摘要:

5th INTERNATIONAL CONFERENCE ON PLASMA SOURCE MASS SPECTROMETRY University of Durham U.K. 15th - 20th September 1996 The conference is organised by the Department of Geological Sciences at the University of Durham and is designed to provide a major forum for the stimulation and interchange of ideas and experiences in plasma source mass spectrometry and its associated topics. Durham is one of the most visually attractive cities in Britain and is a city small enough to be explored on foot. The great Cathedral and its ancient guardian Castle (where the delegates will be staying) are impressive features. Together the Norman Cathedral and its Castle have been designated as a World Heritage site. The University is an integral part of the City and has played a special part in shaping its character.Founded in 1832 it is the third oldest in England after Oxford and Cambridge. Invited Speakers Dr John Olesik (Plasma Dynamics & Analyser Fundamentals) Dr Grenville Holland (Laboratory Instruments) Dr Robert Hutton (Delivery Systems and Sample Introduction) Dr Cameron McLeod (Speciation) Dr Luc Moens (Speciation) Dr Garcia Alonso (Applications) Dr Scott Tanner (Novel and Future Applications) Dr Norbert Jakubowski (Instrumentation) Social Programme Icebreaker Reception Medieval Banquet at Lumley Castle Cathedral Tour Civic Reception (Burns Night) Conference Banquet in Durham Castle Dead1 ines Abstracts 1st August 1996 Registration 1 st September 1996 Submission of manuscripts 1 st November 1996 For further information contact Dr Grenville Holland The Conference Secretary Department of Geological Sciences Science Laboratories South Road Durham City DHI 3LE UK.Tel +44 (0)191 374 2526; Fax +44 (0)191 374 25101997 European Winter Conference on Plasma Spectrochemistry Gent Belgium January 72-17 7997 Since 1980 the Winter Conference on Plasma Spectrochemistry has been organized biennially in the USA and since 1983 has become an annual event which alternates between the USA and Europe. It has acquired an international reputation as the world’s premier meeting covering state-of-the-art developments in all aspects of plasma spectrochemistry. The 1997 conference to be held at the University of Gent (Ghent) Belgium will feature developments in plasma spectrochemical analysis by inductively coupled plasma (ICP) dc plasma (DCP) microwave induced plasma (MIF’) and glow discharge (GD) sources coupled to atomic emission or mass spectrometers.In addition current trends and future directions in novel sample introduction systems plasma system automation and software for data handling will be discussed by recognised world authorities with emphasis on elemental speciation studies high resolution ICP-MS spectrometry accuracy of the results quality assurance and industrial applications. The meeting will comprise oral anld poster presentations short courses and a five day exhibition of spectroscopic instrumentation aind accessories. Scientific Programme The scientific programme will include the major topics of plasma spectrochemistry. Each topic will be introduced by an invited lecturer who is an expert in the field.The main topics are 1) Instrumentation and software; 2) Sample introduction and transport phenomena; 3) Elemental speciation; 4) High resolution ICP-MS; 5) Solid sampling; 6) Glow discharge; 7) Applications; 8 ) Accuracy and quallity assurance; and 9) Stable isotope analysis. S c hed u le of Activities Preliminary title and 50-word abstracts June 15 1996 Notification of accepted papers September 15 1996 Final abstracts November 1 1996 Early pre-registration. Deadline November 1 1996 Hotel pre-registration. Deadline November 1 1996 Late pre-registration. Deadline December 15 1996 Publication of Papers The proceedings of the 1997 European Winter Conference will appear in the autumn of 1997 in a special issue of Journal of Analytical Atomic Spectrometry (JAAS).After peer review manuscripts of accepted papers will be considered for publication in these proceedings. Local Organizing Committee R. Dams University of Gent (Chairman) L. Moens University of Gent (Secretrary) J. Broekaert University of Dortmund Germany R. Cornelis University of Gent R. Gijbels University of Antwerpen F. Vanhaecke University of Gent L. Van ’t dack University of Antwerpen C. Vandecasteele University of Leuven P. Taylor IRMM Joint Research Centre EC P. Quevauviller Measuirements and Testing EC For further information please contact L. Moens Secretariat 1997 European Winter Conference Laboratory of Analytical Chemistry University of Gent Proeftuinstraat 86 B-9000 Gent Belgium. Tel +32 9 264 44 00; Fax +32 9 264 66 99; E-mail plasma97@rug.ac.be; Web page http://www.rug.ac.be.The Society for Applied Spectroscopy. ..KEEP ABREAST OF NEW AND INNOVATIVE TECHNOLOGY .... Our Society can provide you with the latest in research technology and practical knowledge. We also provide the essential link for networking with your peers - with options such as a membership directory internet access and an annual conference. There are awards for achievements student programs and on-line services. Membership entitles you to receive a subscription to Applied Spectroscopy. This monthly publication features papers on all areas of spectroscopy and contains advertisements from leading companies in the field. It is a valuable resource for those who wish to remain informed of today's technology and research and for those providing quality resource materials.You will be eligible to receive reduced rates on other scientdlc journals e.g. Spectrochemical Acta B JAAS and Analytical Chemise. Receive a discount on the registration fees for FACSS the worlds' leading conference in spectroscopy and analytical chemistry. We provide educational courses at a discount to members which can be used as a tool to increase on-the-job performance. Learn hdamental and practical instnunentation analytical methodology and sample applications through these educational courses. We are confident you will be impressed and will want to become a member of our prestigious Society. We look forward to hearing from you in the near hture. Please fill out the form below and fax or mail it to SAS OOl(301) 694-8122 - Phone 201 B Broadway Street OOl(301) 694-6860 - Far Frederick MD.21701 USA TinaKsas@aol.com - E-mail YES enroll me as an SAS member today! 8 8 8 RATES USA CANADA OUTSIDE USA MEMBER $65 .OO $80.00 $105.00 RETIREE $20.00 8 STUDENT $20.00 $35.00 $ 60.00 Please circle one! 8 8 8 Name 8 8 Company 8 8 Province Postal Code Country 8 8 Phone Fax E-mail (include country code) 8 Address 8 8 8 8 MY position fits the following category OAcademic OInstrument Company OConsultant OGovernment ORetiree OStudent OClinical Lab OCommercial Lab OIndustry(Type ) 8 OOther Mycheckisenclosed El Invoice Me 0 Bill my MCNISNAMX 0 8 Credit Card Number 8 8 Expiration Date 8 8 8 8 8 8 8 8 8 8 8 8 8 signature 8 8 8 JAASPROM CHECKS MUST BE IN US FUNDS DRAWN ON A US BANK! 8 8 8 8 8 8 8 . . . 8 8 8 8 8 8 8 8 8 8 8 8 8 8 = = = = 8 8 8 8 8 8 8 8 = 8 8 8 8 8 8 = 8 = 8 8 8 8 8 8 8 = = = = = = =I t Can’t keep up with your reading? Let Annual Reports in the Progress of Chemistry guide you to the latest advances in chemical research. Part C is specifically devoted to physical chemistry. Subscribe to Annual Reports Part C now and create time for yourself. To orclcr plc-nse contact Tlw I<()) al Soc.ic.ly of Clicmistry ‘ I i i r ~ ) i t t 1)islril)rilioii Scrviccs T,td I~lac~l~lioiw I<ontl 1,ctchworth 14rt.1~ S(;O 1 1 IN Unitcd Kingdom “ +44 (0)1402 072555 lG\ +44 ( 0 ) 1402 480047 For further information please contact Stella Grccn Thc Royal Socicty of Chemistry Thomas Graham House Science Park Milton Road Cambridge CB4 4WF Unitcd Kingdom Tcl +44 (0)1223 420066 Fax +44 (0)1223 423429 K-mail sales@rsc..org WWW http://(,hcmistry.rsc..olFJ1sc./ RSC Members should order through thc Membership Administration Department at our Cambridge addrcss.

ISSN:0267-9477    

DOI:10.1039/JA99611BP005

出版商:RSC    

年代:1996

数据来源: RSC

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/JA99611FX017

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/JA99611BX019

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

9611803 804 805 9611806 96/1807 9611808 961 961 809 810 9611811 96/18 12 9611813 Moissette A Shepherd T. J. Chenery S. R. Calibration strategies for the elemental analysis of individual aqueous fluid inclusions by laser ablation inductively coupled plasma mass spectrometry. J. Anal. At. Spectrom. 1996 11(3) 177. (British Geol. Surv. Keyworth Nottingham UK NG12 5GG). Taylor D. B. Kingston H. M. Nogay D. Koller D. Hutton R. C. On-line solid-phase chelation for the determination of eight metals in environmental waters by inductively coupled plasma mass spectrometry. J. Anal. At. Spectrorn. 1996 11(3) 187. (Dept. Chem. and Biochem. Duquesne Univ. Pittsburgh PA 15282 USA). Szpunar J. Schmitt V. O. Lobinski R. Monod J.-L. Rapid speciation of butyltin compounds in sediments and biomaterials by capillary gas chromatography- microwave-induced plasma atomic emission spec- trometry after microwave-assisted leachingldigestion.J. Anal. At. Spectrom. 1996 11(3) 193. (Lab. Photophys. et Photochim. 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ISSN:0267-9477    

DOI:10.1039/JA996110205R

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Equilibrium Plasma Composition in U-shaped DC Argon-stabilized Arc IVANKA HOLCLAJTNER-ANTUNOVIC GORDANA MALOVIC MIRJANA TRIPKOVIC AND ZORAN RASPOPOVIC Faculty of Physical Chemistry P.O. Box 137 11001 Belgrade Yugoslavia Institute of Physics P.O. Box 57 11 001 Belgrade Yugoslavia The calculation of the equilibrium plasma composition of a U-shaped argon-stabilized dc arc burning at 1 bar is given. The calculation procedure based on the minimization of Gibbs free energy was applied in the temperature range 1000-9000 K assuming a state of local thermodynamic equilibrium. The results obtained were compared with experimentally determined values of plasma parameters (temperature electron density) and spectral line intensities with consideration of the local thermodynamic equilibrium state in this arc source.Keywords U-shaped direct current arc; atomic emission spectrometry; equilibrium plasma composition The U-shaped dc arc is a special type of horizontal arc stabilized by the gas vortex technique.' This arc is primarily characterized by a high stability simple experimental set-up and low consumption of gas. It is easy to change the composi- tion of its main components as well as of trace components and thus to influence the chemical reactions which occur under various physical conditions in relatively large plasma volume. The investigations to date point out substantial differences in the spatial distribution of spectroscopic emission of various components as compared with those in conventional arc sources. Plasma parameters as well as the main spectroscopic properties of U-shaped arc as an excitation source are however very similar to the conditions in an inductively coupled argon plasma (ICAP) which is one of the most frequently used spectrochemical sources.The similarity of these two sources is manifested in the existence of a high temperature high electron density core as well as spatial displacement of emitted radi- ation density. However while in the ICAP this displacement is primarily realized in the axial direction; in a U-shaped arc it is realized exclusively in the radial direction. The detection limits of different elements determined by ICAP2 and by the U-shaped arc3 (as an excitation source) are usually of the same order of magnitude. In the case of easily ionizable elements the detection capabilities of a U-shaped arc are much better.4 In this paper the equilibrium plasma composition has been calculated and compared with experimental results. The results help to explain better the mechanisms of formation ionization and excitation of various particles in the system.Spectroscopic and theoretical analyses of plasma composition are given for an arc that burns in air and is stabilized only by an Ar flow as well as in the case of introducing a water aerosol into the plasma. Also the influence on the equilibrium composition of the presence of K and Ti in the water aerosol has been considered. EQUILIBRIUM COMPOSITION CALCULATION In calculation of the equilibrium plasma composition the method based on the location of the Gibbs free energy function minimum was used. The mass action law and quasi-neutrality condition were taken into account.' This is the general method Journal of Analytical Atomic Spectrometry for the determination of the composition in equilibrium systems where chemical potentials e.g.Gibbs free energies of all particles in the system at the given temperatures are known. Supposing that the plasma is in a state of chemical equilibrium including dissociation ionization and radiative capture pro- cesses it is considered to be a monophase system with a constant ratio of main and added components in a stationary state. The composition of neutral (molecules radicals and atoms) and charged (positive and negative singly charged and doubly charged particles) components was calculated by means of a computer using an iterative procedure by the steepest- descent method described in ref.6. The iterative procedure was carried out until the differences in the Gibbs free energy values or molar fractions in two consecutive cycles were lower than a criterion chosen in advance. The necessary Gibbs free energy data were taken from refs. 7 and 8 or calculated for the high temperature region. The number of components in the system was selected so that it included the most probable collision processes in plasma at 1 bar and temperatures corresponding to the radial temperature distribution for this type of discharge in accordance with the results of emission spectroscopic diagnostics. All the calculations were performed for a multicomponent system (the maximum number of components was 33) at a pressure of 1 bar and a temperature range of 1000-9000 K.EXPERIMENTAL The essential parts of the arc device are given in detail elsewhere.' All the measurements were performed in the side- on direction. Photoelectrically measured lateral profiles of spectral lines were transformed radially by means of Abel integral inversion. The spectral analysis of radiation emitted from the plasma was performed in the region from 250 to 750nm. The excitation temperature was determined from Boltzmann plots of argon atomic lines in the central part of the plasma core and of titanium ionic lines in the plasma region from 1 to 4mm from the arc axis. Argon I and Ti I1 spectral lines and their transition probability values were selected from ref. 9.In the plasma periphery the rotational temperature was evalu- ated from the rotational intensity distribution of OH bands. The electron number density was determined from Stark broadening of H in the plasma core applying the theory of Vidal et a1." In the plasma periphery n was determined applying the Saha ionization equation and the ratio of the line pair Mg I1 279.5 Mg I 285.2 nm. RESULTS AND DISCUSSION Equilibrium Composition of 'Dry' Plasma For the calculation of the equilibrium composition of the arc plasma into which the water aerosol has not been introduced (the so called 'dry' plasma) the initial composition system was Journal of Analytical Atomic Spectrometry May 1996 Vol. 1 1 (325-330) 32595% Ar 3.85% N (from air) 1.03% 0 (from air) 0.03% water (due to air humidity) and 0.1% C (from the electrodes). The results obtained for neutral and charged components are presented in Figs.1 (u) and (b) respectively. Stable molecular components such as 02 H N CO present in air exist mainly in low temperature region at about 3000K which corresponds to the plasma periphery. At higher temperatures these components are decomposed. Components such as CN NH NO CO and N2+ are more stable at higher temperatures. These results are in agreement with experimentally determined spectra emitted from a U-shaped arc registered in the region of 250 to 750 nm. Namely the emitted spectra registered from a 'dry' plasma contain the molecular bands of CN N N,' OH NO and NH which is not typical for an arc plasma.'' Also the spectral lines of non-easily ionized elements (NEIE) f ,o oL 520 0 -1 18 16 14 12 10 8 6 4 2 0 0 1 2 3 4 5 6 7 6 9 ~ 1 1 0 ~ K Fig.1 components; (b) charged components Equilibrium plasma composition of 'dry' plasma (a) neutral 326 Journal of Analvtical Atomic Svectrornetrv. Mav 1996. such as Ar H 0 and C are superimposed over the band spectra. The experimentally measured radial distributions of the radiation density of band heads of N N,+ CN NO and NH as well as of spectral lines of Ar 0 and H decrease radially from the plasma centre to the plasma periphery.12 These species are emitted from the plasma core corresponding to the temperature region from 5000 to 7000 K and expanding up to 3 mm from the arc axis. On the other hand the maximum of OH band head intensity is in the plasma periphery where this component is still stable.The equilibrium compositions of charged components show that the ionization of argon is the main process responsible for the production of electrons in plasma core while in plasma periphery the main source of electrons is the ionization of NO. C 18 14 - 12 - 10 - 8 - 6 - 4 - 2 - Fig. 2 Equilibrium plasma composition in the presence of water vapour (a) neutral components; (b) charged components Vol. 11Equilibrium Composition of ‘Wet’ Plasma As the trace elements are introduced into the arc (when it is applied as a spectrochemical source) in the form of aqueous solution it was of interest to calculate the equilibrium composi- tion of an arc plasma in the presence of water aerosols (‘wet’ arc). On the basis of the experimental results it is supposed that the system contains lower levels of nitrogen and carbon than in the case of a ‘dry’ plasma because of Ar i.e.the system consists of 99.3% Ar 0.35% N 0.3% H 2 0 and 0.05% C. The calculations of the equilibrium particle densities for this 25-component system are shown in Fig. 2. When comparing these results with those for a ‘dry’ plasma the only differences in the quantitative ratio of the individual components are those owing to the difference in the composition of the starting system. Thus the particle densities of the components that gave emission in a ‘dry’ plasma are lower in the presence of water owing to the lower quantity of nitrogen. It is also known that the presence of water owing to the high thermal conductivity of hydrogen causes the formation of a high temperature core with a very steep gradient.Therefore it could be expected that the excitation conditions are different as compared with a ‘dry’ plasma. The lower concentrations of all the components except Ar and the change of excitation con- ditions (which are not the most suitable ones for the emission of the present molecular components) can explain the results determined experimentally. That is the spectra emitted by a ‘wet’ plasma are characterized by the disappearance of the molecular bands of N2 N2+ CN NO and NH. The spectra recorded from ‘dry’ and ‘wet’ plasmas in the spectral region from 375 to 400 nm are presented in Fig. 3. It is evident that a ‘wet’ plasma is characterized by the lack of the molecular bands and increase of atomic Ar and H lines.Under these conditions the radiation densities of the OH band heads are increased while their maximum in radial distribution is shifted towards the arc axis. This is in accordance with the fact that the quantity of the OH component is higher in a ‘wet’ plasma particularly in the plasma periphery (temperature about 3000-4000K). Because the presence of water in the plasma causes the formation of a narrow plasma core with a steep gradient the optimal region for the formation of OH radicals is also shifted towards the plasma centre. Under such a condition the emission of Ar atomic lines is improved in the plasma core as compared with that of the ‘dry’ plasma. The fact that in the presence of water aerosols the band spectra of molecules and radicals disappear makes this arc very suitable for spectral analysis. Owing to the formation of a high temperature core and improved ionization of Ar in this region higher electron number density values are also expected for a ‘wet’ plasma.Equilibrium Composition of Plasma in the Presence of Potassium It was of interest to investigate how some easily ionizable elements influence the composition of the plasma. Previous investigations carried out on a U-shaped Ar-stabilized plasma arc revealed that the introduction of K as an aqueous aerosol caused an increase in intensity of all elements except argon a decrease of intensity of the background and a change in ab~orption.~,’~ Thus the addition of K was shown to be very suitable for the optimization of excitation and ionization conditions in this arc when used a a spectrochemical source of radiation as well as an easily ionizable element which modifies the plasma composition. For these reasons the influ- ence of K on the equilibrium composition of plasma was studied and correlated with the results of spectral emission analysis. The initial composition of the system was 99.3% Ar The temperature dependence of particle densities was calcu- lated and is shown in Fig.4. The presence of K in the plasma primarily influences the composition of charged particles in the temperature region below 6000 K. In the high temperature 0.2992% HZO 0.0008% K 0.35% N 0.05% C. I I 1 400 395 390 385 3 80 375 nm’ Fig. 3 Recorder tracing of the spectra of the U-shaped arc burning in (a) air (‘dry’ plasma); (h) the presence of water aerosol (‘wet’ plasma) Journal of Analytical Atomic Spectrometry May 1996 Vol.11 32718 ‘6 . .................... - g’’c 0 1 2 3 4 5 6 7 8 9 ~ 1 1 0 ~ K Fig. 4 (a) neutral components; (b) charged components Equilibrium plasma composition in the presence of potassium zone i.e. in the plasma core there were no changes in either electron density or the density of other charged particles which was in accordance with the experimental re~u1ts.l~ Both the emission and absorption spectroscopic measurements show that atomic K is present mostly in the low temperature zone of the plasma. The ionic K lines were not detected from this excitation source due to their high excitation potentials. However our theoretical calculations have shown that ionic K is the dominant ion among all the charged particles in the same plasma region. It can be concluded that the influence of K is mainly in the low temperature zone where the process of its ionization causes a considerable increase in electron density and thus also in the electric conductivity.Therefore the ioniz- ation equilibrium is shifted in this region in the sense of a decrease in the density of charged components in favour of neutral ones. It is known that the effect of elements with low ionization potentials in thermal plasmas is based on the increase in electron density and the decrease in temperature. As in this arc K is present predominantly in the periphery region it influences by this mechanism the plasma parameters in this region.Decreasing the electron density gradient and cooling the plasma periphery it leads to an increase in the core temperature as was found experimentally. Equilibrium Composition of Plasma in the Presence of Titanium It was of interest to investigate the influence of Ti on the composition of a U-shaped plasma due to its application in plasma technology. Also titanium was used as a thermometric species in excitation temperature determination in the middle plasma zone ( 1 < r < 4 mm). Considering neutral components (the temperature distri- bution of which is given in Fig. 5) it can be noticed that Ti exerts the main influence in plasma periphery. Namely this region (below 4000 K) is characterized by the formation of T i 0 and Ti02 molecules. The density of neutral atomic Ti is highest at 3000-5000K. The presence of molecular T i 0 and TiO causes the emission of T i 0 band spectra in the VIS region.This strong emission can explain the differences that appear in the photographs of an arc plasma for ‘dry’ and ‘wet’ conditions in the presence of Ti. It is visually evident that an increasing quantity of Ti introduced into the plasma causes the broadening of the plasma shining zone as compared with a plasma with pure water aerosols and a ‘dry’ plasma. In the plasma periphery the ionization of Ti strongly contrib- utes to the over-all electron number density so that broader plasma zone is formed. Comparison of Experimental and Calculated Plasma Parameters Starting from the calculation of the equilibrium composition of a U-shaped Ar-stabilized dc arc we tried to compare the obtained results with the experimental measurements.Firstly the excitation temperature determined experimentally from the Ti ionic lines was compared with the value of TLTE from the theoretical calculation of equilibrium composition for those n values corresponding to the values determined e~perimentally’~ from the H linewidth (Fig. 6). The values are in good agree- ment particularly in the case of the arc burning in the presence of 0.5% KCl [Fig. 6(b)]. One can conclude that the addition of K leading to an increase in the electron density particularly in the peripheral region of the plasma causes to a certain extent narrowing of the arc column and thus a slight increase in its temperature. Besides by its ionization K contributes to the further establishment of LTE conditions in plasma.This conclusion is also supported by experimental measurements of the so-called non-equilibrium factor br,15 which in the plasma in the presence of K is nearer to unity than in the presence of water aerosols (Fig. 7). On the basis of the theoretically determined electron density the radial distribution of the ionization degree of the elements of various ionization potentials was calculated (Fig. 8). Within the arc column region there is not a substantial difference in the degree of ionization for trace elements in the presence and absence of K. However in the peripheral region (r > 3.5 mm) owing to the increased electron density in the presence of K suppressed ionization in certain elements causes a decrease in their degree of ionization. Argon as the main plasma compo- nent and an element of high ionization potential is ionized to a somewhat greater extent in the plasma centre in the presence of K owing to the small increase in temperature.Knowing the equilibrium density of the particles and the plasma parameters it was possible to calculate the radial distribution 328 Journal of Analytical Atomic Spectrometry May 1996 Vol. 1120 18 16 14 12 10 a 6 4 2 m- E 2 0 520 0 -I 18 16 14 12 10 8 6 4 2 0 \ Ar',C 0 1 2 3 4 5 6 7 8 9 T/103 K Fig. 5 Equilibrium plasma composition in the presence of titanium (a) neutral components; (b) charged components of the relative intensities for certain elements and to compare them with those determined experimentally.The comparison was carried out for Ar as a major component and phosphorus and magnesium as trace components (Fig. 9). For magnesium results are shown both for atomic and for ionic components. Based on these results it follows that there is a very good accordance in the forms of distribution for elements with high ionization potentials (regardless of whether major or trace components are involved). Discrepancies appear for Mg par- ticularly in the case of an atomic component. One could conclude that in the case of elements ionized in plasma to a greater extent the LTE model is not quite valid particularly outside the plasma core. It is also necessary to take into account transport processes particularly the effect of radial 9000 8000 7000 6000 SO00 4000 3000 .-I..0 1 2 3 4 5 6 rlrnrn Fig. 6 Comparison of experimentally determined and theoretically calculated temperatures (u) water aerosols; (h) aerosols with 0.5% KCl 4 1 QL 2 I 0 A A Fig. 7 Comparison of the radial distribution of the nonequilibrium parameter for water aerosols and 0.5% KCI electric field for the purpose of more complete explanation of the observed phenomena. CONCLUSION The calculation of the temperature distribution of the equilib- rium composition of an Ar-stabilized horizontal arc in addition to the knowledge of radial distribution of plasma parameters ( T ne) enables a detailed explanation to be given of spectral characteristics of this spectral radiation source. The calculations show that the so-called 'dry' plasma is a very complex system in which in the high temperature zone atoms and ions of elements with high ionization potential and electrons formed by means of Ar ionization are dominant while in the low temperature peripheral zone neutral molecular species dominate and electrons originate from NO ionization.Such a plasma equilibrium composition is in accordance with the experimentally registered spectral composition in which the atomic and ionic lines of NEIE together with molecular bands are superposed over a continuum. The calculated equilibrium composition of the so-called 'wet' Journal of Analytical Atomic Spectrometry May 1996 Vol. 1 1 3290 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 r /mm Fig. 8 Radial distribution of trace elements ionization degrees (a) water aerosols; (b) aerosols with 0.5% KCI 0 1 2 3 1.2 1 .o 0.8 0.6 0.4 0.2 0 1 2 3 4 ( d ) P I 253.6 nm -.1.8 . 0 . I 0 1 2 3 4 f /mm Fig. 9 Comparison of radial distribution of experimentally deter- mined and theoretically calculated relative intensities (a) Mg I 285.2 nm; (b) Mg I1 279.5 nm; (c) Ar 1426.3 nm; ( d ) P I 253.6 nm plasma differs from that of the 'dry' plasma in the quantitative ratio of certain components in accordance with the differences in initial composition of these systems. However experimen- tally recorded spectral composition of a 'dry' plasma changes substantially in the presence of water aerosols in that a total disappearance of all the molecular species except OH occurs. This characteristic makes this arc suitable as a spectrochemical radiation source. The explanation of this phenomenon lies in the already mentioned changed initial composition and in changed plasma parameters.The addition of K as an easily ionizable element leads to further changes in the plasma composition particularly in the peripheral low temperature region where an increase in the electron density occurs due to K ionization which results in the suppressed ionization of atomic and molecular species and leads to an increase in 0- and H - concentrations by means of a radiative capture process. In this way in the peripheral region a change in the degree of ionization of certain trace elements occurs and K also leads to an approach to the LTE state. Finally the addition of Ti due to the formation of molecular components causes a change in the spectral characteristics of the plasma and also an increase of n in the periphery.The comparison of theoretical and experimental data shows that the applied theoretical model is satisfactory in the descrip- tion of NEIE spatial distribution. In the case of easily ionizable elements radial distributions of emitted radiation densities cannot be explained completely on the basis of the calculated equilibrium concentrations and measured plasma parameters. The observed displacement of elements across the radius where the radial positions that correspond to the maximum radiation intensities are correlated to the first ionization poten- tial of element cannot be explained without taking into account mass transport of particles particularly in the radial direction. The Ar-stabilized U-shaped arc has the high detection power for traces and provides good reproducibility of results.It is economical to purchase and run using 10 times less argon than an ICAP. The results given in this paper enable a better understanding of excitation processes in this arc source. This work was supported by the Serbian Ministry of Science and Technology under project 0 1 1 1. REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 MarinkoviC M. and Vickers T. J. J. Appl. Spectrosc. 1971 25 519. Winge R. K. Peterson V. J. and Fassel V. A. Appl. Spectrosc. 1979 33 206. MarinkoviC M. and AntonijeviC V. G. Spectrochim. Acta 1980 35B 129. PavloviC M. S. PavloviC N. Z. and Marinkovic M. J. Anal. At. Spectrom. 1989 4 587. White W. B. Johnson S. M. and Dantzig G. B. J. Chem. Phys. 1958 28 751. Radovanov S. B. Holclajtner-AntunoviC I. and TripkoviC M. Plasma Chem. Plasma Proc. 1989 9,445. Stull D. R. and Prophet H. JANAF Thermochemical Tables. Nat. Stand. Ref. Data Ser. 1976 Midland MI vol. 37. Gurvich L. V. Thermodynamic Properties of Individual Substances Izd. A. N. SSSR Moscow 1962 (in Russian). Wiese W. L. and Fuhr J. R. Phys. Chem. Ref. Data 1975 4 320 323 329. Vidal C. R. Cooper J. and Smith E. W. Astrophys. J. Suppl. Ser. 1973 25 37. Pearse R. W. B. and Gaydon A. G. The IdentiJication of Molecular Spectra Wiley New York 1976. Holclajtner-AntunoviC I. MaloviC G. and TripkoviC M. Spectrosc. Lett. 1993 26(6) 1103. MarinkoviC M. and DimitrijeviC B. Spectrochim. Acta 1968 23B 257. MaloviC G. TripkoviC M. and Holclajtner-AntunoviC I. Contrib. Plasma Phys. 1994 34(6) 773. Caughlin B. L. and Blades M. W. Spectrochim. Acta 1984 32B 1583. Puper 610001 8 E Received February 2 1996 330 Juurnul of Analytical Atomic Spectrometry May 1996 Vul. 11

ISSN:0267-9477    

DOI:10.1039/JA9961100325

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Determination of Trace Amounts of Boron by Microwave Plasma Torch Atomic Emission Spectrometry Using an On-line Separation and Preconcentration Technique QUN JIN HANQI ZHANG FENG LIANG WENJUN YANG AND QINHAN JIN* Department of Chemistry Jifin University Changchun 130023 Chinu A new system for the determination of trace amounts of boron by flow injection microwave plasma torch atomic emission spectrometry is proposed. In the system a strongly acidic cation-exchange column is connected in series with a strongly basic anion-exchange column. By the combined function of the two columns interferences (e.g. iron) in the sample solution are removed and the analytical performance improved. Optimization studies illustrate the dependence of the analytical signals of boron on various parameters including observation height microwave forward power flow rates and acidities of the sample solution and the eluents in both columns.The effect of concomitant ions on the relative emission intensity of boron is also examined. Detection limits of 0.0055 mg 1 - ' at 45 samples h-' and 0.0018 mg I-' at 20 samples h-' with a precision of 4.2% at the 0.020 mg I-' level of boron were achieved. With sample columns of 1.25 and 5.0 ml enrichment factors of 22 and 88 were obtained respectively. The proposed system has been applied to the determination of trace amounts of boron in steel samples and the results obtained were satisfactory. Keywords Boron; microwave plasma torch; atomic emission spectrometry on-line separation; preconcentration Several atomic spectrometric techniques including capacitively coupled microwave plasma atomic emission spectrometry (CMP-AES),' microwave-induced plasma (MIP) AES,2 flame atomic absorption spectrometry ( FAAS),3*4 direct current plasma (DCP) AES,' inductively coupled plasma (ICP) AES,6-" ICP mass spectrometry (MS),13 have been developed for the determination of boron.The determination of trace amounts of boron by AAS is not satisfactory as boron is a refractory element. Although ICP-AES and ICP-MS are suit- able for such determinations the purchasing and operating costs are relatively high. In comparison with an ICP micro- wave plasma (MWP) AES is relatively low cost. However very little has been carried out so far on the determination of trace amounts of boron by MWP-AES. Murayama et al.' employed a CMP to determine boron directly.They used a 400 W discharge in argon as an excitation source and the nebulized sample was introduced tangentially into the coaxial waveguide through a sample inlet. Lichte and Skogerboe2 used a low powered (100 W) argon MIP with a desolvation system to determine boron where a design modification to the Evensen cavity was made an impedanse matching device consisting of 20 gauge copper wire was attached to the fine tuning stub insulated with glass tubing to prevent shorting to the cavity wall and extended out from the cavity at nominally 45" to its axis thus the tuning problem was reduced; on the other hand * To whom correspondence should be addressed. Journal of Analytical Atomic Spectrometry the plasma was run in a quartz tube axially through the cavity instead of using the more conventional transverse configur- ation thus ignition and maintenance of the plasma (even when the argon support gas was saturated with water vapour) were possible.An end-on optical arrangement was utilized for both plasmas. However both methods are not sufficiently sensitive (the detection limits of the former and the latter were 0.030 and 0.010 mg 1-' respectively) for the determination of boron and no practical samples especially not those containing large amounts of iron have been analysed using these two tech- niques. The presence of iron in the samples can cause analytical difficulties in the determination of boron because iron has emission lines at 249.77 (Fe 11) 249.65 and 249.70 nm (Fe I) which produce spectral interferences to the more sensitive lines of boron at 249.77 and 249.68 nm. More recently a new excitation source the microwave plasma torch (MPT) has been reported by Jin et al.14 The MPT discharge possesses an ICP torch-like configuration. This configuration greatly improves its tolerance to the intro- duction of wet aerosols'' compared with that of traditional MIPS.However matrix effects are still significant. Matrix interferences in the atomic spectrometric determi- nation of trace amounts of boron have been studied pre- v i ~ u s l y . ~ - ~ * ' ~ These interferences include spectral interferen~e,~ interference from fluorides' and those from other elements present in steeL9.l6 To eliminate the matrix interferences a pre- separation procedure with a column filled with a chelating ion exchanger (Amberlite IRA-743 ion-exchange resin) was employed.16 However this type of resin does not fully meet the requirements as an ideal packing material for the determi- nation of boron in steel samples because a higher pH (5-6) of the sample solution is required for the chelating resin to complex the metals completely and so hydroxide precipitation of Fe3+ cannot be avoided when a large amount of iron is present.Since the concentration ratio of iron to boron in steel samples can exceed lOoOO:l the determination of trace amounts of boron will definitely be affected and this is a well known problem to be solved in the determination of boron in steel because of the spectral interference from iron. Other separation methods employed in ICP-AES for the determi- nation of boron in steels include di~tillation,~ extraction' and pyrohydroly~is.~ Although these methods succeeded in elimin- ating iron interference virtually none of them can be easily automated.In the present work a non-selective strongly acidic cation-exchange column was employed and the separation was performed under acidic conditions (pH 2) in an on-line flow injection (FI) mode. Therefore almost all types of cations were separated from boron and the precipitation of some metal hydroxides was prevented. This is particularly valuable for separating trace amounts of boron from large amounts of iron. To improve the sensitivity of the determination of boron by Journal of Analytical Atomic Spectrometry May 1996 Vol.I I (331 -337) 331ICP-AES anion-exchange chromatography has been employed to adsorb boron as (BF,)- . However the process was an off- line one and the precision was not satisfactory.'2 Boric acid is a weak acid and can exist in various forms ( H2B03- HB03,- BO3,- and H,BO,). Which form dominates amongst them depends on the respective fraction existing in solution (6). The expressions of 6H3R0 6H2BO3- hHBO32- and 6B033- are as follows (1) &,BO3- =ka,CH+ I'IJ (2) 8HB032- = kalka2[Hf1/J (3) 6 R 0 3 3 - = kalka2ka3/J (4) 6 H m 3 = CH + i 3 / ~ where k,,(= k (= 10-'2.74) and ka3(= 10-'3.80) are acid dissociation constants for the first second and third ionizations of boric acid respectively; J = [H+]3+kal[H+]2+kalka2[H+] +k,,k,,k,,; and [H'] is the hydrogen ion concentration.It is indicated in eqns. (1-4) that when [H'] is around 1 x lo-'' (pH 11) boric acid will exist mainly as H2B03- and when [H'] is about 1 x lo- (pH 2) it will exist mainly as H3B03. In the present work a micro- column packed with Type VS-I1 strongly basic anion exchange fibre was added following the cation-exchange column. Because the fibre is a network polymer in which the distance between active groups is larger than that in common anion exchangers and the active groups are on the surface of the fibres the fibre possesses a quicker exchanging and desorbing capability than that of common anion exchangers and the resulting peak shapes of the emission signals (plots of intensity uersus time) are sharper. Thus since peak height was used to measure the emission intensity the enrichment factor ( E F ) for boron is enhanced.Boron is adsorbed on the fibre in the H2B03- form in a basic medium (pH 11.2) and then eluted in the H3B03 form by HCl (1 moll-'). In addition an FI technique was also implemented in the system to improve the sample through- put and absolute sensitivity and to save on sample consump- t i ~ n . " . ' ~ The system has been applied to the determination of boron in some steel samples and the results are satisfactory. EXPERIMENTAL Instrumentation The plasma was sustained with an MPT assembly fabricated in this laboratory the design of which has been described previo~sly.'~ The plasma was operated with argon as both carrier and support gases and was viewed in a side-on mode. The sample introduction system consists of an FI system (Fig.1) with a peristaltic pump (LZ-1010) and two sign rotary valves a pneumatic nebulization (PN) system with a pneumatic nebulizer and a nebulizing chamber (both from the Beijing Vast Time Scientific Manufacturing Laboratory) and a desolv- ation system (DS) with a condenser and a desiccator containing concentrated H2S04. Other equipment used includes a micro- wave generator (WB-WC 2450 MHz Haiguang Instrument) a monochromator (Model WDG 500-11 Beijing Second Optical Instrument) a photomultiplier tube (PMT) (R456 Hamamastu) and its power supply (FH-4268 Factory No. 261 of China) and a chart recorder (Model 056 Hitachi). The operating conditions are as listed in Table 1 unless stated otherwise. Reagents All reagents used were of analytical-reagent grade and prepared with de-ionized water. All solutions were stored in polyethylene bottles.The purity of argon used as both carrier gas and support gas was 99.99%. A stock standard boron solution (loo0 mg 1-') was prepared m~ m i d ml min" Load 0 Elution Fig. 1 FI separation and preconcentration system. S sample; R1 reagent 1 (HCl solution pH2); R2 reagent 2 (1 mol I-' ammonia solution) E l eluent 1 (4 moll-' HCI); E2 eluent 2 (1 mol I - ' HCI); C1 column 1 (separation column); C2 column 2 (preconcentration column); V1 valve 1 (multifunctional valve); V2 valve 2; P pump; W waste by dissolving 2.858 g of anhydrous boric acid ( H3B03) in 0.5 1 of de-ionized water. A Type VS-I1 strongly anionic basic exchange fibre (Liaoyang Institute of Science and Technology China) was employed for preconcentration purposes and a Type 732 strongly cationic acidic exchange resin (Shanghai Resin Factory China) which is similar to Dowex 50W-X8 cation exchanger was used for separation purposes.Procedure The FI separation and preconcentration system consists of an eight-channel multifunctional valve (V 1) and a two-channel valve (V2) a peristaltic pump (P) a separation column (Cl) and a preconcentration column (C2) (Fig. 1). The correspond- ing flow rates in individual channels are also shown in Fig. 1. Column preparation An appropriate amount of anion-exchange fibre was soaked in 2 moll-' HC1 for no less than 6 h taken out and washed with water until no C1- could be detected (with AgNO,) and then fitted into a column [Fig.2(a)]. The preconcentration column was placed in position C2 of Fig. 1. The cation- exchange resin was also soaked in 2mol1-' HCl for about 8 h then washed with water and packed into a column [Fig. 2(b)]. The separation column was placed at position C l of Fig. 1. Separution and preconcentration Whenever a new run was started the multifunctional valve (Vl) was first set at the load position [Fig. l(u)J valve 2 (V2) was set to enable the sample to be pumped and to flow through 332 Journal of Analytical Atomic Spectrometry May 1996 Vol. 1 1Table 1 Operating conditions MPT Monochromator FI system Carrier and support gas Microwave frequency MHz Forward power W Support gas flow rate ml min-l Carrier gas flow rate ml min-' Plasma viewing mode Plasma viewing position Wavelength nm Slit-width pm Slit height mm HCl concentration of eluent 1 moll-' Acid concentration of sample moll-' Flow rate of sample ml min-' HCl concentration of reagent 1 moll-' Flow rate of reagent 1 ml min-' Ammonia concentration in reagent 2 moll-' Flow rate of reagent 2 ml min-' HCl concentration of eluent 2 mol I-' Flow rate of eluent 2 ml min-l Ar 2450 60 500 700 Side-on 6-8 mm above the top of the torch 249.68 25 2 4.0 0.01 2.5 0.01 2.5 1.0 2.5 1.0 1.5 1 Fig.2 (a) Type VS-I1 strongly basic anion fibre conical micro-column with push-fit connections. Conical bottom id 4 mm; od 6 mm. Conical top id 2mm; od 4mm; length 40mm. 1 PTFE tubing; 2 sorbent packing; 3 Tygon tubing; 4 plastic foam; 5 thick walled silicon rubber tubing. (b) Type 732 strongly acidic cation exchange uniform-bored column with threaded-fitting connections.Inner diameter (id) 5 mm; outer diameter (od) 8 mm; length 120 mm the separation column (Cl) where interfering cations were adsorbed. After separation the sample was mixed with reagent 2 (R2 1 moll-' ammonia solution) to reduce the acidity to a pH of 11.2 and then passed through the preconcen- tration column (C2) where boron was enriched by the fibre (the preconcentration time was usually 30 s). At the same time eluent 2 (E2 1 moll-' HCl) was pumped into the MPT through the PN and DS systems. Elution After a certain load time (30 s) V1 was rotated [Fig. l(b)] to allow eluent 1 (El 4mol1-1 HC1) to flow through C1 and the interfering cations to be eluted from C1 into the waste flask.At the same time E2 flowed through C2 and boron was eluted from C2 into the MPT through the PN and DS systems (the elution time was 30 s). Column washing After the signal had been recorded V1 was again rotated to the load position and V2 was rotated [Fig. l(c)] to allow reagent 1 (Rl HCl of pH 2) to flow through C1 then R2 was mixed with R1 and passed through C2 into the waste flask (the washing time was 20s). This stage ensured that both columns were under the same acid conditions as they were at the loading stage and thus guaranteed the RSDs of the method. Emission measurement The emission intensity was recorded with a chart recorder and measured as peak height. In a set of conditioning experiments the most intensive emission signal was indicated as 1.0 and then other emission signals were taken as relative emission intensities relative to the most intensive signal.Sample digestion Steel samples were dissolved in concentrated HCl and concen- trated HN03 (3 + 1 v/v) in a quartz beaker and gently heated on a sand bath until all of the steel had dissolved. Concentrated H,S04 and concentrated H3PO4 (2 + 1 v/v) were then added to the beaker and the sample solutions heated continuously until large amounts of sulfuric acid mist were produced. The residue was then transferred into a calibrated flask and diluted to the mark with de-ionized water. RESULTS AND DISCUSSION Ion-exchange Column Anion-exchange fi bre column The anion-exchange fibre column was designed to meet the requirements for high efficiency of boron enrichment and rapid elution with a minimum volume of eluent.The detailed con- struction of the column is given in Fig. 2(a). Because the adsorbing capacity of the fibre (0.67 mmol g-' of dry fibre) is large enough to eliminate a breakthrough situation a micro- conical cartridge containing about 30mg of dry Type VS-I1 strongly basic-anion exchange fibre was employed. The break- through appears when the concentration of boron exceeds 40 mg 1-l with an EF of 22 (preconcentration time is 30 s) which is much better than when a common strongly basic anion-exchange column was used (4 mg 1-' for the break- through point with an EF of 2) and which indicates why the fibre does not degrade the EF as most strongly basic anion exchangers do and does actually improve the sensitivity.Cation-exchange resin column As a strongly acidic cation exchanger Type 732 cation- exchange resin is not selective thus it can exchange many types of cations. The experimental results indicate that under appropriate acidic conditions the separation column can Journal of Analytical Atomic Spectrometry May 1996 Vol. 11 333adsorb high concentration of the interfering cation Fe3+ (lo00 mg 1-') owing to the higher adsorbing capacity offered by the larger volume of the column [Fig. 2(b)]. Boron Analytical Line Of the few strong emission spectral lines in the wavelength range 200-600nm the strongest boron lines observed from the MPT are at 249.77 and 249.68 nm which are similar to those observed from an ICP." In the present work the spectral line at 249.68nm was chosen as the analytical line.At this wavelength the background emission was shown to originate mainly from an NO molecular band emission." Hence it is clear that measurements at this wavelength will be affected by compounds present in the sample solutions that contain nitro- gen. Thus the ammonia solution remaining in C2 during the preconcentration stage and introduced into the MPT during the elution stage by the eluant would affect the determination of boron. So keeping the concentration of the ammonia solution used at the concentration stage constant is necessary to maintain good precision of the measurements. Plot 2 in Fig. 3(a) was obtained when blank sample solutions were introduced. Because the blanks did not contain the analyte the emission signals recorded were taken as the background emission signals. It is evident from this plot that background signals increase with ammonia concentration. Plot 3 in Fig.3(a) was obtained when sample solutions contain- ing the analyte were introduced. The emission signals (plot 3 ) recorded were taken as the signals for boron emission plus background emission. Plot 1 in Fig. 3(a) was obtained by subtracting signals in plot 2 from signals in plot 3. The 1.0 1 R O.,....,....,....0 . 9 5 ' ~ " " " ~ ~ ' ~ ~ " " ' " ' " ' ~ " " ' ~ ' ~ I . . _ . 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Ammonia concentrationlmol r' Fig. 3 (a) Effect of ammonia concentration on the relative emission intensity of boron. 1 Boron at 249.68 nm; 2 Background emission at 249.68nm; 3 Boron plus background at 249.68 nm.(b) Effect of ammonia concentration on the fraction of H,BO,- present in solution (&,BO -) detection limit for boron is limited by the signal to background ratio (S/B). A lower S/B value is preferred over high S/B values because the lower the S/B the lower the detection limit for boron. Hence the concentration of ammonia solution in R2 should be chosen to be as low as possible. However too low an ammonia concentration can cause a decrease in aHZBO3 - [Fig. 3 ~41. Optimization of the Experimental Conditions Eflect of observation height The effect of observation height on the emission intensity is shown in Fig. 4. The maximum values of the emission intensit- ies as well as the S/B were obtained at an observation height of 6-8 mm above the top of the torch which had been shown to be the best observation zone in previous work.20 Eflect of microwave forward power Microwave power is usually one of the most important param- eters which influences plasma performance such as plasma shape stability and capability of atomization and excitation of analytes. In the present work the effect of microwave forward power on the emission intensity of boron and the S/B was studied (Fig.5). At lower microwave power (< 55 W) the emission intensities of the analytical line increase with an increase in microwave power and at higher power (>55 W) an increase in forward power causes little increase in the emission intensity with slight decrease in the S/B. This result is different from that obtained with an MIP. In the latter case 3-0 1 0 2 4 6 8 1 0 1 2 Observation heighvrnrn Fig.4 Effect of observation height on the relative emission intensity of boron 0. relative intensity; 0 signal to background 2.5 2.0 x v) e .- 5 1.5 e .- c 0 .- .- % 1.0 E W 0.5 0 10 20 30 40 50 60 70 80 Microwave forward powerMl Fig.5 Effect of microwave forward power on the relative emission intensity of boron 0 relative intensity; 0 signal to background 334 Journal of Analytical Atomic Spectrometry May 1996 Vol. 11an increase in the forward power produced a proportionate increase in the net intensity of the spectral emission.2 The reason for this is probably that in the case of an MPT the plasma is formed between the intermediate and the central tubes near the top of the torch and extends into the surrounding air so that the volume of the plasma is enlarged with an increase in the forward power and the energy density in the plasma does not increase sharply.Acid conditions for the separation system In the proposed procedure before being mixed with R2 (ammonia solution) the sample solution has to be passed through the separation column to separate boron from cationic interferences. Of the concomitant elements that affect the emission intensity of boron in steel samples iron is the most troublesome interfering element so the optimum acidity of sample solutions was selected according to the ability of the column to adsorb iron. In the present work to eliminate the interference from iron a separation column (cation-exchange column) was used before the preconcentration of the boron analyte.To examine the sorbing-xtraction of iron on the separation column the eluate from the column was introduced into the plasma and the emission of iron was measured. In the study C2 in Fig. 1 was removed and a 1000 mg 1-’ iron sample solution was pumped through C1 into the PN system directly for about 120s without mixing with ammonia solution. The effect of sample acidity on the relative emission intensity of iron is shown in Fig. 6(a). Too low an HCl concentration (high pH values) were not attempted because in steel samples iron to boron ratios can exceed 1oooO 1 and thus when 0.1 mg 1-’ of boron was determined 1000 mg 1- of iron in the sample would precipitate with hydroxide ion under such acidic con- ditions. It is also indicated in Fig.6(a) that HC1 concentrations higher than 0.1 moll-’ (pH c 1) will cause the break-through of iron this result is consistent with Samuelson’s conclusion:” ‘The break-through capacity is diminished when the acidity of the solution is raised’. Pitts and Beamish” selected pH 1.5 as the sample acidity that would lead to the adsorption of large amounts of Fe3+ on a Dowex 50W-X8 cation-exchange column. In the present work an HCl concentration of 0.01 moll-’ (pH 2) was chosen in order to reduce the con- sumption of ammonia solution. The effect of the acidity of the El on the emission signal of iron is shown in Fig. 6(b). In the study a 1000 mg 1-’ iron solution (pH 2) was preconcentrated on C1 for 120 s and then eluted by El directly into the PN system. It was shown that a concentration of HC1 exceeding 2 moll-’ in El ensured that the emission of iron reached a maximum. This is because the high concentration of HCl facilitates the formation of chloro- complex anions ([FeClJ) which results in the desorption of al Concentration of HCI in 0 1 2 3 4 5 6 Concentration of HCI in sample solution/mol r1 eluent 1/m01 I-’ Fig.6 Effect of acidity of solution in separation system. (a) Effect of concentration of HCI in sample solution on the separation of matrix (iron); (b) effect of concentration of HCI in eluent 1 on the elution of matrix (iron) iron from the cation exchanger. In addition a higher concen- tration of HCl also took less elution time (30 s for 4 moll-’ HCI and 60 s for 2 mol I-’ HC1) and therefore favours an increase in the sample throughput.This result is also fairly similar to that observed with Dowex SOW-XS cation exchanger.23 Thus 4 moll-’ HC1 was selected as the eluent. Acidic conditions for the preconcentration system In the present work the pH value of the sample solution to be preconcentrated was adjusted by R2 (ammonia solution) (Fig. 1). When the concentration of ammonia solution is in the range 0.25-4.00 moll-’ the pH of the sample solution can be adjusted to 10.6-11.8 respectively. The effect of the concentration of the ammonia solution in a mixed sample- reagent solution on the emission intensity of boron and the fraction of H2B03- that exists in solution are shown in Fig. 3(a and b) [constructed according to eqn. (2)]. The similarity between curve 1 in the Fig.3(a) and the curve in Fig. 3(b) indicates that a pH lower than 11.2 (corresponding to 1 moll-’ ammonia solution) will decrease the emission signals because of the incomplete convertion of boric acid into H2B03-. However pH values higher than 11.2 are also not satisfactory because of the higher background emission resulting from the higher concentration of ammonia solution (curve 3) while the net emission intensity of boron will not increase with an increase in the concentration of ammonia solution (curve 1). Hence a pH value of 11.2 was selected for the mixed solution i.e. 1.0 moll-’ ammonia solution was chosen as R2. A study of the effect of acidity of E2 on the relative emission intensity of boron (Fig. 7) indicates that 1.0 moll-’ is the optimum concentration of HC1 for E2.It seems that from this acidity and higher boron exists in solution mainly in the form of H3BO3. In addition the introduction of HCl into the plasma between samples can also result in a rapid clean-up of the system because the memory effects within the desolvation system are greatly reduced through the use of an acid solution.24 Flow rates of sample reagent 2 and eluents The effect of total flow rate of sample and R2 on the relative intensity of boron was investigated while keeping the sample to R2 flow rate ratio (1 1) and the loading time (30 s) constant (Fig. 8). Higher ratios were not beneficial because under such circumstances a higher concentration of R2 was required which would deteriate the precision of the method. Ratios lower than 1 1 were also not attempted in order to avoid excessive dilution of the sample.Increasing the flow rate resulted in an increase in the relative intensity of boron. 1 .o m h 0.8 - 0 u) a e .- e .C 0.6 c v) .- ‘E OA Q) .- i;j 0.2 a - i? d 0.4 0.8 1.2 1.6 2.0 2.4 Concentration of HCI in eluent 2/ml I-’ Fig. 7 of boron Effect of the concentration of HC1 in eluent 2 on the elution Journal of Analytical Atomic Spectrometry May 1996 Vol. 1 1 335; 0.8 L .- v) a C 0 .- E 0.6 .g 0.4 .- E 3 0.2 P) - al LI 0 1 2 3 4 5 Total flow rates of sample and Rdml min-' Fig. 8 Effect of total flow rates of sample and reagent on the elution of boron However owing to the introduction of larger sample volumes at high flow rates the mechanical properties of the anion- exchange fibre would deteriorate as well as large amounts of sample being consumed. Thus a total sample and R2 flow rate of 5.0 ml min-' (at sample to reagent ratio 1 1) was employed.The eluent flow rate is an important parameter in column preconcentration. The effect of the flow rate of El on the relative intensity of iron and E2 on the relative intensity of boron are shown in Fig. 9. The optimum eluent rate for E2 is fairly similar to the normal sample introduction rate of 1-2ml min-' for ICP spectrometric systems." Too high a flow rate of E2 causes a decrease in the emission signal of boron. This could be for kinetic reasons that is the flow rate of E2 is too fast for the boron remaining on the fibre to be eluted into the solution as it is as fast as the rate under thermodynamic conditions will allow.A flow rate change for El within 1-5 ml min-' has no significant effect which proves that for the strongly acidic cation exchanger the flow rate can be chosen over a wide range. Reverse elution was adopted between the loading and elution stages of the preconcentration system to avoid insufficient contact between the fibre and the sample solution which could in turn influence the flow rate and even produce a break- through problem. Effect of Concomitant Ions A continuous sampling mode was adopted without C1 and C2 to investigate the effects of various concomitant ions including easily ionized elements (EIEs) on the emission intensity of 1 .o >r 0.8 c .- v) 0) c. .- 0.6 .- v) '$ % 0.4 .- c. - a LI o.2 I t . . I . . . . I 1 . . . 1 .. . . 1 . . . . 1 0 1 2 3 4 5 Flow rate of eluent 1 (for Fe) and eluent 2 (for B)/ml min" Fig. 9 separation of boron (0) from iron (0) Effect of flow rate of eluent 1 (El) and eluent 2 (E2) on the Table2 Effect of some concomitant ions on emission intensity of boron; emission intensity of boron (0.4 mg I - ' ) is taken as 100 when no other concomitant ions are added Emission intensity of boron Concomitant Concentration/ ion mg I-' None -. K + 1000 Na + 1000 Mg2+ 1000 Ba" 1000 Ca2 + 1000 Fe 200 Fe loo0 Fe 4000 - 1000 PO,^ - lo00 Cr04'- 1000 Without columns C1 and C2 100 140 140 180 124 108 720 1600 2400 90 95 85 With columns C1 and C2 100 100 100 100 100 100 100 103 105 100 100 98 boron (Table2). The most significant effect was shown to come from iron because of its spectral interference (at 249.78 and 249.65 nm).However when the separation column (Cl) and preconcentration column (C2) were used the effects of iron and other elements can be eliminated satisfactorily by the cation-exchange column (C1 ) provided that the concentration of Fe3+ and other ions are not too high (Table 2). The emission intensity of boron is not significantly affected by the existence of EIEs (including Na' K + Ca2+ Mg2+ and Ba2+) and some anions (including CrO,'- SO,'- and at the 1000 mg 1-' level. This situation is not really specific for the MPT. Hoare and MostynZ5 observed that lOOOrngl-' of Na did not affect the emission intensity of boron when determined by ICP-AES. Murayama et al.' and Lichte and Skogerboe2 also proved that the emission signal of boron was little affected by addition of Na into a CMP and MIP.Murayama et al. concluded that the continuum and analytical lines (which are less sensitive to the addition of Na) of boron radiate from the central core of the plasma. Detection Limit and Linear Dynamic Range In the present study the standard deviation of the blank measurement was used to calculate the DL. The DLs (30) for boron obtained by this method as well as others including the DL obtained with MPT-AES without preconcentration are as follows FAAS,3 1.5; ICP-AES (with an electrothermal vaporiz- ation method)," 0.0024; ICP-AES (with a pyrohydrolysis method),' 0.0035; ICP-MS,13 0.0004; MIP-AES,2 0.01; CMP- AES,' 0.03; and from the present work MPT-AES in a continuous sampling mode 0.03 and including separation and preconcentration 0.0018 mg I-'.It is clear that the proposed method is comparable with conventional ICP as far as the DL for boron is concerned. The linear dynamic range was shown to be over three orders of magnitude (0.02-40 mg 1-l). Precision The relative standard deviation (n = 11) for the determination of boron with the proposed method was shown to be 4.2% (at the 0.02 mg I-' boron level) and 0.15% (at 0.10 mg 1-'). Practical Sample Analysis Some standard reference samples of alloy steels were analysed in order to examine the applicability and accuracy of the method. The results obtained are listed in Table 3. 336 Journal of Analytical Atomic Spectrometry May 1996 Vol. 11Table 3 Determination of boron in steel samples using FI-MPT-AES with the on-line separation and preconcentration technique Certified value Sample Found (YO) (”/.I RSD (n = 5) (YO) Steel 1 0.0044 0.0049 3.6 Steel 2 0.0017 0.0015 3.9 Steel 3 0.0098 0.0100 3.8 Steel 4 0.0076 0.0080 4.1 Steel 5 0.0010 0.0012 4.7 CONCLUSION The present study suggests that FI-MPT-AES with on-line separation and preconcentration can greatly improve the per- formance of MPT-AES and successfully eliminate matrix effects on the spectrometric determination of trace amounts of boron even when there is an excess of iron present.The results compare well with those obtained with an ICP except for the slightly more complex mode of operation. However the cost of an MPT is more attractive and thus makes its shortcomings less important. REFERENCES Murayama S.Matsuno H. and Yamamato M. Spectrochim. Acta Part B 1968 23 513. Lichte F. E. and Skogerboe R. K. Anal. Chem. 1973 45 399. Instrumentation Laboratory Data Sheet 1979 09111 1/79. Pickett E. E. and Koirtyohann S . R. Anal. Chem. 1969,41,28A. Barch R. F. Adams D. M. Soloway A. H. Mechetner E. B. Alam F. and Anisuzzaman A. K. M. Anal. Chem. 1991,63,890. 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Coedo A. G. Dorado T. Escudero E. and Cobo I. G. J. Anal. At. Spectrom. 1993 8 827. Molinero A. L. Ferrer A. and Castillo J. R. Talanta 1993 40 1397. Donaldson E. M. Talanta 1981 28 825. Ciba T. and Smolec B. Fresenius’ J. Anal. Chem. 1994,348,215. Hu B. Jiang Z. and Zeng Y. Fresenius’ J. Anal. Chem. 1991 340 435. Hlavacek I. and Hlavackova I. Microchim. Acta. 1989,111 309. Yamada K. Kujirai O. and Hasegawa R. Anal. Sci. 1993,9,385. Date A. R. and Gray A. L. Spectrochim. Acta Part B 1985 40 116. Jin Q. Zhu C. Boer M. W. and Hieftje G. M. Spectrochim. Acta Part B 1991 46 417. Aauilar J. F. C. Garcia R. P. Uria J. E. S. and Medel San A. Spectrochim. Acta Part B 1994 49 6 545. Sekerka I. and Lechner J. F. Anal. Chim. Acta 1990 234 199. Fang Z.-L. Flow Injection Atomic Spectroscopy ed. Buguera J. L. Marcel Dekker New York 1989 ch. 4. Tyson J. F. Spectrochim. Acta. Rev. 1991 169 14. Jin Q. Huang M. and Hieftje G. M. Microwave Plasmas in Analytical spectrometry Jilin University Press 1993 p. 190. Jin Q. Zhang H. Liang F. Jin Q. J. Anal. At. Spectrom. 1995 10 875. Samuelson O. Ion Exchange Separations in Analytical Chemistry Wiley New York 1963 p. 111. Pitts A. E. and Beamish F. E. Anal. Chem. 1969 41 1107. Govindaraju K. Anal. Chem. 1968 40 1. Veillon C. and Margshes M. Spectrochim. Acta Part B 1968 23 503. Hoare H. C. and Mostyn R. A. Anal. Chem. 1967,39 1153. Paper 5/05563F Received August 8 1995 Accepted January 2 1996 Journal of Analytical Atomic Spectrometry May 1996 Vol. 11 337

ISSN:0267-9477    

DOI:10.1039/JA9961100331

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Determination of Thorium and Uranium in Urine With Inductively Coupled Argon Plasma Mass Spectrometry Journal of Analytical Atomic Spectrometry BILL G . TING. DANIEL C. PASCHAL AND KATHLEEN L. CALDWELL Division of Environmental Health Laboratory Sciences National Center for Environmental Health Centers for Disease Control and Prevention (CDC) Public Health Service U S . Department of Health and Human Services Atlanta GA 30333 USA An accurate and simple method has been developed for the determination of thorium and uranium in urine using inductively coupled argon plasma mass spectrometry (ICP-MS). Determination of thorium and uranium was by external calibration using matrix matched standards and high- purity spiking materials. Aliquots of each urine specimen were diluted (1 + 9 ) with 0.2 rnol I-' nitric acid containing iridium as an internal standard. The counts at m/z 232 (thorium) 238 (uranium) and 193 (indium) were measured and ratios of the counts at m/z 232 or 238 to those at m/z 193 were calculated. These ratios were compared with those from urine-based calibration standards to calculate the thorium and uranium concentrations in unknown specimens. The concentrations of thorium and uranium were calculated as pg I-' in the sample and also corrected for dilution via creatinine measurement expressed as pg g- ' of creatinine.The method has been evaluated by determination of reference materials from the Los Alamos National Laboratory as well as of those from the Oak Ridge National Laboratory. The proposed method provides the basis of an accurate method for determining thorium and uranium in unexposed subjects as well as in those considered to be exposed to thorium or uranium through environmental or other pathways.About 40 specimens excluding blanks calibration standards and quality-control materials can be processed in an 8 h day. Keywords Inductively coupled plasma mass spectrometry; thorium; uranium; urine; reference material Uranium is widely distributed in the earth's crust which contains on average about 2 pg of uranium per g of soil.' It is concentrated mainly in the acidic series of magmatic rocks with lesser amounts in basic minerals and sediments.2 Weathering of granite is an important source of soil uranium. Commercial uses of uranium enriched with uranium-235 are primarily as nuclear fuel and in nuclear weapon systems.Thorium is also present in the soil at about 6 pg of thorium per g of Mined principally from monazite a by-product of mineral sands mined for titanium and zirconium thorium has several commercial uses including energy production and refractory applications and as a component of lamp mantles aerospace alloys and welding electrodes. Human exposure to uranium or thorium has many adverse health outcomes some of which have only recently been doc~mented.~*~ Because of suspected adverse health effects from uranium or thorium at locations near mining processing disposal or production facilities assessing human exposure to these radionuclides is an important part of health evaluations. Both uranium and thorium are poorly absorbed by the gastrointestinal tract and most of that which is absorbed is eliminated in the urine.6 Therefore it is important to measure accurately uranium or thorium in urine at concentrations of about 1 pgl-' or less.For the classification of risks to be useful and effective the total measurement error (bias plus variation) must be 10% or better at concentrations of 1 pg 1-' or greater.7 Many laboratories are not currently capable of attaining this level of measurement error. The Centers for Disease Control and Prevention (CDC) has an historic interest in measuring markers of human exposure to a wide spectrum of toxic xenobiotics.' A growing concern is the presence of many widely distributed sites at which energy production nuclear-fuel processing or nuclear waste disposal has occurred.' Various analytical methods have been used to measure uranium and thorium in urine including alpha spectroscopy," fluorescence spectroscopy" and neutron activation analy- s ~ s .' ~ - ' ~ These methods are limited by high sample volume requirements (alpha spectroscopy) expensive and relatively rare equipment (neutron activation) long counting times (alpha spectroscopy) and tedious chemical separation (all three methods). An analytical method has been developed using inductively coupled argon plasma mass spectrometry (ICP-MS) a process that requires a small sample volume is rapid is free from spectral interferences requires no chemical separation and has a low limit of detection to enable quantifi- cation of both uranium and thorium in urine to be made at 'expected normal' concentrations.Accuracy and precision of the method have been estimated by analysis of reference urine pooled samples from Los Alamos National Laboratory (LANL) and Oak Ridge National Laboratory (ORNL) from a pilot study of residents (n=22) living near an historic uranium processing site and from selected subjects participat- ing in a recent population survey (n = 53). In the present paper results for the application of ICP-MS to the determination of uranium and thorium concentrations in urine are presented and compared with those obtained using other analytical methods. EXPERIMENTAL Instrumentation A Perkin-Elmer SCIEX Elan 500/5000 inductively coupled argon plasma mass spectrometer equipped with a peristaltic pump (Perkin-Elmer Norwalk CT USA and SCIEX Thornhill Ontario Canada) and IBM PS/2 Model 70 com- puter for data handling and storage were used.A closed loop water chiller (Neslab Model HX-150 Newington NH USA) was used for cooling with 10% (v/v) ethylene glycol to achieve an approximate coolant temperature of 15 "C. The instrumental settings used optimized for the measurement of uranium and thorium isotopes from m/z 190 to 240 are given in Table 1. Reagents Urine samples were diluted with 0.2 mol I-' redistilled grade ultrapure nitric acid (GFS GS-380 Columbus OH USA). All water used was passed through a Milli-Q system which produces purified water with about 18 Mi2 cm resistance (Millipore Milford MA USA). Uranium iridium and thorium spiking standard solutions were prepared by dilution of SPEX Journal of Analytical Atomic Spectrometry May 1996 Vol.I 1 (339-342) 339Table 1 ICP-MS parameters for determining uranium and thorium in urine Instrument PE SCIEX 500/5000 (updated 500) Nebulizer C3 Type Meinhard Forward power 1.5 kW Reflected power < 5 W Argon flow rates Intermediate 1.35 1 min-' Outer plasma 12 1 min-l Aerosol 0.60 1 min-' B 62 El 98 P 16 S2 29 Ion lens settings (optimum for uranium and thorium) CEM voltage 4.0 kV Measurement parameters 1000 ms per replicate; 5 replicates Time factors (isotope) 193; 232; 238 all set to 1 Dwell time 20 ms (Edison NJ USA) certified stock solutions (1000 mg l-') and from the National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 3 159 Thorium Spectro Soln.(lOOOOmgl-l of thorium) and SRM 3164 Uranium Spectro Soln. (10000 mg 1-l of uranium) for Cali- bration standards and pooled urine samples respectively. Preparation of Pooled Urine Uranium and Thorium Samples All collection and storage containers were screened for uranium and thorium before use. Pools of urine samples were prepared by collection of urine from presumably healthy adult volun- teers the samples were stored at 4°C and filtered immediately before spiking with an NIST diluted solution containing thorium and uranium. The spiked urine labelled as MTE was dispensed into 15 ml plastic screw-capped vials and stored at -20°C. Nitric acid was added to a final concentration of 0.2 moll-l. Uranium and thorium concentrations in the col- lected urine materials were calculated to be about 4 yg 1-1 for MTE.All operations were performed in a specially designed facility under class 100 conditions. In some studies aliquots were sent to other investigators for comparison of the analyt- ical results. Procedure Urine specimens were equilibrated to room temperature and 500yl were diluted with 4.5ml of diluent i.e. a solution of 0.2moll-' nitric acid with lOyg1-1 iridium as the internal standard. Standards were prepared from the pooled urine samples with known concentration increases of thorium and uranium from SPEX diluted solutions produced by spiking. All standards and specimens were diluted in the same way with a 10 yg 1-1 iridium internal standard. Measurements were made of the total counts at m/z 193 for iridium 232 for thorium and 238 for uranium.Ratios of the counts at m/z 232 Table 2 Characteristics of calibration curves or 238 to the iridium-193 internal standard were plotted versus concentration to create calibration curves. To prevent build- up of salts on the sampler and skimmer cones when running successive urine samples a 0.5% (m/v) solution of Triton-X 100 in 0.2mo11-1 nitric acid was used to flush through the system for 300s between the determination of thorium and uranium in each diluted urine specimen. The characteristics of the calibration curves obtained in more than 11 runs conducted on 11 d are shown in Table 2. The correlation coefficients (r2) of both the thorium and uranium calibration curves are greater than 0.999; the slopes and intercepts vary as shown. RESULTS AND DISCUSSION Internal Standard Investigation Inductively coupled plasma mass spectrometry is considered to be more susceptible to matrix effects than inductively coupled plasma atomic emission spectrometry.15 The internal standard method is applied to correct for matrix effects owing to the complexity of the urine matrix and the matrix variation between urine samples.16 This method is based on measuring the isotope ratio of counts measured for the analyte to those of the internal standard to correct not only for sample matrix effects but also for drift or instability of the instrument.The internal standard should be chosen to be as close in nominal relative atomic mass as possible to that of the analyte. A number of elements were considered as the internal standard when measuring thorium and uranium 209Bi 208Pb 205Tl 202Hg lg5Pt and lg31r.Lead thallium mercury and platinum are the toxic elements of interest among the high relative atomic mass group when using iridium as an internal standard for multi-element analysis in this laboratory. Bismuth was found not to be a good internal standard owing to its serious memory effect. Iridium-193 was chosen as an internal standard because its concentration is negligible in human urine and it is similar in chemistry to uranium and thorium in the acidified urine environment. Iridium with a nominal mass of 193 is similar in relative atomic mass to the two nuclides measured uranium at m/z 238 and thorium at m/z 232 and does not create spectroscopic interferences at m/z values of 232 and 238.The performance of lg31r in the urine matrix with respect to 232Th and 238U during ICP-MS with various instrumental parameters was investigated. Before each set of measurements the parameters of the ICP-MS instrument were tuned to maximize the signal intensities for 232Th and 238U. The results of this experiment are shown in Fig. 1. Changes in the peak intensities of lg31r 232Th and 238U are seen as the instrumental parameters are changed. The intensity of lg31r responds in a similar manner to the intensities of 232Th and 238U when the instrumental parameters were varied. These data support the effectiveness of internal standard correction using lg31r. Slope Date 03.24.94 06.21.94 06.28.94 07.25.94 07.27.94 08.02.94 08.09.94 08.10.94 Thorium 0.007120 0.008497 0.01 1753 0.010360 0.010465 0.01 1256 0.01 1125 0.010571 Uranium 0.012332 0.015762 0.0236 15 0.01 5 1 19 0.01 3019 0.022093 0.020278 0.020508 Intercept 'Thorium Uranium -4.546 x loW4 3.691 x 7.390 x 10-5 4.277 x 3.074 x -2.296 x -4.216 x 1.374 x - 1.336 x -2.038 x -~425 x 10-4 - 1.094 x lop3 -1.604 x 10-5 - 1.266 x -4.712 x 10-4 -2.295 x - Correlation coefficient Thorium 0.999996 0.999834 0.999988 0.999946 0.999987 0.999986 0.999927 0.999857 Uranium 0.999993 0.999961 0.999988 0.999913 0.999987 0.999992 0.999992 0.999999 340 Journal of Analytical Atomic Spectrometry May 1996 Vol.1 1B C D E U-238 Th-232 lr-193 0 ,-Background Fig. 1 Internal standard method correction for instrumental param- eter variation. A Aerosol gas flow rate 0.6 1 min-l forward rf power 1549 W; B aerosol gas flow rate 0.5 1 min-l forward rf power 1549 W; C aerosol gas flow rate 0.6lrnin-l forward rf power 1549W D aerosol gas flow rate 0.6lmin-' forward rf power 1420 W; and E aerosol gas flow rate 0.6 1 min-l forward rf power 1549 W Long-term Stability Investigation A long-term stability study of the internal standard method was carried out by measuring the intensities of the three isotopes 1931r 232Th and 238U and the ratios of 232Th lg31r and 238U 1931r in a diluted urine sample over 5 h.A 5 min wash with 0.5% m/v Triton-X 100 in 0.2 mol 1-1 nitric acid was performed between each sample. The plots of intensities of lg31r 232Th and 238U versus time and 232Th lg31r and 238U 1931r versus time are shown in Figs. 2 and 3 respectively.The relative standard deviations (RSDs) of the intensities of 1931r 232Th and 238U over 5 h are 6.3 7.0 and 6.9% respectively. The RSDs for the ratios of 232Th 1931r and 238U 1931r for the 5 h are 2.1 and 1.0% respectively. Clearly this study has shown that the internal standard technique using lg31r as the internal standard effectively compensates for drift or instability of this measurement technique when urine is the matrix. Ave-3741 ;SD=258;CV=6.9 1 1 Fig. 2 Long-term stability test (peak intensity) m iridium-193; + thorium-232; * uranium-238 0.19-1 1 8 Ave=O.I824SD=0.0018;CV=l .O% o 0.16 E 0.15 Fig. 3 Long-term stability test (peak ratio) m 232Th lg31r; and + 238u. 1931r Accuracy To evaluate the accuracy of the proposed method a series of pools of urine samples were diluted and isotope ratios were measured to calculate the uranium and thorium concentrations.These reference samples were prepared by LANL and ORNL as part of their quality-control procedures. Target values for Table 3 Comparison of CDC analyses with certified values (LANL-ORNL) Pool sample LA-30368 LA-30372 LA-30369 LA-30370 LA-30371 LA-30373 OR-A OR-C OR-E OR-G Uranium target value/ 0.499 1.87 2.50 4.99 0.376 3.76 Blank 0.177 1.56 3.66 Pg 1-1 CDC*/ 0.505 1.97 2.68 4.80 0.388 3.97 0.064 0.096 1.46 3.33 Pg 1-1 Bias/ + 0.006 +0.10 +0.18 -0.19 + 0.012 + 0.21 NDt - 0.08 -0.1 -0.33 Pg 1-1 Bias + 1.2 + 5.3 + 7.2 - 3.8 + 3.2 + 5.6 ND - 45.2 - 6.4 - 9.0 ~~ ~ * There were three runs with four replicates per run for the measure- ment of the LA-series and 12 runs with four replicates per run for the measurement of the OR-series.t ND not determined. Table 4 Results of daily quality-control measurements MTE */pg 1-' Date 03.24.94 06.2 1.94 06.28.94 07.25.94 07.27.94 08.02.94 08.09.94 08.10.94 Mean (n= 8) RSD (%) CDC target S LCLt 95% u c L $ 95% Thorium 4.56 4.35 4.19 4.13 4.17 4.59 4.33 4.42 4.34 0.16 3.76 4.51 3.71 4.38 Uranium 3.96 4.00 3.64 3.95 4.05 3.89 3.93 3.94 0.13 3.21 4.05 3.61 4.49 4.08 * Internally prepared urine quality-control pooled sample. t Lower confidence level. $ Upper confidence level. Table 5 Precision of ICP-MS method quality control pooled sample data Pool- analyte 303 7 1 -U 30368-U 30372-U 30369-U 30373-U 30370-U OR-A-U OR-C-U OR-E-U OR-G-U MTE-Th MTE-U Concentration/ 0.384 0.505 1.975 2.676 3.968 4.801 0.064 0.096 1.464 3.329 4.51 4.05 P8 1-' 5 W r 7 Pg 1- 0.037 0.029 0.075 0.113 0.106 0.101 0.025 0.023 0.069 0.08 1 0.208 0.188 SlJ t Pg I-' 0.046 0.027 0.104 0.070 0.135 0.584 0 0 0 0.03 1 0.235 0.142 5t0taq CLg 1- 0.059 0.039 0.129 0.133 0.172 0.593 0.025 0.023 0.069 0.087 0.314 0.236 RSD total (%xi ntT 15.4 3 7.72 3 6.51 3 4.96 3 4.34 3 12.4 3 39.5 12 23.7 12 4.72 12 2.62 12 6.95 21 5.82 21 * Standard deviation within run. t Standard deviation between-run.$ Total standard deviation. 6 Including within-run and between-run RSD. 7 Number of runs. Journal of Analytical Atomic Spectrometry May 1996 Vol. 1 1 341Table 6 Pilot study data (human urine specimens) Number of Minimum-maximum value/ Group su bj -'- Analyte Mean/pg I-' Median Clg I - ' 95 yo UCLt Self referral 2 Uranium 0.0226 0.0 19 0.0 1-0.054 0.042 0.259 NHANES* 111 53 Uranium 0.098 0.082 NHANES* I11 53 Thorium 0.201 0.165 < 0.05-0.765 0.406 < 0.01-0.299 * The National Health and Nutrition Examination Surveys.t 95% upper confidence level. Table 7 Reference intervals reported in the literature"; the analyte was uranium Worker Location Number of subjects Method Mean/pg 1-' Medianjpg 1- ' Hursh-Spoor US (NY Chicago) 37 Fluorimetry 0.110 - Dean UK 300 Unknown 0.217 - Wrenn-Singh US (Salt Lake) 12 a-spectrometr 0.023 9 Welford US (Chicago) 11 Fluorimetry 0.086 64 Fisher us 6 a-spect rometry 0.1 14 0.114 these pools of samples were determined by an alpha- spectroscopic technique. Comparison of the results obtained with those from LANL or ORNL demonstrates good agree- ment.These results are summarized in Table 3. An internally prepared urine quality-control pool sample (MTE) was meas- ured with each run. The results are shown in Table 4. Precision and Detection Limit Precision was estimated using two-way analysis of variance (ANOVA) on data generated from the replicate determination of a series of quality-control pools including those prepared at CDC and those from external laboratories. Both the within- run and between-run components of these determinations are presented in Table 5. The RSDs of the elevated quality-control urine pool sample (MTE) that were measured on eight different days are 3.76 and 3.21 % for thorium and uranium respectively (Table4). The calculated detection limit is defined as three times the standard deviation estimated at a zero concentration by extrap01ation.l~ The detection limits estimated in this way were 10 ng 1-' for uranium in urine and 50 ng 1-' for thorium in urine.Pilot Surveys Two different populations were examined to provide a prelimi- nary estimate of the reference interval for these two urinary metals ( 1) a population (n = 22) of 'self-referred' residents living near to a former nuclear weapons fuel-processing site; and (2) randomly selected subjects (n = 53) who participated in a recent health survey. Group 1 was entirely adults; the ages in group 2 ranged from 1 to 65 years. A summary of the findings from both groups is given in Table 6. These data compare favourably with the previously reported 'reference' intervals for thorium and uranium in urine which are listed in Table 7.'*.19 CONCLUSION The accuracy of the proposed method can be determined by a comparison of the data from the CDC method with data from other laboratories by using well-characterized and accepted methods.The method described is convenient to use. Up to 40 urine specimens can be analysed in a day excluding quality-control pools standards and duplicate blanks. It is anticipated that this method can be used to support future investigations of possible environmental exposures to these metals in a wide variety of settings. 342 Journal of Analvtical Atomic SDectrometrv. Mav 1996. We are grateful to G. Payne of Oak Ridge National Laboratory and N. Koski of Los Alamos National Laboratory for kindly providing reference materials.Use of trade names is for identification only and does not constitute endorsement by the Public Health Service or the US Department of Health and Human Services. REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 VOl. 11 National Council on Radiation Protection and Measurements (NCRP) NCRP Report No. 39 Washington DC 1971. Stokinger H. E. Industrial Hygiene and Toxicology eds. Clayton C . D. and Clayton F. E. John Wiley New York. 3rd edn. 1981 Harmsen K. and De Haan F. A. M. Neth. J. Agric. Sci. 1980 2a,40. Najem G. R. and Voyce L. K. Am. J. Public Health 1990,80,478. Budnick L. D. Sokal D. Falk H. Logue J. N. and Fox J. M. Arch. Environ. Health 1984 39 409. Carson B. L. Ellis H. V. and McCann J. L. Toxicology and Biological Monitoring of Metafs in Humans Lewis Chelsea MI 1986 pp.256 and 273. Dyer F. F. May M. P. Walker R. L. Scott T. G. Caton G. M. and Stokely J. R. Evaluation of Isotope Dilution Mass Spectrometry for Bioassay Measurement of Uranium Plutonium and Thorium in Urine ORNL/TM-9006 Oak Ridge National Laboratory Oak Ridge TN June 1984. Sampson E. J. Needham L. L. Pirkle J. L. Hannon H. Miller D. T. Patterson D. G. Bernert J. T. Ashley D. L. Hill R. H. Gunter E. W. Paschal D. C. Spierto F. W. and Rich M. J. Clin. Chem. ( Winston-Salem N.C.) 1994 40 1376. National Council on Radiation Protection and Measurements (NCRP) Report No. 77 Bethesda MD 1984. American Society for Testing and Materials (ASTM) Water and Environmental Technology ASTM Philadelphia 1986 section 11 Dupzyk I. A. and Dupzyk R. J. Health Phys. 1979 36 526. Pleskach S. D. Health Phys. 1985 48 303. Holzbecher D. and Ryan D. E. Anal. Chim. Acta 1980 119,405. Gladney E. S. Peters R. J. and Perin D. R. Anal. Chem. 1983 55 976. Houk R. S. Anal. Chem. 1986 58 97A. Igarashi Y. Kawamura H. Shiraishi K. and Takaku Y. J. Anal. At. Spectrom. 1989 4 571. Taylor J. K. Quality Assurance of Chemical Measurements Lewis Chelsea MI 1987 p. 81. Wrenn M. E. Ruth H. Burleigh D. and Singh N. P. J. Radioanal. Nucl. Chem. 1992 156 407. Welford G. A. and Baird R. Health Phys. 1967 13 1321. VOI. 2A pp. 1995-2013. VOI. 11.02 pp. 511-15. Paper 5/07605F Received November 21 1995 Accepted December 18 1995

ISSN:0267-9477    

DOI:10.1039/JA9961100339

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Addition of Tertiary Amines in the Semiquantitative Multi-element Inductively Coupled Plasma Mass Spectrometric Analysis of Biological Materials* Journal of Analytical Atomic Spectrometry ANTOANETA KRUSHEVSKA ALEXANDRA LASZTITY MIHALY KOTREBAI AND RAMON M. BARNES Department of Chemistry University of Massachusetts Lederle Graduate Research Center Tower Box 3451 0 Amherst M A 01 003-451 0 USA A semiquantitative inductively coupled plasma mass spectrometric (ICP-MS) analysis protocol for biological materials was developed to include water-soluble tertiary amines with microwave heated sample preparation. Certified reference materials digested with HN03 H202 and HF required addition of H3B03 and a solution of tertiary amines (CFA-C reagent) to dissolve insoluble fluorides and neutralize free fluorides.Commercial semiquantitative analysis software that evaluates the entire m/z range and includes pre- programmed corrections for spectroscopic interferences was applied to investigate matrix interferences resulting from 10% tertiary amines and chlorides (added as 1% HCI). Measurement parameters including m/ z range spectrometer sensitivity and number of elements in the external calibration were evaluated. The accuracy of the semiquantitative analysis improved when the standard solution was matrix matched; interference-free isotopes were selected for some elements instead of scanning the whole m/z range and additional elements with m/z values of under 80 were included for updating the instrument pre-calibration response factor. This semiquantitative analysis approach can be applied successfully for the multi-element analysis of biological materials when optimum instrumental conditions are employed. Thirty-eight elements were determined in six certified reference materials and food samples with a precision of 1-20% and accuracy of 1-50%.The determinations of Al K Na and Si were unreliable. Keywords Inductively coupled plasma mass spectrometry; water-soluble tertiary amines; semiquantitative analysis; biological materials Quantitative determinations with an accuracy of 30-50% are considered semiquantitative and a determination with an accu- racy of less than 10% is quantitative.' In the analysis of food and other biological materials very often a semiquantitative multi-element analysis is expedient for screening or survey needs.Inductively coupled plasma mass spectrometry (ICP-MS) is a valuable technique because it is multi-element and has trace element determination capabilities.2 However interferences and sample pre-treatment can limit its multi- element utility. In the analysis of practical samples ICP-MS exhibits spec- troscopic and non-spectroscopic interferences.2 Isobaric inter- ferences and formation of polyatomic ions with plasma gas components (Ar N2 and 02) sample matrix and sample dissolution acids are recognized as the most intra~table.~?~ Sample preparation and instrumental parameter optimiza- tion techniques can minimize these interferences however. *Presented at the 1994 Winter Conference on Plasma Spectrochemistry January 10-15 1994 San Diego CA USA Additions of gases (N2 O2 or H,) to the Ar reduce matrix effects and increase the analyte signals leading to lower limits of detection for many element^.^-^ Non-spectroscopic inter- ferences are due mainly to the influence of sample transport and ionization effects that can be compensated for usually by matrix matching samples and standards and employing appro- priate internal ~tandardization.~>~*~~ Spectroscopic interferences from polyatomic carbon ions arise in the analysis of biological samples or hydrocarbons,2 because carbon compounds are incompletely destroyed in many sample preparation techniques and/or in the ICP. Some isotopes (e.g.44Ca 24Mg 25Mg 26Mg 52Cr and 53Cr) are subject to significant interferences from polyatomic carbon species.Consequently to avoid spectral overlap an alternative isotope with low abundance is typically substituted." The chloride concentration in certain foods and other biological materials can be high and the elemental determination of As V Cr or Se for example can be limited by polyatomic chlorine ion interferences.2-12 The presence of organic compounds is also found to be beneficial in removing chloride inter- ference~~*'~*'~ and improving the signal and detection limit for some element^.'^.^^ Finally polyatomic ion interferences from major elements (e.g. CaO+ and CaOHf) also can be significant for Fe Ni Zn and Co isotopes.''*12 Appropriate sample preparation is also critical for multi- element determinations. Multi-element ICP-MS determi- nations have been reported for f ~ ~ d ~ ~ - ~ ~ and other biological material^.'^^'^^^^^^ Sample preparation procedures include dry ashing (e.g.in the presence of H2SO4)I7 or wet digestion with conventional and microwave heating.16.'8*20*21.25 The presence of H2S04 restricts multi-element ICP-MS analysis however.2 Dry ashing generally cannot be used for multi-element analysis because of element losses and contamination. These limitations can be minimized by employing closed-vessel digestions especi- ally with microwave heating.25.26 Systematic errors arising from incomplete dissolution of particular elements have been described. 18327 In multi-element ICP-MS screening techniques dissolution procedures require addition of HF. For the determination of Si Ti Zr rare earth elements (REEs) and other metals in inorganic materials HF must be added.To determine A1 accurately in food for example 0.25 ml of HF added per gram of dry mass was required.27 Acid mixtures including HF are used with microwave heating2* or dry ashing2' for preparation preceding the determination of many elements including Si Ti V Cr A1 and Zr in food and other biological materials. When HF is present excess of H2B03 must be added to complex residual HF. However the complexed HF still attacks glassware and glass nebulizer^.^.^' Water-soluble tertiary amines have been employed to neutralize excess of fluoride ions.31 For example the precision and accuracy of an ICP Journal of Analytical Atomic Spectrometry May 1996 VoZ. 11 (343-352) 343atomic emission spectrometric (ICP-AES) determination of Si in food was improved by neutralizing fluoride with tertiary amine~.~' These water-soluble tertiary amines have not been evaluated for the ICP-MS analysis of fluoride-containing solu- tions however.Therefore the addition of these amines was considered in the present investigation. In this study the possible matrix effects resulting from adding water-soluble tertiary amines and biological sample compo- nents are evaluated with ICP-MS multi-element semiquantit- ative analysis techniques. Preliminary investigations of potential interferences with model solutions precede optimiz- ation of instrumental parameters with biological reference materials and food samples. EXPERIMENTAL Instrumentation A programmable ashing furnace (Isotemp 497 Fisher Pittsburgh PA USA) and a closed-vessel microwave system (RMS 150 with pressure control mode 0.1.Analytical College Station TX USA) were employed for sample preparation. For the latter system double-wall medium-pressure ( 1379 kPa maximum pressure) Teflon-perfluoralkoxy ( PFA) vessels were used and 100°/~ applied microwave power corresponded to 850 W. Two ICP-MS systems (Perkin-Elmer Sciex Elan 250 and Elan 5000a Norwalk CT USA) with a standard ICP torch cross flow nebulizer and Ni sampler and skimmer cones were used. Peristaltic pumps (Minipuls 2 Rabbit Rainin Wolburn MA USA) were used to transfer solutions to the nebulizers. The plasma conditions and measurement parameters for investigations of the influence of the matrix are listed in Table 1. Since conditions can vary depending on sample introduction or spectrometer interface conditions,* operating parameters were optimized daily and comparative results were repeated on different days.The plasma was optimized daily with a 1% HNO standard solution of Be Ge In Re and Pb. Sampling depth aerosol carrier gas flow rate and the ion-lens voltages were adjusted to give maximum Ge and In signals compro- mised Be and Pb signals and low signal relative standard deviation (RSD) and background. Lens settings were main- tained for the experiments throughout the day. When the power is unchanged lens settings were not altered.4 The Elan 5000a sampling depth was set at 9 mm. Preliminary experiments for ICP-MS performance optimization indicated that variation of the torch to sampler cone distance was less important than the aerosol gas Row rate.Therefore the distance was fixed ( 3 mm). The Elan 250 sampling depth was adjusted daily and main- tained constant throughout the analyses. Data were acquired with standard system software for multi- element semiquantitative analysis ( Perkin-Elmer TotalQuant II).32 The program utilizes rule-of-thumb and numerical calcu- lation to perform completely automated mass spectrum interpretation. The user specifies a mass (i.e. m/z) range or elemental isotopes. Common isobaric interferences are pre- programmed and corrections are automatically applied. The software has stored pre-calibrated intensities per concentration unit covering the required m/z range. To increase the accuracy these values are updated by running an external standard containing a few selected elements.Table 1 Instrumental operating parameters for ICP-MS semiquantitative analysis (TotalQuant 11) for matrix influence investigations ICP-MS plasma conditions- Rf frequency/MHz Rf forward power/kW Nebulizer Spray chamber Sampling depth (rf coil to sampler distance)/mm Torch to sample cone distance/mm Argon flow rate/l min-' Outer Intermediate Aerosol with HNOJ optimization Aerosol with CFA-C optimization Measurement parameters- Resolution (m/z at 10%) Scanning mode Replicate time/ms Dwell time/ms Sweeps per reading Readings per replicate Number of replicates Points per spectral peak Total estimated time/s Perkin-Elmer Sciex Elan 5000a 40 (free running) 1 .o Cross flow Double pass type 9 3 15.0 0.80 0.94- 1.05 0.8 3 -0.9 5 0.8 (normal) Peak hopping 250 50 5 1 3 1 150 Mass range-m/z Lower Element mass/u 7 23 K 39 42 Ge 74 75 81 In 115 116 Re 187 188 232 Upper mass/u 10 31 70 79 112 184 209 239 External calibration standard (when applied) 0.050 pg ml- of Ca Al Sc Ti Cr Cu V As Se Y Cd Ce Tb Pb and Th 344 Journal of Analytical Atomic Spectrometry May 1996 Vol.1 1Table 2 Evaluation of measurement parameters [m/z range and isotopes mass spectrometer sensitivity (OmniRange)] and external calibrations with semiquantitative analysis (TotalQuant 11) software I I1 I11 IV Element or m/z range 7-10 23-31 39K 43Ca 45sc 47Ti 51-55 57Fe 74Get 75-79 81-112 1151nt 116-194 ls7Ret 1 18-209 232-239 External calibration/ pg ml-' Ca 0.050 Al 0.050 Sc 0.050 Ti 0.050 Cr 0.050 Cu 0.050 V 0.050 As 0.050 Se 0.050 Y 0.050 Cd 0.050 Ce 0.050 Tb 0.050 Pb 0.050 Th 0.050 Element or mJz range 7-10 23-3 1 39K 42-73 74Ge t 75-79 81-1 12 1151nt 116-184 ls7Ret 188-209 232-239 External calibration/ pg ml-' Ca 100.05 A1 0.050 Sc 0.050 Ti 0.050 Cr 0.050 Cu 0.050 V 0.050 As 0.050 Se 0.050 Y 0.050 Cd 0.050 Ce 0.050 Tb 0.050 Pb 0.050 Th 0.050 Na 100 K 40 Mg 20.05 Si 2 Element or m/z range 7-10 23Na* "Mg 'OSi 43Ca* 45sc 4Ti 51v 54Cr 55Mn 57Fe 59-70 74Get 75-79 81-1 12 2 7 ~ 1 39K * 1151n-t 116-184 ls7Ret 188-209 232-239 External calibration/ lg ml-' Ca 100.05 A1 0.050 Sc 0.050 Ti 0.050 Cr 0.050 Cu 0.050 V 0.050 As 0.050 Se 0.050 Y 0.050 Cd 0.050 Ce 0.050 Tb 0.050 Pb 0.050 Th 0.050 Na 100 K 40 Mg 20.05 Si 2 Co 0.050 Mo 0.050 Fe 0.050 Element or mJz range 7-10 23Na* 25Mg 30Si 43Ca* 45sc 46Ti 51v 53Cr 55Mn 57Fe 59-73 74Get 75-79 81-1 12 2 7 ~ 1 39K * 115rnt 116-184 Is7Ret 188-209 232-239 External calibration/ pg ml-' Ca 100.05 A1 0.050 Sc 0.050 Ti 0.050 Cr 0.050 Cu 0.050 V 0.050 As 0.050 Se 0.050 Y 0.050 Cd 0.050 Ce 0.050 Tb 0.050 Pb 0.050 Th 0.050 Na 100 K 40 Mg 20.05 Si 2 Co 0.050 Mo 0.050 Fe 1.05 * Reduced instrument sensitivity applied (Mg and K = 5 Ca = 15 'OmniRange' values).The OmniRange setting is an instrument parameter that permits determination of relatively high elemental concentrations by reducing the instrument measuring sensitivity for a particular isotope or m/z range by varying the voltage applied to the quadrupole mass spectrometer. Typical values are from 15 to 25 for low relative atomic mass elements and from 25 to 35 for high relative atomic mass element^.^' t Internal reference element.Table 3 Optimal instrumental conditions for ICP-MS semiquanti- tative analysis of biological samples with TotalQuant I1 after micro- wave dissolution* ICP-MS plasma conditions- Rf frequency/MHz Rf forward power/kW Rf reflected power/W Nebulizer Spray chamber Sampling depth (rf coil to sampler distance)/mm Argon gas flow rates/l min-' Outer Intermediate Aerosol Sciex Elan 250 27.12 1 .o <5 Cross flow Double pass x 21 11.8 1.40 0.83-0.95 * Measurement parameters (same as Table 1) m/z range Set IV (Table 2). When samples were analysed different measuring param- eters including selected m/z ranges isotopes mass spectrometer sensitivity and the number of elements and their concentrations in the external calibration were compared Four measurement parameter sets (I-IV) are listed in Table 2.Germanium-74 "'In and lE7Re were applied as internal reference elements (Tables 2 and 3). Samples were analysed after microwave dissolution with established optimum instrumental conditions (Table 3). The standard additions method was sometimes used for semiquantitative determinations and verification. Quantitative results for Cr Y Zr La Ce and Nd were also obtained for samples fused in LiB02 with an established food analysis procedure.33 The experimental conditions are listed in Table 4. An ICP-AES instrument (Plasma 11 Perkin-Elmer) was utilized for quantitative measurement of C after microwave d i s s o l ~ t i o n ~ ~ and Si Ti Al Ba and Sr after fusion.33 Instrumental parameters are summarized in Table 5.Myers- Tracy signal compensation3' was used with 50 pg ml-' of Sc Table 4 Instrumental conditions for quantitative ICP-MS analysis of samples after fusion. Instrumental parameters given in Table 3 Measurement parameters Resolution (m/z at 10%) Scanning mode Replicate time/ms Dwell time/ms Sweeps per readings Readings per replicate Number of replicates Points per spectral peak Element Cr Y Zr La Ce Nd In* 0.8 (normal) Peak hopping transient 1800 200 3 3 5 1 Relative atomic mass/u 52 89 90 139 140 142 115 * Internal reference. added as a reference element to the solutions. Four replicate readings were made from duplicate samples (Table 5). Reagents and Samples Samples were weighed and reagents were added in a class 100 clean room.High-purity reagents ( H,02 and HF EM Science Gibbstown NJ USA and 99.997% LiBOz and 99.9995% H3B03 Johnson Matthey Ward Hill MA USA) were used or pre-purified by sub-boiling distillation ( HN03). For the determination of C analytical-reagent grade chemicals were used.34 A 250 pg ml-' Sc solution was prepared from Sc203 (99.99% Scz03 Johnson Matthey). Standard analyte solutions for ICP-AES except C were prepared in 10% HN03 with 50 pg ml-' of Sc and 2% LiB0z.33 Carbon standards were Journal of Analytical Atomic Spectrometry May 1996 Vol 11 345Table 5 Instrumental conditions for ICP-AES measurements ICP-AES instrument Rf frequency/MHz Rf forward power/kW Rf reflected power/W Nebulizer Spray chamber Argon gas flow rates/l min-' Outer Intermediate Aerosol Viewing height/mm Read delay/s Integration time/ms Analytical wavelength/nm Reference wavelength/nm Perkin-Elmer Plasma I1 27.12 1 .o <5 Cross flow Double pass 15 1 .o 1 .o 9 for C 15 for other elements 60 for C 20 for other elements 100 C I 193.091 Si 1251.611 Ti I1 334.941 A1 I 396.152 Ba I1 455.403 Sr I1 421.552 Sc I1 424.683 prepared from mannitol or urea.34 A mixture of water-soluble amines (CFA-C amines Spectrasol McAfee NJ USA) was added to neutralize the excess of fluoride.For the semiquantitative ICP-MS analysis a 1 pg ml-' multi- element standard solution was prepared from an ICP-MS multi-element stock standard solution (ICP-MS1 Spex Industries Edison NJ USA) and from single stock standard solutions containing Al Ba Bi Ca Cd Co Cr Cu Fe Mg Mn Mo Ni Pb Sr Ti Zn and Zr (Spex Industries). The standard solution for ICP-MS quantitative analysis after fusion contained Ce Cr La Nd Y and Zr in 2% HN03 and 1 YO LiB02.In the investigation of spectroscopic interferences a 50 ng ml-' standard solution was prepared in 1% HNO for external calibration. Model solutions containing blank and 5 ng ml-' of the multi-element standard solution were prepared in 1% HNO 1% HCl 10% CFA-C amines+ 1% HN03 and 10% CFA-C amines+ 1% HCl. An external calibration standard solution for sample analysis was prepared from the 1 pg ml-' multi-element standard solu- tion and single element standard solutions of Na Ca K Mg Si and Fe. The final concentrations were 100.05 pg ml-' of Ca; 100 pg ml-' of Na; 40 pg ml-' of K; 20.05 pg ml-' of Mg; 2pgml-' of Si 1.05pgml-' of Fe and 50ngml-' for the other elements.For quality control purposes the standard solution was analysed as a sample after every five samples and the accuracy for 38 elements (i.e. Al Ba Bi Ca Ce Cd Co Cr Cu Dy Er Eu Fe Gd Ho K La Lu Mg Mn Mo Na Ni Nd Pb Pr Sc Si Sm Sr Tb Th Ti Tm Y Yb Zn and Zr) was checked based on 22 elements in the external calibration standard solution. Standard Reference Materials from the National Institute of Standards and Technology (NIST) SRM 157 1 Orchard Leaves SRM 1548 Total Diet SRM 1549 Non-Fat Milk Powder SRM 1577b Bovine Liver SRM 1566 Oyster Tissue and certified reference materials from the National Research Council of Canada (NRCC) Lobster Hepatopancreas TORT-1 and food samples from the Republic of the Marshal Islands were analysed.Two sample preparation procedures were employed. Digestion Procedures Fusion A 5 g sample was weighed into a platinum crucible and 0.25 g of LiB02 (0.2 g for ICP-AES) was added and mixed well with the sample. The crucible was heated in the programmable muffle furnace with the following programme heat at 5°C min-' to 300 "C; hold at 300°C for 30 min; heat at 5 "C min-' to 700°C; hold at 700°C for 120min; heat at 50°C min-' to 980 "C; hold at 980 "C for 60 min; and cool to room tempera- ture. To the fused mixture 2ml of distilled de-ionized water were added followed by 1 ml of HNO and one drop of H202. For ICP-MS measurements the resulting solution was diluted to 25 ml with distilled de-ionized water. For ICP-AES measurements.Two ml of a 250 pg ml-' Sc solution were also added to the fusion preparation along with the HN03 and one drop of H202. The mixture was heated for 10-15 min on a hot-plate with stirring. The solution was diluted to 10 ml in a 15 ml Nalgene tube.33 For ICP-MS measurements. Fused sample solutions and standards were merged on-line through a T-junction in a 1 1 ratio with 100 ng ml-' of an In internal reference solution. Microwace dissolution A 1 g sample was weighed into a PFA vessel and 5 ml of HN03 were added. The vessel was left for at least 4 h (e.g. overnight) in the clean room covered by a plastic rupture disc but not closed. Then 0.5ml of HF and 2ml of H202 were added. The vessel was closed. Six vessels were heated under pressure control. After cooling the vessels were opened in the clean room 5 ml of 4% H3B03 were added and the solution was transferred into a 50ml calibrated flask and diluted to volume with distilled de-ionized water.For determination of C. A 5 ml aliquot of the dissolved sample was transferred into a 50ml glass beaker and evapor- ated gently to a small volume to remove the volatile carbon compounds. One ml of HNO was added along with 5 ml of a 250 pg ml-' Sc solution and diluted to 25 ml with distilled de-ionized water. For ICP-MS measurements. To 10 and 20 ml aliquots 5 ml of a 1 pgml-' Ge In and Re standard solution were added. The solution was neutralized to pH 7-8 with approximately 5 ml of the tertiary amine reagent and diluted to 50 ml with distilled de-ionized water. RESULTS AND DISCUSSION ICP-MS Interferences Amines The addition of alcohols influences metal and polyatomic ion intensities and the position of their maximum signals as a function of the aerosol gas flow rate.6*'3 The influence of the addition of amines on the plasma performance was studied in the present investigation.Results are illustrated in Fig. 1. The addition of amines shifts the maximum of the metal ion signal towards lower aerosol gas flow rates. The shift is due probably to a change in aerosol formation and transport although these properties were not examined. To quantify any matrix effects resulting from the amines the instrumental signal intensities per concentration unit response were obtained daily with a blank and a 0.050 pg ml external calibration standard in 1% HNO (Table 1).Multi-element standard solutions of 5 ng ml-' in 1% HN03 and in 1% HN03 + 10% CFA-C were analysed. The ratios of the concentrations obtained (c~-*-~/ cHNO,) were calculated for 38 elements. Some of the results are presented in Table 6. Values close to one indicate little or no interference; whereas results considerably > 1 could be related to spectroscopic interferences or non-spectroscopic signal enhancement. For some elements a positive systematic error is present and cannot be eliminated by the system software. To determine which isotopes from the whole range used in the measuring parameters are mostly affected additional experiments were performed. The following conclusions could 346 Journal of Analytical Atomic Spectrometry May 1996 Vof.1 I10000 12C35Clf. In the final procedure 46Ti was used. The "Cr+ signal experiences a strong interference from 40Ar12C+. However the 53Cr+ signal is less influenced by the addition of amines. To avoid 40Ar160+ and 40Ca160+ interferences on the 56Fe+ signal and because of the high Fe concentrations in the samples 57Fe was chosen. The 57Fe isotope was found to be better than 56Fe for the analysis of biological materials because of a lower background and only a little degradation in the detection limit." The 75As+ signal is not affected by the presence of C and N. The observed increase in response is a signal enhancement that was also observed previously when organic compounds were present.13-" Selenium as with As exhibits a similar signal enhancement in the presence of organic compounds. The other isotopes investigated are either not affected or are less influenced by the addition of the tertiary amines.The potential internal reference elements Ge In and Re show cn 8000 e + .= 4000 0 P h c .- 6000 .- - a 2000 0 0.65 0.75 0.85 0.95 1.05 1.15 1.25 Nebulizer gas flow rate/l min-' Fig. 1 Signal intensities as a function of the nebulizer (aerosol) gas flow rate in the presence and absence of CFA-C amines H 75As+ in CFA-C; 0 75ArC1+ in CFA-C; A 74Ge+ in CFA-C; + 26CN+ in CFA-C; 0 75A~+ in HNO,; 0 75ArC1+ in HN03; and A 74Ge+ in HNO Table 6 Interference expressed as ( c ~ ~ ~ - ~ / c ~ ~ ~ ~ ) from 5 ng ml-' model solutions using calibration curve and optimization of the aerosol gas flow in 1% HNO n=4 Element C Mg A1 Si Ca sc Ti V Cr Mn Fe Ge As Se Y In Pr Re CCFA-C/CHN03 339 f 224 3.8 f 2.3 6.1 f 3.5 30.6 k 6.0 7.7 + 1.5 1.4f0.3 1.4k0.3 1.1 k0.3 11.4_+ 1.3 1.1 f0.1 1.1 f0.2 0.9f0.1 2.5 0.4 1.7k0.3 1.0 If 0.1 1.0 f.0.1 1.0 & 0.1 1.1 +O.l be made for the isotopes influenced most based on mean values of 2-6 measurements. In the argon plasma 24Mg+ and "Mg+ signals are subject to some '2C12C+ and I2Cl3C + interferences respectively; whereas the 26Mg+ signal is strongly influenced by the forma- tion of 12C14N+. The 27Al+ signal experiences I3Cl4N+ a nd "C1'N+ interferences at low levels when amines are present in the Ar discharge. Both "Si+ and 29Si+ signals exhibit strong spectroscopic interference more from '2C160+ and 13C160+ respectively than l4NI4N+ and 14N15N+. The ,OSi+ signal is less influenced than the other Si isotopes.The 40Ca+ signal was not investigated because of the 40Ar+ interference. Because Ca i s a major element in many biological samples a less abundant isotope (i.e. 43Ca) was selected for the determination of Ca. The 45Sc+ signal is influenced by the formation of 13~160160+ . The 48Ca+ signal overlaps the most abundant 48Ti+ isotope signal. Experience with this isotope and math- ematical correction showed that selecting another Ti isotope is preferable when the Ca Ti ratio is very high. All the other Ti isotopes investigated are less influenced by the matrix. Since correct results were obtained with 47Ti in the analysis of Ca-rich soils after fusion,3o this isotope was chosen first for sample analysis. The results however indicated a strong positive systematic error resulting from the formation of behaviour similar to elements in their m/z range.An internal reference will compensate for most of the transport effects and drift but not for a specific signal enhancement (e.g. As and Se) or spectroscopic interferences. Therefore when analysing samples both the blank and external standard solutions have to be prepared to contain CFA-C amines. Chloride interference Chlorides are commonly present in food and other biological materials and their polyatomic ion interferences with some isotopes in ICP-MS are well documented." Furthermore the addition of organic compounds generally helps to reduce chloride interferences on V As and Se ion signal^.^^^'^^^^ Model solution blanks and 5 ng ml-' standards in 1% HNO 1% HCl 10% CFA-C + 1% HNO and 10% CFA-C + 1% HCl were measured for m/z values with known chloride interference. The ratios of the measured intensities from the solutions in 1% HC1 versus 1% HN03 (ratio A) and in 10% CFA-C + 1% HCl versus 10% CFA-C + 1% HNO (ratio B) are given in Table 7 for Ti V Cry As and Se.A pronounced effect is observed for most V Cr As and Se isotopes in these test solutions. Chloride concentrations in the RMs studied are at least a factor of ten lower than the chloride added to the test solution but in some analysed diet food samples the concen- trations can reach the investigated chloride levels. Without C the presence of chloride in the solution does not influence the Ti signals. When both C and chloride are present however 12C35Cl+ and 12C37Cl+ are formed and spectral interference is observed for the 47Tif and 49Ti + signals.Therefore 46Ti+ is preferred for sample analysis. For V the 35C1160+ interference on "V' signal is not reduced signifi- cantly by the addition of tertiary amines. A major chloride interference appears for both ',Cr+ and 54Cr + signals. Addition of tertiary amines significantly reduces this interference. In practical analyses ',Cr+ and 54Cr+ sig- nals should be compared to verify the absence of chloride interference. The chloride interferences on the 75A~+ signal are also reduced in the presence of tertiary amines. Another strong chloride interference is observed for the 77Se+ signal that as for the 7 5 A ~ + signal is decreased approximately by half in the presence of amines (Table 7).At low aerosol gas flow rates optimized for the CFA-C amines results do not differ significantly from those obtained at optimum flow rates with HNO except for some isotopes (Table 7). Further investigations of chloride interferences on As' and Se+ signals showed that ArCl+ exhibited a maximum signal usually at lower aerosol gas flow rates than polyatomic ions such as carbides and nitrides. This is illustrated in Fig. 1 for 12C14N+ a nd 4oAr35C1+. The reduction of ArCl' formation Journal of Analytical Atomic Spectrometry May 1996 Vol. 11 347Table 7 Chloride interference in 1 YO v/v HCI on some element masses expressed as ratios A = I H a / I H N O 3 and B = ICFA-C + Ha/Ic,A-c Optimization with HN03 Optimization with CFA-C Possible C1 interference I sot ope 46Ti 47Ti 48Ti 49Ti 51v 52Cr 'jcr 54Cr 75As 17Se A 0.9k0.1 1.2f0.2 1.1 fO.1 1.2k0.1 5.8 0.7 1.0k0.2 32.7 k 23.9 6.5 f 0.9 3.4 & 0.5 28.8 f 6.8 B 1.2k0.2 8.0 f 0.4 1.1 fO.1 4.0k0.1 5.1 If 1.1 1 .Of 0.3 6.9 f 4.3 1.1 f0.3 l.5f0.3 11.7 f 3.2 A 0.9k0.1 1.1 fO.1 1.1 kO.1 1.2k0.1 5.2+ 1.1 1.OLt:O.l 16.8 9.2 3.3 f 0.5 6.3 f 2.0 19.8 k 3.5 B 0.9 & 0.1 7.3 k 0.6 1.1 kO.1 4.3k0.1 5.2 f 1.0 1.0 & 0.1 7.9 k 0.6 1.1 k0.2 3.0k0.5 10.2 f.0.9 when organic compounds are present could be owing to the competitive formation of carbides nitrides and oxides.6 Since the optimum signal enhancement and minimal chloride interference for As and Se depend on aerosol gas flow rate the influence of tertiary amines on the As and Se determination has been studied in detail and compared with the addition of N to the Ar outer gas flow el~ewhere.~~.~' Microwave Dissolution The amount of HN03 added to a 1 g sample was varied from 5 to 7ml.Hydrogen peroxide was also added in two sets of experiments (Table 8) because of its positive influence on the sample decomposition without increasing the acid concen- t r a t i ~ n . ~ * Addition of 0.5 ml of HF per 1 g of dry sample previously gave complete recovery of Si in food samples,30 and was chosen for the proposed dissolution procedure. All samples were digested using the same programme with pressure control. Aliquots of the digested samples were taken and the residual C was determined using a previously estab- lished procedure.34 The C remaining in these digested samples is listed in Table 8.Addition of H202 reduces residual C and improves the efficiency of sample destruction. Addition of 7 ml of HNOJ does not significantly decrease the amount of residual C in the solution. By reducing the amount of acid necessary for a digestion the amount of tertiary amines required to neutralize the solution to pH 7-8 also was reduced. With this improved digestion procedure adding about 10% v/v tertiary amines was optimal for ICP-MS measurement~.~~ With higher (i.e. 12 and 20% CFA-C) tertiary amine solution concentrations C deposited on the sampler cone and C and N polyatomic ion interferences were increased. Sample Analysis The importance of choosing an internal reference close in relative atomic mass number to the analytes has been discussed previously." In the present experiments Ge In and Re are used as internal references to cover the entire m/z range.Lithium and B were not determined; the former because of the contamination of the ICP-MS instruments from other measure- ments and the latter was present in the solutions added as H3B0,. Comparison of standard solutions prepared with 10 and 12% tertiary amines confirmed that these internal reference elements compensated sufficiently for small differences in solu- tion viscosity except for As and Se.36 Therefore the solutions used for optimization of aerosol gas flow and calibration were prepared to contain 10% v/v tertiary amines. Precalibrated signal intensity counts per concentration unit were updated by analysing a blank and one standard solution.Two aliquots of different microwave dissolved sample replicates were analysed. Optimal conditions for sample measurements were sought using NIST SRM 1571 Orchard Leaves because of its relatively high Si concentration. The measurement parameters (m/z ranges and isotopes mass spectrometer sensitivity) and the external calibration composition (elements and their concen- trations) were varied (Table 2). The results obtained are pre- sented in Table 9 along with available certified values. For elements without certified values quantitative ICP-AES or ICP-MS results from measurements after sample fusion are included. In an earlier investigation of semiquantitative analysis of water samples external calibration with 15 elements at a concentration of 0.050 pg ml- and measurement of 43Ca 47Ti and 57Fe were required to obtain results with an accuracy of 2-50%. This is measurement parameter set I in Table2 and Table 8 Residual carbon (RCC) after different microwave dissolution procedures for 2-4 sample replicates; results in Yo 7 ml HN0,+3 ml H,O,+0.5 ml HF 5 ml HNO,+2 ml HzOz + 0.5 ml HF 5 ml HNO + O S ml HF Sample Milk powder Canned peaches Canned chicken Doughnut NIST SRM 1573 Tomato Leaves NIST SRM 1566 Oyster Tissue NIST SRM 1548 Mixed Diet TORT 1 Lobster Hepatopancreas NIST SRM 1577 Bovine Liver NIST SRM 1549 Non-Fat Milk Powder Mean 95% CI* RSD 8.9 0.68 11.3 5.8 3.2 4.4 6.8 6.2 4.2 2.3 3.8 0.44 6.4 2.5 1.9 1.9 2.5 2.5 1.9 1.3 4.7 7.2 6.3 4.8 6.7 4.7 4.1 4.2 5.1 6.1 Mean 9.8 0.96 10.2 5.4 3.4 5.6 6.7 5.1 6.5 3.0 95% CI* RSD 1.3 1.5 0.50 5.8 6.4 7.1 3.1 6.5 1.3 4.1 3.2 6.2 4.8 7.9 2.5 5.5 3.8 6.5 1.9 7.1 Mean 95% CI* RSD 14.2 6.4 5.0 5.4 3.8 7.8 15.3 5.0 3.7 20.8 9.5 5.1 12.0 5.1 4.7 ~~ * 95% CI Confidence interval.348 Journal of Analytical Atomic Spectrometry May 1996 Vol. 1 1Table 9 Analysis of NIST SRM 1571 Orchard Leaves with different measurement parameters (from Table 2) and external calibration for 4 sample replicates. Concentrations in pg g-' if YO is not indicated Element* Ca (YO) K (%) Fe Mn Na Pb Sr Zn c u Rb As Sb Cr Ni Mo Cd Ba c o Bi Si (%) Ti A1 Y Zr La Ce Nd Mi? (%I Parameter file Certified ICP-AES ICP-MS value 2.09 f 0.03 1.47 f 0.03 0.62 f 0.02 300 f 20 91 &4 82f6 45f3 3 7 f l 25f3 12f 1 12f 1 10f2 2.9 f 0.3 2.6f0.3 1.3f0.2 0.3k0.1 0.1lfO.01 (44) t (0.2) t (0.1) t - - - - - - - - quantitative - - - - - - - - - - - - - - - - - - - - - - - 0.42 f 0.05 0.80f0.26 1.1 f0.07 0.95 f 0.07 0.71 f 0.20 I 0.009 & 0.001 < 0.001 0.55 f 0.1 1 99+15 92.8 f 4 185 + 100 49.3 f 6 36.2 & 3.6 24.5 Ifr 2.5 14.9 f 1.2 2.3 f0.5 9.6f 1 3.3 f 0.4 9.2 f 3.5 1.9k0.5 0.75 f 0.10 0.08 f 0.05 54f5 0.6 f 0.2 0.03 + 0.02 < 0.05 70+ 10 255 f 55 0.68 f 0.10 0.65 f 0.25 1.0 + 0.05 1.0f0.05 0.74 & 0.18 I1 3.59f0.17 0.66 f 0.32 0.51 f 0.06 114f18 96.6 f 3.7 3283 k lo00 44.2 k 2 30.2 Ifr 0.6 20.8 f 1.2 11.3 f 0.9 3.8 f 0.2 5.3 f 1.1 2.4 f 0.3 26 & 1.5 1.6 f 0.3 0.80f0.10 0.17f0.10 33f3 0.5f0.1 0.3 f 0.05 0.16 f 0.01 45f 12 275 f 48 0.62 & 0.09 1.0 k0.30 0.83 & 0.07 0.83 fO.10 0.57 k 0.25 I11 1.98 f 0.20 1.07 f 0.19 0.55 f 0.08 98f 13 90f3 1845 f 500 47.5 f 3 31 & 1.5 22 f 0.9 11.3 f 1.4 4.3 f 0.2 6.4f 1.1 2.7 f 0.4 189 f 52 2.0 f 0.5 0.18 f0.08 0.111fr0.06 41+3 0.4 f 0.2 0.05 f 0.03 0.21 k 0.03 20f5 323 f 40 0.48 f 0.09 0.85 f 0.28 0.98 f 0.06 1.0 f 0.07 0.72f0.12 IV 2.01 f0.19 1.10 Ifr 0.60 0.56 f 0.05 346 f 28 91 f 4 723 f 108 43f2 35.3 f 1.8 24.7 k 2.4 10.6 f 0.8 7.1f0.6 9.2f1.0 2.8 f 0.3 2.7 f 0.4 1.6 & 0.5 0.28 f 0.10 0.16 f 0.03 40f2 0.3 f 0.1 0.04 f 0.03 0.16 f 0.05 19f4 340 f 43 0.46 f 0.07 0.83 f 0.23 0.95 f 0.05 0.98 f 0.05 0.67 f 0.15 * Hg Se Th U Be Ga Cs and Te are below the limit of determination of ICP-MS (Sciex Elan 250).t Uncertified values. Table 10 Analysis of reference materials. Concentration in pg g-' if YO is not specified (4 replicate samples) Element Certified value NRCC TORT 1 Lobster Hepatopancreas- As 24.6 & 2.2 Cd 26.3 f 2.1 Cr 2.4 f 0.6 c o 0.42 f 0.05 c u 439 f 22 Fe 186f11 Pb 10.4 f 2.0 Mn 23.4 f 1.0 Hg 0.33 f0.06 Mo 1.5 f0.3 Ni 2.3 f 0.3 Se 6.88 f 0.47 Sr 113f5 V 1.4f0.3 Zn 177 f 10 Ca (%) 0.895 f 0.058 Mg (%I 0.255 & 0.025 K (Yo) 1.041 f 0.040 Na (YO) 3.67 f 0.20 Si Ti A1 Ba Y Zr La Ce Nd - - - - - - - - - NISTSRM 1577b Bovine Liver- K (Yo) 0.994 f 0.002 Na (YO) 0.242 f 0.006 Cd 0.50 f 0.03 Ca 116f4 c u 160k8 ICP-MS quantitative - - 2.7 f 0.5 - - - - - - - - - - - - - - - - - - - __ 1.6 f0.3 0.10 f 0.05 4.9 f 0.4 4.2 f 0.2 2.7 k0.3 - - - - - ICP-MS Semiquantitative measurement 18.0 f 5.0 27.2 f 3.6 3.3 f 0.7 (14.8)* 0.47f0.11 327 f 57 197 f 22 9.4 f 1.0 19.0 f 2.0 0.3 f 0.2 1.4 & 0.15 2.5f0.14 6.31 f0.56 111 f 19 0.69 f 0.20 144 f 10 0.83 f 0.14 (<O.Ol)t 0.23 IfI0.03 (0.14)t 0.66 f 0.16 (< 0.Ol)t > 1 (0.72)t 1250 f 866 4.2 f 1 (86)* 83 f 50 2.6 f 1 1.5 f 0.2 0.18 f0.08 4.8 f 0.3 4.1 f0.3 2.5 f 0.3 0.66 f 0.15 (< 0.l)t 1.0f0.5 (0.lO)Jr 0.48 f 0.12 123 Ifr 14 (< 5)f 135 f2a Journal of Analytical Atomic Spectrometry May 1996 Vol.11 349Table 10 (continued) ICP-AES ICP-MS ICP-MS Semiquantitative 1722 18 0.23f0.10 564f86 (8lO)t 10.3 f 1.0 3.7 f 0.3 7.0f 1.8 0.71 f0.15 < 0.05 0.12 f 0.01 105 & 13 <0.1 < 20 < 0.05 < 0.05 0.26 f 0.07 0.15 f 0.05 520 f 260 1.1 f0.5 (95)* 0.03 f 0.005 0.74 f 0.15 (7.5)* 0.010 f 0.004 0.10 f 0.05 0.01 5 f 0.008 0.026 f 0.003 0.008 f 0.004 Fe Pb Mg Mn Mo Rb Se Ag Sr Zn As A1 Sb Hg c o V Si Ti Ba Cr Y Zr La Ce Nd 184f 15 0.129 f 0.004 601 f28 10.5 f 1.7 3.5 f 0.3 13.7f 1,l 0.73 f 0.06 0.039 f 0.007 0.1 36 f 0.001 127 f 16 (0.05 )$ (3E (0.003 )§ (0.003 )$ (0.25 )$ (0.123)$ - - - - 4.8 f 0.2 0.65 f 0.10 <0.1 - 0.70 f 0.06 0.01 6 f 0.03 0.028 f 0.005 0.018f0.004 0.028 f 0.003 0.007 f 0.002 NISTSRM 1549 Non-Fat Milk- Ca (YO) 1.30 f 0.05 Mg (%I 0.120 f 0.003 K (Yo) 1.69 f 0.03 Na (YO) 0.497 fO.010 Cd 0.0005 f 0.0002 Cr 0.0026 f 0.0007 c u 0.7 f 0.1 Pb 0.0 19 f 0.003 Mn 0.26 f 0.06 Hg 0.0003 f 0.0002 Se 0.11 fO.01 Zn 46.1 f 2.2 A1 (2% Sb (0.00027)$ As (0.001 9)$ c o (0.0041 )$ Fe (2.1& Mo (0.34)$ Rb (11R Si (< 50E Ag (0.0003)$ Sn (<5R Ti Sr Ba Y Zr La Ce Nd - - - - - - - - 1.19 f0.26 (0.066)t 0.1 1 f 0.02 (0.086)t 1.30 f 0.26 (0.14)t 0.22f0.12 (<O.l)t NDS N D (8.2)* 0.76 f 0.20 0.55 f0.22 0.3 1 f 0.07 N D N D 43.6 f 4.6 < 209 N D ND 0.12 f 0.08 5.4 f 2 0.32 fO.11 5.5 f 1.6 380 f 160 0.5 f 0.3 4.2k0.8 (91)* 3.0 f 0.3 0.69 f 0.26 0.007 f 0.002 0.07 f 0.04 N D N D N D N D <0.1 - 0.94 f 0.5 - - 8.8f 1 - - 3.0 f 0.5 3.0 f 0.5 0.8 f 0.2 - 0.009 f 0.001 0.025 f 0.005 ND ND ND NISTSRM 1566 Oyster Tissue- Ca (YO) 0.15 f 0.02 Mg ( 7 0 ) 0.128f0.009 K (Oh) 0.969 f 0.005 Na (YO) As 13.4f 1.9 Cd 3.5 f 0.4 Cr 0.69 k 0.27 c u 63.0 k 3.5 Fe 195 f 34 Pb 0.48 f 0.04 Mn 17.5 & 1.2 Hg 0.057 f 0.01 5 Ni 1.03 f 0.19 Rb 4.45 f 0.09 Se 2.1 f 0.5 Ag 0.89 f 0.09 0.5 1 f 0.03 0.14f0.04 0.1 1 f 0.02 0.83 kO.1 1.4 f 0.8 8.6 f 3.2 3.8 f 0.3 0.87f0.4 57f 15 205 f 17 0.70f0.3 18.5 f 2.5 1.4 f 0.4 2.0 f 0.7 2.0 +_ 0.8 0.18k0.05 N D 350 Journal of Analytical Atomic Spectrometry May 1996 Vol.1 1Table 10 (continued) ICP-AES ICP-MS ~~ ICP-MS Semiquantitative 9.2 f 0.8 0.33f0.15 740f 124 0.67 f 0.30 0.19 f 0.07 N D N D 1.5f0.5 0.1 1 f 0.02 6.5f 1.8 266 f 80 6.4 f 2.8 0.42 f 0.04 0.53f0.10 0.23 f 0.09 0.40 f 0.06 0.25 f 0.02 Sr U Zn c o Mo T1 Th v Si (YO) Ti A1 Ba Y Zr La Ce Nd 10.36f0.56 0.1 16 f 0.006 852 14 ( 0.4 % (< 0.2H (0.1% (2.8 % (< 0.005E - - 0.13 f 0.01 10f 1 230 f 20 4.8 f 1.0 - 0.39 & 0.05 0.75 f0.15 0.30 & 0.05 0.42 & 0.03 0.23 f 0.02 NISTSRM 1548 Total Diet- Na (YO) 0.625 f0.026 K (%) 0.606 f 0.028 Ca (YO) 0.174 f 0.007 Mg 556 f 27 Fe 32.6 f 3.6 Zn 30.8 f 3.6 Mn 5.2 f 0.4 c u 2.6 f 0.3 Se 0.245 f 0.005 Cd 0.028 f 0.004 A1 (33% Rb (4.8% Sn (3.6% Ni (0.41 )§ Mo (0.27% Pb (0.05 )$ c s (0.014E Er (O.O0030)$ Si Ti - Sr Ba Cr Y Zr La Ce Nd - - - - - - - - - 1.85 f 0.87 0.67 f 0.29 0.16 f 0.05 544f72 37.0f 3.7 28.8 f 3.9 5.1 f 0.6 2.48 f 0.27 0.24 f 0.09 N D < 20 3.3 f 0.6 3.9 f 0.6 0.70 f 0.25 0.28 f 0.09 N D N D N D 768 f 500 3.9f 1 2.7 f 0.2 0.91 f0.28 0.76f0.04 0.005 f 0.003 0.06 f 0.01 0.006 f 0.003 0.08 f 0.02 ND 73.5 f 2.5 7.5 f 0.7 3.0 f 0.3 1.0Ifr0.2 0.85 f 0.05 0.01 f 0.05 0.07 f 0.02 0.009 f 0.003 0.07 f 0.02 0.001 5 f O.oOO5 * Result when 47Ti is used instead of 46Ti and 54Cr instead of 53Cr.f Result with parameter file 1 (Table 2) (Le. without Ca Mg Na and K in the pg ml-’ range in the calibration solution). $ ND not detected. 8 Uncertified values. it was employed initially in the present extension of the work to biological materials.The results obtained for NIST SRM 157 1 Orchard Leaves (Table 9) are incorrect for Al Ca K Fe Na Cr Mo Co Si and Ti however. A second parameter set (measuring parameter 11) extended the external calibration solution by including Na K Mg Si and Ca at concentrations similar to those expected in biological samples. All isotopes measured were selected by the instrument software default condition. However with this parameter set the concentrations of these ten elements were still incorrect (Table 9). This demon- strated that the measuring parameters must be selected to include specific isotopes to avoid spectral interferences. Furthermore the measurement sensitivity for the major elements had to be reduced.In measuring parameter sets I11 and IV the measured isotopes were selected manually for Mg Ca Si Ti Cr and Fe rather than accepting the instrument default selection. The sensitivity settings for Na K and Ca were reduced to prevent over-range count rates. The most accurate results were obtained with parameter set IV. Therefore the instrumental conditions shown in Table 3 with parameter IV were applied for the analysis of five biologi- cal certified reference materials. Results are summarized in Table 10. For most of the elements the determined values are comparable with the certified or independently determined concentrations. For comparison erroneous results were obtained for Cr Ca Mg and Ti with parameter file I and/or when 47Ti instead of 46Ti and 54Cr instead of J3Cr were used.Some element (ie. Na K Si and Al) determinations were incorrect regardless of the parameter set employed. The recovery of 15 element spikes including some REEs with no certified values was evaluated for NIST SRM 1549 Non-Fat Milk and NRCC TORTl Lobster Hepatopancreas under the same analysis conditions. Two experiments were conducted in which standard additions were made before and after sample dissolution. No significant differences in the recoveries were observed. The recoveries of the semiquantit- ative analysis are in the range of 92-12870 (mean 112%) for the Non-Fat Milk and 78-13270 (mean 116%) for the TORTl Journal of Analytical Atomic Spectrometry May 1996 Vol. 1 1 351RMs. The ability to determine REEs in the presence of fluoride complexed by H3B03 is effective with the addition of tertiary amines.In a practical application of the developed methodology various food samples including meat baked goods and canned fruits were prepared and analysed by ICP-MS. Standard additions were made to evaluate the accuracy and recoveries in the range of 100f25% were obtained. Details of these results will be given elsewhere. The assistance provided by M. D. Argentine and S. F. Durant in operating the ICP-MS instrument is appreciated. Research was supported by the ZCP Information Newsletter. REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Wang M. S. Cave W. T. and Coakley W. S. in Analytical Emission Spectroscopy ed. Grove E. L. Volume 1 Part 11 Dekker New York 1972 vol. 1 part 2 ch. 8.Jarvis K. E. Gray A. L. and Houk R. S. Handbook oflnductiuely Coupled Plasma Mass Spectrometry Blackie Glasgow 1992 pp. 194 206 260 258. Evans E. H. and Giglio J. J. J. Anal. At. Spectrom. 1993 8 1. Xiao G. and Beauchemin D. J. Anal. At. Spectrom. 1994,9 509. Lam J. and Horlick G. Spectrochim. Acta Part B 1990,45 1313. Evans E. H. and Ebdon L. J. Anal. At. Spectrom. 1990 5 425. Durant S. F. Fresenius' J. Anal. Chem. 1993 347 389. Louie H. and Yoke-Peng Soo S. J. Anal. At. Spectrom. 1992 7 557. Wang J. Evans E. H. and Caruso J. A. J. Anal. At. Spectrom. 1992 7 929. Vanhaecke F. Vanhoe H. and Dams R. Talanta 1992 39 737. Friel J. K. Skinner C. S. Jackson S. E. and Longerich H. P. Analyst 1990 115 269. Vanhoe H. Goosens J. Moens L. and Dams R. J. Anal. At. Spectrom.1994 9 177. Goossens J. Vanhaecke F. Moens L. and Dams R. Anal. Chim. Acta 1993 280 137. Hill S. J. Ford M. J. and Ebdon L. J. Anal. At. Spectrom. 1992 7 1157. Allain P. Jaunault L. Maurae Y. Mermet J.-M. and Delaporte T. Anal. Chem. 1991 63 1497. 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 Munro S. Ebdon L. and McWeeny D. J. J. Anal. At. Spectrom. 1986 1 211. Satzger R. D. Anal. Chem. 1988 60 2500. Amarasiriwardena D. Durrant S. F. Lasztity A. Krushevska A. Argentine M. D. and Barnes R. M. presented at the 1994 Winter Conference on Plasma Spectrochemistry San Diego CA USA January 1994. Crews. H. Am. Lab. 1993 25(4) 342. Schmidt J.-P. Massayon Y. and Gelinas Y. Anal. Chim. Acta 1991,249 495. Gunter K. von Bohlen A. Paprott G. and Klockenkamper R. Fresenius' J. Anal. Chem. 1992 342 444. Vandecasteele C. Vanhoe H. and Dams R. J. Anal. At. Spectrorn. 1993 8 781. Vanhoe H. J. Trace Elem. Electrolytes Health Dis. 1993 7 131. Ridout P. S. Jones H. R. and Williams J. G. Analyst 1988 113 1383. Sheppard B. S. Heitkemper D. T. and Gaston C. M. Analyst 1994 119 1683. Introductions to Microwave Sample Preparation ed. Kingston H. M.. and Jassie L. B. American Chemical Society Washington DC 1988. Schelenz R. and Zeiller E. Fresenius' J. Anal. Chem. 1993 345 68. Nadkarni R. A. Anal. Chem. 1984 56 2233. Wang X. Lasztity A. Viczian M. Israel Y. and Barnes R. M. J. Anal. At. Spectrom. 1989 4 727. Krushevska A. P. and Barnes R. M. J. Anal. At. Spectrom. 1994 9 981. Tatro M. E. Spectroscopy 1990 5(2) 16. Users Manual PE-Elan Model 5000 ICP-MS System Perkin Elmer Norwalk CT USA Version 1 May 1992 Rev. B. Krushevska A. and Barnes R. M. Analyst 1994 119 131. Krushevska A. Barnes R. M. Amarasiriwaradena C. J. Foner H. and Martines L. J. Anal. At. Spectrom. 1992 7 845. Myers S. A. and Tracy D. Spectrochim. Acta Part B 1983 38 1227. Krushevska A. Kotrebai M. Lasztity A. and Barnes R. M. presented at FACSS St. Louis MO USA October 1994 paper No. 779. Krushevska A. Kotrebai M. Lasztity A. Barnes R. M. and Amarasiriwardena D. Fresenius' J. Anal. Chem. in the press. Krushevska A. Barnes R. M. Amarasiriwardena C. J. Foner H. and Martines L. J. Anal. At. Spectrom. 1992 7 851. Paper 5108124F Received December 13 1995 352 Journal of Analytical Atomic Spectrometry May 1996 Vol. 1 1

ISSN:0267-9477    

DOI:10.1039/JA9961100343

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Determination of Copper Cadmium and Lead in Biological Samples by Isotope Dilution Inductively Coupled Plasma Mass Spectrometry After On-line Pre-treatment by Anodic Stripping Voltammetry TARN-JIUN HWANG AND SHIUH-JEN JIANG* Department of Chemistry Nutionul Sun Yut-Sen University Kuohsiung Tuiwun 804 Republic of China Flow injection isotope dilution ICP-MS was applied to the determination of Cu Cd and Pb in several biological samples after on-line pre-treatment by anodic stripping voltammetry. The isotope ratios for each injection were calculated from the areas of the flow injection peaks. The influence of the operating conditions of the electrochemical system on the analyte signals was studied. The influence of non-spectroscopic and spectroscopic interferences caused by the matrix on the precision and accuracy of isotope ratio determinations was also investigated.The precision for isotope ratio determinations was better than 2%. Detection limits were 0.07 0.01 and 0.07 ng ml-I for Cu Cd and Pb respectively. The isotope dilution ICP-MS method was successfully applied to the determination of Cu Cd and Pb in National Research Council of Canada CRMs DORM-1 Dogfish Muscle and DOLT-1 Dogfish Liver and NIST SRM 2670 Toxic Metals in Freeze-Dried Urine. Keywords Isotope dilution; inductively coupled plasma muss spectrometry; anodic stripping voltammetry; matrix sepuration; copper; cadmium; lead; biologicul sample ICP-MS is known to be a powerful technique for trace multi- element and isotopic analysis.'*2 However this technique is prone to interferences caused by sample matrix constituents.These interferences may be caused by polyatomic ions with the same nominal mass as the analyte signal suppression or enhancement due to non-spectroscopic matrix effects and blockage of the nebulizer and sampler. In order to achieve accurate and reliable results matrix separation is needed when the matrix elements in the prepared solution interfere with the determination. Methods for elimination of sample matrix effects have been explored including chromatographic ~eparation,~ utilization of a mixed gas and column preconcentrati~n.~,~-~~ Of these studies electrochemical sample pre-treatment for ICP-MS detection appeared pr~mising.'~-'~ In anodic stripping voltammetry (ASV) the elements of interest are selectively deposited out of the sample matrix onto a working electrode at a suitable working potential. Separation is possible if there are sufficient differences between the reduction potentials of the analytes and those of the matrix elements.After a selected period of deposition the analytes collected on the working electrode are stripped back into the solution phase and the oxidation currents are measured." Many matrix elements such as alkali and alkaline earth metals that may cause interference in ICP-MS have reduction poten- tials that are different from those of transition metals. By * To whom correspondence should be addressed. Journal of Analytical Atomic Spectrometry appropriate control of the electrode potential separation of transition metal analytes and matrix elements may easily be accomplished.The use of flow ASV for sample pre-treatment for ICP-AES and ICP-MS detection has been reported previously by Caruso and ~ o - w o r k e r s . ~ ~ - ~ ~ In their studies a reticulated vitreous carbon (RVC) working electrode was used successfully to deposit the analyte elements and to separate the analyte from the matrix elements. In the present work the simultaneous determination of Cu Cd and Pb in biological samples by using an automated flow injection (FI) ASV system combined with isotope dilution ICP-MS detection was studied. Isotope dilution is well-recognized as a definitive analytical technique for the determination of trace elements. The influence of the operating conditions of the electrochemical system on the analyte signals was studied. The influence of non-spectroscopic and spectroscopic interferences caused by the matrix on the precision and accuracy of isotope ratio determinations was also investigated.The method was successfully applied to the determination of Cu Cd and Pb in National Research Council of Canada (NRCC) CRMs DORM-1 Dogfish Muscle and DOLT-1 Dogfish Liver and NIST SRM 2670 Toxic Metals in Freeze-Dried Urine. EXPERIMENTAL ICP-MS Device and Conditions An ELAN 5000 ICP-MS instrument (Perkin-Elmer SCIEX Thornhill Ontario Canada) was used. Samples were intro- duced with a cross-flow pneumatic nebulizer with a standard Scott-type spray chamber. The gas flow rates were controlled by a four-channel mass flow controller. The ICP operating conditions were selected so as to maximize the sensitivity for the isotopes of interest in order to obtain the best precision and accuracy for isotope ratio determinations.The sensitivity of the instrument could vary slightly from day-to-day. The ICP operating conditions used are summarized in Table 1. The mass spectrometer parameters used for isotope ratio measurements are listed in Table 1. The measurements were made by peak hopping rapidly from one mass to another staying only a short time (20 ms) at each mass. After the completion of one sweep additional sweeps were made until the sum of the accumulated dwell times equalled the requested measurement time. The isotope ratios for each element in each injection were calculated from the areas of the FI peaks. The mean isotope ratio and standard deviation were calculated from isotope ratios from several repeated injections.Journal of Anulyticul Atomic Spectrometry May 1996 Vol. 11 (353-357) 353Table 1 Equipment and operating conditions ICP-MS instrument cate. Aliquots (10.0 ml) of the reconstituted solution and appropriate amounts of enriched isotopes were transferred into closed Teflon PFA vessels. After 5.0 ml of nitric acid and 1.0 ml Perkin-E1mer "IEX ELAN 'O0O Plasma conditions Plasma gas flow rate Intermediate gas flow rate Aerosol gas flow rate Rf power Mass spectrometer settings Photon stop lens Bessel box lens Einzel lenses 1 and 3 Bessel box plate lens Resolution Dwell time Sweeps per reading Reading per replicate Number of replicates Points per spectral peak Replicate time 12 1 min-' 0.9 1 min-' 1.08 1 min-' lo00 w - 10.05 V 10.95 V -0.04 v -72.5 V Normal 20 ms 7 100 1 1 14000 ms Flow Injection of hydrogen peroxide had been added the solutions were heated inside a CEM MDS-2000 microwave digester (CEM Matthews NC USA) to decompose the organic components. The digests were then diluted to the desired volume with supporting electrolyte solution after cooling to room tempera- ture.A blank was carried through the digestion procedure as outlined above to correct for any analyte contaminant in the reagent used for sample preparation. The NRCC CRMs were dried as described in the certificates. A 0.5 g portion of DORM-1 and a 0.1 g portion of DOLT-1 were weighed into closed Teflon PFA vessels and digested as follows. To each vessel 10.0ml aliquots of nitric acid 2.0ml of hydrogen peroxide and appropriate amounts of enriched isotopes were added.The mixtures were heated inside a CEM MDS-2000 microwave digester to decompose the organic components. The digests were then diluted to the desired volume with supporting electrolyte solution after cooling to room tempera- ture. A blank was carried through the digestion procedure to In order to investigate the effect of the sample matrix on the precision and accuracy of isotope ratio determinations a simple FI system was built. The system was composed of a Rheodyne (Cotati CA USA) 5041 rotary sample injection valve and a Gilson (Middleton WI USA) Minipuls 3 peristaltic pump. A 100 pl portion of the test mixture solution was injected into a 0.01 mol I-' nitric acid carrier solution and analysed by ICP-MS.correct for any analyte Contaminant in the reagent used for sample preparation. Design of the FI-ASV System An ASV flow cell was designed and constructed as illustrated in Fig. 1. The cell body was machined from a 45.0 mm diameter Teflon rod. A solution flow channel (4mm diameter) was drilled through the cell body. The working electrode was Reagents and Sample Preparation Enriched isotopes purchased from the Oak Ridge National Laboratory (Oak Ridge TN USA) included 65Cu0 "'CdO and 204Pb(N03)2. Stock solutions of approximately 500 mg 1-' of each were prepared by dissolution of an accurately weighed amount of the material in nitric acid and dilution to volume. The concentrations of the spike solutions were verified by reverse spike isotope dilution ICP-MS.All chemicals were used without further purification unless specified otherwise. Stock standard metal solutions (1000mg I-') and nitric acid (70% m/m Trace metal grade) were from Fisher (Fair Lawn NJ USA). Ammonium nitrate (GR) calcium nitrate (GR) sodium chloride (GR) and mercury a 15 mm long 100 ppi (pores per inch) RVC plug (Electrosynthesis Lancaster NY USA). Electrical contact to the RVC working electrode was provided by a platinum wire introduced through the wall of the cell and held by a + in-28 nylon fitting. The RE-4 Ag-AgC1 reference electrode (Bioanalytical Systems West Lafayette IN USA) was held by a stainless-steel retainer (Bioanalytical Systems). The platinum wire counter electrode was introduced through the wall of the cell and held by a ;t in-28 nylon fitting.Each part of the flow cell can easily be removed for storage or replacement. Control of the potential applied to the working electrode was accomplished with a CV-27 potentiostat (Bioanalytical Systems). In order to make the analysis more convenient and precise an automated FI-ASV system was constructed in nitrate solution were from Merck (Darmstadt Germany). this -laboratory. A schematic diagram of the automated Hydrogen peroxide (35% m/v) was from RDH (Seelze FI-ASV-ICP system is shown in Fig. 2. This system was Germany). Triton X-100 was from Sigma (St. Louis MO composed of two peristaltic pumps (Gilson Minipuls 3) and USA). Magnesium nitrate (AnalaR) was from BDH (Poole two PTFE six-port four-way rotary valves (Rheodyne 5041) Dorset UK).The supporting electrolyte solution (0.1 mol 1-' the switching of which was actuated by Rheodyne 5701 pneu- ammonium nitrate) was prepared by dilution of a 1.0 mol 1-' stock solution and was purified by passing it through a laboratory-packed Chelex- 100 cation-exchange column four times. The mercury plating solution was 0.001 mol 1-' in mercury nitrate and 0.1 mol 1-' in ammonium nitrate. After the electrochemical deposition step the analytes stripped were eluted to the ICP-MS system with a solution of 0.01 mol 1-' nitric acid. The tolerance of the matrix separation system for co-existing matrix ions was examined by adding 1OOOpg ml-' Mg2+ and/or 5000pg ml-' Na' to long ml-I of stock metal solutions. Each solution was injected into the FI-ICP-MS and ASV-ICP-MS systems successively and the isotope ratios of Cu Cd and Pb were then determined for comparison.The applicability of the method to real samples was demon- strated by the analysis of NIST SRM 2670 Toxic Metals in Freeze-Dried Urine and NRCC CRMs DORM-1 (Dogfish M I Reference for Trace and Fig. 1 Schematic diagram of ASV flow cell. A Ag-AgC1 reference electrode; B platinum wire counter electrode; C. Dlatinum wire conduc- (Dogfish Liver Reference Material for Trace Metals). The NIST SRM 2670 was reconstituted as described in the certifi- tor to working electrode; D RVC working elecirode 354 Journal of Analytical Atomic Spectrometry May 1996 Vol. 11wl---- Waste Pump 1 Carrier Flow cell Waste acid 1 ( b Sample Valve 1 Pump 1 Waste Carrier Flow cell dl Waste** be 2 TO ICP-MS Pump 2 acid Fig.2 Flow diagram of the FI-ASV system. a Bold line flow path of sample in the deposition step; b bold line flow path of analytes stripped to ICP-MS.The operating procedure is given in the text matic actuators and Rheodyne 7163 solenoid valve kits. The switching between the deposition and the stripping potentials and the automation of the FI system were controlled by a personal computer through a home-made 1/0 card and switching circuit. Procedure Before plating the mercury film the cell was washed with the supporting electrolyte to remove any air trapped inside the RVC. With the potential held at -0.7 V the mercury nitrate plating solution was delivered to the cell at a flow rate of 1.0 ml min-' for 20 min in the forward direction and then for another 20min in the reverse direction.After the plating of the mercury film the solution was switched to 0.01 mol 1-' nitric acid and the potential was switched to 0.2 V for 10 min to strip the impurities deposited during the plating step. At the end of a set of experiments the mercury film was removed by delivering a 1% nitric acid solution to the flow cell while the potential was held at 0.8 V for 1 h. Finally the cell was rinsed with pure water to remove the acidic solution and was ready for storage. The electrochemical system (see Fig. 2) is described below. The first rotary valve was used as the sample injection valve with a 2.0 ml PTFE sample loop. The sample was loaded with a plastic syringe. The contents of the loop were then injected into a stream of the supporting electrolyte solution by rotating the valve and delivered to the cell by Pump 1 as shown in Fig.2(4. The potential applied to the working electrode was switched to - 1.2 V at the moment the sample was injected to start the deposition step. At the same time 0.01 mol 1-' nitric acid solution was supplied to the ICP-MS system by Pump 2. After a selected period of deposition the flow of supporting electrolyte was stopped for 15 s. Valve 1 was then switched back to the loading position for the next sample. The potential at the working electrode was switched to 0.2V and Valve 2 was rotated to allow the nitric acid solution to pass through the flow cell and elute the analytes stripped to the ICP-MS system for analysis [Fig.2(b)]. Isotope Dilution Calculation The analyte concentration in the sample was calculated from the following equation where c is the concentration of analyte c the concentration of the spike Rt the isotope of the spike R the natural isotope ratio R the experimentally determined isotope ratio XB the natural abundance of isotope B X the abundance of isotope B in the enriched spike M the relative atomic mass of the analyte element and M' the relative atomic mass of the spike. Owing to the mass discrimination effect the intensities obtained during isotope ratio determinations of each sample were used to calculate the isotopic abundance of each element. RESULTS AND DISCUSSION Selection of the Operating Conditions of the Electrochemical System Reticulated vitreous carbon was chosen as the working elec- trode material because of its high porosity and large surface area.The electrochemical flow cell constructed was shown to be leakage-free at a flow rate as high as 4.0 ml min-'. The mercury film was coated onto the RVC electrode as described under Experimental. After 5 h of use the ion signal of a 2.0 ml sample containing long ml-' of Pb measured by ASV- ICP-MS was within 90% of the initial value demonstrating that the lifetime of the coated mercury film was sufficient for the experimental requirements. The performance of the RVC electrode may deteriorate after several days of use. How- ever the cell design made the replacement of the working electrode easy. The component of the supporting electrolyte is an important factor that can affect the electrochemical process. Ammonium nitrate potassium nitrate and ammonium acetate were tested as supporting electrolytes.Ammonium nitrate was chosen because of the higher deposition efficiency and lower back- ground noise. The necessity of oxygen removal was also investigated and was found not to be essential in this system. Therefore the samples supporting electrolyte solution and eluent solution were not de-oxygenated during this work. In the work of Caruso and ~o-workers,'~~" the deposition and stripping potentials were chosen so as to provide the optimum conditions for each analyte individually. The elements studied were determined separately. In the present work the deposition and stripping potentials chosen were a compromise that allowed the simultaneous determination of Cu Cd and Pb.Therefore the deposition potential should be as negative as is necessary for the least reducible analyte and the stripping potential should be sufficiently positive so that all the analytes can be stripped from the electrode. In this work a deposition potential of - 1.2 V and a stripping potential of 0.2 V were used. Under these conditions the accumulation of matrix elements such as Na Mg and Ca was not observed. Effect of Sample Flow Rate on Ion Signal Another important factor that affects deposition efficiency is the rate of analyte transport to the working electrode surface during the deposition step. For a given volume of mercury the concentration of the element in the mercury electrode is directly proportional to the limiting current i and deposition time t .Accordingly a greater concentration can be achieved by maximizing i in a given deposition time. An empirical equation" that defines il is il = nFADco/G (2) Journal of Analytical Atomic Spectrometry May 1996 Vol. 1 1 3551.6 I I I Q) I- d a 0.6 0.4 I I I 0.5 1 .o 1.5 2.0 2.5 Sample flow rate/ml min-' Fig. 3 Effect of sample flow rate on the ion signal measured by the ASV-ICP-MS system. The volume of the sample loop was 2.0ml. Sample solution containing 10 ng ml-' Cu Cd and Pb in 0.1 mol I-' ammonium nitrate. Deposition potential was - 1.2 V. Stripping poten- tial was 0.2 V. Analytes stripped were eluted to ICP-MS with 0.01 mol I-' nitric acid at a flow rate of 1.5 ml min-'. Peak areas were integrated and normalized to the first point where n is the number of electrons transferred F the Faraday constant A the surface area of the electrode incm2 D the diffusion coefficient of the analyte in cm2 s-' co the concen- tration of the analyte in the solution phase in molcm-3 and S the thickness of the Nernst diffusion layer.The thickness of the diffusion layer is experimentally controllable. For a flow system the thickness can be decreased by increasing the flow rate of the sample solution. The effect of sample flow rate on the ion signal measured by ASV-ICP-MS is shown in Fig. 3. According to eqn. (2) the ion signal should increase as the flow rate increases if the sample solution is constantly flowing during the deposition. However in this experiment the volume of sample was fixed; hence at higher flow rates the time for the sample solution to contact the working electrode would be shorter whereas at lower flow rates the diffusion layer would be thicker.Therefore an optimum flow rate exists. The optimum sample flow rate was 1.2ml min-' for Cu and Cd and 1.5 ml min-' for Pb. For the simultaneous determination of Cu Cd and Pb the flow rate was set at 1.2ml min-'. Effect of Eluent Flow Rate on Ion Signal Fig. 4 shows the effect of the eluent flow rate on the ion signal. An increased eluent flow rate increased the ion signals slightly and reduced the analysis time. However an increased eluent flow rate could decrease the nebulization efficiency causing the ion signal to decrease. Hence an eluent flow rate of 2.0 ml min-' was selected in subsequent experiments.I r I I I 1 0 B3cu I d r - .d v) al 1.0 1 3 .d a al d IX 0.8 1 I I I I 1 I 1.0 1.5 2.0 2.5 3.0 3.5 Eluent flow rate/ml min-' Fig. 4 Effect of eluent flow rate on the ion signal measured by the ASV-ICP-MS system. Sample flow rate was 1.2 ml min-'. Other conditions as in Fig. 3 Under the selected electrochemical operating conditions a complete analysis cycle was accomplished in less than 6 min. Calibration plots for the elements studied were linear with correlation coefficients better than 0.9994 at levels near the detection limits up to at least 200 ng ml-'. Detection limits calculated from the calibration plots were 0.07 0.01 and 0.07 ng ml-' for Cu Cd and Pb respectively and were based on the conventional definition as the concentration of the analyte yielding a signal equivalent to three times the standard deviation of the blank signal.Better detection limits would be expected if reagents of higher purity were used. Non-spectroscopic and Spectroscopic Interferences As described earlier the reducing potentials of the matrix elements are usually different from those of the analytes thus allowing the analytes to be separated from the matrix and accumulated on the mercury film during the deposition step. The effectiveness of the ASV system in eliminating the matrix was demonstrated in the following experiments. Solutions containing the analytes and matrix elements were analysed by ASV-ICP-MS. The results were compared with those obtained for solutions analysed by a simple FI-ICP-MS system.Table 2 shows the results of adding various concentrations of NaCl and Mg(N03)2 to a test solution containing 10 ng ml-' Cu. As can be seen the 63Cu:65Cu ratio increased when 5000 pg ml-' Na was added which indicated an interference at m/z 63 from ArNaf. Moreover the 63Cu:65Cu ratio decreased when lo00 pg ml-' Mg was added which indicated an interference at m/z 65 from ArMg'. Table 2 also shows that a stable 63Cu:65Cu ratio could be obtained when Na and Mg were separated from the analyte with the ASV system. Hence for the analysis of highly saline samples Na and Mg must be separated before Cu is determined. The precision of isotope ratio determinations was better than 2% with the ASV sample pre- trea tmen t sys tem. Surface-active substances can also decrease the deposition efficiency and ion signal by blocking the working electrode surface.Sample solutions containing 10 ng ml-' of the analytes and different concentrations of Triton X-100 were analysed. The results are shown in Fig. 5. As can be seen the ion signals decreased rapidly as the concentration of Triton X-100 increased although no significant change in the isotope ratio was observed. Table 3 shows the effect of surfactants and UV photolysis on the ion signals. As can be seen the ion signals decreased to 58-80% of the original signals when lo00 pg ml-' of Triton X-100 was added. After photolysis for 1 h with a Metrohm (Herisau Switzerland) 705 UV digester the ion signals were restored to 100% for Cu and Pb although the ion signal of Cd was still less than 100%.In order to obtain the most precise and accurate results for samples containing Table 2 Isotope ratios of Cu in various matrices with different methods of analysis* 63cu T U Sample composition FI ASV 2.14 k 0.04 9.55 k 0.36 2.12 f 0.02 2.1 1 f 0.02 10 ng ml' Cu Cd Pb 1.99 k 0.02 2.1 1 f0.02 10 ng ml-' Cu Cd Pb 10 ng ml-' Cu Cd Pb 10 ng ml-' Cu Cd Pb +5000pgml-'Na + lo00 pg ml-I Mg +5000pgml-'Na + lo00 pg ml-' Mg 2.1 3 f 0.02 4.47 f 0.64 * FI carrier (0.1 mol 1-' ammonium nitrate) flow rate=1.5 ml min-'; 100 pl sample loop. The operating conditions of the ASV- ICP-MS system are given in the text. Results are the mean of five measurements f standard deviation. 356 Journal of Analytical Atomic Spectrometry May 1996 Vol. I 14 Id d 0 63cu 0 '14Cd v 'OePb -20 0 20 40 60 80 100 120 Concentration of Triton X-lOO/pg m1-l Fig.5 Effect of Triton X-100 concentration on ion signals Table3 Effect of the presence of surfactants and of photolysis on ion signals Peak area (counts) Sample composition c u Cd Pb 10 ng ml-' Cu Cd Pb 3.34 x 105 1.20 x 105 6.25 x 105 (100)" (100) (100) 10 ng ml-' Cu Cd Pb 2.68 x 105 7.02 x 104 4.57 x 105 + 1000 pg ml-' Triton X-100 (80) (58) (73) 10 ng ml-' Cu Cd pb 3.28 x 105 1.05 x 105 6.18 x 105 + 1000 pg ml-' Triton X-100 (98) (88) (99) + 1 h UV photolysis * The numbers in parentheses indicate the relative ion signal of each element. The signal of the first solution of each element was assigned a value of 100%. a high concentration of surfactant or organic matrix pre- digestion or pre-photolysis of the sample before the electro- chemical sample pre-treatment step would be necessary.Determination of Cu Cd and Pb in Reference Materials In order to demonstrate the effectiveness of the proposed method for eliminating the interferences from ArNa' and ArMg' three highly saline samples (NIST SRM 2670 NRCC DOLT-1 and NRCC DORM-1) were analysed. The amounts of Cu Cd and Pb in each sample were determined by isotope dilution ICP-MS after on-line sample pre-treatment by ASV. The results of the analysis of the reference materials are given in Tables 4 and 5. The good agreement between the experimen- tal results and the certified values demonstrates the applica- bility of the proposed method to the analysis of real samples. For the normal level freeze-dried urine sample the Cd concen- tration was not determined because of the small signals Table 4 Determination of Cu Cd and Pb in a Freeze-dried Urine reference material (NIST SRM 2670) by ASV-isotope dilution ICP- MS* Concentrationlng ml- ' Sample Element Found Certified value SRM 2670 c u 146 f 2 13Ot-20 normal level Cd -t (0.4)$ Pb 8+1 (lo)$ SRM 2670 c u 374 If 2 370 k 30 elevated level Cd 85f5 88f3 Pb 121 f 7 109$-4 * Mean of five measurements k standard deviation.t Not determined. $ Concentration not certified. Table 5 Determination of Cu Cd and Pb in Dogfish Liver (DOLT-1) and Dogfish Muscle (DORM-1) reference materials by ASV-isotope dilution ICP-MS* Concentration/pg g-' Certified value Element Found Sample DOLT-1 c u 20.2 I.t 0.3 20.8 k 1.2 Cd 4.35 If 0.33 4.18 k0.28 Pb 1.38 & 0.08 1.36f0.29 DORM-1 c u 5.18 f0.40 5.22 f 0.33 Cd 0.088 f0.018 0.086 f 0.012 Pb 0.41 f0.14 0.40 f 0.12 * Values are the mean of five measurements f standard deviation.obtained which may be the result of competition with the high concentration of Cu during deposition. CONCLUSION The effective elimination of the matrix using the proposed ASV-ICP-MS system allowed the simultaneous isotope dilution determination of Cu Cd and Pb in biological samples. Since the deposition of the analyte is not an exhaustive process greater sample preconcentration may require a more efficient cell design. Other applications of the electrochemical sample pre-treatment ICP-MS system are under investigation in this laboratory. This research was supported by a grant from the National Science Council of the Republic of China under Contract No. NSC 83-0208-M-110-027 and NSC 84-2113-M-110-019.REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Houk R. S. Anal. Chem. 1986 58 97A. Jarvis K. E. Gray A. L. and Houk R. S. Handbook of Inductively Coupled Plasma Mass Spectrometry Blackie Glasgow 1992. Plantz M. R. Fritz J. S. Smith F. G. and Houk R. S. Anal. Chem. 1989,61 149. Evans E. H. and Ebdon L. J. Anal. At. Spectrom. 1989 4 299. Alves L. C. Allen L. A. and Houk R. S. Anal. Chem. 1993 65 2468. Xiao G. and Beauchemin D. J. Anal. At. Spectrom. 1994,9 509. Ebdon L. Ford M. J. Hutton R. C. and Hill S . J. Appl. Spectrosc. 1994 48 507. Laborda F. Baxter M. J. Crews H. M. and Dennis J. J. Anal. At. Spectrom. 1994 9 727. McLaren J. W. Mykytiuk A. P. Willie S. N. and Berman S. S. Anal. Chem. 1985 57 2907. Yang H.-J. Huang K.-S. Jiang S.-J. Wu C.-C. and Chou C.-H. Anal. Chim. Acta 1993 282 437. Huang K.-S. and Jiang S.-J. Fresenius' J. Anal. Chem. 1993 347 238. Lu P.-L. Huang K.-S. and Jiang S.-J. Anal. Chim. Acta 1993 284 181. Yang K.-L. Jiang S.-J. and Hwang T.-J. J. Anal. At. Spectrom. 1996 11 139. Bersier P. M. Howell J. and Bruntlett C. Analyst 1994 119,219. Pretty J. R. Blubaugh E. A. and Caruso J. A. Anal. Chem. 1993,65 3396. Pretty J. R. Evans E. H. Blubaugh E. A. Shen W. L. Caruso J. A. and Davidson T. M. J. Anal. At. Spectrom. 1990 5 437. Pretty J. R. Blubaugh E. A. Evans E. H. Caruso J. A. and Davidson T. M. J. Anal. At. Spectrom. 1992 7 1131. Wang J. Stripping Analysis. Principle Instrumentation and Applications VCH Deerfield Beach FL 1985. Kissinger P. T. and Heineman W. R. Laboratory Techniques in Electroanalytical Chemistry Marcel Dekker New York 1984. Paper 5/07386C Received November 9 1995 Accepted January 19 1996 Journal of Analytical Atomic Spectrometry May 1996 Vol. 1 1 357

ISSN:0267-9477    

DOI:10.1039/JA9961100353

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Determination of Trace Amounts of Sulfur in Steel by Electrothermal Vaporization-Inductively Coupled Plasma Mass Spectrometry Journal of Analytical Atomic Spectrometry HIROHITO NAKA Sumitomo Metal Industries Ltd. 1-8 Fuso-cho Amagasaki 660 Japan D. CONRAD GREGOIRE Geological Survey of Canada 601 Booth St. Ottawa Ontario Canada K1 A OE8 A method is described for the determination of trace amounts of S in steel by ETV-ICP-MS. The effect of Fe Cu Al Si V Co Ni Cr Mo Ti Mn and W on S signals and the use of KOH as a chemical modifier were studied. Most concomitant elements affected the intensity and shape of the S ETV- ICP-MS signal. The addition of KOH as a chemical modifier only partially eliminated these interference effects. The use of isotope dilution calibration and the removal of Fe by solvent extraction with 4-methylpentan-2-one were used to compensate for interference effects.A precision of kO.2 pg g-' at an S concentration of 2 pg g-' was achieved. The limit of detection for S in steel was 0.05 pg g-'. Keywords Sulfur determination; electrothermal vaporization; plasma mass spectrometry; steel; solvent extraction; 4-methylpentan-2-one; isotope dilution; chemical modijier The accurate and precise determination of ygg-' levels of S in steels is important to the successful production of high- technology steels because the physical and chemical properties of these steels are significantly affected by small changes in S concentration.' Conventional methods used for the determi- nation of S in steel rely on the infrared absorption of SO2 following combustion in an induction furnace2 or spectropho- tometry using methylene blue after reduction of S to H2S and a distillation step.3 The spectrophotometric method is useful for determining S at concentrations above several yg 8-l.The sensitivity of the spectrophotometric method can be improved by using a 2 m waveguide capillary cell4 or ethylene blue which has twice the molar absorptivity of methylene blue.5 Although the above methods have good sensitivity they involve a complicated and time-consuming H2S evolution step. A more easily applied method was suggested by Yamada et aL6 who used a flow injection technique coupled with an alumina microcolumn and ICP atomic emission spectrometry. Sulfur was determined at the pgg-' level in high-purity iron with a reported limit of detection of 0.3 pg g-'.This method however is difficult to implement because for most samples the method of standard additions is required to compensate for interferences from concomitant elements. Toda et aL7 used on-line H2S evolution gas-phase introduction ICP emission spectrometry for the determination of trace amounts of S in steel and reported a standard deviation of 0.3 yg g-' for an S concentration of 3.5 pg 8-l. The precision obtained however was not adequate for the production of steels containing The isotope dilution calibration technique coupled with MS can measure S more precisely and accurately than can be generally achieved using simple external calibration. Using isotope dilution thermal ionization MS Kelly et aL8 were able to determine 6.4 pg 8-l of S in low S steel with a precision of <5 pgg-' of s.1.2 pgg-l. This method involves the precipitation of S as As2S3 after reduction to H2S and a distillation step. The complexity of the sample preparation procedure may have resulted in the poor precision obtained in spite of using the isotope dilution technique. Solution nebulization ICP-MS (SN-ICP-MS) is a sensitive method for the determination of metallic elements but the measurement of S is hampered by the intense polyatomic ion background produced by oxygen and nitrogen oxides which are isobaric with the four isotopes of S. For example 160229 16021H+ and 160180+ are isobaric with 32S+ 33S+ and 34S+ respectively and 36Ar+ is isobaric with 36S+. ETV as a means of sample introduction can be used to remove water from sample solutions and thus reduce back- ground levels of interfering polyatomic ions.GrCgoire and Nakag reported that for ETV-ICP-MS the background ion count rate at m/z=33 and 34 was only 1500 and 1000 counts s-' respectively and the absolute limit of detec- tion for S was 50 and 20pg using 33S+ and 34S+ signals respectively. This paper reports on the application of ETV-ICP-MS to the determination of trace amounts of S in steel. In order to eliminate or compensate for interferences from Fe Cu Al Si V Co Ni Cr Mo Ti Mn and W in sample solutions on the measurement of S KOH was used as a chemical modifier and calibration was achieved by isotope dilution. Since the addition of KOH as a modifier did not completely remove the inter- ference from concomitant elements the isotope dilution cali- bration was used to compensate for the interference effects.In addition solvent extraction with 4-methylpentan-2-one was used for removing Fe by far the major matrix element from sample solution. EXPERIMENTAL Instrumentation A Perkin-Elmer (Norwalk CT USA) SCIEX Elan 5000 ICP mass spectrometer equipped with an HGA-600MS electrother- mal vaporizer was used. The electrothermal vaporization system was fitted with a Model AS-60 autosampler. Pyrolytic graphite coated tubes were used throughout. A Dionex (Sunnyvale CA USA) Model 4500i ion chromatograph was used for the determination of S as sulfate ion in the isotopically enriched spike solution. A Perkin-Elmer Optima 3000 ICP atomic emission spectrometer was used for the determination of Fe and concomitant elements in the aqueous solution following solvent extraction with 4-methylpentan-2-one.Microwave digestion using a Milestone (Mississauga Ontario Canada) Model 1200 MEGA microwave oven was used to dissolve the S spike and sphalerite. Journal of Analytical Atomic Spectrometry May 1996 Vol. 1 1 (359-363) 359Reagents All solutions were prepared with ultra-pure water obtained from a Milli-Q water purification system (Millipore Mississauga Ontario Canada). Hydrochloric acid (Baker Analyzed J. T. Baker Canada Toronto Ontario Canada) purified by sub-boiling distillation was used. Nitric acid was laboratory-reagent grade (Baker Analyzed). Iron@) sulfate K2S04 and KOH solutions were prepared by dissolving the reagents (Spex Industries Edison NJ USA) in purified water.Stock standard solutions of Fe Cu Al Si V Co Ni Cr Mo Ti Mn and W were supplied by Spex Industries. 4-Methylpentan-2-one (Fisher Scientific Fair Lawn NJ USA) was purified by several extractions with an equal volume of water. Sulfur-34 isotopically enriched spike in the form of elemental S (32S 5.53 atomic %; ,,S 0.11%; 34S 94.33%; 36S 0.03%) was purchased from Oak Ridge National Laboratory (Oak Ridge TN USA). Sphalerite (NIST SRM 8556) used for correcting for instrumental mass discrimination (National Institute of Standards and Technology) had an isotopic com- position of 94.8871 atomic % 32S 0.7563% ,,S 4.3466% 34S and 0.0103% 36S. Japan Iron and Steel (JSS) CRMs were used for the method validation studies.Certified values for S and metallic impurities in the CRMs are listed in Table 1. Preparation of S Spike The method reported by Paulsen and Kelly" was used for the preparation of 34S enriched spike solutions. Five milligrams of enriched S were dissolved with a mixture of 10ml of HNO and 4ml of HC1 in the microwave oven. The solutions were transferred into PTFE beakers and Na2C0 was added to yield an Na S atom ratio of 4. The solutions were evaporated to dryness and the nitrate was destroyed by repeated evapor- ation with HCl. The residue was dissolved in 2mol1-' HCl and made up to a volume of 50 ml. The concentration of S in solution was determined (as sulfate) by ion chromatography. Sample Preparation For samples containing more than 5 pgg-' of S 0.1 g of sample was dissolved in 4 ml of aqua regia [HCI-HNO (3 + 1 )].Following the addition of 0.1 pg of 34S spike sample solutions were diluted to 10 ml in calibrated flasks. For samples containing less than 5 pg g- of S 1.0 g of sample was dissolved in 10ml of aqua regia. The resulting solution was diluted to 25 ml following the addition of 0.25 pg of S spike. The solvent extraction method with 4-methylpentan-2-one reported by Okano and Matsumura" was used for removing Fe from sample solutions. Three millilitres of solution contain- ing 10 g 1-' of sample were transferred into test-tubes and 6 ml of 4-methylpentan-2-one were added. After the mixture had Table 1 Certified values for S and metallic impurities in the JSS CRMs Certified values/pg g- ' S Si Mn Ni Cr Cu Co A1 JSS CRM 002-3 3 9 15 0.6* 2 2* 0.3* 6* Pure Iron Pure Iron Steel for S Determination Steel for S Determination JSSCRM 003-3 1.9* 41 48 8 2 14 10 3* JSS CRM 244-5 15 2600 9800 - - - - - JSSCRM 240-11 60 1900 5500 - - - - - * Refcrence values.360 Journal of Analvtical Atomic Svectrometrv. Mav 1996. been shaken for IOs the aqueous layer containing S was analysed by isotope dilution ETV-ICP-MS. For solutions containing 40 g 1-' of sample the solvent extraction was performed twice because Fe could not be removed completely from sample solutions during a single extraction. Measurement Conditions The experimental conditions for both the Elan 5000 and the HGA-600MS are given in Table 2. As a thermal condition a vaporization temperature of 2500 "C and a 0 s ramp mode were selected to enhance vaporization and transport of analyte.Optimization of plasma and mass spectrometer conditions was accomplished using solution nebulization sample introduction. The HGA-600MS was interfaced to the Ar plasma via an 80 cm length of 6 mm (id) Teflon tubing. During the dry and pyrolysis steps of the temperature programme opposing flows of Ar gas (300 ml min- ') originating from both ends of the graphite tube vented volatiles such as water and acids through the dosing hole of the graphite tube. During the high tempera- ture or vaporization step a graphite probe was pneumatically activated to seal the dosing hole. Once the graphite tube had been sealed a valve located at one end of the HGA workhead directed the carrier Ar flow originating from the far end of the graphite tube directly to the Ar plasma at a flow rate of 900 ml min-".Gregoire and Naka' demonstrated that KOH was effective in converting S-containing compounds into K2S04 and enhancing the S signal intensity. In this work KOH was thus used as a chemical modifier and its effect on S signals studied. Since steel sample solutions contain HCl and HNO which consume KOH KOH was added only after drying sample solutions within the graphite tube. In addition a vaporization temperature of 2000°C and a 1 s ramp time were selected because S signals were suppressed when sample solutions containing KOH were vaporized at higher temperatures and with faster heating rates. Isotope Dilution Analysis The following equation was used where C is the S concentration in the sample (pg g-') M is the sample mass (g) W is the mass of spike (pg) K is the ratio Table 2 Instrumental operating conditions and data acquisition parameters ICP mass spectrometer- Rf power Coolant argon flow rate Auxiliary argon flow rate Carrier argon flow rate Sample volume Dry step Temperature Pyrolysis step Temperature Vaporization step Temperature HGA-600MS electrothermal vaporizer- Data acquisition- Dwell time Scan mode Points per spectral peak (mlz) m/z monitored per measurement cycle Signal measurement MS resolution 7500-1 150 W 15.0 I min-' 900 ml min-' 600- 1 150 ml min- ' 10 p1 10 s ramp 110°C for 30 s 1 s ramp 300 "C for 20 s 0 s ramp (2000°C s - ' ) 2500°C for 5s 20 ms Peak-hopping 1 4 (maximum) Integrated counts 0.7 u at 10% peak height Vol.11of natural relative atomic mass for S to relative atomic mass of the S spike A and B are the atom fractions of 34S and 33S in the sample respectively A and B are the atom fractions of 34S and 33S in the spike respectively and R is the measured ratio of 34S:33S corrected for mass discrimination using the NIST sphalerite solution. Kelly et a/.* described S as one of the few elements which exhibits variability in its isotopic composition in nature. Therefore the ratio of 34S:33S in unspiked samples FeSO and sphalerite solutions was deter- mined to preclude bias from natural sources. The effect was found to be negligible for all of the S-containing solutions and was within the precision of the S isotope ratio measurement (1 %). RESULTS AND DISCUSSION Optimization of Plasma Conditions Optimization of carrier gas flow rate and rf power was accomplished by studying the relationship between the signal intensity for 34S+ as a function of these two parameters.The results of these experiments shown in Fig. 1 indicate that as the carrier gas flow rate is increased from 800 to 1100 ml min- the S signal intensity increases. Variation of rf power gave similar results. Experiments completed in this laboratory for S using SN-ICP-MS9 have shown that as the nebulizer flow rate is increased from 600 to 1150 ml min-' the S+ signal also increased reached a maximum at an Ar flow rate of 950 ml min-' and decreased at higher flow rates. The different results obtained with SN-ICP-MS and ETV-ICP-MS for the Ar flow rate are probably due to water loading of the Ar plasma.For SN-ICP-MS water loading essentially decreased the plasma temperature resulting in increased SO + production and a suppression in S ion production. For ETV-ICP-MS water is not introduced into the plasma during the vaporization step leaving more energy available for S ionization with increased rf power and carrier gas flow rate. Under these conditions however the plasma torch was observed to melt at rf powers > 1200 W during prolonged operation. In addition the gas flow rate was unstable at > 1150 ml min-l because the mass flow controller was rated only to 1000 ml min-l. An Ar carrier gas flow rate of 1100 ml min-l and an rf power of 1150 W were thus selected as standard operating conditions for the measurement of S isotope ratios.rf power/W 800 900 1000 1100 1200 1300 I I I I 3 800 900 1000 1100 1200 Carrier gas flow rate/ml min-' Fig. 1 (b) carrier flow rate Change in the signal intensity of 34S+ with (a) rf power and Effect of Concomitant Elements The effect of Fe as a matrix element and Cu Al Si Co Ni Cr Ti Mn V W and Mo as concomitants on the measurement of S+ ion intensities was examined. The effect of concomitant elements on 34S+ signals derived from the vaporization of 10 pl of sample solution containing 10 ng of S as FeSO in the presence of the above-mentioned elements is shown in Fig. 2. When compared with S vaporized alone the presence of Fe Cu Al Co Ni Cr Ti and Mn did not alter the appearance time but did result in a shift in the position of the maximum of the S signal.The appearance time is defined as the time during the high temperature vaporization step that the analyte signal rises above the background signal. In addition to the above the presence of these elements had a marginal effect on the signal intensity for 34S+ (Table 3). Since the position of the signal maximum marks the point in time when the rate of release of analyte is equal to the rate of removal and transport of analyte from the graphite surface to the Ar plasma it can be concluded that the main effect of Fe Cu Al Co Ni Cr Ti m710 1 2 3 4 0 1 2 3 4 0.0 1 2 3 4 Time/s Fig.2 Effect of concomitant elements on analyte signal pulse for 34S+. Vaporization temperature 2500 "C; 10 ng S; 0 s ramp time; mass of concomitant elements 1.0 pg Table 3 Effect of concomitant elements on the normalized counts of 34S+ for 10 ng of S as FeSO at 2500 "C using 0 s ramp mode Normalized counts Mass of concomitant elements I Fe c u A1 Si V c o Ni Cr Mo Ti Mn W 3.01 pg 1.01 1.07 1.11 0.79 0.90 1.07 0.99 1.01 0.76 1.03 1.02 0.99 0.1 Pg 1 .oo 1.04 1.14 0.73 0.73 1.07 1.14 1.05 0.74 1.01 1.03 0.78 1.0 Pg 1.01 1.13 0.9 1 0.79 0.79 0.99 1.07 1.01 0.71 0.98 0.85 0.76 Journal of Analytical Atomic Spectrometry May 1996 Vol.1 1 361and Mn is to alter the S mass transport efficiency between the plasma and the graphite surface. The presence of Si V Mo and W altered the appearance time as well as the shape of the S ETV-ICP-MS signal. The appearance time was earlier in the presence of V Mo and W and double S peaks appeared with Mo. Silicon formed a small shoulder on the S signal at about 2.2 s into the vaporization step.It is possible that the earlier appearance time the double-peaking and the shoulder can be attributed to the vaporization of a second S-containing compound. The temperature at which iron sulfate decomposes to form Fe203 and SO3 has been reported to be between 500 and 600"C,'2 76OoCl3 and between 680 and 74OoC.l4 VOSO decomposes at 450°C forming V205 SO2 and S03.15 The earlier appearance time can be explained as resulting from the lower decomposition temperature of VOSO compared with that of iron sulfate. Silicon is reported to form SiS in the presence of CaSO with a sublimation temperature of 940°C at 20mmHg.I6 SiS can be formed in the presence of iron sulfate and thus produces the shoulder peak observed.It is unlikely however that the lower appearance temperature S-containing compounds observed in the presence of Mo and W result from the formation of a sulfide since sulfides of Mo and W decompose at relatively high temperature^.'^ An expla- nation for the earlier appearance time in the presence of Mo and W cannot be advanced with the available data. The significant effect of concomitant elements on the vaporiz- ation of S means that the use of external calibration may be difficult unless the chemical form of both analyte S and S calibration standards is the same. Thus the addition of chemi- cal modifiers or the use of an isotope dilution calibration technique is required for quantitative analysis. Since Fe is the major matrix element larger amounts of Fe than those shown in Table 3 can significantly affect S signals.In practice more than 10 pg of Fe resulted in reduced S signal intensities derived from 10 ng of S. The use of chemical modification and isotope dilution calibration will not eliminate signal suppression and thus to obtain adequate sensitivity chemical separation tech- niques are necessary for removing Fe from sample solutions. Effect of Chemical Modifier The effect of KOH on S signals derived from the vaporization of 10 p1 of sample solution containing 10 ng of S (as FeSO,) in the presence of Fe Cu Al Si Co Ni Cr Ti Mn V W and Mo is shown in Fig. 3. The addition of KOH resulted in an enhancement of the S signal and the formation of double peaks in the presence of concomitants except for Si.The first peak cannot be derived from the conversion of S-containing com- pounds because the appearance time and the position of the maximum are in good agreement with S signals obtained without KOH. The second peak can be attributed to the formation of K2S04 because the position of the signal maxi- mum is in good agreement with those obtained for S volatilized as K2S04 in the presence of KOH. It was not possible to eliminate the interference from concomitant elements by using the KOH modifier because the addition of KOH did not quantitatively convert the S-containing compounds into K2S04 when concomitant elements were present. This may be due to incomplete chemical reactions or slow kinetics for the conversion process. Removal of Iron Results obtained from the interference study show that the concentration of Fe in sample solutions should be < lo00 mg 1-' to avoid calibration problems and to ensure good sensitivity. Solvent extraction with 4-methylpentan-2-one was used for removing Fe from 10ml aliquots of sample Tim& Fig.3 Effect of KOH as a chemical modifier on analyte signal pulse for 34S+. Vaporization temperature 2000 " C 1 s ramp time; modifier mass 10 pg; mass of concomitant elements 1.0 pg solution containing 0.1 g of Fe and 10 pg of S as FeSO,. Iron and S remaining in the aqueous layer following the solvent extraction were determined by ICP-AES and ETV-ICP-MS respectively. More than 99% of the Fe matrix was removed and more than 90% of the S was retained in the aqueous layer following solvent extraction. Okano and Matsumura" con- firmed that most elements except for Fe remained in the aqueous solutions after the 4-methylpentan-2-one solvent extraction.For this work since most concomitant elements were observed to remain in the sample solutions after solvent extraction isotope dilution calibration was required to com- pensate for S signal degradation caused by these concomitants. Optimum Spike Mass In order to obtain good precision and accuracy for the isotope dilution analysis the difference between the signal intensities for the two S isotopes determined should be kept to a minimum. In this work since the more abundant S isotope at m/z=34 was added as a spike the signal intensity for 33S+ might be insufficient for accurate analysis when adding small amounts of the S spike.The effect of the added mass of spike on the relative standard deviation (S,) for the analysis of 10ml of sample solutions containing various amounts of S is given in Table 4. On adding both 0.1 and 1.0 pg of S spike to 10 ml of sample solution the S values were less than 4% for 0.5 1.0 and 5.0 pg of S. The S climbed to 7% however for 0.1 pg of S. Higher S concentrations are required in this instance because Table 4 deviation (S,) of sulfur values (n= 7) Effect of mass of 34S+ enriched spikes on the relative standard 0.1 pg of spike 1.0 pg of spike 0.1 pg of s 7.3 7.7 0.5 pg of S 3.6 3.9 1.0 pg of s 2.3 2.1 5.0 pg of S 2.2 1.9 362 Journal of Analytical Atomic Spectrometry May 1996 Vol. 11Table 5 Results of the determination of S in the JSS CRMs.Mean 2% n = 5 Values obtained in this Values obtained by a spectrophotometric Sample Certified values/pg g-l work/pg g-' method4/pg g- JSS CRM 002-3 3 2.9 & 0.2 2.50 JSS CRM 003-3 1.9* 2.2 k 0.2 2.33 JSS CRM 244-5 15 15.5 k0.4 JSS CRM 240-11 60 58.6 t- 1.5 - - * Reference value. the signal intensity for 33S+ was insufficient to obtain adequate precision for sample solutions containing less than 0.5 pg of S. For samples low in S analyte concentrations can be increased 4-fold by using 1.0 g of sample dissolved in 10 ml of aqua regia and diluted to 25 ml. When 1.0 g sample masses were used the 4-methylpentan-2-one solvent extraction was carried out on 3 ml aliquots of sample solutions (recombined following extraction) because more than 1000 mg 1-' Fe remained after a single solvent extraction.After repeating the solvent extraction for a second time less than lOOmgl-' Fe remained. A spike mass of 0.1 pg was added to 10 ml of sample solution because similar precisions were obtained for 0.1 and 1.0 pg spikes. For the determination of less than 5 pg g-' of S in steel 0.25 pg of spike was added to 25 ml of sample solution and the solvent extraction repeated. Determination of S in Steels Results for the determination of S in JSS CRMs 002-3 003-3 244-5 and 240-11 are given in Table 5. The results obtained by the methylene blue spectrophotometric method using a 2 m waveguide capillary cell4 are also given in Table 5. For the analysis of JSS CRMs 002-3 and 003-3 S was preconcentrated by repeated solvent extraction on solutions containing 1 g of sample. The analytical values obtained by the proposed method are in good agreement with the certified values and the values obtained by the spectrophotometric method. The precision was about k0.2 pg g-' for S at the 2 pg g-' concentration level.A limit of detection (3s) of 0.05 pg g-' was obtained. From these results it can be concluded that the proposed method is applicable to the accurate and precise determination of S in steels at the low (< 10) pg g-' concentration level. CONCLUSIONS This work has shown that isotope dilution ETV-ICP-MS coupled with 4-methylpentan-2-one solvent extraction can successfully be used to determine trace amounts of S in steel. The main effect of Fe Cu Al Co Ni Cr Ti and Mn is to alter the S mass transport efficiency between the graphite tube and the plasma whereas Si V Mo and W probably cause chemical effects within the graphite tube.GSC Paper 44995. REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Sasabe M. Refining Limits of Impurities in Steel and Progress in Steelmaking Art Japan Iron and Steel Institute Tokyo 1992 Japanese Industrial Standards G-1215-1982 Methods for Determination of Sulphur in Iron and Steel Japanese Industrial Standards Committee. Narita K. Taniguchi M. Ota N. and Morooka R. Tetsu to Hagane 1981,67 2724. Chiba K. Inamoto I. Tsunoda K. and Akaiwa H. Analyst 1994,119 709. Hinotani S. Endo J. Takayama T. Mizui N. and Inokuma Y. ISIJ Znt. 1994 34 17. Yamada K. McLeod C. W. Kujirai O. and Okochi H. J. Anal. At. Spectrom. 1992 7 661. Toda E. Kubota Y. and Ichikawa G. Bunseki Kagaku 1992 41 453. Kelly W. R. Chen L.-T. Gramlich J. W. and Hehn K. E. Analyst 1990 115 1019. GrCgoire D. C. and Naka H. J. Anal. At. Spectrom. 1995,10,823. Paulsen P. J. and Kelly W. R. Anal. Chem. 1984 56 708. Okano T. and Matsumura Y. Tetsu to Hagane 1991,77 1951. Gallagher P. K. Johnson D. W. and Schrey F. J. Am. Ceram. SOC. 1970 53 666. Safiullin N. Sh. Gitis E. B. and Panasenko N. M. J. Znorg. Chem. USSR 1968 13 1493. Kamel A. E. Sawires Z. Khalifa H. Saleh S. A. and Abdallah A. M. J. Appl. Chem. Biotechnol. 1972,22 591. Dearnaley R. I. and Kerridge D. H. Thermochim. Acta 1983 63 219. Tittarelli P. Biffi C. and Kmetov V. J. Anal. At. Spectrom. 1994 9 443. Handbook of Chemistry and Physics ed. Weast R. C. CRC Press Cleveland OH 56th edn. 1975 pp. 3-25. Paper 510701 8 J Received October 24 1995 Accepted February 9 1996 Journal of Analytical Atomic Spectrometry May 1996 Vol. 11 363

ISSN:0267-9477    

DOI:10.1039/JA9961100359

出版商:RSC    

年代:1996

数据来源: RSC