摘要:

Journal of Analytical Atomic Spectrometry 111 111111111 111111 111 111111111 111111 THE ROYAL C H EM I ST RY Information Services I I JASPE2 11 (1 2) 53N-58N 11 29-1 234 461 R-522R CONTENTS NEWS PAGES Editorial-Steve J. Hill Guest Editors Foreword-Joseph A. Caruso Steve J. Hill Diary of Conferences and Courses Future Issues 53N 53N 54N 55N 57N PAPERS Trace Metal Speciation via Supercritical Fluid Extraction-Liquid Chromatography-Inductively Coupled Plasma Mass Spectrohetry Nohora P. Vela Joseph A. Caruso Low-flow Interface for Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry Speciation Using an Oscillating Capillary Nebulizer Lanqing Wang Sheldon W. May Richard F. Browner Stanley H. Pollock 1129 1137 Effect of Different Spray Chambers on the Determination of Organotin Compounds by High-performance Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry Cristina Rivas Les Ebdon Steve J.Hill 1147 Feasibility Study of Low Pressure Inductively Coupled Plasma Mass Spectrometry for Qualitative and Quantitative Speciation Gavin O’Connor Les Ebdon E. Hywel Evans Hong Ding Lisa K. Olson Joseph A. Caruso 1151 Speciation of Inorganic Selenium and Selenoaminoacids by On-line Reversed- phase High-performance Liquid Chromatography-Focused Microwave Digestion-Hydride Generation-atomic Detection J. M. Gonzalez Lafuente M. L. Fernandez Sanchez A. Sanz-Medel 11 63 Speciation of Organic Selenium Compounds by High-performance Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry in Natural Samples Riansares MuAoz Olivas Olivier F.X. Donard Nicole Gilon Martine Potin-Gautier Investigation of Selenium Speciation in In Vitro Gastrointestinal Extracts of Cooked Cod by High-performance Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry and Electrospray Mass Spectrometry Helen M. Crews Philip A. Clarke D. John Lewis Linda M. Owen Paul R. Strutt Andres lzquierdo Approaches to the Determination of Metallothionein(s) by High-performance Liquid Chromatography-Quartz Tube Atomic Absorption Spectrometry Yanxi Tan Patrick Ager William D. Marshall Hing Man Chan Speciation of Some Metals in River Surface Water Rain and Snow and the Interactions of These Metals With Selected Soil Matrices J. Y. Lu C. L. Chakrabarti M. H. Back A. L. R. Sekaly D. C. Gregoire W. H.Schroeder 1171 1177 1183 1189 Investigations Into Chromium Speciation by Electrospray Mass Spectrometry Ian 1. Stewart Gary Horlick Arsenic Speciation by Liquid Chromatography Coupled With lonspray Tandem Mass Spectrometry Jay J. Corr Erik H. Larsen 1203 1215 Atomic Spectrometry Hyphenated to Chromatography for Elemental Speciation Performance Assessment Within the Standards Measurements and Testing Programme (Community Bureau of Reference) of the European Union Philippe Quevauviller CUMULATIVE AUTHOR INDEX 1225 1233 AT0 M I C SPECTROMETRY UPDATES Industrial Analysis Metals Chemicals and Advanced Materials- James S. Crighton John Carroll Ben Fairman Janice Haines Mike Hinds 461 R References Typeset printed and bound by The Charlesworth Group Huddersfield England 01484 51 7077 509R 0267-9477(1996112:1-6Journal of Analytical Atomic Spectrometry 111 111111111 111111 111 111111111 111111 THE ROYAL C H EM I ST RY Information Services I I JASPE2 11 (1 2) 53N-58N 11 29-1 234 461 R-522R CONTENTS NEWS PAGES Editorial-Steve J.Hill Guest Editors Foreword-Joseph A. Caruso Steve J. Hill Diary of Conferences and Courses Future Issues 53N 53N 54N 55N 57N PAPERS Trace Metal Speciation via Supercritical Fluid Extraction-Liquid Chromatography-Inductively Coupled Plasma Mass Spectrohetry Nohora P. Vela Joseph A. Caruso Low-flow Interface for Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry Speciation Using an Oscillating Capillary Nebulizer Lanqing Wang Sheldon W. May Richard F. Browner Stanley H. Pollock 1129 1137 Effect of Different Spray Chambers on the Determination of Organotin Compounds by High-performance Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry Cristina Rivas Les Ebdon Steve J.Hill 1147 Feasibility Study of Low Pressure Inductively Coupled Plasma Mass Spectrometry for Qualitative and Quantitative Speciation Gavin O’Connor Les Ebdon E. Hywel Evans Hong Ding Lisa K. Olson Joseph A. Caruso 1151 Speciation of Inorganic Selenium and Selenoaminoacids by On-line Reversed- phase High-performance Liquid Chromatography-Focused Microwave Digestion-Hydride Generation-atomic Detection J. M. Gonzalez Lafuente M. L. Fernandez Sanchez A. Sanz-Medel 11 63 Speciation of Organic Selenium Compounds by High-performance Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry in Natural Samples Riansares MuAoz Olivas Olivier F.X. Donard Nicole Gilon Martine Potin-Gautier Investigation of Selenium Speciation in In Vitro Gastrointestinal Extracts of Cooked Cod by High-performance Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry and Electrospray Mass Spectrometry Helen M. Crews Philip A. Clarke D. John Lewis Linda M. Owen Paul R. Strutt Andres lzquierdo Approaches to the Determination of Metallothionein(s) by High-performance Liquid Chromatography-Quartz Tube Atomic Absorption Spectrometry Yanxi Tan Patrick Ager William D. Marshall Hing Man Chan Speciation of Some Metals in River Surface Water Rain and Snow and the Interactions of These Metals With Selected Soil Matrices J. Y. Lu C. L. Chakrabarti M. H. Back A. L. R. Sekaly D. C. Gregoire W. H. Schroeder 1171 1177 1183 1189 Investigations Into Chromium Speciation by Electrospray Mass Spectrometry Ian 1. Stewart Gary Horlick Arsenic Speciation by Liquid Chromatography Coupled With lonspray Tandem Mass Spectrometry Jay J. Corr Erik H. Larsen 1203 1215 Atomic Spectrometry Hyphenated to Chromatography for Elemental Speciation Performance Assessment Within the Standards Measurements and Testing Programme (Community Bureau of Reference) of the European Union Philippe Quevauviller CUMULATIVE AUTHOR INDEX 1225 1233 AT0 M I C SPECTROMETRY UPDATES Industrial Analysis Metals Chemicals and Advanced Materials- James S. Crighton John Carroll Ben Fairman Janice Haines Mike Hinds 461 R References Typeset printed and bound by The Charlesworth Group Huddersfield England 01484 51 7077 509R 0267-9477(1996112:1-6

ISSN:0267-9477    

DOI:10.1039/JA99611FX001

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

XXIX Co I I oq u i u m S pect rosco p i cu m I n t e r na t i on a I e Post - Symposium lCP=MS and I l t h Meeting of the German lCP=MS Users Group September 1-4 1995 Wernigerode Germany And so to Wernigerode the colourful town in the Harz Mountains. Wernigerode is located at the confluence of the Holtemme and Zillierbach rivers and is dominated by its neo-Gothic castle which dates back to the 13th century. The castle is situated high above the town affording excellent views of the Harz mountains and is a repository for many fine works of art as well as examples of interior design from the Renaissance to the 19th century. The town is noted for its splendid half- timbered buildings best typified by the magnificent Town Hall which was the venue for the symposium. Today Wernigerode is a thriving holiday centre but not for delegates from the CSI whose diversion was provided by the mysteries and vagaries of plasma source mass spectrometry.Activities began on Friday evening with a social gathering in the Town Hall Ratskeller a word that seems to convey exactly the kind of event that one can look forward to. Thus local beer and food were provided in abundance and 2 N Journal of Analytical Atomic Spectrometry January 1996 Vol. 11delegates spent the evening learning the names of people they did not know whilst mostly forgetting the names of those they did know! This happy occasion was the prelude to what was to prove a most enjoyable and convivial meeting. The scientific programme began on Saturday morning with an invited paper by G.Knapp on ‘Sample Decomposition for Ultra Trace Analysis’ which set the scene for the first session. After the break the topic for discussion was ‘Chromatographic Separations’ which took us through to a much needed lunch. The afternoon session was devoted to ‘Laser Ablation and ETV’ which was the prelude to the main social events a trip to the castle returning later in the evening for a Gala Buffet. The Sunday programme covered a range of topics under the general heading ‘Instrumentation and Applications’ and began with an invited talk from P. Rommers and P. W. J. M. Boumans entitled ‘ICP-MS versus ICP-AES Competition or a Happy Marriage?-A View Supported by Current Data’. A ‘happy hour’ at the conference hotel concluded the day’s programme offering delegates a final opportunity to look who had been touring Europe promoting the next CSI which will be held in Melbourne) from the CSI in Leipzig but the numbers were swelled by fresh faces to bring the total to about 130.This was undoubtedly a very successful meeting with some excellent science being presented to a specialist audience. Indeed so successful have the pre- and post-symposia become that they are now in danger of detracting both in terms of the science and the numbers of delegates from the main meeting. This problem was discussed at the CSI continuation committee and was again aired at the CSI national delegates meeting. Clearly scientists like to be closeted with kindred spirits and organizers ignore this at their peril. One solution is to bring the pre- and post- symposia into the body of the main meeting which implies many more simultaneous sessions on the FACSS B.Sharp B. Holliday and D. Koppenaal round the posters and the instrument exhibition. On Monday the symposium language changed to German-and the day was given over to the 11 th Meeting of the German ICP-MS Users Group. Most of the delegates attending the symposium were hardened conferees (including the very hardened Dr Les Dale model. Ultimately the decision lies with the organizers and they have to take into account local circumstances. For example the next CSI will be in Australia and given the travel involved delegates may welcome the opportunity to spread the science over a longer period and to see more of the continent in the process. After Australia comes Turkey and once again the circumstances will be different. I am sure that the Managing Editor of JAAS would welcome your letters on this subject which will no doubt be of interest to those involved with the CSI and all who wish it to continue as one of the major international meetings. It remains for me to thank Dr Lieselotte Moenke and her colleagues for organising a really excellent symposium and for affording us the opportunity to enjoy the delights of Wernigerode. B. L. Sharp Chemistry Department Loughborough University of Technology Leicestershire Les Dale champion tour promoter Journal of Analytical Atomic Spectrometry January 1996 Vof. 11 3N

ISSN:0267-9477    

DOI:10.1039/JA99611002Nb

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

FACSS XXII October 15-20,1995 Cincinnati Ohio The FACSS XXII conference on analytical chemistry was held in the attractive city of Cincinnati. The opening of the conference neatly coincided with the closing of the ‘Tall Stacks’ exhibition. This colourful celebration of the steamboat era provided a spectacular welcome to the conference delegates. analytical chemistry conferences in the US and this was reflected by the large FACSS is one of the most prestigious number of papers presented in numerous parallel lecture streams. The lecture program was accompanied by two comprehensive poster sessions. Since physical constraints meant that I could only be in one place at a time the first morning of the conference found me in the Plasma Source-Mass Spectrometry session chaired by Gary Hieftje.The session opened with a detailed lecture by Gary Horlick on the subject of electrospray ionisation in atomic mass spectrometry. The central theme of the presentation was the task of interpreting the complex mass spectra which result from species produced by ion-molecule reactions. The remainder of this session featured lectures discussing the use of alternative mass analysers as opposed to the quadrupole type in ICP-MS. Of particular interest to me was the presentation by Gary Hieftje describing the development of a rapid scanning time-of-flight ICP-MS system. Journal of Analytical Atomic Spectrometry January 1996 Vof. 11 3NSimon Nelms ‘Star of Cincinnati’ cruise ship The afternoon ICP-MS session initially focused on the use of ETV for sample introduction and continued with discussions on the feasibility of slurry sample introduction and analysis of solids by UV laser ablation.This session also incorporated an interesting lecture about a new ICP system using a combined optical emission-mass spectrometer detection system. This instrumentation was shown to be effective in analysing samples containing both low percentage levels of dissolved solids and trace analytes. Sampler and skimmer cone blockage problems which plague standard ICP-MS were shown to be circumvented by using cones of larger orifice diameter. That evening saw the opening of the impressive manufacturers exhibition. On display were a diverse range of instruments and new accessories complete with an equally diverse range of drinks and snacks! This exhibition coincided later in the week with the American Cemeteries Association meeting.Their exhibition consisted of headstones and coffins (fortunately empty ones) providing a very bizarre sight for delegates! The second morning of the conference featured a session on new challenges and applications in ICP-MS chaired by Robert Hutton. The program opened with a detailed lecture on ion-beam extraction and sampling in the ICP-MS interface by Don Douglas. He illustrated how beam scattering by space charge effects is further exacerbated by the high local gas pressure in the skimmer region yielding a beam diameter one order of magnitude greater than ideal behaviour would suggest. Later in the session Sam Houk presented an interesting and informative lecture on the development of a twin quadrupole ICP-MS system to make simultaneous isotope ratio measurements. The morning session closed with an extensive discussion by Scott Tanner on atomisation and ionisation under ‘cold‘ ICP conditions.The dazzling colour scheme of his presentation kept the audience hypnotised while he described the various matrix suppression effects observed in the cold plasma. The afternoon session which was dominated by European speakers comprised further lectures on ICP-MS applications. Helen Crews gave an entertaining presentation on the absorption of selenium by the human body. Dr. Crews demonstrated her dedication to science by revealing that she had volunteered herself to consume selenium enriched foodstuffs for the study! Angelika Raith gave an informative lecture on UV microprobe laser ablation ICP-MS and its application to analysis of geological and environmental samples.The improved capabilities of the UV laser in terms of smaller ablation spot size and ability to couple efficiently with transparent glasses were contrasted with the performance of an IR laser system. Barry Sharp discussed new calibration strategies for excimer laser ablation using aqueous calibration standards and John Marshall closed the session with a lecture on the performance of ultrasonic nebulisation with ICP-MS. Wednesday morning opened with an update on the state-of-the-art flow injection method coupled with atomic spectrometric detection presented by Julian Tyson who was also chairing the session. The first lectures focused on automated hydride generation methods for arsenic and selenium using GFAAS and AAS.Later lectures described applications illustrating the fast sample throughput and on-line chemistry capabilities of flow injection. The session closed with another lecture by Helen Crews her third of the conference describing flow injection ICP-MS with a direct injection nebuliser. A description of the role of solids in flow injection AAS by Miguel Valcarcel was given in the afternoon. Professor Valcarcel illustrated how solids have been used within his group in the form of directly injected slurries sorbent beds for matrix separation and oxidation and as precipitates prepared on-line. The next two lectures focused on the application of novel reagents for on-line preconcentration and matrix separation.After the break attention was directed to on-line digestion procedures for releasing mercury and selenium from biological samples with subsequent on-line detection of the liberated analytes. program many delegates attended the Gala Night on board the ‘Star of Cincinnati’ cruise ship. After the meal diners strolled on deck to admire the impressive landmarks of the city by night. As a relatively impoverished student without a ticket for the Gala Night I was to be found in the slightly less grandiose setting of the local Hooters restaurant! On Thursday morning the ICP-MS session focused on the chromatographic applications. The lecture series detailed the considerations that must be made when using HPLC as the sample introduction system and application of the technique to speciation of chromium and copper in organometallic dyestuffs.On Thursday afternoon an opportunity to visit the famous Cincinnati Zoo presented itself so I seized the chance to see this other feature of the city. The Zoo boasts an impressive collection including bears white Bengal tigers and even a Komodo dragon! Friday morning featured the development of automated sampling systems and instrument developments for reducing certain matrix effects. The use of a modified dynamic scanning lens system to determine trace elements in a uranium matrix was elegantly illustrated. The procedure exploited the As a respite from the awesome lecture The final ICP-MS lecture session on 4N Journal of Analytical Atomic Spectrometry January 1996 Vol. 1 Idifferent extraction profiles observed for elements across the mass range at different extraction voltages. By selecting a voltage which discriminated against higher masses the transmission of lower masses was enhanced giving greater sensitivity . At the end of this session FACSS XXII drew swiftly to a close. It had proved to be an enjoyable and informative week during which new friends were made and many new ideas were generated. After a further few days at Dusquesne University Pittsburgh I set about the long journey back home. Simon Nelms Hull University Hull UK Journal of Analytical Atomic Spectrometry January 1996 Vol. 11 5 N

ISSN:0267-9477    

DOI:10.1039/JA996110003N

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

DIARY OF CONFERENCES AND COURSES 1996 47th Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy March 3-8 Chicago IL USA Details can be found in J. Anal. At. Spectrom. 1995 10 63N. For further details contact The Pittsburgh Conference 300 Penn Center Boulevard Suite 332 Pittsburgh PA 15235-5503 USA. Telephone + 1 412 825 3220; Fax + 1 412 825 3224. Analytica Conference 96 April 23-26 Munich Germany Details can be found in J. Anal. At. Spectrom. 1994 2 69N. For further details contact Messe Munchen GmbH Messegelande D-80325 Miinchen Germany. Telephone +49 89 51 070; Telex 5 212 086 ameg d; Fax +49 89 51 07 177. ASMS Short Course Interpretation of Mass Spectra LC/MS and MS/MS May 11-12 Portland OR USA For further details contact American Society of Mass Spectrometry 1201 Don Diego Avenue Santa Fe NM 87505 USA.Telephone + 1 505 989 4517; Fax +1 505 989 1073. 44th ASMS Conference on Mass Spectrometry and Allied Topics May 12-17 Portland OR USA For further details contact American Society of Mass Spectrometry 1201 Don Diego Avenue Santa Fe NM 87505 USA. Telephone + 1 505 989 4517; Fax +1 505 989 1073. Ninth International Symposium on Trace Elements in Man and Animals May 19-24 Bang Alberta Canada Details can be found in J . Anal. At. Spectrom. 1995 10 58N. For further details contact TEMA-9 The Banff Centre for Conferences P.O. Box 1020 Station 11 Banff Alberta Canada TOL OCO. Telephone + 1 403 762 6308; Fax +1 403 762 6388 or Dr Mary L’Abbe. Telephone +1 613 957 0924; Fax +1 613 941 6182; E-mail Mlabbe@HPB.HWC.CA.Total Reflection X-Ray Fluorescence Analysis June 10-11 (Part 1) E ind ho uen Germany June 13-14 (Part 2) Dortmund Germany Details can be found in J. Anal. At. Spectrom. 1995 10 60N. For further details contact Gesellschaft Deutscher Chemiker TXRF-Konferenz Postfach 90 04 40 D-60444 Frankfurt Germany. Fax + 49 69 7917 475. Resonance Ionization Spectroscopy June 30-July 5 Pennsylvania USA Details can be found in J. Anal. At. Spectrorn. 1995 10 60N. For further details contact Sabrina Glasgow Conference Secretary Department of Chemistry The Pennsylvania State University 184 Materials Research Institute Building University Park PA 16802-7003 USA. Tel +1 814 865 0200; Fax +1 814 863 061 8; E-mail scg4@psuvm.psu.edu. Eighth Biennial National Atomic Spectroscopy Symposium University of East Anglia Norwich UK Details can be found in J.Anal. At. Spectrom. 1995 10 60N. For further details contact Dr S J Haswell School of Chemistry University of Hull Hull HU6 7RX UK. Telephone + 44 (0) 1482 465469; Fax +44 (0)1482 466410. July 17-19 12th Asilomar Conference on Mass Spectrometry Elemental Mass Spectrometry September 20-24 Pacijic Grove CA USA For further details contact American Society of Mass spectrometry 1201 Don Diego Avenue Santa Fe NM 87505 USA. Telephone +1 505 989 4517 Fax +1 505 989 1073. Fourth Rio Symposium on Atomic Spectrometry November 24-30 Buenos Aires Argentina For further details contact Dr Osvaldo E. Troccoli Quimica Analitica Facultad de Ciencias Exactas y Naturales Ciudad Universitaria ( 1428) Buenos Aires Argentina.Telephone 3-541 783 3025; Fax +541 782 0441. 1997 Seventh International Symposiuum on Biological and Environmental Reference Materials April 21-25 Antwerp Belgium Details can be found in J . Anal. At. Spectrom. 1995 9 54N. For further details contact Dr J. Pauwels Institute for Reference Materials & Measurements Management of Reference Materials Unit Retieseweg B-2440 Geel Belgium. Telephone +32 14 571 722; Fax +32 14 590 406; or Wayne R. Wolf Ph.D. Food Composition Laboratory USDA 10300 Baltimore Blvd. Beltsville MD 20705 USA. Telephone + 1 301 504 8927; Fax + 1 301 504 8314. XXX Colloquium Spectroscopicum Internationale September 2 1-26 Melbourne Australia Details can be found in J. Anal. At. Spectrom. 1995 10 58N. For further details contact The Meeting Planners 108 Church Street Hawthorn Victoria 3122 Australia. Telephone +61 3 9819 3700; Fax +61 3 9819 5978. Updated information may be obtained from the XXX CSI homepage on the World Wide Web at http://www.latrobe.edu.au/CSIconf/ XXXCSI.htm1. Journal of Analytical Atomic Spectrometry January 1996 Vol. 11 5 N

ISSN:0267-9477    

DOI:10.1039/JA996110005N

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

FUTURE ISSUES WILL INCLUDE- Speciation of Mercury in Sea-water by Liquid Chromatography With Inductively Coupled Plasma Mass Spectrometric Detection-Martin J. Bloxham Anthony Gachanja Steve J. Hill Paul J. Worsfold Optimization of the Extraction and Determination of Monomethylarsonic and Dimethylarsinic Acids in Seafood Products by Coupling Liquid Chromatography With Hydride Generation Atomic Absorption Spectrometry-Dinoraz Velez N. Ybanez R. Montoro Electrochemical Hydride Generation- Graphite Furnace Atomic Absorption Determination of Total Antimony in Riverwater and Sea-water With In Situ Concentration-W.-W. Ding Ralph E. Sturgeon On-line Solid Phase Chelation for the Determination of Eight Metals in Environmental Waters by Inductively Coupled Plasma Mass Spectrometry- Daniel B.Taylor H. M. Kingston Donald J. Nogay Calibration Strategies for the Elemental Analysis of Individual Aqueous Fluid Inclusions by Laser Ablation Inductively Coupled Plasma Mass Spectrometry- Alain Moissette T. J. Shepherd S. R. Chenery Rapid Speciation of Butyltin Compounds in Sediments and Biomaterials by Capillary Gas Chromatography Microwave Induced Plasma Atomic Emission Spectrometry After Microwave Assisted Leaching/ Diges tion-Richard Lo binski Joanna Szpunar Vincent 0. Schmitt Jean-Louis Monod Direct Determination of Lead in Alcoholic Drinks and Water by Flame Atomic Absorption Spectrometry Using an Atom-trapping Technique-Han- Wen Sun Li-Li Yang 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. The "M.J. Collins Award" for Innovative Microwave Chemistry CEM are pleased to announce the establishment of a biennial prize for the most notable development or exploitation in the field of microwave enhanced chemistry. Applications are invited from individuals groups or institutions working in any field or discipline in which microwaves are being used to enhance or mediate chemical reactivity. A 500-word summary of the work should clearly describe the relevance and originality of the work identifying also potential beneficiaries. There is no restriction on who may apply however the work described in the application should have been carried out in the UK. Typed applications clearly identifying the name(s) and affiliation of the workers followed by a 500- word description of the work should be clearly marked "CEM Prize" and sent to the address below. The 1996 prize will be E2000 and the closing date will be 29th February 1996. The prize will be awarded to the winner on the 18th April 1996 during the SIA London Conference. CEM Microwave Technology Ltd 2 Middle Slade Buckingham Industrial Park Buckingham MK18 1WA Tel 01280 822873 Fax 01280 822342 6 N Journal of Analytical Atomic Spectrometry January 1996 Vol. I 1

ISSN:0267-9477    

DOI:10.1039/JA996110006N

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Glossary of Abbreviations Whenever suitable elements may be referred to by their chemical symbols and compounds by their formulae. The following abbreviations are used extensively in the Atomic Spectrometry Updates. ac AA AAS AE AES AF AFS AOAC APDC ASV BCR CCP CMP CRM cv cw dc DCP DDC DMF DNA ECD EDL EDTA EDXRF EIE EPMA ETA ETAAS ETV EXAFS FAAS FAB FAES FAFS FANES FAPES FI FPD FT FTMS GC GD GDL GDMS Ge( Li) HCL hf HG HPGe HPLC IAEA IBMK ICP ICP-MS alternating current atomic absorption atomic absorption spectrometry atomic emission atomic emission spectrometry atomic fluorescence atomic fluorescence spectrometry Association of Official Analytical Chemists ammonium pyrrolidinedithiocarbamate anodic-stripping voltammetry Community Bureau of Reference capacitively coupled plasma capacitively coupled microwave plasma certified reference material cold vapour continuous wave direct current d.c.plasma dieth yldithiocarbamate N N-dimethylformamide deoxyribonucleic acid electron capture detection electrodeless discharge lamp ethylenediaminetetraacetic acid energy dispersive X-ray fluorescence easily ionizable element electron probe microanalysis electrothermal atomization electrothermal atomic absorption spectrometry electrothermal vaporization extended X-ray absorption fine structure flame AAS fast atom bombardment flame AES flame AFS furnace atomic non-thermal excitation spectrometry furnace atomization plasma excitation spectrometry flow injection flame photometric detector Fourier transform Fourier transform mass spectrometry gas chromatography glow discharge glow discharge lamp glow discharge mass spectrometry lithium-drifted germanium hollow cathode lamp high frequency hydride generation high-purity germanium high-performance liquid chromatography International Atomic Energy Agency isobutyl methyl ketone (4-methylpentan-2-one) inductively coupled plasma inductively coupled plasma mass spectrometry (ammonium pyrrolidin-1-yl dithioformate) spectroscopy ID IR IUPAC LA LC LEAFS LEI LMMS LOD LTE MECA MIP MS NAA NaDDC NIES NIST NTA OES PIGE PIXE PMT PPm PTFE rf REE(s) RIMS RM RSD SEC SEM SFC Si ( Li ) SIMAAC SIMS SR SRM SSMS STPF TCA TIMS TLC TMAH TOP0 TXRF uhf uv VDU vuv WDXRF XRF PPb QC S/B S/N isotope dilution infrared International Union of Pure and Applied Chemistry laser ablation liquid chromatography laser-excited atomic fluorescence spectrometry laser-enhanced ionization laser-microprobe mass spectrometry limit of detection local thermal equilibrium molecular emission cavity analysis microwave-induced plasma mass spectrometry neutron activation analysis sodium diethyldithiocarbamate National Institute for Environmental Studies National Institute of Standards and Technology nitrilotriacetic acid optical emission spectrometry particle-induced gamma-ray emission particle-induced X-ray emission photomultiplier tube parts per billion parts per million polytetrafluoroethylene quality control radiofrequency rare earth element(s) resonance ionization mass spectrometry reference material relative standard deviation signal to background ratio size-exclusion chromatography scanning electron microscopy supercritical fluid chromatography lithium-drifted silicon simultaneous multi-element analysis with a continuum source secondary ion mass spectrometry signal to noise ratio synchrotron radiation Standard Reference Material spark source mass spectrometry stabilized temperature platform furnace trichloroacetic acid thermal ionization mass spectrometry thin-layer chromatography tetramethylammonium hydroxide trioctylphosphine oxide total reflection X-ray fluorescence ultra-high frequency ultraviolet visual display unit vacuum ultraviolet wavelength dispersive X-ray fluorescence X-ray fluorescence 18R Journal of Analytical Atomic Spectrometry January 1996 Vol.1 1

ISSN:0267-9477    

DOI:10.1039/JA996110018R

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Accurate and Precise Measurements of Lead in Bone Using Electrothermal Atomic Absorption Spectrometry with Zeeman-effect Background Correction Journal of Analytical Atomic Spectrometry YAN Y. ZONG Department of Environmental Health and Toxicology School of Public Health State University of New York at Albany Albany N Y 12201 -0509 USA PATRICK J. PARSONS* Wadsworth Center New York State Department of Health P.O. Box 509 Albany N Y 12201-0509 USA and Department of Environmental Health and Toxicology School of Public Health State University of New York at Albany Albany N Y 12201 -0509 USA WALTER SLAVIN Bonaire Technologies Box 1089 Ridgejield CT06877 USA A simple method for measuring trace levels (pg g-') of Pb in bone by electrothermal atomic absorption spectrometry (ETAAS) is described.ETAAS instrumentation equipped with a transverse Zeeman-effect background correction system was used to investigate the effects of bone matrix on Pb atomization. It is shown that Pb can be accurately measured with good precision using aqueous Pb standards containing NH4H,P04 modifier and Ca ( NO3),. Alternatively Mg ( works as well as Ca( N03)2. For rapid and contamination-free sample preparation bone was digested in concentrated HNO using a closed-vessel microwave digestion system. This approach was compared with digestion at room temperature over 48 h. The detection limit (3s) is 0.6 pg g-' dry mass. Typical day-to-day precision is < 5%. Method accuracy is established as better than 1% using NIST SRM 1400 Bone Ash and SRM 1486 Bone Meal which are the only reference materials we have found for bone-Pb measurements.The method was used to analyse various bone specimens (e.g. tibia femur rib and skull) from Pb-dosed animals. Results indicate that Pb is heterogeneously distributed within bone. Keywords Lead poisoning; calibration; accuracy; modifiers; matrix interferences; microwave digestion Lead has been one of the most extensively studied toxic elements. It accumulates in the skeleton where its concen- tration can represent around 90% of the body burden in adults.' It appears that bone-Pb may be a more accurate and appropriate index of long-term cumulative exposure com- pared with blood-Pb. This has led to the development of in uiuo measurements of Pb in bone by X-ray fluorescence (XRF) including K-XRF and L-XRF.2,3 Studies have shown that XRF is a promising approach for the non-invasive assessment of body burden.However before it becomes a valuable screening tool for clinical studies there are still questions that need to be addressed such as the absence of certified reference materials for instrumental calibration and method ~alidation.~. Most studies of in uiuo XRF bone-Pb measurements have relied on the analyses of bone materials by electrothermal atomic absorption spectrometry (ETAAS) for validation purposes. Therefore the development of an accurate and reliable analytical method for the determination of Pb in bone will be helpful not only for assessing the total body burden of Pb but * To whom correspondence should be addressed. also in providing well characterized materials for validating in uiuo XRF measurement^.^^^ The most common and successful technique for measuring Pb in biological samples is ETAAS because of its high sensi- tivity and favourable detection limits.However it has been troublesome for the analysis of bone because of the complex bone matrix and the laborious sample preparation that is required. The direct solid-sampling procedure described by Langmyhr and Kjuus6 for the determination of Pb in bone by ETAAS required the method of standard additions and yielded results with relatively low precision. Thus different sample pre-treatment methods have been utilized. Wittmers et aL7 applied dry-ashing to human bone samples at 450°C which is time consuming (>48 h) prone to contamination errors and may provide low recoveries. Simon and Liese' and Kowal et aL9 digested bone samples by pressure decompo- sition in nitric acid but others"." have reported that bone samples dissolve easily in nitric acid at room temperature over 1-3 d.In order to minimize matrix interferences modifiers have been used to stabilize the analyte during pyrolysis and permit volatilization of the matrix. Kowal et ~ 1 . ~ used NH,H,PO as modifier. Simon and Liese' investigated the effect of atomiz- ation temperature on the absorbance of Pb in bone matrix and they reported that poor reproducibility could result at high atomization temperatures (> 2000 "C) owing to an interference from a major bone matrix constituent Ca3( PO,),. Therefore the method of standard additions was recommended.Wittmers et aL7 chose La3+ and Subramanian et a1.l' chose Pd2+ instead of NH,H2P04 as a modifier for bone-Pb measurements. Both groups concluded that the method of standard additions was required for this analysis. The present work focuses on the use of NH,H,PO as a modifier for the determination of Pb in bone by ETAAS by carefully optimizing the furnace conditions for the bone matrix. The effects of the bone matrix particularly Ca and Mg on the Pb atomic absorption signal during atomization in the presence of NH,H,PO were studied. Finally a reliable and simple analytical method is described that is fast and maintains a contamination-free sample pre-treatment process. More importantly this approach eliminates the requirement for the method of standard additions.Accurate results were obtained by direct calibration with aqueous Pb standards containing the modifier. Journal of Analytical Atomic Spectrometry January 1996 VoE. 11 (25-30) 25EXPERIMENTAL Instrumentation A Perkin-Elmer Model 25100 atomic absorption spectrometer equipped with transverse Zeeman-effect background correc- tion a Massmann-type longitudinally heated HGA-600 graph- ite furnace and an AS-60 autosampler was used for atomic absorption measurements. Perkin-Elmer pyrolytically coated graphite tubes containing a forked L'vov platform (PN B0505057) were used. Instrumental control and data processing were accomplished with a personal computer (80386SX) running Perkin-Elmer's proprietary software (ver- sion 7.1 ). Background-corrected absorbance and background data were extracted from the *.dat and *.pks files created by the Perkin-Elmer software and converted into ASCII format using a separate software program provided by Perkin-Elmer (version 0.6).Instrumental parameters for the Perkin-Elmer Z5 100 instrument are summarized in Table 1. A Perkin-Elmer Model 4100ZL atomic absorption spec- trometer equipped with longitudinal Zeeman-effect back- ground correction and a transversely heated graphite atomizer (THGA) was also used. Pyrolytically coated graphite THGA tubes from Perkin-Elmer (PN 504 033) containing an integral L'vov platform were used. However low recoveries were obtained with the 4100ZL system. It was found that this was caused by a background overcorrection problem which has been reported in an earlier publication.12 Further work with the 4100ZL system will be published subsequently.A CEM Model MDS 81D closed-vessel microwave digestion system with CEM Teflon PFA low-pressure vessels was used for bone sample digestion. Reagents Doubly de-ionized water (Milli-Q Plus Millipore) was used throughout this work. Working standards were prepared by serial dilution of an AAS-grade stock solution (Fisher Scientific) of Pb(N03)2 containing 1000 mg 1-l of Pb2+ with 0.2% v/v HN03 (trace metal analysis grade Baker). The modifier solution was prepared by dissolving 20 g of NH,H2P04 (HPLC-grade Baker) in 0.5% HN03 and diluting to 100 ml to obtain a 20% m/v solution. Separate solutions of 0.2% m/v Mg from Mg( N03)2 (Aldrich analytical-reagent grade) 0.2% m/v Ca from Ca(N03)2 (Johnson-Matthey Puratronic grade) and 0.2% m/v Ca from CaHPO (Aldrich analytical-reagent grade) were also prepared.Triton X- 100 (0.005Y0 v/v) which was used for rinsing the autosampler tip was prepared by diluting Triton X-100 solution (Fisher Scientific Electrophoresis grade) by a factor of 200. Bone Samples and SRM Various bones were obtained post-mortem from Pb-dosed animals for method development purposes and for bone-Pb distribution studies that will be reported elsewhere. These animals were used for preparing blood-Pb pools that are Table 1 Optimized furnace programmes for the 25100 instrument* Ar flow rate/ Step T/"C Ramp/s Hold/s ml min-' Read Dry 180 10 15 300 Atomization 1600 0 5 0 Yes Clean 2650 1 3 300 Pyrolysis 900 10 20 300 * Element Pb; wavelength 283.3 nm; slit 0.7 nm; autosampler AS-60; light source Pb hollow cathode lamp (10 mA); read delay 0.0 s; BOC 1.0; rollover 1.5; injection volume 10 p1; injection temperature 100 "C; pipette speed 100%.distributed in the New York State Department of Health proficiency testing programme. This programme was covered by an NIH-approved animal welfare and care protocol. NIST SRMs 1486 Bone Meal and 1400 Bone Ash were used for validating method accuracy and precision. Experimental Procedures Bone sample preparation Intact long bones (femur tibia etc.,) and samples of skull ribs vertebrae and ilium were removed at autopsy. Fur and muscle were dissected from the long bones and all other adhering tissues were removed with a bone scraper fabricated from ultra-pure tantalum.Bone marrow was also removed. Bone samples were freeze-dried to constant mass and stored at - 70 "C until analysis could proceed. Small samples (z 0.5 g) of freeze-dried bone were cut using a diamond-disc saw (Dremel) except when removing samples from very large bones where it was necessary to use a stainless- steel autopsy saw (Stryker Instruments). Some bone samples were homogenized for internal quality control purposes using a tungsten carbide ball-mill (GlenMills). It was decided to investigate whether reliable results could be obtained by dissolving bone in HN03 at room temperature as reported by others,lO,'l by comparison with a closed-vessel microwave digestion procedure. About 0.5 g of bone was digested in 10ml of concentrated HNO either at room temperature for 48 h or by using a Model 81D closed-vessel microwave digestion system (CEM) using a heating pro- gramme of 8 min at 100% power followed by 10 min at 65% power under a pressure feedback control set to 448 kPa (65 psi). The final digestate was diluted to 50 ml to give lOmgml-' of bone which was the working solution for ETAAS analysis.Data shown later in this paper indicate that either of these two procedures could be used for digesting bone. Atomic absorption measurements Aliquots of the working solution were diluted with modifier solution directly in the AAS sample cup. The autosampler was programmed to deposit 10 pl equivalent to 10 pg of bone on the platform (Table 1). RESULTS AND DISCUSSION Bone Digestion The results from both digestion procedures are shown in Table 2.It can be seen that room-temperature digestion yields similar results to microwave digestion and both techniques produce results that are within the uncertainty limits for the NIST reference materials. Therefore either of these two pro- cedures could be used for digesting bone. The only disadvan- tage with room temperature digestion is that it is very time- consuming. Selection of Modifier Phosphate (Po,,-) and Pd are widely used as modifiers for the measurement of Pb by ETAAS. Since Po43- has been used successfully in our laboratory for the determination of Pb in it was explored first for the determination of Pb in bone using the 25100 instrument. The effect of varying the pyrolysis and atomization temperatures on the integrated absorbance of Pb (Ai) in the presence of bone digestate without a modifier or with addition of modifier (20 pg of NH4H2P04) was studied.The results in Fig. 1 show that without modifier Pb is lost from bone digestate even at very low pyrolysis temperatures. This is surprising because the 26 Journal of Analytical Atomic Spectrometry January 1996 Vol. 11Table 2 Accuracy comparison between two digestion procedures (a) bone + PO4 Pb (ks)/pg g-' dry mass Bone sample NIST SRM 1400 Bone Ash NIST SRM 1486 Bone Meal Goat bone powder Bone mass/ Microwave pg* digestion 10 20 50 100 10 9.1 (k0.2) 9.0 (k0.3) 1.3 (k0.2) 44.5 (k0.6) 1.2 (k0.2) Room temperature digestion 9.0 (f0.2) 8.9 (k0.3) 1.2 (k0.2) 1.2 (k0.2) 44.0 (f0.5) Certified value 9.07k 1.12 1.335 k 0.014 * Dry bone mass in the 10 p1 digestate deposited on the platform.bone + HNOq '* 500 1000 1500 Temperature/"C 2000 Fig. 1 Effect of pyrolysis and atomization temperature on the absorbance of 10 pl of bone digestate (10 pg of bone) without modi- fier (@) and with 20 pg of NH4HzP04 (0) as modifier. (Atomization T = 1600 "C for pyrolysis study pyrolysis T = 800 "C for atomization study) inorganic bone matrix is an endogenous source of phosphate. The modification behaviour of Ca3( PO,) Mg3( PO4) and H3PO4 was also investigated (data not reported here) and provided similar modification properties to NH4H2P04. However the exact chemical structure of the inorganic bone matrix is still a matter for debate. The prevailing view is that it consists of microcrystals of calcium hydroxyapatite which is thought to have the following formula Ca,,( P04)6(OH),.14 Thus we can only state that endogenous phosphate in bone is unavailable for modification following digestion in HN03.As a result a modifier is required for the bone-Pb determi- nation and NH4H2P0 appears to be a good candidate. Phosphate stabilizes Pb up to a pyrolysis temperature of 1200°C. Experiments with a Pd modifier with addition of either Mg or Ca show no advantage over Po43-. Therefore no further studies were conducted with Pd. Thus NH,H2P04 was selected as the optimum modifier for measuring Pb in bone digestate by ETAAS. Effect of Ca and Mg on Pb in Aqueous Standard The standard method suggested by the manufacturer (Perkin- Elmer) for the determination of Pb using the 25100 instrument calls for PO2- and Mg(NO,) as modifier. However some applications have shown that Mg(N03) is not required for measuring Pb in some biological matrices e.g.bl00d.l~ Fig. 1 indicates that PO:- alone could be a suitable modifier for Pb in bone. Bone is a complicated matrix with a large amount of Ca and Mg.14 In order to examine the possibility of eliminating the requirement for standard additions it is essen- tial to investigate the effect of these elements on the integrated absorbance of Pb in simple aqueous standards in the presence of PO:-. Fig. 2 shows that as little as 2 pg of Ca as Ca(N03) or 2 pg of Mg as Mg(N03)2 enhances the stabilization effect P_b + PO Temperat ure/"C Fig. 2 Effect of pyrolysis and atomization temperature on absorbance of 400pg of Pb with 20pg of NH4H2P04 (@) 20pg of NH4HzP04 + 2 pg of Mg (A) or 20 pg of NH,H2P04 + 2 pg of Ca (0) as modifier.(Atomization T = 1600 "C for pyrolysis study pyrolysis T = 800 "C for atomization study) of Po43- to retain Pb at even higher pyrolysis temperatures compared with PO - alone with a small (< 10%) sacrifice in sensitivity. Comparison of the pyrolysis and atomization curves of Figs. 1 and 2 reveals a close match between a real bone matrix and aqueous Pb standards containing both PO:- and either Ca or Mg. In Fig. 3 the absorbance profiles of (a) Pb in bone matrix with PO:- and (b) Pb(aq) with Po43- and 2 pg of Ca are all comparable. If 2 pg of Mg are used in (b) instead of 2 pg of Ca the integrated absorbance remains the o.2i 0.2. 0.1 - 0 1 2 3 4 Time/s Fig.3 Comparison of atomization profiles and absorbance for stan- dard solutions and bone digestate (- atomic background). (a) 10 pl of bone digestate (10 pg of bone) with 20 pg of NH4H,P04 Ai= 0.090 s; (b) 400 pg of Pb+20 pg ofNH4H,P04+2 pg of Ca Ai=0.132 s Journal of Analytical Atomic Spectrometry January 1996 VoL 11 27same and the absorbance profile is also similar to both (a) and (b) except that the signal is delayed and the peak is wider. Therefore the use of aqueous Pb to calibrate ETAAS instru- mentation for bone lead measurements requires a standard that contains a modifier i.e. POZ- +Ca (or Mg) and elirnin- ates the need for the method of standard additions. Optimization of the Amount of Modifier The amount (20 pg) of NH4H2P04 used in the above experi- ment was taken from the blood-Pb method developed in our lab~ratory.'~ Since the matrices for blood and bone are totally different optimized PO2 - concentrations for this work were obtained by observing changes in atomization profiles and integrated absorbance of both aqueous standards and bone samples with increasing amounts of NH4H2P04.The results are plotted in Fig. 4 which indicates that even less than 20 pg of NH4H,P04 (per 10 pl of injection) is sufficient for both standards and samples. To be on the safe side 20pg of NH4H2P04 were used. Effect of Bone Matrix The effect of enriched elements in bone matrix Ca and Mg on the atomization of Pb in the presence of Po43- was investigated in more detail. Figs. 5 and 6 show that even very small amounts (0.2 pg per 10 pl injection) of Mg or Ca have a significant effect on the Pb absorbance profile reducing the absorbance by about 5% and delaying the appearance.Increasing the amount of Mg or Ca to more than 0.5 pg does not produce any further reduction in absorbance but does 0.16 aqueous Pb 0.14 9 - p - - - -I "021 0.W 0 5 10 15 20 25 30 35 40 Amount (pg) of NH4H2P04 added in aqueous Pb (400 pg) or bone digestate Fig. 4 Effect of the concentration of NH,H2P0 on the absorbance of 400 pg of Pb ( 0 ) and 10 pl of bone digestate (10 pg of bone) (0) Amount (pg) of Mg or Ca in 10 pl of injection of STD (400 pg of Pb+20 pg Of NH,H,PO)4 Fig. 5 absorbance of 400 pg of Pb with 20 pg of NH,H,PO Effect of the concentration of Mg ( A ) or Ca (0) on the 0.2 / 400pg Pb+2Opg NH4H2P04 0 1 2 3 4 Ti me/s Fig.6 Effect of the amount of Mg or Ca on the atomization profile and absorbance of 400 pg of Pb+ 20 pg of NH,H,PO (- atomic . . . background) continue to delay the appearance of Pb especially with Mg and increases the background absorbance. The profile for aqueous Pb with 20pg of NH4H,P04 and 2pg of Ca in Fig. 6(c) is most analogous to that of Pb in bone with 20 pg of NH4H2P0 shown in Fig. 3(a) with respect to the appear- ance time for Pb. However there is no difference in the integrated absorbance for 400 pg of Pb with either 2 pg of Ca or 2 pg of Mg. Therefore 2 pg of Ca (10 pl injection) were added to the standards with Po43-. Fig. 7 shows the significance of adding Ca to Pb standards -.- I I Pb concentration (ppb) Fig. 7 Calibration (0) and standard addition [bone ash digestate addition (a); goat bone digestate addition (A)] plots for different standard series.(a) Pb+20 pg of NH,H,PO,; (b) Pb+20 pg of NH,H,PO + 2 pg of Ca 28 Journal of Analytical Atomic Spectrometry January 1996 Vol. 11containing P043- on the calibration graphs used for the determination of Pb in bone. When alone is used with Pb as shown in Fig. 7(a) the calibration slope is different from the slopes obtained by spiking either re-dissolved bone ash or bone digestate. This difference in calibration slopes would certainly result in a low bias. However on addition of Ca to P0,3-containing Pb standards as shown in Fig. 7(b) the calibration slopes are essentially the same and will yield accurate results across the concentration range studied (Table 2).It is interesting that Kowal et aL9 used NH,H2P04 alone as a modifier in the bone-Pb method employed for the Franklin Forensic Project. Method Evaluation The instrumental detection limit for Pb is 0.6 pg 1-'(3s) i.e. 6 pg in 10 p1 aliquots which is equivalent to a method detection limit for bone-Pb of 0.6 pg g-' dry mass. For our purposes however we prefer to use a more conservative minimum reportable bone-Pb concentration of 1 pg g-' dry mass based on 5s. The absolute sensitivity or characteristic mass (rn,,) for Pb was found to be 12.9 pg which was close to the manufac- turer's published value for the 25100 instrument (12 pg). The characteristic mass is defined as the mass of analyte required to produce an integrated absorbance of 0.0044 s.The method precision given in Table 3 shows both within- day and day-to-day precision for different amounts of bone deposited on the platform. Even though the precision becomes slightly poorer as more bone is deposited over-all it is always <6% even with 100 pg of bone deposited on the platform. The accuracy of the method was established up to 9 pg g-' by analysing NIST SRM 1486 Bone Meal and SRM 1400 Bone Ash as shown in Table2. The determined values agree well with the certified values and within the uncertainty limits established for the materials. It will be valuable to have reference materials in the range 20-50 pg g-'. Recovery studies were attempted by spiking different amounts of bone material with 10 20 30 and 40 pg I-' of Pb. Recovery results (Table 4) were in the range 95-105% for 10-100 pg of bone deposited on the platform.The calibration was linear up to 100pgl-l as shown in Fig. 8 although few bone digestate samples analysed were Table 3 Analytical precision for bone-Pb using the 25100 instrument Precision Bone mass/ Within-dayt Day-to-day$ Sample pg Pb/M 8-l sr (%) s (%) 106F(L) 10 27.5 0.8 1.4 2-14H( L) 20 12.5 1.5 2.7 2-1 5F( L) 50 9.0 2.4 3.6 2-1 5H( L) 100 8.8 3.5 5.8 * Dry bone mass in the 10 p1 digestate deposited on the platform. j- Based on five repetitive measurements within a day. $ Based on five-day measurements. Table 4 Recovery of Pb added to bone digestate* ~~ Recovery of Pb (%) at different bone mass (pg)t of Pb spike/ I% 1-1 100 50 20 10 10 9 8 f 3 98f2 9 9 f 2 lOOf 1 20 9 7 f 3 99f2 100 & 2 lOOf 1 30 9812 99+3 99+ 1 100 f 2 40 98+2 9 8 f 3 99+2 99f 1 *The average of four different goat bone digestates in five day's j- Dry bone mass in the 10 pl digestate deposited on the platform.measurements. Pb concentration (ppb) Fig. 8 Plot shows the linear range of the routine calibration line with STD Pb+20 pg of NH,H,PO,+2 pg of Ca 0.20 0.05 0.00 ' 100 200 300 400 Number of firings Fig. 9 20 pg of NH,H,PO Test of tube life using bone digestate (10 pg of bone) with more than lOOpgl-' in Pb. A tube life test was carried out using 10 pl aliquots of bone digestate (i.e. 10 pg of dry bone) and 20 pg of NH,H,PO,. More than 400 firings were possible before the sensitivity was affected (Fig. 9). Analysis of Bone Samples Tibia bone samples from the Pb-dosed animals were prepared and analysed. The results are listed in Table 5.It is clear that this analytical method yields very precise results. It also indicates that tibial bone-Pb concentrations are strongly corre- lated with the cumulative Pb dose. In addition various other bones including femur limb joints skull ribs vertebrae and ilium were analysed for Pb. It was found that Pb was heterogeneously distributed within the skeleton and even within a single bone type such that specimen selection and removal will contribute large variations in the analytical result. Details of our analytical study of Pb distri- bution in bone will be published elsewhere. Table 5 Bone-Pb results from Pb-dosed animals Sample C28 GO-11 G2-11 G2-8 G2-7 G2-5 G1-5 Cumulative Pb dose/g Bone-Pb/pg g-' dry mass* 0 12.7 36.6 40.2 46.8 47.0 53.4 < 1.0 12.8 f0.5 21.5 f0.5 31.4 f 0.5 34.5 0.4 20.0 f 0.3 37.5 f 0.5 * Based on a single 0.5 g bone sample taken from the tibial shaft. Uncertainty is the analytical precision (between-run) expressed at the standard deviation.Journal of Analytical Atomic Spectrometry January 1996 VoZ. I 1 29CONCLUSION Phosphate (NH,H,PO,) is a good modifier for the determi- nation of Pb in bone by ETAAS. However simple aqueous standards containing a modifier such that they are partially matrix-matched should be considered in order to obtain reliable results and avoid the method of standard additions. Either Ca or Mg is effective for this purpose. The method developed here provides a sensitive accurate and precise analytical tool for bone-Pb studies and obviates the need for the method of standard additions.The authors are grateful to the Animal Care staff at the Wadsworth Center’s Griffin Laboratory and to the technical staff of the Center’s Lead Poisoning/Trace Elements Laboratory for assistance with the collection and preparation of animal bone samples. We also thank Shida Tang and Dr. Roland Matthews for technical assistance and helpful discussions. REFERENCES 1 Barry P. S. Br. J. Znd. Med. 1975 32 119. 2 Thomas B. J. Environ. Health Perspect. 1991 91 39. 3 4 5 6 7 8 9 10 11 12 13 14 Todd A. C. and Chettle D. R. Environ. Health Perspect. 1994 102 172. Todd A. C. Landrigan P. J. and Bloch P. Neurotoxicology 1993 14 145. Parsons P. J. Zong Y. Y. and Matthews M. R. Adu. X-ray Anal. 1995 38 625. Langmyhr F. J. and Kjuus I. Anal. Chim. Acta. 1978 100 139. Wittmers L. E. Jr. Alich A. and Aufderheide A. C. Am. J . Clin. Pathol. 1981 75 80. Simon J. and Liese T. Fresenius’ 2. Anal. Chem. 1983,314,483. Kowal W. A. Krahn P. M. and Beattie 0. B. Znt. J. Environ. Anal. Chem. 1989 35 119. Drasch G. A. Bohm J. and Baur C. Sci. Total Environ. 1987 64 303. Subramanian K. S. Connor J. W. and Meranger J. C. Arch. Environ. Contam. Toxicol. 1993 24 494. Zong Y. Y. Parsons P. J. and Slavin W. Spectrochim. Acta Part B 1994 49 1667. Parsons P. J. and Slavin W. Spectrochim. Acta Part B 1993 48 925. Neuman W. F. and Neuman M. W. The Chemical Dynamics of Bone Mineral University of Chicago Press Chicago IL 1958. Paper 5/04559B Received July 7 1995 Accepted October 17 1995 30 Journal of Analytical Atomic Spectrometry January 1996 Vol. 11

ISSN:0267-9477    

DOI:10.1039/JA9961100025

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Determination of Chromium by Electrothermal Atomic Absorption Spectrometry with Various Chemical Modifiers Journal of Analytical Atomic Spectrometry NIKOLAOS S. THOMAIDIS EFROSINI A. PIPERAKI,* CHRISTOFOROS K. POLYDOROU AND CONSTANTIN 0s E. E F STAT H I 0 U Laboratory of Analytical Chemistry Chemistry Department University of Athens University Campus 157 71 Athens Greece The determination of Cr in the presence of various isomorphous metals has been studied. The atomic absorption signal for Cr was increased and stabilized by the presence of 20 pg of Mg(NO& 1 pg Rh and 1 pg Pt. Magnesium Rh and Pt gave comparable characteristic masses of 3.2 3.0 and 2.8 pg respectively when integrated absorbance was measured. The limits of detection were 0.18 0.14 and 0.091 pg l-' respectively. The efficiency of these modifiers was tested with the direct determination of Cr in rain-water and serum samples.Quantification was performed with aqueous standards in the case of the rain-water samples and with matrix- matched standards in the case of the serum samples. Recovery tests and a serum reference material were used to check the accuracy of the proposed methods. Accurate results and good agreement with the certified serum values were found in the presence of platinum as a modifier. Chemical modifiers were not necessary for the determination of Cr in rain water. Keywords Chromium determination; electrothermal atomic absorption spectrometry; chemical modification; rain water; serum Electrothermal atomic absorption spectrometry (ETAAS) is the technique of choice when low amounts of Cr (about 1 pg 1-I) have to be determined.However the determination of Cr is considered to be difficult owing to the following problems (a) background correction with continuum light-sources is difficult owing to the low emission intensity of the deuterium- arc background corrector at the resonance line of Cr (357.9 nm); and (b) pre-atomization losses and decreased sensi- tivity can occur in certain complex matrices. Attempts to solve the first problem led to the use of a modified spectrometer with a quartz-halogen light source for background Extensive s t ~ d i e s ~ . ~ on the back- ground signal showed that the problem arises from the emission caused by Cr together with the main matrix elements (such as K and Na) and probably graphite. The magnitude of this interference depends on the lamp current slit-width and the atomization temperature.Halls and Fell4 and Berndt and Sopczak5 found that using a ramp atomization mode at 2400 "C reduced the interference. Pre-atomization losses and reduced sensitivity are severe in the presence of chlorides of various metal^,^,^ and in the presence of carbide forming elements such as Mo and organic solvents that promote the formation of chromium carbide.' Tungsten has been proposed as a chemical modifier for the determination of Cr in ~ a t e r ~ ' ~ ~ because it enables pyrolysis temperatures of 1500"C9 or 1600°C10 in acidic media to be obtained without losses. Vanadium and a V-Mo modifier have been used for the determination of Cr in serum and lake-water * To whom correspondence should be addressed.samples using peak height measurements." Magnesium nitrate has often been used as a chemical modifier to stabilize Cr during the pre-atomization step8-10y12 and for its determination in water sample^.^^^^^ It has also been used as an ashing aid/ chemical modifier for the determination of Cr in s e r ~ m . ~ ~ ' ~ ~ The Mg-Ca mixed modifier has been used to determine Cr in serum because it has facilitated pyrolysis at higher tempera- tures (1400 versus 1200°C without a chemical modifier) and has given a better characteristic mass (2.56 versus 5.13 pg for integrated absorbance measurements).16 In addition to the above problems very low Cr concen- trations are present in various types of sample even though Cr is a ubiquitous element on the Earth's crust.In order to avoid contamination extreme care is needed and direct methods of determination become necessary. The purpose of the present study was to investigate the direct determination of Cr in various matrices using alternative chemical modifiers (Rh and Pt) to optimize their use and compare them with modifiers that have been proposed pre- viously (Mg and W). The direct determination of Cr in samples with extremely low concentrations such as rain water and serum was investigated and the alternative modifiers proved to be essential especially in the latter type of sample. The choice of potential chemical modifiers was based on the studies of Tsalev and c o - ~ o r k e r s l ~ * ~ ~ on the possible substitution of the modifier atoms by an isomorphous analyte.EXPERIMENTAL Instrumentation A Perkin-Elmer Model 5000 atomic absorption spectrometer equipped with an HGA 400 graphite furnace was used for the atomic absorption measurements at the 357.9 nm resonance line of Cr with a 0.7nm spectral bandwidth. A Cr hollow cathode lamp was employed as the radiation source and was operated at 18 mA. Pyrolytic graphite coated graphite tubes (Perkin-Elmer Part No. B0135653) were used throughout the study. Solution volumes of 20 pl were dispensed into the graphite tubes with an AS-1 autosampler and an Eppendorf micropipette with disposable poly (propylene) tips. A tungsten- halogen light source was used for background correction. The graphite furnace operating conditions are summarized in Table 1.The time-resolved atomic absorption peaks were recorded with an IBM compatible PC Quest 286/16 computer. This system has been described elsewhere." Reagents All chemicals used in this study were of analytical-reagent grade. The glass and poly(propy1ene) apparatus were kept in 10% v/v HN03 for at least one night and then rinsed with 1% v/v HN03 three times and subsequently ten times with Journal of Analytical Atomic Spectrometry January 1996 Vol. 11 (31-36) 31Table 1 Temperature programme for the comparison of chemical modifiers in the determination of Cr Temperature Step 1°C Drying 120 Cooling 20 Pyrolysis Various* Atomization 2300 Cleaning 2650 Ramp time/s 10 10 1 0 1 Hold time/s 20 20 9 4 2 Ar flow ratelm1 min- Read 300 - 300 300 - 0 On 300 - - * Various Tpyr values are presented in Table 3. doubly distilled de-ionized water before use.The acids were of Suprapur grade (Merck). Chromium standards were pre- pared by diluting a 1 g I-' Cr (as CrC1,) stock solution (Titrisol Merck) with doubly distilled de-ionized water and acidified to a final HN03 concentration of 1% v/v. Modifier stock solutions were prepared by dissolving appropriate amounts of their salts in acidic media and diluting to a final volume with doubly distilled de-ionized water. The modifiers studied were Mg Ca Sr Sc Y and La (as the nitrates) Zr (as ZrOCl,) W (as Na,WO,) Re (as HReO prepared by dissolv- ing Re powder in H202) Ru Rh Pd and Pt (as the chlorides). All of these metals are isomorphous with Cr.,' A 1 g I-' NH,SCN solution was prepared from solid NH,SCN (Merck).Procedure Comparison of chemical modiJers For the choice of the maximum pyrolysis temperature (TPyr) and the optimum mass of the modifier 5 or 10 pl of the modifier solution were dispensed into the graphite tube (depending on the mass of the modifier) followed by 20 p1 of the Cr solution (200 pg). The temperature programme in Table 1 was followed. The peak height and the integrated absorbance were recorded simultaneously. Calibration curves were constructed by injecting 20 p1 of standard solutions containing 0.5 1.0 2.0 3.0 5.0 7.5 10.0 15.0 and 20.0 pg 1-' of Cr on to the graphite wall. The characteristic mass m (pg) was calculated from the slope (b) of the calibration curve using the equation m =0.0044 x 20/b for a sample volume of 20 pl.The limit of detection (LOD pg I-') was calculated from the equation LOD = 3 x SB,/b where SBL was the standard deviation of ten blank firings. Determination of Cr in rain water A full description of the type of sampler and methods used for collection has been given in a previous study.21 The samples were acidified with HNO to a final concentration of 1% v/v and stored at 4°C until required for analysis. A 20 p1 volume of the sample was injected into the graphite tube with or without 5 pl of the Pt solution. The temperature programme in Table 1 was followed. The value of Tpyr in the absence of Pt was 1300"C whereas in the presence of 1 pg of Pt it was 1500 "C. Quantification was performed with aqueous solutions containing 0.5 1.0 1.5 2.0 3.0 and 4.0 pg 1-l of Cr and using integrated absorbance measurements.Recovery experiments were carried out by spiking a rain water sample with the same concentrations of Cr. Determination of Cr in serum Serum samples were diluted 1+1 with a 0.2% solution of Triton X-100. A 5 pl volume of the modifier solution (Mg or Pt) was injected into the graphite tube followed by 20p1 of diluted serum. The temperature programme given in Table 2 was followed. The quantification was performed with a matrix- matched calibration curve prepared by spiking a diluted serum 32 Journal of Analytical Atomic Spectrometry January 1996 sample with 0 0.5 1.0 2.0 and 5.0 pg 1-l of Cr. Recoveries were calculated from the matrix-matched curve. The accuracy was tested by analysing a Biological Reference Material (Freeze-Dried Human Serum) with a certified Cr value of 0.76 (0.67-0.87) ng g-' supplied by Dr.J. Viersieck University Hospital Ghent Belgium. The freezed-dried material was taken into solution by simply adding doubly distilled de-ionized water mixing vigorously for 5 min on a Vortex and diluting 1 + 1 with a 0.2% solution of Triton X-100. Various portions of this material were used of different masses giving different Cr concentrations in the final liquid sample. These concentrations are quoted as 'certified values' in Table 7. Serum samples from healthy people (n = 22) and samples from patients with various thoracic diseases (lung cancer tuberculosis and pleurisy n = 15) were analysed using the above procedure with Pt as the chemical modifier taking all necessary precautions to avoid contamination.RESULTS AND DISCUSSION Comparison of Chemical Modifiers Amount of chemical modijier and temperature studies The primary role of a chemical modifier is to stabilize the analyte during the pre-atomization step. Although Cr is a moderately volatile element in oxyacidic media such as the 1% v/v HNO used in the present work with a maximum pyrolysis temperature of 1200"C this temperature has to be decreased when samples with a difficult matrix have to be analysed (e.g. in the presence of high concentrations of chloride salts). Therefore the Tpyr was determined in the presence of various potential chemical modifiers. The results are summar- ized in Table 3 where the optimum amounts of the modifiers are also given. The optimum atomization temperature was found to be 2300"C since the integrated absorbance did not change for higher temperatures and an over-correction of the specific absorbance was seen at temperatures higher than 2500 "C confirming previously described y h e n ~ m e n a .~ . ~ ' ~ The modifiers were tested in sequence according to their position in the Periodical Table and the results are discussed below. Group IIA Mg Ca and Sr. Magnesium was the only element in this group that stabilized Cr. The appearance temperature was shifted to higher values in the presence of 20 pg of Mg(NO,),. As the atomic radius of these metals increased Cr atoms were produced earlier and the maximum pyrolysis temperature decreased. Despite the small increase in sensitivity in the presence of 20 pg of Ca(N03)2 it could not be used as a chemical modifier for the determination of Cr since no stabilization was observed.The influence of increasing amounts of Mg(NO,) on the Cr signal at a Tpyr of 1500°C is shown in Fig. 1. The optimum amount of Mg(N03) was 20 pg because larger amounts produced peaks with tailing and decreased the sensitivity. It is apparent that when peak height absorbance was measured the atomic absorption (AA) signal recovered only in the presence of 20 pg of Mg(NO,) whereas the integrated absorbance signal recovered with only 5 pg of VOl. 11Table 2 Temperature programme for the determination of Cr in serum Temperature Step 1°C Drying Pyrolysis 1 Pyrolysis 2 Cooling Atomization Cleaning 120 600 Various* 20 2200 2650 Ramp time/s 10 5 10 1 0 1 Hold time/s 20 15 20 14 4 2 Ar flow rate/ml min- 300 300 300 300 0 300 1 Read * Various qyr are no modifier 1100 "C; Pt 1300 "C; and Mg 1400 "C.Table 3 Maximum pyrolysis temperature (T,,,) for the determination of 0.1 ng of Cr in the presence of various modifiers of different masses Modifier mass/pg - 20 20 20 20 20 20 20 20 20 10 1 1 5 1 +20 1 +20 Tpyr/OC 1200 1500 1200 1150 1300 1300 1200 1200 1200 1200 1200 1400 1300 1250 1500 1400 * Plus 20 pg of NH,SCN. 0.8 I I I 0.6 0 \o. -- L O I 0 20 40 60 80 100 Mass of Mg (NO&/pg Fig. 1 Influence of increasing amounts of Mg(N03)2 on A the peak height and B the integrated absorbance of 0.2 ng of Cr at a pyrolysis temperature of 1500 "C. The units of integrated absorbance (B) are seconds Mg(NO,),. Thus 20pg of Mg(NO,) were used in the sub- sequent studies.Group IIIA Sc Yand La. This group did not really stabilize Cr. In fact Sc produced erratic and noisy peaks and the background was increased. Yttrium produced flat peaks with increased tailing probably by promoting the formation of chromium carbides and 20 pg of La(NO,) had no effect on the AA signal of Cr. Carbide forming elements (Groups IVA VIA and VIIA) Zr Wand Re. None of these elements stabilized Cr. Zirconium led to slow atomization therefore flat peaks with tailing were recorded. Memory effects were observed and the sensitivity decreased. Zirconium and Cr apparently formed stable mixed carbides. With 20 pg of Re the sensitivity of the determination and Tpyr were not affected. When 20 pg of Na,WO were introduced with the Cr solution in the graphite tube neither significant enhancement of the signal nor thermal stabilization were observed and the appearance temperature did not increase substantially. When the pyrolytic-graphite coated graphite tube was impregnated by a solution containing l o g 1-' of Na,WO following the procedure proposed by Ortner and Kantuscher, an increase of about 20% in the peak height was noticed but the peak area did not alter.Noble metals Ru Rh Pd and Pt. All of these metals enhanced the AA of Cr although to different extents. When masses of their chloride salts of greater than 10 pg were injected the excess of chlorine depressed the AA signal of Cr probably owing to the formation of volatile Cr-chloro compounds' in the atomization step.The same was apparent with lower masses of the Pt modifier. It was found that 20 pg of NH,SCN completely eliminated this interference. It is likely that NH,SCN promoted the early reduction of these compounds to the metals and chlorine was driven off from the graphite tube during the early stage of the pyrolysis step (probably as NH,Cl or HCl). Therefore when masses greater than 10 pg were employed 20 pg of NH,SCN were injected with the modifier solution. Careful optimization of the masses of modi- fier used was carried out because it was shown that the mass of modifier influenced the sensitivity and the Tpyr greatly,19924725 especially in the case of the noble metals. The optimum amounts of modifiers were 1 pg of Rh; 5 pg of Ru; 10 pg of Pd; and 1 pg of Pt.The influence of increasing amounts of Rh on the Cr signal at a Tpyr of 1400°C is shown in Fig. 2. It is evident from this figure that 0.25 pg of Rh were sufficient for restoring the integrated absorbance signal of Cr. The same pattern was also observed with the other modifiers except for Pd. However Ru could not be used as chemical modifier because the background absorption at the resonance line of O L Ll 0 1 2 3 4 Rh mass/pg Fig. 2 Influence of increasing amounts of Rh on A the peak height and B the integrated absorbance of 0.2ng of Cr at a pyrolysis temperature of 1400 "C. The units of integrated absorbance (B) are seconds Journal of Analytical Atomic Spectrometry January 1996 Vol. 11 33Cr was elevated; it also showed a considerable blank value and a decrease in the sensitivity was observed after 30 success- ive injections of 10 pg of Ru.Palladium was useful as a modifier only when 10 pg of Pd were mixed with 20 pg of Mg(N03),. This mixed modifier neither changed the appearance tempera- ture of Cr nor increased the sensitivity but it caused a shift in Tpyr to 1300"C compared with 1500°C achieved with only 20 pg of Mg(N03)2. Therefore the mixed Pd-Mg modifier was not tested further. Only Pt and Rh stabilized Cr during the pyrolysis stage and increased the peak area signal even when using remarkably low masses of modifier. These modifiers were used further in this study. The transient signals of 10 pg 1-l of Cr in the presence of different modifiers are shown in Fig. 3. This figure indicates that both modifiers (Mg and Pt) decreased the peak width and increased the peak height which implies an increase in the rate of atomization in their presence.Moreover the Cr peak showed less tailing which means that the interaction with graphite was less favourable in the presence of Pt. The same phenomena were observed with Rh as a chemical modifier. Various mechanisms have been proposed for the atomization of Cr including the thermal dissociation of its oxides,26-28 and the thermal decomposition of chromium carbide (Cr,C2) and desorption of adsorbed C~(S).~' Magnesium nitrate has been p r o p ~ s e d * ~ ' ~ * ~ ~ ~ ~ ~ as a chemical modifier to stabilize chromium oxide avoiding losses of the volatile suboxide. Since masses of modifiers much larger than the stoichiometric amounts had to be used in order to recover the Cr signal at high Tpyr (Figs.1 and 2) trapping of Cr species in the bulk of the modifier mass and/or the formation of a solid solution of Cr with the modifier is a more probable explanation. It is likely that losses attributed to the formation of volatile CrO at the active sites of graphite are prevented owing to blockage of these sites by the modifiers. AnalyticalJigures of merit Calibration curves were constructed following the procedure described under Experimental and applying the temperature programme given in Table 1. The limits of detection and characteristic masses are given in Table 4. These parameters are in agreement with those previously rep~rted.~."-~~ Both noble metals (Pt and Rh) gave slightly improved characteristic masses.However Pt did not affect the baseline noise giving LOD values similar to those obtained in the absence of a modifier. The relative standard deviations for nine replicate injections of a solution containing 5 pg 1-l of Cr in 1% v/v HN03 were 1.2 and O.8% when peak height and integrated absorbance were measured respectively. The corresponding 1.0 I I I I I 0.8 A 0) c 2 0.6 3 0.4 0.2 0 8 1 2 3 4 Atomization tirnels Fig. 3 Atomization signals for 0.2 ng of Cr in the presence of various chemical modifiers A no modifier Tpyr= 1200 "C peak height 0.587 integrated absorbance 0.269 s; B 20 pg of Mg(N03)2 qyr= 1500 "C peak height 0.746 integrated absorbance 0.277 s; C 1 pg of Pt +20 pg of NH4SCN qyr= 1300 "C peak height 0.866 integrated absorbance 0.312 s.In all instances wall atomization was used at 2300 "C Table 4 Sensitivity and LODs for the determination of Cr LOD/'pg 1-' molpg Modifier PH* IAt PH IA None 0.066 0.072 1.9 3.3 Mg(N03)2 0.17 0.18 1.5 3.2 Na2W04 0.21 0.23 1.9 3.2 Rh 0.11 0.14 1.4 3 .O PtS 0.058 0.09 1 1.4 2.8 * PH peak height absorbance. t IA integrated absorbance. $With NH4SCN. values in the presence of modifiers were 1.4 and 4.0% [Mg(NO,),]; 1.9 and 4.5% (Na,WO,); 1.7 and 1.0% (Rh); and 1.4 and 0.9% (Pt). Determination of Cr in Rain Water The Tpyr in the absence of any chemical modifiers was 1300 "C whereas in the presence of 20 pg of Mg(NO,) it was 1550 "C and in the presence of 1 pg Pt 1500°C. It is likely that the matrix components in combination with Pt allowed Tpyr. to be increased substantially.The increased thermal stabilization of Cr in this type of sample led to the determination being carried out without any interferences. No difference in the slopes of the calibration curves with aqueous and matrix-matched stan- dards was observed therefore quantification was possible with aqueous standards and integrated absorbance measurements. It is shown in Table 5 that excellent recoveries were obtained with or without chemical modification by Pt. The within-batch precisions were 2.8 and 3.2% without and with Pt respectively for 0.55 pg 1-l of Cr (n=5). The between-batch precisions were 3.9 and 4.0% without and with Pt respectively for 0.55 pg 1-l of Cr (n = 5). Rain water samples from two stations one urban (St. A) and one rural (St. B) were analysed and the concentrations ranged from 0.21 to 3.15 pg 1-I in St.A (n= 14) to 0.55 to 1.48 pg 1-l in St. B (n=8). The wet deposition (surface concentration pg m-2) of Cr ranged from 2.7 to 194 pg m-2 in St. A and 6.4 to 148 pg rn- in St. B. Determination of Cr in Serum The pyrolysis and the atomization curves for Cr in a serum sample are shown in Fig.4. The atomic absorption signal of Cr was thermally stable up to 1100°C in the absence of chemical modifiers. The 7byr was 1300°C in the presence of 2 pg of Pt and 1400°C in the presence of 20 pg of Mg(N03),. The optimum mass of Pt was found to be 2 pg (higher than in the case of aqueous solutions) and addition of NH4SCN was not necessary. The organic serum components and/or Triton X-100 probably promoted the early formation of Pt during the drying and /or the pyrolysis step.Recovery experi- ments were carried out with and without modifiers and the results are summarized in Table 6. Consistently better recovery Table5 Recovery of Cr added to rain water with and without Pt using integrated absorbance measurements Recovery (n=3)(%) Cr added/pg I-' No modifier 1 pg of Pt 0.5 97.7 f 3.6 99.0 k 1 .o 1 .o 98.0 i- 2.0 98.3 & 1.2 1.5 99.0 f 3.4 100.1 & 2.4 2.0 101.4 f 1.7 100.9 rfI 2.9 3.0 100.7f 1.0 101.0f 1.1 4.0 99.4k 1.8 99.9 f 1.4 34 Journal of Analytical Atomic Spectrometry January 1996 Vol. 110.20 - u) a V \ 4 -8 c. ; 0.10 2 0.15 - (d E CI) - - 0.05 b I 1000 1200 1400 1600 1800 2000 2200 2400 2600 Temperature/OC Fig. 4 Pyrolysis (hollow symbols) and atomization (full symbols) curves for a 1 + 1 diluted serum sample spiked with 5 pg I-' of Cr in the presence of various chemical modifiers (0) no modifier (0) 20 pg of Mg(NO,) and (0) 1 pg of Pt.Table6 Recovery of Cr added to serum with and without chemical modifiers using integrated absorbance measurements Recovery (n=4) (%) ~~ ~~ Cr added/pg 1-' No modifier Mg(NO,) Pt 0.5 114.4 & 6.6 120.1 k8.9 98.0 & 1.0 1 .o 117.9 5 3.2 120.0 2 3.2 98.3 f 1.2 2.0 109.0 f 1.5 1 14.6 k 2.1 99.9 & 0.9 5.0 102.7f 1.8 104.6+ 1.5 99.7f1.1 was obtained in the presence of Pt. Since Mg(N0,)2 has been used successfully in the past for the determination of Cr in serum the increased recoveries we observed with this modifier could be attributed to the significantly lower concentration range of Cr used in the present study (0.5-5.0 pg l-') compared with those used in previously reported studies (generally 2.0-20.0 pg 1-I).The results for the determination of Cr in the Freezed-Dried Human Serum Reference Material are summar- ized in Table 7. Better agreement with the certified value was obtained in the presence than in the absence of Pt. It was found that build-up of a carbonaceous residue after successive injections affected the sensitivity and frequent recalibration was therefore required. The rn in the absence of a chemical modifier as well as in the presence of 1 pg of Pt or 20 pg of Mg(NO& were 1.7 and 2.9 pg for peak height and integrated absorbance measurements respectively with a new graphite tube. After 50 cycles the m was found to be 3.2 pg and after 150 cycles 3.7 pg for integrated absorbance measurements.The LOD in the absence of a chemical modifier was 0.051 pg Table 7 Determination of Cr in freezed-dried human serum refer- ence material Cr found/pg 1 - ' Certified Sample value/pg 1-' No modifier 1 PLg Pt 72 0.185 0.126 0.178 0.118 0.187 198-1 0.175 0.125 0.147 0.126 0.151 198-2 0.151 0.107 0.156 0.100 0.149 198-3 0.192 0.150 0.199 0.142 0.198 825 0.219 0.180 0.223 0.177 0.25 1 0.170 0.223 1-' whereas in the presence of 1 pg Pt or 20 pg Mg(N0,)2 the LODs were 0.041 and 0.091 pg 1-' respectively for integrated absorbance measurements. The within-batch pre- cisions were 3.0 and 3.8% without and with Pt respectively for 0.90 pg I-' of Cr (n=5). The between-batch precisions were 8.9 and 8.0% without and with Pt respectively for 0.62 pg 1-' of Cr (n=5).The proposed method with Pt as a chemical modifier was used to establish the Cr range in the serum of 22 healthy adults and 15 patients suffering from various thoracic disease^.^' The concentrations in samples ranged for the former group from < 0.05 pg I-' (below the LOD) to 0.69 pg 1-' whereas for the latter group they ranged from 0.18 to 1.13 pg 1-'. CONCLUSIONS Based on the results obtained in the present study it is concluded that several elements can stabilize Cr. The modifiers giving the best results in terms of thermal stabilization and sensitivity were Mg Rh and Pt. Palladium did not stabilize Cr. Tungsten (as 20 pg of Na,WO,) neither increased the Gyr nor the sensitivity. No interferences were observed in the determination of Cr in rain water and quantification could be performed with aqueous standards and integrated absorbance measurments without using chemical modifiers.The successful determination of Cr in serum was accomplished in the presence of Pt. Matrix-matched calibration was essential in order to achieve accurate and precise results. Periodic recalibration was required owing to a small decrease in sensitivity from the build-up of carbon. One of the authors (N. T.) thanks the Greek State Scholarships Foundation for financial support of this work. The Agricultural Bank of Greece is also thanked for providing part of the instrumentation. REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Kayne F. J. Komar G. Laboda H. and Vanderlinde R.E. Clin. Chem. 1979 24 2151. Veillon C. Patterson K. Y. and Bryden N. A. Anal. Chim. Acta 1982 136 233. McAughey J. J. and Smith N. J. Anal. Chim. Acta 1987 193 137. Halls D. J. and Fell G. S. J. Anal. At. Spectrom. 1986 1 135. Berndt H. and Sopczak D. Fresenius' Z . Anal. Chem. 1987 329 18. Matsusaki K. Yoshino T. and Yamamoto Y. Anal. Chim. Acta 1981 124 163. Matousek J. P. and Powell H. K. J. Spectrochim. Acta Part B 1988 43 1167. Castillo. J. R. Mir J. M. and Bendicho C. Fresenius' Z . Anal. Chem. 1988 332 783. Arpadjian S. and Krivan V. Fresenius' 2. Anal. Chem. 1988 329 745. Beceiro-Gonzalez E. Bermejo-Barrera P. Bermejo-Barrera A. Barciela-Garcia J. and Barciela- Alonso C. J. Anal. At. Spectrom. 1993 8 649. Manzoori J. L. and Saleemi A. J. Anal. At.Spectrom. 1994 9 337. Slavin W. Carnrick G. R. and Manning D. C. Anal. Chem. 1982 54 621. Manning D. C. and Slavin W. Appl. Spectrosc. 1983 37 1. Veillon C. Anal. Chim. Acta 1984 164 67. Lewis S. A. O'Haver T. C. and Harnly J. M. Anal. Chem. 1985 57,2 Cimadevilla E. A.-C. Wrobel K. Gayon J. M. M. and Sanz- Medel A. J. Anal. At. Spectrom. 1994 9 117. Tsalev D. L. Slaveykova V. I. and Mandjukov P. B. Spectrochim. Acta Rev. 1990 13 225. Tsalev D. L. and Slaveykova V. I. J. Anal. At. Spectrom. 1992 7 147. Thomaidis N. S. Piperaki E. A. and Efstathiou C. E. J. Anal. At. Spectrom. 1995 10 221. Tsalev D. L. Slaveykova V. I. and Mandjukov P. B. Fifth Journal of Analytical Atomic Spectrometry January 1996 Vol. 11 35Colloquium Atomspektrometrische Spurenanalytik ed. Welz B. Bodenseewerk Perkin-Elmer Uberlingen 1989 pp. 177-205. Smirnioudi V. N. and Siskos P. A. Atmos. Environ. 1992,26B 845. Versieck J. Vanballenberghe L. De Kesel A. Hoste J. Wallaeys B. Vanderhaute J. Baeck N. Steyaert H. Byrne A. R. and Sunderman F. W. Jr. Anal. Chim. Acta 1988 204 63. 23 Ortner H. M. and Kantuscher E. Talanta 1975 22 581. 24 Frech W. Li K. Berglund M. and Baxter D. C. J. Anal. At. Spectrom. 1992 7 141. 25 Mandjukov P. B. Vassileva E. T. and Simeonov V. D. Anal. Chem. 1992,64 2596. 26 L'vov B. V. and Fernandez H. A. Zh. Anal. Khim. 1984,39,221. 27 Frech W. Lindberg A. O. Lundberg E. and Cedergen A. Fresenius' Z . Anal. Chem. 1986 323 716. 21 22 28 Castillo J. R. Mir J. M. and Bendicho C. Spectrochim. Acta Part B 1988 43 263. 29 Fonseca R. W. Wolfe K. I. and Holcombe J. A. Spectrochim. Acta Part B 1994 49 399. 30 Frech W. Lundberg E. and Cedergren A. Prog. Anal. Atom. Spectrosc. 1985 8 257. 3 1 Daunderer M. Metallvergiftungen Diagnostik und Therapie in Kompendium der Klinischen Toxikologie Part III-Volume 9 ecomed Verlagsgesellschaft Landsberg Miinchen 1988. Paper 51035720 Received June 5 1995 Accepted September 20 1995 36 Journal of Analytical Atomic Spectrometry January 1996 Vol. 11

ISSN:0267-9477    

DOI:10.1039/JA9961100031

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Cloud Point Preconcentration and Flame Atomic Absorption Spectrometry Application to the Determination of Cadmium Journal of Analytical Atomic Spectrometry CARMELO GARCIA PINTO JOSE LUIS PEREZ PAVON AND BERNARDO MORENO CORDERO EMILIO ROMERO BEATO AND SOLEDAD GARCIA SANCHEZ Departamento de Quimica Analitica Nutrici6n y Bromatologia Facultad de Quimica Universidad de Salamanca 37008 Salamanca Spain Servicio General de Andisis Quimico Aplicado Universidad de Salamanca 3 7008 Salamanca Spain Cloud point methodology has been successfully used for the preconcentration of trace amounts of cadmium as a prior step to its determination by flame atomic absorption spectrometry. A procedure based on the formation of a complex with 142- pyridylazo)-2-naphthol (PAN) is used for the preconcentration of cadmium in a surfactant-rich phase of Triton X-114.The chemical variables affecting the preconcentration step and the viscosity of the solution affecting the detection process have been optimized. Under the optimum conditions a precision of 3.0% was achieved. The preconcentration of only 15 ml of sample with 0.05% Triton X-114 permits the detection of <0.4 ppb of cadmium with a concentration factor of 120. Keywords Cloud point preconcentration; flame atomic absorption spectrometry; cadmium; tap water; sea water The use of micellar solutions in different areas of analytical chemistry has attracted much attention in recent In particular its use in high-performance liquid chromatography solvent extraction gel filtration ultracentrifugation and capil- lary electrokinetic chromatography has opened up new pos- sibilities for the separation of metal species of biological and environmental interest.6 Aqueous solutions of almost all non-ionic surfactants become turbid when heated to a temperature known as the cloud point.Above this temperature the isotropic micellar solution separates into two transparent liquid phases a surfac- tant-rich phase of very small volume composed mostly of the surfactant plus a small amount of water and an aqueous phase in equilibrium with the former which contains a surfac- tant concentration close to its critical micellar concentration. The exact mechanism through which phase separation occurs remains to be fully This unique surfactant-phase solution-phase separation phenomenon permits the design of simple schemes for extrac- tion preconcentration and purification and has recently been reviewed by Hinze and Pramauro." Any hydrophobic species originally present in water is able to interact with and bind to micelles and become concentrated in a small volume of the surfactant-rich phase.The cloud point methodology has been used for the precon- centration of organic compounds of different types. Recently the compatibility of this method with HPLC both with optical detection (~ltraviolet'~-'~ and fluore~cence'~,~~) and electrochemical d e t e c t i ~ n ' ~ . ~ ~ . ' ~ has been demonstrated. The phase separation phenomenon has also been used for the extraction and preconcentration of metal cations after the formation of sparingly water-soluble complexes." Watanabe * To whom correspondence should be addressed.and Tanaka16 used this method for the first time to preconcen- trate zinc(Ir) using 1-(2-pyridylazo)-2-napththol (PAN) as the hydrophobic ligand and the surfactant PONPE 7.5 as the extracting system. It was later applied in the extraction of metallic chelates for the spectroph~tometric'~ and flow injec- tion" analysis of trace metals in a variety of different samples (tap water sea water soils et~.).''-~l In the present work we report on the results obtained in a study of the cloud point preconcentration of cadmium after the formation of a complex with PAN and later analysis by flame atomic absorption spectrometry using Triton X-114 as surfactant. The proposed method is applied to the determination of cadmium in tap and sea water samples.EXPERIMENTAL Apparatus A Hitachi Model 28000 atomic-absorption spectrometer equipped with Zeeman background correction and a cadmium hollow-cathode lamp as the radiation source was used. A Hitachi 180-0410 micro-sampling device was employed for the injection of 50 or 1OOpl of the sample. The instrumental parameters were adjusted according to the manufacturer's recommendations. A Kokusan H-103 N centrifuge was used to accelerate the phase separation process. Dynamic viscosity was measured with an Ostwald viscometer. Reagents The non-ionic surfactant Triton X-114 was obtained from Fluka and was used without further purification. The stock standard cadmium solution (1000 ppm) was prepared from pure cadmium nitrate (Merck).Working standard solutions were obtained by appropriate dilution of the stock standard solution. mol I-') of PAN (Merck Darmstadt Germany) in Triton X-114 were prepared from the commer- cially available product. Stock buffer solution 0.05 mol l-l was prepared by dissolving appropriate amounts of Na2B407 10H20 (Panreac Barcelona Spain) in water. All the other reagents were of analytical-reagent grade. All solutions were prepared in ultra-high-quality water obtained from an Elgastat UHQ water purification system. The materials and vessels used for trace analysis were kept in 10% nitric acid for at least 48 h and subsequently washed four times with ultra-high-quality water before use. Solutions (5.7 x Journal of AnaEytical Atomic Spectrometry January 1996 Vol. 11 (37-41) 37Procedures Cloud point determination The cloud point for Triton X-114 in the absence and in the presence of 0.05 mol 1-1 borax was determined by observing the appearance of the two phases upon heating different aqueous solutions of surfactant in a thermostated bath.Ratio of phases The volumes of the respective phases were measured in cali- brated tubes (0.4 cm i.d.) for the different amounts of surfactant under the same experimental conditions as those used for phase separation (heating at 40 "C and centrifugation at 3500 rpm). 34 32 - - 28- 18' 1 I 0 5 10 15 [Triton X-l14](%) Cloud point preconcentration Aliquots of 15.0 ml of the cold solution containing the analyte Triton X-114 and PAN buffered at a suitable pH were kept for 5 min in the thermostatted bath at 40 "C.Separation of the two phases was accomplished by centrifugation for 5 min at 3500 rpm. On cooling in an ice-bath the surfactant-rich phase became viscous. The aqueous phase could then be separated by inverting the tubes. Later a given volume of a solution of methanol containing 0.1 mol 1-1 of HNO was added to the surfactant-rich phase. The samples were introduced into the flame by conventional aspiration or by a device designed for microsamples that permits the introduction also by aspiration of a volume of 50 or loop1 of previously diluted surfactant- rich phase. Extraction of cadmium from spiked water samples Tap and sea water samples were filtered using a 0.45 pm pore size membrane filter to remove suspended particulate matter and were then stored at 4 "C in the dark.Aliquots of the water samples studied were 'cloud point preconcentrated' using 0.10% Triton X-114. After phase separation 1.0ml of a methanol solution containing 0.1 mol 1-1 of HNO was added to the surfactant-rich phase. The sample was introduced into the flame by conventional aspiration. RESULTS AND DISCUSSION Phase Diagram of Triton X-114 At a concentration above the critical micellar concentration Triton X-114 in aqueous solution displays a consolution curve above which the micellar solution separates into two isotropic phases. The temperature at which phase separation occurs depends on the concentration of surfactant and the presence and concentration of both organic and inorganic additives. Fig. 1 shows the phase diagram (temperature-concentration) for Triton X-114 in the absence (1) and in the presence (2) of 0.05 mol 1- borate buffer.Across the concentration range studied the presence of the salt decreases the cloud point temperature of Triton X-114. This decrease is more marked for surfactant concentrations below 1 .O% whereas at higher concentrations the difference between the cloud point temperatures is approximately 1 "C. However in both cases the phase diagram shows identical shape. The cloud point temperature remains almost constant (23-25 "C) within the 0.5-5.0% concentration range. Experiments carried out with PAN concentrations similar to those to be used in the preconcentration step did not lead to significant changes in the phase diagram of Triton X-114. Fig. 1 Phase diagram of the surfactant Triton X-114 in aqueous solution in the absence (l) and in the presence (2) of Na,B,O - 10H,O 0.05 mol 1- '.L Single isotropic phase region and 2L two isotropic phase regions Effect of pH The separation of metal ions by the cloud point method involves prior formation of a complex with sufficient hydro- phobicity to be extracted into the small volume of surfactant- rich phase (200 pl) thus obtaining the desired preconcen- tration. Extraction yield depends on the pH at which complex formation is carried out. Fig. 2 shows the effect of pH on extraction yield. It may be seen that for pH values above 8 yield is almost constant and close to 100%. Effect of the PAN Cadmium Molar Ratio The effect of the molar ratio between the complexing agent and the cation was studied for values ranging between 1 and 15 and a cadmium concentration of 3.0 x lop6 mol 1-l.The results obtained on preconcentra ting 15 ml of a solution containing the analyte with a Triton X-114 concentration of 0.25% then adding 1.0 ml of 0.1 mol 1-' HNO after phase separation show that at least a 5-fold excess of PAN over the cadmium concentration was required to obtain maximum and constant recovery. Preconcentration of 15 ml of the solution in the absence of cadmium did not give rise in any case to a cadmium signal. 2 4 6 8 10 12 PH Fig.2 Influence of pH on the extraction recovery (R%) of the Cd-PAN complex. Preconcentration step 3.0 x lop6 mol I-' Cd 3.4 x lo-' moll-' PAN and 0.25% Triton X-114. Other experimental conditions described in text 38 Journal of Analytical Atomic Spectrometry January 1996 Vol.11Effect of Viscosity on the Analytical Signal The small volume (80-400 pl) of surfactant-rich phase obtained after cloud point preconcentration contains a high concen- tration of Triton X-114 (-30%). The solution is therefore highly viscous. Accordingly after phase separation it is neces- sary to decrease the viscosity of the sample in order to facilitate introduction of the sample into the atomizer. Fig. 3(a) shows the variation in dynamic viscosity and in the analytical signal as a function of the Triton X-114 concen- tration initially placed in the solution. In this instance after phase separation 1.5 ml of 0.1 mol 1-l HNO were added to the surfactant-rich volume (between 200 and 300 pl depending on the concentration of surfactant) and the sample was introduced into the flame by conventional aspiration.An increase in surfactant concentration of between 0.10 and 0.50% elicits a strong increase in viscosity reflected in a 70% loss of the analytical signal This decrease can be attributed almost exclusively to the increase in viscosity since the dilution factor between both surfactant concentrations is negligible. However when dilution is carried out by adding 1.5ml of a solution of methanol containing 0.1 mol I-' HNO the 15 10 5 - . 8 0 - P - 1 I I I I I ( b ) l o t \ 1 4 2 - - I I I I I [Triton X-l14](%) 0.25 0.20 0.15 0.10 0.05 0.00 -c 0.20 0.15 0.10 0.05 0.00 Fig. 3 Variation in analytical signal of the Cd-PAN complex (1) and of the viscosity of the sample (2) as a function of the Triton X-114 concentration.Dilution of the surfactant-rich phase with water (a) or methanol (b) containing 0.1 mol 1-' HNO,. Preconcentration step 2.7 x lop7 mol 1-' Cd 2.6 x mol 1-' PAN and 0.10% Triton X-114. Other experimental conditions described in text 1 .oo 0.80 0.60 c 0.40 0.20 0.00 0 300 600 900 1200 1500 Added methanol/pl Fig. 4 Variation in normalized analytical signal (h) corresponding to the Cd-PAN complex as a function of the volume of methanol added. Theoretical plots as a function of the viscosity of the sample (1) and of the dilution factor (2) and experimental curve obtained (3). Preconcentration step 2.7 x lop7 mol 1-' Cd 2.6 x lop6 moll-' PAN and 0.10% Triton X-114. Other experimental conditions described in text increase in viscosity is much less pronounced and the decrease in the analytical signal is only 8% [Fig.3(b)]. Furthermore the effects of the organic solvent on the flame produce a signal enhancement factor that allows an additional increase in sensitivity. Table 1 shows the phase ratios and the signal enhancement factors obtained under different experimental conditions. It may be seen that the presence of methanol produces an increase of approximately 2 in the analytical signal in all cases. The influence of the combined effects of viscosity and dilution are shown in Fig. 4. The figure shows the normalized signals corresponding to the preconcentration of 15 ml of sample with a surfactant concentration of 0.10% as a function of the volume of methanol added to the surfactant-rich phase. Curves 1 and 2 represent the theoretical variations in the signal due to the decrease in viscosity and to the increase in the dilution factor respectively. The experimentally obtained curve (curve 3) depends on the combined effect of these two variables.As can be seen for added volumes of methanol of < 100 pl an important increase in the analytical signal occurs because the effect of decreased viscosity is very strong and clearly predominates over the dilution. However for higher added volumes the decrease in viscosity of the sample is lower and it is essentially the effect of dilution that predominates. Calibration Precision and Detection Limits Calibration curves were constructed by preconcentrating 15 ml of sample with Triton X-114 concentrations of 0.10 and 0.05%.Samples were introduced into the flame by conventional aspiration or using a device for microsamples. When conven- tional aspiration was used the surfactant-rich phase was Table 1 Ratio of phases (solution phase/surfactant-rich phase) and enhancement factor [Triton X-114) ("/.I Dilution of surfactant-rich phase 0.10 0.1 mol I-' HNO in water (1.0 ml) 0.10 0.1 mol 1-1 HNO in methanol (1.0 ml) 0.10 0.1 mol 1-' HN03 in methanol (200 pl) 0.05 0.1 mol 1-' HN03 in methanol (100 p1) 0.10 0.1 mol 1-' HNO in methanol (200 pl) 0.05 0.1 mol I-' HNO in methanol (100 pl) Sample introduction Aspiration Aspiration 50 pl 60 p1 100 pl 100 pl Ratio of phases 11 11 27 60 27 60 Enhancement factor * 10.8 22.7 50 123 48 120 * Relationship of absorbance peak height of preconcentrated samples ( 15 ml) to that obtained without preconcentration.Journal of Analytical Atomic Spectrometry January 1996 Vol. 1 1 39Table 2 Analytical characteristics of the method* Conditions Without preconcentration5 Preconcentration (0.10% Triton X-114)" Preconcentration (0.10% Triton X-114)" Without preconcentration§ Preconcentration (0.10% Triton X-114)** Preconcentration (0.05% Triton X-114)tt Without preconcentration5 Preconcentration (0.10% Triton X-114)** Preconcentration (0.050/ Triton X-114)?? Sample introduction Aspiration Aspiration Aspiration 50 p1 50 p1 50 pl 100 pl loo 1.11 loo p1 Range (PPb) 50- 1000 5.0-100 2.0- 100 100-1000 5.0-100 1 .O-50 50-1000 2.0-100 0.5-50 Slope (9.8k0.1) x lo-' (1.04f0.04)~ (2.09 0.04) x (3.03f0.06)~ lo-' (1.48 k0.06) x (3.1 kO.1) x (4.19k0.05) x lo-' (2.00-tO.04) x (5.06-0.09) x lop3 Intercept (5.0f0.2) x lop3 (5.5f0.2) x lop3 (1.2k0.4) x lop3 ( 2 f 2 ) x 10-3 (4+2) x 10-3 (4rt_4) x 10-3 (2f 1) x 10-3 (2f2) x 10-3 (2.4k0.6) x lop3 r2 0.998 0.998 0.999 0.999 0.997 0.997 0.999 0.998 0.999 s (%)t 2.7 (300) 2.8 (10) 3.1 (5.0) 3.0 (300) 2.9 (10) 3.4 (5.0) 2.8 (100) 3.5 (5.0) 3.2 (5.0) LODS ( PPb) 25 2.3 1.1 80 1.6 0.6 48 1 .o 0.4 * Samples 15 ml.Duplicate injection. t Values in parentheses are the cadmium concentrations for which s was obtained. LOD limit of detection (calculated as twice the noise). Standard solutions of cadmium in 0.1 mol 1-' HNO medium. Dilution of the surfactant-rich phase with 1.0 ml of a solution of 0.1 mol 1-' HN03 in methanol.7 Dilution of the surfactant-rich phase with 1.0 ml of 0.1 mol 1-' HNO,. ** Dilution of the surfactant-rich phase with 200 pl of 0.1 mol 1-' HNO in methanol. tt Dilution of the surfactant-rich phase with 100 pl of 0.1 mol 1-' HNO in methanol. diluted with 1.0 ml of a solution of methanol containing 0.1 mol 1-l HN03. When the device for microsamples was used the surfactant-rich phase was diluted with 100 or 200 pl of the 0.1 moll-' HN03 in methanol solution and 50 pl or 100 pl of the diluted solution were introduced into the flame. In all instances linear relationships were obtained between peak height in units of absorbance and the concentration of cad- mium. The least squares fitting parameters are shown in Table 2 for all conditions studied together with the relative standard deviation for 10 samples to which the complete procedure was applied and the calculated detection limits (twice the noise).The same table shows the calibrations obtained with standard cadmium solutions not subjected to the preconcentration step. Preconcentration of only 15 ml of sample with a Triton X-114 concentration of 0.05% permits a detection limit below 0.4 ppb with a 120 fold increase in the analytical signal. Interferences Two types of interferences affecting the preconcentration pro- cess can be distinguished in the proposed methodology; the cations reacting with PAN and species that form complexes with cadmium including anions and humic acids (potential interferents in water samples). Interference by the foregoing cations that form complexes with PAN can readily be avoided by increasing the concen- tration of PAN.However studies were conducted with the cations alu- minium calcium magnesium lead@) iron(m) nickel and zinc for interferent:cadmium ratios of 1 10 and 100 ([Cd]=18 ppb). The preconcentration step was performed with 0.25% Triton X-114 and a PAN concentration of 4.8 x lop5 mol 1-l. No interferences (error < 3%) were detected in the presence of these cations at the levels described. The results obtained in the study of the interferences pro- duced by the presence of anions and complexing agents for the interferent cadmium ratios previously mentioned shows that sulfate chloride cyanide and ammonia did not cause significant interferences (error < 3 Yo). However the presence of EDTA did lead to a negative interference up to 80% owing to the formation of a water-soluble cadmium complex that competes with the formation of the insoluble Cd-PAN com- plex thereby preventing the preconcentration of cadmium in the surfactant-rich phase.In order to study the interference produced by humic acid in the cloud point preconcentration of cadmium an optically standardized solution (- 10 ppm organic carbon content) was prepared following the procedure described by Johnson et ~ 1 . ~ Different dilutions of this solution spiked with cadmium (10 ppb) were used and the signal obtained after the preconcen- tration step was compared with that corresponding to a solution at the same concentration of cadmium in ultra- pure water. The recoveries obtained for the two different PAN concen- trations are shown in Table 3.For the lowest concentration of reagent the presence of humic acids leads to a decrease in the analytical signal of up to 42%. However when the PAN concentration is higher for dilutions of the humic acid solution between 1 1 and 1 3 no appreciable effect on the cadmium signal can be detected. A decrease of 15% in the signal occurs for a dilution of 1 2 and for an undiluted solution of humic acid the loss in signal is 25%. Although such high concen- trations of humic acids are not usually found in real water samples a sample pretreatment with peroxodisulfate similar to that described by R o y ~ e t ~ ~ was performed. The recoveries obtained in both cases for dilutions of 1 2 and 1 1 were 98 and 97% respectively (see Table 3).Table3 determination of cadmium Effect of humic acid solutions on the preconcentration and Recovery (YO) Dilution [PAN]=2.3 x mol 1-' [PAN]=4.8 x lop5 mol 1-' 1 100 100 1 50 94 99 1:20 98 1 10 85 101 1:5 74 104 1:3 69 102 1:2 60 (98) 85 (97) 1 l 58 (98) 75 (97) * Values in parentheses correspond to recoveries obtained after oxidation with peroxodisulfate of the organic material. 40 Journal of Analytical Atomic Spectrometry January 1996 Vol. 1 1Table 4 Slopes and intercept of the calibration and of the standard additions in tap and sea water Slope Intercept r2 Calibration (2.09k0.04) x (1.2f0.4) x 0.999 Tap water (2.08+0.03)x (4.0f0.6) x lop3 0.999 Sea water (2.05 k 0.04) x (5.7 f 0.7) x 0.998 Determination of Cadmium in Tap and Sea Water In order to test the reliability of the proposed methodology it was applied to samples of tap water (from the drinking water system of Salamanca Spain) and sea water (from the Cantabrico Sea Santander Spain).For this purpose 15 ml of each of the samples were precon- centrated with 0.10% Triton X-114 and a PAN concentration of 2.0 x The samples were spiked at concentrations ranging between 1.0 and 25 ppb obtaining a straight line calibration for the standard addition in the tap water the sea water and ultra- pure water matrices. Table 4 shows the parameters obtained under the different experimental conditions. The slope of the calibrations in ultra-pure water coincides with those of the straight lines obtained by standard addition for both samples; this shows that no matrix effect exists.The highest values of the intercept corresponding to the standard additions indicate that the samples contained cadmium. However it is not possible to quantify these levels properly since the signal obtained for the unspiked samples is almost the limit of detection under these conditions. These results show that the cloud point preconcentration method can be applied to the determination of cadmium in tap and sea water. mol I-' following the proposed method. CONCLUSION This paper shows that the cloud point method can be used to preconcentrate metal cations before their detection by flame atomic absorption spectrometry. The technique offers a simple alternative to other separation and/or preconcentration tech- niques with good yields as regards extraction and a good standard deviation.This work was supported by DGICYT (Project PB94-1393) and the Consejeria de Cultura y Turismo de la Junta de Castilla y Leon (Project SA68/93). REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Pelizzetti E. and Pramauro E. Anal. Chirn. Acta 1985 169 1. Hinze W. L. Sing H. Baba Y. and Harvey N. G. Trends Anal. Chem. 1984 3 193. Moreno Cordero B. PCrez Pavon J. L. and Hernandez Mendez J. Quim. Anal. 1989 8 231. McIntire G. L. Crit. Rev. Anal. Chem. 1990 4 257. Armstrong D. W. Sep. Purg Methods 1985 14 213. Hinze W. L. in Ordered Media in Chemical Separations ACS Symposium Series 342 Hinze W. L. and Armstrong D. W. eds. American Chemical Society Washington DC USA 1987. Degiorgio V. Piazza R. Corti M. and Minero C. J. Chem. Phys. 1985 82 1025. Blankschtein D. Thurston G. M. and Bebedek G. B. J. Chem. Phys. 1986 85 7268. Lindman B. and Wennerstrom H. J . Phys. Chem. 1991,95,6053. Hinze W. L. and Pramauro E. Crit. Rev. Anal. Chem. 1993 24 133. Saitoh T. and Hinze W. L. Anal. Chem. 1991 63 2520. Garcia Pinto C. Perez Pavon J. L. and Moreno Cordero B. Anal. Chem. 1992 64 2334. Moreno Cordero B. PCrez Pavon J. L. Garcia Pinto C. and Fernandez Laespada M. E. Talanta 1993 40 1703. Garcia Pinto C. PCrez Pavon J. L. and Moreno Cordero B. Anal. Chem. 1994 66 874. Garcia Pinto C. PCrez Pavon J. L. and Moreno Cordero B. Anal. Chem. in the press. Watanabe H. and Tanaka H. Talanta 1978 25 585. Kawamorita S. Watanabe H. and Haraguchi K. Anal. Sci. 1985 1 41. Fernandez Laespada M. E. Perez Pavon J. L. and Moreno Cordero B. Analyst 1993 118 209. Saitoh T. Kimura Y. Watanabe H. and Haraguchi K. Anal. Sci. 1989 5 577. Hoshino H. Saitoh T. Taketomi H. and Yotsuganagi T. Anal. Chim. Acta 1983 147 339. Buhai L. and Rigan M. Talanta 1990 37 885. Johnson W. E. Fendinger N. J. and Plimmer J. R. Anal. Chem. 1991,63 1510. Royset O. Anal. Chim. Acta 1986 185 75. Paper 5104083 C Received June 23,1995 Accepted September 24,1995 Journal of Analytical Atomic Spectrometry January 1996 Vol. 1 1 41

ISSN:0267-9477    

DOI:10.1039/JA9961100037

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Characteristics of an Inductively Coupled Argon Plasma Operating with Organic Aerosols Part 3.* Radial Spatial Profiles of Solvent and Analyte Species D. G. WEIR? AND M. W. BLADES1 Department of Chemistry University of British Columbia Vancouver BC Canada V6T 121 The effect of organic solvent load on the radial emission profiles for Mg I Mg 11 C I C and CN was measured. The three dimensional information reveals the observation zones where the emission intensity of these species is proportional to solvent load and plasma excitation conditions. Keywords Inductively coupled argon plasma; organic solvent; solvent plasma load; radial spatial projiles This paper is the third part in a series on the physical characteristics of an inductively coupled argon plasma (ICAP) operating with organic aerosols.The first part described the experimental system for making spectral spatial and temporal measurements and examined the effect of solvent and solvent load on the background spectra and visual features of an ICAP in general.' The second documented the effect of chloro- form load on the axial emission spatial profiles for C (I) C (diatomic carbon) and CN (background species) Mg I Mg I1 (analyte species) and the ratio of Mg I1 to Mg 1.' This paper presents the effects of solvent and solvent load on the radial spatial emission profiles of Mg I Mg 11 C (I) C and CN and the emission intensity ratio of Mg I1 to Mg. Several physical phenomena are evident in the radial data notably air entrainment into the argon jet the result of vortex shedding entrainment of solvent material into the outer argon stream by a recirculation eddy at the base of the discharge and shrinking of the induction region by a thermal pinch effect.The radial spatial structure of analyte emission in the ICAP has been studied by several research group^.^-'^ In order to facilitate spatial studies many ICAP investigators have taken advantage of imaging monochromators equipped with one or two dimensional array detectors mounted vertically in the exit focal plane. This configuration allowed them to record rapidly either vertical or lateral profiles of ICAP emission for a single wavelength channel. For example Koirtyohann et ~ 1 . ' ~ recorded both laterally and axially resolved profiles of calcium emission from the ICAP and studied the effects of concomitant potassium.Blades and Horlick using this methodology were able to classify emission lines according to the behaviour of their axial profile^'^ and to study the radial spatial effects of concomitant easily ionizable elements on analyte emi~sion.~ This general approach has been used for the collection of spatial emission profiles for this paper. The purpose of this paper is to present the effects of solvent load power and nebulizer gas flow rate (or more correctly central gas flow rate) on the radial spatial distribution of emission from Mg 11 Mg I the ratio of Mg I1 to Mg I and * For Parts 1 and 2 of this series see references 1 and 2. t Present address 10228 109 Street Fort Saskatchewan Alberta 1 To whom correspondence should be addressed. Canada.Journal of Analytical Atomic Spectrometry species formed from solvent atomization uiz. C I C2 and CN. The detailed preamble has been presented in the previous publications. A subsequent publication will correlate these observations with more fundamental ICAP properties electron number densities excitation temperatures and excited state population densities. EXPERIMENTAL The instrumentation and procedure for igniting the plasma generating the solvent aerosol preparing solutions controlling the operational parameters and measuring spectroscopic quantities were presented in the previous paper^.'-^,'^*^^ Only the new procedures specific to surveying the spatially resolved parametric response of the solvent loaded ICAP are presented here. Monochromatic images of either the tail cone or induction region of the discharge were recorded with a bandpass of approximately 0.4 nm a lateral resolution of 0.09 mm and a vertical resolution of 0.6mm.Moreover images of the fore- ground background and dark signal were recorded for the purpose of background subtraction. In order to sample the emission profile adequately and to meet the requirements of the numerical Abel inversion procedure,17 up to 200 intensity samples were recorded along the lateral coordinate of the discharge at each observation height. The discharge was trans- lated across the axis of the light collection optics so that the image of the discharge was translated laterally across the entrance slit of the monochromator. The monochromator was equipped with a one-dimensional photodiode array detector mounted with its long axis mounted vertically,' such that several lateral profiles each at different observation heights could be collected simultaneously. As a result an entire monochromatic image of the discharge could be recorded in a single lateral scan.The bandpass of the monochromatic image was determined by the width of the array detector and the reciprocal linear dispersion of the monochromator. For example the width of the detector of 0.506 mm multiplied by the reciprocal linear dispersion of the monochromator at 516 nm (0.76 nm mm-') gave a spectral bandpass of 0.38 nm. This bandpass could easily be reduced by placing a mask over the detector but this was not found to be necessary. The sampling interval along the detector corresponded to 0.6 mm intervals along the axis of the discharge.The total axial range was 25 mm. This range extended either from 5 to 30 mm above the top of the load coil (in the tail cone) or from -15 to 10 mm (the induction region). In the lateral direction the sampling interval was variable but was generally set at 0.045 mm or 0.09 mm in all cases 200 lateral positions were sampled giving a lateral range of 4.5 or & 9.0 mm depending on the region being sampled. In order to generate radially resolved contour plots from Journal of Analytical Atomic Spectrometry January 1996 Vol. 11 (43-52) 43line of sight images the light collection envelope for each point in the image had to approximate to a line integral. The optical train was designed to meet this requirement as follows a planoconvex lens' was fitted with one of three apertures (5 mm diameter 10mm diameter or 5 mm widex30mm high) and was used to form a 0.5 x image of the discharge onto the entrance slit of a 1 m focal length Czerny-Turner monochroma- tor.At 516nm the object distance was 450mm (from the discharge axis to the front principal point of the lens) while the image distance was 225 mm (from the back principal point of the lens to the entrance slit). The lens maker's equation for thick lenses was used to calculate image and object distances at other wavelengths. The planar surface of the lens faced towards the entrance slit in order to minimize spherical aberration. Finally the entrance slit was lined up with the cylindrical axis of the discharge.The spatial response of the monochromator along the entrance slit was determined exper- imentally and was found to be slight over the 25 mm imaging range (k 6.25 mm along the entrance slit) and was not corrected for. Contour plots of the absolute light collection efficiency of the optical system were calculated using an exact ray tracing algorithm developed by Farnsworth et aL1* Beyond providing the light collecting efficiency of the optical train these contour plots confirmed that the light collection optics met the require- ments for Abel inversion. The spectral response function of the detector was also determined using an irradiance standard lamp. The monochromatic images were corrected for background or dark signal contributions by subtracting the background or dark signal images.Next the images were smoothed in both the axial and lateral directions with a digital Because the axis of the discharge reproducibly veered to one side with increasing height the veering was removed by shifting the lateral profile at each observation height by a predetermined number of sampling intervals (< 6 pixels). Once background corrected smoothed and straightened the images were radially inverted. After the profiles had been inverted they were condensed from 200 x 40 intensities to 50 x 40 intensities by taking the average of 4 points in the radial direction. This rendered the images much more manageable for later analysis with little or no significant loss of information. The corrected smoothed radially inverted and condensed images were then converted to topographical contour plots.Radially resolved contour plots were generated for 516.56 nm (C2) 388.34 nm (CN) 247.86nm [C (I)] 257.61 nm (Mn 11) 279.55 nm (Mg 11) 285.21 nm (Mg I) several Fe I and I1 lines Ar I (687.13 nm) and H I (486.16 nm). Some of these were measured for three solvents methanol water and chloroform over a range of inner argon flow rates and forward powers. Spatially resolved intensity contour plots can be regarded as emission from the planar slice through the discharge. Most slices are bounded by z = 5 mm to z =30 mm and r = -7 mm to r = + 7 mm; however a few are bounded by z = - 15 mm to z= + 10 mm and r = -7 mm to r = +7 mm. Obvious shadows of the induction coil reveal which contour plots extend into the load coils (that is those bounded by z= - 15 mm to z= +10mm).Intensity from the planar slice is represented by topographical isocontours as shown in Fig. 1. The isocontours always depict the normalized intensity ranging from 0.1 to 1.0 in increments of 0.1. These isocontours were either normalized to the maximum intensity for individual contour plots or the over-all maximum for a set of contour plots. RESULTS AND DISCUSSION The diagrams in Fig. 1 are a summary of the emission intensity contour plots of all the analyte and background species examined for this paper. These contour plots were measured for an ICAP operated at 1.25 kW with an inner argon flow rate of 0.81 1 min-l and a chloroform load of 4.5 mg s-'. From left to right the first contour plot depicts emission from the CN bandhead at 388.34 nm and second contour plot depicts the Cz bandhead at 516.56nm.These features are concentrated at the boundary regions of the plasma. The CN contour plot is located at the downstream boundary region where air is entrained into the plasma jet. In effect the CN contour plot indicates the interface between the hot atomic plasma and the cold room air. Within the induction coil the C2 contour plot partially outlines the upstream boundary region of the plasma aerosol channel. This region surrounds the base of the plasma and lines the inside of the aerosol channel. The C2 emission may be regarded as a dissociation front between the hot atomic plasma and the relatively cold mixture of argon and undissociated solvent vapour. The next three contour plots in Fig.1 are emission from atomic carbon and argon. The C (I) and Ar (I) emission contour plots essentially define the volume of the atomic plasma (where atomic emission predominates) and reveal how it 'nests' within the molecular boundary region (where molecu- lar emission predominates). Two views of C (I) are provided one within the induction coil and one above the torch rim. Within the induction coil the C (I) isocontour overlaps the toroidal induction region of the plasma. Above the torch rim both Ar I and C (I) contour plots reveal that the toroidal induction region coalesces into a tail cone. As mentioned earlier the isocontours of atomic emission overlap with the boundary layer emission to a greater extent downstream from the torch rim than within the induction coil.It is possible that the temperature gradient downstream is more gradual but more likely that the downstream boundary is time averaged. The next three contour plots on the right side of Fig. 1 are the intensity distribution of analyte emission. The first two plots are the plumes of emission typically displayed by hard lines (atomic ion lines or atom lines with excitation potentials > 6 eV). The intensity distributions of Mn I1 (257.6 nm) and Mg I1 (279.5 nm) are shown. The upstream base of the hard line plume begins at approximately 5-10 mm above the top of the induction coil. From this location the plume extends 15-20 mm downstream up to 25 mm above the induction coil. Typically the hard line plume varied in length width and intensity when one varied the operating parameters.In spite of this the plume retained its distinctive oval shape with no obvious tapering or constrictions upstream or downstream. The oval plume always displayed an unambiguous axial maxi- mum residing well downstream at 10 to 15 mm above the induction coil. The plume extended radially to approxi- mately 3 mm. In general this maximum radius was found at approximately 15 mm above the induction coil. In contrast the third contour plot is the structure typically displayed by soft lines (atom lines with excitation potentials < 6 eV). This plot depicts the spatial distribution of emission from the Mg I (285.2 nm) line an atom line with an excitation energy of 4.35 eV. The most conspicuous differences between this soft line structure and the hard line plumes to its left are the relative positions of their maxima and their characteristic shapes.The maximum for the soft line structure lies signifi- cantly further upstream or at a lower height above the induction coil than the hard line maxima which reside above 10mm above the induction coil. The bases of the hard line plumes also lie well downstream so that the plumes display a characteristic oval shape. In contrast the base of the soft line plume appears to stretch out into a narrow shaft which extends into the torch giving it the characteristic club shape for soft line emission. The last rightmost frame of Fig. 1 is a contour plot of the ratio of Mg I1 (279.55 nm) and Mg I (285.21 nm) line emission. In the previous paper we discussed how this 44 Journal of Analytical Atomic Spectrometry January 1996 Vol.11CN CI Mg Ii MnII MgII Mgl Mg I -8 -4 0 4 8 -0.4 0.0 4.0 -1 5 -a -4 o 4 a Radial distancehrn Fig. 1 Overview of spatially resolved maps of the analyte and background emission from the solvent loaded ICAP. See text for description ratio can be used to diagnose thermal conditions in the plasma and how the ratio is an indicator of robustness of the plasma.' Note that there are two distinctive features of CN emission the central plume and the conical outer mantle. The central plume is absent under conditions of high power and low Emission from CN-The Downstream Boundary solvent load (in the lower left hand plots) but increases in height and extends upwards to meet the outer mantle with The eighteen spatially resolved contour plots of emission from the CN bandhead (388.34 nm) in Fig.2 indicate how CN emission responds to chloroform load and forward power. incieasing load and decreasing power (in the upper right hand plots). On the other hand the outer mantle (which caps the atomic plasma or resides at the boundary between the plasma 1 .OO kW 1.25 kW 1.50 kW 3.4 mg s-l 4.2 mg s-' 6.2 rng s-l 7.4 mg s-' 8.6 mg s-l 10.0 rng s-l 30.0 25.0 20.0 15.0 10.0 Fin -80.0 -40.0 0.0 4.0 8.0-'- Radial distancehm Fig. 2 Isocontour maps of CN (388.34 nm) emission intensity for a chloroform loaded ICAP. Inner argon flow 0.81 1 min-'. The outermost contour in each frame represents a relative emission intensity of 1. The contour interval is 1 relative intensity unit for each frame and the frames can be compared with one another in an absolute sense by counting contours.The power is indicated on the left side of the diagram the solvent load is indicated across the top and the axial and radial scale is provided on the lower right hand map Journal of Analytical Atomic Spectrometry January 1996 Vol. 11 45and the surrounding air) appears to collapse inward and downward with decreasing power and increasing solvent load. Also note the intensity response of the CN emission from left to right or with increasing chloroform load the CN intensity of the mantle increases almost linearly with chloroform load at all locations. The response of CN intensity to power is more ambiguous (power increases from the top row plots to the bottom row plots).Although the CN intensity increases with forward power at specific locations (for example z = 10 mm and r = 6 mm) a linear increase at all locations is not evident. Indeed at some locations the CN intensity appears to decrease with forward power. In an effort to understand the response of CN intensity to chloroform loading and forward power one may first remove the spatial aspects by integrating the intensity over all space in a manner analagous to that of Pan et Alternatively one may choose a spatial location where the structure of the plasma remains fairly constant even when the forward power and chloroform load are varied. On the axis and beyond the tip of the plasma (z=30.0 mm r=0.0 mm) the intensity response appears to be largely determined by how far the atomic plasma extends downstream.Here the effects of power and solvent load are particularly evident. Similarly at a position on the axis and at an intermediate observation height (z = 15.0 mm r = 0.0 mm) the intensity is also determined larg- ely by how far the inner plume extends downstream and whether or not the plume extends past z = 15.0 mm. In contrast the structure of CN emission near z=15.0mm and r = - 5.2 mm appears to be relatively independent of power and solvent load. Because the structure here appears to be constant this is a good location to examine the response of CN intensity to forward power and solvent plasma load. At 1.5 kW the intensity increases almost linearly with solvent load indicating that excitation conditions in the CN mantle are constant and that the amount of solvent material determines the CN inten- sity.At lower powers the CN response departs from direct proportionality and displays a maximum at intermediate load- ing. Evidently high levels of solvent plasma load sap enough energy from the discharge to lower the CN emission intensity. Moreover it is likely that vortex shedding' entrains air into the argon stream effectively mixing N2 with the argon and solvent material so that the solvent carbon combines effectively with the atmospheric nitrogen and the thermal conditions in the boundary region are intermediate between the plasma and the air according to the respective gas temperatures and heat capacities. It should be noted that one can optimize the CN signal as a working diagnostic by selecting the right viewing location; z = 15.0 mm and Y = - 5.2 mm appears to be the best place to monitor solvent plasma during routine analysis.0.6 I min-' 0.7 I min-' m e ' 8 0 lw v- Emission from C,-The Upstream Boundary In contrast to CN the C emission contour plots reveal primarily the upstream boundary of the discharge. This bound- ary is characterized by solvent pyrolysis and a steady recircu- lation eddy rather than air entrainment and vortex shedding. Both processes are evident in the C emission contour plots presented in Fig. 3. This figure depicts C emission within the torch for an ICAP loaded with meta-xylene. For these contour plots the meta-xylene load was 0.2 mg s-' the forward power was set at 1.25 kW and the inner argon flow rate was varied from 0.6 to 1.1 lmin-' in 0.1 1 min-' increments.The inner argon flow rate increases from left to right. At low inner argon flow rates the C2 emission wraps around the base of the plasma while the central plume of C2 emission only extends a short distance along the axis. It is unlikely that diffusion could account for the C emission around the base of the discharge. On the contrary a recirculation eddy near the base of the discharge predicted by computer sir nu la ti on^,^^^^^ could account for convective mixing of solvent material with the outer argon stream. Evidently such a recirculation eddy entrains solvent material quite effectively into the outer argon stream at low inner argon flow rates thus reducing the load in the axial channel. However when the inner argon flow rate is increased the eddy is less effective at entraining solvent material.Interestingly computer simulations predict that at extremely high inner argon flow rates the inner argon stream may actually sweep the recirculation eddy away. Consequently the load on the axial channel increases and the central plume extends farther downstream while the outer C2 emission intensity decreases. Moreover the entire profile settles down into the torch. This indicates that the plasma translates axially when the outer argon flow is loaded with solvent material. C (I) emission contour plots provide further insight into this apparent translation. Contour plots of C emission from an ICAP loaded with other solvents at different rates of solvent plasma load are all consistent with the behaviour depicted in Fig.3. In response to methanol loading the peripheral component of C emission was more intense than the central plume and the central plume extended a shorter distance downstream. Evidently the inner argon stream laden with methanol vapour could not penetrate the recirculation eddy as effectively as an inner stream laden with heavier solvent molecules because the methanol laden stream would have had less momentum. Indeed chloroform loading displayed the opposite response. In summary two features of the flowfield are evident in the parametric response of C2 and CN emission contour plots vortex shedding associated with air entrainment and a recircu- 0.8 I min-' 0.9 I min-' 1 .O I min-' 1 .I I min-' ,-8O.O -40.0 0.0 4.0 8.0 Radial distance/mm Fig.3 Isocontour maps of C (3516.16 nm) emission intensity for a rneta-xylene loaded ICAP. The solvent plasma load was 0.2 mg s - l the forward power was set at 1.25 kW and the inner argon flow rate was varied from 0.6 to 1.1 1 min-' in 0.1 1 min-' increments. The outermost contour in each frame represents a relative emission intensity of 1. The contour interval is 1 relative intensity unit for each frame and the frames can be compared with one another in an absolute sense by counting contours. The axial and radial scale is provided on the right hand map 46 Journal of Analytical Atomic Spectrometry January 1996 Vol. 11lation eddy at the base of the discharge which entrains solvent material into the outer argon stream. The extent to which solvent material is entrained depends on the flow properties of the inner stream.Emission from C (I )-The Atomic Plasma Contrasting quite sharply with the CN results is the response of spatially resolved emission from atomic carbon [from the C (I) line at 247.9 nm]. The fifteen contour plots shown in Fig. 4 indicate how C (I) emission responds. Once again the top row corresponds to the lowest power of 1.00kW the middle row to the intermediate power of 1.25 kW and the bottom row to the highest power investigated of 1.50 kW. From left to right the chloroform load increases from 3.4 to 8.6 mg SKI. The spatial distribution of C (I) is characteristic of the plasma region where atomic line emission predominates over molecular emission indicating that the C (I) emission emanates from hot atomic plasma and not from the molecular flame like conditions of the boundary regions. Nevertheless it is important to note that the spatial distribution of C (I) emission overlaps with the spatial distribution of CN emission.Fig. 5 is a contour plot of C (I) emission from the induction region of the ICAP. The four contour plots on the left reveal the response of C (I) emission to inner argon flow rate and methanol load while the four on the right reveal the response to inner argon flow rate and chloroform load. In each set of four contour plots the inner argon flow rate increases from 1 .OO kW 1.25 kW 1.50 kW 3.4 mg s-’ top to bottom while the solvent plasma load increases from left to right and the isocontours are normalized to the over- all maximum intensity.The contour plots show that the volume containing the C (I) emission shrinks in the axial direction in response to an increase in solvent load or decrease in inner argon flow rate. In fact the volume shrinks in the axial direction by 1Omm when the methanol load is increased and the inner argon flow rate is decreased. In a previous paper it was shown that an enormous increase in electron number density accompanies the axial shrinking.15 For methanol load- ing the electron density between the top and middle turns of the induction coil increases from 8.0 x 1015 cm-3 to 1.3 x cm-j. Evidently the contour plots in Fig. 5 reveal a thermal pinch effect.’ The effect is less conspicuous for chloro- form loading because chloroform is less effectively entrained into the outer argon stream for reasons discussed earlier.Alternatively the bond dissociation enthalpy of the C- 0 bond in methanol may contribute much more significantly to the thermal pinch effect than C-C1 or C-H bonds. Emission from Mg-The Aerosol Channel In general two distinctive responses were observed for contour plots of analyte emission. One response was observed for hard lines or atom lines with excitation potentials > 6 eV and all atomic ion lines and the other response was observed for soft lines or atom lines with excitation potentials <6 eV. Fig. 6 is a plot of hard line emission responding spatially to solvent load (Mg I1 279.55 nm). The outermost contour in 4.2 mg s-’ 6.2 mg s-l 7.4 mg s-’ 8.6 mg s-’ 1 -80.0 -40.0 0.0 4.0 8.0-.- Radial distance/mrn Fig.4 Isocontour maps of C ( I ) (247.61 nm) emission intensity for a chloroform loaded ICAP. The inner argon flow was 0.81 1 min-’. The outermost contour in each frame represents a relative emission intensity of 1. The contour interval is 1 relative intensity unit for each frame and the frames can be compared with one another in an absolute sense by counting contours. The power is indicated on the left side of the diagram the solvent load across the top and the axial and radial scale is provided on the lower right hand map Journal of Analytical Atomic Spectrometry January 1996 Vol. 11 470.61 I m-’ 0.3 mg s-’ methanol 1 .O mg s-’ methanol 3.2 rng s-’ CHCI 10.0 mg s-’ CHCI 10.0 5.0 E E - .- m E -1 0.0 -15 0 . -80.0 -40.0 0.0 4.0 8.0 Radial distancelmm Fig.5 Isocontour maps of C ( I ) (247.61 nm) emission intensity in the induction region for a chloroform or methanol loaded ICAP. The left hand group of four maps are for methanol loading and the right hand group of four for chloroform loading. The inner argon flows were 0.61 (top row) and 1.1 (bottom row) 1 min-’. The rf power was 1.25 kW. The outermost contour in each frame represents a relative emission intensity of 1. The contour interval is 1 relative intensity unit for each frame and the frames can be compared with one another in a absolute sense by counting contours 6.2 mg s-’ CHCI 8.t 4.2 rng s-’ CHCI ,7.\ mg s-’ ..!I3 I mg s-l CHC13 -7 30.0 - 25.0 E E - 20.0 $ .- E 10.0 5.0 -8.0 0.0 8.0 Radial distancelmm Fig. 6 Isocontour maps of Mg I1 (279.55 nm) emission intensity for a chloroform loaded ICAP.The inner argon flow was 0.81 1 min-’ the rf power was 1.25 kW and the solvent load is indicated across the top. The outermost contour in each frame represents a relative emission intensity of 1. The contour interval is 1 relative intensity unit for each frame and the frames can be compared with one another in a absolute sense by counting contours each frame represents the lowest relative emission intensity of 1. The contour interval is 1 arbitrary unit and the frames can be compared with one another in an absolute sense. At the lowest attainable solvent load depicted in the left hand frame the hard line plume displays the lowest intensity presumably because the low condenser temperature required to trap the solvent vapour has also lead to significant sample loss.The entire plume and its intensity maximum also ‘sit’ the furthest upstream at the lowest solvent load. With an increase in solvent load shown in the second frame the over-all intensity increases significantly presumably because the condenser no longer traps a significant amount of analyte. The intensity maximum also moves marginally upstream whereas the plume lengthens significantly so that its tip resides at 25 mm above the top of the induction coil. A further increase in solvent load results in the plume shown in the third frame. With this increase in solvent load the top of the plume extends no further than previously and the intensity maximum only moves marginally upstream by perhaps 1.5 mm.On the other hand the base of the plume moves downstream by 3 mm and clear of the torch while the over-all intensity of the plume decreases significantly. In addition to these major changes the boundary traced out by the outer isocontour has become narrower possibly indicating that the analyte is confined closer to the axis. Further increasing the solvent load to the maximum tolerable load (for chloroform in this case) results in the plume shown in the right hand frame. With this increase in solvent load the plume continues to decrease in intensity and become narrower while the downstream tip of the plume once again extends no further than 25 mm above the top of the induction coil. It is interesting to note that this downstream limit for the tip of the plume overlaps the downstream limit for the atomic plasma as revealed by the C (I) contour plots and by the lowest intensity isocontour for the CN plots.In order to interpret the response of the hard line emission plume to solvent load several physical processes must be taken into consideration. These physical processes determine the local concentration of atomized or ionized analyte and the energy available to excite the analyte so that it emits. Relatively far upstream from the plume the analyte is essentially confined to the aerosol stream because undesolvated particles and droplets must follow the gas stream owing to their minute inertial moments compared with their high viscous drag. 48 Journal of Analytical Atomic Spectrometry January 1996 Vol. 11However once the analyte begins to desolvate and vaporize it becomes free to diffuse across the stream lines of the plasma flow and can disperse radially as it flows across the boundary region of the aerosol channel and into the plasma.Once in the plasma the analyte continues to diffuse across the stream- lines. As the analyte is transported upward and out from the axis by convection and diffusion energy is transported upwards and in towards the axis from the toroidal energy loading region by convection radiation and heat conduction across enormous thermal gradients. As a result the time averaged density of analyte and the time averaged density of energy available to excite the analyte vary enormously throughout the plasma. As a first approximation only two properties determine the local emission intensity of hard line species.These are the time averaged density of analyte and the time averaged density of energy available to excite the analyte. Consequently the maxi- mum in hard line emission resides where the maximum amount of energy is available to excite the hard line species and where the hard line species has not dispersed appreciably by any mass transport process. By similar reasoning the limits of the hard line plume reside where the energy available to excite the hard line is cut off or where the local concentration of hard line species is very low. Accordingly the upper boundary of the hard line plume coincides with the plasma boundary the radial limits of the plume are determined by the radial trans- port of analyte and the base of the plume is determined by vaporization atomization and ionization processes that convert the analyte into hard line species.The contrasting response of a relatively soft line Mg I (285.21 nm) is depicted in Fig. 7. Once again the outermost contour in each frame represents the lowest relative emission intensity of 1. The contour interval is 1 arbitrary unit and the frames can be compared with one another in an absolute sense but the scale is different from that for the Mg 11. In contrast to Mg 11 the soft line plumes depicted here do not extend past the plasma boundary. On the contrary they appear to be nested within the hard line plumes. In fact it appears as though the soft line emission occupies a cooler temperature band in the plasma than the hard line plumes a band that surrounds the hollow inner boundary.This suggests that the geometry of soft line plumes can be rationalized in terms of 4.2 mg s-' CHCI 6.2 mg s-' CHCI 8.6 mg s-l CHCI3 7.4 mg s-l CHC13 I 30.0 25.0 E E 20.0 5 t c .- 15.0 2 m .- 2 10.0 5.0 -8.0 0.0 8.0 Radial distance/mm Fig. 7 Tsocontour maps Mg I (285.21 nm) emission intensity for a chloroform loaded ICAP. The inner argon flow was 0.81 1 min-I the rf power was 1.25 kW and the solvent load is indicated across the top. The outermost contour in each frame represents a relative emission intensity of 1. The contour interval is 1 relative intensity unit for each frame and the frames can be compared with one another in an absolute sense by counting contours norm temperatures as Blades and Horlick have pointed out previo~sly.'~ The norm temperature for an optical transition is simply the temperature at which the emission intensity for that transition displays a maximum.In a thermal plasma one generally encounters a single maximum for line intensity with increasing plasma temperature because of two competing processes. First with the increasing temperature electron collisions increasingly populate an excited bound state for a particular line according to the Boltzmann function. As a result the emission intensity for that line increases with temperature. Second at sufficiently high temperatures the atomic species begins to ionize into the next ionization stage thus depopulating the excited state. Alternatively emitting molecules dissociate with increasing temperature thus depopu- lating molecular excited states.Overall atomic ionic and diatomic emission from the ICAP can be roughly characterized by a norm temperature (if one ignores dynamic processes). As it happens the electron kinetic temperature in the plasma the temperature which largely governs electronic excitation of plasma bound states ranges from approximately 6000 to 9000 K. In general the norm temperatures for molecular species fall below this range by approximately 1000 K whilst the norm temperatures for soft lines fall within this range and the norm temperatures for hard lines exceed this range by approximately 1000 K (see for example references 6 9 and 1 1 ). Consequently molecular emission generally occupies the plasma boundary soft line emission occupies diffuse tempera- ture bands within the plasma (time averaged bands of course) and the most intense hard line emission may generally be found where the most plasma energy is available for electronic excitation. Contour plots of the ratio of ion line to atom line intensity (Mg I1 279.55 nm and Mg I 285.21 nm) are presented in Fig.8. These are consistent with the axial profiles presented in the previous paper but in this case additionally show the off-axis behaviour. It is apparent in these contour plots that the cool regions lie close to the inner boundary and that the excitation environment grows hotter towards the downstream limit where the contour plots become discontinuous. Discussion We have previously discussed the occurrence of a vortex shedding mechanism that is responsible for air entrainment in the tail flame' and as is evident from the isocontour plots presented in this paper these mechanisms are primarily respon- sible for the determination of the location of the downstream boundary of the plasma.It cuts the plasma off by folding cold room air into the argon stream and thus extinguishing the plasma. As a result the tail cone of the plasma cannot be regarded as a region where the plasma decays gradually and steadily owing to microscopic processes such as three body recombination or radiative loss. On the contrary one must consider the possibility of an abrupt fluctuating discontinuous limit at the downstream boundary of the plasma more akin t o the bounds of the potential core in a round jet. The recirculation eddy also has an effect on the radial spatial structure of the plasma discharge.It influences how the solvent load is distributed over the argon stream and hence determines whether the axial channel or the induction region will be heavily loaded with solvent material. The balance between these two extremes determines the temperature and density profile of the plasma gas downstream from the torch. Hence it determines how energy is transported to the analyte. Beyond mass transport by convection and diffusion the effects of heat conduction and heat capacity are evident in the contour plots of C (I) emission from the induction region. Journal of Analytical Atomic Spectrometry January 1996 Vol. 11 494.2 mg s-l CHC13 6.2 mg s-’ CHCI 7.4 mg s-’ CHCI 8.6 mg s-’ CHC13 -8.0 0.0 8.0 Radial distance/mm Fig.8 Isocontour maps of the ratio Mg I1 to Mg I emission intensity (ratio Figs. 6 and 7) for a chloroform loaded ICAP. The inner argon flow was 0.81 1 min-’ the rf power was 1.25 kW and the solvent load is indicated across the top. The outermost contour in each frame represents a relative emission intensity of 1. The contour interval is 1 relative intensity unit for each frame and the frames can be compared with one another in a absolute sense by counting contours Inspection of these contour plots reveals that the plasma volume shrinks in the axial direction in response to solvent loading. This indicates that the discharge responds to solvent loading with a thermal pinch in the axial direction rather than a simple translation downstream.Although such an effect may be obscured in the C (I) contour plots by the mass transport of carbon in the argon stream the thermal pinch effect is corroborated by observations and comparison with similar effects reported in the literature. Phenomena related to heat conduction are also evident beyond the torch rim. For example contour plots of the Mg I1 to Mg I intensity ratio show that solvent dissociation suppresses the transport of energy from the outer regions into the axial channel. Only once all the solvent material has dissociated does an appreciable amount of energy flow from the outer region into the axial channel. However it is not clear how the energy is transported from the outer regions into the channel. Even so the contour plots provide no reason to invoke anything beyond thermal transport or heat conduction.Any further argument about radiation trapping the transport of metastable species or other non-thermal channels of energy transport must be regarded as speculative; after all the results presented here are obscured by temporal averaging. Air Entrainment Vortex shedding has been observed for flame-jets as well as for round jets of cold gas and is most readily observed when the jets are excited acoustically. Becker and Massaro have reviewed the literature on acoustically excited jets up to 1967.24 Their review references work from 1858 when L e ~ o n t e ~ ~ reported that a coal gas flame-jet jumped in response to certain notes from a violoncello and suggested that ‘We must look upon all jets as musically inclined’.The jumping flame was just a manifestation of vortex shedding. Soon afterwards it was found that combustion was not essential for acoustic activity in a gas jet-round jets of cold gas made visible by smoke particles behaved in a similar manner. Later on Lord Rayleigh analysed the instability problem and employed stroboscopic illumination to study it. He found that both varicose and sinuous instabilities could be acoustically excited in round jets. The varicose instabilities took the form of symmetrical swelling and constriction of the jet’s diameter synchronous with the exciting tone while sinuous instabilities took the form of rhythmic undulation or twisting of the jet (vortex evolution is associated with the varicose instability).Varicose instabilities predominate in jets with a flat or top hat velocity profile with a thin boundary region. Becker and Massaro’s literature review also reveals that vortex shedding and the acoustic sensitivity of jets has been extensively studied in more recent times and that the associated theory has also been extensively developed. Becker and Massaro themselves have presented photo- graphic records and detailed observations of vortex evolution in a round jet. Their study focused on an axisymmetric jet of cold gas from a nozzle with a flat flow velocity profile at the nozzle mouth except for a thin boundary layer of laminar flow near the nozzle wall. Their study was very informative because it spanned a wide range of‘ Reynolds numbers for the axisym- metric jet including the range typically encountered for ICAPs.They divided the complete range of Re = 600-20 000 into eight flow regimes. [Incidentally the ICAP (Re = 100-600) resides in the first flow regime of 600<Re< 1450.26-29] They found that successive vortices shed off the jet according to a general 50 Journal of Anahtical Atomic SDectrometrv Januarv 1996. Vol. 11frequency law (or wave velocity law). In general J A - 2 constant UO (5.1) where f is the vortex shedding frequency A is the wavelength of the varicose disturbance and Uo may be regarded as the centre line velocity of the jet. The constant is approximately 0.5 so vortices shed off the jet at approximately half the velocity of the jet stream. Vortex shedding followed this frequency law both in the presence and absence of acoustic excitation.Interestingly they found that when the vortex shedding was excited by pure acoustic tones discrete frequency jumps were observed which turned out to be related to the resonant properties of the nozzle tube. Among other things they found that varicose instabilities were prevalent for thin boundary layers whereas sinuous instabilities were prevalent for fully developed laminar flows. One further point worth mentioning is that they observed the transition from vortex shedding to turbulent flow (vortices need not be turbulent). In certain flow regimes successive vortices would collide then break up into turbulent eddies. In other flow regimes the onset of turbulent flow resided upstream from the tip of the potential core.In which flow regime the ICAP is found if it indeed displays similar phenomena is not known. The ICAP displays many of the characteristics of an axisym- metric round jet in which one would expect vortex shedding. Before the hot argon jet flows out of the confinement tube into the relatively stagnant air of the torch box its flow is essentially laminar rather than turbulent. Its flow profile also appears to have a thin boundary layer and a top hat velocity profile except for the axial channel.23 Moreover the argon exists as unionized gas as a coolant stream close to the torch wall. So at least the outer flow bears similarities to a round jet prone to varicose instabilities. On the other hand it may be dangerous to assume that the flow dynamics of hot plasma bear any similarity to those of cold argon.It should also be noted that the ICAP has both axial and tangential velocity components of flow. It is not understood how tangential components affect varicose instabilities. If the ICAP behaves as a round jet the argon flow remains laminar just beyond the exit of the torch but varicose instabilit- ies arise in the cylindrical surface of discontinuity in the flowfield. As a result the surface of discontinuity eventually folds into a toroidal vortex much like a breaking wave. As this vortex moves downstream it entrains air and radically convolutes the cylindrical interface between the air and the argon. As it continues on its course downstream it grows in thickness folds in on itself and continues to entrain more air into the argon jet at its interior.As the toroidal vortex moves upwards its inner edge makes contact with the hot plasma and probably folds cool material in with the plasma gas quenching the plasma. In other words the plasma is probably confined to the potential core of the jet where the potential core is simply the region of the flowfield unperturbed by air entrainment. In short the plasma boundary is probably defined by a modulated limit or cut-off determined by vortex entrainment of cold air rather than by thermal or radiative dissipation of energy. The time averaged picture of this modulated plasma bound- ary is revealed by the isocontours of CN intensity in Fig. 2. In the outer boundary region the CN emission contour plots and the tail flame observed above the plasma are probably time averaged pictures of the vortex shedding. Within this region the interface between air and plasma over which mass trans- port by diffusion takes place becomes radically convoluted even though the flow may still be laminar (experiments with cold gas jets and diffusion flames reveal that the flow eventually becomes turbulent as the vortices collide with each other and disintegrate at downstream distances of more than two jet diameters from the nozzle).The net result of the vortex shedding is a complex pulsating mixing mechanism with a frequency corresponding to the shedding frequency of the vortex rings which modulates the outer diameter of the plasma. It seems reasonable to conclude then that the overlap of the contours for CN and C (I) contour plots above the torch rim is a consequence of temporal averaging while the minimal overlap between C (I) and C2 isocontours within the torch is characteristic of the steady plasma boundary there.To our knowledge detailed pictures of this vortex shedding process are only available for cold jets and diffusion flames and not for plasma jets. But reliable experimental evidence shows that the ICAP also displays vortex shedding. This evidence includes high speed movie frames in which vortex structures are plainly visible and noise power spectra in which bands corresponding to vortex shedding frequencies are ~nmistakable.~~ Analytical Consequences The spatial relationships between the analyte plumes and background emission are of particular relevance because the ratio between analyte signal and background emission is something that the analyst would like to maximize.Also relevant to the analytical performance is the influence of vortex shedding and air entrainment. Air entrainment influences the analytical signal in several ways. It introduces flame-like conditions to the periphery of the analyte plumes rendering the analyte signal susceptible to all of the matrix interference effects normally encountered with flames. It also introduces noise by modulating the analyte plume. It may even corrupt the analytical blank by entraining dust or other pollutants. Finally vortex shedding and air entrainment are sensitive to acoustic excitation and changes in the flow dynamics of the room air. Consequently environmental sound and changes in the flowfield of the room air may corrupt the analytical signal.Apparently it would be beneficial to eliminate air entrain- ment altogether or to reduce the effect during measurement. End-on viewing is probably one means of achieving this end. The diagnostic usefulness of radially resolved monochro- matic images of emission intensity contour plots for both physical diagnostics and control diagnostics is evident in this paper. The contour plots reveal that emission from C2 CN and C (I) may all be used as control diagnostics for solvent plasma load provided that they are viewed at the appropriate location. For example the C2 intensity is proportional to solvent load when viewed down the axis while CN and C (I) intensity are proportional to solvent load when viewed off- axis.On the other hand for physical diagnostic work the C (I) contour plots within the induction region reveal that the plasma shrinks both axially and radially in response to solvent load. Cz emission within this region indicates how solvent material is distributed over the argon flowstream. From a physical perspective a downstream conical limit is evident in all contour plots of emission intensity at locations above the torch rim. This limit and the overlap between isocontours of different emitting species may be attributed to time averaged varicose instabilities in the plasma jet. In contrast the flowstream within the induction region is appar- ently steady and unperturbed by fluctuations. In contour plots of this region it is evident that the distribution of solvent over the argon stream depends on the inner argon flow rate and the properties of the solvent.Briefly less solvent material is distributed over the outer argon stream when the momentum (flow rate x density) of the inner stream increases. This response may be attributed to a recirculation eddy at the base of the discharge. It is also evident in these contour plots that the Journal of Analytical Atomic Spectrometry January 1996 Vol. 11 51plasma responds to solvent plasma load by shrinking both axially and radially. From an analytical perspective the emission contour plots reveal the analytical usefulness of emission from argon and solvent pyrolysis products. In particular the three dimensional information reveals the observation zones where the emission intensity of these species is proportional to solvent load and plasma excitation conditions. This final aspect will be discussed in a future publication.The authors acknowledge funding from the Natural Sciences and Engineering Research Council of Canada. REFERENCES 1 2 3 4 5 Weir D. G. and Blades M. W. J. Anal. At. Spectrom. 1994 9 1311. Weir D. G. and Blades M. W. J. Anal. At. Spectrom. 1994 9 1323. Blades M. W. Caughlin B. L. Walker Z. H. and Burton L. L. Prog. Anal. Spectrosc. 1987 10 57. Blades M. W. and Horlick G. Spectochimica Acta Part B 1981 36 881. Borghi R. Labbaci K. and Stepowski D. in Turbulent Reactive Flows. USA-France Joint Workshop on Turbulent Reactive Flows 1987 eds. Borghi R. and Murthy S.N.B. Springer-Verlag Berlin 1989 vol. 40 p. 64. 6 Dittrich K. and Niebergall K. Prog. Anal. At. Spectrosc 1984 7 315. 7 Caughlin B. L. and Blades M. W. Spectrochim. Acta Part B 1984 39 1583. 8 Furuta N. and Horlick G. Spectrochim. Acta Part B 1982 31 53. 9 Fister J. C. and Olesik J. W. Spectrochirn. Acta Part B 1991 46 869. 10 Furuta N. J. Anal. At. Spectrom. 1991 6 199. 11 Fister J. C. 111 and Olesik J. C. Spectrochim. Acta Part B 1991 46 869. 12 Hasagawa T. and Winefordner J. D. Spectrochim. Acta Part B 1987 42 773. 13 Koirtyohann S. R. Baber C. and Franklin M. Spectrochim. Acta Part B 1976 31 589. 14 Blades M. W. and Horlick G. Spectrochim. Acta Part B 1981 36 861. 15 Weir D. G. J. and Blades M. W. Spectrochim. Acta Part B 1994 49 1231. 16 Weir D. G. J. Spectrochim. Acta Part B 1990 45 615. 17 Blades M. W. Appl. Spectrosc. 1983 31 371. 18 Farnsworth P. B. Smith B. W. and Omenetto N. Spectrochim. Acta Part B 1990 45 1151. 19 Madden H. H. Anal. Chem. 1978 50 1383. 20 Press W. H. and Teukolsky S. A. Comput. Phys. 1990 4 669. 21 Pan C. Zhu G. and Browner R. F. J. Anal. At. Spectrom. 1990 5 537. 22 Yang P. and Barnes R. M. Spectrochim. Acta Rev. 1990,13,275. 23 Yang P. and Barnes K. M. Spectrochim. Acta Part B 1990 13 275. 24 Becker H. A. and Massaro T. A. J. Fluid Mech. 1968 31 435. 25 Leconte J. Phil. Mag. 1858 15 235. 26 Davies J. and Snook R. D. J. Anal. At. Spectrom. 1986 1 195. 27 Benoy D. A. van der Mu!!en J. A. M. van der Sijde B. and Schram D. C. J. Quant. Spectrosc. Radiat. Transfer 1991,46 195. 28 Benoy D. A. Modelling Thermal Argon Plasmas PhD Dissertation Technische Universiteit Eindhoven 1993. 29 Nowak S. van der Mullen J. A. M. and Schram D. C. Spectrochim. Acta Part B 1988 43 1235. 30 Winge R. K. Eckels D. E. DeKalb E. L. and Fassel V. A. J. Anal. At. Spectrom. 1988 3 849. Paper 51037778 Received June 12 1995 Accepted September 27 1995 52 Journal of Analytical Atomic Spectrometry January 1996 Vol. 1 1

ISSN:0267-9477    

DOI:10.1039/JA9961100043

出版商:RSC    

年代:1996

数据来源: RSC