ISSN:0003-2654    

DOI:10.1039/AN97196FX021

出版商:RSC    

年代:1971

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN97196BX023

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

iV THE ANALYST [June, 1971THE ANALYSTEDITORIAL ADVISORY BOARDChairman: A. A. Smales, O.B.E. (Harwell)*T. Allen (Bradford)*La S. Bark (Salford)*A. G. Jones (Welwyn Garden City)M. T. Kelley (U.S.A.)W. Kemula (Poland)*G. F. Kirkbright (London)*G. W. C. Milner (Harwell)G. H. Morrison (U.S.A.)*G. Nickless (Bristol)S. A. Price (Tadworth)D. 1. Rees (London)E. B. Sandell (U.S.A.)H. E. Stagg (Manchester)E. Stahl (Germony)A. Walsh (Australia)*T. S. West (London)P. Zuman (U.S.A.)R. Belcher (Birmingham)L. J. Bellamy, C.B.E. (Waltham Abbey)L. S. Birks (U.S.A.)E. Bishop (Exeter)*R. C. Chirnside (Wembley)A. C. Docherty (Billingham)D. 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 (Leeds)*Members of the Board serving on the Executive Committee.NOTICE TO SUBSCRIBERSSubscriptions for The Analyst, Analytical Abstracts and Proceedings should be(Other than members of the Society)sent through a subscription agent or direct to:The Chemical Society, Publications Sales Office,Black horse Road, Letc h wort h , He rts.(a) The Analyst, Analytical Abstracts, and Proceedings, with indexes . . ..index), and Proceedings . . .. .. .. .. .. ..index), and Proceedings . . .. .. .. .. .. ..(b) The Analyst, Analytical Abstracts printed on one side of the paper (without(c) The Analyst, Analytical Abstracts printed on one side of the paper (withThe Analyst and Analytical Abstracts without Proceedings-.. . . (d) The Analyst and Analytical Abstracts, with indexes .. ..(e) The Analyst and Anolytical Abstracts printed on one side of the paper (withoutindex) . . . . . . . . . . . . . . . . . . . .(f) The Analyst and Anolytical Abstracts printed on one side of the paper (withindex) . . . . . . . . . . . . . . . . . . . .f 27.50 $66.00f 28.50 $69.00f3475 $84.00f25.00 $60.00€26.00 $63.00f 32.25 $78.00(Subscriptions are NOT accepted for The Analyst and/or for Proceedings alone)Members should send their subscriptions to the Hon. Treasurevi SUMMARIES OF PAPERS I N THIS ISSUE [June, 1971Summaries of Papers in this IssueThe Spectrophotometric Determination of Zirconium in Mildand Low Alloy SteelsThe coloured complex that is formed between zirconium, Eriochromecyanine R and polycyclic ketoamine has been studied and applied in thespectrophotometric determination of zirconium in mild steel at concentrationsranging from 0 to 0-1 per cent.with an estimated precision of f0.003 percent. of zirconium. By preliminary separation of zirconium with phenyl-arsonic acid, other elements that form complexes with Eriochrome cyanine Rand polycyclic ketoamine are partially or totally removed. Provision isalso made for the removal of elements that co-precipitate or adsorb zirconiumin acidic solution, thus extending the method to include more complex steels.Titanium in amounts greater than 0.02 per cent. interferes. The mainadvantages of the method are that residual iron can be effectively maskedwithout any loss in stability of the complex and that the molar absorptivityof the analytical complex is high.D.M. MATHER, F. MILLAR and A. F. POLLOCKBritish Steel Corporation, General Steels Division, Scottish and Shelton Group,Dalzell Works, Motherwell, Lanarkshire.Analyst, 1971, 96, 393-397.An Improved Method for the Determination of Arsenic in SteelThe steel sample is dissolved in hydrochloric and nitric acids and thearsenic reduced with hypophosphorous acid. The resulting arsenic trichlorideis extracted with chloroform and then re-extracted from the organic phase withwater. The aqueous solution of arsenic is allowed to react with ammoniummolybdate, and the molybdoarsenate is reduced to molybdenum blue. Themethod is applicable to high purity iron, carbon steels, low alloy and highlyalloyed steels including rustless, stainless and tool steels.W.R. NALLQuality A4ssurance Directorate (Materials), Ministry of Defence, Bragg Laboratory,Janson Street, Sheffield, S9 2LJ.Analyst, 197 1, 96, 398-402.Further Polarographic Studies of Metal Complexes of Mordantof Beryllium or LeadRed 74: The Masking of Interfering Metals in the DeterminationMordant red 74 in its complexes with beryllium and lead is reducedat a potential 120mV more negative than that a t which the free dye isreduced. Either beryllium or lead can be determined in the presence ofnickel, chromium(II1) and iron(II1) when these latter metals, which alsogive displaced waves with the dye, are masked with EDTA.Thorium(1V)interferes by forming a precipitate with the dye even in the presence ofEDTA, and molybdate interferes by distorting the dye wave.A. G. FOGG, J. L. KUMAR and D. THORBURN BURNSDepartment of Chemistry, Loughborough University of Technology, Loughborough,Leicestershire.Analyst, 1971, 96, 403 -406viii SUMMARIES OF PAPERS I N THIS ISSUE [June, 1971The Extraction and Spectrophotometric Determination of SexavalentUranium with Arsenazo I11 in Aqueous - Organic MediaThe determination of uranium(V1) has been carried out by extraction -spectrophotometric methods based on the use of tributyl phosphate dissolvedin isobutyl methyl ketone and trioctylphosphine oxide in benzene. Arsenazo111 is used as the metallochromic reagent in a medium buffered with mono-chloroacetic acid - sodium monochloroacetate.The effect of many cationsand anions on the procedures has been investigated, including the eliminationof the important interference caused by plutonium.The applicability of the methods evolved has been demonstrated bythe comparative analysis of a series of international secondary uranium orestandards and some other low-content uranium ores that have been analysedby independent chemical methods. The trioctylphosphine oxide - benzene -arsenazo I11 procedure, which has been shown to be greatly superior to theother methods, permits the direct determination of uranium (VI) in thepresence of plutonium when the uranium-to-plutonium ratio is greater than0.2 per cent.The method has also been found suitable for the determinationof uranium in monazitic sands, rare earth concentrates, zirconium-bearingmaterials and phosphoric acid solutions of the type used for the leachingof low-grade uranium ores.J. A. PEREZ-BUSTAMANTE and F. PALOMARES DELGADOJunta de Energia Nuclear, Direccion de Quimica e Isotopos, Ciudad Universitaria,Madrid 3, Spain.A??d3/st, 1971, 96, 407-422.Determination of Iodine and Bromine in Biological Materialsby Neutron- activation AnalysisIodine and bromine have been determined in some biological materialsby neutron-activation analysis. These elements are extracted from irradiatedsamples with a 5 per cent. solution of trioctylamine in xylene, first thebromine being back-extracted with N sodium nitrate solution and then theiodine being back-extracted with N ammonia solution.The extraction yieldis about 94 per cent. for iodine and about 86 per cent. for bromine. Thelimit of detection is about 0.01 pg for iodine and about 0-1 pg for bromine.The precision of the method is about &6 per cent. for both elementsfor concentrations exceeding 0.1 p.p.m.S . OHNONational Institute of Radiological Sciences, 9-1, 4-chome, Anagawa, Chiba-shi,Japan.Analyst, 1971, 96, 423 - 426.Loss of Cobalt and Iron from Lithium Tetraborate Fusions inGraphite CruciblesIt has been found that both iron and cobalt are lost from lithium tetra-borate fusions performed a t 1 200 "C in graphite crucibles. The elementssegregate as tiny pieces of metal near the graphite - fusion interface owingto reduction. The same reaction could well occur with other metals of loweraffinity for oxygen than carbon and so these also would disappear from thefusion,H.BENNETT and G. J. OLIVERThe British Ceramic Research Association, Queens Road, Penkhull, Stolre-on-Trent, ST4 7LQ.Analyst, 1971, 96, 427-43 1 June, 19711 THE ANALYSTAn ‘impossible’ analytical problem?ixtwo minutes from nowyou could be on the way to solving itActivation analysis is a fast-developing technique particularlyhelpful in solving difficult problems of trace element analysis.It offers a unique combination of extreme sensitivity with unam-biguous identification of an impurity. Sample contamination andreagent ‘blank’ errors are avoided and the technique can often beusednon-destructively. An Activation Analysis Unit has now beenestablished a t Harwell in collaboration with the Analytical Re-search & Development Unit. If you would like further details, orwould like the opportunity to discuss ways in which we can helpto solve your particular problems, complete and post the couponor ring Abingdon 4141, Ext.3085.To : Activation Analysis Unit, Harwell, Didcot, Berks.I am interested in the services of the Activation Analysis Unit.I should like to :[7 Receive further information by post Discuss my problem with YOUI am also interested in assistance with :0 IR spectrometry mass spectrometry 0 NMR spectrometrycomputer applications on-line analysis0 other analytical techniques (tick as appropriate)NamePositionAddressTel No.AA 1

ISSN:0003-2654    

DOI:10.1039/AN97196FP093

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

CLASSIFIED ADVERTISEMENTSThe rate for classified advertisements is 35p a line (or spaceequivalent of a line) withan extra charge of l o p for theuse of a Box Number. Semi-disfilayed classifiedadvertisements are $4 for a sin& column inch.ceding date of Publication which is on the 16th of eachmonth. Advertismzeds should be addressed toJ . Arthur Cook, 2 Lloyd Square London, W.C.lCopy required not laler than the 8th of the month pre-Tel.: 01-837 6315.FOR SALEAnalysts, Vol. I & Vols. 8-94, bound; Analytical Abstracts Vols. 1-16,bound; all in excellent condition. Offers please to Box No. 221, c/oJ. Arthur Cook, 9 Lloyd Square, London WClX 9BA.APPOINTMENTS VACANTPlease mentionTHE ANALYSTwhen replying to advertisementsANALYTICAL CHEMIST(ASHTEAD)A qualified Analyst (at least B.Sc.), with several years’ experience in a non-specialist analyticallaboratory, and thoroughly familar with the more common instrumental techniques, is requiredto undertake general analysis of a wide range of materials, especially polymers, a t ASHTEAD,Surrey. A good command of English is essential as the job involves meeting clients and preparing(or checking) informative reports for them.Apply to the PersonnelOfficer, YARSLEY TESTING LABORATORIES LIMITED, a t Clayton Road, Chessington,Surrey. (Tel: 01-397 6111-5).Promotion prospects.REPORTS OF THE ANALYTICAL METHODS COMMITTEEReprinted from The AnalystAdditives in Animal Feeding StuffsThe following thirteen Reports dealing with Additives in AnimalFeeding Stuffs may be obtained direct from The Society for AnalyticalChemistry, Book Department, 9/10 Savile Row, London, WIX IAF(not through Trade Agents), price lop.each t o members of theSociety and I5p. each to non-members.The Determination of Penicillin, Chlortetracycline and Oxytetracycline inDiet Supplements and Compound Feeding Stuffs.The Determination of Stilboestrol and Hexoestrol in Compound Feeding Stuffs.The Determination of Nitrofurazone in Compound Feeding Stuffs.The Determination of Water-soluble Vitamins in Compound Feeding Stuffs.The Determination of Fat-soluble Vitamins in Diet Supplements and Com-pound Feeding Stuffs.The Determination of Amprolium in Animal Feeding Stuffs.The Determination of Sulphaquinoxaline.The Determination of Acinitrazole.The Determination of Ethopabate in Feeds.The Determination of Furazolidone in Feeds.The Determination of Dimetridazole in Animal Feeds.The Determination of Dinitolmide (Zoalene) in Animal Feeds.The Determination of Amprolium, Sulphaquinoxaline and Ethopabate whenPresent together in Animal Feeds (Gratis)xii THE ANALYST [June, 1971Analoid compressed chemicalreagents offer a saving in the use oflaboratory chemicals.The range of over 50 chemicals intablet form includes Oxidizing andReducing Agents, Indicators, andReagents for Colorimetric Analysis.Ful I detai Is of al I Analoid preparationsfree on request from:-RIDSDALE & CO.LTD.Newham Hall, Newby,Middlesbrough, Teesside TS8 9EATel. Middlesbrough 37216 (STD Code 0642)BOOKSMONOGRAPHSREPRINTSorders for all publications ofthe Society (except journals)should be sent direct or througha bookseller to-THE SOCIETY FORANALYTICAL CHEMISTRYBook Department9/10 Savile Row,London, WIX IAF~~Determination of Trace Elementswith Special Reference to Fertilisers and Feeding StuffsA Report of theAnalytical Methods CommitteeRecommended methods for determining traces of-B, Ca, CI-, Cr, Co, Cu, F, I, Fe, Mg, Mn, Mo, Ni, Se, ZnPp.viii + 39 fl-05 netObtainable fromTHE SOCIETY FOR ANALYTICAL CHEMISTRYBook Department9/10 Savile Row, London, WIX IAFMembers of the Society for Analytical Chemistry are entitled tobuy copies at the special Members’ price of 60pRemittances made out to “Society for Analytical Chemistry”must accompany Members’ orderxiv SUMMARIES OF PAPERS I N THIS ISSUEA Sensitive, Specific Method for Determining the RiboflavinContent of Children’s UrineA four-part method based on Wahba’s technique is presented for thespecific determination of the riboflavin content of children’s urine. First,the interfering urinary constituents are precipitated by treating the urinesample with zinc acetate and formalin solutions; they are then removed bycentrifugation.The riboflavin in the resultant supernatant liquid is thenseparated from the other soluble molecular constituents of urine by elutionchromatography, by using a talc column. The riboflavin eluate is nextsubjected to one-dimensional chromatography on silica gel plates to confirmthe identity of the fluorescent spot before the determination.Finally, thethin-layer chromatographic plate is dried and the riboflavin content of theplate is measured fluorimetrically by using the technique of reflectancedensitometry .C. HAWORTH, R. W. A. OLIVER and R. A. SWAILEDepartment of Chemistry and Applied Chemistry, University of Salford, Salford,M5 4WT, Lancashire.Analyst, 1971, 96, 432-436.[June, 1971Analysis of Steroids. Part XVII. A Differential SpectrophotometricVariant of the Diethyl Oxalate Method for the Determination ofKetosteroid ContaminantsA method that consists of spectrophotometry following a Claisen con-densation with diethyl oxalate was used for the determination of ketosteroidcontaminants.Absorption of the main steroid component was eliminatedby a differential spectrophotometric procedure. The proposed method isuseful for the determination of ketosteroid contaminants present at thelevel of 0.1 per cent.S. GOROGChemical Works of Gedeon Richter Ltd., Budapest X, Hungary.Analyst, 1971, 96, 437-441.The Application of Anion- selective Membrane Electrodes inPharmaceutical AnalysisPharmaceutical PreparationsQuantitative reduction or illumination of cyanocobalamin are used toliberate hydrogen cyanide, which is then determined by using the cyanide-selective membrane electrode. The results from this procedure are verysatisfactory, The method is applicable to very low concentrations not onlyof pure cyanocobalamin but also of pharmaceutical preparations.YEHIA M.DESSOUKY and E. PUNGORDepartment of Analytical Chemistry, University of Chemical Industries, Veszprdm,Hungary.Analyst, 1971, 96, 442-446.Part 11. Determination of Cyanocobalamin inA Method for the Determination of Carbon Monoxide, Carbon Dioxide,Sulphur Dioxide, Carbonyl Sulphide, Oxygen and Nitrogen inFurnace Gas Atmospheres by Gas ChromatographyA method is described for the routine analysis of mixtures containingany of the named gases by using a dual-column system and a katharometerdetector. The method is suitable for 1-ml gas samples that may contain from100 per cent. of one of the gases down to at least 7 x per cent. of anyof them, provided that the ratio of carbon monoxide to carbon dioxide ornitrogen to carbon monoxide does not exceed 50: 1.J. B.W. BAILEY, N. E. BROWN and C. V. PHILLIPSDepartment of Minerals Engineering, The University of Birmingham, P.O. Box 363,Birmingham, B15 2TT.Analyst, 1971, 96, 447-451xvi SUMMARIES OF PAPERS I N THIS ISSUEThe Determination of Phosphate in Detergents by Cool- flame[June, 1971Emission SpectroscopyThe total phosphate content of detergent materials is determined bymeasurement of the emission of the HPO molecular species a t wavelength528 nm in a cool hydrogen - nitrogen diffusion flame. Preliminary treatmentwith cation-exchange resin is necessary to remove interference by metals.Analytical results on detergent samples containing up to 20 per cent. ofphosphates (expressed as P,O,) indicates a precision of the order of 2 to 4 percent.for the method.W. N. ELLIOTT and R. A. MOSTYNQuality Assurance Directorate (Materials), Royal Arsenal, London, S.E. 18.Analyst, 1971, 96, 452-456.The Identification of Polyol Base Compounds in PolyurethanePolyethers by Gas ChromatographyThe identification of polyol base compounds of polyurethane polyethershas been carried out by gas chromatography after conversion into theircorresponding acetates. The polyethers are allowed to react with the mixedanhydride of acetic and toluene-p-sulphonic acids (a cleavage reagent), andconverted into the acetates. With gas chromatography the acetate peaksof the polyol base compounds appear at different positions, thus enablingthese compounds to be easily distinguished.KAZURO TSUJI and KAZUO KONISHIIndustrial Research Laboratories, Kao Soap Co. Ltd., 1334 Minato-yakushubata,Wakayama-shi, Japan.Analyst, 1971, 96, 457-459.An Electrometric Method for the Determination of Soil MoistureAn electrometric method for determining soil moisture, based on thereduction of the specific resistance of propan-2-01 that occurs on additionof moisture to it, is described. The soil sample is shaken with pure propan-2-01 and from the fall in the specific resistance of the filtered extract thepercentage of moisture in the soil is read off.V. K. LELEYMaharashtra Association for the Cultivation of Science, Agarkar Road, Poona 4,India.N. J. SAWARKAR and MISS L. K. BADWALInstrument Development and Service Centre, J. N. Agricultural University, Jabalpur(M.P.), India.Analyst, 1971, 96, 460-462

ISSN:0003-2654    

DOI:10.1039/AN97196BP101

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

JUNE, 1971 Vol. 96, No. I143 THE ANALYST The Spectrophotometric Mild and Determination of Zirconium in Low Alloy Steels BY D. M. MATHER, F. MILLAR AND A. F. POLLOCK (British Steel Corporation, General Steels Division, Scottish and Sheltoiz Group, Dalzell Works, Motherwell, Lanarkshire) The coloured complex that is formed between zirconium, Eriochrome cyanine R and polycyclic ketoamine has been studied and applied in the spectrophotometric determination of zirconium in mild steel at concentratioiis ranging from 0 to 0.1 per cent. with an estimated precision of &0.003 per cent. of zirconium. By preliminary separation of zirconium with phenyl- arsonic acid, other elements that form complexes with Eriochrome cyanine R and polycyclic ketoamine are partially or totally removed. Provision is also made for the removal of elements that co-precipitate or adsorb zirconium in acidic solution, thus extending the method to include more complex steels.Titanium in amounts greater than 0.02 per cent. interferes. The main advantages of the method are that residual iron can be effectively masked without any loss in stability of the complex and that the molar absorptivity of the analytical complex is high. PROBABLY the most popular methods published in the past for the photometric determination of small amounts of zirconium in steel have been based on the formation of the zirconium - xylenol orange complex in dilute acid.132 These methods generally involve the preliminary separation of zirconium if it has to be determined in alloy steels, as at least ten elements can possibly interfere, either by forming complexes with xylenol orange or by contributing to absorbance.Rericha and Mayerl found that iron(II1) had to be virtually completely eliminated by cathodic deposition on mercury under controlled conditions, as large amounts of residual iron, when masked by ascorbic acid, caused unstable absorbance. I t is stated that molybdenum(V1) causes interference as it also forms a complex with xylenol orange, and although the authors could suppress its effect by the addition of ascorbic acid, high concentrations of molybdenum tend to retard electrolysis.3 As the method described by CechovA2 for the chemical separation of zirconium with phenylarsonic acid appeared to be more suitable than electrolytic separation for batch analysis, it was decided to adopt this separation procedure and apply a new spectrophoto- metric finish.Hill4 developed a method involving the use of Eriochrome cyanine R with polycyclic ketoamine for the determination of aluminium in steel and listed zirconium as one of the interfering elements. Work in this laboratory showed that the complex formed between zirconium and these reagents has a much higher molar absorptivity than the zir- conium - xylenol orange complex, and it is stable enough to allow residual iron to be effectively masked by thioglycollic acid in the presence of sodium sulphite. EXPERIMENTAL REAGENTS- Standard xivconiztm(1V) solution-Fuse 0-135 1 g of Specpure zirconium dioxide with 2 g of AnalaR potassium hydrogen sulphate in a platinum crucible until a clear melt is obtained.Extract the melt into 4 M hydrochloric acid and dilute to 1 litre with the same acid. Titanium(IV) soZutionAFuse 0.0834 g of Specpure titanium dioxide with 2 g of AnalaR potassium hydrogen sulphate in a platinum crucible until a clear melt is obtained. Extract the melt into 4 M hydrochloric acid and dilute to 100 ml with the same’ acid. AZunzinium(III) solution-Dissolve 0.05 g of aluminium foil in 4 M hydrochloric acid and dilute to 100ml with the same acid. 0 SAC and the authors. 393394 MATHER, MILLAR AND POLLOCK : SPECTROPH OTOMETRIC DETERMINATION [Analyst, Vol. 96 Vanadium( V ) soZzitiow-Dissolve 0.1 14 9 g of ammonium vanadate in 4 M hydrochloric acid and dilute to 100 ml with the same acid. Thioglycollic acid, 2 per cent.v/v-Dilute 20 ml of thioglycollic acid to 1 litre with water. Eriochzrome cyanine R, 0-13 per cent. w/v-Dissolve 0.13g of Eriochrome cyanine R (Merck) in cold boiled-out water and make up the volume to 100ml with the same water. This solution should be freshly prepared. Bufler solution-Mix 1 g of AnalaR anhydrous sodium sulphite, 0-75 g of polycyclic ketoamine (Amchem Products Inc., Ambler, Pa., U.S.A.) and 25.5 g of AnalaR ammonium acetate in a small beaker, dissolve the mixture in water, and make up the volume to 100 ml with water. Adjust the pH of this solution to 7.4 by adding sufficient ammonia solution (sp.gr. 0.88) or glacial acetic acid. This solution should be freshly prepared. Mineral acids-AiialaR grade concentrated acids were used throughout and diluted as necessary. APPARATUS- A Beckmann D.B.spectrophotometer was used for all absorbance measurements. DEVELOPMENT OF PROCEDURE- Rericha and Mayerl found that the minimum concentration of sulphuric acid required to prevent the hydrolysis of zirconium(1V) was 0.1 M. It was therefore decided that the zirconium(1V) should be present in at least 0.1 M sulphuric acid prior to the formation of the analytical complex (i.e., before the addition of the buffer solution). As the method described by CechovA2 provided for the separation of zirconium and its subsequent fusion as zirconium dioxide, the above conditions were achieved by extracting the melt into the requisite amount of sulphuric acid to give an acid concentration of 0.9 M in the parent solution.The optimum conditions for the formation of the analytical complex were found by transferring 2-ml aliquots of a parent solution containing 1 x 10-5gml-1 of zirconium to 50-ml calibrated flasks containing 4 ml of 2 per cent. v/v thioglycollic acid, adding a con- stant excess of Eriochrome cyanine R to the solutions, then buffering each in turn with buffers of constant polycyclic ketoamine and sodium sulphite composition, but with different ammonium acetate concentrations and pH values. After the most suitable ionic environment and the optimum pH value for formation of the complex had been established, the effects of various concentrations of Eriochrome cyanine R and polycyclic ketoamine were studied. These findings are reported under Results and Discussion. PROCEDURE- Transfer a 1-g sample (Note 1) to a 400-ml squat beaker, add 45 ml of 4 M hydrochloric acid, cover the beaker and heat it gently until the sample is dissolved.Oxidise, by dropwise additions of nitric acid (sp.gr. 1-42), and evaporate the solution to dryness; heat the residue at about 200 "C for 10 minutes. Cool, add 30 ml of 6 IVI hydrochloric acid, heat to dissolve the soluble salts, and adjust the volume to 50ml with cold water. Filter the solution on a paper pad and collect the filtrate in a 250-ml squat beaker. Wash the filter with hot 0.2 M hydrochloric acid until it is free of iron and reserve the filtrate and washings. Transfer the filter to a small platinum dish, and then dry, char and finally ignite it at as low a temperature as possible until the residue is carbon-free.Allow to cool (Note Z), add 0.5 ml of 6 M sulphuric acid and 5 ml of hydrofluoric acid (40 per cent. w/w), and evaporate until all the fumes of sulphur trioxide have been expelled. Fuse the remaining residue with 1 g of potassium hydrogen sulphate, and transfer the melt to the reserved filtrate with a minimum of hot 0.2 M hydrochloric acid. Evaporate the filtrate to 100 ml, add 1 g of phenylarsonic acid dissolved in 20 ml of hot 0.2 M hydrochloric acid, boil for 5 minutes, and allow the solution to stand overnight at room temperature (Note 3). Filter on a paper pad and wash the residue thoroughly with a hot solution containing 1 g of phenylarsonic acid in 1 litre of 0.1 M hydrochloric acid until the filtrate runs clear. Transfer the filter to a silica crucible and dry, char and ignite it under a hood at as low a temperature as possible until the residue is carbon-free.Fuse the impure zirconium dioxide with 1 g of potassium hydrogen sulphate until a clear melt is obtained (Note 4). Allow the crucible to cool, add exactly 10 ml of 4.5 M sulphuric acid, heat gently until the melt has dissolved, and transfer the extract to a 50-ml calibrated flask with hot water. Cool the solution to room temperature, dilute to the mark with cold water and mix well.June, 19711 OF ZIRCONIUM I N MILD AND LOW ALLOY STEELS 395 Transfer a 2-ml aliquot to a 50-ml calibrated flask containing 4ml of 2 per cent. v/v thioglycollic acid, add 5 ml of 0.13 per cent. w/v Eriochrome cyanine R solution, rinse down the neck of the flask with a minimum amount of cold water, mix and allow the solution to stand for 5 minutes.Add 5 ml of buffer solution, immediately adjust to the mark with cold water, mix and allow to stand for 15 minutes. Measure the absorbance at 590 nm in a cell of suitable size veysus a blank prepared by carrying 1 g of Specpure sponge iron (Johnson Matthey) through the procedure. NOTES- 1. 2. For high zirconium steels take a proportionately smaller sample weight. If niobium, tantalum or tungsten is present, fuse the residue with 2 g of anhydrous sodium carbonate at 950 “C for 10 minutes, cool, extract with boiling water, filter on a paper pad and wash well with hot water. Discard the filtrate. Transfer the filter to the original platinum dish, and dry, char and ignite it a t as low a temperature as possible until the residue is carbon-frce. Fuse the residue with 1 g of potassium hydrogen sulphate and transfer the melt to the main filtrate with a minimum of hot water.Continue as under Procedure from “Evaporate the filtrate to 100ml. . . .” 3. Alternatively, complete the precipitation by allowing the solution to stand for 2 to 3 hours a t 80 “C. 4. If more than 0.02 per cent. of titanium is present, extract the melt with 30 ml of 5 M hydro- chloric acid, adjust the volume to 100 ml with water and continue as under Procedure from “Evaporate the filtrate to 100ml. . . .” CALIBRATION WITH SYNTHETIC STANDARDS- To six 250-ml squat beakers containing l-g samples of sponge iron, add zirconium(1V) solution and 4 M hydrochloric acid solution according to Table I to maintain constant acidity, and then heat the mixture gently until the iron has dissolved.Oxidise it with a minimum of nitric acid (sp.gr. 1-42), boil the solution until all the nitrous fumes have been expelled, adjust the volume to 100 ml with water and continue as under Procedure from “Evaporate the filtrate to 100ml. . . .’, TABLE I PREPARATION OF SYNTHETIC STANDARDS Zirconium Observed absorbance 4 M Hydrochloric in a 1-g stecl sample, in a l-cm cell a t Zirconium(1V) solution* /ml acid/ml equivalent per cent. 590 nm 0 45-0 0 0 2.0 43-0 0.02 0.105 4-0 41.0 0.04 0.215 6.0 39-0 0.06 0.330 8.0 37.0 0.0s 0-4-10 10.0 35-0 0.10 0.545 * 1 ml of zirconium standard solution contains g of Zr. RESULTS AND DISCUSSION EFFECT OF pH- values the absorptivity decreased rapidly.constant absorptivity was maintained. EFFECT OF ERIOCHROME CYANINE R CONCENTRATION- A molar ratio plot of zirconium(1V) to Eriochrome cyanine K in the presence of an excess of polycyclic ketoamine showed that the analytical complex was completely formed when a 33-fold excess of the dyestuff was present. EFFECT OF POLYCYCLIC KETOAMINE CONCENTRATION- Maximum enhancement of the Eriochrome cyanine R complex was obtained for the highest concentration of zirconium on the calibration graph when a minimum of 0-6 g of polycyclic ketoamine per 100 ml of buffer solution was present. ABSORPTIVITY- The zirconium complex had an absorbance spectrum that was viitually the same as that reported by Hill4 for the aluminium complex, with a A,,,. value between 586 and 592 nm.At 590nm the molar absorptivity of the zirconium complex was approximately 6-0 x 104. Between pH 4.6 and 5-4 the colour formed did not vary a great deal, but at high pH Tests showed that between pH 5.0 and 5.2396 MATHEIZ, MILLAR AND POLLOCK : SI’ECTROPHOTOMETRIC DETERMINATION [ A ?ZdySt, VOl. 96 STABILITY- Colour development was complete after allowing the solution to stand for 15 minutes at room temperature. After the complex had been formed it remained stable for at least 2 hours. ACIDITY- Sulphuric acid (0.9 M) was used for the parent solutions to reduce hydrolysis and poly- merisation of zirconium(1V) before the final colour development. Calibration graphs con- structed from the same parent solutions before and after 2 months were identical and obeyed the Beer - Lambert law.INTERFERENCE EFFECTS- The efficiency of the separation of zirconium with phenylarsonic acid -from the other common elements that form complexes with Eriochrome cyanine R and polycyclic ketoamine, namely aluminium, titanium and vanadium, was studied by preparing synthetic standards and carrying them through the procedure. The composition of these standards and the results obtained are shown in Table 11. TABLE I1 EFFECTS OF POSSIBLE INTERFERING ELEMENTS AFTER ONE SEPARATION WITH PHENYLARSONIC ACID Zirconium taken, per cent. 0.06 0-06 0.06 0.06 0.06 0-06 0.06 0.06 0.06 0.06 0-06 0.06 Aluminium Titanium present, present, per cent. per cent. 0.50 - 0.50 - 0.50 - - 0.05 - 0.05 - 0.05 - 0.50 - 0-50 - 0.50 Vanadium Zirconium present, found, per cent. per cent.- 0.059 - 0-060 - 0.060 - 0.063 - 0.062 - 0.062 - 0.095 - 0.094 - 0-097 0.50 0.060 0.50 0.061 0.50 0-060 Deviation, per cent. - 0.001 0 0 + 0.003 + 0.002 + 0.002 + 0.035 + 0.034 + 0.03 7 0 + 0.001 0 It can be seen from Table I1 that aluminium and vanadium at concentrations up to 0.5 per cent. can be completely removed by a single separation. Titanium on the other hand tends to co-precipitate to an extent of about 25 per cent. of the total content. This effect somewhat limits the applicability of the method, but it can be partially overcome by repeated separations with phenylarsonic acid as shown in Table 111. TABLE I11 REMOVAL OF TITANIUM BY REPEATED SEPARATIONS WITH PHENYLARSONIC ACID Zirconium taken, per cent. 0.06 0.06 0.06 0.06 0-06 0.06 Titanium present, per cent.0.50 0.50 0.50 0.10 0.10 0.10 Zirconium, per cent., present after , 1 1st separation 2nd separation 3rd separation 0.060 0.095 0.069 0.094 0.069 0.060 0.097 0.070 0.061 0.069 0.061 - 0-068 0.060 - 0-070 0.060 - If silicon, tungsten, niobium and tantalum are not removed, low results are obtained, as the oxides of these elements readily precipitate or adsorb zirconium in acidic solution. As it was exceptionally difficult to prepare synthetic standards containing these elements in solution, the efficiency of their removal (by the method described in Note 2 of Procedure) was examined by analysing a series of American steel standards containing them in various proportions. The results obtained are shown in Table IV.June, 19711 OF ZIRCONIUM I N MILD AND LOW ALLOY STEELS TABLE IV DETERMINATION OF ZIRCONIUM IN N.B.S.STANDARD STEEL SAMPLES 397 Standard Interfering elements, No. per cent. A1 0.020, Ti 0.037 Nb 0.096, W 0-053, V 0.058 A1 0.027, Ti 0-010 Nb 0.195, W 0.105, V 0.010 A1 0.005, Ti 0.004 Nb 0.037, W 0.022, V 0.295 A1 0.16, Ti 0-26 Nb 0.29, W 0.20, V 0.041 N.B.S. 1162 N.B.S. 1163 N.B.S. 1164 N.B.S. 1167 Number of Zirconium phenylarsonic certificate acid value, separations per cent. 1 0.063 1 0.20 1 0.010 2 0.094 3 0.094 Zirconium by proposed method, per cent. 0.058, 0.060, 0.061 0.200, 0.196, 0.198 0*009, 0.010, 0.010 0.097, 0.096, 0.096 0.094, 0.092, 0.093 DETERMINATION OF ZIRCONIUM IN MILD STEEL SAMPLES- Unfortunately, no mild or plain carbon steel standards with certified zirconium contents are available in the B.C.S. range so that the accuracy of the method was tested by analysing a series of mild steels produced in a medium frequency furnace and comparing the values obtained by the proposed method with those obtained by X-ray fluorescence on N.B.S. standards to calibrate (1162-1167).The results obtained are listed in Table V. TABLE V COMPARISON OF THE RESULTS OBTAINED BY THE PROPOSED METHOD WITH THOSE OBTAINED BY X-RAY FLUORESCENCE Sample MF. 1656 MI?. 1657 MF.1658 MF.1659 MF.1660 MF.1661 MF. 1662 Zirconium, per cent., by r A > X-ray fluorescence Proposed method 0.026 0.025, 0-024, 0.025 0-048 0.046, 0.044, 0.046 0.069 0.069, 0.069, 0.067 0.078 0.076, 0.079, 0.078 0.091 0.094, 0.092, 0-092 0.112 0.110, 0.112, 0.112 0.001 0.002, 0.003, 0.003 CONCLUSION The proposed method is suitable for the determination of zirconium in plain and low alloy steels with zirconium contents between 0.001 and 0.1 per cent., although this range can be extended by taking a proportionately smaller sample weight.The repeatability of the method is excellent and results compare favourably with those obtained by X-ray fluorescence, as shown in Table V. As the gravimetric determination of zirconium in steel with mandelic acid is suitable only for contents exceeding 0.03 per cent.,5 the present method provides a useful service in enabling low zirconium contents to be accurately determined. The only serious limitation to the method is the fact that titanium present in amounts greater than 0.02 per cent. causes interference. The method is not rapid but a batch of fifteen determinations can be completed by one analyst in 1Q days. The authors thank Dr. J. M. Ottaway, Department of Pure and Applied Chemistry, University of Strathclyde, Glasgow, for his guidance, and Mr. J. Little, now of British Steel Corporation, Strip Steels Division, Ravenscraig Works, Motherwell, Lanarkshire, and Mr. W. Grierson of this laboratory for their support of this work. REFERENCES 1. 2. 3. 4. 5. Rericha, K., and Mayer, V., Hutn. Listy, 1962, 17, 883. CechovA, D., Chemist Analyst, 1967, 56, 94. British Standard, Mercury Cathode Electrolysis, B.S. 1121C : 1955. Hill, U. T., Analyt. Chem., 1966, 38, 654. British Standard, B.S. 1121 : Part 46 : 1965. Received July 27th, 1970 Accepted March 16tlz, 1971

ISSN:0003-2654    

DOI:10.1039/AN9719600393

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

398 Analyst, June, 1971, Vol. 96, pp. 398402 An Improved Method for the Determination of Arsenic in Steel BY W. R. NALL (Quality Assurance Directorate (Materials) , Ministry of Defence, Bragg Laboratory, Janson Street, Shefield, S9 2LJ) The steel sample is dissolved in hydrochloric and nitric acids and the arsenic reduced with hypophosphorous acid. The resulting arsenic trichloride is extracted with chloroform and then re-extracted from the organic phase with water. The aqueous solution of arsenic is allowed to react with ammonium molybdate, and the molybdoarsenate is reduced to molybdenum blue. The method is applicable to high purity iron, carbon steels, low alloy and highly alloyed steels including rustless, stainless and tool steels. MANY existing methods for determining arsenic are based either on reduction to elemental arsenic and subsequent iodimetric titration or distillation of arsenic trichloride to eliminate interfering elements.The British Standard method for determining arsenic in steel1 involves refluxing to ensure complete reduction of arsenic, followed by filtration at an elevated temperature to minimise loss of element. Special pre-treatment of the filtering media with an oxidising agent is required to reduce errors. The titration of the separated arsenic involves the use of 0.01 N solutions of iodine and sodium arsenite, both of which require to be carefully standardised, and in the final titration 1 ml of titrant is equivalent to 0.003 per cent. of arsenic on a 5-g sample. In distillation procedures for determining arsenic, e.g., in lead alloys,2 constant supervision is required to prevent losses caused by erratic distillation and the procedure is time consuming.Submicrogram amounts of arsenic have been determined with silver diethyldithiocarbamate3 by a method involving evolution of arsine and its absorption in pyridine. In this procedure the sample is required to dissolve readily in the solvent if a direct method is to be used or the oxidised arsenic is reduced and arsine evolved together with the hydrogen by adding metallic zinc to the sample solution. A special apparatus for the evolution is used and the amount of arsenic determined is given in the parts per million range. Arsenic has been determined also at trace levels4 by extraction of the yellow molybdoarsenic acid with butanol and its subsequent reduction to the blue complex.Because phosphorus interfered a double extraction with isopentyl alcohol was required when the method was applied to the deter- mination of arsenic in steel and the reduction to molybdenum blue was performed in the organic phase. In another method, based on chloroform extraction of arsenic as the chloride,5 interference from phosphorus required only a single acid wash for complete removal and the reduction to molybdenum blue was carried out in aqueous solution under controlled temperature conditions in a water-bath. The last method5 appeared to offer the most advantageous procedure for accurate deter- minations on a routine basis, but it had been applied only to copper and copper-base alloys.The authors had indicated, however, that from the evidence of limited tests the method had a potential application to the analysis of ferrous alloys. This has been confirmed and the new method proposed gives greatly increased sensitivity (about 60 times on a weight basis) compared with the British Standard method. It is less time consuming and requires a smaller sample weight; no distillation, refluxing or filtration is required and the steps during which adventitious oxidation of arsenic can occur are eliminated. 0 SAC ; Crown Copyright Reserved.NALL 399 EXPERIMENTAL The method is based on the initial dissolution of the sample in an oxidising acid mixture to prevent loss of arsenic as arsine. Subsequent reduction of the quinquivalent arsenic by hypophosphorous acid has been shown to be dependent on the presence of an optimum con- centration of copper ions in the ~olution,~ and it was necessary to confirm that this condition applied also in the analysis of ferrous alloys.The use of copper(1) chloride dissolved in concentrated hydrochloric acid suggested itself as the most convenient way of adding the copper. The copper salt was readily soluble in concentrated hydrochloric acid, in which medium the subsequent reduction of the arsenic had to be made. The copper was then in the lower valency state and did not require further reduction. The effect of increasing copper concentration was investigated by making additions of a copper solution containing 15 g of copper(1) chloride per 100 ml of hydrochloric acid (sp.gr. 1.16) to 0.25-g portions of British Chemical Standard steel No.218/3 containing 0-035 per cent. of arsenic and producing the molybdenum-blue colour by the method described later. The results are shown in Table I. TABLE I EFFECT OF INCREASING COPPER CONCENTRATION ON THE EFFICIENCY OF REDUCTION OF ARSENIC Copper solution/ml . . . . 0.0 2.0 5-0 7.0 10.0 Optical density (2-cm cell) . . 0.55 0-63 0.70 0-75 0.75 From these results it can be seen that the addition of 10 ml of the copper(1) chloride solution (equivalent to about 1 g of copper) gives the maximum optical density in the final solution corresponding to the most complete reduction and extraction of arsenic under the conditions of the method. Fig. 1 shows the transmission curve of the molybdenum-blue solution prepared from from a standard steel (B.C.S. 218/3).Maximum absorption occurs at 840 nm, which is the recommended wavelength for the determination. 0.9 - 0.8 - 0.7 - 0-6 - O*' 0 I 600 700 800 900 1000 Waveiength/nrn Fig. 1. Absorption cume for arsenic EFFECT OF OTHER ELEMENTS- The elements present in steel that may form heteropoly-acids with molybdic acid are boron, silicon, titanium, zirconium, phosphorus, vanadium, arsenic and manganese. Under the conditions of the test those most likely to be extracted and subsequently reduced to molybdenum blue are silicon and phosphorus. Any possible interference from phosphorus is eliminated in the procedure by washing the chloroform extract with concentrated hydro- chloric acid, and the results shown below (Table IV, see p.400) for a wide variety of steels with various phosphorus contents confirm that no interference is caused by this element. To investigate the effect of silicon on the arsenic determination, a standard solution of the element was prepared from high-purity silicon dioxide following fusion with sodium400 NALL: IMPROVED METHOD FOR DETERMINATION O F ARSENIC I N STEEL [A%%dySt, VOl. 96 carbonate in a platinum crucible; 1 ml of this solution contained 0.000 2 g of silicon, equivalent to 0.08 per cent. on the recommended sample weight. B.C.S. 219/3, a low alloy steel containing 0.20 per cent. of silicon and about 0.032 per cent. of arsenic, was chosen for the silicon investigation and additions of standard silicon solution were made to separate 0-25-g portions of the alloy.The arsenic determination was then completed as described in the method. The results are shown below. Arsenic found, per cent. . . 0.033 0.030 0-030 0.027 Added silicon, per cent. . . Nil 0-4 1.2 2.0 British Chemical Standard alloy steels containing vanadium, titanium and manganese are not issued with certified figures for arsenic. The effect of these elements was examined by first determining the arsenic content of the standards and then making an addition of 0.030 per cent. of arsenic and re-determining the total content. In this way it was estab- lished that no interference was caused by these alloying elements, as shown in Table 11. EFFECT OF TITANIUM , VANADIUM B.C.S. No. 211/1 13% Cr (rustless) 220/2 7% W, 5% Mo, 2% V, 5% Cr, 0.3% Mn TABLE I1 AND MANGANESE ON THE MOLYBDENUM-BLUE COLOUR Arsenic Arsenic Arsenic in standard added, recovered, (by this method), per cent.per cent. per cent. 0-023 0.030 0.028 0.020 0.030 0.030 18% Cr, 9% Ni, 0.3% Ti, 0.020 23512 0.9% Mn 261/1 17% Cr, 13% Ni, 0.9% Nb, 043% Mn 0.015 0.030 0.026 0.030 0.028 STABILITY OF THE MOLYBDENUM-BLUE COLOUR- Samples of six British Standard steels were treated by the proposed method and the optical density of the molybdenum-blue colour produced was measured at intervals up to 24 hours. The results given in Table I11 showed that the density of the molybdenum-blue colour remained stable for at least 1 hour and only faded very slowly thereafter. TABLE I11 STABILITY OF THE MOLYBDENUM-BLUE COLOUR Optical density British Chemical Standard 212/1 220/ 1 224/1 322 296 320 After Immediate 30 minutes 0-505 0.505 0-775 0.775 0.78 0.78 0.32 0.32 0.60 0.60 0.785 0.785 After 1 hour 0.50 0-776 0.78 0.32 0-60 0.775 After 2 hours 0.49 0.76 0.77 0-305 0.59 0.775 TABLE IV RESULTS ON STANDARD STEELS Arsenic content f A 1 Sample By proposed procedure, Certified value, British Chemical Standard per cent.per cent. 212/1 220/1 218/3 224/1 239/3 295 320 321 322 325 (Leaded steel) .. .. (Carbon steel). . . . . . (High speed steel) . . . . (Cr-V steel) . . . . . . (Carbon steel) . . . . . . (Mild steel) . . . . . . (Mild steel) . . . . . . (Mild steel) . . . . . . (Carbon steel) .. .. (Mild steel) . . . . .. 0.019 0.032 0.029 0-029 0.029 0-023 5 0.029 0.002 0.01 15 0.012 0.02 0.035 0.030 0-03 0.032 0.024 0.03 1 0.003 0.012 0.013 7 After 24 hours 0.485 0.76 0.77 0.305 0-58 0.76June, 19711 NALL: IMPROVED METHOD FOR DETERMINATION OF ARSENIC IN STEEL 401 APPLICATION OF THE PROCEDURE - Several British Standard steels were examined by the proposed procedure and good agreement with the standard figures was obtained.These results are shown in Table IV. METHOD REAGENTS- Standard arsenic solution-Dissolve 0.132 g of arsenic trioxide, previously dried at 105 "C, in 5 ml of warm 5 per cent. w/v sodium hydroxide solution. Dilute the solution to 100 ml and acidify it with dilute sulphuric acid (1 + 1) until an acidic reaction is obtained with litmus paper. Dilute the solution to 1 litre. Dilute a 25-ml aliquot to 100 ml. Solvent acid-Add 200ml of hydrochloric acid (sp.gr. 1-18> to 100ml of nitric acid (sp.gr.1-42). Copper reagent solution-Dissolve 15 g of copper(1) chloride in 100 ml of hydrochloric acid (sp.gr. 1.18). Ammonium molybdate solution, 1 per certt. w/v-Add, slowly, 14ml of sulphuric acid (sp.gr. 1.84) to 60 ml of water and then dissolve 1 g of ammonium molybdate tetrahydrate in the warm solution. Cool and dilute to 100ml. This reagent must be freshly prepared. Hydraxinium suZ@hate sol.ution, 0.15 per cent.-Dissolve 0.15 g of hydrazinium sulphate in water and dilute to 100 ml. 1 ml of solution = 25 pg (09025 mg) of arsenic. PREPARATION OF CALIBRATION GRAPH- Place separately 1*0,2.0,3*0 and 4.0 ml of the standard arsenic solution (1 ml of solution is equivalent to 0.025 mg of arsenic) in each of four 125-ml conical beakers containing 0.25 g of high-purity iron; use a fifth beaker containing 0.25 g of high-purity iron for a blank deter- mination.Continue with each beaker as described below. Add 10 ml of solvent acid, cover the beakers with a cover-glass and allow the reaction to proceed, warming on the hot-plate as required. When the metal is dissolved, evaporate the solution carefully to dryness, avoiding undue heating. To the residue add 40ml of hydrochloric acid (sp.gr. 1.18) to dissolve soluble salts, warming slightly if necessary, then cool, add 10 ml of copper reagent solution, adjust the temperature to about 20 "C and add 3 ml of 50 per cent. v/v hypophosphorous acid. Set aside the solution for 5 minutes. Transfer the solution to a dry separating funnel with 10 ml of hydrochloric acid (sp.gr.1*18), add 2 5 d of chloroform and shake the mixture vigorously for 1 minute. Allow the two layers to separate and run the lower (chloroform) layer into a dry separating funnel, discarding the aqueous layer. Shake the chloroform extract with 10 ml of hydrochloric acid (sp.gr. 1.18) for 30 seconds. Allow the two layers to separate and run the lower layer into a dry separating funnel; discard the aqueous layer. Add 20 ml of water and shake the mixture vigorously for 1 minute; allow the two layers to separate, discard the lower layer and transfer the aqueous layer to a 125-ml conical beaker, washing the funnel with about 5 ml of water. Add the reagents listed below in the order stated and mix well after each addition: 5 drops of 0.1 N iodine solution; 5.0 ml of 1 per cent. w/v ammonium molybdate solution; and 2.0 ml of freshly prepared 0.15 per cent. W/V hydrazinium sulphate solution. Stand the beaker in a boiling water bath for 10 minutes and then cool the solution to 20 "C. Dilute the solution to 50ml in a graduated flask. Measure the optical density at 840 nm in 2-cm cells. PROCEDURE- "Preparation of Calibration Graph." Dissolve 0.25 g of sample in 10 ml of solvent acid and continue as described under CONCLUSION The proposed method is suitable for determining arsenic in the range 0.001 to 0.05 per cent. in most types of steel. The method allows up to twelve determinations to be completed by one analyst in a normal working day. No distillation, refluxing or filtration is involved.402 NALL REFERENCES 1. 2. 3. 4. 5. British Standard 1121 : Part 38 : 1967. British Standard 3908 : Part 2 : 1967. Vasak, V., and Sedivac, V., Chemickd Listy, 1952, 46, 341. Pakalns, P., AnaZytica Chim. Acta, 1969, 47, 225. Scholes, I. R., and Waterman, W. R., Analyst, 1963, 88, 374. Received August 21st, 1970 Accepted January 12th, 1971

ISSN:0003-2654    

DOI:10.1039/AN9719600398

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

Analyst, June, 1971, Vol. 96, $9. 403406 403 Further Polarographic Studies of Metal Complexes of Mordant Red 74: The Masking of Interfering Metals in the Determination of Beryllium or Lead BY A. G. FOGG, J. L. KUMAR AND D. THORBURN BURNS (Department of Chemistry, Loughborough University of Technology, Loughborough, Leicestershire) Mordant red 74 in its complexes with beryllium and lead is reduced at a potential 12OmV more negative than that at which the free dye is reduced. Either beryllium or lead can be determined in the presence of nickel, chromium(II1) and iron(II1) when these latter metals, which also give displaced waves with the dye, are masked with EDTA. Thorium(1V) interferes by forming a precipitate with the dye even in the presence of EDTA, and molybdate interferes by distorting the dye wave.A RECENT paper1 described the basis of a method for the polarographic determination of beryllium that involves the use of the displaced ligand wave obtained with the o-hydroxy- 0'-carboxyazo dye Mordant red 74 (C.I. 16315) in the presence of beryllium ions. A 10-fold excess of dye over beryllium was recommended to prevent hydrolysis of the complex. The aluminium complex of the dye is reduced at the same potential as the free dye, and an amount of aluminium five times that of beryllium could be tolerated in the determination of beryllium. Lead(II), chromium(III), iron(III), nickel(I1) and uranium(V1) also give displaced ligand waves with Mordant red 74. With the exception of lead(II), all of these metals have been shown previously to give displaced waves with o,o'-dihydroxyazo dyesa To our knowledge this is the first report of a displaced ligand wave with lead.The present paper describes a further investigation of the polarographic behaviour of complexes of Mordant red 74, and includes a study of the effect of interferences on the determination of beryllium or lead with Mordant red 74, EXPERIMENTAL The experimental techniques and conditions used were essentially those described previously; a pure sample of dye was used.l Polarograms were obtained for methanol - water (1 + 1 v/v) solutions that had been heated to 60 "C for 5 minutes to ensure complete complex formation, and then cooled. The most suitable apparent pH at which to buffer the solutions for polarography was determined for each metal by studying the complex formation reaction with Mordant red 74 potentiometrically; acetate buffers were used in the polarographic solutions.Polarograms were obtained with a Cambridge Pen-recording polarograph and a Southern- Harwell, Mark 11, pulse polarograph. The half-wave potential of Mordant red 74 under these conditions at a pH meter reading of 5.5 was -0039V versus S.C.E. LEAD COMPLEX- Potentiometric titrations of Mordant red 74 with sodium hydroxide solution both in the absence and in the presence of lead ions indicated that a 1 : l Mordant red 74-lead complex is formed at pH 5-2 at the concentrations used for polarography. At pH values greater than 8.0 a 2: 1 Mordant red 74 - lead complex is formed. A linear calibration graph for lead was obtained from polaxograms with solutions buffered at a pH meter reading of 5-2 when the height of the displaced ligand wave (AEi = 120 mV) was plotted against the concentration of lead. The height of the displaced wave reached a constant maximum value at lead concentrations equivalent to that required to form a 1 : 1 complex.The limiting current was shown to be diffusion controlled by a study of the effect of the height of the 0 SAC and the authors.404 FOGG, KUMAR AND THORBURN BURNS: FURTHER POLAROGRAPHIC STUDIES [Analyst, Vol. 96 mercury reservoir. Typical polarograms obtained with the Cambridge polarograph showing the displaced ligand wave with lead are given in Fig. 1. C 3 + 2 0 I Ji- 1 Applied potential/\/ Fig. 2. The displaced ligand wave with uranium(V1). Uranium(V1) concentration : 1, 2 x M ; and 2, 4 x M.Mordant red 74 concentration 10-3 MJune, 19711 OF METAL COMPLEXES OF MORDANT RED 74 405 CHROMIUM(III) COMPLEX- Potentiometric titration of a solution of Mordant red 74 and chromium(II1) nitrate with sodium hydroxide solution gave an uncertain result because of the slow rate of reaction of chromium(II1) with the dye at room temperature. When the solution was heated to 65 "C and then cooled before the titration, the formation of a 2 : 1 Mordant red 74 - chromium(II1) complex was clearly indicated at pH values as low as 3.5. The formation of the 2 : 1 complex at pH 5.2 was confirmed polarographically; the height of the displaced wave reached a constant value at the chromium(II1) concentration equivalent to that required for the formation of a 2: 1 complex.INTERFERENCES IN THE DETERMINATION OF BERYLLIUM- All metal ions that form complexes with Mordant red 74, even if they give no displaced wave, will interfere if present in sufficiently high concentration. The present study of inter- ferences in the determination of beryllium was made under the conditions given in the procedure described previouslyJ1 vix., for beryllium concentrations of up to 10-4 M and a dye concentration of 10-3 M. No interference was observed from the following metals when present in an amount five times that of beryllium: Al, Zn, Co(II), Cu(II), Mn(II), Ca, Mg, Sr, V(V), Ba, Ce(III), La(III), Li, W(VI), Ag(I), Hg(I), Hg(II), Ti(IV), Zr(1V) and Sn(1V). Lead(I1) , chromium(III), iron(II1) and nickel(II), which give displaced waves with the dye, interfere when present in amounts similar to that of the beryllium.Uranium(V1) gives a displaced wave at concentrations above 3 x 1 0 - 4 ~ , and therefore interferes only when present in an amount at least three times that of beryllium. Cadmium and thorium interfere by forming a precipitate with the dye. Molybdenum(V1) at M concentration interferes by distorting the polarographic waves. The main interferences, therefore, are lead(I1) , chromium(III), iron(III), nickel(II), cadmium and thorium. The effectiveness of masking with EDTA was investigated. A 10 per cent. w/v solution of EDTA (1 ml) was added to the solutions to be polarographed before the addition of Mordant red 74. Under these conditions no displaced waves were obtained with M solutions of chromium(III), iron(II1) and nickel(I1).Hence, amounts of these metals at least ten times that of beryllium could be tolerated provided that they were masked with EDTA. Cadmium M) was also effectively masked by EDTA, but M thorium and M molybdenum(V1) were not. Significant interference is restricted, th.erefore, to lead, thorium and molybdenum(V1). DETERMINATION OF LEAD- Of the displaced waves obtained with Mordant red 74, that with lead is of particular interest, as to our knowledge no displaced wave with this metal has been reported previously. Analytically, in contrast to the determination of beryllium, there is usually no difficulty in determining lead polarographically, as the hydrated lead ion gives a well defined wave at a convenient potential.Nevertheless, the displaced wave may be of value in certain systems in which another reduction process occurs at the same potential as that for the hydrated lead ion. In particular, lead can be determined with Mordant red 74 at pH 5.5 in the presence of tin(IV), which interferes in the absence of the dye unless an alkaline supporting electrolyte is used.3 The experimental conditions for the determination of lead are the same as those for the determination of beryllium.l The calibration graph for lead is linear, providing that a slight excess of Mordant red 74 is present. This is in contrast to the determination of beryllium for which a tenfold excess of dye over beryllium is necessary to ensure that a linear calibration graph is obtained.Nevertheless, the use of a 10-fold excess of the dye in determining lead may be considered advisable so that larger amounts of other metal ions can be tolerated. The use of only a slight excess of dye, in the absence of interfering metal ions, has the advan- tage that the free dye and complex waves are resolved more completely. The interferences are similar to those for the determination or beryllium. If EDTA is used as a masking agent the only significant interferences are beryllium, thorium and molybdenum(V1).406 FOGG, KUMAR AND THORBURN BURNS CONCLUSIONS The addition of EDTA to the supporting electrolyte used in the polarographic deter- mination of beryllium with Mordant red 74 masks several interfering metal ions, and increases the selectivity of the procedure. Mordant red 74 can also be used to determine lead. Lead is not normally difficult to determine polarographically by means of its own reduction wave but, in instances when this reduction wave is obscured by the reduction of another species present in the solution, the use of the displaced ligand wave with Mordant red 74 may prove advantageous. The authors thank Mr. J. A. Clark of Hopkin and Williams Ltd. for his interest in the project and for supplying a sample of Mordant red 74. REFERENCES 1. 2. 3. Fogg, A. G., Kumar, J. L., and Burns, D. T., Analyst, 1969, 94, 262. Latimer, G. W., Talanta, 1968, 15, 1. Kolthoff, I. M., and Elving, P. J., Editors, “Treatise on Analytical Chemistry,” Part 11, Volume 6, Interscience Publishers Inc., New York and London, 1964, p. 130. Received July 30th, 1970 Accepted March 8th, 1971

ISSN:0003-2654    

DOI:10.1039/AN9719600403

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

Analyst, June, 1971, Vol. 96, $$. 407422 407 The Extraction and Spectrophotometric Determination of Sexavalent Uranium with Arsenazo I11 in Aqueous = Organic Media* BY J. A. PEREZ-BUSTAMANTE AND F. PALOMARES DELGADO (Junta de Energla Nuclear, Direccidn de Quimica e Isdtopos, Ciudad Universitaria, Madrid 3, Spain) The determination of uranium(V1) has been carried out by extraction - spectrophotometric methods based on the use of tributyl phosphate dissolved in isobutyl methyl ketone and trioctylphosphine oxide in benzene. Arsenazo I11 is used as the metallochromic reagent in a medium buffered with mono- chloroacetic acid - sodium monochloroacetate. The effect of many cations and anions on the procedures has been investigated, including the elimination of the important interference caused by plutonium.The applicability of the methods evolved has been demonstrated by the comparative analysis of a series of international secondary uranium ore standards and some other low-content uranium ores that have been analysed by independent chemical methods. The trioctylphosphine oxide - benzene - arsenazo I11 procedure, which has been shown to be greatly superior to the other methods, permits the direct determination of uranium(V1) in the presence of plutonium when the uranium-to-plutonium ratio is greater than 0.2 per cent. The method has also been found suitable for the determination of uranium in monazitic sands, rare earth concentrates, zirconium-bearing materials and phosphoric acid solutions of the type used for the leaching of low-grade uranium ores.ARSENAZO I11 is an organic reagent commonly used mainly for the spectrophotometric determination of many elements,l including thorium, uranium, zirconium, hafnium, scandium, cerium, lanthanum, rare earth elements, plutonium, neptunium, curium, protactinium, niobium, barium, strontium, sulphur, palladi~m~,~ and bi~muth.~ Generally, the colour reactions given by this reagent with various cations are very sensitive, although the main drawback to the use of arsenazo I11 for analytical purposes is its lack of selectivity. Consequently, most of the analytical procedures based on its use include a preliminary stage to increase the selectivity characteristics of the particular reaction considered (e.g., the use of masking agents, solvent-extraction techniques and ion-exchange separations).At present, there is general interest in suitable combined extraction - spectrophotometric methods for the rapid determination of many elements because of the numerous advantages offered by this type of method compared with older procedures that required a larger number of analytical steps. In 1957, White5 pointed out the fundamental requirements, possibilities and some practical applications of extraction - spectrophotometric procedures based on the use of new extractants, different organic metallochromic reagents and non-aqueous media. Some of these methods have already been described for the determination of uranium in connection with the preliminary extraction of the element with trioctylphosphine oxide (TOPO) ,5,6s7 tributyl phosphate (TBP),5ps,s tri-n-octylamine (TOA) and triisooctylamine (TiOA)10 and 8-hydroxyquinolinell diluted with suitable organic solvents.Uranium has been determined so far directly in the corresponding organic extracts with different chromogenic metallochromic organic reagents such as dibenzylmethane,5~6,8 PAN7 and arsenazo I.g HOW- ever, little use has been made of this type of procedure involving arsenazo I11 as the metallo- chromic reagent for uranium, the suitability of which for these purposes has already been demonstrated for thorium12 and p1utonium.l3J4 * Paper presented at the Second SAC Conference, Nottingham, July, 1968. 0 SAC and the authors.408 [Analyst, Vol. 96 As a continuation of other studies carried out in recent years in our l a b o r a t o r i e ~ ~ s ~ ~ ~ the purpose of the investigations described in this paper was to attempt to develop a rapid and simple extraction - spectrophotometric method for determining uranium in various secondary-type uranium ores, leached mineral residues and materials and alloys related to nuclear technology containing various amounts of the elements plutonium, thorium, alu- minium, zirconium, molybdenum, iron, etc.No attempt has been made to tackle the special problems posed by the determination of uranium in cc-, 16- and y-radioactive solutions. We therefore investigated the spectrophotometric determination of uranium(V1) with arsenazo I11 in aqueous - organic media by suitable dilution of organic extracts containing uranium with alcoholic solutions following the preliminary quantitative separation of uranium(V1) from possible contaminants by a single-stage extraction procedure based on the use of TBP- isobutyl methyl ketone and TOP0 - benzene solutions.P~REZ-BUSTAMANTE AND PALOMARES DELGADO : EXTRACTION AND BRIEF REVIEW OF THE REACTIONS OF ARSENAZO I11 WITH URANIUM Both uranium(1V) and uranium(V1) react with arsenazo 111, although the nature of the reaction (stoicheiometry of the complexes formed, molar absorptivities, acidity conditions and effects of anionic and cationic interferences), varies greatly, depending on which oxidation state is involved. The reaction of uranium(V1) with arsenazo I11 can be more readily carried out because of the greater stability of uranium in the higher oxidation state. On the other hand, the use of the uranium(1V) reaction implies the need for reducing the uranium quantitatively to the quadrivalent oxidation state which, at the trace amount level, may be associated with certain practical difficulties.Conversely, the main advantage of the reaction of uranium(1V) with arsenazo I11 compared with that of uranium(V1) is the considerably increased analytical sensitivity and selectivity. REACTIONS OF URANIUM(VI) IN MODERATELY ACIDIC MEDIA- Uranium(V1) undergoes reaction with arsenazo I11 in moderately acidic media (pH 1 to 3) to form a 1 : 1 complex species18s19s20 exhibiting maximum absorption at wavelength 655 to 660 nm and a molar absorptivity of 5-3 to 5-9 x 104 cm2 mmole-l. Under these conditions the reaction exhibits poor selectivity as thorium, zirconium, iron(III), vanadium, chromium, rare earths and actinide elements interfere seriously.The selectivity can be enhanced by the use of various masking agents, e.g., EDTA, phosphate, fluoride and sulphosalicylic a ~ i d . ~ ~ s ~ ~ s ~ ~ Alternatively, the selectivity of the reaction can be increased by carrying out a preliminary extraction of uranium(V1) with TBP - carbon tetra- chloride mixtures in the presence of salting-out agents (usually ammonium, aluminium or calcium nitrates) or masking agents (EDTA, fluoride, etc.), or with TOA or TiOA diluted with ~ y l e n e , ~ ~ and subsequently stripping the uranium(V1) from the organic phase by washing it with aqueous arsenazo I11 solutions11 s25,26 or with dilute hydrochloric acid.24 The selectivity of the arsenazo I11 - uranium(V1) reaction at pH 1 to 3 can also be increased by extraction of the complex with a solution of guanidine in an alcohol (butanol, pentanol, etc.) in the presence of masking agents (EDTA or fluoride), the photometric measurements being carried out directly on the organic phase containing the extracted complex.27 s28 929 REACTIONS OF URANIUM(VI) IN STRONGLY ACIDIC MEDIA- In strongly acidic media (5 to 7 M hydrochloric, nitric and perchloric acids) and in the presence of a large excess of reagent over the stoicheiometric requirements, the reaction of uranium(V1) with arsenazo I11 is more sensitive and selective (the rare earth elements do not interfere) compared with the reaction that takes place at low pH ~ a l ~ e ~ .~ ~ ~ The formation in strongly acidic media of 1 : 1 metal-to-ligand complex species20s30s31 and 1 : 2 specieslO with molar absorptivities for the corresponding complexes ranging from 7-1 to 8.8 x lo4 is r e p ~ r t e d .~ ~ s ~ ~ - ~ ~ , ~ ~ Even the existence of ML,-type uranium(V1) - arsenazo I11 complexes has been postulated by some authors.35936 In strongly acidic media the number of elements that may give rise to interference in the arsenazo I11 - uranium(V1) reaction is considerably reduced (thorium, hafnium, zirconium and plutonium).June, 19711 SPECTROPHOTOMETRIC DETERMINATION OF ~ ( v I ) WITH ARSENAZO 111 409 The arsenazo I11 - uranium(V1) complex species can be quantitatively extracted from strongly acidic solutions with benzyl alcoh01.3~ Generally, the use of concentrated nitric acid solutions is more advantageous than that of hydrochloric acid media as the solubility of the reagent is greater in nitric acid than in hydrochloric acid of the same molarity, and the attain- ment of the maximum sensitivity for this type of reaction necessitates the use of nearly sat- urated arsenazo I11 solutions.21922 When arsenazo I11 is used with concentrated nitric acid solutions it is necessary to destroy any nitrous acid and oxides of nitrogen in equilibrium with the nitric acid.Russian workers37@ usually use urea for this purpose, but for practical reasons we prefer to use small amounts of sulphamic acid. REACTIONS OF URANIUM(IV) IN STRONGLY ACIDIC MEDIA- Although in 0.1 M hydrochloric acid 1 : 1 and 1: 2 metal-to-ligand complex species are formed, in 6 to 8 M hydrochloric acid the formation of 1 : 2 complexesfo and 1 : 3 complexes35 has been reported, the molar a b s o r p t i v i t i e ~ ~ ~ ~ ~ ~ ~ ~ y ~ ~ 9 ~ ~ of which are 1.0 to 1.27 x 105.The main interferences in concentrated hydrochloric acid media are caused by the thorium, titanium(III), plutonium and zirconium, but in 3 to 4 N acid zirconium can be easily masked with oxalate ions, while the interference from thorium and titanium(II1) can be eliminated by carrying out the preliminary extraction of uranium(1V) with TBP41 or with a TiOA - xylene mixture.42 The quantitative preliminary reduction of the total uranium to uranium( IV) is usually effected with zinc in the presence of ascorbic acid and oxalic a ~ i d ~ , ~ ~ ~ ~ ~ ~ b i s m ~ t h ~ , ~ or titanium (I I I) .40 EXPERIMENTAL INSTRUMENTATION AND EQUIPMENT- Shaking machine, Chirana, Model T E I I I .Spectrophotometer, Beckman, Model B, single beam. Recording spectrophotometer, Beckman, Model DK-2A , double beam. Glove boxes, Technochimie and own design-These were used for all experimental work pH meter, Metrohm, Model E388. Combined glass - calomel electrode, Metrohm, Model EA 120UX. Graduated Pyrex tubes, 20 ml, Polythene stoppered. Calibrated $asks, 5 and 10 ml. Calibrated glassware. carried out with solutions containing plutonium. REAGENTS- Arsenaxo III-0.1 per cent. aqueous solutions were prepared from Schuchardt reagent and our own synthesised reagent. Uranium standard solutions-Prepared from acid-free U02(N03) ,.6H20 and U30, stan- dard samples obtained from the Spanish Atomic Commission (J.E.N.).PZutonium solutions-Prepared from low-temperature ignited 239Pu0 samples furnished by the French Atomic Commission (C.E.A.). Plutonium ( I V ) solutions in nitric acid-Prepared by dissolving Pu (OH), in concentrated nitric acid, to give 2 to 6 N acid, and adding an excess of sodium nitrite to ensure complete conversion of the plutonium into the quadrivalent state. Iron(II) sulphamate solutions in 0.2 N nitric acid-solutions containing 10 to 50 mg ml-l of iron(I1) were prepared as described by Eschrich.44 EDTA solution, 15 per cent.-Prepared by the addition of ammonia solution to an aqueous suspension of EDTA to dissolve solids and then of nitric acid until the pH was between 4 and 5. DCTA solution, 10 per cent.-Prepared by the addition of sodium hydroxide solution to a suspension of diaminocyclohexanetetraacetic acid in water to dissolve solids and then of nitric acid until the solution was about neutral.Chloroacetic acid - sodium chloroacetate solutions, 2.5 to 7.5 M equimolar-Prepared by addi- tion of stoicheiometric amounts of sodium hydroxide to aqueous monochloroacetic acid (Merck Union Chimique Belge) solutions that were suitably diluted.4 10 P6,REZ-BUSTAMANTE AND PALOMARES DELGADO : EXTRACTION AND [ATUZZySt, VOl. 96 This type of buffer must be prepared at monthly intervals or more frequently as it decomposes relatively rapidly. However, the best results are obtained, and working is more convenient, when stock monochloroacetic acid and sodium hydroxide solutions of appropriate concentration (5 to 1 0 ~ ) are mixed at the time of preparation of the samples.A detailed investigation of the ageing characteristics of this buffer system will appear elsewhere.45 The following solvents and extractants were used : tributylphosphate (B.D .H.) , thenoyl- trifluoroacetone (TTA) (Fluka), isobutyl methyl ketone (IMK) (B.D.H.), trioctylphosphine oxide (Eastman Kodak), ethanol - butanol and benzene (Merck). PROCEDURES- In all of the extraction studies reported 6 to 9 ml of aqueous phase were usually extracted with 2 to 4 ml of organic phase in 20-ml graduated tubes, TBP (20 per cent.) - IMK (80 per cent.) and 0.05 to 0.1 M TOP0 - benzene solutions being used systematically as extractants. The influence of foreign ions and masking and reducing agents on the extraction of uranium(V1) from 0.1 to 1 N nitric acid solutions was also studied.Solutions were shaken (usually for 10 minutes) to achieve equilibrium between the aqueous and organic phases and, after allowing a few minutes for clean phase separation, aliquots (1 to 2 ml) of the organic extracts were introduced, by pipette, into 10-ml calibrated flasks. The aliquots were then suitably diluted with alcoholic mixtures, followed by the addition of the different reagents and finally by making up to 10 ml With water. The 10-ml aqueous - organic samples resulting from this general procedure were subsequently further investigated as described below. STANDARD EXTRACTION - SPECTROPHOTOMETRIC PROCEDURES EXTRACTION WITH THE TRIBUTYL PHOSPHATE (20 PER CENT.) - ISOBUTYL METHYL KETONE At least duplicate samples containing 15 to 300pg of uranium(V1) are transferred, by pipette, into 20-ml graduated Pyrex glass tubes. If the samples contain plutonium, 1-5 ml ,of a 0.2 N nitric acid solution of iron(I1) sulphamate containing 50 mg ml-l of iron(I1) must be added and the reductant allowed to act for 5 to 10 minutes in the cold.If no plutonium is present, 0.5 ml of each of the following solutions of masking agents should be added instead: EDTA (15 per cent.), DCTA (10 per cent.), tartaric acid (40 per cent.) and sodium fluoride (2 per cent.). Four grams of ammonium nitrate are then added followed by the necessary amount of concentrated nitric acid and water to give 0.5 to 0.75 N nitric acid in a final volume of 8 ml; 3-ml portions of TBP - IMK, previously equilibrated with 0.5 to 0.75 N nitric acid, are then added to each tube and the tubes, after being stoppered, are shaken for 10 minutes at a rate of 250 to 300 strokes minute-l.After clean phase separation, equal 1 to 2-ml portions of each organic extract (duplicated whenever possible) are transferred, by pipette, to 10-ml calibrated flasks and the following reagents are added: 0-1 ml of saturated aqueous sulphamic acid solution, 1.0 ml of 0.1 per cent. aqueous arsenazo I11 solution, 1 ml of 5.3 M recently prepared equimolar monochloroacetic acid - monochloroacetate buffer solution, 4 ml of absolute ethanol and 0-5 ml of 10 per cent. DCTA solution. The solution is then made up to volume with water and, after mixing thoroughly, the samples are measured after 1.5 hours at wavelength 655nm, with 10-mm glass spectrophotometric cells.Measurements are made against the corresponding extrac- tion - spectrophotometric blank samples prepared in exactly the same way as the samples. Measured against distilled water, the blank reference samples normally give an absorbance value of 0.065 0.005. The uranium contents of samples are calculated by interpolation of the absorbance results on a recently obtained calibration graph for the range 0.5 to 10 pg ml-l of uranium(VI), adjusted by the least squares method, or by multiplying the particular absorbance values by the relevant factor obtained from the absorbance values corresponding to the average of triplicate uranium extraction “standards” carried out at two or more suitable uranium concentration levels.(80 PER CENT.) SYSTEM-June, 19711 SPECTROPHOTOMETRIC DETERMINATION OF ~ ( v I ) WITH ARSENAZO 111 EXTRACTION WITH THE 0.1 M TRIOCTYLPHOSPHINE OXIDE - BENZENE SYSTEM- At least duplicate samples containing 15 to 300 pg of uranium(V1) are introduced into 20-ml Pyrex glass tubes. If the samples do not contain plutonium or if it is present in amounts not exceeding 150 pg, there is no need to provide special precautions and 0.5 ml of each of the following masking reagent solutions can be added: 10 per cent. DCTA, 15 per cent. EDTA, 2 per cent. sodium fluororide and 40 per cent. tartaric acid. If the samples contain plutonium in amounts between 0-15 and 5 mg, 50 mg of sodium fluoride and 0.5 ml of 10 per cent.DCTA solution should be added instead as masking agents. If, however, the plutonium content of the samples is between 5 and 20 mg after the extraction step carried out in the presence of 50mg of sodium fluoride and 0.5ml of 10 per cent. DCTA solution, the organic extract should be washed with an equal volume of 0.5 to 1.0 N aqueous nitric acid solution (6 to 9 ml) containing the same amount of sodium fluoride and DCTA, the tube being shaken for 10 minutes. All of the plutonium should be present as pluton- ium(1V). If this is not so, the samples should be treated with 40 per cent. hydrogen peroxide and 9 M sodium nitrite in 5 to 7 M nitric acid medium as described elsewhere.46 According to the nature of the sample solutions, after pre-treatment and addition of masking agents, concentrated nitric acid and water are added to give 0.5 to 1.0 N nitric acid in a final 6 to 9-ml volume of aqueous phase to be extracted; 3-ml portions of 0.1 M TOP0 - benzene, previously equilibrated with 0.5 to 1.0 N nitric acid, are then added and, after stoppering the tubes, the samples are shaken for 10 minutes at a rate of 250 to 300 strokes minute-l.After clean phase separation, 1 to 2-ml samples (duplicated when possible) of the organic extract are introduced, by pipette, into 10-ml calibrated flasks, and the following reagents are added: 0.1 ml of saturated aqueous sulphamic acid solution, 1 ml of 0.1 per cent. aqueous arsenazo I11 solution, 1 ml of 5.3 M equimolar monochloroacetic acid - monochloroacetate solution, 6 ml of an ethanol (80 per cent.) - butanol (20 per cent.) mixture and 0.5 ml of 10 per cent.DCTA solution. The contents are then made up to volume (10 ml) with water, and the solution is thoroughly mixed and measured after 1.5 hours at wavelength 655 nm in 10-mm glass spectrophotometric cells against the corresponding extraction - spectrophoto- metric reagent blanks. The absorbance value of the reference blank solutions measured against distilled water under these conditions is normally 0.150 5 0.010. The uranium contents of the samples should be calculated as described above for the TBP - IMK system. When analysing plutonium-containing samples, it is convenient to reduce the scale by half by using 5-ml calibrated flasks thoroughout, the practical details otherwise remaining unchanged, with the exception that of the amounts of reagents used for the preparation of the spectrophotometric samples, one half of those described under “Standard extraction - photometric procedures” are taken. The reproducibility of the results obtained by using both alternatives (5 or 10-ml calibrated flasks) is in most instances better than +1 per cent.41 1 RESULTS AND CONCLUSIONS ESTABLISHMENT OF THE OPTIMUM CONDITIONS OF THE ARSENAZO 111 - URANIUM(VI) REACTION Following a detailed investigationq7 of the main spectrophotometric and physicochemical characteristics exhibited by the arsenazo I11 - uranium(V1) system in aqueous media buffered by the monochloroacetate ion, additional studies were carried out to establish the experi- mental optimum conditions for this reaction in aqueous - organic media.Accordingly, the influence of the following parameters was investigated : optimum pH for complex formation; nature and amount of buffer; mutual miscibility characteristics of different aqueous - organic media; kinetic features of the complex reaction; conformity with Beer’s law of the arsenazo I11 - uranium(V1) complex; and influence of the extracted acidity on the absorbance of the coloured complex. Generally, the main characteristics of the arsenazo I11 - uranium(V1) system have been shown to be similar both in aqueous and aqueous - organic (alcoholic) buffered media. As described in detail el~ewhere,~’ the arsenazo I11 - uranium(V1) complex of analytical interest (formed with excess of ligand) exhibits two absorption maxima at wavelengths 605 and 655 nm and a maximum molar absorptivity at pH 1.5 j, 0.1 of 5.5 If 0.3 x lo4 at 655 nm.IN AQUEOUS - ORGANIC BUFFERED MEDIA412 [Analyst, Vol. 96 Fortunately, the absorbance of the complex is insensitive towards acidity variations within the pH range 1.3 to 2-2. After testing several buffer solutions, including mono-, di- and trichloroacetic acid - salt systems, we selected the monochloroacetic acid - sodium monochloro- acetate system (equimolecular proportions of acid and salt). This buffer has many advantages within the pH range 1.5 to 3.5 because of its high solubility, which gives a large buffer capacity, and its weak complexing properties towards uranium(V1) .48 Consequently, we have made extensive use of it in a range of spectrophotometric work as described e l ~ e w h e r e .~ ~ , * ~ ~ ~ ~ The arsenazo I11 - uranium(V1) reaction has been shown4’ to exhibit good kinetic features and colour stability, both in aqueous and aqueous - organic media as the absorbance remains almost constant after 1 to 18 hours. The influence of the buffer concentration on the absorbance of the complex has been found4’ to be unimportant up to ionic strengths of 1.5 to 2. For this reason, systematic use has been made throughout this investigation of 2-5 to 7-5 M equimolecular monochloroacetic acid - monochloroacetate solutions (0-5 to 2 ml in a final 10-ml volume of sample). The amount of buffer was sufficient to deal with the acid present in the final volume. A study of the miscibility of the various aqueous - organic mixtures investigated showed that clear and stable 10-ml (final volume) mixtures could be obtained from 1 to 2-ml aliquot samples of organic extract. In the aqueous - organic systems investigated the arsenazo I11 - uranium(V1) complex has been shown to conform to Beer’s law within the range 0.25 to 10 pg ml-1 of uranium(VI), provided that a sufficient excess of reagent (C, : C, > 6) over the stoicheiometric requirements is used.The stability ~ ~ n ~ t a n t ~ ~ ~ ~ ~ ~ ~ ~ , ~ ~ of the complex formed in different aqueous acidic media is about lo4. P~REZ-BUSTAMANTE AND PALOMARES DELGADO : EXTRACTION AND EXTRACTION OF URANIUM(VI) BY THE TRIBUTYL PHOSPHATE (20 PER CENT.) - ISOBUTYL METHYL KETONE (80 PER CENT.) SYSTEM The extraction of uranium(V1) by this system requires the addition of a salting-out component to the aqueous phase to obtain a reasonably high distribution coefficient for uranium into the organic phase.Ammonium nitrate has been used as a salting-out agent (4 g of ammonium nitrate per 8 ml of aqueous phase) for the reasons given el~ewhere.~ The most significant results obtained for the extraction of uranium(V1) by this system in the presence or absence of reducing or masking agents, or both, are reproduced in Table I, from which the following conclusions can be drawn: (i) the extraction of uranium(V1) in the TABLE I EXTRACTION OF 75 pg OF URANIUM(VI) BY TRIBUTYL PHOSPHATE (20 PER CENT.) - ISOBUTYL METHYL KETONE (80 PER CENT.) FROM 0.5 & 0.2 M NITRIC ACID SOLUTIONS SATURATED WITH AMMONIUM NITRATE WITH THE STANDARDISED ARSENAZO 111 SPECTKOPHOTOMETRIC PROCEDURE I N AQUEOUS - ORGANIC MEDIA Aqueous phase Uranium (VI) Minimum Reductants Masking agent per cent. causing interference/mg I A 1 extracted, amount of plutonium(1V) - ..- 97 f: 1 > 0-05 - .. a 89 f 4 2 0.3 - 0 HSCHa.COOH (0.5 ml of 80 per cent.) . . - HSCHa.COOH (0.5 ml of 80 per cent.) . . 0 Ascorbic acid (0.5 g) . . .. .. 78 NH,(OH)Cl (0.5 g) .. .. . . (SO,H.NH),Fe [75 to 150 mg of iron(II)] 83 - (SO,H.NH),Fe [75 to 150 mg of iron(II)] b (?It a a 95 a NH,(OH)Cl (0.5 g) 92 (SO,H.NH),Fe [75 to 150.mg of irbn(1I)j’ - 99 f 1 30.5 < 1* a - Ascorbic acid (0-5 g) . . .. .. - 95 f 3 < 0.3 - - - - - a 0-5 ml of 10 per cent. DCTA + 0-5 ml of 15 per cent. EDTA + 0-5 ml of 2 per cent.NaF b 50 mg of sodium fluoride. * Poor reproducibility for the plutonium interference results. t Most of the uranium remained co-precipitated in the aqueous phase by the PuF, formed. + 0.5 ml of 40 per cent. tartaric acid.June, 19711 413 absence of masking and reducing agents is not rigorously quantitative (about 3 per cent. negative extraction bias), while in the presence of masking agents the extraction charac- teristics of uranium deteriorate considerably (about 89 per cent. of the total uranium(V1) is extracted) ; (ii) in the absence of masking agents, the addition of ascorbic acid or hydroxyl- amine to the aqueous phase brings about a slight increase in the negative extraction bias (about 5 per cent,), while the addition of reductants in the presence of masking agents results in a considerable decrease in the percentage of uranium(V1) extracted; and (iii) in the absence of masking agents, the extraction of uranium(V1) is almost quantitative when iron(I1) sulphamate is added to the aqueous phase.The general conclusion is that the extraction of uranium(V1) by the TBP - IMK system is seldom quantitative in a single extraction step. SPECTROPHOTOMETRIC DETERMINATION OF u (VI) WITH ARSENAZO 111 EFFECT OF FOREIGN IONS- The standard TBP - IMK extraction - spectrophotometric procedure given above tolerates, in the presence of masking agents, at least up to 4 mg of fluoride, 10 mg of thorium, 150 mg of iron(III), 0.5 ml of concentrated acetic acid, 0.5 ml of 10 per cent. DCTA solution, 25 mg each of vanadium(V), molybdenum(VI), cobalt(II), chromium(VI), copper(II), nickel( 11) , manganese (11) , titanium (I I I), arsenic (111) , bismuth( 111) , calcium and aluminium ; various amounts between 2 and 15 mg of strontium, barium, platinum, gold, zirconium, mer- cury, tungsten(VI), cadmium, niobium, tin, platinum-group metals and rare earth elements ; various amounts between 20 and 200 mg of sulphite, chlorate, acetate, phosphate, iodide, borate, oxalate, citrate, thiocyanate, tartrate, sulphate, EDTA, hydroxylamine, hydrochloric acid and DCTA.TABLE I1 EXTRACTION OF 75 pg OF URANIUM(VI) BY 0.1 M TRIOCTYLPHOSPHINE OXIDE - BENZENE FROM 0.5 & 0.2 M NITRIC ACID SOLUTIONS WITH THE STANDARDISED ARSENAZO I11 SPECTROPHOTOMETRIC PROCEDURE IN AQUEOUS - ORGANIC MEDIA Aqueous phase Uranium(V1) r A 1 extracted, Reductants Masking agent per cent... - 100 - .. a 98 f 2 - .. b 100 - .. b 100 Ascorbic acid (0.5 g) . . .. .. a 100 NH,(OH)Cl (0.5 g) .. .. .. a 98 f 2 (SO,H.NH),Fe [75 to 150 mg of iron(1I)J a 92 HSCH,.COOH (0.5 ml of 80 per cent.) . . a 0 - Ascorbic acid (0.5 g) . . .. .. - 100 Ascorbic acid (0-5 g) . . .. .. b 100 NH,(OH)CI (0-5 g) . . .. .. - 100 NH,(OH)Cl (0.5 g) b loo* (SO,H.NH),Fe [75 to 150mg of i&i(II)j' - 100 (SO,H.NH),Fe [75 to 150 mg of iron(II)] b (A) HSCH,.COOH (0.5 ml of 80 per cent.) . . - 8 0.5 ml of 10 per cent. DCTA + 0-5 ml of 10 per cent. EDTA + b 50 mg of NaF + 0.5 ml of 10 per cent. DCTA. + 0.5 ml of 40 per cent. tartaric acid. Minimum amount of plutonium(1V) causing interference/mg 2 0-05 3 0.05 a2.5 < 5 >15 < 25* < 0.5 G 0.6 2 2 .5 < 5 t - 0.5 ml of 2 per cent. NaF * After concluding the extraction step, the organic extract was submitted to a washing cycle with a new aqueous phase of composition identical with that used for the extraction step under the same shaking conditions before aliquots of the organic extract were submitted to spectro- photometric analysis. ?When the reductants were added before the masking agents most of the uranium(V1) remained in the aqueous phase after the extraction cycle (co-precipitation of uranium(V1) on the PuF, precipitate). $ The results obtained gave very poor reproducibility when the interference of plutonium was investigated. 5 Poor reproducibility of results was obtained arising from the probable partial co-precipitation of uranium(V1) in the aqueous phase despite addition of the masking agents before the reductant.414 PAREZ-BUSTAMANTE AND PALOMARES DELGADO: EXTRACTION AND [ArtabSt, VOl.96 PARTICULAR EFFECT OF PLUTONIUM- Table I also summarises the most significant results obtained from a detailed investi- gation of the interference of plutonium on the extraction of uranium(V1). They indicate that in the absence of reductants and masking agents any amount of plutonium(1V) interferes in the extraction of uranium(V1) as a result of co-extraction, and that the only possible way of determining uranium(V1) in the presence of 0.5 to 1 mg of plutonium(1V) is by the use of iron(I1) sulphamate provided that masking agents, especially fluoride, are absent to avoid possible complexation or precipitation of uranium(V1) in the aqueous phase.TABLE I11 EFFECT OF VARIOUS CATIONIC INTERFERENCES ON THE EXTRACTION OF 75 pg OF URANIUM(VI) BY 0.1 M TRIOCTYLPHOSPHINE OXIDE - BENZENE IN 0.5 N NITRIC ACID MEDIUM AS DETERMINED BY THE ARSENAZO I11 SPECTROPHOTOMETRIC METHOD IN AQUEOUS - ORGANIC MEDIA Investigated ion Thorium(1V) . . Thorium(1V) . . Rare earths* . . Rare earths* . . Rare earths* . . Rareearths* .. Zirconium(1V) . . Iron (111) .. Amount/mg 10 to 40 50 2.5 to 30 2 50 >, 7.5 5 to 120 25 to 300 Masking agent C C b b a a a None Uranium(V1) extracted, per cent, 100 - 100 >loot 190 > loot 100 100 Remarks An abundant white precipitate of ThF, was formed in the aqueous phase The formation of persistent emulsions did not permit pipetting of aliquots from the organic extract No appreciable co-precipitation of uranium(V1) could be found on the voluminous rare earth fluoride precipi- tates Increasing amounts of rare earth ele- ments are co-extracted with uranium(V1) as their concentration in the aqueous phase is increased.Insufficient excess of F- in the aqueous phase does not tolerate the presence of rare earths in amounts larger than 5 mg Increasing co-extraction of the rare earths takes place as their concentration in the aqueous phase is increased DCTA acts as the most effective mask- ing agent for zirconium(1V) Regardless of the presence or absence of masking agents in the aqueous phase appreciable amounts of iron(II1) are co- extracted into the organic phase. How- ever, the co-extracted iron is masked quantitatively by addition of 0-5 ml of 10 per cent.DCTA to the aqueous- organic sample to be measured spectro- photometrically (see “Standard extract- ion - photometric procedures”) a 0.5 ml of 40 per cent. tartaric acid + 0.5 ml of 10 per cent. DCTA + 0.5 ml of 2 per cent. NaF + 0.5 ml of 15 per cent. EDTA. b 0.5 ml of 40 per cent. tartaric acid + 0.5 ml of 10 per cent. DCTA + 50 mg of NaF + 0.5 ml of 15 per cent. EDTA. C 50 mg of NaF + 0-5 ml of 10 per cent. DCTA. * A synthetic rare earth solution was used containing the mixture cerium(II1) - lanthanum - neodymium (2 + 1 + 1 w/w). t Results above 100 per cent. for uranium (VI) extract do not arise from errors in the spectro- photometric method but from increased absorbance readings caused by the presence of variable amounts of co-extracted impurities that react with arsenazo 111.EXTRACTION OF URANIUM(V1) BY THE 0.1 M TRIOCTYLPHOSPHINE OXIDE - BENZENE SYSTEM FROM NITRIC ACID SOLUTIONS From the results given in Table 11, it can be readily seen that the extraction of uran- ium(V1) is almost quantitative in a single-extraction step, regardless of whether the extraction is carried out in the presence or absence of different reductants or masking agents, or both.June, 19711 SPECTROPHOTOMETRIC DETERMINATION OF ~ ( v I ) WITH ARSENAZO III 415 This fact, together with its additional advantage of not requiring the use of salting-out agents, causes the TOPO - benzene system to be superior to the TBP - IMK extraction system. Further, the quantitative extraction of uranium(V1) by this sytem is insensitive to variations in the experimental conditions as shown by the results of a detailed factorial investigation involving the extraction of 60 pg of uranium(V1) (in the absence of reducing or masking agents, or both), which indicates that the extraction of the element is almost quantitative in a single-stage operation when the acidity of the aqueous phase varies within 0.5 to 7 N nitric acid (6 to 8 ml of aqueous phase) , even although the extraction is carried out with 2 to 8 ml of organic phase and for any shaking period (250 to 300 strokes minute-1) between 1 and 10 minutes.EFFECT OF DIVERSE IONS- In 0.5 M nitric acid media, and in the absence of masking agents, of the forty different cations tested (2 to 150mg were taken depending on cases) the following were shown to interfere appreciably in the extraction of uranium(V1) : bismuth(III), zirconium, lanthanum, rare earths, iron(III), thorium, tantalum, tungsten(VI), magnesium, niobium, cerium(II1) and plutonium(1V).When the extraction of uranium(V1) was carried out under the same acidity conditions and in the presence of masking agents (see “Standard extraction - spectrophotometric pro- cedures” for details), all of these interferences could be suppressed satisfactorily with the exception of that arising from plutonium(1V). In addition under these conditions, the pre- sence in various amounts (5 to 10 mg) of fifteen anions commonly used for masking purposes did not have an appreciable effect on the quantitative nature of the uranium(V1) extraction.In Tables I11 and IV the results obtained showing the influence of some anions and cations investigated are given. PARTICULAR EFFECT OF PLUTONIUM- As the TOPO - benzene solution is a good extraction system, both for uranium(V1) and plut~nium(IV)~~ within almost the whole acidity range between 0.5 and 10 N nitric acid, it becomes mandatory to discover a suitable way of pre-treating the aqueous phase prior to the extraction step for uranium when both elements are present. The most reasonable alternatives are: the addition to the aqueous phase of suitable masking agents for pluton- ium(1V) that do not complex appreciably the uranium(V1) present (e.g., fluoride, DCTA, etc.) ; the addition of suitable reducing agents for plutonium(1V) that do not alter the sexavalent oxidation state of uranium (e.g., iron(I1) sulphamate, hydroxylamine, ascorbic acid, etc.) ; or the combined addition of both reducing and masking agents.TABLE IV INFLUENCE OF DIFFERENT ANIONIC INTERFERENCES ON THE EXTRACTION OF 75pg OF URANIUM(V1) BY 0.1 M TRIOCTYLPHOSPHINE OXIDE - BENZENE IN 0.5 N NITRIC ACID MEDIUM WITH THE STANbARDISED ARSENAZO I11 SPECTROPHOTOMETRIC METHOD I N AQUEOUS - ORGANIC MEDIA Uranium (VI) extracted, Investigated ion Amount per cent. Remarks SO,%- . . .. .. .. 6to500mg 100 No masking agents were used in the aqueous phase F- . . .. .. .. 2 to30mg 100 No masking agents were used in the aqueous phase F- .. .. .. .. 40mg -98 When the amount of F- in the aqueous phase was increased from 60 to 100mg the uranium(V1) extracted decreased from 79 to 9-6 per cent.H,PO, (sp.gr. 1-71) . . .. < 0-25ml 100 No masking agents were used in the aqueous phase H,PO, (sp.gr. 1-71) . . .. d 0.75ml 100 Al(NO,), (4g) was added to the aqueous phase H,PO, (sp.gr. 1-71) . . . . < 1.0 ml 100 Al(NO,), (8g) was added to the aqueous phase. Amounts of phosphoric acid in excess of 1 ml begin to cause interference regardless of the amount of aluminium nitrate addedTHE REDUCTION AND COMPLEXATIOI TABLE V OF PLUTONIUM AND PERCENTAGE EXTR CTED INTO TRIOCTYLPHOSPHINE OXIDE - BENZENE AND THENOYLTRIFLUOROACETONE - BENZENE SOLUTIONS* Extraction into TOP0 - benzene layer Extraction into r h TTA - benzene layer Composition of aqueous phase 7 f A 3 Arsenazo I11 buffer A# Arsenazo I buffer B# Arsenazo I11 buffer A# Medium : Plutonium/ Reductant used Masking Ethanol - butanol Ethanol - butanol Ethanol - butanol nitric acid, N mg (6 to 10 minutes in the cold) agentt (676 nm) (600 nm) (676 nm) 0.6 to 1.0 0.6 to 1.0 0.6 to 1.0 0.6 to 1.0 0.5 to 1.0 0.6 to 1.0 0.6 to 1.0 0.6 to 1.0 0.6 to 1.0 0.6 to 1.0 1.6 to 2.0 0.6 to 2.0 1.6 to 2.0 1.6 to 2.0 0.6 to 1.0 0.6 to 1.0 0.6 to 1.0 0.6 to 1.0 1.0 to 1.5 1.0 to 1.6 1-0 to 1.5 1.0 to 1.6 0.6 to 1.0 0.6 to 1.0 0.6 to 1.0 0.6 to 1.0 1.0 to 1.5 1.0 - 2.0 1.0 1.0 1.0 1.0 1.0 1.0 2.0 2.0 - 4.0 2.0 4.0 4-0 6-0 6.0 4.0 - 6.0 22 22 22 22 22 22 22 22 44 0.15 - 1-0 - 0.16 - 0.26 NH,(OH)Cl (0.6 to 1.0 g) NH,(OH)Cl (0.6 to 1.0 g) NH,(OH)Cl (0.6 to 1.0 g) NH,(OH)Cl (0.5 to 1.0 g) Ascorbic acid (0.6 g) Ascorbic acid (0.6 g) Iron(I1) as sulphamate (100 mg) Iron(I1) as sulphamate (100 mg) NH,(OH)Cl (0.6 to 1.0 g) Ascorbic acid (1 g) Iron(I1) as sulphamate (160 mg) NH,(OH)CI (0.6 to 1.0 g) NH,(OH)Cl (0.6 to 1.0 g) Ascorbic acid (1 g) Iron(I1) as sulphamate (160 mg) - - - NH,(OH)CI (0.6 to 1.0 g) NH,(OH)Cl (0.6 to 1.0 g) NH,(OH)Cl (0.6 to 1-0 g) Iron(I1) as sulphamate (76 mg) Iron(I1) as sulphamate (76 me) - 99.6 2.0 6.1; 9.9 5.9 2.9; 0.78 > 26 5.7 11.4 2.6 2.7 >8; 7.4 3.1 0.43 >7 >6 >6 >6; >7 21.6 > 26 22.4 20.2 0.46 0.41 - 21.4 34.6 > 2.2 99.2 - - 0.34; 0.20 0.26; 0-21 0.62; 0.06 2-24; 2.20 1.1 - - 1.7 0.10 0.8 1 0.01 0.01 0.60 0.12; 0.28 16.6 1.4 8.2; 7.8 7.0; 6.6 - - - - - - 0.724 F: .g CI ep 4 NOTES-1.No DCTA was added to the aqueous - organic solutions to be measured spectrophotometrically to avoid possible complexation of the extracted E plutonium by this reagent.2. The TOPO - arsenazo I method cannot be used when fluoride is added to the aqueous phase because of the competitive complexing effect brought 4 about by co-extracted fluoride on the extracted plutonium, which leads to inhibition of the reaction of plutonium with arsenazo I in the aqueous - M 0 organic find sample. 3. Addition of reductants prior to the masking agents. If no special remark is made, it is assumed throughout that the masking agents were added 8 prior to the reductants. X 0 4. The addition of ascorbic acid to the aqueous phase often leads to difficulties with the arsenazo I - plutonium reaction in the aqueous - organic 3 medium.E 6. When iron(I1) is added to the aqueous solution, no co-extraction of iron has been detected when TOPO - benzene is used as the extractant. However, 3 with the TTA - benzene system appreciable amounts of iron are co-extracted, which may lead to high plutonium results (the organic extract U occasionally has a more or less intensely blood-red colour) . 6. The organic extract was washed with the same reagents and under the same experimental conditions used for the extraction step, before aliquots 3 M XJ were taken to carry out the spectrophotometric determinations in aqueous - organic media. * Methods involving arsenazo I as the metallochromic agent and trichloroacetic acid - sodium trichloroacetate system as the buffer are similar to those ;d" described in the present paper. z t Masking agent a.Addition of 0.6 ml of 10 per cent. DCTA to the aqueous phase. b. Addition of 60 mg of NaF to the aqueous phase. c. Addition of 100 mg of NaF to the aqueous phase. $ Buffer A. Trichloroacetic acid - trichloroacetate. B. Monochloroacetic acid - monochloroacetate. c: 4 n Y v U U W418 [Analyst, Vol. 96 The lack of reproducible results obtained for the extraction of plutonium(II1) by the TOPO - benzene mixture in 0.5 N nitric acid media makes it unlikely that quantitative reduc- tion of plutonium(1V) to plutonium(II1) will resolve the problem. Our findings indicate that in 0.5 to 2 N nitric acid media about 7 per cent. of plutonium(III), 99 per cent. of pluton- ium(1V) and 90 per cent. of plutonium(V1) are extracted by the 0.1 M TOPO - benzene system. EXTRACTION OF PLUTONIUM(IV) AND PLUTONIUM(III) BY THE P~REZ-BUSTAMANTE AND PALOMARES DELGADO : EXTRACTION AND TRIOCTYLPHOSPHINE OXIDE - BENZENE SYSTEM We have carried out a detailed investigation on the reduction, masking and extraction characteristics of plutonium by determining the amount of plutonium extracted by the 0.1 M TOPO -benzene system as a function of the acidity of the medium, and of the pre- treatment of the aqueous nitric acid solutions with several reductants or masking agents, or both.The results obtained are reproduced in Table V, which includes for comparative purposes results obtained by two additional extraction - spectrophotometric methods de- veloped in recent years in our lab~ratories.~~ These results indicate that in all instances when reductants have been used the reduction of plutonium(1V) to plutonium(II1) seems to be almost quantitative, as the extraction of plutonium by the TTA - benzene system is negligible (under the same acidity conditions the extraction of plutonium(1V) by TTA would proceed quantitatively) ; that the extraction of plutonium(II1) by the TOPO - benzene system is important, even in the presence of a large excess of reductants, while the efficiency with which plutonium is reduced to the tervalent state has been shown to decrease according to the sequence hydroxylammonium chloride > iron(I1) > ascorbic acid; and that the addi- tion of large amounts of fluoride ions (up to 50 mg of sodium fluoride) does not bring about any substantial increase in the amount of plutonium(II1) retained in the aqueous phase but, on the contrary, the larger the excess of fluoride ions the more likely a plutonium trifluoride precipitate will be formed on which uranium(V1) might largely, or even quantitatively, co-precipit at e.EXTENT OF CO-EXTRACTION OF PLUTONIUM I N THE PRESENCE OF MASKING OR REDUCING AGENTS, OR BOTH, ADDED TO THE AQUEOUS URANIUM-CONTAINING PHASE- The main conclusions regarding the interference of plutonium on the extraction of uranium(V1) by the TOPO - benzene system can be readily drawn from consideration of the results included in Table 11: in the absence of reductants and masking agents added to the aqueous phase, plutonium interferes with the uranium(V1) extraction because it is co- extracted; the use of masking agents (especially fluoride) in the absence of reductants allows the tolerance of the method for plutonium(1V) to increase considerably, as the quantitative extraction of microgram amounts of uranium can be carried out in the presence of plutonium, provided that 0.5 ml of 10 per cent.DCTA solution is added to the aqueous - organic sample (quantitative masking of about 50 pg of plutonium per 10 ml.) Further, the tolerance of the method for plutonium(1V) can be increased considerably when, after completion of the extraction step, the organic extract is washed under the same experimental conditions as those used to carry out the extraction; the sole use of reductants for plutonium(1V) does not successfully eliminate the plutonium interference, because of the appreciable co-extraction of plutonium(II1) by the TOPO - benzene system; and the combined use of reductants and masking agents for plutonium in the aqueous phase, prior to the extraction of uranium(VI), gives results similar to those obtained by the use of masking agents alone (upper limit of tolerance 2-5 to 5 mg of plutonium(1V) in the presence of 50 mg of sodium fluoride).CO-PRECIPITATION OF URANIUM (VI) ON PLUTONIUM TRI- AND TETRAFLUORIDES IN THE AQUEOUS When the extraction of uranium(V1) is attempted in the presence of increasing amounts of plutonium (over the 2.5 to 5-mg range), by using both reductants and masking agents for plutonium in the aqueous phase, the extraction of uranium(V1) becomes increasingly less efficient with increasing amounts of plutonium because of the appreciable co-precipitation of uranium(V1) on the plutonium fluoride.It is concluded that uranium(V1) may largely co-precipitate on plutonium tetrafluoride and to a still greater extent on plutonium trifluoride. These findings explain qualitatively the greater tolerance of the method for plutonium when only masking agents (for plutonium (IV)) are added to the aqueous phase compared with the combined addition of reductants followed by masking agents (for plutoninm (111)). PHASE-TABLE VI CORRELATION OF ANALYTICAL RESULTS OBTAINED FOR URANIUM ORES BY USING DIFFERENT METHODS Method (U,O, per cent.) Description “S-I” (Australia) “S-11” (Spain) “S-111” (USA.) ‘IS-IV” (Australia) “La Virgen” (Spain) “Carretona” (Spain) “Alameda de Gordbn” “Fraga” (Spain) “Calaf ” (Spain) ‘‘Cardeisa” (Spain) (Spain) Type of mineral Torbernite Torbernite Carnotite Uraninite Torbernite, autunite, pitchblende Autunite, pitchblende, phosphuran ylite Autunite, renardite Lignite Lignite Autunite, torbernite f TBP - isobutyl TBP - isobutyl methyl ketone - methyl ketone - TOP0 - arsenazo III* arsenazo 1117 arsenazo 1: 0.480 0.487 0.483 0.313 0-309 0.313 0-425 0.415 0.415 0.370 0.371 0.372 0.057 2 0.058 8 0.059 5 0.089 8 0.093 9 0.092 0 0.234 0.238 0.239 0-018 7 - 0.020 2 0.017 8 - 0.018 3 - 0.103 - * Average of twelve determinations.Average of four determinations. $ Average of fifty-six determinations. Dibenzoyl- methane: 0.481 0.311 0.419 0-374 - - - 0.019 7 0.018 1 0.111 OIEA Thio- standard cyanate: values 0.481 0.471 0.318 0.313 0.426 0.418 0.381 0.375 0.057 5 - 0.094 1 - 0.259 - U H n420 PkREZ-BUSTAMANTE AND PALOMARES DELGADO EXTRACTION AND [AnahySt, VOl. 96 Our findings further indicate that when the amount of plutonium(1V) exceeds the 2 6 m g level, the formation of a dark grey precipitate of plutonium tetrafluoride can be easily seen when sufficient fluoride is present, on which uranium(V1) does not co-precipitate appre ciably until the limit of about 20 mg of plutonium(1V) is exceeded.This value constitutes about the upper compatibility limit for the quantitative extraction of uranium(V1) in the presence of plutonium(1V) when the extraction is carried out in the presence of fluoride. According to our results, the co-precipitation of 15 to 150 pg of uranium(V1) on plutonium tetrafluoride becomes quantitative when about 50 mg of plutonium(1V) are present in the aqueous phase.On the other hand, when plutonium(1V) is first reduced to plutonium(III), the co-precipitation of uranium(V1) on the pink precipitate of plutonium trifluoride becomes appreciable for amounts of plutonium larger than 2.5 mg. LIMITS OF APPLICABILITY OF THE EXTRACTION - SPECTROPHOTOMETRIC METHOD FOR URANIUM From Table I1 it is concluded that under suitable experimental conditions (absence of reductants; addition of 50mg of sodium fluoride and 06ml of 10 per cent. DCTA to the aqueous phase; washing of the organic extract following the extraction cycle; and use of DCTA in the aqueous - organic spectrophotometric sample) the TOPO - benzene - arsenazo I11 extraction - spectrophotometric method allows the uranium to be quantitatively separated and determined in samples, provided that the uranium-to-plutonium ratio is greater than 0.1 to 0.2 per cent.at the lower limit of the method (ie., when the total amount of uranium originally present in the sample does not exceed 30 pg) or greater than 1 to 2 per cent. a t the upper limit (total amount of uranium about 300pg per sample). If the uranium content is smaller than the values stated, the method could still be applied, by suitably effecting the preliminary separation of uranium from plutonium ; separation by anion exchange may be suitable for this purpose.msM IN THE PRESENCE OF PLUTONIUM WITHOUT THEIR PREVIOUS SEPARATION- COMPARATIVE STUDY OF THE METHODS WHEN APPLIED TO THE ANALYSIS OF SAMPLES OF URANIUM ORES The practical applicability of the two methods for the determination of uranium des- cribed in the present paper has been tested on several samples of secondary uranium ores, low grade uranium minerals and sterile leached residues, the mineralogical and chemical characteristics of which were well The results obtained from the study of ten such materials are given in Table VI.The method selected for the attack of the samples consisted simply in leaching uranium from the different materials by boiling them under reflux with dilute nitric acid (1 + 1) for prolonged periods (6 to 8 hours), as described el~ewhere.5~ Most of the uranium values included in Table VI, as determined by the arsenazo I, dibenzoylmethane and thiocyanate methods have been taken from an earlier publication54 for comparative purposes.From the results given in Table VI it is apparent that the two methods described in this paper furnish results that agree well with those found for the same samples by other workers who used different methods. The two methods considered here have also been used for the determination of uranium in monazitic sands, “New Brunswick Laboratories” uranium - thorium standards and rare earth concentrates. The results obtained (not included here) indicate that both methods can be applied to the determination of very small amounts of uranium in a large variety of natural mineral samples. DISCUSSION Despite the good agreement shown by the two extraction - spectrophotometric methods for the determination of uranium in different natural and synthetic samples and standards, the TOPO - benzene method exhibits so many practical advantages compared with the TBP - IMK method that only the former is used in our laboratories in routine and research problems. Consequently, only a few specific questions relating to the TOPO - benzene - arsenazo I11 method will be dealt with briefly in this section.Our experimental findings on the extent of plutonium(II1) co-extraction by the TOPO - benzene system and on that of co-precipitation of uranium(V1) on the plutonium trifluoride and plutonium tetrafluoride precipitates have been shown to differ considerably from thoseJune, 19711 42 1 included in the scarce information available on these aspects. Co-precipitation of uranium(V1) on plutonium trifluoride has been reported by Maria,56 although he found tolerance limits much greater than ours by a factor of 10 to 100.Analogously we found the amount of plutonium(II1) co-extracted by the TOPO - benzene system to be 0.3 to 4 per cent., depending on the experimental conditions (Table V) compared with 0-04 and 0.1 per cent. reported by Maria56 and Baltisberger,’ respectively. The characteristic co-precipitation of uranium(V1) on pluton- ium trifluoride so clearly shown by us to occur below the 20-mg plutonium level has not been reported by any of the authors mentioned. Further, the co-precipitation problem is not even mentioned in Baltisberger’s paper. On the other hand, the widely differing charac- teristics shown by the plutonium trifluoride and plutonium tetrafluoride precipitates regarding the extent of uranium(V1) co-precipitation on them do not seem to have been correctly differentiated by previous workers.Contrary to Baltisberger’s findings, our experimental results indicate (Tables I1 and V) that the combined use of iron(I1) sulphamate and fluoride to prevent the plutonium inter- ference in the aqueous phase is unsatisfactory because of the poor reproducibility of the results obtained. Of course, the order of addition of reagents followed in this procedure might give rise to widely varying results, depending on which of the plutonium fluorides is formed as the trifluoride is about ten times more effective as a co-precipitant for uranium(V1) than the tetrafluoride, according to our results.As the main problem encountered in the application of the TOPO - benzene - arsenazo I11 extraction - spectrophotometric method for the determination of uranium(V1) was the direct elimination of the important interference caused by the presence of plutonium, it seems worthwhile to sum up as follows the main facts established experimentally in this connection. (i) The preliminary complexation of plutonium(IV), followed by the addition of reduc- tants, furnishes much more satisfactory results than the reverse order of addition. This procedure largely reduces the risk of losing partially, or even entirely, the uranium(V1) that may be co-precipitated on the plutonium trifluoride and plutonium tetrafluoride precipitates. (ii) When reductants were added, following the use of fluoride plus DCTA as masking agents, no appreciable plutonium trifluoride precipitate formation could be observed when 5-mg amounts of plutonium(1V) were initially present, even after 24 hours had elapsed.(iii) It is concluded that the use of reductants in the aqueous phase to convert plu- tonium(1V) into plutonium(II1) becomes unnecessary because if they are used alone, the plutonium(II1) is appreciably co-extracted; if they are used prior to the addition of masking agents (especially fluoride) plutonium trifluoride is formed on which uranium(V1) may largely co-precipitate ; and, finally, if they are used after preliminary treatment of the plutonium( IV) with a large excess of fluoride, no additional improvement seems to result from their addition.From this, it becomes obvious that the best experimental conditions to suppress the plutonium interference are also about the worst for the quantitative extraction of uranium(V1) into the organic phase. In fact, the order of addition of the reagents (Table V) to the aqueous phase has been shown to be unexpectedly critical in this connection. Finally, there are the following fortunate circumstances concerning the minimisation of the plutonium interference in the uranium (VI) determination when using the proposed extraction - spectrophotometric method: uranium(V1) forms with arsenazo I11 in aqueous - organic monochloroacetic medium a complex compound exhibiting a much higher molar absorptivity than the corresponding plutonium(1V) complex species; the uranium(V1) - arsenazo I11 complex exhibits a very sharp absorption band, the maximum of which appears at 655 nm while that of the equally sharp corresponding plutonium(1V) complex is located at 670 nm; and 0.5 ml of 10 per cent. DCTA solution masks effectively up to 50 pg of plutonium per 10 ml of aqueous -organic phase and has no appreciable effect on the uranium(V1) - arsenazo I11 complex.Since this work was completed it has been found that the use of xylene instead of benzene as a solvent for TOPO in the extraction of uranium(V1) from aqueous nitric acid gives more quantitative results and is to be preferred, even though the mutual solubility of the components of the aqueous - organic system becomes slightly reduced and may result in somewhat more critical conditions for the stability of the final sample from the point of view of emulsion format ion.The authors acknowledge the valuable help given, and careful experimental work carried out, by technical assistant, Mr. M. Tonno Ferrero, in the major part of this investigation. 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Onisk, H., and Sekine, K., Bunseki Kagaku, 1969, 18, 524. Motojima, K., Yamamoto, T., and Kaku, Y., Ibid., 1969, 18, 208; Chem. Abstr., 1969,70,111402 x. Cerrai, E., and Ghersini, G., Analytica Chim. Acta, 1967, 37, 295. Mikhailov, V. M., quoted in Milyukova, M. S., Gusev, N. I., Sentyurin, I. G., and Sklyarenko, I.S., Wolf, P., and Reinhardt, J., Radiochimica Acta, 1969, 11, 128. Vera Palomino, J., Palomares Delgado, F., and Petrement Eguiluz, J., An. Qulm., 1964, 60, 701. Savvin, S. B., Talanta, 1961, 8, 673. Savvin, S. B., and Propitsova, R. F., Zh. Analit. Khim., 1968, 23, 813. BorAk, J., Slovgk, Z., and Fischer, J., Talanta, 1970, 17, 215. Savvin, S. B., Dokl. Akad. Nauk SSSR, 1959, 127, 1231. -, Talanta, 1964, 11, 1. -, Zav. Lab., 1963, 29, 131. Onishi, H., and Toita, Y., Bunseki Kagaku, 1969, 18, 592; Chem. Abstr., 1969, 71, 67115a. Palei, P. N., Nemodruk, A. A., and Davydov, A. V., Radiokhimiya, 1961, 3, 181. Palei, P. N., Nemodruk, A. A., and Deberdeeva, R. Yu., Ibid., 1966, 8, 437. Kuznetsov, V. I., and Savvin, S. B., Ibid., 1960, 2, 682. Kuroha, T., Sakakibara, M., and Sibuya, S., Bunseki Kagaku, 1966, 15, 569; Chem. Abstr., 1967, Opalovskii, A, A., and Kuznetsova, 2. M., Izv. Sib. Otdel. Akud. Nauk SSSR, Ser. Khim. Nauk, Nemodruk, A. A., Novikov, Yu. P., Lukin, A. M., and Kalinina, I. D., Zh. Analit. Khim., 1961, Nemodruk, A. A., and Palei, P. N., Ibid., 1968, 23, 214. Nemodruk, A. A., and Glukhova, L. P., Ibid., 1963, 18, 93. -- , Ibid., 1968, 23, 552. Lukyanov, V. F., Savvin, S. B., and Nikol’skaya, I. V., Ibid., 1960, 15, 311. Nemodruk, A. A., and Palei, P. N., Ibid., 1963, 18, 480. Vykhovtseva, T. T., and Tserkovnitskaya, I. A., “Application of Organic Reagents in Analytical Nemodruk, A. A., and Kochetkova, N. E., Zh. Analit. Khim., 1962, 17, 330. Singer, E., and Matucha, M., 2. analyt. Chem., 1962, 191, 248. Nemodruk, A. A., and Palei, P. N., Zh. Analit. Khim., 1963, 18, 47. Mohai, M., Upor, E., and Jurcsik, I., Magy. Kbm. Foly., 1965, 71, 334. Onishi, H., and Toita, Y., Bunseki Kagaku, 1965, 14, 1141; Chem. Abstr., 1967,67, 39894~. Singer, S., and MareCek, J., 2. Analyt. Chem., 1963, 196, 321. Eschrich, H., Ibid., 1967, 226, 100. P6rez-Bustamente, J. A., 11 Coloquio Franco-Espafiol sobre el tratimento de los Combustibles Ir- - , “Compte Rendu 18‘ Colloque Franco-Espagnol sur le traitement des Combustibles Irradib,” PBrez-Bustamante, J. A., and Palomares Delgado, F. , in preparation. Ahrland, S., Acta Chem. Scand., 1949, 3, 783. P6rez-Bustamante, J. A., Radiochimica Acta, 1965, 4, 61. Tserkovnitskaya, I. A., and Vykhovtseva, T. T., Zh. Analit. Khim., 1967, 22, 1201. Martin, B., Ockenden, D. W., and Foreman, J. K., J . Inorg. Nucl. Chem., 1961, 21, 96. PCrez-Bustamante, J. A., in preparation. Kressin, I. K., and Waterbury, G. R., Analyt. Chem., 1962,34, 1598. Dahlby, J. W., and Waterbury, G. R., U.S. Atomic Energy Commission Report LA-3314, 1965. L6pez Morales, J., Gascb SAnchez, L., and Petrement Eguiluz, J., An. QuZm., 1966, 62, 1265. Maria, A., Compte Rendu du Groupe Technique et Chimie Analytique, H/P/L No. 57 (1967), C.E.A., Received February 4th, 1970 AcceDted Sebtember 2nd. 1970 --- , , Report J.E.N. 139-DQ/I 43, 1964. “Analytical Chemistry of Plutonium’’ (in Russian), Izd. Nauka, Moscow, 1965, p. 173. I , , Ibid., 1966, 62, 293. , , , Ibid., 1966, 62, 301. --- --- 66, 721922. 1965, 1, 130; Chem. Abstr., 63, 17144a. 16, 180. Chemistry” (in Russian), Izd. LGU, Leningrad, 1969, p. 132. -- , , Radiokhimiya, 1968, 10, 324. radiados, Madrid, November 17th to 19th, 1969, in the press. Fontenay-Aux-Roses, November 11th to 14th, 1967, p. 103. La Hague, France.

ISSN:0003-2654    

DOI:10.1039/AN9719600407

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

Analyst, June, 1971, Vol. 96, @. 423426 423 Determination of Iodine and Bromine in Biological Materials by Neutron-activation Analysis BY S. OHNO (National Institute of Radiological Sciemes, 9-1, 4-chome, Anagawa, Chiba-shi, Japan) Iodine and bromine have been determined in some biological materials by neutron activation analysis. These elements are extracted from irradiated samples with a 5 per cent. solution of trioctylamine in xylene, first the bromine being back-extracted with N sodium nitrate solution and then the iodine being back-extracted with N ammonia solution. The extraction yield is about 94 per cent. for iodine and about 86 per cent. for bromine. The limit of detection is about 0.01 pg for iodine and about 0.1 pg for bromine. The precision of the method is about &-6 per cent.for both elements for concentrations exceeding 0.1 p.p.m. MANY investigations have been carried out on iodine and bromine in biological and geological f i e l d ~ , l J ~ ~ ~ ~ J + because both elements have important essential functions in biochemistry. By using the radioactivation technique, Cosgrove, Bastain and Morrison' determined mixed halides in zinc sulphide phosphors and Dimitriadou, Turner and Frasers analysed paper chromatograms of human serum to determine i ~ d i n e . ~ Other workers have determined the concentration of both elements in many materials by this technique. On the other hand, radiochemical separation of radioiodine and radiobromine in irradiated samples has been carried out by solvent extraction and an anion-exchange method. Iodine and bromine have generally been extracted with either carbon tetrachloride or chlorofonn,1° and also distillation methods have been used.However, Moore11t12 mentioned that the application of the technique for the extraction of radioactive simple acids (e.g., hydrochloric acid, sulphuric acid, etc.) would be a potentially useful field of investigation for the radio- chemist because it has not yet been reported by other workers. In this work, iodine and bromine in some irradiated samples are extracted with a solution of trioctylamine in xylene and are determined by neutron-activation analysis. EXPERIMENTAL REAGENTS- All reagents used were of analytical-reagent grade. Trioctylamine - xylene solution-Dissolve 25 g of trioctylamine in 475 g of xylene.Sodium nitrate solution, N. Ammonia solution, N. Potassium iodide standard solution-Prepare an aqueous solution containing 10 pg ml-l Potassium bromide standard solution-Prepare an aqueous solution containing 100 pg ml-l Potassium iodide cawier solution-Prepare an aqueous solution containing 10 mg ml-l Potassium bromide carrier solution-Prepare an aqueous solution containing 10 mg ml-l of iodine. of bromine. of iodine. of bromine. PREPARATION OF SAMPLE- Vegetable sample-Weigh 100 g of fresh vegetable sample, dry it in an oven at 110 "C for 24 hours, and then grind it to a powder. Transfer a portion of the powdered sample into a nickel crucible and fuse it with 5 g of sodium hydroxide and 1 g of sodium peroxide powder 0 SAC and the author.424 OHNO: DETERMINATION OF IODINE AND BROMINE I N [Analyst, VOl.96 in a muffle furnace at 450 "C for 30 minutes. After cooling, dissolve the fused cake in 50 ml of distilled water and warm the solution on a water-bath. After centrifuging it transfer the solution into a 100-ml measuring flask. With a pipette, place 0-5d of this solution on a 3 x 3-cm polythene sheet, evaporate it carefully to dryness with an infrared lamp and then heat-seal it. Urine sam$e-Prepare 1 g of Dowex 1x8 resin (50 to 100 mesh) in a glass column 5 cm long and 1.0 cm in diameter. Wash the column with 100 ml of distilled water followed by 50 ml of N hydrochloric acid solution at the rate of about 2 ml minute-l. Pass 100 ml of urine through the column. Wash the resin with 50 ml of distilled water and then dry it in an oven at 110 "C for 5 hours.After transferring the dried resin into a nickel crucible, fuse it with about 5 g of sodium hydroxide and 1 g of potassium nitrate in a muffle furnace at 450 "C for 5 hours and continue as for the vegetable sample described above. IRRADIATION- The vegetable and urine samples and two standard specimens were packed together in a polythene bag and the irradiation was then carried out in a thermal neutron flux of about 8 x 1013 neutrons cm-2 s-l for 20 minutes in the JRR-2 reactor of the Japan Atomic Energy Research Institute. ACTIVITY MEASUREMENT- A TMC 400-channel pulse height analyser was used for the quantitative measurement of the photopeaks, mainly the 0.45-MeV peak for iodine-128, and 0-55-MeV or 0-78-MeV peak for bromine-82.The photopeak area was evaluated according to Covell's method,l3 and iodine-128 and bromine-82 were identified from their half-lives as determined by following their decay and from .the y-ray energy associated with their radioactive decay. RADIOCHEMICAL SEPARATION OF IODINE AND BROMINE- Open the irradiated sample into a 50-ml glass beaker and add to it the equivalent of 10 mg each of iodine and bromine carrier. Dissolve the sample in 10 ml of distilled water and warm the solution on a water-bath. Then transfer the solution into a separating funnel, wash the beaker with 5 ml of distilled water, and add the washings to the funnel. Adjust the solution to a pH between 4 and 5 with a few drops of 0.1 N nitric acid solution and add 2 ml of 30 per cent. hydrogen peroxide solution.Extract the iodine and bromine with 15 ml of 5 per cent. solution of trioctylamine in xylene, shaking the mixture for 1 minute. Repeat this step twice. Discard the aqueous phase, then back-extract the bromine with 15 ml of N sodium nitrate solution, shaking the mixture for 1 minute. Precipitate the bromine from this solution as silver bromide. After back-extracting the bromine, add 15ml of N ammonia solution to the separating funnel containing the organic phase and then back- extract the iodine, shaking the mixture for 1 minute. Precipitate the iodine as silver iodide. After filtering the precipitates, count the radioactivity of iodine-128 by y-ray spectrometry and then, after allowing the precipitate containing bromine432 to stand for 24 hours, measure TABLE I RESULTS OBTAINED FOR THE DETERMINATION OF IODINE AND BROMINE IN SOME BIOLOGICAL SAMPLES Dried vegetable- Iodine, p.p.m.Bromine, p.p.m. Daucus carota Linn, var. sativa DC . . 0-032, 0.030, 0-031 0.221, 0-215, 0.200 Brassica pekinensis Rupr. .. . . 0.016, 0.017, 0.015 0-157, 0-163, 0.160 Raphanus sativus Linn. . . .. . . 0.009, 0.011, 0.009 0.134, 0.141, 0.138 Allium ce$a Linn. .. .. , . 0.040, 0.041, 0.037 0.455, 0.433, 0.463 Spinaci oleracea Linn. . . .. . . 0.013, 0.014, 0.013 0.118, 0.118, 0.110 Urine (human)- No. 1 0.169, 0.199, 0,181 2.541, 2.688, 2.760 2 0-161, 0.157. 0.163 2.368, 2.476, 2.558 3 0.109, 0.098, 0.093 2.251, 2.347, 2-238 4 0.199, 0.207, 0,213 4.100, 4.125, 4.199 5 0.357, 0,342, 0.311 5.307, 5.321, 5.219June, 19711 BIOLOGICAL MATERIALS BY NEUTRON-ACTIVATION ANALYSIS 425 the radioactivity of bromine-82 by yray spectrometry.The time required for the separation, including that from the end of irradiation to counting, is less than 30 minutes for five samples. As iodine-128 is a short-lived radionuclide, counting of its radioactivity must be carried out without delay. RESULTS AND DISCUSSION The amounts of iodine and bromine contained in some biological materials have been determined by thermal-neutron activation analysis. The results obtained are shown in Table I. A systematic addition method for the determination of these elements has also been examined. Several samples were prepared and spiked with various amounts of standard. The results obtained by the addition method are shown in Table 11.TABLE I1 DETERMINATION OF IODINE AND BROMINE IN URINE AND VEGETABLE SAMPLES BY STANDARD METHOD Sample Vegetable . Amounts of standard added/pg Amounts t-A-, of sample Iodine Bromine - - * 1 g 0.0 1 0.1 0.02 0.2 0.05 1.0 Activity in the precipitate/ counts minute-l Iodine Bromine I o e n e foundlpg found/pg 7 019.5 2 560-8 - - 9 171-5 3 691.7 0.032 0.226 11 125.5 4 646.8 0-034 0.241 17 609.8 7 529.0 0.03 1 0.257 Urine .. 1 ml - - 35 088-0 19 581.8 - - 0.01 1.0 37 351.7 27 447.0 0.155 2.489 0.02 2.0 39 265.1 35 249.0 0.168 2.501 0-05 5.0 46 121.9 58 243-8 0-159 2-53 1 By using this solvent-extraction technique, it appears from the results obtained that the proposed method is simple and rapid, particularly for the determination of iodine. The radiochemical purities of the separated iodine-128 and bromine-82 were checked from their y-ray spectra and decay curves (Fig.1). 1 \ B \--- I 50 100 Channel number Fig, 1. y-Ray spectra of A, bromine-82 and B, iodine-1281 from the irradiated sample after solvent extraction During dry ashing or alkali fusion of biological samples in a muffle furnace it is known that some elements are partially lost; therefore, to determine the loss of iodine and bromine when the samples were prepared for irradiation, the urine and vegetable samples were spiked426 OHNO with known amounts of iodine-131 and bromine-82. These spiked samples, prepared for alkali fusion, were then heated in a furnace at selected temperatures for periods ranging from 5 to 10 hours. After the fused samples had been dissolved in distilled water to give a clear solution, the loss of both elements and the chemical yield were determined by the subsequent procedure as described above.The results obtained are given in Table 111, in which losses after alkali fusion are expressed as percentages. The results show that iodine and bromine are largely retained when the alkali fusion of some biological materials is carried out at temperatures below 450 “C. TABLE I11 LOSS OF IODINE AND BROMINE ON ALKALI FUSION OF URINE AND VEGETABLE SAMPLES IN A MUFFLE FURNACE Ashing time/hours . . 5 10 5 10 5 10 5 10 Loss from urine sample, per cent. Loss from vegetable sample, per cent. Heating r h > t h > temperature/’C Iodine Bromine Iodine Bromine -7 * * - 300 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0-1 400 1-8 2.1 1.0 1.5 1-4 3.1 1.1 1.7 450 6.2 6.9 5.2 5.5 6.6 7.3 5.0 6-9 500 7.0 7.9 6.1 6.5 7.8 9.1 6.0 6.9 550 8-3 8-5 8.0 8.1 8-6 8.8 8.0 8.4 600 12.5 11.9 10.0 10.6 11.8 12.1 9.8 13.2 The sensitivity of detection was calculated on the basis of the minimum detectable photopeak area for iodine-128 and for bromine-82.The sensitivity limits of this method were determined and found to be 0.01 pg for iodine and 0.1 pg for bromine, and the precision was about +6 per cent. for both elements for contents exceeding 0.1 p.p.m. Extraction with carbon tetrachloride will separate radioiodine from the other radio- nuclides, and the same solvent can also be used subsequently to extract the radiobromine. However, use in this work of an amine of high molecular weight, which is a liquid anion exchanger, enabled the iodine and bromine to be extracted and separated with ease.More- over, the radiochemical yield for both elements, particularly that for bromine, is higher than that reported by other workers2 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. REFERENCES Lenihan, J . M. A., and Thomson, S. J., Editors, “Advances in Activation Analysis,” Academic Duce, R. A., and Winchester, J. W., Radiochimica Acta, 1965, 4, 100. Ballaux, C., Dams, R., and Hoste, J., Analytica Chim. Acta, 1967, 37, 164. Wyttenbach, A., von Gunten, H. R., and Scherle, W., Geochim. Cosmochim. Ada, 1965,29, 467. Mulvey, P. F., Cardarelli, J . A., Zoukis, M., Cooper, R. D., and Burrows, B. A., J. Nucl. Med., Ishii, D., and Nakashima, M., Radio-Isotopes, Tokyo, 1970, 19, 129. Cosgrove, J . F., Bastain, R. P., and Morrison, G. H., Analyt. Chem., 1958, 30, 1872. Dimitriadou, A., Turner, P. C. R., and Fraser, T. R., Nature, 1963, 197, 446. Kleinberg, J., and Cowan, G. A., The Radiochemistry of Fluorine, Chlorine, Bromine and Iodine, Moore, F. L., U.S. Atomic Energy Commission Report ORNL-1314, 1952. -, Analyt. Chem., 1957, 29, 1660. Covell, D. F., Ibid., 1959, 31, 1785. Press, London and New York, 1969, p. 190. 1966, 7, 603. 8 , , Ibid., 1963, 198, 576. --- NAS-NS, 3005, 1960. Received June 29th, 1970 Accepted October Eth, 1970

ISSN:0003-2654    

DOI:10.1039/AN9719600423

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

Analyst, June, 1971 , Vol. 96, j?$. 427431 427 Loss of Cobalt and Iron from Lithium Tetraborate Fusions in Graphite Crucibles BY H. BENNETT AND G. J. OLIVER (The British Ceramic Research Association, Queens Road, Penkhull, Stoke-on-Trent, ST4 7LQ) It has been found that both iron and cobalt are lost from lithium tetra- borate fusions performed at 1 200 "C in graphite crucibles. The elements segregate as tiny pieces of metal near the graphite - fusion interface owing to reduction. The same reaction could well occur with other metals of lower affinity for oxygen than carbon and so these also would disappear from the fusion. IN the course of work to develop a spectrographic method for the analysis of high silica materials (sands, etc.) in the solid form, cobalt and manganese oxides were found to be good internal standards.In this method the sample, suitably powdered, is mixed in one of two possible proportions, 1 + 6 or 1 + 9, with a lithium tetraborate flux containing the internal standards. The mixture is fused at 1200 "C in a graphite crucible for 15 minutes, shattered in water, ground, mixed with graphite, pressed into disc electrodes and then excited by an a.c. arc on a direct-reading spectrometer. The graphite crucibles were produced from 24-inch long, 1Q inch diameter Morganite EY9 graphite rods. PRELIMINARY EXPERIMENTS Originally the internal standards were mixed without fusion with the lithium borate flux. In an experiment to determine optimum fusion time for samples, it was found that melts after 20 minutes' fusion appeared appreciably less blue than those after 10 and 15 minutes.On arc-ing the discs prepared from the fusions, not only had the cobalt internal standard intensity decreased for the 20-minute fusion but also the intensity of iron contained in the sample. The variation in the cobalt intensity in the fusions was thought at first to be caused by possible bad mixing. A fresh batch of flux was prepared containing the same amounts of tricobalt tetroxide (Co,O,) (about 1 per cent.) and trimanganese tetroxide (Mn,O,) (about 0.5 per cent.) as the original, but on this occasion the flux was pre-fused in platinum after mixing, and then re-ground. In similar fusion-time experiments with the new flux (5, 10, 15 and 20 minutes) it was found that melts still became progressively paler blue in colour.Intensities of iron and cobalt again decreased with time of fusion, the decrease being appreciable after 15 minutes, although that of manganese appeared to increase slightly (see Fig. 1). As there was an apparent loss of two components, one an internal standard and the other an element to be determined in analysis, it was decided to investigate the phenomena more closely. From visual observations of successive fusions in the same crucible, it appeared that loss of blue colour increased with repeated use of the crucible. Crucibles were therefore pre- treated by carrying out in them several fusions of about 2 g of a mixture of pure silica and pure lithium borate, 1 + 9. After four of these fusions it was found that any fusion of 0.2 g of high silica material and 1-8 g of lithium borate containing 1 per cent.of cobalt oxide would consistently yield a pale blue bead. The beads were much paler in colour than the same mixture fused, say, in a platinum crucible or in a previously unused graphite crucible. It was thought that the iron and cobalt might migrate into the crucibles, so several fusions involving iron and cobalt were performed to test this hypothesis. It was found that, in three crucibles tested, after five successive fusions there was a small amount of movement of iron and cobalt to the graphite but not enough to account for the large losses in colour. 0 SAC and the authors.428 8 - BENNETT AND OLIVER: LOSS OF COBALT AND IRON FROM [Analyst, Vol. 96 A 4 0 5 10 15 20 Fusion tirnehninutes - Fig.1. Change in iron, manganese and cobalt with length of fusion time: A, Mn 2676 A; B, Co 3405 A; and C, Fe 2599A INVESTIGATION In addition to the fact that the loss of cobalt blue colour from fusions became more apparent when the crucible had been used once or twice previously, another phenomenon noted was that the molten fusion product increasingly tended to stick to the crucible. It was decided to “pre-treat” a crucible as described earlier, and then fuse in it a mixture containing cobalt and iron. Each part of the system was then analysed to determine the distribution of cobalt and iron. Initially all of the cobalt is contained in the mixture to be fused and none in the crucible or its lid. Most of the iron is in the mixture to be fused but a small amount is present as an impurity in the graphite (0.48mg of iron oxide (Fe,O,) per l o g of graphite, i.e., 0.0048 per cent.).The components investigated were as follows: (i) lid of crucible; (ii) crucible; (iii) ash produced from burning of the crucible and lid during fusion; (iv) melts that can be poured from the crucible; and (v) melts that stick to the crucible. A mixture of 0.2 g of B.C.S. 267 silica brick (0.79 per cent. of Fe,O,) and 1-8 g of flux (0.86 per cent. of Co304) was fused at 1200 “C for 30 minutes. Table I shows how the cobalt and iron were redistnbuted after fusion. TABLE I MIGRATION OF IRON AND COBALT IN SYSTEM Masses of Fe,O, and Co,O, in fractions Unfused mixture Free melt Sticking melt F ~ s ~ o ~ s - Fe,O,/mg . . . . . . . . . . . . 1.6 0*,6 1.1 Co,O,/mg .. . . . . . . . . .. 16 1 16 Percentage of total mass . . . . . . 100 76 24 Concentration of Fe,O, in cooled melt, per cent. 0.079 0-036 0-23 Concentration of CO,O, in cooled melt, per cent. 0.79 0.067 3.32 Graphite- Migrated FsO,/mg Migrated Co,O,/mg Lid . . . . . . . . . . . . None None Crucible . . . . . . . . . . . . None 0.1 1 Ash . . . . . . . . . . . . None 0.03 nitroso-R-salt and the latter with o-phenanthroline. Co,O, and Fe,O, were determined photometrically by standard techniques, the former withJune, 19711 LITHIUM TETRABORATE FUSIONS IN GRAPHITE CRUCIBLES 429 As can be seen from Table I, no iron has migrated into any part of the crucible or lid and a very small amount of cobalt has been picked up by the crucible. Most of the iron and cobalt has migrated into the sticking part of the melt, which is only a small fraction of the total melt.There is, therefore, a large build-up of these elements in this part of the melt, as is shown by the comparison of concentrations in Table I. Visual examination of the sticking melts revealed that even these had a very pale blue colour. There was, however, a black layer, which was harder than graphite, adhering to the edge of this part of the melt. Further experiments were therefore performed to examine this region. Crucibles were pre-treated as before and the mixtures of 0.2 g of B.C.S. 267 plus 1.8 g of flux were fused in each of them for 50 minutes at 1 200 "C, to allow the effect to develop fully. The melts were allowed to cool in the crucibles and were then removed; they had the appear- ance shown in Fig.2. .... ... Bead .. Matt adhering layer Dark blue region Pale blue region Fig. 2. Appearance of fusions The dark blue regions of cobalt colour were noticeable only where the graphite crucible, or floating graphite powder, had been in contact with the melt. This layer was examined in four ways : by chemical analysis, X-ray diffraction, microscopy and electron probe microanalyser. CHEMICAL ANALYSIS- The adhering layer was removed with a diamond drill; however, it was impossible not to remove with the layer some of the bead produced from the fusion. The amount of the layer removed was about one half of the deposit on the bead. The results of analysis are shown for comparison in Table 11. TABLE I1 COMPARISON OF ANALYSIS OF SURFACE LAYER WITH ORIGINAL UNFUSED MIXTURE Oxide in surface layer (about one half of total layer) Oxide mix before fusion Mass of Co,O,/mg .. . . . . 6-64 15.8 Massof Mn,O,/mg . . . . . . 0.65 N 10 Mass of Fe,O,/mg . . . . . . 0.46 1.68 Concentration of c0~04, per cent. .. 6-75 0-79 Concentration of Mns04, per cent. .. 0-67 N 0.6 Concentration of F%O,, per cent. .. 0-46 0.079 Co,O, Mn,O, and Fe,O, were determined photometrically by standard techniques, CO,o, with nitroso-R-salt, Mn,O, as permanganate by oxidation with periodate and FQO, with o-phenanthroline. It is clear from Table I1 that there is a build-up of cobalt and iron in this layer, which indicates considerable migration to the graphite - fusion interface. It can be calculated that nearly all of the iron and cobalt have appeared in the matt layer.X-RAY EXAM1 NATIO N- An X-ray powder diffraction photograph revealed the presence of cobalt metal, graphite and a little silica in the surface layer.430 BENNETT AND OLIVER: LOSS OF COBALT AND IRON FROM [Analyst, VOl. 96 EXAMINATION BY ELECTRON PROBE MICROANALYSER- Measurements were made of iron Kor and cobalt Ka intensities along a line moving inwards from the edge of the bead (Figs. 3 and 4). It appears that there is a build-up of cobalt and iron into a layer about 10 pm thick at the surface of the bead. This layer consists of metallic particles close to the surface. No manganese was detected in these metallic particles, and the composition of the particles estimated from the intensities was shown to be about 10 per cent.of iron and 90 per cent. of cobalt, which would suggest the formation of metal regions by reduction of the oxides from the bulk of the melt. r 0 0 Surface of bead CoKa Background 10 I,,,-,, d 0 10 20 30 40 1000 1020 1010 1030 rn z L P 0 10 20 lo00 1010 Distance from edge of bead/pm Distance from edge of bead/pm Fig. 3. Logarithmic graph of cobalt Ka Fig. 4. Logarithmic graph of iron Ka intensity against distance from edge of bead intensity against distance from edge of bead EXAMINATION BY MICROSCOPY- Examination under a microscope revealed the presence of metal particles at and near the surface of that part of the bead which had been in contact with either the graphite crucible or the graphite powder floating on the surface. The metal appears as a fern-like structure, which seems to grow inwards from the outside of the bead. Fig.5 shows a section through the bead. Fern-like structures appear at the bottom of the melt and also, to a lesser extent, on the top surface. Fig. 6 shows a magnification of the lower edge of the bead and brings out the fern-like metal structure. Fig. 7 shows part of the top edge of the bead and displays not only the fern-like metal structure but also the bluer area of the bead, which shows as a darker region in the photograph. Fig. 8 shows the lower region of the bead viewed by reflected light. The white regions are metal particles showing through the surface. DISCUSSION From the chemical, microscopic, X-ray and electron probe microanalyser evidence it is clear that the iron and cobalt metals are being produced by reduction with graphite in areas where the flux and graphite are in contact.Manganese does not appear to be reduced noticeably. If a study is made of graphical representations of AGO of formation against temperature for the oxides of iron, cobalt, manganese and carbon, such as those given by Ellinghaml and other workers,2 it is clear that at 1200 "C carbon has a greater affinity than iron or cobalt for oxygen, as the -AGO value for the formation of carbon monoxide is greater than those for iron oxides (Fe,O,, FeO and Fe,O,) and cobalt oxide (COO). Study of similar diagrams for other oxides such as lead oxide (PbO), nickel oxide (NiO), zinc oxide (ZnO) and copper oxides (CuO and Cu,O) reveals that these too can be reduced by carbon at 1200 "C.This would suggest that the fusion process intended as a means of homogenising the sample serves only to segregate several important metallic components contained in it.Fig. 5. Section through bead Fig. 6. Lower edge of bead x 120 To Face p. 4301Fig. 7. Upper edge of bead x 120 Fig. 8. Lower edge of bead viewed by reflected light x 75 [To Face p. 431June, 19711 LITHIUM TETRABORATE FUSIONS IN GRAPHITE CRUCIBLES 431 The mechanism seems to comprise reduction of the dissolved oxides whenever they come into contact with the graphite. The surface must then become depleted of dissolved oxides, and migration of these oxides to this region must occur to maintain the uniformity of their concentrations throughout the fusion. The reaction must ultimately continue to some equilibrium point at which almost all of the iron and cobalt have been reduced. CONCLUSIONS When preparing lithium tetraborate fusions of high-silica materials in graphite crucibles a t 1 200 “C cobalt oxide added as internal standard and iron oxide contained in the sample are lost from the melt. The mechanism of this loss comprises reduction of these metals from their combined state by the graphite of the crucible. The reaction appears to occur more readily if the crucible has been used previously and if the fusion time exceeds 10 minutes. If fusions at 1200 “C are required for an analysis technique it would be advisable not to use graphite crucibles, but to make use of those made of a non-reducing material such as platinum or platinum alloys. The authors thank Dr. N. F. Astbury, C.B.E., Director of Research, British Ceramic Research Association, for permission to publish this paper and also Mr. D. Cooper of the North Staffs Polytechnic for his helpful comments. REFERENCES 1. 2. Ellingham, H. J. T., J . Soc. Chem. Ind., Lond., 1944, 63, 125. Glasher, A., “The Thermochemical Properties of the Oxides, Fluorides and Chlorides a t 2 500°K,” U.S. Atomic Energy Commission Report, ANL 6760, 1957. Received December 7th, 1970 Accepted January 25th 1971

ISSN:0003-2654    

DOI:10.1039/AN9719600427

出版商:RSC    

年代:1971

数据来源: RSC