ISSN:0003-2654    

DOI:10.1039/AN97196FX017

出版商:RSC    

年代:1971

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN97196BX019

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

iV THE ANALYST [May, 1971THE ANALYSTEDITORIAL ADVISORY BOARDChairman: A. A. Srnales, O.B.E. (Ha;well)*T. Allen (Brudford)*L. S. Bark (Salford)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 (Billinghum)D. Dyrssen (Sweden)*W. T. Elwell (6irmingham)*D. C. Garratt (London)*R. Goulden (Sittingbourne)J. Hoste (Belgium)D. N. Hume (U.S.A.)H. M. N. H. Irving (Leeds)*A. G. Jones (Welwyn Garden City)M. T. Kclley (U.S.A.)W. Kcmula (Poland)*G. F. Kirkbright (Londcn)*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 (Germany)A. Walsh (Australia)*T.S. West (London)P. Zuman (U.S.A.)*Members of ;he Board scrving on the Executive Committee.SOCIETY FOR ANALYTICAL CHEMISTRYThe 1971 volume of “Selected Annual Reviews of the Analytical Sciences” will be published shortly.CONTENTSMolecular-sieve Chromatography-D. M. W. Anderson, I. C. M. Dea and A. HendriePhotoluminescence and Chemiluminescence in Inorganic Analysis-L. S. Bark and P. R. WoodRecent Developments in Activation Analysis-T. B. PierceAtomic-absorption Spectroscopy-P. PlattCatalytic Methods in Analytical Chemistry-G. SvehlaORDER FORMTo The Society for Analytical Chemistry,Book Department,9/10 Savile Row,London, W I X IAFPlease send me a copy of the f i r s t (1971) volume of Selected Annual Reviews of the Analytical Sciences as soon as itis published.* I am a member of the Society for Analytical Chemistry and enclose my remittance for f3.00 ($7.50).* I am not a member of the Society for Analytical Chemistry.I enclose a remittance for fS.00 ($12.50)* Delete item that does not apply......................................................................................................................Name.....................................................................................................................Address.........................................................................................................................................................................................................................................vi SUMMARIES OF PAPERS IN THIS ISSUE [May, 1971Summaries of Papers in this IssueThe Determination of Chromium and Molybdenum in a CompleteRange of Steels by Atomic- absorption Spectrometry with aNitrous Oxide - Acetylene FlameInterferences in the absorption of chromium and molybdenum in steelsare overcome in the nitrous oxide - acetylene flame by using perchloric acidas the solvent.The method is rapid and suitable for any level of chromiumor molybdenum found in steels and other metallic alloys. An alternativemethod for the determination of molybdenum is necessary when the tungstenconcentration exceeds 0.5 per cent.; this involves the use of a perchloric -phosphoric - sulphuric acid mixture to retain the tungsten in solution.Adifference read-out technique to obtain good precision for high levels ofchromium is described.D. R. THOMERSON and W. J. PRICEPye Unicam Ltd., York Street, Cambridge.Analyst, 1971, 96, 321-329.The Fluorimetric Determination of Zirconium as 8-Hydroxyquinolinatein the Presence of Titanium, Tungsten and MolybdenumA fluorimetric method is described for the determination of small amountsof zirconium as 8-hydroxyquinolinate. The procedure, which involves extrac-tion of the chelate with chloroform from a hydrofluoric acid - ammoniumtartrate solution at pH 9.0, permits the determination of zirconium in thepresence of titanium, tungsten and molybdenum.Excitation is conducted at 398nm and emission measured at 520nm.Down to 0.1 pg of zirconium can be determined with a coefficient of variationof 2.3 per cent.H.0. SCHNEIDER and M. E. ROSELLIFacultad de Ciencias Exactas, Universidad Nacional de La Plata, La Plata, Argen-tina.Analyst, 1971, 96, 330-334.A Rapid Atomic-absorption Technique for the Determination ofLithium in Silicate MaterialsA simple and rapid atomic-absorption procedure is described for thedetermination of lithium in silicate rocks. Following fusion with sodiumborate, the samples are dissolved in dil.ute nitric acid solution. Determinationsof the lithium contents are made directly. The precision of the method, interms of one standard deviation, was calculated to be 1093 f 13 p.p.m.and 34.5 f 4.6 p.p.m. Accuracy, as indicated by a comparison with publisheddeterminations, is good.JAMES V. O’GORMAN and NORMAN H. SUHRMineral Constitution Laboratories, The Pennsylvania State University, UniversityPark, Pa., U.S.A.Analyst, 1971, 96, 335-337.An Improved Method for the Determination of Bacitracinin Animal FeedsThe determination of small amounts of bacitracin in animal feeds hasbeen studied. It was expected that by using acidified methanol as the onlyorganic solvent in the extraction procedure and phosphate buffer, undesiredproteins would not be dissolved and the use of the toxic solvent pyridinemight be avoided. Bacitracin could then be determined in the final extractby using microbiological methods, in which methanol interferes less thanpyridine. The method reported here has been used for feed mixtures withvarious zinc bacitracin contents in the range from 5 to 350 p.p.m.B. GRYNNEA/S Apothekernes Laboratorium for Specialprzparater, Oslo, Norway.Analyst, 1971, 96, 338-342

ISSN:0003-2654    

DOI:10.1039/AN97196FP077

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

May, 19711 THE ANALYST xiCLASSIFIED ADVERTISEMENTSThe ralc for c:assijkd advertisemcnfs is 35pa line (or spaceyurvaknt o/ a fane) with an extra charge of rop lor theuse of a Box Number. Smri-disp1aye.l rlassifiedadvertisements arc €4 for sinrlc-cohtmn inch.Copy required not later than Lkr 8th of t1w month prc-cedinq date of publication wlruh is on the 16th of cachmonth. Advertiscmcnts should be addressed toJ . Arthur Cook, 9 Lloyd Square, London, W.C.I.Tel.: 01-837 G315APPOINTMENTS VACANTPrincipalLecturer inAnalytical Sciences$2802-$3 14 2A plication form and details from: TR e Establishment Officer,Room TP/6The Polytechnic,Wolverhampton WV1 1LY.PHARMACIST O R CHEMIST(Technical Appointment)OPPORTUNITY IN SMALL SCALEMANUFACTURINGA small company of manufacturing chemists inN.W. London are looking for a live wirepharmacist or chemist who prefers being a bigfish in a small pond.His f i r s t job will be the setting up & operatingof a quality control department. Thereafterhe should within the next two years or soassume responsibility for development & pro-duction and become a director of the companywith the salary and other benefits which thati m p I i es.Replies in strict confidence giving career todate etc. to:Box No. 220, c/o J. Arthur Cook,9 Lloyd Square, London WClX 9BAPlease mention THE ANALYSTwhen replying to advertisementsADDENDUM 1971to the B.P. 1968Publication April 1, 1971Official from October 1, 1971This second Addendum to the British Pharm-acopaia 1968 adds a further 58 new mono-graphs and makes many important alterationsto the specifications in the main volume.Among the substances that are the subjectsof new-monographs are:Alprenolol HydrochlorideAminocaproic AcidCarbamazepineCephalothin SodiumDesferrioxamineMesylateDoxycyclineH yd roch I o rid eDydrogesteroneGentamicin SulphateHuman AntihaemophilicFractionlndomethacinLincomycinHydrochlorideMelphalanMethacyclineHydrochlorideMetyraponeNitrazepamPentagastrinPhenforminHydrochlorideProtri ptyli neHydrochlorideSat butamolSodiumCromogl ycateSulphamethox-azoleTrimethoprimTrimipramineMaleateVin blastineSulphateOther new monographs provide standards fortablets, capsules and injections of the abovesubstances, and for Rubella Vaccine (LiveAttentuated), Sorbitol Injection, Chlormerod-rin ('"Hg) Injection and lodinated (Y) HumanSerum Albumin Injection.Amendments made by the Addendum 1971to 64 monographs of the main volume havethe effect of substituting for the standardsof the British Pharmacopaia those given forthe corresponding substances in Volume 1of the European Pharmacopoeia.Appendices of the Addendum 1971 containa completely revised account of the deter-mination of the ABO and Rh groups of blooddonors, and descriptions of atomicabsorptionspectrophotometry and amino acid analysis.ADDENDUM 1971 to B.P.1968158 pages. S4 post freeAlso availableBRITISH PHARMACOPOEIA 19681454 pages.€8 post freeADDENDUM 1969 to B.P. 1968120 pages. €3.25 post freeThe Pharmaceutical Press17 Bloomsbury Square, London, WC1A 2xii SUMMARIES OF PAPERS IN THIS ISSUEChromatographic Separation and Titrimetric Determinationof the Aphicide Menazon in Paste FormulationsPaste formulations of menazon were chromatographed on a column ofacidic alumina. The emulsifying agents and other active ingredients wereeluted with hexane, diethyl ether and chloroform. Menazon was finallyeluted with dioxan and was then titrated potentiometrically with 0.1 Nperchloric acid in dioxan - acetic acid (1 + 1).PAOLO MAIN1SocietB. Italo Americana Prodotti Antiparassitari, Centro Esperienze e Ricerche,40015 Galliera (Bologna), Italy.A nalyst, 197 1, 96, 343-345.[May, 1971A Rapid and Accurate Method for the Determination ofMolybdenum in Plant Materials with Toluene-3,4-dithiolA rapid and accurate method is described for determining molybdenumin plant materials with toluene-3,4-dithiola The molybdenum is allowed toreact with the reagent in a solution with a sulphuric acid concentration ofabout 6 N.Prior separation of the element from the acid digest of the plantmaterial is unnecessary, there being no loss of sensitivity or accuracy if thisprocess is omitted.H. SSEKAALOAnimal Health Research Centre, P.O. Box 24, Entebbe, Uganda.Analyst, 1971, 96, 346-348.Determination of Sub-microgram Amounts of Cobalt in Plants andAnimal Tissues by Extraction and Atomic-absorption SpectroscopyAtomic-absorption spectroscopy is used to determine cobalt in plantsand animal tissues after solvent extraction of the 1-nitroso-2-naphthol com-plex from an acidic solution of the sample.The solvent is evaporated and thecomplex is dissolved in ethyl methyl ketone for aspiration. The method is moresensitive than, and as accurate and precise as, a colorimetric procedure in-volving nitroso-R salt, and is much less tedious.Cobalt can be determined in the range 0.05 to 1 pg in the final 1-mlsample solution (corresponding to 0.05 to 1 p.p.m.). With a 5-g sample from0.01 to 0.2 p.p.m. of cobalt in samples (dry matter) can be determined.The method can, therefore, be applied readily to pasture samples containing0.1 p.p.m. of cobalt and less, levels that are considered likely to causedeficiency in ruminants. At 0.07 p.p.m.of cobalt the coefficient of variationis 14 per cent. At higher concentrations (0.14 p.p.m.) of cobalt in pastureand liver samples the coefficients of variation are 11 and 6 per cent., respec-tively.J. JAGO, P. E. WILSON and B. M. LEEGovernment Chemical Laboratories, 30 Plain Street, Perth, Western Australia, 6000.Analyst, 1971, 96, 349-353... May, 19711 THE ANALYST xlllMicroanalysisOrganic & InorganicOne-way combustion boats andcapsulesVarious sizes.Various materials (Al. Ag. Sn.)A t interesting prices.For particulars and samples:Labor-Service H. ReinhardtCH 4125 Riehen (Switzerland)136 RainalleeBUREAU OF ANALYSEDSAMPLES LTD.announce the issue of a new l i s t ofBRITISH CHEMICAL tiS P ECTROSCO P I C STAN DA R DSAMPLESNo.437, April, 1971This includes full details of new andreplacement samples issued during thepast year.A copy will be sent free on request.NEWHAM HALL, NEWBY,MIDDLESBROUGH, TEESSIDE, ENGLAND.TS8 9EA,Tel. Middlesbrough 37216 (STD Code 0642)Gas Laser TubesStandard & Custom-builtSI LlCAAPPARATUSStandard & Custom-builtON-SITE REPAIRSAND FABRICATIONSRepair service for G. & E. Bradley gas lasersW. YOUNG(fused silica)P.O. 39, Hemel Hempstead,Hertfordshire. Tel: 3984TRACE ELEMENTANALYSISPRO BL EM S?Activation Analysis could be the answer.technique offers the advantages of high sensitivityand specificity, good accuracy and precision, even atsub-p.p.m.concentrations.obtained, often non-destructively. The maindisadvantage (the need for a nuclear reactor) can beovercome by making use of the Activation AnalysisService provided by the Universities Research Reactor.If you would like to discuss your particular problem,or would like to receive futher details, please contact:Dr. G. R. Gilmore (Activation Analyst),Activation Analysis Service,Universities Research Reactor,Risley,Nr. Warrington,Lancs.Phone, Warr. 32680, 33114ThisA bulk analysis ixiv SUMMARIES OF PAPERS IN THIS ISSUEVoltammetryAnodic stripping voltammetry has been used to study chelates of am-monium 1-pyrrolidinecarbodithioate with metal ions. A technique isdescribed in which polarographic waves are obtained when the chelates arehighly insoluble.The metal is deposited a t a hanging mercury drop electrodein the absence of chelating agent. The chelating agent is then added to thesolution and the anodic stripping peak is recorded. Metal-to-ligand ratiosand dissociation constants are calculated from the shift in the anodic strippingpeak compared with the stripping peak obtained in the absence of chelatingagent. Advantages include ability to use polarographic techniques when thechelates are insoluble (and non-reducible), increased sensitivity, and the possi-bility of using concentrations rather than activities for calculations involvingdilute solutions.[May, 1971Study of Slightly Soluble Metal Chelates by Anodic StrippingPHILLIP H. DAVIS and GARY D.CHRISTIANDepartment of Chemistry, University of Kentucky, Lexington, Kentucky 40506,U.S.A.A ~ n l y s t , 1971, 96, 354-358.The Stability of Dilute Solutions of Mercury(1) PerchlorateCentinormal solutions of mercury(1) perchlorate undergo changes inThese solutions should be standardised reducing normality during storage.frequently or prepared daily from the stable decinormal solution.R. J. MERRER and J. T. STOCKDepartment of Chemistry, The University of Connecticut, Storrs, Connecticut 06268,U.S.A.Analyst, 1971, 96, 359-360.The Amperometric Titration of Submillinormal Concentrationsof Cerium(1V) with Mercury(1) PerchlorateThe amperometric titration with mercury(1) perchlorate of 1 x lod4 Ncerium(1V) in 0.01 N potassium iodide - 0.2 N perchloric acid solution isprecise and accurate to about 2 per cent.R.J. MERRER and J. T . STOCKDepartment of Chemistry, The University of Connecticut, Storrs, Connecticut 06268,U.S.A.Analyst, 1971, 96, 361-363.Polarographic Behaviour of Zinc, Nickel, Copper, Cobalt andCadmium in Monoethanolamine SolutionPolarographic characteristics of copper, cobalt, nickel, zinc and cadmiumin a solution 0.5 M in monoethanolamine and 0.1 M in potassium chloride,at pH 11.0, have been observed, well defined waves being obtained in allinstances. The method described is suitable for the quantitative determinationof these metals individually and for the differentiation of nickel from cobaltand from zinc.A. L. J. RAO and B. K. PURIDepartment of Chemistry, Punjabi University, Patiala, India.Analyst, 1971, 96, 364-366xvi SUMMARIES OF PAPERS IN THIS ISSUEThe Determination of Methanol in Hair SprayInterference by ethanol and other hair spray constituents in the colori-metric determination of methanol is obviated by distillation of the spray,extraction with light petroleum of the sodium chloride saturated distillate,and use of a standard graph of methanol concentration ueysus optical density.CHIA CHWEE LEONG and THENG CHYE YAMDepartment of Chemistry, Ministry of Science and Technology, Outram Road,Singapore, 3.Analyst, 1971, 96, 367-369.[May, 1971Proton Chemical Shifts for Solvents and otherSimple SubstancesThe chemical-shift values for the principal nuclear magnetic resonancepeaks for fifty solvents and other low molecular-weight substances dissolvedin deuterochloroform, deuterodimethyl sulphoxide, benzene (or deutero-benzene), pyridine (or deuteropyridine), trifluoroacetic acid and heavy waterare recorded. The values are useful for the rapid identification and deter-mination of these substances when present as impurities in other organiccompounds.R.A. FLETTON and J. E. PAGEGlaxo Research Ltd., Greenford, Middlesex.Analyst, 1971, 96, 370-373.Fluidic Devices : Design and Applications for AnalyticalSampling ProcessesA range of commercially available fluidic devices has been evaluatedfor application to analytical sampling processes.As a result of this work a modified bistable fluidic element incorporatinga control assembly has been constructed.Details of its design and performanceare given.B. FLEET and L. H. von STORPChemistry Department, Imperial College, London, S. W.7.Analyst, 1971, 96, 374-379.An Attachment to a Simple Trace Reader for Use in ReactionRate AnalysisAn attachment to a commercial chart reader that facilitates the measure-ment of the gradients of sloping traces is described. The performance of theattachment was investigated by using traces generated by the L.K.B. Re-action Rate Analyzer. A measurement rate of ten traces per minute witha coefficient of variation of 1 per cent. was achieved.J. B. DAWSON, G. W. FISHER and W. ANNANDepartments of Medical Physics and of Chemical Pathology, University of Leeds,The General Infirmary, Leeds, 1.Analyst, 1971, 96, 380-383.The Determination of Small Amounts of Fluoride in SolutionReport prepared by the Fluorine Sub-committee.ANALYTICAL METHODS COMMITTEE9/10 Savile Row, London, W1X 1AF.Analyst, 1971, 96, 384-392May, 19711 THE ANALYSTAn ‘impossible’ analytical problem?xviitwo 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 at 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 :Receive further information by post Discuss my problem with youI am also interested in assistance with :IR spectrometry mass spectrometry NMR spectrometrycomputer applications Q on-line analysisother analytical techniques (tick as appropriate)NamePositionAddressTel No.AA 1

ISSN:0003-2654    

DOI:10.1039/AN97196BP085

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

MAY, 1971 Vol. 96, No. I142 THE ANALYST The Determination of Chromium and Molybdenum in a Complete Range of Steels by Atomic-absorption Spectrometry with a Nitrous Oxide -Acetylene Flame BY D. R. THOMERSON AND W. J. PRICE (Pye Unicam Ltd., York Street, Cambridge) Interferences in the absorption of chromium and molybdenum in steels are overcome in the nitrous oxide - acetylene flame by using perchloric acid as the solvent. The method is rapid and suitable for any level of chromium or molybdenum found in steels and other metallic alloys. An alternative method for the determination of molybdenum is necessary when the tungsten concentration exceeds 0.5 per cent. ; this involves the use of a perchloric - phosphoric - sulphuric acid mixture to retain the tungsten in solution. A difference read-out technique to obtain good precision for high levels of chromium is described.EARLIER papers on the determination of chromium and molybdenum in steel with an air - acetylene flame report interferences,l to l 6 in particular, a serious depression of the chromium and molybdenum absorbance by iron itself. Various methods of overcoming these effects were proposed, but none was completely effective for the whole range of elements found in steels. For this reason atomic-absorption spectrometry with an air - acetylene flame for the determination of chromium and molybdenum in iron and steel never achieved the degree of success associated with it in other fields of analysis. With the advent of the nitrous oxide - acetylene flame, new interest was kindled, and with it fresh hopes of success.Even so, compared with the amount of published work on the air - acetylene flame, comparatively little work has been reported in which the nitrous oxide flame was used for the determination of chromium and molybdenum in steel. Kirkbright, Smith and West17 found that the nitrous oxide - acetylene flame overcame many interferences in the determination of molybdenum in alloy steels ; however, their method appears to have some limitations and did not always give consistent results in our hands. Ramakrishna, West and Robinsonla made a comprehensive study of the interferences on molybdenum in the nitrous oxide flame. We confirmed their findings concerning the enhancement effect caused by iron in all media; but we could find no evidence under any conditions of the 30 per cent.enhancement due to perchloric acid that they report. Further studies by McIssac1S~20 showed no interference by iron, but a small enhancement by manganese. Endo, Hata and Nakahara21 found that the molybdenum response was enhanced by the addition of potassium sulphate, which they report as overcoming all in terelement a1 interferences. Only two attempts to determine more than 5 per cent. of chromium in steel were found. The first, by Feldman, Blasi and Smith:z reported the successful determination of 15 per cent. of chromium by using the 425.4 nm line, but no experimental details were given. The second was by WelQ3 who reported low results when using synthetic standards with iron and nickel additions; but when calibration was effected with standard steels, good results were obtained at the 17 per cent.level. A scheme for the determination of chromium and molybdenum in a wide range of steels is therefore considered to be desirable. 0 SAC and the authors. 321322 THOMERSON AND PRICE : DETERMINATION OF CHROMIUM AND MOLYBDENUM [Analyst, Vol. 96 EXPERIMENTAL APPARATUS- All measurements were made with a Unicam SPSOA Series 2 atomic-absorption spectro- photometer, which incorporated a SP91 lamp turret accessory and a SP94 nitrous oxide accessory. Air was supplied through a SP93 air compressor, and nitrous oxide and acetylene were obtained from cylinders. The instrument was also fitted with an inert nebuliser and Unicam high spectral output hollow-cathode lamps. The absorbance peaks were displayed on a SP22 chart recorder.The only non-standard modification was the fitting of 0.125-mm thick metal shims to the nitrous oxide burner to increase the slot width from the normal 0.46 mni to 068 mm. This was necessary to prevent blockage by steel solutions more concentrated than about 0.5 per cent. The fitting of these shims naturally somewhat reduces the previous operating safety margins. Therefore it is important to maintain the gas flow-rates close to the values recommended below. On no account should shims of thickness greater than 0-125mm be used. INTERFERENCES- Interference studies of various acids on the absorbance of chromium and molybdenum showed conclusively that perchloric acid was the best solvent. Unlike other acids (sulphuric - phosphoric, nitric - hydrochloric) it did not interfere with the absorption response.Further- more, experimental evidence was accumulated to suggest that it is essential to obtain both elements in the same oxidation states in both their sample and calibration solutions (otherwise chromium results were on average 10 per cent. low and molybdenum 40 per cent. high), and perchloric acid was also found to ensure complete oxidation. The interference effects of iron have long been realised, and they exist also in the nitrous oxide- acetylene flame. However, in this flame iron enhances the absorption of both chromium and molybdenum, whereas with air - acetylene there is considerable depression. It was found that the enhancement varies with the iron concentration. In the case of molyb- denum this enhancement decreases as the iron concentration increases in the range shown in Fig.1, whereas for chromium, enhancement increases in the same range of iron concen- trations. Therefore, it is still necessary to incorporate iron in the calibration solutions and 0.2 0.5 I I I 1 I I I 1 I I I I Iron concentratiodg per 100 ml Fig. 1. Effect of iron concentration on the absorbance of 20 mg 1-1 of chromium and 60 mg 1-1 of molybdenum: A, chromium; B, molybdenum; and C, aqueous solutions (no iron)May, 19711 IN A COMPLETE RANGE OF STEELS BY ATOMIC-ABSORPTION SPECTROMETRY 323 also to add iron to solutions if dilutions are necessary, in order to maintain a constant concentration of iron in all the samples and calibration solutions. Since most alloyed steels contain only about 60 to 80 per cent.of iron initially in the sample, it is usually necessary to raise their iron content to the equivalent of 100 per cent. in a 1 per cent. sample solution by additions of iron stock solution to the sample solutions before the final dilutions. The improvements in results can be significant. When chromium standards were prepared by simply adding a stock iron solution in perchloric acid to the chromium calibration solutions, low results were always obtained for concentrations greater than about 5 per cent. This effect probably resulted from a difference in the oxidation states and was overcome only by ensuring that the calibration solutions were prepared and oxidised in an identical manner to the sample solutions (see Proposed Method).METHOD DEVELOPMENT- Unfortunately, the presence of tungsten in two of the steels to be analysed posed problems when perchloric acid was used as the solvent. When molybdenum was being determined, the results were only about one-half of their true value. The molybdenum was almost certainly being lost by co-precipitation with the tungsten while the latter was being filtered off as tungstic acid in the preparation of the final solutions. It was, therefore, thought best to retain the tungsten in solution by dissolving the steel sample in a mixture of sulphuric, phosphoric and perchloric acids. This step is the basis of an alternative procedure. Molybdenum was then successfully determined in the presence of 6.9 per cent. of tungsten while the results obtained in the presence of 19.6 per cent.of tungsten were reasonably acceptable. This method of dissolution cannot be employed in a general scheme for chromium and molybdenum as, when the chromium is determined in this solution, an enhancement effect is observed and results are up to 20 per cent. high. For example, B.C.S. 241/1, which contains 20 per cent. of tungsten and 5-03 per cent. of chromium, gave a result of 6.00 per cent. of chromium; and for B.C.S. 220/1, which contains 6-9 per cent. of tungsten and 5-13 per cent. of chromium, our result was 6.16 per cent. of chromium. The other disadvantage of this dissolution is the length of time it needs for completion. For a 1-g sample it could take as much as 2 hours, whereas with perchloric acid the average time is about 20 minutes.Hence, it was decided to adopt the perchloric acid solvent for a scheme for determining chromium and molybdenum in all steels except those for which molybdenum is to be determined in the presence of more than 0-5 per cent. of tungsten. CHOICE OF CALIBRATION RANGE- The reasonably small range of the molybdenum concentrations posed no calibration problems. In general a range of 5 to 50 mg 1-1 (corresponding to 0-05 to 0.5 per cent. of molybdenum in a 1-g sample) was used, and sample dilutions were made when necessary. For higher concentrations of molybdenum, a range of 10 to 100mg1-1 was used with a slightly angled burner, and for lower concentrations 2 to 20 mg 1-1 was used (see Table I) with scale expansion. In all cases the calibration graphs are linear.Chromium, being present over a much greater range of concentrations, needed a different approach. For chromium concentrations up to 5 per cent., a calibration range of 5 to 50 rng 1-1, in conjunction with further dilutions of the sample as necessary, was found to be adequate, but for chromium concentrations between 5 and 25 per cent., large dilutions (of the order of 100 times) were required, and predictably the precision was poor. This position was greatly improved by using a calibration range of 25 to 300 mg 1-1 and a fully rotated burner (which in the case of the SP90 is about 50” from the optical axis). This range is equivalent to a concentration of 1.0 to 12.0 per cent. of chromium in a 0-25-g sample made up to 100ml. The greatest dilution necessary for the range of steels analysed was then five times (Table 11).Rotating the burner also reduced the flame noise, which was sometimes a problem with the 5 to 50 mg 1-1 range and was probably a further reason for the poor precision obtained with results greater than 5 per cent. The calibration graph for the 25 to 300rng1-1 range is slightly curved, while those for the 5 to 50mg1-1 and 10 to 100mg1-1 ranges are linear. OPERATING PARAMETERS- A careful study of the observation height and fuel flow-rates showed that for chromium the fuel flow was not critical. The optimum sensitivity was obtained for a “red-feather”324 THOMERSON AND PRICE: DETERMINATION OF CHROMIUM AND MOLYBDENUM [Amlyst, Vol. 96 I / Acetylene flow rate/l minute-’ Effect of fuel flow-rate on absorbance of chromium and molybdenum: A, chromium $Zus 1 per cent.of iron in perchloric acid: B, aqueous chromium solution; C , molybdenum plus 1 per cent. of iron in perchloric acid; and D, aqueous molybdenum solution Fig. 2. 1 I I I I f I I 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 09 1Q Observation heighthm Fig. 3. Effect of observation height on chromium: A, chromium plus 1 per cent. of iron in perchloric acid; and B, aqueous chromium solutionMay, 19711 325 height of about 0.5 to 1.0 cm. Conversely, for molybdenum, the fuel flow-rate was found to be very critical so that the flame must be carefully adjusted in order to obtain maximum sensitivity. This corresponds to a fuel-rich flame which has a maximum red-feather height without luminescence (Fig. 2).The optimum observation height for chromium is 0.60 cm (Fig. 3); but in practice a height of 0.50 cm was preferred, as this somewhat reduced the level of noise contributed by the flame. Similarly, for molybdenum an observation height of 0.5 cm was preferred in practice to the optimum at 0.4 cm because of flame-noise limitations (Fig. 4). IN A COMPLETE RANGE OF STEELS BY ATOMIC-ABSORPTION SPECTROMETRY I 1 I I I I I I I 0.1 0-2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0.1 Observation height/cm Fig. 4. Effect of observation height on molybdenum: A, molybdenum plus 1 per cent. of iron in perchloric acid; and B, aqueous molybdenum solution PROPOSED METHOD REAGENTS- Analytical-reagent grade acids were used throughout. Perchloric acid, sp.gr. 1.54. Hydrochloric acid, s 9 . g .1.18. Nitric acid, sp.gr. 1-42. Perchloric - ~hos~horic - sul~huric acid mixture-To 300 ml of water add 100 ml of per- chloric acid, 100 ml of phosphoric acid (spgr. 1-75) and 1001111 of sulphuric acid (sp.gr. 1.84). Stock chromium solution, 1 000 mg 1-l-Dissolve 1.000 g of 99.99 per cent. chromium metal in 30 ml of hydrochloric acid and dilute to 1 litre. Stock moJybdenum soZution, 1 000 mg l-l-Dissolve 1.829 g of analytical-reagent grade ammonium molybdate tetrahydrate in water and dilute to 1 litre. Working stock solutions, 100 and 500 mg Z-l-Prepare these solutions when required by diluting the stock chromium and stock molybdenum solutions with water. These should be prepared at least weekly. Stock iron solution, 5 per cent.-Dissolve 5 g of high-purity iron (B.C.S.260/2) in 40 ml of hydrochloric acid and 5ml of nitric acid. When the reaction is complete, add 20ml of perchloric acid and evaporate until fumes of perchloric acid just appear. Cool and dilute to 100 ml with water.326 THOMERSON AND PRICE : DETERMINATION OF CHROMIUM AND MOLYBDENUM [Analyst, Vol. 96 METHOD 1- For all chromium determinations and for molybdenum when the tungsten concentration is below 0.5 per cent. Preparation of sample solutiouts-Weigh 1.0000 g of sample into a 250-ml beaker and dis- solve in 10ml of hydrochloric acid and 5 ml of nitric acid. After the initial reaction has subsided, add 10 ml of perchloric acid and evaporate until the solution is fully oxidised and fumes of perchloric acid appear. If chromium is present at concentrations greater than 0.3 per cent., this can be seen to be achieved when the solution turns red and perchloric acid refluxes on the sides of the beaker.Fume for about 5 minutes, cool, and dissolve the soluble salts in about 50 ml of water. Filter through a Whatman No. 541 filter-paper, wash well with water, and dilute to 100 ml. For chromium concentrations above 5 per cent., take a 25-ml sample, add 15ml of stock iron solution, and dilute to 100ml. This is equivalent to a chromium range of 1.0 to 12.0 per cent. for a calibration range of 25 to 300mg1-l. For chromium concentrations higher than 12 per cent. it is necessary to dilute the sample further and add 5 per cent. stock iron solution to maintain iron at a constant level of 1 per cent. when making dilutions. Preparation of calibration solutions-To each of seven 250-ml beakers transfer 1.0 g of high-purity iron and suitable volumes of chromium and molybdenum stock solutions, depend- ing on the required range of the element to be determined (Tables I and 11).Use the same dissolution procedure as specified above for the samples. It is imperative that the chromium and molybdenum stock solutions be added before fuming takes place. TABLE I MOLYBDENUM CALIBRATION SOLUTIONS (i) For molybdenum up to 0.2 per cent. Volume of 100 mg 1-1 stock solution/ml 0 2.0 5.0 10.0 Molybdenum (l-g sample), per cent. . . 0 0.02 0.05 0.10 Volume of 500 mg 1-' stock solution/ml 0 1.0 2.0 4-0 Molybdenum (l-g sample), per cent. . . 0 0.05 0.1 0-2 Concentration/mg 1-1 . . . . . . 0 2 5 10 (ii) For molybdenum up to 0.5 per cent.Concentration/mg 1-1 . . . . .. 0 5 10 20 Volume of 1000 mg 1-1 stock solution/ml 0 1 2 4 (iii) For molybdenum up to 1.0 per cent. Concentration/mg 1-1 . . .. . . 0 10 20 40 Molybdenum (l-g sample), per cent. . . 0 0.1 0.2 0.4 NOTE- A final volume of 100 ml is used throughout. TABLE I1 CHROMIUM CALIBRATION SOLUTIONS (i) For chromium up to 0.5 per cent. Volume of 500 mg 1-1 stock solution/ml 0 1-0 2.0 Chromium (l-g sample), per cent. . . 0 0.05 0.1 Concentration/mg 1-1 . . . . .. 0 5 10 Volume of 1000 mg 1-1 stock solution/ml 0 1 2 Concentration/mgl-l . . .. . . 0 10 20 (ii) For chromium up to 4.0 per cent. Chromium (0.25-g sample), per cent. . . 0 0-4 0.8 Volume of 1000 mg 1-1 stock solution/ml 0 2.5 5 Concentration/mgl-l . . . . .. 0 25 50 (iii) For chromium up to 12-0 per cent. Chromium (0-25-g sample), per cent. . . 0 1 2 NOTE- A final volume of 100 ml is used throughout. 4-0 0.2 4 40 1.6 7.5 75 3 20 15-0 15 0.15 6.0 0.3 6 60 0.6 30 6.0 0.3 6 60 2.4 30 10 100 4 20.0 20 0.20 8-0 10.0 0.4 0.5 40 50 8 10 80 100 0-8 1.0 8.0 10.0 0.4 0.5 40 50 8 10 80 100 3.2 4.0 20 30 200 300 8 12May, 1971] I N A COMPLETE RANGE OF STEELS BY ATOMIC-ABSORPTION SPECTROMETRY 327 METHOD 2- For molybdenum determinations where the tungsten concentration is above 0.5 per cent. Preparation of sample solutions-Weigh 1*000 0 g of sample into a 250-d beaker, add 50ml of the perchloric-phosphoric-sulphuric acid mixture and heat gently. When the sample has dissolved, oxidise the solution by dropwise additions of nitric acid and evaporate the solutions until the first fumes of perchloric acid appear.Cool, dilute to about 50m1, filter through a Whatman No. 541 filter-paper and dilute to 1OOml. Prefiaration of calibration solutions-To each of seven 250-ml beakers add 1.0 g of high- purity iron and suitable volumes of molybdenum stock solutions, depending on the molyb- denum range (Table I). Use the dissolution procedure specified above for the samples. Solutions prepared according to Method 2 can also be used for the determination of tungsten. In this case the appropriate range of tungsten concentrations should be added to the calibration solutions. TABLE I11 INSTRUMENTAL CONDITIONS Chromium Molybdenum Wavelength/nm . . . . . . 357.9 313.3 Slit width/mm . . . . . . . . 0.05 0.05 Burner .. . . . . . . . . 5-cm NeO with 0.5-mm slot Observation height/cm . . . . 0.5 0.5 Acetylene/l minute-l . . . . 4.2 4.7 Lampcurrent/mA . . . . .. 7 10 Nitrous oxide /1 minute-l . . . . 5.0 5.0 The acetylene flow-rates in the above table should be used only as a general guide. For molybdenum the flow must be carefully adjusted to give a flame with the maximum red-feather height without luminescence. For chromium, a red-feather height of 0-5 to 1.0 cm is sufficient. ANALYSIS- Set up the instrument for each element under the conditions specified in Table 111. Aspirate the blank and calibration solutions followed by the sample solutions. Plot absorbance veysus concentration for each element and read the concentration of the element in the sample. To improve precision of reading at higher concentrations, e.g., above 5 per cent., a difference technique24 can be used.In the case of chromium, calibration standards are prepared for the range 150 to 250 mg 1-l. Zero absorbance is set by using the lower standard and sufficient scale expansion is introduced so that the highest standard gives an absorbance scale reading between 0.8 and 1.0. Samples are then run in the normal way. The low standard should be run between samples so that the operating base-line is maintained and any short-term drifts are immediately detected. TABLE IV DETERMINATION OF CHROMIUM IN STEELS Steel type Carbon steel . . . . Mild steel . . .. Nickel - chromium - Low alloy . . . . Low alloy . . . . molybdenum steel . . Austenitic stainless . . Ferritic stainless .. Austenitic stainless . . Stainless . . . . High-speed steel . . High-speed steel . . B.C.S. No. 218/3 321 252/1 219/3 257/1 336 339 334 341 241/1 220/1 Value found, per cent. * 0.16, 0.16, 0.16 0*12,0.11, 0.11 0.40, 0.40, 0.40 0.72, 0.72, 0.72 2.98, 2.88, 2.94 17.3, 17.5, 17.3 124, 12.4, 12.6 26.4, 25.7, 25.4 24.3, 23.9, 23.7 4.70,4.70, 4.70 5.04, 5-10, 5.08 Zertificate value, per cent. 0.14 0.11 0.42 0.76 2.97 17.6 12.4 25.6 24.0 5.03 5.13 Certificate range, per cent. 0.13 to 0.15 0.10 to 0.11 0.40 to 0.43 0-75 to 0.76 2.95 to 3-01 17.6 to 17-7 12.3 t Q 12.6 25-5 to 25.7 23.9 to 24.1 5-00 to 5.05 5-12 to 5.16 Other major elements present, per cent. - Ni 2.2, Mo 1.1 Ni 2.5, Mo 0.6 Ni 9.5, Mo 2-4 Ni 20.6 - - - W 19.6, V 1-6 W 6.9, V 2-1, MO 5-2328 THOMERSON AND PRICE : DETERMINATION OF CHROMIUM AND MOLYBDENUM [ATUdYSt, VOl.96 DISCUSSION The results obtained for a series of British Chemical Standard steels are summarised in Tables IV and V. The perchloric acid method (Method 1) was chosen for general use because of its speed of operation and accuracy for any steel, except those bearing tungsten, for which a molybdenum determination is required. We feel that this is justified, because one would normally be aware that a particular steel contains tungsten before it is analysed. Even in the presence of large amounts of tungsten chromium is best determined in the perchloric acid solution, though somewhat low results were obtained for B.C.S. 24l/l and B.C.S. 220/1, as will be seen from Table IV. If a range of molybdenum determinations is to be carried out for steels either with or without tungsten, Method 2 can be successfully used throughout for any molybdenum concentration.TABLE V DETERMINATION OF MOLYBDENUM IN STEELS Value found, Certificate Certificate Other major B.C.S. per cent. value, range, elements present, Steel type No. t-A-, per cent. per cent. per cent. Carbon steel . . . . 218/3 0.03, 0.03, 0.03 0.034 0.032 to 0.036 - Mild steel . . . . 321 0.07, 0.07, 0.07 0.068 0.064 to 0.072 - Mild steel . . . . 324 0.17, 0.17, 0.17 0-17 0.16 to 0.18 - Low alloy . . . . 257/1 0.16, 0.15, 0.15 0.17 0-16 to 0.18 Cr 3 Nickel - chromium - molybdenum steel. . 219/3 0.58, 0.60, 0.60 0.60 0.59 to 0.61 Ni 2.5 Low alloy . . . . 252/1 1.08, 1.10, 1.08 1.11 1-09 to 1.13 Ni 2.2 Low alloy .. . . 256/1 0.54, 0.54, 0.53 0.53 0.50 to 0.55 Cr 2.4, Mn 1.0 Austenitic stainless . . 336 2.36, 2.40, 2.36 2.43 2.39 to 2.46 Cr 17.6, Ni 9.5 High-speed steel , . 241/1 0.56, 0.56, 0.56 0.52 0.51 to 0.52 W 19.6, Cr 5.0, CO 5.7, V 1.6 High-speed steel . . 220/1 5.30, 5.30, 5.30 5.20 5.15 to 5.27 W 6.9, Cr 5.0, v 2.1 It may be noticed from Fig. 2 that at one particular gas flow-rate both the chromium and the molybdenum absorption responses are independent of the iron concentration. This suggests that if the particular value could be adhered to, there would be no need for iron to be present in the calibration solutions for either chromium or molybdenum. Unfortunately, the observation cannot be utilised in practice as this value would have to be determined for individual instruments (owing to variations in individual flow meters); and in any case the accuracy of the analysis would be critically dependent upon the gas flow-rates.In the case of chromium, for example, if the error in making the flow-meter setting were 0.1 1 minute-1, the difference between the absorbance value of chromium with iron present and that without iron present would be 0.01, which on a sample absorbance value of, say, 0.3 would be equivalent to an analytical error of about 3 per cent. The addition of iron to calibration solutions is a far simpler method of ensuring accurate results. It is important to use pure chromium metal and not potassium dichromate to make up the chromium standards, as potassium reduces ionisation of chromium in the nitrous oxide - acetylene flame in the standards only, thus causing low results to be obtained for the samples.The method lends itself ideally to a rapid general scheme of analysis suitable for the determination of many elements on one solution. We believe that the problems previously encountered with chromium and molybdenum determinations may now be successfully overcome for a complete range of steels in common use. We have in fact been able to deter- mine high concentrations of chromium in other alloys, specifically Nimonic and Stellite, by the same method, the effects of different compositions always being overcome by maintenance of an iron concentration of 1 per cent. in the prepared solution. As Welz23 has already shown, there is no fundamental reason why atomic-absorption spectrophotometry should not give the precision of some other methods , such as volumetric and potentiometric titrations, for high levels of chromium.This precision may be achieved with a difference technique. Coefficients of variation for 6 results (3 different weighings on each of two different occasions) for each of the 2 highest chromium concentrations, samples B.C.S. 334 and B.C.S. 341, were calculated to be 0.46 per cent. and 0.96 per cent., re spec t ivel y .May, 19711 tion analysis by careful attention to the following- IN A COMPLETE RANGE OF STEELS BY ATOMIC-ABSORPTION SPECTROMETRY 329 High precision in the determination of major components is attainable in atomic-absorp- (1) Reduction of analytical sensitivity so that final readings fall within the most accurate absorbance range. For most instruments this is 20 to 200 times the quoted sensi- tivity value.25 Reading accuracy is improved by using a difference technique.(2) The same care must be taken over sample preparation as in other precision methods. (3) Frequent checks should be made for sources of instrumental drift. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. REFERENCES David, D. J., Analyst, 1961, 86, 730. Kinson, K., Hodges, R. J., and Belcher, C. B., Analytica Chim. Acta. 1963, 29, 134. McPherson, G. L., Proceedings, 17th BISRA Conference, 1964, p. 12. Beyer, M., Atomic Absorfition Newsletter, 1965, 4, 212. Mostyn, R. A., and Cunningham, A. F., Analyt. Chem., 1966, 38, 121. Barnes, L., Ibid., 1966, 38. 1083. Kahn, H. L., J . Metals, N.Y., 1966, 18, 1102. Price, W. J., XI11 Colloquium Spectroscopicum Internationale, Ottawa, Canada, June 1967, Clarke, W. E., and Cooke, P. A., B.C.I.R.A. Report No. 891, 1967. Price, W. J., and Cooke, P. A., Pye Unicam Spectrovision, 1967, 18, 2. David, D. J., Aaalyst, 1968, 93, 79. Scholes, P. H., Ibid., 1968, 93, 197. Slavin, W., “Atomic Absorption Spectroscopy,” Interscience, New York, 1968. Endo, Y., Hata, T., and Nakahara, Y., Japan Analyst, 1969, 18, 832. Knight, D. M., and Pyzyna, M. K., Atomic Absorption Newsletter, 1969, 8, 129. Ramirez-Mufioz, J., and Roth, M. E., Beckman Flame News, 1969, 2, 3. Kirkbright, G. F., Smith, A. M., and West, T. S., Analyst, 1966, 91, 700. Ramakrishna, T. V., West, P. W., and Robinson, J. W., Analytica Chim. Acta, 1969, 44, 437. McIssac, C. L., “The Determination of Molybdenum Sulphide in Siliceous Ores by Atomic Absorp- tion,” Endako Mines Ltd., British Columbia, Canada, October, 1966. -, “Molybdenum Sulphide Determinations by Atomic Absorption Spectroscopy,’’ Endako Mines Ltd., British Columbia, Canada, May, 1967. Endo, Y., Hata, T., and Nakahara, Y., Japan Analyst, 1969, 18, 878. Feldman, F. J., Blasi, J. A., and Smith, S. B.. Analyt. Chem., 1969, 41, 1095. Welz, B., Paper presented at the Society of Analytical Chemistry Anglo-Dutch Symposium on Accurate Methods of Analysis for Major Constituents, Imperial College, London, April, 1970. Thomerson, D. R., Spectrovision, 1971, 25, 12. Roos, J. T. H., Spectrochim. Acta, 1969, 24B, 255. paper no. 94. Received August 27th, 1970 AcceDted November 18th. 1970

ISSN:0003-2654    

DOI:10.1039/AN9719600321

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

330 Analyst, May, 1971, Vol. 96, fq5. 330-334 The Fluorimetric Determination of Zirconium as 8-Hydroxyquinolinate in the Presence of Titanium, Tungsten and Molybdenum BY H. 0. SCHNEIDER AND M. E. ROSELLI (Facultad de Ciencias Exactas, Universidad Nacional de La Plata, La Plata, Argentina) A fluorimetric method is described for the determination of small amounts of zirconium as 8-hydroxyquinolinate. The procedure, which involves extrac- tion of the chelate with chloroform from a hydrofluoric acid - ammonium tartrate solution at pH 9.0, permits the determination of zirconium in the presence of titanium, tungsten and molybdenum. Excitation is conducted at 398nm and emission measured at 520nm. Down to 0.1 pg of zirconium can be determined with a coefficient of variation of 2.3 per cent.BECAUSE of the overlap of the absorption bands (within the range 350 to 400 nm) of the com- plexes formed by 8-hydroxyquinoline with zirconium, titanium, tungsten and molybdenum, the possibility of determining zirconium spectrophotometrically in mixtures of these complexes is excluded unless it is previously separated by extraction , which results in co-extraction of titanium.l $2 The present authors3p4 have studied the luminescence properties of these complexes. At room temperature neither the titanium complex nor the molybdenum complex emits, and emission of the zirconium chelate is much higher than that of tungsten 8-hydroxyquinolinate. Use has been made of the Van Santen, Schlewitz and Toy1 extraction method for deter- mining zirconium in attempts to eliminate the effect of competing absorption as well as of collisional quenching when the ratios of titanium , tungsten and molybdenum to zirconium were too high.The application of this technique to each of these complexes has shown that both titanium and molybdenum are partially extracted and that tungsten is not extracted. Hence, it has proved possible to determine zirconium, within the limits 0.1 to 1-1 pg ml-l, in the presence of the other cations mentioned. Titanium, which causes the most severe inter- ference, can be tolerated up to concentrations ten times higher than that of zirconium. EXPERIMENTAL APPARATUS- Absorption spectra were determined with a Perkin-Elmer 400 spectrophotometer. Fluorescence measurements were made with an Aminco spectrofluorimeter (American Instru- ments Co.), fitted with a 150-W xenon arc lamp and IP28 photomultiplier, and equipped with a X-Y recorder.Silica cells of 10-mm path length were used. REAGENTS- Analytical-reagent grade chemicals and double-distilled water were used throughout. Metal solutions (1 mg ml-l)-These were prepared from ammonium molybdate tetrahydrate (Johnson, Matthey Co.), sodium tungstate (Merck) and zirconium oxychloride (Aldrich). The titanium solution was prepared by dissolving an adequate amount of the metal (Johnson, Matthey Co.) in a platinum dish with a few drops of hydrofluoric and nitric acids. After concentrating the solution nearly to dryness, the residue was taken up in 0.5 M tartaric acid. &Hydroxyquiaol-This reagent (Merck) was purified by crystallisation from ethanol - water (1 + 1) and by final sublimation in a vacuum.0 SAC and the authors.SCHNEIDER AND ROSELLI 331 The chloroform used both for extractions and measurements was purified by washing it successively with 2 per cent. sodium hydroxide and water, drying over anhydrous calcium chloride and distilling with percolation through anhydrous silica gel. The solvent thus obtained shows about a 50 per cent. transmission at 250nm against water and does not fluoresce. PREPARATION OF 8-HYDROXYQUINOLINATES- Chelates were prepared according to the well known techniques of Welche? and Vogel.6 Trace amounts of 8-hydroxyquinoline present in the chelates were eliminated by sublimation under vacuum. The purified complexes were analysed and their formulae were found to agree to within 5 per cent.with those given by the above-mentioned authors, i e . , Zr(8-hydroxy- quinolinate) 4, W02(8-hydroxyquinolinate) 2, TiO(8-hydroxyquinolinate) and MoO&hydroxy- quinolinate),. It is assumed that the composition of the complexes does not change with extraction. SPECTRAL CHARACTERISTICS OF THE 8-HYDROXYQUINOLINATES- The absorption and emission spectra of the complexes were determined by directly dis- solving the 8-hydroxyquinolinates in chloroform, readings being made immediately after dissolution and de-aeration of the resulting solutions by bubbling nitrogen through them (Note). Fig. 1 shows the overlap of the absorption spectra bands of the 8-hydroxyquinolinates, together with the higher wavelength absorption band of 8-hydroxyquinoline.D fn + c 3 .- m 0.300 E g 0.200 .- 4- - --. c.l fn > .- + C m c .- D 2 0.100 3 U. - Wavenumber/pm- 1 I 260 280 300 350 400 Wavelength/nm 300 400 500 600 Fig. 1. Absorption spectra of: A, 3 x 1 0 - 4 ~ 8-hydroxyquinoline; B, 2-5 x 1 0 - 4 ~ Wavelength /n m tungsten 8-hydroxyquinolinate; C, 3 x M molybdenum 8-hydroxyquinolinate ; D, 2 x Fig. 2. Excitation spectrum (A) and fluor- lo-* M titanium S-hydroxyquinolinate ; and escence spectrum (B) of zirconium 8-hydroxy- E, 1 x 1 0 - 4 ~ zirconium S-hydroxyquino- quinolinate. Concentration 1 x M. Solvent linate. Solvent chloroform chloroform The excitation and emission spectra of the zirconium complex can be seen in Fig. 2. Table I includes characteristic values of wavelengths at their maxima, molar extinction coefficients, fluorescence yield and sensitivity for the complexes.The fluorescence yield was calculated according to the method of Parker and Rees7 by measuring it against quinine sulphate, the yield of which8 was taken as equal to 0.55 after correcting the emission spectrum by applying the method of Melhui~h.~332 SCHNEIDER AND ROSELLI : FLUORIMETRIC DETERMINATION OF ZIRCONIUM [AnzaEyst, Vol. 96 NOTE-Fluorescence measurements are not reproducible unless the test solutions are aerated to an equal extent, which could be achieved by saturating the system with air, but readings for the fluorescence of zirconium 8-hydroxyquinolinate would then be about 10 per cent. lower than in a de-aerated atmosphere. Therefore, it is advisable to bubble nitrogen through the tightly capped cell (a sleeve-type rubber stopper was used), by using a pair of hypodermic needles.TABLE I SPECTRAL CHARACTERISTICS OF 8-HYDROXYQUINOLINATES 8-Hydroxyquinolinate Jabs./ E x heXc./ Aem./ E x a) S* nm nm nm (398nm) Zirconium . . .. 385 10.5 398 520 9.2 0.05 460 Tungsten . . .. 35s 4.9 370 486 1.2 0.002 2.4 Titanium . . . . 380 6.4 - 8-Hydroxyquinoline . . 315 3.0 * S denotes the fluorescence sensitivity calculated by multiplying the fluorescence yield by the molar extinction coefficient at the excitation wavelength of the zirconium complex. Both complexes exhibit analogous widths of emission band; consequently this has not been taken into account in the calculation. - - - 5-8 - 2.5 - - Molybdenum . . .. 372 3.5 - - - - - - STUDY OF THE INTERFERENCE OF TUNGSTEN, TITANIUM AND MOLYBDENUM- The sensitivity of emission of the zirconium 8-hydroxyquinolinate is about two hundred times higher than that of the tungsten chelate, when both are excited at 398 nm.Even although the titanium and molybdenum 8-hydroxyquinolinates do not emit at room temperature, the fraction of light these complexes absorb lowers the emission of zirconium as the molar extinction coefficients at that excitation wavelength are: 5.8 x lo9 1 mol-l cm-l for titanium and 2.5 x lo9 1 mol-l cm-1 for molybdenum. The ligand itself does not exhibit fluorescence emission at room temperature; its lower energy band is centred at 315nm and its absorbance diminishes to zero at about 350nm. A reference graph of concentration between 1 x M of solutions of zirconium 8-hydroxyquinolinate in chloroform plotted against emission intensity (relative units), as determined by previous calibration at 100 per cent.emission with a 1 pgml-l solution of quinine sulphate in 0-1 N sulphuric acid, gave a linear relationship for concentrations between 2 x 10-6 and 2 x 1 0 - 5 ~ . The efficiency and course of the extraction procedure were studied by preparing a spectrophotometric calibration graph for each of the complexes, measurements being made at the wavelength of maximum absorbance. Generally, all of them obey Beer’s law at low concentrations. The extraction technique applied is that of Van Santen, Schlewitz and Toy,l which was slightly modified as follows: 10 ml of 2 M hydrofluoric acid in 0.5 M tartaric acid were added to 0.5 ml of a 10 pg ml-l aqueous solution of zirconium, the solution was neutralised to pH 7 with 2 M ammonia solution and the pH finally was adjusted to between 8.9 and 9.0 with 0-1 M ammonia solution.The volume of the aqueous solution was maintained at 45 ml and 1 ml of 1 per cent. solution of 8-hydroxyquinoline in acetone was added. After 30 minutes, the solution was shaken twice, each time for 30 s, with two successive 10-ml portions of chloroform and the extracts were combined and diluted to 25 ml with pure solvent, with the addition of anhydrous sodium sulphate. The fluorescence intensity of zirconium 8-hydroxyquinolinate was measured at different concentrations and the values obtained were plotted against corresponding zirconium con- centrations as determined from the calibration graph from the spectrophotometric readings (Table 11).TABLE I1 RECOVERY OF ZIRCONIUM 8-HYDROXYQUINOLINATE IN THE CHLOROFORM EXTRACT I and 1 x Amount of zirconium (per 45 ml) taken/ Clg 4.95 9.90 14.85 24-75 49-50 Amount of zirconium (per 45 ml) found Fluorescence 4.95 7.2 9.92 18.0 14.83 29.3 24-72 39.9 49.47 50.7 spectrophotometrically/pg intensityMay, 19711 AS 8-HYDROXYQUINOLINATE IN THE PRESENCE OF Ti, W AND Mo 333 The same extraction procedure was applied to each of the remaining chelates individually and the percentage extraction was calculated on the basis of the respective spectrophoto- metric calibration graphs. Under these conditions, titanium 8-hydroxyquinolinate follows zirconium in order of extraction and tungsten extraction is nil, most probably because under the conditions used the pH was too far from the optimum for extraction of the tungsten complex.lO About 11 per cent.of the molybdenum chelate and about 20 per cent. of the titanium complex are extracted. The effect of these elements on the emission of zirconium was studied by using mixtures of zirconium with various proportions of the interfering elements and measuring the emission of the chloroform solutions after extraction (Table 111). TABLE I11 EXTRACTION OF ZIRCONIUM 8-HYDROXYQUINOLINATE IN THE PRESENCE OF Zirconium concentration 0.33 pg ml-l TUNGSTEN, MOLYBDENUM AND TITANIUM Sample NO. 1 2 3 4 5 6 7 8 9 10 11 Concentration of added interfering element in aqueous phaselpg ml-l r A 1 Zirconium Titanium Molybdenum Tungsten found/pg ml-f - 0.31 0.33 0.33 0.33 0.30 0.66 1-65 1.65 0.31 0.99 1-65 1.65 0.30 0.99 3-30 3.30 0.3 1 1.65 3.30 3.30 0.32 1-98 3.30 3.30 0.30 0.33 4.95 4.95 0.3 1 3.30 3.30 3.30 0.27 4.95 3.30 3.30 0.20 0.33 6.60 6.60 0.25 - - Samples 1 to 8: standard deviation as coefficient of variation, 2-3 per cent. Although several other metal 8-hydroxyquinolinates might be capable of being extracted, most of them, mainly the 8-hydroxyquinolinates formed with bivalent cations, could be complexed with cyanide and thus retained in the aqueous phase under the experimental conditions.Other metals, such as aluminium, do not interfere in our simpler system because of the presence of both fluoride and tartrate. However, the proposed technique has been developed with the intention of solving the problem posed by refractory materials and high temperature alloys, such as molybdenum-base alloys, which are of increasing importance in the aerospace industry.RESULTS Measurement of the fluorescence emission of zirconium 8-hydroxyquinolinate permits the determination of zirconium at very low concentrations with good reproducibility. Experimental values obtained in the presence of tungsten, titanium and molybdenum after extraction into chloroform from an aqueous hydrofluoric acid - ammonium tartrate solution at pH 9.0 show that it is possible to determine 0.33 pg ml-l of zirconium in quaternary mixtures in which the contents of molybdenum and tungsten are ten times and the content of titanium is six times as high as the amount of zirconium.Within these ratios, emission values for the zirconium complex are the same as those for the pure 8-hydroxyquinolinate. Titanium interference is found to be much more severe than that of molybdenum, which is in agreement with the values for the molar extinction coefficients of their 8-hydroxyquino- linates at the excitation wavelength for zirconium (398 nm) , as that of the titanium complex is more than twice that of the molybdenum complex. A series of determinations conducted at a concentration level of 0.33 pg ml-l gives a coefficient of variation of 2.3 per cent.334 SCHNEIDER AND ROSELLI Most of the sensitive methods available for the determination of zirconium require the absence of complexing anions such as fluoride, tartrate and citrate, which do not affect the proposed method.Spectrophotometric techniques based on the reaction of zirconium with quercetin are affected by titanium; those based on the reaction with thorin and pyrocatechol violet by both titanium and molybdenum; and interference by titanium, molybdenum and tungsten, among the metals tested, occurs when alizarin is used as the reagent. Also, the well known indirect spectrofluorimetric procedure for determining zirconium with morin, which is greatly dependent on the composition of the system, is affected by fluorides. These limitations therefore preclude the use of these methods without prior application of separation techniques, which outweigh the higher sensitivities claimed for several of them. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Van Santen, R. T., Schlewitz, J. H., and Toy, C. H., Analytica Chim. Acta, 1965, 33, 593. Eberle, A. R., Analyt. Chem., 1963, 35, 669. Schneider, H. O., and Roselli, M. E., An. Asoc. Quim. Argent., 1969, 57, 39. , Ibid., 1970, 58, 191. Welcher, F. J.. “Organic Analytical Reagents,’’ D. Van Nostrand Company Inc., New York; Macmillan 62 Co. Ltd., London, Volume 1, 1947, p. 295. Vogel, A. I., “Quantitative Inorganic Analysis,” Longmans Green and Co., London, 1947, p. 452. Parker, C. A., and Rees, W. T., Analyst, 1960, 85, 587. Melhuish, W. H., N.Z. J . Inst. Technol., 1955, B, 37, 142. -, J . Opt. SOC. AmeY., 1962.52, 1256. Staq?, J.. Analytica Chim. Acta, 1963, 28, 132. , -- Received Jzcly 21st, 1970 Accepted October 16th, 1970

ISSN:0003-2654    

DOI:10.1039/AN9719600330

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

Analyst, May, 1971, Vol. 96, H. 335-337 335 A Rapid Atomic-absorption Technique for the Determination of Lithium in Silicate Materials BY JAMES V. O’GORMAN AND NORMAN H. SUHR (Mineral Constitution Laboratories, The Pennsylvania State University, University Park, Pa., U.S. A .) A simple and rapid atomic-absorption procedure is described for the determination of lithium in silicate rocks. Following fusion with sodium borate, the samples are dissolved in dilute nitric acid solution. Determinations of the lithium contents are made directly. The precision of the method, in terms of one standard deviation, was calculated to be 1093 f 13 p.p.m. and 34.5 f 4-6 p.p.m. Accuracy, as indicated by a comparison with published determinations, is good. ATOMIC-ABSORPTION techniques have been described that enable lithium to be determined successfully in silicate rocks and minerals (Stone and Chesher,l and Ohrdorf2).However, sample preparation is somewhat lengthy and involved, usually entailing dissolution with hydrofluoric and other acids. In our laboratories, a simple scheme of silicate analysis in- volving fusion with lithium metaborate has been successfully used for some time (Suhr and Ingamells: and Medlin, Suhr and Bodkin4). By substituting sodium borate for lithium metaborate, lithium can be determined with adequate precision down to about 5 p.p.m. in the sample. Other elements can be determined with results similar to those already described by Medlin, Suhr and B ~ d k i n . ~ , ~ METHOD INSTRUMENTATION- A Perkin-Elmer, Model 303, atomic-absorption spectrophotometer with an air - acetylene burner of 4-inch path length and a strip-chart recorder was used.A multi-element hollow- cathode device (Ca-Mg - A1-Li, Westinghouse, Type WL23035) was used and the operating conditions were those recommended in the manufacturer’s Analytical Methods Manual. A scale-expansion setting of 3 x was used for lithium values of less than 200 p.p.m. For higher values scale expansion was not necessary. REAGENTS- Analytical-reagent grade chemicals were used throughout. Lithium standards-A stock solution of lithium was prepared by dissolving 0.532 4 g of lithium carbonate in 50ml of dilute nitric acid and diluting to 1 litre with distilled water. This stock solution is equivalent to 5 per cent. of lithium in the sample.Two ranges of standards (equivalent to 0 to 200 p.p.m. and 0 to 2 000 p.p.m. of lithium in the sample) were prepared by making appropriate dilutions of the stock solution with a blank solution (U.S.G.S. Peridotite, PCC-16). This provided lithium standards in a silicate matrix similar to the samples being studied, and eliminated any differences in viscosity between samples and standards . Nitric acid, 3 per cent. A fihydrous sodium borate, Na$,O,. 0 SAC and the authors.336 [Analyst, Vol. 96 PROCEDURE- With the exception of substituting sodium borate for lithium metaborate, the procedure has already been outlined in some detail by Suhr and Ingamells3 and Medlin, Suhr and B ~ d k i n . ~ Briefly, it is as follows : 80.0 mg of 200-mesh sample is mixed with 400 mg of sodium borate by shaking in a plastic vial on a mechanical shaker for about 15 s.The mixture is placed in a graphite fusion crucible (Union Carbide L-4400) and fused for 10 minutes at 1 000 "C in a muffle furnace. The molten bead is poured directly into a beaker containing 40.0 ml of 3 per cent. nitric acid solution. A magnetic stirring bar is added and the mixture placed on a magnetic stirring unit until dissolution is complete (about 10 minutes). This solution, without further treatment, is used for the determination of lithium. If only a few lithium determinations are to be made, a warm-up period of 20 minutes for the atomic-absorption unit is satisfactory. However, as there is a tendency for the energy output of the hollow cathode to change rapidly in the first 15 to 30 minutes of operation, it is wise to allow a warm-up period of 1 hour or more before proceeding with many deter- minations.Ten to twenty samples are run between standards to overcome long-term shifts in absorption in the fashion standards A, B, C . . ., samples 1, 2, 3, . . ., . . ., 3, 2, 1, stan- dards . . . C, B, A. An average of the two readings is then taken. We have found this technique to be successful in overcoming any long-term absorption changes. O'GORMAN AND SUHR : A RAPID ATOMIC-ABSORPTION TECHNIQUE DISCUSSION Stone and Chesherl found no interferences from the common major elements in silicate rocks and minerals. Consequently we did not systematically investigate the effect of various elements and concentrations thereof on the determination of lithium.In addition, the results given in Table I do not indicate any serious interferences. Good agreement is found between our values and other published values, although there are exceptions. Our values for lithium in iron mica and in magnesium mica are slightly lower than those reported. However, the concentrations in these two samples are not established, as indicated in the footnote to Table I. Also, an independent determination of lithium in the iron mica by a chemical separation - flame photometric technique in our laboratories gave 0-10 per cent. of lithium, which substantiates our lower value. TABLE I COMPARISON OF LITHIUM VALUES Sample Diabase W-1 . . . . Granite G-1 . . .. Granite G-2 . . . . Granodiorite GSP-1 . . AndesiteAGV-1 , . . .Basalt BCR-1 . . .. Granite GR . . .. Granite GA .. .. Granite GH .. . . Basalt BR . . .. .. Biotite, iron mica . . .. Phlogopite, magnesium mica Serpentine UB-N . . . . Diorite, DR-N . . . , Syenite S-l .. .. Lithium, p.p.m. atomic-absorption spectrophotometry Present r A I Found by 17 12* 24 24* 35 38t 30 33t 15 13t 12 1 5 t 65 55 $ 88 loor 10 12: 40 42 $ 1090 1400s 114 2505 29 3011 42 4011 120 1207 * Recommended values (Fleischer') . t Average of values reported (Flanagans) . 3 Proposed value (de la Roche and Govindarajus). 9 Preliminary values (de la Roche and Govindaraj~~). 11 Proposed value for UB-N and average of four values for DR-N (de la Roche 7 Mean value reported (Sine et ~ 1 . l ~ ) . and Govindaraj~~).May, 19711 FOR THE DETERMINATION OF LITHIUM IN SILICATE MATERIALS 337 Precision, as indicated in Table 11, and the observed detection limit of 5 p.p.m.in the sample are more than adequate for most geochemical studies. The detection limit could easily be improved by using greater scale expansion, but we did not find it necessary. TABLE I1 PRECISION RESULTS FOR LITHIUM Number of Sample Concentration, p.p.m. Standard deviation, p.p.m. determinations* Granite G-2 . , . . 34.5 4.6 26 Biotite, iron mica . . .. 1093 13 16 * For G-2 determinations were made on ten sub-samples on four different days. For iron mica No results were rejected; the determinations were on three sub-samples on six different days. odd number of determinations is caused by not running all of the sub-samples each day. REFERENCES 1. Stone, M., and Chesher, S. E., Analyst, 1969, 94, 1063. 2. Ohrdorf, R., Geochim. Cosmochim. Acta, 1967, 32, 191. 3. Suhr, N . H., and Ingamells, C. O., Artalyt. Chem., 1966, 38, 730. 4. Medlin, J . H., Suhr, N. H., and Bodkin, J. B., Atomic Absorfition Newsletter, 1969, 8, 25. 5. -,-,- , Chem. Geol., 1970, 6, 43. 6. Flanagan, F. J., Geochim. Cosmochim. Acta, 1969, 33, 81. 7 . Fleischer, M., W d . , 1969, 33, 65. 8. de la Roche, H., and Govindaraju, K., B d . Soc. Fr. Cbyam., 1969, No. 85, 31. 9. - - , Ibid., 1969, No. 85, 35. 10. Sine,’ N . M., Taylor, W. O., Webber, G. R., and Lewis, C. L., Geochim. Cosmochim. Acta, 1969, Received August loth, 1970 Accepted September 29th, 1970 33, 121.

ISSN:0003-2654    

DOI:10.1039/AN9719600335

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

338 Analyst, May, 1971, Vol. 96, pp. 338-342 An Improved Method for the Determination of Bacitracin in Animal Feeds BY B. GRYNNE ( A / S Apothekernes Laboratorium for Sfiecialfira3fiarater. Oslo, Norway) The determination of small amounts of bacitracin in animal feeds has been studied. It was expected that by using acidified methanol as the only organic solvent in the extraction procedure and phosphate buffer, undesired proteins would not be dissolved and the use of the toxic solvent pyridine might be avoided. Bacitracin could then be determined in the final extract by using microbiological methods, in which methanol interferes less than pyridine. The method reported here has been used for feed mixtures with various zinc bacitracin contents in the range from 5 to 350 p.p.m. ZINC bacitracin is frequently used as an additive in animal feeds and has a growth-promoting effect.In the absence of chemical methods for the determination of bacitracin in feeding- stuffs, the antibiotic has to be assayed microbiologically1 after solvent extraction. Although zinc bacitracin is known to be soluble in water,2 experiments show that an acid as well as an organic solvent is required to dissolve all the zinc bacitracin present in a feedingstuff sample .3 The method most widely used for the determination of bacitracin involves the acid- pyridine extraction of zinc bacitracin as described by Craig.* Following this extraction, methanol is added to the extract in order to precipitate proteins and, after removal of the pyridine, the amount of bacitracin present is determined microbio1ogically.l This method is referred to in this paper as the pyridine method.In this work an attempt has been made to simplify the extraction of zinc bacitracin by using an organic solvent that is less toxic than pyridine and would not necessarily have to be removed before the microbiological stage of the assay for bacitracin. METHOD REAGENTS- Phosphate bufler solution, PH 6.5-Dissolve 22 g of potassium monohydrogen ortho- phosphate and 28g of potassium dihydrogen orthophosphate in 1 litre of distilled water. Acidijed methanol-A 2 per cent. v/v solution of concentrated hydrochloric acid (sp.gr. 1-19) in methanol. Bromocresol puyple solution-Dissolve 0-1 g of the indicator in 18.5 ml of 0.01 N sodium hydroxide and dilute the solution to 250ml with water.It is recommended that reagents of analytical-reagent grade are used in the preparation of these solutions. Zinc bacitracin stock solutioni--Dissolve 34 mg of zinc bacitracin of known potency, i.e., 2 500 i.u. of bacitracin (Note l), in 5 ml of 0.1 N hydrochloric acid. Add 10ml of water and adjust the pH to 5 with N sodium hydroxide solution. Dilute the resulting solution to 50ml to give a concentration of bacitracin equivalent to 50 i.u. ml-l. When stored at a temperature between 5 and 8 "C, this solution is stable for 1 week. NOTE 1-The zinc bacitracin was standardised against the Second International Standard for This substance is available from Division of Biological Standards, National Institute Bacitracin. of Medical Research, Mill Hill, London, N.W.7. It contains 74 i.u.mg-l of bacitracin. PREPARATION OF STANDARD SOLUTION- Dilute the stock solution with sufficient phosphate buffer to give a solution containing 0.05 to 0.1 i.u. ml-1 of bacitracin. This solution should be prepared immediately before use. 0 SAC and the author.GRYNNE 339 PREPARATION OF STANDARD SOLUTION MODIFIED WITH EXTRACT OF UNSUPPLEMENTED FEED- Carry out the extraction and dilution of an unsupplemented sample (Note 2) of the feedingstuff under test as described below (under Procedure A or B). Add a suitable amount of stock solution to the diluted extract to give a solution containing 0.05 to 0.1 i.u. ml-l. NOTE &If no unsupplemented samples are available for blanks, the following procedure is recommended. Add a known increment of zinc bacitracin to the unknown sample and determine its recovery by assay.Use the recovery value for calculation of the potency of the unknown sample. An alternative method is the use of autoclaved samples although with this technique it was not always possible to obtain complete inactivation of zinc bacitracin. Also, some feed components decomposed giving dubious blanks. PREPARATION OF ASSAY SOLUTIONS OF FEEDINGSTUFFS- Procedure A for feedingstufs contaiHing 20 to 350 $.p.m. of zinc bacitracin (Note 3)- Weigh a 10-g sample of feedingstuff into a mortar. Triturate the sample for 2 minutes with 25 ml of acidified methanol in order to obtain a solution of pH 2 (if necessary, add concentrated hydrochloric acid dropwise until the required pH is obtained).Then add 25 ml of phosphate buffer and transfer the resulting mixture to a 250-ml Erlenmeyer flask, shaking it for 20 minutes following the transfer. Centrifuge the mixture for 5 minutes at 4000 r.p.m. and dilute the supernatant liquid thus obtained with the phosphate buffer to give a final solution containing 0.05 to 0.1 i.u. ml-1 of bacitracin (Note 4). Procedure B for feedingstufs containing 5 to 20 p.9.m. of zinc bacitracin-Triturate a 10-g sample of feedingstuff in a mortar with 25 ml of acetone in order to remove the fat (if any). Decant the acetone, let the feed sample dry in air at a temperature below 35 "C and carry out the zinc bacitracin extraction as in the above procedure. Transfer 20 ml of the supernatant liquid into a 250-ml round-bottomed flask, add 1 ml of bromocresol purple solution and then add N sodium hydroxide solution dropwise until the indicator has changed colour (at pH 6.5).Immerse the round-bottomed flask in water at 30 "C, connect it to a rotary evaporator and evaporate the extract to dryness at reduced pressure. Next, dissolve the residue in phosphate buffer solution and transfer this mixture quantitatively into a calibrated flask, diluting to the mark. A solution containing 0-05 to 0.1 i.u. ml-l of bacitracin (Note 4) results, e.g., if the residue of a feedingstuff sample containing 5 p.p.m. of bacitracin is dissolved to 10m1, the solution will contain 0.084 i.u. ml-l while the residue from a sample containing 20 p.p,m. yields 0.067 i.u. ml-l when dissolved to 50 ml. NOTE 3-It has recently been shown (Grynne, unpublished work) that this method, with slight modifications, is satisfactory for high-potency feed supplements containing mainly calcium carbonate or kaolin.The potencies of the supplements tested were 104 or 4 x lo* p.p.m. of zinc bacitracin. NOTE &For transforming international units into milligrams of bacitracin most of the feed industry has accepted the definition 42 i.u. = 1 mg, which has been used in this work, but it should be mentioned that the Second International Standard for Bacitracin contains 74 i.u. mg-l. (The potency of the U.S.A. Food and Drugs Administration Working Standard is 62 i.u. mg-l.) MICROBIOLOGICAL DETERMINATION OF THE BACITRACIN CONTENT IN THE ASSAY SOLUTION- SingZe-@oint assay-Test the assay solution against the standard or the modified standard solution by means of the agar diffusion method described in detail by Grove and Randal1,l with the slight modification that test plates with a single layer of about 10 ml of agar should be used instead of two-layer plates.Holes in the agar can be used instead of cylinders, but paper discs should be avoided since these increase the interference by non-antibiotic com- ponents. Calculate the amount of zinc bacitracin in the feedingstuff from the following equation- ' ' ' ' ' Oo0 = p.p.m. of zinc bacitracin in the feed, g x d x 4 2 where c is the concentration of bacitracin found (by assay) in international units per millilitre; v is the volume of the assay solution in millilitres; e is the volume of extraction liquids used (acidified methanol, hydrochloric acid and phosphate buffer) in millilitres; g is the weight of the feed sample in grams; d is the volume of extract diluted to v ml in millilitres; and 42 is the amount of bacitracin in international units per milligram of zinc bacitracin.340 GRYNNE: AN IMPROVED METHOD FOR THE [Analyst, Vol.96 Two-point assay (samples with more than 100 9.p.m. of zinc bacitracin)-Dilute the extract (in the work described in this paper a two-point assay was carried out on samples 13 to 16, see Table 11) to two levels (approximately 0.1 and 0.2 i.u. ml-l of bacitracin) and test against two zinc bacitracin standard solutions with 0.1 and 0.2 i.u. ml-l, by using a satisfactory assay design. For example, twelve agar plates, each with four cylinders filled with the four different solutions, are used for one sample.Carry out the calculation as suggested by Pitton: check the validity of the assay and then, if this is satisfactory, calculate the potency of the test solution. RESULTS AND DISCUSSION The solubility of zinc bacitracin present in feedingstuffs was studied. Several organic extraction liquids (methanol, ethanol, propanol, ethylene glycol monoethyl ether and di- methylformamide) in combination with various amounts of hydrochloric acid were tried and it was shown that methanol had the best properties, i.e., lower toxicity and boiling-point than pyridine, the property of not dissolving undesired proteins, and the ability to dissolve zinc bacitracin. Experiments were initiated to study the possibility of avoiding the time consuming evaporation of the extraction liquids prior to the microbiological test.Preliminary attempts to investigate the influence of the extraction liquids on the size of the inhibition zones were therefore made and by means of zinc bacitracin standard solutions it was demonstrated that the inhibition zones were considerably increased by the presence of more than 1 per cent. v/v of pyridine. Similar experiments with methanol showed that the microbiolopical test was not seriously affected by ihe presence of up to 15 per cent. v/v of methanol in The assay solution (Table I). TABLE I INFLUENCE OF EXTRACTION LIQUIDS ON THE ZONE SIZES Apparent change of Pyridine content Methanol content bacitracin potency? Solution* of assay solution, of assay solution, Zone caused by solvent, number per cent.v/v per cent. v/v diameter/mm per cent. 1 2 3 4 5 6 7 8 9 10 11 12 - - - - - 2 4 8 10 15 20 25 17.10 16.94 17.16 17.24 20.10 16.94 16.96 17-02 16.94 16.94 16.80 16.22 - -5 + 4 + 8 + 320 - 5 -4 -2 - 5 -5 - 10 - 28 * Each of solutions 2 to 12 was tested in thirty-six cylinders against an equal number of cvlinders filled with solution 1. t Bacitracin potency of all solutions = 0.1 i.u. ml-l. Diluent, phosphate buffer solution (pH 6.5). A more detailed examination of the influence of 15 per cent. v/v of methanol was carried out. In this examination, six zinc bacitracin solutions (0-05, 0.1, 0.2 i.u. ml-l of bacitracin, with and without 15 per cent. v/v of methanol) were tested microbiologically in a (3 + 3) design.On the basis of the observed zone diameters (fourteen zones from each solution) statistical calculations were carried out as suggested by P i t t ~ n . ~ It could be shown that the apparent change of antibiotic potency, due to the methanol, was 2 per cent. Further, the two regression lines were found to be parallel and linear. I t was now calculated that when Procedure A was followed, convenient concentrations of methanol (15 per cent. v/v or less) and of bacitracin (0.05 to 0.1 i.u. ml-l) were obtained only for diluted extracts originating from feedingstuffs containing at least 20 p.p.m. of zinc bacitracin. In order to show that the proposed method was suitable for zinc bacitracin in feedingstuffs, assays were carried out on samples with 20 to 350 p.p.m. of zinc bacitracin. The good agreement between the results by Procedure A and the pyridine method is shownMay, 19711 DETERMINATION O F BACITRACIN I N ANIMAL FEEDS 341 in Table 11.Similarly, the results for feedingstuffs containing 5 to 20 p.p.m. of zinc bacitracin (obtained by use of Procedure B, Table 11) were in good agreement with those obtained with the pyridine method. It was thought that soluble ingredients from the basic feed might be able to influence the extraction of bacitracin as well as the formation of inhibition zones by inactivating the bacitracin during its extraction, by reducing the diffusion rate or by affecting the micro- organism. Modified standard solutions were therefore produced by adding blank extracts to the standard solutions. It seemed, however, to make no difference whether a standard or a modified standard was used (Table 11). Unfortunately, there are numerous recipes for the compression of feedingstuffs, most of which are unknown to the analyst, and it is still not fully known whether or not any feed components could interfere in the bacitracin extraction and the microbiological assay.The precise rdle of the zinc atom in the antibacterial activity of bacitracin has also not yet been defined, and attention should be drawn not only to the concentration of zinc, but also to possible metal binding agents6 or other metals' present in the extracts, assay solutions, agar media, etc. Therefore, to minimise inaccuracy in the assay, it is recommended that either modified standards are used, as described in this work or, alternatively, that the quantitative zinc bacitracin recovery of the feed is checked. TABLE I1 COMPARISON OF METHANOL AND PYRIDINE FOR THE EXTRACTION OF BACITRACIN FROM FEEDINGSTUFFS" Sample number? 1 2 3 4 5 6 7 8 9 10 11 12 13§ 14§ 15§ IS§ 17 18 19 20 21 22 23 24 25 26 27 Sample tested against Sample tested against standard modified standard r Procedure A: Bacitracin, Bacitracin, p.p.m.p.p.m. 19 22 20 21 27 31 27 26 25 25 48 42 49 49 51 51 105 113 148 151 233 235 327 347 94 - 132 - 191 - 260 - Procedure Bi 3.6 3.5 5.0 4.6 5.3 5.2 4.5 5.1 10.1 9.5 10.0 10.0 9.0 9.4 9.3 9.0 9.1 9-2 A -I / A .l Pyridine method Baci tracin, p.p.m. 21 21 22 28 23 44 45 48 95 153 221 333 90 131 206 262 3.9 4.8 4.5 5-2 10.6 9.8 9.6 10.0 11.0 20 21 21 21 20 18 28 20 22 24 * Each result is the mean of three determinations, i.e., extraction and biological test.t For assays 1 to 16, 20 and 25 the same basic feed was used. Remaining samples were of 3 Procedure A required no evaporation of methanol prior to the microbiological test, whereas 9 Assays 13 to 16 were two-point assays, while the remainder were single-point assays. various compositions. procedure B did require an evaporation.342 GRYNNE CONCLUSIONS An improved method for the determination of bacitracin in different feedingstuffs con- taining 5 to 350 p.p.m. of zinc bacitracin has been developed. The most suitable organic extraction liquid tried out, in combination with hydrochloric acid, appeared to be methanol. The maximum amount of methanol in feedingstuff extracts that did not interfere in the assay was found to be 15 per cent. v/v. For feedingstuffs containing at least 20 p.p.m. of zinc bacitracin the evaporation of the solvent prior to the microbiological test was unnecessary. The results obtained with this method compared favourably with those obtained with the pyridine method. The author thanks Dr. H. P. Throndsen for valuable discussions and assistance in the preparation of the text, and Mrs. S. Irgens Karlsen, Miss M. Rennaes and Mrs. M. Lehoczky for laboratory assistance during these investigations. REFERENCES 1. 2. 3. 4. 5. 6. 7. Grove, D. C., and Randall, W. A., “Assay Methods of Antibiotics: A Laboratory Manual,” Medical Encyclopedia Inc., New York, 1955, p. 76. Andrew, M. L., and Weiss, P. J., Antibiotics Chemother., 1959, 9, 277. Wright, W. W., and Burton, J. M., J . Ass. 08. Agric. Chew., 1959, 42, 258. Craig, G. H., U.S. Patent No. 3 306 827, 1967. Pitton, J. S., Pharm. Acta Helv., 1966, 41, 658. Weinberg, E. D., Antimicrob. Ag. Chemother., 1964, 5, 120. - , Antibiotics A., 1958-59, 6, 924. Received M a y 12th, 1970 Accepted November 5th, 1970

ISSN:0003-2654    

DOI:10.1039/AN9719600338

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

Autdyst, May, 1971, Vol. 96, $@. 343-345 343 Chromatographic Separation and Titrimetric Determination of the Aphicide Menazon in Paste Formulations BY PAOLO MAIN1 (Societh Italo Americana Prodotti Antiparassitari, Centro Esperienze e Ricerche, 40015 Galliera (Bologna), Italy) Paste formulations of menazon were chromatographed on a column of acidic alumina. The emulsifying agents and other active ingredients were eluted with, hexane, diethyl ether and chloroform. Menazon was finally eluted with dioxan and was then titrated potentiometrically with 0.1 N perchloric acid in dioxan - acetic acid (1 + 1). MENAZON (I. S. 0. common name for S- (4,6-diamino- 1,3,5-triazin-2-ylrnethyl) dimethyl phosphorothiolothionate), which combines high systemic toxicity to aphid species with very low toxicity to humans,l is considered one of the best aphicides currently available.Excluding powders for seed dressing, the formulations containing this active ingredient, because of its very low solubility in any solvent, come in the form of thick pastes or emulsi- fiable suspensions. At the present time, the methods of analysis for menazon, both in formu- lations and residues, are exclusively based on the colorimetric determination of phosphorus after ashing and oxidation of the sample. Paper2s3s4 or thin-laye$ chromatographic methods have been used for the separation and detection of menazon residues; but, in any case, the quantitative determination has been carried out by colorimetry, even though different colorimetric procedures were used. For example, Camoni, D’Antonio, Gandolfo, Leoni, Ramelli and Sampaolo3 used Calderbank and Turner’s technique,2 slightly modified following Beremblum and Chain,6 for determining menazon in olive oil, while Plant Protection Ltd.,4 the European manufacturer of menazon, reports the use of Calderbank and Turner’s method2 based upon the technique of Chen, Toribara and Warner7 for determining menazon residues in various crops.Previously, Calderbank and Turner’s method has been used for formulations also. It provides for a separation of the active ingredient on an ion-exchange resin before the colorimetric determination o€ phosphorus. This method is laborious because of the need for ashing of the sample, its dissolution and its passage through the resin, the last step needing rat her critical conditions.Our laboratories have conducted investigations into an analytical method for a formula- tion containing menazon, other active ingredients and a very high percentage of emulsifying and dispersing agents. It was found that menazon recoveries were not quantitative when Calderbank and Turner’s method was used. In fact, with both pure and technical menazon in paste formulations we have obtained large errors with deviations of -14 to -16 per cent. We were not able to explain such large errors, so to obviate these difficulties we tried other analytical techniques. In view of the weak basicity of the menazon molecule (pK, 3.8): a titrimetric method in non-aqueous medium was tested. Pure menazon gave good results; however, direct determinations on the formulation were not possible because of some inter- ferences caused by the surfactants and by active ingredients other than menazon.Therefore, we thought of exploiting both the very low solubility of menazon in most organic solvents and its polarity characteristics to separate it from the co-formulants by column chromato- graphy. Many chromatographic adsorbents were tested, but only acidic alumina was found to be efficient. The co-formulants were eliminated by elution with hexane, diethyl ether and chloroform. The menazon was finally eluted with dioxan. The active ingredient thus separated was potentiometrically titrated in the non-aqueous solvent dioxan - acetic acid (1 + 1) with 0.1 N perchloric acid by using glass - calomel electrodes.8 The recoveries were quantitative.This method has been successfully applied to the industrial control of only one type of paste formulation, but it seems reasonable to assume that it can be applied to other kinds of liquid, paste or powder formulations based on menazon. 0 SAC and the authors.344 MAINI : CHROMATOGRAPHIC SEPARATION AND TITRIMETRIC [Analyst, Vol. 96 METHOD APPARATUS- Chromatographic column-300 x 25 mm i.d. , fitted with a sintered-glass medium-porosity septum and with a Teflon stopcock. Potentiometer-This is equipped with glass - calomel electrodes. A Beckmann Research pH meter was used. Magnetic stirrer. REAGENTS- A luminium oxide, acidic-Brockmann grade I. Solvents-Diethyl ether, chloroform, glacial acetic acid, dioxan and hexane, all analytical- reagent grade.Perchloric acid-A 0.1 N solution in glacial acetic acid. PROCEDURE- Fill the chromatographic column with sufficient alumina to make a layer 4 cm deep after settling. Wet the column with hexane and allow a 3 to 4-cm layer of this solvent to remain over the alumina. Accurately weigh into a 100-ml beaker sufficient of the sample to contain approximately 0-5 g of menazon. Add to the beaker 5 g of acidic alumina and mix well with a glass rod to a homogenous and dry powder (help the homogenisation if necessary with 8 to 10 drops of diethyl ether). Transfer the powder to the column by using a powder funnel. Add an additional 3 g of alumina to the beaker. Mix well, stirring the mixture and scraping the beaker walls with a glass rod. Transfer this powder to the column.Rinse the beaker, the glass rod, the funnel and the column walls with two 5-ml portions of hexane. Cover the alumina column with a glass-wool plug. Allow the solvent used for the washings to be completely absorbed, then elute sequentially with 150 ml of hexane, 350 ml of diethyl ether and 400ml of chloroform. The elution rate for all the solvents is not important. Discard the three eluates, unless they contain other active ingredients to be determined. (In our case, the hexane fraction contained pyrethrins, while the diethyl ether fraction contained piperonyl butoxide). Finally, elute the menazon with dioxan. Collect 300 ml of eluate in a tall 500-ml beaker, completely evaporate the dioxan on a water-bath with the aid of a curient of air, and take up the residue in 100 ml of dioxan - acetic acid (1 + 1). Titrate this solution with 0.1 N perchloric acid in glacial acetic acid solution, by using a potentiometer equipped with a glass - calomel electrode and with magnetic stirring.Calculation-1 ml of 0.1 N perchloric acid is equivalent to 28.1 mg of menazon (molecular weight 281). a x 2.81 Menazon content of the sample, per cent. = ~ w where a is the volume in millilitres of 0-1 N perchloric acid used, and w is the sample weight in grams. RESULTS AND DISCUSSION The formulations analysed were thick suspensions containing 40 per cent. of active ingredient, together with a high percentage of emulsifying and dispersing agents and with other active ingredients. The accuracy of the method was established by recovery tests on mixtures containing all the ingredients plus pure menazon, and with tests on some industrial formulations.The results are shown in Tables I and 11. TABLE I DETERMINATIONS ON FORMULATIONS CONTAINING PURE MENAZON Menazon added/g Menazon found/g per cent. per cent. Recovery, Mean recovery, 99.25 0.50 0-501 100.2 0.50 0.492 98.4 0.50 0.495 99.0 0.50 0.497 99.4 Three blanks each gave a menazon determination of 0.000.May, 19711 DETERMINATION OF THE APHICIDE MENAZON IN PASTE FORMULATIONS 345 TABLE I1 DETERMINATION ON FORMULATIONS CONTAINING TECHNICAL QUALITY MENAZON Menazon present, Menazon found, Recovery, Mean recovery, per cent. per cent. per cent. per cent. 98.56 40 39.2 98-00 40 39.7 99.25 40 39.2 98.00 40 39.6 99-00 Blank tests were carried out, and no interferences were observed from reagents or co- f ormulan ts.The method is faster and simpler than the commonly accepted colorimetric method. Furthermore, it does not need the preparation of specific reagents. It has been found to give satisfactory results for production control purposes, but impurities arising from decomposition of a formulated sample on long storage may be eluted with the menazon fraction and be titrated with the perchloric acid. The method cannot therefore be recommended on the basis of the work so far carried out for the determination of menazon in stored samples. The method has been shown to eliminate the incorporated co-formulants under examination ; other co-formulants will have to be examined in detail to ensure that there is no interference in the menazon titration. Trace amounts of water present in the sample could interfere in the titration, but they would be adsorbed first by the alumina added to the sample before the transfer to the column. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. Calderbank, A., Edgar, S. C., and Silk, J. A., Chem. & Ind., 1961, 630. Calderbank, A., and Turner, J. B., Analyst, 1962, 87, 273. Camoni, I., D’Antonio, C . , Gandolfo, N., Leoni, V., Ramelli, G. C., and Sampaolo, A., Agrochimica, Plant Protection Ltd. Supplement No. 1 to Data Sheet PP175 (Menazon), April, 1961. Smart, N. A., and Hill, A. R. C., J . Chromat., 1967, 30, 626. Beremblum, I., and Chain, E., Biochem. J . , 1938, 32, 295. Chen, P. S., Toribara, T. Y., and Warner, H., Analyt. Chem., 1956, 28, 1756. Huber, W., “Titrations in Non-aqueous Solvents,” Academic Press, New York and London, 1967. Received June lst, 1970 Accepted November 23rd, 1970 1967, 11, 229.

ISSN:0003-2654    

DOI:10.1039/AN9719600343

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

346 Analyst, May, 1971, Vol. 96,fi+. 346-348 Method for Molybdenum in Plant Materials with Toluene-3,4-dithiol A Rapid and Accurate the Determination of BY H. SSEKAALO" (Animal Health Research Centre, P.O. Box 24, Entebbe, Uganda) A rapid and accurate method is described for determining molybdenum in plant materials with toluene-3,4-dithiol. The molybdenum is allowed to react with the reagent in a solution with a sulphuric acid concentration of about 6 N. Prior separation of the element from the acid digest of the plant material is unnecessary, there being no loss of sensitivity or accuracy if this process is omitted. SEVERAL workers have demonstrated the r81e of molybdenum in the metabolic processes of and higher animalsS5 With the latter much attention has recently been focused on the interaction of this element with copper and inorganic sulphate ions that occur in the In all such organisms molybdenum is needed in small amounts and therefore very sensitive methods must be used for its determination. In addition, speed and accuracy of determination are often necessary in the study of the r6le of this element in these biological systems.In this paper a rapid and accurate, but yet very sensitive, method for determining molybdenum in plants with toluene-3,4-dithiol is described, which does not involve prior separation of the element. METHOD APPARATUS- glass cells. REAGENTS- ToZuene-3,4-dithioZ, 0.2 per cent. solution-warm a 1-g ampoule of dithiol on a steam-bath to melt the yellowish solid. Then pour the molten compound into 0-5 N sodium hydroxide, with stirring to ensure its complete dissolution, and make the volume up to 500ml with 0.5 N sodium hydroxide; add 10 ml of thioglycollic acid (anti-oxidant).This reagent keeps for at least 3 months in completely filled glass-stoppered bottles stored in a refrigerator. Standard molybdenum solution-Prepare a 1000 pg ml-l stock stolution of ammonium molybdate, (NH,),Mo,0,,.4H20 in 0-5 N sulphuric acid; prepare from this solution the required concentrations by appropriate dilution. The other reagents used were of analytical-reagent grade and de-ionised water was used for making the solutions. PROCEDURE- Wet oxidise a suitable weight of oven-dry plant material (1 to 5 g ) with nitric acid (sp.gr. 1-42), sulphuric acid (spgr. 1.84) and 60 per cent.perchloric acid. For each sample weight taken, use an amount of sulphuric acid that will give a concentration of this acid of about 6 N in the final aqueous solution in which the molybdenum - toluene-3,4-dithiol complex is to be precipitated. If the sample weight is between 1 and 2 g, simply pour the cooled sulphuric acid digest directly into a 50-ml Nessler tube in which the complex is to be formed, rinsing the flask with water and adding the rinsings. If the sample weight is more than 2 g, filter the digest through a sintered-glass funnel to remove the silica, if a comparatively large amount of the latter is present, and then transfer the filtrate and rinsings to the Nessler tube. Mix the aqueous solution and make the volume up to about 30 ml. Add 3 ml of 0.2 per cent.A Unicam SP500 spectrophotometer was used for absorbance measurements in 1-cm * Present address : East African Industrial Research Organisation, P.O. Box 30660, Nairobi, Kenya. 0 SAC and the author.SSE KAALO 347 toluene-3,d-dithiol and mix the solution with a glass rod. Allow the tube to stand in a water- bath at a temperature of 75 "C for 20 minutes. Remove the tube, cool it and quantitatively transfer the contents to a 100-ml separating funnel. Add 5.0 ml of carbon tetrachloride and shake the funnel vigorously for 1 minute to extract the green complex into the organic layer. Filter the green solution through cotton-wool and then read the absorbance of the solution at 682nm.s Construct a standard graph for the molybdenum concentration range of 0 to 2.5 p.p.m.RESULTS PRECISION TEST- This work was carried out with replicate determinations of molybdenum on the pasture plants Brachiaria ruxixiensis (l-g samples were used), Chloris gayana, Panicum maximum, Pennisetum fiur$ureum and Pasfialum commersonii (2-g samples were used for the last four). The results obtained are shown in Table I. TABLE I REPLICATE DETERMINATION OF MOLYBDENUM IN LEAVES OF FIVE PASTURE PLANTS Plant Number of Molybdenum Coefficient replicates content, p.p.m. of variation Brachiaria ruziziensis . . . . 20 Chloris gayana . . . . . . 20 Panicum maximum . . . . 20 Pennisetum puypuyeum. , . . 20 Paspalurn commersonii .. 20 4.25 0.25 0.39 0.34 0.39 1.4 10.0 10.2 5.8 7-7 ACCURACY TEST- The accuracy of the method was tested by comparing the molybdenum contents of plant tissues determined by the present method and by Piper and Beckwith's m e t h ~ d .~ The results are shown in Table 11. TABLE I1 MOLYBDENUM CONTENTS OF PASTURE PLANTS BY THE PRESENT METHOD AND BY PIPER AND BECKWITH'S METHOD Plant Plant part Brachiaria ruziziensis . . . . Leaf Chlorisgayana . . . . . . Leaf Panicummaximum .. . . Leaf Stem Brachiaria congo . . . . . . Stem Pennisetum puypureum . . . . Leaf Paspalurn commersonii . , . . Leaf Molybdenum content, p.p.m. r A \ Piper and Present method Beckwith's method 4.25 4.2 1 0-25 0.23 0.39 0.38 0.25 0-27 0.52 0.50 0.34 0-38 0.39 0.4 1 POSSIBLE INTERFERENCE BY COPPER- Piper and Beckwithg noted that a standard copper solution containing about 20 pg, when complexed with dithiol, gave an absorption comparable with that of 2 pg of molybdenum when pentyl acetate was used as the solvent, but in the present work the same copper concentration gave an absorbance equivalent to the blank reading at 682nm.Hence, no appreciable interference from copper is experienced in this method. COMPLETENESS OF EXTRACTION OF THE COMPLEX- Extractions were carried out in two sets of ten replicate determinations of molybdenum in Brachiaria ruziziensis. In one set 10.0 and 5.0-ml volumes of carbon tetrachloride were used in two consecutive extractions of the complex. In the second set 5-0 and 5.0-ml volumes of the solvent were used for the extractions. With both sets, the molybdenum concentration348 SSEKAALO in the second extraction amounted to no more than that found in the blanks, which indicates that the coefficient of extraction of the complex into carbon tetrachloride on vigorously shaking the mixture is very good, especially as the aqueous volume was several times larger than the organic phase.Thus a single extraction of the complex with 5.0 ml of carbon tetrachloride was sufficient. DISCUSSION AND CONCLUSION The results of both the precision and accuracy tests show that molybdenum can be determined accurately with toluene-3,4-dithiol in plant tissues without prior separation of the molybdenum. The high level of acidity at which the complex is formed prevents inter- ference by tung~ten,~ which reacts with the reagent at a much lower acidity levello (pH 0.5 to 2.0). The small amount of silica that may be present in the acidic solution was found to have no effect on the formation and extraction of the complex.Because of the high sulphuric acid concentration small amounts of sulphate tend to precipitate before the addition of the reagent. The good coefficient of extraction of the complex into carbon tetrachloride with vigorous shaking for 1 minute permits a small volume of the organic layer to be used in conjunction with the large aqueous volume in which the complex is formed. Thus there is no loss of sensitivity and a considerable saving in time, which would otherwise have been spent needlessly on the prior separation of the molybdenum. The author is indebted to Mr. A. Okumu of this laboratory for his assistance in this work. This paper is published by permission of the Permanent Secretary, Ministry of Animal Industry Game and Fisheries, Uganda. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. REFERENCES Steinberg, R. A., J . Agric. Res., 1937, 55, 891. Mulder, E. G., PI. Soil, 1948, 1, 94. Hewitt, E. J., Jones, E. W., and Williams, A. H., Nature, 1949, 163, 681. Argawala, S. C., Ibid., 1952, 169, 1099. Bell, M. E., N.Z. Soil News, 1953, [3], 34. Dick, A. T., Soil Sci., 1956, 81, 229. -- , Outl. Agric., 1969, 6, 14. Ssekaalo, H., Lab. Pract., 1970, 19, 603. Piper, C. S., and Beckwith, R. S., J . SOC. Chem. Ind., Lond., 1948, 67, 374. Allen, S. H., and Hamilton, M. B., Analytica Chim. Acta, 1952, 7, 483. Received June 30th, 1970 Accepted October 22nd, 1970

ISSN:0003-2654    

DOI:10.1039/AN9719600346

出版商:RSC    

年代:1971

数据来源: RSC