摘要:

The HP 4500 Benchtop ICP-MS - a Leap Forward. 7- New Leadership in ICP-MS Technology The 111’ 4500 I(’P-MS is riot a redesign of existing I(’I’-MS iiwtrunients. It is a leal) forward. New t cc*hnology has cnabled us to niiiiiat urize niany cmiiponents while hardwarr. and soft wart’ titlsigri inno- vat ions lct us owr(~)nie t hc limitations of c a r i r w i i 1 iiist niiiwnts. It offtlrs iric*rcasd sensitivity (down to suh-ppt lcvcl) a greater dynamic rangc ( 8 orders of rnagiiitude) aid ox(~llcrit signal st ability. b I Its autotuning capabilities - together with the user-friendly software - save time and make the HP 4500 the ideal ICP-MS system for routine measure- ments. The Shield Tomh interface virtually cliniinates polyatomic interferences formed in the plasma enabhg ppt-level quantitation of ’difficult’ elements (e.g.Ca K Fe). The H.ypcr.bolic Qundmpole Rods give niaxiniumtramnlission and peak shape- resulting in excellent sensitivity and high precision isotope measurements. The Quad RE’ Generotor - operating at a high frequency (3.0 Mhz) - gives the HP 4500 an excellent abundance sensitivity. A complete set of fully automated accessories ranging from lascr ablation to the micro concentric nebuliser is available with the HP 4500. The HP 4500 has been designed for maximum reliability. Should a problem occur however it can be rapidly traced and corrected remotely via modem connection to HP’s top- ranked service organisat ion. For details contact Hewlett-Packard P.O. Box 533 A 2130 AM Hoofddorp /p&\ The Netherlands. REGISTERED* HEW LETT@ PAC KAR D c1996 Winter Conference on Plasm a Spe ct roch e m is t ry Fort Lauderdale Florida January 8 = 7 3 7 996 The 1996 Winter Conference on Plasma Spectrochemistry ninth in a series of biennial meetings sponsored by the ICP lnfonnafion Newsletter features developments in plasma spectrochemical analysis by inductively coupled plasma (ICP) dc plasma (DCP) microwave plasma (MIP) and glow discharge (GDL HCL) sources.The meeting will be held Monday January 8 through Saturday January 13 1996 at the Bonaventure World Conference Center in Fort Lauderdale Florida. Continuing education short courses at introductory and advanced levels will be offered Friday through Sunday January 5 - 7. Spectroscopic instrumentation and accessories will be shown during a three-day exhibition.Objectives and Program The continued growth in popularity of plasma sources for atomization and excitation in atomic spectroscopy and ionization in mass spectrometry and the need to discuss recent developments of these discharges in spectrochemical analysis stimulated the organization of this meeting. The Conference will bring together international scientists experienced in applications instrumentation and theory in an informal setting to examine recent progress in the field. Approximately 500 participants from 25 countries are expected to attend. Approximately 300 papers describing applications fundamentals and instrumental developments with plasma sources are expected to be presented in lecture and poster sessions by more than 200 authors.Symposia organized and chaired by recognized experts will include the following topics 1) Sample introduction and transport phenomena 2) Flow injection spectrochemical analysis 3) Elemental speciation with plasma/chromatographic techniques 4) Plasma instrumentation including chemometrics expert systems on-line analysis software and remote-system automation 5) Sample preparation treatment and automation 6) Excitation mechanisms and plasma phenomena 7) Spectroscopic standards and reference materials 8) Plasma source mass spectrometry 9) Glow discharge atomic and mass spectrometry 10) Applications of stable isotope analyses and 1 1) Laser-assisted plasma spectrometry. Six plenary and 18 invited lectures will highlight advances in these areas. Afternoon poster sessions will feature applications automation and new instrumentation.Five panel discussions will address critical development areas in sample introduction instrumentation elemental speciation plasma source mass spectrometry and novel software and hardware directions. Plenary invited and submitted papers will be published in Fall 1996 after peer review as the official Conference proceedings. Schedule of Activities Preliminary Title and 50-Word Abstract Due for Contributed Papers Exhibitor Booth Reservation and Pre-Registration Deadline Conference Pre-Registration October 13 1995 Hotel Pre-Reservation October 13,1995 Late Pre-Registration Deadline December 8,1995 1996 Winter Conference Short Courses January 5 - 7,1996 1 996 Winter Conference on Plasma Spectrochemistry January 8 - 13,1996 July 3 1995 September 11,1995 Further Information For further information return this form to 1996 Winter Conference on Plasma Spectrochemistry %/CP information Newsletter Department of Chemi8try. Lederk GRC Towers University of Massachusetts Box 34510 Amherst MA 01003-4510 USA. AlTN Dr. Ramon Barnes Conference Chairman Telephone (41 311 545-2294 Telefax (41 3) 545-4490. 3 r 0 Send further information. 0 I plan to attend accompanied by 0 I plan to present a paper (D oral 0 poster 0 computer poster). Title 1 9 s w w m CONFERENCE ON PLASMA sPEcrRoctiEMismy Name Organization Address City Telephone Title State/Couritry Telefax Date ZIP/Postal Code EMAlL

ISSN:0267-9477    

DOI:10.1039/JA99510FP018

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

Journal of Analytical Atomic Spectrometry (Including Atomic Spectrometry Updates) JAAS Editorial Board Chairman B. L. Sharp (Loughborough UK) A. T. Ellis (Abingdon UK) J. M. Gordon (Cambridge UK) S. J. Haswell (Hull UK) S. J. Hill (Plymouth UK) R. C. Hutton (Winsford UK) D. Littlejohn (Glasgow UK) J. Marshall (Middlesbrough UK) A. Sanz-Medel (Oviedo Spain) P. D. P. Taylor (Gee/ Belgium) JAAS Advisory Board F. C. Adams (Antwerp Belgium) R. M. Barnes (Amherst MA USA) L. Bezur (Budapest Hungary) M. W. Blades (Vancouver Canada) R. F. Browner (Atlanta GA USA) J. L. Burguera (Merida Venezuela) S. Caroli (Rome Italy) J. A. Caruso (Cincinnati OH USA) H. M. Crews (Norwich UK) A. J. Curtius (Florianopolis Brazil) J. B. Dawson (Leeds UK) M. T. C. de Loos-Vollebregt (Delft The Netherlands) 0.F. X. Donard (Talence France) L. Ebdon (Plymouth UK) M. S. Epstein (Gaithersburg MD USA) Fang Zhao-lun (Shenyang China) W. Frech (UmeA Sweden) A. K. Gilmutdinov (herlingen Germany) G. M. Hieftje (Bloomington IN USA) R. S. Houk (Ames OH USA) R. Klockenkamper (Dortmund Germany) 6. V. L'vov (St. Petersburg Russia) R. K. Marcus (Clemson SC USA) J. M. Mermet (Villeurbanne France) T. Nakahara (Osaka Japan) Ni Zhe-ming (Beuing China) J. W. Olesik (Columbus OH USA) N. Omenetto (Ispra Italy) C. J. Park (Taejon Korea) P. J. Potts (Milton Keynes UK) R. E. Sturgeon (Ottawa Canada) V. Sychra (Prague Czech Republic) P. Van Espen (Antwerp Belgium) R. Van Grjeken (Antwerp Belgium) 6. Welz (Uberlingen Germany) J. Armstrong (Edinburgh UK) *J. R. Bacon (Aberdeen UK) C.Barnard (Glasgow UK) R. M. Barnes (Amherst MA USA) S. Branch (High Wycombe UK) R. Bye (Oslo Norway) J. Carroll (Middlesbrough UK) M. R. Cave (Keyworth UK) S. Chenery (Keyworth UK) *J. M. Cook (Keyworth UK) "M. S. Cresser (Aberdeen UK) H. M. Crews (Nowich UK) J. S. Crighton (Sunbury-on-Thames UK *J. 6. Dawson (feeds UK) J. R. Dean (Newcastle upon Tyne UK) *E. H. Evans (Plymouth UK) J. Fazakas (Budapest Hungary) A. Fisher (Plymouth UK) *J. M. Gordon (Cambridge UK) D. J. Halls (Glasgow UK) *S. J. Hill (Plymouth UK) K. W. Jackson (Albany NY USA) R. Jowitt (Middlesbrough UK) K. Kitagawa (Nagoya Japan) J. Kubova (Bratislava Slovak Republic) Atomic Spectrometry Updates Editorial Board Chairman *A. T. Ellis (Abingdon UK) *J. Marshall (Middlesbrough UK) H. Matusiewicz (Poznan Poland) A.W. McMahon (Manchesler UK) J. M. Mermet (Villeurbanne France) R. G. Michel (Storrs CT USA) *D. L. Miles (Keyworth UK) T. Nakahara (Osaka Japan) Ni Zhe-ming (Beijing China) P. J. Potts (Milton Keynes UK) W. J. Price (Budleigh Salterton UK) C. J. Rademeyer (Pretoria South Africa) A. Sanz-Medel (Oviedo Spain) *B. L. Sharp (foughborough UK) I. L. Shuttler (Uberlingen Germany) S. T. Sparkes (Taunton UK) R. Stephens (Halifax Canada) J. Stupar (Ljubljana Slovenia) R. E. Sturgeon (Ottawa Canada) *A. Taylor (Guildford UK) G. C. Turk (Gaithersburg MD USA) J. F. Tyson (Amherst MA USA) P. Watkins (London UK) 6. Welz (Uberlingen Germany) J. Williams (Egham UK) J. 6. Willis (Victoria Australia) *Members of the ASU Executive Committee Editor JAAS Janice M. Gordon The Royal Society of Chemistry Thomas Graham House Science Park Milton Road Cambridge CB4 4WF UK. Telephone +44 (0) 1223 420066.Fax + 44 (0) 1223 420247. E-mail RSCl @RSC.ORG (Internet) Senior Assistant Editor Brenda Holliday Assistant Editor Ziva Whitelock Editorial Secretary Lesley Turney US Associate Editor JAAS Dr. J. M. Harnly US Department of Agriculture Beltsville Human Nutrition Research Center Beltsville MD 20705 USA. Telephone + 1 301 -504-8560 Asia-Pacific Associate Editor JAAS Prof. N. Furuta Department of Applied Chemistry Faculty of Science and Engineering Chuo University 1-1 3-27 Kasuga Bunkyo-ku Tokyo 112 Japan. Telephone 81 -3-381 7-1 906. Fax 81 -3-381 7-1 895. E-mail nfuruta@apchem.chern.chuo.u.ac.ip Advertisements Advertisement Department The Royal Society of Chemistry Burlington House Piccadilly London W1 V OBN UK.Telephone + 44 (0) 171 -287 3091. Fax + 44 (0) 171 -494 1 134. Information for Authors Full details of how to submit materials for publi- cation in JAAS are given in the Instructions to Authors in Issue 1. Separate copies are available on request. The Journal of Analytical Atomic Spectrometry (JAAS) is an international journal for the publi- cation of original research papers communi- cations and letters concerned with the development and analytical application of atomic spectrometric techniques. The journal is pub- lished twelve times a year including comprehen- sive reviews of specific topics of interest to practising atomic spectroscopists and incorpor- ates the literature reviews which were previously published in Annual Reports on Analytical Atomic Spectroscopy (ARAAS).Manuscripts intended for publication must describe original work related to atomic spectro- metric analysis. Papers on all aspects of the sub- ject will be accepted including fundamental studies novel instrument developments and prac- tical analytical applications. As well as AAS AES and AFS papers will be welcomed on atomic mass spectrometry X-ray fluorescence/emission spectrometry and secondary emission spec- trometry. Papers describing the measurement of molecular species where these relate to the characterization of sources normally used for the production of atoms or are concerned for example with indirect methods of analysis will also be acceptable for publication. Papers describing the development and applications of hybrid techniques (e.g.GC-coupled AAS and HPLC-ICP) will be particularly welcome. Manuscripts on other subjects of direct interest to atomic spectroscopists including sample prep- aration and dissolution and analyte pre-concen- tration procedures as well as the statistical interpretation and use of atomic spectrometric data will also be acceptable for publication. There is no page charge. The following types of papers will be considered. Full papers describing original work. Communications which must be on an urgent matter and be of obvious scientific importance. Communications receive priority and are usually published within 2-3 months of receipt. They are intended for brief descriptions of work that has progressed to a stage at which it is likely to be valuable to workers faced with similar problems.Reviews which must be a critical evaluation of the existing state of knowledge on a particular facet of analytical spectrometry. Every paper (except Communications) will be submitted to at least two referees by whose advice the Editorial Board of JAAS will be guided as to its acceptance or rejection. Papers that are accepted must not be published elsewhere except by permission. Submission of a manuscript will be regarded as an undertaking that the same material is not being considered for publication by another journal. Manuscripts (three copies typed in double spacing) should be sent to Janice M. Gordon Editor JAAS or Dr. J. M. Harnly US Associate Editor JAAS. All queries relating to the presentation and sub- mission of papers and any correspondence regarding accepted papers and proofs should be directed to the Editor or US Editor (addresses as above).Members of the JAAS Editorial Board (who may be contacted directly or via the Editorial Office) would welcome comments suggestions and advice on general policy matters concerning JAAS. Fifty reprints are supplied free of charge. Journal of Analytical Atomic Spectrometry (JAAS) (ISSN 0267-9477) is published monthly by The Royal Society of Chemistry Thomas Graham House Science Park Milton Road Cambridge C64 4WF UK. All orders accompanied with payment should be sent directly to The Royal Society of Chemistry Turpin Distribution Services Ltd. Blackhorse Road Letchworth Herts. SG6 1 HN UK Tel.+44 (0) 1462 672555; Telex 825372 Turpin G; Fax f44 (0) 1462 480947. Turpin Distribution Services Ltd. is wholly owned by The Royal Society of Chemistry. 1995 Annual subscription rate EEA €51 2.00 USA $941 50 Canada f538.00 (+ GST) Rest of World f538.00. Customers should make payments by cheque in sterling payable on a UK clearing bank or in US dollars payable on a US clearing bank. Air freight and mailing in the USA by Publications Expediting Inc. 200 Meacham Avenue Elmont NY 11003. USA Postmaster send address changes to Journal of Analytical Atomic Spectrometry (JAAS) Publications Expediting Inc. 200 Meacham Avenue Elmont NY 11 003. Postage paid at Jamaica NY 1 1 431. All other despatches outside the UK by Bulk Airmail within Europe Accelerated Surface Post outside Europe.PRINTED IN THE UK. @The Royal Society of Chemistry 1995. All rights reserved. No part of this publication may be reproduced stored in a retrieval system or transmitted in any form or by any means electronic mechanical photographic recording or otherwise without the prior permission of the publishers.Journal of Analytical Atomic Spectrometry JAAS Editorial Board Chairman B. L. Sharp (Loughborough UK) A. T. Ellis (Abingdon UK) J. M. Gordon (Cambridge UK) S. J. Haswell (Hull UK) S. J. Hill (Plymouth. UK) R. C. Hutton (Winsford UK D. Littlejohn (Glasgow UK) J. Marshall (Middlesbrough UK) A. Sanz-Medel (Oviedol Spain) P. D. P. Taylor (Geel Belgium) JAAS Advisory Board F. C. Adams (Antwerp. Belgium) R. M. Barnes (Amherst MA USA) L. Bezur (Budapest Hungary) M.W. Blades (Vancouver Canada) R. F. Browner (Atlanta GA USA) J. L. Burguera (Merida. Venezuela) S. Caroli (Rome. Italy) J. A. Caruso (Cincinnati OH USA) H. M. Crews (Norwich UK) A. J. Curtius (Florianopolis Brazil) J. B. Dawson (Leeds UK) M. T. C. de Loos-Vollebregt (Delft The Netherlands) 0. F. X. Donard (Talence France) L. Ebdon (Plymouth UK) M. S. Epstein (Gaithersburg MD USA) Fang Zhao-lun (Shenyang China) W. Frech (UmeB Sweden) A. K. Gilmutdinov (Uberlingen Germany) G. M. Hieftje (Bloomington IN USA) R. S. Houk (Ames OH USA) R. Klockenkamper (Dortmund Germany) B. V. L'vov (St. Petersburg Russia) R. K. Marcus (Clemson SC. USA) J. M. Mermet (Villeurbanne France) T. Nakahara (Osaka Japan) Ni Zhe-rning (Beijing China) J. W. Olesik (Columbus OH USA) N.Omenetto (lspra Italy) C. J. Park (Taejon Korea) P. J. Potts (Milton Keynes UK) R. E. Sturgeon (Ottawa Canada) V. Sychra (Prague Czech Republic) P. Van Espen (Antwerp Belgium) R. Van Grieken (Antwerp Belgium) B. Welz (Uberlingen Germany) Atomic Spectrometry Updates Editorial Board Chairman *A. T. Ellis (Abingdon UK) J. A. Armstrong (Edinburgh UK) *J. R. Bacon (Aberdeen UK) R. M. Barnes (Amherst. MA USA) S Branch (High Wycombe. UK) R. Bye (Oslo Norway) J. Carroll (Middlesbrough UK) M. R. Cave (Keyworth UK) S. R. N. Chenery (Keyworth UK) *J. M. Cook (Keyworth UK) *M. S. Cresser (Aberdeen. UK) H. M. Crews (Norwich. UK) J. S. Crighton (Sunbury-on-Thames UK) *J. 8. Dawson (Leeds UK) J. R. Dean (Newcastle upon Tyne UK) *E. H. Evans (Plymouth UK) J. Fazakas (Budapest Hungary) A.Fisher (Plymouth UK) L. M. Garden (Middlesbrough UK) *J. M. Gordon (Cambridge UK) D. J. Halls (Glasgow UK) *S. J. Hill (Plymouth UK) K. W. Jackson (Albany. NY USA) R. Jowitt (Middlesbrough. UK) K. Kitagawa (Nagoya Japan) J. Kubova (Bratislava Slovak Republic) *J. Marshall (Middlesbrough UK) H. Matusiewicz (Poznan F'oland) A. W. McMahon (Manchester UK) J. M. Mermet (Villeurbanne France) R. G. Michel (Storrs CT USA) *D. L. Miles (Keyworth UKI T. Nakahara (Osaka Japan) Ni Zhe-ming (Beijing China) P. J. Potts (Milton Keynes UK) W. J. Price (Budleigh Salterton UK) C. J. Rademeyer (Pretoria South Africa) A. Sanz-Medel (Oviedo Spain) *B. L. Sharp (Loughborough UK) I. L. Shuttler (Uberlingen Germany) S. T. Sparkes (Taunton. UK) R. Stephens (Halifax Canada) J.Stupar (Ljubljana Slovenia) R. E. Sturgeon (Ottawa Canada) *A. Taylor (Guildford UK) G. C. Turk (Gaithersburg ,!AD USA) J. F. Tyson (Amherst MA. USA) P. J. Watkins (London UK) 8. Welz (Uberlingen Germany) M. White (lspra Italy) J. G. Williams (Egham UK) J. B. Willis (Victoria Australia) *Members of the ASU Executive Committee Editor JAAS Janice M. Gordon The Royal Society of Chemistry Thomas Graham House Science Park Milton Road Cambridge CB4 4WF UK. US Associate Editor J A M Dr. J. M. Harnly US Department of Agriculture Beltsville Human Nutrition Research Center Beltsville MD 20705 USA. Telephone + 44 (0) 1223 420066. Fax + 44 (0) 1223 420247. E-mail RSCl @RSC.ORG (Internet) Telephone + 1 301 -504-8569 Asia-Pacific Associate Editor JAAS Senior Assistant Editor Brenda Holliday Assistant Editor Ziva Whitelock Editorial Secretary Lesley Turney Prof.N. Furuta Department of Applied Chemistry Faculty of Science and Engineering Chuo University 1-1 3-27 Kasuga Bunkyo-ku Tokyo 1 1 2 Japan. Telephone 81 -3-3817-1 906. Fax 81 -3-381 7-1 895. E-mail nfuruta@apchem.chem.chuo.u.ac.jp Advertisements Advertisement Department The Royal Society of chemistry Burlington House Piccadilly London W1V OBN UK. Telephone +44 (0) 171 -287 3091. Fax -44 (0) 171 -494 11 34. Information for Authors Full details of how to submit materials for publi- cation in JAAS are given in the Instructions to Authors in Issue 1. Separate copies are available on request. The Journal of Analytical Atomic Spectrometry (JAAS) is an international journal for the publi- cation of original research papers communi- cations and letters concerned with the development and analytical application of atomic spectrometric techniques.The journal is pub- lished twelve times a year including comprehen- sive reviews of specific topics of interest to practising atomic spectroscopists and incorpor- ates the literature reviews which were previously published in Annual Reports on Analytical Atomic Spectroscopy (ARMS). Manuscripts intended for publication must describe original work related to atomic spectro- metric analysis. Papers on all aspects of the sub- ject will be accepted including fundamental studies novel instrument developments and prac- tical analytical applications. As well as AAS AES and AFS papers will be welcomed on atomic mass spectrometry X-ray fluorescence/emission spectrometry and secondary emission spec- trometry.Papers describing the measurement of molecular species where these relate to the characterization of sources normally used for the production of atoms or are concerned for example with indirect methods of analysis will also be acceptable for publication. Papers describing the development and applications of hybrid techniques (e.g. GC-coupled AAS and HPLC-ICP) will be particularly welcome. Manuscripts on other subjects of direct interest to atomic spectroscopists including sample prep- aration and dissolution and analyte pre-concen- tration procedures as well as the statistical interpretation and use of atomic spectrometric data will also be acceptable for publication.There is no page charge. The following types of papers will be considered. Full papers. describing original work. Communications which must be on an urgent matter and be of obvious scientific importance. Communications receive priority and are usually published within 2-3 months of receipt. They are intended for brief descriptions of work that has progressed to a stage at which it is likely to be valuable to workers faced with similar problems. Reviews which must be a critical evaluation of the existing state of knowledge on a particular facet of analytical spectrometry. Every paper (except Communications) will be submitted to at least two referees by whose advice the Editorial Board of JAAS will be guided as to its acceptance or rejection. Papers that are accepted must not be published elsewhere except by permission.Submission of a manuscript will be regarded as an undertaking that the same material is not being considered for publication by another journal. Manuscripts (three copies typed in double spacing) should be sent to Janice M. Gordon Editor JAAS or Dr. J. M. Harnly US Associate Editor JAAS. All queries relating to the presentation and sub- mission of papers and any correspondence regarding accepted papers and proofs should be directed to the Editor or US Editor (addresses as above). Members of the JAAS Editorial Board (who may be contacted directly or via the Editorial Office) would welcome comments suggestions and advice on general policy matters concerning JAAS. ~~ ~ Fifty reprints are supplied free of charge.Journal of Analytical Atomic Spectrometry (JAAS) (ISSN 0267-9477) is published monthly by The Royal Society of Chemistry Thomas Graham House Science Park Milton Road Cambridge CB4 4WF UK. All orders accompanied with payment should be sent directly to The Royal Society of Chemistry Turpin Distribution Services Ltd. Blackhorse Road Letchworth Herts. SG6 lHN UK Tel. f 4 4 (0) 1462 672555; Telex 825372 Turpin G; Fax +44 (0) 1462 480947. Turpin Distribution Services Ltd. is wholly owned by The Royal Society of Chemistry. 1996 Annual subscription raie EEA f599.00 USA $1136.00 Rest of World f1136.00. Customers should make payments by cheque in sterling payable on a UK clearing bank or in US dollars payable on a US clearing bank. Air freight and mailing in the USA by Publications Expediting Inc. 200 Meacham Avenue Elmont NY 11003. USA Postmaster send address changes to Journal of Analytical Atomic Spectrome?ry (JAAS) Publications Expediting Inc. 200 Meacham Avenue Elmont NY 11 003. Postage paid at Jamaica NY 11431. All other despatches outside the UK by Bulk Airmail within Europe Accelerated Surface Post outside Europe. PRINTED IN THE UK. @The Royal Society of Chemistry 1995. All rights reserved. NO Part Of this publication may be reproduced stored in a retrieval system or transmitted in any form or by any means electronic mechanical photographic recording or otherwise without the prior permission of the publishers.

ISSN:0267-9477    

DOI:10.1039/JA99510FX037

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

Journal of Analytical Atomic Spectrometry JASPE2 lO(9) 51 N-55N 563-698 (1995) CONTENTS NEWS PAGES Atomic Spectrometry Viewpoint Ragnar Bye Diary of Conferences and Courses Future Issues 51N 53N 54N PAPERS PLENARY LECTURE Wavelength Modulation Diode Laser Atomic Absorption Spectrometry in Modulated Low-pressure Helium Plasmas for Element-selective Detection in Gas Chromatography Aleksandr Zybin Christoph Schnurer-Patschan Kay Niemax Some Figures of Merit of a New Double Focusing Inductively Coupled Plasma Mass Spectrometer Luc Moens Frank Vanhaecke Jorgen Riondato Richard Dams Analytical Characteristics of an Inductively Coupled Plasma Mass Spectrometer Coupled With a Thermospray Nebulization System Hans Vanhoe Steven Saverwijns Magali Parent Luc Moens Richard Dams Thermospray Device of Improved Design for Application in ICP-MS Christoph Thomas Norbert Jakubowski Dietmar Stuwer Jose A.C. Broekaert Non-destructive Sampling Method of Metals and Alloys for Laser Ablation- Inductively Coupled Plasma Mass Spectrometry A. Raith R. C. Hutton 1. D. Abell J. Crighton Effect of Laser Parameters and Tooth Type on the Ablation of Trace Metals from Mammalian Teeth Peter M. Outridge R. Douglas Evans PLENARY LECTURE Extraction of Trace Elements in Coal Fly Ash and Subsequent Speciation by High-performance Liquid Chromatography with Inductively Coupled Plasma Mass Spectrometry Jiansheng Wang Medha J. Tornlinson Joseph A. Caruso Determination of Arsenic Species by High-performance Liquid Chromatography-Ultrasonic Nebulization-Atomic Fluorescence Spectrometry Agnes Woller Zoltan Mester Peter Fodor Determination of Trace Amounts of Arsenic Species in Natural Waters by High-performance Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry P.Thomas K. Sniatecki Measurement of Mercury Methylation in Sediments by Using Enriched Stable Mercury Isotopes Combined with Methylmercury Determination by Gas Chromatography-Inductively Coupled Plasma Mass Spectrometry Holger Hintelrnann R. Douglas Evans Janice Y. Villeneuve Stable Isotope Approach to Fission Product Element Studies of Soil-to-Plant Transfer and in vitro Modelling of Ruminant Digestion Using Inductively Coupled Plasma Mass Spectrometry Paul Robb Linda M. W. Owen Helen M. Crews Basic Investigations of Nanosecond Laser-induced Plasma Emission Kinetics for Quantitative Elemental Microanalysis of High Alloys Bela Nernet Laszlo Kozma Cluster Formation Processes in Laser and Spark Plasmas of Rare Earth Oxide-Graphite Mixtures Johanna Sabine Becker Hans-Joachim Dietze 563 569 575 583 591 595 601 609 61 5 619 625 631 637 continued on inside back cover 0267-9477C 1995 19; 1 - V Typeset printed and bound by The Charlesworth Group Huddersfield England 01484 517077Quantitative Analysis of Copper Alloys by Laser-produced Plasma Spectrometry M.Sabsabi P. Cielo Effect of Plasma Pressure on the Determination of Mercury by Microwave- induced Plasma Atomic Emission Spectrometry Jose M. Costa-Fernandez Rosario Pereiro-Garcia Alfredo Sanz-Medel Nerea Bordel-Garcia Coupling Techniques for Inductively Coupled Plasma Optical Emission Spectrometry Using an Array Spectrometer for Laser Solid Sampling and Speciation Joachim Nolte Jorg Schoppenthau Lothar Dunernann Thomas Schumann Lieselotte Moenke-Blankenburg On-line Analysis of Elemental Pollutants in Gaseous Effluents by Inductively Coupled Plasma Optical Emission Spectrometry Thermodynamic Aspects Christian C.Trassy Robert C. Dierniaszonek Preliminary Study of the Role of Discharge Conditions on the In-depth Analysis of Conducting Thin Films by Radiofrequency Glow Discharge Optical Emission Spectrometry Nerea Bordel-Garcia Rosario Pereiro-Garcia Matilde Fernandez-Garcia Alfredo Sanz-Medel Tina R. Harville R. Kenneth Marcus Comparison of Depth Resolution for Direct Current and Radiofrequency Modes in Glow Discharge Optical Emission Spectrometry Frank Praler Volker Hoffmann Joachim Schumann Klaus Wetzig Quantitative Analysis of Iron-rich and Other Oxide-based Samples by Means of Glow Discharge Mass Spectrometry Stefan de Gendt Wim Schelles Rene Van Grieken Victor Muller Comparison Between Direct Current and Radiofrequency Glow Discharge Mass Spectrometry for the Analysis of Oxide-based Samples S.de Gendt R. E. Van Grieken W. Hang W. W. Harrison CUMULATIVE AUTHOR INDEX . . Royal Society of Chemistry Analytical Division Atomic Spectroscopy Group Eighth Biennial National Atomic Spectroscopy Symposium Plenary Lecturers Invited Lecturers Call for Papers social Programme Workshop Further Details 8th BNASS University of East Anglia UK 17-20 July 1996 Dr S J Hill Professor N Furuta Professor F Adam.Professor J M Mermet and Professor G Hieftje Dr 0 Donard. Dr S J P q . Dr S Fairweather-Tait. Dr A Ellis Dr A G Howard Dr J Brenner. Dr J Marshall Dr N J Miller-lhli Dr S Tanner and Professor D Littlejohn Contributed oral and poster presentations on recent developments in both pure and applied atomic spectr~scopy - analytical applications theoretical studies or fundamental advances in AAS AES. AFS. inorganic MS and XRF. Three copies of abstracts must be submitted before 28 February 1996. BNASS has an enviable reputation of being a friendly and dynamic meeting. A number of social events including a Symposium Dinner will form an integral part of the meeting. Immediately prior to the 8th BNASS there will be a Short Course on Sample Pre-treatment and Sample Introduction for Atomic Spectroscopy 17 July a.m. 1996. Ms Brenda Holliday. Royal Society of Chemistry Thomas Graham House Science Park Milton Road. Cambridge. CB4 4WF. UK. Tel +44 (0)1223 420066; Fax +44 (0)1223 420247; E-mail JAAS@RSC.ORG 643 649 655 661 67 1 677 681 689 697

ISSN:0267-9477    

DOI:10.1039/JA99510BX039

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

Department of Pharmacy University of Oslo 031 6 Oslo Norway During the Atomic Spectroscopy Group meeting Bristol UK March 31 1995 Dr Steve Hill (S.H.) a member of the JAAS Editorial Board and Brenda HoIliday (B.H.) Senior Assistant Editor interviewed Dr Ragnar Bye (R.B.) about his own work and science in Scandinavia. B.H. It’s nice to start the interview with a little background information about how you came to be doing what you’re doing now and where. R.B. I have been dealing with chemistry since I was 18 when I was a laboratory assistant and after that I was educated in chemical engineering in 1968. I worked as a chemical engineer for a few years then I started to study science at the University of Oslo. I got my Masters degree in analytical chemistry in 1978 and worked there as an assistant teacher until 1987 when I received a PhD from the same university in analytical chemistry.My thesis was on atomic absorption methods for selenium combined with preconcentration and separation techniques particularly using hydride generation but also electrochemical methods. For three years 1988-90 I was a Senior Lecturer in chemistry at the University of Agriculture then in 1990 I got a position at the University of Oslo again. S.H. How did you end up in the Department of Pharmacy? R.B. Because there was a vacant position which appeared to be more attractive than the one I held. S.H. You have found a home there? R.B. Yes. I work closely with colleagues in the Department of Chemistry where I was educated and worked in the 1980s. The two departments are only a few metres from each other so we are very much a working group. S.H.How many departments that specialize in analytical chemistry are there in Norway and indeed in Scandinavia? R.B. In Norway only the Department of Chemistry at the University of Oslo offers specialized education in analytical chemistry at an academic level. In Sweden there are probably three The University of Umeii where Wolfgang Frech and Douglas Baxter work; the University of Technology in Stockholm where they have been working particularly with flow techniques combined with AS methods as have also Prof. Hansen’s group at the Danish University of Technology; and the University of Goteborg where work is done particularly on ICP-MS. S.H. How close is the community? Do you have regular meetings where people from all three countries come together? R.B.We have only one regular meeting every second year ‘NASTEC‘ (Nordic Atomic Spectroscopy and Trace Element Conference). S.H. Are there many national meetings? You are heavily associated with the regular meetings in Roros. How did that come about? R.B. Every one and a half years we arrange a national meeting in atomic spectroscopy at a small mountain village named Roros and it is quite well known to a lot of British atomic spectroscopists. It started in 1969 I think. At that time Mr. Per Paus was the prime mover. He was a very active man in atomic spectroscopy not only in Norway but also in Europe. Most of the older British atomic spectroscopists will remember him very well. His health was however not very good and it became even worse so in the 1980s I and a couple of colleagues were asked to take over the meeting.S.H. I know many of us who have been there have enjoyed the meeting. The town is also very beautiful. What sort of people do you generally tend to get at these sorts of meetings. Do you get a cross section from technician grades up to well established scientists? R.B. You are perfectly right. The majority of the attendants are technicians and engineers working daily in the laboratory but there is also always quite a large number of academic people there laboratory and institute managers etc. The invited speakers usually come from universities in order to bring the latest ideas and inventions especially those that can help the chemist to solve some of their daily problems.S.H. Do the other Scandinavian countries hold similar meetings? R.B. In the other Scandinavian countries no similar meetings are arranged for some strange reason which could also explain why the Roros meeting is attended by people from other Scandinavian countries (especially Sweden). S.H. While we’re talking about conferences you are a regular visitor to the BNASS meetings. R.B. I’ve attended BNASS since 1986 (it was here in Bristol) and every meeting since. I like the BNASS meeting because of its suitable size combined with a high scientific standard and a very friendly atmosphere. From time to time I bring my wife with me and we combine BNASS with a car holiday in Britain. We do hope to continue to do that. S.H. Of course several years ago you were an invited lecturer at the BNASS meeting.Journal of Analytical Atomic Spectrometry September 1995 Vol. 10 51 NR.B. It was at Loughborough in 1990. The topic of the lecture was hydride generation from alkaline solutions; an approach which was quite new at that time. S.H. How did you get involved with the ASU board? R.B. That was through John Ottaway. The journal (JAAS) had just been established and Per Paus had been a member of the board since the very beginning. However the last time John visited the Rijros meeting (he had been there once before) he realised that Mr. Paus’ health was failing so he asked me if I was willing to take over. S.H. How well is JAAS received in Norway ? R.B. I don’t know how many subscribers there are but I know that everyone who submits papers to JAAS also has the journal themselves in Scandinavia.Nowadays it would be quite impossible to do research work in analytical atomic spectroscopy on an international acceptable level without reading JAAS regularly. S.H. Thinking about your own work I Jirst became aware of it through your papers on hydride generation. What particularly attracted you to that area? Did it come from your background in chemical engineering or from your move into analytical chemistry? R.B. It was an accident because I had not worked with that technique during my Master’s degree but on the combination of GC and AAS for speciation of lead and mercury compounds. Professor Lund had together with one of his graduate students published a method for the determination of selenium in saline water using an electrochemical preconcentration - AAS method and a reader wrote to Professor Lund saying that he wasn’t able to repeat the experiment.Professor Lund asked me to look into it (that was in 1979 just after having finished my Master’s degree). I did and in that connection I proposed to buy a simple batch hydride generator in order to be able to compare the results. S.H. And since the 1980s? R.B. During these years I used that equipment and after a few years also a continuous flow system for my PhD work. I was particularly interested in why certain metals interfere with the hydride generation and how to remove/ minimize such interferences. During the last years we have tried to solve such interference problems by generating the hydrides from alkaline solutions.S.H. I know that you have an interest in hydride formation in graphite tubes. Has that progressed to the stage when you will soon publish? R.B. So far it has not. We have looked into possibilities of elwtroplating and of cathodic sputtering of certain metals inside the graphite tube in order to preconcentrate the hydrides. However many groups are working with those problems and possibilities just now. S.H. How about the speciation side? You said that your own Ph13 studies looked at hyphenated techniques. Are you still working on speciation? R.B. During the last years only on redox speciation of some of i;he hydride elements although I started out in the 1970s with speciation studies of mercury and lead. The big problem with real speciation analysis (organic-metal compounds) is that some sort of chemical treatment is always necessary involving large risks of disturbing the chemical environment of the sample in such a way that chemical alteration of the species in question must be suspected.S.H. Many people have looked at the detector end but veryj’ew people have addressed the problem of sampling. What sort of samples most interest you? I know that you have examined environmental matrices do you look at clinical samples as well? R.B. Yes but only for routine work; not worth publishing. S.H. Do you have any idea of what you would like to do in thej‘uture? R.B. I’m sure I will continue with atomic spectrometry. Besides I should like to do more on decomposition methods of both inorganic and biological materials.As time has gone by the instruments have become more anti more sophisticated whereas not much has happened as to the decomposition methods; they are almost identical with those recommended in the 1960s. The advent of microwave ovens has mostly involved advantages in the time needed for decomposition; as to the chemistry not much has changed. S.H. There are many groups moving into areas like ICP-MS which obviously needs a lot of capital expenditure to get started? R.B. Indeed it does. But fortunately the Department of Chemistry got a grant from the National Council of Research to buy such an instrument. However I am not particularly involved in that project. There are six or seven such instruments in Norway installed at institutions that use them as tools not for research purposes.S.H. How about collaboration with other groups outside Norway? R.B. There are no restrictions. We can establish cooperation with everyone without interference. B.H. Do you think there is any value in moving to another laboratory to work for a period of time? R.B. Indeed yes. On the condition that the period is not too short. One or two weeks will not do. A couple of months is at least needed. S.H. One thing I must ask you about is your passion for old motor cars. On several occasions I know you have brought your car over to the UK. How many cars do you have? R.B. I have three older cars. The one you have seen is not very old - a 30 year- old Volvo. The two other ones are Chevrolets from 1927 and 1939. Finally there is a 1939 motor cycle with side car which my wife and I have just used for a one week holiday in Denmark.S.H. Do you drive them regularly? R.B. Yes! B.H. I imagined you just polishing them that’s all. R.B. Definitely not although I know very well that some people having such vehicles do indeed spend much of their time polishing. S.H. Does your wife share your interest for old vehicles? R.B. Not exactly. She says we have too many old vehicles and too few modern. Our daily car is 15 years old. S.H. You’re giving a talk this afternoon at the Atomic Spectroscopy Group Meeting - on what? R.B. That will be on the present status of atomic spectrometry in the Scandinavian countries and also about its past history. The proposal was that I should say something about my own activity and other AS activities in Norway. But this would probably have taken too short a time so I proposed to expand it include all the Scandinavian countries! B.H. Have you enjoyed the two days that you have been here? R.B. Yes I always enjoy being at meetings in the UK meeting British colleagues. S.H. Thank you for taking the time to talk to us. I look forward to seeing you at the next BNASS meeting in Norwich. R.B. Most certainly I’ll be there! 52 N Journal of Analytical Atomic Spectrometry September 1995 Vol. 10

ISSN:0267-9477    

DOI:10.1039/JA995100051N

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

DIARY OF CONFERENCES AND COURSES 1995 Short Course/Module Statistics and Applied Chemometrics/Statistics for Business October 2-6 Loughborough UK This course may be incorporated into a study programme leading to the award of a postgraduate qualification. For further information contact Dr Barry Sharp Department of Chemistry Loughborough University of Technology Loughborough Leicestershire LEll 3TU UK. Telephone 01509 222 572; Fax 01509 233 163; e-mail B.L.Sharp@LUT.ac.uk Federation of Analytical Chemistry and Spectroscopy Societies Conference October 15-20 Cincinnati Ohio USA Details can be found in J. Anal. At. Spectrom. 1995 10 19N. For further information contact Joseph A. Caruso FACSS National Office 198 Thomas Johnson Dr. Suite S-2 Frederick MD 21702 USA. Telephone (301) 694-8122; Fax (301) 694-6860.Short Course COSHH October 3 1-November 1 Shefield UK Details can be found in J. Anal. At. Spectrom. 1995 10 34N. For further information contact Ms Baldham or Ms Rogers Division of Adult Continuing Education University of Sheffield 196-198 West Street Sheffield S1 4CT UK. Telephone 01 14 2825391; Fax 01 14 2768653. First Mediterranean Basin Conference on Analytical Chemistry November 5-10 Cdrdoba Spain For further details contact Prof. Alfred0 Sanz-Medel Department of Physical and Analytical Chemistry Faculty of Chemistry. University of Oviedo C/ Julian Claveria no 8. 3006 Oviedo (Spain). Telephone 34/85/ 103474-103485; Fax 34/85/103480. Short Course Environmental Auditing in Manufacturing and Process Industries November 7 Shefield UK Details can be found in J.Anal. At. Spectrom. 1995 10 34N. For further information contact Ms Baldham or Ms Rogers Division of Adult Continuing Education University of Sheffield 196-198 West Street Sheffield S1 4CT UK. Telephone 01 14 2825391; Fax 01 14 2768653. Biological Applications of Inorganic Mass Spectrometry November 8-9 Norwich UK Details can be found in J. Anal. At. Spectrom. 1995 10 20N. For further information contact Dr. Fred Mellon Institute of Food Research Norwich Laboratory Norwich Research Park Colney Norwich NR4 7UA UK. Telephone +44(0)1603 255 299 (direct line) +44 (0) 1603 255 000 (switchboard/paging); Fax +44 (0)1603 452578 +44 (0)1603 fred.mellon@BBSRC.AC.UK. 507723; E-MAIL Short Course Safe Storage of Hazardous Substances November 23 Shefield UK Details can be found in J.Anal. At. Spectrom. 1995 10 34N. For further information contact Ms Baldham or Ms Rogers Division of Adult Continuing Education University of Sheffield 196-198 West Street Sheffield S1 4CT UK. Telephone 01 14 2825391; Fax 01 14 2768653. Short Course/Module Quality Management November 27-December 1 Loughborough UK This course will include TQM IS0 900 GLP NAMAS etc and may be incorporated into a study programme leading to the award of a postgraduate qualification. For further details contact Dr Barry Sharp Department of Chemistry. Loughborough University of Technology Loughborough Leicestershire LEll 3TU UK. Telephone 01509 222 572; Fax 01509 233 163; e-mail B.L.Sharp@LUT.ac.uk Short Course Disposal of Hazardous Waste December 5 Shefield UK Details can be found in J.Anal. At. Spectrom. 1995 10 34N. For further information contact Ms Baldham or Ms Rogers Division of Adult Continuing Education University of Sheffield 196-198 West Street Sheffield S1 4CT UK. Telephone 01 14 2825391; Fax 01 14 2768653. International Symposium on Environmental Biomonitoring and Specimen Banking December 17-22 Honolulu Hawaii USA Details can be found in J. Anal. At. Spectrom. 1994 9 59N. For further information contact K. S. Subramanian Environmental Health Directorate Health Canada Tunney's Pasture Ottawa Ontario K1A OL2 Canada (phone 613-957-1874; fax 613-941-4545) or G. V. Iyengar Center for Analytical Chemistry Room 235 B 125 National Institute of Standards and Technology Gaithersburg MD 20899 USA (Telephone 301-975-6284; Fax 301-921-9847) or M.Morita Division of Chemistry and Physics National Institute for Environmental Studies Japan Environmental Agency Yatabe-Machi Tsukuba Ibaraki 305 Japan (Telephone 81-298-51-61 11 ext. 260; Fax 81-298-56-4678). 1996 1996 Winter Conference on Plasma Spec t roc hemis t r y January 8-13 Fort Lauderdale Florida USA Details can be found in J. Anal. At. Spectrom. 1994,9,53N. For further information contact Dr. R. Barnes ICP Information Newsletter Department of Chemistry Lederle GRC Towers University of Massachusetts Box 34510 Amherst MA 01003-4510 USA. Telephone (413) 545 2294; Telefax (413) 545 4490. International Schools and Conferences on X-Ray Analytical Methods January 18-25 Sydney Australia Details can be found in J.Anal. At. Spectrom. 1994,9,47N. For further information contact AXAA '96 Secretariat GPO Box 128 Sydney NSW 2001 Australia. Telephone 61 2 262 2277; Fax 61 2 262 2323; Telex AA 1765 1 1 TRHOST. Journal of Analytical Atomic Spectrometry September 1995 Vol. 10 53 N8th Sanibel Conference on Mass Spectrometry Metal-Containing Ions and Their Applications in Mass Spectrometry January 20-23 Sanibel Island FL USA For further details contact American Society for Mass Spectrometry 1201 Don Diego Avenue Santa Fe NM 87505 USA. Telephone (505) 989-4517; Fax (505) 989-1073. Analytica Conference 96 April 23-26 Munich Germany Details can be found in J. Anal. At. Spectrom. 1994,2,69N. For further information contact Messe Miinchen GmbH Messegelande D-80325 Miinchen Germany.Telephone +49 89 51 07-0; Telex 5 212 086 ameg d; Fax +49 89 51 07-177. ASMS Short Course Interpretation of Mass Spectra LC/MS and MS/MS May 11-12 Portland OR USA For further details contact American Society of Mass Spectrometry 1201 Don Diego Avenue Santa Fe NM 87505 USA. Telephone (505) 989-45 17; Fax (505) 989-1073. 44th ASMS Conference on Mass Spectrometry and Allied Topics May 12-17 Portland OR USA For further details contact American Society of Mass Spectrometry 1201 Don Diego Avenue Santa Fe NM 87505 USA. Telephone (505) 989-4517; Fax (505) 989-1073. Eighth Biennial National Atomic Spectroscopy Symposium July 17-19 University of East Anglia Norwich UK For further informat ion contact Dr. S. J. Haswell School of Chemistry University of Hull Hull HU6 7RX UK.Telephone + 44 (0)4.82-465469; Fax + 44 (0)482-466410. 12th Asilomar Conference on Mass Spectrometry Elemental Mass Spectrometry September 20-24 Pac$c Grove CA USA For further details contact American Society of Mass Spectrometry 1201 Don Diego Avenue Santa Fe NM 87505 USA. Telephone (505) 989-4517; Fax (505) 989-1073. 1997 Seventh International Symposium on Biological and Environmental Reference Materials April 21-25 Antwerp Belgium The Seventh Symposium will continue this series being held on a periodic basis. The excellent exchange of ideas and information documented in the Proceedings of the Sixth Symposium held in April 1994 in Kona Hawaii covered a wide variety and scope of information in this topical area. Activities at the Seventh Symposium are expected to both broaden these discussions and to focus on more specific aspects of further research on problems and progress of projects discussed at the previous symposium.The major aim of this symposium series is to bring together efforts in the production study and use of Reference Materials in the anal:ytical biological biomedical clinical environmental and nutritional communities. Participation in the symposium is open to all who are interested in reference materials and standards in the biological environmental and industrial areas. The registration fee will cover attendance at the symposium lunches and coffee breaks the “Book of Abstracts” and the published proceedings as well as other activities. The city of Antwerp has a large number of hotels of different prices and categories.Bookings have to be made via Brussels International Travel Agency. A social programme is planned to provide an opportunity for informal contacts and discussions among participants. Guest programmes can be organized to take advantage of historical cities of Belgium. Details will be available at a later date. On request of the SMT programme of the European Commission BERM-7 will also include a special session on industrial CRMs. Preliminary titles are requested by July 1 1996. Abstracts of papers intended as contributions to the symposium must be submitted in English (three copies) to the chairman of the Scientific Committee by December 1,1996. Abstracts should be double spaced typed and not exceed one page. Abstracts will be reviewed by the Scientific Commit tee for acceptance and publicaton in the “Book of Abstracts”.Authors of accepted and invited papers will be invited to submit the entire manuscript in English during the symposium for publication in the proceedings. Further details of the publication will be given upon acceptance of abstracts. Acceptance of contribution for publication in the Proceedings will be decided upon by the Scientific Committee J. Pauwels Chairman Belgium; S . Berman Canada; R. Dybczynski Poland; T. Gills USA; B. Griepink B; G. V. Iyengar USA; J. Kumpulainen Finland; P. Mader Czech Rep; H. Muntau Italy; M. Morita Japan; S. Rasberry USA; J. D. Schladot Germany; M. Stoeppler Germany; J. Tanner USA; S. Vandendriessche B; S. Wise USA; W. Wolf USA; R. Zeisler Austria; For further details contact Dr J. Pauwels Institute for Reference Materials & Measurements Management of Reference Materials Unit Retieseweg B-2440 Geel Belgium. Telephone + 32-14-571 722; Fax + 32- 14-590 406; or Wayne R. Wolf Ph.D Food Composition Laboratory USDA 10300 Baltimore Blvd. Beltsville MD 20705 USA. Telephone + 1-301-504 8927; Fax + 1-301-504 8314 54N Journal of Analytical Atomic Spectrometry September 1995 Vol. 10

ISSN:0267-9477    

DOI:10.1039/JA995100053N

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

FUTURE ISSUES WILL INCLUDE- Lowering the Instrumental Detection Limit for Some Electrothermal Atomic Absorption Determinations and Estimation of the Optimum Detection Limit from One Atomization-A. Le Bihan H. Le Garrec J.Y. Cabon Y. Guern Interpretation of the [nterference Mechanisms Occurring in the Determination of Sb ''I* by Hydride Generation Atomic Absorption Spectrometry Based on Normal Redudtion Potentials -M. T. Martinez- Soria J. Sanz Asensio J. Galban Bernal Determination of Selenium by Hydride Generation Atomic Absorption Spectrometry Elimination of Interferences from Very High Concentrations of Nickel Cobalt Iron and Chromium by Complexation-Torild Wickstrom Walter Lund Ragnar Bye 54N Journal of Analytical Atomic Spectrometry September 1995 Vol. 10Continuous Flow Microwave-assisted Digestion of Environmental Samples- Ralph E.Sturgeon Scott N. Willie Bradley A.J. Methven Joseph W. Lam Henryk Matusiewicz Chelation Preconcentration with Resin Analysis by Direct Sample Insertion Inductively Coupled Plasma Spectrometry-Robin Rattray Eric D. Salin Determination of Boron Using Mannitol-Assisted Electrothermal Vaporization for Sample Introduction into Inductively Coupled Plasma Mass Spectrometry-Wei Wen-Ching Chen Chih-Jung Yang Mo-Hsiung Determination of Trace Element Impurities in Nuclear Materials by Inductively Coupled Plasma Mass Spectrometry in a Glove-box-Zlatan Kopajtic Stefan Rollin Beat Wernli Chantal Hochstrasser Guido Ledergerber Petr Jurcek Characterization and Optimization of a Radiofrequency Glow Discharge Ion Source for a High Resolution Mass Spectrometer-Anatolij I.Saprykin J. Sabine Becker Hans-Joachim Dietze Inductively Coupled Nitrogen Plasma Mass Spectrometry Assisted by Adding Argon to the Outer Gas-Hiroshi Uchida Tetsumasa Ito Determination of Cadmium at Ultra- Trace Level by Cold Vapour Atomic Absorption Spectrometry-Guo Xiao- Wei Guo Xu-Ming Computer Simulation of Enclosed Inductively Coupled Plasma Discharges. I. Monatomic Gases-Ana Gaillat Ramon M. Barnes P. Proulx M I. Boulos Computer Simulation of Erwlosed Inductively Coupled Plasma Discharges. 11. Molecular Gases-Ana Gaillat Ramon M. Barnes P. Proulx M I. Boulos Characterization of Ionization and Matrix Suppression in Inductively Coupled ‘Cold’ Plasma Mass Spectrometry-Scott D. Tanner Determination of Silicon by Electrothermal Atomic Absorption Spectrometry Using Platinum as a Chemical Modifier-Masami Fukushima Toshio Ogata Kensaku Haraguchi Kohichi Nakagawa Saburo Ito Masao Sumi Naoto Asami Application of Multi-element Time- resolved Analysis to a Rapid On-line Matrix Separation System for Inductively Coupled Plasma Mass Spectrometry-Simon M.Nelms Gillian M. Greenway Robert C. Hutton Direct Coupling of High-performance Liquid Chromatography to Microwave- induced Plasma Atomic Emission Spectrometry via Volatile Species Generation and Its Application to Mercury and Arsenic Speciation-Jose M. Costa-Fernandez Florian Lunzer Rosario Pereiro-Garcia Nerea Bordel- Garcia Alfredo Sanz-Medel Thermally Stabilized Iridium on an Integrated Carbide-coated Platform as a Permanent Modifier for Hydride- forming Elements in Electrothermal Atomic Absorption Spectrometry. Part 1.Optimization Studies-D.L. Tsalev Alessandro D’Ulivo Leonard0 Lampugnani Marco Di Marco Roberto Zamboni Direct Determination of Nickel in Heroin and Cocaine by Electrothermal Atomic Absorption Spectrometry Using Deuterium Background Correction Combined with Chemical Modification -Pilar Bermejo-Barrera A. Moreda-Pineiro Jorge Moreda- Pineiro A. Bermejo-Barrera COPIES OF CITED ARTICLES The Royal Society of Chemistry Library can usually supply copies of cited articles. For further details contact The Library Royal Society of Chemistry Burlington House Piccadilly London W1V OBN UK. Tel +44 (0) 71-437 8565; fax +44 (0) 71-287 9798; Telecom Gold 84; BUR210; Electronic Mailbox (Internet) LIBRARY@RSC.ORG.If the material is not available from the Society’s Library the staff will be pleased to advise on its availability from other sources. Please note that copies are not available from the RSC at Thomas Graham House Cambridge. Journal of Analytical Atomic Spectrometry September 1995 Vol. 10 55NContinuous Flow Microwave-assisted Digestion of Environmental Samples- Ralph E. Sturgeon Scott N. Willie Bradley A.J. Methven Joseph W. Lam Henryk Matusiewicz Chelation Preconcentration with Resin Analysis by Direct Sample Insertion Inductively Coupled Plasma Spectrometry-Robin Rattray Eric D. Salin Determination of Boron Using Mannitol-Assisted Electrothermal Vaporization for Sample Introduction into Inductively Coupled Plasma Mass Spectrometry-Wei Wen-Ching Chen Chih-Jung Yang Mo-Hsiung Determination of Trace Element Impurities in Nuclear Materials by Inductively Coupled Plasma Mass Spectrometry in a Glove-box-Zlatan Kopajtic Stefan Rollin Beat Wernli Chantal Hochstrasser Guido Ledergerber Petr Jurcek Characterization and Optimization of a Radiofrequency Glow Discharge Ion Source for a High Resolution Mass Spectrometer-Anatolij I.Saprykin J. Sabine Becker Hans-Joachim Dietze Inductively Coupled Nitrogen Plasma Mass Spectrometry Assisted by Adding Argon to the Outer Gas-Hiroshi Uchida Tetsumasa Ito Determination of Cadmium at Ultra- Trace Level by Cold Vapour Atomic Absorption Spectrometry-Guo Xiao- Wei Guo Xu-Ming Computer Simulation of Enclosed Inductively Coupled Plasma Discharges.I. Monatomic Gases-Ana Gaillat Ramon M. Barnes P. Proulx M I. Boulos Computer Simulation of Erwlosed Inductively Coupled Plasma Discharges. 11. Molecular Gases-Ana Gaillat Ramon M. Barnes P. Proulx M I. Boulos Characterization of Ionization and Matrix Suppression in Inductively Coupled ‘Cold’ Plasma Mass Spectrometry-Scott D. Tanner Determination of Silicon by Electrothermal Atomic Absorption Spectrometry Using Platinum as a Chemical Modifier-Masami Fukushima Toshio Ogata Kensaku Haraguchi Kohichi Nakagawa Saburo Ito Masao Sumi Naoto Asami Application of Multi-element Time- resolved Analysis to a Rapid On-line Matrix Separation System for Inductively Coupled Plasma Mass Spectrometry-Simon M. Nelms Gillian M. Greenway Robert C. Hutton Direct Coupling of High-performance Liquid Chromatography to Microwave- induced Plasma Atomic Emission Spectrometry via Volatile Species Generation and Its Application to Mercury and Arsenic Speciation-Jose M.Costa-Fernandez Florian Lunzer Rosario Pereiro-Garcia Nerea Bordel- Garcia Alfredo Sanz-Medel Thermally Stabilized Iridium on an Integrated Carbide-coated Platform as a Permanent Modifier for Hydride- forming Elements in Electrothermal Atomic Absorption Spectrometry. Part 1. Optimization Studies-D.L. Tsalev Alessandro D’Ulivo Leonard0 Lampugnani Marco Di Marco Roberto Zamboni Direct Determination of Nickel in Heroin and Cocaine by Electrothermal Atomic Absorption Spectrometry Using Deuterium Background Correction Combined with Chemical Modification -Pilar Bermejo-Barrera A. Moreda-Pineiro Jorge Moreda- Pineiro A. Bermejo-Barrera COPIES OF CITED ARTICLES The Royal Society of Chemistry Library can usually supply copies of cited articles. For further details contact The Library Royal Society of Chemistry Burlington House Piccadilly London W1V OBN UK. Tel +44 (0) 71-437 8565; fax +44 (0) 71-287 9798; Telecom Gold 84; BUR210; Electronic Mailbox (Internet) LIBRARY@RSC.ORG. If the material is not available from the Society’s Library the staff will be pleased to advise on its availability from other sources. Please note that copies are not available from the RSC at Thomas Graham House Cambridge. Journal of Analytical Atomic Spectrometry September 1995 Vol. 10 55N

ISSN:0267-9477    

DOI:10.1039/JA995100054N

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

Wavelength Modulation Diode Laser Atomic Absorption Spectrometry in Modulated Low-pressure Helium Plasmas for Element-selective Detection in Gas Chromatography* Plenary Lecture ALEKSANDR ZYBIN CHRISTOPH SCHNURER-PATSCHAN AND KAY NIEMAXt Institute of Physics University of Hohenheim Garbenstrasse 30 0-70599 Stuttgart Germany A new technique for element-selective detection in gas chromatography is reported. It is based on wavelength modulation diode laser atomic absorption spectrometry ( WM-LAAS) in modulated low-pressure dc or microwave- induced plasmas (MIP). The double modulation laser atomic absorption spectrometry (DM-LAAS) eliminates not only flicker noise from the laser as well as from the plasma but also etalon effects which limit the detection in WM-LAAS. DM-LAAS allows the measurement of absorbances of about lo-'.The analytical power of the technique is demonstrated by the analysis of haloform samples applying DM-LAAS of metastable chlorine and bromine atoms which are generated in the low-pressure plasmas by dissociation and excitation. Since the species are dissociated completely the signals reflect the relative element concentration in the molecules which allows calibration by internal standards. The detection limits are very low. For example 3s detection limits were found to be below 3 ng ml-' for species such as CHC13 or CC14 applying splitless injection of 0.5 pl samples and DM-LAAS of chlorine in the MIP. The detection limits found in the dc plasma were slightly higher. Keywords Diode laser atomic absorption spectrometry; modulation spectrometry element-selective detection; gas chroma tograph y The signal-to-noise ratio in absorption measurements can be improved significantly if lasers whose wavelength can be modulated with high frequency are used as radiation sources.' This has been demonstrated in atomic absorption spectrometry with semiconductor diode lasers in graphite tube atomizers,' analytical flames3 and low-pressure dc plasmas4 Depending on the radiation power of the fundamental or after frequency doubling in a non-linear crystal of the second harmonic laser wavelength absorbances of 10-4-10-6 have been measured.The reduction of the detection limits in elemental analysis promised improvements of the analytical figures of merit in chromatography with element-selective detection. Recently we have successfully coupled wavelength modulation laser atomic absorption spectrometry (WM-LAAS) of chromium in an analytical flame with high-performance liquid chromatography (HPLC) for the speciation of Cr"' and CrV'.5 Detection limits of about 1 ng ml-' were obtained.Sensitive detection of molecular compounds such as * Presented at the 1995 European Winter Conference on Plasma tTo whom correspondence should be addressed. Spectrochemistry Cambridge UK January 8-13 1995. Journal of Analytical Atomic Spectrometry C2CI2F CCl CHF and 02 has been shown by the WM-LAAS of metastable chlorine fluorine and oxygen atoms which were generated by dissociation and excitation in a low- power dc argon or helium pla~ma.~ In a further paper,6 this technique was coupled with gas chromatography (GC) in order to speciate chlorinated hydrocarbons by the measurement of chlorine.Since other halogens can also be measured by diode lasers element-selective measurements of halogens allow not only the discrimination between halogenated and non- halogenated species but also the halogens. In the preliminary experiment on coupling GC with WM-LAAS a low-pressure microwave-induced plasma (MIP) was used. Although the WM-LAAS signal showed the expected strength low detection limits could not be obtained because of slow fluctuations of the background absorption which could only be partly sup- pressed by the largest possible time constant of 0.1 s. The detection limits for different chlorinated hydrocarbons were only of the order of 1 pg ml-' or 80 pg s-'. The present paper reports on significant improvements of the analytical figures of merit of the coupling of GC and WM-LAAS in low-pressure plasmas (MIP as well as dc plasma).The improvements are the result of the additional modulation of the absorption by switching the plasmas on and off with a frequency of a few kHz. The absorption has to be measured at the sum or difference frequency of the second harmonic of the laser and the first harmonic of the plasma modulation frequency. The modulation of the plasma not only increases the population density in the metastable states but also suppresses wavelength-dependent changes of the laser intensity measured with the detector such as interference effects in the optical path (etalon effects).' It is shown that double modulation laser atomic absorption spectrometry (DM-LAAS) allows absorbances near to the theoretical detection limit given by the shot noise to be measured.EXPERIMENTAL The experimental arrangement for WM-LAAS in a modulated MIP is shown in Fig. 1. The radiation of a semiconductor laser diode (HL 8314 Hitachi or LT15 Sharp; line widths x 20 MHz; power 30 mW) was collimated by a large aperture lens and attenuated by an optical filter to about 0.8 mW. The diameter of the laser beam in the absorption volume was about 1 mm. The attenuation by a filter was necessary to avoid optical saturation of the strong absorption lines in the low- pressure helium plasmas. The MIP was operated in a quartz capillary (diameter 2 mm) placed in a Beenaker-type resonator.The plasma length was about 15cm at optimum operating Journal of Analytical Atomic Spectrometry September 1995 Vol. 10 563Modulator Modulator Microwave Mixer power * I I qy Lens u . Sample injection - u 11 1 Pump Gas - *Y (haloform test solutions from Chromatographie Service) and of CCl and CHCI (both extra pure quality from Merck) in pentane were prepared for the measurements. The concen- trations of the species in the haloform test solutions are listed in Table 1 as well as the chlorine and bromine concentrations in the solutions. RESULTS AND DISCUSSION Photodiode Characterization of the Helium MIP chromatograph I - I L Gas mixture Fig. 1 gas chromatography by DM-LAAS in a low-pressure plasma Experimental arrangement for element-selective detection in condition.The absorption was measured by a low-noise silicon photodiode. The absorption signal was processed by a lock-in amplifier (Stanford Instruments RS 830DS) and stored by a personal computer. When measurements in the low-pressure dc plasma (DCP) were performed the MIP shown in Fig. 1 was replaced by a 15 cm long plasma tube (diameter 3 mm) completely made of Pyrex glass. Near the windows the tube ends were widened in order to have space for large area disc electrodes (diameter 10mm) which minimized the sputtering at a given current. The plasma length was about 13 cm. For the measurement of chlorinated hydrocarbons the laser diode powered by a commercial driver (Melles Griot 56 DLD 403) was tuned to the chlorine absorption line at 837.60nm ( 3s23p44s ,PSi2 + 3s23p44p ,Do7/!) which has a large oscillator strength [f=0.39 (ref.7)]. Bromine compounds were measured by absorption of the Br 827.24nm line (4s24p45s ,P5/? +4s24p45p To our knowledge there are no data available on the oscillator strength of the Br line. However it is expected to be of the same order of magnitude as thef-value of the Cl 837.60 nm line. The wavelength of the laser diode was modulated sinusoidi- The properties of the double modulation scheme were studied by absorption of the C1 827.60nm line using mixtures of C2C1,F and helium as the plasma gas. If the laser is locked to the centre of the line and the plasma is modulated with frequency fi the laser intensity with and without plasma is measured. The output signal of the lock-in amplifier represents the specific element absorption and the non-selective absorp- tion of the plasma which was about 2% in our case.We observed an increase of the specific absorption signal with increasing plasma modulation frequency in the range from a few Hz to about 5 kHz. This behaviour is due to strong changes of the population density in the C1 metastable state during the periods the MIP was burning. The moment the plasma was switched on by the rectangular pulse the absorption reached a much larger value than in the continuous mode and decreased rapidly with time while the plasma was switched on. The time constant of this process was about 10 ps. The increase of the modulation frequency shortened the period of the burning plasma therefore on average a larger absorption was meas- ured.Most probably the high population density at the beginning of each plasma period is due to a smaller collisional deactivation of the metastable levels at a relatively low gas temperature. With time the gas temperature increases and depopulation processes become stronger until the plasma reaches asymptotically the temperature of the stationary case. When the modulation frequency was larger than 5 kHz the time between the plasma shortages and the following re-ignitions was too short for a significant cooling of the gas. Therefore the population densities at the beginning of each plasma period were smaller than for lower modulation ally with a frequency of f l = 11.5 kHz using a commercial power supply (Wavetek FG-5000). To obtain maximum signals modulation amplitudes of 7 and 5 pm were applied for the measurement of the chlorine and bromine lines respectively.A microwave generator (Feuerbacher GMW 24-303 DR) produced radiation at 2.45 GHz with a maximum power of 300 W. Typical powers of about 120 W were applied. The frequencies. Optima absorption signals were obtained at gas flow rates between 3 and 5 ml min-'. The optimum gas pressure was 70 hPa. The absorption signal increased with microwave power between 80 and 200 W. This behaviour is mainly due to an increase of the plasma length with power as was found in our earlier paper.6 However 120 W was chosen as the operation reflected power was about 2 W. The helium MIP was operated between 10 and 100 hPa. A second Wavetek power supply was used for external modulation of the MIP.The plasma was switched on and off by a square wave function. The modulation frequency of the MIP was 5 kHz. The modulation frequency f2 of the plasma was mixed with the second harmonic of the laser modulation frequency to obtain a reference frequency of 2fi -f2 = 18 kHz for the lock-in amplifier. A stabilized power supply (Fug HCN 140-3500) was used for the dc helium plasma. The gas pressure was 40 hPa and the current about 15 mA at a discharge voltage of 900 V. As in the case of the MIP a 5 kHz square wave function was applied to pulse the plasma. The gas chromatograph (Shimadzu GC-14A) was equipped with a fused silica column from Chromatographie Service (type FS-SE-54-CB-1; length 50 m; inner diameter 0.32 mm). Helium was used not only as power because the plasma became unstable at larger powers.As mentioned above the non-selective background absorp- tion in the plasma modulation measurements can be suppressed by additional modulation of the laser wavelength. A spectrum of the chlorine line measured at the frequency 2f1 -f2 is shown as trace 1 in Fig. 2. The concentration of C2C12F4 was 0.4 ppb. The scan time was 30 s and the time constant 3 s. Trace 2 is the blank measured in helium without C,Cl,F admixtures. The difference between the maximum and one of the minima of the second harmonic line profile was recorded as the analytical signal with a large time constant (50 s). The data are presented as full squares in Fig. 3 giving a calibration curve for C2C12F,. The total dynamic range not shown in Fig. 3 was about five orders of magnitude.The 3s detection limit of C2C12F was found to be about 60 ppt. The blank level was about 30 ppt (n = lo) found in preconcentration measurements the plasma gas but also as the carrier gas in the chromatograph (flow rate z 4 ml min-I). Liquid samples of 0.5 pl were introduced manually with a syringe into the splitless injector of the instrument. Two solutions of halocarbons in pentane where C2C12F molecules in a 2 1 volume were condensed in a cold trap and then released by heating to the helium gas flow. The blank was mainly due to contamination of the capillary wall and the tubes of the gas handling system. However there 564 Journal of Analytical Atomic Spectrometry September 1995 Vol. 10Table1 concentrations in 1 and 2 respectively Concentrations of different species in the haloform solutions used.The columns headed chlorine and bromine give the CI and Br Species Dichloromethane (CH,Cl,) Trichloromethane (CHCl,) 1,1,l-Trichloroethane (C,H,Cl,) Tetrachloromethane (CCI,) Trichloroethane (C,HCl,) Bromodichloromethane (CHBrC1,) Dibromochloromethane( CHBr,CI ) Tetrachloroethane (C,Cl,) Tribromomethane (CHBr,) Sample 1/ pg ml-' 200 5 1 0.25 2.5 1 1.5 0.6 4.5 Chlorine/ pg ml-' 4.4 0.79 0.23 2.03 0.42 0.26 0.54 167 - Sample 2/ pg ml-' 158.4 14.9 13.4 15.9 14.6 20.0 24.5 16.2 28.9 Bromine/ pg ml-' - ~ - ~ 9.8 18.8 27.4 - 2 GHz - I I I Optical frequency .- Fig. 2 Spectrum 1 2f chlorine absorption line measured at a concen- tration of 400 ppt C2Cl,F in helium by DM-LAAS and spectrum 2 blank .-1 ,-' /.,m ' I' 7 ,P' -1 3s detection limit 0.01 C2C12F4 in helium (ppb) Fig. 3 gases in the MIP Calibration curve for C2C1,F4 in helium measured with mixed was also a contribution by chlorine-containing polyatomic species in the ultra-pure helium used. It is interesting to note that about 0.05% of all chlorine atoms are in the 3p44s 4P5,2 metastable state at optimum conditions in the continuously operating MIP. These values were evaluated from the absorption spectra taking into account the total number density of chlorine atoms in the plasma the integrated absorption and the oscillator strength of the 837.60nm line. The fraction of metastable atoms can be increased significantly (> 1 YO) by pulsed operation. Coupling of Gas Chromatography and DM-LAAS in the MIP Since the chromatographic spikes were relatively broad at the optimum gas pressure of 70 hPa the helium pressure had to be reduced to 20 hPa to obtain narrow signals. A chromato- gram of haloform solution 1 diluted by a factor of 30 and measured by DM-LAAS of chlorine is shown in Fig.4. Note 1i I / 0 $0 120 180 240 3bO 360 420 Time/s Fig. 4 Chromatogram of a haloform solution measured by DM-LAAS of chlorine in the MIP. Species and concentrations 1 CH,Cl (6.7 pg ml-'); 2 CHCl (150 ng ml-I); 3 C,H,Cl (33 ng ml-'); 4 CCI (8 ng ml-'); 5 C,HCl (80 ng ml..'); 6 CHBrCI (33 ng ml-'); 7 CHBr,C1(50 ng ml-I); and 8 C2C14 (20 ng ml-I) the very low absorbance which can be measured by DM-LAAS. The numbered peaks in the chromatogram correspond to species listed in Table 1.At the start the temperature of the chromatograph was 25°C and increased with a rate of 10 "C min-l up to 105 "C. The start time of the chromatogram was 110 s after injection. Since the concentration of the first component (dichloromethane) was much higher than of the following species the gain of the lock-in amplifier had to be changed. In order to minimize the influence of the solvent to the plasma the plasma was switched on after the major volume of the solvent had passed the capillary of the MIP and before the first species arrived. In our case the plasma was switched on with a delay of about 23 s. Except for the first component where the plasma was still slightly influenced by the solvent the relative signals of the different chlorinated hydrocarbons reflect the chlorine concen- trations given in Table 1.On the basis of six chromatograms the relative chlorine ratios could be reproduced within k 5%. This means that within experimental uncertainty the chlorine atoms were completely dissociated from the species and the population density of the metastable state was proportional to the chlorine density. This can only happen if the plasma does not change its parameters when the species are in the plasma. The correlation between element concentration and signal gives an important advantage of element-selective detec- tion by DM-LAAS in GC i.e. the possibility of calibration by internal standards. Fig. 5 shows calibration curves for solutions with trichloro- methane and tetrachloromethane. The data were obtained by integrated absorbance measurement.The detection limits were 2.8 and 2.5 ng ml-I for CHC13 and CCl respectively. Similar Journal of Analytical Atomic Spectrometry September 1995 Vol. 10 565Concentration/ng ml-' 0 1 I I ' I Fig. 5 Calibration curves for CHCl and CCl measured chromato- graphically by DM-LAAS of chlorine in the MIP J (D 1 x 1 0 ~ ~ ? 2 1x1027 c m 1x101; 13 a l X l O O - to measurements of C2C12F4 in helium the dynamic range of the chromatographic measurements of CHC13 and CC14 was about six orders of magnitude. Taking into account the injected sample volume the detection limit of chlorine was about 0.12 pg s-' or 1.2 pg. 0 ; ; I t Characterization of the dc Helium Plasma The properties of the dc helium plasma were studied with mixtures of C2C12F4 and helium.Similar to that for the MIP the absorption signal had a maximum at a plasma modulation frequency,f2 of about 5 kHz. The laser wavelength modulation frequency fl was again 11.5 kHz. Therefore the same refer- ence frequency ( 2f1 -f2 = 18 kHz) for the lock-in amplifier could be used as in the measurements with the MIP. The dependence of the chlorine line absorption on gas pressure for five different flow rates is displayed in Fig. 6. While the signal was almost independent of pressure for small flow rates e.g. 1.3 ml min-' it increased with pressure for higher flow rates. Unfortunately we could not go far beyond 50 hPa because our current modulator was limited to 1 kV. Higher gas pressures required voltages beyond 1 kV. Fig.7 shows the absorption signal dependence on the gas flow measured at 40 hPa the pressure which is also used in gas chromatography. A calibration curve for C2Cl,F4 in helium measured at 40 hPa and 20 ml rnin-' is given in Fig. 8. The time constant was 50s. A detection limit of about 85ppt was found. This value is comparable to the detection limit obtained with the MIP (60 ppt). Much stronger memory effects were observed in the dc plasma than in the MIP. After measurements of high C2C12F 5 60- c - c .- 50- .- - 2 40- $ 30- 1.3 2 Y - c 2 20 $ . a I O - 13 27 ml min-' 13 ml min-' Fig.6 Chlorine line absorption versus gas pressure measured at different flow rates by DM-LAAS in the DCP Fig.7 Chlorine line absorption versus gas flow rate at 40 hPa by DM-LAAS in the DCP 1 lxlo4i xl o - ~ /3s detection limit I ' ~ " ' ' ~ ' 1 ' " ~ ~ " ~ ' " ' 1 - 3 - ' """.' * ' * * * 0.1 1 l b lb0 1600 10 C2CI2F4 in He (ppb) 100 Fig. 8 Calibration curve for C2C1,F in helium obtained with mixed gases in the DCP concentration the discharge had to be cleaned by flushing pure helium through the tube at high plasma current. Coupling of Gas Chromatography and DM-LAAS in the dc Plasma For optimum coupling of gas chromatography with the DCP an auxiliary helium gas flow of 10ml min-' was used with the flow rate of the gas chromatograph (4ml min-'). The pressure in the plasma tube was 40 hPa. The memory effects were reduced significantly by the additional gas flow. A chromatogram obtained by DM-LAAS of chlorine with halo- form sample 1 (see Table 1) diluted by a factor of 20 is displayed in the upper part of Fig.9. A time constant of 1 s was applied. The calibration curve of CCl obtained by integrated absorbance measurements is given in Fig. 10. The detection limit was 5 ng ml-'. Taking into account the sample volume injected into the gas chromatograph the detection limit for chlorine was about 0.25 pg s-' or 2.5 pg. These data are slightly higher than the values measured in the MIP. However the DCP has an economic advantage. The instrumentation to run a dc plasma is less expensive than for an MIP. As in the experiments with the MIP within small statistical error bars the ratios of the peaks reflected the ratios of the chlorine concentrations in the species. Deviations were only found for the first component where the plasma was still influenced by the solvent.However this has also been observed in the measurements with the MIP. The lower chromatogram in Fig. 9 was measured by element- selective detection of bromine injecting a 20-fold diluted sample volume of the haloform test sample 2 (see Table 1). Bromine peaks were observed at the time when species CHBrCl and CHBr,Cl also gave chlorine signals with sample 1. The peak 566 Journal of Analytical Atomic Spectrometry September 1995 Vol. 101 0 . shows a hyperfine structure splitting with four major compo- nents. The component which was used for absorption rep- resents only about 30% of the total line absorption. Furthermore the population densities in the metastable state and the oscillator strength of the analyte line should be different than for chlorine.In sample 2 the concentration ratios of bromine in CHBrCI2 CHBr,Cl and CHBr are 1 1.84 2.74. These ratios can be found by inspection of the bromine signals in the lower chromatogram in Fig. 9. ' - 1 1 I Timels Fig.9 Upper trace chromatogram of diluted haloform sample 1 measured by DM-LAAS of chlorine in the DCP 1 CH2C1 (10pgml-'); 2 CHC1 (225 ngml-I); 3 C,H,CI (50ngml-'); 4 CCll (12 ngml-'); 5 C,HCl (120 ng ml-I); 6 CHBrCl (50 ng ml-'); 7 CHBr,Cl (75 ngml-I); and 8 C,Cl (30ngml-'). Lower trace chromatogram of diluted haloform sample 2 measured by DM-LAAS of bromine in the DCP 6 CHBrC1 (0.49pgml-'); 7 CHBr,Cl (0.92 pg ml-'); and 9 CHBr (1.37 pg ml-I) 'oool A 1 1000 10600 [ C C I ~ I in pentane/ng mi-' Fig. 10 Calibration curves for CC1 measured chromatographically by DM-LAAS of chlorine in the DCP 9 is due to tribromomethane which does not contain chlorine.Only very few measurements have been made with bromine. Furthermore these measurements were made at the optimum conditions found for chlorine. It is possible that the optimum plasma parameters for Br are slightly different. The preliminary detection limit found for bromine (4.5 pg s-' or 45 pg) was about a factor of 18 higher than for chlorine in the dc helium plasma. The difference is partly due to the higher relative atomic mass of bromine (factor of 2.2 in comparison with Cl) and the fact that the bromine line at 827.24nm Comparison with Other Element-specific GC detectors There are many papers on element-specific detectors based on optical emission spectrometry (OES) of different kinds of plasmas.References to these papers can be found in the literature (e.g. refs. 8-10). Depending on the kind of plasma and the lines used in emission spectrometry the best detection limits for chlorine are typically about 7 pg s-'. This value is much larger than the detection limit for chlorine obtained by DM-LAAS in the MIP and the DCP (0.12 and 0.25 pg s-' respectively). The preliminary detection limit of bromine by DM-LAAS in the dc helium plasma (4.5 pg s-') is comparable to the detection limits by OES in different plasmas!-'0 The best reported detection limits of Br by OES are about 10 pg s-1. REFERENCES 1 Silver J. A. Appl. Opt. 1992 31 707. 2 Schnurer-Patschan C. Zybin A. Groll H. and Niemax K. J. Anal. At. Spectrom. 1993 8 1103. 3 Groll H. Schnurer-Patschan C. Kuritsyn Yu. and Niemax K. Spectrochim. Acta Part B 1994 49 1463. 4 Zybin A Schniirer-Patschan C. and Niemax K. Spectrochim. Acta Part B 1993 48 1713. 5 Groll H. Schaldach G. Berndt H. and Niemax K. Spectrochim. Acta Part B in the press. 6 Schnurer-Patschan C. and Niemax K. Spectrochim. Acta Part B in the press. 7 Wiese W. L. Smith M. W. and Miles B. M. Atomic Transition Probabilities US National Bureau of Standards Washington DC vol. 11 1969. 8 Uden P. C. Element-Specijic Chromatographic Detection by Atomic Emission Spectrometry ACS Symposium Series 479 American Chemical Society Washington DC 1992. 9 Long G. L. Ducatte G. R. and Lancaster E. D. Spectrochim. Acta. Part B 1994 49 75. 10 Skelton R. J. Markides K. E. Lee M. L. and Farnsworth P. B. Appl. Spectrosc. 1990 44 853. Paper 5/01 6270 Received March 14 1995 Accepted May 15 1995 Journal of Analytical Atomic Spectrometry September 1995 Vol. 10 567

ISSN:0267-9477    

DOI:10.1039/JA9951000563

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

Some Figures of Merit of a New Double Focusing Inductively Coupled Plasma Mass Spectrometer* Journal of Analytical Atomic Spectrometry LUC MOENS FRANK VANHAECKE JORGEN RIONDATO AND RICHARD DAMS Ghent University Laboratory ofAnalytica1 Chemistry Proeftuinstraat 86 8-9000 Ghent Belgium An ICP-MS instrument with a quadrupole filter is hampered by its limited resolution in particular polyatomic ions are a major source of interference. With a double focusing magnetic sector mass analyser operated at high resolution most of these interferences are eliminated. In addition these mass analysers are characterized by a low instrumental background yielding superior detection limits at low resolution. In this work a new type of double focusing ICP-MS instrument the 'Element' from Finnigan MAT (Bremen Germany) was tested.The instrument can be used with low resolution (m/Am = 300 10% valley definition) and at high resolution settings (3000 and 7500). At low resolution a linear response uersus mass curve was observed [response of 180 x lo6 counts s-' per pg ml-I (ppm) for U and 6 x lo6 counts s-' for Be]. The sensitivity decreases by roughly a factor of 14 when going from resolution 300 to resolution 3000 and by a factor of 10 from 3000 to 7500. An instrumental detection limit at low resolution of about 8 fg ml-' (8 ppq) was measured at m/z 240. The detection limit for most elements is not determined by the instrument but by the blank level and laboratory procedures will need to be improved in order to make optimal use of the detection power of the instrument.The stability and the relative abundance of oxide and doubly charged ions are comparable to the values found in quadrupole ICP-MS. Matrix effects were compared for measurements with the 'Element' and with a Perkin-Elmer Elan 5000 quadrupole instrument of '"In in the presence of 500 pg ml-' of Cs and of 2.5% of ethanol. Though in the 'Element' ions are accelerated over 8 kV immediately after the skimmer matrix effects were found to be similar to those observed for the 'Elan 5000'. The instrument was used to determine Pt in an environmental material (grass). Keywords Inductively coupled plasma mass spectrometry; high resolution; figures of merit standards; platinum in the environment ICP-MS is a widely used method for trace and ultra-trace analysis of solutions liquids gases and solids.Almost all ICP mass spectrometers are equipped with a quadrupole mass filter allowing fast scanning and multi-element analysis. Precise analytical results can be obtained and if all necessary pre- cautions are taken the highest accuracy is possible.' Two major sources of error that need to be recognized and appropriately taken into account are matrix-dependent signal suppression or enhancement and spectral interferences. Most spectral interferences are caused by polyatomic ions surviving the high temperatures in the plasma or being formed in the cooler interface region. Interfering polyatomic ions originate from the plasma gas the solvent entrained air and the sample matrix. In particular species derived from major sample components need a thorough investigation for each new type of sample material.Various methods have been * Presented at the 1995 European Winter Conference on Plasma Spectrochemistry Cambridge UK January 8-13 1995. proposed to reduce eliminate or correct for spectral inter- ferences. Separating the solvent from the sample aerosol is an efficient method to reduce solvent-induced interferences caused by e.g. MO' MOH' and ArO' when analysing aqueous solutions or by MC' and Arc+ in organic solvents. Desolvation by subsequent heating and cooling of the sample aerosol2-' or electrothermal vaporization (ETV)' can be used to produce largely or completely solvent-free aerosols. Evidently spectral interferences originating from the solvent do not occur when applying solid sample introduction with laser ablationg-" or ETV.'2-'5 The latter method also allows matrix elements to be eliminated by thermal decomposition and ashing of the sample prior to analyte vaporization.In general matrix elements can also be eliminated from sample solutions by chemical separation method^.'^-^^ Other tech- niques that can be used to reduce specific matrix-induced spectral interferences include H 0 or N addition to the plasma or carrier dissociation of polyatomic ions by gas-phase collision30 or addition of ethanol to enhance the intensity of the analyte signal while reducing the interference inten~ity.~' Finally mathematical methods can sometimes be used to correct for spectral interference^?^.^^ An obvious solution to most spectral interference problems in ICP-MS is to use a double focusing mass analyser consisting of a magnetic and an electrostatic sector instead of a quadru- pole filter.Presently available high resolution (HR) ICP-MS machines offer a resolution up to m/Am=10000 (Am is the mass difference between two singly charged ions of average mass m that give rise to equally intense peaks in the mass spectrum which overlap at 10% of the maximum peak height). This is largely sufficient to obliterate most though not all interferences by polyatomic species.34 The first commercial HR-ICP-MS instrument ('Plasmatrace' by VG Winsford UK) was introduced35 in 1989 but the technique was used in only a few mostly industrial laboratories and for a limited number of applications requiring high resolution or making use of the superior detection limits offered by double focusing instruments when used in a low resolution mode (m/Am=300).36-43 The latter feature is due to the low background inherent in the curved ion path in double focusing mass analysers.The large gap between the price of a quadrupole instrument and that of a high resolution instrument hampered a wider use of the latter until recently. Recently ( 1993) two other manufacturers brought a double focusing ICP mass spectrometer on the market the 'JMS- Plasmaxl' (Jeol Tokyo Japan)44 and the 'Element' (Finnigan MAT Bremen Germany)45 whereas the Plasma Trace I1 (VG) will replace the first VG machine. The price of these new instruments is comparable to the price of the first quadrupole ICP mass spectrometers in the eighties and a more widespread use can therefore be expected.In October 1994 the first commercial 'Element' instrument was installed in our labora- tory where it is now being tested. In previous work we have used an 'Element' at the factory in Bremen for the analysis of a human serum reference material thereby making use of its Journal of Analytical Atomic Spectrometry September 1995 Vol. 10 569high resolution capability to determine V Fe Cu and Zn in Samples and Standards 4-fold diluted serum.46 In this work emphasis will be put on the determination of the figures of merit and on the study of some of the operational parameters of the 'Element'. Results can be compared with data obtained for a prototype tested at the Institute for Spectrochemistry and Applied Spectroscopy (ISAS Dortmund germ an^).^',^' EXPERIMENTAL Instrumentation Measurements were carried out on the high resolution ICP mass spectrometer the 'Element' which is equipped with a compact double focusing sector field mass spectrometer of reversed Nier-Johnson geometry.Predefined resolution set- tings of 300 3000 and 7500 allow the adjustment of the resolution depending on the analytical problem at hand. The main feature differentiating this instrument from formerly introduced high resolution ICP mass spectrometers is the new interface design allowing plasma torch sampling cone skim- mer and other mechanical parts to be kept at ground potential. This ensures that the sample introduction side of the instrument is easily accessible facilitating coupling with other sample introduction systems hyphenation and adjustment during operation.The 'Element' is equipped with a Spetec peristaltic pump a Meinhard Tr-30-A3 nebulizer a double-pass Scott- type spray chamber with surrounding liquid jacket maintained at 5°C using a recirculating refrigeration-heating system and a Fassel torch. The instrument settings used are briefly summar- ized in Table 1. In order to compare matrix effects observed using this high resolution instrument with those encountered using a quadru- pole-based instrument some experiments were also carried out on a Perkin-Elmer SCIEX Elan 5000. The latter is equipped with a multi-channel peristaltic pump (Minipuls-3) a GemTip cross-flow nebulizer a Perkin-Elmer Type I1 spray chamber made of Ryton drained by the same peristaltic pump and a Perkin-Elmer corrosion resistant torch with standard alumina injector.Instrument settings for the latter instrument are very briefly summarized in Table 2. Table 1 Instrumental conditions for the Finnigan MAT Element Rf power/W Gas flow rates/l min-' Plasma Intermediate Nebulizer Sample uptake rate/ml min Ion sampling depth Ion lens settings Sampling cone Skimmer 1250 14 0.700 0.675-0.800 (adjusted to obtain maximum signal intensity) 1 Adjusted to obtain maximum Adjusted to obtain maximum nickel 1.1 mm orifice diameter nickel 0.8 mm orifice diameter -1 signal intensity signal intensity Table 2 Instrumental conditions for the Perkin-Elmer SCIEX Elan SO00 Rf power/W lo00 Gas flow rates/l min-' Plasma 15 Intermediate 1.2 Nebulizer 0.870 Sample uptake rate/ml min-' 0.9 Ion sampling depth Sampling cone Skimmer 10 mm from load coil nickel 1.0 mm orifice diameter nickel 0.75 mm orifice diameter All standard solutions used to investigate the performance (e.g. detection limits signal intensities stability matrix effects) of the instrument were prepared by successively diluting commercially available mono-element standard solutions (1 mg ml-I).During these dilutions only water (Millipore Milli-Q) and 0.14 moll-' HNO (obtained by dilution of 14 moll-' HNO purified by sub-boiling distillation with Milli-Q water) of the highest purity available at our laboratory were used. In order to avoid contamination and/or memory effects to the largest extent possible these dilutions were carried out using micropipettes while of course only thoroughly precleaned vessels were used.For the determination of Pt in grass samples were collected at a meadow in a rural area. The grass was dissolved using a stepwise procedure. First 0.625 ml of 10 moll-' HCl (purified by sub-boiling distillation) and 4.0 ml of 14 moll-' HN03 (purified by sub-boiling distillation) were added to about 0.5 g of a dried and ground grass sample in a Teflon bomb which was subsequently subjected to a multi-step microwave heating programme. The latter programme consisted of several steps during which the power applied was gradually increased. An additional 0.5 ml of HNO was added before the last step. After this microwave dissolution procedure the sample solu- tion was quantitatively transferred into a Teflon beaker and 1 ml of HF (500/ Baker Instra-analyzed USA) was added.The sample was evaporated to dryness while during the latter procedure two aliquots of 0.5 ml of Hz02 (30% pro analysi Merck Germany) were added. The residue was dissolved using 3% HC1 quantitatively transferred into a 25 ml calibrated flask and adjusted to volume using 3% HC1. Since the solutions obtained were not completely clear a 'second' destruction step was necessary. Hence 2 ml of 14 moll-' HNO was added to 2ml of the sample solution obtained and the mixture was evaporated to near-dryness again. Finally the residue was quantitatively transferred into a 25 ml calibrated flask and was adjusted to volume using 3% HC1. Blanks were obtained following exactly the same procedure but without sample intake. Measurements For all measurements the parameters used are briefly summar- ized in Table 3.Detection limits were determined according to International Union of Pure and Applied Chemistry (IUPAC) recommendation (3s-criteri0n)~' using 0.14 moll-' HNO as the blank (10 measurements) and 1 or 10 ng ml-' standard solutions as a standard (3 measurements). To evaluate the stability of standard solutions at concentration levels < 1 ng ml-' both freshly prepared standards and standards that were kept stored for periods from a few days up to several weeks were measured and signal intensities were compared. Memory effects were evaluated by registration of the signal of one nuclide for a period of several minutes during which first a blank solution then a standard solution and finally the blank solution again was aspirated.For the determination of Pt in grass the blank sample and standard solutions were measured three times. This measurement sequence also avoided Table 3 Measurement parameters for the Finnigan MAT Element ~ Acquisition mode No. of scans 20 Dwell time per acquisition point/ms No. of acquisition points per mass E-scan - electric scanning over small mass ranges 5 200 1 s per mass segment and segment (per nuclide) Total acquisition time per scan 570 Journal of Analytical Atomic Spectrometry September 1995 Vol. 10important memory effects and hence lengthy rinsing of the sample introduction system. RESULTS AND DISCUSSION Figures of Merit In Fig. 1 the count rates (peak height) measured at low resolution (300) for a number of 1 ng ml-' solutions are plotted as a function of analyte ion mass (mlz). Results were normalized to 100% abundance of the isotopes measured.The figure shows that the sensitivity linearly decreases with decreas- ing mjz. For 238U a sensitivity of 180x lo6 counts s-' per pg ml-' (ppm) U was measured; at mass 9 (Be) the sensitivity was lower by a factor of 30 (6 x lo6 counts s-' per pg ml-' Be). A new skimmer design which was not incorporated in the instrument used here was reported to increase the sensi- tivity by a factor of 2-3.50 In future work results of a comparative study of response curves valid for different exper- imental conditions will be presented and the phenomenon will be discussed in more detail. To obtain a higher mass resolution the width of the entrance and exit slits of the mass spectrometer is reduced.Consequently the transmission and the sensitivity of the instrument will also decrease. When changing the resolution from 300 to 3000 the sensitivity was found to drop to ~ 7 . 5 % of its original value. At a resolution of 7500 the sensitivity is about 10% of the value found at a resolution of 3000. With the instrument considered in this work 52Cr was measured at a resolution of 3000 with a sensitivity of the order of lo6 countss-' per pg ml-' (ppm). Few spectral interferences by polyatomic ions require a resolution of more than 3000 for instance the interferences by 35Cl'60+ on 51V 40Ar'2C+ on "Cr+ or 40Ar'60+ on 56Fe+ are resolved at resolutions of 2572 2375 and 2502 respectively.Of the 155 interferences by polyatomic ions at mlz 24-76 requiring a resolution of between 500 and 10000 and listed by Reed et al.,34 123 can be eliminated with a resolution below 3000 and from the remaining 32,25 require a resolution between 3000 and 7500. A resolution between 7500 and 10000 is necessary to eliminate the interference by 4oAr35C1' on 75As+ (resolution of 7775 required) and of a number of interferences on Ge isotopes (72Ge 73Ge 74Ge and 76Ge). Isobaric nuclides in general cannot be separated with the resolution available on commercially available HR-ICP-MS instruments. The stability of the signal measured at low resolution was found to be similar to values common to quadrupole instru- ments. Ten replicate measurements over a 2 min period show an RSD of 1-2% whereas the long term stability (2 h) is 3-4%.On a day-to-day basis the instrument requires little tuning and once optimized the same lens settings can be used for 200 r 'L t I /" I I I 50 100 150 200 250 01 J 0 d.? Fig. 1 Signal (peak height) obtained when measuring 1 ng ml-' solutions of different elements at low resolution. Results were nor- malized to 100% abundance of the isotopes measured and plotted as a function of analyte ion mass optimal sensitivity and stability over a period of months. Optimal settings for the different resolution modes are stored in the software and can be recovered instantly when needed. The intensities of the signals of doubly charged and oxide ions were measured for Ba. Under gas flow conditions selected for maximal intensity of the Ba+ signal a BaO' Ba' signal ratio of 0.12% was determined.This value is comparable to results obtained for quadrupole instruments. The measured Ba2+ Ba+ signal ratio of 0.95% on the 'Element' is lower than the typical values on quadrupole instruments (2-3%). The background in double focusing machines is substantially lower than that of quadrupole instruments. The curved ion path and the narrow slits effectively prevent photons reaching the detector limiting the background to the level of the electronic detector noise. The background level of the Element is specified to be about 1 count (integrated over a mass window) in every 5 s. For the measurements done in this work the background was higher (approximately 1 counts-'). Detection limits were determined at low resolution applying the 3s criterion.49 Owing to the lower background and the higher sensitivity detection limits can be expected to be superior to those found in quadrupole ICP-MS.Results for a number of elements are represented in Fig. 2. The detection limit at mjz 240 was calculated using the sensitivity measured for U at m/z 238 and can be considered to be an accurate measure for the instrumental detection limit. A value of 8 fg mi-' was found for the present instrument and measuring protocol. Further optimization should allow instrumental detection limits of around 1 fgml-'. Yamasaki et al." reported a 10 times better detection limit for U using a Fisons VG 'Plasmatrace' instrument and integration times of 1 h. Obviously the instrumental detection power of double focusing instruments is sufficiently high for most applications aiming at the determination of concentrations that are sufficiently high to be meaningful from any real life point of view.With this type of instrument blanks are the limiting factor as is clearly demonstrated by Fig. 2 revealing that only for a few of the elements tested (eg. Tb) the instrumental detection limit was reached. For most elements however blanks are an important restriction. The detection limit of 18 pg ml-' for Zn (deter- mined via 66Zn) for instance originated from a signal equival- ent to 100 pg ml-' of Zn in the blank originating partly from contamination of the Milli-Q water produced by the system in our laboratory and partly from polyatomic species elements blanks are not so extravagantly high but in general the above confirms that the introduction of double focusing ICP-MS instruments demands a thorough investigation and efficient reduction of blanks if the instrumental detection power is anted.^' At high resolution detection limits will be higher (as expected ( 3 6 ~ ~ 1 6 0 1 4 ~ + 3 8 ~ ~ 1 4 ~ + 3 40Ar'2C'4N+).For many other 100 . I . . . . . . n . 0.001 Cu Zn La Tb Lu Pt Pb Th U 240 Fig. 2 Detection limits at low resolution determined applying the 3s criterion49 on the results of 10 consecutive measurements of a 0.14 mol I-' HNO blank solution Journal of Analytical Atomic Spectrometry September 1995 Vol. 10 571from the sensitivity drop shown in Fig. l) except when spectral interferences hamper the determination at low resolution.In Fig. 3 the spectrum at m/z 55 of a blank solution (Milli-Q water) measured with a resolution of 3000 is shown together with the spectrum of a 5 ng ml-' Mn solution in 0.14 moll-' HN03. Both spectra reveal the presence of 40Ar'4N'H+ (more abundant in the spectrum of the HNO containing standard solution); probably 38Ar1601Hf contributed to the same peak. In the blank spectrum a very low signal is detected at the mass of 5sMn leading to a detection limit of 4 pg ml-' which is an order of magnitude below the detection limit of 33 pg ml-' obtained at low resolution. The linear dynamic range of the instrument as specified by the manufacturer extends over 9 orders of magnitude. In this work the calibration curve was measured for Cs.A linear relation was found between 1 pg ml-' and 10 pg ml-1 (Fig. 4). To avoid excessive contamination of the instrument no higher concentrations were measured whereas at concentrations below 1 pg ml-' blanks hampered the extension of the cali- bration line. The line shown in Fig. 4 therefore covers only 7 orders of magnitude but extension to 9 orders of magnitude seems possible. Memory Effects As a result of its high sensitivity and low instrumental back- ground the instrument is very susceptible to memory effects. When low concentrations must be measured in the low reso- lution mode careful planning of experiments will be necessary. Memory effects after the continuous introduction of a 10 ng ml-' solution were studied using the low resolution mode (300).Results are shown for U and Pt in Fig. 5. For U r u) 5 80 m$ 60 'u) 100 s 5 40 5 20 " . " 0 0 d Z Fig. 3 Spectra at m/z 55 obtained by measuring a blank solution (Milli-Q water) and a 5 ng ml-' Mn standard in 0.14 moll-' HNO,. Resolution of 3000 @/Am definition); count rates based on counting during 40 ms for each mass channel IE+09 I 1 [Csyng mr' Fig. 4 Calibration line for Cs (133Cs) measured at low resolution IE+06 I Timek Fig.5 Memory effects after the continuous introduction of a 10ngml-' solution of (a) U and (b) Pt; measurements at low reso- lution mode the signal returns to its original blank level within minutes after the nebulization of the 10 ng ml-I solution [Fig. 5(a)]. For Pt however strong memory effects are observed [Fig. 5(b)] hampering accurate measurements at a level below 10 pg ml-'.Fortunately the memory effect seems not to orig- inate from contamination of the lenses as it can be obliterated by cleaning the sample introduction system and the cones. For a 1 ng ml-' Pt solution no large memory effects were observed. The problem of Pt causing memory effects by contamination of glassware and instruments has also been reported for other instruments and method^.'^*'^ The extension of the application field of ICP-MS to the sub-pg ml-' region and the inherent increased risk of errors by memory effects make the use of standard solutions with concentrations of 1 ng ml-I or lower more suitable. The stab- ility over a long period of time of standards at this concen- tration level is now being studied for Ag Au Cd Cr Mn Ni Pt Se and V.Standards with concentrations of 1 ng ml-' and 100 pg ml-' in 0.14 moll-' HN03 and stored in polythene vials have already been measured several times over a period of one month. Some results (V and Au) are shown in Fig. 6. For all elements under consideration the 1 ng ml-' standards turned out to be stable [e.g. shown for Au in Fig. 6(a)]. The same holds for the 100 pg ml-' standards investigated [V Ag Cd Pt and Au; e.g. V shown in Fig. 6(b)] except for Au. As shown in Fig. 6(b) the Au concentration in a 100 pg ml-' Au solution rapidly decreases with time probably by adsorption of the Au onto the walls of the vial. Addition of HCl to the solution is necessary. Matrix Effects Double focusing instruments may solve most problems caused by spectral interferences but also suffer from non-spectral matrix effects originating from the plasma and from the sample introduction system as is the case for quadrupole ICP mass spectrometers.A major difference between both types of instru- 572 Journal of Analytical Atomic Spectrometry September 1995 Vol. 10$ 1.4 I 1 ng mi-' AU I * c 0.8 0.6 I I I I 2 0 / 0 1 1 I I I I I I 0 5 10 I5 20 25 30 35 40 Timeld Fig. 6 Stability of standard solutions containing (a) 1 ng ml-' Au; and (b) 100 pg ml-' Au and 100 pg ml-' V. Measurements at low resolution ments however is the acceleration of the ions by an 8 kV potential applied immediately after the skimmer cone in double focusing instruments. Therefore expansion of the accelerated ion beam by electrostatic repulsion can be expected to be negligible when compared with the same phenomenon in a quadrupole machine and space charge effects should be less prominent with a double focusing instrument.In this work the effect on the ''sInt signal of the addition of 500 pg ml-' of Cs to a solution containing 10 ng ml-' of In in 0.14 moll-' HNO was studied. Measurements were performed as a func- tion of carrier gas flow rate and for two different instruments the 'Element' and the 'Elan 5000' quadrupole instrument. In the 'Element' the load coil is earthed at the end nearest to the sampling cone whereas in the 'Elan 5000' the coil is driven symmetrically. Results are represented in Fig. 7. Upon the addition of 500 pg ml-' of Cs for both instruments the maxi- mum of the carrier gas flow curve shifts to a higher value and the maximum sensitivity increases.Using either instrument measurements at a gas flow rate optimized for 0.14mol1-' HN03 showed almost no signal suppression when 500 pg ml-' of Cs is added. Matrix effects caused by the addition of up to 2.5% of ethanol to the solution are also found to be very similar for both instruments. Results of a systematic study of matrix effects will be discussed in a separate papereS4 At this time it would appear that matrix effects are not significantly different for both types of instruments. Determination of Pt in Grass Whereas the high resolution of double focusing ICP mass spectrometers is an obvious analytical advantage it is not evident that the lower limits of detection obtainable in the low resolution mode are useful.Indeed appropriate sample preparation or chemical pre-treatment can often compensate for the lower detection power of quadrupole instruments. In this work the 'Element' is used for the direct determination of very low concentrations of Pt in grass. The determination of Pt in the environment has been a research topic in this laboratory over the past 3 years. The general introduction of car exhaust catalysts and the concern about the potential hazard of Pt released in the environ- ment55ss6 require preventive monitoring of the Pt concen- trations and a study of the effects on plant animal and human health. When using quadrupole ICP-MS the determination of the Pt concentration in plants from unpolluted or little exposed o ! - I I 0 5 0.6 0.7 0.8 0.9 'F 60 Perkin Elmer Elan SO00 r-4 - \ \ \\ 10 A 0 5 0.9 1.1 1 3 OL 0 7 Carrier gas flow raten min-' Fig.7 '"In+ signal plotted as a function of the carrier gas flow rate for a solution containing 0 10 ng ml-' of In in 0.14 moll-' HNO and A the same solution after addition of 500pgml-' of Cs. Comparison between the 'Element' and the 'Elan 5000'; measurements at low resolution areas requires chemical enrichment procedure^.^^-^^ Such pro- cedures are laborious and involve serious contamination risks. With a double focusing instrument however it was possible to determine Pt directly in digested grass (see above) from an unpolluted area. In Fig. 8 the spectrum of the grass sample and of a 1 ng ml-' standard are superimposed. A concentration of 0.45 pg ml-' was measured in the solution which is far below the detection limit of quadrupole ICP-MS (6 pg ml-').The corresponding concentration in the dry grass sample was calculated to be 700 pg g-'. CONCLUSION It can be concluded that the new instrument for high resolution ICP-MS the 'Element' (Finnigan MAT) allows most spectral interferences by polyatomic species to be eliminated when used d z Fig. 8 Pt peak measured at low resolution in the solution of (a) grass sample and (b) 1 ng ml-' standard solution count rates are based on counting during 40 ms for each mass channel Journal of Analytical Atomic Spectrometry September 1995 Vol. 10 573with a resolution of 3000. In addition the instrument offers drastically improved detection limits down to the fg m1-l level when used in a low resolution mode.Improved detection limits are useful for applications requiring chemical enrichment in quadrupole ICP-MS and for speciation studies at trace element level. To make use of this possibility however it will be necessary to improve laboratory techniques in order to reduce blanks. To avoid memory effects at the sub-pg ml-’ level it is advisable to use standards with concentrations of 1 ng ml-’ or lower. The ‘Element’ and other similar double focusing instruments will probably be more widely used in the future not only for typical high resolution applications but also for the measurement of low concentrations. Matrix effects are obviously not eliminated by high resolution and will continue to be a source of potential error requiring expertise and appropriate correction methods.REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 Moens L. Vanhoe H. Vanhaecke F. Goossens J. Campbell M. and Dams R. J. Anal. At. Spectrom. 1994 9 187. Lam J. W. and McLaren J. W. J. Anal. At. Spectrom. 1990 5 419. Tsukahara R. and Kubota M. Spectrochim. Acta Part B 1994 45 581. Jakubowski N. Feldmann I. and Stuewer D. Spectrochim. Acta Part B 1994 47 107. Alves L. C. Wiederin D. R. and Houk R. S. Anal. Chem. 1992. 64 1164. Alves L. C. Allen L. A and Houk R. S. Anal. Chem. 1993 65 2468. Vanhoe H. Moens L. and Dams R. J. Anal. At. Spectrom. 1994 9 815. Hulmston P. and Hutton R. C. Spectroscopy 1991 6 35. Thompson M. Goulter J. E. and Sieper F. Analyst 1981 106 32. Arrowsmith P. Anal. Chem.1987 59 1437. Denoyer E R. Fredeen K. J. and Hager J. W. Anal. Chem. 1991,63 445A. Voellkopf U. Paul M. and Denoyer E. R. Fresenius’ J. Anal. Chem. 1992 342 917. Wang J. Carey J. M. and Caruso J. A. Spectrochim. Acta Part 8 1994 49 193. Moens L. Verrept P. Boonen S. Vanhaecke F. and Dams R. Spectrochim. Acta. Part B 1995 50 463. Vanhaecke F. Boonen S. Moens L. and Dams R. J. Anal. At. Spectrom. 1995 10 81. Beauchemin D. McLaren J. W. Mykytuik A. P. and Berman S. S. J. Anal. At. Spectrom. 1988 3 305. Plantz M. R. Fritz J. S. Smith F. G. and Houk R. S. Anal. Chem. 1989 61 149. Heithmar E. M. Hinners T. A. Rowan J. 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The Royal Society of Chemistry Cambridge 1991 p.12. 40 Tsumura A and Yamasaki S. in Applications of Plasma Source Mass Spectrometry eds. Holland G. and Eaton A. N. The Royal Society of Chemistry Cambridge 1991 p.119. 41 Takaku Y. Masuda K. Takahashi T. and Shimamura T. J. Anal. At. Spectrom. 1993 8 687. 42 Yamasaki S. and Tsumura A. Water Sci. Techno/. 1992,25 205. 43 Sargent M. and Webb K. Spectrosc. Eur. 1993 5 21. 44 Hertens R. C. Morita T. and Kubota M. Second Regensburg Symposium on ‘Massenspektrometrische Verfahren der Elementspurenanalyse’ 1993 P2. 45 Giessmann U.and Greb U. Second Regensburg Symposium on ‘Massenspektrometrische Verfahren der Elementspurenan- alyse’ 1993 DV1. 46 Moens L. Verrept P. Dams R. Greb U. Jung G. and Laser B. J. Anal. At. Spectrom. 1994 9 1075. 47 Feldmann I. Tittes W. Jakubowski N. and Stuwer D. J. Anal. At. Spectrom. 1994 9 1007. 48 Tittes W. Jakubowski N. Stuewer D. and Tolg G. J. Anal. At. Spectrom. 1994 9 1015. 49 Long G. L. and Winefordner J. D. Anal. Chem. 1983 55 712A. 50 Hamester M. Greb U. and Rottmann L. poster presented at the 1995 European Winter Conference on Plasma Spectrochemistry Cambridge UK January 8-13 1995. Abstract PM79 p. 177. 51 Yamasaki %I. Tsumura A. and Takaku Y. Microchem. J. 1994 49 305. 52 Alt F. Jerono U. Messerschmidt J. and Tolg G. Mikrochim. Acta 1988 299. 53 Hoppstock K. Alt F. Lammann K. and Weber G. Fresenius’ Z. Anal. Chem. 1989 335 355. 54 Vanhaecke F. Riondato J. Moens L. and Dams R. in preparation. 55 Nieper H. Raum und Zeit 1989 Special 2 1. 56 Bartsch A and Schlatter C. Schriftenreihe Umweltschutz 1988 95 1. 57 Wood S. A. Vlanopoulos D. and Mucci A. Anal. Chim. Acta. 1990,229 227. 58 Lee M. L. Tolg G. Beinrohr E. and Tschopel P. Anal. Chim. Acta 1993 272 193. 59 Plantz M. R. Fritz J. S. Smith F. G. and Houk R. S. Anal. Chem. 1989 61 149. Paper 5/01 9736 Received March 29 1995 Accepted June 8 1995 574 Journal of Analytical Atomic Spectrometry September 19!)5 Vol. 10

ISSN:0267-9477    

DOI:10.1039/JA9951000569

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

Analytical Characteristics of an Inductively Coupled Plasma Mass Spectrometer Coupled With a Thermospray Nebulization System* Journal of Analytical Atomic Spectrometry HANS VANHOE STEVEN SAVERWIJNS MAGALI PARENT LUC MOENS AND RICHARD DAMS Laboratory of Analytical Chemistry University of Ghent Institutefor Nuclear Sciences Proeftuinstraat 86 8-9000 Ghent Belgium The analytical characteristics of a thermospray sample introduction system coupled to an inductively coupled plasma mass spectrometer have been evaluated. The results obtained with the thermospray system were compared with those obtained with two other arrangements namely the pneumatic nebulizer coupled with a spray chamber (the conventional arrangement) and the same pneumatic nebulizer coupled with the desolvating unit employed with the thermospray nebulizer.In the presence of salts of Na (NaNO,) or Ca[Ca(NO,),] the non-spectroscopic interferences (analyte ion signal suppression) were more pronounced in the thermospray system than in the conventional arrangement whereas in the presence of mineral acids ( H2S04 H3PO4) both systems gave similar suppressions. The apparent analyte element concentrations due to spectral overlap with MO,' (e.g. SO' SO,' PO' POz+ CaO+) or ArM+ (e.g. ArNa+ ArS' ArP') were lower or similar for the thermospray nebulizer in comparison with those obtained with the conventional arrangement. In order to reduce memory effects a sample flow injection system was used for the analysis of three candidate environmental reference materials [Community Bureau of Reference (BCR) Certified Reference Materials 141R Soil-calcareous loam 144R Sewage sludge-domestic and 146R Sewage sludge- industrial].The accuracy and precision of external calibration with internal standardization standard additions and isotope dilution were compared. Similar results were obtained for the aqua regia soluble content of Cd and Pb in these materials. Keywords Inductively coupled plasma mass spectrometry; thermospray nebulization; memory ejfects; spectroscopic and non-spectroscopic interferences; calibration methods; analysis of environmental samples Although inductively coupled plasma mass spectrometry (ICP-MS) is a well established technique in many analytical laboratories the technique suffers in many instances from some major drawbacks.One of these is the poor efficiency typically 1-2% of the conventional sample introduction system con- sisting of a pneumatic nebulizer and a spray chamber. This feature restricts the sensitivity of the technique. Therefore many researchers have investigated alternative nebulizers with an improved nebulization efficiency. For the introduction of solutions into an ICP-MS system an ultrasonic nebulizer,ls2 a direct injection nebulizer3-' and a hydraulic high pressure nebulizer6*' have been evaluated. All of these nebulizers give an improvement in the sensitivity and the detection limits by one order of magnitude. Recently Montaser et al.' and Vanhoe et a[.' have coupled a thermospray system to an ICP mass spectrometer. In this system the solution is forced to flow through a heated capillary. At the end of the capillary the liquid is partially vaporized and the vapour is expanding * Presented at the 1995 European Winter Conference on Plasma Spectrochemistry Cambridge UK January 8-13.1995. adiabatically producing a heated aerosol. Studies on the funda- mental characteristics of the thermospray have been intensively carried out by coupling the system to an ICP optical emission spectrometer.'-'l As the size of the aerosol droplets (median diameter of 2 pm for the primary aerosol') is lower than for other nebulization systems analyte transport efficiencies of 53% have been reported," resulting in better sensitivities and detection limit^'^^'^ (up to a factor of 2OI4). Coupling of a thermospray system to an ICP mass spectrometer has also led to an improved performance.Montaser et al.' reported detec- tion limits that were improved by a factor of up to 20 for 15 elements whereas Vanhoe et a1.' concluded that the sensitivity and the detection limits were improved by a factor of 10. In addition they reported a decrease in the levels of oxide and doubly charged ions by a factor of 2.5 when an efficient desolvating system is applied. As there is an increased analyte transport to the ICP the solvent transport is also higher so that to avoid solvent overloading of the plasma the thermospray nebulizer must be followed by a desolvating system. Nevertheless from ICP optical emission spectrometry experiments it can be concluded that matrix effects are usually larger for thermospray sample introduction than for pneumatic nebulization even with the use of an efficient desolvating ~ystern.'~.'~ In this work the effects of different matrix salts and mineral acids on analyte element ion signals in ICP-MS were investi- gated.Use was made of a thermospray sample introduction system described in a previous publication' and consisting of a stainless-steel capillary tube with an internal diameter of 180pm and followed by a heated spray chamber and a condenser as desolvating unit. Results are compared with those obtained with a conventional concentric pneumatic nebulizer combined with a spray chamber and with the same pneumatic nebulizer combined with the desolvating unit employed for the thermospray nebulizer. In addition spectroscopic interferences arising from the matrix elements Ca Na P and S were investigated. In order to analyse 'real' samples a sample flow injection system was installed.With this arrangement some environmental samples were analysed and three standardiz- ation procedures namely external calibration in combination with internal standardization standard additions and isotope dilution were compared. EXPERIMENTAL ICP-MS Instrument All measurements were made with a VG PlasmaQuad PQ1 (VG Elemental a division of Fisons Instruments Winsford Cheshire UK). The original interface was replaced by a high- performance interface with a new design of sampling cone and skimmer cone and a better vacuum pumping system in order to improve the sensitivity. The operating conditions for the ICP mass spectrometer are presented in Table 1.Journal of Analytical Atomic Spectrometry September 1995 Vol. 10 575Table 1 ICP-MS operating conditions Conditions Stage Parameter Plasma Pneumatic nebulization system Thermospray nebulization system Ion sampling Vacuum Frequency Rf power Torch Gas flow plasma auxiliary Sample uptake rate Nebulizer gas flow Sample uptake rate Power applied to the capillary Temperature of the aerosol Temperature of the cooling water Carrier gas flow rate Sample cone Skimmer cone Sampling depth Expansion stage Intermediate stage Analyser stage 27.12 MHz 1350 W Fassel-type 14 I min-' 1 1 min-' 0.9 ml min-' 0.720 I min-' 1.33 ml min-' 55 w 120 "C 1 "C 0.820 I min-' Nickel 1.0 mm orifice Nickel 0.75 mm orifice 10 mm (from load coil) 1.6 mbar 1.0 x mbar 2.0 x mbar Pneumatic Nebulization System For comparison with the thermospray nebulization system a Meinhard (TR-30-A3) concentric glass nebulizer and a double pass Scott-type spray chamber with surrounding liquid jacket made of borosilicate glass were used.The spray chamber was thermostated to within 0.1 "C (1 "C) by a recirculating cooling system (Barrington LT6). A peristaltic pump (Gilson Minipuls-2) delivered a constant sample flow rate (uptake rate of 0.9 ml min-l) to the pneumatic nebulizer. Thermospray Nebulization System The thermospray sample introduction system was described in detail in a previous publication.8 The capillary tube (stainless steel with an internal diameter of 180 pm) positioned in a conical flask was followed by a heated L-shaped tube and a modified Friedrichs condenser.The optimum operating con- ditions for the thermospray nebulization system are also given in Table 1. In order to analyse 'real' samples a discrete analyte introduc- tion system was placed between the HPLC pump (Varian 8500 a single-syringe pump) and the capillary tube. It consists of a Valco sample injection valve (six gates) with a 200 p1 sample loop made of PTFE. 'Real' samples were introduced semi-continuously by using a large sample loop of 5 ml. In this way three measurements each lasting 1 min could be made on each sample. Test Solutions For the study of spectroscopic and non-spectroscopic inter- ferences matrix element solutions were prepared using NaNO (Carlo Erba pro analysi) Ca(NO& (UCB pro analysi) H3P04 (Merck pro analysi) and H2S04 (purified by sub- boiling distillation).The respective matrix element solutions- 1 5 50 250 1000 and 5000mg1-' for each matrix element (Na Ca P and S)-were prepared with 0.14moll-' nitric acid. A 10 pg 1-' multi-element solution (Be Al Sc Co In Gd T1 Th and U) was added to all matrix element solutions. This solution was prepared in 0.14moll-' nitric acid from commercially available AAS standard solutions. Water and nitric acid (14 moll-') were purified respectively by a Millipore Milli-Q water purification system (resistivity of 18 MR cm) and by a sub-boiling distillation system. All results were obtained using the scanning mode for data acquisition. The following scanning parameters were chosen mass range between 6 and 256 u 20 channels per u with a dwell time per channel of 320 ps and a total acquisition time of 1 min. The following isotopes were selected 'Be "Al 4'Sc 59C0 "'In 158~d 205T1 232Th and 238U.Sample Preparation and Analysis Procedure for the Reference Materials Three candidate environmental reference materials were ana- lysed namely Community Bureau of Reference (BCR) Certified Reference Materials (CRMs) 141R Soil-calcareous loam 144R Sewage sludge-domestic and 146R Sewage sludge-indus- trial. All materials were treated with aqua regia and the soluble content of Cd and Pb was determined. Therefore approxi- mately 1 g of each candidate reference material was heated under reflux in a mixture of 11.4 ml of aqua regia [9 ml of 10 moll-' hydrochloric acid (purified by sub-boiling distil- lation) and 2.4ml of 14mol1-' nitric acid] and 2-3 ml of Millipore Milli-Q water as described in the DIN 38 41437 procedure," except that the resulting solution was not filtered.The solution obtained was transferred quantitatively into a 100ml calibrated flask and adjusted to volume with 0.14 moll-' nitric acid. A similar procedure was followed for the preparation of a blank solution (without sample). For the determination of the aqua regia soluble content of Cd the standard additions method was applied. All sample solutions were diluted 10-fold with 0.14 mol 1-' nitric acid. For each sample an unspiked solution and a solution spiked with 25 pg 1-' of a Cd standard solution (Cd foil Goodfellow Metals 99.99%) were prepared. Rhodium (100 pg l-' Janssen Chimica AAS standard solution) was added to all solutions as internal standard.Three measurements were made on each solution with the following scanning parameters mass range between 101 and 113 u 20 channels per u with a dwell time per channel of 320ps and a total acquisition time of about 1 min. The isotopes selected were '03Rh '"Cd and "'Cd. For the determination of the aqua regia soluble content of Pb external calibration standard additions and isotope dilution were applied. For each material three sample solutions were prepared an unspiked sample solution (diluted 20-fold for CRM 141R; diluted 40-fold for CRM 144R; diluted 200-fold for CRM 146R) a sample solution spiked with 103 pg 1-' of Pb [National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 983 Radiogenic Lead Isotopic standard (zosPb206Pb =0.013619)] and a sample solu- tion spiked with 25 pg 1-' of Pb [(Pb(NO,) UCB analytical- reagent grade with a natural isotopic composition for Pb].To all solutions-samples and blank-50 pg 1-' of T1 (Alfa 576 Journal of Analytical Atomic Spectrometry September 19!?5 Vol. 10Products AAS standard solution) was added as internal stan- dard. For external calibration Pb standard solutions with a concentration of 10 25 and 50 pg 1-' of Pb [Pb(NO,) UCB analytical-reagent grade] were prepared to obtain a calibration graph. For external calibration and standard additions the ,08Pb isotope was selected for the quantitative determinations. For the isotope dilution method the mass fractionation factor was determined by measuring a Pb standard solution with a certified 208Pb:206Pb ratio (NIST SRM 981 Common Lead Isotopic standard 208Pb:206Pb = 2.168 1).Three measurements were made on each solution with the following scanning parameters mass range between 200 and 210 u 20 channels per u with a dwell time per channel of 3 2 0 p and a total acquisition time of about 1 min. The isotopes selected were ,05Tl ,06Pb and '08Pb. RESULTS AND DISCUSSION Memory Effects A flow injection system with sample loops of 200 1.11 and 5 ml was used to study the memory effects of the thermospray system. Fig. 1 (a) and (b) gives signal plots as a function of time for respectively a 200 p1 loop (filled with 25 pg I-' of T1) and a 5 ml loop (filled with 25 pg 1-' of Rb). For the 200 11 loop a transient signal is obtained with a time basis of about 40 s indicating that the signal almost immediately drops to a normal background level.For five successive analyte injections a relative standard deviation of 1.6 and 0.7% was found based on respectively the peak height and the peak area. As can be seen using a 5ml loop has the advantage that a constant signal can be obtained for 3-4min so that several measure- ments can be carried out. As already mentioned this semi- continuous arrangement was used to analyse some environ- mental samples. For the 5 ml sample loop it can be noticed that the Rb ion signal decreases by three orders of magnitude 1 x 1 0 ~ 7.5~1 O4 5x1 O4 v) 2 . 5 ~ 1 0 ~ ,o c a sr v) c .- L 5 0 C .- - m 0 ijj 1x106 20 40 60 80 TimelS 85Rb-signal 0 3 6 9 Ti m e h i n Fig.1 '03Tl ion signal as a function of time for a 200 pl sample loop filled with 25 pg I-' T1 and 85Rb ion signal as a function of time for a 5 ml sample loop filled with 25 pg I-' Rb within about 1 min. The Cd La and T1 signals behave in the same way. For elements such as Ta Pt and U a longer period of time is required before an acceptable background level is achieved. These plots are similar to those observed with a concentric nebulizer combined with a spray chamber. However Fig. l(b) illustrates that after the initial drop of the analyte signal the background signal (at the mass of the analyte element) is not stable. The short enhancements of the back- ground signal can be reduced by using the 200 pl sample loop or standard solutions with lower concentration.Additional experiments have demonstrated that this memory effect is located inside the desolvating system and not inside the capillary tube and/or the flow injection system. This phenom- enon is probably due to analyte that is left behind in the desolvating unit which is not surprising because of the large volume of this arrangement. Further experiments will be carried out to reduce the size of this unit. Finally as the solution introduced into the thermospray system is heated in the capillary tube for some elements specific memory effects can be observed. For instance Hf will precipitate as hafnium oxide in the heated capillary tube and cause a considerable memory effect. Lowering the power applied to the capillary tube or adding sufficient hydrofluoric acid to the Hf solution will respectively reduce and even eliminate this precipitation as illustrated in more detail elsewhere." Spectroscopic Interferences The polyatomic ions originating from the matrix elements Ca Na P and S that give rise to spectral overlap with analyte elements were examined.This is of particular interest as on the one hand there is undoubtedly an increase in the matrix transport to the ICP resulting in the presence of larger amounts of Ca Na P or S in the plasma On the other hand a decrease in the solvent transport (in our case mainly water) to the ICP was experimentally observed with our desolvating system8 resulting in lower oxide levels. The extent of formation of these polyatomic ions by the thermospray system was compared with that for two other arrangements namely the pneumatic nebulizer coupled with a spray chamber (conventional arrange- ment) and the same pneumatic nebulizer coupled with the desolvating unit employed with the thermospray nebulizer.An example is given in Fig. 2(a) where the 4oCa'60':1'51n+ ratio (In as internal standard) is plotted as a function of the Ca concentration. As can be seen the pneumatic nebulizer com- bined with the desolvating system (used for the thermospray nebulizer) gives the lowest Ca0:In ratios. These ratios are almost a factor of 10 lower than those obtained with a pneumatic nebulizer combined with a spray chamber. Up to a Ca concentration of 1 g l-' the Ca0:In ratios obtained with the thermospray system are significantly lower than those obtained with the conventional arrangement and are higher than those obtained with the combination of a pneumatic nebulizer and the desolvating system.In general for MO' and MOH' it can be concluded that in most instances (CaO' PO' SO') the normalized MO' and MOH' signals are lower for the thermospray system than those for the conventional arrangement and similar to or higher than those for the pneumatic nebulizer combined with the desolvating unit. A similar conclusion can be made for the formation of MO,' and M02H+ as illustrated in Fig. 2(b) for 31P160160+. From these experiments it can be concluded that the decrease in the normalized MO,' signals observed with the thermo- spray system is almost totally due to the use of the desolvating unit. As can be deduced from Fig.2(c) where the ratio of 40Ar23Na':59Co' is plotted as a function of the Na concen- tration the normalized ArNa' signals obtained with the thermospray system are similar to those obtained with the Journal of Analytical Atomic Spectrometry September 1995 Vol. 10 577I " L 10 100 1000 10000 P concentratiodmg r1 0.001 o'o't.-. 10 100 1000 10000 Na concentratiodrng r' Fig. 2 (a) 4oCa'60' :'"In+ as a function of Ca concentration [Ca(NO,)J (b) 31P160160+.45Sc+ as a function of the P concen- tration (H,PO,) and (c) 40Ari3Na+ :5gCo+ as a function of the Na concentration (NaN03) for three sample introduction systems:l ther- mospray system; 2 pneumatic nebulizer combined with the desolvating unit used for the thennospray nebulizer; and 3 pneumatic nebulizer combined with a spray chamber combination of pneumatic nebulizer and desolvating system and lower than those obtained with the conventional arrange- ment up to an Na concentration of 1 gl-'.For higher Na concentrations higher levels of ArNa+ are obtained with the thermospray system. Similar conclusions can be made for ArP+ and ArS'. Hence although there is a higher loading of matrix elements of the plasma the normalized ArM' signal is slightly lower for the thermospray system in comparison with the conventional arrangement. In general it can be concluded that although in some instances the formation of MO,' and ArM' will be higher for the thermospray system the apparent analyte element concentrations due to spectral overlaps will be lower or similar because the normalized MO,' and ArM' signals are lower or similar.Non-spectroscopic Interferences The influence of the matrix of NaN03 or Ca(NO,) (salts) and of H2S0 or H3P04 (mineral acids) on the ion signal intensities was investigated. Again the matrix effects observed with the three sample introduction systems were examined. The relative intensity of the "'Tl ion signal (the "'Ti intensities obtained for all P concentrations are divided by that obtained for 0.14 moll-' nitric acid) as a function of the P concentration (H,PO,) is presented in Fig. 3(a). When using a pneumatic nebulizer in combination with the desolvating system the T1 ion signal is only slightly suppressed up to a P concentration of 1 g 1-l (15%). For the thermospray system however the 205Tl ion signal is suppressed to a greater extent for all P concentrations for 1 g 1-l of P (H,PO,) a suppression of 50% is observed.It is important to note that the extent of suppression observed with the conventional arrangement is comparable to that observed with the thermospray system. Comparable results were obtained for elements with masses over the whole mass range. Similar conclusions can be made for the matrix effects caused by H2S04 which is illustrated in Fig. 3(b). The only significant difference is that above 1 g 1-' of S the suppression is larger for the thermospray system and that for pneumatic nebulization there is an enhancement of the signal up to a concentration of 200 mg 1-' of S. The latter effect can be explained by assuming that the zone of maximum Mt density in the plasma undergoes a spatial displacement under the introduction of H2S04." The situation is different when the influence of NaN0 and Ca(NO,) is investigated.This is illustrated in Fig. 4(a) and (b) for NaNO and Ca(NO,) respectively. Up to an Na concentration of 1 g l-' the 205Tl signal intensity is only slightly decreased when using the conventional arrangement (for 1 g 1-' of Na a suppression of 15% is observed). This is however not the case for the other two systems. The "'Tl ion signal is suppressed to a greater extent for all Na concen- trations for 1 gl-' of Na a suppression of 65 and 90% for respectively the pneumatic system combined with the desolvat- ing unit and the thermospray system is observed. It is clear that the thermospray system gives the most severe suppression I 40 .- aa 1000 10000 10 I00 $ 0 f O.( P concentration (H3P04)/mg r' eo 4 0 - 20 .01 ' I ' l " " ' 8 ' " ' 1 ' 1 ' ' 3 1 ' " ' " I 3 ' 1 ' 1 ' 1 1 I 1 '11U 0.1 1 10 100 1000 10000 S concentration (H2S04)/mg r' Fig. 3 Normalized '05Tl ion signal (0.14 mol I-' nitric acid is used as reference solution) as a function of (a) P concentration (H,PO,) and (b) S concentration (H,S04). See Fig. 2 for explanation of 1 2 and 3 578 Journal of Analytical Atomic Spectrometry September 1995 Vol. 10Na concentratWmg r' 1 120 = I \ I 40 Ca mentratiodmg r1 Fig. 4 Normalized "'TI ion signal (0.14 mol I-' nitric acid is used as reference solution) as a function of (a) Na concentration (NaNO,) and (b) Ca concentration [Ca(NO,),]. See Fig. 2 for explanation of 1 2 and 3 because for this arrangement the Na matrix loading of the plasma is the highest.As a greater suppression is observed with the pneumatic nebulizer combined with the desolvating unit in comparison with the conventional arrangement it is probable that a better transport efficiency of the matrix (Na) to the ICP takes place when the desolvating unit is employed even in combination with a pneumatic nebulizer. As can be seen in Fig. 4(b) Ca(NO,) does not significantly influence the ion signal when the conventional arrangement is used up to a Ca concentration of 5 g I-'. A relatively important suppres- sion is however observed for Ca concentrations above 100 mg 1-' when the desolvating system is used instead of the spray chamber. When the pneumatic nebulizer is replaced by the thermospray nebulizer the extent of suppression is even larger.A significant loss of sensitivity can already be observed at Ca concentrations above 50 mg 1-I. This phenomenon is undoubtedly due to the deposition of Ca salts on the cone and skimmer which was experimentally verified. No mass depen- dency of the matrix effects caused by NaNO or Ca(NO,) is observed which is similar to the results obtained for the matrix effects caused by the mineral acids. From these experiments it can be concluded that for the thermospray system the matrix effects caused by the mineral acids are similar to those observed with the conventional arrangement whereas for the effects caused by salts they are more severe for the thermospray system. The salt matrix effects are in a few instances due to clogging of the cone and skimmer orifice.Some of the observations described above can be explained by plotting the analyte ion signal intensity as a function of the carrier gas flow rate for several matrices. These measurements were carried out for the conventional arrangement and for the thermospray system with the Na and Ca salts and also with the mineral acids H,SO and H3P04. A summary of the results is given in Figs. 5 and 6. For Na and Ca it can be deduced from Fig. S(a) that for the thermospray system the carrier gas flow rate at which a maximum signal intensity is obtained is ( a 1 I20 - 100 - 80 - 60 - Carrier gas flow ratelm1 min-' z m 0 Nebulizer gas flow rate/ml min-' Fig.5 Ion signal intensity for '05Tl as a function of (a) carrier gas flow rate obtained with the thermospray system and (b) nebulizer gas flow rate obtained with the pneumatic nebulizer combined with a spray chamber for L0.14 moll-' HN03; 2 1 g I-' Na (NaNO,); and 3 1 g I-' Ca [Ca(NO,),] ( a 1 200 - 0 600 800 700 800 900 1000 Carrier aas flow rate/rnl rnin-' 600 800 700 800 800 1000 Nebulizer gas flow rate/rnl rnin-' Fig.6 Ion signal intensity for '"Tl as a function of (a) carrier gas flow rate obtained with the thermospray system and (b) nebulizer gas flow rate obtained with the pneumatic nebulizer combined with a spray chamber for 1 0.14 mol I-' HNO,; 2 1 g I-' S (H,SO,); and 3 1 g 1-' P (H,PO,) Journal of Analytical Atomic Spectrometry September 1995 Vol. 10 579shifted towards lower values in comparison with 0.14 mol I-' nitric acid (a reference solution). This behaviour is in contrast to that of the conventional arrangement which does not show a shift in optimum flow rate [Fig.5(b)]. In addition it can be seen that the absolute signal intensity is also affected. It decreases by a factor of 7 and 3 by adding respectively 1 g 1-' of Na and 1 g 1-l of Ca to the 0.14 moll-' nitric acid solution while such a decrease is not observed for the conventional arrangement [Fig. 5(b)]. Obviously with a carrier gas flow rate optimized for 0.14 moll-' nitric acid (760 ml min-I) the analyte ion signal intensities in an Na or Ca matrix decrease significantly when using the thermospray system. These observations provide an explanation for the strong signal suppressions caused by Na and Ca described above for the thermospray system.For H2S04 and H3P04 the situation is different as illustrated in Fig. 6(a) and (b). The optimum carrier gas flow rate at which a maximum signal intensity is obtained is shifted towards higher values when adding H,S04 or H3P04 to the 0.14mo11-' nitric acid solution. This can also be observed for the conventional arrangement although it is less pronounced. Also the absolute signal intensities are inversely affected by the mineral acids. For H2S04 there is a slight increase whereas for H3P04 an increase of up to 50% can be observed. The same trend can be noted for the conventional arrangement. Again these plots provide an explanation for the matrix effects caused by H2S04 and H3PO4 the suppressions are lower than those caused by Na or Ca and they are similar for both the conventional and thermospray arrangements.From the study of the matrix effects it can be concluded that the signal suppressions caused by mineral acids (e.g. HzSO4 and H3P04) are not higher for the thermospray system. Indeed the thermospray and the pneumatic nebulizer give similar non-spectroscopic interferences. For these matrices the improvement in sensitivity by a factor of 10 reported elsewhere* is not deteriorated by strong matrix effects. For the signal suppressions caused by salts [e.g. NaNO and Ca(NO,),] however it is clear that for highly concentrated salt solutions (matrix element concentration above 1 g 1-') no improvement in the sensitivity will be observed. For these matrices thermos- pray nebulization is not preferred to pneumatic nebulization unless a matrix separation is included in the sample preparation step.Analysis of Environmental Reference Materials As in general the non-spectroscopic interferences will be more severe for the thermospray system it is necessary to eliminate these matrix effects. In addition to a separation or a dilution of the matrix several procedures can be used to correct for or to reduce or eliminate the non-spectroscopic interferences. For the reversible matrix effects use can be made of the conventional methods such as internal standardization stan- dard additions or isotope dilution. Deposition of salts on the cone and skimmer can be reduced by using a sample flow injection system so that only minimal amounts of sample are introduced into the system.In order to evaluate the correction procedures mentioned above three candidate environmental reference materials were analysed namely BCR CRMs 141R 144R and 146R. All materials were treated with aqua regia and the soluble content of Cd and Pb was determined. Table 2 summarizes the results for Cd obtained with the conventional arrangement and with the thermospray system. In order to correct for the signal suppression observed with the thermo- spray system which varied from 25% for CRM 144R to 40% for CRM 141R the single standard additions method was applied. Rhodium was used as internal standard to correct for the signal fluctuations during the analysis. As can be seen the results for the three materials obtained with thermospray nebulization are not significantly different from those obtained Table 2 Results of Cd determination for three BCR CRMs uiz.CRM 141R Soil-calcareous loam CRM 144R Sewage sludge-domestic and CRM 146R Sewage sludge-industrial TN-ICP-MS* PN-ICP-MSt Certified value$ CRM 141R 13.6k0.35 13.6 0.1 13.96k0.33 CRM 144R 1.79k0.06 1.76 k 0.04 1.84 k0.07 CRM 146R 18.4k0.3 18.1 k0.3 18.45 k0.35 ~ ~ ~ ~ * TN-ICP-MS use of the thermospray nebulization system. t PN-ICP-MS use of the pneumatic nebulizer combined with a spray chamber. $ Ref. 20. 0 Results are expressed in pg g-' with 95% confidence limits (number of samples = 5). with pneumatic nebulization. The Cd concentrations range from 1.79 pg 1-' for CRM 144R to 18.4 pg g-' for CRM 146R. In addition a similar precision on the results can be noticed.The relative standard deviation (s,) varies from 1.6 to 2.8% (five samples) for the thermospray system in comparison with an s of 0.74-2.3% for the pneumatic system. These results demonstrate that standard additions accurately corrects for the signal suppression and that rhodium is a suitable internal standard to correct for the signal fluctuations. For the determination of the aqua regia soluble content of Pb in the three materials external calibration with internal standardization standard additions and isotope dilution were used. The Pb concentrations which are given in Table 3 range from about 51 pg g-' for CRM 141R to about 570 pg g-' for CRM 146R. In general the results obtained with the three calibration methods agree well with each other.The results for CRMs 144R and 146R obtained by external calibration in combination with an internal standard are higher indicating that the internal standard (Tl) does not accurately correct for the signal suppression caused by the matrix. The precision on the results is similar for the three calibration methods. In addition no significant differences between the results obtained by thermospray and pneumatic nebulization were observed. From the analysis of the three reference materials it can be concluded that although thermospray nebulizers give rise to more severe matrix effects accurate and precise results can be obtained for heavily loaded samples by using a suitable cali- bration method. In order to correct for matrix effects standard additions and isotope dilution are to be preferred to external calibration combined with internal standardization.CONCLUSION From this work it is clear that a significant enhancement of the non-spectroscopic interferences is observed for the thermo- spray nebulizer owing to an increased transport of the matrix to the plasma. This is particularly true for salts such as NaNO and Ca(N03) partially owing to clogging of the orifice of the cone and skimmer. The latter effect can only be reduced or eliminated by using a flow injection system or by diluting or removing the matrix. Less severe suppressions are observed for mineral acids such as H2S04 and H3P04. In addition for these solutions the pneumatic and thermospray nebulizers give similar effects. It can be concluded that although the thermo- spray system offers better sensitivity and detection limits it can only be succesfully applied for sample solutions with a relatively low salt content.This is similar to the performance of the ultrasonic nebulizer. Nevertheless when the matrix effects are not excessively high suitable calibration techniques such as standard additions and isotope dilution can be succesfully applied to correct for the signal suppressions. Although there is a higher matrix loading of the plasma the spectroscopic interferences due to an overlap with polyatomic . 580 Journal of Analytical Atomic Spectrometry September 1995 Vol. I0Table 3 Results of Pb determination for three BCR CRMs viz. CRM 141R Soil-calcareous loam CRM 144R Sewage sludge-domestic and CRM 146R Sewage sludge-industrial TN-ICP-MS* PN-ICP-MSt Certified value$ CRM 141R- 51.3 k 2.0 external calibrations 53.0k 1.47 51.8k 1.2 51.3 1 1.4 51.9 kO.8 standard additions isotope dilution 50.5 jl 1.0 52.4 & 1.0 external calibrations 105.7 i.1.6 98.42 1.6 standard additions 96.0 2.5 97.1 k 0.9 isotope dilution 96.1 jll.1 98.1 k 1.2 external calibration5 588.9 k4.3 576.7 k 6.0 standard additions 511i.11 585.0 2 6.2 isotope dilution 569111 572.4 k 9.4 CRM 144R- 96.0k 1.5 CRM 146R- 583i17 * TN-ICP-MS use of the thermospray nebulization system. t PN-ICP-MS use of the pneumatic nebulizer combined with a spray chamber. $ Ref. 20. 4 External calibration was used in combination with internal standardization (TI). 1 Results are expressed in pgg-' with 95% confidence limits (number of samples=5).ions are not higher for the thermospray system if an efficient desolvating system is used. This results in lower apparent analyte concentrations. By using a flow injection system the washing time is not longer than with pneumatic nebulizers when changing from one sample to another in the thermospray system. Future work will involve the use of smaller capillaries to improve further the analyte transport to the ICP and the use of fused silica tubes positioned inside a stainless-steel capillary to avoid contamination for elements such as V Cr Zn and Mo when samples in acidic medium are analysed. In order to remove more solvent and therefore to reduce matrix effects a more efficient desolvating system will be evaluated. Applications of the thermospray system are anticipated in interfacing HPLC with ICP-MS for separation (of the matrix) and speciation purposes.We thank the National Fund for Scientific Research (Belgium NFWO) and the Interuniversity Institute for Nuclear Sciences (IIKW) for financial support. M. P. is indebted to the Institute for Scientific and Technological Research (IWT) for a research fellowship. REFERENCES Thompson J. J. and Houk R. S. Anal. Chem. 1986 58 2541. Montaser A. Tan H. Ishii I. Nam S.-H. and Cai M. Anal. Chem. 1991 63,2660. Wiederin D. R. Smith F. G. and Houk R. S. Anal. Chem. 1991 63 219. Powell M. J. Quan E. S. K. Boomer D. W. and Wiederin D. R. Anal. Chem. 1992 64 2253. 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Shum S. C. K. and Houk R. S. Anal. Chem. 1993 65 2972. Jakubowski N. Feldmann I. Stuewer D. and Berndt H. Spectrochim. Acta Part B 1992 41 119. Jakubowski N. Jepkens B. Stuewer D. and Berndt H. J. Anal. At. Spectrom. 1994 9 193. Vanhoe H. Moens L. and Dams R. J. Anal. At. Spectrom. 1994 9 815. Koropchak J. and Winn D. H. Appl. Spectrosc. 1987 41 1311. Koropchak J. A Aryamanya-Mugisha and Winn D. H. J. Anal. At. Spectrom. 1988 3 799. Peng R. Tiggelman J. J. and de Loos-Vollebregt M. T. C. Spectrochim. Acta Part B 1990 45 189. Vermeiren K. A. Taylor P. D. P. and Dams R. J. Anal. At. Spectrom. 1988 3 571. Koropchak J. A. and Veber M. Crit. Rev. Anal. Chem. 1992 23 113. Koropchak J. A. Veber M. and Herries J. Spectrochim. Acta Part B 1992 41 825. de Loos-Vollebregt M. T. C. Peng R. and Tiggelman J. J. J. Anal. At. Spectrom. 1991 6 165. Veber M. Koropchak J. A. Conver T. S. and Herries J. Appl. Spectrosc. 1992 46 1525. DIN 38 414-S7 procedure Schlamm und Sedimente (Gruppe S) Aufschluss mit Konigswasser zur nachfolgenden Bestimmung des suureldslichen Anteils von Metallen Germany January 1983. Parent M. Vanhoe H. Moens L. and Dams R. unpublished work. Vanhaecke F. Dams R. and Vandecasteele C. J. Anal. At. Spectrom. 1993 8 433. Quevauviller Ph. Muntau H. Fortunat U. and Vercoutene K. EUR Report Luxembourg Brussels 1995 submitted. Paper 5/01233C Received March I 1995 Accepted M a y 9 1995 Journal of Analytical Atomic Spectrometry September 1995 Vol. 10 581

ISSN:0267-9477    

DOI:10.1039/JA9951000575

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

Thermospray Device of Improved Design for Application in ICP-MS* Journal of Analytical Atomic Spectrometry CHRISTOPH THOMAS NORBERT JAKUBOWSKIt AND DIETMAR STUWER lnstitut fur Spektrochemie und Angewandte Spektroskopie Postfach 10 13 52 0-44013 Dortmund Germany JOSE A. C. BROEKAERT Uniuersitut Dortmund Fachbereich Chemie Postfach 50 05 00 0-44221 Dortmund Germany A new thermospray device for sample introduction in ICP-MS has been developed. Three design principles were followed in order to minimize blank values which originate from chemical erosion of the utilized materials the aerosol comes exclusively in contact with chemically inert materials; a fused silica capillary is used instead of the usually applied steel capillary; and a double desolvation system is applied for an effective reduction of the solvent load to the plasma.With careful optimization of the temperature of the capillary aerosol gas flow rate sample uptake rate operation of the desolvation system and the ICP a considerable improvement was achieved. Blank values in the mass region of Fe as appear with steel capillaries were reduced by orders of magnitude so that this important region became accessible for analytical determination with satisfying detection limits. Sensitivity was improved by a factor of about 20 for the elements measured in comparison with two commercial pneumatic nebulization systems and ICP-MS instruments with low and high resolution. Standard deviations of <3.8% and about 10 times lower detection limits in the mean were achieved for a variety of elements in comparison with pneumatic nebulization.In spite of remaining restrictions from blank values detection limits at pg ml- levels and below were realized for several elements. Keywords Inductively coupled plasma mass spectrometry; sample introduction; nebulization; thermospray; desolvation Owing to its unique combination of true multi-element capa- bility and extremely low detection limits inductively coupled plasma mass spectrometry (ICP-MS) has found increasing interest as a spectrochemical detection technique in direct coupling with various HPLC techniques especially when chro- matography is used for matrix separation and preconcentration in the analysis of complex samples. Recently it is considered more and more often for the challenging task of speciation of heavy metals in environmental and biological samples by direct coupling of chromatography with ICP-MS.l The performance of the usual pneumatic nebulization systems is considerably restricted by a low nebulization efficiency so that sample introduction systems with higher efficiency are a necessary prerequisite to exploit the full analytical benefit of ICP-MS whenever ultimate detection limits are requested.Particularly successful as high efficiency nebulization techniques are ultra- sonic nebulization (USN),’ direct injection nebulization ( DIN)3 and hydraulic high pressure nebulization ( HHPN).4 Thermospray nebulization (TSN) also looks promising as a sample introduction system in ICP-MS and ICP-atomic emis- sion spectrometry (AES). It has primarily been developed as an ion source for direct coupling of liquid chromatography to *Presented in part at the 1995 European Winter Conference on t To whom correspondence should be addressed.Plasma Spectrochemistry Cambridge UK January 8-13 1995. organic mass spectrometry initiated by the work of Blakely and c o - w o r k e r ~ ~ ~ ~ and Vestal,’ but the experiences made in this field cannot be utilized for atomic spectroscopy with an ICP source. Application as an ion source requires total vaporiz- ation whereas a vaporization degree of 40-60% would lead to maximum signal intensity in ICP spectroscopies.* The TSN sample introduction technique for ICP-AES as reviewed by Koropchak and Veber,g was first applied by Schwarz and Meyer’ and by Meyer et a1.l’ in ICP-AES.Aerosol production by TSN requires heating of a flowing liquid for its vaporization as described in more detail else- where.g In most cases this is managed by direct heating of a steel capillary with the result of a partial vaporization of the liquid flowing inside so that an aerosol of fine droplets is finally generated from the mixed phase system by the expansion at the exit of the capillary and additionally by a self desolvation effect due to the hot aerosol droplets,’ so that the number median diameters were typically about 2 pm in comparison with 15 pm for a conventional pneumatic nebulizer.” Several investigations have already been undertaken with the aim to improve the analytical performance of TSN for sample intro- duction in ICP-AES.12-15 It was observed that an increase in the capillary temperature leads to smaller mean droplet diam- eters with the result of an increasing signal intensity and it was found that the signal-to-noise ratio could be significantly improved if the capillary diameter was decreased from 150 to 50 pm.16317 In comparison with pneumatic nebulizers matrix effects are more pronounced in TSN.17-” A slight improvement of the detection limits by up to a factor of five has been obtained for a number of element^'^^'' by direct coupling with the ICP; but with an effective desolvation system a high transport efficiency of 2 50% of the thermospray aerosol generation16 can be exploited to give a significant improvement in sensitivity and detection limitsz1~’’ by more than one order of magnitude because the excessive water load to the plasma is significantly reduced.Although most of the investigations discussed in the literature are related to optimization of TSN some first applications combining HPLC techniques for speci- a t i ~ n ’ ~ . ’ ~ and prec~ncentration,’~ or for microsampling flow injection analysisz6 already show promising properties of TSN. In comparison with ICP-AES examples of application of TSN in ICP-MS2,10-27 are few. Improvements of the detection limits by a factor of up to 13 in comparison with a Meinhard nebulizer were reported for several elements which had been achieved by a self developed TSN unit using a capillary of stainless steel with a length of 30 cm and an inner diameter of 180 pm.z7 With a commercial version of a thermospray device equipped with a membrane separator for desolvation Montaser et aLZ were able to improve the detection limits by a factor of 220.In previous work we adapted HHPN as a sample introduc- tion technique for ICP-MS,z8 which is capable of increasing the aerosol efficiency up to about 30%. We also demonstrated its special capabilities for coupling with HPLC for combined Journal of Analytical Atomic Spectrometry September 1995 Vol. 10 583matrix separation and preconcentrationZ9 and furthermore speciation of Cr"' and CrV'.30 Further improvements of HHPN seem to be possible only if the transport efficiency can be improved or recombination processes of the aerosol droplets can be reduced,28 both by a more effective desolvation system. One approach to improve the desolvation process by directly heating the liquid on the way to the nebulizer has been reported by Berndt and Y a i i e ~ .~ ~ Initial investigations are presented in this paper on a new alternative approach utilizing TSN as a technique for on-line sample introduction from HPLC systems to ICP-MS. The main disadvantage discovered from preceding investigations in this field was the appearance of rather high blank values in particular in a medium mass range so that the determination of for instance Ti V Cr Mn Fe Co Ni Cu Zn and Mo is severely impeded. As this is obviously due to material erosion from the steel capillary by acid solutions it was a primary aim of our investigations to reduce the risk of disturbances from blank values. Therefore we have initially designed a thermo- spray unit using inert materials exclusively for the thermospray device in which a fused silica capillary with an inner diameter of 50 pm is inserted into an outer stainless-steel capillary for resistance heating.Secondly an improved double stage desolv- ation system with Peltier cooling was used to reduce the water load to the plasma significantly. It is the aim of this paper to characterize the analytical performance of this system on the basis of carefully optimizing the most influential parameters of operation. EXPERIMENTAL ICP-MS Systems For the optimization of the TSN a home-made ICP-MS system was used which has been described in previous Two special features different to common commercial instru- ments provide higher flexibility for basic investigations and for operational optimization full xyz-positioning enables opti- mization of the sampling distance; and a variable common bias potential to which all ion optical components are connec- ted enables transmission optimization with respect to ion energies.The differential pumping system is made up of turbomolecular pumps backed by rotary pumps so that a pressure of 2 x Pa is sustained during ICP operation. Operational details are described elsewhere.32 Self-developed software was used for system control data acquisition and data processing. Data may optionally be acquired in a scan mode and multiple-ion detection mode of operation. In the scan mode selected mass intervals are scanned with an increment of usually 0 . 1 ~ . In the multiple- ion detection mode peak jumping is performed according to a list of preselected mass values.The latter was always used if not mentioned otherwise. For ion detection a secondary electron multiplier in an analogue mode was exclusively used. While the development work was carried out with our laboratory instrument detection limits were determined using a prototype of the ELEMENT (Finnigan MAT Bremen Germany) with high mass resolution which has been described in detail elsewhere.33 It was operated with a resolution Rx300. Integration time selection of isotopes and further operational conditions were chosen according to the results of previously performed operational optimization if not mentioned otherwise. Thermospray Nebulization Systems The experimental set-up is represented in Fig.1. A double piston HPLC pump (Knauer Berlin Germany) forces a carrier liquid usually bidistilled water to pass a sample introduction system on its way towards the nebulization unit. By switching hainple loop [I- CE \ heated spray chamber sample injection valve - HPLC pump Ill bldislilled water A Fig. 1 Experimental set-up fused silica capillary 50 pm id and 220 pm od; and steel capillary 250 pm id and 530 pm od the sample introduction valve the analyte solution contained in a sample loop with a volume of 5 ml can be interspersed into the liquid flow to the nebulizer. As well as a pre-filter with 5 pm pore diameter the nebulization system includes a thermospray unit of our own design and a spray chamber. A prerequisite for coupling a thermospray device to an ICP-MS instrument is the application of an effective desolv- ation system in order to reduce the solvent load to the plasma which otherwise will cause strong matrix effects or the risk of instabilities.For this investigation a special two stage desolv- ation system each stage including heating as well as cooling is provided which serves for effective drying of the aerosol before introduction to the ICP torch. Connection is realized by flexible tygon tubing with a length of 80 cm. A sketch of the thermospray device can be found in Fig. 2 and further technical details are available on request. The main component of the self-developed thermospray system is an electrically heated stainless-steel capillary (SGE Weiterstadt Germany) of 9.5 cm length with 250 pm inner and 0.53 mm outer diameter into which a quartz capillary (SGE) with 50 pm inner and 220 pm outer diameter has been inserted.Heating extends over 87 mm of the length; only the last 8 mm at the exit side are without heating owing to technical reasons. The silica capillary protrudes for 0.6 mm above the top of the steel capillary. Temperature control is performed with reference Fig. 2 Themoplast stopper 1 capillary (fused silica and steel); 2 thermoplast stopper; 3 PTFE ferrule; 4 brass fitting; 5 steel screw 584 Journal of Analytical Atomic Spectrometry September 1995 Vol. 10to a measurement point (see Fig. l ) 85 mm from the top using a PID (proportional integral differential) control system of the regulated power supply. A special thermoplast stopper is used to fix the inner capillary simultaneously providing the electrical connection as close to the top as possible.The thermoplast stopper is connected to a self-designed spray chamber with a length of 150mm and a diameter of 40mm. In order to reduce the solvent load of the plasma the back 7 cm of the spray chamber are already heated in transition to the following 'double' desolvation system. This is made up by two U-shaped tubings each with a heating arm followed by a cooling arm. Heating is performed at a temperature of about 130 "C by a heating strip that covers both stages continuously. The cooling temperature is - 5 "C for both stages realized with closed loop liquid cooling in the first stage and Peltier cooling in the second stage. For comparative measurements with a conventional system (Finnigan MAT) a stainless-steel capillary of 58 cm length an inner diameter of 180 pm and an outer diameter of 1.6 mm is alternatively applied.The exit consists of a sapphire orifice with an aperture of 66 pm. The capillary is heated over a length of 48 cm. It is fixed by poly(tetrafluoroethy1ene) (PTFE) spacers in a ceramic holder mounted in a glass tubing as entry to the spray chamber. The quartz connection to the following desolvation system is the first section to be heated. Pneumatic Nebulization System For comparison with conventional pneumatic nebulization a GMK nebulizer (Labtest Ratingen Germany) was used in continuation of previous For this nebulizer normally a peristaltic pump is a prerequisite and has been used unless otherwise mentioned.Only in one case a Meinhard nebulizer with a water-cooled Scott spray chamber (Finnigan MAT) was used in combination with the double focusing instrument. The GMK was operated under standard conditions i.e. with- out desolvation at a sample uptake rate of 0.8 ml min-' and a nebulizer gas flow rate of 0.95 1 min-'. Test Solutions and Optimization Procedure From a stock multi-element standard solution with 1000 ng ml-' of 23 elements a solution with 10 ng ml-' in 0.1 moll-' HN03 was prepared and used as analyte sample in the experiments for operational optimization of the TSN arrangement. This solution was always measured in turn with 0.1 moll-' HN03 as a blank solution. Seventeen elements were taken into account for quantitative evaluation by the following isotopes 7Li 53Cr 55Mn 57Fe 59C0 60Ni 63Cu 64Zn 71Ga *%r lo7Ag l14Cd '''In 13*Ba "'Tl zo8Pb and For optimization the mean signal intensity and the standard deviation of 20 independent measurements were considered.The repetitive measurement of the 17 isotopes was performed with a dwell time of 62.5 ms for each data point. The sample was injected from a polyether ether ketone (PEEK) loop with a volume of 5m1 so that a total registration time of up to 12 min was available. After beginning of the injection it took about 1 min to get a stable signal and data acquisition was started after a further 2 min. Besides generator forward power aerosol carrier gas flow and sample uptake rate the sampling distance has additionally to be optimized; a detailed discussion is given elsewhere.35 The sampling distance was chosen as 6 mm which is typical for a dehumified aerosol but is signifi- cantly lower in comparison with conditions of pneumatic neb~lization;~~ the bias potential was always optimized for "'In.Representation of the results is restricted to the isotopes 55Mn 59C0 and "'In which reflect the general trends for the other elements as well. 209gi Mainly identical conditions were used in the experiments for comparison with pneumatic nebulization. The sample solution was adjusted to 100 ng ml-' in order to achieve about the same intensities as with the TSN system. For the TSN application of an HPLC pump was a prerequisite in order to overcome the resistance of the capillary and the back pressure from the thermospray process and it was used for both systems in order to realize comparable conditions for signal scatter and blank values.Both systems were operated with their optimum sample uptake rate which was 0.4 ml min-' for the TSN unit and 0.8 ml min-' for the GMK nebulizer. RESULTS AND DISCUSSION Operational Optimization Inductively coupled plasma In deviation from pneumatic nebulization systems the aerosol in TSN is generated from the analyte liquid itself without the requirement of a special aerosol gas so that Ar serves only as carrier gas. This may influence the transport and ionization processes in the plasma but not basically the generation of the aerosol. The influence of the aerosol carrier gas flow rate and forward power of the ICP generator on ion intensity is demonstrated by the measurements shown in Fig.3 (a and b). With a forward power of 1.2 kW the intensity maximum in Fig. 3(a) is observed at a carrier gas flow rate of 0.87 1 min-' which for the chosen sampling distance is higher in comparison to the conditions of the pneumatic nebulizer. This is in agreement with experiences from aerosol processing by dehu- midifi~ation,~~ where the maximum ion intensity is shifted towards the front end of the induction coil so that higher flow rates are necessary to realize highest signal intensities. In comparison with pneumatic neb~lization,~~ the maximum ion 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 1.05 Carrier gas flow ratdl min-' r . 3000 - u) --\ .- c - 2500 3 ( b ) + 2 0.g5. z 6 . 2000 ,& s 0.9. 3 * 0.85 - f -1000 5 -1500 i? % L .- c - c .500 0.8.U A ' 0.75 i r O 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 PowerIkW Fig. 3 (a) Dependence of signal intensity on aerosol carrier gas flow rate A "Mn; B 59C0; and C "'In. (b) Dependence of aerosol carrier gas flow rate (left axis) and signal intensity (right axis) on forward power B 55Mn; C 59C0; and A and D "'In Journal of Analytical Atomic Spectrometry September 1995 Vol. 10 585intensity is more pronounced and a variation of the flow rate by i 0.05 1 min-' at the maximum leads to a decrease in signal intensity by about 30%. This pronounced maximum is a peculiarity of a desolvated aerosol which according to our experience can be attributed to a more homogeneous distri- bution of extremely small droplets and as a consequence ionization takes place in a region in the plasma that is not as expanded as in the case of wet aerosols.34 With increasing power the gas flow must also be raised in order to preserve the inten~ity.'~ This is demonstrated in Fig.3(b) showing the result of optimization of the forward power with re-optimized aerosol carrier gas flow rates so as to get maximum ion intensities. A linear dependence of the carrier gas flow rate on the generator forward power was found and an increase of the power by 0.1 kW required an increase of the aerosol carrier gas flow by 0.04 1 min-' to achieve a signal intensity constant over a broad range of variation. From this point of view there is no basic limitation for the choice of the generator power. It should be mentioned that this advantage is offered by the approach of 'combined optimization' which is discussed in more detail elsewhere.36 For further investigations a value of 1.2 kW was selected to warrant comparability with a pneumatic nebulizer usually operated at this value.Thermospray The greatest influence on the operation of the TSN system is the heating temperature of the capillary Tcap which in our case was measured at a selected reference point (cf. Fig. 1). For optimization it was varied in the range 100-200°C. Temperatures below 100 "C were excluded because appearance of droplets at the top of the capillary was observed which resulted in worse reproducibility. Operation above 200 "C was neglected because of the risk of damage of the poly(imide) coating. Furthermore it was observed that a temperature of 195 "C was sufficient to get a totally transparent aerosol which demonstrates nearly complete vaporization.The results of these measurements are represented in Fig. 4 showing the signal intensity as a function of Tcap at a power of 1.2 kW. An identical trend is observed for all elements. In general the signal intensity increases with the temperature up to a value of about 190°C. The relative scatter of the signal (not shown here) is generally between 2 and 8% over the full range of power with an optimum between 150 and 175 "C. The signals for higher temperature are more intense but unstable owing to visible turbulence in the spray chamber so that a compromise value of T, = 167 "C was chosen for further work. 110 120 130 140 150 160 170 180 190 200 Capillaly temperaturePC Fig.4 Influence of capillary temperature (measured at the measuring point cl. Fig. 1) on signal intensity A "Mn; B 59C0; and C "'In Desolvation For optimizing the operational parameters of the desolvation system both signal intensity and signal stability were con- sidered. The temperature of the heating strip Theat for spray chamber and desolvation system was varied from 50 to 190 "C with a cooling temperature Tcool of 0°C for both cooling arms of the two desolvation stages with individual optimization of the bias potential for each temperature. In the results (Fig. 5) the general trend is an increase of the signal intensity with Theat but obviously this trend is weakened at about 9O"C which must be ascribed to increasing transport losses due to an increase in the droplet diameter with decreasing tempera- ture." Although the maximum intensity is reached for highest temperatures a value of 130°C was chosen because of better signal stability in this region.The bias potential included in Fig. 5 displays a decrease with increasing temperature as it is always observed when the amount of water in the aerosol is reduced.33 Adequate optimization was performed always. In the variation of Tcool (Fig. 6) a certain increase of the analytical signal with decreasing temperature down to about 0 "C is found while the bias potential continues to decrease finally reaching negative values. Consideration of the signal scatter did not exhibit a pronounced trend so that a value of Tcool= -5 "C was chosen as optimum value which is lower than in investigations of Vanhoe et aLZ7 where the optimum value was not accessible.It should be mentioned that a lower value would give rise to the risk of freezing if water is used as the solvent. Nevertheless we know from our experiences with HHPN that lower temperatures down to -25 "C are preferable if organic solvents are investigated.'* 5 4.5 - 2000 .e a 2 1500 E 5 1000 3 4 c - 2.5 5 - 2 E .1.5 .P m 1 - 0.5 0 4 8 . . . I . . * . l o 40 60 80 100 120 140 160 I80 200 Heating temperature/"C Fig. 5 Influence of the heating temperature of the desolvation system on signal intensity (left axis) and on bias potential (right axis) A "Mn; B 59C0; and C l151n 4 3 2 3 1 5 2 o # .- - 8 1 -2 -15 -10 -5 0 5 10 15 20 25 Cooling temperaturePC Fig. 6 Influence of the cooling temperature of the desolvation system on- signal intensity (left axis)and on bias potential (right axis) A 55Mn; B 59C0; and C "'In 586 Journal of Analytical Atomic Spectrometry September 1995 Vol.10Sample uptake rate It is well knownz7 that for increasing sample uptake rates the applied power to the TSN device has to be increased. The workz7 was performed with an unregulated power supply but in our case using a temperature controlled unit the power is automatically regulated to stabilize the temperature at the exit of the capillary which guarantees reproducibility of the aerosol generation independent from the sample uptake rate. The optimization results for the sample uptake rate are represented in Fig. 7. The variation range that can be covered is limited to both sides.Measurement of the signal scatter which is included in Fig. 7 shows that operation of the HPLC pump becomes unstable below 0.3 ml min-' and a pressure > 10 MPa becomes necessary for a rate above 0.5 ml min-' in the case of a capillary with an inner diameter of 50 pm. This leads to leak problems at the interface point between the PEEK tubing and the quartz capillary so that a value of 0.4ml min-' was chosen for further investigations which means a certain restriction for this design in comparison to a steel capillary. Analytical Performance Sensitivity The high efficiency of TSN in comparison with conventional pneumatic nebulization (GMK) is demonstrated by the measurements compiled in Table 1 which represents sensitivit- 3000 I 20 2.'I 1000. J 500 - - C. A _ . . A 0 4 0 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.66 Sample uptake rate/ml min-' Fig.7 Influence of sample uptake rate on signal intensity (left axis) and signal stability (RSD) (right axis) A "Mn; B "Co; and C "'In Table 1 Comparison of intensity per ng mi-' and ratio of detection limits (3s) obtained with a TSN equipped with a desolvation system with those obtained by a GMK without desolvation Intensity/counts s-I per ng ml-' Ratio of detection m/z Element TSN GMK Ratio limits GMK:TSN 7 Li 1685 61 28 2.5 53 Cr 45 1 45 16 55 Mn 446 12 37 2.6 57 Fe 15 1 15 9.6 59 c o 412 10 41 4.6 60 Ni 98 2 49 4.4 63 Cu 348 6 58 0.7 64 Zn 334 16 21 0.1 71 Ga 153 4 38 7.5 107 Ag 153 4 38 7.9 114 Cd 73 1 73 19 115 In 234 I 33 6.1 138 Ba 151 3 50 2.0 205 Tl 66 1 66 18 208 Pb 42 1 42 8.0 209 Bi 47 1 41 18 88 Sr 318 7 45 4.2 ies resulting from solutions with different concentrations. The sensitivity gain realized by TSN depends strongly on the element and varies from 15 for 57Fe up to 73 for 'I4Cd.The average for all elements is 43 which is astonishingly high. For reason of comparison with an alternative high efficiency nebulization technique it should be mentioned that an average intensity gain by a factor of 31 in comparison to pneumatic nebulization (GMK) was reported for HHPN in the litera- ture,28 so that from this point of view the thermospray process results in improved sensitivity. But this assessment should not be overstressed HHPN can be significantly improved as has been demonstrated in recent work of Berndt and Yaf~ez.~' The intensity gain is indeed surprising because transpor- tation losses might be expected in the double desolvation system that has a total path length of about 1.7m but the opposite is true.The efficiency of the aerosol transport to the plasma is significantly enhanced by reduction of the droplet diameters owing to the desolvation process.37 This is in agree- ment with the work of Alves and ~ o - w o r k e r s ~ ~ * ~ ~ in which a desolvation device with alternating heating and cyrogenic cooling was applied. Sensitivity improvement is also realized with the double focusing instrument shown in Table 2 from results obtained with a TSN and GMK nebulizer for a selected number of elements. In order to realize that the results are not influenced by differences in blank values the latter was also operated with the HPLC pump as used for TSN.Again the sensitivity gain realized by TSN depends strongly on the element and covers an interval from a value of 8 for "Sr up to 41 for '09Bi. The average for all elements is 18 which is again high but closer to the values obtained for the quadrupole instrument and a Meinhard nebulizer with a mean value of about It should be mentioned that the mean improvement is now a factor of two lower for the double focusing instrument in comparison with results obtained with the quadrupole instru- ment. This may be explained by a stronger influence of water loading at the quadrupole instrument which demonstrates that the improvement may also depend to a certain extent on the instrumentation and differences in the sampling process.For a true assessment of the performance of TSN it should be mentioned that for a Meinhard nebulizer the improvement is not so pronounced as for the GMK nebulizer. But neverthe- less an improvement by a factor of 15 as average for all investigated elements was obtained which is comparable to values in the literature?' For the double focusing instrument the absolute sensitivity measured with a counting system is the best. For example in the case of In 2.7 lo6 counts (in other words 2.7 lo9 counts per s-' per pg m1-I) were registered with a solution containing 1 ng ml-' of In (Table 2 ) . This is more than two orders of magnitude higher in comparison with quadrupole based instru- mentation with conventional nebulization and verifies the Table 2 Comparison of sensitivities obtained with a TSN equipped with a desolvation system and those obtained with a GMK without desolvation determined with the prototype of the ELEMENT Intensity/counts s - l per ng ml-' m/z Element TSN GMK Ratio 7 53 55 59 71 88 115 205 209 Li Cr Mn c o Ga Sr In TI Bi 1492388 135532 1017754 1586947 946805 884102 2754820 1523478 2158865 197251 9915 111548 98686 40366 110298 110860 85100 52554 8 14 9 16 23 8 25 19 41 Journal of Analytical Atomic Spectrometry September 1995 Vol.10 587experience of extraordinary sensitivity improvement discussed by Yamasaki et u I . ~ ~ who used an ultrasonic nebulizer in combination with a double focusing ICP-MS. Stability and repeatability For measurement of the analytical repeatability the whole sample injection procedure including flushing and filling of the sample loop with subsequent injection was repeated 16 times for a solution with 10ngml-l of Mn.The RSD of the analytical procedure was 5% in comparison to 3.8% for the GMK nebulizer although in both cases no internal stan- dard was used. The measurement of the signal stability itself in one of the runs of "'In was greatly improved to 3.8%. Long term stability for TSN is illustrated by the measure- ments in Fig. 8 which were obtained for "Mn "Co and '05Tl with "'In as internal standard over a total measurement time of 5 h. In contrast to pneumatic nebulization for which the signal is mainly constant over the whole measurement time we observed a sudden increase after 2.5 h followed by a generally higher scatter so that the long term stability of the thermospray nebulizer was worse by a factor of 4.This may be ascribed to remaining technical deficiencies of the TSN system. Up to now we cannot be sure whether this is the consequence of a leak problem at the thermoplast stopper (PTFE ferrule) or any disturbing influence at the top of the capillary thereby changing its nebulization properties. Although for the moment the long term stability may be a drawback in comparison with pneumatic nebulization we are sure that this can be overcome in future work. Blank values As already mentioned steel capillaries have been utilized in most cases of technical TSN configurations so far.'*'' Their crucial disadvantage was in the significant blank values obtained for many elements mainly due to material erosion by acidic analyte solutions.In order to verify the advantages of a fused silica capillary over the conventional steel capillary we analysed a 0.3 moll-' HNOB solution with both TSN units. Operation of the steel capillary was optimized individu- ally with respect to both gas flow rate and sample uptake rate. Measurement of the analytical signals was performed in the scan mode. Results are represented in Fig. 9. Comparison of blank values [Fig. 9(a)] shows partial spectra in the mass region between 47 and 72 u for both capillaries. In comparison to the steel capillary the signals for the quartz capillary appear nearly negligible. Some of the signals observed for the quartz capillary must be attributed to interferences from the argide molecule species ArN' and ArO' (54 56 and 58 u); in the - 1 I .. . . . . . . . . . . 0 0.5 1 1.5 2 2.5 3 3.5 4 4.6 5 5.5 Timdh Fig. 8 Time dependence of relative intensity of the analyte signal for thermospray sample introduction ('I5In internal standard) A 55Mn; B 59C0; and C 205TI BE I 0 0 102 104 90 92 94 96 W Z Fig. 9 (a b) Partial mass spectrum of 0.3 Moll-' HNO with different capillary materials fused silica capillary (B) and stainless steel capillary (A). (a) Mass region between 47 and 72 and (b) mass region between 90 and 104 mass interval 63-68 u significant laboratory blank values for Cu and Zn were obtained. These higher blank values can probably be explained by the use of a brass fitting in the stopper although this fitting is not in direct contact with the aerosol.The mass region of Mo is represented in Fig. 9(b) exhibiting once more the strong blank values for TSN with a steel capillary. In summary with the quartz capillary introduced in this work blank values can be reduced by orders of magnitude in comparison with the conventional steel capillaries. As men- tioned before a steel capillary" or a spray chamber made from steelZ have been used in ICP-MS applications up to now so that either the elements in this mass range could not be considered for determination or the use of acids like HNO was necessarily prohibited. Concerning the double focusing instrument one should be aware that owing to its higher sensitivity blank values may affect detection limits which do not become significant with quadrupole instruments. This is also observed for TSN with the fused silica capillary as can be seen from Table 3 showing blank values which resulted with a 0.1 moll-' HNO solution injected by the sample loop.Most of these extremely high Table 3 Blank values obtained for a 0.1 mol 1-' HNO solution and detection limits (3s) using a thermospray nebulizer equipped with a desolvation system determined with the prototype of the ELEMENT mlz I 53 55 59 71 88 115 205 209 Element Li Cr Mn c o Ga Sr In T1 Bi Blank values/ counts s-' per ng ml-' 4559 23576 144875 52329 1530 26374 5302 35568 31504 Detection limits/ pg ml-' 1.2 14 94 10 13 0.4 1.4 4.7 2.1 588 Journal of Analytical Atomic Spectrometry September 1995 Vol. 10values are caused by the HPLC pump which was checked additionally by comparison with the GMK and a peristaltic pump as normally used in this sensitive instrument.This reveals that the pump was not as inert as originally desired and it is surprising that these blank values arise although only bidistilled water is in contact with the pump head. Therefore significant improvements are expected for a new generation of inert pumps with a PEEK head which will be the topic of future work in order to reduce blank values which is the main limitation of TSN. Detection 2imits Although the laboratory prototype instrument which was used for this investigation in analogue mode cannot compete with commercial systems concerning detection limits an improve- ment can nevertheless be demonstrated in the detection limit ratios which are shown in Table 1.In general these ratios depend on the element and have values up to 19 which is realized for li4Cd and ’O’Tl. The improvement corresponds to a factor in the interval 3-10 with a value of 8 as average. In two cases (63Cu and 64Zn) the detection limits with TSN are worse owing to the higher scatter of the higher blank signals. The improvement may appear higher than expected because the TSN system has been operated at only half of the sample uptake rate of the pneumatic nebulizer. Further improvements by higher sample uptake rate may therefore be possible if leak problems can be overcome by ferrules which are more stable against pressure. For all elements not affected from blank values in the case of a steel capillary the ratios obtained in this work are very similar to those obtained by Vanhoe et al.” and by Montaser et a1.’ This shows that the special operational conditions such as diameter of the capillary which were 150 pm and 75 pm respectively and special desolvation arrangements are not the main influence. Preliminary estimations of the detection limits (3s) obtained for the double focusing instrument with TSN and the fused silica capillary were also obtained (Table 3) by application of sensitivity factors which were calculated from measurements of the multi-element standard solution with a concentration of 0.05 ng ml-’ for each element measured.The high blank values (Table 3) as mentioned before are of course reflected in these estimates for the detection limits.For a number of elements the detection limits are at low pg ml-’ levels and these come close to values from the literature.” One should realize that even for Ga with the lowest detection limit and the lowest blank value the intensity of the blank is still a factor of 1.500 above the noise level of the instrument so that a significant improvement of detection limits may be expected for this instrument if limitations from blank values can be overcome. The results obtained here confirm the experience obtained using ICP-AES that inert capillaries with indirect heating can be used to improve detection limits in atomic spectrometry signifi~antly.’~~~~~~~~’~ As shown here there are severe limi- tations due to remaining sources of blank values. For a full exploitation of TSN as an extremely sensitive and powerful sample introduction system in ICP-MS it will be necessary to overcome these disturbing influences.CONCLUSION In this work we have introduced a new thermospray system of improved design which on the basis of careful optimization for both TSN and ICP-MS operation gives a new impetus for the application of TSN as a high efficiency technique for sample introduction in ICP-MS analysis. The improvement was mainly achieved by applying a fused silica capillary instead of the conventional steel capillary. In the design of the new system any risk of the aerosol coming into contact with other than inert materials has consequently been avoided. This leads to a reduction of blank values by orders of magnitude for several elements so that the important range mass 47-70 is now accessible for an analytical determination with satisfying detection limits which at least with acid solutions is not the case with a steel capillary because of the high blank values resulting from chemical erosion of the capillary material.Including an effective two stage desolvation system with Peltier cooling the ion yield could be increased by about a factor of 20 for two different pneumatic nebulizers and ICP-MS instruments with low and high mass resolution. For some elements with significant laboratory blank values exploitation of this high sensitivity as an analytical benefit was limited but on average for the determined elements an improvement in the detection limits by a factor of about 10 resulted so that detection limits at pg ml-’ levels and below could be realized.Blank values which do not originate from the TSN system itself now become significant as a limitation. With respect to sensitivity and detection limits TSN should be included as a choice among the high efficiency techniques for sample introduction in ICP-MS. The work was supported financially by the Ministerium fur Wissenschaft und Forschung des Landes Nordrhein-Westfalen and by the Bundesministerium ftir Bildung Wissenschaft Forschung und Technologie. REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Vela N. P. Olson L. K. and Caruso J. A Anal. Chem. 1993 65 585A. Montaser A. Tan H. Ishii I. Nam S . H. and Cai M. Anal. Chem. 1991 63 2660. 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ISSN:0267-9477    

DOI:10.1039/JA9951000583

出版商:RSC    

年代:1995

数据来源: RSC