ISSN:0003-2654    

DOI:10.1039/AN97398FX041

出版商:RSC    

年代:1973

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN97398BX043

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

ivITHE ANALYST [November, 1973THE ANALYSTE D ITORl AL ADV IS0 RY BOARDChairman: H. J. Cluley (Wembley).*L. S. Bark (Solford)R. Belcher (Birmingham)L. J. Bellamy, C.B.E. (Woltham Abbey)L. S. Birks (U.S.A.)E. Bishop (Exeter)E. A. M. F. Dahmen (The Netherlands)*J. B. Dawson (Leeds)A. C. Docherty (BillinghamjD. Dyrssen (Sweden)*W. T. Elwell (Birmingham)*D. C. Garratt (London)*R. Goulden (Sittingbourne)1. Hoste (Belgium)D. N. Hume (U.S.A.)H. M. N. H. Irving (Leeds)A. G. Jones (Welwyn Garden City)M. T. Kelley (U.S.A.)*J. A. Hunter (Edinburgh)W. Kemula (Poland)*G. F. Kirkbright (London)G. W. C. Milner (Harwell)G. H. Morrison (U.S.A.)*J. M. Ottaway (Glosgow)*G. E. Penketh (Billingham)S. A. Price (Tadworth)D. 1. Rees (LondonjE.B. Sandell (U.S.A.)*R. Sawyer (London)A. A. Smales, O.B.E. (Harwell)H. E. Stagg (Manchester)E. Stahl (Germany)A. Walsh (Australia)T. S. West (London)P. Zuman (U.S.A.)*A. Townshend (Birmingham)* Members of the Board serving on the Executive Committee.NOTICE TO SUBSCRIBERSSubscriptions for The Anolyst, Analytical Abstracts and Proceedings should beThe Chemical Society, Publications Sales Ofice,Blackhorse Road, Letchworth, Herts.Rates for 1973(other than Members of the Society)sent to:(a) The Analyst, Analytical Abstracts, and Proceedings, with indexes . . . . €37.00(b) The Analyst, Analytical Abstracts printed on one side of the paper (without(c) The Analyst, Analytical Abstracts printed on one side of the paper (withindex), and Proceedings .. . . . . . . . . . . . . €38.00index), and Proceedings . . . . . . . . . . . . . . f45.00The Analyst and Analytical Abstracts without Proceedings-(e) The Analyst, and Analytical Abstracts printed OR one side of the paper (without(f) The Analyst, and Analytical Abstracts printed on one side of the paper (with(d) The Analyst and Analytical Abstracts. with indexes . . . . . . . . €34.00index) . . . . . . . . . . . . . . . . . . €35.00. . . . . . . . . . . . . . . . . . index) f42.00(Subscriptions are NOT accepted for The Analyst and/or for Proceedings alonevi SUMMARIES O F PAPERS I N THIS ISSUE [November, 1973Summaries of Papers in this IssueDifferential Electrolytic Potentiometry with Periodic PolarisationPart XXIII.The Effect of Bias and Distortion on Periodic DifferentialElectrolytic Potentiometry, the D.C. Output Produced and Time-biassed Differential Electrolytic Potentiometry in Oxidation -Reduction TitrationsAny departure from the pure, symmetrical, bias-free input waveform ;external d.c. bias; internal d.c. offset, distortion, amplitude or mark-to-space(time) bias ; produces a deterioration in the periodic differential electrolyticpotentiometric titration curve. The peak potential is decreased, the peakbecomes less sharp, the discrimination becomes worse, errors are introducedand the electrodes more quickly become deactivated when any bias or dis-tortion is present in the input current waveform, and this effect is manifestwith 2 per cent.contamination of the waveform and destructive a t 5 percent. A d.c. bias causes the peak to split into two peaks. At the same time,the electrodes produce a d.c. output; the symmetrical polarisation showsno d.c. component in the output; and for d.c. offset and amplitude bias,this d.c. output is the same as for classical d.c. differential electrolyticpotentiometry. With a time-biassed periodic input of any waveform, ad.c. output of unique properties is produced. This output has the same formsas the classical d.c. differential electrolytic potentiometric curves, but theend-points are sharper, the discrimination is better, the end-points are error-free with dichromate and cerium(1V) titrants, the d.c. potential stabilises veryquickly and remains drift-free, even for type I1 (b) curves, the high-qualityend-point persists to very low concentrations, the electrodes retain theiractivity for a long time and the process is independent of frequency.Suchtitrations can be performed as fast as titrations with visual indicators. Thepositive errors in classical d.c. differential electrolytic potentiometric ti trationswith cerium(1V) , chromium(V1) and in zero-current potentiometric titrationswith vanadium(V) are explained.E. BISHOP and T. J. N. WEBBERChemistry Department, University of Exeter, Stocker Road, Exeter, EX4 4QD.Analyst, 1973, 98, 769-776.Monte CarPo Simulation of Matrix Correction EffectsMonte Carlo simulation is useful for the precise evaluation of the effectsof complex systems of matrix correction equations (such as occur in spectro-graphic analysis).If the error distributions for the interfering elements areexperimentally determined, that induced by interaction in the correctionequation system for the elements subject to interference can be predicted.R. J. HOWARTHApplied Geochemistry Research Group, Department of Geology, Imperial Collegeof Science and Technology, London, SW7 2BP.Analyst, 1973, 98, 777-781.Spectrophotometric Determination of Low Levels of Mono-, Di-and Triethylene Glycols in Surface WatersA method is proposed for the determination of mono-, di- and triethyleneglycols in surface waters, based on the oxidation of the glycols to aldehydes.These are made to react with 3-methylbenzotliiazol-2-one hydrazone hydro-chloride to give green cationic chromogens, which are then measured spectro-photometrically a t 630 nm.Sample blank values, to compensate for naturalinterferences, are obtained by omitting the oxidation stage. The methodenables glycol levels of upwards of 0.5 mg 1-1 to be determined, satisfactoryrecoveries of each glycol being obtained for concentrations of 1 to 5 mg 1-1,with a precision of 7 per cent., for a range of water samples. A sensitivevariation of the method, for the determination of monoethylene glycol alone,is described separately.W. H. EVANS and A. DENNISDepartment of Trade and Industry, Laboratory of the Government Chemist, Cornwall,House, Stamford Street, London, SE1 9NQ.Analyst, 1973, 98, 782-791.X THE ANALYST [November, 1973Analytical Standards forTrace Elements AnalysisModern trace analysis techniques more and more frequently call for the use of referencestandards of metals.Spectrography, Atomic Absorption Spectrophotometry, Emission Spectrophotometry, X rayFluorescence are techniques which particularly require the use of these standards.It is however necessary to make a distinction between application of such techniques towater, or to other solutions whatever the basic solvent, oil or hydrocarbon.In fact if one uses the same technique on an aqueous solvent, one must use an aqueoussolution.If one uses a non-aqueous solvent the standards used must be soluble in thissolvent.Standards for atomic absorptionshould actually be called standard solutions for metaltrace anlysis, where the metal is in an aqueoussolution acidified by nitric acid, and may therefore beused as a standard for any analytical techniquerequiring it.Atomic absorption spectrophotometry is now beingused more and more in analysis in both research andindustrial laboratories, as this is the fastest andeasiest independent method for metal determinations.It may be applied to any soluble matrix.As for any instrumental technique, it is important tohave available standards of the metals involved,to set both the method and apparatus, and to revealany interference or positive or negative effects(caused by the matrix, solvent, etc.).In any case a control against a standard is advisablewhen plotting calibration curves.In fact in atomicabsorption spectrophotometry, the theoretical linearrelationship between absorbance and concentration,known as Beer’s law, is effective only within verynarrow limits.It will now be clear how important it is to haveavailable solutions with a known content, at least forthe most frequently determined metals.Carlo Erba STANDARDS for Atomic Absorption are thefollowing concentrated solutions of metal nitratewhich, when diluted to 1000 ml with distilled water,give a slightly acidic solution (about 0.1% HNO,) at aconcentration of metal ion of 1000 ppm:Metallorganic standardsThese compounds are in fact improperly calledmetallorganic, as they are generally metal salts ofcarboxylic organic acids or organic metal complexes;but this expression has been chosen because it givesa more immediate idea of the metal atom being linkedto an organic radical which eases solution in oils,even when the substance involved is not an alkyl oran aryl.They are used as oil-soluble standards in thespectrographic analysis of traces of metals in oils andfats, in petroleum derivatives and in lubricatingagents.The analysis of metals in non-aqueous media iscarried out with spectographs and atomic absorptionspectrophotometers using samples of known contentas controls.Therefore it has been necessary to studyand develop organometallic compounds and organicsalts of metals, having a known metal content.The stability is obtained by the use of solubilisingagents such as 2-1 -Ethylhexanoic acid,6-Methly-2,4-heptandione, 2-Ethyl-hexylarnine, andb is-(2-Et h y I hexy I) d i t h i ocarbam i cacid-bis-(2-ethylhexyl)ammonium salt, with Xylene.Thus, clear and stable solutions in an oil base areobtained, with concentrations up to 500 ppm of metal.It is also possible to prepare solutions containingmore than one metal, bearing in mind that mixtures ofmetals are more soluble than the individualconstituents.Aluminium STANDARD Lithium STANDARDBarium STANDARDCadmium STANDARD M~~~~~~~~ STANDARD vials concern the following elements:~~~~~~i~~ STANDARD Carlo Erba metallorganic standards available in 5 g.Calcium STANDARD NickGI STANDARDChromium STANDARD Potassium STANDARD Aluminium, Barium, Bismuth, Boron, Cadmium,Cobalt STANDARD Silver STANDARD Calcium, Chromium, Cobalt, Copper, Iron,Copper STANDARD Sodium STANDARD Lanthanum, Lead, Lithium, Magnesium, Manganese,iron STANDARD Strontium STANDARD Nickel, Phosphorus, Potassium, Silicium, Silver,Lead STANDARD Zinc STANDARD Sodium, Strontium, Tin, Vanadium, Zinc.Special bookkt available on request( CARLO EBBA I D~V~SIONE CHIMICA I VIA CARLO IMBONATI 24 I 201x1 MILAN

ISSN:0003-2654    

DOI:10.1039/AN97398FP125

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

November, 19731 THE ANALYST xiAPPOINTMENTS VACANTTHE QUEEN’S UNIVERSITY OF BELFASTDEPARTMENT OF CHEMISTRY (ANALYTICAL)DEMONSTRATORSHIPApplications are invited for a demonstratorship in the Departmentof Chemistry (Analytical) from 1st October 1973. The scale is L1,005-E1,086-E1,153. The successful candidate will assist with researchinto fluoride analysis. Initial placing will depend on qualificationsand experience. Applications which should be received by November19 and which should be accompanied by a brief curvzculum vitae andthe names of two academic referees, should be addressed to thePersonnel Officer, the Queen’s University of Belfast, BT7 lNN,Northern Ireland.UNIVERSITY OF BATHSCHOOL OF PHARMACY AND PHARMACOLOGYTECHNICIANrequired to join a research team investigating the interactionsof components of aqueous ophthalmic formulations withplastics.The project is sponsored by the Department ofHealth, initially for a two year period. Applicants shouldpossess experience in analytical chemical techniques orplastics technology.Starting salary (under review) El539 x E51- J;1794 per annum.Application forms are obtainable from the Registrar (S),University of Bath, Claverton Down, Bath BA2 7AY,quoting reference No. 73/145.GLAXOhave an appointmentfor aDEPUTY to the FACTORY ANALYSTAND QUALITY CONTROLLERat their Cambois factory. This is the most recently built factorywithin the large Glaxo Group of companies, having been openedin 1971 for the production of bulk antibiotics by deep-culturefermentation.The Analytical and Quality Control Department provides acomprehensive analytical service including raw material testing,production control, quality control of final products, and variousother work for the ancillary factory services.The person appointed will assist the Factory Analyst andQuality Controller in the smooth and efficient running of thesesections, some of which operate on a 7 day 3 shift system.Hewill also undertake non-routine investigations for the Department.He will be expected to bring to the position a technical expertise,administrative flair and the ability to motivate and lead subordinates,together with a working knowledge of automated and instrumentala n a I yt i ca I eq u i pmen t .Candidates with these requirements are likely to be graduates (orthe equivalent) in Chemistry or Pharmacy, with several yearsappropriate experience in Analytical Chemistry, preferably in thePharmaceutical industry.The position will carry a salary up tof 3055 per annum commensurate with qualifications and experience.The factory is situated in Northumberland within easy reach ofNewcastle, coast and country, and the area provides scope for awide range of sporting and cultural interests. Re-location ex-penses would be paid where appropriate.Candidates should apply to :The Senior Personnel Officer,Glaxo Labaratories Limited,Cambois,Bed I i ngt on,Northumberlandxii THE ANALYST [November, 1973APPOINTMENTS VACANTANALYTICAL CHEMISTCAWTHRON INSTITUTENELSONNEW ZEALANDA permanent position is available in the Chemical Services ServicesSection (10 staff) which offers a wide range of analytical and consultantservices to industry and agriculture.The position would suit a hardworking, versatile chemist interestedin applying knowledge and experience to a wide variety of organic andinorganic analytical problems.Applicants should have a B.Sc.Hons., M.Sc.or A.R.I.C., with someyears of experience in an analytical laboratory, preferably that of aPublic Analyst, and some experience in the supervision of staff.The Institute offers pleasant working conditions in a modem well-equipped laboratory. Instrumentation includes G.C., U.V., I.R. andA. A.Salary will be in the range $5000-$7000 N.Z.(L3040-L4256 U.K.)depending on qualifications and experience.Application Forms may be obtained from the Assistant ProfessionalActivities Officer, Royal Institute of Chemistry, 30 Russell Square,London WClB 5DT, to whom application should, in the first instance,be made.BINDINGHave your back numbers of The Analystbound in the standard binding case.Send the parts and the appropriateindcx(es) together with a remittancefor €2.65 to:J. S. WILSON & SON14a Union Road,Cambridge CB2 I H EHeinz, leaders in the convenience sector of the food industry, require ayoung graduate, preferably with some experience in continuous flowautoanalysis, to carry out development work on foodstuffs analysis by thistechnique.The person appointed must have sufficient experience and initiative toperform this task with minimum supervision.The Heinz Research Centre is situated in a pleasant parkland setting inHayes, Middlesex, and assistance in relocation can be offered ifnecessary.Salary, working conditions and fringe benefits are appropriateto a major food company.Please write in the first instance giving a brief personal and careersummary and quoting present salary to:-Mr. K. S. Chivers,M anager-H. 0. Personnel Services,H. J. Heinz Company Ltd.,Hayes Park, Hayes, Middlesex UB4 8AL.Please mention THE ANALYST when replyingto advertisementxiv SUMMARIES OF PAPERS IN THIS ISSUEA Spectrophotometric Method for the Micro- determination ofPiperonyl Butoxide in the Presence of PyrethrinsA rapid spectrophotometric method has been developed for the micro-determination of piperonyl butoxide in the presence of a wide range ofpyrethrins.A solution of the mixture of piperonyl butoxide and pyrethrinsin a low-boiling fraction of light petroleum is evaporated on a water-bathuntil only a small portion of the solvent remains. The final traces of solventare removed at 50 "C and, to the residue containing piperonyl butoxide andpyrethrins, 18 per cent. nz/V nitric acid is added in order to convert thepiperonyl butoxide content into a soluble yellow-coloured compound. Thequantitative colour reaction has a maximum absorption a t 370nm, andthe method is applicable to the residues in the range 4 to 40 pg ml-l ofpiperonyl butoxide. The method is also applicable to the residues of formu-lated products extracted from grains and paper coatings.H.M. BHAVNAGARY and S. M. AHMEDCentral Food Technological Research Institute, Mysore-BA, India.[November, 1973Analyst, 1973, 98, 792-796.The Determination of Chlorhydroxyquinoline in Medicated Pig FeedsA method has been developed for the determination of chlorhydroxy-quinoline (Halquinol) in medicated pig feeds, Because of the interferenceby feed constituents in simple spectrophotometric and polarographic assayprocedures, a spectrofluorimetric procedure is recommended. Spectrofluori-metric measurements are taken in a methanolic solvent containing 5 per cent.of chloroform, and the fluorescence of chlorhydroxyquinoline, as its mag-nesium chelate, is measured at 500nm, with an excitation wavelength of402 nm.Cyanide is used to suppress interference from copper and zinc saltsthat are commonly added to these feeds. The procedure is not affected bythe presence of other feed additives, such as dimetridazole and arsanilic acid.J. E. FAIRBROTHER and W. F. HEYESSquibb International Development Laboratory, Moreton, Wirral, Cheshire.Analyst, 1973, 98, 797-801.Solvent Extraction of Copper( 11) and Zinc(I1) with1,5- DiphenylcarbazoneThe extraction characteristics of 1,5-diphenylcarbazone and its coni-plexes with the bivalent metal ions copper(I1) and zinc(I1) in an isobutylmethyl ketone - water system have been studied and the extraction curvesof these metal complexes have also been obtained.The copper(I1) complexis extracted from a more acidic solution than is the zinc(I1) complex. Theextraction equilibria have been examined and the extraction constantsdetermined. The spectral properties of the complexes have also been deter-mined and the application of the reagent to the determination of copperand zinc is suggested.HISAHIKO EINAGA and HAJIME ISHIINational Institute for Researches in Inorganic Materials, Niihari-gun, Ibaraki-ken,Japan.Analyst, 1973, 98, 802-810.A Solvent- saving Extraction - Evaporation ApparatusDeveloped for Residue Analysis of PesticidesAn apparatus that simultaneously allows Soxhlet extraction of pesti-cides and concentration of the resulting extract has been designed. Theevaporated solvent is refluxed into the Soxhlet flask where it is utilised againfor the extraction.The major advantages of this cyclic extraction - evapora-tion system are that redistillation of solvents prior to extraction can beomitted, that manual work is reduced, as the solvent evaporation processoccurs simultaneously with the extraction of the sample, and that excess ofsolvent is not wasted but re-utilised for extraction, which is of interestfrom the economic and environmental contamination points of view.G. VOSS and W. BLASSAgrochemical Division, CIBA-Geigy Ltd., Basle, Switzerland.Analyst, 1973, 98, 811-812November, 19731 THE ANALYST xvTRACE ELEMENTANALYSISPROBLEMS?Activation Analysis could be the answer. Thistechnique offers the advantages of high sensitivityand specificity, good accuracy and precision, even atsub-p.p.m. concentrations.A bulk analysis isobtained, 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 I ike to discuss your particular problem,or would like to receive further details, please contact:Dr. G. R. Gilmore (Activation Analyst),Activation Analysis Service,Universities Research Reactor,Risley,Nr. Warrington,Lancs.Phone: Warr. 32680,33114BUREAU OF ANALYSEDSAMPLES LTD.announce the issue of the followingNEW SAMPLESChemical StandardsNo. 384 Hycomax I11 PermanentMagnet Alloy (34% Co,4% Ti, 1% Nb)No.388 Zircon (66% ZrO,, 33% SiO,)Spectroscopic StandardsNos. 661-665 High Phosphorus Engin-eering Irons containingincrements of C , Si, Mn, Sand PFor further details please write to:-NEWHAM HALL, NEWBY,TS8 9EAor Telephone 0632 37216MID D LESBROU GH, TEESSI D E, ENGLANDANNUAL REPORTS ON ANALYTICALATOMIC SPECTROSCOPYVolume 2, 1972This comprehen ive and critical report of developments in analytical atomicspectroscopy has been compiled from more than I000 reports receivedfrom world-wide correspondents who are internationally recognised authori-ties in the field and who constitute the Editorial Board. In addition tosurveying developments throughout the world published in national orinternational journals, a particular aim has been to include less widelyaccessible reports from local, national and international symposia andconferences concerned with atomic spectroscopy.Volume 2 covers the year 1972216 pages Price f5-00 ISBN 0 85990 252 8Obtainable from The Society for Analytical Chemistry,(Book Department), 9/10 Savile Row, London, W1 X 1 AFMembers of The Chemical Society may buy personal copies at the special price of f3.0SUMMARIES OF PAPERS I N THIS ISSUEFractionation and Identification of Commercial HydrocolloidStabilising AgentsPart 11.Identification of the Components of Guar Gum - Locust BeanGum and of Pectinate - Gum Tragacanth MixturesThe limitations of a method for the identification of mixtures of stabilisingagents described previously have been overcome.The method now facilitatespositive identification of pectinate and tragacanth in admixture and of guargum and locust bean gum in admixture.R. G. MORLEY, G. 0. PHILLIPS, D. M. POWERDepartment of Chemistry and Applied Chemistry, University of Salford, Salford,Lancashire, M5 4WT.and R. E. MORGANThe Medical Center, University of Alabama, Birmingham, Alabama, U.S.A.[November, 1973Analyst, 1973, 98, 813-815.Determination of Nicotinamide in Some Injections of B-complexVitamins by Thin-layer ChromatographyNicotinamide in some injections of B-complex vitamins can be separatedon a thin layer of silica gel G by using a solvent mixture of ethanol (98 percent.) - chloroform (25 + 60 V / V ) , eluted from the scraped off area with 0-1 Nhydrochloric acid and the solution measured spectrophotometrically a t261 nni.Results obtained by use of the proposed method are comparedwith those obtained with the ammonia distillation method of the BritishPharmacopoeia 1968.SAAD A. ISMAIEL and DAWOUD A. YASSAResearch Department, Soci6t6 Misr pour 1’Industrie Pharmaceutique, 92 El-MatariaStreet, Post El-Zeitoun, Cairo, Egypt,Analyst, 1973, 98, 816-818.Determination of Balsamic Acids and Esters byGas - Liquid ChromatographyA gas - liquid chromatographic method for the determination of balsamicacids and esters in crude drugs is described. Methylation of free acids isfollowed by a single-stage separation and quantitative determination ofmethyl and benzyl esters of benzoic and cinnamic acids. Results are pre-sented for the column parameters and reproducibility of the method. Theanalysis of a commercial sample of tolu balsam is reported ; the interpretationof the results may offer additional information to that obtained from officialstandards.K. J. HARKISS and P. A. LINLEYPostgraduate School of Studies in Pharmacy, University of Bradford, Bradford,BD7 1DP.Analyst, 1973, 98, 819-822.Application of Gas - Liquid Chromatography to the Analysisof Essential OilsPart 111. The Determination of Geraniol in Oils of CitronellaReport prepared by the Essential Oils Sub-committee.ANALYTICAL METHODS COMMITTEE9/10 Savile Row, London, W1X 1AF.Analyst, 1973, 98, 823-829.Recommended Methods for the Evaluation of Drugs.The Chemical Assay of Cascara Bark and Cascara Dry ExtractReport prepared by the Joint Committee of the PharmaceuticalSociety and the Society for Analytical Chemistry on RecommendedMethods for the Evaluation of DrugsJOINT COMMITTEE OF THE PHARMACEUTICAL SOCIETY AND THESOCIETY FOR ANALYTICAL CHEMISTRY9/10 Savile Row, London, W1X 1AF.Analyst, 1973, 98, 830-83

ISSN:0003-2654    

DOI:10.1039/AN97398BP133

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

NOVEMBER, 1973 Vol. 98, No. 1172 Differential Electrolytic Potentiometry with Periodic Polarisation Part XXIII." The Effect of Bias and Distortion on Periodic Differential Electrolytic Potentiometry, the D.C. Output Produced and Time-biassed Differential Electrolytic Potentiometry in Oxidation - Reduction Titrationst BY E. BISHOP AND T. J. N. WEBBERI (Chemistry Department, University of Exeter, Stocker Road, Exeter, EX4 4QD) Any departure from the pure, symmetrical, bias-free input waveform ; external d.c. bias; internal d.c. offset, distortion, amplitude or mark-to-space (time) bias ; produces a deterioration in the periodic differential clectrolytic potentiometric titration curve. The peak potential is decreased, the peak becomes less sharp, the discrimination becomes worse, errors are introduced and the electrodes more quickly become deactivated when any bias or dis- tortion is present in the input current waveform, and this effect is manifest with 2 per cent.contamination of the waveform and destructive a t 5 per cent. A d.c. bias causes the peak to split into two peaks. At the same time, the electrodes produce a d.c. output; the symmetrical polarisation shows no d.c.-component in the output; and for d.c. offset and amplitude bias, this d.c. output is the same as for classical d.c. differential electrolytic potentiometry. With a time-biassed periodic input of any waveform, a d.c. output of unique properties is produced. This output has the same forms as the classical dlc. differential electrolytic potentiometric curves, but the end-points are sharper, the discrimination is better, the end-points are error- free with dichroniate and ceriuni(1V) titrants, the d.c.potential stabilises very quickly and remains di-ift-free, even for type I1 (b) curves, the high-quality end-point persists to very low concentrations, the electrodes retain their activity for a long time and the process is independent of frequency. Such titrations can be performed as fast as titrations with visual indicators. The positive errors in classical d.c. differential electrolytic potentiometric titrations with cerium(1V) , chromium(V1) and in zero-current potentiometric titrations with vanadium(V) are explained. No previous work on the use of biassed or asymmetrical waveforms has been discovered in a literature search; earlier work on periodic polarisation has been faulted because no effort seems to have been made to ensure purity and symmetry of waveform, or indeed to examine them, except for one attempt to block d.c.by means of a series capacitor in the generator output,l a device that gave very limited success.2 Both the Heathkit and Advance signal generators that were initially used in this ~ o r k ~ , ~ gave unsatisfactory results, which were traced to a d.c. offset in the former and low-frequency distortion in the latter. Addition of a series capacitor did not eliminate all of the d.c. offset, and had no influence on a badly shaped wave, other than to attenuate low frequencies. Moreover, the use of a transformer, even of the constant voltage saturable reactor type, to provide a 50-Hz signal, is productive of waveform distortion and harmonics because of the iron-cored inductance.These observa- tions led to a systematic quantitative examination of the effects of offset and waveform asymmetry on the precision, accuracy and discrimination of end-point location, and on the forms of the titration curves and the speed of electrode response. With a pure periodic waveform, there is no d.c. component in the output from the electrodes, just as there is no periodic component in the output from pure d.c. polarisation. With a biassed or offset waveform, both d.c. and periodic components will be present in the output. * For details of Part XXII of this series, see reference list, p. 776. t Presented a t the Second SAC Conference, Nottingham, 1968.5 Present address : Shell Research Limited, Woodstock Agricultural Research Centrc, Sittingbourne, @ SAC and the authors. Kent. 769770 BISHOP AND WEBBER : DIFFERENTIAL ELECTROLYTIC [Artahst, VOl. 98 Rough predictions of the form of the titration curve for single polarised electrodes veysus reference and zero-current indicator electrodes, and for pairs of polarised electrodes, were made (Fig. 1 in reference 3) on a basis of the titration analogue model,4 for fast reactions and 50 per cent. of the particular bias. For example, if there is a d.c. component in the periodic waveform, then, with an oxidant titrant, for a single electrode the end-point will be displaced from the equivalence point by an amount proportional to the magnitude of the d.c.component, and the error will be positive if the d.c. polarisation is cathodic and negative if it is anodic. For paired electrodes, one electrode will be polarised cathodically and the other anodically, and a d.c. differential potential will exist between them. When observed in the sense anode minus cathode, there will be a periodic peak superimposed on the d.c. peak. The d.c. output will be the sum of the first and second differentials of the zero-current curve, and the periodic output will broaden, eventually splitting to give two peaks. EXPERIMENTAL Various forms of bias were introduced into the pure waveforms, as exemplified in Fig. I, either as an external or internal d.c. offset, or by waveform shaping to give amplitude or time bias. Amplitude bias and d.c.offset are the same for square waves, but not for sine or triangular waveforms. n n Apparatus,3 solutions and procedures2 have been described earlier. Symrnetrical square wave form Fig. 1. Biassing of pure waveforms. Initial pure square wave with: (a), external d.c. offset; ( b ) , a 2: 1 mark-to-space (time) bias; (c), a 2: 1 amplitude bias, which is identical with (a) for square wave forms but not for the other waveforms; and (d), sine wave with a 2: 1 amplitude bias D.C. OFFSET- A limited internal d.c. offset, up to 5 V, could be mixed into the waveform by adjustment of the reference level potentiometer, P9, in the waveform generat~r,~ but greater offset could not be produced in this way without introducing distortion into the output signal. Larger offsets were introduced externally by applying a d.c.potential from a battery and potentiometer across the “low” and “earth” connections (normally strapped together) on the waveform generator. After checking the equality of the duration of the half-cycles with the crystal clock, the amount of d.c. present was measured either directly on the oscilloscope, or by increasing the frequency and applying the signal to a d.c. meter. AMPLITUDE BIAS- As is evident from Fig. 1, the amplitude bias is the same as a d.c. offset for square waves, but not for sine and triangular waves. Limitation of facilities at the time prevented further examination of amplitude bias for sine and triangular waveforms. TIME HAS- Time bias can be obtained by adjustment of the potentiometers P3, P4 and P5 in the generator.3 For square waves, a perfectly symmetrical, pure signal was first obtained, the half-cycles being identical in amplitude and duration, and the selected amount of bias was introduced.The internal adjustments did not permit more than 5 2 0 per cent. relative variation. The crystal clock was then used to measure, the duration of each half-cycle accurately. For sine waves, the clock would not trigger at frequencies less than 14 Hz, and it u7as necessary to trace the shape of an individual cycle from the oscilloscope screen onNovember, 19731 POTENTIOMETRY WITH PERIODIC POLARISATION. PART XXIII 771 to translucent graph paper, and to cut out and weigh the area representing each half-cycle. This method obviously has poor accuracy; the average error determined by replication was less than 5 per cent.The titration cell was then set up,3 with the electrode configuration shown in Fig. 3 in reference 2, so that the d.c. and periodic potentials at each of the periodic electrodes could be measured with reference to a standard half-cell or a zero-current electrode, and the periodic and d.c. potential differences between the two periodic electrodes could also be measured. At the same time, d.c. differential electrolytic potentiometry and zero- current potentiometric potentials could also be monitored for comparison. RESULTS AND DISCUSSION EFFECT OF D.C. BIAS ON THE PERIODIC POTENTIAL CURVE- First, a system showing a modicum of charge-transfer overpotential was examined, the titration of iron(1I) with 0.1 M cerium(IV), with a gradually increasing d.c.offset. The results are shown in Fig. 2, and accord with prediction. These results should be compared with those in Fig. 3 and other figures in reference 2 that show the results with pure, sym- metrical, bias-free waveforms. The presence of a very small (less than 2 per cent.) d.c. offset is sufficient to reduce the sharpness of the periodic potential curve under any given conditions. As the magnitude of the offset increases, the peak gradually broadens, until, at about 30 per cent. offset, it splits into two peaks. The presence of d.c. offset causes deactivation of the electrodes; not only is the relaxation following a concentration perturbation lengthened, but also, after some time, the initially bright and shiny electrodes assume a dull matt surface.With no d.c. offset, potentiometric and periodic end-points agree, but a deviation arises with d.c. offset and increases with increase in d.c. offset. A d.c. offset a d.c. component in the periodic output. I P oten t io me t r IC 1401 ejd-puin:; 120 in the periodic input produces Volume of cerium(lV) added/ml ---t Fig. 2. Variation of the peri- odic differential electrolytic potenti- ometric titration curve with increas- ing d.c. offset in the input signal. Expanded scale end-point region. Titration of 200 ml of 0-0125 M iron(I1) in 0.5 M sulphuric acid with 0.1 M cerium(1V). Sine wave, 3 Hz, r.1n.s. current density, 25 pA cm-2: (a), 2 per cent. d.c. offset; ( b ) , 5 per cent. d.c. offset; and (c), 40 per cent. d.c. offset Further titrations were then performed with periodic inputs containing an increasing time bias, and the deterioration in the periodic output was similar to that above with d.c.offset, although instrumental limitations at the time prevented examination of biasses above 20 per cent.772 BISHOP AND WEBBER : DIFFERENTIAL ELECTROLYTIC [Analyst, Vol. 98 Examination of the effect of offset and time bias was extended to reactions of type I1 (a) [titration of iron(I1) with dichromate] and type I1 (b) (titration of hydrazine with bromate). The results were again similar to those described above for d.c. offset in the titration of iron(I1) and cerium(1V). With increasing bias, the curves became less sharp, the discrimina- tion deteriorated and the periodic end-point deviated increasingly from the zero-current potentiometric end-point.Finally, the influence of d.c. offset on the electrodically fastest reactions, those of the titration of copper(1) with potassium bromate, was examined. The d.c. differential electrolytic potentiometric peak height is 600 mV at 1.0 p A cm-2, and a solution as near as possible to equivalence was prepared (platinum potential versus S.C.E. 520 mV) and a periodic signal of increasing d.c. offset applied to two electrodes; the amplitude of the square wave was maintained constant and the peak to peak output was measured on the oscilloscope. The results are shown in Table I, and indicate that for very fast charge-transfer processes an appreciable d.c. offset at fairly high frequency is necessary before significant reduction in the, probably already clipped, peak potential occurs, although eventually curve splitting into two peaks, as in Fig.2, occurs. TABLE I VARIATION OF PEAK POTENTIAL FOR AN ELECTRODICALLY FAST SYSTEM Applied signal: 10-Hz square wave; ballast resistance 5 x lo6 SZ; current density 10 pA cm-2 WITH INCREASING D.C. OFFSET +41 +42 +43 $48 $50 { 2:; -39 -38 -37 -32 -30 Applied signal/V . . Output signal/mV . . .. 275 275 275 270 200 170 It is therefore abundantly clear that any departure from pure, symmetrical, bias-free periodic waveforms,2 whether d.c. offset, amplitude or time bias, or distortion will cause a deterioration of the periodic output potential titration curve, and appreciable departures will seriously attenuate the precision and discrimination and introduce errors. THE D.C.OUTPUT COMPONENT FROM BIASSED OR OFFSET PERIODIC POLARISATION- By using a d.c. measuring device with a time constant that is long compared with the repetition frequency of the periodic polarising current, any d.c. component can be detected in the output. For an internal or external d.c. offset, the d.c. output produces a differential electrolytic potentiometric curve that is identical with a titration curve produced by classical d.c. differential electrolytic potentiometry at the same current density, but with the differences that in the former instance the electrode response is much faster and the electrodes retain their activity for a longer period. Time biassing, however, produced results of greater benefit and considerable interest.TIME-BIASSED PERIODIC DIFFERENTIAL ELECTROLYTIC POTENTIOMETRY- The periodic component of the output from this biassed waveform showed the usual deterioration and error with increasing bias, but the d.c. component proved to have unique and valuable properties. The range of bias available at the time was too small to permit proper investigation of the effect of its magnitude, and so a 5 per cent. bias was selected for examination, and the d.c. current density arbitrarily assigned a value of 5 per cent. of the periodic r.m.s. current density for comparison purposes. Titrations at customary concentrations-With the time-biassed input, examples of each type of oxidation - reduction reaction were examined, and the precision, accuracy and dis- crimination were compared with those of d.c.and symmetrical periodic differential electrolytic potentiometry. Curves obtained at optimum or near optimum electrical conditions are shown in Fig. 3, on an expanded volume scale in the end-point region, for type I, I1 (a) and I1 ( b ) reactions. The titration curves were appreciably sharper, by a factor of about two, than the corresponding d.c. differential electrolytic potentiometric curves of equivalent peak height, with slopes in excess of 50 000 mVml-l, and also sharper than the symmetrical periodicNovember, 19731 POTENTIOMETRY WITH PERIODIC POLARISATION. PART XXIII 773 3 480 differential electrolytic potentiometric curves. The response of the electrodes to a concen- tration perturbation by an increment of titrant in the region of the equivalence point was extremely rapid and considerably faster than for the classical d.c.differential electrolytic potentiometry, by a factor in excess of ten; this result was confirmed by making potential measurements at 5-s intervals. The increase in response speed was most marked with the type I1 reactions, and is of great benefit. In the iron(I1) titration with cerium(1V) after the end-point, although the speed of response remained, potential drift still occurred, which is indicative of changing charge-transfer kinetic parameters ; it is possible that gold electrodes could be used with benefit in this titration. The titration curves were independent of the frequency used, over the range from 3 Hz to the upper limit of the generator (1200 Hz), and of the waveform used, whether it was square, sine or triangular.At frequencies below about 20 Hz, the mean periodic potential output traced a curve of the same form as the d.c. potential. However, it was again found that in titrations of iron(I1) with cerium(1V) or chromium(VI), the d.c. and periodic peaks failed to coincide. There was again a difference of about 0.01 ml in a 25-ml titration, the pure periodic output peak and the time-biassed d.c. output peak coinciding with the zero-current potentiometric inflection point, and coming before the classical d.c. differential electrolytic potentiometric peak obtained from other electrodes in the same titration. No such differences were found in any of the other titrations examined; all four end-points coincided.Titrations at lower concentrations-Many different titrations were satisfactorily performed with time-biassed differential electrolytic potentiometry at concentrations down to times those just discussed, but the particularly intractable titration of iron(I1) with cerium(1V) was chosen for extensive examination, together with classical d.c. differential electrolytic potentiometry and zero-current potentiometry. 5 x low3 and 5 x 1 0 - 4 ~ cerium(1V) are shown in Fig. 4. The results of these and other titrations are given in Table I1 for titrant concentrations in the region of l O V 4 ~ . The assigned current densities at 5 per cent. bias are again 5 per cent. of the r.m.s. Deriodic current density. Titrations with 5 x 320 280 240 200 160 > E .- + c n 4 120 -0 8D 40 - - - - - - - -.450 300 0 . L - (b 1 - 420 360 300 240 180 120 60 Volume of titrant added/ml- Fig. 3. Titration curve forms ob- tained by using time bias; end-point region on an expanded volume scale. Sine wave, 100 Hz, 5 per cent. mark-to- ‘space bias, resultant mean d.c. density 1.0 pA cm-a: (a), titration of 200 ml of 0.0125 M iron(I1) in 0.5 M sulphuric acid with 0.1 M cerium(1V); (b), titration of 200 ml of 0.0125 M iron(I1) in 0.5 M sulphuric acid with 0.016 67 M chromium- (VI) ; and (c) titration of 200 ml of 0.003 M hydrazine in 0.1 M potassium bromide and 2-5 M hydrochloric acid with 0.01667 M potassium bromate 300 >E 200 r- .- + C + a -=f 100 a 80 a) 60 - 40 - -- I 1 .o 1- Volume of titrant addedhl- Fig. 4. Time bias d.c. differential electrolytic potentiometric curve forms in the expanded end-point region for lower titrant concentrations.Sine wave, 100 Hz, 5 per cent. mark-to-space bias. Titration of 200 ml of iron(I1) in 0-5 M sulphuric acid with cerium(1V) a t various concentrations and assigned current den- sities. Assigned (Celv]/ d.c. density/ mol 1-1 pA cm-8 CFeIII I Curve mol 1-1 6.25 x 10-3 5 x 10-2 1.0 (a) 6-25 x 10-4 5 x 10-3 0.25 6-25 x 10-5 5 x 10-4 . 0.10 (b) (4774 BISHOP AND WEBBER : DIFFERENTIAL ELECTROLYTIC [Analyst, Vol. 98 TABLE I1 TITRATIONS AT LOW TITRANT CONCENTRATION BY TIME-BIASSED DIFFERENTIAL ELECTROLYTIC POTENTIOMETRY . Current density/ Standard Reaction* pA cm-a Titrelml deviationlml 0.1 21.64, 21.59, 21.63, 21.60, 21.60, 21-58 0.02 0.1 23-11, 23.14, 23.12, 23.17, 23.10, 23.14 0.025 0.1 24.48, 24.53, 24.49, 24.47, 24.48, 24.52 0.02 (4 (b) (4 * (a) Titration of 200 ml of a 6.25 x with 5 x lo-* M cerium(1V).(b) Titration of 200 ml of a 1.25 x with 1.67 x M chromium(V1). (c) Titration of 200 ml of a 3 x 2.5 M hydrochloric acid with 1.67 x M solution of iron(I1) in 0.5 M sulphuric acid M solution of iron(I1) in 0.5 M sulphuric acid M solution of hydrazine in 0.1 M bromide plus M bromate. Even with titrant concentrations of 5 x M, the discrimination was still of the same order (about 0.15 per cent.) as the inherent volumetric error, but better than that for d.c. differential electrolytic potentiometry by a factor of about five and much better than that for pure symmetrical periodic polarisation (Fig. 5, reference 2). The response speed of the electrodes, judged by measurement of the time required to reach equilibrium, and the stability of the potentials showed a marked improvement over d.c.differential electrolytic potentio- metry at this concentration level. In Fig. 4, it can be seen that there is an increasing tendency towards type I1 ( a ) curves as the reactant concentrations decrease. This effect arises from the slowing down of the charge-transfer processes, particularly of cerium, on account of the decrease in the concentration terms in the charge-transfer equation and consequent increase in ria. Results for type I1 ( a ) and I1 (b) reactions are given in Table 11; the discrimination was of the same order as for the titration of iron(I1) with cerium(1V) and about twice as good as for d.c.differential electrolytic potentiometry. There was also a marked improvement in response speed and stability of the resultant potentials compared with d.c. differential electrolytic potentiometry. In order to investigate further the prevention of electrode fouling by time-biassed signals, titrations of iron(I1) with 5 x ~ O - * M cerium(1V) solution were performed by the classical d.c. differential electrolytic potentiometric method, and also with a balanced periodic signal of various frequencies of approximately the same r.m.s. current density, 20 p A cm-2, superimposed on the d.c. signal. This produces a synthetic amplitude biassed, but un- symmetrical, signal. There was no appreciable difference in electrode response speed after concentration changes, or any increase in the duration of electrode activity.The effect is similar to, but more deleterious than, that of d.c. offset signals. The special benefits of the time-biassed signal must therefore reside in its particular characteristic of equal anodic and cathodic current excursions of unequal duration. EXPLANATION OF THE SYSTEMATIC ERRORS IN D.C. DIFFERENTIAL ELECTROLYTIC POTENTIO- The systematic errors reported, but not recognised as such, at an early stage,5 occur in titrations of iron(I1) with cerium(IV), chromium(V1) and vanadium(V) , and are real errors as shown by the pipette dilution method2J in which the equivalence point region is traversed in very small increments with diluted titrant. The first peak occurs with symmetrical periodic polarisation and coincides with the d.c.output peak from time-biassed periodic polarisation, both of which coincide exactly with the zero-current potentiometric inflection i n cerium(1V) and chromium(V1) titrations, and these are followed after a voluiiie interval of 040.5 to 0.05 ml (depending on the degree of deactivation of the electrod2s) by the d.c. differential electrolytic potentiometric peak. In vanadium(V) titrations, the zero-current potentiometric inflection comes first, and d.c., symmetrical periodic, and time-biassed periodic d.c. peaks appear simultaneously after an interval that increases with the speed of the titration, i.e., with decreasing dwell time after the addition of an increment oi titrant. Each of the three errors has a different explnnation, none of which could be predicted by computer simulation with the program DEP 10.METRY WITH CERTAIN TITRANTS-Novzmber, 19731 POTENTIOMETRY WITH PERIODIC POLARISATION. PART XXIII 775 Ceriztm(IV)-On adding an increment of titrant immediately after the end-point, as indicated by the time-biassed differential electrolytic potentiometric output, the classical d.c. differential electrolytic potentiometric potential, E,, was observed at first to drift down- wards, but then drifted back upwards until EA became greater than it had been before the addition of the tiny increment of cerium(1V). This behaviour continued for several minute increments, equivalent to 0.0005 or 0-005 ml of the original titrant, after equivalence, so making it difficult to locate the end-point precisely.If the latter be taken as the point at which up-and-down drift of EA after addition of an increment changes to a down-and-up drift, then equivalence and end-points agree, but if the cessation of the drifting is awaited, a positive error of about 0.04 to 0.08 per cent. arises. This error is usually recorded because d.c. differential electrolytic potentiometry, like zero-current potentiometry, is essentially a pseudo-equilibrium technique, whereas the error-free, time-biassed periodic d.c. and the symmetrical periodic potential methods are highly dynamic. The d.c. differential electrolytic potentiometric behaviour is ascribed to a change in the nature of the anode surface when exposed to a minute excess of cerium(IV), leading to a decrease in k and a change in cc so that charge-transfer overpotential, q a , builds up.This process continues as the cerium(1V) concentration increases, the increase in q a being greater than the decrease in qc, until the charge-transfer rate parameters stabilise, and EA decreases as qc falls, but leaving a residual after equivalence. Even with freshly activated electrodes, charge-transfer overpotential is always manifest after the end-point in a cerium(1V) titration, as witness the titration curves for any of the methods. The drifting mentioned does not occur with the time-biassed periodic d.c. output peak, unless the titration is held just past equivalence for many hours; with long waiting periods, the time-biassed periodic d.c. outpeak peak can be persuaded to coincide with the classical d.c.differential electrolytic potentiometric peak, Normally, however, the periodic input current is comparatively large, and so the equilibration of the d.c. potential is very rapid, and the periodicity of the polarisation considerably delays the deactivation of the electrode. Chromiztm(1V)-With this titrant, the error arises from specific adsorption of chro- mium(V1) on the anode surface.6 This adsorption has been shown to be concentration- dependent and to occur at low dichromate concentrations. The adsorption therefore increases as the concentration of excess dichromate builds up after equivalence to the point of complete electrode coverage, and this point corresponds to the false, late d.c. differential electrolytic potentiometric end-point, The specific adsorption is encouraged by electrosorption on the anode, and the conditions at the anode surface represent a progressively more oxidising situation than mass transfer from the bulk of the solution would predict.Again, the accelerated potential equilibration of symmetrical periodic and time-biassed periodic polari- sation are antagonistic to the slow adsorption process, and the large r.m.s. current densities and the periodicity of the polarisation minimise the adsorption and its effect. Vanadium( V)-In this instance, classical d.c., symmetrical periodic, and time-biassed periodic d.c. output differential electrolytic potentiometry all give the correct answer; it is the zero-current potentiometric inflection that is wrong. As an electrode kinetic study of the vanadium(V) - vanadium(1V) system has shown,6 the charge-transfer process is very slow; the exchange current is very small, and so relaxation of the zero-current potential after a concentration perturbation by the addition of an increment of titrant is very slow.It has been reported6 that the zero-current potential, even in heavily poised solutions equi- molar in the two oxidation states, takes an excessive time to reach equilibrium. If, as is commonly the practice with titrimetric reactions of reasonable Q values, “equilibrium” is interpreted as a drift of less than 1 mVmin-l, then the pseudo-equilibrium potential will lag behind the true equilibrium potential by a significant amount, especially in the equiva- lence point region where concentrations are low. The zero-current potentiometric curve therefore rises (or falls) prematurely and the inflection is early.That this fact has not previously been recorded is surprising; zero-current potentiometry has been accepted as the reference method in the titrimetric determination of vanadium for many decades. It can only be concluded that sufficiently pure vanadium and iron compounds have never pre- viously been matched to reveal this, admittedly small, systematic error. It has also been shown that vanadium species, predominantly vanadium(V), are adsorbed on electrodes,G and this adsorption aggravates the deviation explained above. That twin polarised electrodes give the correct answer arises from the enhanced rate of potential equilibration under the776 BISHOP AND WEBBER passage of current , and periodic polarisation further minimises adsorption and encourages the retention of electrode activity.CONCLUSIONS No previous examination of the various types of d.c. bias or of the form and accuracy of the titration curve has been reported, nor, with one exception,l has any effort been made to detect or eliminate d.c. bias. Any form of bias or distortion causes a deterioration in the periodic titration curve as well as introducing errors of end-point location, and, with d.c. offsets, marked electrode deactivation. For optimum results, the periodic waveform must be accurately shaped so as to remove all trace of offset, bias and distortion. There is then no d.c. component in the periodic output, but the presence of even traces of such deviations produces a d.c. output as well as. a periodic output. The most important result of this investigation is the discovery of the unique properties of time-biassing of the periodic signal. Such an input produces a d.c. differential titration curve that shows an improvement in precision and discrimination over both classical d.c. differential electrolytic potentiometry and symmetrical periodic differential electrolytic potentiometry. It retains the advantages of periodic differential electrolytic potentiometry in a great improvement in electrode response speed, stability of the electrode potentials and minimisation of electrode fouling and deactivation. The alternating anodisation and cathodisation of each electrode keeps it active, while the large over-all impressed current density accelerates the electrode response. Both of these factors are important, particularly in dilute solutions, in automatic operation and process control. Also, as with symmetrical periodic polarisation, the end-point is brought into agreement with the equivalence point. Errors that arise in d.c. differential electrolytic potentiometry with cerium(1V) and chromium(V1) titrations, and in zero-current potentiometry with vanadium(V) titrations, have been satisfactorily resolved from electrode kinetic studies. REFERENCES 1. 2. 3. 4. 5 . 6 . Doss, K. S. G., and Agarwal, H. P., Proc. Indian Acad. Sci., 1951, 34, 263. Bishop, E., and Webber, T. J. N., Analyst, 1973, 98, 712. -,- , Ibid., 1973, 98, 697. Bishop, E., in Shallis, P. W., Editor, “Proceedings of the SAC Conference, Nottingham, 1965,” W. Heffer & Sons Ltd., Cambridge, 1965, p. 416. Bishop, E., Analyst, 1958, 83, 212. Bishop, E., and Hitchcock, P. H., Ibid., 1973, 98, 563. NOTE-References 2, 3, 4 and 5 are to Parts XXII, XXI, XVII and 11, respectively, of this series. Received March 5th, 1973 Accepted A p d 12th, 1973

ISSN:0003-2654    

DOI:10.1039/AN9739800769

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

Analyst, November, 1973, Vol. 98, jy5. 777-781 777 Monte Carlo Simulation of Matrix Correction Effects BY R. J. HOWARTH (Applied Geochemistry Research Group, Department of Geology, Imperial College of Science and Technology, London, SW7 2BP) Monte Carlo simulation is useful for the precise evaluation of the effects of complex systems of matrix correction equations (such as occur in spectro- graphic analysis). If the error distributions for the interfering elements are experimentally determined, that induced by interaction in the correction equation system for the elements subject to interference can be predicted. IN spectrographic systems the observed concentrations of both major and trace elements may have been affected by errors that are dependent on the concentrations of other elements present in the sample.The magnitude ef these errors, and the form of the functional relation- ship between the affected element and the interfering elements, will vary with the nature of the sample, the system of correction equations being generally referred to as “matrix corrections.” This functional relationship can be represented in the general form where Ci is the corrected concentration of the j t h affected element; Cj the observed concen- tration of the j t h affected element; xi the observed concentration of the ith interfering element (i = 1, . . ., T Z ) ; andfi ( ) the generalised functional relationship for the j t h affected element. The form of fj ( ) is generally determined by observations made on known samples spiked with various concentrations of the interfering elements.Any element that has been corrected may, in its turn, be used in further’correction equations, so building up a complex system for the simultaneous correction of all the elements being determined. However, direct appraisal of the effects of such equation systems cannot be carried out in more than qualitative terms. The detailed matrix corrections will normally be specific to particular laboratories as they will depend on the instrumentation, the calibration techniques used and the nature of the samples being analysed. The general principles of emission-spectrographic and X-ray fluorescence analysis have been outlined by Ahrens and Taylor1 and Norrish and Chappell,2 respectively, and matrix correction equations have been used in both emission-spectrographic and, to a lesser extent, X-ray fluorescence analysis. The papers of Tennant and Sewell3 and Leake et aL4 may be cited as examples of typical laboratory applications.The purpose of this paper, however, is to indicate how Monte Carlo simulation can be used as a tool to assess quantitatively the effects of error propagation through a battery of matrix correction equations, an aspect that has not previously been investigated. It will be illustrated with examples drawn from an emission-spectrographic system, although the technique could be applied to any situation where complex inter-element interference occurs. MONTE CARL0 SIMULATION- A Monte Carlo simulation is based upon the development of a mathematical model (the matrix correction equation system) that accurately represents the real-world situation to be investigated. The concepts of Monte Carlo simulation are discussed in a number of texts.6-7 The sources of random error are represented in the model by pseudo-random number generators, random values being drawn from populations that have the same prob- ability distribution and parameters (in this instance the mean and standard deviation) as those in the real-world system.The model is translated into a computer program and simulation runs are conducted by the computer to represent randomly selected real-world trials. A suitable basis for the simulation is the Muller method8 of generating pairs of random uncorrelated values ( A and B) from a Gaussian parent population of mean m and standard deviation s, these values having been determined by observation of the real-world system it is desired to simulate.Let U and V be independent random variables uniformly distributed @ SAC and the author.778 HOWARTH : MONTE CARL0 SIMULATION OF [Analyst, VOl. 98 in the interval (0, 1); then, the probability distribution for U and I/ is described by Oify ( 0 { Oify > 1 P ( Y < y ) = yifOQ-3 . The majority of computer centres have library programs for generating uniform random variables of this type. Now .. * (2) .. * * (3) A = m + s d-2 InU cos (z~v> B = m + s 4 - 2 InU sin ( 2 n ~ ) .. .. Because the Monte Carlo simulation involves random values, the results obtained are subject to statistical fluctuations; thus, the larger the number of trials carried out, the more precise will be the final answer.SIMULATION OF AN EMISSION-SPECTROGRAPHIC SYSTEM- As an example of the application of this method to a real system, we will briefly consider simulation of the matrix correction equation system for the ARL 29000B direct-reading optical spectrograph that is being used by the Applied Geochemistry Research Group for rapid, low-precision analysis of approximately 50 000 stream sediment samples in order to compile a regional geochemical atlas of England and Wales. With such an instrument we have the following defects : spectral interference between the lines present for two (or more) elements; a background effect, principally caused by continuous radiation, scattering, or fine spectra due to molecular emission ; and thirdly, the arc effect, which is an intensification or diminution of the intensity of a given spectral line caused largely by variation in the temperature of the arc as a result of differing rock matrix composition.l It is necessary to evaluate the effect that variations in the major element determinations have upon the trace-element values, by acting through the system of matrix correction equations.Analytical control is based on a series of eight representative natural standards (stream sediment samples from streams draining known homogeneous rocks) and two synthetic standards spiked with either a low or a high trace-element concentration. From the initial period of operation of the spectrograph it was possible to obtain the mean and standard deviation values for the element concentrations in all of the standards, based on a large number of replicate determinations for the major elements (aluminium, calcium, iron, potassium, magnesium and silicon) and each of twenty-four trace elements.If we assume, on the basis of the observed behaviour of the element, that the error distribution for the major elements is Gaussian and that for the ith element it is distributed with mean m, and standard deviation si, then we can simulate the major element variation for any matrix type by substituting the appropriate values of mi and si into equations of the form of equations (2) and (3). The observed uncorrected mean trace-element values [Cj of equation ( l ) ] should also be recorded. For each standard, 1000 simulated sets of major element values were drawn at random by, using the Muller method, and the corresponding matrix-corrected trace-element values [C, of equation (l)] were evaluated.The change, or perturbation, of the initial values caused by the correction equations was then calculated as a percentage ratio. For the j t h trace element the perturbation is given by These data were output by the computer program in the form of histograms, together with the mean, standard deviation and maximum and minimum perturbation values for each trace element for each of the ten standards. As an additional check on the validity of the method, the total percentage of oxide was calculated for each set of simulated major element values. These results had means acceptably close to 100 per cent.for all standards. SIMULATION RESCLTS OBTAIKED- It is to be expected that any correction equation of the formNovember, 19731 MATRIX CORRECTION EFFECTS 779 14 1 \- (I 0 - 50 0 50 100 pu, per cent. Fig. 1. Histogram of percentage frequency ( j ) of perturb- ation values (pa, per cent.) for strontium in the limestone-derived stream sediment control sample (where the ai are coefficients) will yield a Gaussian distribution for C;.B That the frequency distributions for the perturbation values were Gaussian in all instances where the nature of the correction equations would indicate it, was confirmed by testing against fitted Gaussian distributions by using the Kolmogorov - Smirnov statistic.1° This reproductive property of the normal distribution does not apply to non-linear correction equations.For example, Fig. 1 shows the positively skewed perturbation frequency distri- + 1- 0 1 pu20, per cent. I 3 Fig. 2. Variation of pcr- centage perturbation at two standard deviations (pu 20, per cent. ,) with increasing aver- age nickel content in the control samples. Lithologies of the stream sediment source rocks are shown: shale (9); sand- stone (0) ; limestone (0) ; gran- ite (+) ; basic igneous (A) ; and synthetic standard ( x )780 HOWARTH: MONTE CARL0 SIMULATION OF [A~zaZyjst, Vol. 98 bution for strontium in the limestone standard, resulting from a correction equation of the form Sr* = (Sr + a,Ca)/(l + a,Al + a,Ca + a,Fe + a&%) The general reduction in the size of the relative perturbation with increase in the trace- element content is typified by the behaviour of nickel (Fig.2). This element is corrected solely for calcium and therefore shows a Gaussian distribution for the perturbation values. The graph shows the relative perturbation at two standard deviations and indicates that we can expect that only 5 per cent. of the nickel determinations would be perturbed by more than the values shown. While it has to be remembered that each analytical system will yield a unique matrix correction system (and hence perturbation effects), it is of interest to note how the behaviour predicted by simulation compared in this instance with the results obtained in practice. Table I shows that, for the majority of elements, the mean perturbation value for the synthetic standard spiked with low element concentrations is close to zero (per cent.).How- ever, there are considerable variations in the magnitudes of the perturbation standard deviation. The spread of values obtained in a typical set of replicate analyses (made on one day, very much later in the project than the data used for the simulation) is indicated by the precision, defined here as twice the element standard deviation divided by the mean, in terms of concentration. It is clear from Table I that for most elements the effect of the matrix corrections has been to increase the precision value to some extent, and that when this increase has been in excess of a factor of 1.3 compared with the uncorrected value (for silver, arsenic, beryllium, cobalt, lithium, molybdenum, phosphorus, tungsten and zirconium) it correlates very well with high-perturbation standard deviations obtained by the earlier simulation of the system.Some difficulty would therefore be expected in obtaining reliable low-level analyses for these elements. It was found necessary in practice to use alternative methods of analysis for arsenic, molybdenum, cadmium and zinc ; silver, phos- phorus, tungsten and zirconium have not been used in the preparation of geochemical maps. The simulation results have therefore been well borne out in day-to-day experience of the rapid, low-precision analytical system necessary to cope with the very large number of multi-element analyses necessary for a geochemical reconnaissance of this type. TABLE I COMPARISON OF SIMULATED AND ACTUAL PERTURBATION EFFECTS FOR Element (i) 2: * ' ..Ba .. Be .. Bi .. Cd .. G 3 .. Cr .. c u .. Ga .. Li .. Mn .. Mo . . Ni . . P .. sc .. Sn . . Sr .. Ti .. V .. W .. Zn .. Zr .. A SYNTHETIC STANDARD - * - c: PUi .. .. i 3 .. .. 719 0 .. .. 146 0 .. .. 26 -1 .. .. 34 0 .. .. 26 -1 .. .. 16 0 .. .. 190 0 .. .. 76 0 .. .. 18 0 .. .. 47 0 .. .. 60 0 .. .. 6 -2 .. .. 166 0 .. .. 496 2 .. .. 21 0 .. .. 262 0 .. .. 197 1 .. .. 312 0 .. .. 240 1 .. .. 164 -1 .. .. 27 2 .. . . 200 2 uDu$ 92 86 6 17 1 28 62 3 1 0 20 4 49 1 69 12 1 13 2 6 19 46 84 +cl4nc§ 3.32 1-81 1.06 1.44 1.00 1.03 2.23 1.10 1.00 1.00 1431 1.03 1.69 1.03 1-64 1.00 1.07 1.02 1-06 1.2 1 1.69 1.16 2.50 * Mean concentration (p.p.m.) of matrix corrected results (11 samples). t Mean simulated perturbation (per cent.) for matrix correction (1000 trials).; Standard deviation of perturbation values (per cent.) for matrix correction (1000 trials). 9 Ratio of precision [$ = 2 (standard deviationlmean percentage)] for corrected ($c) and uncorrected ($uc) results (11 samples).November, 19731 MATRIX CORRECTION EFFECTS 781 CONCLUSION Visual evaluation of the effects of multi-component correction e-quations cannot be carried out in more than qualitative terms. However, Monte Carlo simulation allows the over-all magnitude of the matrix corrections to be evaluated precisely, and affords a method of comparison between the various corrected elements that helps to assess the relative magnitude of the perturbation effects. The method is easily applied to the most complex of matrix correction equation systems.It is economical in computer time and methods are available for determining the optimum number of trials for the evaluation of a given model.ll It is not intended that the specific results reported here should be applied to other emission-spectrographic systems, but rather encourage the investigation of other analytical system interactions by using simulation techniques when it is of interest to separate the effects of errors in the determination of the uncorrected element values from changes induced through the application of multi-component correction equations. The project of which this paper forms a part has been supported by a Natural Environ- ment Research Council grant for an investigation, under the direction of Professor J. s.Webb, into the applicability of computer methods to the analysis of regional geochemical data. The regional geochemical atlas of England and Wales has been made possible by a major grant from the Wolfson Foundation. The experimental determinations on the ARL 29000B system were obtained by Dr. M. Thompson. Computer time was provided by the Imperial College Computer Service. 1. 2. 3. 4. 5. 6 . 7. 8. 9. 10. 11. REFERENCES Ahrens, L. H., and Taylor, S. R., “Spectrochemical Analysis,” Addison-Wesley Co. Inc., London, 1961. Norrish, K., and Chappell, B. W., “X-ray Fluorescence Spectrography,” in Zussman, J., Editor, “Physical Methods in Determinative Mineralogy,” Academic Press, London, 1967, pp. 161 to 214. Tennant, W. C., and Sewell, J. R., Geochim. Cosmochim. Acta, 1969, 33, 640. Leake, B. E., Hendry, G. L., Kemp, A., Plant, A. G., Harvey, P. K., Wilson, J , R., Coats, J. S., Aucott, J. W., Lunel, T., and Howarth, R. J., Chem. Geol., 1969-70, 5, 7. Wagner, H. M., “Principles of Operations Research,” Prentice Hall, Englewood Cliffs, New Jersey, 1969. Hammersley, J. M., and Handscomb, D. C., “Monte Carlo Methods,” Methuen and Co. Ltd., London, 1964. Naylor, T. H., Balintfy, J. L., Burdick, D. S., and Chu, K., “Computer Simulation Techniques,” John Wiley and Sons, New York, 1966. Dillard, G. M., I.E.E.E. Trans. Inf. Theory, 1967, IT-13, 616. Topping, J., “Errors of Observation and their Treatment,” Institute of Physics Monograph, Siegel, S., “Nonparametric Statistics for the Behavioural Sciences,” McGraw-Hill, New York, 1956. Hahn, G. J., I.E.E.E. Trans. Systems Man Cybernetics, 1972, SMC-2, 678. Received February 19th, 1973 Accepted July 2nd, 1973 Chapman and Hall, London, 1957.

ISSN:0003-2654    

DOI:10.1039/AN9739800777

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

782 Analyst, November, 1973, Vol. 98, pp. 782-791 Spectrophotometric Determination of Low Levels of Mono-, Di- and Triethylene Glycols in Surface Waters BY W. H. EVANS AND A. DENNIS (Department of Trade and Industry, Laboratory of the Government Chemist, Cornwall House, Stamford Street, London, SE1 9NQ) A method is proposed for the determination of mono-, di- and triethylene glycols in surface waters, based on the oxidation of the glycols to aldehydes. These are made to react with 3-methylbenzothiazol-%one hydrazone hydro- chloride to give green cationic chromogens, which are then measured spectro- photometrically a t 630 nm. Sample blank values, to compensate for natural interferences, are obtained by omitting the oxidation stage. The method enables glycol levels of upwards of 0.5 mg 1-1 to be determined, satisfactory recoveries of each glycol being obtained for concentrations of 1 to 6 mg l-l, with a precision of 7 per cent., for a range of water samples.A sensitive variation of the method, for the determination of monoethylene glycol alone, is described separately. MONO-, di- and triethylene glycols, frequently mixed with volatile aliphatic alcohols, have been used as de-icing agents for aircraft and airfield runways. Airfield drainage may subse- quently contaminate surface waters with low levels of these glycols. It has been recommended that mono- and diethylene glycol concentrations should not exceed 1 mg 1-1 in water reser- voirs,l but no methods for measurement at these levels appear in the literature. Because of the polarity of the glycols it is not possible to concentrate them quantitatively by solvent extraction, therefore their determination must be accomplished in the aqueous phase.This factor, associated with low sensitivity, excludes many instrumental techniques and also thin-layer and gas - liquid chromatography. For similar reasons, spectrophotometric methods involving the specific reaction of glycols with l-naphthol in sulphuric acid,2 or methods involving general reactions for aliphatic hydroxyl groups, such as dichromate ~ x i d a t i o n , ~ ~ ~ the formation of vanadium(V) hydroxyquinolinates5 or reaction with ammonium cerium( IV) Accordingly, the conversion of the glycols into other compounds has to be considered. This conversion could be achieved by oxidation of the primary alcohol groups to aldehyde or carboxyl groups, but methods for the determination of these functional groups are, in general, equally insensitive.The determination of aldehydes has been reviewed by Alt- shuller, Cohen, Meyer and Wartburg.8 The formation of Schiff’s bases9 or 2,4-dinitrophenyl- hydrazoneslO is not specific to aldehydes and methods based on their formation have low sensitivity, while the reaction with phenylhydrazine and potassium hexacyanoferrate(1II)ll requires the presence of a minimal amount of water. Cleavage of the vicinal glycol group to fonnaldehyde,12 followed by reaction with 1,8-dihydroxynaphthalene-3,6-disulphonic acid (chromotropic acid),13 would enable only one of the glycols to be determined down to the level of 1 mg 1-l.Three reagents that give cationic chromogens with aldehydes are 2-hydrazino- benzothiazole,14 2-hydrazinobenzothiazole with 9-nitrobenzenediazonium tetraflu~roboratel~ and 3-methylbenzothiazol-2-one hydrazone hydrochloride (MBTH) ,16 The first two of these reagents require alkaline conditions and the third requires acidic conditions. The reagents have shown superior sensitivity to aldehydes when compared with chromotropic acid and related compounds.17 2-Hydrazinobenzothiazole and MBTH react only with aliphatic aldehydes, and the latter is more sensitive to a wider range of these compounds. More recently, the sensitivity of MBTH has been greatly improved,l* and the reaction has been applied to the determination of olefins after oxidation,19 to compounds containing 2-aminoethanol and ethylenediamine fragments20 and to sugars containing aldehyde groups or polyhydroxyalde- hyde precursors.21 The sensitivity of MBTH to a wide range of aliphatic aldehydes suggested that, provided suitable conditions for the oxidation of the glycols to aldehydes can be achieved, this reagent @ SAC; Crown Copyright Reserved. are unsuitable.EVANS AND DENNIS 783 might be the basis for a sensitive method for the determination of glycols in surface waters. A method is proposed; based on the investigations described, whereby the three glycols can be monitored in surface waters at concentrations of upwards of 0.5 mg 1-l. METHOD REAGENTS- with de-ionised water. These should be of analytical-reagent grade when available; solutions can be prepared Sulphuric acid, 4 N.Potassium Permangunate solution, 0.0126 M-Dissolve 0.2 g of potassium permanganate in water and dilute the solution to 100 ml. Sodium arsenite solution, 0.07 M-Dissolve 9.1 g of sodium arsenite in 100 ml of water. For use, dilute 10 ml of this solution to 100 ml. 3-Methylbenxothiaxol-2-one hydraxone hydrochloride (MBTH), 2.0 per cent. m/V solution- Dissolve 2 g of reagent in 100 ml of water. Iron(Il1) chloride - sulphamic acid solution-Dissolve 2 g of iron( 111) chloride hexahydrate and 3 g of sulphamic acid in water and dilute the mixture to 100 ml. Standard glycol solutions-Mix 10 g of each glycol with water in separate 1-litre calibrated flasks, and dilute 50 ml of each solution to 1 litre to give solutions containing 500 mg 1-1 of glycol.Immediately prior to use, dilute 5 ml of each of these standards to 500 ml to give standard solutions containing 5 mg 1-1 of glycol. PROCEDURE- Measure 5ml of sample (after allowing it to settle or filtering it through pre-washed cotton-wool), or a suitable aliquot diluted to 5m1, into a 10-ml calibrated flask, and also prepare a reagent blank with 5 ml of de-ionised water. To each flask add 0.5 ml of sulphuric acid followed by 1 ml of potassium permanganate solution, mix well, and immerse the flasks in a boiling water bath for exactly 5 minutes, Withdraw them from the water-bath and remove any unreacted permanganate with 1 ml of sodium arsenite solution. Add 1 ml of MBTH reagent solution and immerse the flasks in the water-bath for a further 6 minutes. Remove them, cool to room temperature, transfer 1 ml of iron(II1) chloride - sulphamic acid reagent by pipette into each flask and dilute to 10 ml in each instance.Allow to stand for 20 minutes and read the optical density of each solution at 630 nm in a clean 2-cm cell with water in the reference cell. The net optical density of the sample is obtained by subtracting the reagent blank value. To compensate for natural interferences in surface waters, a sample blank value should be obtained with the permanganate oxidation stage omitted. Measure 5 ml of filtered or settled sample, or a suitable aliquot diluted to 5 ml, into a 10-ml calibrated flask; also prepare a reagent blank with 5 ml of de-ionised water. Add in order 0.5 ml of sulphuric acid, 1 ml of sodium arsenite solution and 1 ml of MBTH reagent solution, mixing after each addition, and immerse the mixture for 6 minutes in a boiling water bath. Ascertain the optical density of the sample blank, less that due to the reagent blank, by the procedure described previously after the addition of 1 ml of iron(II1) chloride - sulphamic acid reagent.The optical density due to glycols, obtained by subtracting this natural blank value from the net sample optical density, can be expressed as the concentration of the glycol, if known, or in terms of a specific glycol from the calibration graphs. CALIBRATION- To a series of 10-ml calibrated flasks add, with a pipette, 0, 1, 2, 3, 4 and 5 ml of the standard solution containing 5mg1-1 of glycol, and dilute to 5ml with de-ionised water when necessary.Ascertain the optical densities, less that due to the reagent blank, by the procedure described. The resulting calibration graphs of optical density against concentration of glycol are linear in the range from 0 to 5 mg 1-1 for each glycol. DISCUSSION The oxidants used most frequently in organic chemistry include permanganate, chromic acid or systems involving metal ions such as cerium(IV), manganese(III), cobalt(II1) or vana-784 EVANS AND DENNIS : SPECTROPHOTOMETRIC DETERMINATION OF [Analyst, VOl. 98 dium(1V). The magnitudes of the electrode potentials of various oxidising media indicate that cerium(1V) in perchloric acid (E", 1.71 V) or nitric acid (E", 1.61 V) and acidified per- manganate (E", 1-52 V) are more effective for oxidation than acidified dichromate (E", 1.33 V) and other systems.These figures may not reflect, however, the effectiveness of their oxidation properties when applied to organic substrates. Chromium(V1) has been extensively used to oxidise primary alcohols but invariably further oxidation to carboxylic acids, or side-reactions yielding esters via the hemiacetals, occur. Non-substituted 1,2-diols, such as monoethylene glycol, are normally oxidised to the dialdehyde or dicarboxylic acid without cleavage.Z2 Cerium(IV), in an acidic medium, oxidises alcohols via complex intermediates that may not easily be oxidised further, while lJ2-diols may be cleaved22 and would yield formaldehyde from monoethylene glycol with a resulting disproportionately high molar extinctionlS compared with the extinctions obtained with di- and triethylene glycols.I t has been suggested that alkaline conditions are more effective than neutral or acidic conditions for the permanganate oxidation of primary alcohols, while 1,2-diols are not noticeably cleaved to aldehydes with permanganate.22 An oxidising system, involving the use of acidic or neutral conditions, was required that would convert the hydroxyl groups of mono-, di- and triethylene glycol into alde- hyde groups, while, at the same time, minimising further oxidation to the corresponding carboxylic acid compounds. Of several oxidising systems initially investigated, dichromate in dilute acetic or sulphuric acid and neutral permanganate produced no measurable aldehyde at temperatures up to 100 "C; permanganate in dilute sulphuric acid gave a good response for aldehydes for oxidation at 100 "C.One of the factors normally determined in water examination is the 4-hour permanganate value, measured in acidic conditions. For river waters this value has been related empirically to the permanganate consumed on heating the sample for 30 minutes at 100 "C, the consumption being doubled for the latter condi- t i o n ~ . ~ ~ The retention of acidified permanganate as oxidant would therefore be an advantage for this method, an allowance for the normal permanganate consumption of river waters being incorporated in the amount of permanganate used. The total determination involved a number of stages that required careful investigation in order to obtain a reproducible response.For the oxidation stages, the concentration of permanganate, time of reaction required for oxidation, acidity and concentration of reductant for removal of excess of permanganate required particular attention. For the spectrophoto- metric stages the factors that required investigation were the concentration of MBTH reagent, the time of reaction to form the intermediate azine, the acidity and, finally, the conditions for oxidation, with iron(II1) chloride, of the reagent MBTH to a reactive cation and subsequent formation of the final blue or green cationic chromogen. SPECTROPHOTOMETRIC DETERMINATION WITH 3-METHYLBENZOTHIAZOL-2-ONE HYDRAZONE HYDROCHLORIDE (MBTH) An interfering opalescence in the colour development of the MBTH procedure was originally controlled by dilution with acetone, the resulting method losing sensitivity.16 Subsequently, Hauser and Cumminsl* substituted sulphamic acid for acetone for controlling this opalescence and achieved a six-fold increase in sensitivity for formaldehyde, the final reaction volume being reduced to 12 ml.Preliminary work indicated that, as the reagent concentration decreased with increasing volume of solution, so the relative response to the aldehyde precursors decreased; this effect was only partially overcome by increasing the concentration of MBTH. To obtain the necessary sensitivity the final solution volume was therefore limited to 10 ml. Because the addition of several reagents involved up to 5 ml of solution, sample volumes used in this determination could not exceed 5 ml.Each glycol oxidation product on reaction with MBTH produced a green chromogen that gave an absorbance maximum in the wavelength region of 630nm. The effects of variations in the reaction conditions are exemplified by the net optical densities in Table I. Values in italic type are the averages (per mgl-l) of eight series of readings obtained for 1, 2, 3,4, 5 and 6 mg 1-1 of each glycol by a single operator who used the procedure described under Method. The average coefficient of variation from the average response at each level for each glycol for this series of readings was 3 per cent. In no instance did the averages of other operators differ from the average values by more than 3t3 per cent. The sensitivityNovember, 19731 LOW LEVELS OF GLYCOLS I N SURFACE WATERS 785 of each aldehyde precursor to MBTH concentration reached a maximum with 1 ml of 1.5 per cent.of reagent, theoretically a many-fold excess, and declined as the concentration increased further. One millilitre of 2 per cent. MBTH was chosen as being the optimum concentration of reagent, thereby avoiding excessively high optical densities with the higher concentrations of monoethylene glycol, which might prove difficult to read accurately on some spectro- photometers. The extent of the reaction a t 100 "C did not alter over the time span 2 to 10 minutes, although response to the product of oxidation of diethylene glycol declined slightly for a reaction time of 10 minutes; a reaction time with MBTH of 6 minutes was therefore selected. Oxidation of the MBTH reagent to a reactive cation and subsequent formation of the green cationic chromogen was achieved with iron( 111) chloride, the opalescence being con- trolled by sulphamic acid.The response to each aldehyde precursor increased as the volume of 2 per cent. iron(II1) chloride - 3 per cent. sulphamic acid reagent increased. A volume in excess of 1 ml of this reagent produced increases in the reagent blank that were dispro- portionate to the increase in response obtained for both di- and triethylene glycols, and hence 1 ml of the composite reagent was used in this method. It was necessary to cool the reaction mixture to room temperature prior to this addition. The final colour formed reached a maximum response after 15 minutes and remained stable for a further 15 minutes.Measure- ment 20 minutes after addition of the reagent was therefore recommended. CONDITIONS FOR OXIDATION OF GLYCOLS TO ALDEHYDES- The effects of varying the reagent conditions for oxidation are summarised in Table I1 by the net optical densities shown; values in italic type are averages, as in Table I. A constant response was obtained for mono- and triethylene glycols, at the levels indicated, with 1 to 2 mg TABLE I EFFECT OF VARYING REAGENT CONDITIONS ON SPECTROPHOTOMETRIC DETERMINATION WITH MBTH Optical density ( x 1000)* Monoeihylene glycol/mg 1-1 Diethylene glycol/mg 1-1 Triethylene glyc&/mg 1-1 a' 1 1 Variable 2 4 2 4 2 MBTH concentration, t per cent. 0.6 1-0 1.6 2.0 3-0 Time of reaction: / minutes 2 4 6 8 10 Volume of reagent added§/ml 0.5 0.76 1.0 1-25 1-50 220 436 60 138 91 292 580 90 190 115 308 620 104 212 127 260 520 106 212 118 186 374 93 173 98 26 1 528 102 200 121 257 537 97 212 118 260 520 106 212 118 262 624 92 208 117 256 628 96 196 118 142 277 51 115 76 206 442 72 166 98 260 520 106 212 118 274 600 116 234 130 325 670 112 242 136 * Values in italic type are averages.t Concentration in 1 ml of reagent. $ Reaction a t 100 O C with 1 ml of 2.0 per cent. MBTH. 8 2 per cent. iron(II1) chloride - 3 per cent. sulphamic acid reagent. 198 242 259 236 193 246 247 236 234 240 138 200 236 268 274786 [A nalysf, Vol. 98 of permanganate, while a constant level was obtained for diethylene glycol for the range 1.5 to 2 mg of permanganate. The maximum permissible sample volume employed in this procedure is 5 ml and it can be calculated that a water sample with a- 4-hour permanganate value of 10, representing a badly contaminated river water, would consume 200pg of per- manganate.If the empirical relationship of a doubled consumption when heated at 100 "C for 30 minutes is accepted,23 400 pg would be the maximum amount of permanganate used for a 5-ml volume of such a river water. The use of 2 mg of permanganate therefore leaves sufficient reagent to ensure reproducible oxidation of the glycols to their corresponding aldehydes. An increase in the time of oxidation at 100 "C indicated a decrease in response to each aldehyde precursor. This effect can be attributed to the progressive loss of the aldehydes formed as a consequence of their volatility at elevated temperatures.The change in response to di- and triethylene glycols was small between 3 and 7 minutes' reaction time and hence an optimum time of 5 minutes was chosen for oxidation a t 100 "C. A single addition of sulphuric acid and permanganate gave inconsistent results in pre- liminary trials. This inconsistency was partly caused by the instability of permanganate EVANS AND DENNIS : SPECTROPHOTOMETRIC DETERMINATION OF TABLE I1 EFFECT OF VARYING CONDITIONS FOR OXIDATION OF GLYCOLS TO ALDEHYDES Optical density ( x 1000)* A r Monoethylene glycol/mg 1-1 Diethylene glycol/mg 1-1 Triethylene glycol/mg 1-1 Variable Amount of permanganatelmg 0.50 1.00 1.60 2.00 Time of oxidation?/ minutes 1 3 5 7 10 Sulphuric acid concen- t r a t i o n $ / ~ 2 3 4 5 6 Sulphuric acid concentration (effect on MBTH reaction)$/N 4 6 Volume of 0.50 0.75 1-0 1.25 1-50 0.07 M arseniteqlml I - 2 ------? 2 2 4 232 472 73 166 102 217 257 511 96 188 120 233 254 509 103 202 117 236 260 520 106 212 118 236 303 605 95 184 132 259 280 566 109 218 129 254 260 520 106 212 118 236 248 486 108 214 114 246 219 44 1 100 204 111 220 298 596 110 220 124 260 27 1 528 102 206 120 242 260 520 10G 212 118 236 222 466 87 180 100 218 220 458 87 186 104 210 269 547 105 203 120 237 220 463 94 174 111 216 261 534 107 23 1 120 247 263 538 108 216 124 248 260 520 106 212 118 236 250 520 106 218 119 239 261 530 99 203 114 235 * Values in italic type are averages.t Oxidation a t 100 "C with 2 mg of permanganate. $ Volume = 0.5 ml. 9 Volume = 0.5 ml; reaction after oxidation with 0.5 ml of 2 N acid.Effect of use of various volumes of 0.07 M arsenite to reduce the excess of permanganate.November, 19731 LOW LEVELS OF GLYCOLS I N SURFACE WATERS 787 in an acidic medium, with decomposition to manganese(IV), and sulphuric acid was therefore added before the permanganate. As the sulphuric acid concentration increased so the response of each aldehyde precursor decreased. Subsequent variation of this acid. concentration in the reaction stage with MBTH reagent, while maintaining the acid concentration at a constant level during oxidation, indicated that acidity is a factor relevant only to the final reaction stages. The change in response was small for the addition of 0.5 ml of 3 or 4 N sulphuric acid and the latter concentration was selected.The removal of excess of permanganate with arsenite was possible over a relatively wide range of sodium arsenite concentrations and 1 ml of 0.07 M arsenite was finally used in the procedure. This feature was singular, and the need for careful control of reagent additions, and, in particular, the time allowed for oxidation with permanganate must be emphasised in view of previous comments. Different batches of MBTH reagent showed no significant difference in response to each aldehyde precursor, and similarly no difference in sensitivity was apparent when reagents were prepared or dilutions made with demineralised or distilled water. Ageing of reagent solutions (over a period of 7 days) produced no change in response but the reagent blank increased with the age of the reagent; for freshly prepared reagent solutions, the reagent blank should have an optical density not exceeding 0.080.Calibration graphs of optical density against concentration of glycol were linear for the range 0 to 6 mg 1-1 for each glycol, enabling measurements to be made in the range 0 to 5 mgl-l. Typical optical density responses for each glycol, measured by the procedure described, were : monoethylene glycol, 0-130; diethylene glycol, 0.053; and triethylene glycol, 0.059 per mg 1-I. PRODUCTS OF OXIDATION- The molar extinctions of the final chromogenic solutions, obtained by the procedure outlined, were 8060, 5620 and 8850 for mono-, di- and triethylene glycols, respectively. From results obtained for formaldehyde,ls a molar extinction of 1 x lo5 would be expected if complete cleavage of monoethylene glycol to formaldehyde had occurred.Normal oxidation of the glycols would be expected to yield dialdehydes, e.g., glyoxal (biformyl) would be the expected product from monoethylene glycol. Other possible products would be glyoxylic acid (oxoacetic acid), glycollic aldehyde (hydroxyacetaldeh yde) and glycollic acid (hydroxy- acetic acid) or oxalic acid; for the latter two, no aldehyde response would be obtained. A molar extinction of 28000 has been recorded for glyoxal.16 We have found that the reaction of MBTH reagent with glyoxal solutions, prepared from both the polymerised monohydrate and from a 40 per cent. rn/m solution, gave a response, at concentrations of less than 1 mg l-l, corresponding to that obtained by this procedure for monoethylene glycol.Reaction of MBTH with glyoxylic acid monohydrate, however, gave a molar extinction of 59 000, while glycollic aldehyde gave a molar extinction of 36 500. It is emphasised that organic reactions that involve oxidation will invariably give several reaction products, but this evidence suggests that the dialdehyde is the major product of oxidation from mono- ethylene glycol for the conditions defined in this method. It is not certain whether both aldehyde groups react with 2 mol of MBTH initially to give a diazine. A maximum response is, however, obtained with 1 ml of 1.5 per cent. reagent (Table I), representing a very large excess of reagent, whereas previous applications of MBTH to a wide range of aldehydes and aldehyde precursors have involved the use of 1 ml of 0.8 per cent.reagent1g$21; it is not clear whether the latter was the over-all optimum concentration. The molar extinction obtained for diethylene glycol is lower than that obtained for the other two glycols. This effect could arise because of the formation of a monoazine with MBTH reagent, or the presence, after permanganate oxidation, of one aldehyde group only. The relatively slow increase to a maximum response with increasing amounts of permanganate (Table 11) suggests that labile oxidation of one hydroxyl group via the aldehyde to a carboxylic acid group is unlikely. Experimental evidence is inadequate to decide which of the pair of alternatives is the cause of this low molar extinction; it is sufficient that a constant level of response is attainable. SURFACE-WATER SAMPLE BLANKS- Typical water sample blanks, expressed in terms of optical densities, including and excluding the permanganate oxidation stage, are illustrated in Table 111.The good agreement788 EVANS AND DENNIS SPECTROPHOTOMETRIC DETERMINATION OF [AfiPzalyd, VOl. 98 obtained indicates the general absence of a natural level of aldehydes, which would be further oxidised by permanganate, and equally, natural levels of aldehyde precursors (Le., hydroxyl compounds containing primary alcoholic groups). Exceptions to this agreement were noted for domestic effluents. While this agreement holds within our experience, there is a possi- bility that a surface water could prove anomalous because of polluting species.In such an instance, a sample of the surface water immediately before contamination would be required in order to ascertain the surf ace-water sample blank with permanganate oxidation. During the monitoring, over a period of 6 months, of river G with a high constant water flow, this sample blank was consistent (Table 111), but for other river systems subject to large fluctuations in river flow it might vary with the extent of floodwater, e.g., rivers C and D (Table 111). In our experience, volatile alcohols associated with de-icing glycols are seldom encountered in airfield run-offs at water temperatures of greater than 0 "C, because of their volatility, and would not be expected in receiving waters. TABLE I11 COMPARISON OF WATER SAMPLE BLANK VALUES WITH AND WITHOUT THE PERMANGANATE OXIDATION STAGE Optical density ( x 1000) Sample Spring water .. .. .. Well water .. .. .. Treated swimming-pool water . . River water: A . . .. .. B .. .. .. C, October, 1972 . . C, November, 1972 D, April, 1972 . . D, October, 1972 . . Estuary water E . . .. .. River water: F . . .. .. G, June, 1972 . . G, August, 1972 . . G, November, 1972 G, December, 1972 Airfield ditch H . . .. .. Domestic sewage effluent . . Partially treated domestic sewage Airfield ditch J . . .. .. .. .. .. .. .. .. * . .. .. .. .. .. .. .. .. .. * . . . .. Wiih oxidation 0 21 35 7 36 32 75 40 112 77 107 90 96 96 40 140 127 107 a4 Without oxidlation 0 29 37 0 29 37 66 46 104 69 105 80 89 - 34 132 76 55 A SENSITIVE VARIATION FOR DETERMINATION OF MONOETHYLENE GLYCOL INVOLVING CLEAVAGE TO FORMALDEHYDE Cleavage with periodic acid of vicinal diols followed by reaction with chromotropic acid of the aldehydes formed,13 and similarly, cleavage of molecules containing the 2-aminoethanol and ethylenediamine fragments to aldehydes and subsequent measurement with MBTH reagent, have been described.20 A similar oxidation of monoethylene glycol would yield formaldehyde, which would give a coloured cation with a high molar extinction with MBTH reagent.Calculation from values of optical densities obtained previously for forma1dehydel8 indicates that an optical density of 0.660 per mg 1-1, measured at 630 nm in P-cm cells, would be expected from the splitting of monoethylene glycol and subsequent measurement in a final 25-ml volume of solution.In practice, water sample blank values with and without periodate oxidative cleavage disagreed (Table IV) . This disagreement could be explained by the extreme sensitivity of the reaction conditions to polyhydroxyaldehyde precursors, involving both primary and secondary alcoholic groups, which cleaved to form formaldehyde or aldehydes of low relative molecular mass of similar sensitivity. This effect must be com- pared with the absence of aldehyde precursors for acidified permanganate as the oxidation medium, when only primary alcoholic groups are involved. Allowing for this inherent weakness, which implies that monitoring a surface water would require sample blank values before contamination, the extreme sensitivity of this variation commends it for attention.A brief discussion and an outlined procedure is therefore included below for information.November, 19731 LOW LEVELS OF GLYCOLS IN SURFACE WATERS TABLE IV WATER SAMPLE BLANK VALUES WITH AND WITHOUT PERIODATE OXIDATION Optical density ( x 1000) r A I River water . . . . .. c D F G With periodate. . .. .. 19 153 254 96 Without periodate . . .. 0 35 40 27 789 DISCUSSION- The results for different oxidative reagent conditions are shown in Table V. Complete reaction at room temperature was uncertain and results indicated that no disadvantage accrued from heating, consistent response being achieved for 1 to 8 minutes' reaction time at 100 "C; a time of 2 minutes was chosen for this reaction stage. There were no restrictions on oxidation for initial volumes of 0 to 11 ml of solution, thus enabling the monoethylene glycol content of 10-ml samples of surface waters to be determined.Variation of the sulphuric acid concentration for the MBTH reagent stages showed that as acidity increased, sensitivity decreased. It was found that the acid used, 1 ml of 2 N sulphuric acid, was not essential for the initial oxidative cleavage, but it was convenient to use acidified periodate as it increased the solubility of potassium periodate in a cold aqueous solution and reduced the number of solutions that had to be added. Variation in the MBTH reagent concentration indicated that reaction with 1 ml of 2 per cent. MBTH reagent at 100 "C was required; constant response was obtainable fora reaction time of 4 to 8 minutes and 6 minutes was accepted as the optimum time.The response to the addition of the 2 per cent. iron(II1) chloride - 3 per cent. sulphamic acid reagent was a maximum for the addition of 1.0 to 1-25 ml of reagent, stable readings being obtained 15 to 20 minutes after addition. For smaller volumes of the composite reagent, a lower response was obtained, while for larger volumes, fading of the final blue cationic TABLE V EFFECT OF VARYING REAGENT CONDITIONS FOR PERIODATE OXIDATION OF MONOETHYLENE GLYCOL Optical density ( x 1000) A r \ Monoethylene glycol concentration/mg 1-1 . . 0.2 0.6 1.0 Reaction conditions with 1 ml of 0.04 M periodate r 1 Temperature Timelminutes Ambient 5 90 276 10 114 334 15 133 387 20 141 386 30 133 385 100 O C 1 144 414 2 140 412 4 144 417 8 139 417 2 129 404 3 134 394 4 123 370 Sulphuric acid concentration*/N MBTH concentration, per cent.Timelminutes 0.5 4 41 160 1.0 4 89 307 2.0 2 111 31 1 2.0 4 139 404 2-0 8 140 414 * Volume of acid = 1 ml. t Volume of reagent = 1 ml. 500 5 64 669 66 1 662 669 667 674 675 674 672 615 280 485 54 1 671 67 1790 EVANS AND DENNIS : SPECTROPHOTOMETRIC DETERMINATION OF [Analyst, Vol. 98 chromogen occurred within this time span. A volume of 1 ml of composite reagent was therefore selected and the final colour was read 20 minutes after its addition. By using the procedure described, a molar extinction of 1.05 x lo5 is obtained for mono- ethylene glycol, which compares favourably with the value of 7.3 x lo4 obtained previously in a general method for polyhydroxyaldehyde precursors.21 REAGENTS- with de-ionised water.These should be of analytical-reagent grade when available; solutions can be prepared Sulphuric acid, 2 N. Potassium Periodate solution, 0-04 M-Dissolve 0.92 g of potassium periodate in 100 ml of 2 N sulphuric acid. Sodium arsenite solution, 1 M-Dissolve 13 g of the reagent in 100 ml of water. 3-Methylbenzothiazol-%one hydrazone hydrochloride (MBTH), 2 per cent. m/V solution- Dissolve 2 g of the reagent in 100 ml of water. Iron(1II) chloride - sulphamic acid solution-Dissolve 2 g of iron(II1) chloride hexa- hydrate and 3 g of sulphamic acid in water and dilute the mixture to 100 ml. Standard monoethylene glycol solution-Mix 10 g of the glycol with 1 litre of water to give a solution containing 1000Omgl-l. Immediately prior to use, dilute 50ml of this standard solution to 1 litre to give a solution containing 500 mg 1-l; 2 ml of this solution diluted to 500 ml gives a working solution of 2 mg 1-l.PROCEDURE- Measure 10 ml of settled sample (or sample after filtration through pre-washed cotton- wool), of a suitable aliquot diluted to 10 ml, into a 25-ml calibrated flask, and also prepare a reagent blank with 10 ml of de-ionised water. Add 1 ml of periodate reagent to each flask, mix the contents well and immerse in a boiling water bath for 2 minutes. Withdraw the flasks from the water-bath and remove excess of periodate by reaction with 1 ml of sodium arsenite, then add 1 ml of MBTH reagent solution and immerse them in the water-bath for a further 6 minutes. Remove and cool to room temperature, add by pipette 1 ml of iron(II1) chloride - sulphamic acid reagent to each flask and dilute the contents to 25 ml.Stand for 20 minutes and read the optical density at 630 nm in a clean 1-cm cell with water in the reference cell. The net optical density for the sample is obtained by subtracting the reagent blank. To compensate for interference from the natural levels of oxidisable material in surface waters, a sample blank value before contamination must be obtained. The optical density due to monoethylene glycol, obtained by subtracting this natural blank value from the net sample optical density, can be expressed as concentration of glycol by reference to a cali- bration graph prepared by diluting 0, 1, 2, 3, 4 and 5 ml of standard solution containing 2mg1-1 of glycol to 10ml with de-ionised water in 25-ml calibrated flasks.A graph of the optical densities, less reagent blank, plotted against the concentration of glycol is linear for the range 0 to 1 mg l-l, with an optical density of 0.680 per mg 1-1 for monoethylene glycol. RESULTS OF RECOVERY EXPERIMENTS FOR MONO-, DI- AND TRIETHYLENE GLYCOLS Results of recovery experiments, involving the concentration of surf ace-water samples, on a water-bath, suggest that attempts to improve sensitivity by this means cannot be recom- mended. While satisfactory recovery and precision were obtained for uncontaminated water samples, river-water samples gave excessive recovery and low accuracy. This result could be explained by possible biodegradation, in particular of monoethylene glycol, and in part by the inconsistencies of the water sample blanks on concentration.Sample blanks measured after concentration and permanganate oxidation increased according to the degree of concentration. Similar blanks obtained without oxidation were disproportionate to the extent of concen- tration; this disparity could be due to aerial oxidation of the organic constituents to aldehydes during the evaporation. The results of recovery experiments for each glycol in the range 1 to 5 mg l-l, with use of the acidified permanganate procedure, are shown in Table VI. For each glycol, 5 ml of each of 20 and 100 mg 1-1 solutions were diluted to 100 ml with each of the filtered waters indicated. Allowance was made, when necessary, for the water sample blank to account for dilution of water sample with standard. The freshly collected river waters were of varyingNovember, 19731 LOW LEVELS OF GLYCOLS I N SURFACE WATERS TABLE VI RECOVERY OF GLYCOLS FROM FORTIFIED SAMPLES Per- manganate value/ mg 1-1 Spring water.. . . 0.4 Well water . . . . 1-8 Public water supply 1.4 River water: A . . 2.0 C . . 7.0 D . . 2.6 G . . 6.0 G . . 6.0 Monoethylene glycol/mg 1-1 * 1 5 0.90 5-05 1-03 5.23 0.94 4-89 1.02 5-19 0.84 4-87 0-98 5-11 1.19 5-08 0-97 5-04 Diethylene . glycol/mg 1-l i 5 1.05 5.10 0.85 4-63 1.17 4.63 1.07 5-20 1.09 4-78 0.9 1 4-97 0.92 4.70 1.06 5.34 79 1 Triethylene glycol/mg 1-1 * 1 5 1.11 4.94 1.00 4.89 1-05 5.02 1.03 4-84 0.98 5-32 1-11 4.80 1.00 5-20 1-02 6-18 composition from different topographical origins.Rivers A and C originated as upland streams, while rivers D and G were slow-flowing rivers passing through agricultural land into which sewage effluents discharged. The average recovery was 100-5 per cent. with an over-all coefficient of variation of 7 per cent. At the 1 mg 1-1 level this value was 9 per cent., while at the 5 mg 1-1 level it was 4 per cent. Based on these coefficients of variation and those of reagent and sample blanks, a limit of sensitivity of the order of 0.5mg1-1 was indicated. Recoveries from estuary water E, with dissolved solids at a concentration of 15 300 mg l-l, were low and are not included; this low recovery suggests that the method would be invalid for saline waters. The method has been used successfully in these laboratories to monitor the biodegradation of low levels of glycols in river waters. This paper is published with the permission of the Government Chemist. 1. 2. 3. 4. 6. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. REFERENCES Plugin, V. P., Gig. Sanit., 1968, 33 (3), 16; Chem. Abstr., 1968, 68, 117 070. Kaye, S., and Adams, A. C., Analyt. Chem., 1950, 22, 661. Sargent, R., and Rieman, W., Analytica Chim. Acta, 1956, 14, 381. Reese, H. D., and Williams, M. B., Analyt. Chem., 1954, 26, 568. Tanaka, M., and Kojima, I., Analytica Chim. Acta, 1968, 41, 75. Reid, V. W., and Truelove, R. K., Analyst, 1952, 77, 325. Dennis, A., Evans, W. H., and Patterson, S. J., Wat. Treat. Exam.. 1972, 21, 350. Altshuller, A. P., Cohen, I. R., Meyer, M. E., and Wartburg, A. F., Analytica Chim. Acta, 1961, Blaedel, W. J., and Blacet, F. E., Ind. Engng Chem., Analyt. Edn, 1941, 13, 449. Heistand, R. N., Analytica Chim. Acta, 1967, 39, 258. Tanenbaum, M., and Bricker, C. E., Analyt. Chem., 1951, 23, 354. Malaprade, L., Bull. Soc. Chim. Fr., 1928, 43, 683. Speck, J. C., and Forist, A. A., Analyt. Chem., 1954, 26, 1942. Sawicki, E., and Hauser, T. R., Ibid., 1960, 32, 1434. Sawicki, E., and Stanley, T. W., Mikrochim. Acta, 1960, 510. Sawicki, E., Hauser, T. R., Stanley, T. W., and Elbert, W., Analyt. Chem., 1961, 33, 93. Sawicki, E., Hauser, T. R., and McPherson, S., Ibid., 1962, 34, 1460. Hauser, T. R., and Cummins, R. L., Ibid., 1964, 36, 679. Sawicki, E., Engel, C. R., and Guyer, M., Analytica Chim. Acta, 1967, 39, 505. Sawicki, E.. and Engel, C. R., Chemist Analyst, 1967, 56, 7. Sawicki, E., Schumacher, R., and Engel, C . R., Microchem. J., 1967, 12, 377. Wiberg, K. B., “Oxidation in Organic Chemistry,” Academic Press, New York, 1965. Holden, W. S., “Water Treatment and Examination,” Longman Group Ltd., London, 1970, p. 163, Received March 28th, 1973 Accepted June Sth, 1973 25, 101.

ISSN:0003-2654    

DOI:10.1039/AN9739800782

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

792 Analyst, November, 1973, Vol. 98, pp. 792-796 A Spectrophotometric Method for the Micro- determination of Piperonyl Butoxide in the Presence of Pyrethrins BY H. M. BHAVNAGARY AND S. M. AHMED (Central Food Technological Research Institute, Mysore-zA , India) A rapid spectroyhotometric method has been developed for the micro- determination of piperonyl butoxide in the presence of a wide range of pyrethrins. A solution of the mixture of piperonyl butoxide and pyrethrins in a low-boiling fraction of light petroleum is evaporated on a water-bath until only a small portion of the solvent remains. The final traces of solvent are removed a t 50 "C and, to the residue containing piperonyl butoxide and pyrethrins, 18 per cent. m/V nitric acid is added in order to convert the piperonyl butoxide content into a soluble yellow-coloured compound.The quantitative colour reaction has a maximum absorption at 370nm, and the nzethod is applicable to the residues in the range 4 to 40 pg ml-1 of piperonyl butoxide. The method is also applicable to the residues of formu- lated products extracted from grains and paper coatings. PIPERONYL but oxide, 5- [2- (2-but oxyethoxy) et hoxyme t hyl] -6-propyl-l,3-benzodioxole,~ has been widely used in combination with pyrethrins as synergist in various formulations for the protection of grains and foodstuffs, in the control of household insect pests, in food processing plants and warehouses, and for fish preservation. The use of piperonyl butoxide has increased in recent years not only because of its synergism2 with pyrethrins but also because of the low toxicity of such combinations to warm-blooded animals3 A survey of the literature revealed that the gas-chromatographic methods4s5 for the quantitative deter- mination of piperonyl butoxide involved preliminary clean-up procedures, Jones, Ackermann and Webstere have reported a colorimetric method for the determination of piperonyl butoxide alone in which they heated it in purified kerosene with a solution of tannic acid in a mixture of phosphoric and glacial acetic acids in order to produce a quantitative blue colour reaction.This method could not be used in the presence of pyrethrins owing to interference by the latter. In an attempt to avoid this interference, they saponified the pyrethrins content of the mixtures before colour development, but this treatment reduced the colour value.They then suggested that piperonyl butoxide could be separated from pyrethrins by using the partition-chromatographic method. The interference of pyrethrins in the above method was also observed by Williams, Dale and Sweeney,' who considered that it was caused by the red colour produced in the reaction that occurred between the phosphoric acid and pyrethrins. Further, the method of Jones et al. was used by other worker^*^^ only after they had isolated the piperonyl butoxide by means of a column-chromatographic separation in order to prevent interference by the pyrethrins. This procedure again involved the use of additional steps, thus making the method more time consuming and increasing the error.A need was therefore felt to develop a simple spectrophotometric method for the deter- mination of piperonyl butoxide in the presence of pyrethrins. A quantitative colour reaction of nitric acid with piperonyl butoxide has accordingly been developed that forms the basis of a method for its determination. The method is highly sensitive and the coloured compound formed obeyed Beer's law for a suitable range of micro- amounts of piperonyl butoxide down to a minimum concentration of 4 pg ml-l. The method is free from intcrfrrence by pyrethrins. METHOD LIPPARITUS- S~ectro~hotometer-Beckman DU model, with a 10-mm cell. @ SAC a n d the authors.BHAVNAGARY AND AHMED 793 Colorimeter-Bausch and Lomb Spectronic 20, with 12 x 100-mm tubes. For con- venience, measurements were made at 375 nm rather than at the wavelength of maximum absorption (370 nm).Test-tubes-Ground-glass, stoppered test-tubes, with the dimensions 18 x 150 mm, were used for the colour reaction. REAGENTS- piperonyl butoxide. sufficient glass-distilled water to give 1 litre of solution. pyrethrins. compounds, as supplied by Reechem (RC, India). Piperonyl butoxide-Technical material with a minimum content of 80 per cent. of Nitric acid reagent-Add 250 ml of analytical-reagent grade nitric acid (sp. gr. 1.42) to Pyrethrum extract-A standardised commercial extract containing 20 per cent. in/m of Light petrolezcm-Extra pure, with boiling range 40 to 60 "C, and free from aromatic PREPARATION OF STANDARD SOLUTION- For the stock solution, dissolve 0-25 g of technical piperonyl butoxide in light petroleum and make the solution up to 250 ml in a standard flask.With a pipette, transfer 10 ml of the solution into a 100-ml standard flask and make the volume up to the mark with light petroleum, thus giving a solution containing 100 pg ml-l of piperonyl butoxide. PROCEDURE- Preparation of calibration gvaph-Transfer 0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8 and %Om1 of the standard solution into glass-stoppered test-tubes and heat them on a water- bath until the residue obtained is solvent free. Add exactly 5 ml of the nitric acid reagent by means of a pipette and shake the mixture for 1 minute at a temperature not higher than 35 "C. Then measure the absorbance of the solution against a blank solution in the 12 x 100-mm tubes of the Bausch and Lomb colorimeter at 375 nm.Prepare a calibration graph from the results obtained. Preparation of test samples-Dissolve an accurately weighed amount of the samples con- taining pyrethrins and piperonyl butoxide in various proportions, such as 1 to 3, 1 to 5, 1 to 10 and 1 to 15, in light petroleum so as to give solutions that have piperonyl butoxide contents in the range 5 to 50 pg ml-l. Also, dissolve in the same solvent known amounts, within the above range, of piperonyl butoxide alone. COLORIMETRIC DETERMINATION- Transfer an aliquot of 5 ml of the test samples into 18 x 150-mm glass-stoppered test- tubes. Evaporate the solution on a water-bath until a small portion of the solvent remains, then continue to evaporate it in a water-bath adjusted to 50 "C until all of the solvent has been removed.To the residue add exactly 5 ml of the colour-forming reagent, stopper the test-tube and shake it well for 1 minute. Treat 5 ml each of the known sample and reagent blank in a similar manner. Then transfer the coloured solutions to the Bausch and Lomb colorimeter tubes and read the absorbance at 375 nm. Make all determinations in duplicate. CALCULATION OF RESULTS- The piperonyl butoxide content of the sample is calculated as follows. w (c - a) ( b - 4 Piperonyl butoxide content = where IVpg is the amount of piperonyl butoxide in the known sample, a the absorbance of the blank, b the absorbance of the known sample and c the ab; )r'itnce of t'is te;t solution. DISCUSSION COLOUR REAGENT- Under normal conditions, phenolic ethers undergo sulphonation, nitration and chlorina- These reactions were carried tionlo with electropliilic reagents by substitution in the ring.794 BHAVNAGARY AND AHMED : SPECTROPHOTOMETRIC MICRO-DETERMINATION [A%?aZySt, VOl.98 out on piperonyl butoxide by using the appropriate concentrated acids. It was observed that the reaction with nitric acid was quantitative and gave a yellow-coloured nitro compound that was soluble in the excess of nitric acid. Further investigations -with dilute nitric acid revealed that the reaction was complete when nitric acid in the concentration range 10 to 18 per cent. m/V was used for the nitration in aqueous medium. CHARACTERISTICS OF THE COLOUR REACTION- The absorption spectrum of the yellow-coloured nitrated piperonyl butoxide was deter- mined on the Beckman DU spectrophotometer in the wavelength range from 340 to 4-40 nm.Fig. 1 shows the spectra obtained with 30 and 60 pg of piperonyl butoxide present in 1 ml of solution, the maximum absorption occurring at wavelength 370 nm. The relationship between the concentration and the colour intensity obeyed Beer's law in the range 4 to 40 pg ml-l, the graph obtained being a straight line that passed through the origin. For the preparation of the standard graph, both technical and purified grades of piperonyl butoxide can be used as there was no quantitative difference between the colour reactions. The samples of piperonyl butoxide used should be free from organic solvents such as light petroleum, trichloroethylene and benzene, as the nitro compound partitions between these solvents and nitric acid.0.50 - 0.40 - a, C $ 0.30 - 54 Q 0.20 - 0.10.- 340 350 360 370 380 390 400 41 0 420 430 440 Wavelength/nm Fig. 1. Absorption spectra of piperonyl butoxide - nitric acid compound with reagent blank containing 14 per cent. of nitric acid: A, 60 pg ml-1 of piperonyl butoxide; and B, 30 pg ml-1 of piperonyl butoxide STABILITY OF THE COLOURED COMPOUND IN THE TEMPERATURE RANGE 25 TO 30 "C- The stability of the coloured product developed with 20 and 37 pg of piperonyl butoxide per millilitre of nitric acid solution was studied by reading the absorbances at 375nm at intervals of 1 minute for a period of 10 minutes and then at intervals of half an hour for a period of 10 hours. It was found to be stable for a period of up to 10 hours, beyond which time there was a gradual deterioration, as shown in Table I.EFFECT OF HEAT ON THE COLOUR REACTION- The absorbances of the colour developed at various temperatures between 20 and 100 "C with 165 pg of piperonyl butoxide, by adding 5 ml of the reagent, were studied. The relation- ship between the temperature of reaction and the absorbance at 375 nm is shown in Fig. 2. The coloured compound was stable up to a temperature of 35 O C , above which it decomposed 3teadily with increase in temperature. It is therefore necessary to maintain the temperature of the reaction mixture below 35 "C for satisfactory colour development.November, 19731 OF PIPERONYL BUTOXIDE I N THE PRESENCE OF PYRETHRINS TABLE I STABILITY OF THE COLOURED COMPOUND I N THE TEMPERATURE RANGE 25 TO 30 "c Absorbance* Time after development 1 minute 5 minutes 10 minutes 30 minutes 1 hour 5 hours 20 Gg ml-1 37 pg A1-1 of piperonyl of piperonyl butoxide butoxide 0.12 0.22 0.12 0.22 0.12 0.22 0.12 0.22 0.12 0.22 0.12 0.22 795 Time after ( development 10 hours 12 hours 15 hours 18 hours 2 1 hours 24 hours .Absorbance* - 20 pg ml-l 37 pg ml-1 3f piperonyl of piperonyl butoxide bu toxide 0.12 0.22 0.1 1 0.2 1 0.10 0.19 0.09 0-17 0.08 0.15 0.07 0.14 * Measured a t 375 nm in 12-mm tubes against water as reference. EFFECT OF THE NITRIC ACID REAGENT CONCENTRATION- To test-tubes each containing 150pg of piperonyl butoxide, 5 ml of nitric acid a t different concentrations were added and the colour was developed by shaking the mixture for 1 minute.In Fig. 3, the relationship between the concentration of nitric acid and the absorbance is shown. With dilute acids the colour reaction with piperonyl butoxide was incomplete. At an acid concentration of 10 per cent. m/V the absorbance reached a maximum and thereafter remained constant in the range 10 to 18 per cent. m/V, indicating that the colour reaction was complete. The concentration of the nitric acid used as the colour-forming reagent should therefore be above 10 per cent. m/V. 0.20 0.15 b 0.15 m W c m 2 0.10 % a Q 0.05 0 5 10 15 20 Ternperature/OC Nitric acid concentration, per cent. mlV Fig. 2. Effect of temperature on the Fig. 3. Effect of Concentration of absorbance of the piperonyl butoxide - nitric acid on the absorbance of nitric acid coloured compound the coloured compound containing 30 pg ml-l of piperonyl butoxide APPLICATION OF THE METHOD- The rapid spectrophotometric procedure developed has been applied satisfactorily to formulations containing pyrethrins and piperonyl butoxide in various proportions, It can also be used for the determination after extracting the combinations of pyrethrins and piperonyl butoxide from both sorptive and non-sorptive surfaces, such as glass, grains, paper coatings, etc.Either light petroleum or hexane can be used for the extraction and the solvent-free residues taken for the determination by the procedure described. CONCLUSIONS A sensitive and precise method for the determination of piperonyl butoxide in the It is based on the presence of pyrethrins by a spectrophotometric procedure is presented.796 BHAVNAGARY AND AHMED measurement of the yellow colour produced when the samples containing piperonyl butoxide are treated with 10 to 18 per cent.m/V nitric acid at a temperature not higher than 35 “C. There is no interference at any concentration level from pyrethrins, with which it is commonly used in formulations. The authors express their sincere thanks to Shri S. K. Majumder, Chairman, Discipline of Infestation Control and Pesticides, and Dr. H. A. B. Parpia, Director, Central Food Technological Research Institute, Mysore (India), for providing the necessary facilities during the investigations. The colour is stable and appears to be fairly specific for piperonyl butoxide. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. REFERENCES Wachs, H., Science, N.Y., 1947, 105, 530. Dove, W. E., Amer. J. Trofl. Med., 1947, 27, 339. Sarles, M. P., Dove, W. E., and Moore, D. M., Ibid., 1949, 29, 151. Miller, W. K., and Tweet, O., J . Agric. Fd Chern., 1967, 25, 931. Bevenue, A., and Kawano, Y . , J. Chromat., 1970, 50, 49. Jones, H. A., Ackermann, H. J., and Webster, M. E., J . Ass. Off. Agric. Chem., 1952, 35, 771. Williams, H. L., Dale, W. E., and Sweeney, J . P., Ibid., 1956, 39, 872. Williams, H. L., and Sweeney, J, P., Ibid., 1956, 39, 975. Secreast, M. F., and Cail, R. S., J . Agric. Fd Chem., 1971, 19, 192. Kirk, R. E., and Othmer, D. F., “Encyclopedia of Chemical Technology,” Volume 15, Interscience Received March 27th, 1972 Amended May 16th, 1973 Accepted June 19th, 1973 Publishers, New York, 1968, p. 168.

ISSN:0003-2654    

DOI:10.1039/AN9739800792

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

Analyst, November, 1973, Vol. 98, PP. 797-801 797 The Determination of Chlorhydroxyquinoline in Medicated Pig Feeds BY J. E. FAIRBROTHER AND W. F. HEYES (Squibb raternational Development Laboratory, Moreton, Wirral, Cheshire) A method has been developed for the determination of chlorhydroxy- quinoline (Halquinol) in medicated pig feeds. Because of the interference by feed constituents in simple spectrophotometric and polarographic assay procedures, a spectrofluorimetric procedure is recommended. Spectrofluori- metric measurements are taken in a methanolic solvent containing 5 per cent. of chloroform, and the fluorescence of chlorhydroxyquinoline, as its mag- nesium chelate, is measured at 500 nm, with an excitation wavelength of 402 nm. Cyanide is used to suppress interference from copper and zinc salts that are commonly added to these feeds.The procedure is not affected by the presence of other feed additives, such as dimetridazole and arsanilic acid. CHLORHYDROXYQUINOLINE, I, is a mixture of three isomeric chloro-8-hydroxyquinolines that is claimed1 to possess antibacterial and ant ifungal activities greater than those of its individual components : Y OH I ( Halquinol) where X = C1, Y = C1 (57 to 74 per cent. m/m); X = H, Y = C1 (23 to 40 per cent. nz/m); and X = C1, Y = H (not more than 3 per cent. m/m). One of the veterinary uses of chlorhydroxyquinoline is in the treatment of bacterial diarrhoea in weanling pigs. The drug is marketed for this purpose as a pre-mix (“Quixalud,” E. R. Squibb & Sons Ltd.) that is diluted with pig feed.Chlorhydroxyquinoline is readily soluble in chloroform and shows an absorption maximum at 335 nm (&& = about 150). It forms chelates with many cations, in a number of instances (iron, copper, vanadium, titanium and molybdenum) giving coloured products suitable for spectrophotometric determination. The green chelate formed with iron(II1) (with an absorp- tion maximum at 685nm) is soluble in a mixture of chloroform and acetone and can be used (J. E. Fairbrother and W. F. Heyes, unpublished work) for the spectrophotometric determination of chlorhydroxyquinoline in pre-mixes that contain inorganic diluents. The determination of chlorhydroxyquinoline in medicated pig feeds, however, is difficult for two reasons. Firstly, simple solvent extraction in order to remove the active substance from the feed also removes feed constituents that produce a high level of background absorp- tion in both the ultraviolet and visible-light regions of the spectrum.Secondly, in polaro- graphic procedures (J. E. Fairbrother and W. F. Heyes, unpublished work), constituents of medicated feeds either interfere in the assay or prevent the quantitative extraction of chlorhydroxyquinoline. We theref ore decided to examine a spectrofluorimetric procedure for the determination of chlorhydroxyquinoline in a medicated pig feed that contained 600 g ton-l of chlorhydroxyquinoline (about 590 p.p.m.). The procedure had to be capable of determining the active substance in the presence of other common feed additives, such as copper and zinc salts, dimetridazole and arsanilic acid.@ SAC and the authors.798 FAIRBROTHER AND HEYES: THE DETERMINATION OF [AnaZyst, Vol. 98 EXPERIMENTAL The chlorhydroxyquinoline is extracted from the sample of medicated feed by being shaken with chloroform. After the chloroform extract has been filtered an aliquot is treated with a solution of potassium cyanide in methanol, in order to complex any co-extracted copper and zinc. A methanolic magnesium acetate reagent solution is added to the treated aliquot to convert the chlorhydroxyquinoline into its fluorescent chelate with magnesium and the solution is diluted with neutralised methanol containing phenolphthalein indicator. The alkalinity of this solution is adjusted to a defined point by the dropwise addition of methanolic potassium hydroxide solution, then the fluorescence-emission intensity of the solution is measured and compared quantitatively with that of a similarly treated chlorhydroxyquinoline standard.METHOD APPARATUS- A Baird Atomic SF1 spectrofluorimeter was used, with exit and entrance slits set at 8 pm. The scale used (coarse gain, 1000 at 1 s; fine gain, 10; photomultiplier setting, 3 or 4) was adjusted to give a meter reading of 60 for the chlorhydroxyquinoline standard solution. The spectrofluorimeter was coupled with an Advance Electronics X Y pen recorder, Model HR 100, and recorded spectra rather than direct meter readings were used. REAGENTS- All reagents were of analytical-reagent grade, unless otherwise stated. Chlorhydroxyquinoline-A sample of the batch used to medicate the feed, or a suitable reference standard.Chloroform. Magnesium acetate solution-A 0.1 per cent. m/V solution in methanol. Methanol, neutralised-With 0.1 M methanolic potassium hydroxide solution, neutralise 500 ml of methanol containing 0.75 ml of 1.0 per cent. m/V phenolphthalein solution to a faint pink colour. Phenolphthalein solution-A 1.0 per cent. m/V solution in ethanol. Potassium cyanide solution-A 0.5 per cent. mm/V solution in methanol. Potassium hydroxide solution, 0.1 M-weigh 0-561 g of potassium hydroxide into a 100-ml calibrated flask. Dissolve it in, and dilute to volume with, methanol. PREPARATION OF STANDARD- Weigh accurately 120 mg of chlorhydroxyquinoline into a 100-ml calibrated flask. Dis- solve it in, and dilute to volume with, chloroform.Mix the solution thoroughly and transfer 10ml by pipette into another 100-ml calibrated flask, dilute to volume with chloroform, and again mix thoroughly. PREPARATION OF SAMPLE- Weigh accurately 20 g of medicated feed (or an amount containing approximately 12 mg of chlorhydroxyquinoline) into a 250-ml conical flask. Add, by use of a pipette, 100 ml of chloroform, then stopper the flask and shake it thoroughly for 5 minutes. Immediately filter about 20ml of this solution through a fluted Whatman No. 4 filter-paper, rejecting the first 10ml of filtrate. REACTION PROCEDURE- Transfer, with a pipette, 5 ml of each of the standard and sample solutions into separate 100-nil calibrated flasks and treat each in the following manner. With care add, by use of an autonutic pipette, 5 ml of potassium cyanide solution followed by 10 ml of magnesium acetate solution.Mix the solutions and add about 60 ml of neutralised methanol containing phenolphthalein indicator. Then, by using a Pasteur pipette, add 0.1 M methanolic potassium hydroxide solution dropwise until the solution just turns pink. Add a further 1.5 ml of 0.1 M methanolic potassium hydroxide solution from a pipette and dilute each solution to volurne with more neutralised methanol. Mix them thoroughly, then filter, if necessary, through a Whatman No. 1 filter-paper, rejecting the first 1 O m l of filtrate.November, 19731 CHLORHYDROXYQUINOLINE IN MEDICATED PIG FEEDS 799 SPECTROFLUORIMETRIC MEASUREMENT- Scan the fluorescence-emission spectrum of a 1-cm layer of both the sample and standard solutions between 485 and 570 nm, with an excitation wavelength of 402 nm.(The emission peak should occur at approximately 500 nm.) Record the peak heights given by the sample and standard solutions, and calculate the chlorhydroxyquinoline content of the sample. If necessary, a sample of unmedicated feed should be put through the procedure as described for the sample, and a suitable blank correction shouid be made to the reading for the sample of feed. RESULTS AND DISCUSSION REACTION CONDITIONS- Inadequate recoveries of chlorhydroxyquinoline obtained in initial experiments were found to have resulted from a reduction in fluorescence yield, rather than from inefficient extraction from the feed. This result was found to correlate with the co-extraction of acidic components from the feed, and the problem was overcome by controlling the alkalinity of the solution (see Fig.1). The change in fluorescence yield brought about by the addition of alkali was first measured by use of external acid - base indicators. It was then found that the inclusion of the indicator in the reaction mixture did not significantly affect the results, and in view of the necessity to retain methanol as the main solvent, the use of the internal indicator was adopted. Fig. 1. Fluorescence (emission) spectrum of a methanolic solution of chlorhydroxyquinoline - magnesium com- plex neutralised with potassium hydroxide : A, to bromothymol blue external indicator ; B, to phenolphthalein; and C to H, to phenolphthalein with 0.26 (C), 0.6 (D), 0.76 (E), 1.0 (F), 1.6 (G) and 2-0 (H) ml excess of 0.1 M methanolic potassium hydroxide solution per 100 ml of solution. (Subsequent spectra were recorded off-set with respect to the wavelength scale so as to permit comparison) A study of the extraction procedure showed that recoveries of chlorhydroxyquinoline from medicated feeds were dependent on time, values reducing to about 70 per cent.recovery after 30 minutes’ extraction. An examination of the chloroform extracts from medicated feeds by use of atomic-absorption spectroscopy showed that copper and zinc were the main cations co-extracted with the active drug. These ions were found to compete with magnesium800 FAIRBROTHER AND HEYES: THE DETERMINATION OF [Analyst, Vol. 98 acetate reagent for chelation with the chlorhydroxyquinoline, thereby reducing the fluores- cence intensity of the chlorhydroxyquinoline - magnesium chelate solution.A small amount of extracted manganese ion had no significant effect on the fluorescence. When potassium cyanide reagent was added to the chloroform extract the copper and zinc ions complexed with it rather than with chlorhydroxyquinoline, thus overcoming the extraction problem and that of poor recoveries. FLUORESCENCE PHENOMENA- The fluorescence spectra of certain metal chelates of 8-hydroxyquinoline and its deriva- tives have been extensively reported.2-s The fluorescence spectrum of chlorhydroxyquinoline is similar to that of S--hydro~yquinoline,~~8 but its excitation and emission maxima are shifted slightly towards longer wavelengths.The possibility that interfering substances are co-extracted from the feed, as well as the limited availability of solvents of suitable purity, limited the choice of solvents to the chloroform - methanol mixture used. Aluminium, magnesium and lithium were considered as possible chelating cations, and magnesium was selected. Although aluminium was known6 to give the highest fluorescence yield, it was difficult to select an aluminium salt soluble in a chloroform - methanol mixture and also available in a sufficiently pure form for spectrofluorimetric work. Lithium had a lower fluorescence intensity than magnesium and was therefore not examined further. Under the conditions selected , chlorhydroxyquinoline showed an excitation maximum at 402 nm and a corresponding emission maximum at 500 nm.The linearity of the relation- ship between the emission intensity and the concentration of the chlorhydroxyquinoline solution was demonstrated over the concentration range 3-75 to 7.25 pg ml-l, and the fluorescence intensities of the sample and standard solutions remained reproducible for at least 1 hour after their preparation. It was considered valuable to examine the fluorescence characteristics of the three isomeric components of chlorhydroxyquinoline. The changes in fluorescence characteristics caused by variations in the ratio of the component isomers were also examined (see Table I). TABLE I FLUORESCENCE CHARACTERISTICS OF CHLORHYDROXYQUINOLINE AND ITS COMPONENT SUBSTANCES Wavelength of excitation maximumlnm 5,7-Dichloro-8-hydroxyquinoline .. 402 5-Chloro-8-hydroxyquinoline . . .. 402 7-Chloro-8-hydroxyquinoline . . .. 388 Chlorhydroxyquinoline-Batch A . . 402 B .. 402 c .. 400 D .. 402 Wavelength of emission maximumlnm 495 510 487 600 500 497 498 Relative fluorescence intensity 79.3 35.7 60-2 64.6 64-6 62.6 64.2 Although the fluorescence characteristics of the three component isomers are different , the over-all effect of these differences on the fluorescence yield of different batches of chlor- hydroxyquinoline is not critical. However, it is recommended that a sample of the same batch of chlorhydroxyquinoline that was used to medicate the feed be used as a standard in the assay procedure. RESULTS Feed blanks did not appear to make any major contribution to the fluorescence intensity, except for those from feeds that contained a high proportion of meat meal.However, because different feed bases were not studied extensively, such interferences cannot be ruled out for all grades of feed. Recoveries of chlorhydroxyquinoline from different types of feeds medicated in the labmatory are shown in Table 11.November, 19731 CHLORHYDROXYQUINOLINE IN MEDICATED PIG FEEDS TABLE I1 RECOVERY OF CHLORHYDROXYQUINOLINE FROM FEEDS MEDICATED IN THE LABORATORY AT LEVELS BETWEEN 60 AND 140 PER CENT..OF THE THEORETICAL CONTENT (600 g ton-l) 801 Halquinol Feed added/ sample g ton-l 1 600 360 840 2 600 360 840 3 600 360 840 Feed blank, per cent. of contribution of active drug 3.3 5.4 2.4 3.3 5.4 2.4 3-3 5.3 2.4 Recovery of chlorhydroxyquinoline, per cent.(corrected for blank contribution) 97.8, 97.9, 99.0 106.2, 104.2 93.0, 93.8 99.2, 96-6, 96.6 98.8, 98.9 97-9, 96.6 100.2, 102.1, 97.1 102.5, 105.5 94.4, 93.8 The feeds were chosen as being representative of the different cereals and additives used in the manufacture. Deviations from a recovery of 100 per cent. are apparent at levels of 360 and 840 g ton-l of chlorhydroxyquinoline. However, as the procedure described was developed specifically for the assay of feeds containing 600 g ton-l, the deviations encountered (+6 per cent. at 360 g ton-l and -7 per cent. at 840 g ton-l) were considered acceptable. Satisfactory recoveries of chlorhydroxyquinoline (600 g ton-l) were obtained from feeds containing the following additives- Additive Content, p.p.m. Copper . . .. . . .. .. 100 Zinc . , .. .. .. .. 100 Calcium .. .. * . . . 1000 Dimetridazole , . ,. .. .. 100 Arsanilic acid . . .. . . .. 250 The procedure described is not suitable for the determination of Halquinol in pre-mixes and concentrates. Simpler and more precise procedures for these determinations that make use of the spectrophotometric determination of the iron(II1) chelate of Halquinol in a chloroform - acetone solvent can be used (J. E. Fairbrother and W. F. Heyes, unpublished work). 1. 2. 3. 4. 5. 6. 7. 8. REFERENCES British Patent 909,359, 1961. Udenfriend, S., “Fluorescence Assay in Biology and Medicine,” Academic Press, New York, 1962, p. 388. Ohnesorge, W. E., in Hercules, D. M., Editor, “Fluorescence and Phosphorescence Analysis,’’ J. Wiley & Sons, New York, 1966, p. 155. Parker, C. A., “Photoluminescence of Solutions,” Elsevier, London, 1968, p. 475. Stevens, H. M., Analytica Chim. Acta, 1959, 20, 389. Schulman, S. G., Analyt. Chem.. 1971, 43, 285. Schulman, S. G., and Rietta, M. S., J . Pharm. Sci., 1971, 60, 1762. Bratzel, M. P., Aaron, J. J., and Winefordner, J. D., Analyt. Chem., 1972, 44, 1240. Received May 4th, 1973 Accepted June 27th, 1973

ISSN:0003-2654    

DOI:10.1039/AN9739800797

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

802 Analyst, November, 1973, Vol. 98, $y5. 802-810 Solvent Extraction of Copper(I1) and Zinc(I1) with 1,5=Diphenylcarbazone BY HISAHIKO EINAGA AND HA JIME ISHII” (National Institute joor Researches in Inorganic Materials, Niihari-gun, Ibaraki-hm, Japan) The extraction characteristics of 1,5-diphenylcarbazone and its com- plexes with the bivalent metal ions copper(I1) and zinc(I1) in an isobutyl methyl ketone - water system have been studied and the extraction curves of these metal complexes have also been obtained. The copper(I1) complex is extracted from a more acidic solution than is the zinc(I1) complex. The extraction equilibria have been examined and the extraction constants determined. The spectral properties of the complexes have also been deter- mined and the application of the reagent to the determination of copper and zinc is suggested. 1,5-DIPHENYLCARBAZONE has not been widely used as an analytical reagent for the separation and determination of trace amounts of metals in spite of the close similarity of its chemical structure to that of dithizone (1,5-diphenylthiocarbazone). It has been thought that 1,5-di- phenylcarbazone is “far inferior to dithizone for the purpose.”l This structural similarity between dithizone and 1 ,5-diphenylcarbazone, however, implies that the latter possesses considerable potentiality for the formation of complexes with certain of the metal ions that are known to form complexes with the former.Several studies have been made on the reaction between 1,5diphenylcarbazone and several metal ions, such as iron(II), iron(III), cobalt(II), copper(II), mercury(II), cadmium(II), lead(I1) and ~ i n c ( I I ) , ~ - ~ all of which, except iron(III), react with dithizone.It seemed, however, that relatively few details have been reported on the characteristics of solvent extraction of the 1,5--diphenylcarbazone complexes for analytical purposes, which led us to investigate them further. The present paper describes the extraction characteristics of copper( 11) and zinc(I1) with 1,5-diphenylcarbazone, together with those of the ligand itself, in the solvent system isobutyl methyl ketone - water. EXPERIMENTAL REAGENTS- Co@er(II) solution, 1.020 mg ml-1-This solution was prepared by dissolving recrystallised copper(I1) sulphate pentahydrate in water and acidifying the solution with a small amount of sulphuric acid so as to prevent precipitation of copper(I1) by hydrolysis.The solution was standardised by using a complexometric method with 1-(2-pyridylaz0)-2-naphthol as a metallochromic indicator.6 Zinc(1I) solution, 1.150 mg ml-l-This solution was prepared by dissolving pure zinc metal (99-99 per cent.) in hydrochloric acid, a slight excess of which was added in order to prevent precipitation of zinc(I1) by hydrolysis. This solution was also standardised by a complexo- metric method with Eriochrome black T as a metallochromic indicator.’ 1,5-DiphenylcarbazoneJ 0.020 per cent. (8.32 x lo-* M) solution in isobutyl methyl ketone- The 1,5-diphenylcarbazone used to prepare this solution was obtained from Kanto Chemical Co., Inc., Japan, and was purified before use by extraction with diethyl ether so as to remove any lJ5-diphenylcarbazide* and was finally recrystallised from ethanol.Adjustment of the pH and ionic strength of the aqueous phase was carried out by using 0.2 M sodium acetate - 0.2 M acetic acid or 0.05 M sodium borate - 0.1 M hydrochloric acid or sodium hydroxide solution for pH adjustment and 1 . 0 ~ ammonium chloride solution to adjust the ionic strength. * Present address : Department of Applied Chemistry, Faculty of Engineering, Tohoku University, Sendai, Japan. @ SAC and the authors.EINAGA AND ISHII 803 APPARATUS- Absorption spectra and absorbances at the specified wavelength were obtained with a recording spectrophotometer, Model EPS-3T (Hitachi Ltd., Japan); and a spectrophoto- meter, Model 139 (Hitachi Ltd., Japan), respectively, with matched 10-mm silica cuvettes. The pH of the equilibrated aqueous phase was measured with a glass electrode - saturated calomel electrode pair and pH meters, Model HM-5A (Toa Dempa Co. Ltd.) and Model F-5 (Horiba Ltd., Japan).A solution 0.09 M in ammonium chloride and 0.01 M in hydrochloric acid was defined as -log [Hf] = 2.00. Equilibration of both organic and aqueous phases was carried out with a universal shaker (Model KM, Iwaki Ltd., Japan) at the rate of 300 strokes per minute and at a temperature of 25 "C. PROCEDURE- Measurements of extractability (percentage extraction) and distribution ratios of the metal complexes were obtained by the following procedure. A mixture of n ml of the 1,5-diphenyl- carbazone solution and (20.0 - n) ml of isobutyl methyl ketone was equilibrated at various pH values with 20-0 ml of an aqueous solution that contained a definite amount of metal ions and was adjusted to an ionic strength of 0.10 M with ammonium chloride. After separation of the phases, the metal ions extracted into the organic phase were determined by measuring absorbances at a specified wavelength and by making use of the molar absorptivity of each metal ion (see under Extraction characteristics of the complexes of copper(I1) and zinc(I1) with 1,5-diphenylcarbazone). The separated aqueous phase was used for measurement of hydrogen-ion concentration.The concentration of metal ions in the aqueous phase was obtained as the difference between the initial concentration and that in the organic phase, and the distribution ratio, DA, the ratio of the concentration of the metal ions in the organic phase to that in the aqueous phase, was calculated from these results.The above procedure was also applied in the absence of metal ions to the determination of the extractability and distribution ratio of the ligand itself. In this instance the concen- tration of 1,5-diphenylcarbazone in the organic phase was determined by shaking the separated organic phase with an acetate buffer solution (pH 5) and then measuring absorbances at 560 nm (a calibration graph had been constructed by using purified 1,5-diphenylcarbazone). This shaking treatment was necessary in order to obtain reproducible and uniform absorption characteristics of 1 ,5-diphenylcarbazone, the concentration of which in the aqueous phase was obtained as described previously for the metal ions.RESULTS AND DISCUSSION EXTRACTION CHARACTERISTICS OF 1,5-DIPHENYLCARBAZONE- Consideration of the structure of 1,5-diphenylcarbazone suggests that its ketonic and enolic forms are present in tautomeric equilibrium in the solution. From its behaviour on neutralisation with sodium hydroxide it has been reported that 1,5-diphenylcarbazone is a monobasic acid.3 It is, however, reasonable to consider it to be a dibasic acid, just as the structurally closely similar dithizone is a dibasic acid (ha1 = about 2 x loB5 and ka2.< 10-15) .9 Studies were therefore first made on the spectral and extraction characteristics of 1,5-diphenylcarbazone in an isobutyl methyl ketone - water system, and these charac- teristics are shown in Figs.1 and 2, respectively. The absorption spectrum of this re- agent did not vary with change in pH of the equilibrated aqueous phase below 8, and had an absorption maximum at 460 nm, which showed, however, a gradual bathochromic shift when the pH was increased and reached a constant value above pH 11 (Amax. = 505 nm at pH 11-25). The distribution of the reagent from the organic to aqueous phase also became appreciable when the pH was above 8 and gradually increased with increasing pH. The reagent in the aqueous phase had an absorption maximum at 495nm, which was independent of the pH. These results can be qualitatively interpreted as follows : 1,5--diphenylcarbazone is present in the organic phase in ketonic (Amax.= 460 nm) and enolic forms (Amax, = 505 nm) in tautomeric equilibrium, which is, however, gradually shifted in favour of the enolic form by equilibration with an aqueous solution at pH above 8. The enolic form is then distributed into the aqueous phase in which it dissociates into a proton and the anion, HDN- (Amax, = 495 nm), where HzDN represents the undissociated 1,5-diphenyIcarbazone. A series of these equilibria can be represented as follows-804 where the subscript keto represents the ketonic form, enol the enolic form, org the organic phase and absence of subscript the aqueous phase. These equilibria can be exmessed as follows- 0.5 I / / ‘1 3’ / / / / / / I I I I 400 500 600 Wavelength/nm Fig. 1.Absorption characteristics of 1,5-diphenyl- carbazone in the isobutyl methyl ketone - water system. [1,5-Diphenylcarbazone] 4-16 x M ; and [NH4C1] 0.1 M. 1 to 4, absorption spectra of organic phase. pH value of equilibrated aqueous phase: 1, 5.25; 2, 8-80; 3, 10.20; and 4, 11.25. 3’, Absorption spectrum of aqueous phase; pH 10-20 Further, let us define PL as follows- PL = ( [ H a D N ] k e t O , O r g + [ H @ N ] e n o l , o r g ) / [ H 2 D N I e n o l = [H2DN]Org/ [H2DN]enOl - .. .. * (5) where [ H 2 D N ] o r g is the total concentration of 1,5-diphenylcarbazone in the organic phase. The terms Pa and PL can be correlated in the equation .. .. * (6) PL = (1 + Kke) P L ~ ..November, 19731 AND ZINC(I1) WITH 1,5-DIPHENYLCARBAZONE The distribution of 1,5-diphenylcarbazone can then be defined by 805 where the partition coefficient of the ketonic form was assumed to be so large that its effect in the aqueous phase can be neglected as compared with other species, which assumption is considered to be reasonable having regard to our results.By making use of equations (1) and (6), equation (7) can be rewritten in the following logarithmic form- Equation (8) implies that- Log DL = log J'L - log (1 + kal/[H+] + kalka2/[H+I2) . . - ' (8) (;) log D, should have no dependence on log [H+] if H2DN en01 is the principal species in the equilibrated aqueous phase; (G) log DL should have a linear relationship to log [Hf] with a slope of unity if HD,- is the principal species or with a slope of two if D,2- is the principal species; and (G) there should be a non-linear relationship between log DL and log [H+] with a tan- gential slope between 0 and 1 or 1 and 2, depending on whether appreciable concen- trations of both H2DN en01 and HDN- or HD,- and DN2-, respectively, are present in the aqueous phase.Fig. 2 shows the experimental results obtained for log DL and log [H-t]. A linear relationship exists between them with a slope of unity, indicating that HDN- is the principal species in the aqueous phase. Equation (8) can therefore be simplified as follows- Log D L = log P L - log + log [H+] . . .. . . (8a) The extraction constant of 1,5-diphenylcarbazone, Ken, which is expressed by the equilibrium &XL H~DN keto + eno1,org + H+ + HDN- can be defined as follows- .. * . (9) = PL/k,, .. .. .. The value of KexL was calculated by using the results in Fig.2 and was determined as log KeXL = 11.15. lbl - Log [H'] 100 - c; W W Q L $ 50- E .- c, 0 + UJ 0 - Fig. 2. M ; and [NH,Cl] 0.1 M. Extraction characteristics of 1,5-diphenylcarbazone. [ 1,5-Diphenylcarbazone] 4- 16 x (a), Extraction curve of 1,5-diphenylcarbazone; and ( b ) , dependence of distribution ratio on hydrogen-ion concentration GENERAL TREATMENT OF THE EXTRACTION EQUILIBRIA O F METAL(I1) - 1,5-DIPHENYLCARBAZONE COMPLEXES- The terms used below are defined as follows: Keq is the equilibrium constant of the extraction of the metal complex M(HNN)2(H2DN)n-.2, Kex the extraction constant and P, the806 EINAGA AND ISHII : SOLVENT EXTRACTION OF COPPER(II) [Analyst, Vol. 98 partition coefficient of the same metal complex, D, the distribution ratio of the metal, D M = [M(HDN)2(H2DN),-2]or,/[M2+], and D,’ the apparent distribution ratio of the metal, D,’ = [M(HD,)2(H2DN),-Jorg/ [M2+]total ( [M2+]total is the total concentration of the metal in the aqueous phase).I<%%, is the equilibrium constant in the aqueous phase of the metal complex M(DN)nH,c,2+n’-2ra, p series are formation constants of the side reaction of the metal ion with the species indicated, and acoeff the side-reaction coefficient of the metal ion. In the extraction equilibria of bivalent metal ions with 1,5-diphenylcarbazone, both ketonic and enolic forms can be considered to participate to an equal extent in the extraction reaction. It is, however, very difficult from equilibration studies, although unimportant in so far as it affects the extraction equilibria, to elucidate which of the forms is the principal participant in the reaction.Therefore, it was considered that both forms of 1,5-diphenyl- carbazone participate in the reaction involving the extraction of metal complexes. In addition to the assumption made above, it should be considered that the extracted metal complexes are electrically neutral. Under these conditions the principal extraction equilibrium can be represented as follows: Ke q M2+ + ~ H ~ D N org + M(HDN)~(H~DN),-~ org + 2H+ = D, [H+] 2 [H2DNIFn .. . . .. . . (10) The term D,’, which can easily be obtained experimentally, can be defined as follows- D,’ = n‘ n [M(HDN)2(H2DN)n-210Fg (W [h12+]+C C [M(D,),Hn,2+”’-2n ] + 5 [M (NH 3)m2+] + [ M (OAc) p2-”] + 5 [M (OH) a2- a ] 1 1 1 where the following equilibria were taken into consideration- K d M2+ + utHDN- + M(DN)nHn,2+n’--2n + (rt-%‘)H+ .... [ M ( DN) nHn,2+n’-2n] [H+] n--n’ [M2f] [HDN-]” P M Kn,/ = M(HDN)2(H2DN)7a-2 M(HDN)2(H2DN)?Z-2 Ore P, = [M (HDN)2(H2DN) n-2lorg . . . . .. [M(HDN)2(H2DN) 92-21 IN (NH,)m2+1 .. .. .. Bm’= [M2+] [NH,]“ .. .. .. .. .. .. P .. + X 1 /3i’[OAc-]” + 5 1 pql”[OH-]* . .November, 19731 AND ZINC(I1) WITH 1,5-DIPHENYLCARBAZOXE 807 Further, it should be appropriate to assume that the presence in the aqueous phase of lower and higher order complexes for the 1,5-diphenylcarbazone ligand than the electrically neutral complex M(HDN)2(H2DN)n-2 can be neglected and that the neutral complex has a partition coefficient that is high enough to be able to make l/PM < 1.With'these assumptions, equation (17) can be further simplified into logarithmic form- Equation (18) implies that a linear relationship should exist between log DM' + log xcoeff and log [H+] under constant conditions of log [HzDNlorg with a slope of 2 and log Dy' + log acoeff and log [HzDNIorg under constant conditions of log [H+] with a slope of n, which corresponds to the actual number of ligands in the extracted complex. Now let us define the term extraction constant, Kex, as follows: K e x M2+ + HDN- + M(HD,),(H2DN),2 org + (2 - n) H+ [M(HDN)2(H2DN)n-2]Org[H+]2-~ [M2+] [HD,-]" Kex = z= P, K , a(n-1) .. .. .. .. . . (19) Log Kex = log Ke, + n log Kex, .. .. . . (20) The following relationship can be obtained from equations (2), (3), (10) and (19)- The term Kex indicates how easily the complex can be formed in the aqueous phase and extracted into the organic phase, and can be obtained by using the value of Ke,, as determined in the preceding section.EXTRACTION CHARACTERISTICS OF THE COMPLEXES OF COPPER(I1) AND ZINC(I1) WITH 1,5-DI- PHENYLCARBAZONE- Preliminary experiments have shown that zinc(I1) cannot be extracted as its 1,ti-diphenyl- carbazone complex into the organic phase when ammonium salts are absent, although the extraction of the copper(I1) complex was not influenced by the presence or absence of ammonium salts. This difference in behaviour may be due to the formation of hydroxo species of zinc(II), especially the zincate ion, which retards or inhibits the formation of the zinc(I1) complex.It is therefore necessary to add ammonium salt to the aqueous phase i 0 I I I 2 3 4 5 6 7 8 9 10 11 PH Fig. 3. Extraction curves of copper(I1) and zinc(I1) as 1,5-diphenylcarbazone complexes. 1, Extraction curve of copper(I1) : [copper(II)] 8-03 x M ; [1,5-diphenylcarbazone] 2.08 x lo-* M; and [NH,C11 0.1 M. 2, Extraction curve of zinc(I1) : [zinc(II)] 1.76 x M- [i,Ei-diphenylcarbazone] 4-16 x M; and [NH,Cl] 0.1 M808 EINAGA AND ISHII: SOLVENT EXTRACTION OF COPPER(II) [Analyst, Vol. 98 and thus convert the zinc(I1) into the more labile ammine complexes. The presence of ammonium chloride at a concentration of 0.1 M was concluded to be sufficient for the extraction of zinc(I1) as its 1,5-diphenylcarbazone comdex. I 3 4 5 - Log [H'] Fig.4. Extraction characteristics of copper(I1) - 1,5-diphenylcarbazone complex. [Copper(II)] 8-03 x M ; and [NH,Cl] 0.1 M. (a), -Log [H+] 6.12; and ( b ) , -log [H2DN]org 3.70 Extraction curves for the copper(I1) and zinc(I1) complexes are presented in Fig. 3, which show that copper(I1) can be extracted into the organic phase from more acidic solution (pH,,, = 4-30) than is zinc(I1) (pH,,, = 7.02). Under the conditions specified in Fig. 3, copper(I1) was extracted quantitatively (more than 99 per cent.) and zinc(I1) almost quanti- tatively (98 per cent.) by a single extraction. It is therefore necessary to carry out a second extraction for the quantitative extraction of zinc(I1). 4 c $ 3 m - + H Q 2 0) -J 1 6 7 8 - Log [H'] Fig. 5. Extraction characteristics of zinc(I1) - 1,5-diphenylcarbazone com- plex.[Zinc(II)] 1-76 x M; and [NH,Cl] 0.1 M. (a), -Log [H+] 8.90; and (b), -log [H2DN]Org 3-40 The extraction characteristics of copper(I1) and zinc(I1) complexes are presented in Figs. 4 and 5 , respectively; in each instance acoeff was calculated by using the formation constants summarised in Table I with suitable modification for some of the results due to the change in ionic strength. It is evident from Figs. 4 and 5 that linear relationships exist for both copper(I1) and zinc(I1) between log DMf + log acoeff and log [H+], the slope of which is 2, as expected from equation (18). Linear relationships also occur for both metal ions between log D,' + log acoeff and log [H2DNIorg with a slope of 2 (n = 2). Therefore, the extraction equilibrium [equation (lo)] and extraction constant as defined in equation (19) can be simplified as follows- M2+ + 2H2DN org + M(HDN)z org + 2H+ KeqNovember, 19731 and AND ZINC(I1) WITH 1,5-DIPHENYLCARBAZONE 809 .... . . (19a) .. .. . . (20a) Values of Keq for both copper(I1) and zinc(I1) were calculated from the results presented in Figs. 4 and 5, respectively, and they are summarised in Table 11. Values of K e , were also calculated from the values of Keq and KexL, and they are also summarised in Table 11. TABLE I FORMATION CONSTANTS USED FOR THE CALCULATION OF Olcoeff" Ligand r L i Cation Term OAc- NH, OH- H+ pka 4.65 9-37 13.80 1-3 2.27 4.4 4.61 - 2.1 - 7.01 14.4 - 9-06 15.5 Zinc(I1) Log B1 Log B 2 Log Bs Log 8 4 Results were for p = 0.1 except with the hydroxo compIexes of copper(I1) and zinc(II), which were for p = 0 and were converted into p = 0.1 in the usual manner when calculations of ctcoeff were carried out.For acid dissociation of ligands, the acid- dissociation constant, pka, was cited instead of the formation constant. Copper(I1) and zinc(I1) complexes with 1,5-diphenylcarbazone [Cu(HD,), and Zn(HD,),, respectively] thus extracted into isobutyl methyl ketone have their absorption maxima at 530 and 520 nm, respectively, and the very large values of molar absorptivities of 7.6 x lo4 (530 nm) for the copper(I1) complex and 5.8 x 104 (520 nm) for the zinc(I1) complex suggest that the extraction into isobutyl methyl ketone of trace amounts of copper and zinc as their 1,5-diphenylcarbazone complexes can be utilised for their spectrophotometric determination.TABLE I1 EXTRACTION CHARACTERISTICS OF COPPER(II) AND ZINC(II) Composition Absorption maximum, Molar absorptivity, Metal of complex h,,X. /nm Emax. Log Keq Log Kex - 1*11* -7.10* -7.13t } 15*' -1.lOt } 21*2 cu CU ( HDN) 530 7-6 x 104 Zn Zn(HDN), 520 5.8 x 104 Log KexL = 11.15. * Results obtained from the relationship between log DM' + log acoeii and t Results obtained from the relationship between log DM' + log a c o e f f and log [€I+]. log [H,DN]org.810 EINAGA AND ISHII Balt and van Dalen5 reported that copper(I1) and zinc(I1) complexes with 1,5-diphenyl- carbazone have the following characteristics: ,a = 0.1 (NaC10,) at 20 to 22 “C; log Keq = 1.27 for copper(I1) and -6.76 for zinc(I1) ; Amax., 530 nm for copper(I1-) and zinc(I1); and EAmax., 6.8 x lo4 for copper(I1) and 3.7 x lo4 for zinc(II), which were determined by using a toluene - water system. By using these results for log Keq, and partition coefficient (PL = 39) and acid-dissociation constant (Kal = 2.9 x 10-9),5 the values of log K,, were calculated according to equations (9) and (ZOa) to be 21.5 for copper(I1) and 13.5 for zinc(I1).Fairly good agreement can be seen between the results found by Balt and van Dalen5 and those obtained in the present work for log Kex, although the partition systems used were different in the two instances. Some differences in these results, especially in the value for log Kex for zinc(II), and also in other characteristics (for example, molar absorptivity) might be partly due to the differences in the nature of the extraction systems toluene - water and isobutyl methyl ketone - water, which should, however, be elucidated in future from the standpoint of solution theory. The copper( 11) and zinc(I1) complexes showed no photochemical change under ordinary laboratory lighting conditions and are considered to be stable unless exposed to intense ultraviolet radiation. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. REFERENCES Sandell, E. B.. “Colorimetric Determination of Traces of Metals,” Third Edition, Wiley-Inter- Balt, S., and van Dalen, E., Analytica Chim. A&, 1961, 25, 507. science, New York, 1959, p. 178. f , Ibid., 1962, 27, 188. I Ibid., 1963, 29, 466. , Ibid., 1964, 30, 434. -- -- * -- Ueno, K., “Complexometric Titrations (Kireito Tekiteiho),” Nankodo, Tokyo, 1960, p. 260. Krumholz, P., and Krumholz, E., Mh. Chsm., 1937, 70, 431. Sandell, E. B., op. cit., p. 144. Ringbom, A., “ Complexation in Analytical Chemistry, ” Wiley-Interscience, New York, 1963, Received April 27th, 1973 Accepted Jwne 8th, 1973 -, 09. Cit.. p. 233. p. 293.

ISSN:0003-2654    

DOI:10.1039/AN9739800802

出版商:RSC    

年代:1973

数据来源: RSC