摘要:

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.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.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.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.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.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/JA99611BP015

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/JA99611FX037

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

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

ISSN:0267-9477    

DOI:10.1039/JA996110X039

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Journal of Analytical I1 I Atomic Spectrometry I1 THE ROYAL CHEMISTRY Information Services JASPE2 11 (9) 37N-40N 61 3-906 341 R-354R CONTENTS NEWS PAGES Award Announcement Diary of Conferences and Courses Future Issues 37N 37N 39N PAPERS PLENARY LECTURE The Future of Plasma Spectrochemical Instrumentation Gary M. Hieftje PLENARY LECTURE Fundamental Description of Spectrochemical Inductively Coupled Plasmas D. C. Schram J. A. M. Van Der Mullen J. M. De Regt D. A. Benoy F. H. A. G. Fey F. De Grootte J. Jonkers Comparison of Electrospray and Inductively Coupled Plasma Sources for Elemental Analysis With Mass Spectrometric Detection Francine Byrdy Brown Lisa K. Olson Joseph A. Caruso Mass Spectrometric and Theoretical Investigations Into the Formation of Argon Molecular Ions in Plasma Mass Spectrometry J.Sabine Becker Gotthard Seifert Anatoli I. Saprykin Hans-Joachim Dietze Spectrochemical Analysis of Trace Contaminants in Helium (Helium-Fluorine) Pulsed Discharge Plasmas Aleksei B. Treshchalov Andrei S. Chizhik Arnold A. Vill Analysis of Ceramic Layers for Solid Oxide Fuel Cells by Laser Ablation Inductively Coupled Plasma Mass Spectroscopy Jochen Th. Westheide J. Sabine Becker Ralf Jager Hans-Joachim Dietze Jose A. C. Broekaert New Quantitative Approach in Trace Elemental Analysis of Single Fluid Inclusions Applications of Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) A. Mohamad Ghazi Tom E. McCandless D. A. Vanko Joaquin Ruiz Universal Calibration for Analysis of Organic Solutions by Inductively Coupled Plasma Atomic Emission Spectrometry Robert I.Botto Jim J. Zhu Improving Analytical Precision by Utilizing Intrinsic Internal Standards for Determining Minor Constituents by Inductively Coupled Plasma Atomic Emission Spectrometry Jason Li PLENARY LECTURE Status of and Perspectives on Microwave and Glow Discharges for Spectrochemical Analysis James D. Winefordner Eugene P. Wagner II Benjamin W. Smith INVITED LECTURE High-temperature Hydraulic High-pressure Nebulization a Recent Nebulization Principle for Sample Introduction Harald Berndt Jorge Yaiiez Determination of Rare Earth Elements in Wine by Inductively Coupled Plasma Mass Spectrometry Using a Microconcentric Nebulizer Sylvie Augagneur Bernard Medina Joanna Szpunar. Ryszard tobinski 613 623 633 643 649 66 1 667 675 683 689 703 713 continued on inside back cover Typeset printed and bound by The Charlesworth Group Huddersfield England 01484 517077 0267 - 9 ~ 7 7 t 1996 19 I 1 - UDetermination of Iodine Using a Special Sample Introduction System Coupled to a Double-focusing Sector Field Inductively Coupled Plasma Mass Spectrometer Wolfgang Kerl J.Sabine Becker Hans-Joachim Dietze Walter Dannecker INVITED LECTURE Digestion and Extraction of Biological Materials for Zinc Stable Isotope Determination by Inductively Coupled Plasma Mass Spectrometry Claude Veillon Kristine Y. Patterson Phylis B. Moser-Veillon Comparison of Two Different Inductively Coupled Plasma Mass Spectrometric Procedures and High-performance Liquid Chromatography With Electrochemical Detection in the Determination of Iodine in Urine V.Poluzzi 9. Cavalchi A. Mazzoli G. Alberini A. Lutman P. Coan I. Ciani P. Trentini M. Ascanelli V. Davoli Application of Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry to the Study of Protein-bound Lead in Human Erythrocytes lngvar A. Bergdahl Andrejs Schutz Anders Grubb Optimization of Electrochemical Hydride Generation Coupled to Microwave- induced Plasma Atomic Emission Spectrometry for the Determination of Arsenic and its Use for the Analysis of Biological Tissue Samples Claudia Schickling Jinfu Yang Jose A. C. Broekaert Determination of Platinum in Protein-bound CDDP and DBP by Inductively Coupled Plasma Optical Emission Spectrometry and Electrothermal Atomic Absorption Spectrometry Thorsten J. Einhauser Markus Galanski Bernhard K.Keppler Clean Laboratory Chemistry for the Microwave-assisted Digestion of Botanical Samples Charles B. Rhoades Jr. Determination of Trace Elements in Radioactive and Toxic Materials by Inductively Coupled Plasma Mass Spectrometry Fabien Pilon Stephane Lorthioir Jean-Claude Birolleau Silvyane Lafontan Measurement of Lithium Isotope Ratios by Inductively Coupled Plasma Mass Spectrometry Application to Geological Materials D. Conrad Gregoire Barbara M. Acheson Richard P. Taylor Comparative Study of Marine Sediment From Antarctica by Low-pressure Discharge Atomic Emission Spectrometry and Inductively Coupled Plasma- based Spectrometry Sergio Caroli Oreste Senofonte Stefan0 Caimi Peter Karpati Performance of Inductively Coupled Plasma Mass Spectrometric Methods Used in the Determination of Trace Elements in Surface Waters in Hydrogeochemical Surveys Gwendy E.M. Hall Judy E. Vaive Jean-Claude Pelchat Application of a Sequential Extraction Scheme to Ten Geological Certified Reference Materials for the Determination of 20 Elements Gwendy E. M. Hall Gilles Gauthier Jean-Claude Pelchat Pierre Pelchat Judy E. Vaive Comparative Analysis of Aluminium Oxide Powders by Inductively Coupled Plasma Mass Spectrometry With Low and High Mass Resolution Norbert Jakubowski Wolfgang Tittes Dagmar Pollmann Dietmar Stuewer Jose A. C. Broekaert Determination of the Precious Metals in Milligram Samples of Sulfides and Oxides Using Inductively Coupled Plasma Mass Spectrometry After Ion Exchange Preconcentration Zhongxing Chen Brian J.Fryer Henry P. Longerich Simon E. Jackson On-line Method for Inductively Coupled Plasma Mass Spectrometric Determination of Rare Earth Elements in Highly Saline Brines Ludwik Halicz lttai Gavrieli Ethel Dorfman Preconcentration of Rare Earth Elements on Activated Carbon and its Application to Groundwater and Sea-water Analysis D. S. R. Murty G. Chakrapani PLENARY LECTURE Radiofrequency Powered Glow Discharges Opportunities and Challenges R. Kenneth Marcus 723 727 73 1 735 739 747 75 I 759 765 773 779 787 797 805 a i i 81 5 a2 1 continued on facing pageINVITED LECTURE Developments in Glow Discharge Optical Emission Spectrometry Arne Bengtson INVITED LECTURE Pulsed Glow Discharge Time-of-flight Mass Spectrometry W. W. Harrison Wei Hang Relative Sensitivity Factors in Glow Discharge Mass Spectrometry the Role of Charge Transfer Ionization A.Bogaerts R. Gijbels Comparison of Atomization and Ionization Processes in Direct Current Radiofrequency and Microsecond Pulse Discharges Dagmar Pollmann Kristofor Ingeneri W. W. Harrison Use of a Direct Current Glow Discharge Mass Spectrometer for the Chemical Characterization of Samples of Nuclear Concern Maria Betti Analysis of Trace Impurities in Palladium Metal Powders by Glow Discharge Mass Spectrometry David M. Wayne Thomas M. Yoshida Donald E. Vance PLENARY LECTURE Plasma Spectrometry and Molecular Information Olivier F. X. Donard Ryszard lobinski Investigations Into Sulfur Speciation by Electrospray Mass Spectrometry Ian 1. Stewart David A. Barnett Gary Horlick Development of a Gas Chromatography Inductively Coupled Plasma Isotope Dilution Mass Spectrometry System for Accurate Determination of Volatile Element Species. Part 1. Selenium Speciation Stefan M. Gallus Klaus G. Heumann Speciation of Arsenic Compounds by Ion Chromatography With Inductively Coupled Plasma Mass Spectrometry Detection Utilizing Hydride Generation With a Membrane Separator Matthew L. Magnuson John T. Creed Carol A. Brockhoff Laser Ablation Inductively Coupled Plasma Mass Spectrometric Transient Signal Data Acquisition and Analyte Concentration Calculation Henry P. Longerich Simon E. Jackson Detlef Gunther CUMULATIVE AUTHOR INDEX 829 835 84 1 849 855 86 1 87 1 877 887 893 899 905 ATOMIC SPECTROMETRY UPDATES References 341 R

ISSN:0267-9477    

DOI:10.1039/JA99611BX040

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

9613401 9613402 9613403 9613404 96 96 3405 3406 96/3407 9613408 96/3409 9613410 Sadler D. A. Littlejohn D. Perkins C. V. Multi- element optimization of the operating parameters for inductively coupled plasma atomic emission spec- trometry with a charge-transfer device detection system a study of the effects of different response functions. J. Anal. At. Spectrom. 1996 11(7) 463. (Dept. Pure and Appl. Chem. Univ. Strathclyde Glasgow UK G1 1XL). Goodall P. Johnson S. G. Laser ablation-inductively coupled plasma atomic emission spectrometry for the determination of lanthanides and uranium in fuel reconditioning materials problems solutions and impli- cations. J. Anal. At. Spectrom. 1996 11(7) 469. (Argonne Natl. Lab. Idaho Falls ID 83403 USA). Besteman A. D. Lau N. Liu D.-Y. Smith B.W. Winefordner J. D. Determination of lead in whole blood by capacitively coupled microwave plasma atomic emission spectrometry. J. Anal. At. Spectrom. 1996 11(7) 479. (Dept. Chem. Univ. Florida Gainesville FL 3261 1 USA). You J. Depalma P. A. Jr. Marcus R. K. Nebulization and analysis characteristics of a particle beam-hollow cathode glow discharge atomic emission spectrometry system. J. Anal. At. Spectrom. 1996 11(7) 483. (Dept. Chem. Howard L. Hunter Chem. Lab. Clemson Univ. Clemson SC 29634-1905 USA). Olson L. K. Belkin M. Caruso J. A. Radiofrequency glow discharge mass spectrometry for gas chromato- graphic detection a new departure for elemental speciation studies. J. Anal. At. Spectrom. 1996 11( 7 j 491. (The Shepherd Color Co. Cincinnati OH 45246 USA). Chiappini R.Taillade J.-M. Brebion S. Development of a high-sensitivity inductively coupled plasma mass spectrometer for actinide measurement in the femtog- ram range. J. Anal. At. Spectrom. 1996 11(7) 497. (CEA-DIRCENISMSRB Serv. Mixte Surveillance Radiol. et Biol. Homme et Environ. 91311 Montlhery France). Creed J. T. Magnuson M. L. Brockhoff C. A. Chamberlain I. Sivaganesan M. Arsenic determination in saline waters utilizing a tubular membrane as a gas- liquid separator for hydride generation inductively coupled plasma mass spectrometry. J. Anal. At. Spectrom. 1996 11( 7) 505. (Human Exposure Res. Div. Natl. Exposure Res. Lab. US Environ. Prot. Agency Cincinnati OH 45268 USA). Bloxham M. J. Hill S. J. Worsfold P. J. Determination of mercury in filtered sea-water by flow injection with on-line oxidation and atomic fluorescence spectrometric detection.J. Anal. At. Spectrom. 1996 11(7) 511. (Dept. Environ. Sci. Univ. Plymouth Plymouth Devon UK PL4 8AA). Imai S. Hasegawa N. Hayashi Y. Saito K. Indium atomic absorption signals from non-pyrolytic and pyrolytically coated graphite furnaces in electrothermal atomization atomic absorption spectrometry. J. Anal. At. Spectrom. 1996 11(7) 515. (Dept. Chem. Fac. Integrated Arts and Sci. Univ. Tokushima Tokushima 770 Japan). Bavazzano P. Perico A. Rosendahl K. Apostoli P. Determination of urinary arsenic by solvent extraction and electrothermal atomic absorption spectrometry. A comparison with directly coupled high-performance liquid chromatography-inductively coupled plasma mass spectrometry. J.Anal. At. Spectrom. 1996 11(7) 521. (Ind. Toxicol. Lab. Natl. Health Serv. Florence Italy). 961341 1 9613412 9613413 9613414 9613415 96/34 16 961341 7 961341 8 9613419 9613420 9613421 9613422 9613423 9613424 Crain J. S. Kiely J. T. Waste reduction in inductively coupled plasma mass spectrometry using flow injection and a direct injection nebulizer. J. Anal. At. Spectrom. 1996 11(7) 535. (Anal. Chem. Lab. Chem. Technol. Div. Argonne Natl. Lab. Argonne IL 60439-4831 USA). Allen L. B. Siitonen P. H. Thompson H. C. Jr. Aerosol-phase assisted sample digestion for the determi- nation of trace metals in organic samples by plasma atomic emission spectrometry. J. Anal. At. Spectrom. 1996 11(7) 529. (Div. Chem. Natl. Center Toxicol. Res. US Food and Drug Admin.Jefferson AR 72079 USA). Newman A. Elements of ICP MS. Anal. Chem. 1996 68( l) 46A. Kabil M. A. El-Kourashy A.-G. El-Hagrassy M. A. Atomic-absorption-spectrometric investigation and determination of zinc using ethanolamine as a chemical modifier. Anal. Methods Instrum. 1995 2(4) 190. (Chem. Dept Fac. Sci. Mansoura Univ. Mansoura Santoni F. Burelli F. Costa J. Use of a second emission line to improve performance in the determi- nation of an element in an ICP. Analusis 1995 23(8j 389. (Lab. OEHC 20600 Bastia France). Hwang J. D. Wang W. J. Application of ICP AES to analysis of solutions. Appl. Spectrosc. Rev. 1995 30( 4) 231. (Church & Dwight Co. Inc. Princeton NJ 08543 USA). Farah K. S. Sneddon J. Developments and applications of multielement graphite-furance atomic-absorption spectrometry.Appl. Spectrosc. Rev. 1995 30(4) 351. (Dept. Sci. Lasell Coll. Newton MA 02166 USA). Outridge P. M. Hughes R. J. Evans R. D. Determination of trace metals in teeth and bones by solution nebulization ICP-MS. At. Spectrosc. 1996 17(1) 1. (Anal. Chem. Lab. Geol. Surv. Canada Ottawa Ontario Canada K1A OE8). Lust A. Atomic spectroscopy bibliography for July- December 1995. At. Spectrosc. 1996,17( l) 34. (Perkin- Elmer Corp. Norwalk CT 06859-0105 USA). Anderson K. A. Micro-digestion and ICP-AES analysis for the determination of macro and micro elements in plant tissues. At. Spectrosc 1996 17( l) 30. (Anal. Sci. Lab. Dept. Food Sci. and Toxicol. Univ. Idaho Milburn J. W. Automated addition of internal stan- dards for axial-view plasma ICP spectrometry using the Optima 3000 XL.At. Spectrosc. 1996 17(1) 9. (San Jose Tech. Training Center Perkin-Elmer Corp. San Jose CA 95134-1701 USA). Tao G. H. Fang Z. L. Flame atomic-absorption determination of lead in biological materials using a flow-injection online separation and preconcentration system based on ion-pair sorbent extraction. At. Spectrosc. 1996 17( l) 22. (Flow Injection Anal. Res. Center Inst. Appl. Ecol. Acad. Sinica Shenyang 110015 China). Schlemmer G. Graphite-furnace AAS for complex samples detection limits precision long-term stability. At. Spectrosc. 1996 17( l) 15. (Bodenseewerk Perkin- Elmer GmbH 88647 Ueberlingen Germany). Hernandez O. Jimenez F. Jimenez A. I. Arias J. J. Multicomponent analysis by flow injection using a partial least-squares model.Determination of copper and zinc in serum and metal alloys. Analyst (Cambridge Egypt). MOSCOW ID 83844-2203 USA). Journal of Analytical Atomic Spectrometry September 1996 Vol. 1 1 (341 R-354R) 341 R9613 42 5 9613426 9613427 9 61342 8 9613429 9613430 961343 1 9613432 9613433 9613434 9613435 9613436 342 R U. K . ) 1996,121(2) 169. (Dept. Quim. Anal. Bromatol. y Toxicol. Univ. La Laguna 38204 La Laguna Tenerife Spain). Aydemir T. Gucer S. Determination of nickel in urine by flame atomic-absorption spectrometry after activated carbon enrichment. Anal. Lett. 1996,29(3) 351. (Chem. Dept. Fac. Sci. and Arts Inonu Univ. Malatya 44069 Turkey). Tsalev D. L. Slaveykova V. I. Georgieva R. B. Electrothermal atomic-absorption spectrometric deter- mination of volatile elements in biological materials in the presence of a mixed palladium-tungsten chemical modifier.Anal. Lett. 1996,29( l) 73. (Fac. Chem. Univ. Sofia Sofia 1126 Bulgaria). Kabacinski M. Siepak J. Zerbe J. Baralkiewicz D. Comparison of the field and laboratory methods in iron(I1) and iron(II1) speciation studies of water samples. Chem. Anal. (Warsaw) 1996,41( l) 55. (Dept. Water and Soil Anal. Fac. Chem. Adam Mickiewicz Univ. 60-613 Poznan Poland). Matousek de Abel de la Cruz A. Burguera J. L. Burguera M. Wasim S. Rivas C. Flow injection- flame-atomic absorption spectrometry system for the determination of the real stoichiometry of small copper indium diselenide. Fresenius ’ J. Anal. Chem. 1996 354(2) 184. (Andean Inst. Chem. Res. IVAIQUIM Merida 5101-A Venezuela).Weiss Z. Musil J. Vlcek J. Depth profile analysis of minor elements by glow discharge optical emission spectrometry applications to diffusion phenomena. Fresenius’ J. Anal. Chem. 1996 354(2) 188. (LECO Instrumente Plzen 323 18 Plzen Czech Republic). Hiraide M. Mikuni Y. Kawaguchi H. Separation of trace heavy metals from silver matrix by solid-liquid extraction for graphite-furnace atomic absorption spec- trometry. Fresenius’ J. Anal. Chem. 1996 354( 2) 212. (Dept. Mater. Sci. and Eng. Nagoya Univ. Nagoya 464 Japan). Li H. T. Zheng L. M. Determination of beryllium in water with graphite-furnace atomic-absorption spectro- photometry. Guangpuxue Yu Guangpu Fenxi 1995 15( 5) 61. (Zhejiang Province Sanitation and Antiepidemic Stn. Hangzhou 3 10009 China).Shen H. J. Dong Y. G. Weng M. H. Wang L. M. Determination of lead cadmium and iron in magnetic mug by flame atomic-absorption spectrophotometry. Guangpuxue Yu Guangpu Fenxi 1995 15(5) 63. (Changzhou Sanitation and Antiepidemic Stn. Changzhou 213003 China). Zhao Y. K. Zhang Y. X. Lu Y. Q. Zhang Y. J. Analysis of export magnesite by ICP AES and concen- tration ratio variable internal-standard method. Guangpuxue Yu Guangpu Fenxi 1995 15(5) 53. (Exp. Centre Liaoning Normal Univ. Dalian 116029 China). Sun M. X. Shao G. D. Tan B. H. Study on the approaches of various correction coefficients in the XRF mathematical model and its application. Guangpuxue Yu Guangpu Fenxi 1995 15(5) 67. (Dept. Chem. Beijing Univ. Sci. and Technol. Beijing 100083 China). Chen T.W. Photometric evaluation of spectrographic plates. Guangpuxue Yu Guangpu Fenxi 1995 15(5) 103. (Inst. Geophys. and Geochem. Exploration Ministry Geol. and Mineral Resources Langfang 102849 China). Esmadi F. T. Khasawneh I. M. Kharoaf M. A. Attiyat A. S. Sequential atomic-absorption- spectrophotometric determination of binary mixtures of chloride-carbonate chloride-chromate and chloride- oxalate in a flow system using an online preconcen- tration technique. J. Flow Injection Anal. 1995 12( l) 35. (Chem. Dept. Yarmouk Univ. Irbid Jordan). 9613437 9613438 9613439 9613440 9613441 9613442 9613443 9613444 9613445 9613446 9613447 9613448 9613449 9613450 9613451 Renner F. Stratmann K. Problems in the determination of magnesium on multichannel analysers. Comparison of the xylidyl blue method and atomic-absorption spectrophotometry.Labor-Med. 1995,18( 6) 313. (Inst. Klin. Chem. Med. Univ. Luebeck 23538 Luebeck Germany). Ohta Z. Yokoyama M. Ogawa J. Mizuno T. Matrix modification by copper nitrate for the determination of gold by electrothermal atomic-absorption spectrometry with a molybdenum tube atomizer. Mikrochim. Acta 1996 122(1-2) 61. (Dept. Chem. Mater. Fac. Eng. Mie Univ. Mie 514 Japan). Peng T. Z. Sheh L. Q. Wang G. S. Linear scan stripping voltammetry of copper (11) at the chemically modified carbon paste electrode. Mikrochim. Acta 1996 122( 1-2) 125. (Dept. Chem. Hangzhou Chem. Hangzhou 310028 China). Ruiz C. Alegria A. Barbera R. Farre R. Lagarda M. J. Direct determination of calcium magnesium sodium potassium and iron in infant formulas by atomic spectroscopy.Comparison with dry and wet digestions methods. Nahrung 1995,39( 5-6) 497. (Dept. Nutr. and Food Chem. Fac. Pharm. Univ. Valencia 46100 Burjassot Spain). Navarro M. Lopez H. Ruiz M. L. Gonzalez S. Perez V. Lopez M. C. Determination of selenium in serum by hydride generation atomic-absorption spec- trometry for calculation of daily dietary intake. Sci. Total Enuiron. 1995 175(3) 245. (Dept. Nutr. and Bromatol. Granada Univ. 18071 Granada Spain) O’Haver T. C. Atomic spectroscopy online. A collection of Internet resources linking spectrochemists worldwide. Spectroscopy (Eugene Oreg.) 1996 11( l) 12. (Dept. Chem. and Biochem. Univ. Maryland College Park MD 20742 USA). Ball D. W. Widths of lines. Spectroscopy (Eugene Oreg.) 1996 11( l) 29.(Chem. Dept. Cleveland State Univ. Cleveland OH 44115 USA). Skelly Frame E. M. Takamatsu Y. Suzuki T. Characterization of solid particles by helium micro- wave-induced plasma atomic-emission spectrometry. Spectroscopy (Eugene Oreg.) 1996 11( l) 17. (Mater. Characterization Lab. General Electric Corp. Res. and Dev. Schenectady NY 12301 USA). Scheeline A. Resources and references for spectral interpretation. Part IV interpretation or algorithm in atomic spectroscopy? Spectroscopy (Eugene Oreg.) 1996 11(1) 14. (Dept. Chem. Univ. Illinois Urbana IL 61801 USA). Trassy C. Gas control a new application field for ICP. Spectrosc. Eur. 1996 8(1) 20. (Lab. Phys.-Chim. Ind. INSA 69621 Villeurbanne France). Golovko S. A. Tsvetyanskii A. L. Eritenko A. N.Theoretical corrections for taking into account the components not determined in X-ray fluorescence analysis. Zauod. Lab. 1995 61(11) 13. (State Univ. Rostov-on-Don Russia). Gerasimov S. A. Calibration in energy-dispersive X-ray fluorescence spectrometry. Zauod. Lab. 1995 61( 1 l) 17. (Sci.-Res. Inst. Phys. State Univ. Rostov-on- Don Russia). Tatro M. E. Camp L. C. Christenberry R. K. Analysis of trace metals in solid waste using a simultaneous trace analyser ICP. Int. Lab. 1996 26( l) 10. (Spectra Inc. McAfee NJ 07428 USA). Van Britsom G. Slowikowski B. Bickel M. Rapid method for the detection of uranium in surface water. Sci. Total Enuiron. 1995,173( 1-6) 83. (Inst. Ref. Mater. Measurements 2440 Geel Belgium). Laitinen T. Revitzer H. Tolvanen M. Trace metal analysis of coal fly ash collected plain and on a quartz fibre filter.Fresenius’ J. Anal. Chem. 1996 354(4) 436. Journal of Analytical Atomic Spectrometry September .I 996 Vol. 119613452 9613453 9613454 9613455 9613456 9613457 9613458 9613459 9613460 9613461 9613462 9613463 9613464 9613465 9613466 (Chem. Technol. Environ. Technol. 02044 Espoo Finland). Dobrowolski R. Determination of nickel and chromium in soils by slurry graphite-furnace atomic-absorption spectrometry. Spectrochim. Acta Part B 1996 51B( 2) 221. (Central Lab. Maria Curie Sklodowska Univ. 20-03 1 Lublin Poland). Penninckx W. Srneyers-Verbeke J. Vankeerberghen P. Massart D. L. Selection of reference or test materials for the validation of atomic absorption food analysis methods. Anal. Chem. 1996 68(3) 481.(ChemoAC Farm. Inst. Vrije Univ. Brussel 1090 Brussels Belgium). Chau Y. K. Yang F. Maguire R. J. Improvement of extraction recovery for the monobutyltin species from sediment. Anal. Chim. Acta 1996 320(2-3) 165. (Natl. Water Res. Inst. Environ. Canada Burlington Ontario Canada L7R 4A6). Duane M. J. Facchetti S. Onsite environmental water analysis by ICP MS. Sci. Total Environ. 1995,172(2-3) 133. (Dept. Geol. Univ. Natal Dalbridge 4014 South Africa). Whittenburg S. L. Baseline roll removal in NMR spectra using Bayesian analysis. Spectrosc. Lett. 1995 28(8) 1275. (Dept. Chem. Univ. New Orleans New Orleans LA 70148 USA). Hamilton E. I. State of the art of trace element determinations in plant matrices determination of the chemical elements in plant matrices an overview.Sci. Total Enuiron. 1995 176(1-3) 3. (Phoenix Res. Lab. Tavistock Devon UK PL19 OQJ). Bass D. A. TenKate L. B. Wroblewski A. M. Containment attachment for mixed-waste analysis by graphite-furnace AAS. At. Spectrosc. 1996 17( 2) 92. (Anal. Chem. Lab. Chem. Technol. Div. Argonne Natl. Lab. Argonne IL 60439 USA). Xie Z. Z. Xu G. Yuan J. Q. Hu Y. W. Study on the method of digestion of food samples for AAS determination of zinc. Lihua Jianyan Huaxue Fence 1996 32(1) 28. (Dept. Food Hangzhou Inst. Commerce Hangzhou 310012 China). Hoenig M. Critical discussion of trace elements analysis of plant matrices. Sci. Total Enuiron. 1995 176( 1-3) 85. (Inst. Rech. Chim. Ministere Agric. 3080 Tervuren Belgium). Martin G. E. Snow D. D. Kim. E. Spalding R. F.Simultaneous determination of argon and nitrogen. Ground Water 1995 33(5) 781. (Water Sci. Lab. Univ. Nebraska Lincoln NE 68583-0844 USA). Nguyen Thi Hong Hguten Viet Hung Bornan J. Clinical effects of high lead intake by Vietnamese children. J. Trace Microprobe Tech. 1996 14( l) 153. (Dept. Methods Anal. Inst. Mater. Sci. Hanoi Vietnam). Yu F. Jin X. H. Bai M. Jin S. L. GFAAS determination of lead and cadmium in foodstuffs. Lihua Jianyan Huaxue Fence 1996,32( l) 34. (Jilin Province Epidemic Prevention Stn. Changchun 130021 China). Gu M. S. Feng C. L. Luo Y. Determination of elemental ratio in eighteen soporific and sedative drugs by GC AES and its application to the analysis of human whole blood samples. Sepu 1996 14(1) 33. (Inst. Pharm. and Toxicol. Beijing 100850 China).Antonovich V. P. Bezlutskaya I. V. Determination of the chemical speciation of mercury in environmental samples. Zh. Anal. Khim. 1996 51( l) 116. (Bogatskii Phys.-Chem. Inst. Natl. Acad. Sci. 270080 Odessa Ukraine). Soylak M. Doan M. Column preconcentration of trace amounts of copper on activated carbon from natural water samples. Anal. Lett. 1996 29(4) 635. 9613467 9613468 9613469 9613470 961347 1 9613472 9613473 9613474 9613475 9613476 9613477 9613478 9613479 (Dept. Chem. Fen-Edebiyat Fac. Erciyes Univ. 38039 Kayseri Turkey). Szczepaniak W. Szyrnanski A. Sorption and precon- centration of trace amounts of beryllium from natural waters on silica gel with immobilized morin prior to its determination by ETA AAS method. Chem. Anal. (Warsaw) 1996 41(2) 193.(Lab. Instrum. Anal. Fac. Chem. A. Mickiewicz Univ. 60 780 Poznan Poland). Sturnrneyer J. Harazirn B. Wippermann T. Speciation of arsenic in water samples by high-performance liquid chromatography-hydride generation-atomic absorption spectrometry at trace levels using a post-column reaction system. Fresenius’ J. Anal. Chem. 1996,354( 3) 344. (Bundesanstalt Geowissenschaften und Rohstoffe 30655 Hannover Germany). Wang C.-F. Yang J.-Y. Ke C.-H. Multielemental analysis of airborne particulate matter by various spectrometric methods after microwave digestion. Anal. Chim. Acta 1996 320(2-3) 207. (Inst. Nucl. Sci. Natl. Tsing Hua Univ. Hsinchu 30043 Taiwan). Minami H. Honjyo T. Atsuya I. New solid-liquid extraction sampling technique for direct determination of trace elements in biological materials by graphite- furnace atomic-absorption spectrometry.Spectrochim. Acta Part B 1996 51B(2) 211. (Dept. Mater. Sci. Kitami Inst. Technol. Hokkaido 090 Japan). Zhao D. Y. GFAAS determination of arsenic in water. Lihua Jianyan Huaxue Fence 1996 32(1) 47. (Inst. Tap Water Harbin City Tap Water Co. Harbin 150080 China). Palsgard E. Roornans G. Lindh U. Ion dynamics in cells - preparation for studies of intracellular processes. Nucl. Instrum. Methods Phys. Res. Sect. B 1995 B104 (1-4) 324. (Div. Biomed. Radiation Sci. Univ. Uppsala 751 21 Uppsala Sweden). Panday V. K. Hoppstock K. Becker J. S. Dietze H.-J. Determination of rare-earth elements in environ- mental materials by ICP MS after liquid-liquid extrac- tion. At. Spectrosc. 1996 17(2) 98.(Zentralab. Chem. Anal. Forschungszentrum Juelich GmbH 52425 Juelich Germany). Kabil M. A. Ghazy S. E. Lasheen M. R. Shallaby M. A Amar N. S. Spectrophotometric and atomic- absorption determination of nickel(I1) in fresh and sea waters after preconcentration by flotation. Fresenius’ J. Anal. Chem. 1996 354(3) 371. (Chem. Dept. Fac. Sci. Mansoura Univ. Mansoura Egypt). Holmes L. J. Robinson V. J. Makinson P. R. Livens F. R. Multielement determination in complex matrices by inductively coupled plasma-mass spectrometry (ICP MS). Sci. Total Environ. 1995 173( 1-6) 345. (Dept. Chem. Univ. Manchester Manchester UK M13 9PL). Lopez-Artiguez M. Camean A. Repetto M. Preconcentration of heavy metals in urine using chelating ion exchange resin and quantification by ICP AES. At.Spectrosc. 1996 17(2) 83. (Dept. Seville Inst. Nacl. Toxicol. 41080 Seville Spain). Sun L. Yang Y. G. Determination of total sodium in peritoneal dialysate (acetate salt) by AAS. Yaowu Fenxi Zazhi 1996 16(1) 51. (Henan Provincial Inst. Drug Control Zhengzhou 450003 China). Subrarnanian K. S. Determination of metals in biofluids and tissues sample-preparation methods for atomic- spectroscopic studies. Spectrochim. Acta Part B 1996 51B(3) 291. (Environ. Health Directorate Health Canada Ottawa Ontario Canada K1A OL2). Falter R. Schoeler H.-F. New pyrrolidinedithiocarba- mate screening method for the determination of methyl- mercury and inorganic mercury and the relationship between them in hair samples by high-performance liquid chromatography-ultra-violet-post column oxi- dation-cold vapour atomic absorption spectrometry Journal of Analytical Atomic Spectrometry September 1996 Vol.1 1 343 R9613480 9613481 9613482 9613 4 8 3 9613484 9613485 9613486 9613487 9613488 9613489 9613490 9613491 9613492 9613493 344 R (HPLC-UV-PCO-CVAAS). Fresenius ’ J. Anal. Chem. 1996 354(4) 492. (Inst. Umwelt-Geochem. Univ. Heidelberg 69 120 Heidelberg Germany). Guo T. Baasner J. Gradl M. Kistner A. Determination of mercury in saliva with a flow-injection system. Anal. Chim. Acta 1996 320(2-3) 171. (At. Absorption Product Dept. Bodenseewerk Perkin-Elmer GmbH 88647 Ueberlingen Germany). Plantikow-Vossgaetter F. Denkhaus E. Application of an ET-vaporization ICP system for the determination of elements in human hair. Spectrochim.Acta Part B 1996 51B(2) 261. (Instrum. Anal. Chem. Gerhard Mercator Univ. Duisburg 47057 Duisburg Germany). Wei L. H. Determination of ultra-trace mercury in sea water by cold atomic-fluorescence spectrometry. Fenxi Huaxue 1996,24( 2) 247. (Zhejiang Provincial Environ. Monitoring Centre Hangzhou 310012 China). Pedersen-Bjergaard S. Semb S. I. Brevik E. M. Greibrokk T. Capillary gas chromatography combined with atomic emission detection for the analysis of polychlorinated biphenyls. J. Chromatogr. A 1996 723(2) 337. (Dept. Chem. Univ. Oslo 0315 Oslo Norway). Jambers W. Van Grieken R. Message in the dust. Microanalytical techniques for particle analysis. Anal. Eur. 1996 25. (Dept. Chem. Univ. Antwerp 2610 Antwerp Belgium). Luecker E. Schuierer 0. Sources of error in direct solid-sampling Zeeman atomic-absorption spectrometry analyses of biological samples with high water content.Spectrochim. Acta Part By 1996 51B(2) 201. (Inst. Tieraerztliche Naehrungsmittelkunde Justus Liebig Univ. Giessen Germany). Lim H. B. Han M. S. Lee K. J. Determination of trace elements in human serum by inductively coupled plasma atomic-emission spectrometry with flow injec- tion. Anal. Chim. Acta 1996 320(2-3) 185. (Res. Inst. Basic Sci. Dankook Univ. Seoul 140-714 South Korea). Shao H. R. Xu Q. Preparation of standard samples and standard reference materials for micro-beam analy- sis. Nucl. Instrum. Methods Phys. Res. Sect. B 1995 B104 (1-4) 201. (Inst. High-Energy Phys. Beijing 100080 China). Murty D. S. R. Finatallo F. Characterization of the analytical performance of sequential ICP AES by simple diagnostic tests.ICP Inf Newsl. 1996 21(8) 538. (At. Minerals Div. Dept. At. Energy Bangalore 560 072 India). Szpunar J. Schmitt V. O Donard 0. F. X. Lobinski R. Low-power focused microwave technology as a new tool for rapid preparation of solid samples for speciation analysis. Trends Anal. Chem. 1996,15(4) 181. (LPPM CNRS URA 348 Univ. Bordeaux I 33405 Talence France). Lindh U. Cell biology trace elements and nuclear microscopy. Nucl. Instrum. Methods Phys. Res. Sect. B 1995 B104 (1-4) 285. (Centre Metal Biol. Univ. Uppsala 751 21 Uppsala Sweden). Zhang Y. X. Zhang Y. P. Tong Y. P. Qiu S. J. Wu X. T. Dai K. R. Multielement determination in cancellous bone of human femoral head by PIXE. J. Radioanal. Nucl.Chem. 1996,212( 5 ) 341. (Shanghai Inst. Nucl. Res. Acad. Sinica Shanghai 201800 China). Shen J. X. Chai D. L. Wang C. K. GFAAS determination of aluminium in human urine blood and hair. Lihua Jianyan Huaxue Fence 1996 32(1) 50. (Inst. Labor Health Silver Co. Gansu Province 730900 China). Quevauviller P. Kramer K. J. M. Vinhas T. Certified reference material for the quality control of cadmium copper nickel and zinc determination in estuarine 9613494 9613495 9 613 49 6 9613497 9613498 9613499 9613500 9613 50 1 9613502 9613503 9613504 9613505 9613506 9613507 water (CRM 505). Fresenius’ J. Anal. Chem. 1996 354( 4) 397. (Standards Management and Testing Programme European Commission 1049 Brussels Belgium). Van Lierde S. Maenhaut W. De Reuck J. Vis R. D. Study of some analytical-methodological aspects in nuclear micro-probe analysis of soft biological tissues.Nucl. Instrum. Methods Phys. Res. Sect. B 1995 B104 (1-4) 328. (Inst. Nucl. Sci. Univ. Ghent 9000 Ghent Belgium). Pizent A. Telisman S. Analysis of reference materials for serum copper and zinc by flame AAS. At. Spectrosc. 1996 17(2) 88. (Clin. Toxicol. Lab. Inst. Med. Res. and Occup. Health 10001 Zagreb Croatia) Zhang Y. K. Peng T. Yao J. Liu Z. Y. Guang Y. Analysis of inorganic elements in cholelith. Lihua Jianyan Huaxue Fence 1996 32(2) 92. (Dept. Chem. Jishou Univ. Jishou 416000 China). Aminov K. L. Joergensen J. S. Pedersen J. B. Enhanced resolution of depth profiles using two- dimensional XPS data. Surf. Interface Anal. 1996 24(1) 23. (Fysisk Inst. Odense Univ. 5230 Odense Denmark).Wu C. G. Tian C. F. AAS determination of molyb- denum in pure terephthalic acid. Lihua Jianyan Huaxue Fence 1996 32(1) 18. (Prod. Quality Centre Yangzi Petrol. Chem. Ind. Co. Nanjing 210048 China). Demidova M. G. Torgov V. G. Yatsenko V. T. Extraction-atomic absorption methods for the determi- nation of selenium and tellurium in high-purity metals. Vysokochist. Veshchestva 1996 1 83. (Inst. Inorg. Chem. Siberian Div. Russian Acad. Sci. Novosibirsk Russia). Bertolini J. C. Delichere P. Hermann P. Use of LEIS to determine concentration depth profiles in binary alloys application to PtNi( 11 1). Sug. Interface Anal. 1996 24(1) 34. (Inst. Rech. Catalyse CNRS 69626 Villeurbanne France). Richardin P. Contribution of mass spectrometry to the study of cultural heritage.Spectra Anal. 1996 25( 188) 27. (Centre Rech. Conservation Documents Graphiques Museum Natl. Histoire Naturelle 75005 Paris France). Steiner E. Optimizing sampling and analysis conditions in X-ray fluorescence spectrometry by using WinProFX. Spectra Anal. 1996 25(188) 24. (Assoc. Dev. Tech. Nouvelles 75014 Paris France). Allen G. C Brown I. T. Ciliberto E. Spoto G. Scanning ion microscopy (SIM) and secondary-ion mass spectrometry (SIMS) of early iron age bronzes. Eur. Mass Spectrom. 1995 1(5) 493. (Dipt. Sci. Chim. Univ. Catania Catania Italy). Raghani A. R. Smith B. W. Winefordner J. D. Miniature planar magnetron glow-discharge source for analysis of sub-microlitre-volume aqueous samples using atomic-emission spectroscopy. Spectrochim. Acta Part B 1996,51B(4) 399.(Dept. Chem. Univ. Florida Gainesville FL 32611 USA). El-Defrawy M. M. Kabil M. A. Khalifa M. I. Othman A. S. Cyanide as a releasing agent in atomic- absorption-spectrometric determination of lead and cadmium. Analusis 1995 23( lo) 507. (Chem. Dept. Fac. Sci. Univ. Mansoura Mansoura Egypt). Varga I. Csempesz F. Zaray G. Effect of pH of aqueous ceramic suspensions on colloidal stability and precision of analytical measurements using slurry- nebulization inductively coupled plasma atomic- emission spectrometry. Spectrochim. Acta Part B 1996 51B(2) 253. (Dept. Inorg. and Anal. Chem. L. Eotvos Univ. 1518 Budapest 112 Hungary). Ryan C. G. The nuclear micro-probe as a probe of earth structure and geological processes. Nucl. Instrum. Methods Phys. Res.Sect. B 1995 B104 (1-4) 377. Journal of Analytical Atomic Spectrometry September 1996 VoE. 119613508 9613509 9613510 9613511 9613512 9613513 9613514 9613515 9613516 9613517 9613518 9613519 9613520 9613 52 1 (Div. Exploration and Mining CSIRO North Ryde NSW 2113 Australia). Liu D. Y. Zhang Y. L. Determination of chloride in coal by indirect inductively coupled plasma atomic- emission spectrometry. Fenxi Huaxue 1996,24( 2) 244. (Shanxi Int. Coal Chem. Chinese Acad. Sci. Taiyuan 030001 China). Polakovicova J. Medved J. Stresko V. Kubova J. Celkova A. Spectrographic determination of gold in geological materials after preconcentration of Spheron- Thiol. Anal. Chim. Acta 1996,320( l) 145. (Fac. Natural Sci. Comenius Univ. 842 15 Bratislava Slovakia). Yan Q. Y.Ion-exchange atom capture FAAS determi- nation of gallium in bauxite. Lihua Jianyan Huaxue Fence 1996 32(1) 42. (Dept. Chem. Eng. Henan Univ. Kaifeng 475001 China). Satyanarayana K. Determination of rare-earth elements yttrium scandium and thorium in niobate- tantalate carbonatite and fergusonite samples using ICP AES. At. Spectrosc. 1996 17(2) 69. (At. Minerals Div. Dept. At. Energy Chem. Lab. Hyderabad 500 016 India). Ilic Z. Determination of calcium boron and impurities in colemanite by inductively coupled plasma atomic- emission spectrometry (ICP AES). Chem. Anal. (Warsaw) 1996 41(2) 263. (Inst. Nucl. Sci. Chem. Dynamics Lab. 11001 Belgrade Yugoslavia). Guo J. X. Wang L. Li B. Ma C. F. AAS determination of iron nickel and chromium in accumu- lated stains in oil refining reactors.Lihua Jianyan Huaxue Fence 1996 32(1) 45. (Dept. Refining Petroleum Univ. Donying 257062 China). Alteyrac J. Augagneur S. Medina B. Vivas N. Glories Y. Determination of minerals in oak wood by laser ablation ICP MS. Analusis 1995 23(10) 523. (Tonnellerie DEMPTOS Fac. Oenol. Univ. Bordeaux 11 33405 Talence France). Dai Z. N. Ren C. A. Zhang J. J. Ma G. Z. Yang F. J. Comparison of quantitative PIXE and EPMA microanalysis of mineral samples. Nucl. Instrum. Methods Phys. Res. Sect. B 1995 B104 (1-4) 489. (Dept. Nucl. Sci. Fudan Univ. Shanghai 200433 China). Jordanov N. Ivanova Y. Vacuum-thermic extraction (VTE) of toxic and essential elements from rocks with subsequent AAS determination. 11. Fresenius’ J. Anal. Chem. 1996,354(3) 316. (Inst. Gen.and Inorg. Chem. Bulgarian Acad. Sci. Sofia 11 13 Bulgaria). Paksy L. Nemet B. Lengyel A. Kozma L. Czekkel J. Production control of metal alloys by laser spec- troscopy of the molten metals. Part 1. Preliminary investigations. Spectrochim. Acta Part B 1996 51B( 2) 279. (Dept. Qual. Assur. Univ. Miskolc 3515 Miskolc Hungary). Wang J Q. AAS determination of strontium in magnetic alloys. Lihua Jianyan Huaxue Fence 1996 32( l) 46. (Prod. Qual. Control and Anal. Centre Iron Ore Minist. Metallurg. Ind. Maanshan 243004 China). Wagatsuma K. Hirokawa K. Classification of singly ionized iron emission lines in the 160-250nm wave- length region from Grimm-type glow-discharge plasma. Spectrochim. Acta Part B 1996 51B( 3) 349. (Inst. Mat. Res. Tohoku Univ. Sendai 980 China).Ducreux-Zappa M. Mermet J.-M. Analysis of glass by UV laser ablation inductively coupled plasma atomic-emission spectrometry. Part 2. Analytical figures of merit. Spectrochim. Acta Part B 1996 51B(3) 333. (Lab. Sci. Anal. Univ. Claude Bernard Lyon I 69622 Villeurbanne France). Duan Y. X. Zhang H. Q. Jiang X. M. Jin Q. H. A simple innovative method for the determination of iodide by using gas-phase molecular-absorption spec- 9613522 9613523 9613524 9613525 9613526 9613527 9613 52 8 9613529 9613530 961353 1 9613 532 9613533 9613534 trometry after volatile species evolution. Spectrosc. Lett. 1996 29(1) 69. (Dept. Chem. Jilin Univ. Changchun 130023 China). Goyal N. Purohit P. J. Page A. G. Sastry M. D. Atomization mechanism and determination of silver beryllium cadmium lithium sodium tin and zinc in uranium-plutonium matrices by ETA-AAS.Fresenius’ J. Anal. Chem. 1996 354(3) 311. (Radiochem. Div. Bhabha At. Res. Centre Bombay 400 085 India). Zolotovitskaya E. S. Shtitelman E. V. Glushkova L. V. Il&apos;chenko 0. P. Blank A. B. Atomic-emission plasmo-spectral analysis of high-purity substances and monocrystals. Vysokochist. Veshchestua 1996 1 124. (Inst. Single Crystals Ukrainian Natl. Acad. Sci. Khar’kov Ukraine). Mniszek W. Cold-vapour atomic-absorption spec- trometry for total mercury determination in coal sample after oxygen combustion. Chem. Anal. (‘Warsaw) 1996 41(2) 269. (Inst. Occup. Med. and Environ. Health 41-200 Sosnowiec Poland). Khuder A. Maslov L. P. Kutvitskii V. A. The use of non-saturated tungsten phosphates as collectors of the impurities of transition elements for X-ray fluorescence analysis.Vysokochist. Veshchestva 1996 1 121. (M. V. Lomonosov Moscow State Acad. Fine Chem. Tech. Moscow Russia). Ducreux-Zappa M. Mermet J.-M. Analysis of glass by UV laser ablation inductively coupled plasma atomic-emission spectrometry. Part 1. Effects of the laser parameters on the amount of ablated material and the temporal behaviour of the signal for different types of laser. Spectrochim. Acta Part B 1996 51B( 3) 321. (Lab. Sci. Anal. Univ. Claude Bernard Lyon I 69622 Villeurbanne France). Lonardo R. F. Yuzefovsky A. I. Irwin R. L. Michel R. G. Laser-excited atomic-fluorescence spectrometry in a pressure-controlled electrothermal atomizer. Anal. Chem. 1996 68(3) 514. (Dept.Chem. Univ. Connecticut Storrs CT 06269-3060 USA). Oksenoid K. G. Ramendik G. I. Universal approach to studying the mechanisms of ion formation in plasma sources of mass spectrometers. Zh. Anal. Khim. 1996 51( l) 92. (Kurnakov Inst. Gen. and Inorg. Chem. Russian Acad. Sci. 117097 Moscow Russia). Saru F. Montanarella L. Electrospray ionization using magnetic-sector mass spectrometers. Rev. Anal. Chem. 1995 14(4) 205. (Environ. Inst. Comm. Eur. Communities Joint Res. Centre 21020 Ispra Italy). Boudreau D. Ljungberg P. Axner 0. Dens Mat fully time-resolved simulation of two-step pulsed laser exci- tation of atoms in highly collisional media. Spectrochim. Acta Part B 1996 51B(4) 413. (Dept. Chem. Lava1 Univ. Quebec PQ Canada G1K 7P4). Bibicu I. Rogalski M. S. Nicolescu G.A detector assembly for simultaneous conversion-electron conver- sion-X-ray and transmission Mossbauer spectroscopy. Anal. Chem. 1996,7(1) 113. (Inst. At. Phys. Bucharest Romania). Berglund M. The importance of the rollover absorbance and the Zeeman sensitivity ratio-related coefficient for the accuracy in linearization of calibration curves in electrothermal atomic-absorption spectrometry with Zeeman-effect background correction. Spectrochim. Acta Part B 1996 51B(4) 429. (Dept. Anal. Chem. Umea Univ. 901 87 Umea Sweden). Vinas P. Campillo N. Lopez Garcia I. Hernandez Cordoba M. Indirect flame atomic-absorption detection for the liquid-chromatographic separation of alkaline metals. Fresenius’ J. Anal. Chem. 1996 354(4) 497. (Dept. Anal. Chem. Fac. Chem. Univ.Murcia 30071 Murcia Spain). Predecki P. K. Bowen D. K. Gilfrich J. V. Goldsmith C. C. Huang T. C. Jenkins R. Noyan I. C. Smith Journal of Analytical Atomic Spectrometry September 1996 Vol. 1 1 345 R9613 53 5 9613536 9613537 9613 538 9613539 9613 540 9613541 9613542 9613543 9613544 9613545 9613546 9613547 9613 548 9613549 346 R D. K. Advances in X-ray analysis. Vol. 38. Plenum Publishing Co. Ltd. London UK 1995. Pp. 814. Sekine T. Tsuda J. Solvent extraction of thallium(1) with chelating extractants coordinating through oxygen atoms. Bull. Chem. SOC. Jpn. 1995 68(12) 3429. (Dept. Chem. Sci. Univ. Tokyo Tokyo 162 Japan). Sahu R. Sondi S. M. Gupta B. Extraction and separation of mercury using 1 -( T-aminoaryl-4,4,6-trimethyl- 1,4,5,6-tetrahydro- 6-hydroxypyrimidine-2-thiol( HPT) and its application to dental amalgam and medicinal sample.Chem. Anal. (Warsaw) 1996 41(2) 293. (Dept. Chem. Univ. Roorkee Roorkee 247 667 India). Fabry L. Pahlke S. Kotz L. Accurate calibration of TXRF using microdroplet samples. Fresenius’ J. Anal. Chem. 1996,354( 3) 266. (Wacker Chemitronic GmbH 84489 Burghausen Germany). Schofield R. M. S. Applications of ion-beam tomo- graphic element microanalysis (ITEM). Nucl. Instrum. Methods Phys. Res. Sect. B 1995 B104 (1-4) 212. (Phys. Dept. Univ. Oregon Eugene OR 97403 USA). Williams D. B. Goldstein J. I. Newbury D. E. X-ray spectrometry in electron beam instruments. Plenum Publishing Co. Ltd. London UK 1995. Pp. 390. Wu Y. L. Yu B. Zhou T. T. Study on the computational elimination of multi-interferent effects in flame atomic-absorption spectrophotometry.I. Mathematical expression and algorithm for the multi- interferent effect. Fenxi Huaxue 1996,24(2) 202. (Dept. Appl. Chem. Nanjing Inst. Chem. Technol. Nanjing 210009 China). Matusiewicz H. Sturgeon R. E. Atomic-spectrometric detection of hydride-forming elements following in situ trapping within a graphite furnace. Spectrochim. Acta Part B 1996,51B(4) 377. (Dept. Anal. Chem. Politech. Poznanska 60 965 Poznan Poland). Lister T. Modern chemical techniques. Royal Society of Chemistry Cambridge UK 1996. Video 5 min.. Kurfuerst U. Rehnert A. Muntau H. Uncertainty in analytical results from solid materials with electrother- mal atomic-absorption spectrometry a comparison of methods. Spectrochim. Acta Part B 1996 51B(2) 229.(Dept. Nutr. Univ. Fulda 36039 Fulda Germany). Liew S. C. Orlic I. Tang S. M. PIXE tomographic reconstruction of elemental distributions using an iterative maximum-likelihood method. Nucl. Instrum. Methods Phys. Res. Sect. B 1995 B104 (1-4) 222. (Nucl. Microscopy Lab. Dept. Phys. Natl. Univ. Singapore Singapore 051 1 Singapore). Quisefit J. P. X-ray fluorescence spectrometry instru- mentation one hundred years after the discovery of X-rays. Spectra Anal. 1996 25( 188) 14. (LISA Univ. Paris 7 94010 Creteil France). Wu X. K. Zhu J. Q. Lu R. R. Yang F. J. TTSPM a new computer program system for quantitative thick- target analysis by nuclear microprobe. Nucl. Instrum. Methods Phys. Res. Sect. B 1995 B104 (1-4) 196. (Shanghai Inst. Nucl. Res. Chinese Acad. Sci.Shanghai 201800 China). Dai Z. N. Ren C. G. Ni W. H. Yang F. J. Quantitative PIXE and micro-PIXE analysis of thick samples at Fudan University. Nucl. Instrum. Methods Phys. Res. Sect. B 1995 B104 (1-4) 191. (Dept. Nucl. Sci. Fudan Univ. Shanghai 200433 China). Maeda K. Hamanaka H. Influence of sample charging on satellite spectra during particle-induced X-ray emis- sion analysis. Spectrochim. Acta Part B 1996 51B(3) 343. (Inst. Phys. and Chem. Res. (RIKEN) Saitama 351-01 Japan). Yao J. Y. Peng L. Q. Progress in hydride-generation graphite-furnace AAS. Lihua Jianyan Huaxue Fence Journal of Analytical Atomic Spectrometry Septembt 9613550 9613551 9613552 9613553 9613 5 54 9613555 9613 5 56 9613557 9613558 9613559 9613560 9613561 9613562 9613563 9613564 1996 Vol.11 1996 32(2) 118. (Changchun Inst. Appl. Chem. Chinese Acad. Sci. Changchun 130022 China). Ohls K. D. A personal view of the development of solid-sampling emission spectrochemical analysis. Spectrochim. Acta Part B 1996 51B(2) 245. (Krupp Hoesch Stahl AG Dortmund Germany). Shen L. S. Yang S. Yao S. Z. A new adaptive anlaysis method for inductively coupled plasma atomic-emission spectrophotometry. Fenxi Huaxue 1996 24( 2) 188. (Beijing Polytech. Univ. Beijing 100022 China). IUPAC Absolute methods in analytical chemistry. Technical report. Pure Appl. Chem. 1995 67( 1 l) 1905. Moreton P. Scanning micro-sleuth. Lab. Equip. Dig. 1996 34( l) 9. Veillon C. Patterson K. Y. Trace elements in a commercial freeze-dried human urine reference material. Analyst (Cambridge U.K.) 1996 121 983. (US. Dept. Agric. Beltsville Human Nutr. Res. Center Beltsville MD 20705 USA). Konstantianos D. G. Ioannou P. C. Second-derivative synchronous fluorescence spectroscopy for the simul- taneous determination of naproxen and salicylic acid in human serum. Analyst (Cambridge U. K . ) 1996 121 909. (Lab. Anal. Chem. Univ. Athens 15771 Athens Greece). Dobrowolski R. Mierzwa J. Determination of mercury in fluorescent lamp cullet by slurry sampling electrother- mal atomic absorption spectrometry. Analyst (Cambridge U. K.) 1996 121 897. (Central Lab. M. Curie-Sklodowska Univ. 20 03 1 Lublin Poland) Wagatsuma K. Hirokawa K. Yamashita N. Detection of fluorine emission lines from Grimm-type glow- discharge plasmas-use of neon as the plasma gas. Anal.Chim. Acta 1996 324 147. (Inst. Mat. Res. Tohoku Univ. Sendai 980 Japan). Serrano E. Beceiro E. Lopez P. Prada D. Heavy metals determination in atmospheric particulate matter of La Coruna. Quim. Anal. (Barcelona) 1996 15 38. (Anal. Chem. Dept. Fac. Ciencias 15071 La Coruna Spain). Belarra M. A. Resano M. Castillo J. R. Linearization of calibration curve for tin 224.6 nm line in graphite furnace atomic absorption spectrometry. Quim. Anal. (Barcelona) 1996 15 32. (Dept. Anal. Chem. Univ. Zaragoza 50009 Zaragoza Spain). Shukla N. Moitra J. K. Trivedi R. C. Determination of lead zinc potassium calcium copper and sodium in human cataract lenses. Sci. Total Environ. 1996 181 161. (Biolab Central Pollut. Control Board Delhi 110032 India). Richardson D. H. S. Shore M.Hartree R. Richardson R. M. The use of X-ray fluorescence spectrometry for the analysis of plants especially lichens employed in biological monitoring. Sci. Total Enuiron. 1996 176 97. (Saint Mary’s Univ. Halifax Nova Scotia Canada B3H 3C3). Frank A. Madej A. Galgan V. Petersson L. R. Vanadium poisoning of cattle with basic slag Concentrations in tissues from poisoned animals and from a reference slaughter-house material. Sci. Total Enuiron. 1996 181 73. (Centre Metal Biol. ISV Uppsala Univ. 751 21 Uppsala Sweden). Trepka M. J. Heinrich J. Schulz C. Krause C. Popescu M. Wjst M. Wichmann H.-E. Arsenic burden among children in industrial areas of eastern Germany. Sci. Total Environ. 1996 180 95. (GSF- Forschungszentrum Umwelt Gesundheit Inst. Epidemiologie 85758 Oberschleissheim Germany).Diaz-Alarcon J. P. Navarro-Alarcon M. Lopez-Garcia de la Serrana H. Lopez-Martinez M. C. Determination of selenium in cereals legumes and dry fruits from9613565 9613566 9613 567 9613 568 9613569 9613570 9613571 9613572 9613 573 9613 5 74 9613575 9613576 9613577 9613578 southeastern Spain for calculation of daily dietary intake. Sci. Total Enuiron. 1996 184 183. (Dept Nutr. and Bromatology Fac. Pharm. Univ. Granada 18071 Granada Spain). Pharr D. Y. Yen Teh Fu (Ed.) Enhancement effects of surfactants in flame atomic absorption analysis. Ado. Appl. Membr.-Mimetic Chem. 1995 79-94. Satoh Y. Fukuda K. Ohkuma J. Asano T. Taniguchi R. Fujishiro M. Multielement photon activation analysis of a bulk lanthanum sample by a Ge-BGO Compton-suppression spectrometer.Appl. Radiat. Isot. 1995 46(10) 999. (Res. Inst. Advanced Sci. Technol. Univ. Osaka Osaka 593 Japan). Schuetz M. Heitmann U. Hese A. Development of a dual-wavelength dye-laser system for the UV and its application to simultaneous multi-element detection. Appl. Phys. B 1995 B61(4) 339. (Gessellschaft Foerderung angewandter Optik Optoelektronik 12489 Berlin Germany). Sahin U. Ulgen A. Elci L. Determination of phos- phorus and silicon in rock and cement samples by near-infrared absorption spectroscopy with a laser diode. Anal. Methods Instrum. 1995 2(3) 142. (Fac. Art and Sci. Univ. Erciyes Kayseri 38039 Turkey). Cattrall R. W. Scollary G. R. Discontinuous flow analysis generation of fluid flows by differential pump- ing. Anal. Methods Instrum.1995 2(2) 61. (Centre Sci. Instrum. La Trobe Univ. Melbourne 3083 Australia). Gao J. Zhao G. Kang J. Li C. Stabilization induced by gelatin in the spectrofluorometric assay of ter- bium(II1) ions using trimesic acid. Analyst (Cambridge U. K.) 1995 120(8) 2081. (Inst. Chem. Northwest Norm. Univ. Lanzhou 730070 China). Gorbatenko A. A. Kuzyakov Y. Y. Murtazin A. R. Zorov N. Laser microprobe sampling and laser- enhanced ionization spectrometry in flames for surface analysis. AIP Conf. Proc. 1995 329 105. (Dept. Chem. Moscow State Univ. Moscow 119899 Russia). Young J. P. Barshick C. M. Shaw R. W. Ramsey J. M. Application of diode lasers to the isotopically selective determination of uranium in oxides by optogal- vanic spectroscopy. AIP Conf. Proc. 1995 329 111. (Chem.& Anal. Sci. Div. Oak Ridge Nat. Lab. Oak Ridge TN 37831-6142 USA). Groll H. Schnuerer-Patschan C. Zybin A. Kuritzin Y. Niemax K. Sensitive element analysis with semiconductor diode lasers. AIP Conf. Proc. 1995,329 495. (Inst. Phys. Univ. Hohenheim Stuttgart Germany). Matveev 0. I. Cavalli P. Omenetto N. Three-step laser induced ionization of Ir and Hg atoms in an air- acetylene flame and a gas cell. AIP Con. Proc. 1995 329 269. (EC Joint Res. Centre Environ. Inst. Ispra Italy). Lantzsch J. Bushaw B. A. Bystrow V. A. Herrmann G. Kluge H.-J. Niess S. Otten E. W. Passler G. Schwalbach R. et al. Trace determination of 90Sr and 89Sr in environmental samples by collinear resonance ionization spectroscopy. AIP Con$ Proc. 1995 329 251. (Inst. Phys. Johannes Gutenberg Univ.Mainz 55099 Mainz Germany). Butcher D. J. Laser-excited atomic and molecular fluorescence in a graphite furnace. Adu. At. Spectrosc. 1995 2 1. (Dept. Chem. and Phys. Western Carolina Univ. Cullowhee NC USA). Matusiewicz H. Electrothermal vaporization sample introduction into plasma sources for analytical emission spectrometry. Adv. At. Spectrosc. 1995 2 63. (Dept. Chem. Politechnika Poznanska Poznan Poland). Nakahara T. Hydride generation techniques in atomic spectroscopy. Adv. At. Spectrosc. 1995 2 139. (Dept. Appl. Chem. Univ. Osaka Osaka Japan). 9.613 579 9613580 9613581 96 f3582 9613 5 8 3 9613584 9613585 9613586 9613587 9613588 9613589 9613590 9613591 9613592 9613593 9613594 Hoppstock K. Harrison W. W. Spatial distribution of atoms in a dc glow discharge. Anal.Chem. 1995 67( 18) 3167. (Dept. Chem. Univ. Florida Gainesville Hiraide M. Mikuni Y. Kawaguchi H. Solid-liquid extraction with an ammoniacal EDTA solution for the separation of traces of copper from aluminium. Anal. Sci. 1995 11(4) 689. (Dept. Mater. Sci. Eng. Nagoya Univ. Nagoya 464 Japan). Cheng J.-K. Analytical chemistry in China. Bull. Singapore Natl. Inst. Chem. 1994 22 87. (Dept. Chem. Wuhan Univ. Wuhan China). Lim H. B. Hyun J. H. Lee W. Determination of Si in ultra fine A1,0 powder using matrix elimination in inductively coupled plasma-atomic emission spec- trometry. Bull. Korean Chem. Soc. 1995 16( 9) 894. (Res. Inst. Basic Sci. Dankook Univ. Seoul 140 714 South Korea). Bae Z. U. Lee S. H. Lee S. H. Multi-element trace analysis in molybdenum matrix by inductively coupled plasma atomic emission spectrometry.Bull. Korean Chem. Soc. 1995,16( 8) 748. (Dept. Chem. Kyungpook Nat. Univ. Taegu 702 701 China). Hilman K. Goto T. Separation and determination of chromium(v1) and chromium(II1) using trioctylmethyl- ammonium chloride loaded silica gel. Bunseki Kagaku 1995 44( 1 l) 921. (Coll. Eng. Nihon Univ. Koriyama 963 Japan). Rodriguez Pichiling C. E. Valuable elements in Peruvian minerals. BoZ. Soc. Quim. Peru 1995 61(2) 105. (Inst. Ciencias Quim. Univ. Nac. Mayor San Marcos Lima Peru). Leitgeb R. Pichler B. Practical experiences with the determination of boron in highly alloyed steels nickel and cobalt alloys. BHM Berg- Huettenmaenn. Montash. 1995 140(9) 426. (Boehler Edelstahl GmbH 8605 Kapfenberg Austria).Dhawale B. A Rajeswari B. Bangia T. R. Emission spectrographic method for determination of rare earths in plutonium with preliminary separation. Chem. Environ. Res. 1993 2( 3-4) 217. (Radiochem. Div. BARC Bombay 400 085 India). Pearce A. On-line ICP for process and quality monitoring. Chem. N . Z. 1995 59(5) 28. (SciTech Dunedin New Zealand). Krakovska E. Pliesovska N. Florian K. Heavy metals from natural and man-made sources. CLB Chem. Labor Biotech. 1995 46( 8) 368. (Tech. Univ. Kosice Kosice Slovakia). Grosser Z. A. Inorganic methods update. Enuiron. Test. Anal. 1995 4(3) 38. (USA). Luft B. Sattler R. Slickers K. Tasks problems and method orientation of the analytical laboratory in copper metallurgy quality control. Erzmetall 1995 48( 6/7) 435. (Inst. Eisen-Stahltechnol.Tech. Univ. Bergakad. Freiberg Freiberg Germany). Sahuquillo A Rubio R. Rauret G. Griepink B. Determination of total chromium in sediments by FAAS. Fresenius’ J. Anal. Chem. 1995 352(6) 572. (Dept. Quim. Anal. Univ. Barcelona Barcelona Spain). Liang F. Mei E. Zeng X. Wang L. Chen G. Double-encoding Hadamard transform spectroscopy- theory instrument and study on spectroscopic analysis. Fenxi Kexue Xuebao 1995 11(2) 56. (Center Instrum. Anal. Wuhan Univ. Wuhan China). Lin S. Zhao C. Yu G. Design of an online flow injection system with a gravitational phase separator for graphite furnace atomic absorption spectrometry and its analytical performance. Fenxi Kexue Xuebao 1994 10(1) 24. (Dept. Appl. Chem. China Univ. Geosci. Wuhan China). FL 3261 1-7200 USA).Journal of Analytical Atomic Spectrometry September 1996 Vol. 11 347 R9613595 9613596 9613597 9613 598 9613599 9613600 9613601 9613602 9613603 9613604 9613605 9613606 9613607 9613608 9613609 348 R Wang J. Tian L. Application of atomic absorption spectrophotometry in organic analysis. Fenxi Kexue Xuebao 1995 11(2) 74. (Dept. Chem. Xinjiang Univ. Urumqi China). Lin S. Zheng Q. Zhu H. Yin G. Design of a manifold for online solid phase extraction and study of its analytical performance. Fenxi Huaxue 1995 23( 7) 835. (Dept. Appl. Chem. China Univ. Geosci. Wuhan 430074 China). Hou L. Wang S. Li J. Chromatographic separation with tributyl phosphate and inductively coupled-atomic emission spectrometric determination of 22 trace elements in U,Si,. Fenxi Huaxue 1995 23(8) 919.(Mater. Res. Inst. Nucl. Power China Chengdu 610005 China). Oreshkov T. Spectrochemical determination of micro- impurities in bromine. God. Vissh. Khimikotekhnol. Inst. Burgas 1995 24 97. (Bulgaria). Brill M. Robotized ICP-laboratory for the analysis of precious metals. Gold Bull. Gold Pat. Dig. 1995 28(2) 38. (Anal. Lab. W.C. Heraeus GmbH Hanau Germany). Kurfuerst U. Rehnert A. Hollenbach H. Peil B. Uncertainty in analytical results of solid samples by atomic spectrometry. Application of IS0 guide and Eurachem draft. GIT Fachz. Lab. 1995 39(7) 662. (Fachhochsch. Fulda 36039 Fulda Germany). Qiu X. Zhong M. Huang Z. Use of iron hollow cathode lamp to determine iron and platinum simul- taneously by atomic absorption spectrometry. Huaxue Shijie 1995 36(3) 150.(Dept. Chem. Jiangxi Normal Univ. Nanchang 330027 China). Chen H. Cui G. Peng Y. Wu X. Analytical method for trace gold and palladium in silver nitrate. Huaxue Tongbao 1995 4 33. (Inst. Photochem. Acad. Sinica Beijing China). Duan Y. Zhang H. Jiang X. Jin Q. A simple innovative method for the determination of iodide by using gas-phase molecular absorption spectrometry after volatile species evolution. J. Environ. Sci. Health Part A 1995 A30(7) 1577. (Dept. Chem. Jilin Univ. Changchun 130023 China). Liu Z. Chen U. Zhang Z. Li W. Modified computer spectrum-stripping method in inductively coupled plasma atomic-emission spectrometry (ICP-AES) with solid-state detectors. 11. Software. Jisuanji Yu Yingyong Huaxue 1995 12(2) 147. (Dept. Chem. Zhongshan Univ.Canton 5 10275 China). Khuhawar M. Y. Lanjwani S. N. Khaskhely G. Q. Nachnani F. C. High performance liquid chromato- graphic determination of nickel in a nickel aluminium alloy using spectrofluorometric detection. J. Chem. Soc. Pak. 1995 17(2) 97. (Inst. Chem. Univ. Sindh Jamshoro Pakistan). Liu L. K. Cheng T.-h. Young D.-s. Hsieh T.-p. Trace analysis of heavy metals with two new disodium bisdithiocarbamates. J. Chin. Chem. Soc. (Taipei) 1995 42(5) 773. (Dept. Chem. Nat. Taiwan Normal Univ. Taipei 11718 Taiwan). Barna G. G. Quantitative spectral measurement of air leaks into plasma reactors. J. Vac. Sci. Technol. A 1995 13(4) 2285. (Semicond. Process Design Center Texas Instruments Inc. Dallas TX 75265 USA). Panwar 0. S. Mathur S. P. Atomic absorption spectrophotometric determination of molybdenum(v1) after adsorption of its l-hydroxy-l,3-diphenyl- 2-thiourea complex on microcrystalline naphthalene. J.Indian Chem. Soc. 1995 72(8) 563. (Res. Lab. Gov. Coll. Ajmer 305 001 India). Boaventura G. R. Hirson J. da R. Santelli R. E. Preconcentration of molybdenum on activated carbon for the analysis of silicates using the injection method Journal of Analytical Atomic Spectrometry Septembe 9613 6 10 961361 1 9613612 96/36 13 9613614 9613615 9613616 9613617 96/36 1 8 9613619 9 613 620 9613621 9 613 6 22 9613623 1996 Vol. 11 in flame atomic absorption spectrometry. J. Braz. Chem. Soc. 1995 6(3) 317. (Inst. Geociencia Univ. Brasilia Brasilia Brazil). Saraviva Miranda C. E. Freire dos Reis B. Krug F. J. A flow injection system with four ion exchange resin columns for cadmium pre-concentration and determi- nation by flame AAS.J. Braz. Chem. Soc. 1995 6(4) 387. (Inst. Quim. Sao Carlos Univ. Sao Paulo Sao Paulo Brazil). Zheltukhin A. A. Analytical possibilities of intracavity laser dispersion-frequency spectroscopy. J. Anal. Chem. (Engl. Transl.) 1995 50(9) 865. (Lebedev Inst. Phys. Russian Acad. Sci. Moscow 117924 Russia). Sholupov S. E. Ganeev A. A. Timofeev A. D. Ivankov V. M. Zeeman modulation polarization spectroscopy new possibilities in differential absorption analysis. J. Anal. Chem. (Engl. Transl.) 1995 50(6) 589. (Res. Inst. Earth‘s Crust St. Petersburg State Univ. St. Petersburg 199034 Russia). Bel’skii N. K. Nebol’sina L. A. Atomic-absorption hybrid method for the determination of platinum-group metals analysis of copper alloys.J. Anal. Chem. (Engl. Transl.) 1995 50(9) 862. (Kurnakov Inst. Gen. and Inorg. Chem. Russian Acad. Sci. Moscow 117907 Russia). Zolotovitskaya E. S. Potapova V. G. Grebenyuk N. N. Blank A. B. Atomic-absorption determination of aluminium iron and silicon in potassium dihydrogen phosphate with the electrothermal atomizer Grafit-2. J. Anal. Chem. (Engl. Transl.) 1995 50(9) 914. (Inst. Single Crystals. Nat. Acad. Sci. Ukraine Ukraine). Pupyshev A. A. Muzgin V. N. Use of thermodynamics for the investigation prediction and control of thermo- chemical processes in sources of atomization and spectrum excitation. J. Anal. Chern. (Engl. Transl.) 1995,50(7) 632. (Ural State Tech. Univ. Yekaterinburg 620002 Russia). Sen Gupta J.G. Determination of scandium yttrium and eight rare earth elements in silicate rocks and six new geological reference materials by simultaneous multi-element electrothermal atomic absorption spec- trometry with Zeeman-effect background correction. [Erratum]. J. Anal. At. Spectrom. 1995 10(8) 562. (Geol. Surv. Canada Ottawa ON Canada K1A OE8). Samchuk A. I. Extraction-atomic-absorption determi- nation of metals in natural samples. Khim. Tekhnol. Vody 1994 16(4) 421. (Inst. Geochem. Minerol. Ore Formn Nat. Acad. Sci. Kiev Ukraine). Sushida K. Hashimoto H. Mori Y. Practices of analytical techniques. Inorganic analyses course. Kurin Tekunoroji 1995 5(9) 74. (Toray Res. Cent. Inc. Otsu 520 Japan). Singer R. A new inductively-coupled plasma optical emission spectrometer (ICP-OES).LaborPraxis 1995 19(8) 60. (Instruments S.A. GmbH 85630 Grasbrunn Germany). Heyner R. Maennel S. Marx G. GDOS depth profile and trace analysis. Possibilities problems and appli- cations. LaborPraxis 1995 19( 9) 28. (Inst. Chem. Tech. Univ. Chemnitz-Zwichau 09107 Chemnitz Germany). Jorhem L. Dry ashing sources of error and perform- ance evaluation in AAS. Mikrochim. Acta 1995 119(3-4) 211. (Nat. Food Admin. 751 26 Uppsala Sweden). Brill M. Determination of precious metals. Metall (Heidelberg) 1995 49(7-8) 524. (Anal. Lab. W.C. Heraeus GmbH 63450 Hanau Germany). Hasegawa S. I. Kobayashi T. Hasegawa R. Cho K. H. Determination of trace amounts of selenium in Ni-base heat-resisting alloys by graphite furnace atomic absorption spectrometry. Muter. Trans.JIM 1995 36(9) 1157. (Nat. Res. Inst. Metals Ibaraki 305 Japan).9613624 9 613 62 5 9613626 9613627 9613628 9613629 9613630 9613631 9613632 961363 3 9613634 9613635 9 613 6 3 6 9613637 9613638 9613639 Morse D. H. Bench G. S. Freeman S. P. H. T. Pontau A. E. Microbeam PIXE analysis using wave- length dispersive spectrometry. Nucl. Instrum. Methods Phys. Res. Sect. B 1995 99 (1-4) 427. (Sandia Nat. Lab. Livermore CA 94551 USA). Symonds J. Determination of iron in galvanized steel coating. Proc. Chem. Conf. 1993 45 42. (British Steel UK). i Del Monte Tamba M. G. Lo Piccolo E. Luperi N. Novaro E. Zinc-nickel coatings and their analysis techniques (gravimetry ICPAES XRF GDAES). Proc. Chem. Conf. 1993 45 73. (Centro Sviluppo Materiali Rome Italy). Bettinelli M. Spezia S.Baroni U. Bizzarri G. Determination of arsenic bismuth antimony and selenium in steels and nickel alloys comparison between GFAAS and FI-HGAAS. Proc. Chem. Conf. 1993 45 67. (Central Lab. ENEL-DCO Italy). Agrawal Y. K. Rao K. V. Polyhydroxamic acids synthesis ion exchange separation and atomic absorp- tion spectrophotometric determination of divalent metal ions. React. Polym. 1995 25( l) 79. (Sch. Sci. Gujarat Univ. Ahmedabad 380 009 India). Manea F. Pasculescu M. Determination of aluminium and iron in clay minerals by the spectrographic emission method in the UV range. Rev. Rom. Pet. 1995 2(2) 193. (Univ. “Petrol si gaze” Ploiesti Romania). Chung S. W. Lee J J. Lee D. H. Development of low alloy steel reference materials for atomic emission spectrometry.RIST Yongu Nonmun 1995 9(2) 201. (Res. Inst. Ind. Sci. Technol. South Korea). Lee D. H. Lee J. J. Jung S. W. Lee W. B. Determination of Sn in steel by graphite furnace AA. RIST Yongu Nonrnun 1995 9(1) 94. (Res. Inst. Ind. Sci. Technol. South Korea). Jin S. Study of various types of interferences in the flame atomic absorption spectrometry. Shiyou Huagong Gaodeng Xuexiao Xuehao 1995 8(2) 7. (Dept. Appl. Chem. Fushun Petroleum Inst. Fushun China). Guo X.-w. Guo X.-m. Progress in hydride generation- nondispersive atomic fluorescence spectrometry and its application to environment analysis. Shanghai Huanjing Kexue 1995 14(7) 28. (Northwest Inst. Nonferrous Geol. Xian 710054 China). Zheng X. Application of sequential scanning ICP-AES to environmental monitoring. Shanghai Huanjing Kexue 1995 14(4) 24.(Shanghai Environ. Monit. Center Shanghai 200031 China). Ono A. Revision of the standard method (JIS G 1253) for spark discharge atomic emission spectrometry of iron and steel. Tetsu to Hagane 1995 81(9) 869. (Advanced Mater. and Technol. Res. Lab. Nippon Steel Corp. Kawasaki 211 Japan). Cunnane J. C. Lee S. Y. Perry D. L. Tidwell V. C. Schwing J. Nuhfer K. R. Weigand G. Field demon- stration of technologies for characterization of uranium contamination in surface soils. Technol. Programs Radioact. Waste Manage. Environ. Restor. 1993 1 803. (Argonne Nat. Lab. Argonne IL 60439 USA). Di P. Davey D. E. An optimized online preconcen- tration system for determination of trace gold in ore samples. Talanta 1995 42(8) 1081. (Sch. Chem.Technol. Univ. South Australia The Levels SA 5095 Australia). Pinillos S. C. Vicente 1. S. Asensio J. S. Bernal J. G. Simultaneous determination of sulfide and sulfite by gas-phase molecular absorption spectrometry. Comparative study of different calculation methods. Talanta 1995 42(7) 937. (Chem. Dept. Univ. La Rioja Logrono 26001 Spain). Ahmad M. Narayanaswamy R. Development of an optical fiber A~(III) sensor based on immobilized chrome 9613640 9613641 9613642 9613643 9613 644 9613645 9613646 9 613 647 9613648 9613649 96/3650 961365 1 9613 652 9613 65 3 9613654 azurol S. Talanta 1995 42(9) 1337. (Chem. Dept. Univ. Kebangsaan Malaysia Bangui 43600 Malaysia). Manzoori J. L. Sorouraddin M. H. Shemirani F. Chromium speciation by a surfactant-coated alumina microcolumn using electrothermal atomic absorption spectrometry.Talanta 1995 42( 8) 1151. (Fac. Chem. Univ. Tabriz Tabriz Iran). Jones R. D. Jacobson M. E. Jaffe R. West-Thomas J. Arfstrom C. Alli A. Method development and sample processing of water soil and tissue for the analysis of total and organic mercury by cold vapor atomic fluorescence spectrometry. Water Air Soil Pollut. 1995 80( 1-4) 1285. (Dept. Biol. Sci. Florida Int. Univ. Miami FL 33199 USA). Nasimov A. M. Khalmanov A. T. Tursunov A. T. Chekalin N. V. Use of laser atomic-ionization spec- trometers for determination of element traces in various materials. Zavod. Lab. 1995 61(4) 21. (Samark. Gos. Univ. Uzbekistan). Liu H. Determination of 11 trace elements in U,Os certified reference materials by ICP-AES. Youkuangye 1994 13(4) 250.(Beijing Res. Inst. Chem. Eng. and Metall. CNNC Beijing 101149 China). Huang Z. Study on the determination of trace tin in ores by atomic fluorimetry. Yejin Fenxi 1995 15(2) 22. (Res. Inst. Mining Design Wuhan Iron Steel Co. Huangshi 435006 China). Knag J. Determination of trace barium in steel by graphite furnace atomic absorption spectrometry. Yejin Fenxi 1995 15(2) 24. (Dept. Chem. Iron Steel Res. Inst. Ma’anshan Iron Steel Co. Ma’anshan 243000 China). Escobar M. P. Determination of wear metals in lubricating oil by electrothermal vaporization induc- tively coupled plasma spectrometry. Diss. Abstr. Int. B 1996 56( 1 l) 6075. (Univ. Florida Gainesville FL USA). Mochizuki T. Ishibashi Y. Akyoshi T. Sakashita A. Laser spectrometric probe for analysis of melted metals.Jpn. Kokai Tokkyo Koho JP 07,234,211 [95,234,211] (Cl. GOlN33/20) 05 Sep 1995 JP Appl. 93/355,434 30 Dec 1993; 6 pp. (Nippon Kokan Kk Japan). Berndt H. Apparatus for handling of flowing liquids for analytical purposes at high temperatures. Ger. Offen. DE 4,409,073 (Cl. G01N1/28) 28 Sep 1995 Appl. 4,409,073 17 Mar 1994; 14pp. hoe K. Furukawa K. Yokoyama K. Gas absorber and control device for analytical spectrometers. Jpn. Kokai Tokkyo Koho JP 07,181,148 [95,181,148] (Cl. GOlN23/225) 21 Jul 1995 Appl. 93/324,101 22 Dec 1993; 6 pp. (Kobe Steel Ltd. Japan). Okada K. Elemental analyzer. Jpn. Kokai Tokkyo Koho JP 07,229,818 [95,229,818] (Cl. G01N1/28) 29 Aug 1995 Appl. 94119,722 17 Feb 1994; 5pp. (Shimadzu Corp. Japan). Falk H. Plasma manipulator for atomic emission spectrometric analysis.Ger. Offen. DE 4,419,423 (Cl. GOlN21/73) 21 Sep 1995 DE Appl. 4,409,237 18 Mar 1994; 8 pp. (Spectro Anal. Instrum. Gesellschaft fuer Anal. Mesgeraete mbH Germany). Zhu J. System for generating and providing a gaseous phase sample at relatively sequentially constant pressure and flow rate. U.S. US 5,454,860 (Cl. 96-202; B01D19/00) 3 Oct 1995 Appl. 177,219 4 Jan 1994; 7 pp. (Cetac Technol. Inc. USA). Huber B. Atomic absorption spectrometer for mercury determination with improved dynamic range. Ger. Offen. DE 4,411,441 (Cl. GOlN21/71) 5 Oct 1995 Appl. 4,411,441 31 Mar 1994; 12 pp. (Bodenseewerk Perkin-Elmer GmbH Germany). Hirano Y. Matsui S. High frequency induced plasma atomic emission spectrometer and attachments therefor.Journal of Analytical Atomic Spectrometry September 1996 Vol. 11 349 R9613 65 5 9613656 9613657 9613658 9613659 96/3660 9613661 9613662 9613663 9613664 9 613 66 5 9 613 666 9613667 350R Jpn. Kokai Tokkyo Koho JP 07,120,395 [95,120,395] (Cl. GOlN21/73) 12 May 1995 Appl. 93/270,274 28 Oct 1993; 5 pp. (Hitachi Ltd. Japan). Lahmann W. Inductively coupled plasma light gener- ation method for electrothermal atomic absorption spectroscopic analysis and spectrometer system for its realization. Ger. Offen. DE 4,401,745 (Cl. GOlN21/71) 3 Aug 1995 Appl. 4,401,745 21 Jan 1994; 8 pp. (Bodenseewerk Perkin-Elmer GmbH Germany). Akyoshi T. Mochizuki T. Sakashita A. Nimura Y. Myahara H. Composition analysis of steel and appar- atus therefor. Jpn. Kokai Tokkyo Koho JP 07,128,237 [95,128,237] (Cl.G01N21/73) 19 May 1995 Appl. 93/274,590 2 Nov 1993; 8pp. (Nippon Kokan Kk Japan). Yamashita N. Fujimura S. Hiramoto F. Glow discharge emission spectrometric analysis. Jpn. Kokai Tokkyo Koho JP 07,120,394 [95,120,394] (Cl. G01N21/67) 12 May 1995 JP Appl. 931243,701 2 Sep 1993; 4 pp. (Rigaku Denki Kogyo Kk Japan). Awadallah R. M. Ismail S. S. Mohamed A. E. Application of multi-element clustering techniques of five Egyptian industrial sugar products. Aswan Sci. Technol. Bull. 1995 16 37. (Chem. Dept. Fac. Sci. Aswan Egypt). Ikeda M. Zhang Z.-W. Moon C.-S. Imai Y. Watanabe T. Shimbo S. Ma W.-C. Lee C.-C. Guo Y.-L. L. Background exposure of general population to cadmium and lead in Tainan City Taiwan Arch. Environ. Contam. Toxicol. 1996 30( l) 121.(Dept. Public Health Kyoto Univ. Kyoto 606-01 Japan). Careaga-Olivares J. Gonzalez-Ramirez D. Penicillamine produces changes in the acute blood elimination and tissue accumulation of thallium. Arch. Med. Res. 1995 26(4) 427. (Centre Invest. Biomed. Noreste Inst. Mexican0 Seguro Social Monterrey 64720 Mexico). Laryea M. D. Schnittert B. Kersting M. Wilhelm M. Lombeck I. Macronutrient copper and zinc intakes of young German children as determined by duplicate food samples and diet records. Ann. Nutr. Metab. 1995 39( 5) 271. (Univ. Children’s Hosp. Duesseldorf Germany). Krep H. Price D. A. Soszynski P. Tao Q.-F. Graves S. W. Hollenberg N. K. Volume sensitive hypertension and the digoxin-like factor; reversal by a Fab directed against digoxin in DOCA-salt hypertensive rats.Am. J. Hypertens. 1995 8(9) 921. (Harvard Med. Sch. Brigham and Women’s Hosp. Boston MA 02115 USA). Berkovic K. Pavic M. Cikovic N. Gacic M. Corrosion of iron tin and aluminium in fruit juices. Acta Aliment. 1995 24(1) 31. (Fac. Food Technol. and Biotechnol. Univ. Zagreb Zagreb 41000 Croatia). Lemmen P. Weissfloch L. Auberger T. Probst T. Uptake and distribution of the boron-containing ether lipid B-Et-1 1-OMe in tumor-bearing mice. Anti-Cancer Drugs 1995 6(6) 744. (Inst. Org. Chem. Biochem. Tech. Univ. Muenchen D-85747 Garching Germany). Lima J. L. F. C. Rangel A. 0. S. S. Souto M. R. S. Simultaneous determination of potassium and sodium in vegetables by flame emission spectrometry using a flow-injection system with two dialysis units. Anal.Sci. 1996 12( l) 81. (Dept. Quim.-Fisica CEQUP Oporto 4050 Portugal). Lee K.-J. Lim H. B. Preparation and analysis of lyophilized whole blood as external quality control materials for Pb and Cd determination by graphite furnace atomic absorption spectrometry. Anal. Sci. Technol. 1995,8(3) 273. (Coll. Pharm. Ehwa Woman’s Univ. Seoul 120-750 South Korea). Gilon N. Astruc A. Astruc M. Potin-Gautier M. Selenoamino acid speciation using HPLC-ETAAS fol- 96/3668 9613669 96/3670 9613671 96/3672 9613673 9613674 9613 6 7 5 96/3676 9613677 9613678 9613679 9613680 9613681 lowing an enzymic hydrolysis of selenoprotein. Appl. Organornet. Chern. 1995 9(7)? 623. (Lab. Chim. Anal. Univ. Pau Pays Adour 64000 Pau France). Charlot C. Cabanis M. T. Cabanis J. C. Analytical techniques applied to trace elements in foods.Ann. Falsif. Expert. Chim. Toxicol. 1995,88(931) 149. (Lab. Chim. Anal. et Bromatol. Fac. Pharm. 34060/1 Montpellier France). Martin de la Hinojosa M. I. Hitos Natera M. P. Cerezo Rubio M. J. Reyes M. M. Levels of volatile amines histamine and heavy metals in tunafish canned in olive oil. Alimentaria (Madrid) 1995 266 39. (Lab. Arbitral Agroalimentario Spain). Cisneros Garcia M. C. Grafia Gomez M. J. Rodriguez Vazquez J. A. Levels of cadmium in fresh and canned cephalopods. Alimentaria (Mudrid) 1995 266 53. (Dept. Quim. Anal. y Alimentaria Univ. Vigo Vigo 36208 Spain). Moro R. Cabeza J. M. Cuesta M. J. Composition of farmhouse and speciality cheeses of Asturias. VII. Magnesium zinc iron and copper. Alimentaria (Madrid) 1995 263 83.(Fac. Quim. Univ. Uviedo Spain). Celma P. Cabeza L. F. Serrat X. Cot J. Manich A. Detanning process in cycles with hydrogen peroxide in basic medium. AQEIC Bol. Tec. 1995 46(1) 9. (Inst. Quim. Sarria Univ. Ramon Llull Barcelona Spain). Font J. Cuadros R. M. Determination of cadmium and lead in tannery materials. AQEIC Bol. Tec. 1994 45(4) 170. (Escuela Superior Teneria Igualada Barcelona Spain). Alcock N. W. Flame flameless and plasma spec- troscopy. Anal. Chem. 1995 67( 12) 503R. (Dept. Preventive Med. Community Health Univ. Texas Med. Branch Galveston TX 77555-1109 USA). Marquardt B. J. Goode S. R. Angel S. M. In situ determination of lead in paint by laser-induced break- down spectroscopy using a fibre optic probe Anal. Chem. 1996 68(6) 977. (Dept. Chem.and Biochem. Univ. South Carolina Columbia SC 29208 USA). Fukushima M. Nakayasu K. Tanaka S. Nakamura H. Chromium(Ir1) binding abilities of humic acids. Anal. Chim. Acta 1995 317(1-3) 195. (Div. Mat. Sci. Grad. Sch. Environ. Earth Sci. Hokkaido Univ. Sapporo 060 Japan). Tahan J. E. Marcano L. Romero R. A. Anodic stripping voltammetric determination of total lead in anencephalic fetuses after pressure/temperature- controlled microwave mineralization. Anal. Chim. Acta 1995 317( 1-3) 311. (Lab. Instrum. Anal. Dept. Quim. Fac. Exp. Ciencias Univ. Zulia Maracaibo 4003 Venezuela). Ujiie S. Itoh Y. Kikuchi H. Wakui A. Zinc distribution in malignant tumors. Biomed. Rex Trace EEem. 1995 6( l) 45. (Div. Cancer Pharmacotherapy Miyagi Cancer Center Inst. Natori 981-12 Japan).Aquilio E. Spagnoli R. Seri S. Bottone G. Spennati G. Trace element content in human milk during lactation of preterm newborns. Biol. Trace Elem. Res. 1996 51(1) 63. (Inst. Nutr. Univ. L‘Aquila 67100 L‘Aquila Italy). El Sayed Z. A. Identification of inorganic constituents of Saluadora persica using spectroscopic techniques. Bull. Natl. Res. Cent. (Egypt) 1995 20(2) 163. (Spectrosc. Dept. Natl. Res. Centre Cairo Egypt). Springman E. B. Nagase H. Birktdal-Hansen H. Van Wart H. E. Zinc content and function in human fibroblast collagenase. Biochemistry 1995 34(48) 15713. (Inst. Mol. Biophys. Florida State Univ. Tallahassee FL 32306 USA). Journal of Analytical Atomic Spectrometry September j! 996 VoZ. 119613682 9 613 6 8 3 9613684 9613685 9613686 9613687 9613 6 8 8 9613689 9613690 9613691 9613692 9613693 9613694 Schiewer S.Volesky B. Mathematical evaluation of the experimental and modeling errors in biosorption. Biotechnol. Tech. 1995 9( l l ) 843. (Dept. Chem. Eng. McGill Univ. Montreal PQ Canada H3A 2A7). Groen H. J. M. van der Leest A. H. D. de Vries E. G. E. Uges D. R. A. Szabo B. G. Mulder N. H. Continuous carboplatin infusion during 6 weeks’ radio- therapy in locally inoperable non-small-cell lung cancer A phase I and pharmacokinetic study. Br. J. Cancer 1995 72(4) 992. (Dept. Pulmonary Dis. Univ. Hosp. Groningen 97 13 EZ Groningen Netherlands). Bulinski R. Wyszogrodzka-Koma L. Marzec Z. Trace elements in domestic food products. Part XX. Lead cadmium chromium zinc manganese copper nickel and iron content in mead.Bromatol. Chem. Toksykol. 1995,28( 3) 259. (Zakladu Bromatol. Akad. Medycznej Lublin Poland). Bulinski R. Wyszogrodzka-Koma L. Marzec Z. Determination of heavy metals in wine fruit wine and cocktails. Bromatol. Chem. Toksykol. 1995 28( 3) 253. (Zakladu Bromatologii Akad. Medycznej Lublin Poland). Prado G. Alvarez-Leite E. M. De Oliveria M. S. Comparison between the addition and routine atomic absorption spectrophotometric methods for determi- nation of metals in peanuts. Bromatol. Chem. Toksykol. 1995 51(1) 47. (Fac. Farm. UFMG 2360 Belo Horizonte Brazil). Tahan J. E. Sanchez J. M. Rodriguez M. C. Cubillan H. S. Granadillo V. A. Romero R. A. An application of pressureltemperature-controlled microwave heating curves for the mineralization of tuna material prior to spectrometric quantification of mercury.Ciencia (Maracaibo) 1995,3(2) 139. (Fac. Exp. Ciencias Univ. Zulia Maracaibo Venezuela). Peters W. Smith D. Lugowski S. McHugh A. MacDonald P. Baines C. Silicon and silicone levels in patients with silicone implants. Curr. Top. Microbiol. Immunol. 1996,210 39. (Div. Plastic Surgery Wellesley Hosp. Toronto ON Canada). Teuber S. S. Sauders R. L. Halpern G. M. Brucker R. F. Conte V. Goldman B. D. Winger E. E. Wood W. G. Gershwin M. E. Serum silicon levels are elevated in women with silicone gel implants. Curr. Top. Microbiol. Immunol. 1996 210 59. (Dept. Int. Med. Univ. California Davis CA 95616 USA). Oweczkin I. J. Kerven G. L. Ostatek-Boczynski Z. The determination of dissolved organic carbon by inductively coupled plasma atomic emission spec- troscopy.Commun. Soil Sci. Plant Anal. 1996 27( 1-2) 47. (Dept. Agric. Univ. Queensland Queensland 4072 Australia). Masson P. Gomez A. Tremel A. Suitability of open system digestions for the determination of thallium in environmental samples. Commun. Soil Sci. Plant Anal. 1996 27(1-2) 109. (Stn. Agronomie Center Rech. INRA Bordeaux F-33883 Villenave d’Ornon France). Krishnamurti G. S. R. Huang P. M. Van Rees K. C. J. Kozak L. M. Rostad H. P. W. A new soil test method for the determination of plant-available cad- mium in soils. Commun. Soil Sci. Plant Anal. 1995 26( 17-18) 2857. (Saskatchewan Center Soil Res. Univ. Saskatchewan Saskatoon SK Canada S7N 5A8). Swietochowska J. Kosmulska A. Determination of children’s blood serum and urinary copper by flameless absorption atomic spectrophotometry using the Zeeman effect for correction of nonspecific absorption.Diagn. Lab. 1993 29(3) 263. (Zaklad Biochemii Inst. Matki Dziecka Warsaw Poland). Tzatchev K. Lisheva B. Atanasova B. Anke M. (Ed.) Meissner D. (Ed.) Reference values of mana- ganese in blood serum of healthy Bulgarian sub- populations. Defizite Ueberschuesse Mengen- 9613695 9613696 9613697 9613 69 8 9613699 9613700 9613701 9613702 9613703 9613704 9613705 9613706 9613707 Spurenelem. Ernaehr. Jahrestag. Ges. Mineralstofe Spurenelem. 2 0th. Verlag Harald Schubert Leipzig Germany 1994 590-596. Jopke P. Fleckenstein J. Bahadir M. Schnug E. Anke M. (Ed.) Meissner D. (Ed.) Determination of iodine in plants and soils. Defizite Ueberschuesse Mengen- Spurenelem. Ernaehr.Jahrestag. Ges. Mineralstofle Spurenelem. 10th. Verlag Harald Schubert Leipzig Germany 1994 70-78. Husain A. Baroon Z. Al-khalafawi M. Al-Ati T. Sawaya W. Toxic metals in imported fruits and vegetables marketed in Kuwait Environ. Int. 1995 21(6) 803. (Food Resour. Div. Kuwait Inst. Sci. Res. Safat 13109 Kuwait). Belles M. Rico A. Schuhmacher M. Domingo J. L. Corbella J. Reduction of lead concentrations in vegetables grown in Tarragona Province Spain as a consequence of reduction of lead in gasoline. Environ. Int. 1995 21(6) 821. (Sch. Med. “Rovira i Virgil?’ Univ. Reus 43201 Spain). Luwihana S. Widianarko B. (Ed.) Vink K. (Ed.) Van Straalen N. M. (Ed.) Lead content of vegetables grown in fields adjacent to highways in Java Indonesia. Environ.Toxicol. South East Asia. VU University Press Amsterdam Netherlands 1994 185-189. Safaev R. D. Zaridze D. G. Hoffmann D. Brunnemann K. Liu Y. Efficiency and assessment of new cigarette filters. Chemical analysis of some of the toxic and carcinogenic agents in the mainstream smoke. Eksp. Onkol. 1995 17( l) 71. (Inst. Carcinogenesis Cancer Res. Centre Moscow 115478 Russia). Ghia M. Mattioli F. Novelli F. Minganti V. Inhibitory properties of triethylphosphine goldlupinyl- sulfide in adjuvant-induced arthritis in rats. Farmaco 1995 50(9) 601. (Fac. Med. Chirurgia Univ. Genova 16132 Genova Italy). Li S.-x. Huang G.-q. Qian S.-h. Determination of labile lead in foods by graphite furnace atomic absorp- tion spectrometry after electrodeposition on a tungsten loop. Fenxi Kexue Xuebao 1994 10(3) 48.(Dept. Environ. Sci. Wuhan Univ. 430072 China). Kamdem D. P. Gruber K. Freeman M. Laboratory evaluation of the decay resistance of red oak (Quercus rubra) pressure treated with copper naphthenate. For. Prod. J. 1995 45(9) 74. (Dept. Forestry Michigan State Univ. East Lansing MI 48824 USA). Feng J. Pan Z. Liu H. Determination of mercury in milk powder by cold atomic-nonchromatic dispersion atomic fluorescence spectrophotometry. Fenxi Huaxue 1996 24( l ) 74. (Hunan Provincial Sanitary Anti- epidemic Stn. Changsha 410005 China). Soylak M. Saraymen R. Dogan M. Investigation of lead chromium cobalt and molybdenum concen- trations in hair samples collected from diabetic patients. Fresenius Environ. Bull. 1995 4( 8) 485. (Fen-Edebiyat Fakultesi Erciyes Univ.Kayseri 38039 Turkey). Abe K. Studies on the effects of zinc compounds on the bone growth in rats. 11. Effect of zinc compounds on bone metabolism in weanling rats. Gifu Daigaku Igakubu Kiyo 1995 43( 2) 299. (Sch. Med. Gifu Univ. Gifu 500 Japan). Luo H. Gao L. Chen X. Li J. Distribution characteristics of rare earth elements in some ancient porcelain bodies in Zhejiang Province. Guisuanyan Xuebao 1995 23(3) 347. (Northwest Inst. Light Ind. Shaanxi 712081 China). Spencer A. J. Wood J. A. Saunders H.C. Freeman M. S. Lote C. J. Aluminium deposition in liver and kidney following acute intravenous administration of aluminium chloride or citrate in conscious rats. Hum. Exp. Toxicol. 1995 14( lo) 787. (Dept. Physiol. Univ. Birmingham Birmingham UK B15 2TT).Journal of Analytical Atomic Spectrometry September 1996 Vol. 1 1 351 R9613708 9613709 96/37 10 961371 1 9613712 9613 7 13 9613 7 14 9613715 96/37 1 6 96/37 1 7 9613718 96/37 19 9613720 9613721 9613722 352 R Zhang J. Wang S. Qu W. Determination of zinc in hair by a flow-injection system with online anion- exchange preconcentration separation and atomic absorption spectrometry. Huadong Ligong Dame Xuebao 1995 21(4) 507. (Dept. Chem. ECU ST Shanghai 200237 China). Tayel F. T. Trace metals concentrations in the muscle tissue of ten fish species from Abu-Qir Bay Egypt. Int. J. Enuiron. Health Res. 1995 5(4) 321. (Nat. Inst. Oceanography and Fisheries Alexandria Egypt). Prakash P. K. S. Mohan M. R. Rao S. B. Trace metals in cane juice and sugar factory products.Analysis by direct current plasma atomic emission spectrometry. Int. Sugar J. 1995 97( 1160) 362. (Osmania Univ. Hyderabad India). Molnar J. MacPherson A Barclay I. Molnar P. Selenium content of convenience and fast foods in Ayrshire Scotland. Int. J. Food Sci. Nutr. 1995 46(4) 343. (Scottish Agric. Coll. Ayr UK KA6 5HW). Beech I. B. Cheung C. W. S. Interactions of exopoly- mers produced by sulfate-reducing bacteria with metal ions. Int. Biodeterior. Biodegrad. 1995,35( 1-3) 59. (Sch. Chem. Phys. and Radiography Univ. Portsmouth Portsmouth UK PO1 2DT). Yang L.-X. Douple E. B. Wang H.-J. Irradiation enhances cellular uptake of carboplatin. Int. J. Radiat. Oncol. Biol. Phys. 1995 33(3) 641. (Dept. Med. Dartmouth Med. Sch. Lebanon NH USA). Goren Y. Segal I. On early myths and formative technologies a study of pre-pottery Neolithic B sculp- tures and modelled skulls from Jericho.Isr. J. Chem. 1995 35( 2) 155. (Interdisciplinary Res. Div. Israel Antiquities Auth. 91004 Jerusalem Israel). Kawauchi A. Ishida M. Measurement of zeolite silicate and phosphate in laundry detergent products by inductively coupled plasma atomic emission spec- trometry. J. Am. Oil Chem. SOC. 1996 73(1) 131. (Res. and Dev. Dept. Kobe Tech. Center Procter and Gamble Asia Kobe Japan). Day M. Zhang B. L. Martin G. J. Asselin C. Morlat R. Characterization of the region and year of wine production using stable isotopes and elemental analyses. J. Int. Sci. Vigne Vin 1995 29(2) 75. (CNRS Univ. Nantes 44072103 Nantes France). Nixon D. E. Mussmann G. V.Moyer T. P. Inorganic organic and total mercury in blood and urine cold vapor analysis with automated flow injection sample delivery. J. Anal. Toxicol. 1996,20( l) 17. (Metals Lab. Mayo Clinic Rochester MN 55905 USA). Aliyu R. Okoye Z. S. C. Shier W. T. The hepatopro- tective cytochrome P-450 enzyme inhibitor isolated from the Nigerian medicinal plant Cochlospermum planchonii is a zinc salt. J. Ethnopharmacol. 1995,48(2) 89. (Fac. Med. Sci. Univ. Jos Jos Nigeria). Farnum J. F. Glascock M. D. Sandford M. K. Gerritsen S. Trace elements in ancient human bone and associated soil using NAA. J. Radioanal. Nucl. Chem. 1995,196(2) 267. (Res. Reactor Missouri Univ. Columbia MO 65211 USA). James D. W. Hurst C. J. Tindall T. A. Alfalfa cultivar response to phosphorus and potassium deficiency elemental composition of the herbage.J. Plant Nutr. 1995 18( l l ) 2447. (Dept. Plants Soils Biometeorol. Utah State Univ. Logan UT Shakir S. Munshi A. B. Qadri R. B. Studies on mineral content in sea squid species from Pakistan coastal waters. J. Chem. SOC. Pak. 1995 17(1) 31. (PCSIR Lab. Complex Karachi 75280 Pakistan). Touyz R. M. Milne F. J. Alterations in intracellular cations and cell membrane ATPase activity in patients with malignant hypertension. J. Hypertens. 1995 13( 8) 84322-4820 USA). 9613723 9613724 9613725 9613726 9 613 7 27 9613728 9613729 9613 7 3 0 9613731 9613732 96/37 3 3 9613734 9613735 9613 7 3 6 867. (Dept. Med. Univ. Witwatersrand Johannesburg South Africa). Szabo A. S. Golightly D. W. Determination of boron in liquid nutritional foods by ICP-AES.J. Food Compos. Anal. 1995 8(3) 220. (Ross Prod. Div. Abbott Lab. Columbus OH 43215-1724 USA). Poon G. K. Raynaud F. I. Mistry P. Odell D. E. Kelland L. R. Harrap K. R. Barnard C. F. J. Murrer B. A. Metabolic studies of an orally active platinum anticancer drug by liquid chromatography-electrospray ionization mass spectrometry. J. Chromatogr. A 1995 712(1) 61. (CRC Centre Cancer Ther. Inst. Cancer Res. Sutton Surrey UK SM2 5NG). Barclay M. N. I. MacPherson A. Dixon J. Selenium content of a range of UK foods. J. Food Compos. Anal. 1995 8(4) 307. (SAC Ayr UK KA6 5HW). Hong Y. C. Park C. Y. Uptake cytotoxicity and carcinogenicity of nickel compounds on BALB/3T3 cells. K'at 'ollik Taehak Uihakpu Nonmunjip 1994,47( 2) 723. (Med. Coll. Catholic Univ.Seoul South Korea). Chen G. Zhou X. FAAS determination of copper zinc iron manganese calcium and magnesium in fertilizers. Lihua Jianyan Huaxue Fence 1995 31( 5 ) 269. (Dept. Chem. Eng. Northwest Univ. Xi'an 710069 China). Beck P. Determination of magnesium and the trace elements selenium zinc copper and aluminium in the corpuscular components of blood in patients with acute oligo-anuric renal failure. Laboratoriumsmedizin 1995 19(9) 384. (Inst. Klin. Chem. Laboratoriumsmed. Katharinenhospital 70174 Stuttgart Germany). Kruse-Jarres J. D. Ruekgauer M. Schmitt Y. Beck P. Baeuerle-Bubeck A. Moser V. Streit G. Zeyfang A. Simultaneous AAS determinations of selenium and zinc in whole blood and its cellular components as demonstrated in oligo-anuric renal failure.Laboratoriumsmedizin 1995 19( 3) 117. (Inst. Klin. Chem. Laboratoriumsmed. Katharinenhospital 70176 Stuttgart Germany). Hoff T. Gurr E. Determination of electrolytes using the flame atomic emission spectrometer EFUX 5057 in combination with the multichannel analyzer Hitachi 717. Labor-Med. 1995,18( 6) 320. (Zentralkrankenhaus Links Weser Zentrallaboratorium 28277 Bremen Germany). Razniewaks G. Trzcinka-Ochocka M. The use of flameless AAS for determining lead and cadmium in blood and cadmium copper nickel and chromium in urine. Med. Pr. 1995 46(4) 347. (Dept. Biol. Monitoring Prof. Jerzy Nofer Inst. Occup. Med. Lodz Poland). Pun K. C. Cheung R. Y. H. Wong M. H. Characterization of sewage sludge and toxicity evalu- ation with microalgae. Mar. Pollut. Bull. 1995 31(4-12) 394. (Dept.Biol. and Chem. City Univ. Hong Kong Kowloon Hong Kong). Stillman M. J. Presta A. Gui Z. Jiang D.-T. Spectroscopic studies of copper silver and gold- metallothioneins. Met.-Based Drugs 1994 1( 5-6) 375. (Dept. Chem. Univ. Western Ontario London ON Canada N6A 5B7). Touyz R. M. Panz V. Milne F. J. Relations between magnesium calcium and plasma renin activity in black and white hypertensive patients. Miner. Electrolyte Metab. 1995 21(6) 417. (Dept. Med. Univ. Witwatersrand Johannesburg South Africa). Willey J. The effects of desalination on archaeological ceramics from the Casas Grandes region in northern Mexico. Muter. Res. SOC. Symp. Proc. 1995 352 839. (Sherman Fairchild Cent. Objects Conserv. Metrop. Mus. Art New York NY 10028 USA). Milewicz A.Neuberg L. Iwankiewicz G. Blood and tissue magnesium and endogenous estrogen concen- Journal of Analytical Atomic Spectrometry September 11996 Vol. 119613737 9613738 9613739 9613740 9613741 9613742 9613743 9613744 9613745 9613746 9613747 9613748 9613749 9613750 9613751 trations in women with breast cancer. Magnesium 1993 405. (Dept. Endocrinology Med. Acad. Wroclaw Poland). Zeana C. Chirulescu Z. Such A. Pirvulescu R. Carseli C. Zeana C. B. Plasma Mg Zn and Cu in acute myocardial infarction. Magnesium 1993 35 1. (Med. Clin. Emergency Hosp. Bucharest Romania). Sahuquillo A. Lopez-Sanchez J. F. Rubio R. Rauret G. Extractable chromium determination in soils by AAS. Mikrochim. Acta 1995 119(3-4) 251. (Dept. Quim. Anal. Univ. Barcelona Barcelona Spain). Aras N.K. Olmez I. Human exposure to trace elements through diet. Nutrition (Syracuse N. Y.) 1995 l l ( 5 Suppl.) 506. (Dept. Chem. Middle East Tech. Univ. Ankara Turkey). Fujino H. Muguruma M. Oniki H. Ito T. Ohashi T. Studies on available utilization of whey proteins. V. Role of Ca2+ on heat aggregation of whey protein isolate. Nippon Shokuhin Kagaku Kogaku Kaishi 1995 42( lo) 769. (Higashi Chikushi Coll. Kitakyushu 803 Japan). Lu C.-S. Guan Y. Bus-Kwofie R. Metin S. Application of atomic absorption spectroscopy to in situ monitoring of sputtering deposition of dielectric materials.. Proc.-Electrochem. SOC. 1995 95-6 349. (Intelligent Sensor Technol. Inc. Mountain View CA 94043 USA). Korenovska M. Polacekova 0. Distribution of mercury in milk. Sb. UVTLZ Potrauin.Vedy 1995 13(4) 313. (Food Res. Inst. Bratislava Slovakia). Amarowicz R. Grabska J. The content of mineral compounds bound to rape seed dietary fiber. Przem. Spozyw. 1995 49( 8) 268. (Centrum Agrotechnol. Weterynarii 10 718 Olsztyn Poland). Schulze D. G. McCay-Buis T. Sutton S. R. Huber D. M. Manganese oxidation states in Gaeumannomyces- infested wheat rhizospheres probed by micro-XANES spectroscopy. Phytopathology 1995 85( 9) 990. (Dept. Agronomy Purdue Univ. West Lafayette IN 47907 USA). Villafurela Sanz J. J. Ayet Gisbert G. Aluminium a toxic and contaminating element. Quim. Ind. (Madrid) 1995 42(7) 28. (Serv. Nefrologia Hosp. Ramon Cajal Spain). de Abreu C. A. de Abreu M. F. van Raij B. Santos W. R. Comparison of methods to determine the availability of heavy metals in soils.Rev. Bras. Cienc. Solo 1995 19(3) 463. (Secao Fertilidade Solo Nutr. Plantas Inst. Agronomico 13001 970 Campinas Brazil). Aranha S. Nishikawa A. M. Taka T. Salioni E. M. C. Cadmium and lead levels in cattle liver and kidney. Rev. Inst. Adolfo Lutz 1994 54(1) 16. (Lab. Referencia Animal Campinas Brazil). Takasaka M. Analysis for As in beverages by AA-6500s. Shimadzu Hyoron 1995 52( 2) 129. (Chromatogr. Spectrophotom. Instrum. Div. Shimadzu Corp. Hadano 259 13 Japan). Barth A. von Germar F. Kreutz W. Maentele W. Merlin J. C. (Ed.) Turrell S. (Ed.) Huvenne J. P. (Ed.) Three partial reactions of the Ca2+-pumping cycle of the Ca2+-ATPase studied by time-resolved FTIR spectroscopy. Spectrosc. Biol. Mol. Eur. Conf. 6th. Kluwer Dordrecht Netherlands 1995 147-148.Lagarde F. Leroy M. Speciation of trace elements use and suitability. Spectra Anal. 1995 24(185) 32. (CNRS EHICS 67008 Strasbourg France). Zhu B. Tabatabai M. A. An alkaline oxidation method for determining total arsenic and selenium in soils. Soil Sci. SOC. Am. J. 1995 59(6) 1564. (Dept. Agronomy Iowa State Univ. Ames IA 50011 USA). 9613752 9613753 9 613 7 54 9613 75 5 9613756 9613757 9613 758 9613759 9613760 9613761 9613762 9613763 9613764 9613765 Cao J. Wang T. Zhang S. Arrhythmias after cardiopulmonary bypass and treatment with mag- nesium. Shanghai Yike Dame Xuebao 1995 22(4) 288. (Cardiovascular Center Children Hosp. Shanghai Med. Univ. Shanghai 200000 China). ROSSOUW R. J. Grobler S. R. Kotze T. J. v. W. Effect of airborne lead on lead levels of blood tail vertebrae iliac crest and epiphyses of the rat.S. Afr. J. Sci. 1995 91(9) 484. (Oral and Dental Res. Inst. Univ. Stellenbosch Tygerberg 7505 South Africa). du Toit I. J. Grobler S. R. Kotze T. J. v. W. Basson N. J. Fluoride calcium and phosphorus levels in bee honey and water. S. Afr. J. Sci. 1995 91(8) 391. (Fac. Dentistry Univ. Stellenbosch Tygerberg 7505 South Africa). Thompson G. R. The direct determination of phos- phorus in citric acid soil extracts by colorimetry and direct-current plasma emission spectroscopy. S. Afr. J. Plant Soil 1995 12(4) 152. (Dept. Agric. Eisenburg Agric. Dev. Inst. Eisenberg 7607 South Africa). Sapunar-Postruznik J. Bazulic D. Kubala H. Balint L. Estimation of dietary intake of lead and cadmium in the general population of the Republic of Croatia.Sci. Total Enuiron. 1996 177(1-3) 31. (Vet. Inst. Zagreb 41000 Croatia). Kalac P. Niznanska M. Bevilaqua D. Staskova I. Concentrations of mercury copper cadmium and lead in fruiting bodies of edible mushrooms in the vicinity of a mercury smelter and a copper smelter. Sci. Total Enuiron. 1996 177( 1-3) 251. (Fac. Agric. Univ. South Bohemia 370 05 Ceske Budejovic Czech Republic). Tariq M. A. Qamar-un-Nisa Fatima A. Concentrations of Cu Cd Ni and Pb in the blood and tissues of cancerous persons in a Pakistani population. Sci. Total Enuiron. 1995,175( l) 43. (Inst. Chem. Univ. Punjab Lahore Pakistan). White C. Gadd G. M. Determination of metals and metal fluxes in algae and fungi. Sci. Total Enuiron. 1995 176(1-3) 107. (Dept. Biol. Sci.Univ. Dundee Dundee UK DD1 1DN). Gaso M. I. Cervantes M. L. Segovia N. Abascal F. Salazar S. Velazquez R. Mendoza R. 137Cs and 226Ra determination in soil and land snails from a radioactive waste site. Sci. Total Enuiron. 1995 173 41. (ININ 11801 Mexico DF Mexico). Galgan V. Frank A. Survey of bioavailable selenium in Sweden with the moose (Alces alces L.) as monitoring animal. Sci. Total Enuiron. 1995 172(1) 37. (Dept. Chem. Nat. Vet. Inst. 750 07 Uppsala Sweden). Tao G. Fang Z. Online flow injection solvent extraction for electrothermal atomic absorption spec- trometry determination of nickel in biological samples. Spectrochim. Acta Part B 1995 50B( 14) 1747. (Flow Injection Anal. Res. Center Acad. Sinica Shenyang 110015 China). Telolahy P. Morel G. Cluet J. L.Yang J. M. Thieffry N. de Ceaurriz J. An attempt to explain interindividual variability in 24-h urinary excretion of inorganic arsenic metabolites by C57 BL/6J mice. Toxicology 1995 103(2) 105. (Fac. Pharm. Lab. Chem. Toxicol. Environ. 92296 Chatenay-Malabry France). van Warmerdam L. J. C. van Tellingen O. Huinink W. W. ten Bokkel Rodenhuis S. Maes R. A. A. Beijnen J. H. Monitoring carboplatin concentrations in saliva a replacement for plasma ultrafiltrate measure- ments? Ther. Drug Monit. 1995 17(5) 465. (Netherlands Cancer Inst. Antoni van Leeuwenhoek Hosp. Amsterdam Netherlands). Styblo M. Yamauchi H. Thomas D. J. Comparative in uitvo methylation of trivalent and pentavalent arsenicals. Toxicol. Appl. Pharmacol. 1995 135( 2) 172. Journal of Analytical Atomic Spectrometry September 1996 Vol.11 353 R9613766 9613767 9613 768 9613769 9613770 9613771 9613 772 9613773 9613774 9613775 9613776 (Curriculum Toxicol. Univ. North Carolina Chapel Hill NC 27514 USA). Shimmura T. Nakazaki M. Simple measurement of aluminium in serum and urine by palladium ammonium hydroxide dilution and polarized Zeeman atomic absorption spectrophotometry. Toyama-ken Eisei Kenkyusho Nenpo 1994,18,235. (Toyama Inst. Health Toyama 939 03 Japan). Topcuoglu S. Kut D. Erenturk N. Esen N. Saygi N. Some element levels in anchovy bluefish Atlantic mackerel and dolphin. Turk. J. Eng. Environ. Sci. 1995 19(4) 307. (Cekmece Nukleer Arastirma Egitim Merkezi TAEK Istanbul Turkey). Anal. O. Guener G. Gezer S. Ulman C. Taneli N. N. Blood selenium level in healthy children correlation with glutathione peroxidase and interrelation with vitamin E. Turk.J. Med. Sci. 1995 24(3) 201. (Fac. Med. Dokuz Eylul Univ. Izmir Turkey). Paama L. Peraemaeki P. Lajunen L. H. J. Laine K. Pakkonen T. Saari E. Havas P. Spectrochemical determination of trace metals in berries by atomic emission and absorption. Tartu Ulik. Toim. 1993 966( Publications on Chemistry XXI) 153. (Inst. Chem. Phys. Univ. Tartu Estonia). Piiri L. Paama L. Ilomets T. Elemental composition of historical glazes from St. John’s Church of Tartu. Tartu Ulik. Toim. 1994 975 221. (Inst. Org. Chem. Univ. Tartu Estonia). Garcia S. M. C. Jose Javier San Miguel S. Ma. F. Hernandez S. Ma. C. Guillen R. Alberto M. Serrano G. Luis B. Sanchez J. S. A. Determination of arsenic in basic foods in localities affected by arsenic- contaminated water.Tecnol. Aliment. (Mexico City) 1994,29( 5-6) 7. (Fac. Med. Univ. Autonoma Coahuila Coahuila Mexico). Filardo S. Rabling J. P. Zuniga A. A method design for the analysis of lead and cadmium in milk by flame atomic absorption spectrophotometry; from a bibli- ography issued from 1957 to 1980. Tecnol. Aliment. (Mexico City) 1993 28(4 5 6) 29. (Centre Invest. Quim. Univ. Autonoma Hidalgo Pachuca Mexico). Mahalingam T. R. Vijayalakshmi S. Prabhu R. K. Mathews C. K. Shanmugasundaram K. R. Determination of trace elements in blood plasma and red cells by inductively coupled plamsa mass spec- trometry. Trace Toxic Elem. Nutr. Health Proc. Int. Conf. Health Dis. Efl. Essent. Toxic Trace Elem. 4th 1993. Wiley Eastern New Delhi India 1995 438-444.Mathews C. K. Advanced techniques for the determi- nation of trace elements in biological systems. Trace Toxic Elem. Nutr. Health Proc. Int. Conf. Health Dis. Efl. Essent. Toxic Trace Elem. 4th 1993. Wiley Eastern New Delhi India 1995 431-437. Chaudhri M. A. Watling R. J. Young A. The application and potential of inductively coupled plasma mass spectrometry ICP-MS for high sensitivity multi- element analysis of medical samples down to the sub- ppb range. Trace Toxic Elem. Nutr. Health Proc. Int. Conf. Health Dis. Efl. Essent. Toxic Trace Elem. 4th 1993. Wiley Eastern New Delhi India 1995 421-430. Durrant S. F. Mota R. P. Bica de Moraes M. A. Plasma polymerized hexamethyldisiloxane discharge 19613777 19613 778 13613779 (3 613 7 80 ‘961378 1 9613 782 ‘9613783 (9613 784 (961378 5 9613786 ‘9613787 ‘9613788 and film studies.Vacuum 1996 47(2) 187. (Lab. Processos Plasma Fisica Gleb Wataghin 13083 970 Campinas Brazil). Graff L. Muller G. Burnel D. In vitro and in vivo evaluation of potential aluminium chelators. Vet. Hum. Toxicol. 1995 37(5) 455. (Fac. Med. Univ. Henri Poincare 54505 Vandoeuvre les Nancy France). Popov A. I. Gromov K. G. Popkov B. A. Mineral elements of roots and rhizomes of Sanquisorba ojicinalis. Vopr. Pitan. 1995 2 30. (Kemerov. Med. Inst. Kemerovo Russia). Pribilincova J. Maretta M. Janotikova I. Marettova E. The effect of cadmium treatment on breeding hens and cocks and early viability of their chickens. Vet. Med. (Prague) 1995,40( ll) 353. (Inst. Exp. Vet. Med. Kosice Slovakia).Lechuga Galvez D. Rosiles Martinez R. Horta Ramirez J. M. In vitro physicochemical identification and adsorbent efficacy of some commercial aluminosil- icates on aflatoxin B,. Vet. Mex. 1995,26(2) 129. (Fac. Med. Vet. Zootecnia Univ. Nacional Autonoma Mexico Mexico City 045 10 Mexico). Chang H. Schaller K. H. Welter D. Angerer J. Determination of Ag in urine by electrothermal atom- izer with Zeeman-effect background correction. Weisheng Yanjiu 1995 24(4) 201. (Anhui Inst. Occup. Med. Hefei China). Keijzer T. J. S. Loch J. P. G. Accumulation of HN0,- extractable tin in agricultural and nonagricultural soils by the use of triphenyltin acetate. Water Air Soil Pollut. 1995,84( 3-4) 287. (Dept. Geochem. Inst. Earth Sci. Univ. Utrecht 3508 Utrecht Netherlands). Teng J.-H. Wang T.-L.Lin W.-C. Chen M.-T. Chen Z.-S. Investigation on four heavy metal constitu- ents of commercial restorative Chinese medicines. Yaowu Shipin Fenxi 1995 3(3) 193-202. (Dept. Appl. Chem. Chianan Coll. Pharm. Tainan 710 Taiwan). Chen Z.-S. Lee D.-Y. Heavy metal contents of representative agricultural soils in Taiwan. Zhongguo Huanjing Gongcheng Xuekan 1995 5( 3) 205. (Grad. Inst. Agric. Chem. Natl. Taiwan Univ. Taipei Taiwan). Brunner B. Stolle A. Lead- cadmium- and mercury- carry-over to meat products by spices and condiments. Z. Ernaehrungswiss. 1995 34(2) 113. (Inst. Hyg. and Technol. 80539 Munich Germany). Wilhelm M. Lombeck I. Kouros B. Wuthe J. Ohnesorge F. K. Duplicate study on the dietary intake of some metals/metalloids by German children. Part 2. Aluminium cadmium and lead.Zentralbl. Hyg. Umweltmed. 1995 197( 5) 357. (Inst. Toxikol. Heinrich Heine Univ. 40001 Duesseldorf Germany). Wilhelm M. Lombeck I. Kouros B. Wuthe J. Ohnesorge F. K. Duplicate study on the dietary intake of some metals/metalloids by German children. Part 1. Arsenic and mercury. Zentralbl. Hyg. Umweltmed. 1995 197( 5) 345. (Inst. Toxicol. Heinrich Heine Univ. 40001 Duesseldorf Germany). Sabal J. A. Method of hair analysis. PCT Int. Appl. WO 95 28,638 (Cl. GOlN33/20) 26 Oct 1995 US Appl. 228,680 18 Apr 1994; 19 pp. 354R Journal of Analytical Atomic Spectrometry September 1996 Vol. 11

ISSN:0267-9477    

DOI:10.1039/JA996110341R

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

The Future of Plasma Spectrochemical Instrumentation* Plenary Lecture GARY M. HIEFTJE Department of Chemistry Indiana University Bloomington IN 47405 USA Every decade seems to bring with it some important novelty in atomic spectrochemical instrumentation. During the past decade however the changes seemed to be more evolutionary than revolutionary. Emission spectrometric instrumentation has become less expensive and more capable with the introduction of advanced user interfaces lowered detection limits that now approach those for electrothermal atomization in AAS axial-viewing options that provide greater stability and higher sensitivity but at the cost of elevated interferences and multichannel detector arrays that enable an entire emission spectrum to be viewed at once. Similarly MS instrumentation has evolved to a simpler less expensive form even as capabilities have increased.In atomic MS the origins of several troublesome interference effects have been identified and substantially reduced and strategies have been devised to reduce the severity of isobaric overlaps (spectral interferences). Because of these trends sales of emission-based instrumentation have remained brisk while those for atomic mass spectrometers have risen dramatically. The combination of relatively high sales and higher capabilities has encouraged a number of new instrument manufacturers to enter the plasma spectrochemical market while others have been forced to drop out to consolidate or to be acquired. In attempting to project the future of atomic spectrochemical instrumentation it is a safe bet to assume that past trends will continue. Revolutionary changes are of course much more difficult to forecast.Nevertheless some guidance can be derived from reviewing the limitations of current sources and detection techniques that are used for plasma spectrometry. Such a review reveals that detection limits in emission measurements are usually constrained by background noise levels whereas those in MS are bounded by the efficiency of sample utilization and by the transmission of the mass spectrometer and of the interface that separates it from the plasma source. Also although the origin of matrix interferences in both atomic emission and atomic mass spectrometry are not fully understood it seems clear that what is needed is better control of sample introduction atom formation and the plasma environment that fosters atomic excitation and ionization.Further it is obvious that more information must be derived from each atomic spectrometric measurement in order to learn more about sample speciation and to enable the instrument better to monitor its own operation. These needs and likely trends argue strongly for a higher degree of dimensionality in atomic spectrometric measurements. Higher dimensionality represented in other areas of analytical chemistry by the so-called ‘hyphenated techniques’ such as GC-MS can be achieved in atomic spectrometry by using sources and sample-introduction techniques in tandem (either in series or in parallel) by combining emission MS and AF measurements and by employing multi-dimensional calibration and sample-recognition algorithms.For example it can be * Presented at the 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-1 3 1996. 1 Journal of I Analytical I Atomic Spectrometry shown that MS resolution greater than 300 000 can be achieved by means of a relatively simple moderate-resolution mass spectrometer as long as it is preceded by suitable sample-introduction apparatus. Further interference effects and sample-utilization efficiency might be drama tically increased by introducing sample solutions in the form of discrete droplets or as puffs of sample vapour. These and other examples taken from the author’s laboratory and from laboratories of others illustrate these various trends and future projections. Keywords Plasma emission spectrometry; plasma mass spectrometry; inductively coupled plasma; sample-introduction efjiciency ; time-of-jlight mass spectrometry; multidimensional methods; chemometrics It is always dangerous to project the future.It is of course a relatively simple matter to track current trends and to extra- polate them. This approach perhaps the safest has been employed in at least one book series’ and has in retrospect demonstrated a fair degree of reliability. Another approach which was taken in some of our own earlier reviews2y3 applies particularly well to the fields of analytical science and chemical instrumentation. It involves defining an ‘ideal’ device instru- ment or technique and determining criteria by which existing systems fall short. It is then a relatively safe bet to assume that the greatest emphasis in the near future will be placed upon overcoming the most serious of the shortcomings. A third technique to forecast the future is to record notable advances in related scientific or technical areas with the assumption being that those advances will eventually be transferred.Unfortunately none of these established means of forecasting is able to deal with a true ‘breakthrough’. By definition true innovation cannot be predicted. For that reason no one fore- saw for example magnetic resonance imaging matrix-assisted laser desorption/ionization in MS or the deuterium-lamp method for background correction in AAS. Still an informed observer might have foreseen the widespread use of AAS as an analytical technique the attractiveness of ICP-AES and the rapid growth of ICP-MS simply by keeping abreast of the physics literature and by listening attentively to lectures at major international symposia.The forecasting exercise therefore seems to be worthwhile. Predictions in atomic spectrometry are complicated by the blurring of disciplinary boundaries that are affecting all of science. For example it is not simple to decide whether electrospray ionization (ESI) coupled with MS is a form of atomic spectrometry or not. To be sure the method can provide the same sort of information as can ICP-MS and additional details as well. However in its present state of development ESI does not provide complete and unambiguous information about the qualitative and quantitative elemental composition of a sample.Indeed the data it provides are more akin to those offered by ion chromatography than by ICP-MS. Journal of Analytical Atomic Spectrometry September 1996 Vol. 11 (61 3-621) 61 3Similarly the increasing emphasis on speciation in atomic spectrometric analysis precludes a clear definition of the boundaries of the field. Ordinarily speciation is considered to include an indication of the oxidation state of an element; however it might also require information about the degree of complexation the number and type of associated atoms and the sort of bonding in which an atom is involved. Does it then require in its ultimate embodiment also a complete definition of the atomic composition and layout of a sample? If so it would seem to be more competitive with X-ray crystallography than with current techniques such as ICP-AES ICP-MS and AAS.If this degree of speciation is to be the supreme goal of atomic spectometry perhaps our attention should be directed more towards secondary ion mass spectrometry or sputtered neutral mass spectrometry than to these traditional methods. Conveniently both these latter powerful (but expensive) methods and traditional ones can be represented by the scheme shown in Fig. 1 which embodies perhaps the ‘ultimate’ method of atomic spectrometric analysis. In this arrangement a solid liquid or gaseous sample is decomposed quantitatively into its constituent atoms. Those atoms are then sorted by type and by isotope and each of the isotopes subsequently counted.In an ICP mass spectrometer equipped with a laser-ablation accessory for example the laser beam and the ICP together provide the atomization a mass spectrometer performs atom (really ion) sorting and a high-sensitivity low-background detector counts the ions individually. Unfortunately in such an instrument atomization is not quantitative spatial resolution is not possible at the atomic level not all atoms are ionized and transmission losses preclude the detection of every atomic ion. Ideally one might wish to employ a ‘Maxwell’s Demon’ in the scheme of Fig. 1. The demon would pluck atoms one by one from the sample of interest recording at the same time the location from which the atom was withdrawn. Each atom would than be sorted (perhaps by mass) and counted.Because the nearest neighbours of every atom would be recorded and because the demon might be able to register information about bonding and oxidation states at the same time the atom is withdrawn a complete description of a sample would be possible. On the other hand some applications might require greater speed than that of which the Maxwell’s Demon is capable. In such a situation the atomization process might resemble more closely the game-starting ‘break‘ that occurs in pocket billiards (pool). Here the atoms of the sample would be simultaneously liberated and scattered each type (element) Atomic ions fl Atomize C. - Mn U B r Count Atomic Ions Fig. 1 In the ultimate atomic spectrometric instrument the sample would be decomposed quantitatively into its constituent atoms with the location of each atom in the sample being recorded along with its oxidation state degree of complexation and nearest neighbours.The isolated atoms would then be separated by type and by isotope and the individual isotopes counted being directed to its own ‘pocket’ and the atoms counted as they arrive. Interestingly the Maxwell’s Demon concept above is one component of the emerging field of nanotechnology. Ordinarily nanotechnology is viewed as involving the assembly of complex macroscopic materials from individual atoms or molecules. The human body for example is an exquisitely refined nanotechnology factory. However nanotechnology can also involve the disassembly of materials a process which some view as a prerequisite for nanotechnological fabrication.In this concept a nanotechnological ‘disassembler’ would analyse (disassemble) a given sample on an atom-by-atom basis while keeping a nanoscopic record of the position and bonding of each atom. This record or programme stored perhaps in molecular form just as is a biological code in the human genome would then be used to construct perfect replicates of the original object or material. This second (fabrication) step would be carried out by a second type of nanotechnological device an ‘assembler’. Perhaps this nanotechnological direction is where atomic spectrometry will eventually head. For the near term however it is probably more prudent to consider whether and how existing methods can be modified or improved. There is already a substantial array of highly capable sources including glow discharges microwave plasmas inductively coupled plasmas electrospray ionization and others. Similarly a host of alter- native detection methods exists including AAS AES atomic mass spectrometry (AMS) and AFS.In most practical applications of these methods sample preparation plays a crucial role. In many cases this preparation step consists of dissolving the sample and adding to it such things as internal standards or ‘spikes’ to enable standard additions to be used. In other cases sample preparation consists of casting a solid into a suitable form and grinding or other modification of its surface. In still others such procedures as fusion etching or even ion implantation are utilized. Not infrequently sample preparation is the rate-limiting step in performing an elemental analysis. Unfortunately despite the importance of preparing a sample the subject cannot be treated here.Indeed an adequate examination of sample- preparation options for the future deserves a review of similar scope by itself. Considerations will therefore be constrained to likely directions that will be taken in the areas of source and spectrometer development and in signal processing. To begin the most significant shortcomings of the commonly used methods for atomic spectrometry will be reviewed briefly. Trends in both atomic spectrometric instrumentation and in instrumentation overall will then be considered in an effort to project what new instrumental advances are likely.Considering detection limits first it will be seen that improvements in AES will depend upon reducing background emission whereas MS will require gains in sample-utilization efficiency and in instrument transmission. Methods by which other figures of merit can be improved will also be addressed. Figures of merit to be emphasized in this discussion include precision and instrument speed. Other trends that seem likely will then be outlined and will emphasize an increase in the dimensionality of atomic spectrometric instrumentation. Added dimensions might derive from the coupling of atomic methods with others (e.g. ‘hyphenation’) or from the use of multiple sources com- bined atom-detection schemes or multi-spectral correlation. Finally alternative strategies for future plasma spectrometric instrumentation will be suggested.SHORTCOMINGS OF CURRENT TECHNIQUES Lists of the most troublesome shortcomings that currently plague ICP-AES ICP-MS and GD techniques are compiled in Tables 1-3. Of course a person’s orientation and field of 61 4 Journal of Analytical Atomic Spectrometry September 1996 Vol. 11Table 1 Most significant current shortcomings of ICP-AES Modest detection limits (pg 1-') Drift and limited precision Matrix interferences Poor semiquantitative performance Limited for non-metals No isotopic information Sample preparation Micro-samples inconvenient Table 2 Most significant current shortcomings of ICP-MS Matrix and spectral interferences Drift and limited precision Difficulty with micro- or transient samples High cost complexity Need for sample preparation Table 3 Most significant shortcomings of glow discharges Modest detection limits Solution samples inconvenient Microsamples impractical Slow (5-30 min per sample) Complex spectrum (AES or MS) Limited for non-metals interest will dictate which entries will appear on lists such as these.However most would agree that in general even better detection capability improved precision freedom from inter- ferences better semiquantitative performance full elemental and isotropic coverage and freedom from sample preparation would be desirable in all atomic spectrometric techniques. Further most would appreciate the capability to examine micro- or solid samples directly and to obtain spatial resolution in solid specimens. Although one technique might at present meet certain of these needs better than others all could stand improvement.Also the very fact that several alternative methods for atomic analysis coexist and compete testifies convincingly that no single method has a decisive advantage over the others. Clearly a major portion of the fundamental and technical effort in atomic spectrometry in the near future is likely to be devoted to overcoming the limitations listed in Tables 1-3. However the degree to which such goals can be reached will depend upon present and future developments in instrumen- tation particularly of the type useful for atomic spectrometry. Some of these trends will be examined in a bit more detail in an effort to decide which might be of particular importance in atomic spectrometry.TRENDS IN INSTRUMENTATION AND IN ATOMIC SPECTROMETRY In Table 4 are listed a number of trends that can be identified in the development of chemical instrumentation. Of course additional trends could be named; here only those have been included that are especially applicable to atomic spectrometry. It is interesting to compare this list with the one compiled in Table 5 which applies particularly to trends in atomic spectro- Table 4 Trends in instrumentation Faster More specialized Smaller (nano) Spatial resolution More sensitive Microsampling More precise More intelligent Lower reagent consumption Greater dimensionality Integrated ('total analysis systems') Table 5 Present trends in atomic spectrometric instrumentation More sensitive More precise Faster (?) Fewer interferences Less expensive Smaller (?) More automated Fewer vendors (less competition) Increased speciation metric instrumentation.The disparity between these tables will form the basis of a discussion in a later section. Few would dispute that atomic spectrometers over the past few years have become considerably more sensitive and precise. Also especially in AMS both matrix and spectral interferences have been reduced in severity although a number of trouble- some effects still exist. Unfortunately interferences can still pose serious problems in ICP-AES. Interestingly there seems to have been little emphasis on making atomic spectrometers operate more rapidly. Most commonly integration times on the order of 10-60 s are employed although longer times are required when a GD source is used.In part this limited speed could be a result of the relatively long wash-out time of most nebulizer-spray chamber combinations. Similarly modern atomic spectrometers are not a great deal smaller than earlier systems. Although manufacturers have introduced tabletop systems for AMS and AES developments in miniaturization that are actively underway in other fields make one wonder whether additional substantial reductions in size are not possible. Largely because of technological advances instruments have however been made simpler in construction less expensive as a consequence and more user-friendly mainly because of a higher level of automation. This increased emphasis on economy and the realities of a limited market have forced a number of vendors out and have resulted in the acquisition of others.Interestingly despite a high degree of interest in and demand for speciation few commerical packages to perform such an analysis are yet available. It would be useful to evaluate each of the trends listed in Tables 4 and 5 to determine which trends are most likely to be important in atomic spectrometry in the future and to track each trend to its eventual conclusion. Unfortunately space precludes such a comprehensive approach. Instead the sensi- tivity issue will be considered first a trend which appears in both Tables 4 and 5 and that seems to form the focus of much recent work in AES and AM$. The issues of precision and instrumental speed will then be discussed briefly. DETECTION LIMITS IN ATOMIC SPECTROMETRY A fairly simple comparison of ICP emission and mass spectrometry signals reveals the factors that are responsible for governing detection capability.Assume for example that a 1 pg ml-l solution of a chosen element is aspirated into each instrument. Experience shows that a typical mass spectrometer will produce a signal level of roughly 106-107 counts s-I while the emission spectrometer will generate a photocurrent of roughly 10-6A. With a photomultiplier gain of lo6 this photocurrent corresponds to a photon detection rate of 6 x lo6 counts s-'. Interestingly the two techniques produce approximately the same signal level! Where they differ is in the background level. Background count rates expected in AMS seldom exceed 10 counts s-l whereas the background photocurrent in emission spectrometry is of the order of lo-* A which corresponds to a photon detection rate of 6 x lo4 counts s-'. Because the background noise is pro- portional to the square root of the background count rate the signal-to-background noise ratio (S/Nb) of the mass spectro- metric measurement will be lo6 while that for the emission Journal of Analytical Atomic Spectrometry September 1996 Vol.I1 61 5determination will be only lo4. This disparity provides ICP-MS with detection limits that are about two orders of magnitude lower than those of€€ered by ICP-AES. In particular for a given S/Nb (usually three) at the detection limit the mass spectrometer would be expected to yield a sub-ngl-' limit compared with the 0.1 pg1-l detection capability of the emission instrument.These values are roughly what is experienced. Overall then it is the background level rather than the signal magnitude that is responsible for the difference in detection capability of the two techniques. The corollary is similarly clear that MS detection limits can be improved mainly by raising the fraction of atoms in the sample that are eventually detected; in contrast the emission spectrometer could benefit by the same advances but also by lowering the spectral background. Achieving Lower Detection Limits in Plasma Source AES From the foregoing analysis it seems that the most direct route to improving detection limits in AES is to reduce the background level. Of course it is just this end that is sought in the use of on-axis viewing of an ICP.The 'throat' of the discharge is both cooler and less intense than the outer or toroidal region of the plasma. Furthermore end-on viewing enables a greater depth of the centre of the plasma to be viewed so localized instabilities can be averaged out. The result is a lower more stable background reading. Unfortunately with this reduction in background comes a concomitant increase in the severity of inter-element inter- ferences and the likelihood of complications induced by intact aerosol droplets or particles that persist into regions high in the discharge. An alternative means of reducing background intensites in plasma emission spectrometry is to operate the discharge at reduced pressure. Because the recombination continuum in any plasma results from a two-body process (the recombination of an ion and an electron) the frequency of the recombination events and the intensity of the continuum they produce should drop with the square of the ambient pressure.In contrast analyte number densities should drop only linearly with pressure so a gain in S/Nb should be achieved. Further reduced-pressure plasmas are ordinarily more diffuse and stable than those at atmospheric pressure so background fluctuations should be even smaller. Unfortunately when the pressure in a plasma is reduced its ability to volatilize and atomize particulate aerosols or polyatomic species is com- promised rendering the discharge more complicated to use and more susceptible to matrix interferences. It would seem more appropriate therefore to use a reduced- pressure discharge for atomic excitation (or ionization) but to use an auxiliary source to atomize the sample.This 'tandem- source' concept is one that has been discussed in detail earlier4 and does not require elaboration here. Suffice it to say that several alternative tandem sources are attractive. The first source of such a tandem pair could alternatively be one that employs rare-gas sputtering wall volatilization or an atmospheric- pressure plasma for sample atomization. The resulting atoms can then be fed directly (in the case of wall volatilization or rare-gas sputtering) or through a differentially pumped interface (in the case of an atmospheric-pressure atomization source) into a reduced-pressure source for excitation or ionization.Additional tandem-source combinations have been suggested ele~ewhere.~.~ Attainable Detection Limits in Plasma Source Mass Spectrometry As was discussed above improving detection limits in plasma source mass spectrometry is probably achievable only by increasing the fraction of ions that are ultimately detected; background count rates appear unlikely to be lowered signifi- cantly. Accordingly let us first follow the fate of atoms in a sample as they are converted into free atoms in the plasma ionized extracted into the mass-spectrometer interface trans- mitted through the spectrometer and finally detected. Following these steps will allow an assessment of where ion losses occur and which of those loss mechanisms is likely to be improved in the future.In general this discussion will be applicable to most mass spectrometers that are in current use (particularly those that employ a quadrupole mass filter) although specific details will pertain to a time-of-flight mass spectrometer (TOFMS) that has been developed in this laboratory.6-10 In an earlier evaluation," the losses in analyte-ion popu- lations that occur as a sample species moves from the initial solution to the detector in an atomic mass spectrometer were traced. In brief it was found that a 100-fold loss occurs in the aerosol-generation process because of the inefficiency of most nebulizer-spray chamber combinations. However virtually all of the resulting aerosol that enters the plasma and all of the sample vapour it produces ultimately is extracted into the first stage of the vacuum interface to the mass spectrometer.In contrast only about 1 % of that extracted beam passed through the skimmer largely because of geometric (solid angle) con- siderations. For a 1 mg 1-1 analyte-atom concentration in solution delivered at a flow rate of 1 ml min-l into a nebulizer the resulting flow of analyte ions through the skimmer therefore corresponds to roughly lolo analyte atoms s-'. For atoms of moderate ionization energy most will be charged. Yet only about one in lo4 of them is eventually detected in most quadrupole-based instruments. Of course recent advances in interface design have raised the efficiency of these processes somewhat but usually by only an order of magnitude or so. The overall consequence is that only between lo6 and lo7 analyte-ion counts s-l are registered at the dectector even though the initial analyte-atom flow into the nebulizer approxi- mates 1014 atoms s-'.The losses in analyte-atom flux corre- sponding to factors of between lo7 and lo8 can surely be improved. A more detailed analysis of these losses is possible with data recently acquired from the TOFMS instrument in this laboratory. In that instrument it can be assumed that the sample-introduction efficiency constrained mostly by losses in the aerosol-generation process is approximately 1 YO similar to that in most other ICP-MS instruments. Also the efficiency of transmission through the skimmer is unlikely to be better and can therefore be estimated to be 1%. This instrument employs an orthogonal-extraction geometry so transmission losses in both perpendicular sections of the ion beam must be considered.It is estimated that the transmission efficiency of the primary beam is about lo% and measurements have shown7 that the fraction of the remaining ions that are detected after transiting the TOFMS flight tube is of similar magnitude. In addition the current instrument still suffers somewhat from a duty factor which is less than unity; in particular only a little more than 10% of the ions in the primary beam are able to be extracted and ultimately detected because of the finite time it requires for a TOF mass spectrum to be recorded. These estimated losses are summarized in Table 6. Table 6 Losses in an ICP-TOFMS instrument Sample-introduction efficiency = lo-' Skimming efficiency = Ion-optic throughput (estimated) = 10- ' TOF transmission efficiency = lo-' TOF duty factor = lo-' Total losses accounted for = lo-' 61 6 Journal of Analytical Atomic Spectrometry September 1996 Vol.1 IIt is useful to compare the total accumulated losses in Table6 a factor of lo7 with detection limits that have so far been realized with the same instrument. Interestingly detection limits all fall near the level of 107-108 atoms for most sample- introduction schemes that have been explored with the ICP-TOFMS. These methods include the use of ten input ion pulses into the TOFMS instrument from a continuously aspirated sample solution,8 a flow-injection plug and electro- thermal volatilization into the ICP. These values are compiled in Table 7.Because detection limits are approximately at the level of lo7 atoms and because losses of about the same order of magnitude can be ascribed in total to instrumental components or sections virtually all losses in the instrument can be accounted for. It is therefore relatively straightforward to assess in which of these areas gains are likely. Improvements in Sample-utilization Efficiency Advances in sample-utilization efficiency should benefit not only plasma source mass spectrometry but also emission-based techniques. Several attractive possibilities exist including the use of in situ laser ablation,13 more efficient electrothermal vaporization a glass-frit14 or higher-efficiency ultrasonic nebulizer nebulizer starvation and introduction of the sample solution in the form of discrete isolated droplet^'^.'^ or dried monodisperse particle^.'^*'^ Liu and Horlick have shown that signal increases as high as 1000-fold are possible in ICP-AES through use of in situ laser ab1ati0n.I~ In this technique a solid sample is placed high in the ICP torch just below the plasma ‘fireball’.An ablating laser beam focused onto the surface of the sample then generates a cloud of atomic vapour immediately upstream of the discharge. As a consequence sample-transport efficiency into the plasma is virtually loo% yielding an extremely intense but very brief emission signal. Importantly because this brief signal pulse lasts less than 1 ms it is attractive only if coupled with a multichannel detection system such as a direct- reading emission spectrometer an emission spectrograph or a TOFMS instrument.With such instrumentation increases in signal levels up to a factor of lo3 should be possible. Although a number of high-efficiency approaches to nebulization have been introduced and evaluated it seems likely that their higher efficiency could derive as much from a low aerosol density as from any intrinsic properties of the nebulizer of spray-chamber design. Recent work from the research group of Olesiklg has shown that even a conventional glass-concentric nebulizer and a Scott-type spray chamber are capable of delivering sample-introduction efficiencies approaching 90% merely by restricting the sample-solution flow rate into the nebulizer. In part the increased efficiency might derive directly from the production of a finer aerosol which is known to occur under conditions of nebulizer ‘starvation’.However it could also be a result of a greatly reduced aerosol density and a consequent reduction in droplet- droplet collisions. In turn fewer droplet-droplet collisions will cause less coalescence and the resulting loss of large droplets. Table 7 Current limits of detection (LOD) in ICP-TOFMS Importantly this higher efficiency requires extremely low sample-solution flow rates approaching a few pl min-’. As a result the technique is particularly attractive when sample volumes are precious or when it is desired to couple the detection method with for example microbore liquid chroma- tography or chip-based sample-processing systems. These latter systems will be described in more detail later.Virtually 100% of a sample solution can be utilized if it is introduced into a plasma in the form of discrete or dried particle^.'^.'^ Even in the earliest studies in which flame emission spectrometry was employed,15 detection limits as low as 10’ atoms of sodium were obtained and precision levels as high as 0.01% RSD could be achieved by integrating the signal from multiple droplets. Achieving even better detection capability should be possible by using the same system or its dried-particle with an ICP and mass spectrometer. Of course this technique (as with in situ laser ablation) produces a transient sample pulse and will be best coupled with a multichannel emission spectrometer or a rapid-scanning mass spectrometer such as a TOF system.Higher Skimming Efficiency Although skimming efficiency is constrained largely by the geometry of the conventional ICP-MS interface improvements are possible if a low-density reduced-pressure ion source is located in the first vacuum stage of the mass spectrometer. Ion sources can be conceived that maintain most ions on axis and therefore should allow the ions to be more efficiently extracted into the lower-pressure zones of the interface. Of course such a source would not be particularly appropriate for atomizing a sample and would therefore probably be most useful if coupled with a preliminary atomization source. Such a tandem combination was described earlier. Improving Ion-optic Throughput Recent studies by Douglas2’ have shown that the transmission efficiency of an ion-optic train can be improved merely by forming a ‘brighter’ ion source and by reducing the ion density in the beam.In this context a ‘bright’ source implies that the ions must be introduced into the optical system in a very narrow cone and appearing to derive from a very small region in space. Such conditions could be met by a suitably designed reduced-pressure source such as the one just described. Furthermore reductions in ion-beam density would be possible through use of sample-introduction systems that minimize the sample-ion flux but which utilize the available sample ions more efficiently. A ‘starved’ nebulizer system would be one system appropriate for this task. If these sample ions are then carried in a relatively low-density plasma-ion beam trans- mission efficiency could approach unity in the primary ion beam in our TOFMS system.Similarly the transmission of our TOFMS instrument itself should be able to be improved by roughly 10-fold simply by reducing the spread of the ion beam as it travels down the flight tube.7 Indeed most workers in the field feel that a Sample introduction mode Nebulizer multi-element* Nebulizer 10 pulses ETV multi-element Sample volume 170 pl 25 nl 10 ml LODt (atoms) 8 x lo’ ( 5 x 107) 2 x 107 3 x 109 (5 x 106) LODt/mol I-’ (8 x 10-14) 6 x lo-’’ 8 x 3 x 10-9 (2 x 10-13) * Signal-integration time of 10 s taken in flow-injection mode. t Values in parentheses are intrinsic detection limits taken from ref. 12. Journal of Analytical Atomic Spectrometry September 1996 Vol.11 61 7TOFMS instrument should be capable of transmitting and detecting virtually all the ions introduced into it. Also plans are already underway in this laboratory to improve the duty factor of our system. A trivial method which will result at least in a doubling of the duty factor is to employ a shorter flight tube. At present the resolving power offered by the instrument is in excess of what is required for routine AMS. Shortening the flight tube would therefore not result in an unacceptable loss in resolution but will offer both increased flight-tube transmission and a shortened time for acquiring a mass spectrum. Because more mass spectra can be acquired each second the duty factor will increase proportionally. Ultimate Levels of Detection in Plasma Source Mass Spectrometry With all these possibilities for improvement it seems reasonable to expect gains in detection efficiency of analyte ions in the relatively near future of a factor between lo4 and lo5.The resulting detection limits should then approach 100-1000 atoms in the sample to be analysed. It is reasonable to question whether such extraordinary detection capabilities are necessary or even desirable in the real world. After all the likelihood of sample contamination increases as detection limits drop; furthermore at some level virtually every element can be found in every sample solution. However it must be recalled that these detection limits have been cited in terms of the number of detectable atoms (or moles). Therefore they could be exploited either to measure vanishingly low elemental concentrations in a sample of moderate volume (or size) or to determine moderate concen- trations in an extremely tiny sample.The latter option might prove to be the more attractive. The ability to use extremely small sample volumes opens the way to a number of novel and attractive sample-processing alternatives. Many of these options including on-chip sample processing microchromo- tography and others all offer increased speed of analysis smaller equipment closed flow channels to prevent con- tamination and the conservation of chemical reagents a matter that is likely to be of increasing concern in the next century. Of course reduced sample requirements also open the field to the analysis of a greater range of sample types including those from the clinical environment those resulting from biotechnology efforts and those in the nanotechnology arena.IMPROVED PRECISION I N ATOMIC SPECTROMETRY The dominant source of imprecision in plasma source emission or mass spectrometry ordinarily arises from the plasma itself and from the sample-introduction equipment. Peristaltic-pump pulsations temperature-induced drift of the nebulizer and spray chamber plasma tail-flame waver the presence of intact aerosol droplets or solute particles in the discharge and in the case of MS measurements inhomogeneities in the plasma volume that is sampled all constrain precision levels to between 1 and 5% RSD. However because all these sources of fluctuation affect signals from different analyte species in much the same way a considerable improvement in precision can be obtained by a ratioing technique such as internal standardization.Clearly for this ratioing or normalization to work as well as possible the spectroscopic physical and chemical features of the analyte element and its internal standard must be matched as closely as possible. When MS is employed this match can be virtually perfect if an isotope of the analyte element can be employed as the internal standard. This method embodied in isotope dilution techniques can result in tremendous gains in precision. Unfortunately these gains are possible only if the analyte species and its internal standard (or isotope) are measured at the same time. With a sequentially scanned system the tem- poral offset that exists between the measurement of the analyte and internal-standard signals can render the ratioing process imperfect so compensation for relatively rapid fluctuations is impossible.To be sure peak hopping in plasma source mass spectrometry can be extremely fast so precision levels can be improved considerably. However the number of such peak hops that can be achieved in a given measurement interval constrains the number of analyte-internal standard pairs that can be measured at once. The problem is particularly acute when a transient sample is introduced such as that which would be generated by several of the sample-introduction methods just suggested. The conclusion for the future must be that simultaneous or virtually simultaneous instruments will become most attractive.Again such systems include two-dimensional detector arrays for emission spectrometry and any of several alternatives for MS. These alternatives include TOFMS an ion trap a Fourier- transform mass spectrometer and a sector-field system equipped with a multichannel detector array. Unfortunately none of these MS alternatives is yet commercially available. Among them the FTMS seems least attractive in part because of its cost and in part because of the relatively low ion densities that it can contain. This latter complication which the FTMS shares with the ion trap might restrict dynamic range to unaccept- able levels. PROBABLE TRENDS IN ATOMIC SPECTROMERIC INSTRUMENTATION A comparison of Tables 4 and 5 reveals that a number of trends that exists in the development of chemical instrumentation overall are not yet being actively pursued in the field of atomic spectrometry.These missing areas are highlighted in Table 8. Several of the trends listed in Table 8 require no elaboration. However it seems clear that atomic spectrometric instruments like most others will become targeted towards increasingly specialized markets in the future. Because of this trend a number of instrumental requirements will be relaxed. It is of course difficult to design an instrument that is capable of meeting the needs of all users. If a particular class of users strives for a certain group of elements (such as in the metals industry) expects a constrained range of concentrations (as in process-control applications) or must deal with only a single sample form (i.e.solutions) lower-cost special-purpose instru- mentation can be developed. However for this approach to be attractive to vendors the market for a particular application must be sufficient. Accompanying a more specialized or targeted market will come a higher level of integration of the entire analytical operation. A component of this integration will be coupling the output of atomic spectrometric instruments with data provided by complementary analytical methods so the output of an analytical laboratory will be more akin to the solution of a specific problem rather than a mere list of concentrations. Similarly it seems likely that the marriage between sample processing and the atomic spectrometric instrument is likely to be a closer one with particular sample-processing approaches being used for specific customers markets or sample types.Table 8 Probable trends in atomic spectrometric instrumentation More specialized Greater dimensionality Spatial resolution Microsampling Integrated (‘total analysis systems’) Lower reagent consumption 61 8 Journal of Analytical Atomic Spectrometry September I996 Vol. 11The need for spatial resolution and microsampling will similarly be restricted to particular markets or users that are likely to grow in importance in the future. Also the cost of chemical-waste disposal will undoubtedly increase and will encourage conservation of reagents. Integrated-analysis micro- sampling systems will therefore probably grow rapidly in importance and might be implemented by means of the on-chip devices mentioned earlier and discussed in more detail below.A particularly interesting aspect of instrumentation develop- ment outside the field of atomic spectrometry is a trend towards higher dimensionality. This trend represented most obviously by the ‘hyphenation’ that is associated with combi- nations such as GC-MS is leading to measurements that are extraordinarily information-rich. It would seem that multi- dimensionality might be useful in atomic spectrometry also and could provide such advantages as added selectivity lower levels of interference improved speciation sampling con- venience applicability to alternative sample types better pre- cision and detection limits and added confidence in sample identification.Overall multidimensionality should provide more information capability and flexibility. Multidimensional Atomic Spectrometry The components that are common to all atomic spectrometric instruments are portrayed in Fig. 2. Interestingly any of these components can be made multidimensional by employing alternative embodiments of it in either a parallel or serial fashion. For example the sample-processor module could consist alternatively of an aerosol-introduction system an FI device a chromatograph a laser-ablation accessory or others. Moreover in highly flexible instruments several of these modules could be employed in parallel to increase the flexibility and capability of the system. However several of these alternative sample-processing modules produce transient peaks many of which have a duration of less than 1 ms.For the rest of the atomic spectro- metric instrument to accommodate such sample-processing units it must respond rapidly and ideally simultaneously to all elemental concentrations in the sample. In the absence of this capability precision and detection limits will be sacrificed in a multi-element mode. A trade-off will then have to be made between broad elemental coverage or low detection limits and high precision. As was mentioned before the need for this type of flexibility highlights the importance of truly multichannel emission or mass spectrometers. The second module in Fig. 2 the source can also be multidimensional. For example it could alternatively be an ICP a GD an MIP a high-voltage spark or another source.Indeed there have already been commercial offerings in which an ICP or GD could be coupled to the interface of a mass spectrometer. However the tandem-source approach that was already mentioned is another form of multidimensional source that is particularly attractive for the next generation of atomic spectrometric instruments. If properly configured such tandem combinations could yield truly multidimensional information. Just as the combination of GC and MS renders sample identification much simpler by separating and identifying components along two orthogonal (ie. independent) axes Fig.2 Block diagram of an atomic spectrometric instrument. In future-generation instruments each of the blocks would be modular with several alternative devices or schemes for each block being able to operate in parallel or in series.The resulting higher-order instrument should provide far more capability and flexibility than is now available chromatrography and mass spectrometry a tandem source can improve instrument performance. An example of this capability can be found in recent results obtained with our TOFMS system in which the source con- sisted of a tandem combination of an electrothermal vaporizer and an ICP. In this arrangement sample solutions are loaded in the conventional way into a graphite furnace and the solvent driven off from the sample deposit. The sample is then ashed briefly and the temperature of the furnace subsequently ramped to a high volatilization temperature. As has long been experi- enced in AAS it was found that different elements volatilize at distinct times on the temperature ramp.During this atomization process TOF mass spectra were acquired in rapid succession (at a spectral-generation rate of approximately 20 kHz). The result was a two-dimensional map in which the vertical axis consisted of atomization time (related to atomization temperature) and the horizontal axis displayed the mass spectrum. In this two-dimensional map relatively volatile elements such as cadmium appear earlier than those that are more refractory. As a result it became possible to separate otherwise isobaric interferences such as the 112 and 114 isotopes of cadmium and tin. Interestingly to resolve these isotopes mass spectrometrically would require a resolving power of 93 000 for the 112 isotopes and 190 000 for the 114 isotopes.Yet the separation was achieved by this two-dimen- sional technique with a mass spectrometer whose nominal resolving power was less than 2000. Even greater capability is realized by separation on the basis of volatility differences of the 113 isotopes of indium and cadmium. The mass-spectral resolving power required to separate these two species exceeds 300 000. Perhaps a more real-world application of this capability is the separation of ArO’ and Fe’ both of which appear at m/z 56. In most AMS determinations this overlap constitutes one of the most troublesome interferences. However it can be avoided entirely by driving the solvent completely from the sample before the iron is volatilized. Obviously a great many other interferences can be similarly avoided.Other benefits can also be derived from the use of a tandem source especially when it is combined with MS detection. For example either of the two sources in the tandem pair can be modular. Probably the most attractive scheme is to employ the same ionization source (perhaps in a reduced-pressure environment) but to couple to it a group of first sources each of which is tailored for a particular sample type. There could be one first source for the atomization of aerosol-based samples another for solid samples a third for providing spatial resolution in solid samples another for FI applications one for a chromatographic interface a device for handling micro- samples etc. Further the first source in the tandem pair could be modulated so it produces on alternative half cycles fully atomized sample material and merely fragmented sample vapour both of which would pass in alternating fashion into the second (ionization) source.Such a device would yield on one half cycle an atomic mass spectrum and on the other a fragmentation mass spectrum. If these spectra could be generated rapidly enough through use of a sufficiently fast mass analyser such as in TOFMS more unambiguous infor- mation about an entering sample would be available. Such a device would aid greatly for example the identification of eluting constituents from a liquid chromatograph. Multidimensionality is already fairly common in the atom- detection module of an atomic spectrometer. It is routine for example to employ a slew-scan monochromator as an ‘n + 1’ channel in a direct-reading emission system.Also at least one manufacturer has already announced an instrument that couples emission and mass spectrometric detection. An additional scheme that has not been pursued actively however is the combination of MS and fluorimetric detection. Journal of Analytical Atomic Spectrometry September 1996 Vol. 11 61 9This last combination could take several forms but its main advantage would be the ability to provide an extremely high detection efficiency for every analyte atom or ion. Conventional MS detectors are inherently destructive so there is only one chance to detect each ion. As a result it is impossible to distinguish between a single ion and an extraneous detector event.Although such events are relatively infrequent (1-10 per second in a typical instrument) they preclude the detection of less than ten ions or so. In contrast fluorescence is a non- destructive process and each atomic ion is capable of pro- ducing hundreds of millions of detector events per second. The result is truly single-atom detection. One possible combination of fluorimetric detection and MS would be similar in design to an earlier commerical instrument. However in the new arrangement the atoms or ions to be detected would be extracted through a vacuum interface similar to that employed in a modern atomic mass spectrometer. Each extracted ion would then pass through a region irradiated by a high-intensity laser beam. Although some background counts from scattered laser radiation would no doubt exist the passage of an atomic species would be signaled by a brief burst of additional photons.This ‘photon-burst’ mode of detection2’ provides not only the ability to detect single atoms but also a much higher degree of selectivity than could MS by itself. Because it is a truly multidimensional approach MS resolution could be coupled with optical resolution to achieve a much higher degree of selectivity than would otherwise be available. It has been estimated that resolving powers as high as 1014 could be achieved in this fashion.21 Of course such a scheme would compromise multi-element detection unless an array of simultaneous laser beams could be employed. Indeed such capabilities would not seem too far beyond the horizon in view of recent advances that have been made in the development of blue and frequency-doubled diode lasers.Lastly the signal-processing block in the diagram of Fig. 2 might also be multidimensional.2 Likely multidimensional schemes include multi-line and regression-based calibration such as has already been used by a number of commercial manufacturers. However new means of displaying and pro- cessing atomic spectrometric information will no doubt be devised. Similarly element ‘profiles’ of an incoming sample will no doubt be generated; coupling such information with data from other methods will probably be critical in developing special-purpose laboratories that are intended to provide answers to analytical questions rather than simple uninterpreted data.A GLIMPSE OF THE POSSIBLE FUTURE The preceding sections cover relatively straightforward extra- polations of current trends in atomic spectrometry. However is seems appropriate also to cast a bit farther afield to see what the future might bring. For some time physicists have employed crossed laser beams as optical ‘traps’ and optical ‘tweezers’ to manipulate particles in sizes ranging from bacteria tomm spheres. The same type of technology might be profitably applied to analytical atomic spectrometry. For example it is possible to dispense a single microdroplet of sample solution having a volume of less than 1 n1.22 Such a microvolume might be directed into an insoluble liquid with a refractive index different from that of the micro- volume itself. In this medium the droplet could be manipulated by use of laser tweezers and introduced into a selected sample- processing device.Alternatively such a droplet might initially contain not the sample solution but rather a chelating reagent that serves to preconcentrate analyte species from the sur- rounding volume. Similarly a single microscopic ion-exchange particle could be introduced into a larger volume of sample solution and the preconcentrated sample so generated used in a subsequent sample-processing device. To handle such microscopic samples it would be attractive to employ some of the on-chip t e ~ h n o l o g y ~ ~ - ~ ~ that has been used recently in FI analysis in capillary electrophoresis and in sample processing itself. In such devices microchannels are etched into a suitable substrate most commonly silicon or quartz.Electro-osmosis or electrophoresis is then employed to pump samples reagents or diluents about the chip. Injection of a sample plug is possible for example by crossing a sample- containing channel with one filled with a carrier. Because the electrokinetic pump can be switched merely by the application and removal of high voltages a sample plug can be positioned in a desired location (at the junction between the two channels) and carried off in a different direction (if desired) by the carrier stream. In a similar fashion reagents can be added to the sample solution it could be diluted internal standards or standard-additions aliquots could be injected and serial dilution could be implemented. The sample so processed could then be introduced into a multidimensional atomic spectrometer. Lastly is seems likely that future generations of atomic spectrometric instrumentation will become more and more intelligent2 Efforts have been underway for some time to clarify the origins of interference effects in sources such as the ICP.With this information and with knowledge of how an interferent affects the spatial distribution of analyte in a discharge and the characteristics of the discharge itself it should be possible to design an instrument that is truly self- diagnostic one that monitors its own output by means of two- dimensional images spectral information and other sources of data and to feed back control signals to its various inputs. This feedback would be intended both to overcome inter- ferences and to achieve the highest possible signal-to-noise ratios the first time a sample is introduced.Accessible inputs to such an intelligent instrument would include the sample- solution concentration reagents that could be added to it gas flow rates source power alternative methods for sample processing spectrometer resolution and dwell time and detector characteristics. Information available to achieve the necessary feedback would include not only spatial and spectral infor- mation but also details about the sample and its processor that are not now being used. Obviously with these many alternatives available the field of atomic spectrometry holds great promise for the future. The coming of the new millennium should bring even greater challenges and opportunities for its users and students.This work was supported in part by the National Science Foundation through grant CHE 90-20631 and by the National Institute of Health through grant lROl GM 53560. REFERENCES Naisbitt J. and Aburdene P. Megatrends 2000 William Morrow New York 1990. Hieftje G. M. Spectrochim. Acta (Special Supplement) 1989 44 113. Hieftje G. M. Fresenius’ J. Anal. Chem. 1990 337 528. Borer M. W. and Hieftje G. M. Spectrochim. Acta Rev. 1991 14 463. Borer M. W. and Hieftje G. M. J. Anal. At. Spectrom. 1993 8 339. Myers D. P. and Hieftje G. M. Microchem. J. 1993 48 259. Myers D. P. Li G. Yang P. and Hieftje G. M. J. Am. SOC. Mass. Spectrom. 1994 5 1008. Myers D. P. Li G. Mahoney P. P. and Hieftje G. M. J. Am. SOC. Mass. Spectrom. 1995 6 400. Myers D. P. Li G. Mahoney P. P. and Hieftje G. M. J. Am. SOC. Mass. Spectrom. 1995 6 411. 620 Journal of Analytical Atomic Spectrometry September 1996 Vol. 1 110 11 12 13 14 15 16 17 18 19 20 21 Myers D. P. Mahoney P. P. Li G. and Hieftje G. M. J. Am. SOC. Mass. Spectrom. 1995 6 920. Hieftje G. M. J. Anal. At. Spectrom. 1992 7 783. Falk H. Spectrochim. Acta Part B 1994 49 1373. Liu X. R. and Horlick G. Spectrochim. Acta Part B 1995 50 537. Layman L. R. and Lichte F. E. Anal. Chem. 1982 54 638. Hieftje G. M. and Malmstadt H. V. Anal. Chem. 1969 41 1735. Bastiaans G. J. and Hieftje G. M. Anal. Chem. 1973 45 1994. French J. B. Etkin B. and Jong R. Anal. Chem. 1994 66 685. Olesik J. W. and Hobbs S. E. Anal. Chem. 1994 66 3371. Olesik J. W. Ohio State University personal communication 1996. Douglas D. J. presented at the 1995 Chemical Congress of Pacific Basin Societies Honolulu HI USA December 17-22 1995 paper ANYL 226. Keller R. A. Los Alamos National Laboratory personal communication 1994. 22 Shabushnig J. G. and Hieftje G. M. Anal. Chim. Acta 1981 126 167. 23 Ramsey J. M. presented at the 1995 Chemical Congress of Pacific Basin Societies Honolulu HI USA December 17-22 1995 paper ANYL 234. 24 Manz A. Verpoorte E. Busch M. Malone M. Erbacher C. Spielmann A. and Widmer H. M. presented at the 1995 Chemical Congress of Pacijic Basin Societies Honolulu HI USA December 17-22 1995 paper ANYL 38. 25 Harrison D. J. Chiem N. Tang T. and Fluri K. presented at the 1995 Chemical Congress of Pacifc Basin Societies Honolulu HI USA December 17-22 1995 paper ANYL 40. Paper 6/003830 Received January 17 1996 Accepted March 28 1996 Journal of Analytical Atomic Spectrometry September 1996 Vol. 11 621

ISSN:0267-9477    

DOI:10.1039/JA9961100613

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Fundamental Description of Spectrochemical Inductively Coupled Plasmas* Plenary Lecture I Journal of I Analytical Spectrometry 1 Atomic I 1 D. C. SCHRAM J. A. M. VAN DER MULLEN J. M. DE REGT D. A. BENOY F. H. A. G. FEY F . DE GROOTTE AND J. JONKERS Eindhoven University of Technology Department of Physics P.O. Box 513 5600 MB Eindhoven The Netherlands For the determination of the optimum conditions for spectrochemical analysis with plasmas a simple and yet accurate description of the plasma state is essential. In this paper which should be regarded as a review of earlier and more recent work non-equilibrium modelling of slowly flowing atmospheric ICPs and experimental results are described. The results of modelling are in fair agreement with experimental values from the literature in particular for lower excitation frequencies.However for high frequencies the model plasmas tend to remain too close to the wall. It is concluded that even in argon plasmas dissociative recombination of molecular ions gives an additional recombination route close to the wall where the neutral ground state density is high and the temperature low. Results of experimental analysis by active and passive spectrometry are given. In addition the possibilities inherent in time-dependent studies such as in power interruption experiments are indicated. The processes of droplet evaporation and analyte excitation and ionization are also summarized. The virtues of the ICP for spectrochemical analysis are briefly discussed. Keywords Inductively coupled plasma; non-equilibrium; spectroscopy; laser scattering; laser absorption In spectrochemistry plasmas are used to atomize ionize and excite the trace atoms to be analysed. Both the specific spectral response of the various elements and the characteristic mass of the atomic ions are used to identify and quantify the trace elements.',2 Both ways of identification have their own merits3 and thus a consideration of the conditions for effective exci- tation and of ionization as a function of plasma parameters is in order.Plasmas are non-equilibrium systems by definition as the plasma temperature is higher than the ambient tempera- ture and thus transport and radiation will always render the plasma out of eq~ilibrium.~ The measure by which the plasma is out of equilibrium will depend on pressure and on the power density needed to sustain the plasma at the operating pressure. There is a general tendency that at higher pressure higher electron density and associated with that at higher power density the plasma will be more close to eq~ilibrium.~*' This will facilitate the description of excitation and ionization of atmospheric plasmas.However operation at atmospheric pressure is of course not a necessary requirement. Low pressure plasmas have also been considered6 and they may have their virtues in terms of easy operation and relatively low consump- tion of gas and power. Effectiveness of excitation and charge transfer stability of operation predictability of conditions and minimum matrix effects are the criteria on which the choice of plasma has to be made. In order to do so a simple and yet * Presented at the 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-1 3 1996.complete description of the plasma is helpful and this will be the primary concern of this paper. We will therefore review the advances in the understanding of atmospheric plasmas and in particular of ICPs as these plasmas are used most frequently for spectrochemical analysis. It is evident that for mass spectrometric analysis the pro- duction of analyte ions is of primary importance. However also for analyte excitation ions are important as the process of charge transfer from the primary carrier gas ion to the analyte atom is the dominant cause of excitation.' Thus the total number of primary ions produced in the active part of the discharge determine the excitation power of the ICP.Hence the ion density (and electron density) is the most important plasma parameter. Bearing this in mind we will attempt to give a simple description which still takes the non- equilibrium status into consideration. The route to adopt is to characterize the plasma primarily by electron density;?' rather than by electron or excitation temperature. The reasons for this approach are three-fold firstly the electron density varies over at least one order of magnitude whereas the electron temperature varies by only a factor of 1.5 in the same range. Secondly the electron density can be measured with sufficient precision by simple methods such as HP line broadening and the absolute line intensity and also more accurately by elaborate means such as Thomson scattering.l0Y1' Thirdly as stated above the primary ion density which is equal to the electron density is the controlling factor for charge transfer and thus for analyte ion and analyte excitation production.The electron density also determines to a large extent the continuum radiati~n.'~?'~ This source of radiation can be considered as the primary cause for the background which in turn determines the achievable signal-to-background ratio. Of course this reasoning is only approximate as primary plasma production takes place upstream from the analysis process for both the spectral response and ion mass analysis. PLASMA EQUILIBRIUM IN ATMOSPHERIC ICPs IN ARGON The plasma in the ICP is created by induction of an rf current in the plasma.A few windings around the tube carry the primary current with frequencies ranging from several to 100 MHz. At higher electron densities and ionization degrees the conductivity of the plasma is determined by Coulombic collisions between electrons and ions. At lower electron densi- ties and thus lower ionization degrees the collisions between electrons and neutral atoms contribute to the friction and thus the plasma conductivity decrease^.'^,'^ The Coulombic conduc- tivity is proportional to T,3/2 (T = electron temperature) and depends only logarithmically on the electron density n and hence in this regime the conductivity is not dependent on non- equilibrium conditions nor operating pressure. Typical values Journal of Analytical Atomic Spectrometry September 1996 VoZ.11 (623-632) 623are 2 x lo3 R m-l for the highest T values in the ICP.14315 On the other hand for lower n values the conductivity is substan- the ground state deviation’ and can therefore be described by a single non-equilibrium parameter. tially smaller and varies linearly with the ionization ratio n,/n where n is the neutral atom density. It has been found16*17 that reworking the T dependence into an n dependence by using the LTE relationship at 1 bar results in the following approximate dependence with 0.1 < i < 10 and 4 is the electron density in units of The skin depth (6,) for a circular current loop in the plasma (radius Rpl) induced from a coil outside the torch depends on frequency ( ,uo is vacuum permeability) according to a=2 x 102ip.8 (1) 1020/m - 3.Note that here the skin depth of a circular current sheet is taken; this skin depth is smaller than that usually taken; uiz. that for a penetration of the field in a semi-infinite plane conducting sheet. The value of 6 and the location of the annular current carrying the plasma depend on the frequency at higher frequen- cies the plasma is smaller in width and lies closer to the wall than at lower frequencies (dependent on power and operating pressure). For the higher frequency range (f > 1 MHz) the skin depth is smaller than the tube radius which is typically gmm and thus a hollow annular plasma is created at the location of the coil. The hollowness of the plasma is more pronounced at higher frequencies.Hence three regions can be distinguished ( i ) at the wall a tangentially directed protecting flow of gas; ( i i ) halfway between the wall and the tube a hollow active plasma where the induced rf current is dissipated; and ( i i i ) in the centre of the tube a low temperature recombining passive plasma through which the analyte flow passes. To a first approximation the primary ionization and excitation of the plasma can be considered to take place in the carrier gas only and to describe the non-equilibrium ionization we can discuss pure argon plasmas. Note that the relative isolation of the active plasma and the central passive plasma which carries the analyte is particularly evident for atmospheric plasmas. The diffusion coefficient D and the related diffusion time z for neutral particles in a weakly ionized plasma with tempera- tures of a few thousand degrees are typically (A is mass number of neutral particle and R is radial gradient length) D,%-W 10-2 m2 s - l .7,X-N R%0-3s (3) 0.1 JA,- Dn The diffusion times z are of the order of s and thus are longer than or comparable to the drift time over a distance of 1 cm between the active plasma and the analysis position for typical drift velocities of 10 m s-l. Only light gases such as hydrogen can diffuse radially into the plasma within a drift length of 1 cm. (Non)-equilibrium State of Atmospheric Plasmas in Pure Argon Although atmospheric atomic plasmas are close to LTE the deviations from LTE need to be considered for a correct interpretation of measured excited state densities and plasma parameters such as the electron temperature and density.Two deviations are important. ( i ) The electron temperature T is different from the heavy particle (ion and neutral) temperature Th and (ii) the ground state density nl deviates from the LTE density i.e. according to Saha.4,5,17 Also at lower electron densities the values of the lower excited state densities differ from those that would be found in Saha equilibrium with the continuum in particular in the active part of the plasma. These latter deviations in the excited state distribution are related to In this situation we need at least four parameters to describe the plasma state; in practice it is common to use the parameter set pressure p electron temperature T heavy particle tem- perature Th and electron density n,.This is in contrast to the LTE situation where only two parameters are needed uiz. the temperature T= T = l& and pressure p or alternatively elec- tron density n and pressure. The first possibility T is used most frequently whereas it is preferable to use the second possibility n . 5 7 7 9 8 This can be seen immediately in Fig. 1 in which among others the equilibrium relationship between n and T is given for atmospheric argon plasmas. It can be (observed that a variation in n from to 10” m-3 corre- isponds to a variation of only a factor of 1.4 (from 5500 to ‘7500K) in T,. As will be shown below the precision of imeasurement of both T and n is typically 10% or higher and thus it can be concluded that n is the preferred thermodynamic variable in LTE.This becomes even more important under lion-equilibrium conditions where small deviations from either thermal or Saha equilibrium will lead to significantly different 12 values for a specified electron temperature whereas con- versely the variations in T at a specified n remain limited and of the same order as the precision with which T can be ~ n e a s u r e d . ~ ~ . ~ ~ To illustrate this point further actual measure- ments of n and T by Thomson scattering for a 100 MHz 1CPl9 are shown in Fig. 1. The measurements relate to several radial points from the periphery where the density is low through the hot annular zone where the density is maximum to1 the low density centre. Also error bars are indicated; the precision is just sufficiently good to conclude that the plasma is recombining at an observation height (h) of 7 mm.It is therefore preferable to describe the plasma by pressure electron density and two non-equilibrium parameters. One possible choice for these two non-equilibrium parameters is 1 - l&/T for the deviation from thermal equilibrium and a parameter 6bl to describe the deviation from ionization equilibrium i.e. the deviation of the neutral ground state density nl from the Saha value nlSaha 6 0 = 1 - T,/T,; 6bl = nl/nlSaha - 1 (4) in which the Saha density of the neutral ground state nlSaha is equal to (k is Boltzmann constant) ’ $1 lo2’ 4 C” 1O2O -I 10-23 - 5000 6000 7000 8000 9000 10000 TeK Fig. 1 Relationship between n and T for an argon plasma at 1 bar for LTE and partial LTE conditions (pLTE).Also shown is the T dependence of the total ionization rate coefficient K1. The closed squares and dashed curve represent data measured by Thomson scattering at 7mm above the load coil by de Regt.” Conditions 100 MHz ICP 1.2 kW power 18 mm diameter argon flowrates 12 0.3 and 0.6 standard litre min-’. (See under Experimental Results) 624 Journal of Analytical Atomic Spectrometry September 1996 Vol. 11Here gi and ni are the statistical weight and the density of the ion ground state(s) me is the electron mass and Elion is the ionization energy of the neutral ground state. A second possibil- ity probably more appropriate when bl >> 1 and thus 6bl = bl - 1 - b is to use & and bl T,,/T as non-equilibrium parameters in addition to the main parameters p and n,.The primary advantage of such a description is that most transport properties of the plasma are independent of the deviations from equilibrium as long as they are expressed in terms of n at constant pressure. Only in the electron pro- duction terms in the electron mass and energy balances does the deviation parameter b or b,T,/T appear. The net pro- duction term S of electrons and ions is equal to the product of the neutral ground state density n the electron density n and the total excitation and ionization rate coefficient (6) The total ionization rate Kl(T,) is also shown in Fig. 1 and it allows the first conclusion to be drawn. At atmospheric press- ure and heavy particle temperatures of SOOOK the neutral ground state density is around 1024m-3.For the plasma to exist electron production in the active region needs to compen- sate for the electron loss. The electron loss time by convection only is of the order of taking 1 cm for the drift length and a drift velocity of 10 m s-'. Thus the electron production rate Kin needs to be around lo3 s-l and K1 must be larger than m3 s-I. Consequently T must be around 10000 K in the active region which implies an n value of a few times 1021 m-3 in an ionizing plasma. For further details the reader is referred to a recent paper," which treats the higher n range; here it suffices to explore the n dependences of the various transport properties for the lower n range which is valid for ICP plasmas. Before doing so we will first summarize the structure of the transport equations which are used in the two-dimensional modelling of the p l a ~ m a .~ ' - ~ ~ U T ) S = n,(nl - nlSaha)K1(T,) Transport Equations and Two-dimensional Modelling The basis of numerical modelling is the set of conservation equations for mass momentum and energy for the electrons and for the heavy particles complemented by the Maxwell equations for the description of the electromagnetic fields and current. In this description we will concentrate on the situation for the ICP a slowly flowing stationary plasma with electron densities between lo2' and lo2' m-3 and corresponding ioniz- ation degrees between and In the presentation here we will omit various small contributions to the heavy particle balances such as the viscosity contributions (which can always be neglected in the electron momentum balance).Moreover the a/& terms are zero and the mass contribution of ions (and electrons) to the fluid mass is very small compared with the mass in the neutral atom flow. The following set of equations then follow formulated here in the intrinsic f ~ r m ~ . ~ ~ h-mass V nhu = 0 h-mom. nhmh(U v ) U -t v (Ph -t p,) = j"xB- h-energy %nhu V kT = Qeh - V qh e-mass - V - DambV n + V n,u = S ( 7 ) (8) (9) (10) (11) e-mom. j" = aE"; j(O) = 0 ( 12) e-energy aE2=S,(E1+ +~kT,)+Qrad-V.KeVTe+Qeh The equations (7) to (9) describe the heavy particle dynamics with density nh pressure Ph fluid velocity u and heavy particle heat flow qh. This subsystem is weakly coupled to the electron equations (10) to (12) by terms containing p the electron pressure and Qeh the heat transfer of electrons to heavy particles.The Lorentz force j"xB" is the vector products of the rf current density j" and the rf magnetic field strength B". In the electron equations Damb is the ambipolar diffusion coefficient El +- the ionization energy Qrad the radiation losses and K the electron heat conductivity. In this description the possible dc convective currents j(O) are neglected. Although this is commonly done this may not be fully justified and it would be interesting to investigate this more closely. The rf currents and the rf fields must follow from the Maxwell equations with appropriate boundary conditions in which the geometry of the coils and other components are represented. Benoy and co-workers21*22 have used a two- dimensional vector potential equation and have taken the geometry of the coil windings into account (13) (14) in which A"(r t ) is the rf vector potential and j-(r t) reprpsents the current density in plasma and coil windings.In Fig. 2 the structure of these equations is sketched:17 as can be seen there are three weakly coupled sub-systems one for the mass flow one for the non-equilibrium electron pro- duction by ionization and one for the e.m. fields and currents. It should be noted also that the above-given formulation of the conservation laws is in the intrinsic form whereas in the l i t e r a t ~ r e ~ ~ ~ ~ ' ? ~ ~ the extrinsic form is commonly used. The intrinsic form can be obtained from the extrinsic form by subtracting the mass balance from the momentum balance thereby subtracting the drift contribution from the extrinsic form.In a similar way the mass and momentum contributions are subtracted (after proper normalization) from the extrinsic energy balance to obtain the intrinsic form. Before we give an approximate representation we will give first some results of numerical modelling based on the full transport equations. We * Full modelling (p Te ne Th) I 1 1 r C I I j x 8 Mass - h NavierStokers I u Ohm Mass- h I n Navier Stokers Heat and mass flow J" from I q T $ J to active passive region region Maxwell E B Active region Passive region Outer flow Load coil Intermediate flow,\ h Central channel Active region Fig. 2 Structure of the model equations.16 The left-hand side indicates the three sub-systems needed to model the active region; the right- hand side gives the equations needed for the passive region.In the sketch of the ICP the active and passive regions are indicated Journal of Analytical Atomic Spectrometry September 1996 Vol. 11 625will follow here the work of Benoy and co-workers,21*22 but mention also the earlier contributions of Mostaghimi et ~ 1 . ~ ~ In Fig. 3 the model results obtained by Benoy and co-workers for a 3 MHz ICP (radius R = 25 mm) are given and are compared with numerical values from another LTE model.23 The comparison is given here in terms of T the axial flow velocity and the dissipated power density. From the compari- son it can be concluded that the non-equilibrium model of Benoy and co-workers is satisfactory. The only major difference between the two models (and as is observed later also with the experimental results) is found at the periphery the dissipated power remains too high near to the wall.This tendency of the model to locate the plasma closer to the wall than is the case in reality is more pronounced for a 100 MHz ICP for which the skin effect is more pronounced. The proximity of the model plasma to the wall hinders convergence of the 100 MHz model calculations. It is concluded that an additional recombination channel is probably the cause of the discrepancy. For the 3 MHz I.CP the sensitivity of the model to several expressions for the ionization rate and for the radiative losses was tested. As an example the results expressed as contour plots of n T and G of two cases are shown in Fig.4 one with high radiative losses and one with more realistic expressions for ionization and radiative losses. The presentation in the form 0 0 0.043 0.085 0.128 0.170 z /m 15 10 5 0 -5 150 c) 120 E 3 90 z rn 5 6o 30 0 0.043 0.085 0.128 0.170 z Irn 0 0.010 0.020 rlm Fig. 3 Comparison of two models for a 3 MHz ICP 5 cm diameter 5 kW power argon flowrates 21.3 and 1 sl Shown are the axial dependences of temperature velocity and dissipated power density; the open circles are from Mostaghimi et the solid line from Benoy and co-workers.21*22 Shown are the axial dependences of (a) temperature (b) velocity and (c) dissipated power density of contour plots shows that a comparison on the basis of n is inuch clearer and thus more demanding than on the basis of T,.The basic characteristics of an ICP are evident from the contour plots. The plasma is heated in an annular region at the location of the coil; in this region the electron temperature is of the order of 9000K high enough to ensure sufficient electron production. Also the heavy particle temperature G is higher here but still lower than T since the electron density is too low to ensure complete coupling. In this active region also the electron density is at a maximum and thus a hollow profile results. Further upstream the profile flattens out because of ambipolar diffusion and forward flow with typical flow velocities of 10 m s-' and with a diffusion coefficient (in LTE) equal to:'7 Dam = 1.4 x 10-3$0.12 m2 s-' (15) (A in units of lo2' m-')).The time constants involved with ambipolar diffusion [eqn. (4) Tdiff II RV2/Damb] can be estimated to be of the order of s. Radiative recombination and three-particle recombi- nation are weak processes with time constants of 10-2s for the active region and even longer for the passive recombining regions upstream. Three-particle recombination will only be important if T becomes small while n remains high since the three-particle recombination coefficient scales as ne2T,-9/2. Such a case occurs in power interruption experiments to be described later. Since three-particle recombination is the inverse process of ionization it will be contained anyway in the electron production term in the equation which is based on the non-equilibrium parameter 6bl.It can be concluded that in atomic plasmas the electron density decays primarily by convection and for steep gradients by diffusion. This picture changes markedly if molecular ions occur. This may happen even in atomic gases close to the wall where the neutral density is high and the temperature low. In this instance Ar2+ ions may be formed in a three-particle proce~s;~ the newly formed molecular ion will recombine with an electron by the fast process of dissociative recombination Ar' + Ar + Ar + Ar,' + Ar; Ar2+ + e +Ar + Ar*(4p) (16) In the body of the plasma the process becomes less effective for several reasons. First the neutral ground state density decreases rapidly towards the centre and the molecular ion formation rate is proportional to nh2 with an estimated rate coefficient of 1.5 x 10-43-2.5 x m6 s-1.19925 Second at the corresponding higher heavy particle temperature the mol- ecular ion may be dissociated before an electron-induced dissociative recombination occurs.Third the product of disso- ciative recombination viz. an argon atom in the 4p state will be re-ionized if the electron density is high enough. Hence the process is only strong close to the wall and this may be the explanation for the discrepancy observed earlier between the model and experimental results in particular for higher frequency ICPs. As noted above the transport equations presented earlier can be reformulated using an alternative set of parameters p ne 6b and T,/T,. The electron temperature can be calculated from an implicit relationship based on Daltons' law and the Saha expression for the neutral ground state [eqn.( 5 ) ] . For low ionization degrees the contribution of the electron and ion pressure to the total pressure can be ignored (17) Th p N n1kG = bl - kT,nls(n T,; p ) T Thus T is only a function of p n and b Th/T,. we can also write the source terms S in eqns. (10) and (1 1) as a function 626 Journal of Analytical Atomic Spectrometry September 1 !)96 Vol. 110.170 0.127 0.085 0.042 0.170 0.127 0.085 0.042 0 f- zlm f- zlm Fig. 4 Comparison of model results for ne(r7 z) T(r z ) and q ( r z ) of the 3 MHz ICP (cf. Fig. 3) for two different sets of expressions for ionization/recombination and radiative losses. Taken from refs. 21 and 22 of bl and ne2 s = (b - l)[KlnlSaha/ne]ne2 The term between square brackets is plotted as a function of n for argon at 1 bar at LTE in Fig.5. In order to evaluate these equations we need to express the relevant transport coefficients in terms of the plasma para- meters. It appears that for near-equilibrium conditions the transport coefficients are primarily dependent on n at a given pressure and only weakly on the non-equilibrium parameter b and the ratio q/z. In Fig. 5 the n,-dependences of T 0 the ionization production coefficient K nlSaha/ne the heat conductivities q and rc and the ambipolar diffusion coefficient Dam, are given for an argon plasma at 1 bar at LTE. This reformulation makes it clear again that n is the primary plasma quantity. Also the line Q1 and continuum Qei and Qea radiation energy losses were calculated as a function of n,; the results obtained are shown in Fig.6. Again it appears that continuum radiation and line radiation in partial LTE depend primarily on n and weakly on non-equilibrium param- e t e r ~ . ~ ~ ~ ~ ~ ~ ~ ~ For electron densities smaller than lo2' m-3 line radiation is dominant over continuum radiation as is evident from the following approximate power law lo4 I K Nv mK-' 1 0-3 .- 1019 1 O2O 1 02' 1 022 ne/rns Fig.5 n dependences of z B Damb K1nlSaha/ne K and Kh for an atmospheric argon plasma in LTE I I IU 1019 Id0 1 02' 1 on ne/m9 Fig. 6 n dependences of line-(Q,) continuum- (Qei and Qea) and total- (Qtotal) radiation losses (all divided by ne2) and of the inelastic energy loss term coefficient K1 nlSaha(Elion + 5kT/2)ne representations Qline/n? N 2.5 x 10-36de-0.5 (4 in units of lo2' m-3) (19) Qrad/ne2 N 3 x 10-36i,-0-43 (i in units of lo2' m-3) (20) If the lower excited states such as the 4p state deviate from Saha equilibrium then line radiation will change.26 Another aspect of the reformulation is that only two instead of four boundary conditions are needed.This is a consequence of the replacement of T by the non-equilibrium parameter 6bl. The latter parameter appears only linearly in the equa- tions whereas the former appears in a second-order transport term thereby requiring two integration constants and thus boundary conditions. The consequences of this difference are not yet clear. For higher electron densities this formulation was tested on very accurate arc measurements and was also compared with full modelling based on the full transport equations in the extrinsic form.The approximate n,-based model appeared to agree with full modelling and with the experimental re~u1ts.l~ Hence this method also needs to be tested on the lower electron density ICP plasma to support further model studies. Based on the studies described above we can draw some general conclusions. For relatively low excitation frequencies Journal of Analytical Atomic Spectrometry September 1996 Vol. 1 1 627there is good agreement between the model and experimental results. The comparison should be made on the basis of n rather than T because this allows any possible discrepancies between the model and experimental results to be seen more clearly. For higher frequencies the maximum values of the electron density found by experiment agree with those given by the model; however the model predicts that the plasma is too close to the wall.It seems likely that AT2+ ion formation and dissociative recombinationg add an important recombina- tion channel close to the wall and that omission of this process is the reason for the discrepancy. Note that this process if it is the cause is only effective at higher pressures and that scaling with ambient pressure may help to resolve this matter. 0.25 EXPERIMENTAL RESULTS Several groups have in the past few years developed classical and advanced diagnostic techniques to investigate further the ICP plasma. Here we will summarize these techniques and the results obtained in particular for a 100 MHz 1CP.l' Classical techniques include the absolute line intensity and H I line broadening methods.We will summarize first the absolute line intensity method as it has a direct bearing on the non-equilibrium in the excited state distribution discussed earlier. - z =5mm I I I I 1 I I Absolute Line Intensity Method In this method the absolute densities of one or several excited states of the argon carrier gas are The density np per statistical weight g p of an excited state p can be expressed in terms of its Saha density npSaha by the use of the overpopulation of state p b, E ion is the ionization energy of level p. At a specified pressure ( 1 bar) the electron temperature can be expressed in terms of the electron density and the combined non-equilibrium param- eter b Th/T, (22) Th T p z n kT = bl - [kT,nlSaha] If electron excitation is more important than radiative trans- itions then an approximate relationship can be obtained which relates the deviations from equilibrium of both the ground and lower excited state^:^ Epion b - 1 2.0 1.5 1.0 z c" \ 0.6 n - 6 4 - 2 0 2 4 6 in which Co is a constant.The higher excited levels can be assumed to be in Saha equilibrium. The absolute density of an excited level can be directly expressed in terms of the electron density by solving the set of equations (21)-(23). The use of the lower excited states has the disadvantage that the relation- ship ( 2 3 ) is only approximate but the advantage of accurately known transition probabilities. For the higher excited states the reverse is true the levels are in Saha equilibrium but the transition probabilities are known with larger uncertainties.de Regt and ~ o - w o r k e r s ~ ~ * ~ ~ improved the situation by nar- rowing the error margin in the transition probabilities of the higher excited states. Hence absolute measurement of the excited state densities can give the electron density and this method can be characterized as simple yet still relatively precise. As an example of these types of measurements and those of HP line broadening the results of Nowak et a1.28 can be mentioned. These workers measured the higher state densi- ties and determined n and T for several assumed values of b (actually b,T,/T,); the results are shown in Fig. 7. From Fig. 7 and from a comparison with HP line broadening results an estimate of the deviation of the ground state density can be given (see Fig.7) showing that for the active regions the value of bl ranges between 10 and 100 whereas for the passive regions b is smaller than 1. Note that these methods both require Abel inversion. Laser Diode Absorption ,4 more recent method is the determination of the first excited states the 4s levels by laser diode ab~orption.~' In this method lateral profiles of wavelength-resolved absorption are meas- ured. After Abel inversion the radially-dependent density of the considered 4s sub-level and the Doppler and Lorentz broadening contributions can be obtained. Using this method the electron density can be obtained from the 4s density and the heavy particle temperature from the Gaussian part of the broadening. In Fig.8 the heavy particle temperature is shown3' for various power levels. The temperatures obtained agree with values obtained by Rayleigh ~cattering.~ The Lorentz broaden- ing is caused by both Stark and homogeneous broadening effects and is more difficult to use. At lower pressures it has also been used to obtain information on the electron den~ity.~' l'homson and Rayleigh Scattering Thornson scattering has been used to measure locally the electron density and electron t e m p e r a t ~ r e . ~ ~ ~ ~ ~ ~ The measurement is local as it refers to the scattering volume made up by the intersection of the incident laser beam and the detection beam. The total scattering yields the electron Fig. 7 Results for n and T from absolute line intensity method [solid lines for three values of bl (0.1 1 and lo)] and from HP line broadening (dashed line). Measurements refer to z = 5 mm above the load coil.Conditions 100 MHz ICP 0.8 kW power 18 mm diameter gas flow rates 12 0.6 and 0.2 sl min-'; taken from ref. 28 628 Journal of Analytical Atomic Spectrometry September 1996 1Vd. 11- p = 1.2kW - p = 1.5 kW - p = 1.8 kW on . . . . 0 2 4 6 8 rlmm Fig. 8 Experimental values for & by laser diode absorption at 7 mm above the load coil for various rf power levels. Taken from ref. 30. Conditions 100 MHz ICP 18 mm diameter gas flow rates 12,0.3 and 0.6 sl min-l density after subtraction of the scattering at the laser wave- length by Rayleigh scattering on neutral argon atoms. The electron temperature is obtained from the width of the Thomson scattering profile.In the interpretation one has to correct for the partly collective part of the scattering because usually the collectivity parameter 01 = (ksAD)-' is not much smaller than 1 (k is the scattering wavenumber and AD the Debye length). The main problem is the presence of stray light in particular if the incident photon beam has to pass through the glass envelope. The main advantage of this method is that the interpretation is straightforward and that no Abel inversion is required as in line integrated measurements. Pioneers in this respect have been Huang and Hieftje;10,33,34 more recently further data have become available from the work of de Regt and c ~ - w o r k e r s . ~ ~ * ~ ~ The earlier spectroscopic analysis has been c~nfirmed,~' thereby substantiating the close to equilib- rium approach adopted.In Fig. 9 data obtained with Thomson scattering are compared with results from the absolute line intensity met hod.31 Raman Scattering For the interpretation of the Thomson and Rayleigh scattering data new ways had to be found to calibrate the system. 1 02' 1 \ c? 4- Ts 4- AU Fig. 9 Electron density and electron temperature results by Thomson scattering and by the absolute line intensity method; taken from refs. 19 and 31. Conditions as in Fig. 8; power = 1.2 kW Rayleigh scattering on atmospheric gas was not possible in many instances because of the stray light problem. As an alternative Raman scattering on molecular gases such as N2 has been emp10yed.l~ It was shown that this is also a possible way to obtain information on the entrainment of ambient nitrogen in the upper part of the ICP flame; an example is shown in Fig.Absolute concentrations of molecular gases can thus be obtained as well as the ro-vibrational temperature which is equal to the heavy particle temperature &. In Fig. 1 135 an example can be found of the thus obtained pressure profiles of the hot argon central core (Rayleigh) and the ambient air (Raman). The thickness of the transition layer is in agreement with a picture in which the in-diffusing nitrogen molecules are dissociated by charge transfer and subsequent dissociative recombination Ar+ +N2+Ar+N2+ and N2+ + e + N + N (24) This illustrates the strength of combined Thomson Rayleigh and Raman scattering.In this instance scattering in the polarization other than the incident polarization is detected; this approach is only sensitive to molecules with finite polariz- ability and hence molecules can be distinguished from atoms in Rayleigh and Raman scattering. Continuum Radiation A study of continuum radiation is worthwhile for two reasons firstly it gives information on plasma parameters in particular on n,; secondly it forms the ultimate background level for spectrochemical measurements. Continuum radiation in an atomic plasma consists of three contribution^:'^^^^^^^^^^ f ree bound electron ion free free (both e-i) and electron neutral free (e-a) radiation. The first two both result from electron-ion interactions both are proportional to ne2 and can be taken together.The e-a contribution stems from electron-atom elastic collisions and is proportional to n,n,. The ratio of e-i to e-a contributions is of course a function of ne/n and is also a weak function of wavelength. 0 dmm Fig. 10 Density of nitrogen (air) and of argon at 7 mm above the load coil showing clearly the influence of entrainment in the outer layers of the plasma above the rim of the torch; taken from refs. 19 and 35. Conditions as in Fig. 8; power = 1.2 kW 1 .o. A' tinnsrrim torch 1 0.0 . I . I . . - / * . . 0 2 4 6 8 1 0 1 2 1 4 rlmm Fig. 11 taken from refs. 19 and 35. Conditions as in Fig. 8 Partial pressures of argon and air with plasma off and on; Journal of Analytical Atomic Spectrometry September 1996 Vole 11 629INFLUENCE OF HYDROGEN AND NITROGEN Molecular gases may have a marked influence on the ionization degree of the atomic plasma induced in the main gas stream.As analytes are introduced in the form of an aerosol in the central channel a short discussion of the consequences is in order. At atmospheric pressure the diffusion of other gases from the central and outer regions into the mainstream of the annular plasma is slow. Thus to a first approximation the induced argon plasma can be assumed to be still purely atomic. However downstream in the open flame in-diffusion plays a role as has been seen already in the entrainment of air leading to a decrease in the ionization. Similar effects are observed when droplets or hydrogen gas are introduced into a pure argon ICP. In Fig. 13 the area-integrated electron density is shown4' as a function of observation height.It is clear that in the presence of e.g. hydrogen the decay of electron density is much faster than in pure argon. For pure argon electron loss by convection and diffusion are thought to be the dominant processes. However close to the wall molecular ion formation in a three-particle process and dissociative recombination may play a role. In the presence of molecules (as entrained air in the periphery of the flame) recombination by the sequence of charge exchange of an atomic ion with a molecule and dissoci- ative recombination of the resulting molecular ion is the primary process. In the presence of a small amount of molecular hydrogen (or water) in the central flow similar processes occur in the centre of the plasma.The following reaction^^,^^ Ar++Hz+ArH++H and ArH++e-+Ar+H* then lead to an efficient recombination as has also become clear from detailed studies of low pressure expanding plasma^.^^.^^ Usually charge transfer is the rate-limiting pro- cess and the time constant is determined by the rate (typically m3 s-') and the molecular abundance. As molecules are destroyed by this process the decay of electron density comes from the cool regions at the centre and the outside and the process leads to a shrinking of the plasma. Depending on the molecule the process can be observed as the dissociative recombination commonly ends in an excited state of the atomic fragment with the lowest ionization energy in the example of eqn. (25) in an excited state of the hydrogen atom.By detailed study of atomic fragments in excited states or in the ground state by two-photon laser-induced fluorescence (TALIF) further information about these processes can be obtained. (25) :...a. ... ,..... C" I 0 sb Id0 15; Timeims Fig. 12 Reaction of several Ar lines at 5 mm above the load coil to power interruption; taken from refs. 39 and 41. Conditions 100 MHz ICP 0.8 kW power 15 mm diameter argon flowrates 12 0.1 and 1 sl min-l with aerosol injection Since the spectrochemical response is to a first approxi- mation linearly dependent on electron density while the e-i continuum background is proportional to n it is advanta- geous to analyse at the position where the e-i contributions have decayed to the e-a contributions.In atmospheric argon plasmas this situation is reached when n is a few times lozo m-3; this is in fact the value that occurs at the observation height. Continuum radiation can also be used to obtain information on the plasma parameters in particular n,. The power interruption technique (to be discussed in the next section) has also been used to study the continuum radiation. Here full use is made of the additional information contained in the relative time dependence at higher electron densities an n dependence occurs whereas later the decay is of an ne' character. For further details the reader is referred to the l i t e r a t ~ r e . ' ~ . ~ ~ ~ ~ POWER INTERRUPTION AND TIME- DEPENDENT MEASUREMENTS A very powerful extension of the optical probing techniques is the measurement of the reaction to a sudden change in the applied power uiz.the power interruption technique.38 It has been used extensively by Fey and c o - w o r k e r ~ ~ ~ ~ ~ to study the kinetics of argon and of analyte atoms and ions. In its basic form the power is interrupted for a short time (typically 100 ps) long enough to achieve a certain decay but short enough to permit re-establishment of the plasma after the interruption. At first it was thought that during the interruption the electron temperature first decreases to the heavy particle temperature. Recently it became clear that the electron tem- perature during interruption T,* is still substantially higher than the heavy particle temperat~re.'~ The reason why T,* is higher than is probably due to three-particle recombina- tion" as this process is suddenly very favourable because of the still high n but decreased T,.This point needs further study. Nevertheless the electron temperature during power interruption c* is lower than T in the undisturbed situation which leads to an enhancement of the line radiation of excited argon levels. In Fig. 1239 the reaction of several Ar lines is shown; by plotting the relative increase (jump) as a function of the ionization energies of the levels information on T,* and on the deviation from thermal equilibrium can be obtained. IBEHAVIOUR OF ANALYTES DURING POWER HNTERRUPTION From the time dependence of the excited state line emission during power interruption the primary process of analyte excitation can be revealed.Excitation of analyte atoms to excited atoms or ions can basically occur through two pro- Z/mm Fig. 13 Area integrated electron density as a function of observation height; taken from ref.42. With and without aerosol. For ICP con- ditions see Fig. 7 630 Journal of Analytical Atomic Spectrometry September 1996 Vol. 11B I 3500 $9 C 3 30 Energy (eV) 8 Tim elms I \ % \ 25 2O.; rc - - - 15 4P ' Timelms - 10 c 4f- I ' '3d- VHflAW4 0- / O 0 100 200 300 3P- Timelms 0 100 200 300 - 4s 3s3d- - Argon Magnesium '\ 0 100 200 300 Time/ms Y c C s 8"1-r--l 0 O 0 100 Time/ms 200 300 Fig. 14 Reaction of several Mg I and Mg I1 lines. The difference between charge transfer pumped lines (CT) and other lines is apparent; taken from refs. 39 and 41. Conditions as in Fig. 12 but with an inner flow rate of 1 sl min-' with 1 g I-' Mg cesses the reaction of which to power interruption is different.The first is charge exchange of the carrier gas atomic ion and the analyte (An) atom leading to an excited analyte Ar + + An -+ An+* + Ar An example of the reaction to power interruption is shown in Fig. 14 in which the reaction of several levels of Mg I1 (including those nearly resonant with the argon ion) is shown3' together with the reaction of neutral Mg I levels. The reaction differs for the various levels depending on whether the level is populated by charge transfer or by electron excitation from the ground state. A second study concerned the case of Li for which the ion excited states are too high to be reached by energy resonant charge transfer.The kinetics here are totally dominated by electron excitation and thus the so-called Boltzmann reaction prevails4 for the monitored neutral Li I lines.40 Here the reaction depends also on the location in the plasma flame; the production of Li atoms and excitation from the Li ground state first increases as the droplet is evaporated and later relaxes when the evaporation cloud is expanded. In fact what one observes is the evaporation of the droplet in the central channel by the plasma energy and the excitation of the resulting Li atoms. A model based on heating by (heavy particle) heat c o n d ~ c t i o n ~ ~ gives reaction patterns of the Li I excited levels to power interruption that are in agreement with experimental observations. (26) CONSEQUENCES FOR ANALYTICAL USE From this brief summary of model and experimental studies we can make the following comments on the importance of plasma characteristics for the analysis process.( 1) The droplet needs to be evaporated over a distance of about 10mm; this requires sufficient heat conduction and energy content in the plasma and thus a sufficiently high heavy particle temperature. Also the drift velocity of the plasma needs to be high enough to minimize diffusion and recombination ion loss but low enough to ensure evaporation of the small droplets in the aerosol. (2) The ion and thus electron density needs to be high enough to excite the analyte either by charge transfer or by direct excitation over a distance of 10 mm with a flow velocity of 10ms-l; however the electron density needs to be low enough to obtain a continuum background governed by e-a interactions in order to obtain an optimum signal-to-back- ground ratio in the spectroscopic signals.For ion mass spec- trometry similar demands are probably set in order to avoid space charge problems in the mass analyser. Therefore it is clear that all the characteristics of a slowly flowing ICP are needed and that measurements at a location between 10 and 20mm above the coil are optimum in terms of signal-to- background ratio. Further studies along these lines taking both the droplet evaporation and the analyte excitation into account can reveal whether the presently common plasma parameters are optimum. Such studies might show that the use of higher frequencies would offer the possibility to decrease the dimensions of the torch thereby permitting a decrease in power and gas consumption.Another intriguing possibility for analytical use might be the use of modulation of the ICP power. Equivalent analytical power at lower power consump- tion and the use of time integration techniques need further investigation. From this analysis it also becomes clear that in situations where evaporation is not needed the freedom in plasma choice is larger. Also lower pressure plasmas can then be used such as capacitively coupled or inductively coupled rf plasmas. These may have the advantage that it is easier to rf bias the extraction electrode which may be beneficial for ion mass spectrometry. Journal of Analytical Atomic Spectrometry September 1996 Vol.11 631CONCLUSION The state of non-equilibrium of the argon JCP has been investigated in recent years by modelling and by various experimental techniques. The carrier gas plasma is now fairly well understood as are the processes occurring in the plasma if analytes are introduced into the plasma. It has been argued that the ICP in its common form offers a good compromise for effective droplet evaporation and optimum signal-to-back- ground ratio in the analyte determination. Time modulation may offer additional advantages for analyte detection and needs to be investigated further. The technical assistance of H. M. M. de Jong M. J. F. van de Sande and A. B. M. Husken and the contribution by several students is gratefully acknowledged. The research on ICPs has been made possible by support from the ‘Stichting Technische Wetenschappen’ (STW) which is financially supported by ‘Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)’ and by support from Philips.REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Boumans P. W. J. M. Inductively Coupled Plasma Emission Spectroscopy Wiley New York 1987. Date A. R. and Gray A. L. Applications of ICP-MS Blackie Glasgow 1989. Tyler G. Spectrosc. Eur. 1995 7 14. van der Mullen J. A. M. Phys. Rep. 1991 191 109. Schram D. C. Raaymakers I. J. J. M. van der Sijde B. Swenkelaars H. J. M. and Boumans P. W. J. M. Spectrochim. Acta Part B 1983 38 1545. Blades M. W. Spectrochim. Acta Part B 1994,49,47. Raaijmakers I. J. J. M. Boumans P. W. J. M. van der Sijde B. and Schram D.C. Spectrochim. Acta Part B 1983,38 697. Caughlin B. L. and Blades M. W. Spectrochim. Acta Part B 1984,39 1583. Raaijmakers I. J. J. M. Schram. D. C. Schenkelaars H. J. W. Kroesen G. M. W. and Boumans P. W. J. M. Proc. ISPC-7 Eindhoven 1985 823. Huang M. and Hieftje G. M. Spectrochim. Acta Part B 1989 44,739. de Regt J. M. Engeln R. A. H. de Groote F. P. J. van der Mullen J. A. M. and Schram D. C. Rev. Sci. Instrum. 1995 66 3228. Wilbers A. T. M. Beulens J. J. and Schram D. C. Proc. Wilbers A. T. M. Beulens J. J. and Schram D. C. J. Quant. Spectrosc. Radiat. Transfer 1991 46 385. Boulos M. I. Fauchais P. and Pfender E. Thermal Plasmas. Fundamentals and Applications Plenum New York 1994 vol. 1 Qing Z. PhD Thesis Eindhoven University of Technology The Netherlands 1995.de Haas J. C. M. PhD Thesis Eindhoven University of Technology The Netherlands 1986. Schram D. C. de Haas J. C. M. van der Mullen J. A. M. and van de Sanden M. C . M. Plasma Chem. Plasma Process. 1996 16 (Suppl.) 19s. Timmermans C. J. Rosado R. J. and Schram D. C. 2. Nuturforsch. Ted A 1985 40 810. ISPC-10 1991 I 1.1-4. 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 4 1 42 43 44 4.5. de Regt J. M. PhD Thesis Eindhoven University of Technology The Netherlands 1986. Beulens J. J. Milojevic D. Schram D. C. and Vallinga P. M. Phys. Fluids 1991 B3 2548. Benoy D. A. PhD Thesis Eindhoven University of Technology The Netherlands 1993. Benoy D. A. de Jong E. C. J. N. Fey F. H. A. G. van der Mullen J. A. M. and Schram D. C. J. High Temp. Chem.Processes 1992 1 367. Mostaghimi J. Proulx P. and Boulos M. I. J. Appl. Phys. 1987 61 1753. Proulx P. Mostaghimi J. and Boulos M. I. Int. J. Heat Muss Transfer 1991 34 2571. Beulens J. J. de Graaf M. J. and Schram D. C. Plasma Sources Sci. Technol. 1993 2 180. Benoy D. A. van der Mullen J. A. M. and Schram D. C. J. Phys. D 1993 26 1408. van der Sijde B. and van der Mullen J. A. M. J. Quant. Spectrosc. Radiat. Transfer 1990 44 39. Nowak S. van der Mullen J. A. M. van der Sijde B. and Schram D. C. J. Quant. Spectrosc. Radiat. Transfer 1986,41 177. de Regt J. M. Tas R. D. van der Mullen J. A. M. van der Sijde B. and Schram D. C. J. Quant. Radiat. Transfer submitted for publication. de Regt J. M. Tas R. D. and van der Mullen J. A. M. J. Phys. D submitted for publication. de Regt J. M. de Groote F. P. J. van der Mullen J. A. M. and Schram D. C. Spectrochim. Acta Part B submitted for publication. de Regt J. M. Tas R. D. van der Mullen J. A. M. and Schram D. C. Phys. Rev. E submitted for publication. Huang M. and Hieftje G. M. Spectrochim. Acta Part B 1989 44 291. Huang M. and Hieftje G. M. Spectrochim. Acta Part B 1985 40 1387. de Regt J. M. de Groote F. P. J. van der Mullen J. A. M. and Schram D. C. Spectrochim. Acta Part B submitted for publication. de Regt J. M. van Dijk J. van der Mullen J. A. M. and Schram D. C. J. Appl. Phys. 1995 28 40. Benoy D. A. van der Mullen J. A. M. and Schram D. C. J. Phys. D 1993 26 1408. Farnsworth P. B. Rodham D. A. and Ririe D. W. Spectrochim. Acta Part B 1987 42 393. Fey F. H. A. G. Stoffels W. W. van der Mullen J. A. M. van der Sijde B. and Schram D. C. Spectrochim. Acta Part B 1991 46 885. Fey F. H. A. G. de Regt J. M. van der Mullen J. A. M. and Schram D. C. Spectrochim. Acta Part B 1992,47 1447. Fey F. H. A. G. PhD Thesis Eindhoven University of Technology The Netherlands 1993. Nowak S. van der Mullen J. A. M. and Schram D. C. Spectrochim. Acta Part B 1988 43 1235. Graaf M. J. Severens R. J. Dahiya R. P. van de Sanden M. C. M. and Schram D. C. Phys. Rev. E 1993,48,2098. Meulenbroeks R. F. G. Schram D. C. van de Sanden M. C. M. and van der Mullen J. A. M. Phys. Rev. Lett. 1996 26 1840. Fey F. H. A. G. Benoy D. A. van Dongen M. E. H. and van der Mullen J. A. M. Spectrochim. Acta Part B 1995 50 51. Paper 6100827E Received February 5 1996 Accepted April 12 1996 632 Journal of Analytical Atomic Spectrometry September 1996 Vol. 11

ISSN:0267-9477    

DOI:10.1039/JA9961100623

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Comparison of Electrospray and Inductively Coupled Plasma Sources for Elemental Analysis With Mass Spectrometric Detection* FRANCINE BYRDY BROWN LISA K. OLSON AND JOSEPH A. CARUSOT Department of Chemistry University of Cincinnati P.O. Box 2101 72 Cincinnati OH 45221 -01 72 USA Both the qualitative and quantitative aspects of electrospray (ES) and ICP sources were investigated using the same mass spectrometer (originally a VG PlasmaQuad I instrument). While it is well established that ICP-MS is a powerful tool for elemental analysis electrospra y ES-MS has recently become popular as a promising elemental analysis technique that can complement the detection capabilities of ICP-MS. The in-house constructed ES source efficiently produced the bare singly charged metal ion and the optimum ES source conditions varied depending on the charge reduction required to attain the singly charged state.The day-to-day signal reproducibility was excellent (5% RSD) and the removal of the photon stop increased ion transport to the detector. A comparison of the figures of merit for Rb Cs Ba V Cr Ni Co Cu Zn and U showed that the detection limits obtained by ES-MS (ng ml-') are only 2-3 orders of magnitude higher than those found using the ICP source. Additionally Ca was determined in NIST SRM 1643c (Trace Elements in Water) by ES-MS. Keywords Electrospray mass spectrometry; inductively coupled plasma mass spectrometry; elemental analysis Electrospray mass spectrometry (ES-MS) is a versatile and relatively inexpensive technique with considerable potential for elemental analysis.It is therefore not surprising that applications of ES-MS have been prolific in the past few years. Interest within the atomic spectroscopic community was generated with the reported observation by Kebarle and co-worker~'-~ of multiply charged inorganic solution ions (M2+ and M3+). This discovery opened up ES-MS to the field of elemental analysis. To the atomic spectroscopist one attractive feature of ES-MS is the transfer of ions in solution to the gas phase at atmospheric pressure which is accomplished without the use of a high-temperature environment such as a flame furnace or plasma.' While the ICP represents a nearly ideal ion source it has shortcomings. In particular the sample processing steps of the technique including solution and aerosol transport would benefit from new technologies.' For elemental analysis ES-MS may emerge as an attractive inexpensive option to ICP sources.The work of Horlick's group5-'' sparked interest in this technique. They converted a Perkin-Elmer/SCIEX ELAN 250 ICP-MS system into an ES-MS instrument and investigated both the qualitative and quantitative aspects of ES-MS for elemental analysis. Their preliminary results indicated the potential of ES-MS for speciation studies? Later they dis- cussed the quantitative aspects of ES-MS.7 In particular it * Presented at the 1996 Winter Conference on Plasma t To whom correspondence should be addressed. Spectrochemistry Fort Lauderdale FL USA January 8-1 3 1996. Journal of Analytical Atomic Spectrometry was found that a secondary ion of relatively high concentration ( moll-') is necessary to generate quantitative conditions for trace component analyses.Their results favoured the single ion droplet theory (SIDT) over the ion evaporation theory (IET) since they found no solvation energy dependence for ion generati~n.~ In another report they illustrated the typical ion species that could be observed in three positive-ion modes ( 1 ) the 'ion-cluster mode,' (2) the 'intermediate mode' and ( 3 ) the 'bare metal-ion mode.'' The last-named mode was the one most important to our study since this is the mode that produces spectra similar to ICP-MS. In order to perform a valid comparative study of ES-MS and ICP-MS it was necessary to optimize the ES conditions to attain the M+ state.An assessment of ES-MS for elemental speciation measure- ments was reported by Agnes et al.' in 1994. A comprehensive examination of iron@) and iron(rI1) species was described in addition to chlorine iodine and sulfur speciation measure- ments a study of two inorganic complexes and an investigation of the collision-induced dissociation (CID) of peroxodisulfate. More recently Stewart and Horlick" have presented results on several elements in the lanthanide series. The mass spectra observed were highly dependent on the chemical and physical properties of the solution used. Finally in their most recent report Agnes and Horlick" discussed the effect of operating parameters on the analyte signal. The most important interface parameters were found to be the curtain gas flow rate and the sampling plate voltage bias.In this study both the qualitative and quantitative aspects of ES and ICP sources were investigated using the same mass spectrometer (originally a VG PlasmaQuad I ICP-MS instru- ment). No quantitative investigation of this nature has been done to date and to our knowledge this is the first use of a VG PlasmaQuad I ICP-MS instrument as an electrospray mass spectrometer. Initial work included modifications to the electrospray interface in order to improve the signal intensity and day-to- day signal reproducibility. A number of elements were deter- mined in the comparative study including Rb Cs V Cr Ni Co Cu Zn Ba and U. The in-house constructed ES source was found to produce efficiently the bare singly charged metal ion and the optimum ES source conditions varied depending on the charge reduction required to attain the singly charged state.At this early stage of comparison the figures of merit show that ES-MS detection limits are only 2-3 orders of magnitude higher than those found using the ICP source. Potential advantages of the ES source include cost efficiency (e.g. minimal solution and gas consumption) and the ability to determine elements which suffer from argon-based spectral interferences in ICP-MS (e.g. K Ca Fe Se and As). To assess the reliability of the latter statement Ca was determined in NIST SRM 1643c (Trace Elements in Water) by ES-MS. Journal of Analytical Atomic Spectrometry September 1996 Vol. 11 (633-641) 633EXPERIMENTAL Electrospray Source Design and Construction The mass spectrometer used in this study was originally a VG PlasmaQuad I ICP-MS.A diagram of the electrospray source and the interface used to transfer ions into the mass spec- trometer is shown in Fig. 1. Sample solution was pumped through a stainless-steel capillary at a flow rate of 0.8 or 5 pl min-l with a syringe pump (Sage Instruments Model 341 B purchased from Fisher Scientific Fairlawn NJ USA). A glass sample syringe [ 1 ml Hamilton (Reno NV USA) Gastight No. 1001 with removable needle 0.71 mm od x 0.41 mm id] was connected with peristaltic pump tubing (Fisher Scientific 0.025 and 0.020mm id) to the ES capillary. The capillary was made using hypodermic stainless-steel tubing. A piece of smaller bore tubing [HTX-29 type 304 stainless steel 0.33 mm od x 0.18 mm id from Small Parts (Miami Lakes FL USA)] was soldered inside a piece of larger bore tubing (HTX-17 type 316 stainless steel 1.5mm od x 1.1 mm id).The purpose of the larger bore tubing was to have a more rigid piece upon which to make an electrical connection. The ES tip was positioned 8mm from the ES front plate. The interface consisted of a front plate two circular plates (an insulator and the curtain gas plate) and a sampling plate. The sampling plate replaced the normal sampling cone used in ICP-MS experiments. The orifice diameter of the aluminium sampling plate was 0.2 mm and it formed a cone possessing a 60" angle (6 mm wide) behind the orifice. This is different from traditional ICP-MS sampling cones with orifices ranging from 0.75 to 1 mm in diameter.The purpose of the sampling plate is to control the extent of solvent declustering in the jet expansion and the voltage bias of the plate controls the collisional energy of the ion.' An ES front plate made of aluminium and having a 3 mm id hole was mounted 4mm in front of the sampling plate creating a chamber. Nitrogen was introduced into this region as the 'curtain' drying gas through a hole in the curtain gas plate which was made of aluminium. The gas flow rate was 0.2 1 min-' which was controlled using a mass flow controller (Tylan RO-28; Tylan San Diego CA USA). An insulator made of Delrin was placed between the front and curtain gas plates. The curtain gas controls the rate of evaporation of the charged droplets and also reduces the growth of solvent clusters around ions in the jet expan~ion.~~'~ Nitrogen was the Fig.1 into the mass spectrometer (not drawn to scale). The electrospray source and interface used to transfer ions curtain gas of choice since it has a low tendency to cluster with electrosprayed ions. The diatomic gas has several charac- teristics which account for this it lacks a dipole and has low polarizability. If N clusters do form they are weakly bonded.13 Additionally electric discharges are more effectively suppressed using a gas of higher dielectric strength such as nitrogen rather than argon.' The four plates were sandwiched together using nylon screws and washers. They were screwed directly onto a specially designed aluminium interface front plate constructed to replace the normal one used in ICP-MS studies.This plate was 10 mm thick x 123 mm od x 2.8 mm id. Holes for electrical connections were tapped into the front plate curtain gas plate (the voltage bias on the curtain gas and sampling plates was the same) and skimmer cone. The skimmer cone was the usual nickel cone used for ICP-MS work. The only difference was that it was mounted on a piece of Delrin insulator instead of the normal aluminium mount. The whole electrical system was connected to a Plexiglas box equipped with an interlock system. The box itself was screwed onto the front plate of the MS interface. When the door of the box was opened all of the voltage supplies were automatically shut off. This served well as a safety feature. Voltages were applied to the various plates using four different supplies.The front plate employed a Keithley (Cleveland OH USA) 247 HV supply (2999 V maximum). For the sampling plate a Varian (Palo Alto CA USA) Model 80-375 was used (2012 V maximum). A Varian Model 921-0067 (6 kV maximum) supply was utilized for the capillary tip and an in-house constructed low-voltage supply was used to bias the skimmer when necessary. To monitor the current at the capillary tip an in-house constructed ammeter was utilized (2 pA full-scale). This current was monitored to note the onset of a corona discharge at the tip. Such a discharge is unwanted since it is disruptive to the ES process and certain conditions are avoided to prevent its formation (e.g. high voltages or lack of electrolyte in the solvent).' Source and Interface Development In order to optimize the signal intensity a number of modifi- cations were made to the ES source and interface.An investi- gation of two capillary sizes (0.51 mm od x 0.25 mm id and 0.36mm odx0.18mm id) which were larger than that pre- viously used (0.33 mm od x 0.18 mm id) was the only source optimization that was done. In the end the initial capillary size was found to provide the most stable spray. The interface was developed with the aim of maximizing the analyte signal. Originally an interface front plate 8 mm thick x 120 mm od x 2.5 mm id was used. However increasing this to 10 mm thick x 123 mm od x 2.8 mm id provided the best signal-to-noise ratio. A larger diameter O-ring seal pro- vided greater flexibility to vary the distance between this front plate and the skimmer.Two different curtain gas plates were investigated. The gas inlets were made perpendicular to the orifice at 14" and 20" angles rather than in-line with the orifice and sample stream. The original in-line gas stream was found to be optimum however for sample throughput. The last and perhaps most important change to the ES interface involved the construction of a new sampling plate with a smaller orifice. The original sampling plate was of 0.3 mm id and was made of copper. The new plate was more easily constructed of aluminium and had a 0.2mrn id which is closer to the sampling plate orifice size used by Horlick's ,group (0.1 mm). The only change to the mass spectrometer involved utilizing an additional vacuum pump to reduce the pressure in the first stage to 0.27 Torr from the 1.8 Torr originally used.634 Journal of Analytical Atomic Spectrometry September 1996 Vol. 11Mass Spectrometric Considerations The voltages applied to the ion optics of the VG PlasmaQuad I mass spectrometer are adjustable and Table 1 gives the voltage range for the various lens supply elements. Additionally the typical values used for ICP-MS work are given. The extraction lens element may be biased within a - 100 to - 1000 V range by the external controls on the mass spectrometer lens supply. In normal ICP-MS operation the ion extractor is biased at - 190 V. The pressure in the first stage was 0.27Torr. The second and third stage pressures were 7.5 x lo-' and 4.5 x Torr respectively. Reagents To avoid making generalizations from a small number of elements a variety of inorganic ions were investigated. Stock standard solutions (0.1 mol 1-') were prepared by dissolving the following in distilled de-ionized 18 Mi2 cm water (Barnstead Boston MA USA) NaCl (99.9% ACS reagent; Aldrich Milwaukee WI USA); MgC12.6H20 (ACS reagent Fisher Fairlawn NJ USA); KCl (MC/B Norwood OH USA); CaC12.2H20 (99.999% Aldrich); VO( S04).3H20 (Aldrich); Cr(N03)3 -9H2O (MC/B); NiC12.6H20 (J.T. Baker Phillipsburg NJ USA); Co(N0,),-6H20 (Fisher); Cu(NO3),.3H2O (Fisher); Zn(N03)2.6H20 (Fisher); RbCl (99 + % Aldrich); CsCl (MC/B); BaCl (Fisher); and U02(N03)2-6H20 (Fluka Ronkonkoma NY USA). Doubly distilled HNO (GFS Chemicals Columbus OH USA) was added to these solutions so that they had a final concentration of 1 x moll-' H N O ~ to maintain a mini- mum secondary electrolyte concentration as suggested by Agnes and H ~ r l i c k .~ Under the conditions used in this study a pure solvent would create an electric discharge between the electrospray capillary tip and the front plate.14 Addition of the secondary electrolyte increases the voltage bias that can be applied to the capillary before the onset of a corona discharge. As a result one can generate stable charged droplet^.^ Methanol was chosen as the solvent since the voltage biasing conditions are less restrictive than they would be for water.5 'Good quality ES [may be] obtained with methanol and acetonitrile but much poorer or no ES is possible with DMSO and pure water.'15 Separate standards were made for the ES and ICP parts of the comparative study.Dilutions were done in solvents con- sidered optimum for each type of ion source. For the ES procedures dilutions were made using HPLC-grade methanol (Fisher) and nitric acid as discussed above. Three sets of mixture solutions were made to include (1) the alkali metals (Na K Rb and Cs); (2) the alkaline earths (Ca Ba and Mg) plus uranium; and (3) the transition metals (V Cr Ni Co Cu and Zn). The reason for the separation was the need to vary the interface settings to obtain optimum signal for each group. Standards ranged in concentration from 1 x to 1 x moll-' for the alkali metals from 5 x loV7 to Table 1 PlasmaQuad I Voltage ranges for the lens supply elements of the VG Control Voltage/V Extraction (E) -100 to -1000 Collector (C) -100 to +30 Lens 1 (Ll) -100 to +30 Lens 2 (L2) -100 to +30 Lens 3 (L3) Lens 4 (L4) MS front plate (FP) Differential aperture (DA) -200 to - 50 -30 to +30 - 100 to + 30 -100 to +30 Typical ICP-MS setting/V - 190 0 0 - 30 - 120 0 - 50 +4 5 x moll-' for the transition metals and from 1 x to 5 x For the ICP procedures standard solutions were prepared from the same salts used for the ES stock standard solutions and dilutions were made using 2% HN03 from doubly distilled nitric acid (GFS Chemicals).The standard solutions ranged in concentration from 1 x lo-* to 1 x lo-' moll-'. Two sets of mixture standards were made to contain the following (1) Na Rb and Cs; and (2) Ba Mg V Cr Co Ni Cu Zn and U. moll-' for the alkaline earths. Data Collection Analysis procedures within the VG PQ software were set up to aid in data manipulation.For the comparative study the mass range investigated was 8-24Ou. The most abundant isotope of each element was monitored and the results pre- sented are representative of that particular isotope. The dwell time was 320ps with 100 sweeps and 2048 channels giving an approximate acquisition time of 65.5 s. Three replicates were obtained for each standard except for those standards used to acquire reproducibility information. These standards (5 x lo-' mol I-' for ES-MS and 1 x moll-' for ICP-MS) were each run ten times. No skip regions were defined for the ES work. Standard skip regions were however set up for the ICP-MS procedures 4-20 27.8-45 and All ES experiments were run in the positive-ion mode.This means that the potential difference was increasingly more negative (from the capillary to the extraction lens) so that positive ions were produced. It was not possible to monitor negative ions with this mass spectrometer since the equipment required to switch polarity was unavailable to us. 79.5-82 U. RESULTS AND DXSCUSSION Preliminary Results An initial concern involved the applicability of the ES source design of Agnes and Horlick which was developed for a Perkin-ElmerlSCIEX ELAN Model 250 ICP-MS instrument to the VG PlasmaQuad I. The most obvious concern was the difference in the physical geometries of these instruments. In particular the ion optics of the ELAN instrument contain two photon stops and a Bessel box none of which is required for an ES source.A front lens at the base of the skimmer (the extraction lens) is followed by a conventional three-cylinder Einzel lens. This is in sharp contrast to the VG PQ I instrument which contains eight tunable lens elements and only one photon stop. The on-axis photon stop in the VG PlasmaQuad I instru- ment is mounted behind the collector and both are held at the same potential. The purpose of the photon stop is to prevent light from passing down the otherwise unobstructed system axis and being detected by the electron multiplier. If detected the photons would raise the background signal level and hence degrade detection limits. While this is particularly important for ICP-MS work it serves no real purpose in ES-MS since no intense light source is present.Removal of the photon stop increased ion transport to the detector by one order of magnitude. This is clearly evident when one compares Fig. 2(a) (1 x moll-' RbCl) which was obtained with the photon stop in place with Fig. 2(b) ( 1 x mol I-' RbCl) which were obtained after the photon stop was removed. Finally it was necessary to investigate sampling interface theory in order to optimize instrument performance. In particu- lar the distance between the sampling plate and skimmer cone was important. By increasing the sampler-skimmer distance to 4 mm (3.5 mm was originally used) using an additional vacuum pump to lower the first stage pressure and utilizing mol I-' RbCl) and (c) (1 x Journal of Analytical Atomic Spectrometry September 1996 Vol. 11 63590 95 Fig.2 ES mass spectra of RbCl solution in methanol (a) 1 x lop4 mol I-' RbCl with the photon stop in place; (b) 1 x lo-' moll-' RbCl after the removal of the photon stop; and (c) 1 x moll-' RbCl after the removal of the photon stop.the new sampling plate with a smaller id (0.2 mm) an optimum analyte signal was obtained. Summary of Differences At this point it is useful to summarize the differences between our ES design and that of Horlick. The most obvious instru- mental difference is the use of a Fisons VG PlasmaQuad I instead of the Perkin-Elmer/SCIEX ELAN 250. Second our larger sampling plate orifice and increased spacing between the sampling plate and skimmer appear to make the interface optimum for the 'bare' metal ion mode since few clusters were observed (even when 'mild' source and interface conditions were utilized).A lower solution flow rate of the order of 0.8-5 pl min-' compared with 4.5-10 pl min-' facilitates a very stable spray (at 100 nA) and less solution consumption. Also by making the interface plates one complete sandwich each component may be easily dismantled for cleaning pur- poses. In addition the Plexiglas chamber was an excellent safety feature. Finally the moisture content in the area sur- rounding the capillary and orifices may be lowered by simply purging the box with an additional flow of nitrogen. Optimization of Electrospray Operating Parameters A parametric study was initiated to optimize the ES operating parameters. An equimolar solution of the alkali metals (1 x moll-') was studied first.The following voltages were applied to the source and interface components while separately varying the last four ES capillary (+ 4.55 kV) front plate (+ 842 V) sampling plate (+ 250 V) skimmer (+ 11.4 V) and the extraction lens (-689 V). The curtain gas flow rate was maintained at 250 ml min-' and a solution flow rate of 0.8 p1 min-' was used. Fig. 3 shows that all of the alkali metals behaved similarly and the optimum signal was achieved with the front plate voltage held at +832 V. The next variable investigated was the sampling plate voltage bias. The optimum setting was determined to be + 250 V (see Fig. 4). The maximum voltage was limited to +325 V owing to an increase in the probability of arcing to the skimmer and subsequent production of unwanted species (e.g.products of an atmospheric discharge). The skimmer was investigated next. The dependence of the signal on the voltage bias of this component is given in Fig. 5. The skimmer voltage bias was optimum at + 12 V although loo0 1500 0 500 Front plate voltageN Fig. 3 Alkali metal signal intensity versus applied front plate voltage. m 0 glE 100 200 300 400 Sampling plate voltageN Fig. 4 Alkali metal signal intensity versus applied sampling plate voltage. 636 Journal of Analytical Atomic Spectrometry September 1996 Vol. 11Skimmer voltageN Fig. 5 Alkali metal signal intensity uersus applied skimmer voltage. 39K+ 85Rb+ and 133Cs+ actually show three maxima. This same trend is apparent in Fig. 6 for the extraction lens. There are three maxima for each of the alkali metals but the optimum extraction lens setting was determined to be -689 V.The purpose of the skimmer and extraction lens is to facilitate the transfer of atmospheric pressure ions into the mass spectrometer. A similar method was used to obtain the optimum operating parameters for the other elemental groups studied (i.e. the alkaline earths and the transition metals). The optimum ES source conditions vary depending on the charge reduction required to attain the singly charged state. Effect of Operating Parameters on Analyte Signal Species that do not undergo charge reduction (ie. the alkali metals and Ag') yield simpler spectra and do not require 'harsh' ES source and interface conditions to attain the M+ ion. Declustering is fairly simple for these monovalent solution ions.The ion-solvent cluster is in part desolvated by the nitrogen curtain 'drying' gas and additional declustering results via collisions in the region between the sampling plate and skimmer.' Alkali metals The alkali metals 23Na+ 39K+ "Rb+ and 133Cs+ were determined. Lithium was not studied since it has a tendency to adhere to the ion lens elements. The optimum operating conditions are given in Table 2. Relatively mild conditions were used and the solution flow rate was very low (0.8 pl min- ' ) Additionally minimal curtain gas was necessary to decluster these metals fully. Table 3 presents the optimum voltages applied to the lens stack components. For the alkali metals procedure a 'blank' was run eight . - Extraction lens setting Fig.6 Alkali metal signal intensity versus extraction lens setting on the VG PQ I 0 - 101; 2 -282; 4 -463; 6 -644; 8 -825; and 10 -1006 V. times prior to the standards. The blank consisted of 1 x loA3 mol 1-1 HN03 in HPLC-grade methanol and a spectrum of it is shown in Fig. 7(a). Solvated clusters of protonated methanol are visible. The spectrum for an equimolar solution of the alkali metals using the optimum conditions is given in Fig. 7(b). This spectrum is not as clean as desired since the bare singly charged metal ions are not the predominant species in the mass spectrum. There is a species at m/z 149 present in both the blank and blank-subtracted spectra which may be CsO+ . It is difficult to explain why CsO+ would form by CID starting with the singly ionized Cs.Originally the species was attributed to high humidity since the spectrum was obtained on a humid day (> 90% relative humidity). Although pre-purified nitrogen (approximately <4 ppm H20) and the Plexiglas box were used an exchange with any water vapour present in the ambient atmosphere probably occurred. This exchange is possible as the solvated ion clusters drift through the atmos- pheric region." If this were the case however Cs(H,O)+ would be more likely to form. Transition metals Several transition metal ions were determined V Cr Ni Co Cu and Zn. The optimum conditions for these metals differed greatly from those for the alkali metals (see Tables 2 and 3). The source front plate and sampling plate voltages and the solution and curtain gas flow rates were increased substantially.Divalent solution ions such as Co2+ will initially retain their doubly charged state. As a result of solvent evaporation and insufficient solvation energy however the metal ion is unable to maintain the 2+ state. Charge reduction of the cluster is the end result and is depicted Co( MeOH),2+ - Co( MeO)( MeOH) - 2 + + H( MeOH) + A discussion of the electric field gradient between the sampling plate and skimmer is in order. Horlick's group has shown that for their instrument adequate declustering in the CID region is achieved with an electric field gradient of 950 V cm-' for multiply charged species such as iron.g This is calculated by dividing the potential difference between the sampling plate and skimmer by the distance between them.Since the distance used in this study was greater it follows that the potential difference required to attain the same electric field gradient would have to be different. It was calculated that a potential difference of at least 380 V would be necessary to determine the bare transition metal ions. The optimum differ- ence was found experimentally to be 414 V. What this shows however is that Agnes and Horlick's estimation of the required electric field gradient was applicable to our study. Whereas the electric field gradient across the jet expansion was approxi- mately 600Vcm-' for the alkali metals 1000Vcm-' was necessary to decluster the transition metals adequately. Many conditions were tried but unfortunately it was neces- sary to hold the sampling plate at +39OV in order to determine the bare transition metals.This could have resulted in arcing between the sampling plate and skimmer cone. Additionally at the very high capillary tip voltage a corona discharge was possible. These possibilities may explain the discharge products in the following spectra. Fig. 8(a) shows the spectrum obtained by electrospraying the blank nitric acid solution under the operating conditions for the transition metals (see Table 2). The carbon species were formed as a result of the breakdown of the methanol solvent. It is interesting to note the appearance of C+ C,' and C3+ species in this spectrum. The harsher transition metal con- ditions promote the breakdown of the methanol solvent to the ( 1 ) Journal of Analytical Atomic Spectrometry September 1996 Vol.1 1 637Table 2 Optimum ES-MS operating conditions Component ES capillary/kV ES front plate/V Sampling plate/V Skimmer/V Extraction lens/V Solution flow rate/pl min-' Curtain gas flow rate/ml min-' Alkali metals + 832 + 250 + 12 - 689 0.8 250 + 4.2 Transition metals + 5.6 + 900 + 390 - 24 - 735 5 450 Alkaline earths + 5.5 + 900 + 390 - 23 - 780 5 450 Table 3 Optimum lens stack voltages Control Extraction (E) Collector ( C ) Lens 1 (Ll) Lens 2 (L2) Differential aperture (DA) Lens 3 (L3) Lens 4 (L4) Alkali metals - 689 -4 - 25 + 2 - 120 -1 - 65 Transition metals - 735 +1 - 55 +4 - 120 + 34 - 76 Alkaline earths - 780 +2 -21 + 8 - 120 + 32 - 74 20 I I (b' cs' Rb' I 0 50 .i 100 150 200 250 m/Z Fig. 7 (a) ES mass spectrum of 1 x lo- moll-' HNO in methanol and (b) a blank-subtracted ES mass spectrum for a 1 x mol I-' alkali metal solution.The operating conditions are given in Table 2. extent that the bare carbon species are obtained. This may be seen by comparison with Fig. 7(a). The blank-subtracted spectrum for a 1 x lop4 moll-' trans- ition metals solution is presented in Fig. 8(b). While the transition metals are clearly visible between m/z 50 and 70 the N+ ion is the predominant ion in the mass spectrum. Fig. 8(c) shows the former mass region in detail and adequately displays the multi-element potential of the ES-MS instrument. It is interesting to see vanadium at m/z 51 along with its oxide at m/z 67. Since vanadyl sulfate was used to prepare the vanadium solutions it is most likely that the VO' ion is the result of the charge reduction of V02+ in the gas phase.Agnes and Horlick have also observed this and have suggested that this is evidence that direct speciation of solution components is possible with ES-MS.6 Alkaline earths The alkaline earths are similar to the transition metals in that charge reduction is necessary to attain the Mf ion. It follows that the conditions required to produce 40Ca+ and I3'Ba+ would be similar to those used for the transition metals (see Tables 2 and 3). Not surprisingly the blank spectrum obtained was similar to that shown in Fig. 8(a). The blank-subtracted spectrum given in Fig. 9(a) shows the presence of oxide and hydroxide species (products of charge- reduction reactions) for both calcium and barium. Also Ba2 + is just barely apparent.A close-up view of the m/z 130-160 region is shown in Fig. 9(b). Five of barium's seven isotopes are the oxide and hydroxide species of the most abundant is0 tope. The 238U+ ion is also visible in Fig. 9(a). Clearly the conditions were not optimum for this element. In fact two of the expected major uranium species were not observed (UO' and U02+). However even if the conditions had been optimum it would not have been possible to see UO' as a result of the upper mass limitation of this particular mass spectrometer. 137Ba+ and 138Baf) are visible as ( 1 3 4 ~ ~ + 1 3 5 ~ ~ + 1 3 6 ~ ~ + Day-to-day Signal Reproducibility The reproducibility of the analyte signal from day-to-day was impressive. For eight selected days between February 1995 and June 1995 the peak height values for *'Rb+ were recorded.Taking the average of three values per day for the eight days gave a %RSD of 5%. Comparative Study The operating conditions for the ICP-MS system are given in Table 4. The photon stop was replaced prior to experiment- ation with the plasma source and the figures of merit presented in Table 5 are typical for this particular 10-year-old ICP-MS instrument in the normal operating mode. The detection limits 638 Journal of Analytical Atomic Spectrometry September 1996 Vol. 11C+ + a+ - I v) 580 0 m/Z Fig. 8 (a) ES mass spectrum of 1 x lop3 moll-' HNO in methanol (b) a blank-subtracted ES mass spectrum for a 1 x lop4 moll-' transition metal solution and (c) the blank-subtracted ES mass spec- trum from m/z 45 to 75.The operating conditions are given in Table 2. are based on 3cblank calculations in which the standard devi- ation was obtained from eight blank (2% HN03) values for each nominal m/z value. Unfortunately poor low-mass reso- lution precluded the determination of figures of merit for 23Na+ and 24Mg+. This was the case for the ES-MS results also. Linear behaviour was observed over 2.5-3 orders of magnitude for the elements studied with the exception of zinc. Log-log slopes were as follows 0.9865 (Rb) 0.9488 (Cs) 1.044 (V) 1.021 (Cr) 0.9891 (Ni) 1.039 (Co) 1.026 (Cu) 1.054 (Zn) 1.020 (Ba) and 1.028 (U). Zinc was linear over only 1.5 orders of magnitude. L 50 100 W E + 1.; m 200 Y B8+ ho+ \ B&H+ + Fig. 9 (a) Blank-subtracted ES mass spectrum for a 1 x mol 1-1 alkaline earth solution with uranium and (b) the blank-subtracted ES mass spectrum from m/z 130 to 160.The operating conditions are given in Table 2. Table 4 Operating conditions for the ICP-MS instrument Forward rf power Reflected rf power Auxiliary gas flow rate Coolant gas flow rate Nebulizer gas flow rate Spray chamber Nebulizer Solution flow rate 1.25 k W 0.70 1 min-' 0.75 1 min-' Double-pass 5 "C Concentric 0.6 ml min-' <5 w 15 1 min-' The %RSD and detection limits for the elements determined by ES-MS and presented in Table6 are reasonable for this initial study considering the fact that this mass spectrometer was not designed for use with an ES source. In comparison with the ICP-MS results the % RSD is slightly higher for each element. Also the detection limits (calculated in the same way as for the ICP-MS procedures except that the blank was 1 x moll-' HN03 in methanol) are roughly 2-3 orders of magnitude higher than their ICP-MS counterparts.Before directly comparing these detection limits with those reported by Horlick's group it is important to note that they used values at m/z 35 to do standard deviation calculations for the elements of interest rather than using blank ~pectra.~ Linear behaviour over 2-3 orders of magnitude was observed using ES-MS and is represented in the following log-log slopes 0.9882 (Rb) 0.9532 (Cs) 1.018 (Cr) 1.022 (Ni) 1.027 (Cu) and 0.9654 (Ba). Unfortunately the results for V (0.8406) Co Journal of Analytical Atomic Spectrometry September 1996 Vol. 11 639Table 5 Figures of merit for the ICP-MS procedures ~~~ ~ ~~ Element % RSD LOD/ng ml- ' Element Yo RSD LOD/ng ml-' Rb 1 0.04 c o 1 0.05 c s 1 0.03 c u 2 0.2 V 2 0.06 Zn 2 2 Cr 2 0.3 Ba 1 0.04 Ni 2 0.5 U 1 0.02 Table 6 Figures of merit for the ES-MS procedures Element % RSD LOD/ng ml - Element Yo RSD LOD/ng ml-' Rb 3 3 c o 8 30 c s 5 9 c u 6 100 V 4 200 Zn 5 300 Cr 3 30 Ba 3 20 Ni 5 30 U 6 100 (0.8998) Zn (0.8802) and U (1.300) were not as impressive.The high detection limit for vanadium may be a result of the formation of VO' in addition to V' but we have no expla- nation for the non-linearity of Co. Since the conditions were not optimum for the determination of uranium it is not surprising that its detection limit is high. Finally the zinc results were simply not as linear as those for the rest of the elements.No definitive explanation for this is known except that there may have been substantial impurities in the zinc salt used to make the standards. It was particularly challenging to compare the figures of merit for two distinctly different techniques. ES-MS is inherently non-linear whereas ICP-MS possesses a wide linear dynamic range. One of the distinct disadvantages of ES-MS is that it does not possess a wide linear dynamic range and internal standardization is necessary to overcome this prob- lem.7 Part of the problem is that the mechanisms that govern the technique are still not well understood. The most salient point to consider when looking at the detection limits is not their exact value (since a state-of-the-art instrument was not utilized) but the difference between ES-MS and ICP-MS (2-3 orders of magnitude).A potential advantage of the ES source is cost efficiency. In practice solution flow rates of the order of 0.8-5 pl min-' result in far less sample consumption than those of 0.6-1 ml min-' that are typical for ICP-MS studies. Additionally the use of pre-purified nitrogen with flow rates ranging from 250 to 450 ml min-' is cheaper than the use of high-purity argon with flow rates approaching 20 1 min-'. The source design for the ES system is relatively inexpensive to manufacture and the upkeep is negligible. Finally the capillary and interface plates are rugged and durable. Additional advantages of the ES source include the fact that organic solvents are more readily used in ES-MS studies than in ICP-MS work.This makes organometallic studies poten- tially easier to perform. Electrospray ionization is a more efficient way to produce gaseous ions from solution and solution sample history is not altered.5 Perhaps the most impressive advantage is the fact that elements that suffer from argon spectral interferences in quadrupole ICP-MS (e.g. K Ca Fe Se and As) may be easily determined. Fig. 10 which shows the determination of potassium illustrates this point. To assess further the reliability of the above statement calcium was determined in NIST SRM 1643c (Trace Elements in Water) by ES-MS. The low detection limit for calcium (40ngml-') allowed the 1 +99 dilution of a NIST SRM 1643c solution (certified to contain 36.8 1.4 pg ml-' of Ca) with 1 x lo- moll-' HNO in methanol.Taking into account the dilution factor the experimental value obtained for calcium (33.0+ 3.0 pg m1-I) falls within the certified range. QK+ I :I 'A 4 4 4 6 Fig. 10 ES mass spectrum of potassium ( 1 x original source and interface conditions. moll-') under There are some potential limitations for ES-MS. The most pronounced is that aqueous solutions are not easily electro- sprayed. There have been several reports describing techniques to overcome this difficulty but their applications have been lirnited.l7 It may also be difficult to do multi-element determi- nations when the optimum operating conditions vary from element to element. An example of this was uranium in the alkaline earth solution. The conditions that were optimum for barium and calcium were clearly not so for uranium.Multi- element standards containing many elements are not likely. Also there were mass limitations from the quadrupole mass spectrometer used in this study. We could only investigate up to 250 u. Studies of the lanthanides and actinides would appear incomplete if cluster studies were desired. The inability to perform negative-ion mode studies with this instrument is also ii limiting factor since a complete picture of the ions present in solution is unobtainable. Finally the inherent non-linearity of the technique must be addressed. To conclude the in-house constructed ES source efficiently produces the bare singly charged metal ion. Very few clusters were observed throughout the course of this work even when 'mild' ES source and interface conditions were utilized.The optimum conditions varied depending on the amount of charge reduction required to attain the singly charged state. For example 'harsh' conditions were necessary for the transition rnetals study since these ions had to undergo charge reduction. The spacing between the sampling plate and skimmer orifices was found to be critical. It is necessary to take sampling interface theory into consideration in order to optimize the iiis t rumental performance. From the comparative study the figures of merit show that ES-MS may some day complement the detection capabilities 640 Journal of Analytical Atomic Spectrometry September 1996 Vol. 11of ICP-MS for elemental analysis. If nothing else it can certainly provide pieces to puzzles which quadrupole ICP-MS cannot.For example both potassium and calcium were readily determined by ES-MS. Owing to spectral interferences from the argon plasma gas these elements were not detected with the ICP-MS instrument. The day-to-day signal reproduc- ibility the SRM results for calcium and the figures of merit for this initial study are exciting and promising results for ES-MS as an elemental analysis technique of the future. The authors are grateful to Gary Horlick and George Agnes for their assistance in getting this project started and the many helpful discussions which followed. Special thanks are due to the Chemistry and Physics Machine Shops and the Electronics Shop at the University of Cincinnati for building the source and interface components. Finally we acknowledge the National Institute of Environmental Health Sciences for support of this work through grant No. ES04908 Project 5. REFERENCES 1 Jayaweera P. Blades A. T. Ikonomou M. G. and Kebarle P. J. Am. Chem. SOC. 1990 112 2452. 2 3 4 10 11 12 13 14 15 16 17 Blades A. T. Jayaweera P. Ikonomou M. G. and Kebarle P. J. Chem. Phys. 1990,92 5900. Blades A. T. Jayaweera P. Ikonomou M. G. and Kebarle P. Int. J. Mass Spectrom. Ion Processes 1990 102 251. Blades A. T. Jayaweera P. Ikonomou M. G. and Kebarle P. Int. J. Mass Spectrom. Ion Processes 1990 101 325. Agnes G. PhD Thesis University of Alberta Canada 1993. Agnes G. R. and Horlick G. Appl. Spectrosc. 1992 46 401. Agnes G. R. and Horlick G. Appl. Spectrosc. 1994 48 649. Agnes G. R. and Horlick G. Appl. Spectrosc. 1994 48 655. Agnes G. R. Stewart I. I. and Horlick G. Appl. Spectrosc. 1994 48 1347. Stewart I. I. and Horlick G. Anal. Chem. 1994 66 3983. Agnes G. R. and Horlick G. Appl. Spectrosc. 1995 49 324. Bruins A. P. Muss Spectrom. Rev. 1991 10 53. Ikonomou M. G. Blades A. T. and Kebarle P. Anal. Chem. 1990 62 957. Tang L. and Kebarle P. Anal. Chem. 1991 63 2709. Chowdhury S. K. and Chait B. T. Anal. Chem. 1991 63 1660. Blades A. T. Jayaweera P. Ikonomou M. G. and Kebarle P. Int. J. Mass Spectrom. Ion Processes 1990 102 251. Ikonomou M. G. Blades A. T. and Kebarle P. Anal. Chem. 1991,63 1989. Paper 6/00 780E Received February 1 1996 Accepted May 15 1996 Journal of Analytical Atomic Spectrometry September 1996 Vol. 11 641

ISSN:0267-9477    

DOI:10.1039/JA9961100633

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Mass Spectrometric and Theoretical Investigations Into the Formation of Argon Molecular Ions in Plasma Mass Spectrometry* J. SABINE BECKER Zentralabteilung fur Chemische Analysen Forschungszentrum Julich GmhH 0-52425 Julich Germany GOTTHARD SEIFERT Institut fur Theoretische Physik Technische Universitat Dresden 0-01062 Dresden Germany ANATOLI I. SAPRYKIN AND HANS-JOACHIM DIETZE Zentralabteilung fur Chemische Analysen Forschungszentrum Julich Gmb H 0-5242.5 Julich Germany The a bundance and distribution of argon molecular ions (e.g. ArH' ArO' ArN' Ar,' and MAr'; M = metal) in plasma MS (ICP-MS LA-ICP-MS and rf-GDMS) were investigated and compared. In ICP-MS the non-metal argon molecular ions were formed with higher intensity compared with the metal argide ions. This could be explained by theoretical calculations of the binding energies.The ArH' ion can be viewed as an isoelectronic system comparable to HCI. The intensities of diatomic metal argide ions relative to metal ions in ICP-MS are less than A correlation between the intensities of metal argide ions with the bond dissociation energies of diatomic ions was found. The highest intensity of metal argide ions of the order of per cent. values were observed in rf-GDMS. The intensity of the argon molecular ions in an rf-GD varied by up to three orders of magnitude as a function of the plasma parameters (e.g. argon pressure in the GD ion source). The characteristic distribution of diatomic argide ions of REEs in ICP-MS was found to be comparable to the distribution of rare earth oxide ions.Keywords Argon molecular ions; binding energy; inductively coupled plasma; mass spectrometry; metal argide; radiofrequency glow discharge Rare gases play an important role in all plasma techniques when they are used as the plasma gas e.g. plasma-induced deposition plasma sputtering and inductively or capacitively coupled plasma analytical methods such as plasma MS. Argon is normally used in these plasma techniques owing to the low price the high purity that is available and the good plasma formation. The existence of argon molecular ions in these plasma techniques when using argon as the plasma gas can be proved for example by plasma MS,1-3 such as by GDMS or ICP-MS. Plasma MS methods were applied to the sensitive determination of trace and ultratrace elements or precise isotopic analysis of inorganic materials.The determination of chemical elements in the trace and ultratrace concentration range is often difficult and can be disturbed by isobaric interferences of analyte ions by molecular ions such as argon ions oxide carbide hydride or chloride molecular ions formed in a plasma with elements of the matrix or residue gas. These interferences induce an increase in the detection limits. Therefore knowledge of the intensities of molecular ions and their abundance and distribution is of specific interest for MS * Presented at the 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996. Journal of Analytical Atomic Spectrometry trace analysis of inorganic materials. Molecular ion formation processes particularly diatomic ions with a non-metal such as ArH' ArO'? ArN' and Arc' have been studied by numerous groups,4P7 owing to their high ion intensities and the risk of possible interferences in plasma MS.Sakata and Kawabata' found that the argon molecular ions are formed both in the plasma owing to a positive plasma potential induced by capacitive coupling with the coil and also behind the sampling cone where a secondary discharge can exist. Because the relative intensities of the metal argide ions (MAr+/M') in ICP-MS were found to be less than loP4 they play a secondary role in trace analysis especially in highly dilute aqueous solutions. In contrast in GDMS the relative abundance of the metal argide ions is much higher compared with ICP-MS.8 The formation of some metal argide ions (e.g.NaAr+ CuAr' ZnAr' and PtAr') in a GD was investigated by van Straaten' using MS. Whereas the relative abundance of most metal argide ions of interest is usually low (MAr'/M' < for Cu and Zn this ratio can go up to 0.01-0.1 depending on the discharge conditions. Barshick et al.' observed the periodicity of diatomic metal noble gas adduct ions with neon argon and krypton in dc-GDMS. However the measured high intensity of ZnAr' ion currents of 30% relative to Zn' in dc-GDMS cannot be explained. In a previous paper" the energy distribution of different types of atomic ions (Ga' As' Si' and C') and argon molecular ions (ArH' SiAr' Arc' and Ar,') in rf-GDMS were reported. Because singly charged atomic ions of analyte and argon molecular ions were found to have a higher average ion energy (about 10eV) compared with the argon ions (Ar') an effective energy separation of analyte ions of the sample and their argon molecular ions from atomic argon ions can be achieved by setting a particular energy window for the double-focusing mass spectrometer.Although ICP-MS is a widely used MS analytical method the periodic nature of argon molecular ions in an ICP has rarely been investigated. Therefore systematic investigations of the distribution of argon molecular ions in ICP-MS com- pared with LA-ICP-MS and GDMS could be helpful in understanding ion formation processes. High accuracy and precision of analytical results in plasma MS techniques for trace ultratrace and isotopic analysis of inorganic materials can be obtained if the ion interference problems of atomic ions of the analyte with molecular ions are overcome.This is possible by analysing interference-free isotopes of analyte by correcting the results using measured molecular ion intensities or by applying a mass spectrometer Journal of Analytical Atomic Spectrometry September 1996 Vol. 11 (643-648) 64340 6Q 80 100 120 140 160 180 200 Mass (u) Fig. 1 ions from atomic ions of the analyte as a function of mass Mass resolution required for separation of argon molecular with a high mass resolution (e.g. a double-focusing mass spectrometer). The mass resolution required for the separation of argon molecular ions from atomic ions of the analyte as a function of mass where an interference is possible is shown in Fig.1. The mass resolution required for separating argon molecular ions from the atomic ions of the analyte varied between 1800 for the interference of LiAr' and Ti' ions at mass 47 u and 130 000 for the interference of VAr' and Zr' ions at mass 91 u. In the present paper the formation of diatomic argon molecular ions in different types of plasmas is discussed. In order to explain the experimental results obtained ion potential curves for argon molecular ions with the elements of the 2nd and 3rd period in the Periodic Table of elements were calcu- lated by means of the quantum chemical density functional method [linear combination of atomic orbitals-density crk+ pFeAr* functional theory-local spin density approximation ( LCAO-DFT-LDA)] .EXPERIMENTAL An important task in our laboratory is the trace analysis and depth profiling of semi- and non-conducting materials such as high-resistance GaAs compact ceramics and thick non- conducting oxide or ceramic layers. Therefore an rf-GD ion source has been designed which can easily be coupled to a commercial mass spectrometer that was originally used with an ICP ion source. The ICP and the rf-GD ion sources can be changed in 30 min. The mass spectrometer with interchange- able ICP and rf-GD ion sources can be used for the analysis of solids and liquids. The experimental details and analytical capabilities of rf-GDMS have been described previously.lO*" The experimental parameters of the MS methods applied to the determination of argon molecular ions are summarized in Table 1.The rf-GDMS and ICP-MS measurements were carried out using the double-focusing mass spectrometer (Element from Finnigan-MAT Bremen Germany) with reverse Nier-Johnson geometry at different mass resolutions. For comparative ICP-MS and LA-ICP-MS measurements of the abundance distribution of argon molecular ions a quadrupole mass spectrometer (SCIEX ELAN 5000 from Perkin-Elmer) was used. For ICP-MS studies of metal argides a standard solution of the metals in nitric acid [from the National Institute of Standards and Technology (NIST)] was used. The concentration of each metal was 200 pg 1-I. High-purity metals and GaAs were investigated with LA-ICP-MS and rf-GDMS. The reproducibility of the molecu- lar ion intensities measured by ICP-MS LA-ICP-MS and LA-ICP-MS (five determinations) was about & 5%.THE0 RY 'The numerical calculations for the ion potential curves con- sidered in the present paper were performed within the frame- work of the DFT in the LDA. The influence of gradient corrections on the LDA12*13 will be discussed in a forthcoming 13aper.l~ The effective one-particle Kohn-Sahm equations were Table 1 Experimental parameters of MS methods for the determination of' argon molecular ions MS method Ion source ICP-MS Atomization and ionization in ICP- Rf power 1200 w Frequency of generator 27.12 MHz Coolant gas flow rate 14 1 min-' Auxiliary gas flow rate 0.7 1 min-' Nebulizer gas flow rate 1 1 min-' Meinhard nebulizer LA-ICP-MS Laser ablation- Ionization in inductively coupled plasma- Nd-YAG laser Rf power 1050 W Frequency of generator 35 MHz Wavelength 266 nm Coolant gas flow rate 13.5 1 min-' Pulse width 10 ns Auxiliary gas flow rate 0.7 1 min-' Repetition 20 Hz Nebulizer gas flow rate 0.8 1 min-' frequency Cross-flow nebulizer Rf-GDMS Sputtering and ionization in r$GD- Frequency of generator 13.56 MHz Operating pressure 0.5-5 hPa Rf power 20-30 W Electrical Ion separation ion detection Double focusing mass spectrometer SEM (reverse Nier-Johnson geometry) Faraday cup Mass range Mass resolution (m/Am) 300 1-260 u 3000 7500 Quadrupole mass analyser CEM Mass resolution (Am) x0.8 Mass range 6-240 u Double focusing mass spectrometer SEM (reverse Nier-Johnson geometry) Faraday cup Mass resolution (m/Am) 300 Mass range 1-260 u 3000 7500 644 Journal of Analytical Atomic Spectrometry September 1996 Vol.11solved with a wave function. For this the 'Amsterdam density functional' program (ADF) was used which has the following characteristic^:'^^'^ all integrals are evaluated numerically; the densities are fitted to a sum of Slater-type orbitals; and the basic set used had triple-zeta quality. A more detailed discussion will be given in ref. 14. In general rare gas atoms do not form molecules with metals or non-metals (Fig. 3) because the interaction energy of any atom with a rare gas atom is of the order of only a few meV caused by weak van der Waals interactions. However under plasma conditions rare gases can form fairly strongly bound molecular ions. The binding energy in such ions is of the order of that which is usual for chemical bonds a few eV.RESULTS AND DISCUSSION Numerous investigations on the interferences of atomic ions by molecular ions in plasma MS have been rep~rted.'-**'~*'~ In the present work the ion intensities of metal argides in ICP-MS were measured. The intensities of diatomic metal argide ions relative to metal ions are less than 3 x and vary as a function of the metal over about three orders of magnitude in ICP-MS (Table 2). Theoretically calculated binding energies can be helpful to explain metal argide ion stabilities. In Fig. 2 the metal argide ion intensities and calcu- lated binding-dissociation energies from Bauschlicher et a1.l' show a good correlation. The binding energies of molecular ion systems containing transition metals (e.g. NiAr + or CuAr' ions) are generally larger than for metal argide ions with main group metal atoms (e.g. MgAr' or NaAr' ions).Using the curve in Fig. 3 unknown dissociation energies of metal argide ions can be estimated e.g. the relative intensity of AgAr' ions in ICP-MS was determined to be lop6 and the dissociation energy of this metal argide ion can be estimated to about 0.25 eV. Table 2 Relative ion intensities of metal argdes in ICP-MS Argide LiAr + BeAr+ NaAr + MgAr+ AlAr + SiAr+ ScAr+ VAr + CoAr + MnAr+ NiAr+ CuAr' AgAr + Relative ion intensity (MAr+/M + ) 2.6 x 2.0 x 3.6 x 10-7 3.7 x 10-7 3.7 x 1 0 - 5 1.5 x 10-5 1.1 10-5 3.5 1 0 - 5 2.6 x 10-4 1.0 10-5 1.3 x lop6 3.1 x lop6 1.0 x Possible interference with analyte ion 4 6 ~ i + 47Ti+ 49Ti + 63cu + (j7Zn + 68Zn+ 69Ga+ 70Ge+ 85Rb+ 91Zr + 99Tc+ 64zn+ 6 4 ~ i + 65cu + 66zn 7 9 5 ~ ~ + 108pd+ llopd+ 11oCd+ 7 3 103~h + l05pd + l47sm+ 149sm+ 9 7 + 0.1 Q.2 0.3 0.4 0.5 Dolev Fig.2 Correlation of metal argide ion intensities and calculated bindingdissociation energies from Bauschlicher et all9 The potential curves for ArH' and NaAr' ions and the neutral species are illustrated in Fig. 3. The ArH' ion can indeed be compared with the isoelectronic HC1 molecule. The ArH+ ion is not a simple complex of argon with the proton which is bound only by an induced dipole interaction as 60% of the positive charge is located at the argon. A different ion potential curve can be seen for the sodium argide cation (NaAr+) as an example of a metal argide having a metal atom with a low ionization energy.In contrast t a the stable ArH' ion the sodium ion is only weakly bound to the argon atom with a binding energy of 0.2 eV. The calculated high binding energies of the ArH' ion of about 3.4 eV correlate with high ion intensities namely the most abundant argon molecular ion in an ICP is the ArH' ion.20 Owing to the high intensity of ArH' ions isotopic analysis of potassium (determination of the isotopic ratio 39K 41K) under normal plasma conditions (at an rf power of 1400 W) is impossible. By reducing the rf power and increasing the nebulizer argon gas flow (under cold plasma conditions2') the intensity of ArHf ions decreases by 3-4 orders of magni- tude.22 In Table 3 the ion intensities of some argon molecular ions bound with a non-metal relative to argon ions in ICP-MS (measured using the experimental parameters in Table 1 ) are summarized.The effects of varying the experimental parameters (e.g. sampler-skimmer spacing or nebulizer gas flow rate) on the intensities of argon molecular ions are discussed in ref. 23. In general in ICP-MS the argon molecular ions bound with a non-metal were observed to have higher intensities compared with metal argide ions. There seems to be a concentration effect for some non-metal-argon molecular ions (e.g. for ArH + and ArO') because the intensities of H + and O+ ions which arise from the water matrix are higher than those of the metal or other non-metal (e.g. P' S' or C1+) ions from the sample (the concentration of each element in the standard solution was 200 pg 1-l). In order to explain these experimental results in more detail the ion potential curves were calculated for the elements in the 2nd and 3rd period in the Periodic Table of elements by means of the quantum chemical density functional method (LCAO-DFT-LDA).The calculated binding energies as a function of the atomic number for the equilibrium distances are plotted in Fig. 4. The periodicity in the binding energies can be clearly seen small at the beginning of the period for metal argide ions and large at the end of the period which means that the argon molecular ions with non-metal are strongly bound. The trend in binding energies can be under- stood simply by considering the electronegativity of the metal or non-metal. The electronegativities used here are simply Pauling's electronegativities.A high electronegativity supports the formation of a covalent-type of bond between argon and the non-metal in the molecular ion. The low electronegativity of the metals means that the positive charge is strictly located on the metal in the metal argide ion. The calculated binding energies of the ions are in good qualitative agreement with experimental data4 and other theoretical calculation^.^^ A systematic overbinding by about 0.5 eV was obtained which is typical for the LDA-DFT treatment (see for example ref. 25). The only distinct difference appears for ArO+ where the largest binding energy in the series was obtained whereas the experimental values are rather ~maller.~ This cannot be explained by the above-mentioned LDA overbinding. However Journal of Analytical Atomic Spectrometry September 1996 Vol.1 1 6453 . >r F C w 1.5 2 5 3.5 4.5 5.5 8.5 7.5 8.5 Interatomic Distance (a,) 2 . h P C W -2 - 1.5 2.5 3.5 4.5 5.5 6.5 7.5 8.5 9.5 10.5 11.5 Interatomic Distance (ao) Fig. 3 Potential curves for ArH+ and NaAr' ions and the neutral species Table 3 Relative argon molecular ion intensities in ICP-MS Argon Relative ion intensity Possible interference 40ArH+ 4.4 4 0 ~ ~ 0 + 1.0 10-3 56Fe+ 40ArP+ 1.9 x 10-4 llGa' 40ArS+ 2.4 10-4 72Ge+ 73Ge+ 74Ge+ 40ArC1 + 6.3 x 10-4 15As' 77Set molecular ion ( ArX +/Art ) with analyte ion 4 1 ~ + a.o 1 Electronegathrily H LI B N F N8 A1 P CI Ha Ba C 0 Nb Mg Si S X Fig. 4 Binding energies for argon molecular ions as a function of the atomic number for the equilibrium distances and electronegativity of elements more accurate calculations including gradient corrections to the LDA are in progress.14 In Table 4 the relative intensities for the argon molecular ions in different plasma MS methods are compared using a GaAs matrix.In different plasmas ion formation occurs in an argon plasma at different argon pressures with different electron densities and plasma temperatures which results in different degrees of ionization of the elements and formation rates of molecular ions. This is clearly seen for the molecular ion formation in ICP-MS compared with rf-GDMS. In com- parison with ICP-MS higher metal argide ion intensities for the GaAr+ and AsAr' ions and argon dimer ions were observed in rf-GDMS. On the other hand lower ion intensities Table 4 plasmas Comparison of argon molecular ion intensities in different Relative ion intensities ArH+/Art ArO '/Art ArN '/AT+ Ar,+/Ar' GaAr + /Ga ' AsAr +/As ' ICP-MS LA-ICP-MS Rf-GDMS 4.4 N.D.* 9.5 x 10-3t (5 x x 10-2) 1.1 x 10-3 2.5 x 10-5 3 x 10-4t (4 x 10-5-2 x 10-1) 3.5 x 10-5 6.9 x 10-6 1.5 x 10-5t (2 x 10-6-8 x 10-3) 2.5 x 10-3 3.0 x 10-3 8 x lo-'? (1 x 10-1-1) 1.5 x 10-5 4.0 x 10-5 7.7 x 10-3t (4 x 10-2-2 x 10-3) (1.5 io-2-i.o x 10-3) 4.5 x 10-5 4.0 x 10-5 2.6 x lop2? * N.D.not determined. t Under optimal conditions (rf power 25 W and operating argon pressure 2 hPa). were measured for non-metal argon molecular ions ( ArH' ArO' and ArN'). In GDMS a high ArH' ion intensity was observed by Tardy et aLZ6 when hydrogen was added to the argon plasma gas.The difference in the argon molecular ion intensities between ICP-MS and rf-GDMS in the present measurements can be explained by different atomic densities in the ion sources; for instance the density of excited argon AP* in an ICP is about one to two orders of magnitude higher than in an rf-GD whereas the atomic density of the sample atoms (Ga and As) in an ICP is about two orders of magnitude lower compared with an rf-GD. The formation of argon molecular ions can be explained by associative ionization similar to a Hornbeck-Molnar process:27 Arm* + X -+ ArX' + e- where X is a metal or non-metal atom and Arm* is a metastable excited argon atom which induced the Penning ionization in an argon plasma; or by an association reaction of an ion (X') and an argon atom i.e.X' + Ar + ArX' (2) Both reactions for the formation of a molecular ion are more probable in comparison with ionization by electron impact of a neutral argon molecule ArX + e- - ArX' + 2e- (3) Furthermore the association reaction of an atomic argon ion with a metal atom Ar' + X + ArX+ (4) (1) 646 Journal of Analytical Atomic Spectrometry September 19896 Vol. 1 1is improbable. No argon molecular ions were observed by electron beam sputtered neutral mass spectrometry (SNMS) or by bombardment of solid surfaces with argon ions in secondary ion mass spectrometry (SIMS).22 The fact that neither surface-sensitive technique is a plasma MS method must be considered. For the formation of a greater variety of molecular ions (e.g. oxide ions) with high intensities in SIMS other ion formation mechanisms can be assumed to be occurring during the sputtering process.In ICP-MS and LA-ICP-MS similar ion intensities were measured for metal argides (MAr'; M = Ga As Be or V) and argon dimer ions (Ar,'). This can be explained by the same molecular ion formation processes in an ICP in both methods. In contrast for an oxygen- and nitrogen-free matrix (a high- purity GaAs wafer was investigated by LA-ICP-MS) lower absolute intensities of ArO' and ArN' ions were observed in LA-ICP-MS compared with ICP-MS (where the GaAs sample was dissolved in nitric acid). However the relative ArO'/O' and ArN+/N' ion intensities measured by LA-ICP-MS are more similar to those for ICP-MS. Whereas the formation of argon molecular ions as a function of different plasma parameters in ICP-MS is well known in an rf-GD this has rarely been investigated. Therefore the argon molecular ion intensities were measured as a function of the argon pressure in rf-GDMS.The dependence of the relative intensities of GaAr' AsAr' Ga' and As' ions on argon pressure in an rf-GD for a GaAs sample is shown in Fig. 5. The metal argide ion intensity relative to the argon ions (GaAr'/Ar+ and AsAr'/Ar+) varied over about one to two orders of magnitude with a maximum at 2 hPa. The curves for the absolute intensities of metal argide ions (GaAr' and AsAr') and for the atomic ions (Ga' and As') as a function of argon pressure with a maximum sputter rate at 2 hPa correlate with these graphs. Only relative ion intensities are given in Fig.5 to ensure a clear presentation. With increasing argon pressure the metal argide ion intensities relative to the metal ions (GaAr'/Ga' and AsAr '/As+) decrease. The dependence of the relative ion intensity of argon molecu- lar atomic ions with a non-metal argon oxide ions (ArO') and argon nitride ions (ArN') to the intensities of atomic ions 0' and N' or Ar+ ions on argon pressure in an rf-GD is shown in Fig. 6. In contrast to the metal argide ions the non-metal argon molecular ions increase significantly with increasing argon pressure. The distributions of ion intensities t I 1 o-2 L. .g 10" al w - al .- c t lo4 rY 1 o - ~ 2 4 8 Pressure / hPa 1 0 6 ' ; - " . I . . ' I * . . I ' Fig.5 Dependence of the relative intensity of metal ions and metal argide ions on argon pressure in an rf-GD.Sample high-purity GaAs; rf power 25 W 103 1 o2 10' )r loo 4-0 .- v) 5 lo-' 2 10-2 - a a oz - 10" 1 o4 i 0-5 10" 1 2 4 8 Pressure/hPa Fig.6 Dependence of the relative intensities of non-metal ions and non-metal argon molecular ions on argon pressure in an rf-GD. Sample high-purity GaAs; rf power 25 W for non-metal argon molecular ions and atomic non-metal ions as a function of argon pressure are comparable. Consequently from the similar distribution of metal argide ions and non-metal argon molecular ions to the metal ions and non-metal ions respectively the association reaction (2) can be assumed to be dominant for their formation i.e. X' + Ar + ArX'. Furthermore the formation of argon mol- ecular ions by associative ionization reaction (1) is also probable i.e.AP* + X -+ ArX' + e-. More stable non-metal argon molecular ions (see the calculated binding energies in Fig. 4) compared with metal argide ions were formed with higher ion intensities for increasing argon pressure. Finally the argide ion formation of lanthanides in ICP-MS was investigated. In Fig. 7 the dependence of praseodymium argide (PrAr') ion intensity as a function of rf power and nebulizer gas flow rate is demonstrated. A maximum ion formation rate at an rf power of 1250 W and at a nebulizer gas flow rate of 1.1 1 min- in ICP-MS was measured. Similar behaviour was found for all other lanthanide oxide ions in an ICP and has been confirmed by Brenner.,* In Fig. 8 the abundance distribution of lanthanide argide ions as a function of atomic number is compared with the distribution of oxide ions in ICP-MS.The distribution of oxide Nebulizer Gas Flaw Ratell mid 0.95 1 .o 1.05 1.1 1.15 I Pr Ar* 1 200 1250 1300 1350 RF-Power1 W Fig. 7 Dependence of PrAr' ion intensity as a function of rf power and nebulizer gas flow rate 0 = rf power variation; x = variation in nebulizer gas flow Journal of Analytical Atomic Spectrometry September 1996 Vol. 1 1 647MO* La Pr (Pm) Eu Tb Ho Tin Lu Ce Nd Sm Gd Dy Er Yb I I I I I I I Fig. 8 Comparison of the abundance distribution of lanthanide argides as a function of atomic number with the distribution of oxide ions in ICP-MS ion intensities for REEs in ICP-MS is similar to the abundance and distribution in laser ionization and spark source ionization mass spectrometry and correlates with the electronic properties of REEs and bond dissociation energie~.~ The abundance and distribution of argide ion intensities of the REEs is similar to that of rare earth oxide ions.The intensities of argide ions compared with oxide ions of the REEs are about three to four orders of magnitude lower. The experimental or theoretically calculated dissociation energies of lanthanide argides are unknown. It can be assumed that a lower ion intensity for lanthanide argides means lower stability and therefore lower dissociation energies of these species compared with the oxides. CONCLUSIONS A systematic study of the types of molecular ions in ICP-MS LA-ICP-MS and rf-GDMS can be used for estimating mass spectral interferences of molecular ions and atomic ions of the analyte at the same nominal mass.Therefore knowledge of molecular ion formation and abundance and distribution is of considerable importance for MS trace ultratrace and isotopic analysis of inorganic materials. In ICP-MS the non-metal argon molecular ions were formed with higher intensity com- pared with the metal argides. This could be explained by theoretical calculations of the binding energies. A correlation of metal argides with bond dissociation energies of diatomics was found. In ICP-MS and LA-ICP-MS similar intensities of rare gas molecular ions were measured. In rf-GDMS the formation rate of metal argides is higher than in ICP-MS. The abundance and distribution of lanthanide argide ions was found to be similar to the lanthanide oxide ions and can be determined by the electronic structure of the lanthanides.REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Martin T. P. Angew. Chem. 1986 98 197. Mark T. D. and Castleman A. W. Jr. Adv. At. Mol. Phys. 1985 20 65. Becker J. S. and Dietze H.-J. J. Anal. At. Spectrom. 1995,10,637. Nonose N. Matsuda N. Fudagawa N. and Kubota M. Spectrochim. Acta Part B 1994 49 955. Barshik C. M. Smith D. H. Johnson E. King F. L. Bastug T. and Fricke B. Appl. Spectrosc. 1995 49 885. Shao Y. and Horlick G. Appl. Spectrosc. 1992 45 143. Sakata K. and Kawabata K. Spectrochim. Actu Part B 1994 49 1027. Shao Y. and Horlick G. Spectrochim. Acta Part B 1991,46 165. van Straaten M. Dissertation University of Antwerp 1993. Saprykin A.I.Becker J. S. and Dietze H.-J. J. Anal. At. Spectrom. 1995 10 897. Saprykin A. I. Becker J. S. and Dietze H.-J. Fresenius' J. Anal. Chem. in the press. Becke A.D. Phys. Rev. A Gen. Phys. Ser. 3 1988 38 3098. Perdew J. Phys. Rev. B Solid State Ser. 3 1986 33 8822. Seifert G. Becker J. S. and Heinemann A. to be published. Boerrigter P. M. te Velde G. and Baerends E. J. Int. J. Quantum Chem. 1988,33 87. te Velte G. and Baerends E. J. J. Comput. Phys. 1992 99 84. Shibata N. Noriko F. and Masaaki K. Spectrochim. Actu Part B 1992 47 505 Ahmed F. Belt R. F. and Gashurov G. J. Appl. Phys. 1986 60 836. Bauschlicher C. Jr. Partridge H. and Langhoff S. R. Chem. Phys. Lett. 1990 165 272. Gray A. L. in Inorganic Mass Spectrometry ed. Adams F. Gijbels R. and van Grieken R. Wiley New York 1988 p. 257. Tanner S. D. Paul M. Beres S. A. and Denoyer E. R. At. Spectros. 1995 Jan/Feb 16. Becker J. S. and Dietze H.-J. unpublished results. Lam J. W. H. and Horlick G. Spectrochim. Actu Part B 1990 45 1327. Wong M. W. and Radom L. J. Phys. Chem. 1989 93 6303. Johnson B. G. Gill P. M. W. and Pople J. A. J. Chem. Phys. 1993,98 5612. Tardy J. Poitevin J. M. and Lemperiere G. J. Phys. D Appl. Phys. 1981 14 339. Hornbeck J. A. and Molnar K. P. Phys. Rev. 1951,84 621. Brenner I. B. presented at the 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-13 1996 paper FP12. Paper 6/00818F Received February 5 1996 Accepted April 1 1996 648 Journal of Analytical Atomic Spectrometry September 1996 Vol. 11

ISSN:0267-9477    

DOI:10.1039/JA9961100643

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Spectrochemical Analysis of Trace Contaminants in Helium (Helium- Fluorine) Pulsed Discharge Plasmas* Irni Journal of Analytical Atomic Spectrometry I I ALEKSEI B. TRESHCHALOV ANDRE1 S. CHIZHIK AND ARNOLD A. VILL Institute of Physics Riia 142 EE2400 Tartu Estonia Time-resolved spontaneous emission and absorption spectra in the 115-860 nm spectral range were studied for high pressure He and He-F pulsed discharge plasmas the aim being the spectroscopic identification and on-line monitoring of transient and stable gaseous contaminants accumulated in an actual F laser gas mixture. Various radicals (CN CH C OH SiF and CF,) excited atoms (0 C Si N and H) molecules (CO 0 and N2) and molecular ions (N2+ and CO') were identified as contaminants. The accumulation and self- transformation kinetics due to plasmo-chemical reactions between these species were investigated.It is suggested that carbon oxygen and carbon monoxide species are desorbed as primary impurities from the metal electrodes during the sputtering of the electrodes from cathode (anode) hot spots. Secondary impurities such as transient radicals and more complex compounds are formed by plasmo-chemical reactions between primary and other trace impurities (H N and 0,) and fluorine. These reactions might be strongly catalytically activated on the surface of pure nickel particles sputtered from the electrodes. The sensitivity of the spontaneous emission methods was estimated to be better than 1 ppm for the detection of stable CO and N impurities in the He discharge plasma. Under static conditions N2 and 0 impurities accumulate at a rate of about 0.1 mbar d-' in He and He-F gas mixtures due to continuous outgassing of the laser chamber materials. Under F laser running conditions a marked increase in the rate of accumulation of 0 contaminants ( z 0.1 mbar per 5 x 105 shots) was observed.Oxygen is the main contaminant responsible for F laser output energy degradation because of the intracavity absorption at 157.6 nm in the oxygen dissociation absorption band. The strong absorption in the far VUV range (130-115 nm) observed in an aged He-F gas mixture was attributed to stable fluorine-containing compounds (tentatively identified as COF or HF molecules). In addition to the well known molecular fluorine emission band at 157 nm caused by the transition from the ionically bonded D' 3112g state two spontaneous emission bands (structural at 255 nm and continuous at 280 nm) were observed in the discharge of an He-F gas mixture.These new bands were attributed to transitions bet ween covalent 1 y bonded excited electronic states of the fluorine molecule. Keywords Fluorine laser; discharge; gas mixture degradation; vacuum ul traviole t-visi bl e emission-a bsorption spectroscopy ; plasmo-chemical reactions; radicals Molecular discharge lasers (excimers F2) are nowadays the most powerful directly pumped commercially available sources of coherent UV and VUV radiation. It is well known however that the critical component of these lasers is their gas mixture. Laser output power usually declines after the laser chamber has been filled with fresh gas due to highly reactive halogen *Presented at the 1996 Winter Conference on Plasma Spectrochemistry Fort Lauderdale FL USA January 8-1 3 1996.donor depletion and formation of contaminant impurities in the gas mixture caused by discharge-induced plasmo-chemical reactions.'-' Even trace amounts ( z 10 ppm) of some contami- nants manifest themselves in a loss of output energy and cause spatial spectral and temporal degradation of the laser beam due to development of discharge instabilities.8-'' Output par- ameters of VUV gas lasers are particularly sensitive to gaseous impurities which can lead to intracavity absorption of VUV radiation or pre-ionization photons." These contaminants are accumulated continuously and removed from the laser chamber only by refilling with fresh gas.The development of a new generation of 'sealed-off' high pressure gas lasers with a quantitative improvement in gas lifetime'3.14 prompted us to initiate a spectrochemical investigation of the contaminants formed within pulsed discharge-pumped lasers under real operating conditions. Sophisticated gas chromatographic mass spectrometric and Fourier-transform infrared spectrometric methods are usually used for the measurement of specific gaseous imp~rities.~-~ However all these techniques are invasive and they only allow the investigation of stable final plasmo-chemical products accumulated in gas mixtures. Nowadays the most sensitive and more importantly non-intrusive discharge plasma diag- nostic methods are based on spontaneous emission and laser- induced fluorescence techniques characterized by high tem- poral and spatial resolution and species selectivity.It is well known that in a non-stationary He discharge plasma high energy electrons which most efficiently excite and ionize molecular additives are formed mainly at the initial breakdown stage of the discharge. Another mechanism of efficient exci- tation of impurities is connected with fast energy exchange chemical reactions between minor additives and excited helium atoms He* excimer He2* molecules and molecular He2 + ion^.'^*'^ For the formation and investigation of short-lived excited species a high pressure fast pulsed discharge is neces- sary because the formation of transients has to be faster than the possible quenching and radiative decay processes. This paper presents spontaneous emission and absorption spectral data in the range 115-860 nm for high pressure He (He-F,) glow discharge plasmas under fast pulsed excita- tion.The aim was the spectroscopic identification and on-line monitoring of transient and stable gaseous contaminants accumulated in a real VUV fluorine laser gas mixture. EXPERIMENTAL The experimental arrangement for measurement of time-resolved spontaneous emission and absorption spectra in a discharge plasma is shown schematically in Fig. 1. The object of investi- gation is the discharge plasma in a commerci- ally available miniature excimer laser (PSX-100) (MPB Technologies Dorval Canada). A traditional thyratron- switched charge-transfer circuit with a storage capacitor of 12 nF and a charging voltage of 8 kV is used in this laser to generate the pumping pulse for the transverse electrical dis- charge.The length of the active medium is 15 cm; the solid Journal of Analytical Atomic Spectrometry September 1996 Vol. 1 I (649-659) 649Fig. 1 Schematic diagram of the experimental apparatus nickel electrode spacing is 0.3 cm and the discharge width 0.2 cm. Automatic homogeneous UV pre-ionization is performed by a surface discharge on two BaTiO ceramic plates that are placed laterally on both sides of the cathode electrode. Pre- ionization discharge is initiated on the growing front of the main discharge voltage. These ceramic plates also serve as extremely low-inductive peaking capacitors with a total capaci- tance of 12nF for the rapid pulsed homogeneous discharge excitation of the high pressure (up to 10 bar of He) gas mixtures. It was not possible to make reliable and direct measurements of discharge voltage and current temporal behaviour for the very compact design of the pumping circuit used here.From electrotechnical considerations the current rise time can be estimated to be 10ns and the discharge peak current to be 10 kA which gives a maximum discharge current density of ~2 kA an- and a pumping power density of ~ 2 0 MW cm-,. This laser operated with a gas mixture of 6 bar of He and 5 mbar of F gives a pulse energy of M 1 mJ at 157.6 nm (D' 3112g +A' ,112 transition in molecular fluorinelg) with a rep- etition rate up to 100 Hz and a gas lifetime of lo6 pulses.The laser chamber with a volume of ~ 1 5 0 0 cm3 is made from aluminium; Viton O-rings are used for sealing the windows. High voltage insulators mounted inside the laser chamber are made from PTFE. The optical cavity is composed of two uncoated MgF plates. The spontaneous VUV (1 15-220 nm) emission of the dis- charge plasma was detected along the laser axes with a 0.5 m VUV grating monochromator (M-12) (VEMO Tartu Estonia) with a 1/12 relative aperture (resolution of the monochromator 0.05 nm) and an FEU-142 solar blind PMT (time resolution about 20ns). The spontaneous UV-visible (UV-VIS) (220-860 nm) emis- sion was collected with a quartz lens through a diaphragm with a 1/50 relative aperture and focused onto the entrance slit of a 0.5 m grating monochromator (MDR-23) (resolution 0.03 nm) with an FEU-79 PMT (time resolution 10 ns).The signal from the PMT was detected by a BCI-280 box- car integrator interfaced with a computer for data storing and processing. Two different registration regimes were used (1) time-integrated (with an integrator gate of 5 ps) for rec- ording the spectra and (2) time-resolved (with an integrator gate of 10 ns) for detection of the transient kinetics of excited species in the discharge. Relative intensities of measured emis- sion spectra are reported in this paper without corrections for the absolute spectral response of the monochromator and PMT combination. A laser spark was used as a continuum pulsed light source for measurement of low-resolution absorption spectra of stable plasmo-chemical products in the UV-VUV range.20 The light from the laser spark is transmitted through the laser resonator length and compared with the transmission of the evacuated laser chamber.A light pulse with an energy of 2 mJ from a tunable dye-laser (VL-lo) pumped by an excimer XeCl laser was focused inside the gas cell containing Ar at 10 bar and trace amounts of Xe as an impurity. The laser spark is initiated by multiphoton resonance breakdown of the dense gas. The dye-laser wavelength at 440nm is tuned to the four-photon resonance with the 4f states of Xe.21 The emission spectrum of a hot and dense spark plasma consists of an intense black- body continuum and several broad bands (243 220 190 167 160 nm) which presumably belong to excited ion and molecu- lar argon dimers.The VUV cut-off threshold of this source is limited to 112 nm by the transmission of the MgF output window of the gas cell. Particular care was taken to provide a reliable leak-free system for gas filling and pumping of the laser. Stainless-steel and copper tubes with Swagelok fittings were used for He F and other gases. In order to minimize possible impurities such as H,O 02 N2 CO CO and hydrocarbons in the He gas (initial purity 99.99%) additional purification during the gas filling stage was performed by passing the gas through a zeolite trap immersed in liquid nitrogen. Hydrogen which may be present as a contaminant in the He carrier gas at a concentration of up to lOppm is not removed by the cold zeolite trap and is always present in our gas mixture. Other commercially available gases which served as minor additives to our gas mixtures were used without further purification.The laser chamber and gas system were evacuated through a separate cooled zeolite trap to a vacuum of not better than lo-' mbar to avoid 'back-~treaming"~ of oil vapour from the rotary vacuum pump. Flushing of the laser chamber with pure He was usually carried out before refilling it with fresh gas. RESULTS AND DISCUSSION Fresh and Aged Helium Gas Mixtures Spontaneous emission spectra The measurement of the reference spontaneous emission spec- trum of pure He is the first step towards the identification of impurities produced in the discharge plasma. Helium was purified by passing it through a cold zeolite trap and emission spectra were measured immediately after the laser chamber had been filled with the gas at a pressure of 6 bar.A portion of the time-integrated spectrum of pure He in the UV-VIS range is shown in Fig. 2. Most of the observed broad emission 650 Journal of Analytical Atomic Spectrometry September 1996 Vol. 1110 . . I ' " " ' " . ' . fresh gas filling He2 - v) .- 3 - He 6 bar He2 c 300 350 400 450 5 00 Wavelengthhm Fig. 2 Time-integrated spontaneous emission spectrum of the dis- charge in fresh specially purified He. Only molecular He,* bands and trace N2+ CN and HP impurity lines are observed bands belong to transitions between several excited He,* excimer states which are formed after the discharge pulse from the rapid chemical reactions between He+ He* He and electrons under high pressure conditions.All of the observed He2* bands were identified according to the assignments in refs. 23 and 24 and are shown in Table 1. Only trace impurity bands from nitrogen molecular ions N2+* B -+X ,Zg+ and the hydrogen atomic HP line are detected in the initial visible emission spectrum. Some new contaminant bands for example CN* B ,Z+ -+X 2 Z + appear and continuously increase in intensity during the scanning of the spectrum. It was found that after the first several thousand discharge shots significant transformation of the emission spectra (par- ticularly in the VUV range) was observed due to the rapid formation of contaminants in the discharge and accumulation of these contaminants in the aged gas mixture. The spontaneous time-integrated emission spectrum of the same pure He gas mixture after 1.5 x lo6 shots changes markedly due to the accumulation of several impurities in the gas mixture (see Fig.3). Lines originating from atomic or molecular He mostly disappear and very strong emission bands from contaminant radicals (C,* CN* CH* and OH*) molecules (O,*) and molecular ions (N,'*) are observed and can be identified. Positions and assignments of the most intense bands are given in Table 1. For comparison of the fluorescence intensity scales in Figs. 2 and 3 the HP line should be taken as the reference (the intensity of this line does not change during the running of the laser). In the red region of the fluorescence spectrum (see Fig. 4) of an aged He gas mixture at 6 bar after 1.5 x lo6 shots Swan bands of C,* radicals the Ha (656.3 nm) line from atomic hydrogen several lines from He* (587.6 nm is the most intense) several well known red lines from atomic fluorine F* (see Table l) and the 777.5 and 844.6 nm lines from atomic oxygen can be identified. The relative intensities of the oxygen lines should be much higher than is the case in Fig.4; this is due to the poor sensitivity of the PMT cathode and the poor mono- chromator grating efficiency in the infrared region of the spec- trum. Atomic fluorine lines appear in the spectrum of the aged He gas mixture because before these experiments the laser chamber was passivated over a long period by the discharge in the He-F gas mixture. The metal fluoride film which is produced on the inner surface of the laser chamber and on the discharge electrodes provides a continuous source of trace amounts of fluorine during the running of the laser with the He gas mixture.It must be emphasized that all of the vibrational series for both C2* and CN* emission bands are well developed and the hot bands are unusually intense (such as the 1-1 2-2 3-3 2-3 3-4 and 4-5 transitions for CN* and the 1-2 3-4 4-5 5-6 and 6-7 transitions for C2* bands). It is obvious that in He gas at a pressure of 6 bar these radicals do not thermal- ize rapidly after plasmo-chemical reactions which populate selectively highly excited vibronic levels. It is difficult to measure the spontaneous emission spectrum of the He discharge in the VUV region after filling the laser chamber with fresh gas because of the rapid rate of accumu- lation of carbon impurities during the measurement of the spectrum.Fig. 5 shows the time-integrated VUV emission spectrum of the discharge in aged He after 1.5 x lo6 shots. The strong contaminant emission lines (see Table 1) belong to atomic carbon CO* A 'I'I-+X 'Z+ molecular bands and CO+ B 'Z+ +X 'C+ molecular ion bands. It is interesting that fairly strong hot emission lines from (v= 1,2) vibronic levels are observed in the fluorescence spectra of CO* and CO+*. This shows that these electronically excited species are created in highly excited vibronic levels and that at a buffer gas pressure of 6 bar vibrational relaxation is not complete during the radiative lifetime of CO* (7% 10 ns3') and CO+* (7x53 ns3') species. Rotational relaxation is however virtually complete.From the measured rotational contour of the individual CO+ (B-+X) 0-0 emission line the rotational temperature of CO+* ions is estimated to be 380f40 K. Emission lines from atomic nitrogen N* (120.0 and 149.5 nm) oxygen O* (130Snrn) and hydrogen H* (121.5nm) are observed. The relative intensities of the N* and H* lines at wavelengths around or shorter than 120nm should be much higher than they appear in Fig. 5; this discrepancy might be due to the absorption of some of the VUV emission by the thick (8 mm) MgF laser window and to the poor sensitivity of the PMT in the VUV region (PMT cut-off threshold 112 nm). The emission from two weak molecular bands (a structural band at 255 nm and a broad continuous band at 280 nm) is very difficult to attribute to any impurity molecules or radicals. These bands are tentatively assigned to new transitions between excited states of molecular fluorine The nature of these electronic states will be discussed later in this paper.Accumulation kinetics of impurities in the discharge The accumulation and self-transformation kinetics of some identified contaminants in pure He as a function of the number of discharge shots are shown in Fig. 6(a) and (b). On-line monitoring of impurities is controlled by the time-integrated spontaneous emission intensity of their specific spectral lines and bands (see Table 1) C* (193.1 nm) CO* (171.2 nm) CO+* (219.0 nm) O* (130.5 nm) N* (120.0 nm) F2* (255.5 nm) CH* (431.4 nm) C2* (516.5 nm) CN* (387.1 nm) N2+* (388.4 nm) HP* (486.1 nm) and 02* (351.6 nm).The most rapid accumulation rate is observed for C* impurities which quickly reach a maximum after x 6 x lo4 shots and do not increase during further running of the laser. The accumulation kinetics for CO* CO+ CH* and C2* impurities are fairly similar to each other. Emission signals from atomic and molecular nitrogen decrease continuously during the running of the laser. Nitrogen impurities which cause the initial level of the signal are present in He as trace additives. No kinetics were observed for the emission intensity of 02* and H* impurities. Only a slow increase in F,* emission was observed during the running of the laser in a He gas mixture. The emission from CN* radicals increases rapidly during the first 5 x lo4 shots which correlates with the initial rapid increase in the emission from C* species and then decreases slowly which correlates with the decrease in nitrogen impurities during the running of the laser.It is important to note that the formation of impurities is observed only under the discharge conditions. If the running of Journal of Analytical Atomic Spectrometry September 1996 Vol. 1 1 651Table 1 of the most intense characteristic lines are underlined Species Wavelengt h/nm Assignment Species Wavelength/nm Assignment He* 25 388.8 3p3P+2s3S j ~ ~ ~ * 23.24 335.6 5pn3 n +a3 C + 587.6 3d3D + 2p3P0 367.6 4pn3ng+a3Zu+ 706.5 3s3S+2p3PO 399.7 m3Cu+ 4 b3n ~ * 2 5 - 120.0 3s4P+2p3 4s0 445.7 j3Cu+ +b3n 149.5 3s2P+2p3 'Do 464.8 e3n,+a3xuf o* 25 130.5 3s3so+2p4 3P 513.3 E'lI,+A'Z,,+ 777.5 3 p5P + 3 s5s0 573.3 f3A,+b3n 3p3P+3s3SO 639.8 d3 C,+ + b3 l7 844.6 Identified atomic (ionic) emission lines and molecular bands observed for the discharge in He and He-F gas mixtures.The wavelengths ~ * 2 5 121.5 2pZPO-+ lS2S ~ 0 * 2 4 . 2 7 154.4 0-0 A'n+X'EC+ 486.1 4dZD + 2p2P0 157.7 2-2 656.2 3d2D+2p2Po 159.7 0-1 c * 25 156.1 2p3 3D0+2p2 3P 165.3 0-2 247.8 3s'P0 +2p2 'S 174.4 0-4 165.7 3s3P0 +2p2 3P 171.2 0-3 193.1 3s'P0+2p2 'D 173.0 1-4 F* 25 623.9 3p4so +3s4P 179.2 1-5 634.8 3p4so +3s4P 181.1 2-6 685.6 3p4D0 +3s4P 187.8 2-7 3p4D0 +3s4P 189.7 3-8 703.7 3pZPO +3s2P " - 219.0 0-0 B2C+ +X2Z+ 712.8 3pZPO +3s2P 211.2 1-0 739.8 3p4PO +3s4P 213.7 2-1 748.2 3p4PO +3S4P 230.0 0-1 755.2 3p4PO +3s4P 232.5 1-2 22 1.7 3p3 3D0 +3p2 3P 397.3 ,-o+ * 24,27 690.2 757.3 3p4PO 43s4P 235.2 2-3 0-0 Q1B2C+ +A211j 4s3P0 +3p2 'D 395.3 0-0 Qz 251.4 4s3P0 +3p2 3P (z2* 2427 436.3 4-2 d3lIg+a3& 250.6 251.9 4s3P0+3p2 'D 437.1 3-1 252.4 4s3P0 +3p2 3P 466.8 6-5 252.8 4s3P0 +3p2 3P 467.8 5-4 253.2 5S'PO +3p2 'S 468.4 4-3 288.2 4s'Po+3p2 'D 464.7 3-2 217.4 471.5 2-1 225.5 473.7 1-0 226.6 509.7 2-2 228.9 5 12.9 1-1 230.0 516.5 0-0 231.7 301.2 3 10.2 338.1 341.5 3 52.4 361.9 - 385.5 386.2 387.1 388.3 358.4 358.6 359.0 41 5.2 415.8 416.8 418.1 419.7 421.6 CH* 24 431.4 OH * 24.27 287.5 294.5 - - 307.8 312.1 3 18.4 3-3 B2C+ +X2C+ (I2* 24,27 2-2 1-1 0-0 2- 1 1-0 5-6 4-5 3-4 2-3 1-2 $ ; i ~ * 24 0- 1 0-0 A ~ A +x2n 2-1 A2Z'+X211 3-2 0-0 1-1 2-2 3-2 (:F2* 28,29 lq2 + * 2427 543.3 6-7 544.7 5-6 547.0 4-5 550.1 3-4 554.0 2-3 558.5 563.5 - 337.0 351.6 367.3 384.1 284.1 289.4 295.0 300.9 306.9 313.5 320.0 433.4 436.8 440.0 443.0 - 446.2 449.6 358.2 39 1.4 427.8 1-2 0-1 0-14 B3C,- +X3C,- 0-15 0-16 0-17 000-030 A'B1 +XIAl 000-040 000-050 000-060 000-070 000-080 000-090 3-2 A2C+-+X2n 0-0 0-0 1-1 2-2 3-3 1-0 B2C,+ +X2C,+ 0-0 0-1 the laser is stopped and then restarted after several minutes or hours the signals from all the impurities formed remain at the same levels that were achieved immediately before the interrup- and excited by the subsequent discharge shots and give emission signals from specific transient fragmentation products.tion of the running of the laser. This shows that all highly reactive species such as atoms and radicals are transformed Calibrated additions of impurities during the time between the discharge shots to stable gaseous compounds.These accumulated contaminants are destroyed For interpretation of these complicated accumulation kinetics and to reveal the nature of the stable contaminants the 652 Journal of Analytical Atomic Spectrometry September 1996 Vol. 1 1300 350 400 450 500 Wavelengthhm Fig. 3 Spontaneous emission spectrum of aged He (after 1.5 x lo6 shots). Lines originating from atomic or molecular He have largely disappeared. Strong emission bands are observed for CN* C2* CH* CO' N OH* and 02* 550 600 650 700 750 Wavelengthlnm Fig.4 Spontaneous emission spectrum in the red spectral region of aged He (after 1.5 x lo6 shots) I50 200 250 300 Wavelengthhm Fig.5 Spontaneous VUV emission spectrum of aged He (after 1.5 x lo6 shots).The strong emission lines belonbg to C* O* and N* atoms CO* molecules and CO' molecular ions. Two new weak molecular bands (structural at 255 nm and broad continuous at 280 nm) belong to transitions from a covalently bonded fluorine molecular state populated in a neutral energy exchange reaction uiz. F* + F +F,* + F influence of calibrated additions of impurities (02 CO CO N2 and H,) on the emission spectrum of pure He was studied. Fig.7 shows the dependence of the emission intensity from some specific impurity bands as a function of calibrated additions of N to pure He at 6 bar. The emission from N2* molecules N2+* ions and CN* radicals increases linearly with added N up to a pressure of 1 mbar of N2 whereas the 0 150 3 00 450 Number of shots/l000 Fig.6 Accumulation and self-transformation kinetics of some ident- ified contaminants in the He discharge as a function of number of shots I He 6 bar '.OO 0.20 0.40 0.60 0.80 N2 additive/mbar Fig. 7 Dependence of the emission intensity of some specific contami- nants on the calibrated addition of N to pure He emission from C2* and CH* radicals and C* 0* H* CO* and CO+* species remains independent of N addition. Fig. 8(a) and (b) shows the influence of calibrated additions of CO on the emission intensity of some specific species in a discharge of pure He. The emission from CO* CO+* and C2* species increases linearly with CO addition. Some saturation of CO* and CO+* emission signals is observed at a partial pressure of CO higher than 0.5 mbar. The emission from C* 0* CN* and CH* species increases linearly and then levels off for C* and O* at a partial pressure of CO higher than 0.5mbar and for CH* and CN* at a partial pressure of CO higher than 1.3 mbar.The emission intensity for H* N* and N2+* species is independent of CO addition. The influence of CO addition is very similar to that of CO. The addition of O2 to pure He up to a pressure of 0.5 mbar does not have a significant influence on the emission intensity from any of the above-mentioned impurity species except for the O* and 02* emission lines which increase linearly with O2 addition. Journal of Analytical Atomic Spectrometry September 1996 Vol. 11 6532 - C C .- .- m 'Z w 1 10 1 I ! I I (a) He.6 bar 8 - 0.00 0.25 0.50 0.75 I .oo CO additive/mbar Fig.8 nants on the calibrated addition of CO to pure He Dependence of the emission intensity of some specific contami- The addition of H up to a pressure of 1 mbar produces a linear increase in the emission from CH* OH* and H* species and a marked decrease in the emission from C2* CN* CO* CO+* N2* N2+* C* O* and N* impurities. It is interesting that the spontaneous emission spectrum of pure He with 0.5 mbar of added CO is very similar to that obtained for aged He gas after prolonged (1.5 x lo6 shots) running of the laser (see Figs. 3-5). It can therefore be postulated that the CO molecule is one of the main stable contaminants that is accumulated in a He gas mixture after prolonged running of the laser. From these experiments the sensitivity of the spontaneous emission method can be estimated bearing in mind that the geometry conditions used here have not been optimized.A detection limit better than 1 ppm (which is equivalent to 0.006mbar of impurities in our gas mixture) is obtained for the direct monitoring of stable trace impurities such as N or CO molecules. As regards transient species with strong emis- sion bands for example CN* and C,* radicals the sensitivity of their detection by the spontaneous emission method might be even higher; however no attempts were made to measure the absolute density of these transients in the plasma discharge. Time-resolved emission of excited species In order to investigate the mechanisms by which specific contaminant species are produced the time-resolved emission following a short discharge excitation was monitored for several specific impurities accumulated in aged He after pro- longed (1.5 x lo6 shots) running of the laser [see Fig.9(a) and (b)]. For our gas mixture which contains many trace contami- nants and where several competitive chemical reactions take place simultaneously after the initiation of the discharge it is very difficult to reveal all the precursors responsible for the formation of specific species. We will therefore only discuss some of the more probable reactions. The most rapid spontaneous emission kinetics are observed for H* N2* and He* transients which indicates direct high- energy electron-impact excitation of these species at the initial stage of the discharge. The next short-lived components are 10 8 6 4 1 2 2. E3 h c m .- C 5 0 a x v Y l .l . l l . I I I 0 100 200 300 400 500 .- C . 8 - E w .- 6 - 4 - 2 - 0 - & 0 200 400 600 800 1000 1200 Time/ns Fig.9 Time dependence of the spontaneous emission from some identified contaminants in an aged He gas mixture CO+* and N2+* molecular ions which are formed by rapid charge-transfer reactions of He2+ ions (the lowest X 2Cu+ state of the He,' ion has an energy of 22.45 eV) with CO and N r n o l e ~ u l e s . ' ~ ~ ~ ~ The rate of decay of CO+* emission kinetics is attributed to the decay of the CO+* excited electronic state B ,Z+ (radiative lifetime z x 5 3 ns3'). The emission decay time of N2+* ions is significantly shorter than the radiative lifetime of the N2+* excited electronic state B 'XUf (z x 60 ns3') which shows that rapid plasmo-chemical reactions or collisional quenching are important for N2+* ions. An alternative exci- tation mechanism for the emission of CO+* and N,+* ions could be Penning ionization of CO and N2 molecules by 3S1 and 'So metastable states of He (the corresponding energies are 19.82 and 20.62 eV).The emission from 0," impurities has a rapid rise time while the decay time constant of about 120 ns is fairly long. It seems that 0 molecules are directly excited by electron impact in the discharge; however the collisional quenching of the excited electronic state B 3Zu- is much faster than its radiative lifetime (z= 5 x s3'). As regards the emission kinetics of N* O* and C* excited atomic components it should be noted that a certain detectable delay of 15-20 ns is observed for the first emission maximum in comparison with the very rapid emission maximum for H* atoms.It seems that N* O* and C* atoms are produced by direct electron-impact excitation and consequent fragmen- tation of stable O N and CO molecules. Fast electron recombination processes such as CO+ +e+C* + 0 (0" +C)3' and N,++e-'N*+N could also be one of the mechanisms for the production of N* O* and C* atoms. The spontaneous emission decay profiles for these atomic species exhibit a fairly pronounced tailing. A strong second maximum in the emission kinetics of C* atoms and a small second maximum in the emission kinetics of N* atoms are observed at 100-13011s. This stage is a very late phase of the pumping discharge when the plasma has mostly recombined. This maximum can be explained by a chemical reaction between stable CO and N 654 Journal of Analytical Atomic Spectrometry September 1996 Vol.1 1molecules and long-lived highly energetic neutral species for example He2* excimer molecules. These molecules are produced from He* atoms by the following reaction He* + 2He+He2* +He (rate constant 2.5 x cm6 s-' 32). The long-lived triplet He2* electronic states have energies between 18.26 and 20.74eV,24 which is sufficient for the dissociation of CO and N2 molecules and for the resonant electronic excitation of atomic carbon and nitrogen fragments. The spontaneous emission kinetics for CO* impurities [see Fig. 9(a)] show a fast rise time immediately after the discharge excitation pulse and a long decay tail with a small second maximum at about 130 ns.This maximum in the CO* kinetics correlates with a strong second maximum in the emission kinetics of C* atoms. The formation of CO* (A 'II) molecules in the initial stage of the discharge is caused by the direct electron-impact excitation of CO molecules accumulated in the gas mixture from the previous discharge shots. This mech- anism however does not explain the long decay tail in the CO* emission kinetics [see Fig. 9(a)]. The emission A 'II-+X'Z+ transition of CO* molecules has a fairly short radiative lifetime (z M 10 ns3'); therefore the long decay kinetics reflect the destruction of long-lived precursors of the plasmo- chemical reaction for the formation of CO* A 'II molecules. He,* or some other electronically excited neutral molecule with a stored energy higher than 8eV could be such a precursor.It is possible that CO* molecules could also be produced in any fast reactions with the participation of C* atoms for example C* + O2 +CO*(A 'II) + 0. The analogous reaction where C atoms and CO molecules are in the ground electronic state with a fairly high rate constant k = 5 x lo-'' cm3 s-' has been studied by Fairbai~m.~~ In our reaction with the partici- pation of excited C atoms the rate constant might be even higher. The emissions from CH* and OH* radicals [Fig. 9(a) and (b)] have fairly short rise times and exponential decay tails with time constants of 160 and 75 ns respectively. These decay times are much faster than the radiative lifetimes of the investigated transitions (530 ns for the A 2A state of CH* 30 and 700 ns for the A 'C+ state of OH* radicals3').Therefore collisional quenching is very strong for these species. It appears highly unlikely that these radicals are formed from fast plasmo-chemical reactions with the participation of primary discharge-excited atomic species (C* H* 0* . . .). The spontaneous emission kinetics of the C,* and CN* radicals [Fig. 9(b)] have a specific 'incubation' delay time and a very long non-exponential decay tail. Since the radiative lifetimes of the corresponding transitions are fairly short (65 ns for the CN* B2C+ state3' and 12011s for the C2* d 3 n state3') these kinetics do not reflect the radiative decay of excited electronic states but rather the destruction of some long-lived ( M 1 ps) precursors.C,* radicals in the excited d 317 state could be formed from the association of two free carbon atoms by the following reaction C + C + He+C,* + He.34935 According to the potential energy level d i a g ~ a m ~ ? ~ ~ C2* radicals in the d 3 n state could be produced from carbon atoms in either the ground state 3P or in the excited 'D state. CN* radicals in the excited B 2Z+ electronic state could be produced by the reaction of long-lived metastable N2* mol- ecules in the A 3&,+ state with carbon atoms or some carbon- containing contaminant molecule. The highly reactive A &+ state of N is the lowest excited state with an energy of 6.1 eV and a radiative lifetime of about 2 s.~' The influence of meta- stable N as a possible long-lived transient contaminant on the performance of an XeCl laser has been discussed by Gabzdyl et al." This could explain the linear dependence of CN* fluorescence on N addition (see Fig.7) and the connec- tion between the accumulation kinetics of CN* N2+* and C* transients [see Fig. 6(a) and (b)]. If it is assumed that the concentration of carbon-containing impurities is proportional to the emission intensity of the emitted C* species and that the concentration of metastable N is linearly related to the emission of N2+* impurities in the discharge the CN* radicals should be a product of these precursors which is in fact observed in Fig. 6(b). The rise and decay times of the spontaneous emission kinetics of the molecular F2* band at 255 nm depend strongly on the density of the fluorine impurities.For trace concen- trations of fluorine in an aged He gas mixture these kinetics are fairly slow [see Fig. 9(a)]. However for He with fluorine added at a pressure of 4.5 mbar they become very fast (see Fig. 13). A possible reaction for F2* formation will be discussed in the next section. The following explanation for the production in the dis- charge and accumulation in an aged He gas mixture of carbon- containing contaminants is proposed. Carbon 0 and CO impurities which are always present in metals are extensively desorbed as primary contaminants from the main nickel elec- trodes and pre-ionization aluminium plates during the sputter- ing of the metal from cathode (anode) hot spots created under the very high discharge current density. Electron (ion)-bom- bardment desorption of CO from the electrodes36 could also be occurring under our discharge conditions.Hence the purity of the material of the main and pre-ionization electrodes is a very important parameter for a long operational lifetime of the gas mixtures of discharge lasers. Secondary contaminants such as CN C2 CH and OH radicals are formed by plasmo- chemical reactions with other trace impurities (N2 0 and H2). These reactions might be catalytically activated on the surface of pure metal particles sputtered from the electrode^.^^ In an aged He gas mixture the kinetics of the accumulation of contaminants will tend to reach saturation [see Fig.6(a) and (b)]. We believe that after about 1 million shots i.e. for a highly contaminated gas mixture the laser chamber walls serve as both a source and a sink for highly reactive species in the discharge.Surface recombination and pseudo-polymer layer formation reactions on the chamber wall could be an effective channel for the loss of long-lived chemically active radicals such as CN CH C and OH.38 The pseudo-polymer layer itself could act as a source of gaseous contaminants; hence under conditions where there is a dynamic equilibrium between the loss and creation processes the accumulation kinetics will also be saturated. Thus in order to obtain reproducible results in kinetics the purity of the laser chamber walls and their history are very important. Contaminants in an Aged He-F Gas Mixture Spontaneous emission spectra A mixture of He at a pressure of 6 bar with F added at a pressure of 4.5 mbar as investigated in this work is a standard gas mixture usually used in discharge-pumped molecular fluor- ine lasers.After filling the laser chamber with a fresh gas mixture a strong VUV lasing at 157 nm causes a very high level of stray light in the VUV monochromator and it is difficult to measure any spontaneous VUV emission spectrum. The time-integrated spontaneous VUV emission spectrum from an aged He-F gas mixture after 2.5 x lo6 shots when the VUV lasing has disappeared is shown in Fig. 10. Together with the well known molecular fluorine transition D' 3112g -+A' 3112u (157 nm) two new molecular fluorine emission bands at 255 and 280 nm are also observed. The intensity of these two bands is much higher than in the VUV spectrum of aged He containing trace amounts of fluorine impurities (see Fig.5). From the spontaneous VUV emission spectrum in Fig. 10 it is possible to identify also O* and C* atomic lines and CO* molecular bands which are very similar to the impurity lines Journal of Analytical Atomic Spectrometry September 1996 Vol. 1 1 655c) .d C c .- lA Y; ._ f w F He / F (6 bar / 4.5 mbar) F,? after 2.5 lo6 shots C V 150 200 250 300 Wavelengthhm Fig. 10 Spontaneous VUV emission spectrum of an aged He-F gas mixture. Atomic 0* C* and Ni* and molecular CO* contaminant lines are observed. Together with the well known molecular fluorine D 311,g+A' 3112u band at 157 nm two new molecular fluorine bands at 255 and 280 nm are detected in an aged He gas mixture (see Fig. 5). The intensity of these lines remains fairly low until a strong F2* fluorescence band at 157 nm is observed.For a very old He-F gas mixture (after 5 x lo6 shots) when the fluorescence from the 157 nm band is totally absent (but where there are still sufficient F molecules in the aged gas mixture) the emission from C* and CO* contaminants becomes much more pronounced than in Fig. 10. However the emission from the 255 and 280nm bands does not change significantly which shows that the chemical reac- tions responsible for the population of these specific excited electronic states of the F molecule are different. In order to explain our experimental results a schematic potential energy diagram of some F electronic states relevant to the discussion in this paper is proposed in Fig.11. To the best of our knowledge the emission spectra of F2 molecules have not been extensively studied and the determination of the energies of the excited electronic states involved in the emission transitions has still to be ~ompleted.~'-~~ 0 1 2 3 4 5 6 RIA Fig. 11 Schematic potential energy diagram of some F electronic states relevant to the discussion in this paper. Two known absorption transitions at 100 and 290 nm are shown. The upper electronic state for the well known emission band at 157 nm belongs to the ionically bonded D 3112g term. The new molecular fluorine emission bands at 255 and 280 nm originate from the covalently bonded B state It is generally considered that the main process for the formation of the F upper electronic state D 3112g for an F2 laser is a neutral energy exchange reaction viz.F* t F +F2* + F.32943 The rate constant of this reaction is 5.1 x lo-'' cm3 s - ' ; ~ ~ hence the characteristic time constant for the formation of F2* molecules is about 12 ns for our gas mixture. F* denotes both doublet 2P and quartet 4P low-lying excited states of atomic fluorine between 12.7 and 13.0 eV.45 We propose that this reaction can only populate the excited covalent states of the F molecule and not the ionically bonded states (see Fig. 11). Ionic fluorine states in particular the D' 3112g state are populated through the very fast ion-ion recom- bination reaction F+ +F- +He+F2* + He where F+ should be in the 3P2 3P0 or 3P1 lowest electronic states with an energy of about 17.42eV. The rate constant for this reaction in He buffer gas at a pressure of 6 bar is 1.4 x cm3 s - ' .~ ~ Therefore for the efficient pumping of an F laser a significant fraction of the F2 molecules in the He-F gas mixture need to be ionized by the discharge. The main contribution of the ion-ion recombination channel to the pumping of a VUV F2 laser was recently confirmed by Takahashi et aZ.46 In an aged He-F gas mixture with the accumulation of easily ionizable contaminants the ionization of F2 and as a consequence the emission band at 157 nm are depressed strongly. However the pumping of the red atomic fluorine laser lines requires only excited (an energy of about 14.5-14.7 eV) and not ionized fluorine atoms. A reservoir of excited F* atoms with an energy of 12.7-13.0 eV2' is created after the discharge excitation and fast electron-collisional energy-exchange cascades.We believe that this reservoir serves as a precursor for the production of F molecules in the covalently bonded electronic state denoted tentatively as B'. The population of this excited electronic state is responsible for the 255 and 280 nm F emission bands. These bands are not as sensitive to the presence of contaminants in the He-F gas mixture as is the ionic band at 157 nm. The vibronic structure of the 255nm band with a 0-0 transition at 222nm seems to be composed of several over- lapping progressions. The measured sequential distance of 380_+20cm-1 in the short wavelength wing reflects the vib- ronic quantum of the lowest electronic state tentatively assigned as the A3111 state.The vibronic structure of the long-wavelength wing of the 255 nm band is more complicated because of the overlap with the strong carbon (247.8 nm) and several silicon (250.6 251.4 251.9 252.4 252.8 and 253.2 nm) emission lines. We suggest by analogy with the discussion in ref. 19 that more than one near-lying covalent B' elec- tronic state is involved in the 255 nm band transition due to spin-orbit splitting of the F and F* states. Since no vibronic structure is observed for the 280nm emission band the lower electronic state tentatively assigned as B 311u must be a repulsive state producing two ,P fluorine atoms. The fact that there are no observed absorption bands corresponding to transitions to the B and B' states from the X 'Zg+ ground state in indicates that these trans- itions are forbidden by the selection rules.Further evaluation of the molecular F emission spectrum with better resolution is necessary to confirm these suggestions. These investigations are currently in progress. The VUV emission spectrum of an aged He-F gas mixture (Fig. 10) also contains many Ni* atomic emission lines. These lines appear in the spectrum only in the presence of added F in the He gas mixture. This shows that in comparison with pure He the addition of F2 stimulates markedly the sputtering of nickel from the cathode (anode) hot spots created under a very high discharge current density. The most interesting feature in the VUV emission spectrum in Fig. 10 is a strong continuous absorption observed in the far VUV region revealed by the depression of the O* (130.5 nm) impurity emission line in the aged He-F gas mixture.It is 656 Journal of Analytical Atomic Spectrometry September 1996 Vol. 1 1well known that F gas is transparent in the UV-VUV region up to 105 nm (the beginning of absorption in the C 'Xu+ +-X 'Zg+ band4') except for a weak broad continuous A 'nu +-X ' Zg+ absorption of 290 nm1.24 We assign the absorp- tion at a wavelength of less than 140nm in the aged He-F gas mixture to stable fluorine-containing contaminants. The nature of these compounds will be discussed later in this section. The emission spectrum of an aged He-F gas mixture in the UV-VIS region (see Fig. 12) contains together with two fluor- ine emission bands at 255 and 280 nm several specific impurity emission bands.A long progression in the 665 cm-' v,' bending vibrational mode of the CF radical in the ground electronic state is observed for the A 'B +X 'A CF,* emission band." The most intense is the 000+050 vibronic transition at 295.0 nm in accordance with the assignment in ref. 28. Another specific impurity band is connected with the SiF* A 'Z+ +X 'I3 fluorescence band (the radiative lifetime of this transition is z 230 ns 30). According to assignments in ref. 24 the most intense is the 0-0 (440.0 nm) transition. No emission from the well known CF* A 'I=+ +X 2rl[47 fluorescence band with a maximum at 247.6 nm and the NiF* fluorescence band with a maximum at 506.5 nm4* was observed. The molecular bands from 02* CH* and Cz* impurity species are very similar to those observed in the emission spectrum of an aged He gas mixture (see Fig.3). As regards the excited atomic species several very strong Si* emission lines are evident in Fig. 12 and are listed in Table 1. We believe that these silicon contaminants in our laser arise from the sputtering of the aluminium pre-ionization electrodes in the discharge of the He-F gas mixture (silicon is the main impurity in aluminium). A number of Ni* lines the most intense line being at 352.4 nm; the C* line at 247.8 nm together with He* (587.5nm) H/? (486.1 nm) and Ha (656.2 nm) lines several strong red F* lines and the 0" (777.7 nm) line were observed in the emission spectrum of an aged He-F gas mixture. No emission lines from N* N2* Nz+* and CO+* species with an excitation energy higher than that of the added F2 were observed for the aged He-F gas mixture. Time-resolved emission of excited species The time dependence of the specific emission lines (bands) in an aged He-F gas mixture is shown in Fig.13. The atomic fluorine emission lines exhibit fast excitation-decay kinetics which virtually coincide with the kinetics of He*. The same results have been reported by Takahashi et and Peet and Tre~hchalov.~~ It seems that F* atoms are produced 10 3 8 h c) .- v) g .d r 3 6 v x - .- v) c) 5 4 z 2 'Z .- C .d W 0 250 300 350 400 450 500 Wavelengthhm Fig. 12 Spontaneous UV-VIS emission spectrum of an aged He-F gas mixture. The emission bands from C* 02* C2* CH* and HB* Contaminants are similar to those in aged He (see Fig. 3). Lines from Si* SiF* CF2* and F2* appear in the presence of F h v) r~ 1 I I I M h ."FF2 after 5 1 O6 shots He I F (6 bar / 4.5 mbar) 100 150 200 250 0 50 Timehs Fig.13 Time dependence of some specific emission bands in the discharge of an aged He-F gas mixture from very fast energy transfer reactions such as He*( He,*) + F + He-+F* + F + 2He. The rate constant for this reaction is about 2 x s-' (Ref. 43) for a He pressure of 6 bar. The emission from the 255 and 280 nm molecular fluorine bands exhibits fairly fast kinetics similar to the atomic fluorine band but delayed by 15 ns. The emission kinetics of Si* and Ni* atoms exhibit a fast rise time and a long decay time with a time constant of about loons which shows the long exci- tation of these species in the cathode hot spots.SiF* molecules and CF,* radicals exhibit typical kinetics which possibly reflect their production from plasmo-chemical reactions of carbon and silicon atoms with F,. Identification of stable contaminants from absorption spectra In order to identify stable contaminants which accumulate in an aged He-F gas mixture and deteriorate the output energy of an F laser the emission and VUV absorption spectra of the gas mixture were measured during the running of the laser. After filling the laser chamber with fresh gas (6 bar of pure He or an He-F mixture with 4.5mbar of F added) there was no detectable absorption in the spectral range 190-1 15 nm for the gas in a laser chamber with an optical absorption length of 25 cm. Under static conditions (without laser running) N and 0 molecules were detected as the main impurities that are slowly accumulated inside the laser chamber. The absolute concen- tration of N impurities was detected from the fluorescence of N2+* ions.Oxygen molecules were monitored from the strong 0 dissociation continuum absorption band with a maximum at 145 nm.50 The accumulation rate for both N and 0 gases is about 0.1 mbar d-l. The rate of gas ageing is almost identical for pure He and an He-F gas mixture under static conditions but it depends on the quality of the laser chamber passivation. It seems that continuous out-gassing of 0 and N from the laser chamber materials is the main mechanism for the formation of these impurities. Oxygen contaminants accumulate much faster with the He-F discharge running than under static conditions.Fig. 14 shows the absorption spectrum of an aged He-F gas mixture in the VUV spectral region. From the absorption of the oxygen dissociation continuum band the accumulation rate for 0 impurities was estimated to be 0.1 mbar per 5 x lo5 pulses. Running the laser with discharges in pure He does not lead to a considerable increase in the accumulation rate for 0 and N impurities compared with static conditions. It seems that an extensive fluoridation (passivation) process viz. Me0 + F*+MeF + O converts the metal oxide film inside the laser chamber into a stable metal fluorine film and removes 0 from the metal surface into the gas mixture. Highly reactive species such as fluorine atoms are necessary for the passivation process because it is necessary not only to remove oxides Journal of Analytical Atomic Spectrometry September 1996 Vol.I I 657I00 He I F (6 bar / 4.5 mbar) after 5 10’ shots 80 - h 5 - c 60 5 . $ 4 0 - F laser d - .& D 20 0 180 170 160 150 140 130 120 I I . . l l l l . l I . . l l l . _ Wavelengt h/nm Fig. 14 Absorption spectrum of an He-F gas mixture after 5 x lo5 shots. The broad absorption band at 145nm belongs to oxygen contaminants. The F laser line position (157.6 nm) is denoted by an arrow. The strong absorption at 130-120 nm is tentatively assigned to COF or HF contaminants hydrocarbons and water from the surface of the laser chamber but also to produce a corrosion-resistant metal fluorine film. We believe that the strong intracavity absorption at the F2 laser wavelength of 157.6 nm caused by the molecular 0 impurities is the main reason for the degradation of the F laser output.In our laser 0.1 mbar of 0 gives about 40% intracavity absorption at the lasing wavelength. The spectral dependence of the 0 absorption band explains the results obtained by Kakehata e t al.,l2 who investigated the absorp- tion of the active medium of an F discharge-pumped laser. In contrast to the relatively low absorption measured at 168.6nm,12 the energy output of the F laser seems to be limited by the 5-fold greater intracavity absorption. This observation is consistent with the results presented in Fig. 14 where the absorption of oxygen contaminants at 168.6 nm is about five times less than at 157.6 nm. In addition to the 0 absorption band a strong continuum absorption band appears in the range 135-120nm with an extremely large increase in absorption towards the far VUV region. This continuum band only appears when the laser is run with an He-F gas mixture.The identity of the contami- nant responsible for this band is not known. Presumably it could be a stable fluorine-containing compound. We believe that COF or HF molecules could be the contaminant. It is known that CO burns in an atmosphere of F uiz. CO + F + COF2. Hydrogen fluoride is produced by burning trace amounts of hydrocarbons or water in an atmosphere of fluorine. This very effective reaction needs fluorine atoms and is easily initiated by the discharge. Both COF and HF molecules have been identified from Fourier-transform infrared absorption spectra7 and observed in an aged KrF-excimer laser gas mixture (after 2.5 x lo6 shots) at concentrations of about 60ppm for COF and 1OOOppm for HF.The lowest excitation dissocation pathway of COF by analogy with the photolysis of phosgene (COC12),’1 could give after the dis- charge excitation CO CO* and F molecules and FCO radicals.’ The self-transformation reactions between F CO F FCO and COF are not yet fully understood and are cur- rently being investigated in connection with the stratospheric photochemistry of fluorocarbon radical^.'^ In discharge-pumped lasers with fluorine-containing gas mixtures the accumulated COF and HF contaminants have an adverse effect not only because they act as a means of F fuel removal but also because they strongly absorb pre- ionization photons in the far VUV region which seriously deteriorates the spatial homogeneity of the discharge.Indeed the discharge in an He-F mixture after prolonged running of the laser contains visually more pronounced sparks than in a fresh gas mixture. According to the data for the VUV absorp- tion of COF molecules a strong continuous absorption is observed near 131 nm.54 At shorter wavelengths the absorption increases up to the limit of observation of 121.5nm. HF molecules also have a strong X ‘Z+ -+A ‘II photoabsorption band with a maximum at 120nm.55 Both these absorption phenomena are very similar to those shown in Fig. 14. In order to determine whether COF and/or HF is the contam- inant additional experimental studies are necessary. These investigations are currently in progress.CONCLUSIONS This work represents the results of a comprehensive investi- gation of the production and accumulation of transient and stable gaseous contaminant impurities in high pressure He and He-F gas discharge plasmas. Various radicals (CN CH C OH SiF and CF,) excited atoms (0 C Si N and H) molecules (CO 0 and N,) and molecular ions (N,’ and CO + ) were identified as contaminants. The accumulation and self-transformation kinetics due to plasmo-chemical reactions between these species were investigated. Possible mechanisms for the production of the contaminant impurities are proposed. This work was supported in part by the Estonian Science Foundation under Grant No. 2276. REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 Tennant R.Laser Focus 17 65. Gower M. C. Kearsley A. J. and Webb C. E. J. Quantum Electron. 1980 16 231. Mandl A. E. and Hyman H. Appl. Phys. Lett. 1986 49 841. Karwacki E. J. Jr. and Hanton S . D. Laser Focus World 1992 28 81. Hwang H. H. James K. Hui R. and Kushner M. J. J. Appl. Phys. 1991 69 7419. Stevens R. E. Kung C. Y. Kittrell C. and Kinsey J. L. Rev. Sci. Instrum. 1994 65 2464. Jursich G. Rufin D. Von Drasek W. Reid J. and Znotins T. Laser Focus World 1989 25 56. Brannon J. H. J. Quantum Electron. 1982 18 1302. Kimura W. D. and Seamans J. F. J. Quantum Electron. 1988 24 2124. Gabzdyl J. Cleaver K. Stevenson A. OKey M. A. and Osborne M. R. J. Appl. Phys. 1994,75 1213. Shimauchi M. Miura T. and Takuma H. Jpn. J. Appl. Phys. 1994,33,4628.Kakehata M. Ueno Y. Tamura K. and Kannari F. J. Appl. Phys. 1994 75 1304. Endert H. Patzel R. Rebhan U. Powell M. and Basting D. Jpn. J. Appl. Phys. 1995 34,4050. Nikolaus B. Endert H. Rebhan U. Patzel R. Vob F. and Basting D. in Lambda Highlights ed. Brinkmann U. Lambda Physik 1994 44 1. Treshchalov A. B. in Proceedings of the International Symposium on High-Power Lasers and Laser Applications V Vienna Austria April 5-8 1994 314/SPIE 2206 pp. 314-322. Chizhik A. Vill A. and Treshchalov A. in Proceedings of I I International Conference on Laser Physics & Spectroscopy ICLPS’95 Grodno Belarus September 25-27 1995 pp. 96-97. Collins C. B. and Robertson W. W. J. Chem. Phys. 1964,40,701. Richardson W. C. and Setser D. W. J. Chem. Phys. 1973 58 1809. Diegelmann M.Hohla K. Rebentrost F. and Kompa K. L. J. Chem. Phys. 1982 76 1233. Hemici M. Mottin S. Bon M. Roncin J. Y. and Laporte P. J. Phys. III Pr. 1991 1 2061. Peet V. E. Phys. Rev. A 1995 51 3982. Heppell T. A. Vacuum 1987 37 593. Neeser S. Tietz R. Schulz M. and Langhoff H. Z . Phys. D 1994 31 61. Rosen B. Spectroscopic Data Relative to Diatomic Molecules Pergamon Press Oxford 1970. Striganov A. R. and Sventitskij N. S. Tables of Spectrum Lines Atomizdat Moscow 1966. Zaidel A. N. Prokof’ev V. K. and Raiskii S . M. Tables of Spectrum Lines Pergamon Press New York 1961. 658 Journal of Analytical Atomic Spectrometry September 15196 Vol. 1127 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 Pearse R. W. B. and Gaydon A. G. The Identification of Molecular Spectra Chapman and Hall London 1965. Mathews C.W. Can. J . Phys. 1967 45 2355. Mann D. E. and Thrush B. A. J. Chem. Phys. 1960 33 1732. Huber K. P. and Herzberg G. Constants of Diatomic Molecules Van Nostrand Reinhold New York 1979. Wan B. N. and Langhoff H. J. Chem. Phys. 1992 97 8137. Kim Y.-P. Obara M. and Suzuki T. J. Appl. Phys. 1986 59 1815. Fairbairn A. R. Proc. R. SOC. London Ser. A 1969,312,207. Bokor J. Zavelovich J. and Rhodes C. K. J. Chem. Phys. 1980 72 965. Little C. E. and Browne P. G. Chem. Phys. Lett. 1987 134 560. Sandstrom D. R. Leck J. H. and Donaldson E. E. J. Appl. Phys. 1967 38 2851. Zhang J. Wu N. Wang J. Zhao J. and Xu Y. Opt. Laser Technol. 1994 26 355. O’Neill J. A. and Singh J. J. Appl. Phys. 1995 77 497. Porter T. L. J. Chem. Phys. 1968 48 2071. Colbourn E. A. Dagenais M. Douglas A. E. and Raymonda J. W. Can. J . Phys. 1976 54 1343. Levelt P. F. Eikema K. S. E. Stolte S. Hogervorst W. and Ubachs W. Chem. Phys. Lett. 1993 210 307. Bressler C. Lawrence W. Chergui M. and Schwentner N. J. Lumin. 1994 608~61 570. 43 44 45 46 47 48 49 50 51 52 53 54 55 Ohwa M. and Obara M. Appl. Phys. Lett. 1987 51 958. Huestis D. L. Hill R. M. Nakano H. H. and Lorents D. C. J . Chem. Phys. 1978,69 5133. Sumida S. Obara M. and Fujioka T. J. Appl. Phys. 1979 50 3884. Takahashi M. Maeda K. Kitamura T. Takasaki M. and Horiguchi S. Opt. Commun. 1995 116 269. Porter T. L. Mann D. E. and Acquista N. J. Mol. Spectrosc. 1965 16 228. Bouddou A. J. Mol. Spectrosc. 1994 168 477. Peet V. E. and Treshchalov A. B. Laser Phys. 1993 3 88. Okabe H. Photochemistry of Small Molecules Wiley New York 1978 p. 214. Okabe H. Laufer A. H. and Ball J. J. J . Chem. Phys. 1971 55 373. Maricq M. M. and Szente J . J. J. Chem. Phys. 1994 100 8673. Wallington T. J. Ellermann T. Nielsen 0. J. and Sehested J. J. Phys. Chem. 1994 98 2346. Workman G. L. and Duncan A. B. F. J. Chem. Phys. 1970 52 3204. Cacelli I. Chem. Phys. Lett. 1996 249 149. Paper 61003 95 H Received January 18 1996 Accepted May 13 1996 Journal of Analytical Atomic Spectrometry September 1996 Vol. 1 1 659

ISSN:0267-9477    

DOI:10.1039/JA9961100649

出版商:RSC    

年代:1996

数据来源: RSC