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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.1997 European Winter Conference on Plasma Spectrochemistry Gent Belgium January 12- I 7 I997 Since 1980 the Winter Conference on Plasma Spectrochemistry has been organized biennially in the USA and since 1983 has become an annual event which alternates between the USA and Europe.It has acquired an international reputation as the world's premier meeting covering state-of-the-art developments in all aspects of plasma spectrochemistry. The 1997 conference to be held at the University of Gent (Ghent) Belgium will feature developments in plasma spectrochemical analysis by inductively coupled plasma (ICP) dc plasma (DCP) microwave induced plasma (MIP) and glow discharge (GD) sources coupled to atomic emission or mass spectrometers.In addition current trends and future directions in novel sample introduction systems plasma system automation and software for data handling will be discussed by recognised world authorities with emphasis on elemental speciation studies high resolution ICP-MS spectrometry accuracy of the results quality assurance and industrial applications. The meeting will comprise oral and poster presentations short courses and a five day exhibition of spectroscopic instrumentation and accessories. Scientific Programme The scientific programme will include the major topics of plasma spectrochemistry. Each topic will be introduced by an invited lecturer who is an expert in the field. The main topics are 1) Instrumentation and software; 2) Sample introduction and transport phenomena; 3) Elemental speciation; 4) High resolution ICP-MS; 5) Solid sampling; 6) Glow discharge; 7) Applications; 8 ) Accuracy and quality assurance; and 9) Stable isotope analysis.Schedule of Activities Preliminary title and 50-word abstracts Notification of accepted papers Final abstracts Early pre-registration. Deadline Hotel pre-registration. Deadline Late pre-registration. Deadline June 15 1996 September 15 1996 November 1 1996 November 1 1996 November 1 1996 December 15 1996 Publication of Papers The proceedings of the 1997 European Winter Conference will appear in the autumn of 1997 in a special issue of Journal of Analytical Atomic Spectrometry (JAAS). After peer review manuscripts of accepted papers will be considered for publication in these proceedings.Local Organizing Committee R. Dams University of Gent (Chairman) L. Moens University of Gent (Secretrary) J. Broekaert University of Dortmund Germany R. Cornelis University of Gent R. Gijbels University of Antwerpen F. Vanhaecke University of Gent L. Van 't dack University of Antwerpen C. Vandecasteele University of Leuven P. Taylor IRMM Joint Research Centre EC P. Quevauviller Measurements and Testing EC For further information please contact L. Moens Secretariat 1 997 European Winter Conference Laboratory of Analytical Chemistry University of Gent Proeftuinstraat 86 B-9000 Gent Belgium. Tel +32 9 264 44 00; Fax +32 9 264 66 99; E-mail plasma97@rug.ac.be;I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 1 I I I I I I I I I I I I I w K w I J n F I- v) U u I I I I I I I I I I I I I I I I I I I I I I I I I I I I _ I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 1 I I I I I I I I I I I I I- I I I I I I I I I I FOLD HERE JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY OCTOBER 1996 READER ENQUIRY SERVICE For further information about any of the products featured in the advertisements in this issue please write the appropriate number in one of the boxes below. Postage paid if posted in the British Isles but overseas readers must affix a stamp.PLEASE USE BLOCK CAPITALS LEAVING A SPACE BETWEEN WORDS Valid 12 months 1 NAME I ~ l l l l l l l l l l l l l l l l l l l l l l l l l 4 TOWN I1III111I1IIIIIIlIIIIIIIlllllllIJ ~ l l l l l l l l l l l l l l l l l l l l l l l l l 2 COMPANY PLEASE GIVE YOUR BUSINESS ADDRESS IF POSSIBLE IF NOT PLEASE TICK HERE 0 3 STREET 5 COUNTY POSTCODE -1 I I I I I I I I I I I I 1 1 I I I I I I I 1 1 1 6 COUNTRY 7 DEPARTMENT DIVISION -1 I 1 1 1 1 1 I I I I 1 1 I I 1 1 I I I I I 1 1 1 POSITION -1 I I I I I I I I I I 1 1 I I I I I I I I I I I I D m OFFICE USE ONLY REC.D PHOCD 8 YOUR JOB TITLE 9 TELEPHONE NO Postage will be paid by Licensee I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I Do not affix Posaage Stamps if posted in Gt.Britain Channel Islands N. Ireland or the Isle of Man BUSINESS REPLY SERVICE Licence No.WD 106 Reader Enquiry Service Journal of Analytical Atomic Spectrometry The Royal Society of Chemistry Burlington House Piccadil ly LONDON WIE 6WF EnglandRamon M. Barnes Editor Department of Chemistry 701 &GRC Tower University of Massachusetts Box 34510 Amherst Massachusetts 01003-4510 USA Telephone (41 3) 545-2294 fax (41 3) 545-3757 0 bjec tive The ICP lNFORMATlON NEWSLETTER is a monthly journal published by the Plasma Research Group at the University of Massachusetts and is devoted exclusively to the rapid and impartial dissemination of news and literature information related to the development and appli- cations of plasma sources for spectrochemical analysis. Background ICP stands for inductively coupled plasma discharge which during the past 20 years has become the leading spectrochemical excitation source for atomic emission spectroscopy and ion source for inorganic mass spec- trometry.The popularity of this source and the need to collect in a single literature reference all of the pertinent data on ICP stimulated the publication of the ICP INFOR- MA TlON NE WSLETTER in 1975. Other plasma sources such as microwave induced plasmas direct current plasma jets and glow discharges also are included in the scope of the ICP INFORMATION NEWSLETTER. Scope As the only authoritative monthly journal of its type the ICP INFORMA TION NEWSLETTER is read in more than 40 countries by scientists actively applying or planning to use the ICP or other types of plasma spectroscopy. For the novice in the field the ICP lNFORMA TlON NEWS- LETTER provides a concise and systematic source of information and background material needed for the selec- tion of instrumentation or the development of new method- ology. For the experienced scientist it offers a single- source reference to current developments and literature.Editorial The ICP lNFORMATlON NEWSLETTER is edited by Dr. Ramon M. Barnes Professor of Chemistry University of Massachusetts at Amherst with the assistance of a 20- member Board of National Correspondents composed of leading plasma spectroscopists. The Board members from around the world report news viewpoints and developments. Dr. Barnes has been conducting plasma research on ICP and other discharges since 1968. He also serves as chairman of the Winter Conference on Plasma Spectrochemistry sponsored by the ICP INFOR- MATION NEWSLETTER.Reg u lar Features Original submitted and invited research articles by ICP and plasma experts. 0 Complete bibliography of all major ICP publications. @ Abstracts of all ICP papers presented at major US and 0 First-hand accounts of world-wide ICP developments. @I Special reports on dcp microwave glow discharge and 0 Calendar and advanced programs of plasma meetings. * Technical translations and reprints of critical foreign- 0 Critical reviews of plasma-related books. Conference Activities The ICP lNFORMA TION NEWSLETTER has sponsored nine international meetings on developments in atomic plasma spectrochemical analysis since 1 980 in Orlando Fort Lauderdale San Diego San Juan St.Petersburg and Kailua-Kona. Meeting proceedings have appeared as Developments in Atomic Plasma Spectrochemical Analysis (W iley) Plasma Spectrochemistry and Plasma :Spectrochemistry I/-IV (Pergamon Press) as well as in special issues of Spectrochimica Acta Part B and Journal of Analytical Atomic Spectrometry. The 1998 Winter Con- ference will be held January 5-10 1998. Subscription Information Subscriptions are available for 12 issues on either an annual or volume basis. The first issue of each volume begins in June and the last issue is published in May. For example Volume 22 runs from June 1996 through May 'I 997. Back issues beginning with Volume 1 May 1975 also are available. To begin a subscription complete the form below and submit it with prepayment or purchase information.For additional information please call (41 3) 545-2294 fax (413) 545-3757 or contact the Editor. Credit cards are accepted. lSSN 0767-6957 international meetings. other plasm as. language ICP papers. To order complete this section and send it to ICP lnformation Newsletter %Dr. Ramon M. Barnes Department of Chemistry LGRC Tower University of Massachusetts Box 34510 Amherst MA 01 003-451 0 USA. Start a subscription for the following issue OVolume(s)- (June 19- - May 19-) or 13 19 (January - December). Enclosed 13 Prepayment D Check or money order OVI'SA 0 MasterCard Account No. (All 13 or 16 digits) 3 Purchase order (No. ) or 0 Send invoice. Date Cardholder Name Expiration date Cardholder Signature AmountDue$ Mail to Name Organization Address City State/Country ZIP/Postal code Telephone Telex/f ax e-mail Note For each credit-card transaction a 4.26% service charge will be added reflecting our bank charges. Current subscription rates are $65 (North America) $89 (Europe South America) or $99 (Africa Asia Indian/ Pacific Ocean Areas Middle East and Russia). Back issue rates available on request. 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ISSN:0267-9477    

DOI:10.1039/JA99611BP021

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

CONFERENCE REPORT 6th Conference on Total Reflection X-Ray Fluorescence Analysis and Related Methods (TXRF ’96). June 10-1 1 1996 Eindhoven Holland and June 13-1 4,1996 Dortmund Germany The ongoing series of biennial workshops on Total Reflection X-ray Fluorescence Analysis and Related Methods which began at GKSS in Geesthacht near Hamburg in 1986 returned to Europe for its 6th meeting following its one intercontinental excursion to Japan in 1994. TXRF ’96 was held at two venues Eindhoven in Holland and Dortmund in Germany during the week of June 10-14,1996. The first part of the meeting (June 10-11) which was hosted by the Analytical Chemistry Section of the Royal Dutch Chemical Society in cooperation with Philips Research Laboratories Eindhoven was concerned with the analysis of surfaces and thin layers by TXRF and related techniques; the second part (June 13-14) hosted by the Deutscher Arbeitskreis fur Angewandte Spektroskopie in der Fachgruppe Analytische Chemie der Gesellschaft Deutscher Chemiker in cooperation with ISAS Institut fur Spektrochemie und Angewandte Spektroskopie Dortmund was dedicated to the role of TXRF in microanalysis and trace analysis. chaired by Dr.D. K. G. de Boer from Philips and Prof. R. Klockenkamper from ISAS chose to break with tradition not only by opting for a two-venue meeting but also by changing the status of TXRF ’96 from a workshop to a conference. The reason for this tenth anniversary change of status was not announced officially but is presumably a ‘reflection’ of the fact that TXRF and related methods have become ‘totally’ established in numerous scientific disciplines within academia industry and in government and public authority laboratories. With approximately 120 participants from nearly 20 different countries (as well as the bus trip from Eindhoven to Dortmund) TXRF ’96 might well have merited the status of an ‘international conference’! Overall the scientific programme of the conference consisted of 17 invited lectures and some 50 contributed presentations both oral and poster.The The organizing committee this time first part of the meeting which took place in the Koningshof Congress Hotel and Meeting Centre in Veldhoven was organized into sessions devoted to the surface analysis of semiconductors the analysis of thin films and new techniques and instrumentation and was therefore of primary interest to the more ‘physics-oriented’ members of the TXRF community.Much of the work reported in the two sessions on semiconductors was concerned with the use of TXRF for measuring impurity contamination on silicon wafers either on-line or off-line at synchrotron radiation facilities. Although the TXRF technique has served the semiconductor manufacturing industry well in recent years improvements in detection limits reliability arid calibration standards are all issues where further work is needed if TXRF is to retain the foothold it has gained and meet the challenge of the increasingly stringent demands of the future. The contributions to the two sessions on the analysis of thin films and layered materials covered a wide range of applications of TXRF and related methods to a variety of materials including oxide layers thin organic films metallic or oxidic multilayers.Langmuir-Hlodgett films etc. Highlights here were the invited presentations by M. J. Bedzyk on X-ray standing wave and evanescent wave studies and H. Zabel on X-ray reflectometry. The ability of glmcing incidence X-ray techniques 80 provide interpretable informatiori on the composition thickness density and interface-surface roughness of thin film samples was discussed critically and examples of a new approach to obtaining high resolution compositional depth profiles via TXRF in combination with sputtering procedures were presented (H. Schwen ke et al.). The sessions on new techniques and instrumentation for the analysis of surfaces and thin layered materials included presentations dealing with special X-ray sources (including synchrotron sources) for conventional TXRF and other methods such as resonant X-ray reflectivity and XPS Journal of Analytical Atomic Spectrometry PIXE operated in the total reflection mode.Progress with the recently developed GEXRF technique was described in a presentation by P. K. de Bokx et al. on the principles and applications of grazing-emission X-ray fluorescence spectrometry. The poster contributions which were exhibited throughout the two days generally covered similar subject matter to the oral presentations. The location of the poster exhibits and the instrument manufacturers’ information material in the room adjacent to the lecture theatre which was used for coffee and lunch breaks guaranteed a captive audience and lively discussions! The scientific programme of this part of the meeting was finalised with an afternoon visit to the Philips Research Laboratories in Eindhoven.a former cloister set in attractive grounds offered a pleasant working environment and many indoor and outdoor recreational facilities. The relaxed atmosphere (particularly in the bar!) enabled the scientific discussions to be continued well into the night! The highlight of the culinary experience which included a welcoming reception and all meals was the excellent conference dinner (sponsored by Philips) which brought our stay in Veldhoven to an end. On Wednesday the transfer to Dortmund for the second part of the meeting took place within the framework of a ‘supplementary programme’.This programme involved a bus trip to Lennep an attractive small town in Germany whose chief claim to fame is as the birthplace of W. C. Rontgen. After a picnic lunch and a little sight-seeing the afternoon was spent at the ‘Deutsches Rontgen-Museum’ where following a plenary lecture on the ‘Life and Work of W. C. Rontgen’ and afternoon tea the participants were able to tour the museum and marvel at the exhibits. The bus journey to Dortmund was then continued. A glance around the Werksaal of the Dortmunder Stadtwerke during the The venue for this part of the meeting Journal of Analytical Atomic Spectrometry October 1996 VoZ. 11 41 Nfestive musical opening ceremony on Thursday morning was enough to suggest that the scientific programme of the second part of the meeting appealed to yet another section of the TXRF community.Some of the familiar faces from Veldhoven had disappeared only to be replaced by others whose main interests lay in the use of TXRF methods in the areas of microanalysis and trace analysis. The conference continued with sessions on instrumentation and analytical methods which were followed by sessions devoted to industrial biomedical and environmental applications of TXRF. The oral presentations in the former sessions and several of the new poster exhibits (which were again conveniently located adjacent to the lecture theatre and the coffee) covered most aspects of the conventional TXRF analysis technique with respect to optimization of instrumentation (sources and detector systems) specimen preparation quantification procedures etc.The contribution from the GKSS group (A. Prange et al.) on the use of a Mo-W allow anode in combination with a tunable double multilayer monochromator to permit selection of the X-ray excitation energy in TXRF multielement analysis aroused great interest. The work presented in the application sessions and many of the posters served to demonstrate the diversity of scientific disciplines in which TXRF is now being applied. The majority of these were concerned with environmental applications a field in which TXRF has become well established for trace analysis studies of aerosols airborne particulate matter sea and river water and sediment samples of various origins.Here the presentation by R. Van Grieken on the development of procedures for the routine analysis of aerosols using TXRF and the poster by the BSH group (E. Haffer et al.) from Hamburg on the use of hydride generation for matrix separation in TXRF analysis should be mentioned as highlights. Evidence for the growing interest in the TXRF technique in the industrial sector could be found in the presentations concerned with the analysis of pharmaceutical products industrial chemicals spent nuclear fuels oil refinery products and effluents as well as foodstuffs and cosmetics. Biomedical applications of TXRF involved the determination of trace elements in human tissue in enzyme complexes and in plants. In the final session attention returned to more technique-oriented developments such as the use of LA in combination with TXRF for the micro-analysis of solid samples a method for the determination of traces of Hg and the optimization of the SR-TXRF and GEXRF techniques for microanalysis and trace analysis.The meeting drew to a close as Professor Gohshi from the University of Tokyo gave us his vision of future developments in the instrumentation principles and practice of TXRF and related methods. Those delegates not rushing to return home on Friday evening were cordially invited to visit the ISAS laboratories on Saturday morning. programme of this part of the meeting were the reception and buffet at Hovels The highlights of the social Haus Brauerei (sponsored by Atomika Instruments) with guided tours of one of Dortmund’s traditional ‘micro- breweries’ and a lecture on the art and science of brewing beer according to the German Beer Purity Decree of 1516 and last but not least the excellent buffet lunches organized by ISAS. The organizers (and sponsors) are to be congratulated on a ‘conference’ which was smooth-running stimulating and enjoyable. Finally word has it that the next meeting in the series will be held in Austin Texas from September 27th to October 1st 1998 and that the success of this year’s meeting and the continuing growth in interest in the technique have convinced the organizing committee that a further upgrade in status is in order so that TXRF ’98 will be an ‘international conference’! Peter Beaven GKSS Research Centre 21502 Geesthacht Germany 42N Journal of Analytical Atomic Spectrometry October 1996 Vol. 11

ISSN:0267-9477    

DOI:10.1039/JA996110041N

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

BOOK REVIEW Laser Spectroscopy. Basic Concepts and Instrumentation. By W. Demtroder. Springer-Verlag Berlin 2nd edn. 1996. Pp. xvii + 924. Price DM148.00 ISBN 3-540-57171 -X. This is an extremely thorough text focusing first of all on the theory and instrumentation of spectroscopy. This is covered in three comprehensive (introductory) chapters which include details of the theory of absorption and emission spectral line broadening spectrometers and associated detectors. The attention of the book then turns to its main focus lasers and their use and application in spectroscopy. The fundamentals of lasers and their spectral characteristics are covered in generous detail. Eight chapters then follow that cover the rudiments of lasers of different types and configurations for Doppler-limited absorption and fluorescence spectroscopy non-linear spectroscopy Raman spectroscopy molecular beam spectroscopy double-resonance techniques time-resolved spectroscopy coherent spectroscopy and collision processes.‘New developments’ is always a dangerous title to include in any book because of the delays in production and printing. However topics such as the optical cooling and trapping of atoms the spectroscopy of single ions and absolute optical frequency measurements and optical frequency standards should keep the ardent laser spectroscopist happy. Finally and of direct relevance to the practitioner or specialist is a dedicated chapter on applications. This chapter is further sub-divided into five parts focussing on applications in chemistry (including analytical chemistry); environmental research; technical problems; biology; and medical applications.For me this was the most interesting and reader friendly part of the book (probably the analytical chemist part of me). In addition to the comprehensive nature of the text the reader is led through the mathematics by the use of worked examples and additional problems. For students seeking to gain full value from the text the inclusion of the examples is particularly noteworthy. The intense detail of the book does not provide a text that the user will read from cover to cover (unless over a long time period). However as a useful guide for postgraduate students and researchers in the field seeking to reinforce basic theory and principles behind the techniques used it is certainly a useful text. Its relatively high cost will preclude individuals from purchasing their own copies but the text will probably find its way onto library shelves. John R. Dean University of Northumbria at Newcastle Newcastle-upon- Tyne NE18ST UK 42N Journal of Analytical Atomic Spectrometry October 1996 Vol. 11

ISSN:0267-9477    

DOI:10.1039/JA996110042N

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/JA99611FX043

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

I lllll I THE ROYAL Information Services JASPE2 11 (1 0) 41 N-45N 907-1 01 0 355R-408R CONTENTS NEWS PAGES Conference Report-Peter Beaven Book Review-John R. Dean Diary of Conferences and Courses Future Issues 41 N 42N 43N 45N PAPERS Evaluation of Controlled-pore Glass Immobilized lminodiacetate as a Reagent for Automated On-line Matrix Separation for Inductively Coupled Plasma Mass Spectrometry Simon M. Nelms Gillian M. Greenway Dagmar Koller Determination of Physiological Platinum Levels in Human Urine Using Magnetic Sector Field Inductively Coupled Plasma Mass Spectrometry in Combination With Ultraviolet Photolysis Jutta Begerow Martina Turfeld Lothar Dunemann Determination of Trace and Ultra-trace Elements in Saline Waters by Inductively Coupled Plasma Mass Spectrometry After Off-line Chromatographic Separation and Preconcentration Kym E.Jarvis John G. Williams Elena Alcantara Julian D. Wills Determination of Long-lived Radioisotopes Using Electrothermal Vaporization- Inductively Coupled Plasma Mass Spectrometry Jorge s. Alvarado Mitchell D. Eric kson Characterization of Spent Nuclear Fuels by Ion Chromatography-Inductively Coupled Plasma Mass Spectrometry Josefa M. Barrero Moreno J. lgnacio Garcia Alonso Philippe Atbore Georgos Nicolaou Lotar Koch Optimization of Secondary Cathode Thickness for Direct Current Glow Discharge Mass Spectrometric Analysis of Glass Wim Schelles Stefan de Gendt Rene E. Van Grieken Comparison of Systems for Eliminating Interferences in the Determination of Arsenic and Antimony by Hydride Generation Inductively Coupled Plasma Atomic Emission Spectrometry Anna Risnes Walter Lund Behaviour of a Single-bore High-pressure Pneumatic Nebulizer Operating With Alcohols in Inductively Coupled Plasma Atomic Emission Spectrometry Jose L.Todoli Antonio Canals Vicente Hernandis Classification of Emission Lines of the Group IllB Elements Aluminium Gallium and Indium Excited by Grimm Glow Discharge Plasmas Using Several Different Plasma Gases Kazuaki Wagatsuma Comparison of the Analytical Performance of Flame Atomic Magneto-optic Rotation Spectrometry in the Faraday Configuration With That of Flame Atomic Absorption Spectrometry Ahmet T. Ince John B. Dawson Richard D. Snook Short Multifactorial Plan for the Determination of Trace Metals in Complex Matrices by Flame Atomic Absorption Spectrometry Svjetlana Luterotti Thermally Stabilized Iridium on an Integrated Carbide-coated Platform as a Permanent Modifier for Hydride-forming Elements in Electrothermal Atomic Absorption Spectrometry.Part 2. Hydride Generation and Collection and Behaviour of Some Organoelement Species Dimiter L. Tsalev Alessandro D’Ulivo Leonard0 Lampugnani Marco Di Marco Roberto Zamboni 907 913 91 7 923 929 937 943 949 957 967 973 979 Typeset printed and bound by continued on inside back cover The Charlesworth Group Huddersfield England 01484 517077 0 2 6 7 - 9 1 7 7 t 1996 110. 1-0Thermally Stabilized Iridium on an Integrated Carbide-coated Platform as a Permanent Modifier for Hydride-forming Elements ih Electrothermal Atomic Absorption Spectrometry.Part 3. Effect of L-Cysteine Dimiter L. Tsalev Alessandro D’Ulivo Leonard0 Lampugnani Marco Di Marco Roberto Zamboni Spectrometry Vera I. Slaveykova Faramarz Rastegar Maurice J. F. Leroy Rapid Determination of Selenium in Soils and Sediments Using Slurry Sampling-Electrothermal Atomic Absorption Spectrometry lgnacio Lopez- Garcia Mateo Sanchez-Merlos Manuel Hernandez-Cordoba ERRATUM 1007 CUMULATIVE AUTHOR INDEX 1009 989 Behaviour of Various Arsenic Species in Electrothermal Atomic Absorption 997 1003 ATOMIC SPECTROMETRY UPDATES Atomic Mass Spectrometry-Jeffrey R. Bacon Jeffrey S. Crain Adam W. McMahon John G. Williams References 395R 355R Atomic Spectroscopy Group Study Bursaries The Atomic Spectroscopy Group Analytical Division RSC invites applications from UK scientists working in the field of analytical spectrometry for study bursaries. These typically will have a value not exceeding f500 and are intended to afford applicants the opportunity for professional development. Specific activities for which the study bursary might be considered include attendance at meetings workshops and seminars or support for study visits to other laboratories. Applications should include a statement of the purpose for which the bursary is sought (1 page A4) and a summary of recent work (1 page A4). The submission should be sent to Dr S. J. Hill Chairman A.S.G. Department of Environmental Sciences University of Plymouth Drake Circus Plymouth PL4 8AA at least 2 months before funds are required.

ISSN:0267-9477    

DOI:10.1039/JA99611BX045

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Atomic Spectrometry Update- Atomic Mass Spectrometry JEFFREY R. BACON* The Mucauluy Land Use Reseurch Institute Craigiebuckler JEFFREY S. CRAIN Anulytical Chemistry Laboratory Argonne National Laboratory Argonne IL 60439-4831 USA ADAM W. McMAHON Department ofchemistry Munchester Metropolitan University Joim Dalton Building Chester Street Munchester U K M 1 5GD JOHN G. WILLIAMS NERC ICP-MS Fucility Centre for Anulytical Research in the EK*iironment Imperial College Silwood Park Ascot Berkshire UK SL5 7TE berdeen U K AB15 8QH SUMMARY O F CONTENTS 6.6. Applications 1. 1.1. 1.2. 1.3. 1.4. 1.5. 1.6. 1.6.1. 1.6.2. 1.6.3. 1.6.4. 1.6.5. 1.6.6. 2. 2.1. 2.2. 2.3. 2.4. 3. 3.1. 3.2. 3.3. Accelerator Mass Spectrometry (AMS) Reviews Facility Reports Methodologies Isobaric Separation Sample Preparation Applications Dating Hydrology Environmental tracers In-situ production Biomedical High-purity materials Glow Discharge Mass Spectrometry (GDMS) Reviews Fundamental Studies Instrumental Developments Analytical Methodologies Inductively Coupled Plasma Mass Spectrometry Reviews Instrumentation .Sample Introduction (ICP-MS) 3.3.1. Laser and spark ablation methods 3.3.2. Slurry methods 3.3.3. Electrothermal and thermal vaporization 3.3.4. Chemical vapour generation 3.3.5. Nebulization methods 3.3.6. Flow injection matrix separation and analyte 3.3.7. Speciation methods 3.4. Interference Effects 3.5. Applications preconcentration methods 4. 5. 6. 6.1. 6.2. 6.3. 6.4. 6.5. Laser Ionization Mass Spectrometry (LIMS) Resonance Ionization Mass Spectrometry (RIMS) Secondary Ion Mass Spectrometry (SIMS) Reviews Instrumentation Developments Quantification Matrix Effects Depth Profiling and Imaging * Review Co-ordinator to whom correspondence should be addressed.Atomic Spectrometry Update 7. Sputtered Neutral Mass Spectrometry (SNMS) 8. 8.1. Reviews 8.2. Off-line Techniques 8.2.1. Instrumentation 8.2.2. Sample preparation 8.2.3. Analytical methodologies 8.3. GC-Combustion-SIRMS 8.3.1. Instrumentation 8.3.2. Sample preparation 8.3.3. Analytical methodologies 8.4. Other Continuous Flow Techniques 8.4.1. Instrumentation 8.4.2. Sample preparation 8.4.3. Analytical methodologies Stable Isotope Ratio Mass Spectrometry (SIRMS) 9. 9.1. Reviews 9.2. Ion Formation 9.3. Instrumentation 9.4. Sample Preparation 9.5. Analytical Methodologies 9.6.Applications 9.6.1. Isotope dilution (ID) analysis 9.6.2. Environmental studies Thermal Ionization Mass Spectrometry (TIMS) 10. 10.1. 10.2. 10.3. 10.4. 0 ther NIethods Electrospray Mass Spectrometry (ESMS) Fast Atom Bombardment Mass Spectrometry (FABMS) and Gas Chromatography-Mass Spectrometry (GC-MS) Ion Cyclotron Resonance Mass Spectrometry Recoil Mass Spectrometry (ICR-MS) 10.5. Spark Source Mass Spectrometry (SSMS) 10.6. New Methodologies The MS and XRF Updates have been published together since their introduction in 1988. In the last few years however the two sections have been prepared independently of each other and it therefore seemed appropriate to publish the two sections separately. With effect from this issue the MS Update will appear in the October issue of J A A S and the XRF Update in the November issue.The format used for the MS section is broadly similar to Journal of Analytical Atomic Spectrometry October 1996 Vol. 1 1 (355R-393R) 355Rthat used last year with some additional sub-headings. This Update is intended to cover all atomic and stable isotopic MS techniques but not those used in studies of fundamental nuclear physics and 'exotic' nuclei far from stability. Also excluded are those reports in which MS is used as a tool in the study of molecular processes and of gaseous components. The review is based on critical selection of developments in instrumentation and methodology notable for their innovation originality or achievement of significant advances and is not intended to be comprehensive in its coverage. Conference papers are only included if they contain enough information to show they meet these criteria and our policy in general remains one of waiting for a development to appear in a full paper before inclusion in the review. A similar policy applies to foreign language papers unlikely to reach a wide audience.Routine applications of atomic MS are not included in this Update and the reader is referred to the Updates on Industrial Analysis Metals Chemicals and Advanced Materials (96/416) Environmental Analysis (96/ 1444) and Clinical and Biological Materials Food and Beverages (96/2479). Also excluded are those applications even if not routine which use atomic spectroscopy as a tool for the study of a non-atomic property for example the use of stable isotope labelling of carbon or nitrogen in biomolecules in metabolic studies.in the period covered by this update. That of Colodner et al. (95/3890) gave a general review of ion sources in particular GDMS ICP-MS SIMS and TIMS and that of Blades (95/2568 and 95/3077) was a very general overview of some of the techniques covered in this Update. The review of the literature in the period covered by this Update reveals strong advances in all areas with a continuing push to achieve better analyses on smaller samples and in less time. Most advances generally require more sophisticated instrumentation improved sample preparation methods or new methods of sample introduction. This is typified by advances in ICP-MS which see considerable emphasis on sample introduction techniques and a move towards magnetic sector instruments.Most applications of ICP-MS are now highly routine. There is still however a desire to achieve affordable analysis with simplified and cost-effective instruments as illustrated by the development of mobile in-situ isotope MS for environmental studies. There have been few general reviews on atomic MS of note 1. ACCELERATOR MASS SPECTROMETRY 1.1. Reviews A number of well-presented review articles have appeared in the period covered by this Update. Most covered one specific area of application but they also gave details of the general principles of AMS and can be used by the reader to become familiar with the current status of this highly sophisticated technique. The good introductory review by Vogel et al.(96/1490) was somewhat broader in scope. It gave an insight into the development of AMS an explanation of the basic principles and a discussion of precision sensitivity and throughput of analysis. Examples of applications were in radiocarbon dating earth sciences and biological and environ- mental tracing. The review on radiocarbon dating by Donahue (96/1606) was a pleasure to read. It was an excellent introduction to the principles of AMS and the method of radiocarbon analysis and was effectively a primer for those not directly involved in the use of AMS. The review worked through sample prep- aration instrumentation errors and background calibration and typical applications in a clear and concise way using the University of Arizona facility to illustrate the points made.(AMS) The review was of particular value for explaining the principles behind each of the components of the instrumental analysis. The review on AMS in environmental geoscience by Rucklidge (96/1484) was also excellent. The ability of AMS to determine low-level long-lived radionuclides at natural background levels has opened up possibilities for applications in a range of studies of natural and anthropogenic processes. Although the paper concentrated on the use of 1291 in environmental studies and gave several examples of application consideration was also given to the use of 26A1 "Be and 36Cl. A particularly interesting feature of this review was a listing of the 28 AMS laboratories in the world more than half of which share their facility with other accelerator-based techniques.The review of Synal (96/1513) covered the use of radionuclides as environ- mental tracers the use of radiocarbon trapped in tree rings and corals as a record of climate the study of extraterrestrial- cosmogenic processes and in-situ production as a measure of erosion rates. A workshop on the production rates of in-situ-produced cosmogenic nuclides (95/2467) summarized in a clear and comprehensive manner the state of knowledge for this relatively new application. The present understanding of the production rates of the nuclides in-situ in terrestrial samples and how they can be applied to the interpretation of measured radionuclide concentrations were covered. In addition the status of current studies and various models used to describe observations were presented.Aspects of analysis that needed to be addressed included improved detection sensitivities and measurement techniques for the measurement of potentially useful in-situ nuclides such as 59Ni and 32Si increased ion-source output for the determination of 41Ca and improved measurement pre- cision of 26A1 "Be ratios to allow specific erosion rates to be determined. The review on biomedical applications by Freeman and Vogel (96/1607) considered not only the use of elemental tracers (26A1 41Ca) but also l4C-labe1led biomolecules. The need to avoid sample contamination was highlighted. The development of miniaturized accelerator systems and ion sources capable of interfacing to conventional HPLC and GC was foreseen for use in biomedical laboratories.Two reviews on ultrasensitive AMS trace-element analysis by Rucklidge and co-workers (95/4617,95/4630) concentrated on the determination of the platinum group elements (PGEs) in mineralogical studies. The first review covered the current state of the art of AMS analysis in particular detection limits and spatial resolution whereas the second considered in more detail the mineralogical aspects and served as a progress report on current research. In comparison with other microbeam methods AMS had the best detection limit (<cng 8-l) but the poorest spatial resolution. Technical development is required to achieve smaller probing-beam diameters to improve the latter. Other suggested improvements included the use of a dual ion source with enlarged computer-controlled stage and peak-switching magnet software for the automatic determi- nation of several elements.A throughput of 60 targets or more per hour was considered achievable. A good over-all picture of AMS applications was given by the Abstracts of the 209th National Meeting of the American Chemical Society Division of Nuclear Chemistry and Technology held in April 1995. Although the abstracts tended to be short enough detail was given to gain an understanding of the recent advances in AMS. 1.2. Facility Reports Major development has sputter source at Oxford replaced with a spherical within the source. This taken place of the carbon dioxide (95/2451). The coiled ionizer was one to give a more open geometry resulted in immediate removal of 356 R Journal of Analytical Atomic Spectrometry October 1996 Vo!.11material evaporating from the surface of targets and reduced the clean up time to about 4min per target. In addition less recoil implantation of contaminants resulted in consistently low background currents from targets (about 70 nA). Cross contamination between adjacent targets was as low as (1.25% and was considered not to be a problem. Other modific<itions to the source have improved performance so that beams ~ 3 0 0 pA from graphite targets and > 30 pA from cxbon dioxide targets have been achieved. However high ion cu rrents resulted in noticeable space charge effects. These were reduced by neutralization with nitrogen bled through a gas closing valve in the region of the first beam waist.The source was also shown to be potentially useful as a GC detector. Samples containing as little as 3 pg of carbon could be measured to an accuracy of about 3 YO for modern material. Most applic,itions would require a combustion furnace to interface thi GC and AMS. Further details have been reported on the over-all system performance of the new generation radiocarbon system at the Groningen facility which was the first of a line of comniercial AMS instruments and has been in operation since May. 1994 (96/1241). A computer-controlled X-Y sample movemerit was incorporated in the ion source so that up to 64 positicins on the sample surface could be selected and data acquired in time blocks of up to 30 s. The diameter of the caesium beam on the sample surface could be controlled by the distance of the target holder to the ionizer.Beam diameters down to 350 pm could be achieved. High precision and high throughput (up to 3000 samples per year) were achieved through simultaneous detection which not only guaranteed measurement of all three carbon isotopes under the same conditions but also provided an on-line diagnostic tool for the operation of the instrument. The over-all background was 45 ka with a negligible machine component and system performance on 613C and the l4( "C ratio was better than 2%0 and 0.5 pMC respectively. Improvements incorporated in the design of the next instru- ment installed at the University of Kiel included the use of modified and magnetically-suppressed acceleration tubcs the addition of two beam profile monitors and the insertion of an aperture between the 33" electrostatic deflector and the 90" magnet to simplify tuning.Two Australian AMS facilities for radiocarbon measurcments have been described. The CSIRO facility based on a 3 MV Tandetron achieved routine precisions of 2-4% whicli were limited by the low intensity source used and the slow cycling mode of operation (95/2450). The reflected-caesium beam source produced a low intensity (2-4pA) C- beam from graphitized samples. This coupled with the 20-25% trans- mission efficiency for C3+ ions at a terminal voltage of 2 MV resulted in the need for data acquisition over 20-40niin to achieve a 1% statistical error. Better precision (1-1.5%) was achieved at the ANTARES facility (95/2449) through uxe of a high-intensity source which produced a 20 pA 12C- beam and a 5.20 MV accelerator voltage to produce C4+ ions.A slow cycling mode of operation was also used at this facility and consideration was given to use of a fast isotope cycling system in which 12C and 13C would be monitored it the injection magnet during mass 14 injection to achieve precisions of < 1%. 1.3. Methodologies A short paper with 15 authors described the methods used at Erlangen for the determination of strontium radioisotopes in environmental samples (95/3535). Because Sr does not. form negative ions samples were prepared as SrF and the molecular ion SrF3- was used for analysis. Targets containing 10mg of SrF compressed with 20 mg of gold powder gave currents of up to 300nA for 2-3 h.The use of gold powder aY;oided problems of contamination that are possible with the use of silver powder. Rapid switching between 90SrF3 - and 88SrF3 - (injected for 5 ms every 30 ms) was achieved by applying a voltage to the chamber inside the 90" magnet at a constant magnetic field. The beam energy of Sr8+ ions after charge reversal and second acceleration was 43 MeV. Although rapid 90Sr analyses were possible at the 1 in lo9 level for pure starting materials the analysis of environmental samples was limited by the presence of contaminants in particular "Zr which was the source of a small background. The level of 90Zr had to be reduced below and other impurities (for example Ag A1 and Cu) had to be efficiently removed before analysis. The determination of "Sr was also part of a study with the primary aim of developing methodologies for the determination of 41Ca and 1291 in ice cores (95/2470).Iodine was recovered by precipitation as AgI whereas Ca was recovered from a second subsample by precipitation as the oxalate conversion to the oxide by ignition conversion to metallic calcium by reaction with ZrO and final conversion into CaH targets. A sputter negative ion source with 12-sample wheel was used for iodine measurements whereas a high-intensity source with single sample loading was used to produce CaH,- ions. Total energy and TOF signals were used to identify the 129111 + ions; ions were identified by the additional use of a multi- anode ionization chamber. The 1291 I measurement sensitivity was < 1 x that of 41Ca:Ca was limited to about 5 x by the negative ion beam current that could be achieved.Initial feasibility tests of the determination of Sr as SrH,- indicated a "Sr Sr sensitivity limit of 5 x An upgrade in progress at the UNILAC facility Darmstadt including the development of a pilot beam a new ECR ion source and a high-charge-state injector led Henning (95/3570) to reassess the use of AMS for counting ,05Pb ions in geological samples. The new injector would improve over-all efficiency and transmission monitoring would make measurement more reliable although the latter had only been tested for 41Ca. It was estimated that an over-all AMS sensitivity of 1 x lop4 for 205Pb could be achieved but this remained to be demonstrated. Such a sensitivity would however still require 100 kg of sample for measurement assuming 100% efficiency during the geo- chemical extraction step.Knowledge of the properties of the negative ions of actinides is required before the interest in AMS analysis of actinides can be met. The group at Toronto have presented measurements of negative ion intensities of Pa Pu Ra Th and U and of their carbides and oxides using a milli-probe caesium sputter- ing source (95/2454). Use of the + 4 charge state at 1.25 MV terminal voltage resulted in the need to detect low energy (6.27 MeV) ions. Counting rates greater than ten times back- ground and adequate energy resolution ( 13%) were achieved. The results showed that the dicarbide was a good molecule for the determination of Pa Ra and Th whereas the mono- oxide was better for Pu and U.Improvements were foreseen through the use of sources more efficient than the sputtering source which was considered a limitation on analytical performance. Currie (95/2452) has assessed experimentally using AMS data the strengths and weaknesses of four alternative rulesfor estimating (random) uncertainty for counting experiments. Application of the different rules would lead to diverse and sometimes biased uncertainty estimates based on the same experimental data. The most serious differences arose with small degrees of freedom and large confidence levels. Utilization of the maximum variance rule which takes into account knowledge of counting error had a major advantage in avoiding excessively small confidence intervals but led to biased variance estimates and overly conservative confidence intervals.41ca9+ Journal of Analytical Atomic Spectrometry October 1996 Vol. 11 357 R1.4. Isobaric Separation The use of characteristic projectile X-rays as a detection method capable of isobar discrimination has been further investigated by two laboratories independently (96/1240 96/1242). Both groups used similar detector setups in which ions from the spectrometer were incident on a target foil and induced X-rays were detected directly behind the target foil to maximize the solid angle. In some applications additional absorbers were placed between target and detector to stop ions and low energy X-rays. The group at Zurich (96/1240) considered 'projectile X-ray detection' (PXD) to be of limited application because detection limits for 36Cl 59Ni and 12%n were above the natural concentrations of these isotopes and the method could only be used to measure enhanced anthro- pogenic contamination.The use of PXD was considered however to open up the possibility for small (terminal voltage < 3 MV) accelerators for measurement of these heavy radioiso- topes at anthropogenic activity levels. The group at Lawrence Livermore (96/1242) saw more promise in the more grandly titled 'projectile X-ray AMS' (PXAMS) and considered the reduced detection efficiency to be adequately offset by the gains in isobar rejection and simplicity of design. Preliminary work on the detection of 79Se was described and X-ray yields for a number of ions given. For higher mass isotopes the PXAMS system allowed better discrimination of competing atomic isobars than is possible with energy loss detectors but hybrid systems of X-ray detectors in combination with other detection methods was seen as the way forward.Nadeau and Litherland (95/2455) at the IsoTrace Laboratory Toronto have demonstrated the successful use of electric dissociation both as a probe of the structure of negative ions and to destroy the more weakly bound negative ion of a pair of isobars thus making the analysis of the remaining isobar possible. The interfering ion 48Ca- was completely destroyed in the determination of 48Ti- but further develop- ment of analytical protocols was required. The prime consider- ation in the design of the dissociator which was installed between the electric analyser and the injection magnet was the need for a high electric gradient (up to 10 MV m-') and an acceptable transmission over a range of voltages for destruc- tion of negative ions.A voltage of 30 kV was applied success- fully across stainless steel electrodes 1 mm apart. The same authors (96/1243) considered that with MeV ions and high voltage techniques transverse electric gradients approaching 60 MV m-I could be exploited to achieve isobaric separation of isotope pairs such as I3'Ba 135Cs and ,05Pb ,''Tl. 1.5. Sample Preparation Considerable attention continues to be paid to the extraction of radiocarbon from a diverse range of sample matrices. A new sample preparation line incorporated step-wise heating and differential cryogenic techniques to distinguish different sources of I4C associated with meteorites (95/2491).Samples (300-500 mg) were pyrolysed in crucibIes hand made from high-purity molybdenum rod to produce three aliquots of carbon-rich gas contamination below 450 "C terrestrial weath- ering products between 450 and 850°C and the spallation component liberated from the melt. The two dominant species produced CO and CO were separated for each fraction using temperature traps. The analysis of Antarctic meteorites was the first reported measurement on meteorites and showed that I4C was released from the spallation preferentially as CO. This could be used to estimate residence times on Earth. Bradley and Stafford (96/1733) have described an automated pretreatment system for the extraction of radiocarbon from plant fossils.Samples (0.01-0.1 g) were placed in vertical boros- ilicate glass columns (100 mm long x 10 mm i.d.) and reagents contained in pressurized vessels passed through under the control of a personal computer. The system handled three columns simultaneously and up to four different reagents but had the potential to run up to ten samples. The automated apparatus proved to be more than three times faster than the traditional manual procedure and in most cases produced a higher yield. In addition the new system appeared to be more effective in removing humates from the samples. The manual system was considered to be more prone to human error and to have a greater risk of contamination. Changes to be incorporated into an improved system included the ability to use concentration gradients of KOH from 0.01% to OS% flow rates adaptable to the fragility of samples treatments at temperatures up to 80 "C and modified more flexible software. Highly organic peats and lake muds are not well-suited to the traditional methods of sample preparation involving repeated deflocculation selective sieving and final retention of the largest sub-fossil pollen taxa.Richardson and Hall (96/1734) have recommended an optimized procedure for the preparation of such samples with improvements on the estab- lished methods. They have also investigated the novel alterna- tive strategy of microbiological digestion of the fibrous plant types but in fact failed to achieve any appreciable digestion with the proprietary microbiological activator chosen.Further work was being undertaken to identify cellulose-decomposing bacteria which might form the basis of a more successful digestion. Of significance in the determination of'OBe in rocks was the discovery by Middleton et al. (95/2472) that commercial aluminium contains about lo8 atoms of "Be per g of alu- minium. The Be was thought to have been produced in the atmosphere and introduced into aluminium ore deposits by rainwater during ore genesis. To keep blanks down in the determination of ''Be aluminium carrier should be prepared from rocks old enough for "Be to have decayed aluminium vessels for grinding should be avoided and targets should not be loaded into aluminium cathodes. The ''Be concentrations of bauxite ores provide information on the length of exposure to rainfall and the elapse of time since that exposure.A study by Welten et al. (95/2490) of 26A1 and "Be in meteorites employed aluminium carrier and aluminium sample holders and found "Be production rates to be 10-30% higher than calculated using a semi-empirical model. The increased use of 41Ca in biomedical tracing experiments has highlighted some problems experienced in sample prep- aration. Johnson et al. (95/2488) used the somewhat lengthy procedure uia oxalate oxide and metal to produce CaH targets but acknowledged problems in the extraction which resulted in combination with an unstable source in large errors in some data. Samples containing at least 20 rng of Ca were required for analysis. Southon et al. (95/2489) and Freeman et al.(96/1702) on the other hand elected to produce CaF targets because of the difficulties involved for biomedical laboratories in reducing CaO to CaH and in keeping CaH dry. This last group investigated alternative methods for production of CaH which is preferable to CaF for the AMS analysis but were unsuccessful and so developed a procedure based on oxalate precipitation separation of Ca by cation exchange and precipitation of CaF,. Southon et al. left out the cation exchange step but encountered some problems with high count rates and backgrounds. A requirement of 1 mg of Ca in the sample was set as a result of poor ion currents below this level which were attributed to losses by adsorption on container walls. The AMS of CaF targets had in comparison with CaH targets the disadvantages of lower ion currents reduced stripping efficiency and increased interferences.The determination of '"1 in seaweed and algae requires careful preparation techniques to avoid losses and contami- nation. Kilius et al. (95/2476) found an initial alkali leach and fusion method to be preferable to dry ashing because the use 358R Journal of Analytical Atomic Spectrometry October 1996 Vol. 11of disposable iron or nickel crucibles reduced the risk of contamination. However the procedure still involved ignition at 600°C and addition of Na202 to prevent loss of HI This resulted in the formation of insoluble iodate for which an additional digestion step was required. After extraction into chloroform back extraction into water and addition of NaI carrier I was precipitated as AgI.This was subsequently ;mixed with niobium powder to prepare targets. Analysis of samples from the Colombia River estuary Washington State USA found levels of 1291 above background but much diluted ( lo6) from the levels found at the suspected source a nuclear rtfactor storage facility. 1.6. Applications 1.6.1. Dating Although radiocarbon dating is the most established and rou- tine of the AMS techniques there remain uncertainties in its application because of the time dependent fluctuations \if the 14C concentration in the atmosphere in the past. As a result the probabilistic calibration procedure can be ambiguous and interpretation difficult. Niklaus et al. (95/2453) have used a numerical procedure to study the influence of 14C Auctu.4i t' ions on the accuracy of radiocarbon dating. Under favourable conditions of 1-2960 counting statistics and instrumental repro- ducibility of the same order it was possible to obtain a precision of 1.5-3%0 and reduction of the 2a confidence intervals to 140 years. In the more difficult age ranges however 20 confidence intervals of only 425 years were possiblc and were nearly independent of improvement in the precision of radiocarbon measurement. A novel application was the use by Kalish (9512481) ofJish otoliths as a proxy of radiocarbon in seawater. Use of these calcium carbonate gravity and auditory receptors found in the membranous labyrinths of teleost fish was considered to have potential for investigations as diverse as ocean circulation carbon flux fish age determination and paleoclimatc )logy.Because fish occur in almost all aquatic environments and at all depths fish otoliths can provide 14C records from rvgions not covered by hermatypic corals. The prospects of dating using 1291 were found by Schink et al. (96/1700) to be very poor. The proposed method was based on the fact that iodine is concentrated in marine organic matter the 1291 I ratio of which would reflect the ratio in the sea-water at the time of formation. Analysis of seawater samples from the Gulf of Mexico found unexpectedly large variations in 1291 concentrations and fish were found to have higher levels of 1291 than the waters they swam in. 1.6.2 Hydrology Preliminary data have been presented by Fehn et al. (95,2474) on the dating and tracing of fluids using 36CE and lZ91 The introduction which provided a very good review and descrip- tion of the origin of these radioisotopes and their use for the determination of source rocks pathways and residence times of fluids was followed by three clearly explained examples of application.Anthropogenic influence was found to be insig- nificant on fluids from a depth of 4000m in a deep drilling project in Germany and subsurface production of the radioiso- topes was the most likely source. Residence times of > 500000 years were estimated for geothermal brines in the Salton Sea system California. The major source of brines in an Oklahoma system could be identified from the uniquely high 1291 I ratios. The measurement of 36Cl Cl ratios continues to be used to trace the origin and movement of ground and other u'aters.Vogt et al. (95/2477) established the natural meteoritic 36Cl baseline in several shallow perched aquifers in Indiana and concluded from the analysis of two aquifers uninfluenced by anthropogenic sources that recent pre-bomb 36Cl C1 ratios must have been similar to those in modern precipitation. Other aquifers showed clear indications of the presence of bomb- produced 36Cl but residence times were estimated to be 10-15 years longer than inferred from tritium analyses. Salinity in deep groundwaters from fracture zones in a granitic batholith was shown by Gascoyne et al. (95/2475) to be derived by dissolution of soluble salts in the rock matrix. Analysis of surface waters by Milton et al.(95/2473) showed that small quantities of 36Cl were released into the atmosphere by reactor operations at the Chalk River Laboratories in Canada but that most is deposited locally with > 15% falling within 1500 m of the reactor stack. The levels of 36Cl in the Great Lakes (95/2485) could only be explained by the continued presence of bomb test input. The clearing times of the lakes in particular Lake Superior were estimated to be hundreds of years. 1.6.3. Environmental tracers Radiocarbon measurements can be used to trace the origin of deep ocean waters. Jones et al. at Woods Hole (95/2482) routinely obtained precisions of 3-5%0 for the analysis of sea- waters using single targets and nominal 45 min (nine 5 min analysis blocks spread over a period of 12 h) analysis times.The precisions were based on assessment of errors associated with the counting statistics 6 13C correction reproducibility of nine individual runs on each target and measurement of standards. It was suggested that some degree of duplicate analysis was still required to ensure a high quality of data. The results presented showed that the deep waters of the Canada Basin in the Arctic Ocean have a renewal rate of 430 years. Gislefoss et al. (95/2483) obtained precisions of about 6%0 for counting times of 20 min per sample in the analysis of small (0.5 1) samples of sea-water. The origin of atmospheric gases and aerosols can also be investigated by radiocarbon analysis. Preliminary analysis by Eisma et al. (95/2479) of atmospheric 14CH4 in the Netherlands suggested a contribution from nuclear installations other than the suspected pressurized or boiling water reactors.This had the implication that the total emission of 14CH from nuclear activities may be higher than originally estimated. Methane was isolated using cold traps with charcoal and molsieve and preparative GC and then converted to C 0 2 using a CuO oven. The CO was subsequently analysed by AMS using conven- tional graphite targets. The typical sample size of 1 mg could be measured with a precision of 0.5-1%. Radiocarbon measurements of sub-milligram atmospheric aerosol particles have been investigated by Currie et al. (95/2478) as a means to partition individual combustion products between fossil and biospheric sources. Emphasis was given to the need to pay attention to the age and mass of the over-all carbon blank which was the ultimate limitation on AMS analysis.The measurements were used to test a model for the apportionment of mutagenic aerosols to petrol and wood burning sources and to identify tracers for vehicular contributions to the atmosphere now that lead has become unreliable. The results indicated that the tracer potassium previously assumed to be conservative and widely used to assess biomass burning requires local wood-source calibration and may produce erroneous conclusions for certain tempera- ture regimes. Use of 1291 as an oceanographic tracer by Yiou et al. (95/2484) produced the interesting result that over the whole study area around the United Kingdom and in the North Atlantic a single oyster would be sufficient for measurement of '"1.This was attributed to the sensitivity of the method but the substantial emissions from the reprocessing plants at La Hague and Sellafield were also a factor. In the English Channel or North Sea 1 ml of sea-water was sufficient for analysis but elsewhere 11 was appropriate. Some samples Jowrnal of Analytical Atomic Spectrometry October 1996 Vol. 11 359Rneeded to be diluted to bring the 1291 concentrations to a level unlikely to cause problems of contamination. Seaweed samples also analysed were treated by a simplified procedure. They were ashed and leached with water and after oxidation to I iodine was extracted into chloroform reduced back extracted into water and precipitated as AgI for preparation of targets by mixing with niobium powder.The authors reported that the procedure has been used to show that despite extensive dumping of nuclear waste by the former Soviet Union most of the 1291 in the Kara Sea comes from the reprocessing facilities at La Hague and Sellafield. The 129Z concentrations in moss samples down-wind from the reprocessing plant at Sellafield were not only enriched by a factor of four to six times relative to normal background levels but were also highly variable (95/2480). Although approxi- mately 1 g dry mass of moss was used to provide AgI targets for analysis 1 mg would have been sufficient since it was necessary to dilute some samples by a factor of 10 000. The highest concentrations were found close to the plant and in moss over limestone at the extreme end of the traverse.Further work was proposed to understand better the role of alkaline soils above limestone in immobilizing iodine in the environment. 1.6.4. In-situ production The interactions of galactic cosmic-ray particles in the Earth's atmosphere produce a cascade of particles some of which reach the Earth's surface and produce cosmogenic nuclides. The use of these nuclides to study histories of targets or of cosmic radiation is a relatively new and rapidly expanding area of application of AMS which is however often limited by inadequately known production rates. Laboratory simulations of these processes have many limitations for example the inability to reproduce the complex mix of particles and their energies but they do provide controlled irradiation of charac- terized samples.Reedy et al. (95/2459) have simulated the production of 26A1 "Be and 14C in synthetic quartz and silicon exposed to neutrons. The irradiations produced 26Al "Be ratios similar to those measured with documented natural samples. Production ratios varied with the target and with the energy and the nature of the incident particles illustrating the complex nature of predicting such nuclear interactions and their ratios. The same group of authors used both gamma-ray spectroscopy and AMS to study the production of 14C by the irradiation of silicon and silicon dioxide targets using proton beams (95/2492). For the preparation of C02 samples were mixed with an iron combustion accelerator heated to melting in 0 and the gases passed over MnO at room temperature and CuO/-Pt at 400°C.Standard procedures were then used to produce graphite targets for analysis. Cosmogenic "Be produced in the atmosphere known as 'garden variety' "Be attaches to sub-micrometre aerosol par- ticles and is deposited on the Earth's surface by wet deposition. Monaghan and Elmore (95/2471) have used the fact that most "Be in soil is of the 'garden variety' to propose a method to determine bedrock-to-soil conversion rates on a hill slope. Once the decay constant and delivery rate of "Be are known then its abundance in soil can be used to determine the rate of its chemical or physical removal or the exposure age of the soil surface. The principles of the method were presented but this interesting application remained to be tested and used.The "Be concentrations in marine sediment cores from high northern latitudes showed an inverse relationship to the sedi- mentation rate of each climatic stage (95/2439). The sharp contrast of high and low "Be concentrations at climatic stage boundaries indicated that the method could be used for stratigraphic dating of sediment cores in environmental and climatic studies. The in-situ production of 14C in Antarctic ice has implications for the use of 14C to date ice cores. Two groups have been investigating this. Van Roijen et al. from Utrecht (95/2466) used a dry extraction procedure in which CO and C02 released from 5 kg of ice chipped into mg pieces were trapped by a molecular sieve and cold trap respectively. The presence of I4CO in all the ice samples was taken as evidence of in situ production and was used to correct for the presence of in situ produced 14C02.The deduced accumulation and ablation rates were in good agreement with field observations indicating good efficiency of extraction. Jull et al. (95/2465) used similar sample preparation procedures and also concluded that direct dating of accumulating ice cannot be used without correction for in situ produced I4C. They found that most 14C in ice was as a result of in situ production rather than the trapping of 14C02 from air. Although 14C was produced in firn (accumulat- ing snow) as both 14C02 and 14C0 in variable amounts the transformation of CO to CO was rapid and complete before the conversion of firn to ice. La1 and Jull (95/2458) found that in situ production of 14C in terrestrial rocks was predominantly as I4CO.A low- temperature wet extraction method using HF was used to extract 14C and to separate the 14C02 and 14C0 fractions. Digestion vessels made of chlortrifluorethylene proved resistant to the chemicals and unlike other materials including Teflon did not measurably adsorb CO or CO. Silicate samples (50 mg to 50 g) were digested at 60-70°C for 8-10 h under carrier gases of 14C-free CO and CO (nominally 1-2 cm3) and the liberated gases collected in traps. A method for the extraction of total 14C from rock samples (10-60 g) described by Jull et al. (95/2461) involved the destruction of carbonates organic compounds and iron and manganese oxides by acid treatment followed by melting in an rf furnace in a flow of oxygen. The gases evolved were pumped through an Mn02 trap to remove sulfur compounds and Pt-CuO at 450 "C to convert all carbon compounds to C02.The determination of erosion rates using 26Al has been investigated by Strack et al. (95/2463) by analysis of quartz samples from cores of a continental deep drilling project in Germany. In the lithosphere the production of 26A1 in quartz is dominated by spallation reactions on silicon in the first few metres and negative muon capture reactions on silicon at depths below a few metres up to a few hundred metres. The principles of the method were described and the basis of the calculations laid out. The main advantages in the use of 26A1 instead of 36Cl were the absence of exchange by meteoric water and the lack of background reactions. The quartz samples and A1203 carrier were dissolved in HF (190°C 200 bar) AlF converted to Al(OH) in HNO and the Al(OH) converted to A120 by combustion at 900°C.The Al,O was mixed with silver powder for preparation of targets. Although more points needed to be measured and the statistics improved good agreement was obtained with experimental data and this new method seemed promising. A procedure has been described by Knies et al. (95/2468) for the concentration and separation of "Be and 36Cl from rainwater samples. Chloride (3 mg) and Be (2 mg) carriers were equilibrated with the rain sample (6-8 1) and the samples pumped sequentially through a cation exchange column to remove Be and an anion exchange column to remove Cl.The eluted Be was precipitated as Be(OH) and ignited at 900°C to form Be0 for analysis; the eluted Cl was precipitated as AgCl for analysis. The 'Be "Be and 7Be 36Cl ratios can be used to study the mixing of air masses from the troposphere and stratosphere and also provide information on the history of the cosmogenic isotopes and other trace constituents in the atmosphere. The 36Cl data showed a winter minimum followed by a maximum in late spring to early summer which was consistent with the expected enhanced mixing of stratospheric 360R Journal of Analytical Atomic Spectrometry October 1996 Vol. 11air into the troposphere during the late spring. The same pattern of stratospheric-tropospheric mixing was found by Hainsworth et al. (95/2469) in a study of precipitation in Maryland with the aim of providing background information for the use of 36Cl both as a hydrological and stratospheric tracer.1.6.5. Biomedical The medical application of 26A1 continues to be an area of growth but the AMS procedure has become almost a matter of routine. Hohl et al. (95/2487) gave two volunteers oral applications of 100 ng of 26A1 in 100 pg of A1 as AlCL3 and measured the 26A1 concentrations in blood serum and urine. Carrier was added directly to blood serum following t rypsin digestion and urine samples which were ignited at 1000 "C to obtain A120 for targets. Other groups of workers have studied the uptake of A1 into body organs by rats in particular incorporation into brain tissue. Fink et al. (95/2486) digested brain tissue with acid and following addition of carrier precipitated A1 as its 8-hydroxyquinoline complex by atldition of ammonium acetate.The precipitate was ignited to form A120 for targets processed biomedical samples giving ,'Al- currents in the range 50-200nA. A slow cycling mode of operation was used which gave a long-term reproducibility at the 5% level and an over-all sensitivity level of ( 5 + 5 ) ~ 1 0 - ' ~ . Preliminary details have been given by Day et al. (95/( :4301) of a new procedure for the determination of Pu in human i issues. The PuO- ion generated from Pu-Fe(OH) in a conveiitional Cs sputter source was stripped at a low terminal volta!;e and the resulting Pu7+ ions counted in a gas ionization detector. The reported detection limit was lo-'' g equivalent to about Bq of 239Pu and below the levels readily achievable by alpha spectrometry.Improvements were envisaged to in crease sensitivity about ten-fold. The detection limit using 2441'u was about lo-* Bq. 1.6.6. High-purity materials Datar et al. (96/1458) used an innovative procedure to study the dzfusion ofchlorine in silicon wajers. Following implantation of 35Cl ions in silicon wafers at energies of 200 and 400 keV some of the 35Cl atoms were converted by neutron activation into 36Cl atoms which were then measured as a funcrion of depth by AMS. Variable parameters were the implanl dose and the time temperature and atmosphere of annealing The Trace Element Accelerator Mass Spectrometry (TEAMS) system developed by the University of North Texas and Texas Instruments has been used for the depth piojiling analysis of semiconductor materials (96/1701).The system con- sisted of an ultra-clean source based on clean silicon ctjmpo- nents for ion optics and 90" magnetic analysis of the caesium sputtering beam a 3 MV tandem accelerator for ion axeler- ation and charge exchange and post-acceleration magnetic and electrostatic analysis computer controlled to allow automated mass scans of stable isotopes. The depth profiling rale was 0.2 nm s-l with a raster size of 1 mm x lmm a primary Cs+ beam current of 0.5 pA and a Cs beam spot size of 150 pm fwhm. Bulk sensitivities of sub-ng g-' were possible for many elements in the periodic table. 2. GLOW DISCHARGE MASS SPECTROMETRY (GDMS) 2.1. Reviews The only reuiew article of note since last year's Updai:e was the excellent one by King et al.(96/1647). Although tt was intended for the general reader and not for specialists in the field it can be highly recommended for it covered in detail and with clarity all aspects from historical development to recent applications. Sections were included on historical per- spective the glow discharge analyte atomization and ioniz- ation instrumentation quantification analytical performance and applications. The authors made the valid statement that to remain competitive commercial systems must incorporate advances in MS technology to increase analytical performance while decreasing the size complexity and cost. This applies to most of the MS techniques covered in this update. GDMS was one of the techniques covered by Broekaert (96/1402) in his comprehensive review (210 references) on plasma optical emis- sion and mass spectrometry.Application reviews have as in previous years been few in number and not specifically on GDMS. The review (122 references) by Capper and Roberts (95/4431) on the analysis of Hg,-,Cd,Te and related materials included the GDMS analysis of substrate materials. A brief but clear description of the basic principles of GDMS was given by Dietze and Becker (96/1711) in their German review of the mass spectrometric analysis of solids. Of the six MS techniques GDMS was considered to have the best over-all figures of merit with in particular high sensitivity and precision. 2.2. Fundamental Studies In an impressive study on the role of Penning ionization in ion formation in the dc GD plasma Saito (95/3432) determined relative sensitivity factors (RSFs) in a number of metal standard samples using two discharge gases Kr and Xe.The values of the RSFs depended on the degree of Penning ionization which was only apparent if the energies of metastable species were higher than the ionization potentials of the elements. In general the RSF values in Kr and Xe were higher than those previously obtained in Ar because of lower sputtering ratios but were considerably lower for those elements (P S) with ionization potentials above the metastable energies of both Kr (9.82 and 10.5 eV) and Xe (8.91 and 9.12 eV) and for those elements (As Se) with ionization potentials between the metastable energies of Kr and Xe. The relative degree of Penning ionization was estimated to be 7642% for As P and Se and 64% for S.It was concluded that Penning ionization was the main mechan- ism for ionization of the sputtered species in a dc GD discharge but that the relative proportion was dependent on discharge conditions (i.e. current and voltage). Saito (96/1752) has continued to study the use of Ar filler gas containing H for reduction of matrix eflects by measuring RSFs (Fe= 1) for 22 elements in 19 metal RMs. Duplicate samples were analysed alternately using pure Ar or Ar contain- ing 0.2% H with a 200s time interval allowed between measurement with the different gases. The H concentration was lower than the 0.5% used in previous studies in order to decrease the formation of hydrides and resultant suppression of signal.The relative variations in RSFs were reduced from 50 to 20% when the gas mixture was substituted for pure Ar. No explanation was proposed for the decreased matrix effect using the gas mixture. It was suggested that the use of the gas mixture would allow standardless analysis with 10% accuracy if universal RSFs obtained by averaging of values from a wide range of RMs were applied. A systematic study by Barshick et al. (96/1517) on the formation of metal-noble gas adduct ions between 24 metals and three noble gases (Ar Kr Ne) showed in general a periodicity of behaviour for all three gases. The elements Cd Hg and Zn demonstrated anomalous behaviour however with high abundances of MX' ions observed. Although GD press- ure and power were eliminated as an explanation for the phenomenon the increased collision frequency (resulting from higher sputtering rates for these metals) was believed to account for the relative abundance of adduct ions in the discharge.A schematic representation of the basic processes occurring Journal of Analytical Atomic Spectrometry October 1996 Vol. 11 361 Rin a GD was included in a well written and detailed paper by Gijbels and colleagues (95/4727) on the energy distribution of ions bombarding the cathode. The reproducible results obtained for X + X2+ X2+ M+ and MX' where X denotes the gas (Ar Ne) and M the cathode material (Al Cu Mo Ta) illustrated that the cathode was bombarded by low energy singly-charged gas ions and by a significant flux of high energy singly-charged ions of its own material.Singly-charged gas ion motion in the cathode dark space was dominated mainly by charge exchange collisions cathode ions reached the cathode with an energy almost equal to the full discharge potential equivalent due to the low probability of asymmetrical charge exchange. The energy distribution of all kinds of ions at the cathode was determined by the number of charge exchange collisions and was influenced by the mean free path and length of the dark space. The length of the dark space varied more with pressure than the number density of gas atoms. Ion kinetic energies produced in the rf GD were measured by Cable and Marcus (96/1519) using the retarding potential method in which they biased the analyser quadrupole of a double-quadrupole MS to act as a repeller.The study indicated that the plasma conditions under which ions were formed affected kinetic energies and energy spreads to a greater extent than variations in analyser parameters. The kinetic energy of species produced in the rf GD did not vary as a function of ion mass. Tanaka et al. (95/2403) in a study on the effect ofdischarge gasflow rate on RSFs in a dc GD concluded that the gas flow rate should be controlled very precisely. They inserted a diaphragm valve between the discharge cell and vacuum pump so that the gas introduction and evacuation flow rates could be controlled independently. The flow rate could therefore be changed under constant voltage and current and as a conse- quence constant pressure. The signal strength increased with flow rate and resulted in significant differences in RSFs.That for Cr in an alloy was 0.084 at 5 ml min-' but 0.32 at 16.5 ml min-'. The increase in the gas flow rate did not cause an enhancement of the sputtering rate of the samples the variation of the kinetic energies nor the variation of the atomic emission intensities. The mechanism or reason for the effect of the gas flow rate was not found. Alternative plasma gasesfor rf GDMS were studied by Giglio and Caruso (96/1518) in an attempt to reduce problems of interference. Of all the gases studied (Ar He Kr and N2) a He plasma gave the highest intensities for a range of elements in SRM Cu500. Krypton was not a practical alternative gas since analyte intensities were low memory effects were severe and UHP Kr expensive to use.The sputter rates achieved were in the order Ar > He Ne > N2. The detrimental efSects of water vapour in the discharge have continued to be studied by Ratliff and Harrison (96/1516) by pulsed injection of water into an Ar discharge using three different cathode materials (Cu Fe Ti). Metal oxides were observed during and shortly after the pulsed injection the effect being dependent on the reactivity of the cathode with water and its dissociation products. The shortest perturbation period was observed for the titanium cathodes which acted as strong getters. The water dissociated in the discharge to form reactants which could affect the analysis and as in previous studies it was concluded that water vapour should be removed from the discharge for best analytical results.In an important study with implications for the matching of standards Hess et ul. (95/3536) found that ion yield was dependent on the chemical form of the analyte. The relative ion yields for some but not all of the elements measured were greater when the element was deposited as a solution on to a solid matrix than when the element formed part of the matrix. The mechanism by which the enhancement occurred was not well understood but the authors believed it involved a form of reactive etching followed by collisional dissociation of the sputtered molecular species into metal ions. Preliminary investigations suggested that under ideal conditions it might be possible to eliminate the effect on ion yields by holding discharge conditions constant and by closely matching samples and standards in such a way that quantification by standard addition were possible.2.3. Instrumental Developments An yf GD high resolution M S has been built by Becker and co-workers (95/4715) by interfacing a new design of cell directly to a Mattauch-Herzog geometry instrument previously used with a spark source. The cell had a confined electrode geometry and was designed to be coupled to any type of SSMS without the need for reconfiguration of the vacuum and electrical systems. The discharge gas was supplied through the top of the cell so that the resulting radial gas flow prevented redepos- ition and increased sample material transport. As a result the sputtering rate and analyte signal intensities increased signifi- cantly.The electrical interface was designed to provide an effective rf power transfer ensuring rf shielding and grounding and to superimpose the rf potential to the accelerating voltage. The double focusing MS allowed separation of singly-charged atomic ions from discharge and residual gas ions which had an average energy 10 eV lower. Optimum analytical conditions were established by studying the ion yield and energy distri- bution of the ion species in the plasma but it was considered that further investigations were still necessary to make the method viable. Hieftje and colleagues (95/3537) developed an rf GD time of flight ( T O F ) MS by simple modification of the interface to an ICP-TOFMS. The prototype interface was designed to allow simple and rapid exchange of the GD and ICP sources without sacrificing MS performance.The sample-skimmer distance discharge pressure and discharge power were optim- ized at 4 mm 0.3 Torr and 50-60 W respectively. The pressure and power were optimized for signal levels and not to reduce formation of polyatomic ions. As a result interferences were observed. Signals improved marginally with application of a small negative potential to the skimmer cone but both signal levels and resolving power decreased with higher voltages. The current design had poor detection limits in both GD and ICP modes and it was considered necessary to improve instrumental sensitivity and the interface design to achieve ng 8-l sensitiv- ity and the ability to analyse both conductive and non- conductive samples.A linear TOFMS has been designed constructed and coupled with a GD source in microsecond pulsed (MSP) mode by Hang et al. (95/2349). The ion beam was focused by an Einzel lens and compressed from circular profile to elliptical profile by a dc quadrupole to diminish spatial distribution of the ions. A two-stage acceleration field was used to reduce the kinetic energy distribution effect and deflecting pulse tech- niques to remove most Ar' ions. The peak ion current of 100 nA for metal samples compared to that of 0.2 nA in the dc mode. In addition ion transmission was much higher than in the dc mode. Although electron impact and Penning ioniz- ation were thought to dominate ionization it was considered that ion impact and charge transfer ionization should be taken into account because of the high density and momentum of the ions.A major limitation of the system used was the huge argon ion packet still reaching the detectors and attenuation of some peaks. More precise high voltage supplies were also required to obtain position stability for the peaks. Preliminary results have been presented by Steers et nl. (96/C180) for a microwave excited GD. A quartz tube served as a small discharge chamber with one end connected to a vacuum system for evacuation and gas entry and the other 362R Journal of Analytical Atomic Spectrometry October 1996 Vol. 11over the inner conductor of a slab-line cavity operated at 2.45 Hz. The cavity inner conductors were made from the sample in the analysis of metals whereas dielectric samples were machined into caps which were fitted on to the end of the exposed conductor.Good ion count rates were obtained for both types of sample indicating the potential of the source for MS analysis. Two groups have reported the use of a magnetroa glow discharge in which electrons are confined by a magnetic field thereby allowing the discharge to be maintained over a large pressure range (0.66-133 Pa). Confinement of the elcctrons close to the cathode resulted in increased efficiency of ionization of the gas and sputtering rate but also to localized crosion and non-uniform sputtering. Hi et al. (96/1277) operated a planar magnetron discharge under low pressure to allow efficient sputtering and ion production from conducting samples and to simplify the interface with the MS.Sample ion current was found not to be a simple function of dixcharge current but a strong function of sample axial position yelative to the MS sampling cone. Molle et al. (96/286) interraced a magnetron rf GD with a borosilicate glass cathode to a quadrupole MS which could be aligned in either the axial or radial position relative to the discharge. Using an expcrimen- tal design procedure it was possible to obtain rapidly a model expression that translated the influence of a parameter power pressure and sampling distance) on the ion intensity and energy distribution. It was found that the ion energy did not (depend significantly on power but that in the axial position an interaction between pressure and distance had a sigiiificant influence on ion intensity.Variations in the ion energie.; could be explained by changes in the electron temperature. Duckworth (96/C833) reported in a conference abstract on continued studies into the use of ion traps as mass analysers for GD-generated ions. Filtered noise fields (FNFs) wert found to be useful both for selective ion accumulation and for simultaneous polyatomic dissociation over an extended mass range. The FNFs were digitally synthesised broad band noise fields applied to the end-cap electrodes to effect resonance excitation or ejection depending on the trapping well-depth potential and the amplitude of the FNF. Although the introduction of liquid samples continues to be reported at conferences details have yet to appear in the form of a full paper. Marcus and co-workers (95/C3004) toupled an LC to a hollow cathode ion source via a particlth beam interface.The combination of thermoconcentric nebulizer par- ticle beam interface and hollow cathode discharge allowed the efficient introduction of low volatility mobile phases at flow rates up to 1.5 ml min-'. The system could be used for the analysis of organic and organometallic compounds ii nd the determination of elemental species. Use of an rf GD discharge as a detectorfor GC analysis of organometallic compounds has been reported by Olson et al. (95/C2959). The GD was operated with ultra-high purity helium at 3-9 x lo-' mbar and with an aluminium sputtering target. Optimum signal intensity and peak shape for two organotin compounds were achieved when the outlel of the capillary column was aligned with the centre of the sampling orifice of the MS.Detection limits were of the order of 1 pg of Sn. 2.4. Analytical Methodologies Although the formation of doubly-charged and poljlatomic ions in GDMS is lower than in other MS techniques (SIMS or SSMS for example) their formation still provides the opportunity for quantification in those cases where the singly- charged ions suffer from interference. Goodner et al. (96/1615) in a thorough and detailed paper described the novel use (for GDMS) of the alternative ions argide (MAr') dimer (M2+) and doubly charged (M2+) for quantification. All three species behaved similarly to the M+ ion with changing discharge power but to the metal atom (and not M') with changing discharge pressure.The discharge parameters were optimized at 4 W power a compromise between higher power for more intense signals and lower power for lower discharge tempera- tures and 8 mPa pressure a compromise for the relative intensities of the different ionic species. Analysis of three RMs generated RSFs which were applied to the analysis of a fourth RM treated as an unknown to investigate analytical perform- ance. The measured errors were < 5 15 15 and 40% for M + MAr' M2+ and M2+ respectively. The average limits of detection were 60 ng g-l 300 ng g-' 160 pg g-' and 300 pg g-' for M+ MAr' M2+ and M2+ respectively. The authors acknowledged the existence of matrix effects in GDMS by making the interesting comment that matrix matching was important for best analysis. The technique was considered a viable alternative in those cases where the singly-charged ions were interfered with but that it should be used with caution.The analysis of non-conducting materials using either dc or rf GDMS is a subject receiving much attention from Van Grieken and colleagues. They have investigated both the mixing with a conducting powder (95/4188) and the use of a secondary cathode (96/1520) for the dc GDMS of non- conducting samples. In the first study the effects of cooling conducting binder (copper or silver) sample geometry (pin and flat) and analyte material (various iron ore RMs) on the analytical response were evaluated. The values of measured RSFs were dependent on the cooling used and sample geometry but independent (< 25% variation) of both the conducting binder and the sample matrix.When the experimental con- ditions were controlled strictly reproducible (< 10%) and accurate results (<8%) could be obtained for the analysis of oxide-based materials using average RSFs from the analysis of six different iron-rich materials. Optimum analytical con- ditions for the use of secondary cathodes differed significantly for different samples and appeared to be dependent on the electrical resistivity of the sample. An innovative method for preparation of non-conducting samples for dc GDMS analysis was the use by Battagliarin et al. (95/3470) of an injiltration process commonly employed for producing metal-matrix composites for structural appli- cations. Powdered sample and an indium rod of high purity were placed in a pressure vessel similar to a hot isostatic press and heated for 2 h at 190°C and atmospheric pressure.When steady temperature was reached the pressure was raised to 70 bar with N to force liquid indium to infiltrate the sample. Several advantages were seen for the method. Sample was not distributed throughout the resulting pin but within a particular defined section. Heating was sufficient to remove adsorbed water from sample particles thereby improving the analytical characteristics but not high enough to cause problems of losses of volatile elements. No sparks were observed in the plasma because of the physical continuity of the sample. Rapid stabilization of the discharge was achieved so that high detec- tion sensitivities could be reached more quickly than by more conventional methods.Further development was considered necessary and no data were presented on reproducibility for quantitative analysis. De Gendt et al. (95/3524) evaluated the performance of rf GDMS for the direct analysis of nonconducting samples. Samples were prepared either as metal pins (2 mm diameter x 5 mm exposed length) or oxide disks (4.5 mm diameter x 2 mm thickness). Parameters studied were discharge power discharge pressure sample-exit orifice distance and the effect of cryogenic cooling. The last was considered essential to remove interfering gaseous species with a marked improve- ment in the spectrum obtained. The dependence of intensities on discharge pressure and sample distance varied between Journal of Analytical Atomic Spectrometry October 1996 Vol.11 363 Ranalytes and gaseous interferences so it was possible to dis- criminate between the two by appropriate choice of parameters. Under optimized conditions precisions of < 5% were obtained for all measured species in the discharge. The RSFs were in a relatively narrow range of 0.5-3 for different matrices. A semiquantitative analysis gave results within a factor of two of the expected concentration. A comparison between dc and rf GDMS for the analysis of oxide materials by De Gendt et al. (95/4189) found that the two methods gave similar results with uniform RSFs. In the analysis of REE oxides the dc method was less affected by changes in discharge pressure and sample distance than the rf method. Higher power levels were necessary in the rf method to obtain comparable signal intensities and the level of gaseous impurities observed in the spectra was higher.The RSFs by the rf method were more variable than by the dc method. Very stable and reproducible plasma conditions were however obtainable using the rf method when working at a fixed pressure and sample distance so that it was possible to achieve within-sample and between-sample reproducibilities of 5 and 15 Yo respectively. The rf discharge is more prone to the formation of polya- tomic ions than the dc discharge. Three target gases (Ar N Xe) used in collision-induced dissociation (CID) to eliminate polyatomic ions produced in the rf discharge have been fur- ther investigated by Duckworth and colleagues (95/258 l). Collisions with the target gases in the first quadrupole of the double quadrupole system resulted in losses of the discharge species by dissociation symmetrical and asymmetrical charge exchange and scattering.These processes were a function of the relative mass size and ionization potential of the target species in addition to the centre-of-mass energies. Xenon proved to be the most effective target gas because of its relatively low ionization potential and high dissociation efficiency of polyatomic species. Reports are beginning to appear on the analysis of more complex non-conducting materials in comparison with the majority of previous investigations which have been on rela- tively pure matrices. Takahashi et al. (95/2611) analysed sus- pended particulate matter (SPM) by depositing it on high- purity indium electrodes.The results for 34 elements in an SRM from major to trace constituents agreed with the certified values within a factor of two when using typical RSFs. A total of 53 elements including halogens could be determined in 10mg of SPM with sub-pg g-' sensitivity. RSFs for the analysis of soil were found by Teng et al. (96/1278) to depend on the oxygen content and the conducting matrix but not on the soil composition. Good results could be obtained by using a set of RSFs obtained from standard soils with certified compositions. Methods continue to be developed for the analysis of high- purity metals. Venzago and Weigart (95/2617) analysed exten- sively aluminium- and cobalt-based alloys to establish the analytical performance for ultratrace analysis using a dc dis- charge.Strict cleaning protocols were followed so that detec- tion limits in theng g-' and sub-ng g-' ranges could be achieved with precisions of <20% (at < 1 pg g-') and < 10% (at > 1 pg g-') for aluminium-based alloys analysed as pins. Precisions of ~ 7 % were obtained for elements at concen- trations > 10 pg g-' in cobalt-based alloys analysed as flat samples and 20-30% for other elements. Saito et al. (96/1512) found GDMS to be a sensitive and rapid method for the determination of B in high-purity molybdenum with a detection limit of 0.1 ng g-' obtained with a 40 s integration time. The results were low however and this was attributed to the use of incorrect RSFs obtained from the analysis of steels.This was taken as evidence for the matrix dependency of RSFs and the need to ensure the use of correct RSFs. Held et al. (95/4706) investigated the determination of Sc in high-purity titanium as part of a certification programme in which ICP-MS was the primary method of analysis. The detection limit (<25 ng g-') was relatively high as a result of interference from the polya- tomic species 50Ti40Ar2+ for which a correction using the other Ti4'Ar2+ ions was necessary. Although GDMS gave fast analysis (1 h per sample 10 measurements per sample) the need for solid calibration samples was a considerable disadvan- tage in the context of a certification exercise. A thorough study by Riciputi et al. (96/1614) concluded that GDMS was potentially attractive as a technique for the rapid screening of isotope ratios in solid samples. External precisions of <0.1% and 1% were possible for elements at concentrations > 0.5% and 10-20 pg g-' respectively.Isotope ratios of Ag B Cu Pb Re Sb and Sr were measured in a number of RMs mixed with copper or silver powder as conducting matrix if necessary using a peak jumping pro- cedure. The ability to measure isotope ratios in samples with virtually no sample pretreatment is very attractive but severe problems were highlighted which will limit its application at present. Problems included the great dependence of measured isotope ratios on discharge pressure the need to dilute samples with a conducting powder difficulties in obtaining reproducible sample geometry and poor external precision (1-3% for lead isotope analysis for example).Stability of the discharge in particular source pressure was considered critical for obtaining improved analysis. Large day-to-day variations in isotope ratios required daily calibration of the instrument for precise analysis. 3. INDUCTIVELY COUPLED PLASMA SOURCE MASS 3.1. Reviews It could be argued that inductively coupled plasma mass spectrometry (ICP-MS) is a technique entering maturity. In addition to the perennial reviews of current status this year's Update sees the re-publishing of probably the first ever Plasma MS communication by Alan Gray (95/2816) over 20 years ago. It is interesting to note that although higher performance sources and mass spectrometers are used today the basic format of instrumentation has not changed since 1974.The impact of ICP-MS on the analytical community was high- lighted in a 57 reference review by Moens and Dams (95/4558). ICP-MS was compared with NAA and it was concluded that although the former had the potential to replace the latter the future of NAA as a reference technique was assured. Jakubowski and Stuewer (95/2415) reviewed (212 references) fundamentals instrumentation and plasma sources for elemen- tal MS. An additional indication of the maturity of ICP-MS is provided by the appearance of text-books devoted to the subject such as the in-depth monograph by Evans et al. (96/1399) in the RSC Analytical Spectroscopy series. SPECTROMETRY (ICP-MS) 3.2. Instrumentation There has been much interest in alternative mass spectrometers for plasma sources.Hieftje and co-workers have made several reports on the development of a time-of-flight (TOF ,) MS for elemental analysis (95/2580). The TOF-MS produced analogue spectra similar to those from a quadrupole ICP-MS system. The large abundance of Ar ions was deflected away from the detector to reduce dead time and space charge complications. Although the resolving power was 500 the original ion-optics required a trade-off between signal-to-noise ratio and resolving power. Later addition of a quadrupole lens overcame this limitation (95/4642). Mass bias was prominent because of the mass-dependent kinetic energies in the right-angle MS. A constant-fraction discrimination/boxcar integrator effectively rejected noise and accumulated analyte signal resulting in an enhanced signal-to-noise ratio (95/3883).The long-term drift 364R Journal of Analytical Atomic Spectrometry October 1996 Vol. 11of the system was 7-8% with short-term precision at 5 -20%. Precision could be improved to around 0.5% by rzitioing isotopic peaks. Linear dynamic ranges were four orders of magnitude. Limits of detection were 1-2 orders of magnitude poorer than existing commercial quadrupole systems (95,4161). Abundance sensitivities were in the lo6 range for low abun- dance ions that preceded high abundance ions (96/1627). Houk and co-workers (95/2607,95/C2967) reported on their twin quadrupole ICP-MS system. The ion beam from the ICP was split into two parts by a device composed of two electro- static analysers in a back-to-back arrangement.Thus ion ratios could be measured simultaneously without scanning. Isotope ratios for Cu were measured with a precision of 0.14%. Ion signals in the two channels were highly correlated and flicker noise was reduced. Under the circumstances it might be expected that isotope ratio precision would be better given that single quadrupole systems can achieve similar levels of performance. Bias in the measured ratios was substantial but could be corrected by calibration. Magnetic sector MS systems are increasing in popularity in both single collector and multiple collector formats. Giessmann and Grebb (95/2405) and Moens et al. (95/4170) reported some figures of merit for a new commercial double focusing ICP-MS system. It could be operated in low (M/AM=300 10% valley definition) or high (3000 and 7500) resolution modes.At low resolution an almost flat mass responsc was observed. The sensitivity decreased by about a factor of 14 when going from 300-3000 resolution and by a further factor of 10 when the resolution was increased to 7500. The best LOD achieved was <10fgml-’. It was pointed out that the detection limit for most elements was not determined by the instrument but by the blank level and laboratory procedures. Interestingly non-spectral matrix effects were found to be similar to those observed with quadrupole systems. Halliday and co-workers (96/1611 96/1612) reported on precise isotope ratio determinations using a multiple collector ( M C ) magnetic sector ICP-MS system. Trace element ratios such as Rb Sr were made and a wide flight tube allowed Pb and U Pb ratios to be accurately measured simultanecusly. Changing plasma conditions had a significant effect on trace element ratios but not on mass bias.Precise and acciirate isotope compositions for ‘difficult’ and refractory elements such as Mo Sn Te and W could be readily determined. The aul hors believed that this type of instrumentation will greatly enhance the prospect for research on the distribution and isoiopic composition of such elements in terrestrial and mete( )ritic materials. Cromwell and co-workers (95/C2992 96/C’860) reported initial results from a MC system with Mattauch- Herzog geometry and an He ICP. Although system perform- ance was limited by resolution (poorer than a quadrupole) the sensitivity and precision of the system were described as ‘good’.Taylor et al. (95/2398) assessed the linearity and mass discrimination of an MC-ICP-MS system using a set of commercially available and synthetically prepared mixtur1:s of uranium isotopes (IRMM 072). It was found that use 01 the power law and exponential function resulted in the best correction for mass discrimination. The corrected is0 tope abundance ratios for 233U 235U and 233U 238U did not differ significantly from certified values at the 3 x level. The corrected values also gave an indication of the linearity of the measurement system. Caruso and co-workers (95/4745) described a modificcition to the lens system of a commercial quadrupole ICP-MS system. A stainless-steel rod with rounded ends was suspended hy a ceramic insulator (inserted through the photon stop) alone the axis of the lens stack and an optimal negative potential of about 10 V applied.Detection limits for 15 elements across the mass range were improved by two- to ten-fold. Nakagawa and Tetsumasa (96/1792) described a new dt tec- tion system for high ion currents where ion counting was performed by reducing the quantity of ions incident on the detector. The system used a pair of additional electrodes (repeller and assist sic) placed between the quadrupole and detector. Depending on the concentration of analytes to be measured an adjustable potential difference was applied between the two electrodes thereby attenuating high ion counts to the detector. The device was believed to extend the life of detectors allow the measurement of analytes at high concentration (not specified) and reduce costs.Guenther Longerich and Jackson (96/418) reported on the performance characteristics of an enhanced sensitivity quadru- pole ICP-MS instrument. The system was commercially modi- fied by use of additional pumping in the interface region such that the pressure was reduced by a factor of 3. The sensitivity for mono-isotopic elements with moderate ionization potentials was about 5 x 10’ counts per second for a 1 pg g-’ solution. Background signals were found to be about 10 counts s-l leading to LODs of < 10 fg g-’. Tanner Douglas and French (95/2592 95/2593) reviewed the equations describing the pressure density and temperature characteristics of insentropic flow.They also reviewed the formation of a shock structure due to sudden termination of the directed motion of a flowing plasma. The results were applied to describe the flow characteristics of a novel ICP-MS vacuum interface consisting of three apertures conventional sampling and skimmer cones and a third aperture. The last was contained in a blunt support normal to the axis of the primary expansion through the sampling and skimmer cones. The net effect was a reduction in the ion current introduced into the ion optics region of the MS and a corresponding reduction in the magnitude of the space charge field. This resulted in a gain in ion transmission efficiency a more uniform mass response curve and decreased signal suppressions from a high-mass concomitant element.Hieftje and co-workers (96/1646) considered both theoretical calculations and experimental measurements to demonstrate that space charge influences ion transport between the plasma source and mass analyser. By placing a stainless-steel target on the third stage vacuum orifice plate spatial patterns of sample deposition from a microwave plasma source were recorded. Both XRF and SEM were used to examine the spatial maps which showed that analyte deposition was ‘some- what’ element dependent in a way that was correlated with analyte atomic mass. Sawatari et a!. (96/1044) described a ‘versatile’ simultaneous multi-element measurement system which combined ICP-MS with a sequential ICP-AES through an optical fibre. A dynamic range of 9 orders of magnitude from a few pg ml-’ to about 1000 pg ml-’ was obtained.Detection limits for the optical determinations were degraded by 10-50 times compared to a conventional system whereas those for ICP-MS were unaffected. Tanaka et al. (96/1510) demonstrated that a torch with a larger injector orifice diameter reduced oxide ion interferences without affecting analyte sensitivity. The authors concluded that this modification could be useful for analysing complex samples containing elements which readily form oxides such as REEs. Tanner (95/3363 96/266) reported on the ionization and matrix suppression characteristics of a ‘cold’ plasma system operating with an electrically balanced coil configuration. Suppression of analyte (Ca Fe and K) signals by concomitant matrix elements was partially correlated with the ionization potentials of the matrix element.Normalizing analyte signals to NO’ caused suppression to become independent of matrix element. For high concentrations of elements of low ionization potential an additional or enhanced mechanism of ionization was evident. It was concluded that cold plasma conditions Joumal of Analytical Atomic Spectrometry October 1996 Vol. 11 365Rwere most appropriate for the determination of Ca Fe and K in high purity waters and acids. Uchida and Ito (95/4705) developed a nitrogen ICP with a 40.68 MHz generator and a maximum power of 4 kW as an ion source for MS. The plasma was all N with the exception of a small Ar addition to the coolant gas flow to stabilize the discharge. The sampling depth for maximum analyte signal was found to be closer to the load coil than with an all argon plasma and signal increased with carrier gas flow up to 2.0 1 min-'.In the mass spectrum peaks for N' 0' and NO' were significant whereas those for Ar' were minor. Analyte sensitivities for elements with high ionization potentials were inferior to those obtained with an Ar-ICP. Also there was a strong secondary discharge and higher ion kinetic energies leading to high levels of doubly charged and monoxide species. Yasuda and Shirasaki (96/C924) reported on a mixed oxygen-nitrogen MIP for MS. It was found that replacing the carrier gas in a nitrogen based MIP with either an oxygen- nitrogen mixture or 100% oxygen eliminated interferences on Ca Cr and Mg even when organic solvents were introduced. Unfortunately in the analysis of sea-water CaC1' species were present which interfered with As and Se determination.To overcome them mathematical correction had to be applied. 3.3. Sample Introduction Sample introduction continues to be a topic of great interest to practitioners of ICP-MS. The number and variety of sample introduction techniques and their applicability to a diverse assortment of analytical problems have made ICP-MS an important tool in many fields ranging from human nutrition and the earth sciences to semiconductor fabrication and nuclear waste management. In this review period over 250 publications on sample introduction were indexed for review. Included in this section are developments and fundamental studies in solid sample introduction (laser and spark ablation) vaporization (chemical and thermal) nebulization and on-line sample pro- cessing.Method development and validation studies are reviewed elsewhere. 3.3.1. Laser and spark ablation methods The ongoing development of ultraviolet (excimer or frequency- quadrupled Nd YAG) microprobe lasers has continued to stimu- late interest in laser ablation especially among investigators active in high-resolution (pm-scale) spatial analysis. Several new laser ablation systems were described. One commercial frequency-quadrupled Nd YAG system (96/C785 96/C1415) when used in combination with an enhanced sensitivity ICP-MS yielded detection limits below 1 mg kg-' while leav- ing ablation pits less than 10 pm in diameter. Another commer- cial Nd YAG system (95/C2966 96/C718 96/C878) offered a choice of bulk or spatial analysis by allowing user selection of fundamental or frequency-quadrupled Nd YAG wavelengths.A petrographic microscope was included with this system for examination and identification of mineral phases before ablation. A home-made Nd YAG laser ablation system with three selectable wavelengths was also described (95/C3050 95/4669 96/C213); detection limits were found to be between 10 pg kg-' and 1 mg kg-' (depending upon pit diameter) when the system was coupled to an enhanced sensitivity ICP-MS. Fundamental studies continued to improve our understand- ing of the laser ablation process. Jeffries et al. (96/1487) found that UV ablation was less dependent upon sample character- istics (mineral composition crystal structure and crystal orien- tation) than IR ablation.In the case of UV ablation spatial resolution ablation volume and detection limits were shown to be strongly correlated with laser power. The effects of laser parameters and matrix composition were also studied by Outridge and Evans (95/4174) in the context of tooth analysis. Two distinct bulk ablation processes dependent upon laser wavelength and pulse energy were observed. Fractional ablation indicated by energy-dependent variations in matrix- normalized analyte signals was observed below a 2-3 mJ pulse-' threshold for irradiation with green light and a 3-3.5 mJ threshold for irradiation with UV light. Fractional ablation appeared to decrease with pulse frequency and differ- ent ablation characteristics were reported for cetacean (beluga whale) and pinniped (walrus) teeth presumably due to differ- ences in matrix structure.Fractional ablation was also observed during high-resolution spatial analysis of zircons by UV laser ablation (96/1577). In this case fractionation was attributed to changes in laser focal position. These changes presumably due to removal of the specimen surface were corrected by continuous (active) refocusing. A new active focusing system based upon lateral displacement of light reflected from the specimen surface was described by Cousin et al. (95/4658). Studies of the IR ablation process have also continued. Paul (95/2283) studied the influence of Nd YAG laser mode (free- running versus Q-switched) and pulse duration upon ablation.Conducting materials (metals) and pressed powders were tested and microscopic examination of the samples indicated that different processes were responsible for ablation. The effects of pulse energy and multiple laser exposures upon ablation of sulfide minerals were studied by Watling et al. using an Nd YAG laser in free-running mode (95/4280). Electron microscopy and energy-dispersive X-ray analysis of melt annuli (surrounding ablation pits in chalcopyrite) indicated that single low energy pulses (600 V lamp potential) produced an aerosol representative of the bulk mineral whereas additional pulses produced an aerosol markedly different from the sample. Higher energy pulses (900 V lamp potential) also caused elemental fractionation regardless of the number of exposures.Certain minerals (chalcopyrite in particular) appeared to be more susceptible to fractionation. Prior fusion of the mineral into a glass (borate) matrix did not ameliorate the problem. Proponents of laser ablation have historically claimed that reduced sample preparation is an inherent advantage. However a growing body of evidence (including the work cited above) suggests that fractional ablation and matrix-related variations in ablation efficiency must be overcome if quantitative data are desired. Matrix-matched standards (when available) have been one means of compensation (95/2616) but conversion of the sample into a different form (one more amenable to quantification) has been largely overlooked. Lichte (95/4607) has recently described IR (Nd YAG) laser ablation ICP-MS analyses of rock samples fused in a mixture of lithium tetrabo- rate lithium carbonate lithium hydroxide and iron(m) oxide.A suite of internal standard elements (in solution form) was added to the mixture before fusion. Addition of nitrogen to the aerosol carrier gas was found to increase sensitivity; this effect was also reported by Durrant (95/2285). Measurements for 49 elements were found to be accurate to within &5% and detection limits were of the order of 10 pg kg-'. Fire assay techniques were used by Jarvis et al. (95/4277) to concentrate platinum group elements and gold in minerals prior to IR ( N d YAG) laser ablation of the fire assay button. The NiS button was ground prior to ablation and quantifi- cation was achieved using external calibration with standard buttons prepared from mineral reference materials or high purity quartz sand doped with multi-element solution stan- dards.Coefficients of variation for these measurements were found to be 10-15% depending upon the analyte and its concentration and accuracy for most elements was acceptable. Detection limits were less than 90 pg kg-'. Fire assay was also used to concentrate chalcophile elements in minerals prior to laser ablation ICP-MS analysis (96/1489). Recoveries were generally better than 95% and detection limits ranged from 1 pg kg-' for Ag to 100 pg kg-' for Te. 366 R Journal of' Analytical Atomic Spectrometry October 1996 Vol. 11De Carlo and Pruszkowski (95/3838) described the laser ablation ICP-MS analysis of marine ferromanganese oxide deposits.Polished sections of the sample were vacuum- impregnated with epoxy prior to ablation. This process was found to improve the homogeneity of the sample thereby improving the reproducibility of the ablation process. In an unusual study Raith et al. (95/4173) used a diamond lapping disk to obtain metal samples for laser ablation analysis. Metal fragments were transferred to the lapping disk as the sample was polished and the disk (rather than the metal) was analysed. Coefficients of variation were generally better than 10% and detection limits were between 1 and 10 mg kg-'. Despite an improved understanding of the ablation process and efforts to mitigate or compensate for differential ablation calibration techniques and quantijication remain the Achilles heel of laser ablation ICP-MS.This is especially true in -\patial analysis in which any form of sample preparation (beyond cutting and polishing) compromises spatial informatiox I con- tained within the sample. Sharp and Masters (96,C790) described a novel use of aqueous standards for external Cali- bration of UV (excimer) laser ablation analyses. In this work a standard solution was modified to exhibit high molar ahsorp- tivity at the laser wavelength. Subsequent laser vapori #:ation of multi-elemental standards was found to offer improved elemental coverage a constantly-renewing specimen s i trface and tunable response characteristics. Cromwell and Arrowsmith (95/2571) used a two-channel (solution and laser) sample introduction system for semiquantitative analj sis of steel and glass by UV (frequency-quadrupled Nd YAG I laser ablation.High laser fluence and minimal overlap of ablation pits were shown to facilitate representative laser sampling of the specimen thereby making a solution calibration strategy possible. The relative accuracy and precision of the an ilyses were roughly equivalent (about 20%). Shepherd et al. (96/1250 96/1803) also used a dual-channel sample introduction system to evaluate strategies for quail titat- ive UV (frequency-quadrupled Nd YAG) laser ablation i! naly- sis of individual fluid inclusions present in halite fluoritc and quartz. A heated ablation cell was used to ensure coniplete vaporization of the fluid and solution nebulization was used to determine RSFs.Glass SRMs synthetic fluid inclusions and fluid inclusion analogues (microdroplets of multielement solu- tion standards encapsulated in epoxy or plastic micro wells) were used to calibrate instrument response. The epoxy ana- logues were not amenable to ablation at elevated temperciture but elemental ratios in glass synthetic fluid inclusions and microwell inclusion analogues agreed closely suggesting that all of these materials were suitable for instrument calibration and the analysis of natural fluid inclusions. Although laser ablation has been the technique of primary interest for direct solids analysis the development of alternative introduction devices has continued. A new spark ablation system described by Van Hoven et al. (95/4595) was used to determine PGEs in gold and silver fire assay beads.Spark power was found to influence both sampling rate and aerosol transport. Under optimized conditions the sample aerosol was composed of sub-pm size vapour condensates and \mall (<2 pm) spherules. Coefficients of variation for spark abldion signals were found to be between 3 and 6% a minimum linear dynamic range of three decades was demonstrated and detec- tion limits were found to be in the order of 1 mg kg-'. A medium-voltage high-frequency (500 V 400 Hz) spark ablation source was used by Coedo et al. (95/4708) to an,dyse the composition of low-alloy steels. A cyclone separator was used downstream of the ablation source to limit the mass flow rate of ablated particles and control their size distribution thereby preventing condensation of ablated matter on the torch injector and sampling interface.Optimization oi the ablation source and use of 58Fe as an internal standard resulted in detection limits of 0.08-0.32 mg kg-' for metallic analytes and 1.5-2.5 mg kg-' for non-metals (B P and Si) with coefficients of variation in the order of 2.5% or less for analytes present at 10 times the detection limit. These figures of merit were comparable with those obtained from nebulization of a 500 mg 1-' Fe solution. 3.3.2. Slurry methods Broekaert et al. (96/C717) examined slurry nebulization as a means of directly analysing impurities in zirconia and other refractory materials. The diameter of the solid particles was carefully controlled (to assure complete vaporization) and for particles of 1-4 pm diameter slurry nebulization data were indistinguishable from solution data.Franz and Tsourides (96/C875) also studied slurry nebulization of fine particulates with emphasis upon powdered agricultural products (including rice wheat and milk). In general method detection limits were improved (over solution analysis) due to less sample handling (lower blanks) higher sample concentration (versus dissolved solid) and reduced spectral interference. 3.3.3. Electrothermal and thermal vaporizution Ren and co-workers (96/284 96/1557) described a new system for the direct electrothermal vaporization of solids. A solid sample (in powder form) was mixed with purified graphite powder and pressed into a 9 x 4 mm cylindrical pellet. The pellet was placed between two brass contact rings and electro- thermally heated to dry pyrolize and vaporize the sample.A detection limit of 0.1 pg kg-' was determined for Cd but measurement accuracy was unacceptable when external Cali- bration techniques were employed. The authors speculated that the method of standard additions would improve measure- ment accuracy and Giglio et al. (96/C742) indicated that this strategy was indeed the most promising of several calibration alternatives. Factors influencing external calibration of solid sampling ETV measurements have been studied. Vanhaecke and co-workers (96/287) used argon dimer ion signal as a diagn- ostic tool to study electrothermal vaporization of solids. Co-vaporization of matrix constituents was found to have a marked influence upon mass-normalized analyte signals but normalization of the analyte signal against the argon dimer ion signal mitigated this effect.Fonseca and Miller-Ihli (95/C3047 96/C873 96/978) also showed that relative to aqueous solutions (ie. calibration standards) organic matter in the sample matrix enhanced analyte transport for ultrasonic slurry sampling electrothermal vaporization. Oxygen ashing used in combination with a physical carrier (Pd) was found to reduce these differences in transport efficiency thereby improving measurement accuracy. Thermal vaporization techniques have also been used for the Introduction of volatile species and smull (pl-size) solution samples. Several new vaporization devices have been developed. For example a wire loop in-torch vaporization (ITV) device was described by Karanassios and co-workers (95/4587).A 10 yl solution aliquot was deposited and dried upon a rhenium filament and the filament was electrothermally heated to vaporize the sample. The ICP torch was modified slightly (Ar carrier gas was injected through a side arm) to facilitate vapour transport. Absolute detection limits were between 40 and 320 fg for Cd Pb Sr and Zn. An automated system for direct sample insertion was described by Rattray and Salin (95/4703). An aerosol of the sample solution (0.5 ml total) was deposited upon a graphite probe that was inserted directly into the ICP for sample vaporization and subsequent elemental analysis. The effects of ICP and deposition parameters were studied and system performance documented €or aqueous and etha- nolic matrices.Absolute detection limits were 30-900 fg for a Journal of Analytical Atomic Spectrometry October 1996 Vol. 11 367 Rsuite of ten elements and coefficients of variation were of the order of 5% for 500 pg injections of analyte. In a related study Hieftje and co-workers (96/C747) coupled an electrothermal vaporization source with a time-of-flight ICP-MS. The speed and transmission efficiency of the TOF-MS was shown to be advantageous in the measurement of the electrothermal vapor- ization transient. Future improvements in thermal vaporization techniques will depend in large part upon current understanding of the vaporization process. Atomic absorption and ICP-MS were used by Goltz et al. (95/4739) to study the electrothermal vaporization of uranium.Gaseous uranium atoms were observed at about 2700 K whereas gaseous uranium(1v) oxide was produced at lower temperatures (about 1400K). In the range 2500-2900 K uranium was released via decomposition of uranium(1v) oxide; at higher temperatures uranium trans- port was due to carbide decomposition. At a high temperature (about 2300 K) uranium carbide formation was promoted by sodium chloride whereas uranium intercalation into the graph- ite matrix was promoted at a low temperature (500 K). A small amount (3%) of Freon-23 mixed with the argon carrier gas prevented intercalation and carbide formation. Electrothermal vaporization of sulfur was examined by Gregoire and Naka (95/4702). Several sulfur compounds (including sulfuric acid thiourea and sulfate salts) were studied and in most cases thermal decomposition (to sulfur trioxide) was the dominant mechanism for sulfur vaporization. Potassium hydroxide was shown to be the best carrier for sulfur and the absolute detection limit for sulfur (using a 50 pl injection) was found to be 13 pg. Current knowledge of thermal vaporizatiqn phenomena has been used to develop assisted vaporization techniques.Hughes and co-workers (95/4588) described the use of sea-water as a physical carrier in electrothermal vaporization. This technique was applied to the determination of REEs Th and U( 95/4282). Release of HC1 vapour from the sea-water matrix (uia hydroly- sis of MgCl,) enhanced the transport of volatile elements (for example Rb) whereas vaporization of NaCl (less than 70 ng) enhanced the detection of modestly volatile elements.The transport of refractory elements was enhanced by vaporization of MgO. Signal suppression was observed when NaCl was present in excess of 70ng. Mannitol was used to improve the determination of B by ETV-ICP-MS (96/272). The atomization profile for boron in the presence of the modifier was found to contain several maxima (attributed to vaporization of different boron-mannitol complexes). Sensitivity was nevertheless enhanced substantially (about 80-fold) relative to boron vapor- ization from unmodified samples. The absolute detection limit for boron in the presence of mannitol was found to be 4pg. Copper(1) chloride was used by the same investigators as a preconcentration agent and a chemical modifier for determi- nation of As and P in trichlorosilane (96/1308).Other investi- gators determined Bi in iron and steel (95/2583) and found that the intensity of the bismuth atomization profile was markedly different for hydrochloric acid and nitric acid solu- tions. Chemical modification of the sample with nickel reduced the matrix dependence. The method detection limit for bismuth in iron was 10 pg kg-l despite 50% signal suppression due to the presence of the matrix element. Other strategies for improving vaporization in ETV have been examined. Patterson et al. (96/C782) used volatile metal chelates to eliminate the high-temperature atomization step in ETV. The duration of the vaporization transient was increased and thermal variations in carrier gas flow (normally experi- enced during atomization) were reduced.Preliminary trials using zinc-trifluoroacetylacetone produced a constant signal at 373 K and a 4-5-fold improvement in isotope ratio precision was realized. Richner and co-workers (95/2409) used dissolved mineral samples (volcanic erupta) to demonstrate selective electrothermal vaporization of volatile constituents. Byrne et al. (96/C1404) used this strategy to separate NaCl in situ from trace elements present in sea-water. Methods to enhance ETV determinations of Ra and U were also described (95/3366). Dry-tuning novel temperature programs and new furnace mounting techniques were used. Sensitivity was enhanced further by multiple deposition preconcentration and chemical modification of the sample.3.3.4. Chemical vapour generation Chemical vapour generation while less popular then thermal vaporization has remained of use for the determination of certain elements and several new vaporization strategies have been described. Ridgway (96/C804) used controlled potential electrolysis to produce arsenic hydride. The mechanism for hydride production involved electrodeposition of arsenic metal on the working electrode and subsequent attack of the metal by electrochemically-generated hydrogen. Platinum and gold electrodes were shown to be the most effective materials for hydride production from arsenous and methylarsonic acids. Other investigators preconcentrated hydrides on palladium to increase sensitivity (95/4627). A continuous-flow hydride generator for the determination of Se in blood serum was described by Rayman et al.(96/955). A two-channel gaseous introduction system was used to promote mixture of the hydride with argon prior to plasma injection. Dry plasma conditions were found to produce more precise measurements whereas wet conditions gave higher sensitivity. Matrix effects due to iron and copper were negligible and method precision was acceptable (2-3% coefficient of vari- ation). Persistent negative bias was observed however despite careful attention to serum preparation procedures. Duan et al. (96/650) described chemical vaporization procedures for the determination of non-metals (e.g. S). The linear dynamic range of the technique was between four and five decades and detection limits of the order of 1 pg 1-' were reported.Yang and Jiang (96/273) used liquid chromatography with hydride generation for the separation and determination of inorganic and organolead species. Analytical figures of merit using the LC-hydride system were equal to or better than those obtained using LC with pneumatic nebulization. Detection limits for Pb" trimethyllead and tetraethyllead were in the range from 0.6-6ng 1-'. Smichowski and co-workers (95/4701) used anion exchange with hydride generation or nebulization for the separation and determination of inorganic antimony species in water. Detection limits for trivalent and pentavalent Sb were found to be 0.75 ng and 90 pg respectively using pneumatic nebulization and with hydride generation 40 pg and 8 pg. Several interesting applications of hydride generation have also been described.Mercury in urine and biota samples (96/1771) was determined by the method of standard additions. Isotope ratio measurements were also made to assess the feasibility of isotope dilution. Haldimann and Zimmerli (95/2333) used hydride generation with isotope dilution to determine selenium in wheat. The hydrides were generated in a flow injection manifold without pre-reduction. Multilevel spike recoveries were statistically indistinguishable from unity; however an error of about 4% was introduced when the isotope ratios were measured without mass bias correction. Sat0 and co-workers (96/1671) determined the speciation of organotin compounds in sea-water using hydride generation. The sensitivity was highest for inorganic tin and decreased with increasing organic content. The detection limit for inor- ganic tin was 30 pg 1-'.3.3.5. Nebulization methods Considerable effort has been devoted to the development of alternative sample introduction methods but solution nebuliz- 368R Journal of Analytical Atomic Spectrometry October 15196 VoE. 11ation has continued to be the most popular means of sample introduction for routine ICP-MS analysis. Although in the period covered by this Update fundamental properties of the nebulization and aerosol vaporization processes have been studied (95/4719 96/C752) most efforts have been devoted to the development and testing of new high-efficiency nebulizers. For instance an oscillating capillary nebulizer (OCN ) was described by Browner and co-workers (95/C2983).The aixosol produced by the OCN had a mean droplet diameter of 5 pm or less and the OCN operated with unit nebulization efficiency between 1 pl min-' and 2ml min-'. Nebulizer performance was found to be dependent upon gross solution composition and the nebulizer geometry. Assisted pneumatic nebulization (by means of chemical vapour generation) was report :d by Duan et al. (96/641). Samples were mixed with a vaporization reagent in a two-channel delivery system and the mixtuie was pumped directly into a glass concentric nebulizer. Cht mica1 vapour and solution aerosol were concurrently injected into the plasma allowing the simultaneous analysis of deriv,itized and unreacted species. Hernandis and co-workers (9C4643) described the development of a single-bore high-pressure 1 iebul- izer.The performance of the system was documented and compared with that of a glass concentric nebulizer. Primary aerosol droplets were found to be much smaller with thc new nebulizer increasing analyte transport and sensitivity relative to the concentric nebulizer. Strong correlations between nebul- izer behaviour and atomic number were also observed and these observations were explained in the context of inass- dependent radial diffusion rates. The further development of microconcentric nebulizers (including the direct injection nebulizer DIN) also received considerable attention. Kawabata et al. (96/C749) compared microconcentric nebulization and electrothermal vaporizdtion for analysis of sub-ml solution samples. A strategy for choosing the appropriate technique was proposed.Debrah ct al. (96/1457) used microconcentric nebulization (MCN) to tleter- mine a suite of elements in limited volumes (about 0.1 oil) of aqueous solution. Sensitivity polyatomic ion abundanct and background signal from the MCN were comparable with I hose obtained from a crossflow nebulizer; however solution con- sumption was 30-40 times greater with the crossflow. Detection limits for a group of eight elements were 1-30 ng 1-l wit ti the MCN and under cold plasma conditions detection limits for Ca Fe and K were also less than 30ng 1-'. Field and co-workers (96/C880) used an MCN in combination with a batch preconcentration technique to determine REEs in ma irine particulates and seawater.Sensitivity and rinse out times for the MCN were comparable to standard nebulization and absolute detection limits were 1-3Ofg. The MCN was also used by Rivers and co-workers (95/C4341) to determine zinc isotope ratios in sub-ml solution samples. Operating param- eters were optimized for zinc determination and using nal ural (pneumatic) aspiration the 68Zn 66Zn ratio in a 50 ng zinc sample was determined with a 0.1 YO coefficient of variation. Giglio et al. (95/3064) used a home-made DIN for solution introduction into a helium microwave plasma (MIP) MS. Polyatomic ion (e.g. MO' ) abundances were Comparable to those previously found for solution MIP but were substant ially greater than those found in ICP-MS. The elements As Ca K and Se were determined with minimal spectral interference due to the elimination of argon and with element-specific tuning instrument detection limits were of the order of 0.5 pg 1-'.The same home-made DIN was used with microbore HI'LC for ICP-MS detection of chromium species (95lC2933 95/4707). Absolute detection limits for Cr"' and CrV' species were 3 pg and chromium species in urine were determined with minimal sample preparation. A1 though microconcentric nebulizers use sample very efficiently they do not necessarily increase the mass traIisfer rate of analyte into the plasma. For this reason ultrasonic nebulization (USN) continued to be important in ultratrace elemental and isotopic determinations. Tsumura and co-workers (95/3601) illustrated this point by determining U in rainwater with USN and high resolution ICP-MS. An instrument detection limit of 60 fg 1-l (based upon repetitive blank measurements) was achieved and the 235U 238U ratio was determined with coefficients of variation less than 5%.In more general work Marshall and co-workers (96/C791) stud- ied the effects of operating parameters and sample composition upon USN-ICP-MS performance. Variations in polyatomic ion abundance were studied over a range of typical operating conditions and USN performance was compared with that of conventional nebulizers. The effect of speciation upon the ultrasonic nebulization of arsenic was described by Creed et al. (95/3055). Ion chromatography data suggested that the observed differences in species transport were due to the oxidation of As"' to AsV within the USN.Preoxidation of arsenic with sodium hypochlorite eliminated the problem. Thermospray sample introduction has continued to compete with other high-efficiency nebulization methods for a niche in the ICP-MS laboratory. Vanhoe and co-workers (95/4171) evaluated the performance of a thermospray sample introduc- tion system with ICP-MS. Relative to conventional nebuliz- ation signal suppression due to dissolved solids was more significant with the thermospray device whereas viscosity effects (due to phosphoric or sulfuric acid) were similar. Spectral interferences were less than or equal to those observed with normal sample introduction. Thomas et al. (95/4172) described an improved thermospray nebulizer. Blanks were reduced by using inert materials and thoroughly desolvating the aerosol.Sensitivity and background were improved significantly by careful optimization of nebulizer and plasma conditions and instrumental detection limits in the ngl-' range were determined. 3.3.6. Flow injection matrix separation and analyte preconcentration methods Beauchemin (95/3526) developed an FI manifold for on-line standard additions. The sample was injected into two carrier streams (one blank and one standard) and an aliquot of the standard was also injected into the blank. A single multielemen- tal analysis was completed in less than 2.5min and manifold dispersion was such that method sensitivity was comparable to that achieved by continuous sample nebulization. Compared with external calibration the FI precision was slightly poorer; however the FI method adequately compensated for the effect of easily ionized matrix constituents present in solution. Continuous on-line microwave digestion of environmental samples for lead determination was described by Beary and co-workers (96/C85 1).Slurried samples were dissolved or digested and isotope dilution was used for quantification. Method accuracy and reproducibility were comparable to that obtained with off-line sample handling. Automation of the analysis reduced method detection limits and sample size requirements. Seubert et al. (95/2396) described the preparation of an 8-hydroxyquinolinel polystyreneldivinylbenzene resin for FI pre- concentration of trace elements. The resin capacity was some- what low (2.8 pmol of divalent Cu per ml of resin) but was adequate in principle for determination of heavy elements in high ionic strength matrices.Column selectivity was enhanced by concurrent use of a cation exchange column and analyte recoveries were shown to be between 50 and 90%. McLeod et al. (96/C199) described the use of various microcolumns for selective field sampling of elemental species single elements or multiple elements present in natural waters. Flow injection was used later (in the laboratory) for column elution. The Journal of Analytical Atomic Spectrometry October 1996 VoL I 1 369Radvantages of this technique included full automation compati- bility with present FI sample introduction strategies and a stable snapshot in time of the sample composition. The selec- tivity of the sampling process depended upon the choice of column packing material.Flow injection methods were particularly useful for inter- ference management during introduction of dissolved solids. Coedo et al. (95/3557) used FI to determine B in steel. Dispersion within the FI manifold allowed the use of concen- trated ( 5 g 1-') sample solutions and the method detection limit for B was improved six-fold (to 0.2 mg kg-l) as a result. Using Be as an internal standard coefficients of variation were less than 1.5% for 20 mg kg-' of B in steel. The same group used an anion exchange microcolumn to isolate and determine several trace elements in high-purity iron (96/1503). Quantification limits were about 10 pg kg- ' and coefficients of variation were between 0.7 and 3%. Analyte recovery was near unity for all analytes and was reasonably independent of spike concentration.Sayama et al. (96/1309) used anion exchange of iodide complexes to isolate and determine Bi and Cd in high-purity zinc. Detection limits for one sample injection were 75 ng kg-' and 0.81 pg kg-I for Bi and Cd respectively and multiple injections of sample solution were found to improve method detection limits. Analyte recoveries were between 92 and 109%. A trialkylphosphine oxide/cellulose resin was used by Zeng and Zhou (95/3585) to isolate and determine Mo Sn and W in geological samples. Method detection limits for Mo Sn and W were 10 pg kg-l 0.1 mg kg-I and 20 pg kg-' respectively and elemental recoveries were between 98 and 101%. Coefficients of variation were less than 10%.Debrah et al. (96/1436) used flow injection and cold uapour generation to determine Hg in water. The Hg vapour was concentrated by amalgamation on a gold-platinum gauze to enhance sensitivity. The signal was proportional to the mass of Hg and the absolute detection limit for Hg was 5pg in 25 ml of sample. Coefficients of variation were below 1% at 1 pg 1- '. Olivas and co-workers (95/4709) described an FI-HG system for the determination of Se in water. Addition of alcohol (e.g. 5% methanol) reduced polyatomic ion inter- ferences and enhanced the Se signal by an order of magnitude. Under optimized conditions the absolute detection limit for Se was 1 pg (0.2 ml injection) and coefficients of variation were 2% or less. A similar system was also described by Quijano et al.(95/4710) but detection limits were slightly greater (35 ng 1 - I ) owing to the use of a low-sensitivity benchtop ICP-MS. Nelms and co-workers (96/268 96/C786) have developed a fully automated FI system for matrix removal and preconcen- tration of trace elements in sea-water. The principal component of this system was a minicolumn of 8-hydroxyquinoline bonded to controlled-pore-size glass. Preconcentration and column elution parameters were carefully optimized and with five-fold preconcentration coefficients of variation less than 3% were observed for analytes present at 1 pg I-'. Analyte recoveries were 89 to 104%. Dadfarnia and McLeod (95/2569) used a microcolumn of activated alumina to preconcentrate uranium in surface fresh water and sea-water.Uranium was eluted in a small volume of 2 mol HN03 and at 50 ng I-' of U coefficients of variation were below 4.5%. Taylor et al. (96/C675,96/1804) used solid phase iminodiacet- ate chelation to isolate and determine a suite of 8 trace elements in saline and freshwater samples. Absolute detection limits ranged from 8 pg (for Co) to 0.4ng (Cu and Zn). Hall and co-workers (95/3542) also used an iminodiacetate ion exchange resin in the determination of REEs in surface waters. Limits of detection were between 0.2 and 1.0 ng 1-' and coefficients of variation were less than 10% when analyte concentrations were greater than 5 ng 1-'. Chelating ion exchange (on cellulose-bound quinolin-8-01) was used by Yang and co-workers (96/1438) for the preconcen- tration of titanium and vanadium in water.Detection limits were about 10 ng 1-' for Ti and 1 ng I-' for V and coefficients of variation were less than 5%. A microcolumn packed with Chromotrope 2B immobilized on Dowex AGlX8 was used for isolation and determination of A1 in freshwater and saline solutions (95/3528 95/4483). The absolute detection limit for A1 was 200 pg. Capillary electrophoresis (CE) has emerged as an alternative to LC. Olesik Kinzer and co-workers (95/2573) developed an external sheath flow interface for capillary electrophoresis and used the system to determine trace element speciation and metal-ligand formation constants in aqueous and organic solutions. Electrophoretic resolution and analysis time were controlled by varying the flow rate of the liquid sheath (this solution also grounded the downstream end of the capillary).The detection limit for Sr was 8 fg and coefficients of variation for retention time and peak area were less than 3%. In a CE-direct injection nebulization(DINb1CP-MS system described by Liu and co-workers (95/4606) a sheath flow facilitated independent operation of the CE and DIN systems. Preliminary data suggested that detection limits in the ng 1-' range were achievable. A modified concentric nebulizer with sheath flow was also used by Lu et al. for CE-ICP-MS (96/1495). The capillary position within the interface was found to effect resolution and sensitivity and negative pressure was applied to the mobile phase reservoir to counteract pneumatic aspiration by the nebulizer. Detection limits for Cd and Fe (in ferritin) were 4 and 184 fg (respectively) for 74 nl injections.3.3.7. Speciation methods Elution chromatography (as opposed to discontinuous column stripping) remained the most popular means of determining elemental speciation. Recently Kumar et al. (96/1637) used supercritical JEuid chromatography ( S F C ) for the separation and determination of organoarsenic organoanti- mony and organomercury species. Multielemental ICP-MS detection of SFC eluates was superior to flame ionization detection in terms of elemental or isotopic specificity and SFC-ICP-MS detection limits were two to three orders of magnitude lower than those obtained by flame ionization. Given the nature of supercritical carbon dioxide SFC may well be the next speciation alternative to gain a loyal following in the ICP-MS community.Although many investigators use ICP-MS as a detector for chromatography few have used the isotopic selectivity of the mass spectrometer to advantage. The benefits of isotopic detection for chromatography were recently described by Heumann et al. (95/2407) in the context of quantification. On-line isotope dilution with undifferentiated isotopic spikes was used in cases where the identity of the elemental species was unknown. Enriched calibrant species were prepared (and added directly after sampling) in cases where the species was known (e.g. in the determination of iodide and iodate). The preparation of calibrant species using enriched isotopes was also reported by Hill et al. (96/1760) in the context of determin- ing lead and tin species by LC.Rare earth fission products (e.g. lanthanides with markedly non-natural isotopic signatures) in high-level nuclear waste solutions were separated and determined by Garcia Alonso et al. (95/2397) using ion-exchange chromatography and iso- tope dilution with rare earths of natural isotopic composition. Smith and co-workers (96/1657) used a similar chromato- graphic system with ICP-MS and beta particle detection for the same purpose. The benefits of multidimensional detection (primarily with respect to sensitive determination of short- lived fission products) were described. Arsenic is one of several elements receiving considerable 370 R Journal of Analytical Atomic Spectrometry October 1996 Vol. 11attention from chromatographer-mass spectrometrists.Microscale FI coupled with microbore LC was used by Pergantis et al. (96/1500) for the preconcentration and separa- tion of arsenic species found in animal feed additives. Several nebulizers (concentric DIN and a HEN high-efficiency nebul- izer) were evaluated and mu1 tivariate experimental designs were used to optimize detection of the species. A persistent background at m/z 75 (caused by an unspecified spectral interference) was reduced from its original equivalent concen- tration of about 0.3 pg 1-' of As and absolute detection limits were in thefg range. Other benefits of the system included minimal sample consumption ( - 1 pl) on-line matrix elimin- ation and reduced waste generation. Jensen and Bloedorn (96/1319) used a latex anion exchange column for rapid (1-3 min) separation of As species.Isocratic elution with dilute NaOH was used for trivalent and pentavalent As si)ecies gradient elution with NaCO and NaOH for separation of As metabolites in urine. Detection limits for As were in the low pg 1 - range. The 40Ar35C1 interference on 75A~ was rep0 rtedly overcome as a consequence of the separation. Kawabata et al. (95/3600) also found that anion exchange provided excellent separation between six inorganic and organoarsenic species. Absolute detection limits were 4-9 pg and coefficierits of variation were of the order of 5%. Ding and co-wctrkers (95/3610) used micellar LC to separate and determine inorganic and organoarsenic species in urine. The column was eluted with a mixture of propanol cetyltrimethylammonium brctmide and borate buffer; this mixture was fully compatible with the ICP-MS system.The linear dynamic range was three crders of magnitude and absolute detection limits were in the pg range. Reversed-phase ion-pairing and anion-exchange chrornato- graphies were compared by Cai et al. (96/1501) foi the separation and determination of inorganic Se species in fresh and saline water. A small column was placed upstream of the analytical column to preconcentrate the analytes prior to their separation. Conventional pneumatic nebulization was used for sample introduction. Detection limits after preconcentr iition of 2-10ml of sample were about 0.3 pg 1-' for selenitc and 0.1 pgl-' for selenate. These limits were approximately two orders of magnitude better than those achieved with direct injection of a 25 p1 sample aliquot.Takatera and co-workers (95/2529) used LC to separate and determine Se species ill cell culture digests. Metallothioneins were separated by size exclusion metallothionein isoforms were separated on Capcellpak-C and inorganic species were separated by c ition exchange with pH gradient elution. Bricker and Houk (96/1753) also described the separation and determination of selenium species (including metalloproteins) in human scrum using size-exclusion chromatography. Reversed-phase ion-pair- ing chromatography and ultrasonic nebulization were usttd by Yang and Jiang (95/4608) to determine inorganic and oigan- oselenium species in urine. Calibration was linear over 2-3 orders of magnitude.Detection limits were 0.8 pg 1- for selenite 0.5 pg I-' for selenate and 0.2 pg 1-' for trimethylselen- ium. Coefficients of variation were less than 5%. This method was also applied to the determination of inorganic and organotin species (96/58). Absolute detection limits were in the range from 3 to 16 pg with coefficients of variation from 6 to 9% at 50pg 1-' total Sn. Organotin compounds were also separated and determined by micellar LC (95/2 194). Separation of six tin species using an aminododecyl sulfate eluent and a butylsilane column required approxim,ttely 20min and absolute detection limits were in the rmge 20-50 pg. Coefficients of variation were less than 3% foi the determination of all six species. Powell and co-workers (96/1492) used a microcolumn and DIN for the separation and analysis of trivalent and hexavdent Cr.Separation and DIN operating conditions were optimized for best possible performance. The over-all analysis time was less than 10 min and detection limits were 30 ng 1-' 60pg I-' and 180 pg I-' for the determination of total Cr Cr"' and Cr" respectively. Byrdy and co-workers (96/1340) used anion exchange chromatography for Cr speciation. Trivalent chro- mium was stabilized before analysis using EDTA chelation. Detection of the 53Cr isotope was preferred over the more abundant 52Cr due to spectral interference on the latter by SO+ (from the ammonium sulfate mobile phase). Absolute detection limits were 40 pg for trivalent chromium and 100 pg for hexavalent Cr. Buckley and co-workers (95/C2951 96/C723) determined inorganic and organomercury species in soil and sediment extracts using a combination of cation-exchange and reversed- phase chromatography. The organic content of the mobile phase was carefully optimized to reduce problems with plasma instability and carbon deposition.Isotopically enriched mer- cury was used as a tracer to study interconversion between inorganic and organomercury species in soil and sediments. Stable isotope tracers were also used along with purge-and- trap gas chromatography by Hintelmann and co-workers to determine the rate of mercury methylation in sediments (95/4178). Methylmercury was extracted from test samples by distillation and then converted to methylethylmercury. The derivatized mercury was trapped on Tenax and thermally desorbed for analysis.The absolute detection limit for mercury was 1 pg which corresponded to a concentration of 20 ng kg-' of mercury in sediment. Coefficients of variation were approxi- mately 4% for multiple 250 pg injections of methylmercury. 3.4. Interference Effects Houk and co-workers looked at two approaches to overcoming interferences in ICP-MS. Firstly they reported the use of polyatomic ions as internal standards to correct for non- spectral matrix effects (95/4704). It was found that in the presence of a caesium matrix polyatomic and metal oxide ions were suppressed to the same extent as analyte signals at nearby masses. It was suggested that as the count rates for several interfering species are often included in an analysis they could be used in place of some elemental internal standards thereby reducing the number of elements added to samples as internal standards.A second study indicated that metal oxide ions could be attenuated by using a graphite injector inserted directly into the plasma torch in conjunction with desolvated aerosols (95/C3035 96/1261). The hot injector constricted the stream of analyte and prevented it from widening excessively as it travelled through the plasma. This allowed the sampling cone to be deployed several millimetres downstream of the initial radiation zone without substantial loss of analyte signal. The signal ratio for Lao' :La+ was reduced to 0.05% with conventional desolvation and 0.01 YO with cryogenic desolv- ation a considerable improvement on those that could be achieved with a conventional torch injector.Analyte sensitivit- ies were improved by between a factor of 1.5 and 15. Other analytical figures of merit were apparently not compromised. Selby (95/2281) presented the findings of a feasibility study on the prospect of performing elemental analysis in ICP-MS without isobaric or chemical interferences. The approach used the generalized standard additions method (GSAM) which incorporated alternatives to conventional multi-point cali- bration curves using training sets based on statistical exper- imental designs advanced analysis of the data set generated after the calibration and a rapid on-line method for managing the preparation and measurement of training set standards using discontinuous flow analysis (DFA).The GSAM was considered capable of overcoming interferences due to isobaric or chemical effects within the plasma source. Unfortunately Jouiwal of Analytical Atomic Spectrometry October 1996 Vol. 11 371 Rthe GSAM method required that all analytes and interferences be known in advance. 3.5. Applications As highlighted in the introduction of this review only appli- cations with novel content or exciting analytical science are included in this section. For broad reviews of ICP-MS appli- cations the reader is therefore directed to the Atomic Spectrometry Updates concerned primarily with applications. The capability of ICP-MS to make isotope ratio measure- ments was successfully exploited by Vanderpool et al. (95/3548) for B transport in plants rats and humans.The limits of detection for 'OB and "B were 0.11 and 0.40 ng g-' respect- ively. Isotope ratios were measured in faecal samples to a precision of <2% RSD. However memory effects for B were significant with a 1 ng g-' memory after 6 min washout from a 200ngml-' solution. To measure B transport in animal systems 20 pg of loB were fed to a fasted rat. After 3 d 95% of the 'OB was recovered from the urine and 4% from faeces. Urinary isotope ratios "B "B changed from a 'natural' abundance of 4.1140 to an enriched value of 0.9507 a 77% change. The 'OB label in perfused rat livers peaked within 3 h (>90% recovery and a 56% change in "B:loB) and returned to a natural abundance ratio within 24 h. Murphy and Paulsen (95/4544) determined Pb in blood samples using ID.The method was used to certify Pb in four levels of NIST blood SRM 955a. The lowest level of Pb 47.76 ng g-' was measured with an analytical uncertainty of <1% and the highest level 517.9 ng g-' to 0.3%. The uncertainty was attributed to sample inhomogeneity and varia- bility in the analytical blank as isotope ratio measurements had RSDs of <0.2%. The authors believed that the precision and accuracy that could be obtained for blood Pb by ID-ICP-MS was beyond anything that could be obtained with routine methods. In order to determine Cr in biological reference material DOLT-2 McLaren and co-workers (95/3730) had to use a 12% air-Ar mixed nebulizer gas plasma in conjunction with ID to minimize the interference effect of polyatomic species originating from residual carbon in the sample solution.Samples were digested with HN03 in a microwave oven. The limit of detection was 30 pg ml-' and results were considered to agree well with certified values. Takaku et al. (96/1511) described the measurement of I in natural waters. They reported that the element was readily determined without separation or preconcentration to an LOD of 10 pg ml-'. However because of its volatility the I signal was found to be somewhat unstable. Iodine vaporization was attenuated by addition of an organic alkali (e.g. tetramethylam- monium hydroxide) to samples leading to stable signal gener- ation. Results obtained following both external calibration and standard addition were in good agreement. The method was used to determine I in 42 water samples at concentrations of between 0.65 and 35.9 ng ml-'.Jarvis and co-workers (95/460 1) described the measurement of B isotope ratios at low concentration in groundwaters with a precision of between 0.1 and 0.2%. Samples were evaporated to increase the elemental B concentrations to 200 ng ml-' and interfering matrix elements were removed by an adapted cation exchange separation procedure. Using the method the authors felt that a reliable database documenting the natural variation in B isotope composition in aquifers and rain water could be established and may be used to evaluate possible levels of B pollution from anthropogenic inputs into natural aquatic systems. Freydier et al. (96/1563) compared ID with external cali- bration (with and without internal standard) for the determi- nation of Ba by ICP-MS in water and rock samples. The mass bias found to be present was independent of the matrix and stable on a daily time-scale.Barium concentrations determined by ID and external calibration with an internal standard were reported to be in excellent (within f 2 % ) agreement. Indium was considered to be an appropriate internal standard and effective in the correction for matrix effects on Ba. In the absence of an internal standard agreement between the two calibration methods was within f 6% for the determination of Ba. The authors considered that this indicated matrix effects on Ba were small. Thirlwall and Walder (95/4270) reported some Hf isotopic data for ten -0.01 mm2 subareas of zircon crystal separated from the -318 Ma diatrime of Ellie Ness Fife Scotland.In situ analysis was achieved by laser ablation sampling into a multiple collector ICP-MS. Despite large interferences from Yb and Lu 2 standard error precision of 0.000 04-0.000 14 was achieved on 176Hf 177Hf in each subarea each representing the analysis of - 10 ng. Over-all reproducibility of & 0.000 05 (20) was obtained between the ten subareas said to be only 2-3 times poorer than could be achieved by TIMS. Reproducibility of single-spot analysis was about a factor of 2 better than reported for ion microprobe studies of zircon Hf with far less potential for inaccuracies caused by molecular isobaric interferences. Qianli and Kerrich (95/4273) reported on an ID ICP-MS study of Zr and Hf in Komatiites and low abundance RMs in order to evaluate previous data obtained using an external calibration procedure.Isobaric overlaps were negligible and mass bias in spiked samples was corrected using natural ratios from unspiked samples. Results were found to be in good agreement with the previous results but with improved pre- cision. For example Zr was determined in BCRl to a concen- tration of 184 pg g-' and a precision of 0.005% RSD which was comparable to that obtained by TIMS. Enzweiler et al. (96/339) described the development of a method for the determination of Ir Pd Pt and Ru in geological RMs by ID-ICP-MS. After fusion of the sample with sodium peroxide the PGMs were preconcentrated by tellurium copre- cipitation. Results obtained were in excellent agreement with recommended values for elements above the LOD of 0.3-2.0 ng g-'.Although the method only used 0.5 g of sample no errors were found that could be associated with sample hetero- geneity. Additional work showed that the technique could be extended to the determination of Au and Rh by external calibration. El-Jammal and Templeton (96/1506) described a method for processing organosilicone oils and gels for subsequent analysis by ICP-MS. Although the samples were generally 'free' of trace element contamination Pt added as a catalyst during manufac- ture was found to be present at -4.5 pg g-' in a silicone breast implant. Quantitative recovery of Pt from silicone gel was achieved by dispersion in aqua regia extraction of the organosilicone with diethyl ether and back extraction with acid.Hepiegne et al. (96/1758) developed a chemical separation method for the determination of 99Tc in various types of radioactive wastes. The method included fusion with NaOH ex traction in a column containing methyltrioctylammonium chloride extraction by solvent with N-benzoyl-N-phenylhy- droxylamine and measurement by ICP-MS. Recovery of 99Tc using 99mTc as a tracer was >70%. The 30 LOD was 1.9 mBqml-' enabling activities as low as 0.3 Bq g-' to be determined from a 0.2 g sample assuming 70% yield. Studies using ETV-ICP-MS lowered the LOD by a factor of ten. The operation of ICP-MS instruments in glove boxes for the determination of trace elements in nuclear materials has been studied. Kopajtic et al. (96/271) studied the effect of Pu Th U and Zr at concentrations of up to 1OOOpg g-' on the analyte signals.A strong signal suppression effect at concen- trations higher than 100 pg g-' was found for Pu and U. The 372R Journal of Analytical Atomic Spectrometry October 1996 Vol. 11effect of Th and Zr was found to be lower. Special attention was paid to the determination of B in PuO and the LOD was lowered to less than 1 pg g-’. 4. LASER IONIZATION MASS SPECTROMETRY (LIMS) A review of the LIMS technique was provided by Odom ot al. (95/4131) who discussed instrumentation and applications to the microanalysis of solids both bulk and surface analyslis as well as discussing some representative examples. New instruments for LIMS have been described by Gill (95/4115) who reported the development of a laser ablation quadrupole ion-trap MS instrument and by Cuna tit al.(95/4656) who described the less novel use of a Mattauch- Herzog geometry mass analyser. Proposed applications clf the latter instrument were to the analysis of solids inchiding nuclear fuel samples. Work had commenced on the develop- ment of the ion source but the instrument was not complete. Situ (96/1515) described an instrument for long range (3 9 m) LIMS measurements possibly for use on a lunar rover vehicle. The determination of elements in a simulated lunar reference material showed good correlation. The fundamental processes involved in laser ablation were investigated by Zhuang et al. (95/4646) who used doubled and quadrupled Nd YAG radiation ablation of silicon targets. Monatomic ions had a greater average energy and broader energy distribution than neutral species.Higher kinetic encrgies and a greater degree of ionization were observed with the shorter wavelength radiation. The authors discussed their results in the context of a proposed mechanism for silicon ablation. Kozlor et al. (95/4154) also discussed the dependence of ion velocity on laser energy in the context of the mechanism of the ablation process. An unexpected finding was reported by Schriemer and Li (95/4145) who observed that Ar in charge states 66’ and Xe in charge states 69’ could be generated by irradiating the repeller plate in their instrument with 206 nm laser pulses at - lo6 W cm-2. The authors did not give an explanation for the mechanism behind this phenomenon. They discussed the production of photoelectrons from the repeller plate and subsequent acceleration of these electrons ill the applied fields within the source but were unable to account for the 310eV required to produce Ar6+.In multiphoton ionization experiments - lOI4 W cm-’ (at 533 nm) had been required to generate Ar6+ so this did not seem to be a plausible mechanism. The action of a photo-assisted field was also discussed as a possible mechanism but had never been observed at flat electrodes. Their ion source was also exposed to organic ions from a gas chromatograph which yielded the expected electron-impact mass spectra. Ionization of the He carrier gas was not mentioned nor were organic di-cations reported but an unexplained correlation between the formation of multiply charged ions and the absence of background Na’ and K+ ions was reported.A number of investigators have studied the formation of clusters in laser-ablation plasmas which can potentially form isobaric interferences and give rise to other matrix effects. Berardi et al. (95/3717) have used TOF-MS as a diagnostic tool to investigate laser ablation deposition of YBa2Cu307-8 high temperature superconductor films by an XeCl excimer laser emitting 16 ns pulses (40 mJ) at 308 nm. Similar high temperature superconducting materials were investigated by Bulgakov (95/3720) who observed the clusters formed in the laser-ablated plume above YBaCuO using 1-3 J cm-’ pulses focused to a 400 pm spot from an Nd YAG laser. Beckt:r and Dietze (95/4181) have studied the cluster ions formed by laser and spark ablation of REE-graphite mixtures. These were important as potential isobaric interferences in mass spec- trometry. The work was performed on a Mattauch-Herzog instrument with a spark source and a Q-switched Nd:YAG ablation laser using the fundamental emission wavelength. It was observed that the optimum power for C + formation was the same for both ionization techniques.At laser fluences > 1O1O W cm-’ negligible cluster-ion signals were observed either because of their high rate of dissociation or their low rate of formation. The relative intensities of oxide carbide and dioxide clusters were compared with those observed by ICP-MS. Ion ratios were used as a measure of plasma tempera- ture and it was suggested that knowledge of the distribution of cluster ions could be used to correct for isobaric inter- ferences.Laser ionization TOF-MS was used by Kokai et al. (95/4124) to study materials sputtered from (BC,N) films that had been deposited by chemical vapour deposition. An Nd YAG laser producing 1 J cm -2 and an ArF laser yielding 50 mJ cm-’ were used in the experiments. It was found that the low irradiation power of the latter limited post-ablation cluster formation. Al-containing cluster anions incorporating As C 0 P and S generated by laser ablation were studied by Liu et al. (95/4637) who used a dual TOF-MS instrument which allowed the simultaneous determination of cations and anions; however this study was confined to the anions. The distributions of Al,As,- AlC,- A1,0,- Al,P,- and Al,S cluster ions were recorded and discussed in the context of the variation in properties in the transition from small clusters towards the solid state. Casey et al.(95/4651) used Nd:YAG ninth harmonic radiation ( 11 8 nm) to probe Ga As As and As species in the gas phase during molecular beam epitaxy (MBE) processing by LIMS. They reported that the use of such short wavelengths allowed ionization without dissociation of molecular species. Amoroso et al. (96/1628) examined cluster and kinetic energy distributions in the laser ablation plumes of Pb(Tio.48Zro.5,)03 samples. The influence of gas phase oxygen on these distributions was investigated in the context of the laser ablation film deposition process. Gibson (96/1629) has investigated lanthanide oxide and mixed lanthanide ion cluster growth in post-ablation plumes.The analysis of individual airborne particles is extremely important to the understanding of pollutant transport but is technically very demanding. Carson et al. (95/4639) described the application of laser ablation TOF-MS to this problem. They describe their instrument as a ‘Rapid Single Particle Mass Spectrometer’ (RSMS). The instrument was capable of performing both surface and bulk analysis of the particles. The particles triggered the ablation laser as they were detected scattering light from a CW He/Ne laser beam. Determination of the source of S in atmospheric particles from isotope ratio measurements was proposed as a possible application of the instrument. Murphy and Thompson (95/4105) also reported use of the instrument for 0.3-16 pm diameter particles.Direct LIMS analysis of biological matrices has been used by two groups in A1 toxicity studies. Ehmann and Markesbury (95/4648) have reviewed the application of analytical methods to the determination of A1 in biological samples in the context of research into Alzheimer’s disease in their own laboratories. Techniques discussed included GFAAS INAA and LIMS. Schmidt and Barkhaus (95/4649) used the technique in a study of the role of A1 in dialysis osteomalacia. 5. RESONANCE IONIZATION MASS SPECTROMETRY (RIMS) In a review paper Moulin et al. (96/4143) compared the capabilities of RIMS with other analytical techniques particu- larly ICP-MS and laser-induced fluorescence (LIF). The sensi- tivity and selectivity of RIMS were emphasised.A basic introduction to ion sources including resonant laser ionization Jclurnal of Analytical Atomic Spectrometry October 1996 Vol. 11 373Rused for the analysis of inorganic solids and liquids was presented by Colodner et al. (95/3890). The review contained a useful table comparing ion source applicability and perform- ance. RIMS however was written off rather prematurely as a technique that had had its day. The role and importance of both SIMS and RIMS to the study of geological and inorganic materials were briefly addressed in a review of analytical methods by Jackson et al. (95/4348). Tissue (96/1521) reviewed the applications of RIMS to geochemistry and cosmochemistry and Whitaker et al. (96/1624) gave a brief overview of the use of RIMS in trace analysis.Developments of the resonant laser ablation (RLA) technique have been documented by Eiden et al. (95/4132) who discussed the mechanism of RLA and its application to the determination of impurities in copper nickel and rhenium. Johann et al. (96/1706) have described a quadrupole RIMS instrument which sampled by ion-beam sputtering and used a 1 + 1 resonant ionization scheme to achieve sub-ppma detec- tion limits for impurities in metal samples. Turk et al. (96/1470) described a new type of RIMS instru- ment in which the sample was aspirated into an ICP or hydrogen-air flame ionization was resonantly enhanced by laser irradiation and ions were then sampled into the vacuum system of the mass spectrometer. The high pressure environ- ment of ion formation and the expansive cooling on sampling into the spectrometer would presumably reduce selectivity by introducing charge transfer processes and cluster ion inter- ferences. These effects would be in addition to the background signal from these ion sources.A number of groups have used RIMS in studies of the sputtering process. Nicolussi (95/4138) determined the excited state distributions of Ni and Ti sputtered by 8 keV Ar+ ions. The velocity distribution of sputtered ions was found to be independent of the excitation energy being governed by the collision cascade process. Interferences in their measurements arose from the non-resonant dissociation of clusters forming atomic ions which were not directly derived from the sputtering process.The authors emphasised the importance of low-lying metastable states on the distributions observed. He Chun et al. (96/1705) have studied the dependence of neutral-atom excited-state population distributions on Ar + pri- mary ion angle and energy. In the sputtering of an Ni(001) surface they noted significant anisotropy but excellent agree- ment with molecular-dynamics simulations of the sputtering process. They stated that the excitation pattern was not that predicted by the Boltzmann distribution and that valence shell electronic structure was more important in determining the distribution than the excitation energy. Homolka et al. (95/4137) have investigated the sputtering process by LIF and laser ionization sputtered neutral MS (SNMS) using metallic Cr and Ti targets exposed to oxygen pressures in the range 10-6-10-'o mbar.Results from the two techniques for the yield of sputtered monatomic species differed and this was explained in terms of the excited state distribution of the sputtered material and the fact that photodissociation of neutral clusters interfered with the RIMS measurement. The influence of surface oxidation on sputter yield and excited state distribution in sputtered atoms was also addressed. Cluster ions formed in the laser ablation of iron oxide samples were investigated by Maunit et al. (95/4144) who used a laser microprobe with resonant and non-resonant post-ionization. The instrument ablated samples in the transmission mode i.e. the laser beam struck the rear surface of a thin sample film and ions were sampled at the opposite surface.The high sensitivity of resonant post-ionization allowed the use of a lower ablation energy which gave fewer matrix interferences. The ratio of the Fe,' and Fe,O+ cluster ion intensities correlated with the oxide phase ablated. The continued use of RIMS in the field of trace radionuclide determination has been reported by Lantzsch (95/4107 96/1479) who described the use of a dedicated collinear RIMS instrument for the measurement of "Sr in environmental samples containing 'fresh' fission products. Samples collected on air filters were measured after a chemical separation pro- cedure involving the separation of Ba and Ca with crown ethers. Wendt et al. (96/1480 96/1716 96/1719) have reviewed the application of RIMS to the determination of radionuclides.In particular they discussed the triple resonance excitation schemes used by their group for actinide determination their high efficiency Tc ion source (96/1478) which employed reson- ance ionization and the determination of 89Sr and 90Sr in environmental samples by their dedicated collinear RIMS instrument. Trautmann (96/1468) emphasised the importance of RIMS in a comparison of radiometric and non-radiometric methods for the determination of radionuclides. The other techniques discussed included a- p- and y-spectroscopies AMS and ICP-MS particularly for the determination of 89Sr "Sr and Tc. Short-lived radionuclides can also be determined by RIMS Blanc et al. (96/1797) described the collinear ionization technique (COMPLIS-collinear measurement using a pulsed ion source) for high resolution studies and direct ionization of laser-desorbed plumes (PILIS-post-ISOCELE laser isobar separator) for more sensitive measurements.Laser desorption of irradiated refractory samples could be delayed until the parent radionuclide had decayed to give the daughter nuclide of interest. Moulin et al. (95/4143) have reviewed the use of laser spectroscopic methods for the determination of actinides and other radioelements and have compared these techniques with ICP-MS. They emphasised that the highly selective laser- based methods did not require extensive chemical preparation and that measurements were rapid. They did not however draw attention to the rapidity of ICP-MS measurement nor its multi-element capability. The use of diode lasers to excite atoms in RIMS has continued and with advances in diode laser technology promises to play an increasing role in this field.Young and Shaw (96/1652) have used diode lasers in the first three excitation steps of an RIS scheme for La and reported enhancements in isotopic selectivity by a factor of lo3. Bushaw et al. (96/C245) described an RIMS instrument with an atomic beam oven source a quadrupole mass analyser and single ion counting capability. Semiconductor lasers were used for resonant excitation and an isotopic selectivity of lo9 was reported as well as an over- all efficiency of 10- 3 . There is continued interest in RIMS for the analysis of semiconductor devices. The technique is a powerful form of SNMS which offers both highly sensitive and selective analysis and is free from many of the matrix effects that plague SIMS.Downey et al. (96/1663) noted the need for a quantitative tool capable of depth profiling through 4-7 nm SiO gate dielectrics in complementary metal oxide semiconductor (CMOS) devices. The diffusion of dopants through this barrier during the annealing process needed to be closely monitored. Ambiguity arises in 02+ SIMS measurements because the equilibrium sputtering conditions required for quantitative measurements using RSFs may never be reached in these narrow structures. This was not a problem for the RIMS of sputtered atoms using Xe+ primary ions. The spectroscopy of B and P pertinent to these measurements was discussed and the technique demon- strated by recording depth profiles of these elements in silicon substrates.A dynamic range of lo5 was required for these measurements and was achieved by varying the gain of the Daly detector. The problem of exciting atoms with multiplet ground states was addressed by power broadening to excite the components simultaneously. This was demonstrated for the doublet ground state of boron which was split by 16 cm-'. Interferences included the 30SiH+ ion isobaric with 31P+ that was ionized by high intensity UV radiation. The main matrix 374R Journal of Analytical Atomic Spectrometry October 1996 Vol. 11effects observed in sputter-initiated RIMS were due to sputter rate variations which were observed to be particularly pro- nounced across the WSi,-polysilicon boundary. A low energy Xe+ primary ion beam at a high angle of incidence was used to optimize depth resolution. Kong (96/1530) described a two-colour three-photon and a one-colour three-photon scheme for the ionization of Pb.The detection limit of < 100 fg was not outstanding. Telle et ul. (96/1481) used a one-colour three-photon scheme for the determination of Pb isotope ratios and the influence of laser power on these measurements They reported difficulty in determining isotope ratios at low abundances. Geological applications of the laser microprobe included the work of Ma et al. (95/4655) who determined Ti isotope ratios in pm-sized grains of Sic from meteorite samples. Low nitrogen laser power ablation (<20 nJ per pulse 4 ns) and ion-beam sputtering combined with resonance ionization were applied.Wright (95/4682) has reviewed geological applications of the laser microprobe focusing on the measurement of C N 0 and S isotope ratios. Gilmour et al. (96/1688) have applied their RELAX (refrigerator-enhanced laser analysis of xenon) spectrometer to I/Xe chronometry (on the Ma timescale) of meteoritic samples. Xe was desorbed from samples bc CW argon-ion laser heating and then trapped within the low- volume RELAX spectrometer. Over-all detection efficiisncies of were reported for Xe atoms trapped within the spectrometer. The efficiency of CW laser sample degassing and inhomogeneous heating of samples were discussed. Applications of RIMS to biological samples have been described by Bekov and Whitaker (95/C4339) who used a thermal-atomization RIMS instrument for the determination of Pt in blood B in brain tissue and Cr in skin at pg g-' concentrations.A standardless quantification capability for samples of a few milligrams was claimed with little or no chemical treatment. The development of a two stage atomizer to reduce the background of molecular species was planned implying that the current system is subject to such effects. RIMS has also been used for fundamental spectroscopic studies and the determination of ionization potentials by extrapolation of Rydberg series energies. Koehler et al. (96/1475) used a RIMS approach to determine the ionization potentials of Am and Cm with samples of only 10l2 atoms. Huang et al. (96/1651) used a static electric field to ionize Ybf Rydberg states (n = 17-86).The technique allowed the multiphoton background ionization signal to be eliminated and the ioniz- ation potential of Yb" to be measured. 6. SECONDARY IONIZATION MASS SPECTROMETRY (SIMS) 6.1. Reviews A number of reviews of SIMS and its applications in various disciplines have been published and to mark forty ycars of activity in the SIMS field (driven mainly by the needs of the semiconductor industry) a special issue of the Interncztional Journal of Mass Spectrometry and Ion Processes was puhlished (96/1795). A historical review indicating the scope of dtvelop- ments in this period was provided by Honig (96/1599) who discussed the early 'stone-age' SIMS work at RCA Laboratories in Princeton. He reminisced about the days of freedom of research direction and bemoaned unexciting modern-day mass spectrometry with computer control of everything and service contracts that preclude the hands-on approach of those early years.Applications of SIMS with Cs' and 02+ primary ions to microelectronics applications were reviewed by Magee and Frost (96/1601). Problems of varia- bility of RSFs mixing and quantitation at interfaces were discussed as well as recent approaches that addressed cach of these problems. They emphasised the importance of very near- surface depth profiling (< 100) for spatially-resolved analysis of semiconductor devices; also the use of low primary-ion energies and high incidence angles to reduce beam-induced mixing and hence the tailing of sharp profiles. Profiles of N concentration across Si02/Si cannot be reliably measured by SIMS and the use of the CsXf technique was recommended.The presence of A1 contamination from ion implanted samples was compared with that from unimplanted samples to deter- mine its source leading to improvements in implanter design. Applications specific to the analysis of Hg -,Cd,Te (95/4431) for impurity and stoichiometry determination and applications in the field of catalysis (95/4618) have also been reviewed. Ketata et al. (96/1633) have compared TXRF and SIMS for the determination of metallic contaminants particularly A1 and Fe contaminants in silicon wafers. The use of ICP-MS SIMS SNMS and GDMS for precise isotope ratio measure- ment in highly enriched 18'Os samples has been described (96/1691). Although it is of general interest it is not clear that such a capability would be widely applicable! In a review of fundamental aspects of the SIMS technique Migeon et al.(96/1603) discussed ionization efficiencies and matrix effects under Cs' Ga' and 02+ bombardment. Imaging fast acquisition and the reduction of matrix effects using cationic species were discussed. Rastered beam micro- probe instruments were compared with stigmatic imaging instruments that have a single-spot analysis capability. Microscope-type images were more rapid for image acquisition and appropriate where lateral resolutions > 1 pm were required. Although cationization reduced matrix effects because of reduced sensitivity it was not appropriate for the determination of trace elements at sub-micron lateral reso- lution.Wild (96/1459) has reviewed the use of SIMS for surface analysis along with the complementary techniques Auger electron spectroscopy (AES) X-ray photoelectron spectroscopy (XPS) SNMS and laser Raman spectroscopy. Hinton (95/4679) has reviewed the theory and practice of ion microprobe SIMS in the earth sciences. Whilst emphasising the importance of the method the author noted that use of the method has been limited by its high cost and high measurement uncertainty. Sample preparation imaging and depth profiling techniques were discussed as well as applications to the measurement of light elements REEs and to radiometric dating. A review of the basic theory and practice of SIMS was reviewed by MacRae (95/4616) who provided a number of examples of geological interest.6.2. Instrumentation Developments There have been few major developments in instrumentation reported during the review period. Teodoro et al. (96/1769) described a sophisticated instrument that combined Ar + and Cs + ion quadrupole SIMS Al/Mg source XPS AES secondary electron detection and a supplementary electron gun for charge compensation. The instrument had a fast-entry air-lock with a sputter gun for sample cleaning and a variable temperature ( 13&850 K) stage. Low-energy electron-induced desorption measurements were also possible. Examples of spectra were given for anion clusters sputtered by a Cs' ion beam from a graphite surface. The authors planned to develop a time of flight MS capability for the instrument. Konarski (96/1739) described a rotating sample stage which did not require secondary electron imaging.Rotation was used to prevent ion- beam induced surface roughening and was applied to depth profiling in InO~,,A1,,,,As/lnP heterostructures with 5 keV 02+ primary ions (100 pm spot size). The authors reported poor reproducibility of sample position and 'wobble'. Both were of the order of 20pm. Coath and Lang (95/4146) described a cold cathode duoplasmatron source for the pro- duction of Ar' and 0- ions able to generate 0.1 A cm- Ar+ Journal of Analytical Atomic Spectrometry October 1996 Vol. 11 375 Rand 7 mA cm-2 0- on a 4.2 pm spot. Zhou et al. (96/1621) described a primary ion source capable of producing Cs' ions and I - ions without the need to break vacuum. Applications discussed were limited to large molecules.Anthony et al. (95/4141) have described the use of AMS with a SIMS source for the removal of isobaric interferences by using high charge-state ions in the analysis of semiconductor samples and reported sub-pg g-' detection limits. Sugano (96/1790) described an ion source based on an 'X-ray emitting' isotope such as 63Ni or "Sr in a lead container with an aluminium window. 6.3. Quantification The problem of quantification by SIMS is normally addressed through the use of relative sensitivity factors (RSFs) which must be determined for specific elements matrices and instru- mental conditions. Wilson (96/1602) has reported RSFs for Eu Ir Lu Os Pr Re Rh Ru and Tm as well as for molecular secondaries in Si GaAs and diamond. Cameca 3F 4F and 5F instruments were used in this study.The need to monitor ReO' rather than Re' secondary ions was emphasized as Re has the highest molecular ion enhancement of any element (a factor of 4000 in GaAs). Cabri and McMahon (95/4670 95/4672) determined RSFs for lg7Au and lg8Pt in chalcopyrite monoclinic pyrrhotite pentlandite and pyrite. Measurements were performed with a Cameca 4f instrument Cs+ primary ions and negative secondary ions. A matrix effect involving the influence of electronegative mineral components on the suppression of the Au-signal was reported. The determination of '"Ag in chalcopyrite and pyrite with an LOD of 60 ng g-' was also reported (95/4671). Jenett (95/4106) determined RSFs for the quantitative analysis of nitrides embedded in copper pellets by SIMS and electron-gas SNMS.The contribution of all charged and neutral sputtered particles to the matrix effects observed in the analysis of AlN B,C BN Sic and Si9N406 were discussed with particular reference to the role of the light elements B and C and the more electronegative N and 0. Cone formation during sputtering was observed and regions were left unsputtered due to sample charging effects. This latter observation was echoed in the work of Downey and Emerson (96/1464) who reported the deflection of a 2 keV primary ion beam as a result of sample charging. Smith et al. (96/1681) reported the application of SIMS to impurity determination in semiconductors and particularly the ability to measure -2 x lo9 atoms cm- A1 and Fe. The quantitative analysis of oxide ceramics by SIMS has also been briefly reviewed (96/1765).Van der Heide et al. (96/4147) discussed their 'infinite velocity' method for quantijication in SIMS whereby the sputter yield as a function of kinetic energy is extrapolated to the infinite velocity limit where matrix effects are theoretically zero. The authors reported linear calibrations for all elements measured and confirmed the validity of the method by compar- ing integrated depth profiles with known implanted doses. An important application in a number of fields is the determination of the hydrogen concentration in solids. The method is not however particularly sensitive. De Souza et al. (96/1750) discussed problems in the negative ion SIMS measurement of H in perovskite oxides by Cs' primaries.Mass interferences and the use of D were also discussed. Dobrileit (96/1781) used SIMS to investigate metal-hydrogen bonding in SnCo,D and LaNi,H and Madronero (95/4110) used SIMS for the determination of H in carbon fibres. 6.4. Matrix Effects Tomita et al. (95/4148) have determined the sputter yield as a function of energy for six elements in silicon using an 02+ primary ion beam. Sputter yield was found to correlate with surface oxidation and ionization potential. It was suggested that with a knowledge of RSFs and the sputter yield-energy relationships standardless quantitative measurements should be possible. The authors also noted a dramatic change in the As + secondary ion energy at high surface oxygen coverage. Cluster ions represent a potential matrix effect by removing a fraction of the atomic ion signal or by generating isobaric interferences.They can however be used to advantage as certain types of cluster ions are produced in high yield and can be more representative of the solid-phase analyte concen- tration than monoatomic ions. Yang et al. (96/1633) examined the formation of CsX' ions in the very low energy primary ion bombardment regime. They noted that CsX' ions could be formed below the threshold energy for X' secondary ion formation (CsSi+ was cited as an example of this effect). The authors reported that efficient secondary neutral sputtering occurs at these energies (<100eV) and that the cluster ions were formed above the surface. The low energy of the primary ions also leads to minimal penetration and surface damage.The Si( 11 1) surface analysed was partly covered by water and water-derived adduct ions were reported but there was some confusion over the mass-assignment of these ion signals. Chen and Wang (96/1522) applied the MCs' SIMS technique to a study of A1 and 0 diffusion at Ti/Al,O interfaces as a function of sample annealing temperature. Anomalously high Al' A10- 02- and Ti' signals were observed at the interface in normal Cs' SIMS mode. These were eliminated by the use of the MCs' mode. An electron gun was used for charge compensation at the sample. Van de Walle and Joyes (96/1544) reported the very surprising observation that in the liquid- metal ion source (LMIS) sputtering of dimeric copper ions those derived from a pure copper substrate show the expected isotopomer pattern whilst the Cu2' ions sputtered from a Auo.5Cuo.5 alloy were present only as homonuclear isotopo- mers (i.e.63Cu65Cu' dimers were absent). The observation was explained in terms of the different trajectories of the sputtered ions influencing the probability of formation of the different dimer ions. Another application of cluster ions is in the determination of the chemistry of individual solid phases within samples which correlates with cluster distributions in the mass spectrum. Marie et al. (95/4149) investigated the effect of Cs concentration on the MCs' Sics' and Cs2+ yield from Cs-implanted silicon samples bombarded by Cs+ primary ions. Their data were found to be consistent with the recombination model for cluster formation.Daolio et al. (96/1591) investigated cluster ion formation in PbO Ru0,-TiO and IrO,-RuO,-TiO films under Ar' 0' and 0,' primary ion bombardment. The influence of impurities such as alkali metals derived from the electrolytic deposition technique was noted. The positive and negative monatomic and cluster ions observed in each phase were tabulated and the technique was proposed as a tool for characterizing the catalytic activity of these materials. Svetov .and Chmel (96/1777) reported that SIMS could be used to (demonstrate the presence of Si-C1 bonds in silica glass prepared by chemical deposition from C1 enriched vapour. The same feature was not observable by Raman spectroscopy. Electronegative species especially surface oxygen are known ito enhance secondary cation yield.Advantage is taken of this phenomenon by exposing the surface (flooding) to electronega- rive species. Sielanko (96/1770) reported the use of a CF,C1 j'looding technique for SIMS signal enhancement in the analysis of copper and stainless steel samples. Results were compared with the oxygen-flooding method. A signal enhancement factor of 37 was reported.for Cu+ 5 for Cr' 6.6 for Fe' and 4.6 for Ti+ at a CF,Cl of 4 x mbar. Although the authors cited previous work that used CCl no direct comparisons of the two halocarbons were reported. The oxygen-enhancement effect in SIMS was studied (95/4150) by a combination of 376 R Journal of Analytical Atomic Spectrometry October 1996 Vol. 11techniques including ion scattering spectroscopy direct recoil and XPS.The degree of surface oxidation of Co and Fe was found to correlate well with the enhancement effect. Dorozhkin (95/4155) has investigated the influence of residual gas on surface work function and its effect on ionization in SIMS analysis of GaAs under 2 keV Kr+ ion bombardment. Signal enhancement can also be brought about by surface topography modifications; the use of shadow-cone-enhanced SIMS for the analysis of single crystal metal surfaces was discussed by Braun (96/1558). Using the oxygen-flooding technique Smith et al. (96/1681) reported detection limits < 10'' atoms cmP2 for most analytes and - 2 x lo9 for A1 and Fe in particular. Studies of the fundamental processes of ion formation in SIMS included the work of Yamauchi (95/4657) who modelled 0,' bombardment of a copper alloy.Using the LTE inlasma approximation the model agreed with experimental data within an order of magnitude except in the case of heavy elcments. The high energy sputtering process by Ag C Ge m d Si primary ion beams of different charge states and different energies in the range 0.4-10MeV has been investigated by Kyoh et al. (95/3719). The mechanism for multiply-charged secondary ion formation was discussed. 6.5. Depth Profiling and Imaging The demands of the semiconductor industry continually push the SIMS technique to achieve higher depth resolutions in depth-profiling measurements. Tomizuka and Ayame (9b/1523) examined native SiO layers on Si. Insulating SiO layers in MOS devices were expected to become as thin as <?-3 nm and to demonstrate adequate depth resolution native SiO layers (0.57 nm deep) were measured. Resolution was limited by the transient depth an artefact of ion sputtering tliat was less significant for Cs+ than 02-.The transient depth was shown to increase with primary ion energy and angle of incidence due to increased knock-on effects. Crater bottoms were examined by electron spectroscopy for chemical analysis (ESCA) to determine the oxidation state of the silicon. A chemical bevelling technique which allowed 3.1 nm depth resolution to > 1.6 pm below the sample surface has aho been developed (96/1709) for high depth resolution applications. The relationship between depth resolution and primary ion energy was discussed. Tatemachi (96/1788) described in a patent the use of primary-ion-beam induced topography to create a wall around the area under investigation and [hereby reduce edge effect in the etching crater.Franzreb et al. (96/1757) compared reactive ion (Cs' or Ga') SIMS with laser SNMS for ultrashallow depth-profiling. Electrochemically-formed 15 and 30nm Ta205 layers on a Ta substrate and 2nm native oxide layers were examined. Wittmaack (96/1600) uGed the ATOMIKA 4000 in small area profiling for on-chip structure analysis with 0,+ and Cs+ primary ion beams of 25 -30 pm diameter and raster sizes of 140-160 pm. Decay length for Ge in silicon were determined using 1.5 keV and 12 keV primary ions on an Si/Sil-.Ge superlattice with a 27 nm period and a 3 nm SiGe layer. For the determination of C in CiaAs a lower background was observed by monitoring AsC - second- aries rather than C- although a 71Ga160- interference was noted.Small area SIMS was shown to be a valuable approach to the 'vacuum-sensitive' determination of semiconductor impurities such as C and 0 by reducing both residual gas adsorption and cross-contamination. Good beam qua1 tty with neutral beam suppression was required but this did allow high dynamic range (- lo6) measurement. The theoretical limitations on depth resolution have been investigated by Kocanda et al. (96/1514) who tested the modified theory of Zalm and Vriezema which described depth resolution in SIMS in terms of the decay length. Decay lengths were determined at SiO,/Si interfaces for the "SiO signal using Ar' primary ions. Results were compared with the sputtering of Si using reactive 02+ primary ions.Good agree- ment was observed with theory except at glancing angles of incidence. Depth resolution in SIMS is highly dependent upon exper- imental conditions and there is therefore a need for well- defined reference standards. Kajiwara and Shimizu (96/1667) reported on the results of a Japanese round-robin study involving 7 participants. As part of a working group on depth- profiling that contributes to the Committee (TCO1) on Surface and Chemical Analysis of the International Organization for Standardization (ISO) the authors have used AIAslGaAs super- lattices as depth-projiling reference materials for SIMS and the related techniques AES and XPS. The depth and abruptness of the superlattice structures were confirmed by transmission electron microscopy (TEM).SIMS depth resolution was found to show a strong dependence on the nature of the reactive primary-ion used. At shallow depths high depth resolution was reported and this was related to the absence of ion-beam- induced surface ripples observed in their samples. Resolution was found not to degrade with depth in the top 100nm of the sample. A number of multivariate statistical techniques have been applied to image analysis and signal enhancement in SIMS. Latkoczy et al. (96/1692) have applied multivariate image analysis techniques to classify SIMS images and to identify chemical phases within solder joints. Splinter (96/1755) used a multivariate statistical method based on factor analysis to determine from Zr- images the nature of bonding in Zr0,-Zr and ZrN.,-Zr structures the SIMS data were confirmed by Auger depth profiles. Hutter and Grasserbaer (96/C198) have used neural networks to detect distinct chemical phases in SIMS images a maximum entropy algorithm to enhance spatial resolution and wavelet filtering to reduce noise in scanning SIMS images.6.6. Applications SIMS has seen significant application to biological analyses. Goldsmith (96/1553) for example applied the technique to the study of nutrients. Pariot et al. (96/1662) provided an introduction to the basic theory of SIMS and its application to the study of plants. Labelling experiments in the investi- gation of nitrogen metabolism were discussed as well as the study of the role of cell-wall calcium in growth.The role of sodium in the differentiation of secondary cells ionic patterns observed in seeds and the potential for future work were all addressed. Chandra and Morrison (96/1604) have studied Ca2' K+ and Na' transport by imaging SIMS at individual cell level. Ion redistribution artefacts were discussed and the importance of careful sample preparation emphasised. Samples were cryogenically prepared by freeze fracture and freeze drying prior to direct SIMS analysis. The authors also used I3CI5N labelled amino acids and imaging of the distribution of the label using sputtered 13C15N- ions to study the distribution of borocaptates which could potentially be used for boron neutron capture therapy. Approaches to ion immobilization were compared for example precipitation of Ca2' as the oxalate but only cryogenic sample preparation gave satisfac- tory results.The authors also discussed the use of ion ratios as a diagnostic for cell damage and cell death. Morrison et al. (96/1744) also reviewed biological applications of SIMS par- ticularly in the study of Ca2+ which is physiologically very important but is present at low concentrations and of B in the study of boron neutron capture therapy (BNCT) drugs. Larras-Regard (95/C43 16) discussed the use of ion-probe SIMS for Se imaging in biological samples especially in kidney sections. Structures within each section were identified from CN- P- and S- images. Sample preparation techniques Journal of Analytical Atomic Spectrometry October 1996 Vol. 11 377 Rincluded freeze-fixation freeze substitution and embedding in Epon.Gojon et al. (96/1541) reported the use of CN- ions to image the relative distributions of 14N and 15N in soybean samples. Homogeneously doped samples which could be ana- lysed by bulk analytical techniques were used to verify the SIMS data. Background concentrations of 12C15N- were observable by the technique. The authors suggested that SIMS was the only technique capable of such a measurement. Chassard-Bouchard et al. (96/1526) recorded Cr ion images from tissue sections taken from crabs that had been exposed to CrC1,. In some instances a correlation was observed between the Cr and the P distributions. The work demonstrated that the crabs had a low bioaccumulation capability that Cr was largely present in the exoskeleton and that because of moult- ing they did not make good bio-indicators for Cr3+.A related application of environmental relevance was the use by Jeffree et al. (96/1564) to determine Mn uptake in the shell of the freshwater unionid bivalve Hyridella depressa. The molluscs were exposed to 20 mg I-' of Mn for 2 or 6 d. Manganese was observed in the incremental nacre microlamin- ations. The Mn signal was normalized against the Ca signal and showed a phase lag >2-6 d for the shell to reach equilibrium with the water. Arkowa and Imaizami (96/1697) have investigated the source of sulfur in biological samples by 32S 34S isotope ratio measurements. Samples were chemically processed to give a Ag,S film for analysis and determination of 634S values. The ion microprobe has also seen developments and appli- cations to geological studies. Belshaw et al.(96/1595) have used an Isolab 120 ion probe to determine "Be 9Be isotope ratios in environmental materials. The measurement was difficult because the high ionization potential of Be precluded use of surface ionization there was interference from the 9BeH+ ion and a large dynamic range was required (10-7-10-11). At a resolving power of 1400 the 9BeH+ interference could be resolved from the "Be signal yet flat- topped peaks could be maintained. By sputtering the sample from a filament at 1000°C 9BeH+ could be suppressed by a factor of lo4. No CRM was available certified for the "Be 9Be ratio but analysis of NIST SRM-951 demonstrated a 4% deviation from the certified "Be "Be ratio.This was ascribed to instrumental mass discrimination. An over-all ionization efficiency of lo- was reported. Using the ion microprobe mode with a Cameca 4F instrument the measurement of 34S:32S isotope ratios in mineral grains has been reported (96/1605). In the imaging mode dynamic range and sensitivity problems were reported due to the low 34S signal being spread between pixels. The authors also noted the unreliability of quantitation using RSFs when analyte concentration increased to the point that it significantly altered the matrix chemistry. Guo et al. (96/1560) investigated the partitioning of Th isotopes between sea-water and particulate phases. They were able to estimate a residence time for Th in the water column of 5 years. Berry et al.(96/1680) examined the adsorption of Pu and U on to granite diorite and dolerite surfaces from solution noting significantly more U adsorption than Pu adsorption. Didenko (96/1735) reported the measurement of Ag isotope ratios in gold ores which were found to be a useful indicator of ore formation temperature. Kyser (95/4619) reviewed the SIMS measurement of C H N 0 and S isotope ratios in rocks and minerals. Lateral resolutions of < 10 pm were poss- ible but at the expense of measurement precision. The use of laser heating to de-gas samples was also discussed with empha- sis on the inherent problems of fractionation and differential laser power absorption within the sample. Applications to single particle analysis were described by Stowe et al. (96/1695) who examined the surfaces of 20-100 pm particles by spot-probing or rastering microprobe SIMS and reported sub-monolayer depth resolution.Stephan et al. (95/3714) examined interplanetary dust particles collected in the stratosphere by LMIS-TOF-SIMS. RSFs were determined for Al C Ca Co Cr Fe K Mg Mn Na Ni 0 Si Ti V and Zn in homogeneous glass standards. The 10 pm diameter dust particles were embedded in epoxy and sectioned prior to analysis. Enrichment of the particles in S and halogens sug- gested contamination by atmospheric aerosols. Ooishi (96/1785) described in a patent the analysis of dust samples by dissolution and subsequent drying on a conductive plate. Obviously spatial resolution was lost but presumably detection limits could be improved by using many particles and perhaps using chemical separation techniques.The method did not at first sight appear particularly novel. NoveI applications of SIMS have included a study by Hirano et al. (96/353) of the ashing process in graphite furnace AAS. The study focused on the vaporization of In and the influence of Ag Au Cu and Pd as modifiers. Chabala et al. (96/1645) have applied SIMS to the study of photographic gelatins and their interaction with embedded silver halide crystals. They achieved spatial resolutions of < 100 nm and studied the effect of pH on gelatin structure. The SIMS results were discussed in the context of other experimental findings. Stevie et al. (96/1751) reported the use of SIMS to determine contamination sources within ion implantation facilities.Delmore et al. (95/3558) used SIMS to investigate the surface ionization process. Ion sources were examined by SIMS to probe the surface chemistry in conjunction with the use of a purpose- built instrument that projected an ion image from a filament on to a fluorescent plate. The imaging instrument did not incorporate a mass analyser. The Cs+ ions from a zeolite support and Re04- ions from a ceramic source were imaged. Mass spectrometry using a different instrument showed that these were the dominant ions from the filaments used. The technique demonstrated that ionization occurred at the surface of the zeolite support for Cs' and not at the zeolite/Re filament interface. Cracks in the surface coating were seen as bright (i.e. high ion yield). This was interpreted as being due to the higher specific surface area within a crack.SIMS measurements were used to identify features that had been observed on the filaments by the imaging technique. The authors noted that voltage gradients of as little as 0.5 V across the filament could distort the ion focus and suggested the use of indirect heating. They also suggested that less expensive materials including stainless steel could be used to support the zeolite matrix. Corrosion processes have been investigated by Bishop (95/3722) and by Tapping (96/1616) the latter studied the corrosion of zirconium in CANDU reactor pressure tubes and the reaction and diffusional behaviour of H2 and 0 with single crystals of zirconium. 7. SPUTTERED NEUTRAL MASS SPECTROMETRY (SNMS) In a review of developments in SNMS Oeschner (96/1608) emphasised the growing importance of SNMS as a competitor to SIMS.He reported work using the electron gas SNMS technique which in high-frequency mode can be used for the analysis of electrically insulating samples. At frequencies greater than lo5 Hz sample voltage variations due to charging were negligible and did not affect depth resolution. As an example of the technique's capability a depth profile through a W-Si multilayer with a 3.6nm period was shown. Sputter- induced changes in the 70Ge 76Ge signal were reported with the lighter isotope being sputtered at a 5.5% higher rate until equilibrium was reached. Applications of SNMS to optical coatings analysis were reviewed by Weissbrodt et a/. (96/1729) and Kunz et al.(95/4142) reviewed the use of single photon ionization TOF-MS for semiconductor applications. 378R Journal of Analytical Atomic Spectrometry October 1996 Vol. 11Further use of the highfrequency electron gas SNMS method was discussed by Bieck et al. (96/C185) who used a square wave ( lo6 Hz) mode of operation that allowed short electron pulses to reach the sample surface thereby eliminating simple charging. The instrument incorporated a Ga liquid met dl ion gun (LMIG) and allowed microprobe operation with 1 pm spatial resolution. Koch et al. (95/4119) described the of a high frequency sputtering technique for the analysis 01 non- conducting samples especially environmentally important oxide dusts. The compromise between high spatial resolution (i.e very small sample volumes) and detection limit is beconiing a fundamental limitation in some of the most sensitive inicro- probe techniques.Berthold and Wucher (96/1754) discussed the relationship between imaging time and sensitivity in laser- SNMS sputtering with a Ga LMIG. They were able to measure down to 0.1 at.% concentrations at a spatial resolution of 1 pm and a measurement time of a few minutes. The effects of ion-beam-induced surface topography primary ion tluctu- ations and drift were all addressed. SNMS and SIMS allow complementary studies of spiittered neutrals and ions yielding information pertinent to matrix effects in both techniques. Kudryartsev et al. (95/3715) investi- gated the energy dependence of monatomic and diatomic ion yields from 111-IV semiconductors by SNMS with Ar' primary ion bombardment.Bieck et al. (96/1708) have examined Cu and Mo surfaces by electron gas SNMS sputtering wilh Ar' primaries between 40 and 440 eV. Lighter isotopes were found to be preferentially ejected with higher kinetic energies especi- ally at low primary ion energies. Isotopic discriminatlons of several tens of per cent were observed. The difficult problem of atmospheric aerosol analy yis has been tackled by the SNMS technique. Schuricht (90/1799) reported depth profiles for Al K Na and Si within individual particles. Pure salt and oxide standards were used for quantita- tion although the aerosol sample matrix was more cclmplex. Detection limits in the range 35-350 pg g- were reported. Cluster ions were used in characterization of the chemistry of regions within each particle.In the outer layers of particles with carbonaceous cores N was found to be present as (NH,),SO,. The hydrophobic soot cores were rendered hydro- philic by this ( NH,),S04 coating. A knowledge of such particle structures has important consequences for the determination of atmospheric residence times and reactivity. 8. STABLE ISOTOPE RATIO MASS SPECTROMETRY (SIRMS) 8.1. Reviews The only review of note to report since the last Update was that of Barrie et al. (96/1714) on high-throughput techniques. Continuous flow (CF) analysis and GC analysis of gases using packed columns were well covered with good detail of historical development instrumentation sample preparation instrument operation and performance and typical applications.The coverage of capillary column GC systems now well established and widely-used was more limited in detail. A special issue of Organic Geochemistry (Vol. 21 No. 6/7 1994) contained a large number of papers on compound-specijic isotope analysis in biogeochemistry and petroleum research. Although most were applications papers together they gave a good insight into the strong development and wide application of the GC-combustion-SIRMS technique. SIRMS was one of several analytical techniques included in the excellent review with 338 references by Robards and Antolovich (95/3092) on methods for assessing the authenticity of orange juice. Examples of isotope analysis were given for carbon (detection of added cane and corn sugars) hydrogen (detection of added beet sugars) and oxygen (distinction between fresh and reconstituted juices).The review on ozone MS by Mauersberger et al. (95/2589) covered all aspects from analysis using gas expansion systems combined with an MS flown on board balloons through to interpretation of data. A variable ( lo-> 40%) enrichment of "O larger than statistical estimates and a smaller enrichment of have been demonstrated. No satisfactory theoretical explanation has been proposed to explain the large ozone isotope anomaly. 8.2. Off-line Techniques 8.2.1. Instrumentation In a collaborative project between the Institute for Reference Materials and Measurements and a commercial manufacturer a new spectrometer of unprecedented capability in gas isotope abundance measurements has been constructed (de Bikvre et al.95/3598). The instrument a modified conventional spectrometer had five fixed Faraday cups three of which were set for SiF,' analysis and also had an ion counting mode. Interchangeable fixed slits allowed resolutions of 200 1400 3000 and 8000 to be selected. A range of resistors was incorporated for conversion of ion currents to voltages. The instrument had two inlet systems one for viscous flow (four ports) and one for molecular flow. The housing of the EI source was thermostatically controlled to 20.1 K and welded from the inside to reduce de-gassing effects. An improved vacuum system allowed the use of tungsten filaments. A new more flexible software was also developed. Most of the system- atic errors (mass fractionation tail correction or memory effect) were reduced to values so small that individual calibration was not required for some applications.The mass fractionation correction factor could be calculated theoretically to a precision of 5 x lo- leaving only a small experimental correction factor for residual systematic errors. Analysis of synthetic mixtures of enriched Si isotopes previously analysed by conventional methods gave relative uncertainties of < 3 x lo-' for the molar masses. 8.2.2. Sample preparation A method for the ultrasonic extraction of gases from water described by Holt et al. (95/4272) was designed to provide almost complete removal of dissolved gases as an on-line preparation system for isotopic analysis of N 0 and CO,. Absolute ratios of gases could be measured without corrections for differences in solubilities and the completeness of the extraction eliminated potential problems of isotopic fraction- ation.The method could be used to distinguish the 6I3C value and concentration of dissolved CO from those of dissolved (hydr0gen)carbonate. Dolnikowski (96/1715) has investigated use of a new pro- cedure for the preparation of 'H-enriched samples produced by the doubly-labelled water method. Aqueous samples were equilibrated with H gas in the presence of powdered platinum catalyst which increased the rate of deuterium exchange between H20 gas and H gas so that equilibration at 30°C was complete in an hour. The MS sample inlet system was encapsulated by a temperature-controlled air-bath to maintain 30.00 f 0.01 "C for reproducible equilibration.The catalyst was attached to Pyrex rods with silicone glue to facilitate removal and washing between runs. A sample throughput of 20 samples analysed in triplicate per day was possible. Results compared well with those obtained by the traditional zinc reduction method but further comparisons were considered necessary before the new method could be put into routine use. DemCny (95/4265) has identified isotopic fractionation of hydrogen which occurred by absorption by zinc during cooling following the reduction of water. Hydrogen gas bound to the Journal of Analytical Atomic Spectrometry October 1996 Vol. 11 379Rzinc and released by reheating was extremely rich in 2H relative to the gas from which it was absorbed. Differences in fraction- ation were observed for different methods of conversion so it was considered important to use the same reaction procedure and to maintain the same H2:Zn ratio for both samples and standards. It was proposed that the procedure could be modified by heating the zinc to the reaction temperature while the H2 gas was expanded into the MS.A US patent of Villa-Aleman (95/3586) described a simple method for the preparation of hydrogen for isotope analysis. The hydrogen was separated from other gases by using a filter selectively permeable to hydrogen only and then concentrated in a cold trap. The condensed hydrogen was released with pulsed laser energy as the cold finger was rotated. Highly anomalous 13C results can be obtained for C 0 2 in volcanic gases because of the non-reproducible removal of H,S also present. Nishio et al.(95/3530) used synthetic mixtures of gases to study the eflect of H N 2 and H2S on measured 613C and 6l80 values. The 613C values increased with increasing H2S:C0 and H,:CO ratios but were independent of the N,:CO ratio. The 6l80 values were not affected by the presence of the other gases. The purification of C02 was improved by incorporation of a trap containing CuC1 solution to remove H2S. A detailed preparation procedure has been presented by Bird et al. (95/2438) for isotope analysis of soil carbon either organic or occluded by iron nodules. The crushed iron nodule samples (5-10 g) were treated with cold 1 mol I-' HCl (to remove carbonates some amorphous minerals and labile organic compounds) boiling 6 mol 1-1 HC1 (to remove iron oxides and some minerals) 5 mol 1-' NaOH (to remove clay minerals and some alkali-soluble organic matter) and concen- trated HF-HCl(2 1) (to remove all but resistant minerals and refractory carbon compounds).The residues were prepared for MS analysis by combustion with excess CuO and silver wire at 900 "C in evacuated and sealed silica tubes. Organic carbon contents were reproducible to within _+2% and 613C values to within +0.2%0. The carbon isotope composition of chemi- cally resistant carbon in the nodules was the same as that in the surrounding soil so the 6I3C values of organic matter occluded by the iron nodules could be related to the vegetation present at the time of formation of the nodules. Preparation procedures for isotope analysis must be designed to avoid fractionation effects. A method for the isolation of L-ascorbic acid from fruit juices (Gensler et al.96/1626) consisted of reduction of L-dehydroascorbic acid to L-ascorbic acid anion exchange clean up and LC separation on a reversed-phase column. Although the recovery of spiked samples was only 64% the df3C values changed no more than 0.2%0. Concentrations of <20% adulterant in juice could be identified by using this procedure. Both nitrogen and oxygen isotope ratios of N,O could be measured (Inoue and Mook 95/2437) with just slight adjust- ment of the instrument set up for CO analysis. Measurements of the true 615N and 6l80 values were made by two methods. In the first N 2 0 was converted to N2 and CuO by heating over Cu at 650 "C.The CuO was then reduced by H at 400 "C and the resultant water equilibrated with water at 25°C. In the second method N,O was converted to N2 and C 0 2 by reaction with graphite powder on a platinum catalyst in a stainless steel tube at 600°C. The laser-probe method for the isotopic analysis of small samples gives high precision for oxygen isotope analysis. Oxygen can be liberated from laser-heated silicates by fluorin- ating with reagents such as ClF and BrF but the formation of F2 interferes with the isotope measurement. After finding losses of O2 when using a mercury trap (which had implications in the use of mercury diffusion pumps) Akagi et al. (96/1579) found the stainless steel wool trap to be effective in removing F2 generated during Nd YAG laser JEuorination of minerals and therefore in separating 0 from F,. Although a CO laser would have been a more effective source of energy for the reaction the Nd:YAG laser was chosen because it allowed a much simpler construction of the sample chamber and view port.The trap affected neither yield nor the 0 isotope ratio and the precision was better than 0.3%0 for all minerals investigated. A mass fractionation problem was however detected with the Nd YAG laser method of fluorination giving data some 0-2%0 lighter than by conventional methods of fluorination. This problem was associated with the laser fluor- ination reaction and not with the purification procedure. It was proposed that the combination of a C 0 2 laser and a stainless steel wool trap would be a more promising approach than that used.A new method for the isotope analysis of sulfur (Valkiers et al. 95/2290) was based on the ultra-high precision analysis of gaseous juorides. Sulfur hexachloride was formed by the reaction (350"C 1 x mbar 4 h) of silver sulfide with bromine pentafluoride ( 8 x low3 mmol 20-fold excess) and trapped for subsequent analysis. Measurement of the most abundant SF,' ions gave the best analytical precision (2 x lo- on the 33S 32S and 34S 32S ratios). Sources of com- mercial SF6 gas could be differentiated from each other even though in some cases the differences in isotopic composition were very small. Valkiers and de Bievre (95/3576) have used a similar method for determining isotopic abundance of boron and carbon.Boron samples were prepared by producing BF gas either by heating B203 with H2S04 and CaF or by the decomposition of KBF,. Carbon samples were prepared by conversion of CO to BaCO calcination of BaCO and conversion of BaCO to CF gas. Precision of measurement was about 0.004% for both the 13CF3f:'2CF3+ and 1°BF2+ I1BF2+ ratios. 8.2.3. Analytical methodologies Researchers from three leading isotope laboratories (Geel Los Alamos and Seibersdorf ) have correctly drawn attention to the problem of luck of transparency in isotope MS software (96/1620). This lack of transparency does not allow operators to track and troubleshoot obscure or poor programming in the data collection process. The mathematical treatment of data is not always accessible and the parameters used are not archived with the data.The authors proposed a common raw data file which could be used by all operators as a basis for data exchange. The guiding principle was to produce a file which contained all primary measurement information at the time of measurement. Data should not have been altered by subsequent manipulations or statistical rejection of individual data points. These operations were not to be part of the instrument operating software. The proposed file consisted of three parts a descriptive block (filenames date etc.) a measure- ment parameter block (details of measurement protocols) and a data block containing both instrument condition data and actual ion current intensities. Use of such a data file would allow the analyst to perform a proper data reduction and the related uncertainty calculation.It would also allow possible sources of error to be identified. New commercial gas standards produced gravimetrically to a wide range of isotopic compositions have been shown (96/1576) to improve the calibration of gas isotope analysis. A high level of reproducibility and stability of isotopic composi- tion in the production process was achieved. Tanaka et al. (96/1598) have developed a procedure for the measurement of both nitrogen and oxygen isotope ratios in N 2 0 following direct injection into the MS and thereby avoided problems associated with extensive chemistry on small sub- micromolar quantities of samples. Full details were given of 380 R Journal of Analytical Atomic Spectrometry October 1996,. Vol.11the theoretical basis of the procedure which is based on correction for contaminant C 0 2 using the m/z 12 14 and 12:44 ratios. Production of NO2 in the ion source which could be corrected by measuring the m/z 46:44 ratio at different ion source pressures to establish an NO2 slope correction factor could be virtually eliminated by using a high extraction plate voltage and optimizing the settings of electron energy trap voltage and emission current. The internal pre- cision after three years experience with the method was f0.01%0 for nitrogen and +0.03%0 for oxygen. Analysis of a standard gas was accurate to within 0.1%0 of the expected value for both nitrogen and oxygen. An analytical system for the simultaneous determinai ion of nitrogen helium and argon contents and 40Ar 36Ar and 3He 4He ratios in rocks by static MS has been described in detail by Marty et al.(95/3543). Argon is a sensitive tracer for atmos- pheric contamination while helium is a good tracer of Iiiantle volatile geodynamics. Gases were extracted either by steg-wise heating in molybdenum crucibles or by vacuum crushing. A series of charcoal traps cold traps titanium sponge getters and CuO furnaces separated and purified the gases prior to analysis by either a quadrupole or a sector MS whicll were simultaneously connected to the preparation line. Nil rogen purification and atmospheric contamination could be moni- tored by simultaneous measurement of ion intensities *,it m/z 12 14 28 29 and 30 and of the ,'Ar 36Ar ratio. The system was suitable for low levels of gases and for the analysis of samples with low volatile content.Yamamoto et al. (96/1650) have designed a procedure for the measurement of argon isotope ratios using a general- purpose double-focusing MS with high detection sensitivity and precise milli-mass resolution. Argon gas was introduced with helium carrier through a gas inlet port from a glass sample bulb. As the argon gas pressure reduced the ion intensity decreased thereby introducing an error into the peak scanning procedure. The data acquisition and mathematical treatment designed to overcome this inherent error in the system assumed that reduction in intensity was an exponential function of time and that all argon isotopes exhibited the same rate of reduction. Although it was claimed that the procedure was satisfactory for its intended application (the anal! sis of gases from a thermal diffusion column) errors were obherved in the analysis of natural-abundance argon.This was attrr buted to incorrect calibration of the chart recorder used. 8.3. GC-Combustion-SIRMS 8.3.1. Instrumentation Following the initial report in last year's Update on the coupling in parallel of both ion trap MS and gas isotope ,MS to GC Meier-Augenstein (95/3562) has reported on aspects of analytical performance. The system exploited the faci that commercial GC-combustion-SIRMS instruments have a backflush device one outlet of which is permanently open and could be connected to the ion trap MS instrument. Part of the device was a T-piece. This was replaced initially with a commer- cial cross piece but testing of the system highlighted poor chromatographic performance at temperature gradieri ts of >2" min-'.Owing to drastic peak broadening none of the test compounds could be detected by the isotope hlS. A custom-built lightweight cross piece replaced the original and in combination with a home-made open-split resulted in virtually no loss of chromatographic performance. No isotopic fractionation was observed for the new system which gave both isotopic composition and structural information simul- taneously for any compound eluted in a single GC analysis. The design construction and durability of individual compo- nents of the combustion inteflace have been investigated by Merritt et al. (96/1025). Factors affecting the extent of cornbus- tion and efficiency of water removal were examined using two instruments one with a conventional 3 kV ion source and the other with a high intensity 10 kV source.Organic carbon in GC peaks 15 s wide and containing up to 30 nmol of carbon was converted to C 0 2 in tubular combustion reactors (200 x 0.5 mm) packed with CuO or NiO. For all compounds tested except CH equivalent results were obtained for CuO at 850°C NiO plus auxiliary O2 at 1050°C and NiO at 1150 "C. The NiO-based systems were preferred for the analysis of CH,. Good performance was achieved with addition of O2 to the gas stream in the reactor at a level low enough not to threaten the integrity of the filament but high enough to aid oxidation and to re-charge the metal oxide reservoir. Water was removed from the reaction products by differential per- meation through a tubular Nafion membrane.The combustion interface added no additional uncertainty. 8.3.2. Sample preparation The efects of storage on isotopic fractionation have been investigated by Bjorary et al. (95/2423) for individual com- pounds in the C4-CI5 fraction of oils and condensates. Analysis at regular intervals during prolonged storage at elevated temperatures showed no significant affect on the carbon iso- topic composition. Total dissolved inorganic carbon (CC02) in freshwaters was determined (Miyajima et al. 96/1674) by equilibration with He gas (5 ml) and GC-combustion-SIRMS analysis of the headspace gas. Although combustion was not required the furnace was operated at 820 "C to stabilize analytical con- ditions and reduce retention times within the interface. The headspace method had the advantage of being simpler than other methods (for example purge-and-trap) with a reduction in the labour and time required but had the drawback of being based on dissolution equilibrium which could be dependent on the nature of the sample.Only single samples could be taken because the equilibrium was disturbed in doing so. Relatively large errors (& 0.1%0) inherent to the headspace method due partly to the possible presence of H 2 0 and N20 may limit its application. A micro-scale sealed pyrolysis vessel was coupled to a GC injection system by Mycke et al. (95/2422) to obtain insights into the carbon isotopic composition of pyrolytically generated hydrocarbons. Organic material (2-3 mg) was pyrolysed (350 "C 72 h) in sealed glass containers filled with glass beads to reduce the dead volume and the pyrolysates released by crushing the container in the injector were collected at a cold trap.The oxidation catalyst in the combustion reactor was replaced with platinized CuO at 900°C. Two different GC columns (PoraPLOT Q for gases and SE 54 for liquids) allowed determination of the 613C values in C1-C30 in-alkanes in pyrolysates. Isotopic fractionation during sample preparation must be shown to be negligible for any stable-isotope procedure. In a procedure developed by O'Malley et al. (95/2420) for the preparation of PAHs air-dried sediments (15 g) were mixed with Na2S04 (2 g) and extracted with dichloromethane (140ml) in a Soxhlet apparatus for 24 h.The PAHs were subsequently isolated by chromatography on Sephadex and silica columns both of which were topped with activated copper powder (1.5 g) to remove elemental sulfur. The extrac- tion and purification did not alter the 613C values of PAH standards significantly even with in some cases recoveries of < 50%. The precision of analysis was 0.2-0.3%0 for standard compounds but could be up to l.1%0 for poorly separated compounds. The potential of this method for source apportion- ment was highlighted by the distinctly different trend for the isotopic signatures of PAHs from fire soots car soots and crankcase oils. Jownal of Analytical Atomic Spectrometry October 1996 Vol. 1 1 381 R8.3.3. Analytical methodologies The performance of GC-Combustion-SIRMS can be compro- mised by incomplete separation of peaks and difficulties in defining the start and end of peaks.Asymmetric peaks are commonly observed because of the numerous column connec- tions. Goodman and Brenna (95/2413) conducted a systematic study comparing curvejitting with the conventional summation integration algorithm for well resolved small sample injections of fatty acid methyl ester mixtures. The software provided with the instrument was used to process data by the summation method with a rolling five-point linear least squares fit applied to the chromatogram. The commercial Peakfit program was used for curve fitting with the exponentially-modified Gaussian function which reproduced the line shapes and worked well for low signal levels. At all levels curve-fitting produced satisfactory precision and accuracy and was almost immune to the choice of integration time.It was the only method that produced useful isotope ratios at the lowest concentration levels (5 pmol). The conventional summation method became unusable below 30 pmol. Merritt and co-workers (95/2338) have also addressed the issue of acquisition and processing of data. The report described data-processing which included the definition of the start and end of chromatographic peaks and quantitation of background levels allowance for effects of chromatographic separation of isotopically substituted species integration of signals related to specific masses correction for effects of mass discrimination recognition of drifts in MS performance and calculation of isotopic 6 values.The performance of these methods was adequate for determination of isotope ratios with an uncer- tainty of one part in lo5. Merritt et al. (95/2339) have also investigated proceduresfor the introduction of standards for the analysis of n-alkanes. Five different techniques were compared (i) organic compound standards were co-injected with the analytes and carried through chromatography and combustion with them; (ii) CO was supplied from a conventional inlet and mixed with the analyte in the ion source; (iii) CO was supplied from an auxiliary mixing volume and transmitted to the source without interruption of the analyte stream; and (iv) and (v) two methods were used to divert the analyte stream and place the standards on a near-zero background.All methods provided accurate results. Methods not involving interruption gave the best performance (0.06%" for 250pmol C as CO,) but care was required. The co-injection of standards lacked flexibility with a need to maintain a variety of standards to avoid problems of co-elution. Overlap between sample components and stan- dards could cause serious systematic errors which could only be avoided by use of diversion. Techniques involving diversion of the analyte stream were immune to interference from co-eluting sample components and gave high precision Techniques have been developed by Merritt and colleagues (95/2572) for the on-line simultaneous determination of con- centration and carbon isotopic composition of dissolved methane in sea-water and porewater. The method used either headspace equilibration suitable for samples of limited volume (for example porewaters of fine grained sediments) and requiring < 15 min per sample or gas sparging with He more suited to low concentrations in larger volumes and requiring at least 30min per sample.The gases were subsequently dried cry- ofocused separated by capillary column GC on PoraPLOT-Q and combusted at 1000 or 1150°C. The detection limit for 10ml samples was 10nmol 1-' with an isotopic standard deviation of 0.5%0. Analytical blanks associated with the method were negligible. Merritt et al. (95/3614) have also presented methods for the analysis of atmospheric methane. Less than 15 min were (0.1-0.2%0). required for the determination of 613C with a precision of 0.2%" (1%0 single measurement) in 5 ml samples of air contain- ing methane at natural levels (1.7 ppm).Issues examined were methods for preparing samples the withdrawal of samples from flasks injection of samples preconcentration and removal of interferents. Preconcentration performed on a preparative GC column for separation of CH from Ar N and 02 was not necessary for samples containing 100 ppm or more of CH,. Analysis of standards demonstrated that systematic errors were absent and that 6 values were not dependent on sample size. Uncertainties of <0.3%0 could be expected for the analysis of 3-5 ml samples of air containing 1.5 ppm of methane. The analytical performance for the 613C analyses of n- alkanes has been determined by Bake1 et al.(95/2436). Both accuracy and precision for the analysis of standard solutions was <0.5%0. Silica gel gravity LC used for compound class separation introduced no significant isotopic fractionation. Analyses of spiked samples with natural matrix showed that for those compounds (13 of the 21 n-alkanes measured) which gave peaks of adequate size and without co-elution of other components the background could be subtracted accurately by the standard software to give results within 0.05%" of expected. Differences of more than 0.5%" in the 613C values were therefore considered significant but this would not apply to those n-alkanes which co-eluted with other components. Mosandl and colleagues have developed an interesting method using internal standardsfor authenticity control of balm oil (95/3574) and peppermint oil (96/1638).Isotopic analysis is of growing importance for authenticity control in particular of high-value flavour and fragrance compounds but appli- cation of the technique is limited because most cultivated plants belong to the group of C,-compounds and have 613C values close to those of synthetic substances. The method in which fingerprints were constructed by plotting the 613C values of several main components relative to a chosen internal standard identified isotopic discrimination dependent on enzy- matic reactions during the secondary biogenetic pathways rather than fixation during photosynthesis. Criteria set for choosing the internal standard included sufficient concen- tration good isotopic analysis and a biogenetic relationship to the other compounds of interest.It should also be of little commercial value so that it is unlikely to be an adulterant itself. The fraudulent addition of menthyl acetate of an origin other than peppermint oil could be detected unambiguously using this approach. The precision accuracy and linearity of measurement of three commercial GC-combustion-SIRMS instruments have been evaluated systematically by Wong et al. (96/1736). At natural abundance the 613C values of fatty acids were reproducible to within 0.34%" and accurate to -0.38+0.40%0 (mean difference & standard deviation). At enrichment levels of 613C (23-924%") the 613C values were reproducible to within 1.48%" and accurate to - 1.1 1 f 3.16%".All three instruments were linear for 613C values from -30 to 924%". One instrument not identified directly consistently gave more precise and accurate data than the other two. A significant memory effect was found in one instrument. In general the procedure gave precise accurate and linear 613C measurements for as little as pico- and nanogram quantities of sample. Brand et al. (95/2340) have further reported the development of compound-specific isotope analysis of nitrogen-containing compounds using a combination of GC with elemental analyser and MS. Nitrogen was converted quantitatively to N in a post-GC interface which incorporated a micro-oxidation reac- tor for oxidation of organic compounds eluted from the GC a reduction reactor for conversion of NO to N2 and CO removal. Precise and accurate measurements of I5N 14N ratios (+0.4%0) at natural abundance were made on ng quantities of a variety of nitrogen-containing compounds. 382 R Journal of Analytical Atomic Spectrometry October 1996 Vol.11The current status of nitrogen isotope analyses ofamino acids has been reported by Merritt and Hayes (95/2287) and con- sideration given to optimization of the combustion system. The system used was essentially that used for carbon isotope analyses with addition of a cryogenic CO trap between the water separator and open split. In comparison with the study of Brand et al. a reduction reactor was not considered necessary in this study. Amino acids as their N-aceryl n- propyl derivatives were separated on a capillary column (50 m x 0.32 mm) coated with 5% phenyl 95% methyl polysi- loxane and operated with temperature programming from 45 to 280°C at a rate of 3°C min-'.The combustion reactor consisted of an alumina tube (0.5 mm id.) packed either with CuO (operated at 85OOC) or NiO (operated at 1100"Ci. The CuO reactor gave results accurate within 0.35%0 for a sample size some 5000 times less than that required by conventional analysis. The NiO reactor had a higher sample requirement (2 nmol of each amino acid to generate at least 200 pmol of N per component) which could result in overloading of the GC column but good accuracy and precision could be achieved for derivatives of amino acids with high CO,:N ratios. Analytical precision was <0.1%0 for samples larger than 400 pmol < 0.5%0 for samples larger than 25 pmol.In compari- son with carbon isotope analysis the sample requirement was higher and the precision poorer as a result of the low abundance of N relative to C the relatively low natural abundance of 15N and the difficulty associated with quantitative production of N from organic matter. 8.4. Other Continuous Flow Techniques 8.4.1. Instrumentation A major obstacle to the accurate and precise measurement of hydrogen isotopic composition by continuous flow techniques is the interference caused by the 4He+ peak from the carrier gas. Two research groups have chosen quite different solutions to overcome this problem. Prosser and Scrimgeour (96,'149 1 ) took the instrumental route and designed a novel mass spec- trometer with high dispersion so that no interference occurred.The abundance sensitivity of the instrument at m/z 3 was < 1 x The chosen method of sample preparation (equili- bration of water samples with hydrogen gas over a platinum catalyst on alumina) had the disadvantage that it required larger samples (0.1-1 ml) in comparison with the reduction method (1-10 pl) and also introduced a very high fractionation effect. Fractionation was allowed for by equilibrating a refer- ence water under identical conditions to the sample. The procedure was fast (<2 min instrument time per sample) and accurate with a precision of +3.0%0 at natural abundance. The other solution that of using an alternative carrier gas in place of helium was found by Brenna and colleagues (96/1493) to have considerable problems.Two different instru- mental approaches using argon as carrier were taken. In the first water was reduced on-line in a nickel reduction furnace and residual water trapped to minimize memory effects. In the second hydrogen gas was admitted into the instrument through a heated (330 "C) palladium metal foil which acted as a filter to pass the hydrogen but to divert the carrier gas to waste. Argon carrier gas cannot be used routinely until a severe problem of damage to the ion optics caused by rapid sputtering is solved. The palladium filter was very sensitive to ion source pressure so peak intensities had to be matclied for accurate calibration. The quoted precisions of 6-100/11 were several orders of magnitude poorer than those achieved by the high-dispersion instrument.Replicate analysis of 0.4 p1 siimples could be achieved in 3 min. Luke and Schoeller (96/1496) have designed a novel im-line combustion system for dynamic 13C analysis of minute quantit- ies (500 ng) of nonvolatile organic compounds isolated off-line. The sample was loaded on to a tungsten filament sealed in a He-0 carrier gas stream (2-5 ml min-') and heated to combustion at a filament power of 120 W. Lower filament powers and carrier flow rates resulted in severe peak broaden- ing and poor performance. An observed memory effect could be avoided by replacing the filament envelope after each analysis. The accuracy was 1-2%0 for natural abundance and highly enriched samples. The precision limited by the combus- tion process was 1-2%0 at natural abundance and 4%0 at high 13C enrichments.Sample requirement was 100-fold lower than that of the conventional CF techniques. Brand et al. (96/1713) have coupled an elemental analyser to a desktop MS ilia a new design of computer-controlled open-split interface to allow determination of both 15N 13C and N C on u single sample. A limitation on combined analysis using a fixed split ratio would be the approximately 50 times more intense ion beam produced by CO than by Nz. The interface employed a switchable dilution ratio of 0-100 to achieve relatively constant ion intensities for both N and CO gas streams. The interface also allowed the introduction of reference samples for both gases. The authors claimed simul- taneous measurement of the two gases but in fact switching of either the magnetic field or acceleration voltage was employed.8.4.2. Sample preparation Robe et al. (95/2341) have developed a method for puriJication of 15N in inorganic nitrogen amino acids and soluble proteins in small volumes of plant extracts with <5 pg N required for analysis using a nitrogen analyser-MS combination. Soluble protein was extracted from the sap and filtered for analysis. The nitrate and amino acids were subsequently separated by ion exchange chromatography. 8.4.3. Analytical methodologies Small volumes (nmol range) of CO released by a biological microgenerator have been analysed by Lamrini et al. (96/1737) using reverse isotope dilution. Prior to incubation the reactor tubes were flushed with synthetic air containing 3% CO of controlled isotopic abundance which equilibrated with the released gas.A home-made automatic microinjector for gas species was used to transfer microsamples of gas mixtures (50 pl) from the headspace of the microreactor vessel to the GC-SIRMS analysis system. The detection of adulteration using continuous flow tech- niques is relatively rare because of the high precision required at natural abundance but applications are occasionally reported. Gioacchini et al. (96/1738) were able to distinguish between natural and synthetic taurine by determination of the 13C 12C ratio. Neutralized aqueous solutions of taurine (5 p1 containing 500pg of C) were transferred to Chromosorb ( 5 mg) acting as solid support and were analysed by a conventional elemental analyser-SIRMS combination.Saccharose was used as the reference standard. The coefficient of variation ( n = 6) in an intra-assay study was < 2% over a range of 100-500 pg of carbon injected. 9. THERMAL IONIZATION MASS SPECTROMETRY (TIMS) 9.1. Reviews Although there have been relatively few reviews of note in the period covered by this Update that of Crews et al. (95/2562) on the use of stable isotopes in nutrition research can be recommended very highly not just for the application but also for detailed descriptions of several MS techniques. The section on TIMS gave an excellent overview of the technique with explanations of the principles of ion formation mass analysis ion detection and measurement of isotope ratios. Emphasis Jmrnal of Analytical Atomic Spectrometry October 1996 Vol.11 383Rwas understandably placed on those elements of importance in nutritional research but much of the discussion was of wider interest. Recent developments in isotope analysis by TIMS in particu- lar for geological analysis have been covered in the review of Heumann et al. (96/1485). Although somewhat selective and concentrating mostly on negative ionization TIMS the review gave an insight into current trends by describing in some detail significant developments which included new instrumentation for enhanced abundance sensitivity trace element speciation (Cr) by isotope dilution MS the study of Re-0s systematics 1840s isotope variations in meteorites and the use of boron isotopes in environmental studies. The review by de Bievre on isotope dilution MS (95/2362) gave a clear description and explanation of the basic principles of the technique with particular attention given to practical considerations. The amount of detail included and the pro- gression from simple isotopic dilution of a single isotope through bi-isotopic elements to polyisotopic elements made this a particularly useful introduction for the beginner in this subject.Full consideration was given to requirements for analysis calibration assessment of uncertainty and limitations and the choice of optimal conditions. A review by Green (95/2604) on the application of TIMS in the nuclear industry described the author's experience in meas- uring actinide and fission product isotopes at fg to ng levels in nuclear fuels and environmental materials. This included the development of selective chromatography and microextraction techniques for the separation of isotopes of La Li Nd Pu Th and U.Although not intended as a review the paper by Aggarwal and Jain (95/3560) on the use of polyatomic ions for isotope analysis can be used as such. Although the paper contained little original work it brought together various aspects of the use of polyatomic ions and used simple applications taken from the literature to illustrate the principles of choosing the optimum conditions for analysis and the best isotope ratios to measure. 9.2. Ion Formation The silica gel technique is widely used in surface ionization but there is a general lack of understanding of the mechanisms by which this and similar methods enhance ion production. The fascinating and timely work of Huett et al.(96/1610) using model systems based on a Bi' ion emitter has gone some way to clarify these processes and to disprove some widely held concepts for example that ionization must occur at the filament surface. Ion emitters were shown to be molten and highly viscous glasses at ion emission temperatures and the ions originated from the surface of the molten glass. Reactivity with the molten glass rather than work function appeared to be the critical property of the filament material for enhanced ioniz- ation. Rhenium was a better filament material than tantalum for silica gel work because it reacted less with the molten glass and so did not inhibit the emission process. It was not possible to determine the ion formation process in the glasses but it was thought likely that more than one process was in operation.The use of bismuth borosilicate as a model for silica gel and the very high concentrations of measured elements should not lessen the valuable insights this study gave. The level of understanding of many surface ionization sources in regular use is poor and in many cases the regions from which ions are emitted have not been identified. Delmore et al. (95/3558) have described the use of direct imaging of the ion source during ion emission to elucidate the chemistry and physics of surface ionization. The images presented for two refractory emitters (a ceramic source producing perrhenate anions and a zeolite source producing caesium cations) sup- ported the hypothesis that ions originated directly from the surface of the matrix rather than from interstitial regions or the metal support.It was argued that the predominant ion emission process for the two ion emitters studied was the direct sublimation of preformed ions from the solid state to the gas state. 9.3. Instrumentation Instrumental developments required for the achievement of abundance sensitivities of < 1 in lo9 have been described in great detail by van Calsteren and Schwieters (96/1622). Two different instruments were fitted with a redesigned retarding potential quadrupole (RPQ) placed behind the axial position of the multicollectors. The RPQ acted as a very sensitive energy and direction filter lens. A static quadrupole which shaped the beam to a circular cross-section was followed by a funnel and tunnel deceleration lens assembly which rejected ions with incorrect energy or direction.The improved RPQ filter lens incorporated redesign of the most critical region of the ion optics and in comparison with the previous design gave a dramatic increase in transmission and improvement in stability. One of the instruments was equipped with a deflection unit after the RPQ to allow either a Faraday collector or a secondary electron multiplier (SEM) to be used in addition to the standard RPQ configuration with SEM. The Faraday cup allowed evaluation of the transmission stability of the deceler- ation lens independently of the effects introduced by the SEM. The paper also discussed factors which affect abundance sensitivity other instrumental modifications made to improve performance and sources of error.The long term reproduc- ibility of <0.7% for the 234U 238U ratio in a CRM and 1.3% for the low (6.1 x 230Th:232Th ratio was sufficient for the determination of the extreme isotope ratios required for Th and U disequilibrium studies. Stirling et al. (96/1561) replaced the usual high-value (10'' a) resistor in the detectors with a 20 pF air-core capacitor in order to operate in the 'charge collection' mode. This fundamen- tally new technique allowed the measurement range to be extended to below A while preserving the advantages of Faraday cup arrays. With a stable ion beam the charge built up on the capacitor with time ( t ) in a linear fashion. The rate of voltage accumulation (dV/dt) was directly related to ion current so that once the background accumulated charge was removed from the peak signal the atomic ratio of any isotopic pair was directly equal to the ratio of their values of dV/dt.This technique allowed simultaneous measurement of the low level currents of 229Th 230Th and 232Th with high precision (0.25% for the 229Th:230Th ratio collected in one block over 1.5 min). The total procedural blank was 5 & 2 pg of 232Th for a filament load of 15 pg of 230Th. Richter et al. (95/2286) replaced five out of six Faraday cups on their instrument with ion-counting channeltrons in order to work with ion beams as low as A. The channeltrons consisted of a flat ceramic body with a small curved interior channel coated with a thin layer of lead oxide.A high negative voltage (2000 V) was applied to the entrance whilst the exit was earthed so that an ion entering the channeltron generated an avalanche of electrons. The resulting pulse (10 ns duration) was converted into a standard rectangular 600 mV pulse that was registered by counting electronics. Counting efficiencies close to 100% were achieved. Careful monitoring of the behaviour of the channeltrons was required to obtain reliable results. Several sources of spurious pulses were possible for example secondary electron avalanches and ion scattering. Channeltrons needed to be operated at high voltages to obtain flat top peaks but this reduced their lifetime. A decrease in efficiency was observed after a few hour's exposure to a moderate beam current in particular for new channeltrons so 384R Journal of Analytical Atomic Spectrometry October 1996 Vol.11they should only be operated for short periods of time or at low ion beam intensities. Calibration of individual channeltrons also presented problems but the uncertainty was generally c 1%. Precisions of better than 1% could be achieved for the analysis of very small samples for example interstellar &!rains in meteorites using a direct loading technique in which the grains were not dissolved prior to analysis. Freeman (95/3615) has taken out a patent on a new tjpe of surface ionization source which is claimed to have a higher ionization efficiency than the conventional triple filament source. The source incorporates a single evaporation filament and an independently heated ionization coil.The filamcnt is positioned close to one end of the coil so that a major fraction of the evaporated material enters the coil and has a high probability of ionization before escaping from the open end. A voltage gradient between the two ends of the coil helps to steer and accelerate ions towards the open end of the coil. 9.4. Sample Preparation Uranium in water samples was isolated (Efurd et al. 961 1619) using a procedure based on anion exchange chromatography. After elution from Bio-Rad AG MP-1 (50-100 mesh) macrop- orous resin in 8 mol 1-' HNO the uranium was cleaned on a column of the same resin with 0.1 mol 1-' H2S04 0.01 moll-' HF-12 moll-' HC1 and 12 moll-' HCl before elution in 1 moll-' HNO and 14 mol I-' HNO,.The columns were allowed to drain completely between each wash. Proccssing blanks were approximately 2-6ng of U. The uraniunl was electroplated on to rhenium filaments and overplated with platinum. The processing of 100 ml water samples resulted in filament loadings of 10-100 ng uranium. TIMS analyses opti- mized for 10 ng loadings unambiguously separated the uran- ium in pond waters into anthropogenic and naturally-occitrring components. The ultra-clean procedures required for the isotopic analysis ofpg quantities of lead isolated from Greenland and Ant arctic snow and ice as reported by Rosman and colleagues (95/.L259) highlighted the remarkable attention to detail necessary. I Jltra- clean collection storage and processing techniques gave total blanks of < 2 pg of lead.No sample preparation was used in order to avoid addition of higher blanks. Samples were 1t )aded on to filaments using the silica gel technique but with the addition of aluminium which enhanced ion emission some five fold. An ion beam current of 1 x lo-' was achieved for a typical loading of 100 pg. Interference by BaPO,' at m,z 204 was very small but isobaric interference of T1' was possible on the "'Pb added as a spike for IDMS. Precisions of 'ibout 0.2% were achieved for samples containing a few tens ofpg of lead. Problems associated with the conventional methods fG.jr the isolation of hafnium from rocks and zircons include unpredict- able losses of hafnium as fluoro-complexes inconsistent 1 If-Zr separation and difficult removal of Ti.An alternative mcthod developed by Barovic et al. (95/4269) involved three stages of ion exchange separations with H2S04 as eluent. The method produced consistent Ti- and Zr-free separations and was considered particularly suited for rocks with high Ti concen- trations and for zircons. Typical procedural blanks were negli- gible at < 400 pg. A method developed by Na et al. (95/4274) for the isolation of neodymium and strontium from the same sample solution was based on the combination of conventional cation exchange chromatography and HPLC. The initial step was sepal-ation of Sr and the REEs from a rock digest by elution from a cation exchange column using an HC1-HNO3 eluent. Individual REE components were separated by HPLC and quantified with a post-column reaction detector.Separated Nd and Sr fractions were further purified by elution from a cation exchange column using HCl as eluent. Analysis of a series of standard rocks gave precisions of f 0.004% for determination of the 143Nd 144Nd and 87Sr 86Sr ratios. The minute quantities of Rb and Sr inJIuid inclusions pose a considerable analytical challenge in comparison with conven- tional Rb-Sr isotopic studies of mineral grains. Pettke and Diamond (96/1249) synthesized fluid inclusions of known isotopic and elemental ratios in quartz in order to test two fluid extraction procedures for bulk quartz samples. Samples were either crushed in a mortar or decrepitated thermally and then leached. Determination of 87Sr 86Sr ratios was straightfor- ward by both methods but problems were encountered with measurement of the 87Rb 86Sr ratio.Leaching with water was only 93% efficient owing to surface adsorption of Sr but leaching with an La3'-doped acid solution achieved 99.7% recovery. Only crushing could be used to give correct values for 87Rb 86Sr ratios because thermal decrepitation gave repro- ducible but exclusively incorrect values. It was concluded that all published isotopic analyses of fluid inclusions obtained by thermal decrepitation could be in error. Veira and Yergey (96/1499) have tested 25mm membrane filters (both cation and Chelex ion exchange) for the extraction of calcium from water serum and urine samples. Calcium in test solutions was eluted with 6 rnol I-' HCI from cation exchange filters and with 1 mol 1-' HC1 from Chelex filters.In comparison with the alternative oxalate precipitation pro- cedure recoveries were in the range 20% (urine) to 98% (serum) for Chelex filters and 66% (urine) to 86% (water) for cation exchange filters. The method was easy and rapid and required 1 d for sample preparation in comparison with 2 d by the oxalate precipitation method. 9.5. Analytical Methodologies The recommended data transfer protocol for isotopic MS measurement data proposed by de Bievre and colleagues (96/1620) and covered in the SIRMS section of this Update was designed equally for application to the acquisition of TIMS data. The measurement of Pu and U isotope ratios using the total evaporation technique has been performed (Fiedler 96/1617) on both quadrupole and sector instruments.Tantalum was not acceptable as a filament material because isotope ratios dis- played bias as a result of the incomplete consumption of sample. The bias was much less for rhenium and tungsten filaments. The sample drying procedure and the method of attachment of the resin bead to the filament had no significant effect on the total evaporation. The use of peak jumping on a quadrupole instrument required modified procedures includ- ing a heating step in the middle of the scan to maintain the ion beam within a set range. The total evaporation method was susceptible to the presence of isobaric interferences and to insufficiently pure samples. Good analytical data could be obtained for resin beads containingas little as 1 ng of Pu or U. Jain and colleagues have published three papers (95/2319 95/2412 95/4645) on the simultaneous analysis of Pu and U.Many aspects of the study and much of the discussion were common to all three papers. Synthetic solutions containing typically 1 pg of Pu and 10 pg of U as nitrates were loaded on to a rhenium double-filament assembly. The U' and UO' ions appeared at a low evaporation filament current (0.2 A) and before the Pu' ions (at > 2 A) but the latter reached a maximum ion current some 5 to 10 times higher than that of U'. The stability of the UO' ion the intensity of which increased with increasing evaporation filament current was attributed to the dissociation of Pu oxides to provide excess oxygen. Optimized settings of the vaporization filament (for Pu) and ionization filament (for U) allowed simultaneous analysis of the two elements with a precision and accuracy of Journal of Analytical Atomic Spectrometry October 1996 Vol.11 385 R0.2%. The method used initially for the correction of isobaric interference of 238Pu on 238U based on 23sU:239Pu and (238Pu + 238U) 239Pu ratios proved to be unsuccessful whereas the more direct method based on the 239Pu intensity to correct for the presence of 238Pu resulted in much improved precision. A new procedure for the correction of fractionation in lead isotope analysis (Woodhead et al. 95/3098) was based on a double-spike technique in which two highly-enriched isotope spikes were added to samples in order to generate two non- radiogenic isotopes of fixed isotopic abundance. Samples were run in duplicate one without spike and one with spike (207Pb 204Pb = 8.714) added immediately before filament load- ing.The external precisions (two standard deviations) obtained over a four year period for the NBS SRM 981 were 0.004 0.005 and 0.013 for the '"Pb '04Pb '07Pb '04Pb and '08Pb 204Pb ratios respectively. The procedure improved pre- cisions by a factor of three over those obtained by conventional methods but sample throughput was effectively halved. The isotopic compositions of Dy Er Gd La Lu Sm and Yb in pure solutions of single elements not requiring sample preparation have been measured with precisions of 0.005% for most elements by Shima et al. (96/1531). The precisions for La and Lu analysis were poorer because no correction for fractionation was possible.The aiming current of 2 x lo-" A for 1 pg loadings was achieved for all elements and exceeded for La (6 x lo-'' A) and Lu ( 5 x lo-" A). Whereas Dy Er Lu Sm and Yb were loaded on the side filament of a triple rhenium assembly Gd was loaded on the side filament of a Ta-Re-Ta assembly. Lanthanum was loaded on a single rhe- nium filament with an oxygen leak in the source to produce Lao+ ions which were used for measurement. The lS6Gd ls8Gd and lsoSm isotopes in environmental samples are enriched by intensive natural neutron irradiation of '"Gd lS7Gd and I4'Sm respectively which possess extra- ordinarily large neutron capture cross-sections. Hidaka et al. (95/3525) used a static multicollector in two cycles to measure the gadolinium and samarium isotopic compositions in rock samples.Extensive cation-exchange procedures were used to isolate the REEs from samples and then to separate Gd and Sm. A 1 pg loading of Gd on the tantalum side filament of a Ta-Re-Ta filament assembly produced an ion current of 2 x lo-" A with a side filament current of 2.6-2.7 A and centre filament current of 4.5-4.6 A. It was necessary to maintain the source pressure at <5 x bar in order to keep the 1s8Gd'60+ ion intensity below 1 x lo-'' A. The correction for mass fractionation was based on the assumption that lssGd + lS6Gd would remain constant. A 500 ng loading of Sm on the side filament of a triple rhenium filament assembly produced a l5'Smf ion beam current of 2 x lo-" A with a side filament current of 2.2-2.4 A and centre filament current of 4.1-4.2 A.Precisions of 0.001% were achieved for most Gd and Sm isotope ratios in geological SRMs. The method could detect effects caused by a neutron flux of 1 . 3 ~ neutrons cm-' in environmental samples. The absolute isotopic composition of europium was determined by Chang et al. (95/2411) using pure solutions of europium nitrate containing highly-enriched isotopes of europium. The nitrate was prepared from europium oxide treated to remove anionic impurities. The analysis was calibrated by running mixtures of the pure solutions. Samples containing 5 pg of Eu were loaded on to double rhenium filaments which were operated at evaporation and ionization filament currents of 1.5 and 5.5 A respectively to produce ion currents of about lo-'' A.It was not possible to find evidence for isotopic fractionation in terrestrial europium with all '"Eu lS3Eu ratios measured in minerals and chemicals being within 0.0065% of the mean. Zhang and Zhao (95/3545) have developed a method for the isotopic analysis of samarium with the aim of achieving precise measurement of the isotopic abundance values and relative atomic mass. Samples of pure samarium nitrate (10 pg Sm) were loaded on to double rhenium filaments and a beam of 3-5 x lo-" A established with evaporation and ionization filament currents of 2 and 5 A respectively. Isotope ratios were measured by peak jumping between the pairs of ion beams. Mass fractionation was corrected by running filaments of a standard Eu sample under identical conditions. Analysis of six replicate loadings of the samarium sample gave pre- cisions of 0.11 to 0.56% for the different isotope ratios.Procedures for the isotopic analysis of cerium have been developed by two Chinese laboratories with the aim of recalcu- lating its relative atomic mass. Xiao et al. (95/2579) loaded pure solutions of Ce(NO,) CeCl and Ce2(S04) on to tantalum filaments previously coated with graphite ( 100 pg). This procedure enhanced Ce + ion emission significantly and avoided the use of CeO' ions which needed to be corrected for oxygen isotopic composition. After a 14'Ce+ ion beam of ( 1.5-2.0) x 10- '' A had been achieved data were only collected after disappearance of the 137Ba+ peak (about 1 h). No fractionation effect was observed during the usual period of data acquisition (150 min) for the substantial loadings of 20 pg of Ce.A 142Nd . * 14,Nd ratio of 2.2274 was assumed for correc- tion of the significant isobaric interference of 142Nd on '42Ce. Measurement precisions (n = 9) of 0.33 0.17 and 0.012% were achieved for measurement of the '36Ce* . 14'Ce 13Te . * I4'Ce and 14'Ce* . 14'Ce ratios respectively. Chang et al. (96/1597) employed extensive chemical separation to remove the neo- dymium contamination from solutions of highly-enriched cerium isotopes used to calibrate the analysis. Solutions con- taining 4 pg of Ce were analysed by a double rhenium filament procedure to produce Ce' ion currents of about lo-" A. The loading technique as well as measuring program were kept identical for analysis of all samples in order to produce a constant fractionation effect.The relative atomic mass of cerium calculated by the first group 140.1 148( l ) was substan- tially lower than other recent values and also than the value 140.1157(8) found by the second group. The second group claimed that their value was superior to all other values. A procedure for the determination of very low levels of technetium (> lo6 atoms of 9 8 T ~ or 9 7 T ~ and 1.7 x lo7 atoms of 99Tc) by negative ionization TIMS has been reported by Schroeder et al. (95/2603). Lanthanum oxide enhancers and Ca(NO,) were added to single rhenium filaments to achieve ionization efficiencies of > 2% for the formation of Tc04-. Interferences from isobaric impurities or hydrocarbons were equivalent to 5 x lo5 atoms of Tc or less.Concentrations of 14-20 fg I-' of 99Tc were measured in well waters. Negative ionization TIMS was also used by Saumer et al. (95/2596) for the determination of molybdenum isotope ratios following its use as a stable isotope tracer in plant metabolism studies. Plant samples were acid digested the Mo complexed with malonic acid and extracted by liquid-liquid extraction. The Mo (about 1 pg) was loaded on a double rhenium filament assembly and determined as the MOO,- ion (m/z 140-148) using a quadrupole instrument. Levels representing 2.3% of foliar application of tracer molybdate could be detected. High-precision (<0.2%) analysis of the isotope ratios of iron in blood samples has been reported by Abrams et al. (95/2574). Whole blood samples (1 ml only) from young children pre- viously administered stable iron isotopes were digested in acid and the iron isolated by a cation-exchange procedure.The iron was loaded on rhenium single filaments using the silica gel procedure ( 5 pl of silica gel suspension and 8 pl of iron solution containing 20 pg of Fe) and ratios measured at a 56Fe ion current of 5-8 x A. Fractionation correction was based on a normalization factor of 0.063 31 for the s4Fe 56Fe ratio. Some data rejection was employed to achieve the high 386 R Journal of Analytical Atomic Spectrometry October 1996 Vol. 11precision and only the best (that with the lowest standard deviation) of three blocks of 10 scans utilized in calculations. The Cs,Cl+ ion was measured in a new procedure for the determination of chlorine isotopic composition in geological samples (Xiao et al.96/1505). Sample solutions (2 pl) contain- ing about 1Opg of chlorine as CsC1 were loaded 5m to filaments coated with about 100 pg of graphite. Data were collected at a Cs,Cl+ ion beam of 6-8x A by peak switching between m/z 301 and 303. The analysis of NIST SRM 975 gave good precision (0.009?40) but a substantially lower 37Cl:35Cl ratio than that measured by negative ioniz- ation TIMS and reported elsewhere. The Cs,BO,+ method for the determination of boron isi ,topic composition has the disadvantage that the measured peaks have a high mass (up to m/z 309) which must be measuxed by peak jumping procedures. Ding et al. (96/1538) have iitvesti- gated the alternative procedure of measuring the Rb,BO,+ ion.The boron extraction depended on the chemical corriposi- tion of the sample but the final purification step was commonly by anion exchange with elution of boric acid with water. Recovery rates were kept high (99 1%) to minimize isi)topic fractionation during sample preparation. Samples of rubidium borate (2 pl) made by addition of RbOH to the boric acid were loaded on to single rhenium filaments. Data were acquired in a static multicollector mode with an Rb2B02+ ion current at m/z 213 of 0.3 x A. The precision (0.008%) and time (as little as 30 min) of analysis were improvements on the Cs,B02 method. Simultaneous measurement of lithium and boron isotopic com- position is possible by use of the Li,BO,+ ion. Sahoo and Masuda (95/3533) used a Daly detector to measure intensities at m/z 54-57 and applied simultaneous equations to determine the two isotopic compositions.Lithium was separated from the sample matrix by a two stage (cation followed by anion) ion-exchange procedure. Samples of lithium (0.5 pg as LiOH) were loaded on to single rhenium filaments with boric acid and were run at low ion beam currents to reduce fractionation. Lithium and boron isotope ratios were successfully measured simultaneously with precisions of 0.05 and 0.01 YO respectively. Datta et al. (96/1596) found that accuracy of results using the Li2B02+ ions depended on the choice of isotope ratios moni- tored. They presented guidelines for choosing the best ion pairs for the measurement and discussed other requirements for achieving accurate lithium isotopic analysis.The preparation of isotope standards continues to assume considerable importance for accurate analysis. A large inter- national consortium of laboratories has produced three rlatural zircon standards for calibrating the U-Th-Pb geochronc )meter and Hf isotopic analyses (96/1246). The samples chostbn and the analytical procedures used by the various laboratoric>s were described in some considerable detail. 9.6. Applications 9.6.1. Isotope dilution (ID) analysis Kingston (95/4600) has taken out a patent on the isotope dilution process. The originality of the work appeared to be the application to chromium speciation by use of enriched spikes in the oxidation state of the species to be determined. The patent was concerned solely with the spiking process and not the MS measurement.Although the patent contained details of the procedure some statements were inaccurate others questionable and the rest somewhat obscured by the peculiarly legalistic style used including the odd statement that chromium is 'a trace dement.' Iodine speciation in atmospheric particles was the subject of a study by Wimschneider and Heumann (96/1574). Species- specific spike solutions containing 1291- and 129103- were added to water extracts of the particles prior to separation by anion-exchange chromatography of iodate eluted by 0.1 moll-' NaNO and iodide eluted by 1.5 mol 1-' NaNO,. This had the advantage that incomplete recovery would not affect the analytical result but the disadvantage that isotopic exchange between the two species before separation had to be prevented.The iodate fraction was reduced to iodide and iodide precipitated as AgI for analysis by negative ionization TIMS using a quadrupole instrument. The iodide was deposited on the evaporation filament of a double rhenium assembly and 15-20 pg of La as La(NO,) applied to the ionization filament. Detection limits for 3000 m3 sampling volumes of air were 3 and 5 pg m-3 for iodate and iodide respectively. Simultaneous IDMS has been used by Waidmann et al. (95/2563) to determine five metals in homogenized materials from the limnic environment. After addition of spikes the samples were digested or extracted and the metals purified by electrolytic deposition at platinum electrodes. The residue was dissolved in a suspension of silica gel in H3PO4 ( 5 pl) and dried on to single rhenium filaments.The filament current was increased in steps to determine the metals successively at 800 960 1150 1190 and 1300°C for T1 Cu Pb Cd and Zn respectively. Detection limits were 0.03 0.24 0.10 and 1.5 ng for Cd Cu Pb and Zn respectively and 0.6 pg for T1. The determination of iron in zirconium at the pg g-' level is important in the analysis of alloys used in the nuclear industry. A two-stage purification procedure was used by Elliot et al. (96/1618) to isolate Fe from the zirconium matrix. After sample dissolution and addition of 54Fe spike the bulk of the zirconium was removed by anion-exchange chromatography. The eluted iron was further purified by micro-solvent extraction into tributyl phosphate-impregnated resin beads.Iron (0.2-1 pg) was loaded on to a zone-refined rhenium filament coated with silica gel and 0.8 mol I-' boric acid (2 pg) added. An ion current of 2 x A was achieved for loadings >0.1 pg of Fe. Minor signals were observed for Cr+ and organic inter- ferences and corrections of < 0.1 YO and < O S % respectively were required. No attempt was made to correct for fraction- ation because of the lack of isotopic standards. The procedural blank of 20 f 6 ng was sufficiently low to allow determination of pg g-' amounts of Fe in 0.1 g zirconium samples. Analysis of solution standards gave results within 2% of the expected result. The determination of 11 trace elements in high-purity HF by Horn and Heumann (95/2440) required extensive preparation techniques to separate the elements for determination by ID-TIMS.Two preparation schemes were employed. In the first Fe and T1 were extracted into diethyl ether Ag Cu and Pb electrodeposited as one group and Cd Cr Ni and Pb electrodeposited as a second group. In the second scheme Th U and Zn were separated by a strongly basic anion exchanger. The metals were analysed using single rhenium filaments. To increase the ionization efficiency of Cr Fe and Ni 1 pg A1 as AlCl solution 10 pl of silica gel suspension and 1 p1 of boric acid (0.8 mol 1-l) were added to the filament. The boric acid was replaced by phosphoric acid (0.25 mol 1-') for the analysis of Ag Cd Cu T1 and Zn. Either acid could be used for Pb. A more stable ion beam of Cuf was achieved by adding 3 pg of A1 to the copper sample. Detection limits were 70 (Ag) 10 (Cd) 30 (Cr) 20 (Cu) 400 (Fe) 70 (Ni) 16 (Pb) 3 (Th) 1 (Tl) 1 (U) and 1100 (Zn) pg 8 - l .ID-TIMS continues to be the method of choice for the determination of truce element concentrations in RMs. Applications of a less than routine nature have included the determination of Cd in polyethylene (95/2707) K in clinical and geochemical SMs (96/C704) and a range of elements in polyethylene and an alloy (95/2441). The last application was significant in its use of the total evaporation technique to improve the accuracy of ID analysis. The method required Journal of Analytical Atomic Spectrometry October 1996 Vol. 11 387 Ronly low loadings of the elements to avoid excessive analysis times.Ion currents in the range to lo-'' A were obtained for 10 20 10 and 100ng loadings of Cd Ga Pb and Zn respectively. 9.6.2. Environmental studies The large triple-sector TIMS instrument at Richland reported in previous Updates has been used by Stoffel et al. (95/2567) for the environmental monitoring ofefluent radionuclides around a nuclear material production facility. The instrument incor- porated improved ion optics and had an abundance sensitivity of for positive ions and better for negative ions. Femtogram amounts with the prospect of attogram amounts of Pu in 1 g of soil could be detected using a graphitized single rhenium filament. Values of 5 x lop9 for the 1291 1271 ratio in polluted groundwaters could be measured using a triple- filament negative ionization procedure in which AgI was dried on the side filament. The limit of detection was 2fg of 12'1 equivalent to lo7 atoms.Enhanced but radiologically insignifi- cant levels of 1291 were found near a nuclear facility. Stable isotopes have been used for many years to identify the origin of lead in the environment but some novel studies are now beginning to use isotopes to look at the chemical association of lead within sediments and soils. Gobeil et a!. (95/2418) used the original approach of combining sequential extraction procedures with lead isotope analysis to apportion the origin of lead in the different fractions. The results were modelled to determine the specific sources and burden of lead in a coastal marine region of Canada. Lead accumulations in the surface soils from upland Scotland have been shown by Bacon et al.(95/4285) to be anthropogenic in origin with two major sources in present-day deposition. A unique approach was taken by introducing enriched isotopes of lead to soils in the field with the intention of monitoring changes in association of lead with different soil fractions using the lead isotopic composition as a tracer. 10. OTHER METHODS 10.1. Electrospray Mass Spectrometry (ESMS) An acronym for this new technique appears still to be agreed upon with both ES-MS and ESIMS being used in the literature. The former appears to be favoured by the majority but the authors of this review feel that ESMS is more appropriate. In a study of the fundamental operating parameters Agnes and Horlick (95/3065) investigated the effect on analysis of curtain gas flow rate and the voltage biases of the electrospray capillary tip the front plate the sampling plate the skimmer and the barrel ion extractor lens.A minimum flow rate of curtain gas was required in order to observe analyte ion signals and when combined with a low sampling-plate voltage the observed signals were primarily of analyte ion-solvent clusters. As the values of the two parameters were increased in unison the species were declustered and ultimately the mass spectrum became dominated by the singly-charged analyte ion. The same group have continued their investigation of elemen- tal speciation measurements by studying the analysis of the inorganic ionic species of C1 Fe I and S (95/2608). The ionic species of Cl and I were detected as their unmodified molecular ions but some modification dependent on source conditions was observed for S species thereby making interpretation more difficult In general the inorganic ions in solution appeared mainly as their molecular ions in the mass spectra.Problems identified that might affect the speciation of the ions in solution were the need to add an electrospray stabilizer to achieve quantitative analysis the present requirement for methanolic solutions and matrix effects. The authors concluded that the method was 'not an ideal speciation technique' but might have advantages for a wide range of sample types and for samples which present difficulties for other techniques. The pioneering work of Agnes and Horlick in developing the electrospray technique for inorganic analysis has inspired a number of other laboratories to investigate novel approaches for applying the technique.That of Zhou and Van Berkel (96/2012) was particularly original in that the ESMS was effectively an on-line detectorfor electrochemical methods. Three types of cell were coupled on-line and assessed with several applications including the determination of silver by anodic stripping voltammetry using a thin-layer electrode flow-by cell in which solution flowed through a thin channel that separated the planar working electrode from the auxiliary electrode. The constant-potential three-electrode configuration was decoupled from the ES high voltage. Analyte solution (1 ml) was injected into a carrier solution of acetonitrile-water-nitric acid (95 5 0.1 v/v/v) and the silver preconcentrated at - 2.0 V before electrochemically stripping at 1.0 V back into the analyte solution for ESMS detection.The electrochemistry could be used not only to preconcentrate the analyte but also to remove sample matrix species which could interfere with the ESMS detection. A preconcentration period of 3 min which consumed 120 p1 of sample gave a detection limit for Ag' of 1 ngml-l or less. Much of the work on ESMS for inorganic analysis is still in its infancy but some interesting developments were indicated at the Pittcon '95 and FACS XXZZ conferences. Thaxton et al. (96/C726) identified severe chemical matrix effects and complex spectral interpretation in the analysis of inorganic species.Houk and colleagues (95/C3013) have coupled capillary elec- trophoresis with ESMS for the rapid and direct discrimination of elemental isobars such as 23sU and 23sPu. Ketterer and Guzowski (96/C727) measured Ag Pb and T1 isotope ratios of lod4 mol 1-1 solutions of metal nitrates or acetates in methanol. Although conditions could be set up for production of Ag and TI spectra free of polyatomic ions accurate isotopic analysis of lead was precluded by significant yields of PbH' ions. Precisions of 0.1-0.2% were achieved for the isotopic measurements of Ag and TI. Further details of these develop- ments are awaited with interest. 10.2. Fast Atom Bombardment Mass Spectrometry (FABMS) and Gas Chromatography-Mass Spectrometry (GC-MS) There have been no significant developments reported for either of these methods in the period covered by this Update but the review by Crews et al.(95/2562) on the use of stable isotopes in human studies included excellent coverage of both techniques. As application of the two techniques to inorganic analysis has been almost exclusively to isotope analysis in human studies the review can be considered comprehensive. The sections included discussion of the basic principles mass analysis ion detection measurement and correction of isotope ratios sample preparation analytical performance advantages and disadvantages and recommended procedures. 10.3. Ion Cyclotron Resonance Mass Spectrometry (ICR-MS) Kouzes (95/2443) reviewed the application of both Fourier 'Transform ICR-MS and ICR-TOF-MS to precise measurement 'of atomic masses of both stable and short-lived radioactive isotopes.The basic principles and theory were given for both techniques and the limitations of both discussed. FTICR-MS typically required thousands of ions to produce an adequate S/N ratio thereby limiting the sensitivity for radioactive nuclei. (Complete measurements could be made in a short period of .time simultaneously for the elements of interest thereby allowing FTICR-MS to be coupled with GC or LC. In principle ICR-TOF-MS had single-ion sensitivity and was lbetter suited to measurements of a limited number of ions but 388 R Journal of Analytical Atomic Spectrometry October 1996 Vol. 1 1required more time to carry out the resonance mapping. This imposed a requirement of system stability for several minutes.FTICR-MS which is available commercially was considered to be the method of choice except in cases of samples limited to a few ions. 10.4. Recoil Mass Spectrometry Although this technique is primarily associated with the deter- mination of fundamental properties of nuclei far from st tbility it also has a potential application to surface analysis and has recently been attracting interest for elemental profiling of light and medium heavy elements with atomic mass up to about 120. Hammond et al. (96/1666) reviewed the applicaiion to elemental and isotopic surface analysis and found that in some important applications for example the determination of N the method was considerably more sensitive than SIMS. Persson et al. (96/1360) found that mass and energy dispersive recoil spectrometry was suitable for elemental depth p~ ofiling in the characterization of thin film 111-V structures They applied the method to a study of the interfacial rcaction between (100)InP and the metals Ni Pd and Pt.Thy same group of workers (96/1707) have also described methods used to transform the TOF-energy histograms into mass- energy histograms. Special procedures were required to handlt those situations where there was overlap in the isotope signals. The broadening of the mass distributions was well described using a Gaussian distribution. Although these are interesting devel- opments the requirement for highly energetic incident beams produced by accelerators will always present a major limitation on availability of this technique.10.5. Spark Source Mass Spectrometry (SSMS) There has been something of a resurgence in the use of SSMS in the period covered by this Update with developments reported in instrumentation and methodologies. Although there have been no reviews of note that of Dietze and Becker (96/1711) in German gave a clear if brief description of the basic principles of SSMS and other MS techniques. The review included a comparison of the figures of merit for a nunrber of MS techniques for the analysis of solids. SSMS was also one of the techniques considered in a review by Capper and Roberts (95/4431) on the analysis of Hg,-,Cd,Te and ielated materials. Gall' and Kuz'min (96/1778) have investigated the si'ipping discharge as a new method for the analysis of poorly conducting materials and dielectrics.The slipping discharge is a particular variety of surface discharge that takes place when a special configuration of the electrodes creates a strengthened electric field at the cathode. For a 7mm interelectrode gap a pulse voltage of 20 kV with a duration of isolated unipolar pulses of 1-2 ps was sufficient to ionize the material of a dielectric surface and produce a stable discharge ion current. The lcnergy spread did not exceed 100-200 eV in comparison with a b;pread of 700-900 eV for the more conventional rf discharge. 7 he ion current in the analysis of a GeO sample was more stable and more intense than that produced by the spark analysis of conducting samples. Conditions could be set up to redirce the formation of multiply-charged ions.Jochum et al. (95/3551) have replaced the conventional photographic plate detection system with a multi-ion cciunting system designed to consist of 25 separate channeltrons lor ion counting measurements. Each channeltron was mounted at an angle of 45" to the ion optical axis to increase compactness of the system and each was connected to its own individual power source (2100 V) preamplifier and counter. The chan- neltron box was positioned at the high mass end of the image plane of the mass spectrometer to allow the simultaneous determination of up to 25 isotopes from I7'Yb to 238U but the system has only been tested thus far with 5 channeltrons to measure 235U and 238U isotopes in six SRMs. The instrumen- tal vacuum needed to be improved by the use of turbomolecular and ion pumps in order to reduce the level of background caused by charge exchange between ions and neutral molecules.Poor reproducibility of count measurements was caused by differences in electrode positions but the effect tended to be the same for different ions so that the isotope ratios showed much better reproducibility. The extremely impressive analyt- ical performance was a considerable improvement over the photoplate method. Precisions of 1-3% and 10% for U concentrations in the range 1-1Opg g-' and 15ng g-' respectively and an accuracy of about 3 YO for concentrations > 1 pg g-' were achieved in measuring times of 1 min to 1 h and a sample consumption of only 6-2Opg. The very low sample consumption was seen to have drawbacks however in the analysis of coarse-grained materials for which representa- tive sampling might not be achieved.In addition the limited mass range of the new detection system compromised one of the big advantages of SSMS that of simultaneous determi- nation of all elements in the periodic table. The formation of polyatomic and cluster ions by the graphite matrix has been studied by Becker and Dietze (95/4181) for REE oxide-graphite mixtures. The typical alternating abun- dance distributions known since the early development of SSMS were broadly similar to those found for a laser plasma of an equivalent power level. Clusters with an odd number of atoms were more intense than those with an even number of atoms. The maximum cluster formation was found for a power density of about 109-10'0 W cmU2.The knowledge of cluster formation and abundance distributions was considered import- ant for analysis and for an understanding of the chemical and physical processes in the plasma. Jochum and Jenner (95/2442) have determined 29 trace elements in 15 silicate RMsfrom the Geological Survey ofJapan by both SSMS and ICP-MS in a series of studies to reevaluate the compiled data for geological RMs. The multi-element ID technique was used with eleven elements determined directly by the addition of enriched spikes and the remaining 18 determined using RSFs based on the spiked elements. The over-all precision was 3-5% and accuracy judged by the analysis of BCR-1 and W-1 within 5%. Results for the RMs with relatively high trace element concentrations compared well with the compiled data but large discrepancies were observed for the RMs with low trace element concentrations.The results for Nb Th U and Zr in depleted RMs using both SSMS and ICP-MS were significantly lower than the compiled values and called into question the data included in the compilation. A call was made for a more judicious selection of data for those samples with trace element concentrations that push analytical techniques to their limits. SSMS remains a valued technique for the analysis of high- purity materials. A detection limit of 0.01 pg g-' was achieved by Saito et al. (96/1512) for the determination of B in molyb- denum using a tantalum counter electrode and a 30 nC exposure. SSMS was considered sensitive and versatile but to give poor reproducibility (12% internal precision at 2.5 pgg-I).In the determination of C and 0 in high-purity semiconductor materials Wiedemann et al. (95/2614) achieved a precision of +15% but had to calibrate the SSMS method against other analytical techniques because of the lack of suitable RMs. An ultra-high source vacuum of 5 x lo-" mbar was maintained in the upgraded instrument. Two Chinese groups have reported methods published in Chinese for the analysis of high-purity REE oxides. In the analysis of Yb203 Sui et al. (96/1567) extracted the REE impurities by elution with HCl-NH,Cl from P, stationary phase and concentrated them on activated carbon for the preparation of electrodes. Sui et al. (96/1568) found detection limits of <0.01 pg g-' for Journal of Analytical Atomic Spectrometry October 1996 Vol.11 389R40 trace elements in Ho203 and Lu203. In comparison the sum of the detection limits for 13 REEs in Gd203 was reported by Meng et al. (96/1566) to be 8 pg g-'. 10.6. New Methodologies Poths and Chamberlin (96/1613) have reported tests on a microwave plasma ion source for the high sensitivity isotopic analysis of Kr and Xe. The ionization chamber consisted of a ceramic tube (15 cm long x 1.3 cm od) surrounded at one end by a 2.45 GHz h/4 cavity. Gas flowed into one end of the tube via a gas handling system and ions were extracted at 50 kV at the other end into an isotope separator. A minimum gas pressure required to sustain the discharge could be supplied by the analyte gas itself or by an added support gas.Ionization efficiencies were about 5% for pure Kr and Xe and ion currents > 2 x lo-" A of Xe in air could be generated. Further develop- ment work was required before the new source could be used as an analytical tool. An ion optics interface would be necessary to match the ion beam to a magnetic sector MS. The 1% memory effect for Xe needed to be reduced by an order of magnitude probably by replacing the ceramic tube with a quartz tube. The photon burst MS technique (Hansen et al. 96/1730) has been in development for more than ten years and is based on the principle that a single atom or ion in an optically isolated electronic state can absorb and emit a large number or burst of photons as it passes through a resonant laser beam. The instrument used for the determination of 85Kr (half life of 10.76 years and a natural abundance of lo-") consisted of the microwave ion source described above a magnetic sector a decelerator to slow the ions from 50 keV to 400-2000 eV a charge exchange cell containing Rb to convert Kr ions to metastable atoms and a photon burst detector assembly con- sisting of 4-10 light collectors and photomultiplier tubes.Two models were used to analyse the photon burst process. One was a spreadsheet model based on average quantities and using the ion beam diameter as the only variable parameter and the other a more detailed but more time-consuming Monte Carlo simulation. Most attention was being given to reducing the background levels by cooling the photomultipliers and to improving the optical design to remove scattered laser light. Particle inlet MS (PIMS) is a unique application of TIMS first reported in 1986 and recently described by Stoffel et al.(95/2567) for measurement of the isotopic composition of individual particles in heterogeneous particulate samples with- out having to isolate them. The particle beam admitted directly from air via a differentially-pumped inlet entered a rhenium oven in which the particles were vaporized and ionized to produce short bursts of ions for those elements with an ionization potential <8 eV. The capability of the method was demonstrated by the measurement of U isotope ratios in individual particles without isolating them from the hetero- geneous matrix. Kahr et al. (95/C3037) have reported in a conference paper the development of a small portable isotope MS for the determination of Pu and U isotope ratios in the field.The rugged instrument was based on a compact commercial quad- rupole system. Samples were volatilized using fluorination chemistry to convert Pu and U into the volatile hexafluorides. Particular attention needed to be given to the hazardous nature of the fluorination reagents. Details of the analytical performance are still awaited. LOCATION OF REFERENCES The full list of references cited in this Update have been published as follows 95/2276-95/2891 J. Anal. At. Spectrom. 1995 10( lo) 229R-251R. 95/3362-95/4189 J . Anal. At. Spectrom. 1995 10( 1 l) 307R-318R. 95/C4190-95/4746 J. Anal. At. Spectrom. 1995 10( 12) 402R-422R. 96/C1-96/416 J.Anal. At. Spectrom. 1996 11( l) 1R-60R. 96/417-96/C947 J. Anal. At. Spectrom. 1996 11 (2) 49R-59R. 96/948-96/1357 J. Anal. At. Spectrom. 1996 11(3) 87R-101R. 96/1358-96/1802 J. Anal. At. Spectrom. 1996 11(4) 187R-203R. 96/1803-96/2015 J. Anal. At. Speci'rom. 1996 11( 5 ) 205R-212R. 96/2016-96/2799 J. Anal. At. Speci'rom. 1996 11 (6) 239R-269R. Abbreviated forms of the literature references quoted (excluding those to Conference Proceedings) are given on the following pages for the convenience of the readers. The full references names and addresses of the authors and details of the Conference presentations can be found in the appropriate issues of JAAS cited above. Abbreviated List of References Cited in Update 9512281 At. Spectrosc. 1994 15 27. 9512283 At. Spectrosc. 1994 15 21.9512285 Fresenius' J. Anal. Chem. 1994 349 768. 9512286 Int. J. Mass Spectrom. Ion Processes 1994 136 91. 9512287 J. Am. SOC. Mass Spectrom. 1994 5 387. 9512290 Process Technol. Proc. 1994 11 945. 9512319 Int. J. Mass Spectrom. Ion Processes 1994 134 183. 9512333 Mitt. Geb. Lebensmittelunters. Hyg. 1994,85 11 1.9512338 Org. Geochem. 1994 21 561. 95f2339 Org. Geochem. 1994 21 573. 95/2340 Org. Geochem. 1994 21 585. 9512341 Plant Cell Environ. 1994,17 1073. 9512349 Rapid Commun. Mass Spectrom. 1994 8 590. 9512362 Tech. Instrum. Anal. Chem. 1994 15 169. 9512394 J. Anal. At. Spectrom. 1995 10 363. 9512396 J . Anal. At. Spectrom. 1995 10 371. 9512397 J. Anal. At. Spectrom. 1995 10 381. 9512398 J . Anal. At. Spectrom. 1995 10 395. 9512403 Anal. Sci.1994 10 895. 9512405 Fresenius' J. Anal. Chem. 1994,350 186.9512407 Fresenius' J. Anal. Chem. 1994 350 221. 9512409 Fresenius' J . Anal. Chem. 1994 350 235. 9512411 Int. J. Mass Spectrom. Ion Processes 1994 139 95. 9512412 Int. J. Mass Spectrom. Ion Processes 1994 139 111. 9512413 J. Chromatogr. A 1995,689,63.95/2415 Spec. Pub1.- R. SOC. Chem. 1994 154 121. 9512418 Environ. Sci. Technol. 1995 29 193. 9512420 Org. Geochem. 1994 21 809. 9512422 390R Journal of Analytical Atomic Spectrometry October 1996 Vol. 1 1Org. Geochem. 1994,21 787.9512423 Org. Geochem. 1904,21 761. 9512436 Org. Geochem. 1994 21 595. 9512437 Chem. Geol. (Isot. 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Spectrom. 1996,11(3) 187,9612012 Anal. Chem. 1995,67,3643.96/2479 J. Anal. At. Spectrom. 1996 11(4) 103R. Journal of Analytical Atomic Spectrometry October 1996 Vol. 11 393R

ISSN:0267-9477    

DOI:10.1039/JA996110355R

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 A F 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-stripping voltammetry Community Bureau of Reference capacitively coupled plasma capacitively coupled microwave plasma certified reference material cold vapour continuous wave direct current dc plasma diethyldithiocarbamate N N-dimethylformamide deoxyribonucleic acid electron capture detection electrodeless discharge lamp 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 QC rf REE(s) RIMS RM RSD SEC SEM SFC Si (Li) SIMAAC SJMS SIN SR SRM SSMS STPF TCA TIMS TLC TMAH TOP0 TRIS TXRF uhf uv VDU vuv WDXRF XRF LOQ PPb SIB UVfVIS 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 die th yldit hiocarbama te National Institute for Environmental Studies National Institute of Standards and Technology nitrilotriacetic acid optical emission spectrometry particle-induced gamma-ray emission particle-induced X-ray emission photomultiplier tube parts per billion parts per million poly( tetrafluoroethylene) poly(viny1 chloride) quality control radio frequency 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-( hydroxymethyl) propane- 1,3-diol total reflection X-ray fluorescence ultra-high frequency ultraviolet ultraviolet-visible visual display unit vacuum ultraviolet wavelength dispersive X-ray fluorescence X-ray fluorescence Commonly Used Symbols 4 relative atomic mass Mr relative molecular mass r correlation coefficient S standard deviation Sr relative standard deviation Journal of Analytical Atomic Spectrometry October 1996 Vol.11

ISSN:0267-9477    

DOI:10.1039/JA996110394R

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

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ISSN:0267-9477    

DOI:10.1039/JA996110395R

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Evaluation of Controlled-pore Glass Immobilized lminodiacetate as a Reagent for Automated On-line Matrix Separation for Inductively Coupled Plasma Mass Spectrometry SIMON M. NELMS AND GILLIAN M. GREENWAY" University of Hull Cottingham Road Hull N . Humberside UK .HU6 7RX DAGMAR KOLLER VG Elemental Ion Path Road Three Winsford Cheshire UK C W7 3BX A new iminodiacetate chelating reagent immobilized onto a controlled-pore glass support was evaluated as a substrate for on-line matrix separation for ICP-MS. An automated Fi manifold was constructed incorporating a glass mini-column of the iminodiacetate reagent. One compromise set of optimum conditions was obtained for a range of analytes using the variables of matrix separation flow rate buffer pH and concentration and eluent acid concentration.With a sample volume of 3 ml and an elution volume of 0.3 ml a preconcentration factor of 10 was obtained in addition to matrix separation. The range of elements found to be retained by the column included transition metal cations uranium and lead. These could be quantitatively eluted using nitric acid (0.5 mol dm-3). Calibrations prepared from both pure water and artificial sea-water matrices were found to be comparable in terms of sensitivity illustrating that the presence of a saline matrix did not affect the separation process. Both calibration sets showed good linearity with least squares regression coefficients between 0.996 and 0.999 for the analytes measured. The method gave acceptable reproducibility with precisions (s,) at the 5 ng m1-I level of <5% for 5 replicates.Recoveries between 62 and 113% were obtained for all the elements analysed except Mn which gave a very low recovery (< 35%) under the compromise conditions used. The chelating material was found to have a capacity of approximately 0.1 mmol g-' for a range of elements. The procedure was validated by accurate analysis of the National Research Council of Canada CRMs SLEW-1 (Estuarine Water) and CASS-2 (Coastal Sea- Wa ter). Keywords Flow injection; inductively coupled plasma mtiss spectrometry on-line matrix separation; controlled pore glass; immobilized iminodiacerate ICP-MS has rapidly become one of the most sensitive accurate and reliable trace element measurement techniques. Despite the advantages of ICP-MS its principle disadvantages of low tolerance to dissolved solids (<0.2% m/v) and formation of polyatomic interferences are well known.'*2 In addition the presence of easily ionizable matrix elements such as Nit cause ionization suppression because of the increased electron den- sity in the p l a ~ m a .~ Problems with dissolved solids can be alleviated by diluting the sample but this is unsuitable for samples containing very low levels of analyte species such as sea-waters. Polyatomic interferences cannot be removed by dilution and so degrade the accuracy of quadrupole I(:P-MS * To whom correspondence should be addressed. JkS Journal of Analytical Atomic Spectrometry for isotopes such as 63Cu (due to 40Ar23Na) '9C0 (due to 42Ca'601H) and 7'As (due to 40Ar35C1). The use of high resolution magnetic sector ICP-MS instruments allows mass resolution of the interference from the analyte of intere~t,~ but this can be an expensive solution to the problem. More recently use of the shielded 'cool' plasma has been shown to decrease argon based interferences substantially notably 40Ar'60 on 56Fe by eliminating secondary discharges between the plasma and the sampling interface.' This effect may also reduce matrix-related argon interferences such as 40Ar23Na and 40Ar3'C1 thereby permitting accurate measurements of 63Cu and 75As without the need for matrix separation.The disadvantage here however is that cool plasma conditions reduce the ionization efficiency of elements with ionization potentials greater than 8 eV thereby leading to lower sensi- tivity.Furthermore cool plasma conditions favour the forma- tion of some molecular species such as refractory element oxides and suffer more severe matrix effects in place of argon based interferences.6 To counteract the analytical problems outlined above without resorting to new potentially costly instrumentation considerable effort has been invested in the development of on-line matrix separation using chelating ion- exchange resins. Of the many studies which have been per- formed in this area using a range of detection systems two chelating functional groups namely iminodiacetate (IDA) and 8-hydroxyquinoline (8-HQ) have provoked the most interest. Early on-line matrix separation studies used columns of Chelex-100 resin incorporated into the flow manifold to separate several trace metals from sea-water samples with subsequent detection using AAS7 and ICP-OES.* These studies highlighted that Chelex-100 which contains the IDA ligand covalently bonded onto a polystyrene-divinylbenzene support is difficult to use in on-line systems because of the large volume changes it undergoes when it is converted from a salt form to the acid form.It also requires conditioning steps between each sample analysis resulting in an increase in the analysis time. To address this difficulty alternative more highly cross-linked IDA resins which are less susceptible to dimensional changes have recently been employed in system^.'.'^ These resins are amenable for use in on-line systems but like Chelex-100 require conditioning between samples.An alternative support which is not susceptible to dimensional changes with changing solution composition is controlled-pore glass (CPG). This support possesses a reactive surface which can be easily functionalized with chelating groups and can be conditioned rapidly between samples leading to shorter analysis times. Following the benchmark procedure for covalently bonding 8-HQ to CPG described by Hi1l,I1 numerous successful on-line Journal of .4nalytical Atomic Spectrometry October 1996 Vol. 11 (907-912) 907matrix separation studies using CPG-8-HQ combined with flame AAS,I2,l3 ETAAS14 and ICP-MS15 detection have been described. The location of the separation column in the flow manifold is an important factor in on-line matrix separation studies. In systems developed by Bloxham et a!.' and Beauchemin and Berman,15 in which ICP-MS detection was used the column was incorporated in the flow stream and a separate valve was used to direct the matrix to waste downstream from it.Alternatively it has been suggested that by incorporating the column within a loop across one valve to allow direct switching between the sample and eluent streams the need for a separate additional valve can be circumvented.16 Unfortunately this arrangement allows some matrix to pass into the detector on switching the valve but if the connecting tubing is sufficiently short the residual matrix is kept to an acceptably low level. This design facilitates counter current elution of retained analytes yielding sharper less dispersed peaks and resulting in a reduction in analysis time.In this paper a rapid automated on-line matrix separation system for ICP-MS using an FI manifold is described. The manifold incorporates a mini-column of a new CPG-based IDA resin PROSEP Chelating-1 for the determination of several trace elements in saline samples. This novel material combines the advantages of a CPG support with the efficient chelating performance of the IDA ligand. The immobilized chelate is contained within a glass mini-column located in the loop of an automatic Teflon dual 6 port valve. The retained analytes are eluted counter current to the sample flow to yield improved less dispersed peaks. The system described is based on fixed volume injection rather than time based sampling and gives a 10-fold preconcentration in addition to the required matrix separation for a 3 ml sample volume.Data from the transient eluted peaks was collected using the peak jumping data acquisition mode of the instrument with a suitable uptake delay to allow the eluted sample to travel from the column to the plasma. A full optimization of the system is described including recovery and capacity results. Validation of the procedure using National Research Council of Canada (NRCC) CASS-2 (Coastal Sea-water) and SLEW-1 CRMs (Estuarine water) is also presented. EXPERIMENTAL Reagents The iminodiacetate reagent (PROSEP Chelating- 1 Bioprocessing Consett Co. Durham UK) was used as sup- plied. The preparation and structure of this material cannot be described here for commercial reasons. The chelating mate- rial (0.04 g) was packed as a dry powder into a glass mini- column (2.5 cm x 3 mm Omnifit Cambridge UK).High-purity deionized water (18 MR cm resistivity Elgastat UHQ PS Elga High Wycombe Buckinghamshire UK) was used throughout. Elemental stock solutions (1000 pg ml- ' SpectrosoL Merck Poole Dorset UK) were used in the preparation of calibration solutions. Ammonium acetate buffer (Sigma Poole Dorset UK) was prepared from the solid and purified on-line by passing through a column of Chelex-100 (Sigma). Adjustments in pH were made using glacial acetic acid or aqueous ammonia solution as appropriate. Artificial sea-water (Instant Ocean Aquarium Systems Mentor OH USA) was prepared by dissolving approximately 330g of the powder in 101 of water. Samples of the NRCC (Ottawa Canada) CASS-2 and SLEW-1 were introduced into the mani- fold as supplied.Instrumentation ICP-MS measurements were made using a VG Elemental PlasmaQuad 2 Plus (VG Elemental Winsford Cheshire UK). The instrument was calibrated and optimized prior to oper- ation using a solution containing the elements Be Mg Co Y La Eu and Bi at 10 ngml-' in a matrix of 2% nitric acid. The transient analyte peaks were monitored in the peak jumping mode using the data acquisition and instrument operating parameters given in Table 1. The automated matrix separation procedure was carried out using the Preplab unit (VG Elemental). For the PROSEP Chelating-1 capacity evalu- ation measurements were made using a Perkin-Elmer Plasma 40 ICP-OES instrument ( Perkin Elmer Beaconsfield Buckinghamshire UK) the operating parameters of which are given in Table 1.Matrix separation manifold The automated matrix separation manifold is illustrated in Fig. 1. The sample loop (3 ml) was located across the front of the dual 6 port Teflon injection valve (D-6-V) on the Preplab unit. The PROSEP Chelating-1 material was contained within a glass mini-column (2.5 cm x 3 mm id Omnifit Cambridge UK) incorporated in a loop across the rear of the D-6-V. All the manifold connections were made using 0.8 mm id PTFE tubing. The reagents were pumped using the two peristaltic pumps on the Preplab. With the configuration used the matrix separation flow rate could be varied but the eluent flow rate was fixed at 1.5ml min-'. Using the two valves supplied on the Preplab both the sample uptake line and on-line buffer streams could be switched to water to rinse the sample loop between samples and the column after sample loading. Table 1 Operating parameters for the ICP and ICP-MS instruments ICP instrument - Aerosol gas flow rate/l min- ' Intermediate gas flow rate/l min-' Outer gas flow/l min-' Nebulizer Cross flow Spray chamber Ryton ICP emission wavelengths - Element V Cr Mn Fe c o Ni c u Zn Cd Ce Pb U ICP-MS instrument - Forward power/W Aerosol gas flow rate/l min-' Outer gas flow/l min-' Reflected power/W Intermediate gas flow rate/l min-' Spray chamber Glass water cooled 10 "C Nebulizer de Galan type Peak jumping acquisition parameters - Points per peak Dwell time Detector mode Selected isotopes (ICP-MS) - 48Ti 49Ti 51V "Mn "Co 60Ni 63Cu 64Zn 65Cu 114Cd 208pb 2 3 8 ~ 9 x0.75 0.6 12 Wavelength/nm 309.311 205.552 257.610 238.204 238.892 221.647 324.754 213.856 214.438 413.765 220.35 3 385.958 1350 0.939 13.0 0 1 .o 3 10.24 ms Pulse counting 908 Journal of Analytical Atomic Spectrometry October 1996 1/01.1 1SAMPLE WATER Fig. 1 Flow injection manifold Matrix Separation Procedure The automated matrix separation procedure began by opening the D-6-V and valves 1 and 2 (V1 and V2) then starting peristaltic pump 2 (P2). This allowed sample to pass into the sample loop and also eluent acid to pass as a continuous stream through the chelating column. After a period of 50s peristaltic pump 1 (Pl) was started to pump buffer through to the D-6-V via an on-line purification column containing Chelex-100 (A on Fig.1). After a further 30 s buffer had reached the D-6-V and the sample loop was full. At this point V1 closed followed immediately by the D-6-V. Closing V1 stopped the sample uptake by switching to water and c1,osing the D-6-V allowed the sample loop contents to be eluted by water the eluent was then mixed with the buffer (at point B) and finally passed through the chelating column. In this way trace elements in the buffered sample were retained on the column and the matrix and buffer species were passed to waste. Once the sample had passed into the column V2 swiwhed from buffer to water to allow residual buffer and matrix species in the system to be rinsed to waste. After this rinse period the D-6-V and V1 were switched back to open.This allowed acid back through the column thereby eluting the retained analytes into the ICP-MS and simultaneously enabled a new sample to load during the ICP-MS analysis period. As the ICP-MS analysis time was similar to the initial 50s sample loading period the latter could be skipped for subsequent repeats on the same sample by incorporation of a loop command in the Preplab program thereby decreasing the total analysis time. for each element was evaluated using eqn. 1 Determination of Exchange Capacity and Recovery The capacity of PROSEP Chelating-1 was determined for a range of elements using a batch method. Solutions of the selected analytes (200 pg ml- ') were prepared in artificial sea-water (10 ml) then added to ammonium acetate buffer (1.5 mol dm-3 10 ml).Each solution was adjusted to pH 6.5 (pH 8 for Cr and Mn) and added to 0.05 g of the dry chelating material. The mixtures were shaken and left to equilibrate overnight. The reduced concentration of each analyte i n the supernatant solution was then measured uersus the original concentration using ICP-OES. The capacity of the material where C is the capacity (mmol g-') ci and cf are the concen- trations (pg ml-') of the element before and after equilibrium M is the relative atomic mass (g mol-') of the element and u is the volume (ml) of solution equilibrated with a mass m (g) of PROSEP Chelating-1. Recoveries for a range of elements were evaluated dynamically for both a fresh and an aged column of PROSEP Chelating-1 by passing an artificial sea- water solution spiked with the selected analytes at 10 ng ml-' through the automated FI manifold.The aged column had been in use for approximately 240 h before the recovery study. A manual valve (Rheodyne 5020 Supelco Poole Dorset UK) fitted with a 0.3 ml loop was incorporated into the eluent acid stream of the manifold to yield a 10-fold preconcentration on elution. Using this configuration the eluent acid instead of being pumped continuously was injected as a known fixed volume via the manual valve into a water carrier stream. Recoveries were evaluated by comparing samples eluted from the column with a 100 ng ml-' solution prepared in the eluent matrix and injected via the manual valve. RESULTS AND DISCUSSION Optimization of the Matrix Separation Procedure The procedure was optimized with respect to the matrix separation flow rate buffer pH buffer concentration and eluent acid concentration using a univariate approach.For the optimization procedure samples were prepared by spiking a synthetic sea-water solution with the selected analytes (10 ng ml-') followed by acidification with O.lml of concen- trated nitric acid to 100 ml of sample. Acidification was performed to prevent trace element loss from solution by adsorption or precipitation. The optimum conditions for on-line matrix separation were 1.5 mol dm-3 of ammonium acetate (pH 6.5); 0.5 mol dm-3 of nitric acid; matrix separation flow rate 5.0 ml min-'; elution flow rate 1.5 ml min-'; and total analysis time 5 min. The effect of flow rate on the matrix separation procedure is illustrated for selected elements in Journal of Analytical Atomic Spectrometry October 1996 Vol.11 909Fig. 2. Up to a flow rate of 5 ml min-l no significant change in response was observed for the elements analysed. Faster flow rates than 5 ml min-' introduced back pressure problems and slower rates led to increased analysis time. Therefore 5 ml min-l was selected for the rest of this study. The response of the column to selected analytes with changing buffer pH is illustrated in Fig. 3. Since the optimum buffer pH for matrix separation varies between elements a compromise pH must be selected for multi-element analysis. On the basis of the element responses shown in Fig. 3 pH 6.5 was chosen as values below this gave decreased retention of some analytes.Values above this level reduced the capacity of the acetate buffer and also lead to increased retention of Ca as the PROSEP Chelating-1 has some affinity for this element. The effect of the ammonium acetate buffer concentration on the retention of selected elements is illustrated in Fig. 4. The results show that the buffering process is effective for many elements at a concen- tration of 0.05 mol dm-3. However ionogenic retention of Ca at this level is high because the buffer cation concentration is insufficient to displace this element completely. Retention of 48Ca interferes with 48Ti and at zero buffer concentration 63Cu and 'lV are also interfered with because of the formation of 40Ar23Na and 35Cl'60 in the plasma with residual Na and C1 respectively. It was found that a buffer concentration of 1.5 mol dm-3 was required to remove the Ca problem.This high concentration did not affect retention of the selected analytes except Mn and U (as UOzf). These two elements show similar behaviour to Ca on PROSEP Chelating-1 which is expected from the relative positions of these three metals in the Irving-Williams series.17 The effect on analyte elution with increasing eluent acid concentration is illustrated for selected I 2.0 2.5 3.0 3.5 4.0 4.5 5.0 FIOW rate/ml min-' Fig. 2 Effect of matrix separation flow rate. A Mn; B Ni; C Cu; D U and E Zn 30 25 20 15 10 5 0 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 PH Fig.3 D Ni; and E U Effect of ammonium acetate buffer pH. A V; B Mn; C Co; 60 5 50 * 40 2 30 (d Y a v) 4- 8 g 20 10 0 h D 0 0.5 1 1.5 2 [Buffer]/mol dm-3 Fig.4 Co; C Ni; D U; and E Ca Effect of ammonium acetate buffer concentration. A Mn; B analytes in Fig. 5. In this study quantitative elution was observed for all the elements investigated at an acid concen- tration of 0.5 mol dm-3. Acid concentrations greater than 2.0 mol dmP3 were not investigated as these could degrade the column. To determine the! effect on the column of repeated use a second column was prepared from the same batch of PROSEP Chelating-1 and the two columns were compared in terms of element recoveries (Table 2). Recoveries between 62 and 113% were obtained except for Mn for which the recovery was only 30%. This was due to the relatively low affinity of the resin for Mn under the matrix separation conditions used. The results showed that there was a slight reduction in the column performance after use for approximately 240 h.Capacities of the PROSEP Chelating-1 material were evaluated for a wide range of elements (Table 3) and found to be lower (by typically 66%) than those of the polymeric based IDA resin Chelex-100.'8 This is expected as the rigid CPG support cannot expand to allow greater access to the complexation I 0 0.5 1 .o 1.5 2.0 [Acid]/mol dmm3 Fig. 5 D Cu; and E U Effect of nitric acid eluent concentration. A V; B Mn; C Ni Table 2 Recovery comparison between aged and fresh column Recovery (YO) Element Ti V Mn c o Ni c u U Aged column 76 too 30 98 105 71 62 Fresh column 82 101 31 113 110 97 61 91 0 Journal of Analytical Atomic Spectrometry October 1996 Vol. 11Table 3 Capacity results for PROSEP Chelating-1 Element V Cr Mn Fe co Ni c u Zn Cd Ce Pb U Capacity/mmol g- ' 0.22 0.10 0.14 0.29 0.13 0.11 0.1 1 0.13 0.10 0.10 0.13 0.04 sites.Nonetheless the capacity of PROSEP Chelating-1 I S still more than sufficent for use in trace element studies. Evaluation of the Effect of Residual Matrix Species In a previous paper," a procedure for evaluating the influence of residual matrix on the ICP-MS results using the 63Cu 65Cu isotope ratio was described. This procedure was based on the observation that the 63Cu 65Cu isotope ratio is anomalously high if Na is present in the plasma due to polyatomic overlap of 40Ar23Na on 63Cu. However this method of identifjing a residual matrix problem does not cover the possible inter- ference of 33S'602+ on 65Cu which could yield a low 63Cu 65Cu ratio.In this paper this potential inaccuracy has been addressed by presenting data for the 48Ti:4 9Ti ratio in addition to 63Cu 65Cu data to clarify the efficiency of the matrix separation procedure. The 48Ti :"Ti ratio clearly identifies the effect of residual Ca on the process by virtue of the 48Ca/48Ti isobaric overlap. Like 65Cu 49Ti can be affected by a sulfur interference 33S160 but since 33S has a natural abundance of only 0.75% all 33S based interferences will be low. Furthermore since the Table 4 pure saline and matrix separated water samples Isotope ratio measurements for 63Cu 65Cu and 48Ti 4"Ti for Sample description 63Cu 65Cu ratio* 48Ti 49Ti ratio* value 300 pl injected ( 10 ng ml- ') Natural ratio accepted 2.24 13.42 Sea-water (10 ng mi-') 5.55 f 3.07 64.04 & 5.13 0.5 mol dm-3 HNO 2.22 f 0.10 13.45k0.57 injected Matrix separation from 2.21 f 0.05 13.42 f 0.88 spiked pure water ( 5 ng m1-l) spiked sea-water ( 5 ng mi-') Matrix separation from 2.17 f 0.12 13.45 & 0.47 * Values quoted with a range of 2 s (n = 5 ) except natural ratios.Table 5 Comparison between spiked pure and sea-water calibrations sulfate present in the sea-water samples is not retained by the column this source of interference should be negligible. Table 4 illustrates that residual matrix does not affect the isotope ratio measurement for 63Cu 65Cu or 48Ti 49Ti thereby illustrating that the matrix separation procedure is effective with respect to both Na and Ca removal.The results presented for an injected artificial sea-water sample (Table 4) clearly show a severe increase for both the apparent 63Cu 65Cu and 48Ti 49Ti ratios illustrating that FI although effective in reducing block- age problems with high salt samples cannot remove the associated polyatomic interferences. Matrix separation is there- fore essential if accurate results are to be obtained. Calibration and Analysis of Certified Reference Materials Using ICP-MS linear calibrations were obtained over the range 0 to 10 ng ml-' for analytes in both spiked pure water and spiked synthetic sea water matrices as described in Table 5. The two calibration sets compared well therefore validat- ing the use of simple pure water calibration solutions for quantifying analytes in more complex matrices.The matrix separation procedure was validated by analysis of the two certified reference materials SLEW-1 and CASS-2. The analytes were quantified by external calibration against acidified multi-element (Mn Cu Zn Ni Co Cd) pure water standards processed through the manifold. Three repeat analy- ses were made at each concentration and for the reference materials. The calibrations generally showed good linearity with least squares regression coefficients of 0.997 to 0.999 being obtained across the concentration ranges 0-20 ng ml-' (Mn) 0-4 ng ml-' (Cu Ni Zn) and 0-0.1 ng ml-' (Cd Co). Precision (measured as RSD) for the selected analytes were in the range 0.5-5.5 O/O. Results for the certified reference materials analysis are given in Table 6.For both materials good agreement between the found and certified values was obtained for all the elements measured except for Mn. A consistently low result was obtained for this element in both SLEW-1 and CASS-2. This was interpreted to be a consequence of the low affinity of PROSEP Chelating-1 for Mn under the matrix separation conditions used (see Figs. 3 and 4). Direct analysis Table 6 Analysis results for the certified reference materials SLEW-1 and CASS-2 SLEW-1 CASS-2 Element Found* Certified* Mn 7.97k0.72 13.1 f0.8 Co 0.040 f 0.003 0.046 f 0.007 Ni 0.75 1 f 0.074 0.743 f 0.078 c u 1.72 0.30 1.76 f 0.09 Zn 0.74f0.03 0.8650.15 Cd 0.01 5 f 0.002 0.01 8 2 0.003 Found* Certified* 1.84 Ifr 0.07 1.99 k 0.15 0.028 & 0.001 0.025 f 0.006 0.264 & 0.006 0.298 f 0.036 0.704 f 0.10 0.675 k 0.039 1.95 f 0.05 1.97 k0.12 0.017f0.002 0.019f0.004 * Concentrations in ng ml-'.Uncertainties expressed as 2 s of the instrument response to each analyte (95% confidence limit n= 3). Culibrations front spiked pure water - Parameter RSD (YO) at 5 ngml-' ( n = 5 ) Correlation coefficient r Sensitivity ( counts ng-') Detection limit/ng ml- ' ( 5 s n = 5 ) Calibrations from synthetic sea-water- Parameter RSD (YO) at 5 ngml-' (n=5) Correlation coefficient r Sensitivity ( counts ng-' ml) Detection limit/ng ml - 5 s n = 5 ) 55Mn 4.6 0.9997 1.28 0.10 55Mn 3.2 0.9987 1.12 0.56 5 9 c ~ 4.0 0.9998 4.57 0.02 59c~ 2.4 0.9997 5.14 0.0 1 63cu 2.4 0.9990 2.3 1 0.05 63cu 2.3 0.9999 2.58 0.09 64Zn 3.3 0.9989 1.27 0.20 64Zn 1.1 0.9956 1.35 0.44 '14Cd 2.2 0.9998 1.75 0.09 ' 14Cd 2.0 0.9996 1.77 0.07 .Journal of Analytical Atomic Spectrometry October 1996 Vol.11 91 1of the reference materials for comparison with the matrix separation procedure could not be performed because this led to cone and injector blockage and signal suppression in the plasma. Injection of saline samples without prior matrix separa- tion circumvented blockage problems but significant polya- tomic interferences and signal suppression remained. These problems coupled with the low analyte concentrations present made direct injection impractical for the reference material analysis. CONCLUSIONS Batch capacity measurements for a range of elements showed that PROSEP Chelating-1 was comparable and in some cases superior to CPG-8-hydroxyquinoline materials but lower than polymeric based chelators due to the inflexibility of the CPG support.However this rigidity combined with the good chemical stability physical robustness rapid surface reactivity and wide elemental application of PROSEP Chelating- 1 made the material a highly effective reagent for the matrix separation procedure undertaken in this study. A second paper discussing the effects of elemental and humic acid interferences as well as the application of the system to real river water and effluent samples is currently in preparation. S. M. N would like to thank the EPSRC and VG Elemental for their provision of funding and equipment for the project Peter Clarke of Bioprocessing Ltd. for supplying the PROSEP Chelating-1 material and Sarah Dolman for producing Fig.1. REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Beauchemin D. TrAC Trends Anal. Chem. (Pers. Ed). 1991 10 71. McLaren J. W. At Spectrosc. 1993 14 191. Houk R. S. and Olivares J. A. Anal. Chem. 1986 58 20. Reed N. M. Cairns R. O. Hutton R. C. and Takaku Y. J. Anal. At. Spectrom. 1994 9 881. Tanner S. D. Paul M. Beres S. A. and Denoyer E. R. At. Spectrosc. 1995 16 16. Tanner S. D. J. Anal. At. Spectrom. 1995 10 905. Olsen. S. Pessenda L. C. R. Ruzicka J. and Hansen E. H. Analyst 1983 108 905. Hartenstein S. D. Ruzicka J. and Christian G. D. Anal. Chem. 1985 57 21. Bloxham M. J. Hill S. J. and Worsfold P. J. J. Anal. At. Spectrom. 1994 9 935. Taylor D. B. Kingston H. M. Nogay D. J. Koller D. and Hutton R. C. J. Anal. At. Spectrom. 1996 11 187. Hill J. M. J. Chromatogr. 1973 76 455. Malamas F. Bengtsson M. and Johansson G. Anal. Chim. Acta 1984 160 1. Fang Z. and Welz B. J. Anal. At. Spectrom. 1989 4 543. Nakashima S. Sturgeon R. E. Willie S. N. and Berman S. S. Fresenius’ 2. Anal. Chem. 1988 330 592. Beauchemin D. and Berman S. S. Anal. Chem. 1989,61 1857. Fang Z. in Flow Injection Separation and Preconcentration VCH Weinheim 1993 Ch. 4. Shriver D. F. Atkins P. W. and Langford C. H. in Inorganic Chemistry Oxford University Press 1990 Ch. 7 p. 222. Bio-Rad Laboratories Chelex-100 Instruction Manual 1996. Nelms S. M. Greenway G. M. and Hutton R. C. J. Anal. Atom. Spectrom. 1995 10 929. Paper 61041 01 I Received June 11 1996 Accepted August 13 1996 91 2 Journal of Analytical Atomic Spectrometry October 1996 Vol. 11

ISSN:0267-9477    

DOI:10.1039/JA9961100907

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Determination of Physiological Platinum Levels in Human Urine Using Magnetic Sector Field Inductively Coupled Plasma Mass Spectrometry in Combination With Ultraviolet Photolysis Journal of Analytical Atomic Spectrometry JUTTA BEGEROW MARTINA TURFELD AND LOTHAR DUNEMANN Medizinisches Institut fur Umwelthygiene Department of Analytical Chemistry Auf 'm Hennekamp 50 0-40225 Dusseldorf Germany An extremely sensitive and reliable procedure for the determination of physiological (normal ) Pt levels in human urine is described based on UV photolysis of the sample followed by the determination of Pt with magnetic sector field ICP-MS. Owing to the low blank values which are a consequence of the minimal reagent addition required UV photolysis was used to decompose the organic matrix components.Magnetic sector field ICP-MS operated in the low resolution mode afforded detection limits that were 100 times lower than those obtained in the high resolution mode or with conventional quadrupole ICP-MS and was found to be advantageous for the ultratrace determination of non-interfered isotopes. The detection limit in urine samples was 0.24 ng I-' using standard nickel cones. The use of a high performance nickel skimmer cone did not result in an improvement in the detection limit because the analyte and background signals were enhanced to a similar extent. The urinary Pt levels in 16 non-exposed persons ranged between 0.48 and 7.65 ng I-' (arithmetic mean 1.72 ng I-'). Keywords Magnetic sector field inductively coupled plasrrra mass spectrometry; ultraviolet photolysis; platinum; urine With the introduction of Pt-containing automobile exhaust catalysts and anti-cancer drugs the widespread release of Pt into the environment has increased enormously.Belonging to the rarest elements in the Earth's crust Pt has long been denied as an environmental pollutant. Since investigations have shown that it has already accumulated in roadside dust,' airborne dust,2 soil3 and correlating with traffic density and distance from the road there is a growing concern about the possible effects of Pt on humans. The interest in analytical methods suitable for the determination of trace amounts of Pt in biological and environmental matrices has thus rapidly increased. An analytical procedure suitable for this application was first presented by Hoppstock et a/.' using high-pressure acid digestion followed by adsorptive voltammetry.By applying this procedure Messerschmidt et aL6 were able to determine baseline Pt levels in blood and urine. According to these workers,6 normal Pt values in urine ranged between 0.5 and 14.3 ng 1-'; the limit of detection was 0.2 ng 1-'. Because of their insufficient sensitivity other elemental detec- tion methods such as AAS ICP-AES and quadrupole (Q) ICP-MS do not allow the determination of environmental Pt levels in biological matrices without extensive enrichment. Recently a powerful analytical method has been presented offering the possibility of rapid multi-element analysis in com- bination with excellent detection These studies used a new type of magnetic sector field ICP-MS instrument (ELEMENT; Finnigan MAT Bremen Germany) permitting operation in three different resolution modes (m/Am z 300,3000 and 7500 10% valley definition). Irrespective of the possibility to eliminate interferences instrumental detection limits of non- interfered isotopes in the low resolution mode are improved by about two orders of magnitude compared with conventional Q-ICP-MS.7.8 This is mainly a result of the extremely low instrumental background level of < 1 count s-'.Thus the practical detection limits in real matrices are generally not affected by the instrumental background but are mainly limited by the blank concentrations of the reagents memory effects or spectral interferences which become more important with decreasing analyte concentration especially in complex matrices such as blood and urine.Conventional digestion methods such as heating with large amounts of acids in open or closed systems are inconvenient for this application because the background of the acids even at the highest commercial degree of purity and after additional sub-boiling distillation are unacceptably high. Additionally these procedures lead to high acid concentrations in the digestion solutions which are not tolerated by ICP-MS and thus have to be diluted prior to analysis. UV photolysis seems to be a promising alternative using hydroxyl radicals as the oxidizing agent. In principle the mineralization takes place without addition of oxidizing agent but in practice it is useful to add minimal amounts of acid and hydrogen peroxide (up to 1%) to enhance the efficiency and oxidation rate.Owing to the small amounts of reagent required UV digestion results in very low blank values. The major drawback of this digestion method is that its application is limited to fairly simple matrices with a relatively low content of organic matrix such as natural and waste water beverages urine and According to Kroder et al.,13 the carbon content of the sample solutions should not exceed 100 mg 1-'. This paper presents the results of the determination of Pt in human urine at physiological concentrations using UV pho- tolysis and magnetic sector field ICP-MS in the low resolution mode. The relevance and severity of blank values from reagents and spectral interferences in the determination of Pt in urine were investigated. EXPERIMENTAL Instrumentation Magnetic sector field ICP-MS was performed with the ELEMENT instrument (Finnigan MAT).Details of the instru- mental operating conditions are given in Table 1. The instru- ment was operated in an air-conditioned laboratory ( 18-22 "C) equipped with a filter to remove dust particles. Pt was measured at masses 194 195 and 196. Reagents and Standard Solutions In order to reduce the risk of contamination all work was performed on a clean bench. Before use all materials and chemicals were randomly checked for contamination. Journal of Analytical Atomic Spectrometry October 1996 Vol. 1 1 (91 3-91 6) 91 3Table 1 measurements Instrumental conditions for magnetic sector field ICP-MS Instrument Resolution Rf power Pump speed Scan type Integration time Torch Nebulizer Spray chamber Cones Intermediate gas Outer gas Nebulizer gas Wash time Masses Scan time Passes Runs Total scan time Total samples Sample time ELEMENT (Finnigan MAT) m/ Am = 3 00 1.30 kW 1.4 ml min-' Magnetic jump with electric scan 50 ms Fassel torch Meinhardt TR-30-A3 Scott type ('double-pass') at 20 "C Ni (standard or high-performance) Argon 0.76 1 min-' Argon 13.3 1 min-' 0.63 1 min-' 12 min 194 195 196 8 s 5 2 5.08 s 167 0.025 s Polyethylene vials were cleaned with HNO (1 +2 50"C 30 min) rinsed with ultrapure water and dried at 50 "C.Ultrapure HNO from two different manufacturers was checked for Pt background levels Ultrex I1 (70%; Baker GroB-Gerau Germany) was used without further purification; Suprapur ( 6 5 %; Merck Darmstadt Germany) was further purified by sub-boiling distillation in a quartz device.Formation of HfO' interferences (as shown in Fig. 1) was measured using a single-element standard solution in 0.5% HNO containing 10 mg I-' Hf (prepared from a single- element standard solution for AAS; Aldrich Heidenheim Germany). Sample Collection and Storage Morning urine samples from 16 healthy volunteers with no known exposure to Pt were collected in acid-washed poly (propylene) bottles. For stabilization purposes they were acidi- fied with concentrated HNO (Ultrex 11; 1 ml per 100 ml of urine) and stored at - 20 "C until analysis. Digestion UV photolysis was carried out with a UV-1000 digester (Hans Kurner Analysentechnik Rosenheim Germany) using a 1000 W medium-pressure Hg lamp.Before being divided into aliquots the sediment of the urine samples was distributed as homogeneously as possible by rigorous shaking to obtain a representative portion of the specimen. Filtration of the urine samples must be avoided because the sediment may include considerable amounts of analyte. Aliquots (20 ml) of acidified urine were mixed with 500 p1 of H202 (Suprapur; Merck) and digested for 10 min at a water cooling flow of 0.9 ml min-'. A second 500 p1 portion of H202 was then added and photolysis was continued for a further 35 min resulting in a clear colourless solution. Calibration Calibration was performed by the standard additions pro- cedure by adding dilute single-element standard solutions (for AAS; Aldrich) in 0.5% HNO (Ultrex 11) containing 5 10 and 50 ng I-' Pt which were prepared freshly every day.Aliquots (500 pl) of these standard solutions were added to 500 pl of digested sample solution and diluted with 2 ml of ultrapure 91 4 Journal of Analytical Atomic Spectrometry October 1996 water. The linearity of the calibration procedure was checked in the concentration range between 0.5 and 200ng 1-'. In routine use standards lower than 5 ng 1-' were not used for standard additions because the uncertainty of the calibra- tion process increases when the limit of determination is approached. No internal standard was used for calibration because in the lowerng 1-l range it is not possible to find an element that can reflect the behaviour of the analyte (e.g. its ionization energy and monoxide bond strength) and which is at the same time not present in the sample or interfered with by blanks and spectral interferences. lo3Rh for example is in this context unsuitable as an internal standard because its determination in the ng 1-' range is interfered with by spectral interferences caused by 206Pb2+ 63C~40Ar+ and s7Sr'60+ which have been described in detail in a previous paper.7 These spectral inter- ferences resulted in a Rh blank level of about 30 ng 1-' in blood samples.Detection Limit and Reliability Criteria The detection limit was calculated as three times the standard deviation of replicate measurements (n = 10) of blanks contain- ing the same concentrations of HNO and H,02 as the digested urine samples. All analyses were carried out under internal quality control conditions.The within-series imprecision was calculated from a urine sample (geometric mean =0.72 ng 1-' Pt) that was analysed ten times. For internal quality control a control sample with a known Pt concentration was analysed within each analytical series. As a control sample with a known or certified Pt concentration is not commercially available it was prepared in the laboratory by pooling acidified urine samples and stored in portions in a refrigerator at -18°C. External quality control was achieved by participation in an interlaboratory comparison programme (Deutsche Gesellschaft fur Arbeits- und Umweltmedizin Erlangen Germany). The designated Pt concentration of the circulating urine samples was 22.72 ng 1-'; our result was 23.05 ng 1-'.RESULTS AND DISCUSSION By using magnetic sector field ICP-MS in the low resolution mode in combination with UV photolysis as the sample preparation step Pt was detectable in the urine samples of all 16 volunteers. Urinary Pt levels ranged between 0.48 and 7.65 ng 1-' with an arithmetric mean of 1.72ng 1-'. The within-series imprecision of a urine sample (geometric mean 72.3 ng 1-' Pt) that was digested and analysed ten times was 17.7%. Our results are in complete accordance with those of Messerschmidt et ~ l . ~ who determined physiological Pt levels in the urine samples of 14 persons by adsorptive voltammetry. These workers reported Pt concentrations between 0.5 and 14.3 ng 1-' with a geometric mean of 1.1 ng 1-'. The detection limit of our procedure was 0.24ng 1-' using a standard skimmer cone made of nickel.A so-called high-performance (HP) nickel skimmer cone which was reported to enhance the sensitivity by a factor of 2-3,14 was also tested. However no improvement in the detection limit was achieved because the analyte and background signals were increased to a similar extent. With the HP skimmer cone the detection limit for Pt was 0.27 ng I-'. The detection limit obtained here with UV photolysis- magnetic sector field ICP-MS is comparable to that reported for the extremely sensitive voltammetric procedure described in ref. 6 viz. 0.2 ng 1-'. In comparison with magnetic sector field ICP-MS the voltammetric procedure is more susceptible to interferences and more labour-intensive. The voltammetric determination of Pt is severely interfered with by residual carbon surfactants and by HNO,.' In order to eliminate the VOl.11organic matrix a complete mineralization of all the organic sample components is required which was achieved6 by high- pressure ashing with a mixture of concentrated mineral acids including HNO as oxidizing agent. Prior to the determination step the excess of HNO has to be eliminated by heating in open vessels with concentrated H2S04 and HC1,6 a procedure which is prone to interferences caused by contamination or elemental losses. According to Messerschmidt et ul.," the detection limit of their procedure is also limited by blank values from reagents vessels etc. In contrast ICP-MS does not require the complete removal of the organic matrix; in fact the direct analysis of diluted urine samples without any sample pre-treatment has been described.15-17 Mulligan et ~ 1 .' ~ diluted the urine samples 10-fold with 0.28 mol 1-' HNO while Schramel et ~ 1 . ' ~ performed a 1+2 dilution. In our opinion UV photolysis prior to ICP-MS measurements is preferable to direct analysis if solution nebulization is applied for sample introduction. The removal of the organic matrix leads to a reduction of non-spectral interferences such as memory effects or blocking of the sampling cone. The use of UV photolysis for the digestion of urine samples was also employed by Ensslin et al.," who determined urinary Pt in occupationally exposed hospital personnel. They irradiated a mixture of 1 ml of urine 100 pI of concentrated H2S0 and 200 pl of H20z for 2 h.For creatinine contents of > 1.5 g 1-' they had to use smaller urine volumes to obtain complete mineralization. For ICP-MS measurements it is possible to irradiate a mixture of 20 ml of urine 0.7% HNO and 1 in1 of H202 because complete mineralization is not necessary. HNO was chosen because it is generally regarded as the best acidic medium for ICP-MS since the constituent elements (H N 0) are already present in the air entrained by the plasma. 4s a consequence the formation of polyatomic interferences is not increased by HNO addition." Additionally almost all elements form easily soluble nitrates preventing precipitation of salts of low solubility in the sample solution or the sample introduction system resulting in analyte losses memory etrects and blockage of the nebulizer and cones.The detection limit of our procedure is a factor of 4 lower than that reported by Schramel et who determined Pt directly in diluted urine samples (1 +2) by applying ETV-Q-ICP-MS. The proposed procedure is also about two orders of magnitude more sensitive than Q-ICP-MS with conventional pneumatic nebulization which has been used by other ~ o r k e r s . ~ ' ~ ' ~ The lower detection limits of ETV sample introduction over pneumatic nebulization are a result of the higher transport efficiency into the plasma and the possibility to remove interfering matrix component^.'^ According to Schramel et a1.,16 the application of ETV for sample introduc- tion instead of pneumatic nebulization resulted in a 20-fold improvement in the detection limit for Pt determination in urine.The disadvantages of ETV are the transient nature of the signals obtained and the fact that the analytes require different optimum furnace conditions both of which restrict the ability to perform multi-element determinations. Compared with the detection limit for ETV-ICP-AES given by Alimonti et our procedure is better by a factor i)f at least 1000. The detection limit of the procedure described here is lower by a factor of more than 100 than that obtained by ETXAS even after a 25-fold enrichment using solvent extraction8 21 A survey of the detection limits for Pt in urine obtained with different analytical procedures is given in Table 2. Our results indicate that the determination of physiological Pt levels in urine is not hampered by spectral interference$.As illustrated in Fig. 2 the isotope pattern of 194Pt I9'Pt and 196Pt obtained in urine samples is in conformity with the natural pattern. Although the formation of HfO+ interfering at rn/z=194 195 and 196 can be demonstrated by measuring 2.2e+008 1.8e+008 1.4e+008 1 e+008 6e+008 2e+007 0 - - 8000 - - 6000 - - 4000 - - 2000 - +n 176 177 178 179 I80 181 . " - 50 (6) 80HP60" .4e+006 - 40 30 20 10 0 193 194 195 196 197 Mass Fig. I LR mode) Spectral interferences by HfO' (10 mg 1-' Hf in 0.5% HNO,; Table 2 Determination of Pt in urine comparison of detection limits (DLs) obtained with different analytical procedures Method UV photolysis-HR-ICP-MS (LR mode standard Ni cones) UV photolysis-HR-ICP-MS (LR mode H P Ni cones) Dilution-Q-ICP-MS Dilution-Q-ICP-MS Dilution-ETV-Q-ICP-MS High-pressure digestion-adsorptive UV photolysis-adsorptive voltammetry Solvent extraction-ETAAS Dilution-ETV-ICP- AES vol tammetry DL/ ng l-' 0.24 0.27 60 20 1 .o 0.2 1.8 70 500 Ref.This work This work 15 16 16 6 11 8 20 50 Dl DIP1 195Pt I 30 s- 20 10 0 natural Pt abundance urine sample Fig. 2 Determination of physiological Pt levels in urine by magnetic sector field ICP-MS at LR mode-isotope ratios. The urine sample contained 28.7 ng 1-' Pt (calculated as lg5Pt) Jclurnul of Analyticul Atomic Spectrometry October 1996 Vol. 11 915I I 100 400 4501 Mass Fig. 3 Determination of physiological Pt levels in urine-typical mass spectrum. The urine sample contained 7.7 ng I-' Pt (calculated as lg5Pt) Hf standard solutions this interference is in practice of no relevance because of the very low Hf concentrations in urine producing a signal of up to 100 counts s-' at masses 178 179 and 180.The corresponding mass spectrum of a 10 mg 1-' Hf standard solution illustrating the formation of HfO + is given in Fig. 1; the average formation rate (HfO+/Hf+) under stan- dard instrumental multi-element conditions was 0.4% (range O.2-O.6%). Owing to the correct Pt isotope ratios obtained in all urine samples it is concluded that there are no significant spectral interferences at masses 194 195 and 196 (Fig. 3). The determination of Pt at these extremely low concen- trations is mainly affected by blank values originating from reagents such as HN03 and H202.The Pt blank values found in HNO [Ultrex I1 (Baker) and Suprapur (Merck)] and H202 [ p r o analysi and Suprapur (Merck)] related to a HNO concentration of 5% and a H202 concentration of 1.5% are given in Table 3. The given blank values consist of the blank values of the reagent and of the ultrapure water used for dilution and of the blank of the sample introduction system. The results show that Pt blank values originating from HN03 and H,02 are of the same order of magnitude as the lower physiological Pt levels in urine. After UV photolysis blanks containing 0.7% HN03 and 1.5% H202 had a mean total Pt concentration of 0.38 ng 1-' (standard deviation 0.075 ng 1-'). These results show that reagent addition should be restricted to the required minimum. CONCLUSIONS The results presented here clearly indicate the superiority of magnetic sector field ICP-MS for the determination of urinary Pt levels in both unexposed and exposed persons.For elements with non-interfered isotopes such as Pt the full sensitivity of the instrument can be used resulting in detection limits that are comparable to those of adsorptive voltammetry. In contrast to other precious metals such as Rh and Pd,7 the determination of Pt in urine is relatively unaffected by spectral interferences. The practical detection limits are for Pt not affected by the instrumental background but are mainly limited by the blank concentrations of the reagents and Table 3 Mean blank values (ng I-') in ultrapure HNO and H202 solution (LR mode) Aqueous solution 5% HNO [ Ultrex IT (Baker)] 5% HNO [ Suprapur (Merck)] 1.5% H20 [pro analysi (Merck)] 1.5% H202 [ Suprapur (Merck)] Pt/ng I-' (n= 10) 0.15 0.13 0.28 0.18 memory effects.It is expected that detection limits can be further improved if the potential of the ELEMENT instrument is fully utilized. In this context it is necessary to improve the analytical technique to reduce blanks and memory effects. The purity of commercially available reagents should also be improved. UV photolysis was found to be advantageous for the diges- tion of urine. With solution nebulization for sample introduc- tion UV photolysis is preferable to direct urine analysis because the removal of the organic matrix leads to a reduction of interferences such as memory effects and less blockage of the sample introduction system. In contrast to mineral acid digestion techniques or direct urine analysis an extensive dilution of the irradiated samples is not necessary.In order to correct for non-spectral interferences caused by high mat- rix concentrations the standard additions procedure is recommended. The described procedure is also applicable to the simul- taneous determination of other precious metals such as Pd Ag and Au and other environmentally relevant metals such as Cd Pb T1 and Hg." For the monoisotopic element Rh the application is so far restricted to elevated urine levels because its determination is interfered with by spectral interferences which cannot be separated at m/Am 2 7500.7*8 The authors thank Hans Kurner Analysentechnik (Rosenheim Germany) for temporary disposal of the UV digester C.Kranich for technical assistance and A. Landwehr foreign- language correspondent for linguistic revision of the manuscript. REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 Hodge V. F. and Stallard M. O. Environ. Sci. Technol. 1986 20 1058. Schierl R. and Fruhmann G. Sci. Total Environ. 1996 182 21. Zereini F. Zientek C. and Urban H. Z. Umweltchem. Okotox. 1993 5 130. Waber M. Laschka D. and Peichl L. Z. Umweltchem. Okotox. 1996 8 1. Hoppstock K. Alt F. Cammann K. and Weber G. Fresenius' Z. Anal. Chem. 1989 335 813. Messerschmidt J. Alt F. Tolg G. Angerer J. and Schaller K.-H. Fresenius' J. Anal. Chem. 1992 343 391. Begerow J. and Dunemann L. J. Anal. At. Specrrom. 1996 11 303. Begerow J. Dissertation Clausthal-Zellerfeld 1995. Moens L. Vanhaecke F. Riondata J. and Dams R. J. Anal. At. Spectrom. 1995 10 569. Moens L. Verrept P. Dams R. Greb U. Jung G. and Laser B. J. Anal. At. Spectrom. 1994 9 1075. Ensslin A. S. Pethran A. Schierl R. and Fruhmann G. Int. Arch. Occup. Environ. Health 1994 65 339. Saur D. and Spahn E. GITFachz. Lab. 1994 2 103. Kroder H. Bauer K.-H. and Saur D. Vom Wasser 1994,82,269. Hamester M. Greb U. and Rottmann L. poster presented at the European Winter Conference on Plasma Spectrochemistry Cambridge 1995. Mulligan K. J. Davidson T. M. and Caruso J. A. J. Anal. At. Spectrom. 1990 5 301. Schramel P. Wendler I. and Lustig S. Fresenius' J . Anal. Chem. 1995 353 115. Vanhoe H. J. Trace Elem. Electrolytes Heulth Dis. 1993 7 131. Jarvis I. in Handbook of Inductively Coupled Plasma Mass Spectrometry eds. Jarvis K.E. Gray A.L. and Houk R.S. Blackie Glasgow 1992 pp. 172-224. Carey J. M. Byrdy F. A. and Caruso J. A. J. Chromatogr. Sci. 1993 31 330. Alimonti A. Petrucci F. Dominici C. and Caroli S. J. Trace Elem. Electrolytes Health Dis. 1987 1 79. Begerow J. Turfeld M. and Dunemann L. Anal. Chim. Acta submitted for publication. Paper 6/03870K Received June 4 1996 Accepted July 10 1996 91 6 Journal of Analytical Atomic Spectrometry October 1996 Vol. 11

ISSN:0267-9477    

DOI:10.1039/JA9961100913

出版商:RSC    

年代:1996

数据来源: RSC