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/JA99611FX009

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

DIARY OF CONFERENCES AND COURSES 1996 Analytica Conference 96 April 23-26 Munich Germany Details can be found in J. Anal. At. Spectrom. 1994 2 69N. For further details contact Messe Munchen GmbH Messegelande D-80325 Munchen Germany. Telephone +49 89 51 070; Telex 5 212 086 ameg d; Fax +49 89 51 07 177. ASMS Short Course Interpretation of Mass Spectra LC-MS and MS-MS May 11-12 Portland OR USA For further details contact American Society of Mass Spectrometry 1201 Don Diego Avenue Santa Fe NM 87505 USA. Telephone + l 505 989 4517; Fax + 1 505 989 1073. 44th ASMS Conference on Mass Spectrometry and Allied Topics May 12-17 Portland OR USA For further details contact American Society of Mass Spectrometry 1201 Don Diego Avenue Santa Fe NM 87505 USA. Telephone + 1 505 989 4517; Fax + l 505 989 1073.Ninth International Symposium on Trace Elements in Man and Animals May 19-24 Bang Alberta Canada Details can be found in J. Anal. At. Spectrom. 1995 10 58N. For further details contact TEMA-9 The Banff Centre for Conferences P.O. Box 1020 Station 11 Banff Alberta Canada TOL OCO. 'Telephone + 1 403 762 6308; Fax + 1 403 762 6388 or Dr Mary L'AbbC. Telephone + 1 613 957 0924; Fax + 1 613 941 6182; E-mail Mlabbe@HPB.HW C.CA. Total Reflection X-Ray Fluorescence Analysis June 10-11 (Part 1 ) Eindhoven Germany June 13-14 (Part 2!) Dortmund German,y Details can be found in J. Anal. At. Spectrom. 1995 10 60N. For further details contact Gesellschaft Deutscher Chemiker TXRF-Konferenz Postfach 90 04 40 D-60444 Frankfurt Germany. Fax +49 69 7917 475.Resonance Ionization Spectroscopy June 30-July 5 Pennsylvania USA Details can be found in J. Anal. At. Spectrom. 1995 10 60N. For further details contact Sabrina Glasgow Conference Secretary Department of Chemistry The Pennsylvania State University 184 Materials Research Institute Building University Park PA 16802-7003 USA. Telephone + 1 814 865 0200; Fax +1 814 863 0618; E-mail scg4@psuvm.psu.edu. Eighth Biennial National Atomic Spectroscopy Symposium Norwich UK July 17-19 10 N Journal of Analytical Atomic Spectrometry March 1996 Vol. 11Details can be found in J. Anal. At. Spectrom. 1995 10 60N. For further details contact Dr S. J. Haswell School of Chemistry University of Hull Hull HU6 7RX UK. Telephone + 44 (0) 1482 465469; Fax + 44 (0) 1482 466410. 42nd International Conference on Analytical Science and Spectroscopy August 10-13 London Ontario Canada For further details contact Martin Stillman University of Western Ontario Department of Chemistry London ON N6A 5B7 Canada.Telephone + 1 519 661 3821; fax + 1 519 661 3022; E-mail stillman@uwo.ca PRAHA96 14th International Conference on High Resolution Molecular Spectroscopy September 9-13 Prague Czech Republic For further details contact Dr Vladimir Spriko Academy of Sciences of the Czech Republic J. Heyrovsky Institute of Physical Chemistry Dolejskova 3 CZ-18223 Praha 8 Czech Republic. Fax +42 2 858 2307; E-mail praha96@jh-inst.cas.cz or praha96@wcpj.chemie.uni-wuppertal.de 5th International Conference on Plasma Source Mass Spectrometry September 16-20 Durham UK For further details contact Dr Grenville Holland Department of Geological Sciences Science Laboratories University of Durham South Road Durham City DH1 3LE UK.Fax +44 (0)191 374 2510. 12th Asilomar Conference on Mass Spectrometry Elemental Mass Spectrometry September 20-24 PaciJic Grove CA USA For further details contact American Society of Mass Spectrometry 1201 Don Diego Avenue Santa Fe NM 87505 USA. Telephone + 1 505 989 4517; Fax +1 505 989 1073. 12th ICP-MS Applications Meeting September 23-24 Jiilich Germany For further details contact Dr J. S. Becker Forschungszentrum Jiilich GmbH Zentralabteilung fur Chemische Analysen D-52425 Jiilich Germany. Telephone +49 2461 612698; Fax +49 2461 612560. Mass Spectrometry Processes for the Determination of Trace Element September 24-26 Jiilich Germany For further details contact Dr J.S. Becker Forschungszentrum Julich GmbH Zentralabteilung fur Chemische Analysen D-52425 Julich Germany. Telephone + 49 2461 61 2698; Fax + 49 2461 612560. 23rd Annual Conference of the Federation of Analytical Chemistry and Spectroscopy Societies (FACSS) September 29-October 4 Kansas City MO USA For further details contact FACSS 201B Broadway Street Frederick MD 21701-6501 USA. Telephone + 1 301 846 4797 Fourth Rio Symposium on Atomic Spectrometry November 24-30 Buenos Aires Argentina For further details contact Dr Osvaldo E. Troccoli Quimica Analitica Facultad de Ciencias Exactas y Naturales Ciudad Universitaria ( 1428) Buenos Aires Argentina. Telephone + 541 783 3025; Fax +541 782 0441. 1997 1997 European Winter Conference on Plasma Spectrochemistry January 12-17 Gent Belgium For further details contact L.Moens Secretariat 1997 European Winter Conference Laboratory of Analytical Chemistry University of Gent Proeftuinstraat 86 B-9000 Gent Belgium. Telephone +32 9 264 66 00; Fax +32 9 264 66 99; E-mail plasma97@rug.ac. be. Updated information may be obtained from the ‘97 Winter Conference homepage on the World Wide Web at http://www.rug.ac. be. Seventh International Symposium on Biological and Environmental Reference Materials April 21-25 Antwerp Belgium Details can be found in J. Anal. At. Spectrom. 1995 9 54N. For further details contact Dr J. Pauwels Institute for Reference Materials & Measurements Management of Reference Materials Unit Retieseweg B-2440 Geel Belgium. Telephone +32 14 571 722; Fax +32 14 590 406; or Wayne R. Wolf Ph.D. Food Composition Laboratory USDA 10300 Baltimore Blvd. Beltsville MD 20705 USA. Telephone +1 301 504 8927; Fax +1 301 504 8314. XXX Colloquium Spectroscopicum Internationale September 2 1-26 Melbourne Australia Details can be found in J. Anal. At. Spectrom. 1995 10 58N. For further details contact The Meeting Planners 108 Church Street Hawthorn Victoria 3 122 Australia. Telephone +61 3 9819 3700; Fax +61 3 9819 5978. Updated information may be obtained from the XXX CSI homepage on the World Wide Web at http://www.latrobe.edu.au/CSIconf/ XXXCSI. html. Journal of Analytical Atomic Spectrometry March 1996 Vol. 1 1 11 N

ISSN:0267-9477    

DOI:10.1039/JA996110010N

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/JA99611BX011

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

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ISSN:0267-9477    

DOI:10.1039/JA996110087R

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Calibration Strategies for the Elemental Analysis of Individual Aqueous Fluid Inclusions by Laser Ablation Inductively Coupled Plasma Mass Spectrometry Journal of Analytical Atomic Spectrometry A. MOISSETTE British Geological Survey Kingsley Dunham Centre Keyworth Nottingham UK NG12 5GG and CREGU Centre de Recherches sur la Giologie des Matibres Premibres iMinCrales et Energitiques BP 23 54501 Vandoeuvre les Nancy Cedex France T. J . SHEPHERD AND S. R. CHENERY British Geological Survey Kingsley Dunham Centre Keyworth Nottingham UK NG12 5GG Using a combination of synthetic fluid inclusions in halite microvolume aqueous solutions and National Institute of Standards and Technology (NIST ) Standard Reference Material (SRM) 611 Glass calibration graphs were established for the determination of elemental ratios in natural fluid inclusions by laser ablation-inductively coupled plasma mass spectrometry (ICP-MS).For simultaneous multi-element analysis optimization studies demonstrate the necessity to adopt a compromise set of operating conditions since ICP-MS sensitivity (signal backgrouiid) may differ from element to element as a function of argon flow radiofrequency power and spray chamber temperature. Synthetic fluid inclusions were prepared by crystallization from saturated sodium chloride solutions containing up to 13 major and minor cations. The microvolume calibration standards 'microwells' consisted of small holes (3 x 3 x 2 mm3) drilled into plastic sheet filled with a standard solution and hermetically sealed. In order to allow direct comparison between the different test materials all the elements (Li Na Mg K Ca Mn Cu Zn Rb Cs Ba Pb B Cl Br) were ratioed to strontium.The relative standard deviations for the element ratios were generally better than 25% indicating that the nature of the sample (salt glass and aqueous solution) does not markedly affect the consistency of ablation or the efficiency of transfer between the ablation chamber and ICP torch. Element ratios for the synthetic fluid inclusions were linear over several orders of magnitude and in close agreement with those for the NIST SRM 611 Glass and microwell solutions irrespective of inclusion size (20-100 pm) and depth in the sample (up to 80 pm). Statistical t-tests on the mean element ratios confirm that microwells and glasses constitute suitable alternatives to synthetic fluid inclusions for the calibration and routine analysis of natural fluid inclusions.Keywords Laser ablation; inductively coupled plasma mass spectrometry; Juid inclusion; laser microanalysis; calibration For the accurate modelling of palaeofluid-mineral equilibria the limiting factor is often a lack of information on the composition of the fluid phase. Fluid inclusions are known to hold this information but their size abundance and diversity often within a single crystal complicates the acquisition of unequivocal bulk chemical data for fluid(s) in equilibrium with the mineral phase. Analysis of individual fluid inclusions is the most satisfactory solution to this problem. Several techniques have been dewloped for this purpose.' Microthermometry is useful for determining the bulk composition and density of fluid inclusions but detailed interpretation is limited by the need to refer highly complex multi-component geological fluids to very simple (two- three- or four-component) exper- imental sy~tems.~?~ Various spectroscopic techniques have been adapted for single inclusion analysis ultraviolet (UV)-visible or fluorescence spectroscopy for the determination of organic compo~nds;~*~ micro-Raman and infrared (IR) spectroscopy for the determination of polyatomic For the ele- mental analysis of inclusion fluids techniques have included X-ray microanalysis of frozen inclusions;" proton-induced X-ray emission (PIXE) and gamma-ray emission (PIGE) spectro~copy;'~~~~ and synchrotron X-ray fluorescence spectro~copy.'~-~~.The latter techniques although non- destructive and capable of achieving micrometre resolution have detection limits that are highly dependent on the shape and depth of the inclusion in the host material. In order to circumvent these problems significant research is now being directed to the use of laser ablation microprobes interfaced to inductively coupled plasma mass spectrometry ( ICP-MS),17 inductively coupled plasma atomic emission spectrometry ( ICP-AES)14,'8 and direct AES19320 instruments. Although wholly destructive with respect to the inclusion fluid the above techniques combine high element sensitivity high spatial reso- lution and relative simplicity of operation. This paper extends the initial work of Shepherd and Chenery17 and describes in detail the procedures developed for the calibration of laser ablation microprobe-inductively coupled plasma mass spectrometry (LAMP-ICP-MS) for the optimum analysis of single inclusions.One of the principal objectives was to determine if synthetic fluid inclusions in halite glass reference materials and aqueous solutions would be suitable as calibration standards for the determination of elemental ratios in natural fluid inclusions. EXPERIMENTAL Calibration Standards A prime requirement for the quantification of fluid inclusion analyses is the existence of calibration standards that can be analysed under the same or similar conditions as natural inclusions. Synthetic fluid inclusions are the obvious choice. Using quartz as the host matrix inclusions of diverse chemical composition can be synthesized under a wide range of exper- imental pressure and temperature conditions.21 However the procedures are time-consuming and for routine LAMP- ICP-MS analysis prohibitively wasteful of low blank high value calibration material.In order to evaluate the use of aqueous solutions or silicate glasses as alternative calibration standards comparative tests were carried out against synthetic inclusions in halite. Whilst not the ideal matrix for aqueous inclusion analysis the ease of synthesis and abundance of large inclusions in halite more than compensate for the disadvantage of Na and C1 interferences. All three forms of calibration Journal of Analytical Atomic Spectrometry March 1996 Vol. 1 I (1 77-1 85) 177material (synthetic fluid inclusions solutions and glasses) were used to derive elemental ratio working curves.Syntheticfluid inclusions in halite Following the methodology of Pironon,22 synthetic brine inclusions of different composition were prepared from high- purity reagent salts. Up to a maximum of 14 salts were used. For the system NaC1-LiCl-MgCl,-CaCl,-SrCl,-KCl (Mg Li Ca Sr K = 1000 pg g-I) the resultant inclusions were extremely abundant up to lo6 pm3 in volume and distributed in well-defined growth zones. For more complex brines (con- taining additionally Rb Ba Cs Pb Cu Zn Mn B= 100 pg g-') the cation chemistry dramatically influenced the growth kinetics of the halite crystals resulting in anhedral crystal clusters containing fewer smaller inclusions.Brine inclusions with various C1 Br ratios were also prepared C1 Br = 50 100,250 the solutions being saturated with respect to NaCl at room temperature (i.e. M 166000 pg g-' C1 and z 100000 pg g-' Na). Microwells containing aqueous solutions In order to assess the efficiency and performance of direct laser ablation of aqueous solutions use was made of microvolume amounts of aqueous solutions. This approach differs from that of Krishna et aLZ3 in not requiring a continuous flow through of solution. The solutions were pipetted into small 3mm diameter wells drilled into a 2mm thick perspex sheet the base and top being sealed with Sellotape or 100pm thick glass cover-slips using low melting-point wax or a silicone rubber adhe~ive.'~ Such microwells are easy to prepare simu- late very closely the ablation of macro-fluid inclusions and provide excellent matrix-matching of natural inclusions of varied chemical composition.Glass reference materials The third type of calibration standard consisted of the National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 61 1 Glass. This is a certified mater- ial and contains z 500 pg g-' of most elements except for Ca (85 700 pg g-') and Na (140OOO pg g-').25 This was used extensively to optimize the ICP-MS operating conditions described below and as a reference baseline for comparison with the synthetic fluid inclusions and microwells. By adopting a multiple calibration standard approach it was possible to assess variation in ablation efficiency due to material state (liquid versus solid) form of liquid containment (inclusions versus microwells) transfer losses between chamber and plasma torch and possible matrix effects.Instrumentation Fig. 1 shows a schematic layout of the LAMP-ICP-MS analy- sis system. Apart from minor modifications the configuration is as originally described by Shepherd and Chenery.17 UV laser Ablation was carried out using a frequency quadrupled Spectron Nd YAG pulsed laser operating in the far-UV region (266 nm) at 10 Hz. The optical delivery system consists of a high-quality Leitz microscope and Cassegrain x 25 or x 36 reflecting objective lens. Previously Geertsen et a1.26 have suggested that a UV laser-produced plasma is superior in every respect to that of an IR plasma for LAMP-ICP-MS studies.For an IR-induced plasma the plasma is opaque to the incident laser beam. This results in increased heating of INDUCTIVELY COUPLED MASS I PLASMA I MIXER I m Fig. 1 flow sample introduction system used for ICP-MS analysis Schematic diagram of the UV laser microprobe and dual gas the plasma indirect laser-matter interaction uncontrolled ablation selective vaporization of the material and the forma- tion of large ablation craters. By comparison a UV plasma is partially transparent to the laser beam. Laser-matter inter- action is thus more direct resulting in controlled and continu- ous ablation and the formation of craters which are defined by the diameter of the laser spot and not by the size of the plasma. Such mechanisms are still open to investigation and interpretation but for inclusion analysis the most significant advantage is that many inclusion-bearing minerals that are transparent in the IR region (e.g.quartz fluorite) absorb in the UV region. Ablation chamber For this study use was made of a new ablation chamber,27 which has an internal aerodynamic profile and allows smoother and faster transfer of ablated material to the torch. Before reaching the torch the argon flow from the ablation chamber is merged with argon carrier gas from the nebulizer/spray chamber in a glass mixer. Optimization of the different param- eters controlling the dual gas flow ~ystem'~.~*-~' is described below. ICP-MS The ablated material was analysed using a VG PlasmaQuad 2 + ICP-mass spectrometer in peak jumping acquisition mode where only responses at selected masses are analysed.Data processing utilized proprietory VG time-resolved acquisition software that permits identification and integration of the response at each selected mass over time.29*31 Calculation and quantification were performed using custom computer pro- grams. Analyte mass positions were selected to avoid known or suspected polyatomic or isobaric interferences (see Table 1). Optimization of Laser Ablation Conditions In order to optimize the laser ablation conditions for the analysis of inclusions in halite preliminary tests were carried out on inclusion-free halite. These demonstrated that to avoid excessive fracturing of the matrix and potential loss of inclusion fluid (prior to or during inclusion breakthrough) hole forma- tion should be initiated using minimum laser power.Once initiated the power could then be progressively increased to achieve optimum conditions for drilling a clean hole down to the level of the sub-surface inclusion (Fig. 2). These conditions vary from mineral to mineral depending on the position of the absorption edge with respect to the UV wavelength and the Vaporization temperature of the mineral phase. For synthetic inclusions the laser on entering the inclusion was fired for a further 2-10 s according to the size and volume of the inclusion; 178 Journal of Analytical Atomic Spectrometry March 1996 Vol. 11Table 1 analysis. Data taken from ref. 32 Isotope masses (u) and relative abundances used for ICP-MS Relative Isotope Mass/g mol-' abundance (YO) Li 7 92.58 B 11 80.22 Na 23 100 24 78.7 Mg c1 35 Ar 40 99.6 K 39 93.1 Ca 44 2.08 Mn 55 100 c u 63 69.09 Zn 64 48.89 cu 65 30.91 Zn 66 27.81 Br 79 50.54 Rb 85 72.15 Sr 88 82.56 cs 133 100 Ba 138 71.66 Pb 208 52.3 75.53 Fig.2 SEM photomicrograph of a typical laser ablation hole in halite the smaller the inclusion the faster the rate of fluid vaporization. Optimization of ICP Analytical Conditions Since argon flow rates water vapour content of the nebulizer flow and torch power have a marked influence on the tempera- ture and ionization characteristics of the plasma and formation of polyatomic interferences tests were carried out using NIST SRM 611 Glass to determine the optimum dual flow plasma conditions for the determination of different elements.The results expressed as the signal-to-background (S B) ratio are summarized in Fig. 3 and 4. ArgonJEow rates The effects of varying the ablation chamber and nebulizer flow rates are shown in Fig. 3. Wet conditions refer to the injection of a blank solution (1% HN03 solution) from the nebulizer whereas dry conditions refer to zero injection of solution. The best S B ratio under wet conditions corresponds to a nebulizer flow rate of 0.4 1 min-' and a corresponding ablation cell flow WET I DRY I I m 3i I . . 1 2 3 4 Nebuliser and cell argon flow rates Fig. 3 General variation in ICP-MS response [signal background ( S B)] for a range of elements as a function of ablation chamber (cell) and nebulizer (neb) argon flow. Types 1 to 3 refer to wet conditions (1 neb.0.65 min-' and cell 0.3 1 min-'; 2 neb. 0.4 1 min-' and cell 0.6 1 min-l; 3 neb. 0.25 1 min-' and cell 0.9 1 min-'). Type 4 corre- sponds to dry conditions (4 neb. 0.25 1 min-' and cell 0.9 1 min-') Li 1000 1100 1200 1300 1400 Ca Ba $ m v) 80 t 60 20 1000 1100 1200 1300 1400 Plasma power/W Fig.4 Effect of the ICP rf forward power on element intensities [signal backgrounds (S:B)] (a) LiE! and Na +; (b) Cam and Ba+ rate of 0.6 1 min-'. Comparison between wet and dry plasma conditions indicates that wet conditions favour Co Mn and the alkali and alkaline earth elements (except for Sr and Li) whereas dry conditions are more favourable for Cu and Zn. Allowing for a slight reduction in Cu and Zn intensities wet conditions were selected for subsequent calibration tests since they allowed for the introduction of aqueous standard solutions.Spray chamber temperature The spray chamber acts as a dynamic filter for solution droplets produced by the nebulizer. It retains the larger droplets that would otherwise fail to dissociate totally in the plasma and which would increase the noise level and hence the background signal. By varying the temperature of the water-cooled jacket around the spray chamber one can alter the water vapour content of the argon flow and size distribution of the dr0plets.3~ Journal of Analytical Atomic Spectrometry March 1996 Vol. 1 I 179In order to establish the optimum cooling conditions back- ground values were measured for a wide range of elements as a function of temperature from 2.5 to 193°C.Most of the alkali and alkaline earth elements (Be Na K Ca Rb Cs) have their lower background values at around 8.1 "C whilst others appear temperature-independent (Li Mg Sr Ba). The halogens C1 and Br are clearly temperature-sensitive and have their lower background values in the range 2.5-9.4 "C. The background is also lower for B Mn and Fe between 2.5 and 8.1 "C whereas Cu Zn Ce and U show no significant back- ground change with temperature. Thus for most elements 8.1 "C represents a good working compromise. Radiofrequency power to the ICP The radiofrequency (rf) forward power (watts) to the ICP source has been a well-known variable influencing elemental response and singly charged ion to oxide ratios. Gray and Date34 proposed that this was a function of a contraction of the plasma and central channel as power is increased.In order to assess the influence of forward power on those elements of interest S:B ratios were obtained for various power settings (1 100-1325 W). For the alkali and alkaline earth elements S B ratios were optimum at 1100 W (Fig. 4). No significant trend could be discerned for other elements and hence for this study the torch power was set at 1100 W. As demonstrated by these experiments no one set of con- ditions is optimum for all elements. Thus to obtain the maximum chemical information from a single fluid inclusion a compromise set of average instrumental conditions was adopted (Table 2). RESULTS AND DISCUSSION Element intensities were ratioed to Sr since it was not possible to determine quantitatively the concentration of each element in the inclusion fluid.Conventionally when presenting inclusion analyses elements are ratioed to Na the major cation in solution. However in view of the difficulties experienced in measuring Na Sr was selected instead. Sr is considered a suitable alternative because of its generally high concentration Table 2 Operating conditions of the laser ablation microprobe and of the ICP-MS instrument LAMP operating conditions- Laser Wavelength/nm 266 (frequency quadrupled from Maximum energy/mJ Spectron SL803 Nd YAG 1064 nm) 70 (amount of energy used depends on size of crater required) Mode Fully Q-switched TEMOO Laser repetition frequency/Hz 10 Microscope Leitz Aristomet Laser focusing objective Spectrometer VG PlasmaQuad 2+ Gas flow rate/l min-' Pulse length/ns 10 x 25 or x 36 ICP mass spectrometer operating conditions- Forward power/W 1100 Nebulizer 0.4 Cell 0.6 Coolant 13 Auxiliary 0.8 Data acquisition software VG TRA Data acquisition mode Peak jumping Points per peak 3 Dwell time per peak/ms 10 Time unit/s Typically 1-5 in geological fluids17 and in having a low ICP-MS background at m/z 88.Figures of Merit The accuracy of the alternative calibration strategies was evaluated by applying a t-test to the elemental ratios obtained from synthetic inclusions against those from aqueous solutions contained in microwells and glass reference materials (Table 3). The precision of the ratios expressed as the relative standard deviation (&) was evaluated both as within-run repeatability as shown for Li Mg Ca Ba and Br (Table 4) and between- run reproducibility for all elements (Table 5).35 Additionally correlation coefficients (R) were calculated as a test of the coherence of the relationship between elements.In order to display and compare the data for all three calibration materials glass concentrations were normalized to synthetic fluid inclusion and microwell concentrations. In the following sec- tions only the t-tests and between-run S and R values are discussed. NIST SRM 611 Glass The S values for most element Sr ratios range between 5 and 23%. Potassium gives very scattered values (S = 50%) suggest- ing that its concentration in the matrix (500 ppm) is close to the theoretical detection limit (Table 5). Element co-variation plots using raw count data are linear.For most elements R is greater than 0.98 (see Fig. 5) except for K. The corresponding R value for K (0.667) is low reflecting the poor detection limit. Despite having to use the minor Ca isotope 44Ca (2%) because of isobaric 40Ca-40Ar+ interference the Sr and R values are very good. The only problem relates to Na (Fig. 6). At high count rates the Na response exhibits severe non-linearity owing to detector saturation. (N.B. Owing to variations in relative sensitivity resulting from ionization efficiency and mass bias in the quadrupole mass spectrometer the reported signal ratios given in Tables 4 and 5 and Fig. 5 differ from the true mass ratios.) Synthetic Fluid Inclusions in Halite The same procedures were applied to the analysis of synthetic fluid inclusions in halite which range from 20 to 100 pm in diameter and were located up to 80pm beneath the surface (Tables 4 and 5).This is equivalent to a 100-fold variation in inclusion volume. Time-resolved profiles indicate excellent fluid release on laser breakthrough (Fig. 7). Bi-variate plots for Li and Mg against Sr [Fig. 8(a) and (b)] demonstrate very good linearity Table3 Validity of the null hypothesis that assumes mean ratio equivalence (element Sr). Statistical t-test verification; the significance level is indicated by P (i.e. probability)=0.05 (yes) and 0.02 (yes*) Element/Sr Li Mg Ca Rb c s Ba Mn 63cu T U 64Zn 66Zn Pb Br Fluid inclusions- microwells Yes Yes Yes Yes* Yes Yes Yes Yes* Yes Yes Yes Yes Yes ~ Fluid inclusions- glasses Yes Yes Yes* No Yes No Yes Yes Yes Yes Yes Yes Microwells- glasses Yes No No No Yes Yes * Yes No No Yes Yes No 180 Journal of Analytical Atomic Spectrometry March 1996 Vol.11Table 4 LAMP-ICP-MS analyses showing the within-run repeatability for several series of experiments for each type of material (fluid inclusions microwells and NIST SRM 611 Glass)" Elements No. of analyses Li Sr R Mg Sr s (Yo) sr (%) R Ca Sr R Ba Sr R Br Sr s (%) sr (Oh) Fluid inclusions F.I. 1 F.I. 2 F.I. 3 11 16 5 3.57 3.36 3.2 13 14.8 8.7 0.965 0.965 0.996 1.12 1.08 1.19 0.97 0.961 0.98 1.25 1.07 1.26 0.936 0.9 0.944 0.095 0.12 16 7 0.986 0.997 0.036 0.036 9.1 26.5 0.966 0.937 16.2 17.3 21.5 26.3 33.6 16.4 Micro wells NIST SRM 611 Glass Mw. 1 14 3.26 16.1 0.947 1.05 14.3 0.969 1.3 24.2 0.873 0.108 0.93 1 0.037 0.94 16.6 14.5 Mw.2 5 3.22 17.3 0.984 0.9 1 0.986 1.26 0.91 13.7 16.6 Mw. 3 12 3.5 10.1 0.937 1.06 0.9 18 1.31 0.907 10.9 17.1 Gls. 1 11 3.16 7.3 1.25 6.6 1.08 5.1 0.086 6.4 Gls. 2 7 3.24 11.1 0.995 1.02 16.5 0.988 1 8.6 0.992 0.102 8.2 0.987 Gls. 3 10 3.18 5.9 1.1 8.2 0.93 8.1 0.106 8.7 0.034 0.038 0.995 0.883 11.8 14.8 Mass ratio Li:Sr=l Mg Sr = 1 Ca:Sr=l Ba Sr = 0.1 Br Sr = 1.66 * Atomic ratios given in the table correspond to ICP-MS signal ratios and not to mass ratios as described by mass ratio column. over several orders of magnitude. The correlation coefficients are better than 0.96 and the S values of the ratios < 17% across the entire range. As a guide to the applicability to natural fluid inclusions Fig. 8(a) also shows the relationship between inclusion diameter and ICP-MS signal intensities.Some of the deviant points seen in Fig. 8(b) can be attributed to relatively flat inclusions which although large in cross- section had disproportionately low volumes. Other outlying points cannot be so readily explained as there is no apparent correlation with inclusion size or depth in the sample. The reduced precision noted for Ca (S = 28.8%; R = 0.92) is mainly due to the use of the minor isotope 44Ca and the lower concentration of Ca in the synthetic inclusions (1000 ppm). For these experiments 1OOOppm Ca is close to the limit of detection. The S values are poorest for K. Values are 329% and similar to those obtained for the NIST SRM 611 Glass. In both cases there is a high variable background at m/z 39 which is probably due to a combination of the 38Ar-H+ polyatomic interference and K contamination in the spec- trometer.It is estimated that the synthetic inclusions need to contain at least 2000ppm K to provide reliable working calibration graphs for K. For Rb Cs and Ba (100ppm of each) the correlation coefficients are very high (R > 98%). Corresponding S values are also good (Rb 11.05%; Ba 12.5%; Cs 20%). The S and R values for Mn Cu and Zn are slightly higher than for the alkali and alkaline earth elements (25-33% and 3 0.9 respectively). Boron measurements proved unsuccessful. A concentration of 100 ppm B in the synthetic inclusions appears to be close to the detection limit for the instrumental conditions selected. As expected the measurement of Na Sr ratios in an NaCl matrix proved difficult; the average S is > 57%.For a more complete assessment of the Na Sr data see below. For Br Ca Li and Mg a clearer comparison of their respective S values can be seen in Fig. 9 which shows the range in S values for a typical working day and the over- all poorer repeatability obtained for Ca. Data for the halogens are provisional but indicate tremen- dous potential for the direct measurement of Cl Br ratios by ICP-MS. The S and R values for Br are 14.7% and 0.96 respectively those for C1 being poorer ( ~ 3 0 % and 0.89). As with B conditions were not optimized for the determination of the halogens and further improvements in precision and detection limits might be possible. The main limitation is matrix contamination from the host mineral.A notable feature of Fig. 10 is the co-linearity for both 64Zn+ and 66Znf (corrected for isotopic abundance). Similar agree- ment is noted for 63Cu+-88Sr+ and 65C~f-88Sr+. No indi- cation was observed of 23Na40Ar + polyatomic interference on 63Cu+ as is normally the case for analysis of saline solutions by conventional nebulization. This suggests minimal spectral interference and the suitability of these m/z positions for the measurement of pg g-' concentrations of Cu and Zn in NaC1- rich inclusion fluids. Coherent element Sr ratios for inclusions of variable size testify to the precision and efficiency of laser ablation. Reproducible ratios between inclusions and between glass and inclusions show that sampling and removal of material for ICP-MS analysis is not significantly constrained by the depth/ diameter profile of the laser ablation crater.High spatial resolution laser ablation (drilling) to a depth of approximately 60 pm is straightforward. Below 60 ym however the hole can deviate unpredictably from the vertical and it becomes increas- ingly difficult to target 20 ym diameter inclusions. The advan- tages of high spatial resolution and accurate alignment of the laser beam are also relevant to larger inclusions (> 100 pm diameter). During the analysis of large inclusions air bubbles aggregate at the base of the entry hole which shield the liquid phase and give rise to highly erratic vaporization. In order to overcome this problem it is often necessary to re-position the laser and drill a second hole into the inclusion.Unlike the ablation of glass or microwells where the mass of material released is a function of laser power absolute detection limits for inclusions are directly proportional to the absolute mass of the analyte in the inclusion. Thus for a single population of inclusions of various sizes the concentration detection limits are approximately proportional to the cube of the inclusion diameter. Microwells Containing Aqueous Solution In order to facilitate comparison and evaluation of calibration procedures using glass and synthetic fluid inclusions a third approach to test material introduction was adopted namely the laser ablation of microvolume amounts of aqueous solution. A distinct advantage in using microwells is that it is relatively easy to prepare solutions of different composition and molarity especially standards with different C1 Br ratios.For all the elements except for Na (i.e. Ba Br Cs Cu K Li Mg Mn Pb Rb Sr Zn) the microwell data are in excellent agreement Journal of Analytical Atomic Spectrometry March 1996 Voi. I 1 181Table 5 LAMP-ICP-MS analyses showing the between-run reproducibility for each type of sample material* Sample Li Sr Fluid inclusions 3.26 0.972 1.11 0.96 1.16 0.925 1.66 0.743 14.4 17.3 28.8 29.7 212 57.6 0.64 0.89 0.038 0.96 0.108 0.986 0.07 1 0.992 0.064 11.1 0.996 0.1 1 20.4 0.932 0.062 0.904 0.059 0.895 0.02 1 27.9 0.917 0.021 0.878 0.0005 32.3 14.7 12.5 20.3 26.8 31 25.7 157.5 0.08 33.4 0.909 16.9 34.9 0.8 99 Micro wells 3.36 0.966 1.03 13.4 0.963 1.3 19.8 0.906 1.14 15.8 0.9 83 30.2 0.8 0.44 19.5 0.91 5 0.04 0.966 0.108 0.931 0.072 0.972 0.075 0.975 0.08 1 0.927 0.04 9.95 0.986 0.042 0.944 0.019 0.953 0.0 17 0.943 0.024 0.911 0.085 0.872 14.2 14.4 16.6 12.9 11.9 21.5 13.1 17.8 14.6 39.5 23.9 12.5 22.9 0.901 NIST SRM 611 Glass 3.2 7.7 0.995 1.15 0.988 1.01 9.3 0.992 2.58 0.667 12.7 50 117 18.5 0.914 0.096 0.987 0.072 0.978 0.105 0.993 0.105 0.875 0.046 0.979 0.05 18 0.984 0.019 15.3 0.99 0.01 8 0.95 0.025 0.976 0.08 1 0.99 11.6 12.1 22.7 22.7 20.8 17.2 23.8 13.7 Mass ratio Li Sr= 1 Mg:Sr=l Ca:Sr=l K:Sr=1 Na Sr = 100 Cl:Sr=166 Br Sr = 1.66 Ba Sr =0.1 Cs:Sr=O.l Rb Sr = 0.1 Pb:Sr=O.l 63Cu Sr = 0.1 "Cu Sr = 0.1 64Zn Sr = 0.1 "Zn Sr = 0.1 B Sr = 0.1 Mn Sr =0.1 C1 Br = 100 * Atomic ratios given in the table correspond to ICP-MS signal ratios and not to mass ratios as described by mass ratio column.with the glass and synthetic fluid inclusion data. Reproducibilities are generally better than those calculated for the synthetic inclusions owing to the larger masses of test material introduced into the ICP-MS system and for Na and C1 the absence of a solid matrix (Table 5). An unusual and unexplained phenomenon is the difference in slope between the Na-Sr calibration graph for the wells and that for the glass and synthetic inclusions (Fig. 11). For glass the matrix effect increases with laser power (Fig. 6) suggesting preferential vaporization of Na (i.e. chemical frac- tionation). Whilst the synthetic fluid inclusion graph appears superficially similar to that of the glass the enhanced Na signal at high laser power is probably due to contamination from ablation of the matrix.In Fig. 12 the Cl-Sr array for the microwells plots below that of the synthetic fluid inclusions. Since both fluids have identical C1 Sr ratios and allowing for the lower sensitivity of Cl with respect to Na the correlated high Na and C1 responses for the synthetic fluid inclusions would tend to support the matrix effect interpretation. Thus synthetic fluid inclusions in halite are not entirely appropriate for the calibration of Na and C1 in natural fluid inclusions. Further studies are in progress to address the NaCl matrix limitation. Overall microwells present few analytical problems. They confirm the calibration graphs obtained using glass and syn- thetic fluid inclusions and because of the larger solution volumes available for ablation provided data for K (S,= 15.8%; R = 0.90).Several experiments were performed to test the possible virtues of single laser pulse analysis of microwells. For all ratios the S values were >50% indicating the need for continuous pulsed mode ablation to achieve acceptable signal intensities. 182 Journal of Analytical Atomic Spectrometry March 1996 Vol. 11A A 0 2 4 6 8 10 Sr response (a.u.) Fig. 5 Li-Sr and Mg-Sr covariations for NIST SRM 611 Glass 3 1Na A A A Sr 0 2 4 6 8 10 al v) r 0 P v) CT Li I Sr _o L Na L Time (a-u.) Fig.7 Time-resolved ICP-MS spectra for Li Na Mg and Sr for a discrete pulse of fluid released from a 40 pm diameter aqueous inclusion in halite (depth beneath the surface 10 pm) Response ( a d Fig.6 Na-Sr covariation for NIST SRM 611 Glass Statistical Tests In Fig. 13 the data sets of Li versus Sr have been combined for all three calibration materials and procedures. Global correlation coefficients (2 0.9) are statistically very significant for all the elements except for Na. In order to allow rigorous comparison between the synthetic fluid inclusions microwells and NIST SRM 611 Glass a statistical t-test was carried out on the mean ratios for different combinations of the three calibration materials.35 This test measures the truth of a null hypothesis that there is 'no significant difference between the means of two different samples'. The results are given in Table 3 ('yes' and 'no' correspond to adoption and rejection of the null hypothesis respectively).Calculated t-values demon- strate excellent agreement between synthetic fluid inclusions and microwells for all elements. Except for Ba and Rb the NIST SRM 611 Glass also shows good agreement with the synthetic fluid inclusions. The differences in the mean values for Ba and Rb are probably due to a slight change in the ICP-MS responses for two different periods of analysis. However the tests prove conclusively that microwells may be used as calibration standards for the routine analysis of fluid inclusions and that allowing for the poorer results for Ba and Rb NIST SRM 611 Glass may be used accordingly. The degree of statistical agreement between all three calibration materials is shown graphically in Fig.14. This demonstrates that for Mg the data have similar absolute dispersions and approximate very closely to normal distributions the closest match being between the synthetic fluid inclusions and solution microwells. 1Li 70 pm 0 4 8 12 IbMg ' 1 A A A A A A A 0 5 10 1 5 Response (a.u.) Fig. 8 Li-Sr (a) and Mg-Sr (b) covariations for synthetic fluid inclusions in halite. Note in (a) the relationship between inclusion diameter and ICP-MS signal intensities Journal of Analytical Atomic Spectrometry March 1996 Vol. 11 183(Br/Sr)x30 RSD=9O/o 1.5 1 A 1 A A $lA A A A Sr I ' . . . 0 1 2 3 4 Response (a.u.) M&r RSD=16% Fig. 12 Comparison between Cl-Sr covariations for synthetic fluid inclusions and microwells Fig. 9 repeatability of these elements (ratioed to Sr) Spider diagram for Br Ca Li and Mg showing the within-day lLi d 3 W 2 4 a izn A 0 1 2 3 4 Response (a.u.1 0 0 0.5 1 1.5 2 Response (a.u.) Fig.13 Combined element covariation for all three types of cali- bration material (fluid inclusions microwells and NIST SRM 611 Glass) for Li-Sr Fig. 10 Comparison between 64Zn and 66Zn signal intensities. Good agreement indicates absence of significant polyatomic interference. A @Zn Fluid inclusion; A 64Zn fluid inclusion; 64Zn microwells; 0 66Zn microwells; + 64Zn glass; 0 glass SYNTHETIC F.I. MICROWELLS n 4 0 A I I I 1 Sr 0 0 1 2 3 4 Response (a.u.1 0 0.5 1 1.5 2 Mg/Sr Fig. 11 Comparison between Na-Sr covariations for synthetic fluid inclusions microwells and NIST SRM 611 Glass. A Fluid inclusions; A glass; 0 microwells Fig.14 Histogram of measured Mg Sr ratios showing the degree of agreement between all three calibration materials CONCLUSIONS For most purposes microwells containing aqueous solutions and NIST glass reference materials can replace synthetic fluid inclusions as working calibration standards for the elemental analysis of single fluid inclusions. NIST reference glasses are readily available chemically stable and can be used almost indefinitely. Theoretically microwells have less long-term stab- ility (not tested). Their principal advantage however is that they approximate much more closely to the laser ablation of fluid inclusions and can be designed to cover a wider range of chemical compositions and elemental concentrations than MIST glasses. They are also easy to prepare.Synthetic fluid inclusions in halite simulate even more closely the laser response of natural fluid inclusions and for the study of evaporate minerals are the perfect match. Their principal disadvantage is that they cannot be readily used for the calibration of Na and C1 because of host matrix contamination. Techniques for minimizing this problem for the direct measure- ment of C1 Br ratios in inclusions in halite are currently being investigated but for the moment synthetic fluid inclusions in halite are more limited as calibration standards than either 184 Journal of Analytical Atomic Spectrometry March 1996 Vol. 1 1microwells or NIST glasses. Nevertheless all three types of calibration standard yield similar element Sr ratio S values and excellent elemental ratio working curves.Average S values for Li Na K Rb Cs Mg Ca Sr Ba Mn Cu Zn Pb C1 and Br range between 7 and 32% including data for those elements that are close to the detection limit or include a component of matrix contamination. Until the absolute mass of analyte in the inclusion can be determined analyses are best reported as element ratios. However reference to microthermometric data should allow realistic approximation of inclusion fluid concen- trations for geochemical modelling. It is concluded that no one set of instrumental ICP-MS conditions is optimum for all elements and that analysis of more than one inclusion is needed to derive the maximum amount of chemical information from trapped fluid. Nevertheless further studies are in progress to improve the efficiency of fluid release and to optimize the analysis for groups of related elements (e.g.the halogens). A. M. thanks J. Pironon for his help during the synthesis of fluid inclusions. This study was financed in part by the European Union Human Capital and Mobility Programme. Publication is by permission of the Directors of the British Geological Survey (NERC) UK and the Centre de Recherches sur la Geologie des Matikres Premikres Minerales et Energetiques (CREGU) France. REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 Boiron M. 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Paper 51055 221 Received August 21 1995 Accepted November 10 1995 Journal of Analytical Atomic Spectrometry March 1996 Vol. 11 185

ISSN:0267-9477    

DOI:10.1039/JA9961100177

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

On-line Solid-phase Chelation for the Determination of Eight Metals in Environmental Waters by Inductively Coupled Plasma Mass Spectrometry DANIEL B. TAYLOR H. M. KINGSTON* AND DONALD J. NOGAY Department of Chemistry and Biochemistry Duquesne University Mellon Hall Pittsburgh PA 15282 USA DAGMAR KOLLER FI Elemental Analysis Winsford Cheshire UK CW7 3BX ROBERT HUTTON CETAC Technologies Inc. Electra House Electra Way Crewe Business Park Crewe Cheshire U K CWl 1 YX A low-pressure method for the on-line preconcentration of analytes and elimination of matrix elements prior to determination by inductively coupled plasma mass spectrometry (ICP-MS) is described. The method reduces the concentrations of matrix elements in samples to levels that do not interfere with the determination of the first row transition elements at trace levels.The method also reduces biases caused by differences between samples and standards by delivering the analytes to the ICP-MS instrument in a consistent nitric acid matrix. A commercially available low- pressure sample manipulation system was used to perform solid-phase chelation on an iminodiacetate column. The effectiveness of the method is demonstrated for the determination of Cd Co Cu Mn Ni Pb U and Zn in the certified reference materials CASS-2 Near Shore Sea-water; NASS-4 Open Ocean Sea-water; and the Standard Reference Material 164313 Trace Elements in Water. The volume of sample preconcentrated was varied in order to optimize the analyte signal. The detection limits for 10 ml samples ranged from 0.8 ng 1- for Co to 40 ng 1 - 1 for Cu and Zn.Keywords Solid-phase chelation; iminodiacetate; inductively coupled plasma mass spectrometry; matrix elimination; natural water; sea-water The aim of this investigation was to develop and evaluate a reliable method for the analysis of trace elements in environ- mental water samples by inductively coupled plasma mass spectrometry (ICP-MS) using iminodiacetate chemistry and a simple commercially available low pressure sample manipu- lation system. The developed method was used to determine the trace elements in three environmental water samples including sea-water which contain high concentrations of dissolved solids (up to 3% m/v) and low concentrations of analytes (ng 1-l). Analytical chemists in modern laboratories are frequently asked to determine the concentrations of environmentally important and regulated metals in many different types of water samples.ICP-MS has the sensitivity to determine metals at the pg 1-' to ng I-' level but suffers from problems with signal suppression and clogging of the sample introduction system when the sample contains dissolved solids at concen- trations greater than 0.2% m/v.'V2 The matrix elements can also combine with elements in the atmosphere or plasma to * To whom correspondence should be addressed. Journal of Analytical I Atomic 1 Spectrometry 1 form polyatomic species which interfere with the determination of first row transition metals. Several approaches have been used to address these problems including diluting the ample,^.^ flow inje~tion,~ standard additions' and the addition of internal standard^.^.^ These approaches have met with limited success.They correct for suppression and enhancement but they suffer when the isotope of the analyte being determined cannot be spectroscopically resolved from isobaric interference^.^" A more successful approach has been to separate the analytes from the elements causing the interferences and signal suppres- sion. The analytes can be separated from the matrix elements by a variety of techniques but traditionally ion-exchange and chelating resins have been used. Analytes can also be precon- centrated as they are separated from the matrix elements by increasing the volume of sample passed through the column and eluting the analytes from the resin in a minimum volume of eluent for analysis.The preconcentration of analytes from samples has been accomplished off-line using chelating resins including Chelex and silica-immobilized 8-hydro~yquinoline.'~-~~ The iminodiacetate resins traditionally used in the batch mode isolation and preconcentration of analytes namely Chelex 100 Chelex 20 (BioRad Hercules CA USA) and Amberlite IRC-718 (Supelco Bellefonte PA USA) undergo changes of up to 50% in volume when converted from the Hf form into the Na' or NH4+ form." The large volume changes of iminodiacetate resins complicates their use in the small columns often used for on-line preconcentration and solid-phase chel- ation (SPC). Resins with more rigid supports have been developed and used for on-line preconcentration and matrix elimination.Several groups have automated the preconcentration of analytes using various chelating resins. l6 The systems have often been configured for on-line analysis using iminodiacet- ate17-20 and 8-hydro~yquinoline.~~-~~ Much of the initial work in automating the preconcentration was carried out with systems using piston pumps capable of generating the pressures needed to load and elute the analytes from columns packed with particles 50-100 pm in diameter. A commercial system which allows analysts to preconcentrate analytes and eliminate matrix elements has been developed and marketed.'7.19.20.23 The commercial system utilizes piston pumps and pre-packed iminodiacetate columns. A system that preconcentrates ana- lytes on 2-5 pm iminodiacetate-derivatized beads then sub- sequently aspirates the beads into the plasma for analysis has been d e s ~ r i b e d .~ ~ A license for the commercial on-line Journal of Analytical Atomic Spectrometry March 1996 Vol. 11 (I 87-1 91) 107implementation of SPC to remove matrix elements with chelat- ing resins prior to instrument introduction is available from the National Institute of Standards and Technology (NIST)19,20 to anyone. This paper describes the configuration of a simple sample manipulation system that can perform SPC to determine ng 1-' concentrations of analytes in difficult matrices. The volume of sample loaded on the column ranged from 5 to 50ml. The system was used to determine Cd Co Cu Mn Ni Pb U and Zn in the Standard Reference Material (SRM) Trace Elements in Water (1643b) from NIST and the certified reference mate- rials (CRM) Near Shore Sea-water (CASS-2) and Open Ocean Sea-water (NASS-4) from the National Research Council of Canada (NRCC).4 mol I-' NH40Ac buffer pH 5.8 EXPERIMENTAL Pump 2 Waste l'l:d?m +-' - ~~ Cleanup column Apparatus The sample manipulation system used in this work was a PrepLab (Fisons Instruments Winsford Cheshire UK). The sample manipulation system and the ICP-MS instrument were located in a Class 1000 clean room. Fig. 1 shows the configur- ation of the PrepLab and columns for SPC. The peristaltic pump tubing pieces were cut to a length of 75 mm to reduce the volume of tubing in the system. Fittings with female 1/4 inch 28 connections at one end and barbed connectors at the other end (Global FIA Gig Harbor WA USA) were used to attach the peristaltic pump tubing to the 1.6 mm od 0.76 mm id Teflon tubing used throughout the system.The pumps and valves of the PrepLab were controlled by an autosampler (Gilson Middleton WI USA) which was controlled by the PQ Vision Software (Fisons Version 4.1.1 rev a). Two types of column were used in this work. The column used to isolate the analytes from the standards and samples had a PEEK body with the internal dimensions 4.0mm id x 5.0 cm length. The column was packed with 0.1-0.2 mm particles of Chelite C (Serva Heidelberg Germany) and had a capacity of 0.26 mmol. Chelite C is an iminodiacetate derivat- ized polystyrene-dinvinylbenzene resin. The column used to purify the solutions discussed under Preparation of Solutions 1 mol r' HNO;? 5 ng m r 1-1 had an aluminium-clad PEEK body with the internal dimen- sions 4.6 mm id x 7.5 cm long (Upchurch Scientific Oak Harbor WAY USA).The column was packed with the iminodia- cetate resin (50-100 mesh) Muromac A-1 (Muromachi Chemicals Tokyo Japan). The capacity of the column packed with Muromac A-1 was 0.51 mmol. The columns were stored in 2 moll-' ammonia to keep the iminodiacetate functional groups from degrading uia a proposed Claisen condensation. The ICP-MS instrument used for the analysis was an unmodified VG PlasmaQuad 2 + STE unit (Fisons Instru- ments) with a V-groove nebulizer Scott double-pass spray chamber cooled to 278 K and nickel cones. The V-groove nebulizer was used because it was more tolerant of the concen- tration of dissolved solids in the buffer solutions used in the preliminary evaluations than the concentric style Meinhard nebulizer.The buffer was rinsed from the column with water in the final analysis method. The torch position gas flow rates and ion voltage lens settings were adjusted daily for optimum analyte sensitivity following the manufacturer's guidelines. Preparation of Solutions The nitric and glacial acetic acids were prepared by sub-boiling distillation in a Class 100 clean air hood using PFA stills (Savillex Minnetonka MN USA). High-purity 18 Mi2 ASTM Type 1 water was used to make and dilute all solutions. Ammonia solution was prepared by bubbling filtered ammonia gas through high-purity water in an ice-bath until saturation was achieved. The ammonium acetate solution used to buffer the samples and adjust the pH of the column was prepared by combining the high-purity ammonia solution with the sub- boiled distilled glacial acetic acid adjusting the pH to 5.8 and diluting to the desired concentration with high-purity water.'?'' The sea-water samples were prepared by adding 0.5 ml of 4 moll-' ammonium acetate buffer to 90 ml of sea-water.The pH of the sea-water was adjusted to 5.5k0.3 and then diluted to 100ml with high-purity water. The pH of the SRM 1643b Trace Elements in Water was adjusted on-line. All solutions were prepared in a Class 10 or 100 area. The water and buffer solutions used for the sea-water analysis were pumped through a column packed with 50-100 mesh Muromac A-1 at a flow rate of 4mlmin-1 to reduce the levels of analyte contami- nation further.Fig. 1 Diagram of PrepLab configuration for SPC analysis. The PrepLab is a simple system consisting of two dual-channel peristaltic pumps two dual-position pinch selection valves and a dual-stacked six-port valve. The dual-stacked six-port valve position shown by the solid line is the elute column position. The valve position shown by the dashed lines is used to concentrate sample and eliminate the matrix. The double line (**) shows the modification needed to perform on-line neutralization of sample. The clean-up column reduces the level of the analytes in the buffer solution used to adjust the pH of the column and the sample. The sample and the ammonium acetate buffer were pumped at flow rates of 2.4 and 2.0 ml min-l respectively.The water and the analytes eluted by the 1 moll-' nitric acid are delivered to the ICP-MS instrument at a flow rate of 1.0 ml min-' Analysis Procedure The PrepLab was initialized by setting the dual-stacked six- port valve to the position shown by the solid line in Fig. 1. Selection Pinch Valve 2 (SPV2) was set to the sample position and Selection Pinch Valve 1 (SPV1) selected water to rinse away the acid remaining in the column from the previous analysis. The 1 ml loop was filled with buffer. Once the sample selected by the autosampler reached the dual-stacked six-port ,valve the stacked valve was switched. When the valve switched the buffer from the 1 ml loop adjusted the pH of the column. The sample was then loaded onto the column.The volume of sample loaded on the column was determined by the flow rate of sample and the time SPV2 selected the sample. Variations in the flow rate of the sample could lead to bias in the data over the course of the analysis. The flow rate of the sample loaded onto the column was monitored in order to verify that the flow rate did not vary by more than 1% over the course of an 8 h series of analyses. After the buffered sample had been loaded on the column SPV2 selected distilled de-ionized (DDI) water and the unre- tained matrix components were rinsed from the column. The matrix components weakly retained by the column were eluted with 8 ml of buffer. The SPV2 was switched to water and the buffer was rinsed from the column. The analytes were eluted I88 Journal of Analytical Atomic Spectrometry March 1996 Vol.11to the ICP-MS instrument for determination by switching the dual-stacked six-port valve and selecting 1 mol 1-' HN03 with SPV1. The configuration shown by the solid line in Fig. 1 was used to analyse the NASS-4 and CASS-2 sea-water CRMs. The configuration required the pH of the samples to be adjusted to 5.5 k0.3 prior to selection by the autosampler. The matrix components retained by the column were then eluted by the buffer selected by the autosampler. The time to precon- centrate a 10.0 ml sample and elute the matrix retained by the column with buffer was 19min. The modification shown by the double line in Fig. 1 illustrates how buffer can be combined with the sample to adjust the pH on-line. This modified configuration was used to analyse NIST SRM 1643b.The modified configuration eluted the matrix components retained by the column by selecting water with SPV2 and passing buffer through the column with pump 2. The flow rate of buffer was increased from 2.0 to 3.5 ml min-l in the modified configur- ation to allow 2% m/v HN03 solutions to be adjusted to a pH of 5.3. Less than 13 min were required to process a 5 ml sample and 15min for a 10ml sample with the modified configuration.26 The Gilson control language (GCL) files to control the PrepLab can be downloaded from the web site listed in ref. 26. Data Acquisition The data were acquired using the default acquisition param- eters of the ICP-MS instrument. Three points 0.023 u apart were monitored for each mass with a dwell time of 10.24 ms.The masses monitored included "Mn 58Ni "Co 60Ni 63Cu 64Zn 65Cu 66Zn ll'Cd '12Cd '14Cd 206Pb 207Pb 208Pb and 238U. The elution time of the analytes was determined by processing a standard and monitoring the 55Mn signal in the single-ion monitoring (SIM) mode with a dwell time of 100 ms. The SIM signal was used to determine the values for the uptake and acquisition parameters of the acquisition method file. The subsequent samples were analysed using the peak jump mode of the instrument. Temporal information was not collected. Drifts in the sensitivity of the instrument were corrected for by monitoring 5 ng ml-' 69Ga "'In and '"Tb internal standards in the 1 mol 1-1 nitric acid used to elute the analytes. Matrix elements were not added to the standards used for calibration to match the composition of the samples.Table 1 Blanks and limits of detection (LOD)* RESULTS AND DISCUSSION The accurate determination of ng 1-1 levels of transition metals in natural or environmental water samples especially when using a method that preconcentrates the analytes required low and reproducible blanks. Table 1 lists the mass of the analyte blank associated with the SPC preconcentration and matrix elimination of a 10ml sample. The values listed in Table 1 were determined by a standard additions calculation based on three replicate determinations of the calibration standards. The signals from three replicate analyses of 10ml of buffered high-purity water were assigned a concentration of zero. The differences in concentration between the isotopes of the elements listed in Table 1 are within the imprecision of the determination expressed by the standard deviation.The mass of the blank associated with the SPC procedure should remain constant regardless of the volume of sample preconcentrated provided that the volumes of solutions used to process the sample do not change. The concentrations of analytes can be determined at very low levels by increasing the volume of sample loaded onto the column until the analyte signal is sufficiently large to be accurately measured provided that the capacity of the column is not exceeded. It should also be possible to measure the analyte signals from the preconcen- tration of several volumes of sample to optimize the analyte signal for a variety of factors including calibration range blank background signal and instrument sensitivity.Fig. 2 shows the linear increase in the '14Cd signal as the volume of CASS-2 loaded onto the column increased. The right-hand axis of Fig. 2 shows that the mass of Cd detected in each volume of sample preconcentrated was within the 95% confidence limits of the certified Cd concentration. The amount of sample loaded onto the column was changed by editing the GCL file controlling the PrepLab.26 The 30 limits of detection for the isotopes monitored are listed in Table 1. The values are comparable to those reported by McLaren et for a system using either an iminodiacetate or 8-hydroxyquinoline column. The limits of detection of the method could be improved by reducing the blank.The blank could be lowered by further purifying or reducing the volumes of the solutions used to process the sample. Table 1 also lists the limits of detection of the method that could be achieved if larger volumes of sample were preconcentrated. There is clearly a trade-off between analyte signal and the time required to perform the analysis. Blan k/ng Element Manganese Nickel Cobalt Nickel Copper Zinc Copper Zinc Cadmium Cadmium Lead Lead Lead Uranium Isotope 55 58 59 60 60 64 63 66 112 114 206 207 208 238 Mass &standard deviationt 0.190 0.004 0.4 k 0.07 0.005 k 0.003 0.5 * 0.08 0.6k0.2 1.8kO.1 0.4-tO.1 1.8kO.1 0.07 k 0.01 0.07 2 0.01 0.094 t- 0.004 0.104 * 0.002 0.105 & 0.004 0 f 0.04 LOD/ng 1 - Sample size/ml 10 30 50 1.2 0.4 0.3 0.8 0.3 0.2 20 7 4 24 8 5 60 20 12 30 9 5 30 10 6 40 12 7 3 1.1 0.7 4 1.3 0.8 1.3 0.4 0.3 0.5 0.2 0.1 1 1.1 0.4 0.22 11 4 2.0 * Blanks are based on the standard additions analysis of 10 ml samples of buffered water and standards.Limits of detection (ng 1-') are based on three times the standard deviation of the signal for buffered water. Standard deviation of three analyses of the blank. Journal of Analytical Atomic Spectrometry March 1996 V01.11 189Table 4 Analysis of NRCC NASS-4 open ocean sea-water* Concentration/ng ml-'t 80000 - 70000 - 60000 - - 50000- .Cn 40000- 5 30000- 20000 - 10000 - ' 0 I ! I I I I I 0 5 10 15 20 25 30 35 Volume of CASS-2/rnl Fig. 2 '14Cd signal and mass of Cd detected as a function of volume of CASS-2 loaded (n = 5 for samples containing 9.0 ml of CASS-2 n = 3 for samples containing 27.0 ml of CASS-2).The solid lines show the 95% confidence limits of the certified concentration Table 2 Analysis of NIST SRM 1643b trace metals in water* Concentration/ng ml- 't Element Manganese Nickel Cobalt Nickel Copper Zinc Copper Zinc Cadmium Cadmium Cadmium Lead Lead Lead Isotope 55 58 59 60 63 64 65 66 111 112 114 206 207 208 Determined 30f 1.3 50+2 27+ 1.3 51 +2 23 +_ 1.0 67+ 1.4 22 sfr 0.9 67 1 1.8 20 & 0.5 19.9 f 0.3 19.8 k0.4 23 f 0.5 23.9 f 0.4 24.2 f 0.4 Certified 28k2 49*3 26k 1 49f3 21.9 f 0.4 66+2 21.9 h 0.4 66k2 20* 1 201 1 20+ 1 23.7 f 0.7 23.7 -t 0.7 23.7 k 0.7 ~~ * 5.0 ml samples n = 5. t Concentration (ng ml-') & 95% confidence limits. Table2 shows the results of the analysis of NIST SRM 1643b containing ng ml-I concentrations of all the elements determined.The precision of the determination of the metals in SRM 1643b ranged from 1 to 4% relative standard deviation (sr). The concentrations of all the isotopes of all the elements determined by SPC agreed with the 95% confidence limits of the certified values. The agreement between the isotopes of each element indicated that the mg 1-l concentrations of Ca Na Mg and K in the original sample were reduced to the point where they did not interfere with the analysis. Preliminary experiments showed that more than 99% of the Ca from the Table 3 Analysis of NRCC CASS-2 near shore sea-water* Element Manganese Nickel Cobalt Nickel Copper Zinc Zinc Cadmium Cadmium Cadmium Lead Lead Lead Uranium Isotope 55 58 59 60 65 64 66 111 112 114 206 207 208 238 Determined 0.38 k0.012 0.23 k0.015 0.01 1 f 0.001 1 0.22 k 0.03 0.24 + 0.008 0.12+0.03 0.122f0.04 0.016 fO.0018 0.015f0.0014 0.01 5 f 0.0015 0.015 f 0.001 1 0.017 0.0009 0.016f0.0014 2.7 f 0.05 Certified 0.38 f0.023 0.228 fi 0.009 0.009 k 0.001 0.228 1 0.009 0.228 _+ 0.01 1 0.1 15 k 0.018 0.1 15 + 0.01 8 0.016 -t 0.003 0.016 & 0.003 0.0161 0.003 0.013 1 0.005 0.01 3 1 0.005 0.013 f0.005 2.68 f0.12 * Samples containing 9.0 ml of NASS-4 n= 5.t Concentration (ng ml-')+95% confidence limits. samples was eluted from the column with 10 ml of 4 moll-1 buffer. Table 3 shows the results of the analysis of CRM CASS-2. The results of three replicate analyses of samples containing 27.0ml of CASS-2 are also shown. One would expect the precision and accuracy of the analysis of the samples containing 27.0ml of CASS-2 to be better than that for the samples containing 9.0ml of CASS-2 because the analyte signal is larger.The results of the analysis of the samples containing 27.0ml of CASS-2 are closer to the certified concentration than the results of the samples containing 9.0ml of CASS-2 for all the elements except for Cu. The results of the analysis of both the 9.0 and 27.0ml samples agree with the 95% confidence limits of the certified values except for the 9.0ml Zn results. The precision of the results of the 27.0ml samples was not as good as that of the 9.0ml samples. The larger imprecision of the 27.0 ml results was probably caused by the increase in the time needed to perform the analysis from 19 min for the 10 ml samples to 40 min for the 30 ml samples.Table 4 shows the results of the on-line SPC analysis of five samples containing 9.0 ml of NASS-4. The agreement between the results for both the Zn and Ni isotopes indicated that the Ca and Na concentrations were reduced to levels that did not interfere with the analysis of this sea-water CRM. The relative precision for five replicate analyses of samples containing 9.0ml of NASS-4 was better than 10% for all the elements determined except for Zn. The best relative precision was 1.4% for the determination of U the analyte with the Element Manganese Nickel Cobalt Copper Zinc Copper Zinc Cadmium Cadmium Lead Lead Lead Isotope 55 58 59 63 64 65 66 112 114 206 207 208 Concentration/ng ml-'? ~~ 9.0 ml 1.8 f 0.05 0.32 f 0.018 0.033 f 0.002 0.68 f 0.03 1.61 0.05 0.67 f 0.03 1.6 k 0.06 0.020 0.0015 0.020 1 0.0009 0.01 3 f 0.0009 0.014 f 0.0005 0.014 f 0.0006 27.0 ml 1.9f0.2 0.32 f 0.04 0.028 fi 0.003 0.63 1 0.03 1.8 f 0.15 0.6 f 0.05 1.8f0.2 0.019 fi 0.0018 0.0 19 f 0.002 0.019 k 0.001 1 0.019 f 0.004 0.019 fi0.002 Certified 1.99k0.15 0.30 f 0.04 0.025 f 0.006 0.68 f 0.04 1.97f0.12 0.68 f 0.04 1.97k0.12 0.019+0.004 0.0 19 f 0.004 0.019 k 0.006 0.019 +_ 0.006 0.019+_0.006 * The dilution of the sea-water during the adjustment of pH produced 10 ml samples containing 9 ml of sea-water and 30 ml samples containing 27 ml of sea-water.Samples containing 9.0 ml of CASS-2 n = 5; samples containing 27.0 ml of CASS-2 n = 3. Concentration (ng m1-l) & 95% confidence limits.I90 Journal of Analytical Atomic Spectrometry March 1996 V d . 1 1highest concentration and signal. The relative precision of the NASS-4 analysis was less than that of the CASS-2 analysis. One possible explanation is that the concentrations of analytes are lower in NASS-4. The decrease in the relative precision of a determination with the decrease in analyte concentration is illustrated by the determination of Zn in NASS-4. The relative standard deviation was 21% for 64Zn and 24% for 66Zn. The imprecision in the determination of Zn was caused by the combination of the amount of Zn in the blank and the low concentration of Zn in the sample. The Zn blank in Table 1 is 1.8 k0.1 ng but 9.0 ml of NASS-4 contain only 1.0 ng of Zn. Table4 shows that the concentrations of the analytes in NASS-4 determined by on-line iminodiacetate SPC are in agreement with the certified values.The data presented in Tables 2-4 illustrate the agreement between virtually all of the elements determined using on-line SPC in each of the reference materials analysed at the 95% confidence limits. The low- pressure SPC method described here can be applied to the analysis of other samples that traditionally have problems with matrix effects including the digests of biological and geological samples. General analyses of acid-digested samples have been carried out using this method in the authors’ laboratories. The authors acknowledge Fisons for funding this research and for their technical assistance. The authors also acknowledge the members of the Kingston research group especially Karen Taylor Jim Ferguson and Stuart Chalk for their valuable suggestions and help in performing this work and preparing the manuscript.REFERENCES Beauchemin D. McLaren J. W. and Berman S . S. Spectrochim. Acta Part B 1987 42 467. Jarvis K. E. Gray A. L. and Houk R. S. Handbook of Inductively Coupled Plasma Mass Spectrometry Blackie London 1992 p. 125. Toole J. McKay K. and Baxter M. Anal. Chim. Acta 1991 245 83. Klinkhammer G. P. and Chan L. H. Anal. Chim. Acta 1990 232 323. Wang J. Shen W. L. Sheppard B. S. Evans E. H. Caruso J. A. and Fricke F. L. J. Anal. At. Spectrom. 1990 5 445. Henshaw J. M. Heithmar E. M. and Hinners T. A. Anal. Chem. 1989 61 335. 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 Bloxham M.J. Hill S. J. and Worsfold P. J. Anal. Proc. 1993 30 159. Reed N. M. Cairns R. O. Hutton R. C. and Takaku Y. J. Anal. At. Spectrom. 1994 9 881. Kingston H. M. Barnes I. L. Brady T. J. Rains T. C. and Champ M. A. Anal. Chem. 1978 50 2064. Kingston H. M. Quantitative Ultratrace Transition Metal Analysis of High Salinity Waters Utilizing Chelating Resin Separation Interagency Energy Environmental Research and Development Program EPA-600/7-79-174; EPA/NBS National Technical Information Service Springfield VA 1979. Strachan D. M. Tymochowicz S. Schubert P. and Kingston H. M. Anal. Chim. Acta. 1989 220 243. Knapp G. Mueller K. Strunz M. and Wegscheider W. J. Anal. At. Spectrom. 1987 2 611. Akatsuka K. McLaren J. W. Lam J. W. and Berman S . S. J. Anal. At.Spectrom. 1992 7 889. Beauchemin D. McLaren J. W. Mykytiuk A. P. and Berman S. S. J. Anal. At. Spectrom. 1988 3 305. Sturgeon R. E. Berman S. S. Willie S. N. and Desaulneirs J. A. H. Anal. Chem. 1981 53 2337. Huang K.-S. and Jiang S.-J. Fresenius’ J. Anal. Chem. 1993 347 238. Ebdon L. Fisher A. Handley H. and Jones P. J. Anal. At. Spectrom. 1993 8 979. Heithmar E. M. Hinners T. A. Rowan J. T. and Riviello J. M. Anal. Chem. 1990 62 857. Kingston H. M. Siriraks A. and Riviello J. M. A Method and Apparatus for Detecting Transition and Rare Earth Elements in a Matrix US Pat. No. 5126272 June 30 1992. Kingston H. M. Siriraks A. and Riviello J. M. System for Detecting Transition and Rare Earth Elements in a Matrix US Pat. No. 5244634 September 14 1993. Nakashima S. Sturgeon R. E. Willie S. N. and Berman S. S. Fresenius’ Z . Anal. Chem. 1988 330 592. Beauchemin D. and Berman S. S. Anal. Chem. 1989 61 1857. McLaren J. W. Lam J. W. H. Berman S. S. Akatsuk K. and Azeredo M. A. J. Anal. At. Spectrom. 1993 8 279. Seubert A. Petzold G. and McLaren J. W. J. Anal. At. Spectrom. 1995 10 371. CETAC Technologies Improved Detection of Rare Earth Elements in Environmental and Geological Samples by Quadrupole ICP-MS Application Note No. 40 1995. A web site containing the Gilson Control Language (GCL) files used to control the PrepLab http://nexus.chemistry.duq.edu/ sampleprep/prepnet.html. Paper 5/04700E Received July 18 1995 Accepted November 21 1995 Journal of Analytical Atomic Spectrometry March 1996 Vol. 1 1 191

ISSN:0267-9477    

DOI:10.1039/JA9961100187

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Rapid Speciation of Butyltin Compounds in Sediments and Biomaterials by Capillary Gas Chromatography- Microwave-induced Plasma Atomic Emission Spectrometry After Microwave= assisted Leac hing/Digestion Journal of Analytical Atomic Spectrometry JOANNA SZPUNAR VINCENT 0. SCHMITT AND RYSZARD E O B I ~ ~ S K I Laboratoire de Photophysique et Photochimie Moliculaire CNRS URA 348 Universitd Bordeaux I 351 Crs de la Liberation 33 405 Talence France. E-mail Lobinski@frbdxl 1 .cribxl .u-bordeaux.fr JEAN-LOUIS MONOD Laboratoire d'Hydrologie et Molysmologie Aquatique Facultd de Pharmacie Universitd Aix-Marseille 27 Bd Jean Moulin 13 385 Marseille France A rapid procedure for the simultaneous determination of mono- di- and tributyltin in sediments and biological materials is described. The target compounds in sediments were subject to quantitative microwave-assisted leaching with acetic acid.Biomaterials were dissolved in a tetramethylammonium hydroxide solution under the action of a low-power microwave field in such a way that the organotin moiety remained intact. The leaching of the analytes from a sediment as well as the dissolution of a biomaterial in a focused microwave field took only 1-5 min which is much faster than previously reported methods. It was also demonstrated that the leaching efficiency of monobutyltin from certified reference sediments was superior to that of most literature procedures. The butyltins were derivatized with sodium tetraethylborate (NaBEt,) in the aqueous phase and simultaneously extracted into isooctane ( 5 min). The analysis was carried out by capillary gas chroma tograp h y ( GC ) with micr ow ave-induced plasma atomic emission detection.The sample throughput was limited by the duration of the GC run (10 min). The detection limit was 2 ng 8-l for 0.2 g of sample (dry) without preconcentration; it could be improved by a factor 10 if preconcentration was applied. The developed method was applied to a variety of real samples and was validated by analysing three certified reference materials PACS-1 CRM 462 and NIES 11. Keywords Speciation; organotin; microwave-assisted sample preparation; capillary gas chromatography; microwave-induced plasma atomic emission spectrometry; environmental analysis Tributyltin (TBT) which has been used as a biocide in antifouling paints to control the attachment and growth of organisms on the hulls of ships for over 30 years has also been shown to be toxic to non-target b i ~ t a .l - ~ It was found to be responsible for the degradation of edible aquatic resources thus raising economic and ecotoxicological concerns. Legislation has banned TBT on ships smaller than 25 m for over 10 years and has restricted TBT-paints on larger vessels. Some recent studies have shown however unusually high butyltin concentrations in some areas considered clean. Attention has turned to sediments which act as the ultimate sink of organotins. The accumulated species can be released under favourable conditions into the aquatic environment and create an ecotoxicological risk long after the anthropogenic sources have disappeared.For monobutyltin (MBT) and dibu- tyltin (DBT) (products of TBT degradation) no legal environ- mental threshold limits have yet been set but in view of their toxicity and environmental occurrence their simultaneous monitoring is nece~sary.~ The interest in rapid methods for biomaterials has been reinforced apart from ecotoxicological concerns by concerns about their content in foodstuffs. The analytical protocols available are based mostly on the coupling of chromatography and atomic spectrometry Despite the increasing popularity of high-performance liquid chromatography-inductively coupled plasma mass spec- trometry (HPLC-ICP-MS),'-'' the coupling of gas chromatog- raphy (GC) with AS remains the preferred approach owing to good resolution and availability of sensitive detectors. The usual choice for detection is atomic absorption spectrometry (AAS),l1-I4 flame photometric detection ( FPD),15-'' micro- wave-induced plasma atomic emission spectrometry (MIP- AES)19-22 or ICP-MS.23924 These techniques generally show good performance and it is the sample preparation step that determines the duration efficiency precision and accuracy of the over-all analytical procedure. Indeed the procedures reported so far are not only time- consuming but also usually inefficient in terms of analyte recovery and unreliable.As shown by Zhang et only three out of ten sample preparation methods described in the literature for the analysis of sediments were able to recover more than 90% of TBT from a sediment sample whereas none of them was able to recover MBT in a non-erratic and reproducible manner.A high scatter of results caused by leaching problems also prevented certification of MBT in the Community Bureau of Reference (BCR) Certified Reference Material (CRM) 462 Sediment.26 Recently several papers have appeared on supercritical fluid extraction which might be expected to provide a solution to these In addition to the high equipment cost however the extraction step still required 10-50min and the recoveries of di- and especially monosubsituted compounds (even when added as spikes) were far from being quantitative. Microwave-assisted processes have been gaining in popular- ity in analytical and environmental c h e m i ~ t r y . ~ ~ ~ ~ ~ Digestion with a mixture of concentrated acids in a pressurized vessel at temperatures of 200-300°C is commonly used to achieve complete sample dissolution which for biomaterials is associ- ated with the destruction of carbon-containing The potential of microwave heating to enhance the extraction of various compounds from emulsions biomaterials and soils has been reviewed.34 Studies of selective leaching of organic ana- lytes from an inorganic matrix have mainly been confined to Journal of Analytical Atomic Spectrometry March 1996 Vol.11 (1 93-1 99) 193polyaromatic hydrocarbons and pesticides in sediments and A low power microwave field was recently shown to accelerate and enhance leaching of organotin species from a sediment without affecting the C-Sn bonds.37 The poor com- patibility of the determination procedure (GC-FPD) with the leachate required additional steps and resulted in an over-all time for the procedure of more than 1 h which makes it unsuitable for routine analysis.18 The present study was aimed at developing a faster procedure internal standard solution was prepared by diluting the Pr3SnC1 stock solution with methanol to give a concentration of 1 pg m1-l.Two sediments with certified contents of butyltin species were used uiz. PACS- 1 from the National Research Council of Canada (NRCC) and CRM 462 from BCR. A fish tissue NIES 11 from the National Institute of Environmental Studies of Japan with a certified content for TBT was also used. adapted to routine work by optimizing the transfer of organo- tins from a sediment to the organic phase and the application Procedures of a tin-selective detector. Particular attention is given to the Analysis of sediments recovery of MBT the accurate determination of which is still beyond the capability of most procedures published so far.This work also attempts to give a first approach to the microwave-assisted solubilization of tissue samples without the destruction of the Sn-C bond in order to accelerate speciation analysis for organotin in biomaterials. EXPERIMENTAL Instrumentation Organotin compounds were extracted in a 50ml open vessel with a condenser made of borosilicate glass using a Microdigest Model A301 (2.45 GHz maximum power 200 W) microwave digester (Prolabo Briare France) equipped with a TX32 programmer which allows the applied energy to be varied from 20 to 200 W in steps of 10 W.The time of exposure up to 99 min can be set in steps of 1 min. The ethylated species were separated on a DB-210 (J&W) column (30 m x 0.32 mm x 0.25 pm) using an HP Model 5890 Series I1 gas chromatograph (Hewlett-Packard Avondale PA USA) equipped with a split/splitless injection port. Detection was achieved with an HP Model 5921A atomic emission detector. Injections were made by means of an HP Model 7673A automatic sampler. Data were handled using an HP Model 5895A ChemStation. A piece of HP-1 GC column (Hewlett- Packard) (0.32 mm x 0.17 pm) served as transfer line. Reagents Analytical-reagent grade chemicals (Merck Darmstadt Germany) and water de-ionized and further purified in a Milli-Q system (Millipore Milford MA USA) were used throughout unless otherwise stated.The glassware used was cleaned with a common detergent thoroughly rinsed with tap water soaked for 12 h in a 10% nitric acid solution and finally rinsed with de-ionized water just before use. A sample of 0.1-0.2g of dry sediment (or 1-2g of wet sediment) 100 pl of the TPrT solution and 10 ml of acetic acid solution (1 + 1) were placed in an extraction tube and exposed to microwaves at a power of 60 W for 3 min. The supernatant solution was transferred by means of a Pasteur pipette into a narrow-neck 20 ml extraction tube (similar to the design described by Witte et aL3*). Volumes of 10 ml of buffer 5 ml of ammonia 1 ml of NaBEt solution and 1 ml of isooctane containing 20ngml-' of tetrabutyltin were added to the supernatant. The mixture was shaken for 5 min.After separa- tion of the phases (several seconds) sufficient water was added to force the organic phase into the narrow neck to facilitate its recovery. The extract was analysed by GC-AED. Analysis of biomaterials A sample of 0.1-0.2 g of lyophilized tissue (or 1-2g of wet tissue) and 5 ml of 25% aqueous tetramethylammonium hydroxide (TMAH) solution were placed in an extraction tube and exposed to microwaves at a power of 60 W for 3 min. The solution was diluted with 15 ml of water brought to a pH of about 5 by the addition of concentrated acetic acid and buffered with 5 ml of the buffer solution. Volumes of 1 ml of the NaBEt solution and 1 ml of the extracting solvent were added and the tube was shaken for 5 min. The emulsion was broken up by subjecting the extraction tube to the microwave field for 2 min at 20 W.Thereafter the organic phase was recovered and analysed by GC-AED. GC-AED conditions The optimum parameters used for GC-AED are listed in Table 1. RESULTS AND DISCUSSION acetic acid. Standards Individual stock solutions (0.5 mg ml-' as Sn) of BuSnCl (MBT) Bu,SnCl (DBT) Bu3SnC1 (TBT) and Pr3SnC1 (TPrT) (Aldrich St. Quentin Fallavier France) were prepared in methanol. Mixed working solutions were prepared daily by dilution of the stock solutions with methanol. Tetrabutyltin used as internal standard was prepared in the same way. A multi-compound working solution was prepared at 0.25 pg ml-' and diluted with methanol as required. The and was chosen in the present work. The primary concern was focused on the quantitative separation of butyltins from sedi- ment and tissue matrices using a medium suitable for the reaction of the analytes with NaBEt,.Speciation of Butyltins in Sediments Separation of butyltins from the sediment matrix The classical approach is based on the extraction of butyltins from a sediment as their chelate complexes (typically with tropolone) into a water-immiscible solvent.6 Recent studies by 194 Journal of Analytical Atomic Spectrometry March 1996 Vol. 11Table 1 Optimum GC-AED parameters GC parameters Injection port Injection port temperature Injection volume Column head pressure Oven programme Initial temperature Ramp rate Final temperature Interface parameters Transfer line Transfer line temperature AED parameters Wavelength Helium make-up flow Scavenger gases H2 pressure 0 pressure Spectrometer purge flow Solvent vent-off time Column-detector coupling Cavity temperature Splitless 200 "C 1 Yl 130 kPa helium 60 "C (1 min) 20 "C min-l 200 "C (1.5 min) HP-1 250 "C 303.419 nm 240 ml min-'* 50 psi 20 psi 2 1 min-' nitrogen 1.5 min Column-to-cavi ty 250 "C * Measured at the cavity vent.Chau et a1." and Ceulemans and Adams41 showed that the presence of a polar solvent in the extractant mixture is essential for the quantitative recovery of MBT. This makes the analytical procedure a priori time-consuming because of the need for elimination of the polar solvent prior to the Grignard derivatiz- ation which is carried out on the organic phase. For this reason another approach i.e.leaching of native organotin compounds with water or a water-miscible polar solvent was investigated in detail in this work. Although organotin compounds are not involved in mineralogical pro- cesses the presence of acid is essential to destroy surface carbonates and to facilitate the penetration of the leaching agent. Acetic acid was preferred to HCl for this purpose because of the danger of a nucleophilic attack on the organotin compounds by HCl resulting in a possible cleavage of side groups under the microwave field. It was found that in a microwave field acetic acid (1 + 1) alone is able to leach quantitatively all three butyltin species within 3min. The presence of methanol as advocated in a previous was found not to affect the leaching process.However the presence of methanol adversely affected the efficiency of the derivatization/extraction process thereby requiring a large dilution of the leachate prior to extraction." Note also that TBT released from a sediment on sonication with methanolic HCl was reported to resorb on the sediment immediatel~.,~ The use of acetic acid in the present work apparently makes this sorption more difficult. Extraction of butyltins with NaBEt Initially attempts were made to extract the organotins directly from the leachate containing the suspended sediment after pH adjustment and addition of NaBEt and hexane. A literature report showed the possibility of 70-90% recovery of butyltin species from a dilute (0.5-270 dry mass/volume) sediment suspension by using a 30min extraction with fairly concen- trated (0.5%) NaBEt into a large (10 ml) volume of he~ane.~ We found that this procedure failed when the volume of hexane or the extraction time was reduced which was necessary to avoid the lengthy evaporation step and to keep the over-all analysis time short.Further it was observed that the presence of sediment during 5 min of shaking with 1 ml of the NaBEt solution and 1 ml of hexane reduced recoveries to 10-20% for DBT and TBT whereas virtually none of the MBT was recovered. The same result was observed for the extraction with tropolone and subsequent Grignard derivatization. This phenomenon was observed irrespective of whether the sample had been treated in the microwave field prior to extraction or not. It was ascribed to the fact that in the absence of a polar solvent organotin compounds could sorb on the sediment during shaking.It was observed however that when extraction was per- formed from a supernatant free of the suspended sediment spike recoveries approached 100% after a 5 min extraction. Isooctane was preferred to hexane because it allows a higher GC injection port temperature which makes the GC run shorter. GC-AED conditions Most of the work on capillary GC of tetraalkyltin compounds has been carried out using columns with non-polar phases (cross-linked 100% polydimethylsiloxane).6 These columns ensure excellent resolution sharp peaks and good sensitivity in peak height mode. The disadvantage is the fairly long retention times of polyaromatic hydrocarbons (abundant in many sediments) and hence the need to heat the column to 280-300°C. This increases the analysis time up to 15 min and prolonged cooling of the oven is required.In the present work a weakly polar column was chosen. The peaks were broader (the half-width was increased from 0.016 to 0.025 min) and the sensitivity was slightly poorer but the chromatogram was completed at 180-200 "C. No problems were observed in about 200 chromatograms of real sample extracts (including tissues without clean-up) run in this work. Apart from causing the build-up of a black deposit on the injector liner which required periodic cleaning introduction of the crude extracts did not appear to detract from column performance. Another contribution to shortening the analysis time was the use of isooctane in place of the commonly used hexane.The starting temperature of 60 "C not only allowed advantage to be taken of the solvent effect but also decreased the oven cooling time. By using the oven programme in Table 1 four runs per hour (including the data handling) were achieved. Sediment samples tend to contain considerable amounts of sulfur either native (e.g. as s6) or organically bound. Fig. 1 shows a chromatogram for the PACS-1 sediment on the S 181 nm channel which demonstrates the presence of an intense sulfur background and of sulfur compounds at considerable concentrations. In real-life sediments these peaks may occur at random retention times sometimes influencing the analysis. 2 3 4 5 6 7 8 9 10 Retention time/min Fig. 1 Chromatogram obtained for the PACS-1 sediment using the procedure optimized for the butyltins (Table 1) on the sulfur (emission wavelength = 181 nm) channel Journal of Analytical Atomic Spectrometry March 1996 Vol.11 195A desulfurization step is required which makes the analysis time longer; moreover such a procedure does not affect organosulfur compounds that can be co-determined.I8 The advantage of using a tin-selective detector is that it allows the over-all procedure to be shortened. The low selectivity of FPD against sulfur creates a danger of overlap of sulfur peaks with analytical peaks which are impossible to detect unless a truly tin-selective detector is used. Internal standardization Because of the complexity of real-life aquatic sediments the extraction efficiencies may vary with the type of sediment despite the use of the same or a similar extraction pr~cedure.~ An internal standard is necessary.Tripropyltin was chosen. Its main role is to correct for volume changes and spray losses during the microwave heating and the separation of the supernatant. A poor recovery of the internal standard can be considered as an early warning of the malfunction of the procedure. However although the internal standard can contribute sig- nificantly to the correction of errors caused by sorption/ desorption processes on different sediments and of those resulting from the suppression of the extraction caused by the release of an unexpected contaminant from a sediment it should not be used for corrections exceeding 10-15%. Should such a need exist a standard additions run is highly advisable especially when a new batch of sediments is to be analysed.Another internal standard Bu4Sn (TeBT) was added to the extracting solvent (isooctane) to correct for the precision of the injection. Analytical characteristics Typical chromatograms obtained for the reference sediments are shown in Fig. 2. Values of precision and spike recovery are listed in Table 2. Results of the recoveries of standard additions are also included. The method is fast. The throughput is limited by the duration of the chromatographic run and is 4 samples h - l . The detection limit is 2ngg-' for a 0.2g sample size. Evaporation of the extract ten times resulted in a decrease in the detection limit; no additional matrix effects were observed. High volume injection (as described elsewhere6) is thus feasible.Validation of the method Table 3 shows the results for the determination of MBT DBT and TBT in the CRMs. Good agreement with the certified values for DBT and TBT for both sediments is observed. The value for MBT is much higher than the certified value for the PACS-1 sediment and is one of the highest ever reported. This deserves further examination. The highly scattered values for MBT recoveries in the PACS-1 and CRM 462 sediments reported in the literature are summarized in Table 4. It is surprising that none of the values published matches the mean by closer than 20% and only three out of 12 results published hitherto fall within the certified range. Fewer results have been published for CRM 462; three of them (out of five) lie closely together and are close to the certification mean.The most probable reason for this is that MBT is not completely recovered from the sediment by most of the reported procedures. The most reliable assessment of recovery can be made by the method of standard additions the accuracy of which is dependent on whether the analyte and the spike behave similarly. This similar behaviour is apparently not the case for MBT in sediments. Indeed for two intrinsically different procedures recoveries of the MBT spike varied by about 20% (84.7 and 62.3%) but the calculated concentration in the sediment differed by a factor of 2.5 (1.03 196 Journal of Analvtical Atomic SDectrometrv. March 1996. 1 2 l 3 60 50 40 h u) c .- c % 30 .- c 1 s2 34 t IS1 I 2 281 I I 1 I I I I I 0 1 2 3 4 5 6 7 8 9 Retention time/rnin Fig.2 Chromatograms obtained by the optimized procedure for the certified reference sediments. (a) PACS-1; (b) CRM 462; 1 MBT; 2 DBT; 3 TBT; IS1 TPrT; IS2 TeBuT Table2 sample (five experiments) Results of the spike recovery experiments for a sediment Compound Addedlng as Sn MBT - 20 40 DBT - 20 40 TBT - 20 40 Foundlng as Sn 34.0 54.7 72.5 24.5 44.9 63.8 12.2 31.5 49.9 s,* Recovery (Yo) (Yo) 8.5 - 7.3 101 6.8 98.0 5.1 - 6.3 101 4.9 98.9 11.5 - 7.3 102 6.6 97.9 * s = Relative standard deviation. Table3 certified reference sediments (five experiments) Results for the determination of butyltin compounds in PACS-lIpg g-' as Sn CRM 462Jngg-' as Sn Compound Certified Determined Certified Determined DBT 1.16f0.18 1.01+0.06 128k16 122f6 TBT 1.27f0.22 1.19k0.08 70+14 61 +7 MBT 0.28f0.17 0.76k0.05 (12-244)* 172f 15 * Literature data.26 and 0.41 respectively).22 This discrepancy suggests that the spike is not recovered in the same way as the compound in the sediment itself. This is corroborated by the study of Siu et ~ l .~ ~ who showed an 86% recovery of the spike but were not able to detect MBT in PACS-1 despite a sufficiently low experimental detection limit. The value obtained in this work is one of the highest ever VOl. 11Table 4 Literature values for the recovery of MBT from PACS-1 and CRM 462 Procedure* Certified value SFE in the presence of DDTC with CO doped with 5% methanol SFE with C02 doped with 10% methanol Extraction with aqueous NaBEt into hexane Extraction with tropolone into hexane Acidification with HC1 extraction with tropolone into hexane-ethyl Extraction with tropolone into toluene Leaching with concentrated acetic acid acetate Leaching with concentrated acetic acid Microwave-assisted leaching with 0.5 mol 1-' acetic acid in methanol Microwave-assisted leaching with 8.5 mol I-' acetic acid MBT concentration in PACS-l/pg g-' 0.28 f 0.17 0.025 & 0.06 0.41 k 0.04 0.49 f 0.09 0.52 & 0.1 5 0.36 & 0.17 0.94 & 0.06 1.03 50.01 0.55 k 0.05 0.72k0.16 0.59 k 0.06 0.37 & 0.01 0.76 0.05 MBT concentration in CRM 462/ng g-' ( 13-244)t 9.5 & 3.8 NAS NA 102 & 38 126+ 16 NA 8 7 f 4 NA 28 & 4 172k 15 Ref.21 22 23 24 41 22 9 43,44 18 This work * SFE = Supercritical fluid extraction; DDTC = diethyldithiocarbamate.7 The range reported for the certification study.26 The mean value obtained by the laboratories participating in the campaign is 148 f 64. It is 1 NA =Not analysed. neither a certified nor an indicative value. reported. It is slightly lower than the results of Chau et a1.22 and Ceulemans and Adams,,' who have pointed out that their methods extracted three times more MBT from the PACS-1 sediment than the certified value. Our value is also higher than that previously reported using the microwave-assisted pro- cedure.18 This is probably due to the absence of methanol which was found to hamper derivatization and extraction of MBT with NaBEt,. It should be pointed out that it is unlikely that any MBT may be generated by degradation of TBT and/or DBT in a microwave field; the values obtained for the last two compounds match perfectly the certified values.Speciation of Butyltins in Biological Materials In contrast to sediments organotin compounds tend to be incorporated into tissue. Despite some success with leaching reported by several groups,45 the digestion (complete solubiliz- ation) approach was preferred. This was justified because the reports of successful leaching were mostly based on the spike recovery experiments. Intrinsically bound organotin may behave differently. Microwave-assisted dissolution of tissue A recent comparison study showed that hydrolysis with TMAH is superior to acid and enzymic hydrolysis in terms of time and efficacy.46 Biological tissues can be dissolved during 1 h at 40-60°C.46 It was observed in this study that a microwave field can shorten this time to 1-5 min depending on the applied power (100-20 W respectively).Despite rapid (1 min) dissolu- tion at 80-100 W spray losses were considerable and precision was poor. It was preferable to dissolve samples at 60 W under which conditions a transparent solution was obtained after 3 min from the fish oyster and mussel samples investigated. In the last two instances a fine silica-like suspension was sometimes observed at the end. Its presence did not however affect the recoveries of the butyltins. Extraction of butyltin compounds The solution obtained is highly alkaline and must be brought to pH 5 to permit derivatization and extraction. During acidi- fication a white precipitate probably of free fatty acids was formed especially with fish tissue hydrolysates.The precipitate was found to affect precision and its formation should be limited. This was achieved by diluting the hydrolysate 4-fold with water and carrying out the extraction from dilute solu- tions. During shaking a foam was formed which prevented the separation of the phases. Instead of centrifugation exposure to a microwave field at 20 W for 1-3 min was found to break up the emulsion and allowed for clear separation of the phases. Isooctane is required not only for making the GC run shorter but also because hexane evaporates faster during microwave treatment. Injection of 1-2 yl on a routine basis did not require a clean-up when a polar column was used. When a non-polar column was used a clean-up procedure e.g.on an alumina column was indispensable. Analytical characteristics A typical chromatogram of the NIES 11 reference tissue extract is shown in Fig. 3. Table 5 illustrates results from the spike recovery experiments on an uncontaminated oyster tissue homogenate and the NIES 11 tissue. Good precision and linearity can be seen. Table 6 shows the results obtained for the determination of MBT DBT and TBT. Good agreement with the certified value was found for TBT. For MBT and DBT no certified values are available. The pattern is similar to that found by Ceulemans et The method was also validated by a survey analysis (single determinations) of some fish and mussel samples from the Marseille harbour area analysed 6 months earlier using a sample preparation pro- cedure similar to that described by Pannier et ~ 1 .~ ~ The I 46 48 I x 44 c .- 2 42 a .r 40 C .o 38 vl vl 'E 36 W 34 32 30 w 3 I S 4 ms 28 I 1 I 1 I I I I I 0 1 2 3 4 5 6 7 8 9 Retention tirnelmin Fig. 3 Chromatogram obtained for NIES 11 Fish Tissue 1 MBT; 2 DBT; 3 TBT; 4 TPhT; IS TeBuT Journal of Analytical Atomic Spectrometry March 1996 Vol. 11 197Table 5 Results of the spike recovery experiments for biological tissue (five determinations) Sample Compound Fish tissue MBT Southern France DBT TBT NIES 11 MBT DBT TBT Added/ng as Sn - 20 40 20 40 20 40 40 40 40 - - - - - Found/ng as Sn NDt 13.2 21.3 ND 19.5 40.9 ND 17.0 37.6 1.7 39.9 10.9 50.1 88.7 121 s,* (Yo) - 7.9 6.8 5.3 5.1 6.6 6.2 6.5 7.1 5.9 5.7 4.9 - - 10 Recovery (Yo) 66.2 53.2 97.2 - - 102 - 85.2 94.1 95.7 98.4 94.0 - - - * s = Relative standard deviation. ND = Not determined (below the detection limit).Table 6 Results for the determination of butyltin compounds in NIES 11 Fish Tissue (five determinations) Certified/yg g-’ Determinedlpg g-’ Compound as chloride as chloride MBT NA* 0.02 f 0.002 DBT NA 0.14 f 0.01 TBT 1.3f0.1 1.22 f 0.07 * NA = Not available. 0- 1 2 3 4 5 6 7 Concentration (Sn) found by procedure Npg g-’ Fig. 4 Results of an inter-method comparison of TBT determination in mussels and fish (Marseille harbour area). Procedure A this method. Procedure B method based on sample preparation according to ref. 47 followed by GC-AED agreement shown in Fig. 4 can be considered to be good taking into account that an independent set of calibrants was used.CONCLUSIONS This study is the first to present a method for the simultaneous speciation of butyltins in sediments and tissues in which the sample throughput is controlled by the duration of the GC run and not by the sample preparation step. Time-consuming (several hours) sonication and operations such as evaporation and solvent replacement are avoided. Application of micro- waves to leaching of butyltins from sediments not only reduces the time of sample preparation but also enhances the recovery of MBT. Microwave-assisted digestion also reduces the time required for the dissolution of biomaterials 20 times without affecting Sn-C bonds. The proposed method appears promis- ing for routine agricultural and biological speciation analysis.We thank D. Mathe (Prolabo) for the gift of the microwave digester and Dr. Olivier F. X. Donard for valuable discussions. J. S . acknowledges a long-term fellowship from the European Environmental Research Organization (EERO). REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 Maguire R. J. Appl. Organomet. Chem. 1987 1 475. Huggett R. J. Unger M. A. Seligman P. F. and Valkirs A. O. Environ. Sci. Technol. 1992 26 232. Tsangaris J. M. and Williams D. R. Appl. 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Lobinski R. and Adams F. C. Appl. Organomet. Chem. 1994 8 621. 39 40 41 42 43 44 45 46 47 Quevauviller P. Donard 0. F. X. Maier E. A. and Griepink B. Mikrochim. Acta 1992 109 169. Rapsomanikis S. Analyst 1994 119 1429. Ceulemans M. and Adams F. C. Anal. Chim. Acta in the press. Siu K. W. M. Maxwell P. S. and Berman S. S. J. Chromatogr. 1989,475 373. Pannier F. Dauchy X. Potin-Gautier M. Astruc A. and Astruc M. Appl. Organomet. Chem. 1993 7 231. Astruc A. Dauchy X. Pannier F. Potin-Gautier M. and Astruc M. Analusis 1994 22 257. Dirkx W. M. R. Lobinski R. and Adams F. in Quality Assurance in Environmental Analysis eds. Quevauviller Ph. Maier E. and Griepink B. Elsevier Amsterdam 1994. Ceulemans M. Witte C. Lobinski R. and Adams F. C. Appl. Organomet. Chem. 1994 8 451. Pannier F. Astruc A. and Astruc M. Appl. Organomet. Chem. 1994 8 595. Paper 5/06320& Received September 26 1995 Accepted November 1 1995 Journal of Analytical Atomic Spectrometry March 1996 VoE. 11 199

ISSN:0267-9477    

DOI:10.1039/JA9961100193

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Integrated Sample Preparation and Speciation Analysis for the Simultaneous Determination of Methylated Species of Tin Lead and Mercury in Water by Purge-and-trap Injection-Capillary Gas Chromatography-Atomic Emission Spectrometry MICHIEL CEULEMANS AND FREDDY C. ADAMS* Department of Chemistry University of Antwerp (UIA) Universiteitsplein 1 B-2610 Antwerpen Belgium A sensitive and interference-free automated method for the simultaneous speciation analysis of methylated species of mercury tin and lead and also inorganic mercury in water using purge-and-trap injection-gas chromatography-atomic emission spectrometry was developed. The ionic species are volatilized from the sample after ethylation using sodium tetraethylborate in acetate buffer medium of pH 5 and preconcentrated on a capillary cryogenic trap.Desorption is effected by linear heating of the trap followed by separation of the analytes by capillary gas chromatography and selective simultaneous detection by microwave-induced plasma atomic emission spectrometry. Detection limits of 0.15 0.20 and 0.60 ng 1-' for methylated tin lead and mercury species respectively and 2 ng 1-' for inorganic mercury can be obtained on the basis of a 10 ml sample volume. Examples of results for the analysis of river- and soil run-off water samples are given. Keywords Speciation; purge-and-trap injection; gas chromatography-atomic emission spectrometry; methyllead methyltin and (methy1)mercur-y ; sodium tetraethylborate The widespread use of organometallic compounds and their subsequent release into the environment has created great environmental concern in the last few decades.lT2 For lead the major part of the environmental burden is due to the use of tetraalkyllead compounds mainly tetraethyl- tetramethyl- and some related mixed compounds of well documented toxicity as anti-knock additives to petrol. Organotin compounds have more versatile applications.In particular the use of triorgan- otins (R,SnX) in antifouling paints (R = butyl phenyl) and pesticides (R = phenyl cyclohexyl) has led to environmental problems. Industrial uses of mercury compounds such as in seed dressings fungicides and pesticides and in the paint industry have declined owing to concern about mercury toxicity. Methylated species of tin lead and mercury play an import- ant role in environmental pollution as they can be both anthropogenically introduced and naturally formed in the environment via so-called biomethylation processes.The biomethylation of mercury and tin is now well e~tablished.~. Methylation of inorganic mercury is a key process in the biogeochemical mercury cycle. The methylation of mercury in sediments was demonstrated and appears to be higher than in the water c01umn.~*~ Natural formation of organic lead species * To whom correspondence should be addressed. Journal of Analytical Atomic Spectrometry uia biomethylation was tentatively identified in media contain- ing high microbial a~tivity,~,' but still remains c o n t r o ~ e r s i a l . ~ ~ ~ ~ The high toxicity of these compounds has stimulated the development of accurate and sensitive analytical methods.Analytical methods used in organometallic speciation analysis generally involve a chromatographic separation technique such as gas chromatography (GC) liquid chromatography (LC) or supercritical fluid chromatography (SFC) combined with an element-selective detection technique such as atomic absorption spectrometry (AAS) atomic emission spectrometry (AES) mass spectrometry (MS) atomic fluorescence spec- trometry (AFS) or flame photometric detection ( FPD).l1-l4 More recently there has been a trend towards the use of hyphenated techniques offering multi-element detection capa- bilities such as GC coupled to inductively coupled plasma mass spectrometry ( ICP-MS)15 and microwave-induced plasma atomic emission spectrometry ( MIP-AES).16*17 Despite the excellent sensitivity and selectivity provided by these techniques several limitations remain at the level of simul- taneous sample preparation.Sample preparation for alkyltin -lead and -mercury generally requires extraction enrichment and derivatization steps often under conditions strongly differing for each element. With the introduction of sodium tetraethylborate (NaBEt,) as derivatizing reagent in metal speciation analysis the simultaneous derivatization of tin lead and mercury compounds was made possible." This paper describes the optimization of a purge-and-trap injection (PT1)-GC-MIP-AES system for the simultaneous sample preparation and multi-element detection of inorganic mercury and methylated tin lead and mercury species in water at the trace level after volatilization with NaBEt,.The method developed is illustrated by the analysis of environmental water samples. EXPERIMENTAL Apparatus A Model PTI purge-and-trap injector (Chrompack Middelburg The Netherlands) was used for purging the analyte species. Entrained water vapour released from the sample during purg- ing was frozen out in a condenser kept at - 15 "C in order to avoid blocking of the capillary cold-trap.lg Trapping of the analytes was effected in a wide-bore fused-silica liner (10 cm x 0.53 mm id) coated with a 5 pm CP-Sil 8 CB layer. The analytes were separated using an HP Model 5890 Series I1 gas chromatograph (Hewlett-Packard Avondale PA USA) fitted with an HP-1 capillary column and detected by means Journal of Analytical Atomic Spectrometry March 1996 Vol.11 (201 -206) 201Table 1 PTI-GC-AES operating conditions Injector parameters- Purge time Purge flow rate Condenser temperature Trap Trap temperature Desorption temperature Desorption time Clean-up flow rate Injector block temperature GC parameters- Carrier gas Column Column head pressure Oven programme Initial temperature Ramp rate Final temperature Detector block temperature 10 min 25 ml min-' - 15 "C CP-Sil 8 CB 0.1 m x 530 pm id x 5 pm - 100 "C 200 "C 2 min 50 ml min- 200 "C Helium HP-1 25 m x 320 pm id x 0.17 pm 20 psi H pressure 45 "C (1 min) 20 "C min-' 200 "C 200 "C Inter$ace parameters- Transfer line Transfer line temperature AES parameters- Wavelength Hi3 Pb Sn He make-up gas flow rate Scavenger gases 0 pressure 65 psi Spectrometer purge flow Solvent vent-off time Cavity temperature HP- 1 200 "C 253.652 nm 261.418 nm 270.651 nm 270 ml min- ' 20 psi 2 1 min-' of nitrogen 1 min 200 "C of an HP Model 5921A atomic emission detector (AED).Operating conditions of PTI GC and AED are summarized in Table 1. A schematic diagram of the system is shown in Fig. 1. Reagents Methyltin chlorides were purchased from Aldrich (Milwaukee WI USA). Trimethyllead chloride was obtained from Alfa Products (Johnson Matthey Karlsruhe Germany). Dimethyl- lead was synthesized from trimethyllead by reaction of the latter with iodine monohydrochloride.20 Stock standard solu- tions of the individual methyltin and -lead compounds were prepared as described earlier.21*22 Aqueous 1 mg ml- ' solutions of methylmercury chloride and mercury@) chloride were obtained from Alfa Products and Janssen Chimica (Beerse Belgium) respectively. Mixed working standard solutions were prepared daily from the stock solutions by a series of dilutions with de-ionized water.In calibration experiments a known concentration of the mixed working standard solution was introduced into a buffered sample just prior to analysis. Sodium tetraethylborate (NaBEt,) was purchased from Strem Chemicals (Bischheim France). A 0.3% m/v aqueous solution was prepared daily. Acetate buffer (pH 5; 0.1 moll-') was prepared by dissolving to AED r Fig. 1 Schematic diagram of the PTI-GC-MIP-AES system 13.6 g of sodium acetate trihydrate (Merck Darmstadt Germany) in 1 1 of de-ionized water followed by pH adjustment with concentrated acetic acid (Merck).Water de-ionized and further purified in a Milli-Q apparatus (Millipore El Paso TX USA) was used throughout. Procedure A 10ml volume of the sample buffered to pH 5 was placed in the reaction/purge vessel together with 100 pl of the NaBEt solution. The sample was purged for 10min with helium at a flow rate of 25ml min-'. The purged analytes were trapped in the fused-silica liner at - 100 "C. After the purging step the trap was electrically heated to 200°C within a few seconds providing a narrow injection band-width and the compounds were released onto the capillary column. RESULTS AND DISCUSSION Optimization of GC-AES Conditions GC conditions The adapted GC conditions allow an optimum resolution of chromatograms and good peak shapes.Multi-channel detection not only offers an improvement in selectivity but also has its repercussions on chromatographic conditions which can be adapted. Fig. 2 shows a chromatogram of a standard solution of inorganic mercury and methyltin -lead and -mercury species. It can be seen that between 1.0 and 2.6 min a total of seven compounds are eluted. The recording of the signals on three different channels leads to three separate 180 1 4 I 3 I 1.5 2 .o 2.5 3.0 Retention time/min Fig. 2 Chromatogram for the analysis of a standard solution contain- ing 1 Me,Sn'; 2 Me2Sn2'; 3 MeSn3'; 4 MeHg'; 5 Hg"; 6 Me,Pb*; 7 Me2Pb2+ 202 Journal of Analytical Atomic Spectrometry March 1996 Vol. 11chromatograms with optimally resolved peaks. This allows the use of a higher column head pressure and of a higher ramp rate speeding up the analysis compared with single-channel measurements.Preconditioning of the column with mercury compounds often recommended in order to avoid troublesome GC of methylated mercury compounds was not found neces- sary during this study. The temperature of the transfer line and cavity block was kept distinctly above the latest peak elution temperature in order to avoid condensation and peak broadening. AES conditions Analytical line. The software controlling the data acquisition allows recipes to be constructed for the different emission wavelengths for a given element. The tin-emission signal can be measured at 270.651 and 303.419 nm the lead-emission signal at 261.418 and 405.783 nm and the mercury-emission signal at 253.652 and 184.870 nm.The AED is equipped with a photodiode-array spectrophotometer allowing for the deter- mination of up to four elements within the same run provided that the analytical lines are not separated from each other by more than 20-40 nm when measured in the visible-ultraviolet region re~pectively.~~ Therefore simultaneous measurement is only possible on the Sn-271 Pb-261 and Hg-254 channels. Experiments were carried out to compare the characteristics of the two emission lines for each element. For lead it was found that the Pb-406 line was four times more sensitive than the Pb-261 line while for tin and mercury similar sensitivities for both lines were observed. Furthermore it was found that the Hg-185 line was more susceptible to interferences from the carbon matrix originating from purged-and-trapped artifacts formed during the NaBEt derivatization reaction.The reason for this is probably the proximity of the C-193 nm line. EfSect of the helium make-up gasJlow. Auxiliary plasma gas flow has a large effect on the sensitivity and peak shape in the determination of metals. The effect of the helium make-up gas flow on the sensitivity of tin lead and mercury is shown in Fig. 3. The helium flow rate was optimized univariately to give maximum sensitivities by analysis of the same standard mixture for methyltin -lead and -mercury. The helium flow rate was measured at the cavity vent with the ferule purge vent open. From Fig. 3 it can be seen that a reverse effect is observed for the sensitivities of tin and lead compared with that of mercury in agreement with results reported by other worker^.^^^^^ This effect has been attributed to the effect of interactions between tin and lead and the walls of the discharge tube.A similar effect has been observed for the detection of germanium compounds by MIP-AES.24 The decrease in sensitivity at still higher flow rates is due to both dilution effects and cooling v) 0) 3 - 9 .- w 0 m - E z Fig. 3 0 tin; 40 20 0 0 50 100 150 200 250 300 350 He flow / ml min-' Effect of the helium make-up flow rate on the responses of . lead; x Hg 10 20 30 40 50 60 70 80 90 100 H2 pressure / psi Fig.4 Effect of the hydrogen flow rate on the responses of 0 tin; a lead; x Hg of the plasma. Mercury obviously exhibits no such wall inter- action effect and therefore a steady decrease in sensitivity is observed with higher flow rates owing to a reduction of the residence time of the emitting species in the plasma.A similar effect has been observed earlier for the detection of selenium compounds.25 As a result of these observations a compromise had to be made in order to select a working helium flow for the simultaneous measurement of all three elements. A working flow of 270ml min-' was chosen. Under this condition tin and lead sensitivities are close to optimum while for mercury this is 30% of the maximum sensitivity that can be achieved. EfSect of the hydrogen gas flow. Most metals require either hydrogen or a mixture of hydrogen and oxygen as the reagent gas. Oxygen is necessary to prevent carbon from being deposited on the wall of the discharge tube but has no further effect on sensitivity. The effect of hydrogen on the sensitivity of tin lead and mercury can be seen from Fig.4. A univariate optimization was performed by repetitive analyses of the same standard solution at various hydrogen pressures. Again as for the helium make-up flow a reverse effect was observed for tin and lead compared with mercury. A working pressure of 65 psi was selected as a compromise. Optimization of Purge-and-Trap Conditions Derivatization conditions In order to make the analytes sufficiently volatile and amenable to GC it is mandatory to derivatize the polar and ionic organometallic species. Derivatization techniques used in organometallic speciation analysis involve alkylation using Grignard reagents or NaBEt or hydride generation using sodium tetrahydroborate (NaBH,). Simultaneous derivatiz- ation of tin lead and mercury species using a suitable Grignard reagent was recently reported.16 However the use of a Grignard reagent requires a complexation reaction and extraction into an organic solvent as the reaction has to take place in a completely dry medium.Sodium diethyldithiocarbamate (DDTC) is often used as the complexing agent in the extraction of organotin -lead and -mercury compounds. However opti- mum reaction conditions such as pH and buffer medium are different for all three elements and therefore make simultaneous sample preparation impossible.26-28 Hydride generation tech- niques offer the advantage that the species can be derivatized in situ followed by volatilization and trapping of the hydrated species.However the hydrides of organic lead and mercury compounds are not stable and prone to dismutation reac- tions," while for alkyltins the hydridization reaction may be subject to interference in the presence of inorganic metals often encountered in the analysis of contaminated real sample^.^' Table 2 presents derivatization conditions using NaBEt reported by different workers for the elements of interest. From Table2 it becomes clear that in most studies. Journal of Analytical Atomic Spectrometry March 1996 Vol. 11 203Table 2 Overview of reaction conditions in sample preparation procedures for organometallic speciation analysis using NaBEt as derivatizing reagent Analytes Bu3Sn+ Bu2Sn2+ BuSn3+ Bu3Sn+ BuzSn2+ BuSn3+ Bu3Sn+ Bu2Sn2+ BuSn3+ Ph3Sn+ Me,Pb+ MezPb2+ Me,Pb+ MeHg' MeHg' Me,Sn(4-")+ BunSn(4-")+ Ph Sn(4-")+ Me3Pb+ MeHg' Sample matrix Water Sediment Fish mussel Water Water road dust Water Fish Sediment Derivatization medium Tris-solution - acetic acid Acetate buffer pH 4.1 Acetate buffer PH 5 Acetate buffer pH 4.1 Ammoniaxitrate buffer Acetate buffer pH 4.9 Acetate buffer pH 4.5 Acetate buffer pH 5k0.5 pH 6-7 pH 5-8 Reference 30 31 32 33 34 35 36 37 optimum pH values for the reaction are found between 4 and 5 when carried out in acetate buffer medium.Optimization experiments applying the method presented here to standard mixtures confirmed this leading to an optimum pH of 5 in 0.1 mol 1-' acetate buffer medium.The concentration of NaBEt is not very critical and a concentration of 0.003% in the sample proved to be sufficient. Too high a concentration of NaBEt should be avoided because of carbon interference. Derivatization of organometallic species of tin lead and mer- cury was found to be quantitative under the given conditions. Real samples are usually abundant in inorganic lead and tin compared with the concentrations of their organometallic forms. During derivatization inorganic lead and tin may be converted into respectively PbEt and SnEt,. If too large amounts of these compounds enter the discharge tube deposits may be formed on the tube wall resulting in an increased baseline emission intensity and thus negatively influencing detection limits.27 The problem becomes more important when a large number of real samples are analysed in series.Therefore a study on the derivatization of inorganic lead and tin was carried out. It was found that with the given reaction and purging conditions the signals obtained for inorganic lead and tin were only 1.1 and 2.6% respectively compared with the ethylation and purging efficiencies of their methylated forms. None of the real samples analysed in this study showed high inorganic lead and tin emission signals. The reaction and purging of inorganic mercury proceeds with the same efficiency as that of methylmercury and therefore the method could be adapted to the determination of inorganic mercury. Efect of the purge time The time needed to transfer all the species present in the sample onto the cold trap is a combination of two independent processes.The first factor is the time required to form the volatile ethylated derivative of the ionic (organo)metallic species which is determined by the reaction rate between the NaBEt and the (organo)metallic analytes. The second factor is after formation of the ethylated derivatives the time required to transfer the species from the water sample onto the cold trap. This is dependent on the volatility and polarity of the species formed. The effect of the purging time on the signal of all seven species is shown in Fig. 5 which shows that the formation of the ethylated mercury species is the time-limiting factor of the purging process. Experiments showed that a purge flow of 35 ml min-' gave maximum efficiencies for the tin and lead species after 5 min.However mercury efficiencies did not increase at higher flows and remained at about 50% owing to the slower formation of the ethylated mercury derivatives. 204 Journal of Analytical Atomic Spectrometry March 1996 loo 5 t 0 2 4 6 8 10 12 14 16 Purge time / min Fig. 5 Effect of the purge/reaction time on the purging efficiency of 0 Me,Sn+; 0 Me,SnZ+; A MeSn3+; m MeHg'; 0 Hg";+ Me,Pb+ ; x Me2PbZf Therefore a purge time of 10min was required providing maximum signals for virtually all species. For the most volatile derivatives Me,SnEt and MeHgEt longer purge times led to part of the already trapped species being stripped from the cold trap. For 15 min purging at a flow of 25 ml min-' and trapping at - 100°C losses were 60 and 35% for Me,SnEt and MeHgEt respectively.This effect can be circumvented by lowering the trap temperature but the use of very low trapping temperatures must be avoided for reasons of precision as discussed below. Analytical Characteristics of the Method Calibration graphs For calibration a series of standard spiked water samples were ,analysed at five different levels to give concentrations for .the different species ranging from 0 to 20 from 0 to 40 and from 0 to 80ng1-' for tin lead and mercury respectively. Satisfactory correlation was obtained. The analytical figures of merit calculated for all species are presented in Table 3. For inorganic mercury a blank value had to be taken into account explaining the higher intercept value of the calibration graph.The responses defined as emission units per tin lead and mercury mass unit are almost identical within a group of species containing the same metal indicating that no signal discrimination occurs with increasing boiling-point of the eluting species. The larger difference in response for theTable 3 Analytical figures of merit for the calibration graphs y = A + Bx; precision data for five replicate analyses Compound Me,Sn + Me2Sn2+ MeSn3+ MeHg' Hg" Me,Pb+ Me2Pb2+ A - Intercept Standard error 1.220 1.396 1.086 1.135 0.664 0.579 1.800 1.866 2.880 1.051 1.080 1.661 0.940 1.517 Slope 3.104 3.233 2.983 0.596 0.588 2.49 1 2.110 Standard error 0.1 14 0.093 0.047 0.038 0.022 0.068 0.062 B Correlation coefficient 0.9980 0.9988 0.9996 0.9939 0.9980 0.9989 0.9987 Precision 4.1 2.6 2.5 8.1 6.9 2.2 2.0 (Yo) Me,PbEt and Me,PbEt species is probably because the exact concentration of Me,Pb2+ is difficult to estimate as it was synthesized from Me,Pb+ .Precision Replicate analyses (n=5) of a mixed standard solution of 10 20 and 40ng1-1 for tin lead and mercury respectively were carried out to evaluate the precision of the method. The results are presented in Table 3. For the tin and lead species a precision of 2-3% could be routinely obtained. The worse precision observed for the Me,SnEt compound (4.1%) is because under the conditions specified the volatile derivative is beginning to be stripped from the cold trap as can be seen from Fig. 5. For the mercury species precision was a factor of 3 worse than for the tin and lead species.Experiments showed that this was probably due to degradation of the trapped mercury species during linear heating of the trap prior to desorption. This hypothesis was supported by the fact that initially a trapping temperature of - 150 "C was applied leading to precisions of 20 and 16% for MeHgEt and HgEt respectively. A similar observation has also been reported by Liang et a1.,,* who observed thermal decomposition of ethylated mercury species during the desorbing process which could be considerably reduced when trapping was carried out at room temperature. An attempt was made to improve mercury precision further by trapping the purged species at higher temperatures in a capillary trap filled with a 3 cm plug of Tenax. However the maximum trapping temperature could not be increased significantly and the Tenax trap created severe tailing of the mercury signals.Detection limits On the basis of data obtained from the calibration graphs the detection limits (defined as three times the standard deviation of the baseline noise) were calculated. Based on a 10 ml sample volume detection limits of 0.15 0.20 and 0.60ng1-1 can be obtained for methylated tin lead and mercury species. For inorganic mercury a blank value has to be taken into account resulting in a detection limit of 2 ng 1-'. The origin of this mercury blank has still not been elucidated. Intevferences A possible interference in the form of a matrix effect in environmental sample analysis may result from either (i) a different derivatization efficiency of the analyte species in the presence of other contaminants which may also react with the derivatizing reagent; (ii) a change in purging efficiency of the derivatized species owing to interactions of the analytes with other molecules e.g.fats proteins and hydrocarbons which may be present in the sample. Therefore the recovery of spikes in environmental water samples of different origin such as river rain and estuarine water was studied in order to evaluate possible matrix effects. Recoveries were calculated by comparison of the results with those obtained from the analysis of mixed standard solutions spiked in de-ionized water. The waters were spiked prior to analysis to yield concentrations of 10,20 and 40 ng 1-' for tin lead and mercury respectively. Recoveries from the rain water ranged from 97 to 102% those from river water from 85 to 98% and those from the estuarine water from 82 to 93% for all species indicating that matrix effects in the samples studied were minor. However from the result of the estuarine water it may be concluded that it is wise to verify recoveries when real samples are anal ysed.Detector related interferences occurred during the analysis when high amounts of the NaBEt reagent were used owing to the formation of volatile artifacts arriving at the plasma during reaction of the NaBEt,. The interference consisted of an extra peak (retention time about 1 min) appearing in the chromatograms of tin lead and mercury. Confirmation of elemental identity carried out by taking snapshots at the peak apex,39 showed that this peak consisted of carbon and resulted from a carbon background overcorrection on the tin lead and mercury channels.Therefore too high amounts of NaBEt had to be avoided as overlapping of this peak could occur with the first eluting Me,SnEt signal. Further introduction of large amounts of carbon into the plasma must be avoided in order to prolong the lifetime of the discharge tube. Selectivity between the elements of interest was found to be excellent. Only high emission intensities on the tin channel created a slight back- ground overcorrection on the mercury channel resulting in a minor negative baseline distortion as can be seen from Fig. 2. Analysis of Real Samples The developed method was applied to the analysis of two waters sampled at locations where sources of the different organometallics could be expected. The first river water was from the river Elbe sampled near the Czech-German border a site which is known to be highly contaminated with organ~metallics.~~ The sample which contained large amounts of suspended matter was filtered through a 1.2 pm Millipore filter and the filtered water was analysed.The results are presented in Table 4 and show simultaneous detection of methyltin mercury and methylmercury species at low ng 1-' levels. Methyllead species were not detected. A chromatogram of the river water sample is shown in Fig. 6. The second water sample was collected from the draining system of a shipyard containing rain- and soil run-off water. The sample had been analysed earlier using an independent method2 based on liquid-liquid extraction and GC-AAS measurement and was shown to contain butyltin concen- trations at pg 1-' levels.The results of the PTI-GC-AES analysis are presented in Table4 and show the presence of inorganic mercury and methylated lead species in the sample. Methyltin species and methylmercury could not be detected. Journal of Analytical Atomic Spectrometry March 1996 Vol. 11 205Table 4 Results of the analysis of river and soil run-off water Concentration/ng I-'* Compound Me,Sn+ Me2Sn2+ MeSn3 + MeHg' Hg" Me,Pb+ Me2Pb2+ River water 4.08 k 0.29 0.50 0.06 0.3 1 0.04 4.82 _+ 0.55 4.40 k 0.5 1 <DL < DL Soil run-off water < DLt < DL < DL < DL 11.3 & 1.0 14.2 _+ 0.6 1.66 _+ 0.12 ~~ * Mean k standard deviation (n = 4) expressed as metal.t < DL below detection limit. 2 3; 3 75 4 Pb 261 3l I I I I L 1.5 2 a 2.5 3.0 Retention time/min Chromatogram for a sample of river water 1 MeHg'; 2 Hg"; Fig. 6 3 Me,Sn+; 4 Me2Sn2+; 5 MeSn3+ CONCLUSIONS This paper demonstrates the power of in situ ethylation PTI-GC-MIP-AES for the simultaneous sample preparation and multi-element detection of methyltin -lead and -mercury and also inorganic mercury species in water. The low sample volume required and the high sample throughput make the method suitable for routine analysis of environmental samples thereby offering excellent selectivity and detection limits. Further the method developed can be used for the analysis of samples from biomethylation studies in order to provide data that may contribute to a better understanding of natural alkylation processes of tin lead and mercury.A research grant by the N.F.W.O. Belgium to M. Ceulemans is gratefully acknowledged. The authors wish to thank C. Gerbersmann R. Ma M. Heisterkamp W. Van Mol and R. tobinski (University Bordeaux France) for valuable discussions. J. Kuballa (GKSS Geesthacht Germany) is acknowledged for providing the river Elbe sample. REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 .34 :3 5 3 6 3 7 3 8 :r 9 Craig P. J. Organometallic Compounds in the Environment Longman Harlow 1986. Donard 0. F. X. and Michel P. Analusis 1992 20 M45. Craig P. J. and Glocking F. The Biological Alkylation ofHeauy Elements The Royal Society of Chemistry London 1988.Thayer J. S. Appl. Organomet. Chem. 1989 3 123. Jensen S. and Jernelov A. Nature (London) 1968 223 753. Wood J. M. Kennedy F. S. and Rosen C. G. Nature (London) 1968 220 173. Ridley W. P. Dizikes L. J. and Wood J. M. Science 1977 197 329. Chau Y. K. Snodgrass W. J. and Wong P. T. S. Water Res. 1977 11 807. Schmidt U. and Huber E. Nature (London) 1976 259 157. Reisinger K. Stoeppler M. and Niirnberg H. W. Nature (London) 1981,291 228. Harrison R. M. and Rapsomanikis S. Environmental Analysis Using Chromatography Interfaced with Atomic Spectroscopy Ellis Horwood Chichester 1989. Uden P. C. J. Chromatogr. 1995 703 393. Donard 0. F. X. and Martin F. M. Trends Anal. Chem. 1992 11 17. tobinski R. Analusis 1994 22 37. Prange A. and Jantzen E. J. Anal. At. Spectrom.1995 10 105. Liu Y. Lopez-Avila V. Alcaraz M. and Beckert W. F. J. High Resolut. Chromatogr. 1994 17 527. Minganti V. 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ISSN:0267-9477    

DOI:10.1039/JA9961100201

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Use of Signal-to-root Background Ratio as the Optimization Parameter for Inductively Coupled Plasma Atomic Emission Spectroscopy With Charged-coupled Device Detection D. A. SADLER AND D . LITTLEJOHN Department of Pure and Applied Chemistry University of Strathclyde Glasgow UK G1 1 X1 C. V. PERKINS AT1 Unicam Ltd. Cambridge UK CBl 2PX The use of the signal-to-root background ratio (SRBR) of a spectral line as the measurable parameter chosen as the criterion for single-element optimization of an inductively coupled plasma with charge-coupled device detection is described. The theoretical background to the choice of the SRBR rather than the more usual signal-to-background ratio (SBR) is given. Single-element optimization of the carrier gas flow rate and viewing height using both atomic and ionic lines from ten elements is described.The improvement in the detection limit by using the SRBR over the SBR varies by a factor of 1.0-4.8. For example the detection limit for the Mn I1 emission line at 257.610 nm is improved from 13.4 ng ml-' by SBR optimization to 2.8 ng ml-' by maximizing the SRBR. Keywords Inductively coupled plasma atomic emission spectrometry; optimization; charge-coupled device; signal-to-root background ratio For a given inductively coupled plasma (ICP) the critical parameters to be varied to optimize the analytical performance are the radio-frequency (rf) forward power the gas flow rates the sample introduction rate and the observation height in the plasma. Boumans and de Boer' showed that single-element optimization may be achieved by varying one or more of these parameters.They concluded that by holding the rf power constant only two combinations of carrier gas flow rate and viewing height were required to give good detection limits for a wide range of elements. The work of Dickenson and Fasse12 and later Scott et aL3 and Fassel and Kniseley4 demonstrated that a single combination of rf power carrier gas flow rate and viewing height could be found that gave good detec- tion limits for most of the elements normally determined by inductively coupled plasma atomic emission spectrometry In order to select the optimum plasma operating conditions a measurable parameter for each element is required that will act as a criterion of the over-all analytical performance of the chosen set of plasma conditions.This is often chosen as the signal-to-background ratio (SBR). B o ~ m a n s ~ ? ~ has shown that the detection limit is proportional to the relative standard deviation of the background (RSDb) and is inversely pro- portional to the SBR. At background levels where the RSDb is dominated by source flicker noise the RSDb is approximately constant and the detection limit may then be optimized by maximizing the SBR. The use of the SBR for optimization is relatively ~ o m m o n ~ * ~ and has provided good results. In recent years the charge-coupled device (CCD) has success- fully been used for atomic emission spe~trometry.~-'~ Usually (ICP-AES). Journal of Analytical Atomic Spectrometry the CCD is coupled with an echelle spectrograph13 with cross- dispersion as the two-dimensional dispersion plane is ideally suited to the two-dimensional format of the CCD.The full wavelength coverage of a CCD and echelle spectrograph system permits true simultaneous multi-element spectrometry to be performed over a wide spectral range. The simultaneous measurement of the analyte emission and the background spectra can with appropriate data reduction result in the elimination of the plasma background source flicker noise from the RSDb.I4 This has implications concerning the measur- able parameter chosen for single-element optimization of the plasma operating conditions. This paper proposes the use of the ratio of the net line signal to the square root of the background signal as the parameter for single-element optimization.THEORETICAL The basic equation for the detection limit cL using the SBR-RSDb approach derived by bourn an^,^^^ is given by where k is a statistical factor equal to 2 3 2J2 or 3J2 depending on the chosen convention; RSDb is the relative standard deviation of the background; co is the concentration of the analyte in solution and SBR is the resultant signal-to- background ratio. For a scanning monochromator with photo- multiplier tube (PMT) detection the RSDb is given by'' where a is the background source flicker noise coefficient p is the background shot noise coefficient y is the detector noise coefficient and xb is the background signal. If the background signal is sufficiently large such that the dominant noise mechanism is the background source flicker noise then the RSDb may be written as RSDb Z a Substituting the above equation for the RSDb into the detection limit equation eqn.(l) gives the approximation for the detec- tion limit for dominant background flicker noise cL = k x a x - CO SBR As k and co are arbitrary and a can be assumed constant for a given spectrometer and ICP over a wide range of plasma operating parameters,16 the detection limit can be optimized Journal of Analytical Atomic Spectrometry March 1996 Vol. 1 1 (207-21 2) 207by maximizing the SBR. Maximization of the SBR as the sole optimization criterion in ICP-AES is often performed and has provided good results. However as pointed out by Bo~mans,'~ this approach can only be justified if the RSDb is constant. A prerequisite for this is that the background signal is flicker- noise limited over the entire range of background signals covered by the optimization experiment.If this is not the case then both the SBR and the RSDb should be considered during optimization as in the work of Werner and Friege." The full wavelength coverage offered by the use of a CCD detection system provides simultaneous intensity measure- ments of the analyte emission line and of the background signal. As the background source flicker noise is highly corre- lated between neighbouring wavelength^,^' appropriate pro- cessing of the recorded spectra can eliminate the flicker noise that exists in the ICP background spectra. Ivaldi and Barnard2' have described a multivariate data reduction procedure referred to as multi-component spectral fitting which achieves this.Any such multivariate data reduction procedure that makes use of the simultaneous measurement of the background signal to perform background correction will eliminate the flicker noise component of the RSDb. Such data processing will ensure that the RSDb is then strongly dependent on the background signal and hence needs to be considered during an optimization procedure. The sole use of the SBR is then inappropriate for the CCD detection system with multivariate data reduction for the elimination of the background flicker noise. For a CCD system in which appropriate data processing is used to eliminate background flicker noise the RSDb may be written as RSDb = ,/=$ where oR is the root mean square (RMS) detector read-out noise and xd is the average detector dark current signal.Cooling the CCD can reduce the detector dark current to negligible levels and with the very low read-out noise of modern CCDs the RSDb will be essentially shot-noise limited. The equation for the RSDb is then 9000 - 8000 - u) 7000 - 5 6000 - 5000 -2 4000 $ 3000 2000 - - Substitution of eqn. (3) into the detection limit equation eqn. ( l ) gives 7 - - - - c = k x \ / l n - CO Xb SBR By writing SBR = x,/xb where xa is the net analyte signal the equation for the detection limit may then be written as 7 4% cL = k x c0 x - Xa (4) From eqn.(4) it can be seen that in order to optimize the detection limit of a given analyte it is necessary to maximize the signal-to-root background ratio (SRBR) rather than the SBR.The multivariate processing of the simultaneously meas- ured background signal has coupled the RSDb and the SBR together through the background signal. The use of the SRBR then ensures that both the SBR and the RSDb are considered in the optimization of the plasma operating parameters. EXPERIMENTAL Instrumentation A Spectrametrics Spectraspan IIIa echelle spectrograph was modified to accept a Kodak KAF 1300-L CCD (Eastman Kodak Rochester NY USA). The Spectraspan IIIa is a Czerny-Turner configuration with a silica prism for cross- dispersion. The Kodak CCD was controlled with a Photometrics (Photometrics Tucson AZ USA) PXL camera unit and 16-bit analogue-to-digital converter (ADC) connected to a Dell (Dell Computer Austin TX USA) XPS P75 personal computer. PMIS software (Photometrics) was used to interface between the computer and CCD control electronics.All other data analysis software was written in-house using Microsoft (Microsoft Richmond WA USA) FORTRAN version 5.0. The CCD fixed in the exit focal plane of the spectrograph has 1280 x 1024 pixels each of 16 x 16 pm giving an optically sensitive surface area of 20.5 x 16.4 mm. This is not sufficiently large to cover all of the two-dimensional dispersion plane of the spectrograph simultaneously. However by altering the incident angles of the echelle grating and of the cross-dispersive prism any spectral line can be accessed from ~ 2 0 0 to 800 nm. The spectral range covered by the CCD depends on wave- length with typically a fraction of 12-24 orders recorded simultaneously. The entrance slits used were 300 pm tall by 100 pm wide.A Unicam (Cambridge UK) PV8490 50 MHz free-running plasma unit was used to generate the plasma with a standard torch and cross-flow nebulizer for sample aspiration. The plasma was imaged onto the entrance slit of the Spectrametrics spectrograph via a quartz lens with a magnification of 2.7 1 giving an observation zone in the plasma of approximately 0.8mm high. The accuracy of the measurement of the obser- vation height is approximately 0.2mm. The carrier gas flow rate is controlled via a needle valve and the accuracy of the determination of the flow rate is approximately 0.03 1 min-l. Reagents All solutions were prepared from 1000 pg ml-' SpectrsoL [BDH (now Merck) Poole Dorset UK] stock solutions of each element.The optimization solutions were made by serial dilution of the stock solution with 5% v/v nitric acid (AnalaR BDH) diluted with distilled water. RESULTS AND DISCUSSION Background Correction Fig. 1 shows a recorded spectrum around the Mn I1 line at 257.610 nm; each data point is the summation in the direction of the slit height of all the pixels illuminated by the same diffraction order. For a 300 pm tall entrance slit and 16 x 16 pm pixel dimension this was set at 19 pixels. The concentration in solution was 1 pgml-' and the exposure time for the CCD was 10 s. The background correction was performed by fitting a straight line through the background points on either side of the spectral line and subtracting this from the raw data. In A looo t---' L 0 t-- 0 10 20 30 40 50 60 70 Pixel number Fig.1 Spectral profile around Mn I1 257.610 nm line with CCD- based spectrograph 208 Journal of Analytical Atomic Spectrometry March 1996 Vol. 11cases where a separate close lying spectral line was encountered on one side of the main peak only data from the opposite side of the spectral line were used to determine the background level. The intensity value of the fitted line at the analyte peak position was used as the estimate of the background level xb for optimization purposes. In order to determine the RSD the residuals between the fitted straight line and the back- ground data points were used to compute the sum of the squared residuals SSR. The RSDb is then given by JSSR RSDb = x b x ( n - 1) where n is the number of data points used to compute the background level.From a single scan around a spectral line it is then possible to measure the SBR the SRBR and from eqn. ( l ) the detec- tion limit. SBR Detection Limit and SRBR Measurements Fig. 2 is a two-dimensional contour plot of the measured SBR for the Mn I1 257.610nm line as a function of both carrier gas flow rate and viewing height measured above the load coil (ALC). The carrier gas flow rate was varied from 0.5 to 1.1 1 min-' in five steps. The viewing height was varied from 4 to 16.2mm ALC also in five steps The power was held constant during all experiments at 1 kW and the exposure time was set at 10 s. The maximum SBR of the Mn I1 line lies in a region from approximately 0.8 to 1.1 1 min-' for the carrier gas flow rate and from 11 to 14 mm ALC for the viewing height.The actual peak of the SBR occurs at a carrier gas flow rate of 0.9 1 min-' and a viewing height of 13 mm ALC. Fig. 3 shows the measured detection limit determined from eqn. ( l ) for the Mn I1 line as a contour plot and on the same scale as Fig. 2. The value of k was chosen as 3. The minimum in the two-dimensional surface occurs at a carrier gas flow rate of 0.651min-' and a viewing height of between 6 and 11 mm ALC. The actual minimum detection limit is found at a carrier gas flow rate of 0.65 1 min-' and a viewing height of 8.1 mm ALC. A comparison of Figs. 2 and 3 shows that the maximum in the SBR contour plot does not occur at the optimum combination of carrier gas flow rate and viewing height for the detection limit.The difference between the conditions required to maximize the SBR and those required to give the optimum detection limit is much greater than the inaccuracies in the measurements of the carrier gas flow rate or the viewing height. It must then be concluded that optimiz- ation based on the SBR does not result in the lowest detection limit when the analyte and background signals are measured simultaneously. In Fig. 4 the measured SRBR for the Mn I1 line is plotted again on the same scale as Figs. 2 and 3. The maximum in the SRBR plot occurs in an almost identical region to the minimum in the detection limit plot in Fig. 3. The actual maximum occurs at a carrier gas flow rate of 0.65 1 min-' and a viewing height of 8.1 mm ALC. This is the same combination of parameters required to optimize the detection limit.For the Mn I1 line the SRBR contour plot resembles the contour plot for the detection limit as predicted from eqn. (4). The detection limit for Mn 11 at the parameter combination required to maximize the SBR is 13.4 ng ml-' whereas at the parameter combination required to maximize the SRBR the detection limit is 2.8 ng ml-' an improvement by a factor of 4.8. Table 1 shows the detection limits obtained by optimization of the carrier gas flow rate and viewing height based on both 4 8.1 10.8 13.5 Viewing Height Above Load Coil / mm -1.1 B -0.65 -0.5 16.2 I I 0-1 00 100-200 0 200-300 300-400 400-500 500-600 600-7001 Fig.2 Two-dimensional contour map of the SBR for Mn I1 257.610nm line as a function of both carrier gas flow rate and viewing height above the load coil Journal of Analytical Atomic Spectrometry March 1996 Vol.11 209'0.9 p -0.5 4 8.1 10.8 13.5 16.2 Viewing Height Above Load Coil / mm I I 0.002-0.0032mO.0032-0.00440 0.0044-0 .O0560 0,0056-0.0068.0.0068-0.008m 0.008-0.0094 Fig. 3 Two-dimensional contour map of the detection limit (pg ml-.') for Mn I1 257.610 nm line as a function of both carrier gas flow rate and viewing height above the load coil Table 1 both the SBR and SRBR Detection limits (ng ml-') for various elements optimized by Detection limit optimized by Element Cd I1 226.502 Cu 1219.958 Cu I1 224.700 Ni 1232.002 Ni I1 231.604 Fe 1252.285 Fe I1 239.562 Mn I 279.827 Mn I1 257.610 Cr I1 283.563 Mg I1 280.270 V I1 311.071 V TI 311.838 Sn 1283.999 Pb I 280.199 SBR 1.8 54 15 26 15 32 7 10 13.4 2.6 0.21 3 .O 13 22 90 SRBR 1.3 23 9 21 5.2 18 4.9 10 2.8 1.9 0.06 1.2 3.4 13 55 Improvement ratio 1.4 2.3 1.7 1.2 2.9 1.8 1.4 1 .o 4.8 1.4 3.5 2.5 3.8 1.7 1.6 the SBR and SRBR for spectral lines of Cd Cr Cu Ni Fe Mn Mg V Sn and Pb each optimized individually.For all the spectral lines the detection limit is lower when optimizing on the SRBR than the SBR except for Mn I where no change occurred. The atomic lines of Cu Fe Mn Pb and Sn showed no definite peak for the SBR in the two-dimensional parameter space spanned by the optimization experiments. These lines are all 'soft' and require either a higher viewing height ALC or a greater carrier gas flow rate in order for the SBR to be optimized. The detection limits quoted in Table 1 at the maximum SBRs encountered for these spectral lines are prob- ably better than would be expected if the parameter space for the carrier gas flow rate and viewing height was expanded to optimize the SBR for these atomic lines.The minimum in the detection limit and the SRBR was within the spanned param- eter space for all the spectral lines listed in Table 1. The improvement ratios for the lines of Cu I Fe I Mn I Pb I and Sn I are probably lower than might be measured given that the SBR for these lines was not maximized. For some of the spectral lines in Table 1 the improvement in the detection limit is small i.e. Cd I1 exhibits an improve- ment of only 1.4-fold. However Ni 11 Mn 11 Mg I1 and both V I1 lines show improvements in their detection limits by greater than 2.5-fold.The spectra around the Mn I1 line at the parameter combi- nations for maximum SBR and SRBR are shown in Fig. 5. The measured background and peak height signals are given in Table 2 along with the calculated values for the SBR and SRBR for the two parameter combinations. Although the SBR for the SRBR optimized case is lower than the optimized SBR the detection limit is improved owing to the much higher background signal. This higher background signal reduces the RSDb and this more than compensates for the reduction of the SBR. Furthermore optimization solely on the SBR favours low background signals as shown in Fig. 5. At very low background signals the RSDb may have a significant contri- bution from the detector read-out noise or at long exposures from detector dark current.In these situations the RSDb will not be shot-noise limited and the detection limit will be worsened further still. However optimization based on the SRBR considers both the RSDb and the SBR and hence tends to favour both larger background signals and increased line sensitivity. 21 0 Journal of Analytical Atomic Spectrometry March 1996 Vol. 114 v) 80000 -~ L 73 & 60000 v) P E 40000 .- L. -0.5 8.1 10.8 13.5 16.2 Viewing Height Above Load Coil / mm -. - - Fig.4 Two-dimensional contour map of the SRBR for Mn I1 257.610nm line as a function of both carrier gas flow rate and viewing height - * I - . - I I. ,- above the load coil ’zoooo 1 I 100000 I I I 20000 Fig.5 Spectral profile of Mn I1 257.610nm line optimized by both SBR and SRBR CONCLUSION Theoretically the SBR is a poor choice of parameter for single- element optimization of an ICP with CCD detection. Analysis of the equations for the detection limit and the RSDb predict that the SRBR is the parameter which should be optimized.Provided that the background is shot-noise limited optimizing the SRBR will consider both the RSDb and the SBR both of which have an influence on the detection limit. Experimental Table 2 Measured background and peak height signals for the param- eter combinations which maximize the SBR and SRBR for the Mn 11 257.610 nm line Conditions maximized by SBR SRBR Peak height signal (counts) 27 120 101 321 Background signal (counts) 274 1399 SBR 99 72 SRBR (counts’’’) 1638 2709 single-element optimization of ten elements by both SBR and SRBR has shown that the SRBR approach can reduce the detection limit by up to a factor of 4.8.The SRBR as a function of the plasma operating conditions is a smooth changing function with a single maximum. This makes the SRBR ideal for use in a sequential search such as a simplex,” which is often used as an efficient optimization procedure. One of the main advantages in coupling a CCD and an echelle spectrometer together is the ability to perform true simultaneous multi-element spectrometry. As different ele- ments require different plasma operating conditions the chosen set of operating parameters are necessarily a compromise. A future publication will examine the effect that the use of the SRBR has on the choice of compromise plasma operating conditions for a multi-element analysis by ICP-AES.Journal of Analytical Atomic Spectrometry March 1996 Vol. 11 21 1REFERENCES 1 2 3 4 5 6 7 8 9 10 1 1 12 13 Boumans P. W. J. M. and de Boer F. J. Spectrochim. Acra Part B 1972 27 391. Dickenson G. W. and Fassel V. A. Anal. Chem. 1969 41 1021. Scott R. H. Fassel V. A. Kniseley R. N. and Nixon R. N. Anal. Chem. 1974 46 75. Fassel V. A. and Kniseley R. N. Anal. Chem. 1974 46 lllOA. Boumans P. W. J. M. Spectrochim. Acta Part B 1990 45 779. Boumans P. W. J. M. Spectrochim. Acta Part B 1991 46 431. Leary J. J. Brookes A. E. Dorrzapf A. F. Jr. and Golightly J. W. Appl. Spectrosc. 1982 36 37. Moore G. L. Humphries-Cuff P. J. and Watson A. E. Spectrochim. Acta Part B 1984 39 915.Sweedler J. V. Jalkian R. F. Pomeroy R. S. and Denton M. B. Spectrochim. Acta Part B 1989 44 683. Scheeline A. Bye C. A. Miller D. L. Rynders S. W. and Owen R. C. Jr. Appl. Spectrosc. 1991 45 334. Bye C. A. and Scheeline A Appl. Spectrosc. 1993 47 2022. Pomeroy R. S. in Charge-Transfer Devices for Spectroscopy ed. Sweedler J. V. Ratzlaff K. L. and Denton M. B. VCH New York 1994 ch. 10. Zander A. T. and Keliher P. N. Appl. Spectrosc. 1979 33 499. 14 15 16 17 18 19 20 21 Barnard T. W. Crockett M. I. Ivaldi J. C. Lundberg P. L. Yates D. A. Levine P. A. and Sauer D. J. Anal. Chem. 1993 65 1231. Boumans P. W. J. M. McKenna R. J. and Bosveld M. Spectrochim. Acta Part B 1981 36 1031. Winge R. K. Peterson V. J. and Fassel V. A. Appl. Spectrosc. 1979 33 206. Boumans P. W. J. M. in Inductively Coupled Plasma Emission Spectroscopy Part 1 Methodology Instrumentation and Perform- ance ed. Boumans P. W. J. W. Wiley-Interscience New York 1987 ch. 4. Werner P. and Friege H. Appl. Spectrosc. 1987 41 32. Myers S. A. and Tracy D. H. Spectrochim. Acta Part B 1983 38 1227. Ivaldi J. C. and Barnard T. W. Spectrochim Acta Part B 1993 48 1265. Golightly D. W. and Leary J. J. Spectrochim. Acta Reu. 1991 14 111. Paper 5106806 A Received October 16 1995 Accepted December 5 1995 212 Journal of Analytical Atomic Spectrometry March 1996 Vol.11

ISSN:0267-9477    

DOI:10.1039/JA9961100207

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Characterization and Reduction of Silver Matrix Induced Effects in the Determination of Gold Iridium Palladium Platinum and Rhodium by Graphite Furnace Laser-induced Fluorescence Spectrometry ERIC MASERA PATRICK MAUCHIEN" AND BERNARD REMY CEAILaser Analytical Spectroscopy Group CEN Saclay DCCIDPEISPEAISPS 91 191 Gij-sur- Yvette France YANNICK LERAT Kodak European Research Analytical Laboratory Kodak Path6 CRT 71 102 Chalon-sur-SaBne France The determination of ultratraces of Au Ir Pd Pt and Rh in silver nitrate by graphite furnace laser-induced fluorescence (GF-LIF ) spectrometry is subject to strong interference by the formation of condensation. Two kinds of condensation are clearly identifiable diatomic molecules ( AgH Ag,) and condensed particles. In order to find the best analytical parameters for the determination of Au Ir Pd Pt and Rh in silver nitrate by GF-LIF a detailed study of the origin and spa tio-temporal behaviour of these condensations was carried out.Solutions for matrix interference reduction are proposed these include the use of neon as a purge gas a preliminary evaporation of part of the matrix prior to atomization and the use of a transverse heated atomizer. Keywords Graphite furnace laser-induced fluorescence spectrometry two dimensional imaging condensation phenomena silver matrix; gold; iridium; palladium platinum; rhodium Graphite furnace laser-induced fluorescence spectrometry (GF-LIF) is very well adapted to ultratrace determinations in dense matrices because of its high sensitivity and its ability to atomize high salt content samples.'92 For these reasons GF-LIF was chosen for quantitative determination in the ng g-' range of precious metals (Au Ir Pd Pt and Rh) in silver nitrate.The limits of detection obtained for precious metals in silver nitrate depend upon the intrinsic sensitivity of the technique relative to the element and upon matrix interference. Limits of detection down tong I-' can be achieved for precious metals in pure ~ a t e r ~ . ~ thus dilution of silver nitrate with distilled water to a concentration of 1-10 g 1-' is necessary owing to the low levels of precious metals in silver nitrate (ng g-'). When 20 pl of a l o g 1-1 silver nitrate solution are introduced into the furnace the resulting mass of silver after decomposition of the matrix is 130pg.Such a large amount of silver can generate interferences in the determination of precious metals. Indeed the first attempts carried out for the determination of gold in silver nitrate showed that for 130pg of vaporized silver a large non-specific fluorescence signal was superim- posed with the analytical signal of gold. The intensity and the molecular nature of this background was not compatible with the limits of detection required in our study. * To whom correspondence should be addressed. Journal of Analytical Atomic Spectrometry A better understanding of all the processes occuring during the atomization is necessary in order to be able to eliminate the perturbations induced by the silver matrix. Therefore a first assembly of a laser and a gated charge coupled device (CCD) camera was made for the spatio-temporal study of the species present during the atomization.Set-ups dedicated to furnace imaging have already been used suc~essfully~~~ for the investigation of some analyte and matrix distribution in the furnace. Non-uniform atom distri- butions during the atomization of the elements of the alu- minium group were pointed out by Gilmutdinov et al.,' using electrodeless discharge lamps a monochromator and a classical cine camera. Using hollow cathode lamps narrow bandpass filters and a CCD camera more detailed information on aluminium was obtained by Chakrabarti et aL6 The aluminium atoms and the aluminium oxide distributions were determined and atom condensations and oxidations were proved to take place during the atomization of 20 pg of aluminium.Using a dye laser as a probe enables the acquisition of pictures of species distributions in the fluorescence mode as well as in the absorption mode. Measurements performed in the absorption mode allow the visualization of the atom distributions and the condensations of the matrix. The fluores- cence mode is more selective and allows the two-dimensional imaging of each particular species. Thus atoms molecules and condensed particles can be clearly distinguished using the appropriate excitation wavelengths. In a previous paper,7 the first results of this study were presented. Details were given of condensation phenomena occuring in the centre and at the ends of the furnace during the atomization. Two kinds of condensation were identified.Diatomic mol- ecules mostly AgH and Ag are formed during the atomization even for low silver-content samples. These molecules induce strong spectral interferences as their fluorescences overlap the fluorescence of analyte atoms. Condensed particles are observed at the cooled ends of the furnace and in its central part. These condensations strongly affect the gold fluorescence intensity and distribution for very high amounts of silver relative to the case of gold in a pure water matrix. The modifications in the gold fluorescence distribution are attri- buted to the trapping of gold atoms on the condensed particles and to pre- and postfilter effects (absorption and scattering of the incident laser beam and absorption of the gold fluorescence respectively).In order to find the optimum silver matrix atomization Journal of Analytical Atomic Spectrometry March 1996 Vol. 11 (21 3-223) 21 3parameters giving the highest analytical performances for the determination of precious metals a detailed study of the condensations was carried out. The spatio-temporal evolution of the species formed during atomization and their dependance on the atomization temperature and amount of silver are presented in this paper. The origin of the condensation is discussed. The effect on the LIF analytical signal for gold of the condensation is then discussed. Solutions for matrix interference reduction are proposed according to the origin and nature of the condensations involved in the perturbations. The solutions for the reduction of matrix interference are simple due to the necessity to perform routine determinations of precious metals in silver nitrate.Three methods are proposed. The first method concerns the modification of the gas phase different purge gases are tested in order to determine the best thermal and collisional conditions for silver atomization. The second method concerns molecular formation. Since the condensations are completely (condensed particles Ag,) or partially (AgH) linked with the matrix it is possible to reduce their formation by reducing the amount of silver prior to atomization. This reduction of the amount of atomized silver is done using a high temperature pre-heating step. This solution is possible only when the analyte is far more refractory than the matrix and results are discussed according to the physico-chemical properties of the precious metals The third method concerns the use of a Transverse Heated Graphite Atomizer (THGA) which is sup- posed to reduce matrix condensations.Silver atomizations have been performed to evaluate the perturbations induced by the silver matrix in the THGA. EXPERIMENTAL Instrumental Set Up Both the set-up used for the acquisition of pictures and the conventional GF-LiF set-up are described in a previous paper.7 The THGA used is a prototype built in collaboration with the Department of Analytical chemistry Chalmers University of Technology Goteborg Sweden. It has been described by Lundberg et aL8 Temperature Program The same HGA 500 power supply (Perkin-Elmer USA) was used for experiments with the EHGA (End Heated Graphite Atomizer) or the THGA concept.Atomizations were carried out in pyrolytic graphite-coated graphite tubes with a one second ramp time. Unless specified drying was carried out at about 100 "C under 300 ml min-' internal argon flow and ashing was carried out at 1000°C under the same argon flow. Atomizations were carried out at 2200 "C in the gas stop mode. Spectroscopic Data Information on condensed particles was obtained using a CCD camera operated in the absorption mode.7 As condensed particles scatter all wavelengths no special care had to be taken for dye laser tuning. Molecular compounds were studied using either the CCD set-up working in the fluorescence mode or the classical GF-LIF ~ e t - u p . ~ AgH was excited with the laser tuned on a rotational transition of the (0-0) vibrational transition from the electronic systems X to C.Fluorescence was detected at 333 nm corre- sponding to the (0-0) AgH vibrational transition (system A to X). For CCD imaging a 130nm passband filter (maximum transmission 80% at 350 nm) enabled integration of the strong- est fluorescence bands of AgH with good rejection of the laser scattering. 21 4 Journal of Analvtical Atomic Svectrometrv. March 1996 Ag was excited at 264.9 nm (X to C electronic systems). This excitation wavelength gave a strong Ag fluorescence signal at 285 nm (probably B to X electronic transition). For CCD imaging the same passband filter as for AgH was used. This did not enable integration of the strongest band of Ag (low transmission under 300 nm) but enabled rejection of the excitation wavelength with good efficiency.Gold atoms were excited with the laser tuned on the 242.795 nm line. The fluorescence intensity was measured at 312.3 nm using the spectrometer or with the CCD camera using a 10 nm bandwidth interferential filter centred at 313 nm. Laser Probing In the experiments devoted to the acquisition of pictures the laser beam was extended with a divergent lens in order to probe the whole furnace volume. When the classical GF-LIF system was used a 3 mm diameter laser beam was adjusted in the middle of the fur- nace section. Presentation of the Pictures Pictures obtained in the fluorescence mode are presented in 'false' colours. Black corresponds to no fluorescence emission and white to maximum fluorescence emission.Intermediate colours are those of the rainbow. We have chosen to present pictures with as much colour contrast as possible the pictures have been normalized so that all the colours from black to white appear in all the pictures. The raw digital data represen- tative of the true fluorescence intensity of the studied species are presented on diagrams. One vertical and two horizontal sections named respectively VS HS1 and HS2 are extracted from the picture. Fluorescence intensity is presented uersus position in the furnace (expressed in millimetres). Fig. 1 is a scheme of the outline of the furnace showing the location of the extracted sections and positioning of the labels in the furnace (- 3 + 3 and the zero label in the middle of the furnace).Pictures were taken at a 25 Hz repetition rate. Four pictures (tl-t4) representative of an atomization were chosen to illus- trate the spatio-temporal evolution of each compound (Au Ag AgH) studied in the fluorescence mode. Pictures of the condensed particles were obtained in the absorption mode. They are presented in black and white; where dark areas correspond to absorption of the incident laser radiation. For these pictures the corresponding times VS * . . . . . . -3 . . . . . . . Q -3. . . . . . . . . . . . . +3 . . . . . . +3 . . . . . . . . . . HS 1 HS2 Fig. 1 Outline of the furnace and location of the extracted sections VS HS1 and HS2 shown in Figs. 4 6 8 and 13. Labels +3 -3 are expressed in millimetres Vol. 11( t in seconds) are indicated below the pictures.The instant t = 0 corresponds to the beginning of the ramp time. argued to explain the initiation of the condensation cloud. Firstly a slight temperature gradient probably exists between the graphite walls and the argon gas phase and the large silver RESULTS AND DISCUSSION Formation of Condensed Particles At the beginning of the atomization the gas expansion leads to the expulsion of a minor part of the sample through the injection hole and in a second step to the diffusion of the major part towards the water cooled tube ends.' When about 130 pg of silver are volatilized the resulting density of the silver atoms is similar to the initial argon gas density. If the silver atoms meet a colder atmosphere during expansion or diffusion the saturation pressure is reached and condensations appear.These condensations have been dis- cussed for several elements (Au Cu Ag Mn) by Frech and L'vovlo.ll who observed non-specific signals in atomic absorp- tion spectrometry (AAS) measurements not only at the ends of the tube but also in the centre. In the following part a description is given of the condensed particle phenomena observed in the furnace with and without the use of a L'vov platform. Explanations are based on assumptions best supporting the experimental results obtained with the CCD camera. Central condensed particles This type of condensation was observed only when atomiza- tions were performed without a L'vov platform. Pictures of condensations in the centre of the furnace recorded in the absorption mode are presented in Fig.2. In the first picture condensation appears as a diffuse disc centred in the furnace. The disc then becomes more and more dense. In the third picture two different parts of the condensation cloud are clearly visible a very dense central part surrounded by a more diffuse cloud. The dense central part then falls down towards the bottom of the furnace where it dissociates. The diffuse external cloud dissociates before touching the bottom of the graphite tube. The problem of central condensations has already been described in a previous paper,7 but this phenomenon was not completely understood at that time. Pictures of the condensed particles were obtained by recording the black-body emission. Complementary information relative to pictures in absorption was obtained by studying the emission of condensed particles.Pictures in emission showed the same central positioning of the condensed particles but also gave prominence to the presence of a condensation tail going from the injection hole to the centre of the furnace. According to the pictures of the central condensed particles taken in emission and in absorption two major causes can be pressure leads to condensation i n the colder regions. Secondly entrance of cold argon in the furnace (external argon flow) can justify the presence of the condensation tail from the injection hole to the centre of the f ~ r n a c e . ~ After the cloud formation is initiated a chain reaction effect appears. The gas phase heating process occurs mainly by conduction the cloud acting as a thermal shield.Consequently the density of its central part is increased by the trapping of more and more silver atoms. When atomizations are performed with an inserted platform no condensed particles appear. The platform concept was created to achieve better isothermal conditions during the atomization. The sample is mostly heated by radiation and slightly by conduction leading to a delayed atomization which occurs at more isothermal conditions. Peripheral condensed particles It is well known that the EHGA suffers from a non-uniform longitudinal temperature. Even after the temperature equilib- rium has been reached the ends of the furnace walls are about 1000 K colder than its central part. Consequently condensation appears at the ends of the furnace.The expansion of the peripheral condensation in the EHGA when 130pg of silver are atomized under argon atmosphere at 2200 "C is shown in Fig. 3. Condensation occurs at the ends of the tube but only part of those observed in the pictures take place in the furnace volume. Simple naked eye obser- vations of the window support volume proves that the vertical centred stripes (observed until t = 6 s) do not expand in the furnace volume but at the location of the graphite contacts and in the extension tube volume. This makes the results very consistent with gas phase temperature measurements performed at the ends of the furnace by Welz et al.' At the water cooled ends of the furnace a radial temperature gradient is created from the middle of the tube section to the graphite walls.Consequently silver located close to the walls of the furnace condenses at the cooled ends while no condensation appears in the middle of the tube section. Silver is then drained out of the tube volume and condenses in the extension tube volume in the form of verti- cal stripes. Molecular Compounds Only a few reports on molecular fluorescence as a background in analytical LIF spectroscopy can be found in the literature. Sjostrom12 has reported the fluorescence of NaCl as a spectral interference in the determination of gallium. Liang et aL2 have Fig. 2 Pictures recorded in the absorption mode showing the forma- tion of condensed particles in the centre of the furnace during the atomization of 130 pg of silver from the walls at 2200 "C.Times are indicated in seconds Fig. 3 Pictures recorded in the absorption mode showing the forma- tion of condensed particles at the ends of the furnace during the atomization of 130 pg of silver from a platform at 2200 "C. Times are indicated in seconds Journal of Analytical Atomic Spectrometry March 1996 Vol. 11 215t2 t3 t4 Fig. 4 Pictures recorded in the fluorescence mode showing the spatioteniporal distribution of Ag molecules formed during the atomization of 130 pg of silver from a platform at 2200°C (colour key see under Experimental). The excitation wavelength is 264.9 nm. The diagrams below the pictures indicate the raw digital data over three sections of the furnace (cf. Fig. 1). Black line tl red line t black dashed line t and green line t4 reported a molecular fluorescence background in the determi- nation of antimony and tellurium in tap water.Nevertheless most of the backgrounds reported in analytical LIF spec- trometry originate from blackbody radiation stray light and concomitant laser ~cattering.'*'~.'~ In our previous paper,7 we suggested that two molecular species Ag and AgH are generated during the atomization of silver. These molecules induce an important background overlapping the LIF analytical signal. A detailed study of these compounds was performed using the following diagnostics spatiotemporal behaviour of the molecules (CCD laser imaging technique); evolution of the molecular fluorescence intensities versus amount of atomized silver; and evolution of the molecular fluorescence intensities versus atomization temperature.For all the experiments the L'vov platform was used. Ag molecules Silver is vaporized at a temperature lower than those of the precious metals of interest. As a result of this atomization of silver matrix at analytical conditions creates a high silver pressure and consequently the formation of Ag molecules. Spatiotemporal evolution of the Ag molecules. The global evolution of Ag fluorescence when 130 pg of silver are atom- ized in the furnace is shown in Fig. 4. Picture t3 shows that the Ag fluorescence distribution is not homogeneous over the furnace section. The maximum fluorescence intensity is located just above the platform and a minimum intensity appears close to the graphite walls. The reduction of the Ag fluorescence at the vicinity of the walls may come from molecular dissociation on active sites of the heated carbon.Another explanation could be an increase of the fluorescence yield due to better thermal and collisional conditions achieved in the centre of the furnace. Evolution of Ag signal as a function of amount of silver [Fig. 5(a)]. An Ag fluorescence signal is detected even for 20 pg of silver nitrate. When the amount of silver is increased the height of the peak (maximum concentration) and its time duration increase (longer residence time). -Q ? 0 11' I ,'\ -' ' 130 pg 2 4 6 .- E O .- E 0.2 a I@) 2 0.1 5 $ 2 0 0 5 -0.1 -0.2 -0.3 -0.4 -0.5 -0.6 a 1 t -0.7 ' I I I I I I 0 2 4 6 8 Time/s Fig. 5 (a) Evolution of the Ag fluorescence intensity with silver iimount. Atomization from a platform at 2200°C.Peak areas are 260 1500 2500 and 4750 (arbitrary units) for 13 65 130 and 380 pg of silver respectively. (b) Evolution of the Ag fluorescence intensity with the atomization temperature for 130 pg of silver vaporized from a platform 21 6 Journal of Analytical Atomic Spectrometry March 1996 Vol. 11Evolution of Ag signal as a function of atomization temperature [Fig. 5(b)]. For a given amount of atomized silver (130 pg) signals registered at different temperatures (from 1800 to 2800°C) show two different Ag formation rates. For 2200 2000 and 18OO0C an equilibrium is reached (plateau) in the supply and removal of Ag,. For temperatures above 2200°C (Ag boiling point) the Ag fluorescence curves are more sharp. At the same time the heights of the peaks decrease possibly because of thermal dissociation and an increase in the rate of diffusional losses.AgH molecules The origin of the AgH molecules is not as clear as for Ag molecules. Among other hydride compounds AIH molecules have already been identified by Ohlsson et al.” during atomiza- tions in graphite furnaces. Ohlsson et a1.l’ concluded that AlH molecules are formed in the gas phase and that the sample solution is probably the main source of H,. A hydrogen partial pressure of 200-600 Pa was experimentally determined in the atomizer. In our experiments four assumptions can be made to explain the presence of the hydrogen pressure considering the furnace structure and the operating conditions pollution of the purge gas; entrance of air through the injection hole; pollution induced by the dilution water; and desorption of hydrogen by the graphite walls.Experiments have been performed in order to test these different hypothesis. Hydrogen free argon was produced by flowing argon through heated copper oxide (800 K) and then through a cold trap (173K) to condense water. No noticeable difference in the AgH fluorescence amplitude appeared when purified argon was used relative to untreated argon. The second and third assumptions were checked using deuterium as a tracer. A high partial pressure of deuterium oxide vapour was created around the furnace when deuterated water was vaporized in highly divided drops close to the injection hole. No AgD fluorescence appeared in the furnace when the external argon protection flow was on.In the same way when silver nitrate was diluted in deuterated water no tl t2 AgD fluorescence appeared and the AgH fluorescence was not reduced. As the three most probable external hydrogen contributions have been shown to not be responsible for the strong AgH concentration it must therefore be concluded according to our original assumptions that the main part of the hydrogen comes from the graphite crucible itself. When the graphite is brought up to 2000-2400°C hydrogen can desorb from the solid graphite or from the pyrolytic coating made of pyrolysed hydrocarbons. As a consequence it is impossible to avoid the presence of hydrogen in the graphite tube during the atomiz- ation step. Spatiotemporal evolution of the AgH Juorescence (Fig.6). The spatiotemporal evolution of AgH showed the same non- homogeneous distribution as for Ag,. The maximum fluorescence intensity appeared in the centre of the furnace with a decrease of intensity towards the graphite walls. Evolution of AgH signal as a function of amount of silver [Fig. 7(a)]. From the peak heights obtained it is apparent that an instantaneous equilibrium between dissociation and formation of AgH was achieved for 65 pg of silver. For silver amounts above 65 pg lack of hydrogen was the limiting factor for AgH formation. When the amount of silver was increased the residence time and the vaporization time increased. Consequently the integrated AgH fluorescence increased. Evolution of AgH signal as a function of atomization temperature [Fig.7(b)]. Four atomization temperatures were tested from 2000 to 2600°C. As the atomization temperature increased the fluorescence signal occured in a shorter time because the diffusion speed increased. But as hydrogen was certainly emitted over the whole tube length and by the graphite contacts the AgH signal occured over a long time despite the silver diffusion. This study showed that even for low silver content samples Ag and AgH fluorescence signals appear. At the atomization temperatures and silver nitrate concentrations studied the intensities of these fluorescence signals was strong. As these signals are temporally and spatially superimposed with the t3 t4 Fig. 6 Pictures recorded in the fluorescence mode showing the spatiotemporal distribution of AgH molecules formed during the atomization of 130 pg of silver from a platform at 2200 “C (colour key see under Experimental).The excitation wavelength is 242.7 nm. The diagrams below the pictures indicate the raw digital data over three sections of the furnace (cf. Fig. 1). Black line t red line t2 black dashed line t3 and green line t4 Journal of Analytical Atomic Spectrometry March 1996 Vol. 11 21 70 -0.2 -0.4 -0.6 -0.8 3 -1 c .- c E 2 Y -1.4 0- .- v) nr - c .c 0 a 5 -0.2 s -04 -06 3 - -0.8 -1 -1 2 -1 4 - 1 6 L - - r ~ I I I I r 1 0 2 4 6 8 10 Timels Fig.7 (a) Evolution of the AgH fluorescence intensity with silver amount. Atomization from a platform at 2200 "C. Peak areas are 950 2200 3450 and 5100 (arbitrary units) for 13 65 130 and 380pg of silver respectively.(b) Evolution of the AgH fluorescence intensity with the atomization temperature for 130 pg of silver vaporized from a platform analyte fluorescence signal the interference occuring may limit the analytical performance. Consequences of the Condensations on the Determination of Precious Metals Condensed particles and molecular formation induced inter- ference were studied in the case of gold determination. Three types of spectral interferences were created by the silver matrix diatomic molecular fluorescence; condensed particles black- body radiation and laser scattering on condensed particles. The major problem was found to originate from diatomic molecules as their fluorescence overlapped the LIF analytical signal. Condensed particles do not emit fluorescence but only continuous radiations.As the conventional GF-LIF set-up uses a gated detection this continuous background had little effect on the analytical signal. The major spectral problem induced by the condensed particles was strong laser scattering. For elements with excitation and fluorescence wavelengths close to each other strong perturbations can be expected. The spatial interferences observed in the presence of the silver matrix can be attributed to trapping and filters effects. Condensed particles have an important part in this phenomena. Spatial Interferences densed particles at the ends of the tube. When important silver amounts are atomized condensations appear prior to the total diffusion of the gold atoms creating pre- and post-filter effects and a trapping effect.For the same reasons if atomizations are performed without a platform the central condensed particles induce a darkening in the gold fluorescence. Fig. 8(a-c) summarizes these different situations with (a) a homogeneous evolution (b) an atomization perturbed by cen- tral condensed particles and (c) perturbations induced by peripheral condensed particles. For silver amounts giving weak condensations the effect of silver on gold is a decrease in sensitivity. When increasing silver amounts (Fig. 9) from 13 up to 380 yg the signal of 30pg of gold is divided by a factor of two. It appears more and more delayed and trapping quenching and filter effects by silver affect the shape of the fluorescence profile of gold. Spectral Interferences The dye laser used in our experiments is a multimode laser with a 0.2 cm-' ( 6 GHz) spectral bandwidth. The non-linear crystal (BBO) used to produce the UV wavelengths roughly doubled the spectral bandwidth of the dye laser.The Voigt profile of the 242.8 nm gold line has a spectral width of about 4 GHz in the furnace. Consequently maximum sensitivity is achieved in the optical saturation rate as the laser line covers the whole bandwidth of the gold line. The small bandwidth of the dye laser allows a good elemental selectivity. But the selectivity of the laser in excitation might be insufficient for molecular bands as their spectra present numerous transitions. Fig. 10 illustrates this problem. Rovibronic transitions (R and Q branches [0-0) vibrational transition of the [X-C] electronic systems) of AgH were recorded by scanning the laser wavelength in the silver vapour. The fluorescence collected at 333 nm exhibits a maximum each time the laser wavelength corresponds to a molecular transition.All the molecular trans- itions observed in Fig. 10 were identified according to a paper by Ringstrom et In Fig. 10 the 312.3 nm fluorescence signal of a gold hollow cathode lamp was also recorded under the same scanning conditions. It appears that two rovibronic transitions of AgH are very close to the gold line. Consequently excitation of the gold atoms at 242.8 nm (41 174.3 cm-') leads to the excitation of AgH molecules. Fig. 11 shows the resulting fluorescence spectra emitted in the furnace between 250 and 350nm when the laser is tuned on the 242.8 nm gold line. The bands observed above 325 nm are clearly attributable to AgH molecules.Part of the signal around 250 nm is due to incomplete rejection of laser scattered light. The signal at longer wavelengths can be due neither to laser scattering nor to AgH fluorescence and the peak at about 285 nm irnplie~'~ an Ag fluorescence. Laser scanning experiments have proved that Ag is indirectly excited by means of an energy transfer from AgH towards Ag,. The molecular background observed at 312.3 nm for gold determination in silver has two components AgH fluorescence and Ag fluorescence. As a consequence a gold blank cannot be simply evaluated when analysis is performed with the standard additions method. Moreover the background associ- ated noise deteriorates the detection limit of the analyte.This study of the molecular background occuring for gold determi- nation in silver shows that matrix induced effects can be very penalizing in GF-LIF because directly or indirectly induced molecular fluorescence can cover a wide range of wavelengths. In a previous paper' it was shown that spatial interferences (modification of the gold fluorescence distribution over the furnace section relative to the case of gold determination in pure water matrix) in the gold fluorescence signal appear only when high silver amounts (about 500 pg) are atomized. These spatial interferences are attributable to the formation of con- Reduction of Matrix Interferences Use of neon as purge gas Neon has a thermal conductivity three times higher than argon.Consequently a temperature equilibrium between the 218 Journal of Analytical Atomic Spectrometry March 1996 Vol. 11tl t2 t3 t4 Fig. 8 Pictures recorded in the fluorescence mode showing the spatiotemporal distribution of gold atoms in silver. The excitation wavelength is 242.8 nm. (colour key see under Experimental). (a) Atomization from a platform of 20 ng of gold in 130 pg of silver at 2200 "C. The diagrams below the pictures indicate the raw digital data over three sections of the furnace (cf. Fig. 1). Black line t red line t black dashed line t and green line t,. (b) Atomization from the walls of 20 ng of gold in 130 pg of silver at 2200 "C (beginning of the atomization); and (c) atomization from a platform of 40 ng of gold in 1000 pg of silver at 2000 "C (end of the atomization) densed particle elimination is a larger silver evacuation through the ends of the tube.Results obtained with a mixture of neon and helium are not as good as for pure neon. Helium has a high thermal conduc- tivity but a poor heat capacity. Moreover it is far lighter than air and probably rapidly escapes out of the furnace in the gas stop mode thus permitting the entrance of cold external gases. AgH fluorescence emitted from the A to X system is reduced six times by a neon atmosphere relative to an argon atmos- phere. On the other hand no change appears in the Ag fluorescence when using neon instead of argon. Collisional processes are probably involved in this phenomenon and work is now in progress to seek a better understanding of these Removal of the condensed particles under a neon atmosphere is a very interesting point for analytical applications using graphite tubes.For LIF spectrometry the improvement mainly from the reduction of the trapping and filter effects. For AAS spectral interferences can be lowered using neon. cn c 3 the injection hole. Consequently less silver diffuses towards h c .- L. c 2. m .- 0 2 4 6 8 results. Time/s Fig. 9 Evolution of the gold fluorescence intensity (30 pg of gold) with silver amount. Atomization from a platform at 2200°C. Peak areas are 900 730 650 and 470 (arbitrary units) for 13 65 130 and 380 pg of silver respectively graphite walls and the gas phase is more rapidly reached. For this reason central condensed particles are no longer visible with the CCD camera when atomizations are performed using neon.The disappearance of peripheral condensations is more surprising. A temperature gradient probably still exists in a neon atmosphere between the ends of the furnace and its central part. A possible explanation for the peripheral con- High temperature ushing step An elimination of the silver matrix prior to atomization is possible only if it does not imply strong losses of analyte in the same time. The precious metals we wanted to determine have very different refractory properties and all of them are more refractory than silver. Gold is the most volatile element and iridium the most refractory element. Platinum is an intermediate case. These three elements are representative of Journal of Analytical Atomic Spectrometry March 1996 Vol.11 21 941 174.3 cm-' I 41300.5 cm-' I R5 R6 Fig. 10 Scanning of the dye laser between 41 350 and 41 150 cm-' in a silver vapour produced in the furnace showing AgH molecular transitions (R and Q branches). The fluorescence of AgH is collected at 333 nm. The position of the 242.8 nm (41 174.3 cm-') gold line is indicated Gold \ Aa7 (induced by ASH) I IU \ + J \ I \ 1 ' round due to ASH + A@ I 1 I I I I I I I 250 300 Fluorescence wavelength/nrn 350 Fig. 11 Fluorescence spectra of the species in the furnace between 250 and 350 nm with the laser tuned on the 242.8 nm gold line (peaks heights are indicative) Table 1 Analytical parameters for the study of Ir P t and Au in silver the various situations that have to be faced for precious metal determinations.Table 1 presents the atomization conditions (temperature use of inserted platform amount of silver) the nature of the background observed at the wavelength of the analyte and the refractory properties of the element. There is a 1729K gap in temperature between iridium and gold boiling points. Table 2 presents results of an analysis performed for ashing temperatures between 800 "C (minimum temperature for total AgNO decomposition) and 1800 "C. The background (bk) was obtained with free analyte samples. The resulting net fluorescence signals (background subtracted) obtained when precious metals were added to the initial solutions are pre- sented. The signal over background ratio is indicated for each ashing temperature. The higher it is the better the analytical conditions.Iridium. The background continuously decreased when increasing the ashing temperature from 1000 to 1800°C. At Boiling point/K L'vov platform Atomization temperature/'C Origin of the background Amount of atomized silver/pg Iridium 4810 no 2600 molecular 260 Platinum 4097 no 2500 molecular (Ag,) 130 Gold 308 1 Yes 2400 molecular (AgH + Ag,) 260 Table2 Effect of high temperatures ashing step on the backgrounds and on the analytical signals for Ir Pt and Au. The corresponding backgrounds are substracted Mineralization temperature/"C 800 1000 1200 1400 1600 1800 Ir Pt Au Background Net signal (S) for Background Net signal (S) for Background Net signal (S) for (bk) 5 Pg Ir (S)/(bk) (bk) 5 Pg Pt (S)/(bk) (bk) 10 P8 Au (S)/(bk) - - - 580 610 1 710 1160 1.6 4400 900 0.2 650 5 80 0.9 530 1330 2.5 3 700 1300 0.3 760 680 0.9 260 1540 5.9 750 1200 1.6 510 590 1.1 60 1440 24 100 900 9 50 40 0.8 25 1220 49 - - - - - - 220 Journal of Analytical Atomic Spectrometry March 1996 Vol.11the same time the net fluorescence signal of 5 added picog- rammes of iridium first increased until a temperature of 1400 "C was applied and then slowly decreased for higher temperatures. It still remained higher than for 1000°C. For ashing tempera- tures higher than 1400"C iridium was carried out with silver. The best ashing temperature was found to be 1600-1800°C with an improvement of 15-30 in the resulting signal over background ratio relative to direct atomization of the matrix without a pre-heating step. Platinum.The platinum showed similar behaviour to iridium. The large improvement obtained for an ashing temperature of 1600°C was principally due to the reduction of the intense background initially measured for atomization without a high temperature pre-heating step. The net fluorescence signal of platinum in silver increased when the ashing temperature was increased from 1000 to 1200°C. On the contrary when the same experiments were performed in a pure water matrix the fluorescence signal of platinum decreased indicating a loss of atoms during ashing. Consequently in the silver matrix measurements competition was shown to exist between the loss of analyte during the ashing step and the reduction of interference (quenching trapping filters effects) during atomization.Gold. The background observed for gold was reduced only when high ashing temperatures were used (about 1600 "C). Indeed the contribution of AgH for the background was hydrogen and not silver limited. This means that the back- ground was strongly lowered only when most of the silver was preliminarily eliminated. But at the same time owing to the volatile property of gold the gold fluorescence signal strongly decreased. For ashing temperatures below 1600 "C the compe- tition between reduction of the interferences and desorption of gold during the ashing step gave a reasonably constant gold signal. For most refractory elements elimination of a large part of the silver matrix prior to atomization is a solution for the reduction of matrix interferences. For the volatile elements (Au and probably Pd) it leads to strong losses of analytes.This study also showed that the use of a high temperature ashing step for background reduction depends not only on the analyte properties but also on the nature of the background which has to be precisely known. In the case of AgH for example a reduction of the amount of atomized silver gives little improvement on the background intensity (in the case of gold analysis). THGA concept The transverse heated graphite atomizer used in our experi- ments was described by Frech and Lundberg.8 Its performance for matrix interference reduction is briefly described in the following part. This type of furnace reduces matrix condensations thanks to its mode of heating as the longitudinal thermal gradient is suppressed by the lateral heating process.Performances of both atomization techniques are discussed in the case of gold in silver nitrate to using GF-LIF spec- troscopy. Experiments were performed with or without plat- form. The temperature program used for these experiments was similar to the one used for EHGA experiments. Formation of condensed particles in THGA. The THGA was kept under an inert atmosphere by an argon flow blown under the graphite crucible. This argon flow was equivalent to the external flow in EHGA; it was maintained during all the analysis steps (drying ashing atomization). In the THGA concept peripheral condensed particles were no more visible for the CCD camera because of the homogeneous temperature along the tube and because of the external argon flow draining matrix products out of the probing volume.In contrast to EHGA the THGA was not clamped in graphite contacts and after diffusion silver was not confined in a cooled area but diffused out of the tube and was subsequently blown out by the argon external gas flow. Central condensed particles were no more visible in THGA experiments. Even when no platform was used condensations were reduced to the point where they were no more visible with the CCD camera laser imaging technique working in the absorption mode. The THGA probably helped in the reduction of condensation as it was not closed at each end by the MgF windows. Using the AAS technique Frech et ~ 1 . ' ~ observed the forma- tion of condensations in a commercial THGA equipped with longitudinal Zeeman effect background correction. This atom- izer had a relatively small tube housing and cooled magnet poles were positioned close to the tube ends.Therefore these condensations were probably particles at the ends of the tube. These contradictory results may come from differences in the furnace design and in the argon flow patterns. Another expla- nation may be a higher sensitivity in AAS experiments. In our experiments condensed particles were strongly reduced in the THGA relative to the EHGA. Molecular formation in the THGA. Diatomic molecules (Ag AgH) were formed in the THGA as in the case of the EHGA. Roughly the same fluorescence intensities were obtained for Ag and AgH using EHGA or THGA. This is not surprising when the origin of the hydrogen (desorption from the graphite volume) and the partial pressure of silver created during atomization are taken into account.Fig. 12 shows the temporal evolution of the Ag and AgH compounds when 200 pg of silver nitrate are introduced into the THGA furnace. Distributions of gold atoms in the THGA. Very interesting results concerning free atom distribution have been obtained by studying atomization of gold in silver nitrate without using a platform. Fig. 13(a) shows atomization of 40ng of gold in 130 pg of silver. Pictures were recorded in the fluorescence mode. They show that when a one second ramp time tempera- ture program is used trapping and filters effects are very important in the THGA. The two lateral linear graphite contacting bridges create a cold line on each side of the furnace where silver condenses.In these regions no gold atoms fluorescence is emitted until the temperature equilibrium is reached. The pictures in absorption [Fig. 13(b)] have been recorded under the same analytical conditions. They represent the evolution of gold atoms between t = O and the instant tl in Fig. 13(a). When the temperature is high enough atoms trapped on 0 2 4 6 8 Time/s Fig. 12 Fluorescence profiles of AgH (black dashed line) Ag (grey line) and 30 pg of gold (black line) during the atomization of 130 pg of silver from the walls in a THGA at 2200°C Journal of Analytical Atomic Spectrometry March 1996 Vol. 11 221tl t2 t3 t4 Fig. 13 @)Pictures recorded in the fluorescence mode showing the spatiotemporal distribution of gold atoms (40 ng) in 130 pg of silver vaporized from the walls at 2200°C in a THGA.The excitation wavelength is 242.8 nm (colour key see under Experimental). The diagrams below the pictures indicate the raw digital data over three sections of the furnace (cj’. Fig. 1). (b) Pictures recorded in absorption of the 242.8 nm gold line showing the spatiotemporal distribution of gold atoms in the THGA between the beginning of the ramp time and t in Fig. 13(u) condensations are suddenly released (pictures t t 3 ) . Due to a dissymmetry in the graphite crucible positioning or because of an increase in temperature of the cooling water (circular cooling system) gold atoms trapped on each side of the tube were not released simultaneously (time between these two successive releases is roughly 0.1 s).This two-step atomization can be seen in Fig. 12. The fluorescence intensity reaches a plateau (1-2.5 s) until gold atoms trapped on the sides of the furnace are released. This study showed that the same problems are encountered in both kinds of atomizers but to a different extent. The sides of the THGA are equivalent to the cooled ends of the EHGA. Condensations occur in both furnace concepts depending upon their geometry. When atomization is performed with a platform this non- uniform gold fluorescence distribution does not appear any- more because atomization of silver is delayed. In this case the heating process has been long enough to reduce the tempera- ture gradient created by transverse heating and atomization occurs under better isothermal conditions.Consequently for determinations in a dense matrix a platform should be used as far as possible. CONCLUSION Several phenomena induced by the atomization of large amounts of silver were characterized. The origin of all the condensation observed during the atomization was determined. The CCD camera and the use of LIF spectrometry as well as 222 Journal of Analytical Atomic Spectrometry March 1996 Vol. 11 absorption measurements were used as diagnostic tools for the study of the phenomena occuring in the furnace. A good understanding of the perturbations induced by the matrix enabled solutions to be developed for the reduction of matrix interference in the determination of ultratraces of precious metals. The use of neon instead of argon strongly decreases the formation of condensation clouds.To our knowledge neon has never been reported as a purge gas for the reduction of interferences in graphite furnace determinations and a com- parison between argon and neon in AAS would be interesting. The use of a high temperature ashing step is convenient for the determination of elements which are far more refractory than the matrix. Nevertheless in LIF spectrometry determi- nations care must be taken about the origin of the background as it may not be reduced in proportion to the evaporated matrix during the ashing step. The loss of analyte atoms can consequently be too high in proportion to the background reduction. Experiments in the THGA must be continued. As the THGA is not clamped in graphite contacts the removal of silver during a high temperature ashing step is certainly more efficient than in the EHGA.Moreover as it is heated over its entire length deposition of silver at the ends of the tube during the ashing step is unlikely thus reducing the amount of silver vaporized during the atomization. Satisfactory conditions for precious metals determinations using GF-LIF are now available and work is in progress to determine the limits of detection of Au Ir Rh Pt and Pd in silver.REFERENCES Dougherty J. P. Costello J. A. and Michel R. G. Anal. Chem. 1988 60 336. Liang Z. Lonardo R. F. and Michel R. G. Spectrochim. Acta Part B 1993 48 7. Remy B. Verhaeghe I. and Mauchien P. Appl. Spectrosc. 1990 44 1633. Masera E. Mauchien P. and Lerat Y. Spectrochim. Acta Part B submitted for publication. Gilmutdinov A. Kh. Zakharov Yu. A. Ivanov V. P. and Voloshin A. V. J . Anal. At. Spectrom. 1991 6 505. Chakrabarti C. L. Gilmutdinov A. Kh. and Hutton C. J. Anal. Chem. 1993,65 716. Masera E. Mauchien P. and Lerat Y. J. Anal. At. Spectrom. 1995 10 137. Lundberg E. Frech W. and Hardy J. M. J. Anal. At. Spectrom. 1988 3 11 15. Welz B. Sperling M. Schlemmer G. Wenzel N. and Marowsky G. Spectrochim. Acta Part B 1988 43 1187. 10 11 12 13 14 15 16 17 18 Frech W. L'vov B. V. and Romanova N. P. Spectrochim. Acta Part B 1992 47 1461. L'vov B. V. and Frech W. Spectrochim. Acta Part B 1992 48 425. Sjostrom S. J. Anal. At. Spectrom. 1990 5 261. Irwin R. L. Butcher D. J. Takahashi J. Wei G.-T. and Michel R. G. J. Anal. At. Spectrom. 1990 5 603. Butcher D. J. Irwin R. L. Takahashi J. Su G. Wei G. T. and Michel R. G. Appl. Spectrosc. 1990 44 1521. Ohlsson K. E. A. Cedergren A. and Frech W. Spectrochim. Acta Part B 1992 47 1525. Ringstrom U. and Aslung N. Arkiu Fysik 1965 32 19. Rosen B. in Spectroscopic Data Relative to Diatomic Molecules Pergamon Press N.Y. 1970. Frech W. and L'vov B. V. Spectrochim. Acta Part B 1993 48 1371. Paper 5/05086C Received August 1 1995 Accepted October 16 1995 Journal of Analytical Atomic Spectrometry March 1996 Vol. 11 223

ISSN:0267-9477    

DOI:10.1039/JA9961100213

出版商:RSC    

年代:1996

数据来源: RSC