ISSN:0003-2654    

DOI:10.1039/AN97196FX009

出版商:RSC    

年代:1971

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN97196BX011

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

iv THE ANALYST [March, 1971THE ANALYSTEDITORIAL ADVISORY BOARDChairman: A. A. Smales, O.B.E. (Harwell)*T. Allen (Bradford)*L. S. Bark (Salford)M. T. Kelley (U.S.A.)W. Kemuia (Poland)R. Belcher (Birmingham)L. J. Bellamy, C.B.E. (Waltham Abbey)L. S. Birks (U.S.A.)E. Bishop (Exeter)*R. C. Chirnside (Wembley)A. C. Docherty (Billingham)D. Dyrssen (Sweden)*W. T. Elwell (Birmingham)*D. C. Garratt (London)*R. Goulden (Sittingbourne)*G. F. Kirkbright (London)*G. W. C. Milner (Harwell)G. H. Morrison (U.S.A.)*G. Nickless (Bristol)S. A. Price (Tadworth)D. 1. Rees (London)E. B. Sandell (U.S.A.)W. Schoniger (Switzerland)H. E. Stagg (Manchester)E. Stahl (Germany)A. Walsh (Australia)*T. S. West (London)P. Zuman (U.S.A.)J. Hoste (Belgium)D.N. Hurne (U.S.A.)H. M. N. H. Irving (Leeds)*A. G. Jones (Welwyn Garden City)*Members of the Board serving on the Executive Committee.NOTICE TO SUBSCRIBERSSubscriptions for The Analyst, Analytical Abstracts and Proceedings should be(Other than members of t h e Society)sent through a subscription agent or direct to:The Chemical Society, Publications Sales Ofice,Blackhorse Road, Letchworth, Herts.(a) The Analyst. Analytical Abstracts, and Proceedings, with indexes . . . .index), and Proceedings . . .. .. . . . . . . ..index), and Proceedings . . .. .. . . .. . . ..(b) The Analyst, Analytical Abstracts printed on one side of the paper (without(c) The Analyst, Analytical Abstracts printed on one side of the paper (withThe Analyst and Analytical Abstracts without Proceedings-.. . . (d) The Analyst and Analytical Abstracts, with indexes . . ..index) . . . . . . . . . . . . . . . . . . ..index) . . . . . . . . . . . . . . . . . . . .(e) The Analyst and Analytical Abstracts printed on one sidE of the paper (without(f) The Analyst and Analytical Abstracts printed on one side of the paper (with€27.50 $66.00f28.50 $69.00f 34-75 $84.00€25.00 $60.00f 26.00 $63.00€32.25 $78.00(Subscriptions are NOT accepted for The Analyst andjor for Proceedings alone)Members should send their subscriptions to the Hon. TreasureVi SUMMARIES OF PAPERS I N THIS ISSUE [March, 1971Summaries of Papers in this IssueThe Determination of Trace Amounts of Platinum in Glass byColorimetry, Spark-source Mass Spectrography and X-rayFluorescence SpectrometryMethods for the determination of less than 1 ,ug g-l of platinum in glasshave been investigated and evaluated.The p-nitrosodimethylaniline colori-metric method has been adapted to enable 0.2pg g-l of platinum to bedetermined on 2 g of sample, while the tin(I1) chloride colorimetric methodhas been shown to be too insensitive to permit the determination of suchlow concentrations. Spark-source mass spectrography, while confirming theheterogeneous distribution of the platinum throughout the glass, has alsobeen shown to be too insensitive for the direct determination of platinumin this matrix. An X-ray fluorescence procedure has been successfullydeveloped to enable 0-5,ug of platinum in a 1-g sample of glass to be deter-mined with a relative standard deviation of 10 per cent.The time requiredfor the complete analysis is 3 to 4 hours.The proposed methods depend on the pre-concentration of platinum byco-precipitation with tellurium.C. W. FULLER, G. HIMSWORTH and J. WHITEHEADBritish Titan Products Co. Ltd., Billingham, Teesside.Analyst, 1971, 96, 177-185.Rapid Methods for the Determination of Low Concentrations ofTotal Sulphur in Liquids and GasesDistillate by Reduction with Raney NickelGranatelli's method for the determination of sulphur in liquid hydrocarbonshas been modified to permit the determination of total sulphur in purifiedlight petroleum distillate a t concentrations below 4.0 p.p.m. w/v. A mixtureof propan-2-01 and water is used as the reaction solvent in a rapid methodfor the determination of total sulphur in light petroleum distillate in therange 0-1 to 4.0 p.p.m.w/v with a precision of f 9 per cent. of the determinedvalue. For concentrations in the range 0-01 to 0.10 p.p.m. a more lengthymethod is given, which has an absolute precision of +0.01 p.p.m. w/v.A. FENSOM, N. ROBERTS and G. M. S. DUFFResearch and Development Department, Imperial Chemical Industries Limited,Agricultural Division, Billingham, Teesside.Analyst, 1971, 96, 186-193.Part I. The Determination of Total Sulphur in Light PetroleumRapid Methods for the Determination of Low Concentrations ofTotal Sulphur in Liquids and GasesGas and Synthesis GasesA rapid method developed for the determination of total sulphur inlight petroleum distillate is applied to the determination of total sulphur innatural gas.The sulphur compounds present in the gas are adsorbed on toa small amount of active carbon, which is then allowed to react with asuspension of Raney nickel in a propan-2-01-water mixture and the sulphurdetermined as sulphide as described in Part I of this paper, An alternativeprocedure for the determination of total sulphur in gases containing com-pounds that are not reduced by Raney nickel is also described. The compoundsof sulphur are adsorbed on to active carbon, desorbed into a stream ofhydrogen, which then passes through a furnace a t 900 "C, and the resultinghydrogen sulphide is determined as a stain on paper impregnated with leadacetate. Methods involving the use of a carbon adsorption tube give resultswith a precision of 5 0 .5 mg of sulphur on samples of stenched natural gas.A. FENSOM, K. DIMMOCK and G. M. S. DUFFResearch and Development Department, Imperial Chemical Industries Limited,Agricultural Division, Billingham, Teesside.Part 11. The Determination of Total Sulphur in NaturalAnalyst, 197 1, 96, 194-200viii SUMMARIES OF PAPERS I N THIS ISSUE [March, 1971The Determination of Trace Amounts of Sulphide in CondensedSteam with NN- Diethyl-p-phenylenediamineA sensitive colorimetric method has been developed for the determinationof trace amounts of sulphide in condensed steam. For precise work thecolour produced by NN-diethyl-p-phenylenediamine in the presence of iron (111)ions is measured spectrophotometrically covering the range 0-5 to 100 ,ug ofsulphide-sulphur; the standard deviations a t the 100 and 1.0,u.g levels areabout 3 and 0.08 pg, respectively.Reasonably accurate results over the range0.5 to 25 pg of sulphide-sulphur can be obtained “on site” by a simple visualtitration of a reference solution with a methylene blue solution. The NN-di-ethyl-p-phenylenediamine was shown to be superior to the dimethyl homologuenormally used and its use does not appear to have been reported previously.Methods of sampling and the effect of sulphite are also discussed.T. D. REES, A. B. GYLLENSPETZ and A. C. DOCHERTYResearch and Development Department, Imperial Chemical Industries Limited,Agricultural Division, Billingham, Teesside.Analyst, 1971, 96, 201-208.The Determination of Small Amounts of Cyanide in the Presenceof Ferrocyanide by Distillation under Reduced PressureIn the analysis of effluents and waters, the customary use of lead acetateto prevent the decomposition of ferrocyanide during the distillation of cyanideis not sufficiently effective when small concentrations of cyanide (about0.1 mg 1-l) are to be determined.A method is described in which the de-composition of ferrocyanide can be completely prevented by distilling offthe cyanide under reduced pressure in the presence of zinc acetate. Thecyanide in the distillate is determined by the pyridine - pyrazolone method.R. F. ROBERTS and B. JACKSONResearch and Development Department, Imperial Chemical Industries Limited,Mond Division, Northwich, Cheshire.Analyst, 1971, 96, 209-212.The Automated Determination of Silicon and Calcium in PortlandCement and Associated Raw MaterialsThe manufacture of Portland cement clinker is a continuous large scalechemical synthesis of specific compounds.The strength of the hydratedcement matrix in concrete is a function of the original clinker compoundassemblage. Control of the production of the clinker compounds has to berelated to the time of passage of materials through the rotary kiln and theconditions of processing. Continuous control of the major constituents isessential and knowledge of the effects of the variation of the constituentson the physical properties of the product is desirable.Methods are described for the automated determination of calcium andsilicon in Portland cement and associated raw materials with respect to thedemands, scale and nature of the process.J.A. FIFIELD and R. G. BLEZARDTunnel Cement Ltd., West Thurrock, Grays, Essex.Analyst, 1971, 96, 213-219.Determination of Calcium by Radiochemical ReplacementThe determination of calcium ions in solution by radiochemical replace-ment of silver-110 in labelled solid silver oxalate, cobalt-60 in labelled cobaltoxalate and manganese-54 in labelled manganese oxalate has been examined.A one-to-one replacement was observed with manganese oxalate. Thetechnique can be used to determine 2.5 to 100 pmole ml-l(l00 to 4000 pg ml-1)of calcium, and the lower limit is reduced to 16 pg ml-l by using a 50 per cent.methanol solution.Magnesium interferes to only a small extent. Eachdetermination takes less than 5 minutes, and the precision is f 2 per cent.H. J. M. BOWENChemistry Department, The University, Whiteknights Park, Reading, Berkshire.Analyst, 1971, 96, 220-222X THE ANALYSTAn ‘impossible’ analytical problem?[March, 1971two minutes from nowyou could be on the way to solving itActivation analysis is a fast-developing technique particularlyhelpful in solving difficult problems of trace element analysis.It offers a unique combination of extreme sensitivity with unam-biguous identification of an impurity. Sample contamination andreagent ‘blank’ errors are avoided and the technique can often beusednon-destructively. An Activation Analysis Unit has now beenestablished at Harwell in collaboration with the Analytical Re-search & Development Unit. If you would like further details, orwould like the opportunity to discuss ways in which we can helpto solve your particular problems, complete and post the couponor ring Abingdon 4141, Ext.3085.To : Activation Analysis Unit, Harwell, Didcot, Berks.I am interested in the services of the Activation Analysis Unit.I should like to :17 Receive further information by post 0 Discuss my problem with youI am also interested in assistance with :0 IR spectrometry 0 mass spectrometry NMR spectrometry0 computer applications 0 on-line analysisc] other analytical techniques (tick as appropriate)Name ,PositionAddressTel No.AA 1

ISSN:0003-2654    

DOI:10.1039/AN97196FP037

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

xvi SUMMARIES OF PAPERS IN THIS ISSUEMicrodetermination of Mercury in Biological Samples[March, 1971Part 11. An Apparatus for Rapid Automatic Determination ofMercury in Digested SamplesUrine samples that have been cold-digested by potassium perman-ganate - sulphuric acid mixture overnight are analysed in apparatus consistingof an automatic sample changer, pumps for transferring the sample solutionto a purgation tower and adding tin(I1) chloride solution, which reducesmercury( 11) to metallic mercury, and a spectrophotometer. The mercuryvapour is liberated from the solution in the tower by a flow of nitrogen andthen taken through the absorption cell in the spectrophotometer where thelight absorption at a wavelength of 253.7 nm is continuously recorded.Aftercompletion of the purgation, the mercury-free solution is transported backto the original tube in the sample changer by reversing the pumps, and thenext analysis is started. The mercury content in the sample is calculatedfrom standard graphs, drawn from results with known amounts of mercury.Sixty digested samples, each containing 1 ml of urine, are analysed in about2 hours without any manual work or supervision. In each sample about1 ng of mercury can be detected, but normally the working range for urinesamples is 0 to 400 ng ml-l of mercury(I1). The analysis can be applied tobiological or any other samples that can be digested in a similar manner.G. LINDSTEDT and I. SKAREChemistry Department, National Institute of Occupational Health, Fack, S 104 01Stockholm 60, Sweden.Analyst, 1971, 96, 223-229.Propylene Carbonate Extraction of Tris (pentan-2,4- dione)iron (111)from Aqueous Solution : Application to the SpectrophotometricDetermination of IronOrange tris(pentan-2,4-dione)iron(III) is extracted from aqueous solutioninto propylene carbonate a t pH 4.0 to 9.0.Distribution coefficients rangefrom 23.9 to 116, depending on the ionic strength and pH of the aqueous phase.Relative standard deviations of the spectrophotometric methods developedare 1.52 per cent. or less and these methods are applicable to the routinedetermination of 56 to 391 p g of iron. One of the methods was applied tothe determination of iron in wrought aluminium alloy. The importance ofusing non-toxic solvents in analytical chemistry is emphasised.B.G. STEPHENS, JAMES C. LOFTIN, WILLIAM C. LOONEY and KEN-NETH A. WILLIAMSDepartment of Chemistry, Wofford College, Spartanburg, South Carolina 29301,U.S.A.Analyst, 1971, 96, 230-234.Levamisole : Its Stability in Aqueous Solutions at ElevatedTemperaturesFormed in Aqueous Solutions of Levamisole Stored underNitrogen and Oxygen at 100 "CPart I. Isolation and Identification of Decomposition ProductsSolutions of 1-tetramisole (levamisole) buffered over a pH range of 2 to 8were stored under nitrogen and oxygen a t 100 "C. The decomposition thatoccurred was detected by thin-layer chromatography. The decompositionproducts were isolated and their structures elucidated by standard instru-mental procedures.N. A.DICKINSONDepartment of Pharmacy, University of Manchester.H. E. HUDSON and P. J. TAYLORPhariiiaceutical Departmcnt, I.C.I. Pharmaceuticals Division, hlacclesfield, Cheshire.Analyst, 1971, 96, 235-243xviii SUMMARIES OF PAPERS I N THIS ISSUELevamisole: Its Stability in Aqueous Solutions at ElevatedTemperaturesPart 11. An Assay Specific for Levamisole and Applicable toStability StudiesAn assay specific for the anthelmintic drug levamisole is described. Theprocedure depends on the separation of the active constituent by partitioncolumn chromatography in a hexane - water - chloroform - triethanolaminesystem supported on Celite, followed by ultraviolet spectroscopic measurementof the levamisole in selected fractions of the column eluate.N. A. DICKINSONDepartment of Pharmacy, University of Manchester.H. E. HUDSON and P. J. TAYLORPharmaceutical Department, I.C.I. Pharmaceuticals Division, Macclesfield, Cheshire.Analyst, 1971, 96, 244-247.[March, 1971Levamisole: Its Stability in Aqueous Solutions at ElevatedTemperaturesPart 111. A Chromatographic and Polarimetric Study of the Kineticsof DegradationA t 100 "C decom-position is a t a minimum a t pH 2, while a t pH 8 the rate of decompositionis increased about 70-fold. From kinetic studies at pH 4 and 8 the stabilityof the drug a t 25 and 37 "C has been predicted.N. A. DICKINSONDepartment of Pharmacy, University of Manchester.H. E. HUDSON and P. J. TAYLORPharmaceutical Department, I.C.I. Pharmaceuticals Division, Macclesfield, Cheshire.An.aZyst, 1971, 96, 248-253.Levamisole is hydrolysed by both acids and alkalis

ISSN:0003-2654    

DOI:10.1039/AN97196BP047

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

MARCH, 1971 Vol. 96, No. I140 THE ANALYST The Determination of Trace Amounts of Platinum in Glass by Colorimetry, Spark-source Mass Spectrography and X-ray Fluorescence Spectrometry BY C. W. FULLER, G. HIMSWORTH AND J. WHITEHEAD (British Titan Products Co. Ltd., Billingham, Teesside) Methods for the determination of less than 1 pg g-l of platinum in glass have been investigated and evaluated. The p-nitrosodimethylaniline colori- metric method has been adapted to enable 0.2pgg-1 of platinum to be determined on 2 g of sample, while the tin(I1) chloride colorimetric method has been shown to be too insensitive to permit the determination of such low concentrations. Spark-source mass spectrography, while confirming the heterogeneous distribution of the platinum throughout the glass, has also been shown to be too insensitive for the direct determination of platinum in this matrix.An X-ray fluorescence procedure has been successfully developed to enable 0-5 p g of platinum in a 1-g sample of glass to be deter- mined with a relative standard deviation of 10 per cent. The time required for the complete analysis is 3 to 4 hours. The proposed methods depend on the pre-concentration of platinum by co-precipitation with tellurium. A PROGRAMME to prepare high purity silicate glasses that have low light-scattering and absorption properties indicated that glasses prepared by melting the raw materials in platinum vessels were of a lower quality with respect to light attenuation than required. The trans- mittance of a glass is dependent on the concentration of certain trace impurities present, for example, vanadium, chromium, manganese, iron, cobalt, nickel, copper, rhodium and platinum, which absorb light in the ultraviolet, visible and near infrared regions of the spectrum.l The presence of metallic platinum in glass is particularly important to the over-all transmittance of light for, if the platinum particles are very small (less than the wavelength of the light used), substantial absorption of light will occur, while if the particles are larger the light will be scattered.Russell, Spangenberg and Steele2 have recently shown that large amounts of platinum are dissolved by fusing silicate materials with a flux in platinum ware. They showed that of the fluxes investigated the greatest attack was shown by sodium carbonate and that the amount of platinum dissolved was as high as 10 mg per 4 g of glass in some instances.As the glass samples under consideration are made in some instances by the fusion of sodium and calcium carbonates with silica in platinum vessels an accurate method for determining the platinum content is necessary. C ~ l o r i m e t r y ~ , ~ ~ ~ ~ ~ , ~ provides the widest range of methods used for the determination of platinum, but of these only the tin(I1) chloride* and the $-nitros~dirnethylaniline~ methods have been widely accepted. The tin(I1) chloride method lacks sensitivity. The determination levels have been reduced with this method by taking larger samples; up to 20 g have been used.1° This is not practical in glass analysis when 2-g samples are the maximum amounts that can be handled easily.The $-nitrosodimethylaniline method is susceptible to several interferences but is more sensitive. This method is stated to have an optimum range of determination of 0.7 to 2-4 pg ml-l of platinum in 50 ml of solution, which corresponds to the determination of 17-5 to 60 pg g-lof platinum in the glass, when using 2 g of sample. Of the other techniques used for the determination of platinum, atomic-absorption spectro- photometryll ,12 and p~larographyl~ are too insensitive, and X-ray fluore~cencel~ 915 requires further investigation to be of use. Neutron-activation analysis,16 9 1 7 while potentially satis- factory, was not investigated because the necessary equipment was not readily available and the time for analysis would, therefore, be excessive.The aims of the present work were (i) to modify and improve the tin(I1) chloride or $-nitrosodimethylaniline colorimetric methods, and (ii) to develop an instrumental method to simplify the analysis and reduce the analysis time. 0 SAC and the authors. 177178 FULLER, HIMSWORTH AND WHITEHEAD : DETERMINATION [Analyst, Vol. 96 EXPERIMENTAL REAGENTS- Platinum(IV) solution-Prepare a solution containing 1000 pg ml-l of platinum by dis- solving the appropriate weight of chloroplatinic acid in 0-15 M hydrochloric acid, then dilute the solution as required. This solution was standardised gravimetrically by reduction with formic acid.ls Sodium silicate solution-Dissolve the appropriate amount of sodium silicate, Na,O,SiO,, in water as required.Sodium tellurite solution-Prepare a solution containing 0.5 mg ml-l of tellurium by dissolving the appropriate weight of sodium tellurite in water. p-NitrosodimetFYylaniline solution, 0.25 @er cent. w/v-Prepare by dissolving the appro- priate amount of reagent in fresh absolute ethan01.~ BGfler solution, @H 2.2 O.2-Mix 50 ml of 4 M sodium acetate with 53 ml of 4 M hydrochloric acid. Tin(l1) chloride solution-Prepare as required by dissolving the appropriate amount of tin(I1) chloride in 3.5 M hydrochloric acid. Boric acid solution, 5 per cent. w/v-Dissolve the required amount of boric acid in water. APPARATUS- Absorbance measurements were made with a Hilger and Watts Uvispek spectrophoto- meter. Spark-source mass-spectrographic work was carried out with an A.E.I.MS7 double- focusing instrument of the Mattauch - Herzog type, fitted with ion-beam chopping equip- ment.ls Ilford Q2 photographic plates were used for recording the mass spectra. X-ray fluorescence measurements were made with a Philips PW1540 total-vacuum spectrometer . RESULTS AND DISCUSSION COLORIMETRY- Tin(Il) chloride method-The method described by Ayres and Meyer* was followed, pure solutions of platinum and solutions containing the same amount of platinum in the presence of sodium silicate being used. The required volume of standard platinum solution was transferred to a 100-ml calibrated flask and 10 ml of concentrated hydrochloric acid, 25ml of 20 per cent. w/v ammonium chloride solution and 20 ml of M tin(I1) chloride solution were added; the volume was then made up to 100ml. A blank sample was prepared from the same amounts of reagents.The tin(I1) - platinum(I1) chloride complex formed was extracted with isopentyl acetate con- taining 1 per cent. of resorcinol and the absorbance measured at 410 nm with a 4-cm cell. Two series of experiments were carried out in which 10 and 15-ml portions of isopentyl acetate solution were used. The results shown in Fig. 1 (graphs A and B) indicated that the minimum amount of platinum that can be determined with satisfactory precision by this method is 3 to 4pg, which is a small improvement on the previous resultss as 4-cm absorption cells were used in the present work, while Ayres and Meyer used only 1-cm cells. In the presence of sodium silicate the platinum solutions were prepared by evaporating to dryness with 40 per cent.w/v hydrofluoric acid in PTFE beakers and dissolving the residue in hydrochloric acid. Some typical results for platinum recovery in the presence of 1 g of sodium silicate by the tin(I1) chloride method are shown below. Platinum added . . . . . . 0 10 20 30 Platinum recovered . . . . 0, 0 4, <4 12, <4 18, 4 It would seem from these results that either the platinum is lost during some stage of the determination or possibly that a platinum compound is formed, which is inactive in the tin(I1) chloride method. As sodium silicate is soluble in water, the experiments were repeated by using water instead of hydrofluoric acid for the dissolution, and glass beakers instead of PTFE beakers to check if platinum is lost with the dissolution technique. However, low and erratic results were again obtained.The method of Simonsen12 for the dissolution of basic rocks was found to give repro- ducible results, with 80 per cent. recovery of the added platinum in the presence of sodiumMarch, 19711 OF TRACE AMOUNTS OF PLATINUM I N GLASS 179 silicate (Fig. 1, graph C). In this procedure the sample of sodium silicate containing added platinum was heated with 1 ml of concentrated nitric acid and 15 ml of 40 per cent. w/v hydrofluoric acid and evaporated to dryness in a PTFE beaker; 10 ml of aqua regia were added and the beaker covered before heating it for 2 hours, the cover being then removed and the solution evaporated to dryness. Ten millilitres of concentrated hydrochloric acid were added and the solution heated for 10 minutes.The normal procedure for the tin(I1) chloride method was then followed. However, as this procedure is obviously too insensitive for the determination of the platinum levels required, the method was abandoned. 0 -4 0.3 0.2 0.1 0 10 20 30 40 50 Platinurn/pg Fig. 1. Calibration graphs for the determin- ation of platinum by the tin(I1) chloride method after isopentyl acetate extraction of the tin(II) - plati- num(I1) chloride complex: A, 10ml of isopentyl acetate; and B, 15 ml of isopentyl acetate; C, de- termination of platinum in the presence of 2 g of sodium silicate and extraction with 15ml of iso- pentyl acetate 0.6 a3 0.4 8 a A 0.2 .O Fig. 2. Calibration graphs for the determin- ation of platinum by the p-nitrosodimethylaniline method: A, standard platinum solutions made up to a final volume of 25 ml; B, standard platinum solu- tions in the presence and absence of sodium silicate, incorporating separation with tellurium, and with a final volume of 25 ml; and C, standard platinum solutions incorporating separation with tellurium, and with a final volume of 10 ml p-Nitrosodimethylaniline method-The method of Kirkland and Yoeg was investigated by using pure platinum solutions and sodium silicate - platinum standards as before.The pH of the required amount of standard platinum solution contained in a 25-ml calibrated flask was adjusted to between 2 and 3 with 0.1 M hydrochloric acid and the solution diluted to about 10 ml; 0-5 ml of buffer and 0.5 ml of reagent solutions were added and the flask washed down with a few millilitres of water.The solution was then heated in boiling water for 30 minutes to develop the colour of the platinum(I1) - fi-nitrosodimethylaniline complex. The solution was cooled in a bath of cold water, 5 ml of ethanol were added and the volume was made up to 25 ml with water. A blank solution was prepared in an identical way to correct for the excess of reagent in the sample solution. The absorbances of the solutions were measured at 525 nm against the blank, with 4-cm cells. The only difference between this procedure and the original method is that a final volume of 25ml was used instead of 50 ml, with the corresponding alterations to the volumes of reactant solutions. The results, shown in Fig.2 (graph A), indicate that it should be possible to determine 1 pg of platinum. The method was then applied to sodium silicate containing known amounts of platinum, in the range 10 to 30pg. The samples were brought into solution by heating them with 40 per cent. w/v hydrofluoric acid and evaporating to dryness, redissolving the residue in hydrochloric acid and adjusting the pH of the solutions to between 2 and 3 with sodium hydroxide solution before analysing them by the above procedure. No platinum was recovered. As the p-nitrosodimethylaniline method is known to be affected by several interferences a separation technique was introduced, based on the co-precipitation of platinum with tellurium. The method outlined by Sandel12* was followed.180 FULLER, HIMSWORTH AND WHITEHEAD : DETERMINATION [Analyst, Vol.96 SEPARATION OF PLATINUM BY CO-PRECIPITATION WITH TELLURIUM- About 50 ml of solution, 2-5 M in hydrochloric acid and containing 0.5 mg of tellurium(IV), as sodium tellurite, were treated at boiling temperature with 2 ml of a 25 per cent. solution of tin(I1) chloride in 3 M hydrochloric acid. The precipitate was filtered on a sintered-glass crucible, washed with water and then dissolved in 2 ml of aqua regia and evaporated to dryness twice with hydrochloric acid in the presence of a few milligrams of potassium chloride. The residue was dissolved in 5ml of concentrated hydrochloric acid and the pH brought to between 2 and 3 with sodium hydroxide or ammonia solutiong before the determination of platinum was continued.Two problems were encountered in this procedure when it was applied to pure platinum solutions : (i) a white precipitate appeared during the reaction with 9-nitrosodimethylaniline, which had to be removed by filtration before absorbance readings could be taken, and (ii) low and erratic results, with 40 to 60 per cent. recoveries, were observed. The following parameters of the reaction were investigated to determine the causes of these discrepancies: the effect of nitric acid, which might remain after heating to dryness; the amount of potassium chloride used as the carrier; the effect of evaporating the samples to dryness or to small bulk: the effect of tellurium; and the effect of dissolving the potassium chloride residue in hydrochloric acid and adjusting the pH with sodium hydroxide solution.From these experiments several conclusions were reached : recoveries were better by using the carrier and the amount of potassium chloride used was not critical; the precipitate occurring during the f orrnation of the p-nitrosodimethylaniline - platinum complex is caused in some way by the presence of the tellurium. This precipitation could not be avoided but did not affect the recovery of platinum when removed by filtration; consistent results, with 85 per cent. recoveries, were obtained only when the final potassium chloride residue was dissolved by boiling with a few millilitres of water for 10 minutes followed by the addition of 1 drop of 4 M hydrochloric acid to bring the pH of the solution to between 2 and 3.The reasons for the poor recoveries of platinum when the potassium chloride residue was dissolved in hydrochloric acid and neutralised with sodium hydroxide or ammonia solution are not clear as in the original method this appeared to be the correct procedure for neutralising strongly acidic solutions of platinum.9 It is interesting to note that Russell, Spangenberg and Steele2 experienced a similar problem in the determination of platinum by the tin(I1) chloride method when the sample had been in contact with ammonia at any stage during the method. A calibration graph was obtained for the determination of platinum incorporating the separation by co-precipitation with tellurium (Fig. 2, graph B), 85 per cent. recoveries being obtained with a coefficient of variation of 3 per cent.This modified method was tested under simulated conditions for the analysis of glass by taking 1-g samples of sodium silicate to which additions of aliquots of a standard platinum solution had been made. The samples were evaporated to dryness with 5 ml of 40 per cent. w/v hydrofluoric acid in a PTFE beaker on a controlled-temperature hot-plate and the residues then dissolved by heating with 11 ml of concentrated hydrochloric acid before diluting to 50ml of solution with water and again heating on a hot-plate for 15 minutes; 06mg of tellurium was added to the filtered solution and the separation process continued as described previously. Recoveries were again found to be erratic and low, being in the range 5 to 30 per cent. Two variations on the previous procedure were examined to improve these recoveries.(i) The residue after evaporation to dryness with 40 per cent. w/v hydrofluoric acid was dis- solved in water and the acidity then adjusted to 2-5 M with hydrochloric acid. With 10-pg additions of platinum to 1 g of sodium silicate 50 per cent. recoveries were obtained. (ii) The residue after evaporation to dryness with 40 per cent. w/v hydrofluoric acid was evaporated to dryness again with aqua regia. The residue was then dissolved in water as in (2). The results obtained by this method were identical With those obtained in the absence of sodium silicate (Fig. 2, graph B). An attempt was made to improve on the 85 per cent. recoveries obtained by making use of a double precipitation (two 0-5-mg and two 0*25-mg portions of tellurium) and different amounts of tellurium (0.25, 0-50 and 1-00 mg) but no improvement was observed.The sensitivity of the method was finally improved by reducing the volume of solution used for absorbance measurements to 10 ml (Fig. 2, graph C). This enabled 0.4 pg of platinum,March, 19711 OF TRACE AMOUNTS OF PLATINUM I N GLASS 181 in the presence of sodium silicate, to be determined, which gives a minimum determination level of 0-2 pg g-l of platinum with a 2-g sample of glass. RECOMMENDED PROCEDURE FOR THE COLORIMETRIC DETERMINATION OF PLATINUM IN GLASS Weigh 1 g of powdered glass into a PTFE beaker and add 10 ml of 40 per cent. w/v hydrofluoric acid. Evaporate the sample to dryness on a hot-plate thermostatically con- trolled at 220 "C, then evaporate to dryness again with 5 ml of aqua regia.Add 40 ml of water and heat nearly to boiling, then add 11 ml of concentrated hydrochloric acid and heat for a further 15 minutes. Add 0.25 mg of tellurium, as sodium tellurite, and 3 ml of 25 per cent. tin(I1) chloride solution. Heat the solution and precipitate for 30 minutes, to facilitate coagula- tion, and then filter the mixture. Wash the precipitate with water and then dissolve it in 2 ml of aqua regia, returning this solution to the original PTFE beaker. Add about 15 mg of potassium chloride and by heating evaporate the solution to dryness, add 1 ml of hydrochloric acid and evaporate to dryness again. Dissolve the residue in 5 ml of water, by heating the mixture for 15 minutes on a hot-plate and then transfer the solution to a 10-ml calibrated flask.Cool the solution and adjust its pH to between 2 and 3 with 1 drop of 4 M hydrochloric acid, by using pH paper. Add 0.25 ml of buffer solution and 0.3 ml of p-nitrosodimethylaniline solution and immerse the flask in boiling water for 30 minutes. Immediately cool the flask in cold water and filter the solution, returning the filtrate to the calibrated flask, and make the volume up to 10 ml with water. Measure the absorbance of the solution at 525 nm in a 4-cm cell against a blank sample carried through the same procedure. Prepare a standard calibration graph with known amounts of platinum by following the above method, omitting the glass sample. SPARK-SOURCE MASS SPECTROGRAPHY Spark-source mass spectrography is now an established technique for trace-element analysis and has been applied to a wide variety of materials.It was considered therefore to be a potentially useful technique for the determination of platinum in glass. Electrodes prepared by compressing powdered glass samples cannot be used directly because of the insulating properties of a silica matrix. If, however, electrodes are prepared2' by mixing the glass with a conducting material, then it becomes possible to spark these electrodes in the normal way. Graphite and silver powders were both considered for mixing with the glass and proved to be of equal efficiency. Of the two, silver powder is slightly advantageous in that for an investigation of glass for other trace elements there are fewer possible interatomic species that can be formed which might interfere in the analysis. For this reason a silver - glass electrode system was chosen for a thorough investigation. The sparking conditions found to be the most suitable are those shown in Table I.Under these conditions the time required to deposit a mass spectrum on the photographic plate in the range 0.001 to 200 nC was 2 to 3 hours. Increases in the frequency pulse length and spark voltage gave the expected increases in spark intensity but also caused overheating of the electrodes and the emission of electrode fragments, which contributed to a breakdown in the accelerating voltage in the source. As the concentrations of the major constituents of the glass are usually known it was decided to use a minor isotope of one of these elements as the internal standard for the determination of platinum. For this purpose the calcium-42 isotope, at 0.64 per cent.natural abundance, was chosen as this would be present in the glass at a concentration of about 250 p,p.m. None of the isotopes of sodium or silicon could be used as their concentration levels in the glass would be too high. TABLE I EXPERIMENTAL SPARKING CONDITIONS FOR SILVER - GLASS ELECTRODES .. . . 20kV .. . . 100Hz Spark: voltage . . .. .. pulse length . . . . .. . . 100 ps frequency . . .. .. Beam chopper: pulse length . . .. .. 5 p s frequency .. .. . . Variable Vacuum : analyser .. .. .. . . <1 x lO-'torr source . . .. .. .. . . <1 x 10-6 torr182 FULLER, HIMSWORTH AND WHITEHEAD : DETERMINATION [AnaZyst, Vol.96 Despite careful control of all sparking parameters it was impossible to reproduce results with glass samples containing known amounts of platinum. The measured sensitivity factors for platinum-194, 195 and 196 were found to vary by a factor of 2 or 3 between electrodes prepared from the same samples, although for any one electrode the values were in agreement with each other as regards their isotopic abundances. This would indicate two possible sources for the non-reproducibility : the calcium-42 standard line is not being reproduced satisfactorily; and the platinum is not present homogeneously in the samples. As alkali and alkaline earth metals are susceptible to thermal ionisation from the elec- trodes it is possible that small variations in sparking conditions from one analysis to another could cause variations from the true calcium concentration in the ion beam.To overcome this possibility the silver powder was doped with 20pg of niobium pentoxide per gram of silver powder and the niobium-93 line then used as the internal standard. The doped silver powder was sparked in the usual way to confirm that the niobiumpentoxide and the silver powder were thoroughly mixed. When this mixture was used to standardise the method for the determination of platinum in glass inconsistent values were again obtained for the sensitivity factors. This would indicate therefore that the platinum is not homogeneously mixed throughout the glass, which is not surprising considering the method of preparation. Because in a mass-spectrographic analysis only a few milligrams of the electrode are consumed, it is highly probable that in one analysis a non-representative result is obtained even although the powdered glass taken for the analysis is obtained from a much larger sample.The poor reproducibility apart, the lowest level of platinum that could be quantitatively determined by using a maximum exposure of 200nC was about 1Opgg-l. This level of determination and reproducibility could be improved if the platinum was pre-concentrated by the tellurium co-precipitation method described above. It was felt, however, that this procedure would not be of practical use as the time needed for analysis of one sample by this method would be as long as that required for analysis by the chemical method described above.Further, while six glass samples can be analysed chemically in 1 day, 3 days would be required with the mass spectrograph. If, however, at some future date analyses of glasses for the determination of platinum at concentrations less than 0.1 pg g-l were required, then a pre-concentration method could be reconsidered. X-RAY FLUORESCENCE SPECTROMETRY Jenkins and De VriesZ2 have indicated that by using a direct X-ray analytical method the limit of detection for platinum in a typical matrix would be about 20 pg g-l. Examination of a glass sample containing 20 pg g-l of platinum, however, with the conditions outlined below, gave no measurable response, thereby confirming that a pre-concentration technique would be required to determine the low levels of platinum desired.The technique proposed by Luke14 was adopted and co-precipitation with tellurium, as described above, was selected for concentrating the platinum, as this technique had proved to be successful in the $-nitroso- dimethylaniline colorimetric procedure. After co-precipitation with tellurium, by the method described later, the platinum was filtered off on a Pyrex filter holder (supplied by the Millipore Corporation of Bedford, Mass., U.S.A.), as described by Luke,14 with filter discs 25 mm in diameter with a 0.8-pm pore size. The filter discs were then removed from the filtration apparatus and fixed to a glass support disc with silicone grease. These were dried at 105 "C for 15 minutes and the intensity of the platinum La line was measured on the X-ray fluorescence spectrometer.The addition of boric acid to the solutions before co-precipitation of the platinum with tellurium was found to give 90 to 98 per cent. recoveries, while in the absence of boric acid only 59 to 95 per cent. recoveries were observed. The following spectrometer conditions were used for measurements : lithium fluoride crystal, with the 200 plane with a 2d spacing of 0.402 8 nm, scintillation detector; and pulse height analyser with an analysis time of 300 s. The X-ray tube had a 1-kW tungsten anode, operating at 48 kV and 20 mA. A 0.05-mm nickel filter was used over the tube window to eliminate line overlap between platinum L and scattered tungsten L radiation. Samples were examined by using both a 160 and a 480-pm primary collimator.A 1-kW chromium- anode tube was also tried and found to give greater intensity accompanied, however, by a much greater background. Comparative results are tabulated in Table 11.March, 19711 OF TRACE AMOUNTS O F PLATINUM I N GLASS TABLE I1 COMPARISON OF TUNGSTEN-ANODE AND CHROMIUM-ANODE TUBES FOR THE DETERMINATION OF PLATINUM Intensity measurements are in counts s-l Tube Tungsten anode (nickel filter) Chromium anode 183 Collimator size 160 pm Platinum/ pg 0 10 20 30 40 50 I 1 Corrected Intensity intensity 103 50 148 95 193 140 233 180 283 230 - 53 480 pm - Corrected Intensity intensity 187 293 106 377 190 49 7 310 570 383 683 496 - 480 pm & Corrected Intensity intensity 610 - 772 162 926 316 1072 462 1246 636 1451 841 Jenkins and De Vries22 have shown that the percentage error in a determination is given by the product- 100 1 - .dT dFp-VFb where T is the counting time, R, the count-rate of peak and Rb the count-rate of background. From the results given in Table 11, the calculated values of this product show that the tungsten anode with a 480-pm collimator provides the most accurate results. The fractional 20 counting error for a 10-pg platinum standard and an analysis time of 300 s was calculated to correspond to +OQ4 pg. The co-precipitation X-ray technique was found, in practice, to give a relative standard deviation of 10 per cent., with a lower determination limit of 0.5 pg. Some typical results are given in Table 111. The total time required for the analysis is between 3 and 4 hours. TABLE I11 CALIBRATION FOR THE X-RAY FLUORESCENCE DETERMINATION OF 0 TO 10 pg OF PLATINUM I N GLASS BY USING THE CONDITIONS DESCRIBED Intensity/ Corrected intensity/ Platinum/pg counts s-1 counts s-1 0 180 - 2 206 26 4 224 44 6 235 55 8 260 80 10 286 106 RECOMMENDED PROCEDURE FOR THE X-RAY FLUORESCENCE DETERMINATION OF PLATINUM Weigh 1 g of powdered glass into a PTFE beaker and add 10 ml of 40 per cent.hydro- fluoric acid. Evaporate the sample to low bulk on a hot-plate thermostatically controlled at 220 "C. Add 11 ml of concentrated hydrochloric acid and boil the solution for 20 minutes. Cool and dilute the solution to about 50 ml, add 5 ml of 5 per cent. boric acid solution and boil for 5 minutes. Add 0.25 mg of tellurium, as sodium tellurite, and 5 ml of 25 per cent. tin(I1) chloride solution.Collect the precipitate on a 25-mm Millipore filter and wash it with 2 to 3 ml of water. Fasten the filter disc to a glass support with silicone grease and dry at 105 "C for 15 minutes. Finally, measure the intensity of the platinum Lct radiation by using an X-ray fluorescence spectrometer. Use a 480-pm primary collimator and a tungsten-anode tube, fitted with a nickel filter, as the X-ray source. Calibration graphs are constructed by taking standard platinum solutions through the same procedure, omitting the powdered glass. This simpler X-ray fluorescence method of analysis has been adopted in our laboratories for the routine determination of platinum in several different types of glass. The modified dissolution technique used here has not been examined for use in the colorimetric procedure.I N GLASS-184 [A utalyst, Vol. 96 ANALYSIS OF GLASS SAMPLES- The standard glasses were prepared by dissolving known amounts of platinum in aqua regia and adding these to the sodium silicate batch. The batches were dried and mixed and then used to prepare the glasses. The initial melting of the glass was carried out in an alumina crucible but it was necessary to homogenise the glasses for 2 hours in a platinum crucible. Results for the analysis of these standards by the p-nitrosodimethylaniline colori- metric method and the X-ray fluorescence technique are shown in Table IV. The results confirm that platinum is leached from the crucibles in the homogenising stage and also that homogenisation of the platinum within the glass does not take place completely.FULLER, HIMSWORTH AND WHITEHEAD : DETERMINATION TABLE IV ANALYSIS OF PLATINUM STANDARDS BY THE P-NITROSODIMETHYLANILINE COLORIMETRIC AND X-RAY FLUORESCENCE TECHNIQUES Concentration of platinum found/pg g-l Concentration of platinum I A 3 added t o glass/p.g g-1 X-ray fluorescence Colorimetric 0 3.1 5.5 5 7.9 8-0 10 17.2 14.0 20 23.8 23-0 30 29-0 30-5 TABLE V DETERMINATION OF PLATINUM IN GLASS SAMPLES BY THE @-NITROSODIMETHYLANILINE AND X-RAY FLUORESENCE METHODS Platinum/pg g-l, by- I A \ Glass type Colorimetry X-ray fluorescence Sodium - calcium - silica A . . .. 19 B .. .. 19 c .. .. 6.4 D .. .. 0-4 Lead - sodium - silica E . . .. 2.3 F .. .. 0.5 22 17 6.0 0.6 3.0 0-7 Analysis of sodium - calcium silicate glasses and lead oxide - silica glasses have been made by using these procedures and some typical results are given in Table V.The colori- metric and X-ray fluorescence methods give results that are generally in good agreement. This work was carried out under a Post Office Research and Development Contract, and is published by permission of the Directors of British Titan Products Company Limited and of the Senior Director of Development of the Post Office. The authors also acknowledge the technical assistance of Mr. A. Greenhalgh and Mr. S. Townsend. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. REFERENCES Campbell, D. E., and Adams, P. B., Glass Technol., 1969, 10, 29. Russell, B. G., Spangenberg, J. D., and Steele, T. W., Talanta, 1969, 16, 487. Beamish, F. E., Ibid., 1965, 12, 743. Chechneva, A. N., aKd Radushev, A. V., Zh. Analit. Khim., 1968,23, 1059. Gregorowicz, A., and Klima, Z., 2. analyt. Chem., 1968, 239, 87. Manku, G. S., Bhat, A. N., and Jain, B. D., Talanta, 1969, 16, 1421. El-Ghamry, M. T., and Frei, R. W., Ibid., 1969, 16, 235. Ayres, G. H., and Meyer, A. S., Analyt. Chem.. 1951,23, 299. Kirkland, J. J., and Yoe, J. H., Ibid., 1954, 26, 1340. Sen Gupta, J. G., Analytica Chim. Acta, 1968, 42, 481. van Rensburg, H. C., and Zeeman, P. B., Ibid., 1968, 43, 173. Simonsen, A., Ibid., 1970, 49, 368. Beamish, F. E., Ibid., 1969, 44, 253. Luke, C. L., Ibid., 1968, 41, 237. Campbell, W. J., Spano, E. F., and Green, T. E., Analyt. Chem., 1966, 38, 987. Gil’bert, E. N., Pronin, V. A., Sil’vanovich, Yu. A., and Ivanov, G. V., Radiokhimiya, 1968,10,748. Crocket, J. H., Keays, R. R., and Hsieh, S., J . Radioanalyt. Chem., 1968, 1, 487.March, 19711 OF TRACE AMOUNTS OF PLATINUM IN GLASS 185 Hillebrand, W. F., Lundell, G. E. F., Bright, H. A., and Hoffman, J . J., “Applied Inorganic Analysis,” John Wiley and Sons Inc., New York; Chapman and Hall Ltd., London, Second Edition, 1953, p. 378. Jackson, P. F. S., Vossen, P. G. T., and Whitehead, J., Analyt. Chem., 1968, 39, 1737. Sandell, E. B., “Colorimetric Metal Analysis,” Interscience Publishers, New York and London, Third Edition, 1959, p. 721. Jackson, P. F. S., and Whitehead, J., Analyst, 1966, 91, 418. Jenkins, R., and de Vries, J. L., “Practical X-ray Spectrometry,” Philips Technical Library, 1967, Chapter 9. Received August 14t12, 1970 Accepted October 5t12, 1970 18. 19. 20. 21. 22.

ISSN:0003-2654    

DOI:10.1039/AN9719600177

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

186 Artalyst, March, 1971, Vol. 96, @. 186-193 Rapid Methods for the Determination of Low Concentrations of Total Sulphur in Liquids and Gases Part I. TheDetermination of Total Sulphur in Light Petroleum Distillate by Reduction with Raney Nickel* BY A. FENSOM, N. ROBERTS AND G. M. S. DUFF (Research and Development Department, Imperial Chemical Industries Limited, Agricultural Division, Billingham, Teesside) Granatelli’s method for the determinationof sulphur in liquid hydrocarbons has been modified to permit the determination of total sulphur in purified light petroleum distillate at concentrations below 4-0 p.p.m. w/v. A mixture of propan-2-01 and water is used as the reaction solvent in a rapid method for the determination of total sulphur in light petroleum distillate in the range 0.1 to 4-0 p.p.m.w/v with a precision of f9 per cent. of the determined value. For concentrations in the range 0.01 to 0.10 p.p.m. a more lengthy method is given, which has an absolute precision of &O-01 p.p.rn. w/v. THE manufacture of synthesis gas for the production of ammonia and methanol is now largely based on feedstocks of light petroleum naphtha or natural gas. Both feedstocks contain compounds of sulphur that must be removed before they are brought into contact with the nickel-containing reformer catalysts. Light petroleum naphtha usually contains between 40 and 1000 p.p.m. of total sulphur but desulphurised naphtha contains only 1 p.p.m. or less. Total sulphur can be determined in crude liquid feedstocks by a method published by the Institute of Petroleum1 and another by the International Conference of Benzole Producers.2 These two methods are based on that of Wickbold3 and all three methods involve the complete oxidation of the sample with air or oxygen.Complete oxidation is time con- suming and reproducibility is poor with low concentrations of sulphur. Much time can be saved by using when possible the reduction method recommended by Granatelli,* in which the sample is treated first with a suspension of Raney nickel in propan-2-01 to fix the combined sulphur as nickel sulphide and then with hydrochloric acid to liberate the sulphur as hydrogen sulphide, which is then absorbed in alkali and titrated. The method tends to give erratic results with low concentrations of sulphur, but in the modification described below satis- factory results are obtained by using a mixture of propan-2-01 and water instead of pure propan-2-01 as a solvent in the reaction with Raney nickel (Method 1).While the modified procedure gave satisfactory results with concentrations of sulphur in excess of 0.1 p.p.m. its precision was poor at concentrations below that level. Three possible reasons were the imprecise visual end-point, variation of the reagent blank, and the inhibiting effect of the organic phase on the release of hydrogen sulphide from the acidified reaction mixture. The organic phase used could reduce the temperature of the boiling reaction mixture and dissolve trace amounts of the hydrogen sulphide evolved. With the elimination of these sources of error a method was produced that could be used for concentrations of sulphur below 0.1 p.p.m.To make use of a more dilute titrant the final titration with the visual end-point was replaced by a spectrophotometric method based on one used by Rees and Hill5 for the determination of trace amounts of sulphate in water. Preparation of active Raney nickel in sit.u was introduced to eliminate variation in the reagent blank, while inter- ference from the organic phase was prevented by separating the sulphided Raney nickel from the organic liquids by filtration and then boiling it with hydrochloric acid alone to liberate hydrogen sulphide. * Paper presented in part a t the Joint Meeting of the Scottish and North East Sections and the Atomic Spectroscopy and Radiochemical Methods Groups on “Trace Analysis” held at St.Andrews, June, 1970. 0 SAC and the authors.FENSOM, ROBERTS AND DUFF 187 METHOD 1. TITRIMETRIC DETERMINATION OF TOTAL SULPHUR IN LIGHT PETROLEUM NAPHTHA CONTAINING BETWEEN 0.1 AND 4.0 P.P.M. O F SULPHUR APPARATUS- A combined reflux and regeneration apparatus, as shown in Fig. 1, was used. REAGENTS- Sodium hydroxide solution, 4 per cent. wlv, aqueous. ProPan-2-ol - water mixture-Add 5 ml of distilled water to 95 ml of analytical-reagent Hydrochloric acid, 40 per cent. VIV. Dithixone indicator-Dissolve 10 mg of analytical-reagent grade dithizone in 50 ml of analytical-reagent grade acetone. This solution should be made up daily and stored in the dark. Stock standard solution of mercury(l1) acetate-Dry mercury(I1) acetate in an oven at 150 "C (assay not less than 99.0 per cent.on the dried material). Dissolve 3.38 g of the dried reagent in a mixture of 16.5 ml of glacial acetic acid and 25 ml of water. Make the volume up to 500 ml with water. grade propan-2-01. (1 ml of solution = 1000 pg of sulphur.) Dilute standard solution of mercwy(l1) acetate-Dilute 10 ml of the stock solution to 100 ml with water. Dilute 25 ml of this solution to 100 ml with water. (1 ml of solution = 25 pg of sulphur.) Suspension of Raney rcickeLDissolve 10 g of analytical-reagent grade sodium hydroxide pellets in 100 ml of water. Cool the solution in an ice-bath, then add slowly 10 g of nickel - aluminium alloy (B.D.H.) and allow the mixture to stand for half an hour. Decant the aqueous layer, wash three times with 100ml of water by decantation and add 100ml of propan-2-01; preserve in a stoppered flask.It must not be used if more than 3 days old. Nitrogen or argon-Use a supply that is essentially free of oxygen and sulphur. Sintered- glass disc, grade 0. . Absorber with Tip of delivery tube 6 mm from bottom Fig. 1. Apparatus for the determination of sulphur in light distillate by reduction with Raney nickel188 FENSOM, ROBERTS AND DUFF: RAPID METHODS FOR THE DETERMINATION [Analyst, Vol. 96 PROCEDURE- Assemble the apparatus shown in Fig. 1. Measure 20 ml of 4 per cent. sodium hydroxide solution into the absorber with the sintered disc and 50 ml of the dilute hydrochloric acid solution into the tap funnel, then close all the joints and sweep out the apparatus with nitrogen.Raise the tap funnel and measure into the flask, by a pipette with a large delivery jet, 10 ml of a well stirred suspension of Raney nickel. Add 20 ml of propan-2-01- water mixture followed by 50 to 70ml of the sample, replace the tap funnel and reduce the flow of nitrogen to 2 bubbles per second (2 to 3 1 hour-1). Heat the mixture to boiling under reflux for half an hour, then cool it to below the boiling-point and run in the hydrochloric acid from the tap funnel, dropwise, over a period of 10 minutes. Increase the flow of nitrogen to about three times its former rate and boil until all of the Raney nickel has dissolved. Add to the sodium hydroxide solution in the absorber 2 or 3 drops of indicator and 20 ml of analytical-reagent grade acetone. Titrate the absorbed sulphide with the standard solution of mercury(I1) acetate by using a 5-ml microburette, making sure that all of the liquid above and below the sintered disc is titrated (Note 1).Carry out a blank test exactly as above omitting only the sample (Note 2). If A ml is the volume of titrant used for the test, B ml is the volume of titrant used for the blank and I'm1 is the volume of sample taken, then ( A - B) x 25 V p.p.m. w/v Total sulphur (S) = NOTES- 1. The absorption of hydrogen sulphide takes place substantially on the underside of the sintered disc. It is therefore essential that the disc is repeatedly washed with the titrated solution to ensure complete titration of the sodium sulphide. 2. A blank test must be performed on every batch of suspension and when a new supply of propan-2-01 is used.EXPERIMENTAL Granatelli's method has been used successfully for hydrocarbon distillates containing between 100 and 600 p.p.m. of total sulphur. For the analysis of purified petroleum dis- tillates containing about 1.0 p.p.m. of sulphur the method gave erratic results. Increasing the amount of sample taken to improve the sensitivity only resulted in a lower recovery of sulphur. Good recoveries were obtained over a wide range of concentrations when a definite amount of water equivalent to 5 per cent. v/v of the added propan-2-01 was present during the reduction. Factitious samples were prepared by adding, from a l-ml microburette, measured volumes of a crude light petroleum distillate to measured amounts of a light dis- tillate that had been desulphurised completely by refluxing with an excess of Raney nickel.TABLE I DETERMINATION OF TOTAL SULPHUR IN LIGHT PETROLEUM DISTILLATE De- sulphurised (light dis- tillate/ml 70 70 70 70 70 100 100 100 100 100 100 100 Nil Distilled water added/ml 1 1 1 1 1 2 2 2 2 2 2 2 2 Pro- pan-2-01 added/ml 19 19 19 19 19 38 38 38 38 38 38 38 38 Raney nickel sus- pension/ ml 10 10 10 10 10 20 20 20 20 20 20 20 20 Standard added, crude light dis- tillate/ml Nil 0.1 0.5 1.0 1.5 0.2 0.4 0.4 0-6 1.0 Nil Nil Nil Titre/ ml 0.34 0.96 3.24 5.94 8.72 1.74 3.06 3-06 4-34 6.20 0.64 0.60 0.66 Sulphur added/pg Nil 14.2 71-0 142-0 213.0 28-4 56.8 56.8 85.2 142.0 Nil Nil Nil Sulphur re- covered/ Pg 15.5 72-5 140-0 209-0 27-5 60.5 60.5 92.5 140-0 - - - - Re- covery, per cent.Blank 109 102 99 98 97 106 106 108 99 Blank Blank BlankMarch, 19711 OF LOW CONCENTRATIONS OF TOTAL SULPHUR IN LIQUIDS AND GASES. PART I 189 The crude distillate had been analysed by Method 1 (142 p.p.m. w/v as sulphur) and by an oxidation method2 (144 p.p.m. w/v as sulphur). The mixtures were then analysed by the Raney nickel reduction procedure as in Method 1, taking the whole treated volume of 70 ml for each analysis. A further series of factitious samples was prepared by treating 100-ml portions of the desulphurised light petroleum distillate with measured volumes of the analysed crude distillate, but these samples were treated with twice the normal amount of the suspension of Raney nickel during the subsequent analysis. Finally, blank tests were carried out on the desulphurised light distillate, the propan-2-01 and the suspension of Raney nickel.The results in Table I show that over a wide range of concentrations the recovery of sulphur by Method 1 is satisfactory and that there is no great disadvantage in taking rather more of the sample if additional Raney nickel is used. The light distillate chosen as a standard for these experiments contained substantial amounts of only two types of sulphur compound (Table 11, column A). Although this light distillate was fairly typical it was thought desirable to test by the recommended method some material that had a different composition. Two additional samples (Table 11, columns B and C) were analysed by oxidation Method 2 and by Method 1. Methods derived from those of Ball6 were used to determine the concentrations of the types of combined sulphur and the concentration of the elemental sulphur.TABLE I1 TYPES OF SULPHUR COMPOUND IN THREE SAMPLES OF LIGHT PETROLEUM DISTILLATE (P.P.M. W/V) .. .. .. .. .. .. .. .. . . .. 2% . . . . .. R2S2 R,S Elemental Non-reactive . . .. .. .. .. .. .. .. . . Total sulphur by oxidation method Total sulphur by reduction method Sample A .. <2 .. 73 .. 5 .. 59 .. 1 .. 1 .. 144 .. 142 Sample B <2 84 14 71 7 20 191 Sample C (2 61 11 72 24 22 { ;:; The three samples of analysed light distillate were then used to prepare samples containing low concentrations of sulphur, by adding small amounts to measured volumes of desulphurised light distillate. The analyses of these factitious samples by Method 1 are compared in Table I11 where it can be seen that the recovery of sulphur at low levels of concentration is satisfactory.The repeatability of the method is largely dependent on the constancy of the blank for a particular batch of reagents. The coefficient of variation of the nine results shown in Table I is 4.3 per cent., corresponding to a range of &0*09 p.p.m. at the 1.0 p.p.m. level, but this variation includes errors associated with the preparation of the factitious standards; the analytical error would be less. TABLE I11 DETERMINATION OF TOTAL SULPHUR IN THREE SAMPLES OF LIGHT PETROLEUM DISTILLATE Sulphur in 50 ml of distillatel tLg Sulphur, p.p.m. w/v M Introduced Found A 14.2 14.5 0.28 0.29 71.0 69.9 1-42 1.39 B 76.0 8 1.0 1-52 1-62 C 19.0 17.5 0.38 0.35 76.0 7 1-0 1.52 1-42 Sample & (see Table 11) Introduced Found190 FENSOM, ROBERTS AND DUFF: RAPID METHODS FOR THE DETERMINATION [Analyst, Vol. 96 METHOD 2.TITRIMETRIC DETERMINATION OF TOTAL SULPHUR IN LIGHT PETROLEUM DISTILLATE CONTAINING BETWEEN 0.01 AND 0.10 P.P.M. W/V APPARATUS- A combined reflux and regeneration apparatus, as shown in Fig. 1, fitted with the absorber with the spiral baffle, and a Unicam SP600 spectrophotometer or equivalent instrument with special absorption cell fitted with stirrer and burette, as shown in Fig. 2, were used. Microburette li- Stirrer Titration / cell (rnnriifimi I Fin-rni -54 mm- \...--... ._- . -- .... b ea k er 1 Cover made' of Perspex or polythene b LJ Fig. 2. Titration cell, cover and stirrer for spectrophotometric finish with the T lni ra m qPRnn snprtmnh ntnmetpr REAGENTS- with boiled-out water.As in Method 1 except for those listed below. All aqueous solutions must be prepared Sodium hydroxide solution, 10 per cent. w/v, aqueous. Propart-2-02 - water mixtztre-Add 3.5 ml of water to 96.5 ml of analytical-reagent grade Stock standard solution of nzercwy(11) acetate-As in Method 1. Worki.ng standard soZution of mercury(II) acetate-Make the solution up for use as in propan-2-01. Method 1 and dilute 20 ml of this final solution to 250 ml with water. (1 ml of solution = 2 pg of sulphur.) PROCEDURE- Activation in situ of the Raney nickel-Measure 10 ml of 10 per cent. sodium hydroxide solution into the digestion flask of the modified reflux apparatus (Fig.1). Heat it to about 90 "C, allow it to cool and add 1.000 g of nickel - aluminium alloy. Allow the reaction to proceed for 10 to 15 minutes and add 1Oml of distilled water. Decant the aqueous layer and wash the nickel twice with 10 ml of water, once with a mixture of 10 ml of water and 10 ml of propan-2-01 and again with 10 ml of pure propan-2-01. Treatment of sample-Add 50 ml of the sample of light distillate and 30 ml of the propan- 2-01 - water mixture to the flask and place 4-0 ml of 4 per cent. w/v sodium hydroxide solution in the absorber with the spiral baffle. Reduce the sample under reflux for half an hour in an atmosphere of nitrogen, cool, then decant the contents of the reaction flask through a No. 40 Whatman filter-paper. Wash the sulphided nickel on the filter with 20 ml of propan- 2-01 before folding the filter-paper and placing it with the sulphided Raney nickel back into the reaction flask, taking care to remove any nickel adhering to the ground-glass joint.Re-assemble the apparatus with 50 ml of 40 per cent. v/v hydrochloric acid in the funnel, purge with nitrogen and slowly add the hydrochloric acid. Bring the contents of the flaskMarch, 19711 OF LOW CONCENTRATIONS OF TOTAL SULPHUR IN LIQUIDS AND GASES. PART I 191 to boiling and boil for half an hour. Disconnect the absorber and transfer its contents quantitatively to the spectrophotometric cell (Fig. 2) with a minimum amount of boiled-out distilled water. Make this volume up to 50 ml with boiled-out water and then add 25 ml of analytical-reagent grade acetone and 0.50 ml of dithizone solution.Spectrophotometric titration-Place the cell and its contents in a Unicam SP600 spectro- photometer and assemble the stirrer motor and burette unit (Fig. 2). Set the wavelength control to 550 nm, the transmission - density scale to zero and adjust the needle to zero with the dark-current control. Start the stirrer, switch to the “Test” position and re-adjust the needle to zero with the slit width control. Several minutes may elapse before the solution is thoroughly mixed and equilibrium is reached. Add the standard mercury(I1) acetate working solution from a 5-ml microburette in 0.20-ml increments, pausing between each addition to note any deflection of the needle. When the first deflection occurs note the volume of mercury(I1) acetate added and measure the optical density on the transmission - density scale by adjusting the needle back to zero.Continue adding mercury(I1) acetate in 0-20-ml increments, noting the volume added and the optical density in each instance, until a further four readings have been made. Draw a graph relating millilitres of titrant to optical density and determine the end-point to the nearest 0.05 ml from the point of intersection between the rising and horizontal parts of the graph. A blank determination must be carried out exactly as above omitting only the sample. CALCULATION- Let Ts be the number of millilitres of mercury(I1) acetate used for sample titration and then TB be the number of millilitres of mercury(I1) acetate used for blank titration, (Ts - TB) = concentration of sulphur in parts per million w/v.50 EXPERIMENTAL To test the procedure on samples of known sulphur content it was necessary first to prepare sulphur-free light distillate by the repeated distillation of a purified distillate with Raney nickel until no sulphur could be detected in the product by Method 2. The precise sulphur content of a prepared light distillate containing about 5 p.p.m. of sulphur was then TABLE IV SULPHUR DETERMINATIONS ON 50-ml SAMPLES OF LIGHT DISTILLATE (A) (B) Difference between & & (B)-(A)1 duplicates, Sample pg p.p.m. w/v p g p.p.m. w/v p.p.m. w/v p.p.m. w/v Sulphur added Sulphur recovered Reagent blanks (no light Reagents plus sulphur-free distillate) light distillate Factitious samples 1 2 3 4 5 - - Nil Nil 1-13 1-13 2-25 2.25 3-38 3.38 3.38 3-38 4.50 4.50 5-62 5.62 - - Nil Nil 0.023 0.023 0.045 0.045 0.068 0.068 0.068 0.068 0.090 0.090 0.1 12 0.112 3.80 3.90 3-50 3-80 0.85 1.35 2-65 2.45 3.25 3-55 3.35 3.05 5.05 4.75 6.15 6.35 0.076 0-076 0.070 0-076 0.017 0.027 0.053 0.049 0.065 0.071 0.067 0.061 0.101 0.095 0.123 0.127 - 0.006 + 0.004 } + 0.008 + 0.004 } - 0.003 + 0-003 } -0.001 - 0.007 } + 0.01 1 +0.015 } 0.002 0-006 0.010 0.004 0.006 0.006 0.006 0.004192 FENSOM, ROBERTS AND DUFF: RAPID METHODS FOR THE DETERMINATION [Analyst, Vol.96 determined by the same method, except for the final titration for which the procedure detailed in Method 1 was used (i.e., a more concentrated titrant and a visual end-point). This prepared distillate was used as a standard solution (1 ml of solution = 5.62 pg of sulphur) in all subsequent work.To several individual samples of sulphur-free light distillate, each of 50-ml volume, vary- ing amounts of the standard light distillate were added, viz., 0.20, 0.40, 0.60, 0-80 and 1.00 ml, and these samples were analysed in duplicate for sulphur content by Method 2. The results obtained are given in Table IV, where it can be seen that although the differences between added and recovered sulphur ranged from -0.007 to +0.015 p.p.m., the differences between duplicates varied only from 0.002 to 0.010 p.p.m. Thus it is possible to determine total sulphur by this method at concentrations down to 0.01 p.p.m. w/v with a precision of +_O.Ol p.p.m. w/v, although strict attention to detail is essential as the amounts of sulphur to be deter- mined may be less than the amount of sulphur present in the reagents.DISCUSSION Several modifications to Granatelli’s original method have been proposed. Reed7 acti- vated the nickel - aluminium alloy in situ with boiling sodium hydroxide solution and Pitt and Rupprecht* used a colorimetric finish in which the liberated hydrogen sulphide was converted into methylene blue by reaction with an iron(II1) salt and NN-dimethyl-fi-phenyl- enediamine, which was then measured spectrophotometrically. This latter procedure is more sensitive than the titrimetric finish described in Method 1 but the determination takes more time. The titrimetric method has the added advantage of being more readily applicable to samples of widely varying composition.The analysis of a sample with a sulphur content above the prescribed limits can usually be completed by using additional titrant or a more concentrated titrant. Attempts to use a lead sulphide stain finish, as described in a British Standard method for hydrogen sulphide in fuel gas,g were unsuccessful because the range of stains that could be measured accurately was too narrow (1 to 10 pg of sulphur) and the reagent blank was too large. Virtually all of the reagent blank originated from the Raney nickel but some batches of propan-2-01 contained sulphur. Thus in Method 1 it was only necessary to determine a blank on each preparation of active suspension and on each batch of propan-2-01. Sulphur was easily removed from impure propan-2-01 by refluxing it with an excess of Raney nickel.The method has been used successfully for the determination of total sulphur in crude distillates, kerosine and hydrorefined distillates, but not for sulphur in gas oils. According to Granatelli4 olefines interfere in the reaction and compounds such as sulphoxides or sul- phones are reduced with difficulty or not at all. In most instances the interference from olefines is negligible if they are present at concentrations less than 2 per cent., but if oxy- genated compounds are present one of the oxidation procedures already cited should be used. Alternatively, the microcoulometric system used by Martin and Grant,lo in which the sample is first pyrolysed in oxygen, can be used. The Dohrmann microcoulometer C-200A can be used to determine sulphur in naphthas, kerosine and gas oils with a precision of k1.0 p.p.m. if the concentration of sulphur is above 5 p.p.m.A full description has recently been published by Killer and Underhill.ll Method 2 has been used only to determine total sulphur in a few highly refined feedstocks used for experimental work. To obtain satisfactory results it is essential that the experi- mental conditions are strictly adhered to, and on no account should the volume of the sample exceed 50ml. Tests should be carried out in duplicate and in an atmosphere free from volatile compounds of sulphur. Finally it must be emphasised that the method as given applies only to light petroleum distillate, which normally contains no oxygenated compounds of sulphur. Its applicability to other samples must be checked by methods similar to those outlined above before its use can be extended as the efficacy of the Raney nickel reduction procedure cannot be predicted with certainty. REFERENCES 1. 2. Institute of Petroleum, “IP Standards for Petroleum and its Products,” Part 1, Section 1, Method Total Sulphur Working Group of the International Conference of Benzole Producers, Analyt. 107, 1970. Chem., 1964, 36, 339.March, 19711 OF LOW CONCENTRATIONS OF TOTAL SULPHUR IN LIQUIDS AND GASES. PART I 193 3. 4. 5. 6. 7. 8. 9. 10. 11. Wickbold, R., Angew. Chem., 1957, 69, 530. Granatelli, L., Analyt. Chem., 1959, 31, 434. Rees, T. D., and Hill, S. R., Spectrovision, 1969, November 21st, 13. Ball, J. S., U.S. Bureau of Mines, Report Inv. 3591, 1941. Reed, R. H., Analyst, 1963, 88, 735. Pitt, E. H. H., and Rupprecht, W. E., Fuel, 1964, 43, 417. British Standard 3156, Part 2, 1965, 16. Martin, R. L., and Grant, J. A., Analyt. Chem., 1965, 37, 644. Killer, F. C. A., and Underhill, K. E., Analyst, 1970, 95, 505. Received July 22nd, 1970 Accepted September 30th, 1970

ISSN:0003-2654    

DOI:10.1039/AN9719600186

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

194 Analyst, March, 1971, Vol. 96, $9. 194-200 Rapid Methods for the Determination of Low Concentrations of Total Sulphur in Liquids and Gases Part 11. The Determination of Total Sulphur in Natural Gas and Synthesis Gases* BY A. FENSOM, K. DIMMOCK AND G. M. S. DUFF (Research and Development Department, Imperial Chemical Industries Limited, Agricultural Division, Billingham, Teesside) A rapid method developed for the determination of total sulphur in light petroleum distillate is applied to the determination of total sulphur in natural gas. The sulphur compounds present in the gas are adsorbed on to a small amount of active carbon, which is then allowed to react with a suspension of Raney nickel in a water - propan-2-01 mixture and the sulphur determined as sulphide as described in Part I of this paper.An alternative procedure for the determination of total sulphur in gases containing com- pounds that are not reduced by Raney nickel is also described. The compounds of sulphur are adsorbed on to active carbon, desorbed into a stream of hydrogen, which then passes through a furnace at 900 “C, and the resulting hydrogen sulphide is determined as a stain on paper impregnated with lead acetate. Methods involving the use of a carbon adsorption tube give results with a precision of 5 0 . 5 mg m-3 of sulphur on samples of stenched natural gas. MUCH of the natural gas from the North Sea is almost odourless as it is substantially free from compounds of sulphur.1 A few parts per million of sulphur-containing compounds with strong smells are therefore added so that leaks in the distribution system can be easily detected. Tetrahydrothiophen was formerly used as a stenching agent for North Sea gas but this was replaced by a mixture of 90 per cent.of crude dimethyl sulphide and 10 per cent. of mixed thiols known as Calodorant F. Manufactured gases used for the synthesis of ammonia and methanol may contain similar compounds as well as carbonyl sulphide that has been formed by reaction with the carbon monoxide present. The total combined sulphur present in crude or doped gases is not normally more than a few parts per million, expressed as sulphur, and only 0.1 p.p.m. or less in purified gases. Concentrations of sulphur in the part per million range are determined by oxidation methods adapted from those for determining sulphur in liquids but the procedures are inconvenient and slow.Reduction methods are invariably more sensitive and faster than oxidation methods because the conversion of the whole sample is not necessary and the final tests for hydrogen sulphide are much more sensitive than those readily available for sulphate. In the methods to be described advantage has been taken of the adsorptive properties of active carbon for the application of reduction methods to the determination of total sulphur in gases. Non-oxygenated compounds of sulphur are adsorbed on to active carbon and determined by the Raney nickel reduction method developed for the analysis of petroleum distillates, but oxygenated compounds of sulphur must be desorbed from the active carbon and reduced to hydrogen sulphide by reaction with hydrogen at a high temperature.METHOD A. RAPID DETERMINATION OF VOLATILE SULPHUR COMPOUNDS IN NATURAL GAS (REDUCTION WITH RANEY NICKEL) APPARATUS- Adsorption tzlbe-Pack 1 g of prepared active carbon into a Pyrex glass tube, 130 x 5 mm id., keeping it in place with small plugs of glass-wool. Connect the tube with a short piece * Paper presented in part a t the Joint Meeting of the Scottish and North East Sections and the Atomic Spectroscopy and Radiochemical Methods Groups on “Trace Analysis” held at St. Andrews. June, 1970. 0 SAC and the authors.FENSOM, DIMMOCK AND DUFF 195 of silicone rubber tubing to a source of sulphur-free nitrogen and pass the gas through the carbon at the rate of about 30lhour-l while heating the outside of the tube to redness.Continue to pass nitrogen through the tube as it is allowed to cool, then seal it at both ends with silicone rubber stoppers. Hamilton gas syringe, 1 litre. Apparatus for reduction with Rancy nickel-As in Method 1, Part I (this issue, p. 186). REAGENTS- Prepared active carbon-Reflux 50 g of activated carbon (Sutcliffe Speakman Quality 207, Type C, 14 to 18 mesh) with 100 ml of 20 per cent. v/v hydrochloric acid for 1.5 hours. Cool, filter the mixture on a Buchner filter and wash well with de-ionised water. Wash once with propan-2-01 and twice more with de-ionised water. Dry in an oven at 105 "C for 1 hour in a clean sulphur-free atmosphere. Reagents for the reductiopz proceduure with Raney utickel-As in Method 1, Part I.PROCEDURE- With a 1-litre gas syringe pass 2 litres of sample, measured at atmospheric pressure, through a prepared adsorption tube and seal both ends with silicone rubber stoppers. Assemble the apparatus as shown in Fig. 1, Part I. Measure 20ml of 4 per cent. sodium hydroxide solution into the cylindrical absorber and 50ml of dilute hydrochloric acid into the tap funnel. Sweep out the apparatus with a stream of sulphur-free nitrogen. Raise the tap funnel and measure into the flask, by a pipette with an enlarged jet, 10 ml of well stirred Raney nickel suspension, then add 20 ml of propan-2-01 - water mixture. Finally empty the contents of the activated carbon adsorp- tion tube, including the glass-wool plugs, into the flask. Replace the tap funnel and continue the determination of the sulphur in the charcoal as described under Method 1, Part I, for the determination of sulphur in petroleum naphtha.Finally determine the blank on the contents of an adsorption tube prepared from the same active carbon in the same way and with the same reagents. This blank test should be equivalent to less than 2pg of sulphur. If A ml is the volume of titrant used for the test, B ml is the volume used for the blank and V is the volume of gas taken in litres, then or ( A - B) x 25 V mg m-3 Total sulphur (S) = ( A - B) x 18.7 V p.p.m. v/v at 20 "C. EXPERIMENTAL The procedure was tested on gases doped with dimethyl sulphide, thiophen, tetrahydro- thiophen and sulphur dioxide. Standard solutions of dimethyl sulphide (B.D.H. laboratory reagent) were prepared freshly each day by dissolving weighed amounts of the pure liquid in known volumes of sulphur-free light petroleum distillate.The purity of the dimethyl sulphide used was checked by analysing a standard solution that had been made up gravimetrically and was deemed to contain 1.7 g of dimethyl sulphide per 100 ml, expressed as sulphur. Analysis based on total combustion of the sample2 gave a total sulphur content of 1.67 g per 100 ml. As the difference was within the expected precision of the method it was assumed that the dimethyl sulphide was substantially pure and that the standards made up gravimetrically were correct. Several tubes containing activated carbon were prepared as described in Method A. Each tube was then connected to a supply of sulphur-free nitrogen and 30 litres of nitrogen were passed through each tube at a rate of 50 1 hour-l while a calculated amount of standard solution was injected by microsyringe through a rubber septum into the nitrogen up-stream from the carbon.The carbon in each tube was then analysed as described in Method 1, Part I. The results given in Table I have been corrected for the amount of sulphur found in portions of active carbon that had not been exposed to a gas containing compounds of sulphur.196 FENSOM, DIMMOCK AND DUFF: RAPID METHODS FOR THE DETERMINATION [AtZa@t, VOl. 96 TABLE I RECOVERY OF DIMETHYL SULPHIDE FROM A GAS Dimethyl sulphide (expressed as sulphur) Dimethyl sulphide (expressed as sulphur) addedto 30litresof nitrogen/pg , . 25 50 100 150 184 200 368 552 736 920 Nil found/pg .... .. .. 27 48 96 145 175 197 335 535 735 900 2 Further experiments showed that dimethyl sulphide in dry methane or methane saturated with water vapour at 20 “C and at concentrations between 0.4 and 4.0 p.p.m. v/v could be determined with a precision of +7 per cent. of the determined value. Similar studies on the recovery of thiophen and tetrahydrothiophen were carried out in which solutions of the sulphur compounds in methanol were injected into known volumes of nitrogen. From gases containing between 0.8 and 1.6 p.p.m. of thiophen and tetrahydrothiophen the recovery of total sulphur was virtually complete when the volume of sample was not more than 50 litres. Tetrahydrothiophen is resistant to reduction by Raney nickel but amounts of 1OOpg or less can be reduced quantitatively by the procedure used in these tests.The amount of sulphur that could be recovered by this technique from a gas containing volatile sulphur only as sulphur dioxide was negligible. The procedure could therefore be used to determine organic and inorganic sulphides in the atmosphere without interference from the usual excess of sulphur dioxide. (blank) METHOD B. DETERMINATION OF VOLATILE COMPOUNDS OF SULPHUR IN SYNTHESIS GAS (REDUCTION WITH HYDROGEN AT HIGH TEMPERATURE) APPARATUS (see Fig. 1)- Adsorption tube-Pack 1 g of active carbon, which has been acid washed as described under method A, into a piece of silica tubing, 220 x 6mm i.d., and keep it in place with plugs of silica-wool. Activate the tube as described under “Procedure” below.Sleeve furnace to take adsorption tube-This was 150 mm long, wound to give a temperature of 900 “C and fitted with a rheostat control. 8 1-500 mm-1 -350 mm- Hydrogen Fig. 1. Apparatus for the determination of total sulphur in synthesis gas Furnace tube-This consisted of a packed length of silica tubing, 350 x 15mm id., filled with acid-washed silica chips of 3 to 6 mm diameter. Inlet and exit connections were of 6 mm i d . Redzaction furnace to take furnace tube-This was 500mm long, wound to give a tem- perature of 900 “C and fitted with a rheostat control. Holder for lead acetate Pafiers-To enable the exposed part of the paper to be a circle of diameter 12-5 0025mm.March, 19711 OF LOW CONCENTRATIONS OF TOTAL SULPHUR IN LIQUIDS AND GASES.PART 11 197 Lead acetate papers-Prepare an aqueous solution containing 25 g of analytical-reagent grade lead acetate, 12.5 ml of glacial acetic acid and 40 ml of B.P. quality glycerol. Dilute the solution to 250 ml with water. Cut strips 38 mm wide from a sheet of Postlip 633 extra thick white paper (18 x 24, 6076) and soak them in the solution of lead acetate. Suspend the wet papers over a tray to drain and dry at ambient temperature in an atmosphere free from hydrogen sulphide. Cut the dried strips into 50-mm lengths and store them in an air- tight bottle . Rotameters for nitrogen and hydrogen with readings 0 to 50 1 hour-l. Pure nitrogen and hydrogen in cylinders. Silicorte rabbber tNbing, 5 mm id. E.E.L. H,S meter (Evans Electroselenium Ltd., Halstead, Essex). Two Chromel-Alumel thermocouples with indicating galvanometers.Rotary gas meter, 0-5 litre per revolution. PROCEDURE- Preparation of adsorption tube-Assemble the complete apparatus as shown in Fig. 1, making all of the connections with silicone tubing or ground-glass joints. Purge the apparatus with nitrogen at the rate of 50 1 hour-l while raising the temperature of the sleeve furnace and the reduction furnace to 900 "C, by-passing the effluent gas to waste to avoid over-drying of the test paper. After purging with nitrogen for 5 minutes gradually reduce the flow; at the same time cautiously start the hydrogen flow and increase it until a rate of 20 1 hour-l is established when the nitrogen flow is stopped. Any connecting lines that may contain air must be purged to atmosphere with hydrogen before the hydrogen is admitted into the system.Pass hydrogen for 20 minutes with the effluent gases passing through the lead acetate paper, keeping the downstream end of the furnace tube cool with strips of moistened filter-paper. Measure the opacity of the stain obtained on the H,S meter. If this is equivalent to more than 0.1 pg of sulphur (Note 1) continue passing hydrogen until the blank for the active carbon is constant. Reduce the temperature of the sleeve furnace to 600 "C and check the constancy of the blank again. Switch off the sleeve furnace, stop the flow of hydrogen and pass nitrogen through the apparatus at 20 1 hour-l until the sleeve furnace is at ambient temperature. Remove the adsorption tube and seal both ends with silicone rubber stoppers until ready for use.Stop the flow of nitrogen. Analysis of sample-Sample the gas to be analysed by passing a suitable measured volume (Note 2) through the adsorption tube at 50 1 hour-l, by using a rotary gas meter downstream from the tube. Replace the absorption tube in the assembly shown in Fig. 1 and, with the lead acetate paper in position, purge the sytem for 2 minutes with nitrogen at the rate of 50 1 hour-l. Then reduce the flow of nitrogen to zero while starting a flow of hydrogen. When a steady flow of 20 1 hour-l of hydrogen is established switch on the sleeve furnace. Raise the temperature to 600 "C over a period of about 15 minutes and continue to pass hydrogen for a further 15 minutes, keeping the exit tube as cool as possible with wet filter- paper.Stop the hydrogen flow, switch off the sleeve furnace and purge the system with nitrogen as before, allowing the effluent gas to go to waste through the by-pass (Note 3). Measure the opacity of the stain on the H,S meter, with unstained paper to zerotheinstrument, and calculate the concentration of sulphur in the original sample of gas from the amount of sulphur on the paper, allowing for any sulphur found in the blank test. or Micrograms of sulphur on the paper Volume of sample in litres Micrograms of sulphur on the paper Volume of samDle in litres Total sulphur = mg m-3 x 0.75 p.p.m. v/v at 20 "C. L NOTES- 1. The E.E.L. H,S meter is calibrated directly in parts per million v/v of hydrogen sulphide for a gas sample of 2 foot3.The weight in micrograms of sulphur in the stain can be calculated from the meter reading but the instrument can be readily calibrated as follows: Draw 5 ml of hydrogen sulphide from a cylinder into a gas pipette and displace it with pure nitrogen into a large polythene bag by using a rotary gas meter to measure the amount of nitrogen passed into the bag. Make the volume up to 50 litres and close the inlet of the bag with a soft rubber septum. With a gas syringe extract a measured volume from the bag and pass it through a prepared lead acetate paper that has been set up in a holder. Measure the stain produced on the E.E.L. H,S meter. Prepare a series of suitable stains covering the range 1 to 10 ug of sulphur, then construct a graph relating micrograms of sulphur to E.E.L.meter readings.198 FENSOM, DIMMOCK AND DUFF: RAPID METHODS FOR THE DETERMINATION [AfidySt, VOl. 96 2. The volume of gas taken should contain between 1 and 1Oug of sulphur as this is the most suitable range for the operation of the H,S meter. If the required volume is less than 1 litre a gas syringe is to be preferred for measuring the gas passing through the active carbon. The method can be used for the determination of total sulphur in natural gas but not more than 2 litres of the gas must be passed through the carbon. Hydrocarbons of high molecular weight present in natural gas are strongly adsorbed and reduce the capacity of the carbon to adsorb compounds of sulphur. 3. After the determination, when the adsorption tube is cool and filled with nitrogen.it should be a t removed 900 "C. and stoppered immediately as it can be used for a second test without furtiier activation EXPERIMENTAL Method B was tested on measured volumes of nitrogen doped with known amounts of dimethyl sulphide and carbonyl sulphide, either together or independently. A standard solution of dimethyl sulphide in methanol was injected through a rubber septum into the nitrogen by microsyringe; the solution used contained 0.168 g of dimethyl sulphide per 100 ml so that 10 p1 contained the equivalent of 8.7 pg of total sulphur. Gaseous carbonyl sulphide was obtained from a cylinder (supplied by Air Products Ltd.) and found by mass-spectrometric analysis to be better than 99 per cent. pure. Five millilitres of the gas, measured with a gas pipette, were swept into a large polythene bag with nitrogen metered through a rotary gas meter; the volume of gas in the bag was then made up to 50 litres with nitrogen.With the aid of a 100-ml all-glass gas syringe measured volumes of gas were drawn from the bag through a rubber septum and injected into a measured stream of nitrogen, which was then passed through a silica tube packed with prepared active carbon. Between 15 and 60 ml of gas, calculated to contain between 2 and 8 pg of total sulphur, were taken from the plastic bag for a test. The analysis by method B of measured volumes of nitrogen doped with carbonyl sulphide or dimethyl sulphide, or both, is given in Table 11; the sulphur was determined to the nearest microgram. TABLE I1 DETERMINATION OF VOLATILE SULPHUR COMPOUNDS AS TOTAL SULPHUR IN GASES BY HIGH TEMPERATURE REDUCTION IN HYDROGEN Dimethyl sulphide added (calculated)/ pg of sulphur 9 2 9 9 9 0 0 0 0 6 2 2 8 2 Carbonyl sulphide added (calculated) / pg of sulphur 0 0 0 0 0 2 8 8 8 4 8 4 2 2 Volume of nitrogen/ litres 100 100 10 10 50 100 100 10 50 10 10 10 10 10 Total sulphur determined by analysis/ pg of sulphur 8 2 9 9 9 2 8 8 9 9 10 5 10 4 DETERMINATION OF TOTAL SULPHUR IN NATURAL GAS- When natural gas was sampled by the carbon tube technique it was found that adsorption tubes prepared according to the directions given in methods A and B had a breakthrough volume of about 3 litres.High molecular weight hydrocarbons present in the gas in minor concentrations were strongly adsorbed and reduced the capacity of the active carbon to adsorb compounds of sulphur.A sample in a cylinder at 1700 p.s.i.g. was analysed by Methods A and B and again by injecting a measured volume directly into a stream of hydrogen passing through the furnace at 900 "C, as shown in Fig. 1. The resulting hydrogen sulphide was measured as a stain on lead acetate paper by the H,S meter. A l-litre Hamilton gas syringe was used to measure the small volumes ol sample taken, which were 2 litres for the Raney nickel method (Method A), 0.2 to 2 litres for adsorption on carbon and desorption to the Eurnace (Method B) and 0.5 to 2 litres for the direct high temperature reduction method.March, 19711 OF LOW CONCENTRATIONS OF TOTAL SULPHUR IN LIQUIDS AND GASES. PART 11 199 The mean of twelve results by Method A was 4.20 p.p.m.v/v of sulphur, with a standard deviation of 0.31; the mean of ten results by Method B was 4.44 p.p.m. v/v, with a standard deviation of 0-28; and the mean of four results by the direct method was 4.45 p.p.m. v/v, with a range of 0.5 p.p.m. Another sample of natural gas, which was apparently free from high molecular weight hydrocarbons , showed no breakthrough of sulphur when almost 200 litres of gas were passed through an adsorption tube. The mean of six determinations by Method A, by using volumes of sample varying between 18 and 190 litres, was 1.44 p.p.m. v/v of sulphur, with a standard deviation of 0.06. Finally, the two methods for the determination of sulphur in gases were compared over a period of several months with an oxidation method derived from that of the Benzole Pro- ducers Conference2 and a chromatographic method by Gibbons and G ~ o d e .~ The distinctive feature of this chromatographic method is the flame-photometric detector in which the column effluent is passed into a hydrogen-rich flame and the ultraviolet emission at a selected wave- length is monitored by photomultiplier tube. Gas from the West Sole field that had been stenched at Easington was sampled periodically at Immingham and sent in light-alloy cylinders to Billingham where it was analysed by the four methods. Results are shown in Table 111. Date 29.12.69 9.1.70 20.1.70 28.1.70 4.2.70 11.2.70 18.2.70 25.2.70 11.3.70 25.3.70 1.4.70 14.4.70 TABLE I11 DETERMINATION OF SULPHUR IN SAMPLES OF STENCHED NORTH SEA GAS Total sulphur by gas chromatography with flame-photometric detection, p.p.m.v/v 7 7.5 7 7 7 7 7.5 7 6 6 5 6 Total sulphur by carbon tube (adsorption) L 7 -7 Raney nickel Furnace method finish, p.p.m. v/v 7.5 7.5 8 7.5 7.5 7 7 7 7 7.5 7 7-5 8 8 6 7 6 6 6 6 5 5 6 7 finish, p.p.m. v/v Total sulphur by oxidation method, p.p.m. v/v 7 7.5 7 7 7 7 7 6 6 6 5 7 DISCUSSION Tetrahydrothiophen was extracted from fuel gas by Colson4 with a partition sampler containing silicone oil on Chromosorb P, and was desorbed and determined by gas chromato- graphy. Activated charcoal was used by West, Sen and Gibson5 to concentrate atmospheric pollutants which, after subsequent desorption by heat at 200 "C, were analysed cliromato- graphically. Raney nickel was used at 200 "C by Jaworski and Chromniac6 to reduce and fix the volatile combined sulphur in a gas mixture that included an excess of hydrogen.The Raney nickel was then dissolved in hydrochloric acid and the sulphide determined in the evolved gases. Adsorption of the sulphur compounds on carbon followed by treatment with Raney nickel is a convenient way of determining total sulphur in gases if no oxygenated compounds are present and, in the absence of higher boiling hydrocarbons, the method can be made sensitive and precise. It was observed in the course of these investigations that dimethyl sulphide adsorbed on to carbon could be determined more readily by Method 1, Part I, than dimethyl sulphide in solution by the same method, probably because losses by evaporation are prevented if the dimethyl sulphide is adsorbed.Reduction with hydrogen at high temperature has been carried out by Schluter, Parry and Matsuyama,' who passed a gas mixture containing compounds of sulphur and an excess of hydrogen over a nickel catalyst at 1200 "C. Wronsky and Balda and Struchg used a plati- num catalyst for the reaction. This catalyst was also used at 1200 "C by Farley and WinklerlO for the pyrolysis and reduction of liquid hydrocarbons volatilised into a stream of hydrogen, but it was necessary to saturate the hydrogen with water vapour to prevent the deposition of carbon. Method B is intended for the analysis of samples that contain only minor concen- trations of hydrocarbons other than methane. The use of catalysts has been avoided in the200 FENSOM, DIMMOCK AND DUFF interests of simplicity.The results for the samples of stenched natural gas given in Table I11 must be treated with reserve as the composition of the gas in the cylinders may have differed from the composition of the gas in the pipeline from which the sample was taken. The most valuable characteristic of the two procedures detailed above is that the sample can be taken from places close to the main gas stream, adsorbed directly on to carbon and the analysis performed in the laboratory when convenient. Errors caused by adsorption on sample lines and containers can thus be minimised. It will be noted that the temperature specified for the pre-treatment of the carbon is higher in Method B than in Method A. Tests showed that dimethyl sulphide was desorbed completely at 200 OC, but it was necessary to heat activated carbon to 600 "C to desorb carbonyl sulphide. A less rigorous pre-treatment is therefore permissible if the carbon is to be used to absorb non-oxygenated compounds that can be determined by the Raney nickel method.There was evidence that activated carbon sometimes contains sulphates or oxy- genated sulphur compounds, which would not interfere in the Raney nickel method but must be removed if the hydrogen reduction method is to succeed. It was shown experi- mentally that sulphur dioxide was almost unaffected by Raney nickel but that it could be reduced rapidly under the conditions specified in Method B. Methods involving the use of an adsorption tube packed with carbon have some distinct advantages over the other methods cited in Table I11 and, as the apparatus required is inexpensive and simple, they can be used in situations in which the use of more sophisticated methods would not be justified. This is particularly true of Method A, which is convenient for the determination of sulphur in stenched natural gas if only occasional tests are required. If, however, the high temperature reduction furnace is already set up and available it is more convenient to analyse natural gas by Method B as the final instrumental finish is extremely rapid. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. REFERENCES Cooper, L. S., Densham, A. B., de Rose, A. J., and Juren, B., Gas Council Research Communication Total Sulphur Working Group of the International Conference of Benzole Producers, A nalyt. Gibbons, P. A., and Goode, K. A., Gas J., 1968,336, 27. Colson, E. R., Analyt. Chem., 1963, 35, 1111. West, P. W., Sen, B., and Gibson, W. A., Ibid., 1958, 30, 1391. Jaworski, M., and Chromniak, E., Chemia Analit., 1965, 10, 1303. Schluter, E. C., Parry, E. P., and Matsuyama, G., Analyt. Chem., 1960, 32, 413. Wronsky, M., and Bald, E., Chemia Analit., 1967, 12, 863. Struch, C. H., Brennst.-Chemie, 1965, 46, 104. Farley, L. L., and Winkler, R. A., Analyt. Chem., 1968, 40, 962. NOTE-Part I of this series appears on p. 186. GC150, November, 1968. Chem., 1964, 36, 339. Received July 22nd, 1970 Accepted September 30th, 1970

ISSN:0003-2654    

DOI:10.1039/AN9719600194

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

Analyst, March, 1971, Vol. 96, 9fi. 201-208 201 The Determination of Trace Amounts of Sulphide in Condensed Steam with NN-Die th yl-p-phen ylenediamine BY T. D. REES, A. B. GYLLENSPETZ AND A. C. DOCHERTY (Research and Development Defiartment, Imperial Chemical Industries Limited, Agricultural Division, Billingham, Teesside) A sensitive colorimetric method has been developed for the determination of trace amounts of sulphide in condensed steam. For precise work the colour produced by”-diethyl-p-phenylenediamine in the presence of iron (111) ions is measured spectrophotometically covering the range 0-5 to 100,xg of sulphide-sulphur; the standard deviations at the 100 and I.O-,xg levels are about 3 and 0.08 pg, respectively. Reasonably accurate results over the range 0.5 to 25 ,ug of sulphide-sulphur can be obtained “on site” by a simple visual titration of a reference solution with a methylene blue solution.The NN-di- ethyl-p-phenylenediamine was shown to be superior to the dimethyl homologue normally used, and its use does not appear to have been reported previously. Methods of sampling and the effect of sulphite are also discussed. WHEN steam is used as a raw material in catalytic processes, it is necessary to ensure the absence of sulphur compounds and in particular hydrogen sulphide, which is a well known catalyst poison. Although there is no general agreement, some authors have stated that the use of sodium sulphite for the removal of oxygen from boiler feed water can give rise to the production of hydrogen sulphide in the Some raw waters may also contain hydrogen sulphide, which will appear in the steam if not removed in a water treatment plant.Steam contaminated with hydrogen sulphide would adversely affect the I.C.I. steam- reforming process and as many of our boiler waters are conditioned with sodium sulphite it was necessary to analyse samples of steam to determine hydrogen sulphide. To carry out this programme a reliable and sensitive analytical procedure was required. A survey of existing methods suggested that one based on the formation of “methylene blue” would be the most sensitive and suitable for this purpose. Many variations of this method exist and new modifications continue to appear, all of which suggest that improvements are possible.6 to l1 Initial studies were carried out with NN-dimethyl-9-phenylenediamine, but about this time some work had just been completed in which Palin’s DPD method was used to determine chlorine in water. This method involves the use of NN-diethyl-$-phenylene- diamine, which offers advantages over the dimethyl homologue, and it was felt that it might prove to be a better reagent for sulphide also.The use of NN-diethyl-$-phenylenedi- amine for this purpose does not appear to have been reported previously. Subsequent work showed that under our conditions it was about twice as sensitive, with adequate precision. Comparisons were made on several batches of reagent and all of the results obtained confirmed the improved sensitivity with NN-diethyl-9-phenylenediamine. After establishing a suitable laboratory procedure based on the use of this reagent, a simple field test was evolved and the effect of sulphite investigated.EXPERIMENTAL CONDITIONS OF TEST- The procedure selected for examination was that given in the A.S.T.M. method,ll as it had previously been used for effluent analysis. The method, however, was not capable of allowing less than 0.1 p.p.m. of sulphide to be determined and, as we were interested in 0 SAC and the authors.202 REES, GYLLENSPETZ AND DOCHERTY: DETERMINATION OF TRACE AMOUNTS [Analyst, Vol. 96 I I I I I I I 600 620 640 660 680 700 720 740 Wave1 engt h/n m Fig. 1. Absorption curve for ethylene blue colour concentrations down to 0-01 p.p.m. and below, some modification was necessary. Reagents were prepared in accordance with the A.S.T.M.method but sample volumes were increased to 100ml to improve sensitivity. At this dilution, however, the precipitation of iron(II1) phosphate occurred and it was decided to omit the phosphate rather than increase the acidity and incur greater risk of losing trace amounts of sulphide. Phosphate had been used in the original method to destroy the colour of the excess of iron(II1) ions but under the new con- ditions it was unnecessary. Experiments showed that by using 1 ml of 1 per cent. NN-di- methyl-9-phenylenediamine solution and 1 ml of 10 per cent. iron(II1) chloride solution in TABLE I EFFECT OF CONCENTRATION OF NN-DIETHYL-9-PHENYLENEDIAMINE ON FINAL COLOUR IN THE PRESENCE OF 1.0 ml OF 18 PER CENT. IRON(III) ALUM SOLUTION Concentration per cent. w/v, of NN-diethyl-9-phenylenediamine in 50 per cent.sulphuric acid (1.0 ml used) 1.0 1.5 1.8 2.0 2.2 2.5 Blank value 7 4.3 pg of sulphur (40-mm cell) 0.265 0.307 0.336 0.350 0.045 - - Net optical density 80 p g of sulphur (5-mm cell) 0.612 0.700 0-719 0,719 0-722 0.722 0.020 A v 104 pg of sulphur (5-mm cell) 0-734 0.801 0.880 0.880 0.020 - - TABLE I1 EFFECT OF CONCENTRATION OF IRON(III) ALUM ON FINAL COLOUR IN THE PRESENCE OF 1-0 ml OF 2 PER CENT. w/v NN-DIETHYL-@-PHENYLENEDIAMINE SOLUTION Net optical density 18% w/v iron(II1) I A % alum solution/ 4-3 pg of sulphur 100 pg of sulphur ml (40-mm cell) (5-mm cell) 0.5 0.340 0-799 1-0 0.355 0.859 1.5 0.348 0.869 2.0 0.356 0.874 Blank value 0.045 0.020March, 19711 OF SULPHIDE IN CONDENSED STEAM WITH NN-DIETHYL-@-PHENYLENEDIAMINE 203 a final volume of 100 ml, a colour was produced with sulphide which gave an absorption maximum at about 665nm.After allowing about 15 minutes for development the colour was then stable for several hours. Small variations in the amounts of reagents used had no significant effect on the intensity of the colour and a calibration graph over the range 0 to 100 pg of sulphide-sulphur was essentially linear. Because of the instability of dilute solutions of sodium sulphide the standard stock solution was standardised with iodine immediately prior to dilution with de-aerated water. It was also shown that the dilute working solutions were more stable if prepared in dilute de-aerated zinc acetate s ~ l u t i o n ~ , ~ rather than in de-aerated water alone.The final dilute solutions of sulphide contained about 0.05 per cent. w/v of zinc acetate. The results obtained with NN-dimethyl-p-phenylenediamine under these conditions looked promising but at this juncture it was decided to investigate NN-diethyl-P-phenylene- diamine as an alternative. Preliminary tests were therefore carried out under exactly the same conditions and it was found that not only did the latter give satisfactory, stable colours but that they were about twice as intense as those produced with the dimethyl homologue for given amounts of sulphide (e.g., with 49 pg of sulphide values for E,,, were dimethyl 0.192 at 665 nm and diethyl 0.415 at 670 nm). These promising results prompted a more detailed study of NN-diethyl-9-phenylenediamine. As iron(II1) alum was available in a purer form than iron(II1) chloride and shows less tendency to hydrolyse, its use was preferred, in equivalent amounts, in all subsequent work.The absorption curve of the “ethylene blue” complex indicated a maximum at about 670 nm (Fig. 1) and this wavelength setting was used throughout. Experiments designed to study the effect of reagent concentrations were carried out and it was shown that small variations were not critical (see Tables I and 11). Nevertheless, it was decided to standardise on 1.0 ml of 2 per cent. w/v solution of NN-diethyl-9-phenylenediamine in 50 per cent. sulphuric acid and 1.0 ml of 18 per cent. iron(II1) alum solution. It was also established that variations in acidity or alkalinity in the sample solution equivalent to at least 5ml of N acid or alkali caused errors of less than 5 per cent.in the colour. Although theoretical considerations10 would suggest that the order of addition of reagents is unimportant, tests indicated that no colour was produced if the iron(II1) salt was added first. Presumably the sulphide is oxidised under these conditions. Tests were finally carried out to study the effect of the time interval between reagent additions and also the stability of the final colour (see Tables I11 and IV). It was found that 1 minute 2 30 s between the addition of reagents was satisfactory and that full colour development occurred in 10 to 15 minutes. Thereafter the colour was stable for many hours when kept in a stoppered flask in daylight. TABLE I11 TIME BETWEEN ADDITION OF NN-DIETHYL-@-PHENYLENEDIAMINE AND IRON(III) REAGENT Time/s .... .. .. 30 45 60 90 Net optical density for about 40 pg Net optical density for about 4 pg of sulphur (5-mm cells) . . 0.377 0-380 0,369 0.364 of sulphur (40-mm cells) . . 0,288 0-294 0.308 0.300 TABLE IV COLOUR DEVELOPMENT AND STABILITY Time after addition of iron(II1) reagent . . .. .. . . 5 minutes 10 minutes 15 minutes 1 hour Net optical density for about 55 pg of sulphur (5-mm cells) . . 0-506 0.516 0.514 0.507 Net optical density for about 5.5 pg of sulphur (40-mm cells) . . 0.429 0.424 0.423 0,415 Blank on 40-mm cell . . . . 0.045 0.050 0.050 0.050 120 0.357 0.312 18 hours 0.508 0.41 1 0.060204 REES, GYLLENSPETZ AND DOCHERTY: DETERMINATION OF TRACE AMOUNTS [Analyst, VOl. 96 By using the conditions established, calibration graphs were prepared covering the ranges 0 to 10 and 0 to 100 pg of sulphide-sulphur in 40 and 5-mm cells, respectively. Typical results are given in Table V and confirm the linearity in agreement with the Lambert - Beer law.TABLE V TYPICAL CALIBRATIONS WITH NN-DIETHYL-9-PHENYLENEDIAMINE Net optical density - A 3 pg of sulphur per unit optical density Sulphur/pg 40-mm cell 5-mm cell per unit light path 1.1 2-2 4.4 6.6 8-8 9.9 14.4 28.8 43.2 57.6 72.0 86.4 97.2 0.084 - 52.5 0.164 - 53-6 0.342 - 51.5 0.516 - 53.2 0.684 - 51-3 0.756 - 52.4 - 0.136 53.0 - 0.276 52.0 - 0.408 52.8 - 0,544 53.0 - 0.676 53.1 - 0-776 55.5 - 0-870 55.7 Blank value on 40-mm cell 0.044. EFFECT OF SULPHITE- The main purpose of the investigation was to determine sulphide in condensed steam.Under these conditions it was considered that the only interfering substance that might be present in significant amounts would be sulphur dioxide. Because of the mutual interaction of hydrogen sulphide and sulphur dioxide under acidic conditions it was thought that the addition of the acidic NN-diethyl-p-phenylenediamine reagent might therefore give low values for hydrogen sulphide in the presence of sulphur dioxide. Factitious samples were therefore prepared in de-aerated zinc acetate solution containing various but known amounts of sulphite and sulphide. These were allowed to stand for a few minutes to simulate test conditions before the addition of the acidic NN-diethyl-P-phenylenediamine reagent. The colour was then developed in the usual way.The results obtained are given in Table VI and show that amounts up to at least 200 pg of sulphite-sulphur give an error of less than 5 per cent. TABLE VI EFFECT OF SULPHITE ON THE DETERMINATION OF SULPHIDE Approximately Net optical density (5-mm cell) Sulphite-sulphur/ 50 p g of sulphide-sulphur Pg 0 0.495 67 0-490 101 0.485 168 0.479 235 0.475 302 0.440 Approximately 7.5 pg of sulphide-sulphur Net optical density (40-mm cell) 0.564 0-564 0.564 0-564 0.559 0.532 As this work indicated that up to 200 pg of sulphite-sulphur could be tolerated in the sample aliquot a simple test was devised to ensure that this limit was not exceeded. In practice the sample is collected in a 100-ml stoppered measuring cylinder containing 2.0 ml of 0.00625 N iodine solution and a little starch solution or Thyodene (see Reagents, p.206). If the volume of sample required to discharge the blue colour is less than 100 ml, this volume of sample may be taken for the analysis (see “Collection of Sample”). COLLECTION OF SAMPLE- The collection of samples containing small amounts of hydrogen sulphide presents difficulties caused mainly by the ease with which sulphide can be lost by oxidation or volati- lisation. If the “ethylene blue” method is to be used for the completion of the determination,March, 19711 OF SULPHIDE IN CONDENSED STEAM WITH NN-DIE THYL-$-PHENYLENEDIAMINE 205 other problems must also be borne in mind when devising a sampling technique. Thus, the absorbing medium must stabilise the sulphide but the formation of precipitates should preferably be avoided as they may adhere to the walls of the sampling tube and vessel and not readily redissolve.Solutions of cadmium and zinc salts are commonly used to collect hydrogen sulphide, the resulting sulphides being stable. Cadmium salts, are more insoluble and their use is therefore preferable in certain circumstances. In our case, however, we considered that zinc salts were less likely to produce insoluble precipitates and were therefore preferred, the acetate being used to reduce the risk of acidic conditions developing. Standard solutions of sulphide were prepared with dilute sodium hydroxide solution, then made slightly acidic with hydrochloric acid to “liberate” the hydrogen sulphide and transferred, by using nitrogen pressure, to a vessel containing zinc acetate solution to simulate sampling conditions.The results obtained were in good agreement with those obtained with the standard solutions before acidification and confirmed that there was no significant loss of hydrogen sulphide during the transfer. The amount of zinc acetate used was calculated to give an excess even when the maximum recommended amounts of sulphide were being determined. Gustafsson8 has suggested that the zinc acetate should be treated with hydrogen sulphide before use to remove any interfering impurities. It was considered that this could lead to complications with high blank values and was not, in fact, found to be necessary. Nevertheless, it is recommended that blank determinations and fresh standardisations should be carried out with each new batch of reagent.Also de-mineralised water should be used in preference to water from metallic distillation units. DEVELOPMENT OF ON-SITE METHOD- With the conditions established above, the possibility of devising an on-site procedure was investigated. Thus, colours were produced in the usual way in 100-ml stoppered measur- ing cylinders by using known amounts of standard sulphide solution. Instead of measuring the colours spectrophotometrically a compensating solution was prepared in a second cylinder containing all of the reagents with de-mineralised water in place of the standard solutions. It was then found possible progressively to titrate this compensating solution visually with a standardised solution of methylene blue (1 ml being approximately equal to 10 pg of sulphur) until a colour match was obtained.The amount of sulphide that can be measured by this visual technique is limited to about 25pg of sulphide-sulphur in a 100-ml sample volume. With larger amounts of sulphide the matching of colours becomes more difficult. By using solutions of methylene blue (standardised by comparison with colours produced with known amounts of sulphide) a series of samples was examined by the v sual and spectro- photometric methods. The results are given in Table VII. TABLE VII COMPARISON OF ACTUAL SAMPLES BY USING THE SPECTROPHOTOMETRIC AND VISUAL FINISH Sulphide-sulphur, p.p.m. r A * Titration finish .. .. . . 0.12 0.19 0.23 0.014 0.035 0.026 Spectrophotometric finish . . . . 0.08 0-21 0.24 0.011 0.038 0.034 Bearing in mind that the titration method is regarded only as a rapid on-site method and subject to the visual interpretation of the end-point, the above results are considered to be satisfactory.EXAMINATION OF SAMPLES- With volumes of up to 95ml the limit of detection is about 0.005 p.p.m. of sulphide- sulphur (Note 1). For higher concentrations the sample volume can be adjusted accordingly. Some typical results are given in Table VIII (see p. 206), sulphide having been found so far only in steam when contamination could have occurred from extraneous sources. NOTE l-An amount of 0.005 p.p.m. of sulphide-sulphur is equivalent to an increase in optical density of the same order as the blank (Le., about 0.04 in a 40-mm cell). This is regarded as the smallest realistic detectable change a t this level of optical density.206 REES, GYLLENSPETZ AND DOCHERTY: DETERMINATION OF TRACE AMOUNTS [Analyst, Vol.96 TABLE VIII RESULTS ON ACTUAL SAMPLES Sample Sulphide-sulphur, p.p.m. Steam exit boiler A . . . . . . . . . . . . N.D. Steam exit boiler A . . . . . . . . . . . . N.D. N.D. Light distillate vaporiser . . . . . . . . . . N.D. N.D. Export steam from steam reforming plant . . . . . . 0.038 Export steam from steam reforming plant . . . . . . 0.08 Steam just prior to light distillate mixing point A . . . . 1.27 1-36 B . . . . 0.45 0-43 c . . . . 0-21 0.24 N.D. = not detected, Le., <0.005 p.p.m. Where duplicate results are quoted the samples were taken from the same point within 15 to 30 minutes of each other.SPECTROPHOTOMETRIC METHOD REAGENTS- De-ionised water, which has been made oxygen free by boiling and cooling under nitrogen, must be used in the preparation of standard sulphide solutions and for any necessary dilution of the sample before colour development. Other reagents may be prepared from normal laboratory de-ionised water although it may be convenient to use the de-oxygenated water prepared as above. NN-Diethyl-p-phenylenediamine solution-Dissolve 2-0 g of NN-diethyl-p-phenylene- diamine sulphate in 1 O O m l of 50 per cent. v/v sulphuric acid. This reagent is stable for at least 1 month, and should preferably be stored in the dark. Ammonium iron(ll1) sulphate solution-Dissolve 18.0 g of Fe2(S04) ,(NH4)2S04.24H20 in water. Filter if necessary to remove suspended matter and dilute to 100 ml with water.Zinc acetate solution-Dissolve 2-5 g of Zn(CH3C00),.2H,0 in water and dilute to 100 ml with water. Standard iodine solution, 0-00625 N-Prepare freshly by measuring from a microburette 6-25 ml of 0.1 N iodine into a 100-ml stoppered standard flask and diluting to the mark with water. Starch indicator solution, 0-5 per cent. w/v-Triturate 5 g of pure starch and 0-01 g of mercury(I1) iodide with 30ml of water in a mortar. Pour the resulting cream into 1 litre of boiling water, boil the suspension for 3 minutes, allow it to cool and settle and decant off the clear liquid. If preferred, one of the proprietary solid urea - starch mixtures such as Thyodene can be used. Standard sulphide solution-Dissolve 2 to 3 g of analytical-reagent grade Na2S.9H20 in water and dilute to about 1 litre.Determine the sulphide content of the solution by direct titration with 0.00625 N iodine, with the starch indicator solution. Immediately dilute the appropriate aliquot of this solution with water and then add sufficient zinc acetate dihydrate solution to give a solution containing 10 pg ml-l of sulphur and 0.05 per cent. with respect to zinc acetate dihydrate. Standardise this solution with 0-00625 N iodine and adjust if necessary. Dilute standard sd$hide solution-Dilute 10.0 ml of standard sulphide solution to 100 ml with water and sufficient zinc acetate dihydrate solution to give a solution 0.05 per cent. with respect to zinc acetate dihydrate. The two standard sulphide solutions are stable for at least 1 hour.1 ml of solution = 100 pg of sulphur. 1 ml of 0.00625 N iodine solution = 100 pg of sulphur. 1 ml of solution = 1.0 pg of sulphur. COLLECTION OF SAMPLE- The temperature of the sample should not be higher than 20 "C and if sampling from a flowing stream the flow-rate should be between 20 and 50ml minute-l. A stainless-steel cooling coil should be used.March, 19711 OF SULPHIDE IN CONDENSED STEAM WITH NN-DIETHYL-~-PHENYLENEDIAMINE 207 To determine the volume of sample to be taken for analysis it is necessary to limit the amount of sulphite-sulphur present to less than 2OOpg. The following preliminary tests must therefore be carried out. To a 100-ml graduated stoppered measuring cylinder add 2.0 ml of 0.00625 N iodine and 1 ml of starch indicator solution.Collect a sample of water with a dip-tube reaching below the surface of the reagents. Note the volume at which the blue colour is discharged. This volume will contain 200 pg of sulphide and sulphite (expressed as sulphur) and not more than this volume should be taken for the test. If the colour is not discharged when 95 ml of sample have been collected, this volume can be used in the test. PROCEDURE- Prepare calibration graphs freshly for each new batch of reagent. Preparation of calibrationgraph for the range 0 to 1Opg of sulphur-Transfer to seven 100-ml graduated stoppered measuring cylinders, each containing about 50 ml of water and 2 ml of zinc acetate dihydrate solution , amounts of dilute standard sulphide solution containing 0, 1.0, 2-0, 5.0, 7-0, 9.0 and 10.0 pg of sulphide (expressed as sulphur).Dilute to about 97 ml with water and mix gently. Add, from a pipette, 1.0 ml of NN-diethyl-P-phenylenediamine solution and mix. Allow to stand for 1 minute -+_ 30 s then add, from a pipette, 1*0ml ammonium iron(II1) sulphate solution. Mix and dilute to 100ml with water. Allow to stand for at least 10 minutes, then measure the optical density of each solution in a 40-mm cell at the wavelength of maximum absorption (about 670 nm), with water as compensating solution. Correct for the optical density of the solution containing no added sulphide and construct a calibration graph relating optical density to micrograms of sulphur present as sulphide. Preparation of calibration graph for the range 0 to 100 pg of sulphur-Proceed in a manner similar to that outlined above for the preparation of the calibration graph for the range 0 to 10 pg of sulphur, with amounts of standard sulphide solution containing 0, 10.0, 20.0, 50-0, 70.0, 90-0 and 100.0 pg of sulphur and measure the optical density in 5-mm cells.Determifiation-Collect the sample into 2 ml of zinc acetate dihydrate solution in a 100-ml graduated stoppered cylinder until the appropriate volume of sample is collected. Use a glass dip-tube with the tip below the surface of the zinc acetate solution. If necessary add water to give a total volume of 97 ml, then proceed as in “Preparation of Calibration Graph” from “Add, from a pipette, 1.0 ml of NN-diethyl-$-phenylenediamine solution. . . .” Measure the optical density of the solution in 5 or 40-mm cells, as appropriate, at the wavelength at which the preparation of the calibration graph was carried out, with water as compensating solution. Simultaneously prepare a blank solution and a compensating solution , the former con- taining water instead of the sample and the latter containing the same amount of sample as used in the test but adding 1.0 ml of 50 per cent.v/v sulphuric acid in place of the NN-di- ethyl-9-phenylenediamine and ammonium iron(II1) sulphate solutions. Determine the optical density of each of these solutions and apply any necessary correction to the optical density of the sample solution. Read from the appropriate calibration graph the amount of sulphur present as sulphide. CALCULATION- W v Concentration of sulphide (expressed as sulphur), p.p.m.w/v = where W is the weight of sulphide in micrograms, found from the calibration graph, and V is the volume of sample in millilitres used in the test. TITRIMETRIC METHOD With this method sulphur is determined in the range 0.5 to 25pg. Use de-ionised water throughout as for the spectrophotometric determination described Methylene blue stock solzction-Dissolve 1 g of methylene blue in water. This stock solution Dilute methylerte blue solution-Dilute 5.0 ml of the stock solution to 100 ml with water REAGENTS- above. The following additional reagents are required. is known to be stable for several weeks. and standardise before use.208 REES, GYLLENSPETZ AND DOCHERTY STANDARDISATION OF METHYLENE BLUE- Into a 100-ml graduated stoppered cylinder, containing 2.0ml of 2.5 per cent.zinc acetate solution, add from a burette 10 ml of dilute standard sulphide solution containing 1.0 pg ml-l of sulphur. Dilute to 100 ml with water. Add 1.0 ml of NN-diethyl-p-phenylene- diamine sulphate reagent and mix. Wait 1 minute, then add 1.0 ml of iron(II1) alum solution and mix again. As the colour develops in the standard add the dilute methylene blue solution from a semi-micro burette to the blank until this colour matches that of the standard. Full visual colour development occurs in the sample in about 5 minutes. Note the volume of methylene blue required for matching, then Prepare a blank with water in the same way as the standard. 1 ml of dilute methylene blue solution - = A pg of sulphide.Number of micrograms of sulphide taken Volume of methylene blue solution for the colour match - PROCEDURE- Collect the sample in the appropriate manner as described above and dilute to 100 ml with de-aerated water if necessary. Proceed as described in the standardisation of the methylene blue from “Add 1.Omlof NN-diethyl-fi-phenylenediamine sulphatereagent (Note2) .” Note the volume of methylene blue solution used, Y ml. This should not exceed 2-5 ml ( i e . , about 25 pg of sulphur) as matching is difficult above this level, then Y x A Volume of sample taken NOTE %The sample with the colour developed may be retained and measured later by using a spectrophotometer and the sulphide determined in this way, allowance being made for the final volume and volume of sample taken. Concentration of sulphide (expressed as sulphur), p.p.m. w/v = CONCLUSION A method has been established for the determination of traces of sulphide in condensed steam. It has been shown that NN-diethyl-fi-phenylenediamine is more sensitive than the dimethyl homologue normally used. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. REFERENCES Quayle, G. L., “Effluent and Water Treatment Manual, ’’ First Edition, Thunderbird Enterprises Drane, C. W., J . Inst. Fuel, 1954, 27, 502. Andres, R. F., Ind. Engng Chem., 1954,46, 990. Khapaev, V. M., Thermal Engng, 1964, 11, 61. Farley, L. L., and Winkler, R. A., Analyt. Chem., 1968, 40, 962. Kriege, 0. H., and Wolfe, A. L., Talanta, 1962, 9, 673. Polson, D. S. C., and Strickland, J. D. H., Analytica Chim. Acta, 1952, 6, 452. Gustafsson, L., Talanta, 1960, 4, 227. Boltz, D. F., “Colorimetric Determination of Nonmetals,” Interscience Publishers Inc., New York “A.S.T.M. Manual on Industrial Water and Industrial Waste Water,” Second Edition, American Received May 21st, 1970 Accepted September 25th, 1970 Ltd, 1962, p. 216. -, Ibid., 1960, 4, 236. and London, 1958, p. 261. Society for Testing and Materials, Philadelphia, Pa., 1964.

ISSN:0003-2654    

DOI:10.1039/AN9719600201

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

Analyst, March, 1971, Vol. 96, pp. 209-212 209 The Determination of Small Amounts of Cyanide in the Presence of Ferrocyanide by Distillation under Reduced Pressure BY R. F. ROBERTS AND B. JACKSON (Research and Development Department, Imperial Chemical Industries Limited, Mond Division, Northwich, Cheshire) In the analysis of effluents and waters, the customary use of lead acetate to prevent the decomposition of ferrocyanide during the distillation of cyanide is not sufficiently effective when small concentrations of cyanide (about 0.1 mg 1-l) are to be determined. A method is described in which the de- composition of ferrocyanide can be completely prevented by distilling off the cyanide under reduced pressure in the presence of zinc acetate. The cyanide in the distillate is determined by the pyridine - pyrazolone method.AS very small amounts of cyanide can be toxic to fish, the method for the determination of cyanide in concentrations down to about 0.1 mg 1-1 in water and effluent samples should be as precise as possible and free from interference from other constituents. The usual procedure is to distil a large amount of an acidified sample, absorb the evolved hydrogen cyanide in a small amount of sodium hydroxide solution and finally determine the cyanide content spectrophotometrically. If the sample contains ferrocyanide, which is relatively non-toxic, the latter would partially decompose during distillation and release hydrogen cyanide, thus giving rise to positive errors. The use of lead acetate to prevent the decomposi- tion of ferrocyanide is included in certain recommended methods of analysis of sewage and trade effluents.l y2 These methods, however, refer to the determination of relatively large concentrations of cyanide (about 10 mg 1-l).Other work3s4 in which lead acetate was used for this purpose involved milligram amounts of cyanide, which could be determined titri- metrically. Our experience has shown that lead acetate does not completely prevent decom- position of ferrocyanide and is inadequate when small amounts of cyanide are involved. EXPERIMENTAL Several synthetic samples were prepared containing small amounts of potassium cyanide and ferrocyanide. Distillations were carried out on these samples, after adding lead acetate to the distillation flask, and the absorbed hydrogen cyanide was determined spectrophoto- metrically by using a slightly modified form of the pyridine - pyrazolone ~nethod.~ High results were obtained for each sample. Further tests were then carried out in which the lead acetate was replaced by zinc acetate, the use of which has also been recommended6 as a way of preventing the decomposition of ferrocyanide, and although zinc acetate was much more effective than lead acetate, it did not completely prevent the breakdown. Typical results obtained with lead and zinc acetates are given in Table I.TABLE I KNOWN AMOUNTS OF CYANIDE AND FERROCYANIDE DISTILLED IN THE PRESENCE OF LEAD ACETATE AND ZINC ACETATE Test Distillation Ferrocyanide added/ Cyanide added/ Cyanide found/ N O . conditions mg 1-1 of K,Fe(CN), mg 1-1 of CN mg 1-1 of CN 1 With lead acetate 0 0.033 0.034 2 0-033 0-033 0.045 3 6-66 0.033 1-27 4 20.00 0 7.6 5 With zinc acetate 13-3 6 20.0 0 SAC and the authors.0 0.05 0.126 0.04210 ROBERTS AND JACKSON : DETERMINATION OF SMALL [Artalyst, Vol. 96 Various modifications were made to the procedure and finally it was found that the decomposition of ferrocyanide could be prevented by carrying out the distillation at a con- trolled reduced pressure in the presence of zinc acetate. Several synthetic samples were then examined by this method and good recoveries of small amounts of cyanide were obtained, even in the presence of relatively large amounts of ferrocyanide. Typical results are given in Table 11. The procedure used does not prevent the decomposition of all other cyanide com- plexes but in some instances, e.g., tripotassium pentacyanocarbonylferrate (K,[Fe(CN),CO] 1 and disodium pentacyanonitrosylferrate (Na, [Fe(CN),NO] 1, the amount decomposed is reduced.The method has been used effectively on samples of effluents and waters during the last few years. TABLE I1 KNOWN AMOUNTS OF CYANIDE AND FERROCYANIDE DISTILLED AT REDUCED PRESSURE IN THE PRESENCE OF ZINC ACETATE Test No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Ferrocyanide added/ Sample mg 1-1 of K,Fe(CN),, Distilled water 0.033 0.66 0.66 13.3 13.3 13.3 13.3 13.3 20.0 20-0 1.0 1.0 River water 0 Effluent containing 0 CaCl, and NaCl 1.0 1.0 1.0 Cyanide added/ mg 1-1 of CN 0.033 0-033 0-042 0 0.033 0.083 0.167 0.334 0.125 0-500 0 0.056 0.054 0 0 0-062 0.062 Cyanide found/ mg 1-1 of CN 0.033 0.033 0.043 0.002 0.034 0.082 0.168 0.334 0.123 0.500 0-004 0-056 0.055 0.003 0,002 0.060 0.063 Tests 6 to 10 were repeated on samples containing 10 per cent. w/v sodium chloride solution and similar results were obtained.METHOD APPARATUS- An all-glass distillation apparatus is set up as shown in Fig. 1. The components are obtainable from laboratory suppliers, with the exception of the 250-ml absorption flask, which has been modified by means of a thimble-type extension, of about 10-ml volume, to the base of the flask. The delivery tube passes to the bottom of the thimble. This modi- fication ensures that hydrogen cyanide evolved in the early part of the distillation passes into an an adequate column of absorption solution. Manometer vacuum UPPlY Fig.1. Apparatus for distillation of cyanide under reduced pressureMarch, 19711 AMOUNTS OF CYANIDE IN THE PRESENCE OF FERROCYANIDE 21 1 REAGENTS- Sodium hydroxide, 0-1 N. Hydrochloric acid, 0.1 N. Zinc acetate solution, 10 per cent. w/v. Phenolfhthalein indicator solzction, 0-1 per cent. in ethanol - water (1 + 1). Acetic acid solution, 0.5 per cent. v/v. Chloramine T solution, 1.0 per cent. w/v in distilled water-This solution should be prepared daily. 3-MethyL1-phenyL5-pyraxolone solution-Dissolve 2.5 g in 500 ml of distilled water and warm the solution to 70 “C, while stirring. Allow the solution to cool in the dark, and store in a dark bottle; filter before use. Renew the solution after 5 days. Bispyrazolone [3,3’-dimethyZ-lJ1 ‘-diphenyl-(4,4‘-bi-2-pyraxoline)-5,5’-dione] solutiow-Add 0.025 g to 25 ml of analytical-reagent grade pyridine and allow the mixture to stand in the dark, occasionally shaking it until the reagent is dissolved (about 1 hour), Mixed pyridine - pyrazolone reagent-Filter 125 ml of 3-methyl-1-phenyl-5-pyrazolone solution into a brown bottle, add bispyrazolone solution and store in the dark.Prepare daily. Stock standard cyanide solution-Dissolve 0.251 g of analytical-reagent grade potassium cyanide in 1 litre of distilled water containing 20 ml of 0.1 N sodium hydroxide. Dilute standard cyanide solution-Dilute 10 ml of the stock solution to 1 litre with dis- tilled water. This solution should be freshly prepared. 1 ml of solution contains 1-0 pg of cyanide. PREPARATION OF CALIBRATION GRAPH- Into a series of 50-ml standard flasks, introduce accurately measured volumes of the dilute standard cyanide solution containing 0, 2, 4, 6, 8 and 10 pg of cyanide and dilute to about 20 ml with distilled water.Add 2 drops of phenolphthalein solution, neutralise with acetic acid solution and add 0.1 ml in excess. Add 0.2 ml of chloramine T solution and allow to stand for 18 minutes. Then add 15 ml of mixed pyridine - pyrazolone solution, mix and allow the mixture to stand for 30 minutes in the dark. Make up to 50 ml with distilled water and measure the optical density of the solution in a spectrophotometer at a wavelength of 620nm with a 10-mm cell, with distilled water in the comparison cell. Correct the readings for the reagent blank and plot a calibration graph relating net optical density to cyanide content.METHOD OF CARRYING OUT THE TEST- Introduce into the distillation flask a volume of up to 600 ml of a sample of the water or effluent, and connect the apparatus shown in Fig. 1, with the absorption flask containing 10 ml of 0.1 N sodium hydroxide and guard tube 5 ml of 0.1 N sodium hydroxide. Titrate a separate portion of the bulk sample with 0.1 N hydrochloric acid to determine the amount of acid required to neutralise the volume of sample in the distillation flask. Add this amount of 0.1 N hydrochloric acid to the distillation flask followed by an additional 10 rnl. Then add 10 ml of 10 per cent. zinc acetate solution. Connect the air inlet tube to the sodalime column and evacuate the apparatus to reduce the pressure inside to between 127 and 254 mm of mercury, while maintaining slow bubbling from the capillary of the air inlet tube. Heat the flask and boil the solution steadily until a total volume of about 75 ml is collected in the absorption flask.Stop the distillation by removing the source of heat, turn off the vacuum and allow the pressure to return to atmospheric by continuing the bubbling. Combine the absorption and guard tube solutions and make up to volume in a 100-ml standard flask. Measure a suitable aliquot from the 100-ml standard flask (usually 20 ml) into a 50-ml standard flask and proceed with the colour development and optical density measurement as described under “Preparation of Calibration Graph.” Acknowledgement is made to the Directors of I.C.I., Mond Division, for permission to publish this paper.212 ROBERTS AND JACKSON REFERENCES 1. 2. Ministry of Housing and Local Government, “Methods of Chemical Analysis as applied to Sewage and Sewage Effluents,” H.M. Stationery Office, London, 1956. The Association of British Chemical Manufacturers and the Society for Analytical Chemistry, “Recommended Methods for the Analysis of Trade Effluents,” W. Heffer & Sons Ltd., Cambridge, 1958. Jenkins, S. H., Hey, A. E., and Cooper, J. S., Azv Wat. Pollut., 1966, 10, 495. Feld, W., J . SOC. Chenz. Ind., Lond.,1903, 22, 1068. American Public Health Association (American Water Works Association and Water Pollution Control Federation “Standard Methods for the Examination of Water and Wastewater,’ ’ Eleventh Edition, APHA Inc. 1790, Broadway, New York 19, N.Y., 1960. Russell, F. R., and Wilkinson, N. T., Analyst, 1959, 84, 751. 3. 4. 5. 6. Received April 30th, 1970 Accepted September 30th, 1970

ISSN:0003-2654    

DOI:10.1039/AN9719600209

出版商:RSC    

年代:1971

数据来源: RSC

摘要:

Analyst, March, 1971, Vol. 96, $@. 213-219 213 The Automated Determination of Silicon and Calcium in Portland Cement and Associated Raw Materials* BY J. A. FIFIELD AND R. G. BLEZARD (Tunnel Cement Ltd., West Thuwock, Gyays, Essex) The manufacture of Portland cement clinker is a continuous large scale chemical synthesis of specific compounds. The strength of the hydrated cement matrix in concrete is a function of the original clinker compound assemblage. Control of the production of the clinker compounds has to be related to the time of passage of materials through the rotary kiln and the conditions of processing. Continuous control of the major constituents is essential and knowledge of the effects of the variation of the constituents on the physical properties of the product is desirable.Methods are described for the automated determination of calcium and silicon in Portland cement and associated raw materials with respect to the demands, scale and nature of the process. THE analytical importance of the major constituents of a material can be a reflection of inherent specific properties as well as a guide to the completeness of the analysis summation. For example, in the analysis of cast iron or steels it is the minor alloying metals that are studied rather than the major constituent. However, there are other complex systems where there are several phase combinations between two elements and in these instances it may be important to know the elemental analyses with reasonable accuracy. This knowledge may help in deciding which phases are present, or in the continuous monitoring of a dynamic sytem where variables may affect the major constituents.The major oxide constituents of a Portland cement are lime and silica, which together account for 90 per cent. of the total content. Some typical results from the samples regularly analysed in a cement works laboratory are as follows- Lime, per cent. Silica, per cent. Clay . . .. .. 2.0 58-0 Chalk . . .. .. 50.0 2.0 Raw meal . . .. 44-0 15.0 Clinker . . .. .. 67-0 23.0 Cement . . ,. .. 65.0 22.0 On inspection of these results it would appear that methods having a confidence level . of 0.50 per cent. for one standard deviation should suffice for the control of the plant but, in practice, much better precision than this is required. In the cement manufacturing process raw meal is calcined in a kiln into a mixture comprising four main cementitious compounds- Molecular formula Mineralogical abbreviation 3CaO.Si0, .... .. c*s P-2CaO. SiO, .. .. P-C2S 3Ca0.A1,03. . .. .. C3A 4Ca0.A1,0,.Fe,03 . . . . C,AF These formulae are idealised; in practice, the silicate minerals contain interstitial aluminium, magnesium and titanium oxides, alkalis, etc. Early cement microscopists called C,S solid solution alite, C,S belite and the iron complex is now known as ferrite. Cement manufacture is basically a continuous large-scale synthesis of these compounds. The time of passage of the raw material through the rotary kiln may be of the order of 2 hours, and the analytical control system has to be devised with this in mind.* Presented at the symposium on “Accurate Methods of Analysis for Major Constituents,” organised jointly by the Society for Analytical Chemistry and the Analytical Section of the Royal Dutch Chemical Society, London, April 3rd to 4th, 1970. 0 SAC and the authors.214 FIFIELD AND BLEZARD : AUTOMATED DETERMINATION [Auzalyst, Vol. 96 The development of strength of a cement matrix is a function of the compound assem- blage, the relative influence of each of the four main phases being shown in Fig. 1. It must be stressed that strength calculations based on the hydraulic activity of chemi- cally pure cement compounds must be modified as a result of the inclusion of minor elements in solid solution. Compound composition is used as a guide to the potential strength of the finished product and analyses at a rate of at least one per hour are required.N I E E Time/days Fig. 1. Development of strength of pure cement compoundsf EFFECT OF ANALYTICAL ERRORS- Consider the introduction into a kiln of a carbonaceous raw meal having the chemical composition: silica 15-0 per cent., aluminium(II1) oxide 3.0 per cent., iron(II1) oxide 1.5 per cent. and lime 43.5 per cent. Then, under ideal conditions and assuming no ash absorption from the fuel, a clinker will be produced containing: silica 21.3 per cent., aluminium(II1) oxide 4.6 per cent., iron(II1) oxide 2.3 per cent. and lime 67.0 per cent., basing the transposing factor (slurry to clinker) on 100 (100 - ignition loss at 1400 "C) From this chemical analysis it is possible to calculate a theoretical compound composition of the clinker provided the percentage of unreacted or free lime present is known.Hence, the following compound formation can be postulated by using the method enunciated by Bogue2: alite 5843 per cent., belite 23-4 per cent., C,A 8.3 per cent., ferrite 7 per cent. and free lime 1.5 per cent. Assuming no error has occurred in the determination of aluminium and iron, then 0.5 per cent. error in the silica analysis gives rise to a 6 per cent. error in the alite estimate, and 0.5 per cent, error in the lime analysis leads to a 3 per cent. error. Thus the coupled effect of these two errors leads to underestimation of the alite by more than 9 per cent. and over- estimation of belite by the same amount. Alitel has a 7-day strength of 40-68 N mm-2 and a 28-day strength of 49-30 N mm-2 and belitel has corresponding strengths of only 0.69 and 6.90Nmnr2, other phases con- tributing very little to the strength of the cement. Although belite ultimately develops a strength equal to that of alite, it is early strengths that are of importance to the construction industry.The influence of variation of alite content upon compressive strength is shown in Table I. Thus, the 0.5 per cent. analysis errors can lead to strength estimations that may be about 4 N mm-2 low at 28 days. For control of the plant, calculations of compound composi- tion to +2 per cent. of alite are required and it is therefore necessary to use analytical techniques capable of determining silica to +0.07 per cent. and lime to +0*1 per cent.for one standard deviation.March, 19711 OF SILICON AND CALCIUM IN PORTLAND CEMENT 215 Assumptions made in the Bogue calculation are included in this study where a multi- component system (silica - aluminium(II1) oxide - iron(II1) oxide - lime) is being considered under specific conditions. It is assumed that all the iron, aluminium and silicon and the calcium not existing as uncombined lime or as calcium sulphate will be combined as C,S, C,S, C,A and C,AF. The particle-size distribution of the ground compound assemblage in the presence of gypsum is a further contributor to the strength of a hydrating matrix, mainly from the aspects of kinetics and efficiency of hydration. TABLE I INFLUENCE OF VARIATION OF ALITE CONTENT UPON COMPRESSIVE STRENGTH Alite content, * 7-day strength/ 28-day strength/ per cent.Nmm-2 Nmm-a 56.8 28.96 39-10 53.5 27-65 37-62 50.8 26.34 36.61 47.0 25.24 35.10 * The belite content will increase relatively as the alite content decreases. SAMPLE DISSOLUTION FOR AUTOMATED ANALYSIS- Fuse the sample3 with a strong alkali in a gold - palladium crucible and leach with hot water. Pour the alkaline suspension into a solution of sufficient hydrochloric acid to dissolve the calcium and iron hydroxides and, after cooling, dilute to a known volume (500 ml). The range of lime and silica to be measured together with the sample weight required for the various materials is given below in Table 11. TABLE I1 SAMPLE WEIGHT FOR MATERIALS ANALYSED Sample weight/g Lime, per cent. Silica, perlcent. Clay .. .. .. .. 0.250 0 to 6 48 to 64 Raw meal . . .. .. 1.000 42 to 54 12 to 16 Cement and clinker . . .. 0.600 63 to 68 20 to 27 Chalk.. .. .. .. 1.000 30 to 53 0.5 Sampler i - 7 Tube dia. I 1 Wash I I 0.030 mm I t I 10-045mm Sample ' I Hydrofluoric acid ! 10-073mm 1 Air i ;O-O65md i 10.073mm Boric acid i I v- W - Pulse suppressor + Lk;eb~ler drain I I ! I - Ammonium I T0.065mm molybdate I , Water ~ O - 1 0 0 m r n l W R e-sam ple I 10.030mrn I I 30" C 30" C Air i i0.073 mm 1 I 1 I I expander Fig. 2. Flow diagram for the automated determination of silica. Sampler speed 20 hour-l and wash ratio 1:2216 FIFIELD AND BLEZARD : AUTOMATED DETERMINATION [Analyst, Vol. 96 AUTOMATED DETERMINATION OF SILICA For the determination of silica an automated molybdenum blue method has been developed; the required reactions are given by the flow system (Fig.2). 16-0 REAGENTS- fusion (as for samples). Wash reagent-An aqueous solution of 0.22 g 1-1 of pure precipitated silica prepared by Hydrojuoric acid-A solution of 5 ml of 40 per cent. hydrofluoric acid in 1 litre of water. Boric acid-A saturated aqueous solution (approximately 50 g 1-l) . Ammonium molybdate-A solution containing 2-5 g in 1 litre of 0.3 per cent. v/v sulphuric Ascorbic acid-An aqueous solution containing 10 g 1-1 of ascorbic acid. acid. 30 METHOD- The addition of hydrofluoric acid to the flowing sample stream complexes the iron, decomposes any polymerised silicic acids and converts them to a silicofluoride complex. Excess of hydrofluoric acid is then complexed by excess of boric acid, which also decomposes the silicofluoride ion to give fluoroborate and silicate ions.A yellow silicomolybdic complex is formed by adding acidified ammonium molybdate and the product is finally reduced to the molybdenum blue complex by ascorbic acid. Phosphate will interfere but in practice (con- sidering a sample sequence at an individual plant) phosphate content is almost constant and is very low; in the United Kingdom it does not exceed 0.05 per cent. If the phosphate is known to have a detectable variation, any interference that it may cause can be suppressed by the addition of citric acid.4 Initially the analyser was set up to give an optimum performance over the range 0 to 16 per cent. of silica and the charts obtained looked very promising, but a 1 per cent increment of silica concentration was represented by only 2.5 per cent.transmission and interpretation gave errors outside the control limit. For raw meal analysis the range measured is 12 to 16 per cent., so washing with water was replaced by washing with a solution containing silica equivalent to 11 per cent. in the sample. The base-line was set at 98 with the full colour development from 11 per cent. of silica passing through the flowcell and peaks were obtained - 15.0 14.0 Continuous sampling 14.0 Fig. 3. Determination of silica: recorder traceMarch, 19711 OF SILICON AND CALCIUM IN PORTLAND CEMENT 217 for the standards. In this way the resolution improved to 3.5 per cent. transmission per 1 per cent. increment. A x 4 range expander was then employed to boost the resolution to 14 chart transmission units per 1 per cent. of silica.By using this technique the peaks shown in Fig. 3 are obtainable, the base-line varying from peak to peak by less than 1 chart division (+0.035 per cent. of silica). If peaks are allowed to reach their maximum then a precision of +0-035 per cent. of silica can be obtained but, in practice, the sampling time is insufficient to allow a state of equilibrium in the system. However, *0*04 per cent. can be achieved for one standard deviation and this precision meets the requirements of the method; Fig. 4 shows the calibration graph. Having developed this system it was extended to the analysis of clays, chalks and clinkers. 1 I I 1 12.0 13.0 14.0 15.0 11 Silica, per cent.0 Fig.. 4. Determination of silica: calibration graph For clay analysis 0.25 g of sample is used instead of 1 g (see Table 11) so that the 12 to 16 per cent. standards represent a range from 48 to 64 per cent. in the clay, and similarly 0-6 g of cement and clinker is taken to measure the range 20 to 27 per cent. For chalk samples a method of standard addition can be used by adding the equivalent of 11 per cent. of silica to the solution before diluting to volume. In this way the standards range from 1 to 5 per cent. Cement samples have been analysed by the AutoAnalyzer and by the reference B.S.I. m e t h ~ d . ~ Each sample was analysed three times by each technique and thirty samples in all were used. The average deviation between the two methods for the ninety results was 0.03 per cent.and the standard error between the mean of the triplicates 0.06 per cent. AUTOMATED DETERMINATION OF LIME For the determination of lime up to the 70 per cent. level normal colorimetric procedures were discounted because a 1 per cent. increment of lime would be represented by less than 0-5 per cent. transmission. An EDTA titration would seem to be better for this analysis, but in order to achieve a faster output of results, a system that is a compromise between titrimetry and colorimetry has been developed. In Fig. 5 (see p. 218), a manifold for the analysis of lime over the range 0 to 4 per cent. is shown. REAGENTS- Triethanolamiute-A 100 ml 1-1 aqueous solution. Bufer, $H 13-An aqueous solution containing 10 g 1-1 of sodium tetraborate plus 20 g 1-1 Colour reagent-A methanolic solution containing 0.75 g 1-1 of glyoxal bis-2-hydroxyanil.Standard EDTA-An aqueous solution containing 8.35 g 1-1 of EDTA disodium salt of sodium hydroxide. (dihydrate) standardised against B.C.S. 372.218 FIFIELD AND BLEZARD AUTOMATED DETERMINATION [ArtabSt, VOl. 96 - Colour reagent I !O-OSl mm Colori- 570 nm I meter a I I O - O ~ O mm V Recorder Fig. 5. Flow diagram for the automated determination of lime. Sampler speed 20 hour-1 and wash ratio 1 : 2. Colour reagent glyoxalbis-2-hydroxyanil, which must pass only through Solvaflex tubing 60 70 80 90 METHOD- Triethanolamine solution is added to the sample to complex iron and the pH is adjusted to 12.6 by a buffer. A 1 per cent. glyoxal bis-2-hydroxyanil (bis-(2-hydroxyphenylimino)- ethane) solution in methanol3 is then added to produce a red 1 : 1 complex with calcium and the absorbance measured at a wavelength of 570 nm.Fig. 6 shows a typical recorder trace for lime and Fig. 7 illustrates a calibration chart. - 1.6 - 0.8 f - - 0 4-0 3.2 40 'I- 2.4 50 t Continuous sampling 2 4 100' Fig. 6. Determination of lime: recorder trace 2o I I I I 1 0 0.8 1.6 2.4 3.2 1 Lime, per cent. Fig. 7. Determination of lime : calibration graph A calculated amount of EDTA is added to test solutions so that not more than 4 per cent. but greater than zero lime is left uncomplexed in solution. The mixture is then analysed by the AutoAnalyzer for excess of lime content. The EDTA solution is made such that 1 ml is equivalent to 1 per cent. of lime in 50 ml of test solution.So, for raw meal analyses, 42 ml of EDTA (43 to 45 per cent. of lime being determined) are added to 50 ml of test solution, the volume is diluted to 100 ml with water and the mixture is analysed for excess of lime.March, 19711 OF SILICON AND CALCIUM IN PORTLAND CEMENT 219 The percentage of lime in the sample is then 42 @Zus the chart reading. From Table 11, cements and clinkers range from 63 to 68 per cent. of lime, but because 0.6g of sample is used to prepare a test solution and not the l-g standard, the measuring range becomes 37-8 to 40.8 per cent. of lime. To 50 ml of cement solution 38 ml of EDTA solution are added before dilution to 100 ml with water. The excess of lime is determined and 38 + chart reading 0.6 Percentage of lime = Chalk samples range from 30 to 53 per cent.lime content but at a factory site the samples fall into two categories called high and low chalks. Low chalks contain 30 to 34 per cent. of lime and high chalks 49 to 53 per cent. To 50 ml of chalk solution 30 or 49 ml of EDTA, whichever is appropriate, is added before dilution to 100ml with water and measurement of excess of lime. The lime content is then the volume of added EDTA @Zus the chart reading. Clays contain less than 6 per cent. of lime so in this case the neat test solution is analysed directly. As 0.25 g is used and the solution is not diluted further, the results are obtained by multiplying the chart reading by two. Results obtained for cements agree well with results from the B.S.I. rneth~d.~ Triplicate analyses of 30 samples showed an average deviation between methods of 0.05 per cent. with a standard error of 0.13 per cent. CONCLUSION The two methods outlined and also methods395 for aluminium(II1) oxide, iron(II1) oxide, sulphur trioxide and free lime5ps have been used for plant control of two factories for the past 3 years. Samples are analysed at hourly intervals and a considerable improvement in quality stability has been achieved. Some thought has been given to an automated digestion system so that the analyser can be operated in the plant itself, and when this problem has been overcome the system may then find a place in many more factories. REFERENCES 1 . 2. 3. 4. 5. 6. Bogue, R. H., and Lerch, W., Ind. Engng Chem., 1934,26, 837. Bogue, R. H., Ind. Engng Chem., Analyt. Edn, 1929, 1, 1929. Fifield, J. A., and Blezard, R. G., Chem. & Ind., 1969, 1286. British Standard 4550, Part 2 : 1970. Blezard, R. G., and Fifield, J . A., “Advances in Automated Analysis,” Volume 2, Mediad Inc., Fifield, J. A., and Blezard, R. G., Analyst, 1969, 94, 503. Received June 24th. 1970 Accepted October 12th, 1970 Chicago, 1970, p. 283.

ISSN:0003-2654    

DOI:10.1039/AN9719600213

出版商:RSC    

年代:1971

数据来源: RSC