ISSN:0003-2654    

DOI:10.1039/AN95883FX021

出版商:RSC    

年代:1958

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95883BX023

出版商:RSC    

年代:1958

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95883FP093

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

... THE ANALYST XlllCLASSIFIED ADVERTISEMENTSThe rate for classfhed aduertisements i s 5s. a h i e (or spaceequivalent of a line), tottk an extra charge of I s . fur theuse of a Box iyumber. Semi-dtsplayed classi/iedA.F;.R.E., HAKWELLAlETALLUIIGICAL APiAI.E’STrequired for analysis of metals and allo?~ for Kuclear T’owcrProgramme. Scope for initiatib-e and originality in analyiicalmethods in a continually developing field.Applicants should possess G.C.E. (A Ievd). H S.C. orequivalent; experience in nietallnrgical anal>-sis and know-ledge of instrumental inethods essential.Salary rang?: in95 Q,315, according to age arid experience.Send post card to Group l<ecrnitnimt Otlicer [11:;8Yj.%),A.E.K.E., Harwell, Didrot. Berks., for applicatiou forill.-Ml’EIIIAL CHEMICAL ISIICS’TI<lES LIMITED, PlasticsIkivibion.has a vacancy for a TECHSICAL OFFICER inits Analytical Laboratories at Welwyn Garden City.Candidates should hold a good Honours degree in Chemistryor As5ociate5hip of the Royal Institute of CheiniLtry. Theyshonld also be able to nffer sound experience in generalanalytical work.The appointnient carries rneinbenhip of the Staff PensionFund and a profit~sharing scheme is in operation. Forniarried men, spccial mortgage faeilitics can be grantedtowards house-purchase and assistance is given towardsremoval expenses. Temporary lodging allowance alsoavailable for inarried men.Applv bnefiy, to Staff Manager, Imperial ChemicalIndwtrips l.iniited, I’lantics Diviiion, Black Fan Road,M’elwyn Garden City, Hcrt,.OEKTLING Chernical Balance and Weights.Newcondition-t?i (cost L:l.5). Sccn by appointment.Lancaster, 15, Queen’s Gate Gardens, London, S.W.7.IMPERIAL CHEMICAL INDUSTRIES OF AUSTRALIAAND NEW ZEALAND LIMITEDRESEARCH CHEMISTS-ANALYTICALTwo Senior Chemists are required for the Analytical and Physical McthodsSection of our Central Research Laboratories, Ascot Vale, Victoria :1. A wide variety of analytical work is performed for the various sectionsof the Research Laboratories and for the Company’s factories and TechnicalService Scctions. This work is essentially non-routine and is undertakenin cases where the methods and instruments involved are beyond the scopeof the factory laboratories or where methods require to bc checked, improvedor invented..I\ senior man is required t o supervisc this work in detail andt o maintain effective liaison with specialist staff (spectrometry, chromato-graphy, biological analysis). He should be a graduate with considerableexperience in conventional and instrumental methods of analysis. Asuitable man could eventually be called upon t o assume administrativeresponsibilities. Applicants in the early thirties t o middle forties wouldbe preferred.2. .I well qualified man, with post-graduate experience, is required foranalytical research, t o undertake long-range investigations into analyticalmethods and basic research in the field of analysis or associated techniques.Work would be partly by assignment, but also i t is regarded as essentialthat the appointee should have some interest or interests of particularappeal t o himself and be capable of initiating and carrying through workof publication standard.The Company’s policy is liberal with regard t opublication, subject t o protection of its immediate commercial interests.AppIic;itions, giving full details of qualifications, experience and age,should be addressed to-The Staff hlanager,Imperial Chemical Industries of Australia andBox 191 1, C.P.O., A~ELUOURNE, VICTORIA.Sew Zealand Limited,N.B.--l,‘nitctl I<ingdom applicants could make further enquiries andobtain Application €orins from the T’ersonnel Of‘ficer, Australasian Uepart-mcnt, 1mpc:rial Chemical Industries Limited, I.C. House, 3Iillbank, Tanuox,S.IV.1xiv THE ANALYST111 111 Applied Scientists . Iinterested i n working on Instrumenta- 111 tion i n Industrial situations are invitedt o write t oHILGER & WATTS LTD.,who have several interesting vacanciest o offer.The duties will include technical liaison withconsiderable sales content between users,designers, and management, and will entailthe ability to resolve users’ problems, discussdesign requirements resulting from these, andassist management in the formation of policy.The equipment with which the successfulapplicants will need to become familiar includesX-ray diffraction apparatus, spectroscopic andother optical instruments; a basic knowledgeof physics and chemistry is therefore essential,while a knowledge of crystallography andmetallurgy would be an additional advantage.Proficiency in one or more languages otherthan English would also be an advantage asthe Company exports a large proportion ofits production to a wide range of foreign anddominion markets, and personal contact withbuyers from abroad is consequently an integralpart of the duties to be undertaken.Young men with the required background,willing to accept the responsibility of work ofthis nature, and interested in j oining a progressiveCompany with an international reputation oflong standing, should write giving full detailsof education, qualifications and experience, andstating age and salary desired, to:-THE CHIEF PERSONNEL MANAGER,HILGER & WATTS LTD.,98, St.Pancras Way,Camden Road, London, N.W.I.ENIOK LABOKA’TOKY TECHNICIAS, with experiencechemical and biochemical analysts, particularly in thenutrition and toxicological fields, required for the Departmentof Veterinary Hygiene and Preventive Jiedicine, Yniaersityof Edinburgh. Salary scale [590 x pl to L6Sii per anniini,with placement according to qualifications and expericnre.Applications, giving particuiars of age, qualifications andesperience along with two Teceirt testiimmials, sliould besent to the Secretan. of the linivwsitv. I.nivrrsitv of Edin-hnrgh, Old30th June,College, Solith~Br&e, -Edi&ii&h, -not later than1958, quoting reference VH,’STA;.iR, \lay, 1938.THE BRITISH DRIIG HOUSES LIXITED,F3.T). H. Laboratory Cherrricals IXvision,I’oolr, Dorsct,require aIkputy Hrad for the Analytical Department.The Uepartmeiit has a staff of 40 andemploys a wide range of analytical techniquesin tlie exainination of organic and inorganic.chemicals and reagents.Applicants should posscss an Honoum degreein Chemistry or equiralcnt qualificationPrevious industrial analytical cxpcricncr i Fessential, togcther Kith ability to controlstaff. Salary according to cxpcricncc andqualifications.Apply in writing, stating age, experience andqualifications, to the General Manager, B.D.H.Laboratory Chemicals JXvision, West QuayKoad, I’oole, Dorset.S3UTH .41 KICAN COUhLIL I-.OK 5ClhA IIbIL ASDIlDL’STKIAL KE5FAKLHMICRO-ATALYSTPI’LICATIONS are invited from suitably qualifiedPipersons for a post as Micro-Analyst i n the OrganicC irrriistry Division of the NATIONAL CHEMICALRESEARCH LABOKhTOKY in Pretoria, South Africa.The succrssfiil applicant will br required to take chargeof the micro-analytical laboratory attached to the OrganicChrrnistry Division.This laboratory handles a wide rangeof analys~s. Training :and espcrii,nce in niicro-analyticalrliernistry i i essential.The initial salary will be ~ c o r l r i ~ ~ g to qualifications andehperipnrr on thr srale Li50 to L1,2l)il p a . In addition,a vost of living allowance (at present L234 p.a.) is payablctc, married male officers. 4 vacation bo~lus of 2 per cent.on basic s:ilary wac pair1 diiring the past two years.Gcncrous lea\ P privileges, provident fund and a five-dayweek.l’lie Council will contribute an amount of LlXO 111thP racr of :L inarried man, arid LSO in the case of a singleperson towards the total fares and transport costs of thesuccrssful applirant and his family to Pretoria.Applications giving full details of age, niarital status,nationality, knowledge of English and:or Afrikaans,scieutific and techniral qualifications and exycricnce, andof a t least two persons to whom referenre niayhe made, shou!d he addressed to the Illrector, NationalCheinical Krsrarch I.aboratory. Council for Scienilfic andTiidustrial Research, Private Bag J!ll, Pretoria, SouthAirica. .4 copy of the application should be sent to theSouth African Scientific Liaison Offirrr, Africa House,Kingsway, London.bV.C.2.LOXDON PI’ULIC AXALYST requires iiiore staffPLa~id has the following vacancies:-(1) Assistant Aiialyst with experience of food and druganalysis. Very varivd expenencr obtainable. hut accuracyand speed essential. Commencing salary t;S:iO per annuniapproxirnately.(2) Capahlc man as J.aboratory Strward. Part-tinicrricase, if necessary. to obtain instruction. Coniirirnrings;lary about LlO per werk.(3) ,Junior Assistant, pi-eferahly with a good G.C.E.l’art-time rrlcasc for study. Comniencing a t about L6 to L’I per week.The work in this laboratory is very intcrrsting and varied,tliere being practiially no work of a purely routinc nature.Staff are enrouragrrl to pass examinations and to workfor higher qualifications. Apply in nriting in first instanceg:vingdctails of education, expenence, etc., toT.McLachlan,.1 Hanway Place, London, IV.1.BRITISH THOMSON-HOUSTOS CO. LTD.HE British Thonmon-Houston Co. Ltil., have vacancies7rin thnr Research Lalmratory at Rugby for Chemist ~ i t l idegree or A.K.I.C., to develop new methods of analysis.Experieiice in ( I ) polarography and spectrophotonietry or( 2 ) radio-activation and tracer clirniistry would be anad\ antage, hut is not essential.Applicants are invited to writc to the Director of Research,Tie British Thornson-Honston Co. I.td., Rugby, stating agearid qualifications, and quoting reference JAJ.C I T Y OF LEICBSTER IIEALTH DBPAKI’MENI’SENIOR ASSISTAST ASALYSTPPLICAXTS should be members of the Royal Jnstitute&f Chemistry and have had practical experience in thec>aminatmn of wate samples.Salary scale @45,’1025 p a . (.IPT. IIJ). Superannuahlepost. hkdiral exarnination.Applications, togethpr with the names of two referees, tott e I’ublic Analyst 7 , Salisbnry Road, Lricester, within tend, .I)> .. of the app;ar&ice of this advertisement.~.4!iALYTTf24L CHEMISTPPLICATIOm are invited for this position in the Lahora-A t o r v of nnr factorv manufacturing a wide range of productsincludfng Food, Ucug, Cleaning and Toilet preparations.Applicants should possess a minimum qualification of H.N.C.and some experience in any of tlie trades concerned wouldh! an advantage. There i5 conbiderable scope for the righttype of person and an ontstanding opportunity of obtainingcoiuprehensive practical experience is assured. Five dayweek and contributory Superannuation Scheme is inoperation.Applications stating salary reqnired and endorsed“l:hemist” should be submitted to Managcr, S.C.W.S. Ltd.,Chruiical Sundries Uept., Shieldhall, Glasgou, S.W.l

ISSN:0003-2654    

DOI:10.1039/AN95883BP103

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

JUNE, 1958 THE ANALYST Vol, 83, No. 987 PROCEEDINGS OF THE SOCIETY FOR ANALYTICAL CHEMISTRY NEW MEMBERS ORDINARY MEMBERS Desmond Arthur Sidney Barnes, B.Sc. (Lond.) ; Thomas Malcolm Blackwood, B.Sc. (Edin.) ; Bernard Fitzgerald; John Kenneth Fleming, A.R.I.C. ; Neil Robert Francis, B.Sc. (Notting- ham) ; Harry William Houghton, B.Sc. (Nottingham) ; Archie Ronald Javes, B.Sc. (Lond.), F.R.I.C., F.Inst.Pet. ; Charles Edward Roland Jones; Derek Edward Icings, B.Sc. (Hull), A.R.I.C. ; Frederick Lishman, B.Sc. (Sheff.) ; Denis Naylor, B.Sc. (Sheff .) ; John Jonas Nicholls, B.Sc. (Lond.), F.R.I.C. ; Stanley Hope Philpot, A.R.I.C. ; William Crossley Purdy, B.A. (Amherst), Ph.D. (M.I.T.); Herbert Taylor, B.Sc. (Lond.), A.R.I.C.; Walter Westwood, BSc. (Liv.), A.I.M. JUNIOR MEMBERS Elizabeth Jane Hall, B.Sc.(Wales); David Henry Thow, B.Sc. (Edin.). DEATH Daniel Carswell Macpherson. WE record with regret the death of NORTH OF ENGLAND SECTION AND MICROCHEMISTRY GROUP A JOINT Meeting of the North of England Section and the Microchemistry Group with the North Lancashire Section of the Royal Institute of Chemistry was held at 7.30 p.m. on Friday, May 16th, 1958, at Redmans Park House Hotel, North Promenade, Blackpool. The Chair was taken by the Chairman of the North Lancashire Section, Mr. C. D. Lafferty, B.Sc., F.R.I.C. The following papers were presented and discussed: “The Micro Vacuum Fusion Deter- mination of Gases in Metals,” by &I. R. Everett; “The Chemical Determination of Nitrogen in Reactor Metals,” by J. A. Ryan, A.R.I.C.; “The Determination of Naturally Occurring Radioactive Impurities in a Uranium Purification Process,” by M.R. Hayes, A.R.I.C. ; “A Simple Manometric Method for the Determination of Carbon in Metals,” by M. R. Everett (see summaries below). The meeting was preceded at 2 p.m. by a visit to the Chemical Services Department Laboratories of the Springfields Works of the United Kingdom Atomic Energy Authority (Industrial Group). THE MICRO VACUUM FUSION DETERMINATION OF GASES I N METALS MR. M. R. EVERETT said that, in the vacuum fusion technique, a sample was added to a de-gassed graphite crucible or a de-gassed carbon-containing metal bath, maintained at a high temperature in vacuo. The hydrogen, oxygen and nitrogen contents of suitable metals could be calculated from analysis of the evolved gas, which consisted of a mixture of hydrogen, carbon monoxide and nitrogen. Sources of error in vacuum fusion were briefly considered.321322 PROCEEDINGS [Vol. 83 A micro-scale all-mercury-and-glass apparatus was described. This contained a 3.5-g molten-platinum bath at an operating temperature of 1900” C for the analysis of metals such as thorium, zirconium, uranium, niobium, vanadium, molybdenum and tungsten. Sample weights were of the order of 50 mg, and up to twelve samples could be analysed consecutively. A low-pressure circulating-type gas analytical system was used. Limits of detection were approximately 1 1j.p.m. for both hydrogen and nitrogen and 5 p.p.m. for oxygen. The author quoted results that demonstrated the agreement between vacuum fusion and chemical determinations of nitrogen for a large number of zirconium samples. In the analysis of metal of very low gas content, gaseous contamination on the surface of a prepared micro sample could cause an appreciable positive bias, particularly for oxygen, and results that showed the extent of this effect were also quoted.THE CHEMICAL DETERMINATION OF NITROGEN IN REACTOR hlETALS MR. J. A. RYAN said that the applicability of the Allen method for the determination of nitrogen in the reactor metals niobium, vanadium, zirconium, molybdenum and beryllium had been demonstrated by comparison of the performance of the method with the Dumas and caustic-fusion methods. Nitrides of the metals had been prepared and used for the comparison experiments.Although the Allen method could be used satisfactorily for all these elements, it could only be used for the determination of nitrogen in molybdenum on a restricted size of sample. The caustic-fusion method was applicable to fully nitrogenated vanadium, but not to samples of vanadium metal, for which it gave “nil” recoveries. No experiments had been carried out with the Dumas method on beryllium, owing to the hazardous toxic nature of the material, but the method could be applied satisfactorily to the other elements. THE DETERMINATION OF NATURALLY OCCURRING RADIOACTIVE IMPURITIES MR. M. R. HAYES said that pitchblende ore contained the radioactive-decay products of uranium in their equilibrium concentrations, and these radioactive impurities were separated from the uranium during the refining process and appeared in the various plant intermediates and residues.A knowledge of the concentrations of these radioactive impurities was required in order that measures to prevent ur due concentration of radioactivity could be taken and to control the disposal of radioactive wastes. Also, as some of the radioactive im- purities were valuable by-products in the refining of uranium, analytical control was required to permit them to be recovered efficiently. Of the twenty-six radioactive isotopes occurring in the ore, the most important were shown to be thorium-230, polonium-210 and radium-226. The analytical methods used in the determination of these three isotopes were outlined. For thorium-230 and polonium-210, chemical separation followed by alpha counting was used. The methods for radium were purely physical: direct measurement of gamma-ray intensity at the higher levels and separation of radon gas followed by measurement of its activity at lower levels.The concentrations of these radioactive impurities, and mass balances obtained for them over a period of production, were discussed. IN A URANItJM PURIFICATION PROCESS A SIMPLE MANOMETRIC METHOD FOR THE DETERMINATION OF CARBON IN METALS MR. M. R. EVERETT described an apparatus that was simple, compact and portable. It could be used to isolate and determine carbon dioxide in oxygen or nitrogen carrier- gas streams having velocities of up t o 300 ml per minute. The sensitivity range was from 10 to 8000 pg of carbon. An efficient multi-loop cold trap isolated the carbon dioxide, which was afterwards expanded at room temperature in a small evacuated calibrated volume that included an atmospheric-column manometer.SCOTT1 SH SECTION A JOINT Meeting of the Section and the Methods of Analysis Panel (Glasgow) was held at 7.15 p.m. on Friday, April 25th, 1958, in the Royal College of Science and Technology,June, 19581 PROCEEDINGS 323 204 George Street, Glasgow, C.l. The Chair was taken by the Chairman of the Methods of Analysis Panel, Mr. J. H. Love. A lecture on “X-ray Fluorescence Techniques in Analytical Chemistry” was given by E. T. Hall, M.A., D.Phi1. (see summary below). X-RAY FLUORESCENCE TECHNIQUES IN ANALYTICAL CHEMISTRY DR. E. T. HALL said that the use of X-ray fluorescence both in the laboratory and in process control was an accomplished fact in the United States of America.However, in this country, in spite of the existence of the technique since 1914, the importance of the method was only just being realised. The speaker gave an outline of the technique together with some idea of how the physical, mechanical and electronic problems had been solved. Reference was made to commercial equipments available, and how automatic servo-controlled spectrometers could carry out automatic analyses of complex systems. Results could be taken either intermittently in digital form or continuously in analogue form. Some comparisons were made with optical spectrometers, and possible applications to trace analysis were indicated. Examples of suitable problems with their attendant advantages were described.Some mention was also made of the advantages of this technique in non-destructive archaeological analysis of valuable museum objects. SCOTTISH SECTION AND PHYSICAL METHODS GROUP A JOINT Meeting of the Scottish Section and the Physical Methods Group with the Aberdeen University Chemistry Society was held at 7.30 p.m. on Friday, May 16th, 1958, in the Main Lecture Theatre, Chemistry Department, King’s College, Old Aberdeen. The Chair was taken by the Chairman of the Physical Methods Group, Mr. R. A. C. Isbell, A.1nst.P. The following papers were presented and discussed: “The Analysis of Clays Using Ion-exchange Resins,” by Mrs. Jean McAuslin, BSc., A.R.I.C. ; “The Application of Gamma Radiation to the Non-destructive Examination of Coal,” by J.Craig Higgins (see summaries below). During the morning, the Chemistry Department of King’s College was open to visitors and there were demonstrations of a cathode-ray polarograph, a Unicam SP900 flame photo- meter and a high-sensitivity pH meter. In the afternoon, visits were paid to the Macaulay Institute for Soil Research and to the Ministry of Agriculture, Fisheries and Food Experi- mental Factory, THE ANALYSIS OF CLAYS USING ION-EXCHANGE RESINS MRS. JEAN MCAUSLIN described a method of clay analysis in which the sample was decomposed and the silica removed by treatment with hydrofluoric acid. The metallic constituents of the clay were then separated from one another and determined quantitatively. Iron and manganese were converted to anionic chloride complexes, and aluminium to an anionic phosphate complex. These complexes were then adsorbed on anion-exchange resin columns.A cation-exchange resin column was used to separate sodium and potassium from calcium and magnesium. Sodium and potassium were determined by flame-photometric methods, and titanium was determined colorimetrically. The remaining elements were determined by titration with ethylenediaminetetra-acetic acid. The behaviour of titanium had been investi- gated, and provision had been made to prevent its interference in the determination of the other metals. THE APPLICATION OF GAMMA RADIATION TO THE NON-DESTRUCTIVE EXAMINATION OF COAL MR. J. C. HIGGINS said that planning the development of new coalfields required much preliminary proving and survey work.This was carried out to a large extent by exploratory boring. The samples obtained in “core” form from these boreholes provided a valuable cross-section of the coal seams present and their associated strata. The attenuation by coal of gamma radiation from a radioactive source had been utilised as the basis of an experimental non-destructive method of examining the physical structure of coal seams as provided by these core samples. The method had been used as an aid to the visual assessment of seam structure that was carried out before further physical and chemical tests were made.32-1 PROCEEDINGS [Vol. 83 The work done so far demonstrated the practicability of the method and showed it to be capable of differentiating between bands of coal that were closely similar in ash content and specific gravity.Sharp resolution of adjacent thin coal and dirt bands was possible and variations in mineral-matter content had been observed in places where they had not been demonstrated by standard preliminary examination. WESTERN A K I ~ MIDLAXDS SECTIOKS A JOIST Summer Meeting of the Western and Midlands Sections was held on Friday and Saturday, May 16th and 17th, 1958, in the Lecture Theatre, West Midlands Gas Board, Castle Foregate, Shrewsbury. The Chair was taken on Friday by the Chairman of the Mid- lands Section, Dr. R. Belcher, F.R.I.C., 1F.Inst F., and on Saturday by the Chairman of the Western Section, Mr. S. Dixon. MSc.. F. R.1 C. At 7 p.m. on Friday- the following papers were presented and discussed: “The Origins and Growth of Volumetric Analysis” and “The Origins of Quantitative Organic Analysis,” by TY.I. Stephen, B.Sc., Ph.D., A.R.I.C. At 9.30 a.m. on Saturday the following papers mere presented and discussed : “The Historical Development of the Public Analyst,” by G. V. James, IVI.B.E., M.Sc,, Ph.D., F.R.I.C., P.A.I.W.E.; “The Origins of Quantitative Chemical Analysis,” by R. E. Coulson, F.R.I.C. (see summaries below). THE ORIGINS ASD GROWTH OF VOLUNETRIC ANALYSIS DR. W. I. STEPHEN described the early history of titrimetry to show how this branch of chemical analysis had played an (equally as important part in the development of quantitative analysis as had gravimetry. The contributions of Mohr and Penny to the growth of the subject were also discussed.THE ORIGINS OF QVANTITATIVE ORGANIC ANALYSIS DR. W. I. STEPHEN described the contributions of Berzelius, Liebig, Gay-Lussac Subsequent developments in quantitative Some and Dumas to elemental organic analysis. organic analysis had depended entirely on the work of these famous chemists. mention was also made of the histoly of functional-group analysis. THE HISTORICAL DEVELOPMENT OF THE PUBLIC ANALYST DR. G. V. JAMES traced the place of food poisoning and the protection given by select individuals from early times, and described prohibitive legislation in historical times. He mentioned early analyticd tests for adulteration, and described the wide- spread sophistication of the early nineteenth century that led to the Lancet Commission and the first Food and Drugs Act of 1860.Some early books and instrumerts of this latter period were displayed. THE ORIGINS OF QUANTITATIVE CHEMICAL ANALYSIS 11~. R. E. COULSOX said that Klaproth had laid the foundations of quantitative analysis in his work on minerals. He had shown how even the most refractory materials might be brought into solution and the components separated. Berzelius had extended this work and applied current ideas of the structure of chemical compounds to check the analytical results obtained by himself and others, which had led to a clear under- standing of combining proportions. NIDLAKDS SECTIOK A s Ordinary Meeting of the Section was held a t 6.30 p.m. on Wednesday, April 16th, 1058, 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 paper was presented and discussed: “The Analysis of Silicones and Related Organosilicon Compounds,” by J. C. B. Smith. ,4 JOIXT Neeting of the Section with the East Midlands Section of the Royal Institute of Chemistry was held a t 7.30 p.m. on Thursday, April 24th, 1958, in the College of -4rt and Technology, Leicester. The Chair was taken by the Chairman of the East Midlands Section, Dr. A. G. Catchpole, F.R.I.C.June, 19581 OBITUARY 325 The following paper was presented and discussed: “Developments in the Use of Redox Indicators,” by R. Belcher, Ph.D., D.Sc., F.R.I.C., F.1nst.F. BIOLOGICAL METHODS GROUP -4s Ordinary Meeting of the Group was held at 6.30 p.m. on Wednesday, April 16th, 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. -4 discussion on “The Mathematics of Sterility Testing” was opened by D. Xaxwell Bryce, BSc., B.Pharm., F.P.S., A.R.I.C.

ISSN:0003-2654    

DOI:10.1039/AN9588300321

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

June, 19581 OBITUARY 325 Obituary WILLIAM MACRO SEABER IVILLIAM MACRO SEABER died on March 13th, 1958, after a short illness. of age. He was 75 years He had been a member of the Society since 1929, and served on the Council in 1939-40. Having passed the examination for the Bachelor of Science degree of London Cniversity, he was also successful in the Institute of Chemistry’s examination in Branch E in 1907, and was elected to the Fellowship in 1910. In the same year he commenced his career as a con- sultant, setting up jointly with the late Maurice Salamon. In 1912 he married Elsie Eleanor Perry, a sister of the late Lord Perry of Stock Havard. During the first World War he left private practice to go to an explosives works at Hale in Cornwall. In 1919 he left, and, with his wife and two daughters, went to Nexico in the employ of the then Mexican Oil Company, first at the refinery at Minatitlan, and later in Mexico City. In 1923 he returned to England and purchased the practice of Hake and Narshall. Shortly after this he again entered into partnership with Maurice Salamon.Salamon died in 1928, and Seaber was senior partner in Hahe and Marshall and in Salamon and Seaber from that time until his death. He also held a partnership in the firm of John Hughes from 1929 until 1945. His interest was almost entirely confined to his profession, but within that framework he brought a keen mind and wide experience to the many problems that fascinated him. The papers he published show the width of his interest, and include such titles as “The detection of inflammable and explosive gases in ships’ tanks,” “Barium as a normal con- stituent of Brazil nuts,” as well as various papers on the determinations of rotenone, carotene and small amounts of bromine. He was always willing to give practical help to the individual in need, and to give his time and his experience when they were required. Up to the time of his death he was a member of a number of committees, including the British National Committee of the International Commission for Uniform Methods of Sugar -4nalysis, the Essential Oils Committee of the British Standards Institution and the Lonch- ocarpus Panel of the Analytical Methods Committee of the Society for Analytical Chemistry. R. A. RABNOTT

ISSN:0003-2654    

DOI:10.1039/AN9588300325

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

326 WOOD AND CLARK: THE: DETERMINATION OF TUNGSTEN IN [Vol. 83 The Determination of Tiingsten in Titanium, Zirconium and their Alloys BY D. F. WOOD AND R. T. CLARK (Research Defiartment, Imfieria,! Chemical Industries Ltd., Metals Division, Kynoch Works, Witton, Birmingham, 6 ) To fulfil the need for satismfactory methods for the determination of tungsten over the range 0.002 to about 1 per cent. in titanium and its alloys, two absorptiometric procedures have been developed, and subsequently extended to the examination of zirconium and its alloys. A direct procedure, based on the yellow colour produced by the reaction of reduced tungsten with thiocya.nate ions, is suitable for the determination of tungsten from 0.05 to 1.6 per cent. in titanium and many of its alloys, and from 0.01 to 1.6 per cent.in zirconium and its alloys; larger amounts can be determined by using a smaller sample weight. The procedure is simple and rapid, and is also suitable for application on a routine basis. Vanadium and molybdenum interfere, and, when these metals exceed specified limits, the toluene-3 : 4-dithiol pmcedure is recommended. A procedure, which depends on the formation of a bluish green complex with toluene-3 : 4-dithiol, is applicable to the determination of tungsten in both titanium and zirconium-bearing materials over the range 0.002 to 0.8 per cent. Vanadium does not interfere, and interference by molybdenum is overcome by means of a preliminary sulphide separation. TUNGSTEN may be introduced into titanium, zirconium and their alloys either from the parent ores or by contamination from the tungsten electrodes that are frequently used in the arc-melting of evaluation buttons.Its presence is undesirable because of its considerable hardening effect ; further, in zirconium-bearing materials used in nuclear reactors, only small amounts of tungsten (below about 0.005 per cent,) can be tolerated because of its high neutron capture cross-section. The objective was the determination of tungsten in these materials over the range 0.002 to about 1 per cent. Colorimetric procedures based on the use of thiocyanatels2*s and toluene-3 : 4-dithiol (dithiol),4 commonly used for the determination of tungsten in steel, have been applied to the determination of tungsten in titanium metal,516 and these procedures are at present used in this laboratory.’ In the thiocyanate pr~cedure,~ the sample is dissolved in hydrochloric acid and, in order to obtain reproducible blank values, titaniium is completely reduced by boiling the solution with stannous chloride before the addition of thiocyanate.In this procedure, the small absorption of the yellow complex formed between reduced tungsten and thiocyanate ions is measured in the presence of a considerable absorption due to the deep violet colour of titanous chloride, and this limits its application to the determination of tungsten in amounts above about 0.1 per cent. Further, during dissolution in hydrochloric acid, which usually takes several hours, part hydrolysis of titanium sometimes occurs, which results in inconsistent blank values.In order to extend the application of the thiocyanate procedure, modifications to the published method5 were examined. Thew included the use of fluoroboric acid as a sol- vent ; it forms a green-coloured complex fluorotitanate with titanium, and thereby inhibits hydrolysis and minimises blank values, thus allowing the range of the determination to be extended below 0.1 per cent. It was expected that boiling the solution with stannous chloride would be unnecessary because tungsten would be effectively reduced by titanous ions formed during dissolution of the sample. Application of this modified procedure was extended to titanium alloys and, subsequently, to zirconium and its alloys. The dithiol procedure depends on the formation of a bluish green complex of tungsten with dithiol and extraction of the complex: with isoamyl acetate.Although more lengthy than the thiocyanate procedure, it is suitable for the determination of tungsten down to about 0.001 per cent. Examination of titanium - vanadium alloys showed that vanadium This acid ,also expedites dissolution of the metal.June, 19581 TITANIUM, ZIRCONIUM AND THEIR ALLOYS 327 interferes in the dithiol procedures as applied to titanium metal, whereas, in the procedure as applied to steel! it is claimed that vanadium does not interfere. In order to provide a method for the determination of tungsten below about 0.05 per cent. in titanium alloys, including those containing vanadium, and also in zirconium and its alloys, the dithiol procedure, as applied to steel! was selected as a basis for further investigation.EXPERIMENTAL THIOCYANATE METHOD FOR TUNGSTEN IN TITANIUM PRELIMINARY EXPERIMENTS- Initial experiments were made to establish the wavelength at which maximum absorption of the tungsten - thiocyanate complex occurs and then, by using this wavelength, to prepare a calibration graph. The concentrations of hydrochloric acid and ammonium thiocyanate used in these preliminary experiments were those recommended by Bacon.5 Absorption curve-A 0.2-g sample of tungsten-free titanium was dissolved in a mixture of 20 ml of hydrochloric acid, sp.gr. 1.18, and 1 ml of fluoroboric acid; 20 ml of sodium tungstate solution (1 ml 3 0.1 mg of tungsten) were added and the solution was diluted to 100 ml in a calibrated flask. To a 25-ml aliquot in a 100-ml calibrated flask were added 20 ml (making 25 ml in all) of hydrochloric acid and then 10 ml of 15 per cent.ammonium thiocyanate solution. The solution was diluted to the mark and set aside for 5 minutes at 20" C. Optical-density measurements were then made in 2-cm cells with a Unicam SP600 spectrophotometer. Wavelengths between 3700 and 4500 A were used, and it was found that the maximum absorption is at 4 0 0 0 ~ . This procedure was repeated with a solution containing titanium only, and at 4 0 0 0 ~ the absorption, due mainly to fluorotitanate ions, was found to be at a minimum (optical density 0-06). Calibration graph-Solutions containing 0.2 g of tungsten-free titanium and amounts of sodium tungstate solution (1 ml = 0.1 mg of tungsten) ranging from 0 to 32.0 ml were prepared as before.These were diluted to 100 ml and 25-ml aliquots were taken. The reagents were added as before, the solutions were diluted to 100 ml and the optical densities were measured at 4000 A in 2-cm cells. The prepared calibration graph was linear and was suitable for the determination of tungsten in the range 0.05 to 1.6 per cent. The blank value (optical density 0.06) due to the green-coloured fluorotitanate ions was equivalent to only half of that obtained in the method described by Bacon5 The tendency for titanium to hydrolyse was completely prevented, and tungsten was effectively reduced by titanous ions produced during dissolution of the sample. In addition, the sample dissolved in 10 to 20 minutes, compared with about 2 hours when hydrochloric acid is used alone as recommended> EFFECT OF VARIOUS FACTORS- Because the optical density of the complex decreased over the range 18" to 35" C by 0.0015 per "C rise in temperature, solution temperatures were controlled at 20" 1" C while the optical-density measurements were made.Variation in blank values over the same range of temperatures was negligible. The colour was fully developed within 5 minutes of the addition of ammonium thiocyanate solution, and it was stable for about 30 minutes, after which the optical densities slowly decreased, the blank values remaining constant up to 90 minutes after addition of the thiocyanate. Different amounts of hydrochloric acid between 23 and 40 ml had no effect on the optical density.Below 23 ml, optical densities decreased sharply with decrease in acid concen- tration ; the blank value increased slightly with increase in acid concentration. Different amounts of fluoroboric acid between 0.5 and 2 ml had no effect on the optical density of the complex or on blank values. Over the range 8 to 20 ml, the amount of 15 per cent. ammonium thiocyanate solution had no significant effect on the optical density, but, below 8 ml, optical densities decreased sharply with decrease in thiocyanate concentration. There was a marked increase in blank values with increase in the amount of thiocyanate from 5 to 20ml. To ensure full colour development in conjunction with a consistent blank value, 10 ml of ammonium thiocyanate, controlled to within +Om5 ml, was adequate.328 When the procedure was applied to solutions containing titanium in the absence of tungsten, optical densities increased from 0.001 to 0.076 with increase in titanium content over the range 0 to 60 mg, as shown by the following results- WOOD AXD CLARK: THE DETERMINATION OF TUNGSTEX I N [Vol.83 Titanium present, mg . . . . Nil 10 20 30 40 60 ti0 Optical density . . . . . . 0.001 0.010 0.024 0.038 0.062 0.064 0,076 In blank determinations, therefore, it is essential to use a weight of tungsten-free titanium corresponding to the weight of titanium present in the sample. Tests on solutions containing 50 mg of titanium and the equivalent of 0.10 and 0.80 per cent. of tungsten, to determine the effect of common alloying constituents and likely impurities, established that no interference was caused by amounts up to at least 20 per cent.of tin or manganese, 10 per cent. of aluminium, 5 per cent. of iron or chromium and 1 per cent. of copper. Molybdenum above 0.25 per cent, caused high results, but interference by molybdenum up to 2 per cent. can be compensated by adding an equivalent amount of molybdenum to the blank solution. Vanadium introduced a positive error, which became significant above about 0.05 per cent. PRELIMINARY EXPERIMENTS- Initial experiments were made to determine the smallest amount of titanium necessary to effect complete reduction of tungsten and then to prepare a calibration graph in the presence of major amounts of zirconium. Effect of titanium-Samples of tungsten-free zirconium (0.2 g) were dissolved in a mixture of 25 ml of hydrochloric acid, sp.gr.l.lS, and 1 ml of fluoroboric acid. Ten millilitres of sodium tungstate solution (1 ml = 0.1 mg of tungsten) were added, and the solutions were transferred to 100-ml calibrated flasks. Amounts of titanous chloride solution (1 ml = 10 mg of titanium) ranging from 0 to 3 ml were added, followed by 10 ml of 15 per cent. ammonium thiocyanate solution. After dilution to the mark, optical densities were measured at 4000 A in 1-cm cells. Similar tests were made in the absence of tungsten in order to establish blank values. Appropriate blank values were deducted and the results showed that at least 5 mg of titanium111 were required for complete reduction of 1 mg of tungsten (see Table I). To THIOCYANATE METHOD FOR TUNGSTEN IN ZIRCONIUM 'rABLE 1 EFFECT OF TITANOUS CHLORLDE SOLUTION ON THE THIOCYANATE Each solution contained 0.2 g of zirconium PROCEDURE FOR DETERMINING TUNGSTEN I N ZIRCOXIUM Titanous chloride Optical-density Tungsten added, solution added Optical density difference mg ml Nil 0.0 0.002 1.0 0.0 0.031 0.029 Nil 0.26 0.003 1.0 _ .Xi1 1.0 Nil 1.0 Xi1 1.0 Nil 1.0 0.25 0.5 0.5 1.0 1.0 2.0 ~. 2.0 3.0 3.0 0.433 0.007 0.621 0.010 0.630 0.018 0.636 0.025 0.644 0.430 0.614 0.620 0.618 0.619 provide a reasonable safety margin, 1 ml of this reagent was used in all later experiments; this contributes about 0.01 to the optical density. Calibration gma@h-Sodium tungstate solution (1 ml E 0.1 mg of tungsten) in amounts ranging from 0 to 16.0 ml was added to solutions containing 0.2 g of tungsten-free zirconium prepared as before.The reagents were added and the optical densities were measured as before. A satisfactory calibration graph suitable for the determination of tungsten in the range 0.01 to 0.8 per cent. was obtained. EFFECT OF VARIOUS FACTORS- The effects of temperature, acidity, ammonium thiocyanate concentration and stability of the tungsten - thiocyanate complex were studied in the presence of zirconium, and resultsJune, 19581 TITANIUM, ZIRCONIUM AND THEIR ALLOYS 329 agreed with those from similar experiments relating to the determination of tungsten in titanium. Tests on solutions containing 0.2 g of zirconium and the equivalent of 0.10 and 0.80 per cent. of tungsten established that amounts up to at least 20 per cent.of tin, 5 per cent. of nickel or magnesium and 2.5 per cent. of chromium did not interfere. Copper in excess of 0.5 per cent. interfered, owing to precipitation of cuprous thiocyanate. Iron above about 2.5 per cent. interfered, owing to the yellow colour of ferric ions formed during dissolution of the sample, but interference (up to 5 per cent. of iron) was overcome by increasing the amount of titanous chloride to 2 ml. Molybdenum above 0.05 per cent. caused high results, but interference (up to 0-5 per cent. of molybdenum) was overcome by adding an equivalent amount of molybdenum to the blank solution. Vanadium above 0.01 per cent. interfered. EXTRACTION OF THE TUNGSTEN - THIOCYANATE COMPLEX- As a possible means of overcoming interference from alloying amounts of vanadium and molybdenum, and at the same time increasing the sensitivity of the method, attempts were made to extract the complex with organic solvents.Tests with isoamyl alcohol, isoamyl acetate, hexyl acetate, diethyl ether, chloroform and carbon tetrachloride indicated that only isoamyl alcohol extracted the complex to any appreciable extent, but even after four extrac- tions with this solvent it was not completely extracted, and so this possible extension of the procedure was discontinued. APPLICATION OF THE THIOCYANATE PROCEDURES The proposed thiocyanate procedures, see p. 331, were applied to samples of titanium, zirconium and their alloys, and, as shown in Table 11, reproducible results were obtained. TABLE I1 DETERMINATION OF TUNGSTEN IN SAMPLES OF TITANIUM, ZIRCOFIUM AND THEIR ALLOYS Sominal composition Titanium .. . . . . . . .. .. . . Titanium + 2 per cent. of aluminium + 2 per cent. of manganese . . . . . . .. .. .. Zirconium . . . . * . .. .. .. .. Zirconium + 1.5 per cent. of tin + 0.1 per cent. of iron + 0.1 per cent. of chromium + 0.05 per cent. of nickel . . . . .. .. .. .. .. Titanium* . . . . . . .. .. .. .. Titanium + 5 per cent. of aluminium + 2.5 per cent. of tin* . . .. .. . . .. .. .. Titanium + 2.5 per cent. of aluminium + 13 per cent. of tin* . . * . .. .. .. .. .. Titanium + 6 per cent. of aluminium + 4 per cent. of vanadium* .. . . . . .. * . .. Zirconium + 1.5 per cent. of tin + 0.1 per cent. of iron + 0.1 per cent. of chromium + 0.05 per cent. of nickel* . . .. .. .. .. .. Zirconium + 2.5 per cent.of tin* .. * . .. Tungsten found by thiocyanate method, % 0.44, 0.44, 0.44, 0.445, 0.445, 0.44 0.16, 0.16 0.47, 0.46 - 0.07, 0.07 0.40, 0.40, 0.405, 0.40, 0,395, 0.40 Tungsten found by dithiol method, 0.0015. 0.0015 % 0.002, 0.002 0.002, 0.002 0.002, 0.002 0.434, 0.430, 0.435, 0.428, 0.430, 0.430 0.170. 0.170 0.470, 0.475 0.425, 0.420 0.069, 0.070 0.402, 0.404, 0.404, 0.405, 0.400, 0.395 Standard deviation of thiocyanate method at 0.4 per cent. of tungsten = & 0.003 per cent. Standard deviation of dithiol method a t 0.4 per cent. of tungsten = 2 0.003 per cent. * Prepared by an arc-melting process with tungsten electrodes. DITHIOL METHOD FOR TUNGSTEN I N TITANIUM A mixture of sulphuric and phosphoric acids, such as that used for dissolving steel, is not suitable for dissolution of titanium because of the insolubility of titanium phosphate ; a mixture of sulphuric and fluoroboric acids was therefore used in the experimental work.330 [Vol.83 PRELIMINARY EXPERIMENTS- Preliminary experiments were made to establish the wavelength at which maximum absorption of the tungsten - dithiol complex occurs, and then, by using this wavelength, to prepare a calibration graph. Absorption curve-A 0.25-g sample (of tungsten-free titanium was dissolved in a mixture of 50 ml of dilute sulphuric acid (1 + 4) and 0.5 ml of fluoroboric acid, and the solution was oxidised with nitric acid, sp.gr. 1.412. Fifteen millilitres of sodium tungstate solution (1 ml = 0.1 mg of tungsten) were added and, after dilution to 100 ml, a 5-ml aliquot was taken and evaporated to fumes of sulphur trioxide.The solution was cooled, 5 mlof stannous chloride (10 per cent. in hydrochloric acid, sp.gr. 1.18) were added and the solution was heated on a boiling-water bath for 4 minutes. A 10-ml portion of dithiol solution (1 per cent. in isoamyl acetate) was added and heating was continued, with frequent shaking, for 10 minutes. The solution was then cooled, transferred to a separating funnel and the aqueous layer removed. The solvent layer was washed twice with diluted hydrochloric acid (4 + 1) and diluted to 50 ml with isoamyl acetate in a calibrated flask. The optical density of the solution was determined in a 4-cm cell with a Unicam SP600 spectrophotometer at wavelengths between 5000 and 6600 A ; the maximum absorption was found to be at 6300 A.Calibration graph-Solutions containing 0.25 g of tungsten-free titanium and amounts of sodium tungstate solution (1 ml E 0.1 mg of tungsten) ranging from 0 to 20 ml were diluted to 100 ml. Aliquots of 5 ml were taken and examined as described above, but the optical densities at 6300 A were not proportional to the amounts of tungsten added and colour development was not complete. Further tests with solutions containing tungsten only, and iron in addition to tungsten, indicated that the presence of iron is necessary in order to obtain quantitative values for tungsten To investigate the effect of the presclnce of iron, solutions containing 0.25 g of titanium and the equivalent of 1.5 mg of tungsten were diluted to 100 ml.Five-millilitre aliquots of these solutions, to which were added amounts of ferrous sulphate solution (1 ml = 5 mg of iron) ranging from 0 to 5.0 ml, were examined as before. The optical densities were measured at 6300 A. Increase in the amount of iron over the range 0 to 12.5 mg resulted in an increase in optical density of the tungsten - dithiol complex, but from 12.5 to 25.0 mg of iron there was no significant change in optical density and colour development was complete, as shown by the following results- 11 OOD AiXD CLARK: TH 5 DETERMINATION OF TUNGSTEN I N Iron present, mg . . Nil 1.0 5-0 10.0 12.5 15.0 17.5 20.0 25.0 Optical density . . 0.688 0.701 0 712 0.735 0.742 0.748 0.747 0.748 0,749 In all later experiments, 1 ml of ferrous snlphate solution (equivalent to 15 mg of iron) was added to the solutions immediately before evaporation to fumes of sulphur trioxide.By using this modification, satisfactory calibration graphs were prepared covering the ranges 0.05 to 0.8 per cent. and 0.002 to 0.08 per cent. of tungsten. EFFECT OF VARIOUS FACTORS- Tests showed that no significant variation in optical density of the complex occurred over the range 18" to 35" C and strict control of solution temperature during optical-density measurement was therefore not essential. The complex was stable for a period up to 1 hour, after which a decrease in optical density gradually occurred. In further tests, different amounts of sulphuric acid, sp.gr. 1.84, from 0 to 5 ml had no significant effect on the optical density of the final solution.Increase in the amount of 10 per cent. stannous chloride solution over the range 2 to 10 ml had, likewise, a negligible effect. Below 2 ml, the optical density decreased with decrease in the stannous chloride concentration, owing to incomplete reduction of the tungsten. Different times of boiling with stannous chloride from 1 to 6 minutes had no effect on the optical density of the complex. At least 7.5 ml of dithiol solution were required in order to obtain full development of the colour, and no change in the optical density occurred over the range 7.5 to 15 ml. Vari- ation of the time of boiling with this reagent from 3 to 15 minutes had no significant effect. Tests by the proposed dithiol procedure (see p. 332) established that amounts up to about 20 per cent.of tin, manganese or varladium, 10 per cent. of aluminium and 5 per cent. of copper, iron, chromium or nickel did not interfere in the determination of 0-02 and 0.60 per cent. of tungsten.June, 19581 TITANIUM, ZIRCONIUM AND THEIR ALLOYS 331 Molybdenum forms a green complex with dithiol under test conditions and this caused serious interference, Molybdenum has not, so far, occurred as a significant impurity in titanium, but it is used as an alloying constituent and the presence of a large amount of this metal had, therefore, to be considered. Attempts to overcome molybdenum interference in the presence of titanium by extraction of the dithiol complex with isoamyl acetate before reduction of tungsten, in accordance with a published method for the examination of steel,4 were unsuccessful and the results were erratic.Results were also erratic when the method of Short6 was used. High results were attributed to incomplete extraction of molybdenum and low results to extraction of some tungsten during the preliminary separation of molybdenum. Interference was overcome, however, by precipitation of molybdenum sulphide in acid - tartrate solution. In this method, prior oxidation of the solution with potassium permanganate is necessary, otherwise the results are high, due, presumably, to reduction of molybdenum (by titanous ions) to a lower valency state, which results in incomplete precipitation. The results in Table I11 show that this procedure can be satisfactorily applied to solutions containing from 0.1 to 10 per cent.of molybdenum, 0.02 to 0.6 per cent. of tungsten and major amounts of titanium. TABLE I11 DETERMINATION OF TUNGSTEN BY THE MODIFIED DITHIOL PROCEDURE FOR Each solution contained 0.25 g of titanium Molybdenum added, Tungsten added, Tungsten found, Yo % % USE IN THE PRESENCE OF MOLYBDENUM 0.1 1.0 10.0 0.1 1.0 10.0 0.1 1.0 10.0 0.02 0.02 0.02 0.05 0.05 0.05 0.60 0.60 0.60 0.021 0.022 0.023 0.050 0.051 0.051 0.61 0.612 0.611 DITHIOL METHOD FOR TUNGSTEN IN ZIRCONIUM Calibration graphs over the range 0.05 to 0.8 per cent. and 0.002 to 0.08 per cent. of tungsten, prepared from solutions also containing 0.25 g of zirconium, were identical with those prepared in experimental work relating to tungsten in titanium. APPLICATION OF THE DITHIOL PROCEDURE The dithiol procedure for 0.002 to 0.3 per cent.of tungsten was applied to samples of titanium, zirconium and their alloys and, as shown in Table 11, results were reproducible and agreed with those found by the thiocyanate procedures. METHODS THIOCYANATE METHOD FOR THE DETERMINATION OF TUNGSTEX IN TITANUM AND ITS ALLOYS REAGENTS- Hydrochloric acid, sp.gr. 1.18. Fluoroboric acid-To 280 ml of hydrofluoric acid maintained at 10" C add, in small Ammonium thiocyanate solution, 15 per cent.-Dissolve 75 g of ammonium thiocyanate Standard tungsten solution-Dissolve 0,1794 g of sodium tungstate, Na,W04.2H,0, in amounts, 130 g of boric acid and stir well. in about 250 ml of water and dilute to 500 ml. water and dilute to 1 litre. PREPARATION OF CALIBRATION GRAPH FOR 0.05 TO 1.6 PER CENT.OF TUNGSTEN- Transfer 0.2-g portions of tungsten-free titanium to each of seven beakers and dissolve each portion in 20 ml of hydrochloric acid and 1 ml of fluoroboric acid; warm gently to assist Store in a polythene bottle. 1 ml = 0.1 mg of tungsten.332 [Vol. 83 dissolution. Cool and add, separately, 4.0, 12.0, 16.0, 20.0, 24.0 and 32.0ml of standard tungsten solution. Dilute each solution to 100ml in a calibrated flask and transfer 25-ml aliquots to separate 100-ml calibrated flasks. Add 20 ml of hydrochloric acid and 10 ml of ammonium thiocyanate solution to each. Dilute to the mark and set them aside for 5 minutes at 20" i: 1" C. Measure the optical density of each at a wavelength of 4000 A in 2-cm cells. PROCEDURE- Determine a blank value by using a weight of tungsten-free titanium corresponding approximately to the weight of titanium in the sample.Dissolve a 0.2-g sample in 20 ml of hydrochloric acid and 1 ml of fluoroboric acid; warm gently to assist dissolution. (For amounts of tungsten in excess of 1.6 per cent. up to 3.2 per cent., use a smaller weight of sample.) Cool, dilute to 100ml in a calibrated flask and proceed as described for the preparation of the calibration graph. Calculate the tungsten content of the sample from the calibration graph. Note that vanadium above about 0.05 per cent. and molybdenum above about 0.25 per cent. introduce significant positive errors. Molybdenum (up to about 2 per cent.) can be corrected for by adding an equivalent amount of molybdenum to the blank solution.For samples containing vanadium or molybdenum in excess of these limiting amounts, the dithiol method is recommended. THIOCYANATE METHOD FOR THE DETERMINATION OF TUNGSTEN IN WOOD AND CLARK: THE DETERMINATION OF TUNGSTEN I N Use the remaining solution as a blank. ZIRCONIUM AND ITS ALLOYS REAGENTS- The reagents used are the same as for the determination of tungsten in titanium, plus- Titanous chloride solution-Dissolve 1.0 g of titanium in about 50 ml of hydrochloric acid, sp.gr. 1-18. Cool and dilute with hydrochloric acid to 100ml. This reagent must be freshly prepared. Transfer 0.2-g portions of tungsten-free zirconium to each of seven beakers and dissolve each portion in 25 ml of hydrochloric acid ;and 1 ml of fluoroboric acid; warm gently to assist dissolution.Cool and add, separately, 2.0,4*0, 6-0, 8.0, 12.0 and 16.0 ml of standard tungsten solution. Transfer each solution to a 100-ml calibrated flask, washing with about 25 ml of water. Add 1 ml of titanous chloride solution and 10 ml of ammonium thiocyanate solution to each Dilute to the mark and set them aside for 5 minutes at 20" Measure the optical density of each at a wavelength of 4 0 0 0 ~ in 1-cm cells. PROCEDURE- Determine a blank value on the reagents with each batch of samples. Dissolve a 0.2-g sample in 25 ml of hydrochloric acid and 1 ml of fluoroboric acid; warm gently to assist dissolution. (For amounts of tungsten in excess of 0.8 per cent. up to 3.2 per cent., use a smaller weight of sample. When the tungsten content is below 0.05 per cent., use 4-cm cells.) Cool and transfer the solution to a 100-ml calibrated flask with about 25 ml of water, and then continue as described for the preparation of the calibration graph.Calculate the tungsten content of tht: sample from the calibration graph. Note that vanadium above about 0.01 per cent. and molybdenum above about 0.05 per cent. introduce significant positive errors. Molybdenum (up to about 0.5 per cent.) can be corrected for by adding an equivalent amount of molybdenum to the blank solution. For samples containing vanadium or molybdenum in excess of these limiting amounts, the dithiol method is recommended. DITHIOL METHOD FOR THE DETERMINATION OF TUNGSTEN IN TITANIUM, PREPARATION OF CALIBRATION GRAPH FOR. 0.01 TO 0.8 PER CENT. OF TUNGSTEN- Use the remaining solution as a blank.1" C. ZIRCONIUM AND THEIR ALLOYS REAGENTS- 1.84. Mix well and cool. Sulphuric acid, dilute (1 + 4)-To 400 ml of water, add 100 ml of sulphuric acid, sp.gr. Fluoroboric acid-Prepare as described on p. 331.June, 19581 TITANIUM, ZIRCONIUM AND THEIR ALLOYS 333 Nitric acid, sp.gr. 1.42. Iron soZutioH-Dissolve 1.5 g of electrolytic iron in 25 ml of dilute sulphuric acid (1 + 4) and dilute to 100ml. 1 ml z 0.015 g of iron. SnC1,.2H,O, in 100ml of hydrochloric acid, sp.gr. 1.18 100ml of water. water and dilute to 1 litre. For use, dilute 100ml of this solution to 1 litre. PREPARATION OF CALIBRATION GRAPHS- Dissolve 0.625g of tungsten-free metal (titanium or zirconium) in 125ml of dilute sulphuric acid (1 + 4) and 1 ml of fluoroboric acid; warm gently to assist dissolution and then oxidise with a few drops of nitric acid.Boil to remove nitrous fumes, cool and dilute to 250 ml in a calibrated flask. Calibration graph for 0.05 to 0.8 per cent. of tungsten-Transfer five 5-ml aliquots of the solution (titanium or zirconium) to each of five 100-ml conical flasks and add, separately, 2.5, 5-0, 7.5 and 10.0ml of standard tungsten solution. Use the remaining solution as a blank. Cool, add 5ml of stannous chloride solution to each, place them on a boiling-water bath and agitate at frequent intervals over 4 minutes. Add 10ml of dithiol solution and continue heating on the water bath, with frequent agitation, for 10 minutes. Cool to about 30" C and transfer each solution to a separating funnel, rinsing with three 2-ml portions of isoamyl acetate.Shake and allow the layers to separate; run off and discard each lower acid layer. Wash the solvent layers twice with 10-ml portions of diluted hydrochloric acid (4 + 1) and each time discard the lower acid layers. Remove the upper solvent layers containing the tungsten, and transfer them to 50-ml calibrated flasks that have previously been washed free from water with ethanol and then with isoamyl acetate. Dilute each solution to the mark with isoamyl acetate and mix well. Measure the optical density of each solution at a wavelength of 6 3 0 0 ~ in 4-cm cells. Calibration graph for 0.002 to 0.08 per cent. of tungsten-Transfer five 25-ml aliquots of the solution (titanium or zirconium) to each of five 100-ml conical flasks and add, separately, 1-25, 2.5, 3.75 and 5.0 ml of standard tungsten solution.Use the remaining solution as a blank. Add 1 ml of the iron solution to each and continue as described for the preparation of the calibration graph for 0.05 to 0.8 per cent. of tungsten, but transfer the final isoamyl acetate layers containing the tungsten to 25-ml calibrated flasks washed free from water. Dilute each to the mark with isoamyl acetate and continue as previously described. PROCEDURE FOR 0.002 TO 0.8 PER CENT. OF TUNGSTEN- Dissolve a 0-25-g sample in 50 ml of dilute sulphuric acid (1 + 4) and 0.5 ml of fluoroboric acid; warm gently to assist dissolution and oxidise with a few drops of nitric acid. Boil to remove nitrous fumes, cool and transfer to a 100-ml calibrated flask and dilute to the mark.Transfer 5 ml of the solution to a 100-ml conical flask, add 1 ml of the iron solution and con- tinue as described for the preparation of calibration graph for 0.05 to 0.8 per cent. of tungsten. Calculate the tungsten content of the sample from the calibration graph. If the tungsten content of the sample is below 0.05 per cent., transfer a 25-ml aliquot from the remainder of the 100 ml of solution to a 100-ml conical flask, add 1 ml of the iron solution and continue as described for the preparation of the calibration graph for 0.002 to 0.08 per cent. of tungsten. PROCEDURE FOR TUNGSTEN IN SAMPLES CONTAINING MOLYBDENUM- Dissolve a 0.25-g sample in 25 ml of dilute sulphuric acid (1 + 4) and 0.5 ml of fluoro- boric acid; warm gently to assist dissolution and oxidise by dropwise additions of a saturated solution of potassium permanganate, until a permanent brown precipitate is present.Add Stannous chloride solution, 10 per cent. w/v-Dissolve 10 g of stannous chloride, Dithiol solution-Dissolve 1 g of toluene-3 : 4-dithiol in 100 ml of isoamyl acetate. Hydrochloric acid, diluted (4 + 1)-Dilute 400 ml of hydrochloric acid, sp.gr. 1-18, with Standard tungsten solution-Dissolve 0.1794 g of sodium tungstate, Na,W0,.2H,O, in 1 ml = 0.01 mg of tungsten. Add 1 ml of the iron solution to each and evaporate to fumes of sulphur trioxide.334 WOOD AND CLARK [Vol. 83 sulphurous acid dropwise until the precipitate has dissolved and then boil for 2 minutes to remove excess of sulphur dioxide. Add 15 ml of 50 per cent.tartaric acid solution, 250 ml of water and warm to 80” C. Pass a rapid stream of hydrogen sulphide through the solution €or 30 minutes and then allow to cool to room temperature. Transfer the solution and precipitate to a 500-ml calibrated flask and dilute to the mark. Filter an approximately 50-ml portion through a Whatman No. 42 filter-paper, transfer 25 ml of the filtrate to a 100-ml conical flask, add 1.0ml of dilute sulphuric acid (1 + 4) and 1 ml of the iron solution and then evaporate to fumes of sulphur trioxide. Destroy carbonaceous matter by adding nitric acid, sp.gr. 1.42, in 2-ml portions to the hot residue. Continue as described for the preparation of the calibration graph for 0.05 to 0.8 per cent. of tungsten. Calculate the tungsten content of the sample from the calibration graph. If the tungsten content of the sample is below 0.05 per cent., transfer a 100-ml aliquot of the filtrate to a 250-ml conical flask, add 1.5 ml of sulphuric acid, sp.gr.1-84, and 1 ml of the iron solution and then evaporate to fumes of sulphur trioxide. Destroy carbonaceous matter and continue as described for the preparation of the calibration graph for 0-002 to 0.08 per cent. of tungsten. CONCLUSIONS The proposed absorptiometric thiocyariate procedure is satisfactory for the determination of 0.05 to 1.6 per cent. of tungsten in titanium and many of its alloys. Vanadium above 0.05 per cent. and molybdenum above 0.5 per cent. interfere. Interference by molybdenum, up to about 2 per cent., can be overcome by adding an equivalent amount of molybdenum to the blank solution. The proposed thiocyanate procedure for the examination of zirconium and its alloys is applicable over the range 0.01 to 1.6 per cent.of tungsten. Vanadium above 0.01 per cent. and molybdenum above 0.05 per cent. interfere. Interference by molybdenum, up to 0.5 per cent., can be compensated for. Both procedures can be extended to the deter- mination of tungsten up to about 3.2 per cent. by using a smaller weight of sample. The procedures are simple, rapid and particula.rly suitable for control analysis. The dithiol procedure is suitable for the determination of tungsten in the range 0.002 to 0.8 per cent. in titanium, zirconium and their alloys. By using smaller absorption cells, it can be extended to the determination of am.ounts of tungsten up to about 3.2 per cent. The presence of iron is necessary in order to obtain quantitative results. Vanadium does not interfere, and interference by molybdenum can be overcome by incorporating a preliminary precipitation of molybdenum sulphide. The dithiol method is more time-consuming than the thiocyanate method and is, therefore, only recommended in the examination of samples containing amlsunts of vanadium or molybdenum sufficient to cause interference with the thiocyanate procedure, and for general application to materials containing less than about 0.05 per cent. of tungsten. We thank Mr. W. T. Elwell, Division Chief Analyst, for helpful suggestions and assistance in preparation of this paper. REFERENCES 1. 2. 3. 4. 5. 6. 7. Sandell, E. B., “Colorimetric Determination of Traces of Metals,” Second Edition, Interscience Gentry, C. H. R., and Sherrington, L. G., Analyst, 1948, 73, 57. Freund, H., Wright, M. L., and Brookshier, R. K., Anal. Chew., 1951, 23, 781. Bagshawe, B., and Trueman, R. J.. Analy.ct, 1947, 72, 189. Bacon, A., Royal Aircraft Establishment Technical Note N o . MET.119, 1950. Short, H. G., Analyst, 1951, 76, 710. “The Analysis of Titanium and its Alloys,” Imperial Chemical Industries Ltd., First Edition, Received December 12th, 1957 Publishers Inc., h’ew York and London, 1950, Volume 111, p. 584. London, 1956.

ISSN:0003-2654    

DOI:10.1039/AN9588300326

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

June, 19581 SERGEANT 335 The Determination of Chlorinated Hydrocarbon Pesticide Residues in Plant Material BY G. A. SERGEANT (Department of the Government Chemist, Clement's I n n Passage, Straizd, Loitdon, W.C.2) h method is described for the determination of a number of chlorinated hydrocarbon pesticide residues in plant material. After extraction and partial purification, the residues are analysed for total organic chlorine by a modified Stepanow procedure, followed, after the removal of organic matter and excess of sodium ions, by a volumetric determination of chloride by the mercuric oxycyanide method. PROCEDURES for the determination of organic chlorine that involve reduction with sodium by modifications of the original Stepanow methodl have frequently been published, and that described in a recent report of the Analytical Methods Committee of the Society for Analytical Chemistry2 is a typical application.isoPropyl alcohol is now the usual medium for the reduction, although isobutyP and isoamy14 alcohols and a mixture of dioxan and ethanol- amine5 have also been used. In this paper a further modification of the Stepanow method is described, together with its application on the semi-micro scale to the determination of chlorinated hydrocarbon pesticide residues in plant material. The rapid decomposition of organic halogen compounds by reaction with aromatic sodium compounds has been utilised by Liggett6 and others,'*s and is especially advantageous in the analysis of volatile materials, as the reaction proceeds rapidly even in the cold.Reagents such as sodium diphenyl and sodium naphthalene are, however, troublesome to prepare and store, and, in the proposed application of the reaction, sodium naphthalene is generated directly in the reaction flask instead of being added as a prepared reagent. The resulting technique resembles that of Stepanow, but is much more rapid, partly because the end-point of the reaction is self-indicating. From the limited range of solvents in which the formation of aromatic sodium compounds readily takes place, tetrahydrofuran was selected in preference to 1 : 2-dimethoxyethane. Two other solvents of interest noted in the course of the work were isopropylamine and rt-butylamine. The velocity of the reaction increases markedly with the concentration of the aromatic compound, in this instance naphthalene, and it is therefore desirable to keep the volume of solvent as small as possible.The modified Stepanow procedure described later is satisfactory for the semi-micro determination of amounts of organic chlorine up to at least 10mg. The end-point of the reaction, which is indicated by the intense green colour of excess of sodium naphthalene, may become less apparent with the larger amounts of chlorine, as the reacting solution often becomes deeply coloured. Gravimetric determination of chlorine as silver chloride was preceded by part neutralisation of the reaction solution, evaporation to dryness in a platinum basin and gentle ignition to remove all traces of organic matter. The part removal of organic matter by means of an ether separation gave very low results in the analysis of a chlorinated nitro compound, owing to incomplete precipitation of silver chloride.Application of the proposed method to pesticide residues was intended to attain a sensitivity of 10 pg or less of chlorine, and a volumetric finish by the mercuric oxycyanide methodgJO was adopted, as this is simple and, on the semi-micro scale, sufficiently sensitive. To achieve a reasonably sharp end-point in the titration of chloride at high dilutions, it is necessary to remove both the excess of sodium ions, by means of a cation-exchange resin, and, by careful ignition, all traces of organic matter. The extraction with light petroleum of chlorinated hydrocarbon pesticides, added in known amounts to plant material, gave low yields and was abandoned in favour of extraction with a mixture of equal volumes of light petroleum and acetone.Benzene, which is often recommended, has the disadvantage of not being readily removed in a Danish - Kuderna evaporator, The excellent penetrating power for plant tissues possessed by the solvent mixture gives rise to extracts containing considerable amounts of plant extractives, and some degree of chromatographic separation is generally desirable. Activated alumina of suitably controlled water content can be used to effect a part separation of plant colouring336 SERGEANT : THE DETERMINATION OF CHLORINATED HYDROCARBON [Vol. 83 matter without retention, after elution with light petroleum, of any of a number of chlorinated hydrocarbon pesticides tested, with the exception of Kelthane, which is rather strongly adsorbed.The method is not intended for the analysis of materials that have an appreciable fat content. Although it does not appear to be practicable to separate a wide range of the chlorinated pesticides from large amounts of fat by a single method, techniques of limited application have been described,ll~12~13~14 and a combustion method of analysis has recently been recommended in this connection.lt' APPARATUS- Machine for swb-dividing the sample material-A domestic mincing machine of large capacity. Extraction vessels-Flat-bottomed 500-ml or larger flasks with standard ground-glass stoppers held in position by spring clamps. A wide socket, such as a B34, is desirable to facilitate the introduction of the sample material.Before insertion of the stopper, the ground-glass surfaces should be carefully cleaned and the stopper wetted with water to improve the seal. Shaking machine-This should rotate the extraction vessels with an end-over-end motion at a rate of about 1 revolution per second. REAGENTS- METHOD OF EXTRACTING THE PESTICIDE Light petroleum, redistilled-The fraction boiling over the range 60" to 80" C. Acetone, redistilled. PROCEDURE- Introduce 100 to 300g of the minced or shredded sample into the extraction vessel and, for each gram of material, add 1 ml of light petroleum, accurately measured, and 1 ml of acetone. For fibrous absorbent materials, such as grass, these volumes need to be doubled. Insert the stopper, rotate the flask for 1 hour and then pour the liquid through a fast- filtering paper into a separating funnel.Run off and reject any lower aqueous layer and to the remainder add an equal volume of distilled water. Wash the extract free from acetone and water-soluble chloride by shaking first with this and then with two further similar portions of distilled water. Run off the final water washings, add a few grams of anhydrous sodium sulphate and then shake to absorb the remaining water. Run off the liquid into a measuring cylinder and note the volume of light petroleum recovered, or remove by pipette an aliquot calculated to contain not more than 1.5 mg of chlorine. The pesticide is assumed to be distributed uniformly in the total original volume of light petroleum. APPARATUS- Chyomatographic tube-A filter tube, 30mm x 200mm, with a No.1 sintered-glass plate. Evaporator-A simple form of Danish - Kuderna evaporator.ls This consists of a 500-ml round-bottomed flask, the neck of which is fitted with a B24 ground-glass socket, and to the bottom of which is sealed a B14 ground-glass cone. In use, a splash head joined to a condenser for solvent recovery is fitted t o the socket, and a 25-ml round-bottomed flask with a B14 ground-glass socket is attached to the cone and held in place by a spring clamp. The ground-glass joints are moistened with liquid paraffin before assembly and the apparatus is heated by supporting the larger flask on an open-ended cylinder, e.g., made from a tin can, that stands on a steam-bath in such a way that the 25-ml flask and the lower part of the larger flask are surrounded by steam.Some device to prevent bumping of the liquid is necessary, and for this purpose a narrow strip of polytetrafluoroethylene sheeting was found to be effective. REAGENTS- Activated alumina-Heat dry aluminium hydroxide to 800" C and maintain at this temperature for not less than 1 hour; when cool, transfer the ignited material to a stoppered bottle, add 5 per cent. w/w of water and set aside overnight. Shake to mix the prepared alumina before use. METHOD OF TREATING THE EXTRACTJune, 19581 PESTICIDE RESIDUES IN PLANT MATERIAL 337 Sodium sulphate, anhydrous. Light petroleum, redistilled-The fraction boiling over the range 60" to 80" C. PROCEDURE- Transfer 10 g of activated alumina to the chromatographic tube and tap down to ensure that the column is uniformly packed. Cover the alumina with a 1-cm layer of sodium sulphate and arrange to collect the effluent from the column in the evaporator.Introduce the extract carefully, so as not to disturb the column, and, when it has passed completely through the column, add light petroleum rinsings; allow these to drain, and complete the operation by washing the column with 100 ml of light petroleum. Place the evaporator on a steam-bath after adding to the contents 2 drops of liquid paraffin and, when the volume of liquid has been reduced to a few millilitres, remove the evaporator and allow it to cool. Take off the splash head and rinse the apparatus with light petroleum. Detach the 25-ml flask and continue the evaporation on a water bath at 40" C with a stream of dry air until the remaining solvent has been removed.APPARATU s- MODIFIED STEPANOW METHOD FOR THE DETERMINATION OF ORGANIC CHLORINE Re$ux condenser-A small Liebig condenser fitted with a B14 ground-glass cone. Agla micrometer-syringe pipette-A right-angled glass jet is required. A suitable jet can be readily made from drawn-out glass tubing and attached to the syringe by a short piece of capillary plastic or rubber tubing, the flexibility of which protects the jet against accidental breakage or dislocation. Magnetic stirrer. Silica basins-Between determinations these should be kept filled with chromic acid cleaning mixture. REAGENTS- Naphthalene-Analytical-reagent grade. Tetrahydrofuran-Purify by placing 20 ml in a 200-ml Aask fitted with a reflux condenser by means of a ground-glass joint, and add 4 g of naphthalene and 4 g of clean sodium cut into small pieces.Boil the liquid until it becomes dark green, and then for a further 5 minutes. Continue boiling, and, by way of the condenser, add from a dropping funnel a further 100 ml of tetrahydrofuran and then 20 ml of xylene, the additions being made at such a rate that the colour of the solution is not discharged. Finally, replace the reflux condenser by an ordinary condenser with the addition of a fractionating column and distil off the purified tetrahydrofuran, which should be stored away from light. Sodium-To prepare the sodium in a convenient form for use, clean a number of pellets in turn by immersion in isopropyl alcohol and warming on a steam-bath until a vigorous reaction is proceeding.Quickly rinse the pellets with light petroleum and transfer them to a nickel crucible containing liquid paraffin. Heat the pellets until they melt, and then stir gently to assist coagulation into a large globule. Draw up the molten metal into clean dry glass tubes of about 5 mm internal diameter and 300 mm long, wetted internally with liquid paraffin. Allow the tubes to cool thoroughly, and extrude the sodium as required with the help of a glass rod. isoPropyl alcohol, diluted (1 + 1)-Add 1 volume of analytical-reagent grade isopropyl alcohol to 1 volume of distilled water. Screened methyl red indicator solution-Dissolve 0.08 g of water-soluble methyl red in 25 ml of distilled water, and 0.02 g of methylene blue in 25 ml of ethanol.Mix equal volumes of the two solutions for use. Sulphuric acid, 0.1 N, and approximately 0.04 N-A 0.1 N solution of sulphamic acid can alternatively be used; prepare an aqueous solution containing 0-971 g of the pure recrystallised acid per 100 ml. Potassium hydroxide solution-An approximately 0.04 N solution of the analytical-reagent grade material. Mercuric oxycyanide reagent solution-Dissolve 4 g of mercuric oxycyanide in 100 ml of distilled water, stirring on a steam-bath to assist dissolution. Cool and filter the solution, which is slightly alkaline and must be neutralised. For this purpose, carry out the titration procedure described later for chloride determination on 15 ml of distilled water, and thereby338 SERGEANT : THE DETERMINA.TIOX OF CHLORINATED HYDROCARBOS [Vol.83 determine the volume of 0.1 N acid required to neutralise 2 ml of the mercuric oxycyanide reagent under the conditions of the titration. Hence calculate the volume of acid to be added to neutralise the remaining bulk #of the reagent. Ion-exchange resin-Introduce 10 ml (of dry Zeo-Karb 225, (40 to 60-mesh) in the hydrogen form, into a glass tube of 16 mm internal d!iameter and 150 mm long, which tapers at the lower end to a jet and is fitted with a retaining plug of cotton-wool. Regenerate the resin before use and after each determination by running through the column, successively, 15ml of acetone, 15 ml of diethyl ether, 15 ml of 10 per cent. v/v nitric acid and, finally, not less than 40 ml of distilled water.If distilled water from the regular supply is found to contain significant amounts of chloride, it should be made alkaline and redistilled. The resin can be used many times. PROCEDURE- To the residue in the 25-ml flask add approximately 0.4 g of naphthalene, 1.5 to 2 ml of purified tetrahydrofuran and 0.2g of sodium cut into small pieces. Attach the reflux condenser, which should be quite dry, and boil the liquid over the flame of a microburner, e g . , the jet of a bunsen burner, until the appearance of an intense dark green colour indicates the end of the reaction, usually after from 2 to 5 minutes in the absence of appreciable amounts of moisture. Continue heating and add 2 ml of diluted isopropyl alcohol drop by drop. When all the residual sodium has dissolved, remove the flask and add distilled water to a total volume of about 15ml.Cool the flask in ice, then pour the contents into the resin column and collect the effluent in a silica basin. When all the liquid has entered the resin, rinse the flask with about 20 ml of distilled water and add the washings to the column. When the column has drained wash the resin with a further 20ml of distilled water. To the combined effluent and washings add phenolphthalein indicator and 0.04 N potassium hydroxide until just alkaline. Evaporate the liquid to dryness under an infra-red lamp, and then heat the basin, held in tongs over the flame of a bunsen burner, to a temperature just short of redness. It is essential to carbonise organic matter completely, but neither necessary nor desirable to attempt to burn off all the residual carbon.Cool the basin and add about 5 ml of distilled water and 1 drop of screened methyl red indicator solution. Stir the solution and make it just acid with 0.04 N sulphuric acid, then place the basin on a steam-bath for 1 to 2 minutes, with occasional stirring and further additions of acid if the solution turns alkaline. Transfer the solution to a 25-ml beaker, rinse the basin with distilled water and add the washings to the beaker until the total volume is approximately 16 ml. Cool the solution to room temperature and place the beaker on a magnetic stirrer. Add 4 drops of screened methyl red indicator solution and 0.04 N potassium hydroxide until the solution is just alkaline, and then standard 0.1 N acid from the micrometer-syringe pipette to give a persistent pinkish grey tint.Add 2ml of mercuric oxycyanide reagent solution and titrate with the acid to the same end-point colour. Determinatioiz of titration factor-Prepare an aqueous solution of potassium chloride containing 100 pg of chlorine per ml. Place aliquots up to 10 ml of this solution in a series of 25-nil beakers and dilute each to 15 ml with distilled water. Carry out the titration on each aliquot, and on 15 ml of distilled water, in the way described above. Plot graphically micrograms of chlorine taken against micrometer-reading differences less that for the distilled water titration. The relationship is not strictly stoicheiometric, but should be substantially linear over this range.Hence calculate the titration factor in micrograms of chlorine per millimetre on the micrometer scale. Determination of the blank value-Carry out a blank determination to ascertain the correction to be applied for chlorine present in the reagents. With reagents of reasonable purity and a laboratory atmosphere free from chloride fumes, this correction should not be more than 1Opg. R.ESULTS As sample material known to be uncontaminated with pesticide was not conveniently obtainable, and the concentration of any natural organic chlorine was uncertain, cabbage and tomato samples were minced and the minced material was well mixed and divided into halves. One half of each sample was treated as a control and a known weight of pesticideJune, 19581 PESTICIDE RESIDUES IN PLANT MATERIAL 339 was added to the other half in the form of a solution in light petroleum, which was allowed to evaporate.The results in Table I represent over-all recoveries of the various pesticides after deduc- tion of the equivalent of any organic chlorine found in the control samples, and are calculated on the theoretical chlorine contents of the pure crystalline substances and on the chlorine content of the technical materials as determined by analysis. TABLE I RECOVERY OF PESTICIDES ADDED TO PLANT MATERIAL Pesticides were added in the pure crystalline forms, except chlordane and toxaphene, which were added as the technical products Pesticide Pesticide found, Organic chlorine in control, p.p.m. p.p.m. With 1 mg of pesticide added to 100 g of minced cabbage, i.e., 10 +.p.m.of pesticide- y-Hexachlorocyclohexane . . 9.8, 9.4 0.05, 0.05 pp’-DDT . . . . . . . . 9.8, 9.8 0.05, Nil Methoxychlor . . . . . . 9.0, 8.8 0.35, Nil Aldrin . . .. . . . . 9.6, 9.6 0.05, Nil Dieldrin . . .. . . . . 9.2, 9.8 Nil, Nil Endrin . . . . .. . . 9.4, 9.9 Nil, 0.2 Chlorbenside . . . . . . 9.9, 9.4, 9.5 Nil, 0.15, 0.05 Chlordane . . .. . . . . 8.7, 9.2 Xil, 0.05 Toxaphene . . . . . . 9.6, 10.3 0.05, Kil With 1 mg of pesticide added to 100 g of minced tomato, i.e., 10 p.9.m. ofpesticide- y-Hexachlorocydohexane . . 10.0, 10.1 0.05, 0.05 pp’-DDT . . . . . . . . 10.7, 9.9 0.05, 0.05 Chlorbenside , . . . . . 10.0. 10.4, 10.2 0.i. 0.2, 0.05 Toxaphene .. .. . . 10.1, 10.3 0.25, 0.05 With 250 pg of pesticide added to 250 g of minced cabbage, i.e., 1 p.p.m. of pesticide- Aldrin . . .. * . . . 0.91, 0.91, 0.95 0.12, 0.08, 0.08 Dieldrin . . .. .. . . 0.97, 0.85, 0.90 0.08, 0.14, 0.14 Endrin . . .. .. . . 1.09, 0.83, 0.67 0.14, 0.02, Nil I thank the Government Chemist for permission to publish this paper, and also Mr. P. B. Thompson for technical assistance. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. REFERENCES Stepanow, A., Ber., 1906, 39, 4056. Analytical Methods Committee, “The Determination of Small Amounts of Total Organic Chlorine Phillips, W. F., and DeBenedictis, &I. E., J . Agric. Food Chem., 1954, 2 , 1226. Quist, W., and Holmstrom, T., Finska Kemistsanzfundets Medd., 1955, 64, 68. Rauscher, W. R., Ind. Eng. Chem., A?zal. Ed., 1937, 9, 296. Liggett, L. M., Anal. Chem., 1954, 26, 748. Benton, F. L., and Hamill, W. H., Ibid., 1948, 20, 269. Pecherer, B., Gambrill, C. M., and Wilcox, G. W., Ibid., 1950, 22, 311. Viebock, F., B e y . , 1932, 65, 496. Belcher, R., Macdonald, A. Ill. G., and Nutten, A. J., Mikrochim. Acta, 1954, 104. Davidow, B., J . Ass. Og. Agric. Chem., 1950, 33, 130. - , Ibid., 1950, 33, 886. Claborn. H. V.. and Beckman. H. F.. AIzal. Chem.. 1952. 24. 220. in Solvent Extracts of Vegetable Material,” Analyst, 1957, 82, 378. I . Hornstein, I., J. Agric. Food Chem., 1957, 5 , 446. ’ Hudy, J. A,, and Dunn, C. L., Ibid., 1957, 5 , 351. Gunther, F. A., and Blinn, R. C., “Analysis of Insecticides and Acaracides,” Interscience Publishers Inc.. New York and London, 1955, p. 231. Received November 18th, 1957

ISSN:0003-2654    

DOI:10.1039/AN9588300335

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

340 MARTIN AND BATT: THE DETERMINATION OF [Vol. 83 The Determination of DDT in Plant Materials and Soil By J. T. MARTIN AND R. F. BATT (Research Statzon, Long A shtoii, Brzstol) Two procedures, based upon nitration and colour formation with ethanolic potassium hydroxide solution, are described for the determination of DDT in foliage, fruits, grain and soil. In the first, DDT is determined within the range 0 to 360 pg, and in the second, within the range 0 to 30 p g . Inter- ference by wax and pigments is overcome by treatment with alumina and oxidation with acidified permanganate, or by oxidation with acidified permanganate alone. IN work on the chemical control of plant pests and diseases, methods were required for the examination of spray deposits in the assessment of spraying efficiency.Progress reports have been made on the development of techniques for the determination of copper,l sulphur,2 captan (N-trichloromethylthio-4-cyclohexene-1 : 2-dicarboxyimide) ,3 DDT [ l : 1 : l-trichloro- 2 : 2-di($-~hlorophenyl)ethane],~?~ chlorobenzilate (ethyl 4 : 4'-di~hlorobenzilate)~ and of DDT and chlorbenside ($-chlorobenzyl p-chlorophenyl sulphide) occurring together.' The first, called for convenience the macro method, is designed €or the analysis of comparatively large samples of fresh foliage (10 g), fruits or grain (50 g) or soil (20 g), and DDT can be determined when present in amounts within the range 0 to 350pg. The second, a rapid micro method used in studies of the distribution of the insecticide over plants, is suitable for the analysis of single small fruits or samples of between 0.1 and 0-5 g of foliage or 5 g of grain or soil.Both procedures are based upon those of Schechter, Soloway, Hayes and Hailer* and Illing and Stephens~n,~ in which DDT, extracted from plant tissue with a suitable solvent, is nitrated and a colour is formed with sodium methylate or et hanolic alkali. Amsden and Wallbridgelo propose the use of isopropylamine for colour formation after nitration. MACRO METHOD OF EXTRACTING THE DDT- Foliage and fruits-An extraction procedure was used to assess the extent to which DDT could penetrate into plant tissue. To obtain the surface deposits, leaves and fruits were washed four times with carbon tetrachloride at room temperature. Most of the DDT was recovered in the first two washings; none was found in the fourth washing.The plant material was then dried in air, powdered and extracted by hot percolation with carbon tetrachloride, when additional amounts of DDT equivalent to 10 to 20 per cent. of the total deposits on the leaves were recovered." No absorbed DDT was detected in fruits such as blackcurrants and grapes. The ability of DDT to penetrate into foliage should be borne in mind in the analysis of leafy crops. Carbon tetrachloride was preferred as solvent since it removes the DDT with a minimum amount of pigment and gives no interference in the nitration procedure. Grain-The grain was percolated for 30 minutes with hot carbon tetrachloride. Soil-An examination was made of sandy loam soil samples (pH 6.2 to 6.4 and contain- ing 2.5 per cent. of organic matter) in which DDT had been incorporated.The soil was prepared for analysis by drying in air and passage through a &-inch square-hole sieve. Extraction was carried out on 20-g portions in three successive stages: (a) by hot percolation with carbon tetrachloride, (b) by setting the soil aside overnight in a (2 + 1) mixture of carbon tetrachloride and isopropyl alcohol, and (c) by hot percolation with isopropyl alcohol. Samples were also examined by direct hot percolation with acetone or isopropyl alcohol. The results of analysis showed that the treatment with carbon tetrachloride failed to extract all the DDT. Extraction with carbon tetrachloride and then isopropyl alcohol gave values that agreed closely with those obtained with acetone or isopropyl alcohol alone.6 MICRO METHOD OF EXTRACTING THE DDT- made to distinguish between surface and absorbed deposits.Two procedures have been used for the determination of DDT in spray deposits. In this method, the range of DDT covered is 0 to 30 pg. EXPERIMENTAL Foliage and fruits-Because small amounts of plant tissue were used, no attempt was Acetone was used as the solventJune, 19581 DDT IN PLANT MATERIALS AND SOIL 34 1 to obtain the total deposits, five leaf discs, each of 1-cm diameter, or single small fruitlets being extracted by hot percolation for 15 minutes. Grain-Some 5-g samples of grain were extracted by hot percolation with acetone for 15 minutes. Soil-Tests showed that the recoveries of DDT from a sandy loam soil after extraction with acetone of 5 or 20-g samples agreed well with those after extraction with isopropyl alcohol.6 MACRO METHOD OF REMOVING INTERFERENCE BY WAX AND PIGMENTS- The carbon tetrachloride extracts of foliage, fruits and grain were passed through a column of activated alumina to remove pigments and most of the wax.This treatment also effectively removed interfering wax and pigments from extracts of light soils; some soils rich in organic matter and some samples of grain gave highly pigmented solutions, and for these oxidation with acidified potassium permanganate was required after passage through the alumina column. MICRO METHOD OF REMOVING INTERFERENCE BY WAX AND PIGMENTS- The complete removal of interference by pigments and fatty material extracted by the acetone was necessary to obtain significant values for DDT over the range 0 to 30 pg.This was achieved without loss of DDT by oxidation with potassium permanganate in dilute acetic acid. NITRATION OF THE DDT- Tests showed that, after removal of most of the wax, nitration at 100" C was completed in 10 minutes and this period of heating was adopted for both methods. Under the conditions of the test, the product formed is the tetranitro derivative, 1 : 1 : 1-trichloro-2 : 2-di(4-chloro- 3 : 5-dinitropheny1)ethane. SEPARATION OF THE NITRATED DDT- Separation of the nitrated DDT can be effected by extraction with ether, benzene, carbon tetrachloride or any other suitable solvent, In the macro method, we have preferred carbon tetrachloride, which occludes less water than ether and ensures fewer manipulations than when benzene is used.The nitrated DDT has a low solubility in carbon tetrachloride, but with the procedure recommended, which involves extraction from an aqueous solution saturated with salts, the recovery of the nitro- DDT is complete. In the micro method, benzene has been used as solvent for the extraction of the nitro compound. COLOUR FORMATION- Schechter, Soloway, Hayes and Hallers recommended the use of sodium methylate solution, standardised at 10 0.1 per cent., to form a colour with the nitro-DDT in benzene solution. We used ethanolic potassium hydr~xide,~ which forms a blue colour with the nitrated DDT in carbon tetrachloride (macro method) or benzene (micro method). The maximum development of colour occurs after 5 minutes.The concentration of potassium hydroxide is not critical, colours of equal intensity being given over the range 3.5 to 6.5 per cent? METHOD REAGENTS- Carbon tetrachloride-Fractionated before use. Acetone-Fractionated before use. Benzelze-Fractionated before use. Acetic acid, glacial. Potassium permanganate solution-A 2.5 per cent. aqueous solution. Sodium metabisul9hite solution-A freshly prepared 5 per cent. aqueous solution. Aluminium oxide for chromatographic analysis. Nitration acid-Prepared by mixing equal volumes of fuming nitric acid and concentrated Potassium hydroxide solution, 4 N. Sodium sulphate, anhydrous. sulphuric acid.342 MARTIN AND BATT: THE DETERMINATION OF [Vol. 83 Ethanolic potassium hydroxide solution-Prepared by heating 5 g of potassium hydroxide with 100 ml of absolute ethanol under reflux until dissolution is complete.This solution must be freshly prepared and should be filtered immediately before use. MACRO PROCEDURE- Extract the plant material or soil as described under "Experimental," p. 340, using the minimum amount of carbon tetrachloride. If the initial volume is appreciable, reduce it to about 10 ml by gentle distillation over a low flame, or by drawing a current of dry air over the surface of the liquid at about 35" C. If acetone is used for the extraction of soil, evaporate to dryness by passing a current of dry air over the liquid at 35" C and dissolve the residue in 10 ml of carbon tetrachloride with warming, and then cool the solution. Pass the solution through 5 g of aluminium oxide (previously wetted with carbon tetra- chloride) supported on cotton-wool in a glass tube, 150 mm x 18 mm, having a constriction a t the lower end.Gently distil the solvent from the eluate until the volume is about 10 ml and then evaporate to dryness a t 35" C with a current of air. When experience has shown it to be necessary, add 4 ml of acetic acid, warm to dissolve the residue, add 5 ml of potassium permanganate solution and place on a boiling-water bath for 10 minutes. Cool and decolorise by the addition, drop by drop, of sodium metabisulphite solution and then add 10 ml of water. Extract, successively, with vigorous shaking for 30 seconds each time, with 15, 5 and 5-nd portions of carbon tetrachloride. Combine the carbon tetrachloride extracts, add 10 ml of water and then 4 N potassium hydroxide, drop by drop, with shaking, until the aqueous layer is just alkaline to litmus paper.Run off the carbon tetrachloride layer, wash the aqueous layer with a little carbon tetrachloride, combine the carbon tetrachloride layers and wash with 5 ml of water. Run the carbon tetrachloride extract through anhydrous sodium sulphate and wash the water layer and desiccant with a little more solvent. Reduce the volume by gentle distillation to about 5 ml and evaporate to dryness a t 35" C in a current of air. Continue with this residue, or with the residue obtained before addition of 4 ml of acetic icid if the permanganate oxidation procedure was unnecessary, as follows. Cool and slowly add 10 ml of water. Cool again and neutralise by the addition, with swirling and cooling, of 4 N potassium hydroxide until litmus paper just turns blue.Add 2 drops of 4 N potassium hydroxide in excess. Wash the cooled solution into a separating funnel with 5 m l of water. Rinse the flask with 15ml of carbon tetrachloride, add the washings to the funnel and extract with vigorous shaking for 30 seconds. Re-extract with two further 5-ml portions of carbon tetrachloride, rins,ing the flask. Combine the carbon tetrachloride extracts and wash them twice with 5-ml portions of water. Run the carbon tetrachloride solution through anhydrous sodium sulphate and wash the separating funnel and desiccant with a little more solvent. Reduce the volume by dis- tillation over a low flame to 5 ml and then evaporate to 0.5 ml a t 35" C in a current of air.Add 10 ml of 5 per cent, ethanolic potassium hydroxide solution, rotate for 15 seconds, and, after 5 minutes, measure the optical density spectrophotometrically in a 1-cm cell a t a wavelength of 600 m p when a Unicam SI'600 spectrophotometer is used, or with an Ilford No. 607 filter when a Spekker absorptiometer is used. MICRO PROCEDURE- Extract the plant material or soil by hot percolation with acetone as described under "Experimental," p. 340, using the minimum amount of solvent. Evaporate to dryness at 35°C in a current of air. Add 4 ml of acetic acid, warm to dissolve the residue, add 5 ml of potassium permanganate solution and heat on a boiling-water bath for 10 minutes. Cool and decolorise by the addition, drop by drop, of sodium metabisulphite solution.Extract, with vigorous shaking, with 10 and 5-ml portions of carbon tetrachloridc. Run the carbon tetrachloride extracts through anhydrous sodium sulphate and evaporate the solvent to dryness at 35" C in a stream of air. Cool, add 5 ml of water and make just alkaline to litnius by adding 4 A' potassium hydroxide solution. Wash through with five 5-ml portions of carbon tetrachloride. Add 2 ml of nitration acid and heat in a boiling-water bath for 10 minutes. Add 1 ml of nitration acid and heat in a boiling-water bath for 10 minutes.June, 19581 DDT I N PLANT MATERIALS AND SOIL 343 Extract with vigorous shaking for 30 seconds with 10 ml of benzene. Wash the benzene layer with two 3-ml portions of water, run the benzene solution through anhydrous sodium sulphate into a 25-ml graduated stoppered cylinder, wash the desiccant and adjust the volume to 10 ml with benzene and add 5 ml of 5 per cent. ethanolic potassium hydroxide solution.Mix and after 5 minutes measure the optical density spectrophotometrically in a 2-cm cell. RESULTS Calibration curves relating optical density to micrograms of $p'-DDT were prepared from the results of tests on @'-DDT alone, of tetranitro-DDT prepared by the method of Backeberg and Marais,ll of pp'-DDT taken through each method from the nitration stage and of p p -DDT added to the solvent before the extraction of foliage, grain and soil. The degree of concordance was good, indicating no loss in the method and satisfactory recovery of DDT from the extracts of the materials examined. In collaborative work-with the Infestation Control Division of the Ministry of Agriculture, Fisheries and Food at Tolworth, carbon tetrachloride extracts of untreated grain to which known amounts of pure p p -DDT and gamma-hexachlorocyclohexane had been added, were prepared at Tolworth and sent to Long Ashton for analysis by the macro method.The results are shown in Table I. TABLE I RECOVERY OF DDT FROM GRAIN EXTRACTS BY MACRO METHOD Sample DDT added, 7-Hexachlorocyclohexane added, p.p.m. p.p.m. c. 1 4.0 c.2 4.0 11.1 10.0 n.2 10.0 E 20.0 Xi1 Xi1 0.5 S i l 2.0 S i l 4.0 10.0 DDT recovered, p.p.m. 0.5, 0.5 1.6, 1.7 1.5, 1.4 4.1, 3.9 4.0, 3.8 10.0, 9.9 10.0, 10.1 19.7, 19.9 The recovery by the macro method of DDT addea to whole grain and from DDT-treated The recoveries by the micro method of DDT grain taken from storage is discussed later. added to acetone extracts of grain and soils are shown in Table 11.RECOVERY OF DDT Sample Grain . . . . .. Sandy soil . Organic soil . TABLE I1 FROX GRAIN ATD SOIL EXTRACTS BY MICRO METHOD IIDT added, p.p.m, DDT recovered, p.p.m .. 2.0 2.0 4.0 3.9 6.0 6.1 .. 1.5 2.5 3.5 4.5 5.5 1.5 2.5 3.5 4.5 5.5 1.4 2.3 3.1 4.5 5.5 1.6 2.5 3.2 4.3 5.9 For convenience, a standard disc for use with the macro method, which gives the colour intensities produced over the range 25 to 350 pg of DDT, has been prepared in collaboration with Tintometer Ltd. of Salisbury, Wilts., from whom it is available. The disc was designed only for analyses in which the permanganate treatment was not necessary.In the description of the method supplied by the firm, we now recommend the use of 5-g portions of alumina, with washing as described.344 MARTIN AND BATT [Vol. 83 DISCUSSION Certain precautions and some experience in the use of the methods are necessary for satisfactory results. Chemicals of analytical-reagent quality should be used whenever possible and all-glass apparatus should be used throughout. Adequate separations and drainage should be allowed in all liquid - liquid extractions, and the amount of stopcock grease used should be kept to an absolute minimum. In the macro method, an opalescence on dilution of the nitration mixture with water indicates that more than 50pg of DDT are present ; if an appreciable amount of precipitate results, the carbon tetrachloride solution of the nitro compound should be diluted to a specific volume and an aliquot taken for the colour development.The test should be completed with the minimum of delay, particularly after extraction of the nitro compound with carbon tetrachloride. If crystals separate from the small volume of solvent before the addition of ethanolic potassium hydroxide, the test should be rejected. The colour obtained in the examination of deposits on crops that had been subjected to weathering in the field was comparable with that obtained in the analysis of fresh deposits. This was probably due to the fact that any residual 4 : 4’-dichlorobenzophenone, which is formed from DDT under the influence of ultra-violet light and which gives a tangerine colour in the test, is removed by the alumina treatment.of-DDT, which may be present in small amounts in spray deposits, gives a colour of lower intensity than that given by $p‘-DDT and is unlikely to cause any significant error in the determination of the $$‘-isomer. The presence of gamma-hexachlorocyclohexane in grain does not cause interference in the deter- mination of DDT. Work has been carried out by B. S. J. Border and A. Taylor in the Infestation Control Division of the Ministry of Agriculture, ]Fisheries and Food on the recovery of DDT from grain by the macro method and we are indebted to Dr. E. E. Turtle for permission to refer to their results. Weighed amounts of DDT were added to 50-g portions of grain at concen- trations over the range of 4 to 16 p.p.m.and the samples were analysed immediately. Re- coveries of 88 to 110 per cent., with a mean value of 93 per cent., were found. These results are satisfactory in view of the difficulty of ensuring the even distribution of DDT crystals in the grain. Other samples, containing 8, 40 and 76 p.p.m. of added DDT, showed recoveries of 81 to 84 per cent. after storage for 5 weeks; on further extraction of the grain after grinding, the mean recovery of DDT was 88 per cent. The Infestation Control Division workers have also shown that extraction of the tetranitro-DDT with benzene followed by washing the extract with dilute alkali and the use of an aliquot without the removal of solvent in the colour formation gives results agreeing chsely with those by the macro method, but with considerable saving of time. It is desirable that a standard method based upon further collaborative work should be adopted for the determination of DDT in food commodities. Most of our work has been carried out on leaves and fruits from spraying trials, and for these materials the methods have proved to be satisfactory. Further work is required on the recovery of DDT from grain after storage and on the details of the method of analysis to be used. It may be that a combination of the principles of the macro and micro methods, as suggested by the Tolworth workers, would be most acceptable. Fatty materials, such as groundnuts and oil-cake, need special consideration. 1 . 2 . 3. 4 . 5 . 6 . 7 . 8 . 9 . 10. 1 1 . REFERENCES Martin, J. T., Ann. Rep. Agric. Hort. Ref. Sta., Bristol, 1956, 125. Krentos, V. D., Batt, R. F., and Martin, J. T., Ibid., 1956, 122. Martin, J. T., and Pickard, J. A., I b i d . , 1955, 103. Martin, J. T., and Batt, R. F., Ibid., 1953, 121. Batt, R. F., and Martin, J. T., Ibid., 19516, 127. Skerrett, E. J., and Baker, E. A., Ibid., 1956, 130. Martin, J. T., and Batt, R. F., Ibid., 1955, 106. Schechter, M. S., Soloway, S. B., Hayes, R. A., and Haller, H. L., I n d . Eng. Chem., Anal. Ed., Illing, E. T., and Stephenson, W. H., A d y s t , 1946, 71, 310. Amsden, R. C., and Wallbridge, D. J., J . Agric. Food Chem., 1954, 2, 1323. Backeberg, 0. G., and Marais, J. L. C., J Chem. Soc., 1945, 803. 1945, 17, 704. Received December 2nd, 1957

ISSN:0003-2654    

DOI:10.1039/AN9588300340

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

June, 19581 STEPAKEK AND CERNA A Method for the Detection of Traces of Acrylonitrile BY J. 114. STEPANEK AND V. M. CERNA (The Institute of Hygiene, 48 .%obdrova, Prague 12, Czechoslovakia) A chromatographic method is described for the detection and approximate determination of traces of acrylonitrile. The method is based on a reaction between acrylonitrile, thiourea and hydrochloric acid to yield 2-(2-cyano- ethy1)isothiuronium chloride, which is detected by paper chromatography with an ammoniacal silver nitrate spray reagent. The method is widely applicable, specific and highly sensitive; it makes possible the detection of acrylonitrile in amounts of the order of 1 pg. 345 IN the last 10 years, acrylonitrile has achieved many technological applications, e.g., as the raw material for artificial fibres and synthetic rubber, for various organic synthetic products and also as a fumigant insecticide for crops.The need for a suitable method for its detection has consequently extended into various industries. As acrylonitrile is a highly toxic sub- stance, a specific and sensitive method is required for its qualitative detection as well as for the determination of residual amounts of it in industrial raw materials and products, air, industrial waste waters, crops, food-stuffs and also in various physiological systems, in order to follow its metabolism, e.g., urine, blood and blood serum. Of the numerous chemical reactions of acrylonitrile only three have been suggested for its qualitative detection. The first of these makes use of its reaction with piperidine to form P-piperidinopropionitrile,l the picrate of which melts at 161" to 162" C ; this reaction can be used to detect concentrations of acrylonitrile as low as 1 per cent.The second method, a colorimetric test for amides and nitriles, is based on the reaction of acrylonitrile with hydroxyammonium chloride in propylene glycol. In the presence of potassium hydroxide, after being heated and subsequently cooled, a red to violet colour is formed with ferric chloride.2 Finally, a method was suggested for the detection of hydrogen cyanide or acrylonitrile in air or other gases, based on contact with a reagent consisting of o-tolidine and cupric sulphate in glycerol on silica gel. The presence of hydrogen cyanide or acrylo- nitrile causes a colour change to blue or blue-green.s The first of these reactions is not sufficiently sensitive and the others are not specific.Established quantitative chemical methods for the determination of acrylonitrile are based either on titration of the ammonia liberated when acrylonitrile is hydrolysed with concentrated alkali4 or sodium and ethanol5 or else on the oxidation of acrylonitrile with potassium permanganate637ys or a mixture of chromic and sulphuric acids.9 None of these methods is sufficiently specific for the reliable detection of residual traces of acrylonitrile. Beesing, Tyler, Kurtz and HarrisonlO have suggested a method based on the cyanoethylation of dodecyl mercaptan in the presence of potassium hydroxide as catalyst. The reaction is carried out in isopropyl alcoholll and the excess of mercaptan is titrated in an acidified medium with potassium bromate and potassium iodide.If the solution is coloured, the silver salt of the mercaptan can be precipitated and then determined potentiometrically.12 The cyanoethylation reaction between acrylonitrile and dodecyl mercaptan has also been applied to the determination of concentrations of acrylonitrile in air up to 150 mg per cubic metre.13 The ability of acrylonitrile to cyanoethylate isopropyl alcohol and the mercaptan simultaneously in an alkaline medium has been used in a modified method for the simultaneous determination of acrylonitrile and 1-cyano-1 : 3-butadiene.14 A similar quantitative method is based on the reaction between acrylonitrile and sodium or potassium glycocholate.15 For the determination of acrylonitrile, several quantitative methods have recently been suggested.One of these is based on a general reaction of ap-unsaturated compounds, viz., the addition of sodium hydrogen sulphite to acrylonitrile to form a substituted sodium sulphonate; the optimum pH for this reaction is attained by the addition of a measured excess of N sulphuric acid.16 Another method involves the reaction of acrylonitrile (and of @-unsaturated com- pounds in general) with morpholine in the presence of acetic acid to form a tertiary amine, which can be titrated with methanolic hydrochloric acid after the excess of morpholine has been converted to the neutral amide with acetic anhydride.17 Other methods are based on346 STEPANEK AND CERNA: A, METHOD FOR THE DETECTION OF [Vol.83 the addition of sodium sulphite to acrylonitrile and subsequent titration of the sodium hydroxide liberated1*; and also on the addition of sodium hydrogen sulphite, the excess of which is titrated with an alkali solution.1g Physical methods can also be used for the detection and determination of acrylonitrile; spectrophotometric,20 infra-red absorption21@9 and polarographic pr0cedures2~ to 29 have been reported. PRINCIPLE OF THE METHOD It has been reported in a review of the chemical properties of acrylonitrilell that it reacts with thiourea, in the presence oi a basic catalyst, to form 2-(2-cyanoethyl)~seudo- t h i o ~ r e a , ~ ~ j ~ l according to the equation-- NH, OH- I H,N*CS.NH, + CH2 = CH CN --+ NH = C-S-CH,*CH,.CK.According to another report, however, thiourea and acrylonitrile do not react at 100" C in the presence of alkali.s1p32 In the course of our study of acrylonitrile,33 we found that a similar cyanoethylation reaction occurs between acrylonitrile and thiourea in the presence of halogen acids in an aqueous or alcoholic medium. The halogen acid takes part in the reaction, the main product of which is the corresponding isothiuroniiim salt, according to the equation- p N H ) + GN*CH = CH, + H2N*CS*NH2 + HX ----+ CN.CH2.CH2-S-C H / x-, I \NH, J where X represents C1, Br or I. The addition product of acrylonitrile and hydrochloric acid, P-chloropropionitrile, reacts in the same way and forms 2-(2-cyanoethyl)isothiuronium chloride directly with thiourea.s4 It is hoped that details of the probable intermediate formation of P-chloropropionitrile from acrylonitrile and aqueous or alcoholic hydrochloric acid will be dealt with in a separate paper.The homologous methacrylonitrile, when allowed to react with thiourea under the same conditions, does not form a corresponding isothiuronium salt. In the presence of concentrated hydrochloric acid the reaction occurs with quantitative consumption of acrylonitrile. The resulting 2-(2-cyanoethyl)isothiuronium chloride can be detected by paper chromatography with a,n ammoniacal silver nitrate spray reagent. This method is both specific and simple; it permits the detection of amounts of acrylonitrile as small as 1 pg. The corresponding bromide (m.p. 177" C) and iodide (m.p. 131" to 132" C) can also be detected by paper chromatography, as they have different RF values, but the procedure is less sensitive and considerable complications can arise, particularly with the iodide.EXPERIMENTAL To verify the conditions of the reaction between acrylonitrile, thiourea and hydrochloric acid, the optimum ratio of reactants was first studied. It was found that the reaction occurred almost stoicheiometrically when an excess of hydrochloric acid was present. In order to increase the sensitivity of detection of minute amounts of acrylonitrile, e.g., from 1 to 5 pg, it was necessary to increase proportionately the amounts of thiourea and hydro- chloric acid in the reaction solution, up to 35 moles and 50 moles, respectively, per mole of acrylonitrile. Either water or a polar organic solvent can be used as the reaction medium.Ethanol, Iz-propyl alcohol and isopropyl alcohol proved to be the most suitable solvents; isobutyl alcohol, tert.-butyl alcohol and acetone caused the formation of interfering by-pro- ducts, especially at the lower concentration of acrylonitrile. The reaction takes place at ordinary temperatures, but can be accelerated by heating, e.g., under reflux. When different amounts of acrylonitrile are allowed to react with thiourea in the absence of hydrochloric acid, or in an alkaline medium, the isothiuronium salt cannot be detected; this is in accordance with the findings of Hurd and Ger~hbein.~~ It was also found that, after the completion of the reaction, the solution can be diluted with water or an organic polar solvent or, alternatively, concentrated to a certain extent by evaporation, without any apparent effect on the detection of acrylonitrile. Dilution canJune, 19581 TRACES OF ACRYLONITRILE 347 be practically unlimited, but evaporation, which can only be carried out with alcoholic solu- tions, must not be continued after an approximate concentration of 0.1 mg of acrylonitrile per 2 ml of solution has been reached.The chromatographic spots in this instance, however, are less marked, being about half their normal intensity. It is preferable, therefore, to con- centrate the test solution by distilling the acrylonitrile from the original sample, either in a current of pre-heated air or azeotropically with isopropyl alcohol. By using this procedure, it is possible to determine minute amounts of acrylonitrile, when working with specified volumes, down to a minimum of 1 pg.The colour intensity of the isothiuronium spot produced by 1 pg of acrylonitrile corresponds to that produced by 0-3 to 0.5 pg of standard isothiuronium chloride solution. Impurities in commercial acrylonitrile do not affect its detection or determination. METHOD REAGENTS- All reagents should be of recognised analytical grade. Hydrochloric acid, concentrated. Ammonia solution, 10 per cent. aqueous. Sodium thiosulphate solution, 2 per cent.-A 2 per cent. aqueous solution of sodium Thiourea. Ethanol or isopropyl alcohol. n-Butyl alcohol-Saturate with distilled water before use. Ammoniacal silver nitrate solution (Tollens’s reagent)-Prepare by treating a 0.1 S aqueous solution of silver nitrate with an equimolecular amount of 5 per cent.aqueous sodium hydroxide. Add 5 N aqueous ammonia to the precipitated silver oxide, with constant agitation, until the solid just dissolves, and then make the solution slightly ammoniacal by the further addition of aqueous ammonia. This reagent must be freshly prepared before use. 2-(2-Cyanoethyl)isothiuronium chloride, ethanolic standard solution-Dissolve 2 g of the isothiuronium salt, prepared by the procedure described on p. 348, in 1 litre of ethanol. thiosulphate, Na,S20,.5H20. PREPARATION O F THE SAMPLE FOR CHROMATOGRAPHY- By absorption, distillation or extraction from the system containing acrylonitrile, prepare in ethanol or isopropyl alcohol a solution containing 5 to 10 mg of acrylonitrile per 10 ml.Place 10 ml of this solution in a 50-ml flask, add 0.5 g of thiourea and then 0.75 ml of con- centrated hydrochloric acid. Boil the reaction mixture under reflux on a water bath for 30 minutes. When the acrylonitrile is present in the form of an aqueous solution, follow the same procedure, but heat under reflux at a correspondingly higher temperature. When 10 ml of the alcoholic solution contain less than 5 mg of acrylonitrile, follow the same procedure, but make correspondingly smaller additions of thiourea and hydrochloric acid, eg., 5 and 10 times diminished at acrylonitrile contents of 2 and 1 mg per 10 ml of solution, respectively. After 15 to 30 minutes’ boiling under reflux, evaporate the reaction solution on a water bath to a specified volume, not less than 2 ml, and use this for the chromatographic procedure.If the original solution contains more than 10 mg of acrylonitrile per 10m1, dilute it with the solvent until the isothiuronium spot that corresponds to the minimum amount of 1 pg of acrylonitrile is achieved by paper chromatography. In this instance, it is not necessary to alter the additions of thiourea and hydrochloric acid. It is always preferable to estimate the amount of acrylonitrile present in the sample by a pre- liminary experiment, in order to establish the precise conditions for the final procedure. PROCEDURE FOR DEVELOPING THE CHROMATOGRAM- On a strip of Whatman No. 4 filter-paper, 150mm x 300mm, place, by means of a micropipette, at least 0.001 ml of the reaction solution along a line 8 cm from the upper edge of the strip.Allow the solvent to evaporate and then repeat the procedure several times, making any number of additions up to ten and allowing the solvent to evaporate after each addition. Chromatograms are thus prepared from 0.001 to 0.01 ml of the reaction solution, and these can be used to achieve an approximate evaluation of the amount of acrylonitrile present. When cool, use this solution for the paper-chromatographic procedure.348 STEPANEK AND CERNA: .4 METHOD FOR THE DETECTION OF [Vol. 83 To compare the position and character of the isothiuronium spots detected with that of a standard solution, apply simultaneously 0.001 ml of the latter by means of a micropipette. Suspend the strip of filter-paper in i2 chromatographic tank for 2 hours to attain equili- brium with the atmosphere of n-butyl alcohol and water vapours.Dip the upper end of the paper strip in n-butyl alcohol that has been saturated with water and allow the solvent front to travel 25 to 28cm down the paper over a period of about 4 hours. Remove the strip from the tank, mark the position of the solvent front and then allow the paper to dry at room temperature until all the solvent has evaporated (12 to 24 hours). PROCEDURE FOX COLOUR DEVELOPMENT- Spray the dry strip with Tollens’s ammoniacal silver nitrate reagent. The dark brown spot of thiourea, which is the most substantial one on the chromatogram, R, 0.43, appears immediately, owing to the presence of a considerable excess of this substance.As spraying proceeds, a typical yellow spot of 2-(2-c:yanoethyl)isothiuronium chloride appears, RF about 0.25, depending on the concentration of acrylonitrile present. This spot soon darkens until it is dark grey, with a yellow centre at higher concentrations of acrylonitrile. The develop- ment of the spot, particularly at minute concentrations of acrylonitrile, can be accelerated by heating for 5 minutes at 100” C and subsequently washing the chromatogram with a 10 per cent. aqueous solution of ammoni,s and then with distilled water. A faint brownish spot, R, 0.32, which gradually darkens, also appears; this spot corresponds to the reaction of thiourea and hydrochloric acid with the alcohol and appears even in the absence of acrylonitrile. When the standard isothiuroniuin chloride solution is used, only the spot RF 0.25 appears.The spots of isothiuronium chloride have a tendency to “tail” somewhat as the concentra- tion of acrylonitrile increases from 1 pg up to approximately 10 pg per 10 ml, but the position of the solvent front remains constant. The position, character and colour of these spots correspond closely to those obtained from standard solutions at the respective concentrations. When the colours of the spots have developed to maximum intensity, wash the chromato- gram thoroughly with distilled water and allow it to dry at room temperature. The removal of the excess of ammoniacal silver nitrate solution and the fixation of the chromatogram are finally accomplished by washing with a 2 per cent.solution of sodium thiosulphate and water. The presence of any proportion of methacrylonitrile does not interfere with the detection of acrylonitrile. When the chromatograin is treated with ammonia solution after it has been sprayed with ammoniacal silver nitrate solution, methacrylonitrile slowly forms a faint yellowish to brownish spot just above that of thiourea, thus producing an apparent “tailing” of the thiourea spot. To determine approximately the acrylonitrile content of the solution, record the iso- thiuronium spot at which a faint durable grey colour just appears. This spot corresponds to 1 pg of acrylonitrile. From the concentration of the solution examined and the amount of it necessary to produce that spot, calculate the approximate amount of acrylonitrile present in 1 kg of the original sample.REAGENTS- PREPARATION OF 2-(2-CYANOETHYL)iSOTHIURONIUM CHLORIDE Acrylonitrile-Technical grade. Thiowea-Analytical-reagent grade. Hydrochloric acid, concentrated-Analy tical-reagent grade. isoPropyl alcohol-Technical grade. EthanodTechnical grade. PROCEDURE- Dissolve 25 g of acrylonitrile in 200 ml of isopropyl alcohol contained in a 500-ml flask. Add 65 ml of concentrated hydrochloric acid and 40 g of thiourea. Boil the reaction mix- ture under reflux on a water bath for 30 minutes. After it has been cooled and shaken thoroughly, the solution deposits fine needles of 2-(2-cyanoethyl)isothiuronium chloride, which are separated and dried in air. By part evaporation and crystallisation of the mother-liquor, further portions of isothiuronium chloride can be obtained.Purify the product by recrystallisation from ethanol until it melts between 165-5” and 166’ C. This method of preparation gives an approximately 60 per cent. yield of the pure product.June, 19581 TRACES OF ACRYLONITRILE 349 Purity test-The purity of the 2-(2-~yanoethyl)isothiuroniurn chloride can be tested by Only subjecting the material to the above-described paper-chromatographic procedure. one spot, R, 0.25, should be produced. APPLICATION OF THE METHOD The proposed method can be applied for the detection and approximate determination of trace amounts of acrylonitrile in a wide range of materials, such as industrial products, food-stuffs, crops, air and waste waters, and in physiological systems such as urine, blood and blood serum.It is hoped that the respective analytical procedures, together with any interfering effects that arise from the character of the material being examined-crops, urine, blood and so on-will be dealt with in separate publications. The proposed method may find valuable application in food technology by specifying the amount of material under examination that should not produce a coloured isothiuronium chloride spot by the method, and so be in accordance with the official tolerances for acrylonitrile in the material. We thank M.U. Dr. I<. Symon, Cniversity Docent, Director of the Institute of Hygiene, Prague, for his kind permission to publish this paper. REFERENCES Brockway, C. E., Anal. Chem., 1949, 21, 1207. Soloway, S., and Lipschitz, A., Ibid., 1952, 24, 898.McConnaughey, P. W., U.S. Patent No. 2,728,639, 1955; Chew Abstr., 1956, 50, 5470. Peterson, G. W., and Radke, H. H., I n d . Eng. Chem., Anal. E d . , 1944, 16, 63. David, H. S., and Wiedeman, 0. F., I n d . Eng. Chem., 1945, 37, 482. “Deutsche Gesellschaft f u r Schadlingsbekanzpfufung,” Degesch, Frankfurt, 1943, “Ventox,” p. 7. Kroger, E. P., and Schuler, W. A., Dtsch. LebensmittRdsch., 1950, 46, 129. Dal Nogare, S., Perkins, L. R., and Hale, A. H., Anal. Chem., 1952, 24, 512. Kobayashi, Y., YzZki GBsei Kagaku KyBkai Shi, 1956, 14, 673; Chem. Abstr., 1957, 51, 7240. Beesing, D. W., Tyler, W. P., Kurtz, D. M., and Harrison, S. A., Anal. Chem., 1949, 21, 1073. American Cyanamid Co., New York, Cyawamid’s Nitrogen Chemicals Digest, 1951, “The Chemistry Janz, G.J., and Duncan, N. E., Anal. Chem., 1953,25, 1410. Haslam, J., and Newlands, G., Analyst, 1955, 80, 50. de MaldB, M., Ann. Chim. 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ISSN:0003-2654    

DOI:10.1039/AN9588300345

出版商:RSC    

年代:1958

数据来源: RSC