摘要:

Journal of Analytical Atomic Spectrometry 111 111111111 111111 111 111111111 111111 THE ROYAL C H EM I ST RY Information Services I I JASPE2 11 (1 2) 53N-58N 11 29-1 234 461 R-522R CONTENTS NEWS PAGES Editorial-Steve J. Hill Guest Editors Foreword-Joseph A. Caruso Steve J. Hill Diary of Conferences and Courses Future Issues 53N 53N 54N 55N 57N PAPERS Trace Metal Speciation via Supercritical Fluid Extraction-Liquid Chromatography-Inductively Coupled Plasma Mass Spectrohetry Nohora P. Vela Joseph A. Caruso Low-flow Interface for Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry Speciation Using an Oscillating Capillary Nebulizer Lanqing Wang Sheldon W. May Richard F. Browner Stanley H. Pollock 1129 1137 Effect of Different Spray Chambers on the Determination of Organotin Compounds by High-performance Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry Cristina Rivas Les Ebdon Steve J.Hill 1147 Feasibility Study of Low Pressure Inductively Coupled Plasma Mass Spectrometry for Qualitative and Quantitative Speciation Gavin O’Connor Les Ebdon E. Hywel Evans Hong Ding Lisa K. Olson Joseph A. Caruso 1151 Speciation of Inorganic Selenium and Selenoaminoacids by On-line Reversed- phase High-performance Liquid Chromatography-Focused Microwave Digestion-Hydride Generation-atomic Detection J. M. Gonzalez Lafuente M. L. Fernandez Sanchez A. Sanz-Medel 11 63 Speciation of Organic Selenium Compounds by High-performance Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry in Natural Samples Riansares MuAoz Olivas Olivier F.X. Donard Nicole Gilon Martine Potin-Gautier Investigation of Selenium Speciation in In Vitro Gastrointestinal Extracts of Cooked Cod by High-performance Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry and Electrospray Mass Spectrometry Helen M. Crews Philip A. Clarke D. John Lewis Linda M. Owen Paul R. Strutt Andres lzquierdo Approaches to the Determination of Metallothionein(s) by High-performance Liquid Chromatography-Quartz Tube Atomic Absorption Spectrometry Yanxi Tan Patrick Ager William D. Marshall Hing Man Chan Speciation of Some Metals in River Surface Water Rain and Snow and the Interactions of These Metals With Selected Soil Matrices J. Y. Lu C. L. Chakrabarti M. H. Back A. L. R. Sekaly D. C. Gregoire W. H.Schroeder 1171 1177 1183 1189 Investigations Into Chromium Speciation by Electrospray Mass Spectrometry Ian 1. Stewart Gary Horlick Arsenic Speciation by Liquid Chromatography Coupled With lonspray Tandem Mass Spectrometry Jay J. Corr Erik H. Larsen 1203 1215 Atomic Spectrometry Hyphenated to Chromatography for Elemental Speciation Performance Assessment Within the Standards Measurements and Testing Programme (Community Bureau of Reference) of the European Union Philippe Quevauviller CUMULATIVE AUTHOR INDEX 1225 1233 AT0 M I C SPECTROMETRY UPDATES Industrial Analysis Metals Chemicals and Advanced Materials- James S. Crighton John Carroll Ben Fairman Janice Haines Mike Hinds 461 R References Typeset printed and bound by The Charlesworth Group Huddersfield England 01484 51 7077 509R 0267-9477(1996112:1-6Journal of Analytical Atomic Spectrometry 111 111111111 111111 111 111111111 111111 THE ROYAL C H EM I ST RY Information Services I I JASPE2 11 (1 2) 53N-58N 11 29-1 234 461 R-522R CONTENTS NEWS PAGES Editorial-Steve J.Hill Guest Editors Foreword-Joseph A. Caruso Steve J. Hill Diary of Conferences and Courses Future Issues 53N 53N 54N 55N 57N PAPERS Trace Metal Speciation via Supercritical Fluid Extraction-Liquid Chromatography-Inductively Coupled Plasma Mass Spectrohetry Nohora P. Vela Joseph A. Caruso Low-flow Interface for Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry Speciation Using an Oscillating Capillary Nebulizer Lanqing Wang Sheldon W. May Richard F. Browner Stanley H. Pollock 1129 1137 Effect of Different Spray Chambers on the Determination of Organotin Compounds by High-performance Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry Cristina Rivas Les Ebdon Steve J.Hill 1147 Feasibility Study of Low Pressure Inductively Coupled Plasma Mass Spectrometry for Qualitative and Quantitative Speciation Gavin O’Connor Les Ebdon E. Hywel Evans Hong Ding Lisa K. Olson Joseph A. Caruso 1151 Speciation of Inorganic Selenium and Selenoaminoacids by On-line Reversed- phase High-performance Liquid Chromatography-Focused Microwave Digestion-Hydride Generation-atomic Detection J. M. Gonzalez Lafuente M. L. Fernandez Sanchez A. Sanz-Medel 11 63 Speciation of Organic Selenium Compounds by High-performance Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry in Natural Samples Riansares MuAoz Olivas Olivier F.X. Donard Nicole Gilon Martine Potin-Gautier Investigation of Selenium Speciation in In Vitro Gastrointestinal Extracts of Cooked Cod by High-performance Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry and Electrospray Mass Spectrometry Helen M. Crews Philip A. Clarke D. John Lewis Linda M. Owen Paul R. Strutt Andres lzquierdo Approaches to the Determination of Metallothionein(s) by High-performance Liquid Chromatography-Quartz Tube Atomic Absorption Spectrometry Yanxi Tan Patrick Ager William D. Marshall Hing Man Chan Speciation of Some Metals in River Surface Water Rain and Snow and the Interactions of These Metals With Selected Soil Matrices J. Y. Lu C. L. Chakrabarti M. H. Back A. L. R. Sekaly D. C. Gregoire W. H. Schroeder 1171 1177 1183 1189 Investigations Into Chromium Speciation by Electrospray Mass Spectrometry Ian 1. Stewart Gary Horlick Arsenic Speciation by Liquid Chromatography Coupled With lonspray Tandem Mass Spectrometry Jay J. Corr Erik H. Larsen 1203 1215 Atomic Spectrometry Hyphenated to Chromatography for Elemental Speciation Performance Assessment Within the Standards Measurements and Testing Programme (Community Bureau of Reference) of the European Union Philippe Quevauviller CUMULATIVE AUTHOR INDEX 1225 1233 AT0 M I C SPECTROMETRY UPDATES Industrial Analysis Metals Chemicals and Advanced Materials- James S. Crighton John Carroll Ben Fairman Janice Haines Mike Hinds 461 R References Typeset printed and bound by The Charlesworth Group Huddersfield England 01484 51 7077 509R 0267-9477(1996112:1-6

ISSN:0267-9477    

DOI:10.1039/JA99611FX021

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

).{ ROYAL AUSTRALIAN CHEMICAL INSTITUTE AUSTRALIAN ACADEMY OF SCIENCE v XXX COLLOQUIUM SPECTROSCOPICUM INTERNATIONALE World Congress Centre Melbourne Australia September 21st-26th 1997 Participants are invited to submit contributions for presentation on the following topics; Theory Techniques and Instrumentation of :- Atomic Spectroscopy (Emission Absorption Fluorescence) Computer Applications and Chemometrics Electron Spectroscopy Gamma Spectroscopy Laser Spectroscopy Luminescence Spectroscopy Mass Spectrometry (Inorganic and Organic) Methods of Surface Analysis and Depth Profiling UVNisible Spectroscopy NIR Spectroscopy IR Spectroscopy Mossbauer Spectroscopy Nuclear Magnetic Resonance Spectrometry Photoacoustic and Photothermal Spectroscopy Raman Spectroscopy X-Ray Spectroscopy Applications of Spectroscopy to the Analysis of :- Biological and Environmental Samples Food and Agricultural Products Metals Alloys and Geological Materials Industrial Processes and Products Plenary and Invited Speakers To date the following eminent spectroscopists have accepted invitations to present keynote lectures; Freddy Adams Mike Adams Mike Blades John Chalmers Bruce Chase Peter Fredericks Manfred Grasserbauer Mike Gross Mike Guilhaus Peter Hannaford Gary Hieftje Kazuhiro Imai Hiroshi Masuhara Belgium UK Canada UK USA Australia Austria USA Australia Australia USA Japan Japan Andrew Zander Russell McLean Jean-Michel Mermet Caroline Mountford Nicolo Omenetto Mike Ramsey Alfredo Sanz Medel Margaret Sheil Heinz Siesler Richard Snook Yngvar Thomassen Bernhard Welz John Williams Barry Sharp USA Australia France Australia IdY USA Spain UK Australia Germany UK Norway Germany UK In connection with the XXX CSI a number of pre-symposia will be organised the conference will feature an exhibition of the latest spectroscopic instrumentation and associated equipment.Social Programme The scientific programme will be punctuated with memorable :social events and excursions of scientific cultural and tourist interest. The social programme is open to all participants and accompanying persons. sponsors As at August 1995 the following companies have agreed to be major sponsors of XXX CSI 1997; GBC Hewlett-Packard Perkin Elmer and Varian For farther information contact - Secretary Mr P.L. Larkins CSIRO Division of Materials Science & Technology Private Bag 33 Rosebank MDC Clayton VIC 3169 AUSTRALIA Telephone +61 3 95422003 Facsimile +61 3 95441 128 E-mail larkins@rivett.mst.csiro.au Conference Secretariat The Meeting Planners 108 Church Street Hawthorn VIC 31 22 AUSTRALIA Telephone +61 3 98193700 Facsimile +61 3 98195978 Updated information may be obtained from the XXX CSI homepage on the World Wide Web at http://w w w.latro be. edu. au/CSIconf/XXX&I. htm 1 QANTAS has been appointed the sole official carrier to the XXX CSI 1997. When making QANTAS reservations please quote JIF 73Q. The Analyst and JAAS have been appointed as the official journals for publications resulting from CSI ‘97. Authors are encouraged to bring their manuscripts to the conference.).{ ROYAL AUSTRALIAN CHEMICAL INSTITUTE AUSTRALIAN ACADEMY OF SCIENCE v XXX COLLOQUIUM SPECTROSCOPICUM INTERNATIONALE World Congress Centre Melbourne Australia September 21st-26th 1997 Participants are invited to submit contributions for presentation on the following topics; Theory Techniques and Instrumentation of :- Atomic Spectroscopy (Emission Absorption Fluorescence) Computer Applications and Chemometrics Electron Spectroscopy Gamma Spectroscopy Laser Spectroscopy Luminescence Spectroscopy Mass Spectrometry (Inorganic and Organic) Methods of Surface Analysis and Depth Profiling UVNisible Spectroscopy NIR Spectroscopy IR Spectroscopy Mossbauer Spectroscopy Nuclear Magnetic Resonance Spectrometry Photoacoustic and Photothermal Spectroscopy Raman Spectroscopy X-Ray Spectroscopy Applications of Spectroscopy to the Analysis of :- Biological and Environmental Samples Food and Agricultural Products Metals Alloys and Geological Materials Industrial Processes and Products Plenary and Invited Speakers To date the following eminent spectroscopists have accepted invitations to present keynote lectures; Freddy Adams Mike Adams Mike Blades John Chalmers Bruce Chase Peter Fredericks Manfred Grasserbauer Mike Gross Mike Guilhaus Peter Hannaford Gary Hieftje Kazuhiro Imai Hiroshi Masuhara Belgium UK Canada UK USA Australia Austria USA Australia Australia USA Japan Japan Andrew Zander Russell McLean Jean-Michel Mermet Caroline Mountford Nicolo Omenetto Mike Ramsey Alfredo Sanz Medel Margaret Sheil Heinz Siesler Richard Snook Yngvar Thomassen Bernhard Welz John Williams Barry Sharp USA Australia France Australia IdY USA Spain UK Australia Germany UK Norway Germany UK In connection with the XXX CSI a number of pre-symposia will be organised the conference will feature an exhibition of the latest spectroscopic instrumentation and associated equipment.Social Programme The scientific programme will be punctuated with memorable :social events and excursions of scientific cultural and tourist interest. The social programme is open to all participants and accompanying persons. sponsors As at August 1995 the following companies have agreed to be major sponsors of XXX CSI 1997; GBC Hewlett-Packard Perkin Elmer and Varian For farther information contact - Secretary Mr P.L. Larkins CSIRO Division of Materials Science & Technology Private Bag 33 Rosebank MDC Clayton VIC 3169 AUSTRALIA Telephone +61 3 95422003 Facsimile +61 3 95441 128 E-mail larkins@rivett.mst.csiro.au Conference Secretariat The Meeting Planners 108 Church Street Hawthorn VIC 31 22 AUSTRALIA Telephone +61 3 98193700 Facsimile +61 3 98195978 Updated information may be obtained from the XXX CSI homepage on the World Wide Web at http://w w w. latro be. edu. au/CSIconf/XXX&I. htm 1 QANTAS has been appointed the sole official carrier to the XXX CSI 1997. When making QANTAS reservations please quote JIF 73Q. The Analyst and JAAS have been appointed as the official journals for publications resulting from CSI ‘97. Authors are encouraged to bring their manuscripts to the conference.

ISSN:0267-9477    

DOI:10.1039/JA99611BX023

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

tube surface in a liquid form by the scouring action of the flame gases. REFERENCES 1 GiiCer S. and Yaman M. J. Anal. At. Spectrom. 1992 7 179. 2 Satake M. Nagahiro T. and Puri B. K. J. Anal. At. Spectrom. 1992 7 183. 3 Jonas D. M. and Parker L. R. Anal. Chim. Acta 1982 134 389. 4 Lau C. Held A. and Stephens R. Can. J. Spectrosc. 1976 21 100. 5 Khalighie J. Ure A. M. and West T. S. Anal. Chim. Acta 1979 107 191. 6 Khalighie J. Ure A. M. and West T. S. Anal. Chim. Acta 1980 117 257. 7 Khalighie J. Ure A. M. and West T. S. Anal. Chim. Acta 1981 131 27. 8 9 10 11 12 13 14 15 Khalighie J. Ure A. M. and West T. S. Anal. Chim. Acta 1982 134 271. Lau C. M. Ure A. M. and West T. S. Anal. Chim. Acta 1982 141 213. Lau C. M. Ure A. M. and West T. S. Anal. Chim. Acta 1983 146 171. Hallam C.and Thompson K. C. Analyst 1985 110 497. Turner A. D. Roberts D. J. and Le Cor Y. J. Anal. At. Spectrom. 1995 10 721. Hieftje G. M. and Malmstadt H. V. Anal. Chem. 1968,40 1860. Williams F. A. Eighth Symposium on Combustion Williams and Wilkens Baltimore MD USA 1962 p. 50. Roberts D. J. and Kahokola K. V. J. Anal. At. Spectrom. 1989 4 185. Paper 5108281 A Received December 20 1995 Accepted February 8 1996 Journal of Analytical Atomic Spectrometry April 1996 Vol. 11 263tube surface in a liquid form by the scouring action of the flame gases. REFERENCES 1 GiiCer S. and Yaman M. J. Anal. At. Spectrom. 1992 7 179. 2 Satake M. Nagahiro T. and Puri B. K. J. Anal. At. Spectrom. 1992 7 183. 3 Jonas D. M. and Parker L. R. Anal. Chim. Acta 1982 134 389. 4 Lau C.Held A. and Stephens R. Can. J. Spectrosc. 1976 21 100. 5 Khalighie J. Ure A. M. and West T. S. Anal. Chim. Acta 1979 107 191. 6 Khalighie J. Ure A. M. and West T. S. Anal. Chim. Acta 1980 117 257. 7 Khalighie J. Ure A. M. and West T. S. Anal. Chim. Acta 1981 131 27. 8 9 10 11 12 13 14 15 Khalighie J. Ure A. M. and West T. S. Anal. Chim. Acta 1982 134 271. Lau C. M. Ure A. M. and West T. S. Anal. Chim. Acta 1982 141 213. Lau C. M. Ure A. M. and West T. S. Anal. Chim. Acta 1983 146 171. Hallam C. and Thompson K. C. Analyst 1985 110 497. Turner A. D. Roberts D. J. and Le Cor Y. J. Anal. At. Spectrom. 1995 10 721. Hieftje G. M. and Malmstadt H. V. Anal. Chem. 1968,40 1860. Williams F. A. Eighth Symposium on Combustion Williams and Wilkens Baltimore MD USA 1962 p. 50. Roberts D. J. and Kahokola K. V. J. Anal. At. Spectrom. 1989 4 185. Paper 5108281 A Received December 20 1995 Accepted February 8 1996 Journal of Analytical Atomic Spectrometry April 1996 Vol. 11 263

ISSN:0267-9477    

DOI:10.1039/JA996110025N

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Atomic Spectrometry Update- Atomic Emission Spectrometry JOHN MARSHALL* ICI Research and Technology Centre PO Box 90 Middlesbrough Cleveland UK TS90 8JE ANDREW FISHER Department of Environmental Sciences University of Plymouth Drake Circus Plymouth U K PL4 8AA SIMON CHENERY Analytical Geochemistry Group British Geological Survey Keyworth Nottingham UK NG12 5GG SIMON T. SPARKES Somerset ScientiJic Services County Hall Taunton Somerset U K TAl 4DY SUMMARY OF CONTENTS Atomic 1. 1.1. 1.2. 1.3. 1.3.1. 1.3.2. 1.4. 1.5. 1.6. 2. 2.1. 2.2. 2.2.1. 2.2.2. 2.2.3. 2.2.4. 2.2.5. 2.2.6. 2.3. 2.3.1. 2.3.2. 2.3.3. 3. 3.1. 3.2. 3.3. 3.3.1. 3.3.2. 3.3.3. 3.3.4. 3.4. 3.4.1. 3.4.2. 3.4.3. 4. Arcs Sparks Low-pressure Discharges Furnaces and Lasers Arcs Sparks Low-pressure Discharges Glow discharges Hollow cathode discharges Furnaces Lasers Other Sources Inductively Coupled Plasmas Fundamental Studies Sample Introduction Nebulizers Flow injection Chromatography Electrothermal vaporization Solid sampling procedures Chemical vapour generation Instrumental Developments ICP and other related sources Spectrometers Chemometrics and instrument control Microwave-induced Plasmas Fundamental Studies Instrumentation Sample Introduction Direct nebulization Electrothermal vaporization Chemical vapour generation Direct analysis of solids Chromatography Instrumentation Gas chromatography-microwave-induced plasma applications Other chromatographic techniques Direct Current Plasmas This Atomic Spectrometry Update is the latest in an annual series appearing under the title ‘Atomic Emission Spectrometry’.The review describes developments in all aspects of atomic emission spectrometry including fundamental processes and instrumentation reported in the Atomic Spectrometry Updates references published in J A A S in Volumes 10 and 11 (95/183-96/C947). The full references and names and addresses of authors can readily be found in the relevant issues of JAAS. However as an additional service to readers an abbreviated form of each reference quoted (except those of Conference Proceedings) is given at the end of the review. Descriptions of novel dc arc sources for AES continue to appear in the literature. These are either the subject of fundamental spectroscopic or diagnostic study or have been designed to contribute in a particular application.Very few reports of spark AES have been received and it must now be doubtful as to whether the technique will remain of interest in the research domain. The most active area of research in AES concerns the development of glow discharge sources. In addition to further characterization of dc GD sources much of the work reported has focused on the use of radiofrequency powered devices which can be more readily used by application to the analysis of insulators. The use of microwave- and magnetically-enhanced and pulsed GD sources continues to attract attention and effort has also been devoted to modelling sputtering processes. A significant increase has been noted in the use of hollow cathode and glow discharge sources for the analysis of liquids (with desolvation) and gases. The development of solid state array detectors such as charge-injection devices (CIDs) and charge-coupled devices (CCDs) has now affected almost every field of AES including arcs and sparks.The attraction of rapid multi-line analysis with simultaneous background correction capabilities is self- evident and these capabilites have been used to good effect in laser ablation AES where discrimination against a rapidly changing background signal is important. The CCD has also been utilized as an imaging detector in studies of furnace atomization plasma emission spectrometry systems. However the major application of these detectors continues to be in ICP-AES and there has been a growth in the use of multivariate statistics and chemometrics associated with the production of this type of data set.As a result of the introduction of commercial equipment there has been much work emphasizing the benefits of echelle spectrometers with solid state detectors and of the advantages and disadvantages of axial viewing of ICPs. The fundamental study of excitation in the ICP remains a subject of considerable controversy and both LTE and non-LTE behaviour continues to be reported. As in most years the development of sample introduction systems for ICP-AES remains a mainstream topic of research. The greatest over-all impact has been made by the use of ultrasonic nebulizers and desolvation systems. The utilization of HPLC and hydride generation techniques in ICP-AES speciation studies has continued- * Review Co-ordinator to whom correspondence should be addressed. Applications of GC-MIP-AES systems to organometallic Journal of Analytical Atomic Spectrometry June 1996 Vol.11 (213R-238R) 213Rspeciation continue to be reported in significant numbers. Fundamental studies of new higher power MIP sources have been reported but on the whole research has been restricted to elements which are relatively insensitive in ICP-AES (e.g. halogens). Further work has been carried out on direct nebulization into the MIP using desolvation to remove solvent vapour. The demise of the DCP as an AES source has continued and only a few applications papers were received in the year under review. 1. ARCS SPARKS LOW-PRESSURE DISCHARGES FURNACES AND LASERS 1.1. Arcs The dc arc has had a long and successful history as an atomic emission source for bulk solids analysis particularly in indus- trial applications.Despite the emphasis in the primary litera- ture now placed on more modern excitation sources such as the ICP and the GD the dc arc remains a practical alternative for qualitative and quantitative multi-element analysis by AES (95/1920). However conventional application of the dc arc has been restricted by the necessity of utilizing photographic plate detection to achieve full wavelength coverage or by the inflexibility of line selection in a direct-reading spectrometer system. Ching (96/C715) has revived the notion of the ‘dc arc in a new jacket’. It was suggested that the modern dc arc with charge-injection device (CID) detection provided operational benefits over photographic plate detection which allowed niche applications in the aerospace industry to be addressed.The development of CID array detector technology has allowed the multi-element advantage of the dc arc source to be exploited in tandem with the benefits of computer assisted data handling in the determination of trace impurities in precious metals (96/716). Mahan (95/C674 95/C816) illustrated these advan- tages in a discussion of the application of a dc arc CID spectrograph to the direct analysis of soils. The system was reported to provide simultaneous background correction and the ability to detect weak spectral lines in the presence of strong matrix signals. The traditional benefits of full elemental sample fingerprinting with minimal sample preparation were maintained with this system.As a consequence of the non- destructive read-out of the CID both trace elements and matrix elements could be measured in the same burn although the limited dynamic range of the technique required a degree of line selection. The performance of the technique for the analysis of solids was compared with that of EDXRF and LA-ICP-MS and with ICP-AES using liquid sampling although no details are given in the conference abstract. Studies of fundamental processes in arc plasmas continue to be the subject of research interest. Spectral diagnostics for a pulsed high-pressure arc have been examined (95/3074). It was concluded that it was necessary to consider both thermal flux and radiative loss mechanisms through the surrounding gas layers of the arc.A spectroscopic study of the arc parameters in anodic and cathodic excitation has been published (95/3776). The line intensity arc temperature and electron density tem- perature were measured axially and radially for both excitation configurations for the detection of Ag B Be Cu and K in an aluminium oxide matrix. It was found that with anode exci- tation these parameters were at their highest values at the centre of the arc column. In the case of cathode excitation the maxima were observed near the sample cathode. It was also reported that the exposure time taken for complete evaporation of the sample was longer in the case of cathodic excitation and that this led to the observation of a greater background signal. A transferred-arc plasma has been studied and utilized in the synthesis of aluminium nitride (95/1174).Anodic and cathodic arcs were coupled to an aluminium bath under a nitrogen or nitrogen-ammonia atmosphere. The distributions of the densi- ties and temperatures in the plasma were measured by emission spectroscopy. Ultrafine aluminium nitride powder (99.3% pure) was collected in a bag filter and on the reactor walls. A chamber has been developed for the investigation of arc and spark interactions with metals and alloys in a controlled atmosphere (95/2343). The apparatus allowed the acquisition of AE spectral photographic and video data from a single experiment. Non-intrusive optical diagnostics methods have been employed to study the arc jet facility at NASA (95/878). The concentration velocity and temperatures of atomic mol- ecular and ionic species were measured in test facilities designed to simulate atmospheric entry flows.The purpose of this work was to understand heat transfer to thermal protection mate- rials. Absorption methods were used to estimate the copper concentration in the free stream flow. Emission from the free stream and shock layer was used to identify radiating species and also their rotational vibrational and electronic tempera- tures and to provide temperature mapping. Laser-excited fluorescence measurements were used to detect velocity and temperatures in the free stream and the shock layer. A time-resolved method for the determination of trace A1 in steels has been reported (95/3495). By use of an arc-like source the characteristics of the single excitation pulse were examined using a direct reading spectrograph with a time delay of 80 ps at lops intervals.The change of signal and background intensity with respect to time were studied and the S/N for A1 observed at 394.4nm was optimized. An LOD of 2.4ppm of A1 was achieved using this source. A low current U-shaped dc arc plasma has been described for the detection of precious metals in geological samples (95/1844). The analytes were selectively removed from the sample matrix by sequential treatment with acids and Au Pd and Pt were reduced in a boiling solution using tin( 11) chloride and collected. After redissolution in aqua regia the resulting solution was evapor- ated with hydrochloric acid diluted in potassium chloride solution and mixed with graphite powder and lithium carbon- ate.Detection limits obtained using the U-shaped dc arc were reported to be comparable with those obtained by ICP-AES for Au Pd and Pt. A modiJed rotating arc plasma jet has been described for the direct analysis of solid and powder samples by AES (95/1968). The arc column was initiated between a pointed thoriated tungsten cathode and a cylindrical rod sample anode in an argon atmosphere. The arc discharge was forced to rotate reproducibly on the anode surface by introducing the argon gas tangentially to the electrode. Spectroscopic measurements were made in the plume above the cathode. Analytical figures of merit obtained using the source were reported for Ba Ca Fe Mg Pb and Zn. A comparison of dc arc and GDAES for the direct analysis of powders has been published (95/2504).The techniques were applied to the determination of Al B Ca Cr Fe and V impurities in silicon carbide. It was found that LODs for these elements were in the range 10-765 pg 8-l for GDAES and 0.3 to 56 pg g-’ for dc arc AES. However the precision of the dc arc method was poorer than that obtained by GDAES. The accuracy of both techniques was considered to be adequate for the application. Methods for the analysis of zirconium( IV) oxide powder by dc arc AES and the characterization of osmium powder and superconductor material by ac arc AES may also be of some interest (95/240 95/2387). 1.2. Sparks The literature on spark sources for AES remains sparse and it is hard to escape the conclusion that the field is now in terminal decline.A few abstracts were received which continue to challenge this view. As with the dc arc the advent of solid 214R Journal of Analytical Atomic Spectrometry June 1996 Vol. 11state array detectors offers the opportunity of examining the information rich spectrum of the spark source. Thus a custom- built echelle spectrometer-CCD detection system has been used to study the matrix dependence of analyte excitation in a high voltage spark discharge over a wide wavelength range (95/196). The atomic distributions of Cu Fe and Mo were measured. It was concluded that analyte excitation within the source on a time-integrated basis was independent of both the sampled species and the matrix. A new current-controlled source which operated at a frequency of 1000 Hz was claimed to achieve speed gains of about a factor of two (e.g.analysis of steels in 12 s) without loss of analytical precision (95/C4222). This source was coupled with a time resolved spectroscopy measurement system which was used to optimize S/N and improve LODs by a factor of 5-10. The instrument was reported to achieve LODs of the order of 1 ppm for trace elements in a variety of matrices. The use of time-resolved spectroscopy to improve performance in the analysis of solid metals was also considered in a review of spark analysis in the metallurgical industry (95/1008). The principles of the high energy pre-spark and self-regulated pre-spark techniques were outlined and the use of optical light guides and inter-element effects were also discussed.A new AE excitation source for solid sampling known as a sliding spark has been described for the direct in situ analysis of non-conducting material (97251 1 95/C3007). The appar- atus consisted of a spark generator a fibre-linked measuring spark head and a diode-array spectrometer. In this technique positionally stable high temperature sparks were slid over the sample surface. For non-conducting samples a high voltage was applied (up to 20 kV) by the spark generator until dielectric breakdown occurred and then a second circuit was used to generate a current pulse in the range 100-600 A for 5.5 ps. The spark repetition rate was adjustable from 20 to 200 Hz. Spectra were recorded over the range 185-510 nm in a period just less than 1 s using a linear silicon photodiode detector.Applications of the technique which were reported included the identification of plastics and inorganic additives and the determination of heavy metal concentrations in waste water. 1.3. Low-pressure Discharges 1.3.1. Glow discharges It is evident from the number of abstracts received that the major area of growth is concerned with the design and application of radiofrequency glow discharges. The principal advantage of the use of an rf powered source is that it permits the direct analysis of a wider range of sample types including non-conducting materials and insulators. Marcus (95/C630 96/C746,96/C823) has presented broad overviews of the status of rf GD in application to the analysis of conducting and insulating solids derived from industrial sources.Favourable comparisons of the capability of the rf GDAES for the direct analysis ofsolids were made relative to the performance of arc and spark AES (95/C733) and XRF (95/C3005). A summary of developments in rf GDs giving examples of the characteriz- ation of materials such as glass metallic films silicate paint layers and bulk PTFE has been published by the Clemson group (95/1849). The effect of excitation frequency on radiofrequency glow discharge source characteristics was the subject of investigation (95/2120 96/832). For the frequency range 2-30 MHz it was reported that discharge energy was found to be more dissipated at the sample surface at low frequencies and in the negative glow region at high frequencies. As a result sputtering rates were reported to be greater at the lowest frequency used.It was observed in a study of the response for Cu metal that high-lying transitions were optimized at low frequencies whereas resonant transitions showed enhancements at high frequencies. The source background levels were found to decrease and the stability of the plasma was found to improve with increased frequency of applied power. The effect of driving frequency in rf GD-AES was also the subject of a separate study (96/652). It was found that the sample sputtering and analyte emission characteristics of the source were strongly dependent on the rf driving frequency employed. The greatest signals and lowest detection limits for a conducting sample (aluminium matrix) were achieved at an operating frequency of 20 MHz (LOD=O.l ppm) and were substantially poorer at frequencies as low as 3 MHz (LOD = 20 ppm).For an insulat- ing sample the best results were achieved at lower operating frequencies at 6 or 13 MHz depending on sample type although it was stated that the power supply might not have been able to deliver sufficient power to reach the projected optimum voltage at the insulator surface. Detection limits reported for elements present in a Macor ceramic sample ranged from 30 to 110 ppm. Detection power was reported to be limited by detector noise because of the low light throughput of the spectrometer employed. Ion lines were strongest from the lower frequency discharges and this was attributed to the greater electron energies achieved as a result of operating under these conditions.The use of Langmuir probe measurements to characterize an rf GD has been described (95/C3008 96/644 96/C832). A computer-controlled impedance-tuned probe was used to gen- erate undistorted current-voltage curves and collisionless Langmuir theories were employed to evaluate this data and to derive plasma parameters such as electron temperature electron average energy electron density and ion density. It was noted that sputtering of a conductive sample resulted in a plasma with higher electron and ion number densities than for the sputtering of non-conducting samples (95/C3008). However in the latter case the energy of the electrons produced was found to be higher. The optimization of discharge pararn- eters of an rf GD for the examination of dielectric materials has been reported by Parker and Marcus (95/4729). The role of discharge power pressure sample thickness and operating frequency on the production of free gas phase atoms was studied.It was concluded that AAS and AES signals from the source reached a steady state within 20s of plasma ignition for non-conductive oxide samples. Relative standard deviations of < 5% were achieved over a 4 min analysis time. Sample thickness was shown to be a key parameter in the atomization of the non-conductor and SEM examination of the surface topography indicated lower sputtering rates for thicker samples. Lower frequencies were reported to produce larger sputter atom populations within the restrictions of range of the instrumentation used.The characteristics of an rf-powered Grimm-type GD have been investigated (95/2130). The source was operated at argon pressures of 0.6-8 torr and at power levels in the range 10-15OW using a 13.56MHz generator and an L-type matching network. It was reported that sputter- ing rates for metals were obtained at 160-2300 pg min-' whereas the equivalent rates for non-conductors were only 30-100 pg min-' at an rf operating power of 150 W. In all cases except for Pyrex samples the craters formed by the rf source were of the same type as those obtained using the dc glow discharge. The quantitative capabilities of the system were demonstrated in the analysis of low alloy steels. A paper on the analysis of precious metals by rf GDAES may also be of some interest (95/4347).Work on the in-depth analysis of thin conducting films of Al-Zn on steels by rf GDAES has now been published (95/4186). The depth projiling capabilities of glow discharges are well established (e.g. see 95/272 95,4018 95/2325 95/2358 95/3775). However in common with most surface analysis techniques the reliability of analyte quantification by GDAES can be problematic as the matrix composition of samples may Journal of Analytical Atomic Spectrometry June 1996 Vol. 11 215Roften change with depth thus preventing the use of a matrix element as an internal standard. The use of an argon emission line as an internal standard for quantitative depth profiling has been explored (95/C2071). The effect of source parameters such as current voltage and pressure on argon line intensity was studied.It was observed that the argon line intensity was independent of sample composition and source pressure to a first approximation. Nevertheless significant matrix-dependent variations were observed in some cases. The use of a computer- aided interpretation of ion sputtering depth profiling in GDAES has been investigated (95/2155). The conversion of measured signal intensity uersus sputtering time profiles into their concentration uersus depth scale equivalents was achieved by computer simulation of the measuring process. Information on the sample type sputtering conditions and origin trans- mission and registration of analytical signals were used to adapt the model to specific experimental conditions. Calculations were performed on an IBM-compatible PC and the software was electronically published by the authors.The important correlation between depth resolution and the crater formation process has been the subject of a recent publication (95/4187). Both dc and rf glow discharge modes were used in depth profiling of a multilayer metal structure. The best depth resolution was found at the same values of pressure and power for both modes. Under optimum conditions depth resolution was found to increase linearly with the sputtered depth to about 5-10% of the latter. A model was also applied to simulate the intensity time profile in order to examine the depth resolution achieved. A new approach to quantitative depth profiling by GDAES based on the approximation of matrix-independent yields has been proposed (95/47 14).The sputtering rate corrected calibration was calculated directly from raw calibration data using a multi-element calibration algorithm running under Microsoft Windows. It was claimed that much less a priori information was required in comparison with other methods and that the accuracy of the determination of the sample composition approached that for single matrix bulk mode analysis. The effect of the lateral distribution of emission line intensities on quantification in a Grimm-type glow discharge source has been investigated (95/4728). It was found that the species from chemically homogeneous sample surfaces were distributed in the plasma parabolically with the maximum at the centre of the sputtering crater. However species from a coarse inclusion adjusted at different distances from the crater centre to simulate inhomogeneity formed a cone with its apex corresponding to the position of the inclusion on the sample surface in each case.It was noted that the sputtering gas species and impurities therein were evenly distributed over almost the whole excitation area thus indicat- ing position-independent excitation. The use of the source for lateral imaging of surfaces has not been greatly explored. The GD technique does not offer high spatial resolution in comparison with an ion beam technique such as SIMS but it may be suitable for large-scale composi- tional mapping of surfaces of the order of a few hundred square centimetres in area (95/C683). An instrument has been constructed which allows macro-scale elemental mapping with a spatial resolution of 1 mm (95/C2068 96/647).This system was based on a novel GD source capable of sustaining multiple discharges simultaneously. The AE signals arising from these discharges were multiplexed using Hadamard transform spatial imaging and the individual emission intensities were recovered from the data by means of matrix multiplication. It was recommended that the internal standard approach should be adopted to reduce the possibility of mapping errors. There has been some interest in the use of pulsed glow discharge sources for AES. The technique of double-voltage modulation was utilized in conjunction with a GD containing a supplementary cylindrical tube electrode (96/C 176). An abnormal discharge was produced between the anode and cathode of the source when the applied power was modulated on-off at 800V.A second discharge was generated between the supplementary electrode and the sample cathode synchron- ous with the primary system but out of phase by using another power supply in the range 350-4OOV. There was no cathodic sputtering in the second discharge. Argon line inten- sity interferences were compensated for by phase-sensitive detection using a lock-in amplifier. Harrison and co-workers (96/C229) described a high power (2 kV 1 A) microsecond- pulse G D source for AES and MS. It was necessary to reduce the duty cycle to sustain the high power discharge. Gated detection was used to examine atomization excitation and ionization phenomena in the source. The development of a high-current microsecond-pulsed GD for AES has also been pursued by Gong et al.(96/C922). The voltage uersus current operating curves indicated that an intense discharge was generated with a peak current 1-20 A range. It was noted that the frequency of operation (140-800 Hz) and pulse width (0.8-10 ps) had little effect on the voltage uersus current curve. However discharge pressure and operating current were the parameters which were found to be most important in determining cathode sputter rate for pure Cu Cu alloy and pure Nb targets. The operation of a radiofrequency GD with a pulsed power source has also been described (95/C617). The system was used in conjunction with time resolved optical and mass spectrometry. It was found that there was a surge in the intensity of analyte signals arising from sputtered sample and this was attributed to enhancement by radiative decay of metastable argon ions produced in argon-ion recombinations in the plasma.Gated detection of the analytes was used to enhance S/B by up to three orders of magnitude in MS applications. The use of a high dynamic range detector for the analysis of layered materials by rf GDAES has been discussed (95/C3003 95/C3006). The sensitivity of the detector could be automatically adjusted to allow the detection of an analyte present at trace levels in one layer and at major levels in a another layer irrespective of concentration distribution in real time. The application of this system to insulating materials coated with thin films was also discussed (96/C812).Efforts have also been devoted to improving the range of application of GDAES by using microwave-boosted sources (see J . Anal. At. Spectrom. 1995,10 141R). A microwave sputtering device has been described for the examination of insulators and conductors by GDAES (96/C180). The discharge chamber consisted of a quartz tube with a reduced diameter neck at one end which slid over the inner conductor of a slab line cavity (operated at 2.45 GHz) and vacuum sealed with an O-ring. The other end of the quartz tube was connected to the vacuum system for evacuation and gas entry. For the examin- ation of metals cavity inner conductors were made from the sample material. In the case of insulators the samples were machined in the form of a cup which fitted over the exposed end of the conductor.At low argon pressures and low net microwave powers (about 10 W) an intense localized glow was observed directly in front of the end face of the inner conductor resulting in sputtering. Sputtering also occurred when neon was used as the fill gas but the high intensity of the neon AE made the visual observation of the localized glow more difficult. The AE spectra thus produced by the discharge were studied using a quartz spectrograph and a high resolution Fourier transform ultrauiolet-visible spectrometer. The resonance lines emitted from sputtered metals were relatively strong and weak lines from high-lying atomic levels and ionic levels were also observed. In the case of non-conductors such as Macor and boron nitride spectral complexity arising from molecular bands made it difficult to isolate atomic lines but weak signals were observed for A1 and B.Leis (95/C684) also examined the use of a microwave-boosted GD source in argon and helium 216R Journal of Analytical Atomic Spectrometry June 1996 Vol. 11for the analysis of non-conducting ceramics. It was reported that detection limits for many elements were improved by the use of microwave boosting but that the intensity of some lines was hardly affected by the additional excitation source. A magnetically enhanced glow discharge source for AES has been the subject of investigation (95/2181). The device was constructed in such a way as to allow side-on viewing of an rf-powered discharge in the absence and presence of two external magnets which created a transverse field in the GD volume above the cathode surface.The water-cooled cathode blocks (25 mm diameter) were fabricated from standardized nickel-copper and nickelkhromium-iron alloys. A power supply which could be operated at 3.5 6.78 and 13.56 MHz was used to determine the effect of driving frequency on emission intensities. The source was operated over a pressure range of 0.1-1.0 torr at rf power levels between 20 and 50 W. Spatial profiles of argon fill gas emission at 420 nm OH-band emission at 309 nm and Cu emission at 324 nm were recorded using a high-resolution spectrally-segmented diode-array spec- trometer. In the presence of the magnetic field the detection limits obtained using this device were found to be similar to those obtained with a Grimm-type source. Limits of detection for Al Cr Mg and Mn in a Monel 400 nickel-opper alloy were reported to be 30 10 50 and 30ppm respectively.A planar magnetron radiofrequency-powered glow discharge source has also been described by workers from the same group at Indiana (96/651). The effect of the addition of the magnetic field on emission was studied and it was found that sample ablation rates and analyte emission intensities were enhanced compared with those achieved using a conventional rf glow discharge. Sputtering rates were found to be much greater for both conducting and non-conducting samples using this source. A planar magnetron dc glow discharge plasma system has also been developed (95/1540 95/2166). The source was operated over a pressure range of 0.0004-2.5 torr and with discharge currents between 50 and 400 mA.The plasma voltage did not exceed 500V allowing the use of a relatively simple power supply. The surface characteristics of conducting materials such as A1 alloy Cu brass and Au metal were examined by microscopy and the experimental parameters affecting sputter- ing were studied. It was concluded that erosion of samples increased with decreasing support gas pressure increasing discharge currents and increasing atomic number of the sputt- ered elements. It was noted that hillocks were formed at the microscopic level on sample surfaces but no correlation between location and inclusions was observed. The application of a magnetic field was found to enhance sputtering rate in a Grimm-type GD source operated in argon at 4 torr and 1000 V (95/3063 96/C806).When sufficiently thin samples ( 1-2 mm) were used sputtering rates for Cu from a copper-nickel-iron alloy were increased from 100 to 200 pg min-' under the influence of the magnetic field. An increase in intensity was observed for the Cu non-resonance emission line at 282.4 nm and the noise characteristics of the source were also affected. However for resonance lines of Cr and Cu at 324.7nm and 425.7 nm respectively emission intensity decreased in the presence of the magnetic field and this was attributed to self- absorption effects. The effect of$ller gas in the performance of glow discharge sources for AES has been the subject of several investigations. The use of helium-argon plasma gas mixtures in a Grirnm-type discharge has been studied in the sputtering of Cu-Ni and Ni-Co alloy cathodes (95/3820).The matrix element atom lines were detected by AES. It was found that when the plasma gas in the source was pure argon the voltage-current charac- teristics of the discharge were strongly dependent on the cathode materials used. However if the plasma gas mixture was predominantly helium (23 2) the discharge characteristics were found to be almost independent of the nature of the cathode. A comparison has also been made of the effect of various carrier gases on the operating parameters for a dc GD source (95/C2070). It was found that for a given current the highest voltages occurred for helium and the lowest for argon and krypton. In order to avoid excessively high operating voltages for helium and neon carrier gases higher pressures had to be used.Selective interactions with ions and metastable atoms of the inert gas were reported to have a major effect on the ionized spectra and hence on the atomic spectra of sputtered atoms. The energy distribution of ions bombarding the cathode surface of a glow discharge has been determined (95/4727). It was found that the cathode was bombarded by low-energy singly-charged gas ions and by a significant flux of high-energy singly-charged ions from the target material. Gas ion motion in the cathode dark space of the discharge was reported to be largely collisionally dominated limiting and spreading out the energy of the gas ions when they reached the cathode. The theoretically expected variation in the ion energy distribution at the cathode when discharge conditions were altered was in qualitative agreement with experiment a1 data obtained.Reproducible results were obtained for argon and neon filler gas singly-charged ions and cathode material ions (Al Cu Mo and Ta). The effects of small amounts of oxygen on AE from an argon glow discharge plasma were investigated (96/295). The Cu analytical line at 324.7 nm was studied. The addition of 4 '/o oxygen caused a reduction in Cu line intensity by a factor of 800. Gas-sampling glow discharges continue to be the subject of attention (95/1914 95/3881 96/C809) This recent work has focused on the determination of non-metals in molecular gases and organic vapours by AES. Discrete aliquots of the sample were introduced into an exponential dilutor and carried by the support gas through a silica capillary tube into the GD.Radiation from the plasma source was viewed axially. Conditions were established for the simultaneous detection of C C1 F and S. Detection limits for these elements were reported to be in the low ng s-' range. A relative precision of <5% was achieved and the linear dynamic range of the technique was about 2-3 orders of magnitude. The potential of the source for the determination of elemental ratios of organic compounds was also examined. The development of a real-time monitor for the detection of metallic off-gases from a waste processing system using a gas sampling GD has been described (95/C741). The quantification of As and Pb in off- gas was achieved by using hydride generation to calibrate the system (see also J.Anal. At. Spectrom. 1995 10 141R). The detection of As in an argon flow stream at levels of 500 pg mP3 was achieved. A patent application concerning the development of an atomic line emission analyser for hydrogen isotopes has been published (95/873). A sample of hydrogen was introduced to a low pressure chamber and exposed to an electrical discharge. The H atoms were excited by the discharge and the wavelengths of interest were isolated using a Fresnel prism and a photodiode array for detection. The light emitted by the system was filtered to pass only the desired wavelengths. Reviews of the develop- ment of glow discharge sources for atomic spectrometry may also be of interest to the general reader (95/2852 95/2853 95/4433).1.3.2. Hollow cathode discharges Although the application of hollow cathode discharges to the direct analysis of solid samples is well established few abstracts have been received concerning the development of the source in this area. A few papers were devoted to enhancing the intensity of hollow cathode sources for use in AAS but clearly the observations made in these investigations also have xel- evance to AES studies. The addition of nitrogen to the fill gas Journal of Analytical Atomic Spectrometry June 1996 Vol. 11 21 7 Rof a hollow cathode lamp was shown to result in an enhance- ment in excitation and hence observed emission intensity (95/2168). The degree of this enhancement was found to be dependent on the total fill-gas pressure and the lamp operating current typically 1 torr (133.322 Pa) and 5 mA respectively.The increase in emission intensity for Cd levelled off at nitrogen levels above about 10% in the fill gas. The enhancement in excitation was attributed to the generation of active nitrogen which improved efficiency in exciting transitions involving Ca Cd and Fe. The main disadvantage of this approach not surprisingly was that background spectra from the lamp were complicated by the appearance of band systems due to nitro- gen giving rise to the possibility of overlap with analyte spectral lines. In another study argon-helium fill gas mixtures were used for the detection of non-metals by AES in a hollow cathode discharge (96/C774). The intensities of non-metal ionic lines were found to increase as the helium gas concentration was decreased. An aluminium cathode was found to produce much higher analyte emission intensities than those obtained using a copper cathode.The emission background from both the cathode and the plasma were depressed by (presumably) analyte deposits in the cathode. A study of the influence of a magneticfield on AE from a hollow cathode discharge has been described (95/C685). An electromagnet was used to apply an external field with a microcavity hollow cathode discharge in which aluminium and copper metals and aluminium alloys were used as cathodic materials. Enhancements in emission intensities of the atomic lines of aluminium and copper were observed in the presence of the magnetic field whereas argon ion line intensities decreased in comparison to the signals observed in the absence of the field.A compact hollow cathode discharge source incorporating neodymium-iron-boron per- manent magnets which were employed to enhance emission intensities was also described in this presentation (95/C685). The spatial distribution of radiant intensity of hollow cathode lamps has been studied using a digital photodiode array imaging system (95/3879). The intensity distribution of atomic and ionic analyte and filler gas lines was measured over the cross- section of the lamps used. For small cathodes it was observed that the intensity distribution had the shape of a paraboloid with maximum intensity at the hollow cathode axis for all of the lines recorded.In contrast for large cathodes the distri- butions were non-paraboloid and in some cases exhibited a minimum at the cathode axis and a maximum at the cathode walls. It was also noted that the intensity distribution for a given lamp had a very similar shape for all currents applied. The use of secondary circuits to boost emission intensity from hollow cathode lamps has also been described (95/C3023). The use of a second anode was reported to allow a fixed excitation current to be set for every lamp which did not require further operator adjustment. Benefits cited for this arrangement included reduced self-absorption and line broad- ening effects. A Japanese patent concerning the manufacture of hollow cathode lamps using powdered alkaline earth metal halides and a ductile metal particle filler (e.g. aluminium copper magnesium or silver) may also be of interest (95/858).The majority of abstracts received concerned the re-examination of the use of the hollow cathode lamp as an emission source for the analysis of liquid samples. Williams and co-workers (95/C707 96/343 96/C737 96/C8 10) have con- tinued their studies of a hollow cathode emission source for applications in solution microanalysis. It was found that pre- conditioning of the hollow cathode and careful electrical control of the discharge were important factors in achieving detection limits in the low- to sub-pg range. Application of the source to the determination of Ca C1 K Mg Na and P in nanolitre volumes of physiological fluids was described. It was reported that pulsing of the discharge improved analytical precision (96/C8 10).The effect of conditioning of the hollow cathode by sputtering was investigated as a function of time using a two-piece demountable source unit (95/C705). It was observed that argon gas pressure and the pulse width of the conditioning current had the greatest effect on the conditioning of the spherical hollow. A computer-controlled hollow cathode discharge source was used in conjunction with a triple mono- chromator to compare relative intensities of selected atom and ion lines of non-metals (95/C704). The operation of the system for simultaneous detection of metals and non-metals by AES was described. Details of a hollow cathode atomic emission source designed for continuous solution nebulization have now been published (95/2228; see also J. Anal.At. Spectrom. 1995 10 140R). Liquid samples were introduced to a Meinhard nebulizer and Scott-type spray chamber arrangement using a peristaltic pump. The aerosol thus produced was passed through a heated desolvation unit at 270°C and then uia a water-cooled condenser at 17 "C to the hollow cathode dis- charge. The transition from atmospheric pressure to discharge pressure occurred directly at the hollow cathode discharge so that the tip of the introduction tube was right inside the hollow cathode. The discharge itself was powered via a high voltage dc supply which could deliver a maximum of 300mA and 2 kV and the enclosure was evacuated using a rotary vacuum pump. The helium plasma discharge was found to be stable at current densities up to 0.64 A crnp2.The emission signal was observed along the axis of the hollow cathode uia an imaging lens (1 1) and a 0.35 m spectrometer fitted with either a photodiode array or photomultiplier detector. By use of this system detection limits were obtained for 11 elements in the range 0.03ngml-' for Li to 200ngml-' for Zn. The adap- tation of this system to incorporate a laser ablation unit for solid sampling has also been described (95/C680). An Nd YAG laser was used to introduce the ablated solid to the discharge in the form of a dry aerosol stream. An LC-MS particle beam interface was used as a means of introducing liquid samples into a hollow cathode discharge prior to AE measurement (95/C681 95/C2986 95/3414). Sample solutions were intro- duced to a thermoconcentric nebulizer and passed to a heated desolvation chamber and then through a two-stage momentum separator to separate the analyte and solvent.The resultant analyte particles were directed into a heated steel block flash vaporized and carried in a helium or argon gas flow to the hollow cathode discharge. The system was applied to the measurement of Cs and Na as nitrates and background equivalent concentrations (BEC) for these elements in aqueous solution were reported as 0.74 and 0.53 ppm respectively. It was reported that in the use of this source for the determination of Cs in simulated nuclear waste water solutions (5.0 mol 1-l sodium nitrate and 0.1 mol 1-l potassium hydroxide diluted lOOO-fold) the addition of excess chloride rather than nitrate as a counter ion resulted in an improvement in BEC by about a factor of 100.The detection limit in this latter case was reported to be 8 ppb of Cs (95/3414). An all-electronic spec- trometer has been described which combined a hollow cathode discharge and an acoustooptic tunable filter (AOTF) for AES (96/C808). The hollow cathode source was designed to allow the introduction of samples as aerosols generated via pneu- matic nebulization and desolvation or laser ablation. The filter was electronically tunable and narrow band covering a wave- length range of 350 to 600nm. The complete spectral region could be scanned in less than 1 s and any wavelength accessed randomly in 0.1 ms thus allowing scanning and peak hopping functions. Spectral resolution was reported to be 0.2nm at 350 nm.Clearly the potential for such a system is great if the wavelength range can be extended to incorporate more lines in the UV region of the spectrum. 1.4. Furnaces Graphite furnace atomizers are traditionally associated with AAS but high sensitivity multi-element analysis can be 21 8 R Journal of Analytical Atomic Spectrometry June 1996 Vol.11achieved with a variety of electrothermal devices using AES. An excellent review of the application of furnaces as thermal excitation sources in emission spectrometry has been published by Baxter and Frech (95/4730). The major limitation of the graphite furnace when used as a thermal excitation source for AES is that a number of elements (e.g. non metals metalloids) with transitions in the low UV region of the spectrum exhibit relatively poor sensitivity. The furnace performs very well as an atomizer but is lacking in thermal capacity and electron temperature for the excitation of more energetic transitions. In recent years the development of plasma excitation sources contained within the furnace enclosure has led to a new field of research in AES.A furnace atomic non-thermal excitation source (FANES) was the first such device based on excitation by a low pressure hollow cathode discharge occurring between the graphite tube (cathode) and a ring anode. The determi- nation of Hg at trace levels using FANES has been described (95/2223). It was found that the direct analysis of microvolume samples could be improved by the use of chemical modifiers such as iridium or palladium to stabilize the Hg during thermal pretreatment. A cold vapour generation system and an amalgam attachment was also coupled to the FANES source and this arrangement allowed a detection limit of 22 ng 1-' to be obtained for sample volumes up to 10 ml.However the best results were achieved using the cold vapour technique and in situ enrichment of Hg onto the surface of the graphite tube which has been impregnated with iridium. Under these conditions a detection limit of 0.9 ng 1-l was obtained. The technique was validated using a variety of reference materials following microwave digestion sample pretreatment. The FANES source has also been used to carry out a study of the atomization of B (95/321). A total pyrolytic graphite tube was coated with tungsten carbide or lanthanum carbide and this procedure was found to result in an increase in the pyrolysis temperature for B from 850 to >2200 "C. It was found that the addition of a calcium-magnesium modifier to boron solu- tions increased the maximum pyrolysis temperature to 1200 "C but that a titanium-ascorbic acid modifier had no effect.Atomic emission signals for B were obtained at <800°C by hollow cathode furnace atomic non-thermal excitation with a 30 torr helium plasma. A detection limit for B of 71 pg was reported in the absence of a modifier. It was concluded that the atomization of B occurred through molecular dissociation rather than solely by sublimation and that poor detection limits for B in ETAAS resulted from inefficient thermal dis- sociation of B-containing oxides and carbides produced by dissociative desorption of boron( 111) oxide.A comparison has been made of FANES and ETV-ICP-MS for simultaneous multielement analysis (95/318). In this study the FANES source was used as the electrothermal vaporization device coupled to the ICP-MS. Interferences from sodium on analyte signals in ETV-ICP-MS were compared with those for FANES operated in the AES mode. An electrothermal excitation source similar to the FANES system employing a micro-scale hollow cathode cup instead of a graphite tube has been improved to achieve better reproducibility and S/N (95/2317 see also Papp L. Magy. Kem. Foly. 1990 96 179). The S/B of this source was enhanced by using excitation current modulation low gas pressure (133 Pa in argon) and computer correction for interference signals observed during excitation pauses.The response of the system was linear for Cr Cu Mn and Ni in the concentration range 5 ppb to 10 ppm for 40 pl sample volumes and precision was of the order of 2-6% relative. Detection limits obtained using the instrument in multi-element AES mode were in the range 50-200pg depending on the element. An electrothermal hollow cathode glow discharge atomic emission spectrometer has been described for the in situ monitor- ing and trace analysis of up to 20 elements in waste water (96/C669). Continuous sample introduction into the hollow cathode was achieved by using an ultrasonic nebulizer. The system was also applied to the spectrochemical analysis of actinides and REEs (95/C678).An AE method based on the excitation of atoms by the electron flux in an electrothermal atomizer has been described (95/4740). The atomic vapour was produced by a tungsten coil cathode-atomizer and a second electrode made of glassy carbon or graphite was used as the anode positioned to achieve a 1-3 mm gap between the two. The image of this gap was focused on the slit of a high resolution monochromator. It was possible to control the electron energy of the source by varying the voltage between the cathode and the anode. Helium was used as the shielding gas allowing efficient excitation for a range of elements (Ag B Cd Co Cr Cu Fe Mn Ni Pb Sr and Zn). Detection limits achieved using the source were reported to be in the pg range and were similar to those obtained by ETAAS. Furnace atomization plasma emission spectrometry (FAPES) is a combined source in which a radiofrequency plasma usually sustained in helium at atmospheric pressure is formed within a graphite furnace (95/536,95/C804,96/C736).Analyte atomiz- ation takes place within the conventional graphite furnace and subsequent excitation is achieved in the plasma discharge. Sturgeon et al. (95/C732) have reported the use of Langmuir probes to derive diagnostic FAPES plasma data. Probes were inserted axially through an enlarged sample injection port of the graphite furnace into the atmospheric helium plasma in order to obtain radially resolved electron temperature and density data. The effect of rf forward power reflected power frequency (13.56 and 40 MHz) and centre electrode dc bias voltage on the results was investigated.Pavski et al. have utilized a charge coupled device imaging system to obtain two-dimensional distributions of analyte and plasma gas species in FAPES (95/536 95/C804). Imaging of the He 667.82 nm support gas line revealed the presence of an intense luminous zone located around the central electrode and a diffuse plasma near the furnace tube walls. In a graphite tube at room temperature the plasma system exhibited a significant dependence on the dc bias of the centre electrode for a constant forward rf power of 50 W. It was observed that polyatomic background species exhibited similar over-all distri- butions and response to changes in the centre electrode dc bias. For the atomization of Ag primary condensation and re-evaporation occurred at the centre electrode for plasma powers of 30 and 50 W.When the system was operated at 70 W the effect was removed and this was attributed to plasma induced heating of the centre electrode. It was noted that optimum sensitivity could be obtained for some elements at pressures slightly higher than atmospheric and consequently part of the study was carried out over a pressure range of 200-2000 torr (95/C804). The distribution of analyte atom and oxide species in FAPES was also investigated using this imaging technique (96/C736). Blades and co-workers (95/C825) carried out monochromatic imaging of the FAPES discharge using a CCD camera. A combination of interference filters or a high resolution monochromator was used to examine the spatial and temporal evolution of the emission signal from the plasma and analyte species (Ag).The spatial and temporally resolved gas and excitation temperatures were measured to assess the effect of furnace temperature (thermi- onic emission from the tube wall) on the plasma. In a related study spatially resolved atomic emission intensities from helium and molecular emission intensities from OH were used to monitor the effect of increasing the rf power applied to the centre electrode of the FAPES source and to calculate rotational temperatures (96/C776). The intensity measure- ments indicated that there was a significant thermal gradient in the source in the range 680-1920 K when 60 W rf power was applied. The line ratio method was used to estimate excitation temperatures for Pb.This temperature was found Journal of Analytical Atomic Spectrometry June 1996 Vol. 11 219Rto be in the range 4800-5200 K for power settings of 35-70 W. The FAPES source is also being developed in a form suitable for environmental mobile laboratory field applications (95/C825). The system described was based on a graphite furnace-capacitiuely coupled plasma source coupled to a photo- diode array AE spectrometer. Applications discussed included the determination of hazardous metals and radionuclide iso- topes in soil matrices using slurry sampling and microwave digestion. The determination of C1 P Pb and T1 at the sub pg levels has also been described using a graphite furnace- capacitively coupled plasma AES system (95/C735).Argon was used as the discharge gas rather than helium to improve sensitivity. The detection limit for P claimed for this instrument was reported to be three orders of magnitude better than that achievable by ETAAS. 1.5. Lasers Interest in laser ablation (LA) for direct AES is growing steadily. This appears to result in part from the incorporation of array detectors in spectrometers allowing simultaneous detection of many emission lines and more importantly real- time background correction. However the development of more robust excimer laser systems has also contributed. This is reflected in the number of papers and conference abstracts appearing in the literature. Thus Radziemski (95/2872) was able to review (61 references) the analytical applications of laser plasmas and laser ablation from 1987-1994.The review was confined to lasers producing pulse energies less than 1 J. Additionally Uebbing et al. (95/205) have discussed the requirements for quantitative matrix independent elemental analysis by LA-AES. The field of LA-AES can be considered in terms of studies based on the different laser types since these provide different properties and applications. Sneddon (95/2553) has discussed and reviewed (21 references) the theory of excimer lasers and their advantages and disadvantages compared with lasers generating light of longer wavelengths. Recent work was described generating excimer laser ablation plasmas for the determination of metals and non-metals by direct AES. Fundamental aspects such as the spectrometric observation position of the plasma the nature of the surrounding gas and its pressure were considered in comparing experimental data with theoretical models.The technique was claimed to offer a precision of +/-lo% and an accuracy of 5-10%. Lee and Sneddon (95/1890) have demonstrated the capabilities of an argon fluoride excimer laser with an energy of 150 mJ at 193 nm coupled with a photodiode array based spectrometer system to observe the plasma resulting from the laser ablation of NIST trace element reference glasses. Three glass reference materials NIST 610 612 and 614 were ablated in a helium atmosphere with the laser firing single shots. The best S/B was found by analysing the edge of the inner plasma sphere. A linear calibration graph was produced for K (764.6 nm line) and RSD values of 8.6% at 461 pg gel rising to 10.2% for 30 pg g-' were obtained.The calculated detection limit was 0.13 pg 8-l. Emission line spectra were observed to be compli- cated at lower wavelengths by the large number of elements in the matrix. The Rb peak was also observed to be free of interference at 778.1 nm. A report concerning the application of a pulsed laser for the vaporization of human blood cells in order to determine individual Na and K concentrations by AES was particularly novel (95/336). A 193 nm argonjuoride excimer laser operated at an energy of 0.5-5 mJ with a pulse length of 10 ns at a rate of 1 Hz was focused onto a flowing stream of 4% glucose on water. The flowing stream was a combination of two individual flows where an inner flow at 9-21 ml min-' was used to drag the outer sample flow of 6-50 p1 min-'. The laser pulse war; focused onto a spot 1 mm x 0.1 mm.The pulse energy density was such that cells absorbed the laser light and were vaporized but the bulk liquid did not break down. The emitted light was separately focused onto a 590nm filter and a 766nm filter placed in front of collimating pinholes. Photomultiplier tubes behind the pinholes were used for detection of K and Na signals respectively. The electronically integrated signals were digitized and passed to a PC for data processing. The detection limits obtained using the system (approximately 10 fmol) were not good enough for individual cells to be analysed. By careful use of Poisson statistics it was possible to separate out the average concentration of Na or K per cell and the variation of that concentration in cells from the analytical variance.The variations of +/-1550/ and +/-55% in K and Na could not be explained by changes in cell volume and only a weak correlation between K and Na was found. The results were believed to reflect the age distribution of the cells in the sample. Andre et al. (95/2197,96/C242,96/C253) have developed an ICP-AES system using a xenun chloride excimer laser emitting at 308 nm with a measured beam energy of approximately 150 mJ and a pulse duration of 28 ns. The laser was focused on the test material surface with a plano-convex lens with a focal distance of 50cm and at an angle of 80". Accurate focusing within 0.1 mm was ensured by use of a novel ultrasonic emitter-receiver.This laser ablation system resulted in a laser spot size of 400 x 700 pm. The large spot size was necessary to avoid inhomogeneity in the aluminium test samples and pre- cluded the use of frequency-multiplied Nd YAG lasers. The plasma was produced in air at atmospheric pressure and the AE from the laser plasma was focused onto the spectrometer slit perpendicular to the test material surface. This configur- ation was chosen because it was most suitable for in situ measurements and as the laser ablation crater got deeper the part of the plasma sampled did not change. The emission spectra were recorded with a diode-array spectrometer ( 1024 diodes) over a range of 13 nm. This was found to be sufficient to allow the detection of several elements in an aluminium matrix but of limited application to other matrices i.e.iron. Analytical results demonstrated that with internal standardiz- ation the method was quantitative with a reproducibility of 2%. The main limitations on reproducibility were found to be precise control of laser power densities (by measurement of the distance between lens and test material) and of the total number of pulses delivered before and during intensity measurements. Images of the plasma obtained with a time- gated CCD showed that the time delay after the laser pulse had to be long enough to avoid background emission but not so long (<5 ps) that the plasma stabilized. Laserna et al. (95/193) reported the measurement of spatially resolved emis- sion spectra from the laser ablation plasma of noble metals.A pulsed xenon chloride excimer laser delivered a fluence between 2.3 and 4.7 J cm-2 at 308 nm onto gold copper and mercury targets. Measurement of AE was performed using a charge coupled device as a detector. The emission spectra of 18 carat gold materials were discussed. Kagawa et al. (95/901) investi- gated a shock waue plasma induced by a xenon chloride excimer laser. The characteristics of the plasma were examined using time-resolved spectroscopy. It was found that the plasma was an excellent source of emission from metals since the back- ground intensity was low and the atom excitation occurred purely as a thermal process. A linear relationship was observed between emission intensity and element concentration.Laser ablation atomic emission spectrometry has begun to reach the industrial arena. Peng et al. (95/C745) have employed laser AES for the analysis of solid particles and fine liquid droplets in streams of air for the purposes of industrial process control. The ablation of graphite using a krypton fluoride laser was examined as a method for producing fullerenes (95/207). Ablations were carried out in helium neon argon and xenon 220R .lournu1 of Analvtical Atomic Svectrometrv. June 1996 Vol. 11atmospheres at 300 torr. The processes which took place were investigated using fast imaging of the plasma characterization of the soot produced and spectroscopy. The measurement of rotational and vibrational spectra of electronically excited C2 in the plasma was achieved.Rotational temperatures of 3000 K and vibrational temperatures of 6000 K were calculated. Theim et al. (95/198) performed simultaneous quantitative analysis of NIST transition metal alloys in high vacuum using laser-induced breakdown spectroscopy (LIBS). An Nd YAG laser was used to ablate the sample and AE was measured using an optical multichannel analyser. Linear calibration curves were obtained for Al Cu Fe Ni and Zn at concen- trations from fractions of a per cent. to tens of per cent. levels using a non-resonant line. Reported LODs ranged from 0.0001% for Ni in copper to 0.16% for A1 in a complex granular matrix. The analysis of liquids by absorption onto paper was achieved using the same system. Sabsabi and Cielo (95/C2083 95/3880 96/C249) used a Q-switched Nd:YAG laser operating at 1064 nm with a pulse length of 8 ns in air at atmospheric pressure for the examination of aluminium alloys. The plasma generated from ablating the alloys was characterized in terms of its appearance emission spectrum excitation temperature and electron density. The electron density was inferred from Stark broadening of A1 ion lines and the temperature was obtained by Boltzmann plots of neutral Fe lines.Calibration curves for Cu Mg Mn and Si were produced and detection limits were element dependent and of the order of 10ppm. Further work was reported concerning the examination of copper alloys using this system (95/4182). Calibration curves for Ag Fe and Ni were generated. The precision achieved ranged from 2-10% of the analyte concen- tration and LODs of 1 20 and 10ppm were obtained for Ag Fe and Ni respectively.Wisbrun et al. (95/1864) have investigated the development of a field portable laser ablation atomic emission spectrometer. Soils sand and sewage sludge were ablated using a Nd:YAG laser and the emission from the plasma was carried to the detector head using a fibre optic. An optical multi-channel analyser recording in a time-resolved fashion was employed for detection. The effects of persistent aerosols crater forma- tion grain size timing laser pulse power gas above the sample and water content were studied. Multivariate calibration pro- grams were devised to improve reproducibility. The determi- nation of Ba and Cr in pressed powder compacts of soils was carried out in a separate study using similar equipment (96/346).Calibration graphs were obtained for spiked samples. The precision of the technique was in the range 6-2O% and LODs of 26 and 50ppm were reported for Ba and Cry respectively. In order to improve the analytical performance of this system the laser plasma produced was examined using spectral imaging (96/C777). Kuzuya et al. (95/1926) studied time and spatially resolved spectra of laser induced plasmas at low pressures of argon and helium in order to find the optimum emission intensity and S/B from test materials. The best experimental conditions found were an argon atmosphere of 200 torr an observation position 1.5 mm above the test material and a gate delay time of 2 ps after the initiation of the laser pulse.Kagawa et al. (95/195) described a transversely excited atmospheric pressure carbon dioxide laser beam with an energy of 500 mJ and a pulse length of loons which was focused onto a Zn target at reduced gas pressures. The resultant laser ablation plasma was confined in a tube that had been placed just in front of the target. Temporally and spatially resolved measurements of zinc emission intensity showed it rapidly increasing with a distinct jump near the front of the plasma. The experimental results supported the supposition that the plasma was excited by a shock wave. The authors suggested that the plasma confinement technique might improve sensi- tivity in laser-microprobe AES. In further work a pulse energy of 700 mJ was used in the analysis of steel and a pulse of 300 mJ energy was employed for the ablation of glass (95/3837).Using an internal standard method a linear relationship was found between Cr content and Cr emission. The calibration response for Ni was linear up to 4% m/m. Boron was determined in glass using silicon as an internal standard. A ruby laser has also been employed for plasma generation (95/1929). The strongest emission lines for Br C1 and I in an atmospheric emission plasma were found to be in the range 390-560nm and these could be used for the identification of halogens. The application of a theta-pinch discharge to aid the excitation process in LA-AES may also be of some interest (95/C827 96/C705). 1.6. Other sources Only a few reports of the study or application of flame excitation sources (FES) for AES are worthy of mention here.A method of imaging the temperature zones of flames by IR emission spectroscopy has been proposed (95/1171). Methods of how to obtain temperature information from distinct spectral entities were discussed although it was noted that these were not suitable for precise calculations. The characterization of a swirl-stabilized methane-air diffusion flame using AES and planar laser-induced fluorescence ( LIF) has been described (95/1172). The experimental arrangement was devised to simu- late combustion processes in a gas turbine chamber. The parameters which governed the mechanisms of formation of NO were studied. Methods with high spatial and temporal resolution were required to follow the microscopic processes driving the macroscopic behaviour of the gas flows.Spectroscopic aspects of the use of flame photometric detec- tors as element-specific detectors in chromatography have been reported (95/1870 95/1975). Patents concerning the FES measurement of chlorine in gaseous compositions (95/855) and the detection of metal particles in combustion gases (95/874) may be of some interest. 2. INDUCTIVELY COUPLED PLASMAS 2.1. Fundamental Studies Blades and Wier (95/2879) have reviewed (46 references) on fundamental studies of the inductively coupled plasma including analytical plasma spectroscopy torch design excitation mech- anisms and temperatures electron number densities and the state of thermodynamic equilibrium. Boumans (95/186) has produced a more focused review (38 references) concerning detection limits and spectral interferences in ICP-AES.Lopez-Molinero et al. (95/1034) have used principal compo- nents analysis (PCA) to classify 39 analytically useful lines from an ICP. The lines selected were electronic transitions between states of ions and atoms and more than one line per element was considered in some cases. The spectral constants investigated were wavelength; the energy of the upper and lower atomic levels or for ionic levels the sum of ionization energy and the upper and lower ionic energy levels; the statistical weights of the upper and lower levels; and the transition probability. The PCA resulted in two significant factors. Factor 1 represented the influence of the statistical weight from the upper and lower levels and factor 2 represented the influence of energy.The lines were then divided into two groups based on the influence of these two factors. The first group were distinguished by a negative value of factor 2 and in most cases by a negative value of factor 1. The second group were defined by a positive value of factor 2. Those in group 1 could be identified as ‘soft lines’ whereas those in group 2 were categorized as ‘hard lines’. It should be noted that this study employed statistical weights as well as energy considerations for spectral line classification. Journal of Analytical Atomic Spectrometry June 1996 Vol. 11 221 RIn recent years many researchers have come to the con- clusion that the argon ICP under the conditions normally employed for analytical AES is not in local thermal equilibrium (LTE).It has been suggested that Fe atoms often used to measure ICP temperatures are neither at LTE nor distributed according to Boltzmann populations. Nakamura (95/3059) has now published evidence which indicates that the function of the number of excited Fe atoms has a linear relationship to the upper level energies of Fe atoms. This study was based upon measurements from 69 wavelength lines emitted from an ICP operated under analytical conditions. It was concluded that the Fe atoms were distributed according to Boltzmann populations and that the temperature of Fe atoms in the plasma could be obtained from the Boltzmann distribution equation. Van der Mullen and de Regt (96/C211) also advo- cated the retention of the LTE model.A study of absolute intensities revealed that the bulk of the ICP is in LTE and more careful studies were needed to unravel subtle LTE deviations. The use of the interrupted plasma method was recommended. This technique was also used to compare experimental data with the atomic distribution of Li as modelled by a time-dependent collisional radiative model a model of the vaporization of droplets and analyte and a model of the plasma velocity and temperature in the central channel. Theory and practice were found to be in agreement. Yang et al. (95/3664) in contrast reasserted that LTE was not valid and non-Boltzmann distributions occurred in the ICP and proposed that the atomic excitation process could be approxi- mated by a stepwise model. In this way the non-Boltzmann distribution of the population and de-population in the exci- tation process was considered to be an essential feature of an optically thin plasma. A formula for the non-LTE Boltzmann distribution and the corresponding bottleneck energy was also discussed.In the second part of this study on non-LTE in ICP-AES non-Saha ionization equilibrium processes were considered (95/1954). Three parameters were introduced to modify the Saha ionization equilibrium in order to account for the temperature difference between heavier particles and electrons for the emission in an optically thin ICP and for the ambipolar diffusion of ion-electron pairs. It was concluded that the overpopulation of electron number density in the cool channel of the ICP was caused principally by the charge exchange process between argon ions and analyte atoms and this in turn was enhanced by the ambipolar diffusion process.Mingzhao and Zhanxia (96/C925) re-evaluated the rate model for ICP excitation mechanisms and concluded that it could not account for non-LTE phenomena in the ICP. Perry and Fannin (96/C771) used a quantum statistical model rather than a Boltzmann model to describe the population distri- bution of electronically excited states in the ICP. This model used Fermi-Dirac counting and a single temperature to model the distribution of electronic states of both the argon support gas and first row transition elements as analytes. The role of chemical potential that arose as a fitting parameter in the model was also discussed. To avoid the need to consider whether a plasma is at LTE or not for temperature measurements a new method that involved the measurement of apparent excitation rate constants associated with different upper energy levels has been devel- oped (95/C73 1).These results were obtained using sinusoidal modulation of the magnitude of the applied rf waveform and monitoring the magnitude and phase of the resultant emitted radiation for selected transitions. A rate constant indicative of the plasma being in a thermodynamic steady-state was obtained. Carnahan et al. (95/C730 96/C686 96/C775) devel- oped an integrated approach to the investigation of monomer ion induced charge transfer in plasmas. The significance of the charge transfer mechanism was found to depend on the degree of ionization predicted by the Saha equation.Charge transfer was expected to be unimportant in situations where the analyte was predicted to be highly ionized. However if the analyte was predicted to be poorly ionized then charge transfer was likely to be significant. The authors attempted to predict the degree of charge transfer ionization based upon a knowledge of charge transfer cross-sections related electronic state con- figurations and the energy defects involving the production of those states. Comprehensive tables were constructed to corre- late these defects and determine which states were allowed charge transfer. Zhang et al. (95/2186) have extended previously published (Spectrochim. Acta 1989 44B 175) algorithms and computer programs for the determination of electron number densities (n,).The determination of n was accomplished by a least squares fitting of the entire emission profile or the wing portions of the emission profile of the H line (486.12 nm) to the theoretical Stark broadened profiles compiled at different electron temperatures.Wlsir and Blades (95/2188) surveyed the tail cone of the ICP for the distribution of n using the intensity of a single argon line assuming the atomic state distribution function lay close to LTE. Simultaneously measurements of n were made using the more conventional Stark line broaden- ing method. The spatially resolved data from the single argon line method allowed a rapid investigation of the effects of injector gas flow rate rf power and solvent plasma load (both aqueous and organic).Thomson and Rayleigh scattering have been used to study the el€ect of the sample matrix on electron densities (ne) electron temperatures (T,) and gas temperatures (T,) in a spatially resolved fashion (95/1023 95/C2988). The injector gas flow rate the observation height and the presence and absence of matrix elements (caesium lithium silver and zinc) with different ionization potentials on the analyte (Ca) were considered. Aerosols of desolvated analyte interferent and water vapour were introduced using a cooled spray chamber (14°C). The results implied that the magnitude of the change in n and Tg was typically an inverse function of the matrix ionization potential. Enhancements in n in the central channel were attributed to electron redistribution rather than matrix ionization.I[t was considered unlikely that large changes in n could result solely from matrix ionization. Changes in n and Tg were correlated with axial Ca atom and ion emission profiles. Work on interferences in ICP-AES has continued with a theoretical approach to finding the optimal observation zone in order to minimize eusily ionizable elements (EIE) matrix effects (95/1033 95/C773). The methodology was based on data from high-resolution two-dimensional radially- and lat- erally-resolved images of Ca (I) and Ca (11) emission in the presence and absence of lithium. The spatial distribution of EIE matrix effects,and the consequences for the experimental degree of analyte ionization and the excitation temperature have been studied (95/2316). It was found not surprisingly that the enhancement effect in the low regions of the plasma resulted from both e1eci:rons and ions.Enhancement effects observed in the ICP tailflame were considered to result from ion-electron recombinatlion. Suppression effects of aluminium on the alkaline earth elernents were attributed to solute vapor- ization interference. Matrix efSects associated with mineral acids have been investi- gated for many years. Brenner et al. (95/4721) found that atypical depressive effect:; on REE responses in ICP-AES could be observed in matrices containing nitric and hydrochloric acids. In the presence of nitric acid the REEs were not found to respond as a coherent group with the intensity of each REE line responding differently for increasing acid concen- trations whereas in the presence of hydrochloric acid all REE spectral lines responded similarly.These effects were observed regardless of the mode of aerosol generation. On the introduc- tion of 7 mol 1-1 nitric acid the excitation temperature of the 222 R Journal of Analytical Atomic Spectrometry June 1996 Vol. 11plasma was observed to drop from 7500 K to 7000 K. It was noted that the depressive effects were not directly correlated with the thermal and spectroscopic characteristics of the REE lines employed. The addition of 10 mol 1-’ hydrochloric acid was not observed to change the plasma temperature and consequently the depressive effects were attributed to a physical effect in the aerosol transport system. The nitric acid depressive effect was studied further and the interference was attributed to a decrease in the energy transfer from the plasma to the analyte (95/C2944 95/4722).Principal components analysis was performed on data to differentiate the behaviour of REEs and this highlighted the influence of oxide bond strength and the ionization energy in the acid effect. Similar behaviour was obtained if a sheathing gas was used. Canals et al. (95/4720) have conducted an in-depth fundamental study on the efect of mineral acids on emission intensity in ICP-AES particularly with respect to pneumatic nebulization and aerosol transport. Five mineral acids were evaluated at concentrations between 0 and 30% v/v. To investigate the causes of the matrix effects the emission signals for Ca Mn and Zn ion and atom lines were measured as were the plasma excitation temperature and the physical parameters of sample uptake rate primary and tertiary drop size distributions and total analyte transport rate.The authors came to a number of conclusions some of which confirmed the work of others and some of which contradicted previous work. The physical properties of the acid solutions were found to be at the root of the matrix effect and the degree of effect depended on the nature of the acid and whether the nebulizer system was fed by natural uptake or controlled with a pump. The sample uptake rate drop size distributions transport rates and plasma excitation conditions all contrib- uted to the matrix effect. It was found that the acids could be divided into two groups based on the degree of effect i.e.hydrochloric nitric and perchloric acids and sulfuric and phosphoric acids in accordance with their viscosities. In both natural and controlled uptake it was postulated that the cooling effect on the plasma could arise from the presence of increasing amounts of acid. In natural uptake mode an increase in acid concentration caused a decrease in uptake rate and a slight decrease of drop size in the primary aerosol. These would have opposite effects on the emission intensity but the over-all effect would be a reduction. In the controlled uptake situation the uptake rate was constant and an increase in the primary drop size distribution occurred producing a decrease in emission intensity. In addition it was considered possible that density effects could contribute to a decrease in the amount of sample reaching the plasma. Olesik and Hobbs (95/1865) have further demonstrated the potential of the mono-disperse dried droplet microparticulate injector (MDMI) for studying fundamental processes in the ICP (see also section 2.2.1.).The sizes of particles produced by this device were varied by the temperature of the drying furnace and gas flow rate. Spatially and temporally resolved emission intensities from such particles in the ICP were reported. The emission intensity peak heights and areas obtained from the individual droplets had an RSD of 1-6% except at the point of analyte vaporization. Strontium atom line emission intensity appeared to be high only during vaporiz- ation and occurred only over a region of 4 mm in the plasma for a given particle size; vaporization also appeared to take less than 80 ps.The Sr ion intensity started at a height in the plasma consistent with the onset of vaporization and continued for at least 20 mm for the same particles. By changing the size of particle it was possible to estimate the height at which they survived in the plasma; results suggested that a 5 pm drop would be vaporized within 2 mm of the load coil but a 35 pm drop would survive to 20 mm above the load coil. Horner and Hieftje (96/C671) using data of this type have produced computer simulations of the effect of rf power central channel flow rate and droplet size on the height of complete vaporiz- ation of an individual droplet. The effect of organic solvents on the ICP continues to be of interest for both practical and theoretical reasons.McCrindle and Rademeyer (95/293) investigated the effect of an ethanol loaded solution aspirated into an ICP. It was found that increasing concentrations of ethanol resulted in a proportional increase in the intensity of the Ha line and of the electron density (nJ. Mass flow rates of the aerosol also increased with ethanol concentration resulting in a relative mean droplet size increasing from 2 pm in pure water to >4.5 pm for 25% ethanol. The effect of ethanol concentration on the excitation temperature in the plasma was determined from hydrogen emission signals in a further study (95/2399). Increasing the amount of ethanol introduced to the plasma produced an increase in excitation temperature up to a concentration of 15 % v/v and thereafter the temperature decreased with increas- ing ethanol concentration.This was observed to correlate with changes in sensitivity LODs and background equivalent con- centrations (BECs) for many elements. The flow rate of the nebulizer gas was demonstrated to be more significant when ethanol was present than with pure water. Weir and Blades (95/525) considered the effect of solvent and solvent load on the background spectra and visual features obtained from an argon ICP. Solvents studied were water methanol and chloro- form at solvent loads from the maximum to minimum obtain- able. The most conspicuous features observed were emission from atomic carbon diatomic carbon and cyanide. A thermal pinch and a recirculation eddy created by the introduction of organic solvents at the base of the torch were characterized.In the second part of the study the axial spatial profiles of solvent and analyte species in a chloroform-loaded plasma were determined (95/526). The effect of chloroform load on profiles for C (I) C2 CN Mg (I) and Mg (11) was measured. The emission ratio of Mg (I) Mg (11) was used to indicate the robustness of the plasma at various rf powers and injector gas flow rates. The C2 and CN emissions were used to mark the boundaries of the aerosol channel and edge of the atomic plasma in the ‘tail-flame’ region. Liu et al. (95/1961) showed experimentally that changes in the Boltzmann factor and activity coefficient contribute to enhancement effects of ethanol in ICP-AES.On a more analytical note Boumans (95/886) discussed the different methods of estimating detection limits based on S/N S/B and S/B/(RSD of background) methods. The latter was favoured as the easiest for cross-comparison. Yngstrom (95/905) derived a relationship involving detection limits of ionic lines in an ICP from principles applied in determining atomic transition probabilities from intensity measurements in arc experiments. A new theory of spectral line intensity previously shown to support arc experimental data was extended and shown to be consistent with results of detection limits obtained in ICP spectrometers. Perkins and Gamaury (95/C2047) considered the effect of integration time on the RSD of signals in ICP-AES. It was noted that from a theoretical standpoint flicker noise may not give rise to invariance of RSD with integration time even when a strictly l/f pro- portionality in the noise power spectrum occurs but that RSD depends on the mode of data collection.From a practical point of view noise power spectra from modern ICP-AE spectrometers showed a significant variation from that pre- dicted from l/f when far from the detection limit. This was considered to be particularly significant for short integration times with CCD detectors when measuring solutions with a high concentration of analyte. Fundamental spectroscopic data has been provided by Schierle and Thorne (95/3471). This included a table of UV-visible wavelengths wavenumbers S/N and full width half height (fwhm) values for 2229 lines of 33 elements Journal of Analytical Atomic Spectrometry June 1996 Vol.11 223Rdetermined by ICP-FTS. Fourier transform and grating spectra were briefly compared. Ghazi et al. (95/1534) have observed and recorded 8361 lines of U emission between 235-500 nm by ICP-AES. Patwardhan et al. (95/2812) obtained the wavelength shift of 233U with respect to 238U and used this for the quantitative detection of 233U with high resolution ICP-AES. 2.2. Sample Introduction As well as nebulizers other components of the sample introduc- tion system i.e. peristaltic pumps spray chambers and desolv- ation devices have also been studied in this review period. In two conference presentations the problem of peristaltic pump noise has been addressed (95/C813 and 96/C915) whilst other papers have described methods for improving the transport of organic solvents to the nebulizer (95/C690) and the develop- ment of a corrosion resistant pump (95/C2985).Desolvation devices have been designed optimized and evaluated by Conver et al. (96/C732) and Akinbo and Carnahan (96/C733). Parameters investigated included the effects that the membrane drier has on noise the counter current gas flow rate tempera- ture and composition and the transport efficiency of the analyte. A fast clearing spray chamber has been described by Legere and Salin (95/908). The system utilized a nozzle situated within the spray chamber that could be used to wash the nebulizer. A high volume gas flush was also used to ensure that memory effects were kept to a minimum. It was reported that the memory effects of a 500ppm Fe or Zn solution decreased to below 10 ppb in about 20 s.2.2.1. Nebulizers Browner (95/3867) has published an overview (19 references) concerning advances made in sample introduction over the last 20 years. Some possible future developments were also discussed. As always this has been a prolific area of research with a wide variety of nebulizers being investigated. One field of active research has concerned applications of ultrasonic nebuliz- ation. This is presumably because of the high efficiency (> 25%) of ultrasonic nebulizers (USNs) which of course leads to detection limits that are improved by an order of magnitude when compared with conventional pneumatic nebulizers. Various applications have been reported. These include the analysis of water (96/319) in which the precision was 0.5-2% and recovery was 98.2 and 97.9% for Ca and Mg respectively; the analysis of canned cherries for A1 to determine whether or not the cherries contained the colorant carmine (95/2516)(in Japanese); the determination of Cd Co Cu Mo Ni Pb and Zn in 1 mol 1-l hydrochloric acid (95/2555) (in French) and the analysis of gaseous effluents for As Cr Cu Fe Mn Ti and Zn (95/4185).In this last paper the reported detection limits were 25 pg m-3 for As and below 1 pg mP3 for the other analytes. In another application a USN was used during the analysis of hydrogen chloride gas for metals leached from the walls of the gas cylinder (95/C621). Several papers have commented on the fact that USNs are so efficient that the amount of solvent reaching the plasma has to be decreased by the use of a desolvation device.A significant amount of work has been devoted to the use of on-line membrane desolvation (95/C52,95/C734,95/C756,95/C2950,96/C558). The perform- ance of USNs has also come under inspection. The use of organic solvents has been reported by Castillano and Caruso (95/C699). These authors determined the effects of desolvation conditions sample flow rates and the concentration of several organic solvents on the analyte signal. Desolvation of the aerosol to improve the performance of a USN has also been achieved by Wiederin et a!. (95/C779). The use of the desolv- ation device resulted in improved stability during the analysis of high purity acids and environmental samples. The concentric pneumutic nebulizer has received limited attention during the period under review.Olesik and Bates (95/47 19) have characteriized the aerosols produced by two such nebulizers and determined the effects of liquid and gas flow rates on the drop size distribution. An interesting appli- cation using a concentric pneumatic nebulizer has been pub- lished by Nomizu et al. (95/2265) who determined the Ca content of individual biological cells. A cell suspension in ethanol-water was sprayed by the nebulizer into a drying chamber. The dried cells which were suspended in air were then introduced to the plasma. Calibration was achieved using monodisperse calcium acetate aerosols prepared by a vibrating orifice monodisperse aerosol generator. The LOD of the system was -0.01 pg.A glass pneumatic nebulizer was also used to determine total organic carbon (95/2882). The sample was sprayed into a combustion region coated with nickel foil to prevent thermal shock. The spray introduction reportedly gave a more symmetrical signal less signal tailing and less noise when compared with conventional drip sample introduction. Monodisperse dried purticulate injectors (MDMI) have received substantial attention from Olesik and co-workers (95/1865 see also section 2.1). In this form of sample introduc- tion the drops travel along a reproducible path and virtually 100% of the sample reaches the plasma. Once in the plasma sample vaporization takes place in a well defined location (between 30 mm above the load coil to below the load coil) and therefore high sensitivity can be obtained from only a very small amount of sample. There have been several presentations that have discussed the relative merits of this technique (96/C752 95/C840 95/C841 95/C780 95/C2099 and 95/C2987). In a further publication the injector was used during time-resolved emission measurements using a solution of strontium carbonate (95/1865).The MDMI could control the size of the droplets formed and this control over the introduction of the aerosol enabled precisions of 1-6% to be obtained. Thermospray nebulizers have continued to receive some attention. This type of sample introduction technique has also been used to enhance salmple transport efficiency improve detection limits and increase sensitivity. A fused silica aperture thermospray (FSApT) has been described in 2 papers by Koropchak (96/C694,96/(2779).The device was able to intro- duce sample to the plasma at a rate in excess of 5 ml min-l. The performance was optimized by altering parameters such as the aperture diameter the sample flow rate the carrier gas flow rate and the desolvation system. The device was reported as having a poorer precision when used with a 40 MHz plasma compared with a 27 MHz one. In another report the same group of workers have described the use of a thermospray that could nebulize sample at up to 9 ml min-' (95/C838). An electrospray device for coupling chromatography with ICP-AES has been descriibed by Gotz et al. (95/2182). The system could cope with sample uptake rates as low as 10 pl min- '.The neutralization of the highly positively charged droplets of the aerosol produced by the electrospray enabled its transport to the plasma. The interface was tested by the analysis of metal acetylacetonates in methanol-water (8 2 v/v). Over a period of 1 h no drifting was observed and although the detection limit was worse than for either thermospray or conventional pneumatic nebulization the absolute amount of the analyte that could be determined was lower (because of the low uptake rate). The characteristics of aind the figures of merit produced by high efJiciency nebulizers (HENS) have been described by several groups. Olesik et al. (95/2530) described the use of a HEN that had a sample uptake rate of 50 p1 min- ' . Detection limits for the majority of lines were within a factor of 3 of those produced by conventional nebulizers using an uptake rate of 1 ml min-'. In all cases the LOD was within a factor of 8.224R Journal of Analytical Atomic Spectrometry June 1996 Vol. 1 1The aerosol characteristics were determined and it was found (by laser diffraction) that over 90% of the aerosol droplets were < 10 pm. Sample transport efficiency was 20% compared with the 1.5-2% obtained for conventional nebulizers. Phase- Doppler diagnostic studies of primary and tertiary aerosols produced by a HEN (a pneumatic type with a 79 pm capillary) have been published by Liu and Montaser (95/C834 and 95/1526). The authors used both a 2-beam and a 4-beam interferometer to measure droplet size and velocity distri- butions size-velocity correlation aerosol span droplet number density volume flux and a volume fraction of droplets <8 pm of the aerosols before injection into the plasma.The results were compared with those obtained from an aerosol produced by a conventional nebulizer. It was found that the Sauter mean diameter of the tertiary aerosol from the HEN was 2-3 pm smaller than those from the conventional nebulizer over an uptake rate of 10-1200 pl min-'. Coupling of some chromatographic techniques with ICP- AES can be difficult especially when the flow rate of the chromatography is at the pl min- ' range. Under circumstances such as these a measurable signal can only be obtained if close to 100% of the sample is transported to the plasma. The oscillating capillary nebulizer has been described by Browner and co-workers (95/C2983,95/C661 and 95/C843).This nebul- izer had a mean droplet size of less than 5 pm so the transport efficiency was nearly 100%. In addition it could operate with a sample uptake of between 1 pl min-' and 2 ml min-'. Hydraulic high pressure nebulization (HHPN) has been used as an alternative means of achieving high analyte transport efficiency. It is ncessary to use a desolvation device with this type of nebulizer because the efficiency can be >20%. A desolvation device utilizing a heater followed by a Peltier cooling system that has a 97% desolvation rate for aqueous samples and a 94% rate for methanol has been described in a paper by Luo and Berndt (95/1022). The cooling system enabled temperatures of between 15 and -40°C to be obtained.This desolvation device when used with an HHPN yielded improvements in sensitivity and LODs of an order of magnitude. A modification to the HHPN has been reported by Berndt (96/C207). A high temperature HHPN in which the solvent was heated above its boiling-point was used. The method was described as having the advantages of both HHPN and thermospray techniques (very fine droplets high aerosol yield and nebulization of saturated salt solutions). A single-bore high-pressure pneumatic nebulizer has been evaluated by Todoli et al. (95/1897). The performance of this nebulizer was found to be very favourable when compared with a conventional all-glass concentric nebulizer. Analyte transport rates were improved 1.8-3.4 fold LODs were 2-5 times better and sensitivity was enhanced by a factor of between 2.8 and 3.8.The nebulizer also exhibited no tendency to block when solutions of high salt content were nebulized and the aerosol it generated had a lower mean Sauter diameter than that produced by the Meinhard. Only two conference presentations on direct injection nebuliz- ers (DINS) have appeared during the period under review. In one application the high throughput of samples containing high solids was described (95/C573). Memory effects were reported to be minimal multi-element determinations required less than 30 s per sample and by the use of an in-line filter larger particles could be trapped thereby preventing injector blockage. In the other application (95/C620) total organic carbon was determined simultaneously with other elements.Using this technique the LOD for carbon was <0.5 ppm. Several authors have compared the performance character- istics of a range of diflerent nebulizer types. Browner (95/C660) has compared monodisperse aerosol generators thermosprays and the oscillating capillary nebulizers. The effects of con- trolling the drop size on transport efficiency desolvation vaporization excitation and ionization were discussed. A com- parison of the sensitivity and interference effects arising from USNs and Meinhard nebulizers has been published by Magi et al. (95/4350). These authors confirmed that the USN had improved sensitivity but that it also led to increased inter- ferences. Desolvated aerosols from USNs and thermosprays have been compared using scanning mobility particle spec- trometry by Koropchak et al.(95/C783). Thermospray operating temperatures USN uptake rates and the effects of dissolved solids on particle size were all addressed. In a similar paper Conver and Koropchak compared the performance of pneumatic USN and thermospray nebulizers (95/4581). The pneumatic nebulizer produced LODs that were 14-16 times inferior and sensitivities of 39-58 times inferior compared with the other systems. Acid effects (ie. the change in signal when acid concentration changes or a different acid is used) have been studied using a variety of pneumatic nebulizers (Meinhard cross-flow and conespray). The data was compared with the results obtained from a USN working with a desolv- ation system (95/4718 see also section 2.1).The effects were found to be more severe with the USN system but the data obtained using the pneumatic nebulizers indicated that the effects were caused by a change in the aerosol density and by a variation in the analyte concentration in the fraction of aerosol that reached the plasma. 2.2.2. Flow injection Flow injection (FI) has again been a relatively quiet area of research in this review period. An overview of FI as a means of sample introduction for ICP-AES ICP-MS DCP and MIP has been published by Gine et al. (95/2854). The publication also included interfaces and the use of FI to overcome inter- ferences and matrix effects. In another overview (95/3515) the advantages of using FI the development and current status of sample introduction devices and the different time- and volume-based devices were all discussed.The reliability flexi- bility robustness automation capabilities and sample con- sumption of the methods were emphasized. Flow-through microwave digestion has been the subject of investigation. A microwave heated digestion chamber has been developed and used to prepare biological materials on-line in a stopped flow manner (95/898 95/221). The device was used for the determination of several analytes in milk blood and urine. Results were reported to be quantitative and comparable to those obtained using a high-pressure ashing method. The manifold design method development and optimization of a flow-through microwave digestion system for the determi- nation of analytes in soils sediments and sludges has also been described (95/C755).The use of pow injection for analyte preconcentration and matrix separation in ICP-AES continues to remain popular. The most common type of method has involved the use of a mini-column containing either a chelating resin or ion exchange resin. Chelating resins such as iminodiacetic acid ethylcellulose have been used to retain a range of analytes (Cd Co Cu Fe Mn Ni Pb Ti V and Zn) in rain water (95/2540). In a related paper (95/2241) the same method was used to preconcentrate Ni by a factor of 100 and measure Cr. An off-line batch pre- concentration was also performed. Results of the analysis of the CRM CASS 2 nearshore seawater by this method were found to be in good agreement with certified values. Detection limits of 0.05 and 0.14 pg 1-' were reported for Cr and Ni respectively.The preparation of a new poly(acry1amidrazone- hydrazide lacmoid) chelating fibre for the preconcentration and separation of Cr Ga In and Ti from solutions has been described by Chang et al. (95/2507). The analytes were eluted from the fibre using a 3 mol 1-' hydrochloric-0.6 mol 1-' sulfuric-0.5 mol 1- nitric acid mixture. After regeneration the Journal of Analytical Atomic Spectrometry June 1996 Vol. 11 225 Rfibre could be re-used up to 10 times. Recovery of the analytes was reported to be 98-100% and there was no significant interference observed from a 20-200 fold excess of most cations. Precision was typically found to be in the range 1.4-4.6% for this method. The results obtained in the analysis of waste water and ore samples were in good agreement with those found by a GFAAS method.The synthesis and use of an epoxy-tannin chelating resin for the determination of Be Bi Cr Ga In La Sn Ti V and Y has also been described (95/4257). The precision of the method was found to be in the range 0.5-4.5%. Little interference was observed from other cations and the results reported were comparable to those obtained by a GFAAS method. A paper in Russian has described the preconcentration of REEs using diethylenetri- aminetetraacetate sorbed onto either polystyrene or cellulose (95/257). The use of a masking agent (5-sulfosalicylic acid) was required in both cases. Anion exchange resins have also been used to effect pre- concentration/matrix removal.A paper written in Chinese described the preconcentration of Mo from tap water using a micro-column (30 x 3 mm) containing Dowex 1 resin (95/963). Recovery of Mo was reported to be in the range 90-110% and the precision achieved for the method was 5.3%. The technique was also applied to soil samples. Arsenic(V) and monomethylarsonate have been preconcentrated and speciated on an AGl-X8 anion exchange resin by Ochsenkuhn-Petropolu and Schramel(96/60). Recovery was described as being 'nearly quantitative' after sequential elution using 0.05 moll-' sodium acetate-0.05 mol I-' acetic acid and 1 mol I-' hydrochloric acid. The use of this system in conjunction with a USN enabled LODs at theng 1-' level to be achieved. The procedure was applied to the analysis of BCR standard reference materials soil and sludge. Preconcentration has also been used in ICP-AES with on- line desolvation utilizing a heating and condensation device as described in a paper published in Chinese (95/3391).After optimization of the operating parameters and using a desolv- ation temperature of 120 "C the desolvation efficiency was 34.2%. A preconcentration factor of 7 was achieved with LODs being at the ng ml-' level and below. The fundamentals of flow injection ICP-AES have been studied by Israel and Barnes (95/3415,95/1886). In the former paper the dispersion characteristics were studied by measuring the width of the FI peak at 10 and 61% of the transient's height. Deviations from conventional behaviour of the disper- sion heights and widths for FI parameters were observed and differences between normal and reversed modes occurred at low flow rates or large reactor volumes.In the follow-up paper (95/1886) a similar approach was used to determine the influence of flow modes and manifold configuration. A simple and inexpensive method of achieving controlled-dispersion flow analysis has been reported by Wu et al. (95/903). The system used a computer controlled peristaltic pump coupled to an autosampler. Precision of 4.2% was achieved with an injection volume of 10 pl or larger; calibration graphs were linear over 3 orders of magnitude and a series of standards could be prepared automatically from one stock standard (10 pg ml-' of Ca). Applications of flow injection ICP-AES to appear during the period under review included the analysis of tea for Al Fe Mg Mn and Zn (95/2704) (in Chinese) the determination of base metals in gold bullion (96/417) and the determination of Cu Fe Mn and Pb in organic solvents such as methanol acetone ethanol butanol cyclohexane formaldehyde and others (95/4520) (in Chinese). Typical precision achieved for each of these analyses was 0.5-4%.The coupling of flow injection with hydride- or cold uapour generation has also received attention during this review period. A cation exchange column was used to separate the matrix (copper) from the analytr (As) prior to HG-ICP-AES (95/3786 in Chinese). The method was able to remove up to 10 mg ml-' of copper. Up to 25 samples per hour could be analysed and an LOD of 0.9 pg g-' As was reported. A similar procedure has been used to determine As Sb and Se in cobalt (95/2146). A reverse flow injection approach coupled with CV-ICP-AES has been adopted by de Andrade and Bueno to determine Hg in samples of human hail- (95/2184). The calibration was linear to 50ngml-' and a sampling rate of 120 h-' was achieved. There was negligible carry-over observed and the precision obtained was typically 1.6% RSD.Field sampling strategies have been developed by two groups of workers. Fairman et 611. (95/1505) used 8-hydroxyquinoline at pH 5 to complex the fast reactive A1 fraction from waters. The Al-complex was then adsorbed onto mini-columns (50 x 1.5 mm) containing Amberlite XAD-2 non-ionic resin. Analyte elution was carried out with 1 mol I-' HCl. Results were comparable to those obtained by an established HPLC method and the LOD was 10 pg 1-'.Problems were encoun- tered though for moorland waters because of the poor sensi- tivity of the technique. McLeod et al. (95/C771) have also discussed the use of field sampling strategies. 2.2.3. Chromatography There appears to have be:en another increase in the number of papers published on on-line chromatographic separations for ICP-AES during the review period. The majority of reports concern the use of liquid chromatography but a small number are beginning to use newer separation techniques such as capillary electrophoresis. There have been several applications of liquid chromatogra- phy (LC) coupled with ICP-AES published recently. These include the analysis of polymers (95/C721,96/C822,95/C2949) the determination of Cu compounds in metallic dyes (96/C722) the determination of protein bound B (95/2836) and the determination of cis-diarnmine (glycolato) platinum and its metabolites in urine (95/2669).In this last paper written in Japanese a Carbonex column was used to separate the Pt compounds from samples of filtered urine. The detection limit for a 1OOpl sample injection was 48 ng of Pt. In another application REEs in rockx were determined (95/4368). In this paper a cation exchange column was used with an eluent of 2-hydroxy-2-methylpropanoic acid to separate the analytes prior to detection. Limits of detection obtained were between 0.4 and 30ngml-' and precision was in the range 2-20%. The procedure was validated by the analysis of CRM's.Ion chromatography has been coupled on-line with ETV-ICP-AES and ETV-ICP-MS to determine 27 different elements in a high purity rhenium sample (97953). Recoveries were reported to be - 100% for AES but curiously > 100% for MS detection. In another investigation REEs were determined in a variety of geological materials (95/3522). The chromatography was combined with a simultaneous evaporation process in a proto- type device that also rec:overed the acid eluent. The whole process took 1 hour and fifteen minutes which was apparently an improvement by a factor of 30. The accuracy and precision of the procedure was determined by the analysis of 7 geological CRMs. Results were not significantly different from certified values and the precision obtained was in the range 1.8-18.2%.Arsenobetaine has been determined in seafood samples using ICP-AES by Ybanez et al. (95/3058). A strong anion exchange column was used for the separation. Recovery for the arseno- betaine from cockles sole and prawns was reported to be approximately 87%. The method was also used to analyse the CRM DORM-1 dogfish reference muscle. Results were achieved which were in agreement with those obtained by other workers. The precision obtained ranged from 2 to 8 YO relative. Schlegel et al. (95/3477) speciated As and Se using 226 R Journal of Analytical Atomic Spectrometry June 1996 Vol. 11anion chromatography. Hydride generation was used post- column as a method of sample introduction to the ICP in order to increase sensitivity. The calibration was linear over 2 orders of magnitude and LODs were reported to be 0.017 0.64 0.23 and 0.1 1 pg ml-' for As"' AsV Se" and dimethylar- sinic acid respectively.A similar procedure was used for Ge speciation (95/3851). A Hamilton PRP-1 column was used to separate inorganic Ge dimethyl- diethyl- trimethyl- and trie- thylgermanium. Detection limits obtained in a saline matrix were reported at the ng ml-' level. The separation of Cr"' and CrV' by HPLC using an anion exchange column has been achieved using 2 different methods by Prokisch et al. (95/3476). The procedures used gave a linear response up to 40 pg ml-' for both species and the LODs obtained were typically below 1 pg ml-'. Chromatography linked with ICP-AES has also been applied to the analysis of food samples (95/1379 and 96/C794).Vesicle mediated high-performance liquid chromatography has been applied in conjunction with ICP-AES to the speciation of toxic metals such as As Hg Se and Sn (95/3475). The chromatography was carried out on a reversed-phase column that had been modified by passing 1 mmol 1- didodecyldime- thylammonium bromide through it. The mobile phase used was dihexadecyl phosphate containing methanol. The method was applied to the speciation of As compounds in tap water and urine butyltin compounds and to Hg species in seawater. Software designed for the use of HPLC with ICP-AES has been developed in a report written in Chinese (95/2836). Unfortunately the software appears to be designed specifically for one instrument but the authors have used it successfully in the speciation of As.Less common types of chromatography have also been coupled with ICP-AES. An improvement in the recovery of Lu Tm and Yb after preconcentration using countercurrent chromatography has been reported by Pukhovskaya et al. (95/3469). The procedure was applied to the analysis of rocks. Extraction chromatography has received considerable attention recently. In this approach the bulk matrix is retained on a column whilst the analyte impurities are eluted. Applications reported included the determination of Ce Nd Pr and Sm in lanthanum oxide using a P, resin (95/232) (in Chinese); the determination of Al Ca Co Cr Cu Mg Mn Ni Pb and Zn in europium oxide using a di-( 2-ethylhexyl) phosphoric acid- Levextrel resin (95/4447); the determination of Ta in uranium compounds using a Levextrel resin (95/289)(in Chinese) and the analysis of radioactive mixed waste using a TRU-SPEC column (95/1386).Most of these techniques yielded recoveries in the range 88-106% and exhibited precision of better than 5 7 0 relative. Capillary electrophoresis (CE) has been coupled with ICP- AES to achieve elemental speciation (95/C739 95/2573). This work included the development of an interface with negligible dead volume that produced a fine aerosol of the eluate from the CE. The technique was used for the speciation of inorganic ions organometallic species and metal-ligand complexes. 2.2.4. Electrothermal vaporization A review of solid sampling electrothermal vaporization (ETV) for sample introduction in ICP-AES containing 70 references has been published by Moens et al.(95/4589). This review concentrated on the methods of standardization and described the different types of ETV device that have been coupled to the plasma. The use of matrix modifiers in electrothermal vaporization is still proving to be a popular subject for investigation. A number of different types of modifier have been used and broadly these may be classed as either the type that assists in analyte volatilization or the type that assists in matrix removal. The most common of the former type are the fluorinating agents. Freon gases have been used for many years to assist in the vaporization of refractory analytes. Ren and Salin (95/1026) have described the use of CCl,F to volatilize 1% slurries of aluminium oxide silicon(1v) oxide tantalum carbide and zir- conium(1v) oxide. In all cases the boiling-point decreased when the sample was converted from the oxide or carbide to a halide.The same was also true for tungsten carbide if an additional modifier of barium chloride was used. Freon-12 was used as a modifier in the analysis of real samples in a follow- up paper (95/1027). Four marine sediments reference materials and one coal fly ash reference material were analysed for 8 determinants. The precision obtained for the analysis was between 3 and 15%. Solid fluorinating modifiers have also been used. Hu Bin et al. (95/1841 see also J. Anal. At. Spectrom. l995,10,146R) have continued to use PTFE slurries this time to facilitate the determination of A1 in biological materials.The absolute LOD obtained was 5 pg and at a concentration of 0.2 pg ml-' the precision achieved was 2.2%. The protocol was validated by the analysis of CRMs of mussel bovine liver and serum. Results were in reasonable agreement with certified values. The same group of workers have also used PTFE to assist in the determination of A1 in waters (95/1942) (in Chinese) and B in botanical samples (95/3628). The procedures were again validated by the use of CRMs. A study (in Chinese) of the transport process of fluorination assisted ETV has also been published (95/3823). The influences of the carrier gas flow rate transport tube length and heating rate of the furnace on the analyte signal were determined and a transport mechanism proposed. Fluorination has also been used to determine Cu in biological materials (95/4254).The use of alkylation has gained in popularity as a means of sample introduction. Tao and co-workers have produced a series of papers where in-situ alkylation has been used to volatilize analytes including Be (95/1868) Cd (96/306) Ga(95/3646) and Zn (95/4498). For the cadmium and gallium work the method involved mixing the sample solution (10 pl) with 15 pl of ethylmagnesium bromide in THF. The resulting solution was dried and then vaporized at 900°C into the plasma. The LOD and linear range were 11 pg and up to 50ng for Cd and 1.9ng and up to 100ng for Ga. Precision was typically 2-3%. For Be an LOD of 1.1 pg was obtained. A different method was applied for the determination of Zn (95/4498). In this case the sample was mixed with 1.7 mol 1-' butyllithium dried and then vaporized at 500 "C.The LOD was 0.2ng and the precision for 5ng of Zn was 3.2%. The results obtained in application to the determination of Zn in pharmaceutical preparations compared well with those obtained using a GFAAS method. Palladium(II) chloride has been used as a matrix modifier during the optimization of ETV experimental parameters in the determination of impurities in silicon carbide (95/4593). A 7-stage heating program was used to analyse 5mg samples. The LODs reported for Al Fe Ti and V were 4.4 1.7 1.4 and 0.3 pg g-' respectively. An ETV device was employed which utilized exchangeable graphite cups that could be used for the examination of solid or liquid samples without the need for sample pre-treatment. Zaray and Kantor (95/4592) have employed sodium selenite and toluene vapour (introduced to the internal furnace gas) as a matrix modifer during the determination of As Cd Pb and Zn in soils and sediments by ETV-ICP-AES.The authors claimed that similar results were achieved by calibration using standard solutions solid CRMs or by the method of standard additions. The background equivalent concentration was reported to be 20 times better than that achieved by pneumatic nebulization. The cobalt fluoride-barium oxide (1 1) modifier has been used in ETV- ICP-AES for the analysis of ceramic powders (95/3433). Nickel and Zadgorska (95/4724 see also J. Anal. At. Journal of Analytical Atomic Spectrometry June 1996 Vol. 11 227 RSpectrom. l995,10,146R) have described an ETV device where the transport path between the orifice of the crucible and the base of the injector was shortened to 9mm.This device was used to analyse ceramic powders using the modifier described above. Limits of detection were reported to be at the pg level. The design of an improved ETV-ICP-AES device has been described by Kantor and Zaray (95/3450). A horizontal graph- ite tube was enclosed in a glass envelope and this enclosure made possible the transportation of the vapour from the sample injection port to the torch. The effects of the furnace temperature the flow rate of both internal and external argon the use of a sample boat and the effect of sodium selenite and CC1 and toluene vapours on the cadmium signal were exam- ined (see also 95/4592).Several applications of ETV-ICP-AES have been published. Up to 16 analytes were determined in organometallic semicon- ductor grade reagents and process chemicals (95/299,95/19 12 95/1397). The sample types investigated included trimethylind- ium trimethylgallium trimethylaluminium dimethylzinc trichloroethane and phosphorus tribromide. The furnace pro- gram started at either 0 or -2O"C and the tube was then heated to 100 and then 450 "C to remove volatile analytes and the matrix and then finally raised to 2400-2800 "C to vaporize the less volatile analytes. The authors concluded that the determination of the non-volatile analytes may be 'reasonably performed' but that for the volatile analytes the results could only be regarded as semi-quantitative.An ultrasonic agitator has been employed to ensure sample homogeniety in the analysis of slurries by ETV-ICP-AES (95/C781). The hardware employed appears to derive directly from that used in ETAAS. The method was validated by the analysis of certified coal fly ash a diet sample and oyster tissue for analytes such as Cu Mn Ni Pb and V. Mercury has been determined directly in solid samples including soil and sludge by Golloch and Goetzen (96/C919). Up to 200 mg of material could be analysed without any sample preparation and the method gave a detection limit at the pg level. A Meinhard nebulizer has been employed for sample precon- centration in ETV-ICP-AES. The nebulizer was used to spray sample onto the inner wall of a graphite furnace tube that was heated to 160°C (95/4586).The water vapour formed was removed continually by a stream of argon. After a set nebuliz- ation period the analytes were vaporized into the plasma. The method yielded an improvement in sensitivity of 2 orders of magnitude when compared with conventional nebulization. Limits of detection for Cd Cu Pb and Zn were reported as 0.06 0.04 0.3 and 0.02 ng ml-' respectively. Electrothermal vaporization has been compared with a new in-torch uaporiz- ation system in a paper by Karanassios et al. (95/4587). A manually operated rhenium wire loop had 10 pl of sample injected onto it. This was then placed in the base of the torch and heated to vaporize the sample. Initial results indicated that sensitivity achieved using this arrangement was better than that obtained by pneumatic nebulization and yielded results comparable to conventional ETV-ICP-AES.Limits of detection reported for Cd Pb Sr and Zn were 41 25 0.12 and 26 pg respectively. An ETV device connected to a capacitively coupled helium plasma was used to determine C1 in aqueous solutions and in pesticides (95/4591). A detection limit using the 837.6nm line of 5 ng was obtained and precision at 25 pgml-1 C1 was 3.2% RSD. The results achieved for C1 were in good agreement with those obtained by ion chromatography. 2.2.5. Solid sampling procedures The origins and brief history of laser ablation has been reviewed with 20 references by Miller (95/3117). Although the author admits that the explosion of papers using LA did not occur until 1985 the review emphasized the very early stages during the 1960s.An overview i n French of LA coupled with AES laser-induced fluorescencle spectrometry and ICP-AES has been published by Mauchien et al. (95/2877). The publication contained only 8 references but covered the advantages and disadvantages of the techniques. The use of laser ablation (LA) in ICP-AES now seems to be in decline following the development of LA-ICP-MS and direct LA-AES. However Noelte et al. (95/2506 95/4184) described solid sampling of steel and soils using laser ablation- ICP-AES. The spectrometer incorporated an echelle grating and a solid-state detector. Pulsation of the ablated material was compensated for by rieal-time background correction and internal standardization resulting in good accuracy and pre- cision.Caetano (96/C773) discussed the spatial emission profile in the ICP resulting froni the introduction of laser ablated material. The emission profile was studied to determine whether changes in the laser ablation conditions affected the particle size distribution OF removed material. Fernandez et al. (95/C828) compared direct AE from the laser ablation plasma with the emission intensity from an ICP-atomic emission spectrometer coupled to the laser ablation system. Results supported the hypothesis that there were two different ablation mechanisms a less efficient interaction of laser beam and test material at higher power d,ensities (> 1 GW cm-2) and a more efficient interaction at lower power densities. A xenon chloride excimer laser and a frequency tripled/quadrupled Nd:YAG laser were compared in the examination of polymers (96/C244) and glass (96/C247) by laser ablation ICP-AES.Characteristics such as the erosion rate dlepth and surface of the crater and the amount of ablated material were studied as functions of laser parameters. Analytical figures of merit including detection limit precision and accuracy were also studied as functions of these parameters. The design construction and operation of a laser ablation cell and plasma torch withiH a glove box has been described in French by Masseau (95/34.03). The system enabled the direct analysis of toxic or radioactive materials. The sample was irradiated by an externally mounted xenon chloride excimer laser operating at 308 nm and the aerosol produced was transported to the plasma by a stream of argon gas.The system was evaluated by the analysis of several alloys and high purity beryllium. The authors claimed that their ablation cell exhibited an aerosol transport efficiency of 35% which was higher than the 25% of typical cells. Detection limits were comparable to those obseirved for conventional nebulization using the same spectrometer. Liu and Horlick (95/4725 95/C836) have described an in situ LA sampling system. The sample was placed within the torch immediately below the plasma discharge uia a direct sample insertion probe. A Q-switched Nd:YAG laser was focused on the sample by a lens above the plasma. The ablated material entered the plasma directly eliminating the need for an aerosol transport step with all its concomitant errors.The emission signal had a duration of 0.7 ms in comparison with conventional LA where the signal may last for several seconds. The sensitivity of the analysis was therefore improved with limits of detection for several analytes in aluminium alloy steel and brass reported in the range from 0.015 pg g-' for Ca to 12 pg g-' for Mo. Several applications papers have also been published which concern the use of LA-ICP-AES. Noelte et al. (95/2506) have examined soil and steel samples by LA-ICP-AES using a high resolution echelle spectrometer jitted with a solid-state detector. Certified steel samples were analysed for C Cr Cu Mn Ni P S Si and V using iron as an internal standard. Linear calibrations were obtained for all analytes except for carbon and good agreement with certified values was also obtained.Precision was found to be below 1% for most analytes but less than 9% in all cases. Reference soils were analysed for Al 228R Journal of Analytical Atomic Spectrometry June 1996 Vol. 11Fe Mg Mn and Ti and again good agreement with certified values was obtained. Russo et al. (95/1669) used a krypton fluoride excimer laser with a 10Hz repetition rate to sample the same spot of a glass. Silicon was used as the internal standard and precision in the range 1-3% was obtained. Quantitative analysis was successfully demonstrated by the analysis of glasses with known composition. In another study of glass an Nd:YAG laser was used at a repetition rate of 10 Hz and at 5 mJ to ablate material for the determination of Ba Ca Co Cu K Mg Na Ni Pb Si and Zn (95/C3742).Laser ablation has also been used for the analysis of certified aluminium and manganese ores and manganese nodules for the determination of Al Ca Cu Fe K Mg Mn Si and Ti (95/2873). A comparison of conventional nebulization TIMS and LA-ICP-AES for isotopic uranium determination has been made by Goodall et al. (96/C916). The results of the determinations agreed within experimental uncertainty. The use of the intrinsic internal standard zirconium improved the precision of the sequential determination of the intensities of 235U and 238U from 1.6% to 0.17%. The determination of lanthanides and actinides in a eutectic mixture of lithium chloride-potassium chloride by LA-ICP-AES has also been reported (96/C778). A comparison of LA- and spark ablation-ICP-AES for the analysis of precious metals has been published (95/4574).It was concluded that spark ablation was the preferred method for the analysis of reference materials because of its ease of operation long-term stability high sample throughput and because there was no limitation on sample size and shape. A similar comparison has been made by Moenke-Blankenburg et al. (95/3811). Both techniques were used for the analysis of the certified geological materials galena (GFl) sphalerite (SF1) and pyrite (PS1). It was found that LA and spark ablation both produced systematic errors of less than 3% but that random errors were 9% and 5% relative respectively. Spark ablation has had only limited attention in this review period. Geological samples and related non-conducting mate- rials have been analysed using this technique by Brenner et al.(95/4726). The analysis of several reference materials for Al Ba Ca Cr Fe Mg Mn Sr Ti V Zn and Zr using silicon as an internal standard resulted in a significant improvement in accuracy. The presence of water vapour was found to increase interference effects. Fundamental questions concerning spark ablation sampling were addressed in two conference presen- tations. The effect of particle size on the analytical performance was assessed in one paper (96/C743). In the other it was described how individual optimization of the sampling and the excitation processes led to improved performance (96/C744). Slurry nebulization is still attracting attention as a means of sample introduction.The research interest in this method is split between applications and theory. Nebulization efficiency and its relationship with slurry particle size has been studied in an excellent paper by Goodall et al. (95/247). It was concluded that the maximum particle size permissible to enable representative sampling depended on the density of the mate- rial. The particle size maximum for a material with density of 1 g cm-3 was 2.9 pm but this decreased to 1.5 pm for a material with density of 7 g ~ m - ~ . It was also stated that for some carbonaceous materials micro-flocculation may occur i.e. a loose assembly of 5-10 particles would form and that this could behave in a similar manner to single particles of a much greater diameter. This would inevitably lead to lower transport efficiency and lower recovery.This micro-flocculation problem was overcome by the use of a more concentrated dispersant. The work was validated by the successful analysis of a number of different CRMs. The problem of particle size control and analytical recovery has also been tackled by Chen and McCreary (95/902). A fundamental difference was observed between the method of conversion of slurry and solution droplets to gas phase atoms. It was demonstrated that there was a reduction in the emission signal of refractory analytes in a slurry when compared with the same concen- tration in an aqueous solution. It was concluded that unit transport was not necessarily guaranteed to produce unit recovery. Ebdon et al. have optimized the multi-element analy- sis of several environmental samples by slurry atomization using a segmented array charge coupled device detector (95/4263).Simplex optimization was compared with on-board computer algorithms. Very similar operating parameters were obtained using both optimization methods. The results of the analysis of MESS 1 and BCSS 1 (sediments) BCR 145 sewage sludge and two certified rocks yielded excellent agreement with certified values. However for the sewage sludge carbonization of the sample prior to grinding and the use of a custom-built reduced-volume double-pass spray chamber were required. Simplex optimization has also been used for the analysis of ceramic powders by Broekaert et al. (95/2510). It was stated that the slurry particle size should be less than 5-10 pm.In a related paper the analysis of ceramic powders was again considered and it was noted that any particle in excess of 8 pm was not fully vaporized in the plasma (96/C717). It was recommended that the maximum size of particles introduced to the ICP should not exceed 1-4 pm. Direct sample insertion (DSI) for ICP-AES has again been included in a few papers although most of them have been conference presentations. Rattray and Salin (96/288) have pre- concentrated Cd Cu Pb and Zn on Chelex-100 resin and then inserted the analyte-laden resin directly into the plasma. For both Cu and Zn the ratio of the signal before and after pre- concentration approached the theoretical pre-concentration factor but this was not achieved for the other two analytes.This failure was attributed to the adverse effect of the remnants of the resin after ashing on the excitation properties of the plasma. The performance of the technique was improved by increasing the forward power to the plasma. Two different types of DSI devices have been compared by Karanassios and Wood (95/C837). One device employed a car aerial to bring the sample cup to the plasma and the other used a computer controlled stepper motor. The development and characteristics of the devices were described. A novel method of DSI and ETV has been developed by Rattray et al. (95/C835). A Meinhard nebulizer was used to spray the sample onto a heated graphite surface (see also section 2.2.4.). After sufficient accumulation of the sample it was vaporized into the plasma.This approach yielded improvements of sensitivity in excess of two orders of magnitude. Direct powder introduction has been described by De Silva et al. (95/C839). Dry powders were introduced to the plasma as a continuous stream of particles. Both environmental and geological samples were analysed. 2.2.6. Chemical vapour generation Two reviews have been published on the use of chemical uapour generation for ICP-AES. In one paper written in Japanese (95/1535) the use of solid phase reactions to generate hydrides halides or organometallic compounds has been reviewed (14 references). An overview containing 32 references of some less commonly used HG techniques has also been published (95/2242). The overview included the use of FI on-line electro- chemical HG HG in non-aqueous media simultaneous deter- mination of hydride and non-hydride generating analytes and the use of a cyclone-nebulizer-hydride generator. Hydride generation is still the most commonly used vapour generation technique for ICP-AES and a large number of applications of the technique continue to be published.Such applications have included the determination of As in drinking water (95/3633) As (95/3834) and Se (95/2627) in soil Sb in environmental samples (95/3490) Se in natural waters Journal of Analytical Atomic Spectrometry June 1996 Vol. 11 229R(95/C2019) and Te in plasticizers (95/3897). The determination of As Sb and Se in waters has been carried out sequentially (95/4416). Detection limits were reported in the range 0.7-6.7 pg 1-I. The calibrations graphs were linear to 1 mg 1-' and precision was typically 3%.In another publication the determination of As Bi Sb and Se in certified reference waters was discussed (95/918). A continuous flow hydride generator was used (the construction of which was described) which yielded acceptable recoveries for all analytes except Te. An HG-ICP-AES method for the determination of As in foods was described (96/347). The foodstuffs were dry ashed using magnesium nitrate-magnesium oxide as an ashing aid and the ash was then dissolved in 9 mol 1-l hydrochloric acid. This was followed by an on-line continuous separation and HG-ICP-AES determination. The procedure yielded LODs of arsenic of 0.5 ng g-' in beer 2 ng g-' in tomatoes and 50 ng g-' in mussels. The precision of these methods was found to be in the range 4-11% RSD.The procedure was validated by the analysis of certified reference materials and good agreement with certificate values was obtained. Hydride gener- ation has also been used to effect speciation (see also sec- tion 2.2.3.). Germanium was speciated in a saline matrix using LC-HG-ICP-AES (95/385 1). The operating parameters were optimized and the procedure yielded LODs at the pg I-' level. Arsenic(v) and As"' have been speciated using L-cysteine to reduce the AsV to As"' and then using a subtraction method to determine As"' itself (95/2527). This work also made use of a small co-centric hydride generator without a gas-liquid separator. For AsV and As"' the LODs and precision for a lOOngml-' standard were 3.4 and 0.7ngml-' and 1.45 and 1.21 YO respectively.Much research has been concentrated on the removal of interferences during HG-ICP-AES determinations. Thiourea has been used to mask the interference effects exerted by iron(m) cobalt(rI) nickel@) copper(Ir) zinc@) silver(I) cad- mium@) and lead(11) on the determinations of As Bi Sb Se and Te (95/24OO). The thiourea proved successful in removing interferences on As Bi and Sb but not for Se and Te. The thiourea was also used to reduce As and Sb from the penta- valent to the trivalent state. Thiourea or 1,lO-phenanthroline were used to mask the effects of iron during the determination of germanium in iron meteorites (95/2327). Although the addition of either of these complexing agents was fairly success- ful in the removal of interferences it was still recommended that standard additions should be used.In addition it was reported that the most appropriate reaction medium for ger- mane production was 0.02 mol 1-' phosphoric acid. This acid improved the sensitivity by approximately 3 orders of magni- tude when compared with conventional nebulization. The LOD was reported to be 0.063 ng ml-' for this determination. The calibration graph was linear over 5 orders of magnitude and the precision at 5 and 500 ng ml-I was 1.4 and 1.2% respectively. Complexing agents were also used for the determi- nation of Se in nickel alloys and low alloy steels (95/4700). The complexing agents effectively masked the interferences from a suite of transition metals. The protocol was validated by the analysis of CRMs.A different approach to overcoming interferences in HG-ICP-AES has been published by Wang et al. (95/2146). A flow injection approach was employed for the determination of As Se and Sb in cobalt using an on-line cation exchange resin to remove the bulk matrix. The analytes passed through the column and on elution were reacted with sodium tetrahydroborate and hydrochloric acid. The hydrides thus formed were then swept to the ICP for detection. The column had sufficient capacity to retain 10 mg ml-' of cobalt. The LODs reported for As Sb and Se were 1 2.2 and 1.3 ng ml-' respectively. Only a few papers were received concerning thefundamentals of hydride generation and its optimization for ICP-AES. A paper in Chinese (95/201) discussed the influences of the molar ratios of the reactants on the yield of germane.It was concluded that partial neutralization assisted in the production of ger- mane and that the optimum conditions existed between pH 2-12. A study (in Chinese) of the influence of ICP operating parameters and the hydride generating conditions on the signals of As Ge and Se has been made by Wu and Shao (95/3390). In addition a study of the interference effects exerted by a suite of metals was also made. It was found that the presence of copper increased the Ge signal. The simultaneous determination of As and Pb hydrides and an investigation into the reaction medium has been reported by Chen et al. (95/4550). A comparison of two reaction media was made. One consisted of 1% nitroso R salt in 0.3 moll-' hydrochloric acid and the other consisted of 5% potassium hexacyano- ferrate(u1) and 2% sodiurn tetrahydroborate in 0.3 mol 1-' hydrochloric acid.Detection limits for As"' AsV and Pb" for both systems were tabulated and it was found that the potassium hexacyanoferrate medium yielded better LODs. A solid-phase hydride generation technique for silicon determi- nations has been described by Kumamaru et al. (95/3061). An aqueous sample was dried on a sample cuvette and lithium aluminium hydride was added. After further drying the cuvette was heated to 7OO0C and the silane formed was introduced directly to the ICP. Optimization of the amount of reagents the heating program and the argon carrier gas flow yielded an LOD of 0.03 ng. The calibration graph was linear to at least 100 ng and the precision (of ten measurements of a 1 ng Si sample was 2.7%.The method was applied to the determi- nation of Si in river water. Other types of vapour generation have also been studied. The alkaline mode of hydride generation has again been investi- gated by Qiu et al. who have followed last year's conference presentation with a paper written in Chinese (95/975 see also J. Anal. At. Spectrom. 1995 10 147R). Thus As Bi Ge Pb Sb Se Sn and Te have all been mixed with sodium hydroxide sodium tetrahydroborate and hydrochloric acid to form their respective hydrides and 1 he optimum conditions for this formation were established. Interferences from the VIII and Ib group elements were reporledly avoided by the method. Cold vapour generation has been used to determine Hg in a variety of environmental samples (plants soil and water) (95/985).The samples were digested in nitric acid and potassium dichro- mate and then treated with potassium permanganate until the solution remained purple 01- until a brown precipitate formed. After heating oxalic acid was added until the solution went clear or turned milky. Vapour generation occurred on mixing the digest with 10 mol 1-l hydrochloric acid and 6% sodium tetrahydroborate in 5% sodium hydroxide. The LOD was reported as being 0.2 pg 1-' and recoveries ranged from 64.8 to 97%. Iodine has again been determined by the oxidation of iodide-containing solutions with nitric acid (95/3783) (in Chinese). The iodine contaiining solution was then nebulized and the vapour produced lby this method entered the torch directly.This method reputedly enhanced the sensitivity of the analysis by over two orders of magnitude with the LOD improving from 192.5 to 0.85 pg ml-'. 2.3. Instrumental Developments Beauchemin et al. (95/185) reviewed all aspects of plasma emission spectrometry including sample pre-treatment sample introduction atomization and excitation sources detection ;systems and data acquisition and processing. Zander (95/3680) reviewed (20 references) fifty years of commercial instrumen- tation for atomic emission spectrometry. The key features of developments were identified and put into context with demands on manufacturers for equipment. The development of ICP spectrometry from 19'74 to the present day particularly 230R Journal of Analytical Atomic Spectrometry June 1996 Vol.11of techniques was reviewed (20 references) by Tappe and Ohls (95/979). Plasma conditions aerosol introduction and spectro- scopic detectors were discussed. 2.3.1. ICP and other related sources The beginning of the commercial battle between axial and radial viewing of plasmas was reported last year. Assessments of axial viewing have predominated at conferences in the year under review (95/C618 95/C624 95/C2074 95/C2081 95/C2973 95/C2974 95/C2975 95/C2976 96/C826 96/C827 96/C828 96/C830 and 96/C831). The sole riposte came in the form of a presentation pointing out the benefits of optimizing plasma parameters in the radial mode (96/C829). This rather artificial debate looks like being resolved commercially at least by the introduction of dual-view optics.Elsewhere academic researchers continue to develop specialist and novel spectroscopic sources. Hornsby and Farrell (95/147 1 95/3086) described modified reflectometer based systems for coupling ICP sources and rf generators to ensure minimum reflected power and therefore best efficiency of power transfer. The reflectometer signal was used to adjust the frequency of a free running generator and minimize reflected power irrespective of plasma conditions. The system was expected to work best with solid state rf generators with a low power variable frequency oscillator feeding a high powered amplifier. Inductively coupled plasmas with low argon consumption continue to be developed. Yang et al. (95/4366) detailed the analytical characteristics of a low flow/low power ICP.Although the net intensity of the signals was lower the S/B improved because the background decreased faster with decreasing rf input power. The detection limits were compar- able to those of a moderate-power ICP. Ionization interferences were observed to increase with carrier gas flow rate but did not vary with changes in rf power. Dudnikov et al. (96/377) described a new instrument with an argon consumption of only 5 1 min - '. The spectroanalytical characteristics of several types of torch using water cooling were discussed (96/379). Detection limits were reported for Cu Mn and Zn these were 2-4 times better than those obtained using a conventional Fassel-type torch. Luge et al. (95/4590 95/C2084) reported analytical figures of merit for different sample introduction methods when using a low power stabilized capacitative plasma (SCP) source for atomic emission spectrometry.The source operated at 27.12 MHz with a power of 150 W and gas flows between 1 and 2 1 min-'. Argon helium and an argon-hydrogen mixture were tested as support gases. Sample introduction by electro- thermal evaporation was compared with that from hydride generation and pneumatic nebulization with subsequent desolvation. In most cases detection limits using all three support gases were similar and were in the 10-500ngml-I range for all the sample introduction techniques employed. Using electrothermal vaporization absolute detection limits were obtained which were approximately 1OOpg for Cu Ca and Mg.It was concluded that the dry methods of sample introduction were superior for this source. When these figures of merit were compared with literature data for a number of different MIP sources the SCP source was claimed to show much potential. A similar system was described by Katschthaler et al. (95/4591) using a helium support gas and graphite furnace electrothermal introduction. The analytical feasibility of the system was tested for the determination of C1 (using atomic emission at 837.6 nm) as chloride in aqueous solutions and as chlorinated hydrocarbons in methanol. The detection limit for chloride was 5 ng and the precisian at the 25 pg ml-' level was 3.2%. Good agreement with ion chroma- tography was found in a series of natural water test materials.Cordos et al. (95/3107) have produced a novel capacitively coupled plasma (CCP)-atomic emission spectrometer. The rf generator operated at 27.12 MHz with a power of 185 W and this was fed to a torch with a central water cooled tungsten electrode. A counter electrode was placed on the outside of the 15mm quartz tube used to contain the discharge. The support gas both for the plasma and nebulization was argon with a total flow between 0.4 and 1.5 1 min-'. Aqueous test solutions were nebulized with a conventional Meinhard nebul- izer and peristaltic pump the aerosol being fed into a PTFE mixing chamber where additional gas could be added. The aerosol entered the torch through 12 holes placed concentri- cally around and inclined towards (at 12.5") the tip of the centre electrode.The plasma was observed using a conventional 35 cm focal length scanning monochromator with photomul- tiplier detection. Limits of detection for Cu Pb and Zn were 28 450 and 700 ng ml - ' respectively. This system was used in a selective extraction study of sedimented dusts and soil; results were found to be comparable with those obtained by AAS. Beale et al. (95/3070) investigated a low pressure planar inductively coupled plasma source using argon as a support gas for materials processing. The source was excited at one end by a spiral antenna feed with rf energy at 13.6 MHz. Ar atomic emission was measured over pressure ranges of 10-100 mtorr and at rf power levels between 100 and 200 W. Abel inversion of line-integrated intensities yielded two-dimensional emission profiles and in all cases the emission intensity was found to peak in a ring-shaped region close to the antenna where the rf field was strongest.A local emission intensity was also observed near the centre of the plasma where the electron density peaked. The fundamentals of mixed gas plasmas have been studied by Sesi et al. (95/2190). It was shown that adding helium nitrogen or hydrogen to a conventional argon ICP caused significant changes in the spatial distributions of electron density electron and gas temperatures as well as calcium ion emission. The degree of these changes was dependent on the gas its introduction rate and whether it was introduced into the auxiliary or injector gas flow of the ICP torch. The additional gas was also observed to affect the rate at which the sample was volatilized and might be used to minimize associated volatilization matrix effects.It was also considered that there might be opportunities to eliminate inter-element matrix effects over a region larger than the normal cross-over point of suppression/enhancement by manipulation of electron densities and temperatures and heavy particle temperatures. Okino et al. (95/ 925) observed that a conventional torch for use with argon did not produce a stable plasma when used with helium. A new torch was designed with an improved vortex flow that had a smaller diameter gas inlet and a reduced distance between gas inlet and plasma generating region. The new plasma was formed at 40.68 MHz using >500 W of rf power a plasma gas flow rate of >16 1 min-' and a carrier gas flow rate of > 1.0 1 min-'.Spectrochemical measurements on this plasma were made (95/2549) including electron number densities helium excitation temperature and hydroxy radical rotation temperature. Introduction of the carrier gas was observed to increase the electron number density and decrease the rotational temperature and it was concluded that the introduction of aqueous solutions would have a more severe effect than on an argon plasma. A toroidal 'Gas Insulated Plasma' source was developed by Okino et al. (95/3084). The initial argon plasma was obtained at a gas pressure of a few torr in a toroidal discharge tube by an rf field and then the gas pressure was raised gradually down the tube. A secondary vortex gas flow was added to the outside of the discharge to insulate the tube wall.This allowed a stable toroidal plasma to be formed up to 760 torr. The plasma was characterized by Journal of Analytical Atomic Spectrometry June 1996 Vol. 11 231 Rspectroscopic measurement of emission intensity excitation temperature and electron number density. The fundamental properties of a helium plasma were measured using high resolution Fourier transform spectrometry (95/2151). The helium ICP was formed using a conventional 27.12 MHz rf generator and Fassel-type torch. The He ICP was sustained with rf powers of 1.4-1.5 kW and plasma and injector gas flows of 7 and 1 1 min-l respectively. The emission observation height was 25 mm above the load coil. ‘Wet’ samples of Fe were introduced by a glass frit type nebulizer and spray chamber; for ‘dry’ plasma measurements gaseous Fe,(CO)4 was sublimed from solid in an enclosed container.A number of important conclusions were drawn as to the efficacy of a helium ICP. Line widths of 3-4 pm for Fe (I) were similar to those from an argon ICP. The ‘average’ Doppler temperature estimated for a wet helium plasma was 3900 K compared with 7500 K for an argon plasma. Both the OH and N,’ rotational temperatures were less for the helium plasma and because of these lower gas temperatures current helium ICP sources will not atomize refractory elements as well as argon ICP systems. A lack of Boltzmann equilibrium was observed and the Fe excitation temperature measured was lower than that from an argon ICP.It was considered that this should not be an indicator of lower excitation capability as electron temperature is a better gauge of this. Finally electron number densities were observed to be higher in both the wet and dry helium plasma than in an argon plasma. This work was further extended to the measurement of rotational temperatures of argon-nitrogen mixed gas plasmas (95/2154). The lowest rotational temperature of 5500 K was measured with a 100% nitrogen plasma gas and the highest of 10000 K was obtained with a 17% mixture of nitrogen in argon plasma gas. This compared with a rotational temperature of 7800K for a pure argon ICP. The results of this work were broadened and the state of the art for different plasma gases reviewed by Montaser et al.(96/C215). Wagatsuma et al. (95/1879) con- sidered not only argon-nitrogen binary gas mixtures for ICP source but also argon-nitrogen-helium ternary mixtures. Atomic emission for seven different elements with different ionization potentials were considered. It was concluded that when compared with an argon plasma the argon-nitrogen binary gas mixtures required higher carrier gas flow rates to obtain best S/B and the ternary mixture had a better S/B due to suppression of the background from nitrogen by the helium. Pack and Hieftje (95/C596) considered the requirements of a tandem ICP-MIP source for AES when using mixed gas plasmas i.e. the first source should have a high thermal temperature for vaporization and atomization while the second source should have high excitation and ionization potential.It was noted that the MIP was susceptible to problems with the addition of foreign gases and therefore in mixed gas tandem sources the choice of gas additive should be to increase the excitation temperature or create a more stable plasma. Research on the sealed inductively coupled plasma sources by Barnes and co-workers has moved on all fronts and a number of publications have appeared on this subject in the literature. To avoid tedious cycles of experimental work computer simu- lation has been used to investigate fundamental processes in the enclosed ICP such as thermodynamic and fluid flow fields when monatomic support gases are used (96/269). The use of these sources with molecular gases was also considered (96/270 95/C2097).The application of this technology appears to be of particular interest in the characterization of high specifica- tion gases for the electronics fabrication industry. The use of sealed source ICPs has been reported in the analysis of chlorine gas (95/1536 95/21 85) and anhydrous hydrogen chloride (95/329). Goldberg and co-workers (95/C592 95/C593 95/C4746) have continued development work on high frequency capacit- ative discharge plasma gun sources for AES. The S/B was found to be optimized for the plasma gun source when using the highest energy low inductance discharges to achieve efficient atomization. Atomic em:ission was collected and integrated only from the upper reaches of the plasma plume (>10mm) after the first emission pulse (>75 ps) in order to discriminate against continuum background signals and maximize S/B.2.3.2. Spectrometers Ciurczak (95/1038) has reviewed the components required for building the perfect spectrometer including sources mono- chromators and detectors. A number of interesting studies have been made on individual spectrometer components that may lead to improved performance in the future. Woods et al. (95/1226) observed that the primary contributor to diflraction grating based spectrometer scattered light was the grating itself It was concluded from measuring the scattered light properties of 10 diffraction gratings and applying this to 3 different spectrometers that there are two components of grating scattered light. These two components are a Lorentzian type predicted from diffraction theory and a constant back- ground consistent with Rayleigh scattering from microscopic surface defects. It was also discovered that multiple replicas from a master grating had a 1.1-2 fold increase in scattered light.Loewen et al. (95/3067) performed a detailed experimen- tal theoretical and numerical study on several echelle difSrac- tion gratings that work at low (8-13) to very high (660) diffraction orders. Noticeable deviations from the scalar model were detected both experimentally and numerically. Several reasons for differences be tween real and theoretical echelles such as material index profile and groove angle deviations were considered and their effects on performance studied. The influence of the width of an intermediate slit on optical transfer functions between two identical monochromators was investi- gated by Mattei and Gil (95/1236).The special case of a double-pass parabolized Ebert monochromator was con- sidered. Florek and Becker-Ross (95/1484) have designed a water-filled reflection prisrn as part of their high-performance double-echelle monochromator system. Although intended for AAS the technology may have applications in ICP-AES. Yang et al. (95/4249) reported the results of an experimental study on an echelle-CCD based ICP-atomic emission spectrometer. An observed S/N enhancement was considered important due to the poor sensitivity of the charge coupled detector used. Correction methods for the effect of the CCD noise pattern on dark current and sensitivity were described. The dynamic range of the detector was extended to six orders of magnitude by multiple-time or multiple-line integrations.Sadler et al. (95/1501) have devised an automatic wavelength calibration procedure for echelle spectrometers with cross-dispersion and CCD-CID detectors. The novelty of this approach was to model the difference between an ideal conceptualized spec- trometer and the physical instrument rather than the more conventional modelling of spectrometer dispersion. The pro- cedure was intended to compensate for both manufacturing tolerances and laboratory conditions such as temperature and pressure. Although not yet tested in practice simulation sug- gests that sub-pixel accuracy in the prediction of spectral lines on the detector should be possible. Morrisey et al.(96/173) reported an average quantum efficiency of 40% from 116.4 to 520 nm using a modified commercial 24 pm-pixel CCD device. The device was thinned and the backside illuminated. The measured quantum efficiencies were compared with models based on UV reflectivities measured on the device. With the current eclipsing of photomultiplier tubes by CCD/CID detec- tors it is heartening to see that some workers are at least investigating potential prloblems. Koirtyohann and Yates (95/C563 and 95/C2048) investigated what happens when 232R Journal of Analytical Atomic Spectrometry June 1996 V01.11individual pixels of semiconductor light detectors become saturated. It was concluded that when saturation was due to long integration times of lines with moderate intensity no blooming to adjacent pixels could be observed even at charge levels of 1000 times saturation.Therefore analytically useful data could be collected from the line wings or close-by weak lines of a second element providing appropriate background correction could be made. Extremely intense light levels that caused saturation in a few milliseconds yielded a more complex behaviour and correct data depended on the readout method- ology but could be explained on the basis of the fundamental characteristics of the detector. In a promising development of ICP-AES technology a novel high resolution spectrometer using an acousto-optic tunable filter (AOTF) as a prefilter with a lens-less fibre-optic Fabry- Perot interferometer was described (95/C2971). There were no mechanical tuning elements in the system and all wavelength selection was computer controlled.The AOTF was tuned to transmit a spectral window of approximately 0.6 nm around the elements emission line from the ICP. The transmitted light was then focused on the input face of a single mode fibre-optic of the FFB. The optical coatings of the interferometric cavity were directly on the fibre faces. The cavity was tuned by scanning a concentric piezoelectric element. The output of the FFB was directed onto a photomultiplier tube for detection. The output of the PMT was amplified and counted using a multichannel scalar averager. An emission spectrum for a 1 1 mixture of uranium-235 and uranium-238 demonstrated the ample resolution of the system for determining actinide iso- topes and was comparable to that achievable using a 1.5 m monochromator. Supich and Carnahan (96/C914) also used a acousto-optic device within a ICP spectrometer.An acousto- optic modulator was placed at the exit slit of a spectrometer; frequency and/or amplitude modulation of the high frequency sound source allowed the atomic emission light to be either modulated in wavelength or amplitude. In this way efficient background correction could be performed in microseconds. 2.3.3. Chemometrics and instrumental control The use of chemometrics and computerized data processing continues in its rise in popularity perhaps because a more powerful PC is much cheaper than buying a new spectrometer with better dispersion. This rise in interest seems likely to increase particularly for multi-dimensional chemometrics with the advent of array detectors for simultaneous multi-line data acquisition in AES.Mermet (95/2193) has returned to basics and investigated the quality of calibration in a scanning monochromator system. A procedure based on confidence limits rather than a regression coefficient was proposed to be more appropriate for assessing calibration quality. Application of this procedure indicated that the use of three standards for calibration should be discouraged and that four or five were needed to determine concentrations adequately at both the high and low end of the range. Instrument manufacturers were taken to task for usually supplying software that used unweighted regression. It was recommended that this should only be used over calibration ranges of a decade and for greater ranges weighted regression should be used.Whether manufacturers take any notice of this significant conclusion given that others have tried to convince them previously remains to be seen. It was noted that the procedure would only concern the confidence limits due to the regression but not account for systematic errors resulting from unmatched test solutions and standards. Zhang and Karanassios (95/C814) have evaluated the use of partial least squares (PLS) to correct for spectral inter- ferences theoretically and practically with a scanning mono- chromator and polychromator systems. Kalny and Have1 (95/C3756) also evaluated PLS using a spectrometer with an echelle grating. Model mixtures of REE solutions were used because of the demanding nature of their rich line spectra.A calcium matrix was also investigated to model non- spectroscopic interferences. Salit (96/C910) studied the per- formance of a simple multiple least squares (MLS) approach under real-world conditions to multivariate calibration of spectrometers with array type detectors. Performance limi- tations were identified in several areas including poor fits of the components because of contamination sensitivity to wave- length drift and noise artefacts in low S/N spectra. Luan et al. (95/4738) applied the generalized standard additions method (GSAM) to an echelle based polychromator system with a segmented-array charge coupled device detector allowing direct visual examination of spectral overlaps.A slit translation capability added the possibility of using all spectral information throughout the spectrum to reduce noise through signal averaging. Pure spectra of each sample component were extracted through GSAM calculations. The validity of the GSAM procedure to produce a pure spectrum was confirmed by comparison with the original experimental spectrum. Several limitations of GSAM were identified. It is necessary to know the approximate concentration of analyte in the sample to calculate the amount of spike to be added. Contamination can be a problem particularly when adding multi-element spikes. The present form of GSAM will not correct for a completely unknown spectral interference but the use of the generalized rank annihilation method (GRAM) was posed as a possible solution to this particular problem.Al-Ammar (95/2855) has detailed a method for the selection of internal reference lines in ICP-AES derived from GSAM and the parameter-related internal standardization method (PRISM). Danzer and Venth (95/2850) claimed an improvement in some analytical parameters such as sensitivity and detection limit when determining minor elements such as Cry Mn and Ni in low alloy steels using multivariate techniques such as principal component regression (PCR) and partial least squares regression (PLR). The problem of colinearity was discussed. Schierle and Otto (95/1002) developed a combined qualitative and semi- quantitative approach to analysis using multivariate cali- bration. Elements were first qualitatively eliminated from the analysis by the absence of their most prominent line.Quantitative analysis of the remaining elements was performed by multivariate calibration with the most prominent line of each element and possible interferences being noted. Multivariate detection limits were then applied as a criterion for the true presence of an element. Principal component analysis (PCA) has found a variety of uses in ICP-AES. Riley et al. (95/1036) have followed up previous work (see 94/2052 and 94/C3445) with a computer program ‘Spectral Line Interference Modelling’ that uses the relative intensities of more than 3 lines to predict spectral interferences without knowledge of test material matrix elements. Lopez-Molinero et al. (95/1034) have revisited the work of Ramsey and Thompson in the early 1980s to use PCA to identify ‘soft’ and ‘hard’ line behaviour.Cave (95/C2046) has also extended their PCA work to use background emission lines of Ar H 0 and OH as internal standards rather than added elements. Karanassios et al. (95/2159 95/C712) applied Fourier trans- form based cross-correlation for the automated detection of elements in microlitre samples introduced by wire loop in-torch vaporization (ITV) into an ICP-atomic emission spectrometer. The cross-correlation of multi-component sample and library single element spectra (obtained using a photodiode array) allowed rapid automatic identification of the presence of elements. Artificial neural nets have been used for diagnostic purposes by Morgan et al. (95/3071). After first considering neural network concepts and algorithms their use was illus- trated in the determination of plasma electron temperatures Journal of Analytical Atomic Spectrometry June 1996 Vol.I 1 233Rand by the analysis of spectral data. Neural networks were considered to be an efficient way of handling the large amounts of data produced by plasma spectroscopic instrumentation. Catasus et al. (96/345) applied traditional multi-layer per- ceptron neural networks and generalized regression neural networks (GRNN) to the problems of spectral interference matrix effects and measurement drift in ICP-AES analysis. The performance of these networks was compared with multiple linear regression (MLR). The GRNN reduced the error due to Fe interference on Zn from 81% to 24% compared with 49% by MLR.It was less successful in reducing the matrix effects by 10000 pg g-’ Mg from 67% to 55%. But GRNN also reduced drift due to fluctuating power levels from 2.3% to 0.6%. The related area of pattern recognition has been investigated by Branagh et al. (96/342) for sample classification using elemental composition. Three pattern recognition tech- niques k-nearest neighbour Bayesian analysis and the C4.5 inductive learning algorithm were compared for their ability to classify 71 reference materials. The C4.5 inductive learning algorithm had the best performance in terms of classification accuracy result clarity and speed. The Bayesian analysis performed worst but had the advantage of providing a ‘good- ness of fit’ statistic. The possibilities of improved background correction through chemometrics has been investigated by several groups.Mattee and Visser (95/4741) attempted automatic background correc- tion by means of repetitive sinusoidal wavelength scanning and Fourier analysis but with specific restrictions. Salit et al. (95/2169) evaluated two algorithms for fully automated back- ground correction. The first was a ‘heuristic’ approach which attempted to mimic the analyst selecting background correc- tion intervals for each test material and standard. Each sample had unique wavelengths selected from which the intensity of the background was estimated. These were chosen according to qualitative guidelines as opposed to explicit quantitative rules. The second was a ‘statistical’ background estimation.The statistical background correction algorithm iteratively identified those data which did not represent the spectral background using rigorous statistical tests and then masked them out. The data remaining were used for estimating the background from a least-squares curve fit. The heuristic approach proved to be robust in performing the correction but produced a bias in the background estimates. It was concluded that with further work the statistical approach was expected to demonstrate superior robustness and precision with respect to the heuristic approach. Chen et al. (95/4390) compared a polynomial model for fitting backgrounds with a statistical approach when using diode-array detectors. They observed when the background contained structure or line overlap wings that the statistical method produced superior results without the need for prior knowledge of test material composition or visual inspection of the data.Coles et al. (96/330) described a procedure for improving detection limits during transient signal analysis by correlated background correction. It was observed that fluctuations in the atomic emission background for many lines was correlated with respect to time. This allowed the changes in backgrounds under transient signals to be estimated from lines that exhib- ited no analyte or interference responses. Detection limits typically improved by a factor of 5 over those estimated without any correction of background fluctuations. Kalman Jiltering is still providing a significant input to the literature after more than a decade of research (95/C812 96/C920).Background and interference correction continue to rcprcscnt thc main thrust of the research interest. The practi- cality of this technique must now be in question as it has yet to be taken up as a routine analytical methodology despite much work. Interested readers are referred to recent publi- cations in this field (95/248 95/1934 95/1959 95/2187 9513623 95/4244). Zheng and co-workers (95/1958) have used the Monte Carlo technique for studying chemical and physical processes in ICP- AES. A computer program was described which was used to assess the impact of the physical properties of the analyte solution the operating conditions and dimensions of the nebulizer on nebulizer efficiency and total mass transport.The effects of parameters such as sample introduction rate carrier gas flow rate and nebulizer geometry on nebulizer efficiency and mass transport rate were investigated using Cd as an analyte (95/3859). This teclinique was finally applied (95/3665) to the simulation of evaporation processes in the plasma itself. Various software packages have been described to aid in ICP-AES analysis. Yang et al. (95/3669) produced an electronic consultant for the selection of analytical spectral lines. It could simulate a predicted interference spectrum using a combination of a line database and knowledge of the ICP discharge and the atom and ion excitation processes. The system was intended to allow the choice of (optimal analytical lines or verify experimental results for particular matrices. Ba’nhidi and Paksy (95/3441) have developed a modular package of statistical tests for preliminary data treatment including drift normality t and F tests. Proposals for the choice and sequence of tests were made on the basis of experimental results.Galley et al. (95/3473) developed a program that allowed automated sim- plex optimization of rf power intermediate and nebulizer argon flow and sample uptake rate for a monochromatic imaging ICP-AES. A 2-13 detector system simultaneously collected responses across the plasma. Surovell (95/4048) described a spreadsheet macro that accessed data files to display visible emission spectra for more than 80 elements. 3. MICROWAVE-INDUCED PLASMAS 3.1. Fundamental Studies The number of papers reporting investigations of plasma characteristics has shown a slight increase on previous years.Madrid et al. (95/2170) described the noise characteristics of an argon plasma discharge using nebulizer-based sample intro- duction with and without dlesolvation. Flicker noise was domi- nant below 1 Hz and white noise was dominant below 100 Hz but discrete noise peaks welre found in the range up to 300 Hz. The noise frequency characteristics were strongly dependent upon argon flow rate and it was proposed that gas flow turbulence from argon leaving the torch was the source. Pak and Koirtyohann (95/1029) have characterized a 500 W He MIP producing spatial profiles of excitation temperature ionization temperature roltational temperature and electron number density. As would be expected the apparent tempera- tures varied considerably depending upon the measurement method.The experimental data indicated overpopulation of the upper energy levels of the rotational energy distribution which the authors suggested was to support the existence of high energy electron species in the plasma. 3.2. Instrumentation Sanz-Medel and co-workers have performed a detailed examin- ation of microwme-induced plasma instrumentation for the determination of Hg (95/’1021) and of chlorinated hydro- carbons (95/1026). Argon and helium plasmas in conjunction with a Beenaker cavity with capillary and tangential torches a surfatron and a microwave plasma torch were compared and their performance evaluated in terms of plasma operating parameters and interferences.For the determination of Hg the authors considered that the surfatron system offered the best LOD 10 pg ml-’ whilst for the determination of chlorinated hydrocarbons the Beenak:er cavity was the most sensitive although the microwave plasma torch gave greater stability 234 R Journal of Analytical Atomic Spectrometry June 1996 Vol. I Iwith high levels of organic compounds. The group at Jilin University continue to report work with their microwave- induced plasma systems in this instance reporting the analytical characteristics of a 70 W He MIP for the determination of REEs. The same group also reported upon the spectroscopic behaviour of Br C1 I P and S (95/237). Spencer and Winefordner (95/332) have described a CCP torch and its application to the determination of Si in organic matrices.The torch was comprised of two concentric quartz tubes the inner of which held the electrode coupled to the microwave field. Moisan et al. (95/4737) have described a surfatron based microwave plasma torch which enables a wide range of operating conditions to be used and reduces torch erosion at higher power densities. The construction of the device and the experiments performed to improve power transfer to the plasma and to improve the stability of the discharge under a range of conditions were described in detail. Instrumentation for the continuous monitoring of Hg in flue gases has been described by Siemens et al. (95/3373). The Hg was trapped in a potassium dichromate-nitric acid absorption solution and then determined by vapour generation MIP-AES.3.3. Sample Introduction 3.3.1. Direct nebulization A Hildebrand nebulizer has been used without aerosol desolv- ation for the direct analysis of urine by MIP-AES (95/1177). Suppression of analyte signal by matrix components was significant but was corrected by calibration using the standard additions method. Spencer et al. (95/906) have investigated the determination of halogens in organic and aqueous media using an 850 W He CCP. Organochlorine and organofluorine com- pounds in kerosine or inorganic salts in water were nebulized directly into the plasma. Limits of detection of 0.4 and 1 mg ml-1 were reported for C1 and F respectively in organic compounds. For aqueous samples C1 emission was weak and no F emission was found. The determination of platinum group metals has been reported by Yu et al.(95/203) who used ultrasonic nebulization and desolvation prior to analysis by argon MIP-AES. Limits of detection were reported in the 1-10ngml-I range. Jankowski (95/930) has also studied these determinands using pneumatic nebulization directly linked to a 150 W He MIP to achieve LODs between 0.05 and 0.5 mg ml-I. On-line anion preconcentration coupled with MIP-AES has also been reported (95/3778 95/4711 96/C766). Chloro- complexes for a range of analytes were concentrated on an anion exchange resin and subsequently eluted and introduced into an argon MIP using pneumatic nebulization with desolv- ation. Other reports concerning nebulization of samples into MIPs included the determination of A1 and Fe (95/2369) Cu (95/397) and Hg (95/284).3.3.2. Electrothermal vaporization Wensing et al. have described an electrothermal vaporization microwave induced plasma atomic emission method for the determination of lead in whole blood (95/2237). A 5 ml aliquot of the sample was placed on the plasma supporting electrode of a CCP dried using microwaves ashed using a low power plasma then atomized and excited with a higher power plasma. The method gave an LOD of 7 mg 1-1 (35 pg) using calibration by standard addition. 3.3.3. Chemical Vapour Generation Continuous flow hydride generation has been used for the determination of As Sb and Se in a 115 W Ar MIP at 50 torr (6.5 kPa). Detection limits of 0.7 0.9 and 4.1 ng ml-' were reported for As Sb and Se respectively (95/1671). Luge and Broekaert (95/2330) have compared continuous flow and discrete sample introduction for the determination of As.The discrete procedure gave an LOD of 1 mg 1-1 for As whilst the continuous flow method gave an LOD of 50 ng ml-I As. Interference effects were also investigated. A comparison of atmospheric pressure and reduced pressure microwave plasmas for the determination of Hg has been made (95/4183). The reduced pressure argon MIP yielded an LOD of 0.7 pg ml-' compared with 8 pg ml-' for the argon plasma at atmospheric pressure. The helium MIPs studied gave com- parable LODs of 3 and 4 pg ml-I at reduced and atmospheric pressure respectively. Both argon and helium reduced-pressure MIPs demonstrated greater stability with the introduction of other gases. Nakahara et al.(95/4585) have described a continuous flow system for the determination of S using an atmospheric pressure helium MIP combined with a nitrogen-purged monochroma- tor. Limits of detection were reported of 0.13 ng ml-l for H,S and 1.3 ng ml-I for SOz. 3.3.4. Direct analysis of solids Pak and Koirtyohann (95/330) have reported the use of spark ablation for sample introduction to an argon MIP. A spark was formed between two electrodes in the sampling chamber and the products were swept into the MIP. Limits of detection of approximately 10mg 8-l were obtained for a range of elements in low alloy steel and aluminium alloy. Other reports which may be of interest include the analysis of individual particles using helium MIPs from two laboratories ( 95/C780 95/C781).3.4. Chromatography Long et al. (95/1218) have reviewed the application of atmos- pheric pressure helium MIPs as element specijic detectors in chromatography including GC HPLC and SFC. Goode and Thomas (95/3368) have discussed the potential applications of GC-MIP systems. 3.4.1. Instrumentation The number of reports addressing developments in instrumen- tation in this area has reduced in this review period probably reflecting the relative maturity of the field. Farnsworth et al. (95/1899) reported the development of a two-channel optical system to allow simultaneous background correction for the determination of sulfur species. Similar instrumentation for the determination of Cl has been described by Rieping et al. (95/4391). Valente and Uden (95/2302) have compared argon- helium plasmas with pure helium plasmas as GC detectors with a concentric flow torch.Benefits were found in reductions in the formation of products eroded from the torch wall and cost savings in the use of argon sheathing. Performance was only marginally degraded compared to that with an all-helium plasma. A low resolution near-IR monochromator has been evaluated for the GC-MIP determination of Br C1 I P and S containing species (95/4415). It was found that selectivity of the determinand from carbon was good but that spectral interferences from other atoms were significant. 3.4.2. Gas chromatography-microwave-induced plasma applications The determination of organornetallic species has been the subject of much attention during the period under review.Several laboratories have reported GC-MIP-AES methods for the determination of organotin compounds in environmental samples (95/983 95/1866 95/3905 95/3948 95/C2921). Other workers have reported methods for the determination of organotin organolead and organomercury species (95/3670 95/3808 95/3855 95/C2199). Reports concerning the determi- nation of organomercury compounds have appeared (95/3852 Journal of Analytical Atomic Spectrometry June 1996 Vol. 11 235 R95/3947 95/C2922 95/C4277). In most of these studies detec- tion limits in the pg range were reported. The high selectivity and sensitivity of GC-MIP systems has been shown to offer distinct advantages in the speciation of organoselenium com- pounds in foods (95/2108 95/C2923 95/C4199). The determi- nation of selenium compounds in environmental waters following ethylation has also been reported (95/1479). An LOD of 8 ng I-' was achieved for a 5 ml sample.The potential advantages of the element-specific nature of the MIP appear to be becoming accepted for the determination of a wide range of organic compounds including reports concerning the measurement of pesticide residues (95/432 95/1071 95/3474). Advantages cited include the avoidance of potential false positives (presumably generated by competing techniques). Detection limits of 0.2 ng g-' were reported for the determination of PCB residues in environmental samples (95/3479 96/125). Other applications reported in the year under review included the use of GC-MIP for the analysis of 0 containing compounds (95/1225 95/C599) the detection of S in organic compounds (95/3946) N 0 and P in hydro- carbons (95/3799) and halocarbons in landfill gases (95/C2926).The ability of GC-MIP systems to determine 13C in pharmaceutical tracer studies has been described (95/425 95/2636). A detection limit of approximately 2 pg ml - ' was reported. Details of instrument optimization studies and the determination of drug metabolites were also reported. 3.4.3. Other chromatographic techniques The use of MIP detection for supercriticaljluid chromatography has declined in comparison with previous years. A single report appeared which favoured the use of a concentric plasma torch to overcome some of the plasma perturbations that occur with carbon dioxide or nitrogen as mobile phases (95/954).The combination of HPLC and MIP-AES was reported by Sanz- Medel et al. (96/283 95/C2059). The determination of As and Hg species following vapour generation was described. 4. DIRECT CURRENT PLASMAS Ek et al. (95/1481) have reported the use of a sequential injection analysis system for the determination of As Bi and Ge as hydrides by DCP-AES. The analytes were separated from the liquid in a piston burette which allowed isobaric reaction and pumped by the piston into the analytical zone of the plasma. Limits of detection of 0.15 mg 1-' for As 0.08 mg 1-' for Bi and 0.03 mg I-' for Ge were reported. Other publications that may be olf interest included the simultaneous determination of Ca Cd (20 Cr Cu Fe K Mg Mn Na Ni P Pb V and Zn in dog urine (95/429) Ca Mg and P in rat tissue (95/3480) and B in whole blood by dilution with Triton X-100 (95/3894).LOCATION OF REFERENCES The full list of references cited in this Update have been published as follows 951183-951469 J. Anal. At. Spectrom. 1995 10( 2) 49R-59R. 95/470-95/C849 J. Anal. At. Spectrom. 1995 10(4) 113R-125R. 951850-9511 159 J. Anal. At. Spectrom. 1995 10( 5 ) 127R-138R. 9511 160-9511597 J. Anal. At. Spectrom. 1995 10(6) 155R-171R. 95/1598-95/C2275 J. Anal. At. Spectrom. 1995 10( 7) 173R-198I.t. 9512276-9512891 J. Anal. At. Spectrom. 1995 10( 8) 229R-251R. 95/C2892-95/3361 J. Anal. At. Spectrom. 1995 10( lo) 31 lR-328R. 9513362-9514189 J. Anal. At. Spectrom. 1995 10( 1 l) 329R-358R.. 9512892-9513361 J. Anal. At. Spectrom. 1995 10( 12) 402R-422R.. 96/C1-96/416 J.Anal. At. Spectrom. 1996 11( l) 1R-17R. 96/417-96/C947 J. Anal. At. Spectrom. 1996 11(2) 67R-85R. Abbreviated forms of the literature references quoted (excluding those to Conference Proceedings) are given on the following pages for the convenience of the readers. The full references names and addresses of the authors and details of the C'onference presentations can be found in the appropriate issues of JAAS cited above. Abbreviated List of References Cited in Update 951185 Anal. 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ISSN:0267-9477    

DOI:10.1039/JA996110213R

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

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Lab. Clemson Univ. Clemson SC 29634-1905 USA). 96/C2040 Bogaerts A. Gijbels R.Relative ion yields in glow discharge mass spectrometry the role of charge transfer ionization. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. Antwerp B-2610 Wilrijk-Antwerp Belgium). 96/C2041 Bengston A. Developments of glow discharge optical emission spectrometry. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Swedish Inst. Metals Res. S-11428 Stockholm Sweden). 96/C2042 Marcus R. K. Radio frequency glow discharges opportunities and challenges from aluminium to zeo- lites. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Clemson Univ. Clemson SC 96/C2043 Goodner K. L. Eyler J. R. Watson C. H. Barshick C.M. Smith D. H. 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ICP-AES determination of trace impurities in silicon carbide after fusion decomposition. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Lederle Grad. Res. Center Univ. Massachusetts Amherst MA 01003-4510 USA). 96/C2047 Sikharulidze G. G. Lezhnev A. E. Ion source for direct analysis of solutions in a glow discharge mass spec- trometer. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Inst. Microelectron. Technol. and High Purity Mater. Russian Acad. Sci. 142432 Chernogolovka Moscow District Russia). 96/C2048 Einhauser T.J. Keppler B. K. Pharmacokinetic studies into cis-diammine [bis( phosphonatomethy1)amino)- acetato( 2-)-0' N'] platinum(rr) DBP a newly synthe- sized tumour-inhibiting compound in mice by atomic spectroscopy. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Anorg-Chem. Inst. 69120 Heidelberg Germany). 96/C2049 Toukhvatoulline R. Feldmann G. Mhnchen R. J. Determination of the self-absorption coefficients of spectral lines for some elements. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Fis. 240R Journal of Analytical Atomic Spectrometry June 1996 Estatistica e Mat. UNIJUI-Univ. Reg. Noroeste do Estado do RS Brazil). 96/C2050 Le Blanc C. W. Blades M. W.Plasma spatial structure in a FAPES source. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. British Columbia Vancouver British Columbia Canada). 96/C2051 Eiden G. C. Barinaga C. J. Koppenaal D. W. Argon ion and matrix polyatomic ion loss phenomena in ICP/MS and ICP/ITMS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Pacific Northwest Lab. Richland WA 99352 USA). 96/C2052 Bogaerts A. Gijbels R. Mathematical modelling of the behaviour of the sputtered atoms and corresponding ions in a direct current glow discharge. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. Antwerp (UIA) B-2610 Wilrijk- Antwerp Belgium). 96/C2053 Schram D.C. van der Mullen J. A. M. de Re@ J. M. Benoy D. A. Jonkers J. Fey F. H. A. G. Fundamental description of spectrochemical ICP dis- charges. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Phys. Eindhoven Univ. 5600 MB Eindhoven Netherlands). 96/C2054 Botto R. I. Breniier I. B. Broekaert J. A. C. Donard 0. F. X. Mermet J. M. Moens L. How to handle hard sample anal ysis-a panel discussion. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Exxon Chemicals Baytown TX 77522 USA). 96/C2055 Kotrebai M. Amarasiriwardena D. Zhu E. Krushevska A. Barnes R. M. 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Fundamental performance of UV laser ablation ICP-MS.1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Hewlett-Packard Co. Wilmington DE 19808 USA). 96/C2059 Moy M. M. Crerners D. A. Junk C. P. Effect of soil matrix on elemental analysis using laser induced breakdown spectroscopy (LIBS). 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13,1996 (Los Alamos Natl. Lab. Los Alamos NM 87545 USA). 96/C2060 Ghazi A. M. Vanko D. A. McCandless T. E. Ruiz J. New quantitative approach in trace elemental analysis of single fluid inclusion applications of laser ablation ICPMS (LA-ICPMS). 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Geol. Georgia State Univ. Atlanta GA 30303 USA).96/C2061 Cremers D. A. Foster L. Fereis M. Effect of sampling geometry on elemental analysis using laser-induced breakdown spectroscopy. 1996 Winter Conference on Vol. 11Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Los Alamos Natl. Lab. Los Alamos NM 87545 USA). 96/C2062 RUSSO R. E. Mao X. L. Caetano M. Shannon M. A. Chan W.-t. Leung A. Laser ablation inductively coupled plasma atomic emission spectroscopy factors influencing the amount and composition of the ablated volume. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Lawrence Berkeley Natl. Lab. Berkeley CA 94720 USA). 96/C2063 Einhauser T. J. Galanski M. Keppler B. K. New investigations into the plasma protein binding proper- ties of cis-diammine [( bis( phosphonatomethy1)amino)- acetato( 2-)-0' N']platinum(~~) DBP and cisplatin by ICP-OES and ETAAS.1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Anorg. Chem. Inst. 69120 Heidelberg Germany). 96/C2064 Schickling C. Broekaert J. A. C. Optimization of an electrochemical hydride generation technique coupled to microwave induced plasma atomic emission spec- trometry for the determination of arsenic. 1996 Winter Conference on Plasma Spectrochemis try Fort Lauderdale FL USA January 8-13 1996 (Fachbereich Chem. Univ. Dortmund D-44221 Dortmund Germany). 96/C2065 Szpunar J. Schmitt V. O. Lobinski R. Monod J.-L. Rapid speciation of butyltin compounds in sediments and biomaterials by capillary gas chromatography- microwave induced plasma atomic emission spec- trometry after microwave assisted leaching/digestion.1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Lab. Photophys. et Photochim. Mol. CNRS Univ. Bordeaux I 33405 Talence France). 96/C2066 Heumann K. G. Gallus S. Selenium speciation by GC/ICP-IDMS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Inst. Inorg. Chem. Univ. Regensburg D-93040 Regensburg Germany). 96/C2067 Bol'shakov A. A. Barnes R. M. Diagnostics of the enclosed inductively coupled plasma in chlorine- argon mixtures. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. Massachusetts Amherst MA 01003-4510 USA).96/C2068 Popescu S. Pressure a critical parameter in the process of molecular dissociation using successive multiphotonic excitation-photoionization appearance. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Res. Inst. Electr. Eng. RO-4400 Bistria Romania). 96/C2069 Treshchalov A. B. Chizhik A. S. Vill A. A. Spectrochemical analysis of trace contaminants in He (He/F,) pulsed discharge plasmas. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Inst. Phys. Estonian Acad. Sci. EE 2400 Tartu Estonia). 96/C2070 Tepe R. Jacksier T. Barnes R. M. Qualitative analysis of anhydrous hydrogen bromide by enclosed inductively coupled plasma-atomic emission spectroscopy.1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Air Liquide Countryside IL 60525 USA). 96/C2071 Yan X.-m. Tanaka T. Kawaguchi H. Investigation of reduced pressure inductively coupled plasma mass spectrometry. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Sch. Eng. Dept. Mater. Sci. and Eng. Nagoya Univ. Nagoya 464-01 Japan). 96/C2072 Sanz-Medel A. Gonzalez J. M. Fernandez M. L. Fernandez de la Campa M. R. Marchante J. M. Vesicles-mediated hybrid techniques for element speci- ation using plasma detection. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Quim. Fis. y Anal. Fac. Quim. Univ. Oviedo 33006 Oviedo Spain). 96/C2073 Halicz L.Gavrieli I. Dorfman E. On-line ICP-MS analyses of REE in highly saline brines. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Geol. Surv. Israel Jerusalem 95501 Israel). 96/C2074 Winefordner J. Smith B. Wagner E. I1 Future of microwave and glow discharges for spectrochemical analysis of discrete samples. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. Florida Gainesville FL 3261 1 USA). 96/C2075 Pucci P. Caimi S. Caroli S. Mura G. Role of Chirocephalus diaphanus for the early recognition of environmental pollution by trace elements. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (1st. Superiore di Sanita 00161 Rome Italy).96/C2076 Hoppstock K. Becker J. S. Dietze H.-J. High resolution ICP-MS used for the determination of "Se after hydride generation. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Zentralabteilung Chem. Anal. Forschungszentrum Julich GmbH D-52425 Julich Germany). 96/C2077 Kerl W. Hoppstock K. Becker J. S. Dietze H.-J. Dannecker W. Determination of stable and long-lived radioactive halides using high resolution ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Zentralabteilung Chem. Anal. Forschungszentrum Julich GmbH D-52425 Julich Germany). 96/C2078 Debrah E. Denoyer E. R. Practical benefits of a new ICP-MS lens system determination of trace elements in uranium. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Perkin-Elmer Corp.Wilton CT 96/C2079 Klaue B. Blum J. B. Applications of a high-resolution ICP-MS for analysis of toxic metals in the northeast from biological to environmental implications. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Earth Sci. Dartmouth Coll. Hanover NH 03755 USA). 96/C2080 Reed N. M. Mennie D. Brown P. Optimisation of data acquisition parameters for high resolution ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Fisons Elemental Analysis Winsford Cheshire UK CW7 3BX). 96,422081 Sigsworth P. T. Gilmour D. Gregson D. Routinely solving the non-routine problem.1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Fisons Instruments Elemental Analysis Winsford Cheshire UK CW7 3BX). 96/C2082 BCrubC D. BrBlC D. Determination of silicon/alu- minium ratio in drinking water supplies by low resolution ICP-MS. 1996 Winter Conference on Plasma Spectrochemis try Fort Lauderdale FL USA January 8-13 1996 (Environ. Health Centre Health Canada Ottawa Ontario Canada K1A OL2). 96/C2083 Woods G. D. McLeod C. W. Jones B. Owens R. Microcolumn field sampling and ICP mass spectro- metric analysis of seawater. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Centre Anal. Sci. Dept. Earth Sci. Univ. Sheffield Sheffield UK S3 7HF). 96/C2084 Nixon D.E. Moyer T. P. Collection of capillary whole blood on filter paper and subsequent heavy 06859-0215 USA). Journal of Analytical Atomic Spectrometry June 1996 Vol. 11 241 R96/C2085 96/C2086 96/C2087 96/C2088 96/C2089 96/C2090 96/C209 1 9 6/C 209 2 96/C2093 96/C2094 96/C2095 9 6/C209 6 242 R metal analysis by ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Metals Lab. Div. Clin. Biochem. and Immunol. Mayo Clinic Rochester NY 55905 USA). Nixon D. E. Moyer T. P. Determination of mercury in urine and whole blood by ICP-MS using conven- tional cross-flow nebulization and standard unthermo- stated spray chamber. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Metals Lab.Div. Clin. Biochem. and Immunol. Mayo Clinic Rochester MN 55905 USA). Settembre G. Koch S. A. Sample introduction by direct injection nebulization in high resolution ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Microelectron. Div. IBM Corp. Hopewell Junction NY 12533 USA). Wiederin D. R. Rapid screening for trace metals in biological samples using direct injection nebulization high resolution ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (CETAC Technologies Omaha NE 68107 USA). Plantz M. Georgitis S. J. Comparison of sensitivity reduction techniques for ICP-MS analyses. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Varian Instruments Wood Dale IL 60191 USA).Georgitis S. J. Anderson S. Plantz M. Comparison of techniques for the reduction of ArO interferences in ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Varian Instruments Englewood CO 80012 USA). Houk R. ICP-MS status and future. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Ames Lab.-US Dept. Energy Dept. Chem. Iowa State Univ. Ames IA 50011 USA). Koppenaal D. W. Barinaga C. J. Eiden G. C. Plasma sources and ion traps-present status and future vision. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Pacific Northwest Lab. Richland WA 99352 USA). Betti M. Critical evaluation of the use of a D.C.glow discharge mass spectrometer for the characterization of nuclear samples. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (European Commission JRC Inst. Transuranium Elements D-76125 Karlsruhe Germany). Karanassios V. Horlick G. Blades M. Farnsworth P. Teaching spectroscopy with computers. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Univ. Waterloo Waterloo Ontario Canada). O’Connor G. Ebdon L. Evans E. H. Design and optimisation of a low pressure inductively coupled plasma mass spectrometer. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Environ. Sci. Univ. Plymouth Plymouth UK PL4 8AA). Engelhart W.G. Total microwave sample preparation for atomic spectroscopy-a systematic approach. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Milestone MLS Riviera Beach FL 33404 USA). Poling J. Moshiri B. Innovations in closed vessel microwave sample preparation. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8- 13 1996 (Questron Corp. Mercerville NJ 08619 USA). 96/C2097 96/C209 8 96/C2099 96/C2 100 96/C2 101 96/C2102 96/C2103 96/C2104 96/C2105 96/C2106 96/C2 107 96/C2108 Journal of Analvtical Atomic Suectrometrv. June 1996. V01.11 Moshiri B. Poling J. Rapid sample preparation techniques for analysis by ICP and ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Questron Corp.Mercerville NJ 08619 USA). Glavin G. G. Barnes R. M. Analysis of hydrogen bromide using enclosed inductively coupled plasma atomic emission spectrometry. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. Massachusetts Amherst MA 01003-4510 USA). Emily J. N. Goode S. R. Spatial changes in the helium microwave induced plasma during sample introduction from a gas chromatograph. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. and Biochem. Univ. South Carolina. Columbia SC 29208 USA). Siemens V. Larjava K. Study of mixed-gas and molecular gas microwave-induced plasma in optical emission spectrometry. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (VTT Chem.Technol. Environ. Technol. FIN-02044 VTT Espoo Finland). Li G.-z. Barnes R. M. Electronic excitation and rotational temperatures in the argon microwave plasma torch. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. Massachusetts Amherst MA 01003-4510 USA). Li G.-z. Barnes R. M. Determination of free electron kinetic tempera1 ures and free electron number densities in the argon microwave plasma torch. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FI USA January 8-13 1996 (Dept. Chem. Univ. Massachusetts Amherst MA Hamier J. Salin E. D. Direct solid sample digestion and introduction using halogenating reagents.1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. McGill Univ. Montreal Quebec Canada H3A 2K6). Chalk S. J. Lorentzen E. M. Jiang W.-c. Kingston H. M. Performance based atmospheric pressure micro- wave methods for analytical sample preparation. 1996 Winter conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. and Biochem. Duquesne Univ. Pittsburgh PA Skinner C. D. Salin E. D. Axial viewing of a direct sample insertion probe for ICP-AES. 1996 Winter Conference ori Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. McGill Univ. Montreal Quebec Canada HA3 2K6). Karanassios V. Drouin P. Kellerman R. 2-D cross- correlation signal processing in ICP-AES.1996 Winter Conference or1 Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. FVaterloo Waterloo Ontario Canada N2L 3G1). Roine J. Asik.ainen M. Harju T. Siemens V. Larjava K. New radio-frequency inductively coupled plasma. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (VTT Chem. Technol. Environ. Technol. FIN-02044 VTT Espoo Finland). Samuel O. Powssel E. Mermet J. M. Long term quality control and diagnosis of inductively coupled plasma sequential emission spectrometers. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Instrum. SA Div. Jobin Yvon F-91165 Longjumeau France). 01003-4510 US.4). 15282-1503 USA).96/C2109 Li J. Improving analytical long-term and short-term Drecision bv utilizing intrinsic internal standard for 8-13 1996 (Fisons Instruments Elemental Analysis Winsford Cheshire UK CW7 3BX).kalyzing minor components by ICP-AES. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Tech. Assistance Lab. Osram Sylvania Inc. Beverly MA 96/C2110 Barnes K. W. Prusak E. Analysis of biomedical matrices using a dual view inductively coupled plasma- optical emission spectrometer. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Perkin-Elmer Corp. Norwalk CT 06859-0215 USA). 96/C2111 Houk R. S. Winge R. K. Praphairaksit N. Axial viewing of an ICP with a graphite torch injector. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept.Energy Dept. Chem. Iowa State Univ. Ames IA 50011 USA). 96/C2112 Tsourides D. Evaluation of end-on plasma ICP-AES for the analysis of high dissolved solids. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8- 13 1996 (Spectro Analytical Instruments Fitchburg MA 01420 USA). 96/C2113 Flajnik-Rivera C. Shkolnik J. Comparison of internal standard and standard additions for difficult samples by axial ICP. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Varian OSI Wood Dale IL 60191 USA). 96/C2114 Schramel P. Experiences with the new JY66P ICP- AES spectrometer with axial torch. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (GSF-Res.Center Environ. and Health Inst. Ecol. Chem. D-85758 Oberschleissheim Germany). 96/C2115 Sartoros C. Salin E. D. Automatic sample recognition. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (McGill Univ. Montreal Quebec Canada H3A 2K6). 96/C2116 Zimmer B. S. Gaston C. M. Heitkemper D. T. Wolnik K. Elemental analysis in the investigation of counterfeit pharmaceutical compounds. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (US Food and Drug Admin. Cincinnati OH 45202 USA). 96/C2117 Goode S. R. Quantitative methods for choosing internal standard elements in ICP-AES. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept.Chem. and Biochem. Univ. South Carolina Columbia SC 29208 USA). 96/C2118 Horlick G. Fulton G. S. Shi L. Atomic spectroscopy CD-ROM-preliminary report. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. Alberta Edmonton Alberta Canada T6G 2G2). 96/C2119 Salin E. D. Alary J.-F. Sartoros C. Mermet J. M. ICP-AES system diagnosis using QUID. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. McGill Univ. Montreal Quebec Canada H3A 2K6). 96/C2120 Greb U. Rottmann L. Schroder E. Direct solid sampling with laser ablation ICP-MS and glow dis- charge mass spectrometry-principles and applications. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Finnigan MAT GmbH D-28 197 Bremen Germany). 96/C2121 Reed N.M. Raith A. Brown P. Comparison of quadrupole and magnetic sector ICP-MS for laser ablation studies. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 019 15- 1068 USA). 96/C2122 Figg D. Brink C. Kahr M. Laser ablation-inductively coupled plasma mass spectrometry for PuO analysis. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Los Alamos Natl. Lab. Los Alamos NM 87545 USA). 96/C2123 Raith A. Sigsworth P. Performance of a new UV laser ablation microanalysis system for ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Fisons Instruments Elemental Analysis Winsford Cheshire UK CW7 3BX).96/C2124 Brenner I. B. Zander A. Geolaser probe-a versatile laser ablation system for the direct analysis of geological materials by ICP-AES and MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Ginzton Res. Center Varian Assoc. Palo Alto CA 94304 USA). 96/C2125 Westheide J. Becker J. S. Dietze H.-J. Broekaert J. A. C. Analysis of ceramic layers for solid oxide fuel cells by LA-ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-1 3 1996 (Zentralabteilung Chem. Anal. Forschungszentrum Julich GmbH D-52425 Julich Germany). 96/C2126 Mahoney P. P. Li G.-q. Ray S. J. Hieftje G. M. Analysis of laser generated transients with an inductively coupled plasma time-of-flight mass spectrometer.1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Indiana Univ. Bloomington IN 47405 USA). 96/C2127 Sharp B. L. Masters B. J. Studies of new calibration strategies for excimer laser ablation ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Loughborough Univ. Technol. Loughborough Leics. UK LEll 3TU). 96/C2128 Goodall P. Johnson S. G. Laser spectrometry and laser ablation-an ideal solution for the analysis of nuclear materials? 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Argonne Natl. Lab.-West Idaho Falls ID 83403 USA). 96/C2129 De Silva N.Guevremont R. Direct powder introduc- tion into the ICP a window for the lost analytical information? 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Miner. Resour. Div. Geol. Surv. Canada Ottawa Ontario Canada K1A OE8). 96/C2130 Miller-Ihli N. J. Fonseca R. W. ETV-ICP-MS trans- port wars oxygen ashing us. palladium. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (USDA Beltsville Human Nutr. Res. Center Beltsville MD 20705 USA). 96/C2131 Michalke B. Schramel P. Combination of CE and ICP-MS for metal speciation. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Inst. Okol. Chem. GSF Forschungszentrum Umwelt und Gesundheit GmbH Neuherberg D-85758 Oberschleissheim Germany).96/C2132 Alary J.-F. Rattray R. Brown E. Salin E. D. Spray deposition for ICP-AES and MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8- 13 1996 (Chemistry Dept. McGill Univ. Montreal Quebec Canada H3A 2K6). 96/C2133 Karanassios V. Willeke M. Zhang Z. Direct elemental analysis of solids by spark ablation ICP-AES. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. Waterloo Waterloo Ontario Canada N2L 3G1). Journal of Analytical Atomic Spectrometry June 1996 Vol. 11 243R96/C2134 96/C2135 96/C2 136 96/C2137 96/C2 138 96/C2139 96/C2 140 96/C2 14 1 96/C2 142 96/C2143 96/C2 144 96/C2 145 244 R Lu Q.-h. Barnes R. M. Detection and quantification of metal-binding proteins in different buffers by capillary electrophoresis (CE) and inductively coupled plasma mass spectrometry (ICP-MS).1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. Massachusetts Amherst MA 01003-4510 USA). Gomez J. Using the DIN with ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Yokogawa Anal. Systems Musashino-shi Tokyo 180 Japan). Keohane B. M. Christodoulou J. Li H.-y. Kashani M. Kumarsingh R. Murdoch P. del S. Sadler P. J. Sun H.-z. Recognition of metallodrugs by blood plasma proteins investigations using chromatography linked to ICP-MS with direct injection nebulization. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem.Birkbeck Coll. Univ. London London UK WClH OPP). Jantzen E. Prange A. Cryofocusing-GC-ICP-MS as an easy and powerful hyphenated technique for the multielemental speciation of volatile organometallic compounds. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (GALAB Technol. Centre GKSS D-21502 Geesthacht Germany). Heitkemper D. T. Mulligan K. J. Elemental speciation in dietary supplements. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Forensic Chem. Center US Food and Drug Admin. Cincinnati OH 45202 USA). Thomas P. Hutton R. HPLC-ICP-MS determination of arsenic and selenium species using time resolved analysis and chromatographic software.1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13,1996 (Inst. Pasteur de Lille Serv. Eaux-Environ. F-59019 Lille France). Yehl P. M. Tyson J. F. Speciation studies using ICP- atomic fluorescence for the determination of generated hydrides following liquid chromatographic separation. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. Massachusetts Amherst MA Ebdon L. Feasibility of in-vivo metal speciation. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Environ. Sci. Plymouth Anal. Chem. Res. Unit Univ. Plymouth Plymouth Devon UK PL4 8AA). Tao H. QuCtel C. R. Tominaga M. Miyazaki A. On-line matrix removal for the determination of trace metals in highly-salted waters by ICP-MS.1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Hydrospheric Environ. Prot. Dept. Natl. Inst. Resour. and Environ. Tsukuba Ibaraki 305 Japan). Smith F. G. McLeod C. Polymer reagent chemistries for automated preconcentration-matrix elimination in ICP-mass spectrometric analysis of seawater. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (CETAC Technologies Inc. Omaha NE 68 107 USA). Lasztity A. Horvith Z. Bertalan EO. PerCnyi K. Trace metal analysis of highly mineralized waters by FI-GFAAS and ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Inorg.and Anal. Chem. Eotvos L. Univ. H-1518 Budapest 112 Hungary). Wiederin D. Gutierrez A. G. Comparison of cooled plasma and desolvation both separate and combined as approaches for trace analysis with ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort 01003-4510 USA). 96/C2146 96/C2147 96/C2148 96/C2 149 96/C2150 96/C2 15 1 96/C2152 96/C2 15 3 96/C2154 96/C2 1 5 5 96/C2156 96/C2 157 Journal of Analytical Atomic Spectrometry June 1996 Vol. 11 I Lauderdale FI USA January 8-13 1996 (CETAC Technologies Inc. Omaha NE 68107 UK). Wiederin D. R. Brennan J. Gjerder D. T. Low pressure ion exchange separation of chromium arsenic and selenium with detection by ICP-MS. 1996 Winter Conference om Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (CETAC Technologies Inc.Omaha NE 68107 USA). Larsen E. H. Corr J. J. Role of HPLC-ICP-MS and HPLC-ionspray -MS in speciation research. 1996 Winter Conference 011 Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Inst. Food Chem. and Nutr. Natl. Food Agency Denmark DK-2860 Snrborg Denmark). Winn J. W. Hobbins B. Performance comparison of commercial pneumatic and ultrasonic nebulizers. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Precision Instrumentation Englewood CO 801 12 USA). Caruso J. A. New departures for elemental speciation at ultra-trace levels. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. Cincinnati Cincinnati O’Hanlon K.Foulkes M. Ebdon L. Silicon speciation using high perfoirmance liquid chromatography-induc- tively coupled plasma atomic emission spectrometry. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Environ. Sci. Pllymouth Anal. Chem. Res. Unit Univ. Plymouth Plymouth UK PL4 8AA). Crews H. M. Fairweather-Tait S. J. Elemental speci- ation in human studies the role of hyphenated techniques. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (MAFF CSL Food Sci. Lab. Colney Norwich UK NR4 7UQ). Packer A. P. GinC M. F. Miranda C. E. S. dos Reis B. F. Automated on-line preconcentration system for plasma spectrometry. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Centro Energia Nucl.Agric. CENA-USP 13400-970 Piracicaba-SP Brazil). Browner R. F. Nebulizer characteristics and aerosols. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Sch. Chem. and Biochem. Georgia Inst. Technol. Atlanta Krause P. Prange A. Lead isotope ratio measurements by ICP-MS a way to follow the pollution history in sediment-cores of the river Elbe? 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (GKSS Res. Centre Geesthacht Inst. Phys. and Chem. Anal. D-21502 Geesthacht Germany). Kozerski G. E. Fiorentino M. A. Ketterer M. E. Electron self-exclhange studies of Fe(m/II) and Ni(m/II) redox couples using stable isotopes and ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL.USA January 8-13 1996 (Dept. Chem. John Carroll Univ. University Heights OH 44118 USA). Gregoire D. C. Acheson B. M. Taylor R. P. Measurement of lithium isotope ratios in geological materials by incluctively coupled plasma mass spec- trometry. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Ged. Surv. Canada Ottawa Ontario Canada K1A OE8). Byrdy F. A. Ohon L. K. Caruso J. A. Comparison of electrospray and ICP sources for elemental analysis with mass spectrometric detection. 1996 Winter Conference on Plasma Spectrochemistry Fort OH 45221-0172 USA). GA 30332-0400 USA).96/C2158 96/C2 159 96/C2160 96/C2 16 1 96/C2162 96/C2163 96/C2 164 96/C2165 96/C2 166 96/C2167 96/C2168 96/C2169 Lauderdale FL USA January 8-13 1996 (Dept.Chem. Univ. Cincinnati Cincinnati OH 45221-0172 USA). Hamester M. Rottmann L. Greb U. Haveresch- Kock M. Analysis of ultrapure chemicals with high- resolution ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Finnigan MAT GmbH D-28197 Bremen Germany). Hearn R. Cox R. Haines J. Reed N. Applications of high resolution ICP-MS in a contract analytical laboratory. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Analytical Services Group Didcot Oxon UK OX11 ORA). Blades M. W. Future prospects in plasma spectrochemi- stry. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept.Chem. Univ. British Columbia Vancouver British Columbia Canada V6T 1Z1). Chartier F. Dubois J.-C. Pilier M. Fission products and actinides analysis by ICP-MS and TIMS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (CEA/ SACLAY DCC/DPE/SPEA/SAIS 91 191 Gif-sur- Yvette France). Hall G. S. Orquita C. Multielemental analysis of ice cubes from fast-food restaurants using ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Rutgers State Univ. New Jersey New Brunswick NJ 08903 USA). Yu S.-I. Hall G. S. Persuad D. Marcus S. Jennis T. Chronology of Pb isotope ratios and concentrations in biological fluids from a gun-shot victim. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept.Chem. Rutgers State Univ. New Jersey New Brunswick NJ 08903 USA). Nonose N. Kubota M. Precise determination of metal impurities in sulfamic acid by isotope dilution method coupled with ETV-ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Natl. Inst. Mater. and Chem. Res. Tsukuba Ibaraki 305 Japan). Buckley B. Heintz M. Fang W. Johnson W. Determination of isotope ratios for individual mercury species. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (EOHSI-Busch Campus Rutgers Univ. Hughes R. J. Evans R. D. Anomalous results in the determination of San Joachin soil reference material. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Environ.and Resour. Studies Trent Univ. Peterborough Ontario Canada K9J 7B8). Patino L. C. Feigenson M. D. Detailed study of rare earth elements of lavas from Hawaiian volcanoes using ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Geol. Sci. Dept. Rutgers State Univ. New Jersey New Brunswick NJ 08903 USA). Hoffmann E. Ludke C. Scholze H. Stephanowitz H. Application of laser-ICP-MS as a means of obtaining information on spatial changes in element concentration in plant tissue. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13,1996 (Inst. Spektrochem. Angew. Spektrosk. Lab. Spektrosk. Meth. Umweltanal. 12489 Berlin Germany).Koskelo A. Figg D. Mahan C. Wayne D. Thornton D. Los Alamos National Laboratory Center for direct chemical analysis of materials. 1996 Winter Conference NJ 08855-1179 USA). on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Chem. Sci. and Technol. Div. Center Direct Chem. Anal. Los Alamos Natl. Lab. Los Alamos NM 87545 USA). 96/C2170 Amarasiriwardena C. Rokho K. Lupoli N. Hu H. Sinik K. Youngsoo C. Kwangsik P. Jaeman H. Environmental correlates of tooth lead in South Korea. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Channing Lab. Harvard Med. Sch. Boston MA 02115 USA). 96/C2171 Augneran S. MCdina B. Szpunar J. Lobinski R. Direct ICP-MS determination of the rare earth elements in wine using a microconcentric nebulizer.1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Lab. Reg. Repression des Fraudes 33405 Talence France). 96/C2172 Dams R. Riondato J. Vanhaecke F. Moens L. Determination of spectrally and not spectrally interfered ultra-trace elements in biological reference materials by high resolution ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Lab. Anal. Chem. Ghent Univ. B-9000 Ghent Belgium). 96/C2173 Hsiung C.-s. Andrade J. D. Ash K. 0. Optimization of ICP-MS for quantitative multi-element analysis of biological specimens. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Mater. Sci. and Eng.Univ. Utah Salt Lake City UT 84112 USA). 96/C2174 Duckworth D. C. Barshick C. M. Smith D. H. McLuckey S. A. Quadrupole ion traps what do they hold for glow discharge mass spectrometry?. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Chem. and Anal. Sci. Div. Oak Ridge Natl. Lab. Oak Ridge TN 96/C2175 Tanner S. D. Houk R. S. Ion trajectory modelling (including space charge) of the ion deposition experi- ment. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (PE-SCIEX Concord Ontario Canada L4K 4V8). 96/C2176 Nadolny R. Becker J. S. Dietze H.-J. Saprykin A. I. Broekaert J. A. C. Application of RF GDMS for trace element analysis of non-conducting samples. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Zentralab.Chem. Anal. Forschungszentrum Julich GmbH D-52425 Julich Germany). 96/C2177 Prassler F. Hoffmann V. Bartsch K. Wetzig K. Quantitative analysis of PA-CVD multilayer-coatings by radio frequency and direct current glow discharge optical emission spectroscopy. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Inst. Festkorper. u. Werstofforschung Dresden D-01171 Dresden Germany). 96/C2178 Betti M. Lagerwaard A. Studies on single particles by glow discharge mass spectrometer. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13,1996 (Eur. Comm. JRC Inst. Transuranium Elements D-76125 Karlsruhe Germany). 96/C2179 Ye Y.-c.Marcus R. K. Effects of limiting orifice (anode) geometries on an analytical RF-glow discharge (GD) analysis by Langmuir current and voltage probes. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Clemson Univ. Clemson SC 96/C2180 Saprykin A. I. Becker J. S. Dietze H.-J. Radiofrequency glow discharge ion source for high resolution mass spectrometry “element”. 1996 Winter 37831-6375 USA). 29634-1905 USA). Journal of Analytical Atomic Spectrometry June 1996 Vol. 11 245R96/C218 1 96/C2182 9 6/C2 1 8 3 96/C2 184 96/C2 185 96/C2186 96/C2187 96/C2188 96/C2189 96/C2 190 96/C2 19 1 246 R Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Zentralab. Chem. Anal. Forschungszentrum Julich GmbH D-52425 Julich Germany).Ingeneri K. Hang W. Harrison W. W. Comparison of the atomization and ionization efficiencies of DC RF and microsecond pulse discharges. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. Florida Gainesville FL 3261 1 USA). Horlick G. Zhao Y.-h. Spectral study of charge transfer in glow discharges. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. Alberta Edmonton Alberta Canada T6G 2G2). Obenauf R. H. Kocherlakota N. Considerations in the design manufacture and use of chemical reference materials for sub-ppb trace metal analysis. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (SPEX Chemical Metuchen NJ 08840 USA).Collins L. W. Applications using alternative tempera- ture control in analytical microwave systems. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (01 Analytical College Station TX 77842-9010 USA). Amarasiriwardena D. Kotrebai M. Krushevska A. Barnes R. M. Determination of trace elements in human milk by ICP-MS and ICP-AES after high pressure high temperature digestion. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Sch. Nat. Sci. Hampshire Coll. Amherst MA 01002 USA). Gercken B. Fille M. Emmenegger G. Suter O. Pave] J. ICP-MS TXRF and ZGFAAS complemen- tary techniques in analysis of trace elemental impurities in photoresists.1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Central Anal. Dept. Ciba-Geigy Ltd. CH-4002 Basel Switzerland). Michael J. D. Excited mercury density measurements in a Hg-Kr inductively coupled discharge. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (GE Lighting Cleveland OH 441 12 USA). Maso G. N. Galkin A. A. Glavin G. G. Thermodynamic approach to the optimization of instrumental parameters in inductively coupled plasma atomic fluorescence spectrometry for the analysis of superconductors. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Inorg. Chem. Div. Dept. Chem. Moscow State Univ. GSP Moscow 119899 Russia). 96/C2192 Tanner S.D. Mechanism of ionization in the inductively coupled “cold” plasma interpreted through matrix suppression effects. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (PE-SCIEX Concord ON Canada L4K 4V8). 96/C2193 Farnsworth P. B. Duersch B. S. Optical diagnostics inside an ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13,1996 (Dept. Chem. and Biochem. Brigham Young Univ. Provo UT 84602 USA). 96/C2194 Gerth D. J. Analysis of waste isolation pilot plant (WIPP) brines for target analytes using a charge injection device (CID) equipped ICP-AES part I method development. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Los Alamos Natl. Lab.Los Alamos NM 87545 USA). 96/C2195 Coleman G. N. Harris C. J. O’Boyle M. Steiner J. D. Direct determination of halogens in organic and aqueous solutions by ICP-AES in the VUV region. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Fisons Instruments North America Beverly MA 01915 USA). 96/C2196 Franz S. F. Low UV performance of ICP-AES for oil analysis. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Spectro Analytical Instruments Inc. Fitchburg MA 01420 USA). 96/C2197 Karanassios V. Wood T. J. Development and charac- terization of an automated direct sample insertion-ICP- AES system. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Guelph-Waterloo Center Graduate Work Chem.Dept. Chem. Univ. Waterloo Waterloo Ontario Canada N2L 3G1). 96/C2198 Merten D. Broekaert J. A. C. Le Marchand A. Application of the image system for analysis of materials with line-rich emission spectra by sequential ICP-OES. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. Dortmund D-44221 Dortmund Germany). 96/C2199 Dymott T. C. Neal P. Booth P. K. Possibilities of PPT analysis in ICP-AES. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (AT1 Unicam Cambridge UK CB1 2PX). 96/C2200 Shipman M. Wilbur S. Closer look at interference correction and EPA method 6020. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Pace Inc.Petaluma CA 94954 USA). Gaillat A. Barnes R. M. Pressure dependence of the 96/c2201 Hoffmann E.9 Lfidke c.9 Skole J. Determination of element contents in single airborne particles by ETV- ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13,1996 (Inst. Spektrochem. Angew. Spektrosk. Lab. Spektrosk. Meth. Umweltanal. 12489 Berlin Germany). Laser ablation microprobe-inductively coupled plasma mass spectrometry (LAM-ICP-MS) of geological mate- rials. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Earth Sci. and Center Earth Resour. Res. Memorial Univ. Newfoundland St. John’s Newfoundland Canada A1B 3x5). discharge characteristics in an enclosed ICP.1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Greenfield Community Coll. Greenfield MA 01301 USA). Kingston H. M. S. Walter P. J. Link D. Taylor D. environmental sample preparation for ICP-MS includ- ing total and speciated elemental analysis. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. and Biochem. Duquesne Univ. Pittsburgh PA 15282 USA). Hue DSmw. Nogay D. Chalk S. Larget B. Robust 96/c2202 Longerich p*9 Jackson s* E* Forsythe La Horn 1. Becker J. S. Seifert G. Saprykin A. I. Dietze H.J. Mass spectrometric and theoretical investigations on formation of rare gas molecular ions in different plasmas. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA Januarv 8-13 1996 (Zentralab.Chem. Anal. 96/C2203 Koskelo A. Gamble T. Lippert T. Laser induced breakdown spectroscopy of geological materials. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8- 13,1996 (Los Alamos Natl. Lab. Los Alamos NM 87545 USA). Forschbngszentrum Julich GmbH D-52425 Julich Germany). Journal of Analvtical Atomic Svectrometrv. June 1996. Vol. 11 96/C2204 Drouin P. Karanassios V. Spiers G. User interface for 1-D cross-correlation signal processing in ICP-AES.1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Guelph-Waterloo Center Graduate Work Chem. Dept. Chem. Univ. Waterloo Waterloo Ontario Canada N2L 3G1). 96/C2205 Branagh W. Whelan C.Salin E. D. Automatic operating parameter and methodology selection for ICP-AES. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. McGill Univ. Montreal Quebec Canada H3A 2K6). 96/C2206 Horlick G. Stewart I. I. Barnett D. Plasma mass spectrometry are we using the right source? 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. Alberta Edmonton Alberta Canada T6G 2G2). 96/C2207 Mermet J.-M. Current status of laser ablation ICP- AES. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Lab. Sci. Anal. Univ. Lyon I F-69622 Villeurbanne France). 96/C2208 Ketterer M. E. Kozerski G. E. Ritacco R. Painuly P. Alternatives to chromatography capillary free-flow electrophoresis applied to elemental speciation for plasma spectrochemistry.1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. John Carroll Univ. University Heights OH 441 18 USA). 96/C2209 Bergdahl I. A. Schutz A. Grubb A. Protein-bound lead in erythrocytes studied by use of LC-ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Occup. and Environ. Med. Univ. Hosp. S-221 85 Lund. Sweden). Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Chem. Metrol. Group Inst. Natl. Measure. Standards Natl. Res. Council Canada Ottawa Ontario Canada K1A OR6). 96/C2217 Brenner I. B. Ebdon L. Salin E.Broekaert J. Marcus K. Zander A. Solids analysis dead or alive?. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Geochem. Div. Geol. Surv. Israel Jerusalem 95501 Israel). 96/C2218 Hoppstock K. Becker J. S. Dietze H.-J. Mercury determination at trace and ultratrace level using cold vapour generation coupled to high resolution ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Zentralabteilung Chem. Anal. Forschungszentrum Julich GmbH D-52425 Julich Germany). 96/C2219 Titov V. V. Detailed study of the quadrupole mass analyzer operating within the first second and third (intermediate) stability regions. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8- 13 1996 (Russian Federation Tech.Phys. and Automation Res. Inst. 115230 Moscow Russia). 96/C2220 Hall G. E. M. Capabilities and limitations of ICP-MS in hydrogeochemical exploration for base metal and gold deposits. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Geol. Surv. Canada Ottawa Ontario Canada K1A OE8). 96/C222 1 Tittes W. Pollmann D. Jakubowski N. Broekaert J. A. C. Analysis of A1,0 ceramic powders by low and high resolution ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January -8-13 1996 (Inst. Spektrochem. Angew. 96/C2210 Bird S. M. Barnes R. M. Evaluation of adsorption of Spektrosk. D-44013 Dortmund Germany). metals to electrophoresis capillaries using inductively coupled plasma mass spectrometry. 1996 Winter 96/C2222 Bakowska E.Ultra trace analysis of semiconductor Conference on Plasma Spectrochemistry Fort materials by ICP-MS. 1996 Winter Conference on Lauderdale FL USA January 8-13 1996 (Dept. Plasma Spectrochemistry Fort Lauderdale FL USA Chem. Lederle Graduate Research Center Univ. January 8-13 1996 (Hewlett-Packard Co. Wilmington Massachusetts Amherst MA 01003-4510 USA). DE 19808 USA). 96/C22 96/C22 11 Abou-Shakra F. R. Rayman M. P. Churchman D. R. Ward N. I. Analysis of selenium in blood serum by ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. Surrey Guildford Surrey UK GU2 5XH). 12 Vanhaecke F. Moens L. Dams R. Held A. Taylor P. D. P.ICP isotope ratio measurements using a high resolution instrument an evaluation. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Lab. Anal. Chem. Gent Univ. B-9000 Gent Belgium). 96/C2213 Veillon C. Patterson K. Y. Moser-Veillon P. B. Stable isotope ICP-MS in biological materials. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Human Nutr. Res. Center US Dept. Agric. Beltsville MD 20705 USA). 96/C2214 Caroli S. Senofonte O. Caimi S. Comparative study of marine sediments from Antarctica by GD-AES and ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (1st. Superiore di Sanita 00161 Rome Italy). 96/C2215 Kogan V. V. Hinds M. W. Analysis of V Cr Mn and As in gold by ICP-MS.1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Royal Canadian Mint Ottawa Ontario Canada K1A OG8). 96/C2216 McLaren J. W. Lam J. W. H. Hioki A. Methven B. A. J. Environmental applications of inductively coupled plasma mass spectrometry. 1996 Winter 96/C2223 Poluzzi V. Lutman A. Trentini P. Cavalchi B. Coan P. Ascanelli M. Mazzoli A. Alberini G. Ciava G. Determination of iodine in urine by two different ICP-MS procedures and instrumentation and by HPLC with electrochemical detection. Comparison of results. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (P.M.P. A.U.S.L. RE 42100 Reggio Emilia Italy). 96/C2224 Panday V. K. Hoppstock K.Becker J. S. Dietze H.-J. Determination of rare earth elements in materials by inductively coupled environmental plasma mass spectrometry. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Zentralabteilung Chem. Anal. Forschungszentrum Julich GmbH D-52425 Julich Germany). 96/C2225 Milgram K. Shalosky J. A. Goodner K. L. Watson C. H. Smith B. W. Winefordner J. D. Eyler J. R. Ultra-high resolution ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. Florida Gainesville FL 3261 1-7200 USA). 96/C2226 Harrison W. W. Hang W. Atomic mass spectrometry of solids-critical new developments. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept.Chem. Univ. Florida Gainesville FL 3261 1-7200 USA). 96/C2227 Mahan C. Direct analysis of soil samples using DC arc CID spectroscopy. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January Journal of Analytical Atomic Spectrometry June 1996 Vol. 1 1 247R96/C2228 96/C2229 96/C2230 96/C2231 96/C2232 96/C2233 96/C2234 96/C223 5 96/C2236 96/C2237 96/C2238 96lC2239 8-13 1996 (Inorg. Trace Anal. Los Alamos Natl. Lab. Los Alamos NM 87545 USA). Hoffmann V. Prassler F. Wetzig K. Dependence of line intensities of selected elements on the plasma parameters. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Inst. Festkorper. und Werstofforschung Dresden e.V. D-01171 Dresden Germany). Pan X.-h.Harville T. R. Marcus R. K. Analysis of simulated nuclear waste by glow discharge atomic emission spectrometry. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Clemson Univ. Clemson SC 29634-1905 USA). Mahoney P. P. Ray S. J. Li G.q. Hieftje G. M. Continuum background reduction in time-of-flight mass spectrometry with continuous ion sources. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Indiana Univ. Bloomington IN 47405 USA). Hang W. Smith B. W. Winefordner J. D. Harrison W. W. Glow discharge time-of-flight mass spectrometry. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. Florida Gainesville FL 32611 USA).Horlick G. Zhao Y.-h. Excitation and emission characteristics of neutral atoms in glow discharges with comparisons to inductively coupled plasmas. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. Alberta Edmonton Alberta Canada T6G 2G2). Marcus R. K. Shick C. R. Jr. Effect of driving frequency (2-30 MHz) on source characteristics in radio frequency glow discharge mass spectrometry. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Howard L. Hunter Chem. Lab. Clemson Univ. Clemson SC 29634-1905 USA). Leikin S. V. Grillo A. C. Barnes R. M. Applications of automated microwave digestion system for ICP-AES analysis. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Questron Corp.Mercerville NJ 08619 USA). Rhoades C. B. Jr. Clean laboratory chemistry for the microwave assisted digestion of botanical samples. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 [ R.J. Reynolds Tobacco Co. Winston-Salem NC Amarasiriwardena D. Krushevska A. Barnes R. M. Microwave assisted vapour-phase nitric acid digestion of small biological samples for the determination of trace elements by inductively coupled plasma atomic emission spectrometry. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Sch. Nat. Sci. Hampshire Coll. Amherst MA 01002 USA). Carey J. M. Mattern J. J. Methods for improving ICP-AES analysis of lubricating oils containing vis- cosity modifiers.1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (The Lubrizol Corp. Wickliffe OH Rahman M. M. Blades M. W. Trace element analysis using radio-frequency capacitively coupled discharges coupled with electrothermal sample introduction. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. British Columbia Vancouver British Columbia Canada V6T lZl). Rider M. E. Goode S. R. Evaluation of optical systems used for spatial mapping and their effects on Abel 27102-1487 USA). 44092-2298 USA). inverted maps. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept.Chem. and Biochem. Univ. S. Carolina Columbia SC 29208 USA). 96/C2240 Gaillat A Barnes R. M. Proulx P. Open flow enclosed inductively coupled plasma a mathematical simulation. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Greenfield Community Coll. Greenfield MA 01301 USA). 96/C2241 Clemons P. S. Houk R. S. Praphairaksit N. Fundamental properties of an ICP with a graphite torch injector. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Ames Lab. US Dept. Energy Iowa State Univ. Ames IA 50011 USA). 96/C2242 Ohls K. D. Procedure of spectrochemical analysis how to achieve accuracy?. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept.Anal. Chem. Univ. Munster D-44267 Dortmund Germany). 96/C2243 Knapp G. Sample preparation progress and challenges. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Anal. Chem. Micro- and Radiochem. Tech. Univ. Graz A-8010 Graz Austria). 96/C2244 Hieftje G. M. Sesi N. N. Interelement interference effect in inductively coupled plasma spectrometry. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Indiana Univ. Bloomington IN 47405 USA). 96/C2245 Olesik J. W. Current descriptions of fundamental processes that control ICP-OES and ICP-MS signals. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept.Geol. Sci. Lab. Plasma Spectrochem. Laser Spectrosc. and Mass Spectrom. Ohio State Univ. Columbus OH 43210 USA). 96/C2246 Paama L. Peramaki P Lajunen L. H. J. Determination of aluminium in environmental samples by ICP-AES. Comparison of factors affecting the line intensity of different emission lines. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Inst. Chem. Phys. Tartu Univ. EE-2400 Tartu Estonia). 96/C2247 Botto R. I. Zhu J. J. “Universal calibration” for analysis of organic solutions by ICP-AES. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Baytown Chem. Plant Lab. Exxon Chem. Co. Baytown TX 77520 USA). 96/C2248 Shkolnik J. Brenner I. B. Zander A Kim S. Direct determination of Pb in gasoline using emulsification and Ar and Ar-oxygen ICP-AES.1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Varian Optical Spectroscopy Instruments Wood Dale IL 60191 USA). 96/C2249 Goldstone L. C. Samuel O. Deraede C. Yvon J. Influence of resolution on the sensitivity of ICP-AES a non-axial approach to ultratrace detection limits. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (JY Emission/Instruments SA Inc. Edison NJ 08820 USA). 96/C2250 Schwartz R. S. Carnes D. M. Hecking L. T. Sheehan T. D. Sullivan J. L. Evaluation of multivariate software packages for the analysis of trace element data for geographic origin determination of agricultural prod- ucts. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (US Customs Service Washington DC 20229 USA). 248 R Journal of Analytical Atomic Spectrometry June 1996 Vol.1196/C2251 Gerth D. J. Windows based automated quality control svstem for the ICP-AES analvsis of waste isolation 8-13 1996 (Inst. Spektrochem. Angew. Spektrosk. D-44013 Dortmund Germany). iilot plant (WIPP) brines. 1998 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Los Alamos Natl. Lab. Los Alamos NM 87545 USA). 96/C2252 Cousin H. Giinther D. Wanner B. Magyar B. Heinrich C. Laser ablation process in LA-ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Lab. Inorg. Chem. Swiss Fed.Inst. Technol. CH-8092 Zurich Switzerland). 96/C2253 Masters B. J. Sharp B. L. Excimer LA ICP-MS for the analysis of biological materials using aqueous standards. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Loughborough Univ. Technol. Loughborough Leics UK LE11 3TU). 96/C2254 Evans R. D. Casselman J. M. Monitoring historical changes in water quality in Lake Erie an application of laser ablation microprobe ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Environmental Sci. Centre Trent Univ. Peterborough Ontario Canada K9J 7B8). 96/C2255 Salit M. L. Yates D. A. Analysis of soils using multivariate signal quantitation ICP-OES. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Chem.Sci. and Technol. Lab. Anal. Chem. Div. Natl. Inst. Stand. Technol. Gaithersburg MD 20899 USA). 96/C2256 Sesi N. N. Galley P. Hanselman D. Horner J. Huang M. Hieftje G. M. Development of an imaging- based instrument for plasma studies. 1996 Winter Conference on Plasma SDectrochemistrv Fort 96/C2263 Fairman B. Catterick T. Development of an HPLC- ICP-MS method for the determination of organotin compounds is speciation analysis ready for accreditation? 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Lab. Government Chemist Teddington Middx. UK TW 11 OLY). 96/C2264 Buckley B. Heintz M. Fang W Johnson W. Mercury speciation with an IC/ICP-MS system a marriage of convenience.1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (EOHSI-Busch Campus Rutgers Univ. Piscataway NJ 08855-1179 USA). 96/C2265 Betti M. Barrero Moreno J. M. Koch L. Garcia Alonso J. I. Determination of low levels of plutonium in presence of uranium and other actinides by IC-ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Eur. Comm. JRC Inst. Transuranium Elements D-76125 Karlsruhe Germany). 96/C2266 Chamberlain I. Creed J. T. Magnuson M. L. Brockhoff C. A. Determination of arsenic in saline waters by hydride generation utilizing a membrane based gas liquid separator and ICP-MS detection. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (US Environmental Protection Agency Port Orchard WA 98366 USA).96/C2267 Grote B. Heinrichs H. Simon K. Analysis of acid digested geological samples by MCN-ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (FMS CETAC D-57258 Freudenberg Germany). Lauderdale FL USA JanuirY 8-13 1996' (DePt. Chem. Indiana Univ. Bloomington IN 47405 USA). 96/C2268 Koller D. Sigsworth P. Abell I. Sample preparation for ICP-MS past present and future. 1996 Winter 96/C2257 Cromwell E. F. Sensitivity and resolution enhancements in small-spot laser ablation ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (IBM Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Fisons Instruments Elemental Analysis Winsford Cheshire UK CW7 3BX).Storage Systems Div. San Jose CA 95193 USA).' 96/C2269 Rosenberg E. Peck M. A. Grasserbauer M. 96/C2258 Alexander M. L. Smith M. R. Mendoza A. Koppenaal D. W. Optical characterization of laser ablation particle production and plasma digestion processes in laser ablation ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Pacific Northwest Lab. Richland WA 99352 USA). 96/C2259 Hieftje G. Future of plasma spectrochemical instrumen- tation. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Indiana Univ. Bloomington IN 47405 USA). 96/C2260 Kirlew P. W. Caruson J. A. Capillary electrophoresis with ICP detection utilizing an ultrasonic nebulizer interface.1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. Cincinnati Cincinnati 96/C226 1 Reitznerova E. Amarasiriwardena D. Kopcakova M. Barnes R. M. Determination of trace elements in enamel layer of human teeth by inductively coupled plasma emission and mass spectrometry. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. Massachusetts Amherst MA 96/C2262 Jakubowski N. Dettlaff I. Schram J. Stuewer D. Speciation of selenium by inductively coupled plasma mass spectrometry with hydraulic high pressure nebuliz- ation. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January OH 45221-0172 USA).01003-45 10 USA). Optimization of a microwave-induced He-plasma as a gas chromatographic detector in trace organic analysis. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Inst. Anal. Chem. Vienna Univ. Technol. A-1060 Vienna Austria). 96/C2270 Vanhaecke F. De Smaele T. Moens L. Dams R. Capillary gas chromatography inductively coupled plasma mass spectrometry (CGC-ICP-MS) for elemen- tal speciation. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Lab. Anal. Chem. Ghent Univ. B-9000 Ghent Belgium). 96/C2271 QuCtel C. R. Tao H. Tominaga M. Miyazaki A. Separation and elemental analysis of volatile com- pounds by capillary gas chromatography coupled to a bench-top inductively coupled plasma mass spec- trometer.1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Water Anal. Div. Hydrospheric Environ. Prot. Dept. Natl. Inst. Resour. and Environ. Ibaraki 305 Japan). 96/C2272 Krushevska A. Kotrebai M. Barnes R. M. Slurry nebulization and ICP-AES analysis of food. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. Massachusetts Amherst MA 96/C2273 Tyson J. F. Fitzgerald N. Jassie L. B. Towards a new sample introduction device for plasma spec- troscopy. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 01003-4510 USA). Journal of Analytical Atomic Spectrometry June 1996 Vol.11 249R96/C2274 96/C2275 96/C2276 96/C2277 96/C227 8 96/C2279 96/C2280 96/C228 1 96/C2282 96/C2283 96/C2284 96/C2285 250 R 8-13 1996 (Dept. Chem. Univ. Massachusetts Amherst MA 01003-4510 USA). Berndt H. Yanez J. Aerosol generation for sample introduction by high temperature/hydraulic high- pressure nebulization (HT-HHPN). 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Inst. Spektrochem. Angew. Spektrosk. D-44139 Dortmund Germany). Olson L. K. Belkin M. Caruso J. A. Gas chromatogra- phy using radio frequency glow discharge mass spectro- metric detection. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. Cincinnati Cincinnati Roehl R. Recent advances in the speciation of selenium in petroleum refinery and municipal waste waters using ICP-MS and ICP-MS coupled with liquid chroma- tography.1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (California Public Health Foundation Berkeley CA 94704 USA). Donard 0. F. X. Lobinski R. Plasma spectrometry and molecular information. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Lab. Photophys. et Photochim. Mol. Univ. Bordeaux I F-33405 Talence France). Foner H. A. Halicz L. Yoffe O. Ehrlich S. Barnes R. M. Determination of bromine and iodine in natural waters and related materials by ICP-MS and FIAS- ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8- 13,1996 (Geochem.Div. Geol. Surv. Israel Jerusalem 95501 Israel). McLeod C. W. ICP atomic and mass spectrometry the FIA way. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Centre Anal. Sci. Dept. Earth Sci. Univ. Sheffield Sheffield UK S3 7HF). Heithmar E. M. Pergantis S. A. Hinners T. A. Effect of spray-chamber design on pFI/ICP-MS with a high efficiency nebulizer. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Characterization Res. Div. Natl. Exposure Res. Lab. US Environmental Protection Agency Las Vegas NV 89193-3478 USA). Berndt H. New high pressure nebulizers for ICP spectrometry. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-1 3 1996 (Inst.Spektrochem. Angew. Spektrosk. D-44139 Dortmund Germany). Gras L. Bordera L. Todoli J. L. Mora J. Hernandis V. Canals A. New applications of microwave radiation to the sample introduction in atomic spectrometry. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Quim. Anal. Univ. Alicante 03071 Alicante Spain). Lam J. W. H. McLaren J. W. Sturgeon R. E. Micro- volume sample introduction devices their role and performance. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Inst. Natl. Measurement Standards Natl. Res. Council Canada Ottawa Canada K1A OR6). Dillen H. Novel sample introduction systems for high resolution ICP mass spectrometry. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (OCAS N.V.(Res. Centre Appl. Steel) B-9060 Zelzate Belgium). Brenner I. B. Zander A. Zhu J. Gutierrez A. Plantz M. R. Evaluation of a membrane desolvation interface for trace element detection by solvent extraction and ICP-AES and ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA OH 45221-0172 USA). 96/C2286 96/C2287 96/C228 8 96/C2289 96/C2290 96/C2291 96/C2292 96/C2293 96/C2294 96/C229 5 96/C2296 Journal of Analytical Atomic Spectrometry June 1996 Vol. 11 January 8-13 1996 (Ginzton Res. Center Varian Assoc. Palo Alto CA 94305-1025 USA). Jakubowski N. Thomas C. Stuewer D. Comparison of high efficiency nebulizers for coupling HPLC and ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Inst.Spektrochem. Angew. Spektrosk. D-44013 Dortmund Germany). Moens L. Vanhaecke F. Boonen S. Dams R. Direct determination of trace metals in solid samples by electrothermal vaporization ICP mass spectrometry (ETV-ICP-MS). 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Lab. Anal. Chem. Ghent Univ. B-9000 Ghent Belgium). Zlatan K. Stefan R. Determination of spallation and fission products in UOz and Tho targets by FI-ICP-MS and HPLC-ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Paul Schemer Inst. (PSI) CH-5232 Villigen PSI Switzerland). Greb U. Rottmann L. Analysis of small sample volumes by high resolution ICP-MS.1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Finnigan MAT GmbH D-28197 Bremen Germany). Behlke M. K. Uden P. C. Wise S. A. Schantz M. M. Methylmercury in whale livers kidneys and blubber as determined by gas chromatography with atomic emission detection (GC-AED). 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. Massachusetts Amherst MA 01003-43510 USA). Ebdon L. Elemental speciation-extending capability by new instrumental approaches. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Environ. Sci. Univ. Plymouth Plymouth Devon UK PL4 8AA). Olesik J. W. Kinzer J. A. Grunwald E. Thaxton K. Olesik S.Elemental speciation using capillary elec- trophoresis inductively coupled plasma mass spec- trometry and electrospray mass spectrometry. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13,1996 (Lab. Plasma Spectrochem. Laser Spectrosc. and Mass Spectrom. Dept. Geol. Sci. Ohio State Univ. Columbus OH 43210 USA). Moens L. Van Holderbeke M. Vanhaecke F. Dams R. Evaluation of a microconcentric nebulizer (MCN-100) for ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Lab. Anal. Chem. Inst. Nucl. Sci. B-9000 Ghent Belgium). Botto R. I. Gutierrez A. Volatile element species in volatile organic matrix direct determination by ICP- AES and ICP-MS. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Baytown Chem.Plant Lab. Exxon Chem. Co. Baytown TX 77520 USA). Hyun J. H. Lim H. B. Lee K. M. Lim C. H. Analysis of ceramics by inductively coupled plasma atomic emission spectrometry using slurry sample introduction technique in low power and mini torch. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Dankook Univ. Seoul 140-714 North Korea). Camuna-Aguilar J. F. Montes M. Pereiro R. Sanchez-Uria J. E. Sanz-Medel A. Katschthaler C. Knapp G. Microwave induced plasma and stabilized capacitive plasma atomic emmission for total halogens content determinations. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA,96/C2297 96/C2298 96/C2299 96/C2300 96/C230 1 96/C2302 96/C2303 96/C2304 96/C2305 9612306 9612307 96/2308 January 8-13 1996 (Dept.Quim. Fis. y Anal. Fac. Quim. Univ. Oviedo 33006 Oviedo Spain). Hintelmann H. Evans R. D. Measurement of relative bioavailability of mercury species in sediments by using a multiple traces isotope technique. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Environ. Sci. Centre Trent Univ. Peterborough Ontario Canada K9J 7B8). Carrilho E. N. V. M. Gilbert T. R. Mozeto A. A. Preconcentration of trace metals on the marine algae Pilayella Littoralis. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Barnett Inst. Northeastern Univ. Boston MA 02115 USA). Lund W. Methods for minimizing interferences in hydride generation atomic spectrometry.1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept. Chem. Univ. Oslo N-0315 Oslo Norway). Magnuson M. L. Creed J. T. Brockhoff C. A. Speciation of arsenic compounds by ion chromatogra- phy with ICP-MS detection utilizing hydride generation with a membrane separator. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (US Environmental Protection Agency Cincinnati OH 45268 USA). Farmer 0. T. 111 Smith M. R. Wyse E. J. Barinaga C. J. Koppenaal D. W. Separation and quantitation of radionuclides in Hanford environmental and waste tank samples using IC-ICP-MS techniques. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Pacific Northwest Lab.Richland WA 99352 USA). Handley H. Compton N. Determination of bromate and chlorate in drinking waters by coupled ion chromatography inductively coupled plasma mass spec- trometry. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dynamco Scientific Services Camberley Surrey UK GU16 6HZ). Hall G. Caughlin B. Hoffman E. Horowitz A. Longerich H. Geochemistry with plasma source mass spectrometry. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Geol. Surv. Canada Canada). Hall G. S. Rabinowitz M. Use of ICP-MS to characterize lead-based paints using stable lead isotopes and multielemental analyses. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Dept.Chem. Rutgers State Univ. New Jersey New Brunswick NJ 08903 USA). Smith M. R. Alexander M. L. Hartman J. S. Koppenaal D. W. Laser ablation laser parameters frequency pulse length power and beam charter play signigicant roles with regard to sampling complex samples for ICP-MS analysis. 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 (Pacific Northwest Lab. Richland WA 99352 USA). Anisimov V. N. Baranov V. Yu. Grishina V. G. Derkach 0. N. Sebrant A. Yu. Stepanova M. A. Interaction of laser ablation plasma plume with grid screens. Appl. Phys. Lett. 1995 67(20) 2922. (Inst. Laser Phys. Moscow 107078 Russia). Cromwell E. F. Arrowsmith P. Fractionation effects in laser ablation inductively coupled plasma mass spectrometry.Appl. Spectrosc. 1995,49( 1 l ) 1652. (IBM Storage Systems Div. San Jose CA 95193 USA). Steiner R. Stingeder G. Hutter H. Grasserbauer M. Haubner R. Lux B. Imaging SIMS for the investigation of substrate surfaces for CVD diamond deposition. Fresenius' J. Anal. Chem. 1995 352(3-4) 313. (Inst. 9 612 3 09 96/23 10 96/23 1 1 9612 3 1 2 96/23 13 9612314 96/23 15 96/23 16 9612 3 1 7 9612 3 1 8 96/23 19 96/2320 9612321 Anal. Chem. Tech. Univ. Vienna A-1060 Vienna Austria). Balaram V. Ramesh S. L. Anjaiah K. V. Comparative study of the sample decomposition procedures in the determination of trace and rare earth elements in anorthosites and related rocks by ICP-MS. Fresenius' J. Anal. Chem.1995 353(2) 176. (Natl. Geophys. Res. Inst. Hyderabad 500 007 India). Jin D.q. Zhou X.-h. Chen Q.-c. Gu Z.-n. Mass spectrometric analyses of 13C and "0 at microgram levels of calcium carbonate. Beijing Daxue Xuebao Ziran Kexueban 1995 31(4) 426. (Dept. Chem. Peking Univ. Beijing 100871 China). Liu L.-f. Cheng X.-w. Zhou W.-n. Hu M.-j. Sun G.-y. Wang N.-x. Formation of cross sections of "Be measured by accelerator mass spectrometry. Gaoneng Wuli Yu Hewuli 1995 19(9) 786. (Inst. Nucl. Res. Chinese Acad. Sci. Shanghai 201800 China). Ishijima A. Morohashi T. Kudo M. Ion induced alteration at lead-tin and lead-tin-silver alloy surfaces investigated by AES and SIMS. Hyomen Kagaku 1995 16(7) 422. (Fac. Eng. Seikei Univ. Musashino 180 Japan). Kriebel A. Levi-Setti R. Chabala J.Gutmannsbauer W. Haefke H. Topological and chemical analysis of AgBr microcrystals. ICPS' 94 Phys. Chem. Imaging Syst. IS&T's 47th Annu. Conf.. IS&T Springfield VA Rondon S. Wilkinson W. R. Proctor A. Houalla M. Hercules D. M. Characterization of Mo/C catalysts by XRD XPS and TOF-SIMS. J. Phys. Chem. 1995 99(45) 16709. (Dept. Chem. Univ. Pittsburgh Pittsburgh PA 15260 USA). Zhou M.-f. Qin Q.-z. Isotope determination of lead and bismuth by pulsed laser evaporation and resonance ionization time-of-flight mass spectrometry. J. Radioanal. Nucl. Chem. 1995 201(4) 303. (Nucl. Sci. Dept. Fudan Univ. Shanghai 200433 China). Takeshita H. T. Tomii Y. Suzuki R. O. Ono K. Local quantitative SIMS analysis of small amount of oxygen in titanium. Nippon Kinzoku Gakkaishi 1995 59(9) 973.(Dept. Eng. Sci. and Eng. Kyoto Univ. Kyoto Japan). Franzke B. Beckert K. Eickhoff H. Nolden F. Reich H. Schaaf U. Schlitt B. Schwinn A. Steck M. Winkler T. Schottky mass spectrometry at the experimental storage ring ESR. Phys. Scr. T 1995 T59 176. (Gesselschaft Schwerionenforschung mbH Darmstadt D-64220 Germany). de Saint Simon M. Thibault C. Audi G. COC A. Doubre H. Jacotin M. Kepinski J.-F. Le Gac R. Le Scornet G. et al. Orsay radio-frequency mass spectrometer. Phys. Scr. T 1995 T59 406. (Centre Spectrom. Nucl. Spectrom. Masse CNRS Orsay F-91405 France). Heavner T. P. Zuo M. Hayes P. Dunn G. H. Jefferts S. R. JILA Penning trap mass spectrometer. Phys. Scr. T 1995 T59 414. (JILA Univ. Colorado Boulder CO 80309-0440 USA). Vandervorst W.Kapeldreef I. Secondary-ion mass spectrometry a tool for surface and in-depth analysis. Proc.-Electrochem. Soc. 1995 30(Analytical Techniques for Semiconductor Materials and Process Characterization 11) 252. (B-3001 Louvain Belgium). Maurice V. Marcus P. Mason B. Lu Z. H. Sproule G. I. Rao T. S. Graham M. J. Characterization of (100)InP after surface passivation as studied by AFM XPS and SIMS. Proc.-Electrochem. SOC. 1995 30(Analytical Techniques for Semiconductor Materials and Process Characterization 11) 253. (Lab. Phys. Chim. Surfaces Ecole Natl. Superieure Chim. Paris 7523 1 Paris France). USA 1994. 0-89208-177-5. 216. Journal of Analytical Atomic Spectrometry June 1996 Vol. 11 251 R9 612 3 2 2 9 612323 9612324 9612325 9612326 9612327 9612328 9612329 9612330 961233 1 96/23 32 96/23 3 3 9612334 96/23 3 5 Koelbl G.Krachler M. Kalcher K. Irgolic K. J. Carapella S. C. (Ed.) Oldfield J. E. (Ed.) Palmieri Y. (Ed.) Determination of selenium compounds in biological and environmental samples using HPLC with selenium-specific detection. Proc. Int. Symp. Uses Selenium Tellurium 5th. Selenium-Tellurium Dev. Assoc. Grimbergen Belgium 1994. 291. Holmes L. J. Robinson V. J. Makinson P. R. Livens F. R. Multi-element determination in complex matrixes by inductively coupled plasma mass spectrometry (ICP-MS). Sci. Total Enuiron. 1995 173( 1-6) 345. (Dept. Chem. Univ. Manchester Manchester UK M13 9PL). Maemoto T. Yamashita T. Yano M. Inoue M. Sakamoto H. Watanaba M. Masuda K. RBS and SIMS analyses of BiPbSrCaCuO superconductor thin films by halide-CVD.Shinku 1995 38(3) 239. (Osaka Inst. Technol. Osaka 535 Japan). Niu HA. Luan S. Pang H.-m. Houk R. S. Langmuir probe measurements of the ion extraction process in inductively coupled plasma mass spectrometry. Part 2. Measurements of floating voltage and radiofrequency voltage. Spectrochim. Acta Part B 1995 50( lo) 1247. (Ames Lab. US Dept. Energy Dept. Chem. Iowa State Univ. Ames IA 50011 USA). Stevens R. J. Laughlin R. J. Allen J. (Ed.) Voges R. (Ed.) Nitrogen-15 gas-phase methodology and its applications to soil nitrogen research. Synth. Appl. hot. Labelled Compd. 1994 Proc. Int. Symp. 5th 1994. Wiley Chichester UK 1995. 317. Ristolainen E. O. Puga-Lambers M. Panthangay B. Holloway P. H. Depth profiling of thin film heterostruc- ture materials by secondary ion mass spectrometry.Vacuum 1995 46( 8-10) 1025. (Centre Chem. Anal. Helsinki Univ. Technol. FIN-02150 Espoo Finland). de Boer J. L. M. Verweij W. van der Velde-Koerts T. Mennes W. Levels of rare earth elements in Dutch drinking water and its sources. Determination by inductively coupled plasma mass spectrometry and toxicological implications. A pilot study. Water Res. 1996 30(1) 190. (Natl. Inst. Public Health Environ. Protection Bilthoven 3720 BA Netherlands). Liu Z.-y. Wang C.-r. Huang R.-b. Zheng LA. Mass distribution of cluster ions produced from laser ablation of metal-composite-oxides Y-M-Cu-0 (M =Ba Sr Ca Mg). 2. Phys. D At. Mol. Clusters 1995 34(4) 257. (State Key Lab. Phys. Chem. Solid Surface Dept. Chem. Xiamen Univ. Xiamen 361005 China).Hu K. Kunselman G. C. Hoffman C. J. Inductively coupled plasma optical emission mass spectrometric system and methods for trace analysis. Ger. Offen. DE 19512793 A1 12 Oct 1995 14pp. (Thermo Jarrell Ash Corp. USA). Ootsuka K. Iwanga M. Inductively coupled plasma mass spectrometer. Jpn. Kokai Tokkyo Koho JP 07240169 A2 12 Sep 1995 Heisei 4pp. (Nippon Electron Optics Lab. Japan). Goodner K. L. Dejsupa C. Barshick C. M. Eyler J. R. High magnetic field glow discharge ionization source. Report Order No. AD-A279 972 1994 5 pp. (Dept. Chem. Florida Univ. Gainesville FL USA). Wise M. L. Emerson A. B. Downey S. W. Detection of sputtered neutrals by ultrahigh-intensity postioniz- ation in the near-infrared. Anal. Chem. 1995 67(22) 4033. (AT & T Bell Lab. Murray Hill NJ 07974 USA).Hastings D. W. Emerson S. R. Nelson B. K. Determination of picogram quantities of vanadium in calcite and seawater by isotope dilution inductively coupled plasma mass spectrometry with electrothermal vaporization. Anal. Chem. 1996 68(2) 371. (Sch. 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Wiley Eastern Delhi India 1995. 448. 961278 1 96/2782 9612783 9612784 96/27 8 5 96/27 8 6 96/27 8 7 9612788 9 612 7 89 9612790 961279 1 9612792 9612793 9612794 Journal of Analytical Atomic Spectrometry June 1996 Vol. 11 Lewis D. G. Kilic A. Ogg C. A. Adaptation of the EGS4 Monte Carlo code for the design of a polarized source for X-ray fluorescence analysis of platinum and other heavy metals in viuo.Adv. X-Ray Anal. 1995 38 579. (Dept. Phys. Univ. Wales Swansea UK SA2 8PP). Roels H. Konings J. Green S. Bradley D. Chettle D. Lauwerys R. Time-integrated blood lead concen- tration is a valid surrogate for estimating the cumulative lead dose assessed by tibia1 lead measurement. Environ. Res. 1995 69(2) 75. (Unit Ind. Toxicol. and Occup. Med. Med. Sch. Catholic Univ. Louvain B-1200 Brussels Belgium). Parsons P. J. Zong Y.-y. Matthews M. R. Development of bone-lead reference materials for validating in vivo XRF measurements. Adv. X-Ray Anal. 1995 38 625. 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ISSN:0267-9477    

DOI:10.1039/JA996110239R

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

GLOSSARY OF ABBREVIATIONS Whenever suitable elements may be referred to by their chemical symbols and compounds by their formulae. The following abbreviations may be used without definition. ac AA AAS AE AES AF AFS AOAC APDC ASV BCR CCP CMP CRM cv cw dc DCP DDC DMF DNA ECD EDL EDTA EDXRF EI E EPMA ETA ETAAS ETV EXAFS FAAS FAB FAES FAFS FANES FAPES FI FPD FT FTMS GC GD GDL GDMS Ge( Li) HCL hf HG HPGe HPLC IAEA IBMK ICP ICP-MS ID IR IUPAC LA LC alternating current atomic absorption atomic absorption spectrometry atomic emission atomic emission spectrometry atomic fluorescence atomic fluorescence spectrometry Association of Official Analytical Chemists ammonium pyrrolidinedithiocarbamate anodic-stripping voltammetry Community Bureau of Reference capacitively coupled plasma capacitively coupled microwave plasma certified reference material cold vapour continuous wave direct current dc plasma diethyldithiocarbamate N N-dimethylformamide deoxyribonucleic acid electron capture detection electrodeless discharge lamp e t h ylenediamine te traace tic acid energy dispersive X-ray fluorescence easily ionizable element electron probe microanalysis electrothermal atomization electrothermal atomic absorption spectrometry electrothermal vaporization extended X-ray absorption fine structure flame AAS fast atom bombardment flame AES flame AFS furnace atomic non-thermal excitation spectrometry furnace atomization plasma excitation spectrometry flow injection flame photometric detector Fourier transform Fourier transform mass spectrometry gas chromatography glow discharge glow discharge lamp glow discharge mass spectrometry lithium-drifted germanium hollow cathode lamp high frequency hydride generation high-purity germanium high-performance liquid chromatography International Atomic Energy Agency isobutyl methyl ketone (4-methylpentan-2-one) inductively coupled plasma inductively coupled plasma mass spectrometry isotope dilution infrared International Union of Pure and Applied Chemistry laser ablation liquid chromatography (ammonium pyrrolidin- 1-yl dithioformate) spectroscopy LEAFS LEI LMMS LOD LOQ LTE MECA MIP MS NAA NaDDC NIES NIST NTA OES PIGE PIXE PMT PPm PTFE PVC QC rf REE(s) RIMS RM RSD SEC SEM SFC Si ( Li) SIMAAC SIMS SR SRM SSMS STPF TCA TIMS TLC TMAH TOP0 TRIS TXRF uhf uv VDU vuv WDXRF XRF PPb SIB SIN UV/VIS laser-excited atomic fluorescence spectrometry laser-enhanced ionization laser-microprobe mass spectrometry limit of detection limit of quantification local thermal equilibrium molecular emission cavity analysis microwave-induced plasma mass spectrometry neutron activation analysis sodium diethyldithiocarbamate National Institute for Environmental Studies National Institute of Standards and Technology nitrilotriacetic acid optical emission spectrometry particle-induced gamma-ray emission particle-induced X-ray emission photomultiplier tube parts per billion parts per million poly (tetrafluoroethylene) poly(viny1 chloride) quality control radiofrequency rare earth element(s) resonance ionization mass spectrometry reference material relative standard deviation signal-to-background ratio size-exclusion chromatography scanning electron microscopy supercritical fluid chromatography lithium-drifted silicon simultaneous multi-element analysis with a continuum source secondary ion mass spectrometry signal-to-noise ratio synchrotron radiation Standard Reference Material spark source mass spectrometry stabilized temperature platform furnace trichloroacetic acid thermal ionization mass spectrometry thin-layer chromatography tetramethylammonium hydroxide trioctylphosphine oxide 2-amino-2-( hydroxymethy1)propane- 1,3-diol total reflection X-ray fluorescence ul tra-high frequency ultraviolet ultraviolet-visible visual display unit vacuum ultraviolet wavelength dispersive X-ray fluorescence X-ray fluorescence Commonly Used Symbols 4 relative atomic mass Mr relative molecular mass r correlation coefficient S standard deviation Sr relative standard deviation Journal of Analytical Atomic Spectrometry June 1996 Vol.11

ISSN:0267-9477    

DOI:10.1039/JA996110270R

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Laser-enhanced Ionization Detection of Magnesium Atoms by a Combination of Electrothermal Vaporization and Flame Atomization Journal of Analytical Atomic Spectrometry KEN L. RITER WENDY L. CLEVENGER LEAH S. MORDOH BEN W. SMITH OLEG I. MATVEEV AND JAMES D. WINEFORDNER* Department of Chemistry University of Florida P.O. Box 11 7200 Gainesville FL32611-7200 USA A system for the electrothermal vaporization flame atomization laser-enhanced ionization ( ETV-FL-LEI) detection of Mg was optimized and completely characterized. The vaporization transport atomization probing and detection efficiencies were all determined experimentally. The overall efficiency of the system was found to be 0.00251%. The experimental detection limit of 2 ng ml-I (20 pg) for Mg was limited by noise due to the blank signal.A detection limit of 590 fg ml-' (5.9 fg) could be achieved in the absence of the blank and a reduction of radiofrequency noise. Keywords Magnesium; laser-enhanced ionization; electrothermal vaporization ; flame atomization The first observation of the phenomenon that has become known as laser-enhanced ionization spectroscopy (LEIS) was made almost twenty years ago.' Since then the mechanism has been well studied2-6 and the technique has been used to detect ultra-trace (sub-ppb) amounts of at least 34 element^.^ One of the main features offered by this technique is its selectivity owing to resonantly pumped ionization that is then collisionally assisted in a flame. This advantage becomes even greater when two laser-pumped excitation steps are used resulting in a four-level energy system.When two laser-pumped excitation steps are used the selectivity is extremely good although for complex and especially easily ionized matrices the detection capability suffers due to background generated from excitation in the wings of absorption lines belonging to the matrix species. In addition degradation in charge collection efficiency can occur due to modifications in the charge collec- tion process. These problems have been studied and brought under some degree of control by improvements in electrode design.'-'' Another advantage of LEIS over other trace analysis methods is the nonoptical nature of the detection system which avoids sources of noise and interference usually encoun- tered in flame techniques as well as interference due to laser scatter." In addition total charge collectiod2 and near-total ionization13 suggests the possibility of absolute or standardless analysis in certain cases.In approaching this goal it is neces- sary to examine the various processes that ultimately control the fate of the analyte from vaporization to detection. The generally accepted theoretical limit of detection14 for LEIS is in the order of 1 fg ml-I or about 100 atoms ~ m - ~ . Typically the laser beams occupy a volume in the flame of about 0.1 cm3; this corresponds to an absolute detection limit of about 10 atoms. This implies an ionization yield (defined as the number of charge pairs produced per atom in the probe volume) near unity and indeed ionization yields of this * To whom correspondence should be addressed.magnitude have been rneas~redl',~~ and have been predicted the0retical1y.l~ In some cases the theoretical detection limit was close to being obtained. The collisional rate in the flame is sufficient to provide complete ionization for atoms within about 1 eV (about 5 kT for an air-acetylene flame) of the ionization limit. The efficiency of charge collection has also been shown to be unity.12 In general when the ultimate detection capability has not been achieved it has been due to a poor choice of excitation wavelengths (to levels further than 1 eV from the ionization limit) low laser pulse energy (insufficient to saturate the transitions involved) or to unusual sources of limiting noise particularly rf noise. In properly designed experiments all of these difficulties can be overcome.Nevertheless despite the phenomenal detection capability LEIS has found limited use as an analytical method. This can be attributed to three problems (1) the requirement of a dual dye laser system (2) unpredictable interferences and ( 3 ) the poor atomization efficiency of many elements in suitable combustion flames.17 The first problem once considered a substantial complexity is no longer a serious disadvantage especially as tunable solid-state lasers become available in useful wavelength regions. The second problem caused in large part by complex matrices present in real samples has limited LEIS mostly to simple aqueous samples. The third problem is unavoidable if one wishes to induce and observe ionization at atmospheric pressure since the flame provides the necessary collisional redistribution.No other atom reservoir has been found to be practical for LEIS measurements. Because of these last two problems attempts have been made to observe LEI in alternate atom reservoirs including the inductively coupled plasma (ICP)'* and the graphite furnace (GF).19,20 The ICP achieved limited success due to its large rf noise background. The GF is an attractive option because of its superior atomiz- ation efficiency as well as indications of improved sampling and probing efficiencies compared to the flame. However its disadvantages include a large background current induced by the high current used to electrically heat the GF along with thermionic emission from the GF that is directly detected.In addition the ionization yield in the GF is probably lower than that observed in a combustion flame because of the lower collisional rate available in the furnace environment. The signal was also observed to suffer a suppression due to the presence of sodium in the matrix.21 A more successful approach was made by placing the GF directly into the LEI In this method the sample is rapidly vaporized into the probe region and is very efficiently detected. Liquid powder and solid micro-samples may be directly analysed. Recently Chekalin and c o - ~ o r k e r s ~ ~ have obtained detection limits of 0.1 to 1 ng g-' for Co Cr Mn and Ni in a complex fluorine matrix using direct solid sampling. In a technique coupling LEI with liquid chromatography Epler and co-workers2* have Journal of Analytical Atomic Spectrometry June 1996 Vol.11 (393-399) 393determined organolead compounds in NIST SRM Oyster Tissue 1566 at 0.5 to 1 ngg-l. Another successful method involving the introduction of samples into an air-acetylene flame from a tungsten electrothermal vaporizer was developed to analyse thallium in water samples with detection limits in the sub-ppb range.29 An alternative approach is to couple a graphite furnace with a flame by a sample transfer line.26 A GF is interfaced to the LEI flame via a 1 m length of tubing through which a stream of argon flows. The GF performs the vaporization while atomization ionization and detection take place in the flame. This allows one to exploit the advantages of both processes while maintaining independent control of each. The purpose of the present work was to study the various processes that affect the atom from its vaporization in the furnace to its detection in the flame. THEORY The amount of charge that should be created per mole of analyte is given by the Faraday constant F which is equal to 96485 C mol-I.The signal (in C) for GF-Flame-LEI may be expressed as:4,30 where W is the mass (8) of analyte in the sample A is the atomic weight of the analyte (g mol-l) E~ is the vaporization efficiency of the furnace E~ is the transport efficiency between the furnace and the flame E is the atomization efficiency (or free atom fraction fi) of analyte in the flame cp is the laser probing efficiency and Ed is the detection efficiency (efficiencies are all dimensionless.) Before considering the possibility of using this technique as an absolute method each of these efficiencies must be fully characterized.The transport efficiency E ~ describes how effectively the analyte vaporized in the furnace is transported to the flame. This value must be experimentally determined as it is a characteristic of the experimental set-up. The probing efficiency of the laser beams E ~ is a product of the spatial probing efficiency E ~ and the temporal probing efficiency E,. The spatial probing efficiency describes what portion of the flame the laser beams encompass. If the lasers encompass the entire flame then E = 1. The temporal probing efficiency can be calculated as Dbf E = ~ U where Db is the diameter of the laser beam (cm) f is the frequency of the pulsed laser (Hz) and u is the flame velocity (cm s-').The vaporization efficiency of the furnace eV is assumed to be approximately loo% provided the proper temperature and ramp times are chosen to control the GF. The atomization efficiency E describes the portion of the sample that is actually present in the flame as free atoms capable of being ionized. This is a function of the analyte and the flame conditions and can be found in tables or experimen- tally determined.31-33 The detection efficiency Ed describes the charge collection by the electrode and the ionization efficiency induced by the laser in the flame. It is calculated as Ed = x & D (3) where is the ionization yield and E~ describes the efficiency of charge collection.The actual signal detected in our case is the induced charge QI which is related to the total charge QTut by the equation (4) where AV is the actual potential in the flame at the point of ionization and V is the potential applied to the electrode.34 The fraction AV/V describes the efficiency of charge collection cD in our case so AV ED=- V The ionization yield describes the fraction of atoms which becomes ionized in the flame due to the laser induced process. According to Omenetto et al.,35 when the second excitation transition reaches a Rytlberg level from which collisional ionization occurs very rapidly the ionization yield can be determined by measuring what is known as the fluorescence dip. This parameter describes the decrease in resonance fluo- rescence from the first excited level that occurs when adding the second pumping process.This second excitation process depletes the atomic population of the first excited level such that they do not return to the ground state. The resonance fluorescence signal is always proportional to the number density of excited atoms in the first excited state.36 As it has been shown from simple theoretical consideration^,^^-^^ the ionization yield will approach unity when an optically saturat- ing laser pulse has a duration that significantly exceeds the reciprocal of the effective ionization rate of the laser populated excited state. However before using the fluorescence measure- ment to directly evaluate the ion yield one must be sure that there is no loss due to quenching collisions into a metastable level.In the absence of collisional quenching the ionization yield can be calculated as where I is the signal intensity for the resonance fluorescence. EXPERIMENTAL A block diagram of the experimental set-up used is shown in Fig. 1. Two dye lasers (Model Scanmate 1 Lambda Physik Acton MA USA) were pumped by an excimer laser (Model LPX-24Oi Lambda Physik Acton MA USA) operated with XeC1. The beams were directed into a mini-flame by quartz prisms and lenses. Sample aliquots (10 pl) of Mg solutions were vaporized with a graphite furnace (Finnigan MAT/SOLA Bremen Germany) and swept into the mini-flame through a PTFE transfer tube by a flow of carrier argon. Two-step LEI was performed on Mg in the air-acetylene mini-flame. The LEI signal was observed by measuring the induced charge between a cylindrical water-cooled high voltage electrode immersed in the flame and the burner head.The LEI signal was then amplified by a pre-amplifier and recorded by a computer. Typical characteristics of the experimental set-up and experiments performed are given below. I -Hv ETV I+' To Fig. 1 Block diagram of the experimental set-up 394 Journal of Analytical Atomic Spectrometry June 1996 Vol. 11Lasers The excimer pump laser was operated at a repetition rate of 30Hz. The two laser dyes used were Coumarin 153 and Coumarin 120 (Lambda Physik Acton MA USA). Both dyes were dissolved in high purity methanol (Optima grade Fisher Scientific Pittsburgh PA USA). The output of the Coumarin 153 at 570.4 nm was frequency doubled with a BBO I11 crystal (Lambda Physik Acton MA USA).Laser pulse durations were approximately 40 ns (full width at half maximum) rather than the LPX-24Oi nominal duration of 14ns. Pulse energies were typically 150 mJ for the excimer 3 mJ for the Coumarin 153 50 pJ for A (Coumarin 153 doubled by BBO 111) and 4 mJ for 2 (Coumarin 120). Conversion efficiencies were typi- cally 8% for Coumarin 120 6% for Coumarin 153 and 2% for the BBO I11 crystal. i C285.213 nm 3s2 ' S - + ~ S ( ~ S ) 3p 'Pl0 A2,=4.95 x 10' s-'1 was focused into a 5 times beam expander (Model 15600 Oriel Corporation Stratford CT USA) by a quartz cylindrical lens [focal length (fl)=3.5 in]. i2 C435.191 nm 3s(,S)3p 1P,o+3s(2S)6d 3D2 A,,= 2.1 x lo7 s-'1 was focused with a quartz lens (fl=41 in) into the flame. At the flame i1 is a square beam approximately 4mm wide and 1 is a round beam approximately 6mm in diameter encompassing A,.Both laser beams were positioned immediately below the high voltage electrode for efficient charge collection. Flame The burner used for these studies was designed in our labora- tory and is shown in Fig. 2. The burner produces a cylindrical mini-flame into which a stream of argon is injected up the centre. The carrier argon and the vaporized sample flow up the central stainless-steel capillary (od = 0.095 in id = 0.077 in). The premixed flame gases acetylene and air flow out around the central capillary (0.125 in hole). Air acetylene and carrier argon flow rates were optimized with respect to the signal-to- noise ratio.All gas flows were calibrated with a mass flowmeter (Model ALK-SOK Teledyne Hastings-Raydist Hampton VA USA) at experimental conditions. Average flame gas velocity was measured by observing the LEI signal at two different positions in the flame and measuring the time differential between the two ion pulses.40 For this experiment the burner head was grounded and an iridium wire (diameter = 0.012 in) was inserted into the flame above the laser beams. The Ir wire was connected to the circuit and transimpedance amplifier used for the regular LEI experiments described below. The amplified signal was observed and recorded on a digital storage oscilloscope (Model 620A Tektronix Beaverton OR USA). A Electrode cm and air T Ar and sample Mini-burner design and relative position Fig.2 Ion pulses for 10 pl samples of 100ppb Mg solution were observed on the oscilloscope. The Ir wire was moved a distance d of 1 mm in the z-direction (up and down) and the time differential z between the ion pulses was determined. The flame gas velocity was calculated by the following formula (7) where u is the flame gas velocity (cm s-'). Flame temperature was measured using the two-line m e t h ~ d ~ ~ v ~ ~ with iron. This procedure has been described in detail elsewhere.43 The absolute temperature T can be calcu- lated from the equation 0.6247 ( E l - E2) T= where El and E are excitation energies (cm-') g and g are statistical weights of the states A and A are transition probabilities for the lines v1 and v2 are frequencies of the lines and 1 and I are the relative intensities of the two lines.The photomultiplier tube (Model R928 Hamamatsu Photonics Japan) response was calibrated using a standard light source (Model FEL-C Optronic Laboratories Orlando FL USA) as described by Schneider and G0ebe1.~~ All iron solutions were introduced into the mini-flame using a laboratory con- structed ultrasonic nebulizer. The relative line intensities of Fe emission at 382.043 nm and 371.994 nm were measured. The temperature was calculated using values for the statistical weights and transition probabilities obtained from the litera- ture4' and the relative line intensities measured. A profile of the relative atom concentrations in the flame was obtained by observing the saturated resonance fluores- cence (285.213 nm) at various positions in the flame.The beam expander and cylindrical lens were removed from A,. A plano- convex quartz lens (fl=4.5 in) was then inserted in order to focus the beam down to a very small spot in the flame. Resonance fluorescence was collected at 90" with a fused-silica collection lens (fl=3.5 in) which was used to image the flame onto the monochromator (Model EU-700 GCA/McPherson Instrument Acton MA USA) slit. Fluorescence was detected at 285.213 nm. Saturation of the fluorescence was checked by insertion of neutral density filters into the excitation beam. Saturation was confirmed at several different positions within the flame. The burner was translated in the x- y- and z- directions and a relative spatial distribution of Mg atoms in the flame was obtained from the relative fluorescence intensities.Graphite Furnace A graphite furnace (System 3000 GBC Scientific Instruments Melbourne Victoria Australia) modified by Finnigan (Finnigan MAT/SOLA Bremen Germany) for use with an ICP-MS was used to vaporize all samples for flame LEI. Pyrolytic graphite coated graphite tubes were used for all LEI experiments. The temperature of the graphite furnace was monitored by measuring the emission from the heated graphite tube with a photodiode mounted just outside the right window. The sample was transferred from the graphite furnace to the burner by a flow of argon through a PTFE transfer tube (Cat. # AP-06375-02 Cole-Parmer Instrument Company Niles IL USA) approximately 1.7 m long (id = 5/32 in od = 1/4 in).The graphite furnace was modified by separating the argon flow through the centre of the graphite tube from the flow around the tube and replacing the left window of the furnace with a sample transfer interface. The argon flow through the graphite tube was adjusted with a mass flow controller. The Journal of Analytical Atomic Spectrometry June 1996 Vol. 11 395sample transfer interface consisted of a tantalum tube placed about 5 mm from the graphite tube a stainless-steel holder that fitted into the original window housing and a PTFE adapter to connect the holder to the transfer tubing. This interface was modified by extending the tantalum tube to within 2mm of the graphite tube and eliminating the PTFE adapter by threading the transfer tubing so that the tubing could be directly attached to the stainless-steel holder.A sharpened 1/8 in diameter graphite electrode (Part # L4236 Spectrographic Services Sussex NJ USA) was used to plug the injection hole of the graphite tube during e~perirnents.~~ Fig. 3 shows a cross-sectional view of the graphite furnace with the tantalum sample extraction probe at the left. In order to optimize the vaporization efficiency of the furnace a study of the ETV temperature program was made. Temperatures ranging from 1850 to 3000 "C were examined. Matrix Modifier Once all of the optimizations were performed solutions of different concentrations of magnesium were introduced to check the linearity of the system response. It was observed that at lower concentrations of Mg (< 100 ppb) the precision was worse than that observed for the higher concentrations.Therefore the feasibility of using a matrix modifier to act as a physical carrier for the lower concentration samples was evaluated. Although the process that allows signal enhance- ment with a matrix modifier in the furnace is not well under- stood one theory47 involves the aerosol formed by the modifier acting as a physical carrier for the sample to condense upon forming aggregates of large enough size to be transported out of the furnace. Since formation of insufficiently sized aggregates due to the small amount of sample present in the furnace seemed possible a matrix modifier was chosen. The main criterion for making this choice was to find a carrier with negligible Mg contamination (less than our blank contami- nation of about 3 pg ml-').Ultrapure methanol (Optima grade Fisher Acton MA USA) was chosen as a possibility. Subsequent analysis indicated that no detectable Mg was present but a blank LEI signal (not due to Mg) was obtained with the methanol carrier. However this signal was reproduc- ible and was therefore subtracted from the sample peak signals. The temperature program was changed so that the time between the drying and vaporization steps would be long enough (90 s) to allow the tube to cool so that the methanol could be injected. A volume of 6 p1 was found to be optimal. The inclusion of methanol as a physical carrier for the low concentration samples resulted in a noticable improvement in precision and sensitivity. It was subsequently used with all Mg concentrations below 100 ppb.Transport Efficiency In order to determine the transport efficiency (which actually included the vaporization efficiency of the furnace) from the I/ Graphite plug window housing1 I Fig. 3 Cut-away view of the graphite furnace showing the tantalum sample extraction probe furnace to the flame a trapping technique modelled after that described by Schmertmarin et was used. Cotton was used to trap the particulates transported by the carrier argon. Various types of cotton were digested in 50% high-purity nitric acid (Optima grade HNO Fisher Scientific Acton MA USA) and analysed by atomic absorption to find the one containing the least amount of Mg. PADCO cotton (non-surgical bleached cotton ACCO Valley Park MO USA) purchased from Fisher Scientific was selected for use.The trapping apparatus was made up of two glass bubblers connected in tandem to the end of the transfer tubing leading from the ETV. The conriection between the tubing and first bubbler included a 1 in length of stainless-steel capillary to make it as similar as possible to the connection between the tubing and the mini-burner. The connection between the two bubblers was a two-inch length of Tygon tubing (id=0.375 in od=0.625 in). A 1.60 g sample of the cotton was placed into the bottom of each bubbler to trap the particulate produced by the furnace. Since the resulting trapping solution was to be analysed via atomic absorption the final concentration had to be in the range of 1-1000ppb. This was achieved by the injection of 100 samples of 100 ppm Mg solution (10 p1 each).The cotton was then digested in 60ml of 50% high-purity HNO in a 70 "C water bath for 30 minutes. The resulting solution was then hot filtered into a 100 ml volumetric flask and diluted to the mark with high-purity water (Milli-Q Plus Water System). To check the validity of the trapping system we used the LEI system to analyse Mg standards from 1 ppb to 100 ppm and confirmed that the signal remained linear over this range. This supports the theory that an increase in sample mass and vapour concentration will result in an increase in particle concentration rather than particle size and therefore the transport efficiency will not significantly change with the sample mass.38 We also compared the LEI signal of 100 ppm Mg to the signal detected with a trap placed between the furnace and flame and found that >99.9% of the Mg that travelled through the tubing was being trapped.An effort to account for the analyte losses incurred during transport included analysing residue in the transport tubing since larger particles formed in the vapour can become deposited on the tubing by gravitational or streaming forces. The transfer tubing was rinsed with 50% high-purity HNO and the subsequent solution was analysed by atomic absorp- tion spectroscopy. To measure the loss of magnesium due to diffusion through the graphite walls of the furnace magnesium in the shroud gas flowing around the outside of the furnace and discharged through the opening of the furnace encasement around the dosing hole was measured.The PTFE tubing leading to the flame was interfaced to the dosing hole opening such that this shroud gas would be sent to the flame for analysis by LEI. The argon flow was matched to that which flowed through the graphite tube. An additional study which examined laser excited atomic fluorescence along the length of the tube both top and bottom was performed to confirm diffusion losses and to give a spatial indication of the diffusion losses. Fluorescence DipIonization Yield The fluorescence at 285.213 nm was collected at 90" as described earlier. To determine the ionization yield the fluo- rescence dip for the 285.213 nm line of Mg was measured. Measurements were made by aspirating the solutions into the flame via a laboratory-constructed ultrasonic nebulizer described earlier.First the blank (high-purity water) signal was measured to determine the scatter (background) from the laser. Next a concentrated solution of Mg was aspirated into the flame and the resonance fluorescence detected on the 396 Journal of Analytical Atomic Spectrometry June 1996 Vol. 11oscilloscope. A2 (435.191 nm) was then added and for the same solution a decrease in the fluorescence intensity was observed. To ensure that there was no loss of atoms from the first excited level due to collisional quenching saturation of the fluorescence signals from three different positions within the flame was confirmed. This same procedure was then repeated using ETV sample introduction rather than the nebulizer and the LEI signal was monitored simultaneously as shown in Fig.1. A solution of 10 ppb Mg was injected in volumes of 10 pl which is a much lower concentration than that which was aspirated via the nebulizer. The fluorescence dip at 285.213 nm was observed with the addition of A2 (435.191 nm) simultaneously with the LEI signal enhancement. From this measurement the ioniz- ation yield for Mg in the flame was estimated. In order to determine the ionization yield in terms of laser induced rates an LEI simulation program called DENSMAT49 was used to model the experiment. After importing all experimental param- eters characteristic of our system (including an unusual laser pulse shape) the theoretical ionization yield was calculated. Detection System A water-cooled stainless-steel electrode (od = 3 mm) was immersed in the flame and a negative high voltage (-800 V) was applied.An aluminum box was used to partially shield the system from extraneous rf noise. During optimization studies of the applied electric field the high voltage to the electrode was varied from 0 to 2000V. In addition to finding the optimal value the shape of the signal versus electric field served as an indication of whether or not complete charge collection was occurring. The induced charge was collected through an electrical connection to the central burner capillary and transferred to a circuit consisting of a 10 ki2 resistor to ground and a 1 nF capacitor in series. The signal then passed through a transimpedance amplifier (Model Al THORN EM1 Gencom Fairfield NJ USA) low noise preamplifier (Model SR560 Stanford Research Systems Sunnyvale CA USA) and a boxcar averager (Model SR250 Stanford Research Systems Sunnyvale CA USA).The theoretical detection limit of the transimpedance pre- amplifier was calculated by determining the equivalent noise charge (ENC) of the ~reamplifier.~' A pulse generator (Model PG501 Tektronix Beaverton OR USA) was connected to the input circuit consisting of a capacitor C (1 pF) which was connected in series to the Thorne A1 preamplifier. Some parasitic or stray capacitance C in parallel was also present in the circuit. The value of C is typically around 15 to 30 pF. An input voltage Uin of 55.4 mV (50 ns pulse width) was delivered by the pulse generator. If C >> C then Q = Uin - C where Q is the charge.The ENC can be calculated by the equation (9) where SN=RMS noise of the preamplifier and S=the output of the preamplifier. To determine SN the preamplifier input was disconnected and the RMS noise of the preamplifier measured using an oscilloscope. The charge response of the detection system was measured using the following scheme. The pulse generator described above was connected to a calibration circuit consisting of a 50Cl resistor in parallel and a capacitance C in series. A parasitic or stray capacitance C was again present in parallel within this circuit. The calibration circuit was then connected to the original input circuit and the A1 preamplifier. A voltage pulse Uin was applied and the output of the preamplifier S was measured for each value of C,.If C,>> C then Qc= Uin C where Q = the charge applied. Values of 1 pF and 2 pF were used for C,. A 55.4 mV pulse was used for Uin (50 ns pulse duration). The average signal output S from the pre- amplifier corresponding to a 1 pF charge was recorded. The amount of charge Q was calculated and divided by S to give the charge response of the detection system. RESULTS AND DISCUSSION General Studies Graphite furnace vaporization Little difference was observed in signals using vaporization temperatures from 1900 to 2200 "C; 2000 "C was chosen as the vaporization temperature because the best precision was obtained at this temperature and 2500°C was chosen as the temperature for the cleaning step. Table 1 lists the character- istics of the entire optimized furnace temperature program.Gasjlow rates and applied high voltage Optimal volumetric gas flow rates with respect to S/N were found to be about 622 cm3 min-' for air 85 cm3 min-' for acetylene and 357 cm3 min-' for the carrier argon. The stoi- chiometric air-to-fuel mole ratio of this flame was 6.9 indicating that it was fuel lean. Flow rates for carrier argon 2700 cm3 min-' resulted in a shorter residence time for the analyte in the flame which resulted in small signals. Flow rates for carrier argon < 200 cm3 min- ' gave larger signals but with poorer precision. A flow of 357 cm3 min-l was chosen as it appeared to result in signals with the best signal-to-noise ratio. The best S/N and precision were obtained with an applied electrode voltage of - 800 V. Flame temperature and gas velocity The flame temperature measured using the two-line method with iron was found to be about 1973 "C.This is cooler than a normal air-acetylene flame (temperature 2267 "C). However this result was expected since our flame is much smaller than a normal air-acetylene flame and because of the stream of cold argon injected up the centre of the flame. The flame gas velocity was measured using an LEI based rneth~d.~' The time differential z was found to be 240 ps for a distance d of 1 mm. The flame gas velocity was then calculated to be 4.2 m s-'. Spatial profile of magnesium atoms in theflame A spatial profile of the relative fluorescence intensities for Mg in the flame is shown in Fig. 4. The fluorescence intensities can be related to the relative Mg atom concentrations in the flame so this profile gives us an indication of where the Mg atoms reside in the flame.It appears that the laser beams should be centered about 10 mm above the burner head. This is expected since it should take a certain distance for the cold argon and sample to thoroughly mix with the flame gases. The data shown in Fig. 4 also indicate that over 80% of the Mg atoms Table 1 Electrothermal vaporization temperature program for magnesium Step TemperaturePC Ramp time/s Ramp hold/s 1. Drying 90 2. Cool Down 20 (add carrier) 3. Vaporization 2000 4. Cool Down 20 5. Cleaning 2500 6. Cool Down 20 10 60 10 90 3 6 1 20 3 6 1 10 Journal of Analytical Atomic Spectrometry June 1996 Vol. 11 39720 18 - 16 - E E 2 E 3 14 - n n d 2 1 2 - a c .- 0 10 - 8.6 Relative fluorerscence intensities n 5.00-12.5 12.5-20 0 20.0-27.5 275-35.0 35.0-42.5 42.5-50.0 50.0-57.5 57.5-65.0 I I I I -2 -1 0 1 2 Distance from centre (in) Y-directionlmm Fig. 4 Magnesium fluorescence profile of the flame reside within a 4 mm width. Over 99% of the Mg atoms reside within approximately a 6 mm flame diameter. Theoretical detection limit The theoretical detection limit of the transimpedance amplifier was calculated by determining its equivalent noise charge (ENC). The ENC was found to be about 3700 electrons. Therefore if the transimpedance amplifier noise is the limiting noise in the experimental system the minimum number of detectable electrons should be 3700. The charge response of the detection system was calculated to be approximately 3.3 x lo4 electrons mV-l. The signal S corresponding to an input potential Uin of 55.4 mV and a capacitance C of 1 pF was found to be 10.5 mV.The applied charge Q of 5.5 x C (3.44 x lo5 electrons) was divided by the signal S to obtain the charge response. Vaporization Efficiency After the vaporization temperature was optimized the vaporiz- ation efficiency was checked by attempting to observe the LEI signal associated with the cleaning step. However no signal was observed from the cleaning peak even after increasing the preamplifier gain ten times. Therefore the vaporization efficiency was deduced to be > 99.9% ( E ~ > 0.999). Transport Efficiency The results of the transport study indicated that the transport efficiency was 0.17. It was determined that about 8% of the analyte was being lost due to adhesion to the tubing and about 24% due to diffusion through the graphite walls of the furnace.From the laser induced fluorescence study it appears that the primary loss through the graphite was through the dosing hole. The rest of the analyte loss during transport was not accounted for. It is suspected that the unaccounted analyte is either depositing very early in the tantalum tube or is escaping through the 2 mm gap between the graphite tube and the tantalum tube at the ETV. The transport efficiency decreased at low concentrations (< 100 ppb). The use of methanol as a carrier improved the transport efficiency at very low concentrations and was there- fore used. Probing Efficiency The probing efficiency of the laser beams E ~ is the product of the spatial probing efficiency E ~ and the temporal efficiency E ~ .The probing efficiency was determined to be 0.023. The spatial probing efficiency was estimated from the fluorescence profile of the flame at a distance of 10mm above the burner head and was found to be 0.81. The temporal probing efficiency can be calculated from the diameter of the laser beam the frequency of the pulsed laser and the velocity of the flame gases. The diameter of the laser beam was measured and found to be approximately 4 mm. The laser repetition frequency used was 30 Hz. The velocity of the flame gases was calculated earlier to be 420 cm s-'. The calculated temporal probing efficiency E was 0.0286. Detection Efficiency The detection efficiency E d is the product of the ionization yield x and the efficiency of charge collection cD.The detection efficiency was found to be 0.675. The fluorescence dip observed when adding the second excitation step to the first resulted in a ~ 9 9 . 9 % dip in the fluorescence signal. This indicates a high degree of ionization within the flame as the only other source of fluorescence dip collisional redistribution to other excited levels contributes <2-3%. To ensure the accuracy of these results the gain on the boxcar was increased by a factor of ten and the measurements repeated. To confirm the absence of collisional quenching as a source of decreased fluorescence measurements were made at several incident laser powers confirming that near saturation was always achieved.From DENSMAT the LEI simulation program an ionization yield of 0.984 was calculated. From these results the ionization efficiency of Mg in the flame was found to be 20.984. The actual potential in the flame at the level of the laser beams was determined b y measuring the potential using an iridium wire inserted directly into the flame. The actual poten- tial AV was found to be - 540 V. The potential applied to the electrode V was -800V. Therefore the efficiency of charge collection E ~ was calculated to be 0.675. Atomization Efficiency The atomization efficiency was calculated using the equation SAa & =- a 96485 W a ~ V ~ T ~ p ~ d where the symbols were defined earlier. The signal from a 100 ppb Mg sample (10 p1) and the previously determined efficiencies were used.The atomization efficiency was found to be 0.0096. Previously reported values of E (or p) for air- acetylene flames range from 0.59 to 1.06.'4,32,51 The value obtained for our flame is lower than these but this is expected since our mini-flame is substantially cooler than a normal air- acetylene flame. Also the cold stream of argon injected up the centre of the flame probably decreased the atomization efficiency. Analytical Curve and Limits of Detection The analytical curve was rectilinear for 2.5 to 100ppb of Mg in 2% HN03. A slope of .2.46 C mol-' was obtained and the 398 Journal of Analytical Atomic Spectrometry June 1996 Vol. 1 1experimental limit of detection (LOD S/N = 3) was estimated to be 2 ng ml-I (20 pg). This LOD was limited by the blank signal from the 2% HNO and methanol carrier.The limiting non-blank noise level was found to be 9.8 fC rms. This limiting noise level was primarily due to rf noise from extraneous sources. Using this limiting instrumental noise the LOD for Mg was calculated to be 29 pgml-I (290 fg). The rf noise may be reduced by the design and construction of a better metal shielding box. If the rf noise can be reduced to a level below that of the A1 preamplifier noise then the theoretical LOD would depend on the A1 noise. For this case the theoretical LOD for Mg was calculated to be 590 fg ml-’ (5.9 fg). This compares favorably with LODs recently deter- mined for Mg with ETV-ICP-AES (0.1 ~ g ) ’ ~ ETV-ICP-MS and FANES (20 ~ g ) ’ ~ and ETV-AAS (0.4 ~ g ) .~ ~ CONCLUSION The combination of an ETV source with a small flame LEI detection system has been shown to have an over-all detection efficiency of 2.51 x The most significant inefficiency (ca= 0.0096) occurred in the formation of free atoms in the flame. It may not be possible to improve this further without increas- ing the noise introduced by the flame background current. The probing efficiency (8 = 0.023) was primarily limited by the inefficient temporal excitation due to the 30 Hz repetition rate of the laser which was used. This could be significantly improved simply by using a laser system operating at higher repetition rate. In this experimental system a rate of about 1 kHz would be needed to bring E = 1. In order to access the potential for standardless analysis by this technique the stab- ility of the over-all efficiency with time must be established as well as the possible influence of varied matrices.This research is supported by a grant from the National Institutes of Health R01-GM49638-03. REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Green R. B. Keller R. A. Schenck P. K. and Travis J. C. J. Am. Chem. Soc. 1976 98 8517. Havrilla G. J. and Carter C. C. Appl. Opt. 1987 26 3510. Omenetto N. Berthoud T. Cavalli P. and Rossi G. Anal. Chem. 1985 57 1256. Marunkov A. G. Reutova T. V. and Chekalin N. V. Zh. Anal. Khinz. 1986 41 681. Green R. B. and Seltzer M. D. in Laser-induced Ionization Spectrometry ed. Sneddon J. JAI Press Tnc. Greenwich CT 1992 vol. 1. Axner O. Rubinsztein-Dunlop H. and Sjostrom S. Mikrochim.Acta 1989 3 197. Axner O. and Rubinsztein-Dunlop H. Spectrochim. Acta Part B 1989 44 835. Trask T. O. and Green R. B. Spectrochim. Acta Part B 1983 38 503. Turk G. C. Anal. Chem. 1981 53 1187. Axner O. Magnusson I. Petersson J. and Sjostrom S. Appl. Spectrosc. 1987 41 19. Turk G. C. Travis J. C. DeVoe J. R. and O’Haver T. C. Anal. Chem. 1979 51 1890. Schenck P. K. Travis J. C. Turk G. C. and O’Haver T. C. J . Plzys. Chem. 1981 85 2547. Omenetto N. Smith B. S. and Hart L. P. Fresenius’ J . Anal. Chem. 1986 324 683. Matveev 0. I. and Omenetto N. Con5 Proc. #329 (RIS 94) 1994 515. Smith B. W. Hart L. P. and Omenetto N. A d . Chem. 1986 58 2147. Axner O. and Berglind T. Appl. Spectrosc. 1979 43 940. Smith B. W. Petrucci G. A. Badini R. G. and Winefordner J.D. Anal. Chem. 1993 65 118. 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 Turk G. C. and Watters R. L. Anal. Chem. 1985 57 1979. Magnusson I. Axner O. Lindgren I. and Rubinsztein- Dunlop H. Appl. Spectrosc. 1986 40 968. Magnusson I. Sjostrom S. Lejon M. and Rubinsztein- Dunlop H. Spectrochim. Acta Part B 1987 42 713. Butcher D. J. Irwin R. L. Sjostrom S. Walton A. P. and Michel R. G. Spectrochim. Acta Part B 1991 46 9. Chekalin N. V. Pavlutskaya V. I. and Vlasov I. I. Inst. Phys. Con5 Ser. 1991 114 283. Chekalin N. V. and Vlasov I. I. J. Anal. At. Spectrom. 1992 7 225. Chekalin N. V. Pavlutskaya V. I. and Vlasov I. I. Spectrochim. Acta Part B 1991 46 1701. Chekalin N. V. Marunkov A. G. Pavlatskaya V.I. and Bachin S. V. Spectrochim. Acta Part B 1991 46 551. Chekalin N. V. Marunkov A. G. Vlasov I. I. and Kalmanov A. T. Khim. Vys. Energ. 1994 28 465. Chekalin N. V. Khalmanov A. Marunkov A. G. Vlasov I. I. Malmsten Y. Axner O. Dorofeev V. S. and Glukhan E. Spectrochim. Acta Part B 1995 50 753. Epler K. S. O’Haver T. C. and Turk G. C. J. Anal. At. Spectrom. 1994 9 79. Miyazaki A and Hiroaki T. Anal. Sci. (1991 Suppl.) 1991 7 1053. Omenetto N. Spectrochim. Acta Part B 1989 44 131. Slavin W. Manning D. C. and Carnick G. R. At. Spectrosc. 1981 2 137. Metal Vapors in Flames ed. Alkemade C. Th.J. Hollander Tj. Snelleman W. and Zeegers P. J. Th. Pergamon Press Oxford 1982. deGalan L. and Winefordner J. D. J. Quant. Spectrosc. Radiat. Transfer 1967 7 251. Semiconductor Detectors In Experimental Physics ed.Akimov Yu. K. Tguatiev 0. V. Kalinin A. I. and Kushniruk V. F. Energoatomizdat Moscow 1989. Omenetto N. Turk G. C. Rutledge M. and Winefordner J. D. Spectrochim. Acta Part B 1987 42 807. Omenetto N. Smith B. W. Farnsworth P. B. and Winefordner J. D. J. Anal. Atom. Spectrom. 1992 7 89. Travis J. C. Turk G. C. DeVoe J. R. Schenck P. K. and Van Dijk C. A. Prog. Anal. At. Spectrosc. 1984 7 199. Travis J. C. Turk G. C. and Green R. B. Anal. Chem. 1982 54 1006A. Travis J. C. J. Chem. Educ. 1982 59 909. Kuzyakov Yu. Ya. Matveev 0. I. and Novodvorskii 0. A. Zh. Prikl. Spektrosk. 1984 40 145. Ornstein L. S. and Brinkman H. K . Acad. Wet. Amsterdam Proc. 1931 34 33. Ornstein L. S. and Brinkman H. Physica (Amsterdam) 1934 1 797. Kirkbright G. F. Peters M. K. Sargent M. and West T. S. Talanta 1968 15 663. Schneider W. E. and Goebel D. G. Laser Focus Electro-Op Mag. 1984 20(9) 82. Reif I. Fassel V. A. Kinseley R. N. and Kalnicky D. J. Spectrochim. Acta Part B 1978 33 807. Escobar M. P. Smith B. W. and Winefordner J. D. Anal. Chim. Acta 1995 in the press. Kantor T. Spectrochim. Acta Part B 1988 43 1299. Schmertmann S. M. Long S. E. and Browner R. F. J. Anal. At. Spectrom. 1987 2 687. Ljungberg P. Boudreau D. and Axner O. Spectrochim. Acta Part B 1994 49 1491. Gillespie A. B. in Signal Noise and Resolution in Nuclear Counter AmpliJers McGraw-Hill New York 1953. Zeegers P. J. Th. Townsend W. P. and Winefordner J. D. Spectrochim. Acta Part B 1969 24 243. Ng K. C. and Caruso J. A. Anal. Chim. Acta 1982 143 209. Hoffman E. Liidke C. and Scholze H. J. Anal. At. Spectrom. 1994 9 1237. Perkin-Elmer Corp. Analytical Techniques for Graphite Furnace Atomic Absorption Spectrometry. Publication No. B332; Perkin- Elmer Corp. Norwalk Ct 1984. Paper 51081 66A Received December 15 1995 Accepted Murch 15 1996 Journal of Analytical Atomic Spectrometry June 1996 Vol. 11 399

ISSN:0267-9477    

DOI:10.1039/JA9961100393

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Laser Ablation-Inductively Coupled Plasma Mass Spectrometry With a Time-of-flight Mass Analyser PATRICK P. MAHONEY GANGQIANG LI* AND GARY M. HIEFTJET Department of Chemistry Indiana University Bloomington IN 47405 USA Laser ablation has been employed for sample introduction into an ICP-time-of-flight (TOF ) mass spectrometer. The transients generated by the ablated material are generously sampled by the 10 kHz repetition rate of the TOF instrument. A detection limit of 10 ppb for Pb in a cast-iron standard is calculated from integration of a 0.3 s transient signal generated by a single laser pulse. By simultaneously acquiring and rationing the signals from two isotopes of Zn the substantial pulse-to-pulse power fluctuations from the laser are virtually eliminated. Although some of the data are presented in a single- or double-channel acquisition mode the results demonstrate the sensitivity and rationing abilities available for all elements and isotopes simultaneously from a single laser pulse.Use of a digital oscilloscope provides a full elemental spectrum for each laser pulse as the laser is rastered across a lava sample that contains plagioclase crystals. The relative spatial distributions for 11 elements of interest contained in this sample are plotted over an 11 mm distance. This paper is not intended to be a display of state-of-the-art laser-ablation techniques as the large beam divergence of the ruby laser limits the spatial resolution to 1 mm. However the ability of the plasma-source TOF mass spectrometer for analysing transient signals is clearly demonstrated.Keywords Elemental analysis; time-of-flight mass spectrometry; laser ablation; inductively coupled plasma mass spectrometry ICP-MS has found widespread applications in the elemental and isotopic analyses of geological industrial medical biologi- cal and food samples.'P2 By far quadrupole mass analysers have been chosen over other types of mass analysers in the development of commercial instruments owing to their high sensitivity low operating costs modest vacuum requirements and the fact that the ions need not be accelerated to high energy. Although quadrupole-based instruments have achieved great success several limitations still exist.3 These limitations include only moderate mass resolution and the inability to perform truly simultaneous multi-element analysis.As a result of the latter fact the precision with which isotope ratios can be measured is compr~mised.~ In order to overcome these limitations a time-of-flight (TOF) mass analyser has been presented as an alternative to quadrupoles for ICP-MS.S-9 The TOF instrument offers both higher resolution (with the use of an ion reflectron) and the ability simultaneously to determine all elements and isotopes. A technique that has been successfully coupled to ICP-MS for the direct analysis of solids is LA.1° LA-ICP-MS can greatly reduce or eliminate sample preparation and can provide spatial resolution with high sensitivity for elemental and iso- topic analysis of both conductive and non-conductive solid samples. In practice the ablated material is carried into the * Present address Hewlett-Packard Laboratories 3500 Deer Creek t To whom correspondence should be addressed.Road Building 26U MS 26U-6 Palo Alto CA 94303 USA. Journal of I Spectrometry I L I ICP by the central channel gas flow. The result is a transient signal with a half-width from less than 1 s up to several seconds depending on the carrier gas flow rate and the dimensions of the ablation cell and transport tube. Since a quadrupole mass analyser must be scanned to cover a desired mass range a compromise between sensitivity and mass cover- age must be made for these transient signals. Usually a high repetition rate laser is used to generate a nearly steady-state signal to avoid this compromise. However this approach precludes spatial-dependent analysis. TOFMS is ideally suited for detecting transient signals" and no compromise between sensitivity and mass coverage is necessary.In this paper a previously described LA apparatus12 is used to demonstrate the abilities of ICP-TOFMS for the simultaneous multi-element and isotopic analysis of transient signals. The results are not intended to be a demonstration of state-of-the-art LA techniques but rather of the LA-TOFMS combination. TOFMS generates a complete mass spectrum with each repetition cycle; further this spectral information can be acquired at a very high repetition rate (10-20 kHz). Of course a suitable data acquisition system is needed. Three different data acquisition schemes were employed here to evaluate the performance of the LA-TOF mass spectrometer.Specifically a digital oscilloscope two boxcar averagers and a single- channel ion-counting method were used to demonstrate the multi-channel capabilities isotope-ratio measurement pre- cision and sensitivity respectively. Ideally a single data acqui- sition system such as an integrating transient recorder ( ITR),13 could perform as all three. Unfortunately such an ITR is not yet commercially available. Although two of the schemes mentioned above allow only single- or double-element/isotope coverage the results reflect the information available for all elements and isotopes from the same laser pulse. Because of the simultaneous multi-channel detection inherent in TOFMS ratioing the signals from two isotopes of Zn can greatly reduce imprecision caused by laser power fluctuations. With the ion counting method a detection limit of 10 ppb is calculated for Pb in a cast-iron standard.This value was obtained with a 0.3 s integration of the signal resulting from a single laser pulse. With the use of a digital oscilloscope the relative spatial distributions of 11 elements were determined in a plagioclase-rich flood basalt lava sample. EXPERIMENTAL Laser ablation apparatus The LA apparatus has been described previously in connection with an LA-ICP emission studyI2 and is a combination of those described by Arrowsmith and Hughes14 and Carr and Horlick." The glass cell consists of two concentric Pyrex tubes; the outer tube carries the gas flow down to the sample surface while the inner tube carries the ablated material away from the sample to the ICP. Two modified designs of the cell in ref.12 were employed in an attempt to improve the transport Journal of Analytical Atomic Spectrometry June 1996 Vol. 11 (401 -405) 401Table 1 Typical operating conditions between the second and third stage is now positioned 55 mm Plasma parameters- ICP forward power ICP reflected Dower Central channel flow rate Intermediate flow rate Outer flow rate Sampler-load coil distance Sampler aperture diameter Skimmer aperture diameter 3rd stage aperture diameter Repeller frequency Laser parameters- Energy per pulse Pulse width Spot size Irradiance ReDetition rate TOFMS parameters- 1.3 kW 1.5-1.7 1 min-' 1.0 1 min-' 13.5 1 min-' 15-20 mm <5 w 1.0 mm 0.9 mm 1.3 mm 10 kHz 100 mJ 1 ms 400 pm 2 x lo4 W cm-' Manual ( z 0.1 Hz) - behind the skimmer aperture.As a result the conductance of the second stage is raised the gas flow into the third stage is reduced and a skimmer with a larger aperture can be employed. A commercial skimmer (Spectron Oxnard CA USA) with a 0.9 mm aperture has replaced the earlier7 labora- tory-built 0.5 mm aperture skimmer. The diameters of the three apertures that define the interface pressures are listed in Table 1. The third-stage pressure is 3 x lop6 Torr (with the plasma on) under these interface conditions. These modifi- cations have increased the ion current measured after the extraction region' from less than 2 nA to approximately 50 nA (with solution nebulization). For better time resolution of the transient LA signals the repeller-pulse repetition rate of the TOFMS instrument was raised from 7 to 10 kHz.A further increase in repetition rate is not currently possible because of limitations in the repeller- pulse circuitry. Specifically at the present width (1 pi) and amplitude (z 500 V) of the repeller pulse with a repetition rate of 10 kHz the pulser (DEX Model FPX 800 Fort Collins CO USA) is operated at its maximum recommended duty cycle. With a more suitable pulser a repetition rate of up to 20 kHz could be employed on the instrument because the flight time of the heaviest ions is about 50 ps. The data presented in this paper were collected exclusively in the reflectron mode of TOFMS ~peration.~ efficiency. The first design is similar to the previous design; the difference is that the centre tube was shortened 0.5 mm relative to the outer tube.The second cell resembled the first but with the centre tube removed completely. Both cells produced time- dependent mass spectral profiles of similar amplitude and shape but the cell with the central channel removed produced a wider profile owing to its larger internal volume. Unless otherwise indicated the cell with the shortened centre tube (the first design) was used throughout this study. Table 1 lists the operating conditions for the ICP TOFMS and the free-running- ruby laser [ Korad Laser Systems (Santa Monica CA USA) Model 890171-9011 that were employed in this study. The laser was operated manually at a maximum repetition rate of about 0.1 Hz limited by the charging time of the 5 kV flashlamp capacitor.A 10 cm focal length plano- convex glass lens was used to focus the laser beam onto the sample surface. One operating condition different from those in ref. 12 is that the carrier gas (ICP central channel) flow rate was increased from 0.7 to 1.5-1.71min-' to improve the sample transport efficiency and reduce the temporal width of the signal peak. In order to accommodate the increased flow rate the distance between the sampling plate of the mass spectrometer interface and the ICP load coil was increased from 10 to approximately 15 mm. Cast iron standards from the Research Institute CKD (Prague Czech Republic) and A1 standards from Alcoa (Alcoa Center PA USA) were analysed in these experiments. ICP-TOF Mass Spectrometer The ICP ion source and TOF mass spectrometer have been described in detail However modifications to both the ion optics and interface have been made.Plasma conditions and modified spectrometer parameters are listed in Table 1. Ref. 7 describes performance improvements that are associated with the installation of an electrostatic quadrupole lens among the ion optics leading to the extraction region. In an attempt to increase both ion throughput and resolving power a quadrupole doublet now replaces the earlier7 single lens. Preliminary studies suggest only modest increases in both performance features. A dramatic increase in the sensitivity of the instrument Data acquisition In order to evaluate the performance of the TOF mass spectrometer for transient signals three different data acqui- sition schemes were employed.For multi-element analysis a 500 MHz digital oscilloscope (Tektronix Model TDS520 Beaverton OR USA) was used to average and store successive spectra. The oscilloscope is interfaced to a Macintosh computer (Quadra 950) through a GPIB interface and LabVIEW I1 (National Instruments Austin TX USA) software. A synch- ronizing pulse from the ruby laser power supply was used to trigger the oscilloscope after a sufficient delay time to allow the ablated material to reach the plasma. Unfortunately the oscilloscope cannot average full spectra at a rate of 10 kHz. The averaging rate can be increased through a reduction of the record length but this reduction limits the number of elements that can be observed. Real-time averaging requires an alternative data acquisition scheme.In one such alternative two boxcar averagers [Stanford Research Systems (Sunnyvale CA USA) Model SR2501 were triggered by the repeller pulse (10 kHz) and had delays that were adjustable over the entire atomic flight-time range (0-50 ps) so that any two desired elements or isotopes could be monitored simultaneously. The width of the boxcar gates was set to a value just 1.arger than the base of the peak (20-50 ns depending on the ion mass). The averaged signal was read out by the computer at the end of every 300 cycles (30 ms for a 10 kHz repetition rate). For high-sensitivity measurements a single-channel ion- counting detection scheme was employed. A constant-fraction discriminator (Model TC454 Oxford Instruments Oak Ridge TN USA) was gated open with a function generator at a time corresponding to the m/z of interest with a function generator.accompanied the replacement of the -third-stage vacuum aperture/ion optic. Previ~usly,~ a cylindrical optic that had a conical tip with a 1.3 mm aperture was positioned 15 mm behind the skimmer aperture to separate the second and third stage vacuum regions. The new third-stage optic is flat with the same aperture diameter and has a cylindrical optic mounted 10 mm in front of it. The conductance-limiting aperture rate meter gain on a higher sensitivity setting. The function generator in turn was triggered by the repeller pulse. The output pulses of the discriminator were sent to a rate meter [Ortec (Oak Ridge TN USA) Model 9349). The time constant of the rate meter was set to 30 ms and its output was read out with the computer.The background and noise counts were measured in the absence of a laser pulse with the 402 Journal of Analytical Atomic Spectrometry June 1996 Vol. 11RESULTS AND DISCUSSION With the gated ion-counting method time-dependent signal pulses produced by a single laser shot appear similar to that in Fig. 1. The signal in Fig. 1 is from 208Pb. Lead is present at 30ppm in the cast iron standard analysed. At a carrier gas flow rate of 1.6 1 min-' the width of the peak at half maximum is 0.3 s. With a repeller-pulse repetition rate of 10 kHz the signal is sampled 3000 times by the TOFMS instrument during this period. Clearly the TOFMS instrument could be used to analyse signals of much shorter duration since the period between repeller pulses is short (100 ps).If the distance between the ablation cell and the plasma were reduced not only would the signal profile become much narrower but also the sample transport efficiency would increase.16 In the limit LA of a sample mounted just below the ICP on a direct sample insertion probe could be performed such as was demonstrated by Liu and Horlick." Even with a transient width of 0.7 ms,I7 seven spectra are available from the TOFMS instrument. Fig. 1 demonstrates a single-channel measurement; however a similar profile can be generated for all elements and isotopes simul- taneously with a suitable data acquisition system. Such a multi-channel measurement could be performed with the same sensitivity as the single-channel measurement demonstrated here.Integration of the signal peak in Fig. 1 (0.3 s integration) yields a detection limit (3s) of 10 ppb for Pb. The background and noise counts were measured during a laser pulse at an adjacent m/z value where no peak was present since no suitable blank was available. In the previous experiment,12 10 pg of material were removed with each laser pulse. If it is assumed that 10 pg of material are also ablated in the present experi- ment this detection limit corresponds to 100 fg of Pb. Although this experiment is based on single-laser-pulse analysis the S/N could be improved by the integration of signals from several laser pulses. A 10 s integration (33 laser pulses) should yield about a 6-fold (square root of 33) improvement or a detection limit of about 2 ppb or 11 fg for Pb in cast iron.A drawback of ion counting in TOFMS is that pulse pile- up is much more of a problem than when a quadrupole mass analyser is used. For good mass spectral resolution ions of a particular m/z value are required to hit the detector at approxi- mately the same time. In order to minimize pulse pile-up with the rate meter employed in this experiment count rates must therefore be kept below 1 ion for every 10 repeller pulses. Therefore at count rates above 1000 counts s-l (for a 10 kHz repeller-pulse repetition rate) detector pulse pile-up becomes 10000- aooo- 3 6ooo 8 4000 2000- 0 *''P b 03 s i W H M + 6 i . ~ ~ ~ ~ . . . . . . . 1~ Fig. 1 Typical signal profile obtained with gated ion counting from a single laser pulse impinging on a cast-iron standard.The profile is from 208Pb; Pb is present at 30 ppm. Integration over the 0.3 s FWHM of the profile yields a detection limit (3s) of 10 ppb. For this detection limit assessment the background and noise counts were measured with a higher sensitivity setting on the rate meter significant. Although the cast-iron standard used in this deter- mination had the lowest concentration of Pb of those available for analysis the count rates displayed in Fig. 1 suggest that pulse pile-up might be occurring and that the true detection limits may be slightly lower than the values quoted above. Another consequence of pulse pile-up is that the dynamic range with ion counting becomes very limited. Clearly an analogue detection scheme with sensitivity equal to that avail- able with ion counting is preferable.With the dual boxcar averagers the response for Cu was measured to be linear over three orders of magnitude (0.06-6.0% by mass). This range is limited at the high- concentration end by saturation of the microchannel plate detector. The low-concentration end could not be investigated owing to a lack of suitable standards. The dynamic range could be extended at the high-concentration end by observing a less-abundant isotope by reducing the gain on the detector or by de-tuning the ion optics. The digital oscilloscope offers full spectral coverage but cannot average spectra at 10 kHz; a compromise in sensitivity therefore occurs. For the 0.3 s transients it was found that a maximum of only 20 averages could be obtained with the record length of 50000 points needed to cover the entire elemental mass range.This limitation has important conse- quences for the attainable S/N. Fig. 2 shows the difference in S/N between the average of 20 and 3000 spectra. In this demonstration only the mass range containing the Pb isotopes is shown. Because the laser could not be used to generate a steady-state signal these plots were obtained by ultrasonic nebulization of a 100 ppb Pb solution. A 12-fold improvement in S/N would be expected with an increase from 20 to 3000 averages. However because not all of the influential noise sources are random in nature an improvement of only 6-fold is observed. Clearly for multi-element analyses of the highest sensitivity a faster digital oscilloscope or an ITR13 is needed.However the oscilloscope is still useful for qualitative multi- element analysis as will be seen later. Because the digital oscilloscope offers only modest precision the pair of boxcar averagers was used to demonstrate the ratioing capabilities of the instrument. Again although only two channels were ratioed in the present experiment a more suitable data acquisition system would permit all elements and isotopes present to be ratioed to each other or to suitable internal standards; the performance would be expected to equal that of the two-channel case. Fig. 3 shows simultaneously acquired signals from 64Zn and 66Zn during multiple laser pulses. Zinc is present at 0.1% by mass in the A1 standard that was analysed.It should be noted that the laser pulses do not occur as frequently as is implied in Fig. 3. The plots were 3000 Averages 20 Averages I I I I I I I 1 2 0 3 2 0 4 2 0 5 2 0 6 2 0 7 2 0 8 2 0 9 2 1 0 d z Fig. 2 Difference in S/N in spectra of Pb obtained from 20 and 3000 averages with the digital oscilloscope. Because the laser could not be used to generate a steady-state signal these data were taken during ultrasonic nebulization of a 100 ppb Pb solution Journal of Analytical Atomic Spectrometry June 1996 Vol. 11 4030.61 I 1-0- - - - 1'5' Tirnds Fig. 3 Two boxcar averagers were used to monitor simultaneously 64Zn and 66Zn present at 0.1% in the A1 standard analysed during multiple laser pulses. Each point is the result of 300 averages (30ms at a 10 kHz repetition rate).Owing to laser power fluctuations the RSD values of the 64Zn and 66Zn peak areas are 25 and 24% respectively. The ratio of the peak areas however has an RSD of 1.6% software-edited so the peaks appear closer together. The cell with no centre tube was used for these data; the greater volume of this cell broadened the profiles slightly. It is immediately obvious that the laser power fluctuations are fairly severe. The peak areas for 64Zn and 66Zn change with an RSD of 25 and 24% respectively. Because the signals were obtained simul- taneously however their ratio virtually eliminates fluctuations induced from the unstable laser. In Fig. 3 both the peak heights and the peak profiles track each other well for the two isotopes. The RSD of the ratioed peak areas is 1.6%.The small peaks following each profile are not always present and are thought to arise from changes in laser pulse shape and/or shifts in gas-flow patterns as the cell is moved across the sample to enable successive ablation events to be produced. With high sensitivity and excellent ratioing capabilities LA-ICP-TOFMS is suitable for bulk analysis of solids but its abilities are best exploited when spatial resolution is desired. In order to demonstrate the wealth of information available on a pulse-by-pulse basis multi-element analysis was per- formed on a geological sample with a known spatial distri- bution. The sample is a plagioclase-rich flood basalt lava from the Steens Mountains in South Central Oregon.I8 Table 2 lists the approximate concentrations of elements in both the lava and crystal portions of the sample.Fig. 4(a) shows a spectrum (average of 20 cycles) from a plagioclase crystal obtained from a single laser shot. Fig.4(b) shows a background spectrum taken under the same conditions but in the absence of a laser pulse. The ringing following abundant species such as Ar' Si+ Na' or N' is due to detector saturation. A comparison of Fig. 4(u) and (b) suggests that it is possible to determine Ca through measurement of the Ca2+ peak at rn/z=20. In the background spectrum [Fig. 4(b)] the Ar2+ peak at this rn/z value was not observed. The digital oscilloscope was used to acquire a spectrum similar to that in Fig. 4(u) for each laser pulse as the laser was rastered across the lava sample.A photograph of the sample is shown in Fig. 5 (upper part). The narrow white lines are the plagioclase crystals. The laser was rastered across several crystals; the path of the laser beam is indicated in Fig. 5 (upper Table 2 presented in mass YO oxide* Approximate concentration of lava and crystal matrices SiO TiO Al,O FeO MnO MgO CaO Lava 48.10 2.94 14.80 13.77 0.21 5.07 8.05 Crystal 52.56 NDP 29.9 0.57 ND? NDt 13.13 * Ref. 18. Not determined. 8 0 CI) 3 0 2 0 1 0 -:li 30 1 0 5 1 0 0 Si' 3 2 1 nJZ A r+ + Mn+ \ b P t Y 4 8 cu+ A 6 4 2 0 3 0 4 0 5 0 6 0 7 0 8 0 Ar2' Fig.4 (a) Spectrum obtained from the average of 20 cycles (repeller pulses) following a single laser pulse incident on a plagioclase crystal contained in a lava sample. The ringing following abundant peaks is due to detector saturation. (h) Background spectrum obtained under the same conditions as (a) but in the absence of a laser pulse part) by the black line.The peak heights for 11 elements of interest are plotted as a function of distance in Fig. 5 (lower part). In order to reduce the effects of laser power fluctuations the peak heights were all normalized to the 29Si+ peak height which is present in both the matrix and crystal at similar concentrations. This internal standard is used only to reduce signal fluctuations caused by laser sampling and does not correct for changes in the 29Si concentration across the sample. For each element the most abundant isotope was measured except for Si and Mg. The 29Sif peak was used to avoid the isobaric overlap of I4N2+ with "Si' .Because of detector saturation 26Mg' was used instead of 24Mgf. The spatial resolution of Fig. 5 (lower part) is 1 mm. Because the laser spot size was about 400 pin the sample was moved 1 mm after every pulse to avoid sampling redeposited material from the previous laser pulse. This limited spatial resolution is a result of the large beam divergence of the laser and can certainly be improved by use of a different laser system. From Fig. 5 (lower part) it can clearly be seen whether a laser pulse hits the lava matrix or a crystal. The crystal contains higher concentrations of Al Na and Ca while the matrix contains higher concentrations of Fe Mg P K and Mn. Although the concentrations of Cu and Zn are not listed in Table 2 it can be seen that the lava matrix contains more Cu and Zn than does the crystal.Visual inspection with a micro- scope supports the results of Fig. 5 (lower part). Laser shots on the lava matrix occurred at 0 1 4 5 6 and 9 mm. Laser shots on the crystal occurred at 2 3 7 8 10 and 11 mm. CONCLUSIONS Although much of the data presented here are in a single- or double-channel acquisition mode several important features 404 Journal of Analytical Atomic Spectrometry June 1996 Vol. 11P ' O m E 0 . 2 v - g 0 . a 0 . wl .- 0 . Distancdmm Fig. 5 (Upper) Picture of plagioclase-rich lava sample that was analysed by LA-ICP-TOFMS. The black line indicates the 11 mm path of the laser beam across several crystals (white zones). (Lower) Relative distributions of 11 elements (normalized to 29Si ) across the 11 mm distance.Visual inspection under a microscope supports the distributions suggested in the plot. Laser shots on the lava matrix occurred at 0 1 4 5 6 and 9 mm while laser shots on the plagioclase crystals occurred at 2 3 7 8 10 and 11 mm. Approximate concen- trations of elements in the lava matrix and in the plagioclase crystals are presented in Table 2 of TOFMS for the simultaneous multi-element and isotopic analysis of transient signals have been demonstrated. With an improved data acquisition system such as an ITR the sensi- tivity and ratioing capabilities of the instrument would be available for all elements and isotopes simultaneously. Future work is planned with an Nd YAG laser which with its wavelength-selectable output will provide better focusing properties a more stable output higher power and the ability to perform analyses on a wider range of sample types.The authors thank Dr. James Brophy of the Indiana University Department of Geological Sciences for providing the plagio- clase-rich lava sample the approximate concentrations listed in Table 2 and valuable consultation. This research was funded by the National Institutes of Health through grant R01 GM 46853. One of the authors (P.P.M.) also thanks the Department of Education for fellowship support. REFERENCES 1 2 7 8 9 10 11 12 13 14 15 16 17 18 Handbook of Inductively Coupled Plasma Mass Spectrometry ed. Jarvis K. E. Gray A. L. and Houk R. S. Chapman and Hall New York 1992 ch. 8. pp. 225-264. Bacon J. R. Ellis A. T. McMahon A. W. Potts P. J. and Williams J. G. J. Anal. At. Spectrom. 1993 8 261R. Hieftje G. M. J. Anal. At. Spectrom. 1992 7 783. Furuta N. J. Anal. At. Spectrom. 1991 6 199. Myers D. P. and Hieftje G. M. Microchem. J. 1993 48 259. Myers D. P. Li G. Yang P. and Hieftje G. M. J . Am. SOC. Mass Spectrom. 1994 5 1008. Myers D. P. Li G. Mahoney P. P. and Hieftje G. M. J. Am. Soc. Mass Spectrom. 1995 6 400. Myers D. P. Li G. Mahoney P. P. and Hieftje G. M. J. Am. Soc. Mass Spectrom. 1995 6 411. Myers D. P. Mahoney P. P. Li G. and Hieftje G. M. J. Am. SOC. Mass Spectrom. 1995 6 920. Denoyer E. R. Fredeen K. J. and Hager J. W. Anal. Chem. 1991 63 445A. Cotter R. J. Anal. Chem. 1992 64 1027A. Richner P. Borer M. W. Brushwyler K. R. and Hieftje G. M. Appl. Spectrosc. 1990 44 1290. Holland J. F. Newcombe B. Tecklenburg R. E. Jr. Davenport M. Allison J. Watson J. T. and Enke C. G. Rev. Sci. Instrum. 1991 62 69. Arrowsmith P. and Hughes S. K. Appl. Spectrosc. 1988 42 123. Carr J. W. and Horlick G. Spectrochim. Acta Part B 1982,37 1. Moenke-Blankenburg L. Spectrochim. Acta Rev. 1993 15 1. Liu X. R. and Horlick G. Spectrochim. Acta Part B 1995 50 537. Brophy J. Department of Geological Sciences Indiana University Bloomington IN 1994 personal communication. Paper 510551 8K Received August 18 1995 Accepted February 12 1996 Journal of Analytical Atomic Spectrometry June 1996 Vol. 11 405

ISSN:0267-9477    

DOI:10.1039/JA9961100401

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Determination of Selenocystine Selenomethionine Selenite and Selenate by High-performance Liquid Chromatography Coupled to Inductively Coupled Plasma Mass Spectrometry Journal of Analytical Atomic Spectrometry M. ANGELES QUIJANO ANA MARIA GUTIERREZ M. CONCEPCION PEREZ-CONDE AND CARMEN CAMARA Departamento de Quimica Analitica Facultad de Quimicas Universidad Complutense de Madrid 28040 Madrid Spain An analytical method has been developed for the determination of selenocystine selenomethionine selenite and selenate. Separation of the four Se species was achieved by HPLC on a Spherisorb 5 ODs-AMINO column using a concentration gradient from 3.5 to 7.0 mmol 1-' phosphate buffer of pH 6.0 as the mobile phase at a flow rate of 1.0 ml min-'. Detection was carried out using an on-line inductively coupled plasma mass spectrometer.The chromatographic parameters and the chemical factors affecting the separation of the Se species were optimized. The detection limits using a 100 p1 sample loop volume and expressed as Se were found to be 2.0 1.0 1.6 and 1.2 pg 1- for selenocystine selenomethionine selenite and selenate respectively. The precision was better than 5% in all instances. The method was successfully applied to the determination of the four Se species in water samples certified for selenite and selenate to which selenocystine and selenomethionine had been added. Keywords Inductively coupled plasma mass spectrometry; high-performance liquid chromatography; selenium speciation; water Since the first reports in 1957 that Se was an essential element continued progress has been made in identifying the natural seleno compounds in biological media and in elucidating their function.' Selenium has been identified as an essential element in many species including humans in which it is a component of glutathione peroxidase which is necessary for the removal of hydrogen peroxide and lipid peroxidases from cells.Selenium is also known to prevent the appearance of. toxic effects normally caused by elements such as As and Hg.2 There is a narrow range of Se intake that is consistent with health; outside this range deficiency diseases and toxicity occur. At higher doses Se is toxic diets containing more than 5 mg kg-' of Se are considered to be poisonous to man and animals.' In the aqueous environment selenite and selenate are the most common Se compounds and in biological samples both inorganic and organic Se species can be p r e ~ e n t .~ Several chromatographic methods for the separation of seleno compounds with non-specific and specific detectors have been re~iewed.~-~ Volatile Se compounds (dimethyl selen- ide dimethyl diselenide diethyl selenide methanoselenol) have been separated by gas chromatography.6 For the speciation of non-volatile Se compounds both liquid and gas chromatogra- phy are used. The latter requires a prior derivatization step to convert the Se species into volatile forms. Various reagents are available such as trimethylsilylacetamide cyanogen bromide and ~-phenylenediamine.~~~ Liquid chromatography is preferred for the separation of non-volatile species without prior derivatization.In most publi- cations selenite and selenate are separated using an ion- exchange chromatography column. Separation is based on a strong anion exchange with elution using different buffers.*-" Some researchers who include the elution of trimethyl- selenonium (TMSe') in the dead volume using either hydride generation," or electrothermal8 atomic absorption spec- trometry as the method of detection give detection limits of about 1.27 0.76 and 1.67 ng of Se for selenite selenate and TMSe+ respectively. Selenocystine (SeCys) and selenomethionine (SeMet) have been separated using either ion-exchange" or ion-pair12 chro- matographic methods. Potin-Gautier et ~ 1 . ' ~ have carried out the separation of SeCys and SeMet by ion-pair chromatography with electro- thermal atomic absorption spectrometric detection with detec- tion limits of 1.0 and 0.8 ng of Se respectively.Using this method selenite and selenate were not well resolved interfering in the separation of seleno-amino acids. The use of Se specific detectors is preferred to reduce the interferences and improve the detection limits. Hydride gener- ation (HG) coupled to any type of atomic detector requires the prior conversion of seleno species into SeIV," while electro- thermal atomic absorption spectrometry requires fraction col- lections after elution or a sophisticated design,I2 in order to connect the chromatographic column and graphite furnace. The aim of the present work was to design a simple procedure for the simultaneous separation of the four Se species mentioned above all of which may be present in real samples.It was decided to use ICP-MS detection with the aim of facilitating very low detection limits and allowing easy interfacing through a direct connection between the HPLC column and the nebulizer. The coupling of HPLC to ICP-MS has previously been used in the analysis of metal-containing species for As Pb Sn and Hg.l3*I4 The use of ICP-MS detection requires certain modifications to the chromatographic method compared with those pre- viously used with other types of detector. Buffer concentrations must be decreased to prevent salt deposition and clogging of the sampling orifice while the concentrations of organic sol- vents must be controlled to avoid plasma in~tabi1ity.l~ EXPERIMENTAL Instrumentation The chromatographic system used consisted of a Milton Roy CM4000 HPLC pump with a Milton Roy six-port sample injection valve fitted with a 100 pl loop (Milton Roy LDC Division Riviera Beach FL USA).Separations were per- formed on a 5 pm Spherisorb ODS (octadecyl silica)-AMINO Journal of Analytical Atomic Spectrometry June 1996 Vol. 11 (407-41 1 ) 407column (250 x 4.6 mm id) (Phenomenex Torrance CA USA). In this mixed column the stationary phase consists of an equimolar mixture of octadecyl and amino groups on a silica support operating as a reversed-phase weak anion-exchange or ion-pairs chromatographic column. Separation was achieved with a phosphate buffer of pH 6.0 as the mobile phase using a concentration gradient from 3.5 to 7.0 mmol l-l.Detection was performed using an Eclipse ICP-MS instru- ment (Fisons Instrument Uxbridge Middlesex UK). The Eclipse instrument was first optimized independently of the chromatographic system for nebulizer gas flow rate ion lens voltages quadrupole resolution and pole bias using a standard solution containing elements across the mass range from Be to U at concentrations of 10 pg 1-'. The optimization was also checked using a 25 pg 1-' Se standard solution in order to improve optimization further. The chromatographic system was then coupled to the ICP-MS instrument with 20 cm of poly( tetrafluoroethylene) capillary tubing (0.5 mm id) from the column outlet to the inlet of the standard Meinhard nebulizer. During the HPLC-ICP-MS runs only the ion at m/z=78 was monitored since it presents a better signal-to-noise ratio than the other Se isotopes.16 The chromatographic peaks were evaluated by their areas.The conditions used are summarized in Table 1. Reagents and Standards Selenium stock standard solutions (1000 mg 1-l as Se) were prepared from sodium selenate ( SeV') sodium selenite (Se") SeCys and SeMet which were purchased from Aldrich (Milwaukee WI USA). The use of 3% v/v HC1 was necessary to solubilize SeCys. Stock solutions were stored in the dark at 4°C. Working standards were obtained daily by dilution of the stock solutions with de-ionized Milli-Q water (Millipore Bedford MA USA). The eluents used for the separations were phosphate buffers of pH 6.0 at concentrations of 3.5 and 7.0 mmol l-l. Solutions were prepared by mixing independent solutions of Na,HPO and NaH2P04 (Panreac Barcelona Spain) until the desired pH was reached.Artificial serum to test the ionic strength effect was prepared by dissolving 3.5 g of NaCl (Merck Darmstadt Germany) 1.5 g of KCl (Merck) 2.5 g of NaHCO (Merck) and 20 g of glucose (Merck) in 0.5 1 of de-ionized water. Water (BCR CRM 603) certified for SeIV and Sev' (35.33 and 44.82 pg 1-' respectively) was used for validation of the method. Table 1 Optimum ICP-MS and chromatographic operating conditions I CP- MS- Forward power Reflected power Coolant gas flow rate Auxiliary gas flow rate Carrier gas flow rate Data collection mode Integration time C hromut ogr up hy- Analytical column Mobile phase Phosphate buffer pH Gradient concentration Gradient time Flow rate Sample injection volume 1150 W <0.5 W 14 1 min- 0.7 1 min-' 0.8 1 min-' Single monitoring 1.0 s Spherisorb 5 ODs-AMINO Phosphate buffer 6.0 3.5-7.0 mmol 1-' 1.0 min 1.0 ml min-' 100 p1 All solutions were filtered through a 0.45 pm membrane filter and de-gassed before use.Procedure The chromatographic separation of SeCys SeMet selenite and selenate standards was performed by injecting solutions con- taining the four compounds onto the column and initially eluting with 3.5 mmol 1-' phosphate buffer of pH 6 at a flow rate of 1.0 ml min-'. After 5 min the eluent was changed to 7 mmoll-' phosphate buffer of pH 6 using a linear concen- tration gradient over a 1 min period. Detection of each eluted Se species was carried out by ICP-MS using the operating conditions given in Table 1.The analytical peaks obtained were evaluated by peak area measurements. RESULTS AND DISCUSSION Column Selection A previous paper' has described the separation of SeCys and SeMet using ion-pair chromatography. In the present work this method was developed for the separation of the four Se species using cationic ion-pairing reagents. Studies were per- formed on a 5 pm Hamilton PRP-1 styrene-divinylbenzene column (150 x 4.1 mm id) eluting the Se compounds with an aqueous mobile phase containing the ion-pairing reagent and a low percentage of acetonitrile (1-5% v/v). Two reagents were tested tetraethylammonium bromide at various concentrations ( 10-4-10-2 moll-') and tetradecyltri- methylammonium bromide at concentrations below its critical micellization concentration (about 4 x mol 1-') but with poor resolution in both instances.Selenite and selenate were not well separated from each other and eluted between SeCys (first peak) and SeMet (last peak) interfering with both. With the use of anionic ion-pairing reagents only cationic species can be retained. At the recommended pH for the stability of the columns utilized SeCys and SeMet exist as zwitterions whereas selenite and selenate are in the anionic form and therefore elute in the dead volume. Other workersg,10 have used a strong anion-exchange column for the separation of selenite and selenate employing a variety of buffers as the mobile phase. The use of a Hamilton PRP-X100 column was attempted in this work; however SeCys and SeMet eluted in the dead volume.Finally a mixed column was tested uiz. Spherisorb ODS- AMINO on which amino groups can be protonated by the use of an appropriate buffer in the mobile phase. The separation of the four Se species was achieved with this column using a concentration gradient of phosphate buffer as described in detail later. The elution order was SeCys followed by SeMet selenite and selenate. According to the acidity constants for selenous acid (pK,= 2.46 and pKl=7.31) and selenic acid (pK1= 1.92) in the pH range recommended for the stability of the column (2.0-KO) selenite and selenate are predominantly present as HSe0,- and SeO,,- respectively; hence the observed elution order suggests an anion-exchange chromatographic mechanism. In the pH range 2.0-8.0 SeCys and SeMet exist as zwit- terions; the former molecule contains terminal polar and ionized functions with two negative charges.Although this should lead to longer retention SeCys elutes first followed by SeMet. This could be due to a reversed-phase mechanism for the retention of seleno-amino acids in which SeMet would be retained longer since its alkyl chain is more accessible than that of SeCys. The dead volume of the system was determined by passing a 20 yg 1- LiCl solution through the column at various flow rates. The Li+ ion which should not be retained by the 408 Journal of Analytical Atomic Spectrometry June 1996 Vol. 11column was monitored by ICP-MS at m/z=7. The dead volume of the system was calculated to be 2.04+0.01 ml. Effect of pH In order to evaluate the influence of pH on the retention times of the analytes different 5.0 mmol 1-' phosphate buffer solu- tions in the pH range 2.5-7.0 were used as mobile phases.The retention ability of the column is related to the capacity factor (k') This parameter is independent of the flow rate and the dimensions of the column. The results obtained are presented in Fig. 1 in which it can be seen that the inorganic Se species do not elute at pN values below 6. Within the pH range studied selenite and selenate are present as HSe0,- and Se042- as mentioned above and the predominant phosphate species are H2P04- and HP042-. Above pH 6 the predominant phosphate species is HP042- which is able to compete with the Se species retained which are then eluted.Below pH 6 the predominant anion H,P04- is not able to remove the inorganic Se species from the column. This suggests that the retention-elution of selenite and selenate on the column is due to an anion-exchange mechanism which is governed by the protonation of Se and phosphate anions. These anions compete for the NH,' groups of the stationary phase where the H P 0 2 - species is responsible for the elution. Furthermore the significant decrease in K' on increasing the pH from 6 to 7 for both inorganic Se species is in good agreement with the proposed mechanism. Since good resohtion was not achieved for SeMet and Se'" at pH 6 the separation of the four Se species was attempted using a 5 mmoll-' phosphate buffer over a pH gradient from 2.7 to 6.0. The main problem encountered with the type of column used here was the long equilibration period required to reach the desired pH (about 1 h).Considering these results it was decided to work with isocratic pH elution at pH6. Resolution of the chromatogram was improved by varying the buffer concentration as described in the following section. Concentration Gradient of Phosphate Buffer and Flow Rate In order to evaluate the optimum concentration of the mobile phase different phosphate buffer concentrations within the range 2.5-7.0mmoll-' were tested. The use of high buffer concentrations was limited to prevent salt deposition and clogging of the sampling and skimmer orifices. It was not necessary to modify the adjusting parameters in the ICP-MS instrument when the effect of the different phos- phate buffer solutions used was evaluated.Fig. 2 shows the influence of the concentration of phosphate buffer on the k' values of the four Se species at a constant pH of 6.0. The k' values for SeCys and SeMet are independent of \ I 2 3 \ C :j ' *? 2 3 4 5 6 7 Phosphate buffer pH Fig. 1 Effect of pH of phosphate buffer (5.0 mmol 1- ') on the capacity factor (k'). A Selenocystine; B selenomethionine; C selenite; and D selenate (20 pg I-' Se each) 2 3.1 4.2 5.3 8.4 7.5 Phosphate buffer concentration/rnmol I-' Fig. 2 Effect of phosphate buffer concentration at pH 6.0 on the capacity factor (k'). A SeCys; B SeMet; C Se"; and D SeV' (20 pg 1 - l Se each) this parameter because of their separation mechanism. The k' values for selenite and selenate decrease when the mobile phase concentration is increased particularly from 2.5 to 4.2 mmol I-'.From the results shown in Fig. 2 it can be concluded that a low phosphate buffer Concentration is necessary for the opti- mum separation of SeMet and Se". Although the use of a low phosphate buffer concentration for the elution of selenate is possible it produces long analysis times whereas an increase in the phosphate buffer concentration reduces the retention time for SeV1 and therefore the analysis time. For this reason it was decided to use a concentration gradient of phosphate buffer from 3.5 to 7.0 mmol I-' at pH 6. All these results agree with the mechanism proposed above. The resulting chromatog- ram is shown in Fig. 3. Gradient elution was used for all subsequent experiments.In order to determine the optimum flow rate values in the range 0.6-1.2 ml min-' were tested. This flow rate range was compatible with ICP nebulization flow rates. The best reso- lution was obtained with a flow rate of 1.0 ml min-'. Effect of Ionic Strength Sodium chloride and artificial serum were chosen to evaluate the effect of ionic strength the first because it is a common electrolyte in environmental samples and the second because it contains some common electrolytes and organic material. Different NaCl and artificial serum concentrations were added to the Se working standards for the evaluation of the 12000 1 1 10000 o ! I I I I 0 200 400 600 800 1000 Time/s Fig. 3 (2) SeMet ( 3 ) Se" and (4) Se"' (20 pg 1- Se each) HPLC-ICP-MS trace of a standard mixture of (1) SeCys Journal of Analytical Atomic Spectrometry June 1996 Vol.11 409effect of the ionic strength (1.6-850 mmol 1 - I ) on the separa- tion of the seleno compounds. No significant differences between addition of either NaCl or artificial serum were found. Table 2 shows the relative signals for the Se species at different ionic strengths with respect to those obtained without electrolyte. Above an ionic strength of 27 mmol l-l the relative signal of selenate begins to decrease whereas the signals of the other three Se species are not affected in the range studied. On the other hand Fig.4 shows the effect of the ionic strength on the k' values of the four Se species. An increase in the ionic strength does not affect the elution of SeCys or 12 1 0 94 189 283 378 412 567 661 156 850 Ionic strength/mmol I-' Fig. 4 Effect of the ionic strength on k' A selenocystine; B selenome- thionine; C selenite; and D selenate (20 pg 1-' Se each) Table 2 Effect of ionic strength on the signal of Se (20 pg 1- ') for the four species.Relative signal is the ratio between the Se signal in the absence and presence of NaCl or artificial serum expressed as a percentage Relative signal (YO) Ionic strength/mmol 1-' 1.6 4.0 8.0 16.0 18.0 27.0 40.0 55.0 80.0 110.0 170.0 220.0 340.0* 850.0* SeCys 9 9 f 2 9 3 f 3 99+3 91f5 9 2 f 3 9 3 f 3 9 5 f 4 9 4 f 3 8 9 f 4 9 6 f 4 101 f 3 9 5 f 4 105 f 4 104 k 3 SeMet 9 8 f 3 102 f 4 9 4 f 4 9 9 f 3 103 f 4 9 4 f 3 101 f 3 102f4 9 6 f 3 9 7 f 4 98+3 102f4 9 8 f 3 10314 SeIV 102 k 3 9 9 f 2 103 f 4 101 f 3 look3 102f4 9 8 f 3 101 k 3 9 8 f 4 102 f 3 100 f 5 103 f 3 101 f 4 102 f 3 SeV' 9 2 f 4 99*3 9 7 f 2 96+3 91 f 4 8 8 f 3 8 0 f 4 70+5 6 5 f 4 5 4 f 4 50+4 4 5 f 3 42+4 38+3 ~~ * Ionic strength obtained only with NaC1. Table 3 Analytical characteristics SeCys SeMet Se" SeV' Detection limit/ng 0.20 0.10 0.16 0.12 S,* (%) (50 pg I-') 3.6 4.3 3.8 2.0 (20 pg 1-7 3.9 4.7 4.0 3.4 Retention time/s 181 253 378 732 * Relative standard deviation.Table 4 Selenium recovery study (pg 1-'); n = 3 SeMet but produces an increase in the retention times of selenite and selenate at values higher than 88 mmol 1-'. The retention times of the seleno-amino acids are indepen- dent of this parameter because of their partition mechanism whereas the inorganic species are more affected by their ionic mechanism.Analytical Characteristics The analytical characteristics were evaluated for the four Se compounds. The precision of the method was tested using two standard solutions containing 20 and 50 pg 1-' of each species. The relative standard deviations were calculated from five replicate measurements under the conditions listed in Table 1 and were better than 5% in all instances. The detection limit is defined as three times the standard deviation obtained from ten replicate blank determinations. In this work the signal from the blank was negligible; therefore the detection limits were calculated using a 5 pg 1-' Se standard solution. Detection limits using a 100 pl injection volume were 0.20 0.10 0.16 and 0.12 ng of Se for SeCys SeMet selenite and selenate respectively.Table 3 shows the analytical characteristics for the four Se species. Sample Analysis The proposed method was successfully applied to the analysis of BCR CRM 603 containing 20.0 g 1-1 of NaC1; this CRM contains concentration levels of 35.33 and 44.82 pg 1-1 of selenite and selenate respectively. Method validation for SeMet and SeCys was achieved by adding known amounts of these compounds to the certified water. Calibration was carried out by the method of standard additions owing to the effect of the ionic strength on the selenate signal. The results obtained are shown in Table4. The recoveries of SeCys and SeMet from spiked samples were 96-103%. Further investigations with regard to species extraction in more complex samples are in progress. CONCLUSION The acidity constants and the order of elution suggest a reversed-phase mechanism for the retention of seleno-amino acids and an anion-exchange chromatographic mechanism for the retention of selenite and selenate in the column used in this work.The separation of the four Se species studied using a pH gradient is not feasible owing to the long equilibration period with respect to this variable whereas a concentration gradient allows the separation to be carried out in less than 13 min. Retention times of inorganic Se species are considerably affected by a change in the ionic strength. The proposed method allows the on-line separation and detection of SeCys SeMet selenite and selenate and provides high sensitivity and selectivity using a single chromato- graphic run.Compound Certified value/pg 1-' Addedjpg 1-1 Found/pg 1-' Se" 35.33 f0.40 36.3 f 1.3 41.9 f 1.2 SeV' SeCys - 20.0 20.3 f 0.5 SeCys - 40.0 41.42 1.2 SeMet - 20.0 19.6 f 0.8 SeMet - 40.0 38.5 & 1.4 44.82 f 0.70 - Recovery (%) - 101 & 2.5 103 f 3.0 98.0 f 4.0 96.2 & 3.5 41 0 Journal of Analytical Atomic Spectrometry June 1996 Vol. 11The authors are grateful for financial support from CICYT under project PB 92-0218 and the Measurements and Testing Programme (EC) under project MAT1-CT930006. We also thank Ma Jose Mancheiio and Mark Austin for revision of the manuscript. REFERENCES 1 Merian E. Clarkson T. W. and Fishbein L. Metals and their Compounds in the Environment VCH Verlagsgesellschaft Weinheim 1991 pp. 1153-1190.2 Shibata Y. Morita M. and Fuwa K. Adv. Biophys. 1992,28 31. 3 Muiioz Olivas R. Donard 0. F. X. Camara C. and Quevauviller P. Anal. Chim. Acta 1994 286 357. 4 Kolbl G. Kalcher K. Irgolic K. J. and Magee R. J. Appl. Organomet. Chem. 1993 7,443. 5 Dauchy X. Potin-Gautier M. Astruc A. and Astruc M. Fresenius’ J. Anal. Chem. 1994 348 792. 6 Gui-bin J. Zhe-ming N. Li Z. Ang L. Heng-bin H. and Xiao- quan S. J. Anal. At. Spectrom. 1992 7 447. 7 8 9 10 11 12 13 14 15 16 Johansson K. Ornemark U. and O h A. Anal. Chim. Acta 1993 274 129. Laborda F. Chakraborti D. Mir J. M. and Castillo J. R. J. Anal. At. Spectrom. 1993 8 643. Kolbl G. Kalcher K. and Irgolic K. J. Anal. Chim. Acta 1993 284 301. Cobo-Fernandez M. G. Palacios M. A. Chakraborti D. Quevauviller P. and Camara C. Fresenius’ J. Anal. Chem. 1995 351 438. Martin J. L. and Gerlach M. L. Anal. Biochem. 1969 29 257. Potin-Gautier M. Boucharat C. Astruc A and Astruc M. Appl. Organomet. Chem. 1993 7 593. Larsen E. H. Pritzl G. and Hansen S. H. J. Anal. At. Spectrom. 1993 8 557. Vela N. P. and Caruso J. A. J. Anal. At. Spectrom. 1993 8 787. Hill S. J. Bloxham M. J. and Worsfold P. J. J. Anal. At. Spectrom. 1993 8 499. Quijano A. Gutierrez A. M. Perez-Conde C. and Camara C. J. Anal. At. Spectrom. 1995 10 871. Paper 51047963 Received July 21 1995 Accepted February 16 1996 Journal of Analytical Atomic Spectrometry June 1996 Vol. 1 1 41 1

ISSN:0267-9477    

DOI:10.1039/JA9961100407

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

On-line Removal of Interferences via Anion-Exchange Column Separation for the Determination of Germanium Arsenic and Selenium in Biological Samples by inductively Coupled Plasma Mass Spectrometry FU-HSIANG KO AND MO-HSIUNG YANG* Department of Nuclear Science National Tsing Hua University Kuang-Fu Road Hsinchu 30043 Taiwan A method was developed for the determination by inductively coupled plasma mass spectrometry of germanium arsenic and selenium in urine and blood after microwave acid digestion and on-line anion-exchange separation. After acid digestion the analytes exist mainly as H,GeO H,AsO H3As04 H2Se03 and H2Se04 in the resulting sample solution. Separation of the analytes is achieved by adsorption of the analytes as anionic species on the column in relatively alkaline media with subsequent desorption of the analytes from the column as undissociated neutral species in acidic media.By loading the digested sample adjusted to about pH 11.5 onto the column of the on-line separation system the analytes as well as C1 and S which may cause spectral interference in the inductively coupled plasma mass spectrometric determination are retained on the column. In the subsequent elution step with eluent of about pH 1.6 the analytes are desorbed from the column while C1 and S are still retained. With this on-line analytical system the determination of 72Ge and 75As could be completely free from the interference caused by 35CP7C1 and 40Ar35C1 respectively. By following the established microwave digestion and on-line separation process the detection limits obtained for Ge As and Se were as low as 0.07 0.13 and 0.3 ng mi-' respectively.The analytical reliability of the proposed method was evaluated by analysing commercially available urine and whole blood standards and the results obtained were found to be in reasonably good agreement with the literature values. Keywords Germanium; arsenic; selenium; inductively coupled plasma mass spectrometry; on-line removal of interference In recent years the demand to find lower limits of detection for elements with environmental and biological significance has been greater than ever before. Germanium As and Se are among those elements which can form volatile hydrides and which are considered to be of important environmental and biological significance. The contamination of public water supplies by As is known to cause skin pigmentation changes keratoses and carcinoma.' Arsenic is also recognized as a cumulative poison and The presence of Se in water has also been linked to a number of human diseases notably cancers and Keshan disease for people living in Se deficient areas of China,4 although Se in trace amounts is found to be essential for both humans and animals and its deficiency has been linked to some types of muscular degener- a t i ~ n .~ The germanium compounds on the other hand have been taken as an elixir by various people in Japan and their toxic effects to the kidney muscle and nervous system have * To whom correspondence should be addressed. Journal of Analytical Atomic Spectrometry 1 I also been r e p ~ r t e d .~ - ~ Since concentrations of these elements existing even in sub-pg g-' orng g-' levels can exhibit significant effects on environmental and biological systems highly sensitive and reliable methods for their determination in various samples need to be developed. For trace element analysis inductively coupled plasma mass spectrometry (ICP-MS) in comparison with other techniques possesses several advantages such as simultaneous multi- element capability and excellent detection However in a large number of applications it suffers from matrix induced spectral overlap problems and matrix induced signal intensity The latter interference can be generally overcome by standard addition internal standardization isotope dilution or sample preparation techniques.l3 The spectroscopic inter- ferences are caused by atomic or polyatomic ions that have the same nominal mass as the analytes of interest. In biological samples many of these interferences are mainly caused by the matrix elements C1 and S and a few others by C Ca P N and Na.'2,'4,15 These elements give rise to polyatomic species leading to spectral overlap with the analyte elements. A survey of these interferences for the determination of' As Se and Ge in biological samples is presented in Table 1. Extensive studies have so far been made on the alleviation of this matrix spectroscopic interference pr0b1em.I~ The use of the alternative plasma gases (e.g. He)'6 or an addition of N to the Ar plasma gas17 can result in shifting some of the interfering species to other mass regions or reducing the formation of some polyatomic species.Alternatives are the introduction of As and Se as hydrides into the ICP,'8-'9 chromatographic de-salting2' or the coupling of an aerosol desolvation system to the ICP-MS instrument.21 The benefits of coupling ICP-MS with chromatography are well recognized; these include element specificity real-time chromatograms the ability to separate interferences from peaks Table 1 Polyatomic interferences for germanium arsenic and selenium Element Isotope Germanium 70Ge(21.23%) 72Ge( 27.66 %) 73Ge( 7.73 %) 74Ge( 35.94%) 76Ge( 7.44%) Arsenic 75As ( 100%) Selenium 74Se( 0.89%) 76Se(9.36%) 77Se( 7.63%) 78Se( 23.78 %) "Se( 49.61 %) 82Se (8.7 3 "/a) Possible polyatomic interferences 35C12 36Ar34S 38Ar32S 35C137C1 40Ar32S 40Ca160 40Ar33S 36Ar37C1 38Ar35C1 37C12 40Ar34S 40Ar35C1 38Ar37Ci 37C12 40Ar34S 36Ar40Ar 40Ar36S 31P2'4N 40Ar37C1 40Ar36Ar'H 38Ar40Ar 31P2160 3 6 ~ ~ 4 0 ~ ~ 4 0 ~ ~ 3 6 ~ 31p 1 4 ~ 40Ar2 31~2180 12 C 35 Cl2 34S'"03 Journal of Analytical Atomic Spectrometry June 1996 Vol.11 (413-420) 413of interest multi-element capability and low levels of detection. Although there have been no reports published so far on the determination of As Se and Ge in biological samples by the hyphenated system several off-line s t ~ d i e s ' ~ ~ ~ have been car- ried out on the determination of As and Se from urine and blood using ion-exchange separation for the elimination of the spectral interferences caused by C1 and S in ICP-MS. In these studies the interference eliminating technique is basically based on the retention of Cl and S as anions on a strong base anion- exchange resin in NO3- form while the analytes as undissoci- ated forms of H,AsO H,AsO and H,SeO are eluted with dilute acid and collected in the eluate for determination by ICP-MS. However this separation process is not applicable when Se in the sample solution is not present solely as Se".This is because Se presented in the higher oxidation state as SeIV dissociates into HSe0,- and Se042- in diluted acid media and is strongly retained together with Cl- on the resin. Consequently it is necessary to add a reductant (such as SnCl,) to the sample to reduce Se"' to Se" prior to elution in order to facilitate complete separation of the analytes from the interferences.In an attempt to further improve the method for the determination of Ge As and Se in biological samples an on-line anion-exchange separation-ICP-MS procedure was developed for the separation of C1 S and other concomitants from analytes based on different principles from the method described above. A sequence of separation processes was optimized by prior adsorption of analyte anions (as HGe0,- H,AsO,- As04,- Se03,- Se04,- etc.) as well as Cl- and S042- on the column by adjusting the sample solution to an appropriate pH (about pH 11.3 while allowing elution of cationic species from the column at this specific pH. Further separation of analytes from the interferents (C1 and S) was possible by adjusting the pH of the eluent (at about 1.6) to allow the elution of analytes as undissociated species (such as H,Ge03 H3As0 and H,SeO,) from the column.The main advantages of this on-line system are that the analytes irrespec- tive of their oxidation states can be effectively separated from the potential interferences of cationic and anionic species in the ICP-MS measurement simply by pH adjustment of the eluent solutions and rapid sample throughput is achievable. EXPERIMENTAL Reagents and Vessels All reagents used were of analytical or higher grade (E. Merck Darmstadt Germany). Water was treated by reverse osmosis and mixed-bed ion exchange (Milli-RO 10 PLUS Millipore MA USA) followed by double distillation in a quartz still equipped with a quartz immersion heater (Heraeus Destamat Germany). High purity nitric and perchloric acids were pre- pared by sub-boiling distillation of reagent grade acids and then stored in Teflon bottles.Stock standard solutions (1000 ppm) of Se"' and As"' were prepared by dissolving sodium selenate and sodium arsenite (Aldrich Milwaukee WI USA) in water. Other standard solutions (1000 ppm) of Gel" As" and Se" were purchased from Aldrich or E. Merck. Standard solutions of each element were prepared fresh daily from stock solutions. The anion exchange resin (AG2-X8 100-200 mesh chloride form) was purchased from Bio-Rad. Sample preparations were carried out on a clean bench providing a class 100 working environment. The eluents at pH 1-3 and 11-13 were prepared by diluting nitric acid and sodium hydroxide respectively. The test sample solutions at pH 4-7 and 7-11 were adjusted by addition of ammonium acetate-acetic acid and ammonium hydroxide-ammonium acetate buffer solutions respectively.For the adjustment of pH beyond 11-13 a sodium hydroxide solution was used. Prior to their use all the buffers were purified by passing through an anion-exchange column. Polytetrafluoroethylene (PTFE) and polypropylene (PP) containers were used throughout. The vessels were cleaned by immersion in 20% v/v nitric acid overnight and steaming successively with nitric acid and water vapour before use. Apparatus Microwave digestion of biological samples was accomplished with the use of a commercial oven Model MDS-2000 (CEM Corp. Matthews NC USA) equipped with a Teflon-coated oven cavity and removable 12-position sample carousel. The oven has a variable power range (up to 630 W) adjustable in 1% increments.The existing turntable was rotated at 3.5 rev min-l and a pressure line was installed with a transducer for pressure monitoring. The pressure limit was set at 150 psi (1 psi = 6895 Pa) a gas pressure in the vessel of over 150 psi resulted in the power being turned off; when the pressure dropped to 148 psi the power was restarted to heat the sample. The sample was digested in a lined digestion vessel (100 ml volume maximum operating pressure 200 psi) consisting of a chemically resistant inner liner (Teflon PFA) and cover to contain and isolate the sample solution from a higher strength outer pressure vessel body (Ultem polyetherimide). In order to protect the digestion vessel from excessive pressures a rupture membrane (Part number 324350 CEM) was used to direct the escape gases through the exhaust port if the safety rupture membrane broke.A dual beam UV/VIS spectrometer (Model Cary lE Varian Australia) equipped with quartz cells of 1 cm path length was used to measure the absorbance at 200-900 nm. The ICP mass spectrometer used was a Perkin-Elmer Sciex Elan 5000 (Thornhill Ontario Canada) equipped with a cross- flow pneumatic nebulizer and a Scott-type spray chamber. The element elution profiles were recorded in real-time with 'graph- ics' software and stored on an IBM PS/2 computer. The data was acquired in multielement mode by peak hopping over the analytical masses using a 1 s measurement time a 20 ms dwell time and 1 measurement per peak. The data as ASCII files was first processed using a program developed in this labora- tory the raw count rates were then smoothed with a five-point Savitzky-Golay method.Peak area was calculated by integrat- ing the total counts above the baseline using points on both sides of each peak. Sample Decomposition Urine and blood samples were digested in a closed system to prevent sample loss from vaporization. For the digestion of urine 1.0ml of sample together with 1.0ml of hydrogen peroxide (30%) and 1.0 ml of concentrated nitric acid were dispensed into the Teflon PFA lined vessel. Twelve vessels were put into the microwave cavity for sample digestion at maximum power (630 W) for 30 min. The pressure was monitored by means of a transducer connected to one of the sample vessels the pressure limit of which was set at 150 psi.After digestion the sample was cooled for 30 min and transferred into a 7 ml Teflon vessel. The solution was irradiated with an infrared lamp on a clean bench (class 100) to evaporate to incipient dryness (with gradual addition of water). The residue was diluted with 3 ml of water and adjusted to pH 11.5. The sample solutions were used either for evaluating the completeness of the digestion process by UV/VIS spectrometry or for the determination of the analytes using the on-line analytical system described in the next section. For the digestion of blood a two-step digestion procedure was performed. Twelve samples were processed at a time. A 41 4 Journal of Analytical Atomic Spectrometry June 1996 Vol. 110.5 ml portion of sample 2ml of nitric acid and 0.5 ml of HC104 were placed in a Teflon PFA lined vessel and digestion was carried out at maximum power (630 W) for 25 min with the pressure limit setting at 150psi.After finishing the first digestion step the digest was cooled for 30 min the vessel cap was opened and 1 ml of hydrogen peroxide was added to the digest. The sealed vessel was then heated again at 630 W for 15 min. After cooling the digested sample was further treated as described for the urine sample. On-line Separation and Measurement by Inductively Coupled Plasma Mass Spectrometry An anion-exchange resin column was prepared by pouring a slurry of resin into a 4.6 mm id x 25 cm polyether ether ketone (PEEK) column (Alltech Associates Arlington Heights IL USA) using a packing machine obtained from Alltech.The prepared column was subsequently washed with 100ml of 10% v/v HNO and 100 ml of water. A schematic diagram of the manifold of the on-line analytical system is shown in Fig. 1. Three metal-free valves were used. A (4 + 1)-port switching Teflon valve (No. 11 18 Omnifit USA) was installed between various solution reservoirs (designated as A B C and D respectively for pH 11.5 carrier solution water and eluents of pH 1.6 and 4% HN03) and a Dionex Model DQP-1 pump (Pump 1). A sample injection valve (Model 9125 Rheodyne Cotati CA USA) with a 2 ml sample loop was connected with Teflon tubing between DQP-1 pump (Pump 1) and the anion-exchange column. A six-port switching valve (Model 9000 Rheodyne Cotati) which served as a four way valve in this work was installed for conveying the effluent from the column to the waste and water from the peristaltic pump (Pump 2) to the ICP-MS instrument during the sample pretreatment stage.The on-line separation procedure was carried out as follows. During the sample uptake step 2ml of sample solution of pH 11.5 was injected into the sample loop with a syringe; meanwhile a carrier solution of pH 11.5 (A in the figure) was passed through the column at an optimum flow rate of 1.72 ml min-'. The sample was then loaded onto the column by switching the sample injection valve to allow the carrier solution to flow through the sample loop. After sample loading (about 70 s) the (4+1)-port valve was rotated to the water port (B) for washing the line for about 150s.During the sample uptake and column washing steps the effluent from the column was directed through the six-way valve to the waste bottle; meanwhile water was carried by the peristaltic pump to the ICP-MS instrument. During the elution step the six-way valve was first switched to direct the column effluent to the ICP-MS instrument and the (4+ 1)-port valve was then rotated to the acid solution (pH 1.6 C) port for the desorption S B ~ D I C iniection valve (Rheodyne 9 125) waste I P Ample loop $-Port Vslvc I,,,.,,] Fig. 1 Schematic diagram of the proposed hyphenated system. A carrier solution (pH 11.5); B washing solution (H,O); C eluent (pH 1.6) and D eluent (4% HNO,) Table 2 Instrumental parameters and operating conditions Instrumental conditions Rf power/W Reflected power/W Plasma gas flow rate/l min - Auxiliary gas flow rate/l min-' Nebulizer gas flow rate/l min-' Sampling depth/mm Sampler cone Skimmer cone Bessel box lens/V Bessel box plate lens/V Photon stop lens/V Einzel lenses 1 and 3/V Column (4.6 mm id x 25 cm) Liquid chromatography conditions Eluent flow ratelm1 min-' 1050 <5 15 0.9 0.9 18 Nickel 1.14 mm orifice Nickel 0.89 mm orifice 10.95 - 73.8 - 10.05 1.57 Strong anion exchanger 1.72 (AG2 x 8 100-200 mesh) of Ge As and SerV.After this elution process (about 300 s) the (4+1)-port valve was again switched to the 4% nitric acid solution port (D) for the desorption of the remaining species of SeV' from the column. After finishing the complete elution procedure the (4+ 1)- port valve and the four-way valve were restored to their original sample uptake positions for processing the next sample.The ICP-MS operating conditions including power nebulizer gas flow rate and ion lenses were optimized to achieve maximum sensitivity for the analytes by flow injecting 50 ppb of mixed standard analytes. The instrumental param- eters and operating conditions of the on-line system thus obtained are summarized in Table 2. RESULTS AND DISCUSSION Sample Decomposition Urine and blood samples contain various types of proteins which combine with Ce As and Se to form various organo- complexed compounds. It is unlikely that the complexes can be retained by the anion-exchange resin mainly because of their size configuration and charge.24 In addition the protein molecules existing in the biological samples may be tightly sorbed on the resin surface and lead to pressure build-up eventually shortening the column lifetime.25*26 This indicates that in order to achieve complete separation of Ge As and Se from body fluid samples by ion-exchange chromatography a prior decomposition of the organic matrix is a prerequisite.Microwave digestion of biological samples with acids at elevated temperatures and pressures rapidly destroys the organic matrix. Under these conditions the oxidizing power of the acid is significantly increased and contamination loss of volatile elements and dissolution time are reduced. In this work the microwave digestion of biological samples was per- formed basically following the established literature methods. For the digestion of urine a mixed reagent of HN03 and H202 was ~ s e d ; ~ ~ ~ ~ for the digestion of blood a two step process with prior digestion with HNO and HC104 followed by addition of H202 was The digestion was performed at a maximum power of 630 W at a pressure upper limit setting of 150 psi as was described in Experimental.As described above the destruction of organic matter is one of the most critical steps in trace analytical techniques in which ion-exchange processes and solvent extraction are employed as the separation method^.'^,^^ However to what extent the matrix is destroyed by a specific decomposition method has been so far seldom evaluated quantitatively. Conventionally when clear and colourless solutions are obtained or when total recovery of some elements is obtained it has been Journal of Analytical Atomic Spectrometry June 1996 Vol.11 41 5assumed that oxidation of the organic matter has been com- pleted for practical purposes. However such assumptions are not necessarily reliable in all cases. More conclusive and direct information as to the presence and identities of residual matter retained by the acid solution is certainly desirable especially if such matter might interfere in any subsequent measurement. To investigate the wet oxidation efficiency of biological and botanical samples with the use of HNO Kingston and J a ~ s i e ~ ~ evaluated the completeness of dissolution by measuring the free amino acid resulting from protein hydrolysis in the samples. In some other st~dies,,~,,~ the total residual carbon in a number of digested biological samples was measured and used as a relative measure of the efficiency of the various digestion schemes.Evaluation of the peak shape and back- ground behaviour of the different voltammograms was also used to judge the quality of the digestion p r ~ c e d u r e . ~ ~ In our previous report^,^^,,^ we developed a method combining radio- tracer techniques with paper electrophoresis to investigate the effectiveness of the decomposition process of 65Zn-labelled liver samples. In this study a UV/VIS spectrophotometric method was tested for its applicability to evaluate the completeness of destruction of the sample matrix. Biological samples which contain various kinds of protein and other high molecular weight substances exhibit distinct absorption spectra in the UV/VIS region.Destruction of the organic matrix may conse- quently result in a decrease in the intensity of UV/VIS absorption and the measurement of decreasing absorption of the digested sample can probably provide useful information to evaluate the effectiveness of sample decomposition. Fig. 2 shows the UV/VIS absorption spectra from 200 to 900 nm for urine and blood samples prior to and after digestion. Fig. 2(a) shows that urine (diluted 1 200) exhibits strong absorption at 200 to 300nm while the same sample after treatment by microwave digestion with acid mixture (HN03 and H202) 2 1.5 1 0.5 1.5 I 0.5 0 200 300 400 500 600 700 800 900 Wavelengthhm Fig. 2 UV-VIS absorption spectra of (a) urine samples where A is original urine (1:200 dilution) and B is urine after digestion (no dilution); and (b) whole blood samples where A is original blood (1 200 dilution) B is blood after stage one digestion (1 25 dilution) and C is blood after stage two digestion (no dilution) exhibits only appreciably low absorption in the same wave- length region.This may provide a preliminary indication of the effectiveness of this digestion procedure for urine. For undigested blood [Fig. 2(b)] a much more intense and complicated absorption spectra extending from 200 to 450 nm was observed as compared with urine. The remarkably high absorption may indicate abundant existence of complex organic species and consequently more drastic digestion con- ditions should be exerted in order to achieve complete digestion of blood.The same figure also shows the absorption spectra resulting from the first step of blood sample digestion with a strong oxidizing acid mixture (HNO and HC104) followed by the second step of digestion with a further addition of H202. From the result it can be seen that after the first step of the digestion procedure the majority of the absorption spectra disappears but an intense broad peak at 300nm still remains. By further digestion with the use of H202 this specific absorption peak can be effectively reduced to a very low level (only about 1 70 remains). In order to verify if the disappear- ance of the absorption can be a correct reflection of the complete destruction of the organic matrix the recovery of Se in certified urine (National Institute of Standards and Technology Toxic Metals in Urine NIST SRM 2670) and blood (Seronorm Trace Elements in Whole Blood Batch Number 205052) (subjected to the digestion procedures described above) was examined with on-line separation and determination by ICP-MS.Recoveries obtained for Se in the digested urine sample in blood subjected to the first step and second step of digestion were 94 60-70 and 95% respectively. The somewhat good correlation obtained between the recovery of the analyte and the exhibiting absorbance of the digested sample solutions may provide a feasible means to identify the extent of digestion efficiency based on UV/VIS spectrophoto- metric measurement. Anion-exchange Separation of the Analytes After acid digestion the digest was treated by anion-exchange chromatography in order to separate the analytes from the matrix.The chemical forms of the analytes in the wet oxidation digested samples most probably exist in the forms H2Ge03 H3As03 H3As04 H2Se03 and H,SeO,. The chemical behav- iours of these species toward the anion exchanger is basically predictable from their respective acid dissociation constants pK,. It is generally believed that the analytes in the alkaline media exist as 0x0-anionic forms that can be strongly retained by the anion exchanger; whereas in relatively acidic media these ions will be protonated to become neutral species that will be inactive to the resin phase. Table 3 summarizes the stepwise dissociation constants of these analytes from the 1iteratu1-e.~' Though the value of pK1 of H2Se04 was not found in the literature it could be expected to be lower than its pK2 value (i.e.1.7). In order to investigate the adsorption behaviour of the respective analytes on the anion-exchange resin batch experi- ments were carried out in this study. Analyte solutions adjusted to pH 1.0 to 13.0 were introduced into the anion-exchange Table3 Literature values for pK of H2Ge03 H,As03 H,AsO H,SeO and H2Se0 (Ref. 24) ~ PKI PK2 PK3 Species H2Ge0 9.01 (8.87) 12.30 H3As03 9.29 (9.24) H,AsO 2.26 (2.32) 6.76 11.29 H2Se0 2.62 (2.73) 8.32 H2Se0 * (1.08) 1.70 * Not reported. Data in parenthesis was obtained in this work. 41 6 Journal of Analytical Atomic Spectrometry June 1996 Vol. 11column (4.6 mm id x 25 cm) at 1.72 ml min-I and the eluates collected from each elution were determined by ICP-MS.Fig. 3 shows the effect of pH on adsorption efficiency for each analyte on the anion-exchange column. From the figure it can be seen that adsorption yields for AsV and Se" abruptly increase to nearly quantitative values between pH 2 and 3.5 and are quantitative up to pH 13 (maximum pH tested) for SeV1 adsorption yield abruptly increases to nearly quantitative at about pH 1.5 and is quantitative up to pH 13. The abrupt increase in adsorption at relatively lower pH regions (pH 1.2 to 3.5) for these species can be explained on the basis of their respectively lower pK values as seen in Table 2. These analytes are supposed to dissociate into singly ionic species as H,AsO,- HSe03- and HSe0,- which can be adsorbed on the resin in the relatively lower pH region and successively dissociate with an increase in pH into AsO;- Se032- and Se042- in accordance with their respective pK and pK3 values.It is also noted from the figure that the adsorption behaviours of GelV and As"' are very different from the above three ions. It shows that quantitative adsorption for the latter two ions can be achieved only at a pH of about 10 which is obviously attributable to the relatively higher pK1 values for H,Ge03 (9.01) and H3As03 (9.29). The results shown in Fig. 3 indicate that it may be possible to separate the analytes as a group from the matrix by anion- exchange chromatography simply by adjusting the sample solution to a pH greater than 10. The matrix substances which do not exist as anions at this specific pH region will flow through the column while the analytes as well as some other anionic species adsorbed can be subsequently eluted out of the column either as undissociated neutral species or ionic forms with eluents of appropriate pH.By referring to the curves of pH uersus adsorption yield shown in Fig. 3 the acid dissociation constants (pK,) of the analytes can be roughly estimated. The first dissociation con- stant (pK,) of a dibasic acid H2A can be expressed as in the following equation Under the specific conditions when the equilibrium concen- tration of the [H2A] analyte form is equivalent to the [HA-] form the pK value can be determined from the pH of the solution. The pK values of the respective species so obtained from the equivalent points at 50% adsorption on the respective curves shown in Fig.3 are included in Table 3. The data estimated are in reasonably good agreement with the literature values and the pK1 of H2Se04 which was not found in the literature is roughly estimated to be 1.08. Establishment of the On-line Separation System In an attempt to improve the detection sensitivity and through- put for sample analysis a hyphenated technique combining anion-exchange separation of analytes from the sample matrix with ICP-MS determination was developed. The on-line system as shown in Fig. 1 was first tested for its applicability for the analysis of biological samples with the use of a standard solution comprising the estimated concentrations of the major matrix elements Na C1 and S at mg ml-' levels and trace analytes at ng ml-I levels in the digested sample solution.Considering the possible existence of various oxidation states of the analytes in the digested sample the adsorption behaviour of GetV As"' AsV Se" and SeV' on the column was also examined in this on-line separation system. In order to understand the chromatographic behaviour of the analytes and matrix elements in the on-line system the full-time scale elution chromatogram from sample loading to analyte desorption was investigated by directing the effluent to an ICP-MS instrument for mass detection. Fig. 4 shows the chromatograms for Na C1 S Ge" As"' and AsV and SeIV and SeV' so obtained. The m/z for 23Na 35Cl 33S 75As and 72Ge are only shown in the above figure. It can be seen from this figure that during the sample uptake and washing steps which take about 250 s only 23Na and 40Ar38Ar appear in the chromatogram thereby confirming the expected elution order of cationic species from the column.In the subsequent desorption step with an eluent of pH 1.6 shown in the time scale from 250 to 550 s GelV As"' and AsV and Se" are seen to be completely eluted from the column while SeV1 and potentially interfering elements like C1 and S are still not observed. By further increasing the acidity of the eluent to 4% HN03 as shown from 550 to 900 s Se" which is attributable to its lower pK1 together with 35Cl 33S (as SO,") 35C137C1 and 40Ar35C1 can now be observed in the chromatograms. The fact that C1 and S are eluted out only in the second elution step is beneficial in that spectral interference of 75As by 40Ar35Cl and 72Ge by 35C137C1 is prevented. This ensures complete removal of matrix interference by this on-line separa- tion and ICP-MS method.It is noted that the presence of S 100 80 60 0 +AS(III) - W V ) -+ Se(1v) * Se(V1) -8- Ge(1v) 0 2 4 6 8 10 12 14 pH value Fig. 3 Dependence of recovery of the analytes on pH of the sample solution Journal of Analytical Atomic Spectrometry June 1996 Vol. 11 41 733s L l l i . _ I 800000 lmmmy) 0 7 2 G e j 2000 (4 - 78SeOrI) 0 ' 82& 1000 0 500 Time/s Fig. 4 Chromatograms of Na C1 S Ge" As"' and AsV and Se'" and SeV' in test sample solutions at concentrations of 5 mg ml-' for Na and C1 1 mg ml-' for S 5 ng ml-' for Ge" 2.5 ng ml-' for AS'" 5 ng ml- ' for AsV 20 ng ml-' for Se" and 30 ng ml-l for SeV1 at levels of mg ml-' in the sample solution do not cause any perceivable interference (no perceivable peak of 40Ar32S) and can thus be neglected in the present work.The effect of different charge states of the analytes on the chromatographic behaviour was also investigated. It can be seen from the figure that the peaks of As"' and AsV appear in the same time interval while those of SeIV and SeV' appear at different elution times. The notable difference in the chromato- graphic separation of Se species can be attributed to their different pK values. After acid digestion of the biological sample Se in the digest may exist as in SeIV or SeV' depending on what acid mixture and digestion procedure was employed. Even when two Se species are present in the digest the total concentration of Se can still be determined simply by summing up the respective concentrations of SeIV and SeV' determined by this analytical system. For the purpose of analysis of the standard reference material sample the operating conditions for the on-line system were as follows.In the sample loading stage the sample solution (adjusted to pH 11.5) was loaded onto the column for adsorp- tion of the analytes the eluate comprising the neutral and cationic species was directed to waste. Meanwhile water was continuously pumped through an alternative path to the ICP-MS instrument to clean the sample loop. Such an oper- ation can provide advantages of preventing possible clogging of the nebulizer orifice and sampling cone by the dissolved solid substances and also the memory effect caused by the previously analysed samples and can thus ensure the long term analytical precision of the system.The reactions involved in the separation scheme as shown in Fig.4 can be plausibly explained by Eqns. 2-4. In the sample loading step at pH 11.5 all the analytes and matrix elements of S and C1 are adsorbed as anions on the column possibly following Eqn. 2. As the eluent of pH 1.6 was applied to the column analytes such as Ge" As"' AsV and Se" were protonated as neutral species and were eluted as shown in Eqn. 3. Finally as the acidity of the eluent was further increased to 4% HNO SeV1 as well as Cl- and S042- were eluted as in Eqn. 4. By following the on-line analytical process estab- lished the sample throughput can be achieved to about 4 samples h-'.Sorption step n [ Resin] + + M"' X" - = [ Resin],X + M" + where X"- = HGeO - H2As0 - AsO - Se0,2- (pH 11.5) (2) Se042- C1- ... M"+=Na+ K' Ca2+ Mg2+ ... Desorption step 1 [ Resin],X + nH + = n [Resin] + + H,X (pH 1.6) where H,X= H,GeO H,AsO H,AsO H2Se0 (3) Desorption step 2 [Resin],X+nH+ =n[Resin]+ +H,X (4% HNO,) (4) where H,X=H2Se04 HCl H2S04 ... Analysis of Urine and Blood With use of the established on-line column separation system the digested urine and blood samples were analysed. Fig. 5 shows the typical elution profiles for standard samples of urine (NIST SRM 2670 of normal levels) and blood (Seronorm Trace Elements in Whole Blood Batch Number 205052 Level I) respectively. As can be seen Ge As and Se" appear at the same elution time between 350 and 550 s after sample loading.For urine there is no appreciable peak for Ge thereby indicating its insignificant content in the urine sample; however there is one distinct peak for As and three peaks of mass 78 corresponding to one ,*Ar4OAr peak and two peaks of Se" and Se" respectively. The peaks of Ge As and Se can all be observed in the chromatogram of the blood sample. It is noticeable that both the peaks of Se" and SeV1 can be observed in the digestate of the urine and blood samples but at different peak intensity ratio which is attributable to different acid mixtures used for the digestion of the samples. By following the established microwave digestion of the sample matrix followed by on-line removal of the interferences the analytical performance of this method was evaluated in terms of detection sensitivity and analytical reliability.The method detection limits defined as the analyte concentration that gives a signal that is three times the standard deviation of the procedure blank (n=7) were calculated to be 0.07 0.13 and 0.3 ng ml-' for Ge As and Se" and SeV' respectively. The percentage differences of slopes between the external calibration and standard addition curves were all within f 3% for Ge As and Se which may indicate that the multiplicative interferences caused by the matrix substance can be effectively eliminated by this on-line separation system. Consequently the external calibration method was used throughout this work. For evaluation of data reliability two certified reference urine samples (NIST SRM 2670 of normal level and elevated level) and two certified whole blood standards (Seronorm Trace Elements in Whole Blood Batch Number 205052 Level I and 205053 Level 111) were used.Among the four standards cited above no certified values of Ge in the two urine samples and of Ge and As in the two whole blood samples were provided. Table4 shows the results for the analysis of the reference materials. The data for Se shown in the table are the 41 8 Journal of Analytical Atomic Spectrometry June 1996 Vol. 1 1Table 4 Analytical results for Se As and Ge in certified urine and whole blood samples (n= 3) [Se]/ng ml-' [As]/ng ml-' [Ge]/ng ml-' Sample* Found Certified Found Certified Found Certified Urine standard 1 31.2f 1.4 30+8 60.3 f4.5 ( 60 )t ND -$ Urine standard 2 451 f 18 460 f 30 486 k 25 480 f 100 ND -1 Blood standard 1 87.2 + 6.2 83 4.0 0.7 - f 4.7 f 0.5 (4.3 f 0.2B Blood standard 2 87.7 '.6.2 82 27.8 3.0 (X+25fl 4.5 0.4 -1 * Urine standard 1 NIST SRM 2670 of normal level; Urine standard 2 NIST SRM 2670 of elevated level Blood standard 1 Seronorm Trace Elements in Whole Blood Batch Number 205052 Level I; Blood standard 2 Seronorm Trace Elements in Whole Blood Batch Number 205053 Level 111. t Suggested value. $ No certified value available. 8 Independent result obtained by ETV-ICP-MS. 1 Addition of 25 ng ml-' of As to As sample 'Level I' (non-certified for As). 2000 2000 1500 500 7 I v) t 0 9 1000 500 0 500 1000 Time/s Fig. 5 Chromatograms for the digested biological sample solutions.(a) urine and (b) blood sum of the respective concentrations of Se" and SeV' deter- mined. The results found in this work are in good agreement with the certified values. For the evaluation of the accuracy of the data of which no reference values are available from the standard samples alternative verification processes either by using a different analytical method or by spike addition were adopted. The result for Ge determination in whole blood (standard 1) obtained by an independent method of ETV-ICP- MS39 is in good agreement with the result obtained by the proposed method. Spike recovery tests were also performed by adding equivalent amounts of Ge As and Se as those found in this work (as shown in Table 4) to the whole blood standard 1 and urine standard 1 followed by microwave digestion and on-line separation.The recoveries for all the elements tested were of 95 to 100%. The authors gratefully acknowledge the financial support of the National Science Council (NSC 84-2621-M-007-007 ZA) of Taiwan. 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ISSN:0267-9477    

DOI:10.1039/JA9961100413

出版商:RSC    

年代:1996

数据来源: RSC