ISSN:0003-2654    

DOI:10.1039/AN95883FX013

出版商:RSC    

年代:1958

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95883BX015

出版商:RSC    

年代:1958

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95883FP051

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

THE ANALYST SVCLASSIFIED ADVERTISEMENTSThe rafefor classified adzwfkemenfs is 5s. a line (or spaceeyniuulenl uf a line), with a n exlra charge uf Is. for lhem e uf a Box Sumber. Semi-displayed classifiedRESEARCH CHEhllST with expcriciicc in riirtallurgicalA a n a i y s i s and an a 1 ysis of gasfs iii inctals, is rrqiiirrd b y theRritibti \Vilding I<cst,arch Association a t Abington nrarC'aliilJridgt.. Some txpvricncr of sp"ctroscopy also an advan-tag<'. l h i , work covi'rs a wirlv rangc of techniques andiiiatcrials including titaniuin, zirconium, copper, stccl and:iliiiiiininiii alloys. Opportunitirs to pursui' indrpmdciitresvarch, or to collahorat(, with othrr invistigators, in;iddition to takingchargrof wcllrquippcrl chcniical laboratorydoing analysis work for a11 rcsrarch projects.Apply with fullparticiilars of agv, qualifications, and cxpcrimci., to thc?Sccrctary, B.W.K.A., %!I Park Crisctmt, London, \\'.I.THE GEKEIIAL ELECTRIC CO>ll'.lSYLIhIITSD\VITTOS, BIRMISGHAM, tiS .4SAI,YTICAL CHEMIST who prefersvarifty of intrrrsting work ratht,r thanspccialisiiig in a particular field or carryingoii t routin? procedures, is required for problmisconnt~tcd with tlir chcmistry of rriattrialiu s d in ekctrical tngincvring. The positionis a r<.bponsiblv onc m d calls for adapt.ibrlity:ind invcntivrn(=,s.Applicants should possrss a dr.gry orA.R.I.C. an(l havc some analytiral cxpcrimc?..-\pplications giving details of age, qualifica-tions am1 cxpt,ri(mc? should be wilt to th?Staff Managw, Thv Gi.nr,ral Eii,ctric Co.Ltd.,tyitton, Birriiinghaiii, ti.wi[Jloyiiitmt or ( h ) on trriiporary tcriiis. Salary scale(including inrlncruit~~t addition) ( a ) L;i4 rising to E1,ZX.I ayear, or ( h ) &U:34 rising to jl,38ti a yi'ar with gratuity at rat?L l l i r i / L l $ i a year. Comnencing salary according t o quali-fications antl txpcrimce. Outfit allowanw &60. Prcepassages for oflicr,r and will,. .Assistancr: towards chiltlrm'spassage's and grant tip to Ll.XJ annually towards maintenancein { J . K . Lil,cml lravi: on full salary. Candidate iiiust beA.I.S.T. or cquivalcnt arid have good knnwli,dge of botanyand cheniistry with a sound grounding in physics and inathi,-iiiatics 'Training in analytical work or expmienrr in r~xprri-nirntal fir111 of biological research an advantag<,.Frmnlccari(lid,it<.s iiiust be singlc Writ? to the Crown Agmts,'4, Millbank. London, S.\V.l. State, aai', nanic' in blockICtt(.rs, full qualifications and expt.rimct. and quotc\5Z:JC/442iO/AAD.~ ~~~~~ -~ ~~~'IXE PATSTOCK M.ARl<k:'l'ISG CORPORA?'ION L l D .XPANDIXG suhsidiarv group handling and procrssingEaninbal by-products rcquiws qualitiid chemist. Thia 15a pr<rgrr,s.;ivc position \rith prospects of advanccrnrnt to ainure srnior appointnwnt. Dutics will bc primarily con-c t ~ n c d with analysis arid quality control of cxistirig productsantl assisting iiranagrincnt in improving prrsrnt handling1111 thods. Dutics will also include, krrping abreast of tvch-nical dt~urlopnirnts i n the ariiiual by-products firld.Appli-cants should havi. an Honours Dt,grw in Chemistry, withknuwkdgi. of bactr,riology, and havv had at lrast five yeari'indiistrial rxpvriencr. with a coniinc~rcial organisation. Theccmiinf~ncing salary will bc acrording to qualifications and willtx. suhitct to annual rrvicw. Particination in the PtmsionSchi?n~'~. Applications shouki be ima'dc to th,. 1'wsonni.lKinager. F.1t.C. Ltd., Agriculturv Housr, 25/31, Knights-txklgt., S.\V.l.COUSTY BOROUGH UP SOC'fH SHIELDSPPLICA'I'IONS art. invitrd from suitably qualifirtlA1nmons for thv appointment of Part Titlie Public Anaiystnnrlfr the Food and h u g s Act, 1Y.G, and Part 'l'imr Agri-cultural Analyst u r n l i ~ thi, Ft~tilisers aiid E'r,rding Stuffs Act,1326 Tha scak of fws payahlc will be in accordanas Withtht, Joint Nrgotiating Committrc for Public Analysts.Applications should reach the undcmign<d by 2nd Way, 1 ' J hI<.s. Yoosc,(;I.AXO L.mor<r\mtur;s LTD.rcquirc1'N'O ANALYTICAL CHEMISTSat thrir factory a tBARNARD CASTLE(Co. Durham)\I hich is cmgag<,d on the nianufacturc.filling and packing of antibiotics.I'PLICAS'TS i i i i i s t posscss a n honoursAilc,gri,c in Chemistry or thc Associateshipof lhr Koy;il Inatitutt, of Lhwnstry. TheyIitust have had rxpc,rii.ncc i n thr iise ofiiiodc-rn physical instrnincnts. A d d d rccoiii-iiimdations would I)? fariiiliaritv with thrprol)lt.iiis and rcquirvrncnts of thr pharma-cvutical industry arid thc provtd ability toorganist, thc work of a gronp.Onc post issmtabk for a iiidn; thr srconcl calls for theservicrs of a wonian.4 starting salary in the rang? of jS1)iI to& l , f i I i ( i is visisalisrd. It would bi, progri,ssivr.'1'11~ timiis of srrvicr which go with the postarc lilx,ral and includc a Pmsion Schi,inr aridthu opportunity to participate in thr Coiii-paiiy's profit;ibility.Apphcatioiis should be Addrc,ssid to the,--Prrsonnrl Manager,Glaxo 1,aboratorics Ltd.,Greenford. ?diddlrscx.Town Hall,South Shic,lds.T o m Clerk.~~~~ I ~ BKITISII IKDUSI'RIAL PLASTICS LIII'I'ED('HIFF CHF\IIS'f ! B.I.1'. Ch~iiiicals Ltd. invitr applications for ~~~~ ~ ~~~ ~graduate chemist (ag? u p to 311 ymra) with several yvars 1Sorth Midlands area, to takr chargr of several new lahora- ,tor1cs concernrd u.ith the analysis of an important rawinaterial connectid u,ith the nuclear powrr ilrdustry.Hewill be rvspoii.itrlr for guiding a tram of assistants, and willbe givrn the opportnnitv to ndvicc on thr lay-out andsvttingup of nrw laboratorit -.This appointnitnt provides a unique opt-ning in this ficldIposts a5 Kescarcli Chemists in~thrirrsearchtalmratories at Oldlwrv Birmingham. hliiii-11111111 qiialifications-Hononrs Degree or.-\.R,I,C. Acadrmic or industrial rrsearchexpeririici, is drsirablt-. l'hc, vacanclrs in-clude one for an analytical cheiiiist to drvdopnew niethods of analyhis. 'I'hr con>pany~iiannfactures iiioulding pow-dcr, and urea,riielaniiiic and polvestvr rebin,.Interestingwork is offcr~rl with auod prospects aridattractive cruiditions of etiplo).inrnt in- . .. - . . . and offers a four fiaurr salary for this position.('on1ril)utory prnsion and free lifr assurance schmir inopc,ration.Apply with full details of past experienci,, erlrication andqualifications. marked Private and Confidrntial, to Rrf. QC/S.Box No. 3!161, the Analyst, 47, Grrsham Street, London, E.C.2.cludrrrg a gi'nf'roiis t'enilon antl Life Assur-ance Schrini,. .Applications shortld br madein writing to:Prrsoiinel Manager. B.I.1'. Cheinicals l.td., Oldbury,Birniirighnibii v i THE AKALYSTASALTTIC.AL LHEXlISIV.AC4S('\' eyi,tc in the Analytical Di\ramu of tA#c>earch Orgarribation fix Sriiitli 'Y.Sephew AasociatCoiiipariies 1-td., iiiariiifac tiirers of biirgiciil dressings, adhesibaidaxes and plasters, pl.iatic iiliris, rosiitetic. toilet artliic2l phaririaceiitical preparatioIih. Thr vwh. whichprogre,>ive in character, is eoncernpd with the inwitigatioo f sprciticationc and test iiiethods relating to the I :Imterials, intrrmediatec and bnal prodirrts iiiade by r i i e i ~ ~ h<>f the Group. The i i i i i i i r i r i i i i i qualifications art' a LniversiIkgrrr or the equivalent qiialihcations of the In,tituteCheiiiiitry. Sotlie induatrial expi~rieuce 15 (leairable L u t nrsseiitial. Salary will be according to age and cspericn(Write to: The Technical Secretary, Siiiith CY l q > l > e v ResearLtd., Huiisloii I.ahoratoric~, Ware, Herts..lSALYTICAL CHEMISTSLLOYDS RESEARCH LTD.annoiincc that the following mctallo-chromic indicators for complcxometricanalysis have now been addcd to therange of indicators made in theirlaboratorics :SYLESOL OR.ASGE>I E TI I Y LT I I Y3101, HI I. I<-411 equiri?s lo:LLOYDS RESEARCH LTD.,CLERK GREEN, BATLEY, YVRKS.HEFFER'SO FCAMBRIDGEpublish from time to timecatalogues and lists of bookson various subjects, andannouncements of individualnew books of special impor-tance. Let us add yourname to our mailing list.W. HEFFER & SONS, LIMITED3 & 4 PETTY CURY, CAMBRIRG

ISSN:0003-2654    

DOI:10.1039/AN95883BP063

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

APRIL, 1958 THE ANALYST Vol. 83, No. 985 PROCEEDINGS OF THE SOCIETY FOR ANALYTICAL CHEMISTRY ORDINARY MEETING AN Ordinary Meeting of the Society, organised by the Physical Methods Group, was held a t 7 p.m. on Wednesday, April Znd, 1958, in the meeting room of the Chemical Society, Burlington House, London, W.l. The Chair was taken by the President, Dr. J. H. Hamence, MSc., F.R.I.C. The subject of the meeting was “Gas Chromatography,” and the following papers were presented and discussed : Introductory Talk by C. S. G. Phillips, M.A. ; “,4pplications of Gas Chromatography in the Halogenated Hydrocarbon Field,” by R. Hill, B.Sc., A.R.I.C. ; “Gas Chromatography in the Petroleum Industry,” by D. H. Ilesty, B.Sc. NEW MEMBERS ORDINARY MEMBERS Philip Atherton, A.R.I.C., A.R.T.C.S.; Thomas William Brandon, BSc.(Lond.), F.R.I.C.; Chuni La1 Chakrabarti, B.Sc. (Calcutta) ; Isaac Hodara, M.Sc. (Jerusalem) ; Edward Albert Hontoir, B.Sc., A.I.M. ; Jeffery Michael Llewellin, B.A. (Cantab.) ; Fred Ridgway, B.Sc. (Lond.) ; Allan Neal Smith, M.Sc. (Dunelm.), A.R.I.C. ; William John Williams, B.Sc., Ph.D. (Lond.). JUNIOR MEMBE~~ Terence Dwyer, A.R.I.C. DEATH Arthur Gordon Francis. WE record with regret the death of SCOTTISH SECTION AN Ordinary Meeting of the Section was held at 7 p.m. on Friday, February 28th, 1958, in the George Hotel, George Street, Edinburgh. The Chair was taken by the Chairman of the Section, Dr. Magnus Pyke, F.R.I.C., F.R.S.E. A lecture on “The Solvent Extraction of Metal Complexes” was given by F. J. C. Rossotti, B.Sc., M.A., D.Phi1. MIDLANDS SECTION THE third Annual General Meeting of the Section was held at 6.30 p.m.on Tuesday, March 4th, 1958, in the Mason Theatre, The University, Edmund Street, Birmingham, 3. The Chair was taken by the Chairman of the Section, Dr. R. Belcher, F.R.I.C., F.1nst.F. The following appointments were made for the ensuing year :-Chairman-Dr. R. Belcher. Vice-Chairman-Dr. S. H. Jenkins. Hon. Secretary-Mr. G. W. Cherry, 48, George Frederick Road, Sutton Coldfield, Warwickshire. Members of Committee-Messrs. A. S. Beidas, H. E. Brookes, W. T. Elwell, J. R. Leech, W. M. Lewis, Dr. Alison M. G. Macdonald, Messrs. R. Sinar and J. H. Thompson. Miss M. E. Tunnicliffe and Mr. H. J. Alcock were re-appointed as Hon. Auditors. AN Ordinary Meeting of the Section was held at 7 p.m.on Thursday, March 13th, 1958, in the Gas Showrooms, Nottingham. The Chair was taken by the Chairman of the Section, Dr. R. Belcher, F.R.I.C., F.1nst.F. 185 Hon. Treasurer-Mr. F. C. J. Poulton.186 PROCEED tNGS p o l . 83 The following paper was presented and discussed : “The Analytical Chemistry of Synthetic Detergents,” by W. B. Smith, BSc. WESTERN SECTION A JOINT Meeting of the Section and the South Wales Section of the Royal Institute of Chemistry was held a t 6.30 p.m. on Friday, Marc:h 14th, 1958, at the Chemistry Department Lecture Theatre, University College, Singleton Park, Swansea. The Chair was taken by the Chairman of the Western Section, Mr. S. Dixon, M.Sc., F.R.I.C. A lecture on “Sequestration and its Analytical Applications” was given by R.L. Smith, B.Sc., Ph.D. MICROCHEMISTRY GROUP THE Fourteenth Annual General Meeting of the Group was held at 6.30 p.m. on Friday, February 7th, 1958, in the meeting room of the Chemical Society, Burlington House, London, W.l. The following Officers and Committee Members were elected for the forthcoming year :-Chairman- Mr. D. F. Phillips. Hon. Secretary-Mr. D. W. Wilson, Department of Chemistry, Sir John Cass College, Jewry Street, Aldgate, London, E.C.3. Hon. Treasurer-Mr. G. Ingram. Members of Committee-Mr. E. Bishop, Mrs. D. Butter- worth, Messrs. R. Goulden, J. A. Hunter, C. Whalley and C. L. Wilson. Dr. L. H. N. Cooper and Mr. H. Childs were re-appointed as Hon. Auditors. The Annual General Meeting was followed by an Ordinary Meeting of the Society, organised by the Group. The Chairman of the Group, Mr.D. F. Phillips, F.R.I.C., presided. Vice-Chairman-Mr. F. Holmes. PHYSICAL METHODS GROUP THE sixty-first Ordinary Meeting of the Group was held at 6.30 p.m. on Tuesday, February 18th, 1958, in the meeting room of the Chemical Society, Burlington House, London, W.l. The Chair was taken by the Chairman of the Group, Mr. R. A. C. Isbell, A.1nst.P. The subject of the meeting was “Solid-sou~:ce Mass Spectrometry” and the following papers were presented and discussed : “Solid-source Mass Spectrometry-Instrumentation,” by G. H. Palmer, B.Sc., A.1nst.P. ; “Solid Analysis Using a Spark-source Mass Spectrometer,” by R. D. Craig, R.Sc.; “Stable-isotope Dilution Analysis,” by R. K. Webster, B.A. (see summaries below).SOLID-SOUIICE MASS SPECTROMETRY-INSTRUMENTATION MR. G. H. PALMER described the techniques in mass spectrometry for the isotopic analysis of elements available as solids having very low vapour pressures. A com- parison was made between furnace and thermal-emission ion sources and a description was given of how the latter source could be used in conjunction with a high-sensitivity ion collector to analyse sub-microgram amounts of material. The causes of error in the measurements were examined and methods for minimising these errors were described. The main features were given of a modern instrument designed for rapid routine analysis. SOLID ANALYSIS USING A SPARK-SOURCE MASS SPECTROMETER MR. R. D. CRAIG described a spark-source mass spectrometer, type M.S.7, designed according to the geometry of Mattauch for use with either photographic or electrical detection, which had been developed for the general analysis of solids.The instrument had been widely applied to impurity analysis with photographic plates as detectors. An exposure range of a.t least lo6 to 1 could be attained, and the sensitivity was such that impurities down tcl the level of 0.01 p.p.m. could be detected in favourable cases. The use of the technique for impurity analysis was indicated in four main fields of application : (i) general metallurgical problems (e.g., steels; nimonic alloys), (ii) pure metals (e.g., aluminium), (iii) reactor materials (e.g., carbon) and (iv) semi-conductors (e.g., silicon).April , 19581 0 BIT UARY 187 STABLE-ISOTOPE DILUTION ANALYSIS MR.R. B. WEBSTER said that the method of stable-isotope dilution had been used as early as 1935 for hydrogen determination, but for a number of years it had been restricted to the few elements for which enriched isotopes were available. The develop- ment of solid-source mass spectrometers and the use of electromagnetic separators to prepare enriched isotopes had permitted a large expansion of the method in the last ten years. The author described the basis of the method, its scope and its limitations. The method was very sensitive, and limits of detection in the range lo-* to 10-l2 g were feasible for many of the elements. It was also very specific, and one of its chief features was the nearly complete freedom from interference problems; as a result it was one of the more accurate general methods of trace analysis. The main drawback was contamination, either from reagents or from the atmosphere, and it was often this quantity that determined the sensitivity for a particular element. The value of the method seemed to lie in the determination of trace concentrations, or higher concen- trations when only very small samples were available; it could also provide standards for other methods of analysis. BIOLOGICAL METHODS GROUP AN Ordinary Meeting of the Group was held at 6.30 p.m. on Wednesday, February 19th, 1958, in the restaurant room of “The Feathers,” Tudor Street, London, E.C.4. The Chair was taken by the Chairman of the Group, Dr. S. K. Kon, F.R.I.C. A discussion on “The Stage at which a Biological Assay can be Replaced” was opened by \IT. 1.. bl. Ycrry, O.B.E., M.11.

ISSN:0003-2654    

DOI:10.1039/AN9588300185

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

April , 19581 0 BIT UARY Obituary JULIAN LEVETT BAKER JULIAN LEVETT BAKER, who edited The Analyst from 1907 to 1920, died at his home in Xaidenhead on January 29th, 1958, at the age of 84. Julian Baker was born in London on February 24th, 1873, and educated a t the City of London School, to which he was unable to return after the Easter vacation of 1888, as he had been in contact with a case of scarlet fever. This proved actually to his advantage. Tcnowing that Julian was set on becoming a chemist, his father consulted R. J. Friswell, then managing chemist to the old dyestuffs firm of Brooke, Simpson and Spiller, and Friswell advised having the boy coached for the next entrance examination to Finsbury Technical College, where Meldola, who had formerly been on Friswell’s staff, had recently succeeded L4rmstrong as Professor of Chemistry.The boy passed in, as he would not have done had he remained at school another term. At Finsbury in the eighties, the chemical students had not only their professor to look to, for Meldola had on his staff Streatfeild and Castell-Evans. What the students thought of Streatfeild is shown by the institution of the Streatfeild lectures. If Castell-Evans was less spoken of, he was not forgotten, as was shown by M. 0. Forster in the course of his 1938 Streatfeild lecture. M. 0. Forster was a man of Baker’s year and remained throughout his life one of the most intimate of Baker’s friends. G. T. Morgan was Baker’s senior by a year at Finsbury, but was another life-long friend. It was during Baker’s time at Finsbury that Meldola invited E.R. Moritz, the well-known consulting brewer, to deliver five lectures on brewing, lectures subsequently embodied in a printed book and later translated into German. Young Baker was kept at Finsbury for three years, the normal course in those days being of two years only, but he had been very young at entrance and was still under nineteen when he was appointed assistant chemist to the London Beetroot Sugar Association, under A. R. Ling, who subsequently became Professor of Brewing at Birmingham. Association with such a man as Ling was another piece of good fortune. Ling had been one of Armstrong’s earliest pupils at Finsbury and Armstrong kept in touch with such of his old students as could be persuaded to engage in some research, so far as their other duties permitted.Thus 4rmstrong would drop into the laboratory of the Sugar Association and advise these young men as to what they might usefully do. So began that long intimacy with Armstrong that has led the writer of another obituary to state that Baker was one of Armstrong’s students.188 PRIBIL RECENT DEVELOPMENTS I N CHELATOMETRY [Vol. 83 That he never was, but he was one of the people the old man welcomed even when helay a sick man. At first Ling and Baker published work on the halogen derivatives of quinone, but their interest lay increasingly in the degradation of starch. They published one or two papers on this subject, but were not encouraged to work in this field, which some of their seniors thought should be reserved to Horace Brown.In 1900 Baker, who had been for some time chief chemist to the Sugar Association, did what he had long hoped to do. He gained entrance to the brewing industry, being appointed chemist (at first, sole chemist) to Watney, Conibe, Reid and Co. Before taking up this appointment, he spent some months in the laboratory of Adrian Brown, then Professor of Brewing at Birmingham, and thus began another life-long friendship. His duty to his Company permitted him to publish many papers in the chemical and brewing journals. His services to his Company may be judged by outsiders by the facts that he deferred his retirement until after the war and that for many weeks he and his chairman, a near neighbour and as old as Baker, drove daily between Maidenhead and London when railway services could not be depended on.From 1920 until 1948, he edited the Journal of She Institute of Brewing. Baker had been a Member of the Council of the Chemical Society and of the Institute of Chemistry as well as a Vice-president of the Society of Chemical Industry and of the Institute of Brewing. As Honorary Secretary of the London Section of the S.C.I. in 1905, he was largely responsible for the success of the (for those days) ambitious programme for the Annual Meeting of the Society in London. Members went by launch to Woolwich, to be shown over the Arsenal, all the men of the party in frock coats and silk hats. Baker was one of the few Finsbury men to be elected a Fellow of the City and Guilds of London Institute. Another honour that fell to him and gave him pleasure was the award of the Horace Brown Medal of the Institute of Brewing. Aged 84, he would sometimes say, after visiting his London club, “I hardly saw a man I knew.” But a generation ago, among a crowd of chemists, the writer remembers reflecting that “Baker seems to know everyone here and everyone knows Baker.” No one who saw Baker at work in his laboratory, or for that matter in his garden, which he loved, can have failed to note that he had very nice hands. In 1948 he married Mrs. Catherine St. Paul, who died in 1956. Those were days. He married Eveleen Daniels in 1901 ; she died in 1945. He is survived by a daughter and two sons. G. C. JONES

ISSN:0003-2654    

DOI:10.1039/AN9588300187

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

188 PRIBIL : RECENT DEVELOPMENTS IN CHELATOMETRY [Vol. 83 Recent Developments in Chelatometry* BY RUDOLrF PRIBIL (Analytical Laboratory of the Czechoslovak Academy of Sciences, Jilska 16, Prague 1, Czechoslovakia) LESS than ten years have passed since Professor Schwarzenbach of Zurich surprised the analytical world with his volumetric determination of calcium and magnesium.l As is well known, this was based on the use of a standard solution of disodium dihydrogen ethylene- diaminetetra-acetate-a reagent now known by a variety of names, the commonest being “Complexone” or EDTA. As indicators for these titrations, he suggested Eriochrome black T and murexide. Schwarzenbach not only thorclughly studied the physico-chemical properties of the reagent and its complexes, as well as of a number of related compounds, but also laid the foundations of a new branch of volumetlric analysis-complexometry.The extent to which this unique new method underwent development and gained acceptance within a very short time is without parallel in the history of analytical chemistry. To-day, both the principles and the experimental techniques of complexometry are so widely known that it will surely be unnecessary for me to deal with these aspects. I have in mind the number of cations (or anions) that can be determined by this highly elegant method. Practically the whole Periodic System comes within its scope-except, naturally, for the rare gases, some few elements of the first, fifth and sixth groups, and beryllium, boron and In a certain sense, complexometry is now at the peak of its development.* Presented at the meeting of the Society on Tuesday, November 5th, 1957.April, 19581 PRIBIL : RECENT DEVELOPMENTS IN CHELATOMETRY 189 silicon. This very universality, however, on the other hand, seriously hampers attempts to determine a given metal in a more complex solution-a common requirement, for instance, in the analysis of alloys, ores, minerals and many similar materials. Many theoretical analysts regard the universal nature of the method as a serious drawback, and they belittle its practical significance by pointing out that any complex- forming reagent might be used in a similar way, by reference to the obsolescent theory of functional analytical groups, and so on. However, it would be pointless in this lecture to polemize with those holding such views.The main aim of complexometry at the present time is to find ways and means of carrying out complexometric titrations with the maximum of selectivity. The problem is best dealt with if we analyse the factors that may affect, or prevent, complex formation by individual metals in solution. The most important of these factors will no doubt be pH and the presence of strongly complex-forming agents in the solution. EFFECT OF pH ON COMPLEX FORMATION BY EDTA The stability of complexes formed by EDTA is expressed by their stability constant, defined as follows- (The ionic charges are omitted here for the sake of simplicity.) The stability constants (or complexity constants) , many of which have been carefully measured by Schwarzenbach and his school under precisely defined conditions (for instance, in decinormal potassium nitrate solutioiis), are a good guide in comparing the relative stability of various complexes.The most unstable complexes are those of the alkaline-earth metals, with pK values hardly reaching 10. Next in the series are the complexes of manganese and bivalent iron (pK = 14). For the majority of metals, the pK values lie between 16 and 19. The most stable complexes appear to be those of bivalent mercury, with a pK of 21, scandium and thorium (pK = 23), and indium, ferric iron and tervalent vanadium (pK = 26). The concentration term, [Y], in equation (1) is only identical with the concentration of free complexone in alkaline solution of a pH greater than 12, where ethylenediaminetetra- acetic acid is practically fully dissociated to the quadrivalent anion Y4-. At lower pH values, there will be an equilibrium between the individual ionic species formed by the progressive dissociation of EDTA so that the real concentration of Y4- ions will be much lower than the concentration of free complexone. This must be taken into account in calculating the stability constants at any given pH.The relation between the concentration of the ion Y4- and the concentration of free complexone in its dependence on pH is the so- called ccH function- The measured stabilities vary very greatly. . . B y dividing the stability constants defined by equation (1) by the value of aH we get the so-called pH-dependent stability constants. (The calculated values of aH for various values of pH are shown in Table I.) If we take it as established that the lowest stability constant that permits complexometric determination is 108, then we can, by applying the aH function, readily derive the lowest pH value at which a given titration will still be practicable.Ringbom has plotted these values for individual cations in a curve that we shall refer to as Ringbom’s curve. It not only permits us to estimate the lowest pf-1 at which a given cation can be determined, but also to what extent any other cation will interfere with this determination. As a corollary, it also demonstrates that there are combinations of cations that will not be titratable in presence of each other however carefully the acidity is adjusted and maintained.The theoretical interpretation of Ringbom’s curve is not, of course, precise. For instance, his calculations do not take into account the initial concentrations of the cations or the sensitivity of the indicator. However, the curve is useful for the practical worker. From what I have said it might appear that the theory of complexometric titration is completely settled and that any complexometric problem might be solved by purely Their course is analogous to that of the function aH and is shown in Fig. 1. Ringbom’s curve is very instructive.190 PkIBIL RECENT DEVELOPMENTS IN CHELATOMETRY [Vol. 83 mathematical considerations. The pH is not the only factor influencing the “useful” stability constant. There is a large number of further effects, which, with certain misgivings, we include in a further factor /?.This covers, for instance, the ionic concentration o’f the solution, the effect of less polar solvents, the influence of competing equilibria involving the component ions of the complex and other effects. In practice these effects are so closely interconnected that it would be quite a waste of time to attempt their exhaustive physico-chemical treatment. For this reason, the effect of the factor /3 as a whole is evaluated purely empirically at present and is expressed in the accuracy of the results, the description o f interfering effects, concentration limits for the ion being determined and so on. TABLE I Unfortunately, the situation is not so simple as that. CALCULATED VA:LUES OF Q~ PH 0.0 0.4 0.8 1.0 1.4 1.8 2.0 2.4 2-8 3.0 3-4 3.8 4.0 4.4 4.8 5.0 UH 21.18 19.59 18.0 1 17-20 15-68 14-21 13-52 12-24 11.13 10.63 9.71 8.86 8.04 7.64 6.84 6-45 PI3 5-4 5.8 6.0 6.4 6.8 7.0 7.5 8.0 8.5 9.00 9.50 10.0 11.0 12.0 13.0 14.0 a1-I 5.69 4-98 4.65 4.06 3-56 3-32 2.78 8-26 1-77 1.29 0.83 0.45 0.07 0.00 0.00 0.00 [Me Yl [Me] [YI log K = log .- Fig.1. Ringborn’s curve Let us return now for a moment to Ringborn’s curve. As I have already pointed out, this curve indicates the pH that must be chosen to eliminate interference by as many other cations as possible. However, a further practical requirement is the availability of an indicator that will give a good end-point at the chosen pH. Now, over the past three years much attention has been given to the question of com- plexometric indicators.More than one hundred #compounds have been proposed for service as metal indicators in more or less specific instances. These compounds differ widely notApril, 19581 PfiIBIL : RECENT DEVELOPMENTS I N CHELATOMETRY 191 only in their chemical structure, but even in their mechanism of action. They include a number of well known and simple compounds that form complexes whose colour can be ascribed to the deformation of the cation; examples are the reaction of salicylic acid or tiron with iron. A further group of compounds may form coloured precipitates or colloidal solutions, or give rise to turbidity with certain cations or groups of cations. The largest group, however, are dyes that form soluble complexes differing in colour from the free dye; this group now includes also the “classical” indicators, Eriochrome black T and murexide; for this type of compound we have introduced the term “metallochromic indicator.” By reviewing the properties of these compounds we have arrived at certain conclusions regarding the structural pre-requisites of metallochrome action ; these considerations in turn have stimulated the synthesis of a number of new compounds that have already proved themselves to be excellent indicators, with brilliant colour changes at the end-point.Our conclusions can be summarised in the following points- All metallochromic indicators behave as acid - base colour indicators, under some conditions at least, even though they may not be used as such for one reason or other. In addition, however, the metallochromic indicators have marked complex-forming properties, which are entirely absent in the normal run of acid - base indicators.More- over, the complex-forming grouping must be attached directly to the conjugated system of the dye. We further observe that the change in colour induced in a metallochromic indicator on formation of a complex lies within the limits of the acid - base colour change. This indicates a fundamental relation between protonation or dissociation on one hand and formation of the complex on the other. Our conclusions regarding the mechanism of action of metallochromic indicators, briefly speaking, give the following picture- The colour changes of acid - base indicators are due to changes in the electronic structure of the dye system. If the auxochrome responsible for such colour changes in addition also forms part of a chelating group, then formation of a complex will lead to the same type of change in the electronic structure and hence also to the same kind of colour change.This analysis indicates the points that should be borne in mind in searching for, or designing, new metallochromic indicators. Consideration along these lines led us to the conclusion that a dye system eminently suitable as a basis for the synthesis of metallochromic indicators was that of the sulphonphthalein and phthalein type; some azo dyes have also been examined in this respect. A suitable complex-forming group seemed to be the imino- diacetic acid grouping, which is in accord with Schwarzenbach’s experience.Even the intro- duction of the aminoacetic acid (glycine) grouping has been found to confer marked metallochromic properties on acid - base indicators. SOME NEW INDICATORS AND THEIR COLOUR CHANGES Perhaps I might now briefly mention some of the new indicators and demonstrate their end-point colour changes. XYLENOL ORANGE- 3 : 3’-Bi~-di(carboxymethyl) aminomethyl-o-cresolsulphonphthalein (xylenol orange, I)2 s3 is obtained by the condensation of cresol red with formaldehyde and iminodiacetic acid. In acid solution up to about pH 5-6 to 6 it is yellow; in alkaline solutions it has a deep reddish purple colour. The colour transition at the end-point is extremely sharp, probably better than that of any other indicator proposed so far. The stability of the individual metal - indicator complexes is, of course, dependent on the acidity, so that a certain pH range must be maintained for each metal.So far, titrations with this indicator have been described for bismuth at pH 1 to 2, thorium at pH 2.5 to 3.5 and for lead, zinc, cadmium, lanthanum and scandium at pH 5 to 6, most conveniently in solutions buffered with hexamethylenetetramine. Excellent results have also been obtained in the titration of mercury: and an indirect method is available for aluminium5 based on the back-titration of the excess of complexone with zinc, lead or thorium salts. Kinnunen and Wennestrand6 have shown that tin can be determined in its alloys with copper by back-titration with thorium, the copper being screened with thiourea. Its use as an indicator is therefore confined to the acid pH region.192 PgIBIL : RECENT DEVELOPMENTS I N CHELATOMETRY [voi.83 The same authors, in unpublished work,' have allso shown xylenol orange to be an excellent indicator for the indirect complexometric determination of iron, nickel, cobalt, copper, quadri- valent uranium and vanadium, and tervalent chromium, indium, gallium and thallium. For the determination of titanium they recommend back-titration with a thalliumIl1 salt at pH 4.4 to 6 , and for aluminium back-titration *with zinc acetate at pH 5 to 6 in ammonium acetate solution. Nickel and cobalt can be determined in presence of each other by a rela- tively simple procedure.s Kinnunen has also developed an indirect determination of phos- phate' based on the precipitation of thorium phosphate with a known amount of thorium nitrate and back-titration of the excess of thorium with EDTA to xylenol orange; if copper is screened with thiourea the method can be use'd for the analysis of phosphor bronzes.CH, CH, By suitable adjustments of the acidity, pairs of metals such as bismuth and lead, and Xylenol orange is used as a 0.1 to 0.5 per cent. aqueous solution, which is stable for bismuth and cadmium can be individually determined in a single solution. several months; one or two drops of this solution are used for each titration. METHYLTHYMOL BLUE- 3 : 3 '-Bis-di (carboxymet hyl) aminome th ylth ymolsulphonpht halein (me thylt hymol blue, II)9,10 is prepared in the same way as xylenol orange, but from thymol blue as the starting material.This compound also retains the acid - base indicator properties of the parent dye; it is yellow in acid solution, turning light blue at pH 6-5 to 8.5 and grey at 10.5 to 11.6. Above pH 12.7 it forms a dark blue anion. I t can not only be used in acid solution for titration of all cations mentioned under xylenol orange, but can also be used in strongly alkaline solution for alkaline-earth metals. Methylthyrnol blue undergoes a very sharp metallo- chromic colour change from yellow to blue, this being the maximum possible range of the visible spectrum. The exceedingly wide pH range over which this compound functions as a metal indicator makes it possible to titrate to successive end-points in strongly acid, weakly acid and alkaline solution. Thus we can successively titrate bismuth, zinc and magnesium-a combination that frequently occurs in pharmaceuticals-or zinc and magnesium in alloys, and so on.CH, CH, CH, CEI, '.c/H \/H (11) Methylthym 01 blue Another example is the evaluation of calcium ethylenedianiinetetra-acetate injections -used as an antidote in lead poisoning-involving the titration of the excess of free com- plexone or calcium, and of the total complexone or calcium in a single solution.ll The indi- cator can also be used for the titration of lead in urine, an important analytical index in the treatment of lead poisoning.April, 19583 PRIBIL : RECENT DEVELOPMENTS IN CHELATOMETRY 193 Aqueous solutions of methylthymol blue are not very stable and it is therefore more convenient to use an intimate mixture (1 + 100) with potassium nitrate.A number of further indicators having similar properties-xylenol purple, methyl- xylenol blue and others-can be prepared from other sulphonphthalein dyes; they have recently been listed in Chemistry and Industvy.12 THYMOLPIITHALEXONE AND FLUOREXONE- Another dye system suitable for use as a basis for the synthesis of new metallochromic indicators is the phthalein system. The Mannich condensation with iminodiacetic acid can again be used to introduce the chelating group. Owing to the presence of a rather stable lactone ring, these indicators operate only in alkaline solution. This is not to say that no complex formation takes place in acid solution, but the cation on entering into the chelate complex is not capable of forcing the lactone ring to open in order to form the coloured indicator ion.The first indicator of this group, Cresolphthalein Complexone or ph thalein purple, was prepared by Schwarzenbach some years ago? Its drawbacks as an indicator in the complexometric determination of strontium and barium are well known. The colour effect at the end-point is merely hypochromic, Le., there is a decrease in the intensity of the purple colour of the solution. The colour of the free indicator can be suppressed by the addition of alcohol, but this again may lead to precipitation, e.g., of barium carbonate. CH, CH, CH, CH, 'A XI (IIIa) Thymolphthalexone (IIIb) Glycinethymol blue Our new indicator thymolphthalein complexone or Thymolphthalexone (IIIa) ,I* which is the analogous derivative of thymolphthalein, has a great advantage in this respect. Its acid - base colour change lies at much more alkaline pH values, so that the end-point in the titration of alkaline-earth cations is marked by a sharp colour change from deep blue to greyish yellow or almost colourless.The corresponding derivative of phenolphthalein, Phenolphthalexone, is much less satisfactory. (IV) Calcein A very interesting compound is the metal indicator derived in the same way from fluorescein. This compound was first obtained-though evidently in an impure state-by Diehl and Ellingboe15 and has been marketed under the name Calcein. A much purer product has been obtained in our laboratories by Korbl and called Fluorexone.lG The compound differs from the parent dye in showing in acid solution a green fluorescence that is quenched by alkali; however, the fluoresence reappears if traces of calcium are present.The end-point of a titration with complexone in alkaline solution is therefore marked by a quenching of the fluoresence, and the resulting solution is almost colourless or faintly pink, according194 P ~ I B I L : RECENT DEVELOPME‘NTS IN CHELATOMETRY [Vol. 83 to the concentration of the indicator. Spectral measurements have shown that there is no change in colour at the end-point, but only a sudden change in fluorescence. Fluorexone is a suitable “metallofluorescent” indicator for the titration of calcium in strongly coloured solutions, and also serves for fluorimetric detection and determination of minute traces of the alkaline-earth metals.GLYCINETHYMOL BLUE AND GLYCINECRESOL RED- In the synthesis of new indicators we are, of course, by no means limited to the chelating grouping formed by the phenolic hydroxyl group together with the iminodiacetic acid group. If other amino acids are used in the same type of synthesis, we obtain further indicators of much greater selectivity. For instance, we have prepared compounds containing a carboxy- methylaminomethyl group in a suitable relationship to the phenolic hydroxyl group by using glycine in the Mannich condensation. The glycinethymol blue (IIIb)17 obtained by applying this reaction to thymol blue is highly selective in its action. The removal of one of the carboxylmethyl groups of the original chelating grouping leads to a decrease in the range of cations with which the indicator will react, and to a displacement of the pH stability region of the complexes formed by others.In a weakly acid medium, the indicator will react with copper to give an intense blue colour. The reaction is very much more sensitive than that with ammonia or glycine alone. A very simple complexometric determination of copper can be based on this reaction. Complex formation between glycinethymol blue and nickel takes place very slowly and only in presence of high concentrations of the metal. We can therefore use the indicator to detect traces of copper in the presence of nickel, cobalt and other metals, and even for the colorimetric determination of copper. The recently prepared compound glycinecresol red also proinises to have very interesting properties.By varying the amino acid component in the condensation we get a whole series of very interesting derivatives, which differ in the sensitivity of their colour reactions and the rate of complex formation. THE AZO-DYE INDICATORS- The third dye system that we have used as a basis for the construction of metallochromic indicators is the azo-dye system. The simplest compounds having metallochromic properties are two indicators1* in which the complex-forming grouping consists of two phenolic hydroxyl groups in ortho positions, vix., 3 : 4-dihydroxy-4’-nitroazobenzene (Vaj and 3 : 4-dihydroxy- azobenzene-4’-sulphonic acid (Vb) . As had been expected, these compounds resemble in many respects the indicator pyrocatechol violet, which has the same chelating grouping.They form coloured complexes with bismuth, thorium and copper, and may indeed serve as indicators in the complexometric determination of these metals. /OH .OH (V> (a) 3 : 4-Dihydroxy-4’-nitroazobenzene The condensation with iminodiacetic acid or glycine can also be carried out in this dye As examples I will mention naphthol violetlg and glycinenaphthol violet ,20 which (6) 3 : 4-Dihydroxyazobenzene-4’-sulphonic acid series. might find practical application to titrations in acid and alkaline solutions. EFFECT OF FURTHER COMPLEX-FORMING COMPOUNDS Permit me now to say a few words about the screening of cations in complexometric titrations. By using certain reagents capable of forming very stable complexes we can, in principle, screen a number of cations and thereby make these titrations more selective.This approach is certainly very tempting, but also rather difficult. The screening reagent must fulfil a number of conditions: it must form complexes that are many times more stableApril, 19581 P ~ I B I L : RECENT DEVELOPMENTS IN CHELATOMETRY 195 than those formed with EDTA, the complexes should be colourless and water soluble, their formation should be quantitative at stoicheiometric ratios and should proceed without side reactions, and so on. Quite a number of such reagents are now known, but the use of most of them is limited to the alkaline pH region. The use for this purpose of potassium cyanide, ammonium fluoride ,21 triethanolamine,22 2 : 3-dimer~aptopropanol~~ and other compounds was reviewed in an article in 1955.24 As I have mentioned, with the introduction of new metallochromic indicgtors it has become possible to move outside the alkaline pH region in complexometry. This leads not only to new possibilities, but also to new demands being made for screening reagents for this pH region.There is the possibility of screening iron by fluoride, copper by thiourea and mercury by thiosemi- carbazide25; this last reaction in particular is highly selective and makes possible the indirect determination of mercury in the presence of practically all the other elements. As an example of the further possibilities that exist in this direction, I should like to show you a reaction that might make it possible to screen bismuth and thorium in the presence of zirconium: so far this is only in the qualitative stage.From the theoretical point of view a number of objections can be raised to the screening of cations in solution. It would appear necessary to calculate equilibria in various complicated systems, take account of the indicator sensitivity and so on. In any case, this field of complexometry certainly deserves increased attention. In solu- tions of a complex qualitative and quantitative composition we cannot usually resort to complexometry without previous chemical treatment. By this I have in mind the separation, by some means or other, of various components of the solution. This can often be done by applying classical methods such as those established in gravimctric analysis, or more modern ones, such as extraction, ion exchange and so on.Here it is important to stress that such separations can frequently be speeded up considerably if we bear in mind the particular requirements and possibilities of complexometry. Often, for instance, it is quite unnecessary laboriously to achieve the complete separation of two components, but it is sufficient to reduce the concentration of the dominant component to such an extent that the residual amount can be dealt with by the usual methods of complexometry. This applies, for instance, to ion-exchange methods , which , incidentally, have not yet been applied in complexometry to any great extent. This and numerous other possibilities await development at the hands of analytical chemists. The state of affairs in this respect is by no means satisfactory yet.This account does not, of course, exhaust the possibilities of complexometry. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. REFERENCES Schwarzenbach, G., and Biedermann, W., Helv. Chim. Acta, 1948, 31, 678. Korbl, J., Piibil, R., and Emr, A., Chem. Listy, 1956,50, 1440; Coll. Czech. Chem. Comm., 1957,22, Korbl, J., and Piibil, R., Chemist-Analyst, 1956, 45, 102. Pribil, R., and Koros, E., Acta Pharm. Hungarica, 1957, 27, 1; see also Piibil, R., Koros, E., and Bazcza, L., Acta Pharm. Hungarica, , 1957, 27, 145. Houda, M., Korbl, J.: BaBant, V., and PFibil, R., Chem. Listy, 1957, 51, 2259. Kinnunen, J., and Wennestrand, B., Chemist-A nalyst, 1957,46, 34. Piibil, R., and Korbl, J., unpublished data. Korbl, J., and Piibil, R., Chem. Listy, 1957, 51, 1061. Korbl, J., Ibid., 1957,51, 1304; see also Korbl, J., and KakG, B., Ibid., 1057 51, 1680. Buben, F., Korbl, J., and Pribil, R., Ibid., 1957, 51, 1307. Korbl, J., and PTibil, R., Chewz. & Ind., 1957, 233. Anderegg, G., Flaschka, H., Sallmenn, R., and Schwarzenbach, G., Helv. Chinz. Acta, 1954,37, 113. Korbl, J., and Ptibil, R., Chem. Listy, 1957, 51, 1804. Diehl, H., and Ellingboe, J. L., Anal. Chem., 1956, 28, 882. Korbl, J., and Vydra, F., Chem. Listy, 1957,51, 1457. Korbl, J., Kraus, E., and PTibil, R., Ibid., 1957, 51, 1809. Korbl, J., Kraus, E., Janeik, F., and Piibil, R., Ibid., 1957. 51, 311; Coll. Czech. Chem. Comm., BudGinsklj, B., Chem. Listy, 1957, 51, 726. -, Ibid., in the press. Pi.ibi1, R., Ibid.. 1954, 48, 41; Coll. Czech. Chem. Comm., 1954, 19, 65. -, Chew. Listy, 1953, 47, 1333; Coll. Czech. Chem. Comnz, 1954, 19. 57. Piibil, R., and Roubal, Z., Chem. Lisly, 1954, 48, 818; Coll. Czech. Chem. Comm., 1954, 19, 1 162. Ptibil, R., Chem. Age, 1955, 72, 141. Korbl, J., and Pribil, R., Chem. Listy, 1957, 51, 667; Coll. Czech. Cltem. Comm., 1957,22, 1771. 961. 8 , Ibid., in the press. -- - 1957, 22, 1416.

ISSN:0003-2654    

DOI:10.1039/AN9588300188

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

196 HASLAM AND HALL : THE SEMI-MICRO DETERMINATION OF [Vol. 83 The Semi-micro Determination Chloride) of Chlorine and Related in Polymers BY J. HASLAM AND J. I. HALL (Imperial Chemical Industries Ltd., Plastics Division, Welwyn Garden City, Herts.) A semi-micro method has been developed for the determination of chlorine in polymers and copolymers of vinyl chloride. A sample of the polymer is fused with sodium peroxide in a small electrically fired bomb. After dissolution of the melt, removal of excess of peroxide and acidification, the chlori,de is titrated with standard silver nitrate, use being made of an automatic titrimeter. RECENTLY we were called upon to develop a very rapid method for the semi-micro deter- mination of chlorine in small samples of poly(viny1 chloride) and related polymers, e g ., copolymers of vinyl chloride with vinylidene chloride or vinyl acetate. A method applicable to large numbers of samples at one time when iche amounts of sample available for test are only about 20mg was required. Methods such as the micro Carius test, which we have used for some time, were obviously inapplicable, owing to the rather long time required for the determination. Moreover, the methodl developed by Soppet and one of us (J.H.) for the macro-determination of chlorine in polymers could not be used directly on the semi- micro scale, owing to the relatively high blank values as compared with sample titrations when a 15-g charge of sodium peroxide is used. Attempts to apply Bather's method2 on the rnicro scale to the problem were unsuccessful; the results were invariably low whatever concentration of sulphuric acid was used in the breakdown of the polymer with ammonium ceric sulphate and acid.Ultimately, it was decided to reduce the macro method to the semi-micro scale. In doing so it was necessary, in co-operation with Messrs. Chas. W. Cook & Sons (University Works, Walsall Road, Birmingham), to design a small electrically fired bomb for sodium peroxide fusion, in which 20 mg of the polymer sample could quickly be broken down with 1 g of sodium peroxide. The bomb was made o'f stainless steel and the capacity of the cup was approximately 2 ml. A thorough search of the literature carried out subsequent to our work has shown that Eger and Yarden3 have designed a similar bomb of capacity 8 ml for the semi-micro deter- mination of fluorine in organic fluoro compounds.Further, in order to retain both speed and accuracy, it has been necessary to carry out the final titration of the ionised chloride with standard silver nitrate, use being made of an automatic titrimeter as described by Squirrel1 and one of us (J.H.).415 The small reference electrode used in this work consists of an 18 s.w.g. silver wire im- mersed in a solution containing a very slight excess of silver ions. The reference electrode is maintained in contact with the solution to be titrated by means of a ground-glass sleeve, which is kept moistened with the solution contained in the electrode vessel. The indicator electrode is an 18 s.w.g. silver wire. In order to avoid false potentials, this electrode is kept in a position touching the stirrer and i!; therefore continually vibrated during the titration.The silver nitrate is standardised against sodium chloride that has been fused with sodium peroxide in exactly the same way as the sample. APPARATUS- in Fig. 2. Instruments Limited. REAGENTS- Chemical Industries Limited) was used. use was used. METHOD A diagram of the semi-micro bomb is givien in Fig. 1 and of the reference electrode The automatic titrimeter used in this work was manufactured by Messrs. Electronic Sodium $erode-Sodium peroxide of low chlorine content (manufactured by Imperial Stadz catalyst-AnalaR soluble starch that had been heated for 3 hours a t 100" C beforeApril, 19581 CHLORINE IN POLY(VINYL CHLORIDE) AND RELATED POLYMERS 197 Nitric acid, concentrated-The AnalaR reagent was used.Nitric acid, 2 N-Dilute 12.5 ml of concentrated nitric acid to 100 ml with water. Sodium hydroxide solution, 10 per ceizt. w/v-Dissolve 10 g of sodium hydroxide in water, The AnalaR reagent was used. MethyZ red indicator solution-A 0.05 per cent. w/v solution in ethanol. Silver nitrate solution, 0.02 N-Prepare by dilution of a 0.1 N stock solution. Sodium cldoride solution, 0-02 N-Prepare by dilution of a 0.1 N stock solution. Sodium chZoride-AnalaR sodium chloride that had been heated for 4 to 5 hours at 270" & 10" C before use was used. Reference electrode solution-Prepare a solution containing 64 ml of saturated sodium sulphate solution, 6.0 ml of 2 N nitric acid, 30 ml of 0.1 N sodium chloride solution and 30.1 ml of 0.1 N silver nitrate solution.Mix the solution and allow to stand until the bulk of the silver chloride has settled out. cool and dilute the solution to 100 ml with water. Fill the reference electrode with this solution. P.T. F.E. - --t Im 8 s.w.g. silver wire 100 m m 1- - - - - Sleeve made from 14mm cut down B7 L ]..I socket Fig. 1. Cross-section of semi-micro bomb Fig. 2. Reference electrode PROCEDURE- Weigh 20 mg of the sample into the cup of the bomb and add 0.06 g of dried starch together with 1-Og of sodium peroxide. Mix intimately the contents of the cup, fire elec- trically by using 3 cm of fuse wire and a current of 2 to 3 amperes and then allow to cool in a bath of distilled water. After fusion, place the cup and top in a 50-ml beaker containing 10 ml of distilled water and cover the beaker with a watch-glass.Warm the beaker carefully to assist dissolution. When the melt has completely dissolved, remove the top of the bomb and cup and carefully wash them with a minimum of distilled water. Bring the solution just to the boil and maintain for 15 minutes to destroy the excess of peroxide. After cooling, make the solution just acid by adding concentrated nitric acid dropwise from a burette, using methyl red as indicator, again cool, add a further few drops of methyl red indicator solution and make the solution slightly alkaline by adding 10 per cent. w/v sodium hydroxide solution. Neutralise the solution with 2 N nitric acid and add 0.25 ml of acid in excess, The volume of the solution will be about 30 ml at this stage.Titrate the chloride with 0.02 N silver nitrate solution to a pre-set end-point, using the automatic titrimeter with the FAST - SLOW change-over control set at 50 mV before the end-point is reached. In this titration, use a burette that has a fine capillary jet kept below the surface of the solution being titrated. Carry out a blank determination on the reagents, omitting only the sample. Determine the pre-set end-point by an initial manual potentiometric titration as follows. Measure 15 ml of 0.02 N sodium chloride solution into a 50-ml beaker and add 15 ml of distilled water. Acidify the solution with 0.25 ml of 2 N nitric acid and titrate with 0.02 N198 HASLAM AND HALL [Vol. 83 silver nitrate solution, using the manual control of the titrimeter.When the end-point is approached, make additions of silver nitrate solution in 0.1-ml increments and note the millivolt readings after each addition. Note the potential difference at which - plotted with respect to V is a t a maximum, and use this as the pre-set end-point on the titrimeter. In our experience, the end-point is usually at a setting of about +SO mV. When large numbers of determinations are involved, it is our practice to determine the pre-set end-point daily. Standardise the 0-02 N silver nitrate solution against 20 mg of dried sodium chloride that has been fused with sodium peroxide and subsequently titrated with the silver nitrate solution in exactly the same way as described folr the sample. RE s u LT s The results of applying the proposed procedure to the determination of chlorine in poly(viny1 chloride) and to copolymers of vinyl chloride with vinyl acetate and with vinylidene chloride are given in Table I.For comparison, results of corresponding determinations by the micro Carius method are included. AE AV TABLE I CHLORINE CONTENTS OF VARIOUS POLYMERS AND CO~OLYMERS OF VINYL CHLORIDE Chlorine found by the Substance micro Carius method, % Poly(viny1 chloride) . . .. .. .. .. 56.7 49.8 Copolymer of vinyl chloride with vinyl acetate 48.5 46.8 57.2 59.8 I 63.3 . . { Copolymer of vinyl chloride with vinylidene chloride . . Chlorine found by the proposed method, 66.6, 56.6, 56.7 49.6, 49-9, 50-0 48.4, 48.4, 48-8 46.6, 46.7, 46.8 56.9, 57.2 69.8, 59.9, 59.9 63.3, 63.7 % Since this paper was originally prepared, it has been shown that the method can be extended to the determination of chlorine in copolymers containing chlorine and nitrogen. The result of the determination of chlorine in a copolymer containing 24-4 per cent. of nitrogen by the micro Carius method was 24.3 per cent., and the results of replicate determinations by the proposed method were 24.1, 24-2 and 24.3 per cent. It is suggested that the method may find application in the determination of chlorine on the semi-micro scale in other materials. We are indebted to Miss M. Clark for her assistance in this investigation. REFERENCES 1. 2. 3. 4. 6. Haslam, J., and Soppet, W. W., J , SOC. Chem. i'nd., 1948, 67, 33. Bather, J. M., Analyst, 1956, 81, 536. Eger, C., and Yarden, A., Anat. Chem., 1956, 28, 512. Haslam, J., and Squirrell, D. C. M., Amlyst, 1954, 79, 689. -,- , Ibid., 1957, 82, 511. Received Sefitembev 20tla, 1967

ISSN:0003-2654    

DOI:10.1039/AN9588300196

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

April, 19581 DIXON, HANDS AND BARTLETT 199 A Field Method for the Rapid Determination of Hydrogen Cyanide in Air BY B. E. DIXON, G. C. HANDS AND A. F. F. BARTLETT (Department of the Government Chemist, Clement’s I N n Passage, Strand, W.C.2) A field test for determining small amounts of hydrogen cyanide in industrial atmospheres is based on formation of a Prussian blue colour on test paper impregnated with ferrous sulphate and sodium hydroxide. The test is specific for hydrogen cyanide. The behaviour of a number of possibly interfering gases has been investigated. The test is sensitive to slightly less than 1 p.p.m. of hydrogen cyanide in air and has an error of f 10 to 20 per cent. Test papers properly prepared and stored retain their activity for a t least 10 months. The blue stains obtained are permanent.TWO field tests for the detection and approximate estimation of hydrogen cyanide in air are described in “Methods for the detection of toxic gases in industry-Leaflet No. 2” (Department of Scientific and Industrial Research).l One of these, the benzidine - copper acetate test, has been widely used, but it has certain drawbacks, e g . , difficulty in controlling the critical moisture content of the test paper, instability of the reagents, of the prepared test paper and of the stains on the test paper after treatment with hydrogen cyanide, and lack of specificity. The alternative Congo red-silver nitrate test shares some of these drawbacks. Tests based on formation of a Prussian blue colour from hydrogen cyanide, which would have the advantages of specificity and permanence of pigment, have usually been regarded as insufficiently sensitive and unsuitable for use as field tests.2 Gettler and Gold- baum3 determined the amount of hydrogen cyanide in solutions by aerating at 90” C and passing the gas through test paper previously impregnated with ferrous sulphate and sodium hydroxide to form blue stains of various intensities. These authors claimed that the test papers would retain their usefulness for several weeks if stored in a cool dark place.Our tests showed, however, that test papers prepared as described were sometimes unsatisfactory, and that anyway the papers could not be relied upon to retain their full activity after a few hours. We finally succeeded in establishing the conditions necessary for a test based on formation of a Prussian blue colour, which was free from the various drawbacks already mentioned.EXPERIMENTAL TEST PAPERS- The success of the method depends largely on the correct preparation and storage of the test papers. These are prepared by immersing filter-paper in ferrous sulphate solution, drying, immersing in sodium hydroxide solution and again drying. Reactions within the test fi@ev-The two reagents that are incorporated in the test paper can react with each other and with atmospheric carbon dioxide or oxygen. Ferrous hydroxide, which is initially formed by the action of sodium hydroxide on the ferrous sulphate, can be preserved for long periods in spite of a reputation for instability. Shipko and Douglas4 have shown that ferrous hydroxide in contact with saline solution containing either excess of hydroxide or of ferrous ions is stable for periods up to 6 months if oxygen is rigorously excluded. When the dried paper already impregnated with ferrous sulphate is soaked in alkali solution, about 50 per cent.of the sulphate ion passes into the solution. Only a few per cent. of the ferrous iron on the paper is oxidised to ferric iron during both this procedure and the subsequent drying of the paper. The sodium hydroxide on the test paper will readily absorb carbon dioxide, which has an inhibitory effect on the subsequent formation of the blue stain. In fact, if the test papers after impregnation with sodium hydroxide are allowed to dry in air, as recommended by Gettler and G~ldbaum,~siifficient atmospheric carbon dioxide may be absorbed to cause faulty stains to be obtained later. This risk can be reduced by careful drying under an infra-red lamp, but can only be completely eliminated by drying in a vacuum- desiccator.The dried papers can be stored by inserting them in glass tubes, which are then sealed under vacuum. Test papers should be used within 1 hour of preparation or of withdrawal from storage tubes. Papers so stored have an effective life of at least 10 months.200 Penetration of the stain-Cross-sections of test papers that had been used in the detection of hydrogen cyanide were examined under a microscope. Paper that had been freshly prepared showed a deep blue stain on the exposed face extending inwards for a distance approximately equal to two or three times the fibre diameter; beyond this point the paper was colourless.On the other hand, paper the upper face of which had been exposed to carbon dioxide before use in the field test showed only a faint blue colour that pene- trated 30 to 5 0 p inwards from the exposed face, and had a band of more intense blue in the central region of the cross-section. It is clear that, unless the whole of the hydrogen cyanide in the sample is trapped on the surface of the test paper, i.e., within a depth of about ZOp, depending on the texture of the pa.per, the amount of gas present cannot be properly estimated b y visual examination of the stain. The importance of an adequate concentration of reagents in the test paper and of proper protection of the critical outside layer before use is obvious.It was found that the proposed method of preparation produced test papers of average composition 10 mg per sq. cm of Whatman No. 50 filter-paper, 0.3 mg per sq. cm of total iron (including at least 50 per cent. as ferrous iron), as Fe, 0.2 mg per sq. cm of sulphate, as SO,, and 4.5 to 5.5 mg per sq. cm of alkali, as sodium hydroxide. Papers of this composition were invariably satisfactory. Occasionally, satisfactory stains were obtained with papers containing as little as either 0.05 mg per sq. cm of ferrous iron or 1 mg per sq. cm of sodium hydroxide. SAMPLING RATE- In order to obtain an even coloured stain it is essential that the rate of flow of gases passing through the test paper does not exceed 6 ml per second.It is very difficult to main- tain this slow steady flow with a hand pump, and even occasional bursts of speed can result in pin points of deep blue colour on the test pape!r where the gas has streamed through larger pores. CALIBRATION OF STAINS- To prepare standard stains, a stream of air mixed with hydrogen cyanide in the desired proportions was prepared as described by McKelvey and Hoelscher.5 The hydrogen cyanide was supplied from a gas cylinder. Alternatively, a static concentration of mixed gases was prepared by sucking a stream of air into an evacuated 10-litre bottle together with the hydro- gen cyanide liberated by the action of concentrated sulphuric acid on a known amount of 0.0.5 per cent. w/v potassium cyanide solution. The concentration of hydrogen cyanide in the mixed gases was determined by taking samples in an evacuated 2-litre flask containing 0.05 N sodium hydroxide. After prolonged shaking an aliquot of the alkaline liquor was withdrawn by pipette and analysed by the Lubatti method.6 The results were checked occasionally by the Liebig argentimetric method, the end-point being determined photo- electrically.A series of five standard stains representing 2-5, 5, 10, 20 and 60 p.p.m. of hydrogen cyanide in a 360-ml sample was found 1.0 be adequate. APPARATUS- DIXON, HANDS AND BARTLETT: ,4 FIELD METHOD FOR THE [Vol. 83 The use of a rubber-bulb aspirator avoids this difficulty. METHOD A spirator-A rubber-bulb hand aspirator of approximately 120-ml capacity was used. Test-paper hoEder-A suitable form of holder is shown in Fig.1. The paper is placed between two smooth-faced rubber washers held in position by two parallel brass plates carrying wing-nuts and bolts. Plates and washers are drilled to take a hole of 1 cm diameter and the sampled air enters inlet tube A to pass through the paper and leave by the outlet tube, B. Dish-A glass, porcelain or plastic dish of about 200 ml capacity was used. Glass tube containers for fest Papers-These were about 6 cm long and of 6 mm internal Filter-papers-Whatman No. 50 filter-paper in sheets approximately 4 inches >: 3 inches diameter. was used. REAGENTS- grade hydrated ferrous sulphate. grade sodium hydroxide free from carbonate. Ferrous sulphate solution-A 10 per cent. w/v aqueous solution of analytical-reagent Sodium hydroxide solution-A 20 per cent.'w/V aqueous solution of analytical-reagent Sulphuric acid, 30 fier ceizt. v / v .April, 19581 R4PID DETERMINATION OF HYDROGEN CYANIDE IN AIR 201 PREPARATION O F THE TEST PAPERS- Immerse a sheet of filter-paper for at least 5 minutes in a shallow vessel containing about 100 ml of ferrous sulphate solution. Remove the filter-paper and dry it by suspension over a radiator. Cut off and discard a strip 2 cm wide from the lower edge of the filter-paper and cut the remainder of the sheet into rectangular pieces of 3.5 cm x 2.5 cm. Immerse the pieces of paper singly in the sodium hydroxide solution for about 15 seconds. Remove the papers, partly dry them with absorbent paper and transfer them quickly to a vacuum-desiccator. Evacuate the desiccator and leave the papers until they feel dry to the touch, but are not brittle.Satisfactory papers are greyish green to pale brown in colour. The paper should then be white or off-white in colour. For storage, vacuum seal each test paper in a piece of glass tubing. Fig. 1 . Test-paper holder: A, inlet tube; €5, outlet tube PROCEDURE- Fix the test paper between the rubber washers of the test-paper holder and screw up the two wing-nuts until they are finger- tight. Attach the holder to the aspirator by means of a piece of rubber tubing and draw the sample of air through the paper at a rate not exceeding 6ml per second until 360ml have passed. Remove the test paper from the holder and immerse it in 30 per cent. sulphuric acid contained in the dish. If hydrogen cyanide is present a blue colour develops on the paper in 30 seconds to 1 minute and an approximation of the hydrogen cyanide content of the atmosphere can be made by reference to the stain chart while the test paper is still in the dish.For a more accurate determination, remove the paper from the dish, wash it well with water, dry it and compare it with the stain chart. Break the sealed glass tube and remove the test paper. DISCUSSION OF THE METHOD SPECIFICITY- The Prussian blue reaction is specific for hydrogen cyanide and the test papers are not stained blue except by this gas or by substances that could react to produce the cyanide ion, e g . , cyanide dust or cyanogen. Cyanide dust can be removed from the gas sample before passage through the test paper by means of a cotton-wool filter.Neither hydrogen chloride nor ammonia appears to interfere with the test even when present in concentrations up to 400 p.p.m. Sulphur dioxide and hydrogen sulphide in amounts less than 50 p.p.m. do not appreciably affect the colour of the stain. Hydrogen sulphide can, if required, be removed by interposing a dry lead acetate paper in front of the hydrogen cyanide test paper in the holder. Chlorine inhibits the reaction of the test papers with hydrogen cyanide; if chlorine is likely to occur in the atmosphere under examination a qualitative test should be carried out. SCOPE- The test is sensitive to slightly less than 1 p.p.rn. of hydrogen cyanide in air. There is little difficulty in comparing stains as the background colour is white and the With the recommended stains themselves differ only in the intensity of a single colour.202 RUSSELL AND HART: THE DETERMINATION OF COPPER I N GEL-4TIN [Vol.83 series of standard stains, the error is estimated to be about + l o per cent. for concen- trations of hydrogen cyanide above 10 p.p.m. and about *SO per cent. for concentrations below 10 p.p.m. By increasing or reducing the volume of saniple, the concentration range of hydrogen cyanide that can be covered is about 1 to 500 p.p.m. The blue stains are permanent, and, after having been thoroughly rinsed and dried, test papers can be kept for reference purposes. Care should be taken to keep them out of contact with alkalis. They are unaffected by further exposure to an atmosphere containing hydrogen cyanide. Papers can be safely used within 1 hour of preparation or of brea.king the protective seal.No decrease has been detected in the activity of papers kept in vacuum-sealed glass tubes for at least 10 months. Although the preparation of the test papers’ is not complicated and involves the use of fairly stable reagents, it is definitely a laboratcry operation. If previously prepared and sealed papers are used, however, the method is simple, can be operated wholly by hand and is suitable for use as a field test. The test has the advantages that the test paper is virtually unaffected by small amounts of hydrogen cyanide in the atmosphere during the 30 seconds or so needed to break the sealed tube and put the paper in the holder, and that after immersion in the acid bath the stained paper is unaffected by hydrogen cyanide.Hence it is unnecessary for the operator to be in fresh air either for insertion of the paper in the holder or for subsequent examination of the stain. An approximation of the hydrogen cyanide content can be made in 6 minutes and a more accurate one in 10 minutes. The test should prove useful for the determination of small amounts of hydrogen cyanide in industrial atmospheres generally, and also when it is required to determine fairly accurately, rather than very rapidly, concentrations of residual hydrogen cyanide, This work was carried out on behalf of the Committee on Tests for Toxic Substances in Air, and the Ministry of Labour and Nationa.1 Service. We thank the Government Chemist for permission to publish this paper. REFERENCES 1. 2. 3. 4. 5. 6. D.S.I.R., “Methods for the Detection of Toxic Gases in Industry, LeuJet No. 2: Hydrogen Cyanide,” Jacobs, M. B., “Analytical Chemistry of Industrial Poisons, Hazards, and Solveiits,” Interscience Gettler, A. O., and Goldbaum, L., Anal. Chem., 1947, 19, 270. Shipko, F. J., and Douglas, D. L., J . Phys. Chcm., 1956, 60, 1519. McKelvey, J. M., and Hoelscher, H. E., Anal. Chem., 1957, 29, 123. Lubatti, 0. F., J . SOC. Chem. Ind., 1935, 54, 4 % ~ . H.M. Stationery Office, London, 1943. Publishers Inc., New York, 1949. Received November 27th, 1957

ISSN:0003-2654    

DOI:10.1039/AN9588300199

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

202 RUSSELL AND HART: THE DETERMINATION OF COPPER I N GEL-4TIN [Vol. 83 The Determination of Copper in Gelatin BY G. RUSSELL AN:D P. J. HART (Chemical Research Laboratory, Ilford Limiteal., Woodman Road, Brentwood, Essex) Some newer methods for the determination of traces of copper have been applied to gelatin and results are compared with those obtained by present procedures ; the advantages over the use of substituted dithiocarba- mate-type reagents are discussed. The :preferred procedure is with 2: 2’- diquinolyl as reagent. TRACES of impurities in raw materials may have profound effects on photographic emulsions. It is desirable to have a method capable of determining the copper content of various gelatins in the range 0 to 15 p.p.m. The method to be selected had to fulfil the following conditions- (i) the reagents to be used should be readily available in a reasonably pure state; (ii) the procedure should be specific, yet simple and sensitive;April, 19581 RUSSELL AND HART: THE DETERMINATION OF COPPER I N GELATIS 203 (iii) it should preferably involve an extraction stage; the partition coefficient should (iu) the coloured complex produced should be stable, especially to light.The reagents used in well known methods and their shortcomings may be summarked Dithizone is non-specific,l unstable and has an intense colour of its own. Sodium diethyldithiocarbamate is used in the British Standards method.2 It is less sensitive than dithizonel and is not specific. An extraction stage into chloroform or carbon tetrachloride is often used, but the partition coefficient is small.The complex with copper is unstable to light.3 This type of reagent has been used in conjunction with ethylene- diaminetetra-acetic acid to increase specificity,4p5 but interference still occurs. Zinc dibenxyldithiocarbamnte also suffers from non-specificity6 and instability of the complex with copper to light. It has the advantage over sodium diethyldithiocarbamate that it can be used at a lower pH. More recently, other methods have become available, some of which have been examined. These include methods in which 2 : 2'-diquinolyl, biscyclohexanone oxalyldihydrazone or 2 : 0-dirnetliyl-1 : 10-phenaiithroline is used. Polarographic methods have also been examined. be high in favour of the organic phase; as follows- &THOD OF DESTROYING ORGANIC MATTER REAGENTS- &411 reagents should be of recogiiised analytical grade.Nitric mid, concentvnted. Perchloi.ic acid, 73 pev cent. Sulphziric acid, concentvated. PROCEDURE- Heat 2 g of gelatin and 10 ml of nitric acid in a 100-m1 conical flask on a hot-plate until vigorous evolution of brown fumes O C C U ~ S . ~ I t is advisable to renove the flask from the hot-plate at this stage. Add 2 ml of sulphuric acid and continue heating until no more brown fumes are evolved and charring begins. Add 4 m l of perchloric acid and continue heating until the liquid is colourless or very pale yellow and then maintain the solution at the same temperature for a further 3 to 4 hours to ensure the removal of excess of perchloric acid. Little attention is required at this stage and several digestions can be conducted simultaneously.After the solution has cooled, dilute with about 10ml of water, boil for a few minutes and then cool. The solution is now ready for the determination. COLORIMETRIC METHODS All colorimetric measurements were made with a Gallenkamp photo-electric colorirneter. 2 : 2'-Diquinolyl gives a magenta-coloured complex with cuprous copper, which can be extracted into isoamyl alcohol. isoAmy1 alcohol is said8 to give a slightly greater colour intensity than n-amyl alcohol. The complex of 2 : 2'-diquinolyl with cuprous copper is remarkably stable to atmospheric oxi&dtion.9 The partition coefficient is largelo and is relatively slightly affected by high salt concentrations. The solubility of isoamyl alcohol in water at room temperature is appreciable, hence temperature control is desirable at the extraction stage.The reagent is sensitive to oxidising agents that may occur in the isoamyl alcohol or remain after the digestion with perchloric acid.ll The alcohol is subjected to the pre-treatment described later and the digestion is prolonged to overcome these effects. It is claimed12 that the extraction and reduction stages can be combined by adding the solvent cliniethylformamide to the solution, but we have preferred to retain the advantages of CN traction. FVITH Z : 2'-DIQUINOLYL AS REAGENT- Reagents- 2 : 2'-DiqzainolyZ solution-A 0.02 per cent. w/v solution of analytical-reagent grade The commercial grade reagent, m.p. 186" According to Dr.J. Hoste the solution 2 : 2'-diquinolyl, m.p. 196" C,13 in isoamyl alcohol. to 192" C was also used without recrystallisstion. is stable for several months if stored in a brown bottle.204 RUSSELL AND HART: THE DETERMINATION OF COPPER IN GELATIN [VOl. 83 isonmy1 alcohol-Analytical-reagent grade, b.p. 128" to 132" C. This was treated before use in accordance with a communication from Dr. J. Hoste, as follows. An 800-ml portion was shaken with 100ml of a 10 per cent. solution of sodium metabisulphite, the layers were separated and the alcohol layer was, dried overnight in contact with anhydrous magnesium sulphate. After filtration, the alcohol was distilled and the fraction boiling over the range 128" to 132" C was collected and stored in a brown bottle.Tartaric acid solution, 50 per cent. w/v. Iiydroxylamine hydrochloride solution, 15 per cent. w/v-Prepare freshly each week.8 Sodium hydroxide solution, 30 per ccnt. wlv. Proccdure- After digestion to destroy the organic matter, treat the solution with 2 ml of tartaric acid solution and 2 ml of hydroxylamine hydrochloride solution. Adjust the pH to between 4 and 7 with sodium hydroxide solution (test by spotting micro drops on pH papers). Dilute the solution to 50 ml and transfer it to a thermostatically controlled water bath at 25" & 0.5" C for 10 minutes. Add 10 ml of 2 : 2'-diquinolyl solution, also at 25" C, and shake the mixture for 3 minutes. Separate the organic layer and measure its optical density, using an Ilford No. 625 filter. ReszLlts-Calibration curves with simple aqueous copper solutions and with known additions of copper to a de-ionised copper-free gelatin are shown in Fig.1. The displacement of one curve from the other is due to copper in the digesting acids and the sodium hydroxide used for neutralisation. 40 II Copper added, yg Fig. 1. Calibration curves for copper by 2: 2'-diqujnolyl method: curve A, digested with gelati~l; curve B, no digestion WITH BISC~C~OHEXANONE OXALYLDIHYDRAZONE AS REAGENT- known, it is not extractable. mining copper in paper and pulp15 and in plants.l6 of the metal hydroxide. Reagents- ethanol, warmed to dissolve the solute and filtered before use. freshly prepared each day. This reagent gives a blue colour with copper in the pH range 7 to 9 and, so far as is I t is highly specific for copper14 and has been used for deter- Citrate is added to prevent precipitation Biscyclohexanone oxalyldihydrazone solution--A 0.5 per cent.w/v solution in 50 per cent. This solution should be Ammoniwn citrate solution, 10 per cent. w/v. Ammonia solution, sp.gr. 0.880-Analytical-reagent grade. Neutral red indicator solution, 0.05 per cent. wlv. Sodium hydroxide solution, 50 per cent. w/:Y. Hydrochloric acid, concentrated-Analytical-reagent grade. Procedwc- Prolonged digestion is not necessary and, after a clear solution is obtained, heating for 1 hour is sufficient. After it has cooled, transfer the solution to a 25-ml calibrated flask, add 0.5 ml of ammonium citrate solution and 4 drops-about 0.15 ml--of ammonia solutionApril, 19581 205 and then 1 drop of indicator.Adjust the pH with sodium hydroxide or hydrochloric acid until the solution is just yellow (pH 7 to 9). Cool the solution frequently to minimise loss of ammonia. Add 1 ml of biscyclohexanone oxalyldihydrazone solution and dilute to the mark. Occasion- ally, cloudy solutions are obtained, which require filtration into the colorirneter cell. The calibration curves obtained in this way resemble those shown in Fig. 1. WITH 2 : 9-DIMETHYL-1 : 10-PHENANTHROLINE (NEOCUPROINE) AS REAGENT- used for 2:Z'-diquinolyl. tungsten.lg extracted by the same solvent. RUSSELL AND HART: THE DETERMINATION OF COPPER I N GELATIN Measure the optical density after 15 minutes, using an Ilford No. 626 filter. This reagent gives a yellow colour with cuprous copper under similar conditions to those It has been used for determinations of copper in paper1' and It is subject to the same interference from oxidising agents and the complex is I t is advisable17 to store the reagent solution in a refrigerator.Reagent s- Buffer solution, p H 5-Dissolve 57 g of anhydrous sodium acetate and 17.0 ml of glacial acetic acid in water and dilute almost to 1 litre. Adjust the pH to 5.0 and then dilute to 1 litre. Neocuproine solzction-Dissolve 75 mg of 2 : 9-dimethyl-l : 10-phenanthroline in 100 ml of buffer solution with vigorous shaking. *4 SCOY bic acid. Tartaric acid solution, 50 per cent. w/v. Procedure- After digestion, add 2 ml of tartaric acid solution. Adjust the pH to approximately 6, and add 10 ml of buffer solution. Treat the solution with 3 ml of neocuproine reagent and about 50mg of solid ascorbic acid, dilute to about 50ml and then place the solution in a thermostatically controlled water bath at 25" 0.5" C for 10 minutes.Add 10 ml of isoamyl alcohol (purified as for use with 2: 2'-diquinolyl), also at 25" C, and shake the mixture Store the reagent in a refrigerator. for 3 minutes. No. 622 filter. Separate the alcohol laye; and measure its optical density, using an Ilford POLAROGRAPHIC METHOD A polarographic method in which dry oxidation is used has been described.19 However, dry oxidation is not suitable for gelatin. The material froths considerably, and, on burning, leaves a mass of porous carbon, which is only slowly oxidised. The operation is tedious and requires considerable attention from the analyst, apart from the known risks of loss in such a procedure. The wet-oxidation procedure described is suitable for the purpose.Prolonged digestion is necessary and decomposition products of the perchloric acid may give spuriously high diffusion currents for the copper wave. Such effects have been noted by other workers.18 APPARATUS- A Tinsley pen-recording polarograph was used. TABLE I DETERMINATION OF COPPER IN GELATIN BY VARIOUS METHODS Copper found by- A - I._.--- _____ 7- ~ biscy clohexanone zinc dibenzyldithio- 2 : 2'-diquinolyl oxalyldihydrazone neocuproine polarographic carbamate method, method, method, p.p.m. p. p. in. p.p.m. 14.5 11.7 12.2 3.5 1.9 3.5 8.0 7.8 8.1 3.0 1-4 3.4 3.0 1.8 3.3 1.0 0.0 0.7 1.0 0.0 1.0 After digestion, transfer the cooled solution to mark with distilled water.This solution, which Pi<OCEDL?RE-- - metlhod, p.p.m. 13-4 3-3 8-6 2.4 2-8 0.5 1.0 method, p.p.m. 14.5 2.4 8.1 1.5 1-4 0-0 0.0 a 10-ml calibrated flask and dilute to the is approximately 5 N in sulphuric acid,206 RUSSELL AND HART: THE DETERMINATION OF COPPER IK GELATIN [VOl. 83 is used directly for the polarographic determination. No maximum suppressor is required. I t is convenient to use a mercury pool as anode; the half-wave potential of the copper wave is at -0.34 volt against the pool. Preliminary experiments showed that variations in sulphuric acid concentration from 3 to 8 N did not seriously affect the wave heights. RESULTS The results by these four methods on seven commercial gelatins are shown in Table I.Figures obtained with the zinc dibenzyldithiocarbamate procedure of AndruslS with special precautions to minimise light fading are included for comparison. In a series of recovery experiments, known amounts of copper were added to the gelatins before digestion. The average recoveries were as follows- 2 : 2’-Diquinolyl method . . .. .. . . . . 101 & 5 per cent. Biscyclohexanone oxalyldihydrazone method . . 96 5 per cent. Neocuproine method . . .. .. . . . . 99 i 5 pcr cent. Zinc dibenzyldithiocarbamate method. . . . . . 96 & 5 per cent. The results shown in Table I are reasonably satisfactory, considering the low coimn- trations involved and the simplicity of the instruments used for measuring. COMPARISON OF THE METHODS S E NSI TI v ITY - According to the values given in the literature, zinc dibenzyldithiocarbamate6 has about the same sensitivity as biscyclohexanone oxalyldihydrazone,20 when both complexes are measured with a spectrophotometer.In this work, with the best filter available, the zinc reagent was only about one-third as sensitive. On the other hand, biscyclohexanone oxalyldihydraz- one was found to be about 2i-times as sensitive as 2:2’-diquinolyl. This figure is in agreement with those of other However, this advantage is offset by the “concen- trating” effect of the extraction stage in the latter case. Like other workers,17 we have found 2 : 2’-diquinolyl and neocuproine to be very similar in sensitivity. Caution must be exercised in comparing sensitivities with filter iiist ruments.I ” I I ‘ I I OLI-.--L 0 5 10 50 100 500 IOOC Time, rnhutes Fig. 2. Colour stability: curvc ~1, sodium diethyldithiocarbamate in fluorescent light; curve B, sodium diethyldithiocarba mate i n diffuse day- light; curve C, 2 : 2’-diquinolyl and neocuproine in all lighting : curve D, biscyclohexanone oxalyldi- hydrazone in all lighting; curve E, sodium diethyl- dithiocarbamate in sunlight INTERFERENCE- The only known interference when the 2 : 2’-diquinolyl and neocuproine methods are used is from ferric iron, and this can be masked by tartaric acid. The zinc dibenzyldithio- carbamate method is affected by the presence of bismuth, cobalt and nickel, and the polaro- graphic method may be affected by stannous tin. There is no known interference with the biscyclohexanone oxalyldihydrazone method.April, 19581 RVSSELL AND HART: THE DETERMINATION OF COPPER IN GELA4TIN 207 STABILITT OF THE COMPLEX TO LIGHT- The relative stabilities of the various complexes to light of different kinds are illustrated in Fig.2 (note the logarithmic time scale). A curve is shown for sodium diethyldithio- carbamate ; the zinc dibenzyldithiocarbamate reagent complex fades almost as quickly in bright light. As has been reported,21 the biscyclohexanone oxalyldihydrazone complex fades slowly; this may be partly due to high salt ~0ncentration.l~ The 2:T-diquinolyl and neo- cuproine complexes are stable to light for at least several days. STABILITY OF THE REAGENT- Carbamate-type reagents deteriorate on keeping.22 J~~ 2 : 2’-Diquinolyl solution, when prepared as described, is stable for a t least 3 months.Biscyclohexanone oxalyldihydrazone solution is less stable and becomes yellow after a few days. A freshly prepared solution of this reagent, with the addition of a standard amount of copper, gave a reading of 25.2 colori- meter units; when 4 days old, with the same amount of copper, it gave a reading of 20.6 units. The need to keep neocuproine solution in a refrigerator has been mentioned. When the solution was kept at laboratory temperature, the reading with a standard amount of copper fell from 25.7 units when fresh to 22.0 units at 4 days old. PKICE OF THE REAGENT- the difference in the concentrations used, they are about the same cost. oxalyldihydi-zone is about the same price as carbamate reagents. 2 : 2’-Diquinolyl and neocuproine are fairly expensive reagents; by taking into account Biscyclohexanone CONCLUSIONS 2 : 2’-Diquinolyl and neocuproine are equivalent in most respects except for the stability of the reagent.The stabilities of the complexes to light favour these reagents; simplicity, sensitivity and economy favour biscyclohexanone oxalyldihydrazone. All these reagents have advantages over sodium diethyldithiocarbamate. The polarographic method is simple and convenient , although possibly not so generally attractive as a colorimetric method. By taking into account all the above factors, the preferred reagent is 2:2’-diquinolyl. The procedure described, used in place of the British Standard method, has given satisfactory results during 6 months. We thank the Directors of Ilford Limited for permission to publish this paper, and Miss M.E. Bell, Miss P. T. King and Mrs. G. A. Nichols for technical assistance. The value of the 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. communication frGm DF, J. Hoste of Ghent University is greatly appreciated. REFERENCES Sanclell, E. B., “Colorimetric Determination of Traces of Metals,” Second Edition, Interscience “Sampling and Testing of Gelatin,” British Standard 757 : 1944. Ovenston, T. C. J., and Parker, C. A., Anal. Chim. Acta, 1950, 4, 135. Sedivek, V., and VaSAk, V., Coll. Czech. Chem. Compz., 1950, 15, 260. Forster, W. A,, Analyst, 1953, 78, 614. Johnson, m’. C., Editor, “Organic Reagents for Metals,” Fifth Edition, Hopkin and Williams Ltd., Chadwell Heath, Essex, 1955, p. 188. Reed, J. l?., and Cummings, R. W., I n d . Rng. Chem., A~zal. E d . , 1041, 13, 124. Guest, R. J., Anal. Chenz., 1953, 25, 1484. Gahler, A. R., Ibid., 1954, 26, 577. Hoste, J., Eeckhout, J., and Gillis, J., Anal. Chim. A d a , 1953, 9, 263. Ferrett, D. J., and Milner, G. W. C., Analyst, 1956, 81, 193. Pflaum, R. T., Popov, A. I., and Goodspeed, N. C., Anal. Chenz., 1955, 27, 253. Iloste, J., Anal. Claim. Acta, 1950, 4, 24. Nilsson, G., Acta CJzem. Scand., 1950, 4, 205. Wetlesen, C. U., and Gran, G., Sveizsk Papperstidn., 1952, 55, 212. Williams, T. R., and Morgan, R. R. T., Chetn. G. I n d . , 1954, 461. Zak, B., and Ressler, N., Anal. Ckenz., 1956, 28, 1158. Crawley, R. H. A., Anal. Chim. A d a , 1955, 13, 373. Rlichel, G., and Maron, N., Ibid., 1960, 4, 542. Peterson, K. E., and Bollier, M. E., Anal. Chew,., 1955, 27, 1195. Somers, E., and Garraway, J. L., Chenz. & I n d . , 195‘7, 395. Johnson, W. C., Editor, op cit., p. 172. Martens, R. I., and Githens, R. E., 4naZ. Chein., 1952, 24, 991. Publishers Inc., New York, 1950, p. 300. Received November 1 lth, 1957

ISSN:0003-2654    

DOI:10.1039/AN9588300202

出版商:RSC    

年代:1958

数据来源: RSC