摘要:

THE ANALYSTTHE ANALYTICAL JOURNAL OF THE CHEMICALZSOCIETYh.EDITORIAL ADVISORY BOARD"Chairman: J. M. Ottaway (Glasgow, U.K.)R. Belcher (Birmingham, U.K.)E. Bishop (Exeter, U.K.)L. R. P. Butler (South Africa)"H. J. Cluley (Wembley, UX.)E. A. M. F. Dahmen (Thehletherlands)A. C. Docherty (Billinghan, U.K.)D. Dyrssen (Sweden)G. Ghersini (Italy)"P. Gray (Leeds, U.K.)R. Herrman (West Germany)J. Hoste (Belgium)M. T. Kelley (U.S.A.)H. V. Malmstadt (U.S.A.)G. W. C. Milner (Harwell, U.K.)G. H. Morrison (USA.)E. J. Newman (Poole, U.K.)"J. H. Knox (Edinburgh, U.K.)"J. N. Miller (Loughborough, U.K.)H. W. Nurnberg (West Germany)"G. E. Penketh (Wilton, U.K.)"T. B. Pierce (Harwell, U.K.)E. Pungor (Hungary)D. I. Rees (London, U.K.)P. H.Scholes (Middlesbrough, U.K.)S. Siggia (U.S.A.)A. A. Smales, O.B.E. (Thornaby, U.K.)A. Walsh, K.B. (Australia)T. S. West (Aberdeen, U.K.)* J . White head (Stockton-on- Tees,A. L. Wilson (Medmenham, U.K.)P. Zuman (U.S.A.)"W. H. C. Shaw (Greenford, U.K.)"D. Simpson (Thorpe-le-Soken, U.K.)"A. Townshend (Birmingham, U.K.)U. K, )"Members of the Board serving on The Analyst Publications CommitteeREGIONAL ADVISORY EDITORSDr. J . Aggett, Department of Chernistry, University of Auckland, Private Bag, Auckland, NEW ZEALAND.Professor L. Gierst, Universit6 I-ibre de Bruxelles, Facult6 des Sciences, Avenue F.-D. Roosevelt 50,Professor H. M. N. H. Irving, Department of Theoretical Chemistry, University of Cape Town, Ronde-Professor W. A. E.McBryde, Faculty of Science, University of Waterloo, Waterloo, Ontario, CANADA.Dr. G . Rossi, Chemistry Division, Spectroscopy Sector, CEC Joint Research Centre, EURATOM, lspraDr. 1. Rubegka, Geological Survey of Czechoslovakia, Kostelni 26, Praha 7, CZECHOSLOVAKIA.Professor J. RGZiGka, Chemistry Department A, Technical University of Denmark, 2800 Lyngby,Professor K. Saito, Department of Chemistry, Tohoku University, Sendai, JAPAN.Professor P. C. Uden, Departmtmt of Chemistry, University of Massachusetts, Amherst, Mass. 01 003B ruxelles, B ELGlU M.bosch 7700, SOUTH AFRICA.Establishment, 21 020 lspra (Varese), ITALY.DEN MARK.U.S.A.Published by The Chemical SocietyEditorial: The Director of Publications, The Chemical Society, Burlington House,London, W1 \I OBN. Telephone 01 -734 9864. Telex No. 268001Advertisements: Advertisement Department, The Chemical Society, Burlington House, Piccadilly,London, WIV OBN. Telephone 01 -734 9864Subscriptions (non-members): The Chemical Society, Distribution Centre, Blackhorse Road,Letchworth, Herts., SG6 1 HNVolume 104 No 1242 September 1979@ The Chemical Society 197

ISSN:0003-2654    

DOI:10.1039/AN97904FX033

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

ANALAO 104 (1 242) 801 -896 (1 979)ISSN 0003-2654September 197980181 2822831837846853860865THE ANALYSTTHE ANALYTICAL JOURNAL OF THE CHEMICAL SOCIETYCONTENTSIonic Polymerisation as a Means o f End-point Indication in Non-aqueous Thermo-metric Titrimetry. Part X. Acrylonitrile Indicator Reactions in theDetermination of Acids-E. J. Greenhow and L. A. Dajer de TorrijosIdentification and Determination o f Titanium Sulphide and CarbosulphideCompounds in Steel-W. R. Bandi and George KrapfCorrection System f o r Spectroscopic Determination o f Trace Amounts o fCadmium Using the Atomic Faraday Effect w i t h Electrothermal Atomisation-K. Kitagawa, T. Koyama and (the late) T. TakeuchiDetermination of Aluminium, Calcium, Iron and Magnesium in Sewages andSewage Effluent by a Rapid Electrothermal Atomic-absorption Spectro-scopic Method-M.J. T. Carrondo, J. N. Lester and R. PerryDetermination o f Nitrate in Raw, Potable and Waste Waters by UltravioletSpectrophotometry-P. J. Rennie, A. M. Sumner and F. B. BasketterCombined Gas Chromatography - Chemical-ionisation Mass Spectrometry o fSome Phthalate Esters-J. B. AddisonPolarographic Determination of Some Linear Alkylbenzene Sulphonates-J. P.Hart, W. Franklin Smyth and B. J. BirchDetermination o f the Amino Acid Contents o f Coalworkers' Lungs After Correc-t i o n f o r Blood, Fat, Dust and Collagen-Roy LoxleyNaphthidines and o-Dianisidine as Redox Indicators in Titrations rwith N-Bromosuccinimide-H. Sanke Gowda, R. Shakunthala and U. SubrahmanyaSHORT PAPERS873 Non-aqueous Titration of Substituted N-o-Tolylbenzohydroxamic Acids-Y.K.Agrawal875 Trace Determination of Carbonyl Compounds in Air by Gas Chromatography o ftheir 2,4-Dinitrophenylhydrazones-R. A. Smith and 1. Drummond878 Effect o f Ammonium Nitrate on the Gas-chromatographic Determination o fSome Pesticide Residues in Soils-E. G. Cotterill880 Spectrophotometric Determination of Iodide Ion Using Palladium andr2-Nitroso-5-diethylaminophenol-Shoichi Hamada, Shoji Motomizu and Kyoji TBei883 Electroanalytical Study o f Zinc - L-Citrulline Complex a t a Dropping-mercuryElectrode-K. M. Suyan, S. K. Shah and C. M. GuptaCO M M U N ICATIONSDetermination of Trace Amounts of Sulphate by Molecular Emission CavityAnalysis Using a Vaporisation System-S.L. Bogdanski, lssam M. A. Shakir,W. I . Stephen and Alan Townshend890 Novel Reagent f o r the Determination o f Atmospheric Isocyanate MonomerConcentrations-Horace L. Hardy and Ronald F. Walker892 Book Reviews886Summaries of Papers in this lssue-Pages iv, vi, vii, x, xii, xivPrinted by Heffers Printers Ltd Cambridge EnglandEntered as Second Class at New York, USA, Post Offic“ A N A L O I D ”COMPRESSED CHEMICALREAGENTSoffer a saving in the use of lab-oratory chemicals. A range of over50 chemicals includes Oxidizingand Reducing Agents, Reagents forColorimetric Analysis and Indicatorsfor Complexometric Titrations.For full particulars send for ListNO. 458 to:-RIDSDALE & CO. LTD.Newham Hall, Newby,Middlesbrough,Cleveland TS8 9EAortelephone Middlesbrough 31 721 6CLASSIFIED ADVERT1 SEMENTSThe Rate, for Classified Advertisements isL2.50 per single column centimetre.Box Numbers are charged a n extra 6op.Deadline for classified copy i s 20th of themonth preceding month of issue.All space orders, copy instructions andenquiries should be addressed toThe A dvertisement Department,The Chemical Society, Burlington House,Piccadilly, London WIV oBN.Telephone 01-734 9864 Telex 268001FOR SALE1.Analytical Abstracts 1954-1972 (bound).2 . Analyst 1946-1974 (bound).Telephone Nottingham 256398.1975-present (unbound).Notice to SubscribersFor information on subscription rates for The Analyst, AnalyticalAbstracts and Proceedings write to:The Marketing Department,The Chemical Society,Burlington House,London WIV OBN, England.Telephone 01 -734 9864.Telex: 268001.Orders and claims for missing issues should be sent to:The Chemical Society, Distribution Centre,Blackhorse Road, Letchworth, Herts., SG6 1 HN, Englan

ISSN:0003-2654    

DOI:10.1039/AN97904BX035

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

iv SUMMARIES OF PAPERS I N THIS ISSUE Septembev, 1979Summaries of Papers in this IssueIonic Polymerisation as a Means of End-point Indicationin Non- aqueous Thermometric Titrimetry.Determination of AcidsPart X. Acrylonitrile Indicator Reactions in theThe mechanism of the reaction marking the end-point when acrylonitrile isused as the indicator reagent in the thermometric titration of acids withsolutions of potassium hydroxide and alkoxides in alkanols has been investi-gated. Two indicator reactions occur : cyanoethylation of alcohols andanionic polymerisation of the acrylonitrile. The relative contribution ofthe two reactions is shown to depend on the nature and concentration ofalcohols in the titrand solution. Cyanoethylation is more important withrespect to end-point sharpness, when primary and secondary alcohols arepresent, and polymerisation predominates in the presence of tertiary alcohols.Anomalous titration values obtained in the determination of thiols andsulphanilamide can be explained by the effect of the structure of the samplecompound on the reversibility of its reaction with acrylonitrile.The experimental findings are used to devise combinations of titrand solventsand titrants leading to “ideal” titration curves.Keywords : Non-aqueous thermometric titrimetry ; end-point indication ; ionicpolymerisation ; acrylonitrile indicator reactions ; weak acid determinationE.J. GREENHOW and L. A. DAJER DE TORRIJOSDepartment of Chemistry, Chelsea College, University of London, Manresa Road,London, SW3 6LX.Analyst, 1979, 104, 801-811.Identification and Determination of Titanium Sulphide andCarbosulphide Compounds in SteelAs part of the experimental work to identify titanium compounds formed tocontrol sulphide morphology in high-strength low-alloy steels, heats withspecial additions of titanium were melted.It was determined that fivetitanium compounds could be distinguished from one another by differentialthermal analysis - evolved gas analysis techniques. Further, by analysingresidues obtained by using both the acid and the ester - halogen methods ofdissolving the matrix, it was possible to quantify the results for the fivetitanium compounds.The results showed that every experimental heat or experimental alloyexamined contained Ti,C,S, and that one sample contained both Ti,C,S,and y-Ti,S.Another unidentified titanium sulphide was thought to bepresent in one of the steels.Keywords : Titanium compounds ; high-strength low-alloy steel ; diflerentialthermal analysis ; evolved gas analysis ; ester - halogen extractionW. R. BAND1 and GEORGE KRAPFUnited States Steel Corporation, 125 Jamison Lane, Monroeville, Pa. 15146, USA.Analyst, 1979, 104, 812-821Se@tembcr, 1979 THE ANALYST VORGANICS ANALYSIS USING GASCHROMATOGRAPHY/MASSAND PROCEDURES MANUALby W.L. Budde and J.W. Eichelberger,Environmental Monitoring and Support Laboratory,US Environmental Protection Agency, Cincinatti.A practical guide for scientists, managers, andtechnicians who perform or contract to performanalyses of organic pollutants in water, air,sediment, or fatty tissue samples. It emphasizesquality control and the versatility of the powerfulgas chromatography/mass spectrometry tech-nique.In Press approx.242 pages0250 4031 8 8 approx. $22.00/f 1 1 .OOPublished by Ann Arbor Science Inc., and dis-tributed by John Wiley & Sons Ltd.SPECTROMETRY - A TECHNIQUESARCHEOLOGICAL CHEMISTRY:A Sourcebook on the Applications ofChemistry to Archeologyby Z. Goffer, Soreq Nuclear Research Centre,Yavne, Israel.A description of the ways in which chemistrycan beused as an aid in the study of archaeology. Itpresents a unified treatment that includes not onlymethods and techniques, but case histories as well.Results obtained from laboratories and theirinterpretation are emphasized and there isdiscussion of such topics as: ancient technologyand materials, decay and restoration, dating,prospecting, ancient temperatures and palaeo-climate, and authentication of antiquities.(Analytical Chemistry Series Vol.55)In Press approx. 390 pages0471 05156 X approx. $33.20/f 16.70INTRODUCTION TO POWDERSURFACE AREAby S. Lowell, Quantachrome Corporation.A highly specialized book - written by a leadingauthority - which provides a concise introductionto the theory and experimental methods used tostudy the surface area and porosity of solidsurfaces. Part 1 covers the important theoriesassociated with the measurement of surface area,along with the factors that affect it.Part 2 describesand compares various experimental methods.In Press appiox. 200 pages0471 04771 6 approx. $23.90/f 12.05KIRK-OTHMER ENCYCLOPEDIA OFCHEMICAL TECHNOLOGY 3rd Ed.VOl. 7Editorial Board: H.F. Mark and D. Othmer, both ofthe Polytechnic Institute of New York;C.G. Overberger, University of Michiganand G.T. Seaborg, University of California,Berkeley; Executive Editor: M. Grayson;This volume - covering Copper Alloys toDisinfectants and Antiseptics - spans the 15-yeargap between the previous edition and the presentone and brings thasubjects covered completely upto date. The new Third Edition has been completelyrewritten and updated. Two hundred and fifty newsubjects are included reflecting the growth andchanges in chemical technology through the1970s.In addition the new edition emphasizes major topicsof current concern to all industrial and appliedchemists.Some areas in which coverage has beenexpanded include chemical engineering, coatingsand inks, ecology and industrial hygiene, energyconversion and technology, plastics and elasto-mers, semiconductors and electronic materials,and water supply, purification, and reuse. TheThirdEdition also includes: approximately 1000 new orrevised articles by over 1200 distinguishedspecialists - both SI and Imperial units; ChemicalAbstracts Service’s Registry Numbers; and interimindexes to be supplied with every fourth volume.In Press approx. 900 pages0471 02043 5 approx. $1 20.00/f60.00(subscription price)(single-volume price) approx.$150.00/f 75.00Associate Editor: D. EckrothVi SUMMARIES OF PAPERS IN THIS ISSUE September, 1979Correction System for Spectroscopic Determination ofTrace Amounts of Cadmium Using the Atomic Faraday Effectwith Electrothermal AtomisationThe effect of background absorption of radiation on the signal obtained inFaraday-eff ect atomic spectroscopy has been overcome by comparing theenergies transmitted when the optical polarisers are in crossed and parallelconfigurations. Two systems were developed: one was a static system inwhich a Glan prism was used to divide the optical beam into two beams oforthogoually polarised radiation that were detected by two photomultipliers ;the other system used a rotating prism to rotate the plane of polarisation ofthe optical beam and a single photomultiplier with time-sharing electronicsto separate the required signals.Cadmium in a starch matrix was deter-mined using the spectral line a t 228.8 nm and losses of incident radiation ofup to 99% were corrected successfully.Keywords : Atomic spectroscopy ; electrothermal atomisation ; Faraday effect ;cadmium determination ; background correctionK. KITAGAWA, T. KOYAMA and (the late) T. TAKEUCHIDepartment of Synthetic Chemistry, Faculty of Engineering, Nagoya University,Furo-cho, Chikusa-ku, Nagoya, Japan.Analyst, 1979, 104, 822-830.Determination of Aluminium, Calcium, Iron and Magnesium inSewages and Sewage Effluent by a Rapid ElectrothermalAtomic-absorption Spectroscopic MethodThe methods currently used for the determination of aluminium, calcium,iron and magnesium in sewages and final effluent are time consuming.Arapid electrothermal atomic-absorption spectroscopic procedure utilisinghomogenisation of samples as the only pre-treatment has been compared withdigestion methods followed by flame atomic-absorption spectroscopic analysisin a statistically designed experiment. Low-sensitivity (secondary absorp-tion) lines were used for the electrothermal atomic-absorption analysis. Thetime saved by the use of this method is substantial and it could be usedadvantageously for routine analysis.Keywords Electrothermal atomic-absorption spectroscopy ; aluminium,calcium, iron and magnesium determination ; sewages and sewage ejluent ;pe-treatment by homogenisation ; low-sensitivity linesM.J. T. CARRONDO, J. N. LESTER and R. PERRYPublic Health and Water Resource Engineering Section, Civil Engineering Depart-ment, Imperial College of Science and Technology, London, SW7 2AZ.Analyst, 1979, 104, 831-836September, 1979 SUMMARIES OF PAPERS I N THIS ISSUEDetermination of Nitrate in Raw, Potable and Waste Waters byUltraviolet SpectrophotometryviiA method is proposed for the determination of nitrate in raw, potable andwaste waters using ultraviolet spectrophotometry. The use of an activatedcarbon filter at an elevated pH eliminates interference from organic matter,i.e., substances commonly assumed to be responsible for the related absorb-ances a t 275 and 210nm.The procedure also removes the interferences ofseveral cations that are precipitated out of solution. The development workleading up to the proposed method is discussed with reference to the relevantbehaviour towards organic matter and the nitrate ion of activated carbonmaterials. The method has a limit of detection of 0.006 mgl-1 N and atotal standard deviation of 0.016mg1-I N at a nitrate concentration of1.05 mg 1-l N in potable water. No statistically significant difference wasdetected between the proposed method and an established automated methodfor a wide range of samples.Keywords : Nitrate determination ; water ; waste water ; ultvaviolet spectro-Photometry ; activated carbonP. J. RENNIE and A. M. SUMNERNorth West Water Authority, Southern Division, Allport Road/Bridle Road, Brom-borough, Wirral, Merseyside, L62 6AB.and F.B. BASKETTERNorth West Water Authority, Directorate of Scientific Services, Dawson House,Great Sankey, Warrington, WA5 3LW.Analyst, 1979, 104, 837-845.Combined Gas Chromatography - Chemical-ionisation MassSpectrometry of Some Phthalate EstersA sample mixture of seven phthalate esters was analysed using combinedgas chromatography - chemical-ionisation mass spectrometry (GC - CIMS) .Separation of the various components of the mixture was effected by gaschromatography and subsequent identification by chemical-ionisation massspectrometry using methane and isobutane as reagent gases.Comparison of electron-impact (EI) spectra and the CI spectra was under-taken in order to illustrate the advantage of CIMS over EIMS in identifyingthese phthalate esters. CIMS with isobutane gives abundant quasi-molecularions, [M + HI+, with no adduct ions formed, in contrast to CIMS withmethane, and thus provides a means of distinguishing between isomericphthalate esters.Keywords : Phthnlate ester analysis ; gas chromatography - chenaical-ionisntionmass spectrometryJ. B. ADDISONAtlantic Regional Laboratory, National Research Council of Canada, 141 1 OxfordStreet, Halifax, N.S., B3H 321, Canada.Analyst, 1979, 104, 846-852

ISSN:0003-2654    

DOI:10.1039/AN97904FP073

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

X SUMMARIES OF PAPERS I N THIS ISSUEPolarographic Determination of Some LinearAlkylbenzene SulphonatesSeptember, 1979The linear alkylbenzene sulphonate content of sewage samples has beendetermined by an indirect polarographic method. Recoveries made onsewage samples spiked with between 25 and 100 pg of 4-phenyldodecanesulphonate ranged from 82.0 to 104.1y0, respectively, showing the methodto be reliable when concentrations were of the order of 0.5 pg ml-l or greater.This was also confirmed by recoveries made on tap water.Keywords : Linear alkylbenzene sulphonate determination ; polarographyJ. P. HART and W. FRANKLIN SMYTHChemistry Department, Chelsea College, Manresa Road, London, SW3 6LX.and B. J. BIRCHUnilever Research, Port Sunlight Laboratory, Port Sunlight, Wirral, Merseyside,L62 4XN.Analyst, 1979, 104, 853-859.Determination of the Amino Acid Contents of Coalworkers’ LungsAfter Correction for Blood, Fat, Dust and CollagenThe amino acid contents of dust-affected coalworkers’ lungs, complicatedpneumoconiotic lesions, the remainder of the lungs from which the lesionshad been removed and dust-free control lungs have been determined.Theresults have been corrected for blood, dust, fat and collagen content, but nosignificant differences between dust-free and dust-affected lungs were found.The residual amino acid results, after correction, closely resembled the resultsfor glycoprotein extracted from human lung pleura and aorta.analysis ; PnewmoconiosisROY LOXLEYHealth and Safety Executive, Safety in Mines Research Establishment, Red Hill,Sheffield, S3 7HQ.Analyst, 1979, 104, 860-864.Keywords : Amino acid determination ; coalworkers’ lungs ; human lungNaphthidines and o-Dianisidine as Redox Indicatorsin Titrations with N- BromosuccinimideThe optimum conditions for the successful uge of naphthidine, 3,3’-dimethyl-naphthidine, 3,3’-dimethylnaphthidinedisulp>onic acid and o-dianisidine asindicators in macro- and micro-titrations of hexacyanoferrate(II), iron(I1) ,hydroquinone, metol and ascorbic acid with N-bromosuccinimide have beenestablished.The indicators give a very sharp reversible colour change at theequivalence point and have advantages over the existing redox indicators.Hydrazinium sulphate and hydroxylammonium chloride have been determinedindirectly.Anhydrous hexacyanoferrate(I1) and iron(I1) are suggested for thestandardisation of N-bromosuccinimide solutions.Keywords : Naphthidine and o-dianisidine indicators ; N-bromosuccinirnideand hexacyanoferrate (11) standardisationH. SANKE GOWDA, R. SHAKUNTHALA and U. SUBRAHMANYADepartment of Postgraduate Studies and Research in Chemistry, Manasa Gangotri,University of Mysore, Mysore, India.Analyst, 1979, 104, 865-872.September, 1979 THE ANALYST xiCOBALT IN BIOLOGYAND BIOCHEMISTRYRoland S. YoungAugust/September 1979, x + 148pp., ;E11.80 0.12.772750.7Although cobalt plays an important role in ruminant nutrition and functions as a key element invitamin BIZ, information on its biology and biochemistry has not, until now, been collected together inbook form.placed to make a critical assessment of such published investigations.This book takes the form of areview of the literature of cobalt and a reference manual that will enable researchers to benefit froman insight into the techniques employed and data obtained by others working in different areas ofscience. The cobalt content of fertilizers, waters and plants, cobalt in human and animal nutritionand the effects of cobalt on enzymes and microorganisms are the subjects of just some of thechapters.throughout the world and the relationship between the cobalt content of soils and ruminant health.The text is well documented with over a thousand references, allowing the agricultural, medical,biological and chemical researcher or student ample scope to pursue his own particular interest andto acquire ideas from other areas of science which may be applicable to his own.With over forty years of experience of all aspects of cobalt, Dr.Young is eminentlyA lengthy chapter on soils reviews the total and available cobalt in various soilsAcademic PressLondon New York Toronto Sydney San FranciscoA Subsidiary of Harcourt Brace Jovanovich, Publishers24-28 Oval Road, London NW1, England11 1 Fifth Avenue, New York, NY 10003, USAPO Box 300, North Ryde, NSW 2113, AustraliaAnalytical Sciences Monograph No. 2The Chemical Analysis of WaterGeneral Principles and Techniquesby A. L. Wilson( Water Research Centre, Medmenhem Laboratory)BRIEF CONTENTS:Introduction. Information requirements of Sampling and Analysis Programmes.Sampling.The Accuracy and Reporting of Results. Choice and Sources of Analytical Methods.General Precautions in Water-analysis Laboratories. Manual Analytical Techniques.Automatic and On-line Analysis. Data-handling.Pp. viii + 188 f 7.50Clothbound ISBN 0 85990 502 0 CS Members' price f5.75Orders should be sent through your usual bookseller or direct, enclosing remittance, to-Distribution Centre,THE CHEMICAL SOCIETYBlackhorse Road, Letchworth, Herts., SG6 1 HNCS Members must write direct to the above address enclosing the appropriate remittancxii SUMMARIES OF PAPERS IN THIS ISSUENon-aqueous Titration of Substituted N-o- TolylbenzohydroxamicAcidsSeptember, 1979Short PaperKeywords ; Non-aqueous titration ; substituted N-o-tolylbenzohydroxamic acidsY.K. AGRAWALPharmacy Department, Faculty of Technology and Engineering, Maharaja Sayaj iraoUniversity of Baroda, Kalabhavan, Baroda 390 001, India.Analyst, 1979, 104, 873-875.Trace Determination of Carbonyl Compounds in Air by GasChromatography of their 2,4-DinitrophenylhydrazonesShort PaperKeywords ; Trace carbonyl determination ; air analysis ; 2,4-dinitrophenyl-hydrazones ; gas chromatographyR. A. SMITH and I. DRUMMONDOccupational Health and Safety Division, Alberta Labour, 10158-103 Street,Edmonton, Alberta, Canada, T5 J 0x6.Analyst, 1979, 104, 875-877.Effect of Ammonium Nitrate on the Gas-chromatographicDetermination of Some Pesticide Residues in SoilsShort PaperKeywords : Pesticide residue determination ; soil analysis ; gas chromnto-graphy ; ammonium nitrateE.G. COTTERILLAgricultural Research Council, Weed Research Organization, Begbroke Hill, Yarnton,Oxford, OX5 IPF.Analyst, 1979, 104, 878-880.Spectrophotometric Determination of Iodide Ion Using Palladiumand 2-Nitroso - 5- diethylaminophenolShort PaperKeywords : Iodide determination ; spectrophotometry ; palladium ; 2-nitroso-5-die thy larnino phenolSHOICHI HAMADA, SHOJI MOTOMIZU and KYOJI T6EIDepartment of Chemistry, Faculty of Science, Okayama University, Tsushima-naka,Okayama-shi, Japan.Analyst, 1979, 104, 880-882xiv SUMMARIES OF PAPERS IN THIS ISSUEElectroanalytical Study of Zinc - L- Citrulline Complexat a Dropping-mercury ElectrodeSeptember, 1979Short PaperKeywords : Polarography ; zinc - L-citrulline complexK.M. SUYAN, S. K. SHAH and C. M. GUPTAChemical Laboratories, University of Rajasthan, Jaipur, India.Analyst, 1979, 104, 883-886.Determination of Trace Amounts of Sulphate by Molecular EmissionCavity Analysis Using a Vaporisation SystemCommunicatioaKeywords : Hydrogen flame ; molecular emission cavity analysis ; sulphatereduction ; tin - orthophosphoric acidS. L. BOGDANSKIRonalstan Chemical Consultants, Temple House, New Street, Birmingham, B2 4LH.and ISSAM M. A. SHAKIR, W. I. STEPHEN and ALAN TOWNSHENDDepartment of Chemistry, University of Birmingham, P.O. Box 363, Birmingham,B15 2TT.Ayzdyst, 1970, 104, 886-890.Novel Reagent for the Determination of AtmosphericIsocyanate Monomer ConcentrationsCommunicationKeywords : Isocyanate determination ; 1,( 2-pyridyl)pipevazine reagelzt ;atmospheric pollution ; high-performance lzquad chromatogvaphyHORACE L. HARDY and RONALD F. WALKERHealth and Safety Executive, Research and Laboratory Services Division, 403Edgeware Road, London, NW2 6LN.Analyst, 1979, 104, 890-891

ISSN:0003-2654    

DOI:10.1039/AN97904BP079

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

September 1 979 The Analyst Vol. 104 No. 1242 Ionic Polymerisation as a Means of End-point Indication in Non-aqueous Thermometric Titrimetry Part X.” Acrylonitrile Indicator Reactions in the . Determination of Acids E. J. Greenhow and L. A. Dajer de Torrijos Department of Chemistry, Chelsea College, University of London, Manresa Road, London, SW3 6LX The mechanism of the reaction marking the end-point when acrylonitrile is used as the indicator reagent in the thermometric titration of acids with solutions of potassium hydroxide and alkosides in alkanols has been investi- gated. Two indicator reactions occur : cyanoethylation of alcohols and anionic polymerisation of the acrylonitrile. The relative contribution of the two reactions is shown to depend on the nature and concentration of alcohols in the titrand solution.Cyanoethylation is mofe important with respect to end-point sharpness, when primary and secondary alcohols are present, and polymerisation predominates in the presence of tertiary alcohols. Anomalous titration values obtained in the determination of thiols and sulphanilamide can be explained by the effect of the structure of the sample compound on the reversibility of its reaction with acrylonitrile. The experimental findings are used to devise combinations of titrand solvents and titrants leading to “ideal” titration curves. Keywords : Non-aqueous thermometric titrimetry ; end-point indication ; ionic polymerisation ; acrylonitrile indicator reactions ; weak acid determination In the initial investigation of the use of acrylonitrile as an indicator reagent for the thermo- metric titration of weak acids,1$2 it was suggested that both anionic polymerisation of the acrylonitrile and cyanoethylation reactions could be responsible for the rise in temperature marking the end-point.However, in subsequent studies of the applications of this indicator reagent, it has been assumed that the polymerisation reaction predominates. In a recent preliminary communication3 we reported that significant amounts of cyano- ethylation products were present in the final titration solutions when acrylonitrile was used as the indicator reagent, and primary and secondary alcohols were introduced into the sample solution, either as the titrant solvent or as an original constituent of the solution.This investigation is concerned with the nature of the indicator reaction and the means by which it can be modified to obtain sharp end-point inflections in the titration of weak acids. Particular attention is paid to the effects of the titrant, titrant solvent and sample solvent on the shape of the titration curve. An attempt is made to explain these effects in terms of the mechanisms and rates of the reactions involved. Weak acids, such as phenols, thiols and sulphonamides, can undergo cyanoethylation and, in earlier paper^,^^^ it was suggested that the low reaction stoicheiometries observed in the titration of some thiols and sulphanilamide could be explained in terms of the complete or partial cyanoethylation of the weak acid. This analytical problem is examined in this paper.Experimental Reagents Toluene, pyridine, methanol, propan-2-01 and n-butanol were of analytical-reagent grade ; acrylonitrile, morpholine and other solvents were of laboratory-reagent grade. All liquid reagents were dried over molecular sieve 4A before use. * For Part IX, see Analyst, 1976, 101, 777. 801802 GREENHOW, DAJER DE TORRIJOS IONIC POLYMERISATION FOR END-POINT Analyst, VOL. 104 Titrants Potassium hydroxide and alkoxide solutions were prepared in the usual manner by dissolving the solid hydroxide and metal, respectively, in the appropriate alkanol. Tetra- methylammonium hydroxide reagent, 0.025 M in pyridine - propan-2-01 (1 + l), was pre- pared from a 25% aqueous solution by evaporating off most of the water a t 28 “C under reduced pressure, adding pyridine, continuing the evaporation until all of the water had been removed and diluting the pyridine solution with pyridine and propan-2-01.Cyanoethyl Derivatives These derivatives were prepared by the addition of acrylonitrile to the alkanols, phenol, 2-mercaptobenzothiazole and sulphanilamide in the presence of benzyltrimethylammonium hydroxide. The procedures described by Utermohlen,6 Bachman and Levine,’ Hurd and Gershbeins and Misra and Raog were used for the preparation of 3-alkoxypropionitriles, 3-phenoxypropionitrile, S-(2’-cyanoethyl)-2-mercaptobenzothiazole and NN-bis(Z’-cyano- ethyl)-4-aminobenzenesulphonamide, respectively. Apparatus The automatic apparatus described in Part IIIlO was used, but with unsilvered Dewar beakers (capacities 14 and 30 ml) instead of foam-insulated titration flasks.A variable- speed syringe, driven by a stepper motor, was used in investigations of the effects of titration rate on observed reaction stoicheiometries. Procedure Thermometric titrimetry Prepare a solution of benzoic acid in acrylonitrile, pipette an aliquot of the solution into the titration beaker and add additional acrylonitrile, if required, and any other solvents. Introduce the titrant a t a constant rate (0.2 ml min-l) unless otherwise required, and record the temperature and titrant volume on a millivolt chart recorder (500-mV scale) a t a chart speed of 600 mm h-l. Gas - liquid chromatogyaphy After completion of the catalytic thermometric titration, acidify the titration solution with glacial acetic acid (2 ml), filter off any precipitated polymer and inject about 0.5 p1 of the filtrate into the gas chromatograph. Use a stainless-steel column (2 m x 2 mm i.d.) packed with 2.5% OV-17 on Chromosorb G (80-100 mesh), and a flame-ionisation detector.Programme the column temperature from 60 “C to an upper value appropriate for the higher boiling constituents of the sample solution. Results and Discussion Effect of Alcohols in the Titrant and Titrand Solutions Acrylonitrile alone and solutions of benzoic acid in acrylonitrile were titrated with solutions of potassium hydroxide in methanol and propan-2-01, and potassium alkoxides in the corresponding alkanols. The titration curves obtained are shown in Fig. 1. The anions present in the potassium hydroxide solutions are essentially alkoxide and not hydroxide because the equilibrium in the titrant solution, represented by the equation OH- + ROH .+ OR- + H,O strongly favours the right-hand side.ll As observed in earlier studies of solvent effects,lZ the titration curves for the solvents only [Fig.l(a)-(e)] reveal more clearly the influence of different reagents on end-point sharpness than do the corresponding curves for the benzoic acid solutions [Fig. l(a’)-(e’)]. In the blank titrations of acrylonitrile, steeper rises in temperature are obtained with potassium hydroxide in methanol, potassium n-butoxide in n-butanol and potassium tert- butoxide in tert-butanol than with potassium hydroxide in propan-2-01 and potassium sec- butoxide in sec-butanol as the titrants.The induction period before the indicator reactionSeptember, 1979 INDICATION IN NON-AQUEOUS THERMOMETRIC TITRIMETRY. PART X 803 is initiated is about 1 min when the last two titrants are used, and about 0.3, 0 and 0 min with the potassium n-butoxide in n-butan-ol, potassium hydroxide in methanol and potassium tert-butoxide in tert-butanol, respectively. There is evidence13J4 that the catalytic "/ I I I I I I I I I I I I ;\ a I!, a I d / , Titrant/ml (1 division = 1 rnl) Fig. 1. Effect of the nature of the alcohol titrant solvent on the titration graph. Titrand solvent: acrylonitrile, 10 ml. Sample: benzoic acid, 61.1 mg. Titrants (0.5 M) : a, potassium hydroxide in methanol ; b, potassium hydroxide in propan-2- 01; c, potassium n-butoxide in n-butanol; d, potassium sec- butoxide in sec-butanol; and e, potassium tert-butoxide in tert-butanol.Graphs a-e are the blank titrations and a'-e' are the sample titrations. activity of alkali metal alkoxides for the cyanoethylation reaction increases in the order CH30- < n-C,H,O- rn n-C,H,O- < iso-C,H,O- < tert-C,H,O-. On the other hand, the acidities of the corresponding alcohols increase in the reverse order.14 Thus, although the methoxide ion may be a less effective catalyst than the secondary and tertiary alkoxide ions, the titrant solvent, methanol, is more reactive than the secondary and tertiary alcohols. It is these alcohols that are required to complete the cyanoethylation process : RO- + CH,=CHCN + ROCH2-6HCN . . . . . . (1) ROCH~CHCN + ROH + ROCH,CH,CN + RO- .. ' . (2) and it seems probable that the sharp rise in temperature seen in titration curves Fig. l(a) and (c) is caused by cyanoethylation rather than polymerisation. In contrast, the sharp temperature rise in curve (e) in Fig. 1 must be attributed to anionic polymerisation because tert-butanol does not yield cyanoethylation products at the temperature of the titration process. Titration curves (b) and (d) in Fig. 1 could represent a combination of both cyanoethyla- tion and anionic polymerisation, although there is considerable evidence from kinetic and other s t u d i e ~ ~ ~ - l * that, in general, cyanoethylatiori will precede the anionic polymerisation of acrylonitrile when primary and secondary alcohols are present. Gas - liquid chromatographic analysis of the titration solutions, after they have been acidified with acetic acid to prevent decyanoethylation reactions on the column of the chromatograph, confirms the absence of a cyanoethylation product when the tert-butoxide titrant is used, and the presence of a significant amount of cyanoethylation product when titrants containing primary and secondary alkanols are employed [Table I, experiments l(a)-(e) and l(a')-(e')].The higher yield of polymer when potassium hydroxide (effectively isopropoxide) in propan-2-01 is the titrant suggests that the relatively long induction period corresponds more to polymerisation than to a cyarioethylation reaction. This possibility is supported by the appearance of a yellow colour, associated with the formation of p l y - acrylonitrile,15 which is seen to develop when the end-point is indicated.804 GREENHOW, DAJER DE TORRI JOS IONIC POLYMERISATION FOR END-POINT Analyst, Val.104 TABLE I COMPOSITION OF TITRATION SOLUTIONS IN THE CATALYTIC THERMOMETRIC TITRATION OF SOLVENT MIXTURES AND BENZOIC ACID SOLUTIONS WITH ACRYLONITRILE AS INDICATOR Conditions: the final solutions from titrations described in Figs. 1 and 2 [l(a)-(d’) and 2(d)-(f’)] are used after acidification with acetic acid (2 ml). Composition of the final solution Titrantt M K N S B B B B M N S B B B Initial solvent system v-----7 Acrylo- nitrilelg Co-solvent:/g 8.06 - 8.06 8.06 - 8.06 - 8.06 c 8.06 R1, 2.09 8.06 R2, 1.02 8.06 R3, 0.95 8.06 8.06 - 8.06 - 8.06 RI, 2.09 8.06 R2, 0.91 8.06 R3, 0.80 - - Acrylo- nitrile/g 7.06 5.58 7.84 7.71 7.90 6.10 5.00 2.05 5.60 7.59 7.31 5.60 4.60 4.98 Alkanol/g Trace 0.11 0.03 0.097 0.53 0.00 0.45 0.09 0.21 0.07 0.21 0.00 0.00 0.08 Cyano- ethylation products/g 0.37 0.40 0.48 0.67 0.00 3.11 0.74 0.00 3.16 1.03 1.44 3.11 1.17 0.00 Polymer$/g 0.77 2.29 0.02 0.07 0.16 0.94 2.90 6.01 0.49 0.04 0.15 1.44 3.19 3.08 * 1 and 2 refer to Fig.1 and Fig. 2, respectively. Curves l(a)-2(f) are for the solvent mixtures only; t 0.5 M titrants: M = KOH in methanol; K = KOH in propan-2-01; N = n-BuOK in n-butanol; S = $ R1 = benzyl alcohol; R2 = diphenylmethanol; R3 = triphenylmethanol. 5 By difference. curves l(a’)-2(f’) are for solutions containing 61.1 mg of benzoic acid. sec-BuOK in sec-butanol; R = tert-BuOK in tert-butanol. Although a significant amount of polymer is formed in addition to 3-methoxypropio- nitrile in the titration of acrylonitrile with potassium hydroxide (methoxide) in methanol, there seems little doubt, from the kinetic studies of Feit and Bigon,16 that cyanoethylation must be the initial step.Not only did they establish that cyanoethylation was a faster reaction than anionic polymerisation, but by quenching the reaction at an appropriate time they were able to show the presence of the cyanoethylation product before any polymerisa- tion had occurred. Consideration of the gas - liquid chromatographic analysis of the titration solution and the shape of the titration curve for the titration of acrylonitrile, when the potassium sec- butoxide reagent is used [Fig. l(d)], leads US to believe that the indicator reaction in this instance is mainly a relatively slow cyanoethylation reaction.The titration curves for the solutions of benzoic acid in acrylonitrile [Fig. l(a’)-(e’)] do not differ as much as the blank titration curves, possibly because at the end-point there is present a significant amount (about 10% by volume) of the alkanol, which makes the con- ditions favourable for cyanoethylation. The encl-point inflection is sharpest when potassium n-butoxide is the titrant, and is the least s h a q with potassium sec-butoxide as the reagent. The differences in the shape of titration curt’es (a’) and (c’) in Fig. 1 can be explained if it is assumed that the highly reactive methanol added in the titration represented in Fig. l(a’) yields a cyanoethylation product before the alkoxide appears in excess in the titration solution, i.e., the cyanoethylation is catalysed by the weakly basic benzoate ion.The polymer formed does not precipitate from the :solution and must have a low degree of polymer- isation. The inflections in titration curves (c’) and (d’) in Fig. 1, at approximately the half- neutralisation stage, correspond to the point where potassium benzoate is precipitated from the titration solution. The effect of including primary, secondary and tertiary alkanols and arylalkanols in the original titrand solution has also been investigated. Cyanoethylation reactions involving the titrant have been avoided by using the solution of potassium tert-butoxide in tert-butanol.Se$tember, 1979 INDICATION IN NON-AQUEOUS THERMOMETRIC TITRIMETRY.PART x 805 Titration curves and gas-chromatographic analyses are shown in Fig. 2 and Table I [2(d)-(f) and 2(d’)-(f’)], respectively. As in Fig. 1, it can be seen that a very rounded end-point is obtained in the blank titration when sec-butanol is present in the titration solution [Fig, 2(b)], whereas the end-point is rounded, but not to the same extent, in the titration of the benzoic acid [Fig. 2(b’)]. This small improvement in end-point sharpness can be attributed to the effect of the added tert-butanol. Sharp end-point inflections are achieved not only when the primary alcohols n-butanol and benzyl alcohol are present, but also in the presence of diphenylmethanol, a secondary alcohol. I t is interesting that virtually all of the added diphenylmethanol is cyanoethylated in the benzoic acid titration [Table I, 2(e’)] and there is a high yield of cyanoethylation product also in the blank titration [2(e)].Benzyl alcohol is completely cyanoethylated in both the blank and benzoic acid titrations [Table I, 2(d) and (d’)]. On the basis of these analyses, there is strong evidence that the indicator reaction is cyanoethylation when these arylalkanols are present. In contrast to the results obtained when the primary and secondary arylalkanols are present, the presence of the tertiary aryl- alkanol, triphenylmethanol, as a co-solvent leads to rounded end-point inflections [Fig. 2(f) and (f’)], and there is no evidence for the formation of a cyanoethylation derivative. Only about 10% of the triphenylmethanol can be accounted for in the gas - liquid chromatographic analysis, and there is a high yield of polymer [Table I, 2(f) and (f’)].I t must be concluded that the triphenylmethoxy anion initiates the polymerisation of acrylonitrile, and this reaction, which is slower than cyanoethylation , is responsible for the rounded end-point inflections. - 0.5 M Potassium tert-butoxide in tert-butanollrnl ( 1 division = 1 ml) Fig. 2. Effect of the nature of the alcohol titrand solvent on the titration graph. Sample solvent: a, 5 ml of acrylonitrile plus 2 ml of n-butanol; b, 5 ml of acrylonitrile plus 2 ml of sec- butanol; c, 5 ml of acrylonitrile plus 2 ml of tert-butanol; d, 10 ml of acrylonitrile plus 2 ml of benzyl alcohol; e, 10 ml of acryloni- trile plus 1.0 g of diphenylmethanol; and f , 10 ml of acrylonitrile plus 0.8 g of triphenylmethanol.Sample: benzoic acid, 61.1 mg. Titrant : 0.5 M potassium tert-butoxide in tert-butanol. Graphs a-f are the blank titrations and a’-f’ are the sample titrations. In the titrations summarised in Fig. 2, equilibria will be established when the tevt-butoxide titrant mixes with the co-solvent in the titrand solution and the co-solvent alkoxide is likely to be an important constituent of the catalyst system. The effect of increasing the concentration of alkanol in the titrand solution is demonstrated in Fig. 3. sec-Butanol was chosen as the co-solvent because it is known to affect the end- point inflection adversely. Fig. 3 shows that an increase in alkanol concentration not only reduces the end-point sharpness but also causes an increasing rise in temperature before the temperature rise associated with the presence of an excess of titrant.In the blank titrations [Fig. 3(a)-(d)] there is at first a gradual increase in temperature when sec-butanol is present, and later the temperature increases more rapidly. In the absence of the alcohol [Fig. 3(a)] there is an induction period before the temperature rise, and it can be assumed that a slow cyanoethylation reaction is initiated immediately in the presence of the alkanol. The effect806 GREENHOW, DAJER DE TORRIJOS: IONIC POLYMERISATION FOR END-POINT Analyst, VOZ. 104 of increasing the content of the sec-butanol is clearly to reduce the rate of the indicator reaction. This is in accord with the findings of Feit and Bigon16 and Feit et aZ.,18 who established that the rate of cyanoethylation o-E methanol was inversely proportional to the a’ I- 0.5 M Potassium tert-butoxide in rert-butanollml ( 1 division = 1 ml) Effect of the ratio of acrylonitrile t o sec-butanol in the titrand solvent.Sample solvent: a, 4 ml of acrylonitrile; b, 3 ml of acrylonitrile plus 1 ml of sec-butanol; c, 2 ml of acrylo- nitrile plus 2 ml of sec-butanol; tl, 1 ml of acrylonitrile plus 3 ml of sec-butanol. Sample : benzoic acid, 61.1 mg. Titrant : 0.5 M potassium tert-butoxide in tert-butanol. Graphs a-d are blank titrations and a’-d’ are the sample titrations. nth power of the methanol concentration, where n depends on the nature and concentration of other solvents present in the cyanoethylation reaction.They consider that solvation of the alkoxide ion by the methanol reduces the catalytic activity of the former. The value of n is related to the desolvating power of other solvents in the reaction mixture; thus dimethylformamide, an effective “desolvating” solvent because it readily solvates alkanols and prevents them from solvating the alkoxide ions, causes a reduction in n when it is included in the cyanoethylation mixture. In addition, dimethylformamide solvates the potassium cation but not the alkoxide anion, thereby enhancing the dissociation of the catalyst ion pair and increasing the catalytic activity of the anion. The effect of including dimethylformamide in the titrand solution is shown in Fig. 4. By Fig. 3. 0.5 M Potassium tert-butoxide in tert-butanollml (1 division = 1 ml) Fig.4. Effect of the acrylonitrile : sec-butanol : dimethyl- formamide ratio in the titrand solvent. Sample solvent (millilitres of acrylonitrile : sec-butanol : dimethylformamide) : a, 4 : 0 : 2; b, 3 : 1 : 2; c, 2 : 2 : 2 ; d, 1 : 3 : 2. Sample: benzoic acid, 61.1 mg. Titrant: 0.5 M potassium tert-butoxide in tert- butanol. Graphs a-d are the blank titrations and a’-d’ are the sample titrations.September, 1979 INDICATION I N NON-AQUEOUS THERMOMETRIC TITRIMETRY. PART x 807 comparing Fig. 4(a)-(d) with Fig. 3(a)-(d) it can be seen that the addition of dimethyl- formamide to mixtures of acrylonitrile and sec-butanol gives rise to considerably sharper end-point inflections. The effect is similar in the titrations of the benzoic acid solutions [compare Fig.4(b’)-(d’) with Fig. 3(b’)-(d’)]. When the sec-butanol is omitted [Figs. 4(a’) and 3(a’)] the dimethylformamide has the effect of initiating the anionic polymerisation before the end-point is reached [Fig. 4(a’)]. The decreasing influence of the dimethyl- formamide with increasing concentration of sec-butanol in both the blank and benzoic acid titrations is an indication of the limit of the desolvating power of this dipolar solvent; apparently dimethylformamide will “desolvate” about an equal volume of sec-butanol [compare the slopes of curves (c) and (d) or (c’) and (d’) in Fig. 41. Greenhow and Nadjafi19 observed that the rise in temperature marking the end-point in the titration of benzoic acid with tetramethylammonium hydroxide reagent when pyridine is used as the co-solvent with acrylonitrile was much less than when alcohols or dimethyl- formamide were the co-solvents.A “normal” rise in temperature at the end-point was achieved by adding a significant amount of propan-2-01 to the initial sample solution (e.g., 1 ml per 2 ml of pyridine). The retarding effect of pyridine on the indicator reaction was believed to be due to the pyridine forming an adduct with the growing polymer chain : This type of adduct formation was proposed by Yagi et aL20 to explain the retarding effect of pyridine on the anionic polymerisation of styrene. We find that a further, significant, rise in temperature occurs immediately on the addition of propan-2-01 to the titration solution after the end-point is indicated [Fig. 5(a,), (a2) and (a3)].Apparently, the propan- 2-01 displaces pyridine from the adduct and undergoes chain transfer to continue the cyano- ethylation, oligomerisation and polymerisation reactions at a faster rate. There is evidence, therefore, that alkanols can be useful in preventing certain solvents from retarding the acrylonitrile reaction. In titrations of benzoic acid with n- and sec-alkoxides in the corresponding alkanols, the end-point sharpness was found to be influenced by the titrant molarity. Thus, it can be seen in Fig. 6 that whereas a sharp end-point inflection is obtained by using 0.1 M potassium hydroxide in propan-2-01 for the titration of 0.1 M solutions of benzoic acid, significant rises a2 -- I I I 0.025 M Tetrarnethylarnrnoniurn hydroxide reagendrnl ( 1 division = 0.5 ml) Fig.5. Effect of propan-2-01 when pyridine is a titrand solvent. Sample solvent : 4 ml of acrylonitrile plus 2 ml of pyridine. Propan- 2-01 added (1 ml) : a (solid line), none; al-a3 (broken lines), a t the points indicated by the arrows; b, to the original sample solution before the titration. Sample: benzoic acid, 1.5 mg. Titrant: 0.025 M tetramethylammonium hydroxide in pyridine - propan-2-01 (1 + 1).808 GREENHOW, DAJER DE TORRI JOS : IONIC POLYMERISATION FOR END-POINT Analyst, VOt?. 104 in temperature occur before the inflection point when 0.5 and 1.0 M titrants are used for the titration of 0.5 and 1.0 M benzoic acid solutions, respectively. These premature rises in temperature are not apparent when 0.5 M potassium tert-butoxide in tert-butanol is used as the titrant [Fig.6(d)]. I t must be concluded that the acrylonitrile competes with the benzoic acid for the alkoxide ion when the titrant is present, momentarily, in high concentra- tion. This hypothesis was confirmed by adding the 0.5 and 1.0 M potassium hydroxide titrants at a slower rate, e.g., 0.02 instead of 0.2 ml min-l, when titration curves similar to to that in Fig. 6(c) are obtained. Titrant/mI ( 1 division = 1 ml) Fig. 6. Effect of titrant molarity. Sample: benzoic acid in 2 ml of acrylonitrile plus 2 ml of pyridine. Titrant, milligrams of benzoic acid: a 0.5 M potassium hydroxide solution in propan-2-01, 61.1 ; 11, 1.0 M potassium hydroxide solution in propan-2-01, 122.1; c, 0.1 M potassium hydroxide solution in propan-2-01, 12.2; d, 0.5 M potassium tert-butoxide in tert-butanol, 61.1.Cyanoethylation Effects in the Determination of Phenols, Thiols and Sulphanil- amide As phenols, thiols and some sulphonamides can be cyanoethylated with acrylonitrile in reactions that replace their acidic hydrogen functions by the non-acidic cyanoethyl group, it might be expected that the use of acrylonitrile as an indicator reagent could lead to erratic or negligible titration values in the determination of these weak acids. In our previous studies we found no evidence of a reduction in the acidity of phenols when they were titrated in the presence of acrylonitrile, and the titration values obtained by the catalytic thermo- metric method were comparable with, and sometimes higher than, those obtained by non- aqueous potentiometric titration.However, alkylthiols and thiophenols could not be titrated when acrylonitrile was present4 and a. titration value corresponding to a stoicheio- metric reaction was obtained for sulphanilamide only with certain titrant - solvent combina- t i o n ~ . ~ Unexpected results were obtained iin the titration of some heterocyclic thiols, including 2-mercaptobenzothiazole.4 These compounds could be titrated without difficulty to give a titration value corresponding to the neutralisation of the thiol function, although they are known to be cyanoethylated readily by acrylonitrile.8 The effect of cyanoethylation on titration values was investigated by preparing and titrating the cyanoethylation derivatives of phenol, sulphanilamide and 2-mercaptobenzo- thiazole. The titration curves, and titration values, obtained are compared with those of the parent compounds in Figs.7 and 8. I t can be observed (Fig. 7) that cyanoethylated and uncyanoethylated phenol and 2-mercaptobenzothiazole give rise to very similar titration curves and identical titration values corresponcling to the neutralisation of one acidic function. It must be concluded that decyanoethylation of the two cyanoethylation derivatives occurs readily under the conditions obtaining in the titration. Titration curves for an arylalkyl thiol, toluene-a-thiol, and an arylthiol, toluene-4-thiol, are included in Fig. 7 for comparison ;September, 1979 INDICATION IN NON-AQUEOUS THERMOMETRIC TITRIMETRY.PART x 809 d'el . i / I / C \ 1 0.5 M Potassium hydroxide in propan -2-01 ( 1 division = 1 ml) Titration graphs for cyanoethylated and uncyano- ethylated weak acids. Sample (in 4 ml of acrylonitrile plus 2 ml of dimethylformamide), mg : a, 2-mercaptobenzothiazole, 83.6 ; b, S-(2-cyanoethyl)-2-mercaptobenzothiazole, 110.0; c , phenol, 47.1 ; d, 3-phenoxypropionitrile, 73,5 ; e, toluene- a-thiol, 58.2; f, toluene-4-thio1, 523.0. Titrant: 0.5 M potassium hydroxide solution in propan-2-01. Fig. 7. these compounds clearly form very stable cyanoethylation derivatives. Titration curves for the biscyanoethylsulphanilamide in two solvent systems (Fig. 8) show that only partial decyanoethylation occurs during the titration. Although the rounded form of the curves suggests that the decyanoethylation process is occurring slowly, no significant increase in the measured reaction stoicheiometry was achieved by reducing the rate of titrant addition to 0.02 ml min-l.Another difficulty that can arise when acrylonitrile is used as the indicator reagent is the ready cyanoethylation, in the absence of a catalyst, of some solvents that are used success- fully in the non-aqueous potentiometric titration of weak acids, namely primary and secondary alkylamines. The use of such solvents leads to a large rise in temperature during the course of the thermometric titration, before the end-point is indicated.21 However, in a re-examination of this problem we found that, although the use of an amine solvent I 0.1 M Potassium hydroxide in propan-2-01 (1 division = 1 ml) Fig.8. Titration graphs for dicyanoethylated and uncyanoethylated sulphanilamide. Sample : a and b, NN-bis(2'-cyanoethyl)-4-aminobenzenesulphonamide, 27.8 mg; c and d, sulphanilamide, 17.2 mg. Sample solvents : a and d, 3 ml of acrylonitrile plus1 ml of dimethyl- formamide; b and c, 4 ml of acrylonitrile. Titrant: 0.1 M potassium hydroxide solution in propan-2-01.810 GREENHOW, DAJER DE TORRIJOS: IONIC POLYMERISATION FOR END-POINT Analyst, VoZ. 104 (morpholine) causes a premature temperature rise, acceptably sharp end-point inflections can still be achieved with solvent mixtures containing morpholine and acrylonitrile in equal volume, particularly when dimethylformamide is present (Fig. 9). Conclusions This investigation has revealed that primary and secondary alcohols present in the titrant or sample solutions during the catalytic thermometric titration undergo cyanoethylation when acrylonitrile is the indicator reagent.There is strong evidence that these cyanoethylation reactions occur before the anionic polymerisa tion of acrylonitrile. When highly reactive alcohols are present some cyanoethylation may occur before the end-point of the determina- tive reaction, and this will affect the end-point adversely. Thus, although it is desirable that the primary or secondary alcohols should be reactive they should not be too reactive. The results obtained with potassium tert-butoxide in tert-butanol as the titrant show that cyanoethylation is not an essential requirement for an acceptably sharp end-point inflection, provided that the titrant is sufficiently active to initiate the anionic polymerisation after a very brief induction period.0.1 M Potassium hydroxide in propan-2-ol/ml (1 division = 1 ml) Fig. 9. Effect of morpholine in the titrand solvent. Sample: benzoic acid, 12.2 mg. Sample solvent (millilitres of acrylonitrile - morpholine - dimethylformamide) : a, 2 : 0 : 4; b, 2 : 1 : 3; c, 2 : 2 : 2; d, 2 : 4 : 0. Titrant: 0.1 M potassium hydroxide solution in propan-2-01. The solvating properties of the alcohols and other co-solvents have an important effect on the rate of the indicator reaction and, therefore, on the sharpness of the end-point inflection. As solvation of the catalyst anion by alcohols reduces the rate of the cyanoethylation reaction the concentration of alcohols should not be too high.In addition, the presence of dipolar aprotic solvents, such as dimethylformamide, that reduce the solvating effect of thc alcohols and solvate the cation but not the anion of the titrant - catalyst is advantageous When 0.5 M titrants are used, there is evidence that the presence of dimethylformamide can promote premature rises in temperature, before the end-point, when alcohols are absent from the sample solution. This suggests that alcohols have a modifying effect on the dimethylformamide. The premature rises in temperature with more concentrated titrants is related to the competition between the determinative and indicator reactions, and they can be reduced or eliminated by adding the titrants at a slower rate than is used with less concentrated titrants.In devising a combination of titrant and sample solvent in order to achieve the ideal end- point inflection in these titrations, the aim is to minimise the extent of reactions other than the determinative reaction before the end-point, and to maximise the rate of the indicator reaction immediately the titrant is present in excess. Suitable reagent - solvent combina- tions will have, as the titrant, either a higher primary alkoxide in a higher primary alkanol or a tertiary alkoxide in a tertiary alkanol arid, as the sample solvent, a mixture of acrylo-September, 1979 81 1 nitrile, a dipolar aprotic solvent (dimethylformamide, dimethyl sulphoxide or hexamethyl- phosphorotriamide) and, when the tertiary alkoxide reagent is used, a higher primary alkanol to promote a rapid cyanoethylation reaction.Titration curves obtained with these titrant - solvent combinations are shown in Fig. 10. INDICATION I N NON-AQUEOUS THERMOMETRIC TITRIMETRY. PART x 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. a I: Titrant/ml (1 division = 1 ml) Fig. 10. Ideal titration curves. Sample: benzoic acid, 12.2 mg.* Sample solvent? and titrant:: a, I, A; b, 11, B; c, 111, A; d, IV, C. *d = 61.1 mg. TI = 4 ml of acrylonitrile plus 2 ml of dimethylformamide; I1 = 3 ml of acrylonitrile plus 2 ml of dimethylformamide plus 1 ml of n-butanol; I11 = 4 ml of acrylonitrile plus 2 in1 of dimethyl sulph- oxide; IV = 4 ml of acrylonitrile plus 1 ml of dimethylformamide plus 1 ml of n-butanol. :A = 0.1 M potassium n-butoxide in n-butanol; B = 0.1 M potas- sium tert-butoxide in tert-butanol; C = 0.5 M potassium tert-butoxide in tert-butanol. References Greenhow, E. J., Chemy Ind., 1972, 422. Greenhow, E. J.. Chemy Ind., 1972, 466. Greenhow, E. J., Nadjafy, A., and Dajer de Torrijos, L. A., Analyst, 1978, 103, 411. Greenhow, E. J., and Loo, L. H., Analyst, 1974, 99, 360. Greenhow, E. J., and Spencer, L. E., Analyt. Chem., 1975, 47, 1384. Utermohlen, W. P., J . Am. Chem. SOC., 1945, 67, 1505. Bachman, G. B., and Levine, H. A., J . Am. Chem. SOC., 1948, 70, 599. Hurd, C. D., and Gershbein, L. L., J. Am. Chem. SOC., 1947, 69, 2328. Misra, G. S., and Rao, M. V. R., J . Indian Chem. SOC., 1976, 53, 953. Greenhow, E. J., and Spencer, L. E., Analyst, 1973, 98, 98. Caldin, E. F., and Long, G., J . Chem. SOC., 1954, 3737. Greenhow, E. J., and Shafi, A. A . , Analyst, 1976, 101, 421. Feit, €3. A., and Zilkha, A., J . Org. Chem., 1963, 28, 406. Zilkha, A., Feit, B. A,, and Frankel, M., J . Chem. SOC., 1959, 928. Maerker, G., Kenney, I i . E., and Donahue, E. T., J . Am. Oil Chem. SOC., 1968, 45, 72. Feit, B. A,, and Bigon, Z., J . Org. Chem., 1969, 34, 3942. Feit, B. A,, and Zilka, A,, J . Appl. Polym. Sci., 1963, 7, 281. Feit, €3. A., Sinnreich, J., and Zilkha, A., J . Org. Chem., 1967, 32, 2570. Greenhow, E. J . , and Nadjafi, A,, t o be published. Yagi, K., Tsuyama, S., Toda, F., and lwakura, Y., J . Polym. Sci., Polym. Chem. Ed., 1976, 14, Greenhow, E. J., and Spencer, L. E., Analyst, 1973, 98, 90. 1097. NOTE-References 4, 10, 12 and 21 are t o Parts VI, 111, VIII and I1 of this series, respectively. Received January 25th, 1979 Accepted April 6th, 1979

ISSN:0003-2654    

DOI:10.1039/AN9790400801

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

812 Analyst, September, 1979, Vol. 104, pp. 812-821 Identification and Determination of Titanium Sulphide and Carbosulphidle Compounds in Steel W. R. Bandi and George Krapf United States Steel Corporation, 125 Jamison Lane, Mowoevalle, Pa. 15146, USA As part of the experimental work to identify titanium compounds formed to control sulphide morphology in high-strength low-alloy steels, heats with special additions of titanium were melted. I t was determined that five titanium compounds could be distinguished from one another by differential thermal analysis - evolved gas analysis techniques. Further, by analysing residues obtained by using both the acid and the ester - halogen methods of dissolving the matrix, it was possible to quantiEy the results for the five titanium compounds.The results showed that every experimental lieat or experimental alloy examined contained Ti,C,S, and that one sample contained both Ti,C,S, and y-Ti,S. Another unidentified titanium sulphide was thought to be present in one of the steels. Keywords : Titanium compounds ; high-strength low-alloy steel ; dijferential thermal analysis ; evolved gas analysis ; ester - halogen extraction For several years a metallurgical investigation directed toward controlling the sulphide morphology of high-strength low-alloy (HSLA) steel has been in progress at the United States Steel Research Laboratory. I t was presumed that addition of titanium to the steels would result in a change in the sulphide morphology as the result of reaction of part of the sulphur with titanium rather than with manganese.By means of a recently developed chemical method,l it was possible to show tha.t the manganese(I1) sulphide content of the steel was reduced, but it was not possible to determine what titanium sulphide phases were present. 13ecause knowledge of the amount and type of titanium compounds precipitated in these steels was needed in order to understand the mechanical properties of the steel, work was initiated to determine the concentration and crystal structure of the titanium precipitates. The literature on titanium sulphide compounds found in steel is confusing and incomplete. Although sulphides are often studied by microscopic, diffraction and microprobe procedures, the separation and determination of sulphides by chemical methods has been ignored to a large extent.According to a recent survey of the literature,2 the most likely sulphide precipitates in titanium-bearing steel are hexagonal TiS (often written TiS,-,), y-Ti,S and Ti,C,S,. However, misidentification is common when microscope, microprobe and particu- larly X-ray diffraction procedures are used because the diffraction patterns of y-Ti,S and Ti,C,S2 are similar. Over the last 15 years, differential thermal analysis - evolved gas analysis (DTA - EGA) procedures have been developed for the determination, after isolation from the steel matrix, of approximately 35 second-phase compo~nds,~-6 some of which had not previously been identified. Because sulphur dioxide and carbon dioxide can be differentiated when residues isolated from steel are combusted in oxygen, it appeared possible to differentiate between y-Ti,S and Ti,C2S, by DTA - EGA procedures.Therefore, the chemical isolation and DTA - EGA identification and quantitative determination of these precipitates were investigated. This paper summarises this work and further describes the quantitative DTA - EGA deter- mination of titanium nitride and titanium carbide, and also two niobium carbides, which are present in some HSLA steels. Materials and Experimental Work The first two steels were experimental heats made for the purpose of identifying titanium compounds ; all alloying metals that form carbides and sulphides, except titanium, are present only in residual concentrations. Steels 3 and 4 were two HSLA experimental heats that were used in the study of sulphide shape control.Table I shows the partial composition of the steels used in this study.BAND1 AND KRAPF TABLE I 813 COMPOSITION OF SAMPLES (yo) Element c . . . . Mn . . . . Si . . . . Ti . . . . Mo . . . . A1 (total) . . Nb . . . . N, . . . . 0, . . . . . . . . . . . . . . . . . . . . . . 1 0.025 t 0 . 0 1 0.064 0.60 <0.01 <0.005 <0.002 0.001 N.D.* Steel No. 2 3 0.21 0.13 (0.01 1.49 0.064 0.024 0.53 0.053 <0.01 0.33 <0.005 0.042 (0.002 0.016 0.001 0.009 N.D.* 0.007 h 7 4 0.11 1.45 0.026 0.13 0.33 0.030 0.053 0.007 0.011 * N.D. = not determined. Residues from the steels were isolated in bromine - methanol ( l + 3 V / V ) , 10% m/V iodine in methanol solution, 10% hydrochloric acid and fuming perchloric acid. Of these isolation procedures the most useful is that with hydrochloric acid because it is easier to identify the presence of phases such as y-Ti,S and/or Ti4C,S, in the residues by chemical and X-ray diffrac- tion procedures.I t has also been established from past experience that the best DTA - EGA results are obtained when residues are isolated in hydrochloric acid because smaller amounts of interfering phases such as Fe,C, MnS, (MnTi)S and FeS will be present. Therefore, acid- isolated residues have higher concentrations of phases such as y-Ti,S, Ti,C,S, and TiC,Ny, and ultimately a smaller percentage of these phases can be detected in the steel because the DTA - EGA response is more sensitive, less complicated and more easily resolved into the individual components.Finally, because residues isolated in acid contain smaller amounts of amorphous carbon and Fe,C than those from most other isolation procedures, there is less tendency for rapid combustion of Fe,C. Such combustion can cause uncontrolled temperature changes in the DTA sample holder and lead to pre-ignition of other carbides or nitrides. Residues isolated in bromine - methanol, iodine - methanol and fuming perchloric acid were analysed for titanium, sulphur and niobium. The results were compared with similar values obtained on hydrochloric acid residues in order to gain qualitative and quantitative information about the phases present in the steel and to verify the qualitative interpretation of the DTA - EGA peaks. The microchemical analysis was also used to confirm the quantita- tiveness of the EGA results. As an example, Fe,Ti is insoluble in 10% hydrochloric acid, and if the amount of titanium dissolved in iodine - methanol is greater than that dissolved in the acid, it would indicate the possible presence of Fe,Ti in the steel.If more sulphur and titanium are present in an iodine - methanol residue than in a 10% hydrochloric acid residue, i t indicates the possible presence of (MnTi)S or hexagonal TiS in the steel. If the titanium phase is insoluble in fuming perchloric acid, it is probably TiO, or titanate. Before any attempt was made to isolate residues, the steel specimens were surface-ground to remove oxide scale and were then machined to produce the finest possible millings for treatment with bromine - methanol, 10% hydrochloric acid and perchloric acid.Acid- isolated residues were obtained by treating 2-4 g of steel with 10% hydrochloric acid at 38 & 2 "C. (For samples containing niobium, 10 g of tartaric acid were added to each 100 ml of 10% hydrochloric acid.) To prevent oxidation of the solution and precipitation, oxygen was removed from the dissolving reagent by bubbling argon through it, and an argon atmosphere was maintained during dissolution of the isolated residue. Filtration was accomplished by using a Millipore filtration apparatus and a 500-nm methylcellulose organic filter membrane. Details of the filtration and weighing of these residues have been published previously . 9 7-g To isolate (MnTi)S or hexagonal TiS, together with y-Ti,S and Ti,C,S2, solid pieces of steel ( 1 0 g or more) wcrc shaken for 3 h with 10% m/V iodine in methanol solution.The solid piece was removed from the iodine solution with the aid of a magnet, treated ultrasonically in methanol t o remove adhering residue and then re-weighed. The residue was filtered on a Gelman Alpha 8 membrane according to previously described pr~cedures.~*~-~ Titanium814 Analyst, V o l . 104 was determined by ignition of the residue, fusion with sodium hydrogen sulphate and applica- tion of the ASTM method for the photometric determination of titanium as peroxytitanic acid.10 Sulphur was determined by heating the residue with Escha's mixture and applying the grat-imetric barium sulphate method to the leached solution.ll To determine which sulphides could be isolated in bromine - methanol, fine drillings were treated with 5 ml of bromine and 15 ml of methanol per gram of sample.Filtration has been described previou~ly.~*~*~ Titanium and sulphur were determined in the bromine- isolated residues in the same manner as described above for the iodine - methanol residues. The presence of TiO, or titanate in the steels was determined by dissolving the steel in perchloric acid and vigorously fuming the resulting solution. After filtration and ignition, titanium was determined in the ignited contents by fusion with sodium hydrogen sulphate and determination of titanium photometrically as peroxytitanic acidlo in the acid-disolved fusion. Titanium in acid-isolated residues was determined by the photometric peroxytitanic acid method.10 Sulphur in the acid-isolated residues was determined by the combustion method.12 The DTA - EGA curves for the combustion of the isolated second phases were obtained with an instrument described in detail p r e v i ~ u s l y ~ , ~ , ~ ~ and summarised for this paper as follows.An R.L. Stone, Model 12EC,, instrument was modified to limit the gas volume and increase the sensitivity of the EGA system by substituting a specially built Inconel sample holder. This sample holder included an 8-min Inconel gas exit tube, which allowed the evolved gas to flow upwards out of the sample holder through the top of the furnace and into the EGA thermal conductivity cell. A hole €or the exit tube was drilled through the top of the furnace. The sample and reference material were placed on 6-mm platinum dishes situated on top of thermocouple rings. The insulated thermocouple wires were enclosed in a 5-mm Inconel tube, which was inserted donwards through the 8-mm exit tube into the sample compart- ment, and a gas seal outside the DTA furnace was obtained with an O-ring fitting. The total volume of the gas train was about 21 ml.The sensitivity was set so that the evolution of 5 ng of carbon dioxide in 10 min could be measured by thermal conductivity with an oxygen flow-rate of 3 ml min-l. Changes in the thermal conductivity were measured with a Gow-Mac TRIIIA thermal conductivity cell. A bridge current of 6 mA and a tempera- ture of 25 "C were maintained while recording the thermal conductivity changes on a 1-mV recorder. In some instances it was necessary to use a DuPont 310 curve resolver to deconvolute overlapping EGA carbon dioxide responses and determine the area associated with a specific carbide.In resolving the individual areas associated with a specific carbide, use was made of previously established knowledge of the EGA combustion temperature peaks for the specific carbides. Also, the appearance of the simultaneously recorded DTA response was used to interpret the EGA response. Attempts were also made to correlate the EGA response with the composition and heat treatment of the steel, the EGA temperature peaks of com- pounds identified by microchemical analysis of the acid-isolated residue, the EGA temperature peaks of compounds identified by X-ray diffraction examination of the acid-isolated residue, the solubility of phases in dilute warm hydrochloric acid and knowledge that minor amounts of Fe,C and amorphous carbon will contaminate acid-isolated residues.To establish the DTA - EGA responses caused by the decomposition of y-Ti,S and Ti,C,S,, 1-3 mg of the hydrochloric acid isolated residue were transferred into a 3 mm diameter platinum dish and placed on the platinel thermocouples. Alumina was used in the reference pan. The DTA thermogram was recorded on a 1 mV in-l recorder at a sensitivity of 0.33 "C in-l and a heating rate of 10 "C min-l. An initial EGA response was recorded without the sulphur dioxide trap in the evolved gas train so that the thermal conductivity changes caused by the evolution of both carbon dioxide and sulphur dioxide could be recorded. After a small sulphur dioxide trap (75 x 51 mm diameter plastic tube) containing man- ganese(1V) oxide had been placed in the EGA gas train, a second thermal conductivity for the carbon dioxide evolved was recorded.By comparison of the DTA - EGA responses, both sulphide and carbosulphide responses were discerned. The sulphur dioxide trap installed in the EGA exit gas train was small because the gas volume and gas-flow charac- teristics of the evolved gas would be changed by installation of a large sulphur dioxide trap and such a change would affect the shape, area, sensitivity and peak temperature of the EGA response. BAND1 AND KRAPF: IDENTIFICATION AND DETERMINATION O FSeptember, 1979 TITANIUM SULPHIDE AND CARBOSULPHIDE COMPOUNDS IN STEEL 815 The determination of TIN and N, as TiC,N, was accomplished by use of an automatic sampling gas chromatograph placed in the evolved gas train to separate nitrogen from oxygen. A description of this apparatus has been published p r e v i ~ u s l y .~ ~ ~ The same acid- isolated residue was used for the nitride determination. The EGA gas flow-rate was 3 ml min-l; helium (75 ml min-l) was used as the carrier gas in the gas-chromatographic column. The EGA sefisitivity was set so that as little as 0.0003~0 of nitrogen as TIN could be detected by using the same Gow-Mac thermal conductivity apparatus described for carbon dioxide detection. Results and Discussion Table I1 shows the X-ray diffraction identification of the precipitates in residues isolated with hydrochloric acid.The similarity in the diffraction patterns of Ti4C,S, and y-Ti,S prevents differentiation. The identification of TIN, TIC and NbC, particularly in the HSLA steels, was expected because past experience indicated that such precipitates should be present. The fact that no titanium - sulphur compounds were identified in the HSLA steels does not mean that none were present because small amounts of the precipitate could escape detection in the presence of large amounts of carbides, nitrides, amorphous carbon and oxides. TABLE I1 PRECIPITATES IDENTIFIED BY X-RAY DIFFRACTION Steel No. Component 1 y-Ti,S or Ti4C,S,, TiN 2 y-Ti,S or Ti4C,S,, TIC 3 4 TiN, Tic, plus some unidentified lines TiN, Tic, NbC, plus some unidentified lines The amount of titanium found in the residues isolated by treating the steels with various dissolution media is shown in Table 111.If it is assumed, for example, in steel 1 that the titanium compounds present are TIC and y-Ti,S, then about half of the titanium in the steel (0.30%) should be present in the hydrochloric acid residue. However, if it is assumed that Ti4C,S, instead of y-Ti,S is the primary precipitate, then less than one third of the titanium in the steel (0.18%) would have been precipitated. Table I11 shows that for steel 1, 0.14% of titanium was precipitated, which indicates Ti,C,S, to be the predominant precipitate. Steel 2 contains a compound insoluble in hydrochloric acid but soluble in iodine and methanol. For steel 4, there is a difference in the amount of titanium found to be insoluble in iodine - methanol in comparison with bromine - methanol and hydrochloric acid.This difference indicates that some titanium compound partially or wholly dissolves in both bromine - methanol and hydrochloric acid. The difference probably represents a titanium sulphide such as hexagonal TiS or (Mn,Ti)S. Table I11 also shows that only steel 4 contains titanium compounds that are insoluble in fuming perchloric acid. This could be Fe,Ti or a similar compound. Therefore, this sample contains titanium as the oxide or titanate. TABLE I11 AMOUNT OF TITANIUM IN RESIDUE AFTER TREATMENT OF STEEL WITH VARIOUS ISOLATING REAGENTS Titanium isolated, % of steel I 7 h Steel No. In HCl In Br, - CH,OH In I, - CH,OH In HC10, 1 0.14 N.h.* 0.14 N.D.t 2 0.44 N.A.0.30 N.D. 3 0.026 0.026 0.025 N.D. 4 0.083 0.088 0.12 0.012 * N.A. = not analysed. N.D. = none detected (<0.01%).816 BAND1 AND KRAPF: IDENTIFICATION AND DETERMINATION OF Analyst, Val. 104 N b J 3 Resolution EGA response 610°C TiC,N, C (Nb,lVlo)C I Fe,C of EGA 600 500 400 300 Temperature/ "C Fig. 1. Resolution of EGA carbon dioxide response for 1.91 mg of residue isolated from steel sample 4. Fig. 1 shows the EGA response obtained for steel 4. It is typical of the responses used to determine TiC,N1/, Nb,C, and (Nb,,,Mo,,)C in HSLA steels and illustrates the use of the DuPont curve resolver to deconvolute the E.GA response into the peaks shown for the isolated residue. The resolution and identification of Nb,C, and (Nb,,,Mo,,,)C are con- sistent with past experience in the analysis, of precipitates in niobium - molybdenum- bearing steel^^,^ and also agree with the microchemical analysis results for the residue.X-ray diffraction was unable to differentiate between these two niobium carbide precipitates, but a diffraction pattern for cubic niobium carbide was obtained (Table 11). Similarly, an X-ray diffraction pattern was obtained for TIC, but DTA - EGA results showed that in some instances the compound was TiC,N,. The temperatures for the Fe,C, C, TIC and TiC,N, responses are also consistent with past experience.798 TIN and N, in TiC,N, were deter- mined from Fig. 2, and the results agree with ithose described in previous publication^.^^^^^^^^ I 400 500 - I I 600 700 800 Be0 Tern per atu re/ "C 1000 Fig.2. EGA nitrogen response for 4.78 mg of residue isolated by acid dissolution from steel sample 3. Table IV shows the results obtained for TiC, TiC,N,, TIN, Nb,C, and (Nb,,Mo,,,)C from However, Fig. 1 shows unidentified evolution of carbon dioxide Figs. 3 and 4 show DTA - A sulphur The difference in the responses figures such as Figs. 1 and 2. at 610 "C, which was observed for residues from all four steels. EGA responses for residues isolated in hydrochloric acid from steels 1 and 2. dioxide trap was used in obtaining these EGA responses.September, 1979 TITANIUM SULPHIDE AND.CARBOSULPHIDE COMPOUNDS IN STEEL 817 TABLE IV AMOUNTS OF TITANIUM AND NIOBIUM PRESENT AS TiC,Ny, TIC, TIN, Nb,C,, AND (Nbo.,Moo.,)C (70) Ti as Tic and Nb as Steel No. TiC,N, Ti as TIN Nb as Nb,C, (Nb,.,Mo,.,)C 1 0.004 N.D.* N.D.N.D. 2 0.09 N.D. N.D. N.D. 3 0.01 1 0.006 0.006 0.003 4 0.018 0.010 0.042 0.015 * N.D. = none detected (<0.001%). reflects the fact that there is 10 times more carbon in steel 2 than in steel 1. Therefore, the residue from steel 2 contains much more amorphous carbon, cementite and titanium carbide than the residue isolated from steel 1. Fig. 5 shows the resolution of the EGA responses and the response for the TIC identified by X-ray diffraction in steel 2. Temperature/"C Fig. 3. DTA - EGA resDonses for 2.04 ma of residue isolated TemDerature! "C Fig. 4. DTA - EGA response for 2.31 mg of residue isolated by acid dissolution from steel sample 2 (sulphur trap in the system).818 BAND1 AND KRAPF: IDENTIFICATION AND DETERMINATION OF AnaLyst, Vol 104 E 6 -.MC Fe,C 620 "C 600 500 400 Temperature/"C Fig. 5. Comparison of carbon dioxide evolved at 620 "C from (a) steel sample 1 ; and (b) steel sample 2. To determine whether any sulphur dioxide was simultaneously evolved with the carbon dioxide at 610-630 "C, the sulphur dioxide trap was removed from the evolved-gas train and the DTA - EGA responses were again recorded for the residues heated in oxygen. Figs. 6 and 7 show larger EGA responses at 610-630 "C than were observed in Figs. 3 and 4. The increase in magnitude is more noticeable for steel 1 than for steel 2. The EGA response and resolution for steel 1 with and without the sulphur dioxide trap are presented in Fig. 8. Not only is the response at 610-630 "C larger when no sulphur dioxide trap is used in the combustion of TiaC2S2, but also the resolution shows a second EGA response is present at 580 "C.Because of the composition shown in Table I, the X-ray diffraction results shown in Table I1 and the analytical results shown in Tables I11 and V, it is possible to state that the response at 580 "C is produced by the combustion of y-Ti2S. There is also an indication that the y-Ti2S may contain some carbon, because even with the sulphur dioxide trap inserted I I 100 200 300 400 500 600 700 800 Tempe rature/"C DTA - EGA response for 1.96 mg of residue isolated by acid dissolution from steel .,ample 1 (no sulphur trap in the system). Fig. 6.September, 1979 TITANIUM SULPHIDE AND CARBOSULPHIDE COMPOUNDS IN STEEL 819 i! DTA I I I I I I 1 I 100 200 300 400 500 600 700 800 Temperature/"C Fig.7. DTA - EGA response for 2.25 mg of residue isolated by acid dissolution from steel sample 2 (no sulphur trap in the system). in the gas train, a small carbon dioxide response was observed at 580 "C. This could be due to inefficiency of the trap as it had a small absorption capacity and had to be renewed every day. Although no thermal conductivity response for Ti,S could be observed visually in the EGA trace for steel 2 (Fig. 9), when the response was resolved into its component parts a small EGA peak at 580 "C was needed in order to obtain a good fit. It therefore appears that steel 2 contains a small amount of y-Ti,S and a larger amount of Ti,C,S,. In practice we do not use the EGA apparatus to determine sulphur dioxide, because it is known that some of the sulphur dioxide will condense in the train and eventually either react with the metal tubing to form sulphur trioxide or form this gas by another mechanism.Further, it is known that thermistors operating- with a bridge current of 6 mA deteriorate in the presence of sulphur dioxide. obtained by conventional gravimetric or combustion procedures. Therefor6 quantitative sulphur dioxide values were 1 / '\ 58O"CSO, inrTi,S Fe,C Residual CO, or SO, in yTi,S CO, in C ---- _ _ ., CO, in Fe,C -- ___ - ~- - Temperature/"C Fig. 8. Effect of SO, on thermal conductivity of gas evolved from residue of steel sample 1. Resolution of EG-4 responses for 2 mg of residue isolated by acid dissolution from steel sample 1 : (a) without SO, trap; and (b) with SO, trap.820 BAND1 AND KRAPF : IDENTIFICATION AND DETERMINATION OF Analyst, Vol.104 600 500 400 Temperature/"(= Fig. 9. EGA response and resolution for 2.25 mg of residue isolated by acid dissolution from steel sample 2 (no sulphur trap in the system). Tables V and VI summarise the distribution of sulphur and titanium precipitates found in the steels. For steel 1, Table V shows that the quantitative results obtained for Ti,C,S, from the EGA response and sulphur calculated to be y-Ti,S from the classical chemical determination agree with the total sulphur content in the steel, the X-ray diffraction data and the calculation of the y-Ti,S concentration from results in Table 111. TABLE V COMPARISON OF Ti,C,S, CALCULATED FROM DTA - EGA RESULTS WITH SULPHUR FOUND AS TITANIUM - SULPHUR COMPOUNDS BY CHEMICAL METHODS (70) S found as y-Ti,S DTA - EGA C as S equivalent and Ti,C,S, by Amount of S as Steel No.Ti,C.,S, DTA - EGA. C chemical methods y-Ti,S 1 0.005 0.014 0.051 0.037 2 0.023 0.060 0.059 0.000 3 0.0005 0.001 3 0.003 0.002 4 0.003 9 0.010 0.018 0.008 For steel 2 the calculation of the sulphur equivalent of Ti,C,S, in Table V indicates the absence of y-Ti,S, although it was indicated as present in the EGA resolutions. A probable explanation is that some of the sulphur dioxide passed through the trap, causing the EGA TABLE VI DISTRIBUTION OF TITANIUM IN SAMPLES (yo) Total Ti Total Ti as Tic, TIN, found in Steel As Tic As As TiO,,Ti,CIS, residue, No. TiC,N,, As TIN As TiO, Ti,C,S, y-Ti,S and y-Ti,S I, - CH,OH Difference Remarks 1 0.004 <0.001 <0.005 0.042 0.10 0.15 0.14 - 0.01 All titanium precipitated as Tic, Ti,C,S, and y-Ti,S 2 0.09 <0.001 t0.005 0.18 ? 0.27 0.30 +0.03 HCl difference 0.17.Some titanium precipitated as Fe,Ti, M,C; y-Ti,S also present 3 0.011 0.006 <0.005 0.004 0.005 0.026 0.026 - 0.000 Results agree 4 0.018 0.010 0.012 0.030 0.018 0.088 0.12 +0.032 Some titanium present (0.088 total TI in Br, - CH,OH) probably as TiS or (MnTi)SSeptember, 1979 TITANIUM SULPHIDE AND CARBOSULPHIDE COMPOUNDS IN STEEL 821 result for carbon dioxide for Ti4C2S2 to be high and therefore the sulphur equivalent, which is based on the premise that only carbon dioxide was being detected, is also high. When this high sulphur result is subtracted from the total sulphur present as Ti,C,S,, no sulphur as y-Ti,S is detected.The isolation of 0.17% more titanium in hydrochloric acid (Table 111) than is shown in column 7 of Table VI indicates the presence of titanium in other precipitates such as (Fe,Ti),C and does not necessarily indicate an error in the analysis of the titanium - sulphur precipitates. The chemical value shown in Table V for the total amount of sulphur associated with titanium is greater than the amount found to be present as Ti,C,S, in steel 3. This indicates the possibility of a trace amount of y-Ti,S being present. However, because the sulphur bound as Ti,C2S, was calculated on the basis of detecting 0.0005% of carbon, it is impossible to say with certainty that a titanium - sulphur compound other than Ti,C,S, is present in this steel.The results shown in Table VI for the residues isolated from steel 4 definitely confirm that the steel contains a third unidentified titanium - sulphur compound, as indicated by the results in Table 111. Additional DTA - EGA runs confirmed the carbon dioxide value for Ti,C,S2, and the determinations of total titanium isolated in bromine - methanol agree with acid isolations and DTA - EGA results. Therefore, the larger amount of titanium precipitate isolated in iodine - methanol indicates the presence of TiS or (Mn,Ti)S. Conclusions In conclusion, two Fe - Ti - C - S alloys and two experimental HSLA steels containing titanium additions for the purpose of forming titanium - sulphur compounds were examined by X-ray diffraction, DTA - EGA and classical chemical methods.The results showed that every sample contained Ti4C,S2 and that one also contained y-Ti,S. A second unidentified titanium sulphide was found in the HSLA steels. I t was demonstrated that DTA - EGA is the best method for identifying Ti,C,S,. It is also the best method for differentiating between Ti,C,S, and y-Ti,S because their thermal responses are different, even though the X-ray diffraction patterns are similar. Finally, DTA - EGA has been used to differentiate Nb4C, and (Nbo,,Moo,,)C from each other and from cubic NbC and also has been used to differentiate between TIC and TiC,N,. The authors acknowledge the assistance of P. A. Stoll and R. P. Bacco of the Research Laboratory who provided the X-ray diffraction results. 1. 2. 3. 4. 6. 6. 5. 8. 9. 10. 11. 12. 13. References Bandi, W. R., Lutz, J . L., and Buyok, E. G., in deBarbadillo, J. J., and Snape, E., Editors, “Sulfide Kiessling, R., and Lange, N., “Nonmetallic Inclusions in Steel,” Part 11, Iron and Steel Institute, Karp, H. S., Bandi, W. R., and Melnick, L. M., Talanta, 1966, 13, 1679. Bandi, W. R., Straub, W. A., Buyok, E. G., and Melnick, L. M., Analyt. Chem., 1966, 38, 1336. Bandi, W. R., Science, N . Y . , 1977, 196, 136. Lloyd, M. H., and Shanahan, C. E. A., J . Thermal Analysis, 1977, 12, 321. Bandi, W. R., Lutz, J . L., and Melnick, L. M., J . Iron Steel Inst., 1969, 207, 348. Krapf, G., Lutz, J . L., Melnick, L. M., and Bandi, W. R., Thermochim. Acta, 1972, 4, 257. Bandi, W. R., and Krapf, G., Analyt. Chem., 1977, 49, 649. “1978 Annual Book of ASTM Standards, Part 12, Chemical Analysis of Metals; Sampling and Analysis of Metal-bearing Ores,” American Society for Testing and Materials, Philadelphia, Pa., 1978, p. 25. Lundell, G. E. F., Hoffman, J. I., and Bright, H. A., “Chemical Analysis of Iron and Steel,’’ John Wiley, New York, 1931, p. 612. “1978 Annual Book of ASTM Standards, Part 12, Chemical Analysis of Metals; Sampling and Analysis of Mctal-bearing Ores,” American Society for Testing and Materials, Philadelphia, Pa., 1978, p. 527. Randi, W. R., Buyok, E. G., Krapf, G., and Melnick, L. M., in Schwenker, R. F., Jr., and Garn, P. D., Edztors, “Thermal Analysis,” Volume 2, Academic Press, New York, 1969, p. 1363. Received October 4th, 1978 Accepted February 27th, 1978 Inclusions in Steel,” American. Society for Metals, Metals Park, Ohio, 1975, p. 178. London, Publication 100, 1966, p. 138.

ISSN:0003-2654    

DOI:10.1039/AN9790400812

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

822 Aqzalyst, September, 1979, Vol. 104, $9. 822-830 Correction System for Spectroscopic Determination of Trace Amounts of Cadmium Using the Atomic Faraday Effect with Electrothermal Atomisation K. Kitagawa, T. Koyama and (the late) T. Takeuchi Department of Synthetic Chemistry, Faculty of Engineering, Nagoya University, FuYo-cho, Chikusa-ku, Nagoya, Japan The effect of background absorption of radiation on the signal obtained in Faraday-eff ect atomic spectroscopy has been overcome by comparing the energies transmitted when the optical polarisers are in crossed and parallel configurations. Two systems were developed: one was a static system in which a Glan prism was used to divide the optical beam into two beams of orthogonally polarised radiation that were detected by two photomultipliers ; the other system used a rotating prism to rotate the plane of polarisation of the optical beam and a single photomultiplier with time-sharing electronics to separate the required signals.Cadmium in a starch matrix was deter- mined using the spectral line at 228.8 nm and losses of incident radiation of up to 99% were corrected successfully. Keywords : A tomic spectroscopy ; electrothevmal atomisation ; Faraday eflect ; cadmium determination ; background covrectio:n In a previous paper1 we described, as a novel technique of atomic spectroscopy, an applica- tion of the Faraday effect to the determination of trace amounts of cadmium with an electrothermal atomiser. It was shown that the technique gave a detection limit for cadmium comparable to that of atomic-absorption spectroscopy and wa-, insensitive to the background scattering frequently encountered in atomic-fluorescence spectroscopy.There was, however, a problem in the direct atomisation of biological samples where background absorption caused a reduction in the transmitted energy and led to negative interference. This problem was briefly stated in the previous paper and the principle of a method for correction was suggested. In this study, correction systems based on this principle were constructed and their performances evaluated. Three types of information were obtained either by time or spatial separation of the signals. These data consist of signals arising from the optical rotation due to the Faraday effect, the background absorption and the black-body radiation emitted from the electrothermal atomiser.Theoretical As discussed previously,l the intensity, I J , transmitted through the Faraday configura- tion when the number of atoms in the light beam is small can be expressed as follows: . . * * (1) I1 cc (NLB)21, J’p’(k)F(k,H)2dk . . . . s where N L is the number of atoms in the light beam, I? the transition probability, IB the source intensity, p ’ ( k ) the profile function of the source radiation, F ( k , H ) the Faraday function, s the band pass of the monochroma.tor and k the angular frequency. If any back- ground species are present in the light beam, equation (1) must be modified by multiplying it by a damping term, e-abLb: IL cc (NLB) 21se--a2Jp’( k ) F (k,H) 2dk . . .. * * (2) s where Mb is the apparent absorption coefficient for the background component and L b the length of its cloud in the light beam.If the atomic absorption is small enough, the intensity, 111, transmitted when the plane of polarisation of the polariser is parallel to that of the analyser can be expressed as follows:KITAGAWA, KOYAMA AND TAKEUCHI 823 .. * . (3) 111 oc I,e-"bLbJp'(k)dk . . .. .. S As the integral term is unity, If we take a ratio of Il to 111, defined as T,, then T , cc (NLB)2Sp'(k)F(k,H)2dk . . . . .. ' * (5) S Therefore, under the condition of a constant strength magnetic field and a definite line profile of the source radiation, the corrected term T , becomes and hence 2/Fc K N L B .. .. . . . . * * (7) Thus, the square root of the corrected term is proportional only to the number of atoms in the light beam and is independent of the presence of background components and variation in the source intensity.Experimental TO embody the principle stated above in a rapidly responding system, two kinds of optics were tentatively constructed and compared. One of them, illustrated in Fig. 1, incorporates a Glan-type prism with an escaping window on the lateral face (Karl Lambrecht Co. Ltd.) as the analyser and two photomultiplier tubes behind the exit slit of the monochromator. The other optical elements, the electromagnet, the electrothermal atomiser and the polariser are the same as those used in the previous experiment.l The analyser passes the ordinary ray along the optical axis and the extraordinary ray at an angle of about 24" to the axis in the ultraviolet region.The polariser and the analyser were set in such a fashion that the ordinary ray coincided with I , and the extraordinary ray with 111. The separated radiations were detected by separate photomultiplier tubes (Hamamatsu TV Co. Ltd., R928). The source radiation was chopped at a frequency of 285 Hz by a mechanical chopper (Varian- Techtron Co. Ltd.) located between the source and the polariser. The resulting photo- currents were fed to the electronic system, the circuit diagram of which is shown in Fig. 2. Each of the photocurrents was converted into voltage and amplified through an ax. amplifier. The coupling capacitor between the photomultiplier tube and the amplifier D . Fig. 1. Schematic diagram of static system for correction of energy loss.A, EDL and microwave cavity; B, chopper; C, lens and polariser; D, electro- magnet and electrothermal atomiser ; E, monochromator; F, analyser (Glan prism with escape window) ; and G, photomultiplier tube (H'I'V K928).824 KITAGAWA et al. : CORRECTION SYSTEM FOR SPECTROSCOPIC Analyst, Vol. 104 I- - 1 I’ . -. & l i i . Off-set Operation :.vj, V ~ ~ i T $ - ~ ; R e c o r d e r __o J s R1 R2 Fig. 2. Circuit diagram of electronic system for the static system. removes the d.c. voltage resulting from the black-body radiation emitted by the electro- thermal atomiser. The operational amplifier employed was a bi-FET IC, LF356 (Intersil Co. Ltd.), the high input impedance of which allowed it to be the load of the photomultiplier tube.Because of the large difference in energy between I , and I,!, the gain factor for the former was set higher (100) than that for the latter (10). Following a buffer amplifier, each of the a.c. signals was fed through a band-pass filter tuned to a frequency of 285 Hz with a Q-factor of 10 and rectified by an ideal diode circuit. The resulting d.c. signals were operated upon by a programmable multifunction analogue module (Analog Devices Co. Ltd., Model 433 J) according to the equation where m = R2/(Rr + R2). Let V , GC I,, V , cc 111, m = 4 and Vy = 0-9 V for adjusting the over-all gain factor. Then, VOUt cx: d I ~ ~ , , and Vout oc NL. Therefore, if the strength of magnetic field and the profile of the absorption line are defined, the output voltage varies proportionally only with the number of atoms in the light beam.However, a problem arose C B A I U Fig. 3. Schematic diagram of time-sharing system for correction of energy loss. A, EDL and microwave cavity; B, modulation system; C, electromagnet and electro- thermal atomiser; D, analyser and lens ; E, monochromator; and F, photomultiplier tube (HTV R928). in that the monochromator partially depolarised the incident radiation. current even if the atomic vapour was absent. was inserted between the rectifier and the function module. voltage is modified as in equation (9) : This caused a bias To offset this current, an additional circuit Consequently, the output {September, 1979 DETERMINATION OF Cd USING THE ATOMIC FARADAY EFFECT 825 where k,Iil is the additional term for cancelling the voltage resulting from the depolarisation. When atoms are absent, the numerator is pre-set to zero.The alternative system is illustrated in Fig. 3, the details of its mechanical modulator are shown in Fig. 4 and the circuit diagrams of the gating and signal processing electronic circuits in Fig. 5 . The mechanical modulator consists of a disc rotor for chopping the source radiation and a holder for the polariser. The holder is rotated by a synchronous motor at 3600 rev min-l through a belt drive and the disc linked to it by gears. The correlation in time sharing is shown for the detected radiations veysus the rotational angle of the plane of polarisation of the polariser in Fig. 6. At positions a and c the rotor blinds the detector from the source radiation and only black-body radiation from the electrothermal atomiser falls on the detector.Synchronously, an analogue switch Sb is closed and the voltage corresponding to the black-body radiation is sampled and stored in the capacitor Cb. At the instant b, the source radiation is allowed to pass through an aperture in the rotor and reach the polariser. As the polariser and the analyser are in the crossed configuration at this moment, the detected energy is the magnetically rotated radiation, I,, plus the black-body radiation, Ib. The following operational amplifier subtracts the voltage Ib from this voltage, giving the output voltage as the net energy of the magneto-rotation. Concurrently, a switch SI operates and the voltage is sampled and held in the capacitor C,.At moment d, the rotor allows the source radiation to reach the polariser and the plane of polarisation of the polariser is now parallel to that of the analyser, so that the resulting voltage is the reference voltage, I , , , plus the voltage owing to the background radiation, I b . After subtracting Ib, the net voltage Ill is sampled and held in the capacitor CII by closing and opening the analogue switch S,,. The resulting signals I , and I , , are fed to the same function module as that used in the preceding system. The sequence of operations is repeated during the remaining half cycle. Fig. 4. Schematic diagram of modulator in the time- sharing system. E, EDL; L, small lamp; D, rotatory disc; PH, phototransistor; G, gear system; P, polariser; S, stripes for synchronisation; and M, motor.In the preliminary experiment, the triggering pulse for the synchronous operation of the analogue switches was generated by detecting radiation from a small lamp after passing through holes bored on the rotor. However, the stability of the pulses was not satisfactory, partially attributable to fluctuations in the gear system. To improve the stability, the radiation from the small lamp was detected by a phototransistor after reflection by stripes marked on a drum mounted on the axis of the polariser. Another pulse was taken to define the sequence of the operation of the analogue switches. As the photocurrent is significantly different in magnitude between the parallel and crossed configuration, the gain of the pre- amplifier is synchronously altered by switching the resistance in the feedback network.826 KITAGAWA et al.: CORRECTION SYSTEM: FOR SPECTROSCOPIC Analyst, Vol. 104 +5 v H -;a Pre-amplifier .v Blank hold Operation V, \/\I hold Subtract I -15 V U 48, B Q 741 21 Recorder Fig. 5. Circuit diagrams of (a) analogue and (b) digital electronic circuit for the time-sharing system. C, capacitor; P, switching pulse; and S, switch. Results andl Discussion The operating conditions were similar to those used in the previous work1 and were as follows: wavelength, Cd I, 228.8 nm; band-pass width of monochromator, 2.5 nm; drying temperature, 120 "C; atomisation temperature, 1800 "C; and strength of magnetic field, 4 kG. The two systems presented similar results from the standpoint of correction ability.However, in the first system, probably because of the depolarising property of the mono- chromator prism, a considerable leak of energy (about 2% of the incident radiation) was observed in the crossed configuration. This generated a bias photocurrent in the photo- multiplier tube intermediate in form between the continuous and pulse modes. The con- tinuous current was offset electrically according to equation (9) but the noise level on the base line was increased owing to the pulse current. The following results therefore relate mainly to the time-sharing system.September, 1979 Optimisation of Switching Pulses Fig. 6 shows a trace of the photocurrent (Vt) displayed on a cathode-ray oscilloscope (Iwasaki Tsushin Co. Ltd.) and synchronised with those of the switching pulses for the analogue gates of Sb, S, and St[.To offset the blank signal due to the black-body radiation, the switching pulses P b were set as close to P, and as possible; the time interval between the pulses of P b and P, or PI, was synchronised to be 1 ms. DETERMINATION OF Cd USING THE ATOMIC FARDAY EFFECT 827 a.l 0-l CI 0 - > p, v, n v b VI Pb 4 I , J-T-Tl c d 43 , I I I O0 90" 1 80° Rotational angle of the plane of polarisation of the polariser Fig. 6. Traces of photocurrent and pulses for analogue switching. V,, Photocurrent converted into voltage ; PL, switching pulse at crossed configuration ; VL, voltage sampled and held at crossed configuration ; PiI, switching pulse at parallel configuration; Vll, voltage sampled and held at parallel configuration ; Pb, switching pulse for sampling black-body radiation ; Vb, voltage of black-body radiation sampled and held; and P,, pulse for switching gain of pre- amplifier.Fig. 7 is the oscilloscope trace of the I , signal as a function of the width of the switching pulse. For greater widths, however, the noise level increased progressively. This increase may be attributed to the wider pulse sampling the transmitted radiation at moments when the polariser and analyser are incompletely crossed, and to some vibration in the mechanical system of modula- tion. Up to a 50-ps pulse width no variation in the energy of the stored signals was found when atomising 25 pg of cadmium at 1800 "C. Taking into account the slew rate Jf the operational amplifier, we determined the optimum pulse width to be 25 ps.Up to a width of 50 pus, no significant change in noise level was found. loops 1 5 0 ~ ~ 200~s Fig. 7. Oscilloscope trace of I, signal to show dependence of base-line noise on width of switching pulse with crossed polariser configuration. Effectiveness of Correction with Constant Optical Rotation that was stretched unidirectionally to produce optical activity. The corrective ability was estimated using 0.05 mm thick film of low-density polyethylene The film was mounted828 Analyst, vd. 104 between the pole pieces of the electromagnet and, by means of its optical activity, allowed a constant signal to be transmitted through the optical system. The microwave power supplied to the cadmium EDL was varied from 100 to 70 W.Fig. 8 shows traces of the reference signal, I,,, and of the computed signal, z/z, when cigarette smoke was introduced between the pole pieces. The peaks on the reference signal trace correspond to the loss of energy due to scattering by the smoke; these peaks, however, do not appear on the computed signal traces. KITAGAWA et d. : CORRECTION SYSTEM FOR SPECTROSCOPIC These results illustrate three important aspects for practical analysis : (1) the system does not respond to radiation scattered by non-atomic species; (2) the system corrects for the influence of changes in source intensity; (3) the system corrects for the reduction in incident and transmitted energy arising from background absorption. The noise on the corrected signal increased as the source intensity decreased.This effect is attributable to the decrease in the signal to noise ratio in the numerator and denominator of equation (9), due to the reduction in the radiation output of the lamp. 3 0 Time Fig. 8. Traces showing correction for energy loss Arrows and variation in intensity of source radiation. indicate the introduction of cigarette smoke. Correction in Electrothermal Atomisation Fig. 9 shows oscilloscope traces of the corrected response for pyrolysis of different amounts of starch a t the atomisation temperature of 1800 "C. As no ashing procedure was applied, a concentrated cloud of background species was generated in the electrothermal atomiser. In practice, the reference signal 11, was rapidly reduced as shown in Fig.9, but no background signal appeared on the dTc trace, except an increase in the noise level. Partly because of imperfection in the transient response of the electronic circuit for the static system, an errone- 0 0 Fig. 9. Oscilloscope traces of the corrected response for pyrolysis of different amounts of starch at the atomisation temperature of 1800 "C, showing the background scattering. 1, No starch; 2, 2 . 5 p g of starch; 3, 5 pg of starch; and 4, 10 pg of starch.September, 1979 829 ous signal equivalent to 5 pg of cadmium was generated by the correction system when the loss of the incident energy reached 99%. From this point of view, the “box-car” circuit employed for the time-sharing system gave better results than the combination of band-pass filter and rectifier employed in the two-detector system.Fig. 10 shows oscilloscope traces of the response of the system to 50 pg of cadmium in solutions to which starch was added in various concentrations to produce background absorption. After drying at 120 “C for 1 min, 5 p1 of the solution were atomised at 1800 “C without ashing. The traces of the reference signal, I,,, [Fig. 10 (c)] are a measure of the energy loss due to the resulting background component and the absorption by atomic cadmium. When starch was present in a concentration of 0.3%, only 5% of the incident radiation was transmitted by the smoke generated by the pyrolysis of starch. The base-line drift is assigned to the variation in the source intensity. The traces in Fig. 10 ( b ) are the uncorrected response corresponding to IL, and it is obvious that the resulting smoke reduces the transmitted intensity and causes the negative interference.In Fig. 10 (a) it can be seen that the use of the function .\/T, buffers the interference. DETERMINATION OF Cd USING THE ATOMIC FARADAY EFFECT Fig. 10. Correction of energy loss and variation in intensity of source radiation for electro- thermal atomisation. 1, 50 pg of cadmium; 2, 5 pg of starch added; 3, 10 pg of starch added; and 4, 15 p g of starch added. See text for explanation of (a), (b) and (4. Signal to Noise Ratio As the system involves a “box-car” circuit, the photocurrent that is sampled and held has a value corre- sponding to the moment for which the gate is open. Most of the noise included in the output voltage can be attributed to the pulses generated in the photomultiplier tube.When the radiation does not reach the photomultiplier tube, the pulses are assignable to thermal noise. When the number of photons is small, the photocurrent becomes a series of pulses. In this instance, the sample and hold circuit leads to significant variations in the peak response. In either instance, a short current pulse is held and converted into a longer voltage pulse. This leads to a disadvantage in that it is difficult to remove the noise by a circuit of low pass filter. The problem of the thermal noise can be reduced by cooling the photomultiplier tube. To resolve the problem of low light levels, it seems to be more promising to employ a modified photoelectron counting circuit of short cycle time.Another possibility lies in the enchancement of the source intensity for a short period. A possible There remains, however, a problem inherent in the time-sharing system.830 KITAGAWA, KOYAMA AND TAKEUCHI version of this is the use of the hollow-cathode lamp synchronously driven by a giant current pulse. An electronic system based on this technique is under investigation and will be dis- cussed elsewhere. On the other hand, although the system using two detectors did not give better results than the time-sharing system, an alternative configuration is possible that is potentially free from the bias current due to depolarisation. In this system, after separation by a Wollaston or Rochon prism located in front of the entrance slit of the monochromator, the ordinary and extraordinary rays can be dispersed and each detected by a photomultiplier tube. Conclusion The performance of the instrumental systems that we have developed for the determina- tion of cadmium using the Faraday effect has been shown to be sensitive and independent of changes in light-source intensity, scattering of radiation by smoke and absorption of radiation during atomisation of the sample matrix. The limitation of the system has been found to lie in the noise in the systems arising from low light levels and incomplete extinction when the planes of the polariser and analyser are crossed. This work was supported by a grant from the Ministry of Education of Japan. We are indebted to Dr. J. B. Dawson and Professor T. S. West for helpful discussions and advice. Reference 1. Kitagawa, K., Shigeyasu, T., and Takeuchi, T., Analyst, 1978, 103, 1021. Received January 3rd, 1979 Accepted February lst, 1979

ISSN:0003-2654    

DOI:10.1039/AN9790400822

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

Analyst, September, 1979, Vol. 104, pp. 831-836 83 1 Determination of Aluminium, Calcium, Iron and Magnesium in Sewages and Sewage Effluent by a Rapid Electrothermal Atomic-a bsorption Spectroscopic Method M. J. T. Carrondo, J. N. Lester and R. Perry* Public Health and Water Resource Engineering Section, Civil Engineering Department, Imperial College, of Science and Technology, London, SW7 2AZ The methods currently used for the determination of aluminium, calcium, iron and magnesium in sewages and final effluent are time consuming. A rapid electrothermal atomic-absorption spectroscopic procedure utilising homogenisation of samples as the only pre-treatment has been compared with digestion methods followed by flame atomic-absorption spectroscopic analysis in a statistically designed experiment.Low-sensitivity (secondary absorp- tion) lines were used for the electrothermal atomic-absorption analysis. The time saved by the use of this method is substantial and it could be used advantageously for routine analysis. Keywords : Electrothermal atomic-absorption spectroscopy ; aluminium, calcium, iron and magnesium detevmination ; sewages and sewage efluent ; pre-treatment by homogenisation ; low-sensitivity lines Atomic-absorption spectroscopy is probably the most commonly used method for the determination of aluminium, calcium, iron and magnesium in waste waters and effluents.1-3 Other methods, such as neutron-activation a n a l y ~ i s , ~ , ~ X-ray fluorescence6 and spectrophoto- metry,' have also been applied to the determination of these metals in waters, waste waters or sewage sludges.As samples of this nature contain organic and inorganic matrices, some form of treatment is required prior to flame atomic-absorption analysis. Of the methods availab1e,8s9 a limited number have achieved general use. Digestion with perchloric acid in conjunction with nitric acid is claimed to yield high recoveries.lO Procedures based on the use of sulphuric acid and nitric acid have been recommended' for waste waters, but some metals may be lost as insoluble ~ulphates.~ Digestions using hydrogen peroxide and nitric acid have been applied successfully to environmental samples.l19l2 The use of electrothermal atomisers allows pre-treatment to be minimised for samples with mainly organic matrices.l39l4 As electrothermal atomisers are more sensitive than flame atomisers, low-sensitivity (secondary absorption) lines must be used when the con- centration of the analyte is high, thus avoiding the need for excessive di1uti0n.l~ The use of a rapid electrothermal atomic-absorption method for the determination of cadmium, chromium, copper, lead, nickel and zinc in sewage sludges16-18 and sewages and effluents has been reported,Ig and its application to the determination of aluminium, calcium, iron and magnesium in sewage sludges has also been described.20 The results presented here were obtained from a statistically designed experiment to compare the rapid electrothermal atomic-absorption method of analysis using low-sensitivity lines with flame atomic- absorption analysis of acid-digested samples using high-sensitivity absorption lines.Two digestion procedures have been used, a sulphuric acid - nitric acid method and a nitric acid - hydrogen peroxide method. Experimental Apparatus spectrophotometer equipped with deuterium background correction. analysis and the working ranges used are presented in Table I. Flame analysis was undertaken using a Perkin-Elmer, Model 603, atomic-absorption The conditions for In order to remove inter- * To whom all correspondence should be addressed.832 CARRONDO et al. : DETERMINATION OF Al, Ca, Fe AND Mg IN Analyst, Vol. 104 TABLE I CONDITIONS FOR FLAME ATOMIC-ABSORPTION ANALYSIS Spectral Working Wavelength/ band width/ range/ Metal nm nm Flame type mg 1-l A1 . . . . 309.3 0.7 Nitrous oxide - acetylene, 1-50 reducing (rich, red) oxidising (lean, blue) oxidising (lean, blue) oxidising (lean, blue) Ca .. . . 422.7 0.7 Air - acetylene, 0.05-5.0 Fe . . . . 248.3 0.2 Air - acetylene, 0.05-5.0 Mg . . . . 285.2 0.7 Air - acetylene, 0.005-0.5 ferences or suppress ionisation, the samples and standards to be analysed for aluminium were made up to 2000mgl-1 in potassium chloride and those to be analysed for calcium and magnesium were made up to 0.5% in lanthanum.21 Electrothermal analyses were undertaken using the same spectrophotometer in conjunc- tion with a Perkin-Elmer HGA-76 heated graphite atomiser. The conditions and working ranges for electrothermal atomic-absorption analysis are presented in Table I1 ; the values reported were obtained with the less sensitive lines indicated.The atomisation programme used was identical for all metals and consisted, for the 20 x 10-6 1 samples used, in a drying stage at 100 "C for 30 s, a double-stage thermal decomposition with temperature ramping from 100 to 400 "C in 45 s (rate 2), followed by isothermal decomposition at 1200 "C for 30 s and atomisation at 2770 "C for 5 s for all metals except aluminium, for which an 8-s atomisation was used. The ramping stage during the thermal decomposition avoided spattering of the sample that would otherwise have occurred if the temperature had been suddenly increased from 100 to 1200 "C. TABLE I1 CONDITIONS FOR ELECTROTHERMAL ATOMIC-ABSORPTION ANALYSIS Wavelength/ Metal nm A1 . . . . 309.3 Ca . . . . 422.7 Fe . . . . 248.3 Mg . . . . 285.2 257.5* 239.9* 305.9* 202.6* Spectral band width/ nm 0.7 0.2 0.7 0.7 0.2 0.2 0.7 0.7 Sample volume Working range/ x 10-6/1 mg 1-1 20 0.05-1.0 20 0.20-4.0 20 0.01-0.08 20 1.00-20.0 20 0.05-0.5 20 0.20-5.0 20 0.002-0.04 20 0.02-0.50 * Spectral lines used in this work.Reagents Aristar-grade reagents were used for all analyses. Nitric acid, Toy0, sp. gr. 1.42. Sulphuric acid, 98%, sp. gr. 1.84. Hydrogen peroxide, 100 volume. Standard metal solutions. Standards were prepared by serial dilution of 1000 mg 1-1 All standard solutions were prepared so as to contain the same metal stock solutions. reagents as those added to the samples. Homogenisation Approximately 250 ml of undiluted raw sewage, settled sewage and final effluent samples were acidified to 1% V/V with nitric acid and homogenised in a 2-1 tall-form Pyrex beaker&?fitember, 1979 833 with an Ultra Turrax T45N homogeniser (Scientific Instrument Co.Ltd., London) for 5 min at 8000 rev min-l. This ultrasonic homogeniser works on the stator - rotor principle (centrifugal turbine) and produces a very finely homogenised suspension. Aliquots of 20 x 10-6 1 were injected into the electrothermal atomiser with an Eppendorf micropipette (Anderman & Co. Ltd., East Molesey, Surrey). Analysis was performed by direct compari- son with standards in 1% V/V nitric acid. SEWAGES AND SEWAGE EFFLUENT BY RAPID ELECTROTHERMAL AAS Sulphuric Acid - Nitric Acid Digestion7 A sample of 100 ml was digested in a 500-ml flask using an electric isomantle with 5 mI of 70% nitric acid until the volume was reduced to 10 ml; after cooling, 2.5 ml of 98% sulphuric acid were added and the digestate was heated until white fumes were evolved.If the digestion was not complete, a further 1 ml of 70% nitric acid was added until the digestate turned a pale straw colour. The digestate was filtered through a Whatman GF/C glass-fibre filter-paper. Nitric Acid - Hydrogen Peroxide Digestionll until the volume was reduced to 10 ml and then allowed to cool. of 70% nitric acid and hydrogen peroxide were added until the digestion was complete. A sample of 100 ml was digested on a thermostatic hot-plate with 5 ml of 70% nitric acid Subsequently, 2 ml each Results and Discussion Samples of raw sewage (387 mg 1-1 suspended solids), settled sewage (76 mg 1-1 suspended solids) and final effluent (17 mg 1-1 suspended solids) were collected in polythene containers, previously leached in 10% V/V nitric acid, and acidified to 1% V/V with nitric acid.For each of the pre-treatments (digestions and homogenisation) and for each sample type, five replicates and two blanks were examined. As the concentrations of aluminium in sewages and effluents were below the sensitivity of flame analysis (approximately 1 mg 1-1 for 1 yo absorption), these samples were analysed by electrothermal atomic-absorption spectroscopy. The homogenised samples were analysed by electrothermal atomic-absorption spectro- scopy. The results obtained were compared with those obtained by a method of standard additions and found to be in good agreement. The values reported are those.obtained by direct comparison with aqueous standards. The results were statistically evaluated ; the mean values, within-group relative standard deviation and the results of an analysis of variance by the F-test22 are reported in Table 111.Tukey’s test22 was used to identify which means were statistically different at the 0.05 significance level. The repeatability of the electrothermal analysis based on ten injections of the same sample (diluted, if necessary) is indicated in Table IV. No significant differences were found between the treatments for iron and aluminium in all samples. However, highly significant differences were obtained for calcium in all samples and for magnesium in settled sewage and final effluent samples. A comparison of the means by Tukey’s test indicated that the sulphuric acid - nitric acid digestion yielded lower results for the determination of calcium in all samples. Results obtained by flame atomic-absorption spectroscopy and the hydrogen peroxide - nitric acid digestion procedure and electrothermal atomic-absorption spectroscopy in conjunction with homogenisation were always in agreement.Moreover, these two methods yielded higher recoveries than the sulphuric acid - nitric acid digestion procedure. For the determination of magnesium in settled sewage and final effluent, the results obtained by the hydrogen peroxide-nitric acid digestion were comparable to those obtained by both of the other methods. However, a statistically significant difference exists between the sulphuric acid - nitric acid digestion followed by flame atomic-absorption spectroscopy and homogenisation followed by the electrothermal method, the former method yielding lower results than the latter.For unknown reasons, all values seem to be in good statistical agreement for the determination of magnesium in raw sewage. The lower results obtained for the determina- The digested samples were analysed by flame atomic-absorption spectroscopy.834 CARRONDO et aL. : DETERMINATION O F Al, Ca, Fe AND Mg IN AnaZyst, VOZ. 104 TABLE I11 COMPARISON O F ALUMINIUM, CALCIUM, IRON AND MAGNESIUM CONCENTRATIONS I N SEWAGES AND EFFLUENT USING SULPHURIC ACID - NITRIC ACID DIGESTION AND HYDROGEN PEROXIDE - NITRIC ACID DIGESTION FOLLOWED BY FLAME ATOMIC-ABSORPTION ANALYSIS WITH HOMOGENISED SAMPLES ANALYSED BY ELECTROTHERMAL ATOMIC-ABSORPTION ANALYSIS Metal Sample A1 . ... Raw sewage Settled sewage Final effluent Ca .. . . Raw sewage Settled sewage Final effluent Raw sewage Settled sewage Final effluent Mg . . . . Raw sewage Settled sewage Final effluent Fe . . Pre- treatment* H,02 - HNO, Homog. H,S04 - HNO, H202 - HNO, Homog. H2S04 - HNO, Homog. H2S0, - HNO, H,02 - HNO, Homog. H202 - HNO, Homog. H,02 - HNO, Homog. H202 - HNO, Homog. H2S04 - HNO, H,02 - HNO, Homog. H2S04 - HNO, Homog. H2S04 - HNO, Homog. H2S04 - HNO, Homog. H2S04 - HNO, H202 - HNO3 H2S04 - HNO, HZSO4 - HNO, H2S04 - HNO, H202 - HNO, H20, - HNO, HZO, - HNO, H2S04 - HNO, H202 - HNO, Homog. Mean F-test level of concentration/ Modet significance: mg I-'§ F F E E E E E E E F F E F F E F F E F F E F F E F F E F F E F F E F F E N.S.N.S. N.S. 0.01 0.01 0.01 N.S. N.S. N.S. N.S. 0.01 0.01 3.2a 3.la 3.2a 0.52a 0.53a 0.52a 0.14a 0.15a 0.15a 78a 90b 90b 75a 88b 91b 7 7a 88b 90b 1.9a 1.8a 1.8a 0.52a 0.50a 0.54a 0.15a 0.13a 0.14a 10. la 10.4a 11.0a 9. la 9.3ab 10.4b 8.6a 9.5ab 10.2b Relative standard deviation, yo 6.5 6.4 6.1 11.0 13.0 13.2 14.4 9.4 10.5 5.5 4.3 5.4 7.5 7.3 5.0 6.9 5.5 3.8 5.0 5.9 6.1 6.8 6.0 8.0 10.0 12.0 9.5 7.6 6.2 4.8 7.0 6.6 4.3 10.2 5.3 4.6 peroxide - nitric = hydrogen H2O2 - HNO, * H2S04 - HNO, = sulphuric acid - nitric acid digestion; acid digestion ; Homog. = pre-treatment by homogenisation. t F = flame atomic-absorption analysis ; E = electrothermal atomic-absorption analysis. : N.S. = not significant a t the 0.05 significancelevel.9 Means not followed by a common letter are statistically different at the 0.05 significance level. tion of calcium and to a lesser extent magnesium after digestion by the sulphuric acid - nitric acid method are probably due to the formation of insoluble sulphatesg that were retained in the filter or were not aspirated into the flame. The relative standard deviations obtained for the electrothermal atomic-absorption analysis of the homogenised samples compared well with the values obtained for flame analysis of digested samples. The repeatability of the electrothermal method reported in Table IV indicates that for the determination of aluminium in settled sewage and final effluent and iron in final effluent the relative standard deviations were high.This is in part the consequence of working close to or below the lower limit of the recommended working range [Table 11). For these two metals the repeatability of analysis in final effluent wasSeptember, 1979 835 also examined at the higher sensitivity (primary absorption) lines (Table 11) and the relative standard deviations were found to improve from 9.4% to 6.5% and from 8.0% to 4.8% for aluminium and iron, respectively. Thus, the homogenisation - electrothermal atomic- absorption method can yield more precise results if high-sensitivity lines are used for the determination of the lower concentrations. SEWAGES AND SEWAGE EFFLUENT BY RAPID ELECTROTHERMAL AAS TABLE I V REPEATABILITY OF ELECTROTHERMAL ATOMIC-ABSORPTION ANALYSIS OF RAW SEWAGE, SETTLED SEWAGE AND FINAL EFFLUENT SAMPLES (ONE OF EACH) INJECTED TEN TIMES Concentration/mg 1-1 Relative I standard A Metal Sample Mean Standard deviation deviation, yo Al .. . . Raw sewage 3.1 0.17 5.5 Settled sewage 0.54 0.05 9.3 Final effluent 0.16 0.015 9.4 Ca . . . . Raw sewage 9.1 0.35 3.9 Settled sewage 9.0 0.32 3.6 Final effluent 8.8 0.25 2.8 Fe . . . . Raw sewage 1.74 0.08 Settled sewage 0.52 0.034 Final effluent 0.15 0.012 4.6 6.5 8.0 Mg . . . . Raw sewage 0.43 0.013 3.0 Settled sewage 0.41 0.012 2.9 Final effluent 0.40 0.012 3.0 The repeatability of the results obtained for the analysis of aluminium varied slightly with time; this could have been due to variations in voltage that resulted in slight tempera- ture variations in the furnace at the time of atomisation.There was also an increase in sensitivity as the tubes became older; this type of interference effect can probably be explained by Fuller’s kinetic theory of at0misation.~3 Thus, a standard had to be injected more often than was required for other metals (every five as opposed to fifteen injections). Reported values for the electrothermal atomic-absorption analysis of biological samples quote relative standard deviations of 8% for the determination of aluminium in whole blood2* at 0.4 mg 1-’ and 10% in biological tissue13 at approximately 1 mg ml-l. The use of low-sensitivity lines for the determination of iron, calcium and magnesium by electrothermal atomic-absorption spectroscopy eIiminates, or substantially reduces, the extent of dilution that would be needed and so the amount of contamination that could occur if sensitive lines were used.The analysis is simple and there is no need to use the deuterium background corrector, which agrees with results reported previously for iron15 and calcium and magnesium.25 Conclusions The rapid electrothermal atomic-absorption method described here compares well with flame atomic-absorption spectroscopy in conjunction with the digestion methods tested. Homogenisation takes only 5 min as opposed to 3-6 h needed for digestion; this more than compensates for the additional time (2-3 min) required in the electrothermal as opposed to the flame method. The proposed method has the further advantage over flame atomic- absorption spectroscopy that it dispenses with the need to add interference removal agents to samples and standards prior to analysis. Deuterium background correction is not required for the determination of the metals indicated.The authors acknowledge the financial support for this work provided by the Department of the Environment and the Department’s approval for the publication of these results. One of us (ill. J. T. Carrondo) is also grateful to the Instituto Nacional De InvestigaCZo Clentifica, Lisboa, Portugal, for the award of a postgraduate scholarship.836 CARRONDO, LESTER AND PERRY References Welz, B., and Wiedeking, E., 2. Analyt. Chem., 1973, 264, 110. Department of the Environment/National Water Council, “Magnesium in Waters and Sewage Effluents by Atomic Absorption Spectrophotometry, 1977,” HM Stationery Office, London, 1978, Department of the Environment/National Water Council, “Calcium in Waters and Sewage Effluents by Atomic Absorption Spectrophotometry, 1977, Tentative Method,” HM Stationery Office, London, 1978, 12 pp.Lieser, K. H., Calmano, W., Heuss, E., and Neitzert, V., J . Radioanalyt. Chem., 1977, 37, 717. Nadkarni, R. A., and Morrison, G. H., Envir. Lett., 1974, 6, 273. Smits, J., and Van Grieken, R., Analytica Chim. Acta, 1977, 88, 97. Department of the Environment, “Analysis of Raw, Potable and Waste Waters,” HM Stationery Gorsuch, T. T., “The Destruction of Organic Matter,” Pergamon Press, New York, 1970. Hanson, N. W., Editor, “Official, Standardised and Recommended Methods of Analysis,” Second Agemian, H., and Chau, A. S. Y., Analyst, 1976, 101, 761. Geyer, D., Martin, P., and Adrian, P., Korresp. Abwass., 1975, 22, 369. Krishnamurty, K. V., Shpirt, E., and Reddy, M. M., Atom. Absorption Newsl., 1976, 15, 68. Krishnan, S. S., Quittkat, S., and Crapper, D. R., Can. J . Spectrosc., 1976, 21, 25. Lord, D. A., McLaren, J. W., and Wheeler, R. C., Analyt. Chem., 1977, 49, 257. Olsen, E. D., Jatlow, P. I., Fernandez, F. J., and Kahn, H. L., Clin. Chem., 1973, 19, 326. Lester, J. N., Harrison, R. M., and Perry, R., Sci. Total Envir., 1977, 8, 153. Stoveland, S., Astruc, M., Perry, R., and Lester, J . N., Sci. Total Envir., 1978, 9, 263. Carrondo, M. J. T., Perry, R., and Lester, J . N., Analytica Chim. Acta, 1979, 106, 309. Carrondo, M. J. T., Perry, R., and Lester, J. N., Sci. Total Envir., 1979, 12, 1. Carrondo, M. J . T., Lester, J . N., and Perry, R., Talanta, 1979, in the press. Kirkbright, G. F., and Sargent, M., “Atomic Absorption and Fluorescence Spectroscopy,” Academic 12 PP- Office, London, 1972. Edition, Society for Analytical Chemistry, London, 1973. Press. London. 1974. 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. Bowker; A. H., ‘and Lieberman, G. J ., “Engineering Statistics,” Prentice Hall, Englewood Cliffs, N.T.. 1972. Fullgr,‘C. W., Analyst, 1976, 101, 798. Langmyhr, F. J., and Tsalen, D. L., Analytica Chim. Acta, 1977, 92, 79. Pardhan, S. I., and Ottaway, J. M., Proc. Analyt. Div. Chem. Soc., 1975, 12, 291. Received February 28th, 1979 Accepted March 29th, 1979

ISSN:0003-2654    

DOI:10.1039/AN9790400831

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

Analyst, September, 1979, VoL. 104, pp. 837-845 837 Determination of Nitrate in Raw, Potable and Waste Waters by Ultraviolet Spectrophotometry P. J. Rennie and A. M. Sumner* North West Water A uthority, Southern Division, Allport RoadlBridle Road, Bromborough, Wirral, Mersey- side, L62 6AB and F. B. Basketter North West Water Authority, Directorate of Scienti=fic Services, Dawson House, Great Sankey, Warrington, WA5 3 L W A method is proposed for the determination of nitrate in raw, potable and waste waters using ultraviolet spectrophotometry. The use of an activated carbon filter a t an elevated pH eliminates interference from organic matter, i.s., substances commonly assumed to be responsible for the related absorb- ances a t 275 and 210 nm. The procedure also removes the interferences of several cations that are precipitated out of solution. The development work leading up to the proposed method is discussed with reference to the relevant behaviour towards organic matter and the nitrate ion of activated carbon materials.The method has a limit of detection of 0.006 mg 1-1 N and a total standard deviation of 0.016 mg 1-l N at a nitrate concentration of 1.05 mg 1-1 N in potable water. No statistically significant difference was detected between the proposed method and an established automated method for a wide range of samples. Keywords : Nitrate determination ; water ; waste water ; ultraviolet spectro- Photometry ; activated carbon The various methods at present employed for the determination of nitrate in water fall into one of five main categories: the reduction of nitrate to ammonia; manual methods using chromogenic reagents; direct spectrophotometry ; ion-selective electrode methods; and reduction to nitrite.Of these techniques, one of the most reliable, simple and rapid is direct spectrophotometry in the ultraviolet (UV) region, but its range is limited by inter- ferences and the work described in this paper was intended to extend this range. The use of direct UV methods is widespread and especially suitable for waters of low organic content, although waters containing organic matter can be analysed by use of established correction factor technique~l-~ In this and previous ~ o r k , l - ~ “organic matter” is commonly assumed to be those materials responsible for related absorbances in the region of 200-300 nm.In this work, absorbances at 210 and 275 nm have been selected to indicate the presence of nitrate and “organic matter,” respectively. It should be pointed out however, that strictly the reference to “organic matter’’ means “materials absorbing at 275 nm.” We have used the absorbance at 275 nm as an indicator of the presence or absence of “organic matter’’ that could absorb also at 210 nm. The term “organic matter” is therefore used throughout the paper for brevity and because, as will be shown in the method validation section, it is believed that “organic matter” content is represented fairly accurately in the water samples of interest by “absorbance at 275 nm.” The inter-relationship of absorbances at 275 and 210 nm due to organic matter is based on observations of the similarity in absorption spectra of water samples in the region of 300 nm and below.For example,6 both synthetic solutions of humic and fulvic acid extracts and real samples illustrate well this inter-relationship, and we have also obtained UV spectra that support these findings. The correction factor techniques already mentioned involve the use of an arbitrary factor that corrects for the UV absorbance of organic matter at the wavelength selected for nitrate-ion determination. This approach cannot be used when the nitrate concentration is low and the organic content is high. The reason for such failures of the correction factor approach arises from the variability of the different organic compounds * Present address : North West Water Authority, Western Division, Merton House, Bootle, Merseyside, L20 3NH.838 Analyst, VoL.104 likelv to be present in different types of water. The variability of the correction factors and-the possible lowering of precision by the dilution required to bring the absorbances within the linear range of UV spectrophotometric analysis thus necessitate a non-arbitrary method with improved accuracy. Such a method is proposed, which removes not only the organic matter prior to absorbance measurement, but also some cationic interferences that normally affect the spectrophotometric determination of the nitrate ion. RENNIE, sUMNER AND BASKETTER: DETERMINATION OF NITRATE Methods of Dealing with Organic Interference In addition to the factor methods already briefly mentioned, three other methods have been proposed to deal with interferences by organic matter.7 These methods involve the chemical reduction of the nitrate ion, the coagulation of organic matter with aluminium sulphate and the adsorption of organic matter by activated carbon.Two methods were attempted for the elimination of nitrate by its reduction in a sample to ammonia. These result in a solution, the UV absorbance of which when subtracted from the absorbance of the unreduced sample gives the absorbance directly attributable to the nitrate ion. Both methods were attempted on samples of raw water and for the zinc - copper couple method on nitrate standard solutions also. In the reduction by a zinc - copper couple,2?* it was inferred that organic matter was also reduced as the absorbance at 275 nm was decreased, The other reduction method involved heating the raw water with hydrazine hydrate in a boiling water-bath and then boiling, after the addition of sodium hydroxide, to expel ammonia.On acidification, the resultant solution exhibited an interfering absorbance at 210 nm, which was shown to be due to undestroyed hydrazine. These procedures cannot therefore be used to estimate the absorbance at 210 nm due to species other than nitrate and hence to deduce the nitrate concentration. So far as the aluminium sulphate coagulation methodS~l0 is concerned, there is evidence7 that removal of organic matter is only approximately 85% and indeed the APHA publicationlo recommends coagulation for removal of colour but still retains a correction factor for the remaining dissolved organic matter that absorbs at 275 nm.Recently, Brown and Bellingerll proposed a method for improving the correction factor procedure in the presence of humic acids and also suggested the use of an anion-exchange resin for the removal of most of the UV-absorbing organic materials. The difficulties encountered in dealing with organic matter and the potential effectiveness of activated carbon, particularly in view of the recent paper by Slanina et aZ.,12 prompted us to concentrate on the investigation of activated carbon methods. The adsorption of organic matter by activated carbon is well known but a less appreciated fact is that there is some e ~ i d e n c e ~ ~ ~ ~ ~ ~ ~ that nitrate ions are removed from aqueous solutions by activated carbon and that the effect may be pH dependent.In fact, activated carbon has been recommended13 for removing dissolved colour at alkaline pH prior to nitrate determination with chromogenic reagents. Although Slanina et aZ.12 investigated a number of carbons and recommended a particular one, they did not indicate the behaviour of the other carbons. It was therefore necessary for our purpose to investigate the organic matter content, nitrate content as received and the extent of nitrate retention of about 20 types of activated carbon. It was found that most of the carbons tested contained nitrate and organic matter that was easily leached out, and all the carbons retained nitrate to variable extents (19444% retention) under acidic conditions.Nitrate retention tests were made after washing the carbons free of nitrate and/or organic matter. One of the materials, ADC 33 (Sutcliffe, Speakman & Co.), was in regular use at a treat- ment plant and earlier work had indicated that under alkaline conditions contamination could be removed and nitrate was not retained. The effect of altering the pH was investi- gated in more detail with this carbon. The tests consisted of adding aliquots of carbon to a water of known nitrate concentration and containing organic matter, at several pH values between 1.5 and 12.6, mixing for 5 min, removing the carbon by filtration through Whatman GF/C paper and reducing the pH to 1.5-1.9 by adding the same volume of mixed acid reagent to each test solution before measuring the absorbance at 210nm (for mixed acid reagent, see Reagents and Interference efects sections).The absorbances were compared with those of samples that had not been treated by the addition of carbon. The results (Table I) confirm the pH dependence of nitrate retention and organic matter adsorption; the nitrate retention appears to show a complex relationship with variation in pH but this was notSeptember, 1979 I N RAW, POTABLE AND WASTE WATERS BY UV SPECTROPHOTOMETRY 839 TABLE I EFFECT OF pH ON THE ADSORPTION PROPERTIES OF AN ACTIVATED CARBON (ADC 33) PH 1.5 3.0 5.8 7.3 10.4 12.0 12.6 Organic removal, yo 90 90 90 99 97 98 100 Nitrate-ion retention, % 41 59 24 63 57 0 0 investigated further. In the pH range 1.5-1.9, the variation of adsorption5 of nitrate solutions with pH is less than 7% of the absorbance reading and is therefore not significant in the present context.Removal of Organic Matter with Activated Carbon Methods investigated were (a) batchwise addition of powdered or granular activated carbons followed by filtration to remove the carbon, (b) use of a carbon column and (c) construction of a filter stack using materials impregnated with carbon. Firstly, a method was developed using ADC 33 activated carbon that consisted in membrane filtration of the sample and addition of powdered carbon (0.5 g) to 100 ml of filtrate adjusted to pH >12 by the addition of sodium hydroxide solution. This mixture was stirred for 5 min before removing the carbon by filtration. The pH of the filtrate was reduced to below 2 and the absorbance was measured at 210 nm against distilled water. There was no absorbance due to organic matter, i.e., at 275nm.A calibration graph was constructed using standards treated in the same manner. The drawbacks to this procedure were the need to weigh out the carbon, contamination of the glassware and the need for two filtrations. In an attempt to produce a less tedious method and to optimise the conditions used, a carbon column was prepared from granular carbon supported on a glass-wool plug. It was not possible to achieve a sufficiently long contact time for total removal of organic matter and so this approach was abandoned. Several materials impregnated with carbon, viz., filter-paper, fibreboard, woven fabric and polymer beads, were examined for organic matter and nitrate content and for the extent of nitrate retention under acidic conditions.It was found that these materials behaved in a similar manner to the granular activated carbons in that varying degrees of contamination with nitrate and/or organic matter were observed. Of the carbon filter media tested, an analytical-grade filter-paper (Schleicher & Schull No. 508 active carbon paper; Schleicher & Schiill, Dassel, West Germany; Anderman & Co. Ltd., East Molesey, Surrey) proved to be the most satisfactory with regard to the ease of construction of a filter stack (see Fig. l), the least cleansing required prior to use and the efficient removal of organic matter. I t was therefore decided to pursue a development of the method using the Schleicher & Schull paper under the alkaline conditions previously investigated with ADC 33 carbon.Preliminary tests with four, eight and sixteen layers of the carbon paper showed that sixteen layers were required in order to allow a sufficient contact time for the removal of organic matter from samples (the initial and residual absorbances at 275 nm were 0.152 and 0.004, respectively, using 10-mm cells). The extents of removal of organic matter with four and eight layers were 79 and goyo, respectively. At the same time tests with standard nitrate solutions showed that nitrate ion was not absorbed under alkaline conditions by the increased number of layers. Using this information we have developed the following proposed method using the filter assembly shown in Fig. 1.The extent of nitrate retention varied between 19 and 66%. Proposed Analytical Method Apparatus An ultraviolet spectrophotometer capable of measuring absorbances at 210 nm and a pair of matched ultraviolet-grade silica cells (path length 10 mm) were used. The filtration apparatus shown in Fig. 1, consisting of sixteen layers of 60 mm diameter Schleicher & Schiill No. 508 active carbon papers sandwiched between two 60mm diameter Whatman840 A n a l y s t , vol. 104 GF/C papers in a Carlson-Ford filter holder (Gallenkamp & Co. Ltd., London), was used in conjunction with a suitable vacuum source and a Biichner flask. To prepare a new carbon filter stack for use, wash with 400ml of 3.5% m/V sodium hydroxide solution followed by 200 ml of distilled water.This treatment gives reagent blank values of the order of 0.025 absorbance unit. Between batches of analyses, contact with a laboratory atmosphere may result in contamination of the filter stack with UV- absorbing substances and it may be necessary to clean the filter stack by the above alkaline procedure in order to maintain satisfactory reagent blank values. The top GF/C paper may be changed between samples if the filter exhibits significant headloss. The operational life of the prepared filter stack is dependent on the organic content of the samples; a typical capacity is 100 samples with an absorbance of 0.045 at 275 nm before organic breakthrough occurs. Glass bottles should be used for samples; these bottles and other glassware used for the method should be cleaned by treatment with concentrated sulphuric acid followed by thorough rinsing with distilled water.RENNIE, SUMNER AND BASKETTER: DETERMINATION OF NITRATE Section I elevation 80 ml capacity stainless- m- steel funnel -60 mm diameter GF/C ~ filter-papers 16 layers, 60 mm diameter, d+p Schleicher & Schull No. 508 active carbon ~ papers Filter base __ - Stainless-steel gauze Alkali-resistant bung (e.g., silicone rubber) for connection to 250-ml Buchner flask (vacuum required >/ 98 kPa) Fig. 1. Activated carbon filter assembly. Reagents Reagents of analytical-reagent grade are preferable unless otherwise stated. Distilled water should be used rather than de-ionised water, which could contain UV-absorbing materials derived from the ion exchangers and from organic matter present in the feedstock.I t is advisable to check that the reference distilled water does not contain materials that absorb at 210 nm. A 500-ml volume of the distilled water should be re-distilled from an all-glass apparatus and 200-, 50- and 150-ml sequential portions of distillate collected. Using the 50-ml portion in the reference cell, the other portions and the residue should have an absorbance reading of less than 0.01 for the original distilled water to be considered accept- ably free from UV-absorbing materials. Store in a polyethylene bottle (stable for about 3 months). 0.1 g of sulphamic acid in 500 ml of 5% V/V sulphuric acid. Prepare freshly by 50-fold dilution of a 100 mg 1-1 N stock standard solution (stable for 3 months) of potassium nitrate (0.721 8 g of dried potassium nitrate per litre).Dilute the standard solution as appropriate to produce 0.25, 0.5, 0.75, 1.0, 1.5 and 2.0 mg 1-1 N standard solutions. Borosilicate glass containers should be used. Sodium hydroxide solution, 3.5% m/V. Mixed acid reagent. Dissolve 5 Standard nitrate solution, 2 mg 1-1 N. This solution should be stored in borosilicate glass (stable for at least 2 months). Procedure than 2 mg 1-1 N of nitrate in a calibrated flask and mix. Add 5 & 0.1 ml of sodium hydroxide solution to 100 ml of sample containing not more Pass 30 ml of this solution throughSeptember, 1979 841 the filter and discard it, then filter 50ml of the solution and keep the filtrate. Pipette 40 ml of this filtrate into a 50-ml calibrated flask containing 5 ml of the mixed acid reagent, dilute to 50 ml with distilled water and measure the absorbance at 210 nm against water in the reference cell.Absorbances corrected for the reagent blank are then converted into milligrams of nitrogen per litre using a regressed equation from standards and a reagent blank treated in the same manner. A blank determination must be carried out with each batch of analyses by taking 100 ml of distilled water through the full procedure in place of the sample. Linear regression of the calibration graph gave a mean correlation coefficient of 0.9996 for a y = mx + c equation and the mean standard error of estimate was 0.016mg1-I N. An absorbance reading of about 0.4 is given by a 1 mg 1-1 N standard solution treated as described above.I N RAW, POTABLE AND WASTE WATERS BY UV SPECTROPHOTOMETRY The calibration graph is linear up to at least 2.0 mg 1-1 N. Validation of the Proposed Method Statistical evaluation of the method was carried out according to the procedures given by Cheeseman and Wilson1* (viz., precision of standards and samples and spiking recovery). The method was compared with an established method and several specific interference effects of substances known to absorb in the UV region were investigated. Precision and recovery tests The precision target for the determination of nitrate in potable water had been set at a total standard deviation of an individual determination of 5% of concentration or 0.01 mg 1-1 N, whichever was the greater. To test the performance of the proposed method against this target, duplicate analyses were carried out, on each of five days, of distilled water, 0.5 and 1.0 mg 1-1 N standards, treated water from Lamaload reservoir (an upland impounded reser- voir in the Macclesfield area fed by the River Dean) and treated water from Lamaload reservoir spiked with a 0.474 mg 1-1 N addition.The results obtained from the last two samples were used to calculate the spiking recovery. The results were analysed to derive the corresponding within-batch (sw), between-batch (sb) and total (st) standard deviations. The results are summarised in Table 11; the number of degrees of freedom were derived14 from duplicate analyses on each of five days and are given in parentheses. TABLE I1 PRECISION OF ANALYTICAL RESULTS Standard deviation*/mg 1-1 N A f , Mean concentration Solution SW s b S t found/mg 1-l N 0.00 mg 1-l N .. .. . . . . . . 0.001 (5) - - 0.01 1.00 mgl-l N . . . . .. . . . . 0.011 (5) N.S. (4) 0.017 (6) 1.00 0.50 mg 1-1 N . . .. . . . . . . 0.012 (5) N.S. (4) 0.019 (6) 0.50 Treated Lamaload watert . . . . . . 0.005 (5) 0.015 (4) 0.016 (4) 1.053 Treated Lamaload water + 0.474 mgl-l N 0.012 (5) 0 (4) 0.012 (7) 1.551 * Figures in parentheses are the degrees of freedom. N.S. indicates that the result is not statistically f The absorbance of “Treated Lamaload water” plus reagents but without carbon filtration is of the significant. order of 0.065 at 275 nm. Analysis of variance14 showed that in only one instance (the sample) was there a signifi- cant component of between-batch variability, possibly reflecting unusually consistent deter- minations within each of the batches.A limit of detection of 0.006mg 1-1 N was calculated by using the formula 2t2/2(sw), where t is Student’s single-sided t for 0.10 probability and sw is the within-batch standard deviation of the blanks. The spiking recovery was 105 ~f 1.1%, where 1.1% is the 95% confidence interval (equal to s t / 4 5 , where s is the total standard deviation of the spiking addition, t is Student’s double- sided t for 0.10 probability and there were five batches). It must be remembered that This easily satisfies a target for potable waters of 0.02 mg 1-1 N.842 Analyst, vol. 104 because the method involves what is effectively a non-specific UV absorbance characteristic, even if interferences are present they will probably not be detected by a simple spiking recovery test based on additive absorbances.RENNIE, SUMNER AND BASKETTER: DETERMINATION OF NITRATE Comparison with established method Samples of raw, potable and waste waters from throughout the North West Water Authority area were taken. These samples were carefully split between two bottles; one sample was analysed in the Authority’s Rivers Division, Warrington Laboratory, using an automated analyser for nitrate determination, and the other was analysed by the proposed method. Both samples were stored in a similar manner at 4 “C and the nitrate determinations carried out at the same time using the respective methods. The automated method consisted in the reduction of nitrate by means of a cadmium column and determination of the total nitrite using 1-naphthylethylenediammonium chloride - acid sulphanilamide reagent, the original nitrite concentration being subtracted to obtain the nitrite derived from the nitrate content.The performance characteristics of the auto- mated method were as follows: range, 0-10 mg 1-1 N ; total standard deviations, 0.038 and 0.080 mg 1-1 N at concentrations of 1.0 and 7.5 mg 1-1 N, respectively (with 19 degrees of freedom) ; spiking recovery, 1oo.4y0 at a concentration level of 3 mg 1-1 N; maximum possible bias, 2.7% in a UK inter-laboratory exercise involving 19 laboratories. The results obtained by the two methods and the absorbances at 275 nm before and after carbon treatment as an indication of the efficiency of removal of organic matter are sum- marised in Table 111.The results indicate that there is good agreement between the two methods for the wide range of sample types considered. The differences (UV method minus automated method) between the pairs of results in Table I11 were examined using Student’s t-test.14 The results were dealt with in two groups, chosen such that the variance within each group was constant. This subdivision corresponded to the degree of dilution, which conveniently divides the samples into “water supply samples and Crewe effluent” and “sewage works effluents excluding Crewe,” i.e., “low” and “high” dilutions, respectively. For each group the t-value was calculated using the equation where 3 is the mean of the differences, n is the number of pairs and s is the standard deviation of the differences between pairs. The results of the examination are summarised in Table IV, which shows that the calculated t-values for each group are less than the tabulated, double-sided Student’s t for 0.05 probability and the respective number of degrees of freedom (n - 1).This indicates that there is no evidence of a statistically significant difference between the two methods over the wide range of sample types considered. The 275-nm absorbance readings (Table I I I) without carbon filtration are relatively so high that few samples could be analysed with confidence using the direct UV method1°,15 with a factor correcting for the presence of organic matter. This conclusion is based on the assumption of a correction factor of 3, i.e., the absorbance due to organic matter at 210 nm is three times that at 275 nm, and using the absorbance at 210 nm of nitrate ion as 1 mg 1-1 N = 0.4 unit.As an example, from Table 111, the Lamaload raw water sample absorbance due to organic matter at 210nm (without carbon) would be 3 x 0.104 = 0.312; the total absorbance measured (without carbon) at 210nm was in fact 0.626. Now, by using the correction factor method, the net absorbance at 210nm would be 0.214, which gives a nitrate concentration of 0.79 mg 1-1 N. This is approximately 75% of the actual concentra- tion, thus showing how the use of an assumed correction factor is unreliable. The results (Table 111) therefore illustrate how the proposed method extends the applicability of the UV method for nitrate determination to samples that contain significant amounts of organic matter.It is pertinent here to discuss how the results in Table I11 may be used in support of the assumption made in the introduction concerning the inter-relationship of absorbance readings at 210 and 275 nm, defined for the present context as “organic matter” but understood to mean “UV-absorbing substances.” The results given in Table 111, which cover a wide range of sample types (and therefore it may be expected that the samples will contain different organic species), show that for samples for which the absorbance at 275nm is significantSeptember, 1979 843 before carbon filtration, the absorbance falls to zero after carbon filtration.This indicates (according to the above assumption) that the organic matter has been totally removed by the carbon. Now, if any species absorbing at 210 nm (other than nitrate) were present, the UV method would give a higher “apparent” nitrate concentration than the automated method, which is specific for nitrate and is free from bias. There is no such bias between the two methods (see Table IV) and so this validates the assumption that absorbances at 210 and 275 nm are inter-related such that absence of absorbance due to organic matter at 275 nm indicates absence of absorbance at 210 nm. Further evidence is given by the sample from Hooton Borehole (Table 111), which has a negligible organic matter content as indicated by the absorbance at 275 nm without carbon filtration.The agreement between the results of the UV and automated methods confirms the absence of organic matter (and any other UV-absorbing material) that absorbs at 210 nm. The 275-nm absorbance readings with carbon filtration (Table 111) show that there are no significant amounts of organic matter remaining in the filtrates, thus confirming the absence I N RAW, POTABLE AND WASTE WATERS BY l J V SPECTROPHOTOMETRY TABLE I11 COMPARISON OF RESULTS OBTAINED BY THE PROPOSED METHOD AND BY AN ESTABLISHED AUTOMATED METHOD FOR RAW AND POTABLE WATERS Sample* Raw surface waters- Lamaload . . Sutton Hall (1 T’ 1) . . Alwen . . . . . . Goyt . . . . . . Langthwaite (1 + 1) . . Cant Clough . . . . Worthington (1 + l j . . Llangollen Canal (1 + 1) Stocks . . . .. . Arnfield . . . . . . Treated surface waters- Sutton Hall (1 + 1) . . Lamaload . . * . Alwen . . . . . . Langthwaite . . . . Hooton (1 + 1) . . Slag Lane . . . . Borehole waters- Haydock (1 + 3) , . Sewage works final efluents f- Adderley (1 + 19) . . Bunbury (1 + 19) . . Haslington ( 1 + 9) . . Crewe (1 + 3) . . . . Elton (1 + 19) . . AND FINAL EFFLUENTS Nitrate content/mg 1-I N - Automated Proposed method? method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Little Budworth South (1 + 9) Doddington ( 1 + 19) . . . . Mickle Trafford (1 + 9) . . Thornton Hough ( 1 + 9) . . Capenhurst (1 + 9) . . . . Wrenbury (1 + 19) . . . . Audlem (1 + 19) . . . . 1.05 3.15 0.30 0.85 0.80 0.55 4.00 3.10 0.45 0.80 1.11 3.04 0.47 0.80 0.70 0.50 4.00 3.06 0.40 0.70 2.40 2.70 1.05 1.04 0.40 0.52 0.80 0.72 3.20 3.20 7.40 7.40 0.05 0.06 35.5 0.1 28.9 33.5 16.95 18.8 39.4 19.5 25.4 12.3 23.9 23.6 32.4 0.2 30.9 32.5 16.9 18.9 38.3 19.8 25.0 13.1 24.3 22.9 Absorbance a t 275 nm - Without carbon filtration 0.104 0.097 0.151 0.040 0.067 0.080 0.079 0.115 0.062 0.048 0.030 0.064 0.044 0.036 0.006 0.021 0.023 0.016 0.033 0.007 0.019 0.020 0.018 0.007 0.016 0.018 0.016 0.009 0.006 With carbon filtration 0.000 0.000 0.005 0.000 0.000 0.001 0.005 - 0.001 0.003 0.006 0.000 0.000 0.000 0.000 -0.001 0.001 0.004 0.000 0.000 0.000 0.000 0.000 0.002 0.003 0.003 0.000 - 0.002 0.000 0.000 * Figures in parentheses show the dilution used in the proposed method.Results by the automated method were supplied by the North West Water Authority, Rivers $ The results for sewage works final effluents obtained by the proposed method were supplied ’Division Laboratory, Dawson House, Warrington. by the North West Water Authority, Southern Division, Hurleston Laboratory.844 Analyst, vol.104 of interference from organic matter. Throughout the initial running of the proposed method, further measurements of absorbance at 275 nm with and without carbon were made, and showed that the high efficiency of removal of organic compounds on the carbon has been maintained. RENNIE, SUMNER AND BASKETTER: DETERMINATION OF NITRATE TABLE IV STATISTICAL ANALYSIS OF RESULTS IN TABLE I11 Sample group Water supply samples and Crewe effluent (low dilution) Number of pairs, n . . . . . . . . . . 18 Mean of differences, Z mgl-1 N .. .. . . 0.009 Tabulated t (0.05 probability) . . . . .. 2.11 Standard deviation of differences, s mg 1-1 N Calculated t* . . . . . . .. . . . . 0.37 . . 0.107 * Calculated t = Z&/s. Sewage works effluents excluding Crewe (high dilution) - 0.105 1.30 0.27 2.23 11 Interference efects To avoid interference from nitrite, sulphamic acid was employed as used in a draft sub- mitted to the Standing Committee of Analysts99l5; the pH was adjusted to 1.8 to eliminate interferences from hydroxyl and carbonate ions.1° To determine the effects of other inter- fering substances on the method, graphs of absorbance at 210 nm against concentration were obtained (using the experimental conditions of the proposed method) of potential water contaminants known to absorb in the region of 210 nm.The effects of certain concentrations of the adventitious contaminants are summarised in Table V and the concentration that gave an absorbance at 210 nm equivalent to 0.02 mg 1-1 N is defined as the interference limit for the proposed method (denoted by an asterisk) in Table V. The lack of an inter- ference effect, compared with that found by direct UV spectrophotometry, of the sodium salt of dodecylbenzenesulphonic acid is due to the effectiveness of removal of organic matter by the filter. Whereas Fez+ and Fe3+ interfere significantly in direct UV methods, such interference is eliminated in the proposed method as a result of the formation of insoluble TABLE V INTERFERENCE EFFECTS Interfering substance r A Species Chloride (Cl-) .. . . .. . . Bromide (Br-) . . .. . . . . . . Iodide (I-) . . .. . . . . . . Iron (Fe2+) . . . . .. .. . . Iron (FeS+) . . .. . . .. . . Dichromate (Cr20,2-) . . . . . . . . Manganese (Mn2+) . . . . . . . . Dodecylbenzenesulphonic acid, sodium salt 1 Concentration/ mg 1-’ 2 500* 5 000 1.0* 2.0 0.65* 1.30 13.5 27 1ooot 1 ooot 0.2 0.4 0.15* 0.30 100 1ooot 1ooot 3.5 7.0 Interference effect/mg 1-’ N With Without carbon filtration carbon filtration 0.02 0.02 0.06 0.06 0.02 0.02 0.04 0.04 0.02 0.02 0.05 0.05 (0.02 (0.02 (0.02 0.08 <0.02 1.4 (0.02 <0.02 <0.02 0.08 (0.02 1.75 0.02 0.02 0.08 0.08 (0.02 <0.02 (0.02 0.4 <0.02 (0.02 (0.02 0.06 (0.02 1.8 A I \ * Indicates “interference limit.” f Indicates highest concentration investigated.September, 1979 IN RAW, POTABLE AND WASTE WATERS BY UV SPECTROPHOTOMETRY 845 hydroxides at the elevated pH, the precipitates being removed by the GF/C paper on the filter.I t is apparent that the interference effects of anions are not reduced by carbon treatment. This effect could indicate that an anion-exchange mechanism is responsible for the retention of nitrate (and other) anions by activated carbon under neutral or acidic conditions. In the presence of alkali, such anion-exchange sites may not be available and so nitrate, chloride, bromide, etc., pass through unhindered, a situation that is analogous to “anion slip” and “regeneration” of anion-exchange resins. Conclusions The precision of the proposed method is satisfactory and the results for water samples, when compared with those obtained by the automated method, show good agreement.The method is less tedious and subject to fewer interferences than methods using chromogenic reagents, and is therefore more suitable for a wide variety of samples. The method is more economical on capital and running costs than an automated method and is therefore particu- larly recommended for small laboratories and low-throughput analyses. The authors thank their colleagues in the North West Water Authority, particularly Messrs. P. Morries, J. Collins and M. D. Nicholson, for useful discussions and for comparative inter-laboratory evaluation work, and Mr. J. Heron of the Freshwater Biological Association, Windermere, and Mrs. L. Newman, of the Water Research Centre, Information Services, for literature work. They are also grateful to Mr. G. Ainsworth, Director of Scientific Services, North West Water Authority and Mr. N. H. Girnson, Manager, Southern Division, North West Water Authority, for permission to publish this paper. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. References Hoather, R. C., and Rackham, R. F., Analyst, 1959, 84, 548. Morries, P., Proc. SOC. Wat. Treat. Exam., 1971, 20, 132. Sekiguchi, K., and Takishima, T., Nippon Kagaku Kaishi, 1975, 4, 642. Sekiguchi, K., Nippon Kagaku Kaishi, 1976, 10, 1553. Soares, M. I. V., Pereira, P. G. S., and Antunes, A. M., Revta Port. Quim., 1971, 13, 151. Wilson, A. L., J . Appl. Chem., 1959, 9, 501. Waters, W. F., Proc. Soc. Wat. Treat. Exam., 1964, 13, 298. “Approved Methods for the Physical and Chemical Examination of Water,” Institution of Water Engineers, London, 1960, p. 21. Cawse, P. A., Analyst, 1967, 92, 311. American Public Health Association, American Water Works Association and Water Pollution Control Federation, “Standard Methods for the Examination of Water and Wastewater,” Fourteenth Edition, American Public Health Association, New York, 1976, p. 420. Brown, L., and Bellinger, E. G., Wat. Res., 1978, 12, 223. Slanina, J., Lingerak, W. A,, and Bergman, Id., 2. Aitalyt. Chem., 1976, 280, 365. “Methods of Chemical Analysis Applied to Sewage and Sewage Effluents,” HM Stationery Office, Cheeseman, I<. V., and Wilson, A . L., “Manual on Analytical Quality Control for the Water “Methods for Examination of Water and Associated Materials. Nitrate in Some Nonsaline Waters London, 1956, p. 22. Industry,” Water Research Centre, Medmenham, 1978, TR66. and Effluents by Direct UV Spectrophotometry,” HM Stationery Office, London, in preparation. Received October 4th, 1978 Accepted April 9th, 1979

ISSN:0003-2654    

DOI:10.1039/AN9790400837

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

846 Analyst, September, 1979, Vol. 104, pp. 846-852 Combined Gas Chromatography - Chemical= ionisation Mass Spectrometry of Some Phthalate Esters J. B. Addison Atlantic Regional Laboratory, National Research Couvzsil of Canada, 141 1 Oxford Street, Halifax, N.S., B3H 321, Canada A sample mixture of seven phthalate esters was analysed using combined gas chromatography - chemical-ionisation mass spectrometry (GC - CIMS) . Separation of the various components of the mixture was effected by gas chromatography and subsequent identification by chemical-ionisation mass spectrometry using methane and isobutane as reagent gases. Comparison of electron-impact (EI) spectra and the CI spectra was under- taken in order to illustrate the advantage of CIMS over EIMS in identifying these phthalate esters.CIMS with isobutane gives abundant quasi-molecular ions, [M + HI+, with no adduct ions formed, in contrast to CIMS with methane, and thus provides a means of distinguishing between isomeric phthalate esters. Keywovds : Phthalate estev analysis ; gas chvovnatogvaphy - chemical-ionisation mass spectvometvy No ionisation technique since electron impact (EI) has had as great an acceptance and use in mass spectrometry as chemical ionisation (CI) and the quadrupole mass spectrometer was the first instrument reported that utilises this technique for gas chromatography - mass spectrometry (GC - MS) work.1,2 The use of GC - EIMS for the separation and elucidation of the structure of phthalate esters has been r e p ~ r t e d , ~ and recent work has shown that these compounds are found in the envir~nment.~-~ The use of CIMS is meanwhile being increasingly applied as an aid to structural elucidation by virtue of the prominence of quasi-molecular ions, [M + HI+, and simple fragmentation patterns in the resulting Most of the CI work carried out so far has employed the direct insertion probe technique in identifying phthalate esters.1° This paper presents results obtained by the use of CIMS coupled with GC to obtain representa- tive mass spectra including quasi-molecular ions, [PI + HI+, and other pertinent mass fragments at source temperatures and reagent gas pressures that unequivocally identify the components of typical phthalate ester sample mixtures, and the technique could be used on components of a mixture of phthalate esters separated by gel filtration from lipids or bio- logical and environmental materiakll Experimental All phthalate esters were obtained from Analabs (North Haven, Conn., USA) with a commercial purity of over 98%.Distilled diethyl ether was used to dissolve the esters for GC - CIMS analysis. A mixture of seven phthalate esters (total concentration 100 ng p1-l) was analysed on a Finnigan, Model 4023, system, which includes a Finnigan, Model 4000, quadrupole GC - MS system equipped with dual EI and CI ion sources and a Finnigan Incos data system. Chromatographic separations were achieved using a 1.8-m glass column packed with 3% OV-1 on Chromosorb Q (100-120 mesh) interfaced to the mass spectro- meter via an all-glass jet separator maintained at 280 "C.The reagent gas pressure was regulated at 0.35-0.45 Torr and the injection port temperature was maintained at 220 "C. The temperature programming parameters were as follows : initial temperature, 150 "C for Zmin, then programmed to a final temperature of 240 "C at the rate of 5 "Cmin-l; the final hold time was 5 min and the helium carrier gas flow-rate was 30 ml rnin-l. Methane and isobutane reagent gases were introduced into the mass spectrometer source as make-up gases through a solenoid valve; methane could be used as a carrier gas.ADDISON (a 1 x2 - QI:::::: 847 I I m k Fig. 2. Mass spectra of dimethyl phthalate: (a) EI; (b) CI with methane; and (c) CI with isobutane.848 ADDISON : COMBINED GAS CHROMATOGRAPHY - CHEMICAL- Analyst, VOZ. 104 In the identification of phthalate esters in the environment, the primary interest is to determine the relative molecular mass of the compounds in a sample mixture.Conventional GC - EIMS of these compounds gave weak molecular ions, or no molecular ions with the higher homologues, thus making the specific identification of these phthalate esters from their EI spectra difficult or impossible. Figs. 2-8 clearly show the advantage of GC - CIMS over GC - EIMS for the analysis of these compounds. The former technique provides excellent confirmation of the relative molecular masses. The CI spectra indicate quasi-molecular ions corresponding to the various esters. This result was expected, as the direct insertion probe work by Fales et aZ.10 has shown that at a source temperature of 150 "C and high reagent gas pressures of about 0.8- 1.0 Torr, strong quasi-molecular ions, [M + HI+, were produced with little breakdown of these ions.CI spectra obtained with methane show quasi-molecular ions, [M + HI+, together with adduct ions that sometimes correspond to relative molecular masses of higher homologues, which might therefore interfere with the identification of chromatographically separated components of a sample mixture of phthalates. For example, butyl phthalate produced significant fragment ions at m/e 279 [M + HI+ and 307 [M + 27]+, with the latter adduct corresponding to the quasi-molecular ion of dipentyl phthalate. 50 0 x2 13 a, [M+H] + I . 1 1 . 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 /x2 - (C) 1 [M+H]+ I I I I I I Fig. 3. Mass spectra of diethyl phthalate: (a) EI; (b) CI with methane; and (c) CI with isobutane.CI with isobutane, however, produced far fewer peaks and more intense protonated mole- cular ions without interfering adduct ions, thus making CI spectra obtained with isobutane much easier to interpret than the corresponding CI spectra obtained with methane, and with sufficient information for the identification of these phthalate esters. The conditions under which these CI spectra were collected suggest an advantage in using isobutane as reagent gas in phthalate ester analysis; this observation has also been made in direct insertion probe CI work. Isobutane provides reactant ions of lower energy upon ionisation and therefore exhibits lower exothermic ion - molecule reactions, with the result that fewer fragment ions are produced, which thereby enhances the abundances of ions in the relative molecular mass region concerned.September, 1979 IONISATION MASS SPECTROMETRY OF SOME PHTHALATE ESTERS 50 0 - 849 (4 x2 - [M+Hl+ I ‘ I 1 - I ’ .r - l I I I ‘ # [ I I I I , 1 I - (a 1 - x2 COOC4 Hg COOC4 Hg (6) x2 I . - I. 1 . ,.& , I , ,_ ,\ , . , [M+H] + I I , l mle Fig. 5. Mass spectra of dibutyl phthalate: (a) EI; (b) CI with methane; and (c) CI with isobutane.850 50 . (C) ADDISON : COMBINED GAS CHROMATOGRAPHY - CHEMICAL- Analyst, VoZ. 104 x2 [M+Hl* (6) x2 [ M+H] + I ) . lI . , I ; I . . I .l I . , . , I. . . , 1 ,L . . 0 I I l , ' I . , I 1 1 1 1 40 100 200 mle 300 400 Fig. 7. Mass spectra of di(2-ethylhexyl) phthalate: (a) E I ; (b) CI with methane; and (c) CI with isobutane.September, 1979 85 1 CI spectra obtained with methane and isobutane for dimethyl phthalate and diethyl phthalate show that the most abundant fragments are m/e 163 and 177, corresponding to the loss of OCH, and OC,H,, respectively.The fragment m/e 149 was the most abundant ion in the CI spectra of the other phthalate esters, except for the CI of dioctyl phthalate with isobutane, which gives the quasi-molecular ion [M + HI+ as the most abundant ion. Molecular adducts formed in CI with methane are mainly of the form [M + C,H,]+, [M + C,H,]+ and [M + HI+ as expected when methane is confined to the source chamber of the mass spectrometer at a high pressure.12 Although the adducts formed could interfere with interpretation, as explained above, they could be used as a parity check on particular quasi-molecular ions.IONISATION MASS SPECTROMETRY OF SOME PHTHALATE ESTERS 50 0 40 100 200 mle 300 400 Fig. 8. Mass spectra of dioctyl phthalate: (a) EI; (b) CI with methane; and (c) CI with isobutane. CI of dioctyl phthalate with methane illustrates the case where the spectrum of a com- pound exhibits fragmentation that does not follow the simple scheme of functional group elimination. In contrast to CI with methane, the CI spectrum of dioctyl phthalate with isobutane shows an abundance of quasi-molecular ions and no interference from adducts, therefore making it easy to detect and clarify the presence of ions in the molecular region even with the high GC and manifold temperature requirements.Hence the isomeric dioctyl phthalate and di(2-ethylhexyl) phthalate could be distinguished on the basis of their CI mass spectra obtained with isobutane. Direct insertion probe CI of di(2-ethylhexyl) phthalate at a source temperature of 150 "c and a pressure of about 1 Torr is reportedlo to give strong [M + HI+ ions with both methane and isobutane reagent gases, but no adducts were observed for this GC-CIMS study at 270 "C and reagent gas pressures of 0.35-0.45 Torr. This observation seems to suggest that the formation of adduct ions is temperature dependent at a constant reagent gas pressure. Also, the above low temperature - high reagent pressure probe CI conditioii gave a quasi-molecular ion with 100% relative abundance for di(2-ethylhexyl) phthalate. The GC - CIMS work gave a weak protonated molecular ion and could be due to the high source temperature used for this work.An increase in temperature is known to cause a decrease in CI [M + H]+ ion intensity13; hence, considering that all conditions are satisfactory for chromatographic separations, the temperature requirements for separation dictate the852 ADDISON operating temperatures of the interface and manifold of the mass spectrometer. Although protonation of dicarboxylic acids could be achieved under mild probe CI conditions, the results presented show that protonation could also occur with stable species being formed at high GC - CIMS temperature condtions. Under these conditions, isobutane is highly recommended as the reagent gas for phthalate esters.TABLE I RETENTION TIMES AND RELATIVE ABUNDANCES OF QUASI-MOLECULAR IONS Compound Dimethyl phthalate Diethyl phthalate Diisobutyl phthalate Dibutyl phthalate Dipentvl phthalate .. .. . . . . . . Relative abundance, % r A \ Retention time/ [M + HI+, CI CI . . 0.6 195 3.8 33.2 . . 2.3 223 6.8 37.9 . . 5.0 279 7.8 29.3 . . 6.0 279 8.3 22.2 .. 7.9 307 9.4 18.3 min m/e with methane with isobutane Dii2-ethyihexyl) phthalate , . 11.9 391 6.5 12.9 Dioctyl phthalate . . .. 15.5 391 4.7 100 Table I gives the relative intensities of the quasi-molecular ions, [M + HI+. Other fragment ions are formed from the breakdown of [M + HI+, as reported by workers using the magnetic probe CI technique.13 Elimination of water caused by bifunctional inter- action in protonated dicarboxylic acids1* was not observed in this work; the reason might be that the sample pressures were kept below the normal CI running conditions, and there- fore no protonated dimers were formed.I am grateful to the National Research Council of Canada for financial support and to Mr. Dale Johnson for drawing the figures. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. References Arsenault, G. P., Dolhun, J. J., and Biemann, K., Chem. Commun., 1970, 944. Story, M. S., Paper presented a t the 20th Annual Conference on Mass Spectrometry and Allied Blum, W., “Application Tips,” Finnigan Corp., Sunnyvale, Calif., 1972, p. 42. Blumer, M., Contam. Control, 1965, 4, 13. Chem. Engng News, Sept. lath, 1972, 14. Mayer, F. L., Stalling, D. L., and Johnson, J. L., Nature, Lond., 1972, 238, 411. Field, F. H., and Munson, M. S. B., J . A m . Chem. SOG., 1965, 87, 2289. Field, F. H., and Munson, M. S. B., J . A m . Chem. SOG., 1966, 88, 4337. Field, F. H., J . Am. Chem. Soc., 1969, 91, 2827 and 6334. Fales, H. M., Milne, G. W. A,, and Nicholson, R. S., Analyt. Chem., 1971, 43, 1785. Baker, R. W. R., J . Chromat., 1978, 154, 3. Vander Velde, G., and Ryan, J. F., J . Chromat. Sci., 1975, 13, 322. Week, D. P., and Field, F. H., J . Am. Chem. SOL, 1970, 92, 1603. Grmneberg, T., Org. Mass Spectrom., 1977, 12, 769. Topics, Dallas, Texas, June 4-9th, 1972. Received March 20th, 1979 Accepted April 20th, 1979

ISSN:0003-2654    

DOI:10.1039/AN9790400846

出版商:RSC    

年代:1979

数据来源: RSC