摘要:

THE ANALYSTTHE ANALYTICAL JOURNAL OF THE ROYAL SOCIETY OF CHEMISTRYADVISORY BOARD"Chairman: J. M. Ottaway (Glasgow, U.K.)"L. S. Bark (Salford, U.K.)E. Bishop (Exeter, U.K.)W. L. Budde (U.S.A.)D. T. Burns (Belfast, U.K.)L. R. P. Butler (South Africa)H. J. Cluley (Wembley, U.K.)E. A. M. F. Dahmen (The Netherlands)L. de Galan (The Netherlands)A. C. Docherty (Billingham, U.K.)D. Dyrssen (Sweden)G. Ghersini (Italy)J. Hoste (Belgium)A. Hulanicki (Poland)"G. W. Kirby (Glasgow, U.K.)W. S. Lyon (U.S.A.)H. V. Malmstadt (U.S.A.)G. W. C. Milner (Harwell, U.K.)"A. C. Moffat (Aldermaston, U.K.)E. J. Newman (Poole, U.K.)H. W. Nurnberg (West Germany)"T. B. Pierce (Harwell. U.K.)E. Pungor (Hungary)P. H. Scholes (Middlesbrough, U.K.)D. Simpson (Thorpe-le-Soken, U.K.)"J.M. Skinner (Billingham. U.K.)'J. D. R. Thomas (Cardiff, U.K.)K. C. Thompson (Sheffield, U.K.)*A. M. Ure (Aberdeen, U.K.)A. Walsh, K.B. (Australia)G. Werner (German Democratic Republic)T. S . West (Aberdeen, U.K.)'P. C. Weston (London, U.K.)'J. Whitehead (Stockton-on-Tees, U.K.)J. D. Winefordner (U.S.A.)P. Zuman (U.S.A.)'G. J. Dickes (Bristol, U.K.)"Members of the Board serving on the Analytical Editorial BoardEditor: P. C. WestonSenior Assistant Editor: R. A. YoungAssistant Editors: Mrs. J. Brew, Miss D. ChevinREG I ONAL ADVl SORY ED IT0 RSDr. J. Aggett, Department of Chemistry, University of Auckland, Private Bag, Auckland, NEW ZEALAND.Professor L. Gierst, Universit6 Libre de Bruxelles, Facult6 des Sciences, Avenue F.-D.Roosevelt 50,Professor H. M. N. H. Irving. Department of Theoretical Chemistry, University of Cape Town, Ronde-Professor W. A. E. McBryde, Faculty of Science, University of Waterloo, Waterloo, Ontario, CANADA.Dr. 0. Osibanjo, Department of Chemistry, University of Ibadan, Ibadan, NIGERIA.Dr. G. Rossi, Chemistry Division, Spectroscopy Sector, CEC Joint Research Centre, EURATOM, lspraDr. 1. Rubeika, Geological Survey of Czechoslovakia, Malostranskk 19, 118 21 Prague 1 , CZECHO-Professor J. R&icka, Chemistry Department A, Technical University of Denmark, 2800 Lyngby,Professor K. Saito, Department of Chemistry, Tohoku University, Sendai, JAPAN.Professor L. E. Smythe, Department of Chemistry, University of New South Wales, P.O. Box 1 ,Professor P.C. Uden, Department of Chemistry, University of Massachusetts, Amherst, MA 01 003,Editorial: Editor, The Analyst, The Royal Society of Chemistry, Burlington House,Piccadilly, London, W1 V OBN. Telephone 01 -734 9864. Telex No. 268001Advertisements: Advertisement Department, The Royal Society of Chemistry, Burlington House,Piccadilly, London, W1 V OBN. Telephone 01 -734 9864. Telex No. 268001The Analyst (ISSN 0003-2654) is published monthly by The Royal Society of Chemistry, BurlingtonHouse, London W1V OBN, England. All orders accompanied with payment should be sent directly toThe Royal Society of Chemistry, The Distribution Centre, Blackhorse Road, Letchworth, Herts. SG6 1 HN,England. 1983 Annual subscription rate UK f93.50, Rest of World f99.00, USA $201 .OO. Purchased withAnalytical Abstracts UK f 226.50, Rest of World f 238.50, USA $487.00. Purchased with AnalyticalAbstracts plus Analytical Proceedings UK f251 .OO, Rest of World f265.00, USA $539.00. Purchasedwith Analytical Proceedings UK fll7.50, Rest of World f 124.50, USA $253.00. Air freight and mailingin the USA by Publications Expediting Inc., 200 Meacham Avenue, Elmont, NY 1 1 003.USA Postmaster: Send address changes to: The Analyst, Publications Expediting Inc., 200 MeachamAvenue, Elmont, NY 11003. Second class postage paid at Jamaica, NY 11431. All otherdespatches outside the UK by Bulk Airmail within Europe, Accelerated Surface Post outside Europe.PRINTED IN THE UK.Volume 108 No 1283 @ The Royal Society of Chemistry 1983 February 1983Bruxelles, BELGIUM.bosch 7700, SOUTH AFRICA.Establishment, 21 020 lspra (Varese), ITALY.SLOVAKIA.DENMARK.Kensington, N.S.W. 2033, AUSTRALIA.U.S.A

ISSN:0003-2654    

DOI:10.1039/AN98308FX005

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

ANALAO 108 (1283) 137-296 (1983) February 1983THE ANALYSTTHE ANALYTICAL JOURNAL OF THE ROYAL SOCIETY OF CHEMISTRYCONTENTSFIRST BIENNIAL NATIONAL ATOMIC SPECTROSCOPY SYMPOSIUMSHEFFIELD, UK, JULY 13-15,1982137 Editorial-J. M. Ottaway138 Glassy Carbon Tubes in Electrothermal Atomisation - Atomic-absorption Spectrometry145 Intensities of Some Spectral Lines from Hollow-cathode Lamps-Christopher Howard,153 Flow Injection Sample Introduction Methods f o r Atomic-absorption Spectrometry-159 Development Progress in Plasma Source Mass Spectrometry-Alan R. Date and Alan L. Gray166 A Pneumatic Recirculating Nebuliser System f o r Small Sample Volumes-Peter Hulmston171 Trace-metal Determinations in Concentrated Electrolyte Solutions-a ComparativeStudy-Peter R.Skidmore and Susan S. Greetham178 Simultaneous Multi-element Analysis by Carbon Furnace Atomic-emission Spectrometry-John Marshall, David Littlejohn, John M. Ottaway, James M. Harnly, Nancy J. Miller-lhli andThomas C. O'HaverDetermination o f Trace Impurities i n Sodium Coolant from a Fast Breeder Reactor byInductively Coupled Plasma Atomic-emission Spectrometry-Thomas Berry, KennethC. Macleod, Alistair C. Christie and James A. CunninghamDetermination of Trace Elements in Biological Materials Using a Hollow-cathode Dis-charge : Comparative Study of Matrix Effects-Sergio Caroli, Oreste Senofonte andPietro Delle FernmineA Critical Comparative Study of Atomic-spectrometric Methods (Atomic Absorption,Atomic Emission and Inductively Coupled Plasma Emission) f o r DeterminingStrontium in Biological Materials-Alfred0 Sanz-Medel, Rosa Rodriguez Roza andConchita Perez-CondeInvestigations on Atomisation Mechanisms o f Volatile Hydride-forming Elements in aHeated Quartz Cell.Gas-phase and Surface Effects; Decomposition andAtomisation o f Arsine-Bernhard Welt and Marianne MelcherA New Design o f Graphite Furnace f o r Rapid Cycle Electrothermal Atomisation - Atomic-absorption Spectrometry-Mohammad-Hossein Bahreyni-Toosi and John B. DawsonDetermination o f Lead in Blood by Flame Atomic-fluorescence Spectrometry-Prem R.Sthapit, John M. Ottaway and Gordon S. FellDetermination of Lead in Whole Blood by Electrothermal Atomic-absorption Spectro-metry Using Graphite Probe Atomisation-Shree K.Giri, Charles K. Shields, DavidLittlejohn and John M. Ottaway254 Analysis of Used Lubricating Oils for Wear Metals by Wavelength Dispersive X-rayFluorescence Spectroscopy-Edward Searle and Christopher M. Thompson261 Determination of Lead in Soil by Graphite Furnace Atomic-absorption Spectrometry withthe Direct Introduction o f Slurries-Kenneth W. Jackson and Alan P. Newman265 Re-usable Sampling Tubes for Monitoring Airborne Mercury Vapour Concentrations:Sample Collection and Analysis by Cold Vapour Atomic-absorption Spectrometry-Mark Taylor277 Extraction o f Metals from Soils and Sewage Sludges by Refluxing with Aqua Regia-Michael L. Berrow and Winnie M. Stein286 Application of Optical Emission Source Developments in Metallurgical Analysis-Hugh Hughes-Leo de Galan, Margaretha T.C. de Loos-Vollebregt and Rent5 A. M. OosterlingMarjorie E. Pillow, Edward B. M. Steers and Donald W. WardJulian F. Tyson, John M. H. Appleton and Ahyar B. ldris18919620421 3Part 1.225235244293 BOOK REVIEWSSummaries of Papers in this lssue-Pages iii, iv, v, vi. vii. viii. ix, X. xiiPrinted by Heffers Printers Ltd Cambridge EnglandEntered as Second Class at New York, USA, Post Officf 4NON FREEZINGN20GAS REGULATORNo heaters requiredNo ElectricalconnectionsNo freeze-upThis specially designed regulator eliminates pressureand flow fluctuations caused by internal icing whichnormally affects ordinary regulators. Gives a smoothreliable gas flow. Trouble free unattended operationeven outdoors at low ambient temperature.Available for immediate delivery at only€104.50 + VAT.HIGH PURITY CARRIER GASREGULATORSFor gas chromatography etc.Diffusion resistantregulators with stainless steel diaphragms designed togive accurate pressure control while maintaining gaspurity. Minimum inboard leakage and diffusion. Singlestage and two stage models from €120.00.For orders and further information contact:NEWBURY RG14 5DT - TEL (0635) 49903. TLX 848668ELECTROCHEM LTD - MAIDENHEAD HOUSE - electrochem - SPECIALITY CHEMICALS AND GASESA205 for further information. See page xviiiTHE QUEEN’SUNIVERSITYOF BELFASTMSc COURSE inANALYTICAL CHEMISTRYApplications are invited for admission to thisestablished 12 month full-time MSc coursewhich provides a comprehensive training inthe theory and practice of modern chemicaland instrumental methods of analysis.Applicants should normally possess anhonours degree (or equivalent) in chemistryo r cognate subjects.Part-time courses areavailable.The Science and Engineering ResearchCouncil has recognised the course for tenureof its Advanced Course Studentships.A description booklet and application formscan be obtained from Professor D. ThorburnBurns, Dept. of Chemistry, Queen’s Universityof Belfast, Belfast BT7 1 NN, Northern Ireland.A208 for further information. See page xviii12th - 14th October 1983BARBICAN CENTRE, LONDONThe Conference, which has the strong support of theRoyal Society of Chemistry, is intended for scientistsand technologists from all branches of industrial scienceand the related disciplines where analytical techniquesplay a significant role.‘ANALYTICON 83’ has the added attractions of beingstaged alongside the successful and expanding seriesof ‘LABORATORY’ exhibitions as well as the use of theexcellent conference facilities at the new BarbicanCentre.The organisers are pleased to welcome ProfessorJohn 1.G. Cadogan, President of the Royal Societyof Chemistry, to act as Chairman for the Conference.He will be supported by many eminent plenary andkeynote speakers who will form the foundation for thisimportant event.Six-Theme Plenary Lectures:Organic Structure: Prof. C.J.W. Brooks, University of Glas-gowTitle: To be confirmed.Chromatography: Dr D.R.Deans, I.C.I. Wilton, ClevelandTitle: ‘Quantitative GC - a decade of progress’.Surface Analysis: Dr V.E. Coslett, Cavendish Labs., Univ. ofCambridgeTitle: ‘Microanalysis, Auger and Photoelectron Spectroscopy’.Elemental Analysis: Prof. T.S. West, Macaulay Inst., Aber-deenTitle: ‘Elemental Analysis - an overview of problems and theirresolution by physical chemical techniques’.Computers In Analytical Chemistry: Prof. D. Betteridge,British Petroleum, Sunbury-on-ThamesTitle: To be confirmed.Clinical Analysis & Bio-Sciences: Dr F.L. Mitchell, C.R.C.,HarrowTitle: ‘New technology and the changing scene in clinicalchemistry’. -------- c o obtain a copy of the Call for Papers and /or RegistrationForms, please return this coupon to:Mr G.C. Young, S.I.M.A., Leicerter House, 8 Leicester St., I London, WCPH 70N or Telephone: 01-437-0678. IIII Surname:Prof/Dr/Mr/Mrs/Miss/Ms: I Company/Organisation:II I Address: II Postcode: 1IJI Please return a copy of 0 Call for Papers0 Registration FormsA206 for further information. See page xvii

ISSN:0003-2654    

DOI:10.1039/AN98308BX007

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

February, 1983 SUMMARIES OF PAPERS IN THIS ISSUESummaries of Papers in this IssueGlassy Carbon Tubes in Electrothermal Atomisation -Atomic-absorption SpectrometryPreliminary results are presented on the use of glassy carbon tubes of standarddimensions for electrothermal atomisation - atomic-absorption spectrometry.In comparison with pyrolytically coated graphite tubes, the glassy carbontubes show similar limits of detection provided that the same atomisationtemperature can be realised. Glassy carbon tubes promise the followingadvantages : more uniform heating ; resistance against chemical attack ; a life-time of several thousands firings ; and a remarkably constant sensitivity.Keywords : Glassy carbon ; electrothermal atomisation ; atomic-absorptionspectrometryLEO de GALAN, MARGARETHA T.C. de LOOS-VOLLEBREGT andRENS A. M. OOSTERLINGLaboratorium voor Analytische Chemie, Technische Hogeschool, Jaffalaan 9,2628 BX Delft, The Netherlands.Analyst, 1983, 108, 138-144.Intensities of Some Spectral Lines from Hollow-cathode LampsThe relationship between spectral line intensity I and discharge currenti is examined as part of an investigation of low pressure (1-20 Torr) hollow-cathode discharges in neon, for various cathode dimensions. An equation,I = Ai (1 + Ci)/(l + Bi), deduced by balancing likely excitation and de-excitation processes, can be fitted within the limits of experimental accuracy tomeasured I vevs'sus i graphs. Here, A depends on one-stage excitation, C on therelative importance of two- and one-stage excitation, and B on the relativeimportance of collisional and radiative de-excitation.The values of B and Cfor individual lines, and their dependence upon pressure and upon cathodedimensions, together with the possible role of self-absorption, are discussed.Keywords ; Hollow cathodes ; excitatiop processes ; spectral intensity ; neonCHRISTOPHER HOWARD, MARJORIE E. PILLOW and EDWARD B. M.STEERSSchool ofN7 8D8.Applied Physics, The Polytechnic of Northand DONALD W. WARDCathodeon Ltd., Nuffield Road, Cambridge, CB4 1TF.London, Holloway, London,iiiAnalyst, 1983, 108, 145-152iV SUMMARIES OF PAPERS I N THIS ISSUEFlow Injection Sample Introduction Methods forAtomic-absorption SpectrometryFebruary , 1983The essential features of flow injection analysis are described and the use offlow injection methodology for sample introduction for flame atomic-absorp-tion spectrometry is briefly reviewed.A flow injection analogue of thestandard additions method has been devised and applied to the analysis ofchromium in some BCS standard steels. The results showed good agreementwith the certificate values. The use of a concentration gradient formingmixing chamber to provide a novel method of rapid, single-standard cali-bration is described and the results of preliminary experiments with magnesiumshow the method to be viable, The potential usefulness of both methods iscritically evaluated.Keywords : Flow injection ; atomic-absorption spectrometry ; standard additionsmethod ; sample introduction ; concentration gradient generatorJULIAN F.TYSON, JOHN M. H. APPLETON and AHYAR B. IDRISDepartment of Chemistry, Loughborough University of Technology, Loughborough,Leicestershire, LE11 3TU.Analyst, 1983, 108, 153-158.Development Progress in Plasma Source Mass SpectrometryDevelopment work in the application of the inductively coupled plasma toplasma source mass spectrometry is described. Preliminary results obtainedunder continuum (or bulk plasma) sampling conditions are illustrated andcompared with previously published boundary layer sampling work. Thetechnique is now shown to be viable for multi-element analysis of complexsamples.Keywords : Plasma source mass spectrometry ; inductively coupled plasma ;continuum (or bulk plasma) sampling mode ; multi-element trace analysisALAN R.DATEInstitute of Geological Sciences, 64/78 Gray’s Inn Road, London, WClX 8NG.and ALAN L. GRAYDepartment of Chemistry, University of Surrey, Guildford, Surrey, GU2 5XH.Analyst, 1983, 108, 159-165.A Pneumatic Recirculating Nebuliser System for SmallSample VolumesThe nebuliser spray chamber described generates an aerosol, for use with aninductively coupled plasma, on as little as 1 ml of sample solution for over10 min. The nebuliser has direct application to inductively coupled plasmaoptical emission spectroscopic analysis in those instances where economy ofsample solution is important. The performance of the nebuliser spraychamber was tested and it was found that the sensitivity and precision are asgood as those obtained with a conventional nebuliser system.Memory effectsare readily overcome by including a system that allows rapid, thoroughflushing and flooding of the spray chamber.Keywords : Inductively coupled plasma ; optical emission spectrometry ;pneumatic nebuliserPETER HULMSTONAnalytical Chemistry Branch, Chemistry Division, MOD(PE) , Atomic WeaponsResearch Establishment, Aldermaston, Berkshire, RG7 4PR.Analyst, 1983, 108, 166-170February , 1983 SUMMARIES OF PAPERS IN THIS ISSUETrace-metal Determinations in Concentrated ElectrolyteSolutions-a Comparative StudyVThe results presented here are typical of those obtained during an extendedstudy of methods for determining trace amounts of cationic contaminants inthe two most commonly used dry-cell electrolytes (aqueous 7 M solutions ofzinc chloride and potassium hydroxide).The results show that when dilutioneffects are taken into account there is little to choose between inductivelycoupled plasma atomic-emission and flame atomic-absorption spectroscopyas far as.sensitivity is concerned but the precisions of results obtained from adirect reading (simultaneous) inductively coupled plasma spectrophotometerare significantly better than those obtained by flame atomic absorption, andthe time taken to analyse samples for a number of elements is greatly reducedby the simultaneous inductively coupled plasma method.At lower levels, significant reductions in sensitivity of the electrothermalatomic-absorption technique, amounting to 3-4 orders of magnitude in someinstances, are caused by the presence of large excesses of these electrolytes,but where ultimate sensitivity is of less importance than sample throughputthis technique has advantages over electroanalytical techniques.Wheresensitivity, high precision and/or low capital costs are the prime considerationthen electroanalytical techniques have much to offer.Keywords : Direct current plasma ; inductively coupled plasma ; atomic-absorption spectrometry ; trace elements ; electrolyte solutionsPETER R. SKIDMORE and SUSAN S . GREETHAMBritish Ever Ready Company Ltd., Group Technical Centre, St. Ann’s Road,Tottenham, London, N16 3TJ.Analyst, 1983, 108, 171-177.Simultaneous Multi- element Analysis by Carbon FurnaceAtomic-emission SpectrometryThe application of carbon furnace atomic-emission spectrometry (CFAES) tosimultaneous multi-element analysis has been investigated using a direct-reading spectrometer system.A computer-controlled wavelength modulationsystem employing a quartz refractor plate is used to provide automatic back-ground correction in both the single and multi-element modes. Detectionlimits obtained using a three-step square-wave modulation waveform with thissystem are comparable to those previously obtained using the rotating sectormethod of modulation. The linear range of calibration graphs has beenextended to 4-5 orders of magnitude by measurement of emission intensitiesoff the centre of the line profile.The potential of CFAES as a technique forsimultaneous multi-element analysis is demonstrated by the determinationof trace elements in NBS standard reference materials and orange and pine-apple juice samples.Keywords : A tomic-emission spectrometry ; electrothermal atomisation ; simul-taneous multi-element analysis ; wavelength modulation ; fruit juiceJOHN MARSHALL, DAVID LITTLEJOHN and JOHN M. OTTAWAYDepartment of Pure and Applied Chemistry, University of Strathclyde, 285 CathedralStreet, Glasgow, G1 1XL.JAMES M. HARNLYNutrient Composition Laboratory, Beltsville Human Nutrition Centre, US Depart-ment of Agriculture, Beltsville, MD 20705, USA.NANCY J. MILLER-IHLI and THOMAS C. O’HAVERDepartment of Chemistry, University of Maryland, College Park, MD 20742, USA.A ~ z a l y ~ t , 1983, 108, 178-188vi SUMMARIES OF PAPERS IN THIS ISSUEDetermination of Trace Impurities in Sodium Coolant from a FastBreeder Reactor by Inductively Coupled Plasma Atomic-emissionSpectrometryFebruary , 1983Trace impurities in samples of the liquid sodium coolant from the DounreayFast Reactor are determined by inductively coupled plasma (ICP) atomic-emission spectrometry of vacuum distillation residues.A 72-channel vacuumspectrometer with a l-kW argon plasma source, fed by a coaxial capillarynebuliser, simultaneously measures 59 elements with a precision varying from(1% at concentrations 20 times the detection limit to 30% a t detectionlevels. The ICP torch box is enclosed in a fume-cupboard fitted with afiltered extract system to allow safe handing of the radioactive solutions.Comparisons of some results have been made with spark-source mass spectro-metry, d .c.arc emission spectrography, neutron-activation analysis andatomic-absorption spectrometry.Keywords : Liquid sodium ; sodium distillation ; inductively coupled plasma ;atomic-emission spectrometry ; impurity determinationTHOMAS BERRY, KENNETH C. MACLEOD, ALISTAIR C. CHRISTIEand JAMES A. CUNNINGHAMUnited Kingdom Atomic Energy Authority (Northern Division) , Dounreay NuclearPower Development Establishment, Thurso, Caithness, KW14 7TZ.Analyst, 1983, 108, 189-195.Determination of Trace Elements in Biological Materials Using aHollow-cathode Discharge: Comparative Study of Matrix EffectsAn emission source that does not appear to be significantly prone to matrixeffects is the hollow-cathode discharge.In order to elucidate its effectivepotential a number of elements (aluminium, arsenic, calcium, copper, galliumand zinc) were determined in the presence of various compounds (ortho-phosphoric acid, sodium nitrate and potassium nitrate) over a wide range ofconcentrations and internal ratios. The same elements were determined inliquid samples resulting from mineralisation of biological materials (kidney,liver, brain and blood of mice). The results showed that the hollow-cathodeemission source is affected by this type of interference to a lesser extentthan atomic-absorption spectrometry and arc-emission spectrography.Keywords : Hollow-cathode discharge ; emission spectroscopy ; atomic-absorp-tion spectrometry ; matrix effectsSERGIO CAROLI, ORESTE SENOFONTE and PIETRO DELLE FEMMINEIstituto Superiore di Sanith, 299 Viale Regina Elena, 00161 Rome, Italy.Analyst, 1983, 108, 196-203February, 1983 SUMMARIES OF PAPERS IN THIS ISSUEA Critical Comparative Study of Atomic- spectrometric Methods(Atomic Absorption, Atomic Emission and Inductively CoupledPlasma Emission) for the Determination of Strontium inBiological MaterialsviiAs part of a general research plan, aimed at establishing tolerable doses ofstrontium and its distribution in selected soft tissues of rats and hamsterstreated with stable strontium, a comparative study on the analytical per-formance of flame atomic absorption, flame atomic emission and inductivelycoupled plasma (ICP) emission for biological strontium assays, especially inblood serum, has been carried out.Optimum conditions for the variousmethods were established and analytical performance characteristics wereevaluated for each method in terms of limits of detection, dynamic range,selectivity and precision attainable using the same basic instrument (thePerkin-Elmer ICP/5000),ICP emission spectrometry appeared to be the best method as it provides asensitivity of about 100 times better than the next most sensitive method, alinear calibration graph over five orders of magnitude, good precision in realsample analysis and virtual absence of spectral or chemical interferences(although nebulisation and transport effects have to be allowed for) fromthose elements and organic matrices common in biological materials.Adinitrogen oxide - acetylene flame, in the presence of a sodium contentapproximating the blood sodium content, increases sensitivity and selectivitywhen compared with an air - acetylene flame, flame emission being aboutfour times more sensitive than flame atomic absorption for both flames.Results for the determination of strontium in blood serum, brain and liverof rats and hamsters treated with stable strontium are also reported.Keywords : Strontium determination ; biological materials ; jlame atomic-absorption spectrometry ; flame atomic-emission spectrometry ; inductivelycoupled plasma emission spectrometryALFRED0 SANZ-MEDEL and ROSA RODRIGUEZ ROZADepartment of Analytical Chemistry, Faculty of Chemistry, University of Oviedo,Oviedo, Spain.and CONCHITA PEREZ-CONDEDepartment of Analytical Chemistry, Faculty of Chemistry, Universidad Com-plutense, Madrid, Spain.Analyst, 1983, 108, 204-212.Investigations on Atomisation Mechanisms of Volatile Hydride-forming Elements in a Heated Quartz Cell. Part 1.Gas-phaseand Surface Effects; Decomposition and Atomisation of ArsineThe atomisation of gaseous hydrides in a heated quartz cell is not caused bya thermal decomposition but by collision with free hydrogen radicals. Theseradicals are formed in a reaction with oxygen a t temperatures above 600 “C.In a “clean” environment, the concentration of radicals is well above theequilibrium concentration because their formation is a much faster processthan their recombination.Several materials, however, can catalyse radicalrecombination and therefore have a depressing effect on the observed signal.In the absence of hydrogen, arsine is not atomised but thermally decomposed,probably with the formation of As, and As,.Keywords : A tomic-absorption spectrometry ; hydvide generation technique ;atomisation mechanisms ; arsine atomisation and decomposition ; hydrogenradicalsBERNHARD WELZ and MARIANNE MELCHERDepartment of Applied Research, Bodenseewerk Perkin-Elmer & Co. GmbH,D-7770 ftlberlingen, Federal Republic of Germany.Analyst, 1983, 108, 21 3-224... Vlll SUMMARIES OF PAPERS IN THIS ISSUEA New Design of Graphite Furnace for Rapid Cycle ElectrothermalAtomisation - Atomic-absorption SpectrometryFebruary, 1983The design and performance of a new furnace developed for electrothermalatomisation - atomic-absorption spectrometry is described.The furnaceconsists of a segmented graphite rod. Sample solutions may be atomiseddirectly from the rod without prior drying and pyrolysis, with the resultthat the time interval between sample injections is reduced to <30 s. Theperformance of the segmented-rod atomiser with direct sample atomisationwas investigated for the determination of silver, gold, aluminium, bismuth,cadmium, chromium, copper, mercury, manganese, lead, vanadium and zincin complex matrices containing salts and organic material.In all instancessensitivities comparable to those associated with conventional furnacesystems were achieved. The coefficient of variation ranged from 4.0% forcadmium in 0.1 M nitric acid to 9% for gold in 1% sodium chloride solution.Keywords : A tomic-absorption spectrometry ; electyothermal atomisation ; seg-mented graphite rod ; direct atomisationMOHAMMAD-HOSSEIN BAHREYNI-TOOSI and JOHN B. DAWSONDepartment of Medical Physics, General Infirmary, Leeds, LS1 3EX.Analyst, 1983, 108, 225-234.Determination of Lead in Blood by Flame Atomic-fluorescenceSpectrometryA simple, rapid method is described for the determination of lead in blood.Dilution 1 + 4 with Triton X is the only sample preparation required andmeasurements are carried out using a purpose-built atomic-fluorescencespectrometer with a nitrogen-separated air - acetylene flame. The prepara-tion and operation of the lead electrodeless discharge lamps used as theexcitation source have been optimised by a ten-factor Simplex procedure. Adetection limit of 6 pg 1-l has been achieved for lead in aqueous solution. Nosignificant chemical interferences were observed from the major constituentsof the blood matrix and a second continuum source is used to achieve auto-matic background correction for scattered radiation. Aqueous lead standardsare used for calibration. Accuracy was established by satisfactory comparisonwith values reported for quality control blood samples.Keywords : Flame atomic-fluorescence spectrometry ; lead determination ; bloodanalysis ; electrodeless discharge lampsPREM R. STHAPIT and JOHN M. OTTAWAYDepartment of Pure and Applied Chemistry, University of Strathclyde, CathedralStreet, Glasgow, G1 1XL.and GORDON S. FELLDepartment or' Clinical Biochemistry, Royal Infirmary, Glasgow, G4 OSF.. - . - ^ - - ~ - - --- ^.

ISSN:0003-2654    

DOI:10.1039/AN98308FP013

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

February , 1983 SUMMARIES OF PAPERS IN THIS ISSUEDetermination of Lead in Whole Blood by Electrothermal Atomic-absorption Spectrometry using Graphite Probe AtomisationAtomisation from a pyrolytic graphite probe, placed in a hot and constant-temperature HGA 70 furnace, was used for the direct determination of leadin diluted whole blood. Substantial reductions in the classical vapour-phaseinterference effects by up to 2% m/V magnesium chloride and calcium chlorideand 1.5% wz/V sodium chloride allowed the use of aqueous standard solutionsfor analytical calibration. Good agreement with national (UK) mean valueswas obtained for the analysis of quality control blood samples. The analyticalprecision is equivalent to that with conventional atomisation, but withimproved sensitivity.ixKeywords : Lead determination ; whole blood analysis ; electrotlaermal atomisa-tion ; atomic-absorptio n spectrometry ; probe atomisationSHREE K.GIRI, CHARLES J. SHIELDS, DAVID LITTLEJOHN andJOHN M. OTTAWAYDepartment of Pure and Applied Chemistry. University of Strathclyde, CathedralStreet, Glasgow, G1 1XL.Analyst, 1983, 108, 244-253.Analysis of Used Lubricating Oils for Wear Metals by WavelengthDispersive X-ray Fluorescence SpectroscopyAnalysis of used lubricating oils for wear metals by X-ray fluorescence spectro-scopy has always been difficult when the deterinination of many elements hasbeen required. Problems have been mainly caused by the nature of the sample,selection of standards and presentation of samples and standards to theinstrument in a suitable form.The method described largely overcomes theseproblems, is simple and convenient to use and is suitable for a wide range oflubricating oils. Repeatability is good and readily available standards can beused for calibration purposes. A correlation programme has been carried outusing flame atomic-absorption and direct-reading emission spcctroscopy onchromium, tin, lead, copper and iron.Keywords ; Wear metals ; lubricating oils ; wax medium ; X-ray fluorescencespectroscopyEDWARD SEARLE and CHRISTOPHER M. THOMPSONResearch laboratory, London Transport Executivc, 566 Chiswick High Road, London,W4 5RR.Analyst, 1983, 108, 254-260X SUMMARIES OF PAPERS I N THIS ISSUEDetermination of Lead in Soil by Graphite Furnace Atomic-absorption Spectrometry with the Direct Introduction of SlurriesFebruary, 1983A simple procedure is described whereby 5-20mg of a powdered soil aremixed with 25 ml of water and, while stirring, 20-pl aliquots of the slurryare pipetted into a graphite furnace electrothermal atomiser.Calibrationwith aqueous standards gives the total lead concentration of the soil. Thisis much simpler than the complex hydrofluoric acid digestion proceduresnormally required to obtain complete recoveries from soil. The over-allprecision of the analysis (8% relation standard deviation) is adequate forthis application, as is the sensitivity. A characteristic concentration ( A =0.0044) of 0.5 pg 1-1 is equivalent to 0.62 pg g-1 soil in a typical slurry.Keywords Lead determination ; soil analysis ; solid-sample introduction ;electrothermal atomisation ; atomic-absorption spectrometryKENNETH W.JACKSONDepartmentS1 1WB.of Chemistry, Sheffield City Polytechnic, Pond Street, Sheffield,and ALAN P. NEWMANDepartment of Geography and Environmental Studies, Sheffield City Polytechnic,Wentworth Woodhouse, Rotherham, S62 7T J.Afialyst, 1983, 108, 26 1-264.Re-usable Sampling Tubes for Monitoring Airborne MercuryVapour Concentrations : Sample Collection and Analysis byCold Vapour Atomic-absorption SpectrometryA re-usable sampling tube with silvered alumina as the collection medium isused to monitor concentration levels of airborne mercury vapour. Thedevice is ideally suited for personal sampling over long or short periods andits mercury blank is negligible.Analysis is by cold vapour atomic-absorptionspectrometry, using thermal desorption to release the mercury from thesampling tube for subsequent measurement, and a novel and convenientmeans has been devised for altering the measurement range of the analyticalsystem. A detection limit of 3 ng, equivalent to 0.5 pg m-3 for a 6-1 airsample, has been achieved but this could easily be improved further bymaking small modifications to the analytical apparatus. The sampling andanalytical procedures have been validated by comparing results obtained forsamples from mercury standard atmospheres and for factory samples withthose obtained by established procedures.Keywords : Airborne mercury vapour ; silvered alumina ; re-usable samplingtube ; cold vapour atomic-absorption spectrometryMARK TAYLORHealth and Safety Executive, London and Home Counties North Field ConsultantGroup, 14 Cardiff Road, Luton, LU1 1PP.Analyst, 1983, 108, 265-276February, 1983 THE ANALYST xiCOMPUTERS IN AUTOMATION ANDLABORATORY MANAGEMENTThe 5th Summer School ofAutomatic Chemical AnalysisA residential course at the University of Sussex,Falmer, Brighton, England.10th to 15th July 1983For the past four years this highly acclaimed coursehas been held at the Universiw College of Swansea.The new venue will provide an opportunity toexpand the scope of the course while retaining theproven format which includes a balanced mixtureof theory, practice and personal tuition.The programme will include lectures, tutorials andpractical sessions on the following broad topics:AutomationComputingData handlingManagementMicro-electronicsDetailed information and registration forms from:The 5th Summer School ofAutomatic Chemical Analysis,176A North View Road,London, N8 7NB.England.A Handbook ofICP SpectrometryM Thompson, Imperial College, London,andJ N Walsh, King's College, London.This important new book, the first t o bedevoted entirely t o inductively coupledplasma atomic emission spectrometry (ICPAES),reviews the theory and practice of this impres-sive analytical technique.Beginning with a review of the developmentof ICPAES, its analytical characteristics andadvantages and the instrumentation used, thebook goes on t o concentrate on how thetechnique can be applied t o the geological andenvironmental sciences.Appendices summarize the determination ofthe elements and list all publications concernedwith geological and environmental analysis byICPAES.Publication June 1983c.23Opp ISBN 0 2 16 9 1436 1 c.f 35.00 netBlackie Et Son LtdBishopbriggsGlasgow 664 2NZUK1 Scientific, educational, medical andindustrial laboratory equipment, servicesand supplies.2 Medical electronics.3 Analytical, Biochemical and ResearchInstrumentation.4 Electronic measuring and testingequipment.5 Measurement control systems andinstrumentation.IT ALLADDS UPTOTHE INT€RNATIONALLABORATORY SHOWi nco r po ra t i ng La bex and La bTec h no logy14 - 17 June 1983.€arts Court, London.Opening times: 14th-16th June. . . .0930 - 173017th June. . . .0930 - 1600Or anised by:Industrial an% Trade Fairs Limited,Radcliffe House,Blenheim Court,&-& Solihull, West Midlands B912BGTel: 021-70s 6707. Telex: 337073. r - i - - - - - - - - - m - Please send me further details on Tectronica '83. 7I NAME II COMPANY II ADDRE55 II A 2 1I Post to: Industrial and Trade Fairs Limited, Radcliffe House, IBlenheim Court, 5olihull, West Midlands B91 2BG England.A203 for further information.- - - - - - - - - - - - - . J ISee page xviii A207 for further information. See page xviixii SUMMARIES OF PAPERS I N THIS ISSUE February, 1983Extraction of Metals from Soils and Sewage Sludges byRefluxing with Aqua RegiaThe analysis of soils for total metal content using various acid digestionprocedures and flame atomic-absorption spectroscopy has been investigated.Refluxing with aqua regia was more effective than digestion in an open vesseland produced results comparable to those obtained by bomb digestion, themost vigorous method used.Refluxing with aqua regia extracted at least80% of the total chromium, copper, lead and manganese from sewage sludgesand sludge-treated soils. Analysis of the uncontaminated Canadian Referencesoils showed that a similar proportion of the total cadmium, iron and zincwas also extracted. Results for the analysis of six typical Scottish topsoilswere in agreement with the conclusions obtained with the Canadian soils.Keywords ; Trace metal determination; soils ; sewage sludges ; acid digestions ;atomic-absorption spectro$hotometryMICHAEL L.BERROW and WINNIE M. STEINDepartment of Spectrochemistry, The Macaulay Institute for Soil Research, Craigie-buckler, Aberdeen, AB9 2Q J.Analyst, 1983, 108, 277-285Febrzcary, 1983 THE ANALYST xiiiThe Market Leader for ICP Sourcesand AccessoriesNEW f I950 per unitA m t e d Hydride GeneratorRapid analysisof As, Bi, Sn, Sb, Se, Te, Ge, Hg, & Pb. Detectionlevels in region of . l PPB for above elements. Stable contin-uous hydride generation allows greater precision and relia-bility. Simplevisual checking of instrument performance.Sample levels measuredagainst background.Easy and simpleto interface to any plasmaor atomic absorption instrument.Additional pumpingchannel available for introductionof HzOz orIodide solution. Stand-alone or remote operation fromcomputer or auto sampler.Plasma-Therm ICPSources, which have become the standardof the industry are ideal sources for macro or trace, single ormultielement analysis. The heart of each system is a crystalcontrolled RF generator (27.1 2 or 40.68 MHz) designed forstability, reliability. serviceability, simplified control and safety.Automatic power control; impedance matching; and preciseflow meter control of plasma, auxiliary, and nebulizing gasesensure high spectroanalytical stability and reproducibility. Allsystems are easily adapted to most commercial spectro-meters.The recently introduced Compact Single Phase 40 MHzSystems available as 1 KW and 2KW versions offer increasedstability, reliability and performance.PlASMAmTHERM LTD213 Kangley Road Lower Sydenham sE26 5AR Tel: 01-778 6798A202 for further information.See Page xviiiSecond-hand -Copies? -RSC members have the advantage thatthey may subscribe to this journal at amost attractive discount price.The convenience of having yourpersonal copy, rather than borrowinga library copy, is obvious but there aremany other advantages of member-ship. Details of membership will besent if you write 200 in one of theboxes on the Reader Enquiry Servicepage.BUREAU OF ANALYSEDSAMPLES LTDannounce the availability ofNEWCERTIFIED REFERENCEMATERIALSfor twelve trace elementsinNICKEL BASE ALLOYSBCS/SS 345 for normal trace levelsBCS 346/SS 346A for enhancedtrace levelsFor full details write, telephoneor telex to:BAS Ltd., Newham Hall, Newby,Middlesbrough, Cleveland, TS8 9EATelephone: Middlesbrough 31 721 6Telex: 587765 BASRIDA200 for further information.See page xviii A209 for further information. See page xviixiv THE ANALYST Febrzlayy, 1983Analytical Sciences MonographsNo. 4 ElectrothermalAtomisation for AtomicAbsorption Spectrometryby C. W. FullerSince the introduction of atomic absorptionspectrometry as an analytical technique, by Walsh,in 1953, the use of alternative atomization sourcesto the flame has been explored.At the present timethe two most successful alternatives appear to bethe electrothermal atomiser and the inductively-coupled plasma. In this book an attempt has beenmade to provide the author's views on the historicaldevelopment, commercial design features, theory,practical considerations, analytical parameters of theelements, and areas of application of the first ofthese two techniques, electrothermal atomisation.Hardcover 135pp 0 851 86 777 4f 18.00 ($34.00) RSC Members fl3.50No. 5 Dithizoneby H. M. N. H. IrvingThe author of this monograph, who has beenclosely associated with the development ofanalytical techniques using this reagent for manyyears, and who has made extensive investigationsinto the properties of its complexes, has gatheredtogether a body of historical and technical data thatwill be of interest to many practising analyticalchemists.Hardcover 11 2pp 0 851 86 787 1f12.50 ($24.00) RSC Members f9.50No.6 lsoenzyme AnalysisEdited by D. W. MossThis monograph attempts to draw together the mostimportant experimental techniques which haveresulted from the modern recognition that enzymesfrequently exist in multiple molecular forms. Thismonograph also indicates the advantages andlimitations in isoenzyme studies of these modernexperiments.Brief Contents:Multiple Forms of Enzymes; Separation of MultipleForms of Enzymes; Selective Inactivation of MultipleForms of Enzymes; lmmunochemistry of MultipleForms of Enzymes; Catalytic Differences betweenMultiple Forms of Enzymes, Methods of ObtainingStructural Information, Selection of Methods ofAnalysis.Hardcover 171 pp 0 85186 800 2f12.00 ($23.00) RSC Members f9.00No.7 Analysis of AirbornePollutants in WorkingAtmospheresThe Welding and SurfaceCoatings Industriesby J. Moreton and N. A. R. FallaThis Monograph covers the following:Part I The Welding Industry: Airborne Pollutantsin Welding; Sampling of Welding WorkshopAtmospheres; Analysis of Welding Fumes andPollutant Gases.Part II The Surface Coatings Industry: Origin ofAirborne Pollutants in the Surface CoatingsIndustry; Collection and Analysis of GaseousAtmospheric Pollutants in the Surface CoatingsIndustry; Collection and Analysis of ParticulateAtmospheric Pollutants in the Surface CoatingsIndustry; Future Trends Relating to Sampling andAnalysis in the Welding and Surface CoatingsIndustries.Hardcover 192pp 0 85186 860 6f15.00 ($29.00) RSC Members f12.00No.8 The Sampling of BulkMaterialsby R. Smith and G. V. JamesThe literature of analytical chemistryexhaustively covers the many techniques nowavailable to the analyst.feature common t o a l l analyses, is in contrastonly sparsely documented. Comparatively feworiginal papers on this subject have beenpublished in the last fifty years; there are veryfew reviews available, and perhaps as a resultsampling is badly neglected in most instructionalcourses in analytical chemistry. ThisMonograph will go some way towards filling agap in the literature and should stimulateinterest in the development of sampling as afield of study.Brief ContentsIntroduction; Glossary of Terms; Establishment of aSampling Scheme; Sampling Theories; Apparatusfor Sampling; Sampling Methods; Appendices 1-4.Hardcover 200pp 0 851 86 81 0 Xf16.50 ($32.00) RSC Members f10.75Orders:RSC Members should send their orders to:The Membership Officer, The Royal Society of Chemistry30 Russell Square, London WC1 B 5DTAll other orders should be sent to:The Royal Society of Chemistry, Distribution Centre,Blackhorse Road, Letchworth, Herts. SG6 1 HNSampling, the oneThe Royal Society ofChemistrFebruary, 1983 THE ANALYST xvWiley Heyden J O U R ~ - _Announcing a new quarterly journalComputer En hanced CES SpectroscopyAn International JournalEDITOR-IN-CHIEF: REGIONAL EDITORS:Dr.H.A. Willis NORTH AMERICA: JA PA N:4 Sherrardspark Road, Professor G. Levy, Professor S. Sasaki,Welwyn Garden City,Herts, AL8 9JP, Syracuse University, School of Materials Science,England. Bowne Hall, Tempaku - Cho,EDITORIAL ADVISORY BOARDU.K.: Dr. A. Braithwaite, Nottingham, Dr. A. Carrick,Manchester, Dr. A.F. Fell, Edinburgh, Dr. B.J. Millard,BerkhamsteadU.S.A.: Professor R.E. Dessy. Blacksburg. Virginia,Professor P. Griffiths, Riverside, California,Dr. T . Hirschfeld, Livermore, California, ProfessorF. McLafferty, New York, Dr. R. Shaps. Philadelphia,Pennsylvania, Professor C.L. Wilkins, Riverside. California,Department of Chemistry,New York, NY 132 7 0.USA.To yohashi Institute of Technology,TOYO Lashi, Japan.GERMANY: Dr. W. Brernser, Ludwigshafen.Dr. K. Holland-Moritz, KolnJAPAN: Professor S. Minarni, Osaka, Dr. Y. Kudo,TokyoRUSSIA: Professor V.A. Koptyug. NovosibirskAIMS AND SCOPEComputer Enhanced Spectroscopy is devoted to therapid publication of papers describing novel practicalwork in which the performance of a spectrometer or achromatograph/spectrometer combination is enhancedwith a computer. Contributions centre on minicomputersand microcomputers, their application in the control andoperation of spectrometers, the acquisition andevaluation of data, the relevant software and user-developed programmes and the associated hardwareand interfaces. Papers on more sophisticated computersand spectrometers will also be welcome, especiallywhere the object is to interrelate the output of a numberof instruments or to involve data bases and SpectraCollections, or where there are implications for thesmaller installation.Short communications and Lettersto the Editor are also invited so that an interchange ofideas and results can be established. Reviews on topicsof special interest will be included.PAPERS APPEARING IN EARLY ISSUESH. Abe, T. Fujiwara, T. Nishimura, T. Okujama, T. Kidaand S. SasakiRecent advances in structure elucidation systems'CHEMICS'.J.D. Lipscornbe and R.W. SaloElectron Paramagnetic Resonance Spectrometer DataAccumulation and Reduction system for microcomputersR.S. Stradling, P.A. Ryan and J.D.WoodAutomated control of a mass spectrometer using a centralminicomputer and distributed microprocessors.H.D. Kronfeldt and S. WasserothComedy: A microcomputer based system for controllingpulsed dye laser experiments.D. Bianchi, F. Cavatorta and G. LenziData acquisition and spectrometer control with aRockwell AIM 65 microcomputer.D. Michailovic, J.F. Ryan and W.J. SiersternaA multipurpose computer interface for a scanning opticalspectrometer.P.L. Mains and M.J. HughesUsing a Hewlett-Packard minicomputer for the processingof gamma ray spectra from neutron activation analysis.A.F. Mehlkopf, A. Bax, J. Schmidt and T.A. TiggelrnanDesign, control system and software organisation ofmultipurpose nmr spectrometers.M . Carleer and J.P.WalgraeveMicroprocessor synchronisation of multichannel analyserto a monochromator.Subscription details: quarterly f50.00/$110.00A. Wiley Heyden journal published by John Wiley andSons Ltd.For a specimen copy and/or further informationplease write to the most convenient address below~~A201 for further information. See page xviixvi THE ANALYST February, 1983The Royal Society of ChemistrySpecialist Periodical ReportsEnvironmentalChemistry Vol. 2Senior Reporter: H. J. M. BowenThe first volume of this series was published in1975 and emphasized environmental organicchemistry whereas this second volume is deliber-ately slanted towards inorganic chemicals,covering the broad fields of the atmosphere andthe hydrosphere, soils, and human diets.Reviewers of all these subjects agree that far toolittle information is available on the chemicalforms of the elements in environmental reservoirs,thus laying down a challenge to analyticalchemists.A broad review of mycotoxins is how-ever included partly to redress the balance ofinorganic topics.Brief Contents :Inorganic Particulate Matter in the Atmos-phere :Methods of Sampling and Analysis; GeneralPhysical and Chemical Composition of Particu-lates; Characteristics of Emissions from SpecificSources; Atmospheric Transport and Dispersionof Particulates; Removal of Particulates from theAtmosphere; Effects of Airborne and DepositedParticulates; Future Research Needs and Con-clusions;The Elemental Content of Human Diets andExcreta :Outline of Ingestion, Absorption, Excretion;Met h odolog ica I Problems, In puts, 0 u tpu ts,Deficient Concentrations, and Oral Toxicities ofthe Elements;The Elemental Constituents of Soils:The Alkali Metals: Lithium, Sodium, Potassium,Rubidium, and Caesium; The Alkaline EarthElements: Beryllium, Magnesium, Calcium,Strontium and Barium; Titanium, Zirconium, andHafnium; Vanadium, Niobium, and Tantalum;The Lanthanides or Rare Earth Elements, andYttrium and Scandium; Molybdenum andTungsten; Chromium, Manganese, Iron, Cobalt,and Nickel; Copper, Zinc, and Cadmium; TheNoble Metals; Mercury; Boron, Aluminium,Gallium, Indium, and Thallium; Carbon, Silicon,Germanium, Tin, and Lead; Nitrogen, Phos-phorus, and Sulphur; Hydrogen and Oxygen;The Halogens: F, CI, Br, and I; Arsenic, Selenium,Antimony, and Bismuth; Thorium and Uranium;Radionuclides, Organic Soils;M ycotoxi ns :Biogenesis of Mycotoxins; The Importance ofMycotoxins in the Environment; Analysis ofMycotoxins; Occurrence in Food and AnimalFeed; Metabolism and Mode of Action of Myco-toxins; Control of Mycotoxins in the Food Chain;Occurrence, Distribution, and ChemicalSpeciation of some Minor DissolvedConstituents in Ocean Waters :Individual Elements; Additional Aspects ofChemical Speciation;Hardcover 301 pp 0 851 86 765 0Price f33.00 ($63.00) RSC Members f19.00Still available:Volume 1.Hardcover 21 2pp 0 851 86 755 3Price f15.50 ($30.00) RSC Members f7.50Special Package Price (Vols 1 & 2)Non-RSC Members only f39.00 ($75.00)Miscellaneous PublicationsThe Periodic Table ofthe ElementsThe Royal Society of Chemistry has produced acolourful wall chart measuring 125cm x 75cmcovering the first 105 elements as they existtoday.Each group is pictured against the same tintedbackground and each element, where possiblephotographed in colour and discussed withregard to its position in the hierarchy of matter.Additional information for each element includeschemical symbol, atomic number, atomic weightand orbits of electrons.This chart is particularly useful for both teachersand students and would make a worthwhileaddition to any establishment.Price f2.20 ($4.00) RSC Members f1.00Teacher Members f4.60 for 10Prices for The Periodic Table subject to VAT in the UK~~RSC members should send their orders to: The Royal Society of Chemistry, The Membership Officer, 30 RussellSquare, London WC1 B 5DT.Non-RSC members should send their orders to: The Royal Society of Chemistry,Distribution Centre, Blackhorse Road, Letchworth, Hens SG6 1 HN. Z,!M *The Royal Society of ChemistryBur lington HouseLondon W1V OBFe braary , I983 THE ANALYST xviiAnnual Reports on AnalyticalAtomic Spectroscopy Vol. 11Edited by M. S. Cresser and 6. L. SharpThis volume reports on current developmentsin all branches of analytical atomic emission,absorption and fluorescence spectroscopywith references to papers published andlectures presented during 1981. Much of theinformation is in tabular form for ease ofreference.Brief ContentsAtomization and ExcitationArcs, Sparks, Lasers and Low-pressure Dis-charges; Plasmas; Flames; ElectrothermalAtomization; Vapour Generation;InstrumentationLight Sources; Optics; Detector Systems;Instrument Automation; Complete Instru-ments; New Commercial Instruments;MethodologyNew Methods; Detection Limits, Precision andAccuracy; Standards and Standardization;ApplicationsChemicals; Metals; Refractories and MetalOxides, Ceramics, Slags, Cements; Minerals;Air Analysis; Water Analysis; Soils, Plants andFertilizers, Foods and Beverages; Body Tissuesand Fluids;Hardcover 388pp 0 85186 707 3Price f48.00 ($88.00) RSC Members f32.00RSC members should send their orders to: The Royal Society of Chemistry, The Membership Officer,30 Russell Square, London WClB 5DT.Non-RSC members should send their orders to: The RoyalSociety of Chemistry, Distribution Centre, Blackhorse Road, Letchworth, Herts SG6 1 HN. ,,~”.~The Royal Society of ChemistryBurlington HouseLondon WIV OBNNotice to SubscribersSubscriptions for The Analyst, Analytical Abstracts andAnalytical Proceedings should be sent to:The Royal Society of Chemistry, Distribution Centre,Blackhorse Road, Letchworth, Herts., SG6 I HN, EnglandRates for 1903 (including indexes)u K/Eire USA... 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ISSN:0003-2654    

DOI:10.1039/AN98308BP019

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

FEBRUARY 1983 Analyst Vol. 108 No. 1283 First Biennial National Symposium Atomic Spectroscopy Sheffield, UK, July 13-1 5, 1982 In July 1982, the above symposium was organised jointly by the Atomic Spectroscopy Group of the Analytical Division of the Royal Society of Chemistry and the Spectroscopy Group of the Institute of Physics. Judged by the number of delegates attending the meeting and the quality of the scientific presentations, the symposium represented a very successful new ven- ture, which will undoubtedly become a regular feature in the Society’s programmes. The aim of the symposium was to promote developments in fundamental and applied atomic spectroscopy in the UK, by providing an opportunity for academic and industrial workers to take part in both formal and informal exchanges of ideas.The scientific programme con- sisted of five Plenary Lectures, a number of specially invited lectures and sessions of contri- buted and poster papers. A special feature of the symposium was the Round Table Discus- sions conducted in an informal and relaxed atmosphere as a result of refreshments provided by Perkin-Elmer Ltd. in celebration of 25 years of their UK operation. These discussions yielded some interesting and important conclusions and they are reviewed in the current (February 1983) issue of AnaZyticaZ Proceedings. The Plenary Lectures were given by V. A. Fassel on “Inductively Coupled Plasmas : Their Future as Atomisation, Excitation and Ionisation Cells for Atomic Emission, Fluorescence and Mass Spectroscopy” ; J. M. Ottaway on “The Revolu- tion in Electrothermal Atomisation” ; R.Jenkins, on “Current Trends in Instrumentation and Techniques for XRF Analysis” ; T. C. Rains on “AAS : a Challenge in the Analysis of Environ- mental and Biological Materials” ; and G. F. Kirkbright on “Some Perspectives in Analytical Spectroscopy.” Invited papers were presented by L. de Galan, A. M. Ure, P. H. Scholes, G. S. Fell, B. Welz, B. J. Price, K. C. Thompson and K. Ohls. In the sense that most of these special lectures provided a review of a particular technique or field of application of atomic spectroscopy, it was the contributed and poster papers that presented a more informed view of current research and developments in analytical atomic spectroscopy in the UK and to some extent elsewhere.In collaboration with the organisers of the Symposium, the Analytical Editorial Board invited authors of original papers presented at the conference to publish their work in The Analyst. The result is this Special Issue of the Journal, which will provide a permanent record of some of the new material presented at the meeting. The publication of such a Special Issue is a new venture for The Analyst, but one which we believe will be of interest and benefit to both subscribers and authors. Individual copies of this issue are also available for personal purchase from the Royal Society of Chemistry Distribution Centre, Rlackhorse Road, Letchworth, Herts., SG6 1HN. The Atomic Spectroscopy Symposium was held at the Collegiate Crescent Site of Sheffield City Polytechnic, which provided an attractive and convenient location for the meeting. Both the national organising committee led by Dr. L. Ebdon and the local and scientific committees worked hard to ensure that the symposium was both scientifically worthwhile and informative, and that it was held in a relaxed and enjoyable atmosphere. All participants will be looking forward t o the Second Biennial National Atomic Spectroscopy Symposium, which is to be held in Leeds in 1984. J. M. OTTAWAY 137

ISSN:0003-2654    

DOI:10.1039/AN9830800137

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

138 Analyst, February, 1983, Vol. 108, $p. 138-144 Glassy Carbon Tubes in Electrothermal Atomisation - Atomic-absorption Spectrometry Leo de Galan, Margaretha T. C. de Loos-Vollebregt and Rene A. M. Oosterling Laboratorium UOOY Analytische Chemie, Technische Hogeschool, Jaffalaan 9, 2628 BX Delft, The Netherlands Preliminary results are presented on the use of glassy carbon tubes of standard dimensions for electrothermal atomisation - atomic-absorption spectrometry. In comparison with pyrolytically coated graphite tubes, the glassy carbon tubes show similar limits of detection provided that the same atomisation temperature can be realised. Glassy carbon tubes promise the following advantages : more uniform heating ; resistance against chemical attack ; a life- time of several thousands firings ; and a remarkably constant sensitivity.Keywords : Glassy carbon ; electrothermal atomasation ; atowic-absorption spectrometry The impressive performance of electrothermal atomisation (ETA) - atomic-absorption spectro- metry (AAS) for trace analysis relies to a large extent on the material from which the atomiser tube is fabricated. Traditionally, graphite has been and still is widely used, because it is strong, easily machinable and chemically pure, it has good electrical and thermal conductivity and it can be heated to 3300 K. A disadvantage of graphite is its permeability and affinity for chemicals. This property is exploited in adsorption columns, but forms a serious source of interferences in ETA - AAS, as has been documented in a recent and extensive review by Slavin and 1Manning.l The porosity of graphite can be reduced by the application of protec- tive coatings.Pyrolytic coatings, originally applied iiz sit% but nowadays supplied by the manufacturer, have shown more promise. Rapid deterioration of the pyrolytic coating and the graphite substrate under chemical attack from perchloric acid and ammonium nitrate has been ~bserved,~ but appears to have been overcome by improvements in the coating t e c h n i q ~ e . ~ Better resistance to chemical attack may be expected when solid pyrolytic graphite is used. This is confirmed by recent work on interference reduction through the use of platforms made from pyrolytic g r a ~ h i t e . ~ Complete ETA tubes have also been made entirely from pyrolytic graphite, but as a result of the anisotropy of the material only in experiments with very fast heating.6 However, there is an alternative carbonaceous material that is isotropic and lends itself easily to the fabrication of complete tubes.This is called glassy carbon or vitreous carbon. The material derives its name from its glassy surface, its strength and hardness, its impermea- bility to gases and its resistance to chemical attack. The latter two properties combined with acceptable electrical and thermal conductivity warrant exploration of glassy carbon as ETA material. The preparation of glassy carbon for use as ETA tubes has been described in a patent.' Tubes of standard dimensions can be obtained from various manufacturers and chemical purity, which was insufficient some years ago,8 has been improved lately.The review by Van der Linden and Diekerg is valuable for the information it contains of the material itself. Only a few references have been found to the application of glassy carbon in ETA - AAS. The potential utility was demonstrated by Yanagisawa and Takeuchi,lo who used a strip of glassy carbon enclosed by a Pyrex dome to observe signals from copper and strontium. In a later study by the same group,ll a glassy carbon tube was used to measure degrees of atomisation in ETA - AAS, but the analytical potential was not discussed. In the meantime, Volland et aZ.12 investigated different carbonaceous tube materials and found that their glassy carbon tubes were thermally too unstable to last more than a few firings.Prech and co-workers, who like Yanagisawa and Takeuchi used Tokai material, have been more successful. In a largely fundamental study on the atomisation of phosphorus the use of a glassy carbon tube was briefly mentioned.13 In another, more detailed study on arsenic Metal-lined tubes2 are restricted in upper temperature. Glassy carbon is widely used in electrochemical analysis.DE GALAN, DE LOOS-VOLLEBREGT AND OOSTERLING 1 39 some interesting differences between glassy carbon and ordinary graphite were observed.14 In glassy carbon arsenic is released at a lower temperature, to a large extent as molecules, so that the analytical sensitivity is lower than in graphite tubes. On the other hand, the atomic-absorption peak is much more symmetrical in glassy carbon, because volatilised arsenic is not re-deposited, as is confirmed by radioactivity measurements.In the absence of contrary information it seems that in all of these s t ~ d i e s l ~ - ~ ~ the graphite and the glassy carbon tube have mutually similar dimensions and heating characteristics. In view of the different electrical and thermal properties of the two materials, this is surprising and raises questions as to the nature of the glassy carbon used. It appears that glassy carbon is a potentially highly suitable material for electrothermal atomisers, but has not yet been thoroughly investigated. Therefore, we have started a systematic study of glassy carbon for ETA - -4AS. Some preliminary results are reported in this paper. Experimental Glassy carbon tubes of standard dimensions (length 28 mm, 0.d.8 mm, i.d. 6 mm) were obtained from Le Carbone-Lorraine (Paris, France), Tokai (Tokyo, Japan) and Sigri Elektro- graphit GmbH (Meitingen, Germany). Holes were drilled for sample introduction and the ends were machined to fit the tubes into a standard HGA 500 housing. All experiments were performed with Perkin-Elmer equipment, i.e., a Model 5000 atomic-absorption spectro- meter, a Model 500 power supply for ETA and a Model AS 40 autosampler. Data were fed into a Model 3500 Data Station, modified by us to display both the net signal and the back- ground absorbance. For comparison, standard Perkin-Elmer pyrolytically coated tubes were used with a temperature programme taken from the manufacturer's manual. Unless otherwise stated maximum power heating was used with either tube.Standard chemicals of analytical- reagent grade were introduced as aqueous solutions in a volume of 20 pl. Over a period of 3 months most experiments were carried out with a single tube from Le Carbone-Lorraine. So far only a few data have been obtained with the Tokai and Sigri tubes. Hard-copy output was recorded with an HP 7225 A plotter. Results and Discussion Heating Characteristics of Glassy Carbon Some relevant properties of different brands of glassy carbon are compared with time of ordinary graphite in Table I. The mechanical properties are largely similar, i . c . , a density of 1.5 g ~ m - ~ , a strength of 500 N cm-2 and a thermal expansion coefficient of 2 x 10k6 K The glassy carbon described in tlie patent' still has a high porosity and significant gas permeability.However, after thermal treatment, as has been done for the other two entries in Table I, glassy carbon has a much lower porosit; and gas permeability than ordinary graphite. Finally, glassy carbon also differs from ordinary graphite in having a lower thermal conductivity and a higher electrical resistivity. For electrothermal atoinisers of equal dimensions this leads to different heating characteristics. The data in Table I refer to room temperature. IVhereas tlie electrical resistivity o f ordinary graphite is virtually independent of temperature, Fig. 1 shows that the resistivity of glasI;. carbon decreases with increasing temperature. In fact, at common atomisation temperatures the resistivity may come even closer to that of graphite.This behaviour has several consequences. TABLE I PROPERTIES OF GLASSY CARBON Gas Thermal Electrical Deiisitv/ Porosity, permeability/ conductivity/ resistivity/ 0 cn12 s ' \\' c111-l K 10 12 cni l<eference hhterial g c111-~ 0' Graphite . . .. 1.7 -20 0.1-1 0 1 0.6-1 15 . . 1-1 4 -50 10-3-10-7 0 . 1 1 0 7 . . 1.5 0 35 -10-1' 0 0s 5 16 . . 1.45 0.3 10-7-10 9 0.1 3.5 17 Glassy carbon140 DE GALAN et a2. : GLASSY CARBON TUBES Analyst, Vol. 108 With increasing temperature the local resistance decreases and heat dissipation becomes more pronounced at the ends. The low thermal conductivity reduces the heat losses to the cooled electrodes. As a result, the combination of a low thermal conductivity and a negative temperature coefficient of the electrical resistance may produce a more uniform heating of the glassy carbon tubes.When power is supplied to the tube, it will initially heat up in the centre. Le Carbone-Lorraine 4- m ll Graphite G I , , I 1000 2 000 3 000 0 Tern peratu re/K Fig. 1. Variation of electrical resistivity of glassy carbon and graphite with temperature, from information supplied by the manufacturers.15-1’ Although this assumption has not yet been verified by actual temperature measurements along the tube, it might explain the absence of lead deposits at the ends of the tube, a phenomenon that is frequently observed with graphite tubes. Of course, the smooth and impenetrable surface of the glassy carbon also minimises the formation of deposit^.'^ For voltage-controlled power supplies the comparatively high resistance of glassy carbon predicts a relatively low heating rate, at least initially.Indeed, when the ashing step is deleted from the temperature programme, a slow initial heating is readily observed. With increasing tube temperature the decreasing resistance will enhance the heating rate. Conse- quently, when an ashing step is included] as is customary in ETA - AAS analysis, the effect of slower heating during atomisation will be small. According to the manufacturer’s specification, glassy carbon, grade V 25, from Le Carbone- Lorraine can be used up to 2800 K, whereas the grade GC-30s Tokai material can be heated to 3300 K. No upper limit is specified for the Sigri tube, but after a few runs with maximum power (i.e., 2500 K, see below), this tube was destroyed.In this study very high tempera- tures were not realised. The HGA 500 power supply is limited to a maximum voltage of 7 V, designed to heat a graphite tube to 3300 K. The higher resistance of the glassy carbon tube lowers the power dissipation and hence the final tube temperature. An estimate of the final temperature of the glassy carbon tube was obtained with the facilities of the HGA 500. The voltage control corresponds to a temperature scale calibrated for graphite. With the maximum power mode the voltage is regulated by the signal from a photodiode focused at the ETA tube. The surface of well used glassy carbon tubes looks similar to graphite tubes. Therefore, for the present, we assume that glassy carbon and graphite have equal emissivity.I t is now possible to draw up a temperature scale for glassy carbon. For example, with a graphite tube installed let the photodiode be adjusted to have the power supply heat the graphite tube to 2300 K. Next, the graphite tube is replaced by a glassy carbon tube and the voltage is increased until the photodiode lights up again. At this voltage (corresponding to 3000 K on the graphite scale) we know that the glassy carbon tube has reached a tempera- ture of 2300 K. The curve was confirmed by direct temperature measurements.18 Obviously, for a certain setting of the HGA 500 power supply graphite is heated to a higher temperature than glassy carbon, in agreement with the differences in electrical resistivity. The maximum temperature reached for glassy carbon is In this way, the complete graph in Fig.2 was constructed.February, 1983 I N ELECTROTHERMAL ATOMISATION AAS 141 2500 K. As has been noted in the introduction, previous reports on the use of glassy carbon tubes in ETA - AAS1°-14 devote little attention to the heating characteristics of glassy carbon. However, recently Styris and Kayelg published a heating curve for a vitreous carbon tube with a wall thickness of 2 mm and a length of 39 mm using another commercial power supply. The heating curve rises fairly slowly and levels off at 2500 K. There are two ways to reach higher temperatures: one is to decrease the resistance of the glassy carbon tube by increasing the wall thickness and the other, more attractive, possibility is to increase the upper voltage of the power supply to, e.g., 15 V.3000 I CJ I I I Fig. 2. Temperature reached with glassy carbon and graphite tubes of equal dimensions for the same setting of the HGA 500 power supply. Analytical Results I t can be seen that during the first ten firings the peak height and hence the analytical sensi- tivity increase steadily and then become constant. This phenomenon was observed each day. Possibly the structure of glassy carbon is slightly modified during the first few firings and returns to its original state slowly overnight. Curiously, it is necessary to execute a sequence of ten (blank) firings. Simply heating at maximum power for an equivalent amount of time is not sufficient. However, with this daily pre-treatment the sensitivity remains remarkably constant.Over a period of 3 months and a succession of more than 2500 firings the sensitivity remained constant to within 5%. The glassy carbon tubes from Le Carbone-Lorraine, Tokai and Sigri show equal sensitivity for the determination of cadmium. Moreover, the same sensitivity has been obtained with two different tubes from Le Carbone-Lorraine. When inspected visually, no degradation of the inner surface of the tubes is observed. In contrast, the outside of the tube reveals some Fig. 3 presents the peak height of the cadmium signal observed in successive firings. The reasons for this behaviour are not clear. U 0 0.4 4 z 2 0.2 Y I 1 500 2 500 a O ' 2 4 6 8 1 8 1 0 0 500 ' Number of firings Fig. 3. Variation of analytical sensitivity with number The measure- of firings of a single glassy carbon tube.ments extended over 3 months.142 A~zal_vst, VoL. 108 deposit of carbon dust. So far, we have not been able to determine the lifetime of a glassy carbon tube. The specimen used for the data in Fig. 3 was destroyed when the plastic tube alignment tool was accidently left in the sample injection hole during atomisation. However, over this period the tube was subjected to heavily salted and strongly acidic solutions (1 M perchloric acid). Although chemical interferences were noted, the tube did not suffer and the sensitivity was restored when aqueous solutions were analysed again. These observations demonstrate the resistance of glassy carbon to chemical attack. Sensitivity data for a number of elements are presented in Table I1 for pyrolytically coated graphite tubes and Le Carbone-Lorraine glassy carbon tubes. A few elements were also run on glassy carbon tubes from Tokai and Sigri.No significant variations in sensitivity were observed between tubes from different manufacturers. The results obtained with the pyrolytically coated tubes using the temperature programme advised in the Perkin-Elmer manual were generally and sometimes significantly better than the sensitivity checks provided in that manual. DE GALAN et al. : GLASSY CARBON TUBES The data in Fig. 3 refer to pure aqueous solution. This demonstrates that the instrument is functioning properly. TABLE I1 CHARACTERISTIC CONCENTRATIONS (pg 1-1 FOR 0.0044 ABSORBANCE UNIT) I N GLASSY CARBON AND PYROLYTICALLY COATED TUBES Wavelength/ Elemcnt nm Ag .. . . 328.1 A1 . . . . 309.3 Bi . . . . 223.0 Cd . . . . 228.8 co . . . . 240.7 Cr . . . . 357.9 c u . . . . 324.7 Fe . . . . 248.3 Mn . . . . 279.5 Ni . . . . 232.0 Pb . . . . 283.3 Sb . . . . 217.6 Si . . . . 251.6 sn . . . . 224.6 Ti . . . . 365.3 v . . . . 318.4 Pyrolytically coated graphite T a r a c t c r i s t i c ’ Tat concentration 1500 0.03 2 700 0.5 1400 1 1500 0.1 2 500 0.25 3 000 0.15 2 500 0.4 2 300 0.4 2 200 0.1 2 600 0.3 2 300 1 2 300 1.1 2 300 4.5 3 000 4.5 2 850 2.2 3 000 57 Glassy carbon r-----Characteristicl T*at concentration 1850 0.07 2 500 0.8 1850 2 2 350 0.1 2 500 0.7 2 500 0.7 2 500 0.9 2 500 1.3 2 500 0.3 2 500 5 2 500 1 2 500 1.2 2 500 3 2 500 2.2 2 500 200 2 500 11 * Limited to 2500 K (see Fig.2). 7 Ordinary graphite. When the data for glassy carbon are considered, two general conclusions can be drawn. Those elements which atomise at a relatively low temperature (c.R., Cd, Mn, Sb) yield sensi- tivities that are comparable to the values observed with pyrolytically coated graphite tubes. Differences of up to a factor of two in favour of pyrographite may be attributed to the slower heating of glassy carbon, especially at low atomisation temperatures. On the other hand, and not surprisingly, elements that require atomisation temperatures over 2500 K (e.g., Ni, Ti) yield appreciably poorer sensitivity with the glassy carbon tubes as used in this investigation. For some of these elements (Cu, V, Ti) incomplete volatilisation of the analyte was also apparent from memory effects observed in consecutive blank firings. Significant improvement may be expected when the atomisation temperature for glassy carbon tubes can be increased over its present upper limit of 2500 K as discussed above.A pronounced influence of the tube material is also apparent from the differences in peak shape observed between pyrographite and glassy carbon. Some examples are shown in Fig. 4. These signals were obtained with the atomisation temperatures indicated (cf., Table 11) and following a brief ashing step at 800 K to enhance the heating rate of the glassy carbon tube. For the 28 mm long tubes used in this study the removal of the analyte from the atorniser is probably fast enough to identify the peak shapes as the analyte introductionFebruary, 1983 I N ELECTROTHERMAL ATOMISATION AAS 143 0.4 0.2 0 0.4 0.2 $ 0 10 p.p.b.Cd Glassy carbon 2350 K Pyrog raphite 1500 K 1 1 20 p.p.b. Cu 0.2 I Glassy carbon I 2500 K Pyrographite 2500 K 0.1 I I 1 2 0 1 2 3 0 1 2 3 4 5 L 0 2 0.6 a 0.3 0 0.6 0.3 0 *O0 P.Pmb* si Glassy carbon Pyrographite Pyrographite 3000 K 2300 K 0 1 2 0 1 2 3 4 5 Time/s Fig. 4. Examples of atomic-absorption signals measured in glassy carbon and pyro- lytically coated graphite tubes. Atomisation temperatures are indicated. function.20 The peak shape is then determined by a combination of analyte release from the tube wall and atomisation reactions in the gas phase. The rapid release of the very volatile cadmium reflects the non-adhesive character of glassy carbon, even more so than pyrolytically coated graphite.For the less volatile antimony this effect is not observed, probably as a result of the lower heating rate of glassy carbon. A t the present stage of investigation it is too early for a fruitful discussion of peak shapes, because for most elements the temperature programme is not optimal. This is certainly so for copper, where observed memory effects stress the need for higher atomisation temperatures. Some preliminary experiments on matrix effects demonstrated the presence of chemical interferences. However, a closer investigation has been postponed until the glassy carbon tubes can be heated to optimuin temperatures. A blank signal for silicon was observed with the Sigri tube. According to the manufacturer's specification ,17 the Tokai tubes contain aluminium, iron and silicon at the parts per million level and copper, magnesium and boron at sub-parts per million trace levels.No blank signal was observed for copper, but aluminium, iron and silicon gave strong blank signals that persisted even after several hundred firings: aluminium, 0.26; iron, 1.5; silicon, 0.1 absorbance unit. In contrast, the glassy carbon from Le Carbone-Lorraine is remarkably pure. For none of the elements listed in Table I1 was a blank signal observed with tubes from Le Carbone-Lorraine. The purity of the glassy carbon materials deserves attention.8 Conclusion The results obtained so far have shown that glassy carbon is a very interesting material for Tubes of customary dimensions electrothermal atomisers in atomic-absorption spectrometry.can be obtained from several sources and at a similar cost to graphite tubes.144 DE GALAN, DE LOOS-VOLLEBREGT AND OOSTERLING The full potential of glassy carbon can be appreciated only when the tube dimensions or, preferably, the ETA power supply has been adapted to the different electrical and thermal properties of glassy carbon. With such modifications it should be possible to reach tube temperatures of 3300 K relatively fast. Peak shapes and detection limits might then be comparable to or better than those observed in ordinary or pyrolytically coated tubes. It would then be possible to exploit the major advantages of glassy carbon observed so far, i.e.. the great resistance to chemical attack, the extremely long lifetime of the tube and, probably most important, the constancy of the analytical sensitivity during the tube’s lifetime.The financial support of one of the authors (M.C.T. de L.-V.) and the instrumentation put at our disposal by Perkin-Elmer, Norwalk, CT, USA, are gratefully acknowledged. Dr. W. Slavin of the same company verified the temperature dependence of the glassy carbon tube shown in Fig. 2. Prof. A. Cedergren, Dr. W. Frech and Dr. E. Lundberg of the Depart- ment of Analytical Chemistry, University of Umei, Sweden, are thanked for helpful dis- cussions and comments. Useful information on the electrothermal properties of glassy carbon was provided by ing. J. W. M. van Uffelen from the Department of Electrical Engineering, Technische Hogeschool, Delft . 1. 2.3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. References Slavin, W., and Manning, D. C., Prog. Anal. At. Spectrosc., 1982, 5, 243. L’vov, B. V., and Pelieva, L. A., Can. J . Spectrosc., 1978, 23, 1 . Montgomery, J. R . , and Peterson, G. N., Anal. Chim. Acta, 1980, 117, 397. Slavin, W., Manning, D. C., and Carnrick, G. I<., Anal. Chem., 1981, 53, 1504. Slavin, W., Carnrick, G. R., and Manning, D. C., Anal. Chem., 1982, 54, 621. Chakrabarti, C. L., Wan, C. C., Hamed, H. A . , and Bertels, P. C., Anal. Chern., 1981, 53, 444. Knippenberg, W. F., Lersmacher, B., Lydtin, H., and Schelhas, K., Offenlegungsschrift N E 2702189, Frech, W., personal communication. Van der Linden, W. E., and Dieker, J . W., Anal. Chim. Acta, 1980, 119, 1 . Yanagisawa, M., and Takeuchi, T., Anal. Chim. Acta, 1974, 23, 364. Kitagawa, K., Ide, Y . , and Takeuchi, T., Anal. Chim. Acta, 1980, 113, 21. Volland, G., Kolblin, G., Tschopel, P., and Tolg, G., 2. Anal. Chem., 1977, 284, 1 . Persson, J. A., and Frech, W., Anal. Chim. Acta, 1980, 119, 75. KoreEkova, J., Frech, W., Lundberg, E., Persson, J . A., and Cedergren, A., Anal. Chim. Acta, 1981, Manufacturer’s information, Ringsdorf, Bonn-Had Godesberg, Gcrniany, 1982. Manuiacturer’s information, Le Carbone-Lorraine, Paris, France, 1982. Manufacturer’s information, grade GC-30 material, Tokai, Tokyo, Japan, 1982. Slavin, W., and Manning, D. C . , personal communication. Styris, D. L., and Kaye, J. H., Anal. Chem., 1982, 54, 864. Van den Broek, W. M. G. T., and de Galan, L., Anal. Chem., 1977, 49, 2176. BRD, 1978; US Pat., 4 204 769, 1980. 130, 267. Received July 14th, 1982 Accepted September 20th, 1982

ISSN:0003-2654    

DOI:10.1039/AN9830800138

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

Analyst February 1983 Vol. 108 pp. 145-152 145 Intensities of Some Spectral Lines from Hollow-cathode Lamps Christopher Howard Marjorie E. Pillow and Edward B. M. Steers* and Donald W. Ward School of Applied Physics The Polytechnic of North London Holloway London N 7 8013 Cathodeon L t d . Nu$eld Road Cambridge CB4 1TF The relationship between spectral line intensity 1 and discharge current i is examined as part of an investigation of low pressure (1-20 Torr) hollow-cathode discharges in neon for various cathode dimensions. An equation, I = Ai ( 1 + Ci)/(l + Bi) deduced by balancing likely excitation and de-excitation processes can be fitted within the limits of experimental accuracy to measured I versus i graphs. Here A depends on one-stage excitation C on the relative importance of two- and one-stage excitation and B on the relative importance of collisional and radiative de-excitation.The values of B and C for individual lines and their dependence upon pressure and upon cathode dimensions together with the possible role of self-absorption are discussed. Keywords Hollow cathodes ; excitation pyocesses ; spectral intensity ; neon Hollow-cathode discharges have been used for many years for the production of intense, narrow spectral lines and in more recent years have been extensively employed in analytical atomic spectroscopy mainly as sealed lamps forming the line source in atomic-absorption spectroscopy but also as a demountable source for samples in emission spectroscopy. Despite this the details of the excitation processes are as yet imperfectly understood; this paper presents some preliminary results from a continuing extensive study of hollow-cathode lamps.In hollow-cathode and other low-pressure low-current sources thermodynamic equilibrium does not exist and the populations of the excited states of the carrier gas and of the atoms sputtered from the cathode cannot be characterised by a “temperature.” A possible method of studying excitation processes under actual discharge conditions is the investigation of the relationship between the intensity of specific spectral lines and the discharge current. In this paper a theoretical interpretation of such relationships with physically significant parameters, is deduced by balancing excitation and de-excitation processes and shown to be in good agreement with experimental results for a number of Ne I and Ne I1 lines.Discussion of the intensity of spectral lines emitted by sputtered cathode atoms is reserved for later work; whilst most of the applications of hollow-cathode lamps involve such lines their intensities depend on two further processes (the sputtering of the atoms and the diffusion and excitation of the sputtered atoms) and can only be considered satisfactorily when the basic processes occurring in the carrier gas have been established. I n a review on hollow-cathode discharges Pillowl has pointed out that whilst in the lamps now used for atomic-absorption spectroscopy and emission spectroscopy the cathode is typically of 3 mm bore most of the published work on the physical properties of hollow-cathode discharges (electron energy distributions field strengths etc.) has been carried out using much larger cathodes (10-30 mm bore).The results presented in this paper are part of a wider investigation currently in progress which includes the effects of cathode dimensions and carrier gas pressure on the electrical and spectral properties of the discharge. The “similarity principle” predicts that geometrically similar discharge tubes typified by linear dimensions d, d would exhibit the same electrical behaviour if the gas pressures used PI P2 were such that P,d = P2d2. This is unlikely to hold exactly in instances where as in a hollow cathode, photo-emission has a significant role in cathode emission; however it was found here that a large cathode at low pressures gave results closely resembling those for a smaller cathode at correspondingly higher pressure.It is clear from a visual examination of a hollow-cathode discharge that the intensity varies within the cathode; previous workers such as Lompe et aZ.2 and Kagan and c o - ~ o r k e r s ~ - ~ have shown that the radial intensity distribution varies greatly with pressure and from line to * To whom correspondence should be addressed 146 HOWARD et al. INTENSITIES OF SOME Analyst Vol. 108 line and that this can be linked with electron energy distributions. This variable intensity distribution complicates the measurement of line intensity; three approaches may be used a small image on the spectrometer slit may be used to give the total intensity; with a larger image the intensity from a diametral or other slice may be recorded; and by restricting the slit height a particular region of the discharge (frequently the axial region) may be studied.In the present investigations radial intensity distributions were recorded so that total, diametral and axial intensities could be derived. The results in this paper are based on axial intensities recorded as discussed below. Experimental Some preliminary measurements were made using sealed hollow-cathode lamps from Cath-odeon Ltd. Some of these were of routine manufacture and some were provided specifically for this work. The majority of the work was carried out using a demountable hollow-cathode lamp (Fig. 1 ) ; the experimental chamber formed part of a specially designed metal high-vacuum system which could be evacuated to Torr for the de-gassing of the hollow-cathode chamber.After de-gassing a charge of research-grade neon could be introduced at the desired pressure and gas purity maintained with a non-evaporable getter (Societa Appar-ecchi Electtrici e Scientifici Stl71TM). Various sizes of mild-steel cathodes were used with a stainless-steel ring anode. Mica and glass screens were used to prevent unwanted discharges. All the intensity measurements were made using a 0.8 m focal lengthf/10 Ebert mono-chromator (Philips) with a 1200 lines mm-l grating used in the first order and an EM1 9789QA photomultiplier. The signal was amplified and recorded on a Honeywell Brown chart recorder. An image of the central plane of the cathode was focused on the entrance slit of the monochromator using two plane mirrors and a concave mirror operated close to its axis.The magnification of the system was adjusted according to the cathode size and this influenced the solid angle accepted from the source. The radial intensity distribution was recorded by rotating the concave mirror slightly by a slow mechanical drive to scan the diameter of the cathode image horizontally across a short slit (height about one tenth of the image diameter). The centre of the image yielded the “axial intensities.” Cathode dimensions Bore/mm Depth/mm 3 10 6 20 15 50 Fig. 1. Sectional view of demountable hollow-cathode lamp. A Stainless-steel ring anode; C cathode; G getter; L insulated lead-throughs M mica disc Q, fused quartz viewport; S, S, glass sheaths; S, fused silica sheath; V connection to high-vacuum system February 1983 SPECTRAL LINES FROM HOLLOW-CATHODE LAMPS Results and Discussion Experimental Results 147 In the preliniinary experiments with a sealed iron hollow-cathode lanip axial intensity versus current graphs were plotted for a number of spectral lines and showed a wide variety of form; typical graphs are shown in Fig.2. For Ne I lines a linear graph was obtained for a few lines with upward curvature for some others but many showed pronounced downward curvature even when self-absorption was not likely. Ne I1 lines usually gave a straight line or upward curving graph whilst the spectral lines of the cathode material showed very pronounced upward curvature. Similar results were obtained for copper and molybdenum cathodes.20 15 VI t 3 .l- .-2 2 .= 10 -e i 5 0 ilmA Fig. 2. Experimental intensity ( I ) vettius current (2) graphs for a sealed iron hollow-cathode lamp (cathode 3 mni bore 10 mm deep). The arbitrary intensity units differ for each line. Wavelength 1 Ne I 363.4; 2 Xe I 470.9; 3 Ne I 665.2; 4 Ne I 614.3; 5 Ne I1 337.4; and 6 Fe I 382.7 nm. On the basis of this survey the spectral lines listed in Table I (and for Ne I lines sliown 011 the energy level diagram Fig. 3) were chosen for more detailed study with different cathode dimensions at various gas pressures in the demountable discharge lamp. The radial intensity distributions were recorded in all instances and were compatible with other published pressure has a marked effect on these distributions whilst for most lines current has a very limited effect.Accordingly axial intensities have been considered for this first treatment of the results. Smooth trends were observed with pressure and cathode size. TABLE I NEON LINES STUDIED IN DETAIL (OR REFERRED TO IN THIS PAPER) Species A/nm Transition Upper level/eV N e I . . . . 363.4 4p[+lo + 3s’[8]! 20.3 470.9 5d[$]! -+ 3~5$!,~ 21.0 588.2 3p’[Q] + 3s[1&]; 18.7 614.3 3p[13l2 += 3s[l&]O 18.6 665.2* 3p[Ql0 -+ 3s’[+]; 18.7 585.2 3p’[+] -+ 3s [2]1 19.0 Ne I1 . . . . 337.4* 3d 4D3,2 + 3p 4D,,2 21.6 + 34.9 348.1 3~”~P,,,-t 3s” ‘ S ) 21.6 + 37.7 348.2 3p ‘P*” + 3s 2P3,2 21.6 + 31.4 * Sealed lamps only 148 Analyst Vol. 108 Theoretical Interpretation In a paper that gives probably the most extensive previous coverage of intensity current relationships MushalO used a log - log plot for his results; he obtained very approximately straight lines of differing gradients but there is no physical reason suggested for the various fractional powers obtained.Computer curve-fitting techniques showed that power laws were not adequate to describe the present results and the basic processes involved were therefore, considered in detail. For a discharge in a steady state the population of an excited state is determined by a balance between the rates of radiative and collisional processes. The latter depend upon the number density (No) of atoms in the ground state the number density (n) of electrons their velocity and energy distributions and the relevant excitation and de-excitation cross-sections; n is related to the current density i / S (S being the effective cross-sectional area of discharge) by the equation ;/S = nvd.The electron drift velocity ud will be approximately constant at a given pressure if the voltage across the relevant section of the discharge is constant; hence for a given pressure and discharge configuration n will be approximately proportional to i. HOWARD et al. INTENSITIES OF SOME 16.8 16.6 An excited level Ex (Fig. --M I I -M lonisation 22.0 1 k k Ground state 0 Fig. 3. Partial energy level diagram for Ne I showing transitions discussed in the text. Note the expanded sections of the energy scale. M denotes the meta-stable levels.Wavelengths in nano-metres. 4) may be populated from the ground state E in a single step by 00 electron collisions and the rate of this process will be proportional to NoJn(E)v(E)QOz(e)de where n(E) is the number density of electrons of energy E and velocity u(e) and Qoz(E) is the excitation cross-section from the ground state to level x for such electrons. This expression can be written as No ni?jox. The rate at which the level x is de-populaled by radiation will be N,/T where T is the radiative lifetime of the state and its value is independent of the collision processes. February 1983 SPECTRAL LINES FROM HOLLOW-CATHODE LAMPS t 149 Fig. 4. Excitation (single- and two-stage) and de-excitation pro-cesses. If these were the only processes determining the steady condition it would follow that N = No nvQ0,7 and hence that N is proportional to n and therefore to current.In such an instance the intensity of a line originating from level x should be proportional to current. A two-stage process via an intermediate level E may also be possible and by similar reasoning this would give an additional excitation rate proportional to No n2 v Qoz v Qyx and line intensity would include a term proportional to the square of the current and could be written I = ai + pi2. For lines in the spectrum of a neutral atom the two-stage process is possible if metastable levels exist as in neon to provide a suitable intermediate levely. For a singly ionised spec-trum the level y might be the ground state of the ion or a metastable state of the neutral atom or ion.Whilst the expression I = ai + piz gave an adequate description of the behaviour of some Ne I1 lines it was not generally satisfactory for the upward curving lines; moreover the major-ity of the Ne I lines showed a downward curvature at least under some conditions; this curvature was more marked for lines with higher upper levels for which collisional de-excitation, either to the ground state or to adjacent states becomes more probable. The rate for colli-sional de-excitation to the ground state is N n$, and the total collisional de-excitation rate is N n qxz. Balancing rates of single and two-step excitation processes against rates of collisional de-excitation and radiative de-excitation leads to the expression - -Hence it can be shown that I = Ai(1 + Ci)/(l + Bi) where A depends on the magnitude of single-step excitation B on the relative importance of collisional and radiative de-excitation and C on the relative importance of two-stage and single-stage excitation.Application to Experimental Results The above expression has been fitted to the results from the demountable hollow-cathode tube in which the pressure was independent of current using both graphical and least-squares methods. The agreement is very satisfactory for many examples as illustrated in Figs. 5-8, with the deduced values of the constants listed in Table 11. In some instances where the cathode dimensions and pressure used led to very low axial intensities the experimental scatter was too large for satisfactory fitting and additional experimental work is being carried out.For lines showing pronounced downward curvature ( A 363.3 470.9 and 585.2 nm) good fits are obtained with a large value of B and with C having a smaller value appreciably different, however from zero. The relative magnitudes of B and C are certainly significant and it is clear that for these lines collisional de-excitation is very important and there is a small amoun 150 HOWARD et al. INTENSITIES OF SOME Analyst Vol. 108 of two-step excitation. The absolute values of the constants are less well defined with the current ranges used in this preliminary investigation; it can be seen from the equation that as the current increases the ratio of the constants becomes more important than the absolute values and further work is in progress to extend the current range to lower values and to obtain more accurate results for the lower intensities.30 25 v) 4- 'C 20 .- L- 1 5 -- 2 40 ---/x'x X / YM 10 0 5 10 15 20 ilmA Fig. 5. Intensity Z I ~ Y S U S current graph for demountable hollow-cathode lamp. The lines arc graphs of 1 = Ai (1 + Cz)/(l + Bi), with the values of the constants derived by a least-squarcs fit (sce Table 11) ; the symbols indicate experimental results. The arbitrary intensity units are constant for a given wave-length and cathode size. Wavelength Nc I, 363.4 nm. Cathode 3 mrn bore 10 mm deep. Pressures A 3.5; B 5 ; C 7.5; D 10; and 141 20 Torr. Where the I 'UCYSUS i graph shows upward curvature the fit is often rather less satisfactory, but it appears that for Ne 11 lines the best fit occurs for B zero whilst for Ne I lines a small non-zero value of B is required for a good fit.iImA Fig. 6. As Fig. 5. Wavelength Ne I, 363.4 nm. Cathode 15 mm bore 50 mm deep. Prcssures A 1 ; B. 2; and C, 5 Torr February 1983 SPECTRAL LINES FROM HOLLOW-CATHODE LAMPS 151 Where the experimental data yield a straight line A is accurately determined but whilst it is clear that B and C are approximately equal they cannot be determined uniquely and such data have not been analysed in detail. From Table I1 it can be seen that for h 363.4 nm there is a smooth variation of A and B with pressure for the small cathode (3 mm bore x 10 mm depth) and almost constant values for the large cathode (15 x 50) whilst for h 470.9 nm a marked variation with pressure occurs in the large cathode.Such apparently erratic behaviour is not surprising as the excitation and de-excitation cross-sections depend on electron energy in differing ways for various spectral lines, and changing the pressure has a marked effect on the axial electron energy distribution as is shown by the variation in radial intensity distributions. The detailed reasons for these trends in A B and C are still under consideration. 0 5 10 15 20 ilmA Fig. 7. As Fig. 5. Wavelength Ne I, 470.9 nm. Cathode 15 mm bore 50 mm deep. Pressures A 1 ; B 2 ; and C , 5 Torr. Effect of Self-absorption In neon the visible and near ultraviolet spectra are due to transitions between highly excited levels and resonance transitions lie in the vacuum ultraviolet region.However two of the lower levels involved in the visible and ultraviolet spectra are metastable (Fig. 3) and appreciable populations of metastables could lead at higher currents to self-absorption or self-reversal of transitions to these levels and hence reduced intensity. In this work two such lines ( A 614.3 and 588.2 nm) originally chosen for their upward curvature consistently yielded I versus i graphs that were slightly S-shaped (Fig. 2). In a separate experiment the profiles of these lines emitted from sealed lamps recorded using a pressure-scanned Fabry Perot inter-ferometer showed at high currents self-absorption and self-reversal the magnitude of which depended on the lamp used and was not observed for lines with non-metastable lower levels.0 5 10 15 2c ilmA Fig. 8. As Fig. 5 . Wavelength Ne 11, 348.1 nm. Cathode 6 mm bore 50 mm deep. Pressures A 2.5; B 5; and C, 7.5 Torr 152 HOWARD PILLOW STEERS AND WARD It has been shown further that with a sealed lamp the ratio of the intensities of lines A 614.3 and 630.4 nm (from the same upper level and the former terminating on a metastable level) varies with current by a factor if (1-yi) implying a metastable concentration proportional to current; y is an experimentally determined constant that varies with the particular lamp used. Appli-cation of such a factor can account for the S shape of curves and further work on this will be carried out on the demountable system. TABLE I1 VALUES OF CONSTANTS A B AND C FROM I VERSUS i GRAPHS Cathode Species X/nm (bow x depth)/mm Pressure/Torr A arbitrary units* l3IrnA-I N e I 363.4 3 x 10 3.5 39 1.6 5 15 0.6 7.5 10 0.4 10 6.5 0.3 20 3.0 0.2 16 x 50 N e I 470.9 15 x 50 Ne I1 .. 348.1 6 x 20 1 2 5 1 2 5 2.5 5 7.5 8.1 0.5 3.0 0.5 0.5 0.5 17 0.9 5.7 0.6 1.2 0.3 1.5 0.03 0.28 0.00 0.07 0.00 C/mA-I 0.05 0.04 0.04 0.05 0.02 0.07 0.08 0.08 0.04 0.02 0.00 0.04 0.12 0.20 * Arbitrary units constant for a given line and cathode. Conclusions The expression I = Ai(1 + Ci)/(l + Bi) derived for the dependence of intensity on current, is shown to hold for a number of spectral lines under a wide range of experimental conditions in hollow-cathode discharges. I t is suggested that the values of A B and C can be used to characterise the behaviour of individual spectral lines in a discharge and interpreted in terms of the processes controlling this behaviour.Some preliminary work has shown that the expression can also be fitted to the different I zleysuus i graphs obtained for spectral lines from a positive column discharge. Experimental work on hollow-cathode and positive-column dis-charges is continuing with measurements over a wider current range to yield more reliable determinations of the constants and to link them where possible with excitation cross-sections. The work described formed part of an SERC CASE project with Cathodeon Ltd.; C. H. thanks the Science and Engineering Research Council for a studentship. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. References Pillow M. E. Spectrochim. Acta Part B 1981 36 821. Lompe A. Seeliger R. and Wolter E. Ann. Phys. (Leipzig) 1939 36 9. Borodin V. S. Gerasimov G. N. and Kagan Yu. M. Sou. Phys. Tech. Phys. 1967 12 283. Gofmeister V. P. and Kagan Yu. M. o p t . Spectrosc. (USSR) 1968 25 185. Gofmeister V. P. and Kagan Yu. M. Rev. Roum. Phys. 1968 13 19. Gofmeister V. P. and Kagan Yu. M. Opt. Spectrosc. (USSR) 1969 26 379. Gofmeister V. P. Desai S. K. and Kagan Yu M. 9th Int. Conf. Phenomena Ioniz. Gases 1969, Howorka F. and Pohl M. 2. Naturforsch Teil A 1972 27 1425. Kuen I. Howorka F. and Stori H. Phys. Rev. Sect. A 1981 23 829. Musha T. J . Phys. SOC. Jpn. 1962 17 1440. contributed papers p. 167. Received September 9th 1982 Accepted October 18th 198

ISSN:0003-2654    

DOI:10.1039/AN9830800145

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

Analyst, February, 1983, Vol. 108, pp. 153-158 153 Flow Injection Sample Introduction Methods for Atomic-absorption Spectrometry Julian F. Tyson, John M. H. Appleton and Ahyar B. ldris Deflartment of Chemistry, Loughborough University of Technology, Loughborough, Leicestershire, LE11 3T zi The essential features of flow injection analysis are described and the use of flow injection methodology for sample introduction for flame atomic-absorp- tion spectrometry is briefly reviewed. A flow injection analogue of the standard additions method has been devised and applied to the analysis of chromium in some BCS standard steels. The results showed good agreement with the certificate values. The use of a concentration gradient forming mixing chamber t o provide a novel method of rapid, single-standard Cali- bration is described and the results of preliminary experiments with magnesium show the method to be viable.The potential usefulness of both methods is critically evaluated. Keywords : Flow injection ; atomic-absorption spectrometry ; standard additions method ; sample introduction ; concentration gradient generator The term “flow injection analysis” (FIA) is generally understood to encompass analytical techniques in which a discrete sample volume is injected into a continuously flowing carrier stream after which the sample undergoes controlled mixing with a reagent (or reagents) and finally the reaction product is measured by a flow-through detector. The concept of FIA was first proposed by RtiiiiEka and Hansen in 1975,l although a variety of non-segmented flow systems had been described earlier.In its simplest form, the mixing of sample and reagent is achieved by using the reagent as a carrier stream and controlling the dispersion of the sample between the point of injection and the downstream detector. In general, dispersion is a function of volume injected, tube dimensions (both length and diameter) and flow-rate. The predominant mechanisms are (a) the convective flow patterns developed in the laminar flow of a fluid in a closed circular pipe (the stream lines at the tube walls have zero velocity and that in the centre has twice the average velocity, with a parabolic velocity profile between these two extremes) and ( b ) the radial diffusion of the sample molecules. The latter mechanism allows molecules to move from one stream line to another and thus all the mole- cules in the sample zone are eventually transported down the tube and cross-contamination from one sample zone to another may be avoided by suitable timing of the injection cycle.In this basic format, FIA may be considered to be high-performance liquid chromatography without the column, whereas the more complex manifolds that allow merging zone and other reagent addition procedures may be considered as AutoAnalyzer systems without the air bubbles. Most FIA methods are based on a spectrophotometric measurement of the reaction product. As a steady-state signal is not achieved, the FIA system must consist of a high-precision sample injection valve and pumping unit so as to achieve good reproducibility of the peak height.In practice, the precision achievable depends on the particular pumps and injection valve used, the nature of the detection system, complexity of the flow injection manifold, etc. Values of less than 1% relative standard deviation are routinely reported for the over- all precision based on peak height. This high precision, which may be achieved at a relatively modest cost, allows some of the kinetic restrictions governing the use of reactions forming the basis of a spectrophotometric method of analysis to be relaxed and thus as well as adapting existing methods for FIA, new chemistries may be devised. Further, the peaks may be only a few seconds wide and very rapid sample throughputs are possible with suitably automated equipment.Not surprisingly, given the emphasis on controlled chemical reaction through the controlled dispersion of FIA, these techniques have not found much use as sample introduction methods for atomic-absorption spectrometry. Such applications that have been reported have either used flow injection techniques as a precise method of introducing small sample volumes to the instrument2 or as a means of adding spectroscopic buffers, releasing agents, e t ~ . , ~ and may be thought of as the flow injection analogues of “discrete nebulisation” and “branched capillary nebulisation.”154 TYSON et al. : FLOW INJECTION SAMPLE Analyst, Vol. 108 However, it is suggested here that the controlled, precise dispersion characterisation of FIA has considerably more to offer and in this paper the possibilities of FIA for calibration purposes are outlined and results presented for (a) the determination of chromium in steel by the standard additions method (in which iron exerts a depressive effect) and (b) calibration for magnesium using a variable dispersion device.Quantifying Dispersion Although Gaussian shaped peaks are expected from FIA systems, in practice the dispersion necessary for analytical purposes is rarely large enough for the peaks to achieve a Gaussian shape. In most FIA systems the peaks are skewed with the rising and falling curves approxi- mating to exponentials. This is particularly true when an atomic-absorption spectrometer is used as a detector as the basic action of the nebuliser and the instrument response charac- teristics play a major role in determining peak shape.A simple model has been proposed to account for these peak shape^^-^ and these will not be discussed further here. It is common practice in FIA not to quantify dispersion in terms of the peak width at some particular height (as is done in chromatography) but to define dispersion, D, as the ratio of the con- centration injected, Cm, to the concentration at the peak maximum, Cp. Thus for a sample plug in a reagent stream, .. * . (1) D = Cm/Cp .. .. .. The carrier stream reagent concentration will also vary across the-sample plug from Cz to CpR at the peak maximum. The reagent dispersion, DR, is defined in an analogous manner, a.e., and on the basis of the simple model mentioned above it has been shown6 that .... - * (2) DR = CzlC; .. .. .. D DR = - D - 1 " (3) FI Standard Additions Method In this method the sample is used as the carrier stream and the standards are injected in sequence. If the concentration of a standard, 0, is lower than the sample carrier stream concentration, Cx, then the change in concentration at the peak maximum, AC,, will be negative. Thus a graph of AC, veysus Cs will intersect the CS axis at Cx. In order for the method to compensate for any interference effect in the sample, the dispersion must be such that the concentrations at the peak maximum are such that the interference also affects the added standard to the same extent as it does the sample. The effect of varying the dispersion has already been described for the interference of phosphate on calcium.5 If the required minimum ratio of interferent to analyte species, RiIa, is known, the relationship between concentration of interferent, sample concentration, Cx, and standard concentration, Cs, may be readily calculated from equations (1)-(3) above,6 bearing in mind that the analyte concentration at the peak is made up of contributions from carrier stream and injected solution, as follows : Also, if Cs > Cx then AC, > 0 and if C* = Cx then AC, = 0.c: = [C",(D - 1) + CX]R . . .. .. .. (4) where CE is the concentration of interferent in the carrier stream and Ci is the concentration of the top standard in the calibration sequence. The validity of this approach was evaluated by using it to adjust the concentration of iron (interferent) in the determination of chromium in steel.Variable Dispersion Calibration Methods The dispersion may be varied by either changing the volume injected or by changing the tube dimensions between the injection point and the nebuliser, the. flow-rate being kept constant at a value giving a satisfactory nebuliser performance. Previously it had beenFebruary, 1983 INTRODUCTION METHODS FOR AAS 155 observed4 that a graph of signal vemm flow-rate showed a broad maximum at a flow-rate slightly greater than the nebuliser’s “natural” flow-rate. Experimentally, varying the volume injected required the sample loops on the injection valve to be changed and although this is a straightforward procedure it has nothing to recommend it as an alternative to serial dilution in calibrated flasks as a means of producing solutions of known concentration for calibration points.However, changing the tube dimensions by switching the injected volume down a set of lines in parallel is experimentally simple and rapid and is, at present, being evaluated’ as a calibration method. As different points along the rising part of a peak represent, in effect, different dispersions, the possibility of generating a concentration - time profile suitable for calibration purposes has been proposed4-6 and is also currently being investigated.s The initial experiments have used a small glass vessel as a continuously stirred mixing chamber. Passage of a sharp concentration boundary through such a mixing chamber produces an exponential gradient according to the following equation : C = C,[1 - exp(-ut/V)] .. . . . where C is concentration at time t, C, is the concentration at the high concentration side of the boundary (the other concentration being zero), u is the volume flow-rate and V is the volume of the mixing chamber. If the concentration boundary is in the opposite sense the exponential decrease in concentration follows the equation C = C, exp(-ut/V) .. .. This method is analogous to that proposed by Horvai et aL9 for the calibration of ion-selective electrodes. Experimental Apparatus For the studies of the standard additions method a Shandon Southern A3300 atomic- absorption spectrometer was used together with a Gilson Minipuls 2 peristaltic pump, an Altex, Model 201-25, eight-port injection valve (with two external loops) and 0.58 mm i.d.tubing as the basis of the flow injection manifold. For the concentration profile study, a Perkin-Elmer 290B atomic-absorption spectrometer was used together with two home-made constant-head vessels and a Rheodyne, Type 5011, six-position rotary valve as the flow injection manifold. The mixing chamber was a small enclosed cylinder with the inlet located radially on a base diameter and the outlet axially at the top. The solution was stirred with a magnetic stirrer. The arrangement is shown schematically in Fig. 1. Air - acetylene flames were used throughout with both instruments. Reagents stock solutions (BDH Chemicals Ltd.). 149/3) according to the method of Nall et aZ.1° Chromium and magnesium standards. I r o n ( I I 1 ) solution. These were prepared by dilution of 1000 p.p.m.This was prepared by dissolution of high-purit y iron granules (BCS Procedure For the standard additions studies, the effect of varying the volume injected and tube length on the sample dispersion was first investigated using the conventional mode of separation (k., injecting the “sample” into a water carrier stream). With the apparatus used in these studies the injection-loop volume was varied from 13 to 5 0 0 ~ 1 and the con- necting tube lengths from 3 to 200 cm. A dispersion of 4 was used in the standard additions experiments described here. Substitution of appropriate values into equation (4) enabled a suitable concentration of iron to be calculated. Iron was added to the samples if necessary to increase the concentration to this level. The sample solutionlo was used as the carrier stream and the standards were injected in turn.A graph of change in absorbance, AA, versus concentration of standard, 0, was plotted and the value of the sample concentration found from the intercept on the CS axis.156 -- I- A -- -- -- B -- r Analyst, Vol. 108 - - For the exponential dilution flask calibration method, the instrument output was recorded continuously as the solution aspirated was switched from 0 to 2.5 p.p.m. of magnesium. Solutions for analysis were introduced at the same flow-rate and the time corresponding to the steady-state absorbance was obtained from the chart recording; this was then converted into a concentration using equation (5). The over-all procedure is shown schematically in Fig.2. 0 0 Fig. 2. Use of concentration gradient for cali- bration. (a) Concentration of the solution entering the mixing chamber is switched rapidly from zero to Cm; (b) an exponential concentration gradient is introduced to the nebuliser and corresponding absorbance - time graph is recorded; (c) an unknown solution is introduced at the same flow-rate and the steady-state absorbance Ax obtained; (d) from the absor- bance - time graph the corresponding time, t X , is found. Finally this is converted into a con- centration by substitution in equation ( 5 ) , the values of Cm, u and V being known. Results and Discussion The variation of dispersion as a function of volume injected and tube length is shown in Construction of such graphs enables appropri- It is suggested that wider use Fig.3 for selected values of these parameters. ate values to be chosen so as to achieve a desired dispersion. of such graphs would be valuable in comparing flow injection systems.February, 1983 INTRODUCTION METHODS FOR AAS 157 14 12 10 4 2 - 1 C t \<=- 1 I I 1 Volume i njected/pI 0 50 100 150 200 Tube lengthkm I I Fig. 3. Variation of dispersion, D, measured as the ratio of steady-state absorbance to peak absorbance with tube length, L, and volume injected, Vi. Volume injected: A, 13; B, 50; and C, 200 p1. Tube length: 1, 200; 2, 100; and 3, 3 cm. It was found that in the determination of chromium in the presence of iron, a constant depression in the chromium absorbance was observed when the iron to chromium mass ratio, Rila, exceeded 30.The top standard in the calibration sequence was 20 p.p.m., hence for a sample containing 10 p.p.m. of chromium, the concentration of iron required on the carrier stream to ensure successful application of the standard additions method was calculated from equation (4) to be 500 p.p.m. The results for the analysis of some BCS steels are shown in Table I. Although the analysis reported here and that reported previously5 (the deter- mination of calcium in iron ore) may be artificial applications of the standard additions TABLE I ANALYSIS OF STANDARD STEELS BY FLOW INJECTION STANDARD ADDITIONS METHOD Certificate value Sample of chromium, yo Chromium found, yo BCS 220/2 . . .. 5.12 5.13 f 0.02 BCS 261/1 .. .. 17.3 17.4 f 0.1 BCS 241/2 . . .. 5.35 5.34 f 0.02 method in atomic absorption, in that the various interference effects can generally be over- come by the use of a dinitrogen oxide - acetylene flame, they serve to illustrate the principle of the flow injection analogue of the standard additions method.This has advantages over the conventional method in that the necessary volumetric manipulations are reduced and the result is obtained by interpolation, a more accurate procedure than the normal extrapolative procedure. I t should perhaps be pointed out that, in any format, the standard additions method will not work unless there is a constant depression plateau Tie., a graph of absorbance (or other analytical parameter) for a fixed concentration of analyte vemts concentration of interferent levels off to a measurable value above a certain interferent concentration]. This fact is often omitted in text-book explanations of the method. The results of the calibration based on the exponential concentration gradient mixing chamber are shown in Table 11.The accuracy of the method depends on the accuracy of158 TYSON, APPLETON AND IDRIS TABLE I1 CALIBRATION FOR MAGNESIUM BY EXPONENTIAL CONCENTRATION GRADIENT FORMATION Actual concentration, p.p.m. . . 0.125 0.250 0.500 1.00 1.50 2.00 Concentration found, p.p.m. . . 0.128 0.255 0.520 1.04 1.55 2.07 the flow-rate and, of course, on maintaining this constant. With the constant-head vessels used in these experiments it was found that the flow precision was about 1.574 relative standard deviation. The rate of stirring is also important, as at lower rates the mixing chamber behaves as though its volume were less than the measured volume.There is an additional possibility of error in deciding where the zero time point is; however, with the values of the parameters in equation (5) used in these experiments (C, = 2.5 p.p.m., z t = 5.04 ml min-l and V = 7.18 ml) the recorded absorbance - time graph covered a period of about 200 s and hence this error becomes important only at lower concentrations. This method has a number of advantages over the conventional method of constructing a calibra- tion graph through a limited number of points. The calibration function is continuous and therefore no curve-fitting procedures are necessary ; further, no assumptions need be made about the nature of the absorbance - concentration relationship.A single concentrated standard is used that again reduces the volumetric manipulation necessary and, as the pro- cedure is rapid, re-calibration over the same or a new concentration range takes a minimum of time. Further, the use of a microcomputer to store the graph and perform the calculations should be a straightforward procedure. Conclusions In addition to the rapid, precise transport of small sample volumes to an atomic-absorption spectrometer it has been demonstrated that flow injection based sample-introduction pro- cedures, involving relatively simple and inexpensive apparatus, offer a number of possibilities for the manipulation of sample and reagent concentrations through control of the appropriate dispersion.This opens up new possibilities for calibration procedures that have the potential for considerably reducing the volumetric manipulation necessary for the corresponding con- ventional procedure, hence considerably reducing the time spent on dilution of samples, addition of reagents and preparation of calibration solutions, etc. This could be an important consideration for the present generation of atomic-absorption spectrometers that incorporate automated sample introduction and data handling facilities. It is unlikely at this stage that all the possibilities of flow injection for calibration procedures have been exhaustedll as there are several ways in which dispersion may be varied and reproducible concentration gradients produced. A. B. Idris and J. M. H. Appleton gratefully acknowledge financial support from the National University of Malaysia and the Zimbabwe Government Department of Manpower Training and Social Services, respectively. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. References RbiiEka, J., and Hansen, E. H., Anal. Chim. Acta, 1975, 78, 145. Wolf, W. R., and Stewart, K. K., Anal. Chem., 1979, 51, 1201. Zagatto, E. A. G., Krug, F. J . , Bergamin F*. H., Jorgensen, S. S., and Reis, B. F., Anal. Chim. Tyson, J. F., Anal. Proc., 1981, 18, 542. Tyson, J. F., and Idris, A. B., Analyst, 1981, 106, 1125. Tyson, J. F., Idris, A. B., and Appleton, J. M. H., Anal. Chim. Acta, in the press. Tyson, J. F., and Adeeyinwo, C. E., work in progress. Tyson, J. F., and Appleton, J. M. H., work in progress. Horvai, G., Toth, K., and Pungor, E., Anal. Chim. Acta, 1976, 82, 45. Nall, W. R., Brumhead, D., and Whitham, R., Analyst, 1975, 100, 555. Olsen, S., RbiiCka, J., and Hansen, E. H., Afial. Chim. Ada, 1982, 136, 101. Acta, 1979, 104, 279. Received August loth, 1982 Accepted September lst, 1982

ISSN:0003-2654    

DOI:10.1039/AN9830800153

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

Analyst, February, 1983, Vol. 108, pp. 159-165 159 Development Progress in Plasma Source Mass Spectrometry Alan R. Date and Alan L. Gray Institute of Geological Sciences, 64/78 Gray’s Inn Road, London, WClX 8NG Department of Chemistry, University of Surrey, Guildford, Surrey, G U2 6XH Development work in the application of the inductively coupled plasma to plasma source mass spectrometry is described. Preliminary results obtained under continuum (or bulk plasma) sampling conditions are illustrated and compared with previously published boundary layer sampling work. The technique is now shown to be viable for multi-element analysis of complex samples. Keywords : Plasma source mass spectrometry ; inductively coupled plasma ; continuum (or bulk plasma) sampling mode ; multi-element trace analysis Plasma source mass spectrometry is a rapidly developing technique that combines the speed and convenience of sample introduction to a plasma source with the simple spectra and isotope ratio capability of atomic mass spectrometry.In this context, the technique is applied to solution samples, introduced to the inductively coupled plasma source (ICP) using a conventional pneumatic nebuliser with an uptake rate of 1.5 ml min-l. Samples may be processed at a rate of one every few minutes. Two modes of operation have been identified by us, boundary layer sampling and continuum (or bulk plasma) samp1ing.l Previously published work describing development of the ICP as an ion source2-5 has been limited to the boundary layer sampling mode. Boundary Layer Sampling Mode Ions extracted from the tail flame of the ICP into the vacuum system of the mass spectro- meter have to traverse a boundary layer of cool gas which forms over the sampling aperture.The formation of this boundary layer is discussed else~here.~9~ The boundary layer sampling mode is characterised by: (a) high signal to background ratios; (b) excellent detection limits (see Table I) ; (c) operation with aerosol desolvation ; (d) serious ionisation suppression ; (e) formation of oxide and hydroxide ions; and (f) aperture blocking at high salt concentrations. However, the unique configuration of plasma torch, sampling cone, ion lens and detector we have developed for use in the boundary layer sampling mode5 leads to the almost complete removal of stray background. Although the technique is limited to the analysis of simple solutions, there are several possible applications.The rapid determination of lead isotope ratios in galena (natural PbS) samples has been described and the potential of the technique for elements forming volatile hydrides illustrated.1 The high signal to background ratio achieved in this mode suggests that time spent in sample enrichment will be rewarded in terms of the speed and convenience of subsequent mass analysis. Continuum Sampling Mode The two advantages of boundary layer sampling, high signal to background ratios and excellent detection limits, are off-set by the inability of the system to accept solutions with total salt concentrations greatly in excess of 10 pg ml-1. For the analysis of complex samples it is necessary to induce sufficient flow from the plasma gas to break through the cool boundary layer.Simply increasing the sampling aperture diameter in order to effect this, results in the formation of a “pinch” discharge in the aperture mouth caused by compression of the free electron population of the plasma gas. By regulating the pressure immediately behind the sampling aperture it is possible to suppress the discharge and achieve controlled expansion of the plasma gas into the vacuum system. Development work in the continuum sampling mode is described in detail elsewhere.6160 DATE AND GRAY: DEVELOPMENT PROGRESS Aaalyst, Vol. 108 RF power supply Multi-channel analyser and display X - Y Teletype Cassette plotter recorder A Fig.1 . General system diagram : continuum sampling mode. The general system diagram, incorporating a controlled expansion stage, is shown in Fig. 1, and the new plasma sampling interface in Fig. 2. A blank spectrum (1% V/V nitric acid) obtained in the continuum sampling mode is illustrated in Fig. 3, taken with the total trans- mission reduced to avoid saturation in the major peaks. Although broadly similar to the equivalent boundary layer spectrum (see Fig. 3 in reference 5), the 190H,+, 30NO+ and 8oAr,+ peaks are much smaller, and the 81Ar,H+ peak is not detected. P2 = Water-cooled front plate - Extraction electrode Expansion Stage 2 -Torch box U ~ ~ ~ ~ a r t z bonnet C - \ Sampling - cone r coil torch ll - atm ’ cm Fig. 2. Plasma sampling interface : continuum sampling mode.At the present stage of development, the continuum sampling mode is superior to the boundary layer sampling mode in all but two characteristics, (a) and (b) above. Although the signal to background is lower by one or two orders of magnitude, and detection limits in most instances are inferior (see Table I), desolvation of sample solutions is unnecessary,February, 1983 I N PLASMA SOURCE MASS SPECTROMETRY 161 41 (2 968617 counts s-’1 16 Fig. 3. Blank spectrum (1% V/V nitric acid) : continuum sampling mode. ionisation suppression is much less significant (Fig. 4), oxide formation is limited, even for strongly bound oxides such as thorium (Fig. 5 ) , and salt condensation is insignificant. The upper limit in the dynamic range for the system is controlled by the detector and counting chain.The response for cobalt, shown in Fig. 6, is closely linear over six orders of magni- tude. TABLE I DETECTION LIMITS (30, ng ml-l) IN PLASMA SOURCE MASS SPECTROMETRY Element Lithium . . Boron . . Magnesium Aluminium Titanium . . Vanadium. . Chromium. . Manganese Iron .. Cobalt . . Copper . . Zinc .. Germanium Arsenic . . Selenium . . Rubidium . . Silver . . Cadmium . . Indium . . Tellurium . . Caesium . . Barium . . Lanthanum Cerium . . Tungsten . . Gold . . Mercury . . Lead . . Bismuth .. Thorium . . Uranium . . . . .. . . .. .. .. .. .. .. .. .. .. .. . . .. . . . . . . .. .. .. .. .. .. .. .. .. .. .. .. .. Boundary layer mode 0.4 0.2 0.3 0.3 0.1 0.06 0.5 0.1 0.3 2.0 0.1* 0.2 0.1 0.2 - - - - - - 0.2 - - 2.0 0.2 - 0.05 Continuum mode 5.0 2.0 0.7 0.9 0.5 0.6 0.2 1.3 0.8 4.3 1.6 - - 11 23 0.4 0.3 0.7 0.2 0.7 0.2 0.4 3.4 0.3 1.5 0.7 0.2 0.6 0.4 0.3 1.5 0.3 0.5 0.5 * Hydride generation.162 lo7 DATE AND GRAY DEVELOPMENT PROGRESS Analyst, Vol.108 ! - /' '"10 20 50 100 200 500 1000 Sodium concentration/pg m1-l Fig. 4. Effect of up to 1000 pg ml-l of sodium on 10 pg ml-1 of cobalt. I 232Th (86 767 counts s-l) Fig. 5 , Spectrum for thorium at 100 pg ml-1, showing small oxide peak. 10' 0.001 0.01 0.1 1.0 10 100 1000 Cobalt concentration/yg ml- ' Fig. 6. Calibration graph for cobalt, with background correction, and gain adjustment (to overcome counting losses at high count rates). Broken line: corrected for background (1% nitric acid blank). Detection limit (20, blank), 0.001 pg ml-1.Febraary, 1983 IN PLASMA SOURCE MASS SPECTROMETRY 163 In order for plasma source mass spectrometry to find ready application to multi-element trace analysis of complex samples, several criteria must be satisfied.The technique must be capable of simultaneous analysis of a wide range of elements in a variety of matrices. 2 4 6 8 10 12 14 lonisation energylev Fig. 7. Relationship between response (counts s-l a t 1 pgml-') and ionisation energy, Vi (ev), for 25 elements in the range m/z 7-209 (corrected to lOOyo abundance in each instance). Sensitivity is within a factor of three for elements with Vi below 11 eV. Elements: Li, B, Al, C1, V, Cr, Mn, Fe, Co, Zn, Ge, As, Se, Br, Rb, Ag, Cd, In, Te, I, Cs, Au, Hg, Pb, Bi. To supplement detection limit data, presented in Table I, the relationship between response (counts per second at 1 pg ml-l) and ionisation energy (electron volts) for 25 elements in the range 7-209 m/z (corrected to 100~o abundance in each example) is illustrated in Fig.7. Sensitivity lies within a factor of three for elements with ionisation energies below 11 eV. The two elements outside this range, bromine and chlorine, have ionisation energies of 11.85 and 6 3 ~ u + (sampling aperture) 238u + ..a - 3 Fig. 8. Spectrum in 2048 channels over the range rn/z 0-260 for a solution containing 10 pg ml-l each of Al, Co, As, Br, Rb, In, Te, I, Cs, La, W, Au, Pb, Bi and 17 in 1% V / V nitric acid. With a dwell time per channel of 800 ps and only 60 sweeps, the total spectrum was taken in just over 1 min.Each isotope occupies approximately seven channels and was therefore addressed for about 0.2 s.164 DATE AND GRAY: DEVELOPMENT PROGRESS Analyst, Vol. 108 13.02 eV, respectively. The ionisation equilibrium of the plasma flame is controlled princi- pally by the plasma support gas argon, with a first ionisation energy of 15.76 eV. Elements with second ionisation energies below 15.76 eV will be partially doubly ionised. This is illustrated in Fig. 8, which shows a spectrum in 2048 channels over the range 0-260 m/z for a solution containing 10pgml-l each of Al, Co, As, Br, Rb, In, Te, I, Cs, La, W, Au, Pb, Bi and U in 1% V/V nitric acid. Lanthanum and uranium show significant double ionisa- tion, while lead (second ionisation potential, 15.03 eV) is only slightly doubly ionised.With a dwell time per channel of 500 ps and only 60 sweeps, the total spectrum was taken in just over 1 min. Each isotope occupies approximately seven channels and was therefore addressed for about 0.2 s. I 75As+(65 000 I counts s-l) 79Br+ 85Rb+(79133 counts s - l ) 8 1 ~ ~ + Fig. 9. Scale expansion (128 channels) of the region in Fig. 8 covering arsenic, bromine and rubidium. Count rates were calculated from the peak channel count in each instance. J U L Although it is possible to identify most of the isotopes present in Fig. 8, the region o1 the spectrum covering arsenic, bromine and rubidium is subjected to vertical ( x 16) and hori- zontal ( x 16, 128 channels) scale expansion in Fig. 9. All isotopes may be readily identified by this approach. Count rates (calculated from the peak channel integral count in each instance) are shown for 75As+ (65000 counts s-I) ands5Rb+ (79 133 counts s-l).The apparently shortened appearance of the 80Ar-Ar+ dimer peak is caused by peak fold-over at high gain in the data system used (Canberra Series 40). In order to make a preliminary assessment of performance with a complex matrix, the solution used in the above example was diluted with a synthetic geological-matrix solution i (16367 counts s-') Fig. 10. Scale expansion (128 channels) for the same solution as in Fig. 8 diluted to 5 pg ml-1 showing the lead isotopes and bismuth (A), com- pared with a similar dilution in the presence of a synthetic geological matrix containing Na and K at 50 pg ml-l and Mg, Al, Ca and Fe at 100 pg ml-l (B).Fe brzGary , 1983 IN PLASMA SOURCE MASS SPECTROMETRY 165 prepared from BDH atomic-absorption standard solutions.A scale-expanded spectrum of the region covering the lead isotopes and bismuth (at 5 pg ml-l) is illustrated in Fig. 10, and compared with a similar dilution in 1% V/V nitric acid. The concentrations used for the synthetic matrix, 50 pg ml-l of Na and K and 100 pg ml-l of Mg, Al, Ca and Fe, were limited by the available stock solution concentrations. They represent a dilution factor of 1000 (0.1 g in 100 ml) for a solid sample containing 5% Na and K and 10% Mg, Al, Ca and Fe. The negligible effect of this matrix addition on lead and bismuth is shared by all but two of the trace elements. Iodine is a serious contamination in the synthetic matrix and is probably present in one of the BDH standard solutions (probably the potassium solution).Although the system is far from optimised, and much research and development remain, these data suggest that a viable multi-element technique for the analysis of complex samples will soon be more widely available, a technique having far-reaching implications in fields as diverse as geochemical research, the life sciences, pollution monitoring and the nuclear power industry. Gold has disappeared from both solutions (see Fig. 10). This work was supported by the Institute of Geological Sciences and the European Com- munity Research and Development Programme on “Uranium Exploration and Extraction” (contract No. EXU 033-81-UK). The paper is published with the approval of the Director, Institute of Geological Sciences (NERC) . References 1. 2. 3. 4. 5. 6. Date, A. R., and Gray, A. L., Spectrochirn. A d a , Part B, in the press. Houk, R. S., Fassel, V. A., Flesch, G. D., Svec, H. J., Gray, A. L., and Taylor, C. E., Anal. Chem., Houk, R. S . , Fassel, V. A., and Svec, H. J., in Price, D., and Todd, J . F. J., Editors, “Dynamic Gray, A’,?., and Date, A. R., in Price, D., and Todd, J. F. J., Editors, “Dynamic Mass Spectro- Date, A. R., and Gray, A. L., Analyst, 1981, 106, 1255. Gray, A. L., and Date, A. R., in preparation. 1980, 52, 2283. Mass Spectrometry,” Volume 6 , Heyden, London, 1981, pp. 234-251. metry, Volume 6 , Heyden, London, 1981, pp. 252-266. Received July 27th. 1982 Accepted September 14th, 1982

ISSN:0003-2654    

DOI:10.1039/AN9830800159

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

166 Analyst, February, 1983, VoE. 108, $9. 166-170 A Pneumatic Recirculating Nebuliser System for Small Sample Volumes Peter Hulmston Analytical Chemistry Branch, Chemistry Division, 11.300( PE) , Atomic Weapons Research Establishment, Aldermaston, Berkshire, RG7 4PR The nebuliser spray chamber described generates an aerosol, for use with an inductively coupled plasma, on as little as 1 ml of sample solution for over 10 min. The nebuliser has direct application to inductively coupled plasma optical emission spectroscopic analysis in those instances where economy of sample solution is important. The performance of the nebuliser spray chamber was tested and it was found that the sensitivity and precision are as good as those obtained with a conventional nebuliser system. Memory effects are readily overcome by including a system that allows rapid, thorough flushing and flooding of the spray chamber.Keywords : Inductively coupled plasma ; optical emission spectrometry ; pneumatic nebuliser The most common method of introducing sample solutions into an inductively coupled plasma (ICP) source is to generate a fine aerosol by pneumatic nebulisation. With con- ventional nebulisers, less than 5% of the solution actually enters the source, the remainder, which consists of a coarse spray, being trapped in the spray chamber and allowed to drain to waste. This poor efficiency in sample transfer to the plasma is normally of little importance as the amount of sample solution available is not limited, but there are occasions when the volume is limited by the amount of sample available or the amount that can be dissolved.Further, with the application of photographic recording1s2 and of sequential multi-element analysis3 there is a need to nebulise a sample into the plasma for long, uninterrupted periods of time. I t is obvious that a considerable gain in efficiency in sample use can be achieved by recovering the bulk of the solution that normally drains to waste and recycling it to the nebuliser. The use of pneumatic nebulisers where the waste solution is recovered is almost as old as spectroscopy itself4p5 and was particularly popular in flame photometry up to 30 years ago, after which their use declined, probably because the inconvenience of changing samples became more important as rapid monochromator and photoelectric detection systems took over from photographic recording.Many of the systems used metal components, most required a considerable volume of solution (10-20 ml) and all required a high gas flow-rate, which is not suitable with ICPs. Novak6 constructed a recirculating fixed cross-flow nebuliser for use with ICPs on the Rauterberg and Knippenberg design,’ but this requires more solution and its construction would require the service of a very high quality glassblower. No reference to a system using commercially available nebulisers using small volumes of sample for ICP could be identified and, to meet some of our current analytical requirements, a nebuliser design based on the Meinhard concentric system has been investigated. Design Requirements A number of factors were considered to be of importance in designing the iiebuliser spray chamber. Nebulisers for ICPs are made t o fine tolerance because of the limited volume of gas available for nebulisation and it could be expected that a consistent performance could be most easily achieved by using a commercial nebuliser such as the Meinhard glass concentric nebuliser.For our analytical requirements the maximum volume of sample available was 2 ml and to operate on this volume the hold-up of sample in the spray chamber should be small, as should be the drainage time. The spray chamber design should also allow for Crown Copyright.HULMSTON 167 rapid and effective flushing to eliminate contamination of a solution by a previous sample. Low-power argon - argon plasmas are adversely affected by the ingress of air and it would be necessary to prevent air from entering the spray chamber during sample changeover and to provide an uninterrupted flow of argon to the plasma to maintain its stability.Finally, the precision and sensitivity of the system should not be significantly worse than those of a con- ventional nebuliser spray chamber, and the system should be easy to operate routinely. Apparatus ICP Equipment The ICP source used was a Plasma-Therm system, Model HFP 2500D. The generator of this system was a crystal-controlled type operating a t 27.12 MHz with a maximum output of 2.5 kW. The plasma torch used was an integral Plasma-Thenn, Model T1.5. Solutions are introduced into the plasma using either the prototype recirculating nebuliser or the concentric nebuliser (taken from the recirculating nebuliser) in a conventional spray chamber.Radiation emitted from the plasma was focused on to the entrance slit of a 1-m Czerny- Turner monochromator (Spex) as a 1 : 1 image. The detection system employed consisted of an EHI 9862 photomultiplier in conjunction with a Spex DPC 2 digital photometer, which also supplied the EHT to the photomultiplier. Optimised conditions are listed in Table I. TABLE I OPTIMISED CONDITIONS FOR ICP R.F. power . . Viewing height Plasma gas . . Auxiliary gas Injector gas . . Entrance slit Exit slit . . DPC 2 range.. Integration time .. . . 1.0kW .. . . 23 mm above load coil .. . . 12lmin-l .. . . 1.2 lmin-1 .. . . 32 lb in-2 for both nebuliser systems .... 20pm .. .. 35pm .. . . 0.01-0.1 pA .. .. 5 s Prototype Recirculating Nebuliser Figs. 1 and 2 illustrate the design features of the prototype recirculating nebuliser. The return of waste solution to the nebuliser inlet is facilitated by moving the nebuliser and spray chamber vertically. The Meinhard concentric nebuliser operates efficiently in this position and is small enough to be readily accommodated within the spray chamber. The nebuliser sprays into a central inner tube, which traps the bulk of the coarse spray and the fine spray passes through a hole a t the top of this tube on its way to the plasma. Rapid drainage is assisted by trapping most of the coarse spray inside the central tube, by angling the bottom edge of this tube and by coating all the interior surfaces with silicone.Efficient cleaning of the system between sample nebulisation is achieved by filling the spray chamber completely with de-ionised water with argon passing through the nebuliser during the earlier stages of filling. One system, consisting of a drain valve and water inlet valve, is used for rapid flushing and flooding of the spray chamber. The second system is used for controlling the argon by-pass system, which allows the ICP source to be sustained during sample changeover. The following description of the operation of the system should be read in conjunction with Fig. 2. Sample introdzcction. A 1-ml volume of sample solution is injected by syringe into the nebuliser chamber. With only valve 1 open, the nebuliser will generate the required aerosol for the ICP source.Sample removal. After analysis, valves 3 and 4 are opened to operate the by-pass system and, by opening valve 5, the sample can be drained into a container and stored for future analysis if required. Flztshing andjooding. With the pump switched on and valve 2 open, de-ionised water enters the spray chamber and flushes out residual sample. Valve 5 is then closed to allow The purpose of the two sets of valve systems is as follows.168 HULMSTON : PNEUMATIC RECIRCULATING Analyst, Vol. 108 the chamber to fill with water. During the earlier stage of flooding the concentric nebuliser remains pressurised. This allows argon to bubble through the water thus improving the effectiveness of the washing process. Valve 1 is closed before the nebuliser chamber becomes completely flooded to avoid splashing solution into the plasma tube.With valve 2 closed and valve 5 open the system can be drained. The flushing, flooding and drainage procedure may be repeated to ensure total removal of the previous sample. With valve 5 closed and valve 1 open the next sample can then be injected into the nebuliser and by closing valves 3 and 4 normal nebulisation of the sample is restored. Fine aerosol p----- 1-ml syringe Screw-top and silicone IU septum lasses . ..I.......... 220 mm 28 mm diameter 35 mm diameter 83435 Quickfit joint concentric nebuliser 3-mm glass valve va Ive Fig. 1. Prototype recirculating nebuliser. Performance Nebulising Characteristics The nebulising characteristics of the recirculating and conventional nebulisers were com- pared by measuring the sensitivity, the limit of detection and the precision of each of the three elements, zirconium, titanium and copper.The sensitivity, i.e., the net signal above background for unit concentration of an impurity in solution, does not differ significantly between the two nebulisers, and the intensities of the background emissions are also the same. The limit of detection, defined as the concentration equivalent to twice the standard deviation of the background, and the precision, obtained by repetitive readings taken from one portion of standard, were calculated for each element and the results are shown in Table 11. I t is concluded that the amount and size of spray reaching the plasma from either nebuliser system are not sufficiently different to affect the performance of the ICP.Again, no significant difference between the two systems was observed.February, 1983 NEBULISER SYSTEM FOR SMALL SAMPLE VOLUMES To ICP source Valve 4 (fine adjustment valve) Argon in I J Fig. 2. Schematic representation systems used during operation. U showing valve 169 Memory Effects In the practical application of the recirculating nebuliser the efficiency with which all traces of a previous solution can be removed from the spray chamber is important. This can be tested by monitoring the level of sample present after each flushing and flooding cycle. This was carried out by recording the detector response of the 327.9-nm zirconium emission from 1 ml of a 100 pg ml-l zirconium solution.After a flooding and flushing cycle, the response from 1 ml of a blank solution injected into the nebuliser was also recorded. This latter procedure was repeated until a reading equivalent to a blank level was reached. The results show a decontamination factor of 5 x 10-3, i.e., the actual zirconium content of the l-ml blank solution recorded after the first wash was 0.02 pgml-1. Thus in most practical instances, two washing and flooding cycles would eliminate contamination. TABLE I1 COMPARISON OF DETECTION LIMITS AND STABILITY ACHIEVED BY CONVENTIONAL AND RECIRCULATING NEBULISERS Short-term precision/pg ml-1 (mean concentration 0.125 pg ml-l) Detection limitlpg ml-1 r \ I I Element Wavelength/nm Recirculating Conventional Recirculating Conventional A A Zr.. .... 343.8 0.02 0.02 0.002 6 0.0020 T i . . .. .. 338.4 0.01 0.02 0.007 8 0.007 7 cu .. .. 327.4 0.003 0.004 0.002 6 0.003 4 Precision The short-term precision described under Nebulising Characteristics does not take into consideration the error associated with sample changeover, in particular the recirculating system where injection of sample and efficiency in drainage can significantly contribute to precision. The precision of the nebuliser systems was compared by making ten replicate170 HULMSTON determinations of a 2.5 pg ml-l zirconium solution. The standard deviations obtained were 0.06 and 0.05 pg ml-l for the recirculating and conventional nebulisers, respectively, which are not significantly different. Conclusions The nebuliser described operates successfully on as little as 1 ml of sample for at least 10 min. The performance of this recirculating nebuliser, in terms of precision and sensitivity, is not significantly different from that of a conventional system. The working procedure devised has reduced the memory effects to insignificant levels. No deterioration in the quality of results for multi-elemental analysis has been observed. The success of this prototype justifies the construction of a further system employing improved control systems to simplify its operat ion. References 1. 2. 3. 4. 5. 6. 7. Karser, M . , Spectrochim. Ada, 1978, 33, 536. Witmer, A., Philips Tech. Rev., 1974, 34, 322. Boumans, P., Analyst, 1976, 101, 587. Arrhenius, S., Ann. Phys. Chem., 1891, 42, 18. Gouy, G., Ann. Phys. Chem., 1879, 18, 5. Novak, J., Anal. Chem., 1980, 52, 576. Rauterberg, E., and Knippenberg, E., Angew. Chem., 1940, 54, 477. Received July 14th, 1982 Accepted September 17th, 1982

ISSN:0003-2654    

DOI:10.1039/AN9830800166

出版商:RSC    

年代:1983

数据来源: RSC