ISSN:0003-2654    

DOI:10.1039/AN96691FX029

出版商:RSC    

年代:1966

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN96691BX031

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

i V SUMMARIES OF PAPERS IN THIS ISSUE [August, 1966Summaries of Papers in this IssueRapid Automated Determination of Biphenyl in Citrus Fruit RindA totally automated analytical procedure for determining the fungistatbiphenyl in citrus fruit rind has been developed. Small pieces of hand-peeledrind are automatically homogenised in water and steam-distilled to liberate thebiphenyl, which is trapped in cyclohexane solution ; this solution is exhaustivelyextracted'to remove interfering steam volatiles and the biphenyl remaining isread a t 246nip in a continuous flow recording spectrophotometer. Timerequired from the introduction of rind samples to read out of biphenyl presentis 9 minutes, with about 15 minutes for the first sample. The useful range isfrom 1 to about 150 p.p.m.on a whole-fruit basis with a reproducibility ofabout 3 per cent. The method has been applied most extensively to Valenciaoranges.F. A. GUNTHER and D. E. OTTDepartment of Entomology, University of California Citrus Research Center andAgricultural Experiment Station, Riverside, California.Analyst, 1966, 91, 475-481.Determination of Carbon in Steel by a Dynamic Infrared SystemA simple, automatic apparatus has been developed for the rapid deter-mination of carbon in steel. I t is based upon the continuous measurementof carbon dioxide evolved during the high temperature combustion of steeli n oxygen by using a specially designed infrared gas analyser and integrationsystem. When this is used in conjuction with a conventional resistance-tubefurnace, the speed of the determination varies from 40 to 55 seconds for mildand low alloy steels, and slightly longer for highly alloyed materials.G.WHITE and P. H. SCHOLESBritish Iron and Steel Research Association, Metallurgy Division, Hoyle Street,Sheffield 3.Analyst, 1966, 91, 482-489.The Determination of Aluminium in Iron and SteelVarious colorimetric reagents have been examined for their suitabilityin a standard method for determining aluminium in ferrous metals. Inter-fering elements are removed by a mercury-cathode separation followed bycupferron - chloroform extraction. In the method adopted, aluminium isdetermined by measuring the optical density of its complex with Alizarinred S - calcium reagent. The method has been tested with a wide rangeof steels.J.A. CORBETTPhysical Metallurgy Section, Commonwealth Scientific and Industrial ResearchOrganization, Australia.and B. D. GUERINMetallurgy Department, University of Melbournc, Australia.A n~Zy.~t, 1966, 91, 490-498vi SUMMARIES OF PAPERS I N THIS ISSUEA Chemiluminescence Method for Determining Ozoneh method for determining ozone is described which is characterised bythe direct recording and automatic determination of ozone within a widerange of concentrations. The development of this method is based on theuse of a chemiluminescent solution that is stable, and shows a linear relation-ship between the light emitted and the ozone concentration. A combinationof rhodamine B with gallic acid in ethanol is satisfactory in operation and doesnot itself emit light.The electronic instrumentation used is relativelysimple. Other methods of ozone analysis based on this principle meet withmuch difficulty, owing to the direct oxidation of the chemiluminescent com-pound. The present method, by contrast, involves the use of gallic acid asan ozone acceptor, and rhodamine B, which remains unchanged during themeasurement, as a photon emitter. Observations made with an oscillographof the light emitted by single bubbles of ozonised air passing through the chem-iluminescent solution give valuable information about the response-timeof the system.D. BERSIS and E. VASSILIOUNuclear Research Center “Democritus,” Aghia Paraskevi Attikis, Athens, Greece.[August, 1966A nalyst, 1966, 91, 499-505.The Determination of Tantalum by the Solvent Extractionof a Tantalum - Pyrogallol ComplexA colorimetric procedure for determining up to 1.2 mg of tantalum inthe presence of up to 20 mg of niobium, or up to 180 mg of tungsten, hasbeen developed.The colourless tantalum - pyrogallol complex is extractedinto ethyl acetate a t pH between 4-5 to 6.0 by means of tetrahexyl or tetra-butyl ammonium iodide and back-extracted with acidified ammonium oxalate(pH 2.0). The yellow complex obtained is measured spectrophotometricallyat 400 mp.BETSY BIRABEN SCOTTFacultad de Quimica y Farmacia, Universidad Nacional de La Plata, Argentina.Analyst, 1966, 91, 506-510.Flame-photometric Determination of Sodium and Potassiumin Manganese OresTwo procedures are described; in one, the sample is dissolved in hydro-chloric acid, interfering elements are precipitated with 8-hydroxyquinolinein ammoniacal solution, and the precipitate then extracted into chloroform.Sodium and potassium are determined in the aqueous phase by means ofa filter flame photometer.The second procedure is more suitable for routine use and involves thedissolution of the sample in hydrochloric acid, followed by the addition ofsulphuric acid and aluminium nitrate to suppress interferences, and thedirect evaluation of the sodium and potassium contents of the solution bymeans of either a prism or a filter flame photometer.Comparative resultsobtained by this alternative procedure on instruments of these two typesare given.B. G.RUSSELLThe National Institute for Metallurgy, Yale Road, Milner Park, Johannesburg.Analyst, 1966, 91, 511-519.Determination of Cyclamate in Soft Drinks byGas ChromatographyShort PaperM. L. RICHARDSON and P. E. LUTONJohn & E. Sturge Ltd., Lifford Chemical Works, Kings Norton, Birmingham 30.Analyst, 1966, 91, 520-521viii SUMMARIES OF PAPERS I N THIS ISSUEThe Determination of Cyclamate in Soft Drinks by Titrationwith Sodium NitriteShort Paper[August, 1966M. L. RICHARDSON and P. E. LUTONJohn & E. Sturge Ltd., Lifford Chemical Works, Kings Norton, Birmingham 30.Analyst, 1966, 91, 522-523.The Determination of Ethanolamine and Serine inPhospholipidsShort PaperA. J. de KONINGFishing Industry Research Institute, University of Cape Town, Rondebosch, CapeTown, South Africa.AnaZyst,1966, 91, 523-525.The Paper Chromatography of Some Purines, Pyrimidinesand ImidazolesShort PuperM.N. KHATTAK, N. T. BARKER and J. H. GREENDepartment of Nuclear and Radiation Chemistry, University of New South \Vales,Kensington, Sydney, Australia.Analyst, 1966, 91, 526-528.The Determination of Total Sulphur in Soil and Plant MaterialShort PaperI. A. CHAUDHRY and A. H. CORNFIELDChemistry Department, Imperial College of Science and Technology, London, S.W. 7.Analyst, 1966, 91, 528-530.A Simple Colorimetric Finish for the Johnson - NishitaMicro-distillation of SulphurShovl PaperG. A. DEANCommonwealth Scientific and Industrial Research Organization, Division of Soils,W.A.Regional Laboratory, Nedlands, \Vestern Australia.Ancrlyst, 1966, 91, 530-532.The Oxidation of Hydroxylamine in Sodium Hydroxide in thePresence of Copper(1r)Shovt PaperJ. H. ANDERSONLong Ashton Research Station, University of Bristol, Somerset.Analyst, 1966, 91, 532-535x SUMMARIES OF PAPERS IN THIS ISSUE [August, 1966Limits of Sensitivity of Detection of Aluminium in Amorphous andCrystalline Aluminium Oxide by X-ray DiffractometryShort PaperC. J. TOUSSAINT and G. VOSEuratom, Chemistry Department, Analytical and Mineral Chemistry Section,Ispra, Italy.Analyst, 1966, 91, 535-537.Nitrogen Factor for KidneyReport prepared by the Meat Products Sub-committeeANALYTICAL METHODS COMMITTEE14 Belgrave Square, London, S.W.1.Analyst, 1966, 91, 538-539.Nitrogen Factor for Cod FleshReport prepared by the Fish Products Sub-committeeANALYTICAL METHODS COMMITTEE14 Belgrave Square, London, S.W.1.Analyst, 1966, 91, 540-542.Methods for the Analysis ofNon-Soapy Detergent (NSD) ProductsbyG. F. LONGMAN, B.SC., F.R.I.C. & J. HILTON, B.Sc., A.R.I.C.(Unilever Research Laboratory, Port Sunlight)Society for Analytical Chemistry Monograph No. I-0-This Monograph describes in detail the methods of analysisdeveloped in Unilever’s Laboratories for the identificationand assay of components of NSD Products.-0-Available ONLY fromThe Editor, “The Analyst,” I 4 Belgrave Square, London, S.W. I(Not through Trade Agents)Price 15s.or U.S. $2.00 Post freeA remittance made out to “Society for Analytical Chemistry” should accompany every order.Members of the Society may purchase copies at the special price of 5s., post freeAEl SCIENTIFIC APPARATUSBULLETIN NO. 4ANALYSIS OF SOLIDS BY SPARKSOURCE MASS SPECTROMETRYSince the possibility of using spark source ionization for the analysis of solidswas first recognised ten years ago, the design of the double focusing massspectrometer using Mattauch geometry has been considerably improved. Andtoday one instrument-namely the AEI MS7-is capable of detecting im-purities at levels as low as 1 part in IO@. As a result the MS7-which, incident-ally, was the first commercially available double focusing instrument to bebuilt expressly for the analysis of solids-has found wide applicationsparticularly where overall coverage of all elements and comparison analysiswithout standards are valuable.Now the MS7 technique has been further improved by the careful control ofcertain parameters, and very good reproducability and accuracy can beguaranteed.This bulletin reviews the parameters affecting analytical accuracyand outlines the methods of control developed by AEI engineers.I t has been shown that the sensitivityof the majority of elements differs fromsome standard such as iron by no morethan a factor of 3 . In other words, mostrelative sensitivity factors lie between0.3 and 3 . In the case of the MS7, thedetermination of relative sensitivityfactors is considerably simplified bythe fact that the response of the instru-ment is linear over a very large rangeof concentration.Indeed Hannay &Ahearn established linearity over therange 104 to 1 using doped siliconsamples. More recently, W. A. Wolsten-holme (AEI Consultant Lab.) hasreported on the investigation of golddoped titanium samples covering a con-centration range from 0.5% to .02 ppmby weight; a range of more than lo5to 1.These samples were chosen because oftheir suitability for neutron activationand wet chemical analysis. Figure 1shows the relative ion intensity of goldplotted against the concentration de-+,ermined by chemical or neutron acti-FOOTNOTE :I Hannay and Ahenrn (1954) Anal. Chem 261956.reported in tables 1 and 2.In copper and steel relative sensitivitiesare very similar for chromium (1 -8 and1.4) and for tin ( 1 -3 and 1.1).Only forsome low BP elements is there amarked dependence on the matrix, e.g.(1.4 and 2.6) for lead.Homogeneity ofstandards and samplesCare has to be taken to use homo-geneous standards or alternatively toincrease the rate of consumption ofsample above the usual 5 to 10 milli-grams.As it happens, however, the possibilityof inadvertently using an inhomogene-ous sample has been materially reducedby the introduction of more reliablemethods of sample preparation.FIG. 1TABLE 1RELATIVE SENSITIVITIES ANDREPRODUCIBILITY OF R.F. SPARKSOURCE ANALYSIS OF COPPER:JOHNSON MATTHEY CA230kV r f.; 19.5kV accel. volts; pulse length andrepetition rate varied in the analytical plates,vation techniques.The “just detect-able” line is an individual assessmentfor ion intensity and the “densito-metric” line indicates that a micro-densitometer was used to scan thespectral lines; the two graphs havebeen displaced for the sake of clarity.Matrix effects are generally very small,as is illustrated by the relative sensi-tivities for copper and steel standards11014013016021 0250110 --lelativensitivit)3.851.41 .I1.31.43.11.8 -O htandard deviationseparatcnalyses31303225232720 -5 repealrposure131 1189.2211321 ReproducibilityThe most important improvements inreproducibility have been achieved bycareful control of certain instrumentalparameters.As a result of recent in-vestigationse it is now clear that themost important factor is one that iscomparatively simple to control ; name-ly, the ion accelerating voltage. Whenthis is always set to the same value, andother source conditions are kept asconstant as possible, reproducible ana-lytical results are obtained. The princi-pal reason is the improved constancyof the relative sensitivity factors fordifferent elements. Table 2 shows howclose agreement with known values isobtained when such relative sensitivityfactors are measured and used to cor-rect observed concentrations.Variations in PhotoplateThe standard deviations on identicalexposures on a photoplate using ahomogeneous aluminium standard in-dicate that the best standard deviationobtained for the different elements isabout loo/,.The standard deviation onisotope .ratios, i.e. where the relativeFOOTNOTE :2 Halliday, Swift and U'olstenholme; Quantita-tire Analysis by Spark Source Mass Spectro-metry, International Mass SpectrometryConference, Paris 1964.TABLE 2ACCURACY OF ANALYSIS AFTERZALIBRATION: BUREAU OF ANALYSEISTANDARDS LTD. MILD STEELRESIDUAL SERIES SPECTROGRAPHICSTANDARD SSl4Pulse length 100 microsecs ; 300 pulses/sec. :30kV r.f.; 19.5kV accel. volts.Concenrration % wtInpurityCrcoNicuZrNbMoSnPbLIST. average of MS7, CONeCtOd liven Spectmeight analyses using SSl2 graphic value0.26 0.18 0.1850.1 9 0.18 0.190.1 0 0.13 0.130.047 0.029 0.040.017 0.007 (0.005)0.072 0.025 (0.05)0.053 0.060 0.070.019 0.017 0.020.01 8 0.007 (0.0075)( ) not certified-approximatesensitivity factor is not involved andwhere a limited area of plate is used,show better figures of 3 to 4%.Thisindicates the likely variation due to theplate itself, and represents a limit thatwould remain even if a calibrationspectrum of a standard was placed onthe same photoplate as the sample tobe analysed.Reproducibility of AnalysesWhen different photoplates are used inseparate analyses the standard devia-tion increases.In repeat analyses different photoplateswill be used and also source conditionsmay vary slightly. To cover the fullrange of exposures (10' to 1) it is some-times necessary to vary the pulse lengthand repetition rate of the spark whichmight also contribute to the variations.An internal standard, although notessential, eliminates the need for sucha wide range of exposures.When the spark pulse-length and repe-tition rates for the analysis of a copperstandard shown in Table 1 were heldconstant throughout the series of suc-cessive analyses of one of the standards,the minimum standard deviation did infact decrease towards the minimumvalue previously obtained for repeatexposures (about 1 PA).Accuracy of AnalysisThe accuracy which can be attainedwith the MS7 when all parameters areproperly controlled is perfectly exem-plified by the data set forth in Table 2.In this case, of course, a standard ofreasonable homogeneity has been usedto establish relative sensitivity factorsfor the impurities in the given matrix.It will be noted that only one standardis used, and that the levels of concen-tration in the standard do not corres-pond too closely to those in the un-known.A steel matrix has been takenas an example because studies of sourceconditions indicated that it seemed themost likely (compared with the alu-minium and copper standards) to givepoor results should the source con-ditions change. It is clear, however, thatthe results once corrected for relativesensitivity factors are in excellent agree-ment with those given by chemicalanalysis.Further information on the MS7can be obtained from AssociatedElectrical Industries Ltd., ScientificApparatus Department, BartonDock Road, Urmston, Manchesteror your nearest AEI off ice.8 I01

ISSN:0003-2654    

DOI:10.1039/AN96691FP155

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

August, 19661 THE ANALYST xvCLASSIFIED ADVERTISEMENTSThe rate for classified advertisements i s 7s. a line (or spaceequivalent of a line), with a n extra charge of 2s. for theuse of a Box Number. Semi-displayed classifiedadvertisements are 80s. for single-column inch.Copy required not later than the 20th of the month pre-ceding date of publication which i s on the 16th of eachmonth. Advertisements should be addressed to TheAnalyst, 47 Gresham Street, London, E.C.2. Tel.:MONarch 7644.-CITY OF BIRMINGHAM PUBLIC HEALTHDEPARTMENTAssistant Analyst (male) required in thc City Analyst’sLaboratories for interesting work of a general analyticalnature. Qualifications required are a degree in Chemistryor Graduateship of the Royal Institute of Chemistry.Persons taking their degrees this summer are invited toapply.Salary: Graduate--A.P.T.Grade I1 (f;920-L1125)G.R.1.C.-A.P.T. Grade I11 (Ll090-iC;1340)Post permanent, pensionable and subject to medicalexamination.Applications giving details of age, qualifications andexperience together with the names of two persons to whomreference may be made should be sent to the Medical Officerof Health, Public Health Department, Trafalgar House,Paradise Street, Birmingham 1, by August 29th, 1966.NEW ZEALANDDEPARTMENT OF SCIENTIFIC AND INDUSTRIALRESEARCH.4pplications are invited for the undermentioned vacancy :Vacancy B 13/18/45/2526: Forensic Chemist. TheChemistry Division, Department of Scientific and IndustrialResearch, New Zealand, undertakes the scientific investiga-tion of crime for the Police Department.Applications areinvited for the position of chemist in the Division’s AucklandLaboratory. The appointee will be required to work with asmall group of spccialists in the scientific investigation ofdrugs and poisons in forensic toxicology.Salary: Up to L2065 p.a. is offered according to qnalifica-tions and cxperience, with opportunity for a further advancc-ment on scientific merit up to L2710 p a .Qualifications desired: B.Sc.(Hons.). Independent researchis encouraged. Modern physico-chemical techniques such asinfra-red, gas chromatography are available.Passages: Fares for appointee and his wife and family, ifmarried, will be paid.Incidental expenses: Up to E35 for a single man and &lo0 fora married man can be claimed to cover the cost of takingpersonal effects to New Zealand.Application forms and general information are availablefrom the High Commissioner for New Zealand, New ZealandHouse, Haymarket, London, S.W.1, with whom applicationswill close on August :iOth, 1966.Please quote refercrlce B 13/18/48/2526 whrn enquiring.COUNCIL OF EUROPEThe European Pharmacopoeia Commission will shortlyrequire a Scientific Officer as Head of the Laboratory soon tobe opened in Strasbourg.Full information and applicationforms may be obtained from the Establishment Division,Council of Europe, Strasbourg, France. Closing date forapplications September 30th, 1966.BRITISH PHARMACOPOEIA COMMISSIONSCIENTIFIC ASSISTANTApplications arc invited from graduatcs (pharmacy orchemistry) with experience in pharmaceutical analysis forappointment to thc staff of the Commission’s laboratoryworking on the investigation of analytical methods andspecifications for drugs.Commencing salary within therange L996 toA1462 according to qualifications and experience,Applications, marked “Appointment”, giving full detailsto The Secretary, British Pharmacopoeia Commission,General Medical Council, 44 Hallam Street, London, W.l.BSTRACTORS required Ability to prepare abstractsAfrom papers in French or‘Gcrrnan would be an advaiitagc.Apply to-The Editor, Analytzral Abstrartc, 14 BelgravcSquare, London, S.W.I.CHIE‘; ANALYST/DEPUTY required by Consultant withApplicants must holdthe Branch E Diploma (though an applicant about to take itmight be considered) and have at least two or three ytwsexperience in a Public .4nalyst’s laboratory ; they shouldpreferably be under 35.The person appointed must hecompetent to take charge of the day-to-day rumiing o f thelaboratory and to act as Deputy Public Analyst immediatt4yor in the very near future. Initial salary in the &SO00 toL2.500 range, with excellent prospects; the right man C R I Iexpect a major share in the practice at a later stage. Applica-tions i n full detail will be treated in strict confidence. Dr.E. C. Wood, Clarence House, Clarence Road, Norwicli,NOR 29T.appointments as Public Analyst..4NALYTICAL ASSISTAST also required. Applicants musthave H.X.C.at Irast, preferably L.R.I.C. or Grad.R.1.C.Initial salary L800 to L1200; some knowledge of food anddrugs analysis is nccrssary, prcferably g.tintd in a P.A.laboratory. The work is very varied and the prospects grwd,particularly for a man whose ultimate target is the Diplomain Branch E. Applications as above.THE UNIVERSITY OF SUSSEXTHE CHEMICAL LABORATORYM IC ROAN A LY STThere is a vacancy for an experienced rnicroanalyst to takecharge of the microanalytical laboratory. This position isgraded i n the Chief Technician salary range of L1242 toLl423 per annurn.Applications giving the namcs and addresses of tworeferees and a brief resume of previous experience aridqualifications, at the earliest opportunity, to the LaboratorySuperin tendent, Chemical Laboratory, thc University ofSusses, Falmer, Brighton.NL4LYST for silicate analysis rcquircd for GeologyADepartment for work initially in emission spectrography(experience preferred) and latrr co-operation in chemical andx-ray Auorescence analysis.Degree, H.N.C. or equivalentrequired. Appointment as Assistant Experimental Officer(~XOX-Ll243 p a . ) or Experimental Officer (Ll:i65-&17:14 p.a.)according to agr and qualifications. Write to AssistantBursar (Personnel), University of Reading, Reading,Berkshirc.CHELSEA COILEGE OF SCIENCE AND TECHNOLOGYManresa Road, London, S.W.3DEPARTMENT OF CHEMISTRYPOSTGRADUATE COURSES(i) Analytical Chemistry, il1.S~. (University of London)Applications are invited from graduatcs, or persons withequivalent qualifications, for admission to the above coursecommencing on October 3rd, 1966.The coiirse coiisists oflcctures, seminars, tutorials and laboratory work at a post-graduate level. Candidates who fulfil the entry requirementswill be registered for thc M.Sc. dtxgrcc (University of London)and other candidates for thc, Diploma of Chelsea College(D.C.C.).ljull-time students complete the course in one academicyear (October to July). The course may be taken part-time.Thc full-timr Analytical Chemistry course has hrenapproved by the S.R.C. for the award of Advanced CourseStudentships to suitably qualified studcn ts.Vacancies are strictly limited. Furthcr details may beobtained from thc Academic Registrar, to whom applicationsshould be scnt as soon as possible.(ii) The Chcmistry and Microscopy of Food, Drugs and WaterA special postgraduate evening course of lectures andpractical work based on the syllabus for the examinationleading to the Diploma of the Royal Institute of Chemistry(Branch E) will be given during the academic year commenc-ing October 3rd, 1966. The course is primarily intended forstudents who wish to prepare for this examination, but is alsosuitable for other chemists and pharmacists who have aninterest in the analysis of food and drugs.Full particulars can be obtained on application to theCollege Academic Registrar

ISSN:0003-2654    

DOI:10.1039/AN96691BP167

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

AUGUST, 1966 THE ANALYST Vol. 91, No. 1085 Rapid Automated Determination of Biphenyl in Citrus Fruit Rind* BY F. A. GUKTHER AND D. E. OTT (Department of Entomology, University of California Cztrus Research Center and Agricultural Experiment Station, Riverside, California) A totally automated analytical procedure for determining the fungistat biphenyl in citrus fruit rind has been developed. Small pieces of hand-peeled rind are automatically homogenised in water and steam-distilled to liberate the biphenyl, which is trapped in cyclohexane solution ; this solution is exhaustively extracted to remove interfering steam volatiles, and the biphenyl remaining is read a t 246 mp in a continuous flow recording spectrophotometer. Time required from the introduction of rind samples to read out of biphenyl present is 9 minutes, with about 15 minutes for the first sample.The useful range is from 1 to about 150 p.p.m. on a whole-fruit basis with a reproducibility of about 3 per cent. The method has been applied most extensively to Valencia oranges. THE fungistat biphenyl has been used commercially since about 1935l to protect citrus fruits from the normally extensive post-harvest decay caused principally by the so-called blue- green moulds, PeniciZZium digitaturn and P. notatztm. Despite the objectionable odour of biphenyl it is still used in immense tonnages, wherever citrus is grown, as a mould inhibitor on the multi-billion dollar citrus crops in storage and transit around the world. A com- bination of fortuitous properties makes the chemical biphenyl unique for this purpose: it is non-toxic, non-carcinogenic,2 inexpensive, its vapour tension - temperature relationships1 are ideal for the purpose, it can be easily handled and is a sublimable solid, and its vapour is highly fungistatic to the omnipresent blue and green moulds in their rind locales.With any of the usual methods of application to citrus fruits it does not penetrate through the ntact rind but resides in the wax “layers” and oil sacs of the rind until the fruits are adequately aired, allowing it to escape slowly by vaporisation. Because of its strong and persistent odour, however, much effort during the past 20 years has been expended to find a less offensive but otherwise satisfactory substitute for biphenyl. Thousands1 (Souci, S.W., private communication ; Eckert, J. W., private communication) of candidate chemicals have been screened in many laboratories for this purpose, but an equally efficient and acceptable substitute citrus fruit fungistat or fungicide has not yet been found. Because of its unusually low mammalian toxicity2 the United States’ legal tolerance for biphenyl on and in citrus fruits and products is 110 p.p.m. on a whole-fruit basis; this is the highest specific tolerance value yet assigned to any pesticide by the U.S. Food and Drug -Administration, except for some organobromine fumigants calculated as inorganic bromide. To stimulate efforts to find a less offensive substitute, however, some other countries have accorded lesser tolerance values to biphenyl in this usage.For example, Great Britain and France allow a still realistic maximum of 70 p.p.m., whereas in 1965 The Netherlands’ government legislated3 the completely unrealistic and fungistatically ineffective (Eckert, J. W., private communication) maximum of 30 p.p.m. Absolute enforcement of any pesticide tolerance restriction requires the extensive use, with confidence, by both the producing agency and the ultimate consuming agency-whether * Universitj- of California Citrus Research Ccntcr and A4gricultural Experiment Station Paper No. 1698. This material was presented in part at the Scptember, 1985, Technicon Symposium “Automation in Analytical Chemistry,” New York. 475476 GUNTHER AND OTT : RAPID AUTOMATED DETERMINATIOK ;Analyst, TTol. 91 it be wholesale buyer, importer or regulatory official-of an adequate residue analytical method.Adequacy in this instance relates to satisfactory reproducibility in many different laboratories, to a minimum detectability that will comfortably bracket the lowest amount permissible, to simplicity of operation because of the world-wide shortage3 of trained residue analysts and to rapidity because of the thousands of samples that should be involved. I t should also relate to the ability of the operation and required apparatus to be standardjsed so as to circumvent the unfortunate errors4 almost always introduced when a residue analytical method produced by one laboratory is adapted to the always slightly different equipment, supplies, conditions and personnel training in another laboratory.Because of the importance of biphenyl over three decades, there are dozens of residue analytical methods for this fungistat; Rajzmanl has reviewed in detail the most acceptable ones, and has pointed out the advantages and disadvantages of the many analytical approaches involved. Because it was readily adaptable, one5 of these methods has now been totally automated, from fruit or fruit rind to p.p.m. of biphenyl present, to provide a method that is fast, reliable, operationally simple, and unique in that it is a standardisable biphenyl-residue screening m e t h ~ d . ~ This method represents the near-ultimate in pesticide residue analysis. It is the first example of complete automation, from homogenisation in water of the fruit or fruit rind to recorder read out 9 minutes later of the amount of biphenyl present in that sample relative to fortified control samples, within the range of 1 to about 150 p.p.m.on a whole-fruit basis. METHOD APPARATU s- as shown in Fig. 1, and are listed as follows. AutoAnalyzer modules (Technicon Controls Inc., Ardsley, Xew York) are connected Solidprep sampler. Proportioning pzwzps, two. Digestor, with accessories f o r d i s t i l l a n h use. 6 0 PS4 @ 0 Proportioning Waste Proportion i ng Pump I 1 Ultraviolet spectrophotorneterT IO-mm quartz rectangular f j c 246 mp I Recorder Fig. 1. Automated system for biphenyl residues in citrus fruit rind. to pump 45ml of water as homogcnising fluid, and the rate of sampling is 7 per hour. in inches = Acidflex tubing; S = Solvaflex tubing) The Solidprep sampler is set Tube sizes are-lugust, 19661 OF BIPHENYL I N CITRUS FRUIT RIND 477 Evacuated separator (see Fig.2)--For simplicity in drawing this figure, the waste digestant liquid a t the end of the helix is shown as being aspirated into the vacuum source; in practice, however, the most convenient disposal is to pass to waste through an all-glass or plastic water aspirator. Distillables plus added cyclohexane Pump cyclohexane phase $i n sleeve ,lip j o i n t vacuum trap t 1 Pump aqueous 5 cm phase t o waste Fig. .2. Details of cxracuated separator essential to the biphenyl-residue automated system I'ltraviolet s#ectro#hotometer-The spectrophotometer is dual beam, with a 10-mm light Strip-chart recorder, 10 mV. Glassware and tubing (see Fig. 1). ASSEMBLY OF APPARATUS- The detailed flow diagram for the apparatus is schematically presented in the standard manner in Fig.1 ; a few minor changes may be needed in a particular system for smooth and reliable operation. Thus, the flow-rates controlled by some of the tubings in the two pumps may need to be: varied from those shown in the figure in order to achieve optimum flow characteristics. In particular, the diameter of the pump tubing at position 11 on the left-hand pump may need to be increased for maximum flow, or decreased to keep air bubbles out of the spectrophotometer cell. Also, the rate of flow of material pumped from the bottom of the evacuated separator may have to be varied to achieve good separation within the 5eparator. Acidflex sleeving over joints and transmission tubing is used throughout the system where there is possibility of contact with concentrated sulphuric acid, except where indicated otherwise.,411 joints (glass to glass, flexible-tubing to glass, or flexible-tubing to flexible- tubing) associated with the sampling system from the homogeniser vessel to the pipette which introduces sample and digestant into the digestor helix must be butt joints (no con- necting nipples) to avoid blockage by particles of orange rind. For the same reason the tubing from the mixing coil in this same stream to this introduction pipette should be Acidflex sleeving rather than transmission tubing. The introduction pipette should be long enough to introduce the sample directly into the heated zone ; accumulation of rind and other particles occurs if introduced into an unheated zone.Biphenyl-exhausted particles will accumulate in the cool downstream end of the helix, however, but here there is no risk of their subsequent dislodgement and contamination of another sample; the helix must be cleaned after about 1 week when in constant use to remove these gross accumulations. path rectangular quartz flow-cell in the sample side, and nothing in the reference side.478 GUNTHER AND OTT: RAPID AUTOMATED DETERMINATIOK [ArtdySt, VOl. 91 PROCEDURE- This system utilises either analytical-reagent grade or spectrograde cyclohexane” for extrac- tion of the distillate, and analytical-reagent grade sulphuric acid for the cyclohexane wash series. The Solidprep sampler is set to pump 45 ml of water as homogenising fluid, and is operated with a standard factory set programmer; the homogeniser motor is set for medium speed during the sampling cycle. The vacuum pump connected to the evacuated separator (Fig.2) is set for about 2 inches of mercury, the requirement for the separator, which in turn supplies the vacuum to collect the vapours in the collection funnel. This funnel is inserted into the exit end of the digestor helix which rotates a t 20 r.p.m. and is heated by setting the heater controls 1 and 2 at 3.0 and 5-0 amps, respectively. The ultraviolet spectrophotometer is set at the pre-determined absorption maximum for biphenj-1 in cyclohexane solution (246 mp under the present conditions, although Gunther et aZ.5 specify 248 mp). A 0.062-inch horizontal aperture slit is used in the air path of the reference side of the dual-beam spectrophotometer.To keep the measuring cell clean, the following procedure when shutting down the system is suggested: as rapidly and nearly simul- taneously as possible, the transmission tubing that is connected to the cell and to the pump tube which pulls the continuous stream of cyclohexane through the cell, is disconnected at the nipple joint from that pump tube, while a small pinch clamp is tightened over the three tubings which are connected collectively to the spectrophotometer (see Fig. 1) ; finally, a similar pinch clamp on the waste line connected to the bottom of the BO glass fitting is loosened to by-pass the contents in that fitting to waste. M7hen starting the system up, and after equilibrium conditions are reached, a continuous stream of cyclohexane pours into the BO fitting, and the foregoing procedure is performed in reverse. The chart drive of the recorder is turned on, and when the base-line becomes stable after about 15 minutes the Solidprep sampler is started with an empty cup in the first position followed by samples of previously chopped fruit rindt weighed into sample cups in every third successive cup, with two intervening empty cups between each sample for “wash” purposes; in this mode of operation the rate of sampling is 7 per hour.For routine screening analyses one empty “wash” cup will probably suffice, thus decreasing the time required per analysis by one-third. 1Vith series of samples containing both very high and very low levels of biphenyl, however, two cups for washing are necessary (see diffusion on Fig.4). DISCUSSIOS OF THE METHOD A simplified flow diagram of the basic steps in this biphenyl analytical system is shown in Fig. 3. The rind previously chopped into approximately Q-inch or smaller cubes is auto- Citrus rind Solidprep sampler - Digestor E Condenser Digestion-distillation Condensation of biphenyl and other distillables in cycloh exan e (C y c I o h e xan e p h as e) Ultraviolet spectrophotorneter (measurement at 246 mp) Fig. 3. Simplified flow diagram of the basic steps in citrus fruit rind c Separator Extractors Conc. H2S04 extraction of cyclohexane phase t HzS04 t o waste in the automated system for biphenyl residues matically homogenised in water, and then steam-distilled in the presence of sulphuric acid to liberate the biphenyl PLUS citrus oils (mostly terpenoids) and waxes.These steam volatiles are trapped in cyclohexane, the oils and waxes are quantitatively extracted into concentrated sulphuric acid, and the biphenyl left in the cyclohexane is determined at 246 mp. In the original manual method” some p-cymene escaped the room-temperature acid washing or was * The manual method5 requires thc iisc of spectrogradc cyclohexane. t $-inch or smaller cubes prepared by a Hobart or similar food chopper.August, 19661 OF BIPHENYL I N CITRUS FRUIT RIND 479 formed6 from other terpenoids ; to minimise this highly variable interference it was oxidised with permanganate, then washed out with more sulphuric acid.The present continuous acid extraction step at 45" C either removes @-cymene without the necessity for an oxidation step, or else the small-sized starting sample (2 g of rind against 150 g of whole fruit for the manual method) effectively reduces this particular background contribution to nil in this measuring system. One of the major obstacles in the development of this automated procedure was the problem of continuously separating an aqueous phase from an immiscible solvent phase, while at the same time having these two phases under reduced pressure. This was overcome with a special glass evacuated separator. As it is new as well as essential for the biphenyl system it has been shown in detail in Fig. 2. This device does not guarantee an absolutely non-aqueous stream out of the top.After the slip joint has been optimally set under equili- brium and fixed conditions for vacuum pump and digestor temperature, the occasional small amounts of aqueous phase and occasional air bubbles are entrained in the emergent cyclo- hexane solution; these are either sufficiently constant, or in such small amounts that the net reproducibility of results is not affected. Typical chart recordings are produced in Fig. 4, and were obtained from 1 or 2-g starting samples of chopped Valencia orange rind. These recordings are from the system operated for 7 consecutive, noise-free hours according to the flow diagram in Fig. 2. Thirty-four samples and 8 controls and fortified controls were run that day with no special (single) operator attention.The average time interval was therefore 9 minutes per test, exclusive of about 30 minutes for warm-up and 15 minutes for shut-down, Note the absence of significant background (Fig. 4) from even 2 g of control rind, and also the close agreement between '"I 20 I- - F Time Chart recordings obtained from the biphenyl-residue automated sytem: A, 1 g of Valencia orange rind control; B, 2 g of rind; C, 1 g of rind fortified with biphenyl a t 350 p.p.m.; D, 2 g of rind fortified with biphenyl a t 350 p.p.m.; E, 1 g of rind from the biphenyl-treated carton of fruit; F, sampling cycle origin of last peak Fig. 4. replicates by comparison of ordinate intercepts of peak maxima alone. For greater precision, peak height (or area) in absorbance units should be used: this is the difference in absorbance units between the peak maximum and a base-line drawn in the usual manner beneath the peak.Absorbance unit - peak height measurements were obtained in this way for a series of controls (rind from untreated samples) fortified in the range 35 to 700 p.p.m. to establish a fortified-control standard curve. To 1 or 2-g portions of chopped control rind, weighed into every third sampler cup, were added appropriate volumes (up to 2 ml) of a standard solution of 350 pg per ml of biphenyl in 95 per cent. ethanol, or a standard volume of solutions of varying strengths. There were no measurable differences between the 1 or 2-g samples of control rind run alone through the system and the 1 or 2-g samples of control rind each containing 1 ml of 95 per cent.ethanol. The resultant standard curve had a slope of 195 p,p.m. of biphenyl per 0.1 absorbance unit. Reproducibility results were as follows. The lowest point, 35 p.p.m. in the rind (a value which is roughly equivalent to 7 pp.m. based on the480 GVNTHER AXD OTT RAPID AIJTOMATED DETERMINATION [,4?2dySt, lrO1. 91 U.S. Food and Drug Administration practice of weight of whole fruit,” and well below The Netherlands’ tolerance of 30 p.p.m. mentioned earlier), was replicated six times jielding a mean value of 0.017 i 0.001 absorbance unit; a next higher value at 70 p.p.m. was replicated four times, with a mean value of 0.037 t 0.004 absorbance unit; the mean value at a 175 p.p.m. level, from three replicates, was 0.082 0.005 absorbance unit; other absorbance values averaged 0-200 at 350 p.p.m.and 0-350 at 700 p.p.m. These values were not corrected for a background of 0.003 absorbance unit per gram of control rind. For greater minimum detectability, 2-g samples of rind can be used routinely, or a recorder range expander can be added with l-g samples: the 2X position is feasible but noise and base-line shifting usually exclude the 4X and 1OX positions. Two-gram samples of grapefruit and lemon rind are necessary for adequate sensitivity and precision when AutoAnalyzing these citrus fruits. To examine samples representative of commercial practice, half of a field box of tree- ripened Valencia oranges was stored for 6 days at 25” to 30” C in a standard vented citrus fruit shipping carton. Standard, commercial, biphenyl-treated liners were placed in the bottom and top of the carton, and for extreme dosage one was placed in the middle with oranges above and below it.The other half box of oranges was kept in a separate room’as a control. Fruits were sampled from the top of the “treated” carton for AutoAnalysis, producing the two peaks labelled E in Fig. 4. From the fortified-control standard curve, 175 8 p.p.m. of biphenyl were in and on the rind of this treated fruit, equivalent to 33 & 2 p.p.m. on a whole-fruit basis. The primary problem that has occurred with the present system is that occasionally there is excessive signal noise to the recorder associated with the physical composition of the stream flowing through the measuring cell. However, if the cell tubing connections are all clamped off when this noise appears, and the cyclohexane stream is momentarily by- passed (according to directions in the shut-down procedure) to leave in the light path a full and static-condition cell, the noise immediately stops, yet there are no visible air bubbles or other contaminants.This problem is more annoying than serious, however, as peaks recorded during these periods quantitate comparably to smooth peaks from equivalent samples if a curve drawn midway through the noise is used for measurement purposes. The noise rarely lasts longer than 30 minutes at a time; if it starts in the middle of a peak that peak will probably be lost for quantitative purposes because there is a marked base-line shift at the start of the noisy period. At present it is not possible to relate directly and simply the slope of the fortified control standard curve to that of a primary standard curve with biphenyl alone.Without a “keeper,” (e.g., orange oil), biphenyl alone shows large and variable losses during the Solidprep homo- genisation cycle. The reason for lower responses from the few exploratory samples of fortified grapefruit and lemon rind, compared (Table I) with fortified l’alencia orange rind, may be due to lower amounts of oils and waxes as “keepers” in the first two varieties. Thus, standardisation must always be in terms of fortified controls of the same variety as the unknowns. Both automated and manual5 methods are compared in Table I. Background values from untreated (control) samples are collated in Table I1 in com- parison with corresponding samples run by the manual5 method.I t is clear from these results that variable backgrounds from grapefruits and lemons were not a cause of the lower recoveries shown in Table I. Despite these minor disadvantages, the advantages of speed, convenience, precision and reproducibility, coupled with more than adequate sensitivity for monitoring purposes, result in an automated system that should merit further evaluation for eventual adoption bj- control laboratories around the world as a screening method for biphenyl residues in citrus fruit rind. With this system, speed of analysis is reduced to minutes-per-sample rather than the hours-by-sample required by the several manual methods at present being used both in the United States and in Europe. With cups in the Solidprep sampler arranged as recom- mended, the time lapse between successive samples is 9 minutes.This was the loading used in the present investigation to achieve the maximum accuracy from assured adequate purging of the system between samples containing, at random, from none to more than 175 p.p.m. of biphenyl each on a whole-fruit basis. In screening operations routine samples * Mature Valencia orangcs contain 18.7 1 6-3 per cent. rind based upon 297 measurements, Navel oranges contain 22.1 5 7.3 per cent. rind (567 mcasurements), lemons contain 30.0 1 8.5 per cent. rind (632 measurements), and grapefruit contain 2 3 4 & 3.2 per cent. rind (47 measurements).August, 19661 OF BIPHENYL IN CITRUS FRUIT RIND 481 would contain from about 30 to about 120 p.p.m., and this meticulous purging might not be necessary; in this situation every other cup could contain a sample with consequent reduction of average time per analysis to 6 minutes.In its present form this method should also work with whole fruit that has been made into a purke and commercial fruit products, but these applications should be checked with fortified samples for reproducibility, sensitivity and efficiency before routine application. Applications to grapefruits and lemons should incorporate enough fortified controls to establish a reliable recovery value as related to Valencia oranges at 100 per cent. TABLE I ILLUSTRATIVE COMPARATIVE RECOVERIES AND REPKODUCIBILITIES O F AUTOMATED AND MANCAL BIPHENYL METHODS ON COMMERCIALLY TREATED FRUITS I N THE APPROXIMATE RANGE OF 30 TO 150 P.P.M.ON A WHOLE-FRUIT BASIS Avcrage recovery, per cent. Reproducibility, per cent. (- Automated* Manual Automated Manual h _7 r--- 7 Variety (2-g sample) 1. ( 150-g sample) (2-g sample) 7 (1 50-g sample) Grapefruit . . . . . . 38 (44 p.p.m.) 100: 1.2 1 3 : Lemon . . . . . . 52 (58 p.p.m.) 99 1 2 5 1 Orange, Valencia . . . . 100 98 f 3 *1 Orange, Navel . . . . c3 100 8 5 1 * From standard curves prepared from fortified controls, compared to Valencia oranges at t Rind only. assumed 100 per cent. recovery. Unpublished results developed in 1959 by Gunther and co-workers in routine application 5 Navel oranges were not in season at the time of this study; the manual results illustrate to commercial shipments in Hamburg, %‘.Germany. recoveries for possible comparisons by others in routine applications of the present method. TABLE I1 ILLUSTRATIVE BACKGROUND VALUES FROM CONTROL SAMPLES WITH AUTOMATED AKD MANCAL METHODS OX A WHOLE-FRUIT BASIS Background Absorbance units Equivalent, p.p.m. I h > 7 <----- 7 ----- Automated M anii a1 Automated Manual I’arie t y (2-g samples) * (1 50-g samples) t (2-g samples) * (150-g samples) t Grapefruit . . . . . . 0-004 0.001 0.005 0.003; 1.9 & 0.3 1.5 0.6: Lemon . . . . . . 0.004 i 0.001 0.008 & 0.002 2.6 f 0.5 1.8 5 0.4 Orange, Valencia . . . . 0.003 & 0-001 0.010 0.004 1.1 f 0.2 3.1 0.9 Orange, NaXTel . . . . § 0.004 & 0.001 § 1.0 i 0.2 * Kind only. t \:hole fruit. L-npublishcd results developed in 1969 by Gunther and co-workers in routine application S Navel oranges were not in season a t the time of this study; the manual results illustrate to commercial shipments in IIamburg, FV. Germany. recoveries for possible comparisons by others in routine applications of the present method. REFERENCES 1. 2. 3. 4. 5. 6. Gunther, F. A., Adv. Pest Control Res., 1962, 5 , 191. Rajzman, X., i9t Gunther, F. A., Editov, “Residue Reviews,” Springer-T’erlag, Heidelberg and New York, Volume 8, 1965, p. 1. van Stratum, I?. G. C., “The Toxicity of the Citrus Fungistat Diphenyl,” Central Institute for Nutrition and Food Kesearch T.N.O., Report No. R1838, The Netherlafds, November, 1964. Gunther, F. A., and Ott, D. E., “Automation in Analytical Chemistry, 1965, Technicon Sym- posium, New York, N.Y., 1965. National Academy of Sciences-National Research Council, Pesticide Residues Committcc, Report on “no residues” and “zero tolerance,” Fiashington, D.C., June 1965. Gunther, F. A., Rlinn, R. C., and Barkley, J . H., Analysf, 1963, 88, 36. Received February 14th, 1966

ISSN:0003-2654    

DOI:10.1039/AN9669100475

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

482 WHITE AND SCHOLES: DETERMINATION OF CARBON I N [Ana&St, VOl. 91 Determination of Carbon in Steel by a Dynamic Infrared System BY G. WHITE AND P. H. SCHOLES (Bvitish Iron and Steel Research Association, Metallurgy Division, Hoyle Street, Shefield 3) A simple, automatic apparatus has been developed for the rapid deter- mination of carbon in steel. I t is based upon the continuous measurement of carbon dioxide evolved during the high temperature combustion of steel in oxygen by using a specially designed infrared gas analyser and integration system. When this is used in conjunction with a conventional resistance-tube furnace, the spced of the determination varies from 40 to 55 seconds for mild and low alloy steels, and slightly longer for highly alloyed materials. CONSIDERABLE progress has been made during recent years in the development of com- bustion apparatus for determining carbon in steel.There are now several analysers available commercially in Europe and North America.1 These new instruments are entirely automatic. The operator has only to place a weighed sample into a refractory container and insert this into a combustion furnace. From this stage the determination proceeds automatically, the operator being required only to read a meter and perform a simple conversion to the percentage of carbon. The commercial analysers can be classified into three groups according to the technique used to measure the carbon dioxide evolved during the high temperature combustion of steel samples in oxygen. These measuring systems are (a) electrochemical, mainly those of German origin, (b) thermal conductivity (used in instruments made in North America), and (c) infrared absorption (used in a British and a French instrument).Current developments in the tech- niques available for the rapid sampling of molten steel permit the use of these analysers for process control purposes, and another rather arbitrary grouping is possible in terms of instru- ment time. For the electrochemical instruments this is normally 2& to 4 minutes, being rather longer for the French infrared analyser, and 60 to 90 seconds for the thermal-con- ductivity instruments and the British infrared analyser. With instruments of the latter group it is, therefore, possible to determine the carbon content of, for example, large open- hearth furnaces at 5-minute intervals.With the exception of the Canadian Thermocarb,2 the commercial process analysers incorporate a static measurement system in which the combustion gas is first collected before measurement. One of the disadvantages of this approach is that conditions must be carefully pre-arranged to ensure that combustion is completed before measurement of carbon dioxide takes place. For maximum speed it seemed preferable to use a dynamic approach, in which the carbon dioxide content of the combustion gas is monitored continuously by using a fast-response detector with electronic integration. Previous work by the authors had shown that remarkably fast combustion of samples, in the form of turnings and solid pins, could be obtained with an inexpensive resistance-tube furnace.In the system used, combustion takes place in the presence of excess oxygen, and the combustion gas is pumped from the furnace at a fixed rate. Measurement of the evolved carbon dioxide by infrared absorption is an attractive alternative to thermal-conductivity measurement, and is free from many of the difficulties arising from the instrumental instability of the latter technique. The principle is not new, it was first proposed by Lay3 in 1955, Le Controle de Chauffe of Paris published a brochure in 1962 describing a prototype carbon analyser based upon infrared measurements, and in the following year, Tipler4 described an analyser designed principally for determining low carbon contents in steel and silicon - iron.The latter instrument has now been modified by Hilger-I.R.D. Limited for more general appli~ation.~ Both instruments incorporate static measurement systems of the type mentioned earlier. In early 1963, an infrared analyser was kindly made available to the authors by Hilger-I.R.D. Limited for initial experiments on the dynamic measurement of the evolved carbon dioxide. In this paper, the development of a dynamic carbon-in-steel analyser, the Dynacarb, is described. The primary consideration in design is that the apparatus should be inexpensive, have a rapid throughput time and be capable of application to all types of steel. Sometimes this is unnecessary as the percentage of carbon is shown directly.August , 19661 STEEL BY A DYNAMIC INFRARED SYSTEM 483 EXPERIMENTAL Preliminary experiments were carried out with a standard single range, direct-reading infrared analyser supplied by Hilger-I.R.D. Limited. Combustion patterns for various types of steel were recorded with a moving-chart potentiometer, and it was found that, with furnace temperatures in excess of 1300" C and high oxygen flow-rates, combustion of most samples was complete in less than 1 minute. The recorded pattern of carbon dioxide concentration versus time was extremely symmetrical, but from attempts to relate carbon content to integrated peak area it was clear that the response of the analyser was not adequate to detect all of the carbon dioxide present in the gas. Experiments designed to slow down the rate of carbon dioxide evolution and its subsequent introduction to the analyser were not successful, and the obvious requirement was an analyser with a much more rapid response- time.A second infrared analyser was obtained that had a response-time of about 200 milli- seconds, and was suitable for measuring concentrations of carbon dioxide up to 12 per cent. by volume. This instrument, which incorporated a high speed recorder suitable for obtaining combustion patterns, had previously been used as a prototype for experimental work in determining carbon dioxide in respiratory gases. ( a ) 0.29 percent. of carbon Time, seconds Fig. 1. Typical combustion patterns. Temperature 1350" C, flow-rate 900ml per minute In general, the recorded patterns showed a reasonable degree of symmetry, but, in a few instances, irregular combustion conditions caused minor rapid fluctuations in the carbon dioxide content of the evolved gases.The maximum carbon dioxide concentration at any one instant did not exceed 8 per cent. by volume. Typical combustion patterns are presented in Fig. 1. Measurement of the area under the peak gave reproducible values, provided that the oxygen flow-rate through the analyser was maintained at a constant level. Mixing tubes of various capacities were inserted into the flow system at the entrance side of the analyser, in order to decrease the proportion of carbon dioxide in the combustion gas. The values obtained were similar to those obtained in the absence of expansion tubes, confirming that instrument response was sufficient to detect all of the carbon dioxide passing through the analytical cell.484 WHITE AND SCHOLES: DETERMINATION OF CARBOX IS [L4naZyst, Vol.91 These experiments showed that dynamic infrared measurement of carbon dioxide was feasible, and an apparatus based upon these principles was designed in conjunction with Hilger-I. R.D. Limited. 10- Resistance tube O ~ I I I I I I Infrared anal yser Electronic linearising and integrating device Flow controller Fig. 2. Block diagram of prototype apparatus AFPARATUS- A block diagram of the Dynacarb apparatus is shown in Fig. 2. Gas analyser-The gas analyser is a modified, general-purpose instrument incorporating a specially designed analytical cell for the measurement of high velocity gas streams. I t is suitable for use with carbon dioxide concentrations up to 10 per cent.by volume in oxygen, and has a response-time better than 200 milliseconds. As the electrical output of infrared analysers is logarithmic in function, it was necessary to incorporate a linearising circuit in order to produce a signal that could be integrated and displayed on a meter. This was accomplished by dividing the curve relating meter-reading to voltage-output into a number of segmenk6 Each segment has an associated printed circuit card with a silicon diode and an adjustable potentiometer. Bias is applied to each diode to ensure that it will pass only current higher than the voltage of selected ordinates of the meter reading - voltage relationships; the voltage of each segment is then adjusted by its potentiometer to give an over-all linear relationship.During combustion of a sample, the linearised signal is stored by a suitable condenser, and is continuously displayed on a meter throughout the determination. OxygenJEow-A pump maintains a constant flow of gas through the apparatus. Fluctu- ations in flow-rate, caused by irregular combustion, are avoided by the supply of a large excess of oxygen during ignition of the sample. Excess oxygen escapes from the mouth of the tube, and provides an adequate seal against the atmosphere without the need for any form of closure. Large fluctuations in the percentage of carbon dioxide evolved are smoothed by passing the gas through a small pre-mixing vessel attached to the analyser. The effect of changes in flow-rate was studied by injecting identical volumes of carbon dioxide into the flexible tubing of the apparatus by means of a Hamilton gas-tight syringe, and recording the meter deflections at various flow-rates. In Fig.3, it can be seen that there is a plateau region between 900 and 1000 ml of oxygen per minute. The reasons for this areAugust, 19661 STEEL BY ii DYNAMIC IKFRARED SYSTEII 485 obscure, but Bartley (in a private communication) has suggested that it may be caused by a change in the nature of the gas flow through the analytical cell. It seems probable that, at flow-rates below 900 ml per minute, the flow is laminar, but above this value a certain amount of turbulence is introduced and, while the over-all flow-rate is unaffected, there is some slowing down in the passage of carbon dioxide through the cell.A flow-rate of 950ml per minute was, therefore, used in subsequent work; this was achieved by means of a rotary pump and adjustable flow regulator. FORMATION OF IRON OXIDES- When combustion of samples takes place at high temperatures with fast oxygen flow- rates carry-over of iron oxide becomes troublesome and it is essential to filter the gas stream efficiently before passing it through the analyser. Filters made from cotton-wool and glass- wool become blocked and cause fluctuations in the flow-rate. The problem was overcome by using a calico filter-cloth in a small glass container of the type used with American high frequency furnaces. This proved to be most effective and may easily be cleaned by tapping the container or gently brushing the filter-cloth.CHOICE OF FLUX AND BLANK DETERMINATION- The pick-up of carbon from extraneous sources arises from ( a ) the oxygen supply, (b) the combustion boat and (c) the fluxing materials. After purification of the oxygen supply and pre-ignition of the combustion boat, the contribution from ( a ) and ( b ) is negligible at the carbon levels investigated.’ Pre-ignition of the boats is best performed in one tube of a twin-tube furnace. After cooling in air for a few minutes, the boat is loaded with the sample and flux and then ignited in the second tube. Under these conditions the blank value can be attributed solely to the flux. Two fluxing materials, tin powder and lead foil, have proved satisfactory. The addition of lead foil to carbon and low alloy steel gives a fairly smooth combustion and a minimum carry-over of iron oxide.With careful handling the blank is of the order of 30 p.p.m. of carbon. For more complex steels and solid-pin samples, lead is not suitable and additions of tin powder must be made. Combustion is not as smooth and carryover of iron oxide is greater, but the blank values are lower, and are in the range of from 10 to 20 p.p.m. of carbon. CALIBRATION OF THE ANALYSER- The infrared analyser is initially set up with a gas mixture nominally containing 8.6 per cent. of carbon dioxide in oxygen. With the prototype, it is not possible to adjust the inte- grator meter to obtain a direct reading of the percentage of carbon for a specified sample. Scale calibration may be achieved by burning a number of standard steels in oxygen, and constructing a graph relating meter divisions to carbon content.I t is preferable, however, that calibration should be independent of standardised steels and, therefore, it is better to inject varying volumes of high purity carbon dioxide (volume corrected to S.T.P.) into the system with a Hamilton gas-tight syringe. The relationship between integrated meter reading and carbon dioxide is linear and remains constant over long periods, provided that the infrared analyser is free from electronic drift. This possibility must be checked several times during the course of each working day by using the setting-up gas mixture. A simple slide-rule conversion after each test is all that is necessary to obtain the percentage of carbon. The instrumental precision of the analyser was assessed by injecting a series of identical volumes of carbon dioxide into the system. The coefficient of variation of measurements, obtained for repetitive injections, is about 1 per cent.: this value is, however, limited by the precision of the injection syringe used in these tests. ANALYTICAL PERFORMANCE WITH RESISTANCE AND HIGH FREQUENCY COMBUSTION FURNACES For reasons of economy and simplicity, the Dynacarb apparatus is primarily intended to be used with a resistance-tube combustion furnace. Tests have also been made with a high frequency furnace and a comparison of analytical speeds is given in Table I.486 WHITE AND SCHOLES: DETERMIXATION OF CARBON I N (Analyst, Vol. 91 TABLE I COMPARISON OF ANALYSIS TlMES WlTH RESISTANCE AND HIGH FREQUENCY COMBUSTION FURNACES Instrument time, seconds f-y------ Resistance High frequency Millings and drillings heating heating Mild and medium-carbon steel .. . . . . 40 to 50 35 to 45 Low alloy and high-carbon steel . . . . .. 45 to 55 40 to 50 Stainless steel . . . . . . . . . . . . 45 to 50 30 to 40 High-carbon alloy steel . . . . . . . . 65 to 76 50 to 60 Pin sambles- 1 5-mm diameter Mjld steel . . . . . . 55 to 70 35 to 45 3-mm diameter {Carbon and low alloy steel . . 50 to 65 35 to 45 1-High-carbon steel . . . . 65 to 80 45 to 55 40 to 50 { High-carbon steel . . . . 60 to 80 RESISTANCE HEATING- There was no difficulty in obtaining the complete combustion of samples of even the most complex alloy steel in the form of millings and drillings, with a conventional tube furnace.The best results were obtained by using 26-mm i.d. aluminous-porcelain combustion tubes that were maintained at a temperature of 1350" to 1400" C by silicon carbide heating rods. Instrument time, from the time of inserting the loaded refractory boat into the tube up to the time taken for reading the integrated signal from the meter, varied from 40 to 55 seconds for carbon and low alloy steel, to 65 to 75 seconds for alloy steels containing about 1 per cent. of carbon. Samples of stainless steels ignited quite readily with analysis times rarely exceeding 55 seconds, and a limited number of tests indicated that nickel-base alloys could be analysed within about 60 seconds. For maximum speed in steelworks process control, suction samples are taken in preference to a small cast sample which requires milling or drilling before analysis.One method is to insert the tip of an evacuated tube into a spoon sample of de-oxidised molten steel. The high temperature leads to fusion at the tip, and the sudden suction that is produced causes the metal to enter and fill the tube, so producing a solid rod of 3 to 4-mm diameter. A suitable alternative procedure is to aspirate the molten steel into a glass tube by suction from a rubber bulb. A piece, weighing approximately 1 g, is then cut from the cooled rod or pin and used for analysis. A number of pin samples have been analysed with the Dynacarb apparatus. Preliminary tests on samples of low alloy steels from Samuel Fox & Company indicated that complete combustion was obtained in a resistance furnace, provided that the sample was covered with tin powder.Analysis time, for 3 and 5-mm diameter samples, was related to the carbon content of the sample, and varied from 60 to 80 seconds. Modern tube furnaces are capable of continuous operation at temperatures well in excess of 1400" C ; it was possible to reduce the minimum analysis time to about 50 seconds by increasing the furnace temperature to 1450" C. During subsequent trials of the instrument at the English Steel Corporation Ltd., suction samples were taken alongside the conventional samples that were intended for direct- reading spectrographic analysis. Excellent comparisons with spectrographic results were obtained on steels of different steel-making compositions.HIGH FREQUENCY HEA~ING- Comparative tests were made with a Radyne 5-Mc generator, fitted with a quartz- glass combustion chamber containing a movable refractory pedestal to support the com- bustion crucibles. The speed of combustion, by high frequency heating, is dependent upon the method of passing oxygen through the combustion chamber. When oxygen entered the bottom of the chamber below the refractory crucible, combustion times were found to be of the same order as those obtained with resistance heating. When the flow was reversed and passed through a jet directly above the crucible, extremely rapid ignition was achieved and theAugust , 19661 STEEL BY A DYNAMIC INFRARED SYSTEJI 487 total analysis time was approximately 30 seconds. With such rapid evolution of gas, however, the localised concentration of carbon dioxide may exceed 10 per cent.by volume, thereby overloading the infrared analyser, particularly when high-carbon steels are being analysed. It was, therefore, necessary to design a special oxygen-delivery jet that would ensure adequate mixing and dilution of the carbon dioxide in the combustion chamber. This was made from 4-mm glass tubing with a tapered jet of 2 to 3-mm diameter. Several 1-mm holes, bored into the wall of the tube above the orifice, created sufficient turbulence in the chamber to maintain the carbon dioxide level at below 10 per cent. As described earlier, the combustion gases were pumped through the analyser, and excess of the oxygen was allowed to escape into the atmosphere through one arm of a T-piece situated in front of the combustion chamber.\f'ith high frequency heating, all types of steel in the form of millings or drillings could be analysed within 50 seconds. Solid-pin samples required a further 5 seconds for complete combustion. KESULTS Many standard steels have been analysed; the results of the analyses are presented in Table 11, and are based upon instrument calibration by injection of high purity carbon dioxide. Good agreement was obtained with certified values, and analytical precision varied from about 1 per cent. coefficient o f variation at the 1 per cent. level of carbon content, to 3 or 4 per cent. at the 0.05 per cent. carbon level. There was no significant difference in precision for samples analysed with both the resistance and high frequency combustion furnaces.TABLE I1 RESVLTS OBTAINED iV1TH KESISTASCE AND HI(;H FREQUENCY C 0 31 B U ST I 0 N FLl R X ACE S Certificate value, B.G.S. percentage s o . Type o f carbon 260/1 Iligh purity iron . . . . 0.014 265/1 Carbon steel . . . . 0.043 295 Carbon stcel . . . . 0.263 23X/1 Carbon stcel . . . . 0.21 193 Carbon steel . . . . 0 . 6 3 I N / S Carbon stcel . . . . 0.54 215/l Carbon steel . . . . 0.925 221/1 Chrome - vanadium steel . . 0-50 290 13 per cent. manganese steel 1.17 241jl 1Iigh speed steel . . . . 0.8.5 E 0 / 1 High speed steel . . . . 0.93 :!3.5/1 Stainlcss steel . . . . ct.042 2 3 5 / 2 Stainless steel . . . . 0 . 0 5 2 310 Ximonic 90 . . . . . . 0.098 "1 Stainless steel . . . . 0.083 247/3 \2'hite cast iron . . . . 3 4 0 203/l Ferrochrome alloy .. . . 0.045 203j2 Ferrochrorne alloj- . . . . 0.027 ?39/2 Carbon steel . . . . 0.295 138/1 Carbon steel . . . . 0.81 Rcczrlts olitaiiit)d ztz tvzals at E.S.C. Ltd- 293 Carbon stcel . . . . 0.63 Resistance heating - ~ 2 ~~~~ l'ercentage Standard of carbon tie\ iation 0.01 0 0.002 0.043 0.001 0 . 2 1 0.004 0.64 0.00Fi 0.54 0.009 0.93 0.006 0.50 0.008 1-17 0.016 0.85 0-01 1 0.94 0.008 0.042 0.002 0.071 0.00 1 0.098 0.00 I 0486 0 a 003 2.95 0.028 0.042 0.001 0.02t.i 0.002 7 - __ 0.294 0.008 0.207 0-010 0.64 0.008 High frequency heating f-----l l'ercentage Standard o f carbon deviation - 0-26 0.63 0-54 0.92 0-5 1 1-15 0.84 -~ - 0.054 0.097 - 0-004 0.004 0.003 0.015 0.012 0*010 0.009 - - - 0.002 0.003 X s a further confirmatory test of performance under steelworks conditions, 15 samples of stainless steel, 4 nickel-base alloys and 10 samples of high-speed tool-steel were analysed at the English Steel Corporation, and the results were compared with those obtained by using the !$'ostoff Carmhograph conductimetric analyser for low carbon contents,' and the British Standard gravimetric methodB for the high-carbon tool-steels.The results in Table 111 are in favourable agreement with these alternative procedures. During these tests, 3 standard steels were each analysed by 3 operators at frequent intervals over a period of 2 weeks, in order to provide a more realistic assessment of precision, which ~ o u l d include variation between different operators (see Table TI).488 WHITE AND SCHOLES: DETERMINATION OF CARBON IN [A?tUlJt5t, VOl.91 RESULTS OBTAINED Cast No. Stainless-steel samdes- 5157 . . .. 2509 . . . . 4085 . . . . 2507 . . . . 2603 . . . . 2719 . . . . 2497 . . . . 4080 . . . . 4090 . . . . 4091 . . . . 4092 . . .. 4093 . . . . FW 14 .. FW 2515 . . FK 07 . . .. Nickel-base alloys- Nimonic S207. . NimonicS85 . . Nimonic H8707 Nimonic Y1041 . . . . . . . . . . . . . . .. . . . . . . . . .. .. .. . . .. . . . . TABLE I11 DURING STEEL WORKS ROUTINE OPERATION .. . . . . . . . . . . . . . . . . . . . . . . .. . . .. . . . . . . .. High speed tool-steel samples- R A 4 4 . . . . . . . . RA 45 . . .. . . . . RA 46 . . . . . . . . RA 47 . . . . . . . . RA 53 . . . . . . .. RA 54 . . . . . . . . RA 55 . . . . . . . . RA 56 . , . . . . .. RA 57 . . . . . . ..RA 58 . . . . . . . . .. .. .. . . . . .. . . . . . . . . . . . . .. .. . . Wosthoff Carmhograph, percentage of carbon 0.017 0.035 0.068 0.049 0.057 0.095 0.078 0.027 0.04 1 0.052 0.056 0.27 0.037 0.059 0.051 .. 0.042 . . 0.012 . . 0.029 . . 0.28 Standard method, percentage of carbon .. 0.74 . . 0.74 . . 0.73 . . 0.75 . . 0.78 . . 0.83 . . 0.83 . . 0-8 1 .. 0.83 .. 0.83 I) ynacarb, percentage of carbon 0.019 0.037 0.069 0-055 0.059 0.098 0.080 0.037 0.044 0.053 0.053 0.35 0.036 0.065 0.060 0.045 0.008 0.03 1 0.28 0.75 0.72 0.72 0.74 0.80 0.84 0.84 0.83 0.8 1 0.84 The full-scale meter deflection of the Dynacarb is nominally equivalent to 1.2 per cent. of carbon on the basis of a l-g sample weight, and a “ x 4” scale expansion is provided giving full-scale deflection, equivalent to 0-3 per cent.of carbon. For samples containing more than about 1 per cent. of carbon, a smaller sample weight must be used. The lower level of detection is of the order of 0-005 per cent. of carbon and, a t this percentage, the 95 per cent. confidence limits for the mean of two results is +0.0015 per cent. of carbon. CONCLUSIONS The application of infrared absorption to the determination of carbon in steel by a dynamic system has been shown to be feasible. Precise and accurate results may be rapidly obtained on a wide range of steel-making compositions, by using samples in the form of millings, drillings and solid pins. The proposed apparatus may be used either with a high frequency or resistance combustion furnace, but as the advantages of the former are marginal, a simple resistance-tube furnace is recommended. Capital costs are lower than with alternative instruments that incorporate high frequency heating and automated gas collection. The system is continuously flushed with oxygen, and there is no possibility of the carry-over of carbon dioxide from one sample to the next. Combustion processes can be followed, and completion of the analysis is immediately obvious. A further advantage is the use of an open tube, excess of oxygen providing a seal against the atmosphere during combustion. We acknowledge with gratitude the full co-operation of Mr. W. Bartley, Managing Director, and his colleagues of Hilger-I.R.D. Limited. In addition, thanks are given to Mr. L. Kidman for his permission to make trials at English Steel Corporation, to Mr. R. Staham, Samuel Fox and Company, who supplied pin samples, and to Mr. P. Barker, who performed some of the experimental work. The chief advantages of a dynamic system are simplicity and economy.August, 19661 STEEL BY A DYNAMIC INFRARED SYSTEM 489 REFERENCES 1. Scholes, P. H., “Proceedings of the Sixteenth Chemists’ Conference,” British Iron and Steel 2. 3. 4. 5. Waldock, P., Hilger J . , 1965, 9, 18. 6. 7. 8. British Standard 1121 : Part 1 1 : 1948. Research Association, London, 1963, p. 26. Hines, W. G., Addinall, R. L., and Orten, J . P., J . Metals, 1964, 165. Lay, J. O., Metallurgia, 1955, 51, 109. Tipler, G. A., Analyst, 1963, 88, 272. Rippon, K. P., and Smith, F., Brit. Irzsttz Radio Euzgrs J . , 1962, 24, 127. Scholes, P. H., Rep. B.I.S.R.A., MG/D/244/62. Received January 24th, 1966.

ISSN:0003-2654    

DOI:10.1039/AN9669100482

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

490 CORBETT AND GLTERIN: I)ETERJII?iATION O F [,4nalyst, 1701. 9 1 The Determination of Aluminium in Iron and Steel BY J. A. CORBETT (Plzj~sicnl ;lIetallu~,qy Secttoit, Conawotiwealth Scieiztifc atad Idatstrial Resravcli Oiyatzisatioiz, 4 Icstvalia) Various colorimetric reagents have been examined for their sensitivity in a standard method for determining aluminium in ferrous metals. Inter- fering elements are removed by a mercury-cathode separation followed by cupferron - chloroforni extraction. In the method adopted, aluminium is determined by measuring the optical density of its complex with -Alizarin red S - calcium reagent. The method has been tested with a wide range of steels. THIS project was undertaken at the request of the Committee on Sampling and Analysis of Ferrous Metals, Standards Association of Australia, as part of its programme of developing standard methods for the analysis of steels.After a survey of published methods the authors concluded that none was completely satisfactory as a standard method applicable to all types of steels. As a result, the investigation described here was undertaken. The determination of aluminium at low levels is particularly susceptible to errors arising from the introduction of extraneous aluminium, and a high degree of analytical skill is required to prevent contamination by minute traces of this ubiquitous element. In addition to this avoidable random introduction of aluminium, there is an unavoidable pick-up of aluminium from impurities in reagents and from dissolution of aluminium from glassware.This need not be a serious problem because, in the hands of an experienced analyst, the blank from these sources can be quite reproducible. The method of analysis should be designed to keep the magnitude of this aluminium pick-up within reasonable limits. As so many analytical reagents can be a source of minute traces of aluminium, a method should in general require only small additions of reagents, restricting, in particular, the use of alkaline reagents and avoiding their contact with glass. The storage of all reagents in polythene containers reduces the risk of contamination. I t should be emphasised, however, that it is the reproduci- bility of the blank rather than its magnitude that imposes the lower limit to the range of aluminium that can be determined, and, in fact, the blank may be greater than the net amount of aluminium in the sample aliquot at very low levels of aluminium.I t is unlikely, howe\rer, that satisfactory reproducibility will be attained with very high aluminium pick-up. P R E: L I hi I N A K Y s E PA K A T I o N s There are no known colorimetric reagents that are specific for aluminium. On the contrary, with all reagents there is only a rather restricted Iist of elements that do not interfere with the colour-forming reaction, and an efficient separation of most of the elements occurring in steels will be necessary. Several methods' 9 * have been described, in which interfering elements form complexes instead of separating. Such methods involve the use o f large amounts of reagents and are applicable only to certain types of steels.For a standard method to deal with all classes of steels and irons, an efficient separation of most of the elements present will be necessary. Blair, Power, Griffiths and M.'ood3 have discussed previously published separations of aluminium from iron which they have classified under the headings : precipitation ; solvent extraction; chromatography; and mercury-cathode electrolysis. They selected the last as the most suitable technique for their method for determining trace amounts of aluminium. \Then used with a c1.c. supply of sufficient power output, electrolysis in a perchloric acid medium over a mercury cathode provides a rapid and elegant method o f removing many alloying elements, including manganese, nickel, chromium and molybdenum, as well as the iron.In view of the requirement to keep reagent additions to a minimum this electrolytic technique is the obvious choice for a preliminary separation.August, 19661 ALChlINIUJl IK IROK AND STEEL 49 1 AIERCURY-CATHODE ELECTROLYSIS- The design of a mercury-cathode apparatus for rapid electrolysis should allow the use of high currents and reasonably low electrolyte temperatures, both factors increase the hydrogen o\-er-voltage on mercury, and contribute to current efficiency. Metals amalgamating with the mercury tend to lower the hydrogen over-voltage so that the use of contaminated mercury may result in imperfect separations. The use of a magnet beneath the cell to attract deposited ferro-magnetic metals below the surface of the mercury can thus improve cell efficiency.In this investigation we used a water-cooled Rfelaven cell operating at 10 amps and a magnetic mercury-cathode cell (similar to the design of Center, Overbeck and Chase4), operating at 12 to 15 amps. Both designs have proved satisfactory for this work, as no doubt would other types of cells designed to operate at these current levels. Electrolysis of 0-5-g samples of plain carbon steels were completed in less than 15 minutes, but molybdenum-bearing stainless steels may require up to 1 hour for completion. Blair3 and his colleagues showed that traces of chloride interfere with the electrolysis, and that repeated fuming with perchloric acid is needed to remove such traces when the composition of the steel, in particular its chromium content, necessitates the use of hydro- chloric acid in the attack of the sample.We have found that if the solution is boiled to allow perchloric oxidation of chromium to its higher valency state, double fuming at this high temperature will remove the chloride. During electrolysis there is a tendency for elements to be deposited in the order of their electrode potentials, although some simultaneous deposition does occur. With stainless steels it is found that complete deposition of nickel and then iron will occur before that of chromium. Molybdenum, if present, will be the last of these alloying elements to be completeljr deposited. Spot tests should be used to test for the completeness of deposition of iron, chromium and molybdenum (see Notes).The spot test for chromi~m,~ in which one drop of solution is used, will detect the presence of 50 pg of chromium in the electrolyte. Tt has not been found necessary to include a spot test for manganese. With steels con- taining up to 2 per cent. of manganese, less than 0-2 mg of manganese remains in the elec- trolyte when deposition of iron is complete. With 12 per cent. manganese steels the presence of manganese in the electrolyte becomes obvious because of the anodic oxidation to perman- ganate or oxides of manganese. When electrolysis is continued until the electrolyte becomes colourless, up to 1.3 mg of manganese remains in the electrolyte. However, even this amount of manganese is below interference level with the principal colorimetric reagents for aluminium.FINAL SEPARATION Of the elements that have been mentioned in the literature as steel constituents, those that would be present in solution after electrolysis are titanium, vanadium, zirconium, beryllium and phosphorus. There could also be traces of iron, manganese, chromium or molybdenum, at levels below the limits of detection of the spot tests. Various methods are available to isolate aluminium from these elements. Sodium hj-droxide was used by Scholes and Smith,6 Hill' and Studlar and Eichleri to precipitate, as hydroxides, some of the elements listed above. The remainder were complesed with hydrogen peroxide to prevcnt interference with the colorimetric reagent used. The probabilitj- of aluminium pick-up from alkaline reagents has been mentioned.A further danger with this technique is the possibility of loss of aluminium as aluminium phosphate when a high phosphorus alloy is encountered. Claassen, Bastings and Visser' used a series of solvent extraction separations with 8-hydroxyquinoline and chloroform, with complexing reagents and different values of yH. A knowledge of the sample composition is necessary, and with some steels a further separation with cupferron is required. A cupferron - solvent extraction seemed preferable to the above techniques and has been widely used for this type of separation. I t was decided to investigate its application tothe present method. CUPFEKKON PRECIPITATION - CHLOROFORM EXTRACTION- Blair, Power, Griffiths and Wood3 have been concerned to remove residual traces of iron which cause severe interference with the Eriochrome cyanine R reaction with aluminium.They made a small addition of cupferron with chloroform extraction of cupferrates to rernox-e492 CORBETT AXD GUERIN : DETERMINATION OF [Analyst, Vol. 91 traces of iron, titanium and vanadium. As an additional precaution they added hydrogen peroxide to ensure that any excess of titanium or vanadium was in the non-interfering oxidised state. If titanium is present in greater than trace amounts it will react with all of the added cupferron and will be extracted, leaving iron present in the aqueous layer. Those workers’ restriction on the amount of cupferron apparently arose from their desire to keep the total aluminium pick-up as low as possible. We preferred to ensure the complete removal of iron, titanium, zirconium, molyb- denum and vanadium at this stage by repeating the addition of cupferron and chloroform extraction until the chloroform extract was colourless.Hydrogen peroxide, which interferes with some colorimetric reactions of aluminium, can now be omitted, so the choice of colori- metric reagent is widened. The acidity of the aqueous phase during chloroform extraction of cupferrates should be controlled. Slight losses of aluminium by extraction occur if the pH is above 0.4, and the extraction of iron is retarded in solutions that are too strongly acid.* Our experiments have indicated that a satisfactory separation can be effected in molar acid solution, so an appropriate addition of acid is made before the separation. The repeated cupferron - chloroform extraction necessary with some alloy steels may result in a slightly increased, but reproducible, pick-up of aluminium. Provided the blank determination for such steels is given identical treatment no error is introduced by this technique.It should be noted that any traces of manganese and chromium in the electrolyte after mercury-cathode electrolysis will not be removed by the cupferron - chloroform extraction. The only other elements likely to be present in irons and steels, and which are not removed by the two separations described or by a preliminary filtration of the insoluble matter, are the aluminium, and also magnesium, beryllium and phosphorus. Assuming that the sample weight is limited to 0 5 g , and the aliquot taken for colour development is not greater than one-fifth of the electrolyte, the levels at which elements could be present in the aliquots are as follows- There is a possibility of error in this technique.Beryllium . . . . . . 200 pg for 0.2 per cent. beryllium alloy Chromium . . . . . . 10 pg assuming the spot test is effective Magnesium . . . . . . 200pg for 0.2 per cent. alloy Manganese . . . . . . 300 pg for 12 per cent. manganese steel Phosphorus . . . . . . 1000 pg for 1 per cent. phosphorus alloy COLORIMETRIC REAGENTS A Unicam spectrophotometer SP600 was used for all colorimetric work described. After studies of the published colorimetric reagents used for aluminium, five reagents were considered to merit detailed investigation. These were- Alizarin red S - calcium reagent. Arsenazo.Eriochrome cyanine R (Solochrome cyanine RS), 8-H ydrox y quinoline. S tilbazo. The investigation of each of these reagents has included: (a) the determination of the optimum wavelength for photometric measurement, from a study of graphs of optical density against wavelength for the reagent and the aluminium complex; (b) conformity with Beer’s law ; (c) calculation of sensitivity, which has been expressed : (i) as the extinction coefficient E with respect to 1 gram atom of aluminium per litre of solution (as advocated by International Union of Pure and Applied Chemistry), and (ii) as the concentration range of aluminium corresponding to the optical density range 0 to 1.0 in the cell size recommended for the particular reagent; (a) interference studies, for the most part confined to those elements which could be present following the two major separations.Elements given as not inter- fering have been tested at least to the levels listed above. The results of the above work are shown in Table I.Alizarin red S - calcium reagent Optimum wavelength 490 mp for colour measurement pH for colour development 4.4 to 4-65 TABLE I RESULTS OF INVESTIGATIONS ON COLORIMETRIC REAGENTS Eriochrome cyanine R Arsenazo (Solochrome cyanine RS) 8-Hydroxyquinoline Stilbazo 580 mp 532 mp 392 mp 520 mp 6.1 t o 6-11 Approximately 6- 1 Extraction Approximately 6.8 a t pH 4.9 t o 5.0 Conformity to Beer’s Conforms Conforms Slight but consistent Conforms Deviations suggesting the the existence of more (0 t o 100 pg of aluminium per 100 ml) law. (Range tested (0 t o 80 pg of aluniinium (0 to 100 pg of aluminium deviations detected shown in brackets.) per 100 ml) per 100 ml ) (0 to 60 pg of aluminium per 100 ml) than one compound (0 to 300 pg of aluminium per 100 ml) E a t optimum wavelength 1.8 x 104 1.2 x 104 6-75 x 104 6.7 x lo3 3.8 x 104 Concentration range 0 t o 80 pg of aluminium per 100 ml in 2-cm cells 0 to 100 pg of aluminium per 100 ml in 2-cm cells 0 to 60 pg of aluminium pcr 100 ml in 0-5-cm cells 0 to 100 pg of aluminium per 100 ml in 4-cm cells 0 t o 70 pg of aluminium per 100 ml in l-Cm Cells and cell size Interferences : Effect on optical density a t optimum wavelength- { Slight increase 40 pg Be = lpg A1 None Slight increase Drastic increase Drastic increase ( a ) Beryllium { 0 * 7 p g R e = l p g A l ‘ (2 pg Be = 1 pg A1 (b) Other elements None None.Higher levels of None. Higher levels of None None { 4 0 p g H e - l p g A l listed on page 492 chromium cause increase chromium cause decrease a t levels specified Notes on reagent The reaction of sodium The orange coloured Acidified (nitrated) alizarin sulphonate aqueous solution forms solutions of Merck’s with aluminium in the a cherry-red complex Eriochrome cyanine R presence of calcium with a1urnini~m.l~ (The and Gurr’s Solochrome ions has been used in reagent used was from cyanine RS were found analysis of rocks, slags Tokyo Kasei Kogyo to give identical re- and coal ash.l0~l1~l* Co. Ltd., Japan.) actions. This reagent has been widely used for aluminium deter- minations in steel^.^^^*^ Aluminium hydroxy- quinolinate is extracted from the aqueous phase with chloroform vielding a pale yellow analyses.16J7 solution.This reaction has been used in steel14 and cast-iron16 analyses. The reaction with alu- minium to form a reddish brown complex has been used in steel G 0 Z v1 4 M M r bP CD W494 C‘ORBETT AND GVERIK DETER311KL4TIOK OF [Analyst, lrol. 91 PRACTICABILITY- In addition to the investigations outlined above we have introduced the concept of the “practicability” of a colorimetric reagent and have considered the five reagents in this respect. Under this term we have included rapidity of development of the coloured complex and its stability, the stability of the reagent solution and the effect on the optical densit?.of slight changes in conditions such as pH and buffer concentration. All of these factors play a part when the reproducibility of a method is determined experimentally. Another factor is the optical density of the reagent. If the reagent absorbs appreciably at the optimum wavelength it is not practicable to use a large excess of reagent and there is a tendency for the calibration graph to deviate from linearity towards the upper end, unless the equilibrium constant for the complex formation is high. Absorption by the reagent reduces the slope of the calibration graph, and also, in the type of instrument used here, limits the cell size that can be used without unduly opening the slit. CHOICE OF COLORIMETRIC REAGEXT- Each of the 5 colorimetric reagents investigated in detail has sufficient sensitivitj- for determining aluminium in steels and irons.We have found that the lower limit of detection of aluminium is determined by the reproducibility of aluminium pick-up in the blank and sample rather than by the sensitivity of the colorimetric reagents tested. I t would seem, then, that the choice of reagent for this standard method should depend primarily on the reproducibility of the colour-forming reaction rather than its sensitivity. One criterion for a standard method is that it should give satisfactory results in the hands of a competent analyst. On this basis all of the above reagents can be considered as satisfactory as it is possible to obtain accurate reproducible results for aluminium with each reagent, provided the relevant conditions are sufficiently closely controlled.The factors affecting repro- ducibility are different for each reagent, and with some of the reagents are difficult or irksome to control in practice. I t was therefore considered that reproducibility tests, made under the ideal conditions for each reagent, would not provide a realistic basis for comparison. The factors affecting reproducibility, that we have discussed in the section on “Practicability,” provide results for a more realistic appraisal of the reproducibility which could be expected under laboratory conditions, and it was consideration of these factors that guided our final choice of reagent for the standard method. Close control of pH and buffer concentration should present no difficulty provided that the analyst takes the elementary precaution of preparing a sufficient volume of buffer solution to deal with all samples, blanks and standards in the batch of analyses.Close control over time of standing is, however, irksome, when measurements are being made against a reference solution whose density is also time-dependent. Strict adherence to Beer’s law is desirable as it obviates the need for close plotting of the calibration graph with each batch of analyses. With Eriochrome cyanine R close control over time of standing is essential because the optical densities of both the aluminium complex and reference solutions decrease on standing. There are slight deviations from Beer’s law. Stilbazo has similar defects, the deviations from Beer’s law being slightly more severe.The lower sensitivity of the 8-hydroxycluinoline complex is compensated by the low absorption of the reference solution which permits the use of larger cells and smaller dilutions for absorption measurements. The colour development in\wlving a chloroform extraction is not as simple as with the other reagents, and the coloured solution is light sensitive and subject to the disadvantage of a volatile liquid. Aqueous solutions of arsenazo are stable, and the optical density of the aluminium complex remains constant in the interval from 1 to 5 hours after d o u r development. The reagent itself has a low absorption at the wavelength used. I t suffers from severe interference from beryllium. This is not regarded as a serious defect; however, this element is found in a few special stainless alloys and experimental batches of steels. Aqueous solutions of Alizarin red S are stable for about 2 weeks and the optical density of the calcium - aluminium complex remains constant in the interval from 1 to 4 hours after colour development.Absorption by the excess reagent is not severe. We are of the opinion that arsenazo and Alizarin red S - calcium reagent are the two most suitable reagents for use in a standard method for determining aluminium. The latterAugust, 19661 ALUMINIUM I N IRON AND STEEL 495 has the slight advantage that interference from beryllium is almost negligible. In deciding to recommend the Alizarin red S - calcium reagent to the Australian Committee on Analysis of Ferrous Metals we were further influenced by the wealth of experience in its use by analytical chemists in the analysis of non-metallic materials.APPLICATION OF ALIZARIN RED s - CALCIUM REAGENT TO THE METHOD- The aluminium, before colour development, is in dilute perchloric acid solution. The pH for colour development may be in the range 4-4 to 4.65, but it must be kept uniform to within +0-02 units. The acid solution can be brought directly to the required pH by adding a high concentration of buffer solution, but this addition was found to cause a marked decrease in the optical density of the aluminium complex. As with the other colorimetric reagents for aluminium the buffer concentration must be kept reasonably low for efficient colour de- velopment. With the resulting low buffer capacity it is necessary that before colour develop- ment the solution is neutralised with sodium hydroxide followed by a small measured excess of acid to re-dissolve the aluminium.The addition of 10 ml of a buffer of M sodium acetate - M acetic acid (pH 4.75) brings the final pH within the required limits. As sodium hydroxide is a likely source of trace aluminium, the amount required to neutralise the solution has been kept to a minimum by evaporating the perchloric acid solution almost to dryness before neutralisation. The addition of 7 mg of Alizarin red S provides sufficient excess of reagent to ensure linear calibration over the range 0 to 80 pg of aluminium. Ideally, 0-5-g portions of high purity iron should be used in the blank and standard. As “pure” irons, commercially available, contain traces of aluminium, this addition is not recommended.The time required to complete the determination of aluminium in a single steel sample is approximately 8 hours. METHOD The method is applicable to all steels and irons, and has a range from 0.002 to 10 per cent. of aluminium. APPARATUS- 10 amps and should be water-cooled. solution at 490 mp may be used. Mercury-cathode cell-The cell should be designed to operate at a current of at least Spectro$hotometer-Any instrument suitable for measuring the optical density of a REAGENTS- All reagents should be of the highest purity obtainable and distilled water should be used throughout. Certain types of analytical-grade reagents are unsuitable because of the presence of either aluminium or other impurities.All solutions should be stored in polyethylene or polypropylene containers. Cupferron, 2 per cent. w/v-Dissolve 2 g of cupferron in 50 ml of water and dilute the solution to 100 ml. This solution should be colourless and must be prepared each day. Sodium hydroxide, 2 M-Dissolve 80 g of sodium hydroxide pellets in 700 ml of water in a polyethylene container, cool the solution and dilute it to 1 litre. Hydrochloric acid, 0.2 M-Dilute 18 ml of hydrochloric acid (sp.gr. 1.18) to 1 litre. PhenolphthaZein indicator-Dissolve 0.1 g of phenolphthalein in 50 ml of ethanol and dilute the solution to 100ml with water. Calcium chloride-Dissolve 14 g of calcium carbonate in 50 ml of hydrochloric acid (50 per cent. v/v). Boil the solution for 2 minutes. Cool and dilute to 1 litre.Bufler solution-Dissolve 140 g of hydrated sodium acetate (CH3COOWa.3H,O) in water. Add 60 ml of glacial acetic acid and dilute to 1 litre. Alizarin red S solution, 0.14 per cent. w/v-Dissolve 140 mg of Alizarin red S in 75 ml of water and dilute the solution to 100ml. Chromium spot-test, solution A-Dissolve 10 g of sodium hydroxide pellets in 50 ml of water, cool the solution and add to it 50 ml of hydrogen peroxide (6 per cent.). Chromium spot-test, solution 23-Dissolve 0.5 g of diphenylcarbazide in 50 ml of glycerol. (This solution is satisfactory for several days.) To 5 ml of the glycerol solution add 5 ml of Filter if necessary.496 CORBETT AND GUERIN: DETERMINATION OF [Anahst, VOl. 91 sulphuric acid (25 per cent. v/v) and 5 ml of glacial acetic acid.(This solution is satisfactory for 1 to 2 hours.) Iron and molybdenzm spot-test solution C-Dissolve 5 g of tin(I1) thiocyanate (SaSCS.H,O) in 50 ml of water and dilute the solution to 100 ml. Iron and molybdenum spot-test solzition D-Dissolve 32 g of stannous chloride l(SnC1,.2H,O) in 40 ml of hydrochloric acid (sp.gr. 1-18) and dilute the solution to 100ml with water . PROCEDURE- Transfer 0-5 g of sample to a 100-ml beaker, add to it 10 ml of nitric acid (50 per cent. v/v) and allow it to digest until the solvent action ceases (Sote 1). Add 5 ml of perchloric acid (60 per cent.) and evaporate to fumes of perchloric acid. Allow the mixture to fume for 1 minute with the cover removed (Note 2). Cool the residue, add to it 10 ml of water, heat to dissolve soluble salts and filter the mixture through a small filter-paper.Wash the filter- paper with hot water and reserve the filtrate (A) (Note 3). Transfer the paper to a platinum crucible, char, then ignite it at a temperature not exceeding 1000" C. Cool, and moisten the residue with 5 or 6 drops of dilute sulphuric acid (20 per cent. v/v), add to the residue 2 ml of hydrofluoric acid and evaporate to dryness. Heat the residue to 800" C for several minutes, then fuse it with 0-5 g of sodium hydrogen sulphate. Cool the mixture, add 10 ml of water and dissolve the solid by heating (Kote 4). If the total aluminium is required add this extract to filtrate (A). If separate results are required for acid-soluble and acid-insoluble aluminium, treat the extract as described in Xote 5.Transfer the solution to the mercury-cathode cell with a minimum amount of water. The volume of electrolyte should not exceed 70 ml. Electrolyse at 10 to 15 amps, washing down the cover and inside of the cell with water after 30 minutes. Continue the electrolysis until deposition is complete, i.e., until spot tests indicate that iron or, if present, chromium and molybdenum have been removed from the electrolyte (Note 6). Remove the electrolyte and filter it immediately into a 100-ml standard flask (Kote 7) with the minimum volume of water for washing, and make the solution up to the mark. Transfer by pipette a 20-ml aliquot (Xote 7) into a 200-ml separating funnel. Add to the solution 2 ml of hydrochloric acid (50 per cent. v/v) and mix. Introduce 1 ml of cupferron solution (2 per cent.w/v), shake the mixture, and allow it to stand for 5 minutes. Add 15ml of chloroform, shake the solutions for 30 seconds, allow the two phases to separate and run the chloroform layer into a beaker. Extract the aqueous layer with a further 10 ml of chloroform, then run off the chloroform layer. Add 1 ml of cupferron (2 per cent. w/v) to the aqueous portion, mix, and allow the solutions to stand for 5 minutes. Add 10 ml of chloroform and shake the solutions for 30 seconds, allow the layers to separate, note whether the chloroform layer is coloured (Note 8) and run off the chloroform layer. Run the aqueous layer into a 100-ml beaker. Evaporate the aqueous portion to about 5 ml, add 1 ml of nitric acid (50 per cent. v/v) and evaporate to fumes of perchloric acid.Continue the evaporation until no free liquid is visible although fumes of perchloric acid are still being emitted. If drops of perchloric acid remain on the beaker wall, carefully wash down with water and repeat the evaporation. Cool, add 10 ml of water and warm to dissolve salts. Cool, add two drops of phenolphthalein solution and add sodium hydroxide (2 M) from a polythene wash-bottle until the colour just changes to pink. KO more than 2 to 4 drops of sodium hydroxide should be required. Titrate with 0-2 M hydrochloric acid until the solution becomes colourless and add 1.0 ml in excess. Add, in order, with a burette and shaking the solution after each addition, 2 ml of calcium chloride solution 10 ml of buffer solution and 5 ml of Alizarin red S solution (0.14 per cent.w/v); dilute the solution to the mark with water. Allow the solution to stand for 1 hour, transfer it to a 2-cm cell and measure the optical density a t 490mp against the reference solution. (See under Calibration.) Transfer the solution to a 100-ml calibrated flask and dilute to 50 ml. REAGENT BLANK- Each sample must be accompanied by a reagent blank solution. The treatment of the blank must be identical with that of the sample throughout the method. Measure the optical density a t 490 mp against the reference solution. (See under Calibration.)August, 19661 ALUMINIUM I N IRON AKD STEEL 497 CALIBRATION- Aluminium solution-Dissolve 1.757 g of aluminium potassium sulphate (A1,(S0,),K2S0,.24H,0), in distilled water, add 1 ml of sulphuric acid (sp.gr.1.84) and dilute to 1 litre. Dilute 100 ml of the above solution to 1 litre with water. 1 ml = 10 pg of aluminium. Calibration procedure-To 50 ml of water in a 100-ml calibrated flask add 1.0ml of 0.2 M hydrochloric acid, and proceed with colour development as described under “Pro- cedure.” Allow the solution to stand for 1 hour. Each sample must be accompanied by a standard. This is prepared by measuring with a burette a 35-ml portion (Note 9) of the diluted aluminium standard solution into a 100-ml beaker, and proceeding through all steps of the method. The treatment of the standard must be identical with that of the sample. Measure the optical density a t 490mp against the reference solution and deduct the reagent blank to give the optical density due to 70 pg of aluminium in the aliquot.CALCULATIONS- Deduct the reagent-blank optical density from the test-solution optical density and convert to weight of aluminium in the aliquot taken, by reference to the calibration standard. Hence calculate the percentage of aluminium in the sample. This is the reference solution. NOTES- An addition of 5 ml of hydrochloric acid (sp.gr. 1.18) is suitable. Evaporate to fumes of pcrchloric acid, and with the cover on the beaker boil the solution vigorously for 30 seconds to oxidise the chromium. Remove the cover and allow the mixture to fume freely for another 30 seconds. Cool, wash down the sides of the beaker with water and repeat this evaporation to fumes, boiling and fuming, to remove the last traces of chloride. 3.If tungsten is present remove the filtrate and wash the paper with 10 ml of ammonia solution (50 per cent. v/v), then with water. 4. The fused residue from some complex alloys may not completely dissolve in water. If i t does not, transfer the extract to a 100-ml beaker and boil i t to dissolve the residue as far as possible. Add the solution and the insoluble residue to the main filtrate A. 5. For the determination of acid-insoluble aluminium, add to the extract, filtered if necessary, 1 ml of perchloric acid (60 per cent.), 2 ml of hydrochloric acid (50 per cent. v/v) and continue with the cupferron extraction as described under “Procedure.” 6. In each of the following spot tests, 1 drop of the electrolyte is placed in a small porcelain crucible or in the depression of a porcelain spot plate.I ~ o n - ~ i d d 1 drop of nitric acid (50 per cent. v/v) and 1 drop of the sodium thiocyanate solution C. A red colouration indicates the presence of iron. Chromium--Add 1 drop of solution A , mix and then add two drops of solution B, and mix. The resulting solution should be acid. An immediate purple colouration indicates the presence of chromium. MoZybdenum--hdd 1 drop of solution C and 2 drops of solution D. ,4 pink to red coloration indicates the presence of molybdenum. 7 . The aliquot must not contain more than 7 0 pg of aluminium. When necessary the sample weight, the dilution, or the aliquot can be adjusted to conform to this limit. If the aliquot is less than 20 ml i t should be diluted to 20 in1 with water.The aliquot should be approximately 0.5 molar with respect to perchloric acid. If necessary, make an appropriate addition of perchloric acid (60 per cent.). 8. If this chloroform extract is coloured, repeat the addition of 1 ml of cupferron (2 per cent. w/v) and the extraction \vith chloroform, until the chloroform extract is colourlcss. 9. The aliquot for colour development should contain 70 pg of aluminium. With standards accompanying steels containing more than 0.07 per cent. of aluminium a proportionately larger initial amount of aluminium will be necessary. 1. The addition of hydrochloric acid is necessary to effect dissolution of some alloy steels. 2. If hydrochloric acid has been used special care must be taken to remove it. RESULTS Tests were made on a group of X.B.S.and B.C.S. steels with aluminium contents ranging from 0.002 to 6.98 per cent. The results are shown in Table IT. These results show that aluminium can be determined with satisfactory accuracy. Statistical tests at low levels of aluminium indicated that the lower limit of detection of the method should be not greater than 0.001 per cent. of aluminium. At this lower limit a pick-up of 6 pg of aluminium in the blank-determination aliquot was sufficiently reproducible to enable an additional 1 pg of aluminium in the sample aliquot to be detected.498 CORBETT AND GUERIN [Anazyst, VOl. 91 TABLE I1 RESULTS OF TESTS ON N.B.S. AND B.C.S. STEELS, ALUMINIUM CONTENT Certificate value, percentage of Sample aluminium N.B.S. 106 . . . .1.06 N.B.S. 55e f . . . 0.002 N.B.S. l7Oa . . . . 0.046 (low alloy steel) (ingot iron) (open hearth steel) (high speed steel) (mild steel) (magnet alloy) (1 8/ 12 stainless with niobium, molybdenum) * B.C.S. 241/1 . . .. B.C.S. 271 .. . . 0.008 B.C.S. 2337 . . . . 6.98 B.C.S. 246 ,. .. t 0.02 TO 6.98 PER CENT. Laboratory 1 Laboratory 2 Mean result 1.060 0.0032 0.0483 0.0229 0.0083 7.05 0.0027 No. of deter- mina tions 5 5 3 5 5 5 3 I Standard deviation 0.009 0*0009 0.0006 0.0019 0*0002 0.041 0*0002 Mean result 1.064 0-001 3 - 0.0246 0*0080 7.07 0.0026 No. of deter- Standard minations deviation 5 0.01 1 5 0.0005 0.00 13 5 5 0*0005 5 0.059 - 2 * No certificate value is given for B.C.S. 241/1. Scholes and Smith6 found 0.024 per cent. of aluminium. 7 Certificate and experimental values for B.C.S. 233 are for soluble aluminium. $ No certificate value is given for B.C.S. 246. Further reproducibility tests are now being carried out by a panel of fellow members of the Ferrous Analysis Committee in order to determine the 95 per cent. confidence limits for incorporation in the proposed standard. The authors wish to acknowledge helpful discussions a t meetings of the Committee on Sampling and Analysis of Ferrous Metals, Standard Association of Australia. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. REFERENCES Claassen, -4., Bastings, L., and Visser, J., Analytica Chim. Acta, 1954, 10, 373. Hill, U., Analyt. Chem., 1959, 31, 429. Blair, D., Power, K., Griffiths, D. L., and Wood, J. H., Talanta, 1960, 7, 80. Center, E. J., Overbeck, R. C., and Chase, D. L., Analyt. Chem., 1951, 23, 1134. Evans, B. S., and Higgs, D. G., Analyst, 1945, 70, 75. Scholes, P. H., and Smith, V. D., Iron Steel Inst., 1962, 200, 729. Studlar, K., and Eichler, V., Chemist Analyst, 1962, 51, 68. Short, H. G., Analyst, 1950, 75, 420. Parker, C. A., and Goddard, A. P., AnaZytica Chim. Acta, 1950, 4, 517. Shapiro, L., and Brannock, W. W., Bull. U.S. Geol. Surv., 1956, No. 1036-C. Archer, K., Flint, D., and Jordan, J., Fuel, Lond., 1958, 37, 421. British Standard 1016 : Part 14, 1963. Kuznetsov, V. I., and Golubstova, R. €3.. Zav. Lab., 1955, 21, 1422. Sandell, E. B., “Colorimetric Determination of Traces of Metals,” Third Edition, Interscience Rooney, R. C., B.C.I.R.A. J. Res. and Dev., 1958, 7, 436. Jean, M., Analytica Chim. Acta, 1954, 10, 526. Wetlesen, C. U., Ibid., 1962, 26, 191. Publishers Inc., New York, 1959, 243. Received May 26th, 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100490

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

August, 19661 BERSIS AND VASSILIOU 499 A Chemiluminescence Method for Determining Ozone BY D. BERSIS AND €3. VASSILIOU (Nuclear Research Center “Democritus,” Aghia Paraskevi A ttikis, Athens, Greece) A method for determining ozone is described which is characterised by the direct recording and automatic determination of ozone within a wide range of concentrations. The development of this method is based on the use of a chemiluminescent solution that is stable, and shows a linear relation- ship between the light emitted and the ozone concentration. A combination of rhodamine I3 with gallic acid in ethanol is satisfactory in operation and does not itself emit light. The electronic instrumentation used is relatively simple. Other methods of ozone analysis based on this principle meet with much difficulty, owing t o the direct oxidation of the chemiluminescent com- pound.The present method, by contrast, involves the use of gallic acid as an ozone acceptor, and rhodamine B, which remains unchanged during the measurement, as a photon emitter. Observations made with an oscillograph of the light emitted by single bubbles of ozonised air passing through the chemiluminescent solution give valuable information about the response- time of the system. THE increasing interest in the applications of ozone, and their importance in the fields of radiation chemistry, upper atmosphere technology, industrial organic chemistry, etc., gives rise to a constantly growing number of projects dealing with basic research in ozone chemistry. Therefore, the development of good and rapid methods of ozone analysis is required.The methods for the determination of ozone that have been developed so far are mainly chemica1,l $2 e l e c t r ~ c h e m i c a l ~ ~ ~ ~ ~ - ~ and optical.’ ,8 Each of these methods has advantages and disadvantages, so that the method that is to be used must be selected according to the individual requirements and conditions. In general, however, the direct and continuous indication or, better, automatic recording of the results is desirable. Methods with procedures of this kind can be found in the l i t e r a t ~ r e , ~ ~ ~ ~ ~ but most of them are relatively slow in response, or require complicated instrumentation, Some methods are also hindered by the presence of gases, such as nitrogen dioxide and sulphur dioxide, which interfere more or less strongly.Within the range of optical methods, a field at present being developed, is one in which the light emitted by chemiluminescence reactions is used. The use of modem techniques of photon-counting combined with chemilurninescent systems of high efficiency can give rise, mainly from the point of view of sensitivity and response-time, to an ideal method of analysis. Nevertheless, a method based on these principles has not been developed to the extent expected, at least for ozone, owing to the fact that the chemilurninescent compound formed is constantly being destroyed during analysis, thus complicating the results. Re-cycling of the solution containing the chemiluminescent compound causes further complications.AIR SUPPLY- a manometer and a flow-meter were attached to control the pressure and the flow-rate. taining granulated potassium hydroxide and silica gel, respectively. OZONE PRODUCTION- EXPERIMENTAL A small rotary compressor, fluid metering type 8, Weldon Tool Co., was used, to which The air stream was freed from carbon dioxide and dried by means of two columns con- Ozonised air was produced by the following systems according to requirement- (a) A conventional Siemens ozoniser (Pyrex glass) with a wall thickness of 1 mm, gap distance of 3 mm and total volume of 11 ml. The two electrodes were filled with a sodium chloride solution (10 per cent. w/v). (b) A 5-fold ozoniser, i.e., five ozonisers, each like the one described above, connected in such a manner as to split the air stream into five equal streams as it enters.The five streams meet again at the common outlet of the ozonisers. By means of a suitable H.T. commutator switch, it was possible to energise any number of the individual ozonisers, as required by the experiment.500 BERSIS AND VASSILIOU: A CHEMILUMINESCENCE [Analyst, VOl. 91 The high voltage was supplied by a H.T. transformer (50 c/s) and controlled by means of a Variac connected to a suitable stabiliser, and was continuously monitored. To exercise additional control over the ozone concentration in the ozonised air stream, a suitable trap, K, (Fig. 1 ( b ) ) , containing granules of dry potassium hydroxide was used. The volume of ozone decomposed could be regulated by two taps, TI and T,, connected to suitable micrometric screws for fine adjustment.I Air photomultiplier ( 0 ) (b) K = Potassium hydroxide trap S = Silica gel trap C = Pyrex glass bubbler T, and T, = Taps M = Manometer Fig. 1. Apparatus for the automatic determination of ozone: (a), calibration unit; ( b ) , analysis unit CALIBRATION OF THE OZONISER- The calibration of the ozoniser, with respect to ozone production, was carried out as described by Ehmert .6 According to this method, a suitable reaction vessel containing a neutral 2 per cent. potassium iodide solution and a certain amount of dilute sodium thiosulphate solution is attached to the apparatus. The ozonised air bubbling through this vessel reacts with the potassium iodide, so liberating free iodine, which in turn reacts with the sodium thiosulphate.The residual sodium thiosulphate is then measured and compared with that of a blank. For this measurement, 4 platinum electrodes are used. An electric potential of about 0.18 volt is applied between two of them. At this voltage no electrolysis takes place as long as sodium thiosulphate is present, because of polarisation. The second pair of electrodes is connected to a suitable current source, so that iodine is liberated by electrolysis, and this reacts immediately with the sodium thiosulphate present. When the whole of the sodium thiosulphate has been consumed, the free iodine causes depolarisation of the first pair of electrodes, and a current flows which is linear with time. By using Faraday’s constant, the amount of iodine can be calculated from the values of current and time.PHOTOMETRIC ASSEMBLY- A Pyrex glass bubbler, C, (Fig. 1 (b)), of approximately 20 mm i.d., containing 10 ml of chemiluminescent solution, was used as a photometric cell. The porous diaphragm was of the G2 type. A second bubbler was connected in series with the first to ensure that no ozone escaped observation. An RCA 931 A photomultiplier, connected to a Varian G 11 A pen recorder through a pre-amplifier, or to an oscilloscope, and to a stabilised d.c. high tension supply, (Fig. 1 ( b ) ) , was also used.August, 19661 METHOD FOR DETERMINING OZONE 501 SOLUTION- of rhodamine B in 1 litre of ethanol (96 per cent. v/v). PROCEDURE- The gas stream to be analysed with respect to ozone concentration is passed through trap K, (Fig.1 (b)), if required (i.e., if the ozone concentration is too high), and is then bubbled through the reaction cell, C. The light emitted energises the photomultiplier, which in turn gives a signal to the recorder. This signal, as will be seen later, is proportional to the ozone concentration when the stream flow remains constant. The recorded area is used to determine the absolute amount of ozone passed through the reaction cell. CALIBRATION OF THE APPARATUS- in Fig. 1 (a). cent. v/v under the following conditions- The chemiluminescent solution was prepared by dissolving 2.5 g of gallic acid and 0.03 g METHOD AND RESULTS To calibrate the ozone-analysis apparatus, use was made of the calibration unit shown I t was found, by using Ehmert's method,6 that the production of ozone was 0-17 per gas, air; high tension, 7 kV; stream flow, 64 ml per minute; pressure, 17 inches of The ozonised air stream was led into the photometric cell, and the d.c.high tension supply connected to the photomultiplier was regulated so that the recorder showed an indication in support of the direct reading, e.g., of 17. LINEARITY AND LIMITS- To examine the linearity of the method, use was made of the calibration unit (Fig. 1 (a)), in which the single ozoniser was replaced by the 5-fold one. The five single ozonisers, as already indicated, were connected in such a manner that equal amounts of gas could pass through each. Equivalent amounts of ozone, therefore, were produced in each ozoniser under the same conditions. In practice, small differences occurring in the production of ozone by each ozoniser were corrected by fine adjustment of the high tension acting on each ozoniser.The concentration of ozone produced by each ozoniser was 0-07 per cent. v/v under the conditions described above. The percentage concentration of ozone was calculated with respect to the total stream flow, which was 64 ml per minute, and must not be confused with the flow through each ozoniser, which was approximately 13 ml per minute. water; temperature, 20" C. -l Number of operating ozonisers Fig. 2. Operation of the five-fold ozoniser The tap TI, (Fig. 1 ( b ) ) , was entirely closed; T, was opened and the d.c. high tension adjusted so that the recorder gave a reading of 100 when all five ozonisers were operating. By switching off one, two, three and four ozonisers the recorder gave readings of 80, 60, 40502 BERSIS AND VASSILIOU : A CHEMILUMINESCENCE [AutdySt, VOl. 91 atid 20, respectively, (Fig.2), It can, therefore, be concluded that in the region between 0.07 and 0.35 per cent. v/v, the light emitted b y the chemiluminescence reaction is linearly related to the ozone concentration. To determine whether this function is also linear in lower concentrations of ozone, the following operations were carried out- With all five ozonisers switched on, the ozone decomposition trap, K, (Fig. 1 ( b ) ) , was adjusted by means of taps T, and T,, so that the recorder gave a reading of 20. This repre- sented an ozone concentration of 0-07 per cent. v/v. On increasing the photomultiplier sensitivity by means of the d.c.high tension supply, a reading of 100 was given (the ozone concentration remaining at 0-07 per cent. v/v). Switching off afresh one, two, three and then four ozonisers, the recorder gave readings of 80, 60, 40 and 20, respectively. The function, therefore, is also linear within the region 0.07 to 0-014 per cent. v/v. Adopting the same technique, an ozone concentration of 0-0003 per cent. v/v was reached, the function remaining linear. STABILITY OF THE CHEMILUMINESCENT SOLUTION- Experiments with the continuous bubbling of ozonised air luminescent solution showed that the readings are stable for at stream flow is 64 ml per minute, and the ozone concentration 0.0 being made for the evaporation of alcohol. through 10ml of chemi- least 20 hours when the per cent.v/v, allowance INFLUENCE OF TEMPERATURE- This lack of effect with temperature change applies to the chemiluminescent solution only, and not to the ozonisers that were used in developing the method. Temperature change in the ozonisers largely affects the rate of ozone production. Change of temperature by * 10" C does not influence the results of analysis. INFLUENCE OF OTHER GASES- As may be appreciated, nitrogen, oxygen and similar gases do not interfere at all. Nitrogen dioxide and sulphur dioxide were each mixed with air and the mixtures were passed separately through the chemiluminescent solution to test whether they would (a) react with simultaneous emission of light, (b) destroy the solution. I t was found that in neither instance was light emitted; nor was the chemiluminescent solution destroyed, for, after passing ozone through it again, the reading remained un- changed, i e ., the reading was the same before and after nitrogen dioxide and sulphur dioxide had been passed through the solution. Ozonised - air S = Silica gel T = Tap Apparatus for increasing the stream flow without Fig. 3. change in the absolute volume of ozone per time-unit INFLUENCE OF THE STREAM FLOW- The apparatus outlined in Fig. 3 was used to study the effect of the gas-stream flow on the emitted light. The flow was increased at the outlet of the ozoniser in order to avoidlo change in the rate of ozone production.August, 19661 METHOD FOR DETERMINING OZONE 503 It was found that increasing the flow up to 200ml per minute does not influence the reading of the recorder when the rate of ozone production remains constant and within the limits already mentioned.RESPONSE-TIME OF THE CHEMILUMINESCENT SOLUTION- To determine the response-time of the solution, oscillographic observations of the light emitted by single bubbles were made (Fig. 4 ( a ) ) . Similar experiments were also conducted by using a second solution which contained no gallic acid (Fig. 4 ( b ) ) , and to make a better comparison of the results obtained, the heights of the pulses given by this second solution were arbitrarily equalised with those given by the first solution by adjusting the sensitivity of the oscilloscope. It can be seen that the time of fall, considerable (approximately second) for rhodamine B, (Fig.4 ( b ) ) , becomes almost zero for the mixture with gallic acid, (Fig. 4 ( a ) ) . I I tI % I , , I , , I I I I -1 -- Time, seconds - I 1 I . . - - Time, seconds Fig. 4 (u).. Light emitted by single bubbles of ozonised air through a mixture of gallic acid and rhodamine B in ethanol Fig. 4 (b).. Light emitted by single bubbles of ozonised air through rhodamine B in ethanol REPRODUCIBILITY OF RESULTS- It was found from a large number of recordings conducted at several ozone concentration levels under constant conditions, that the chemiluminescent solution (within its stability limits, as already stated) showed a fluctuation smaller than 21 per cent. DISCUSSION Although some attempts have been made to use the light emitted during chemi- luminescence reactions as a means of ozone analysis, all have encountered serious difficulties, mainly arising from ( a ) the continuous decrease of the concentration of the chemiluminescent compound that results in non-linear response of emitted light as a function of ozone concen- tration, and (b) the low level of the intensity of light emitted during the chemiluminescence reactions used.It must, therefore, be concluded that an analytical method based on the conversion of chemical energy into light, with measurement of the latter, can be successful only if the concentration of the chemiluminescent compound remains unchanged during analysis, i.e., if the chemiluminescent compound does not take a direct part in the chemical reactions occurring in the reaction vessel. Because such a change occurs, solutions like those used by Biswas and Dahr,ll and Briner,12 although emitting light under the influence of ozone, are nevertheless not suitable for ozone analysis.To avoid this difficulty, Bernanose and R&n&13 used chromatographic paper impregnated with solutions of luminol or rhodamine B. Even so, however, although regular luminescence is observed, this method cannot be used for continuous recording as the concentration of the light-emitting compound diminishes rapidly. Bernanose’s method also encounters another difficulty. Chromatographic paper-discs were used, containing only a small amount of chemi- luminescent compound (of the order of 1 pg) so that the intensity of the light emitted should have been accordingly low. This may have been the reason why a Lallemand 18-step photo- multiplier, which has a sensitivity about 10 times higher than that of the IP 21 RCA, was used.In the present work it was realised that only the protection of the chemiluminescent substance by another compound could lead to the solution of the problem. The latter com- pound should react with ozone more easily than does the former and its concentration should They are mainly useful for continuous recording of the results.504 BERSIS AND VASSILIOU A CHEMILUMINESCENCE [Ana&St, VOl. 91 be relatively high. Further, during the reaction with ozone either the compound itself or its reaction products, should be able to transfer to the chemiluminescent compound an amount of energy such that the latter would be only temporarily excited, and then return to its ground state by emitting a photon.A combination of rhodamine B, as a chemiluminescent compound with gallic acid in ethanol, was found to possess the desirable properties. Use was made of gallic acid for the following 8 reasons- It contains three hydroxyl groups and therefore? has a good quantum yield. It has no induction time because of the presence: of a carboxyl group. It protects rhodamine B from direct oxidation. The oxidation products of gallic acid are not coloured and, therefore, no screening effect Its solution in ethanol is not affected at all by the atmospheric oxygen. I t is not characterised by self-emission of light. The excited molecules or reaction products of gallic acid seem to be at such energy levels (under the influence of ozone) that the energy transfer to rhodamine B, which is finally responsible for the emission of light, becomes possible with a satisfactory quantum yield.The reaction of gallic acid with ozone, the energy transfer to rhodamine B and the subsequent emission of light have, in total, a much faster response than does the reaction of rhodamine B alone with ozone (cf. Fig. 4 (a) with Fig. 4 ( b ) ) . takes place. Rhodamine B was used because- (i) It appears to be a good acceptor of the energy provided by the reaction of gallic acid with ozone. (ii) It is stable to oxygen. (iii) Unlike luminol, it does not self-emit (although the self-luminescence of luminol can be inhibited16 by using a-naphthol or 3-indazolinone-4-carboxylic acid, other com- plications arise).(iv) The light that it emits is suited to the S4 surface of the photomultiplier that was used. ( v ) It is not oxidised directly by ozone in the presence of gallic acid. The authors of the present work have produced unpublished evidence that the reactions taking place may be summarised as follows- gallic acid + ozone --+ A* + oxygen rhodamine B + A* --+ rhodamine B* + B rhodamine B* -+ hu + rhodamine B where A* is an excited intermediate, or excited intermediates, resulting from the reaction between gallic acid and ozone and B is the final product, or products, of the oxidation. Taking into account (a) the sequence of the reactions, (b) the fact that rhodamine B remains unchanged during the process, and (c) that the concentration of gallic acid is much higher than that of rhodamine B (50 : 1), the advantages of this system can be readily apprecia- ted when it is compared with other methods in which direct oxidation of a chemiluminescent compound is used.The following conclusions can be drawn- As regards the use of the 5-fold ozoniser, it can be said that it is the most dependable source of ozone in that concentrations are kept constant and related accurately by certain ratios (e.g., 1 to 2, 1 to 3, 1 to 4 and 1 to 5 ) . If, instead of the taps TI and T, of the potassium trap (Fig. 1 ( b ) ) , a capillary tube is used in one or the other branch of the apparatus, a fixed proportion of the ozone would be destroyed. Partial decomposition of the ozone could also be achieved thermally. This method, however, requires closer control.t It has been observed that in reactions of polyphenols with ozone the light sum increases rapidly In the presence of carboxyl groups, the emission of light begins simultaneously with the reaction. with increasing numbers of hydroxyl groups. The delay otherwise observed is called the induction time.August, 19661 METHOD FOR DETERMINING OZONE 505 A G2 porous diaphragm was used in the construction of the bubbler, which acted as the reaction cell, C (Fig. 1 ( b ) ) , as this grade of diaphragm gives fine bubbles without the need to increase considerably the pressure of 17 inches of water of the ozonised air. It must be pointed out that the production of ozone in the ozoniser falls as the pressure increases and, therefore, all experiments must be carried out at the same pressure.For the single ozoniser that was used in the present work, it was found that by changing the pressure from 5 to 35 inches of water (the stream flow being constant and equal to 64 ml per minute), the ozone concentration changed from 0.10 to 0.08 per cent. v/v. I t has already been mentioned that the time of linear response of 10ml of the chemi- luminescent solution is 20 hours for a stream flow of 64ml per minute, and an ozone con- centration of 0.01 per cent. v/v. This time can be extended, either by increasing the dimensions of the reaction cell, or by suitable adjustment of the potassium hydroxide trap, K (Fig. 1 ( b ) ) . If by the latter, the time of linear response can easily become 700 hours with the conditions described above.In the instance of the solution containing gallic acid (Fig. 2), the occurrence of light fluctuation, which is almost entirely absent from similar curves taken by using rhodamine B alone in ethanol, is an additional measure of the fast response of this solution. The incidental noise originates from the statistical behaviour of the bubbles passing through the chemiluminescent solution. The intensity of light emitted is a measure of the ozone concentration only if the stream flow is constant. Generally, however, it is a measure of the absolute amount of ozone passing through the reaction cell per unit of time. The fact that by this method concentrations of ozone down to 0.0003 per cent. v/v only were recorded, does not exclude at all the possibility of measuring much lower con- centrations.For example, the modern low noise photomultipliers make it possible to count photons readily, one by one. A rough calculation of the quantum yield of the system used in the present work, shows that an emitted photon corresponds to about lo5 molecules of ozone, i.e., about 10-11pg of ozone. These extreme figures, which lie beyond the limits even of radioactivation analysis, show the future possibilities of chemiluminescence as a tool in analytical chemistry. This work was done under the auspices of the Greek Atomic Energy Commission. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. REFERENCES Morozov, N. M., Zh. Analit. Khim., 1960, 15, 367. Zehender, F., and Stumm, W., Mitt. Geb. Lebensmittelunters. u. Hyg., 1953, 44, 206. Wartburg, A. F., Brewer, A. W., and Lodge, J. P., jun., A i r & Wat. Pollut., 1964, 8 (l), 21. Mast, G. M., and Saunders, H. E., 1.S.A. Trans., 1962, 1, 325. Hersch, P., and Deuringer, R., Analyt. Chem., 1963, 35, 897. Ehmert, A., in “Ozone Chemistry and Technology,” Advances in Chemistry Series 21, American Osherovich, A. L., and Rodionov, S. F., A t m . Ozone (Moskow: Mosk. Univ.), Sb., 1961, 72. Alway, C. D., and Slomp, G., jun., in “Ozone Chemistry and Technology,” Advances in Chemistry Regener, V. H., Ibid., 1959, 21, 121. Bersis, D., and Katakis, D., J . Chem. Phys., 1964, 40 (7), 1997. Biswas, J., and Dhar, N., 2. anorg. allg. Chem., 1928, 173, 125. - _ _ , Ibid., 1931, 199, 400. Brink, E., Helv. Chim. Acta, 1940, 23, 320. Bernanose, A. J., and R h 6 , M. G., in “Ozone Chemistry and Technology,” Advances in Chemistry Bersis, D. S., 2. phys. Chem., 1969, 22, 328. Uemura, K., Science and Crime Detection, 1954, 7, 6. Chemical Society, Washington, D.C., 1959, p. 128. Series 21, American Chemical Society, Washington, D.C., 1959, p. 108. Series 21, American Chemical Society, Washington, D.C., 1959, p. 7. Received J u l y 5th, 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100499

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

506 BETSY BIRABEN SCOTT: DETERMINATION OF TANTALUM BY THE [ArtdySt, VOl. 91 The Determination of Tantalum by the Solvent Extraction of a Tantalum - Pyrogallol Complex BY BETSY BIRABEN SCOTT (Facultad de Quimica y Farmacia, Universidad Nacional de La Plata, Argentina) A colorimetric procedure for determining up to 1.2 nig of tantalum in the presence of up to 20mg of niobium, or up to 180 mg of tungsten, has been developed. The colourless tantalum - pyrogallol complex is extracted into ethyl acetate a t pH between 4.5 to 6.0 by means of tetrahexyl or tetra- butyl ammonium iodide and back-extracted with acidified ammonium oxalate (pH 2.0). The yellow complex obtained is measured spectrophotometrically at 400 mp. TANTALUM can be determined colorimetrically when admixed with niobium and tungsten by selectively extracting a colourless tantalum - pyrogallol complex, in the presence of tetrabutyl or tetrahexyl ammonium iodide, into ethyl acetate and back-extracting with acidified ammonium oxalate.The molar extinction coefficient of the yellow complex is 2135 at 400 mp. Vanadium, chromium and molybdenum interfere less than in the original procedure of Hunt and Wells. Titanium remains as a serious interference. Nudelmanl has studied the effect of quaternary ammonium compounds on the extraction of metal - pyrogallol complexes into ethyl acetate. He observed that a colourless tantalum complex was extractable in the presence of tetrahexyl or tetraheptyl ammonium iodide. This observation has been developed into a method for the determination of tantalum in the presence of excess niobium and other ions.Usually corrections have to be applied to pyro- gallol absorptiometric methods for determining tantalum when niobium or tungsten are p r e ~ e n t , ~ , ~ but in the new procedure 1 mg of tantalum can be determined in the presence of 20 mg of niobium and 180 mg of tungsten. Titanium interferes with the determination and must be removed. EXPERIMENTAL THE EFFECT OF pH AND QUATERNARY AMMONIUM IODIDE ON EXTRACTION- Aliquots of a tantalum solution containing 0.9 mg of metal were extracted at different pH’s with additions of tetrahexyl ammonium iodide (THAI), or the tetrabutyl salt (TBAI) into ethyl acetate and then back-extracted with ammonium oxalate solution acidified to pH 2. The measured absorbances at 400mp are given in Tables I and 11.TABLE I EFFECT OF pH ON EXTRACTION OF TANTALUM (043mg) IN THE PRESENCE OF THAI AND TBAI PH 4.0 4.2 4.3 4.5 4.9 5.0 5-6 6 4 6.8 ,4bsorbance - THAI TBAI 0-490 0.500 0.515 - 0.522 0.525 0.525 - 0-520 0.527 0.535 - 0.525 - 0.522 0.532 0.500 0,518August, 19661 SOLVENT EXTRACTION OF A TANTALUM - PYROGALLOL COMPLEX TABLE I1 EFFECT OF THAI AND TBAI ON THE EXTRACTION OF TANTALUM (0.9mg) AT pH 4.5 TO 5-0 THAI, mg Absorbance TBAI, mg Absorbance 5 0.200 20 0-480 8 0.528 40 0-526 15 0.531 80 0.532 30 0-520 100 0-53 1 45 0.500 120 0.520 507 A certain amount of quaternary salt is required for extraction into the organic phase, but an excess prevents back-extraction into the aqueous phase. INTERFERENCE BY NIOBIUM- Amounts of niobium up to 4 mg are without effect; between 4 and 8 mg a larger amount of tetrahexyl ammonium iodide must be taken to ensure quantitative extraction of tantalum ; above 9 mg too much tetrahexyl ammonium iodide (required for extraction into the organic phase) prevents quantitative stripping.Tetrahexyl ammonium iodide can be used successfully with 9 mg of niobium but only over a restricted range of pH. Tetrabutyl ammonium iodide allows up to 20 mg of niobium to be present, and extraction is possible over a wider pH range than with tetrahexyl ammonium iodide (see Tables I11 and IV). TABLE I11 EFFECT OF THAI AXD TBAI ON THE IXTERFERENCE OF NIOBIUM IN THE DETERMINATION OF TANTALUM (0-9 mg) AT pH 4.5 TO 5.0 Niobium, mg 0.45 0.90 3.6 3-6 6.3 9.0 9-0 9-0 9.0 18.0 2 7.0 36.0 36.0 - THAI 15 15 15 15 30 30 8 15 40 50 - Absorbance 0.53 1 0.530 0.53 1 0.527 0.526 0.5 13 0.258 0.470 0.492 0.450 - TRAI 80 80 80 80 - - - - - - 80 80 120 200 Absorbance 0.530 0.528 0.530 0-530 - - 0.535 0.470 0.460 0.442 TABLE IV EFFECT OF pH ox THE INTERFERENCE OF 9mg OF NIOBIUM IN THE DETERMINATIOK OF TANTALCM (0.9 mg) PH 4.5 4.7 4.9 5.3 5.5 5.9 6.2 5.8 Absorbance in the presence of- r - THAI, 40 mg TBAI, 80 mg - 0.531 0.490 - 0.491 0.530 0.458 - - 0-532 0.340 - - 0.528 - 0.529 IKTERFERENCE BY TUNGSTEN- Although the tungsten - pyrogallol complex is insoluble in ethyl acetate in the presence of tetrahexyl ammonium iodide, it can interfere because extractable coloured products are formed.Spectral studies on the reaction between tungsten, pyrogallol and quaternary ammonium ions show that the existence of a definite stoicheiometric compound is dubious, and suggest the oxidative nature of the process as the colour intensity increases, not only508 BETSY BIRABEN SCOTT: DETERMINATION OF TANTALUM BY THE [Analyst, Vol.91 with acidity (Table V) and ammonium salt concentration, but also with time. Thus when niobium is present, the restricted pH allows only 11 mg of tungsten to be present without TABLE V EFFECT OF pH ON THE INTERFERENCE BY 18.4mg OF TUNGSTEN IN THE DETERMINATION OF TANTALUM (0.9 mg) Absorbance in the presence of- PH THAI, 15 mg TBAI, 60 mg 4-5 4.7 5.0 5-2 6-1 6-5 6.6 - 0.580 - 0.558 0.590 - 0.562 - 0.555 0.547 0.530 - - 0-542 interference. In the absence of niobium, up to 180 mg of tungsten do not cause interference if the pH is maintained at 6, and a minimum amount of tetrahexyl ammonium iodide is used.TABLE VI EFFECT OF TUNGSTEN IN THE DETERMINATION OF TANTALUM (0.9mg) AT A pH OF 4.5 TO 5.0 Absorbance in the presence of- Weight of I A 1 tungsten, mg THAI, 15 mg TBAI, 80 mg 5.5 0.531 0.532 9-2 0.529 0.551 11.0 0.530 0.570 12.9 0.538 - 18.4 0.590 - TABLE VII EFFECT OF TUNGSTEN ON THE DETERMINATION OF TANTALUM (0.9mg) AT A pH OF 6 Weight of tungsten, mg Absorbance in the presence of 15 mg of THAI Te t rabu t yl ammonium tractability of the tungsten OTHER INTERFERENCES- 18 0.528 92 0-527 184 0.532 202 0.548 iodide is unsuitable for use with tungsten because of the ex- - pyrogallol complex. The interferences studied only include those which usually accompany tantalum after a hydrolytic concentration starting from more complex materials.Molybdenum, vanadium and chromium interfere to a lesser extent than in Hunt and Wells’ technique (see Table VIII). Concentrations of fluoride and phosphate as high as 5 x M cause insignificant errors in the procedure. Boric acid interferes by retaining tantalum in the aqueous phase; sulphate does not interfere. TABLE VIII INTERFERENCE OF CATIOKS IN THE DETERMINATIOK OF TAKTALUM Tantalum oxide equivalent, mg 7 A \ 1 mg of metal oxide Hunt and Wells Proposed method Molybdenum trioxide . . .. 0.68 0.015 Chromic oxide . . .. .. - 0.06 Vanadium pentoxide . . . . 0.44 0.12August, 19661 SOLVENT EXTRACTION OF A T.4NTALUM - PYROGALLOL COMPLEX COLOUR PRODUCTION AND STABILITY- Colour measurements were made after 30 minutes in order to obtain perfect separation of phases; the colour was stable for a t least 1 day.The absorbance is linear up to 1.2 mg of tantalum. 509 PROCEDURE- M) and niobium ( M) solutions were prepared by dissolving the appropriate amount of spectrographically pure metal in a platinum dish with 5 ml of 48 per cent. hydrofluoric acid and a few drops of concentrated nitric acid. After concentration on a steam-bath to about 2 ml, 5 ml of concentrated sulphuric acid were added, evaporating to sulphur trioxide fumes. The diluent was 4 per cent. ammonium cxalate solution. Tungsten (5 x M), vanadium and chromium (5 x 10-2 M) solutions were prepared by dissolving the corresponding salt in distilled water. A titanium (1 x M) solution was prepared in the same way as tantalum except that titanium dioxide was used as the starting material.The molar solutions of phosphate and fluoride were prepared by dissolving the respective ammonium salt in distilled water. Test solutions-Tantalum ( M and 1 M), molybdenum (1 x PREPARATION OF CALIBRATION GRAPH- The standard curve was prepared by taking aliquots of the 0.2 mg per ml tantalum solution and proceeding as indicated in Method ( a ) or ( d ) . The curve was plotted over the range 0 to 1.2 mg of pure metal. REAGENTS- Ammonium oxalate solution, 4 per cent. w/v, aqueous. Sodium sulphite solution 30 per cent. w / v , aqueous. Sulphuric acid solution, 5 per cent. w / v , aqueous. Pyrogallol reagent (A)-Dissolve 10 g of pyrogallol in 100 ml of analytical-reagent grade ethyl acetate (this solution keeps well for several weeks).Pyrogallol reagent (B)-Dissolve 10 g of pyrogallol and 0.1 g of tetrahexyl ammonium iodide in 100 ml of analytical-reagent grade ethyl acetate. Pyrogallol reagent (C)-Dissolve 10 g of pyrogallol and 0.3 g of tetrahexyl ammonium iodide in 100ml of ethyl acetate. Tetrabutyl ammonium iodide solution-Dissolve 1 g in 100 ml of 4 per cent. ammonium oxalate solution. Acid ammonium oxalate-Acidify 4 per cent. w/v ammonium oxalate solution with con- centrated sulphuric acid until a pH of 2 is attained. METHOD- Prepare the sample solution by dissolving the metal with hydrofluoric acid and a few drops of nitric acid (see Test solutions), or by fusing the oxides with potassium bisulphate. After preparing the solution and evaporating, dilute with ammonium oxalate solution.Use an amount of sample solution containing not more than 1 mg of tantalum. ( a ) Samples containing niobium up to 4 mg and tungsten up to 11 mg-Introduce an aliquot of sample solution into a 100-ml separating funnel and dilute to 20 ml with ammonium oxalate solution after adjusting the pH to between 4-5 and 5.0 with sodium sulphite solution (if necessary correct with sulphuric acid solution). Extract with a 10-ml portion of p>.rogallol reagent (B) and shake the mixture vigorously for at least 2 minutes. Re-extract the clear aqueous phase with 5ml of the same reagent. Combine the organic layers and wash twice with 2-ml portions of 4 per cent. ammonium oxalate, waiting each time until the aqueous solution is clear.Add 20ml of acid ammonium oxalate solution to the organic layer and shake them together vigorously for 2 minutes. Wait for 30 minutes and read the absorbance at 400 mp in a 1-cm cell against a blank similarly prepared. (b) Samples containing niobium between 4 and 8 mg and tungsten up to 11 mg-All condi- tions are the same except that it is necessary to extract the first time with 10 ml of pyrogallol reagent (C). The second extraction is performed with 5 ml of reagent (B). ( c ) Samples containing tungsten up to 180 mg and niobium ztp to 1 mg-This is essentially the same procedure as in (A), but the extraction is performed at a pH of 6.0 to 6.5.510 BETSY BIRABEN SCOTT [Analyst, VOl. 91 ( d ) Sawaples containing niobium up to 20 mg and tungsten up to 6 mg-Add the sample and 5 ml of tetrabutyl ammonium iodide solution to a 100-ml separating funnel.Add ammonium oxalate solution to a total volume of about 20 ml, Correct the pH as above to between 4.5 and 6.5. Extract initially with 10 ml of pyrogallol reagent (A), and then with 5 ml of the same reagent after adding 3ml of tetrabutyl ammonium iodide solution. Treat the collected extracts in the same manner as when reagent (C) is used. REsurrs AND DISCUSSION By using the appropriate procedure the figures obtained for the determination of 0.9 mg of tantalum in the presence of excess niobium and tungsten are collected in Table IX. TABLE IX DETERMINATION OF TANTALUM (0.9mg) I N THE PRESENCE OF NIOBIUM AND TUNGSTEN Niobium, Tungsten, THA41, TBAI, mg mg mg mg pH Absorbance 4 11 15 - 4-6 0.528 7 11 35 - 4.7 0.527 0.9 180 15 - 6.2 0.530 18 5.5 - 80 5.8 0.531 The extraction of the tantalum complex into ethyl acetate is quantitative.Absorbances for the same concentration, with and without extraction, show an insignificant difference (less than 2 per cent.). An unstable yellow colour appears on acidifying the residual aqueous phase with sulphuric acid, which resembles the yellow4 complex TaO(C,O,)Yy-, but tests show that it is caused by reaction between pyrogallol and bisulphite. The residual aqueous solution remains colourless after acidification when extraction is carried out a t a lower pH of between 4.0 and 4.5. In agreement with Lucachina5 it was found that the oxalate ion must be present in the final aqueous phase ; the yellow complex was not formed when the organic phase was extracted with sulphuric acid of the same pH as the oxalate extractant. Other quaternary ammonium salts such as tetraheptyl ammonium iodide, tetrahexyl and tetrabutyl ammonium bromides give similar results. I wish to thank R. A. Wells, former Director of the National Chemical Laboratory, Teddington, for providing the facilities to carry out the work. I am also indebted to A. Woolf for his reading of the manuscript and to J. A. Catoggio and G. Smith for their helpful suggestions. REFERENCES 1. 2. 3. 4. 5. Nudelman, O., Thesis, 1964 (unpublished paper), Facultad de Quiniica y Farmacia, La Plata, Catoggio, J. A., and Rogers, L. B., Talanta, 1962, 9, 387. Hunt, E. C., and \X7ells, R. A., Afaalyst, 1954, 79, 345. Rabko, A. K., and Lucachina, V. V., Ukr. Khirn. Zh., 1962, 28, 371; Chem. Abstr., 1962, 57, 9445e. Lucachina, V. V., I b i d , , 1963, 29, 689; Chern. Abstr., 1963, 59, 14574g. Received May 24th, 1965 Argentina.

ISSN:0003-2654    

DOI:10.1039/AN9669100506

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

August, 19661 RUSSELL 611 Flame-photometric Determination of Sodium and Potassium in Manganese Ores BY B. G. RUSSELL (The lZiational Institute for Metallurgy, Yale Road, Milner Park, Johannesburg) Two procedures are described; in one, the sample is dissolved in hydro- chloric acid, interfering elements are precipitated with 8-hydroxyquinoline in ammoniacal solution, and the precipitate then extracted into chloroform. Sodium and potassium are determined in the aqueous phase by means of a filter flame photometer. The second procedure is more suitable for routine use and involves the dissolution of the sample in hydrochloric acid, followed by the addition of sulphuric acid and aluminium nitrate to suppress interferences, and the direct evaluation of the sodium and potassium contents of the solution by means of either a prism or a filter flame photometer. Comparative results obtained by this alternative procedure on instruments of these two types are given.GROWING importance is being attached to the reliable determination of sodium and potassium contents of South African manganese ores, and this problem is aggravated by the widely discrepant results currently reported by suppliers and customers on the same sample. TABLE I RESULTS OF THE DETERMINATION OF SODIUM AND POTASSIUM IN SOUTH AFRICAN MANGANESE ORES Analysis by suppliers Analysis by customers A 7- r 7 Sample Sodium oxide, Potassium oxide, Sodium oxide, Potassium oxide, No. per cent. per cent. per cent. per cent. 0.56 0.48 0.65 0.44 0.51 0.89 0.76 1-14 0.51 0.62 0.41 0.36 0.46 0-12 0.14 1-08 0.61 0-46 0.61 0.93 The classical gravimetric procedures of J.Lawrence-Smith1 and Berzelius2 for determining sodium and potassium were found to be too time-consuming and inaccurate for present purposes. Grimaldi3 has successfully applied a “standard-addition” method to the determination of sodium and potassium in siliceous rocks, but we were unsuccessful in applying this procedure to the analysis of manganese ores, owing to the non-linear relationship between emission and alkali content of the sample. The choice of a flame-photometric procedure for determining sodium and potassium is largely dictated by the type of instrument available. Instruments involving the use of a prism are invariably more expensive than those in which filters are used. If a simple filter instrument typified by the “EEL” flame photometer (obtainable from Evans Electroselenium Ltd., Harlow, Essex), can be used, it has economic advantages. The “EEL” flame photometer has been described in detail by Collins and Polkinhorne,* and was used in the investigational work described in this paper.To obtain further informa- tion on the performance of this instrument many of the solutions examined on it were also examined on a Beckman Model DU spectrophotometer that had been fitted with a flame attachment. The mutual interferences of alkali metal^,^ calciumJ6 9’ ,8 and some anions4 have already been investigated. Farrow and Hill9 have also studied the effect of cations in the determina- tion of alkali metals, and reported interferences by the chief constituents of manganese ores, i.e., iron and manganese.512 RUSSELL : FLAME-PHOTOMETRIC DETERMINATION OF [Analyst, Vol.91 The relatively cool air - coal gas or propane - butane flame of the “EEL” instrument excites fewer elements than the higher temperature flames of other instruments. Cationic interferences are therefore less with an “EEL” instrument ; however, a filter instrument is not sufficiently selective for accurate determination of sodium and potassium, because emissions due to iron and manganese are known to pass through the filter^.^ Bond and Staces found that the use of narrow wavelength-band filters largely eliminates emission from calcium and strontium and, although the use of such filters might be an advantage in eliminating interference from iron and manganese emissions, these filters were not readily available.METHOD I-SUPPRESSION OF INTERFERENCE BY SOLVENT EXTRACTION EXPERIMENTAL PREPARATION OF A SOLUTION OF THE SAMPLE- Hydrochloric acid was used to dissolve the samples because sodium and potassium are present in manganese ores as cryptomelane and ephesite, both of which are readily soluble in this acid. This was later verified by the good agreement of the sodium and potassium values obtained in repeat tests in which the samples were decomposed with hydrofluoric acid. SEPARATION OF INTERFERING SUBSTANCES- Manganese is the major interfering element in the analysis of manganese ores. It is not readily absorbed on a cation-exchange resin unless it is present in solution as permanganate. This, however, presents difficulties that arise from the marked tendency for manganese in solution to precipitate as manganese dioxide during oxidation.Few reagents, other than 8-hydroxyquinoline, precipitate manganese quantitatively. Many other metals are also quantitatively precipitated by 8-hydroxyquinoline in alkaline solution, but alkalis tend to co-precipitate, and errors are introduced if the precipitate is removed by filtration. If, however, the precipitate is extracted into chloroform, no such loss of alkalis occurs. If calcium and magnesium are present, it is essential to use a large excess of 8-hydroxy- quinoline, but it is claimed that the presence of butyl Cellosolve increases the solubility of the magnesium complex in chloroform,lO and so reduces the amount of chloroform required for the extraction. Butyl Cellosolve also has the advantage of reducing the amount of chloro- form necessary for the extraction of other metal 8-hydroxyquinolinates ; it also aids separation of the organic and aqueous phases.If only a small amount of calcium is present, the calcium precipitate may be removed by filtration after the chloroform extraction. The precipitation of manganese is quantitative only if the pH of the solution is between 7 and 9.5, and a reducing agent, e.g., hydroxylamine,ll is present. When an acetic acid solution of 8-hydroxyquinoline was used, the extraction of manganese was incomplete, and subsequent removal of the large amount of ammonium acetate formed was difficult and time-consuming. When, however, an alcoholic solution of the reagent was used, these problems were not encountered.PREPARATION OF STANDARDS- To minimise error, acidities were adjusted so that each solution contained 3 per cent. v/v of perchloric acid before it was sprayed into the flame. Standard solutions containing known amounts of both sodium and potassium oxides, in the ratio of 1 to 4, were used for calibration purposes, as this was approximately the ratio of sodium to potassium found in the samples investigated. It has been shown5 that wide variations in this ratio are permissible because the mutual interference of sodium and potassium is negligible if the amount of either does not exceed that of the other by a factor of more than 10. METHOD REAGENTS- All reagents should be of the highest purity obtainable.Ammonia solution-Pass ammonia gas into water in a plastic bottle until a saturated This reagent, as supplied, usually has an unacceptably solution of ammonia is obtained. high sodium content.August, 19661 SODIUM AND POTASSIUM I N MANGANESE ORES 513 8-Hydroxyquinoline (8 per cent. w/v)-Dissolve 100 g of the reagent in 70 ml of 96 per cent. ethanol, then add 900 ml of water. Filter the solution through a Biichner funnel, and wash the precipitate with water. Continue to draw air through the precipitate for about 30 minutes, then transfer it to a dark bottle and store it, preferably in a refrigerator. Dissolve 8 g of the purified reagent in 100 ml of ethanol; prepare the reagent solution daily. Standard sodium solution-Dissolve 1.8860 g of sodium chloride (dried at 105" C) in Dilute this solution 10 times for use.water, add 5ml of perchloric acid (spgr. 1-58), and dilute the solution to 1 litre. 1 ml of solution = 0.1 mg of sodium oxide Standard potassium solution-Dissolve 1.5830 g of potassium chloride (dried at 105" C) in water. Add to this solution 5 ml of perchloric acid (sp.gr. 1-58) and dilute the solution to 1 litre. Dilute this solution 10 times for use. 1 ml of solution = 0.1 mg of potassium oxide Keep the volumes of all reagent solutions to a minimum and ensure accurate com- pensation for the blank by standardising the amount of each reagent added at each stage of the procedure. APPARATUS- funnels. detectable error. Use quartz apparatus wherever possible, and make extractions in Pyrex separating Calibrated flasks made of soda-glass were used, but these did not introduce any Use a filter (e.g., "EEL") flame photometer with an air - coal gas flame.PROCEDURE- Determine a blank on the reagents with each batch of samples. Transfer the sample (see Note 1) to a 150-ml quartz beaker, and add 15 ml of hydrochloric acid (spgr. 1.16). Evaporate the solution to dryness on a hot-plate, then cool it slightly. Add about 2 drops of hydrochloric acid (sp.gr. 1.16) and 20 ml of water. Boil the solution gently to dissolve soluble salts; allow to cool. Transfer the entire contents of the beaker to a calibrated flask and dilute the solution to the mark. Filter the solution through a dry filter-paper into a dry quartz beaker, and transfer a 20-ml aliquot, representing not more than 0.29g of sample, to a 250-ml quartz beaker.Add 2 g of hydroxylammonium chloride, dilute the solution with water to about 150 ml, then add 10 ml of the 8-hydroxyquinoline solution. Adjust the pH of the solution to between 7 and 9, testing with indicator paper; heat it to about 60" C (do not boil), then cool. Transfer the entire contents of the beaker to a 150-ml Pyrex separating funnel, and add to the solution 2 ml of butyl Cellosolve and 15 ml of chloroform. Shake the funnel for about 30 seconds, then draw off and discard the chloroform phase. Repeat the extraction twice, with 5-ml portions of chloroform. Transfer the aqueous solution to a 150-ml quartz beaker; if necessary, filter the solution through a Whatman No. 40 filter-paper ; wash the filter-paper sparingly with water.Add 3 ml of nitric acid (spgr. 1.42), evaporate the solution to dryness, then cool. Add 2 ml of perchloric acid (sp.gr. 1-54), again evaporate the solution to dryness, volatilise the excess of perchloric acid and then cool. Add 1.5 ml of perchloric acid (sp.gr. l a % ) , warm gently to dissolve soluble salts, then transfer the clear solution to a 50-ml calibrated flask and dilute with water to the mark. Determine the sodium and potassium emissions of the solution a t 589 and 766.5 mp, respectively, and calculate the sodium and potassium oxide contents of the sample from calibration graphs prepared by using the appropriate standard sodium and potassium solutions. XOTE 1- When analysing batches of samples containing the same approximate ratios of sodium and potassium, it is advantageous to prepare calibration standards containing both sodium and potassium in similar ratios to the samples.When the ratio of the one element to the other exceeds 10 to 1, this technique becomes necessary to compensate for mutual interference of the two elements.514 RUSSELL FLAME-PHOTOMETRIC DETERMINATION OF [ A nabst, VOl. 91 PRECISION OF THE METHOD- The samples contained about 45 per cent. of manganese, and 13 per cent. of iron, 3.5 per cent. of silica, 1.1 per cent. of barium oxide and 4 per cent. of alumina. This is shown in Table 11. TABLE I1 DETERMINATION OF SODIUM AND POTASSIUM BY PROPOSED METHOD Sodium oxide Potassium oxide - - Sample number . . .. 2 4 2 4 Determinations . . .. 11 7 14 7 Mean value . . .. . . 0.193 per cent. 0.207 per cent. 0.843 per cent. 0.682 per cent. Standard deviation . . . . 0.016 0.014 0.022 0.030 Coefficient of variation . . 8.3 per cent. 6.8 per cent. 2-7 per cent. 4-4 per cent. COMPARISON OF RESULTS- The standard deviation was higher for the determination of sodium than it was for the potassium determination. A probable explanation lies in the proportionately higher blank in the sodium determination: the mean of 5 determinations was 0.072 per cent. of sodium oxide; the corresponding blank in the potassium determination was a mean of 0-036 per cent. of potassium oxide for 6 determinations. RECOVERIES OF ADDED SODIUM AND POTASSIUM- To assess the extent of any loss of alkalis in the proposed procedure, additions equivalent to 2.0 mg of sodium oxide and 5.0 mg of potassium oxide were made to a series of 0.5-g samples of purified manganese dioxide.Recoveries of sodium oxide varied between 98-1 and 100.6 per cent. and the blank values between 22 and 65 pg; the standard deviation was 0-035 pg, and the coefficient of variation was 1.7 per cent. Recoveries of potassium oxide varied between 92.0 and 102.0 per cent. and the blank values were between 8 and 49 pg; the standard deviation was 0.167 pg, and the coefficient of variation was 3.5 per cent. These recoveries show that there is no appreciable loss of sodium or potassium in the proposed procedure and emphasise the necessity to make frequent blank determinations, especially with each batch of samples. CONCLUSION The method is satisfactory for determining sodium and potassium in manganese ores.The procedure is, however, time-consuming and not suitable for application on a routine basis. As very few elements interfere, the method is ideally suited for establishing the sodium and potassium content of samples of manganese ores of variable composition. The investi- gation of a batch of 7 samples and a blank can be completed in about 10 working hours. METHOD II-SUPPRESSION OF INTERFERENCES BY THE ADDITION OF ALUMINIUM EXPERIMEKTAL LIMITATIONS OF A FILTER FLAME PHOTOMETER- The main limitation of a filter instrument is due to the transmission of iron and man- ganese emissions through the sodium filter, and iron emission through the potassium filter. Evans Electroselenium Ltd. reported that the presence of aluminium suppresses interference due to and it was decided to investigate the suppression effect of aluminium on iron and manganese emissions.According to Collins and P~lkinhorne,~ hydrochloric acid and chlorides seriously suppress sodium and potassium emissions when the chloride concentration exceeds 0-012 N. Therefore, chlorides introduced during the dissolution of the sample should be removed by evaporating the sample solution with a measured excess of sulphuric acid.August, 19661 SODIUM AND POTASSIUM I N MANGANESE ORES TABLE I11 FLAME PHOTOMETER READINGS SHOWING THE EFFECT OF SULPHURIC ACID ON EMISSION OF SODIUM AND POTASSIUM Sulphuric acid, normality Nil 0.05 0-1 0.4 0.5 0.7 1.0 1.5 2.0 3.0 Sodium oxide, 30 p.p.m. “EEL” Beckman 66.5 60.5 - 61-5 - 62.0 - 62.0 65.0 - - 62.0 63.5 62.0 61.0 60.0 58.5 57.0 - - Potassium oxide, 30 p.p.m.“EEL” 58.0 - 61.0 59.0 59.0 58.0 56.0 52.5 Beckman 63.0 63.0 66.0 64.5 62.5 57.5 53.0 - - - 515 Both instruments were adjusted to give 100 divisions deflection equivalent to sodium oxide and potassium oxide, each at the 50 p.p.m. level. Results in Table I11 show, in general, that sulphuric acid does not have an erratic or pronounced effect on the emissions of sodium and pot4assium, provided that the strength of this acid is about 0-7 N. It was decided, therefore, to standardise the amount of sulphuric acid present at 0.8 N, and avoid an excessive loss of this acid when solutions were evaporated to remove chlorides. The next aim was to establish the effect of added aluminium, and the tests made are summarised in Table IV; the strength of sulphuric acid in these and all subsequent tests was maintained at 0.8 N.TABLE IV FLAME PHOTOMETER READINGS SHOWING THE EFFECT OF ALUMINIUM (AS NITRATE AND SULPHATE) ON EMISSIOXS OF SODIUM AND POTASSIUM Aluminium added, p.p.m. 0 25 50 75 100 150 200 300 500 1000 1500 2000 3000 4500 5000 6000 30 p.p.m. of sodium oxide with aluminium added as- A f > Nitrate Sulphate 3 E - z G z GzBeckman’ 66-5 66.5 66.5 66.5 - - 67.0 - - 66.5 - 65.0 67.0 66.5 67-0 66.5 - 67.0 67.5 69.0 67-0 __ - - 67.0 68.0 66.6 68-0 66.0 66.0 - - 62.0 64.0 66.5 66.0 59.0 62.0 66.5 63.0 - 66.5 63.0 - 66.5 63.0 - - - - - - - - - - - - - - - - - - 30 p.p.m. of potassium oxide with aluminium added as- Nitrate 5zF-ZGz 58.0 63.0 - - - - 58.5 - - - - - 58.5 65.0 58.0 65-0 58-0 60.0 58.0 - 54.5 55.0 53.0 55.0 - 55.0 - - - - Instrumental settings as for Table 111.Sulphate Gr-kzBeckmaI: 58.0 63.0 - 62.0 59.0 - 59-0 64.0 59.5 - - 66.0 60.0 - 59-5 68.0 59.0 66.0 58.6 66.0 56.5 63.5 - - - - The results contained in Table IV show that the sodium emission is constant when the concentration of aluminium (as nitrate) exceeds 1000 p.p.m. and that the potassium emission is reasonably steady for concentrations of aluminium (as nitrate) up to 3000 p.p.m. If the aluminium is added as sulphate, the emissions of both sodium and potassium vary. The sulphate concentration must therefore be kept constant, and this requirement precludes the use of aluminium sulphate in place of aluminium nitrate to suppress inter- ferences arising from the presence of iron and manganese.516 RUSSELL : FLAME-PHOTOMETRIC DETERMINATION OF [AnaZySi!, VOl.91 TABLE V FLAME PHOTOMETER READINGS SHOWING THE EFFECT OF IRON AND MANGANESE ON EMISSIONS OF SODIUM AND POTASSIUM Iron or manganese added, p.p.m. 0 1000 2000 4000 5000 8000 10,000 30 p.p.m. of sodium oxide, with added- 30 p.p.m. of potassium oxide, with added- A r > I h Iron Manganese Iron Manganese e- 5 B e c k m z - n 66.5 66-5 66.5 66.5 61.5 63.0 61.5 63.0 75.5 - 70.5 63.0 - 63.0 83.0 65.0 74.5 71.0 66.0 61.0 61.5 63.5 - 66.0 - 65-5 79.0 - - 62.5 61.5 - - 66.5 - - 73.0 - - 68.0 92.0 75.5 - 64.0 70.0 67.0 - - > 100 - - 71.5 83.0 - - - Concentration and instrumental settings as for Table VI. Table V shows that the potassium emission is unaffected by up to 5000 p.p.m.of man- ganese] although the presence of iron at the 1000 p.p.m. level causes high readings to be obtained. Interference due to the presence of iron is satisfactorily suppressed in the presence of between 2000 and 5000 p.p.m. of aluminium (as nitrate)] as shown in Table VI. TABLE VI FLAME PHOTOMETER READINGS SHOWING THE EFFECT OF ALUMINIUM NITRATE ON THE COMBINED INTERFERENCE OF IRON AND MANGANESE ON THE EMISSIONS O F SODIUM AND POTASSIUM Aluminium Sodium oxide, added 30 p.p.m. (as nitrate), p.p.m. 1 d e n 0 - 79.5 150 - 81.0 300 - 78.0 500 - 76.5 600 - 76.0 1000 92.0 75.0 2000 88-0 - 3000 86.0 75.0 5000 84.0 75.0 10,000 84.0 82.5 12,000 84.0 - The solutions contained 1400 p.p.m. of iron and Instrumental settings were as for Table IV. Potassium oxide, 30 p.p.m.- “EEL” Beckman 76.0 72.0 76.5 71.0 74.0 - 72.5 69.5 66.5 65.5 66.5 61.5 - 61.5 66.5 61.5 66.5 < 60.0 58.0 - - - 4880 p.p.m. of manganese. Interference effect on the sodium emission by both iron and manganese (Table V) is probably a result of the light from the respective emission lines at 586.8 mp and 586.0 mp passing through the sodium filter. The presence of aluminium (as nitrate) in concentrations TABLE VII DETERMINATION OF SODIUM AND POTASSIUM IN THE PRESENCE OF MANGANESE AND IRON Sodium oxide, Potassium oxide, Manganese p.p.m.* p.p.m.* added, & 7-- p.p.m. “EEL” Beckman “EEL” Beckman 1000 33.0 30.0 30.4 30.8 2000 33.6 30.3 30.4 30.2 3000 35.0 36.5 30.7 30.7 4000 36.8 30.0 30.2 30.6 Iron added, p.p.m. 1000 36.0 30.0 30.6 30.4 2000 37.6 30.1 29.9 30.0 3000 39.9 30.4 30.4 30.8 4000 41.8 31.4 30.5 30.6 * 30 p.p.m. added: aluminium, 5000 p.p.m.August, 19661 SODIUhl AND POTASSIUM I N MANGANESE ORES 517 above about 3000 p.p.m.partly suppresses this interference (Table VI), but, as the results in Table VII show, errors are incurred if the amounts of iron and manganese are variable, therefore, iron and manganese equivalent to the amounts of these elements present in the sample must be added to the standards used for calibrating the instrument. This is not necessary for potassium determinations as the interference of iron and manganese is com- pletely suppressed by the addition of between 2000 and 5000 p.p.m. of aluminium (as nitrate). COMPARISON OF A FILTEK INSTRUMENT WITH A PRISM INSTRUMEKT- Experiments conducted on the “EEL” instrument (Table V) were repeated on the Beckman instrument and, for convenience, the two series of results are placed side by side in Table V.A comparison of these results shows that interference arising from the presence of manganese and iron is less pronounced with a prism instrument than it is with a filter instrument. At this stage, it was thought that valuable information could be obtained by repeating the experiments, the results of which are shown in Tables 111, I V and VI; on this occasion a prism instrument was used, and, for convenience, the two series of results are placed side by side in these tables. The monochromator of a prism instrument enables a narrow band-pass to be obtained that largely eliminates emission bands at 586.8 and 586-0 mp.Conclusions reached from these additional experiments with a prism instrument make it possible for both sodium and potassium to be determined in the presence of manganese and iron without compensating for these elements in the standards used to prepare the calibration graph. COMPARISON OF THE TWO METHODS WITH OTHER METHODS- Each of the 5 manganese ore samples examined (Table VIII) contained about 3.5 per cent. of silica, 1.1 per cent. of barium oxide and 4-7 per cent. of alumina, The manganese contents ranged from 40 to 45 per cent. and the iron contents from 12 to 17 per cent. Results obtained by procedures given in the references and by the recommended methods referred to in this paper are shown in Table VIII. The samples were South African man- ganese ores.METHOD REAGENTS- All reagents should be of the highest purity obtainable. Aluminium nitrate solution-Dissolve 713 g of hydrated aluminium nitrate (A1(NO,),.9H2O) in water, and dilute the solution to 1 litre. This solution contains 50,000 p.p.m. of aluminium. Standard sodium and potassium solutions-See Method I. APPARATUS- with a flame attachment and an oxy - hydrogen flame. Use an “EEL” flame photometer with an air - coal gas flame, and a Beckman Model DU PROCEDURE- Determine a blank on the reagents with each batch of samples. Transfer the sample (see Kote 1 under Method I) to a 250-ml quartz beaker, add 20 ml of hydrochloric acid (sp.gr. 1.16) and boil the solution for about 15 minutes. Add 10 ml of 8 N sulphuric acid and evaporate the solution until fumes of sulphuric acid begin to appear (avoiding any significant loss of this acid), then cool the solution.Dilute the solution with water to about 30 ml, then filter it quantitatively through a Whatman No. 40 filter-paper into a 100-ml calibrated flask containing 10 ml of the aluminium nitrate solution (see Xote 2 ) . Dilute the solution with water to the mark. Determine the sodium and potassium emissions of the solution a t 589 and 766.5 mp, respectively, on either of the two types of flame photometer, and calculate the sodium and potassium oxide contents of the sample from appropriate calibration graphs prepared by using the standard sodium and potassium solutions. If a filter instrument is used for the determination of sodium oxide, add, as nearly as possible, the same amount of iron and manganese as that present in the sample solution, to the standard sodium solution before preparing the calibration graph.518 RUSSELL FLAME-PHOTOMETRIC DETERMINATION OF [ A PZUlySt, VOl.91 XOTE 2- After taking into account the aluminium content of the sample, this addition should provide a final 100-ml solution containing between 3000 and 5000 p.p,m. of aluminium, if a prism flame photometer is used; otherwise, the range should be between 3000 and 6000 p.p.m. of aluminium. PRECISION OF THE METHOD- This is shown in Table IX. The samples were similar in composition to those analysed in Table 11. Sample number 1 2 3 4 5 1 2 3 4 5 r Method given in Ref. 1. 0.50 0.48 0.47 0.41 0.5 1 TABLE VIII COMPARISON OF METHODS Sodium oxide, per cent.L > Method I1 Method given Method I, in Ref. 3 "EEL" Beckman 0.28 0.22 0.22 0.22 0.39 0.19 0-17 0.17 0.42 0-20 0.20 0.20 0.50 0.2 1 0.2 1 0.2 1 0.41 0-23 0.20 0.19 Potassium oxide, per cent. f h \ 1-12 1.18 1.01 1.01 1.00 0.96 0.93 0.84 0.79 0-80 1-02 1-14 1.11 0.95 0.94 0.74 0.68 0-68 0.66 0.62 1-58 1.22 0.98 0.92 0.91 TABLE IX DETERMINATION OF SODIUM AND POTASSIUM BY PROPOSED METHOD 11 Sodium oxide Potassium oxide Beckman Beckman Determinations . . .. . . . . 12 12 12 12 Mean value, per cent. . . . . . . 0*212 0.2 13 0.670 0.632 Standard deviation . . . . . . 0.007 0.006 0.007 0.00 1 Coefficient of variation, per cent. . . 3.3 2.6 1.1 1.7 Table X shows the results obtained by another laboratory on six international standard samples with a Zeiss PMQ I1 spectrophotometer with flame attachment. TABLE X DETERMINATION OF SODIUM AND POTASSIUM IN INTERNATIONAL STAXDARDS BY METHOD I1 Sodium oxide, per cent.f A 7 Value by Sample Method 11 Accepted mean value T-112 . . .. . . 4.46 4-39 SY-113 .. . . 3.40 3.24 G-114 . . . . . . 3.37 3.39 N.B.S. NO. 9115 . . 8.48 8.48 STD-GH" . . . . 3.82 3.75 STD-GR" . . . . 3.90 3.80 Potassium oxide, per cent. r 7 Value by A Method I1 Accepted mean value 1-28 1.23 2.64 2.75 5.60 5.52 3.22 3.25 4.62 4-70 4.48 4.50 CONCLUSIONS The direct determination of both sodium and potassium by Method I1 is reliable if a prism instrument is used. With a filter instrument, iron and manganese interfere in the determination of sodium only, but this interference can be overcome by adding iron and manganese to the calibrationAugust, 19661 SODIURf AND POTASSIUM I N MANGANESE ORES 519 solutions.For the determination of potassium only, a filter instrument can be used with advantages in speed and simplicity and without any serious loss of precision. Results obtained by Method I1 (and Method I) are more reliable than those obtained by alternative procedures examined.l j3 I thank Dr. R. E. Robinson, Director of the National Institute for Metallurgy, for valuable advice and for permission to publish this paper, Mr. T. W. Steele for his helpful suggestions throughout this project, and Mr. J. Ferguson of the Geology Department, Witwatersrand University, for the results quoted in Table X. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. REFERENCES Lawrence-Smith, J., Amer. J . Sci., 1871, 50, 269. Berzelius, J. J., A n n l n Phys., 1824, 1, 169. Grimaldi, F. B., Prof. Pap. U.S. Geol. Surv., 1965, No. 400B, 226. Collins, G. C., and Polkinhorne, H., Analyst, 1952, 77, 430. Bond, R. D., and Stace, H. C. T., Ibid., 1958, 83, 679. Leaflet Reference No. 1704.16 “EEL” 1162, Evans Electroselenium Ltd., Harlow, Essex. Bond, R. D., and Hutton, J . T., Analyst, 1958, 83, 684. Leaflet Reference No. 1704.8, Evans Electroselenium Ltd., Harlow, Essex. Farrow, R. N. P., and Hill, A. G., Talanta, 1961, 8, 116. Umland, F., and Hoffman, W., Analytica chim. Acta, 1954, 11, 120. TVelcher, F. J., Editor, “Organic Analytical Reagents,” Vol. I, D. van Sostrand Co. Inc., New Tanganyika Geological Survey, Standard Geochemical Sample T-1, Supplement No. 1 ( 1961). Webber, G. R., Geochim. cosmochim. Acta, 1965, 29, 229. Ingamells, C . O., and Suhr, N. H., Ibid., 1963, 27, 897. Natn. Bur. of Stand., IVashington, D.C., Standard Sample KO. 91, “Opal Glass.” Roubault, H., and Govindaraju, H. de la R., Sciences Tewe, 1963, 9 , No. 4, 339. York, 1947, p. 264. Received September Oth, 1963 Amended, April 26th, 1966

ISSN:0003-2654    

DOI:10.1039/AN9669100511

出版商:RSC    

年代:1966

数据来源: RSC