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)' G . J. Dickes (Bristol, U.K.)A. C. Docherty (Billingham, U.K.)D. Dyrssen (Sweden)'L. C. Ebdon (Plymouth)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)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.)'Members of the Board serving on the Analytical Editorial BoardEditor: P. C. WestonSenior Assistant Editor: R. A. YoungAssistant Editors: Mrs. J. Brew, Miss D. ChevinREGIONAL ADVISORY EDIT0 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. Rubegka, Geological Survey of Czechoslovakia, Malostransk6 19, 1 1 8 21 Prague 1 , CZECHO-Professor J . R&ikka, 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, W1V 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 f 99.00, USA $201 -00.Purchased withAnalytical Abstracts UK f 226.50, Rest of World f 238.50, USA $487.00. Purchased with AnalyticalAbstracts plus Analytical Proceedings U K f 251 .OO, Rest of World f 265.00, USA $539.00. Purchasedwith Analytical Proceedings UK f 1 1 7.50, Rest of World f 124.50, USA $253.00. Air freight and mailingin the USA by Publications Expedi?ing 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 a t Jamaica, NY 11431. All otherdespatches outside the UK :,y Bulk Airmail within Europe, Accelerated Surface Post outside Europe.PRINTED IN THE UK.Q The Royal Society of Chemistry, 1983. All rights reserved. No part of this publication may be reproduced,stored in a retrieval system, or transmitted in any form, or by any means, electronic, mechanical,photographic recording, or otherwise, without the prior permission of the publishers.Bruxelles, BELGl UM.bosch 7700, SOUTH AFRICA.Establishment, 21 020 lspra (Varese), ITALY.S LOVA K I A.DEN MARK.Kensington, N.S.W. 2033, AUSTRALIA.U.S.A

ISSN:0003-2654    

DOI:10.1039/AN98308FX029

出版商:RSC    

年代:1983

数据来源: RSC

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ANALAO 108 (1 289) 905-1 032 (1 983) August 1983THE ANALYSTTHE ANALYTICAL JOURNAL OF THE ROYAL SOCIETY OF CHEMCONTENTSSTRY905 Combination o f Flow Injection Analysis w i t h Flame Atomic-absorption Spe trophoto-metry: Determination of Trace Amounts of Heavy Metals in Polluted Seawater-Svend Olsen, Luiz C. R. Pessenda, Jarornir R82iEka and Elo H. HansenDetermination o f the Chemical Forms o f Cadmium and Silver i n Sediments by ZeemanEffect Flame Atomic-absorption Spectrometry-Ken R. Lum and Duart G. EdgarDetermination o f Caesium and Rubidium by Flame and Furnace Atomic-absorptionSpectrometry-2. Grobenski, D. Weber, B. Welz and J. WolffPyridine-2-aldehyde 2-Furoylhydrazone as a Fluorogenic Reagent f o r the Determina-t i o n of Nanogram Amounts o f Gallium-Eloisa Requena, Jose J.Laserna, Aurora Navasand Francisco Garcia Sinchez939 Spectrophotometric Determination o f Arsenic i n Biological Tissues and SedimentsAfter Digestion w i t h Nitric, Sulphuric and Perchloric Acids and Pre-concentrationby Zinc Column Arsine Generation and Trapping-W. A. Maher944 Spectrophotometric Determination o f Phosphorus and Arsenic i n Steel by SolventExtraction o f their Heteropolyacids w i t h Ethyl Violet-Shoji Motomizu, ToshiakiWakirnoto and Kyoji T6ei918925933952959966971978904991997100310071013Extraction and Spectrophotometric Determination of Titanium(lV) w i t h N-Phenyl-laurohydroxamic Acid and Phenylfluorone-H. Dasaratha GunawardhanaSpectrophotometric Determination o f Rhodium(l1l) in Aqueous and Alcoholic MediaUsing 2-Thiobarbituric Acid-Basilio MorelliRapid Spectrophotometric Determination of Saccharin i n Soft Drinks and Pharma-ceuticals Using Azure B as Reagent-P.G. Rarnappa and Anant N. NayakInterfacing an Automatic Elemental Analyser w i t h an Isotope Ratio Mass Spectro-meter: the Potential f o r Fully Automated Total Nitrogen and Nitrogen-I5Analysis-Thomas Preston and Nicholas J. P. OwensDetermination o f Phosgene in Methylene Chloride After Cyclisation w i t h a 2-Hydroxy-amine and Gas Chromatography w i t h Nitrogen-selective Detection-Olle Gyllen-haalSimultaneous Gas-chromatographic Analysis o f Lower Fatty Acids, Phenols andlndoles i n Faeces and Saliva Using a Fused Silica Glass Capillary Column-Yasuyuki Hoshika and Ninzo MurayamaIonic Polymerisation as a Means of End-point Indication i n Non-aqueous ThermometricTitrimetry.Part XI. The Reaction Mechanism o f lodimetric End-point Indica-tion and an Evaluation o f a Copolymerisation Indicator Reaction-Edward J.Greenhow and G. Louis JeyarajVoltammetric Studies o f Zomepirac Sodium and i t s Determination i n Tablets byDifferential-pulse Polarography-Leslie G. Chatten, Stanley Pons and LawrenceArnankwaTransient Potential Shifts w i t h pH Glass Electrodes Due t o Divalent Cations-Colin D.KennedyInfluence o f Instability o f Thiocyanate in Argentimetry and Mercurimetry-EdrnundBishop, David Darker, Michael D. Jones, Paul M. Stewart and Salah M. SultanFlow Injection Analysis System f o r Determining Soil pH-Tony E. Edmonds and GraceCouttsSHORT PAPERS1018 Rapid Spectrophotometric Determination o f Nitrate w i t h Phenol-Noel Velghe andAlbert Claeys1022 lodimetric Micro-determination o f Aliphatic Acids by a Potentiometric TitrationMethod and Comparison w i t h Acid - Base Potentiometry-Anjou Wadhwa and RajMohan VerrnaDetermination of Nitrate in Lake Water by the Adaptation o f the Hydrazine - CopperReduction Method f o r Use on a Discrete Analyser: Performance Statistics and anInstrument-induced Difference from Segmented Flow Conditions-John Hiltonand Eric Rigg1029 BOOK REVIEWS1026Summaries of Papers in this Issue-Pages iv, v. vi, vii, viii, ix, x, xiiPrinted by Heffers Printers Ltd Cambridge EnglandEntered as Second Class at New York, USA, Post Offic

ISSN:0003-2654    

DOI:10.1039/AN98308BX031

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

iv SUMMARIES OF PAPERS I N THIS ISSUE August, 1983Summaries of Papers in thisCombination of Flow Injection Analysis with Flame Atomic-absorption Spectrophotometry : Determination of Trace Amountsof Heavy Metals in Polluted SeawaterA simple flow injection system, the FIAstar unit, was used to inject samplesof seawater into a flame atomic-absorption instrument allowing the deter-mination of cadmium, lead, copper and zinc a t the parts per million level a ta rate of 180-250 samples per hour. Further, on-line flow injection analysispre-concentration methods were developed using a microcolumn of Chelex- 100resin allowing the determination of lead a t concentrations as low as 10 partsper loB (p.p.b.) and 1 p.p.b. for cadmium and zinc. The sampling rate wasbetween 30 and 60 samples per hour and the readout was available within60-100 s after sample injection; the sampling frequency depended on thepre-concentration required.Keywords : Heavy metals determination ; flow injection analysis ; flameatomic-absorption spectrophotornetry ; trace awnlysis ; polluted seawaterSVEND OLSEN, LUIZ C.R. PESSENDA, JAROMIR RfikICKA andEL0 H. HANSENChemistry Department A, The Technical University of Denmark, Building 207,DK-2800 Lyngby, Denmark.Analyst, 1983, 108, 905-917.Determination of the Chemical Forms of Cadmium and Silver inSediments by Zeeman Effect Flame Atomic-absorptionSpectrometryA polarised Zeeman flame atomic-absorption spectrometer has been used forthe determination of cadmium and silver in chemical extracts of sedimentsusing a procedure designed to provide information on the potential availabilityof trace elements.The limit of determination for complex solution matriceswas found to be 1.1 pg 1-1 for both cadmium and silver. Minimum base-linenoise for the instrument afforded very good stability of the calibration con-ditions a t the 10 pg 1-1 level for the two elements. Accuracy tests performedwith standard reference materials showed good agreement for the determi-nations in the extracts. The analysis of suspended and bottom sediments isused to demonstrate the value of this instrumental technique.Keywords : Zeeman game atomic-absorption spectrometry ; chemical forms ;cadmium determination ; silver determination ; sedimentsKEN R.LUMEnvironmental Contaminants Division, National Water Research Institute, CCIW,P.O. Box 5050, Burlington, Ontario L7R 4A6, Canada.and DUART G. EDGARNissei Sangyo Canada Inc., 89 Galaxy Blvd., Suite 14, Rexdale, Ontario M9W 6A4,Canada.Analyst, 1983, 108, 918-924August, 1983 SUMMARIES OF PAPERS I N THIS ISSUE VDetermination of Caesium and Rubidium by Flame and FurnaceAtomic- absorption SpectrometryCaesium and rubidium have been determined by flame and furnace atomic-absorption spectrometry. It was found that both techniques are reasonablyfree from interferences and accurate enough for the routine analysis of varioustypes of samples.Keywords : Caesium determination ; rubidium determination ; atomic-absorptionspectrometry2. GROBENSKI, D.WEBER, B. WELZ and J. WOLFFBodenseewerk Perkin-Elmer & Co. GmbH, Postfach 1120, D-7770 Uberlingen,Federal Republic of Germany.Analyst, 1983, 108, 925-932.Pyridine-2-aldehyde 2-Furoylhydrazone as a Fluorogenic Reagentfor the Determination of Nanogram Amounts of GalliumThe synthesis, characteristics and analytical applications of pyridine-2-aldehyde 2-furoylhydrazone (PAFH) are described. This compound hasbeen examined to evaluate its usefulness as a selective and sensitive spectro-fluorimetric reagent for gallium. The method is applied in 0.8% ethanolicsolution a t pH 4.5. Under these conditions the fluorescent species haveexcitation and emission maxima a t 380 and 445 nm, respectively. Thedetection limit is 0.8 ng ml-l and the range of application is between 1 and50ngml-l.The method has been employed to determine gallium in syn-thetic mixtures and its recovery from human urine samples.Keywords: Gallium determination; pyridine-2-aldehyde 2-furoylhydrazonereagent ; spectrofluorimetryELOISA REQUENA, JOSR J. LASERNA, AURORA NAVAS andFRANCISCO GARCfA SANCHEZDepartment of Analytical Chemistry, Faculty of Sciences, University of MAlaga,MQlaga-4, Spain.Analyst, 1983, 108, 923-938.Spectrophotometric Determination of Arsenic in Biological Tissuesand Sediments After Digestion With Nitric, Sulphuric andPerchloric Acids and Pre- concentration by Zinc Column ArsineGeneration and TrappingA procedure for the determination of total arsenic in environmental extractsis described.Arsenic is converted into arsine using a zinc reductor column,the evolved arsine trapped in a potassium iodide - iodine solution and thearsenic determined spectrophotometrically as an arsenomolybdenum bluecomplex. The detection limit (based on four times the standard deviationof six blank measurements) is 0.024 p g and the coefficient of variation is 5.1 yoat the 0.1- pg level. The method is free from interferences by other elementsa t levels normally found in environmental samples.Keywords : Arsenic determination ; hydride generation and trapping ; mole-cular-absorption spectrophotometry ; environmental materialsW. A. MAHERDepartment of Oceanography, University of Southampton, Southampton, SO9 SNH.Analyst, 1983, 108, 939-943vi SUMMARIES OF PAPERS IN THIS ISSUESpectrophotometric Determination of Phosphorus and Arsenic inSteel by Solvent Extraction of their Heteropolyacids with Ethyl VioletAugust, 1983Under the same conditions, orthophosphate and ortlioarsenate react withmolybdate to form molybdophosphate and arsenomolybdate, which areextracted into a cyclohexane - 4-methylpentan-2-one mixture (1 + 3) withethyl violet.The absorption spectrum of each ion pair, extracted into theorganic phase, is almost the same in the visible region and the molar absorp-tivity of each ion pair in the organic phase is 2.8 x lo6 1 mol-l cm-l a t 602 nm.In determining phosphate, arsenate can be masked with thiosulphate andhydroxylamine. The arsenate concentration was obtained by subtractingthe phosphate concentration from the total concentration of phosphate andarsenate.Steel samples (less than 0.25 g in mass) were dissolved in aquaregia and the solution was diluted to 11 with distilled water. In the deter-mination of phosphorus (about 0.003y0) and arsenic (about 0.007~0) in steel,the relative standard deviations were 2.5 and 2.1 Yo, respectively. Fifteenstandard steel samples were analysed, and the results obtained for phosphorusand arsenic were in good agreement with their certified values. The resultsfor the recovery test were also good. The limit of detection for both phosphorusand arsenic is about O.OOlyo in steel.Keywords Phosphorus and arsenic determination ; solvent extraction ; hetero-polyacid; steel analysis ; ethyl violetSHOJI MOTOMIZU, TOSHIAKI WAKIMOTO and KYOJI TOE1Department of Chemistry, Faculty of Science, Okayama University, Tsushima-naka,Okayama-shi, JapanAnalyst, 1983, 108, 944-951.Extraction and Spectrophotometric Determination of Titanium( IV)with N- Phenyllaurohydroxamic Acid and PhenylfluoroneN-Phenyllaurohydroxamic acid reacts with titanium(1V) in 9-10 Mhydrochloric acid to give a coniplex that is completely extractable intosolvents such as hexane and chloroform.The chloroform extract of thetitanium complex, on second extraction from a dilute hydrochloric acidmedium (0.1-0.5 M), in the presence of phenylfluorone and isoaniyl alcohol,forms an intensely coloured complex possessing an absorption maximum at540 nm. Even though the molar absorptivity of the complex under optimumconditions at 540 nm is 2.33 x lo5 1 niol-l cm-l, the measurements are moreprecise at 560 nm with a molar absorptivity of 1.23 x lo5 1 mol-l cm-l.Thesystem obeys Beer’s law for up to 0.4 p.p.m. of titanium(1V). Considerableamounts of many cations and anions including a 350-fold molar excess ofiron(II1) can be tolerated. Interference from zirconium(1V) can be mitigatedor even eliminated by the addition of fluoride ions. The method can beapplied to the determination of titanium present at 10 parts per lo9.Keywords : Titanium(I V ) determination ; spectrophotometry ; N-phenyllauro-hydroxamic acid; Phenyljuorone ; liquid - liquid extractionH. DASARATHA GUNAWARDHANATrace Analysis Research Centre, Chemistry Department, Dalhousie University,Halifax, Nova Scotia, B3H 4 J 1, Canada.Analyst, 1983, 108, 952-958August, 1983 SUMMARIES OF PAPERS IN THIS ISSUESpectrophotometric Determination of Rhodium(II1) in Aqueousand Alcoholic Media Using 2- Thiobarbituric AcidA spectrophotometric study of the rhodium(II1) - 2-thiobarbituric acidsystem is presented.Rhodium(II1) forms 1 : 2 and 1 : 4 complexes with 2-thio-bartituric acid in water and 98% ethanol, respectively. Conformity toBeer’s law a t 327 nm was observed for up to 14 pg ml-l of rhodium in waterand for up to 12 p g ml-l in 98% ethanol and the detection limits were 0.24and 0.34 pg ml-l of rhodium, respectively. Molar absorptivities at 327 nmin aqueous and alcoholic media were 1.04 x lo4 and 1.08 x lo4 1 mol-l cm-land Sandell’s sensitivities were 0.009 8 and 0.099 5 pg cm-2, respectively.The tolerance of the system to platinum metals and other common cationsis reported, the method is evaluated and a comparison with the maincolorimetric methods for rhodium determination developed in recent years ispresented.Keywords : Rhodium determination ; 2-thiobarbituric acid ; spectrophotometryBASIL10 MORELLIUniversitk degli Studi di Bari, Dipartimento di Chimica, Via Amendola 173, 70126-Bari, Italy.Analyst, 1983, 108, 959-965.ViiRapid Spectrophotometric Determination of Saccharin in SoftDrinks and Pharmaceuticals Using Azure B as ReagentSaccharin reacts quantitatively with Azure B in disodium hydrogen ortho-phosphate - citric acid buffer forming a blue product that can be extractedinto chloroform.Beer’s law is valid over the concentration range 2-68 pg ml-lof saccharin and the molar absorptivity is 2.4 x lo3 1 mol-l cm-l. Reasonableamounts of ingredients that are likely to be present in soft drinks and pharma-ceuticals do not interfere. Recoveries of saccharin from soft drinks andpharmaceuticals were satisfactory.Keywords : Saccharin determination ; spectrophotometry ; soft drinks ; fiharma-ceuticals; Azure BP. G. RAMAPPA and ANANT N. NAYAKDepartment of Post-Graduate Studies and Research in Chemistry, University ofMysore, Manasa Gangotri, Mysore-570006, India.Analyst, 1983, 108, 966-970.Interfacing an Automatic Elemental Analyser with an Isotope RatioMass Spectrometer: the Potential for Fully Automated TotalNitrogen and Nitrogen- 15 AnalysisAn interface between an automatic nitrogen analyser and an isotope massspectrometer is described.The interface enables total nitrogen analyses andnitrogen isotope ratio measurements to be made semi-automatically, a t therate of 12 h-l. The precision of the measurements was a t the detection limitof the mass spectrometer (0.00026 atom-% 15N; &0.7O/oO). No significantcross-contamination between samples was observed (< 0.02% carry over).The potential for full automation and extension of the interface for otherstable isotope measurements is discussed.Keywords : Nitrogen- 15 isotope mass spectrometry ; automatic nitrogen analysis ;elemental gas chromatograph - mass spectrometer interfaceTHOMAS PRESTONScottish Universities Research and Reactor Centre, N.E.L. Estate, East Kilbride,Glasgow, G75 OQU.and NICHOLAS J.P. OWENSNatural Environment Research Council, Institute for Marine EnvironmentalResearch, Prospect Place, The Hoe, Plymouth, PL1 3DH.Analyst, 1983, 108, 971-977viii SUMMARIES OF PAPERS I N THIS ISSUEDetermination of Phosgene in Methylene Chloride AfterCgclisation With a 2-Hydroxyamine and Gas ChromatographyWith Nitrogen-selective DetectionAugust, 1983A convenient and simple method for the determination of phosgene inmethylene chloride has been developed. An aliquot of the sample is mixedwith a solution of metoprolol or 2-aminophenol, in an excess. After a reactiontime of 10 min the solution is taken to dryness and the cyclic derivativeanalysed by gas chromatography with nitrogen-selective detection.Theprecisions (relative standard deviation) a t the 40 and 10 ng nil-l levels were3.9 and 7.3% for metoprolol and 3.3 and 3.6% for 2-aminophenol, respec-tively. The absolute yields at the 40 ng ml-l level were 91 and 95%, respec-tively. The present limit of detection is approximately 1 ng ml-1. Phosgeneappeared in methylene chloride (> 2 ng ml-l) stabilised with 20 p.p.m. ofamylene within 3 d if stored in clear glass in the presence of daylight. After15 d the 100 ng ml-l level was reached.Keywords : Phosgene determination ; 2-hydroxyamines ; gas chromatography ;nitrogen-selective detection; methylene chlorideOLLE GYLLENHAALAnalytical Chemistry, AB Hassle, S-431 83 Molndal, Sweden.Analyst, 1983, 108, 978-983.Simultaneous Gas- chromatographic Analysis of Lower Fatty Acids,Phenols and Indoles in Faeces and Saliva Using a FusedSilica Glass Capillary ColumnThe simultaneous gas-chromatographic separation of a mixture of 14 lowerfatty acids, 11 phenols and 7 indoles was performed by using a fused silicaglass capillary column of Carbowax 20M (50 m x 0.2 mm i d ., Carbowax20M deactivated). Complete separation of the mixture was obtained, exceptfor the peaks of phenols and o-cresol, o-ethylphenol and 3,5-xylenol andpelargonic acid, 2,3-xylenol and lt2-dimethy1indole, whose peaks overlapped,and 2- and 3-methylindoles, which were poorly separated. The optimumconditions are as follows: column temperature, held for 1 min at 100 "C;column oven, heated at 4 "C min-1 from 100 to 220 "C, maintained at 220 "Cfor 9min for standard compounds or 29min for sample specimens, thencooled to 100 "C; and carrier gas (nitrogen) flow-rate, 0.97 ml min-l. Themethod was applied to the analysis of the lower fatty acids, phenols andindoles in cat and human faeces and non-smoker saliva.Keywords : Gas chromatography ; fused silica glass capillary column ; faecesanalysis ; lower fatty acids, phenols and indolesYASUYUKI HOSHIKA and NINZO MURAYAMADepartment of Hygiene, Shinshu University School of Medicine, 3-1-1, Asahi,Matsumoto-shi, Nagano, 390, Japan.Analyst, 1983, 108, 984-990

ISSN:0003-2654    

DOI:10.1039/AN98308FP077

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

August, 1983 SUMhIARIES OF PAPERS IN THIS ISSUEIonic Polymerisation as a Means of End-point Indication inNon-aqueous Thermometric Titrimetry. Part XI. The ReactionMechanism of Iodimetric End -point Indication and an Evaluationof a Copolymerisation Indicator ReactionixThe mechanism of the reactions marking the end-point when ethyl vinylether is used as the indicator reagent in the thermometric titration of iodine-reactive analytes with solutions of iodine in dimethylformamide has beeninvestigated by capillary gas chromatography - mass spectrometry. Threemajor constituents, ICH,CH (OEt) CH,CH(OH) (OEt), I [CH,CH(OEt)],CH,CH-(OH) (OEt) and I[CH,CH(OEt)],CH,CH(OH)(OEt) have been identified,confirming the occurrence of a polymerisation process initiated by the iodoniumion.The hydroxy group in the molecules arises from the use of aqueousthiosulphate to terminate the polymerisation.An improvement in end-point sharpness using this catalytic thermometricprocedure is effected by using a mixture of ethyl vinyl ether and 1,3-dioxolaneas the indicator reagent instead of ethyl vinyl ether alone. The temperaturerise in this copolymerisation reaction is greater than in the ethyl vinyl etherhomopolymerisation, and the end-point inflection is sharper.Keywords : Non-aqueous thermometric iodimetry ; end-point indication ; ethylvinyl ether ; 1,S-dioxolane ; copolymerisationEDWARD J. GREENHOW and C. LOUIS JEYARAJDepartment of Chemistry, Chelsea College, University of London, Manresa Road,London, SW3 6LX.Analyst, 1983, 108, 991-996.Voltammetric Studies of Zomepirac Sodium and its Determinationin Tablets by Differential-pulse PolarographyA simple differential-pulse polarographic method has been developed for thedetermination of zoniepirac sodium in tablets.Britton - Robinson bufferof pH 1 1 0, containing 5:o I./ I’ of methanol, was employed as the supportingelectrolyte. The peak potential occurs a t - 1.50 V. Results obtained bythe proposed method are in excellent agreement with those provided by bothtlie official and tlie manufacturer’s methods of assay. It was found thatcommonly used tablet escipients did not interfere in the analyses.Keywords : Zomepirac sodzuiiz detewuination; dinerendial-pulse polarography ;controlled-potential coulowetvy ; cyclic voltnvlznzetry ; tabletsLESLIE G.CHATTEN, STANLEY PONS and LAWRENCE AMANKWAFaculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton,Alberta, T6G 2N8, Canada.Analyst, 1983, 108, 997-1002X SUMMARIES OF PAPERS IN THIS ISSUETransient Potential Shifts with pH Glass ElectrodesDue to Divalent CationsAugust, 1983The introduction of low concentrations of Cu2+, Ni2+, Co2+, Mn2+, Zn2+, Cd2+and Hg2+ salts into unbuffered aqueous solutions gave rise to transientpotential shifts with glass pH electrodes. These shifts mimic transitory pHdecreases in solution. Removal of the added cation gave rise to a transientpotential shift in the opposite direction. The relative order of magnitude dueto the added cations was studied.The quasi-pH shifts were shown to beparticularly serious in flow cells where the vigour of mixing was less andcould easily lead to the inipression that an actual pH transient had occurred.The effects were shown to be due to a surface action at the glass membrane.A possible mechanism is suggested.Keywords : pH glass electrodes ; divalent cations ; pow cell; transient potentialsCOLIN D. KENNEDYDepartment of Biochemistry, Physiology and Soil Science, Wye College, (Universityof London), Wye, Ashford, Kent, TN25 5 h H .Analyst, 1983, 108, 1003-1006.Influence of Instability of Thiocganate in Argentimetryand MercurimetryThe silver - thiocyanate and mercury(I1) - thiocyanate reactions have beenexamined by precise mass titrimetry for possible errors arising from decomposi-tion of thiocyanate in nitric acid media.For silver, potentiometric titrationin either direction in 0.15 mol kg-l nitric acid is free from error provided stepsare taken to overcome adsorption, but thiocyanate cannot be stored a t thisacid concentration. Using iron(II1) as the indicator, visual titration in theVolhard direction (thiocyanate titrant) is unaffected by time delay, acid con-centration and indicator concentration ; in the reverse direction an error of theorder of 0.5% is incurred and increases as time, acid and indicator concentra-tion increase. For mercury(II), potentiometric titration is unsatisfactory inboth directions. Standard mercury( 11) ion solutions hydrolyse in nitric acidless than 4.0 mol l-l, while thiocyanate is unstable in solutions contakingmore than 0.05 mol 1-1 of nitric acid.Neutral thiocyanate solution andmercury(I1) solution in 4.0 mol 1-1 nitric acid can be titrated in eitherdirection using iron(II1) as the indicator, but the precision is poor and timedelays are not tolerated. Higher indicator concentrations favour betterprecision through increased ease in locating the end-point.Keywords : Thiocyanate titrations ; Volhard titration ; mercury(II) - thio-cyanate titration; iron(III) - thiocyanate indicator; stability of mercury(II)ion and thiocyanate solutionsEDMUND BISHOP, DAVID DARKER, MICHAEL D. JONES, PAUL M.STEWART and SALAH M. SULTANChemistry Department, University of Exeter, Stocker Road, Exeter, EX4 4QD.Analyst, 1983, 108, 1007-1012xii SUMMARIES OF PAPERS I N THIS ISSUE August, 1983Flow Injection Analysis System for Determining Soil pHA flow injection analysis system is described for the determination of soilpH in filtered 0.01 M calcium chloride solution extracts. The system is con-structed entirely from off -the-shelf components and is capable of analysingup to 90 samples in 1 h.The unbuffered nature of filtered soil extracts causesproblems in terms of electrode response times and imposes restrictions onthe composition of the carrier-stream buffer and reference standards.Keywords : Flow injection analysis ; soil p HTONY E. EDMONDS and GRACE COUTTSThe Macaulay Institute for Soil Research, Craigiebuckler, Aberdeen, Scotland.Analyst, 1983, 108, 1013-1017.Rapid Spectrophotometric Determination of Nitrate with PhenolShort PaperKeywords ; Nitrate determination ; spectrophotometry ; phenol ; nitriteNOgL VELGHE and ALBERT CLAEYSLaboratory of Analytical Chemistry, University of Ghent, B-9000 Ghent, Belgium.Analyst, 1983, 108, 1018-1022.Iodimetric Micro - determination of Aliphatic Acids by aPotentiometric Titration Method and Comparison withAcid - Base PotentiometryShort PaperKeywords : Aliphatic acid micro-determination ; potentiometry ; iodate, iodideand sodium hydroxide reagentsANJOU WADHWA and RAJ MOHAN VERMADepartment of Post-Graduate Studies and Research in Chemistry, University ofJabalpur, Jabalpur 482001 (M.P.), India.Analyst, 1983, 108, 1022-1025.Determination of Nitrate in Lake Water by the Adaptation of theHydrazine - Copper Reduction Method for Use on a DiscreteAnalyser : Performance Statistics and an Instrument-inducedDifference from Segmented Flow ConditionsShort PaperKeywords : Nitrate determination ; hydrazine - copper reduction ; lake water ;discrete analyser ; flow injection analysisJOHN HILTON and ERIC RIGGFreshwater Biological Association, Windermere Laboratory, The Ferry House,Far Sawrey, Ambleside, Cumbria, LA22 OLP.Analyst, 1983, 108, 1026-1028

ISSN:0003-2654    

DOI:10.1039/AN98308BP083

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

AUGUST 1983 The Analyst Vol. 108 No. 1289 Combination of Flow Injection Analysis with Flame Atomic-absorption Spectrophotometry: Determination of Trace Amounts of Heavy Metals in Polluted Seawater Svend Olsen Luiz C. R. Pessenda," Jaromir RfiziCka and Elo H. Hansen Chemistry Department A The Technical University of 3enmark Building 207 DK-2800 Lyngby Denmark A simple flow injection system the FIAstar unit was used to inject samples of seawater into a flame atomic-absorption instrument allowing the deter-mination of cadmium lead copper and zinc at the parts per million level at a rate of 180-250 samples per hour. Further on-line flow injection analysis pre-concentration methods were developed using a microcolumn of Chelex- 100 resin allowing the determination of lead at concentrations as low as 10 parts per los (p.p.b.) and 1 p.p.b.for cadmium and zinc. The sampling rate was between 30 and 60 samples per hour and the readout was available within 60-100 s after sample injection; the sampling frequency depended on the pre-concentration required. Keywords Heavy metals determination ; flow injection analysis ; flame atomic-absorption spectrophotometry ; trace analysis ; polluted seawater Atomic-absorption spectrophotometry (AAS) is a well established extremely valuable tech-nique for the determination of trace amounts of metals. Since its introduction by Walsh,l the method has gone through a number of development stages aiming at obtaining an increase in reliability ease of operation and above all improvement in the limit of detection.Hence, atomisation by a flame has been supplemented or replaced by the graphite furnace technique, background correction has been introduced to compensate for non-specific absorption phenomena and most recently background correction has by exploiting the Zeeman effect, become more sophisticated by incorporating a polariser and a magnetic field into the commer-cial instruments. However despite all these improvements the assay of trace amounts of metals in samples with high salt content such as seawater still remains a time-consuming and difficult task. Because the high salt content in evaporated samples might result in clogging of the burner or poisoning of the inner surface of a graphite tube heavy metals generally have to be pre-separated from the salt matrix either by solvent extraction or by ion exchange.While diethyldithiocarbamate extraction into isobutyl methyl ketone is widely used this method is far from ideal because besides being laborious it also requires very careful work if blank values are to be kept low. Further analysis of a large number of samples yields along with the analytical results considerable volumes of used organic solvents that have to be disposed of in environmentally acceptable ways. Therefore there is a marked tendency to use another pre-concentration technique that is ion exchange on Chelex-100 resin,2 which is efficient and yields low blanks3 A recent paper by Danielssen et and an older yet much more detailed paper by Kingston et aZ.,5 have summarised the present state of seawater assays based on ion exchange.Thus a typical procedure requires 100-500 ml of seawater which is to be passed through a column containing 5 g of Chelex-100 at a rate of 2 ml min-l, followed by elution into 10 ml of 5 M nitric acid. Hence pre-concentration of a single sample by a factor of ten will require over 1 h while one 1-1 sample volumes have to be pre-concen-* Present address Centro de Energia Nuclear na Agricultura (CENA) Universidad de Sao Paulo, 13.40O-Piracicaba S.P. Brazil. 90 906 OLSEN et &. FIA WITH FLAME AAS DETERMINATION ANabySt vd. 108 trated overnight. Using this pre-concentration procedure and graphite furnace atomic-absorption spectrophotometry lead and cadmium concentrations down to the 0.5 parts per 109 (p.p.b.) level have been determined in seawater.Flow injection analysis (FIA)6 in combination with atomic-absorption spectrophotometry was first suggested and used by Zagatto et aZ.' as a means to dilute and to add lanthanum solution prior to sample introduction into the flame. As the reagent addition was done in the zone-merging mode both reagent and time economy were improved; indeed a sampling fre-quency of 300 samples h-l was achieved. Independently Wolf and Stewarts replaced aspira-tion by sampling via an FIA system achieving a sampling rate of 180 samples h-l. Standard addition and matrix effect compensation using FIA was recently suggested by Tyson and I d r i ~ ~ while the unique ability of FIA - AAS to handle samples with high salt contents (up to 25% magnesium chloride solution) was demonstrated by Mindel and Karlberg.lo The use of FIA as an on-line pre-concentration for flame-atomic absorption (FAA) has so far been based on low-flow solvent extraction and has been applied to assay for copper.ll However the flow system requiring solvent separation and re-injection seems to be complicated.The purpose of this work was to develop a rapid and reliable technique for screening of a large number of seawater samples while determining their lead cadmium zinc and copper contents. At levels of 10-4.1 p.p.m. this has been done by direct sampling of seawater into the flame using the FIAstar system.12 However samples with lower heavy-metal contents had to be pre-concentrated within a more sophisticated FIA system that was equipped with peristaltic pumps and microcomputer control.The method was to be used for the environ-mental control of an area around Marmorilik in Greenland where the water contamination, caused by extensive mining activity must be strictly controlled. This involved analysis of a large number of water samples collected at the mining plant itself and in the adjacent fjord system and therefore economy of time reagent consumption and acquisition of instrumenta-tion were besides the reliability of the method the important design parameters. Experimental Apparatus The atomic-absorption spectrophotometer (Varian Model AA-1275) was connected in parallel to a recorder (Radiometer Servograph REC 80 furnished with an REA 112 high-sensitivity module) and via a home-made interface to a computer (PET Commodore Model 3032 combined with a Commodore CBM Model 2040 dual-drive floppy disk) and a printer (Tractor Model 3022).For the FIA systems shown in Figs. 4 and 7 and for the automated system (Fig. 10) the contact to the computer was triggered by a microswitch in the injection valve of the FIA system which served to inform the computer of the sequence of events. The automated system in Fig. 10 additionally included a timer that controlled the timing of the stop - go intervals of the two attached peristaltic pumps (Ismatec Model Mini-S-840). The flow injection system consisted of a FIAstar unit details of which have been published elsewhere12 (for actual manifold designs used in this study see Results and Discussion). All connecting tubes consisted of 0.5 mm i.d. Microline.As the FIAstar valve is furnished with an external loop in order to regulate the injected sample volume change of volume was simply effectuated by changing the external loop. For small sample volumes (less than 200 p1) the sample loop consisted of 0.5 mm i.d. tubing while tubes of larger i.d. were used for larger sample volumes (up to 1.57 mm i.d. for sample volumes exceeding 1 ml). Reagents All chemicals were of analytical-reagent grade and re-distilled water was used throughout. All reagent and standard solutions were stored in clean polyethylene bottles. Standard solutions of lead(II) cadmium(II) zinc(I1) and copper(1I) were made up by suitable dilutions of 1000 p.p.m. aqueous standard solutions for AAS (BDH Chemicals), certified by the manufacturer to contain 1000 & 5 mg 1-1 of the metal.In order to simulate the matrix of the actual water samples all standards were prepared by dilution with water containing 31.3 g 1-1 of sodium chloride and 3 ml l-1 of concentrated nitric acid. The samples originated from a mining plant at Marmorilik in Greenland collected partly in the fjord system near the plant and partly in the plant itself where large volumes of seawate August 1983 OF HEAVY METALS IN POLLUTED SEAWATER 907 from the fjord are used in the flotation process for separating the minerals from the parent rock material. Prior to shipment from Greenland to Denmark all samples were preserved by adding 3 ml of concentrated nitric acid per litre of sample solution. The ammonium acetate buffer solutions used in the FIA system were prepared by aqueous dilutions of a 2 M stock solution made by mixing 55.5 ml of 99% acetic acid with 112.5 ml of 25% ammonia solution; re-distilled water was added to a total volume of 500 ml.Any re-adjustment of the pH in the diluted solutions (see Results and Discussion) was done by the addition of ammonia. The Chelex-100 cation-exchange resin 50-100 mesh (sodium form) was purchased from Bio-Rad Laboratories. Preparation of Chelex- 100 Microcolumn The microcolumn was made from the FIAstar gradient tube which is a Perspex block into which is drilled a 50 mm long channel of 2 mm i.d. furnished at both ends with threaded term-inals so that the connecting tubes can be securely attached by means of screws and gaskets as used for all FIAstar connections.12 Prior to packing the Chelex-100 resin was converted to the ammonium ion form by storing it in a large volumetric excess of 0.05 M ammonium acetate buffer solution for 2 d shaking the slurry intermittently and renewing the buffer solution 2-3 times each day.Being now ready for packing the resin in the ammonium ion form may be stored in the buffer solution for extended periods of time but it is recommended that the resin is washed with fresh buffer solution 2-3 times prior to packing. For packing the column the resin - buffer slurry was aspirated into a l-ml syringe the con-tents of which were then carefully emptied into the column. At the end of the column a small piece of polyurethane foam was inserted to entrap the resin particles mechanically within the column.The process was repeated until the column was completely filled with resin each time taking care that the introduction of air was avoided. Fully packed and closed at both ends by polyurethane foam the column contained about 25 mg of resin. As a routine all new columns were conditioned in the FIA system for about 10 min during which time ammonium acetate buffer solution and 2 M nitric acid solution were pumped through the column inter-mitt en tly . Results and Discussion Direct Injection of Sample Material The simplest approach to the water assays was tested by combining the Varian AA-1275 FAA spectrophotometer with the simplest FIA unit commercially available the FIAstar. The FIAstar unit originally developed for students teaching and research,12 is a robust modular system consisting of an injection valve (loop type so that the injected volume may be varied) assorted connectors coils and a carrier stream propulsion unit.The carrier stream is propelled by gas (air or nitrogen) and the very low pressure (0.1-0.5 bar) is maintained by means of a precision regulator. In this work the FIA system serves mainly as a means of Fig. 1. Single-line FIA - FAA manifold where the carrier solution (C) (5 x M sulphuric acid) is propelled by gas main-tained at a pressure P of 0.5 bar corresponding to a flow-rate of 4.9 ml min-l. A sample volume of 150 pl is injected by means of valve S and then passed through the shortest possible length of line (20 cm) to the FAA instrument. In order to obtain optimum performance of the system it is necessary to operate the pro-pulsion of the FIA system a t a higher flow-rate than the aspiration rate of the nebuliser of the FAA instrument (3.1 ml min-l).W = Waste 908 OLSEN ef at!. FIA WITH FLAME AAS DETERMINATION Analyst Vd. 108 transport and of exact timing and so a single line limited dispersion configuration6 was chosen and assembled (Fig. l) using tubing of 0.5 mm i.d. between the injection valve (S) and the FAA instrument. The useful calibration range for each of the four metal species was established by injecting a series of standards into the continuously flowing non-segmented carrier stream of 5 x 10-4 M sulphuric acid while the absorbance as measured by the FAA instrument was continuously recorded [Fig. 2 ( a ) ] . In all instances plots of the peak height zlenus concentration yielded strictly linear calibration graphs.Calculating the limit of detection (LOD) according to the recommendations in reference 13 a value of 0.010 p.p.m. was found for zinc while the maximum attainable sample frequency was 250 samples h-l with the readout available within 5 s after sample injection [Fig.- 2(6)j Copper cadmium and lead yielded equally satisfactory results (Table I). TABLE I PERFORMANCE DATA OF THE FIA - FAA SYSTEM WITH DIRECT INJECTION OF SAMPLE The sample volume was 150 pl. Element assayed Par am e ter Wavelength/nm . . LOD* (20),t p.p.m. . . LOD (20),$ p.p.m. . . LOD (34 p.p.m. . . LOQS (loo) p.p.m. . . Characteristic concentration tq p.p.m. . . Characteristic concentration $ p.p.m.. . . . Sensitivity,ll AA/Ap.p.m. . . Correlation coefficient. . Cadmium 228.8 0.007 0.001 5 0.009 0.030 0.01 1 0.01 0.220 0.9990 Copper 324.7 0.001 0.003 0.005 0.032 0.035 0.03 0.100 0.999 1 Lead 217.0 0.01 0.01 0.032 0.227 0.049 0.1 0.037 0.996 3 7 Zinc 213.9 0.007 0.000 8 0.010 0.026 0.011 0.008 0.498 0.999 2 * Limit of detection based on a 95.5% (20) and 99.7% (30) confidence level. t As found in this work. # As reported by the manufacturer. § LOQ limit of quantitation.13 7 Characteristic concentration defined as that concentration of the element which gives rise to 11 Sensitivity (the slope of the calibration graph) and correlation coefficient as found when operating 0.0044 absorbance unit (z.e.1 % absorption). the FIA - FAA system within the working range of the AA-1275. Whenever a flow injection system is being combined with a conventional instrumental method a natural question is asked “What is the trade-off between the increased sampling frequency and the loss of sensitivity caused by the readout of peak height rather than at the steady state?” The answer for this FIA - FAA combination is given in Fig. 2(b) where the recorder response is shown as obtained with a 1.5 p.p.m. zinc standard solution continuously aspirated in the conventional mode (B) and injected with a 15O-pl sample volume (A). It is obvious that the FIA peak is only 20% lower than the steady-state plateau but being much narrower with a standard deviation of ut = 1.5 s it allows theoretically a sampling fre-quency (Smax.) as high as 600 samples h-l [Sma,.= 3600/kut where k = 4 (reference S ) ] . In other words “the peak value for any given time f is as good a measure of the concentration of the analyte as the final steady state reached,” as already stated in the first paper on FIA.14 This feasible trade-off between sensitivity and sampling frequency is the result of careful design of the geometry of the flow channel of the injection unit and of the injected sample volume. Indeed the dispersion coefficient D = Co/Cmax. = 1.3,15 where C the concentra-tion [Fig. 2(b)] has a value confirming that a limited dispersion of the injected sampling plug has been achieved. Examination of the effects caused by the seawater matrix which in the samples originating from the coastal waters of Greenland may reach up to 3.3% salinity was the next step in th August 1983 OF HEAVY METALS IN POLLUTED SEAWATER 909 1 1.3 Q 2 Scan + Fig.2. Recordings obtained with the single-line FIA - FAA system of Fig. 1 and the flow charac-teristics detailed there. (a) Calibration run for zinc as obtained by the injection of 0.1 0.2 0.5, 0.75 1.0 1.5 and 2.0 p.p.m. zinc standards (sample volume 150 pl). (b) Recorder response for the 1.5 p.p.m. zinc standard as obtained by (A) injection via the FIA system and (B) continuous aspiration in the conventional mode. For the sake of comparison the aspiration rate in (B) was increased to 4.9 ml min-l corresponding to the propulsion rate used in (A) where S is the point of injection.Wavelength used in (a) and (b) 213.9 nm. D represents the dispersion number which in (B) is equal to 1. development of the method. Thus Fig. 3 shows a set of calibration recordings for a series of lead standards prepared with and without the addition of sodium chloride simulating the actual matrix of the seawater samples. Because the sampling period is only a fraction of each measuring cycle during the length of which the carrier stream flows uninterruptedly the nebuliser and the burner are effectively washed and therefore no salt deposit is being built up. Thus as originally observed by Mindel and Karlberg,lo large series of seawater samples may be analysed by FAA with no 2 0% T 3.3% Scan + b) 10.05 0.5 0.25 p.p.m. Fig. 3. Calibration runs for a series of lead standards (2 5 10 15 and 20 p.p.m.) as obtained with the FIA - FAA system of Fig.1 and the conditions rendered there recorded (a) 1 without and 2, with sodium chloride added to the standards to simulate the matrix of seawater. (b) With increased amplification the output for two lead standards containing 0.5 and 0.25 p.p.m. respectively, and the calculated values for the limit of detection (LOD) and the limit of quantitation (LOQ) attain-able with the FIA - FAA system. Wavelength used in both (a) and (b) 217.0 nm 910 OLSEN et al. FIA WITH FLAME AAS DETERMINATION Analyst VoZ. 108 adverse effect caused by the matrix. The limit of detection LOD (defined as 3 u where u is the standard deviation of the base-line fluctuation~l~) was 0.032 p.p.m.of lead and the limit of quantitation LOQ (defined as 100 of the base-line fluctuations) was 0.227 p.p.m. of lead [Fig. 3(c)]. Although these values are higher than the detection limits quoted occasionally in the literature on FAA they truly reflect the realistic limits obtained with an advanced instrument such as the Varian AA-1275 tuned to optimum performance. On-line Pre-concentration Using a Microcolumn of Chelex-100 The main advantage of using on-line pre-concentration is that all samples and standards are subjected to exactly the same treatment from the moment of injection to the moment of detection and that the same ion-exchanger column is used for all samples and standards. As all time events the geometry of flow and the ensuing chemical reactions are strictly controlled and reproducibly maintained in an FIA system; there is no need to achieve quantitative adsorption of metals from the injected sample zone although the subsequent elution must be completely effective otherwise carry-over from one sample to the next will occur.Because a number of critical parameters had to be investigated to optimise the conditions the method had to be developed in three stages as described under Single-line Two-valve System. Single-line Two-valve System This is a logical extension of the FIAstar system the components of which were used to build up the system described earlier as the direct single-line system (Fig. 1). For the FIA on-line pre-concentration procedure three units were added (Fig. 4) which were a second injection valve a mixing coil and a microcolumn (volume 150 pl 5.0 cm long) filled with Chelex-100.The carrier solution was 0.05 M ammonium acetate with which the sample zone (volume 1 .O ml) was mixed during the passage from the injection valve (S) through the coil and the bypass conduit of valve A to the Chelex-100 microcolumn. The trace amounts of metal to be assayed were adsorbed on the chelating group of the resin which has the selectivity sequence Cu 2+ > > Pb2+ > Fe3+ > AP+ > Cr3+ > Ni2+ > Zn2+ > Ag+ > Co2+ > Cd2+ > Fe2+ > Mn2+ > Ba2+>Ca2+>>Na+>H+.2 Thus metals adsorbed in neutral media can be desorbed by strong acid and by injecting 180 pl of 2 M nitric acid solution by valve A the metals originally present in the 1 ml sample volume can be released into the much smaller volume of the acid zone and then be transported into the flame where they absorb the light emitted by a hollow-cathode lamp and are measured in the usual way.Thus when samples containing 20-500 p.p.b. of lead were injected pre-concentrated and then eluted a calibration record was obtained (Fig. 5) which showed no evidence of carryover. This yielded a straight-line relationship between absorbance ( A ) and concentration (C) with a regression coefficient of 0.9999 a sensitivity of AA/Ap.p.m. = 0.517 LOD = 0.004 p.p.m. of lead and LOQ = 0.015 p.p.m. of lead. A closer examination of a single assay cycle recorded at a high chart speed [Fig. 5(b) (A)] revealed several interesting details. Each assay cycle consists of two periods the first and longer one (S-E 55 s) is the pre-concentration step and Fig.4. Single-line two-valve FIA - FAA system for on-line pre-concentration using a microcolumn of Chelex- 100. The metal-contain-ing samples (volume 1 ml) are injected by valve S into the carrier stream C (0.05 M CH,COONH,) propelled by a gas pressure P corresponding to a flow-rate of 3 ml min-l. The two components are mixed in the 1-m coil before being passed via the by-pass of valve -4 to the column (CH-100). After pre-concentration valve S is closed and a small zone of 2 M nitric acid (volume 180 p1) is injected by valve A the acid zone eluting the metal and transporting i t into the FAA instrument. During the latter sequence valve S is closed being ready for loading of the next sample.W = Waste Augzcst 1983 OF HEAVY METALS IN POLLUTED SEAWATER 911 0.25 -Q, C lu e s 2 0 - I B Scan -b Fig. 6 (a) Calibration runs for lead with a series of acidified standards (20 60 100 200 360 and 500 p.p.b.) prepared in a matrix of sodium chloride (31.3 g 1-l) using the system of Fig. 4. (b) High-speed recording of the 600 p.p.b. lead with-out (A) and with (B) background correction both sample injections started at S and the elution sequences started at E. Wavelength used in (a) and (b) 217.0 nm. the second and shorter one is the elution step (beginning at E and lasting 5 s). Two peaks appear during each assay cycle the first one low and wide the second one high and narrow the latter increasing with increasing content of lead. As the low peak appears during the pre-concentration period and can be completely eliminated by operating the FAA Varian AA-1275 spectrophotometer with background correction [Fig.5(b) (B)] it is obvious that this peak is due to non-selective absorption of light emitted by the hollow-cathode lamp by sodium atoms originating from the sample matrix (which passes through the column into the flame). The sodium interference and the influence of pH on the recovery of heavy metals on Chelex-100 has been discussed already in the first comprehensive work by Riley and Taylor,3 when it was shown how the uptake of metal increases with pH. The upper pH limit was set to 9.1, at which value calcium and magnesium precipitation was said to interfere. Although a number of papers have been published since (e.g.reference IS) Kingston et aL,5 in a more'recent work, still point out the difficulty of the complete separation of sodium which is present in high levels in seawater from heavy metals when a pH of 5.5 is used in their procedure. Having now at hand a tool to resolve the contribution of sodium to the peak height veysus that of heavy metal (Fig. 5) it was decided to investigate the influence of pH on the recovery. For this purpose solutions containing 10 20 50 and 100 p.p.b. of cadmium were prepared in 3.3% sodium chloride and subsequently injected (in duplicate) in the system depicted in Fig. 4. As already mentioned each sampling cycle consisted of a pre-concentration period, which commenced by the switching of the sample injection valve (S) followed by an elution period commencing by the injection of acid by means of valve A.Similarly to the system in Fig. 5 first the sodium and then the cadmium peak appeared during each cycle. The calibra-tion run was repeated four times (Fig. 6) using as carrier stream a 0.05 M ammonium acetate solution the pH of which was adjusted to 7.0 9.0 and 10.0. Obviously the peak height and the recovery of cadmium increased with increasing pH with an optimum at pH 10. Closer examination of the first smaller and broader (ie. sodium) peaks revealed that their height is constant only at pH 10 while at lower pH values most notably at pH 7 their height increases with increasing cadmium content showing that at low pH cadmium cannot be quantitatively retained on the Chelex-100 resin under the prevailing flow conditions and column geometry; hence the non-retained cadmium appears as part of the sodium peak.At pH 10 the recovery is quantitative and the high content of sodium in no way affects the second high and narrow peak of cadmium. This is best seen on the last experimental run where the four cadmium standards were injected in an increasing concentration sequence while the FAA spectrophoto-meter was operated without background correction. Afterwards another series of the stand-ards was injected in a decreasing concentration sequence while the FAA spectrophotometer was operated with background correction. The equal height of the comparable cadmiu 912 OLSEN et al. FIA WITH FLAME AAS DETERMINATION Analyst VoE. 108 Scan + Fig. 6. Influence of pH on the recovery of cadmium as obtained by using the system of Fig.4. The acidified cadmium standards injected in all experiments contained 10 20 50 and 100 p.p.b. respectively in a matrix of sodium chloride (31.3 g 1-I). (a) pH 7; (b) pH 9; and (c) pH 10 showing the influence of increasing pH on the cadmium peaks; and (d) also pH 10 depicting the Cali-bration series run without (left) and with (right) back-ground correction applied. Wavelength used in (a) (b), (c) and ( d ) 228.8 nm. peaks and the absence of any deviation on the base line when the background correction was applied confirm the complete recovery of cadmium from the carrier stream during the pre-concentration period and the complete elution of the cadmium from the column during the elution period.Thus two advances have been made at this stage (1) the LOD and the sensitivity of measurement have been increased compared with the direct injection of sample system; and (2) the sodium interference has been eliminated. The single line experimental set-up used so far has however certain shortcomings. The first is due to the fact that the ion exchanger undergoes a drastic change of volume any time the Chelex-100 changes from the NH,+ to the H+ form. This swelling has been reported to be more than 100% of the resin volume2 and causes tighter and tighter packing of the column because the flow in the single line system is uni-directional. Therefore the downstream end of the column eventually becomes blocked while the upstream end becomes void. The second shortcoming of the single-line system lies in its inappropriateness to mix the centre of the sample zone sufficiently with the carrier stream (unless a long mixing coil is used).While this was not a problem when synthetic seawater samples were injected the single-line system could not be used to handle seawater samples that have been acidified by nitric acid after collection, in order to preserve them (3 ml of 14 M nitric acid per litre of seawater). These shortcomings are eliminated in the system described under Two-line FIA - FAA System with a Directional Valve and Peristaltic Pumps. Two-line FIA - FAA System With a Directional Valve and Peristaltic Pumps There are two distinct features of the two-line system depicted in Fig. 7. The first is the confluence arrangement that allows continuous addition of the ammonium acetate buffer to the aqueous carrier stream in pre-selected proportions at the merging point M.This and the passage through the subsequent mixing coil ensure stabilisation of pH along the whole length of the injected sample zone even when acidified seawater samples are injected. The second feature is the use of an additional FIAstar valve used exclusively for diversification of the flow, which allows the flow to be directed through the Chelex-100 column (CH-100 Fig. 7) in one direction during the pre-concentration step and in the opposite direction during the subsequent elution step. Hence all directional functions symbolised by circles in Fig. 7 are executed by one standard FIAstar valve that has two positions (A) pre-concentration and (B) elution August 1983 OF HEAVY METALS I N POLLUTED SEAWATER 913 Fig.7. Two-line FIA - FAA system with directional valve and peri-staltic pump (a) pre-concentration cycle during which the sample (volume 2 ml) injected by valve S is merged with the ammonium acetate buffer (0.6 M) and then directed to the column; A the corresponding position of valve for cycle (a) ; and (b) elution cycle where the metal adsorbed on the Chelex-100 column is countercurrently eluted by 2 M nitric acid and subsequently measured in the FAA instrument; B the corresponding position of valve for cycle (b). M is the merging point and the lines propelling liquids into the FAA instrument in (a) or (b) are drawn thick. W = Waste. The pre-concentration cycle is shown in Fig.7 (a) where the thin line depicts the pre-concentra-tion line into which the sample has been injected; note that the flow line drawn solidly continuously washes the nebuliser and burner with pure carrier stream of eluting acid. When the rotor is turned [A + B Fig. 7 ( b ) ] the flow into the FAA (again drawn as a solid line) is diverted through the column in the former reverse direction and then into the FAA thus bringing the eluted metal into the flame for measurement; during this period the FIAstar sampling valve can be reloaded. It must also be noted that the flow arrangement never allows the seawater matrix to enter the flame because during the pre-concentration cycle the 30 min 500 20 50 1 500 Scan Fig. 8. Assay of lead in seawater samples using the FIA - FAA system of Fig.Shown are 6 samples bracketed by two series of standards the numbers All samples and stardards were 7. depicting the concentrations in p,p.b. of lead. injected in triplicate. Wavelength 217.0 nm 914 OLSEN et al. FIA WITH FLAME AAS DETERMINATION TABLE I1 COMPARATIVE RESULTS FOR ASSAY OF LEAD AS OBTAINED BY FIA - FAA Analyst VoZ. 108 AND BY POTENTIOMETRIC STRIPPING ANALYSIS (PSA) Lead p.p.b. Sample NO. ‘FIA - FAA* PSA’ 1 100 93 2 237 243 3 333 332 4 372 373 6 43 41 *As obtained with the FIA-FAA system of Fig. 7. sample plug enters the column and continues to waste [Fig. 7(a) top line] Therefore the two-line FIA - FAA system obviates the necessity for any background correction which in turn reduces the cost of the apparatus.The system was tested for lead zinc and cadmium assays in real seawater samples and performed so well that several hundred analyses have so far been executed with the same column, In Fig. 8 is shown a recording obtained for lead with a set of five seawater samples (pre-served by nitric acid) bracketed by two series of standards (20 50 100 200 and 500 p.p.b. of lead). All samples were injected in triplicate. The range encompassed satisfactorily covers the lead levels encountered in the samples from the mining process (where seawater is used for flotation). As the LOD was determined to be 10 p.p.b. the system could also be used for assay of the samples from the adjacent fjord. In a typical analysis much larger runs than the five samples shown in Fig.8 would of course be bracketed by standards the record shown here was merely shortened for graphical presentation. For the purpose of actual pollution control the FAA values were re-checked by another method i.e. potentiometric stripping analysis.17J8 A comparison of the results obtained by the FIA - FAA and by the potentiometric stripping analysis is shown in Table 11. The ion-exchange capacity of the miniaturised column was calculated and compared with a “breakthrough” graph obtained under prevailing experimental conditions with the aim of exploiting the limitation of the present technique. The microcolumn contains about 25 mg of Chelex-100 an amount much smaller than usually ~ s e d . ~ - ~ This amount is in a stoicheiometric excess of over 30 times that which would be needed to accommodate the amount of lead con-tained in 1 ml of a 500 p.p.b.lead standard. The experimental breakthrough graph was obtained by injecting increasing volumes of the 500 p.p.b. acidified lead standard and the 50 p.p.b. acidified cadmium standard in seawater matrix using the system shown in Fig. 7 and a carrier stream of 0.5 M ammonium acetate adjusted to a pH of 10 and is shown in Fig. 9. 1 .o al C Q e 8 0.5 9 0 5 10 15 Sample volume/ml Fig. 9. “Breakthrough” graphs for the miniaturised column of Chelex-100, containing 26 mg of resin as obtained by injecting increasing volumes of standard solutions containing (A) 500 p.p.b. of lead and (B) 60 p.p.b. of cadmium Azcgzcst 1983 OF HEAVY METALS IN POLLUTED SEAWATER 915 Sample volumes up to 2ml can readily be accommodated the breakthrough limit being reached at 4-5 ml.Thus further pre-concentration and an increase in the detection limit for the method can be achieved only by increasing the column size and the amount of Chelex-100 contained within it. Fully Automated System With several hundreds of seawater samples to be assayed the last task was the further automation of the system because exact timing during each cycling period was strenuous and labour demanding when performed manually. Therefore a single-valve two-pump system was designed. This was equipped with an electronic timer capable of sequencing pump 1 and pump 2 in a stop - go mode each pre-concentration - elution cycle being initiated by the turn of the injection valve (Fig.10). During the pre-concentration cycle pump 1 (Pl) was going while the sample was injected by turning the valve (S). Afterwards the injected zone was mixed with buffer in the coil and passed through the microcolumn. In the next sequence, pump 1 was stopped and pump 2 (P2) started permitting the eluting acid to move through the column in the opposite direction and thereby transport the eluted metal into the FAA spectro-photometer. Note that when pump 1 is stopped the liquids in the thus closed circuit cannot move in either direction. The sampling cycle is completed when the peak appears whereupon pump 2 may be stopped and pump 1 reactivated thus establishing the high pH inside the microcolumn and thereby making it ready for the next pre-concentration step. Note also that, as in the previous system the seawater matrix never enters the FAA spectrophotometer and that the microcolumn is carefully regenerated prior to each sampling cycle while being operated in countercurrent fashion.Typical calibration runs for series of lead and cadmium Fig. 10. Fully automated FIA - FAA system operated via two peristaltic pumps the stop and go sequences of which are controlled by an electronic timer (T). The stated pumping rates are in ml min-l with sample volume 2 ml. Similarly to the system of Fig. 7 the operation consists of a pre-concentration cycle and an elution cycle, during which the metal is desorbed from the column counter-currently. For further details see text 916 OLSEN et al. FIA WITH FLAME AAS DETERMINATION Analyst YoZ.108 Scan __+ Fig. 11. Calibration runs for (a) lead (217.0nm) (20, 50 100 200 350 and 500 p.p.b.); and (b) cadmium (228.8 nm) (2 5 10 20 35 and 50 p.p.b.) as executed in the FIA - FAA system of Fig. 10. standards are shown in Fig. 11. The slight increase in sensitivity as compared with the results of the manually operated FIA - FAA system shown in Fig. 7 is due to the improved flow geometry of the system. The manifold components shown within the shaded area of Fig. 10 were all incorporated into an integrated microconduit,lg which is a new way of fabricating flow-through systems. In the integrated microconduit all connectors mixing coil and the ion-exchange column are imprinted within a plastic block which is then permanently sealed by a second plate. Therefore con-necting tubing and Swagelock-type connectors are eliminated as the whole structure is em-bedded within a 7 x 4 x 1.5 cm thick plastic block with four inlets and two outlets.Such a micro-flow injection manifold can then be placed within and operated by a BIFOK - Tecator FIA 5020 instrument which has two pumps injection valve with variable volume and appro-priate timing and sequencing facilities. It is fitting to conclude this section by referring to a serious deficiency from which all methods for the determination of trace amounts of metals in natural waters and seawater suffer. At the parts per billion level and below there may be a substantial fraction of the lead or cadmium present in forms that have been described as “bound,”20-22 thus being inaccessible to determination because these metals are present in colloidal form insoluble in acid or in the form of strong complexes that are not dissociated.As only the “labile” and “free” metals can be electro-deposited extracted or adsorbed on Chelex-100 only these fractions are measurable by the present analytical techniques because the seawater matrix itself interferes in the direct measurement by flame or graphite furnace atomic absorption. It is of course questionable whether lead and cadmium concentrations below the parts per billion level present in either forms are objectionable from an environmental viewpoint as they approach the levels of natural abundance in ~eawater.~3,~4 This subject is however outside the scope of this paper, except that it allows us to put into perspective the usefulness of the FIA - FAA combination as a pollution-screening technique at realistic levels.Conclusion Seen from a practical viewpoint the FIA - FAA combination results in time saving because it allows an unprecedented sample throughput at the parts per billion level. As the analyti-cal readout is available within 5 s for the direct assay and the latest within 110 s for the system including pre-concentration (Fig. lo) smaller sample series can be treated expediently by manual injection. The saving in terms of equipment is not limited to a sample changer. Graphite furnace and background correction are no longer needed while the necessary FIA equipment may be acquired at a fraction of the cost of a graphite furnace. Truly the graphite furnace is still more sensitive than the FIA - FAA system by a factor of about 50 yet for sea-water assays a manual solvent extraction or Chelex separation nevertheless has to be performed.On the other hand it may still be possible to increase the sensitivity of the FIA - FAA system by a factor of five by increasing the injected sample volume to 10 ml and the size of the column about %fold while redesigning the geometry of flow in the microconduit August 1983 OF HEAVY METALS IN POLLUTED SEAWATER 917 Much effort has rightfully been made in the past to improve atomic-absorption equipment as far as computerisation electronics optics and sample atomisation are concerned. It is time now to turn attention to automation of the sample treatment prior to sample entry into the FAA instrument.While FIA as a simple means of transport is certainly useful the on-line FIA pre-concentration technique by ion exchange as described here or via hydride generation as developed by ~ h t r o m ~ ~ are amongst the significant future trends which are not limited only to FAA but naturally can be extended to ICP also. The authors express their gratitude to Greenex A/S and the Danish Academy of Technical Sciences for providing the funds for S. Olsen to DANIDA for a scholarship to L.C.R. Pessenda and to the Danish Council for Scientific and Industrial Research which together with the above-mentioned institutions financed part of the equipment used in these studies. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.19. 20. 21. 22. 23. 24. 25. References Walsh A. Spectrochim. Acta Part A 1955 1 108. Bio-Rad Laboratories Product Information 2020 March 1981. Riley J. P. and Taylor D. Anal. Chim. Acta 1968 40 479. Danielsson L.-G. Magnusson B. and Zhang K. At. Spectrosc. 1982 3 39. Kingston H. M. Barnes I. L. Brady T. J. and Rains T. C. Anal. Chem. 1978 50 2064. RhZiEka J. and Hansen E. H. “Flow Injection Analysis,’’ Wiley-Interscience New York 1981. Zagatto E. A. G. Krug F. J. Bergamin FO. H. Jergensen S. S. and Reis B. F. Anal. Chim. Wolf W. R. and Stewart K. K. Anal. Chem. 1979 51 1201. Tyson J. F. and Idris A. B. Analyst 1981 106 1025. Mindel B. D. and Karlberg B. Lab. Pract. 1981 30 719. Nord L. and Karlberg B. Anal. Chim. Acta 1981 125 199. Rbiitka J. Hansen E. H. and Ramsing A. U. Anal. Chim. Acta 1982 134 55. ACS Committee on Environmental Improvement Anal. Chem. 1980 52 2242. RbfiCka J. and Hansen E. H. Anal. Chim. Acta 1975 78 145. Hansen E. H. Rhiitka J. Krug F. J. and Zagatto E. A. G. Anal. Chim. Acta 1983 148 111. Florence T. M. and Batley G. E. Talanta 1975 22 201. Jagner D. and Graneli A. Anal. Chim. Acta 1976 83 19. Jagner D. and ArBn K. Anal. Chim. Acta 1978 100 375. ROZiEka J. Janata J. and Hansen E. H. in preparation. Florence T. M. and Batley G. E. Talanta 1976 23 179. Batley G. E. and Florence T. M. Anal. Lett. 1976 9 379. Abdullah M. I. El-Rayis 0. A. and Riley J. P. Anal. Chim. Acta 1976 84 363. Bruland K. W. and Franks R. P. Anal. Chim. Ada 19‘79 105 233. Jones P. G. W. Anal. Proc. 1982 19 565. Astrom O. Anal. Chem. 1982 54 190. Acta 1979 104 279. Received January 31st 1983 Accepted March 2nd I98

ISSN:0003-2654    

DOI:10.1039/AN9830800905

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

918 Analyst August 1983 Vol. 108 $9. 918-924 Determination of the Chemical Forms of Cadmium and Silver in Sediments by Zeeman Effect Flame Atomic-absorption Spectrometry Ken R. Lum Environmental Contaminants Division National Water Research Institute CCI W P.O. Box 5050 Burlington, Ontario L7R 4A6 Canada and Duart G. Edgar Nissei Sangyo Canada Inc. 89 Galaxy Blvd. Suite 14 Rexdale Ontario M9W 6A4 Canada A polarised Zeeman flame atomic-absorption spectrometer has been used for the determination of cadmium and silver in chemical extracts of sediments using a procedure designed to provide information on the potential availability of trace elements. The limit of determination for complex solution matrices was found to be 1.1 pg 1-1 for both cadmium and silver. Minimum base-line noise for the instrument afforded very good stability of the calibration con-ditions at the 10 pg 1-1 level for the two elements.Accuracy tests performed with standard reference materials showed good agreement for the determi-nations in the extracts. The analysis of suspended and bottom sediments is used to demonstrate the value of this instrumental technique. Keywords ; Zeeman flame atomic-absorption spectrometry ; chemical forms ; cadmizcm determination ; silver determination ; sediments The toxicity of cadmium and its dissemination into the environment are of considerable current intere~t.l-~ In freshwaters silver is regarded as one of the most toxic metals to aquatic Because metal ion toxicity in aquatic systems can be influenced by sorption and binding to suspended and bottom sediments much work has been done on determining the chemical form and potential availability of elements associated with these substrates.2J-9 The determinations rely on a variety of extraction scheme^^^^-^^ that require the use of high ionic strength solutions such as 1 M magnesium chloride 1 M sodium acetate 0.2 M barium chloride or 0.22 M sodium citrate - 0.11 M sodium hydrogen carbonate - 1 .O g sodium dithionite.The large number of extracts that result from these procedures precludes the use of electro-thermal atomisation atomic-absorption spectrometry (ETA-AAS) techniques because of the additional time that is required to separate the elements of interest from the complex matrix, e.g. by chelation and solvent extraction. The advantages of greater sensitivity in ETA-AAS can in addition be minimised by contamination during the separation step and the longer analysis time needed for these analyses.The direct aspiration flame AAS approach thus offers a simple and rapid analytical tool which further calls for less skill on the part of the operat or. In the procedure12 adopted by us for studies of trace metal availability the flame detection limit for cadmium was reported to be 0.012 pg ml-1 which represents a detection limit of 0.3 pg g1 for a 1.0-g sample subjected to this sequential extraction scheme and a final volume of 25 ml. These detection limits are generally inadequate because background total cadmium concentrations for soils and sediments are in the range 0.4-0.6 pg g-1.13J4 Apart from grossly polluted sediments total cadmium concentrations are usually less than 10 pg g1.14 More-over for chemical extraction procedures the concentration of cadmium in the fractions that are deemed readily or potentially available does not normally exceed 50% of the t o t ~ d .~ ~ ~ J ~ Although there are few data on the chemical forms of silver in soils and sediments total con-centrations of silver in estuarine sediments are ca. 1 pg g1.9 Recent work on the application of the Zeeman effect to atomic-absorption analysis has shown that significant reductions in base-line noise can be attained.l7J8 The superior capability of such instruments for the correction of non-atomic absorption compared with systems relying on deuterium lamp correction is now well documented.l+l LUM AND EDGAR 919 In this paper we report the results of an evaluation of a polarised Zeeman atomic-absorption spectrometer for the determination of cadmium and silver in sediment extracts.Experimental Instrumentation Atomic-absorption measurements were made on a Hitachi Model 180-80 polarised Zeeman instrument using a water-cooled pre-mix burner with air - acetylene. Hamamatsu hollow-cathode lamps were used. The configuration and operation of the Zeeman flame system has been described previou~ly.~~ Instrumental parameters were those recommended by the manufacturer and are given in Table I. Analytical results were obtained using three 5-s integrations of each sample. The data processing unit stores the absorbances of a blank and three standards and gives a mean concentration standard deviation and coefficient of variation (in yo) for each analysis.TABLE I INSTRUMENTAL PARAMETERS FOR THE DETERMINATION OF CADMIUM AND SILVER Element Wavelength/nm Slit width/nm Burner height/cm Flame composition Cadmium 228.8 1.3 7.5 Air 9.4 1 min-I Silver . . 328.1 2.6 7.5 Air 9.4 1 min-1 C,H 2.3 1 min-l C,H 2.3 1 min-l Reagents AnalaR-grade or equivalent quality reagents were used except for the following lithium chloride and caesium chloride Aldrich gold label (99.999%) ; sodium acetate E. Merck Suprapur ; nitric and hydrochloric acids prepared by sub-boiling distillation; and acetic acid, Baker Instra-analysed grade. Standards were made up in 0.16 M nitric acid by serial dilution of 1000 mg 1-1 stock solutions (Fisher Scientific Co.) .Sequential Chemical Extraction Procedure A five-part sequential scheme12 was followed except for the lake sediments for which a reagent composed of 0.75 M lithium chloride and 0.25 M caesium chloride in 60% methanol was used instead of 1 M magnesium chloride. The volumes of extractants used were identical with those recommended by Tessier et ~ 1 . 1 ~ and the procedure was applied to ca. 1-g (dry mass) samples of sediment (Fig. 1). The sequential extractions simulate to a certain extent various environmental conditions to which sediments and similar materials may be subjected Although these extraction schemes are not perfectly selective they can provide valuable information on the mobility and avail-ability of elements in soils sediments and Dissolution of Standard Reference Materials A modified room-temperature dissolution procedure was used for solubilising several stand-ard reference materials to assess the accuracy of the instrumental determination and the extrac-tion process.23 The samples were weighed into 125-ml acid-cleaned polyethylene bottles, wetted with 2 ml of doubly distilled water then 3 ml of aqua regia and 20 ml of hydrofluoric acid were added.The bottles were agitated on a wrist-arm shaker for 16 h then 75 ml of saturated boric acid solution were added and the bottles were replaced on the shaker for a further 4 h. The supernatants were analysed after allowing the small amounts of residue to settle. Five replicate 1-g samples of NBS SRM 1577 (bovine liver) were digested in PTFE beakers using 10 ml of 1 + 1 sulphuric acid and heating to white fumes.After allowing the beakers to cool sufficient 30% hydrogen peroxide was added in 0.2-ml aliquots to obtain a yellow extract. The solution was heated for a further 30 min cooled and made up to 25ml with doubly distilled water 920 LUM AND EDGAR DETERMINATION OF CHEMICAL FORMS Analyst VoZ. 108 Triplicate 0.2-g samples of the National Institute for Environmental Studies (NIES Japan) Certified Reference pond sediment were muffle ashed at 500 "C for 3 h. A separate 0.2-g sub-sample was dried in a forced air oven at 110 "C for 24 h to determine moisture content. The ashed samples were carefully wetted with doubly distilled water transferred into PTFE beakers and 20 ml of freshly prepared aqua regia were added.The digests were reduced nearly to dryness 15 ml of hydrofluoric acid were added and heating was continued until the samples were dry care being taken to avoid baking. Hydrochloric acid (15 ml) and 15 ml of doubly distilled water were then added and the solutions were heated for 1 h to reduce the volume to ca. 15 ml. After cooling the volumes were made up to 25 ml in a calibrated flask. Results and Discussion Cadmium Calibration graphs were obtained for cadmium concentrations of 0.0 10.0 40.0 and 100.0 pg 1-l. The absorbances were stored in the instrument's data processing unit and for three separate days (and for standards of 0.0,20.0,40.0 and 60.0 pg 1-l) the computed correla-tion coefficient for the best linear fit line was 0.99. Using the former calibration range stand-ards run as samples gave the concentrations shown in Table 11.The data processing unit is capable of computing (within 4%) concentrations that were ten times that of the highest stored standard. Calibration stability and analytical reproducibility were assessed by aspirating the 10.0 pg 1-1 Sample a 0.75 M LiCl - 0.25 M CsCl - 60% CHBOH 10 min Room tem peratu re Residue Q 1 M CH,COONa,pH 5.0 Room temperature Extract I Residue 1 M NH2OH.HCI -25% CH3COOH 2h Room temperature Extract rn Residue H202 PH 2 90 "C 5 h Extract 1.2 M CH3COONHd - 20% HNO3 Residue 9 I Aqua regia - HF - HCI - H202 I Extract Readily exchangeable ions (A) Carbonate-bound su rface-oxide bound ions (B) Ions bound to Fe -Mn oxides (C) Organically and sulphide-bound ions (0) Ions bound to the residual phase Fig.1. Outline of the sequential chemical extraction procedure August 1983 OF CD AND AG IN SEDIMENTS BY ZEEMAN EFFECT AAS TABLE If LINEARITY OF CADMIUM CALIBRATION CONDITIONS 921 Concentration of standard/pg 1-1 10.0 25.0 40.0 60.0 100 250 500 1000 Concentration determined by instrument*/pg 1-1 11.6 f 1.1 24.7 f 0.8 42.6 f 1.7 61.3 f 0.9 101 f 0.4 246 f 0.8 480 f 1.6 961 f 0.6 * The data processing unit prints out the mean concentration of three 5-s integra-tions and the standard deviation. standard periodically during the analysis of sediment extracts. The standard was determined ten times over a 2-h period and the concentration measured varied from 10.0 to 11.6 pg 1-1 with a mean value of 10.8 5 0.6 pg 1-l.These data were obtained without any update of the calibration graph. In spectrochemical analysis the concentration of an element that will absorb 1% of the incident resonance energy of that element is defined as its reciprocal sen~itivity.~~ The absorbance of the 10.0 pg 1-1 cadmium standard was 0.001 5 which is below that required by this definition and which therefore is not applicable to this analysis in a calculation of the detection limit. A limit of determination was obtained from the analysis of 35 sediment extracts (seven samples of five fractions each) for which the majority (77%) gave concentra-tions less than 10.0 pg 1-1 (the range was 0.5-17.7 pg 1-l). The average of the standard deviations for the 35 analyses was 1.1 pg 1-1 and is used here as the instrumental limit of determination for cadmium in the complex matrices analysed in this study.A particularly valuable feature of this instrument was the low base-line noise observed even after aspirating samples containing 0.32 M magnesium chloride and 0.32 M sodium acetate. At no time during the three days of operation was it ever necessary to dismantle and clean the burner chamber and nebuliser. Occasional clogging of the nebuliser by particles in some of the samples was promptly rectified by the insertion of a cleaning wire. The accuracy of the determination was evaluated by analysing several standard reference materials (Table 111). The solution concentrations calculated from the certified values (pg g-') are compared with the measured concentrations.The recovery of cadmium from the coal fly ash (NBS SRM 1633) is in excellent agreement with the certified value and that reported by G l a d n e ~ . ~ ~ Similarly the determination of cadmium in digests of bovine liver (NBS SRM 1577) showed good agreement with the certified value. The lower than expected recovery for the river sediment (NBS SRM 1645) and the urban particulate matter (SRM 1648) is in part the result of their organic contents. For a similar room-temperature dissolution procedure the mass of the undissolved residue was found to be correlated with the carbon content of the ~ample.~3 The river sediment contains 1.71 yo of Freon-extractable oil and grease whereas the urban particulate matter contains 1.19%.An estimate of the organic content can be obtained from the loss on ignition (800 "C) value which is 10.72y0 for the river sediment; no value is provided for the urban particulate matter. In contrast the coal fly ash would be expected to contain very little organic matter. TABLE I11 ACCURACY OF THE DETERMINATION OF CADMIUM BY ZEEMAN EFFECT FLAME AAS Reference material NBS SRM 1633 coal fly ash 1 . . 2 3 . . NBS SRM 1645 river sediment . . NBS SRM 1648 urban particulate matter NBS SRM 1577 bovine liver (n = 5) . . Expected Measured Recovery, concentrationlpg 1-1 concentration/pg 1-1 yo 5.4 5.8 f 0.8 107 7.0 7.4 & 0.6 106 6.2 6.3 f 0.8 102 185 148 f 0.2 80 329 291 f 0.7 88 10.8 10.6 f 0.8 9 922 LUM AND EDGAR DETERMINATION OF CHEMICAL FORMS Analyst Vol.108 The possible effect of the high dissolved solids content (e.g. 0.7 M for boric acid) on nebulisa-tion and atomisation efficiency was checked by serial dilution and analysis. The concentra-tions obtained for 0 2 4 10 and 15x dilutions were 152 151 149 154 and 159 pg 1-1, respectively which indicate that such effects do not markedly suppress the cadmium atomic absorption. The accuracy of the determination was further assessed by analysing the NIES pond sediment26 and as shown in Table IV reasonable agreement was obtained for concentra-tions ca. five times the detection limit. It should be noted that the expected concentration has been corrected for a moisture content of 9.0%. TABLE IV ACCURACY OF THE DETERMINATION OF CADMIUM AND SILVER IN THE NIES CERTIFIED REFERENCE SEDIMENT Cadmiumlpg 1-1 Silverlpg 1-1 - Expected Measured Expected Measured Pond 1 .. 6.1 5.8 6.4 5.6 Pond2 . . 6.1 5.7 6.4 5.7 Pond 3 . . 6.1 5.7 6.4 5.6 Chemical forms of cadmium in suspended sediments Seven samples each of suspended sediments were collected by continuous-flow centrifugation from Hamilton Harbour and western Lake Ontario during the summer of 1981. The material was freeze-dried and 0. l-g sub-samples were subjected to the sequential extraction procedure. Total cadmium contents were obtained from the sum of the concentrations found in each extract. The distribution of the chemical forms in each fraction were then expressed as a percentage of the total. The results (Table V) show that the distribution of the chemical forms of cadmium is dominated by the iron and manganese oxide phase in Hamilton Harbour, which is to be expected as the harbour front is the location of the largest steelworks in Canada.For both areas the first two fractions are very important accounting for 28% and 48% for the harbour and lake respectively. The fact that for these fractions the solution concentrations (20 out of 28 extracts) were less than 10 pg 1-1 demonstrates the value of the Zeeman effect AAS determination at these low levels. TABLE V DISTRIBUTION OF THE CHEMICAL FORMS OF CADMIUM IN SUSPENDED SEDIMENTS FROM HAMILTON HARBOUR AND WESTERN LAKE ONTARIO Hamilton Harbour Lake Ontario Exchangeable forms % . . 10 f 3 17 f 6 Carbonate and surface-oxide bound yo .. 18 f 12 31 f 10 Bound to Fe and Mn oxides yo . . f . 53 f 8 34 f 7 Bound to organic matter % . . 7 f 3 12 f 5 Residual forms % . . ,. 12 f 9 6 f 3 Total cadmium concentration rangelpg g-l . . 5.0-8.0 3.5-8.0 Silver Calibration graphs were obtained for silver concentrations of 0.0 20.0 40.0 and 60.0 pg 1-l. Correlation coefficients ranged from 0.95 to 0.99. Although the absorbance of the 20 pg 1-1 standard is not displayable (<0.00099) the microprocessor has been designed to record and calculate concentrations based on detecting absorbances to six significant figures. Calibration stability was ascertained by aspirating a 10.0 pg 1-1 standard periodically during the analysis of sediment extracts. The average value for ten measurements for this standard was 9.3 & 0.8pg.l-l.The limit of determination was calculated from the average of the standard demations of the analysis of 16 sediment extracts that contained less than 10.0 pg 1-1 of silver (nine of which were between 0.5 and 2.0 pg 1-l) and found to be 1.1 pg 1-l. None of the reference materials examined in this study have been certified for silver content Augwst 1983 OF CD AND AG IN SEDIMENTS BY ZEEMAN EFFECT AAS 923 However the NIES pond sediment has been analysed for this element by isotope dilution mass spectrometry. As for cadmium the measured concentrations are in reasonable agreement with those calculated from the value provided by the NIES (Table IV). Although the con-centrations of silver in these samples yield “undetectable” absorbances <O.OOO 99 the high spectral intensity of the hollow-cathode lamp permits a very low gain to be used.The resulting low noise enhances the ability of the microprocessor to discriminate atomic-absorption signals at silver concentrations below 10 pg 1-l. For the urban particulate matter (SRM 1648) a value of 6 pg g1 is provided by the NBS as information only. We obtained 6.4 pg g-l for a single sample subjected to the room-tempera-ture dissolution procedure which is in good agreement with the value reported by Greenb~rg.~’ Data on the chemical extraction of a sediment core from Moira Lake Ontario and coal fly ash (SRM 1633) are presented in Table VI. There is no value given by the NBS for the silver content of the coal fly ash. G l a d n e ~ ~ ~ reported a range of 0.25-1.3 pg g1 for coal fly ash with a 1975 certificate date.No value was listed for the SRM having a 1979 certificate date that was analysed in this study. Nevertheless the concentrations obtained here demonstrate the value of the polarised Zeeman effect AAS system for the determination of silver in extracts of environmental materials. In a recent study of weak acid-soluble silver in marine sediments,% the determination by direct aspiration AAS was considered unreliable for samples containing less than 2.5 pg g1 of silver. It was therefore necessary for these workers to resort to an ammonium tetramethylene dithiocarbamate - isobutyl methyl ketone extraction in order to determine silver in the range 0.1-2.5 pg g-l. As with the cadmium determinations the high concentrations of alkali and alkaline earth elements in our extracts did not cause burner problems as was noted in a determination of silver in corrosion test solutions containing 0.9% and 3% of sodium ~hloride.~g TABLE VI DISTRIBUTION OF THE CHEMICAL FORMS OF SILVER IN A SEDIMENT CORE AND IN COAL FLY ASH (SRM 1633) Total concentration/ Sediment depth/cm rg 8-l 0-1 .. 5.63 9-10 . . 8.05 14-15 ,. . . 6.60 18-19 . . 3.66 21-22 . . 4.30 32-33 . . 1.00 Coal fly ash 1 . . . 0.15 Coal fly ash 2 . . . . 0.14 Exchangeable forms/ r g g-l 0.52 0.63 0.90 0.12 0.10 0.03 0.02 0.02 Carbonate surf ace oxide bound/pg g-l 0.03 0.03 0.03 0.03 0.03 0.03 0.02 0.02 Fe Mn oxide bound/ 0.03 0.03 0.03 0.03 0.03 0.03 0.02 0.02 rg g-l Organic sulphide bound/ 2.31 2.02 1.30 0.24 0.36 0.16 0.03 0.02 r g l2-l Residual forms/ 2.70 5.40 4.40 3.30 3.84 0.12 0.12 Clg g-l 0.84 Hence using this instrumental technique it is now possible to determine directly the distri-bution of the chemical forms of silver and cadmium in environmental materials such as sus-pended and bottom sediments atmospheric particulates and soils.The data in Table VI show that significant amounts of silver can be found in sediments as readily extractable forms (mean value 7% of the total silver concentration; range 2-14y0). These forms are regarded as bioavailable because they are weakly bound and may equilibrate rapidly in water.2 The environmental significance of these results is at present being considered in a study of the factors affecting trace metal availability in aquatic systems.We are grateful to the referees for their helpful comments. The sample of NIES pond sediment was kindly supplied by Dr. Kensaku Okamoto. References 1. Associate Committee on Scientific Criteria for Environmental Quality “Effects of Cadmium in the Canadian Environment,” National Research Council of Canada Ottawa 1979 Issued as NRCC No. 16743. Forstner U. in Hutzinger O. Editor “The Handbook of Environmental Chemistry,” Volume 3, Part A Springer-Verlag New York 1980 p. 59. 2 924 LUM AND EDGAR 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28.29. Nriagu J. O. Editor “Cadmium in the Environment Part 1 Ecological Cycling,” Wiley-Inter-science New York 1980 682 pp. Davies P. H. Goettl J. P. and Sinley J . R. Water Res. 1978 12 113. Birge W. J. Hudson J . E. Black J. A. and Westerman A. G. in Samuel D. E. Hocutt C. H., and Mason W. T. Editms “Surface Mining and Fish/Wildlife Needs in the Eastern United States,” US Department of the Interior Fisheries Wildlife Service FWS/OBS-78/81 1978 p. 97. Lima A. R. Curtis C. Hammermeister D. E. Call D. J. and Felhaber T. A. Bull. Environ. Contam. Toxicol. 1982 29 184. Symeonides C. and McRae S. G. J. Environ. Qual 1977 6 120. Luoma S. N. and Jenne E. A. in “Biological Implications of Metals in the Environment,” Luoma S. N. and Bryan G. W. Sci. Total Environ. 1981 17 165.Gibbs R. J. Science 1973 180 71. Gupta S. K. and Chen K. Y. Environ. Lett. 1975 10 129. Tessier A. Campbell P. G. C. and Bisson M. Anal. Chem. 1979 51 844. Ure A. M. and Berrow M. L. in “Environmental Chemistry,” Volume 2 Specialist Periodical Katz A. and Kaplan I. R. Mar. Chem. 1981 10 261. Forstner U. in Nriagu J . O. Editor “Cadmium in the Environment Part 1 Ecological Cycling,” Brodie K. G. and Liddle P. R. Anal. Chem. 1980 52 1059. Fernandez F. J. and Giddings R. At. Spectrosc. 1982 3 61. Dawson J. B. Grassam E. Ellis D. J. and Keir M. J. Analyst 1976 101 315. Koizumi H. Yamada H. Yasuda K. Uchino K. and Oishi K. Spectrochim. Acta 1981 363 608. Tessier A. Campbell P. G. C. and Bisson M. Can. J . Earth Sci. 1980 17 90. Harrison R. M. Laxen D. P. H. and Wilson S. J. Environ. Sci. Technol. 1981 15 1378. Lum K. R. Betteridge J. S. and MacDonald R. R. Environ. Technol. Lett. 1982 3 57. Silberman D. and Fisher G. L. Anal. Chim. Acta 1979 106 299. Price W. J . “Spectrochemical Analysis by Atomic Absorption,” Heyden London 1979 p. 142. Gladney E. C. Anal. Chim. Acta 1980 118 385. Okamoto K. Editor “Preparation Analysis and Certification of ‘Pond Sediment’ Certified Research Report No. 38 National Institute for Environmental Studies, Greenburg R. R. Anal. Chem. 1979 51 2004. Dillon J. J. and Martin E. A, At. Spectrosc. 1982 3 66. Varma A. Talanta 1981 28 701. CONF-75029 US NTIS Springfield VA 1977 p. 213. Report Royal Society of Chemistry London 1982 p. 9. Wiley-Interscience New York 1980 p. 305. Reference Material, Japan 1982 112 pp. Received November 22nd 1982 Accepted March 22nd. 198

ISSN:0003-2654    

DOI:10.1039/AN9830800918

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

Analyst August 1983 Vol. 108 pp. 925-932 926 Determination of Caesium and Rubidium by Flame and Furnace Atomic- absorption Spectrometry Z. Grobenski D. Weber B. WeIz and J. Wolff Bodenseewerk Perkin-Elmer & Co. GmbH Postfach 1120 0-7770 Oberlingen Federal Republic of Germany Caesium and rubidium have been determined by flame and furnace atomic-absorption spectrometry. It was found that both techniques are reasonably free from interferences and accurate enough for the routine analysis of various types of samples. Keywords ; Caesium determination ; rubidium determination ; atomic-absorption spectrometry Several general problems arise in the determination of caesium and rubidium by atomic-absorption spectrometry (AAS). The primary resonance lines at 852.1 nm (Cs) and 780.0 nm (Rb) are at the beginning of the infrared region of the spectrum and therefore at the limit of normal atomic-absorption instruments that utilise only one grating and a wide-range photo-multiplier.Nevertheless almost every commercially available atomic-absorption spectro-photometer has a specified wavelength range up to 870nm. However there is a great difference between spectrophotometers for determinations in this region of the spectrum. It can generally be said that double-grating monochromator instruments having one grating optimised for the UV range and a second for the visible range of the spectrum are much better. Ruled and illuminated areas blaze wavelength and other characteristics of the visible-range grating are of importance. The performance of an instrument can be considerably improved for the determination of rubidium and caesium by selecting a photomultiplier that is more sensitive in the visible range near-infrared part of the atomic-absorption spectrum.The next very important contribution comes from the radiation sources used. For most elements metal-vapour lamps have lost significance in atomic-absorption work except for rubidium and caesium. Their radiant intensity is considerably higher than that of the corresponding hollow-cathode 1amps.l Electrodeless discharge lamps for caesium and rubidium have an even higher radiant intensity thus improving the signal to noise ratio and detection limits. Even more important metal-vapour lamps emit extensively broadened lines because of self-absorption and self-reversal while electrodeless discharge lamps emit narrow lines with very little self-absorption.Sensitivities and linearity of the analytical curves obtained with the latter are therefore considerably better. A cut-off filter (opaque to wavelengths below 650 nm) is usually inserted in front of the monochromator thus improving further the signal to noise ratio. Ionisation potentials for caesium (3.893 eV) and rubidium (4.176 eV) are very low2 and very pronounced ionisation interferences therefore occur in flame atomic absorption. To suppress ionisation it is essential to spike standard and analyte solutions with a large excess of other easily ionised elements (e.g. 2-5mgml-l of potassium). Ottaway and Shaw3 found an extensive ionisation of alkali metals in electrothermal atomisation using atomic emission.This strongly influences the atomic line emission intensity and ionisation buffers should be added to prevent it.394 In contrast no ionisation interferences were found in atomic ab~orption.~ This can be explained by the fact that ionisation in the graphite furnace occurs only after the atomic-absorption signal has already been measured and thus has no practical influence on the analyte signal. Only a few papers dealing with the determination of caesium and rubidium by atomic-absorption methods have been published. To determine these elements in silicate rock samples by flame AAS a separation from the bulk of the matrix by coprecipitation with ammonium 12-molybdophosphate was recommended.6 In the determination of caesium in river and sea waters by graphite furnace AAS interferences from cobalt and iron were observe 926 GROBENSKI et al.DETERMINATION OF CAESIUM Analyst VoZ. 108 and chromatographic separation on a strong cation-exchange resin was recommended.’ For silicate rocks atomisation of the solid samples was investigated8 and compared with the analysis of dissolved samples using graphite furnace and flame techniques. Both papers7s8 discussed briefly the requirement for background correction in the visible range without really applying it. Some modern instruments provide such background correction by means of a tungsten lamp. Experimental Instrumentation Perkin-Elmer Model 5000 and 4000 atomic-absorption spectrophotometers were used. These are double-beam instruments having Czerny - Turner monochromator design with a focal length of 408 mm.The spectral range is a t least 180-900 nm covered by two gratings, each used in the first order. The visible grating has 1440 lines mm-1 with a large ruled area (84 x 84 mm) and blazed at 580 nm. A cut-off filter is automatically inserted into the optical path for measurements above 650 nm. The photomultiplier detector has a multi-alkali metal cathode with a UV-transmitting window covering a wavelength range from 185 to 930 nm. Electrodeless discharge lamps for caesium and rubidium were used and the slit employed had a spectral band width of 1.4 nm (with a graphite furnace the same slit with a reduced height was used). For electro-thermal atomisation a Model HGA-500 graphite furnace and an AS-40 autosampler were used.The background signal (using the tungsten lamp as a continuous light source for background correction) was recorded simultaneously with the analyte signal on a Perkin-Elmer Model 56, two-pen recorder. Integrated or peak absorbance was printed using a Model PRS-10 printer sequencer. Primary resonance lines at 852.1 nm (Cs) and 780.0 nm (Rb) were used. Reagents All reagents used were of the highest purity available (e.g. Merck Suprapur acids). Work-ing solutions of the required concentrations were prepared from stock standard solutions (Merck Titrisol) as required. Results and Discussion “State of the art” limits of detection are presented in Table I. Different pre-analysed samples were measured by flame and furnace AAS depending on the element concentration in the particular sample.TABLE I DETECTION LIMITS FOR DIFFERENT TECHNIQUES IN ATOMIC SPECTROSCOPY Technique Rb/mg 1-1 Cs/mg 1-1 Flame AAS with vapour discharge lamp . . . . 0.002 0.05 Graphite furnace AAS with electrodeless discharge lamp (100 pl) . . 0.00005 0.000 05 Flame AAS with electrodeless discharge lamp . . . . 0.001 0.01 (contamination problems) FlameAES* . . 0.0003 0.008 Graphite furnace AESS . . . . 0.000 1-0.0002 0.02-0.07 * AES atomic-emission spectroscopy. Determinations by Flame Atomic-absorption Spectrometry An oxidising lean blue air - acetylene flame was used. Determinations by AAS are simple and straightforward if sample decomposition is complete and a sufficiently high concentration of an ionisation buffer is added to samples and standards.Rubidium measured in different pre-analysed rock samples after conventional decomposition with hydrofluoric-sulphuric acid serves as an example. To 0.2-g samples 10-15 ml of hydrofluoric acid (40%) (depending on the silicon concentration) and 0.5 ml of sulphuric acid were added in a platinum vessel and the mixture was slowly heated to dryness. Hydrochlori August 1983 AND RUBIDIUM BY FLAME AND FURNACE AAS 927 acid (4 ml) was added to the residue and heated until a volume of about 0.5 ml remained. The solution was transferred into a 50-ml flask and diluted to volume with 2000 mg 1-1 potassium solution. For the blank 2000mg1-1 potassium solution was measured and there was no difference from the signal obtained on aspirating de-ionised water.Direct calibration against aqueous standards was applied and generally good agreement with certified values was found (Table 11). Only with the basalt BCR-1 was too high a value found; there is no evident explanation for the difference from the reported values. Only in the grandiorite sample MA-N of the International Working Group (IWG) was the caesium level very high and therefore measured by flame AAS. The values found of 547 and 536 pg g-1 were slightly too low (proposed value13 640 pg g-l). Higher values have been reported for flame emission a1~0.l~ Caesium was further measured in a soil extract with nitric acid using the analyte addition technique (method of additions 10 x scale expansion) and 0.15 mg 1-1 of caesium was found.This result was later confirmed using the graphite furnace technique. TABLE I1 DETERMINATION OF RUBIDIUM BY FLAME AAS IN STANDARD ROCK SAMPLES Each reported value represents the mean value of multiple determinations for separate decomposition. Sample G-2 granite USGS . . USGS GSP-1 granodiorite IWG MA-N granodiorite USGS AGV-1 andesite . . USGS BCR-1 basalt . . IWG BE-N basalt . . Found/pg g-l 171 172 112 . 260 259 266 . . 3352 3242 65 67 I1 61 69 48 50 Reported values P Value/pg g-l Reference 168 9 166 6 161 10 170 11 114 12 254 13 260 11 265 9 3 600 14 67 9 69 6 67 11 61 13 47 11 46.9 9 41.6 6 46.6 13 41.6 14 (3 120-4600) (24-61) Determinations by Graphite Furnace Atomic-absorption Spectrometry Conditions for both elements were established using electrodeless discharge lamps uncoated and pyrolytically coated graphite tubes conventional and maximum power (fast) heating for atomisation and different argon flow-rates (Table 111).A sensitivity check is the concentra-tion of the element in milligrams per litre that would generate a signal of 0.2 A when a 20-4 aliquot is dispensed. Values were established with an argon flow-rate of 50 ml min-l during atomisation. The quoted concentrations serve as reference values that should be obtained to within approximately 25%. A further sensitivity increase could be obtained for the normal heating mode by increasing the atomisation temperature. This would however decrease the tube life (especially for pyrolytically coated tubes).The use of fast heating provides higher sensitivities (up to a factor of 2) compared with normal heating. A pyrolytically coated tube provides higher sensitivities (4-10 fold) and this effect is even more pronounced when the gas stream is interrupted during atomisation. Atomisation off the L’vov platform was introduced into graphite furnace AAS to achieve freedom from vapour-phase interferences.16-19 A L’vov platform was inserted into a pyro-lytically coated graphite tube and similar conditions were used to those for atomisation off the wall of a pyrolytically coated tube with maximum power heating (Table 111) 928 GROBENSKI et d. DETERMINATION OF CAESIUM Analyst Yol. 108 TABLE I11 GRAPHITE FURNACE CONDITIONS FOR CAESIUM AND RUBIDIUM WITH 0.2% OF NITRIC ACID AS DLLUENT Conditions A pyrolytically coated tube with platform maximum power heating; B, pyrolytically coated tube off the wall maximum power heating; C pyrolytically coated tube off the wall normal heating; D uncoated tube off the wall maximum power heating; and E uncoated tube off the wall normal heating.Platform conditions can be recommended as the best. Element cs * . TemperaturelOC --- Conditions Pre-treatment Atomise A 900 1900 B 900 1900 C 900 2 700 D 900 2 200 E 900 2 700 Characteristic amountlpg m A r peak height peak height 4.0 -5.0 (PA) 3.6 7 4.5 12 30 41 46 77 No. of mgl-l (20 p1) for 0.2 absorbance 0.005 0.01 0.03 0.09 0.18 Rb A 800 1900 1.4 - 0.003 B 800 1900 1.3 2.7 0.008 C 800 2 700 1.6 4.5 0.01 D 800 2 100 6 10 0.03 E 800 2700 10 17 0.04 2.3 (PA) A 105-fold excess of rubidium was added to a 5 ng 1-1 caesium standard (and vice versa) to check for the presence of ionisation interferences.There was no difference in the signal with and without the ionisation buffer. A 105-fold excess of caesium increased slightly the signal for rubidium but this was attributed to the contamination obvious from the blank measurement. Rabidiam Rubidium was determined in different pre-analysed samples (Fig. 1) and it was found that in instances of signal depression application of the L'vov platform is beneficial. The analyte 0.3 0.2 8 e n rn a 0.1 0 B A C - I r I I -E E -OI E 0 0 -m m I - ' I ' - E Fig 1. Recorder tracings for the determination of rubidium in (A) NBS SRM bovine liver (10 p1 standard + 10 pl sample); (B) orchard leaves (10 pl standard + 10 p1 sample); and (C) acid standard (20 pl).A L'vov platform and maximum power atomisation at 1900 "C under gas interrupt (0 ml min-1 argon) were used. An autosampler was used for the automatic addition of sample into the tube and calculation of results was done off-line with a desk mini-computer August 1983 AND RUBIDIUM BY FLAME AND FURNACE AAS 929 addition technique was applied to check for the absence of depression and integrated absorbances were evaluated using linear regression. As there was no depression direct calibration was valid. It was found that a thermal pre-treated temperature of 900 "C was too high and minor losses were observed when longer thermal pre-treatment times were applied.This was observed only in the presence of a matrix. Because of this a temperature of only 800 "C can be recommended for thermal pre-treatment. A fast heating rate of up to 2000 "C s-l was used routinely for atomisation off the L'vov platform in a pyrolytically coated graphite tube. Biological and botanical samples [0.2 g of NBS Standard Reference Materials (SRMs) bovine liver spinach and orchard leaves] were decomposed in an autoclave (Perkin-Elmer Autoclave 3) with 6 ml of nitric acid (1 + l) and made up to 50 or 100 ml. Results for rubidium are presented in Table IV. Good agreement with certified values was obtained. Without the L'vov platform the values found were systematically lower.In addition, rubidium was determined in two US Geological Survey standard rock samples (AVG-1 and BCR) previously measured by flame AAS (see Table 11) and a value of 69 pg g-l was found for andesite (AGV-1) and 66 pg g1 for basalt (BCR-1). TABLE IV RESULTS FOR THE DETERMINATION OF RUBIDIUM USING GRAPHITE FURNACE AAS Sample Certificate valuelpg g-l Found/pg g-l NBS SRM 1577 bovine liver 18.3 f 1.0 18.9 f 0.8 NBS SRM 1571 orchard leaves . . 12 f 1 11.6 f 0.9 NBS SRM 1570 spinach . . . . 12.1 f 0.2 12.2 f 0.7 11.8 f 0.8* * Via solid sampling. The sensitivity for rubidium with pyrolytically coated tubes is so high that environmental contamination may cause a problem. This is also the main reason why the detection limit for rubidium is not better than that for caesium (see Table I).Rubidium was determined in water samples taken from Lake Constance (stabilised with 0.1 % of nitric acid) using 50-pl sample aliquots pyrolytically coated tubes atomisation off the wall and direct calibration against acid standards. The concentration found was 1.24 pg 1-1 (Fig. 2). Solid sampling was applied to the determination of rubidium in NBS spinach.lB The half as sensitive line at 794.7 nm maximum power to 2 100 O C atomisation off the wall and an argon flow-rate of 200 ml min-1 during atomisation were applied. In routine analysis carbon build-up was avoided using an ashing step at 500 "C with oxygen as alternate gas before going to the maximum pre-treatment temperature of 800 "C. Direct calibration against ordinary standards gave excellent agreement with the certified value when integrated absorbance values 0.2 E 4? 8 0.1 a m 0 +lo0 pg Rb Fig.2. Recorder tracings for the determination of rubidium in lake water. Sample aliquots 60.p1, pyrolytically coated tubes maximum power atomsa-tion at 1900 O C and a flow-rate of 30 ml min-l of argon were used 930 GROBENSKI et al. DETERMINATION OF CAESIUM Analyst Vol. 108 were used (found 11.8 & 0.8 pg gl; certified 12.1 If more than one element has to be determined in spinach and a number of samples are available, determination after decomposition is faster than solid sampling and more suitable for automa-tion. 0.2 pg gl) (see Table IV). Caesiwn Caesium was determined inUSGS rock sample (Fig. 3) and the results are presented in Table V.The decomposition method was the same as previously described for flame determinations. Pyrolytically coated graphite tubes and maximum power atomisation were applied. A signal depression caused by the matrix was observed for atomisation off the wall and integrated absorbance could only partially compensate for it. Only after 10 pl of sulphuric acid (96%, Suprapur) had been added to 1 ml of decomposed rock sample solution was depression no longer observed and direct calibration could be applied. The same amount of sulphuric acid was added to the calibration solutions but there was essentially no influence on their peak height and area values. For atomisation off the L’vov platform the addition of sulphuric acid was still required. The same water samples from Lake Constance were also analysed for caesium.With a 10-fold scale expansion pyrolytically coated tubes a sample aliquot of 50 p1 and maximum power atomisation at 1900 OC a concentration of lower than 0.1 mg 1-1 was found (Fig. 4). Caesium was measured by graphite furnace AAS in the same nitric acid soil extract as with the flame technique. Because of much lower sensitivity (10-fold) uncoated graphite tubes TABLE V DETERMINATION OF CAESIUM IN STANDARD ROCK SAMPLES BY GRAPHITE FURNACE AAS Each value represents a mean value of multiple determinations for a single decomposition. Reported value USGS GSP-1 granodiorite . . 0.9 1.1 1.0 1.0 USGS AGV-1 andesite 1.23 1.24 1.23 1.6 1.4 1 .o 1.3 IWG BE-N basalt . . 0.7 0.7 Sample USGS G-2 granite .. Found/pg g-l Valuelpg g-l 1 .o 2.1 0.9 1.3 1.0 1.4 1.4 1.0 1.23 1.24 1.33 1.22 1.7 1 .o 1 1.0 0.8 0.88 1.00 1.03 0.98 1.4 1.2 1 .o 1.27 1.26 1.34 1.23 0.96 0.96 1.2 1.22 0.96 1.03 0.96 0.8 Reference 6 8 13 11 20 21 22 23 24 6 13 11 20 21 22 23 24 16 13 20 21 22 23 24 16 13 11 20 22 23 24 16 1 August 1983 AND RUBIDIUM BY FLAME AND FURNACE AAS 93 1 Fig. 3. Recorder tracings for the determination of caesium in standard rock samples of USGS granite G-2 granodiorite GSP- 1 and andesite AGV- 1. Pyrolytically coated tubes and maximum power atomisation a t 1900 O C under an argon flow-rate of 50 ml min-’ were applied. were used and sulphuric acid was added for the reasons mentioned above.The result obtained of 0.15 mg 1-1 was in excellent agreement with that obtained by the flame technique. All determinations were performed using the tungsten lamp background corrector. Owing to the absence of background however it was not required for the samples investigated. Only when the possibility of analyte modification for caesium with phosphoric acid was investigated were non-specific signals observed and had to be corrected. With the addition of a 10000-fold excess of cobalt and iron no spectral interferences for caesium were observed. 0.04 I 0.03 8 +50 pg Cs 4 L Fig. 4. Recorder tracings for the determination of caesium in lake water. Sample aliquots 50 pl pyrolytically coated graphite tubes maximum power atomisation a t 1900 “C under gas interrupt (0 ml min-l argon) were used.Conclusion The satisfactory agreement with pre-analysed samples indicates that the determination of caesium and rubidium by AAS is reasonably free from interferences and is accurate enough for the routine analysis of the various types of samples. An essential prerequisite is good instru-mentation optimised for analysis in the near-infrared region of the spectrum as well as intense and stable spectral line sources For flame AAS control of ionisation interferences by using effective buffers is required in addition. Graphite furnace atomisation off the L’vov platform using maximum power heating and peak-area integration helps to eliminate vapour-phase interferences.References 1. 2. 3. Welz B. “Atomic Absorption Spectroscopy,” Verlag Chemie y n h e i m and New York 1976. Weast R. C. Editor “Handbook of Chemistry and Physics, Ottaway J. M. and Shaw F. AppZ. Spectrosc. 1977 31 12. Fifty-third Edition CRC Press, Cleveland OH 1973 932 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. GROBENSKI WEBER WELZ AND WOLFF Ottaway J. M. Hutton R. C. Littlejohn D. and Shaw F. Wiss. 2. Karl-Marx-Univ. Leipzig, Sturgeon R. E. and Berman S. S. Anal. Chem. 1981 53 632. Das A. K. Banerjee S. and Chowdhury A. N. 2. Anal. Chem. 1978 290 319. Frigieri P. Trucco R. Ciaccolini I. and Pampurini G. Analyst 1980 105 651. Langmyhr F. J. and Thomassen Y. 2. Anal. Chem. 1973 264 122. De Laeter J. R. and Rosman K. J. R. Geostand. Newsl. 1977 1 35. Govindaraju K. Mevelle G. and Chouard C. Chem. Geol. 1971 8 131. Abbey S. Geostand. Newsl. 1978 2 141. Flanagan F. J. Geochim. Cosmochim. Acta 1969 33 81. Flanagan F. J. Cosmochim. Acta 1973 37 1189. Govindaraju K. Geostand. Newsl. 1980 4 (l) 49. Goguel R. Geostand. Newsl. 1981 5 95. Slavin W. and Manning D. C. Anal. Chem. 1979 51 261. Vollkopf U. Lehmann R. Grobenski Z. and Welz B. Appl. At. Spectrosc. 1980 26. Grobenski Z. Lehmann R. Tamm R. and Welz B. Microchim. Acta 1982 1 115. Kaiser M. L. Koirtyohann S. R. and Hinderberger E. J. Spectrochim. Acta Part B 1981 36 773. Govindaraju K. Analusis 1975 3 164. Randle K. Chem. Geol. 1974 13 237. Katz A. and Grossmann L. U.S. Geol. Surv. Prof. Pap. 1976 No. 840 49. Steinnes E. J . Radioanal. Chem. 1972 10 65. Terashima S. and Mita N. Geostand. Newsl. 1981 5 71. Math.-Naturwiss. Reihe 1979 28 367. Received June llth 1982 Accepted February 25th 198

ISSN:0003-2654    

DOI:10.1039/AN9830800925

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

Analyst August 1983 Vol. 108 pp. 933-938 933 Pyridine-2-aldehyde 2-Furoyl hydrazone as a Fluorogenic Reagent for the Determination of Nanogram Amounts of Gallium Eloisa Requena Jose J. Laserna Aurora Navas and Francisco Garcia Sanchez Department of Analytical Chemistry Faculty of Sciences University of Mdlaga Mdlaga-4 Spain The synthesis characteristics and analytical applications of pyridine-2-aldehyde 2-furoylhydrazone (PAFH) are described. This compound has been examined to evaluate its usefulness as a selective and sensitive spectro-fluorimetric reagent for gallium. The method is applied in 0.8% ethanolic solution a t pH 4.5. Under these conditions the fluorescent species have excitation and emission maxima at 380 and 445 nm respectively. The detection limit is 0.8 ng ml-1 and the range of application is between 1 and 50 ng ml-l.The method has been employed to determine gallium in syn-thetic mixtures and its recovery from human urine samples. Keywords; Gallium determination; pyridine-2-aldehyde 2-furoylhydrazone reagent ; spectro$uorirnetry Organic reagents containing the atomic arrangement -CO-NH-N=CH- namely aroylhydra-zones have been widely used for the spectrophotometric determination of metal ions because of their great complexing ~apacity,l-~ forming coloured complexes with transition metal ions. However a search of the relevant literature revealed that these compounds had not been widely applied to spectrofluorimetric analysis. The ability of these reagents to undergo conformational transformations in the reaction between their ionised particles and metallic ions leads to the formation of complexes with coplanar structures This allows the formation of rigid structures that facilitate the fluores-cent emission from the complex.Taniguchi et aL6 synthesised 32 aroylhydrazones and studied the relationship between fluorescence and structure of the chelates formed with gallium aluminium scandium and zirconium. By means of these studies they concluded that the =CONH- group has a relevant participation in the formation of fluorogenic chelates. On the other hand the possibility of keto - enolic tautomerism which increases the conjugation of the molecule in the enolic form, and also the ability to co-ordinate with metal ions contribute greatly to the production of fluorescent phenomena with the co-ordination process.This paper also gives details of the synthesis properties and analytical behaviour of pyridine-2-aldehyde 2-furoylhydrazone (PAFH) together with a description of the more interesting chromogenic and fluorogenic reactions of this compound with metal ions. The detailed development and testing of a fluorimetric method for the determination of gallium is described below. The method has been applied to the determination of gallium in synthetic mixtures and in human urine samples. The antiturnour activity of gallium,' and its use as a tumour-scanning agent,8 as well as gallium toxicity,gJo have created the need for sensitive and reliable methods of determining gallium in tissues and biological fluids.ll Experimental Reagents Unless otherwise stated the reagents were of analytical-reagent grade.PAFH was synthesised by refluxing equimolar amounts of pyridine-2-aldehyde and 2-furoyl hydrazide (Ega Chemie) at 60-70 "C for 2 h. After cooling to room temperature the reaction mixture was placed in a refrigerator and after a short time brown crystals formed. These were filtered washed with cold water and ethanol repeatedly and redissolved in ethanol -water (1 + 1). The reagent was characterised by its infrared spectrum purity being con 934 REQUENA et al. PYRIDINE-%ALDEHYDE 2-FUROYLHYDRAZONE Analyst Vol. 108 firmed by elemental analysis (required for C,,H902N3 C 65.67 N 13.93 H 4.48%. Found: C 65.60 N 14.00 H 4.40%). The yield of the synthesis was 75%. The melting-point of the reagent was 108 & 1 "C.Solutions of the reagent were prepared weekly in absolute ethanol (Merck) . A stock solution of gallium was prepared by dissolving 0.9978 g of Ga(N03),.8H,0 in 250 ml of 2 M hydrochloric acid solution. The exact gallium content was determined by titration with EDTA. Solutions of lower concentrations were made by dilution with de-ionised water. Buffer solutions of pH 4.5 consisted of sodium acetate - acetic acid (0.1 M). Apparatus Fluorescence measurements were performed on a Perkin-Elmer Model MPF-43A spectro-fluorimeter equipped with an Osram XBO 150-W xenon lamp excitation and emission grating monochromators 1 x 1 cm quartz cells R-777 photomultiplier (Hamamatsu) and a Perkin-Elmer 023 recorder. A set of fluorescence polymer samples were used daily to adjust the spectrofluorimeter and compensate for changes in source intensity.The fluorescence data are given without spectral correction. An ultrathermostatic water-bath circulator (Frigiterm S-382) was used for temperature control. The absorption measurements were performed on a Shimadzu UV-240 Graphicord spectro-photometer . Procedure Into a 25-ml calibrated flask transfer 2.5 ml of pH 4.5 buffer solution and 0.2 ml of the appropriate PAFH ethanolic solution to make the final solution between 2 x and 2 x 10" M. Add an aliquot of sample solution containing 0.025-1.25 pg of gallium and dilute to volume with de-ionised water. Store in the dark for 30min; afterwards measure the fluorescence intensity a t 445 nm with excitation at 380 nm against a reagent blank at 15 "C.Preparation of Urine Sample Solutions A 10-ml volume of human urine was digested by treatment with concentrated nitric acid, evaporated to a small volume and diluted to 50 ml with de-ionised water after an aliquot of gallium standard solution had been added. Results and Discussion Acid - Base Equilibria of PAFH The absorption spectra of 0.8% ethanolic solutions of PAFH registered in the 250-400 nm spectral range show that for values of pH ranging from 1.5 to 12.1 the absorption spectra are unaffected. They show a maximum at 310 nm and two isosbestic points at 330 and 280 nm. From these experimental data the Pease and Williams12 method allows the determination of pK = 3.10 &- 0.08 and pK = 9.60 & 0.13. In agreement with literature data13-15 for similar reagents these values can be assigned as pK for the de-protonation of pyridinium hydrogen and pK for the de-protonation of enolic hydrogen.The species distribution diagram which corresponds to the prototropic behaviour of PAFH is shown in Fig. 1. Fig. 1. Species distribution diagram of PAFH. cc = Molar ratio August 1983 AS A FLUOROGENIC REAGENT FOR GALLIUM 935 Main Chromogenic and Fluorogenic Reactions of PAFH with Metal Ions The reactions of PAFH with 30 cations at three pH values (4.5 7 and 10) were investigated in a 0.8% ethanolic solution. The characteristics of the most important complexes are summarised in Table I. The data were obtained from the appropriate spectra which were measured in the presence of a 5 M excess of the reagent at those pH values which facilitate the formation of the different complexes.As shown the chromogenic reactions of PAFH are not very sensitive but on the other hand the reagent is selective. TABLE I ANALYTICAL CHARACTERISTICS OF THE MAIN COLOUR REACTIONS OF PAFH Concentration/ Ion pg ml-l pH hmax./nm AX*/nm Emax. x 10-4/1 mol-l cm-I Ni . . 1 10 360 50 3.80 Zn . . 5 10 350 40 0.84 c o . . 1 10 350 40 3.33 Cu(I1) . . 2 10 355 45 2.05 CU(I1) . . 2 4.5 365 55 2.16 Pd . . 5 4.5 405 95 1.59 * Colour contrast (AX) = Am, (complex) - Amax (reagent) under identical conditions of measurement. The fluorescent reactions were tested in a similar way and for those complexes that fluor-esced most strongly a fluorescent titration was performed. A summary of the main spectral characteristics of the fluorogenic reactions of PAFH with metallic ions is given in Table 11.The concentration of all the metallic ions in these experi-ments was 1 pg ml-l with a reagent concentration 5 M in excess. It is noteworthy that the relative fluorescence intensity of the PAFH chelates with gallium and scandium is higher than with aluminium. This is unusual because the heavy-atom effect tends to make the reactions of the lighter metal ions more sensitive. TABLE I1 ANALYTICAL CHARACTERISTICS OF THE MAIN FLUOROGENIC REACTIONS OF PAFH Ion pH Xexc./nm hem./nm RFI* A1 . . . . 4.9 382 442 350 Ga . . . . 4.5 380 446 4 100 In . . . . 6.9 393 452 15 s c . . . . 4.5 382 460 3 400 Zn . . 7.8 395 454 20 Y . . 7.5 384 430 80 * The relative fluorescence intensity of 0.1 p.p.m.quinine sulphate is 22. Spectrofluorimetric Study of the Gallium - PAFH System an intense blue fluorescence is formed immediately. the gallium - PAFH complex in a 0.8% ethanolic solution at pH 4.5 are shown in Fig. 2. reagent excitation and emission spectra are also given. When dilute gallium(II1) solutions and a 1 x M solution of PAFH in ethanol are mixed, The excitation and emission spectra of The Effect of Experimental Variables In order to evaluate the effect of pH a fluorescent titration was carried out in 0.8% ethanolic solution. The pH was changed by addition of small amounts of dilute hydrochloric acid and sodium hydroxide solutions. The results are shown in Fig. 3 which shows that oscillations in fluorescence intensity about the peak at pH 4.5 are within 3% in the pH range 4.44.55; the intensity diminishes strongly at both lower and higher pH values 936 REQUENA et al.PYRIDINE-%ALDEHYDE 2-FWROYLHYDRAZONE Analyst VOZ. 108 Wavelengthlnm Fig. 2. Uncorrected excitation (A,A') and emission (B,B') of complex (A,B) and free ligand (A',B') a t pH 4.5. [Gal = 4 x M and [PAFH] = 8 X 1 0 - ' M . 3 4 5 6 PH Fig. 3. Effect of pH on the formation of the gallium -PAFH chelate. [Gal = 4 x M and [PAFH] = 8 x M. Other experiments were carried out at pH 4.5 to determine the optimum percentage of ethanol. The results show that the ethanol concentration in the reaction solution must be carefully controlled because the fluorescence intensity decreases continuously by 70% as the ethanol concentration increases from 0.8 to 40%.Between ethanol concentrations of 40 and goy, the fluorescence intensity decreases by 15%; there is little or no fluorescence in 90% ethanolic solutions. The 0.8% ethanolic solutions are satisfactory. The fluorescence behaviour of the gallium chelate with solvent composition suggests that an increase in the polarity (0.8% ethanol) raises the energy of the n-n* state above the T-T* state and thereby facilitates deactivation by fluorescence emission.16 Generally if a carbonyl-containing molecule has an Sn,x. lowest state it will not fluoresce but will phosphoresce. The phosphorescence can originate from either a Tx,n* or a Tnmx. state. If an Sx,x* state is lowest both fluorescence and phosphorescence occur.17 Solvents can affect the emission properties in terms of both A,,,.and quantum efficiency. This results from a change in the nature of the energy relationship between the lowest Sn,n* and SxIx* statesla During the experiments a chelate photolytic phenomenon was observed that seriously affects the time necessary for stable fluorescence intensity. In order to evaluate the effect of instrumental parameters on the stability two solutions were continuously exposed to lamp-light at 380 nm with different excitation slits; another was stored in the dark until its fluores-cence intensity was measured. From the results obtained it was evident that to ensure better reproducibility small excitation slits and storage of the solutions in darkness until measurement were important Under the recommended experimental conditions the fluorescence emission remains stable for 90 min 30 min after preparation.The effect of PAFH concentration on the intensity from the 4 x 10-6 M gallium solution was also studied under conditions similar to those of the recommended method. The intensity of the fluorescence increases with concentrations of PAFH up to 8 x 1 0 - 4 ~ . For greater concentrations the intensity decreases steadily because of fluorescence inversion phenomena. The wide anomalous range of PAFH concentrations in which the fluorescence intensity increases can be ascribed to the low stability of the chelate which necessitates a large reagent excess for full development of the complex. The 2 x 10-4 M PAFH concentration was selected for further investigation as this impedes the fluorescence inversion phenomena and ensures a sufficient reagent excess.The dependence of the fluorescence intensity on temperature is critical showing a dramatic fall (70%) on increasing the temperature from 18 to 30 "C. A temperature increase from 5 to 18 "C diminishes the fluorescence intensity by 5%. This effect can be explained by the higher internal conversion as temperature increases facilitating non-radiative deactivation of the excited singlet state. In addition the contribution of the higher inter-system crossing rate as temperature increases may be effective. The presence in the PAFH molecule of a carbonyl group lends some support to this hypothesis because compounds of this naturelg often show these energy-transfer mechanisms. This work was carried out a t 15 & 0.5 "C Azlgust 1983 AS A FLUOROGENIC REAGENT FOR GALLIUM 937 Composition of the Complex The metal to ligand ratio in the complex was studied under the established working condi-tions by the method of continuous variation.This method was applied to a series of solutions in which the total concentration of reactants (gallium + PAFH) was kept constant at 4 x The maximum occurred at a 0.32 molar fraction of gallium indicating that the composition of the complex is 1 2 (metal to ligand) so, according to the structure of the ligand and the co-ordination number of the gallium ion a charged complex is formed (I) in which the ligand acts as a tridentate planar chelating agent. M but the molar fractions were varied. I I Analytical Parameters Linear calibration graphs passing through the origin were obtained for two ranges of gal-lium(II1) concentrations covering a total range of 1-50 ngml-l with two concentrations of PAFH.Two series of 11 measurements on 36 and 10 ng ml-l of gallium(II1) gave relative errors of 1.96 and 2.6% and relative standard deviations of 2.95 and 3.91y0 respectively. The limit of detection defined as the concentration of gallium giving a signal to noise ratio of 2 1 was 0.8 ng ml-l of gallium. Effect of Foreign Ions The effect of various ions on the determination of gallium at the 30 ng ml-l level was investi-gated by first testing a 100-fold m/m ratio of interferent to gallium and if interference occurred, reducing the ratio progressively until interference ceased.The criterion for interference was a variation of fluorescence intensity of more than &4% from the value expected for gallium alone. The results are given in Table 111. Interferences in this method arise from two main chemical sources and also from an inter-action at the excited state level. The latter occurs with Mo(VI) V(V) Ni(I1) and Fe(III), because of their paramagnetic character. The chemical sources are In(II1) and Sc(III) which form fluorescent chelates with PAFH; EDTA and citrate give moderately stable chelates with gallium ions at pH 4.5. Higher ratios were not tested. TABLE I11 EFFECT OF FOREIGN IONS ON THE DETERMINATION OF 30 ng ml-l OF GALLIUM (ERROR 4%) Tolerance/ ng ml-' Foreign ion or species Tl(I) Ag Be Mg Sr Ba Pb Ca Se(VI) As(V) SCN- S20a2-Hg(II) La Th Zn Mn Tl(III) Sb(III) Y Cd .. 1600 . . 3000 Cu(II) Pd Al Ti Os Co Bi POq3- F- . . 300 Ni . . . . 150 Mo 60 v(v) iie(III);+In citrate . . . . 30 EDTA Sc . . . . 16 Applications The recommended procedure for the determination of gallium was applied in a variety of situations to evaluate its effectiveness. For this purpose synthetic mixtures of common metal ions that usually accompany gallium in natural and manufactured samples were prepared an 938 REQUENA LASERNA NAVAS AND GARCIIA SANCHEZ TABLE IV DETERMINATION OF GALLIUM IN THE PRESENCE OF SYNTHETIC MIXTURES OF FOREIGN IONS Mixture of foreign ions/ng ml-l 150 A1 + 750 Zn . . 150 Cu(I1) + 750 Zn . . 150 Cu(I1) + 1500 Cd . . 750 Zn + 1500 Cd + 15 In .. 150 A1 + 15 In + 760 Tl(II1) . . 150 Cu(I1) + 1500 Cd + 750 Zn 750 Zn + 1500 Cd + 750 Hg . . 150 A1 + 15 In + 750 Hg . . * . . . Ga added/ ng ml-l 30 30 30 30 30 30 30 30 Ga found*/ ng ml-1 29.45 28.00 27.50 32.66 35.00 28.00 29.84 35.00 * Results are the means of three determinations. analysed (Table IV). Also a series of recovery experiments were carried out by adding standard pure gallium solutions to aliquots of human urine samples treated as indicated in the experimental section (Table V). The results obtained indicate that the method would be effective for the analysis of samples of similar complexity. TABLE V DETERMINATION OF GALLIUM IN HUMAN URINE Gallium added/ng ml-l Gallium found/ng ml-l Recovery % 0 0.19* -1 .oo 1.22 103.0 2.00 2.03 92.0 4.00 4.01 95.5 6.00 5.77 93.0 8.00 8.25 100.8 * Triplicate determination.1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. References Katiyar S. S. and Tandon S. N. Talanta 1964 11 892. Vasilikiotis G. S. and Tossidis J. A. Microchem. J . 1969 14 380. Uno T. and Taniguchi H. Bunseki Kagaku 1971 20 997. Gallego M. Garcia Vargas M. and Valchrcel M. Analyst 1979 104 613. Silva M. and Valckrcel M. Analyst 1980 105 193. Taniguchi H. Tsuge K. and Nagano S. Yakugaku Zasshi 1974 94 759. Hart M. M. and Adamson R. H. Proc. Natl. Acad. Sci. USAI 1971 68 1623. Hoffer P. B. Bekerman C. and Henkin R. E. Editors “Gallium-67 Imaging,” John Wiley, Newman R. A. Brody A. R. and Krafoff I. H. Cancer 1979 44 1728. Kelsen D. P. Alcock N. Yeh S. Brown J. and Young C. Cancer 1980 46 2009. Nakamura K. Fujimori M. Tsuchiya H. and Orii H. Anal. Chim. Acta 1982 138 129. Pease B. F. and Williams M. D. Anal. Chem. 1959 31 1044. Dolgorev A. V. Sivak N. S. Pal’nikova T. I. and Gurevich L. M. Zh. Anal. Khim. 1979 34 106. Luque de Castro M. D. and Valckrcel M. Talanta 1980 27 645. Cejas M. A, G6mez Hens A. and Valckrcel M. Anal. Chim. Acta 1981 130 73. Lippert E. Angew. Chem. 1961 73 695. Becker R. S. “Theory and Interpretation of Fluorescence and Phosphorescence,” John Wiley New Eastman J. W. Spectrochim. Acta Part A 1970 26 1545. Schulman S. G. “Fluorescence and Phosphorescence Spectroscopy Physicochemical Principles and New York 1978. York 1969. Practice,” Pergamon Press Oxford 1977. Received January 6th 1983 Accepted March 17th 198

ISSN:0003-2654    

DOI:10.1039/AN9830800933

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

Analyst Aqgust 1983 Vol. 108 pp. 939-943 939 Spectrophotometric Determination of Arsenic in Biological Tissues and Sediments After Digestion with Nitric Sulphuric and Perchloric Acids and Pre-concentration by Zinc Column Arsine Generation and Trapping W. A. Maher" Department of Oceanography University of Southampton Southampton SO9 5NH A procedure for the determination of total arsenic in environmental extracts is described. Arsenic is converted into arsine using a zinc reductor column, the evolved arsine trapped in a potassium iodide - iodine solution and the arsenic determined spectrophotometrically as an arsenomolybdenum blue complex. The detection limit (based on four times the standard deviation of six blank measurements) is 0.024 p g and the coefficient of variation is 5.1% at the 0.1-pg level.The method is free from interferences by other elements at levels normally found in environmental samples. Keywords Arsenic determination ; hydride generation and trapping ; mole-cular-absorption spectrophotometry ; environmental materials The continuing interest in arsenic in the en~ironmentl-~ has led to a need for methods of improved simplicity and precision for the determination of arsenic in environmental materials. Many methods for the determination of arsenic in environmental extracts use arsine genera-tion after the prior destruction of the matrix to isolate and concentrate arseni~.~,5 Arsine generation methods usually utilise the addition of zinc magnesium aluminium or sodium tetrahydroborate(II1) in the forms of solutions slurries or pellets to acidified solutions.The main problems with using arsine generation separation methods is that severe interferences, affecting both the extent and the rate of hydride generation are caused by the presence of large amounts of other element@-7 and strong oxidising acids.* Interferences in the deter-mination step may also be caused by other hydride forming elements (selenium tellurium, tin antimony and germanium) which are co-generated. Published methods also often require long generation times and suffer from imprecision owing to the variable evolution of hydrogen. The use of a zinc reductor column to generate arsine that can tolerate high concentrations of foreign ions and allow a rapid throughput of prepared samples with little evolution of hydrogen has been reported.9 In this paper the use of a zinc column to generate arsine and the subsequent trapping of the gas have been investigated.This method of separation and concentation has been combined with the determination of arsenic as arsenomolybdenum blue to give a convenient method for determining total arsenic in solutions obtained from biological and sediment samples. Experimental Instrumentation and Apparatus 4-cm microcuvettes (capacity less than 2 ml). was prepared by filing zinc sticks to pass through a 2-mm sieve. 10-20 mesh. Absorbance measurements were made with a Zeiss PMQ 2 spectrophotometer using 1- and The reductor column used to generate and trap the arsine is shown in Fig. 1 . Zinc powder The Drierite (CaSO,) was Reagents All chemicals were of analytical-reagent grade.* Present address Department of Physical and Inorganic Chemistry University of Adelaide Adelaide 5001 Australia 940 MAHER SPECTROPHOTOMETRY OF As IN BIOLOGICAL TISSUES Analyst VoZ. 108 Dissolve 1.3204 g of arsenic(II1) oxide in 1000 ml of 0.1 M sodium hydroxide solution. A reducing solution was prepared by dissolving 15 g of potassium iodide and 15 g of ascorbic acid in 100 ml of distilled water . A trapping solution was prepared by dissolving 1 g of potassium iodide and 0.5 g of iodine in 100 ml of distilled water. A mixed spectrophotometric reagent was prepared by adding 2.2 nil of 18 M sulphuric acid 5 ml of 5% m/V ammonium molybdate solution 1 ml of 0.3% m/V antimony potassium tartrate solution and 12 ml of 15% m/V ascorbic acid solution to 29 ml of distilled water in the order indicated.Arsenic(II1) standard solution 1 000 pg ml-l. Potassium iodide (15% m/V) - ascorbic acid (15% m/V) solution. Potassium iodide (1% m/V) - iodine (0.5% m/V) solution. Mixed reagent. Syringe ll Zinc i 1 ml) - Drierite Pasteur pipette Centrifuge tube Potassium iodide -solution iodine Fig. 1. Apparatus to generate dry and trap arsenic hydride. Procedure Biological tissues and sediments were freeze-dried and ground (to less than 200 pm) before analysis. A weighed sample (less than 0.5 g) was placed in a 30-ml Pyrex centrifuge tube 5 ml of concentrated nitric acid were added and the mixture was allowed to stand for at least 12 h at room temperature to ensure complete dissolution (this avoids foaming on heating).The tube was then placed in an aluminium heating block and refluxed until the evolution of brown fumes ceased. After cooling 5 ml of a nitric - sulpliuric - perchloric acid mixture (5 + 1 + 3 V / V ) were added and heating continued until dense fumes of sulphur trioxide appeared. The digest was diluted with 5 nil of 1.5 M hydrochloric acid 1 ml of reducing solution was added and the solution allowed t o stand for 40 min to reduce all of the inorganic arsenic to the trivalent form. The solution was then made up to 25 ml in a calibrated flask with 1.5 M hydrochloric acid. The apparatus was assembled as in Fig. 1 with 1.5 ml of the potassium iodide - iodine solution in the centrifuge tube. The nitrogen gas flow-rate was adjusted to 150 ml min-l, 1 ml of sample was injected on to the zinc column and the evolved arsine collected for 2 min.Between each sample 1 ml of 1.5 M hydrochloric acid was injected to prevent any accumulation of potentially interfering material on the column. After the arsine had been trapped the centrifuge tube was removed and 0.5 ml of the mixed spectrophotometric reagent added. The solution was mixed by means of a vortex mixer and allowed to stand for 30 min to develop the arsenomolybdenum blue. Calibration graphs of absorbance veyszts amount of arsenic (0-1 and 0-5 pg) were prepared by using arsenic standards carried through the entire analytical procedure. The absorbance was measured at 866 nm August 1983 AND SEDIMENTS AFTER ACID DIGESTION AND PRE-CONCENTRATION Results and Discussion Optimisation of Hydride Generation and Trapping 90 80 70 941 ---To optimise the conditions for hydride generation and trapping the effects of acid concentra-tion gas flow-rate and trapping solution composition on the evolution and trapping of arsine were investigated.Sample solutions containing 5 pg ml-l of arsenic (1 ml injections) and 1.5 ml of 1 % m/V potassium iodide - iodine trapping solution were used for the optimisation of acid concentration and the gas flow-rate. The effects of flow-rate and acid concentration are shown in Figs. 2 and 3. It was desirable to use the lowest acid concentration possible as an excess of acid necessitated the frequent replacement of zinc and also caused excessive entrain-ment of water and acid vapour which resulted in the rapid clogging of the absorbent.Hydro-chloric acid was preferable to sulphuric acid which consumed larger amounts of zinc during hydride evolution. A hydrochloric acid concentration of 1.5 M and a gas flow-rate of 150 mlmin-l were chosen for all further work. Under these conditions the collection of arsine was complete within 2 min. A trapping solutioii containing 1% nz/V potassium iodide and 0.5% m/V iodine quantitatively trapped up to 5 pg of arsenic (from a 1-ml injection) as arsine; no arsenic was found in a second bubbler trap in series with the first. The iodine concentration was not critical as long as an excess was present. The equilibrium I + I- + 13- produces 13- which traps the arsine. Recoveries of arsenic added to the zinc column were all greater than 97% (97 & 1 97.6 &- 0.5 and 98.2 & 0.8% for 0.1 2.0 and 5.0 pg ml-l of arsenic respectively using the proposed conditions).The use of smaller capillary tubing for trapping did not increase the trapping efficiency. 100 I s! -. 100 F 8 90 L I I Gas flow-rate/mI min-’ Fig. 2. Effect of gas flow-rate on hydride generation and trapping. Hydrochloric acid concentration 2 M. I I I I I 1 2 3 4 Acid concentrationlhn Fig. 3. Effect of acid concentration on hydride generation and trapping. A, Hydrochloric acid media ; B sulphuric acid media. Spectrophotometric Determination The conditions for the determination of arsenic as arsenomolybdenum blue were investigated by Portmann and RileylO and the optimum concentrations that they recommended have been used in this study.It was thought possible that the absorption spectrum of arsenomolybdenum blue might be modified in the presence of an excess of potassium iodide. The spectrum was plotted and no shift in the absorption maximum was found; thus all measurements were made at 866 nm. The calibration graph of absorbance versus arsenic injected on to the zinc column was linear in the range 0-5 pg for 1-cm cells and 0-1.25 pg for the 4-cm cells. Interferences Possible interference by other elements was investigated by measuring the arsine generated and trapped in the presence of elevated concentrations of other elements. The concentrations at which certain elements interfere are shown in Table I. Various other elements [Al(III), B(III) Ca(II) Cd(II) Co(II) Cr(VI) Fe(III) K(I) Li(I) Mg(II) Mn(II) Na(I) Ni(II) 942 MAHER SPECTROPHOTOMETRY OF As IN BIOLOGICAL TISSUES Analyst VoZ.108 TABLE I EFECT OF INORGANIC IONS ON THE GENERATION AND TRAPPING OF ARSINE All tests used 0.1 p g of As(II1) in 1 ml of 1.5 M hydrochloric acid. generation and trapping conditions were used. Optimised hydride 22 Species . . . . . . Cu(I1) Hg(I1) Mo(V1) Sb(II1) Se(1V) Si(1V) Interference level/pg . . . . 50 2.5 400 25 0.1 50 Pb(II) S(VI) Sn(I1) and Zn(II)] showed no significant interference at the 500-pg level. Only low selenium concentrations in extracts can be tolerated. However few environmental samples contain appreciable amounts of selenium. As selenium is not reduced to hydrogen selenide on the column selenium will not interfere in the final determination step but probably suppresses either arsenic reduction or arsine formation.Selenium appears to suppress arsine generation at high arsenic concentrations but causes a slight enhancement at low arsenic concentrations (around 0.1 pg) which could not be traced to arsenic impurities in the selenium standard used. Accuracy Precision and Detection Limit The accuracy of the method was assessed by recovery experiments and the analysis of standard reference materials (orchard leaves NBS SRM 1571 and oyster tissue NBS SRM 1566). As shown in Table 11 complete recovery of added arsenic was obtained within experi mental error for selected biological tissues and a sediment. The arsenic concentration obtained by replicate analysis of the orchard leaves (9.7 & 0.3 pg g-l) and oyster tissue (13.2 0.4 pg g1) were in agreement with the certified values of 10 & 2 and 13.4 & 1.9 pg gl, respectively.The precision was determined from replicate analyses of arsenic standards carried through the entire procedure. The relative standard deviation at the lowest concentration examined (0.1 pg of arsenic) was 5.1%; for 2.0 and 5.0 pg ml-1 of arsenic the relative standard deviations were 3.7 and 2.4% respectively. The standard deviation of the blank (6 determinations) corresponded to 0.006 pg of arsenic. TABLE I1 RECOVERY OF ARSENIC ADDED TO SELECTED BIOLOGICAL TISSUES AND A SEDIMENT Arsenic added as inorganic arsenic. Arseniclpg 1 Sample kdded Found Recovery % Macroalgae Ecklonia radiata (0.25 g) .. 0 21.3 f 0.9 10 30.9 f 0.9 96 20 51 f 1 99 5 21.8 f 0.6 100 10 26.6 f 0.4 98 5 7.9 f 0.3 96 10 12.9 f 0.6 98 Crayfish J a w s novae hollandiae (0.5 g ) . . . . 0 16.8 f 0.6 Sediment (0.5 g) . . 0 3.1 -+ 0.2 Conclusion The experimental method described in this paper allows the determination of arsenic down to 0.1 pg with a relative standard deviation of 5.1%. The advantages of this method are the inexpensive equipment required and the high concentration of foreign ions that can be present without causing an interference. References 1. 2. Penrose W. R. CRC Crit. Rev. Environ. Control 1914 4 465. Lunde G. Environ. Health Perspect. 1977 19 47 August 1983 AND SEDIMENTS AFTER ACID DIGESTION AND PRE-CONCENTRATION 943 3. 4 5. 6 . 7. 8. 9 . 10. Benson A. A. and Summons R. E Science 1981 211 482. Talmi Y and Bostick D. T. J . Chromatogr. Sci. 1975 13 231. Yamsmoto Y . Kumamaru T. Hayashi Y. and Kamada T. Bull. Clzem. SOC. Jpn. 1973 46 2604. Smith A. E. Analyst 1975 100 300. Guimont J. Pichette M. and Rhekume N. A t . Absorpt. Newsl. 1977 16 53. Kang H. K. and Valentine S. L. Anal. Chem. 1977 49 1829. Maher W. A. Talanta 1982 29 532. Portmann J. E. and Riley J. P. Anal. Chim. Acta 1964 31 509. Received November 8th 1982 Accepted March loth 198

ISSN:0003-2654    

DOI:10.1039/AN9830800939

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

944 Analyst August 1983 Vol. 108 pp. 944-951 Spectrophotometric Determination of Phosphorus and Arsenic in Steel by Solvent Extraction of their Heteropolyacids with Ethyl Violet Shoji Motomizu Toshiaki Wakimoto and Kyoji Toei Department of Chemistry Faculty of Science Okayama University Tsushima-naka Okayama-shi Japan Under the same conditions orthophosphate and orthoarsenate react with molybdate to form molybdophosphate and arsenomolybdate which are extracted into a cyclohexane - 4-methylpentan-2-one mixture (1 + 3) with ethyl violet. The absorption spectrum of each ion pair extracted into the organic phase is almost the same in the visible region and the molar absorp-tivity of each ion pair in the organic phase is 2.8 x lo5 1 mol-l cm-l a t 602 nm. In determining phosphate arsenate can be masked with thiosulphate and hydroxylamine.The arsenate concentration was obtained by subtracting the phosphate concentration from the total concentration of phosphate and arsenate. Steel samples (less than 0.25 g in mass) were dissolved in aqua regia and the solution was diluted to 11 with distilled water. In the deter-mination of phosphorus (about 0.003y0) and arsenic (about 0.007~0) in steel, the relative standard deviations were 2.5 and 2.1 yo respectively. Fifteen standard steel samples were analysed and the results obtained for phosphorus and arsenic were in good agreement with their certified values. The results for the recovery test were also good. The limit of detection for both phosphorus and arsenic is about O . O O l ~ o in steel.Keywords Phosphorus and arsenic determination ; solvent extraction; hetero-polyacid; steel analysis ; ethyl violet Almost all of the methods for the spectrophotometric determination of phosphorus depend on the formation of the heteropolyacid which is formed in an acidic medium by the reaction between orthophosphate and molybdate. A reduced species of molybdophosphate (molyb-denum blue) and of molybdophosphovanadate have also been used. The molar absorptivities of such heteropolyacids are less than 3 x lO41mol-1 cm-1 when these are determined spectrophotometrically in aqueous solution or in an organic phase by solvent extraction. Molybdophosphate has been extracted into an organic phase with cationic dyes such as safranine T,112 crystal violet or iodine green,3 methylene blue4 and rhodamine B.5 Recently, we studied the solvent extraction of molybdophosphate with ethyl violet.6 The method has the following advantages (1) high sensitivity (the molar absorptivity in cyclchexane -4-methylpentan-2-one mixture at 602 nm is 2.8 x lo5 1 mol-1 cm-1); (2) a simple and less time-consuming procedure (the procedure involves a single extraction and does not require washing the organic phase after extraction) ; (3) good reproducibility; (4) relatively low absorbance of the reagent blank (about 0.1) ; and (5) few interferences from co-existir g ions except for arsenate.In the previous work,6 several parts per 1 0 9 (p.p.b.) of phosphorus in waters were determined. In the course of further study for the extraction of the heteropoly-acid we found that arsenate could be extracted into an organic phase with ethyl violet under the same conditions as phosphate and the absorption maximum and molar absorptivity at 602 nm of the ion pair of molybdophosphate - ethyl violet were the same as that of arseno-molybdate - ethyl violet.It was also found that arsenite did not interfere in the deter-mination of phosphate and arsenate could be easily reduced to arsenite with sodium thio-sulphate. In the simultaneous determination of phosphate and arsenate by the molybdic acid - spectrophotometric method Johnson' and Johnson and Pilsons masked arsenate with sodium thiosulphate and sodium disulphite which reduce arsenate to arsenite. In this work sodium thiosulphate and hydroxylammonium sulphate were used and phosphorus and arsenic in steel were determined simultaneously by solvent extraction -spectrophotometry MOTOMIZU WAKIMOTO AND T6EI Experimental 945 Apparatus The absorptiometric measurements were made on a Hitachi 139 spectrophotometer with glass cells of 10-mm path length.An Iwaki Model V-S Type KM shaker was used for the horizontal shaking of the 25-ml stoppered test-tubes. Reagents A stock solution of phosphate was prepared by dissolving disodium hydrogen orthophosphate (anhydrous) which had been previously dried at 50 "C under reduced pressure (about 5 mmHg) until a constant mass had been reached in distilled water to give a The working solution was prepared daily by diluting the stock solution accurately . Dissolve 0.19 g of arsenic(II1) oxide in 20 ml of 5% sodium hydroxide solution.Acidify with 3 M sulphuric acid. Boil and add 1% potassium permanganate solution until the solution is slightly coloured. Neutralise with 5% sodium hydroxide solution and dilute to 100 ml with distilled water. The working solution was prepared daily by the appropriate dilution of the stock solution. MoZybdate solution. Ammonium molybdate [(NH,),(Mo,O,,) .4H,O] (31 g) was dissolved in distilled water and the solution was made up to 1 1. Ethyl violet solution. Commercially available ethyl violet was recrystallised twice from water. The crystals (0.13 g) were dissolved in distilled water and the solution was made up to 200 ml. Redacing (masking) a g e d . Hydroxylammonium sulphate [(NH,OH),SO,] (0.41 g) was dissolved in distilled water and the solution was made up to 50 ml (0.05 M).Sodium thio-sulphate pentahydrate (0.025 g) was dissolved in distilled water and the solution was made up to 50 ml (2 x These solutions were prepared daily. Ethylenediaminetetraacetic acid disodium salt (dihydrate) (3.7 g) was dissolved in distilled water and the solution was made up to 500 ml. A mixture of 100 ml of cyclohexane and 300 ml of 4-methylpentan-2-one was prepared and was used as the extraction solvent. Standard Phosphate solution. M solution. Standard arsenate solution. A stock solution of arsenate was prepared as follows. M ) . EDTA solution. Extraction solvent. Preparation of the samfle solution Add about 3 ml of aqua regia and dissolve the steel by heating on a hot-plate (at about 100 "C).After dissolu-tion add 10 ml of 2.5 M sulphuric acid and heat for about 30 min on a hot-plate at about 150 "C in order to remove the excess of nitric acid. The solution is then accurately diluted to the required volume with distilled water. Weigh the required amount of the steel sample into a 50-ml beaker. Procedure f o r the determination of phosphorus and arsenic Transfer an appropriate aliquot (<lo ml) of the sample solution containing up to 1 pg of phosphorus into a stoppered test-tube and dilute with distilled water to 10 ml. Pipette 0.1 in1 of 0.05 M hydroxylammonium sulphate solution into it and mix then pipette 0.1 ml of 2 x 10-3 M sodium thiosulphate solution into it and mix again. Mix thoroughly and leave for about 10 min. Pipette 1 ml of EDTA solution 1 ml of ethyl violet solution and 5 ml of the extraction solvent into it.After shaking for 25 min measure the absorbance of the organic phase at 602 nm in a 10-mm glass cell against a reagent blank. The phosphate concentration was calculated from the calibration graph for phosphate which had been obtained previously according to the same procedure. Transfer an appropriate aliquot of the sample solution (<lo ml), containing up to 0.03 pmol of total orthophosphate and orthoarsenate into a stoppered test-tube and dilute with distilled water to 10ml. Add the same amounts of sulphuric acid, molybdate EDTA ethyl violet solution and extraction solvent as those for procedure A and carry out according to this procedure. The total concentration of phosphate and arsenate was calculated from the calibration graph for either phosphate or arsenate.The arsenate Procedure ( A ) f o r phosphorus. Pipette 1 ml of 5 M sulphuric acid and 1 ml of molybdate solution into it. PTocedure (B) f o r arsenic 946 MOTOMIZU et aZ. SPECTROPHOTOMETRY OF P AND As IN STEEL Analyst VoZ. 108 concentration was obtained by subtracting the phosphate concentration from the total concentration. Results and Discussion Absorption Spectra and Calibration Graphs Each absorption spectrum of the ion pair formed between molybdophosphate and ethyl violet and between arsenomolybdate and ethyl violet in the organic phase was obtained by procedure B. Both spectra were identical and the maximum absorbance occurred at 602nm. The calibration graphs were linear in the range 0-3 x 1 0 - 6 ~ of phosphate and arsenate and the molar absorptivity calculated from the slope of the graph was 2.8 x lo5 1 mol-l cm-l.Effect of the Reducing Agent on the Reduction of Arsenic(V) to Arsenic(II1) Of these sodium dithionite and sodium thiosulphate can effectively reduce arsenic(V) to arsenic( 111). However when sodium dithionite was used the absorbance of the reagent blank became larger than the absorbance obtained with sodium thiosulphate. In view of this further experiments were carried out using sodium thiosulphate. In the range 0-2pmol of sodium thiosulphate added the absorbances of the reagent blank were almost equal and were about 0.105. In the range below 0.1 pmol of sodium thiosulphate, the greater the concentration of the sodium thiosulphate the smaller the absorbance of the ion pair extracted into the organic phase becomes and the differences in absorbance between the solutions with and without arsenate are almost equal in the range 0.1-2.0 pmol of sodium thiosulphate; this small difference in absorbance may be due to the phosphate in arsenic solution resulting from impurities in such reagents as sulphuric acid sodium hydroxide and potassium permanganate.As in this work iron and steel samples are dissolved in aqua regia iron may exist as iron(II1) in the sample solution. Iron(II1) may consume sodium thiosulphate. As shown in Fig. 1 the addition of large amounts of sodium thiosulphate causes an increase in the absorbance of the reagent blank. As can be seen from Table I, hydroxylammonium sulphate hardly reduces arsenic(V) to arsenic( 111) ; this reagent can effectively reduce iron(II1) to iron(II).g The effect of hydroxylammonium sulphate is shown in Table 11.It can be seen that more than 90% of the arsenate can be masked with only 0.2 pmol of sodium thiosulphate even when 36 pmol of iron(II1) are present. Such a result is interesting but is not explained on the basis of standard oxidation - reduction potentials of thiosulphate arsenate and iron(II1) ions. At present we cannot give a reasonable explanation for “the selective masking of arsenate with thiosulphate.” Also it is found Several reducing agents were examined (Table I). The effect of sodium thiosulphate can be seen in Fig. 1. TABLE I REDUCING AGENTS FOR REDUCTION OF ARSENATE TO ARSENITE Reducing agent None NaBH (0:0013’mol) .. Zn (0.0015 mol) + NaH (0.001 3 mol) . . Zn (0.001 5 mol) . I . . Zn (0.0015 moll + KI’ i0.01 Zn (0.0015 mol) + KI (0.01 pmol) + NaB€€ (0.0013 ,hi) KI (0.01 pmol) + Na,SO (0.0001 mol) . . . . Sb (0.001 mol) + KI (0.01 pmol) . . . . . . (NH,OH),SO (60 pmol) + KI (0.01 pmol) . . L-Ascorbic acid (60 pmol) + KI (0.01 pmol) SnC1 (0.05 pmol) + KI (0.01 pmol) Na,S,O (2 pmol) + KI (0.01 pmol) . . Na,S,O (2 pmol) . . . . HCOONa (2 pmol) . . . . (COONa) (2 pmol) . . ,. Na,S,O (2 pmol) . . . . . . . . * Reference solvent. Reference reagent blank. As(V) 0.012 pmol. Absorbance of reagent blank* . . 0.106 . . 0.119 . . 0.209 . . 0.178 . . 0.092 . .0.162 . . 0.185 . . 0.205 . . 0.165 . . 0.149 . * 0.110 . . 0.168 . . 0.109 . . 0.184 . . 0.101 . . 0.150 Absorbance? 0.672 0.458 0.225 0.299 0.344 0.281 0.125 0.542 0.629 0.519 0.457 0.005 0.013 0.355 0.331 0.03 August 1983 BY EXTRACTION OF HETEROPOLYACIDS WITH ETHYL VIOLET 947 Sodium thiosulphate/ymol 2 4 I 1 I I t 0 0.05 0.1 0.2 0.4 0.6 0.8 1.0 Sodium thiosulphate/pmol Fig. 1. Effect of sodium thiosulphate on reduction of arsenic(V) to arsenic(II1). (1) and (2) reagent blank reference solvent; and (3) and (4) 10 ml of 1.2 x M As(V) reference reagent blank. that the absorbance becomes gradually smaller as the hydroxylammonium sulphate content is increased and is almost constant in the region above 5 pmol of hydroxylammonium sulphate.The absorbances obtained in the region of 5-30 pmol of hydroxylammonium sulphate are in good agreement with those expected for the phosphate content. In deter-mining phosphorus in the presence of iron(II1) ion arsenate was masked with sodium thio-sulphate and hydroxylammonium sulphate. Here the absorbance of the reagent blank was about 0.04 larger than that in the absence of the reducing agents. This increase in the reagent blank may be caused by the phosphate contained in the agent. TABLE I1 EFFECT OF HYDROXYLAMMONIUM SULPHATE ON THE REDUCTION OF IRON(III) TO IRON(II) Sample 36 pmol of iron alum [Fe,(S04),(NH4),S04.24H,0] + 0.008 pmol of phosphate + 0.008 pmol of arsenate. This iron alum contains 0.008 pmol of phosphate per 1 g of salt that is 36 pmol of iron alum contains 0.0027 pmol of phosphate.Sodium thio-sulphate content 0.2 pmol. Amount of (NH,OH),SO,/pmol 0 1 2 3 4 5 10 20 30 Absorbance of reagent blank* Absorbancet 0.124 0.621 0.130 0.620 0.126 0.614 0.139 0.608 0.140 0.602 0.136 0.590 0.138 0.583 0.150 0.580 0.155 0.578 * Reference solvent. t Reference reagent blank. Effect of Co-existing Ions In determining phosphorus and arsenic the following ions produced absorbances contri-buting less than 0.01 unit Mg2+ (0.4 mg) ; Ca2+ (0.6 mg) ; Co2+ (0.9 mg) ; Zn2+ (1 mg) ; Cd2+ (0.7 mg) ; Mn2+ (0.8 mg) ; Cu2+ (1 mg) ; Ni2+ (0.9 mg) ; A13+ (0.4 mg) ; Ba2+ (1.4 mg) ; .Cr3+ (0.1 mg); Fe3+ (0.1 mg); Pb2+ (20 pg); W(V1) (1 pg); Sn2+ and Sn4+ (1 pg); and Si(1V) (14 pg).The effects of these ions were examined by using the metal chlorides which are commercially available. As these chlorides are more or less contaminated with phosphat 948 MOTOMIZU et al. SPECTROPHOTOMETRY OF P AND As IN STEEL Analyst vol. 108 0.6 I RI 0.4 2 0.2 - ~~ 0 2 4 6 8 10 Volume of sample solution/ml Fig. 2. Effect of volume of sample taken. (1) and (2) NBS 55e 0.496 g l-l (1) for phosphate (2) for phosphate and arsenate; (3) JSS 232-3 0.1982 g l-l for phosphate; (4) FeC13.6H,0 0.0536 g per 100 ml for phosphate; and (5) Fe,(SO,),.xH,O 0.0801 g per 100 ml for phosphate. and arsenate the results obtained by using such chlorides do not necessarily indicate the upper limit of a tolerable concentration of the co-existing ion. In order to examine the interference of iron the relationship between the absorbance and the amount of iron was obtained by using several iron(I1) and iron(II1) salts and standard steel samples.The examples are shown in Fig. 2. From graphs 1 and 2 in Fig. 2 it seems that in the region below about 4 mg of iron in procedure A and 3 mg of iron in procedure B the graphs are linear and each intercept of the y-axis is in good agreement with each reagent blank. Other graphs are also linear and each intercept is in good agreement with the reagent blank. From these results it can be seen that amounts below 3 mg do not interfere in the determination of phosphorus and arsenic. TABLE I11 DETERMINATION OF PHOSPHORUS AS PHOSPHATE IN IRON (11) AND IRON (111) SALTS Solution/ Sample Grade* Procedure g per 100 in1 FeSO,.H,O .. a A 0.055 8 FeS04(NH4),S04.6H,0 . . . . a A 0.0782 Fe,(S04),.xH,0 . . a B 0.080 1 Fe,(S04),(NH4),S04.24H,0 . . a A 0.096 9 a B 0.0964 FeC13.6H,0 e A 0.053 6 Solution takenlml 6 8 10 6 8 10 6 8 10 6 8 10 6 8 10 6 8 10 Absorbance? 0.011 0.014 0.026 0.021 0.035 0.042 0.047 0.067 0.082 0.021 0.026 0.035 0.012 0.018 0.023 0.061 0.076 0.103 Phosphorus content yo 2.3 x 10-4 2.1 x 10-4 3.0 x 10-4 3.1 x 10-4 3.7 x 10-4 3.5 x 10-4 6.9 x 10-4 3.1 x 10-4 2.6 x 10-4 2.6 x 10-4 1.4 x 10-4 1.5 x 10-4 1.2 x 10-3 1.2 x 10-3 6.8 x 6.6 x 1.6 x lo-' 1.3 x * a and e denote analytical-reagent grade and extra-pure reagent respectively.t Reference reagent blank August 1983 BY EXTRACTION OF HETEROPOLYACIDS WITH ETHYL VIOLET 949 Determination of Phosphate in Commercially Available Iron Salts The iron salts were dissolved in 0.01 M sulphuric acid and used as the sample solution. Phosphate was determined by procedure A. As the arsenate content in iron(II1) salts is less than one tenth of the phosphorus content the arsenate content cannot be determined accurately by procedure B. The results obtained are shown in Table 111. Iron salts contain 10-4-10-3 yo of phosphorus as phosphate. Preparation of Steel Sample Solution Dissolution 1 Steel samples (0.1-0.2 g) were dissolved by adding 10 ml of sulphuric acid (2.5 M) and 1 or 2 ml of about 10% hydrogen peroxide at room temperature. After dissolution potassium permanganate solution was added until the solution was coloured.An excess of perman-ganate was decomposed by adding hydrogen peroxide and boiling for 30 min. The solution was diluted with distilled water to 11. Phosphate and arsenate were determined by pro-cedures A and B. From Table IV it is found that not all of the phosphorus and arsenic in steel is converted into orthophosphate and ortho-arsenate. The values obtained are shown in Table IV. TABLE IV RESULTS OBTAINED BY DISSOLUTION WITH DILUTE SULPHURIC ACID AND HYDROGEN PEROXIDE (DISSOLUTION METHOD 1) AND NITRIC ACID (DISSOLUTION METHOD 2) Sample solution taken 10 ml. Certified value % (-*- Concentration of Steel sample* P As steel/g 1-1 JSS 230-4 . . 0.0124 0.096 7 JSS 231-3 .. 0.0223 0.099 6 JSS 030-2 . . 0.0179 0.0046 0.2030 0.2054 JSS 050-3 . . . . 0.0186 0.0113 0.1966 0.196 8 0.198 8 JSS 061-2 . . 0.0104 0.0056 0.201 0 Found % Dissolution (-*-, method P As 1 0.0100 1 0.0156 1 0.009 4 0.002 5 2 0.0136 0.0037 1 0.0095 0.0054 2 0.0186 0.0089 1 0.0068 0.002 7 2 0.0074 0.002 9 * Japanese Standards of iron and steel. Dissolution 2 Steel samples (0.1-0.2 g) were dissolved by adding 5 ml of dilute nitric acid (about 4 M). After dissolution 10 ml of 2.5 M sulphuric acid and potassium permanganate solution were added until the solution was coloured. The solution was boiled for 5 min 1 ml of 15% hydrogen peroxide was added and the solution was boiled for about 30 min and diluted with distilled water to 11. Phosphate and arsenate were determined by procedures A and B.The contents of phosphorus and arsenic obtained were about 40% lower than the certified values (see Table IV). Dissolution 3 Steel samples (masses less than 0.25 g) were dissolved in 3 ml of aqua regia on a hot-plate (at about 50 "C). After dissolution 10 ml of 2.5 M sulphuric acid were added and the solution was boiled on a hot-plate for about 20 min to remove the excess of nitric acid. The solution was then diluted with distilled water to 1 1. In this way the preparation of sample solution can be made within 2 h. Determination of Phosphorus and Arsenic in Steel Samples Sample solutions were prepared using dissolution 3 and phosphorus and arsenic were determined by procedures A and B. The results obtained are shown in Tables V VI and VII 950 MOTOMIZU et al.SPECTROPHOTOMETRY OF P AND As IN STEEL Analyst VoZ. 108 TABLE V REPEATABILITY OF THE EXPERIMENTS Sample NBS 55e; certified values phosphorus 0.003% and arsenic 0.007%. Absorbance Sample solution/ ,-A-, g per 500 ml P As 0.097 1 0.101 0.084 0.0974 0.106 0.086 0.099 8 0.102 0.090 0.100 2 0.104 0.092 0.097 1 0.106 0.086 0.096 5 0.103 0.088 0.098 0 0.101 0.087 0.099 0 0.106 0.086 0.100 5 0.107 0.086 Mean : Relative standard deviation : Found, v P 0.003 1 0.003 2 0.003 0 0.003 0 0.003 2 0.003 1 0.003 1 0.003 2 0.003 2 0.003 1 2.5 % I As 0.006 3 0.006 4 0.006 5 0.006 6 0.0064 0.006 6 0.006 4 0.0063 0.006 2 0.0064 2.1 In Table V the result for repeatability of the method proposed in this work is shown.The relative standard deviations for the determination of o.oo3y0 phosphorus and o.007y0 arsenic in the NBS 55e sample are 2.5 and 2.1yo respectively. In Table VI the results obtained for phosphorus and arsenic in steel samples are shown. The results obtained for phosphorus and arsenic are in good agreement with the certified values except for JSS 232-3. Although the result obtained for JSS 232-3 is about 25% smaller than the certified value for phosphorus the values obtained vary as narrowly as the values obtained for other steel samples. Further as shown in Fig. 2 the graph of absorbance against volume of sample solution taken shows good linearity from 0 to 10 ml, and the result for the recovery test of phosphorus is 96-101y0 (see Table VII).Hence the value for the phosphorus content of JSS 232-3 of 0.028y0 obtained in this work would appear to be the correct value. In Table VII the results for the recovery test are shown. To 5 ml of sample solution known amounts of phosphorus as phosphate and arsenic as arsenate were added and the recovery of phosphate or arsenate was examined. The results for this test are recoveries of 96-101y0 for phosphorus and 95-101y0 for arsenic respectively. TABLE VI DETERMINATION OF PHOSPHORUS AND ARSENIC IN STANDARD STEEL SAMPLES Steel sample JSS 230-4 . . JSS 231-3 JSS232-3 JSS 030-2 JSS 050-3 * . JSS 061-2 JSS 159-3 . . JSS 160-3 . . JSS 161-3 . . NBS 19g . . NBS lOle . . * . NBS 362 . . NBS 364 .. NBS 126b . . High purity steel . . . . ,. Certified value % & P As 0.0124 0.022 3 0.0389 0.0179 0.0046 0.0186 0.0113 0.0104 0.0056 0.10 0.051 0.01 0.046 0.025 0.041 0.092 0.01 0.052 Found % P As r A \ 0.0135 (0.0002)* 0.022 4 (0.000 5) * 0.0284 (0.0004)* 0.0167 (0.0002)* 0.0048 (0.0003)* 0.0177 (O.OOOO)* 0.0091 (0.0001)* 0.0096 (0.0001)* 0.0040 (0.0001)" 0.010 0.096 0.004 6 0.047 0.001 4 0.0104 0.002 0.0442 (0.0003)* 0.0226 (0.000 1)* 0.006 1 0.039 8 0.0874 0.0099 0.049 8 0.0049 0.007 8 0.001 6 (0.000 1)* Not detected * These are the means of three determinations. The values in parentheses are the mean n A=l deviations which are given by Z I X - 8 I In where 8 is the mean August 1983 BY EXTRACTION OF HETEROPOLYACIDS WITH ETHYL VIOLET TABLE VII RESULTS OF RECOVERY TESTS ON PHOSPHORUS AND ARSENIC 951 A 5-ml volume of sample solution was taken and phosphate or arsenate solutions were added to it and diluted to 10 ml with distilled water.Steel sample Sample solution/g 1-1 NBS 55e . . 0.196 0 0.1980 0.201 0 JSS 232-3 0.2048 0.196 8 0.1962 NBS 126b . . 0.199 0 NBS 364 . . 0.099 6 NBS 362 . . . . 0.0394 JSS 159-3 . . 0.0373 JSS 161-3 . . 0.1005 JSS 160-3 0.099 4 Added/pg & P As 0.241 0.522 0.241 0.522 0.241 0.522 0.241 0.241 0.241 0.120 0.261 0.120 0.261 0.120 0.261 0.120 0.261 0.120 0.261 0.120 0.261 Recovery % Y-7 P As 98 95 96 95 101 96 98 101 96 99 97 100 98 96 97 98 98 96 101 96 95 Conclusion The proposed solvent extraction - spectrophotometric method for the determination of micro-amounts of phosphorus and arsenic was applied to the determination of phosphorus and arsenic in commercially available iron(II1) and iron(I1) salts and steel samples.The steel samples were advantageously dissolved in aqua regia. In determining phosphorus, co-existing arsenic(V) is masked with sodium thiosulphate and hydroxylammonium sulphate. In the absence of thiosulphate and hydroxylamine phosphate and arsenate each react with molybdate to form heteropolyacids which are extracted into a mixture of cyclohexane -4-methylpentan-%one with ethyl violet. The advantages of this method are as follows (I) high sensitivity; (2) simple and less time-consuming procedure ; (3) the procedure is scarcely subject to interferences by co-existing ions ; and (4) good reproducibility of determination of phosphorus and arsenic at the level in steel samples. 1. 2. 3. 4. 5. 6. 7. 8. 9. References Ducret L. and Drouillas M. Anal. Chim. Acta 1959 21 86. Sudakov F. P. Klitina V. I. and Dan’shova T. Ya. Zh. Anal. Khim. 1966 21 1333. Babko A. K. Shkaravskii Yu. F. and Kulik V. I. Zh. Anal. Khim. 1966 21 196. Matsuo T. Shida J. and Kurihara W. Anal. Chim. Acta 1977 91 385. Kirkbright G. F. Narayanaswamy R. and West T. S. Anal. Chem. 1971 43 1434. Motomizu S. Wakimoto T. and TBei K. Anal. Chim. Acta 1982 138 329. Johnson D. L. Environ. Sci. Technol. 1971 5 411. Johnson D. L. and Pilson M. E. Q. Anal. Chim. Acta 1972 58 289. TBei K. Motomizu S. and Korenaga T. Analyst 1975 100 629. Received November 29th 1982 Accepted January 31st 198

ISSN:0003-2654    

DOI:10.1039/AN9830800944

出版商:RSC    

年代:1983

数据来源: RSC