ISSN:0003-2654    

DOI:10.1039/AN96691FX025

出版商:RSC    

年代:1966

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN96691BX027

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

iv SUMMARIES OF PAPERS IN THIS ISSUE [July, 1966Summaries of Papers in this IssueSeparation and Determination of Small Amounts of TinA REPORT OF WORK UNDERTAKEN ON BEHALF OF THE METALLIC IMPURITIES I N ORGANIC MATTERSUB-COMMITTEE OF THE ANALYTICAL METHODS COMMITTEE.A method is presented for the selective extraction of tin(1V) iodide fromsulphuric acid solution into toluene. Tin(1V) is then returned to aqueoussolution by shaking the toluene extract with dilute sodium hydroxide solution.The metal is finally determined by spectrophotometric measurement of thecolour of the complex formed between tin(1V) and catechol violet.method is quick, simple, sensitive and highly selective.E. J. NEWMAN and P. D. JONESAnalytical Laboratories, Hopkin and Williams, Ltd., Freshwater Road, ChadwellHeath, Essex.TheAnalyst, 1966, 91, 406-410.Determination of Trace Amounts of Copper in Niobium andTantalum by Atomic-absorption SpectroscopyCopper may be determined in niobium and tantalum a t the 1 to 10 p.p.m.level by extraction of copper 8-hydroxyquinolinate from a fluoride mediuminto ethyl acetate a t pH 4.5, and by direct atomic-absorption spectroscopy ofthe extract in an air - propane or air - acetylene flame at 3247 A.Optimumconditions of pH, reagent concentration and solvent composition have beenestablished, and a study of the effect of other cations and anions is presented.Only titanium(1V) and molybdenum (VI) cause interference when present in100-fold excesses, but even these may be masked by the addition of hydrogenperoxide.G.F. KIRKBRIGHT, M. K. PETERS and T. S. WESTChemistry Department, Imperial College, London, S.W.7.Analyst, 1966, 91, 411-417.The Analysis of Titanium Dioxide Pigments by Spark- sourceMass SpectrographyGraphite, silver and gold powders have been investigated as conductingmedia in the analysis of titanium dioxide pigments for trace elements by solid-source mass spectrography. It is concluded that graphite and silver a.resatisfactory, and that by using both these electrode systems the only elementsthat cannot be determined are sodium and copper.It has been shown that by using niobium in low concentration as aninternal standard, quantitative analysis is possible ; the coefficient of vari-ation of the results being approximately 15 per cent.Sensitivity factors for44 elements relative to niobium in a graphite matrix, and 3 elements relativeto niobium in a silver matrix, have been determined. The results of thedetermination of 27 elements commonly present in titanium dioxide pigmentsare given. The total time for a quantitative analysis is approximately 3hours, and it is possible to analyse up to 8 samples in a working day of 8 hours.P. F. S. JACKSON and J. WHITEHEADBritish Titan Products Company Ltd., Billingham, Co. Durham.Analyst, 1966, 91, 418-427Vi SUMMARIES OF PAPERS IN T H I S ISSUEDetermination of Tetra-alkyl Lead Vapour and Inorganic LeadDust in AirMethods are described for the determination of particulate lead and oftetra-alkyl lead vapour in air, by passing the atmosphere under test through aglass-fibre filter and then through a hydrochloric acid solution of iodine mono-chloride.Tetraethyl lead and tetramethyl lead are collected in this solutionby means of their reaction with iodine monochloride to give the correspondingdialkyl lead ions. The lead collected on the filter is extracted with a nitricacid - hydrogen peroxide reagent, and the amount present is determinedcolorimetrically as lead dithizonate. This may be done automatically withthe Technicon Auto-Analyzer, or manually with a comparator and a standarddisc.Manual and automatic procedures are also given for the determination ofthe amount of tetra-alkyl lead collected. The manual method involvesreaction of the dialkyl lead ions with dithizone a t high pH and matching thecolour of the dialkyl lead dithizonate with a standard disc.In the automaticprocedure, the dialkyl lead is converted to the inorganic state before reactionwith dithizone and colorimetric measurement as lead dithizonate.The methods are designed for the measurement of lead-in-air concentra-tions down to 0.1 mg of lead per 10 cubic metres of air, with sampling periodsof a t least 8 hours. A modified method based on a sampling period of halfan hour, and having a sensitivity of 0.3 mg of lead per 10 cubic metres, isalso described.R. MOSS and (the late) E. V. BROWETTThe Associated Octel Co. Ltd., Ellesmere Port, Chcshire.[July, 1966Analyst, 1966, 91, 428-438.An Examination of Some of the Factors Affecting the Determinationof Carbon Dioxide by Non-aqueous TitrimetrySome of the factors, including choice of absorbent, indicator and titrant,that affect the determination of carbon dioxide by non-aqueous titrimetryare examined experimentally.The results of this examination are used togive a procedure that is recommended for the determination of milligramamounts of carbon dioxide.The method involves absorption of the carbon dioxide in a 5 per cent. v/vsolution of ethanolamine in formdimethylamide, followed by titration withstandard tetrabutyl ammonium hydroxide in benzene - methanol solutionto a visual end-point with thymolphthalein indicator.P. BRAID, J. A. HUNTER, W. H. S. MASSIE, J. D. NICHOLSON andB. E. PEARCEHeriot-Watt University, Chambers Street, Edinburgh 1.Analyst, 1966, 91, 439-444.Thin-layer Chromatography of Epoxide ResinsA simple thin-layer chromatographic technique is described for separatingcommercial epoxide resins into their various components.A method isclcscribed for the quantitative determination of the monomer content ofbisphenol A - epichlorohydrin resins. The various components present inepoxide resins are separated on glass plates coated with silica gel G withchloroform as developing solvent. Optimum separation is achieved by givingtwo developments in chloroform. Details are given of a method for detectinghydrolysable chlorine containing components present in the resin. By themethod described it is possible to distinguish between similar resins fromdifferent manufacturers.R.G. WEATHERHEADYarsley Research Laboratories, Chessington, Surrcy.Analyst, 1966, 91, 445-448viii SUMMARIES OF PAPERS I N THIS ISSUEThe Determination of Diethyl Phthalate in Cosmetic PreparationsAs alternatives to simple hydrolysis and titration, three methods forthe determination of diethyl phthalate in ethanolic preparations such asperfumes, lacquers, deodorants, varnishes and paints are described. A methodsuitable as a screening test for large numbers of samples involves the use ofdirect gas chromatography. Another method involves a simple clean-up ofthe sample followed by column chromatography and determination of theester by its absorption in the ultraviolet. A further and more accurate methodis based on hydrolysis of the ester and gravinietric determination of thephthalic acid after conversion to phthalanil.W.HANCOCK, B. A. ROSE and D. D. SINGERMinistry of Technology, Laboratory of the Government Chemist, Cornwall House,Stamford Street, London, S.E. 1.Analyst, 1966, 91, 449-454.[July, 1966The Analysis of Fats Containing Cyclopropenoid Fatty AcidsCyclopropenoid compounds are labile in the presence of acidic reagents,silver nitrate and mercuric acetate; they are partially destroyed in the courseof gas - liquid chromatographic analysis; and they give a mixture of straightand branched-chain acids on hydrogenation.The difficulties associated with the isolation of methyl sterculate andof the analysis of fats for sterculic and malvalic acids are discussed.T.W. HAMMONDSTropical Products Institute, Gray’s Inn Road, London, W.C. 1.and G. G. SHONENorth Staffordshire College of Technology, Stoke-on-Trent, StaffordshireAnalyst, 1966, 91, 455-458.The Determination of Vitamin D in the Presence of Vitamin AA method has been developed for eliminating vitamin A interference inthe determination of vitamin D. The procedure depends upon the oxidationof vitamin A alcohol by means of manganese dioxide to vitamin A aldehyde,which reacts with p-aminobenzoic acid to form a derivative that is readilyextracted from organic solvents with aqueous sodium hydroxide solution.Vitamin D remains in the organic solvent. Final traces of impurities thatinterfere in the vitamin D determination are removed by chromatography onfloridin earth and on alumina. Vitamin D is determined by the antimonytrichloride colour reaction.F.SAID. M. K. SALAH and P. GIRGISAnalytical Chemistry Department, Faculty of Pharmacy, Cairo University, Egypt,U.A.R.Analyst, 1966, 91, 459-463.Primary Analytical Standards for Plutonium: Quantitative Separationof Plutonium from Dicaesium Plutonium HexachlorideShort PaperF. J. MINERThe Dow Chemical Co., Rocky Flats Division, P.O. Box 888, Golden, Colorado 80401.Analyst, 1966, 91, 464-465.The Micro Determination of Isoniazid by N-BromosuccinimideShort PaperM. 2. BARAKAT and MONIER SHAKERBiochemistry Department, Faculty of Veterinary Medicine, Cairo University, Giza,Cairo, Egypt.Analyst, 1966, 91, 466-467.An Ultraviolet Spectrophotometric Method for Determining3-Amino- 1H- 1,2,4-triazoleShort PaperB.D. WILLSIvon Watkins-Dow Limited, Box 144, New Plymouth, New Zealand.Analyst, 1966, 91, 468-470July, 19661 THE ANALYST ixN O T I C E TO SUBSCRIBERSIt has proved necessary t o increase the annual subscription rates for The Analyst and AnalyticalAbstracts for 1967 and subsequent years, as follows-The Analyst plus Analytical Abstracts, including both indexes . . . . . . . . f15both indexes .. . . . . .. . . . . .. .. . . €17The Analyst plus Analytical Abstracts, printed on one side of the paper only, includingThe 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. . . . .. .. ..Analytical 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 I s t , 1967, prices of all single copies will be increased as follows-Single copies of The Analyst . . .. .. .. .. .. ..Single copies of Analytical Abstracts . . . . .. .. .. ..Single copies of Analytical Abstracts printed on one side of the paper only..Index t o The Analyst . . .. .. . . .. .. .. ..Index to 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 . ... €15.. €10.. €120 00 05 00 00 0.. f10 10 0.. € I 10 0* . € 1 2 0. . € 1 10 0.. fl 10 0.. 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ISSN:0003-2654    

DOI:10.1039/AN96691FP135

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

N E U E K S C H E I N U N GGe rba rd Spitelle rMassenspektrornetrischeStrukturanalyseorganischer VerbindungenEine EinfuhrungImmer wieder steht der Chemiker vor dem Problem, Molekulargewicht, Zusammensetzung und Struktur einer Sub-stanz bestimmen zu miissen, die nur in aul3erst geringer Menge vorhanden ist. Hier helfen ihm vor allem die in denletzten Jahrzehnten auBerordentlich verfeinerten spektroskopischen Methoden. Eine von diesen ist die Massenspek-trometrie, die besonders bei der Untersuchung der Struktur organischer Verbindungen standig an Bedeutunggewonnen hat. Der geringe Substanzbedarf und die bescheidenen Reinheitsanforderungen machen die Methodevor allem fur den Naturstoffchemiker zu einem unentbehrlichen Hilfsmittel. Ein ebenso grofies Anwendungsfeldbeginnt sich der Massenspektrometrie bei der Schnellanalyse roher S yntheseprodukte zu erschlienen : Das Ziel dessynthetisch arbeitenden Chemikers ist die Darstellung des Endproduktes in moglichst hoher Ausbeute. Eine Er-hohung der Ausbeute gelingt nur, wenn die Bildung von Nebenprodukten durch Anderung der Reaktionsbedin-gungen so weit wie moglich eingeschrankt wird.Dies setzt die Kenntnis der Struktur der Nebenprodukte voraus.Zur Auffindung dieser Nebenprodukte und zur Aufklarung ihrer Struktur direkt aus dem Reaktionsansatz ohnevorhergehende Reinigungsoperationen kann die Massenspektrometrie vie1 beitragen.Uber Einaelheiten und Variationen dieses Verfahrens sowie vor allem uber die Spektren verschiedener Substanz-klasscn, uber die im Massenspektrometer ablaufenden Vorgange, uber ihre Beeinflussung durch Substituenten unduber die Deutung der Spektren unterrichtet das Buch von Professor G.Spiteller. Zahlreiche Spektren und Formcl-bilder erleichtern das Verstandnis des Textes. Die erworbenen Kenntnisse konnen an Hand von Ubungsaufgabenam Ende des Buches, zu denen ausfuhrliche Losungen angegeben sind, uberpriift und gefestigt werden.1966. XU, 355 J’eiien mit 91 Abbildzlgen zlnd 2 Tabellen. Ganxleinen DM 44,-.2% uusjuhrlicher Prospekt siehi au f A n forderung xur Verfugung.V E R L A G C H E M I E G M B HWEIN HE1 M / B E R G STRXX THE ANALYST [July, 1966Thrifty people saveMONEYSPACE andHAN DLI N G withLIQUID REAGENTSin bulkYou can now buy BDH solvents and other liquidchemicals in 5 gallon cans. Compared withwinchesters these containers offer such economiesin filling and transport costs that BDH standardmaterials can be offered at substantiallyreduced prices.The metal containers are robust and stack easilyfor compact storage. They occupy considerablyless space than the equivalent volume of liquidchemicals in winchesters.Users will appreciate the ease of handling bothin transit and storage. The containers are now astandard B DH package, delivered free whereverthe BDH delivery service operates.~JOIN THEMBY WRITING NO WFOR THEBDHPRICE LIST OF LIQUID REAGENTS IN BULK @THE BRITISH DRUG HOUSES LTD. B D H LABORATORY CHEMICALS DIVISION POOLE DORSE

ISSN:0003-2654    

DOI:10.1039/AN96691BP145

出版商:RSC    

年代:1966

数据来源: RSC

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JULY, 1966 Vol. 91, No. 1084 THE ANALYST Editorial IN common with many other learned societieh that foitei- the international propagation of scientific knowledge by the publication of research papers and abitracts, the Society for A4nalytical Chemistry is now facing a financial situation causing much concern. This is the direct result of the continuing increases in abstracting, editorial and printing costs, coupled with increasing overheads and distribution expenses. ‘These difficulties are also accentuated by the steady growth of analytical rcsearch, which demand\ a concomitant expansion of publication space in both The A tzalvst and ‘4 ~zaZ~vticnZ ‘4 bstvncts if adequite coverage of this rapidly developing field is to be maintained. These two publications hai-e already won world-wide scientific acclaim and the Council of the Society is determined to maintain the high standard of past achieirements. The Council is assured that all the Society’s corporate members and subhcribers, being fully aware of present economic trends, will accept and endorse those increases in subscription rates, which of necessity have to be introduced from Ja-nuary lst, 1967. Alembers of the Society are being advised in the current issue of The Proceedings of the reiised subscription rates. Proportionate increases are to be made in the cost of the Society’s journals, the new annual subscription being raised to fJ15. A full list of the modified charges will be found on page ix of the advertisement section of this issue. 405

ISSN:0003-2654    

DOI:10.1039/AN9669100405

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

Separation and Determination of Small Amounts of Tin A method is prcscntecl for the selective extraction of tin(l\‘) iodicic from sulphuric acid solution into toluene. Tin(I\-) is then returned to aqueous solution by shaking the toluene cstr-act \\.it11 dilute sodium hydroxide solution. The metal is finally determined h y spcctropliotometric measurement of the colour o f t h e complex formed between tin( and catcchol x-iolet. The method is cliiick, siniplc, sensitivv and highly selcctive. CXTECHOL violet is one of the more sensitive colorimetric reagents that have been used to determine tin. I t forms a red-coloured complex with tin(1V) in weakly acidic solution. The complex is water-soluble, and this property a11c)ws the use of simpler manipulative techniques than can be used with some other colorimetric reagents for tin, such as dithiol and phenj-1- fluorone, which produce colloidal systems.Other metallic species that would also be expected to produce colours with catechol violet, at the same p11 as that used for determining tin, have been listed by Suk and Nla1at.l These include aluminium, gallium, indium, titanium( I\’), zirconium, thorium, antimony( 111), bismuth(III), molybdenum(VI), tungsten(\’I) and iron(II1). Ross and LlThite,2 who first described the use of catechol violet for determining tin, showed that these metallic species in fact caused serious interference. They also showed that copper, zinc, lead, arsenic and nickel did not interfere, and that tin(1I) did not give a coloured product with catechol violet provided that it was protected by adding a reducing agent ; in the absence of a reducing agent, however, the tin was rapidly and quantitatively osidised to the quadrivalent state, presumably by atmospheric oxidation, and accordingly gave the colour reaction with catechol violet.Our own experiences with this reagent confirm completely these findings of Ross and White. Obviously a preliminary separation procedure is required in order that a highly selective determination of tin with catechol violet may be made. Ross and White2 suggested that the distillation of tin(1V) bromide, according to the method of Onishi and Sandell,3 would be suitable, but 110 report of its use in this connection has appeared in the literature. Ross and White4 have also described a highly selective method in which tin was extracted from acidic solution with a cyclohesane solution of tris-(%ethylhexyl) phosphine oxide.The extract was diluted with ethanol, and treated with catechol violet to produce the coloured tin( 11’) complex. Gilbert and Sandells described a procedure for the solvent extraction of tin (IV) iodide into benzene. This method separated tin from most elements, but “salting out” n.ith perchlorate was required for efficient extraction and the sulphuric acid concentration of the aqueous phase was restricted to below 0.5 31. The method that seemed most suitable for our purpose, how- ever, ivas that reported by Tanaka,G who found that tin(1V) iodide could be extracted quanti- tatively into benzene from sulphuric acid solutions of concentrations greater than 8 N , con- taining 0.1 M potassium iodide.This method ought to be readily adaptable to the scparation of tin from the sulphuric acid digestion residues produced by the wet oxidation of organic materials. Tanaka and E’amayoshi7 have also reported the use of catecliol violet for the determina- tion of tin. Their method was slightly different from that of Ross and White and, in our hands, it proved to be more reliable. Later, Tanaka8 combined his separation and colori- metric procedures in a photometric method for the determination of tin in iron and steels. In this paper we present our procedure for the extraction of tin(I1’) iodide from sulphuric acid solution and the subsequent determination of the tin with catechol violet. Basically, our procedure is the same as that of Tanaka, but it contains modifications that, in OUT experience, improve the method. * Present address: lkpai-tmcnt of (kology, Inipci-ial Collegc, I,ondon, S,l\‘. 7 .July, 1966: DETERMINATION OF S3IBLL AMOCSTS OF T I N 407 EXPERIMENTAL In the method of Ross and WhiteJ2 catechol violet was added to a dilute hydrochloric acid solution containing tin( IV).Potassium hydrogen phthalate buffer was then added, and the pH of the solution adjusted to 2.6 by the addition of ammonia solution. The solution was set aside for 15 minutes for full development of the colour before the absorbance was measured at a wavelength of 555 mp. The order of addition of the reagents was important, and the presence of chloride appeared to be necessary for full colour development.The calibration graph was linear over the range 0-24 to 1.6 pg of tin per ml, but deviated from linearity in more dilute solutions. Preliminarj. experiments carried out by this method confirmed all the results of Ross and \\'bite, but we found that many of our replicate calibration figures were rather low. The potassium hydrogen phthalate had a very low buffer capacity and, when ammonia was added to raise the pH, momentarily high pH values were obtained. We attributed our erratic results to this behaviour because of the ease with which tin(I\’) is hydrolysed. Tanaka and Yamayoshi’s methods gave much more satisfactory results. This method was almost the same as Ross and White’s, except that acetate, which has a much greater buffer capacity than phthalate, was used to buffer the solution at pH 3.8, and optical measure- ments were made at a wavelength of 552 mp. The calibration graph we obtained by the procedure described below under “Method,” was linear over the range 0 to 1.2 pg of tin per ml, and the ionic molar extinction coefficient calculated from this graph was approximately 68,500. An indication of the reproducibility of the method is provided by the calibration figures given in Table I.TABLE I CALIBILITIOX FIGURES OBTAINED BY PROPOSED METIIOI) .\mount of tin taken, Ph” 5 10 1 5 20 25 30 Optical densities obtained (quadruplicate determinations) 0.114 0.109 0.110 0.108 0-226 0.235 0.231 0.228 0.336 0.351 0.351 0.342 0.460 0.474 0.464 0.450 0.572 0.578 0.570 0.572 0.680 0.672 0.682 0.680 Mean value 0 .1 10 0.230 0.345 0.462 0.573 0.679 We also examined the behaviour of three different batches of catechol violet. Two batches behaved identically, but the third had a sensitivity towards tin of only about four- fifths of that quoted above; the correct colour was still produced, however, and the calibration graph was linear, but the decrease in sensitivity could not be overcome by adding more reagent. I t is desirable, therefore, to check calibration figures whenever a different batch of catecho1 violet is used. Full de\Telopment of the coloured complex occurred within about 15 minutes with all three batches of catechol violet. We also modified the separation procedure described by Tanaka,x but chose toluene as the extractant instead of benzene because of its much lower toxicity.Tanaka took half the extract and re-extracted the tin to the aqueous phase by shaking it with dilute hydrochloric acid. To simplify the procedure and enable it to be performed in only one separating funnel, we preferred to take the whole extract, but did not obtain quantitative recoveries by reversion with dilute hydrochloric, sulphuric or perchloric acids. Instead, we re-extracted the tin with dilute sodium hydroxide solution because tin( II?) is readily converted into water-soluble stannatc in this way. By this means we were able to develop an extraction and reversion procedure that gave quantitative recoveries of tin. Inevitably, during the extraction stage when iodide was added to 9 N sulphuric acid, oxidation by air caused some iodine to be liberated, and this was also extracted into the toluene and subsequently re-extracted into the sodium hydroxide solution as hypoiodite. Acidification with hydrochloric acid, which is the nest essential stage of the procedure, caused iodine to be liberated, and this had to be removed because catechol violet is easily oxidised, even by iodine.At first we added sodium sulphite to discharge the iodine colour and warmed the solution to expel sulphur dioxide, but later we found that ascorbic acid was effective without reducing the tin(1V) to the tin(T1) state. We chose to make our measurements after 30 minutes.408 NE'CVMAN AND JOKES: SEPARATION AND [ A ?lazyst, \'ol. 91 Recoveries of known amounts of tin that were put through the whole procedure described below are given in Table TI.Excellent recoveries were obtained. TABLE IT RECOVERIES OF TIN OBTAINED BY PKOPOSED METHOD .Amount of tin taken, 5 10 15 20 25 30 Optical density 0.105 0.228 0.338 0.464 0.576 0.680 A 111 ou n t of tin found, tLg 4-8 9.9 14.6 20.0 25-2 30.0 Recovery, per cent. 96.0 99.0 97.3 100.0 101.0 100.0 Tests for interference were made with a wide variety of anions and cations, in which the ions under investigation were added to sulphuric acid solutions containing 20 pg of tin. Each test solution was treated by the whole of the procedure described below, and the results are given in Table 111. TABLE 111 No significant interference was found. INVESTIGATION OF INTERFERENCES Each test was conducted on a solution containing 20 pg o f tin(1V) Recovery of tin -4mount Optical ,-*--- 7 per cent.lons added added density Bcryllium . . . . . . . . . . . . 100 pg 0.435 18.8 94.0 Calcium . . . . . . . . . . . . 10mg* 0.430 18.6 93.0 Magnesium . . . . . . . . . . 5 mg 0.443 19.3 '36.5 Barium . . . . . . . . . . . . 100 pg 0.439 18.9 94.5 Cadmium . . . . . . . . . . 100 pg 0.449 19.6 97.5 hlercury(1) . . . . . . . . . . 100 pg 0.456 19-7 98.5 JZercury(I1) . . . . . . . . . . 100 pg 0.463 20.0 100.0 T,anthanuin(LII) . . . . . . . . . . 100 pg 0-457 19.8 99.0 Cerium(II1) . . . . . . . . . . 1oopg 0.460 19.9 99.5 Thorium(1V) . . . . . . . . . . 100 pg 0.460 19.9 99.5 Germanium(1V) . . . . . . . . . . 100 pg 0-473 20-5 102.6 Lead . . . . . . . . . . . . 100 pg 0.452 19.6 98.0 Arsenic(II1) . . . . . . . . . . 100 pg 0.460 19.9 99.5 Antimony(II1) .. . . . . . . . . 100 pg 0.46 1 20.0 100,o Bismuth . . . . . . . . . . . . 100 pg 0.440 19.1 95.5 .\lumlnizm . . . . . . . . 5 mg 0.443 19.3 96.5 Cerium(1V) . . .. . . . . . . 100 pg 0.444 19.2 96.0 Titanium(1V) . . . . . . . . . . 100 pg 0.448 19.4 97-0 Arsenic(V), antimony(V), vanadatc and selenium(V1) . . . . . . . . . . 100 pg 0.443 19.3 96.5 of cach Chromium(II1) . . . . . . . . . . 100 pg 0.439 18.9 94.5 and uranium(V1) . . . . . . . . 100 pg 0.460 19.9 99-6 Manganesc(II), cobalt, nickel, copper and zinc 100 pg 0.445 19.3 96.5 Iron(I1) . . . . . . . . . . . . 100 pg 0.439 18.9 94.6 Fluoride, chloride and nitrate . . . . . . 1 mg 0.45i 19.8 99.0 mg 0.439 18.9 94.5 Pyrophosphatc . . . . . . , . . . Chromium(VI), molybdenum(VI), tungsten(V1) of each of each Iron(Il1) .. . . . . . . . . . . 5 mg 0.443 19.3 96.5 of each 19.9 99.5 Orthophosphate . . . . . . . . . . 3 mg Citrate . . . . . . . . . . . . 5mg 0.464 20.1 100.5 0.460 and borate . . . . . . . . . . p g I * Filtcrcd to remove calcium sulphate bcforc extraction. ME THO D REAGF.NTS- All reagents should be of analytical-reagent quality. Water-Purify glass-distilled water further by passing it through a mixture of strongly acidic cation-exchange resin and strongly basic anion-exchange resin.July, 19661 DETERMINATION OF SMALL AMOUKTS OF TIN 409 Sulphuric acid, approximately 9 N-Cautiously mix 250 ml of sulphuric acid, sp.gr. 1.84, with 500 ml of water, cool to room temperature, and dilute to 1 litre with water. Potassium iodide, approximately 5 M-Dissolve 83 g of potassium iodide in water to produce 100 ml.Tolitene. Sodium hydroxide, approximately 5 N and approximately 0-1 N. Hydrochloric acid, approximately 5 N. Ascorbic acid solution-Freshly prepare a 5 per cent. w/v, aqueous solution. Catechol violet solution-A 0.05 per cent. w/v aqueous solution. Sodium acetate trihydrate solution--A 20 per cent. w/v aqueous solution. Ammonia solzition, approximately 5 N. Tin(1V) stock solution-Dissolve 0.1000 g of pure granulated tin in 20 ml of sulphuric Cool, cautiously dilute with 150 ml of Add 65 ml of sulphuric acid, sp.gr. 1.84, again cool, and transfer to a Prepare freshly each day. Prepare freshly each week. acid, sp.gr. 1-84, by heating until fumes appear. water, and cool again. 500-ml calibrated flask.Dilute to the mark with water. 1 ml of solution = 200 pg of tin. Tin(IV), dilute standard solzction-Dilute 5-0 ml of tin(1V) stock solution to 100 ml with water in a calibrated flask. Prepare freshly each day. 1 ml of solution = 10 pg of tin. PREPARATION OF CALIBRATION GRAPH- Transfer by pipette, or small-capacity burette, suitable volumes of dilute standard tin solution, to cover the range of 0 to 30 pg of tin, to a series of 50-ml beakers and treat each as follows: dilute to 7 ml with water, add 1 ml of 5 N sodium hydroxide, and mix. Add 2-5 ml of 5 ?u’ hydrochloric acid, mix, add 2.0 ml of catechol violet solution, mix again, and add 5 ml of sodium acetate solution. 0.1 units, with the aid of a pH meter. Transfer to a 25-ml calibrated flask, dilute to the mark with water, mix thoroughly and set aside for 30 minutes.Measure the optical density of the solution in a 1-cm cell at a wavelength of 552 mp, with the solution containing no added tin in the reference cell. Construct a graph relating the quantity of tin to the optical density. The graph should be rectilinear and pass through the origin. Adjust the pH of the solution with 5 N ammonia to 3.8 PROCEDURE- Dilute the sulphuric acid solution containing not more than 30 pg of tin to approximately 9 N, cool, and transfer it to a separating funnel. For each 25 ml of solution add 2.5 ml of 5 M potassium iodide, mix, and add 10 ml of toluene. Stopper and shake the funnel vigorously for 2 minutes, allow the layers to separate, and discard the aqueous phase. Wash the toluene layer, without shaking it, with 5 ml of a solution prepared by mixing 25 ml of 9 N sulphuric acid and 2.5 ml of 5 M potassium iodide, and discard the washings.The toluene layer will be coloured pink with extracted iodine. Add 5 ml of water to the toluene extract and then add 5 is sodium hydroxide dropwise, with shaking, until the toluene layer is colourless. Add 2 drops in excess (usually a total of 8 to 10 drops is required). Stopper and shake the funnel for 30 seconds, allow the phases to separate and run the aqueous layer into a 50-ml beaker. Shake the toluene layer with 3 ml of 0.1 s sodium hydroxide for 30 seconds, allow the layers to separate, and add the aqueous layer to the contents of the 50-ml beaker. Acidify the aqueous solution in the beaker with 2.5 ml of 5 N hydrochloric acid and de-colourise the liberated iodine by the dropwise addition of ascorbic acid solution. Add 2.0 ml of catechol violet solution, and mix.Wash the toluene retained above, without shaking, with 5 ml of sodium acetate solution. ,4dd the washings to the contents of the beaker, mix, and adjust the pH of the solution to 3.8 0.1 with 5 x ammonia, by means of a pH meter. Transfer to a 25-ml calibrated flask, and complete the determination of tin as described above under “Preparation of Calibration Graph.’’ Calculate the amount of tin found by reference to the calibration graph. Retain the organic (toluene) phase.410 NEWMAN AND JONES [A~zalyst, Vol. 91 CONCLUSIONS A simple and accurate method for the separation and spectrophotometric determination of microgram amounts of tin(1V) has been described. The method proved to be specific for tin in the presence of a wide variety of other metals and several anions, and should be applicable to the determination of tin in organic matter after wet decomposition in which a sulphuric acid residue is produced. We thank the Directors of Hopkin and Williams, Ltd., for permission to publish this paper, and Mrs. June H. Jones for assistance with part of the experimental work. KEFEREXCES 1. 2. 3. 4. 5. 6. 7. 8. Suk, V., and nlalat, JI., Chemist Analyst, 1956, 45, 30. Ross, W. J., and White, J . C., Analyt. Ckein., 1961, 33, 421. Onishi, H., and Sandell, E. R., Anal-yfica Chinz. Acta, 1956, 14, 153. Ross, W. J., and White, J. C., AnaZvf. Chem., 1961, 33, 424. Gilbert, D. D., and Sandell, E. R., iWicvochem. J . , 1960, 4, 491. Tanaka, K., Japan Analyst, 1962, 11, 332. Tanaka, K., and Yamayoshi, I<., Ibid., 1964, 13, 540. Tanaka, I<., I b i d . , 1964, 13, 725. Received Januavy 20th, 1966

ISSN:0003-2654    

DOI:10.1039/AN9669100406

出版商:RSC    

年代:1966

数据来源: RSC

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July, 19661 KIRKBRIGHT, PETERS AND \YEST 41 1 Determination of Trace Amounts of Copper in Niobium and Tantalum by Atomic-absorption Spectroscopy BY G. F. KIRKBRIGHT, M. K. PETERS AND T. S. WEST (Chemistry Department, Imperial College, Loizdol.2, S . W.7) Copper may be determined in niobium and tantalum a t the 1 t o 10 p.p.m. level by extraction of copper 8-hydroxyquinolinatc from a fluoride medium into ethyl acetate at pH 4.6, and by direct atomic-absorption spectroscopy of the extract in an air - propane or air - acetylene flame a t 3247 Optimum conditions of pH, reagent concentration and solvent coniposition have been established, and a study of the effect of other cations and anions is presented. Only titanium(1Vf and molybdenum (VI) cause interference when present in 100-fold excesses, but even these may be masked by the addition of hydrogen peroxide.THE rapidity , sensitivity and relative freedom from interference of at omic-absorp t ion spectroscopy for the determination of traces of metals is now well recognised. The technique has been applied to the determination of copper in sea-water,l brass and b r o n ~ e , ~ ? ~ 0res~9~ and agricultural materials6 Our studies have been concerned with the application of atomic- absorption spectroscopy to the determination of trace elements in metals that form refractory oxides in air - propane and air - acetylene flames, and which are, therefore, difficult to determine by direct aspiration of a solution of the sample into such a flame. This paper reports the determination of traces of copper in niobium and tantalum.The copper is extracted into ethyl acetate as copper(I1) 8-h\idroxyquinolinate, and the organic phase is then aspirated directly into an air - propane or air - acetylene flame for absorbance measurements . An unmodulated atomic-absorption spectrophotometer was used for the air - propane flame, but a modulated instrument had to be used for the air - acetylene flame because of the background emission from the flame. Although the analysis of copper in niobium was carried out in air - propane, it could be done equally well in the air - acetylene flame. It was also found that a smaller volume of liquid sample was required to obtain reliable absorb- ance values with the modulated instrument fitted with a recorder. This effective increase in sensitivity enabled a 2-g sample of metal to be taken by using the modulated instrument in place of a 10-g sample required for the unmodulated instrument.EXPERIMENTAL APPARATUS FOR THE DETERMINATION OF COPPER IN XIOBIUM- A Hilger and Watts Uvispek (H700) and the unmodulated atomic-absorption attachment (H1100) with a copper - zinc hollow-cathode lamp (FL165) were used. The flame used was a regulated supply of compressed air and propane. The optimum instrument control settings were determined with a standard 10 p.p.m. copper 8-hydroxyquinolinate solution. These were: lamp current, 4 mA; wavelength, 3247 A ; slit width, 0.2 mm; air pressure, 25 lb per sq inch (1.75 kg per cm2) ; propane pressure, sufficient to produce a flame that was just non- luminous; burner height, Uvispck position 1 (optical path just above the cones in the flame) ; effective burner-head dimensions, 10 cm long and 1.5 cm wide.APPARATUS FOR THE DETERMINATION OF COPPER IN TANTALUM- A Unicam SPSOOA, fitted with a recorder and copper - zinc hollow-cathode lamp (FL165, Hilger and Watts Ltd.), was used. The flame used a regulated supply of compressed air and acetylene. The optimum instrument control settings were determined with a standard copper 8-hydroxyquinolinate solution. These were : lamp current, 5 mA ; wavelength, 3247 A ; slit width, 0.05 mm; air pressure to atomiser, acetylene pressure to burner and burner height, as above; effective flame dimensions, approximately 7 cm long and 3 mm wide.412 [Analyst, Vol. 91 REAGENTS- Copper solution-Dissolve 3.929 g of analytical-reagent grade copper sulphate (CuS0,.5H20) in 1 litre of distilled water from an all-glass distillation apparatus to produce a stock solution containing 1000 p.p.m, of copper.Dilute this solution to 10 or 100 p.p.m. when required. Tantalum solution-Dissolve 10 g of tantalum metal (Murex Ltd., Rainham, Essex) in a mixture of 30 ml of 40 per cent. hydrofluoric acid and 3 ml of nitric acid (sp.gr. 1-42). Dilute the solution to 500 ml with distilled water and add 4 N ammonia to raise the pH to 4.0. Finally, dilute the solution to 1 litre to produce a 10,000 p.p.m. tantalum solution. Niobium solution-Dissolve 50 g of niobium metal (Murex Ltd., Rainham, Essex) in a mixture of 150 ml of 40 per cent. hydrofluoric acid and 100 ml of concentrated nitric acid (sp.gr.1.42). Dilute the solution to 450 ml with distilled water, and add 10 per cent. of sodium hydroxide to raise the pH to 4.0. Dilute the solution to 1 litre to produce a 50,000 p.p.m. niobium stock solution. KIRKBRIGHT, PETERS AND WEST: DETERMINATION OF COPPER 8-Hydroxyquinoline reagents, 0.1 and 0.025 per cent., in ethyl acetate. Sodium acetate - acetic acid bufer, pH 4.5, All other reagents used should be of analytical-reagent grade. PROCEDURE- Calibration curve for niobium-Transfer 1 to 10-ml aliquots of a 10 p.p.m. copper solution to a series of 500-ml separating funnels. Add 200 ml of 50,000 p.p.m. niobium solution, 10 ml of pH 4.5 buffer and 30 ml of 0-1 per cent. 8-hydroxyquinoline reagent solution to each flask. Shake the funnels for 1 minute.Allow the phases to separate, run off the lower aqueous layer and spray the ethyl acetate phases directly into the air - propane flame. Measure the absorbances at 3247 A against a 0.1 per cent. solution of 8-hydroxyquinoline in ethyl acetate as a blank. Preparation of sam$Zes-Dissolve 10 g of niobium metal in 30 ml of 40 per cent. hydro- fluoric acid and 20 ml of concentrated nitric acid (sp.gr. 1-42). Dilute the solution to 100 ml with distilled water and add 10 per cent. of sodium hydroxide solution to raise the pH to 4-0. Dilute the solution to 200 ml with distilled water. Calibration curve foy tantalum-Transfer 0.5 to 2.5-ml aliquots of a 10 p.p.m. copper solution to a series of 500-ml separating funnels. Add 10 ml of pH 4-5 buffer, 200 ml of the 10,000 p.p.m.tantalum solution and 30 ml of 0.025 per cent. 8-hydroxyquinoline solution to each funnel and shake them for 1 minute. Reject the lower aqueous layer and add 10 ml of 0.1 N hydrochloric acid to the organic phase. Shake them for 30 seconds, allow the phases to separate and collect the aqueous layer in a 50-ml separating funnel. Add 1 ml of N am- monia, 5 ml of pH 4.5 buffer and 2 ml of ethyl acetate. Shake together for 1 minute, allow the phases to separate, and spray the organic phase directly into the air - acetylene flame. Measure the absorbance at 3247 against a 0.025 per cent. solution of 8-hydroxyquinoline in ethyl acetate as the blank. Preparation of samples-\treigh 2 g of tantalum metal and dissolve it in a mixture of 6 ml of 40 per cent.hydrofluoric acid and 0.5 ml of nitric acid (sp.gr. 1.42). Dilute the solution to 100 ml with distilled water and add 4 N ammonia to raise the pH to 4.0. Dilute the solution to 200 ml with distilled water. RESULTS AND DISCUSSION OF THE DETERMINATION OF COPPER IN NIOBIUM During the initial experiments an attempt was made to determine copper in aqueous solution in the presence of niobium. I t was expected that the presence of niobium would decrease the absorbance values for copper owing to the formation of refractory niobium oxide in the flame. No interference of this type was obtained in the presence of a 100 or 1000-fold excess of niobium, in fact the absorbance values for copper obtained in the presence of niobium were slightly higher than those for aqueous copper solutions alone.This effect was subsequently shown to be due to traces of copper in the niobium. Siobium itself does not contribute to the absorbance at 3247 A. It is not possible, however, to determine copper in niobium directly in aqueous solution at the 1 to 10 p.p.m. level owing to (a) insufficient sensitivity for the determination of copper by atomic-absorption even when a 10-g metal sample is dissolved in 200 ml of solution, and (b) the presence of between lo5 and 106-fold excesses of niobium and fluoride which reduce the atomiser efficiency and cause the formationJuly, 19661 IN NIOBIUM AND TANTALUM BY ATOMIC-ABSORPTION SPECTROSCOPY 413 of undissociated refractory oxide particles in the flame, so inhibiting absorption. The pre- liminary separation of the copper by extraction of copper 8-hydroxyquinoline into ethyl acetate was therefore adopted to provide a concentration of the copper, and to take advantage of the higher spraying efficiency of the organic solvent. EXTRACTION PROCEDURE- (a) Efect of pH-Below pH 2, copper is not extracted as its 8-hydroxyquinolinate, and above pH 5 it is not possible to retain large amounts of niobium in solution as its fluoride.The niobium thus precipitated hinders the extraction procedure owing to co-precipitation of copper. As shown in Fig. 1, quantitative extraction is obtained between pH 4 and 5, pH 4.5 was chosen as the most favourable pH for extraction. Fig. 1. Effect of pH on the extraction of copper as copper 8-hydroxyquinolinate from a fluoride medium ( b ) Effect of reagent concentration-As shown in Table I, the use of a large excess of 8-hydroxyquinoline produces high blank absorbance values in relation to those from copper 8-hydroxyquinolinate solutions.The greatest difference between sample and blank absorbances in the extraction of 200 pg of copper was obtained with the most dilute (0.1 per cent.) ethyl acetate solution of 8-hydroxyquinoline. With the recommended procedure and volume of reagent solution (30 ml), this concentration provides a 300-fold excess by weight of 8-hydroxy- quinoline over the amount of copper present a t the top of the calibration curve. It was thought advisable not to use less reagent in an attempt to increase the sensitivity further, because, in the presence of high concentrations of foreign ions, insufficient reagent might be left to permit quantitative extraction of the copper.TABLE I EFFECT OF REAGENT CONCENTRATION ON ABSORBANCE AT 3247 A OF 20 p.p.m. COPPER AND BLANK SOLUTIONS IN ETHYL ACETATE Concentration of of 8-hydroxyquinoline, Blank absorbance Absorbance from Net absorbance per cent. (against ethyl acetate) 10 p.p.m. of copper due to copper 1 1.55 1-70 0.15 0.5 1.04 1-50 0-46 0.25 0.45 1.32 0.SS 0.1 0.095 1-02 0.925 (c) Efect of length of shaking time-A shaking time of 45 seconds is required for maximum extraction, but no further increase in absorbance occurs on longer shaking. A time of 1 minute was subsequently chosen as a satisfactory equilibration period. (d) Organic solution efect-The extraction of copper into ethyl acetate as its 8-hydroxy- quinolinate before absorption measurements should result in an increase in the over-all sensitivity because of concentration of the copper in the organic phase, and a further increase in sensitivity from the increased spray-rate of organic solvents relative to aqueous solutions.The expected increase in sensitivity from the latter effect may be calculated from a com- parison of the rates of atomisation of water and ethyl acetate. As shown in Table IT, the rate of atomisation of ethyl acetate is almost 4.8 times that of water. Consequently, the414 KIRKBRIGHT, PETERS AND WEST: DETERMINATION OF COPPEK [Analyst, VOl. 91 absorbances produced by ethyl acetate and water containing the same concentration of copper should approximate to the ratio 4.8 to 1.For ethyl acetate and water containing 10 p.p.m. of copper, the absorbance ratio is, in practice, only 3 to 1. I t is probable that the ratio is lower than that expected owing to saturation of the ethyl acetate with water following the extraction, and because of the presence of the dissolved reagent. TABLE I1 THE RATE OF ASPIRATION OF ETHYL ACETATE AS COMPARED WITH WATER Volume taken, ml . . .. . . .. .. 10.0 10.0 Volume recovered, ml . . . . . . .. 8.2 3.5 Volume atomised, ml . . . . . . . . . . 1.8 6.5 Time taken, seconds . . . . . . . . . . 248 166 Rate, ml per second (throughput x lo2) . . . . 0.726 3.49 Throughput ratio relative to distilled water . . 1.00 4.8 1 Solvent system Distilled water Ethyl acetate A stock solution of copper 8-hydroxyquinolinate in ethyl acetate (containing 10 p.p.m.of copper and 0.1 per cent. with respect to 8-hydroxyquinoline) was diluted with various organic solvents to determine whether any increase in rate of atomisation, and consequently absorbance, could be obtained. One volume of the stock solution in ethyl acetate was diluted with 2 volumes of organic solvent, and the absorbance produced was measured against a blank solution of 0-1 per cent. of 8-hydroxyquinoline diluted similarly. As shown in Table 111, ethyl acetate produces the highest absorbance values. TABLE 111 EFFECT OF DIFFERENT ORGANIC SOLVENTS ON ABSORBANCE OF STANDARD COPPER 8-HYDROXYQUINOLINATE SOLUTION IN ETHYL ACETATE (1 VOLUME OF COPPEK 8-HYDROXYQUINOLINATE + 2 VOLUMES OF SOLVENT) Solvent added Ethyl acetate . . .... Pentyl acetate . . .. .. Ethyl methyl ketone . . .. Isopropyl methyl ketone . . lsobutyl methyl ketone . . . . Isopentanol . . .. .. Isopropanol . . . . . . .. Pentanol . . . . . . . . Hexanol . . . . . . . . Butanol . . . . .. . . Diethyl ether . . . . .. Di-isopropyl ether . . . . Cyclohexanone . . . . . . Acctylacetone . . . . . . Light petroleum (b.p. 100" to 120") .. .. . . .. . . I . .. .. . . .. .. . . . . . . . . .. .. . . . . . . . . .. . . . . . . .. . . . . . . Absorbance 0.230 0.075 0.183 0.156 0.068 0.074 0.154 0.079 0.068 0.104 0.1 10 0.214 0.190 0.105 0.084 CALIBRATION CURVE AND SENSITIVITY- The calibration curve obtained is linear in the range 10 to 100 pg of copper, and corre- sponds to the added 1 to 10 p.p.m. of copper in the sample taken, which is equivalent to 10 g of niobium metal.The absorbance values corresponding to these concentrations are 0.115 and 0-540, respectively, and the curve passes above the origin. This positive blank arises owing to the presence of traces of copper in the niobium metal used in this work. The addition of EDTA (5 ml of 10-1 M) to the niobium blank to complex these traces of copper reduces this blank absorbance to zero. By virtue of this device the copper content of the different samples of niobium metal used in these experiments was readily established to be 1.6, 1.8 and 4-2 p.p.m. PRECISION AND ACCURACY- To obtain the precision of the method, a solution equivalent to 5 p.p.m. of copper (50 pg) in niobium metal was analysed 11 times by the recommended procedure over a period of several weeks during the course of the investigation.The average absorbance obtained wasJuly, 19661 IK NIOBIUM AND TANTALUM BY ATOMIC-ABSORPTION SPECTROSCOPY 415 Fig. 2. Calibration curves for copper: curve -4, extracted from pure solution; curve B, extracted from niobium solution 0.233, and the standard deviation was 0-011 or 4.8 per cent. A measure of the accuracy of the method was obtained by the determination of copper in synthetic niobium solutions containing foreign ions and treated as unknown samples. The results of these analyses are shown in Table IV. TABLE IV DETERMINATION OF COPPER IN SIMULATED NIOBIUM SAMPLES TREATED AS UNKNOWNS Copper in niobium, p.p.m. 3.5 6.1 5.4 5-3 7.8 3.2 4.9 3.8 5.8 5.6 Copper found, * p.p.m. 3.8 6.7 7.25 4.6 7.2 3-25 5.0 3.86 6.0 8.5 Error, per cent.t 8.5 1 10-0 - 2.0 - 13.0 ~ 5.5 -; 1.6 + 2.0 + 1.5 + 3.6 + 12.0 7- Zinc, 250 Molybdenum, 100 \.‘anadium, 100 Lead, 250 Iron, 800 Cobalt, 250 Aluminium, 250 Lead, 150 Zirconium, 100 Xickel, 100 Foreign ions added, p. p. m . Manganese, 100 Zinc, 150 Manganese, 100 Manganese, 100 Titanium, 50 Aluminium, 100 Tantalum, 100 Chromium, 150 Iron, 100 Tungsten, 50 Nickel, 100 Iron, 150 Tantalum, 100 * Obtained from corrected calibration curve. RESULTS AND DISCUSSION OF THE DETERMINATION OF COPPER IN TANTALUM A limitation of the recommended method for the determination of copper in niobium is the need for a relatively large (10 g) niobium sample. During the course of application of the method to the determination of copper in tantalum, it was decided to incorporate a further extraction step so that a smaller sample might be taken.In this procedure, the copper 8-hydroxyquinolinate is extracted into ethyl acetate from the tantalum in a fluoride medium at pH 4.5, back-extracted into 0.1 N hydrochloric acid, and re-extracted into a small volume of ethyl acetate. This extract is then aspirated into an air -acetylene flame for atomic-absorption measurement at 3247 A. EXTRACTION PROCEDURE- A pH of 4-5 was again found to be most favourable for extraction of the copper 8-hydroxy- quinolinate and retention of the tantalum in the aqueous fluoride medium. Hydrochloric acid, 0.1 N, was found to back-extract the copper completely from the ethyl acetate phase. As reported above, it was found that the use o f a large excess of 8-hydroxyquinoline produces high blank absorbance values in relation to those from copper 8-hydroxyquinolinate solutions. The introduction of a second extraction - concentration step in the procedure magnifies this effect.It was, therefore, found necessary to utilise a 0.025 per cent. solution of 8-hydroxyquinoline in ethyl acetate in place of the 0-1 per cent. solution used for niobium samples.416 [ A d y s t , Vol. 91 CALIBRATION CURVE AND SENSITIVITY- The calibration curve obtained is linear in the range 2 to 25 pg of copper and, in relation to the 2 g of tantalum added, corresponds to 1 to 12 p.p.m. of copper in metallic tantalum. The absorbance values corresponding to these concentrations are 0.1 10 and 0.772, respectively, and the curve passes above the origin.The positive blank due to the presence of traces of copper in the tantalum metal used may be eliminated by means of EDTA as described above. By this method the copper content of the different samples of tantalum metals used in this study was found to vary between 2-7 and 3 p.p.m. KIRKBRIGHT, PETERS AND WEST: DETEKMINATION OF COPPER PRECISION AND ACCURACY- To obtain the precision of the method, a solution equivalent to 5 p.p.m. of copper (10 pg) in tantalum metal was analysed 6 times by the recommended procedure. The mean absorbance obtained was 0-443 and the standard deviation was 0.023 or 5.2 per cent. A measure of the accuracy was obtained by the determination of copper in synthetic tantalum solutions, some containing foreign ions and treated as unknown samples.The results of these analyses are shown in Table V. TABLE V DETERMINATION OF COPPER I N SIMULATED TANTALUM SAMPLES TREATED AS UNKNOWNS Copper in tantalum, p.p.m. 7-3 16.5 16.5 5.0 13-8 18.5 12-0 19.0 11.9 18.0 20.0 8.0 23.0 7.0 14.0 2 5 0 10.5 18.0 21.0 Copper found, p.p.m. 8-4 16.3 17.7 5.7 14.7 19.0 11.9 17.7 12.8 17.6 19.1 8.0 25.0 7.8 15-5 27.0 11.5 16.7 20.5 Error, per cent. + 13-0 - 1.2 + 8.0 + 14.0 + 7.0 + 2.7 0.8 - 7.0 + 7.0 - 2.2 - 4.5 0.0 + 2.5 + 10.0 + 10.0 + 8.0 + 9.0 - 7.0 - 2.5 Foreign ions added, p.p.m. 7- A 7 Aluminium, 400 Zirconium, 200 Nickel, 300 Zinc, 400 Cobalt , 400 Tin, 300 Tungsten, 300 Iron, 300 Magnesium, 300 Lead, 300 Chromium, 300 Manganese, 250 Titanium, 300 Aluminium, 500 Nickel, 300 Pulolybdenum, 300 Vanadium, 300 Zinc, 200 Aluminium, 500 Nickel, 300 Molybdenum, 800 Vanadium, 300 Zinc, 200 INTERFERENCES (BOTH DETERMINATIONS)- The effect of foreign ions on the determinations was investigated by observing their influence on the absorbance produced in the determination of 5 p.p.m.of copper (50 pg) in niobium (10 g) and 5 p.p.m. of copper (10 pg) in tantalum (2 g) by the recommended procedure. For the purpose of this study an ion was considered not to interfere when less than 5 per cent. error in absorbance was produced. The presence of a 100-fold excess by weight of the following ions produced no interference : aluminium, cobalt (TI), chromium( 111) , iron( 111) , potassium, magnesium, manganese(II), sodium, ammonium, nickel, tin( IIr), vanadium(\.‘), tungsten(VI), zinc, zirconium( TI’), acetate, chloride, fluoride, nitrate and sulphate.Low results were obtained in the presence of a 100-fold excessof titanium(I\’) and molybdenum(VI), but the interferences were eliminated by the addition of 5 ml of 20 volume hydrogen peroxide to the aqueous solution before extraction. DISCUSSION The methods recommended for the determination of copper in niobium and tantalum are selective. The selectivity may be attributed to the inherent freedom from interference of the atomic-absorption spectroscopy of copper at 3247 A, and to the masking action of the high concentration of fluoride present during the extraction procedure with 8-hydroxy- quinoline. The sensitivity of the method for tantalum] enhanced by the final extractionJuly, 19661 IN NIOBIUM AND TAPU’TXLUM BY ATOMIC-ABSORPTION SPECTROSCOPY 417 of the copper 8-hydroxyquinolinate into a volume of ethyl acetate of only 2 ml, is sufficient to allow the determination of 1 to 12 p.p.m. of copper in tantalum metal when a 2-g sample is taken. The sensitivity of the method for the analysis of niobium metal allows the deter- mination of 1 to 10 p.p.m. of copper in niobium when a 10-g sample is taken. The concen- tration step incorporated in the analysis of tantalum metal could, however, equally well be applied to a 2-g sample of niobium. We are grateful to the Ministry of Aviation for supporting this work and to the Science Research Council for a grant for atomic-absorption equipment. We thank Messrs. Murex Ltd., of Rainham, Essex, for gifts of samples of niobium and tantalum metal. REFERENCES 1 . 2. ;Llenzies, A., -4naZvt. Chew., 1960, 32, 898. 3. ~ , Spectvochinz. L4cta, 1957, 11, 106. 4. 5 . 6. Allan, J . E., Spectrochiin. Acta, 1961, 17, 469. Magee, R. J., l’alaizta, 1965, 12, 409. Stumpf, K. E., and Gonsior, T., “Colloquium Spectroscopium Internationale IX,” Lyons, June, Strasheim, A . , Strehlow, F. W. E., and Butler, L. K. P., J. S. Afr. Chem. Imt., 1960, 13, 73. 1961. Received December 15th. 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100411

出版商:RSC    

年代:1966

数据来源: RSC

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418 JACKSOK AND 1YHITEHEAD: ANALYSIS OF TITANIUM [A%dySk, VOl. 91 The Analysis of Titanium Dioxide Pigments by Spark-source Mass Spectrography BY P. F. S. JACKSON AND 'J. WHITEHEAD (British Titan Products Company Ltd., Billingham, Co. Dwham) Graphite, silver and gold powders have been investigated as conducting media in the analysis of titanium dioxide pigments for trace elements by solid- source mass spectrography. I t is concluded that graphite and silver are satisfactory, and that by using both these electrode systems the only elements that cannot be determined are sodium and copper. It has been shown that by using niobium in low concentration as an internal standard, quantitative analysis is possible ; the coefficient of vari- ation of the results being approxiniatcly 15 per cent.Sensitivity factors for 44 elements relative to niobium in a graphite matrix, and 3 elements relative to niobium in a silver matrix, have been determined. The results of the determination of 27 elements commonly present in titanium dioxide pigments are given. The total time for a quantitative analysis is approximately 3 hours, and it is possible to analyse up to 8 samples in a working day of 8 hours. THE presence of trace amounts of certain elements has a considerable effect on the colour and photochemistry of titanium dioxide pigments. Barksdalel refers to the need for reducing the concentration of impurities such as chromium, vanadium, manganese and iron to the minimum possible level to improve the colour of the product. Stonhil12 has published information on the effect of tungsten, molybdenum, chromium and vanadium on the relative brightness of titanium dioxide pigments.He concluded that, although a concentration of several parts per million of tungsten has little effect, up to 10 p.p.m. of chromium and vanadium can cause noticeable deterioration in the whiteness of the pigment. With reference to the photochemistry of titanium dioxide, LVeyl and Forland3 have investigated the effects of elements such as niobium, antimony, tantalum and tungsten, and McTaggart and Bear4 have discussed the effects of iron, chromium, nickel, manganese, cobalt, praseodymium, yttrium, neodymium and copper. The determination of impurities such as these at very low concentrations presents considerable difficulties when conventional methods are used.The amount of sample that may be used for analysis is restricted to a few grams because of the difficulty in dissolving titanium dioxide pigment, and because of the tendency for hydrolysis to occur in titanium solutions. The large amounts of reagents that are necessary to dissolve the sample give rise to high blank values. Therefore, at low impurity levels, the accuracy of the method may be seriously impaired. As separate methods have to be used for each element, the time required to carry out a complete examination of a sample is long. Spark-source mass spectrography has been reported to be a useful technique for the examination of semiconductor9 for trace-element concentrations, and it was considered that it would be equally useful for the analysis of titanium dioxide pigments.The method is extremely sensitive, and is capable of determining down to 0.001 p.p.m. in favourable cases. The sample does not require any chemical treatment, thereby eliminating troublesome blank values. The mass spectrum is relatively simple to interpret, and may be arranged to include all elements within the normal mass range. The method is relatively rapid, and a mass spectrum can be obtained down to the lowest possible level within 2 hours of receiving the sample. EXPERIMENTAL The work described in this paper was carried out with an Associated Electrical Industries MS7 double-focusing instrument of the Mattauch type, and specially designed for spark- source analysis. An ion beam, which may be positive or negative and is representative of the composition of the sample, is formed by passing a pulsed radio-frequency voltage of up to 100 kV amplitude between two electrodes of the sample.The components of the ion beam areJuly, 19661 DIOXIDE PIGMENTS BY SPARK-SOURCE MASS SPECTROGRAPHY 419 separated into fractions of similar mass - charge ratios by electrostatic and magnetic fields, and collected on a photographic plate. By adjusting the magnetic field intensity, the mass - charge range on the photographic plate may be adjusted from 1/35 to 7/245. The working pressure inside the instrument is approximately 1 x lo-* torr in order to reduce plate con- tamination caused by collisions between ions and gas molecules. The ion beam intensity is monitored, and by the use of an integrator and beam deflector, a series of spectra may be obtained corresponding to a charge range of lo7 to 1.By comparing the line densities of elements present in unknown concentration with those of an internal standard, the amount of each unknown may be calculated. A semi-quantitative assessment may be obtained by cornparing the exposures of just-detectable lines for isotopes of the unknown and principal elements. This method, however, does not take into account the variation in sensitivity factors for each element, and in order to obtain reliable quantitative results, it is necessary to use a densitometer for measuring the line intensities, and to determine the sensitivity factors for each element relative to the standard element. The concentration of impurity may then be obtained from the following equation6- E .I . X M Es I s 100 M Impurity concentration in p.p.m. by weight = --a x 2 x S x - x -5 x lo6 where Ei = exposure of internal standard for a given line intensity of a singly charged E , = exposure of impurity element 1 element; I i = percentage abundance of isotope of internal standard; I , = percentage abundance of isotope of unknown element; S = relative sensitivity factor of unknown to internal standard; X = percentage atomic concent1,ation of internal standard ; M = average atomic weight of sample; M s = atomic weight of unknown element. For exact analysis, the areas under each line should be used to obtain Ei and E,. In practice, if the lines used for comparison are chosen carefully, accurate results may be ob- tained by using peak heights.PREPARATION OF ELECTRODES- Electrodes made by compressing titanium dioxide pigments cannot be used because of the low electrical conductivity of titanium dioxide. Although the conductivity of titanium dioxide increases as the titanium is chemically reduced, it has not been found possible to make an electrode of suitable mechanical strength from the reduced product. There is also a risk of losing impurities in the reduction process. Graphite has been recommended for this purpose because it is conducting, obtainable in a pure state at the right particle size and has good adhesive properties. The graphite and sample are mixed together in a polytetrafluoroethylene capsule, containing a pestle of the same material, by means of a vibratory mixing machine.The mixed powder is then placed in a die and compressed to form a solid electrode by using pressures of approximately 50 tons per sq. inch. The electrodes produced by this procedure have satisfactory mechanical strength and can be handled without difficulty. The introduction of a sccond material into the electrode system, however, gives rise to complications owing to the additional lines caused by the material and its associated impurities. In addition, the interpretation of mass spectra produced when compound electrode systems are used, may be hindered by the presence of heterogeneous polyatomic species whose mass - charge ratio is equal to that of the element or elements under investigation. These complex ions cannot always be differentiated from the elemental ion by their mass defect, and hence lead to interfering lines of considerably higher intensity than the detection limit. For example, in the spectra produced from graphite - titanium dioxide electrodes, the presence of titanium carbide ions at masses 58 to 62, and titanium monoxide ions at masses 62 to 66, masks nickel, cobalt and copper which are present in titanium dioxide at very low concentrations and, therefore, cannot be deter- mined.Similarly, low concentrations of magnesium cannot be determined because of inter- ference by the diatomic species, 12C,+, (12C13C)+ and 13C2+. Although elimination of the oxygen complex is impossible, the carbon complexes can be eliminated by selection of an alternative matrix. The suitability of silver and gold powders (supplied by Koch-Light Laboratories Ltd.) as well as graphite was therefore investigated.The technique of incorporating a conducting powder7 was therefore adopted.420 JACKSON AND WHITEHEAD ANALYSIS OF TITAKICM [AndySt, VOl. 91 Reasons for the selection of silver and gold as alternative matrices are that (i), both silver and gold are obtainable as very high purity powders of suitable particle size; (ii), neither silver nor gold had previously been detected in titanium dioxide by mass spectrography in a graphite matrix; (iii), the mass numbers of the silver isotopes (107 and 109) and of the gold isotope (197) are prime numbers, hence, any polycharged species will not occur at whole mass numbers, thus eliminating any overlap. Gold has the additional advantage of existing as a single isotope; (iv), both are good conductors of electricity; (v), silver is comparable in cost to graphite.Gold, however, is considerably more expensive than the other two and would require to be outstanding, technically, before its price could be justified. Gold costs L1000 per 1000 samples, but graphite and silver cost E30 and E90, respectively. In an attempt to eliminate electrode inhomogeneity, the sample mixtures were made up to 50 per cent. by volume of titanium dioxide. Table I shows the weight of matrix element, the weight of titanium dioxide and the relevant per cent. by weight of titanium dioxide in each mixture. TABLE I COMPOSITION OF ELECTRODES Mixture I, Mixture 11, Mixture IJI, g g g Titanium dioxide . . . . ... . . . 0.51 0.40 0.19 . . . . . . . . 0.30 - - Graphite . . . . . . . . - 1-18 - Silver . . . . . . . . Gold . . . . . . . . . . . . . . - 0.92 Titanium dioxide (per cent. by weight) . . . . 63 2 5 17 - The resulting mixtures were examined under an optical microscope to confirm that the distribution of titanium dioxide to matrix element was uniform. When using silver and gold, preparation of the electrode presented a problem in that the metal - titanium dioxide electrodes, unlike the graphite - titanium dioxide electrode, tended to stick to the walls of the die, and to fracture slightly during ejection. These factors eventually led to fragmentation of the electrode. This problem was partially solved by the application of much greater pressures when compressing the electrode and by using a reversed die-set technique.This technique is not recommended for general use, as the die-piece tends to buckle at pressures in excess of 110 tons per sq. inch. However, electrodes capable of use were eventually made by this technique. This should not be taken to mean that the electrodes were entirely satisfactory, as metal - titanium dioxide electrodes, in particular, were fragile and brittle. They shattered on impact and great care had to be exercised in mounting them in the source. The gold - titanium dioxide electrodes proved the most difficult to mount, owing to their extreme sensitivity to pressure. SPARKING OF ELECTRODES- The production of a sufficiently continuous spark was achieved without difficulty for graphite and silver, but the gold electrode tended to give an intermittent spark.Variation of the spark voltage between 400 and 1000 V made no apparent difference to the ease of sparking and an arbitrary figure of 800 T‘ was selected. Increases in the pulse-repetition rate and in the pulse length gave the usual increase in spark intensity, but it was found that the continuity of the spark with the metal - titanium dioxide electrodes broke down when the pulse-repetition rate exceeded 100 pulses per second with the pulse length set at 100 microseconds, I t was also noticed that welding occurred between the electrodes when the pulse-repetition rate exceeded 100 pulses per second, and so the loss of spark continuity was attributed to electrode overheating. This was borne out by the fact that red-hot frag- ments of the electrodes were seen to “fly” in the source, and that stalagmitic and stalactitic deposits were observed on electrodes made from metal - titanium dioxide mixtures.With the silver electrode, a satisfactory ion beam could be maintained without difficulty, and the time taken to complete an analysis was comparable to that when graphite - titanium dioxide electrodes were used. The intermittent nature of the spark between gold - titanium dioxide electrodes made the signal at the monitor collector-plate vary considerably, and consequently, no figure for an ion beam could be quoted, but the total time taken to complete an analysis was approximately 2 hours, compared with the 20 to 30 minutes for the graphite and silver electrodes.July, 19661 DIOXIDE PIGMENTS BY SPARK-SOURCE MASS SPECTROGRAPHY 42 1 TRANSMISSION OF THE ELECTRODE SYSTEM- The electrodes were weighed before and after the exposure of a complete plate, and the total weight loss recorded.From a knowledge of the total charge deposited, it is possible to calculate values for the transmission of each electrode system and to obtain a relative guide to the uniformity of the electrode composition. The experiments were carried out with identical instrument settings and the vanadium mass 51 line was used. The values, which are listed in Table 11, were calculated from the following equation8- V.d.$.Ii N 108p Ai A = where A = number of ions consumed per ion deposited on the plate. V = volume of electrode consumed (ml). d = matrix density (g per ml).p = concentration of impurity (p.p.m. by weight). I1 = isotope abundance (per cent.) of impurity element. N = Avogadro's number. p = number of ions deposited for a measurable line (e105). Ai = atomic weight of impurity. The results given in Table I1 are approximate because of the fragility of the electrodes and the tendency, particularly with the gold electrode, for the electrode to fragment when sparking. They indicate, however, that the three electrode systems exhibit approximately similar transmission characteristics, and require approximately the same degree of homo- geneity in the electrode. TABLE I1 ELECTRODE TRANSMISSION RESVLTS Graphite Silver Gold Total weight loss, g . . . . . . . . 0.0026 0.0044 0.0052 Exposure for detectable line (nanocoulombs) .. 0.9 1.7 0.52 Number of ions consumed per ion deposited on Total charge deposited (nanocoulombs) . . . . 250 250 200 the plate . . . . . . . . . . 1 1 x 107 35 x 107 16 x lo5 (Volume of electrode consumed)+, p . . . . 140 150 90 INTERPRETATION OF SPECTRA In the interpretation of the mass spectra, only those elements usually present in titanium Table I11 shows those elements that are masked in dioxide samples have been considered. the graphite - titanium dioxide matrix. TABLE I11 ELEMENTS WHICH CANNOT BE DETERMINED AT LOW LEVELS IS TITANIUM DIOXIDE - GRAPHITE ELECTRODE SYSTEMS Element Line RIagncsium . . . . . . 24 23 26 Sickel . . . . . . . . 58 60 61 62 Cobalt . . . . . . . . 59 Copper . . . . . . .. 63 65 T nterf erencc 48Ti2+, 12C,+ 50Ti2+, (12C13c) t 12C2H,+, I3C2+ (Separable with resolution of 1000) (46Ti12C) + (I8Til2C) + (49Ti12C) + (46Ti160) + (47Ti12C)+ (49Ti160)+ ( 4 7 ~ ~ 6 0 ) + -\pproximate concentration of interference, p.p,m.> 1000 > 1000 100 50 150 50 400 20 400 400 It can be seen that with magnesium, nickel and cobalt, the use of a silver or gold matrix would be advantageous as the limits of detection would be very much lower than in graphite.422 JACKSON AND WHITEHEAD: ANALYSIS OF TITANIUM [A?UZiySt, VOl. 91 TABLE IV A COMPARISON OF THE LIMITS OF DETECTION, IN THE THREE MATRICES, OBTAINED AT DECREASE THESE BY A FACTOR OF 10) EXPOSURES OF 300 NANOCOULOMBS BY MICRO DENSITOMETRY.* (VISUAL ANALYSIS WILL Element Graphite Silver Gold Aluminium . . 0.1 0.1 0.1 Silicon . . . . 10 1 1 Potassium .. 0.05 0.05 0.05 Calcium . . 0-15 0.15 0.16 Vanadium . . 0.2 0.2 0.2 Zinc . . . . 2 2 2 Arsenic . . 0.5 0.5 0.5 Zirconium . . 0.2 0.2 0 . 2 Niobium . . 0.2 0.2 0.2 Molybdenum . . 1 1 1 Tin . . . . 1 High 1 Phosphorus . . 0.2 0.2 0 . 2 -Antimony . . 0.15 owing to 0.5 black- ening * All results are expressed as p.p.m, by weight. Element Chromium Manganese Iron . . Nickel . . Cobalt Copper Barium Hafnium Tantalum Tungsten Lead . . . . . . . . . . . . . . . . . . . . Graphite Silver 0.2 0.2 0.2 0.2 0-1 0.1 50 0.1 20 0.1 10 10 1 1 4 4 2.5 2.5 4 4 2 2 Gold 0.2 0.2 0.1 0-1 0.1 10 1 4 2.5 4 High owing to black- ening Table IV gives a comparison of the limits of detection of those elements which may be present in titanium dioxide samples. An exposure of 300 nanocoulombs was used each time, and the method of detection was by micro densitometry with the Model IIIC Joyce - Loebl recording instrument.Apart from the dis- advantages of the graphite system already noted, the silver system has the disadvantage that low levels of tin and antimony cannot be detected because of the diffusion of silver ions. I t is therefore apparent that in the analysis of titanium dioxide samples complete analysis cannot be achieved by a single electrode system, and it is necessary to use two conducting matrices, viz., graphite and silver. Gold is unsatisfactory because of the electrode quality and high cost. Visual examination will decrease the levels by a factor of ten. THE USE OF GRAPHITE AS CONDUCTING MATERIAL Three samples of titanium dioxide of known composition were made into electrodes, and mass-spectrographic plates prepared for each sample.Each plate was assessed visually and the results were compared with the known composition of each sample. The agreement between the two sets of results was unsatisfactory. The line intensities were measured by densitometry, and the sensitivity factors of the elements were then calculated relative to titanium for one of the samples. These were used to calculate the impurity concentrations in the other two, but again, the agreement was not satisfactory. No improvement was obtained when peak areas were used instead of peak heights. It was considered that the probable reason for the discrepancy was the difficulty of accurately measuring the densities of titanium lines. To produce satisfactory densitometer curves, it is necessary to use the short exposure lines for titanium as the concentration of the least abundant isotope is still relatively high, and the accuracy of measurement of the ion current required to produce these lines is not very great.Accordingly, an alternative standard was sought which was present at much smaller concentrations. Kiobium was found to be most suitable because it was present at a concentration of 0-14 per cent.; it has a mass approximately in the middle of the atomic weight scale, and it has only one natural isotope. The sensitivity factors for the elements were determined relative to niobium, and the results used to calculate the composition of the other two samples. The results obtained were in satisfactory agreement with those obtained by other methods.DETERMINATION OF SENSITIVITY FACTORS Niobium was selected as the internal standard because, in addition to the factors listed above, it is present in all titanium dioxide pigments made by the sulphate process from ilmenite, or ilmenite beneficiates. The typical concentrations range from 100 p.p.m. to approximately 0-6 per cent. as niobium pentoxide. Furthermore, niobium may be deter- mined quickly and accurately by X-ray spectroscopy.July, 19661 DIOXIDE PIGMENTS BY SPARK-SOURCE MASS SPECTKOGKAPHY 423 With titanium dioxide pigments made from titanium tetrachloride, which contain very little niobium, it is necessary to make a known addition, and this is best incorporated at the graphite and sample mixing stage.Hydrolysis of a solution of this material produced a precipitate of hydrated titanium dioxide to which addi- tions were made. A solution of the compound was prepared and the required volume was mixed with the titanium dioxide slurry. This was then dried, lightly calcined and well ground. The level of addition in most cases was 100 p.p.m. of the element and, when possible, the actual concentration was checked by another method. Electrodes were prepared from a mixture of 0-25 g of niobium standard, 0.25 g of element standard and 0.5 g of graphite, so that the final niobium concentration in titanium dioxide was 50 p.p.m. Two separate electrode mixtures were prepared, and two electrodes were made from each mixture, making four determinations for each element.The sensitivity factors relative to niobium were then calculated for each plate. The results are given in Table V which lists the elements, the compounds used for addition, the analyses of the standards by other methods, when possible, and the relative sensitivity factors. TABLE V Titanyl sulphate of high purity was used as the starting material. The purest available materials were used to make the additions. SENSITIVITY FACTORS RELATIVE TO NIOBIUhl I N TITANIUM DIOXIDE - GRAPHITE MATRIX Sensitivity factor relative to niobium 7 Analysis, r- L--- Element Added as p.p.m. 1 2 3 4 Lithium . . . . . . I,i,SO, 93 0.52 0-40 0.41 0.49 Boron . . . . . . H,BO, 65 0.47 0.46 0.46 0.49 Magnesium . . . . . . MgSO, 80 0.26 0-28 0.22 0.28 Aluminium . . . . . . Xl,(SO,), 130 0.35 0.38 0.35 0.37 Silicon .. . . . . SiO, 3400 0.58 0-57 0.55 0.52 Phosphorus . . . . . . NH,H,I'O, 115 0.68 0.68 0.78 0.72 Potassium . . . . . . K,SO, 2300 0.24 0.2 1 0.24 0.19 Calcium . . . . . . Ca(CH,COO), 100 0.19 0.18 0.19 0.21 Scandium . . . . ' * sc'2(s04)3 70 0.70 0-67 0.65 0.69 Vanadium . . . . . . VOSO, 106 0.57 0-56 0.64 0.60 Chromium . . . . * cr2(s04)3 103 0.50 0.5 1 0.53 0.49 Manganese . . . . . . MnSO, 108 0.57 0.58 0.61 0.59 Iron . . . . . . FeSO, 102 0.32 0-39 0.36 0.35 Nickel . . . . . . NiSO, 1000 0.91 0-77 0.85 0.84 Gallium . . . . . . GaCl, 60 0.17 0-15 0.17 0.15 Zinc . . . . . . ZnSO, 8000 1.12 1-06 1.19 0.98 Germanium . . . . . . GCO, - 0.22 0-24 0.19 0.21 Arsenic . . . . . . NaAsO, 110 0.85 0.83 0.83 0.8 1 Rubidium . . . . . . Rb,SO, - 0.10 0.14 0.18 0.16 Strontium . .. . . . SrCl, - 0.14 0.15 0.16 0.17 Yttrium . . . . ' . Y,(SO,), - 0-56 0.53 0.52 0.53 Zirconium . . . . . . Zr(SO,), 90 0-81 0.79 0.77 0.78 Rhodium . . . . . . KhLl, - 1.18 1.27 1.32 1.40 Molybdenum . . . . (NH,),MoO, 100 1.07 1.10 1.08 1.22 Palladium . . . . . . PtlCl, - 0.95 1-03 1.03 0.99 Silver . . . . . . ;IgNO, - 1.00 0.96 0.91 0.98 Ruthenium . . . . . . RuCI, 100 1.1 1 1.27 1.3 1 1-15 -Antimony . . . . . . Sb,(C,H,W, 100 0.77 0.79 0.7 7 0.83 Cadmium . . . . . . CdSO, 86 2.20 1.90 2.00 1.95 Indium . . . . . f 1 3 S 0 4 ) 3 - 0.27 0.31 0.28 0.29 Tin . . . . . . . . Sn(NO,), 110 0.70 0.72 0.70 0.71 Barium . . . . . . BaCl, 116 0-39 0-43 0.42 0.42 Cerium . . . . . . Ce(SO,), 90 0.35 0-33 0.34 0.3 1 Ytterbium . . . . . . Yb,(SO,), - 0.40 0.46 0.52 0.46 Tantalum .. . . . . Ta(HC,O,), 110 1.38 1-33 1.34 1-35 Tungsten . . . . . . (NH4)6\V,024 119 1-62 1.58 1.62 1.49 Rhenium . . . . . . Re(NO,), 40 1.53 1.51 1.30 1.30 Platinum . . . . . . H,PtCl, - 2.10 2.90 2.50 2.50 - 0.23 0.24 0-30 0.35 - 1 *40 1-70 1.30 1.50 Lead . . .. . . Pb(NO,), Uranium . . .. * * U02(N03)2 - 0.93 0.94 1.04 1.05 Hafnium . . . . . . Hf(SO,), - 2.34 2.68 2.17 1.85 Iridium . . . . . . (NH4),1rCl6 - 2.40 2.20 2.40 2.20 Thallium . . . . . . T12(S04)3 Thorium . . . . . . ThCI, - 0.96 1-0 0.98 0.93424 JACKSON AND IVHITEHEAD ANALYSIS OF TITANIUM [ A ?Zd_?lsf, jrol. 91 The agreement obtained between the sensitivity factors is generally satisfactory, although the range is sometimes rather wide. In these instances, the concentration of the element in titanium dioxide pigments is so small that the scatter in sensitivity factor is relatively unimportant.THE USE OF SILVER AS CONDUCTING MATERIAL- levels with graphite, were investigated by using silver as the conducting material. of the niobium standard and 1-000g of silver. relative to niobium and these were found to be: magnesium, 0.22 and cobalt, 0.60 0.05. are similar to the results obtained with graphite. are shown in Table VI. The three elements, magnesium, nickel and cobalt, which cannot be determined at low Electrodes were prepared from a mixture of 0.100 g of the standard pigment, 0.100 g The sensitivity factors were determined 0.02; nickel, 0.87 0.04; It is noted that the sensitivity factors for magnesium and nickel when silver was used These factors were then used to analyse pigments of known composition and the results TABLE I’I DETERMINATION OF RIAGSESIURI, COBALT AXD xIcKErd IN TITAPiICIll DIOXIDE WITH SILVER hlATRIX 1 2 r--L 7 r-pA-- Added, Found, Added, Found, p.p . m. p. p. m . p.p.m. p.p.m. 7 Cobalt . . . . . . 5 4 5 4 Magnesium . . . . 20 15 20 1s Nickel . . . . . . 5 7 5 7 ANALYSIS OF PIGMENT SAMPLES- Eight different samples of titanium dioxide pigment were then analysed by the mass - spectrographic method with graphite as matrix, and the results are compared with those obtained by X-ray spectrometric and colorimetric methods. These results are shown in Table VII. TABLE 171 COMPARISON OF MASS-SI’ECTROGKAPHIC RESCLTS BY USING GRAPHITE MATRIX \VITH I n i s . 1o.M. ~ 0 .R . I . 1 O.M. J M.S. 1 0.M. (h1.S. ~ 0 . 3 1 . J M.S. (M.S. J1M.S. 1 O.M. JM.S. 1 O.M. JM.S. 1 O.M. Alu- minium oxide, per cent. 2.52 2.49 2.5 2.2 0.3 1 0-29 1.9 1.86 1.Oi 0.96 1.3 1-56 0.07 1 0.070 0.31 0.29 THOSE OBTAINED BY OTHER METHODS Phos- phorus Zir- Silicon pent- Zinc Calcium Potassium conium dioxide, oxide, oxide, oxide, oxide, Iron, oxide, per cent. per cent. per cent. per cent. per cent. p.p.m. per cent. 0.83 0.37 1.30 0-02 0.02 40 0.01 0.80 0.38 1.28 0.03 0.02 54 0.011 0.90 0.14 0.99 0.025 0.015 65 0.016 0.7 1 0.15 1-03 0.02 0-oox 80 0.017 0.04 0.61 0-0015 0.02 0.3 1 18 0.039 0.03 0.66 0-002 0.01 0.27 20 0*0:3x 1.1 0.24 1.1 0.0 1 0.01 55 0.014 0.94 0 . 2 2 0.93 0.0 1 0.0 1 73 0.015 0.053 0.50 C)-O010 0.012 0.1% 40 0.036 0.05 0.65 0~0020 0.012 0.15 23 0.036 0.055 0.27 0 .0 0 2 9.015 0.02 45 0.031 0.058 0.25 0.002 0.014 0.02 6 i 0.035 0.08 0.35 0.009 0.03 0.42 43 0.01 0.06 0.28 0.010 0.04 0.41 27 0.01 0.04 0.61 0.0015 0.02 0.31 18 0.039 0.03 0.66 0.002 0.01 0.27 20 0.038 M.S., mass-spectrographic method. OM., other methods. .\nti- mony oxide, Tin, per cent. p.p.m. 0.001 40 -<0.002 40 0.002 7 0.002 <: 20 0.014 10 0.02 ( 2 0 0.0:3x 45 0*039 44 0.017 10 0.016 <:20 0.01 I0 0.011 .;20 0.14 50 0.12 40 0.014 10 0.02 ( 2 0 ATCURACY OF RESULTS- In order t o assess the reproducibility of the method, the complete procedure for obtaining a mass spectrum, starting with the weighing of the graphite and sample, was repeated ten times on the same sample. It is noted that the reproducibility of the determination will probablyJuly, 19661 DIOXIDE PIGMEKTS BY SPARK-SOURCE MASS SPECTKOGKAPHY 425 be better than the quoted figures, because the sample itself may not be completely homo- geneous with reference to all the impurity elements.The mass spectra were measured, and the concentration of all the measurable elements calculated. The results are given in Table VIII. DISCCSSION O F RESCLTS Examination of the results listed in Table 1'111 indicates that the average coeficient of variation is 15.0 per cent., which is acceptable for elements present in parts per million con- centration. I t was not anticipated, however, that similar values for the coefficient of variation would be obtained for elements present at higher concentrations, as the method is specifically designed for trace amounts; in this connection it is interesting to note that the method can also be used to give an estimate of the concentration of elements, such as aluminium, zinc and silicon, which are present in the range 1 to 2 per cent. Although a higher level of accuracy is normally required at this level of concentration, nevertheless, an indication of the results to the accuracy achievable by the mass-spectrographic method is sufficient for many purposes.1i'hen it is possible to compare the results with other methods, the agreement between sets of results is satisfactory. I t is not possible, however, to make this comparison each time because of the difficulties in establishing methods for determining many of the elements at the concentrations in which they are present. In Table 1'11, the results of the analysis of 8 different samples of titanium dioxide pigments by the mass-spectrographic methods are compared with results obtained bj.other methods. Although the agreement is generally satisfactory, some discrepancies are evident in the results for iron which occasionallv show wider differences than would be expected. The possibility that the variation was due to surface contamination of the electrode from the die was eliminated by pre-sparking. I t is most probable that these differences are caused by heterogeneous distribution of iron in the samples, and they serve to illustrate one of the dis- advantages of the mass-spectrograpliic method. From Table I and 11, it can be seen that approximately 1 mg of titanium dioxide is used to deposit 250 nanocoulombs of charge, which is the amount required to produce a typical mass spectrum.Therefore, to obtain reliable results it is essential that the milligram of sample consumed represents the composition of the sample. In the colorimetric determination of iron a sample weight of 2 g is used, lvhich offers a much better chance of obtaining a representative sample. If, therefore, it is suspected that the sample is not homogeneous, an alternative technique in which the sample is homo- genised by solution, or fusion, must be adopted in order to ensure that a representative sample is used. This apparent disadvantage, however, can be turned to advantage if it is required to study the distribution of impurities in a specimen. The results in Table VI indicate satisfactory recovery of added amounts of cobalt, magnesium and nickel when a silver electrode system is used.I t is of interest to note that the sensitivity factors relative to niobium, for magnesium and nickel in a silver electrode system, are similar to the values found in graphite. I t is concluded that the technique of mass spectrography enables a comprehensive quantitative examination of a pigment sample to be carried out in a relatively short space of time. The only elements which cannot be determined at low level are sodium and copper because of interference by 4sTi2+ and titanium - oxygen complexes, respectively. A typical breakdown of the total time (in minutes) required to carry out Time taken for calcination of sample a t 600" C to eliniinstc Tvatcr and organic matter is as follows: Time taken for grinding of calcined sample .. . . . . . . . . . . Timc taken for weighing of sample and graphite . . . . . . , . . . . . Time taken for forming of electrode . . . . . . . . . . . . . . Time taken for mounting of electrodes . . . . . . . . . . . . . . Time taken for exposure (100 nanocoulombs of charge) . . . . . . . . . . Time taken for removal and development of plate . . . . . . . . . . . . . . . . . . . . r .. lime taken for mixing of sample and graphite . . an analysis 35 5 30 2 5 30. 5 3 11 7 minutes Visual examination of the plate takes a further 10 minutes so that a semi-quantitative assessment of a sample may be achieved in a total time, from receipt of sample, of approxi- mately 2 hours 10 minutes.A complete quantitative assessment of the plate with calculationTABLE VIII THE RESULTS OF 10 DETERMINATIONS ON THE SAME SAMPLE 1 Boron trioxide, p.p.m. . . 0.07 Magnesium oxide, p.p.m. . . 40 Aluminium oxide, per cent. . , 1-8 Silicon dioxide, per cent. . . 1.6 Phosphous pentoxide, per cent. 0.15 Potassium oxide, p.p.m. . . 80 Vanadium pentoxide, p.p.m. 5 Manganous oxide, p.p.m. . . 0-14 Arsenic trioxide, p.p.m. . . 15 Strontium oxide, p.p.m. . . 3 Zirconium oxide, p.p.m. . .120 Molybdenum trioxide, p.p.m. 10 Antimony trioxide, p.p.m. , .550 Lanthanum oxide, p.p.m. . . 0.21 Ceric oxide, p.p.m. . . . . 0.4 Hafnium dioxide, p.p.m. . . 8 Tantalum pentoxide, p.p,m. . . 65 Tungsten trioxide, p.p.m. . . 60 Thorium dioxide, p.p.m. . . 0.8 Calcium oxide, p.p.m.. .550 Chromic oxide, p.p.m.. . . * 2.2 Zinc oxide, per cent. . . . . 0.94 Tin, p.p.m. . . . . . . 90 Barium oxide, p.p.m. . . * . 5 Lead, p.p.m. . . . . . . 95 Uranium oxide, p.p.m. . . 0.8 Iron, p.p.m. , . .. . . 55 2 0-04 1.8 1.1 0.10 40 81 540 5 2.2 0.16 1.4 12 3 140 10 90 620 5 0.25 0.5 8 90 40 70 0.8 0.9 80 3 0.05 2.5 1-3 0.12 50 86 680 4.5 2.1 0.11 1.3 15 3 130 9 130 750 5 0.22 0.4 7 65 50 110 0.7 0.8 65 4 0.05 2.6 1.5 0.12 45 82 770 6.0 2.2 0-17 0.84 14 4 130 12 95 550 6 0.27 0-6 9 80 50 85 0.8 0.8 55 5 0.04 1-6 1.4 0.11 45 85 720 6.5 3-1 0-13 0.81 18 5 130 12 110 590 6 0.32 0.6 8 80 60 110 0.9 0.9 60 6 0.07 2.0 1.5 0.13 45 95 730 6.0 2.3 0.19 1.1 18 4 140 10 110 630 6 0.30 0.3 6 80 45 82 0.8 0.8 55 7 8 0.04 0.05 1.8 1.8 1.1 1.0 0.14 0-13 50 40 72 70 670 580 4.5 4.5 2.0 2.0 0.15 0-12 0.9 1.0 15 12 4 3 120 110 10 10 80 95 530 500 8 5 0.20 0.30 0.3 0.6 5 9 70 60 45 40 83 100 0.7 0.9 0.8 0.9 55 60 9 10 0.05 0.05 2.5 1-7 1.4 1.4 0.14 0.14 55 50 95 70 540 720 6.0 5-5 2.9 2.8 0.16 0.13 1.1 1.1 14 19 4 5 140 140 9 12 90 110 500 625 4 7 0-32 0.29 0.5 0.6 9 8 70 65 45 60 100 110 1.0 0.9 1.0 0.9 70 55 Mean 0.05 46 2-01 1.33 0.13 82 650 5.4 2.4 0.15 1.05 3.8 10.4 15 130 100 585 5.7 0.27 0.48 7.7 72 50 95 0.83 0.86 61 Standard deviation 0.01 5.2 0.37 0.20 0.015 8.9 0.75 0.40 0.025 0.19 2-5 0.79 10.5 1.2 14.7 76 1.1 0.04 0.12 1.3 9.5 7.8 15.5 0.09 0.07 8.4 89 Coefficient of variation 20.0 11.3 18-4 15.1 11.5 10.8 13-7 13.9 16.6 16.6 18.1 16.7 20.8 8.2 11.5 14.7 13.0 19-3 14.8 25.0 16.5 13.2 15.6 16.3 10.8 8.1 13.7 Other methods - 52 2.3 1.4 0.14 < 100 700 6 4 0.2 0.90 15.1 - 130 11 110 650 - 0 w 3 d x n bJuly, 19661 DIOXIDE PIGMENTS BY SPARK-SO WRCE MASS SPECTROGKAPHY 427 of the results takes approximately 60 minutes, so that an accurate analysis takes a total time of approximately 3 hours. Many of the above operations can be carried out concurrently, so that it is possible to examine up to eight samples in an 8-hour working day.The authors are indebted to the Directors of British Titan Products Company Limited, for permission to publish this paper. REFERENCES 1. 2. 3. 4. 5. 6. 7 . 8. Barksdale, J., “Titanium,” The Ronald Press Company, New York, 1949, Chapter 12. Stonhill, L. G., Chemist Analvst, 1958, 47, 68. Weyl, W. A., and Forland, T., I n d . Engng Chem., 1950, 42, 257. McTaggart, F . K . , and Bear, J., J . appl. Chem., 1955, 5, 643. Cali, J . P., Editor, “Trace Analysis of Semiconductor Materials,” Pergamon Press, Oxford, London, New York and Paris, 1964, p. 188. Waldron, J. D., Editor, “Akdvances in Mass Spectrometry,” Pergamon Press, Oxford, London, New York and Paris, 1959, p. 143. Brown, R., and Wolstenholme, W. A., “Publication No. 2030/73,” -4ssociated Electrical Industries, Scientific Apparatus Department, Traff ord Park, Manchester, 17. Halliday, J. S., Swift, P., and Wolstenholme, W. A., “Quantitative analysis by spark source mass spectrometry,” Associated Electrical Industries, Scientific Apparatus Department, Trafford Park, Manchester, 17. Paper presented a t Conference on Mass Spectrometry, Paris, Sep- tember, 1964. Received July 27th, 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100418

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

428 MOSS AND BROIVETT DETEKMINATION OF TETKA-ALKYL [Arsalyst, Yol. 91 Determination of Tetra - a€kyl Lead Vapour and Inorganic Lead Dust in Air R u R. MOSS AND (THE LATE) E. 1’. BROIJ‘ETT (The Associated Ocfel Co. L t d . , Ellesvneve Port, ChesAive) AIethods are described for the determination of particulate lead and of tetra-a1kj.l lead vapour in air, by passing the atmosphere under test through a glass-fibre filter and then through a hydrochloric acid solution of iodine monc chloride. Tetraethyl lead and tetramethyl lead are collccted in this solution by mcans of their reaction with iodine monochloride to give thc. corresponding dialkyl lead ions. ’l’he lead collected on the filter is extracted with a nitric acid - hj-drogen peroxide reagent, and the amount present is determined coloriiiietrically as lead dithizonate.This may be donc automaticall>- with the Technicon Xuto-Xnalyzer, or manually with a comparator a n d a standard disc. Manual and automatic procedures are also given for the determination of the amount of tetra-alkyl lead collected. The manual method inrwlL-es reaction of the clialkyl lead ions with dithizone a t high pH and matching the colour o f the dialkyl lead dithizonate with a standard disc. In the automatic procedure, the tfialkyl lead is conr-erted to the inorganic state before reaction with dithizone and colorimetric measiircment as lead dithizonate. The 111 e t ho cl s are designed for t hc ni ea su reni cn t o f 1 cad - i n -air con cent r a- tions down to 0.1 nig o f lead per 1 0 cubic metres of air, with saiiipling pcriods of at least 8 hours.;Z modified method based on a sampling period of half an hour, and having a sensitivity of 0.3 mg o f lead per 1 0 cubic metres, is also descritxxl. BOTH tetraethyl lead and tetramethyl lead are manufactured on a large scale for use as anti-knock additives to gasoline. Owing to the toxicity of organo lead compound\ it ih neces- sary to monitor the atmosphere for tetra-alkyl lead content where manufacturing operations are performed. Both tetraethyl lead and tetramethyl lead react with iodine to yield inorganic lead by means of a series of reactions indicated below- PbR, + PbR,+ ++ PbRZ2+ + Pb2+ The reaction rate between tetraethyl lead and iodine is such that tetraethyl lead can be collected quantitatively by passing the air under test through aqueous iodine solution under controlled conditions.Tetramethyl lead reacts less readily and more severe conditions are required for its collection. Snyder and Heridersonl recommend the use of a tube packed with solid crystalline iodine for “spot” testing the atmosphere for organic lead content. Linch et aZ.2 have shown that solid iodine and solutions of iodine in methanol are both effcxtive in collecting tetramethyl lead when using the “Uni-jet” air sampling equipment for sampling over short periods of time. Solutions in methanol obviously cannot be used for routine monitoring over periods of 8 to 24 hours owing to the volatility of the solvent. The use of solid iodine for this purpose has a number of disadvantages, the main ones being the difficultj- of packing the tube so as to avoid channelling, the possibility of variable “blank” values from one tube to another, and the volatilisation of iodine from the collecting tube during the sampling period.An investigation into possible alternative collecting agents led to a study of the beha1Tiour of solutions of iodine monochloride in this application. EXPERIMENTAL PREPARATION OF IODINE IUONOCHLORIDE REAGENT- potassium iodide and potassium iodate in strong hydrochloric acid solution. The preparation of the solutions of iodine monochloride is based on the reaction between KIO, + 2KI + 6HC1+ 3IC1 4- 3KC1 + 3H,OJuly, 19661 LEAD VAPOUR AND INORGANIC LEAD DUST IN -4IR 429 Solutions prepared in this way that are 5 N with respect to hydrochloric acid and 1.0 hi with respect to iodine monochloride are stable, and may be diluted ten times without hydrolysis occurring.h slight excess of potassium iodate is used to ensure complete reaction of the iodide. REACTION OF IODINE RIOXOCHLORIDE WITH TETRAETHYL LEAD AND WITH TETRAMETHYL LEAD- In order to follow the reaction between iodine monochloridc and the two tetra-alkyl lead compounds, the method of Henderson and Snyder3 for the determination of triethyl lead, diethyl lead and lead ions in the presencc of one another was modified and extended to the analogous methyl compounds. I t was found that all the alkyl lead dithizonates are sensitive to light. A 100-ml portion of 0.1 11 iodine monochloride reagent was treated with an ammoniacal buffer solution containing cyanide, citrate and excess sulphite over that required to reduce all the iodine monochloride present.The ammonia content was such as to give a pH value of 10-1 in the final solution. *Absorption spectra of the trialkyl lead and dialkyl lead dithizonates were obtained by adding a known amount of the appropriate chloride, equivalent in each case to 100 pg of lead, to the solution prepared as above, and then extracting with a solution of dithizone in a solvent comprising 1 volume of chloroform and 4 volumes of carbon tetrachloride. Under these conditions, the excess dithizone partitions into the aqueous phase. The absorption spectra of the solutions of the dithizonates were determined over the range 400 to 600 mp by means of a ITnicam SP500 spectrophotometer.The spectra obtained are shown in Fig. 1, together with the spectrum of an equivalent amount of lead dithizonate. Iodine monochloride solutions of 0.05 and 0.1 M were prepared, and amounts of tetraethyl lead and of tetramethyl lead equivalent to 100 pg of lead were added to 100-ml portions of these solutions. The solutions were then allowed to stand at room temperature for varying lengths of time. Reaction was stopped by adding the solution to the ammoniacal buffer contained in a darkened separating funnel. The dithizonates were then extracted under the conditions described above. The lead species present were identified by scanning the spec- trum in the visible range. Wavelength, mp Fig. 1. A4bsorDtion mectra of lead dithizonates ) 450 500 550 600 Wavelength, mp Fig.2. Absorption spectra of the dithizonates with a"l0-mm hg6t path' optical cell and 20 ml of of the yroducts of -reaction of iodine monochloride chloroform and carbon tetrachloride (1 + 4) : curve with tetraethyl lead and \\.it11 tetramethyl lead a t A, 100 pg of lead as triethyl lead dithizonate; room temperature: cur\.e -2, diethyl lead dithi- curve B, 100 pg of lead as trimethyl lead dithi- zonate; curve B, dimethyl lead dithizonate zonate; curve C, 100 pg of lead as diethyl lead dithizonate; curve D, 100 pg of lead as dimethyl lead dithizonate; curve E, 100 pg of lead as lead dithizonate430 MOSS AND BROWETT: DETERMINATION OF TETRA-ALKYL [A~alyst, T701. 91 The absorption spectra obtained, as shown in Fig. 2, were identical with those of diethyl lead dithizonate and dimethyl lead dithizonate, respectively, in amounts equivalent to 100 pg of lead.There were no differences between the spectra obtained after reaction times varying from 10 minutes to 1 week at room temperature. Thus both tetraethyl lead and tetramethyl lead are rapidly and quantitatively converted to the corresponding dialkyl lead ion by the iodine monochloride reagent. There was no evidence of any further reaction at room temper- ature. Exposure of the solutions to light had no effect on the course of the reaction. ,4t this temperature the dimethyl lead and the diethyl lead ions were stable in the iodine monochloride solution for at least 3 days. After this time there was evidence of further reaction to ionic lead. Similar trials were performed in which the solutions were maintained at 30" C.I I INTERFERENCE DUE TO INORGAKIC LEAD- Inorganic lead compounds may be present as dust in atmospheres that are monitored for tetra-alkyl lead vapour. Most of these compounds are soluble in the acid solution of iodine monochloride and would, therefore, interfere in the subsequent determination of dialkyl lead ions derived from tetraethyl lead or tetramethyl lead. Filtration of the air under test, prior to contact with the iodine monochloride reagent, will avoid the possibility or this inter- ference. The solids collected on the filter may also be analysed for lead content to give more complete results on the total toxic hazard of the atmosphere under test, n 4 Air inlet via charcoal anc ica - G n H silica gel scrubbers I A = Rotameter B = Vent line C = U-bore stopcock D = Bleed valve t o control suction E = Dreschel-type scrubbers connected by spherical ground-glass joints \ 'E' I ./ F = Atomiser G = Reservoir H =Teflon T-bore stopcock I = Palmer continuous slow injector operating an Agla syringe of cap- acity 0.5 ml.Fig. 3. Apparatus for the preparation of standard atmospheres and deter- mination of collection efficiency of absorbing solutions COLLECTIOX EFFICIENCY OF IODINE MONOCHLORIDE SOLtJTIONS- The apparatus shown in Fig. 3 was used for drawing atmospheres of constant tetraethyl lead or tetramethyl lead content through a series of scrubbers. The syringe was filled with a solution of tetraethyl lead or tetramethyl lead in ethanol, and the solution was injected at a slow, steady rate, via an atomiser, into an air stream that had been previously passed through activated charcoal and silica gel scrubbers.The air-flow was controlled at 4 cubic feet per hour by a bleed valve on the vacuum pump inlet. The alkyl lead concentration was adjusted by varying the concentration of the tetraethyl lead or tetramethyl lead solution injected by the syringe. The air stream containing the alkyl lead vapour was passed through a Dreschel- type scrubber, details of which are shown in Fig. 4, containing 100ml of the absorbing solution under test. This was followed by a sufficient number of similar scrubbers, eachJuly, 19661 LEAD VAPOUR AND INOKGANIC LEAD DUST IN AIR 431 containing 100 ml of iodine monochloride solution, to ensure complete collection of the alkyl lead compound.At the end of each trial the alkyl lead compounds collected were converted to inorganic lead by reaction with iodine, and the amount of lead collected in each scrubber was determined spectrophotometrically as the dit hizonat e. Each trial was of about 6 hours’ duration. The collection efficiency was calculated as- amount of lead collected in first scrubber - x 100 per cent. total amount of lead collected The results obtained when using 0.05 and 0.1 hi iodine monochloride solutions as the collecting agents are given in Table I. A further series of similar trials was performed in which the collection efficiency of aqueous iodine solutions was determined under exactly similar conditions. The values obtained for a 0.2 K iodine solution were 90 to 95 per cent.for tetraethyl lead and 40 to 50 per cent. for tetramethyl lead. The values obtained for a N iodine solution were 99 to 100 per cent. for tetramethyl lead and 86 to 89 per cent. for tetramethyl lead. Thus 0.1 M iodine monochloride solution was the only reagent tested that will give quanti- tative collection of both tetraethyl lead and tetramethyl lead when 100ml of the reagent is contained in a Dreschel-type scrubber, as shown in Fig. 4, and the air stream under test is drawn through at a rate of 4 cu. ft. per hour. The collection efficiency of 0.1 M iodine monochloride solution contained in a “midget impinger” (as supplied with the “Uni-jet” lead-in-air analyser) was then determined under conditions that would apply to tests made over a short period of time.Three midget impingers, each containing 15 ml of a 0.1 M iodine monochloride solution, were connected in series by spherical glass-joints. An air stream of constant tetraethyl lead or tetramethyl lead concentration was passed through at a rate of 4 cu. ft. per hour using the apparatus shown in Fig. 3. The results of these trials are given in Table 11.432 MOSS AND BRO\\rETT : DETERMINATION O F TETRA-ETHYL [A4~zalyst, 1'01. 91 TABLE I COLLECTION EFFICIENCY OF 100 MI, OF IODINE MOKOCHLORIDE SOLTJTIOK CONTAINED IN ,4 DRESCHEL-TYPE SCRUBBER, AT AN AIR RATE OF 4 C r . FT. PER HOCR Strength of iodine mono- chloride solution 0.05 hl 0.05 XI 0.1 a l Volume .4lkyl of air lead sampled, present CU. f t . Tetraethyl 22-7 lead 22.7 23.0 24.0 20.0 20.0 Tetramethyl 26.0 lead 21-3 20.0 20.0 14.7 14.7 T,ead collected in first scrub 11 er , Pg 60 145 382 780 1061 2060 58 150 289 460 699 1438 Lead collected in sccond scrubber, Pg 1 1 (1 < 1 6 19 4 10 2 0 35 56 97 Lead collected in third scrubber, c Pg n.d.n.d. n.d. n.d. 1 2 n.d. 1 2 3 3 5 Tetramethpl 24.3 6 0 11.d. n.d. lead 24.3 145 n.d. n.d. 26.0 353 6 n.d. 26.0 688 12 n.d. 20.0 1086 33 n.d. 20-0 2131 28 n.d. n.d. is used t o indicate not detected. Total lead .ollec ted, Pg 61 146 382 780 1068 208 1 62 161 311 498 758 1540 60 145 359 700 1119 2159 Per- centage Lead of lead in air collected concentra- in first tion, mg scrubber per 1 0 cu.m. 98 0.95 99 2.3 100 5.9 100 11.5 99 18.9 99 36.7 94 0.85 93 2.7 93 5.5 92 8.8 92 18.2 93 37.0 100 0.85 100 2.1 98 4-9 98 9.5 97 19.8 99 38.1 TABLE I1 COLLECTIOK EFFICIENCY OF 15 MI, OF 0.1 11 I o r l I N E NONOCHLORIDE SOLUTION COSTXISED IK A MIDGET IMPINGER, AT AN AIR RATE OF 4 CTT.FT. PER HOUR Awiyl lead present Tetraethyl lead Tetramethyl lead Volume of air sampled, cu. f t . 8.0 4-4 4.0 4.0 2.0 2.0 4-0 2-0 2.0 2.0 2.0 Lead first impinger, Pg 19.7 24.1 47.3 96.8 collected in ( 104 204 21.2 21.3 42.5 92.7 165 Lead :ollected in sccond impinger, Pg 1.2 1.0 4.1 3.9 4.2 7.6 1.8 2.4 2.5 7 . 2 15.0 Lead collected in third Pg 0.6 0.8 0.7 0.9 0.6 2.9 0.2 0. f i 1.3 0.9 0.8 impinger, c Total lead ,ollected, Pg 21.5 25.9 52.1 102 109 215 23-2 24.3 46.6 101 181 Percentage of lead collected in first impinger 92 93 91 95 95 95 91 88 92 92 91 Lead in air concen- tration, mg per 10 cu.m.0.95 2.1 4.6 9.0 19.2 38-0 2.0 4.3 8.2 17.8 32.0 T H E T)ETERhIISATION OF DLILKYL LEA11 IOSS 1s SOLCTIOK- -4s tetraethyl lead and tetramethyl lead, when collected in iodine monochloride solution, are converted to the corresponding dialkyl lead salts, and as the solutions obtained are stable at room temperature, one would expect to be able to determine the amount of the tetra-alkyl lead compounds collected by direct measurement of the dialkyl lead ions in solution. Alterna- tively, an additional btep of converting the dialkyl lead ions to inorganic lead would have to be incorporated in the analytical scheme. The wavelength of maximum absorption by diethyl lead dithizonate is 490 mp and that by dimethyl lead dithizonate is 483 mp, as shown in Fig. 1. Calibration curves were prepared for both species at both wavelengths.These showed that Beer's Law was obeyed, but the slope of the calibration lines differed slightly, thus making impracticable any accurate deter- mination of total lead content by a single spectrophotometric measurement. Solutions of both the dialkyl lead dithizonates in the carbon tetrachloride - chloroform solvent are orange in colour, that of the diethyl lead dithizonate being slightly more red than that of the dimethyl lead dithizonate.July, 19661 LEAD VAPOUR AND INORGANIC LEAD DUST I N AIR 433 Standard solutions of diethyl lead chloride and dimethyl lead chloride in iodine mono- chloride reagent were prepared, containing amounts from 10 pg of lead to 240 pg of lead per 100 ml of solution. These solutions were buffered and then extracted with 20 ml of dithizone solution as in the method given below.The colour values of the dialkyl lead dithizonate solutions so obtained, and also of a “blank” determination, were noted. Messrs. Tintometer Ltd. prepared standard glasses, incorporated in two discs, that were intermediate in shade between the two series of solutions. It was possible to match solutions of either of the dialkyl lead dithizonates against these discs within the normal precision of visual matching when viewing against a white light screen. \\.’hen using an automatic technique of analysis by means of the Technicon Auto-Analyzer it is necessary to analyse a series of standards with each batch of samples. The provision of standard solutions of pure diethyl lead or dimethyl lead salts for this purpose would be difficult.The alternative procedure of reacting with iodine to convert the dialkyl lead ions to lead, extracting with dithizone and measuring as lead dithizonate was, therefore, developed. This has the advantage that the same Auto-Analyzer pump manifold assembly can be used for the determination of both the tetra-alkyl lead content and the inorganic lead content of the atmosphere under test. Double crook Extraction coil 12-ft. flat spiral tubing of 2 7 mm i.d. Vent to \ De-bubbler No 2 atmosphere \ $ ‘ Recorder Fig. 5. air samples Manifold assembly and flow diagram for the automatic determination of lead collected from A series of trials was performed in which solutions of tetraethyl lead or tetramethyl lead in iodine monochloride reagent were fed into the analytical system, shown in Fig.5 , mixed with potassium iodide solution and passed through a standard single coil heating-bath maintained at 50“ C. The effluent from the heating-bath outlet was collected and the excess iodine removed by reaction with sulphite. The solution was buffered to a pH value of 10.1 and then extracted with dithizone solution. Examination of the absorption spectra of the dithizonates obtained showed that diethyl lead and dimethyl lead ions were quantitatively converted to lead by reaction with iodine under the conditions used. The retention time in the coil at the flow-rates used is about 8 minutes. METHOD FOR THE DETERMINATION OF LEAD-IN-AIR CONCEKTRATION (LONG PERIOD SAMPLIKG) REAGENTS- 25 per cent.w / v potassium iodide solution-Dissolve 500 g of potassium iodide in about 1 litre of distilled water. Make slightly alkaline by the drop-wise addition of ammonia solution and then “de-lead” by shaking with successive portions of dithizone solution until the green colour of the dithizone solution is unchanged. After separation of the organic phase,MOSS AND BROWETT : DETERMINATION OF TETRA-ALKYL [Analyst, Vol. 91 434 make the solution slightly acidic by the drop-wise addition of dilute nitric acid and wash with chloroform to remove any dissolved dithizone. Separate off the chloroform layer and make up the volume to 2 litres with distilled water. 1.0 M iodide monochloride stock solution-Mix 445 ml of de-leaded 25 per cent. w/v potassium iodide solution with 445 ml of AnalaR concentrated hydrochloric acid.Slowly add 75 g of analytical-reagent grade potassium iodate with cooling, stirring the solution until all free iodine has re-dissolved to give a clear orange-red solution. Dilute to 1 litre with distilled water, 0.1 M iodine monochloride reagent-Dilute 1 volume of iodine monochloride stock solution with 9 volumes of distilled water. Note: (i) Rubber bungs must never be used to stopper vessels containing iodine monochloride s o h t ions. (ii) Iodine monochloride will react with ammonium ions under certain conditions to yield nitrogen tri-iodide. It is important, therefore, that ammonia and ammonium salts are excluded from solutions containing iodine monochloride except when an excess of reducing agent is also present.Standard lead solutions .for automatic organic lead determination-Prepare a solution of analytical-reagent grade lead nitrate, containing 100 pg of lead per ml, in 0.1 per cent. v/v nitric acid. With a pipette transfer 10 ml of this solution and 10 ml of the iodine monochloride stock solution into a 100-ml Pyrex calibrated flask. Make up to volume with distilled water. This solution contains 10 pg of lead per ml, and has the same iodine monochloride and hydrochloric acid content as the 0.1 M iodine monochloride reagent. Measure volumes of this solution corresponding to 50, 100, 150, 200 and 250 pg of lead, respectively, into 100-ml Pyrex calibrated flasks and make up to volume with 0.1 M iodine monochloride reagent. Sulphite - cyanide solution-Dissolve 250 g of anhydrous sodium sulphite and 25 g of potassium cyanide in about 1800 ml of distilled water.“De-lead” the solution by extraction with successive portions of dithizone solution until the green colour of the dithizone solution is unchanged. Wash the solution with chloroform to remove any dissolved dithizone, separate off the chloroform phase and make up the volume to 2 litres with distilled water. 46 per cent. w / v ammonium citrate solution-Weigh 400 g of citric acid monohydrate into a beaker, add about 100 ml of distilled water and place the beaker in an ice and water cooling- bath. Add just sufficient o-cresol red indicator solution to give a definite colour, and then add concentrated ammonia solution (spgr. 0.88) slowly, with stirring, until the alkaline (red) colour of the indicator is just developed.Dilute the solution to 1 litre with distilled water and “de-lead” the solution by extraction with successive portions of dithizone solution until the green colour of the dithizone solution is unchanged. Wash the solution with chloroform to remove any dissolved dithizone. Allow to stand until the aqueous phase is clear and separate off the chloroform phase. If necessary, filter the solution through a glass-wool plug to remove any particulate matter present. UtifSer solution KO. 1-This is used for the manual method of lead determination. Mix 400 ml of sulphite - cyanide solution, 20 ml of 46 per cent. w/v ammonium citrate solution, 350 ml of concentrated ammonia solution (sp.gr. 0.88) and 230 ml of distilled water.Bzifer solution N o . 2-This is used for the automatic method of lead determination. Mix -300 ml of sulphite - cyanide solution, 200 ml of 46 per cent. w/v ammonium citrate solution, 75 ml of concentrated ammonia solution (sp.gr. 0.88) and 525 ml of distilled water. l\ritric acid - hydrogen Peroxide reagent-Mix 200 ml of concentrated analytical-reagent grade nitric acid with 1600 ml of distilled water, and add 200 ml of “100 volume’’ hydrogen peroxide. Hydroxylamnzoniunz chloride reagent-Dissolve 200 g of hydroxylammonium chloride in 750ml of distilled water and add 200 ml of concentrated ammonia solution (spgr. 0.88). “De-lead” this solution by shaking with successive portions of dithizone solution until the green colour of the dithizone is unchanged.Wash the solution with chloroform to remove any dissolved dithizone, separate off the chloroform phase and make up the volume to 1 litre with distilled water. This reagent is stable for several weeks when stored in amber glass bottles. Acid stock solution-Heat 1 litre of nitric acid - hydrogen peroxide reagent to boiling point and boil gently for 5 minutes. Slowly add 400ml of hydroxylammonium chloride reagent and continue boiling for 10 minutes. Cool, and make up the volume to 2 litres withJU~Y, 19661 LEAD VAPOUR AND INORGANIC LEAD DUST I N AIR 435 distilled water. This provides an acid stock solution for the preparation of the wash solution and of standards. Wash solution for automatic inorganic lead determination-Prepare the wash solution by diluting the acid stock solution with an equal volume of distilled water.Standard lead solutions for automatic inorganic lead determination-Prepare a solution of analytical-reagent grade lead nitrate containing 25 pg of lead per ml, in 0.02 per cent. v/v nitric acid. Measure volumes of this solution corresponding to 50, 100, 150, 200 and 250 pg of lead, respectively, into 100-ml Pyrex calibrated flasks. Add to each 50ml of the acid stock solution (above) and make up to volume with distilled water. 50 mg per litre dithizone sol.ution for manual lead determinations-Dissolve 100 mg of dithizone, Eastman Kodak, in 400 ml of chloroform, then add 1600 ml of carbon tetrachloride and mix thoroughly. 20 w g per litre dithixone solution for automatic lead determinations-Dissolve 40 mg of dithizone, Eastman Kodak, in 400 ml of chloroform, then add 1600 ml of carbon tetrachloride and mix thoroughly.PROCEDURE- Collection of sanzple-Place a Gelman glass-fibre filter-paper, of 1-inch diameter, type E, in a Gelman open filter-holder and attach it to the inlet of a Dreschel-type scrubber (Fig. 4). Measure 100 ml of iodine monochloride reagent into the scrubber and place it in the sampling position. Connect the outlet of the scrubber via a second scrubber containing sodium thio- sulphate solution to a gas meter that is connected to a suitable vacuum system. Draw air through the filter and the iodine monochloride reagent at a rate of 3 cubic feet per hour for a period of 8, 12 or 24 hours. Disconnect the scrubber from the sampling train and note the total volume of air that has passed through it. The amounts of inorganic lead collected on the filter and of the tetra-alkyl lead collected in the iodine monochloride reagent may be determined automatically or manually in each case.AUTOMATIC METHOD FOR DETERMINING TETRA-ALKYL LEAD COLLECTED APP-IRATUS- The apparatus consists essentially of standard Auto-Analyzer modules but with a constant-head device, an extraction coil, a phase separator and an optical cell as described previously for the determination of lead in urine.4 A single-coil heating-bath in which the on - off temperature controller had been replaced by a proportional controller is also included in the system. The prin- ciple of "de-bubbling" the sample-wash stream and then re-segmenting with air was again incorporated in the analytical system in order to achieve a constant pH value in the buffered aqueous phase from which the lead is extracted.The manifold assembly and flow diagram is shown in Fig. 5. PROCEDURE- with 0.1 h i iodine monochloride reagent for use as wash solution. of the heating-bath is steady at 50" C & I" C, and that cooling water is flowing through the cooler immediately after the heating-bath. Switch on the machine with the crook of the sampler in the wash solution, the cell waste receiver inlet tap closed and the pump tubing from this receiver disconnected. Pump all reagents through the system to waste via the phase separator overflow until a steady flow pattern is achieved. Then connect the cell waste receiver pump line, open the tap and pump the chloroform - carbon tetrachloride phase through the cell.Switch on the recorder chart drive and position the cell to give maximum deflection on the chart before adjusting the base- line. Fill alternate sample cups in the sample tray with 0.1 h i iodine monochloride reagent and transfer a series of standard lead solutions to the first 5 available spaces on the sample tray. Remove the insert from each scrubber used to collect the sample and make up the volume in the scrubber to the 100-ml calibration mark with distilled water. Shake the scrubber to mix and then, by using the insert as a dropping pipette, transfer about 2 ml of solution to a sample cup. Place the sample cups containing the sample solutions in the remaining available spaces on the sample tray.A water-cooled coil is fitted on the outlet from the heating-bath. .Issemble the apparatus as shown in the flow diagram and fill the constant-head device Check that the temperature436 MOSS AND BROWETT: DETERMINATION OF TETRA-ALKYL [A~zaL’yst, Vol. 91 With the sampler set to operate at a rate of 40 per hour, switch on when a steady base- line is being drawn on the recorder chart. After aspiration of the last sample, allow iodine monochloride reagent to be aspirated until the recorder pen has returned to the base-line. The time interval from aspirating the sample to recording the corresponding peak is about 17 minutes. The buffer composition and the pumping rates of the reagents are designed to bring the pH value of the aqueous phase to about 9.4 for the dithizone extraction stage.The aqueous effluent from the phase separator must be tested periodically to ensure that the extraction is taking place at a pH value within the range 9.2 to 9.6. Draw a calibration curve relating peak height to micrograms of lead per 100 ml of standard lead solution and read off the total amount of lead collected in each iodine monochloride scrubber from this curve. The calibration curve is not linear. AUTOMATIC METHOD FOR DETERMINING INORGANIC LEAD COLLECTED APPARATUS- As for the automatic determination of organic lead content escept that the constant-level device is filled with nitric acid - hydrogen peroxide - hydroxylamine wash solution and the 25 per cent. w/v potassium iodide reagent is replaced by distilled water. PROCEDURE- Dismantle the filter holder and transfer the glass-fibre paper to a Pyrex beaker by means of a pair of forceps.Add 25 ml of nitric acid - hydrogen peroxide reagent and heat the solution to boiling. Boil gently for 5 minutes, cool slightly and add 10 ml of hydroxylammonium chloride reagent. Cool and filter through a sintered-glass crucible in a Witt filtration apparatus, into a 100-ml Pyrex calibrated flask. Wash the crucible with several portions of distilled water and make up to volume with distilled water. Assemble the Auto-Analyzer with the appropriate reagents and wash solution. Fill alternate sample cups in the sample tray with the nitric acid - hydrogen peroxide - hydroxyl- amine wash solution and the remaining alternate available spaces in the tray with a series of the appropriate standards and the samples.Operate the machine as described above, and determine the amount of inorganic lead in each sample solution by reference to the calibration curve obtained from the standards. Allow for the amount of lead extracted from the paper when calculating the amount of lead collectcd on each filter. MANUAL METHOD FOR DETERMINING TETRA-AIXYL LEAD COLLECTED Re-heat to boiling and boil gently for a further 10 minutes. The calibration curve obtained is not linear. Perform periodic “blank” determinations on the glass-fibre filter-papers. APPARATUS- “ All-Purpose” Lovibond comparator with 5-mnz and 13-5-mm all-glass fused cells. White light viewing cabinet-Use with the Lovibond comparator. Comfiarator discs-These are used to match standard solutions of dimethyl lead and diethyl lead dithizonates, ranges 0 to 100 pg of lead and 80 to 240 pg of lead, respecti\-ely, together with brightness screen. PROCEDURE- Remove the insert from each scrubber used to collect a sample and make up the volume in the scrubber to 100 ml with distilled water.To a 250-ml Pyrex separating funnel, painted black, transfer 20 ml of 25 per cent. w/v potassium iodide solution and 50 ml of buffer solution No. 1. Shake the funnel to mix and then add the contents of the scrubber to the funnel. Wash the scrubber with about 10ml of distilled water and add the washings to the separating funnel. Swirl the container to mix and then add 20 ml of 50 mg per litre dithizone solution. Fill the 13.5-mm cell with the lower non-aqueous phase and place the cell in the right-hand compartment of the Lovibond comparator.Place the 0 to 1OOpg of lead disc and the brightness screen in position. Place the comparator in the white light cabinet and rotate the standard disc until a colour match is obtained. Shake the funnel for 30 seconds and then allow the layers to separate.July, 19661 LEAD VAPOUR AND INORGANIC LEAD DUST I N AIR 437 If the depth of colour of the non-aqueous phase is greater than that of the glass corre- sponding to 100 pg of lead, transfer a further portion of the non-aqueous phase to a 5-mm cell and repeat the procedure, using the disc corresponding to 80 to 240 pg of lead. A “blank” determination on the reagents alone should give a disc reading corresponding to less than 1Opg of lead with the 13.5-mm cells and 20 ml of dithizone solution, if the reagents have been properly “de-leaded.” The disc reading corresponding to a colour match gives the total amount of lead collected in the sample.MANUAL METHOD FOR DETERMINING INORGANIC LEAD COLLECTED APPARATUS- “ All-Purfiose” Lovibond comparator with 5-mm all-glass fused cells. W h i t e light viewing cabinet-Use with the Lovibond comparator. Lovibond Comparator disc Reference 5/17-This disc was calibrated against standard amounts of lead under the conditions of test, with various volumes of dithizone solution. When using the 5-mm optical cell, the following relationship was obtained- pg of lead present = disc reading x volume of dithizone (ml) x 330 PROCEDURE- Dismantle the filter holder and transfer the glass-fibre paper to a Pyrex beaker by means of a pair of forceps.Add 25 ml of nitric acid - hydrogen peroxide reagent and heat the solution to boiling. Boil gently for 5 minutes, cool slightly and add 1Oml of hydroxyl- ammonium chloride reagent. Re-heat to boiling and boil gently for a further 10 minutes. Allow to cool and filter through a sintered-glass crucible in a Witt filtration apparatus. Collect the filtrate in a beaker and neutralise it by the drop-wise addition of concentrated ammonia solution (sp.gr. 0.88). Transfer the neutral solution to a separating funnel and add 60 ml of buffer solution No. 1. Mix the solutions and then add 20 ml of 50 mg per litre dithizone solution. If sufficient dithizone has been added the aqueous phase will have a definite orange colour.If this is so, transfer a portion of the chloroform - carbon tetrachloride phase to a 5-mm optical cell. Place the cell in the comparator and match the colour against the standard disc with the white light viewing cabinet. If the aqueous phase, after shaking with 20 ml of dithizone solution is colourless or has a pale yellow colour, add further 20-ml portions of dithizone solution until the aqueous phase has a definite orange colour after shaking for 30 seconds. Match the colour of the chloroform - carbon tetrachloride phase against the standard disc, as above. Shake the funnel for 30 seconds and allow the layers to separate. Perform a “blank” determination on the reagents using a clean paper. Calculate the amount of inorganic lead collected from the relationship- pg of lead collected : (disc reading - blank) x volume of dithizone (ml) x 330 METHOD FOR “SPOT” TESTING FOR TETRA-ALIWL LEAD-IN-AIR CONCENTRATION REAGENTS- 0.1 hi iodine monochloride reagent.Rufer solution No. 1-For the manual method of lead determination. 50 mg per litre dithizopie solution. These reagents are prepared by the methods given above. APPARATUS- rate of 4 cu. ft. per hour, with a midget impinger for containing the absorbing liquid. “ [Jni-jet” air sampling apparatus or equivalent equipment-To obtain an air sample at the Gelman open jilter holder and glass-jibre papers, type E , 1-inch diameter. clAll-Purjbose” Lovibond comparator with 13.5-mm all-glass fused cells. Comparator discs f o r tetraethyl lead and tetramethyl lead in air, yange 0 to 100 pg of lead, White light viewing cabinet-Use with the Lovibond comparator.and brightness screen.438 MOSS AND BROWETT [Amlyst, Vol. 91 PROCEDURE- Measure 15 ml of 0.1 M iodine monochloride reagent into the midget impinger and fit a Gelman open filter holder with a glass-fibre paper, type E, on to the inlet of the impinger. With the “Uni-jet” air sampling apparatus or any otheI suitable equipment, draw 2 cu. ft. of air through the sampling train at a rate of 4 cu. ft. per hour. Disconnect the filter and the midget impinger and transfer the iodine monochloride solution to a separating funnel. Wash out the impinger with three successive 10-ml portions of distilled water and add the washings to the separating funnel. Add 10 ml of buffer solution No.1 and swirl the contents until all the free iodine initially formed is re-dissolved. Add 4 ml of 50-mg per litre dithizone solution, shake the funnel for 30 seconds and then allow the layers to separate. Run the lower non-aqueous phase into a 13.5-mm optical cell and place the cell in the right-hand compartment of the comparator, Place the 0 to 100 pg of lead disc and brightness screen in position. Place the comparator in the white light viewing cabinet (or, alternatively, facing North light) and rotate the disc until a colour match is obtained. Sote the disc reading. The concentration of tetra-alkyl lead in air- (i), as pg of lead per cubic foot = disc reading x 0.10. (ii), as mg of lead per 10 cubic metres = disc reading x 0.035. SCOPE AND APPLICATION OF THE METHODS The concentrations of both tetra-alkyl lead vapour and particulate lead in air may be measured separately by the method described above with a sensitivity of 0.1 mg of lead per 10 cubic metres when a sampling period of 8 hours (or longer) is used. The values recom- mended by the American Conference of Governmental Industrial Hygienists5 for the maximum allowable concentrations of tetraethyl lead and for inorganic lead are 0.75 mg of lead per 10 cubic metres and 2.0mg of lead per 10 cubic metres, respectively. Therefore this method may be used to follow trends in average daily lead-in-air concentrations well below the “threshold values. ” The method based on a sampling period of half an hour allows a fairly quick check to be made on atmospheres where a toxic hazard due to tetra-alkyl lead vapour may exist, The sensitivity of this method (0-3 mg of lead per 10 cubic metres) is adequate to determine whether such a hazard does exist. The maximum concentration that can be measured is 3.5 mg of lead per 10 cubic metres when the volume of the air sample is 2 cu. ft. Even higher concentrations may be measured, but with less precision, if smaller samples are taken. We acknowledge the assistance given by Messrs. Tintometer Ltd., in making the com- parator disc for the manual method for determining tetra-alkyl lead in air. We thank The Associated Octel Co. Ltd., for permission to publish this paper. REFERENCES 1. 2. 3. 4. 5. Snyder, L. J., and Henderson, S. R., Anal-yyt. Chem., 1961, 33 1175. Linch, A. L., Davies, R. B., Stalzer, R. F., and A h d o t t i , W. F., ,4mel~. Ind. H?y. -32s~. J . , 1964, Henderson, S. R., and Snyder, L. J., Analvt. Chem., 1961, 33, 1172. Browett, E. V., and Moss, R., Analyst, 1965, 90, 715. Archs Enviv. Hlth, 1964, 9, 545. 25, 81. Received Jirvze lOtli, 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100428

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

July, 19661 BRAID, HUNTER, MASSIE, NICHOLSON AND PEARCE 439 An Examination of Some of the Factors Affecting the Determination of Carbon Dioxide by Non-aqueous Ti trime t ry BY P. BRAID, J. A. HUKTER, W. H. S. MASSIE, J. D. NICHOLSON AND B. E. PEARCE (Heviot- Watt Univevsity, Chambers Street, Edinburgh 1) Some of the factors, including choice of absorbent, indicator and titrant, that affect the determination of carbon dioxide by non-aqueous titrimetry are examined experimentally. The results of this examination are used to give a procedure that is recommended for the determination of milligram amounts of carbon dioxide. The method involves absorption of the carbon dioxide in a 5 per cent. v/v solution of ethanolamine in formdimethylamide, followed by titration with standard tetrabutyl ammonium hydroxide in benzene - methanol solution t o a visual end-point with thymolphthalein indicator.THE direct titrimetric determination of carbon dioxide with visual indications is possible when carried out in non-aqueous solvents. Attempts to increase the accuracy of the method have usually involved changing the combination of reagents or conditions of absorption or titration in order to improve retention of the carbon dioxide, or to facilitate observation of the equivalence point. Changes that have been made appear to have resulted from trial and error rather than from any systematic examination of the various factors involved. Grant et aZ.1 used formdimethylamide as the absorbing solvent instead of acetone or pyridine as used by Blom and Edelhausen.2 They also reported more satisfactory end-point detection with thymolphthalein as indicator in place of thymol blue.LTarious titrants have been tried, and Grant et aZ.l found that potassium methoxide in benzene - methanol solution was superior to sodium methoxide. The method described by White3 involves continuous titration of the carbon dioxide as it is introduced into the solvent to prevent its removal by the carrier gas, whereas Patchornick and Shalitin4 overcame this difficulty by the use of a solution containing benzyl- amine to retain the carbon dioxide, probably as benzylamine N-benzyl carbamate. The Steel Company of Wales (private communication, 1964) found that retention in formdimethyl- amide could be improved by the addition of an unspecified amount of ethanolamine.Indicator fading has been described by White3 who applied a time-dependent “fade correction” to the volume of titrant used; a procedure that was later adopted by Boyle, Stevens and Sunderland.5 This paper describes experiments that have been carried out to examine the absorption of carbon dioxide by various organic amines in order to select the most suitable for addition to formdimethylamide to improve its carbon dioxide retention characteristics. A semi- quantitative comparison of different indicators in the selected solvent system has also been made, and the conclusions resulting from experience gained with various non-aqueous titrants during the course of this section of the work are given. The procedure finally chosen is suitable for the determination of carbon dioxide produced in various ways, and some results for the micro determination of carbon in O.A.S.compounds by rapid combustion are included to show how the titrimetric method could be applied to a standard system. EXPERIMENTAL ABSORPTION AND RETENTION OF CARBON DIOXIDE- The reactions of a number of amines with carbon dioxide were examined by passing the gas sequentially into undiluted samples of diethylamine, diamino-ethane, butylamine, benzylamine, cyclohexylamine and ethanolamine.440 BRAID et al. : AN EXAMINATION OF SOME OF THE FACTORS AFFECTING [Analyst, Vol. 91 A vigorous exothermic reaction occurred each time, producing a syrupy liquid with ethanolamine and white solid products with each of the other amines. The compounds formed differed in stability ; those from diethylamine and diamino-ethane decomposed rapidly but the others were more stable, the ethanolamine compound appearing unchanged after 24 hours.Infrared spectra of the 4 relatively stable products were obtained by using the potas- sium bromide disc techniques with a Perkin-Elmer infracord spectrophotometer. For each product the twin-SH, peaks (3500 to 3300 per cm) were replaced by a single peak correspond- ing to a =NH group. The -NH, peaks at 1650 and 1580 per cm vanished, and new peaks were observed in the region of 1600, 1300 and 800 per cm, which would indicate the presence of a -?r'H,' group, and at 1610 to 1550 and 1420 to 1300 per cm as would be expected for a COO- group. It therefore seems likely that substituted ammonium carbamates are formed. There are two possible reactions for the titration of carbamates by a strong base such as potassium methoxide- (a) H,NR.oOC.NHR + KOCH, = RHN.COOK + RNH, + CH,OH or (b) H,hR.OOC.NHR + KOCH, = SRNH, + KCH,CO,.Patchornick and Shalitin4 favour (a), but either gives the equivalence relationship- 1 litre of N base = 44-01 g of carbon dioxide. The absorption efficiencies of the different amines for carbon dioxide were next examined for solutions of the amines of different concentrations in formdimethylamide. The initial proportion of amine to formdimethylamide used was 3 per cent. v/v, but if good recovery of carbon dioxide was obtained the concentration was lowered to 1 per cent. v/v, whereas if poor recovery resulted with the 3 per cent.solution the concentration was raised to 5 per cent. v/v. Known amounts of carbon dioxide, obtained by heating weighed milligram amounts of sodium hydrogen carbonate, were swept into 10-ml samples of the chosen absorbent contained in a small flask by a stream of purified nitrogen maintained a t a flow-rate of about 50 ml per minute. After 15 minutes the absorbed carbon dioxide was titrated with approxi- mately 0.02 N standard tetrabutyl ammonium hydroxide in benzene - methanol. The titrant was introduced from a 5-ml microburette until a faint blue colour was obtained with thymol- phthalein indicator. The results are summarised in Table I. TABLE I RECOVERY OF CARBON DIOXIDE ABSORBED Carbon dioxide range calculated froin weights of Proportion sodium hydrogen of solvent in carbonate, formdimethylamide mg 3*& v / \ ~ of cyclohexylamine.. 1.691 to 3-676 5 O / O v/v of cyclohexylamine. . 2-302 to 3.550 30,, x ~ / v of ethanolamine . . 2.061 to 2.919 lo/, \-/v of ethanolamine . . 1.855 to 2.601 3"/, v/v of benzylaminc . . 2.320 to 2.874 l:,, v/v of benzylaminc . . 2.288 to 2.807 3*, v/v of butylaniinc . , 2.405 to 3-119 l o b v/v of butylamine . . 2.579 to 2.818 3 O ; v/v of diethylamine . . 2-546 to 2.800 5:& v/v of diethylamine , . 2-583 to 2.736 Number of deter- minations 3 3 5 9 5 9 7 7 9 9 BY DIFFERENT SOLVENTS Carbon dioxide range found, mg 0.595 to 1.330 0.63 1 to 0.95 1 2.062 to 2.905 1.825 to 2.565 2-297 to 2.813 2.321 to 2.804 2-353 to 3-145 2.572 to 2.795 2.380 to 2.687 2.556 to 2.717 Error range, per cent.-69.6 to -57.5 -74.1 to -70.5 - 0.75 to + 1.45 - 1.62 t o + 1.83 - 3.95 to - 0.99 - 2.79 to -+ 1.44 - 2.17 to + 1.95 - 0.82 to + 0.04 - 8.25 to + 0.04 - 4.39 to + 2.12 The most accurate determinations were those with 1 per cent. butylamine or 3 per cent. ethanolamine. Those with 3 per cent. butylamine were less satisfactory, but this is attributed to increased difficulty in discerning the end-point of the titration rather than to any decrease in the efficiency of absorption of the carbon dioxide. Tndeed, all of the amines tended to make the end-point colour changes less sharp than when they were absent. This effect was least evident with ethanolamine, with which satisfactory end-points could be obtained a t a 5 per cent. concentration in the fonndimethylamide, although they became less satisfactory if the amine concentration were further increased.July, 19661 DETERMINATION OF CARBON DIOXIDE BY YON-AQUEOUS TITRIMETRY 441 SPECTROPHOTOMETRIC EXAMINATION AND COMPARISON OF DIFFERENT INDICATORS- Titrations of carbon dioxide with alkali in the presence of various indicators with visual observation of the colour changes had revealed that in some instances the changes of colour were rather gradual.To permit the selection of the most suitable indicator the end-point characteristics of a number of indicators were compared by spectrophotometric titration of carbon dioxide solutions. A Unicam SP600 spectrophotometer was used with a specially constructed glass cell (see Fig. 1) suitably supported on a wooden block. The cell was fitted with a 5-ml microburette with drawn-out jet, and with a suitably bent polythene tube for entry of nitrogen to stir the solution.Burette I V I Good en block Fig. 1 . Titration cell for spectrophotometric examination of indicators Indicators whose colour change in aqueous solution occurred at pH values above 7 were chosen, as in aqueous solution these would be likely to be suitable for the titration of a relatively weak acid with a strong base. Azo violet, which has been recommended by Beckett and Tinley6 for similar titrations in non-aqueous solvents, was also examined. The absorption spectra of suitable solutions containing equal concentrations of the chosen indicators in the “acid” and “base” forms, respectively, were examined, and from the results the wavelengths of greatest increase in absorbance on passing from “acid” to “base” forms were found.Several 1-ml portions of an approximately 0-3 M solution of carbon dioxide in ethanol- amine - formdimethylamide were diluted to 40 ml with the solvent mixture in the titration cell. After the addition of the amount of indicator that had been found by trial and error to give a change in optical density of about 0.8 units during the titration, the carbon dioxide was titrated with an approximately 0.1 N non-aqueous base. The end-point colour change was followed spectrophotometrically by a procedure similar to that described by Hunter and Miller.7 The results obtained with different indicators in 3 and 5 per cent. v/v solutions of ethanolamine in formdimethylamide are shown in Fig.2. Similar graphs were obtained when benzoic acid (used for standardisation of basic non-aqueous titrants) was titrated instead of carbon dioxide. With either acid the sharpest change was found to be that from colourless to blue with thymolphthalein. This change corresponds to the easily discernible first appearance of a blue colour in a previously colourless solution, and confirms the qualitative conclusion of Grant et aZ.l that thymolphthalein gives end-points superior to those obtained with thymol blue.442 BRAID et al.: AN EXAMINATION O F SOME OF THE FACTORS AFFECTING [Ana&St, YO]. 91 Volume of basic titrant I division = I ml Fig. 2. Spectrophotometric titration curves for different indicators in carbon dioxide - ethanolamine - formdimethylamide solutions: curve I\, phenolphthalein in 3 per cent.ethanolamine - formdimethylamide ; curve B, phenolphthalein in 5 per cent. ethanolamine - formdimethylamide ; curve C , thymolphthalein in 3 per cent. ethanolamine - formdimethylamide; curve D, thymolphthalein in 5 per cent. ethanolamine - formdimethyl- amide; curve E, m-cresol purple in 3 and 5 per cent. ethanol- amine - formdimethylamide; curve I;, azo violet in 3 and 5 per cent. ethanolamine - formdimethylamide ; curve G, thymol blue in 3 per cent. ethanolamine - formdimethylamide; curve H, thymol blue in 5 per cent. ethanolamine - formdimethylamide The possible difference between the observed end-point and the true equivalence point is, in practice, rendered less significant by titrating always to about the same intensity of the blue colour, and by the use of the same end-point in titrations of carbon dioxide and in standardisations.CHOICE OF TITRANT- In the course of the investigations several different titrants were tried, including solutions of the alkali methoxides in benzene - methanol, alkali hydroxides in various alcohols and tetrabutyl ammonium hydroxide in benzene - methanol. Difficulties were variously encountered due to precipitation of (presumably) alkali alkyl carbonates, to marked day- to-day variations in the results of standardisations even when maximum precautions were taken to preserve the freshness of the solutions (suggesting the occurrence of decomposition reactions), and to “fading” of the end-points. The phenomenon of “fading” of end-points in non-aqueous titrations of carbon dioxide has been reported by White,3 who attributed it to the presence of water and found that an empirical correction factor could be applied.Boyle et aZ.5 have similarly applied an empirical correction factor to allow for “fading.” The occurrence of fading in the various experiments of this work was not found to be in any way reproducible, and no satisfactory explanation for it could be found despite numerous experiments involving the alteration of a variety of conditions. The effect seemed to be connected in some way with the presence of methanol in the titrated system, but reproducible results could never be obtained. Standard solutions of tetrabutyl ammonium hydroxide in benzene - methanol were, however, essentially stable and did not react with carbon dioxide contamination to give rise to precipitates.More benzene (and consequently less methanol) could be present and still maintain a clearer solution than with the alkali methoxides, and fading effects were found to be essentially absent with this titrant.July, 19661 DETERMINATION OF CARBON DIOXIDE BY NON-AQUEOUS TITRIMETRY 443 In some of the preliminary experiments use was made of solutions obtained by dilution of the commercial tetrabutyl ammonium hydroxide of about 0.1 N to about 0.02 N by the addition of benzene, but it was later found that equally satisfactory results could be obtained with the 0.1 N solution in a 1-ml microburette. By virtue of the smaller increase in volume of liquid in the absorber, this facilitated the performance of a greater number of titrations (about 10) with the one sample of absorbent.PROCEDURE FOR THE DETERMINATION OF CARBON DIOXIDE APPARATUS- Titrationjask-This is essentially similar to that used by Grant et aZ.l and consists of a 50-ml Pyrex conical flask with side-tubes to lead the gas stream to the bottom of the flask and to allow the carrier gas to escape after absorption of the carbon dioxide. Stirring is done magnetically, and the burette tip is immersed in the absorbant to facilitate the addition of small increments of titrant. Burette-A grade A burette, of 1-ml capacity, fitted with a suitable reservoir, is used. Polytetrafluoroethylene stop-cocks are used ; these greatly facilitate the prolonged use of the burette by eliminating the sticking that results from the washing of lubricant from glass taps by the non-aqueous titrant.Soda-lime tubes are attached to prevent ingress of atmospheric carbon dioxide. REAGENTS- A bsorbent-Prepare a 5 per cent. v/v solution of ethanolamine in formdimethylamide ; ordinary-reagent grade. A 20-ml sample is adequate for up to about 10 carbon dioxide deter- minations of 5 to 10mg each, after which the titration flask is almost full and the ethanol- amine content of the absorbant has been reduced to 3 to 2.5 per cent. Titrant-This is a 0.1 x tetrabutyl ammonium hydroxide in benzene - methanol solution. I t is an approximately standard solution supplied by British Drug Houses, Poole, Dorset. Indicator-Prepare a 0.05 per cent. w/v solution of thymolphthalein in formdimethyl- amide; use 5 drops per 20 ml of absorbent.AZkaZimetric standard-Fuse O.A.S. benzoic acid on a platinum lid and break into small pieces to facilitate the addition of milligram amounts to the titration flask for standardisations. PROCEDURE- Standardisation of the 0.1 N tetrabutyl ammonium hydroxide-Milligram amounts of the fused O.A.S. benzoic acid are dissolved in 20-ml portions of the absorbent (previously brought to the first observable blue of the indicator) in the titration flask in a carbon dioxide- free atmosphere, and titrated with the titrant to the same blue end-point. C,H,COOH + C,H,NOH = C,H,COo + C,HgG + H,O The reaction is- whence 1 litre of N C,H,NOH = 122-1 g of C,H,COOH. Several standardisations may be performed without renewing the solvent, although the end-point deteriorates after a time, probably owing to the accumulation of water formed in the reaction.Titration of carbon dioxide-The procedure is similar to that of the standardisation. The carbon dioxide is flushed into the absorbent (previously titrated to pale-blue and stirred by the magnetic stirrer) by the carrier-gas stream, and then titrated to the same pale-blue end-point. The reactions are probably- kH,(CH,),(OH)(CO~)(OH)(CH,),NH + C,H,NOH = 2KH,(CH,),OH + C,H,NHCO,, 2NH2(CH,),0H + CO, = ~H,(CH,),(OH)(CO~)(OH)(CH,),NH i.e., effectively CO, + C,H,NOH = C,H,NHCO, whence 1 litre of N C,H,NOH = 44-01 g of CO,. Results obtained for carbon dioxide produced by heating milligram amounts of sodium hydro- gen carbonate are given in Table 11.Table I11 summarises the results obtained by applying the method to the determination of carbon in O.A.S. compounds by the rapid combustion process.444 BRAID, HUNTER, MASSIE, NICHOLSON AND PEARCE [A%dySt, 1:Ol. 91 TABLE I1 SOX-AQUEOUS TITRIMETRIC DETERMINATION OF CARBON DIOXIDE PRODUCED BY HEATING WEIGHED AMOUNTS OF SODIUM HYDROGEN CARBOXATE AND ABSORBED I N 5 PER CENT. V/V ETHANOLAMINE IN FORMDIMETHYLAMIDE Sodium hydrogen carbonate, mg 3.268 7.958 6.116 4.928 8-979 3-701 4.903 4.862 5.369 5-802 6-250 5.332 20.439 15-129 8.992 7.303 Carbon dioxide calculated, mg 0.854 2.084 1.601 1.290 2.351 0.969 1.283 1.273 1.406 1.519 1.636 1.396 5.348 3.961 2.355 1.912 Carbon dioxide found, mg 0.859 2.128 1.609 1.286 2.342 0.964 1.282 1.277 1-404 1.546 1-634 1.404 5-340 3-951 2.367 1.932 Error, mg + 0.006 + 0.044 + 0.008 - 0.004 - 0.009 - 0.005 - 0.00 1 + 0.004 - 0.002 + 0.027 - 0.002 + 0.008 - 0.008 -0~010 +0*012 + 0.020 TABLE I11 NON-AQUEOUS TITRIMETRIC ANALYSIS OF CARBON IN O.A.S. COMPOUNDS Number Weight Carbon Standard of range (found), Carbon deviation, deter- taken, percentage Mean, (calculated), percentage Compound minations mg range per cent. per cent. units Benzoic acid . . 9 3.6 to 4.7 67-45 to 68.44 67.91 68.84 0.36 Sucrose . . . . 10 4.3 to 5-8 41.70 to 42.84 42-15 42.10 0.34 Saphthalene . . 10 2.5 to 4.5 92.45 to 94.45 93.36 93.71 0.52 REFERENCES 1. 2. 3. iihite, D. C., Talanta, 1963, 10, 737. 4. 5. 6. 7. Grant, J. A., Hunter, J. A., and Massie, W. H. S., Analyst, 1963, 88, 134. Blom, L., and Edelhausen, L., Analytica Chim. Acta, 1955, 13, 120. Patchornik, A, and Shalitin, Y., Analyt. Chem., 1961, 33, 1887. Boyle, W. C., Stephens, F. B., and Sunderland, M’., Ibid., 1965, 37, 935; Beckett, A. H., and Tinley, E. H., “Titration in Non-aqueous Solvents, Hunter, J. A., and Miller, C. C., Analyst, 1956, 81, 79. Third Edition, British Drug Houses Ltd., Poole, Dorset, p. 35. Received September 9th, 1965

ISSN:0003-2654    

DOI:10.1039/AN9669100439

出版商:RSC    

年代:1966

数据来源: RSC