ISSN:0003-2654    

DOI:10.1039/AN96691FX045

出版商:RSC    

年代:1966

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN96691BX047

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

iv SUhlhlARIES OF PAPERS IS THIS ISSUE [December, 1966Summaries of Papers in this IssueThe Determination of Iron(I1) Oxide in Silicate and RefractoryMaterialsPart I. A ReviewSUMMARY OF CONTENTSIntroductionAcid decomposition in a sealed tubeAcid decomposition in an inert atmosphereAcid decomposition in the presence of an oxidantEvolution methodFusion methodCombustion methodConclusionH. N. S. SCHAFERDivision of Coal Research, CSIRO, P.O. Box 175, Chatswood, New South Wales,Australia.Analyst, 1966, 91, 755-762.REPRINTS of this Review paper will soon be available from the Secretary, The Society forAnalytical Chemistry, 14 Belgrave Square, London, S.W.1, a t 5s. per copy, post free.A remittance for the correct amount, made out to The Society for Analytical Chemistry,MUST accompany every order; these reprints are not available through Trade Agents.The Determination of Iron(I1) Oxide in Silicate and RefractoryMaterialsOxide in Silicate MaterialsA description is given of an apparatus of simple construction that canbe made from plastic, in which the decomposition of silicate materials byhydrofluoric acid can be carried out.The procedure for the titration of iron(I1)with dichromate under conditions that eliminate the risk of oxidation isoutlined.A comparison has been made between dichromate titres obtainedpotentiometrically and with diphenylamine sulphonate as indicator. Errorsassociated with the latter in the titration of small amounts of iron(I1) arediscussed. The method of sample decomposition and titration of iron(I1)has been assessed by determining the iron(I1) oxide content of the diabaseW-I, and has been applied to the determination of iron(I1) oxide in slagsfrom a boiler fired with pulverised fuel.H. N.S. SCHAFERDivision of Coal Research, CSIRO, P.O. Box 175, Chatswood, New South Wales,Australia.Part 11. A Semi-micro Titrimetric Method for Determining Iron(I1)Analyst, 1966, 91, 763-770.The Determination of Fluorine or Phosphorus in OrganicCompounds by a Micro-titrimetric MethodA method is described for determining fluorine or phosphorus in organiccompounds synthesised for medical research. After combustion of thecompound in an oxygen flask and absorption of the decomposition productsin water, the contents are diluted with isopropanol, and titrated with thoriumnitrate solution with a Solochrome cyanine R screened indicator.The additionof buffers is unnecessary. The removal of elements that interfere in thetitration of fluorine is also described.F. H. OLIVERChemical Research Department, Parke, Davis & Co., Staines Road, Hounslow,Middlesex.A n ~ l y s t , 1966, 91, 771-774i V SUMMARIES OF PAPERS I N THIS ISSUE [December, 1966Summaries of Papers in this IssueThe Determination of Iron(I1) Oxide in Silicate and RefractoryMaterialsPart I. A ReviewSUMMARY OF CONTENTSIntroductionAcid decomposition in a sealed tubeAcid decomposition in an inert atmosphereAcid decomposition in the presence of an oxidantEvolution methodFusion methodCombustion methodConclusionH.N. S. SCHAFERDivision of Coal Research, CSIRO, P.O. Box 175, Chatswood, New South Wales,Australia.Analyst, 1966, 91, 755-762.REPRINTS of this Review paper will soon be available from the Secretary, The Society forAnalytical Chemistry, 14 Belgrave Square, London, S.W.l, at 5s. per copy, post free.A remittance for the correct amount, made out to The Society for Analytical Chemistry,MUST accompany every order; these reprints are not available through Trade Agents.The Determination of Iron(I1) Oxide in Silicate and RefractoryMaterialsOxide in Silicate MaterialsA description is given of an apparatus of simple construction that canbe made from plastic, in which the decomposition of silicate materials byhydrofluoric acid can be carried out.The procedure for the titration of iron(I1)with dichromate under conditions that eliminate the risk of oxidation isoutlined.A comparison has been made between dichromate titres obtainedpotentiometrically and with diphenylamine sulphonate as indicator. Errorsassociated with the latter in the titration of small amounts of iron(I1) arediscussed. The method of sample decomposition and titration of iron(I1)has been assessed by determining the iron(I1) oxide content of the diabaseW-1, and has been applied to the determination of iron(I1) oxide in slagsfrom a boiler fired with pulverised fuel.H. N. S. SCHAFERDivision of Coal Research, CSIRO, P.O. Box 175, Chatswood, New South Wales,Australia.Analyst, 1966, 91, 763-770.Part 11.A Semi-micro Titrimetric Method for Determining Iron (11)The Determination of Fluorine or Phosphorus in OrganicCompounds by a Micro-titrimetric MethodA method is described for determining fluorine or phosphorus in organiccompounds synthesised for medical research. After combustion of thecompound in an oxygen flask and absorption of the decomposition productsin water, the contents are diluted with isopropanol, and titrated with thoriumnitrate solution with a Solochrome cyanine R screened indicator. The additionof buffers is unnecessary. The removal of elements that interfere in thetitration of fluorine is also described.F. H. OLIVERChemical Research Department, Parke, Davis & Co., Staines Road, Hounslow,Middlesex.Analyst, 1966, 91, 771-774viii SUMMAIIIES 01; PAPICI<S I N THIS ISSUE [December, 1966The Proportion of 2-Methylbutanol and 3- Methylbutanol in someBrandies and Whiskies as Determined by DirectGas ChromatographyStationary phases suitable for the separation of 2-methylbutanol (“active”pentanol) and 3-methylbutanol (isopentanol) are discussed.The mostsuitable for the determination of these alcohols in potable spirits by directinjection of samples are diethyl tartrate and polyethylene glycol 200. Poly-ethylene glycol 200 is preferred because other congeners can be determined a tthe same time. With n-pentanol as an internal standard, 65 samples ofcognac brandies, Scotch and other whiskies have been examined on one orother of these stationary phases.The sum of the two pentanol isomersdetermined separately agrees well with their determination as a single peak onpolyethylene glycol 1500. The ratio of the concentrations of the isomersappears to be characteristic of the type of spirit.D. D. SINGERLaboratory of the Government Chemist, Ministry of Technology, Cornwall House,Stamford Street, London, S.E.l.Analyst, 1966, 91, 790-794.An Instrument for the Continuous Determination of CarbonDioxide in High Purity WaterAn instrument for the continuous determination of carbon dioxide in highpurity water is described. The instrument consists essentially of a device fortransferring the carbon dioxide from the water to a gas stream, which is thenpassed through an aqueous suspension of calcium carbonate.The pH ofthis suspension, which is proportional to the concentration of carbon dioxidein the gas stream and hence the original water, is recorded continuously.Precision tests a t levels of 20 and 60 pg per litre had a standard deviationof about 4pg per litre.K. H. WALLCentral Electricity Generating Board, South Eastern Region, Cockfosters, Herts.Analyst, 1966, 91, 795-801.The Determination of Salt in Bacon by Using a Sodium-ionResponsive Glass ElectrodeRapid determination of the salt content of cured meat products with asodium-ion responsive electrode is described and discussed. The methodenables the percentage of salt on water content to be measured directly on themeat in a few minutes. Many determinations can be made cheaply andaccurately enough for purposes of routine factory control.J.H. HALLIDAYT. Wall & Sons (Meat and Handy Foods) Ltd., Willesden.and F. W. WOODUnilevcr Research Laboratory, Colworth House, Sharnbrook, Bedford.Analyst, 1966, 91, 802-805.Mobile Laboratory Methods for the Determination of Pesticides in AirPart I. PhosphorothiolothionatesShort PaperG. A. LLOYD and G. J. BELLPlant Pathology Laboratory, Hatching Green, Harpendcn, Herts.Analyst, 19GG, 91, 806-808X SUMMARIES OF PAPERS I N THIS ISSUE [December, 1966Mobile Laboratory Methods for the Determination of Pesticides in AirPart 11. ThionazinShort PaperG. A. LLOYD and G. J. BELLPlant Pathology Laboratory, Hatching Green, Harpenden, Herts.Analyst, 1966, 91, 808-809.Determination of Thiourea in Sewage and Industrial EffluentsShort PaperDENIS DICKINSONCity Laboratories Service, Shortley Road, Coventry.Analyst, 1966, 91, 809-811.Absorptiometric Determination of Fenitrothion Residuesin Cocoa BeansShort PaperS.H. YUENImperial Chemical Industries Ltd., Agricultural Division, Jealott's Hill ResearchStation, Bracknell, Berkshire.Analyst, 1966, 91, 811-813.Spectrophotometric Determination of Complexed DibenzoylmethaneShort PaperS. INCITTI and A. LA GINESTRAComitato Nazionale per L'Energia Nucleare, Laboratory F. Giordani, Departmentof Chemistry, University of Rome, Italy.Analyst, 1966, 91, 814-816.Detection of Some 2-Hydroxy and 2-Methoxy Estrogens and OtherShort PaperPhenolic Compounds by a Modified Folin - Ciocalteu TestR.L. RISACHER and A. M. GAWIENOWSKIDepartment of Chemistry, University of Massachusetts, Amherst, Massachusetts.Analyst, 1966, 91, 816-817.A Rapid Infrared Spectrophotometric Method for the Analysisof pp'-DDT in Formulations of Technical DDTShort PaperD. J. HAMILTON and T. J. BECKMANNAgricultural Chemical Laboratory Department of Primary Industries, Brisbane,Queensland, Australia.Analyst, 1966, 91, 817-819December, 19661 THE ANALYST xiN O T I C E TO SUBSCRIBERSThe annual subscription rates for The Analyst and Analytical Abstracts for 1967 and subsequentyears will be as follows-The Analyst plus Analytical Abstracts, including both indexes . . . . . . . . f15 0 0The Analyst, plus Analytical Abstracts printed on one side of the paper only, includingboth indexes .... * . .. .. . . * . . . .. f17 10 0The Analyst, plus Analytical Abstracts printed on one side of the paper only, includingThe Analyst index but excluding the Analytical Abstracts index . .Analytical Abstracts alone, including the index. . . . .. .. . .Analyticof Abstracts printed on one side of the paper only, including the indexAnalytical Abstracts printed on one side of the paper only, without index . .From January Ist, 1967, prices of all single copies will be as follows-Single copies of The Analyst . , .. .. .. .. .. ..Single copies of Analytical Abstracts . . .. * . .. * . ..Single copies of Analytical Abstracts printed on one side of the paper o n l y . .Index t o The Analyst , . .. .. .. .. . . . . ..Index t o Analytical Abstracts . . .. .. .. .. .. -.Prices of unbound complete volumes of back numbers will be as follows-The Analyst, including the index , . .. .. .. .. ..Analytical Abstracts, including the index . , .. .. .. ..Analytical Abstracts printed on one side of the paper only, including the indexAnalytical Abstracts printed on one side of the paper only, without index . .* .. ........ .... ...........f15 15 0f10 0 0f12 0 0f10 10 0€1 10 0fl 2 0fl 10 0f l 10 0f3 15 0f15 15 0f I 2 0 0f16 10 0f12 10

ISSN:0003-2654    

DOI:10.1039/AN96691FP239

出版商:RSC    

年代:1966

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN96691BP249

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

DECEMBER, 1966 T H E ANALYST Vol. 91, No. 1089 The Determination of Iron(I1) Oxide in Silicate and Refractory Materials Part I. A Review* BY H. N. S. SCHAFER (Division of Coal Research, CSIRO, P.O. Box 175, Chatswood, New South Wales, Australia) SUMMARY OF CONTENTS Introduction Acid decomposition in a sealed tube Acid decomposition in an inert atmosphere Acid decomposition in the presence of an oxidant Evolution method Fusion method Combustion method Conclusion THE determination of iron(I1) oxide presents a number of difficulties. Two of special im- portance are the method of bringing the sample into solution and the prevention of oxidation of iron(I1) in the process. With materials that are readily soluble in sulphuric or hydro- chloric acids, the determination should present no great difficulty because it is possible to carry out decomposition in glass apparatus, and maintain an atmosphere of a suitable gas (carbon dioxide or nitrogen) to prevent oxidation.This is not so with materials resistant to a simple acid attack, and some procedures designed to overcome the difficulties associated with the determination of iron(I1) oxide in such materials are dealt with here. A third difficulty inherent in all methods is the possibility of the oxidation of iron(I1) oxide during sample preparation, especially if grinding in air is used. According to Hillebrand et aZ.,l if on simple crushing of the material a product is obtained that leaves little or no residue when gently boiled with hydrofluoric acid, then no further preparation of the sample is needed.If, on the other hand, there is considerable residue, then the sample should be ground under alcohol only long enough to yield a powder that leaves little or no residue. The main characteristics of each of the methods considered here are used as the basis for the arbitrary headings under which the methods are discussed. Usually the differences in the methods relate to the initial decomposition stage. ACID DECOMPOSITION IN A SEALED TUBE The method described by Mitscherlich2 y 3 involves the decomposition of the material by heating with sulphuric acid in a sealed glass tube at temperatures up to 200" C. In this procedure, exclusion of oxygen (air) should present no difficulty, but complete dissolution of some of the materials is not always achieved.In Hillebrand's modification1 of the original method, a weaker sulphuric acid solution is used and the air in the tube is replaced with carbon dioxide. The determination of iron(I1) oxide is subject to errors arising from the presence of sulphides and carbonaceous matter. With sulphides the error can be quite large because of the reduction of the iron(II1) that may be present. Pyrite is normally resistant to boiling dilute acids, but under the conditions of increased temperature and pressure that prevail in the sealed-tube method, and in the presence of iron(TII), it will go into solution with reduction of the iron(II1) to iron(I1). These difficulties with the method were fully discussed by Hillebrand, who concluded that, in the absence of sulphides and when the material is fully decomposed, the sealed-tube method is almost ideal; otherwise its application is limited.* Reprints of this paper will be available shortly. For details see Summaries in advertisement pages. 755756 SCHAFER: DETERMINATION OF IRON(II) OXIDE IN [Analyst, Vol. 91 For the decomposition of resistant silicate minerals, Riley4 proposed a method that can be regarded as an extension of the sealed-tube method of decomposition. The resistant mineral is decomposed with hydrofluoric and perchloric acids in a Teflon bomb, which is placed in a steel vessel fitted with safety valves and containing water. The apparatus is maintained at 150" C in an oil-bath for 3 to 4 hours. Riley and Williams5 suggested that this method of decomposition is suitable for the micro determination of iron(I1) oxide in resist ant minerals.ACID DECOMPOSITION IN AN INERT ATMOSPHERE This method generally (but not always) implies the use of hydrofluoric acid to decompose the sample. As originally devised by Cooke6 it involved decomposition of the sample with hydrofluoric and sulphuric acids in a platinum crucible heated in a specially designed water- bath. The crucible was surrounded by an atmosphere of carbon dioxide to prevent aerial oxidation of the iron(I1) during decomposition of the sample. The iron(I1) was titrated with permanganate. One of the difficulties associated with Cooke's method is the tendency for iron(I1) to be readily oxidised in air in hydrofluoric acid solution, and this can occur during the titration. Another is the oxidation of bivalent manganese by permanganate in the presence of hydro- fluoric acid.For reliable results the latter difficulty must be overcome by removal of the hydrofluoric acid or the elimination of its effect. Barnebey' used boric acid to eliminate the effect of the hydrofluoric acid by the formation of undissociated fluoroboric acid. Pratts dispensed with Cooke's apparatus, and, to prevent oxidation of iron(II), carried out the de- composition in a large platinum crucible fitted with a perforated cover under which carbon dioxide was introduced. Hillebrand modified the method by introducing carbon dioxide only at the beginning, relying upon the evolution of steam from the boiling acid mixture to prevent entry of air during the dissolution of the sample.Various other modifications designed to prevent oxidation have been proposed. Tread- wellg carried out the decomposition in a platinum crucible supported in a lead box in which an atmosphere of carbon dioxide was maintained. The box was heated in a paraffin-bath, and the temperature at the end of the decomposition period could be raised to 120" C to remove hydrofluoric acid and so prevent it from interfering in the permanganate titration. BarnebeylO dispensed with carbon dioxide as used in the Cooke apparatus and relied upon the generation of steam to displace air. Instead of permanganate, Sarverll used dichromate to titrate iron( 11), with diphenylamine as internal indicator and a platinum crucible fitted with a tight transparent bakelite lid for the sample decomposition.The lid was provided with a bakelite tube and funnel to enable the carbon dioxide and acid to be introduced into the crucible, The decomposition procedure used was as in Pratt's method. After cooling in a current of carbon dioxide, a measured excess of dichromate was added; the solution was then transferred to a beaker containing boric acid, and the excess of dichromate back-titrated with iron(I1) sulphate with diphenyl- amine as indicator. Soule13 dispensed with the use of platinum ware and carried out the decomposition with hydrofluoric and sulphuric acids in a Pyrex flask in a current of carbon dioxide. He applied a correction for the glass dissolved by conducting a blank determination on ammonium iron(I1) sulphate. In a later paper14 he discussed possible errors in the determination arising from the presence of arsenic in the glass, and claimed that these could be avoided by titrating with cerium(1V) sulphate instead of permanganate.In considering the effects of sulphides in met hods in which hydrofluoric acid decomposition is used, Hillebrand suggested that hydrogen sulphide evolved from soluble sulphides would probably be expelled without reducing iron( 111), but with sulphides containing iron the iron(I1) oxide content would be in error by the amount of iron(I1) they contained. This would be especially significant for pyrrhotite. The insoluble sulphide, pyrite, is resistant to attack by hydrofluoric acid in the absence of air, but Stokes15 showed that in the presence of iron(I1) it is attacked, with the oxidation of the sulphide and reduction of iron(II1).The extent of this reaction depends on the amount of iron(II1) present, and on the degree of fine- ness of the pyrite. Hillebrand considered the influence of pyrite on the iron(I1) oxide determination in most rocks to be negligible, a view that was shared by Dittler.16 The latter maintained that carbon dioxide should, liowever, be introduced into the bottom of the crucible to remove any trace of hydrogen sulphide that might be formed. Schollenberger12 applied the technique developed by Sarver.December, 19661 SILICATE AND REFRACTORY MATERIALS. PART I 757 The effect of organic matter can be minimised if the titration of iron(I1) is carried out with dichromate instead of permanganate, because, according to Sarver,ll dichromate reacts much less readily with organic matter. Densem,17 in modifying Pratt’s method, developed a rather complex apparatus designed to eliminate air during sample decomposition and during the subsequent titration of iron(I1).This apparatus was subsequently modified by Harris.18 In an attempt to overcome oxidation during sample decomposition, Smirnov and Aidinyanlg proposed dissolution of the sample with hydrofluoric and sulphuric acids while it was under a layer of toluene. They claimed that this could be achieved without “bumping” and without forming reaction products that would affect a permanganate titration of iron(I1). Modification of procedures in which hydrofluoric and sulphuric acids are used for sample decomposition has been made to enable micro or semi-micro determinations to be made of iron(I1) oxide. Titrimetric methods were developed by Shioiri and Mitsui,20 Das Gupta21 and Meyrowitz.22 Riley and Williams5 used a spectrophotometric method in which the sample is decomposed in a stoppered Teflon tube heated in a boiling water-bath, the iron(I1) being determined with dipyridyl.In a similar procedure, Shapi1-0~~ decomposed the sample with hydrofluoric and sulphuric acids in the presence of o-phenanthroline in a small plastic bottle. This reagent was designed to react with the iron(I1) as it was released, with the formation of the iron(I1) - o-phenanthroline complex, and so minimise aerial oxidation. The fact that heating affects the stability of the colour seems to militate against obtaining reliable results.N i c h o l l ~ ~ ~ determined iron( 11) oxide in carbonaceous shales by decomposing the sample in sulphuric acid - hydrofluoric acid solution, adding boric acid, and pouring the resulting solution into hydrochloric acid containing iodine monochloride. The iodine liberated was extracted into carbon tetrachloride and titrated with potassium iodate. I t is claimed that the method is applicable in the presence of organic matter equivalent to up to 4 per cent. of carbon. The decomposition of materials that cannot be brought into solution with hydrofluoric acid has been achieved with phosphoric acid. Konopicky and Caesar25 determined iron(I1) oxide in chrome ore by decomposing the sample by heating it with phosphoric acid in an atmosphere of carbon dioxide, the resulting solution being titrated with permanganate.For the determination of iron(I1) oxide in ferrites Kleinert and Funke26 applied a similar method in which nitrogen was used to prevent oxidation. Clemency and Hagner2’ departed from the general practice of determining iron( 111) as the difference between iron(I1) and total iron; instead they determined it by using coulo- metrically generated titanium(II1) ion as titrant, with an automatic spectrophotometric apparatus devised by Malmstadt and Roberts.28 For the determination of iron(II1) in the rocks G-1 and W-1, dissolution of the sample was achieved by heating it to just below the boiling-point with hydrofluoric and concentrated sulphuric acids. Initially, this decomposition was carried out in a specially constructed box in which an inert atmosphere could be main- tained.The results were erratic and always low, but this was evidently not because of the incomplete dissolution of the sample, as a total-iron analysis showed a virtually complete recovery of iron. The low results were presumed to he caused by reduction of iron(III), perhaps by some constituent of the rocks. Subsequently the decomposition was carried out in a covered crucible. The heating time proved critical, 3 to 4 minutes being the optimum. With heating times in the range of 4 to 5 minutes results were low and erratic, andreduction of iron(II1) appeared to occur. Heating times in excess of 5 minutes gave gradually increasing iron( 111) values, presumably because o f the predominance of air oxidation over the reduction observed.Evidently, therefore, in this instance the problems associated with the determination of iron(I1) are not overcome by carrying out a determination of iron(II1) instead. ACID DECOMPOSITION IN THE PRESEKCE OF AN OXIDANT To overcome difficulties with iron( 11) oxide determinations arising from aerial oxidation, many methods have heen proposed for decomposing the sample with acids in the presence of an oxidising agent. A known amount of oxidant is used, which oxidises the iron(I1) as it is brought into solution, and the excess of oxidant, or the product of its reduction, is then determined by a suitable (usually titrimetric) method. This was suggested (but never tried) by H a ~ k l , ~ ~ who proposed decomposing the sample with hydrofluoric acid in the presence758 SCHAFER: DETERMINATION OF IRON(II) OXIDE IN [Analyst, Vol.91 of potassium dichromate and subsequently titrating the excess of dichromate. The first practical application of such a procedure was carried out by Shein,30 who used it for the analysis of iron(I1) oxide in chromite. He decomposed the sample by heating (360” to 380” C) with phosphoric and sulphuric acids in the presence of a weighed amount of vanadium pentoxide, and then titrating the excess of vanadate with iron(I1) sulphate. Modifications of Shein’s method have been used by many other workers for determining iron(I1) oxide, generally in chromite and chrome - magnesite materials. These materials are not decomposed by hydrofluoric and sulphuric acids but can be brought into solution with phosphoric acid.31 to 38 Most of the applications of acid decomposition in the presence of an oxidant reported in the literature are based on the use of phosphoric acid and vanadium pentoxide, as in Shein’s method.However, other oxidants have been used. G o ~ w a m i ~ ~ claimed that a considerable amount (16 to 20 per cent.) of vanadium pentoxide underwent decomposition during sample dissolution, and proposed the use of cerium(1V) sulphate as oxidant. Although cerium(1V) sulphate undergoes some decomposition, Goswami obtained consistent and reproducible results for the determination of iron(I1) oxide in chromite. The volume of iron(I1) sulphate required for the cerium(1V) sulphate added was multiplied by a derived factor, which pre- sumably allows for the slight decomposition of cerium(1V) sulphate under the conditions used.Ingamells40 based his method on the stability of both bivalent and tervalent manganese in phosphoric acid - pyrophosphate mixtures. A measured excess of potassium permanganate is incor- porated in the phosphoric acid reagent containing bivalent manganese, which is oxidised by the permanganate to tervalent manganese. After addition and dissolution of the sample, the excess of tervalent manganese is titrated with iron(I1) sulphate. Nagato41 developed a spectrophotometric method based on the decomposition of the sample with phosphoric acid in the presence of manganese(II1) oxide; the optical density of the resulting solution containing tervalent manganese was read at 525 mp.used an oxidant prepared from ammonium cerium( IV) nitrate treated with phosphoric acid. For the determination of iron(I1) oxide in ferrites he decomposed the sample with phosphoric acid containing a measured amount of the phosphatocerate reagent and determined the excess of reagent by titration with iron( 11) sulphate. Cheng claimed that phosphatocerate was stable at the temperature and for the time recommended for sample decomposition. For samples decomposed by cold hydrochloric acid or hydrochloric - hydrofluoric acids mixture, Hey43 used iodine monochloride as the oxidant. The iodine formed by reaction with iron( 11) was determined by titration with potassium iodate. Ishibashi and Kusaka4* decomposed silicates by heating with hydrofluoric and sulphuric acids in the presence of ammonium metavanadate, and titrated the excess of vanadate with iron(I1) sulphate.Wilson45 used the same approach but carried out the decomposition at room temperature, extended periods being required for the dissolution of some samples. Under these conditions vanadate was considered to be stable in hydrofluoric acid. Later,46 he adapted the method for micro-scale work by titration, as well as by introducing a colorimetric method based on the regeneration at pH 5 of iron(I1) when the reaction V4+ + Fe3+ + V5+ -1- Fe2+ proceeds to the right. The removal of iron(I1) by the formation of a complex with dipyridyl assisted the reaction to proceed in the desired direction. The colour developed was then measured spectrophotometrically. Wilson’s volumetric method has been adapted by Jackson47 on a semi-micro scale for determining iron(I1) in the ash and slag from pulverised- fuel boilers. Potassium dichromate as the in situ oxidant was used by Reichen and FaheV8 for deter- mining iron(I1) oxide in rocks and minerals.Decomposition was effected with hydrofluoric and sulphuric acids, at a temperature between 65” and 70” C. However, under these conditions dichromate was found to decompose slightly by reaction with hydrofluoric acid. This effect could be minimised by adding an iron(TT1) salt. The destruction of dichromate appeared to be proportional to the amount in excess, and so a correction based on the simple subtraction of a blank could not be applied. The alternative procedure was therefore adopted of multi- plying the volume of iron(I1) solution used to titrate the excess dichromate by the ratio of the volume of dichromate to iron(I1) solution used in the blank determination.The determination of iron(I1) oxide in materials that can be decomposed by acids in the presence of an oxidant, although attractive in principle, may in practice give rise to a It must be assumed that the extent of decomposition is reproducible. More recently He termed the resulting product “phosphatocerate.”December, 19661 SILICATE AND REFRACTORY MATERIALS. PART I 759 number of difficulties, the most important of which is the stability of the oxidant under the conditions used. If decomposition of oxidant occurs it must be reproducible, and therefore rigid control of the conditions is required to ensure the same degree of decomposition in both sample and blank determinations.In addition, the possible effect of other constituents in the sample on the decomposition of an oxidant should not be overlooked. Some workers have tried to eliminate the possibility of oxidant decomposition by carrying out the acid treatment at room temperature. The disadvantage here is that while some materials are readily dissolved, others require long periods of digestion. A possible advantage is that oxidation of organic matter, such as carbonaceous material, may be less likely at room temperature. SUMMARY OF METHODS IN WHICH ACID DECOMPOSITION IS USED IN THE PRESENCE OF ADDED OXIDANT Material Acid decomposition Silicates, Heating with including H F - H,SO, rocks and minerals room temperature HCl or fICJ - HE' a t Heating with H F a t room tempera- H F a t room tempera- H F - H2S04 ture ture Heating with H3P04 - NaH,P04 Heating with HF - H,S04, 65" to 70" C Chromite Heating with (and chrome - H,PO, - H,SO,, magnesite 360" to 380" C refractories) H,PO, - H,SO, heated a t 360" C Heating with Heating with H3P04 - H2S04 H,PO, - H2S04 heated a t 290" to 300" C HSPO, - H2SO4 HSPO, - H2SO4 Heating with H3P04 - H2S04 Heating with H3P04 Ash and slags HF at room tcmpera- ture Tourmaline Heating with H3PO4 - H2S04 Ferrites H,PO4 a t 250' C H,P04 a t 250" to 300" C Transition H,SO, metal oxides Oxidant Method of determination Reference K2Crz07 Titration of exccss di- H a ~ k l ~ ~ chromate potassium iodate with iron(I1) sulphate NH4V0, Exccss vanadate titrated Wilson45 with iron(1I) sulphate KH,VO, Micro titration of excess Wilson46 vanadate, and also spectrophotometric Tervalent Titration of excess man- Ingamell~4~ manganese ganese with iron(I1) IC1 Iodine formed titrated with Hey43 V,O, Excess vanadate titrated Ishibashi and Kusaka44 sulphate chromate with iron(I1) sulphate K,Cr,O, Titration of excess di- Reichen and Fahey* V205 Excess vanadate titrated Shein30 with iron(I1) sulphate V,O, Titration of excess vana- Samanta and Sen36 V,O, Titration of excess vana- Balyuk and Mirakyan31 V,05 V4+ formed titrated with Nagaoka and Yamazaki3s date date permanganate Cerium (IV) Excess cerium( 1V) titrated Goswami39 sulphate with iron(I1) sulphate V,O, Titration of excess vana- Sasuga and Iidaa7 V,O, Amperometric titration of Kondrakhina el aZ.34 date excess vanadate with iron( IT) sulphate V,O, Titration of cxcess vana- DippeP2 date NaVO, Excess vanadate titrated Jacksond7 with iron(1I) sulphate V,O, Titration of excess vana- Gekht and Putoka3 date with iron (I J) sulphate Mn2O3 Spectrophotometric deter- Nagato,' mination of excess tervalent manganese Phosphato- Excess cerate titrated Cheng'* cerate with iron(I1) sulphatc VzO, V4+ titrated with per- Wickham and WhippIe3B manganate760 SCHAFER: DETERMINATION OF IRON(II) OXIDE IN [AaaZyst, Vol.91 The use of phosphoric acid enables many refractory materials to be brought into solution, but at the temperatures used (up to 380" C) there may be extensive decomposition of the oxidant as well as oxidation of organic matter.Another difficulty that can affect iron(I1) oxide determinations is the presence of sulphides, which may result in consumption of oxidant and thus in high values for the iron(I1) oxide content. A summary of methods involving acid decomposition in the presence of an oxidant is given in Table I. EVOLUTION METHOD Sei149 proposed a completely different approach to the determination of iron( 11) oxide ; he suggested decomposing the finely ground material in phosphoric and sulphuric acids in a stream of carbon dioxide, and passing the resulting vapours through absorption tubes containing a measured amount of standard dichromate solution. According to Seil, sulphur dioxide was evolved by reaction of iron(I1) oxide and the acids. This reduced the dichromate, and the excess of dichromate could then be determined by titration.More recently Tikhomi- rova et aL50 applied this method to the determination of iron(I1) in chromium ores and slags. They thought that the reduction of dichromate was due to absorption of sulphur dioxide and phosphine formed by reaction 01 iron(T1) oxide with the acid mixture. I t is apparent that other substances such as sulphides and organic matter, which could result in the reduction of sulphuric or phosphoric acid with the evolution of the gases mentioned above, must be absent. FUSION METHOD For the decomposition of refractory silicates and the subsequent determination of iron( 11) oxide Rowledge51 investigated the application of a number of fluxes, the most satisfactory being a fluoroborate (NaF),.B,O,.He heated the sample which was mixed with the flux in a sealed glass tube at 900" C, dissolved the melt in dilute sulphuric acid and titrated the iron(I1) with permanganate. He applied the method to refractory silicates such as staurolite, tourmaline, axinite and garnet, and compared the values obtained by decomposition in hydrofluoric and sulphuric acids with those obtained by using the fluoroborate fusion procedure. Because these refractory materials were only partly decomposed by the acid treatment, the iron( 11) oxide contents were determined by weighing the undecomposed material and calculating from the weight of mineral decomposed (obtained by difference). This procedure may be acceptable for homogeneous minerals, but it is unsatisfactory because of doubt about the composition of the undecomposed material.The comparisons made by Rowledge are rather confusing. With tourmaline the results obtained by the two methods agreed ; for garnet the fusion method gave a value of about 1 per cent. higher than that by acid decom- position, and for staurolite and axinite the method gave a value of about 1 per cent. lower. In an attempt to apply the Rowledge fusion method on a micro scale, Hey43 encountered difficulties arising from the oxidation of iron(I1) by air enclosed in the fusion tube, as well as those arising during the slow process of dissolving the melt in sulphuric acid. He overcame the former by conducting the fusion in an evacuated tube, and the latter by dissolving the melt in an excess of iodine monochloride in hydrochloric acid in a stoppered flask and titrating the liberated iodine with potassium iodate.By carrying out the fusion in a platinum boat placed in a silica tube at 950" C through which a current of carbon dioxide was passed, Groves52 excluded the possibility of oxidation. The iron(I1) was then determined by permanganate titration or, better still, by the iodine monochloride method of Hey. Groves regarded the combination of fusion in carbon dioxide, followed by dissolution of the melt in hydrochloric acid containing iodine monochloride, as probably the best method available for determining iron( 11) oxide in refractory materials. More recently Mikhailova et aZ.53 used the method of fluoroborate fusion in an atmosphere of carbon dioxide as developed by Groves for determining both bivalent and tervalent iron in rocks that are difficult to decompose.The solution obtained by dissolving the melt in a mixture of 10 per cent. sulphuric acid and saturated sodium oxalate was subjected to polaro- graphic reduction. The heights of the waves corresponding to Fe2+ and Fe3+ were measured and the content of each form calculated. S~bsequently~~ the fusion was carried out in a platinum crucible into which carbon dioxide was introduced.December, 19661 SILICATE AND REFRACTORY MATERIALS. PART I 761 COMBUSTION METHOD This is based on the oxidation of iron(I1) oxide to iron(II1) oxide when the former is heated in a current of oxygen. In the method originally developed by S h e i r ~ , ~ ~ the sample was heated in a current of dry oxygen or air in an electric furnace maintained at 1000" C.The water and carbon dioxide evolved were collected in an absorption tube and weighed. The oxygen used in the oxidation of iron(I1) oxide was then calculated from the increasein weight of the ignited residue. In a later modification the sample was heated first in pure nitrogen to expel volatile matter; it was then weighed, and finally re-ignited in oxygen. The iron(I1) oxide content could then be calculated from the increase in weight. An investigation of Shein's method as applied to chrome ores by Sasuga and Iida37 with a thermobalance showed that, for samples low in aluminium and magnesium, the increase in weight reached a maximum at 800" to 900" C and that the weight decreased at higher temperatures.They concluded that the temperature at which the weight increase is recorded must be changed according to the sample analysed. De Wet and van Niekerk56 adapted the method on a semi-micro scale for the analysis of iron(I1) oxide in South African chromites. In a study of the rapid analysis of chromite and chrome ores, D i r ~ n i n ~ ~ compared iron(I1) oxide determinations made by the Sliein com- bustion method, the Shein method with vanadium pentoxide as oxidant , and the evolution method of Seil. In a different approach, Habashy5* determined the iron(I1) oxide content of material that is difficult to dissolve, by ignition at 1000" C in a limited, known volume of oxygen. He then calculated the iron(I1) oxide content from the volume of oxygen used in the oxidation of iron(I1) oxide to iron(II1) oxide.He claimed that interferences could be overcome by applying suitable corrections. CONCLUSION The diversity of publications on the determination of iron(I1) oxide in silicate and refractory materials is indicative of the extent of the problem, and it would be unwise to assume that it has been solved. There does not appear to be any one method applicable to all types of materials. All methods suffer from some disadvantages, but perhaps the one most closely approaching the ideal is that of Rowledge, as modified by Groves. However, its application to some materials would amount to the use of unnecessarily severe conditions for sample decomposition that could be readily achieved by some simpler method. The extent of interference arising from the presence of organic matter in a sample would depend on the method of sample decomposition used.I t could be quite serious with decom- position in the presence of an added oxidant, especially if heating were required. With other titrimetric methods the degree of interference would be dependent on the type of organic matter and the oxidising power of the titrant used for the iron(I1). With materials containing sulphides, particularly iron sulphides, errors in the deter- mination of iron(I1) oxide seem unavoidable. Their magnitude is dependent on several factors, such as type and amount of sulphide, the iron(II1) content and the method of sample decomposition. Apart from the likely sources of errors mentioned above, interference with iron( 11) oxide determination could occur because of the presence of oxidising substances such as manganese dioxide, which would lead to low results arising from the oxidation of iron( 11) during sample dissolution.On the other hand, Hillebrand has cited the interference of tervalent vanadium, which would consume the titrant used for iron(I1) and lead to high results. These two sources of error are unlikely to be of common occurrence. However, given an awareness of the problems involved, and a knowledge of the range of methods available for the determination of iron(I1) oxide, it should be possible to select the method best suited to the type and number of samples to be analysed. The author thanks Dr. D. J. Swaine for helpful discussions. REFERENCES 1. 2. 3.___ , Ibid., 1861, 83, 445. 4. 6. 6. Hillebrand, W. F., Lundell, G. E. F., Bright, H. A., and Hoffman, J. I., "Applied Inorganic Mitscherlich, A., J . 9rakt. Chem., 1860, 81, 116. Riley, J. P., Analytica Chim. Ada, 1958, 19, 418. - , and Williams, H. P., Mikrochim. Acta, 1959, 516. Cooke, J. P., Amer. J . Sci., 1867, 44, 347. Analysis," Second Edition, John Wiley and Sons Inc., New York, 1953, p. 907.762 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58. SCHAFER Barnebey, 0. L., J . Amer. Chem. SOC., 1915, 37, 1481. Pratt, J. H., Arne:, J . Sci., 1894, 48, 149. Treadwell, F. P., Barnebey, 0. L., J . Amer.Chem. SOC., 1916, 38, 374. Sarver, L., Ibid., 1927, 49, 1472. Schollenberger, C. J,, Ibid., 1931, 53, 88. Soule, B. A., Ibid., 1928, 50, 1691. -, Ibid., 1929, 51, 2117. Stokes, H. W., Bull. U.S. Geol. Surv., 1901, 186. Dittler, E., Z . anorg. allg. Chem., 1926, 158, 264. Densem, N. E., J . SOC. Glass Technol., 1936, 20, 303. Harris, F. R., Analyst, 1950, 75, 496. Smirnov, V., and Aidinyan, N., Dokl. Akad. Nauk SSSR, 1937, 14, 353. Shioiri, M., and Mitsui, S., Mikrochim. Acta, 1938, 3, 291. Das Gupta, J., Sci. Cult., 1941, 6, 677. Meyrowitz, R., Amer. Miner., 1963, 48, 340. Shapiro, L., Prof. Pap. U . S . Geol. Surv., 1960, [400-B], 496. Nicholls, G. D., J . Sedim. Petrol., 1960, 30, 603. Konopicky, K., and Caesar, F., Ber. dt. keram. Ges., 1939, 20, 362. Kleinert, P., and Funkc, h., Z , Chemze., 1962, 2 , 155.Clemency, C. V., and Hagner, A. F., Analyt. Chem., 1961, 33, 888. Malmstadt, H. V., and Roberts, C. B., Ibid., 1956, 28, 1884. Hackl, O., 2. analyt. Chem., 1925, 67, 197. Shein, A. V., Zav. Lab., 1937, 6, 1199. Ralyuk, S. T., and Mirak’yan, V. M., Ibid., 1949, 15, 1004. Dippel, P., Silikattechnik, 1962, 13, 51. Gekht, I. I., and Putok, S. I., Vest Akad. i\Tauk. Kazakh. S.S.R., 1960, 9, 68. Kondrakhina, E. G., Egorova, L. G., and Songina, 0. A., Izv. Akad. Nauk. Kazakh. SSR, 1957,1, 45. Nagaoka, T., and Yamazaki, S., j a p a n -4nalyst, 1954, 3, 408. Samanta, H. B., and Sen, N. B., Traws. Indian Ceram. Soc., 1946, 5, 97. Sasuga, H., and Tida, Y., Japan A4nalyst, 1958, 7, 248. Wickham, D. G., and Whipple, E. R., Talanta, 1963, 10, 314. Goswami, N., Sci. Cult., 1957, 22, 398. Ingamells, C. O., Talanta, 1960, 4, 268. Nagato, H., Japan AnaZyst, 1961, 10, 985. Cheng, I<. L., Analyt. Chem., 1964, 36, 1666. Hey, M. H., Mineralog. Mag., 1941, 26, 116. Ishibashi, I. M., and Kusaka, Y., J . Chem. Sor. Japan, 1950, 71, 160. Wilson, A. D., Bull. Geol. Survey, Gt Brit., 1955, 9, 56. -, Analyst, 1950, 85, 823. Jackson, P. J., J . A p p l . Chem., Lond., 1957, 7, 605. Reichen, Laura E., and Fahey, J . J., Bull. U.S. Geol. Surv., 1962, 1144-B. Seil, G. E., Ind. Engng Chem. Analyt. Edn, 1943, 15, 189. Tikhomirova, 0. F., Strebulaeva, E. N., and Sazonova, 2. V., Sb. Trud. Tsent. Naztchne-Issled. Rowledge, H. P., J . Proc. Roy. Sor. West. Aust., 1934, 20, 165. Groves, A. W., “Silicate Analysis,” Second Edition, George Allen and Cnwin Ltd., London, 1951, Mikhailova, 2. M., Mirskii, R. V., and Yarushkina, A. A., Z h . Analit. Khim., 1963, 18, 856. Mikhailova, 2. M., Yarushkina, A. A,, Mirskii, R. V., and Shil’dkrot, E. A., Trudy Kuibyshev. Shein, A. V., Zav. Lab., 1937, 6, 505. Wet, J . F, de, and h’iekerk, J. N. van, J . Chpm. Metall. M i n . SOC. S . Afr., 1952, 53, 10. Dinnin, J., Bull. U.S. Geol. Surv., 1969, 1084-R. Habashy, M. G., Analyt. Chem., 1962, 34, 1015. Kurzes Lehrbuch analytischen Chemie,” 1913, Volume 2, p. 425. Inst. Chern. Mettall., 1963, 31, 180. pp. 88 and 181. Gos. n’aulhnc.-Issled. Inst. Neft. Prom., 1963, 20, 124. Received October 28th, 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100755

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

Analyst, December, 1966, Vol. 91, $9. 763-790 763 The Determination of Iron(I1) Oxide in Silicate and Refractory Materials Part 11. A Semi-micro Titrimetric Method for Determining Iron(I1) Qxide in Silicate Materials BY H . N. S. SCHAFER (Division of Coal Research, CSIRO, P.O. Box 175, Chatswood, New South Wales, Australia) A description is given of an apparatus of simple construction that can be made from plastic, in which the decomposition of silicate materials by hydrofluoric acid can be carried out. The procedure for the titration of iron(I1) with dichromate under conditions that eliminate the risk of oxidation is outlined. A comparison has been made between dichromate titres obtained potentiometrically and with diphenylamine sulphonate as indicator. Errors associated with the latter in the titration of small amounts of iron(I1) are discussed. The method of sample decomposition and titration of iron(I1) has been assessed by determining the iron(I1) oxide content of the diabase W-1, and has been applied to the determination of iron(I1) oxide in slags from a boiler fired with pulverised fuel.IN Part 1 of this paper methods are reviewed for determining iron(I1) oxide in refractory materials. A simplified analytical procedure comprising dissolution of the sample followed by direct titration of iron(I1) is now considered. Its application is restricted to silicate materials that are decomposed by hydrofluoric acid. The method described here was developed after consideration had been given to the methods of Wilson1 and Reichen and Fahey,2 both of which involve sample decomposition in the presence of an oxidant. The former method,l in which vanadate is used as added oxidant with subsequent colorimetric determination of iron( 11), gives satisfactory results when complete decomposition of the sample can be achieved at room temperature.However, most of the samples studied decomposed only very slowly under these conditions. In the method proposed by Reichen and Fahey,2 in which dichromate is used as oxidant with subse- quent titration of the excess, reproducible results could not be obtained for the titration of dichromate in the blank determination and the method was, therefore, not examined further. DEVELOPMENT OF THE METHOD APPARATUS- The apparatus for sample decomposition was required to be of simple construction, to have provision for maintaining an inert atmosphere, to be suited to operation at temperatures above room temperature and to be capable of being used as the titration vessel.The con- struction of an all-plastic apparatus satisfying most of these requirements is fully described under Experimental, and is illustrated in Fig. 1. This apparatus is similar in application to that devised by Sarver3 and further described by S~hollenberger,~ who used a platinum crucible, which enabled the solution to be boiled, for sample decomposition ; an inert atmosphere was maintained by carbon dioxide introduced above the solution through a tube in a bakelite lid. DICHROMATE TITRATION OF IRON(II)- The titration of iron(T1) with dicliromate was examined in the presence of phosphoric acid, of hydrofluoric acid after addition of boric acid and phosphoric acid, and of hydrofluoric acid.In all titrations sulphuric acid was present and sodium diphenylamine sulphonate was used as indicator, the titrations being carried out in an atmosphere of nitrogen. The same dichromate titre was obtained each time. As the titration in hydrofluoric acid solution gave sharp and distinct end-points, removal of hydrofluoric acid by forming complexes with boric acid appeared to be unnecessary. Accordingly all subsequent titrations were performed764 SCHAFER: DETERMINATION OF IRON(II) OXIDE IN [Analyst, Vol. 91 Stopper Funnel (neck from bottle) Cap (base from bott I e) Body of 100-ml bottle Fig. 1. Sample decomposition apparatus (poly- thene) directly in solutions containing hydrofluoric acid.This acid acts in the same way as phosphoric acid in lowering the redox potential of the iron(I1) - iron(II1) system. These observations confirm those of Schollenbergel"' who examined the titration of iron(I1) with dichromate, with diphenylamine as indicator. He noted that the presence of hydrofluoric acid sharpened the end-point ; and maintained that in the determination of iron(I1) oxide in minerals it was preferable to perform a direct titration with dichromate, and that the addition of boric acid to inactivate the hydrofluoric acid used in the decomposition of a silicate should be omitted. TITRATION OF DIFFERENT VOLUMES OF IRON(II) SOLUTION- The next aspect studied was the effect of varying the amount of iron(I1) titrated.Meyrowitz5 observed that the reverse titration was disproportional. There was an apparent change in the normality of an iron(I1) solution as the volume of dichromate was changed; the normality gradually increased as the volume of dichromate titrated increased. This disproportion was found to be more pronounced in large volumes (300 ml) than in small volumes (100 ml). To overcome this effect in an iron(I1) oxide determination, a sample weight was chosen that required about the same volume of dichromate as was used in the standardisation of ammonium iron( 11) sulphate. TABLE I TITRATION OF APPROXIMATELY 0-02 S IRON(I1) SULPHATE WITH 0.02 N POTASSIUM DICHROMATE UNDER NITROGEN IN A HYDROFLUORIC - SULPHURIC ACID SOLUTION (10 mi of 1 + 3 H,SO, and 5 ml of HF diluted to 25 ml) Iron( 11) solution, ml 1.00 2.00 3.00 4.00 5.00 6-00 8-00 10.00 Potentiometric titration Potassium Apparent dichromate, iron(I1) ml normality 0.97 0.01940 1.95 0.0 1950 2.93 0.01953 3.91 0.01955 4.88 0.01 952 5.85 0.01950 7.80 0.01950 9.76 0.01952 Y Diphenylamine sulphonate Potassium - s t dichromate, iron(I1) ml normality 1.01 0.02020 2.00 0~02000 2.95 0-01967 3-93 0.01965 4-89 0.01956 5.86 0.01953 7.80 0-01950 9.77 0.01954 Ferroin Potassium? - Apparent dichromatc, iron (I I) ml normality 0.98 0.0 1960 1-96 0.01960 2.94 0.01960 3.93 0.01965 4.90 0.01960 5.88 0.01960 7.84 0.01960 9-80 0.01960 * Corrected for blank of 0-02 ml of 0-02 N potassium dichromate.t Corrected for blank of 0.08 ml of 0.02 N potassium dichromate.December, 19661 SILICATE AND REFRACTORY MATERIALS. PART 11 7 65 A similar effect has been reported by Rodden6 and De Sesa7 in the determination of small amounts of uranium, in which quadrivalent uranium is reacted with iron(II1) ions, and the iron(I1) ions formed are titrated in sulphuric acid - phosphoric acid solution with dichromate.No satisfactory explanation was offered for this disproportion. Toni,8 in a study of the disproportion in uranium determinations, showed that the indicator, diphenylamine sul- phonate, was responsible, and overcame the problem by determining the end-point potentio- metrically. Earlier, Kolthoff and Sarver9 had discussed the possibility of side reactions occurring when diphenylamine was used as indicator in dichromate titrations. In the present study the titration of iron(I1) solutions in the presence of hydrofluoric acid with dichromate, with diphenylamine sulphonate as indicator, also proved to be dis- proportional for small amounts of iron(I1). In view of the findings of Toni, comparisons were made between titres obtained when the end-point was determined potentiometrically, with diphenylamine sulphonate, and with ferroin.If the disproportion observed in titrations in which diphenylamine sulphonate was used arose from side reactions occurring on oxidation of this indicator, it was thought that this would not occur with ferroin with which the colour change on oxidation is caused by the oxidation of iron(I1) to iron(II1) within the o-phenan- throline complex. The apparent iron( 11) normality, as well as the dichromate titres, obtained for different volumes of iron(I1) solution are shown in Table I.The disproportion observed in the titration of small amounts of iron( 11) with dichromate, with diphenylamine sulphonate as indicator, is not apparent when the end-point is detected potentiometrically or when ferroin is used as indicator. In the latter case an apparently higher normality for the iron(I1) solution was obtained. I t would appear that, as the potential of the iron(I1) - iron(II1) - o-phenanthroline system is about 1-06 volts, the indicator ferroin is not really suitable for use with dichromate as oxidant at the acidity used (3-6 N) when the chromium(II1) - dichromate potential is about 1-11 volts (Smith and KichterlO). Because of this the solutions were possibly over-titrated in reaching the point of colour change of the indicator, which would account for the apparently higher normality of the iron(I1) solution.Disadvantages of ferroin as indicator are the large indicator blank and the gradual colour change from the orange of the iron(I1) form through a virtually colourless stage to the blue of the iron(II1) form. The change in potential during a potentiometric titration of iron(I1) with dichromate in the presence of hydrofluoric acid is particularly large and abrupt. A typical titration graph is shown in Fig. 2. End-points were calculated from the second derivative. 0 I 2 Millilitres of 0.02 N potassi um dich romate yig. 2. Typical potentiometric titration curve766 SCHAFER: DETERMINATION OF IRON(II) OXIDE IN [Analyst, Vol.91 Plotting dichromate titres, obtained by using potentiometric end-point detection, against millilitres of iron(I1) solution (about 0.02 N) gives a linear relationship. A similar procedure in which dichromate titres, obtained with diphenylamine sulphonate as indicator, are used shows a change of slope occurring at approximately 5 ml of iron(I1) solution. By using the titres shown in Table I the following equations may be derived- P = 0.9758 M - 0.001 P = 0.9780 M - 0.006 P = 0.9761 M - 0-004 D = 0.9690 M + 0.049 D = 0-9756 M + 0.007 . . . . . . . . . . where P = dichromate titres obtained potentiometrically ; D = dichromate titres obtained with diphenylamine sulphonate; and M = millilitres of about 0.02 N iron(I1) solution. (1) (2) (3) (4) (5) (For the range 0 to 10 ml of iron(1J) solution.) (For the range 0 to 5 ml.) (For the range 5 to 10 ml.) (For the range 0 to 5 ml.) (For the range 5 to 10 ml.) From equations (2) and (4) the relationship between potentiometric and indicator titres for volumes of iron(I1) solution in the range up to 5ml is given by- Similarly, from equations (3) and (5) for volumes of iron(I1) solution in the range 5 to 10 ml, the relationship is- Thus in this range titres obtained with the indicator diphenylamine sulphonate tend to be about 0.01 ml higher than those obtained potentiometrically.This is probably because the potentiometric end-point is more easily detected than the indicator end-point, slightly more titrant being required with the latter to develop a perceptible colour change.However, P = 1.0093 D - 0.055 . . . . . . - * (6) P = 1.0005 D - 0.011 . . . . .. * * (7) TABLE I1 IRON(II) OXIDE DETERMINED IN W-1 500 ml minute per Sample Nitrogen weight, Time, flow-ra te mg minutes 100 ml 75.95 60 per 72-75 50 minute 74.75 50 75.00 60 71-22 60 69.10 60 70.10 30 74.85 60 7 1.05 60 72.15 30 77.75 60 79.95 30 80.80 30 79.25 30 69.30 60 68-70 15 70.18 60 68.00 70 70.50 60 69.80 60 67-22 120 73-40 60 71-91 30 71-76 30 73.57 30 72.84 30 73.43 30 Standard deviation . . Average . . . . .. 0.02 N Potassium dichromate, ml 4.44 4.30 4.36 4.55 4.30 4.06 4.19 4.5 1 4-28 4-36 4.69 4.89 4.93 4-83 4-18 4-19 4.28 4.14 4.28 4.25 4.06 4.47 4.36 4.34 4.48 4-43 4.44 Iron (11) oxide, per cent. 8-40 8-49 8.42 8.72 8-68 8.44 8-59 8-66 8.66 8.68 8.67 8.79 8.77 8.76 8.67 8.76 8-76 8.75 8.72 8-75 8.68 8-75 8.71 8.69 8.75 8-74 8.69 .. .... 8.72 .. . . .. 0.04 95 per cent. confidence limits for average . . 8.72 f 0.02 Iron( 11) * oxide, per cent. 8-38 8.47 8-40 8.70 8.66 8.40 8.55 8-64 8.64 8.66 8-65 8.77 8.75 8.74 8.63 8-72 8.74 8.7 1 8470 8.73 8.64 8.73 8.69 8.67 8.73 8.72 8-67 8.70 0.04 8.70 f 0.02 * Calculated from the relationship between potentiometric and diphenylamine sulphonate titres according to equation (6).December, 19661 SILICATE AND REFRACTORY MATERIALS. PART 11 767 within the limits of experimental error it is considered that for titrating volumes of iron(I1) solution in the range 5 to 10 ml, the difference in dichromate titres between the two methods is not significant. Equation (6) shows that for up to 5-ml volumes of iron(I1) solution the difference between the dichromate titres is significant.Accepting potentiometric titration as the reference method, equation (6) may be used to correct titres obtained with diphenylamine sulphonate as indicator and thus overcome the disproportion. In practice, the error in determining an iron(I1) oxide content will only be significant for low titres and low sample weights. In Table 11, in which iron(I1) oxide determined in W-1 is shown, titres were in the range of 4 to 5 ml for the sample weights taken. These titres, corrected on the basis of equation (6), are on the average 0-01 ml less than un- corrected titres, and accordingly the percentage of iron(I1) oxide is lower by 0.02. There- fore, the correction at this level is no greater than the probable experimental error.For practical purposes titres greater than 4 ml need not be corrected, but to ensure wider applica- tion of the method it is desirable to establish the relationship between potentiometric and diphenylamine sulphonate titres. EXPERIMENTAL APPARATUS- Sample decomposition apparatzcs-This was constructed from 100-In1 polythene bottles, and its structure may be clearly seen in Fig. 1. For potentiometric titrations the cap shown was replaced by one with holes for the insertion of the platinum electrode and salt bridge, and for the addition of nitrogen. Platinum electrode-This consisted of thin-sheet platinum, 15 x 5 mm, welded to a platinum wire and sealed into a glass tube, which was covered with thin-walled plastic tubing to protect it from hydrofluoric acid vapours (see Fig.3). Salt bridge-A length of polythene tubing, to one end of which a plug of tightly rolled filter-paper had been fitted, was filled with saturated potassium chloride solution. A dip-type calomel electrode could be inserted tightly into the other end of the tube (see Fig. 3). Potentiometer-Potentiomctric measurements were made with a pH meter (supplied by W. G. Pye and Co., England) in conjunction with a dip-type calomel reference electrode. Burette-A 10-ml Class A burette graduated at 0.02 ml intervals. Copper / wire V Platinum Plastic sheath D i p-type Saturated Filter-paper SGI ut ion calomel electrode potassium chloride Fig. 3. Platinum electrode and “salt bridge” REAGENTS- Hydrojuoric acid, analytical-reagent grade, 40 per cent.Sulphztric acid, 1 + 3-One volume of concentrated sulphuric acid poured into three Potassium dichromata, 0.02 N-Prepare by powdering analytical-reagent grade potassium Weigh 0.9807 g, Diphenylamiize sulflhonate solution, 0.3 per cent .-Dissolve 0.3 g of sodium diphenylamine Ferroin indicator, 0.025 M-Dissolve 1-485 g of o-phenanthroline monohydrate in 100 ml volumes of distilled water. dichromate and drying it at 120” C for 2 hours; cool it in a desiccator. dissolve it in distilled water and dilute the solution to 1 litre. sulphonate in 100ml of distilled water. of a solution containing 0.695 g of iron(T1) sulphate, I;eS0,.7H,O.768 SCHAFEII: DETERMINATION OF IRON(II) OXIDE IN [Analyst, Vol. 91 PROCEDURE- Weigh, to the nearest 0.01 mg, a 20 to 100-mg sample depending on the expected iron(I1) oxide content.Transfer to the decomposition vessel, assemble the apparatus and flush with nitrogen at a rate of about 100 ml per minute. Carefully add 10 ml of freshly boiled, 1 + 3, sulphuric acid solution, and increase the nitrogen flow to 500ml per minute. Make sure that the nitrogen inlet is below the surface of the acid. Swirl the apparatus to disperse the sample, then add 5 ml of hydrofluoric acid from a small plastic vial. Place the stopper loosely in the funnel and immerse the apparatus to about half its depth in a water-bath maintained at 80" C. During sample dissolution swirl the flask occasionally. When dissolution is complete (generally in about 30 minutes) remove the apparatus from the hot water-bath and place it in a cold water-bath.Remove the funnel, and wash down the inner surface of the vessel with freshly boiled and cooled distilled water until the volume is about 25 ml. Allow the apparatus to cool for 10 to 15 minutes. Remove it from the cooling bath, add one drop of diphenylamine sulphonate indicator and immediately titrate with dichromate until a definite purple colour is reached. Correct the volume of dichromate used by subtracting the titre obtained in a blank determination. The percentage of iron(I1) oxide in the sample is given by- Dichromate (ml) x 143.7 Sample weight (mg) For dichromate titrations of less than 4 ml, correct the titre on the basis of equation (6). If a potentiometric titration is desired, the cap fitted with platinum electrode and salt bridge is used in place of the normal cap.The electrode and bridge are withdrawn to the top of the cap during sample dissolution and lowered into the solution before titration. TABLE I11 EFFECT OF SAMPLE WEIGHT ox THE DETERMINATIOK OF IRON(II) OXIDE IN W-1 0.02 N Sample Potassium Iron(I1) oxide, End-point weight, dichromate, per cent. detection mg rnl Potentiometric 19.62 1-19 8.72 7 38-14 2.30 8.67 8-70 73.73 4.47 8.71 } Average 78.47 4.74 8.68 J Ferroin 20.29 38.58 74.59 79-30 Diphen ylamine 20.20 sulphonate 37.63 77.17 1.24 8.78 2.33 8.68 '1 8.71 4.50 ::3; J Average 4.82 1.26 8.96 8-68* 2-31 8.82 8.71* 4-88 8-71 8*70* * Corrected on basis of equation (6). RESULTS AND DISCUSSION INFLUENCE OE- KITROGEN FLOW-RATE- To prevent oxidation of iron( 11) during decomposition of a silicate material, "oxygen- free" nitrogen was used to displace air from the apparatus.On testing the method for the determination o f iron(I1) oxide in the diabase U-1, it was found that the variation in results initially obtained occurred because the nitrogen flow-rate of 100 ml per minute was insufficient, especially when, during the course of sample dissolution, the apparatus was swirled to ensure dispersion of the sample. Consistent results were obtained when the flow-rate was increased to 500 ml per minute, which ensured a good flushing of the apparatus and in addition served to keep the sample dispersed. Passing the nitrogen through a saturated iron( 11) sulphate solution and then through a bubbler containing reduced anthraquinone p-sulphonic acid did not significantly change the results as compared with those obtained by using nitrogen directly from the cylinder.Tests on an iron(I1) sulphate solution treated in the apparatus in the same way as a sample for periods up to 1 hour gave dichromate titres averaging about 99.5 per cent. of those obtained by immediate titration. The results obtained for the iron(I1) oxide content of W-1 under numerous different conditions are shown in Table 11.December, 19661 SILICATE AND REFRACTORY MATERIALS. PART 11 769 VARIATION IN SAMPLE WEIGHT- In view of the disproportion evident in the titration of iron(I1) in amounts equivalent to less than 4 ml of 0.02 N dichromate when diphenylamine sulphonate is used as indicator, various weights of W-1 were taken for the determination of the iron(I1) oxide content, with three methods of end-point detection.The results of these determinations are shown in Table 111. The iron(I1) oxide contents of 8.96 and 8.82 per cent. obtained for sample weights of approximately 20 and 38 mg, respectively, with diphenylamine sulphonate are significantly higher than the average value of 8.70 per cent. obtained for 20 determinations with sample weights averaging about 72 mg. However, if the dichromate titres found in these determina- tions with the lower sample weights are corrected on the basis of equation (B), iron(I1) oxide contents become 8.68 and 8.71 per cent., respectively, in agreement with the average value. In the determination of iron(I1) oxide in a sample with diphenylamine sulphonate as indicator, it is necessary to take a sample weight which will require a dichromate titre of not less than 4 ml of 0.02 N solution, or alternatively to correct the titre on the basis of the relationship between potentiometric and diphenylamine sulphonate titres.The use of ferroin for end-point detection does not suffer from this limitation, but the tendency towards over- titration and the difficulty of observing the exact colour change are disadvantageous. Potentio- metric titration is by far the most reliable method of end-point detection, as it is not subject to the disproportion effect when small volumes of iron(I1) are titrated, and because the potential break is so distinct. APPLICATION OF THE METHOD The method of sample decomposition and subsequent direct titration of iron( 11) with dichromate, with diphenylamine sulphonate as indicator, has been applied to the determination of iron(I1) oxide in a number of slags from a boiler fired with pulverised fuel.The results of the determinations shown in Table IV are compared with iron(I1) oxide contents obtained by Wilson’s colorimetric method. In general, the titration procedure gave slightly higher contents than the colorimetric method. Two samples allowed to stand at room temperature for 4 hours did not give complete decomposition, and a large increase in iron(I1) oxide contents was obtained in repeat determinations left overnight, CONCLUSION The determination of iron(I1) oxide in silicate materials decomposed by hydrofluoric acid can be easily performed in an inexpensive apparatus under conditions that prevent oxidation. Difficulties associated with the titration of small amounts of iron( 11) with dichromate, with diphenylamine sulphonate as indicator, can be avoided by using adequate sample weights or, if this is not possible, by application of a correction where necessary, based on the relationship between potentiometric and diphenylarnine sulphonate titres of an iron( 11) solution.For the most precise determinations potentiometric titration is recom- mended. In the determination of iron(l1) oxide in W-1, an average of 8.70 per cent, was TABLE I V DETERMINATION OF IRON(II) OXIDE IN SLAGS FROM PORT AUGUSTA POWER STATIOK, SOUTH AUSTRALIA Proposed Sample method A 5*17* 5*26* B 9-48 9-45 C 9.74 9.67 D 10-99 10-92 E 7.78 7.85 Wilson’s colorimetric method r 4 hours 16 hours - - - - - - 9.25 8.74 7-07 6-67 5.01 5.01 9.12 9.18 9.62 9.47 10.69 10.10 7.89 7.60 * Corrccted on basis of equation (6).770 SCHAFER found in 20 determinations, with a standard deviation of +0-04 per cent.The 95 per cent. confidence limits for the average are 8-70 Ifr 0.02 per cent. The preferred value for the iron(I1) oxide content of W-1 as given by Fleischer and Stevensll is 8.74 per cent., whereas Ingamells and Suhrl2 give a preferred value of 8-71 per cent. It should be possible to extend the application of the method by using an apparatus constructed of PTFE, to enable the acid to be boiled during decomposition. The author thanks Dr D. J. Swaine for helpful discussions, and Mr. R. J. Cosstick for providing results of iron( 11) oxide determinations by Wilson’s colorimetric method. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. REFERENCES Wilson, A. D., Analyst, 1960, 85, 823. Reichen, L. E., and Fahey, J . J., Bull. U.S. Geol. Surv., 1962, 1144-B. Saxver, L., J . Amer. Chem. Soc., 1927, 49, 1472. Schollenberger, C. J., Ibid., 1931, 53, 88. Meyrowitz, R., Amer. Miner., 1963, 48, 340. Rodden, C. J , , in Susano, C. D., House, 33. S., and Marler, M. -4., Editors, “First Conference on Analytical Chemistry in Nuclear Reactor Technology,” Report TlD-7555, U.S. Atomic Energy Commission, p. 25. De Scsa, M. A., in Susano, C. D., lIousc, H. S., and Marler, M. A., Editors, op. cit., p. 58. Toni, J . E. -4., Analyt. Chem., 1962, 34, 99. Kolthoff, I . , and Sarvcr, L., J . Amer. Chem. Soc., 1931, 53, 2902. Smith, G. F., and Richter, F. P., “Phenanthroline and Substituted Phcnanthroline Indicators,” G. Frederick Smith Chemical Co., Columbus, Ohio, 1944. Fleischer, M., and Stevens, K. E., Georhim. Cosmochim. Acta, 1962, 26, 525. Ingamells, C. O., and Suhr, N. H., Ibid., 1963, 27, 897. Received October loth, 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100763

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

AnaZyst, December, 1966, Vol. 91, $9. 771-774 77 1 The Determination of Fluorine or Phosphorus in Organic Compounds by a Micro-titrimetric Method BY F. H. OLIVER (Chemica2 Research Department, Parke, Davis G. Co., Staines Road, Hounslow, Middlesex) A method is described for determining fluorine or phosphorus in organic compounds synthesised for medical research. After combustion of the compound in an oxygen flask and absorption of thc decomposition products in water, the contents are diluted with isopropanol, and titrated with thorium nitrate solution with a Solochrome cyaninc R screened indicator. The addition of buffcrs is unnecessary. The removal of elements that interfere in the titration of fluorine is also described. IN the determination of the elements in organic compounds by micro-analytical techniques it is desirable that the methods used should be both accurate and simple.This is not achieved in the determination of fluorine or phosphorus; known methods are accurate, but there is a need for greater simplicity. With the oxygen-flask1 method, the decomposition of organic compounds has been simplified, but the final determination of the ionised fluorine or phosphorus is elaborate. The hydrofluoric acid formed by combustion of fluorine compounds that contain no other acid-forming elements can be titrated directly with 0.01 N sodium hydroxide.2 An alternative method that was found to give good results is to add potassium iodate and then potassium iodide to the acid solution and titrate the liberated iodine with a standard solution of sodium thiosulphate.Attempts made by the author, when using the oxygen flask for combustion, to find a titration finish applicable to organic compounds containing fluorine or phosphorus that have been synthesised for medical research are described in this paper. No reports in the literature could be found relating to the titration of orthophosphate with thorium, but, as thorium forms an insoluble phosphate, it was thought that a thorium solution could be used as a titrant for phosphorus and the same method used as that used for fluorine, especially as phosphate was found to interfere with the determination of fluorine. Sulphate also interfered, but as the interference was not quantitative it could not be used as a method for the determination of sulphur.EXPERIMENTAL Metals that form insoluble fluorides and phosphates were chosen for examination. These are : thorium, zirconium, lanthanum, cerium, yttrium, bismuth and iron. Indicators that form coloured complexes with one or more of them are: Alizarin red S, acid Alizarin black S, Solochrome (Eriochrome) cyanine R, * pyrocatechol violet , methylthymol blue, xylenol orange, thoron, PAN , SPADNS, Zincon, Tiron, phenylfluorone, arsenazo and purpurin. Complexes of these metals and indicators have all been used in the spectrophotometric determination of either the metal or fluorine, but reports on them in the literature are too numerous to quote. The majority of these failed in the present work for one or more of the following reasons: some required very close pH control as the indicators are also acid - base indicators; end-points with some were slow; and in many instances the colour change was gradual from one tone to another with no sharp change taking place.In nearly all of these combinations the metals formed highly insoluble lakes that separated out, and end-points were masked. The most promising results, however, wcre obtained by titrating fluoride and ortho- phosphate ions with thorium nitrate and Solochrome cyanine R as indicator. Willard and Horton3 state that the preferred order of indicators for the titration of fluoride with thorium nitrate is (i) purpurin sulphonate, (ii) Alizarin red S, and (iii) Solochrome cyanine K. * The indicator is referred to by the suppliers as “Solochrome cyaninc I<” and this designation will be used throughout.772 [Analyst, Vol.91 Alizarin red S is the most widely mentioned indicator used for the determination of fluorine. In no instance, however, when used on the micro-scale in the author's laboratory, was it possible to detect a reliable end-point with this indicator by straight titration, and at all times it was necessary to exercise strict pH control by the use of buffers. The recom- mended method was that of Dahle et aZ.,4 and is based on colour matching by comparison and described in full by Clark,5 and Milton and Waters.6 It was therefore decided to investigate more fully the use of Solochrome cyanine R. Supplies of this indicator were obtained from three sources, A, B and C. A 0.25 per cent. aqueous solution of each indicator was prepared and 3 drops of indicator and 1 drop of 2 N nitric acid were added to three separate flasks, each of which contained 25 ml of distilled water.The colour of each solution was golden brown and changed, for the solutions con- taining A and B, to red - purple on the addition of 1 drop of 0.01 N thorium nitrate, although with C, 0.1 ml of the thorium solution was required to give a colour change. Visual inspection of the solid indicators showed that a second compound was probably present in each. Any such compound was water-soluble as no residue was left when the solutions were filtered. A 0.25 per cent. solution of each indicator was then prepared in 96 per cent. ethanol and, on filtering, A and B left a small amount of a white organic crystalline material, while C left an inorganic residue amounting to about 66 per cent.of the dye. This was shown to be sodium sulphate. A and R were used for further investigations. A standard solution of 0.01 N sodium fluoride was used for the titration with thorium nitrate, but the colour change at the end-point was not considered satisfactory. Cheng' has shown that in the determination of chlorine and bromine, the colour of the end-point is greatly enhanced if the determination is carried out in a mixture of water and an organic solvent such as ethanol, methanol or isopropanol. Experiments on these lines were then conducted for the titration of fluoride with thorium nitrate, and, as isopropanol was the solvent chosen by Cheng for determining chlorine and bromine, this solvent was used in the present work.To each of two flasks, one of which contained 25 ml of isopropanol and water (4 + I), and the other, 25 ml of distilled water, were added 3 drops of indicator (A or B) and 1 drop of 2 N nitric acid. The isopropanol solution turned yellow, but the aqueous solution showed no change. Both solutions turned purple on adding 1 drop of thorium nitrate solution, but the colour of the propanol solution was much more intense. Screening the indicator with methylene blue made the end-point even more distinctive, and in the titration of fluoride the colour change was from green to blue - purple. Successive titrations of 2 ml of 0.01 N hydrofluoric acid in a mixture of 3 ml of water and 20 ml of isopropanol with 0.02 N thorium nitrate required 0.98, 0.99, 0.98, 0-98 and 0.99 ml.Similar experiments conducted with orthophosphoric acid solutions gave excellent end- points. In the titration of sulphate solutions, however, the end-points were poor, and as they were not quantitative this titration was not investigated further. The presence of phosphorus and sulphur interferes with the determination of fluorine and their removal is described later in this paper. METHOD OLIVER: DETERMINATION OF FLUORINE OR PHOSPHORUS IN All combustions were carried out in 250-ml silica oxygen flasks.8 Solochrome cyanine R-Prepare a 0.25 per cent. solution in 95 per cent. ethanol and filter illethylene blue solution, 0.05 per cent., w / v , aqueous. Thorium nitrate, 0-02 N (0.005 M)-Dissolve 2.7610 g of thorium nitrate tetrahydrate, Th(NOJ4.4H,O, in distilled water and make up to 1 litre.Isopropanol-Use AnalaR grade. DETERMINATION OF FLUORINE- Weigh accurately sufficient of the compound to give approximately 1 mg of ionised fluorine. Wrap it in a square of filter-paper and place it in the platinum spiral. Transfer 4 ml of distilled water into a 250-ml silica flask and flush it with oxygen, Light the tab and plunge the spiral into the flask. When the combustion is complete, shake the flask well and allow it to stand for 10 minutes. Wash down the spiral and stopper with the minimum amount of water (1 to 2 ml) and gently boil the contents of the flask for about 10 seconds REAGENTS- into a bottle. The solution is quite stable.December, 19661 ORGAKIC COMPOUNDS BY A MICRO-TITRIMETRIC METHOD 773 to expel carbon dioxide.Cool the flask and add 20 ml of isopropanol. Then add 0-3 ml of Solochrome cyanine R indicator and 3 drops of methylene blue. The colour should now be green; if not, add 1 drop of 2 N nitric acid. Titrate with 0-02 K thorium nitrate to a blue - purple end-point (when the green colour begins to darken, the thorium nitrate should be added slowly with vigorous shaking of the flask). The thorium nitrate is standardised empirically by combusting standard organic fluorine compounds. The results obtained by this method are shown in Table I. TABLE I DETERMINATION OF FLUORINE IN THE ABSENCE OF SULPHUR AND PHOSPHORUS Compound Trifluoroacetanilide M.A.S. . . . . . . p-Fluorobenzoic acid M.A.S. . , . . . . Trifluoromethylbenzoic acid M.A.S.. . . . 2,5-Di-(2-fluorophenyl)-oxadiazole 1,3,4 . . 2-(2-FIuorophenyl)-5-phenyloxadiazole 1,3,4 Fluoxymesterone . . . . . . . . C14H10N02F3 * * . . . . . . . . C21H2i"20F3 . . . . .. . . . . C21H29N08F3 - * . . . . . . . . CloHl2NO2F . . . . . . . . . . C,H,NO,F, . . . . * . . . .. . . . . . . . . . . . . . . . . . . .. Weight, mg 2.983 3.125 3.068 3.130 2.979 3.111 5.300 4.857 3.155 5.879 7.082 8.290 9.237 3.736 5.264 5.278 6.100 3.922 Fluorine r A - found, required, per cent. per cent. 30.25 30.14 30.33 30.14 29.92 30.14 30.04 30.14 30.20 30.14 29.95 30.14 13.64 13.56 13-62 13-56 29.93 29.98 14.92 14.72 7.56 7.92 7-72 7.92 5-76 5.65 20.32 20.25 15.0 15.0 14.38 14.2 18.9 18.9 9.62 9.64 Difference, per cent. so.11 +0*19 - 0.22 -0.10 + 0.06 -0.19 + 0.08 + 0.06 - 0.05 + 0.20 - 0.37 - 0-20 + 0.10 + 0.08 Nil f0.18 - 0.02 Nil REMOVAL OF PHOSPHORUS AND SULPHUR- Soluble salts of barium, lead, zinc, magnesium and silver were used for the attempted removal of phosphorus (assumed to be present as orthophosphate), and barium and lead for the removal of sulphur as sulphate.Only silver gave complete recovery of fluoride in the presence of phosphorus, and neither barium nor lead gave complete recovery of fluoride in the presence of sulphur. However, complete removal of sulphate was obtained by the use of benzidine. REMOVAL OF PHOSPHORUS- The method of Colsong for the removal of phosphorus in the determination of sulphur was used, except that the ion-exchange resin procedure was omitted as excess of silver ions has no effect on the titration with thorium nitrate.REAGENT- Silver oxide-Prepare as described by Colson. After the contents of the flask have been briefly boiled, add about 50 mg of silver oxide sludge and boil for about 1 minute. Cool the flask and filter through a small Hirsch funnel into a titration flask. Wash out the flask with the minimum amount of water and add isopropanol to give a final strength of 70 to 80 per cent. Carry out the titration as for fluorine. The addition of 1 drop of 2 N nitric acid is necessary to neutralise the slight solubility of the silver oxide. Determine the blank value. REMOVAL OF SULPHUR- Bring the contents of the flask to the boil and add 2 ml of 1 per cent. w/v solution of pure benzidine in 96 per cent. ethanol; boil for a further 15 seconds.Allow the flask to cool under running tap water for a minimum of 1 hour, and then filter into a titration flask as above and carry out the titration as for fluorine.774 OLIVER The excess benzidine will need to be neutralised with 2 N nitric acid. Table I1 shows the results obtained with some compounds that contain fluorine and either phosphorus or sulphur. TABLE I1 DETERMINATION OF FLUORINE WHEN SULPHUR OR PHOSPHORUS IS PRESENT Weight , Compound mg Trifluoroacetanilide . . . . . . . . 3.160 (+ phenylthiourea) . . . . . . . . 3.288 3.362 5.444 Cl,Hl,N,O,SF . . . . .. . . 8.317 C,,H,,NPF, . . . . . . . . . . 3.504 3.890 C1,Hl,F3SN3HCl.H,0 . . . . . . 4-848 C18H16N202SF3 . . . . .. . . 4.485 Fluorine =required: per cent. per cent. 29.7 30.14 30.65 30.14 30.0 30-14 18.16 17-94 18.0 17-94 15.78 16.00 6.18 6-20 25.1 24.6 24-88 24.6 Difference, per cent.+0.51 + 0.22 + 0.06 - 0.22 - 0.02 + 0*50 + 0.28 - 0.44 -0.14 DETERMINATION OF PHOSPHORUS- The method and reagents are the same as those described under Determination of Fluorine. Standardise the thorium nitrate empirically with standard organic phosphorus compounds. Owing to the lack of organic phosphorus standards only triphenylphosphine can be quoted, although research compounds have been successfully analysed. Table 111 shows the results obtained with triphen ylphosphine. TABLE I11 DETERMINATIOK OF PHOSPHORUS I N THE ABSENCE OF FLUORINE AND SULPHUR Phosphorus - Vl‘eight, found, required, Difference, Compound mg per cent. per cent. per cent. Triphenylphosphine . . .. .. . . 4.068 11-70 11.80 -0.10 4.614 11-85 11-80 + 0.05 3.977 12-06 11-80 + 0.26 4.893 11-70 11.80 -0.10 DISCUSSION The method described gives excellent results for fluorine or phosphorus when no inter- fering elements are present. It is not necessary to add buffers to maintain a definite pH. Although phosphorus and sulphur can be removed when the determination of fluorine is required, it has not been found possible to remove fluorine or sulphur when requiring to determine phosphorus. 1. 2. 3. 4. 5. 6. 7. 8. 9. REFERENCES Schoniger, W., Mikrochinz. Ada, 1955, 123. Wilson, C. T,. , and Wilson, D. W., Editors, “Comprehensive Analytical Chemistry,” Elsevier Willard, H. H., and Horton, C. A., Analyt. Chem., 1950, 22, 1190. Dahle, D., Honnar, K. V., and Wiechmann, H. J., J . Ass. Off. Agric. Chem., 1938, 21, 459. Clark, S. J., “Quantitative Methods of Organic Microanalysis,” Biitterworths Scientific Publica- tions, London, 1956, p. 132. Milton, R. F., and Waters, W. *4., Editors, “Methods of Quantitative Micro-Analysis,” Edward Arnold & C o , London, 1949, p. 191. Cheng, F. W., Microchem. J . , 1969, 3, 537. Johnson, C. A,, and Leonard, M. A., Analyst, 1961, 86, 101. Colson, A. F., Tbid., 1963, 88, 26. Piiblishing Co., Amsterdam, London, New York and Princeton, Volume lB, p. 558. Received November 17t8, 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100771

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

Analyst, December, 1966, Vol. 91, pp. 775-778 775 The Colorimetric Determination of Boron in Soils, Sediments and Rocks with Methylene Blue BY R. E. STANTON AND ALISON J. McDONALD (Defiartment of Geology, Imperial College of Science and Technology, London, S . W.7) A method is presented for the determination of boron in soils, sediments and rocks. The sample is decomposed by a mixture of hydrofluoric and sulphuric acids, and the complex formed between fluoroborate ions and methylene blue is extracted with 1,S-dichloroethane. Boron is determined either by visual colour of the blue complex, or by spectrophotometry. The method is rapid and sensitive. THE reaction of the fluoroborate ion with methylene blue has been applied to the deter- mination of boron in soils, sediments and rocks, following its use in the analysis of iron and steel,1,2 and the procedure described below has been developed.METHOD REAGENTS- Sulphuric acid, 10 N-Prepare from analytical-reagent grade acid. Hydrojuoric acid, 40 per cent. w/w, analytical-reagent grade. Methylene blue, 0.08 per cent. w/v, aqueous. 1,2-Dichl oroet hane . Sodium tetraborate-Decahydrate, analytical-reagent grade. Standard boron solutions-Dissolve 0.4408 g of sodium tetraborate in 10 N sulphuric acid, and dilute with this acid to 500 ml in a calibrated flask to give a solution containing 100 pg of boron per ml. Dilute further with 10 N sulphuric acid to give solutions containing 2, 5 and 1Opg of boron per ml. PROCEDURE- Weigh 0.1 g of sample into a polythene beaker, and add 2-5 ml of 10 N sulphuric acid and 0.5 ml of 40 per cent.hydrofluoric acid. Stir the solution with a polythene rod, cover and leave to stand at room temperature for 2 hours. Add 2 ml of water, mix and leave t o stand for 15 minutes. Transfer 1 ml of the clear solution by pipette into a test-tube calibrated at 15 ml. Add 1 ml of 0.08 per cent. methylene blue and dilute to 15 ml with water. Add 5 ml of 1,2-dichloroethane, stopper the tube and shake it vigorously for 30 seconds. Allow the phases to separate and compare the intensity of colour in the organic layer with a standard series. A reagent blank must be determined. PREPARATION OF THE STAKDARD SERIES- Into eleven polythene beakers transfer by pipette, from the dilute standard solutions, 0, 1.0, 2.0, 3.0, 4.0, 5-0, 7.5, 10.0, 15-0, 20.0 and 25.0 pg of boron, respectively.Add sufficient 10 N sulphuric acid to each beaker to give a total volume of 2-5 ml. Add 0.5 ml of 40 per cent. hydrofluoric acid, mix well and leave to stand for 2 hours. Then add 2 ml of water and mix. Remove 1 ml from each solution with a pipette and treat as described for a sample solution in Procedure. DISCUSSION OF THE METHOD This method was developed for geochemical research studies in which the boron was derived from the mineral colemanite, and was readily attacked in the cold by a mixture of dilute hydrofluoric and sulphuric acids. Consequently, application of the method to other materials may be restricted by this method of sample decomposition.776 STANTON AND MCDONALD : COLORIMETRIC DETERMINATION [Analyst, VOl.91 TABLE I COMPARISON BETWEEN CRUSHED AND UNCRUSHED SAMPLES Sample - Sample +- Boron, p.p.m. Boron, p.p.m. No. - 20 mesh - 80 mesh No. -20 mesh -80 mesh 1 38 45 2 105 100 3 220 240 4 320 330 5 340 340 6 280 200 7 200 180 8 180 190 Formation of fluoroborate takes place as the sample is being attacked. The acid con- centrations are not critical, but must be kept at the same constant level for both samples and standards, and 10 N sulphuric acid is used so that alkaline samples produce no significant variation in acidity. The volume of 40 per cent. hydrofluoric acid is kept low to minimise the colour extracted from the zero standard, The time allowed for this stage is not critical; some samples went completely into solution within 1 hour, whereas others appeared unaltered, even after standing overnight.Nevertheless, boron was always completely converted into the soluble fluoroborate within 2 hours. Samples have been left in contact with the acids for up to 3 days without ill effect, although there is great danger of volume loss by evaporation. Complete recovery was achieved when boron was added to samples as sodium tetraborate ; it was also found possible to increase the sample weight to 250 mg without any other alteration to the procedure. As it was necessary for geological reasons to analyse the -20-mesh fraction of many samples, a comparison was made between results obtained when this fraction was crushed to pass 80 mesh and on the uncrushed material. From the results given in Table I it will be seen that, in general, there is no significant difference, although analysis of the coarser material may introduce greater sampling errors.There is always a slight colour extracted from the zero standard that is dependent upon the final aqueous phase acidity, decreasing with decreasing acidity while the efficiency of TABLE I1 EFFECTS OF VARIOUS ELEMENTS ON THE DETERMINATION OF BORON Amount Boron added, present, Element mg CLg Aluminium . . . . 5.0 0 5.0 1-0 Arsenic (as 0.1 0 Na2HAs0,.7H.01 0.1 1.0 Barium . . Calcium . . Chloride . . Chromium (as Chromium (as CrC1,) K2Crd-3,) Cobalt . . Copper . . Iron(I1) . . Iron(I1J) . . Magnesium . . - I . . 0.1 0.1 . . 5-0 5.0 . * 1.0 1.0 0.04 0.04 1.0 1.0 0.1 0.1 . 0.1 0.1 . . 0.1 0.1 . . 5-0 5.0 . . 5.0 5.0 . . 5.0 5.0 0 1.0 0 1.0 0 1.0 0 1.0 0 1.0 0 1.0 0 1.0 0 1.0 0 1.0 0 1.0 0 1.0 Boron found, CLP (0.1 1.0 3.5 4.5 <om1 1.0 0.1 1.0 0.2 1.0 <o-1 1-0 >5*0 B5.0 >5*0 >5-0 0.2 1.0 (0.1 1.0 <0.1 1.0 <o-1 0.9 <0*1 1.0 Element Manganese .. .. Mercury( 11) .. Molybdenum (as Na2M00,.2H20) Nickel . . . . Nitrate . . . . Potassium , . .. Silicon (as SiO,) Silver . . Sodium . . Titanium . . Tungsten (as Na,W0,.2H20) Vanadium .. ,. Zinc .. .. Amount Boron added, mg 1.0 1.0 0.1 0.1 0.1 0.1 0.1 0.1 1.0 1.0 1.0 1.0 2.5 2.5 0.1 0.1 5.0 5.0 1.0 1.0 0.1 0.1 0-1 0.1 0.1 0.1 present, CLg 0 1-0 0 1.0 0 1-0 0 1.0 0 1.0 0 1.0 0 1.0 0 1.0 0 1.0 0 1.0 0 1.0 0 1.0 0 1.0 Boron found, CLg <0.1 1.0 0.4 1.2 t 0 . 1 1.0 <0.1 1.0 3.0 4.0 < O . l 1.0 <0*1 1.0 <o-1 1.0 <0*1 1.0 (0.1 1.0 tom1 1.0 <0*1 1.0 < O * l 1.0December, 19661 OF BORON IN SOILS, SEDIMENTS AND ROCKS WITH METHYLENE BLUE 777 extraction of the fluoroborate complex increases.It is therefore important that the final acid concentration should be constant, and if more than 1 ml of sample solution is used for analysis, the preparation of the standard series must be adjusted to obtain similar conditions. Likewise, when less than 1 ml is used, compensating amounts of hydrofluoric and sulphuric acids must be added with the aliquot. The standard series shows an increasing intensity of blue from a slightly blue zero. The molarity of methylene blue in the final aqueous phase must not be less than four times that of the boron, an increase of 50 per cent. having no effect upon the intensity of colour in the organic phase.The complex is readily extractable, agitation for 15 seconds is probably adequate, and it is stable for 2 days. Benzene, carbon tetrachloride, chloroform, isopentyl acetate, isopentanol, toluene, various petroleum spirits and white spirit were tried unsuccessfully as alternative solvents. I t was found convenient to use polythene ice-cube trays for the acid treatment of the sample, a second tray being used as a cover; pipettes were made from quartz glass or poly- thene. Borosilicate glassware must, of course, be avoided, and even soft glass can contain a few per cent. of boron and so cause contamination. Quartz glass test-tubes were used for the colorimetry, although lead glass is also satisfactory and such test-tubes are much cheaper.Bark corks were unsatisfactory as they absorbed a considerable amount of methylene blue which did not wash out and could be liberated during a later test to give high results; the use of silicone rubber stoppers eliminated this source of error. A spectrophotometric finish could be adopted, the boron - methylene blue complex exhibiting an absorption maximum a t 640 mp. A blank determination should be used as reference. INTERFERENCE FROM OTHER ELEMENTS- Dichromate, nitrate, arsenate and mercury (11) ions have adverse effects, but the concentrations at which interference occurs are unlikely to be obtained in normal samples. RE s u LTS The effects of various ions are shown in Table 11. The reproducibility of the colorimetric stage was tested by using several aliquots from one sample solution.A mean value of 177.5 p.p.m. was obtained, with a standard deviation of k6.1 p.p.m. Replicate analyses on three samples gave mean values of 32-5, 177-5 and 233 p.p.m., with standard deviations of -I 2.8, & 6-1 and I_t 12.1 p.p,m., respectively. Several samples, including the standard rocks G1, W1 and Syl, were analysed by the proposed method and by the official A.O.A.C. m e t h ~ d . ~ The results are shown in Table 111, Sample No. G l w 1 SYl 1 2 3 4 6 6 7 8 9 10 11 TABLE I11 COMPARISON OF RESULTS FROM VARIOUS METHODS Boron, p.p.m. Proposed A.O.A.C. Mass procedure method Spectrography spectrometry 2.8 <2 < 10 12 23 17 18 72 69 70 - 184 173 80 80 92 91 122 137 134 137 166 160 188 182 186 182 182 182 188 182 44 46 r A - - - - - - - - - - - - - - - - - - - - - - - together with some spectrographic4 and mass spectrometric5 determinations on the standard rocks. The low values for G1 and W1 are likely to be caused by the inadequacy of the acid treatment of the particular mineral containing the boron.778 STANTON AND MCDONALD The work described forms part of the programme of the Applied Geochemistry Research Group under the direction of Professor J. S. Webb. REFERENCES 1. 2. 3. Pasztor, L., Bode, J. D., and Fernando, Q., Analyt. Chem., 1960, 32, 277. Goto, H., and Takeyama, S., Nippon Kink. Gakk., [ J . J a p . Inst. Metals], 1961, 25, 588. Horwitz, W., Editor, “Official Methods of Analysis of the Association of Official Agricultural Chem- ists,’’ Eighth Edition, The Association of Official Agricultural Chemists, Washington, D.C., 1955, p. 38. 4. Heier, K. S., Norsk Geol. Tidsskr., 1964, 44, 205. 5. Brown, R., and Wolstenholme, VT. -4., Nature, 1964, 201, 598. Received June 28th, 1966

ISSN:0003-2654    

DOI:10.1039/AN9669100775

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

Analyst, December, 1966, Vol. 91, pp. 779-782 779 The Analysis of the Organophosphorus Pesticide, Fenitrothion, an Infrared Method BY R. B. DELVES ( Woodstock Agricultural Research Centre, “Shell” Research Limited, Sittingbourne, Kent) AND v. P. WILLIAMS (Milstead Laboratory, “.Shell” Research Limited, Sittingbourne, Kent) An infrared method is described for determining the fenitrothion [00-di- methyl-0-( 3-methyl-4-nitrophenyl) -phosphorothioate] content of technical material after chromatography over silica gel. The fenitrothion is eluted with mcthylene chloride, and after evaporating the eluate to dryness the residue is dissolved in carbon disulphide to give a concentration of fenitrothion in the range 0.8 to 1 . 1 per cent. w/v. Measurements taken a t three absorption peaks in conjunction with related minima are used to calculate the fenitro- thion content from previously prepared calibration graphs that relate absorbance to fenitrothion content.The standard deviation of this method, based on ten samples of technical material, is 0.53 per cent. THE increasing use of organophosphorus pesticides necessitates the development of more specific methods of analysis. Non-specific methods, such as those based on the reduction of the nitro group, for example the method of O’Keeffe and Averelll for technical parathion, tend to give erroneously high results owing to the presence of “related impurities.” A search of the literature has revealed some general papers on fenitrothion [00-dimethyl-0-(3-methyl-4-nitro- phenyl)-phosph~rothioate]~~~~~~~ and two concerned with its analytical determinatiom6 p 7 One of these analytical methods involves polarography after separation of technical material by thin-layer chromatography, and the other utilises gas - liquid chromatography for residue analysis.Neither method was considered suitable for our purposes, and the object of our work has been to develop a rapid, specific infrared method for determining the fenitrothion content of technical and formulated materials (Notes 1, 2 and 3). EXPERIMENTAL In an attempt to isolate fenitrothion from associated impurities, preliminary separations were carried out by loose-layer chromatography. Examination of several solvent systems on the adsorbents, alumina, silica gel and Florisil, showed that a good separation could be obtained on silica gel by using methylene chloride as developing solvent.Chromatography over a column of silica gel (50 g) with methylene chloride as developing solvent isolated the major component from technical material (0.5 6). After elution of this material, which represented about 95 per cent. w/w recovery, a clear fraction was obtained NOTES- 1. This method of determination can also be applied to liquid formulations as follows- Make a slurry of 60 g of silica gel with petroleum spirit (boiling range 40” to 60” C) and methylene chloride (1 + 1 viv) and place it in the chromatographic column; drain off exress solvcnt. Take a sufficient formulation to contain 0-2 g of fenitrothion and transfer i t quantitatively with a minimum amount of petroleum spirit - methylene chloride t o the top of the silica gel column.Place a beaker under the column and allow the sollition to percolate into the adsorbent. -4dd small amounts of solvent t o ensure complctc adsorption of the fenitrothion into thc silica gel. Continue to elute with petroleum spirit - methylcne chloride (about 1.50 ml) until the formulation solvent is removed. Elute with 250ml o f methylene chloride and continue from this point as directed under Chromato- graphic Separation of Penitrothion. 2, Normally, formulation ingredients and decomposition products (if any) that are formed on storage will be retained on the adsorbent. 3. Possible interference will be detected if the conccntration of fenitrothion with any one of the peaks differs by more than & 3 per cent.(relativc) of thc mean. If this occurs, the particular value should be discarded and the remaining concentrations averaged.780 DELVES AND WILLIAMS: ANALYSIS OF THE ORGANOPHOSPHORUS [Analyst, Vol. 91 before the first impurity was eluted. The other impurities remained on the column as four separate zones. PROOF OF STRUCTURE OF THE MAJOR COMPONENT- The major component isolated by chromatography was examined by (a) mass spectro- metry with an A.E.I. Ltd. M.S. 2H mass spectrometer, (b) infrared spectrometry with a Grubb Parsons spectrometer and (c) thin-layer chromatography, by using a thin layer (275 p) of silica gel G and chloroform or methylene chloride - benzene (1 + 1, v/v) as develop- ing solvents. The chromatoplate was sprayed with 2,6-dichloro-~-benzoquinone-4-chlorimine, which appears to be specific for the P + S group by forming a red coloured derivative.* The mass spectrometer showed a parent peak at m/e 277 (fenitrothion) and intense fragment ions at m/e 260, m/e 125 and m/e 109.The fragment ion at m/e 260 was attributed to the elimination of OH from the 3-methyl-4-nitro substituents of fenitrothion. Beynon et aL9 have reported that o-nitrotoluene eliminates OH and this is accompanied by ring closure. This evidence confirms that the methyl and nitro groups are ortho to one another in the aromatic ring of fenitrothion. The fragment ion at m/e 125 was formed by the cleavage of the P-0 bond in the P-0-aromatic group to give a substituted phenoxy ion. The intensity of the ion a t m/e 109 was comparable to that of the ion a t m/e 125.It appears that there is a re-arrangement within the mass spectrometer followed by elimination of the phosphorus moiety to produce an ion at m/e 109. The infrared spectrum showed the presence of P-0-aromatic, P-0-methyl and probably P -+ S groupings. P -+ 0 and P-S-aromatic groupings were absent. The P -+ S group was confirmed by thin-layer chromatography, which showed one component only to be present. Infrared analysis of the phenol isolated after hydrolysis of the major component showed this to be identical with 4-nitro-m-cresol (Sadtler infrared spectrogram No. 23685). This confirmed that the methyl and nitro groups are in the 3 and 4 positions, respectively. Thus, the analytical evidence obtained by mass spectrometry, infrared spectrometry and thin-layer chromatography shows that the major component is fenitrothion, the structure of which is- APPARATUS- NO, I I I CH,O-P+ S OCH, METHOD Infrared s#ectrophotomcter-An instrument capable of quantitative analysis in the 2 to Sealed liquid absorption cell-0.4-mm path length.Hypodermic syringe-Glass, Luer type, 2-ml capacity. Chromatographic columns-15 x 500 mm, fitted with a glass tap and a solvent reservoir 15-p region is required. of approximately 500 ml. REAGENTS- Silica geLWhatman Chromedia SG3 1. Benzene, general-purpose reagent grade. Methylene chloride, general-purpose reagent grade. Carbon disulphide, R.D. H . Ltd. general-purpose reagent grade or equivalent. Fenitrothion-Analytical standard material of purity greater than 99 per cent.Prepare material suitable for analytical calibration purposes by using the chromatographic separation method.December, 19661 PESTICIDE FENITROTHION BY AN INFRARED METHOD 781 CHROMATOGRAPHIC SEPARATION OF FENITROTHION- Prepare a slurry of 50 g of silica gel with methylene chloride and transfer it to a chromato- graphic column with a cotton-wool plug to retain the adsorbent. Allow the solvent to pass through the column until the meniscus reaches the top of the adsorbent. Weigh, to the nearest 0.1 mg, an amount of sample that contains approximately 0.2 g of fenitrothion. Dissolve the fenitrothion in a minimum of benzene (3 ml) and transfer the solution quantitatively to the top of the column by using methylene chloride. Allow the solvent to percolate into the silica gel, then wash the inside of the chromatographic column with three 5-ml portions of solvent, allowing each portion to penetrate the adsorbent independently.Elute with 250 ml of methylene chloride and collect the eluate in a tared 400-ml beaker. When the solvent reaches the top of the adsorbent, stop the flow of solvent, wash the tip of the column with solvent and replace the 400-ml beaker with a 100-ml beaker. Evaporate the solvent contained in the 400-ml beaker at room temperature by using a forced draught. This is the fenitrothion residue. Collect a further 50-ml fraction and evaporate to dryness in a forced draught to confirm the complete elution of fenitrothion by the absence of residue. In the unlikely event of a residue being present, examine it by infrared spectroscopy as it may be a related impurity.Calculate the percentage extract (to give a guide to the fenitrothion content) and submit the extract to quantitative infrared analysis. Re-weigh the tared 400-ml beaker and obtain the weight of the extract. INFRARED ANALYSIS CALIBRATION OF APPARATUS- Into each of several 20-ml calibrated flasks, weigh (to the nearest 0.1 mg) 160, 180, 200 and 220-mg amounts of the standard sample of fenitrothion. Dissolve each in carbon di- sulphide, dilute to the marks, and mix thoroughly. The strengths of these solutions will therefore be 0.8, 0.9, 1.0 and 1.1 g per 100 ml. Fill the 0.4-ml cell with the most dilute of these standard solutions by means of the hypodermic syringe. Adjust the spectrophotometer to the optimum instrument settings with respect to gain, slit width, balance, response, chart speed and wavelength-scanning speed.Make duplicate scans over the 7.0 to 9.0-p region. Flush out the cell with carbon disulphide, dry, re-fill, in turn, with each of the remaining calibration solutions and, without changing instrument conditions, repeat the duplicate scans over the 7-0 to 9-0-p region. For each of the scans of the calibration solutions measure the transmitted radiant power, as a proportion of the incident radiant power, at the following wavelengths- (;) From the absorption peak at about 7-45 p to the minimum, i.e., reference point at (ii) From the absorption peak at about 8.05 p to the minimum, i.e., reference point at (iii) From the absorption peak at about 8.05 ,U to the minimum, i.e., reference point at (iv) From the absorption peak at about 8-55 p to the minimum, i.e., reference point at Construct a calibration graph for each absorption peak by plotting the percentage transmission on a logarithmic ordinate zleysus the corresponding concentration (g per 100 ml) on a linear abscissa.about 7.60 mp. about 7-95 p. about 8.30 p. about 8-50 p. Construct the line of best fit through each set of four points. PROCEDURE- Dissolve the material obtained from the chromatographic procedure in a volume of carbon disulphide sufficient to give a concentration of fenitrothion in the range 0-8 to 1-1 per cent. w/v. Fill the same 0.4-mm path-length cell that was used in calibrating the instrument with each sample solution in turn, and make duplicate scans over the 7.0 to 9-0-p region.The same instrument conditions must be used as for the calibration. Calculate the percentage transmission of the three specified peaks for each sample.782 DELVES AND WILLIAMS CALCULATION- fenitrothion in each solution. differ by more than 4 per cent. of the mean. Read from the appropriate calibration graph the concentration, in g per 100m1, of Take the average of the four concentrations thus obtained. Concentrations should not Calculate the fenitrothion content by using the following equation- c x v w Fenitrothion content per cent. by weight = ~ where C is the average concentration as read from calibration graphs, g per 100 ml; V is the volume of sample solution, ml; and W is the original weight of sample taken for chromatographic “clean-up,” g.RESLJLTS AKD CONCLUSIONS The results obtained by using the method described are shown in Table I. TABLE I FENITROTHION CONTENT OF TECHNICAL MATERIAL Technical Fenitrothion content, per cent. w/\v Standard fenitrothion, -h- deviation, sample number Individual Mean per cent. 1 92.4, 93.4, 92.6, 93.4, 92.5, 93.1 0.53 2 96.9, 97.5 97.2 - 3 96-4, 97.3 96.8 - 4 96-9, 97.3 97-1 - 92.8, 92.7, 93-8, 93.8, 93.1 The method described is specific and is used routinely for determining the fenitrothion content of technical material and its formulations. I t has proved to be satisfactory. The standard deviation of the method, which includes adsorption chromatography and infrared spectroscopy, is 0-53 per cent. We thank Mr. F. Wirtz-Peitz of Cologne University who, as an overseas student under IAESTE (U.K.), carried out much of the experimental work reported in this paper. 1. 2. 3. 4. 5. 6. 7. 8. 9. REFERENCES O’Keeffe, K., and Averell, P. R., Analyt. Chem., 1951, 23, 1167. Nishizawa, Y., Fujii, I<., Kadota, T., Miyamoto, J., and Sakamoto, H., Agric. & Biol. Chem., Nishizawa, Y., Nakagawa, M., Suzuki, Y . , Sakamoto, H., and Mizutani, T., Ibid., 1961, 25, 597. Schrader, G., “Die Entwirklaing neuer inseklizider Phosphorsaure-Ester, ” J‘erlag Chcmie GmbH, LTchijama, M., and Okui, S., J . Fd Hyg. Soc. Japuw, 1962, 3, 277; Chrm. -4bsti/., 58, 3839b. Kovac, J., J . Chvomat., 1963, 11, 412. Dawson, J . A,, Dvriegan, L., and Thain, E. M., r2nalysf, 1964, 89, 495. Braithwaite, n. P., h’utzrr~, 1963, 200, 1011. Beynon, J . H., Saundcrs, R. A., and li~illiams, A . E., Tiidiistrie Chifl2. Belge, 1964, 4, 311. 1961, 25, 605. WeinheimiBergstr., 1963, p. 292. Received November loth, 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100779

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

Analyst, December, 1966, Vol. 91, p p . 783-789 783 The Thermal Analysis of Lichens Growing on Limestone BY B. D. MITCHELL, A. C. BIRNIE (The Macaulay Institute for Soil Research, A berdeen, Scotland) AND J. K. SYERS (Department of Soil Science, Lincoln College, New Zealand) In an investigation of the pcdogenic activities of lichcns growing on limestones it was found that they varied greatly in their calcium oxalate content. As chemical methods of determining calcium oxalate in such material are somewhat tedious, detailed qualitative and quantitativc studies of oxalate in specific lichen species were made by using differential thermal and thermogravimetric analysis. The results show that in a controlled atmosphere of oxygen-frec nitrogen, thermal methods provide a rapid means of identifying and determining calcium oxalate in lichens, and.also enable an assessment to be made of the non-oxalate derived carbonate in the sample. IT has been recognised for some time that there is a correlation between the amounts of calcium and oxalate in many plants, and it has been claimed that calcium oxalate is abundant in all plant species inhabiting limestone. However, in the course of an investigation of the pedogenic activity of lichens, Syersl found that those growing on limestone varied widely in their oxalate content. Chemical methods of determining oxalate in plant materials are tedious, especially for small amounts. Recently, Mitchell and Knight2 demonstrated that oxalate in higher plants, for example, Beta vulgaris and Efiilohizcm Zaizceolatiinz, may be conveniently monitored by thermal methods, and in view of this a detailed study of calcium oxalate in specific lichen species was conducted by using thermal methods.Because the energy changes occurring in a material when heated may vary according to the atmosphere enveloping it, the thermal characteristics of lichen species were determined in oxygen, nitrogen and carbon dioxide to ascertain under which of these atmospheres the calcium oxalate reactions were distinct from other pyrolysis reactions occurring in the lichens. Further, as the area of a peak in a thermal curve is indicative of the amount of reactant, it was necessary to establish which of the thermal peaks associated with the decomposition of calcium oxalate was the most satisfactory for its quantitative determination.METHODS MATERIALS- Seven lichen species were examined, namely, Asfiicelia calcaria, Calofilaca hefipiana, Physcia adscendem, Physcia caesia, Rhizocavpon calcaveii m, Verrzccaria 12 ipescens and Xantlzoria parietina. The samples, which were obtained by scraping the surface of lichen-colonised limestone, were dried at 40" C and ground to pass through a O.5-rnm sieve. PROCEDURES- The differential thermal analysis curves were determined under controlled-atmosphere conditions ; equipment and experimental details have been described elsewhere by Stewart, Birnie and MitchelL3 The tliermogravimetric characteristics of the lichens in a nitrogen atmosphere were also determined by using a TR 01 Stanton thermobalance from which the differential thermogravimetric curves were derived.RESULTS The complete-combustion curve for calcium oxalate monohydrate (Fig, 1 , curve D) exhibits an endothermic peak at 243" C, indicating the loss of water of hydration. The series of exothermic effects between 450 and 500" C traces the oxidation of the oxalate to carbonate, and the decomposition of the latter to calcium oxide is shown by the 900" C endothermic peak.784 MITCHELL, BIRNIE AND SYERS: THERMAL [Analyst, Vol. 91 In an inert atmosphere calcium oxalate decomposes in the following three stages- CaC,O,.H,O = CaC,O, + H,O.. . . . . * * (1) . . - * ( 2 ) . . . - (3) CaC,O, = CaCO, + CO . . . . CaCO, = CaO + CO, . . . . All three reactions are endothermic and the heats of reaction (H" 298" K, kcal. per mole) are 13.3, 15.5 and 42-5, respectively (Simons and Newkirk,).Under the dynamic heating con- ditions of differential thermal analysis, the peaks associated with these reactions occur at about 235O, 500" and 900" C (Fig. 2, curve D). Thus, in the interpretation of the thermal curves of lichens, endothermic effects in the 150" to 250" C region are regarded as indicative of the dehydration of calcium oxalate, effects between 400" and 600" C of oxalate decomposi- tion, and in thc 700" to 900" C range of carbonate decomposition. Reasons for the fluctu- ations between the peak temperatures of calcium oxalate alone and the peaks on the lichen curves due to the presence of calcium oxalate will be dealt with later. The thermal characteristics of the seven lichen species fall into three well defined groups, depending on the amount of calcium oxalate and calcium carbonate present. Thus Physcia adscendens, Physcia caesia and Xanthoria parietina, which contain small amounts of calcium oxalate, have closely similar thermal curves, as do the oxalate-rich species Rhizocarpoiz calcareum, Aspicilia calcaria and Caloplaca heppiana.The Verrucaria nigrescens sample is unique in that it contains an appreciable amount of calcium carbonate. EFFECTS IN AN OXYGEN ATMOSPHERE- The complete-combustion curves for Physcia adscendens and Verrucaria nigrescens (Fig. 1, curves A and B) exhibit exothermic peaks at about 300", 430" and 500" C and the peak areas decrease with increasing temperature. Complete-combustion patterns of this type are common for fresh plant material and are thought to reflect concentrations of carbohydrates of high molecular weight.2 The combustion curve of Rhizocarpon calcareum (curve C) is D .I- v 900 243 I A Temperature, "C - Fig.1. Differential thermal analysis curves in an oxygen atmosphere (10 ml per minutc) for: -4, Physcia adscendens; B, Verrucaria nagrescens ; C, Khizocavfion calcareurn ; and D, calcium oxalate monohydrate, (15-mg samples diluted with 50 mg of calcined kaolin, loosely packed : recording sensitivity, 170 pvolts pcr inch; hcating rate, 10" C per minute)December, 19661 ANALYSIS OF LICHENS GROWING ON LIMESTONE 785 markedly different. The endothermic peak at about 150" C indicates the dehydration of calcium oxalate, and the exothermic system is limited to peaks at 296" and 447" C.The latter peak, from a comparison with that of curve D, is affected by the combustion of calcium oxalate, but the complete-combustion curves are obviously not satisfactory for the un- ambiguous detection of calcium oxalate. EFFECTS IN A NITROGEN ATMOSPHERE- Temperature range 150" to 250" C-The small endothermic peaks at 175" and 177" C on the pyrolysis curves of Physcia adscendens and Verrucaria nigrescens indicate that these materials contain only small amounts of oxalate (Fig. 2, curves A and B). The dehydration of the oxalate in these two lichen species occurs 50" to 60" C lower than that in Rhizocarpon calcareum (curve C ) and that of pure calcium oxalate (curve D). Further, the dehydration of the oxalate in Physcia and Verrucaria occurs in a single stage.The reason for the doubling of the dehydration peak, which is particularly marked in the curve for Rhizocarpon (Fig. 2, I Temperature, "C - Fig. 2. Differential thcrmal analysis curves in a nitrogcn atmosphere (200 ml per minute) for: A, Physcia adscendens ; B, Verrucaria nigrescens ; C, Khizocarpon culcareum ; and D, calcium oxalatc monohydrate, (50-mg samples diluted with 120 mg of calcined kaolin, hard packed; recording sensitivity, 70 pvolts per inch; heating rate, 10" C per minute) curve C), is not absolutely clear. Substantial amounts of magnesium oxalate dihydrate are known to accumulate in certain plant tissue. This magnesium salt dehydrates in the 200" C region. The presence of magnesium oxalate in the lichens would result also in an endothermic peak between 600" and 700" C, marking decomposition to magnesium carbonate, and there is no indication of such a peak.Further, the magnesium contents of these lichens were determined chemically and found to be very low, indeed that of Rhixocarpon was the lowest, being 149 p.p.m. Physcia and Verrucaria contained 500 and 974 p.p.m., respectively. De- hydration of oxalic acid dihydrate occurs at 100" C and the monohydrate decomposes between786 MITCHELL, BIRNIE AND SYERS : THERMAL [Analyst, Vol. 91 180" and 190" C. Free oxalic acid, however, cannot be present in the lichens because the exchangeable calcium is high : Rhizocarpon, 898 milli-equivalents per 100 g ; Physcia, 120 milli- equivalents per 100 g; and Verrucaria, 946 milli-equivalents per 100 g.From evidence of infrared-absorption spectroscopy, not only is calcium oxalate the only oxalate present, but it appears to be exclusively in the monohydrate form. Although the energy changes shown on a differential thermal analysis curve that indicate the loss of sorbed moisture in the sample are not necessarily reflected exactly by the differential thermogravi- metric curve, it is nevertheless significant that the differential thermogravimetric curves of Rhizocarpon calcareum and calcium oxalate (Fig. 3, curves C and D) give no indication of a two-stage dehydration of oxalate. The variation in the dehydration pattern of oxalate, as reflected by the differential thermal analysis curve, may be related to the dilution and hard-packing technique developed for examination of the sample under inert-atmosphere conditions.Hard packing would tend to restrict the egress of water vapour and the effect would be enhanced by increased concentration, particularly in the initial stages. Temperature, "C - Fig. 3. Uiflcrcntial thermogravimetric curvt's in a nitrogen atmosphere (200 1111 per minute) for: 4 , PIzyscia adscrrzdezzs; €3, Verrucavza 9zigvescens; C, Hizizocavpon cnlcaveunz ; and I), calcium oxalatc monohydrate, (sample weight, 100 mg; heating rate, 4' C per minute) Temperature raizge 250" to 400" C-Substantial weight losses between 300" and 400°C are shown on the differential thermogravimetric curves of lichens determined in an inert atmos- phere (Fig. 3, curves A to C), Physcia adscendens losing 52 per cent., and Rhizocarpon calcareum, 21 per cent, Infrared spectroscopy indicated that the Physcia species contained considerably larger amounts of carbohydrate than the Rhizocurpon species.The pyrolysis curves of cellulose and carbo- hydrates of low molecular weight exhibit well defined endothermic peaks about 300" C,5 and attributing, therefore, the weight loss in the 350" C region to carbohydrate decomposition, it is noteworthy that no endotliermic effect is recorded in this region of the differential thermal analysis curves of lichens under inert atmosphere conditions (Fig. 2, curves A to C). There There is no weight loss in this region for calcium oxalate (curve D).December, 19661 AKALYSIS OF LICHENS GROWING ON LIMESTONE 787 is, however, an exothermic reaction, whose intensity decreased with reduction in carbo- hydrate content.As a peak on a differential thermal analysis curve need not necessarily represent a single reaction, but may be the record of the summation of simultaneous reactions, it is conceivable that the endothermic effect associated with the initial decomposition of the carbohydrate component is completely masked by an exothermic reaction involving the products of decomposition. As care was taken to exclude oxygen in these determinations, the exothermic peaks probably resulted from auto-oxidation by organic components of the lichens. Temperature range 400" to 600" C-The absence of an endothermic peak in the region of 500" C on the differential thermal analysis curves of Physcia adscendens and Verrucaria nigrescens (Fig.2, curves A and B) is in accord with a low calcium oxalate content. However, the differential thermogravimetric curve of the former (Fig. 3, curve A) shows a weight loss about this temperature which, by comparision with that for calcium oxalate, corresponds to a content of less than 5 per cent. The corresponding weight loss for Rhixocarpon (curve C) is equivalent to a calcium oxalate content of 60 per cent. Temperature range 700" to 950" C-The pyrolysis curves of Verrucaria izigrescens and Rhixocarpon caZcareum in a nitrogen atmosphere (Fig. 2, curves B and C) exhibit a large endothermic peak at 800" C resulting from the decomposition of calcium carbonate, which in the latter species is derived from calcium oxalate. However, for the Verrucaria sample the calcareous substratum is probably the principal source.The carbonate decomposition peak on the curve of Yhvscia adscendens (curve A) is much smaller and occurs at a considerably lower temperature (705" C), both features being in accord with a lower calcium oxalate content. 3 20 Tern pera t u re, "C -I-- Fig. 4. Differential thermal analysis curves in a carbon dioxide atmosphere (200 ml per minute) for: A, Physcia adscendens ; B, Verrucaria nigrescens ; C , Rhizocarpon cakareum ; and D, calcium oxalate mono- hydrate; E, 1 + 1 mixture of Physcia adscendens and calcium oxalate monohydrate, (50-mg samples diluted with 120 mg of calcined kaolin, hard packed: recording sensi- tivity, 70 pvolts per inch; heating rate, 10" C per minute)788 MITCHELL, BIRNIE AND SYERS: THERMAL [Analyst, Vol.91 EFFECTS IN A CARBON DIOXIDE ATMOSPHERE- The differential thermal analysis curves of lichens determined in a carbon dioxide atmosphere (Fig. 4, curves A to C) are similar to those observed in a nitrogen atmosphere, except in the 700" to 950" C range of curves B and C for Verrucaria and Rhizocarpon, respec- tively, where a doubling of the peak reflecting carbonate decomposition occurs. Although the curves for Physcia and calcium oxalate monohydrate (curves A and D) do not show this doubling phenomenon, that of a mixture (1 + 1) of these materials (curve E) does possess a complex high temperature - peak system, but only when the lichen and oxalate have been intimately mixed (ground for 1 minute in a vibratory ball mill). The lichen samples on reaching 700" C consist essentially of a carbonaceous residue PLUS calcium carbonate and, as the temperature is raised, increasing amounts of carbon dioxide will be produced as decomposition of the latter proceeds.The high temperature - peak pattern could arise from the oxidation of the carbon residue by carbon dioxide, and consequently would represent an endothermic effect with a superimposed exothermic reaction. This effect, however, only occurs under a dynamic carbon dioxide atmosphere when an additional and substantial amount of carbon dioxide is produced in situ, as in the decomposition of samples containing appreciable amounts of calcium carbonate. Under these conditions, the voids in the sample well are completely filled with carbon dioxide. The doubling effect is not observed when nitrogen is the con- trolling atmosphere, but in this instance the carbon dioxide from carbonate decomposition would diffuse more easily from the reaction site.DISCUSSION The results show that calcium oxalate in naturally occurring materials such as lichens may be unambiguously identified on the differential thermal analysis curve, but only when determined in a nitrogen atmosphere. Comparison of the weight loss in the 500" C region of the differential thermogravimetric curves of the lichens with the corresponding weight loss on the differential thermogravimetric curve for a known quantity of calcium oxalate provides a simple and direct estimate of the oxalate in the lichens. The oxalate content of these plants was also determined chemically by a micro method6 and it will be noted (Table I) that while agreement between thermogravimetry and the chemical method is good for high concentrations of oxalate, at low levels the former method is less satisfactory.TABLE I AMOUNTS (PER CENT.) OF CALCIUM OXALATE AND CALCIUM CARBONATE IN LICHENS DETERMINED BY DIFFERENTIAL THERMOGRAVIMETKIC, DIFFERENTIAL THERMAL ANALYSIS AND CHEMICAL METHODS Calcium oxalate, per cent., determined by- differential thermo- gravimetric method Physcia adscendens 5 Rhizocarpon calcareum 60 Verrucaria nigrescens nil Aspicelia calcarea 42 differential* thermal analysis chemical method method 2.7 2.2 0.8 1.4 60 56 48 39 Calcium carbonate, per cent., determined by- - diff erentialt thermo- gravimetric chemical: method method 2.3 ( 5 52 54 7.0 11 21 24 * Determined from 170" C peak area for Physcia and Verrucaria (Fig.2, curves A and B) t Obtained by subtracting the calculated weight loss for calcium oxalate derived carbonate Obtained by treating the dry matter with 0.1 N hydrochloric acid overnight, filtering, and and from 500" C peak area for Rhizocarpon (Fig. 2, curve C). from total weight loss between 700" and 800°C (Fig. 3, curves ,4 to C). then back-titrating the unused acid with alkali. Differential thermal analysis can also provide a quantitative result as the area enclosed by a peak is proportional to the amount of reactant. As the 500" C peak on the differential thermal analysis curve of calcium oxalate resulting from the oxalate - carbonate reaction is, unlike the dehydration peak, invariably free from doubling, it may be used for the quantitative determination of oxalate by simply measuring the area of this peak on the lichen curve and comparing this with the peak area for the known amount of calcium oxalate monohydrate (see, e.g., Rhizocarpon calcareum, Table I). For low levels of oxalate this 500" C peak is eitherDecember, 19661 ANALYSIS OF LICHENS GROWING ON LIMESTONE 789 absent or poorly defined (Physcia adscendens and Verrucaria nigrescens, Fig.2, curves A and B). Here, however, oxalate dehydration is recorded as a single peak (170” C), and integration of this provides a good assessment of the oxalate content of the lichen (Table I). Indeed, the agreement between differential thermal analysis and the chemical determinations of oxalate is remarkably close.Finally, consideration of the weight losses on the differential thermogravimetric curves associated with carbonate decomposition in relation to the effects on these curves resulting from the first and second stages of calcium oxalate decomposition, enables an assessment to be made of the non-oxalate derived carbonate (Table I), which is in good agreement with the chemical determination of this component. Ability to distinguish these two forms of calcium in the sample has shown that the three lichen species containing appreciable amounts of calcium oxalate, namely, A spicelia calcaria, Calofilaca heppiana and Rhizocarpovt calcareum are confined to calcareous rocks (i.e., obligate calicoles) , whereas Physcia adscendens, Physcia caesia and Xaizthoria fiarietina, which contain 5 per cent. or less of calcium oxalate, are ubiquitous. These results, supported by other unpublished evidence, show that thermal techniques provide a rapid and reliable means of determining oxalate in plant materials. Magnesium oxalate commonly occurs with calcium oxalate in plants; however, there is no indication of the presence of magnesium salt in the lichen species examined, all the evidence pointing to the oxalate being present exclusively in the form of the calcium oxalate monohydrate. REFERENCES 1 . 2. 3. 4. Simons, E. L., and Newkirk, A. E., Talanta, 1964, 11, 649. 5. Mitchell, R. D., Sczent. Proc. R. Dubl. Soc., i3, 1960, 1, 105. 6. Syers, J, K., “Study of Soil Formation on Carboniferous Limestone with Particular Reference t o Lichens as Pedogenic Agents,” 1’h.D. Thesis, L’nivcrsity of Durham, 1964. Mitchell, €3. D., and Knight, A. H., J . Exp. Rot., 1965, 16, 1 . Stewart, J. M., Rirnie, A. G., and Mitchell, B. n., Agrochimica, in the press. Joy, K. W., Ann. Bot., 1964, 28, 689. Received February 25th, 1966

ISSN:0003-2654    

DOI:10.1039/AN9669100783

出版商:RSC    

年代:1966

数据来源: RSC