ISSN:0003-2654    

DOI:10.1039/AN97398FX045

出版商:RSC    

年代:1973

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN97398BX047

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

... December, 19731 THE ANALYST 111Modern Analytical Methods is one of TheChemical Society’s series of paperbackmonographs which present concise andauthoritative accounts of selected welldefined topics in chemistry for those whoteach the subject at ‘A’ level and above andfor students of further and higher education.It discusses the principles underlying themost important methods of quantitative andqualitative analysis used today. Samplesfor analysis may arise from diverse sourcesand contain a variety of molecules orelements at various levels of concentration.Thus separation methods, organic reagents,nuclear, electrochemical, spectroscopic andtitrimetric methods are amongst those dealtwith in some detail. Within the bounds ofelementary algebra, equations are developedwhich show how the optimum conditions forthe application of a method may be deducedand conditional constants are usedthroughout. The numerous illustrationssupport the text by clarifying principles or byexemplifying important methods which aredealt with briefly because they do not involvenew principles.234pp 75 diagrams f2.00 I (CS Members S1.50)ISBN 0 85186 759 6MONOGRAPHSFOR TEACHERSModernAnalyticalMethodsby D.BETTERIDGEand H. E. HALLAMOrders enclosing the appropriateremittance, should be sent to:The Publication Sales Officer, TheChemical Society, Blackhorse Road,Letchworth, Herts SG6 1HN.For information on other titles in the serieswrite to: The Marketing Officer,The Chemical Society, Burlington House,London WIV OBN.THE CHEMICALSOCIETYS PECl ALlST ABSTRACTJOURNALSpublished bySCIENCE AND TECHNOLOGY AGENCYAtomic Absorption and FlameEmission Spectroscopy AbstractsVol.5,1973, bimonthly €30X-Ray Fluorescence SpectrometryAbstractsVol. 4,1973, quarterly €28Thin-Layer Chromatography AbstractsVol. 3, 1973, bimonthly €28Gas Chromatography-MassSpectrometry AbstractsVol. 4, 1973, quarterly €37Nuclear Magnetic ResonanceSpectrometry AbstractsVol. 3, 1973, bimonthly €30Laser-Raman Spectroscopy AbstractsVol. 2, 1973, quarterly €30X-Ray Diffraction AbstractsVol. 1-2,1973, quarterly €30Neutron Activation Analysis AbstractsVol. 2-3, 1973, quarterly €30Electron Microscopy AbstractsVol. 1,1973, quarterly €30Liquid Chromatography AbstractsVol.1, 1973, quarterly €30Electron Spin Resonance SpectroscopyAbstractsVol. 1, 1973, quarterly €30Sample copies on request from:SCIENCE AND TECHNOLOGY AGENCY,3 HARRINGTON ROAD,SOUTH KENSINGTON,LONDON, SW7 3ES01-584 808iV THE ANALYST [December, 1973THE ANALYSTEDITORIAL ADVISORY BOARDChairman: H. J. Cluley (Wembley)*L. S. Bark (Salford)R. Belcher (Birmingham)L. J. Bellamy, C.B.E. (Waltham Abbey)L. S. Birks (U.S.A.)E. Bishop (Exeter)E. A. M. F. Dahmen (The Netherlands)*J. B. Dawson (Leeds)A. C. Docherty (BillinghamjD. Dyrssen (Sweden)*W. T. Elwell (Birmingham)*D. C. Garratt (London)*R. Goulden (Sittingbourne)J. Hoste (Belgium)D. N. Hume (U.S.A.)H. M. N. H. Irving (feeds)M.T. Kelley (U.S.A.)*J. A. Hunter (Edinburgh)W. Kemula (Poland)*G. F. Kirkbright (London)G. W. C. Milner (Warwell)G. H. Morrison (U.S.A.)*J. M. Ottaway (Glasgow)*G. E. Penketh (Billingham)S. A. Price (Tadworth)D. 1. Rees (London)E. B. Sandell (U.S.A.)*R. Sawyer (London)A. A. Smales, O.B.E. (Warwell)H. E. Stagg (Manchester)E. Stahl (Germany)A. Walsh (Australia)T. S. West (London)P. Zuman (U.S.A.)*A. Townshend (Birmingham)* Members of the Board serving on the Executive Committee.NOTICE TO SUBSCRIBERSSubscriptions for The Anolyst, Analytical Abstructs and Proceedings should beThe Chemical Society, Publications Sales Office,Blackhorse Road, Letchworth, Herts.Rates for 1973(other than Members of the Society)sent to:(a) The Analyst, Analytical Abstracts, and Proceedings, with indexes .. . . €37.00(b) The Analyst, Analytical Abstracts printed on one side of the paper (withoutindex), and Proceedings . . . . . . . . . . . . . . €38.00(c) The Analyst, Analytical Abstracts printed on one side of the paper (withindex), and Proceedings . . . . . . . . . . . . . . €45.00The Analyst and Analytical Abstracts without Proceedings-(d) The Analyst and Anolytical Abstracts, with indexes . . . . . . . . €34.00(e) The Analyst, and Analytical Abstracts printed on one side of the paper (withoutindex) . . . . . . . . . . . . . . . . . . f35.00(f) The Analyst, and Analytical Abstracts printed on one side of the paper (withindex) . . . . . . . . . . . . . . . . . . €42.00(Subscriptions are NOT accepted for The Analyst and/or for Proceedings aloneDecember, 19731 THE ANALYST VWhy not use“COLLOID TITRATIQN”for simple and rapid determination ofCOLLOID PARTICLES in the field ofAgar and Alginic Acid IndustryLeather IndustryFood IndustryPaper and Pulp IndustrySu rfactant IndustryWater Treatmentfor detailed brochure and reagentswrite soon to-DOJINDO CO., LTD.Research LaboratoriesP.O.Box 41, KumamotohigashiKumamoto (862)JAPANTelex-7627-76 DO J I N LINDIDTABSTablets of pre-mixed chemicals. A simpleand economical way of adding indicators toyour titration flask.One hundred tablets each of twelve differentindicators are contained in each of two kitsfor titration of Aluminium, Bismuth,Cadmium, Calcium, Cobalt, Copper, Magne-sium, Nickel, Zinc, etc.etc.Details on request from:-RIDSDALE & CO. LTD.suppliers of “Analoid” compressed chemicalreagentsNewham Hall, Newby,Middlesbrough, Teesside, TS8 9EATel. Middlesbrough 0642 37216~ ~~~~~~~~~SELECTED ANNUAL REVIEWSof theANALYTICAL SCIENCESVolume 2 - 1972CONTENTSThe Techniques and Theory of Thermal Analysis Applied to Studies on InorganicMaterials with Particular Reference to Dehydration and Single Oxide Systems -D. DollimoreDevelopments in Ion Exchange - F. VernonThermometric and Enthalpimetric Titrimetry - L. S. Bark, P. Bate and J. K. GrimeObtainable from-Pp. vi + 149 €5.00; U.S. $13.00 ISBN 0 85990 202 1The Society for Analytical Chemistry, Book Department,9/10 Savile Row, London WIX I A FMembers of The Chemical Society may buy personal copies at the special price of f3.00; U.S.$8.0vi SUMMARIES OF PAPERS I N THIS- ISSUE [December, 1973Summaries of Papers in this IssueApplication of the Carbon Cup Atomisation Technique in WaterAnalysis by Atomic-absorption SpectroscopyA modified, laboratory-made carbon cup (small-scale Massmann) atomiseris described, with particular reference to the atomic-absorption determinationof copper, lead and cadmium in water samples.Several parameters such as sample volume, time and temperature ofthe atomisation steps, and sample composition, have been investigated. Itwas found that injection of a 10-p1 sample in one portion is the most con-venient technique with respect to sensitivity and speed of operation.Additionof EDTA causes an enhancement of sensitivity, which is considerable whendetermining lead. The adsorption of these elements on the polyethylenecontainers has also been examined in order to evaluate possible errors thatmay arise after sample storage.The detection limits are 0.45 ng ml-l of lead, 1.7 ng ml-l of copperand 0.04 ng ml-l of cadmium, and the average precision is 5 3 per cent. ina single measurement. The method permits the direct and rapid determinationof these elements in various water samples, which determinations are frequentlyrequired in pollution control.F. DOLINSEK and J. STUPARThe “ Jo2ef Stefan” Institute, University of Ljubljana, Ljubljana, Yugoslavia.Analyst, 1973, 98, 841-850.Absorptiometric Determination of Trace Amounts of SulphideIon in WaterA sensitive and rapid method is described for the determination ofminimal concentrations of soluble sulphide in water.It is based on thereduction of iron(II1) to iron(I1) by sulphide at pH 3 in the presence of1,lO-phenanthroline reagent, forming the orange - red complex [(C12H,N2)3Fe]2+.The method is subject to some interferences, which fortunately are not usuallypresent in water supplies. Interferences of many acidic and basic radicalscan be successfully overcome by recovery of hydrogen sulphide by steamdistillation from the samples acidified with sulphuric acid. Down to 0.5 pgor a concentration of 33 pg 1-1 of sulphide, if 15 ml of sample are available,can be detected by the method.S.A. RAHIM, A. Y. SALIM and Mrs. S. SHEREEFDepartment of Chemistry, College of Science, Mosul University, Iraq.Analyst, 1973, 98, 851-856.A Spectrofluorimetric Procedure for the Assay of CarrageenanA spectrofluorimetric procedure for the determination of carrageenanin the presence of salts, many polysaccharides, and proteins has been de-veloped. It involves the binding of acridine orange to the polyanion andobservation of the decrease in green fluorescence from free monomer dyein solution.The method offers many advantages over the available chemical assays,and is a simple, accurate and rapid technique for determining carrageenanin a conventional hydrocolloid stabiliser mixture. Its successful application,after minor modifications, in the presence of protein and salts indicates itsdirect applicability to commercial milk products.R.B. CUNDALL,Department of Chemistry, University of Nottingham, Nottingham, “ 2 7 2RD.G. 0. PHILLIPS and D. P. ROWLANDSDepartment of Chemistry and Applied Chemistry, University of Salford, Salford,M5 4WT.Analyst, 1973, 98, 857-862December, 19731 SUMMARIES OF PAPERS I N THIS ISSUEGas - Liquid Chromatographic Determination of Alpha-, Beta-,Gamma- and Delta-BHC Levels in Human Blood, Depot Fat andVarious Organs with the Use of 2,2-Dimethylpropane- 1,3-diolSuccinate as the Stationary Liquid PhaseThe presence of various BHC isomers in the human organism has receivedrelatively little attention, and studies were often restricted to only one BHCisomer.A previously described one-step extraction and clean-up procedurebefore gas - liquid chromatographic determination of organochlorine pesticideresidues in human blood has now been applied to various organs and depotfat. The identification of the BHC isomers was performed by gas - liquidchromatography with several stationary liquid phases. 2,2-Dimethylpropane-1,3-diol succinate was found to be the most satisfactory stationary liquidphase for the present purpose, as it gave distinctly separated peaks andcharacteristic relative retention times.viiG. CZEGLEDI- JANKOInstitute for Chemistry and Food Analysis, H-1022 Hermann Ott6 u. 15, Budapest,Hungary.Analyst, 1973, 98, 863-872.Simultaneous Determination of Actinide Nuclides in EnvironmentalMaterials by Solvent Extraction and Alpha SpectrometryActinide analysis based on the selection of groups, instead of separationof individual elements, has been applied to monitoring and control of theincreasing variety and amounts of actinide nuclides in environmental materialscontaminated by controlled discharges of liquid wastes.Multi-element acti-nide analysis is achieved by extracting the whole group, or part of it, in thetri-n-octylphosphine oxide - n-heptane - nitric acid - sodium nitrate system,stripping into ammonium carbonate solution and electrodeposition, followedby solid-state alpha spectrometry, with unusual actinide nuclides as yieldtracers. This system gives efficient separation from virtually all commonelements.Common operations for the several functions of sample dissolution, tracerexchange, solvent extraction and electrodeposition have been developed,which are suitable for the group from actinium to curium.Detailed procedures,with variations, for simultaneous measurement of these actinides are stated,in order to allow application to biological materials and radioactive effiuentsin two combinations, the first in valency states 111, IV and VI, and thesecond in valency states IV and VI with valency state I11 eliminated. Theyhave been fully evaluated for plutonium-239 plus -240 with plutonium-236as tracer, and americium-241 with americium-243 as tracer, and the scopeis indicated for other members of the group. Up to 2 kg of edible seaweedor 10 kg of fish flesh can be handled, with detection limits (in terms of activityto double background) of 2 x and 4 x lO-'pCig-l, respectively, fora 1-week counting time. Sensitivities for precision with 4 per cent. standarddeviation are 4 x lo-* and 8 x 10-5 pCi g-l, respectively, which correspondsto levels associated with fallout.B. L. HAMPSON and D. TENNANTMinistry of Agriculture, Fisheries and Food, Fisheries Radiobiological Laboratory,Hamilton Dock, Lowestoft, Suffolk.Analyst, 1973, 98, 873-885

ISSN:0003-2654    

DOI:10.1039/AN97398FP141

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

December, 19731 THE ANALYST ixFOR SALE~~THE ANALYST 1890 to 1956continuous, with a few copies 1885 to 1889. Two copiesmissing Dec. 1946 and Jan. 1952. V,'ell bound annuallyexcept 1946 and 1952-1956.Offers invited (including delivery).Box no. 234c/o J. Arthur Cook9 Lloyd SquareLondon WClX 9BASpecimen copies supplied in advance if desired.APPOINTMENTS VACANTPARTICLE SIZEANALYSIS1970THE Society for Analytical Chemistryhas published in this book all paperspresented at the Second Particle SizeAnalysis Conference, held in Bradfordin September 1970, and the full discus-sions on them.The 35 papers cover all aspects ofresearch into the subject, basicallycovering the 4-year period since the firstconference was held in Loughboroughin 1966, and include plenary lectures bythe late Professor H.Heywood and byProfessor K. Leschonski. The volumeis a companion to "Particle SizeAnalysis" - the report of the First Con-ference, also published by the Society.Pp. x + 430Price S7.750 btai nable from-THE SOCIETY FORAN ALYTI c A L CHEMISTRY,(Book Department),9/10 Savile Row, London, W1X 1AFMembers of The Chemical Society may buypersonal copies at the special price of S6.2X THE ANALYST [December, 1973APPOINTMENTS VACANTDEVELOPMENTCHEMISTWe manufacture feeds for farm livestock in our nine factories inEngland and Ulster. Our Research and Advisory Department inlpswich carries out development work and provides a technicalservice to our branches, there is close liaison with UniversityAg ricu I t u ra I Depart men ts and other organ isa ti ons.Following a recent promotion, we are looking for a man to work in ourlaboratories on problems on animal nutrition.He will work closelywith graduate staff specialising in this field and may be involved intrials at our experimental farm.You will need sound practical analytical experience and the ability towork with minimum supervision on a wide variety of projects. Wewould prefer you to be qualified to R.I.C. standard, but will consider alesser qualification backed by experience in food or feed analysis, or ina consultant laboratory.Conditions of service are excellent and include annual bonus, pensionand insurance schemes. Initial salary will be based on qualificationsand experience.Please write for an application form to C.S. Drake, Group PersonnelOfficer, Pauls and Whites Limited, P.O. Box 39, lpswich 1 P4 1 BX.Telephone (0473) 5671 1.BINDINGHave your back numbers of The Analyst bound in the standard binding case.Send the parts and the appropriate index(es) together with a remittance for€2.65 to:I. S. WILSON & SON14a Union Road, Cambridge CB2 I H December, 19731 THE ANALYST xiAPPOINTMENTS VACANTAnalytical ChemistThe Union International Co. Ltd. has a vacancy at the St. Albans ResearchCentre for an Analytical Chemist.The work will involve the development of new methods and the analysisof a wide range of materials associated with the food and pharmaceuticali nd u st r i es.Applications are invited from recently qualified Chemists and also fromthose who have had several years analytical experience.A good salary will be offered to the successful applicant and there are theusual fringe benefits.Please write giving age and full details of qualifications and experience tothe Staff Manager (AD 5763), 14 West Smithfield, London, E.C.1.ANALYTICAL SCIENCES MONOGRAPHNo.IH ig h- Precision Titri met ryby C. Woodward and H. N. RedmanImperial Chemical Industries Limited (Agricultural Division)BRIEF CONTENTS:lntro ductionVisual Titrations, with sections on Apparatus, Standard Substances and their preparation andassay, and Standard Solutions.Instrumental Methods, with sections on Photometric Titrations, Electrometric Titrations andMiscellaneous Techniques.References to the literature of high-precision titrimetry.Price f2.50Pp.viii+63 ISBN 0 85990 50: 2Society for Analytical Chemistry, Book Department,911 0 Savile Row, London, W1 X 1 AFMembers may buy personal copies at the special price of f2.0xii SUMMARIES OF PAPERS I N THIS ISSUEVoltammetric Determination of Tocopherols by Use of a NewlyDeveloped Carbon Paste ElectrodeA voltammetric method is described for determining tocopherols invegetable oils, foods and pharmaceuticals by a newly developed carbon pasteelectrode. The samples are saponified and the unsaponifiable fraction isextracted and determined voltammetrically. No elaborate purification methodis necessary as the substances that interfere with photometric proceduresare electrochemically inactive in the potential range of operation.Detailedprocedures for the preparation and the working of the electrode, and resultsfor the precision of the method, are presented.SAMUEL S. ATUMA -and JORGEN LINDQUISTDepartment of Analytical Chemistry, University of Uppsala, Box 531, S-751 21,Uppsala 1, Sweden.Analyst, 1973, 98, 886-894.[December, 1973Polarographic Studies of the Zinc(I1) Complex Formed withTyrosine in Aqueous and Mixed Aqueous and Non-aqueous MediaThe reduction of zinc(I1) in tyrosine solutions has been studied a t adropping-mercury electrode in aqueous and mixed aqueous and non-aqueousmedia. The effects due to variation of pH, temperature, ligand concentrationand height of the mercury column on the wave characteristics have beeninvestigated and the results interpreted.Under all experimental conditionsthe reduction has been found to be irreversible and diffusion controlled.Hence, the kinetic parameters, transfer coefficient (M,,) and formal rateconstant (Kof,h) have been calculated by use of Koutecky's method as im-proved by Meites and Israel. The analytical implication of the sytem hasalso been suggested.DAYA NAND CHATURVEDI and C. M. GUPTAChemical Laboratories, University of Rajasthan, Jaipur-4, India.Analyst, 1973, 98, 895-899.Determination of Organoisothiocyanates Alone and in Mixtureswith Organoisocyanates or ThioureasAn iodatometric method for the determination of organoisothiocyanatesis described.The isothiocyanates are quantitatively converted with n-butyl-amine in dimethylformamide medium into the corresponding symmetricalNN-disubstituted thioureas, which are titrated visually or potentiometricallyin acidic medium with potassium iodate solution. Methods have also beendeveloped for the analysis of isothiocyanate - isocyanate and isothio-cyanate - thiourea mixtures on the same sample solution. A known excessof the standard n-butylamine solution added to the mixture in dimethyl-formamide converts the isothiocyanate and isocyanate into the correspondingdisubstituted thiourea and urea, respectively. Acidimetric titration of theexcess of amine, and iodatometric titration of the thiourea present andformed, enable the particular mixture to be analysed for both constituents.The end-points can be detected both visually and potentiometrically.Themethods described are simple, accurate, reliable and widely applicable.BALBIR CHAND VERMA and SWATANTAR KUMARDepartment of Chemistry, Punjabi University, Patiala, India.Analyst, 1973, 98, 900-905December, 19731 SUMMARIES OF PAPERS I N THIS ISSUE xiiiDetermination of Bacitracin in Animal Feeds that Contain CopperA modification of the method involving the use of acidified methanolfor the analysis of animal feeds that contain bacitracin and copper sulphateas additives has been developed. Because of the interference of copper inthe bacitracin assay, the copper is precipitated by the addition of 3 to 4 molof sulphide ions per mole of copper.The method has been used for feedsamples that contain 5 to 20 p.p.m. of bacitracin and 100 to 300 p.p.m.of copper.B. GRYNNE, E. HOFF, T. SILSAND and K. VAAJEA/S Apothekernes Laboratorium for Specialpraeparater, Oslo, Norway.Analyst, 1973, 98, 906-907.The Determination of Nifursol in Animal FeedsReport prepared by the Prophylactics in Animal Feeds Sub-committee.ANALYTICAL METHODS COMMITTEE9/10 Savile Row, London W1X 1AF.Analyst, 1973, 98, 908-911.ANNUAL REPORTS ON ANALYTICALATOMIC SPECTROSCOPYVolume 2, 1972This comprehensive and critical report of developments in analytical atomicspectroscopy has been compiled from more than 1000 reports receivedfrom world-wide correspondents who are internationally recognised authori-ties in the field and who constitute the Editorial Board.In addition tosurveying developments throughout the world published in national orinternational journals, a particular aim has been to include less widelyaccessible reports from local, national and international symposia andconferences concerned with atomic spectroscopy.Volume 2 covers the year 1972216 pages Price f5.00 ISBN 0 85990 252 8Obtainable from The Society for Analytical Chemistry,(Book Department), 9/10 Savile Row, London, WIX IAFMembers of The Chemical Society may buy personal copies at the special price of €3.0xiv THE ANALYST [December, 1973Reprints of Review PapersREPRINTS of the following Review Papers published in The Analyst since January, 1963, areavailable from The Society for Analytical Chemistry, Book Department, 9/10 Savile Row, London,W1X 1AF (not through Trade Agents).Orders MUST be accompanied by a remittance for thecorrect amount made out to “Society for Analytical Chemistry.”“Classification of Methods for Determining Particle Size,” by the Particle Size Analysis“Methods of Separation of Long-chain Unsaturated Fatty Acids,” by A. T. James (August,“Beer’s Law and its Use in Analysis,” by G. F. Lothian (September, 1963).“A Review of the Methods Available for the Detection and Determination of Small Amounts“Circular Dichroism,” by R. D. Gillard (November, 1963).“Information Retrieval in the Analytical Laboratory,” by D. R. Curry (November, 1963).“Thermogravimetric Analysis,” by A. W. Coats and J. P. Redfern (December, 1963).Price“Some Analytical Problems Involved in Determining the Structure of Proteins and Peptides,”“The Faraday Effect, Magnetic Rotatory Dispersion and Magnetic Circular Dichroism,” by“Electrophoresis in Stabilizing Media,” by D. Gross (July, 1965).“Recent Developments in the Measurement of Nucleic Acids in Biological Materials,” by“Radioisotope X-ray Spectrometry,” by J , R. Rhodes (November, 1966).“The Determination of Iron(I1) Oxide in Silicate and Refractory Materials,” by H. N. S.“Activation Analysis,” by R. F. Coleman and T. R. Pierce (January, 1967).“Techniques in Gas Chromatography. Choice of Solid Supports,” by F. J . Palframan“Heterocyclic Azo Dyestuffs in Analytical Chemistry,” by R. G. Anderson and G. Nickless“Determination of Residues of Organophosphorus Pesticides in Food,” by D.C. Abbott and“Radioactive Tracer Methods in Inorganic Trace Analysis : Recent Advances,” by J . W.“Gamma-activation Analysis,” by C. A. Baker (October, 1967).“Precipitation from Homogeneous Solution,” by P. F. S. Cartwright, E. J. Xewman andD. W. Wilson (November, 1967).“Industrial Gas Analysis,” by (the late) H. N. Wilson and G. M. S. Duff (December, 1967).Price 35p.“The Application of Atomic-absorption Spectrophotometry to the Analysis of Iron andSteel,” by P. H. Scholes (April, 1968).“Inorganic Ion Exchange in Organic and Aqueous - Organic Solvents,” by G. J . Moody andJ . D. R. Thomas (September, 1968).“Radiometric Methods for the Determination of Fluorine,” by J . K. Foreman (June, 1969).Price 25p.“Techniques in Gas Chromatography.Developments in the van Deemter KateTheory of Column Performance,” by E. A. Walker and J. F. Palframan (August, 1969).Price 25p.Choice of Detectors,” by T. A. Gough andE. A. Walker (January, 1970)’.Sub-committee of the Analytical Methods Committee (March, 1963).1963). Price 25p.Price 25p.Price 25p.of Cyanide,” by L. S. Bark and H. G. Higson (October, 1963). Price 25p.Price 15p.Price 15p.25p.by Derek G. Smyth and D. F. Elliott (February, 1964).J . G. Dawber (December, 1964).Price 25p.Price 25p.Price 25p.H. N. Munro and A. Fleck (February, 1966). Price 25p.Price 25p.Schafer (December, 1966). Price 25p.Price 25p.Part I.and E. A. Walker (February, 1967).(April, 1967). Price 25p.H. Egan (August, 1967).McMillan (September, 1967). Price 25p.Price 25p.Price 25p.Price 25p.Price 25p.Price 25p.Price 35p.Part 11.“Techniques in Gas Chromatography.Price 25p.“Laser Raman Spectroscopy,” by P. J . Hendra and C. J . V e n (April, 1970).“Ion-selective Membrane Electrodes,” by Ern0 Pungor and KlAra T6th (July, 1970). Price“X-ray Fluorescence Analysis,” by K. G. Carr-Brion and K. W. Payne (December, 1970).“Mass Spectrometry for the Analysis of Organic Compounds,” by A. E. Williams and H. E.“The Application of Non-flame Atom Cells in Atomic-absorption and Atomic-fluorescence“Liquid Scintillation Counting as an Analytical Tool,” by J. A. B. Gibson and A. E. LallyPart 111.Price 35p.35p.Price 25p.Stagg (January, 1971). Price 35p.Spectroscopy,” by G. F. Kirkbright (September, 1971).(October, 1971). Price 25p.Price 25p

ISSN:0003-2654    

DOI:10.1039/AN97398BP147

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

DECEMBER, 1973 THE ANALYST Vol. 98, No. 1173 Application of the Carbon Cup Atomisation Technique in Water Analysis by Atomic-absorption Spectroscopy BY F. DOLINSEK AND J. STUPAR (The " Jofej Stefan" Institute, University of Ljubljana, Ljubljana, Yugoslavia) A modified, laboratory-made carbon cup (small-scale Massmann) atomiser is described, with particular reference to the atomic-absorption determination of copper, lead and cadmium in water samples. Several parameters such as sample volume, time and temperature of the atomisation steps, and sample composition, have been investigated. It was found that injection of a 10-pl sample in one portion is the most con- venient technique with respect to sensitivity and speed of operation. Addition of EDTA causes an enhancement of sensitivity, which is considerable when determining lead.The adsorption of these elements on the polyethylene containers has also been examined in order to evaluate possible errors that may arise after sample storage. The detection limits are 0.45 ng ml-l of lead, 1-7 ngml-l oi copper and 0.04 ng nil-I of cadmium, and the average precision is f3 per cent. in a single measurement. The method permits the direct and rapid determination of these elements in various water samples, which determinations are frequently required in pollution control. CONCENTRATIONS of several heavy metals such as lead, cadmium and copper in public water supplies are limited to certain safe levels because of the toxic character of these metals. For example, by several national criteria for water quality the following levels are permitted: lead 50, cadmium 5 to 10 and copper 10 to 1OOOngml-l.Different industrial wastes, particularly such as those from plating, zinc and lead smelting, etc., discharge significant amounts of these elements in various forms. The concentration of these metals in waters may therefore rise to a level that can be hazardous to livestock. Monitoring of natural waters and industrial effiuents is thus becoming increasingly important, particularly in highly industrialised areas. The determination of metals at nanogram levels, however, presents a difficult task. In addition to the need for high sensitivity, a rapid analytical method is required that will enable the large number of samples involved in water pollution control to be dealt with. Among the various analytical methods available, anodic stripping polarography,l neutron a~tivation,~*~ flame atomic-absorption spectro~copy~-~~ and spectroph~tometryl~-~~ seem to be the only suitable techniques for the determination of lead, cadmium and copper at the parts per billion ( lo9) level.However, pre-concentration of solutions (for flame atomic- absorption spectroscopy) or chemical treatment prior to the determination (for polarography and spectrophotometry) restrict the lower limit of detection because of the relatively high blank values. Neutron activation requires expensive instrument facilities and is not sensitive enough to permit direct determination of cadmium and lead at the desired concentration. The possibility of direct analysis and the high sensitivity achieved by flameless atomic-absorption spectroscopy make this technique particularly advantageous for the determination of these elements in liquid samples.Fernandez and Manning15 determined twelve elements directly in natural waters by using a Massmann-type graphite atomiser (HGA-70); 50 to 100 pl of sample were used for a single measurement. The standard addition method was used in order to calculate the results. Pickford and Rossi16 designed an automatic sampling system in conjunction with a graphite atomiser (HGA-70). A high degree of sensitivity was reported as a result of the large sample volumes (100 to 500 pl) taken. The aim of the present work was to develop the carbon cup technique into a speedy and reliable tool for the determination of these elements in actual water samples, concen- trating especially on the parameters that affect its accuracy and sensitivity.841 Also, the accuracy and speed of analysis are seriously affected. @ SAC and the authors.842 EQUIPMENT- Hollow-cathode lamps (lead, cadmium, copper and hydrogen) were operated at the currents recommended by the manufacturer (Varian). The burner was replaced by a locally made carbon cup attachment that was similar to the Varian carbon cup atomiser, Model 63. A Perkin-Elmer 165 chart recorder (10 mV, full-scale response time 1 s) was connected to the instrument. The power unit supplied a maximum of 600 A at 1OV to the carbon cup atomiser. In Fig. 1 the circuit diagram of the power unit is shown. In order to achieve the various temperatures required for atomisation of different samples, the current passing through the atomiser can be varied by changing the voltage on the primary coil of a step-down transformer. Five different temperatures can be selected for drying, five for ashing and five for the final atomi- sation.The timers automatically control the sequence of operations. DOLINSEK AND STUPAR: CARBON CUP ATOMISATION TECHNIQUE IN [Analyst, Vol. 98 EXPERIMENTAL The atomic-absorption instrument used was the Varian AA-5 model. 220-V auto-transformer 7 carbon cup I heating I n I I step-down L - - - - - - _ _ - _ A transformer b b To carbon cup Fig. 1. Circuit diagram of the power unit The details of the carbon cup attachment are shown in Fig. 2. The graphite cup (Ringsdorf, RW OOZ), of 6.5 mm 0.d.and 9 rnrn in height with 1 6 m m wall thickness, is held by two support rods clamped between massive water-cooled stainless-steel blocks (1) , which also serve as electrical terminals. The distance between the blocks can be varied by means of a screw (6) , which enables the graphite cups to be exchanged. Spring-loaded support rods ensure good and constant electrical contact. The carbon cup and part of the support rods are continuously purged with argon so as to minimise the oxidation of the carbon. The pro- tective action of argon was observed to be significantly improved by mounting a curved quartz roof (4) above the cup. Normally, about 200 measurements can be made with a single cup but the number of measurements depends on the operating temperature in the atomisation step.By using a quartz roof more than 600 measurements were possible. The carbon cup device was found to be very convenient for solution analysis, although the carbon tube or rod has normally been used for this purpose. Larger volumes (up to 30 p1) can be introduced into the cup if higher sensitivity is required. This sampling pro- cedure is more reproducible as the injected solution always collects at the tapered bottom of the cup. A Hamilton 10-pl syringe and an Oxford 10-p1 micropipette were used for sampling solutions.n 2 3 'p Fig. 2. Carbon cup atomiser: 1, stainless-steel blocks; 2, water-cooling system; 3, electrical connections; 4, quartz roof; 5, argon inlet tube; and 6, adjusting screw r, 03 n IuDecember, 19731 WATER ANALYSIS BY ATOMIC-ABSORPTION SPECTROSCOPY SELECTION OF OPERATING CONDITIONS- Instrument parameters used in the measurements are summarised in Table I.TABLE I OPTIMAL INSTRUMENT SETTINGS 84 3 Element Wavelength/nm Spectral band pass/nm Lamp currentlmil Copper . . .. .. .. 324.8 0-33 3 Cadmium .. . . .. .. 228.8 0.66 3 Lead .. .. .. .. 217.0 0.66 6 Hydrogen background corrector. . - - 3 to 15 Several factors such as the volume and the volatility of the sample were considered in selecting the appropriate conditions for atomisation of water samples. The following procedure for atomisation of a 10-pl sample, introduced in one portion, was found to be the most suitable: drying at approximately 90 "C for 30 s, ashing at 300 "C for 15 s and atomisation at 2500 "C for 2-2 s.With copper, the duration of the atomisation step was extended to 3 s. It is preferable to introduce the sample solution into a slightly warm cup so as to minimise the risk of soaking of the solution into the porous carbon walls. On the other hand, too high a temperature during the drying period causes rapid disintegration of the sample solution inside the cup, which may result in sample losses and a non-reproducible absorption signal. ABSORPTION MEASUREMENTS ON AQUEOUS LEAD, COPPER AND CADMIUM SOLUTIONS- Appropriate solutions were prepared from lead, copper and cadmium stock solutions (1 mg ml-l, prepared by using Specpure grade metal) by dilution with doubly distilled water. Water was taken as the blank solution. A linear relationship between the concentration and absorbance was observed for all three elements in the range up to 50 per cent.absorption. Because the sensitivity can be increased by taking larger sample volumes, an examination of the relationship between sample volume and absorbance was made. Four different lead solutions were measured for this purpose; two (5 and 10 ng ml-l of lead) in the range 10 to 30 p1 and the other two (25 and 50 ng ml-l of lead) in the range 2 to 10 pl of sample volume. The solution was injected into the cup either in one portion or in successive small portions (10 or 2 p1, respectively). These experiments are illustrated in Figs. 3 and 4. o'20 I Sam p I e vo 1 u me/,uI Fig. 3. Variation of absorbance with sample volume a t constant lead concentra- tion: A, A' 25 and B,B' 50 ng ml-1 of lead; A,B, solution injected in one portion; and A,'B,' solution injected in several 2-p.1 portions in succession 0 10 20 30 Sample volume/pl Fig.4. Variation of absorbance with sample volume a t constant lead concentra- tion: C,C' 5 and D,D' 10 ng ml-l of lead; C,D, solution injected in one portion; and C',D', solution injected in several 10-pl portions in succession844 DOLINSEK AND STUPAR: CARBON CUP ATOMISATION TECHNIQUE I N [Autabst, vol. 98 It can be seen that a linear relationship between sample volume and absorbance is generally established, although the injection of sample in successive small portions (2 or 10 pl) always results in a higher sensitivity (curves A', B', C', D' in Figs. 3 and 4). A satisfactory explanation of the latter phenomenon can be found by considering sample losses to result from penetration of the solution into the cup walls during the drying step.It can be assumed that these losses are approximately proportional to the retention time of the solution in the cup, and to the surface area of the cup in contact with the solution. The results for the evaporation times of particular sample volumes are summarised in Table 11. TABLE I1 DURATION OF THE DRYING STEP AS A FUNCTION OF THE SAMPLE VOLUME Sample volume/pl Duration of the drying step*/s 2 to 4 15 6 19 8 23 10 30 20 80 to 90 30 110 to 120 2 x 10 60 3 x 10 90 * Temperature below 100 "C. Increasing the temperature of the drying step to slightly above 100 "C would certainly reduce the evaporation time significantly, but the figures given in Table I1 will still retain their relative values.A sample volume of 3Opl was considered for practical purposes to be the upper limit for use with the carbon cup atomiser, although the technique of successive injection of 10-pl portions can be successfully used. EFFECT OF EDTA AND VARIOUS ORGANIC REAGENTS ON THE SENSITIVITY OF THE DETER- MINATION- Measurements of copper, lead and cadmium in various streams and relatively unpolluted river waters by using the standard addition method have shown that poor sensitivity is obtained in comparison with doubly distilled water, particularly for cadmium and copper. Acidification of the water prior to analysis has been frequently adopted,12 which slightly improves the sensitivity but also increases the risk of contamination. The effect of different organic reagents (EDTA, ammonium tetramethylenedithiocarbamate and sodium diethyl- dithiocarbamate) that form metal chelates was investigated for this purpose.A substantial enhancement of absorbance was obtained for lead and copper in natural water samples, while only lead showed a considerable improvement in distilled water. During measurements of the effect of these organic reagents on the peak height of the absorption signals of the elements concerned, appreciable day-to-day variations were found, which may be ascribed to variation in instrument parameters. Table 111 summarises some typical results of these experiments ; TABLE I11 RELATIVE ABSORBANCE OF LEAD, CADMIUM AND COPPER IN DISTILLED AND NATURAL 10-pl sample volume WATER, AS INFLUENCED BY THE ADDITION OF DIFFERENT ORGANIC REAGENTS Distilled water r--------h--? 0.2 ml of 1 per cent.Element EDTA (concen- No solution tration/ng ml-l) addition per 50 ml Cd (2.5) 100 115 Pb (50) 100 358 Cu (150) 100 110 Mountain stream water r A 0.2 ml of 1 per cent. 0.2 ml of 2 per cent. No solution solution addition per 50 ml per 50 ml 64 112 115 78 113 120 95 332 343 EDTA APDC - 0-2 ml of 1 per cent. NaDDTC solution per 50 ml 110 109 338 APDC = Ammonium tetramethylenedithiocarbamate. DDTC = Sodium diethyldithiocarbamate.Decern ber, I 97313 WATER ANALYSIS BY ATOMIC-ABSORPTIOS SPECTKOSCOP\- 846 the relative values given are true atomic absorbances. Correction for non-specific absorption was made a t the resonance line wavelength by using a hydrogen hollow cathode.A 1 per cent. solution of EDTA (free acid) was selected as an additive to water samples and standard solutions in order to normalise the sensitivity. The concentration of EDTA in the water sample that was necessary to cause the enhancement of sensitivity was deter- mined from curve A in Fig. 5; 0.2 ml of the EDTA solution in 60 ml of sample was chosen, as this value lies well on the plateau of the curve and should not cause appreciable contamina- tion. In order to determine any measurable contamination that may have been caused by the addition of EDTA solution, different volumes of the latter were added to the stream-water sample and the absorbance of lead was measured (Fig. 5, curve 13). The constant absorbance observed over the range 0.3 to 4 ml of EDTA solution indicated that no risk of lead con- tamination should be expected when 0-2 ml are added to 50 ml of the sample.Similar tests were made with copper and cadmium and no detectable amounts of these elements were found in the EDTA solution. 0 0.5 1.0 " 4.0 EDTA solution/ml Fig. 5. Variation of lead absorbance with volume of added 1 per cent. aqueous EDTA solution: A, stream water, 100 ng ml-1 of lead; and 13, stream water The enhancing action of organic reagents, which proved to be particularly strong in the determination of lead and copper in both natural and distilled water, can be explained by the formation of clielates. These compounds, although stable in solution, are easily decomposed at elevated temperature during the atomisation step, which results in a transient, high atomic population inside the cup.SENSITIVITY, PRECISION AND DETECTION LIMITS- Sensitivity, defined as the concentration that gives 1 per cent. absorption, was derived from the calibration graphs obtained for lead, copper and cadmium standard solutions (distilled water) in the presence of EDTA. Detection limits were calculated on the basis of the following relationships- Ac AA Detection limit = kub - ( k = 3) (n = 11, 15) where CTb is the standard deviation of the blank solution (distilled water PLUS EDTA) and &/AA is the reciprocal value of the slope taken from the calibration graphs. A scale expansion846 DOLIXSEK AND STUPAR: CARBON CUP ATOMISATION TECHNIQUE I N [AfialySt, VOl. 98 (factor of 2) was used for determination of the detection limits.The results obtained are presented in Table IV. TABLE IV SENSITIVITIES AND DETECTION LIMITS OBTAINED WITH CARBON CUP GRAPHITE ATOMISER AT lo-$ SAMPLE VOLUME Sensitivitylng ml-l per Detection Element 1 per cent. absorption limit*/ng ml-1 Lead . . .. .. 1.2 Copper . . .. .. 4-4 Cadmium . . .. .. 0.1 * Scale expansion 2 x . 0.45 1.7 0.04 The precision of the determination with the carbon cup atomiser was evaluated by taking eleven to fifteen successive measurements of 50 ng ml-l of lead, 2.5 ng ml-l of cadmium and 300 ng ml-l of copper solutions (distilled water plus EDTA). Coefficients of variation of 2.3, 1-9 and 3.9 per cent., respectively, were calculated, which are reasonable for the atomisa- tion technique used.The recorder trace shown in Fig. 6 demonstrates the precision typical of the carbon cup atomiser; a 10-pl sample volume injected in one portion was used for these measurements. W L 30- c 0 - .- w ,n 20- a - 2 10- - - - - - - - - - L - --. -. 1 . 0 - Fig. 6. Reproducibility of measurement typical of the carbon cup atomiser (sample volume 10 pl, 50 ng ml-l of lead, 2-5 ng ml-l of cadmium and 300 ng ml-l of copper) INTERFERENCES- Although the time available for atomisation in the carbon cup is significantly longer in comparison with the flame technique, several chemical interferences could still be observed. In addition, molecular absorption and light scattering often present a serious problem. In our experiments the influence of different salts commonly present in natural waters was studied.The effect of the addition of EDTA was also investigated. The results are sum- marised in Tables V and VI. Values given in these tables are relative absorbances produced by particular kinds of atoms, while those in parentheses are relative absorbances measured with the continuum light source. All values for a particular element are expressed relative to the absorbance of a pure solution containing no EDTA. Non-specific absorption was frequently observed when different salts were present in the solution; in some instances it was easily resolved from the atomic peak. Addition of EDTA had no, or very little, influence upon the absolute value of the non-specific absorption, although considerable changes were observed in the interference effects of various salts.The interferences of the various salts investigated in the determination of copper, cad- mium and lead, which manifested themselves in an enhancement or decrease of the peak absorption value, can generally be attributed to the change in the rate of atomisation. ADecember, 19731 WATER ANALYSIS BY ATOMIC-ABSORPTION SPECTROSCOPY TABLE V EFFECT OF VARIOUS SALTS (CATIONS) ON THE RELATIVE ABSORPTION SIGNAL 847 O F LEAD, CADMIUM AND COPPER Lead (200 ng ml-l) Cadmium (5 ng ml-l) Copper (300 ng ml-I) & +--7 +- Concen- 1 per cent. 1 per cent. 1 per cent. tration of EDTA EDTA EDTA 0.2 ml of 0.2 ml of 0.2 ml of Salt - NaCl KCl CaCl, MgCb MgSO, FeCI, -41*(S04), cation/ No solution NO solution N O pgml-1 EDTA in 50 ml EDTA in50ml EDTA - 100 360 100 116 100 200 87 3 60 150 152 95 100 73 260 102 126 103 200 266 168 170 138 106 200 81 72 66 61 103 200 31 216 116 161 79 60 105 62 95 62 120 50 95 370 179 148 103 * Non-specific adsorption easily resolved from the atomic peak.(12) (12) (250)* (250) * (0) (0) (0) (17) (17) (0) (106) (106) (131)* (131)* (0) (37) (37) (34) (34) (0) (40) * (40) * (34) (34) (0) ( 7) (71 (17) (17) (0) (13) (13) (17) (17) (0) detailed study of these salt systems should perhaps be undertaken by using a fast-response instrument so as to obtain more knowledge of the mechanism of interference. However, any resultant interference effect that may be expected in measurements of actual water samples cannot be predicted, as the concentration and chemical character of particular matrix elements differ widely.TABLE VI EFFECT OF VARIOUS SALTS (ANIONS) ON THE RELATIVE ABSORPTION SIGNAL OF LEAD, CADMIUM AND COPPER Lead (200 ng ml-l) Cadmium (5 ng ml-I) r------h--? - r---A--7 Copper (300 ng ml-l) 0-2 ml of 0.2 ml of 0.2 ml of Salt - NaCl Na,CO, NaNO, Na,SO, Na,HP04 Concen- 1 per cent. sodium/ No solution No pgml-I EDTA in50mI EDTA - 100 170 100 50 100 170 99 50 55 157 39 50 100 157 101 60 26 77 89 50 98 170 83 tration of EDTA (0) (0) U3)* (0) (0) (2) (0) (0) (2) (0) (0) (2) (0) (0) (2) * Non-specific absorption easily resolved 1 per cent. EDTA solution NO in 50 ml EDTA 110 100 114 104 77 64 114 105 115 101 108 83 from the atomic peak. (13)* (0) (2) (0) (2) (0) (2) (0) (2) (0) 1 per cent. EDTA solution in 50 ml 100 110 (0) 85 (0) 108 (0) 110 (0) 95 (0) DETERMINATION OF LEAD, COPPER AND CADMIUM IN NATURAL WATERS AND INDUSTRIAL Preliminary studies with the carbon cup atomiser showed that direct determination of these elements in a variety of water samples should be possible at the nanogram per millilitre WASTES-848 [Analyst, Vol.98 level. Several river and stream waters, effluents from different industries and tap water samples were analysed in order to demonstrate the feasibility of the carbon cup flameless atomic-absorption method. SAMPLING PROCEDURE- In the determination of nanogram amounts of an element, special care should be taken in sample collection if significant errors from losses or contamination are to be prevented. The effect of adsorption of lead on polyethylene was therefore investigated. For this purpose, two water samples (1000 ml) containing different amounts of lead were collected in 1-litre polyethylene bottles and stored at 4 "C for 3 weeks.The lead concentration was determined periodically. The absorbance of the sample (A,) was divided by the average absorbance of two standard lead solutions (Ast) containing 60 ng ml-l of lead, which were prepared freshly each time from the lead stock solution. The ratio ASIAs, was plotted against time and is shown in Fig. 7. Curves A and B have a slight negative slope, which indicates that the lead concentration in the solution decreased slowly with time. Although the absolute amount of lead lost in 3 weeks is approximately the same in both solutions, the relative error produced by this loss is significant only at low lead concentrations (see Table VII).DOLINSEK AND STUPAR: CARBON CUP ATOMISATION TECHNIQUE IN 0.1'- A I I I I I I I I I ~ 2.1 r 1 0.2 1 TABLE VII RELATIVE ERROR CAUSED BY LOSS OF LEAD FROM SOLUTION AFTER 3 WEEKS' STORAGE IN POLYETHYLENE BOTTLES Lead concentration in the solution/ng ml-l -7 Relative Sample collection collection per cent. 1 hour after 3 weeks after loss of lead, Tap water . . .. .. .. . . .. .. 6.6 5.7 13.5 Doubly distilled water left overnight in a polyvinyl tube 120.5 120.1 0-3December, 19731 WATER ANALYSIS BY ATOMIC-ABSORPTION SPECTROSCOPY a49 0 n 6Q Concentration of added lead/ng ml-l Calibration graphs of lead in different river and industrial waste waters : A, River MeZa (contamination from lead smelter); B, River Sava; C, Stream Voglajna (highly polluted by different industrial effluents) ; and D, effluent from zinc plant (five times diluted) Fig.8. a zinc plant. It can be seen that the latter two curves have a significantly lower slope (curve C 1/2 and curve D 1/3 of the slope of curves A and B) due to interference effects caused by the different sample compositions. Therefore, it is obviously necessary to prepare a calibration graph for each particular type of water if accurate results are desired. TABLE VIII LEAD, COPPER AND CADMIUM CONTENTS OF SOME REPRESENTATIVE WATER SAMPLES ANALYSED BY CARBON CUP ATOMIC-ABSORPTION AND COMPARATIVE METHODS Sample 21 23 11 27 31 34 38 24 Cadmium, ng ml-l, by & absorption absorption absorption spectroscopy spectroscopy spectroscopy * * - cup Flame graphy* cup Flame graphy* cup Flame graphy* activation Lead, ng ml-l, by Copper, ng ml-l, by L.I > 7Gz-- Atomic- Atomic- Carbon Polaro- Carbon Polaro- Carbon Polaro- Neutron 4.3 2.9 4.5 20.5 20 14 24 40 (6) (2) 0.30 0-5 - 5100 4600 - 10 6 0.17 0-5 - 2.2 <D.L. - 6 5 (16) (16) (9) 0.05 0.5 <0*3 8 6 5.5 21 25 (50) (5) (9) (2) 20.3 20 - 1040 1150 - 3.5 3 (2) (1.3) (2) (1.8) 0.40 0.5 0.5 9s 113 96 5 6 (1.9) (1.8) 0-35 0.5 0-3 48 48 45 4 3 4-5 160 240 5.1 5.0 3-4 6.0 (2.6) (9) (1.5) (0.9) (3.5) - (9) (17) * Anodic stripping polarography. D.L. denotes detection limit. Values given in parentheses are percentage standard deviation. 24 - 220 -850 DOLINSEK AND STUPAK In order to determine the accuracy of the method some representative samples were analysed by comparative analytical methods : flame atomic-absorption spectroscopy, polaro- graphy and neutron activation, with the first of which the use of an extraction procedure was necessary.The results obtained by these methods are summarised in Table VIII. Generally, satisfactory agreement was obtained between the results by the various analytical methods in those instances when comparison was possible. Unfortunately, the sensitivity of the comparative methods was not sufficient to enable them to be used for deter- mining cadmium in most of the water samples. The relatively high blank readings involved in flame atomic-absorption spectroscopy and polarography have a significant influence on the accuracy and detection limits of these techniques. CONCLUSION Carbon cup, flameless atomic-absorption spectroscopy has been demonstrated to be ;t rapid and sensitive technique that permits the direct analysis of natural waters and industrial wastes.Only a single set of standard solutions is necessary for each type of water sample. The precision of the method is as good as that given by other analytical methods with which it was compared, while its accuracy is satisfactory. The low cost of the equipment used and the extreme speed of analysis make the proposed method superior to these other methods for monitoring lead, copper and cadmium in various water samples. The authors thank the “Boris KidriE” Foundation for providing financial support, and are also indebted to the late Dr. I. Sink0 and to Dipl. Ing. V. Ravnik, who performecf the polarographic and neutron-activation analyses, respectively. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. REFEREKCES Siriko, I., and Dolefal, J., J . Electroanalyt. Chem., 1970, 25, 299. Perkin-Elmer Instyurn. News Sci. Ind., 1970, 21, 4. Das, H. A., and Van der Sloot, H. A., in “Proceedings of the Symposium on Nuclear Activation Robinson, J. L., Barnekow, G., jun., and Lott, P. F., Atom. Absorption Newsl,, 1969, 8, 60. Nix, J., and Goodwin, T., Ibid., 1970, 9, 119. Jones, J. L., and Eddy, R. D., Analytica Chim. Ada, 1968, 43, 165. Midgett, ill. Ii., and Fishman, M. J., Atom. Absorption Newsl., 1967, 6, 128. Mansell, 13. E., and Emmel, H. W., Ibid.. 1965, 4, 365. Sprague, S., and Slavin, W., Ibid., 1964, 3, 37. Kuwata, K., Hisatomi, K., and Hasegawa, T., Ibid., 1971, 10, 111. Mansell, K. E., Ibid., 1965, 4, 276. “Standard Methods for the Examination of Water,” A.P.H.A., A.W.W.A. and W.C.P.F., Geneva, Dozanska, W., Roczn. Pa&. Zakl. Hig., 1963, 14, 433. Saltzman, B. E., Analyt. Chem., 1953, 25, 493. Fernandez, F. J., and Manning, D. C., Atom. Absorfltion Newsl., 1971, 10, 65. Pickford, C. J., and Rossi, G., Analyst, 1972, 97, 647. Techniques in the Life Science,” Ljubljana, Yugoslavia, 10-14 April, 1972. Switzerland, Second Edition, 1963. Received Januavy 2&h, 1973 Accepted July rjth, 1973

ISSN:0003-2654    

DOI:10.1039/AN9739800841

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

-4 nalyst, December, 1973, 1701. 98, $$. 851-856 851 Absorptiometric Determination of Trace Amounts of Sulphide Ion in Water BY S. A. RAHIM, A. Y. SALIM* AND MRS. S. SHEREEF (Depavtment of Chemistry, College of Science, M o d University, Iraq) A sensitive and rapid method is described for the determination of minimal concentrations of soluble sulphide in water. It is based on the reduction of iron(II1) to iron(I1) by sulphide a t pH 3 in the presence of 1,lO-phenanthroline reagent, forming theorange - red complex [(C,2H,N2)3Fe]2+. The method is subject to some interferences, which fortunately are not usually present in water supplies. Interferences of many acidic and basic radicals can be successfully overcome by recovery of hydrogen sulphide by steam distillation from the samples acidified with sulphuric acid.Down to 0-5 pg or a concentration of 33 pg 1-1 of sulphide, if 15 ml of sample are available, can be detected by the method. ANAEROBIC decomposition of sulphur-bearing organic materials produces hydrogen sulphide, the presence of which, or its salts, is an indication of poor water quality. The rotten-egg odour of hydrogen sulphide is very offensive. Its odour threshold is as low as 0.0011 mg 1-l.l The toxicity of hydrogen sulphide to aquatic life has been reported to have widely ranging values. It can be toxic to some fresh-water fish in concentrations well below 1 mg 1-1.2 Corrosion of metallic and concrete structures by sulphides is important and costly. Sulphides also corrode a wide variety of metals and alloys rapidly.Oxidation of hydrogen sulphide produces sulphuric acid that will attack concrete. Few methods are available for the determination of small amounts of sulphide in water. The best known are probably the titration method involving the use of iodine and thiosul- hate,^ and the colorimetric method based on the reaction that takes place under suitable conditions between 9-amino-NN-dimethylaniline and sulphide ions in the presence of iron( 111) , which results in the formation of methylene blue.4 The accuracy of the latter method is reported to be &lo per cent. if very careful use of the technique is made.4 A fluorimetric method has been described5 in which the sulphide ion is caused to react with the non- fluorescent palladium complex of 8-hydroxyquinoline-5-sulphonic acid at pH 9.2, thus liberating the strongly fluorescent free ligand.More recently6 an absorptiometric method has been described based on the green colour that is formed when sulphide ions are treated in ammoniacal solution with iron(II1) in the presence of excess of nitrilotriacetic acid, colloidal basic iron(II1) sulphide solution being used as a reference. The recommended procedure can be applied down to 8mg1-1 of sulphide, but the absorbance has to be measured 2 to 12 minutes after carrying out the test. In this paper, we describe a method for the determination of small amounts of sulphide, based on the reaction between sulphide ion and iron(II1) at pH 3 in the presence of 1,lO-phenanthroline. In the course of an investigation of the elimination of sulphides from natural water7 by chemical treatment, it was observed that with the gradual addition of iron(II1) chloride t o sulphide solutions the following series of reactions occurs : ( a ) A dark green coloured solution is first formed when up to one molar proportion of iron(II1) is added to the sulphide at high pH.(b) Addition of a slight excess of iron(II1) results in the immediate formation of a black precipitate. (c) Further addition of iron(II1) causes gradual dissolution of the black precipitate, until its complete dissolution when a total of two molar proportions of iron(II1) have been added with respect to the original sulphide, together with the precipitation of colloidal sulphur. Increasing the molar proportion of iron (111) to more than 2 has no effect.(d) * Present address : Faculty of Engineering, Alexandria University, Alexandria, Egypt. (Q SAC and the authors.852 RAHIM, SrZLIM AKD SHEREEF : ABSORPTIOMETKIC 1)ETERMINATIOS 01; [ A nalyst, \-d. 98 The reactions that take place are very probably as follows: (a) S2- + Fe3+ + OH- = Fe(0H)S (b) 3Fe(OH)S + 4Fe3+ = 6Fe2+ + Fe(OH), + 3s 3Fe(OH)S Fe(oH!, 2FeS + Fe(OH), + S 2Fe3+ + FeS = 3Fe2+ + S 2Fe3+ + S2- = 2Fe2+ + S (c) with the probable over-all equation : The determination of small concentrations of sulphide ion in solution by methods previously described in the literature was inconvenient because these methods lacked sensi- tivity, simplicity or stability. Determination of sulphide from the iron(I1) liberated by the reaction of sulphide with excess of iron( 111) was considered, but of the different methods available,8 the colorimetric method in which 1,lO-phenanthroline is used is probably the most satisfactory.Both iron(I1) and iron(II1) form coloured complexes with 1,lO-phenanthroline ; the reddish orange iron(I1) complex absorbs at 510nm, and both the iron(I1) and the yellow iron(II1) complexes have identical absorbances a t 396 nm, the amount being additive. Thus the reading a t 396 nm gives the total iron, while that at 510 nm gives iron(I1) only, which is equivalent to the original sulphide. EVOLUTION OF THE ANALYTICAL PROCEDURE- When a solution containing about 1 mg of sulphide was mixed with about 10 mg of iron(II1) in the presence of 1,lO-phenanthroline, a very deep orange - red colour (characteristic of ferroin) developed, accompanied by a slight turbidity due to colloidal sulphur.The colour was so intense that the mixture could be diluted to more than 10 litres and the solution was still distinctly coloured. It was therefore possible to decrease the concentration to a very low value, and it was surprising that, when dealing with 0.1 mg of sulphide or less in a total volume of 50 ml, no formation of colloidal sulphur was observed, a clear orange - red solution being obtained, which was stable for long periods. As the colour intensity is proportional to the concentration of iron(II), resulting from the reduction of iron(II1) by sulphide, the above observation suggests that it may be made use of for the determination of small amounts of sulphide. These experiments revealed that if appropriate solutions were mixed to give 1 to 100 pug of sulphide, 200 to 700 pg of iron(II1) and 3 to 10 mg of 1,lO-phenanthroline in a total volume of 25 ml, clear orange-red solutions were obtained that could be read.It was also found that it was best to maintain the pH between 3 and 4 (preferably at 3) because at higher pH values slight turbidity resulting from the presence of iron(II1) hydroxide occurred, and at lower pH values gradual fading of the colour took place. A buffer solution of pH 3 was used to control the pH. A study was then carried out in order to determine the conditions of maximum absorption, e.g., optimum time of colour development, sequence of addition of reactants, time between additions and proportions of reactants.Only a slight variation in absorption was observed when the standing time was extended from 30 minutes to 2 hours, as shown in Table I for the determination of 15 pg of sulphide in a final volume of 25 ml. TABLE I ABSORBANCE IN THE IRON(III) - SULPHIDE - 1 ,~O-PHENANTHROLINE SYSTEM 15 pg of S2- + 0-2 mg of Fe3+ + 3 mg of 1,lO-phenanthroline + 5 ml of acetate buffer in a final volume of 25 ml Standing time . . . . 0 15 30 45 1 2 24 Absorbance (1-cm cell) . . 0.36 0-368 0.370 0-370 0.370 0.372 0-45 Attempts were then made to find the optimal concentrations of reactants. minutes minutes minutes hour hours hours Also, only slight changes in absorbance were observed with different standing times (0 to 30 minutes) between additions of subsequent reagents or between the mixing of the reagents and dilution to the mark.A composite solution containing iron(II1) and acetate buffer wasDecember, 1973; TRACE AMOUKTS O F SULPHIDIS I 0 9 I?; WATER 853 made for simplicity. A composite iron(II1) - buffer - 1,1O-phenanthroline solution was un- suitable because it developed a red colour on standing for long periods. It was found that the best procedure was to mix 1,lO-phenanthroline solution with iron(II1) - buffer reagent, add sulphide, dilute to the mark and read the absorbance after 30 minutes to 2 hours against a reagent blank, Having thus established the best conditions for the determination, a test was made to check the adherence to the Beer-Lambert law. It was found that this law was obeyed (Table 11) in the range 0-5 to 25 pg of sulphide in a final volume of 25 ml.On extrapolation, the calibration graph passed almost through the origin when the readings were made against a reagent blank (with all materials except sulphide). Readings with amounts of sulphide above 25 pg showed slight negative deviation. The molar absorptivity of sulphide ion corresponds to 1-98 x 10' 1 mo1-1 cm-l. TABLE I1 ABSORBAXE OF THE IRON(III) - SULPHIDE - 1, 10-PHENANTHROLINE SYSTEM 7 ml of iron(II1) - buffer reagent containing 0.2 mg of iron(II1) + 3 ml of 0.1 per cent. 1,lO-phenanthroline + 0-5 to 25 pg of S2- diluted to final volume of 25 ml. Readings taken after 1 hour, with a l-cm cell, against reagent blank Sulphide solution/ml 0.1 0.2 0-3 0-6 0.8 1.0 2.0 3-0 5.0 Sulphidelpg . . . . 0.5 1.0 1.5 3.0 4.0 5.0 10 15 25 Absorbance .. . . 0.010 0.022 0.036 0.070 0.10 0-12 0.25 0.37 0.62 In order to facilitate interpretation, a calibration graph of iron(I1) was required. Iron(II1) chloride solutions containing from 10 to 70 pg of iron(II1) were reduced with hydroxyl- ammonium chloride and 1 , 10-phenanthroline was added.s Comparison of the calibration graph for sulphide with that for iron [the molar absorptivity of iron(I1) was founds to be 1.03 x 1041mol-lcm-l] showed that similar absorbances were obtained with 1 part of sulphide and 3.35 parts of iron, corresponding to a molar ratio of Fe3+ to S2- of 1.92: 1, which is slightly lower than that expected according to the equation ~ 2 - + 2~e3f = 2Fe2+ + S In order to test the accuracy and precision of the proposed method, recovery experiments were carried out on sulphide solutions containing 7, 10 and 15pg of sulphide.The results (Table 111) showed that both precision and accuracy were good. TABLE I11 RECOVERY OF SULPHIDE ADDED TO DISTILLED WATER Sulphide Sulphide Standard deviation Coefficient of added1 Number of Mean found r variation, per cent. PF: determinations absorbance (mean)/ pg Absorbance Irg 7 10 16 I5 0.172 6-94 0.0073 0.295 4.2 17 0.248 10.00 0.008 0.32 3.2 11 0.370 14.90 0.013 0.52 3.5 The interfering effect of cations was not examined in detail as most of them are not compatible in solution with the sulphide ion. Of the anions examined (Table IV), however, the following did not interfere in 100-fold excess on a mass basis relative to sulphide: chloride, sulphate, carbonate, hydrogen carbonate, bromide and nitrate.Many oxidising, reducing and complexing agents were found to interfere seriously, e.g. ., thiosulphate, sulphite, nitrite, citrate, tartrate and oxalate. Fortunately, it has been found that in the presence of most interfering agents, except those which react with sulphide in acidic medium, the determination can be carried out easily by acidifying the sample with sulpliuric acid in a micro-Kjeldahl distillation apparatus and steam distilling the liberated hydrogen sulphide, which is directly absorbed in a solution containing iron(II1) - buffer and 1,lO-phenanthroline. Losses of hydrogen sulphide are 15 per cent. or less and can be minimised by taking the usual precautions to prevent oxidation by atmospheric oxygen.Phosphate, cyanide and EDTA had little effect.854 RAHIM, S.4LIM AND SHEREEF: ABSORPTIOMETRIC DETERMINATION OF [,4ndySt, VOl. 98 TABLE IV INTERFERING EFFECT OF SOME ANIONS ON THE ABSORBANCE OF SULPHIDE SOLUTIONS Added anion Chloride Sulphite Phosphate Nitrite Sulphate Hydrogen Carbonate Oxalate Citrate Tartrate Thiosulphate Fluoride Iodide Cyanide EDTA Nitrate Bromide carbonate Absorbance of sulphide solution containing the anion tested in- control l0-fold excess 102-fold excess 103-fold excess 104-fold excess - - - - - Sample Blank Sample Blank Sample Blank Sample Blank Sample Blank - - 0.21 0.04 0-21 0-04 0.21 0.04 - 0.21 0.04 0.24 0.31 0.94 1-08 - - - - 0.21 0.04 0.21 0.04 0.22 0.07 0.23 0.12 0.25 0.18 0.21 0.04 - - 0.04 0.06 0.06 0.06 0-08 0.08 0.21 0.04 - - 0.21 0.04 0.22 0.04 0.22 0.05 f A \ - 0.20 0.04 0.20 0.04 0.20 0.04 0.20 0.04 - - 0.20 0.04 0.19 0.03 0.20 0.04 0.20 0.04 - - 0.20 0.04 0.20 0.18 0.39 0.31 0.45 0.43 - - 0.22 0.04 0.37 0.13 0.41 0.28 0.34 0.31 - - 0.22 0.04 0.21 0.08 0.32 0.19 0.51 0.43 - - 0.22 0.04 0.31 0.10 1.08 1-05 - - - - 0.22 0.04 0.21 0.04 0.21 0.06 0.98 0.04 - - 0.22 0.04 0.24 0.04 0.24 0.05 0.34 0.21 - - 0.22 0.04 0.23 0.04 0.24 0.05 0.30 0.11 - - 0.22 0.04 0.22 0.04 0.20 0.01 0.19 0.01 - - 0.19 0.04 - I 0.18 0.03 0.17 0.03 0.17 0.03 0.19 0.04 - I 0.19 0.04 0.19 0.04 0.19 0-04 The blank contained all the reagents except the substance to be determined (sulphide), and was measured against distilled water.Although it is recommended that the absorbance should be measured against a reagent blank, the absorptions of each sample and its blank were measured separately against distilled water in order to show the effect of each inter- fering ion examined and its corresponding blank (containing no sulphide).However, sub- traction of the absorption of each blank from its corresponding sample absorption (both measured against distilled water) gives the absorption of the sample against the reagent blank. This procedure is preferred to that of driving off the liberated hydrogen sulphide with a slow stream of nitr~gen,~ because (i) the apparatus is simple and compact, (ii) the use of extremely pure nitrogen is avoided, (iii) recovery of hydrogen sulphide takes place in a shorter time, e.g., 20 minutes, and (iv) the hydrogen sulphide recovered is directly absorbed in the test reagent. The presence of excess of zinc ions interferes in the determination as zinc forms a complex with l,lO-phenanthroline.a Consequently pre-treatment with zinc a ~ e t a t e , ~ ~ ~ in order to preserve and purify or concentrate, or both, the sulphide, should be followed by the above steam-distillation procedure. METHOD APPARATUS- Readings werelmade on a Unicam SP500 spectrophotometer. REAGENTS- All reagent solutions should be prepared with recently boiled and cooled distilled water, and protected from atmospheric oxygen as much as possible. Stock sodium sulphide solution-Add 10 per cent.sodium hydroxide solution dropwise to a saturated solution of hydrogen sulphide in water, until a pH of 11 is reached. Determine the exact molarity of the solution i~dimetrically~ (0.1 M).The stock solution can be kept for 2 to 3 days but its concentration should be checked immediately before each dilution. Dilute sodium sulphide solation-Dilute 10 ml of the above solution with water to 200 ml. This solution should be freshly prepared. Standard sodium sulphide solution, 5 mg Z-1(1.56 x M)-Ddute sufficient stock sodium sulphide solution (1 to 2 ml, measured to the nearest 0.005 ml; alternatively, 20 to 40 ml of dilute sodium sulphide solution) with water to 1 litre. This solution should be freshly prepared daily. 1 ml of solution = 5 pg of S2-.December, 19731 TRACE AMOUNTS OF SULPHIDE ION IK WATER 855 Stock iron(I1I) chloride solution, 0.5 M-Dissolve 10 g of anhydrous iron( 111) chloride in water, make the volume up to 100 ml, leave the solution overnight, then filter it.Determine the molarity of the iron solution gravimetrically. Standard iron(II1) chloride solution, 100 mg l-l (1.79 x M)-Dilute sufficient stock iron(II1) chloride solution (3 to 4 ml, measured to the nearest 0.01 ml) with water t o 1 litre. Acetate bufer solution, pH 3-Dissolve 35 g of crystalline sodium acetate in 200 ml of 1,lO-Phenanthroline solution, 0.1 per cent.-Dissolve 0-1 g of the monohydrate in hot Iron(III) - bufer composite reagent-Mix 2 volumes of standard iron(II1) chloride 1 ml of solution = 100 pg of Fe3+. water, then add glacial acetic acid until a pH of 3 is reached. water (70 "C). solution with 5 volumes of acetate buffer solution. PROCEDURE- Pyeparation of calibration graph-Transfer 7-ml portions of iron(II1) - buffer reagent to 25-ml standard flasks.To each flask add 3 ml of 0.1 per cent. 1,lO-phenanthroline solution, then add 0-1 to 10-ml aliyuots of the 5 mg 1-1 sulphide test solution (i.e., 0.5 to 50 pg of S2-) and dilute the contents of the flasks to 25ml. Measure the absorbance of each solution 4 to 2 hours from the time of preparation in l-cm cuvettes a t 510 nm against a reagent blank. Use this procedure for unknown solutions containing 0-03 to 100 mg 1-1 of sulphide by using sample volumes containing 0.5 to 25 pg of sulphide. After cooling the solution, make the volume up to 100 ml. APPLICATION TO SOME KATURAL WATERS The sulphide contents of two natural waters were determined iodimetrically arid by the The results given in Tables V and VI show that a satisfactory recovery of present method.sulphide was obtained in the presence of high concentrations of several interfering ions. TYPICAL TABLE V Results expressed in mg 1-l ANALYSES O F TWO NATURAL WATERS FROM THE VICINITY OF MOSUL Val Lie determined 13 arnmam Al- A1 il p l l . . . . . . . . 6.8 Total solids . . . . . . 570 Total hardness* . . . . 130 MgCO, . . . . . . 29 CaCO, . . . . . . 97 Na,CO, . . . . . . Na,SO, . . . . . . 35.5 __ NaCl . . . . . . . . 330 * Calculated as CaCO, (mg 1-l). .\in Kibrit 5.4 1650 265 160 88 83 1183 - CONCLUSIONS The proposed method for determining sulphide can be applied down to 0.03 mg 1-l of ulphide if 15 ml of sample are available, and up to 100 mg 1-1 in 25-ml test samples. The nsitivity is high and the accuracy is good.The method is specially recommended for the termination of sulphide in natural waters in which almost all interfering materials are not kely to be present. TABLE VI ANALYSES OF THE NATURAL WATERS FOR SULPHIDE CONTENTS Sample volume Sulphide present in sampIe by Sulphide found in sample by \\'ater analysed taken/ml iodimetric method/pg present method/ pg ammam A1-Alil 0.5 1 2 Iiibrit 0.1 0.5 I 2-25 4.5 9 1.6 8.01 16.03 2.15 4.4 9.08 1.2 7.20 16.6856 RAHIM, SALIM AND SHEREEF The exact composition of the red absorbing species is known and is referred to as (C,,H,N,) ,Fez+. Stoicheiometry of the reaction between sulphide and iron( 111) ions indicates that 1 mol of S2- produces 2 mol of Fe2+, probably according to the equation 2Fe3+ + S2- = S + 2Fe2+ Although when present in higher concentrations sulphur separates in colloidal form, at low concentrations no turbidity arising from separation of sulphur is observed. The precision of the method was tested by replicate analyses of a 1-58 x low4 M sulphide solution, which gave a mean coefficient of variation of 3.6 per cent. The sensitivity was 0-0016 pg ml-1. 1 . 2. 3 . 4 . 5. 6. 7 . 8. 9. REFERENCES Klein, L., “River Pollution 11: Causes and Effects,” Butterworths, London, 1962. Doudoroff, P., and Katz, M., Sewage Ind. Wastes, 1950, 22, 1432. Vogel, A., “A Text Book of Quantitative Inorganic Analysis,” Third Edition, Longmans, London, 1966, p. 370. A.P.H.A., A.W.W.A. and F.S.I.W.A., “Standard Methods for the Examination of Water and Waste Water,” Thirteenth Edition, American Public Health Association, New York, 197 1, pp. 555 and 336. Hanker, J. S., Gelberg, A., and Witten, B., Analyt. Ckem., 1958, 30, 93. Rahim, S. A., and West, T. S., Talanta, 1970, 17, 85. Salem, A. Y., and Rahim, S. A., Report to Mosul University, 1971. Sandell, E. B., “Colorimetric Determination of Trace Metals,” Third Edition, lnterscience Pub- Pomeroy, R., Analyt. Chern., 1954, 26, 571. lishers, New York, 1959, p. 520. Received Octobev 30th, 1972 Amended April 27th. 1973 Accepted July 27th, 1973

ISSN:0003-2654    

DOI:10.1039/AN9739800851

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

d4nalyst, December, 1973, Vol. 98, pp. 857-862 857 A Spectrofluorimetric Procedure for the Assay of Carrageenan BY R. B. CUNDALL, G. 0. PHILLIPS AND D. P. ROWLANDS (Department of Chemistry, Uniuersity of Nottingham, Nottingham, NG7 2RD) (Defiartment of Chemistry and Applied Chemistry, University of Salford, Salford, 1%?5 4 WT) A spectrofluorimetric procedure for the determination of carrageenan in the presence of salts, many polysaccharides, and proteins has been de- veloped. It involves the binding of acridine orange to the polyanion and observation of the decrease in green fluorescence from free monomer dye in solution. The method offers many advantages over the available chemical assays, and is a simple, accurate and rapid technique for determining carrageenan in a conventional hydrocolloid stabiliser mixture.Its successful application, after minor modifications, in the presence of protein and salts indicates its direct applicability to commercial milk products. CARRAGEENAN is the broad designation given to closely similar sulphated polysaccharides derived from certain types of seaweeds. This material, which is widely used as a stabiliser in ice cream and allied frozen milk products, is generally added in concentrations between 50p.p.m. and 1 per cent. Its quantitative determination in the presence of other carbo- hydrates (which assist the carrageenan in improving texture) and proteins is important, and there is a need for procedures for the rapid quality control of commercial samples. Several methods are already available for the quantitative determination of carra- geenan ,1-3 most of which involve removal of interfering cations and isolation of the carrageenan as an insoluble salt. These methods are tedious and time consuming.Stone, Childers and Bradley4 have determined the ester sulphate content of various plant polysaccharides by the interaction of anionic sites with cationic dyes. On becoming bound to polyelectrolytes the dyes may show a shift in their absorption spectra to shorter wavelengths ; this phenomenon, known as metachromasia, is due mainly to dye aggregation on the polymer molecules, although other factors also influence the intera~tion.5,~ Anionic groups in several polyanions7s8 can be accurately titrated on this basis. When bound, some cationic dyes, for example acridine orange or proflavine, either become non-fluorescent or show a fluorescence emission that is shifted to longer wavelengths and can easily be separated from the fluorescence of the unbound dye.The relative binding affinities towards a cationic dye with respect to the type of anionic site present increases in the order C02- < C02- + 0.S03- < C02- + 0.S03- + NHS03- < 0.S03-.9p1@ For the sulphated polysaccharide carrageenan, concentrations of metallic ions up to 1 M do not interfere with dye binding. A suitable dye for use in the determination of carrageenan is acridine orange. It binds strongly to polyanionsll and has been used extensively in histological staining and studies of metachromasia. The free dye is strongly fluorescent and on binding to anionic palysac- charides the green fluorescence is shifted to the red.It is the fluorescence of the unbound dye (Abr. 530nm) which is used in the following assay method. Metal ions can release the bound dye by competing for anionic sites. EXPERIMENTAL APPARATUS- Fluorimetric measurements were made with either an Aminco-Bowman instrument or a fully corrected spectrofluorimeter constructed at Nottingham University.12 The right-angle viewing mode was used with both instruments. @ SAC and the authors.858 CUND-ILL, PHILLIPS AND ROWL-Ih'DS -4 SPECTROFLUORIMETRIC [-4ilndyS/, 1'01. 98 REAGENTS- A specimen of A-carrageenan was also supplied by Dr. D. A. Rees, Unilever Ltd. . Other stabilisers used were gum arabic powder (BDH Chemicals Ltd.), guar gum MM (Meers Corporation), locust bean gum (Meers Corporation), pectinate as apple pectin, 250 grade (BDH Chemicals Ltd.), gum tragacanth (Griffin and George Ltd.) and the sodium salt of carboxymethylcellulose (Hercules Inc.).Acridine orange was purified by the method of Lamm and Ne~ille.1~ The extinction coefficient at a given concentration was calculated from the formula given by Stor,e and Bradley.s De-ionised water was used and all other reagents were of the purest grade obtain- able. Enzymes used were trypsin (Seravac) , subtilisin Carlsberg (Novo Industre, Copenhagen) and a-chymotrypsin (Seravac). A-, K- and L-Carrageenan samples were supplied by Copenhagen Pectin Co. METHOD Solutions of the different carrageenan-containing samples were prepared by dissolving amounts of sample that gave about 50 mg of carrageenan per 50 ml of solution.The standard solutions were stable for up to 3 days when stored a t 5 "C. Determinations were made by two different procedures. In one, 1 ml of diluted ( x 10) polyanion stock solution was added t o 5 ml of 1.54 x lo-* M solution of acridine orange and the mixture was immediately diluted to 50 ml and gently shaken. No precipitation occurred and a series of solutions was prepared by using increasing amounts of polyanion. In another procedure carrageenan solution was added in 0.01-ml portions to standard dye solution by using an Agla micrometer syringe. Both methods gave reproducible and consistent results. The absorption spectrum was measured in the range 400 to 500 nm and the fluorescent emission intensity was determined relative to a sample of unbound dye.In the fluorescence measurements the dye was excited on the short wavelength edge of the monomer absorption at 400 nm in order to achieve a low optical density, of about 0.06. Under these conditions, with right-angle viewing, the intensity of fluorescence is directly related to the concentration of free monomer dye. Fluorescence is viewed at 540 nm, rather than at the maximum inten- sity of 530 nm, so as to minimise inner filter effects from self-absorption of the fluorescence. For the experiments on the effect of the presence of other stabilisers or additives, the additive was added to the carrageenan before mixing the latter with the acridine orange solution. Bovine milk - carrageenan samples (5 g) were digested with 5 mg of trypsin, 5 mg of a-chymotrypsin and 5 mg of subtilisin Carlsberg at 27 "C and pH 6.5 to 7 for at least 6 hours before titration.Carboxymethylcellulose also binds acridine orange but less strongly than carrageenan. In the presence of carboxymethylcellulose determinations of carrageenan could be made in acidic solutions in which ionisation of the carboxyl group is suppressed,2 the optimum pH for this purpose being between 3.0 and 3.5. RESULTS Fig. 1 shows that increasing amounts of carrageenan decrease the absorption of mono- iiieric dye at 492 nm and a new band due to bound dye aggregate appears at about 462 nm. As the polymer concentration increases to a 1 : 1 equivalence of anionic sites to dye the spectrum becomes principally due to bound dye.It is, therefore, possible to plot the decrease in monomer absorption against carrageenan concentration and obtain a curve that indicates the number of sites on the polysaccharide. Sharper end-points were obtained by using spectrofluorimetric data, and typical results are shown in Fig. 2. The end-point is accurately determined by locating the point of inter- section of the two linear sections of the curve. The second section of the curves corresponds l o the concentration of dye that remains free in solution in the presence of excess of polyanion and is usually less than 5 per cent. of the total dye present. The effect of addition of calcium ions on the procedure for the determination is shown in Fig. 3. End-points were satisfactory when the polyanion was present in up to 1 0 - l ~ calcium chloride solution.High concentrations of calcium chloride removed increasing amounts of acridine orange from the carrageenan.December, 19731 PROCEDURE; FOR THE ASSAY OF CARRAGEENAN 0.8 0.6 Q) 8 m e a 0.4 0.2 0 400 420 440 460 480 500 520 540 Wavelength/nm Fig. 1. The effect of K-carrageenan on the absorption spectrum of acridjne orange. Dye concentration 1.55 x M. 1, No additive; 2, 75; 3,150;4,225; 5, 300; and 6, 375 pg in 50 ml 859 The different samples of carrageenan were titrated in the presence of six-fold excesses of five other commonly used stabilisers and a twelve-fold excess of carboxymethylcellulose. The results obtained are shown in Table I as the equivalent mass (relative molecular mass per unit dye-binding site) of the carrageenan sample.The proportions of additive used are only typical values, for example carboxymethylcellulose can be added up to a 200-fold excess and the carrageenan still successfully determined. Only one of the additives, gum arabic, decreased the sharpness of the end-point. Preliminary dialysis gave improved results with Carrageenan solution addedlml Fig. 2. Spectrofluorimetric titration of &-carrageenan - locust bean gum (1 : 6 wz/m), acridine orange 1-45 x M. Graph of de- crease in dye fluorescence intensity with in- creasing c-carrageenan 0 1.0 2.0 Ratio, site dye Fig. 3. The effect of calcium ions on the spectrofluorimetric titration of &-carrageenan with acridine orange, 0, 1 0 - a ~ CaC1,; 0, 1 0 - 1 ~ CaCl,; and x, 1 M CaCl,860 CUKDALL, PHILLIPS AND KOWLA4K11S SPHCTROPLCOKIILIETRIC [i!!na~ySt, VOl. 98 all of the carrageenan samples.In all instances the recovery is 100 per cent. within the limits of experimental error. TABLE I EQUIVilLENT MASSES OF VARIOUS CARRAGEENAN SAMPLES WITH EXCE. <ss OF ADDITIVES AS DETERMINED BY ACRIDINE ORANGE TITRATION Carrageenan solution, 0.05 per cent. m/m Additive Locust bean . . . . . . Pectinate . . . . . . Guar gum . . . . . . Gum arabic (dialysed) . . Gum tragacanth . . . . Mixure of above 5 additives Carboxymethylcellulose . . Bovine milk (enzyme digested) Mass of additive Mass of carrageenan 6 6 6 6 6 25 12 - Equivalent mass of carrageenan sample+ 7- Lambda 264 (1) 267 (1) 266 (1) 269 (2) 265 (1) 280 (6) 269 (2) - A Kappa 390 (1) 392 (1) 388 (1) 400 (2.5) 392 (1) 407 (4) 395 (1.5) __ -1 Iota 285 (2) 288 (1) 292 (1) 292 (1) 302 (4) 293 (1) 303 (4) 294 (2) * Figures given in parentheses are the mean percentage deviations of the values determined Fig.4 shows the improvement in the determination made by enzyme digestion of the milk proteins before titration; the lower curve is for an undigested milk - &-carrageenan (0-05 per cent.) sample and the upper curve for a sample that has been digested with enzyme at 27 "C for 6 hours. Results obtained with milk and digested milk samples showed that acridine orange binds to milk proteins at pH 6.5, but enzymic treatment limits the interaction with protein to an extent such that it does not interfere with the stronger binding to carra- geenan. No attempts were made to remove the polypeptides by complete digestion and dialysis.from known concentrations of carrageenan. Fig. 4. Bovine milk - 1-carrageenan titration with acridine orange. Acridine orange, 1.5 X 1 0 - 5 ~ and carrageenan, 0.05 per cent. 0, undigested milk - carrageenan cqmplex; and @, enzyme digested DISCUSSION The calculated equivalent masses determined by our method are of the order expected from the structure of the polymer and are in good agreement with the values obtained from elemental analyses of all the samples (Table 11). In order to use the method as an assay procedure it is necessary to know the equivalent mass per anionic site for each carrageenanDecember, 19731 PROCEDURE FOR THE ASSAY O F CARRAGEENAN 861 sample, which value is directly available from the titration procedure described.Other workers4S7J have obtained similar results, particularly with acridine orange, on a variety of strongly binding polyanions. Weakly binding polyanions, such as sodium carboxymethyl- cellulose, cannot be titrated in the manner described because of the large amount of unbound dye present at the equivalence p ~ i n t , ~ , ~ which is a useful advantage when carrageenan must be determined in the presence of carboxylated polysaccharides. With carrageenan and other strong binders there are only small amounts of unbound dye, as shown by the results given in Fig. 2. TABLE I1 EQUIVALENT MASSES PER REPEATING POLYSACCHARIDE UNIT FOR VARIOUS CARRAGEENAN SAMPLES Equivalent mass per sulphate group r - 3 Carrageenan sample From sulphate content By acridine orange titration Lambda (i) .. * . 286 298 Lambda (ii) .. .. 258 266 Kappa .. .. .. 370 390 Iota .. .. .. 296 290 Fluorimetric measurements have important advantages over those of absorption. Stone, Childers and Bradley4 in their absorption studies on sulphated polysaccharides did not always obtain good end-points, and we have also found that when salt was present in any of the samples only spectrofluorimetry gave satisfactory results. This effect is due to the changes in the shape of the absorption spectrum of the bound dye, which arise from variation in ionic strength. The analysis of fluorescence from monomer dye is simpler and no manipulation of the results is necessary in determining the equivalence point. In addition, it is possible, by using fluorimetry, to analyse samples containing as little as 5 p.p.m.of carrageenan even in the presence of other additives and cations. It has also been established that the method is applicable to systems involving carrageenan in the presence of other stabilisers, both neutral and charged, and proteins. The fluorescence method can also be used for determining the sulphate group content of different carrageenan samples. With protein-free samples the titration procedures can be carried out in triplicate in less than 1 hour. The results show that the method is suitable for the determination of carrageenan in enzyme-digested samples that contained protein, no removal of cations or clarification treatment being necessary for titration with the dye solution.The method is also applicable to other strongly binding polyanions such as dextran sulphate and polystyrene sulphonate. For stabilising a number of milk products the mixture of hydrocolloids studied by us is used, namely, carrageenan, carboxymethylcellulose in the presence of one or more of the neutral gums, mar, tragacanth, locust bean, etc.14 Fractionation of such mixtures is complex and is generally required before particular stabilisers can be individually determined.15 As carrageenan is a primary material for controlling stabilisation, its ready determination in a product such as, for example, infant milk, is of considerable practical value. The method we have described is simple, accurate and rapid for determining carrageenan in a conventional stabiliser mixture.The success of the method, when slightly modified even in the presence of protein, salts and other materials that may be present in the final commercial product, shows that the procedure could also prove of value in these circumstances. We thank the Copenhagen Pectin Co. and Dr. D. A. Rees (Unilever Research) for the well characterised samples of K-, L- and h-carrageenan. REFERENCES 1. 2. 3. 4. 5. 6. 7. Hansen, P. M. T., and Whitney, E. McL., J . Dairy Sci., 1960, 43, 175. Graham, H. D., J . Fd Sci., 1968, 33, 390. - , J . Dairy Sci., 1972, 55, 1675. Stone, A. L., Childers, L. G., and Bradley, D. F., Biopolymers, 1963, 1, 111. Phillips, G. O., in Balazs, E. A., Editor, “Chemistry and Molecular Biology of the Intercellular Matrix,” Volume 11, Academic Press, London and New York, 1970, p. 1033. Moore, J. S., Phillips, G. O., Power, D. M., and Davies, J. V., J . Cheun. SOG. ( A ) , 1970, 1155. Vitagliano, V., Costantino, L., and Zagari, A., J . Phys. Chem., 1973, 77, 204.862 8. 9. 10. 11. 12. 13. 14. 15. CUNDALL, PHILLIPS AND ROWLANDS Stone, A. L., and Bradley, D. F., J . Amer. Chem. Sm., 1961, 83, 3627. Davies, J. V., Dodgson, K. S., Moore, J. S., and Phillips, G. O., Biochem. J., 1969, 113, 465. Scott, J. E., and Willett, I. H., Nature, Lond., 1966, 209, 985. Lewis, C., Cundall, R. B., Llewellyn, P., and Phillips, G. O., J . Phys. Chem., 1970, 74, 4172. Cundall, R. B., and Evans, G. B. ,J. Scient. Instrum. ( J . Phys., E ) , 1968, 1, 305. Lamm, M. E., and Neville, D. M., J . Phys. Chem., 1965, 69, 3872. “Natural Plant Hydrocolloids,” Adv. Chem. Ser., 1954, No. 11. Morley, R. G., Phillips, G. O., Power, D. M., and Morgan, R. E., Analyst, 1972, 97, 315. Received May 8th 1973 Accepted June 2nd, 1973

ISSN:0003-2654    

DOI:10.1039/AN9739800857

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

Analyst, December, 1973, Vol. 98, $9. 863-872 863 Gas - Liquid Chromatographic Determination of Alpha-, Beta-, Gamma- and Delta-BHC Levels in Human Blood, Depot Fat and Various Organs with the Use of 2,2=Dimethylpropane- 1 ,3-diol Succinate as the Stationary Liquid Phase BY G. CZEGLEDI- JANKG (Institute for Chemistry and Food Analysis, H-1022 Hermann Ottd u. 15, Budapest, Hungary) The presence of various BHC isomers in the human organism has received relatively little attention, and studies were often restricted to only one BHC isomer. A previously described one-step extraction and clean-up procedure before gas - liquid chromatographic determination of organochlorine pesticide residues in human blood has now been applied to various organs and depot fat. The identification of the BHC isomers was performed by gas - liquid chromatography with several stationary liquid phases.2,Z-Dimethylpropane- 1,3-diol succinate was found t o be the most satisfactory stationary liquid phase for the present purpose, as it gave distinctly separated peaks and characteristic relative retention times. OF the investigations that have been carried out on the accumulation of organochlorine pesticide residues in the human organism, only a few have dealt with the presence of BHC isomers and most papers have been concerned with DDT and its metabolites. For instance, the presence of gamma-BHC in the depot fat of the French population was first demonstrated by Hayes, Dale and LeBreton,l but they treated the results with some reservation. Their findings were later confirmed by other studies, but nevertheless the presence of the various BHC isomers in human biological material has not received great attention.Many workers do not mention the presence of BHC isomers in the human organism at all, and Table I, which is far from complete, demonstrates that some authors who have investigated this problem restricted their study to only one BHC isomer. TABLE I REFERENCES TO BHC ISOMERS IN THE HUMAN ORGANISM Authors Reference BHC isomer mentioned Specimen Hayes, Dale and LeBreton . . .. 1 Dale, Curley and Cueto . . .. 4 Dale, Curley and Hayes . . .. 5 DBnes and TarjAn . . . . .. 6 Engst, Knoll and Nickel . . .. 7 Abbott, Goulding and Tatton . . 8 deVlieger et al. . . .. .. 9 Curley, Copeland and Kimbourgh . . 10 Milby, Samuels and Ottoboni .. 11 Dacre . . . . .. . . . . 12 Kadis, Breitkreitz and Jonasson . . 13 Samuels and Milby . . .. . . 14 Radomski et aE. . . .. . . 15 Egan, Goulding, Roburn and Tatton Radomski and Fiserova-Bergerova . . 2 3 Gamma Beta + “total BHC” Gamma Beta Beta, gamma Alpha, beta, gamma Gamma Beta + “total BHC” Alpha, beta, gamma Gamma Gamma Alpha, beta, gamma Alpha Gamma Alpha, beta, gamma Adipose tissue Adipose tissue, milk Adipose tissue, organs Blood Blood Foetal liver (one case) Adipose tissue Adipose tissue Adipose tissue, organs, blood Adipose tissue Blood Adipose tissue, organs, blood Adipose tissue, organs Blood Blood The intention of the present study was to investigate the determination of the four important BHC isomers in human biological material by means of an appropriate gas - liquid chromatographic method.@ SAC and the author.864 MATERIALS- Brain, liver, kidney and gonad and abdominal depot fat samples taken from ten healthy persons killed in accidents and dissected at the Institute of Forensic Medicine of the Semmel- weis Medical School, Budapest, were investigated. The specimens were selected randomly from subjects of both sexes (aged 32 to 66 years) and stored in a refrigerator between dissection and processing. Whole blood samples were taken from ten healthy donors and investigated without delay. CZEGLI~DI-JANK~ : GAS - LIQUID CHROMATOGRAPHIC DETERMINATION [Analyst, Vol. 98 EXPERIMENTAL METHODS- In a previous paper,16 a one-step extraction and clean-up procedure for the gas - liquid chromatographic determination of organochlorine pesticide residues in human blood samples was described.This method was modified so as to be suitable for the determination of alpha-, beta-, gamma- and delta-BHC isomers in human blood, adipose tissue (depot fat) and various organ samples by altering the composition of the material used for the clean-up (sodium sulphate and Florid were not used) and by using several different stationary liquid phases. Extraction and clean-up of samples-Organ samples containing about 0.01 to 0-1 g of fat were ground with an equal amount of sand and then dehydrated by lyophilisation in an Edwards High Vacuum Ltd. centrifugal freeze dryer, Model 30 PI-512, with a secondary drying unit, Model 30 SI-332, or equivalent equipment. The blood samples (2 to 10 ml) were lyophilised without pre-treatment.One-step extraction and clean-up was carried out in the apparatus described previously.16 In the present study, only 1.8 ml of fuming sulphuric acid (10 per cent. of SO,) mixed with 2 g of Hy-Flo Super Cel was used in the clean-up and 25 to 30 ml of light petroleum (boiling range 35 to 40 “C) or n-pentane (gas-chromatographic purity) was used as the extraction solvent. Adipose tissue samples were also lyophilised and subsequently extracted with light petroleum. The extracted pure depot fat (0-1 g) was placed in the apparatus above the clean-up material and processed as described above. With extracted depot fat, solvent extrac- tion for 30 minutes was sufficient. Most of the light petroleum or n-pentane in the flask was evaporated by means of a rotary evaporator, and the remainder was transferred into a conical tube and 1 ml of n-hexane was added.After the evaporation of the residual light petroleum (n-pentane), the 1 ml of n-hexane solution (diluted, if necessary) proved to be suitable for gas - liquid chromatographic analysis. Determination of the fat content of organ samples-The organochlorine pesticide level can be expressed in parts per million of wet organ tissue or of extractable fat, as recommended by Kadis, Breitkreitz and Jonasson,13 and the fat content of the organs therefore had to be determined. For this purpose, organ samples were ground with sand, lyophilised and extracted with light petroleum. Hence in this study the “fat content” represents the lipids extracted with light petroleum from the lyophilised organs (see Table VI).Gas - liquid chromatographic analysis of puyi$ied extracts-A Packard gas chro- matograph, Model 7934, was used. The general operating conditions were as follows- detector: electron capture, tritium foil, 200 mC, applied potential 50 V; electrometer range : 1 x A; column: Pyrex glass, 4 mm i.d., on-column injection; solid support : Chromosorb W HMDS, 60 to 80 mesh; carrier gas: nitrogen, high purity; temperature: inlet, 235 “C; detector, 200 “C; outlet, 235 “C; chart speed: 30 in h-l. Operating conditions that were varied for the different columns are given in Table 11. The extraction time was 3 hours. IDENTIFICATION AND RECOVERY OF BHC ISOMERS IN HUMAN BIOLOGICAL MATERIAL- The BHC isomers were identified by comparing the retention times on each of the four columns with the retention times of the reference substances. Figs.1 to 4 show the chromato- grams obtained from a human liver extract (female, 46 years old) on the four columns, together with the peaks and retention times of pure alpha-, beta-, gamma- and delta-BHC isomers and of Pp’-DDE as the internal standard. Table I11 gives the retention times of the BHC isomers relative to those of gamma-BHC and to pP’-DDE. pp’-DDE was chosen because it was present in all of the samples examined owing to environmental pollution.December, 19731 OF BHC IN HUMAN BLOOD, DEPOT FAT AND VARIOUS ORGANS TABLE I1 OPERATING CONDITIONS FOR GAS - LIQUID CHROMATOGRAPHY 865 Column r A \ Variable . . .. .. .... I I1 I11 IV Stationary liquid phase . . .. * . QF-1 Concentration of liquid phase, per cent. Column length/cm . . .. .. 180 Inlet pressure/p.s.i. . . . . .. 10 (silicone resin) 5 Carrier gas flow-ratelm1 min-1 . . .. 50 Column temperature/”C . . .. .. 170 OV- 1 7 (silicone resin) 5 60 50 6 185 XF-1112 (silicone nitrile resin) 120 60 13 180 2.5 2,2-Dimethyl- propane-1,3- diol succinate 2 120 70 12-5 185 For the identification of the BHC isomers thin-layer chromatography, according to Kov~cs,~’ was used as a complementary method. The extracts of each organ were mixed together and, after evaporation of the solvent in a rotary evaporator, a suitable amount of the residue was placed on a thin layer of alumina G. The developed chromatograms were compared with those for a series of standard BHC isomers, for which the RF values of the standards were: alpha-BHC 0.28, gamma-BHC 0.21, beta-BHC 0.04 and delta-BHC 0.02.F R.eference substances K, I X I 4 L Fig. 1. Gas -liquid chromatogram of an acid-cleaned extract from 2 g of lyophilised human liver. Volume of extract, 1 ml; volume injected, 10 pl; liquid phase, QF-1 silicone resin. Peaks: A, alpha-BHC (0.004 ng) ; B, gamma-BHC (0.02 ng) ; C, beta-BHC (1.1 ng) : D, delta-BHC (0.005 to 0.01 ng) ; E, pfi’-DDE; F, pp’-DDD; G, pp’-DDT; and X, unidentified. Reference substances: H, alpha-BHC (0.05 ng) ; I, gamma- BHC (0.05 ng) ; J, beta-BHC (0.5 ng) ; K, delta-BHC (0.1 ng) ; and L, pp’-DDE (internal standard) The reliability of the one-step extraction and clean-up of the lyophilised samples and extraction time have been discussed in a previous paper,16 and it was shown that the recovery of added gamma-BHC was highly unsatisfactory owing to its evaporation during lyophilisation.Therefore, it was necessary to investigate whether or not the BHC isomers, transferred through metabolic pathways to the organs, would be lost during lyophilisation. (Dale, Miles and Gained8 used compounds labelled with carbon-14 and found that DDT incorporated by metabolic pathways is bound more strongly to biological material than is added DDT).X ,Injection point X Fig. 2. Gas - liquid chromatogram of an acid-cleaned extract from 2 g of lyophilised human liver. Volume of extract, 1 ml; Peaks: A, alpha-BHC; B, gamma-BHC ((3.02 ng); C, beta-BHC (1.0 ng); Reference substances: H, alpha-BHC volume injected, 10 p1; liquid phase, OV-17 silicone resin. D, delta-BHC (0.005 to 0.01 ng) ; E, pp'-DDE; F, pp'-DDD; G, pp'-DDT; and X, unidentified.(0-025 ng) ; I, gamma-BHC (0.025 ng) ; J , delta-BHC (0.05 ng) ; and K, pp'-DDE (internal standard) Z 's 0 Z 3A n ‘Injection point F I II 1 Fig. 3. Gas - liquid chromatogram of an acid-cleaned extract from 2 g of lyophilised human liver. Volume of extract, 1 ml; volume injected, Peaks: A, alpha-BHC; B, gamma-BHC (about 0.02 ng) ; C, beta-BHC (1.2 ng) ; D, delta-BHC Reference substances: G, alpha-BHC (0.025 ng) ; H, gamma-BHC 10 pl; liquid phase, XF-1112 silicone nitrile resin. (about 0.015 ng) ; E, pp’-DDE; F, pp’-DDT plus fip’-DDD; and X, unidentified. (0.025 ng) ; I, beta-BHC (0.5 ng) ; J, delta-BHC (0.05 ng) ; and K, fip’-DDE (internal standard)868 CZEGLkDI-JANK6 : GAS - LIQUID CHROMATOGRAPHIC DETERMINATION [AflaZySi!, VOl.98 X -Injection point Reference substances I F Fig. 4. Gas - liquid chromatogram of an acid-cleaned extract from 2 g of lyophilised human liver. Volume of extract, 1 ml; volume injected, 5 pl; liquid phase, 2,2-dimethyl- propane-1,3-diol succinate. Peaks: A, alpha-BHC (0.002 ng) ; B, gamma-BHC (0.01 ng) ; C , pP’-DDE; D, delta-BHC (0.005 ng) ; E, beta-BHC (0.52 ng) ; and F, pp‘-DDT plus pp’-DDD. Reference substances: G, alpha-BHC (0.005 ng); H, gamma-BHC (0.005 ng); I, pp’-DDE (internal standard) ; J, delta-BHC (0.01 ng) ; and K, beta-BHC (0.05 ng) In this study, such evidence could be obtained only by applying an indirect method of recovery, i.e., the method described by Stanley and LeFavoure.l9 The samples were digested with a 1 + 1 mixture of acetic acid and 70 per cent.perchloric acid. The final clean-up step of this method was modified by using our circulation apparatus with the clean-up material described above. Amounts of 0.01 p.p.m. each of alpha-, gamma- and delta-BHC and 0.1 p.p.m. of beta-BHC were added to whole blood, homogenised liver and homogenised adipose tissue samples, which TABLE I11 RELATIVE GAS - LIQUID CHROMATOGRAPHIC RETENTION TIMES OF BHC ISOMERS AND P$’-DDE Relative retention times Stationary liquid phase* Stationary liquid phaset A A r 3 \ Compound OF-1 OV-17 XF-1112 DPDSt OF-1 01-17 XF-1112 DPDSZ alpha-BHC 0.28 0.18 0.26 0.30 0.79 0.75 0.79 0.68 beta-BHC 0.42 0.29 0.33 1.64 1-16 1.20 2.17 3-72 delta-BHC 0.47 0.34 0.79 1.34 1.32 1.44 2.44 3.11 pp’-DDE 1.00 1.00 1.00 1.00 2.78 4.20 3.10 2.27 gamma-BHC 0.36 0.24 0.7 1 0.44 1.00 1.00 1.00 1.00 * Relative to pp’-DDE = 1.00.t Relative to gamma-BHC = 1-00. # 2,2-Dimethylpropane-1,3-diol succinate.December, 19731 869 were then exarnined by the method of Stanley and LeFa~0ure.l~ Samples without added isomers were also examined. Our results for recovery were expressed as the means of results from three samples, as recommended by Kadis, Jonasson and Breitkreitz2* Table IV shows that the recovery of added BHC isomers was satisfactory. OF BHC IN HUMAN BLOOD, DEPOT FAT AND VARIOUS ORGANS TABLE IV RECOVERY OF BHC ISOMERS FOLLOWING THE ADDITION OF 0.01 p.p.m.OF ALPHA-, GAMMA- AND DELTA-BHC AND 0.1 p.p.m. OF BETA-BHC TO WHOLE BLOOD, HOMO- GENISED LIVER AND HOMOGENISED ADIPOSE TISSUE, USING THE MODIFIED METHOD OF STANLEY AND LEFAVOURE19 Results are mean values & standard deviations, from three samples. Results obtained by gas - liquid chromatography with 2,2-dimethyIpropane-l,3-dio~ succinate as the stationary liquid phase Recovery of pesticide added, per cent. A I \ Sample alpha-BHC beta-BHC gamma-BHC delta-BHC Whole blood . . . . 96.4 f 2-8 98.0 f 0.8 98.7 f 1.2 94.2 f 2.4 Liver . . .. . . 92.6 f 7.6 95.6 f 1.2 101.2 & 0.2 97.2 f 1.0 Adipose tissue* . . 88.4 f 7.2 105.2 f 0.8 89-8 & 3.2 90.0 f 3.6 * The results in this trial are referred to the total adipose tissue. Subsequently, samples were examined repeatedly by means of our lyophilisation and one-step extraction - clean-up method and by the method of Stanley and LeFavoure. The results of our lyophilisation method and those obtained by the perchloric acid digestion (the latter confirmed by the recovery of added BHC isomers) are in good agreement, with the usual accuracy achieved in gas - liquid chromatographic analyses (see Table V).RESULTS Quantitative determinations were made by comparing the gas - liquid chromatographic peak areas of the BHC isomers with those of the reference substances, and the results are summarised in Table VI for 2,2-dimethylpropane-1,3-diol succinate as the stationary liquid phase. As the amounts of BHC isomers in the samples differ considerably, it cannot be assumed that all of the BHC isomers are in the linear range of detection in the solution injected into the chromatographic column.The results therefore do not refer to a single reference solution, but to a series of standards of various concentrations, which were prepared so as_ to cover the range of the sample peaks. The results in Table VI also show the agreement between the results obtained following the two methods of preparation. Owing to the large number of investigations that would be necessary, it was not possible to obtain all of the corresponding results following lyophilisa- tion and perchloric acid digestion, but the range and mean values of the results verify the agreement between the two methods. DISCUSSION In applying the modified one-step method to demonstrate the presence of BHC isomers in human biological material, the following difficulties had to be overcome.Firstly, the original procedurel6 proved suitable for the recovery of added DDT, its metabolites and dieldrin, but not for that of added BHC. We therefore had to find an indirect method by which we could prove reliably that although added gamma-BHC would evaporate during lyophilisation, gamma-BHC and other BHC isomers incorporated through metabolic pathways would be retained. Lyophilisation, subsequent one-step extraction and clean-up in the circulation apparatus have the advantages that the lyophilised samples can be stored without refrigeration and can be easily and cleanly processed. The volume of solvent needed for extraction is not more than 25 to 30 ml. The second problem was to find the optimum gas - liquid chromatographic operating conditions that would result in good separations and make the identification of BHC isomers reliable.The chromatographic columns in general use for determining organochlorine pesticide residues from biological materials have relatively short retention times for BHC isomers.870 CZEGLBDI- JANKd GAS - LIQUID CHROMATOGRAPHIC DETERMINATION [Analyst, VOl. 98 On OV-17 as the stationary liquid phase, the determination of alpha-BHC is very uncertain owing to interference by an unknown component extracted from acid-cleaned biological material. In the present study, four stationary liquid phases were used in the identification of BHC isomers. It was found that for the separation of BHC isomers, the use of 2,2-dimethylpropane- 1,3-diol succinate as the stationary liquid phase has the particular advantage that it gives distinctly separated peaks and characteristic relative retention times, especially for beta- and delta-BHC.Dale, Curley and Cueto4 and McClure21 have already reported that diethylene- glycol succinate has the same advantage, but it has not been widely used. Its main dis- advantage is its volatility and its tendency to contaminate the electron-capture detector. The use of 2,2-dimethylpropane-1,3-diol succinate as the stationary liquid phase enables temperatures above 200 “C to be used without the risk of rapid “end-blooding.” As shown in Figs. 1 to 4, acid-stable DDT, its metabolites and unidentified peaks, which were probably due to co-extracts or artifacts, also appeared in the gas - liquid chromatograms.In this paper, however, only the gas - liquid chromatographic analytical problems with BHC isomers are considered. TABLE V REPEATED INVESTIGATIONS OF ALPHA-, BETA-, GAMMA- AND DELTA-BHC CONTENTS OF LIVER, ADIPOSE TISSUE AND WHOLE BLOOD SAMPLES I N ORDER TO COMPARE THE LYOPHILISATION AND PERCHLORIC ACID DIGESTION METHODS Gas - liquid chromatographic analysis with 2,2-dimethylpropane-1,3-diol succinate as the stationary liquid phase Sample Method alpha-BHC beta-BHC gamma-BHC delta-BHC Liver* Lyophilisation 0.0008 0.320 0.0052 0.0003 0.0009 0.340 0-0068 0.0003 0*0010 0.342 0.0060 O*OOO 25 0.00 12 0,334 0.0064 0*0003 0.0012 0.340 0.0058 0.0003 0~0010 0.330 0.0062 0.0003 0~0010 0.338 0.0068 0*0003 0.0260 7.16 0.124 0.0062 0,0265 7.84 0.142 0.0062 0.0300 7.30 0.134 0.0080 0.0284 7.42 0.120 0.0060 0.132 0.0042 0.0280 7.24 0.0320 7.46 0.1 10 0.0068 0.0250 7.32 0.118 0*0080 0.0264 7.38 0.138 0.0056 0.012 24.6 2.44 0.026 0.016 24.0 2.00 0.020 0-015 24.2 2.16 0.022 0.015 24.9 2-28 0.032 0.010 24.8 2.00 0.024 0.020 25.0 2.22 0.026 0.018 24.8 2-24 0.020 0.014 24-0 2.22 0.024 Perchloric acid digestion 0.00 10 0.328 0-0056 0~0002 Adipose Lyophilisation tissue? Perchloric acid digestion Whole Lyophilisation blood $ Perchloric acid digestion * Pesticide content expressed in p.p.m.t Pesticide content expressed in p.p.m., referred t o the total adipose tissue. 1 Pesticide content expressed in p g 1-l. We also used thin-layer chromatography as a complementary method. The thin-layer chromatograms alone, especially those for compounds with low RF values, such as beta- and delta-BHC, would not provide conclusive evidence of identification. However, proof of identity was provided by the four gas - liquid chromatographic columns, and corresponding evidence was obtained when spots with the same RF values as those of the reference substances, and with corresponding areas as expected, also appeared on the thin-layer chromatograms.The results of the representative runs given in Table VI do not include the results of preliminary experiments and ancillary investigations. Nevertheless, it is worth noting thatDecember, 19731 87 1 these other results fell within the range of the tabulated results for the representative runs, except for the blood used to compare the lyophilisation and perchloric acid digestion methods of preparation, which had a lower alpha-BHC content than the lowest alpha-BHC level recorded for the ten samples in the representative series.OF BHC I N HUMAN BLOOD, DEPOT FAT AND VARIOUS ORGANS TABLE VI PESTICIDE CONTENT (p,p.m.) IN VARIOUS ORGANS AND PURE DEPOT FAT OF HEALTHY PERSONS KILLED IN ACCIDENTS AND IN WHOLE BLOOD (pg I-') OF HEALTHY DONORS Mean values and ranges are given for ten determinations, except where stated otherwise. Gas - liquid chromatography with 2,2-dimethylpropane-2,3-diol succinate as the stationary liquid phase Mean fat content, Specimen per cent. Method Brain, frontal 3.68 Lyophili- sation Liver Perchloric acid digestion 4.67 Lyophili- sation Cerebellum 5.62 Kidney Gonads 6-24 1.64 Abdominal - depot fat Whole - blood? Perchloric acid digestion Lyophili- sation Perchloric acid digestion Lyophili- sation Perchloric acid digestion Lyophili- sation Perchloric acid digestion Lyophili- sation Lyophili- sation Value Mean Range Mean Range Mean Range Mean Range Mean Range Mean Range Mean Range Mean Range Mean* Range* Mean* Range* Mean Range Mean Range alpha-BHC 0~0010 0-0001 to 0.0034 o*ooo 73 0*0001 to 0.0029 0.001 39 0~0002 to 0.0033 0.001 30 0.0002 to 0.0029 0.002 22 0~0002 to 0.0057 0.002 27 0.0002 to 0.0060 0.001 85 0.0003 to 0.0043 0.001 67 0-0003 to 0-0042 0.000 78 0.000 03 to 0.0021 0.000 77 0.000 06 to 0.0018 0.041 0.009 to 0.086 0.334 0.06 to 0.80 beta-BHC 0.0512 0.0323 to 0.1060 0.051 86 0.0296 to 0.1114 0.3842 0.0620 to 0.7721 0.3308 0.0543 to 0.6412 0-106 10 0,0161 to 0.2985 0.068 60 0.0169 to 0.2870 0.297 73 0.0337 to 1.040 0.2784 0.0345 to 0.8563 0.172 37 0.0783 to 0.3910 0.166 08 0,0756 to 0.3801 9.39 3.56 to 16.3 25.9 16.0 to 36.0 gamma-BHC 0,005 79 0.0023 to 0-0234 0.006 71 0.0027 to 0.0248 0.005 32 0.0009 to 0-0223 0.0055 0.0006 to 0.0286 0.005 80 0.0008 to 0.0268 0,005 75 0.0007 to 0.0280 0.006 49 0.0017 to 0.0224 0.006 39 0.0017 to 0.0192 0.001 99 0*0009 to 0.0048 0.001 89 0.0006 to 0.0048 0-135 0.020 to 0-348 1.628 0.149 to delta-BHC 0.000 22 0.000 05 to 0.0005 0~000 21 0.000 05 to 0.0005 0-000 47 0~000 02 to 0.0015 0.000 40 0.000 02 to 0.0014 O*OOO 38 O*OOO 03 to 0*0020 0.000 50 0.000 03 to 0.0024 0.0006 0-000 02 to 0.0033 0.000 64 0.000 02 to 0.0036 0-000 144 0~000 02 to 0.0004 0.000 15 o*ooo 02 to 0*0004 0.008 0.001 to 0.034 0.104 0.0 (not 2.88 detectable) to 0.63 * Five determinations.t Results expressed in pg ml-l. In this study, the gas - liquid chromatographic analytical problems of the BHC isomers in biological materials were considered from the point of view of their satisfactory separation. However, we did not deal with the problem of the separation of other organochlorine com- pounds from the BHC isomers; these compounds have recently become important in the pollution of the environment, e.g., hexachlorobenzene, chlorine-containing plasticisers and polychlorobiphenyls. These compounds can appear as interferents in both thin-layer and gas - liquid chromatography. At present in Hungary, the presence of these compounds in the environment and in the general population does not cause any problems, as confirmed by other investigations. Nevertheless, if the presence of these compounds cannot be neglected872 CZEGLI~DI- J A N K ~ in the gas - liquid chromatographic separation of BHC isomers, one should remove such interfering materials, such as in pesticide residue analysis in the presence of polychlorobi- phenyls, as described by Reynolds,22 or in the investigation of the identity of hexachloro- benzene according to Zemann.23 The scope of the present study does not permit a statistical evaluation to be made of the results in terms of the sex and age of subjects. Also, it was not our aim to discuss the toxicological implications of the BHC isomers, to study the possibility of post mortem changes in BHC, mentioned by French and Jefferies,Z4 or to consider the problem of large amounts of beta-BHC. Our aim was simply to develop a method by which we could separate the BHC isomers from human biological materials with good reproducibility.The author expresses his thanks to Dr. Zsuzsanna Balla for making available the organ samples, Mr. A. Ho116 and Miss Zsuzsanna Pksztor for technical assistance and Mr. K. Krajcziir for lyophilisation of samples. This work was carried out in the State Institute of Hygiene, Budapest. 1. 2. 3. 4. 5. 6. 7 8 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22 23 24 REFERENCES Hayes, W. J., jun., Dale, W. E., and LeBreton, R., Nature, Lond., 1963, 199, 1189. Egan, H., Goulding, R., Roburn, J., and Tatton, J. O’G., BY. Med. J., 1965, 2, 66. Radomski, J . L., and Fiserova-Bergerova, V., Ind. Med. Surg., 1965, 34, 934. Dale, W. E., Curley, A., and Cueto, C., jun., Life Sci., 1966, 5, 47. Dale, W. E., Curley, A., and Hayes, W. J., jun., Ind. Med. Surg., 1967, 36, 275. DCnes, A., and TarjAn, R., Magy. Tudom. Akud. V . Osztdly Kozl., 1967, 18, 379. Engst, R., Knoll, R., and Nickel, B., Pharmazie, 1967, 22, 654. Abbott, D. C., Goulding, R., and Tatton, J. O’G., BY. Med. J., 1968, 3, 146. deVlieger, K. M., Robinson, J., Baldwin, M. K., Crabtree, A. N., and Dijk, M. C., Archs Envir. Curley, A., Copeland, M. F., and Kimbourgh, D. R., Ibid., 1968, 19, 628. Milby, T. H., Samuels, A. J., and Ottoboni, F., J . Occup. Med., 1968, 10, 584. Dacre, J. C., Proc. Univ. Otago Med. Sch., 1969, 47, 74. Kadis, V. W., Breitkreitz, W. E., and Jonasson, 0. J., Can. J . Publ. Hlth, 1970, 61, 413. Samuels, A. J., and Milby, T. H., J . Occup. Med., 1971, 13, 147. Radomski, J. L., Astolfi, E., Deichmann, W. B., and Rey, A. A., Toxic Appl. Pharmuc., 1971, CzeglCdi- Jank6, G., and Cieleszky, V., Analyst, 1968, 93, 445. Kovacs, M. F., J . Ass. 08. Analyt. Chem., 1950, 33, 130. Dale, W. E., Miles, J. W., and Gaines, T. B., Ibid., 1970, 53, 1287. Stanley, R. L., and LeFavoure, H. T., Ibid., 1965, 48, 666. Kadis, V. W., Jonasson, 0. J., and Breitkreitz, W. E., Can. J . Publ. Hlth, 1968, 39, 357. McClure, V. E., J . Chromut., 1972, 70, 168. Reynolds, L. M., Residue Rev., 1971, 34, 27. Zemann, A., Naturwissenschaften, 1971, 58, 276. French, H. C., and Jefferies, D. J., Nature, Lond., 1968, 219, 164. Hlth, 1968, 17, 759. 20, 186. Received July 29th, 1971 Amended June 18th, 1973 Accepted July 19th, 1973

ISSN:0003-2654    

DOI:10.1039/AN9739800863

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

Analyst, December, 1973, Vol. 98, pp. 873-885 873 Simultaneous Determination of Actinide Nuclides in Environmental Materials by Solvent Extraction and Alpha Spectrometry BY B. L. HAMPSON AND D. TENNANT (Ministry of Agriculture, Fisheries and Food, Fisheries Radiobiological Laboratory, Hamilton Dock, Lowestoft, Suflolk) Actinide analysis based on the selection of groups, instead of separation of individual elements, has been applied to monitoring and control of the increasing variety and amounts of actinide nuclides in environmental materials contaminated by controlled discharges of liquid wastes. Multi-element acti- nide analysis is achieved by extracting the whole group, or part of it, in the tri-n-octylphosphine oxide - n-heptane - nitric acid - sodium nitrate system, stripping into ammonium carbonate solution and electrodeposition, followed by solid-state alpha spectrometry, with unusual actinide nuclides as yield tracers. This system gives efficient separation from virtually all common elements. Common operations for the several functions of sample dissolution, tracer exchange, solvent extraction and electrodeposition have been developed, which are suitable for the group from actinium to curium.Detailed procedures, with variations, for simultaneous measurement of these actinides are stated, in order to allow application to biological materials and radioactive effluents in two combinations, the first in valency states 111, IV and VI, and the second in valency states IV and VI with valency state I11 eliminated. They have been fully evaluated for plutonium-239 $us -240 with plutonium-236 as tracer, and americium-241 with americium-243 as tracer, and the scope is indicated for other members of the group.Up to 2 kg of edible seaweed or 10 kg of fish flesh can be handled, with detection limits (in terms of activity to double background) of 2 x 10-6 and 4 x lo-7pCig-1, respectively, for a 1-week counting time. Sensitivities for precision with 4 per cent. standard deviation are 4 x lo-* and 8 x 10-5 pCi 8-1, respectively, which corresponds to levels associated with fallout. MEASUREMENT of actinide nuclides in environmental materials is becoming increasingly important as nuclear power programmes build up. Comprehensive actinide analysis is needed for control measures associated with the discharge of these radionuclides in liquid effluents, and also for radio-ecological research. The artificial nuclides of most concern are 238Pu, 239Pu, 240Pu, 241Am and 242Cm, although others, for example, 237Np, may occur.Members of the thorium and uranium series, which are constituents of the natural background, are conveniently measured at the same time. The range of sensitivity required varies from derived working limits in marine foodstuffs (typically of the order of lo2 pCi g-l) down to levels associated with natural activities or fallout (as low as In hazard assessment, all actinide nuclides should be detected and measured simul- taneously. The aim with most current chemical methods is to separate individual actinides, although with some several are separated sequentially, e.g. , by fractional elution from solid1 or liquid2 ion exchangers, followed by total alpha counting.Yield tracers have previously been used only in exceptional instances, e.g., 236Pu, so as to assess the recovery3 of 239+240Pu; their universal adoption is essential. Alpha spectrometry has been used in two ways for collective measurement of actinides in environmental materials, namely, with the Mayneord- Hill large-volume gridded ionisation chamber,4 and co-precipitation with barium sulphate com- bined with solid-state alpha spectrometry.5,6 However, the sensitivity of these methods (detector limits of about 0.1 pCi per g of ash) is insufficient for the materials mentioned above, because only small samples can be handled (in the latter method calcium, aluminium, etc.interfere). The present method combines highly selective actinide group separation with sensitive alpha spectrometry, by using yield tracers throughout , and sensitivity is increased at least 103 times. pCi g-l). @ SAC; Crown Copyright Reserved.874 HAMPSON AND TENNANT : SIMULTANEOUS DETERMINATION OF [Analyst, VOl. 98 A review of actinide separation indicates that neutral rather than ionic extractants are best suited to actinide group selectivity. Separation of all actinides together in a single operation cannot be achieved by ion exchange as both cation and anion exchange are required, with widely varying conditions for different actinides. The actinides are particularly prone to form strong ion-association complexes with neutral organophosphorus extractants, with reaction mechanisms not directly dependent on hydrogen-ion concentration (a main cause of differentiation with ionic extractants), and broad ranges of conditions are available for separation of actinides of valency states 111, IV and VI, or of sub-groups from almost all other elements under common conditions.The actinide selectivity derives from combination with the strongly nucleophilic phosphoryl 0 atom whose basicity is dependent on substituents, and is most highly developed in the c8 to C,, straight-chain trialkylphosphine oxides in similar hydrocarbon diluents. Electrostatic-type binding occurs with the actinide ion acting as a “hard” Lewis acid, and simultaneously n-bonding due to the actinide inner transition d orbitals. With the comparable nucleophilic amines, of which the tertiary and quaternary amines are the most potent, the latter effect is prevented.Of the many neutral extractants tri-n-octylphosphine oxide (TOPO) gives the highest extraction coefficients for americium(II1) ,7 c~rium(III),~ plutonium(IV)s and uranium(V1) .8 Of the TOPO - nitric, hydrochloric and sulphuric acid systems the nitric acid systems are the best c h ~ i c e , ~ as they give the most efficient extraction and separation of actinides from other elements. Nitric acid systems are also the most satisfactory for the best extraction of most actinides from quaternary amines, although not always from tertiary amines. However, in all instances, the use of nitric acid systems is necessary for effective separation from iron(II1) and other matrix elements.TOPO gives higher extraction efficiency for actinides of valency states 111, IV and VI, which is much higher for tervalent actinides, than the optimum tertiary and quaternary amines, and better separation from iron(II1); in fact, it gives effective separation from all significant biological matrix elements. EXPERIMENTAL Because of the separate demands of spectral resolution and sensitivity, the actinides must be extracted together, with high distribution coefficients for effective volume reduction and high separation factors from matrix elements so as to provide thin sources from massive samples. Some of the separation factors from individual interfering elements need to be very high, e.g. 107 for iron, and the over-all factor lo6 or more.Actinide valencies vary with redox conditions in such a way that in order to deal with the group from actinium to curium under common conditions it is necessary to separate actinides in a t least the 111, IV and VI valency states together. The behaviour of the bivalent oxy-cations is often intermediate between that of the ter- and quadrivalent cations. Most of the lighter common elements of valency I, I1 and I11 will be present in the matrix, but lanthanides and elements of higher valency, e.g., titanium, zirconium and niobium, can generally be ignored. The central issue is to obtain adequate separation between tervalent actinides and tervalent iron and aluminium, which tend to overlap in a scheme in which the elements of high valency are separated from the remaining elements.Sample dissolution, chemical exchange between sample nuclides and yield tracer nuclides, pre-concentration of actinides from bulky samples and removal of silica, solvent extraction and stripping and electrodeposition must each be carried out by successive processes that are commonly valid for all actinides. Uncommon nuclides used as tracers include 236Pu, 243Am and others (see under Scope). Actinides may co-exist in several valency states including both simple and oxygenated ions, which hinder free interchange with tracers. Some, for example, plutonium(IV), which are intimately bound to the insoluble fraction of ash from biological material,l* may be in polymeric or refractory form. Complete dissolution and tracer exchange are ensured by first reducing all actinides to the lowest states that can exist in aqueous solution, followed by re-oxidation.Boiling hydrochloric acid complexes most actinides well and was chosen in preference to nitric acid or nitric - hydrofluoric acid mixture+ for leaching the main salts and reducing the ferri-manganese component of ash from biological material. For reduction ascorbic acid was preferred to magnesium and agents of comparable potential,12 as its action is prolonged and the products are eliminated in the subsequent oxidation. Direct conversion Extraction with TOPO meets the above requirements.December, 19731 ACTINIDE NUCLIDES IN ENVIRONMENTAL MATERIALS 875 of plutonium and neptunium into valency IV,13 and uranium into valency VI by the nitrite - nitrate systems,14 leaving americium and curium in the tervalent state, was satisfactory, and gave results that were similar to those obtained by preliminary oxidation of uranium, nep- tunium, plutonium and americium to valency VI with silver peroxide and persulphate.12 The nitrite - nitrate stabilisation was preceded by hydrogen peroxide treatment so as to prevent formation of nitroso compounds of iron(I1) ; it also brings plutonium and neptunium to valency IV.Pre-concentration of the actinides from large samples of ash from biological material disposes of the bulk salts, and so simplifies the removal of silica; if left, these salts would form insoluble fluorides that carry actinides, and would interfere during extraction by com- plexing action and precipitation, as would phosphates.Sensitivity is improved by selective separation of tervalent actinides from iron at this stage. After the initial equilibration, two quantitative co-precipitations (to combine the actinides from the soluble and siliceous frac- tions) were adopted in order to suit the two variants of the procedure, according to whether tervalent actinides were included or excluded. With the latter the pH was raised to about 2 to permit the formation of a small amount of iron(II1) phosphate precipitate, which carried plutonium(1V) quantitatively but was unsuitable for tervalent actinides, because their phosphates precipitate at higher pH than the corresponding iron compounds. With the former at pH 1.5, oxalate carried all actinides without phosphate precipitation, kept iron complexed in solution, and was subsequently destroyed by nitric acid. Complete elimination of silica ensures the release of bound actinides and prevents their removal by colloid formation during the subsequent extraction.The hydrofluoric acid digest is evaporated with nitric acid in order to minimise the level of fluoride and the residue dissolved in nitric acid - boric acid mixture so as to complex any remaining fluoride before repeating the treatments with ascorbic acid and nitrite in order to effect exchange and stabilisation of valency state. CONDITIONS FOR ACTINIDE EXTRACTION WITH THE TOPO - NITRIC ACID SYSTEM- Distribution coefficients for actinides and matrix elements in this system are influenced by several factors, nitric acid concentration, the nature of the cation, the total nitrate-ion concentration, the TOPO concentration and nature of the diluent being the most important.By choosing appropriate conditions, separation procedures can be devised to meet particular needs in respect of actinide selection and matrix element rejection, For the present purpose two selections have been made: (1) all actinides together with valency states adjusted to 111, IV and VI, and (2) actinides of valency states IV and VI with I11 eliminated. The latter combination is needed so as to discriminate between plutonium-238 and americium-241, whose spectra could not be resolved from a mixture. The conditions chosen for full actinide group selection were 0-4 M nitric acid - 4 M sodium nitrate for biological materials or 0-2 M nitric acid - 4 M sodium nitrate for effluents, with an organic phase of 0.5 M TOPO in n-heptane. For actinides of valency states IV and VI with I11 eliminated the phases were 2 M nitric acid and 0.1 M TOPO in n-heptane.The first system gives distribution coefficients of lo2 to lo3 for actinides of valency state I11 and much higher values for actinides of valency states IV and VI, while the latter gives distribution coefficients of about for americium(III), curium(III), etc., but more than lo2 for plutonium(1V) and plutonium(VI), and other actinides of higher valency. Matrix element distribution coefficients range from to Amounts of transition elements, iron, etc., are easily reduced to less than 1 pg so as to prevent inter- ference with electrodeposition.There is a large margin of separation after prior elimination of most of the iron, etc., from large biological samples (100 g to 10 kg) by preliminary co-precipitation, especially in the presence of oxalate. STRIPPING OF ACTINIDES FROM TOPO SOLUTION, AND SOURCE PREPARATION BY ELECTRO- The actinides must be stripped from the TOPO prior to electrodeposition, preferably into a solution that can serve directly as the electrolyte. The two stripping agents that best satisfy the dual criteria are ammonium oxalate and ammonium carbonate. The oxalate complexes of actinides of valency states 111, IV and VI are much stronger than the TOPO binding, and they can be stripped into a small volume for plating. Carbonate complexes are even stronger, and this ligand was adopted for stripping; it was also more suitable for DEPOSITION-876 HAMPSON AND TENNANT: SIMULTANEOUS DETERMINATION OF [AnabSt, VOl.98 electrodeposition as oxalate15 could be destroyed easily only if chloride was added to generate chlorine electrolytically. (The platinum anode was attacked by chlorine and deposited on the cathode, thus degrading the source.) Formate is another effective electrolyte for all the actinides, is easily destroyed without using chlorine, but is not a good stripping agent from TOP0 for all the valency states. Electrodeposition could follow slight acidification of the ammonium carbonate stripping solution with nitric acid, because all actinides then migrate to the cathode. However, ammonium formate was usually added as an additional complexing agent for electrodeposition so as to destroy any excess of nitric acid, which can otherwise degrade the source during prolonged electrolysis.INSTRUMENTATION- The alpha spectrometer was developed so as to have sufficient stability to maintain a constant resolution of 35 keV or better over yearly or longer periods. Drift was limited to h3.5 keV in the 5-MeV region over counting periods of 10 000 minutes. It consisted of silicon surface barrier detectors, a charge-sensitive transistorised pre-amplifier with field-eff ect transistor input stage, and Intertechnique 400 channel pulse-height analyser (SA 40B) or Northern Scientific 256 channel (NS 601). Source - detector distance was controlled by using an adjustable source mount holder based on a 1-mm pitch screw.The vacuum chamber (Fig. 1) was redesignedl6 for continuous operation over long periods. The instrument was maintained at 20 & 0.5 "C, and provided with smoothed stable power supplies. The system gave a resolution of 14 keV with 25-mm2 detectors, with an americium-241 source, and noise determined with a mercury pulser was less than 5 keV. The empirical relationship (Fig. 2) between counting efficiency and resolution was evalu- ated for detectors of various sizes (for example, 100-mm2 Ortec A series and 300-mm2 20th Century Electronics) with various source - detector spacings, as both are functions of the solid angle subtended. Detectors that gave the highest efficiency for a specified limiting resolution were chosen; the larger detectors are not necessarily the most suitable, particularly when low background is required.A C E 0 1 2 inches 0 1 2 3 4 5 cm A= Glass feed-through B=Signal feed-through C=lnsulator D = O-ring E= Spring-loaded brass finger for applying potential to sample F = Detector G =Copper face H =Acrylic sample holder J =Threaded support K=Toggle clamp Fig. 1. Section of detector chamberDecember, 19731 ACTINIDE NUCLIDES IN ENVIRONMENTAL MATERIALS 877 ANALYSIS OF SPECTRA- Alpha spectra from environmental materials containing several artificial and natural nuclides are complex, and individual peaks are not always completely resolved. Spectra from individual nuclides are typically band spectra, with about 95 per cent. of the emission from two or three major lines within about 40 keV, and more than 70 per cent.of it from the primary line. Two types of interference occur, that from partial overlapping of the main bands from two or more nuclides, and that from the low-energy continua of scattered radiation from higher-energy nuclides. There is also broadening due to incomplete instru- mental resolution. Of the several unscrambling methods applicable to gamma spectrometry,17 simultaneous matrix solution was best suited to alpha spectrometry, and is capable of correcting both types of interference simultaneously . r 50 - 40 - 10 20mm , I I 0 5 10 15 Counting efficiency, per cent. Fig. 2. Relationship between reso- lution and efficiency for detectors of varying diameter. Marked distance on point denotes source - detector spacing : A, 300-mm2 detector; B, 100-mma detec- tor; and C, 25-mm2 detector Instrumental resolution remained constant at 30 to 35 keV (full width at half maximum; F.W.H.M.) and long-term stability was controlled at several points in the range to &0.5 channel (7 keV per channel).This arrangement did not cause significant broadening of the nuclide emission bands, and enabled routine analysis to be carried out with once-for-all calibration. In order to analyse spectra by the simultaneous matrix method, characteristic channel groups (equivalent to energy bands) are selected for each nuclide. The spectra of pure sources of each nuclide are first recorded over the entire energy range covered by all the nuclides. By comparing these spectra, nuclide channel groups are chosen; they are spaced so as to maximise the counts from that nuclide, and rninimise the counts from others, taking into account the expected activity ratios (e.g., 10: 1).Interference must not be a major component of any peak. The counts are expressed as rates in each channel group, norrnalised to unity in the characteristic channel group of each particular nuclide, and represented as a matrix. For example, for nuclides A, B, C, and characteristic channel groups a, b, c : where K is the response of pure nuclide in each channel group, X is the unknown sample count-rate of each nuclide in the channel group and M is the measured count-rate of the sample in the channel group.878 HAMPSON AND TENNANT : SIMULTANEOUS DETERMINATION OF [Analyst, VOl. 98 The inverse matrix is then obtained: (Z) = (1;: : :::) x (5) kca kc, kcc where k is the nuclide factor in each channel group. The elements of the inverse matrix are then used as parameters in order to evaluate the digitally recorded spectra from the sample sources ; for example, xA = kAa MA + kAb M B + kAc MC The degree of interference depends on the proximity of the primary emission lines of the nuclides, and also on which side of these lines the secondary lines occur (i.e., whether on the same or opposite sides of the primary lines).The extent of interference indicates the practical performance of matrix analysis in particular instances of closely spaced nuclides. However, in general, interference is only a minor fraction of peaks spaced more than 70 keV apart at a peak height ratio of 10: 1, and is readily corrected (see below).But when the primary lines differ by less than 40 keV the spectra cannot be resolved. In these situations it is necessary to distinguish between the nuclides by chemical means. RESULTS Although the method is generally applicable to actinides the two procedures discussed below have been particularly tested for plutonium-238, plutonium-239 plus -240, and americ- ium-241, the most common actinides arising in controlled discharges. Some of the results that indicate their validity are given here. SPECTRAL INTERFERENCE : ASSESSMENT AND CONTROL OF ERRORS THAT ARISE- procedures A and B (see under Methods). (F.W.H.M.). The spectra shown in Fig. 3 (a), ( b ) and (c) are typical of those obtained by using Resolution in all instances is 30 to 35 keV An evaluation of the major interferences is shown in Table I for the particular I ( c ) 23"u 1 Alpha energy/NleV Fig.3. Alpha spectra of actinides: (a), separated from 10 ml of nuclear power station cooling pond effluent by procedure A; ( b ) , separated from 5 g of Porfihyra ash from Sellafield, Cumberland, by procedure A; and (c), separated from 75 g of Porphyra ash from Bude, Cornwall, by procedure BDecember, 19731 ACTINIDE NUCLIDES IN ENVIRONMENTAL MATERIALS 879 measurement of plutonium-239 and americium-241, with plutonium-236 and americium-243 as yield tracers, in materials that have curium-242 as the only other important alpha-emitter. Interference between pairs may be up to 36 per cent. for ten-fold activity ratios, but errors after matrix correction are about twenty times less because each correction has been esti- mated to be 3 2 to 5 per cent. The greatest neighbouring-pair interference is normally between plutonium-239 plus -240 and americium-243, for which diverse ratios can be avoided by judicious spiking.TABLE I SPECTRAL INTERFERENCE BETWEEN NEIGHBOURING PAIRS IN THE MEASUREMENT OF PLUTONIUM AND AMERICIUM NUCLIDES 230+240pu 243Am 241Am 23Spu 242Cm 238pu Energy band for 95 per cent. emission 5.099 to 5.224 to 5.433 to 5.717 to 6-066 to 5.452 to Energy gap between neighbouring 74 167 240 303 Energy band chosen/MeV 5-04 to 5-21 to 5.39 to 5.64 to 5.99 to 5-17 5-31 5.53 5-80 6.13 Width of energy band/keV 130 100 140 160 140 6.110 5.495 - - - - - with primary line underlined/MeV 5.150 5.266 5.476 5.763 primary or secondary lines/keV Energy gap between neighbouring 40 80 110 190 Emission appearing in neighbouring - 0-7 0.4 3.3* -0.1 Emission appearing in neighbouring 0.01 0.06 0.02 0.02 - Estimated maximum individual 7.4 3.7 32.7 1 channel blocks/keV nuclide band below, per cent.nuclide band above, per cent. interference component for ten-fold activity ratio, per cent. - * Includes typical component of 238Pu impurity in 236Pu tracer. Accuracy of measurement of americium-241 and plutonium-238 by the joint use of procedures A and B depends on the decontamination from americium by procedure B. Current ratios of plutonium-238 to plutonium-239 PZus -240 in discharges are typically 0.1 to 0-2, while the ratio of americium-241 to plutonium-238 may vary from less than 1 to 100.Minimum decontamination factors needed to guarantee an error of less than 1 per cent. are 104 for americium-241 and 105 for plutonium-238 measurement, with the “difference” method inapplicable at an americium-241 to plutonium-238 ratio of less than 0.1. A decontamination factor of lo6 was achieved, and was established by adding known amounts of americium-241 prior to analysis. Curium decontamination is probably similar, and will prevent further ingrowth of plutonium-238 from curium-242. PRECISION OF MEASUREMENT BY PROCEDURES A AND B- Precision by the two procedures (Table 11) was estimated by using samples of the seaweed Porphyra from the Cumberland coast with various concentrations of radionuclides and in- soluble components. Counting statistics were 3 per cent.(standard deviation) for individual nuclide activities, equivalent to 4 per cent. (standard deviation) for nuclide and tracer together. The estimate of 6 to 8 per cent. over-all precision, including all errors for the more silty samples, gives confidence with less exacting biological materials, e.g., fish tissues. When plutonium alone is required procedure B should be used because of its precision and simpler operation. ACCURACY OF MEASUREMENT O F PLUTONIUM-239 PlUS -240 AND AMERICIUM-241 BY PROCEDURES A AND B- The critical processes in which bias of plutonium results might occur are dissolution and exchange. Different modifications of procedures A and B were compared and are referred to in Table I11 as methods Al, A2, B1, B2, C2 and D2. Two reducing agents were investigated, metallic magnesium, a very rapid reductant for plutonium,12 and ascorbic acid, which is effective with insoluble iron compounds and man-880 HAMPSON AND TENNANT : SIMULTANEOUS DETERMINATION OF [AndySi!, VOl.98 TABLE I1 PRECISION OF 239+240PU AND 241AM MEASUREMENTS IN POYphyYU TAKEN FROM THE CUMBERLAND COAST BY PROCEDURES A AND B 23s+240pu =*lArn Sample No. 1 1 2 3 3 4 5 6 7 8 Mean . . Mean .. CoefficieI;t of Mean/ variation, Procedure minations pCi g-1 per cent. pCi g-l per cent. Number I n t of of deter- Mean/ variation, A B A A B B B B B B A B 10 2 5 4 2 3 3 2 2 2 19 16 0.530 0.567 0- 194 0-899 0.960 0.260 0-181 0.104 0.040 0.022 * 23sPu corrections applied, based on determination by procedure B. ganese(1V) oxide. Both hydrochloric and nitric acids were tested; the former is the better reducing medium, although nitric acid is completely effective in conjunction with nitrite for interchange and stabilisation of plutonium in the quadrivalent ~ t a t e .1 ~ Combinations of these reagents, also various acid concentrations, were tried out on a range of Porphyra samples. Results in Table I11 are expressed in relation to the highest plutonium-239 plus -240 content, corresponding to the most complete release and exchange with tracers. The lowest recoveries occurred when 1 M acid was used, probably resulting from losses by hydrolysis. Otherwise the range, of about &6 per cent., showed that, provided the acid concentration is maintained at 2 M, both reducing agents are equally effective. Nitric acid, however, provided better conditions for subsequent re-oxidation. Sodium carbonate fusion applied to the insoluble matter from a silty ferruginous Porphyra sample after the primary dissolution - exchange stage, but before hydrofluoric acid treatment, released no additional plutonium-239 PLUS -240, indicating that total extraction had already been achieved.Tests on the co-precipitation step by equilibrating the acid-soluble fraction with the nuclides used for spiking showed the precipitation to be complete. The phosphate precipita- tion of procedure B was not in doubt because plutonium is quadrivalent and the pH of the solution is relatively high. The oxalate precipitation of procedure A for both plutonium and americium (Table IV) was found to be virtually complete in a single stage but a second precipitation was included as a safety precaution.An estimate of accuracy by comparing the sum of plutonium and americium present with that of total alpha-activity, making allowance for minor alpha-emitters, was made on Cumberland Porphyra (Table V) in which samples 9 to 12 are bulked from nine locations for average matrix composition. Total alpha-activity was measured with 200 mg of ash (less than 22 pm particle diameter) spread over a 200-cm2 source area, by using a Beckman proportional alpha counter with adequate discrimination against beta- and gamma-radiation. Measurements of uranium, thorium (and daughter products) polonium, neptunium and curium TABLE I11 EXCHANGE OF ENVIRONMENTAL PLUTONIUM IN Porphyra ASH WITH 236Pu TRACER Number of Method Solution conditions samples tested Bias * A1 Mgo - 1 M HNO, 6 0.817 B1 Mgo - 1 M HC1 6 0.774 B2 MgO - 2 M HC1 5 0.927 c 2 Ascorbic acid - 2 M HNO, 5 0.965 D2 Ascorbic acid - 2 M HC1 5 0-885 * Degree of incomplete exchange in relation to method A2 taken as 1.A2 Mgo - 2 M HNO, 5 1.000December, 19731 ACTINIDE NUCLIDES IN ENVIRONMENTAL MATERIALS 881 nuclides on occasional samples of Porphyra from the area indicate that the sum of such activities corresponds approximately to the mean “unaccounted” activities in Table V. Thus errors caused by bias are not serious. TABLE IV COMPLETENESS OF PRECIPITATION OF PLUTONIUM AND AMERICIUM AS OXALATES FROM SOLUTIONS OF SEAWEED ASH AT pH 1.5 Recovery as percentage of total nuclide recovered each with 200 mg of oxalic acid 23sPu z43Am First 95.7 98.1 Second 2-92 1-34 Third 1.34 0.54 Consecutive co-precipitations, r- For effluents, curium-242 was also measured as a major nuclide.Its recovery was calculated from the americium-243 spike, as a curium tracer was not then available. The mean results are shown in Table VI and involved variants of acidic media and redox agents in the dissolution - exchange operation, but showed only small differences, the conditions giving the highest activity values being those given in the procedure. Small differences between methods imply that the dissolution - exchange stage is efficient. Two other variants were tested. In one, with the redox cycle omitted, results varied widely; in the other 1 0 ~ nitric acid - 0.1 M hydrofluoric acid mixture was used for the pre-exchange leaching of actinides from insoluble matter, as recommended by other workers.18 Results were invariably low, indicating that actinides are not completely available under these conditions : they must be leached and equilibrated before the introduction of hydrofluoric acid.Total alpha measure- ments on effluents were made from thin evaporated sources with a zinc sulphide alpha scintillation counter gated not to register beta- and gamma-radiation and calibrated with a similar standardised source. The comparison of the sum of plutonium-239 PZNS -240, americium-241 and curium-242 with total alpha-activity (Table VI) shows only a small discrepancy accountable to uranium, neptunium and other nuclides noted in the spectra, and indicated accuracy to within a 10 per cent.limit. TABLE V MEASUREMENT OF PLUTONIUM , AMERICIUM AND TOTAL ALPHA-ACTIVITY IN Porphyra Sample No. 9 10 11 12 13 14 0.75 1-16 0.86 0.74 0.60 1.07 z3spu - 2 4 1 ~ ~ / pCi 8-l 0-72 1.77 0.87 0.81 0.32 0.46 Mean .. * . 238+239+240pu - 24lAm/ pCi 8-1 1.47 2.93 1-73 1-55 0.92 1.53 1.69 Total alpha- activitylpci g-’ 1.37 4.11 1.96 1.40 1.93 1.82 2.10 SCOPE- The method is applicable to all the actinides except the quinquivalent oxy-cations, and, by maintaining all in one of the other states, most of them up to curium have been measured. Convenient nuclides for spiking include actinium-225 , thorium-229 , uranium-233, neptun- i~m-235,~~ plutonium-236 ,19 americium-243 and curium-244. On occasions when energies conflict alternatives can sometimes be used; otherwise differential extraction procedures are readily developed.Successful application to natural waters had been made after suitable pre-concentration. SENSITIVITY- Attainable sensitivity depends on sample size, extent of chemical recovery and counting efficiency. Amounts of seaweed samples up to 2 kg, and of fish flesh up to 10 kg, have been handled. Chemical recoveries are virtually 100 per cent. at the precipitation stages and882 HAMPSON AND TENNANT: SIMULTANEOUS DETERMINATION OF [Analyst, VOl. 98 75 to 90 per cent. at the solvent-extraction and electrodeposition stages, with more than 50 per cent. overall. In this work 300-mm2 detectors with 25 to 30 keV (F.W.H.M.) nominal alpha energy resolution were used. With the 10 mm diameter sources, discrimination factors were chosen equal to 12 per cent.of 47r geometry (Table I). With counting periods up to 1 week, ultimate sensitivity relative to a standard deviation on counting of 4 per cent. is 4 x pCi g-l for the 10-kg samples. Nominal detec- tion limits, in terms of the activity to double background, are 2 x and pCi g-l, respectively. Sensitivity for measurements of plutonium-239 and americium-241 to 4 per cent. (stan- dard deviation) precision when using 100-g samples of foodstuffs and counting for 100 minutes is about 0.8 pCi g-l. Measurements on marine foodstuffs, fish flesh or Porphyra, can thus be made at concentrations of about 1 per cent. of the derived working limits for consumption by the general public.20 Actual concentrations in individual Cumberland Porphyra samples are currently 0.001 to 5 pCi g-l, and about 0.005 pCi g1 in fish flesh from the vicinity of the Windscale outfall.Up to l-kg samples are needed for 4 per cent. precision in 24-hour counts. The fallout concentration in seaweed estimated at 2 to 5 x 10-4pCig-1 can be measured with 4 per cent. (standard deviation) precision with a 2-kg sample in 1 to 2 weeks’ counting time, although in fish, about In conclusion, actinide analysis by solvent extraction and solid-state alpha spectrometry is sufficiently selective and accurate for control of actinides in foodstuffs, and for surveillance of their spread in aquatic organisms. TABLE VI MEASUREMENT OF MAJOR INDIVIDUAL ALPHA-EMITTERS IN EFFLUENTS, AND COMPARISON (MEAN OF THREE DETERMINATIONS) pCi g-l for the 2 kg and 8 x pCi g1 can be detected with lower precision.O F THEIR SUM WITH TOTAL ALPHA-ACTIVITY MEASUREMENTS Effluent No. 1 2 3 4 5 6 Mean . . 2 3 9 + 2 4 O P ~ - pCi ml-l per cent. 1.46 4.2 0.217 12.2 0.825 13-4 0.605 20.7 0.893 12.8 0.361 12.9 12-7 Coefficient Mean/ of variation, 238pu - 241Am f - - ~ - - - - - ? Coefficient Mean/ of variation, pCi ml-l per cent. 0.855 1.2 0.1 13 6.7 0.531 12.9 0.406 21.7 0.605 9.9 0.242 8.2 10.1 249Cm, single Sum of determina- 23*+239+240Pu, tions/ 2r1Am and 2a2Cm/ pCi ml-1 pCi ml-l 4-12 6.43 0.443 0.773 2-10 3.46 1.66 2-67 2.5 1 4.0 1 0.870 1-47 3.14 Total alpha-activity/ pCi ml-1 6.17 1.26 4.20 2.73 5.42 1.40 3-46 METHODS Two types of procedure for group selection of actinides of valency states 111, IV and VI, and for sub-group selection of actinides of valency states IV and VI with I11 eliminated, have been developed for application to biological materials and effluents.Most of the details of the four routines are similar, and that for actinides with valencies 111, IV and VI in biological materials is stated in full. The points of difference in the other procedure, and in the sub-routines then follow. REAGENTS- Plutonium-236 solution in 2 M hydrochloric acid. Americium-243 solution in 2 M hydrochloric acid. Tri-n-octylphosphzine oxide. n-Heptane. PROCEDURE A FOR THE SEPARATION OF PLUTONIUM, AMERICIUM AND OTHER ACTINIDES TOGETHER AS A GROUP FROM BIOLOGICAL MATERIALS- Sample dissolution and exchange of actinides with tracers-Weigh 5 g* of carbon-free ash * For amounts of sample larger than 5 g (up to 100 g) the amounts of reagents used should be varied in proportion.December, 19731 ACTINIDE NUCLIDES IN ENVIRONMENTAL MATERIALS 883 into a centrifuge tube and spike it with standardised solutions of suitable nuclides, pluton- ium-236, americium-243 and others as required (see under Scope).Boil the mixture for 5 minutes with 40ml of 4111 hydrochloric acid, cool and dilute to 80ml. Add 500mg of ascorbic acid and leave the solution for 5 minutes in the cold, then heat it. After cooling, add 1 ml of 30 per cent. hydrogen peroxide solution, and then dissolve 10 g of sodium nitrate and 1 g of sodium nitrite in the solution. Allow it to stand for 5 minutes, then heat it. Adjust the pH of the solution to 1.5 with ammonia solution, then add 4 ml of 5 per cent.oxalic acid solution, and leave the mixture to stand until a precipitate forms. Collect the precipitate, together with acid-insoluble matter, by spinning it in a centrifuge. Repeat the precipitation with a further 4 ml of oxalic acid solution. Combine the precipitates, and wash them with 50 ml of 2 per cent. ammonium oxalate solution. Transfer the combined precipitates into a 50-ml capped PTFE centrifuge tube with 20 ml of 16 M nitric acid. Add 20 ml of hydrofluoric acid (70 per cent. m/m if a pure grade is available) and digest the mixture at 100 "C so as to dissolve all siliceous matter. Transfer the solution, in portions, to a platinum crucible and evaporate it under radiant heat. Complete the transfer with nitric acid so as to ensure dissolution of all fluorides, etc.Evaporate just to dryness two or three times with mixed nitric and hydrofluoric acids, and then two or three times with nitric acid. Dissolve the dry residue in 20 ml of 0.4 M nitric acid that is half-saturated with boric acid. (A larger volume may be needed if much acid-insoluble matter was originally present. This volume should be kept small, but without approaching the solubility limit). Treat a 20-ml volume of the solution with 50 mg of ascorbic acid, or larger volumes with 100 mg, for 5 minutes. Make the solution 4 M in sodium nitrate. Treat it for 5 minutes with 150 mg of sodium nitrite for a 20-ml volume, or 300 mg for larger volumes. Centrifuge or filter the solution if it is not absolutely clear. Extraction with TOPO and stri$$ing-Decant 10 ml of freshly prepared 0.5 M solution of TOPO in n-heptane into a separating funnel, and purify it by washing it in turn with 5 per cent.sodium carbonate solution, 2 M nitric acid (three times) and 0.2 M nitric acid - 4 M sodium nitrate solution. Shake the aqueous phase prepared from the sample with the purified TOPO solution for 5 minutes. After separating the phases, scrub the TOPO solution three times with 10 ml of 0.2 M nitric acid - 4 M sodium nitrate solution for 5 minutes each time. Strip the actinides by shaking the TOPO solution three times, each for 5 minutes, with 3ml of 10 per cent. ammonium carbonate solution. Wash the combined aqueous phases once for 1 minute with 10 ml of n-heptane and transfer them to a plating cell.ELECTRODEPOSITION- Prepare a disposable plating cell, which can be made from the cut-off top and screw-cap of a polythene bottle (e.g., hydrofluoric acid type). Degrease a polished stainless-steel disc, 27 mm in diameter and 22 s.w.g. (0.711 mm) thick, in trichloroethylene, and mount it as the cathode, with a polythene gasket to expose a central 8 mm diameter area for a 10-mm detector, or 1Omm diameter area for a 20-mm detector. Complete the cell with a loop of 0-040-inch (1-mm) thick platinum wire to serve as the anode, inserted through a polythene foil cover. Acidify the stripping solution in the cell to pH below 2 with 16 M nitric acid, by using wide-range indicator paper in order to ensure that the excess of acid does not exceed one drop.Add 1 ml of 40 per cent. ammonium formate solution and electrolyse the solution at 3.5 mA mm-2 for 8 to 16 hours. The pH of the final bulk solution should be above 10. On dismantling the cell rinse the disc rapidly with methanol and dry it. A good source will be almost invisible. MEASUREMENT AND ANALYSIS OF THE ALPHA SPECTRA- Set the spectrometer to the required alpha energy range by using a multi-nuclide source. Make regular checks for spectral resolution, linearity and drift so as to ensure that all sources are counted on exactly the same channel settings. Calibrate with an absolutely standardised source that is similar to the sample sources (obtainable from the Radiochemical Centre Ltd., Amersham). Count a set of individual sources of all alpha nuclides in the samples and tracers,884 HAMPSON AND TENNANT: SIMULTANEOUS DETERMINATION OF [Analyst, Vol.98 by using the actual batches of the latter to correct automatically for impurities. Prepare and invert a matrix based on chosen channel groupings so as to correct for spectral inter- ference arising from all the nuclides present. For close pairs check that acceptable error limits will not be exceeded. Count the sample sources to acceptable statistics, allowing for count-rates of required and tracer nuclides, and measure background between batches. Calculate the results by detecting background effect and calculating the activity due to each nuclide, by using the inverse matrix and the absolute calibration. Correct for yields on the basis of measured tracer recoveries.For samples containing both plutonium-238 and americium-241, measure the pluton- ium-238 (and plutonium-239 plus -240) by procedure B, spiking with plutonium-236. Obtain the americium-241 (and also plutonium-239 plus -240) by procedure A, spiking with americ- ium-243 and plutonium-236. Correction for plutonium-238 has to be made from its measure- ment by procedure B because it cannot be resolved from americium-241. In a batch of samples in which the 238Pu to 239+240P~ ratio is found to be constant, this ratio may be inserted into the matrix and the americium441 then measured by procedure A. PROCEDURE B FOR THE SEPARATION OF PLUTONIUM AND OTHER QUADRI- AND SEXAVALENT ACTINIDES, WITH ELIMINATION OF AMERICIUM AND OTHER TERVALENT ACTINIDES , FROM BIOLOGICAL MATERIALS- Sample dissolution and exchange of actinides with tracers-Carry out the spiking, leaching and chemical exchange stages as above, by using samples of any size up to 1OOg of ash.Neutralise the resulting solution with ammonia solution until an amount of precipitate of 100 to 200 mg forms on top of any acid-insoluble matter. Allow to stand so as to enable the precipitate to coagulate and collect it by spinning the mixture in a centrifuge. Wash the precipitate with 50 ml of 2 per cent. ammonium nitrate solution made slightly alkaline with ammonia solution. Dissolve the dry residue con- tained in a platinum crucible in 10 ml of 2 M nitric acid half-saturated with boric acid. A larger volume may be needed if much acid-insoluble matter was present originally.Carry out the reduction and re-oxidation as described above, by using the amounts of reagents given for solution volumes of less than and more than 20 ml, respectively. Extraction into TOP0 and stripping-Prepare the 0.1 M TOPO phase as above, but use only 2~ nitric acid for the final wash. Shake the aqueous phase prepared from the sample with the purified TOPO solution for 5 minutes. Separate the phases and scrub the TOPO solution four times with 10 ml of 2 M nitric acid, for 5 minutes each time. Strip the actinides as described above. APPLICATION OF PROCEDURES A AND B TO EFFLUENTS- Make effluent samples 4~ in nitric acid and store them in polythene bottles. Transfer 10 ml of suspension to a 50-ml PTFE tube, and spike with standardised solutions of yield tracer nuclides, Dilute the mixture to 20 ml and add 100 mg of ascorbic acid.Allow the mixture to stand for 5 minutes, then heat it. Add 500 mg of sodium nitrite, allow to stand for 5 minutes and again heat. Digest and complete the removal of silica, dissolution and valency adjustment as described above, but making the dissolution media only 0-2 M in nitric acid half-saturated with boric acid for procedure A, or 2 M nitric acid - boric acid for procedure B. The remaining operations for tracer exchange and extraction are as for biological materials described above. Carry out the dissolution and removal of silica as above. Add 10 ml of fuming nitric acid and 15 ml of hydrofluoric acid. REFERENCES 1. 2. 3. 4. 5. 6. 7. Magmo, R. J., Kauffman, P. E., and Schleien, B., Hlth Phys., 1967, 13, 1335. Butler, F. E., Ibid., 1968, 15, 19. Pillai, K. C., Smith, R. C., and Folsom, T. R., Nature, Lond., 1964, 203, 576. Hill, C. R., Hlth Phys., 1962, 8, 17. Gomm, P. J., and Eakins, J. D., Analyst, 1968, 93, 228. Sill, G. W., Hlth Phys., 1969, 17, 89. Gureev, E. S., Dedov, V. B., Karpacheva, S. M., Lebedev, I. A., Shvetsov, I. K., Yakovlev, G. N., Ryzhov, M. N., and Trukchlayev, P. S., Proc. 3rd Int. Conf. Peaceful Uses Atom. Enevgy, Geneva, 1964, p. 348.December, 19731 ACTINIDE NUCLIDES IN ENVIRONMENTAL MATERIALS 885 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. Coleman, G. K., “The Radiochemistry of Plutonium,” Rep. Nat. Acad. Sci., Wash., NA S-NS-3058, White, J . C., and Ross, W. J., “Separations by Solvent Extraction with Tri-n-octylphosphine Toribara, T. Y . , Predmore, C., and Hargreve, R. A., Talanta, 1963, 10, 209. Ballada, J ., “Determination Analytique du Plutonium dans l’Environment,” Rapp. CEA R3220, Katz, J . J . , and Seaborg, G. J., “The Chemistry of the Actinide Elements,” Methuen, London, Weaver, B., and Horner, 13. E., J . Chem. Engng Data, 1960, 5, 260. Dukes, E. K., J . Amer. Ckem. Soc., 1960, 82, 9. Brooks, R. 0. R., Rep. U.K. Atom. Energy Auth., AM 60, 1960. Perry, K . E. G., in “Proceedings of the Symposium on Radioisotope Sample Measurement Tech- O’Kelley, G. D., “Detection and Measurement of Nuclear Radiation,” Rep. Nut. Acad. Sci., Black, R. M., and Drummond, J. L., Rep. U.K. Atom. Energy Auth., TRG 1072 (D), 1965. Jenkins, J . L., and Wain, A. J., Ibid., A E R E R5790, 1968. Preston, A., and Jefferies, D. F., Hlth Phys., 1969, 16, 33. 1965. oxide,” Ibid., NAS-NS-3102, 1961. 1967. 1957. niques in Medicine and Biology, Vienna, 1965,” I.A.E.A., Vienna, 1966, pp. 687-698. Wash., NAS-NS-3105, 1962. Received October 18th, 1971 Amended April 9th, 1973 Accepted June 26th, 1973

ISSN:0003-2654    

DOI:10.1039/AN9739800873

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

886 Analyst, December, 1973, Vol. 98, fip. 886-894 Voltammetric Determination of Tocopherols by Use of a Newly Developed Carbon Paste Electrode BY SAMUEL S. ATUMA AND JORGEN LINDQUIST (Department of Analytical Chemistry, University of Uppsala. Box 531, S-751 21, Uppsala 1, Sweden) A voltammetric method is described for determining tocopherols in vegetable oils, foods and pharmaceuticals by a newly developed carbon paste electrode. The samples are saponified and the unsaponifiable fraction is extracted and determined voltammetrically. No elaborate purification method is necessary as the substances that interfere with photometric procedures are electrochemically inactive in the potential range of operation. Detailed procedures for the preparation and the working of the electrode, and results for the precision of the method, are presented.THE importance of vitamin E calls for specific and simple quantitative analytical techniques for determining both the total tocopherols and the various individual forms in natural and enriched products. Among the most common naturally occurring tocopherols are CC-, P-, y- and 6-tocopherol, of which a-tocopherol exhibits the highest biological potency. The parent compound, from which they are derived, is tocol [2-methy1-2-(4’,8’,12’-trimethyltridecyl)- chroman-6-01] and a-t ocopherol is 5,7,8- trimet hylt ocol, P- t ocopherol 5,8-dimet h ylt ocol, y-tocopherol 7,8-dimethyltocol and 6-tocopherol 8-methyltocol. The purpose of this study was to develop a quantitative voltammetric method for the determination of tocopherol involving the use of a newly developed carbon paste electrode. Most of the existing methods are either too tedious, incomplete or non-specific. Until recently the best known method for the quantitative determination of tocopherol in biological materials and pharmaceutical preparations has been the direct or modified application of the Emmerie-Engel colorimetric method.l-15 This method depends on the reduction of the iron(II1) ion to iron(I1) by the tocopherols and subsequent reaction with 2,2’-bipyridyl to form the red iron(I1) complex, the absorbance of which is measured at 520nm in a spectrophotometer. Prior to measurement the tocopherols are purified and separated into the individual forms.The several techniques that have been used in the separation procedure involve the use of column chromatography on different materials,*-11J3 paper chromat~graphy~s~*~~J~-~~ or thin-layer ~hromatography.~J~J~~~~~~1-~5 The best separa- tion seems to have been obtained by S t ~ w e , ~ ~ who used a five-component solvent system for chromatographing tocopherols on thin layers of silica gel and was able to separate 18- from y-tocopherol.The application of these separation techniques does not necessarily preclude the general preliminary treatment of tocopherol samples by saponification and adsorption chromato- graphy on to floridin earth. The Emmerie-Engel reaction is, however, susceptible to many interferences. Booth16 has pointed out that tocopherol simulators from fat solvents and adsorbents could give spurious results with the Emmerie-Engel method, thus making the method highly non-specific and unreliable. The “nitroso” method of Quaife26 and the “dianisidine coupling” method of Weisler, Robeson and B a ~ t e r ~ ~ for determining individual tocopherols are tedious and suffer from certain Recently gas - liquid techniques for separating and determining quantitatively the major tocopherol forms have been described and a ~ p l i e d .~ l - ~ ~ Some of the work reported is con- centrated on pharmaceutical^^^-^^ in which the tocopherol content is high and interferences are limited, and in many instances only cc-tocopherol is present. In applying gas - liquid chro- matography to naturally occurring mixtures, initial purification is of the utmost importance as sterols and cholesterols appear in the region of the tocopherols in gas chromatograms.40s41 The polarographic method for determining tocopherols was introduced by Smith, Spillane and Kolthoff .42 They found that a-tocopherol was oxidised at the dropping-mercury anode.@ SAC and the authors.ATUMA AND LINDQUIST 887 The anodic waves of p- and y-tocopherol did not give a diffusion current because the oxidation occurred at too positive potentials. The same authors43 also showed that a-tocopherol could be determined at the dropping-mercury cathode by first oxidising a-tocopherol to a-tocopheryl quinone with iron(II1) chloride. This polarographic technique has been-used, with modifica- tions, to determine tocopherols in vegetable oils, fats and pharmaceutical^.^^-^^ In these instances, the tocopherols were oxidised with cerium(1V) sulphate and the resulting tocopheryl quinones analysed polarographically at a mercury electrode.Tocopherols have also been determined by amperometric titration with gold( 111) chloride by using a dropping-mercury electrode as the indicator ele~trode.~’ Cospito, Raspi and Lucarini48 titrated the tocopherols with cerium( IV) sulphate and used a bubbling platinum electrodegg as the indicator electrode. Amperometric titrations are carried out only with samples containing a high tocopherol concentration and do not distinguish between the various forms of tocopherol. The application of a voltammetric method has been reported by Lucarini, Cospito and Raspi.50 By using a platinum electrode, with “periodic surface renewal ,” as indicator elec- trode51 they were able to determine the individual tocopherols in fats, oils, pharmaceuticals and foods.The electrode system in this method seems, however, to be rather complicated, and the poisoning effect of the electrode surface is not eliminated. The use of a wax-impregnated graphite electrode in the polarography of organic com- pounds was introduced by Gaylor, Conrad and Landerl,52 and Nash, Skauen and Purdy53 applied it to the study of the polarographic behaviour of certain antioxidants, including a-tocopherol. The need for an easily renewable stationary electrode for organic compounds in the anodic region has been greatly felt because surface film formation and adsorption of reactants or intermediates are known to influence the reproducibility of peak current measurements. Platinum has been the most widely used material for solid electrodes in anodic voltammetry, but it is far from being ideal for quantitative measurements. Its pre-treatment is of the utmost importance and it is very difficult to reproduce the surface accurately.For this reason wax-impregnated graphite52 and carbon paste electrodes54 seem to be the most practical solid electrodes for analytical work. The surface of the paste electrode is easily reproducible within 1 per cent.55956 A new carbon paste, impregnated with ceresin wax, has, however, been developed in this Department for use in all of the common solvents used in electrochemistry. In the present study of the voltammetric determination of tocopherols, this electrode was used as the working electrode.EXPERIMENTAL INSTRUMENTATION- The voltammetric measurements were made with a three-electrode system polarograph for linear-sweep voltammetry, built at this Department. It is a solid-state device with an analog section based on operational amplifiers, and a control logic section with transistor gates, reed relays and manual switches. The intention with this system has been to facilitate easy and safe operation with some consideration of possible automation. A full description of the polarograph and its electronics can be obtained on request. Any commercial three- electrode polarograph could, however, be used (even a two-electrode polarograph would suffice if corrections were made for eventual I R drop). The voltammograms were recorded with a Philips recorder (PM 8100) and a Houston Instrument XY-recorder (Model 2000).CELL AND ELECTRODES- The electrolyte consisted of a 0.2 M solution of sulphuric acid in 75 per cent. ethanol. The reference electrode was a calomel electrode with a salt bridge containing a saturated, aqueous solution of lithium chloride (Radiometer). A platinum wire served as the counter electrode. The working electrode was the newly developed carbon paste electrode prepared in the following way. An amount (0-5 g) of ceresin wax was dissolved in 20 ml of warm n-hexane (40 to 50 “C) in a beaker placed on a water-bath and 9.5 g of graphite powder were added with stirring. The dry graphite powder, now containing 5 per cent. m/m of ceresin wax, was carefully mixed with silicone oil MS 510 in the proportions 5:3 m/m to give a homogeneous paste.In any case, interference can be very trouble~orne.~~ The stirring was continued until all of the n-hexane had evaporated.888 ATUMA AND LINDQUIST : VOLTAMMETRIC DETERMINATION OF [Analyst, VOl. 98 The paste was then tamped into an electrode holder,55 care being taken to ensure that the paste was not too firmly packed. The electrode surface, with an area of 0-31 cm2, was smoothed by cutting off the excess of paste with a stretched length of a 0.2 mm piano wire while the electrode was being rotated. After each voltammetric measurement the electrode surface was easily renewed by pressing out about 1 mm of the paste and repeating the cutting procedure. In Fig. 1 are shown the anodic ranges of the electrode in 85 per cent.ethanol, acetonitrile, acetic acid and dimethyl sulphoxide. The supporting electrolytes were sodium perchlorate, ammonium acetate, sodium acetate and lithium chloride. Potential versus S.C.E./V + 1.5 +- 1.0 D I 2 14 3 > Background currents for the carbon paste electrode in different solvents: a, 85 per cent. V / V ethanol; b, acetonitrile; c, acetic acid ; and d, dimethyl sulphoxide Fig. 1. REAGENTS- Pure tocopherols (Hofman L a Roche Inc.). Tocol (Koch-Light Laboratories Ltd.). Floridin earth X S . Graphite. Ceresin wax, white. Silicoae oil MS 510. Pyrogallol solution-A 5 per cent. m/V solution in ethanol was prepared daily. Sodium ascorbate solution-A 5-g amount of sodium ascorbate was dissolved in 10 ml of distilled water. Potassium hydroxide solution-A 160-g amount of potassium hydroxide was dissolved in 100ml of distilled water.All the electrolytes used were of analytical-reagent grade. CALIBRATION GRAPH- A standard solution was made by dissolving pure cc-tocopherol in absolute ethanol. From this solution a series of solutions was prepared, by serial dilution, in the concentration range of a-tocopherol from 3 X lov6 to 7 X loA4 M, with a 0.2 M solution of sulphuric acid in 75 per cent. ethanol as solvent. Each solution was transferred into a polarographic cell (Metrohm, 20 ml) and thermostatically controlled at 20 & 0.1 "C. At least three voltammo- grams were recorded for each solution, with the electrode surface renewed after each run. Fig. 2 shows a typical voltammogram for a-tocopherol. The voltage scan was 0.5 V min-1.The peak current, i,, was measured for each solution and the blank subtracted. The height of the peak was a linear function of the concentration of tocopherol in the solution (Fig. 3). All samples were saponified in the presence of ethanolic pyrogallol or aqueous sodium ascorbate with potassium hydroxide solution for 15 minutes and the unsaponified material was extracted and determined voltammetrically. The method of saponification used was a modified version of that recommended by the Analytical Methods Committee.17 A small amount of the sample (0.5 to 3 g, depending on the tocopherol content of the sample) was weighed into a round-bottomed flask. Next, 1 ml of sodium ascorbate or 4 ml of pyrogallol solution and 20 ml of methanol were added, and the mixture was heated on a water-bath under reflux.Then 1 ml of potassium hydroxide solution (2 to 3 ml if 2 to 3 g of oil sample were saponified) was added and the refluxing continued for 15 minutes with occasional swirling. After cooling, 20 ml of distilled water were added and the unsaponified material was extracted with 75 ml of diethyl ether, about 25 ml being ALKALINE HYDROLYSIS AND ANALYSIS OF SAMPLES-December, 19731 TOCOPHEROLS BY USE OF A CARBON PASTE ELECTRODE Potential versus S.C.E./V 0.7 0.6 0.5 0.4 .Oh3 889 Fig. 2. A typical anodic voltammogram for the oxidation of a-tocopherol in 0.2 M sul- phuric acid solution in 75 per cent. ethanol. used for each extraction. The combined ether extracts were washed with 25-ml portions of water until neutral to phenolphthalein; the ether was then removed by evaporation under reduced pressure, while warming the solution on a water-bath.The dry residue was dissolved in 10 ml of 80 per cent. ethanol (20 ml if the tocopherol content was high), and 0-7 ml (or 1.4 ml) of 3 M sulphuric acid added to give a solution in 75 per cent. ethanol that was 0.2 M in sulphuric acid. This solution was then transferred into a polarographic cell and subjected to voltam- metry. ACID HYDROLYSIS- 12 ml of 2.5 M sulphuric acid in 55 per cent. ethanol were added. for 3 hours. 150-ml calibrated flask. tocopherol determined directly. The sample was dissolved in 10ml of absolute ethanol in a round-bottomed flask and This solution was refluxed The flask was cooled and its contents were transferred quantitatively into a The final volume was adjusted with 75 per cent. ethanol and the 1 10 100 Concentration/pMol Calibration graph for a-tocopherol Fig.3. RESULTS AND DISCUSSION The voltammetric behaviour of cc-tocopherol in a 0-2 M solution of sulphuric acid in 75 per cent. ethanol is shown in Fig. 2. De-aeration of solutions prior to voltammetric recording was found to be unnecessary as the results obtained with de-aerated and un- de-aerated solutions were essentially the same.890 ATUMA AND LINDQUIST : VOLTAMMETRIC DETERMINATION OF [Analyst, VOl. 98 On the basis of their structural relationship the various forms of tocopherol could be assumed to have approximately the same diffusion coefficient. A calibration graph for the a-form could therefore suffice for the determination of the other forms.Solutions to be analysed should contain 1.5 to 240 pg ml-l of tocopherol. Table I contains the peak and half-peak potentials for the four forms of tocopherol that were considered in this study. The voltammograms from which these potentials were calculated were recorded with a Houston Instruments XY-recorder (Model 2000), with a calomel in saturated potassium chloride electrode as reference electrode. TABLE I PEAK (E,) AND HALF-PEAK POTENTIALS OF THE DIFFERENT TOCOPHEROL FORMS E , versus S.C.E./V EP12 veisus S.C.E./V a-Tocopherol .. .. 0.473 0.445 fi-Tocopherol . . .. 0.550 0.520 y-Tocopherol .. .. 0-555 0.525 &Tocopherol . . .. 0-623 0.59 1 Tocol . . .. . . .. 0.646 0.614 Hedenburg and Freiser5’ have shown that an alkyl substituent in the meta position in a phenol ring has little effect on the ease of oxidation of phenol, but the inductive effects of alkyl groups in the ortho and para positions render substituted phenolic compounds more easily oxidisable than phenol itself.The work of Suatoni, Snyder and Clark58 on voltammetric studies of phenol and aniline ring substitution is in agreement with Hedenburg and Freiser’s conclusions. This phenomenon explains the order in which the tocopherols are oxidised at the carbon paste electrode. The small difference between the oxidation potentials of 18- and y-tocopherols can then be understood as they both have a methyl group in one ortho position and another methyl group in the meta position of the same ring.No doubt, the oxidation potential of the parent compound, tocol, lies very close to (possibly a little more positive than) that of &-tocopherol because the methyl group in the meta position of &tocopherol contributes very little to the ease of its oxidation. This belief was eventually confirmed (Table I). PURE TOCOPHEROLS- Pure tocopherol was treated as described under Alkaline hydrolysis and analysis of samples and the voltammograms were recorded after thermostatic control of the solution temperature in a polarographic cell. The results shown in Table I1 indicate that no significant losses of tocopherol were encountered during the saponification and extraction processes. TABLE I1 RECOVERY OF PURE a-TOCOPHEROL AFTER SAPONIFICATION AND EXTRACTION 0.108 0.106 0.001 0.115 0-115 0.001 0-615 0.616 0.001 1.184 1.181 0.003 1-648 1.649 0.002 2.283 2.280 0.003 Taken/mg Foundlmg Standard deviation TOCOPHERYL ACETATE- The tocopheryl acetate did not give a peak if it was not first hydrolysed.Acid hydrolysis of the ester gave as good a result as alkaline hydrolysis, the only disadvantage with the acid hydrolysis procedure being the length of time required for complete hydrolysis. PHARMACEUTICALS- All the tablets analysed in this work contained a rather high concentration of cc-toco- pherol; none of them contained any other form of tocopherol. The tablets were thoroughly ground and mixed, then about 0.5 g was saponified directly and the unsaponifiable matter extracted and analysed. Pre-extraction before the saponification procedure was found to be unnecessary.The results obtained with some tablets are shown in Table 111.December, 19731 TOCOPHEROLS BY USE OF A CARBON PASTE ELECTRODE TABLE I11 COMPARISON OF VOLTAMMETRIC AND EMMERIE-ENGEL ASSAYS FOR a-TOCOPHERYL ACETATE I N MULTIVITAMIN TABLETS. 891 Voltammetric assay Emmerie-Engel assay Declared & ----7 potency/ Found/ Standard Found/ Standard Sample mg per tablet mg per tablet deviation mg per tablet deviation 1 5 to 6 5.10 0-04 5.02 0-24 2 5 to 6 5.58 0.01 5-61 0.1 1 3 5 to 6 5.76 0.09 5.83 0.24 4 5 to 6 5.58 0.03 5-33 0.3 1 5 5 to 6 5.23 0.06 5.21 0.09 6 5 to 6 5-55 0.07 5-27 0-28 7 10 11.24 0.06 10-27 0.33 OILS- All the oils examined had to undergo saponification in order to remove as much of the oil base as possible because the presence of oil in the final solution could affect the peak current of the tocopherol present.The results obtained when oils of corn germ, sunflower, linseed and wheat germ were examined are shown in Table IV. TABLE IV VOLTAMMETRIC ASSAY OF TOCOPHEROLS I N SOME NATURAL PRODUCTS Product Corn germ oil Sunflower oil Linseed oil Micromilk Wheat germ Wheat germ oil Mixed tocopherols Declared tocopherol content/ mg g-l 1.0 0.9 0.25 0.15 to 0.3 2.5 About 500 - U-TOCO- pherol Trace 0.900 - - 0.145 2.09 314 Tocopherol content found/mg g-1 p- and/or y- S-Toco- tocopherol pherol Total 0.968 0.083 1.050 Trace - 0.900 0.781 - 0.781 0.160 0.073 0.233 0.073 - 0.2 18 0-30 - 2.39 157 41 512 A 1 Standard deviation 0,018 0.018 0.021 0.002 0.003 0.025 10 TOCOTRIENOLS AND OTHER REDUCING SUBSTANCES- The behaviour of tocotrienols, which are structurally related to the tocopherols, has not yet been studied.It is presumed that they may be electrochemically active in the same potential region as the tocopherols. Studies were carried out on vitamins A and D, /3-carotene and cholesterol, but these substances did not give rise to any waves in the region of operation. TOCOPHEROL MIXTURE- The determination of the different forms of tocopherol in a mixture presented some difficulties as their peak potentials are rather close to one another (Table I and Fig. 4). The second peak lies on the slope of the first and the third peak on the slope of the second, and this gives an incorrect interpretation of the heights of the subsequent peaks. In addition, these subsequent peaks are affected by the poisoning effect of the electrode surface, resulting from the recording of the first peak or peaks. A method has been developed for determining two tocopherol forms from a single voltam- mogram.In very rare cases three forms may be present, but the third is usually either present as a trace amount or so little is present that its approximate concentration can be obtained by graphical extrapolation. Fig. 5 shows voltammograms of wand P-tocopherol, both singly and in a mixture. The first peak current, AB, is measured without difficulty. The true value of i p for the second peak corresponds to CE and not to CD. By plotting a graph of EF, is, v m u s the con- centrations of a-tocopherol corresponding to the various heights of AB, a linear relationship is obtained between is and the a-tocopherol concentration over the range 3 x lo4 to 7 x 1 0 - 4 ~ (Fig.6). It is very important that i, values should be measured at the peak Usually only one or two tocopherol forms occur in any one natural product.892 -\ -1 _----I-- \ '\ \ ATUMA AND LINDQUIST : VOLTAMMETRIC DETERMINATION OF [A%dySt, VOl. 98 - 4 2, - 6 :: 5- Potential versus S.C.E./V 0.8 0.7 0.6 0.5 0.4 0.3 - - -I 3 - 8 2 z -10 3, 2 D 12 14 16 Fig. 4. A voltammogram of a-, /?-, and 8-tocopherol in a mixture. Electrolyte : 0.2 M sulphuric acid solution in 75 per cent. ethanol. 1, a-Tocopherol ; 2, /?-tocopherol; and 3, 6- tocopherol Potential . C Fig. 5. Voltammo- grams of a- and /3- tocopherol when present separately (dotted line) and in a mixture (solid line) potential of /3-tocopherol.When AB is known, EF is obtained from the calibration graph. In any mixture of cx- and @-tocopherol, therefore, the true value of i p is obtained by subtracting EF from CF. The value of i p can be expressed mathematically in the following way: where k = i,/iM. The mixtures of cc- and &tocopherol and @- or y- and 8-tocopherol are treated in a similar way. p- and y-tocopherol have approximately the same oxidation poten- tials and it was impossible to separate them by use of this method. It is very rare, however, for these two tocopherol forms to appear in the same natural product. i, = Z'CF - k x ~ A B 10 Y Q, a Concentration/pMot A, peak current of a-tocopherol as a function of concentration; B, limiting current of a-tocopherol a t the peak potential of /3-tocopherol as a function of concentration Fig.6. In Table V the results obtained when a mixture of pure or-tocopherol and linseed oil was analysed by using the method outlined above are shown. The value of &)-tocopherol in linseed oil is in agreement with the value obtained without the addition of a-tocopherol. These results indicate the high precision of the method. A series of samples of differentDecember, 1873_ TOCOPHEROLS BY USE OF A CARBON PASTE ELECTRODE 893 tocopherol contents was analysed in triplicate and the mean results are shown in Table IV. All of the oils analysed were bought in a local shop. TABLE V RECOVERY OF WTOCOPHEROL ADDED TO LINSEED OIL a-Tocopherol a-Tocopherol Standard p( y)-Tocopherol Standard Sample added/mg recovered/mg deviation found/mg g-l deviation 0.021 1 2 0.171 0.173 0.002 0-780 0.019 3 0.560 0.559 0.001 0-779 0.015 4 1.950 1.953 0.010 0.782 0-015 - 0.781 - - For comparison purposes some pharmaceutical tablets were also analysed by the Emmerie-Engel reaction method.With this method, all of the blank solutions, as well as the sample solutions, were run through the column of floridin earth to correct for any toco- pherol simulatorslS from the adsorbents. Table I11 is a summary of the results obtained with the different methods. CONCLUSION I t is worthy of note that this voltammetric method coinpletely obviates the need for column, thin-layer or paper chromatography as a necessary clean-up procedure for the samples prior to analysis.Carotenoids, vitamin A, steroids and other reducing substances, which interfere in other methods, are completely inactive electrochemically in the potential range of operation. The method is sensitive, simple and specific and its high precision in comparison with the widely used Emmerie-Engel method can be seen from Table 111. The insolubility of the electrode paste in all the common organic solvents and the very low background currents that are obtained over a very wide range of potentials make this electrode unique among the existing solid electrodes used in the study of organic compounds dissolved in organic solvents. It would appear that the great reliability and simplicity of the electrode should make this method a most suitable tool for the determination of toco- pherols. The authors thank Professor Bengt Nygard and Professor Folke Nydahl for their kind interest in this work.Grants from The Swedish Association for the Pharmaceutical Prepar- ation Industry and the Faculty of Mathematics and Natural Sciences, University of Uppsala, are greatly appreciated. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. REFERENCES Emmerie, .I., and Engel, C., Nature, 1938, 142, 873. Tsen, C. C., Analyt. Chem., 1961, 33, 849. Green, J., and Marcinkiewicz, S., Analyst, 1959, 84, 297. Marcinkiewicz, S . , and Green, J., Ibid., 1959, 84, 304. Edisbury, J . I<., Gillow, J., and Taylor, R. J., Ibid., 1954, 79, 617. Tosic, J., and Moore, T., Biochem.J., 1945, 39, 498. Lambertsen, G., and Braekkan, 0. R., Analyst, 1959, 84, 706. Lambertsen, G., Myklestad, H., and Braekkan, 0. R., Acta Agric. Scand., 1967, 17, 13. Bro-Rasmussen, F., and Hjarde, W., Acta Chem. Scand., 1957, 11, 34. -- , Ibid., 1957, 11, 44. Lambertsen, G., Myklestad, H., and Braekkan, 0. R., J . Fd Sci., 1964, 29, 164. Whittle, K. J., and Pennock, J. F., Analyst, 1967, 92, 423. Eggitt, P. W. R., and Norris, F. W., J . Sci. Fd Agric., 1955, 6 , 689. Sturm, P. A., Parkhurst, R. M., and Skinner, W. S., Analyt. Chem., 1966, 38, 1244. Crawford, R. K., Naramore, D. C., and Esmerian, 0. K., J . Pharm. Sci., 1968, 57, 1716. Booth, V. H., Analyt. Chem., 1961, 33, 1224. Analytical Methods Committee, Analyst, 1959, 84, 356. Brown, F., Biochem. J.. 1952, 52, 523.Eggitt, P. W. I<., and Ward, L. D., J . Sci. Fd Agric., 1953, 4, 569. Green, J., Marcinkiewicz, S., and Watt, P. R., Ibid., 1955, 6, 274. Dilley, K. X., Analyt. Biochevut., 1964, 7, 240. Lambertsen, G., Myklestad, H., and Braekkan, 0. R., J . Sci. Fd Agric., 1962, 13, 617. Schmandke, H., J . Chromat., 1964, 14, 123. Stowe, H. D., Archs Biochem. Biophys.. 1963, 103, 42. Herting, D. C., and Drury, E. E., J . Chromat., 1967, 30, 502. Quaife, M. L., J . Biol. Chem., 1948, 175, 605. Weisler, L., Kobeson, C. D., and Baxter, J. G., Analyt. Chem., 1947, 19, 906. Lehman, R. W., Meth. Biochem. Analysis, 1955, 2, 153.894 ATUMA AND LINDQUIST Polister, B. H., Analyt. Chem., 1954, 26, 407. Eggitt, P. W. R., and Norris, F. W., J . Sci. Fd Agric., 1956, 7, 493.Wilson, P. W., Kodicek, E., and Booth, V. H., Biochem. J., 1962, 84, 524. Libby, D. A., and Sheppard. A. J., J . Ass. 08. Agric. Chem., 1964, 47, 371.. Slover, H. T., Lehman. J., and Valis, R. J., J . Amer. Oil Chem. SUC., 1969, 46, 417. Nelson, J. P., and Milun, A. J., Ibid., 1968, 45, 848. Pillsbury, H. C., Sheppard, A. J., and Libby, D. A., J . Ass. Off. Analyt. Chenz., 1967, 50, 809. Kovensky, B. J., and Day, R. I., J . Chrumat. SGZ‘., 1971, 9, 442. Bowman, P. B., and West, W. E., J . Pharm. Sci., 1968, 57, 470. Sheppard, A. J., Hubbard, W. D., and Prosser, A. R., J . Ass. Off. Analyt. Chenz., 1969, 52, 442 Mahn, F. P., Viswanathan, V., Plinton, C., Menyharth, A., and Senkowski, B. Z., J . Pharm. Sci. Nair, P. P., and Turner, D. A., J . Amer. Oil Chenz. SOC., 1963, 40, 353. Carroll, K. K., and Herting, D. C., Ibid., 1964, 41, 473. Smith, L. I., Spillane, L. J., and Kolthoff, I. M., J . Amer. Chem. SOC., 1942, 64, 447. --- , Ibid.. 1942, 64, 644. Knohoch,’E., Macha, F., and Mnoucek, K., Chemicke’ Listy, 1952, 46, 718. Niederstebruch, A., and Hinsch, I., Fette Seifen Anstr-Mittel, 1967, 69, 559. Wisser, K., Heimann, W., and Fitsche, C., 2. analyt. Chem., 1967, 230, 189. Smith, L. I., Spillane, L. J., and Kolthoff, I. M., J . Amer. Chem. Soc., 1942, 64, 646. Cospito, M., Raspi, G., and Lucarini, L., Analytica Chim. Acta, 1969, 47, 388. Cozzi, D., Raspi, G., and Nucci, L., J . Electroanalyt. Chem., 1963, 6, 275. Lucarini, L., Cospito, M., and Raspi, G., Farrnacu Edizione Practica, 1969, 25, 39. Cozzi, D., Raspi, G., and Nucci, L., J . Electroanalyt. Chem., 1966, 12, 36. Gaylor, V. F., Conrad, A. L., and Landerl, J. H., Analyt. Chem., 1957, 29, 224. Nash, R. A., Skauen, D. M., and Purdy, W. C., J . Amer. Pharm. Ass., 1958, 47, 433. Adams, R. N., “Electrochemistry at Solid Electrodes,” Marcel Dekker Inc., New York, 1969. Lindquist, J., J. Electroanalyt. Chtem., 1968, 18, 204. Marcoux, L. S., Prater, K. B., Prater, B. G., and hdams, R. N., Analyt. Chem., 1965, 37, 1447. Hedenburg, J. F., and Freiser, H., Ibid., 1953, 25, 1355. Suatoni, J. C., Snyder, R. E., and Clark, R. O., Ibid., 1961, 33, 1894. 1968, 57, 2149. Received March 29th, 1953 Accepted July 4th. 1973 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58.

ISSN:0003-2654    

DOI:10.1039/AN9739800886

出版商:RSC    

年代:1973

数据来源: RSC