ISSN:0003-2654    

DOI:10.1039/AN96691FX017

出版商:RSC    

年代:1966

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN96691BX019

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

... May, 19661 THE ANALYST 111'ORGANIC REAGENTSFOR METALSAND OTHER REAGENTM ONOG RAPHS'VOLUME 2,1964. Published by Hopkin & Williams Limited, price 30/-d.A companion to Volume 1, 1955, price 15,'-d, the second volumecontains all monographs in the series "Organic Chemical Reagents"issued since Volume 1 together with many new ones and representsworkverified or originated in our own Laboratories. It deals with 28colorimetric and gravimetric reagents and includes a section oncompleximetry, with 1 5 metallochromic indicators.'BIOCHEMICALS'A CATEGORISED PRICE-LIST OF SUBSTANCES USED IN BIOCHEMISTRYFor many years the H €t W Chemical Catalogue has included sub-stances of biochemical interest. These, together with a preliminaryrange of over 60 additional biochemicals, selected on the advice ofour biochemical consultants, are now published as a separate price-list with technical information and specifications where appropriate.T Hopkin & Williams Limited, Freshwater Road, Chadwell Heath,Essex, England.Please send me ..................... copy(s) of "OrganicReagents for Metals and Other Reagent Monographs" Volume 2,1964 price 30/-d and ..................... free copy(s) of "Biochemicals"0NAME ..........................................................................................................................................................................POSlTl ON ..............................................................................................................................................................COMPANY ...........................................................................................................................................................ADDRESS ..............................................................................................................................................................All substances mentioned inthese publications are available from :HOPKIN & WILLIAMS LIMITED, Chadwell Heath, Essex, England.Telephone : GOOdmayes 2436CHEMICALS FOR RESEARCH, ANALYSIS AND INDUSTRYTRADE MARK TAR/HW.3iv SUMMARIES OF PAPERS I N THIS ISSUE [May, 1966Summaries of Papers in this IssueThe Quantitative Microanalysis of Carbonyl Compoundsseveral published methods for preparing 2,4-dinitrophenylhydrazonesand determining them colorimetrically have been examined, and a practicalsystem of analysis has been devised from them.The key step is the use ofa 2,4-dinitrophenylhydrazine - 66 per cent. phosphoric acid column elutedwith benzene, as well as light petroleum.The results of an analysis in the difficult case of a butter fat are described.A. M. PARSONSUnilever Research Laboratory, Welwyn, Herts.Analyst, 1966, 91, 297-305.Calibration of a Fisher Air-permeability Apparatus forDetermining Specific SurfaceCalibrating the Fisher sub-sieve sizer at a single particle-size level doesnot ensure accuracy a t other levels unless several variables are controlled.Instrument modifications that give better control of the several variables,and a calibration method that ensures accurate air-flow measurement withoutdepending on a particle-size standard, are described.The modified instrumenthas good precision over the range 2 to 40,~. A method for extending thisrange is given.I. C. EDMUNDSONGlaxo Laboratories Ltd., Greenford, Middlesex.Analyst, 1966, 91, 306-315.A Study of the Macroscopic Distribution of Oxygen in a Steel Rodby Neutron- activation and Vacuum Fusion TechniquesThe distribution of oxygen was determined along the length of a steelrod. Neutron-activation and vacuum fusion techniques were used alterna-tively, and the relevant pieces of apparatus and methods are described. Theover-all average oxygen content determined by neutron-activation analysiswas 129 p.p.m., in excellent agreement with 128 p.p.m.found by vacuumfusion. The results further show the continuity between the two sets of results,and also a definite inhomogeneity in the macroscopic distribution of oxygen.JUSTUS M. van WYK,* MARC Y. CUYPERS,? LLOYD E. FITEt andRICHARD E. WAINERDIt* Basic Research Division, Research and Process Development, South African Iron?Activation Analysis Research Laboratory, Texas A and M University, CollegeAnalyst, 1966, 91, 316-323.and Steel Industrial Corporation, Pretoria, South Africa.Station, Texas, U.S.A.Quasi-quantitative Separation of Paraffins and OlefinsBy the addition of iodine monochloride to a mixture of paraffins and olefins,an easy chromatographic operation on silica gel of the two is made possibleby virtue of the olefin adduct being much more strongly adsorbed.Theolefins are regenerated by refluxing the halogenated derivative with ethanoland excess sodium iodide.The efficacy of the method has been proved on the total aliphatics oflow temperature tars and on pairs of pure n-paraffins and 1-olefins of thesame carbon number. The small losses incurred are almost entirely inthe olefins.J. A. SPENCE and M. VAHRMANNorthampton College of Advanced Technology, St. John Street, London, E.C. 1.Analyst, 1966, 91, 324-327vi SUMMARIES OF PAPERS I N THIS ISSUEA Study of the Determination of Thiamine in Breakfast CerealsThe method of determining thiamine that involves the purification bybase-exchange on sand is satisfactory for materials of the “breakfast cereal”type.Traces of materials responsible for errors in the direct determinationremain after treatment, but the errors are greatly reduced and oppose oneanother, so that they may reasonably be neglected.H. N. RIDYARDThe Research Association of British Flour-Millcrs, Ccrcals Research Station, OldLondon Road, St. Albans, Herts.Analyst, 1966, 91, 328-332.[May, 1966The Assay of NeomycinShort PaperR. A. HOODLESSMinistry of Technology, Laboratory of the Government Chemist, Cornwall House,Stamford Street, London, S.E. 1.Analyst, 1966, 91, 333-334.Removal of Polyphenolic Compounds Interfering with CarbohydrateDeterminations in Plant Extracts with an InsolublePolyphenol AdsorbentShort PaperG.W. SANDERSON and B. P. M. PERERATea Research Institute of Ceylon, Talawakelle, Ceylon.Analyst, 1966, 91, 335-336.The Detection of Dinitro and Trinitro Aromatic Bodies inIndustrial Blasting ExplosivesShort PaperS. A. H. AMAS and H. J. YALLOPRoyal Armament Research and Development Establishment, Fort Halstead, Kent.Analyst, 1966, 91, 336-337.The Use of Molecular Sieve 5A for Collecting Fractionsfrom a Gas ChromatographShort PaperM. CARTWRIGHT and A. HEYWOODImperial Chemical Industries Ltd., Dyestuffs Division, Hexagon House, Blackley,Manchester 9.Analyst, 1966, 91, 337-338AEl SCIENTIFIC APPARATUSBULLETIN NO. 4Ag 1 150 210 1 1.4 23Ga ~ 80 250 3.1 1 271IMPROVED ACCURACY IN THEANALYSIS OF SOLIDS BY SPARKMASS SPECTROMETRY2113Since the possibility of using spark source ionization for the analysis of solidswas first recognised ten years ago, the design of the double focusing massspectrometer using Mattauch geometry has been considerably improved.Andtoday one instrument-namely the AEI MS7-is capable of detecting im-purities at levels as low as 1 part in lo9. As a result the MS7-which, incident-ally, was the first commercially available double focusing instrument to bebuilt expressly for the analysis of solids-has found wide applicationsparticularly where overall coverage of all elements and comparison analysiswithout standards are valuable.Now the MS7 technique has been further improved by the careful control ofcertain parameters, and very good reproducability and accuracy can beguaranteed.This bulletin reviews the parameters affecting analytical accuracyand outlines the methods of control developed by AEI engineers.It has been shown that the sensitivityof the majority of elements differs fromsome standard such as iron by no morethan a factor of 3. In other words, mostrelative sensitivity factors lie between0.3 and 3. In the case of the MS7, thedetermination of relative sensitivityfactors is considerably simplified bythe fact that the response of the instru-ment is linear over a very large rangeof concentration. Indeed Hannay &Ahearn’ established linearity over therange lo4 to 1 using doped siliconsamples. More recently, W. A. Wolsten-holme (AEl Consultant Lab.) hasreported on the investigation of golddoped titanium samples covering a con-centration range from 0.5% to .02 ppmby weight; a range of more than l o 5to 1.These samples were chosen because oftheir suitability for neutron activationand wet chemical analysis.Figure 1shows the relative ion intensity of goldplotted against the concentration de-termined by chemical or neutron acti-FOOTNOTE :I Hannay and Ahearn (1954) Anal. Chem 261956.FIG. 1 /vation techniques. The “just detect-able” line is an individual assessmentfor ion intensity and the “densito-metric” line indicates that a micro-densitometer was used to scan thespectral lines; the two graphs havebeen displaced for the sake of clarity.Matrix effects are generally very small,as is illustrated by the relative sensi-tivities for copper and steel standardsreported in tables 1 and 2.In copper and steel relative sensitivitiesare very similar for chromium (1.8 and1.4) and for tin (1.3 and 1.1). Onlyforsome low BP elements is there amarked dependence on the matrix, e.g.(1.4 and 2.6) for lead.NOTE :Relative Sensitivity = uncorrected MS7known valueHomogeneity ofstandards and samplesCare has to be taken to use homo-geneous standards or alternatively toincrease the rate of consumption ofsample above the usual 5 to 10 milli-grams.As it happens, however, the possibilityof inadvertently using an inhomogene-ous sample has been materially reducedby the introduction of more reliablemethods of sample preparation.Cr ! 60 110 1 1.8 1 20 1 2

ISSN:0003-2654    

DOI:10.1039/AN96691FP097

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

May, 19661 THE ANALYST xiiiThe rate for classified advertisements is 7s. a line (or spaceequivalent of a line), with a n extra charge of 2s. for theuse of a Box Number. Semi-displayed classifiedadvertisements are 80s. for single-column inch.Copy required not later than the 20th of the month pre-ceding date of publication which i s on the 16th of eachmonth. Advertisements should be addressed to ?’he 11 Analyst, 47 Gresham Street, London, E.C.2. Tel.:MONarch 7644.ANALYTICAL CHEMISTSDue to thc demands of increased production, vacancies havearisen in the analytical laboratories for four analyticalchemists. The company manufacture a wide variety ofinorganic and organic compounds, both for the Home andOverseas markets.The analytical techniques used in the laboratories rangefrom the classical to the latest instrumental techniques.These coupled with the diversity of chemicals to be analysed,ensure variety and interest in the work.Chemists betweenthe ages of 1 9 years and 25 years having either O.N.C. orH.N.C. in Chemistry preferably with experience in analysisare invited to apply.Salaries will be commensuratc with age and experience.Please write quoting reference number 34 to:-The Personnel Manager,HOPKIN & WILLIAMS LTD.,Freshwater Road,Chadwell Heath,Essex.RENTOKIL LABOR..ZTOlZIES LID.,Webbcr Road, Kirkby Industrial Estate, Liverpool.require an ANALYTICAL CHEMIST to develop methods ofanalysis for quality control. Candidates, preferably agcdbetween 21 arid 25 years, should posscss degree, L.K.I.C.orH.N.C. and havc similar previous expcricnce.This is a responsible appointment and high standards areessential, Salary will be commcnsuratc with qualificationsand experience. Conditions of employment within theCompany, spccialists in the manufacture and application ofPESTICIDES, arc above average arid include 3 weeks’annual holiday, pension and bonus schemes after qualifyingperiod.Write for application form to Miss A. Keating.THE CITY ANALYST’S DEPARTMENTKINGSTON C‘PON HULLApplications are invited for the post of Assistant Chemist inSalary on scale A.P.T. IIl/IV, Ll,ON-L1,555.Commencing salary dependcsnt upon experience.Minimum qualification required is G.R.I.C. (or equivalent).Recently qualified applicants will be considered.Encourage-ment is given to stiidy for Branch E Diploma of RoyalInstitute of Chemistry.The usual Local Government Conditions of Service willApplication fornis can be obtained from the City Analyst,the above department.apply.184 High Street, Kingston upon Hull.CHIEF ANALYSTThe Union International Co Ltd. wishes to appoint an experienced man aged about 35/40 to take charge of itsThe post is permanent and pensionable and an attractive salary will be offered to the rigllt applicant whoThis year’s holiday arrangements will be respected. Please write fully to Staff Manager, 14, Wtst Smithfield,well equipped Analytical Laboratory in London.must be a F.R.I.C. (Branch E).London, E.C.l.RESEARCH ANDDEVELOPMENTA SENIOR CHEMIST is required to take charge of the analytical depart-ment of the food research laboratories of the Ranks Hovis McDougallGroup at High Wycombe.The work involves the examination of a variety of food products togetherwith research into analytical techniques, and the post carries with it anattractive salary and excellent prospects of advancement in an expandingorganisation.Candidates should preferably be between the ages of 30 and 35, and shouldpossess either a Ph.D.or FRIC (branch E). Previous experience in foodanalysis and familiarity with modern techniques together with an aptitudefor research are essential. Applicants must also possess qualities of leader-ship and the abiltiy to control staff.APPly in writing t o :The Research Manager,Cressex Laboratories, Lincoln Road, High Wycombe, Bucks.Ranks Hovis McDougall (Research) Ltd.[May, 1966 xiv THE ANALYSTNALYTICAL CHEMIST.Young Graduate or equivalentArequired by Public Analysts and Consulting Chemistsfor analysis of wide variety of materials including foods,drugs, waters, trade effluents. Professional salary offered.Bostock Hill & Rigby, 37 Birchfield Road, Birmingham, 19.SSISTANT ANALYSTS, who are not interested in repeti-Ative routine work, but in experience and variety, requiredfor an expanding laboratory.The work covers samples undcr the Food and Drugs Act,the National Insurance Drug Testing Scheme, control analysesfor manufacturers, and advisory and legal problems. Appli-cants should preferably possess H.N.C., but a t least several‘0’ level certificates with practical experience.Part-timerelease for study if required. Salary according to age,qualifications, and experience. Apply Thomas McLachlan,4 Hanway Place, London, W.l.BRITISH CHEMICALSTANDARDSNew Thermochemical StandardB.C.S. No. 190j Benzoic AcidWith Calorific Value certified by theNational Physical Laboratory.Full particulars sent on request.BUREAU OF ANALYSEDSAMPLES LTD.Newham Hall, Newby, Middlesbrough, Yorks.Allen & HanburysLi m itedControl DivisionThe following vacancies exist in the Control Division of Allen &Hanburys Limited at Ware, Hertfordshire.(a) A GRADUTE CHEMIST is required in the Spectroscopy Sectionof the Analytical Research Department.Applicants should haveexperience or interests in physical organic chemistry, particularlyin infra-red and n.m.r. interpretation. Applications would also beconsidered from recently graduated chemists who have an interestin this work and who are keen to gain experience in this field.(b) A TECHNICAL ASSISTANT is required in the Analytical ResearchDepartment. Previous experience of instrumental analyticalmethods, especially infra-red and n.m.r. spectroscopy, would be anadvantage, especially if combined with a knowledge of organicand physical chemistry. Applicants should preferably possess arecognised qualification, such as L.R.I.C., H.N.C. or O.N.C.(6) AN EXPERIENCED ANALYTICAL ASSISTANT is required inthe Laboratories of the Analytical Control Department to under-take a variety of careful determinations, including the use of in-strumental techniques, applied to pharmaceutical dosage forms andmedicinal chemicals.Applicants should have had at least five years’experience in the analysis of pharmaceutical or allied products andshould preferably possess a recognised qualification, such asL.R.I.C. or H.N.C.Applicants are invited to write to the Personnel Manager, givingdetails of age, qualifications and experience and state clearly in whichof the three they are interested, quoting reference number TA2xvi THE ANALYST [May, 1966CENTRAL RESEARCH DEPARTMENTANALYTICAL CHEMISTSREF. W.R.To cope with the work required by this growing groupof companies, a planned expansion of the department isin progress.We require:SENIOR INVESTIGATOR(Graduate or equivalent)SENIOR ASSISTANT(H.N.C.or equivalent)for the development of physico-chemical methods ofsteel and slag analysis.Candidates must have experience in one or more of:-Chemical analysis, instrumental methods, gases in steel,statistics.Write for an application form to:-Staff Recruitment Officer,Colvilles Limited,Dalzell Steel Works,MOTHERWELLxviii THE ANALYST [May, 1966Pergamon International Series of Monographs in Analytical ChemistryGeneral Editors:Ronald Belcher, D.Sc., Professor of Analytical Chemistry, University of Birmingham, and LouisGordon, Ph.D., Professor of the Department of Chemistry, Case Institute Technology, Cleveland, Ohio.This series supplies the first really effective and authoritative account, in an accessible and definiteform, of those important new developments in analytical chemistry which occur so rapidly in thefield.These works, furnishing in useful detail the theory and practice of (1) special techniques, (2)rapiding expanding branches of analytical chemistry, and (3) applied methods widely used inparticular industries, should be of great value to all chemists.MONOGRAPHS PUBLISHED IN THIS SERIES:Microanalysis by the Ring Oven Technique by H. Weisz1 12 pages 3OS./$5.00Applied Gamma-Ray Spectrometry edited by C. E. Crouthamel443 pages 5Os./$6.50Analytical Chemistry of the Rare Earths by R. C. Vickery139 pages 40s./$6.50Photometric Titrations by J. B. Headridge131 pages 45s./$7.50The Analytical Chemistry of Indium by A.I. Busev288 pages 84s./$12.50Atomic-Absorption Spectrophotometry by W. T. Elwell and J. A . F. Gidley1 10 pages 30s./$5.00Gravimetric Analysis, Parts 1, 2 and 3 by L. ErdeyPart 1 : 332 pagesPart 2: 790 pagesPart 3 : 3 12 pages50s./$7.50S6/$18.5050s./$7.50Organic Functional Group Analysis by F. E. Critchfierd196 pages 42s./$6.50Analytical Chemistry of the Actinide Elements by A. J. Moses138 pages 45s./$6.75The Analytical Chemistry of Thorium by D. I. Ryabchikov and E. K. Gol’braikh332 pages f5/$14.00Trace Analysis of Semiconductor Materials edited by J. P. Cali292 pagesOrganic Polarographic Analysis by P. Zuman316 pages 50s./$7.50Controlled-Potential Analysis by G. A. Rechnitz86 pages 35s./$5.00Analysis of Petroleum for Trace Elements by 0. I. Milner128 pagesInorganic Ultramicroanalysis by J. P . Alimarin and M. N. Petrikova151 pages 40s.lE6.00Analytical Chemistry of Niobium and Tantalum by R. W. Moshier284 pages 9Os./$12.75~~~Gas Analysis by Gas Chromatography by P. G. Jefrey and P. J . Kipping228 pages 70s. 1% 10.00Kinetics of Precipitation by A. E. Nielsen164 pages 4Os./$6.00Analysis of Ancient Metals by E. R. Caley188 pages 70s./$10.00Nuclear Techniques in Analytical Chemistry by A. J. Moses152 pagesOscillometry and Conductometry by E. PungorNewer Redox Titrants by J. Zyka, A. Berka and J. Vulterin256 pages 6Os./$10.00242 pages 70s./$12.00Gas Chromatography of Metal Chelates by R. W. Moshier and R. E. Severs172 pagesThe Analytical Chemistry of the Noble Metals by F. E. Beamish616 pages f6/$18.50Kinetic Methods of Analysis by K. B. Yatsimirskii176 pages 50s./$7.50The History of Analytical Chemistry by F. Szabadvary416 pages July 1966 f6/$18.50PERGAMON PRESS LTD., Headington Hill Hall, Oxfor

ISSN:0003-2654    

DOI:10.1039/AN96691BP107

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

MAY, 1966 THE ANALYST Vol. 91, No. 1082 The Quantitative Microanalysis of Carbonyl Compounds BY A. &I. PARSOYS ( Unilever Research Laboratory, Welwyn, H u t s ) Several published methods for preparing 2,4dinitrophenylhydrazones and determining them colorimetrically have been examined, and a practical system of analysis has been devised from them. The key step is the use of a 2,4-dinitrophenylhydrazine - 66 per cent. phosphoric acid column eluted with benzene, as well as light pctroleurn. The results of an analysis in the difficult case of a butter fat are described. IN connection with flavour and other work a procedure was required for the quantitative microanalysis of complex mixtures of carbonyl compounds. Winter et aZ.l found that at least twelve carbonyl compounds were removed from butter by steam distillation.The amounts involved ranged from 18-8 p.p.m. for acetoin to less than 0.01 p.p.m. for hexanal, nonanal and nonan-2-one. Low ~oncentrations~9~ of monocarbonvl compounds have been im- plicated in the reversion flavours of edible oils4q5 and in the fishy flavour of dairy product^.^^^^^ Although other suggestionsg ,lo have been made, the colorimetric determination of 2,4-dinitrophenylhydrazones was selected as being the most generally useful technique. A great deal of work has been published on the chromatographic separation and spectro- photometric examination of 2,4-dinitrophenylhydrazone~, but the strictlv quantitative preparation of the derivatiL7es with 2,4-tlinitrophenylhydrazine has received relatively little attention. In a comparative study, Begemann and de JongL1 showed that the reaction of a dilute ethereal solution of a carbonyl compound with 2,4-dinitrophenylhydrazine in mineral acid gave an incomplete conversion, the yield in homogeneous solution12 being worse than that obtained when the solutions were partially13 or almost completely imrni~cib1e.l~ Water was present in all three solutions, and unless sufficient carbonyl compound was present for the derivative to separate, the equilibrium mixture obtained presumably fell far short of complete conversion into the 2,4-dinitrophenvlhydrazone.Henick et aZ.15916 carried out the reaction under essentially anhydrous conditions in benzene with trichloroacetic acid as the catalyst. There seems to be no reason why this reaction should not go to completion; a Dean and Stark apparatus can be used toremove water if necessary.17 However, the blank values were high (optical density in benzene - ethanolic potassium hydroxide, E = 0.35) and it was not clear whether thiswas due to excess reagent or to an artifact consequent upon the use of trichloroacetic acid.In addition, the presence of dicarbonyl compounds causes a large error in the calculation of carbonyl content, and therefore the procedure is largely useless for the empirical examination of oiIs for which it was originally proposed.l* Pool and Kloselg claimed a quantitative reaction of aldehydes in benzene with 2,4-dinitro- phenylhydrazine that had been adsorbed on to an alumina column, but their extinction coefficient ( E = 19,200 at 435 mp in benzene - ethanolic potassium hydroxide at zero time) appears to include a correction factor; the now accepted value1* (6 = 20,930 at 430 mp after 10 minutes) is significantly higher.Hegemann and de Jongll obtained a 90 per cent. con- version of heptanal into its 2,4-dinitrophenylhydrazone (assuming E = 22,500 at 358 mp in chloroform) but only 20 per cent. for nonan-%one on this column. Keith and L)ayls obtained 75 per cent. yields with alkanals, 65 per cent. with alk-2-enals and 60 per cent. with alka-2,4-dienals. The loading of this column is very low. Pool and KloseI9 recommended 0-05 to 0.50 pmole and Keith and Day1* up to 1 pmole of carbonyl compounds for a 10-g column, although the amount of reagent present is about 25 pmoles. In addition, decomposition may occur; for example, Lea and Jackson20 found that hydroperoxides give some carbony1 cornpounds under these conditions.298 PARSONS : QUANTITATIVE MICROANALYSIS OF CARBONYL COMPOUNDS [Andyst, VOl.91 Forss et appear to have been the first to prepare 2,4-dinitrophenylhydrazones by shaking 2,4-dinitrophenylhydrazine in 2 N hydrochloric acid with solutions of carbonyl compounds in light petroleum. Under these conditions the derivatives are obtained free from excess reagent in a surprisingly short time. Begemann and de Jongll found that the reaction with undecan-%one was frequently complete in 4 hours. However, the results were more reproducible and the reaction still more rapid if the petroleum solution was percolated through a column of the aqueous phase supported on Celite. In this way, 0.3 to 5 pmoles of heptanal, heptan-2-one, non-2-enal, undecan-2-one, tridecanal and pentadecan-%one gave almost complete conversion into their respective 2,4-dinitrophenylhydrazones in 1 hour with 2,4-dinitrophenylhydrazine (about 250 pmoles) in 7-5 ml of 2 N hydrochloric acid on 15 g of Celite.Subsequently, Schwartz and Parks22 suggested that the solution of 2,4-dinitrophenyl- hydrazine in 2 N hydrochloric acid could be replaced advantageously by 2,4-dinitrophenyl- hydrazine in 66 per cent. phosphoric acid. This column contained a relatively large amount of reagent (about 100 pmoles per g of stationary phase), from which impurities were removed by washing with benzene. A further advantage, particularly for the analysis of oils, is that the column does not decompose hydroperoxides to carbonyl whereas the 2 N hydrochloric acid column2* does (80 to 88 per cent.), either because hydrochloric acid is stronger than phosphoric acid, or because of the catalytic effect of the chloride ion.25~26527 All workers in this field have stressed the importance of the ubiquitous nature of carbonyl compounds and the necessity for the careful purification of the solvents used.EXPERIMENTAL 2,4-DINITROPHENYLHYDRAZINE- The commercially available material (e.g., 2,4-dinitrophenylhydrazine AnalaR, British Drug Houses Ltd., m.p. 196" to 199" C) was suitable for most purposes, any impurities being removed from its solution in aqueous mineral acid by filtration and washing with carbon tetrachloride28 or a carbonyl-free petroleum solvent.However, this method of purification was not possible for solutions in ethanol or benzene, and the reagent was purified as described under Method. Xn alternative procedure, extraction with light petroleum in a Soxhlet apparatus,ll gave material which still imparted a colour to the organic phase when distributed between 2 N snlphuric acid and purified light petroleum. Little purification could be effected by simple re-crystallisation from methan01.l~ CYCLOHEXANE AND LIGHT PETROLEUM- Useful indications of the carbonyl contents of these solvents were obtained by shaking samples with a saturated solution of 2,4-dinitrophenylhydrazine in 2 N hydrochloric acid overnight, in a Griffin wrist-action flask shaker (Messrs. Griffin and George Ltd.).The resulting concentration of 2,4-dinitrophenylhydrazones in the organic phase was obtained by dividing the value of the optical density at its maximum (about 340 mp) by the value of E = 23,700. It should be noted that not only is the adsorption maximum 20mp lower in hesane than it is in chlor~form,~~ ethanol or benzene, but the extinction coefficient is 5 per cent. higher. \Ye found that the lowest value for E occurred in a 4 to 1 v/v mixture of benzene and ethanol. The heavily contaminated samples of cyclohexane and light petroleum gave precipitates which were taken up in benzene and determined after dilution with ethanolic potassium hydroxide.17 The results obtained are shown in Table I. TABLE I CARBONYL COMPOUNDS IN SOME LABORATORY SOLVENTS Solvent Carbonyl concentration, pmolar Hexane .. . . .. .. . . . . 3000 Hexane (spectroscopic grade) .. .. 14 Light petroleum (b.p. 60" to 80" C) . . 320 Light petroleum (b.p. 40" to 60" C) . . 330 Light petroleum (aromatic free) . . .. 17 Cyclohexane . . . . . . .. .. 37 , - - - - I - I . ~ - - ~ - ~ I ~ . . ~ ~ + ~ ~ ~ ~ ~ ~ ; ~ m,.3ao\ i n .. ..May, 19661 PBRSONS QUANTITATIVE MICROANALYSIS OF CARBONYL COMPOUNDS 299 Thus a good grade of cyclohexane or light petroleum was adequate for most purposes. By using the procedure described by Van der Ven and de Jonge30 the carbonyl content of aromatic-free light petroleum was still further reduced to 2 pmolar. BENZENE- Carbonyl compounds in benzene were found to react incompletely when shaken overnight with a solution of 2,4-dinitrophenylhydrazine in mineral acid.They were therefore determined by adding 1 mg of purified 2,4-dinitrophenylhydrazine and 10 mg of trichloroacetic acid to a 10-ml sample, leaving to stand overnight and measuring the adsorption at 430mp after dilution with 1-8 per cent. ethanolic potassium hydroxide. The results of an investigation into the accuracy of this procedure are described in the next section. I t was found that consistent results could best be obtained by adding the benzene solution to an equal volume of freshly prepared 1.8 per cent. ethanolic potassium hydroxide (obtained by shaking 5 potassium hydroxide pellets with 25ml of re-rectified ethanol at room tem- perature, and filtering) and reading the optical density with a self-recording spectrophotometer (Cnicam SP800) after exactly 10 minutes.At low carbonyl concentrations, absorption due to unchanged reagent was too large to be ignored31; so measurements were also made at 360 mp, and calculations performed after determining the appropriate extinction coefficients- %som~* E ~ ~ o ~ I J . 2,4-Dinitrophenylhydrazine . . . . 1860 1180 2,4-Dinitrophcnylhydrazones. . . . 3400 22,300 The last figure is significantly higher than that used by Keith and Day,19 but is consistent with the values obtained by Jones et aZ.32 if it is assumed that solvents, unlike oils, are liable to contain more ketones than aldehydes. The formulae derived from the above extinction coefficients were as follows- 2,4-Dinitrophenylhydrazine = (594 E,,,, - 90 E,,,) pmolar 2,4-Dinitrophenylhydrazones = (49-7 E,,, - 31.4 E,,,) pmolar The carbonyl content of sulphur-free benzene proved to be variable (10 to 500 pmolar), even with bottles labelled with the same batch number.One or two distillations from 2,4-dinitrophenylhydrazine - trichloroacetic acid17 reduced this value to less than 4 pmolar. Details of this purification are given under Method. REACTION OF CARBONYL COMPOUNDS \VITH 2,4-DINITROPHEh'YLHYDRAZINE AND TRICHLORO- ACETIC ACID I N BENZENE- An attempt was made to check the Henick p r o c e d ~ r e l ~ ? ~ ~ by following the reaction with a model compound at room temperature. Purified 2,4-dinitrophenylhydrazine (2.6 mg, 12.9 pmoles), in 10 ml of carbonyl-free benzene, was added to nonan-2-one (101 pg, 0-72 pmole) and trichloroacetic acid (186 mg, 1-14 pmoles) in 15 ml of the same solvent.At intervals a sample was withdrawn, diluted with an equal volume of 1.8 per cent. ethanolic potassium hydroxide, and examined after 10 minutes in the self-recording spectrophotometer (time of scan was 2 minutes) against a blank of trichloroacetic acid in benzene - ethanolic potassium hydroxide. A control was run under the same conditions, the nonan-%one being omitted. The net apparent quantities of saturated and unsaturated carbonyl 2,4-dinitrophenylhydra- zones obtained are shown in Table 11. TABLE IT APPAREXT EXTEST OF REACTIOB BETITEEN NONAN-2-ONE AND 2,4-DINITROPHENYLHYI)KAZINE I N BENZENE IN THE PRESENCE OF TRICHLOROACETIC ACID Time of reaction a t 23" C 5 minutes 30 minutes 23 hours saturated carbonyls, pmoles .. . . 0.79 0.79 1.03 Saturated carbonyls, per cent. . . . . 110 110 143 Unsaturated carbonyls, pmoles. . . . - 0.05 - 0.07 - 0.24 Unsaturated carbonyls, per cent. . . - 7 - 10 - 33 The negative values are a consequence of the magnitude of the readings given by the control. In another experiment, purified 2,4-dinitrophenylhydrazine (2.5 mg, 12-5 pmoles) in 10 ml of carbonyl-free benzene was added to trichloroacetic acid (146 mg, 900 pmoles) in the same solvent. Samples were withdrawn and examined as before, and the optical densities obtained are shown in Table 111.300 PARSONS : QUANTITATIVE MICROANALYSIS OF CARBONYL COMPOUKDS [ A d y s t , Vol. 91 TABLE I11 REACTION BETWEEX 2,4-DI?;ITROPHEKYLHYDRAZINE AND TRICHLOKOACETIC ACID I N BENZENE Time of reaction at 23" C E360 Ed30 &60 5 minutes 0.63 0.30 0.18 30 minutes 0.6 1 0.30 0.18 6 hours 0.63 0.32 0.2 1 24 hours 0.68 0-39 0.26 47 hours 0.70 0.43 0.30 120 hours 0.75 0.5 I 0.37 The explanation of the high readings of the control appears to be that 2,4dinitrophenyl- hydrazine reacts with trichloroacetic acid to give a pigment which is green in alkaline solution.It is possible to allow for this effect by assuming that the pigment has similar absorption (at 360 and 430 mp) to 2,4-dinitrophenylhydrazine and by using the formulae given in the preceding section. This method for computing the results was applied to the original experiment and the results are set out below- Time of reaction a t 23" C 6 minutes 30 minutes 23 hours Carbonyl 2,4-dinitrophenylhydrazones, pmoles .. 0.67 0-(i9 0.73 Carbonyl 2,4-dinitrophenylhydrazones, per cent. . . 93 96 101 Applied in this way the procedure gives reasonable results with much larger concen- trations of carbonyl compounds. By using 2,4-dinitrophenylhydrazine (2.5 mg, 12.5 pmoles) and nonan-2-one (1-01 mg, 7-2 pmoles) under conditions similar to those described in the foregoing section, the results are shown below- Time of reaction a t 23" C 5 minutes 30 minutes 24 hours Carbonyl 2,4-dinitrophenylhydrazones, pmoles . . 4.7 6.9 7 . 1 Carbonyl 2,4-dinitrophenylhydrazones, per cent. . . 65 96 99 For analyses involving subsequent fractionation of the derilratives by chromatography, however, the presence of artifacts from the reagents was clearly undesirable. For example, it was observed that a solution of 2,4-dinitrophenylhydrazine in 2 s aqueous trichloroacetic acid deposited a crystalline precipitate on standing at room temperature, and after 2 weeks the supernatant liquid was almost colourless.REACTIOY BETWEEN 2,4-DINITROPHEXYLHYDKAZINE IN AQLJEOCS ACID AND SOh'AX-?-ONE IN \'A RI 0 LT S SOLVENTS- (a) Light PetroZeztm-By using the wrist-action shaker under standard conditions it was possible to follow reactions in systems involving two immiscible liquids. The reaction between nonan-2-one (210 pg, 1.46 pmoles) in 5 ml of light petroleum and 2,4-dinitrophen~~lhydrazine (about 5 pmoles) in 5 ml of 2 N sulphuric acid proceeded as shown in Table 1iT. TABLE IC: REACTION BETM'EEN NONAN-2-OX;E 13 LIGHT PETIIOLEUM AKD 2,4-DINITKOPHENYLHYDK.~Zl~E I N 2 h' SVLI'HrRIC ACID Time, in minutes Percentage conversion Time, in hours Percentage conversion 0 0 1 39 5 2.8 2 58 10 5.0 5 85 30 24.7 16 102 Thus the reaction was essentially (95 per cent.) complete in 6 hours, as was also the case with the carbonyl compounds studied by Forss et aZ.21 and by Begemann and de Jongell under similar conditions. ( b ) Hexune - benzene-The reaction between nonan-2-one (470 pg, 3.3 pmoles) in 10 ml of hexane - benzene and 2,4-dinitrophenylhydrazine (about 4 pmoles) in 10 ml of 5 per cent.v/v sulphuric acid was studied in a similar manner with the ethanolic potassium hydroxide procedure to determine 2,4-dinitrophenylhydrazones in the presence of 2,4-dinitrophenyl- hydrazine. The results, set out below, clearly show the retarding effect of benzene on the reaction- Benzene, per cent.. . 0 20 50 90 Percentage conversion in 16 hours . . 33 10.2 4.1 2.5 Percentage conversion in 65 hours . . 56 28 14.6 9.1May, 19661 PARSONS : QUANTITATIVE MICROANALYSIS OF CARBONYL COMPOUNDS 301 REACTION BETWEEN 2,4-DINITROPHENYLHYDRAZII\;E IN AQUEOUS ACID AND VARIOUS CARBONYLS IN LIGHT PETROLEGM- Shaking experiments-A saturated solution of 2,4-dinitrophenylhydrazine (about 5 pmoles) in 5 ml of 2 N sulphuric acid was shaken with the carbonyl compound (1 to 3 pmoles) in 5 ml of light petroleum for a suitable time. A sample was withdrawn from the organic phase and examined in the spectrophotometer. The concentrations of the 2,4-dinitrophenylhydrazones of nonan-2-one, acetophenone and benzophenone were calculated, assuming E = 22,600, 24,100 and 28,300, re~pectively.~~ IVith benzaldehyde, however, a precipitate separated at the interface ; benzene was therefore added and the concentration of 2,4-dinitrophenylhydrazone was obtained by the ethanolic potassium hydroxide procedure, assuming E = 33,300.32 The results are set out in Table 1'.The relative rates of reaction were benzaldehyde > nonan-2-one > acetophenone > benzophenone. These results agree with those of Belcher and Fleet,33 who found that benzophenone reacted very slowly with hydroxylamine in homogeneous solution. REACTION BETWEEN 2,4-L)INITROPHENTLHIDKAZINE IN 2 N SULPHURIC ACID AND VARIOUS CARBONYL COMPOCKDS I N LIGHT PETROLElJM Concentration (time = O), pmolar Carbonyl compound Renzaldehyde .. . . 570 Nonan-2-one . . . . 197 Acetophenone . . .. 490 .4cetophenone . . . . 490 Acetophenone . . . . 490 Benzophenone . . . . 268 Benzophenone . . . . 268 Time, in hours 2 2 2 16 67 16 67 Percentage conversion 04 61 48 63 83 20 9.9 T H E 2,4-DINITROPHENYLHYDRAZINE - 66 PER CENT. PHOSPHORIC ACID COLIJMN- This column was made up as described22 and gave a quantitative conversion of benzo- phenone (3-9 pmoles and 0.39 pmoles) in 10 ml of cyclohexane into its 2,4dinitrophenyl- hydrazone at a flow-rate of 22 ml per hour. Higher rates of flow gave lower yields, only 19 per cent. conversion being obtained at 97 ml per hour. A second column, 1.0 x 18.5 cm, was made with 10.0 g of stationary phase, i.e., at least 900 pmoles of 2,4-dinitrophenylhydrazine after washing.This column gave 73 per cent. conversion of 3.9 pmoles of benzophenone into its 2,4-dinitrophenylhydrazone at 8 ml per hour. Nonan-2-one (6-0 pmoles) was quantitatively converted at 20 ml per hour, which is the flow- rate laid down by Begemann and de Jongell with a column of similar size containing 2,4-dinitrophenylhydrazine - 2~ hydrochloric acid. The reaction is reversible. A solution of butanone 2,4-dinitrophenylhydrazone (8.25 pmoles) in cyclohexane was decolourised completely by passage over a 1.0 Y 9 6 c m column of Celite impregnated with 66 per cent. phosphoric acid. Octanol 2,4-dinitrophenyl- hydrazone (6.9 pmoles) was 33 per cent. hydrolysed at a flow-rate of 7 ml per hour, and decan-%one 2,4-dinitrophenylhydrazone (6.0 pmoles) was 26 per cent. hydroly-sed at 8 ml per hour.The foregoing result suggested that, although a short chain carbonyl compound would react much more rapidly than benzophenone it might not react completely. Indeed, when a solution of 41 pmoles of acetone was percolated over the 2,4-dinitrophenylhydrazine column, the effluent had no more colour than a blank treated in the same way. It seems probable, therefore, that the values given by Schwartz and Parkes22 for the aliphatic monocarbonyl contents of various organic solvents do not include acetone, and it is not possible to say from the details given in their paper whether or not acetone is removed from solvents which have been percolated over a 2,4-dinitrophenylhydrazine - 66 per cent. phosphoric acid column. THE 2,4-DINITROPHENYLHYDRAZINE - 2 N HYDROCHLORIC ACID COLUMN- Gaddis et a1.N prepared 2,4-dinitrophenylhydrazones in 2,4-dinitrophenylhydrazine - 2 N hydrochloric acid, followed by extraction with carbon tetrachloride and with benzene ; both extracts were then washed with 2 N hydrochloric acid and with water.It appears from a302 PARSONS : QUANTITATIVE MICROANALYSIS OF CARBONYL COMPOUNDS [,4 nalyst, J701. 91 subsequent paper by Gaddis and Ellis35 that the 2,4-dinitrophenylhydrazones of formaldehyde, acetaldehyde, acetone and butanone are extracted by the benzene but not by the carbon tetrachloride, and these authors commented that the quantitative aspects of the procedure required further study. Begemann and de Jongll purified light petroleum, first by the method described by Van der Ven and de J~nge,~O and then by passage over a 2,4-dinitrophenylhydrazine - 2 N hydrochloric acid column, followed by distillation.Begemann and de Jong stated that a very small amount of acetone was still present. We have found that this column gives a 95 per cent. yield of 2,4-dinitrophenylhydrazone with acetone, and an 84 per cent. yield with diacetone alcohol. The column procedure is thus a considerable improvement over the simple extraction procedures, both for slow reactions and for reactions giving unfavourable equilibria. The use of benzene as the mobile phase would be unfavourable for slow reactions and would tend to strip the reagent from the column. However, its use by Gaddis and Ellis34 suggested how the 2,4-dinitrophenylhydrazine - 66 per cent. phosphoric acid column, which has several advantages over the 2,4-dinitrophenylhydrazine - 2 N hydrochloric acid column, might be modified to give an improved yield with acetone.METHOD REAGENTS- Cyclohexane and light petroZezlm-Cyclohexane for ultraviolet spectroscopy (as supplied by British Drug Houses Ltd. or Hopkin and Williams Ltd.) is used without further purification. For more exact work, light petroleum (b.p. 40" to 60" C, aromatic free, Carless, Capel and Leonard Ltd.) is rendered carbonyl free in the following manner. 350 ml of fuming nitric acid, density 1-51, and 350 ml of sulphuric acid, density 1.84, are added, with stirring, to 3.5 litres of light petroleum, contained in a 5-litre flask fitted with a reflux condenser. The mixture becomes warm, and stirring is continued overnight. The mixed acid is removed by aspiration, and the organic phase is washed22 twice with 700 ml of water, nine times with 700 1111 of 20 per cent.potassium hydroxide and twice with 700 ml of water. The washed solvent is distilled over 350ml of refined coconut oil (Van Den Berghs and Jurgens Ltd., Purfleet), and percolated firstly through a 3-5 x 22-cm column of 100 g of alumina (P. Spence, grade H) and then through a second column of alumina activated by heating at 800" C for 4 hours (a personal communication from H. J. Duin, H. W. A. E. Groeneweld and H. Van der Wel). In order to obtain a stable product it was found to be essential to remove both the carbonyl compounds and their precursors in the foregoing manner and to store in brown bottles in the dark.Benzene-A mixture of 2-5 litres of thiophene-free benzene (Carless, Capel and Leonard Ltd.), 12.5 g of 2,4-dinitrophenylhydrazine and 2.5 g of trichloroacetic acid are refluxed for 4 hours under a Dean and Stark trap. The mixture is then distilled with constant stirring and use of a double splash head. If the mixture is not stirred, the reagent bakes on to the sides of the flask and is carried over into the receiver to give a coloured distillate. The distillation is repeated as necessary. 2,4-DinitropIze~zyZ~~~drazine--C:ommercial 2,4-dinitrophenylhydrazine and 100 ml per g of N hydrochloric acid are refluxed for 30 minutes, and the solution is then filtered. The filtrate is made alkaline with ammonia and cooled. The purified 2,4-dinitrophenylhydrazine is collected and re-crystallised from 200 ml per g of methanol to give leaflets of m.p.195" C. 98 per cent. nezitval alumina-A 2-ml portion of hydrochloric acid of density 1-16, and 98g of alumina (P. Spence, grade H) are shaken together for 30 minutes and then allowed t o stand overnight in a stoppered flask. 1.8 per cent. ethanoZic potassiz~m hydroxide-Five potassium hydroxide pellets are dis- solved in 25 ml of re-rectified ethanol by shaking mechanically in an Erlenmeyer flask. The solution is filtered through a Whatman No. 541 filter-paper and used within 2 hours. The alumina should be used within 1 week. PREPARATION OF 2,4-DINITROPHENYLHYDRAZONES- Impregnate 10-0 g of analytical-grade Celite (Johns - Manville) with a solution of 2,4-di- nitrophenylhydrazine (500 mg, 2-5 pmoles) in 6 ml of 88 to 93 per cent.orthophosphoric acid of density 1.75, diluted with 4ml of water. Transfer this stationary phase to a column of 2.1-cm internal diameter, fitted with a B24 socket and cone and a sintered-glass plate,May, 19661 PARSONS : QUANTITATIVE MICROANALYSIS O F CARBONYL COMPOUNDS 303 containing cyclohexane and tamp it down to a height of 9.5 cm.22 Wash with 50 ml of benzene to remove some of the reagent together with residual impurities. However, at least 2.2 pmoles of 2,4-dini t rophen ylhydrazine will remain. Fit this column to a swan-necked column36 containing 35 g of 98 per cent. neutral alumina. Apply the sample (containing between 1 and 100 pmoles of carbonyl compounds) in 5 to 10 ml per g of cyclohexane to the celite column and elute with the same solvent at 20 ml per hour (total volume 175 ml), the 2,4-dinitrophenylhydrazones being retained on the columns.Up to 10 g of triglycerides and other non-polar materials may be present in the sample and are recovered in the eluate. Elute both columns with 175 ml of benzene and examine an aliquot in the spectrophoto- meter, either directly or after adding to an equal volume of 1.8 per cent. ethanolic potassium hydroxide and leaving to stand for exactly 10 minutes. Approximate values for the wave- length maxima and extinction coefficients under neutral and basic conditionslg 335 (A. M. Parson, unpublished results) are given in Table 1’1. TABLE 17 WAVELENGTH MAXIMA AND EXTINCTION COEFFICIENTS OF 2 ,4-DIN ITROPHENYLHY DRAZONES 3,4-Dinitrophenylhydrazone h ~ ~ l l c , mp fniax.xmax. mP Emax. KOH - C,H,OH, Allcan-2-ones . . . . . . 36 1 21,500 43 1 22,200 Alkanals . . . . . . 354 21,000 430 20,900 Alk-2-enals . . . . .. 372 27,900 460 30,000 Allra-2,4-dienals . . .. 388 36,000 480 41,000 When the various classes of carbonyl compounds are present together, their total concentrations may be obtained29 with c2H50H = 21,000, or the separate concentrations of alkanals, alk-2-enals and alka-2,4-dienals may be obtained by measuring the absorptions at 430, 460 and 480mp and applying the equations derived by Keith and Cnfor- tunately, the absorption maxima of alkan-%one 2,4-dinitrophenylhydrazones are too close to those of alkanal 2,4-dinitrophenylhydrazones to permit separate determination by this means.However, by taking additional readings after 2 hours, further information may be obtained on this point, because only acetone and alkanal 2,4-dinitrophenylhydrazones fade appreciably under these condition^.^^ 935 For detailed analysis, the remainder of the benzene eluate may be fractionated into classes by adsorption chromatography on dry paper,37 magnesium o ~ i d e , ~ ~ ? ~ ~ or 92 per cent. alkaline alumina.40 Separation according to chain length may then be achieved by partition chromatography on paper,41 942 thin layers of Kieselguhf13+ or column^.^^^^^ 947 Xumerous thin-layer adsorption systems have also been d e ~ c r i b e d . ~ ~ y ~ 9 ~ ~ 349 I t is necessary to repeat the whole procedure, with omission of the sample, in order to allow for residual carbonyl compounds in the solvents and for artifacts produced on the columns.I t is found, for example, that two pigments < 320 mp) are obtained which are less polar than ketone 2,4-dinitrophenylhydrazones on adsorption chromatography. Winter et al. have noted several such artifacts50 and have pointcd outs1 that 2,4-dinitroaniline could arise from the reaction between acetoin and 2,4-dinitrophenylhydrazine. For polar compounds when the 2,4-dinitrophenylhydrazine column is eluted with benzene, the 2,4-dinitrophenylhydrazones of polar carbonyl compounds are transferred to the 98 per cent. neutral alumina column, together with some unchanged reagent. The alumina column may subsequently be eluted with benzene containing between 1 and 10 per cent of ethanol and aliquots of the solutions examined in the spectrophotometer as before. The absorption maxima for acctoin5l and for the two 2,4-dinitrophenylhydrazones of d i a ~ e t y l ~ ~ are shown in Table VII.TABLE iTII WAVELENGTH MAXIblA AND EXTINCTION COEFFICIENTS OF DINITROPHENYLHYDRA4ZONES OF ACETOIN AND DIACETYL 2,4-Dinitrophenylhydrazone X ~ ~ ~ ~ f o n n , m p Ernax. XI,,,. mCc Emax. Acetoin . . . . .. 357 33,000 433 Diacetyl-mono . . .. 351 29,100 50 1 38,000 Diacetyl-bis . . .. .. 393 47,000 556 54,000 KOH - C,H,OH, 435 40,000 - - (shoulder)304 PARSONS : QUANTITATIVE MICROANALYSIS OF CARBONYL COMPOUNDS [Analyst, Vol. 91 The reagent 2,4-dinitrophenylhydrazine has A::: - CzH50H = 360 mp, E = 1,860. There are, however, more satisfactory methods for determining acetoin and diacetyl which do not involve preparation of 2,4-dinitrophenylhydrazones.53 755 RESULTS Application of the method to model compounds gave good yields of products; even acetone gave 84 per cent.ANALYSIS OF BUTTER FAT The method also worked well with the molecular distillates of 200 g of butter fat obtained with a 2-inch wiped wall molecular still (Edwards High I'acuum Ltd.), 10-20 p (b.p. 160" C), fitted with liquid nitrogen cooled traps. The values (Table VIII) agreed closely with those obtained after subsequent chromatography. A 10-g sample of New Zealand butter fat was also examined directly, but in this case we were unable to separate the classes by chromatography. Schwartz et al. claim56 that this separation can be performed after a preliminary fraction on a partition column but, as can be seen from the last column in Table VIII, the quantity of involatile carbonyl compounds in this fat is so large that it would place great demands on any technique to require it to carry out a separation at this stage.TABLE 1~111 CARBOKYL CONTEST OF BUTTER FAT AND BUTTER FAT VOLATILES New Zealand Danish New Zealand volatiles, volatiles, butter fat, pmoles per kg pmoles per kg pmoles per kg Alkan-2-ones and alkanals . . 2.2 8-1 730 A1 k-2-enals . . . . . . 1.0 1.0 130 Alka-2,4-dienals . . . . . . 0.4 0.6 30 More recently, Schwartz and co-workers5' have shown that keto-glycerides can be removed from butter fat by adsorption chromatography, and that these glycerides amount to no less than 0.045 per cent. by weight (550 pmoles per kg as keto-tripalmitin).We have removed polar material from 20 g of Kew Zealand butter fat in this way, and have converted the remaining carbonyl compounds to 2,4-dinitrophenylhydrazones by the method described above. The carbonyl compounds still amounted to over 120pmoles per kg and, judging by their behaviour on subsequent chromatography, consisted largely of keto-glyceride 2,4-dinitrophenylhydrazones. The polar fraction was also examined in the same way, except that a strongly acid (2 N perchloric acid) 2,4-dinitrophenylhydrazine column was used in order to decompose acid labile carbonyl precursors.5s The 2,4-dinitrophenylhydrazones gave two bands on mag- nesium oxide,38 939 in similar positions to those given by pentanal 2,4-dinitrophenylhydrazone and by dec-2-enal 2,4-dinitrophenylhydrazone. The spectral properties given in Table IX, however, indicate an alkanone and an alkanal fraction (Amax.= 430 mp in each instance, and the latter fading rapidly) amounting to 165 pmoles per kg and 36 pmoles per kg, respectively. TABLE TX WAVELENGTH MAXIhfA AND FADING OF L)INI?'ROPHENYLHYL)RXZONES OF POL-iR CARBONYL COMPOUNDS FROM BUTTER FAT Fading, Fraction GZ:'& Amax., ml* per cent. 1 362 430 2 0 540 3.4 2 360 430 15 635 24 KOH - C,H,OH It therefore appears that, despite the use of a strongly acid reaction column, the carbonyl compounds still contained polar groups and were probably keto-glycerides and aldehydo- glycerides, respectively. The author thanks Dr. I. D. Morton for his interest and encouragement, and Mr.D. J. Moore and others for technical assistance.May, 19661 PARSONS : QUANTITATIVE MICROANALYSIS OF CARBONYL COMPOUNDS 305 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 40. 50. 51. 52. 53. 54. 55. 56. 57. 68. REFERENCES Winter, M., Stoll, M., Warnhoff, E. W., Greuter, F., and Buchi, G., J . Fd Sci., 1963, 28, 554, Lea, C. H., and Swoboda, P. A. T., Chem. & Ind., 1958, 1289. Meijboom, P. W., J . Amer. Oi2 Chem. SOC., 1964, 41, 326. Hoffman, G., Ibid., 1961, 38, 1. Forss, D. A., Dunstone, E. A., and Stark, W., J . Dairy Res., 1960, 27, 211. Commonwealth of Australia, Commonwealth Scientific and Industrial Research Organisation, Forss, D.A, J . Dairy Sci., 1964, 47, 245. Braun, P. A, and Mosher, W. A., J , Amer. Chenz. SOC., 1958, 80, 3048. Chen, P. S., Analyt. Chem., 1959, 31, 296. Haverkamp Begemann, P., and de Jong, K., Recl Trav. Chim. Pays-Bas Betg., 1959, 78, 275. Dana Johnson, G., J . Amer. Chem. SOC., 1951, 73, 5888. Shriner, R. L., and Fuson, R. C., “Identification of Organic Compounds,” Third Edition, John Buss, C. D., and Mackinney, G., J . Amev. Oil Chem. Soc., 1955, 32, 487. Henick, A. S., Benca, 54. F., and Mitchell, J . H., Ibid., 1954, 31, 88 and 447. , Ibid., 1956, 33, 35. Skeriett, E. J., and Baker, E. A., Analyst, 1959, 84, 376. Keith, R. W., and Day, E. A., Ibid., 1963, 40, 121. Pool, M. F., and Klose, A. A., J . Amer. Oil Chem. Soc., 1951, 28, 215.Lea, C. H., and Jackson, H. A. F., Chem. & Ind., 1964, 1429. Forss, D. A., Pont, E. G., and Stark, W., J . Daivy Res., 1955, 22, 91. Schwartz, D. P., and Parks, 0. W., Analyt. Chem. 1961, 33, 1396. Schwartz, D. P., Haller, H. S., and Keeney, M., Ibid., 1963, 35, 2191. Horikx, &I. RI. J , Appl. Chem. Lond., 1964, 14, 50. Chang, S. S., and Watts, €3. M., “Flavour Chemistry Symposium,” Campbell Soup Co., Camden, Loftus Hills, G., and Thiel, C. C . , J . Dairy Res., 1946, 14, 340. RlcDowell, A. K. R., Ibid., 1964, 31, 221. Bennett, A., May, L. G., and Gregory, R., J . Lab. Clin. Med., 1951, 37, 613. Stitt, F., Seligman, R. B., Resnik, F. E., Gong, E., Pippen, E. L., and Forss, D. A., Spectrochim, Van der Ven, B., and de Jonge, A. P., Red Trav. Chim. Pays-Bas Belg., 1957, 76, 169.Mendelowitz, A., and Riley, J . I?., Analyst, 1953, 78, 704. Jones, L. A., Holnies, J. C., and Seligman, R. B., Analyt Chem., 1956, 28,191. Belcher, R., and Fleet, B., J . Chem. SOC., 1963, 5720. Gaddis, A. M., Ellis, R., and Currie, G. T., Fd Res., 1959, 24, 283. Gaddis, A. M., and Ellis, R., Ibid., 1959, 24, 392. Bush, I. E., “The Chromatography of Steroids,” Pergamon Press, 1961, p. 149, Gaddis, A. M., and Ellis, R., A n a l y f . Chem., 1959, 31 870. Schwartz, D. P., Parks, 0. W., Keeney, M., Ibid., 1962, 34, 669. Schwartz, D. P., and Parks, 0. W., Microchem. J . , 1963, 7, 403. Van der Yen, B., Haverkamp Begemann, P., and Schogt, J . C. M., J . Lipid Res., 1963, 4, 91. Horner, L., and Kirmse, W., Justus Liebigs A n n l n Chem., 1955, 597, 48. Klein, F., and de Jong, I<., Red Trav. Chim. Pays-Bas Belg., 1956, 75, 1285. Badings, €1. T., and M’assink, J . G., Xeth. Afilk G. Dairy J . , 1963, 17, 132. Urbach, G., J. Chromat., 1963, 12, 196. Kramer, P. J . G., and Van Duin, H., R e d Trav. Chim. Pays-Bas Belg., 1964, 73, 63. Corbin, E. )I., Schwartz, D. P., and Keeney, >I., J. Chvowiat., 1960, 3, 322. Freytag, W., Fefie Seifen, 1963, 65, 603. Radings, H. T., J . Amer. Oil Chem. SOC., 1959, 36, 648. Ilhont, J. H., and de Rooy, C., .4$zaZyst, 1961, 86, 74. Winter, M., and Sundt, E., Helv. Chim. A c f a , 1962 45, 2195. Winter, RI., and Enggist, P., J . Fd Sci., 1963, 28, 685. Jones, L. A,, and Kinney Hancock, C., J . An7er. Chein. Soc., 1960, 82, 105. Pien, J., Baisse, J . , and Martin, R., Lait, 1937, 17, 675. Kimphorst, L. C. E., Kruisheer, C. I., 2. Unters. Lebeizsmitfel, 1937, 73, I . Owades, J . L., and Jakavac, J. L4., Proc. Amer. SOC. Brew. Chem., 1963, 22; A n a l y f . Abstr., 1964, Schwartz, D. P., Haller, H. S., and Keeney, M., A n a l y f . Chem., 1963, 35, 2191. Parks, 0. W., Keeney, M., Katz I., and Schwartz, D. P., J . Lipid Res., 1964, 5, 232. Schogt, J. C. M., Haverkamp Begemann, P., and Koster, J., Ibid., 1960, 1, 232. -, Ibid., 1962, 39, 439. Division of Dairy Research, Annual Report 1961-1962, Melbourne, 1962, p. 10. Wiley and Sons Inc., 1948, p. 171. -- ___ -- New Jersey, 1961, p. 145. Acta, 1961, 17, 51. 3363. R w e i v d Novdmher 16th. 1965.

ISSN:0003-2654    

DOI:10.1039/AN9669100297

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

306 EDMUNDSON CALIBRATION OF A FISHER AIR-PERMEABILITY [Analyst, VOl. 91 Calibration of a Fisher Air-permeability Apparatus for Determining Specific Surf ace BY I. C. EDMUNDSON (Glaxo Laboratories Ltd., Green ford, Middlesex) Calibrating the Fisher sub-sieve sizer at a single particle-size level does not ensure accuracy a t other levels unless several variables are controlled. Instrument modifications that give better control of the several variables, and a calibration method that ensures accurate air-flow measurement without depending on a particle-size standard, are described. The modified instrument has good precision over the range 2 to 4 0 ~ . A method for extending this range is given. THE air-permeability apparatus of Gooden and Smith,l available commercially as the Fisher sub-sieve sizer (Fisher Scientific Company, Pittsburg, Pa., U.S.A. ; Kek Ltd., Ancoats, Manchester 12), is widely recognised as a convenient means of determining specific surface.Its advantages include an automatic calculator and the ability to give readings on a single sample compressed to successively lower porosities. We found considerable variation in the results for identical samples tested on different instruments. Some of the variation arises from fundamental errors in the usual method of calibrating and using the Fisher instrument. An alternative calibration method described by Dubrow2 is indirect, and takes no account of some important factors. The Fisher instrument, like other types of air-permeability a p p a r a t u ~ ~ ~ ~ ~ ~ ~ ~ is a means of measuring flow-rate of air through a powder sample.In this paper it is shown how So modif!, and calibrate the instrument so as to ensure accurate flow-rate measurement. The instrument (Fig. 1) consists of an air-supply section, a sample tube and a flow-meter. The water manometer, P, is not part of the standard instrument, but was added for the investigation and is now retained by us because it increases the instrument's accuracy and precision. The flow-meter consists of a capillary resistance, a water manometer, F, and a chart. A second flow-meter resistance can be opened to double the range. D/' A''' . P' I I t + I -TL E H a \ K \ J '\ M A = Pump B = Air filter C = Pressure control D = Standpipe P = Water manometer E = Drying tube G = Sample tube H = Flow-meter resistances F = Flow-meter manometer J = Zero control K = Chart M = Sample-height line Fig.1. Modified Fisher sub-sieve sizerMay, 19661 APPARATUS FOR DETERMINING SPECIFIC SURFACE 307 ’IVhen the sample is compressed, a pointer indicates the sample height, L , and the corresponding bed porosity, E, on the chart. After the sample tube is inserted in the air line, the water in one arm of the F manometer (a) rises to a level (&F) that depends on the flowrate. This level is read directly as average particle diameter (dvs) on the chart, which is mounted behind the manometer arm and on which there is a series of curves relating $F and E to dvs. A rack-and-pinion device for compressing the sample and indicating L and &F on the chart is not shown in Fig.1. THE INSTRUMENT EQUATIONS The Fisher instrument is based on the equation1- where d , , is the volume-surface mean diameter in p (specific surface in sq. cm per cc = 60,000/dV,), 7 is the viscosity of air in poises, C is the conductance of the flow-meter resistance in cc per second unit pressure per drop, p is the sample density, L is the sample height in cm, , ! ! is the sample weight in g, A is the cross-sectional area of the sample tube in sq. cm, P is the air pressure entering the sample and I; is the pressure drop across the flow-meter resistance, all pressures being expressed as centimetres of water. Therefore, The sample weight is standardised at a value numerically equal to p. equation (1) can be simp1 where c is an instrument - - fied to the form- constant that combines factors from equation (1)- c = L .. . 6o 14 Oo0 JZ (3) I f the flow-meter resistance is a capillary tube of suitable dimensions, C is given by the simple form of Poiseuille’s equation- where Y is the radius and I the length of the capillary, g is the gravitational constant and 7 is the viscosity of air. CONSTRUCTION OF THE CHART The base-line of the chart is graduated in values of E from 0-80 to 0.40. The L ordinates (cm) of the sample-height line are given by- .. .. .. . . 0.7893 L = - l - A ( l - € ) 1--E where A has the nominal value 1-267 sq. cm. The equation for the d,, ordinates, which are equal to $F cm, is obtained by combining equations (2) and ( 5 ) , and substituting the nominal values of c = 3.SO and P = 50.0 cm- ACCURACY OF THE INSTRUMENT All the factors of equations (1) and (2) are possible sources of systematic error.It is apparent from the form of dj77-T) in equation (2) that small errors in P or F can result in large errors in dvs, especially when P and F are nearly equal. It will be shown also that c is not independent of P and F when the instrument is calibrated in the usual way. The remaining factors ( A , L , ,!W, 7 and p ) are less important. The effect of error in measuring or standardising these factors on the apparent particle size indicated by the chart, dvs’, can be calculated after appropriate substitution in equations (1) or (2).308 EDMUNDSON : CALIBRATION OF A FISHER AIK-PERMEABILITY [AlZa&St, VOl. 91 THE INSTRUMENT CONSTANT- The flow-meter resistance in Fisher instruments is either a capillary tube whose resistance can be varied by a sliding wire in its lumen, or an adjustable needle-valve.Either type is usually calibrated against an artificial standard sample supplied with the instrument. This calibrator is a small ruby orifice-plate mounted in a sample tube. I t is inserted in place of the normal sample, and the flow-meter resistance is then adjusted until the chart d,, reading equals the value stamped on the calibrator; the instrument constant is then, nominally, equal to 3.80. The ruby's labelled value is usually about 5.8 p at porosity 0.75, corresponding to about 15 p at porosity 0.5. Porosity has no real meaning in reference to an orifice; essentially, the ruby produces a constant I; value on the flow-meter manometer when other factors are constant.This F value corresponds to different d,, values, which depend merely on the porosity setting of the chart. If the accuracy of this calibration is in doubt, a direct check of the ruby's nominal value is difficult. Since the orifice length-to-diameter ratio is small and the air flow turbulent, the flow-rate and its equivalent d,, cannot be related to the orifice dimensions by any simple equation. However, an accurate and constant value of c can be achieved by replacing the variable resistances with simple capillary tubes of dimensions calculated to give the required con- ductance. Substituting6 q = 0.000183 poise at 25" C and c = 3-80 in equation (3) gives the normal-range conductance, C = 0.004298 cc per second per cm pressure drop at 25" C.The conductance of the double-range capillary is three times that of the normal-range. Sub- stituting in equation (4) gives the required length and radius. Accurate resistances can be made from precision-bore tubing after selecting for uniformity of bore and determining the average radius by filling with mercury. Suitable nominal bore- diameters are 0.03 cm and 0.04 cm for the normal-range and double-range capillaries, respec- tively, with corresponding lengths of about 25 cm and 26 cm. Errors due to turbulence, molecular flow and end effects are negligible with these dimensions at the maximum pressure involved. Mounted vertically in the instrument, the capillaries are protected from chance contamination by dust and have maintained their constants during continual use for sevei a1 years.AIR PRESSURE- The Fisher instrument's constant-pressure device consists of a control valve and a standpipe filled with water. In use, the valve is adjusted until a regular stream of bubbles rises through the water. Since the air pressure depends on the height of water (approxi- mately 50 cm) and on the bubble rate, the standpipe is engraved with a water-level line by the manufacturer, and the bubble rate is directed to be adjusted to between 2 and 3 per second. The reliability of this system was checked by means of the P manometer specially fitted for this purpose, as shown in Fig. 1. The P manometer is made from precision-bore tubing, with a narrow-bore section (1-5 mm), to damp oscillations caused by the pump, and two expansion bulbs to accommodate the initial surge before the standpipe begins to bubble.When the bubble rate was adjusted to 2.5 per second by careful timing with a stopwatch, the manometer gave a steady reading of 50.0 cm. But when different operators attempted to produce a steady bubble rate of 2 to 3 per second by unaided visual judgment, the reading varied between 49.5 and 51-0 cm. It is preferable, therefore, to standardise P by ignoring the bubble rate and adjusting the pressure control valve to give a manometer reading of 50.0 cm during each determination of particle size. Gooden and Smith' adopted the standpipe from an earlier design by Traxler and 1Ba~m.~ Although the latter claimed that such a pressure regulator is highly accurate, they included a manometer in the system and used its readings in their calculations.The real function of the standpipe is to reduce pulsation in the air flow by allowing a bubble to escape at each stroke of the pump, Since the stroke rate is usually about 4.5 per second, a steadier flow is obtained if the water level in the standpipe is lowered by about 0-5 cm, or until one bubble is given for each stroke while the manometer is at 50-0 cm. The upper curve in Fig. 2 shows the error in indicated diameter at porosity 0-5 when P' = 51 cm instead of the standard 50.0 cm used to calculate the chart ordinates. The usual method of calibrating the variable flow-meter resistance against a standard sampleMay, 19661 APPARATUS FOK DETERMINING SPECIFIC SURFACE 309 Fig. 2. Error of indicated particle size a t porosity 0.5 due to error in air pressure (P’ = 51 cm) or to inequality of flowmeter manometer arm radii ( Y ~ / Y ~ = 0.98): curve A, error uncompensated ; curve B, error partially compensated by calibrating with a 15-p standard compensates the error in P’ by introducing an equal and opposite error in the instrument constant, c.But the compensation is complete only at the chart level corresponding to the standard sample. The lower curve in Fig. 2 shows a residual error varying from -56 per cent. to +9.3 per cent. at other diameters when the original error is compensated with a standard equivalent to 15 p at porosity 0.5. Thus a subtle disadvantage of the usual cali- bration method, when either the ruby standard or an actual fine-particle standard is used, is that it is a one-point calibration and gives the operator a false sense of accuracy.ERROR IN MEASLTIIING FLOW-METER PRESSURE DROP- Maizometev error-The Fisher method for determining 4F by observing the rise in one manometer arm, while ignoring the fall in the other arm, leads to error if the two arms are of unequal internal radius. Nanometer-arm inequality has the same effect as error in standardis- ing P’. Hence Fig. 2 also shows the effect of the manometer error when the arms have a radius ratio (ra/~b) of 0.98, corresponding to a maximum difference of 1 cm between the rise and fall in the two arms. Inequality of Ya and Yb may be detected by fitting millimetre scales to both arms of the manometer. In this way, errors of more than 1 and 2 cm in F were found in two of the instru- ments mentioned in paragraph 1 above.I t was not known whether the faulty tubes were original fittings, though the instruction manual refers to the need to use matched pairs. Since the relationship of d,, to F varies with E according to equation (6), Fig. 2 is valid for any porosity if values of F corresponding to E = 0.5 are substituted for dvS‘ in the abscissa. Chart ervor-The accuracy of the drawing and reproduction of the principal d,, curves on the chart was checked by measuring the ordinates with a travelling microscope and com- paring them with the \dues given by equation (6). The ordinates of the principal curves were found to have consistently 99-2 per cent. of the theoretical values at all porosities. The effect of this error on dvs’ at E = 0-5 is shown in Fig.3. As before, partial compensation occurs if the flow-meter resistance is calibrated against a standard sample. JTalues of F may be substituted for dvS’ in the abscissae as in Fig. 2. Some of the intermediate d,, curves on the chart are less precisely drawn, in particular those from 3.1 to 3-3 p at E = 0.47. Drainage error-Drainage error in setting the manometer zero and in taking the sample reading is difficult to differentiate from error due to manometer-tube radius. However, these errors are eliminated simultaneously if manometer tubing is selected so that a rise in one arm is equalled by a fall in the other under standard drainage conditions. In this way, and by applying corrections for measured chart errors, good accuracy is achieved for routine work.Compensation occurs in the same way as for P’.310 EDMUNDSON : CALIBRATION OF A FISHER AIR-PERMEABILITY [A ?Za/$St, 1'01. 91 c A Average particle size (dv;),p Fig. 3. Error of indicated particle size a t porosity 0.5 due to - 0.8 per cent. error in the chart d,, ordinates: curve A, error uncompensated; curves B and C, error partially com- pensated by calibrating with 15 and 5.5-p standards, respectively If greater accuracy and precision are required at the expense of convenience, the errors of the Fisher manometer - chart system can be eliminated by calculating d,, via equation (2) from direct F readings on a separate manometer, so fitted that both arms can be read against a single millimetre scale. VISCOSITY OF AIR- If the viscosity of air is assumed to be constant within the range of pressures used, 7 cancels out when equation (4) is substituted in equation (I), and the instrument reading should be unaffected by temperature changes (cf.Lea and Nurse3). This was confirmed experimentally for constant ambient temperatures between 10" and 30" C and for flow-rates within the instrument range. OTHER FACTORS- The form of equation (1) is such that small percentage errors in A , L , -21 or p result in larger percentage errors in the apparent particle size, dvs', indicated by the chart. The dvS' errors are independent of particle size, but increase as porosity is reduced (see Table I). Sample-tube diameter-The nominal cross-sectional area of the sample tube, A = 1.267 sq. cm, corresponds to an internal diameter, D = 1.270 cm.The internal diameters of the effective portions of three sample tubes measured with a travelling microscope were each found to be 0.31 per cent. high. Table I shows the factoIs by which this percentage error must be multiplied to give the corresponding percentage eriors in dvs'. TABLE I EFFECT OF ERROR I N SAMPLE TVBE DIAMETER, SAMPLE HEIGHT ASD SAMPLE UTIGHT ON dvsf AT DIFFERENT POROSITIES Multiply the percentage error in D, L. or ,iM by the factors shown below to obtain the corresponding percentage error in dvS' Porosity 0.80 0.70 0.60 0.50 0.40 D + 3.8 + 4.3 +5.1 $6.1 + 7.6 L + 0.9 + 1.3 + 1.5 + 2.0 + 2.8 M - 1.4 - 1.7 - 2-0 - 2.5 - 3.3 Sample height-The sample height, L, is equal to the ordinate of the sample-height line on the chart, provided that the compression mechanism is properly adjusted in the usual way.The errors in the L-ordinates on a typical Fisher chart were found to vary from +0.2 to -0.7 per cent. over the porosity range 0-50 to 0.80, with a maximum error of - 1.1 per cent. a t porosity 0-40. Table I shows the factors by which these errors must be multiplied to give the corresponding errors in dvs'.May, 19661 APPARATUS FOR DETERMINING SPECIFIC SURFACE 31 1 Sample demity aizd weight-The standard sample weight for the instrument is equal t o the density of the sample material ( M = p). Any systematic error in density, e.g., by round- ing-off, therefore results in a systematic error in sample weight, and the effect on dvS’ is increased by the factors shown in Table I.The factors are negative because an excess sample weight results in a low value of dV8’. THE FLOW-METER RESISTANCE- A normal-range flow-meter resistance was made, as described previously, from selected precision-bore tubing. Substituting the measured radius and length in equation (4) gave the conductance as 0.004299 :c per second per cm pressure drop at 25” C, or 100.1 per cent. of the desired nominal value. The conductance at that temperature was measured by a bubble meter method8 at constant pressures of about 50 cm as indicated on the P manometer. Four replicate determinations ranged from 0-004296 to 0.004320 cc per second per cm, the mean being 100.26 per cent. of the value by equation (4) or 100-33 per cent. of the desired nominal value of 0-004296 cc per second per cm.The same result was obtained for P values down to 5 cm. From equation (l), d,, is proportional to 4 C ; it is therefore probable that the error of the calibration is not more than 0.16 per cent. in terms of d,,. Further confirmation was sought by using the capillary tube to determine the tiYS’ of a standard Portland-cement sample No. 114j from the Xational Bureau of Standards, Washington, D.C., U.S.A. Chart errors were avoided by measuring F and L directly, as described above; the result was calculated from equation (2) after determining c from the measured dimensions of the capillary and gwing A the value found by measuring the sample-tube diameter. Duplicate results were 99.9 and 98-7 per cent. of the value, 5.755 p at E = 0-500, assigned to the sample by the Bureau, or 100.1 and 98.9 per cent.when calculated by the bubble meter calibration factor. The bubble meter and cement results confirm the calibration accuracy within the limits of their respective experimental errors. THE RUBY CALIBRATOR- Substituting measured values of F in equation (2) gave d,, results about 2 per cent. lower than the rubies’ labelled values. I t is possible that this discrepancy is due to the makers’ method of calibrating each production batch of rubies on a standard instrument that has itseli been calibrated against a fresh K.B.S. Portland-cement sample. If the chart d,, ordinates in the standard instrument have the -0.8 per cent. error reported above (Error in Measuring Flow-meter Pressure Drop), and that error is compensated at 5-5 p by calibrating the instrument against cement of that value at porosity 0-5, curve C in Fig.3 shows that the labelled value of a ruby, equivalent to 15 p at porosity 0.5, will be 2-15 per cent. high. PRECISION OF THE MODIFIED INSTRUMENT CONFIRMATION OF ACCURACY OF CALIBRATION Several calibrators were checked with the calibrated capillary tube. The over-all precision of d,, determinations depends on the precision of measuring or standardising the factors previously mentioned. In the treatment below, it is assumed that when a quantity is measured to the nearest graduation on a linear scale, the measurement error is distributed rectangularly, and that the standard error is equal to the scale interval multiplied by 41/12 for a single reading, or by d l j 6 for a measurement by difference.CALIBRATION BY THE MERCURY METHOD- The instrument constant, c, depends on the capillary radius and length. The precision of c therefore depends on weight and length measurements. The standard error of the Calibration, in terms of d,,‘, is k0.17 per cent. in the single-range, or +0-08 per cent. in the double-range, if weighings (of mercury) are made to the nearest 0.001 g, and length is measured to the nearest 0-002 cm (by travelling microscope). SAMPLE-TUBE DIAMETER- The error in d,,’, when D differs from its nominal value, can be corrected by applying factors calculated from the measured value of D. The standard error of the corrected dVB’, due to error in measuring D with a travelling microscope graduated to 0.002 cm, ranges from t-0-24 per cent.at porosity 0.80 to $_O-47 per cent. at porosity 0.40.312 EDMUNDSON CALIBRATION O F A FISHER A41R-PERMEARILITY [Analyst, VOl. 91 PRECISION OF dvS‘ DETERMINATION- The precision of d,,’, determined on a single modified instrument, with a singIe sample tube, depends on the precision of five successive operations : weighing the sample, standardising P a t 50.0 cm, setting the pointer to the sample-height line, setting the reference bar of the pointer to the flow-meter meniscus, and reading the dvS’ indicated on the chart by the pointer. Sample weight-Weighing to the nearest 0.001 g gives M a standard error of k0-03 per cent. when 211 = 1.5 g. This is smaller than the errors in other factors, but caution is necessary because this error must be multiplied by the factors given in Table I to obtain the standard error of dvs’, Air firesszrre-Tf the P-manometer levels are set to the nearest 0.1 cm, the standard error of P’ will be k0-04 cm.This error has been used to calculate the d,,’ error shown in Fig. 4, but greater precision can be obtained in practice. Since the manometer has no adjustment for the effective volume of contained water, it is impossible to set the pressure so that both menisci will coincide with scale graduations; if one coincides exactly, the other will fall at random between two graduations. But the 0.04 cm standard error can be reduced to the extent that the operator can judge both menisci to be equally displaced from the appropriate graduations. Sample height-The precision with which twenty operators could set the instrument pointer to the sample-height line was determined with a sensitive clock-gauge.The standard deviation from the mean setting was 0.003 cm, equal to one-fifth of the line thickness, or approximately equivalent to the limit of unaided visual resolutiong at 15 cm. The same error occurs in setting the zero; combining both errors gives the standard error of I , at porosity 0.5 as i 0 - 2 7 per cent. F-manometer settifig-In a similar clock-gauge experiment the standard deviation of the meniscus setting was 0.009 cm. This is larger than that for the sample height, probably because the parallax error is greater. The equivalent standard error of F’ is k0.026 cm. Chart dvS’ readiizg-The spacing between dvs curves on the chart is sufficient to permit visual estimation of the reading to the nearest one-fifth interval between successive curves.If we assume that such interpolation is accurate, the standard error of the reading will be +0.22/1/12 multiplied by the interval, in microns, between successive curves. This is the minimum theoretical error and has been used in the calculations for Fig. 4. After some training in recognising the appearance of the pointer in different positions between the curves, a careful operator can reduce the error to about 1.2 times the theoretical error. The individual and combined effects of these errors on dV,’ at porosity 0.5 are shown in Fig. 4. The P , F and d,, effects depend essentially on the F-manometer level. When the instrument is used in the double-range, a sample of given average paficle size produces an F level equivalent to half the average size, and the chart reading must therefore be doubled.Hence the double-range error curve is obtained by doubling the abscissae of the single-range curve. The steps in the d,, curve correspond to changes in the micron intervals between successive chart graduations. The precision for samples over 40 p can be increased, and the instrument range extended somewhat beyond 50 p, by using an over-weight sample in order to obtain a lower F reading and so increase the value of (P - 1;) in equation (2) ; the indicated E and dv,’ can be corrected for the excess weight by means of the equations given in an earlier paper.1° Since the curves intersect at 8 p, it is advantageous to use the double-range for all samples over 8 p at porosity 0.5.The precision of the modified instrument cvas determined experimentally by testing four weighed samples from each of six procaine penicillin batches. The batches were prepared by grinding one lot of crystalline material at different pressures in a fluid-energy mill; they were therefore similar in general characteristics but differed in d,,. Each batch was well blended to ensure uniformity between samples. Each weighed sample was tested at seven porosity levels obtained by compressing the same sample bed to successively lower porosities. The detailed results for one batch are shown in Fig. 5 (a), and are typical of the results for each batch. They show two kinds of random error, an instrument error revealed by the small scatter of the points for a given sample about a smooth curve drawn through them, and a larger error between samples.The results for each batch, expressed as the mean of four samples, are shown in Fig. 5 ( b ) , and show a trend towards a minimum dvs‘ at porosities between 0.56 and 0.48.May, 19661 APPARATUS FOR DETERMINING SPECIFIC SURFACE I I c C a, U L aJ a . > , l o - > -D 0 L L 2 -Y aJ -0 C 0 d": u i L U C (u L aJ a - L n > -3 0 L 0, 7 0) -0 C id CI I/) Single rang I I Double range I I I I I I I I I I 5 10 15 20 25 L-+-Lb+ Average 20 p a r t i c l e size 30 ( dy[, ),p 40 Average p a r i i c i e size (d,,:),~ O ] t Intersection at 8~ 313 Fig. 4. Precision of a single determination a t porosity 0.5 on a single modified instrument with a single sample tube as affected by the determined precision of: M , sample weight; P, air pressure; L , sample height ; F , flow-meter manometer setting; d,, chart reading.The effect of sample variability is not included. (a) Individual effects of the five factors in the single range ( b ) Combined effect (root sum of squares) of the five factors in the single and double range The combined effect of the instrument error and the error between samples is shown by the standard deviations of the sample results from their corresponding batch means, calculated separately for each porosity and expressed as percentages of the over-all batch means- Porosity . . . . . . . . 0.60 0.58 0.56 0.54 0.52 0.50 0.48 Over-all mean db.s' . . . . 7.96 7.80 7.70 7.70 7.71 7-72 7.72 Standard deviation, per cent.. . 4-73 3.13 2.99 2.74 3.17 2.98 3-49 The several sources of variation are isolated by the analysis of variance summarised The analysis is confined to the porosity range, 0.56 to 0.48, within which the in Table 11. porosity effect appears, from Fig. 5 ( b ) , to be negligible. TABLE I1 ANALYSIS OF VARIANCE OF dvs' RESULTS FOR 24 PROCAINE PENICILLIN SAMPLES AT FIVE POROSITY LEVELS (E = 0.56 TO 0.48) Degrees of Mean Significance Source of variation freedom square level Porosity . . . . . . . . 4 0-0023 not 'significant Batches . . . . . . . . 5 25.4231 0.1 per cent. Interaction . . . . . . 20 0.0021 not significant Samples within batches . . . . 18 0.2696 0.1 per cent. Error . . . . . . .. 72 0.0033 Total . . ..119EDMUNDSON : CA4LIBRATION OF A FISHER AIR-PERMEABILITY [Analyst, VOl. 91 I I I I I I I ‘ ?“I 0 56 0 52 0 18 Pot-OSl t y 1 I I I I I I 0 60 0 56 0 51 0 48 Porosity Fig. 5. Average particle size, dv8‘, of six pro- caine penicillin batches as determined after com- pression of each weighed sample to successively lower porosities, (a) single determinations on four weighed samples of one batch, showing a small within-samples scatter and a larger between-samples scatter. Similar scatter occurred with the other batches: (b) means of four determinations on each of six batches Instrzcment error-The square root of the error mean square (0.0033) is the standard error of the instrument (and the operator’s ability to read it) after eliminating the sample error and the variation due to porosity, batches and their interaction.Expressed as aper- centage of the over-all mean dvS’ for all batches in the porosity range, 0.56 to 0.48, it is -10.74 per cent., which agrees well with the estimate in Fig. 4 (b) if the small effect of M is neglected. Error betmeen sumpZes-The samples-within-bat ches mean square (0.2696) = 5 x samples variance - error mean square. Hence the samples standard error, excluding all other sources of variation and expressed as a percentage of the over-all mean dvS’ for allbatches in the porosity range 0.56 to 0.48, is 3.0 per cent. This is too large to be explained as weighing error. I t is probably due, not so much to inhomogeneity within batches of powder, as to variation in the uniformity of packing in successive sample beds as suggested by R i g d e ~ ~ The analysis of variance shows that the slight upward trend between porosity 0.56 and 0-48 is not significant.However, when the analysis was repeated over the range 0-60 to 0.48, the porosity effect was significant at the 0.1 per cent. level; the interaction between porosity and batches was also significant at the same level, indicating that the trend of dvS’ with porosity is not constant for all batches. DISCUSSION The calibration method described above is absolute in the sense that it standardises the instrument variables in terms of c.g.s. units, without depending on an external particle- size standard. It therefore permits an accurate measurement of sample permeability. The The porosity efect-Fig. 5 (b) shows that dvs’ varies with porosity.May, 19661 -4PPtlRATUS FOR DETERMINING SPECIFIC SURFACE 315 equation by which the Fisher instrument, like other apparatus such as those of Rigden or Lea and Nurse, relates permeability to mean particle size is adapted from the original Kozeny - Carman equation.ll All such instruments, if properly calibrated, should therefore give the same result for mean particle size. The question of the validity of the Kozeny - Carman relationship between permeability and particle size is not one of instrumental accuracy and is beyond the scope of this paper.In this respect, the X.B.S. Portland-cement sample is to be regarded as a permeability standard rather than a particle-size standard. The modified instrument approaches the standard Lea and Nurse a p p a r a t u ~ ~ 9 ~ in accuracy and precision, provided that the significant variables are standardised or calibrated as described.The ability to compress a single sample to successively lower porosities and obtain corresponding diameter readings is a further advantage of the Fisher instrument. Other workersl0?l2 have observed a variation of apparent diameter with porosity, and it has been suggested that the minimum diameter may have special significance. The effect can be observed more readily with the Fisher apparatus than with apparatus that requires separate sample weighings for each porosity level; with the latter, the combined sampling and instru- mental errors may obscure a trend in apparent diameter. The porosity level, 0.56 to 0-54, at which the apparent particle size is a minimum and the wide range over which the size is almost constant in Fig. 5 ( b ) , are characteristic of the particular batches used in this study; other batches and materials may show their minimum at a different level and over a narrower porosity range.1° I thank Mr. H. Gresley Grey for the analysis of variance, and Mr. J. W. Mitchell of the Fisher Scientific Company for information about their methods of calibrating standpipes and ruby orifices. I t has the additional convenience of permitting direct reading. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. REFERENCES Gooden, E. L., and Smith, C. M., Ind. Engng Chem., Analyt. Edn, 1940, 12, 479. Dubrow, B., Analyt. Chem., 1953, 25, 1242. Lea, F. M., and Nurse, R. W., J . SOC. Chem. Ind., Lond., 1939, 58, 277. Rigden, P. J., Ibid.. 1943, 62, 1 . Dubrow, B., and Nieradka, M., Analyt. Chem., 1955 27, 302. “Portland Cement,” British Standard 12 : 1958. Traxler, R. N., and Baum, L. -4. H., Physics, 1936, 7 , 9. Levy, A., J . Scient. Instrum., 1964, 41, 449. Hooke, Robert, 1674, quoted by Gage, S . H., “The Microscope,’’ Seventeenth Edition, Comstock Edmundson, I. C., and Tootill, J. P. R., Analyst, 1963, 88, 805. Carman, I?. C., J . SOC. Chem. Ind., Lond., 1938, 57, 225. Hutto, F. B., jun., and Davis, D. W., Off. Dig. Fed. Paint Varn. Prod. Clubs, 1959, 31, 429. Publishing Co. Inc., New York, 1943, p. 279. First submitted, March Ist, 1965 Amended, December 22nd, 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100306

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

316 VAN WYK, CUYPERS, FITE AND WAINERDI: [Analyst, Vol. 91 A Study of the Macroscopic Distribution of Oxygen in a Steel Rod Neutron-activation and Vacuum Fusion Techniques BY JUSTUS M. VAN WYK (Basic Research Division, Research and Process Development, South African Iron and Steel Industrial Corporation, Pretoria, South Africa) MARC Y. CUYPERS,* LLOYD E. FITE AND RICHARD E. WAINERDI (Activation Analysis Research Laboratory, Texas A and M University, College Station, Texas, U.S. A . ) The distribution of oxygen was determined along the length of a steel rod. Neutron-activation and vacuum fusion techniques were used alterna- tively, and the relevant pieces of apparatus and methods are described. The over-all average oxygen content determined by neutron-activation analysis was 129 p.p.m., in excellent agreement with 128 p.p.m.found by vacuum fusion. The results further show the continuity between the two sets of results, and also a definite inhomogeneity in the macroscopic distribution of oxygen. THE importance of oxygen determination in modern steelmaking has become increasingly apparent as the need for cleaner steels arose during the last few years.192y3 It is the purpose of this study to show the variation of oxygen content along the length of a steel rod. Thereby, a picture is obtained of the degree of homogeneity that can be expected in a finished steel product. Two methods for oxygen determination have been applied, viz., neutron-actil-ation and vacuum fusion analysis. Concurrently with the oxygen distribution, an evaluation could therefore be made of the respective merits of the two methods.MATERIAL AND SAMPLING SELECTION OF STEEL- Because a high manganese content interferes with the vacuum fusion determination of oxygen in steel by gettering of carbon m ~ n o x i d e , ~ ? ~ ~ ~ ~ ~ ~ ~ a steel with a very low manganese content was selected for this study. The composition of the steel was: 0.08 per cent. carbon, 0.16 per cent. manganese, 0.020 per cent. phosphorus, 0.021 per cent. sulphur and 0 4 1 per cent. silicon, and it was produced as a normal semi-killed grade in an l8-ton basic electric furnace from an all-scrap charge at the ISCOR steelworks in Pretoria. From the rolled stock of this heat a 50-mm square billet, corresponding to the central part of a 4-ton ingot, was selected, and one end was hot forged to a rod approximately 14 mm in diameter a d 2-5 m in length. SAMPLING- The 14-mm rod was divided into 10 bars, numbered consecutively from 1 through to 10, and each bar was machined to 12-mm diameter.From each bar, 8 samples of approximately 18 g (19 mm) each, and then 10 samples of approximately 7 g (7 mm) each, were cut consecu- tively. The 18-g samples were analysed by neutron activation, and the 7-g samples by vacuum fusion techniques. Each sample was numbered according to its original position i n the 2-5-m rod and the method of analysis utilised. Thus, the first sample cut from the rod would be 1x1, the second 1N2, and the last two samples 1OV9 and 10V10, respectively. Just before analysis, each sample was etched for 1 minute in concentrated hydrochloric acid to remove surface oxide, rinsed consecutively in distilled water, ethanol and acetone, and finally dried in an air stream.* On leave from the University of Liege, Belgium.May, 19661 DISTRIBUTION OF OXYGEN I N A STEEL ROD 317 APPARATUS- For the neutron-activation part of this research, an apparatus for general activation analysis at the Activation Analysis Research Laboratory (AARL), Texas A and M University, was adapted for possible routine use in a steel production plant for on-line analysis and in-process control. The analysis is based on the l60 (n,p) 16N reaction that has previously been proposed and used for oxygen determination.* to l7 The apparatus consists basically of a neutron source, a sample transfer sytem and detecting equipment (see Fig.1). NEUTRON-ACTIVATION ANALYSIS I I I -L L A = Programmer G,, G, = Transfer boxes B,, 6 2 = Scalers H,, H, = Solenoid air valves C, = Amplifier I = Flux monitor counter C, = Amplifier discriminator J = Sample positioning pin D,, D, = Photocells K = Neutron generator E = Detecting head L = Compressed air F,, F, = Detectors with pre-amplifiers Fig. 1. Block diagram of neutron-activation analysis system Nezdroiz source-A Texas Nuclear Corporation EO-kV, 1-mA maximum, Cockcroft - Walton deuteron accelerator with a tritiated titanium target is used as a neutron source. The 3T (d,n) 4He reaction yields an essentially isotropic and mono-energetic flux of 14.7-hIeV neutrons. At full output, the generator, K, in the present case, is capable of producing a total flux of 10lo 14-MeV neutrons per second.To extend the target life the acclerator is, however, operated at a beam current of only 0-2 mA. A boron trifluoride counter, I, coupled through an amplifier, C,, to a scaler, B,, is used to monitor the neutron flux during irradiation. Transfer system-The short half-life (7.35 seconds) of the product nuclide, nitrogen-16, makes rapid detection imperative. A pneumatic system was constructed for this purpose. I t consists of a compressed air source which connects at L, a 16-mm i.d. plastic tube, solenoid air valves, H, and H,, transfer boxes, G, and G,, to direct the air flow,18 a pin, J, and a detecting head, E, to position the sample at the irradiation and counting sides, respectively, and photocells, D, and D,.Detecting eguifiunent-The 6-13 and 7.12-MeV y-rays of nitrogen-16 are detected by two horizontally opposed and matched Harshaw Integral Line 3-inch x 3-inch thallium-activated sodium iodide crystal and photomultiplier assemblies with pre-amplifiers, Fl and F,. The remainder of the system consists of an amplifier discriminator, C,, a scaler, B,, and a pro- grammer, A. Shielding-The neutron-generator target is surrounded by 25 cm of paraffin wax. The generator is situated in a room with 60-cm concrete walls. The y-ray detectors are enclosed318 VAN WYK, CUYPERS, FITE AND WAINERDI: [L-lrzaZyst, 1'01. 91 in a lead castle of wall thickness 7-5 cm. Between the detectors and the generator room, another 25 cm of paraffin wax and 60 cm of concrete are used to minimise activation of the crystals during irradiation.PROCEDURE- At the beginning of an analysis cycle, a sample is introduced into the pneumatic system at the transfer box, G,, (Fig. 1). The rest of the cycle is controlled by the programming unit, A, in the following sequence. The sample positioning pin in the detector head, E, is raised for a short time and the sample blown through the pneumatic tube (air pressure 80 to 100 p.s.i.) against the sample stop pin, J, at the target. A signal from photocell D, turns on the neutron generator, K, and the flux monitor scaler, B,, for an irradiation time of 20 seconds. At the end of irradiation the air flow is reversed by transfer boxes G, and G,, and the activated sample is blown back against the positioning pin in the detector head, E.After a set delay time of 2 seconds, scaler B, is turned on for 20 seconds only if photocell D, has signalled the arrival of the sample at the detector. The amplifier discriminator, C,, is set to pass only pulses corresponding to 7-ray energies above 4-6 MeV. A continuation of the air flow for a few seconds after arrival of the sample at both the target and the detector eliminates the possibility of the sample bouncing back from the respective positioning pins. The flow of air during the 2-second delay period purges the system of any activated air still present. Standards-Weighed amounts (ranging from 3 to 1750 mg) of dry Specpure ferric oxide (Fe,O,), sealed in polythene vials, were used as standards. Sealed vials filled with air were run to determine the blank value.The possible increase in the blank value as a result of the absorption on the polythene of recoil nitrogen-16 nuclei, stemming from the activation of the air layer around the vial,13 could be ignored at the lel7el of activity in this experiment. The error introduced by assuming a constant volume of enclosed air in all the standards was insignificant. General-The sharp edges of the steel samples were rounded with emery paper to facilitate their transport in the pneumatic system. Each sample and standard was irradiated and counted five times, and a background count, followed by a check determination on a standard, was made at hourly intervals. The linear distance between the detectors and the neutron generator is about 7 m with the shielding as described.There is still, however, a slight build-up of activity in the crystals during a day of continuous operation, which gradually increases the background. On a routine basis a single determination can be made in 1 minute and, allowing 1 to 2 minutes for the manual calculation, a result can be reported every 4 minutes lor duplicate analyses. I VACUUM FUSION ANALYSIS APPARATUS- A slightly modified conventional vacuum fusion apparatus was constructed in the Research and Process Development Department of ISCOR, Pretoria. A schematic diagram is given in Fig. 2. The furnace assembly, A, consists of a water-cooled quartz tube joined, via a ground-glass joint, to a Pyrex-glass cross. A graphite crucible, thermally insulated from the quartz with coarse graphite powder (about 0-5-mm granular size), is heated inductively by a 15-kIl' radio- frequency unit.A four-stage, high speed, high backing pressure, mercury diffusion pump, B, is used for gas extraction, circulation and collection. The all-glass gas analysis equipment consists of a manometer, C, with dibutylphthalate as manometric fluid, a furnace-heated (400" C) vessel, D, containing cupric oxide (CuO) in wire form, a vapour trap, E, filled with granular magnesium perchlorate (Mg(ClO,),), and a cold trap, F. A Dewar flask with liquid nitrogen for cooling F is raised and lowered by means of a motor-driven hoist. Stopcocks S1 to S, and the mechanical fore-pump, which connects as indicated, complete the apparatus. METHOD- Primiple of anaZysis-The oxygen in the sample is reduced by carbon at 1600" C and evolved as carbon monoxide together with nitrogen and hydrogen.The carbon monoxide and hydrogen are oxidised to carbon dioxide and water, respectively, by cupric oxide at 400" C. The water vapour is trapped in magnesium perchlorate and the pressure of theMay, 19661 DISTRIBUTION OF OXYGEN IN ,4 STEEL ROD 319 carbon dioxide and nitrogen mixture measured. The carbon dioxide is then frozen out at -190" C by liquid nitrogen, and the pressure of the nitrogen alone is measured. The pressure of the carbon dioxide is determined by a ddference calculation. f t E To fore-pump A = Furnace assembly B = Diffusion pump C = Manometer E = Vapour trap (magnesium per- ch lo rate I F S,, S,, S,, S, = Stopcocks = Cold trap iliquid nitrogen) D = Furnace heated copper oxide con- tainer Fig.2. Schematic diagram of vacuum fusion analysis equipment Calibration-The collection volume (1') was calibrated by introducing a known volume of pure nitrogen at room temperature and pressure at the cross arm of the furnace assembly, and expanding it through the diffusion pump into the volume 1'. The pressure in V was measured on the manometer, which has a scale calibrated in millimetres of mercury. By arbitrarily assuming normal room temperature (25" C) in volume V, most of which is in- corporated in the lower part of the diffusion pump at an unknown temperature, V was calcu- lated from the ideal gas equations. PROCEDCRE- A maximum of fifteen 5 to 10-g samples at a time are etched, weighed and introduced into the sample loading arm of the furnace assembly, together with about 30 g of nickel.The whole system is then evacuated with the crucible at 1800" C until the blank l-alue is less than 1 per cent. of the expected gas content of a steel sample; this takes about 2 hours. The crucible temperature is then lowered to 1600" C, and the nickel (in part or in total) introduced into the crucible through the quartz funnel (Fig. 2) with a magnet. This nickel is necessary for quick de-gassing and quantitative reduction of aluminium oxide.5 After blank measurement the samples are dropped into the crucible and analysed. The evolved gas is extracted for 2 minutes and then circulated through the hot cupric oxide and the magnesium perchlorate for 1 minute to remove hydrogen. A pressure reading (nitrogen and carbon dioxide) is taken to the nearest 0.02 mm of mercury.The cold trap is subsequently immersed in liquid nitrogen and the final pressure (nitrogen alone) read after 3 minutes. To conclude the analysis, the cold trap is heated to room temperature in an air stream and the whole system evacuated by the diffusion pump (backed by the fore-pump) for 2 minutes, during which time the oxygen content of the sample is calculated. The determination, complete with calculation, is thus completed in 8 minutes.320 VAN WYK, CUYPERS, FITE AND WAINERDI: [Analyst, VOl. 91 RESULTS AND DISCUSSION ACTIVATION ANALYSIS- After correcting for background, the observed counts for the five activation analyses of each sample were normalised with respect to the neutron flux and the average and standard deviation calculated.Oxygen, mg Fig. 3. Neu tron-activation analysis calibration curve The calibration curve obtained with the ferric oxide standards is shown in Fig. 3. The straight line, calculated by the least squares method, gives a calibration constant of 189 counts per mg of oxygen, and fits the results points very well throughout the entire range, i.e., from 1 to 525mg of oxygen. TABLE I Bar : Sample 1 2 3 4 5 6 7 8 Average of bar (U in p.p.m.) Bar : Sample 1 2 3 4 5 6 7 8 OXYGEN FOUND BY NEUTRON-ACTIVATION ANALYSIS 1N 2N 3N 4N 5N & r_----h----, r---J-, r----h--- (--A-, Oxygen, 0, Oxygen, u, Oxygen, u, Oxygen, u, Oxygen, 0, p.p.m. percent. p.p,m. percent. p.p.m. percent. p.p.m. percent. p.p.m. percent. 137 137 136 145 145 151 172 136 10 5 4 2 9 12 13 5 135 6 115 125 5 119 103 0 113 106 4 118 116 6 107 120 4 129 122 4 113 131 7 102 14 114 8 123 2 122 4 116 3 111 5 122 4 114 10 117 125 138 139 143 132 145 151 147 145 f 12 120f 11 115 -J= 8 117 + 4 140 f 8 TABLE I-continued GN 7N 8N 9N 1 ON 7+ r----h--7 r----A-, ( P A - - - - , f-h-, p.p.m.per cent. p.p.m. per cent. p.p.m. per cent. p.p.m. per cent. p.p.m. per cent. Oxygen, a, Oxygen, u, Oxygen, u, Oxygen, a, Oxygen, 0, - 152 7 - - - - - - - - - - 139 2 - 163 12 - - 157 12 136 3 133 5 136 3 147 4 135 4 Average of bar (0inp.p.m.) 149 f 11 136 f 1 Over-all average : 170 9 145 143 4 112 140 6 107 125 8 121 123 4 111 145 11 111 111 10 102 112 8 114 134 f 20 115 f 13 129 p.p.m. f 17 p.p.m. 166 20 129 6 120 6 123 9 122 7 131 G 143 12 130 3 133 f 15May, 19661 DISTRIBUTION OF OXYGEN IN A STEEL ROD 32 1 The oxygen content and percentage standard deviation for each sample are listed in Table I, and are grouped according to the sampling sequence described in the paragraph on sampling.The oxygen content varies from 102 to 172 p.p.m. Samples with visible cracks due to the forging of the original steel billet were not analysed (cf. bars 6N and 7N). Typically, 625 counts and a background of 64 counts were observed per sample. The standard deviations quoted for the samples in Table I compare favourably with an expected value of 6 per cent., and the reproducibility is sufficient for routine analysis. In a few instances, somewhat higher standard deviations were observed. This fact is attributed to local inhomogeneity in the samples concerned. In Table I a value is also given for the average oxygen content of each bar.The standard deviation in this case was calculated from the oxygen contents of the samples constituting the particular bar, and it is given directly in p.p.m. of oxygen. To test the validity of the calibration with ferric oxide, 26 apparently homogeneous steel samples were analysed independently by two other laboratories, namely at Texas Nuclear Corporation and at Kaman Nuclear. In the first laboratory, titanium with a known oxygen content (certified by the N.B.S.) was used for calibration, whereas a synthetic sample consisting of a stack of alternating mylar and steel discs, was used as a standard at Kaman N~c1ear.l~ The average oxygen content of the 26 samples (5 determinations on each) found by the Texas Nuclear Corporation and the Kaman Nuclear were 124 pap.m. 11 p.p.m.and 123 p,p.m. 1 13 p.p.m., respectively, which are in excellent agreement with the value of 125 p.p.m. 5 14 p.p.m. found in our system (Table II), thus justifying the calibration with ferric oxide. TABLE I1 COMPARISON OF RESULTS OBTAINED IN THREE LABORATORIES FOR 26 HOMOGENEOUS SAMPLES Laboratory : AARL Sample 1N2 137 1N4 145 1N8 136 2N4 106 2N6 120 Oxygen, h p.p.m. TNC KN 128 138 132 106 119 120 138 124 103 125 2N7 122 132 130 3N3 113 113 120 3N4 3N5 3N8 4Nl 4N4 4N8 5N2 5N5 5x8 6N4 6N7 7N6 7N7 8N2 8N3 9N3 9N6 10N3 10N5 Mean . . .. 118 107 102 11.1 116 117 135 132 147 139 133 136 136 143 140 107 111 120 122 125 f 14 116 120 109 124 111 I24 127 127 153 138 128 131 123 137 12s 106 112 122 131 124 f 11 119 112 107 121 128 132 145 135 161 133 118 125 12.2 124 121 95 106 117 124 123 f 13 In the three systems concerned there are significant differences in irradiation geometry.In the Kaman nuclear system a double-axis rotator is used to minimise the effect of in- homogeneity in the sample, whereas no sample rotation during irradiation occurred in the cases of the Activation Analysis Research Laboratory and the Texas Nuclear Corporation. Further, the minimum distance between sample and target is about 0.4mm in the Texas Nuclear Corporation system (which was constructed for maximum sensitivity) as compared with about 6mm for the other two. One would therefore expect sample inhomogeneity to322 VAN WYK, CUYPERS, FITE, AND WAINERDI: ‘,41zalyst, Vol. 91 have a greater affect in the Texas Nuclear Corporation system and a smaller effect in the Kaman nuclear apparatus in comparison with the Activation Analysis Research Laboratory system.This is reflected clearly in the different standard deviations for 5 determinations on the same sample as found in the three laboratories, namely 13 per cent. (Activation Analysis Research Laboratory), 25 per cent. (Texas Nuclear Corporation) and 5 per cent. (Kaman nuclear) for an inhomogeneous sample, and 4, 8 and 2 per cent., respectively, for a homo- geneous sample. VACUUM FUSION- As stated in the paragraph on the principle of analysis, one oxygen atom in each resultant carbon dioxide molecule originates from the sample being analysed.Thus, one gram mole of carbon dioxide (22,400ml at S.T.P.) contains one gram atom (16g) of sample oxygen. Assuming validity of the ideal gas equations, the oxygen content of a sample with mass M g is thus related to the carbon dioxide pressure reading by- P 273 lo6 16 p.p.m. of oxygen = - V - ~ - - M 298 760 22,400 where V = calibrated collection volume in ml, P = pressure of carbon dioxide in V (mm of mercury) (typically 4.2 mm of mercury). The collection volume ( V ) was found to be 253 ml. Therefore, the oxygen content of the analysed sample is- P p.p.m. of oxygen = 218 - n/r ’ The results of the vacuum fusion oxygen determinations are given in Table 111. Again, the results are listed according to the sampling sequence, and a value for the average oxygen content of each bar is given, together with the standard deviation.There was only one sample containing a visible crack, and this was not analysed. The values range from 96 to 172 p.p.m. TABLE 111 OXYGEN FOUND BY VACUUM FUSION ANALYSIS Oxygen, p.p.m. Bar : Sample 1 2 3 4 5 6 7 8 9 10 Average of bar Bar : Sample 1 2 3 4 5 6 7 8 9 10 Average of bar iv 2 v 3 v 117 131 127 131 172 136 136 136 151 145 138 f 15 101 111 121 128 131 125 122 127 117 119 120 f 9 110 110 109 102 99 96 106 119 128 125 110 & 11 TABLE TII-contiizzied Oxygen, p.p.m. h -_ r 6V 7 v 8V 132 122 108 142 123 105 143 132 109 144 130 116 137 129 109 142 127 133 - 125 115 156 127 127 130 128 122 133 123 109 140 f 8 127 f 3 115 f 9 Over-all average: 128 f 15. 4 v 10s 123 114 115 126 135 147 171 134 126 130 18 5 v 138 166 154 134 137 133 139 136 144 138 142 & 10 9 v 114 125 118 137 134 108 110 139 151 169 131 f 19 1 oG 126 124 119 134 128 117 140 120 121 145 127 f 9May, 19661 DISTRIBUTION OF OXYGEK IN A STEEL ROD 323 COMPARISON AND CONCLUSIONS- 17 p.p.m., and is in striking agreement with 128 p.p.m.15 p.p.m. found as the average for the 99 vacuum fusion analyses (Tables I and 111). In Fig. 4, the two sets of results are combined and plotted as the oxygen content along the length of the original steel rod. The continuity between the two sets of results is evident. The continuous curve, drawn in Fig. 4 through the points representing the average values of the 20 sub-groups, illustrates the large-scale distribution of oxygen content around the over-all average for the complete rod.I t clearly indicates an almost periodic fluctuation of the oxygen content around the over-all average for the complete rod, instead of the random scatter that would normally be expected in such a case. The average of the 73 neutron-activation determinations is 129 p.p.m. I --T-’ -- 0 50 I00 I50 200 250 Distance from end of steel rod, cm Fig. 4. Distribution of oxygen along the length of a steel rod The figure shows that, in this rolled and forged steel rod which is a fair example of a finished steel product, there exists a definite inhomogeneity in the macroscopic oxygen dis- tribution. This distribution can be determined with equal accuracy by both neutron-acti1.a- tion and vacuum fusion techniques, but faster, non-destructively and more conveniently by neutron activation.The authors wish to express their thanks to the Activation Analysis Research Labora- tory, Texas A and 1c.I University, and the Research and Process Development Department of the South 14frican Iron and Steel Industrial Corporation, as well as their appreciation to Texas h’uclear Corporation and Kaman Xuclear for their kind co-operation dexribed above. I . 3. 4. ti. 7. S. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 7 1. 9. REFERENCES Chepn. Engizg News, 1965, 43, KO. 11, 38. Etterich, O., Taxhet, H., and Thoniich, I\’., Arch. EisenAuttTYes. 1964, 35, 613. Kraus, T., Ibid., 1962, 33, 527. Sloman, H. .4., J . Iron Steel Inst., 1941, 143, 298. Kraus, T., Frohberg, 31. G., and Gerhardt, -%., Avch. EisenhzittWes., 1964, 35, 30. Beach, A. L., and Cruldner, W. G., A n a l j ~ t . Clzcin., 1959, 31, l i 2 2 . Sperncr, F., and Koch, I<.-H., iWetrrlZ, 1964, 18, i01. Koch, R. C., “-tctivation Analysis IIandbook,” A4cademic Press Inc., Xew 170rk, 1060, p. 3 0 . Steelc, E. L., and Meinke, 121. W., Aual\d. Chem., 1962, 34, 185. Veal, D. J., and Cook, C. F., Tbid., 19G2, 34, 178. Coleman, I<. F., arid Perkin, J. L., Analyst, 1959, 84, 233. F3-ud’homnie, J. T., “Texas Nuclcar Corporation Neutron Generators,” Tesas Nuclear Corporation, Anders, 0. U., and Briden, D. W., A ?zalvt. CIwiz., 1965, 37, 530. Wood, D. E., and Pasztor, L. C., “Proceedings of the 1965 International Conference on JIoclern Nickel, H., Rottmann, J., Stdcker, 13.- J., Koster-Pflugmacher, A., and Frohberg, Rf., Avch. Kopineck, H.-J., Sommerltorn, G., Bass, R., and Presser, G., Ibid., 1964, 35, 957. Coleman, R. F., Analysl, 1962, 87, 590. Fite, I>. E., Steele, E. L,., and Wainerdi, R. E., Report No. TEES-2671-2, U.S. Department of Corn- Received Sepfeinber 28th, 1965 Austin, 2962, p. 91. Trends in Xctilration Analysis,’ 31cGraw-Hi11, New York, z ?a the press. Eisetihiitt W e s . , 1964, 35, 637. merce, Office of Technical Services, 1962.

ISSN:0003-2654    

DOI:10.1039/AN9669100316

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

324 SPENCE AND VA%HRMA4K : QUASI-QUANTITATIVE [AwaZyyst, VOl. 91 Quasi-quantitative Separation of Paraffins and Olefins BY J. A, SPENCE AND M. VAHRMAN (Northampton College of Advanced Technology, St. John Street, London, E.C. 1) By the addition of iodine monochloride to a mixture of paraffins and olefins, an easy chromatographic separation on silica gel of the two is made possible by virtue of the olefin adduct being much more strongly adsorbed. The olefins are regenerated by refluxing the halogenated derivative with ethanol and excess sodium iodide. The efficacy of the method has been proved on the total aliphatics of low temperature tars and on pairs of pure n-paraffins and 1-olefins of the same carbon number. The small losses incurred are almost entirely in the olefins. THE problem of the quantitative separation of paraffins from olefins, and retention of the identity of the latter, arises in the examination of their mixtures in fractions from petroleum and coal tars.In the latter, saturated and unsaturated aliphatic hydrocarbons exist in quantity in low temperature tars and in those of a type intermediate between low and high temperature tars.l Adsorption chromatography is well established as a method of determining hydrocarbon types, especially in lower boiling mixtures, e.g., the fluorescent-indicator adsorption method.2 Liquid chromatography has been used for the separation of paraffins and olefins, from C, or C,, up to C,,, from the lower boiling neutral portion of low temperature That the total neutral components in such tars could also be separated by this method was shown by Boyer et u Z ., ~ if three fractional distillation cuts were separately chromatographed. In the higher molecular weight hydrocarbons, where the lone double bond of the olefins was considerably “diluted” in the long chains, not more than 5 per cent. of paraffins contaminated the separated olefin fractions. Hydrocarbons up to about C,, were then determined by gas chromatography. The original aim of the work reported here was the quantitative separation of paraffins and olefins from the total aliphatic hydrocarbons of low temperature tars, without prior frac- tionation of these hydrocarbons. The method devised, however, is applicable to such mixtures of hydrocarbons from a wide variety of sources. For example, we have applied it successfully to the analysis of hydrocarbons from coal extracts and to waxes from plants and soils.EXPERIMENTAL The total aliphatic hydrocarbons were first prepared by liquid chromatography on silica gel (column length, 20 cm; diameter, 2 cm; weight of charge, 2 g) of the neutral, light petroleum-soluble oil of a low temperature tar1 from the carbonisation of Thoresby coal (Sational Coal Board classification KO. 801) by internal heating of the charge with hot gas. The soft wax thus obtained contained n-, iso- and cyclo-paraffins and a corresponding series of olefins, the range being from C,, to &. In all subsequent chromatographic separations, the same ratios of column length to diameter were used, the actual dimensions being appro- priate to the weight of charge.The bulk of the solvent was removed each time by atmospheric distillation on a steam-bath, the small amount remaining being eliminated by vacuum desiccation (5 mm of mercury) to constant weight of the cooled flask. The basis of the method of separation of the paraffins from the olefins was the selective addition of iodine monochloride to the latter, the subsequent easy separation of the paraffins from these addition compounds by liquid chromatography, and the regeneration of the olefins. A 70 to 90 per cent. molar excess of Wijs’ reagent (0.2 N iodine monochloride in glacial acetic acid) was added to a 2 per cent. solution in carbon tetrachloride of the whole aliphatic hydrocarbon fraction in a stoppered, brown glass bottle, and the whole allowed to stand for 30 minutes.The scheme of analysis is shown in Fig. 1.May, 1!166] SEPARATIOX OF PA%RA%FFINS AND OLEFINS TOTAL ALIPHATIC HYDROCARBONS lodrrie monochloride i Unreacted paraffins Halogenated olefin derivatives + Liquid chrornotography on silica gel 1 + TOTAL PARAFFINS Vtc todo-chloro olefin derivatives Sodium iodide in boiling ethonol 1 Crude regenet-ated olefins 325 I TOTAL OLEFINS Fig. 1 . Scheme for the separation of olefins and paraffins At the end of the reaction period, excess of 15 per cent. potassium iodide solution was added to convert the unconsumed iodine monochloride reagent to iodine and potassium chloride; a large volume of distilled water was also added. The liberated iodine was finally titrated with sodium thiosulphate solution.The carbon tetrachloride layer was separated from the aqueous acid, which was then further extracted with carbon tetrachloride to ensure complete removal of the sample. The combined carbon tetrachloride solutions were washed with distilled water until free of acid, dried over anhydrous sodium sulphate, and the solvent distilled off. The residual brown wax, a mixture of paraffins and halogenated olefins, was dissolved in sufficient light petroleum (40" to 60" C) to make a 10 per cent. solution; this was then poured on to an activated silica gel (100 to 200 mesh) chromatographic column. Elution was continued with light petroleum until the faint purple-brown colour, the front of the halogenated olefin derivatives, approached the bottom of the column. The colourless first eluate contained the total paraffins, which were recovered by evaporation of the solvent.The coloured, halogenated olefins were completely eluted with ethanol and the original olefins regenerated by boiling the solution gently under reflux with excess sodium iodide. Most of the ethanol was removed by evaporation under reduced pressure, and the regeneration mixture partitioned between light petroleum (40" to 60" C ) and dilute aqueous sodium thiosulphate solution: the latter removed the iodine which had been liberated, while the regenerated olefins passed into the light petroleum phase. After washing the light petroleum solution with distilled water and drying over anhydrous sodium sulphate, the solvent was evaporated off if a determination of the crude olefins was required.To obtain the pure product, a 10 per cent. solution of the crude olefins in light petroleum (40" to 60" C) was chromatographcd on silica gel with the same solvent as eluant. The olefins were recovered by distilling off the light petroleum from the total eluate. For comparison, paraffin contents were also determined by sulphuric acid extraction. A 20 per cent. w/v solution of the sample in cyclohexane was extracted repeatedly at room temperature with equal volumes of 98 per cent. sulphuric acid until no further colouration was imparted to the acid layer (about 10 extractions). The acid extracts were combined, washed twice with cyclohexane, and then discarded. The combined cyclohexane solution and washings were evaporated to give an approximately 10 per cent.solution of paraffins and then chromatographed on silica gel with cyclohexane as eluant. The pure paraffins were then recovered from the total eluate by evaporation of the solvent. Infrared absorption spectroscopy was used throughout as a guide to the completeness of separation of the olefins from the paraffins.326 SPENCE AND VAHRMAK QUASI-QUANTITATIVE [Analyst, VOl. 91 The results of a separation by the iodine monochloride method of 10 g of the aliphatic hydrocarbon fraction from the tar are given in Table I. TABLE I RESULTS FOR THE SEPARATION INTO ITS PARAFFINIC AND OLEFINIC COMPONENTS OF THE ALIPHATIC HYDROCARBON FRACTION FROM A LOW TEMPERATURE TAR Percentage by weight Paraffins . . .. .. . . .. . . .. 49-1 Purified olefins .. .. . . . . .. . . 43-9 Losses . . . . . . . . .. . . . . .. 7.0 Paraffins (by removal of olefins with sulphuric acid) 51.1 . . G. Clubb and M. Vahrman, in this laboratory, working on a different aliphatic fraction from a low temperature tar, investigated the effect on the separation by this method of using different amounts of iodine monochloride, and ascertained the reproducibility of the results with the optimum excess of reagent (Table 11). TABLE I1 RESULTS OF SEPARATIONS OF ALIPHATIC HYDROCARBONS FROM TAR BY IODINE MONOCHLORIDE METHOD Molar excess Weight of Weight of Weight of monochloride, material, recovered, recovered, per cent. per cent. of iodine starting paraffin olefin Paraffin, Olefin, per cent. g 6 10* 2.4916 1.8070 0.4760 72.4 19.1 30* 2.5085 1.6872 0.5637 67.2 22-4 50 2.5110 1.5138 0.6088 60.4 24.2 67 2-4751 1.5732 0.6366 63.6 25.8 80 2.4936 1.5757 0.7069 63-2 28.4 80 2.4694 1.5536 0,6232 63.2 25.2 80 2.4957 1.5632 0.6845 62.8 27.4 80 2.5299 1.5983 0.6942 63.1 27.4 80 2.4863 1.5572 0.6489 62.5 26.0 80 2.5138 1.5802 0.661 1 62.9 26.3 80 2.4588 1.5480 0.6552 63-0 26.7 so 2-4688 1.5602 0.6509 63.2 26.4 THE Recovery, per cent. 91.5 89-6 84.6 89.4 91.6 88.4 90.2 90.5 88.5 89.2 89.7 89.6 * The infrared spectra of the recovered unreactcd materials showed the presence of olefinic unsaturation.Paraffin content (by extraction with 98 per cent. sulphuric acid): 63.0 per cent. w/w. The iodine monochloride addition method, with 80 per cent. excess of reagent, was tested on binary mixtures of n-paraffins and 1-olefins of the same carbon number (Table 111).TABLE I11 RESULTS OF SEPARATIONS BY THE IODINE MONOCHLORIDE METHOD OF BINARY MIXTURES O F PURE PAKAFFINS AND OLEFINS Percentage by Percentage by 20 weight of paraffin or Hydrocarbons mixture nD olefin recovered nL, 'LO weight in synthetic n-Tetradecane . . . . 52.3 1.4272 61.9 1.4269 1.4341 Tetradec-1-enc . . . . 47.7 1.4342 45.3 n-Eicosane . . . . 72.1 1.4306 72.0 1.4308 Eicos-1-ene . . .. 27.9 1-4363 25.8 1.4362 DISCUSSION A minimum of 50 per cent. excess of iodine monochloride was necessary to effect complete separations of olefins from paraffins: 80 per cent. excess is considered to give a safe margin. The recovery of paraffins is virtually complete; the losses, mainly in the olefinic fraction, are probably due to irreversible substitution reactions with the halogen reagent, together with the retention of olefins on the column during purification.Losses diminish with increase in weight of original sample. No further yields of olefins could be obtained with ethanol and sodium iodide from the material left on the chromatographic column after removal of the pure olefins.May, 19661 SEPARATION OF PARAFFINS AND OLEFINS 327 As both the addition and elimination of halogens in. ethylenic compounds are specifically trans, and result in the regeneration of the original isomers, the method can be used if the structures of the olefins are to be investigated. That no isomerisation of the olefins occurred by the method described was confirmed from the infrared absorption spectra of the original aliphatic material and of the separated, regenerated olefins. The authors are grateful to Rexco Research and Development Company Ltd., for a grant to one of them (J.A.S.), and for samples of their tar. REFERENCES 1. 2. 3. Coppens, L., Bricteaux, J., and Ncuray, M., Annls Mines Belg., 1961, 121, 1156. 4, Lewis, H. R., Chem. & Ind., 1959, 1049. 5. Boyer, A. F., Ferrand, R., Ladam, X., and Payen, P., Chim. Ind., 1961, 86, 523. Blunt, G, V., and Vahrman, M., J . Inst. Fuel, 1960, 33, 522. A.S.T.M. Designation D 1319-61T, A .S.T.M. Special Technical Publication, No. 332, 1963. Received April 6th, 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100324

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

328 RIDYARD: A STUDY OF THE DETERMINATION [Analyst, Vol. 91 A Study of the Determination of Thiamine in Breakfast Cereals BY H. N. RIDYARD* ( T h e Reseavch .4 ssociatioii of British Flour-Millers, Cereals Research Siatiov, Old 1.ondon Road, S t . A lbans, flevts.) The method of determining thiamine that involves the purification by base-exchange on sand, is satisfactory for materials of the “breakfast cereal” type. Traces of materials responsible for errors in the direct determination remain after treatment, but the errors are greatly reduced and oppose one another, so that they may reasonably be neglected. PROCESSES such as pressure cooking and subsequent baking, when applied to many cereal foods, result in the destruction of thiamine. At the same time, materials are produced that give a high fluorescence on treatment with sodium hydroxide and subsequent extraction with isobutanol (“blank fluorescence”l), and also substances that interfere with the fluorescence of thiochrome.2 These effects rendered the “direct”l determination of thiochrome in unpurified extracts of such foods of little value until a more detailed study was made.The “blank” used was usually slightly greater than the total fluorescence that was developed after oxidation of the thiamine to the thiochrome, and although the blank and interferences opposed one another the relative magnitudes of the effects were unknown. Recently, the addition of synthetic thiamine to such products during manufacture has become common practice, and a more detailed and prolonged study of one such product has been made which has given interesting results.Confirmatory results of a much less detailed nature have been obtained with five other products. METHOD APPARATIJ S- were used. The apparatus used has been previously de~cribed.~ y 4 In addition, 100-ml conical flasks REAGEXTS- Extract-This is prepared as described for flour,l but with 30 g of the product in a 1000-ml conical flask and 750 ml of 0.2 N acid. Large amounts are used to compensate for the probable uneven distribution of thiamine; 30 g is a convenient approximation to 1 oz, and the rate of fortification of flour is commonly expressed in terms of mg per oz. The extract is filtered next day through a large fluted filter-paper. Thiamine additions for recovery ex$erimenfs-Place 5 ml of a 200 pg per ml solution of thiamine (stage 1 in preparation of standards1) in a 100-ml calibrated flask and fill to the mark with the extract.Mix the solutions by emptying the flask turbulently, inverting it in a dry 200 or 250-ml conical flask equipped with a glass stopper. Shake the flask, as vigorously as is possible without the formation of a lasting foam, for about 3 minutes. Return the liquid to the measuring flask, and repeat this process at least twice more. Dilute 10 ml of this solution to 100 ml with the extract. Mix the solutions as before, then dilute 10 and 20 ml of this solution to 100 ml with the same precautions, to give extracts with +0.1 and +0.2 pg per ml of added thiamine. REAGENTS, STANDARDS AND PROCEDURE- The same as those used for the “direct” method as described.l The same as those used for the “sand” method, as previously de~cribed,~ omitting those that were only used for digestion (unless this is to be undertaken).* Present address: “Silverwood,” 55 Bucknalls Drive, Rrickctt IYood, Watford, HertsMay, 19661 O F THIAMINE I N BREA4KFAST CEREALS 329 RE s u LTS At first, recoveries with the sand technique seemed disappointingly erratic but, after four sets had been examined (eight additions), it was found that the mean recovery in the eight results was 98.8 per cent., although extreme results were 108 per cent. and 90 per cent. One difficulty in recovery experiments is that each result expresses the sum of two errors of deter- mination, and it was later decided that the mixing of solutions was still a source of error, in spite of the stringent precautions laid down previously, and hence the shaking in a conical flask, as described above, was prescribed as an additional precaution.Duplicate eluates, washed with 3 portions of isobutanol, gave a higher mean recovery, but the results were not less erratic. Examination of these earlier results suggested that both fluorescent and interfering substances were held on the column, probably with varying tenacities. Some were possibly held by base exchange, others only by loose adsorption. To test this hypothesis a large uniform bulk of extract was prepared and, to portions of this, additions of thiamine were made in the manner described above. A set of 8 sand columns was prepared for each solution (+0.0, +0*1, $0.2 pg per ml of added thiamine) and 10 ml of solution were applied to each column (a total of 24 columns). Four columns of each set were then washed with 200 ml of 0.2 x hydrochloric acid, and the remainder with 500 ml of this acid.All the columns were then eluted, giving six sets of eluates. Two eluates from each four were then washed with 4 portions of 25 ml of isobutanol. The eluates were then arranged in the order 1,2,3,4, corresponding to Table I, oxidised and extracted with four portions of isobutanol and the fluorescence measured on 3 successive days as already de~cribed.~ With the isobutanol-washed eluates, the fluorescence found was multiplied by a factor of 1-09 to allow for the increase in volume of the isobutanol owing to the smaller loss of isobutanol into the isobutanol-saturated aqueous phase.The fluorescence of the washings was measured separately. The results are given in Table I. TABLE 1 EFFECT OF \VASHIKG THE COLUMN \VITH ACID AND THE ELUATE WITH ISOBUTANOL I. Eluates not washed with isobutanol 200 ml of acid-wash of column. 500 ml of acid-wash of column Order of measuring r---- A -- ~ ---L------ 7 fluorescence . . 1 3 A 4 Added B, . . . . +o.o f0.1 t 0 . 2 fO.0 +om1 +0.2 +O.O f0.1 t 0 . 2 +0*0 +0*1 +0*2 Percentage recovery - 94 89 -- 03 05 - 0 R,, pg per nil . . 0.362 0.456 0.340 0.365 0.458 0.554 0.362 0-457 0.558 0.359 0.462 0.555 95 88 - 103 98 Mean 92.75 Mean 06.0 11. Eluates washed with isobutanol B,, pg per ml . . 0.340 0453 0.547 0.355 0.454 0.548 0.355 0.4.54 0.554 0.360 0.453 0.565 Percentage recovery - 113 104 - no 97 - 99 100 - 03 103 Mean 103.25 Mean 98.75 It will be seen that the washing of the columns with 500 ml o f acid results in a slight improvement in the recovery.This indicates the slow removal of adsorbed interfering substances. The washings from the eluates, when examined in the fluorimeter, showed a remarkably constant level of 0.026 pg per ml with a maximum deviation of 0.001,, mean 0400,. The blank was reduced to 0.017 on eluates from both the 200-ml and 500-ml acid-washed columns. The blank on the isobutanol-washed eluates was reduced to 0-007 pg per ml. These figures support the view that the column holds traces of both fluorescent and interfering bodies with varying degrees of tenacity, and that these small variations may contribute to the erratic recovery.iVashing the columns with 500 ml of acid will improve the recovery but it will give much the same basic level, because of the balancing opposition of blank and interference. In order to demonstrate still further the validity of these concepts, the isobutanol extracts were concentrated by distillation i n V ~ C U O by using an oil pump. Solid carbon dioxide and alcohol were used as a condensing refrigerant, and a trickle of carbon dioxide was passed from a Kipp's apparatus into the distilling liquid to prevent bumping and also to render330 KIDYARD: A STUDY OF THE DETERMINATION [AIZazyst, Vol. 91 the alkali less soluble in the isobutanol. When the contents of the distillation flask had been reduced to a paste, it was stirred with dry isobutanol and spun in a centrifuge.The super- natant liquid was poured into a small flask. The solid was extracted three times in all in this way, and the combined extracts were then distilled again amost to dryness. The distillation residue was extracted with 4 portions of 0.5 ml of dry isobutanol, which were then transferred to an ignition tube and stored in a desiccator containing a small beaker of dry isobutanol to maintain a saturated atmosphere. The liquid was then chromatographed on paper pre- viously extracted with flowing wet butanol for 48 hours and dried. The chromatogram was developed with water-saturated hutanol in descending flow. The isobutanol extract of a 200 pg per ml thiamine solution was used as a marker without concentration. The chromato- grams when developed and dried were exposed to ultraviolet light and the fluorescence photographed.Fig. 1 is composed from two such chromatograms, and shows the results of chromatographing extracts from: ( I ) , autoclaved wheat ; (11), autoclaved wheat after the addition of thiamine ; (111), autoclaved wheat after final toasting ; (IV), pure thiamine. In order to show more clearly the nature of the interferences remaining after sand purification, 500 ml of the isobutanol washings of the eluates before oxidation were concen- trated to 2ml without being spun in a centrifuge as described above. The chromatogram of the liquid is shown in F-ig. 2, A l ; that of the liquid after stirring in some solid is shown in Fig. 2, A2. Fig. 2, A3 is the chromatogram of a pure thiochrome marker, and A4 is the washing of an eluate from sand alone.The chromatogram shows the presence of fluorescent material (blank) in the washings of the cereal eluates. The subsidiary spots on the pure thiochrome line are attributed to a repeating pair of faint spots that were noticed in such runs from time to time, and have not yet been explained. The chromatogram was then sprayed with the highly fluorescent isobutanol extract of an oxidised thiamine standard containing 200 pg per ml, and then photographed with a shorter exposure. Thus the quenching effects are developed more clearly, as in Fig. 2, B. The same chromato- gram was then sprayed with dipicrylamine to show the location of potassium on the paper (Fig. 2, C.) and finally with potassium ferrocyanide to show the location of ferrous iron (Fig.2, D). These ions are important, not for themselves but as carriers of the chloride ion which is a notorious quenching agent. The four photographs together show the quenching on the paper due to each ion, and also the presence of discrete spots which are presumably due to the presence of organic components from the washings. These are the quenching components which persist throughout the determination. The presence of both blank fluores- cence and quenching materials are thus shown clearly. I t can be seen that traces of iron in the washing from the eluates of the breakfast cereals run further than in the sand blank, where they remain at the origin. This appears to be due to the presence of organically combined iron. In the isobutanol extracts from oxidised eluates, iron is completely, or almost completely, removed by precipitation with sodium hydroxide, and the potassium (or sodium) chloride concentration is reduced by greater aqueous dilution. However, traces of potassium or sodium chloride will remain, but the quenching that arises from this is extremely small, and acts as compensation to the blank.I t has been found with this particular product, after frequent examination for about two years by both the direct and sand methods, that the direct method gives much the same result as the sand method if th.e value for the blaizk is izot deducted. This was observed previously with uncooked wheat p r ~ d u c t s , ~ ? ~ and it is interesting that it should be true with the much higher blank obtained with this cooked material.In the examination of 63 extracts of 52 samples of one wheat product it was found that the blank had a mean value of 0.083 pg per The dark spots near the origin are due to the quenching of the fluorescence. Fig. 1 . Fig. 3. Fig. 2 . Chromatograms of extracts from: ( I ) , autoclaved wheat; (11), autoclaved wheat after the addition of thiamine; (III), autoclaved wheat after final toasting; (IT), pure thiamine Chromatograms o f isobutanol extracts : E, pure thiamine; F, G, H, foods prepared from wheat; J, food prepared from rice; K, food prepared from maize Chromatograms of jsobutanol washings of eluates before oxidation: A, run in water-saturated jsobutanol ; B, sprayed with thiochrome ; C, sprayed with hexanitro-diphenyl- amine (dipicrylamine) ; D, sprayed with potassium ferrocyanide after spraying with dipicryl- amine.I . Eluate washings, solution alone; 11. solution and solids; 111. 200 pg per ml of B; IV. washing of eluate from sand aloneE F G H J K Fig. 3May, 19661 OF THIAMMIIVE I N BREAKF-AST CEREALS 331 ml (the maximum value was 0-120 and the minimum value 0.060). Where the thiamine content was in the region of 0.4 pg per ml, the value, as determined by the sand method, was on the average 0.015 pg per ml higher than that determined by the direct method (mean of 2) witliozd deductioit q f f h e blank value. The maximum differences were +Om046 and -0.022 pg per ml. In three tests, however, when the thiamine content rose to 0.5, 0.6 and 0.7 approximately, the corresponding excesses of the sand values were 0-030, 0.087 and 0.133.I t appears likely that with high interferences the quenching is proportional to the square of the thiamine concentration, as with Therefore, at certain concentrations of this material, a measure of the dircct value without deducting the blank value could be a valuable rapid routine check on the thiamine content. However, the balance of errors is not the same with other foods, even if they are prepared from wheat (see Table 11). The matter should be carefully checked by the sand method with manjT samples. TABLE I1 THIAMIKE DETERMINATION OK BREAKFAST CEREALS 30 g per 750 ml acid extracts Cereal : B8619 RIaize B8620 IVheat B8623 Wheat I38624 Wheat B8625 Rice Direct determination- pg per ml .. . . . . 0-289 0.326" 0.11 0*101* 0.093 0.075 0.311 0.290* Blank . . . . . . . . 0.105 0.092 0.070 0-055 0.070 0.070 0.070 0.08," - 0.396 Addition + 0.1 pg per ml . . 0.408 0.20 7 - - 0.460 Alddition + 0 2 pg per ml . . 0.492 0.277 - mg per 100 g blank deducted 0.46 0.56 0.11 0.12 0.06 0.01 0.60 0.52 mg per 100 g blank not deducted 0.72 0.79 0-28 0.26 0.22 0.19 0.78 0.72 Sand determination- pgpqc: ml . . . . . . 0.230 0.2l9 0.057 0.073 0.072 0-030 0.284 0.209 Addition + 0.1 pg per ml . . 0.345 0.165 - Addition + 0.2 pg per ml . . 0.425 0.263 - II'ashed eluates, pg per in1 . . 0.212 0.0s 1 - - - IVashings, pg per ml . . . . 0.041 0.035 - - 0.30; - 0--110 - - mg per 100 g . . . . . . 0-57 0.62 0.28 0.18 0.18 0.08 0.71 0.51 Manufacturers claim, mg per 100 g 0.60 0.60 * Figures in italics were obtained from difierent extracts of the sample, and lack of corre- spondence of these values with the first determinations are indicative of an erratic distribution of vitamin in the original sample.The value of taking a large amount (30g) for the extract was shown by examining duplicate extracts of 26 samples of one brand of cereals for 15 months. Mean deviations of the results from means of their respective pairs was 0.02 on a general level of 0-9 mg per 100 g, with a maximum deviation of 0.07. Six extracts of each of 5 samples were prepared with only 2 g. Mean deviation from the means was 0.07 mg per 100 g with a maximum of 0.17. Two 5-g portions of a single sample of one fortified breakfast cereal were digested, purified by base exchange on Decalso, and the thiamine determined bv using the method des- cribed by the Aneurine Panel of the Analytical Methods Committee.6 The mean of the t1z.o results obtained was 0-86 mg per 100 g.The same fluorirneter readings interpreted from a curve prepared from five standards, instead o f by calculation from a single 0-2 pg per ml standard as prescribed by the Analytical Methods Committee method, gave a mean result of 0.93. The mean value obtained from two 30-g portions examined by the sand technique was 0.95 mg per 100 g. The low result by the above calculation is due to variation with concentration of the response of the fluorimeter used, as is shown by the sigmoid form of the calibration curve.] Thus, if the calculation is performed with the reading from the 0.4 pg per ml standard in the five mentioned above, a mean value of 0.90 is obtained.Single samples of five other brands of "breakfast cereal'' have been examined by both the direct and sand methods. As one of these brands was a wheat product that was believed to have had only part of the cooking and treatment given to the brand most studied, and two of the other brands were maize and rice products, respectively, these three were examined a second time with additions, and the results from these are included in Table I1 (the columns in italics). As the distribution of thiamine when added to these prodccts t c r d s to be erratic, repeat figures on different extracts are valueless as The results are given in Table 11.332 RIDYARD [A4Tzazyst, Vol.91 a guide to reproducibility of the method. The recovery results are the best guide to this, as these are based on one extract with and without additions. The isobutanol extracts from the original determinations of these five products were concentrated and separated by chromatography. Fig. 3 has been composed from the two chromatograms so prepared, and shows: E, pure thiamine; F, G, H, foods prepared from wheat; J, food prepared from rice; K , food prepared from maize; the last two being fortified in manufacture. It is concluded that the method involving the purification by base exchange on sand is satisfactory for cereal foods that have been manufactured by pressure cooking and subsequent baking or toasting. Traces of fluorescent material are held on the column, apparently by base exchange. Traces of fluorescence-quenching substances and possibly also traces of light-absorbing materials, which may be the same as the quenching substances,2 are held on the column in a less firm and reproducible manner. These last effects oppose the blank however, and both being small are advisedly neglected, as attempts to remove them by washing the eluates with isobutanol are somewhat tedious and liable to give rise to small errors owing to partition and volume effects. I t was found that the procedure previously laid down for mixing solutions prepared in measuring flasks,l stringent though it was, was quite inadequate for the somewhat viscous solutions, and this appears to have been the main cause of erratic recoveries. Hence the more extreme methods laid down in this paper were found to be essential. The direct method may have value as a rough routine check, but the balance of blank and interference varies according to the treatment and nature of raw material. I thank Mr. K. H. IVillis for carrying out the analyses and the photography. REFERENCES 1. 2. 3. 4. 5. 6. Ridyard, H. N., i3 izalvst, 1949, 74, 18. - , Ihzd., 1030, 75, 634. - , Ibzd., 1961, 86, 723. -, Ibztl., 1!340, 74, 24. __ , J . SOC. Cliem. I n d . , 1946, 65, 92. Analytical Methods Committee, A nalyst, 1951, 76, 127. Received Novenabev 225~2, 1963

ISSN:0003-2654    

DOI:10.1039/AN9669100328

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

May, 19661 SHORT PAPERS 333 SHORT PAPERS The Assay of Neomycin BY R. A. HOODLESS (Ministry of Technology, Laboratory of the Government Chemist, Cornwall House, Stamford Street, London, S.E. 1) COMMERCIAL neomycin consists of true neomycins, which are glycosides yielding ribose on hydrolysis, with some admixture of the relatively inactive neamine, which yields no ribose. Neomycin is normally assayed microbiologically. However, various methods have been described for the chemical determination.l~~*~ Most of these are based on the fact that when neomJ-cins are heated with a strong mineral acid, furfural is formed from the ribose as one of the decomposition products. method has been developed which is less time consuming than the other published methods and yet is of the same order of reproducibility.The determination is based on the reaction of ribose with phloroglucinol in a mixture of concentrated hydrochloric acid and glacial acetic acid.4 Optimum conditions for the determination of neomycin are found in heating a solution of neomycin with a mixture of 110 ml of glacial acetic acid, 4 ml of concentrated hydrochloric acid, 1 ml of a 0.8 per cent. aqueous solution of glucose and 5 ml of a 5 per cent. alcoholic solution of phloroglucinol in a boiling water-bath for 15 minutes, and measuring the extinction a t 552 mp. If a higher concentration of hydrochloric acid is used the blank becomes much darker. TYhen neomycin is heated with glacial acetic acid and concentrated hydrochloric acid in the ratio used in the reagent, the maximum amount of furfural is formed after heating for 45 minutes at 100" C.Therefore it seemed unlikely that the determination depended on the formation of furfural. This is confirmed by the fact that furfural does not react with the reagent. Hydrolysis of neomycin with 1.5 N hydrochloric acid and determination of the released ribose with the phloroglucinol reagent gave very erratic results for the ribose content. Hence it is more satisfactory to carry out the hydrolysis and development of the colour with phloroglucinol simultaneously. 5-Hydrosymethylfurfural has been used as a qualitative test for sugars, and it was thought that this might be used for determining neomycin. However, although ribose reacted with 5-hydrosymethylfurfural under the conditions outlined by Love5 to give a straight line relation- ship between extinction and concentration of ribose, neomycin did not react with 5-hydroxy- methylfurfural.METHOD REAGEXTS- Glacial acetic acid, mzalvtical-veagrnt gyacle, fvactionallv distilled. Coircentvated h?ldrorhlovic acid, analytical-reagent gvade, sP.gv. 1- 18. Glucose solittion-Prepare a 0.S per cent. w/v solution in distilled water. Phloitoglzrcinol solution-Prepare a 5 per cent. w/v solution in 95 per cent. alcohol just before use. Phlovoglztcznol reagent-bIix together in a stoppered flask 110 ml of glacial acetic acid, 4 ml of concentrated hydrochloric acid, 1 ml of glucose solution and 5 ml of phloroglucinol solution. This solution must be freshly prepared. A-eomycin standavd-The International Reference Preparation for Neomycin obtained from the National Institute for Medical Research was used.1 mg of this preparation is equivalent to 680 international units. Scorn-ycin samples-These were dried over phosphorus pentoxide in a vacuum desiccator for 24 hours. PROCEDURE- Transfer by pipette 1 ml of test solution containing about 200 pg of neomycin sulphate per ml into a glass-stoppered test-tube. Add 10 ml of the phloroglucinol reagent, mix the solutions, and place the tube in a boiling water-bath with the water level above the liquid level in the tube,334 SHORT PAPERS [A~zal.t)st, Vol. 91 for 15 minutes. against a blank prepared with water instead of test solution. sulphate, and carry them through the procedure a t tlie same time as the sample solutions. After this time cool tlie tube and immediately measure the extinction a t 552 mp Prepare a series of standard solutions containing between 80 and 400pg per ml of neomj-cin Determine the amount of neomycin sulphate in the samples by referring to the standard curve.RESULTS The results obtained from separate assays on samples of neomjcin sulphate pouder are shown in Table I. Thcse are compared with the results obtained by using the methods of Korchagin TABLE I INTERNATIONAL USITS OF SEOMYCIS PER mg OF SAMPLE 2 3 4 Sample Proposcd method 1 65 1 655 665 687 662 648 694 687 653 662 656 637 699 708 694 695 714 707 655 668 658 638 674 637 Method of Korchagin et al. 64 1 622 683 652 645 694 7 00 710 703 689 71 1 682 707 700 699 650 648 659 628 64 1 - - - - Method of Brooks, Forist and Loehr 652 734 662 642 655 829 717 637 - 856 704 683 668 802 661 805 728 - et al., and Brooks, Forist and Loehr on the same solutions.Both the latter methods take longer to carry out owing to the greater hydrolysis time required and the need to make up to a known \-olume after hydrolysis. The over-all time required to carry out an assay by the proposed method is about 1+ hours, as compared with about 2 hours by the method of Korchagin et al., and about 3 hours by the method of Brooks, Forist and T,oehr. The method as proposed is not specific for neomycin because other amino sugar antibiotics yielding ribose on hydrolysis, e.g., paramomycin, will also react with the phloroglucinol reagent. The author thanks thc Govcrnment Chemist for permission to publish this paper. REFERENCES 1. 3. 3. 4. 5. Brooks, A. X., Forist, A. A., Loehr, B. F., Analyt. Chwz., 1936, 28, 1788. Korchagin, I-. R., Iiorobitskaya, A. A,, Uruzhinina, E. N., and Semenor, S. M I Aiztibioliki, 1962, Foppiano, R., Brown, B. B., J . Pharm. Scz., 1965, 54, ( 2 ) , 206. Dische, Z., Borenfreund, E., Baochim. Biophys. Ada, 1957, 23, (3), 639. Love, R. M., Analyst, 1953, 78, 733. 7, (2), 124. Received July 1 2 h , 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100333

出版商:RSC    

年代:1966

数据来源: RSC