摘要:

THE ANALYSTTHE ANALYTICAL JOURNAL OF THE CHEMICAL SOCIETYEDITORIAL ADVISORY BOARD*Chairman: J. M. Ottaway (Glasgow)R. Belcher (Birmingham)L. J. Bellamy, C.B.E. (Wa/tham Abbey)L. S. Birks (U.S.A.)E. Bishop (Exeter)L. R. P. Butler (South Africa)E. A. M. F. Dahmen (The Netherlands)A. C. Docherty (Billingham)D. Dyrssen (Sweden)W. T. Elwell (Birmingham)J. Hoste (Belgium)H. M. N. H. Irving (Leeds)M. T. Kelley (U.S.A.)W. Kemula (Poland)'J. H. Knox (Edinburgh)G. W. C. Milner (Harwell)*H. J. Cluley (Wembley)'P. Gray (Leeds)G. H. Morrison (U.S.A.)H. W. Nurnberg (West Germany)E. Pungor (Hungary)D. I. Rees (London)"R. Sawyer (London)P. H. Scholes (Sheffield)"W. H. C. Shaw (Greenford)S. Siggia (U.S.A.)"D. Simpson (Thorpe-le-Soken)A. A.Smales, O.B.E. (Harwell)"A. Townshend (Birmingham)A. W a Is h (Australia)T. S. West (Aberdeen)A. L. Wilson (Medmenham)P. Zuman (U.S.A.)"G. E. Penketh (Billingham)*J. Whitehead (Stockton-on- Tees)*Members of the Board serving on The Analyst Publications CommitteeREGIONAL ADVISORY EDITORSDr. J. Aggett, Department of Chemistry, University of Auckland, Private Bag, Auckland, NEW ZEALAN D.Professor G. Ghersini, Laboratori CISE, Casella Postale 3986, 201 00 Milano, ITALY.Professor L. Gierst, Universitk Libre de Bruxelles, Facult6 des Sciences, Avenue F.- D. Roosevelt 50,Professor R . Herrmann, Abteilung fur Med. Physik., 63 Giessen, Schlangenzahl 29, W. GERMANY.Professor W. A. E. McBryde, Faculty of Science, University of Waterloo, Waterloo, Ontario, CANADA.Dr.W. Wayne Meinke, KMS Fusion Inc., 3941 Research Park Drive, P.O. Box 1567, Ann Arbor,Dr. I. Rubeika, Geological Survey of Czechoslovakia, Kostelni 26, Praha 7, CZECHOSLOVAKIA.Dr. J. R&iEka, Chemistry Department A, Technical University of Denmark, 2800 Lyngby, DENMARK.Professor K. Saito, Department of Chemistry, Tohoku University, Sendai, JAPAN.Dr. A. Strasheim, National Physical Research Laboratory, P.O. Box 395, Pretoria, SOUTH AFRICA.Bruxelles, BELGIUM.Mich. 48106, U.S.A.Published by The Chemical SocietyEditorial: The Director of Publications, The Chemical Society, Burlington House,London, WIV OBN. Telephone 01 -734 9864. Telex No. 268001Advertisements: Advertisement Department, The Chemical Society, Burlington House, Piccadil!y,London, W1 V OBN. Telephone 01 -734 9864Subscriptions (non-members): The Chemical Society, Distribution Centre, Blackhorse Road,Letchworth, Herts., SG6 1 HNVolume 103 No 1233 December 1978@ The Chemical Society 197

ISSN:0003-2654    

DOI:10.1039/AN97803FX045

出版商:RSC    

年代:1978

数据来源: RSC

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ANALAO 103 (1 233) 1 185-1 280 (1 978)ISSN 0003-2654December 1978THE ANALYSTTHE ANALYTICAL JOURNAL OF THE CHEMICAL SOCIETYCONTENTS11 8511 951199Continuous Monitor for Measuring Toxic Gases in Steelworks Atmospheres-H. J. Boniface and R. H. JenkinsGas-chromatographic Determination of Phosphine i n Ambient Air-A. Vinsjansenand K. E. ThraneRapid Method for the Determination of Benzo(a)pyrene in the ParticulatePhase o f Cigarette Smoke by High-performance Liquid Chromatographywith Fluorimetric Detection-N. M. Sinclair and B. E. FrostReproducible Method for the Preparation and Operation of Microwave-excitedElectrodeless Discharge Lamps for Use i n Atomic-fluorescence Spectro-metry. Additional Experience w i t h Cadmium Lamps-R. G. Michel, J. M.Ottaway, J.Sneddon and G. S. FellSelective Spectrophotometric Determination of Trace Amounts o f MolybdenumWith 2.2’-Dihydroxybenzophenone Thiosemicarbazone-J. M. LopezFernandez, D. Perez-Bendito and M. Valcarcel3,3’-Dimethylnaphthidinedisulphonic Acid as a Selective and Sensitive Reagentfor the Spectrophotometric Determination o f Vanadium(V) and i t sApplication t o Vanadium-bearinbg Minerals and Alloys-H. Sanke Gowda andR. Shakunthala1221 Modified Fenton‘s Reagent for the Destruction o f Organic Matter in theSpectrophotometric Determination of Lead, Cadmium and Mercury inSodium Carboxymethylcellulose-R. Cela Torrijos and J. A. Perez- BustamanteSpectrophotometric Determination o f Amidopyrine and Antipyrine by Charge-transfer Complex Formation-H. Abdine, M.Abdel-Hady Elsayed, I . Chaabanand M. E. Abdel-Hamid1233 Determination o f Trace Organic Pollutants in Water by Proton MagneticResonance Spectroscopy of Solvent Extracts-J. K. Becconsall1239 Separation o f Uranium from Seawater by Adsorbing Colloid Flotation-W. J.Williams and A. H. Gillam1244 Determination of Lead in Paint by Differential-pulse Anodic-stripping Voltam-metry-P. C. Lai and K. W. Fung1249 High-frequency Microtitrimetric Determination of Acidic and Basic Constit-uents in Lubricating Oils. Part 1. Determination of Total Acid Number-T. FernBndez, J. M. Rocha, N. Rufino, A. Garcia Luis and F. Garcia Montelongo1204121 0121 51227SHORT PAPERSShape of the Atomic-absorption Calibration Graphs for Chromium Using anAir - Acetylene Flame-K. C. ThompsonDetermination of Furazolidone i n Pig and Poultry Feeds by High-performanceLiquid Chromatography-A. D. Jones, E. C. Smith, S. G. Sellings and I . W. BurnsFluorimetric Determination of Triphenyltin Compounds in Water-S. J. Blundenand A. H. ChapmanFreezing-point Data on Aqueous Solutions o f Sucrose and Sodium Chloride andthe Hortvet Test: a Reappraisal-J. H. Prentice12581262126612691274 Book Reviews1277 Instructions t o AuthorsSummaries o f Papers in this Issue-Pages iv, v, vi, vii, viii, i xPrinted by Heffers Printers Ltd Cambridge EnglandEntered as Second Class at New York, USA, Post Offic

ISSN:0003-2654    

DOI:10.1039/AN97803BX047

出版商:RSC    

年代:1978

数据来源: RSC

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December, 19 7s THE ANALYST ...111 RS solvents forUV and IRspedrophotome t ryAcetone UV and IRAcetonitrile UV and IRBenzene UV and IRCarbonium sulfideUV and IRCarbonium tetrachloridUV and IRChloroform UV and IRCyclohexane UV and IRN-N-DimethylformamideUV and IRDichloroethane IRDimethylsulfoxide UVDioxane UVEthyl acetate IREthyl alcohol UV9 5 O and abs.Ethyl ether UVn-Heptane UVn-Hexane UVlsoctane UV and IRlsopropyl alcohol UVMethylene chlorideUV and IRMethyl Alcohol UVn-Pentane UVPotassium bromide IRTetrachloroet hylene IRTetra hydrof uranUV and IRToluene IRTrichloroetilene IRCHEMICALS DIVISIONP.O. Box 3996/20159 Milano/Via lmbonati 24 (Italy)Telex Erba Mi 36314lTel. 6995$$ MONl EDISON S p A REG. TRADEMARiv SUMMARIES OF PAPERS I N THIS ISSUE December, 1978Summaries of Papers in this IssueContinuous Monitor for Measuring Toxic Gases inSteelworks AtmospheresPortable instruments are described for the continuous determination ofsulphur dioxide and carbon monoxide in air.For sulphur dioxide, the gasis absorbed in an aqueous electrolyte containing an acid - base indicator.Resulting changes in the indicator colour are monitored photoelectricallyand the detector current, after amplification, is used to titrate the reactionproduct. The titration current can be used to calculate the gas concentrationa t a given flow-rate, on a coulometric basis. The changing current is displayedon a chart recorder, which provides a record of concentration against time.Carbon monoxide, after conversion into carbon dioxide, is determined in asimilar manner using a partially aqueous electrolyte.Ranges of 100 and 20 mg m-3 for sulphur dioxide and 250 and 50 p.p.m.by volume for carbon monoxide are provided.These ranges cover theThreshold Limit Values for the gases. The instruments, which are batterypowered, can be left unattended on-site for periods of at least 8 h. They havebeen used successfully for occupational hygiene studies in steelworks environ-ments.Keywords : Continuous gas monitor ; sulphur dioxide ; carbon monoxide ; toxicgases ; steelworks atmospheresH. J. BONIFACE and R. H. JENKINSBritish Steel Corporation, Welsh Laboratory and Strip Mill Products, Port Talbot,Glamorgan.Analyst, 1978, 103, 1185-1194.Gas-chromatographic Determination of Phosphine in Ambient AirAir samples taken in the neighbourhood of a chemical plant manufacturingdicyanamide from calcium carbide, of which process phosphine is a by-product,were collected in polyester bags and brought to the laboratory for analysis.A gas chromatograph equipped with a nitrogen - phosphorus-selective detectorwas used. The working range was 0.5-5 p.p.b.(parts per lo9) V/V and thedetection limit was 0.03 p.p.b. V / V . The stability of the samples was invest-igated, and different calibration gases were compared. The results obtainedwith this method in the field agreed with results obtained with a continuousflame photometer.Keywords ; Phosfihine determination ; ambient air analysis ; gas sampling bag ;gas chromatografihyA.VINSJANSEN and K. E. THRANENorwegian Institute for Air Research, P.O. Box 130, N-2001 Lillestram, Norway.Analyst, 1978, 103, 1195-1198December, 1978 SUMMARIES OF PAPERS IN THIS ISSUERapid Method for the Determination of Benzo[a]pyrene in theParticulate Phase of Cigarette Smoke by High-performanceLiquid Chromatography with Fluorimetric DetectionA method is described for the rapid determination of benzo[a]pyrene in theparticulate phase of cigarette smoke. The particulate matter from fivecigarettes is fractionated on Florisil and a concentrated fraction injectedon t o a high-performance liquid chromatography column of Partisil.Benzo[a]pyrene is detected in the eluate fluorimetrically. Quantification isachieved by means of a standard-additions method.VKeywords ; Benzo[a]pyrene determination ; cigarette smoke ; high-performanceliquid chromatography ; jluorimetvic detectionN.M. SINCLAIR and B. E. FROSTCarreras Rothmans Limited, Research Division, Nevendon Road, Basildon, Essex.Analyst, 1978, 103, 1199-1203.Reproducible Method for the Preparation and Operation ofMicrowave- excited Electrodeless Discharge Lamps for Use inAtomic-fluorescence Spectrometry. Additional Experience withCadmium LampsResults are presented of experience with a previously reported method forthe preparation and operation of cadmium microwave-excited electrodelessdischarge lamps. The method can be used while employing alternativemicrowave-excitation equipment but it is necessary to alter the levels of thefactors that control the preparation and operation of the lamps.Lamps ofidentical performance are produced with the alternative equipment. A meanatomic-fluorescence detection limit of 0.07 p g 1-1 with a relative standarddeviation of 25% was achieved for 12 cadmium lamps prepared in two batchesof six with a time interval of 4 months between them.Keywords : A tomic-Puorescence spectrometry ; microwave-excited electrodelessdischarge lamps ; cadmium lawpsR. G. MICHEL, J. M. OTTAWAY and J. SNEDDONDepartment of Pure and Applied Chemistry, University of Strathclyde, CathedralStreet, Glasgow, G1 1XL.and G. S . FELLDepartment of Clinical Biochemistry, Royal Infirmary, Glasgow, G4 OSF.Analyst, 1978, 103, 1204-1209.Selective Spectrophotometric Determination of Trace Amounts ofMolybdenum with 2,2’-Dihydroxybenzophenone Thiosemicarbazone2,2’-Dihydroxybenzophenone thiosemicarbazone reacts with molybdenumin solutions in mineral acids in the presence of tin(I1) chloride to produce ared 1 : 1 complex (Amax.= 500nm, E = 3.3 x 1031mol-1 cm-l). Thiscomplex is used for the spectrophotometric determination of trace amountsof molybdenum. The interferences of many metallic ions have beenexamined and a procedure for the determination of molybdenum in syntheticmixtures is proposed. Interfering metals can be removed by a preliminaryextraction with dithizone.Keywords : Molybdenum determination ; visible spectrophotometry ;2,2’-dihy droxybenzop Jaenone thiosemicarbazoneJ.M. LOPEZ FERNANDEZ, D. PEREZ-BENDITO and M. VALCARCELDepartment of Analytical Chemistry, Faculty of Sciences and E.T.S.I.A., Universityof Cbrdoba, Cbrdoba, Spain.Analyst, 1978, 103, 1210-1214vi SUMMARIES OF PAPERS I N THIS ISSUE3,3‘- Dimethylnaphthidinedisulphonic Acid as a Selective andSensitive Reagent for the Spectrophotometric Determination ofVanadium(V) and its Application to Vanadium- bearingMinerals and Alloys3,3’-Dimethylnaphthidinedisulphonic acid is proposed as a selective andsensitive reagent for the spectrophotometric determination of vanadium(V) .It forms a violet coloured species with vanadium(V) in 8-13 M orthophosphoricacid medium. A 2-fold molar excess of reagent is necessary for the fulldevelopment of the colour.The violet species exhibits an absorption maxi-mum a t 555 nm with a molar absorptivity of 1.94 x lo4 1 mol-1 cm-l.Sandell’s sensitivity is 2.6 ng cm-2. Beer’s law is obeyed for the range0.08-3.5 p.p.m. of vanadium(V) with an optimum concentration range of0.1-3.1 p.p.m. The proposed method offers the advantages of simplicity,high sensitivity, good selectivity and the opportunity t o carry out the deter-mination at room temperature without the need for an extraction step. Themethod has been used successfully for the determination of vanadium inilmenite and vanadium steels.Keywords : Vanadium( V ) determination ; ilmenite ; vanadium steels ; spectro-December, 1978photometry; 3,3’-dimethylnaphthidinedisulphonic acidH.SANKE GOWDA and R. SHAKUNTHALADepartment of Post-graduate Studies and Research in Chemistry, Manasa Gangotri,University of Mysore, Mysore-570 006, India.Analyst, 1978, 103, 1215-1220.Modified Fenton’s Reagent for the Destruction of Organic Matterin the Spectrophotometric Determination of Lead, Cadmium andMercury in Sodium CarboxymethylcelluloseA modification of Fenton’s reagent has been applied successfully to the rapidand safe mineralisation of samples of up to 10 g of sodium carboxymethyl-cellulose in order to determine lead, cadmium and mercury by spectrophoto-metric methods based on the use of dithizone. Recoveries and reproducibilitywere satisfactory a t the 0.05-1.5 p.p.m. levels.Keywords : Wet oxidation ; modi$ed Fenton’s reagent ; trace metal deter-mination ; sodium carboxymethylcellulose analysis ; spectrophotometryR.CELA TORRIJOS and J. A. PEREZ-BUSTAMANTEUniversidad de Sevilla, Facultad de Ciencias de CAdiz, Departamento de QuimicaAnalitica, Duque de Najera s/n, CAdiz, Spain.Analyst, 1978, 103, 1221-1226.Spectrophotometric Determination of Amidopyrine andAntipyrine by Charge- transfer Complex FormationThe charge-transfer complex formed by the interaction between the electronacceptor dichlorobenzoquinone and an electron donor amidopyrine (amino-phenazone) or antipyrine (phenazone) was adopted for the assay of thesedrugs in tablets. The conditions suitable for the complex formation weredetermined. The determination o f the molar ratio of the reactants and ofthe association constant are also described. The method can be convenientlyapplied to assay individual dose units of amidopyrine and antipyrine withgood accuracy and precision.Keywords : Amidopyrine determination ; antipyrine determination ; dtraviolet -H. ABDINE, M. ABDEL-HADY ELSAYED, I. CHAABAN and M. E. ABDEL-HAMIDDepartment of Pharmaceutical Analytical Chemistry, Faculty of Pharmacy, Uni-versity of Alexandria, Alexandria, Egypt.Analyst, 1978, 103, 1227-1232.visible spectrophotometry ; tablets ; charge-transfer complex formatio

ISSN:0003-2654    

DOI:10.1039/AN97803FP113

出版商:RSC    

年代:1978

数据来源: RSC

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December, 1978 SUMMARIES OF PAPERS I N THIS ISSUEDetermination of Trace Organic Pollutants in Water by ProtonMagnetic Resonance Spectroscopy of Solvent ExtractsviiExtraction with carbon tetrachloride followed by proton magnetic resonancespectroscopy, using a pulsed Fourier transform spectrometer with externalfield-frequency lock, has been investigated as a method for identifying anddetermining trace organic pollutants in water. The resulting spectra canbe used as fingerprints in order t o identify pollutants, and for quantitativemeasurements on specific compounds. The method is useful for all hydrogen-containing compounds that are efficiently extracted by the solvent, includinghydrocarbons, halogenated hydrocarbons and organochlorine pesticides.Measurements can be made over a wide range of pollutant concentrations,from heavily polluted effluents t o waters containing as little as 15 pg 1-1 ofalkanes.Keywords : Organic pollutant determination ; proton magnetic resonancespectroscopy ; water analysisJ.K. BECCONSALLImperial Chemical Industries Limited, Corporate Laboratory, P.O. Box 11, Runcorn,Cheshire, WA7 4QE.Analyst, 1978, 103, 1233-1238.Separation of Uranium from Seawater by AdsorbingColloid FlotationHydrated titanium oxide has been investigated for use as a collector in theseparation of uranium from seawater using adsorbing colloid flotation. Themain recovery is 91% and the optimum pH 6.6 f 0.2.Keywords ; Uranium sepavation ; seawatev ; adsorbing colloid $otation ;hydvated titanium oxideW.J. WILLIAMS and A. H. GILLAMSchool of Chemistry, University of Bath, Bath, BA2 7AY.Analyst, 1978, 103, 1239-1243.Determination of Lead in Paint by Differential-pulseAnodic- stripping VoltammetryA procedure for the determination of lead in paints by differential-pulseanodic-stripping voltammetry is presented. Only a few milligrams of sampleare required for the analysis. Dry ashing with sodium carbonate as the fluxhas been found to be a simple and effective method for the destruction of theorganic matrix. Samples of the dried paint of small particle size should be usedand the sample solution is adjusted to pH 4.0-4.6 with a buffer solution beforeanalysis. Loss of lead by retention in a porcelain crucible is significant inanalysis for trace levels of lead and a platinum crucible is recommended asthe container in the ashing process.The inexpensive porcelain crucible canonly be used if the lead content is of the order of 10-1 g.Keywords : Lead determination ; paint ; differential-pulse anodic-styippingvoltarnrnetryP. C. LA1 and K. W. FUNGDepartment of Chemistry, University of Hong Kong, Hong Kong.Analyst, 1978, 103, 1244-1248...V l l l SUMMARIES OF PAPERS I N THIS ISSUEHigh-frequency Microtitrimetric Determination of Acidic and BasicConstituents in Lubricating Oils. Part 1. Determination ofTotal Acid NumberDecembe~, 1978A high-frequency microtitration method is described for the determinationof total acid number in new and used lubricating oils. The sample, dissolvedin toluene - ethanol (7 + 3), is titrated with standard alcoholic tetramethyl-ammonium hydroxide solution.A study of solvents, titrants, sample sizeand other experimental parameters is reported. This method providessharp breaks a t the end-point and more repeatable results faster than thoseobtained with the standard potentiometric method. The method can beexpanded to the macro-scale using a commercially available titrator and offersan alternative to the ASTM and IP methods for the determination of totalacid number.Keywords : Total acid number determination ; lubricating oils ; high-frequencytitrationT. FERNANDEZ, J. M. ROCHA, N. RUFINO and A. GARCfA LUISCompaiiia Espaiiola de Petr6leos SA, Research Laboratory, Santa Cruz de Tenerife,Canary Islands.and F.GARCfA MONTELONGODepartment of Analytical Chemistry, University of La Laguna, Tenerife, CanaryIslands.Analyst, 1978, 103, 1249-1257.Shape of the Atomic- absorption Calibration Graphs for ChromiumUsing an Air - Acetylene FlameShort PaperKeywords Chromium determination, ; atomic-absorption spectrophotometry ;calibration graph shape; air - acetylene pameK. C. THOMPSONMalvern Regional Laboratory, Severn-Trent Water Authority, Malvern, Worcester-shire, WR14 2AN.Analyst, 1978, 103, 1258-1262.Determination of Furazolidone in Pig and Poultry Feeds byHigh-performance Liquid ChromatographyShort PaperKeywords : Furaxolidone determination ; high-perfovmance liquid chromato-graphy; pig feed; poultry feedA.D. JONES, E. C. SMITH, S. G. SELLINGS and I. W. BURNSUnilever Research, Colworth House, Sharnbrook, Bedfordshire, MK44 1LQ.Analyst, 1978, 103, 1262-1266December, 1978 SUMMARIES O F PAPERS I N THIS ISSUE ixFluorimetric Determination of Triphenyltin Compounds in WaterShort PaperKeywords : Triphenyltin compound determination ; 3-hydroxyflavone ; spectro-Juorirnetry ; water analysisS. J. BLUNDEN and A. H. CHAPMANInternational Tin Research Institute, Fraser Road, Perivale, Greenford, Middlesex,UB6 7AQ.Analyst, 1978, 103, 1266-1269.Freezing-point Data on Aqueous Solutions of Sucrose andSodium Chloride and the Hortvet Test: a ReappraisalShort PaperKeywords : Sucrose solution ; sodium chloride solution ; freezing-point ; Hortvettest; milkJ.H. PRENTICENational Institute for Research in Dairying, Shinfield, Reading, Berkshire, RG2 9AT.Analyst, 1978, 103, 1269-1273X THE ANALYST December, 1978ANALYTICAL SCIENCES MONOGRAPH No. 5Dithizoneby H. M. N. H. IrvingThe author of this volume has gatheredtogether a body of historical and technicaldata that will be of interest to many practisinganalytical chemists.Brief contentsThe Properties of Dithizone; Metal-DithizoneComplexes and Their Formulae; The Photo-chemistry of Metal Dithizonates; The Extrac-tion of Metal Dithizonates; The Less FamilarDithizone Complexes; Organometallic Dithi-zonates; Practical Considerations; SomeAdditional Applications of Dithizone; SomeUnresolved Problems; Bibliography.Clothbound 112pp 83” x 5s“0 85186 787 1f7.25 (CS Members f5.50)THE CHEMICAL SOCIETY,Distribution Centre,Blackhorse Road, Letchworth,Herts., SG6 1 HN“ A N A L O I D y yCOMPRESSED 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,M idd les b r o ug h,Cleveland TS8 9EAortelephone Middlesbrough317216ANALYTICAL SCIENCES MONOGRAPH No. 4Electrothermal Atomization forAtomic Absorption Spectrometryby C. W. FullerAt the present time the two most successful alternatives to the flame appear to bethe electrothermal atomizer and the inductively-coupled plasma. In this book anattempt has been made to provide the author‘s views on the historical develop-ment, commercial design features, theory, practical considerations, analyticalparameters of the elements, and areas of application of the first of these twotech n iq ues, electrot her ma I atomization.The chapter headings are as follows: History; Theoretical Aspects of theAtomization Process; General Experimental Conditions; Analytical Conditionsfor the Determination of the Elements by Atomic Absorption Spectrometry;Applications (Oil and Oil-Products; Metals; Rocks, Minerals and Soils; Waters;Plants; Food and Drugs; Biological Fluids; Biological Tissues; Air Particulates;Refractory Oxides and Related Materials; Other Analytical Applications;Theoretical).Clothbound 135pp 89” x 5” 0 85186 777 4 f6.75 ($13.50)CS Members f5.50THE CHEMICAL SOCIETYDistribution Centre, Blackhorse Road, Letchworth,Herts., SG6 1 HN, Englan

ISSN:0003-2654    

DOI:10.1039/AN97803BP117

出版商:RSC    

年代:1978

数据来源: RSC

摘要:

DECEMBER 1978 The Analyst Vol. 103 No. 1233 Continuous Monitor for Measuring Steelworks Atmospheres Toxic Gases in H. J. Boniface and R. H. Jenkins British Steel Corporation, Welsh Laboratory and Strip Mill Products, Port Talbot, Glamorgan Portable instruments are described for the continuous determination of sulphur dioxide and carbon monoxide in air. For sulphur dioxide, the gas is absorbed in an aqueous electrolyte containing an acid - base indicator. Resulting changes in the indicator colour are monitored photoelectrically and the detector current, after amplification, is used to titrate the reaction product. The titration current can be used to calculate the gas concentration a t a given flow-rate, on a coulometric basis. The changing current is displayed on a chart recorder, which provides a record of concentration against time.Carbon monoxide, after conversion into carbon dioxide, is determined in a similar manner using a partially aqueous electrolyte. Ranges of 100 and 20 mg m-3 for sulphur dioxide and 250 and 50 p.p.m. by volume for carbon monoxide are provided. These ranges cover the Threshold Limit Values for the gases. The instruments, which are battery powered, can be left unattended on-site for periods of at least 8 h. They have been used successfully for occupational hygiene studies in steelworks environ- ments. Keywords : Continuous gas monitor; sulfihur dioxide ; carbon monoxide ; toxic gases ; steelworks atmospheres The effect of toxic gases in the atmosphere on the health of workers in the steel industry has been studied by the occupational hygienists in this laboratory for many years.Reliable methods for determining gases such as sulphur dioxide and carbon monoxide are basic requirements for this work and improvements in techniques are being sought continually. Not only is it important to measure gas concentrations in areas surrounding the plant installations, but also within buildings and moving vehicles. Traditionally, the technique for measurement of sulphur dioxide has been based on absorbing the gas from a stream of air into a solution of hydrogen peroxide and determining the resulting sulphuric acid by manual titrati0n.l This gives a cumulative value for sulphur dioxide collected during the sampling period (usually 8 h) and gives no information on short-term variations or high instantaneous concentrations, which may be extremely important physiologically. A device for continuously recording the sulphur dioxide con- centration was needed, and the developments described in this paper were initially under- taken for this purpose.Carbon monoxide can be determined continuously and specifically using infrared absorption and instruments for this purpose are installed in many of the major hazard areas of steel- works. However, such instruments are not portable and they are expensive and require mains electrical supplies. Development of semiconductor devices is proceeding rapidly. These are portable and some can be worn on the person, but they are not specific for carbon monoxide and act only as alarms without giving a record of concentration over a period.The need for a continuous portable monitor was therefore clearly demonstrated. Coulometry had previously been applied in this laboratory to the determination of sulphur in steel2 and carbon in steel3 and the techniques seemed to offer good possibilities for the measurement of sulphur dioxide and carbon monoxide in air streams. The principle of the steel method was therefore modified so as to provide a continuous measuring device. This was achieved by feeding back the amplified photometric end-point detection output as a coulometric titration current. With sulphur dioxide, sodium hydroxide is generated a t the cathode at a rate equivalent to the rate of formation of sulphuric acid (reaction of sulphur 11851186 BONIFACE AND JENKINS : CONTINUOUS MONITOR FOR Analyst, VOl.103 dioxide with hydrogen peroxide) and at equilibrium the current is proportional to the concentration of sulphur dioxide in the air. Provided that efficient conversion of carbon monoxide into carbon dioxide can be achieved, the same principle can be applied to its determination. It was found in the steel analysis work that absorption of carbon dioxide was best carried out in a nearly non-aqueous medium, and an electrolyte based on dimethylformamide, ethanolamine and potassium iodide was used. A search of the literature showed that the principle of feeding back an amplified signal from the indicator output to produce a titration current was used prior to 1948 by Shaffer, et aZ.4 for the determination of mustard gas in air.It was later applied to the determina- tion of sulphur dioxide by Landsberg and Escher5 and de Veer et aL6 and it has also been used for the determination of organic reducing agents.' In all of these instances potentio- metric indication of the end-point was employed and the amplified current was used to generate bromine. However, small amounts of volatile bromine are constantly removed by the incoming stream of air and consequently there is always a small titration current flowing, even in the absence of sulphur dioxide. In the proposed apparatus, photometric indication is used and sodium hydroxide is generated to titrate sulphuric acid, thus enabling lower levels of sulphur dioxide to be determined, provided that a sufficiently stable d.c. amplifier is available.An apparatus has been constructed that can be used for either of these measurements. The electronic circuitry, optical systems and pumping arrangements are common and only the pre-absorption tubes and electrolytes are different. The instrument is battery operated, portable and will function for more than 8 h without attention. However, for monitoring carbon monoxide the electrolyte life depends on the concentration encountered. The instrument for sulphur dioxide is suitable for the ranges 0-100 and 0-20mgm-3, which cover most situations encountered in steelworks environments. The Threshold Limit Value for sulphur dioxide is 5 p.p.m. (approximately 13.5 mg m-3). The ranges for carbon monoxide are 0-250 and 0-50 p.p.m., the Threshold Limit Value being 50 p.p.m.It is considered that the same principles can be applied to the determination of other gases, such as ammonia, hydrogen sulphide, hydrogen chloride and oxides of nitrogen. Apparatus* components. 1. Absorption and electrolysis cell (Fig. 1) The system generates an organic base. Sulphur Dioxide The apparatus, housed in a wooden or metal case, is portable and consists of the following The cell consists of a 50-ml cylindrical glass vessel with stopper which carries the following. ___Silver wire diameter / 12 mm 1 mm diameter Fig. 1. Absorption and electrolysis cell. * An instrument based on this design which is patented world-wide (BY. Put., 1612002) is being manu- factured under licence of the British Steel Corporation by Analysis Automation Ltd., Oxford.December, 1978 MEASURING TOXIC GASES IN STEELWORKS ATMOSPHERES 1187 (a) A gas outlet tube through which air is drawn by means of a battery-operated pump.(b) Gas inlet tube terminating in a jet. The tube is surrounded by a tube of larger diameter with an outlet hole at the surface of the electrolyte. This guard tube keeps air bubbles away from the body of the solution. (c) Platinum-wire working electrode (cathode) wound around the inlet tube (b). (d) Silver-wire anode mounted in a glass tube (anode chamber) sealed at the base with a sintered-glass disc (porosity No. 4) and containing an agar plug. 2. Optical system (Fig. 2) This consists of two selenium barrier-layer photoelectric cells (Evans Electroselenium Ltd.), in front of which are mounted interference filters (Ban and Stroud Ltd.), Type MD6, 620 nm.The light source is a 24-V, 2.5-W lamp. The absorption cell is positioned as shown in Fig. 2. L I I- ’ I Fig. 2. Diagram of apparatus for measurement of sulphur dioxide. A = Absorption cell; B = lens; C = lamp; D = optical filter; E = photocell; F = amplifier; G = chart recorder; H = pump; J = flow meter; K = tube containing sulphamic acid; L = filter. 3. Amplifier The circuit is shown in Fig. 3. The amplifier is powered by two re-chargeable Sonnersclle Dryfit PC 6FX35 batteries, which also feed the lamp. 4. Chart recorder n A Rustrak Model 288 recorder is used, with full scale 1 mA, chart speed 4 in h-l and strike It is powered by a 6-V supply drawn from the batteries described Shunts are fitted to switch the range from 1 to 5 mA.rate 4 strikes per second. under (3) using Zener diode circuits. 5. Airfiump the Sonnerschein batteries, with a Zener diode circuit. The Casella Personal Sampler pump, Type C, is suitable, powered by a 5-V supply from 6. Flow meter Flow meter capable of measuring air flow-rates of up to 1000 ml min-l. 7. Control panel This panel bears “on - off,” “set zero” and range switches. positions, 100 and 20 mg m-3, which indicate full-scale deflections. The range switch has two 8. Air pre-treatment tubes A glass-fibre filter in an appropriate holder (Gelman, 25 mm) is positioned at the end of1188 BONIFACE AND JENKINS : CONTINUOUS MONITOR FOR Analyst, Vd. 103 the flexible sampling line (PVC tubing connected to the cell inlet tube). A glass absorption tube containing sulphamic acid to remove ammonia (if the concentration is less than 100 p.p.m.) is also placed in this line.100 kS2 1 MR i 100 kR - I 0 turn) 1 MR Chart +12”recorder Connections to absorption cell electrodes Q /I < / /,rr Fig. 3. D.C. amplifier circuit. I.C. 1, 2, 3 and 4 = 741 operational amplsers; D1 = diode 1N914; T1 = transistor 2N3063; P.C. 1 and 2 = potted photocells, catalogue No. 058 99 004, (Evans Electro- selenium Ltd.) . Absorption Solution Dissolve 20 g of sodium chloride in water, add 25 ml of bromocresol green solution (0.1% m/V) and 25 ml of hydrogen peroxide solution (6% m/V), mix and dilute to 1 1. Adjust the pH to 3.94.0 by the dropwise addition of hydrochloric acid (1% V/V). Partially fill the anode chamber with sodium chloride solution (2%) adjusted to pH 4.0.The sintered-glass disc of the anode chamber should be sealed with a small plug of agar gel made by boiling 1 g of agar powder with 30 ml of the anode chamber solution. Operating Procedure Fill the absorption - electrolysis cell (50 ml) and anode chamber (to the same level) with thn Qnnrnnrigto cnliitinnc P l ~ r o tho roll in tho nntirQl cxrctnm c n thgt lirrht frnm tho lQmn Y C L I b UyyLVyIIC&C\r d V I U L I V I L 0 . .L A L . . b b L I I b bbIL AAL L A I V W y L A b - UJ U L b L A I UW C L A U C U g L A L .LIVIIl LIIV IL4111 can pass through the cell without obstruction by the probes. Connect the air inlet and outlet tubes as shown in Fig. 2. Complete the connections between the amplifier and the anode and cathode points on the cell, select the 5-mA range and switch on the power.Adjust the pump flow-rate to 1000 ml min-l and adjust the “set zero” control knob to give a small positive reading on the chart. Allow this reading to decay to zero while aspirating a sulphur dioxide-free atmosphere (if necessary remove sulphur dioxide from ambient air by attaching to the inlet a tube packed with BDH microanalytical-grade manganese dioxide, 10-30 mesh). The instrument is now ready to be moved to the test site. The appropriate range is selected and monitoring can be commenced. Discussion Interferences The apparatus responds to sulphuric acid produced by reaction between sulphur dioxide and hvdrnrren neroxidt. and i s sensitive to mnst other alknlis 2nd arid4 rnntained in the airDecember, 1978 MEASURING TOXIC GASES IN STEELWORKS ATMOSPHERES 1189 Sulphuric acid mist and sulphur trioxide can be removed by inserting a paper or glass- fibre filter in the line; hydrogen sulphide is not absorbed at the pH of 4 used and carbon dioxide interferes only at concentrations greater than 1 yo V/V.Ammonia at concentrations less than 100 p.p.m. is effectively removed by sulphamic acid or at higher concentrations by sulphuric acid on a solid support (Merck, Catalogue No. 717). Hydrochloric acid and oxides of nitrogen are the most likely interferents, owing to the formation of hydrogen ions in solution. In the presence of hydrogen chloride, sulphur dioxide can be measured by using an alternative redox system. The following electrolyte has been found to be suitable: dissolve 20 g of potassium iodide, 10 g of potassium hydrogen phthalate and 10 ml of 1% V/V sodium starch glycollate solution in water and dilute to 1 1.The polarity of the cell must be reversed. Reactions Sulphur dioxide reacts with hydrogen peroxide to form sulphuric acid : SO, + H,O, = H2S04 = 2H+ + SO,,- . . .. .. - (1) When current flows through the absorption cell, the reaction at the cathode is 2Na+ + 2H,O + 2e- = 2NaOH + H, . . .. .. * * (2) and the sodium hydroxide generated neutralises the sulphuric acid : 2NaOH + H,SO, = Na,SO, + 2H,O . . .. .. - * (3) An alternative cathodic reaction is .. .. .. (4) 2H+ + 2e- = H, . . .. which has the same resultant effect as reaction (2). The reaction at the silver anode is .. .. * - (5) C1- + Ag = AgCl + e- .. .. Relationship between titration current and sulpht,w dioxide concentration From reactions (l), (2) and (3), it can be seen that two electrons are equivalent to one molecule of sulphur dioxide. From Faraday's law, 2 x 96487 C of electricity are equiva- lent to 64 g of sulphur dioxide. Therefore, a current of 5 mA (full scale on the upper range) is equivalent to (64.06 x 5)/(2 x 96487) mg s-l of sulphur dioxide. At a flow-rate of 1000 ml min-l a current of 5 mA is equivalent to (64.06 x 5 x 60 x 106)/(2 x 96487 x 1000) = 99.5 mg m-3. As the measurement of flow-rate is not easily controllable to within 1% of its value, it is convenient to approximate 99.5 to 100 mg m-3. On the lower range, the full-scale deflection is equivalent to a sulphur dioxide concentration of 20 mg m-3.Concentrations are sometimes expressed in parts per million by volume. Conversion of parts per million by volume into milligrams per cubic metre of sulphur dioxide in air Therefore, 1 p.p.m. by volume (1 v.p.m.) at 1 atm is equivalent to 2.9 mg m-3 at 0 "C or 2.7 mg m-3 at 20 "C. The density of sulphur dioxide8 at 0 "C and 1 atm pressure is 2.927 g 1-l. Performance Tests were carried out using the following mixtures of sulphur dioxide in air: cylinder 1, 100 -+ 5 p.p.m. by volume or 270 mg m-3 at 20 "C (Rank Hilger, Margate) ; and cylinder 2, 5.7 p.p.m. by volume or 15.4 mg m-3 at 20 "C (BOC Special Gases, London). The 100 mg m-3 range was tested by passing 300 ml min-l of the gas from cylinder 1 into the air stream being drawn into the instrument.When equilibrium was reached, a current of 3.97 mA was observed on an accurate meter in series with the recorder. This current was equivalent to 97.5 p.p.m., i.e., within the 5% tolerance of the certified value.1190 BONIFACE AND JENKINS :, CONTINUOUS MONITOR FOR Analyst, VoZ. 103 The 20 mg m-3 range was tested by passing the undiluted gas from cylinder 2 at a flow- rate of lo00 ml min-1. An average equilibrium current of 0.73 mA was observed, which is equivalent to 14.5 mg m-3 or 5.4 p.p.m. (24 "C) and is within 6% of the certified value (no tolerances given). I 1 Time Fig. 4. Recorder trace showing approxi- In- mately 70 mg m--3 of sulphur dioxide. strument set on 100 mg m-3 range. Time Fig. 5. Recorder trace showing approximately 13 mg m--3 of sulphur dioxide.Instrument set on 20 mg m-3 range. Typical traces (Figs. 4 and 5) show response times (to 90% of the full signal) of about 5 The instrument has been used successfully at various sites within steelworks, e.g., blast- A and 7 min for the 100 and 20 mg m-3 range, respectively. furnace casting bays, annealing-furnace environments and soaking-pit atmospheres. typical chart record is shown in Fig. 6. Time Fig. 6. Recorder trace obtained while moni- Instru- toring sulphur dioxide within a steelworks. ment set on 20 mg m-3 range. Carbon Monoxide Apparatus minor modifications to permit its use for carbon monoxide measurement. The apparatus described above for sulphur dioxide measurement needs only the following 1. The cell consists of a 30-ml cylindrical glass vessel similar in shape to that used for sulphur dioxide but smaller.The agar plug is omitted from the anode chamber. 2. The pump is arranged to force the sampled air through the cell at a flow-rate of 300 ml mi&. 3. The pre-treatment tube containing sulphamic acid is omitted. A series of air pre- treatment tubes are fitted in the inlet as follows: (i) silica gel to remove moisture; (ii) soda-asbestos to remove atmospheric carbon dioxide ; (iii) molecular sieve (Type 13X, pellet size 4 in) to remove trace amounts of hydro- (iv) silica gel and soda-asbestos to remove the last traces of moisture and carbon (v) Schutze's reagent [supplied by Strohlein & Co. or Leco Instruments (UK) Ltd.] Optical system: arranged as for sulphur dioxide but fitted with Ilford 607 filters.Control panel: as for sulphur dioxide, but with three range positions, labelled 20 mA and. 250 and 50 p.p.m. of carbon monoxide. The 20-mA position is for setting-up purposes only. carbons ; dioxide; and to oxidise carbon monoxide to carbon dioxide. 4. 5.December, 1978 MEASURING TOXIC GASES IN STEELWORKS ATMOSPHERES 1191 6. Absorption solution: to 780 ml of dimethylformamide in a 1-1 bottle add 20 ml of 0.1% m/V thymolphthalein dissolved in dimethylformamide, 30 g of potassium iodide (analytical-reagent grade) dissolved in 30 ml of water and 30 ml of monoethanolamine and mix the solution well. Caution-Wash off any dimethylformamide or absorption solution in contact with skin and avoid inhaling the vapour. Operating Procedure to the same level.light path by the probes. Connect the air inlet tube as shown in Fig. 7. nections between the amplifier and the anode and cathode points on the cell. Transfer 30 ml of absorption solution into the cell and add solution to the anode chamber Place the cell in the optical system, avoiding any obstruction of the Make the con- L I I‘ I Fig. 7. Diagram of apparatus for measurement of carbon monoxide. A = Absorption cell; B = lens; C = lamp; D = optical filter; E = photocell; F = amplifier; G = chart recorder; H = pump; J = flow meter; L = filter; M = tube containing silica gel; N = tube containing soda-asbestos ; 0 = tube containing molecular sieve (type 13X); P = tube containing soda-asbestos and silica gel; Q = tube con- taining Schutze’s reagent. Select the 20-mA range, switch on the pump and adjust the flow-rate to 3OUmlmin-l.Allow any carbon dioxide in the electrolyte to be neutralised. The meter and recorder reading will soon return to zero in a carbon monoxide-free atmosphere. The instrument is now ready to be moved to the test site. Choose the appropriate range (250 or 50 p.p.m) and proceed with monitoring the carbon monoxide concentration. Discussion Gases such as sulphur dioxide, hydrogen chloride, carbon dioxide and other acidic gases are removed by the soda-asbestos pre-treatment tube. Small amounts of hydrocarbons are removed by the molecular-sieve tube, but excessive concentrations could pass through and be oxidised to carbon dioxide by Schutze’s reagent. Exhaustion of the electrolyte is indicated by the formation of a white precipitate.Under the conditions described it will accept 25 p.p.m. continuously for 8 h or proportionately more for shorter periods. During use the colour of the Schutze’s reagent along the length of the tube changes from yellow to dark brown, indicating exhaustion of the reagent. The electrolyte life is limited by the total amount of carbon dioxide absorbed. Catalyst Although Schutze’s reagent is efficient and is self-indicating of exhaustion, it is expensive and has a short shelf life when the container is unsealed. Alternative catalysts are being1192 investigated. efficiency than for Schutze's reagent. ment, can be recovered for further use, thus providing a cost advantage. BONIFACE AND JENKINS: CONTINUOUS MONITOR FOR Analyst, Vol. 103 Silver oxide is a promising alternative although tests so far show a lower However, the spent material, after suitable treat- I 1 c=o I + KOCH2CH2NHZ- 0- Reactions The following reactions are thought to occur: II 0 KI --+ K+ + I- .... .. * . * (6) K++e--+K .. .. .. .. .. . * (7) * ' (8) .. .. .. Ag + I- -+ AgI + e- . . K + HOCH,CH,NH, -+ KOCH,CH,NH, + iH2 . .. ' (9) HOCH,CH,--NH I CO, + 2HOCH,CH,NH, -+ I c=o .. .. I 0- . . (10) I HOCH,CH2-NH3+ 5CO + 1,0, -+ 5c0, 51, .. .. .. . . (13) For the purpose of this reaction, Schutze's reagent is represented by iodine pentoxide. Relationship between titration current and caybon monoxide concentration of carbon monoxide. From the reactions shown, it can be seen that one electron is equivalent to one molecule The efficiency of these reactions has previously been established to be From Faraday's law, 96487 C of electricity are equivalent to 28.01 g of carbon monoxide.Therefore, a current of 1 mA is equivalent to 28.01/96487 mg s-1 of carbon monoxide. At a flow-rate of 300 ml min-l a current of 1 mA is equivalent to (28.01 x 60 x 106)/(96487 x 300) = 58.1 mg rn-, of carbon monoxide. The density of carbon monoxide is 1.250 g 1-1 at 0 "C and normal atmospheric pressure.8 A mixture containing 1 p.p.m. by volume of carbon monoxide is equivalent to 1.250 mg m-3 of carbon monoxide at 0 "C or 1.165 mg m-3 at 20 "C. Therefore, at 20 "C 1 mA is equiva- lent to 58.1/1.165 = 49.8 p.p.m. by volume. This value can be approximated at 50 p.p.m. by volume as the flow-rate is not easily controllable to within 1% of its value. Full-scale deflection on the high range is produced by a current of 5 mA, which is therefore equivalent to 250 p.p.m.by volume. looyo .3December, 1978 MEASURING TOXIC GASES IN STEELWORKS ATMOSPHERES 1193 Results The analytical performance of the apparatus was measured by using mixtures of carbon monoxide in nitrogen. It was found that in the absence of oxygen falsely high readings were obtained after continuous measurement for about 90 min. For this reason, the nitrogen - carbon monoxide mixtures were further mixed with air for measurement over long periods. Gas mixtures containing 10, 100, 200 and 400 p.p.m. by volume of carbon monoxide were tested (cylinders supplied by Air Products Ltd.). The results in Table I show that with the TABLE I CARBON MONOXIDE CONCENTRATIONS FOUND FOR VARIOUS STANDARD GAS MIXTURES Certificated concentration, p.p.m.by volume 12 106 109 205 366 Measured concentration, p.p.m. by volume Recovery, 14.4 120 109 103 106 97 203 99 374 102 exception of the 12 p.p.m. mixture all results lie within 3% of the certificate value. In practice, the flow-rate would be difficult to maintain within 5 3 % and the perfonnance is therefore considered to be satisfactory. Response times (to 90% of full signal) were found to be about 2 and 8 min for the 250 and 50 p.p.m. ranges, respectively (Figs. 8 and 9). -??!Ez.d Time Time Fig. 8. Recorder trace showing approxi- Fig. 9. Recorder trace showing approxi- mately 150p.p.m. of carbon monoxide. In- mately 25 p.p.m. of carbon monoxide.strument set on 250 p.p.m. range. Instrument set on 50 p.p.m. range. The instrument has been used successfully in a variety of steelworks environments, including moving cranes and other vehicles. A typical trace is shown in Fig. 10. Time Fig. 10. Recorder trace obtained while monitoring carbon monoxide within a steelworks. Instrument set on 250 p.p.m. range. Conclusions A portable instrument has been developed to measure continuously the concentration of toxic gases in the atmosphere. It has been applied successfully to monitoring the sulphur dioxide and carbon monoxide in steelworks environments. The ranges of 0-100 and 0-20 mg m-3 for sulphur dioxide are suitable for occupational hygiene investigations. Work is in progress to improve the sensitivity to provide ranges of 0-2 mg m--3 and 0-200 pg m--3, which would be applicable to urban environment concentrations.1194 BONIFACE AND JENKINS In the carbon monoxide mode, the instrument covers the ranges 0-50 and 0-250 p.p.m. Its intended use is for monitoring hazardous areas, rather than to provide an alarm or warning of high concentrations. The electrolyte has a limited life. The authors thank the Manager, Welsh Laboratory, British Steel Corporation, for per- mission to publish this paper and also the staff of the Laboratory’s Electronics and Instru- mentation Section, who designed the amplifier circuit. References 1. 2. 3. 4. 5 . 6. 7. 8. BS 1747 : Part 3 : 1969, British Standards Institution, London, 1969. Boniface, H. J., and Jenkins, R. H., “The Coulometric Determination of Sulphur in Steel,” Report Boniface, H. J., and Jenkins, R. H., Analyst, 1971, 96, 37. Shaffer, P. A, Briglio, A., and Brockman, J. A., Analyt. Chem., 1948, 20, 1008. Landsberg, H., and Escher. E. E., Ind. Engng Chem., 1954, 46, 1422. de Veer, S. M., Brouwer, H. J., and Zeedijk, H., 62nd Annual Meeting, Air Pollution Control Associ- Br. Pat., No. 1 098 992. Weast, R. C., Editor, “Handbook of Chemistry and Physics,” Fifty-third Edition, CRC Press, No. SM/235/A, British Steel Corporation, Sheffield, 1975; Analyt. A bstr., 1975, 29, 5B233. ation, New York City, 1969, Paper 69-6. Cleveland, Ohio, 1972-73. Received May 15th, 1978 Accepted June 26tlt, 1978

ISSN:0003-2654    

DOI:10.1039/AN9780301185

出版商:RSC    

年代:1978

数据来源: RSC

摘要:

Analyst, December, 1978, Vol. 103, pp. 1195-1198 1195 Gas-chromatographic Determination of Phosphine in Ambient Air A. Vinsjansen' and K. E. Thrane Norwegian Institute for Air Research, P.O. Box 130, N-2001 Lillestrerm, Norway Air sampIes taken in the neighbourhood of a chemical plant manufacturing dicyanamide from calcium carbide, of which process phosphine is a by-product, were collected in polyester bags and brought to the laboratory for analysis. A gas chromatograph equipped with a nitrogen - phosphorus-selective detector was used. The working range was 0.5-5 p.p.b. (parts per loQ) V/V and the detection limit was 0.03 p.p.b. V/V. The stability of the samples was invest- igated, and different calibration gases were compared. The results obtained with this method in the field agreed with results obtained with a continuous flame photometer.Keywords : Phosphine determination ; ambient air analysis ; gas sampling bag; gas chromatography Most of the measurements of phosphine reported in the literature have been made in con- nection with fumigation, where the concentrations of phosphine in air have been in the parts per million range. A search was made for possible methods for the determination of phosphine that would be applicable at the expected low concentrations of 0.5-5 p.p.b. (parts per lo9) V/V estimated from the emission rate of a chemical plant manufacturing dicyanamide from calcium carbide, of which process phosphine is a by-product. Colorimetric, continuous flame-photometric and gas-chromatographic methods were considered.were found to lack the desired sensitivity, specificity and adaptability. Flame-photometric detectors for continuous measurements of phosphorus compounds are very sensitive, but are not specific for phosphine. Different gas-chromato- graphic methods for the determination of phosphine have been published.s-ll DumasGJ measured phosphine in the range 0.5-10 mg 1-1 (33-667 p.p.m.) using a thermistor detector, but air interfered when the concentration was below 0.5mg1-1 (33 p.p.m.). He later changed the dimensions of the column and used a thermionic (phosphorus) detector, which is selective to phosphorus compounds. It is a special type of a flame-ionisation detector in which an alkali metal salt evaporates slowly into the flame jet, and in which the electrodes in the detector are repositioned.The detection limit in the Dumas study' was 0.005 mg 1-1 (0.33 p.p.m.), but oxygen and carbon dioxide interfered. Berck et a1.8 compared micro-coulometric, thermionic and flame-photometric detectors for the gas-chromatographic determination of phosphine. They concluded that the flame- photometric detector was the most sensitive and that it also gave the most rapid linear response and the best reproducibility. Since that paper was published, thermionic detectors have been improved and detectors selective for phosphorus compounds have been used for the determination of low concentrations of phosphine.ll The sensitivity of these detectors is comparable to that of a flame-photometric detector, but the thermionic detector is more versatile and less expensive. No report of the use of this detector for the deter- mination of phosphine in ambient air has been found in the literature.The colorimetric Experimental Sampling Procedure Air samples were collected in 2- and 5-1 gas sampling bags made of aluminium and poly- ester, obtained from Calibrated Instruments Inc., Ardsley, N.Y., USA. The bags were filled through PTFE tubing by an adjustable peristaltic pump or a pump equipped with a timer from Calibrated Instruments Inc. Samples were collected at different locations outside the chemical plant, the sampling time being 12-24 h. Gas-tight syringes made of * Present address: Research Laboratory of the Norwegian Canning Industry, P.O. Box 68. N-4001 Stavanger, Norway.1196 VINS JANSEN AND THRANE : GAS-CHROMATOGRAPHIC Analyst, Vol.103 glass and PTFE were used for taking instantaneous air samples. After sampling, the bags and syringes were sealed and sent to the analytical laboratory. Analytical Procedure The analyses were carried out on a Carlo Erba Model Fractovap 2101 AC gas chromato- graph, equipped with a nitrogen - phosphorus-selective detector (NPSD) and a 3-ml injection valve, also from Carlo Erba. The NPSD is a thermionic detector selective for nitrogen and phosphorus compounds. The selectivity and sensitivity for these compounds are adjusted by altering the positions of the electrodes and the alkali metal salt source. In this study, the alkali metal salt was potassium chloride and the detector was used in the phosphorus mode. The column (3.5 m x 4 mm id.) was made of glass and packed with 30% squalane on Chromosorb P DMCS (40-60 mesh).The temperature in the oven was 50 "C. In order to prevent condensation of water in the detector housing, the detector temperature was as high as 225 "C. Nitrogen was used as the carrier gas at a flow-rate of 25 ml min-1 and the hydrogen and air flow-rates to the detector were 30 and 300 ml min-l, respectively. Samples from the bags were transferred into the 3-ml sampling loop with a gas-tight syringe. A typical chromatogram is shown in Fig. 1. The retention time for phosphine was 220 s and the detection limit was 0.03 p.p.b. Phosphine - \ -1njectior 1 Fig. 1. Typical chromato- gram of phosphine in air. Attenuation, x 8. Sample size, 3 ml; concentration, 1.4 p.p.b. V / V .Calibration A gas mixture of 9.71 p.p.m. of phosphine in nitrogen with a certificate was obtained from MG Scientific, Kearny, N.J., USA. The concentration was not checked by any analytical method. The mixture was diluted with air (purified with activated carbon) in bags of theDecember, 1978 DETERMINATION OF PHOSPHINE I N AMBIENT AIR 1197 same make as those used for sampling. Standards of concentration 0.25, 0.5, 1.0 and 5.0 p.p.b. were prepared, 3-ml volumes of these standards were transferred into the gas chromato- graph and a calibration graph (see Fig. 2) was prepared by measuring the peak height. A calibration graph was also prepared from a gas mixture obtained from Alfax A/B con- taining 0.1 p.p.m. of phosphine in hydrogen. This calibration graph was comparable to that in Fig.2. The gas mixture from Alfax was not used in the routine work because of the risk of explosion. 120 100 Y a m 40 20 0 0.2 0.4 0.6 0.8 1.0 A 0 1 2 3 4 5 B Concentration, p.p.b. V/V Fig. 2. Calibration graphs re- lating the phosphine content to the peak height. Attenuation x 16 (A) is used for concentrations up to 1 p.p.b. V/V and x 128 (B) for concentrations between 1 and 5 p.p.b. V / V . Results and Discussion The average concentration of 24-h samples from 61 days was 2.2 p.p.b. and the standard deviation was 2.0 p.p.b.; the maximum 24-h average was 10.2 p.p.b. All of the samples concerned were taken at one monitoring station about 200 m from the plant. The samples were mailed to the analytical laboratory and were analysed several days after sampling.It was important to test the stability of the air samples, and four samples with different concentrations of phosphine were therefore stored at room temperature and analysed four times during 1 month. No change in the phosphine concentration was detected. The analytical results varied within 10% for the low concentration, i.e., 0.1 p.p.b., and &4% for concentrations above 1 p.p.b. This test showed that samples of phosphine in air can be stored in bags of this type for at least 1 month. For about 1 month three different methods for the determination of phosphine (the method described above, a wet-chemical method and a flame photometer for continuous measure- ment) were used simultaneously and the results were compared. For the wet-chemical method, air was drawn through a filter-paper to retain particles and through a gas-washing bottle in which phosphine was oxidised to phosphate in sodium hypochlorite solution.The sampling time was 24 h and the size of the air sample was 2-3 m3. The phosphate concentration was determined colorimetrically.12 The recovery of phosphine was found to be satisfactory (100%) when this method was tested in the labora- tory, but the exposed solution was not stable. Therefore, this method should be applied only when the samples can be analysed immediately after sampling. In this study the samples were analysed several days after sampling and the results from the wet-chemical method did not agree with those from the other two methods. The flame photometer was a Meloy Model SA160 instrument, from Meloy Laboratories Inc., equipped with a filter with maximum transmittance at 526nm.This detector and the sampling equipment for the gas-chromatographic analyses were working simultaneously1198 VINS JANSEN AND THRANE at the same monitoring station for 29 days. The 24-h average concentrations from the flame photometer and the results from the 24-h samples analysed by the gas-chromato- graphic method are given in Table I. The correlation coefficient was 0.82 with 95% confidence limits of 0.66-0.91. The regression line, FP = 0.7GC + 0.2 (where FP is the concentration determined by flame photometry and GC is that determined by gas chromato- graphy), showed that the gas-chromatographic method gave a higher concentration than the flame-photometric method for concentrations above 0.7 p.p.b.TABLE I COMPARISON OF 24-h AVERAGE CONCENTRATIONS OBTAINED BY FLAME PHOTOMETRY (FP) AND RESULTS OBTAINED BY GAS CHROMATOGRAPHY (GC) Month Date March 10 11 12 13 14 17 18 26 27 2 3 4 5 6 April 1 Concentration of phosphine, p.p.b. V/V -7 GC FP 3.1 2.1 1.9 0.8 5.7 4.4 2.1 1 .o 1.5 1 .o 0.8 0.5 1.1 0.6 1.7 1.8 0.2 0.0 0.2 0.1 0.1 0.1 0.7 0.8 1.5 2.5 0.3 0.4 3.0 1.3 Month Date April 7 8 9 10 11 13 14 16 17 18 20 21 23 l5 1 Concentration of phosphine, p.p.b. V / I‘ 1 GC FP 2.3 0.5 3.3 1.8 0.2 0.7 1.4 0.6 1.5 2.0 0.0 0.2 1.2 1.7 2.1 2.0 0.4 1.1 0.0 0.1 2.9 3.0 2.1 2.7 3.6 3.6 1.5 0.5 Conclusion The results show that ambient air samples for the determination of phosphine can be collected in the field and brought to the laboratory for analysis.The sampling method is simple and does not require heavy and expensive equipment in the field. Because the sample handling is uncomplicated there is very little chance of contamination of the samples prior to analysis. The gas-chromatographic analysis is rapid and sensitive and no inter- ference from other constituents in the air could be detected. The authors are grateful to Mr. J. Schaug for. permission to use unpublished data. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. References BS 642 : 1965, British Standards Institution, London, 1965, Appendix E, p. 20. Dechant, R., Sanders, G., and Graul, R., Am. Ind. Hyg. Ass. J., 1966, 27, 75. Muthu, M., Majumder, S. K., and Parpia, H. A. B., J . Agric. Fd Chem., 1973, 21, 184. Hartkamp, H., “Landesanstalt far Immissions- und Bodennutzungsschutz des Landes Nordrhein- Kashi, K. P., and Muthu, M., Pestic. Sci., 1975, 6, 511. Dumas, T., J. Agric. Fd Chem., 1964, 12, 257. Dumas, T., J. Agric. Fd Chcm., 1969, 17, 1164. Berck, B., Westlake, W. E., and Gunther, F. A., J . Agric. Fd Chem., 1970, 18, 143. Berck, B., and Gunther, F. A., J . Agric. Fd Chem., 1970, 18, 148. Chakrabarti, B., and Wainman, H. E., Chemy Ind., 1972, 300. Dumas, T., J. Ass. Off. Analyt. Chem., 1978, 61, 5. Murphy, J., and Riley, J. P., Analytica Chim. Acta, 1962, 27, 31. Westfalen, Schrifttenreihe der LIB,” Heft 32, Verlag W. Girardet, Essen, 1974, p. 37. Received April 6th, 1978 Accepted June 19th, 1978

ISSN:0003-2654    

DOI:10.1039/AN9780301195

出版商:RSC    

年代:1978

数据来源: RSC

摘要:

Anabst, December, 1978, Vol. 103, pp. 1199-1203 1199 Rapid Method for the Determination of Benzo[a]pyrene in the Particulate Phase of Cigarette Smoke by High-performance Liquid Chromatography with Fluorimetric Detection N. M. Sinclair and B. E. Frost Carreras Rothmans Limited, Research Division, Nevendon Road, Basildon, Essex A method is described for the rapid determination of benzo[a]pyrene in the particulate phase of cigarette smoke. The particulate matter from five cigarettes is fractionated on Florisil and a concentrated fraction injected on to a high-performance liquid chromatography column of Partisil. Benzo[a]pyrene is detected in the eluate fluorimetrically. Quantification is achieved by means of a standard-additions method. Keywords : Benxo[a]pyrene determination ; cigarette smoke ; high-performance liquid chromatography ; fluorimetric detection Benzo [alpyrene (benzo [deflchrysene) occurs in many environments, such as forest soils, river water and marine flora and fauna,l and it has been found in industrial effluents,l atmospheric particulate matter,2 car-exhaust fumes3 and foodstuff s.*3 Benzo [alpyrene is also present in cigarette-smoke condensate, together with over 300 other polycyclic aromatic hydrocarbons (PAHs) and alkyl-substituted PAHS.~ The biological properties of PAHs have been extensively studied7-9 and, owing to its potency and wide occurrence, benzo [alpyrene has received particular attention, especially with regard to its metabolism and activation by microsomal enzymes.lO~ll Methods for the separation of PAHs include thin-layer ~hrornatography,l~9~~ gas chromato- g r a p h ~ ~ ~ and high-performance liquid chromatography (HPLC) Benzo [a] pyrene has been determined by thin-layer chromatography,16 by gas chromatography on a nematic liquid crystal,l7 by HPLC using cellulose acetate columns and an ultraviolet detectorl8 and also by HPLC on an octadecylsilane bonded phase with a fluorimetric detector.19 There was a demand in our laboratory for a rapid, routine method of assay for benzo[a]- pyrene in cigarette-smoke condensate.Most published methods did not meet our require- ments as they are time consuming, require the smoking of large numbers of cigarettes20921 or involve extensive clean-up procedures.22923 A rapid analysis for benzo [alpyrene has been described that involves fluorimetric detection of benzo [a] pyrene after separation by either paper chromatography or thin-layer ~hromatography.~~ However, this method, in our hands, was unsatisfactory as HPLC of the benzo [alpyrene band from the thin-layer chroma- tographic plate demonstrated a 40-50y0 loss of benzo [alpyrene during thin-layer chromato- graphy and the presence of other fluorescent material in the benzo[a]pyrene band.A method is described here for the rapid determination of benzo[a]pyrene in cigarette- smoke particulate matter by means of HPLC on Partisil and fluorimetric detection. Only a limited clean up is required and the complete analysis, including cigarette smoking, can be carried out in one day. Experimental Materials further purification. that fraction distilling between 67 and 69 "C.Carbon tetrachloride, acetone and diethyl ether (AnalaR grade) were used without Hexane. General-purpose reagent (Hopkin and Williams) distilled once in glass, collecting Acetonitrile. Puriss grade, obtained from Koch-Light and used without further purification. Florid. Partisil, 5 pm. This was not activated This was not activated prior to use. Obtained from Whatman Laboratory Sales. prior to packing into the column.1200 SINCLAIR AND FROST: RAPID DETERMINATION OF BENZO[a]PYRENE Analyst, VOl. 103 Apparatus All glassware used for PAHs was made from amber glass. A Waters M6000 liquid-chromatography pump was used. Stainless-steel (316) columns, 250 x 4.6mm i.d., from Anachem, Luton, were equipped with a MACC I1 injector from Phase Separations, Queensferry, Clwyd.The fluorimeter was an Aminco Fluorocolorimeter, fitted to our own specification with a mercury lamp and a square-section flow cell, 8 x 3 x 3 mm (84 pl in volume). A 365-nm excitation filter was used and fluorescence emission was measured at 404 nm. Both filters, of approximately 20-nm peak width at 10% peak height, were obtained from Balzers, Fiirstentum, Liechtenstein. The output from the fluorimeter was recorded on a Servoscribe chart recorder at 300 mm h-l. Column Preparation and Equilibration The columns were slurry packed with 3 g of Partisil in 30 ml of carbon tetrachloride. The column top was fitted with a 20-pm stainless-steel mesh disc and a MACC I1 injector packed with silanised glass-wool. The water content.of the adsorbent was adjusted by passing 400 ml of acetone (2% water content) through the column. This procedure gave a retention time of 8.5min for benzo[a]pyrene in subsequent chromatography. The water content of the Partisil, and hence the retention time of benzo[a]pyrene, was held constant by using hexane - acetonitrile (1 1 + 200 pl) as the mobile phase for subsequent chromatography. Method The particulate matter from five cigarettes was collected on a 55-mm Cambridge filter by using a Filtrona 300 smoking machine, which gave a 35-ml puff of 2-s duration every 60 s. (Although the method is sufficiently sensitive to detect benzo [alpyrene from one cigarette, it is considered that five cigarettes is the minirnum number required in order to account for variations in individual cigarettes.) The filter was then sliced into small pieces and these were placed on top of a column of Florisil (100 x 10 mm), which had been packed in hexane.The column was eluted with 5% of ether in hexane and the first 100 ml of eluate were collected and reduced to a volume of 1.0 ml; benzo[a]pyrene was completely eluted in this fraction. A 5-pl aliquot was then examined ‘by means of HPLC on Partisil, eluting with oxygen-free hexane - acetonitrile at 1.5 ml rnin-l. The eluate from the HPLC column passed directly into the fluorimeter flow cell and the emission at 404 nm, caused by excitation at 365 nm, was recorded. Injections (5 pl) were made in triplicate. A further four Cambridge filter pads were prepared simultaneously and analysed in an identical manner.One of these pads was a duplicate of the first sample while known amounts of benzo[a]pyrene (typically 40, 80 and 120 ng) were added to the remaining three pads immediately after collection of the smoke, Confirmation of the retention time of benzo[a]pyrene on Partisil was provided by the chromatography of those fractions containing standard additions of benzo [alpyrene ; typical elution profiles obtained from untreated and treated pads are shown in Fig. 1. The peak produced by emission due to benzo[a]pyrene projects from a broad envelope caused by the fluorescence emission from a large number of other smoke products with similar chromato- graphic properties. Nevertheless, the peak height down to the broad envelope can be mea- sured, as shown in Fig.l. Results In Table I are given the peak heights obtained from seven replicate series of 15 injections of the eluate resulting from a UK filter cigarette in the middle-tar band. A statistical analysis of the regression plot obtained from the standard-additions method was carried out in order to determine the variance of the benzo[a]pyrene content of the untreated pads. The variance of this value x, the zero-point value, is given by where jj = the fitted values of y (the peak height) from the linear regression equation y = a + bx and n is the number of observations.December, 1978 IN CIGARETTE SMOKE BY HPLC WITH FLUORIMETRIC DETECTION 1201 Retention time/min Fig. 1. Chromatograms obtained by HPLC of cigarette-smoke condensate containing standard additions of benzo- [ulpyrene: (a), 0 ng; ( b ) , 40 ng; (c), 80 ng; and ( d ) , 120ng.Using the data in Table I the linear regression equation was found to be y = 0.308% + 28.20, giving a mean zero-point value for benzo[a]pyrene on each filter as 91.3ng, with a standard error of 7.6 ng. As five cigarettes are smoked on to each filter pad the benzo[a]- pyrene content of the cigarette was determined to be 18.3 ng. TABLE I FLUORESCENCE INTENSITIES FOR BEN20 [a]PYRENE OBTAINED BY HPLC ANALYSIS OF A MIDDLE-TAR UK FILTER CIGARETTE USING UNTREATED AND TREATED FILTER PADS Each intensity is the arithmetic mean of the results obtained from three injections. Amount of Series benzo[u]pyrene added A 1 to filtering 1 2 3 4 5 6 7 0 26* 26* 28* 28* 27* 26* 29* 40 40 47 41 47 44 37 42 80 63 68 54 57 47 60 47 120 68 70 64 70 61 60 61 * Mean of six injections from two fiIter pads.Discussion Clean-up of Particulate Matter Attempts to separate a narrow benzo [alpyrene band from earlier eluting less polar material on Florisil were not successful owing to activity variations in batches of Florisil, and it was not possible to control Florisil activity to the critical value required for this separation. Therefore, benzo [alpyrene was eluted in a fraction together with less polar smoke components and the Florisil served only to retain polar material that would otherwise rapidly degrade the HPLC column.1202 SINCLAIR AND FROST : RAPID DETERMINATION OF BENZO[a]PYRENE Analyst, 'Vd. 103 A standard sample of benzo[a]pyrene was applied to a Cambridge filter pad and eluted through a Florisil column.Injection of an aliquot of the sample on to the HPLC column before and after passage through the Florisil column demonstrated that 90-100% of the benzo [a] pyrene was recovered from the Florisil clean-up stage. High-performance Liquid Chromatography It was found that retention times for PAHs on Partisil, using hexane alone as solvent, increased steadily over a period of days and became unacceptably long after about five days. The cause was a decrease in the water content of the Partisil. A simple method used to overcome this problem was to add acetonitrile: to the hexane, the amount required being that which gives a retention time of 8-10 min for benzo[a]pyrene. This amount was found to be 200 pl of acetonitrile to 11 of hexane.Fluorimetric Detection A large number of PAHs elute from the HF'LC column in the region of benzo[a]pyrene and most of these are strongly fluorescent. Selective detection of benzo[a]pyrene is obtained, to some degree, by suitable choice of excitation and emission wavelengths. The mercury lamp of the Aminco fluorimeter produces a strong line emission at 365 nm, which coincides with a benzo [alpyrene absorption maximum. Narrow-band filters remove all other lamp emissions and allow fluorescence detection at 404 nm, a maximum for benzo[a]pyrene emission. With the detection system described here, a 4-pg injection of benzo [alpyrene could produce full-scale deflection with a signal to noise ratio of 10: 1. The benzo[a]pyrene peak projects from a broad envelope due to other fluorescent material and therefore justification was needed for taking the base of the benzo[a]pyrene peak to be its point of contact with the envelope (Fig.1). This justification was achieved by changing the excitation and emission filters on the fluorimeter so that benzo[a]pyrene did not give a response. Under such conditions the over-all shape (but not intensity) of the fluorescence envelope remained virtually constant, no dip was observed in the profile at the point where benzo[a]pyrene elutes and no other projecting peaks were observed at this position. Another means of producing some selective enhancement of benzo [a] pyrene fluorescence is to remove all dissolved oxygen from the HPLlC solvent. Oxygen is effective in quenching the relatively long lifetimes of PAH excited :singlets and compounds will vary in their susceptibility to oxygen quenching as this qulenching is proportional to the fluorescence lifetime. A four-fold enhancement of benzo [alpyrene fluorescence is produced by removing oxygen from the HPLC solvent by a continuous flow of nitrogen at a low rate. Anthracene and pyrene, which also fluoresce at 404 nm when excited at 365 nm, are enhanced to a much smaller degree; this finding has been reported by other workers2 Finally, the possibility of fluorescence quenching being caused by smoke components renders suspect a direct comparison of peak heights for the sample and a standard.In such a case the method of standard additions is preferable. Conclusion The method described is a rapid and reliable one for the determination of the concentration of benzo [alpyrene in the particulate matter of cigarette smoke.It involves high-performance liquid chromatography combined with fluorimetric detection and the result is calculated by a st andard-additions method. The authors thank Dr. D. H. Jones for assistance in the preparation of this manuscript, Miss J. A. Williamson and Mr. G. F. Plummer for technical assistance and the Directors of Carreras Rothmans Limited for permission to publish this work. Ref erenices 1. 2. 3. 4. 5. Harrison, R. M., Perry, R., and Wellings, R, A., Wat. Res., 1975, 9, 331. Fox, M. A., and Staley, S. W., Analyt. Chem., 1976, 48, 992, Sawicki, E., Meeker, J. E., and Morgan, M., Archs Envir. Hlth, 1965, 11, 773. Haenni, E. O., Residue Rev., 1968, 24, 41.Tilgner, D. J., and Daun, H., Residue Rev., 1969, 27. 19.December, 1978 IN CIGARETTE SMOKE BY HPLC WITH FLUORIMETRIC DETECTION 1203 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 23. 23. 24. Snook, M. E., Severson, R. F., Higman, H. C., Rrrendale, R. F., and Chortyk, 0. T., Beitr. Heidelberger, C., Adv. Cancer Res., 1973, 18, 317. Hoffmann, D., and Wynder, E. L., Cancer, 1971, 27, 848. Lee, P. N., Rothwell, K., and Whitehead, J . K., BY. J . Cancer, 1977, 35, 730. Chouroulinkov, I., Gentil, A., Grover, P. L., and Sims, P., BY. J . Cancer, 1976, 34, 523. Hundley, S . G., and Freundenthal, R. I., Cancer Res., 1977, 37, 244. Zoccolillo, L., and Liberti, A., J . Chromat., 1976, 120, 485. Woidich, H., Pfannhauser, W., Blaicher, G., and Tiefenbacker, K., Chromatographia, 1977, 10, 140. Severson, R. F., Snook, M. E., Chortyk, 0. T., and Arrendale, R. F., Beitr. Tabakforsch., 1976, 8, Lochmuller, C. H., and Amoss, C. W., J . Chromat., 1975, 108, 85. Klimisch, H.-J., and Kirchheim, E., Chromatographia, 1976, 9, 119. Janini, G. M., Shaikh, B., and Zielinski, W. L., Jr., J . Chromat., 1977, 132, 136. Klimisch, H.-J., Analyt. Chem., 1973, 45, 1960. Walters, D. B., Chamberlain, W. J., Snook, M. E., and Chortyk, 0. T., Analytica Chirn. Acta, Severson, R. F,, Snook, M. E., Arrendale, R, F., and Chortyk, 0. T., Analyt. Chewz., 1976, 48, 1866. Klimisch, H.-J., and Ambrosius, D., Analyt. Chem., 1976, 280, 377. Davis, H. J., Lee, L. A., and Davidson, T. R., Analyt. Chem., 1966, 38, 1752. Ayres, C. I., and Thornton, R. E., Beitr. Tabakforsch., 1966, 3, 285. Oakley, E . T., Johnson, L. F., and Stahr, H. M., Tob. Sci., 1972, 16, 19. Tabakforsch., 1976, 8, 250. 273. 1974, 73, 194. Received March 16th, 1978 Accepted June 16th, 1978

ISSN:0003-2654    

DOI:10.1039/AN9780301199

出版商:RSC    

年代:1978

数据来源: RSC

摘要:

I204 Analyst, December, 1978, "01. 103, @p. 1204-1209 Reproducible Method for the Preparation and Operation of Microwave-excited Electrodeless Discharge Lamps for Use in Atomic-fluorescence Spectrometry. Additional Experience with Cadmium Lamps R. G. Michel, J. M. Ottaway and J. Sneddon and G. S. Fell Department of Pure and Applied Chemistry, University of Strathclyde, Cathedral Street, Glasgow, G1 IXL Department of Clinical Biochemistry, Royal Infirmary, Glasgow, G4 OSF Results are presented of experience with a previously reported method for the preparation and operation of cadmium microwave-excited electrodeless discharge lamps. The method can be used while employing alternative microwave-excitation equipment but it is necessary to alter the levels of the factors that control the preparation and operation of the lamps.Lamps of identical performance are produced with the alternative equipment. A mean atomic-fluorescence detection limit of 0.07 pg 1-L with a relative standard deviation of 25% was achieved for 12 cadmium larnps prepared in two batches of six with a time interval of 4 months between them. Keywords : A tomic-fluorescence spectrometry ; microwave-excited electrodeless discharge lamps ; cadmium lamps Recently Michel et a1.l critically defined a reproducible method for the preparation and operation of microwave-excited electrodeless discharge lamps (EDLs) . The method included ten factors that had a known or postulated effect on the radiant output and stability of EDLs. A cadmium EDL was taken as an example and the ten factors optimised using the simplex algorithm.2 It was found that no EDLs failed and atomic-fluorescence detection limits, obtained when using optimised cadmium EDLs and an argon-separated air - acetylene flame,l were as good as the best reported in the past.Moreover, the detection limits obtainable for successively prepared EDLs were reproducible with a 25% relative standard deviation. This paper describes the use of the same method but with different microwave excitation. Michel et al.1 used an A antenna during the preparation and operation of the cadmium EDLs. In this paper the use is reported of a $-wave Broida cavity but with otherwise identical equipment and procedure. The characteristics of these microwave coupling devices have been described as has their use in atomic-fluorescence spectroscopy.5-7 Experimental Neglecting details, which can be obtained from the original publication,l the method involves the addition of an aqueous solution of cadmium iodide into the EDL blank followed by freeze drying under vacuum.The material is then sublimed inside the lamp blank by initiating a microwave discharge while the lamp is still on the vacuum system. In order to support this discharge either an A antenna or .a co-axial cavity can be used. However, the A antenna directs a diffuse microwave field around the EDL whereas the cavity produces a more localised microwave field, which is coupled more efficiently to the plasma. During initial attempts to prepare cadmium EDLs with a $-wave cavity it became clear that the more efficient coupling was causing the sublimation of cadmium iodide to occur more rapidly than when an A antenna was used.Too rapid sublimation can cause the loss of material from the blank during the discharge and will also affect the equilibrium between cadmium metal and cadmium iodide in the resulting 1amp.l As a result lamps prepared with optimum factor levels identical with those in reference 1 but using the $-wave cavity gave inferior detection limits. This difference demonstrated that the different excitation conditions inMICHEL, OTTAWAY, SNEDDON AND FELL 1205 the cavity were sufficient to make significant changes in the optimum levels of factors affected by the microwave excitation. Hence it was considered necessary to re-determine the optimum conditions for the preparation and operation of the cadmium EDL in order to allow for the use of the $-wave cavity. A full ten-factor optimisation requires the construction of over 100 EDLs., However, it was not considered necessary to repeat the optimisation of all ten factors as they are not all directly involved in the two discharge stages of the method (preparation and operation).Therefore, an optimisation was attempted that involved the variation of only five factors. It was assumed that the remaining five non-discharge stage factors could be kept constant at the optimum levels reported in reference 1 without compromising the location of the same over-all optimum found in the earlier work., The results of the optimisation presented here do indicate that the assumption was acceptable.Moreover, the five-factor optimisation required the construction of fewer EDLs and showed a consequent saving of time over a full ten-factor optimisation. The discharge during the preparation of the lamp is affected by three inter-related factors,l the time during which the discharge is continued, t,; the microwave power used during the discharge, P,; and the argon fill pressure used for the discharge, A,. (The notation used here for each factor is identical with that used in reference 1.) The operation of the lamp after preparation is also affected by the choice of coupling device. Accordingly it was necessary to optimise the microwave power for operation, P,; and the temperature at which the EDL was controlled during operation, T. The relationship between P, and T is detailed elsewhere8 and was verified for cadmium by Michel et a2.1 The simplex optimisation was therefore applied to the five factors t,, A,, P,, P, and T.The remaining five factors were kept at their optimum levels reported in reference 1. A large step size, five-dimensional, initial simplex was constructed by defining the necessary six points in factor space. The Nelder and Mead2 variable size simplex algorithm was then followed in order to search for optimum levels of the five factors. After termination of the simplex it was possible to obtain more information about the response surface in the region of the optimum EDL by carrying out a univariate search similar to that in reference 1. Each of the five factors was varied in turn while the remaining ones were kept constant at the simplex optimal levels found either in reference 1 (W,, t,, t,, t, and A,) or in this study In order to verify that the reproducibility of preparation and operation of EDLs was the same whether the A antenna or the $-wave cavity was used, 12 identical cadmium EDLs were made and their atomic fluorescence detection limits measured.These 12 EDLs were made in two batches of six. The second batch was made 4 months after the first. This enabled both the short- and long-term reproducibility to be estimated. Instrumentation and operating conditions are detailed in Table I. The instrumentation used and procedure followed were modelled closely on those employed in references 1 and 9. The instrumental arrangement was similar to that used by Johnson et aL9 except that the rapid-scan computer-controlled facility was not available and the EDL replaced the continuum source.(A,, p,, t,, p, and T). Results The five factor simplex search generated 34 vertices and involved the construction of 46 EDLs. This result can be compared with 80 vertices and 116 EDLs for the ten-factor search of reference 1. In both instances the difference between the number of vertices and the number of EDLs is a function of the progress of the simplex.2J0y11 Two EDLs gave the best detection limits (0.19 and 0.20 pg l-l, vertex numbers 28 and 30) and both sets of factor levels were nearly identical (Table 11). The set of 12 identical EDLs, prepared using the optimum conditions of vertex 30, gave a mean detection limit of 0.23 pg 1-1 with a relative standard deviation of 25% (Table 111), which, using the t distri- bution and a 99% confidence level, results in a confidence interval of 0.18-0.28 pg 1-l.These two EDLs, vertices 28 and 30, were used as the basis for the univariate search the results of which are shown in Table 11. From these results it was possible to infer the range over which each factor level could be varied while maintaining the detection limit within the confidence interval. This range defined the degree of control that is necessary for each1206 factor in order to maintain the optimum detection limit. factors optimised can be compared with the same ranges in reference 1. this comparison is set out in Table IV. MICHEL ef al. : PREPARATION AND OPERATION OF CADMIUM Analyst, Vol.103 The ranges obtained for the five For convenience TABLE I 1 NSTRUMENTATION AND 0P:ERATI NG CONDITIONS Component Model No. Double monochromator . . 1672 Photomultiplier . . .. 9789QB Photomultiplier housing . . .. .. PR1400RF Photomultiplier power supply . . .. .. PM.28A Photon counting system . . 6C1 Synchronous sampler . . 6C21 Pre-mix flame system Capillary burner and flame separator .. Manufacturer Spex Industries, Metuchen, N.J., USA EMI, Electron Tube Division, Hayes, Middlesex Products for Research, Danvers, Mass., USA EM1 Ortec Brookdeal, Bracknell, Berks . Perkin-Elmer Laboratory constructed Operating conditions Spectral band pass 0.5 nm, grating 1200 groove mm-l, blaze 300 nm High-voltage supply, 1100 V Count time 1 or 10 s Nitrogen-separated air - acetylene flame operated under stoicheiometric conditions.Signals observed 30 mm above burner head Chopper. . .. .. Laboratory constructed Modulation frequency 300 Hz Broida &wave cavity . . 210L Electromedical Supplies, Wantage, Oxon. Microwave generator . . Mark 111 Electromediczd Supplies Discussion Control Range for Optimised Factors Referring to Table IV it can be seen that the optimum range for factor A,, the argon pressure used for the discharge during the preparation, remained unchanged when compared with the results in reference 1. However, the optimum range for the time factor, t,, dropped from approximately 24 to approximately 11 s. This fall is in accordance with the initial observation that the cadmium iodide was being sublimed out of the EDL bulb more rapidly when using the $-wave cavity than when using the A antenna.The two factors involving control of the microwave power, P, and P,, both dropped to ranges about 10 W below those reported by Michel et aZ.1 This fall indicates that the more efficient coupling of the &wave cavity relative to the A antenna reduces the power require- ment. With regard to P, it appears that a simple drop in power was not sufficient to compensate for the coupling efficiency effect, a ccirresponding drop in t, was also necessary. This effect cannot be explained adequately without carrying out a detailed factorial study in the region of the optimum but it is clear that it relationship between t, and P, does exist as postulated by Michel et al.1 Any further relationship with A , would also be revealed by such a factorial experiment. Referring to Table IV, it can be seen that T , the operating temperature, appears to have dropped considerably compared with the range reported in reference 1.However, from Table I1 it can be seen that an optimum in P, of 50 W exists when the temperature T is within the control range 210-230 "C. This situation simultaneous optima in the levels of P, andDecember, 1978 MICROWAVE-EXCITED ELECTRODELESS DISCHARGE LAMPS FOR AFS 1207 TABLE I1 RESULTS OF SIMPLEX OPTIMISATION AND OF UNIVARIATE SEARCH The optimum electrodeless discharge lamps, vertices 28 and 30, which were a result of the simplex optimisation were used as the basis of the univariate search. Each factor was varied in turn while the remaining ones were kept constant a t the simplex optimum levels.Electrodeless Factor* Unit discharge lampt 4 Torr us us V28 V30 us us Watt Second Watt T Degree Celsius us us V28 V30 us us us V30 V28 us us us us V28 V30 us us US us us V28 V30 us Factor level 0.5 1 2.5 2.5 3 4 75 80 88 89 100 7 8.5 9.5 10.5 12.5 15 40 45 51 51 55 60 170 190 210 220 222 230 Detection limits/pg 1-I 0.62 0.25 0.20 0.19 0.22 0.59 0.43 0.21 0.20 0.19 0.36 0.45 0.50 0.19 0.20 0.16 0.40 0.35 0.23 0.20 0.19 0.20 0.39 0.67 0.48 0.24 0.20 0.19 0.28 * Factors W,, t,, t,, t+ and A , are not included in this table but were kept constant throughout both the simplex search and the univariate search at the optimum levels reported in reference 1 and shown here in Table IV.t V = vertex, US = univariate search. T , occurs only when the temperature is at a true over-all optimum level as indicated in Figs. 7 and 8 of the paper by Michel et aZ.1 If the temperature was indeed too low there would be no optimum level for P, at low powers. The fluorescence signals would simply increase with increasing microwave power in order to take advantage of the microwave heating effect and compensate for the low operating temperature, The lower optimum temperature obtained here can be explained in terms of the heat losses between the heater itself and the EDL. Michel et al. measured the temperature of the air stream just after the heater,l whereas here the temperature of the air stream was measured using a thermometer placed at the EDL position after removal of the EDL.The latter measurement results in a lower temperature. It is clear that it is not possible to make accurate comparisons and conclusions concerning the control range of the operating temperature in the two situations. A repro- ducible position for the temperature measurement is currently being investigated. EDL Performance Michel et aZ.l the earlier study1 and 0.07 pg 1-1 in this. In every respect EDLs performed identically in both this study and that carried out by Detection limits, measured on very similar instrumentation, were 0.08 pg 1-1 in A 10-s counting time on a photon counter and a1208 MICHEL et al.: PREPARATION AND OPERATION OF CADMIUM TABLE I11 REPRODUCIBILITY AND DETECTION LIMITS Twelve identical electrodeless discharge lamps were prepared using factor levels resulting from vertex 30 (Table 11).Detection limits measured as in references 1 and 9 but with a 1 s counting time.* Analyst, Vol. 103 Detection limit! Lamp tcg 1-1 1 0.20 2 0.23 3 0.18 4 0.14 5 0.28 6 0.21 Detection limit/ Lampt LLg 1-1 7 0.21 8 0.28 9 0.19 10 0.23 11 0.21 12 0.36 Mean detection limit . . . . 0.23 p g 1-1 Standard deviation . . . . 0.06 pg 1-1 Relative standard deviation. . 25% *With a 10-s counting time a mean detection limit of t EDLs 7-12 were prepared 4 months after EDLs 1-6. 0.07 pg 1-1 was obtained. band pass of approximately 0.5 nm was used in both studies. The 25% relative standard deviation in the detection limit found for successively prepared EDLs (Table 111) was identical with that reported in reference 1.Moreover, the two sets of EDLs used in the reproducibility determination (Table 111) were prepared several months apart. The differ- ence between the means of the detection limits of the two sets was not statistically significant (t distribution, 99% confidence). Therefore, both long- and short-term reproducibilities in the preparation and operation of the cadmium EDLs are statistically identical. The temporal stability of EDLs was also similar to th.at reported by Michel et aZ.l in Fig. 3, after the first 100 min of lifetime EDLs were stable and the detection limits reproducible. In view of the similarity between the EDLs produced in both the optimisation procedures discussed here it is probable that the same over-all optimum had been found in both instances.Hence, it appears that it was valid to keep those five factors constant that were thought not to be affected by the different excitation conditions. TABLE 1:V CONTROL RANGE FOE: EACH FACTOR The range of control for all factors is given for the results obtained in reference 1 and for the factors re-determined in this work. For the definition of control range see text. Factor* Mass of cadmium . . .. .. .. . . . . Time under vacuum after water removal .. .. Argon pressure under microwave excitation during Microwave power for discharge during preparation . . Time interval for microwave discharge during prepara- tion .. ,. .. .. . . . . .. Time for EDL to cool before evacuation.. .. .. preparation . . .. .. .. . . . . Time under vacuum after cooling period .... Final argon fill pressure . . .. .. .. .. Operating microwave power . . .. .. .. Operating temperature . . .. .. .. .. Control range I A I A antenna, $-Wave cavity, Symbol reference 1 this work 680-750 p.Cg 715 pgt 0-1000 s 300 s t 1.0-2.5 Torr 1.0-3.0 Torr 95-100 W 80-90 w Wl tl A1 Pl tz 20-28 s 9.5-12.5 s t3 240 s 240 s t to 0-500 s 500 s t T 290-330 "C 6-9 TOIT 8 Torrt 55-65 W 45-55 w 210-230 "C A2 p2. * For description of factors see reference 1. t For both simplex optimisation and univariate search factors W,, t,, t3, t4 and A , were kept constant a t the levels indicated. These levels were within the coritrol range reported in reference 1.December, 1978 MICROWAVE-EXCITED ELECTRODELESS DISCHARGE LAMPS FOR AFS 1209 Conclusions The different excitation characteristics of the $-wave cavity when compared with the A antenna alter the optimum levels of the factors that control the preparation and operation of cadmium EDLs using the method described by Michel et aZ.l However, both microwave excitation devices can be used to produce EDLs with identical performance.This work has confirmed that all of the factors need to be controlled carefully within defined limits in order to manufacture successive cadmium EDLs with a t least a 25% relative standard deviation in their atomic-fluorescence detection limits. Assuming that the levels of the factors are controlled within the ranges defined by Michel et aZ.1 and in this paper, then excellent reliability can be expected from this method of prepara- tion and operation of cadmium EDLs.The application of the method t o the optimisation of selenium EDLs in this laboratory has demonstrated similar reliability and good detection limits for the atomic-fluorescence spectrometry of selenium and the preparation of optimised EDLs for other elements is in progress. The authors acknowledge the support of the Scottish Home and Health Department for the purchase of the equipment used in this project and for the award of a Postdoctoral Fellowship (to support R. G. M.). They also thank the Eastern District, Greater Glasgow Health Board, for a maintenance grant in support of J. S. I . 3. 4. 5. 6 . 7. 8. 9. 10. 11. 3 I . References JIichel, R. G., Coleman, J., and Winefordner, J. D., Spectvochim. Acta 1978, 33B, 195. Nelder, J. A., and Mead, K., Comput. J . , 1965, 7 , 308. Fehsenfeld, F. C., Evenson, K. M., and Broida, H. P., Rev. Scient. Instrum., 1965, 36, 294. Fehsenfeld, F. C., Evenson, K. M., and Broida, H. P., Nat. Bur. Stand. Rep., No. 8701, US Dept. of Mansfield, J. M., Bratzel, M. P., Norgordon, H. O., Knapp, D. O., Zacha, K. E., and Winefordner, Cooke, D. O., Dagnall, R. M., and West, T. S., Analytica Chim. Acta, 1971, 54, 381. Aldous, K. M., Alger, D., Dagnall, R. M., and West, T. S., Lab. Pvact., 1970, 587. Browner, R. F., and Winefordner, J. D., Spectrochim. Acta, 1973, 28B, 263. Johnson, D. J., Plankey, F. W., and Winefordner, J. D., Analyt. Chem., 1975, 47, 1739. Morgan, S. L., and Deming, S. N., Analyt. Chem., 1974, 46, 1170. Deming, S. X., and Morgan, S. L., Analyt. Chem., 1973, 45, 278.4. Commerce, 1964. J . D., Spectrochim. Acta, 1968, 23B, 389. Received May 31st, 1978 Accepted July lath, 1978

ISSN:0003-2654    

DOI:10.1039/AN9780301204

出版商:RSC    

年代:1978

数据来源: RSC

摘要:

1210 Analyst, December, 1978, Vol. 103, pp. 1210-1214 Selective Spectrop hotometric Determination of Trace Amounts of Molybdenum With 2,2'- Dihydroxybenzophenone Thiosemicarbazone J. M. Lopez Fernandez, D. Perez-Bendito and M. Valcarcel Department of Analytical Chemistry, Faculty of Sciences and E.T.S.I.A ., University of Cdrdoba, Cdrdoba, Spain 2,2'-Dihydroxybenzophenone thiosemicarbazone reacts with molybdenum in solutions in mineral acids in the presence of tin(I1) chloride to produce a red 1 : 1 complex (Amax. = 500 nm, c = 3.3 >: lo3 1 mol-lcm-1). This complex is used for the spectrophotometric determination of trace amounts of molybdenum. The interferences of many metallic ions have been examined and a procedure for the determination of molybdenum in synthetic mixtures is proposed.Interfering metals can be removed by a preliminary extraction with dithizone. Keywords Molybdenum determination ; visible spectrophotometry ; 2,2'-dihydroxybenzoP henone t hiosemicarbazone The work described in this paper forms part of an investigation into the use of hydroxy- benzophenone thiosemicarbazones. In a previous paper1 we described the synthesis and properties of the thiosemicarbazones of 2-hydroxybenzophenone, 2,2'-dihydroxybenzo- phenone and 4,4'-dihydroxybenzophenone and their reactions with some cations. We have now used 2,2'-dihydroxybenzophenone thiosemicarbazone (2,2'-DHBT) for the spectro- photometric determination of trace amounts of molybdenum. Some other hydroxylated thiosemicarbazones have been used as photometric ligands especially for cobalt ions.293 2,2'- D H BT The red complex obtained between molybdenum(V1) and 2,2'-DHBT in mineral acids in the presence of tin( 11) chloride appears to be specific to thiosemicarbazones with hydroxyl groups in positions adjacent to the C=N- group.Thus, a complex with salicylaldeliyde thiosemicarbazone and its application to the determination of molybdenum in steels has been de~cribed.~ A similar complex is obtained with 2-hydroxybenzophenone thiosemi- carbazone, but 4,4'-dihydroxybenzophenone thiosemicarbazone does not react with molybdenum(V1) under similar conditions. However, thiosemicarbazones of pyridoxal, 3-hydroxypicolinaldehyde and dihydroxyphthalimide do not give this reaction. It is possible that the presence of other groups in these reagents prevents the development of the red chelate.The proposed method for the determination of molybdenum is superior to the classical molybdenum - thiocyanate complex method because an extraction step is not necessary and the results are more reproducible. Experimental Reagents All solvents and reagents were of analytical-reagent grade. 2,2'-Dihydroxybenxophenone thiosemicarbazone solution, 0.2% ml V in etlza?zol. This reagentLOPEZ FERNANDEZ, PEREZ-BENDITO AND VALCARCEL 121 1 was prepared by dissolving 2 g of 2,2'-dihydroxybenzophenone in 100 ml of ethanol and condenser the solution with 1.40 g of thiosemicarbazidedis solved in 100 ml of hot water; 3 ml of concentrated hydrochloric acid were added and the solution was refluxed for 3 h. The condenser was removed and heating continued until the volume had been reduced to half.A yellow crystalline product was obtained on cooling and was recrystallised from ethanol - water (1 + 1). The melting-point was 163 "C, and elemental analysis gave C 57.90, H 4.70 and N 14.10%; C,,H,,N,SO, requires C 58.54, H 4.54 and N 14.63%. A 1.5000-g amount of molybdenum(V1) oxide (pre- pared by heating ammonium molybdate at 500 "C) was dissolved in 0.1 M sodium hydroxide solution and hydrochloric acid was added to a concentration of 2 PUI in 1 1 of solution. Tin(I1) chloride solution. This solution contained 2% m/V of tin in 2 M hydrochloric acid; it was replaced frequently. Diphenylthiocarbazont! (dithizone) solution, 0.1 yo m/ V iit carbon tetrachloride. Molybdenum( V I ) standard solution.Apparatus cells. used for pH measurements. Spectro$lzotometcr. Digital pH meter. A Perkin-Elmer 124 spectrophotometer was used with 1 .O-cm silica A Philips PW 9408 instrument, with glass - calomel electrodes, was Procedure ( a ) Determination of molybdenum To a solution containing 50-1000 pg of molybdenum(V1) add 20 ml of 0.2% m/V 2,2'- DHBT solution in ethanol, 20ml of 0.5 M hydrochloric acid and 0.05 ml of 2% tin(I1) chloride solution. Allow the mixture to stand for 8 min, then dilute to 50.0 ml with water and measure the absorbance a t 500 nm against a water blank. (b) Determination of molybdenum after removal of foreign metal ions by dithizone extraction Place a volume of solution containing 50-1 000 pg of molybdenum(V1) in a separating funnel and add 5 ml of 0.1% dithizone in carbon tetrachloride.Shake the mixture for 2 min and allow it to stand for 10 min. Transfer the aqueous phase into a 50.0-ml calibrated flask and add 20 ml of 0.2% reagent solution in ethanol, 20 ml of 0.5 M hydrochloric acid and 0.05 ml of 2% tin(I1) chloride solution. Allow to stand for 8 min, dilute the solution to the mark with water and measure the absorbance at 500 nm against a water blank. Results and Discussion Reaction of 2,2'-DHBT with molybdenum The reagent has the advantages that it is stable, slightly coloured, readily available, selective and sensitive. 2,2'-DHBT reacts with molybdenum(V1) in mineral acid solution in the presence of tin(I1) chloride, to produce a red 1 : 1 complex with maximum absorption at 500nm.The reagent does not absorb a t this wavelength and water can be used as a blank. If other reducing agents such as iodide, hydroxylamine or ascorbic acid are used no complex is formed. A complex is not formed when metallic zinc or tin is used, in contrast to the behaviour of salicylaldehyde thiosemicarbazone, which slowly forms a complex with molybdenum. A yellow solution is obtained with 2,2'-DHBT in the absence of a reducing agent . At pH values above 2, the tin(I1) chloride is removed by hydrolysis and the molybdenum complex is destroyed. The order of addition of reagents is important, and affects both the sensitivity and stability of the complex. I t is necessary to add the reagent before the tin(I1) chloride, otlienvise the red complex is not formed. The sequence molybdenum, reagent , hydrochloric acid, tin(I1) chloride gives maximum sensitivity and stability of the complex.The compound is formed quantitatively only in a strongly acidic medium. The absorbance - pH graph shows a useful working pH range of 0.7-1.8. Order of addition of reagents.1212 LOPEZ FERNANDEZ et al. : SELECTIVE SPECTROPHOTOMETRIC Analyst, vol. 103 Efect of the acid employed. The anion of the acid employed influences the formation of the complex probably owing to its taking part in the co-ordination reaction. Hydrochloric, sulphuric, perchloric and acetic acids have been used and the results are shown in Table I. With all four acids the absorbance decreased slowly with time, but hydrochloric acid gave a more sensitive reaction. Orthophosphoric acid prevented the development of the colour, probably by formation of heteropolyacids.TABLE I EFFECT OF THE NATURE AND CONCENTRATION OF ACID ON ABSORBANCE OF COMPLEX AT 500 nm AFTER 10 min Solution contained 10 p.p.m. of molybdenum, 10 ml of 0.2% reagent solution, 20 ml of acid and 1.0 ml of 2% tin(I1) chloride solution. Concentration of acid addedlllr I 1 Acid 0.1 0.25 0.5 1.0 2.0 HCl .. . . 0.470 0.493 0.510 0.500 0.400 H,SO, .. .. -* 0.350 0.310 0.320 0.300 HClO, .. . . 0.330 0.360 0.330 0.300 0.225 CH,COOH . . 0.260 0.250 0.260 0.235 0.275 * No reading possible as precipitate formed. Efect of concentrations of hydrochloric acid and tin(1I) chloride on the stability of the molybdenum - 2,2'-DHBT complex. In order to obtain maximum stability of the molyb- denum(V1) - 2,2'-DHBT complex, the effect of changes in the concentrations of both hydrochloric acid and tin( 11) chloride was studied.Solutions were prepared containing 10 p.p.m. of molybdenum(VI), 10 ml of 0.2% reagent solution, 20 ml of a range of hydro- chloric acid solutions having concentrations between 0.25 and 2.5 M and various volumes between 0.2 and 0.5ml of 2% tin(I1) chloride solution. The absorbance of each sample was measured at 2-min intervals. The results are given in Table I1 and show that the best stability is attained when 0.5 M hydrochloric acid and 0.05 ml of 2% tin(I1) chloride solution are added. When prepared under these conditions the complex is stable for 4-12 min and a time interval of 8 min before making the photometric measurements was adopted.TABLE I1 EFFECT OF CONCENTRATIONS OF HYDROCHLORIC ACID AND TIN(I1) CHLORIDE ON ABSORBANCE OF COMPLEX AT 500 nm Concentra- Volume of Time of standing/min tion of 2% SnCl, < A \ 2.5 0.25 0.100 0.080 0.080 0.078 0.076 0.076 0.074 0.35 0.370 0.400 0.400 0.370 0.360 0.358 0.350 0.50 0.470 0.460 0.420 0.370 0.355 0.340 0.300 HCI/M solution/ml 0 2 4 6 8 10 12 1.5 0.05 0.260 0.320 0.330 0.330 0.310 0.290 0.285 0.10 0.210 0.230 0.230 0.230 0.225 0.225 0.210 0.20 0.300 0.340 0.355 0.355 0.340 0.338 0.320 1 .o 0.50 0.200 0.280 0.350 0.350 0.348 0.345 0.340 0.10 0.260 0.380 0.410 0.410 0.400 0.390 0.370 0.5 0.05 0.180 0.280 0.340 0.345 0.345 0.345 0.342 0.10 0.230 0.340 0.390 0.420 0.420 0.400 0.380 0.25 0.50 0.140 0.200 0.230 0.250 0.250 0.260 0.245 0.10 0.230 0.320 0.370 0.390 0.390 0.380 0.375 0.20 0.250 0.370 0.420 0.430 0.410 0.400 0.390 The effect of the solvent on the stability of the complex was also tested.It was observed that the stability increased with a water - ethanol solution of increased polarity and there- fore a mixture containing a high proportion of water is preferred.December, 197'8 DETERMINATION OF TRACE AMOUNTS OF MOLYBDENUM 1213 Extraction. The complex is not extracted by benzene, hexane, carbon tetrachloride, dibutyl phosphate or diethyl ether. It is not extracted by the carbon tetrachloride- 3-methylbutan-1-01 (1 + 1) mixture that is employed in other molybdenum-complex extrac- tion methods.5 The complex is extracted into 3-methylbutan-1-01, tributyl phosphate and 4-methylpentan-2-one, but a green colour is developed.The best extraction was obtained with benzyl alcohol, but the stability of the red complex is no better than that in the aqueous medium. Job's plots at 500 nm show that molyb- denum and 2,2'-DHBT combine in a 1 : 1 molar ratio (Fig. 1). The reagent probably behaves as a terdentate ligand, forming a charged complex with molybdenum, which explains why it is not extracted by organic solvents. A single hydroxyl group seems to take part in the co- ordination complex, in agreement with the fact that the 2-hydroxybenzophenone thiosemi- carbazone forms a similar complex. Stoickeiometry of the formation of the complex. 1.00 E 8 0.80 Ln c, Q, 0.60 e El 2 0.40 - - - - 0.201 ' ' ' . ' ' ' 0 0.2 0.4 0.6 0.8 [Mo] + [2,2'- DHBT] [ Mol Fig. 1.Stoicheiometry of molybdenum - 2,2'-DHBT complex. (Continuous-variations method.) The initial concentration of molyb- denum was M. Determination of Molybdenum with 2,2'-DHBT Beer's law is obeyed between 1 and 22 p.p.m. of molybdenum(V1). The molar absorptivity is 3.3 X lo3 1 mol-l cm-l. A Ringbom plot shows that 1-20 p.p.m. of molybdenum(V1) is the range for minimum error. The relative error of the method (P = 0.05) is 0.3%. In order to assess possible analytical applications of the molybdenum - 2,2'-DHBT complex, the influence of foreign metal ions was examined. A series of synthetic samples containing equal amounts of molybdenum and a foreign metal were prepared. The results are summarised in Table I11 and the following conclusions can be drawn. Sodium, potassium, calcium, magnesium and manganese(I1) do not interfere in the spectrophotometric determination of molybdenum, but iron( 11)' cadmium(I1) and bismuth(II1) interfere and cause an error of about 5% if all foreign metallic ions are extracted previously with dithizone as described in Procedure (b).Copper(I1) produces an error of less than 7%, but the interference of vanadium(V) is considerable. No interferences occur for mixtures containing chromium (11) and cobalt(I1) or sodium and potassium, but cadmium(I1) and bismuth(II1) produce an error of about 10% in the value for molybdenum after their extraction with dithizone. A mixture of chromium(III), cobalt(I1) and nickel(I1) does not interfere. A mixture of sodium, potassium and calcium does not interfere if EDTA is added, but a mixture of cadmium(II), bismuth(II1) and iron(II1) produced errors of about 10% in the values for molybdenum after their extraction with dithizone.The conditions given in the recommended procedure were determined empirically. Efect of foreign metal ions. Binary mixtures. Ternary mixtures. Quaternary mixtures.1214 LOPEZ FERNANDEZ, PEREZ-HENDITO AND VALCARCEL TABLE 111 MOLYBDENUM WITH 2,2’-DHBT IN MIXTURES INFLUENCE OF FOREIGN METAL IONS ON THE DETERMINATION OF Composition of mixture Mo(V1) . . .. .. .. .. . . Mo(V1) + Cu(I1) .. . . .. .. . . Mo(V1) + Bi(II1) .. .. .. .. .. Mo(V1) + Cd(I1) .. .. * . .. . . Mo(V1) + V(V) . . .. .. .. .. .. Mo(V1) + Cd(I1) + Bi(II1) . . .. .. .. Mo(V1) + Cd(I1) + Bi(II1) i- Fe(II1) . . . . Mo(V1) + Cr(II1) + Co(I1) + Ni(I1) + Zn(I1) + Al(II1) .. .. . . M ~ ( V I ) + Cr(II1) + C ~ ( I I ) + Ni(I1) ‘-i- Zn(I1) + Al(II1) + Sb(II1) . . . . Mo(V1) + Cr(II1) + Co(1I) + Ni(I1) Al(II1) + Sb(II1) + Ba(I1) . . .. .. .. Mo(V1) + Na .. .. .. .. .. M ~ ( V I ) + Cr(II1)’ ’ .. .. .. .. .. Mo(V1) + Cr(II1) + Co(I1) .. .. .. M ~ ( V I ) + Cr(II1) + C ~ ( I I ) + ‘rji(I1) Mo(V1) -!- Na + K + Ca . . .. .. . . Mo(V1) + Na + K + Ca + Mg .. .. .. Mo(V1) + Na + K +- Ca +- Mg + Mn(I1) Mo(V1) + Na + K . . .. .. .. .. M ~ ( V I ) + i&(II) .. .. .. .. .. Zn(1i) $- .. Mo(V1) + Cr(II1) + Co(I1) + Ni(I1) -I- Zn(I1) . . .. .. * I n the presence of 1 ml of 0.1 M EDTA. Amount of molybdenum, p.p.m. A I 3 Found A Added 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 Method (a) 10.0 2.5 2.5 4.5 7.5 0.8 4.5 1.8 9.2 9.2 9.2 10.0 10.0 10.0 10.0 10.0 10.0* 10.0* 10.0 10.1 Method (b) , preliminary extraction with dithizone 9.9 9.8 9.3 9.5 9.7 1.0 9.0 9.0 9.6 9.5 9.6 Other mixtures. Mixtures of molybdenum with chromium( 111), cobalt( II), nickel(I1) and zinc(I1) or with manganese(II), calcium, magnesium, sodium and potassium do not interfere. Mixtures containing sodium, potassium, calcium and magnesium do not interfere in the presence of EDTA. The error in the presence of chromium(III), cobalt(II), nickel(II), zinc(II), aluminium(II1) and magnesium was about 8% but if all foreign metallic ionsare extracted previously with dithizone, the error decreased to 5%. References 1 . 2. 3. 4. 6. Lopez Fernandez, J. M., Perez-Bendito, D., and Valcarcel, M., Quim. Analit., in the press. Can0 Pavon, J. M., Lavado, A., and Pino, F., hlikrochim. Acta, 1976, 11, 233. Gonzdez Ruiz, A. J., Thesis Licenciature, University of Seville, 1974. Perez-Bendito, D., and Pino-PCrez, F., Mikrochim. Acta, 1976, I, 613. Johnson, C. M., and Arkley, T. H., Analyt. Chem., 1954, 26, 572. Received February 13th. 1978 Accepted May 8th, 1978

ISSN:0003-2654    

DOI:10.1039/AN9780301210

出版商:RSC    

年代:1978

数据来源: RSC

摘要:

Analyst, December, 1978, Vol. 103, pp. 1215-1220 1215 3,3‘-Dimethylnaphthidinedisulphonic Acid as a Selective and Sensitive Reagent for the Spectrophotometric Determination of Vanadium(V) and its Application to Vanadium-bearing Minerals and Alloys H. Sanke Gowda and R. Shakunthala Defiartment of Post-graduate Studies and Research in Chemistry, Manasa Gangotri, University of Mysore, My S O Y ~ -570006, India: 3,3’-Dimethylnaphthidinedisulphonic acid is proposed as a selective and sensitive reagent for the spectrophotometric determination of vanadium(V) . It forms a violet coloured species with vanadium(V) in 8-13 M orthophosphoric acid medium. A 2-fold molar excess of reagent is necessary for the full development of the colour. The violet species exhibits an absorption maxi- mum at 555 nm with a molar absorptivity of 1.94 x lo4 lmol-l cm-l.Sandell’s sensitivity is 2.6 ngcm-2. Beer’s law is obeyed for the range 0.08-3.5 p.p.m. of vanadium(V) with an optimum concentration range of 0.1-3.1 p.p.m. The proposed method offers the advantages of simplicity, high sensitivity, good selectivity and the opportunity to carry out the deter- mination at room temperature without the need for an extraction step. The method has been used successfully for the determination of vanadium in ilmenite and vanadium steels. Keywords : Vanadium( V ) determination ; ilwenite ; vanadiuw steels ; spectro- Photometry ; 3,3‘-dinzethylnafihthidinedisulphonic acid There is conflicting evidence concerning the value of 3,3’-dimethylnaphthidine (DMN) as a spectrophotometric reagent for the determination of vanadium(V) .l-4 Bannard and Burton5 arbitrarily selected a 3 M orthophosphoric acid medium for the spectrophotometric deter- mination of vanadium(V) with DMN, although the absorbance and Amax.varied with the orthophosphoric acid concentration. Our investigation of the reaction between DMN and vanadium(V) in orthophosphoric acid showed that the absorbance and Amax. increased over the range of orthophosphoric acid concentration 1-8 M and remained almost constant in 8-13 M orthophosphoric acid solution. However, DMN gave a violet colour slowly in the blank containing 8-13 M orthophosphoric acid. This erratic reaction of DMN with vanadium(V) stimulated the investigation of 3,3’-dimethylnaphthidinedisulphonic acid (DMNS) as a spectrophotometric reagent for vanadium(V).Belcher et al. discussed the sensitivity of the reaction of DMNS with vanadium(V) .6 Experimental Reagents Vanadium( V ) standard solution. Prepare a stock solution of vanadium(V) from AnalaR- grade ammonium metavanadate in doubly distilled water and standardise it with standardised iron(I1) solution. Dilute this stock solution suitably to give a standard solution containing 20 pug ml-1 of vanadium(V). 3,3’-Dimethylnaphthidinedisul~~onic acid. Prepare a 0.1 yo ynlV solution of 3,3’-dimethyl- naphthidinedisulphonic acid (DMNS) by the procedure described by Belcher et aL6 and store it in an amber-glass bottle in a refrigerator. Prepare solutions of various ions of suitable concentrations by using analytical-reagent grade reagents.Solutions of foreign ions.1216 SANKE GOWDA AND SHAKUNTHALA: SELECTIVE SPECTROPHOTOMETRIC Analyst, VoZ. 103 Instrument A Beckman, Model DB, spectrophotometer with matched l-cm silica cells was used for absorbance measurements. Procedure for the Determination of Vanadium Transfer 04.5-ml aliquots of the 20 p.p.m. vanadium(V) solution into a series of 25-ml calibrated flasks. Add 1 ml of 0.1% DMNS solution to each and dilute to the mark with 12 M orthophosphoric acid in order to give an over-all acid concentration of 8 M. Mix well and measure the absorbance of each solution a t ti55 nm in l-cm cells against a reagent blank prepared under similar conditions. The plot of absorbance versus the concentration of vanadium is a straight line passing through the origin.Determine the absorbance of the sample containing vanadium by the method described for the preparation of the calibration graph. Deduce the vanadium concentration of the sample solution from the standard calibration graph. Procedure for the Determination of Vanadium in Ilmenite Fuse carefully about 0.5 g of finely powdered ilmenite in a silica crucible with about 10 g of sodium hydrogen sulphate until the sample is completely decomposed. Cool the melt and dissolve it in 50 ml of hot 2 M sulphuric acid. Filter the solution and dilute the filtrate to 250 ml in a calibrated flask. To a 25-ml aliquot of this solution, add 0.01 M potassium permanganate solution dropwise until the solution appears pink in order to oxidise any vanadium(1V) to vanadium(V).Allow the solution to stand for 5 min then warm and add 0.005 M oxalic acid solution slowly, with stirring, until the pink colour of the solution disappears. Transfer the solution into a 100-ml calibrated flask and dilute to the mark with doubly distilled water. Use aliquots of this solution for reaction with the DMNS as described in the Procedure for the Determination of Vanadium. Measure the absorbance at 555 nm and read the vanadium concentration from the calibration graph. Results on two samples of ilmenite are given in Table I. TABLE I DETERMINATION OF VANADIUM IN ILMENITE Vanadium content of solution, p.p.m,t f n \ Sample Certified composition, % * Certified value Found Q Grade . . . . TiO,, 60.6; Fe,O,, 24.18; FeO, '9.25; 0.42 0.48 A1,0,, 0.96; MnO, 0.39; Cr,O,, 10.12; 0.84 0.84 MgO, 0.89; P205, 0.21; ZrO,, 0.90; 1.68 1.67 SiO,, 0.40; rare earths, trace: loss on ignition, 2.00; V,O,, 0.15 MK Grade.... TiO,, 54.2; Fe,O,, 14.2; FeO, 216.6; FeO, 26.6; A1,0,, 1.25; MnO, 0.4; Cr,O,, 0.07; MgO, 1.03; P,O,, (2.12; ZrO,, 0.8; SO,, 0.68; rare earths, 0.12; loss on ignition, 0.34; V,05, 0.16 0.64 1.28 2.56 0.64 1.28 2.57 * These analyses were given by the suppliers of the samples. t A known mass of sample was dissolved and aliquots of the solution were diluted to give solutions con- These values, calculated from the vanadium content certified The results quoted as found are the means of five taining three different levels of vanadium. by the supplier, are expressed as certified values. determinations on each solution. Procedure for Determination of Vanadium in Vanadium Steels Transfer an accurately weighed amount of vanadium steel (approximately 0.5g) into a covered 250-ml beaker and treat with 15 ml of 5 M sulphuric acid, 2 ml of orthophosphoric acid (sp.gr. 1.75) and 1 ml of concentrated nitric acid. Boil the solution gently to dissolve the sample and expel the oxides of nitrogen, then cool, dilute to 50 ml with doubly distilled.&Ct?mber, 1978 DETERMINATION OF VANADIUM(V) I N MINERALS AND ALLOYS 1217 water, treat with potassium permanganate and then determine the vanadium content according to the Procedure for the Determination of Vanadium in Ilmenite. Results for six samples of steel are given in Table 11. TABLE I1 DETERMINATION OF VANADIUM IN VANADIUM STEELS Vanadium content of solution, P*P*m.t Sample EO 300 .. .. T 1OOV25 .. AISI H-11 . . 20 Cr I Mo 95 V 8 5 T i B .. Heat No. 7 2034, 15 CDV, Heat No. 6 4828, 58 CrV, Certified composition, yo * .. C, 1.01; Si, 0.059; Mn, 1.11; P, 0.018; S, 0.012; Ni, 0.11; Cr, 1.13; Mo, 0.033; Cu, 0.1; V, 0.1 C, 1.04; Si, 0.17; Mn, 0.36; P, 0.015; S, 0.008; Ni, 0.1; Cr, 0.2; Mo, 0.03; Cu, 0.1; V, 0.245 C, 0.41; Si, 0.99; Mn, 0.27; P, 0.019; S, 0.011; Ni, 0.14; Cr, 5.06; Mo, 1.20; Cu, 0.14; V, 0.49 .. . . . . C, 0.21; Si, 0.35; Mn, 0.41; P, 0.017; S, 0.011; Ni, 0.16; Cr, 1.25; Mo, 0.94; Ti, 0.06; B, 0.0046; Cu, 0.11; V, 0.96 .. C, 0.14; Si, 0.10; Mn, 0.88; P, 0.027; S , 0.01; Ni, 0.37; Cr, 1.32; Mo, 0.81; Al, 0.032; V, 0.19 .. C, 0.61; Si, 0.29; Mn, 0.86; P, 0.033; S, 0.011; Ni, 0.14; Cr, 1.12; Mo, 0.12; Al, 0.017; V, 0.09 r Certified value 0.48 0.82 1.64 0.64 0.96 1.62 1.22 1.86 2.54 0.88 1.34 2.12 0.58 1.16 1.74 0.64 1.28 1.92 1 Found 0.48 0.81 1.65 0.53 0.96 1.63 1.20 1.87 2.52 0.87 1.33 2.12 0.58 1.15 1.73 0.64 1.27 1.91 * These analyses were given by the suppliers of the samples.t A known mass of sample was dissolved and aliquots of the solution diluted to give solutions con- These values, calculated from the vanadium content certified The results quoted as found are the means of five taining three different levels of vanadium. by the supplier, are expressed as certified values. determinations on each solution. ResuIts and Discussion DMNS is readily oxidised by vanadium(V) at room temperature in sulphuric, hydro- chloric, orthophosphoric and acetic acids to a violet species, which is believed to be a di-radical di-cation.' Ion-exchange studies showed that the violet species is cationic. The intensity and stability of the violet colour depend on the nature and concentration of the acid employed.The violet species is unstable in hydrochloric acid or acetic acid. It is stable for 1-2 h in sulphuric acid, in which the sensitivity of the reaction is lower. Ortho- phosphoric acid has therefore been selected for further studies because of the higher sensitivity of the reaction and the longer stability of the coloured species in this medium. Effect of Orthophosphoric Acid Concentration The effect of varying the concentration of orthophosphoric acid was investigated. The results in Table I11 show that the rate of colour development and the sensitivity increase with increasing acid concentration from 1 to 4 M and then remain constant over the range 5-13 M. The maximum colour development takes place instantaneously at room tempera- ture (27 "C) in 5-13 M acid, The stability of the coloured species increases from 2.5 h to 2 d as the acidity increases from 5 to 13 M.Absorption Spectra phosphoric acid are shown in Fig. 1. The absorption spectra of DMNS, vanadium(V) and the violet species in 8~ ortho- The coloured species exhibits maximum absorbance1218 SANKE GOWDA AND SHAKUNTHALA : SELECTIVE SPECTROPHOTOMETRIC Analyst, Vd. 103 400 450 500 550 600 650 700 750 Wavelengthhm Fig. 1. Absorption spectra of vanadium- (V) -DMNS system. Graph A, 2p.p.m. of vanadium(V) in 8 M H3P0, measured against distilled water; graph B, 1 mnl of 0.1% DMNS in 8 M H,PO, measured against distilled water; and graph C, 2 p.p.m.of vanadium(V) and 1 ml of 0.1% DMNS in 8 M H,P04 measured against reagent blank. at 544-566 nm (Table 111). DMNS and vanadium(V) show little absorbance at this wave- length. The effect of reagent concentration was examined by measuring the absorbance of solutions containing 0.8 p.p.m. of vanadium and various amounts of DMNS. A 2-fold molar excess Subsequent studies were made at 555 nm. TABLE 111 SPECTRUM OF THE VANADIUM(V) - DMNS SYSTEM EFFECT OF ORTHOPHOSPHORIC ACID CONCENTRATION ON ABSORPTION Concentration of acid/M 1 2 3 4 5 6 8 9 10 12 13 Time taken for colour development/ min 15 10 3 2 Immediate Immediate Immediate Immediate Immediate Immediate Immediate Colour Reddish violet Reddish violet Reddish violet Reddish violet Reddish violet Reddish violet Violet Violet Intense violet Intense violet Intense violet ~?nax./nm 540-550 540-550 540-550 540-550 544-552 544-554 548-562 552-566 550-562 654-566 554-666 Absorbance 0.1675 0.181 5 0.192 6 0.221 8 0.251 8 0.251 8 0.261 8 0.251 8 0.251 8 0.251 8 0.251 8 Molar absorptivity/ 1 mol-I cm-1 9.67 x 103 1.05 x 104 1.12 x 104 1.28 x 104 1.94 x 104 1.94 x 104 1.94 x 104 1.94 x 104 1.94 x 104 1.94 x 104 1.94 x 104 Stability of colour/h 1.0 1.0 1.5 2.0 2.5 2.5 2.6 2.6 4.0 24.0 48.0 of the reagent was necessary in order to produce maximum colour intensity.The optimum amount of 1 ml of 0.1% reagent solution was used in a final volume of 25 ml of solution, The order of mixing vanadium (M), orthophosphoric acid (A) and DMNS (L) has some effect on the development of the colour.If the mixing of the reagents follows the orderDecember, 197s DETERMINATION OF VANADIUM(V) IN MINERALS AND ALLOYS 1219 LAM, LMA, MLA or ALM, the maximum absorbance is obtained instantaneously. If the mixing of the reagents follows the order AML or MAL, the maximum absorbance is not obtained. It is therefore recommended that DMNS and vanadium(V) are mixed prior to the addition of orthophosphoric acid. Above 40 "C, the absorbance gradually decreases with increasing temperature. The absorbance values are not affected by temperature over the range 8 4 0 "C. Calibration, Range, Sensitivity and Precision Beer's law is obeyed over the range 0.08-3.5 p.p.m. of vanadium(V) with an optimum concentration range of 0.1-3.1 p.p.m.The molar absorptivity is 1.94 x lo4 1 mol-l cm-l. Sandell's sensitivity is estimated to be 2.6 ng cmA2. The standard deviation calculated from 10 determinations on a solution containing 0.8 p.p.m. of vanadium(V) is 0.0025. Effect of Foreign Ions In order to assess the possible analytical applications of this colour reaction, the effect of some foreign ions that often accompany vanadium were examined by carrying out deter- minations of 0.8 p.p.m. of vanadium(V) in the presence of each of these ions. The results in Table IV show that DMNS is selective for vanadium(V), but cerium(IV), chromium(VI), nitrite and iodide interfere strongly. TABLE IV EFFECT OF FOREIGN IONS ON THE DETERMINATION OF VANADIUM(V) Tolerance Tolerance Ion added limit, p.p.m.* Ion added limit, p.p.m.* Fe( 111) 5 200 Zr(1V) 150 Cu(I1) 350 As (111) 100 Ni(I1) 400 Fluoride 10 000 Co(I1) 240 Chloride 5 000 ARM Cr (I 11) 1000 Nitrate 10 000 Mn(I1) 2 000 Sulphate 10 000 WVI) Mo(V1) 240 Bromide 6 000 Ti(1V) 1 Iodide 0.3 400 Nitrite 0.1 200 Acetate 10000 200 Tartrate 5 000 Zn(I1) Ca(I1) 1500 Oxalate 3 500 1000 Citrate 2 500 220 Borate 4 000 10 000 EDTA 2 000 2@) 5 000 W I ) (1) * Amount of foreign ions causing an error of less than 2% in the determination of 0.8 p.p.m.of vanadium. Analysis of Ilmenite and Vanadium Steels The results in Tables I and I1 show that the associated substances'in ilmenite and the other metals present in vanadium steels do not interfere in the determination of vanadium.The values obtained with DMNS compare favourably with the certified values for vanadium. The sensitivity of the proposed method is higher than that with N-phenylacetylsalicylo- hydroxamic acid,8 2-et hoxycarbonyl-5-hydroxy- 1 - (4-tolyl) pyridin-4-0ne,~ 1,2,3-phenyloxy- amidine,lO disodium salt of dimercaptomaleonitrile,ll N-4-tolyl-2-furohydroxamic acid,12 t hio t heno y It rifluoroace t one ,I3 ant h ranilic acid isopropylidineh ydrazide, l4 4-phenyl-7,8-di- hydroxycoumarin,l5 sodium salt of N-(2-sulphobenzoyl)-N-phenylhydroxylamine,16 thio- salicylic acid1' and picraminazo N,18 which have been proposed as sensitive spectrophoto- metric reagents for vanadium(V). The authors thank Indian Rare Earths Limited for supplying ilmenite and Mahindra Ugina Steel Co.Limited and Hindustan Steel Limited, India, for supplying vanadium steels.1220 SANKE GOWDA AND SHAKUNTHALA References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. Milner, G. W. C., and Hall, W. R., Analytica Chim. Acta, 1952, 6, 420. Scholes, P. H., Analyst, 1957, 82, 525. Forrester, J . S., and Jones, J. L., Analyt. Chem., 1960, 32, 1443. Macmillan, E., and Samuel, B. W., Analyt. Chem., 1966, 38, 250. Bannard, L. G., and Burton, J. D., Analyst, 1968, 93, 142. Belcher, R., Nutten, A. J., and Stephen, W. I., J . Chem. Soc., 1952, 1269. Bishop, E., “Indicators,” Pergamon Press, Oxford, 1972, p. 571. Savariar, C. P., and Joseph, J., J . Indian Chem. SOL, 1973, 50, 14. Tamhina, B., and Herak. M. S., Mikrochim. Acta, 1975, 45. Satyanarayana, K., and Mishra, R. K., Analyt. Chcm., 1974, 46, 1609. Chatterjee, A. B., Basu, A., and Bag, S. P., Mikrochim. Acta, 1974, 275. Rowland, R., and Meloan, C. E.. Analyt. Chem., 1970, 42, 1261. Solanke, K. R., and Khopkar, S. M., Talanta, 1974, 21, 245. Dolgorev, A. V., and Karpova, 0. I., Zav. Lab., 1974, 40, 771. Kalra, A. K., Singh, H. B., and Singh, R. P., J . Indian Chem. Soc., 1972, 49, 97. Bhargava, S. P., and Sogani, N. C., Bull. Acad. Pol. Sci., S ~ Y . Sci. Chim., 1972, 20, 741. Sikorska-Tomicka, H., and Lewicka, M., Chemia Aaalit., Warsaw, 1973, 18, 551. Zadumina, E. A., and Cherkesov, A. I., Izv. V p s h . Ucheb. Zaved., Khim. Khim. Tekhnol., 1969, Received March 29th, 1978 Accepted June 16th, 1978 12, 1483; Analyt. Abstr., 1971, 20, 1624.

ISSN:0003-2654    

DOI:10.1039/AN9780301215

出版商:RSC    

年代:1978

数据来源: RSC