ISSN:0003-2654    

DOI:10.1039/AN95176FX041

出版商:RSC    

年代:1951

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95176BX043

出版商:RSC    

年代:1951

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95176FP097

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

NOVEMBER, 1951 Vol. 76, No. 908 THE ANALYST PROCEEDINGS OF THE AND OTHER SOCIETY OF PUBLIC ANALYSTS ANALYTICAL CHEMISTS DEATHS WE regret to record the deaths of Bernard Cracroft Aston (Honorary Member) Charles Wesley Bayley The Titrimetric Determination of Carbon Dioxide Liberated in the Ninhydrin Reaction with Amino-Acids BY A. M. SMITH AND A. H. AGIZA The a-amino nitrogen in single amino-acids or in mixtures can be accurately determined by measuring the carbon dioxide released by ninhydrin. A simple and convenient unit for the purpose and experimental conditions suitable for a quantitative .reaction are described. Recoveries of from 97 to 102 per cent. were attained with amounts corresponding to about 0.15 mg of a-amino nitrogen. ONE of the standard methods of determining amino-acids is based upon the determination of the carbon dioxide liberated in their decarboxylation by ninhydrin.This reaction is practically confined to the carboxyl carbon adjacent to the amino group and under suitable conditions most of the a-amino-acids, including glutamic acid, liberate one molecule of carbon dioxide; proline and hydroxyproline react similarly, but aspartic acid and cystine give two molecules of carbon dioxide, and the carboxyl group of p-alanine is only slightly reactive. The method is, therefore, extremely useful for measuring the total a-amino nitrogen in a mixture of amino-acids and other nitrogenous compounds likely to occur in a protein hydro- lysate. In this respect the method is complementary to that involving the measurement of the colour produced by the ninhydrin, a method that is more sensitive than the determina- tion of the carbon dioxide but is not so specific and can be used only for individual amino-acids whose identity is known (Smith and Agizal).Mason2 and Van Slyke, Dillon, MacFadyen and Hamilton3 have shown how the carbon dioxide may be measured manometrically with great precision, but the equipment is necessarily rather elaborate and simpler techniques for the titrimetric determination of the carbon dioxide have been devised by Christensen et ~ 1 . ~ 1 ~ and Van Slyke, MacFadyen and H a m i l t ~ n . ~ I t is obvious that in the measurement of the small amounts of carbon dioxide corresponding to less than 1 mg of a-amino nitrogen, special care must be taken to avoid contamination with atmospheric carbon dioxide, and the apparatus and procedure described below were designed to provide a convenient means of achieving this throughout the analysis. 619620 SMITH ASD AGIZA: THE TITRIMETRIC [Vol.76 METHOD APPARATUS- The reaction tube, A, and the absorption flask, B, 26 or 50 ml, are connected to each other by capillary tubes X and Y through the stopcock, S, which in turn connects them through capillary tube 2 with either a vacuum pump or a test tube, C, containing sodium hydroxide. The normal precautions were taken over the selection The apparatus is illustrated in Fig. 1. A‘ s. position t A s, position 2 =!&+ 4 s, position 3 -FEY- 1 . \ - _ , Fig. 1. Reaction and absorption apparatus and cleansing of rubber connections. A small burette is fitted to the stopper of the reaction tube and the whole apparatus is made air-tight, the stopcocks being lubricated with a high- vacuum grease.A sheet of asbestos between A and B helps to preserve the temperature gradient during the distillation of the carbon dioxide. A compact and practically continuous form of aspirator is shown in Fig. 2. Two bottles of 1 litre capacity are built into a rigid unit by means of stoppers and glass tubing. The rubber tubing A connecting the two bottles is long enough to allow either bottle to be turned uppermost so that when the lower one has filled with water, the bottles are inverted, the appropriate stopcocks being closed or opened to maintain the ctlrrent of air through the solution of sodium hydroxide in the flask B.REAGENTS- The reagents are selected according to the approximate quantity of amino-acids taken, namely, (a) “macro,” (b) “micro” and (c) “submicro” for 3 to 5, 0.15 to 1.0 and less than 0.15 mg of a-amino nitrogen respectively. Niahydri.n-Solutions containing (a) 150, (b) 100 and (c) 50 mg of ninhydrin in 1 ml of a citrate buffer of pH 5 are freshly prepared each week.Kov., 19511 DETERMISATION OF CARBON DIOXIDE 62 1 Barium hydroxide-(a) Approximately 0.25 N containing 2 per cent. of barium chloride, (b) approximately 0.125 N containing 2 per cent. of barium chloride and (c) approximately 0.016 N containing 10-5 per cent. of barium chloride. Hydrochloric acid-(a) 0.1428 N , (b) 0.07138 N , (c) 0.02855 or 0.01428 N . These con- centrations are convenient since 1 ml is equivalent respectively to 1.0, 0.5, 0.2 or 0.1 mg of a-amino nitrogen.- Fig. 2. Continuous aspirator Im?icators-For (a) and (b), 1 drop of a 1 per cent. solution of phenolphthalein in 95 per cent. ethanol; for (c), 1 drop of a 0-04 per cent. solution of cresol red in water. Bufers-A solid buffer of pH 4.7 is added to the amino-acid solution ; it consists of 17.65 g of tri-sodium citrate (Na,C,H5O,.2H,O) and 8.40 g of citric acid (C,H,O,.H,O) separately ground and then intimately mixed in a mortar. As a standard of pH 8 for the “submicro” titration, 10-3 g of sodium veronal are dissolved in 500 ml of water, and 7 ml of this solution are mixed with 4 ml of 0.07138 N hydrochloric acid. PROCEDURE- Place 2 to 3 ml of the amino-acid solution and about 100 mg of the solid citrate buffer in the reaction tube, insert the stopper and put a solution of ninhydrin in the burette.Remove the carbon dioxide from the tube by placing it in boiling water and connecting it through XZ (Fig. 1) to the suction pump; turn the appropriate stopcocks and allow air, free from carbon dioxide, to enter the tube by way of the sodium hydroxide solution in C. Repeat this procedure a t least three times. Remove carbon dioxide also from the absorption flask by passing a current of air, free from carbon dioxide, from an aspirator and, while the current is still passing, add 1 to 3 ml of barium hydroxide from a protected automatic burette. Attach the flask to tube Y and evacuate the whole system, refill with air, free from carbon dioxide, and again evacuate with the tap S at position 1.Turn S to position 2, add a suitable amount of ninhydrin solution (usually 1 ml) to the tube A and seal the burette with a drop of mercury. Immerse flask B in an ice-bath and the reaction tube in boiling water for 6 or 7 minutes until the reaction is complete and the carbon622 SMITH AND ACIZA: T H E TITRIMETHIC [Vol. 76 dioxide has distilled with most of the water from the tube to the flask. Shake the flask frequently during the process to bring the carbon dioxide into contact with the barium hydroxide. Turn S to position 3 so that any unabsorbed carbon dioxide in Y may be washed into the flask by a current of carbon dioxide-free air from C. Disconnect the flask, add the indicator and titrate the excess of barium hydroxide immediately with acid while a current of air, free from carbon dioxide, is passing through the solution from the aspirator.Risk of contamination with atmospheric carbon dioxide is eliminated by the careful evacuation of the apparatus before the reaction and by filling the absorption flask with carbon dioxide-free air before disconnecting it for the titration. Blank experiments with carbon dioxide-free water in place of amino-acid solution are carried out from time to time, and the amount of amino nitrogen in milligrams is simply (a - b) x c, where a and b are the amounts of hydrochloric acid in millilitres required to neutralise the excess of barium hydroxide in the blank and in the experimental solutions, respectively, and c is the factor for the acid.The presence of the barium chloride facilitates the precipitation of the carbonate, and with “macro” and “micro” quantities the titration is carried out to the first disappearance of the colour of the phenolphthalein. For “submicro” quantities, the end-point of the titration is matched against the colour of an equal volume of the veronal buffer containing 1 drop of cresol red. DISCUSSION OF RESULTS The time required for a quantitative reaction is not the same for all amino-acids and is shorter at pH 4-7 than at pH 2.5 or 1. Van Slyke, Dillon, MacFadyen and Hamilton2 found, however, that prolonged heating of a protein digest at pH 4.7 was liable to give a result higher than the maximum reached under more acid conditions. This was possibly due to a ‘secondary slow formation of carbon dioxide from glutamic acid and lysine. Those authors, therefore, preferred to carry out the reaction at pH 2-5 and considered that a result approaching the theoretical one would be obtained by adhering closely to the prescribed reaction time, on account of a compensation of errors with the few amino-acids that did not give a theoretical value in that time.Their results for individual acids certainly show smaller discrepancies with acids like cystine and lysine at pH 2.5 than at pH 4.7. In the present investigation it was found that a buffer of pH 4-7, 50 mg of ninhydrin per millilitre of amino-acid solution and a reaction time of 6 to 7 minutes gave very uniform results with twenty-two amino-acids. They were examined separately and in a mixture of equal quantities of each in terms of a-amino nitrogen.Determinations were carried out in quintuplicate, the amount of a-amino nitrogen taken being 150 pg in 1 to 2 ml of solution on each occasion. Replicates did not differ from each other by more than 2 per cent., the average recovery varied from 97.3 per cent. for tryptophan to 102.0 per cent. for aspartic acid and the general average was 99-9 per cent. for all the individual acids. For an unknown reason the recovery from the mixture was higher Lit 102.5 per cent. A selection of the results is given in Table I. TABLE I RECOVERY OF AMINO-ACIDS BY DETERMINATION OF CARBON DIOXIDE Acid a-Amino nitrogen I A I Taken, Found, Recovery, tG P6 % Alaninc . . Threonine . . Cystine . . Methionine . . Aspartic acid Arginine .. Lysine . . Pheny lalanine Tryptophan Proline . . Mixture .. .. .. 150 .. .. 150 .. .. 150 .. .. 150 .. .. 150 .. . . 150 . . .. 150 . . . . 150 .. .. 150 .. .. 150 .. .. 150 150 147 150 150 153 148 151 149 146 150 154 150 147 14‘3 150 I52 150 152 149 1+6 150 154 149 147 150 150 154 151 151 149 146 149 154 150 147 150 149 153 151 152 149 146 151 154 7 151 148 161 151 153 150 152 150 146 150 153 100.0 98.1 100.0 100.0 102.0 100.0 101.1 99.8 97.3 100.0 102.5Nov., 19511 DETERMISATIOS OF CARBOS DIOXIDE 623 The method was used to determine the proportion of total nitrogen in a-amino form in a series of hydrolysates of proteins extracted from grassland species. Preliminary tests indicated that the apparatus might be convenient for the determination of small amounts of calcium carbonate. REFERENCES 1. Smith, A. M., and Agiza, A. H., Analyst, 1951, 76, 623. 2. Mason, M. F., Biochem. J., 1938. 32, 719. 3. Van Slyke, D. D., Dillon, R. T., MacFadyen. D. A., and Hamilton, P., J . Biol. Chem., 1941, 141, 4. Van Slyke, D. D., MacFadyen, D. A., and Hamilton, P., Ibid., 1941, 141, 671. 5. West, E. A., Christensen, B. E., and Rinehart, R. E., Ibid., 1940, 132, 671. 6. Christensen, B. E., West, E. S., and Dimick, K. P., Ibid., 1941, 137, 735. 627. EDINBURGH AND EAST OF SCOTLAND COLLEGE OF AGRICULTURE First submitted, January, 1951 Amended, June, 1951

ISSN:0003-2654    

DOI:10.1039/AN9517600619

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

Nov., 19511 DETERMISATIOS OF CARBOX DIOXIDE 623 The Determination of Amino-Acids Colorimetrically the Ninhydrin Reaction BY A. M. SMITH AND A. H. AGIZA The coloured compound produced in the reaction between amino-acids and ninhydrin can be used as a quantitative measure of the amino-acid decomposed. The depth of colour is not the same for all the common amino-acids, but the results are reproducible to within 3 per cent. and the curve is linear for all the acids examined in the range 5 to 25 pg of amino nitrogen. Hence the reaction provides a convenient method of determining the sub-micro quantities of amino-acid obtained from a drop of a protein hydrolysate fractionated by two-dimensional chromatography on paper. IN the reaction between amino-acids and ninhydrin (triketohydrindene hydrate), each of the products, aldehyde, ammonia, carbon dioxide and the coloured compound, can provide a convenient measure of the amount of decomposed amino-acid.The determination of a volatile aldehyde can be carried out,' but the method is, of course, applicable only to certain acids; ammonia may be detemr~ined,~~~ but apart from the fact that several amino-acids do not give the theoretical amount, the results are not as accurate as those obtained by determining the carbon dioxide. The liberation of carbon dioxide is highly specific and its determination is sufficiently precise for assessing micro amounts of all free a-amino-acids and a number of closely related c o m p ~ u n d s . ~ ~ ~ ~ ~ ~ ~ Nevertheless, it would be convenient in many circumstances if amino-acids could be measured in terms of the coloured compound formed in the reaction.Ruhemanns was the first to examine the nature of the blue or purple compound and considered that it was formed by the condensation of the reduced ninhydrin with the ammonia liberated from the amino-acid and with the excess of ninhydrin. Harding and MacLeanO devised a quantitative technique that gave accurate results for several amino-acids in the range 5 to 50 pg of nitrogen per ml. Later they and Warneford showedlotll that the colour reaction was not specific for a-amino-acids but also occurred with ammonium salts, peptides and certain classes of amines. These compounds, however, are not as reactive as amino- acids, which alone are sensitive, in the absence of a base, when the concentration of nitrogen is less than 0.1 mg per ml of solution.The question of specificity does not arise in the deter- mination of individual amino-acids separated and identified by a chromatographic procedure. Wieland and Wirth,12 for example, have used the method to determine aspartic and glutamic acids separated in a column of aluminium oxide, and Moore and Stein13J* have fractionated the amino-acids in synthetic mixtures and in protein hydrolysates on a starch column and measured their concentrations in the eluate. The mechanism of the reaction has received a good deal of attention, and recent spectro- photometric studies16,16 of ninhydrin and various derivatives have indicated that the purple colour is due to the anion of diketohydrindamine-diketohydrindylidene, the red and blue624 SMITH AKD AGIZA: THE DETERMISATIOX OF AMISO-ACIDS [Vol.7ti components being respectively the mono- and di-valent anions of indanone-enediol. Prolinck and hydroxyproline, from which ammonia is not produced by reaction with ninhydrin, arc exceptional in giving a yellow or red compound.17 The depth of colour is not constant for equivalent amounts of different amino-acids, so the method is not accurate for the determination of the total amino nitrogen in a mixture, but this does not present any difficulty with individual acids, since a standard curve can btb prepared for each and, with proper precautions, the results are reproducible without difficulty and the curve is linear over the range 5 to 25 pg of nitrogen. Differences in shade of colour are probably due to the condensation of the aldehydes produced from different acids with the 1 :3-diketohydrindamine to give the orange - brown dyes (1 :3-diketo-2-arylidene-hydrind- amines) described by Ruhemanns and referred to more recently by Atkinson, Stuart and Stuckey.18 In the course of the present investigation, it was observed that the colour was altered in both depth and shade when traces of aldehydes were added to mixtures of glycine or alanine or ammonium salts with ninhydrin.Moore and Stein13 were of the opinion that difficulties in obtaining a good correlation between amount of amino-acid and depth of colour were caused by oxidation changes and consequently they took precautions to exclude oxygen from the reactants and also added a reducing agent, first hydrindantin, which is formed on the reduction of ninhydrin, and later stannous chloride.In their comprehensive study of the conditions of the reaction they found that the absorption spectrum rose to a maximum value at 570 mp (440 mp for proline and hydroxyproline), and that maximum colour development occurred at pH 5 for all acids except tryptophan (pH 6) after 5 to 20 minutes’ heating at 100°C. These authors were especially interested in the recovery of the individual amino-acids in successive fractions of the eluate from a starch column, and they used three different solvents. They added the amino-acid solution to a mixed solution of ninhydrin in methyl Cellosolve and buffered stannous chloride in a photometer tube, raised the temperature to 100°C for 20 minutes and then shook the solution with a diluent of water and n-propano1 before measuring the colour absorption.In the present work several modifications were made in this procedure. For example, the amount of ninhydrin used by Moore and Stein, about 20 mg for amounts of amino nitrogen of the order of 3 pg, seemed to be an unnecessarily large excess; less than a tenth of that quantity was found to be adequate. I t was also found more convenient to dissolve the ninhydrin in the buffer solution and keep it separate from the stannous chloride than to keep a mixture of the two reagents under nitrogen. The method finally adopted is described below. REAGENTS- Citrate bufer, PH &Dissolve 21.008 g of citric acid (C,H,O,.H,O) in 200 ml of distilled water, add 200 ml of N sodium hydroxide and dilute to 500 ml; add 15 to 20 ml of n-butanol to prevent fungal growth. Ninhydrin solution A-Dissolve 550 mg of Iiinhydrin in 100 ml of citrate buffer.Ninhydrin solution B-Dissolve 100 mg of ninhydrin in 100 ml of n-butanol, saturated This solution is for spraying on to the paper chromatogram. Stannous chloride-Dissolve 0-5 g of stannous chloride in 250 ml of citrate buffer and This solution must be renewed METHOD with water. add a layer of n-butanol to the surface to reduce oxidation. at intervals of about 5 days. PROCEDURE FOR PURE AMINO-ACIDS- Place 1 to 2 ml of the solution of the amino-acid, containing 5 to 20 pg of amino nitrogen, in a test tube graduated at 5, 10 and 15 ml and neutralise if necessary with sodium hydroxide, using phenolphthalein as indicator. Add 1 ml of the buffer solution, or 2 ml if it has bee11 necessary to neutralise the solution, and then add 1 or 2 ml of ninhydrin solution A , according to the amount of amino-acid taken.Place the test tube in boiling water and add 1 ml of the stannous chloride solution. Continue heating for 15 minutes and then remove the tube from the boiling water and allow it to cool in the dark for 10 minutes. Make the solution UP to a volume of 10 ml with a saturated solution of sodium chloride. Add between 4 and 5 ml of n-butanol to the tube, stopper it tightly, shake and set aside for 5 minutes. By this treatment the colour is extracted from the aqueous phase and appears A red colour is first produced, but this changes to blue.Yov., 19511 COLORIMETRICALL\i BY THE SISHYDRIS REACTIOS 625 in the supernatant alcohol layer.Adjust the volume of the aqueous phase to 10 ml by adding water saturated with butanol, and adjust the volume of the upper layer to 5 ml by addition of butanol. With a pipette, transfer 3 to 4 ml of the clear butanol solution into a colorimeter tube and compare the purple colour with that of a blank prepared under the same conditions. 0 5 10 15 Amino nitrogen, p g 20 25 Fig. 1. Relationship between colour and amino nitrogen An Evans Electroselenium colorimeter was found to be satisfactory, with yellow filter No. 626 (maximum transmission at a wavelength of 570 mp), for all acids except proline and hydroxy- proline, which gave a yellow - red colour and for which violet filter No.621 (maximum transmission at 460 mp) was used. With cystine it was necessary to double the amount of ninhydrin in order to obtain reproducible results and a depth of colour similar to that from the other amino-acids. Cysteine yielded only about 15 per cent. of the colour given by an equivalent amount of leucine, an observation previously recorded by Moore and Stein.13 This may be due to the presence of the HS- group, and the following modification in the method was found to over- come the effect. A drop of phenolphthalein was added to the solution of cysteine (or cystine) in the tube and then enough sodium hydroxide to give a pink colour. One drop of dilute bromine solution was then added and this formed sufficient hypobromite to effect an oxidation to cysteic acid.The normal procedure for the other amino-acids was then followed, and the development of the colour was of the same order.626 SMITH A S D AGIZA: THE DETERMISATIOS OF AMISO-ACIDS [l'ol. TG RESULTS For each of twe?ty-three amino-acids, a series of concentrations ranging from about 4 to 20 pg of amino nitrogen was examined by the above method and the results were repro- ducible to between 1 and 3 per cent. of the mean of five determinations for all except glutamic acid (5 per cent.) and tryptophan and tyrosine (4 per cent.). A linear relationship between colour and quantity of acid was found over this range, and five typical curves are shown in Fig. 1. In common with other i n v e ~ t i g a t o r s , ~ l ~ ~ ~ ~ ~ ~ ~ ~ we found that equivalent amounts of different amino-acids did not give the same depth of colour.The relative values interpolated on each curve at 15pg of amino nitrogen are shown in Table I. On the same scale, proline and hydroxyproline gave values of 58 and 57 respectively, but these figures are not comparable with the others as the colours were different. TABLE I RELATIVE DEPTHS OF COLOUR FROM AMINO-ACIDS Relative depth of colour Amino-acids 100 glycine, leucine, isoleucine, norleucine 96 serine 93 phenylalanine, cysteine 90 lysine 89 glutamic acid, tyrosine. tryptophan 88 arginine, histidine. methionine 86 aspartic acid, ornithine 85 alanine 81 threonine, valine, itorvaline 79 cystine DISCUSSION OF RESULTS- The above results differ substantially from the corresponding values reported by Moore and Stein,13 although the analytical procedure was similar except in certain respects previously noted.For example, the figures given here are much lower for alanine, arginine, glutamic acid, histidine, lysine, methionine, threonine and valine, and higher for phenylalanine, tryptophan, cysteine and cystine. Moore and Stein used various solvents to elute the amino- acids from a starch column, added a much larger proportion of ninhydrin to develop the colour and determined the depth of colour with a spectrophotometer a t 570 mp. Fowdenlg has recently reported the results of a study of the reaction with amixed reagent of equal volumes of a 4 per cent. solution of ninhydrin in methyl Cellosolve and a 0-16 per cent. solution of stannous chloride, saturated with hydrindantin and stored under nitrogen.He took 20 to 30 mg of ninhydrin for quantities of acid containing 1 to 10 pg of a-amino nitrogen, heated for 25 minutes, made up the solution to 10 or 25ml with water and acetone, and estimated the colour with a spectrophotometer at 570mp. His method, therefore, closely resembled that of Moore and Stein, and his list of relative depths of colour is similar to theirs except that his values are higher for aspartic acid, glutamic acid, tyrosine, histidine, phenylalanine, serine and valine. The reason for the discrepancies in the three sets of results is not clear, apart from those for cysteine and cystine, because when the leucines are taken as a standard, the present values are in close agreement with those of Moore and Stein in respect of glycine, serine, aspartic acid and tyrosine, and with those of Fowden in respect of glycine, serine, phenyl- alanine and tryptophan.Obviously the method may not give a reliable result for a mixture of amino-acids, but it can nevertheless give reproducible results for individual acids, and is sufficiently sensitive to be suitable for the determination of the very small amounts of amino- acids obtained in the fractionation of a protein hydrolysate by partition chromatography on filter-paper. APPLICATION TO PROTEIN HYDROLYSATES About 170 samples of protein extracted from various species of grassland herbage were subjected to acid hydrolysis and the individual amino-acids were separated by two-dimensional chromatography on Whatman No.54 filter-paper by means of the solvents (a) phenol - 0.2 N formic acid, in an atmosphere of ammonia, and ( b ) n-butanol- glacial acetic acid - glycerol - water (in the ratio 83 : 2.5 : 2.5 : 12) in an atmosphere of coal gas and hydrocyanic acid.Sov., 19511 COLORIMETRICALLY BY THE SI.; HYDRIS REACTIOS 627 After drying at 80" C, the paper was lightly sprayed with ninhydrin solution B and again dried at 80" C for two minutes. The colour developed by the ninhydrin marked the positions of the individual acids, which could be identified from their RF values and from their positions with respect to proline, whose characteristic yellow or yellowish-red spot was a useful guide. Fifteen of the acids included in Table I (and also proline) were identified in this way.One millilitre of the buffer solution was added to each tube and then 1 to 2ml of ninhydrin solution A. The subsequent procedure was exactly the same as that described on p. 624 for pure amino- acids. This method differs from that of Naftalin,20 who developed the colour at pH 7, at which pH tyrosine and cystine are insoluble, and extracted it with 75 per cent. acetone. For various reasons, cysteine, cystine, histidine, hydroxyproline, methionine and tryptophan were not determined on these chromatograms. The sulphur compounds were sometimes difficult to identify on chromatograms of protein hydrolysates, histidine was rather insensitive to development with ninhydrin, and hydroxyproline occurred only in extremely small amounts. The tryptophan could not be determined in an acid hydrolysate and was determined separately after hydrolysis of about 150 mg of the protein in 1 ml of 5 N sodium hydroxide in a sealed tube at 110" C for 90 minutes.The hydrolysate was brought to an acidity of 1.2 N with hydrochloric acid, filtered, and an aliquot was diazotised and then treated with S-( 1-naphthy1)-ethylenediamine &hydrochloride. The red - purple colour was salted out, extracted with n-butanol and measured in the colorimeter with green filter No. 404 (maximum transmission at 530 mp). The curve was linear over the range 0-05 to 0.20 mg of tryptophan, corresponding to 3.5 to 14 pg of a-amino nitrogen. This method differed from that described by Eckert21 only in some minor details adopted for convenience in routine determinations, and the results were not affected by the other compounds likely to occur in a grass-protein hydrolysate.Tyrosine, for example, had no effect on the colour unless it was added in considerable excess. Although this method of determining the individual amino-acids in a mixture does not attain the remarkable standard achieved by Moore and Stein1* with a starch column, it is rapid and convenient for routine analysis and sufficiently accurate for a comparison of the relative amounts of amino-acids present in different hydrolysates. The percentage recoveries of the individual acids from a synthetic mixture were as follows: arginine and lysine, 91; serine and valine, 93; aspartic acid, 94; alanine and tyrosine, 96; glutamic acid, 07; threonine, 99; tryptophan, 100; glycine, 101; the leucines and phenylalanine, 103; proline, 105.In an analysis of a mixture of ten of these amino-acids, separated from two-dimensional chromato- grams, Fowdenls obtained a similar range of figures (93 to 102) although the individual values differ markedly in five instances. The individual spots were cut out and placed under water in test tubes. 1. 3. 4. 5 . 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 3 -. REFERENCES Virtancn, A. I., and Rautancn, X., Biochm. J . , 1947, 41, 101. Schlenker, F. S., Anal. Chem., 1947, 19, 471. Sobel, A. E., Hirschman, A., and Besman, L., J . Biol. CJieiw., 1945, 161, 99. Mason, M. F., Biochem. J . , 1938, 32, 719. Van Slyke, D. D., Dillon, R. T., MacFadyen, D. -4., and Hamilton, P., J . BioZ. Sci., 1941, 141, 637. Van Slyke, D. D., MacFadyen, D. -4., and Hamilton, P . , Zbid., 1941, 141, 671. Smith, A. M,, and Agiza, A. H.. Analyst, 1951, 76, 619. Ruhemann, J., J . Chenz. SOC., 1911, 99, 792, 1310, 1486. Harding, V. J., and MacLean. R. M., J . Biol. Client., 1915, 20, 217. -- , Zbid., 1916, 25, 337. Harding, V. J., and Warneford, F . H. S . , Zbid., 1916, 25, 319. Wieland, T., and Wirth, L., Bey. chem. Ges., 1943, 76B, 823. Moore, S., and Stein, W. H., J . Biol. Chem., 1948, 176, 367. -- , Ibid., 1949, 178, 63. MacFadyen, D. A., Zbid., 1950, 186, 1. MacFadyen, D. A., and Fowler, N., Zbid., 1950, 186, 13. Grassmann, W., and von Amim, K., Ann. Chew., 1934, 509, 288. Atkinson, R. 0.. Stuart, R. G., and Stuckey, R. E., .4izaZysf, 1950, 75, 447. Fowden, L., Biochem. J., 1951, 48, 327. Naftalin, L., Kature, 1948, 161, 763. Eckert, .H. W., J . Biol. Chem., 1943, 148, 203. THE EDINBURGH AND EAST OF SCOTLAND COLLEGE OF AGRICULTURE March, 1951

ISSN:0003-2654    

DOI:10.1039/AN9517600623

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

628 HASLAM, WHETTEM A S D SOPPET: THE DETERMISATION OF [Vol. 76 The Determination of Methyl a-Chloro-acr yla te in the Atmosphere BY J. HASLAM, S. M. A. WHETTEM ASD W. W. SOPPET Colorimetric and volumetric methods have been devised for the deter- mination of methyl a-chloro-acrylate in the atmosphere. The colorimetric method, which is suitable for the range of concentrations 0.5 to 25 mg of methyl a-chloro-acrylate per cubic metre of air (0.1 to 5 p.p.m. v/v at 20" C and 760 mm pressure), is based on the passage of a known volume of the atmosphere through 0.00 1 N potassium permanganate solution. The colour of the resulting solution is compared either with that of standards prepared from known amounts of methyl a-chloro-acrylate in 0.00 1 h- potassium permanganate solution or with standard colour discs in a Lovibond comparator.The volumetric method, which is suitable for the range 25 to 100 mg of methyl a-chloro-acrylate per cubic metre of air (5 to 20 p.p.m. v/v at 20" C and 760 mm pressure), is based on the passage of a known volume of the atmosphere through 0.02 N potassium permanganate solution and determination of the volume of potassium permanganate consumed, by addition of an excess of 0.02 N potassium oxalate solution and titration of the excess of potassium oxalate with 0-02 N potassium permanganate solution. THE production of the new polymer poly-methyl a-chloro-acrylate necessitated a rapid and accurate method for the determination of small concentrations of methyl a-chloro-acrj.latc in the atmosphere. I t was hoped that the method ultimately worked out would be simple and capable of rapid application on a plant engaged in the manufacture of the polymer.PRELIMISARY EXPERIMENTS ON THE ABSORPTION OF METHYL a-CHLORO-ACRYLATE BY POTASSIUM PERMASCANATE SOLUTION I t was known that methyl a-chloro-acrylate reacted readily with aqueous potassium permanganate solution and preliminary tests were performed to find out whether advantage could be taken of this reaction in working out a suitable method. In these preliminary experiments about 0.03 g (accurately weighed) of methyl a-chloro-acrylate was placed on glass wool contained in a small stoppered flask. This flask was connected to two jet bubblers, each containing 25 ml of 0.1 N potassium permanganate solution, which were connected to a Rotameter and suction pump.Air was aspirated through the apparatus for 10 minutes at the rate of 1 litre per minute. By weighing the flasks before and after the aeration it was shown that the methyl a-chloro-acrylate was completely removed in the air stream. After aeration the bubblers were disconnected, and 20 ml of 20 per cent. v/v sulphuric acid solution and 25 ml of 0.1 N potassium oxalate solution were added to each. The decolorised solutions were washed out into two 250-ml flasks and heated to 80" C, after which the excess of oxalate was titrated with 0.1 N potassium permanganate solution. In these experiments the absorption of methyl a-chloro-acrylate by potassium perman- ganate solution was very efficient. For examplc, in one experiment the volume of potassium permanganate solution consumed in the first bubbler was 17-05 ml, whereas in the second bubbler but 0.3 ml of 0.1 N potassium permanganate was consumed.Duplicate tests were in good agreement and indicated that 1.46 mg and 1.50 mg of methyl a-chloro-acrylate required 1 ml of 0.1 N potassium permanganate. DEVELOPMEXT OF A VOLUMETRIC METHOD- I t was considered that the concentration of the vapours in the atmosphere of a plant might be in the range of 25 to 100mg of methyl a-chloro-acrylate per cubic metre of air, i.e., 5 to 20 p.p.m. v/v at 20" C. Further, it was thought that a practical test should not involve the passage of the suspected atmosphere through permanganate solution for longer than 15 minutes. This would involve the absorption of amounts of methyl a-chloro-acrylate of the order of only 0-5 to 2-Omg.On consideration of these factors further experimentsSov., 19511 METHYL a-CHLORO-ACRYLATE I 5 THE ATMOSPHERE 629 were carried out with a weaker permanganate solution, 15 ml of 0.02 N potassium perman- ganate solution being placed in each bubbler. In this second set of experiments an amount of methyl a-chloro-acrylate within the range of 0.5 to 2.0 mg was first weighed out accurately in a stoppered micro weighing bottle. The stopper was removed and the bottle and stopper dropped into a 100-ml flask. The flask, preceded by an Arnold bubbler containing 0.01 N potassium permanganate, which served as a guard tube, was connected immediately to the absorption train. The absorption train (Fig. 1) consisted of two jet bubblers, each containing 15ml of 0.02 N potassium permanganate solution, a Rotameter and pump, all connected in series.The flask containing the sample was immersed in a bath of water at 50" C and air was aspirated through the apparatus at the rate of 1.5 litres per minute, the temperature of the water being gradually raised to 80" C. To each .4t the end of 15 minutes the air was turned off. Air intake I for of flow Fig. 1 . -4bsorption train for the determination of methyl a-chloracrylate in the atmosphere of the bubblers 5 ml of 10 per cent. v/v sulphuric acid and then 20 ml of 0.02 N potassium oxalate solution were added and the contents of the bubblers were allowed to stand until the permanganate became decolorised. The contents of each bubbler were then washed into 250-ml conical flasks with water and heated to 80" C, after which the excess of potassium oxalate was titrated with 0.02 N potassium permanganate solution.A blank determination was made by measuring 15 ml of 0.02 N potassium permanganate solution into another flask, adding 5 ml of 10 per cent. v/v sulphuric acid, 20 ml of 0.02 N potassium oxalate solution and titrating the excess of potassium oxalate with 0.02 N potassium permanganate solution at 80" C as before. The results indicated that the absorption of the vapours within the range considered, 25 to 100 mg of methyl a-chloro-acrylate per cubic metre of air, was efficient when judged by the small amount of permanganate consumed in the second bubbler; e.g., in one experiment the volume of 0-02 N permanganate solution consumed in the first bubbler was 6.0 ml and in the second bubbler it was 0.4 ml.Duplicate tests were in good agreement and indicated that 0.285 mg of methJ.1 a-chloro-acrylate required 1 ml of 0.02 N potassium permanganate solution. Confirmation that the absorption of methyl a-chloro-acrylate by 0-02 N potassium permanganate solution under the above conditions is accompanied by complete ionisation of the chlorine of the chloro-acrylate was given by the following experiment. After aeration of 0.487 mg of methyl a-chloro-acrylate, the contents of the permanganate bubblers were transferred to a beaker and diluted to 30 ml with distilled water. To this was added 1 ml of concentrated nitric acid, A.R., and then N hydrogen peroxide solution until the perman- ganate solution was just decolorised. The excess of hydrogen peroxide was removed by boiling, and the solution was allowed to cool and was then diluted to 50 ml with water.To630 HASLAM, WHETTEM ASD SOPPET: THE DETERMIXATION OF [Vol. 76 the dilute solution 1 ml of a 5 per cent. w/v solution of silver nitrate, A.R., was added, and after 5 minutes the turbidity was compared with previously prepared permanent “Perspes” standards.1 The turbidity of these standards corresponded with those obtained on addition of 1 ml of the 5 per cent. w/v solution of silver nitrate to 50 ml of a solution containing a known amount of 0.01 N hydrochloric acid and 1 ml of nitric acid, A.R. The turbidity comparison was performed against a background of black matt filter-paper.These experiments indicated that the turbidiity obtained in the experiment of 0-487 mg of methyl a-chloro-acrylate, containing 0.143 mg (of chlorine, matched that of the permanent standard prepared from 0.4 ml of 0.01 N hydrochloric acid, containing 0-142 mg of chlorine. The volumetric method was satisfactory for the range of concentrations considered, i e . , from 25 to 100 mg of methyl a-chloro-acrylate per cubic metre of air, and could un- doubtedly be extended to the determination of smaller concentrations by the passage of larger volumes of air. Xevertheless, the passage of larger volumes of air would involve an increase in the time taken for the test beyond the desired maximum of 15 minutes. Certain observations that had been made on the effect of adding increasing amounts of methyl a-chloro-acrylate solution to the same volume of potassium permanganate solution suggested that the colours produced might be used in a colorimetric test, particularly if the permanganate solution was relatively weak.A standard solution of methyl a-chloro-acrylate in water was prepared as follows. /4 0.25-ml portion of methyl a-chloro-acrg-late was shaken in a graduated flask with 500 ml of water at room temperature and the solution was filtered. To 10ml of this solution were added 40 ml of 0.02 N potassium permanganate solution. The mixture was well shaken, 10 ml of 10 per cent. v p sulphuric acid and 50 irnl of 0-02 N potassium oxalate were added and the excess was titrated with 0.02 N potassium permanganate solution as described on p.629. On the basis of previous experiments, which had indicated that 1 ml of 0.02 N potassium permanganate was equivalent to 0.285 mg of methyl a-chloro-acrylate, it was shown that the filtered solution contained 0.17 g of methyl a-chloro-acrylate per 500 ml. This solubility figure of 0.034 per cent. w/v may be useful in other work. A standard solution of methyl a-chloro-acrylate in water was then prepared by diluting 5.85 ml of the strong solution, i.e., 2.0 mg of methyl a-chloro-acrylate, to 100 ml with water. One millilitre of this standard solution contained 0.02 mg of methyl a-chloro-acrylate. Colour calibrations were made by taking 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0 and 5-0 ml of this standard solution of methyl a-chloro-acrylate, diluting each to 5.0 ml with water and adding to each 5.0 ml of 0.002 N potassium permanganate solution.Reaction with the permanganate took place immediately and the colours that developed ranged from red through orange - red to orange - yellow as the concentration of methyl a-chloro-acrylate increased. The Lovibond colour values of these solutions were measured in a Lovibond tintometer with 1-cm cells, and readings are shown in Tab1.e I. DEVELOPMENT OF A COLORIMETRIC METHOE- Experiments were therefore performed to test this. TABLE I COLOURS PREPARED BY THE REACTIObi OF METHYL E-CHLORO-ACRYLATE ON 5 ml OF 0.002 N POTASSIUM: PERMASGANATE SOLUTION Volume of standard solution, ml 0.5 1.0 1-5 9.0 2.5 3.0 4-0 5.0 Weight of methyl r or-chloro-acr ylate, mg 0.01 0.02 0.03 0.04 0.05 0-06 0.08 0.10 Lovibond colour values Red Yellow A 7 4.5 4.1 3.9 3.7 3.6 3.4 2.9 2.4 0.0 0-3 1.1 2.7 3.1 4.2 6.6 8.5 To obtain some information about the reproducibility of the test and the stability of the colours, standards corresponding to 0.05 mg and 0-10 mg of methyl a-chloro-acrylateNov., 19511 METHYL a-CHLORO-ACRYLATE IN THE ATMOSPHERE 631 were prepared on successive days.The Lovibond colour values of these standards were determined 10 minutes and 3 hours after preparation. The results are shown in Table 11, from which it was concluded that a satisfactory colorimetric method could be based on examination of the coloured reaction products of methyl a-chloro-acrylate and potassium permanganate after colour development for 5 minutes. TABLE I1 EFFECT OF TIME ON THE COLOURS PREPARED BY THE METHYL a-CHLORO- ACRYLATE - POTASSIUM PERMANGANATE REACTION Lovibond colour values Weight of I A > Volume of methyl After 10 minutes After 3 hours standard ot-chloro- & & solution, acrylate, Red Yellow Red Yellow 2-5 0.05 3.3 3.1 3.3 5.6 5.0 0.10 2.2 8.9 2.5 9.2 ml "g 2.5 0.05 3.3 3.1 3-0 5.0 5.0 0.10 2.0 8.5 3.1 8.9 Attention was next directed to the efficiency of absorption of methyl a-chloro-acrylate vapour by weak solutions of potassium permanganate.To set up a known weak concentration of methyl a-chloro-acrylate vapour, in order to check the efficiency of the absorption of the vapour in very weak solutions, would be a matter of some difficulty. Instead of doing this, an experiment was made with an unknown concentration, which was then determined by the volumetric method with 0.02 N potassium permanganate solution and by the colorimetric method, 0.001 N potassium permanganate solution being used for the absorption.The concentration of methyl a-chloro-acrylate vapour in the laboratory fume cupboard, which contained chloro-acrylate residues in an open vessel, was used for the experiment. A point was chosen for the tests, and for the colorimetric method air was drawn at the rate of 1-5 litres per minute through two jet bubblers each containing 10 ml of 0-001 N potassium permanganate solution. After 3 minutes the potassium permanganate solution in the first bubbler had changed colour appreciably and the test was stopped. A range of standards containing from 0.0 to 0.10 mg of methyl a-chloro-acrylate by O*Ol-ml steps was prepared as before and the colours of the sample bubblers were matched against the standards.The first bubbler was equivalent to the 0.06-mg standard and the second was equivalent to the 0.02-mg standard, i.e., 4.5 litres of air contained 0.08 mg of methyl a-chloro-acrylate. Hence the concentration was calculated as 18mg of methyl a-chloro-acrylate per cubic metre of air. The air was tested at the same point by the volumetric method. Again air was drawn at the rate of 1.5 litres per minute through two jet bubblers, each containing 15 ml of 0.02 N potassium permanganate, for 15 minutes. The total permanganate consumed amounted to 1.6 ml of 0.02 N potassium permanganate solution, which is equivalent to 0.456 mg of methyl a-chloro-acrylate, i.e., 22.5 litres of air contained 0.456 mg of methyl a-chloro-acrylate.From this the concentration was calculated as 20 mg of methyl a-chloro-acrylate per cubic metre of air. The close agreement between these results was sufficient evidence that the methyl a-chloro-acrylate vapour was completely absorbed by 0.001 N potassium permanganate solution in the method described. It was concluded from these results that a colorimetric method based on the procedure used in the above experiments would be suitable for the determination of concentrations of methyl a-chloro-acrylate in air ranging from 0.5 to 25 mg per cubic metre (0.1 to 5 p.p.m. v/v) by absorbing the vapours in 0.001 N potassium per- manganate solution at the rate of 1.5 litres per minute over periods ranging from 3 to 16 minutes.Initially it was proposed that the colour matching should be made against standards prepared in the laboratory by interaction of known volumes of potassium permanganate solution with known amounts of methyl a-chloro-acrylate solution. I t was realised, however, that much time would be saved if a colour disc suitable for use in a Lovibond comparator could be obtained, The co-operation of Mr. Chamberlin of The Tintometer Ltd. was sought,632 HASLAM, WHETTEM AND SOPPET: 1HE DETERMINATION OF [Vol. 76 and a satisfactory colour disc was made. I t consists of nine individual coloured glasses that have been prepared to match the colours obtained by the interaction of 10 ml of 0.001 N potassium permanganate solution and the following amounts of methyl a-chloro-acrylate : 0.00, 0.01, 0.02, 0.03, 0.04, 0.05, 0-06, 0.08 and 0.10 mg.I t is necessary to view the test solution in the 13.5-mm comparator cells 5 minutes after colour development, the screen provided being used on the sample side. Full details of the colorimetric method are given below. The method includes a description of both procedures, ie., that using standards prepared in the laboratory from known amounts of methyl a-chloro-acrylate and permanganate, and that using the Lovibond comparator. Although it is probable that most of the problems that arise will be dealt with satis- factorily by the colorimetric procedure, it may be necessary on occasions to determine very high concentrations of the order of 25 to 100 mg of methyl a-chloro-acrylate per cubic metre of air, For this reason the volumetric procedure is also given after the colorimetric method.COLORIMETRIC METHOD APPARATUS- Jet bubblers-Two of these are required. Their dimensions are: length, 26 cm; internal diameter, 22 mm; tube diameter, 6.5 mm, drawn out to 1 to 1-5 mm at the tip (see Fig. 1). Rotameter-This is calibrated to measure rates of flow from 1.5 to 0.1 litres per minute a t 20" C and a pressure of 760 mm of mercury. REAGENTS- Potassium permanganate solutions, 0.02 N , 0.002 N and 0.001 N . Potassium oxalate solution, 0.02 N . Sulphuric acid, 10 per cent. v / v . Standard solzition of methyl a-chloro-acrylate in water (1 ml = 0.02 mg)-Prepare the standard aqueous solution of methyl a-chloro-acrylate as follows.Measure from a I-ml graduated pipette 0.25 ml of methyl a-chloro-acrylate into a 500-ml measuring flask. Dilute with water to 500ml and shake well. Filter into a dry flask and transfer, by means of a pipette, 10 ml of the filtered solution to a 250-ml conical flask. Add 40 ml of 0.02 N potassium permanganate solution, shake well and add 10 ml of 10 per cent. v/v sulphuric acid and then 50 ml of 0.02 N potassium oxalate solution from a pipette. When the solution has decolorised, heat it to 80" C and titrate the excess of potassium oxalate with 0.02 N potassium per- manganate solution. From the volume of 0.02 N potassium permanganate consumed, calculate the strength of this solution as milligrams of methyl a-chloro-acrylate per millilitre of solution. 1 ml of 0.02 N potassium permanganate = 0,285 mg of methyl a-chloro-acrylate. Measure from a burette, reading to 0.01 ml, an amount of this standardised solution equivalent to 2-0mg of methyl a-chloro-acrylate into a 100-ml graduated flask and dilute to 100 ml with water.This is the standard solution used in the colour comparison, and 1 ml of it contains 0.02 mg of methyl a-chloro-acrylate. SAMPLING PROCEDURE- Measure 10 ml of 0.001 N potassium permanganate solution into each of the two jet bubblers and connect these in series to the Rotameter and suction pump (Fig. 1). Aspirate the air to be tested through the apparatus at the rate of 1.5 litres per minute until the colour of the permanganate solution in the first bubbler appears to be satisfactory for colour com- parison (usually 3 to 15 minutes).Stop the air flow and drain the solutions from each bubbler carefully into 50-ml Nessler cylinders. Note the volume of air passed. COLOtlR COMPARISON- While the aeration through the permanganate is proceeding, prepare methyl a-chloro- acrylate colour standards as follows. Into nine Nessler cylinders measure, by means of a graduated pipette, the following amounts of the standard solution of methyl a-chloro- acrylate: 0.0, 0.5, 1.0, 1-5, 2.0, 2-5, 3.0, 4.0 and 5.0 ml. Dilute each solution to 5.0 ml with water and add 5.0 ml of the 0.002 N potassium permanganate solution. Visually match the colours of the permanganate solutions from the test with the prepared standards. Com- bine the two results and calculate the final result to milligrams of methyl a-chloro-acrylate per cubic metre of air sampled.Nov., 19511 METHYL a-CHLORO-ACRYLATE IN THE ATMOSPHERE 633 RAPID COLORIMETRIC METHOD WITH THE LOVIBOND COMPARATOR- Drain the contents of the first bubbler into one of the 13.5-mm glass comparator cells and fill the other comparator cell with water.Place the cells in the comparator so that the colour glasses of the methyl a-chloro- acrylate colour disc cover the water cell. See that the screen supplied with the disc is in position covering the sample cell and rotate the disc until the colours of the sample solution and colour disc match. Read the value shown on the disc, which represents milligrams of methyl a-chloro-acrylate in the 10 ml of 0.001 N potassium permanganate solution. Match the colour of the solution in the second bubbler in the same way.Combine the two results and calculate the final result to milligrams of methyl a-chloro- acrylate per cubic metre of air sampled. Carry out the sampling procedure described above. VOLUMETRIC METHOD APPAriATCs- As for the colorimetric method. REAGEKTS- Potassium permanganate solution, 0.02 N. Potassium oxalate solution, 0.02 N . Sulphuric acid, 10 per cent. v / v . PROCEDURE- Measure 15 ml of 0.02 N potassium permanganate solution into each of the two jet bubblers and connect these in series to the Rotameter and suction pump (Fig. 1). Aspirate the air to be tested through the apparatus at the rate of 1-5 litres per minute for 15 minutes. Add 10 ml of 10 per cent. v/v sulphuric acid and 20 ml of 0.02 N potassium oxalate solution and allow to stand until the permanganate is decolorised.Wash out each bubbler separately into 250-ml conical flasks. Titrate the excess of oxalate with 0.02 N potassium permanganate solution after heating the contents of each flask to 80" C. Carry out a blank titration by measuring 15 ml of 0.02 N potassium permanganate solution into another flask, adding 10 ml of 10 per cent. v/v sulphuric acid, 20 ml of 0.02 N potassium oxalate solution and titrating the excess of oxalate with 0.02 N potassium permanganate solution as before. Calculate the volume of 0-02 N potassium permanganate solution con- sumed in each bubbler by subtracting the blank titration from the sample titration. The total permanganate consumed is the sum of these two figures.The total volume in millilitres of 0.02 N potassium permanganate consumed multiplied by 0.285 gives the weight in milligrams of methyl a-chloro-acrylate in the volume of air passed. Calculate the result to milligrams of methyl a-chloro-acrylate per cubic metre of air. APPLICATION OF THE COLORIMETRIC METHOD TO THE DETERMINATION OF METHYL A test was carried out by the colorimetric method on the atmosphere inside a fume chamber . An open beaker containing 6 g of methyl a-chloro-acrylate was placed inside the chamber and the ventilating fan was switched on. The two jet bubblers containing the 0.001 N potassium permanganate solution were set up inside the fume chamber so that the air intake was 15 inches vertically above the beaker. This height corresponded approximately to mouth level.Air was aspirated through the bubblers at the rate of 1 litre per minute. While this was in progress the colour standards were prepared in 50-ml Nessler cylinders. The air flow was stopped after 30 minutes and the permanganate solutions were drained from the bubblers into two similar 60-ml Nessler cylinders. RESULTS- a-CHLORO-ACRYLATE IK THE ATMOSPHERE I N A FUME CHAMBER Rate of flow of air = 1 litre per minute. Time for which air was aspirated = 30 minutes. Volume of air aspirated = 30 litres. On matching the colour of the solution from the first bubbler against the standards, it was found to be between the 0.03 and O-OPmg standard and was estimated to be 0.033 mg634 HASLAM, WHETTEM AND SOPPET [Vol. 76 of methyl a-chloro-acrylate.The solution from the second bubbler matched the 0-O-mg standard and therefore contained no methyl a-chloro-acrylate. Hence 30 litres of air contained 0.033 mg of methyl a-chloro-acrylate and 1000 litres of air contained 1.10 mg of methyl cr-chloro-acrylate, i e . , the concentration was 1.1 mg of methyl a-chloro-acrylate per cubic metre of air, or 0.22 p.p.m. v/v at 20" C and 760 mm pressure of mercury. THE EFFECT OF METHYL METHACRYLATE ON THE COLORIMETRIC METHOD Two sets of standards were prepared in 10 ml of 0.001 N potassium permanganate solution, one set containing 0.02, 0.04, 0.06, 0.08 and 0-10 mg of methyl a-chloro-acrylate and the other set containing the same weights of methyl methacrylate. The methyl a-chloro- acrylate standards were normal, i.e., their colours ranged from permanganate tint to orange - yellow with increasing amounts of chloro-acrylate. The methyl methacrylate standards, however, all retained the permanganate tint, the intensity of which diminished with increasing amounts of methacrylate. Tests were also carried out on known amounts of methyl a-chloro-acrylate with and with- out added amounts of methyl methacrylate. As a result of these tests it is our opinion that 4 parts by weight of methyl methacrylate have the same effect on the chloro-acrylate test as 1 part of methyl a-chloro-acrylate. In other words if, for example, the atmosphere contained 4mg per cubic metre of methyl a-chloro-acrylate and 4mg per cubic metre of methyl methacrylate, the application of the colorimetric method to this atmosphere would give a result of 6 mg per cubic metre of methyl a-chloro-acrylate. This method for determining the lachrymatory methyl a-chloro-acrylate is designed for use on a plant producing it, where contamination of the atmosphere would be due entirely or almost entirely to the ester. If used in other circumstances, positive results in the test would not necessarily be indicative of the ester without confirmatory evidence. Incidentally, we have shown that methyl a-chloro-acrylate reacts extremely rapidly with weak potassium permanganate solution at concentrations in which such substances as ethyl alcohol and form- aldehyde have a negligible effect. REFERENCE The behaviour of the two sets of standards was quite different. 1. Haslam, J., and Squirrell, D. C. M., Biochem. J., 1951, 48, 48. IMPERIAL CHEMICAL INDUSTRIES LIMITED PLASTICS DIVISION WELWYN GARDEN CITY, HERTS. May, 1961

ISSN:0003-2654    

DOI:10.1039/AN9517600628

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

Nov., 19511 HODGSON AND GLOVER 636 The Determination of Alcohol, Ether and Water in Ternary Mixtures BY H. W. HODGSON AND J. H. GLOVER A method is described for the analysis of all mixtures of alcohol, ether and water with an accuracy of 0.2 per cent. The composition is obtained from a calibration graph constructed from data obtained by boiling-point determina- tions and “cloud-point” titrations. A modification to the 3-tube for the boiling-point determination has effected an improvement in technique. The . method is simple and rapid in operation, and would be applicable to other ternary mixtures containing water. IN connection with the evaluation of the performance of rectification columns a rapid method was required that would be applicable to mixtures of all compositions of alcohol, ether and water.Existing methods1s2~3~4s6se~7 depend on separation or chemical means of estimation and consequently are time consuming and lack the flexibility necessary to cover all proportions of the constituents. Among the physical methods, Andress8 determined the specific gravity and surface tension and then evaluated the composition from a calibration diagram, and Scotta used refractive-index and specific-gravity measurements. These methods were found unsuitable owing to the volatility of mixtures that contain a high proportion of ether and to the fact that it is difficult to define the exact point of intersection of the lines on the graph owing to the small angle between them. The Andress method has the further disadvantage that several mixtures have the same specific gravity and surface tension.The advantage of indirect methods for the analysis of ternary mixtures lies in the accuracy and speed with which certain physical properties can be determined. The choice of properties for measurement is governed by the calibration diagram and so, to avoid difficulties such as are encountered in the Andress and Scott methods, two constants were selected, of which each is dependent on a different component of the mixture. Hence, in the calibration diagram, the two sets of lines cross almost at right angles, so permitting accurate location of any mixture. The properties determined are (i) a titration value that depends on the solubility of dibutyl phthalate in the sample and (ii) the boiling-point of the sample.The titration is carried out by adding a solution of dibutyl phthalate to the sample and then titrating, at constant temperature, with water until precipitation of the phthalate begins. This is a simple and reproducible procedure and the titration is influenced mainly by the water content of the mixture. The boiling-point of the sample is determined by measuring the temperature at which the vapour pressure is 760 mm of mercury. The apparatus is a modified &tube designed for easy filling. The accuracy of the proposed method depends on the scale and accuracy of the calibration diagram, and is 0-2 per cent. in the method described. However, for mixtures in which one component predominates a variation of the dibutyl phthalate reagent would provide greater accuracy over a narrower range.The proposed method could be applied to other ternary mixtures of which water is a component, and the titration technique alone can be employed to analyse binary mixtures containing water. METHOD APPARATUS- bore except for the portion from E to H which is 1-mm capillary tubing. fitting stopcock. tions directly opposite each other. The boiling-point is affected most by the ether content of the sample. The &tube is constructed as shown in Fig. 1 of thin-walled Pyrex tubing of 4 to 5 mm Tap C is a well- A millimetre scale is etched on the U portion of the tube with the gradua-636 HODCSON AND GLOVER: THE DETERMINATIOK OF ALCOHOL, [I-ol. 76 REAGENT- Dibutyl PhthaZate solution-A 1 per cent. w/v solution in ethanol previously adjusted with water to sp.gr. (15.6" C/155" C) 0.8070 PROCEDURE- Determination of the titration value-Weigh 10 g * 0.1 g of the sample into a dry 150-ml conical flask modified by the addition of a vertical side arm to take a thermometer.Add by pipette 10 ml of dibutyl phthalate reagent, the temperature having been previously adjusted to 20" & 1" C. Insert a thermometer, adiust the temperature to 19" C, and then 0.0002. "t F- Imm I.D. 7mm O.D. \ A 5mm I.D. 7mm O.D. -G Scale graduated in mlllimetres D Fig. 1. Modified d-tube for boiling-point determination (half-scale) titrate wiih distilled water, maintaining the tem- perature at about 19" C, until one drop of water produces a permanent opalescence in the solution. Adjust the temperature to 20" & 0.1" C, when the solution should become clear, and then continue the titration dropwise until a permanent opalescence is again produced.This point is taken as the end- point. Duplicates should be reproducible within 0.1 ml. Determiizat ion of the boiling-Po i d . --Introduce pure, dry, mercury into the limb A of the J-tube, attach B to a vacuum line and carefully open tap C so that mercury is drawn up to the tap without being allowed to enter the tap itself. The amount of mercury used should be such that the tube is now filled from C to a point just round the bend at D. Close tap C, disconnect B from the vacuum line, arid apply the vacuum at A to bring the mercury to approximately the same level in both limbs. Gently waJm the U portion of the tube to remove occluded air, and then carefully break the vacuum at A so that the mercury returns slowly to its original position.All the air is now trapped below the stopcock C. Introduce two drops of the sample on to the mercury surface at D in limb A by means of a capillary pipette. Carefully tilt the tube to transfer the sample into limb B so that it is trapped at E. A capillary thread of mercury separates the sample from the trapped air at C. Immerse the filled tube in a bath of water to the level FG. Slowlv raise the temDerature of the water, stirring it continuously until the mercury levels in (he tube begin to'alter. At this point reduce the rate of heating to about 1°C per minute. Note the temperature at which the vapour in limb B is at 760 mm pressure, this point being determined from the difference in height of the mercury levels in relation to the atmospheric pressure.Duplicates should be reproducible within 0.1" C. CALIBRATION GRAPH- The calibration graph (Figs. 2 and 3) was prepared from the results described in the experimental section below. The ordinate of the graph is the percentage of water and the abscissa the percentage of ether in the mixture, the percentage of alcohol being obtained by difference. A series of titration lines connect points representing mixtures with the same titration value, and a similar series of boiling-point lines are drawn connecting mixtures of the same boiling-point. I t has been found more convenient to adopt the use of rectilinear co-ordinates rather than the more usual triangular form. Interpretation of results is simplified and the angle of intersection between the two sets of lines is larger.The scale adopted in the construction of the graph is made consistent with the accuracy of the method, 1 mm on the scale corresponding to 0.2 per cent. except in the region of high water content (50 to 100 per cent.), where the ether scale was doubled, 1 mm corresponding to 0.1 per cent., toALCOHOL - ETHER - WATER CALIBRATIQN DIAGRAM WATER 50 TO 100 PER CENT Titre, ETHER Fig. 2Tit re, Qc w I- s ETHER Fig. 3Nov., 19511 ETHER AND WATER IN TERNARY MIXTURES 637 facilitate the reading of the boiling-point lines. The boiling-point lines have been labelled at 5" C intervals and the titration lines at intervals of 1 ml, but intermediate values can easily be interpolated.EXPERIMENTAL DETERMINA4TION OF THE TITRATION VALUE- A large number of mixtures of alcohol, ether and water were prepared and titrated as Examination of the results indicated that the titre depended on two described above. factors- (a) the water content of the sample, and (b) the E value of the sample. The E value is defined by the following expression- 100 A E = A = the weight of ether in l o g of sample, and B = the weight of water in l o g of sample. (10 - B) + 7.6 where- The E value defines the slope of the line relating titration to water content. The constant 7.6 in the equation is the weight of alcohol added in 10ml of dibutyl phthalate reagent. The E value of any known mixture can thus be calculated. For mixtures containing up to 80 per cent.of water, the relation between the titre and water content was found to be linear for a fixed E value. For mixtures containing more than 80 per cent. of water, the relation between the titre and the water content is almost independent of the E value since, owing to phase restrictions, this cannot exceed 5; and the change in slope of the line relating titration to water content over a range of E from 0 to 5 is negligible for the small titrations obtained for mixtures containing more than 80 per cent. of water. Results illustrating these points are shown in Table I. The effect of a change in E value is illustrated by mixtures 22 to 27. For mixtures having E values of 0 to 15 the increase in titration is linear with increase in E value for a fixed water content, a titration maximum is reached at E = 18 and then the titration decreases in a smooth curve as E increases further.Mixtures of E value greater than 34 cannot be titrated, as phase separation occurs before the end-point is reached. Such mixtures may be analysed after addition of an equal weight of alcohol (of known water content) to a portion of the sample. This modified material is analysed by boiling-point determination and titration and its composition read from the calibration graph. The composition of the original sample can then be calculated by allowing for the alcohol added. The occurrence of phase separation is easily distinguished from the true titration end-point. Mixtures 28 to 37 illustrate the independence of titration and E value if the water content is above 80 per cent.Hence the results of the titration of known mixtures of alcohol, ether and water can be summarised as follows- (1) A plot of titration against water content for mixtures containing less than 80 per cent. of water gives a series of straight lines whose slopes depend on the E value of the mixtures, i.e., all mixtures having the same E value lie on the same line. (2) Mixtures containing more than 80 per cent. of water give titrations very nearly independent of their E value. (3) Mixtures with an E value greater than 34 cannot be titrated without prior dilution with alcohol. DETERMINATION OF THE BOILING-POINT- It was originally intended to determine the vapour pressure of the sample at a fixed temperature, but attempts to carry out such a determination in a simple manner led to results lacking in reproducibility.It was therefore decided that a logical alternative would be the determination of the temperature at which the vapour pressure of the mixture was a fixed value, and this was chosen as 760mm of mercury for convenience.638 HODGSON AND GLOVER: THE DETERMINATION OF ALCOHOL, [Vol. 76 The &tube apparatus was first investigated, but was found to be very difficult to fill. It was almost impossible to confine the sample above the mercury in the sealed limb without the introduction of air bubbles, and the initial charging of the tube with mercury was subject to the same difficulties. TABLE I DEPENDENCE OF TITRATION ON WAfER CONTENT AND E VALUE Mixture No. 1 2 3 4 6 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 26 26 27 28 29 30 31 32 33 34 35 36 37 Alcohol, 100 80 60 40 20 10 0 % Ether, Yo 0 0 0 0 0 0 0 Water, % 0 20 40 60 80 90 100 34 6 60 53 7 40 72 8 20 91 9 0 45.95 14.06 40 63.95 16.05 20 81-96 18-06 0 30.4 19.6 50 38.9 21.1 40 55.9 24.1 20 72.9 27.1 0 31.9 47.9 63.9 28.1 32.1 36.1 90 10 80 20 70 30 60 40 50 50 46 54 8.0 9.0 10.0 5.0 6.0 6.5 7.0 4-0 4.6 5.0 2.0 1.0 0 2.0 1.0 0.5 0 1.0 0.5 0 40 20 0 90 90 90 93 93 93 93 95 96 95 E value 0 0 0 0 0 0 0 Titration a t 20° c, ml 30.9 24.56 18.15 12-05 6-86 2.90 0.45 5.2 12.1 5.2 18.6 5.2 2646 5-2 31.6 10.4 10-4 10.4 19.0 26.6 32-3 15.6 15.9 15-6 18-95 15.6 26-1 15.6 32.8 20.8 20.8 20.8 19.25 26.1 32.85 5.7 31.7 11.35 32-75 17.05 32.85 22.7 32.6 28.4 31.15 30.7 30- 15 1.22 1.1 1 0 2.3 1-15 0.57 0 1.18 0.59 0 3.1 3.1 2.9 2.35 2-35 2.35 8.3 1.76 1.75 1.75 Finally, a modified &tube was evolved, the design of which allowed easy charging with mercury and removal of occluded air; this has been described on p.635. By the method described on p. 636, the boiling-points of a large number of ternary mixtures were determined. Mixtures were prepared by dilution with water of a series of solutions each containing a fixed ratio of alcohol to ether. As the work proceeded it became apparent that a number of unusual results were being obtained. For example, in the series containing alcohol and ether in the ratio of 9 to 1, maxima were obtained with mixtures containing 2, 54 arid 97 per cent. of water. With mixtures in the ratio of 8 to 2, maxima were obtained at water contents of 2, 4, 57 and 97 per cent.; similar maxima were obtained with the 7 to 3 and 6 to 4 ratios, except that the maximum at about 50 per cent.disappeared. The effect of ether on the boiling-point is quite considerable, but an increase in water content has little effect; the boiling-point for mixtures containing up to 70 per cent. of water changes by only a few degrees.Nov., 19511 Alcohol, % 100 95.5 91 80 74 69 64 59 ETHER AND WATER I N TERNARY MIXTURES TABLE 11 RESULTS OF BOILING-POINT DETERMINATIONS Binavy mixture (no . h e y ) - Water, B.p. (760 mm), % " C 0 78.4 4.5 78.1 9 78.2 20 78.8 26 79.4 31 79.8 36 80.2 41 80-6 Mixtures of alcohol - ether ratio 9 to 1- Alcohol, Ether, 90 10 88.85 9.9 88-2 9.8 85.5 9.5 82.8 9.2 81.0 9.0 72.1 8.0 62.9 7.0 53.8 6-0 49.6 5-5 44.9 5.0 42-65 4.85 41.4 4.6 40.5 4.5 38.25 4-26 36.2 4-0 264 3.0 18.0 2.0 13.6 1.5 % % 9.15 1 -05 6.76 0.76 4.5 0.5 3.6 0.4 2-7 0.3 2.25 0.25 Mixtures of alcohol - ether ratio 8 to 2- Alcohol, Ether, 80 20 78.8 19.7 78.1 19.5 77.6 19.4 76.7 19-2 76-2 18.8 73.6 18.4 71.7 17.9 63.8 15.9 56.7 13.9 48.0 12-0 40.0 10.0 36.4 9.1 36.0 9.0 36-2 8-8 34.2 8.6 33.5 8.4 32.0 8.0 24.0 ' 6.0 16.0 4.0 8.0 2.0 4.0 1.0 76.8 19.0 % % Water, 0 1.25 2.0 5.0 8.0 10.0 19.9 30.1 40.2 44.9 60.1 52-6 54.0 55.0 57.5 59.8 70.1 80.0 86.0 89.8 92.6 96.0 96-0 97.0 97.5 % Water, 0 1.5 2.4 3.0 4.1 6.0 8.0 10.4 20.3 30.4 40.0 60.0 54.5 65.0 66.0 67.2 68.1 60.0 70.0 80.0 90.0 96.0 6-2 30.1 % 56-9 14.0 -~ ~ 634 16.0 20.1 Alcohol, Water, % 50 45 41 30 20 15 10 5 % Fi 0 55 59 70 80 85 90 95 639 B.p.(760 mm), "C 81-2 81.6 82-0 83.5 86.0 88.0 90-0 94.5 B.p. (7,gO mm), C 68.0 68-3 (maximum) 68-0 67.8 68.0 68.3 68.8 69.0 69.3 69.1 68.7 69.8 70.4 (maximum) 68.3 67.7 68-0 69.8 74.7 78.5 81.0 86.0 90.9 92.8 95.2 (maximum) 94-6 B.p. (760 mm), O C 59.2 60.2 (maximum) 59-9 58-9 60.8 (maximum) 60.4 60.4 60.3 60-3 59.5 57.6 57-1 67.3 57.6 68.2 59-6 (maximum) 67.6 66.9 58.8 63.8 70.4 86.2 60.6 69.5 60.3640 HODGSON AND GLOVER: THE DETERMINATION OF ALCOHOL, [Vol. 76 TABLE I I-continued Mixtures of alcohol -ether ratio 7 to 3- Alcohol, Ether, 70 30 68.7 29.5 67.9 29.1 66.9 28.7 66.2 28.3 644 27.6 62.7 26.9 69.2 25.3 56.9 24.1 35.1 15.1 33.3 14.3 31.7 13.6 29-4 12.6 28.2 12.1 20.8 8.9 14.2 6.1 7.3 3.2 10.5 4.6 % % Mixtures of alcohol - Alcohol, 60 59.7 59.3 68.8 58-5 57.9 67.4 66.6 66.9 86.2 64.0 52-6 50.4 45-6 40.8 39.6 38-4 37.2 34-8 32.4 30.0 27.6 3.6 3.0 1-8 1.6 % ether ratio 6 lo 4- Ether, % '40 39.8 39.6 39.2 39.0 38.6 38.2 37.8 37-3 36.8 36.0 35.0 33.6 30.4 27.2 26.4 26.6 24.8 23.2 21.6 20.0 18.4 2-4 2.0 1.2 1.0 Water, 0 1-8 3.0 4-4 5.6 8.0 10-4 15.5 19.0 49.8 52.4 54.7 58.0 59.7 70.3 79.7 89.6 85-0 % Water, 0 0.5 1.2 2.0 2-5 3.5 4.4 6.6 6.8 8.0 10.0 12.4 16.0 24.0 32.0 34.0 36.0 38.0 42.0 46.0 60.0 54.0 94.0 95.0 97.0 97.6 % B.p.(760 mm), OC 62.5 64.2 64.3 53.9 63-2 64-1 54.5 54.3 63.8 48.5 48.0 47.7 48.1 48.3 49.8 51.5 69.5 53.6 B.p. (7060 mm), C 48.2 48.4 48.6 48.8 48.9 49.4 49.4 49.1 49.1 49.5 48.9 49.2 48.6 47.1 46.2 46.1 46-0 45.5 45.0 43.6 42.6 41.6 76-6 80.0 90.0 92.5 Mixtures of alcohol - ether ratio of less than !3 to 1 show a decrease in boiling-point with increasing water content up to about 50 per cent.of water. Difficulty was found in repro- ducing the boiling-points of 8 to 2 ratio mixtures in the vicinity of the maximum at 57 per cent. of water; this maximum is presumably due to an unstable phase equilibrium at this composition. Results are shown in Table 11. All other points were found to be reproducible. CALCULATION OF TITRATION LINES- The fact that the titration bears a linear relation t o the water content for mixtures containing less than 80 per cent. of water can be used to calculate the -titration lines up toNov., 19511 ETHER AND WATER IN TERNARY MIXTURES 641 this water content. The equation relating titration to water content over the range 0 to 80 per cent.of water can be written- where- T = T O - m W T is the titration value; W is the water content; To is the titration when water = 0; m is a constant depending on the E value of the mixture. where- T, is the titration for mixtures containing 80 per cent. of water. This is constant Values of m and To for various E values calculated in this manner are shown in Table 111. for all values of E. TABLE I11 CALCULATED VALUES OF To AND m FOR VARIOUS VALUES OF E E To m 0 30.9 0.3131 6 31.55 0.3212 10 32.2 0.3294 15 32.8 0.3369 18 32-9 0.3381 20 32.8 0.3369 22 32-06 0.3350 25 32.1 0.3281 28 31.26 0.3175 30 30.45 0,3075 32 29.3 0.2931 34 27-6 0.2719 TABLE IV CALCULATED VALUES FOR TITRATION LINES (VALUES OF W) Titra- tion 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 E=O - - 2.9 6.1 9.3 12.5 15-6 18.8 22.0 25.2 28-4 31.6 34.8 38.0 41.2 44.4 47.6 50.8 54.0 57.2 60.4 63.6 66-8 70.0 73.1 76-3 79.5 82.5 86.2 89.6 93.2 97.2 E=;S 1.7 4-8 7.9 11.1 14.2 17.3 20.4 23.5 26.6 29.7 32.8 35.9 39.1 42.2 46.3 48.4 51.5 54.6 57.8 60.9 64.0 67.1 70.2 73.4 76.4 79.6 82.5 86.2 89.6 93-2 97.2 - E=lO 0.62 3.6 '6.7 9-7 12.7 15-8 18.8 21.8 24.9 87.9 30-9 34.0 37-0 40.1 43.1 46.1 49.2 52-2 55.3 68.3 61.3 64.4 67-4 70.4 73.5 76.5 79.5 82.5 86-2 - - - E= 15 2.4 5.3 8.3 11.3 14.2 17.2 20.2 23.1 26.1 29.1 32.0 35.0 38-0 40.9 43.9 46.9 49.9 62.8 55.8 68.7 61.7 64-7 67.7 70.6 73.6 76.6 - - - - - E=18 2.7 5.6 8-6 11.6 14.5 17.5 20.5 23.4 26.4 29.3 32.3 3 5 3 38.1 41.1 44.1 47.0 50.0 63-0 55.9 58.9 61.8 64.8 67.7 70.7 73.7 76.6 - - - - - - E=20 2.4 5.3 8.3 11-3 14.2 17.2 20.2 23.1 26.1 29.1 32.0 36.0 38.0 40.9 43.9 46.9 49.9 52.8 55.8 58.7 61.7 64.7 67.7 70.6 73.6 76.6 - - - - - - E=22 1.9 4.9 7.9 10.9 13.9 16.9 19.9 22.8 25.8 28.8 31.8 34-8 37.8 40.7 43.7 46.7 49.7 52.7 55.7 58.7 61.6 64.6 67-6 70.6 73.5 73.5 - - - - - - E=26 0.3 3.3 6.4 9.4 12.6 15.5 18.6 21-6 24.7 27.7 30.8 33.8 36.8 39.9 42.9 46.0 - - - - - - - - - - - - - - - -642 HODGSON AND GLOVER: THE DETERMINATION OF ALCOHOL, [Vol.76 Titration lines are drawn from points calculated by substituting the above values for m and To in the equation TO - T w =-- m This gives W for fixed E values, and hence the percentage of ether can be calculated. For example, if the titration line for 20 ml is being constructed, points are obtained as (a) E = 0, To = 30.9, m = 0.3131.follows- 30.9 - Water = W = - = 34.8 per cent. As the E value = 0, the percentage of ether = 0 Therefore, by difference, the percentage of alcohol = 65.2 per cent. (b) E = 5, To = 31-66, m = 0.3212 Water = W = o.3212 = 35.95 per cent. Since the E value = 6, the percentage of ether = 7.0 per cent. Therefore, by Merence, the percentage of alcohol = 57-06 per cent. 31.55 - 20 A series of points can be obtained in this way and the titration line constructed. The calculation of the ether content of a mixture from the E value and water content can be done graphically. This is the most convenient way when a large number of points are required. Water, % 0 1 2 3 4 6 8 10 12 16 20 24 28 32 36 40 44 60 52 54 56 58 60 64 70 75 80 86 90 92 94 96 97 98 48 46' C 50.4 - - 48.0 50.0 (46" C) 51.0 (46" C) 50.4 48.5 39.6 42-5 33-8 31.5 29.4 27.1 24.3 21.8 19.0 17.7 16.7 16.1 14.4 11.8 14.2 12.4 10.5 - - - - - - - - - - 50" C 35.6 36.9 36.5 34.6 37.0 35.0 35.8 34.2 33.2 3 1.4 29.4 26-2 24.3 22.1 20.1 18-4 17.0 15.1 14.0 13.2 12.0 12.4 11.8 10.9 10.2 8.8 7.5 6.3 - - - - - - - 55" c 25.9 28e.5 28.3 26.8 27.1 26.6 26.0 26.0 25-7 24.0 22.0 20.1 18.7 17.0 15.4 13.9 12.7 11.6 11.1 10.5 10.2 10.3 9.7 8.4 8.0 7.2 6-4 5.5 4.4 - - - - - - TABLE V BOILINGPOINT LINES Values for ether contents 60" C 19.0 20.2 20.1 18-0 19.6 19.4 19.4 18.4 18.0 17.3 16-3 15.1 14.1 12.8 11.6 10.6 9.6 8.8 8.6 8.3 8.2 5-8 7.3 6.4 6.0 5.6 5.2 4.6 4.1 - - - - - - 66" C 13.0 13.6 13.5 12.8 12.8 12-7 12.8 12.4 12.2 11.8 11.5 10.7 10.1 9.3 8.5 7-8 7.1 6.5 6.5 6.2 6.4 5.5 5 .2 4.8 4.4 4.0 3.8 3.8 3-6 - -- - - - - 70' C 7.8 7.9 7.9 7.5 7.3 7.0 7.0 7.0 7.0 7.0 7.0 6-8 6.4 6.2 3.8 5.5 5.1 4.5 4.5 4.3 4.8 3.6 3.4 3.3 3.0 2.7 2.8 2.8 5.7 - - - - - - 76" C 2-7 2.8 2.7 2-4 2.2 2.2 2.2 2.3 2.4 2.9 2.8 3-1 3.1 3.1 3.0 2.9 2.7 2.7 2.6 0.5 3.0 2.0 2.0 9.0 1.8 1.6 1-8 1.8 2.0 2-4 2.6 2.8 - - -. 80" C 85" CNov., 19511 ETHER AND WATER I N TERNARY MIXTURES 643 The titration lines of mixtures containing more than 80 per cent. of water are most easily obtained from a graph of experimental results. I t will be noted that the higher titrations will give negative values for W when the above equation is used at various E values. A negative result indicates that the titration line does not cover mixtures of the E value in question.Table IV shows points for titration lines calculated in this manner. CONSTRUCTION OF THE BOILING-POINT LINES- The boiling-points of known mixtures already listed in this paper are used in the con- struction of the boiling-point lines on the calibration graph. First the boiling-points of mixtures are plotted against their water content for fixed ratios of alcohol to ether. From the resulting curves, points may be obtained for the construction of a series of graphs relating the percentage of ether to the boiling-point for fixed water content mixtures. Finally, the boiling-point lines may be constructed from points obtained from the series of graphs. The composition of all mixtures boiling at any given temperature can readily be found by this method. Where maxima and minima are encountered in the first set of curves a sufficient number of points must be taken for the fixed water content curves to cover the effect of the minima and maxima on the boiling-point lines. Points obtained by this method are shown in Table V. The authors thank the Directors of the British Oxygen Company Limited for permission to publish. REFERENCES 1. Juzikhin, A. N., Zavod. Lab., 1937, 6, 1013. 2. “Allen’s Commercial Organic Analysis,” Fifth Edition, J. & A. Churchill Ltd., London, 3. Szeberenyi, P., 2. anal. Chem., 1916, 54, 409. 4. 5. 6. 7. 8. Andress, G. M., Chcm. Met. Eng., 1944, 114. 9. RESEARCH AND DEVELOPMENT DEPT. BRITISH OXYGEN COMPANY LTD. Volume I, p. 160. Johnson, J. J., Ind. Eng. Chem., Anal. Ed., 1932, 4, 20. Bonner, T. G., Analyst, 1947, 72, 47. Shaefer, W. E., Znd. Eng. Chem., Anal. Ed., 1944, 16, 432. - , A7tal. Chem., 1948, 20, 661. Scott, T. A., J. Phys. COIL Chent., 1946, 50, 406. ANALYTICAL LABORATORY LONDON, S.W.19 March, 1961

ISSN:0003-2654    

DOI:10.1039/AN9517600635

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

64.4 LONG: THE ESTIMATION OF TANTALUM IN MIXTURES p o l . 76 The Estimation of Tantalum in Mixtures by Neutron Activation Analysis BY J. V. P. LONG A neutron activation method is described for the determination of tantalum in mixtures containing niobium, zirconium, iron, tin, titanium and silicon. The method depends on the pile irradiation of the sample followed by measurement of the filtered y-ray activity. An accuracy of approximately k 3 per cent. can be achieved for mixtures containing more than 1 per cent. of tantalum. IT is known that whereas tantalum has a large slow-neutron activation cross-section and that the decay radiation includes a hard y-ray, many elements commonly associated with tantalum, for example, titanium, niobium, iron, tin, zirconium and silicon, have low activation cross- sections or give rise to isotopes with a short half-life, or with a short half-life combined with low-energy radiations.These facts, summarised in Table I, provide the basis for a neutron irradiation method for the determination of tantalum in the presence of the elements named above; but caution TABLE I ACTIVATION DATA Atomic activation Type and energy Target cross- Isotope of radiation Element nucleus Abundance, section, produced Half-life (in MeV) % barns Tantalum . . 18lTa 100 20.6 18Ta 120 days 8- 0.5 y 1.13, 1.22 Niobium . . OSNb Titanium . . &OTi Tin . . . . l12Sn U6Sn 120Sn 122Sn lZ4Sn Zirconium . . O*Zr Q8Zr Iron . . . . 64Fe 5@Fe 100 5.34 0.96 14.2 24.0 33.0 4.7 6.0 17.8 2.8 5.9 0.33 0.0099 - 0.01 ? ? ? ? 0.15 0.07 0.2 0.04 0.0026 MNb lUSn 85 Zr &I?e 5QFc 6.6 min.I.T. 100 years 6 minutes 112 days 14 days 100 days 27 hours 130 days 10 days 66 days 17 hours 2.9 years 47 days ,!3- 1-35 X /I- 1.6 K I.T. e Y ,!3- 0.4 18- 1.4 y 0.4 ,!3- 2.4 /3- 0.4, 1-0 y 0.7 0.8 8- 2.2 K /3- 0.26, 0.46 y 1-1, 1.3 is necessary in applying the method to minerals and ores of unknown composition, or to tantalum concentrates derived from them, because several other elements could, if present, cause interference. Some interference might be expected from the 17-hour half-life zirconium- 97 if zirconium is present in large amounts, but this can be easily overcome by delaying counting until several half-periods of this isotope have elapsed. In the absence of elements other than niobium and tantalum, niobium can be determined by difference.This method for the estimation of niobium and tantalum has provided in some instances a useful alternative to the difficult chemical separation of the two elements.Nov., 19511 BY NEUTRON ACTIVATION ANALYSIS 64.5 EXPERIMENTAL In the experiments described in this paper, materials for irradiation were sealed in silica capsules of 5 mm outside diameter and approximately 1.5 cm long. Other experiments have been carried out with graphite capsulesf (see Fig. l), which have since been found more section of for silica tubes aluminium holder section of graph i te capsule 0 I 2 3 cm I 1 1 Fig. 1. Details of apparatus convenient. These holders were constructed by drilling longitudinal holes in aluminium rod and then turning the rod in a lathe so that the holes were partially exposed and the holder would fit in a standard 30-ml irradiation can.Graphite capsules were arranged round a central graphite rod and tied in position with thread before insertion in the aluminium can. The samples were irradiated for one week in the Harwell pile a t a neutron flux of approximately loll neutrons per sq. cm per second. Unless otherwise stated, all oxides used were Johnson Matthey “Specpure” materials. The silica capsules were loaded into holders of the type shown in Fig. 1. Weight of Tho,, mg Fig. 2. Relation between counting rate and weight of tantalum646 LONG [Vol. 76 Gamma-ray measurements were made after four days had elapsed from the time of removal from the pile; this allowed isotopes of short life to decay.The experimental arrangement consisted of a copper y-ray tube screened with 5 mm of lead to filter out soft radiations from the source, which was placed in a light wooden trough at 10 to 15cm from the Geiger tube. A preliminary irradiation was carried out to determine the effect of the presence of other elements on the activity of the tantalum, 5-mg quantities of tantalum oxide being used together with 5 mg of an added oxide. Two sets of tubes were irradiated, the first containing 10 mg of the mixed oxides and the second 10 mg of the mixed oxides together with 30 mg of high-purity graphite. Oxides of tin, silicon, iron, titanium, zirconium and niobium were investigated. The values obtained for the specific activity of the tantalum showed a mean deviation of & 1.8 per cent.without graphite and &1.6 per cent. with graphite. These results indicate that the oxides of the elements investigated will have only a small effect on the tantalum activity . Two further experiments have shown that the activity as measured is proportional to the quantity of tantalum present. In the first, the tantalum oxide was mixed with niobium oxide before irradiation. In the second, the base material consisted of a matrix composed of the oxides listed above in the proportions in which they might be expected to occur with tantalum in the first stage of its separation from naturally occurring materials. The counting rates from these two series have been normalised to correct for different pile factors and are shown in Fig. 2.These results give a linear relationship between counting rate and weight of tantalum. In one further irradiation the specific activity was found to decrease with increasing weight of tantalum. Subsequent experiments have failed to confirm this effect and it is thought to have been due to the position of the tubes during irradiation. The standard deviation of the results used in plotting the graph in Fig. 2 indicates that tantalum can be estimated by this method to a standard deviation of approximately &3 per cent. on single determinations for a standard deviation of &l per cent. in the counting. The lower limit is set more by the variation in constitution, and consequently in the activity, of the base material than by the cosmic and y-ray background. For this reason the range covered extends upwards from approximately 0.2 per cent. of T+O, in the matrix used, and the method is probably of most use above 1 per cent. of T+O,. The work described was carried out on behalf of the Ministry of Supply, by whose permission it is published. REFERENCE 1. Long, J. V. P., J . Sci. Instv., 1961, 28, 191. CHEMICAL RESEARCH LABORATORY TEDDINGTON, MIDDLESEX Apvil, 1961

ISSN:0003-2654    

DOI:10.1039/AN9517600644

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

Nov., 19511 HARRIS AND LINDSEY 647 Vibrating Electrodes in Amperometric Titrations Part I The Determination of Thiosulphate, Iodine and Tervalent Arsenic J ~ Y E. D. HARRIS AND A. J. LINDSEY (Preseutcd at the meeting of the Physical Methods Grot@ on Tuesday, April loth, 1951) The use of vibrating electrodes is extended to amperometric titrations. The apparatus consists of a simple polarising unit with a galvanometer to measure the diffusion currents and a vibrating micro-electrode in conjunction with a saturated calomel electrode. Amperometric titrations of 0.001 N solutions of iodine, sodium thiosulphate and tervalent arsenic give results that, in suitable supporting electrolytes, are comparable in accuracy with titrations in which starch is used as indicator. IK earlier publications’ j 2 the behaviour of vibrating platinum micro-electrodes was described and essential conditions for their use in polarography were established. These electrodes can be used as substitutes for the dropping-mercury electrode, which cannot be used for anodic reactions occurring at potentials more positive than +0.4 volt with reference to the saturated calomel electrode because mercury is attacked in such circumstances.Platinum electrodes, however, can be used up to a potential of +1.1 volts without attack3 and they have been used in this potential range by a number of e x p e r i r n e n t e r ~ . * ~ ~ ~ ~ , ~ In addition they can be used for electrode reactions where the presence of mercury is undesirable, such as the polarographic reduction of alkyl peroxides.’ Permanent polarisation and electrode “poisoning,” which are disadvantages of the platinum micro-electrode in quantitative polarography, are less troublesome in amperometric titrations where the electrode is used as an indicator for an end-point.If no current flows until after the end-point is reached, this difficulty does not occur. As the vibrating electrode is insensitive to external vibration, it has considerable advantage over a stationary electrode or a dropping-mercury electrode. Another advantage is that the vibrating electrode gives a much greater diffusion current than a stationary electrode of the same area. The use of vibrating electrodes does not differ greatly from the well-established techniques for mercury electrodes or rotating platinum micro-electrodes. APPARATUS- The electrodes for this work were constructed as described else~here2,~ and were driven by means of an electromagnetic massage vibrator from the alternating-current mains.They were made of platinum wire sealed into glass tubing of 4 mm diameter, and were 0.5 mm in diameter and 2 mm long. The electrodes were vibrated at constant amplitude greater than 3 mm, which conforms to the conditions recommended elsewhere.2 The electrical circuit is shown in Fig. 1, and is similar to that previously described. This simple polarising circuit can be replaced by the unit described by Stock.8 PROCEDURE- substance being titrated. a change in the direction of the diffusion current - titre curve. was best found by plotting current readings against those of the burette. The polarising voltage was set to correspond to the limiting diffusion current of the The titrating solution was then run in, with stirring, until there was The location of the end-point It is advisable648 HARRIS AND LINDSEY: VIBRATIKG ELECTRODES IN [Vol.76 always to plot a current - voltage curve as a preliminary to any new type of determination in order to determine the characteristics of the electrode process under the conditions of the experiment. Although the diffusion current changes with temperature and thermostatic control is necessary for quantitative polarography, there is seldom any need to control or n il Fig. 1. Circuit for polarising vibrating electrodes A 2-volt accumulator. and two potentiometers provide a variable voltage that is measured by the voltmeter, V, and applied to the cell, which consists of a calomel half-element, a salt bridge and the vibrating electrode.A galvanometer, G, in series with the cell measures the current measure the temperature in amperometric titrations. unnecessary in the titrations described in this paper. Oxygen removal was shown to be DETERMINATION OF IODINE IN ACID SOLUTION A study of the current - voltage curve of 0.0001 N iodine in N hydrochloric acid con- taining 0.004 N potassium iodide as supporting electrolyte showed that a limiting diffusion current due to reduction of iodine is attained at from +0-05 to +040 volt with respect to the saturated calomel electrode, The vibrating electrode was therefore held at this potential and various amounts of iodine were added to fiOml of supporting electrolyte.In Fig. 2 is shown the diffusion current plotted against the concentration of iodine after allowing for volume changes. The range over which diffusion current was directly proportional to iodine concentration was from 2.5 x N, but if this part of the curve is extrapolated to zero current it does not pass through zero volume. The error is small, however, (equivalent to 0.3 per cent. of the full titre) and may be neglected for many analytical purposes. If more accurate results are required the figure may be used as a calibration curve. At the chosen potential the products of a sodium thiosulphate - iodine titration gave no diffusion current when added to the electrolyte even at a concentration corresponding to 0.01 N.As this titration is carried out at zero potential the electrical circuit can be modified considerably and the galvanometer only is needed in addition to the electrolytic cell. Fig. 3, which is representative of manj. experiments, shows the relationship between current and burette readings obtained when 100 ml of 0.001 Ai iodine, N with respect to hvdrochloric acid and 0.004N with respect to potassium iodide, were titrated with 0.01 N sodium thiosulphate solution from a micro-burette. l h e micro-electrode was held at the potential of the saturated-calomel reference electrode and current readings were taken over the whole titration, although they are only necessary during the last part. The end-point was taken as the extrapolation of the line to zero current, and corresponds to 10.22 ml of thiosulphate solution.Check titrations on the iodine and thiosulphate with starch as indicator gave an end-point of 10.24 ml, after correcting for an indicator blank. DETERMISATIONS IN NEUTRAL SOLUTIONS When 0.1 N potassium chloride and 0.004 N potassium iodide was used as supporting electrolyte, the current - voltage curve with iodine at a concentration of 0-0001 N was similar to that obtained in acid solution, so that a titration with 0.01 N iodine of 100 ml of approxi- mately 0.001 N sodium thiosulphate in this supporting electrolyte can be carried out under the same electrical conditions. In these circumstances no current is observed until the end- point is reached, after which the diffusion current is proportional to the iodine concentration over the same range as previously found.To obtain a rcproducible end-point it is recom- mended that a number of current readings be taken and the plotted values be extrapolated to 7.5 xNov., 19511 AMPEROMETRIC TITRATIONS. PART I 649 back to zero current. In a series of determinations with 10ml of iodine solution the end-points differed by 0.01 ml from those in which starch indicator was used. DETERMINATIONS IN SUPPORTING ELECTROLYTE CONTAINING SODIUM BICARBONATE- By the same procedure, 100 ml of approximately 0.001 N sodium thiosulphate, 0.1 N with respect to potassium chloride and sodium bicarbonate and 0.004 N with respect to potassium iodide, were titrated. A diffusion current was obtained for the end-point and its . . Iodine.ml Iodine. ml Fig. 2. Diffusion current - concentration curve Fig. 3. Diffusion currents measured when 100 ml of 0.001 N iodine in supporting electrolyte is titrated with 0.01 N sodium thiosulphate for iodine in a supporting electrolyte of N hydro- chloric acid and 0.004 N potassium iodide magnitude was proportional to the amount of iodine added for the range 2.5 x lW5 to 7.5 x In a series of determinations with 10 ml of iodine the end-points differed by 0.02 ml from those in which starch indicator was used. N . DETERMINATION OF TERVALENT ARSESIC BY IODIYE- By the same procedure, 100 ml of 0.001 N sodium arsenite, 0.1 N with respect to both potassium chloride and sodium bicarbonate and 0.004 N with respect to potassium iodide, were titrated with similar results.In a series of determinations the end-points differed by 0-03 ml from those in which starch indicator was used. These experiments show that the vibrating micro-electrode is satisfactory as an indicator electrode in amperometric titrations with iodine as the electro-active material and that results are within 0.3 per cent. of the values obtained when starch is used as an indicator. The authors wish to state that the experimental work was approved as part of a thesis for the degree of Master of Science in the University of London.9 They also wish to record their thanks to Imperial Chemical Industries Ltd., for a grant used for the purchase of chemicals. REFERENCES 1 . Harris, E. D., and Lindsey, A. J., Natzcve, 1948, 162, 413. 2. Lindsey, A. J., J . Phys. Coll. Cheni.. in the press. 3. Morris, C. J . 0. I<., Analyst, 1947, 72, 298. 4. Randle, J. E. B., Ibid., 1947, 72. 301. 5. Airey, L., Ibid., 1947, 72, 304. 6. Miller, S. D., Trans. All-Union Conf. Anal. Chem., 1943, 2, 551. 7. Roberts, E. R.. and Meek, J. S., Analyst, in the press. 8. Stock, J. T.. Ibid., 1946, 71, 585. 9. Harris, E. D., M.Sc. Thesis, University of London, 1949. SIR JOHN CASS COLLEGE LONDON, E.C.3

ISSN:0003-2654    

DOI:10.1039/AN9517600647

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

650 HARRIS AND LINDSEY: VIBRATING ELECTRODES I N [Vol. 76 Vibrating Electrodes in Amperometric Titrations Part I1 Bromometric Determinations of Antimony and Arsenic BY E. D. HARRIS AND A. J. LINDSEY (Presented at the meeting of the Physical Methods Group on Tuesday, April loth, 1951) The reduction of bromine at a vibrating platinum micro-electrode in N hydrochloric acid containing 0.05 A- potassium bromide commences at +0.75 volt with reference to the saturated calomel electrode, and a region of constant diffusion current is reached at +0*20 volt. Tervalent antimony and arsenic yield no diffusion current and may be determined by amperometric titration with potassium bromate and a vibrating electrode polarised to 0-2 volt. With 0.01 N potassium bromate and 0.001 N solutions of the metals an accuracy of +0-1 per cent.can be attained. TERVALENT arsenic and antimony compounds are readily oxidised by potassium bromate in acid solutions, and when the reaction is complete, additional bromate is converted into bromine by the reaction- BrO,' + 5Br' + 6H' = 3H,O + 3Br, This has been made the basis of a method of determination by using an indicator such as methyl orange to show the liberation of bromine,' but since the appearance of the yellow colour of the end-point is a slow reaction and is not reversible the titration is tedious and it is easy to overshoot the end-point. A recent paper2 refers to quinoline yellow as a reversible indicator in such titrations. The liberation of bromine is, however, readily and immediately detected by a vibrating electrode polarised to +0.2 volt with reference to a saturated calomel electrode. ESTABLISHMENT OF SUITABLE CONDITIONS FOR THE DETERMINATIONS Solutions of tervalent antimony and arsenic (0.001 N ) were titrated with a 0.01 N solution of potassium bromate in a supporting electrolyte of N hydrochloric acid containing 0.05 N potassium bromide.Current - voltage curves for the supporting electrolyte without and with bromate are shown in Fig. 1 as curves A and B, respectively. It will be noted that the bromine wave begins at +0.75 volt with reference to the saturated calomel electrode and that the currents reach a constant value in the region of +0.2 volt. It was therefore decided to polarise the electrode to this voltage in determinations of the metals. To confirm this choice, 60ml of supporting electrolyte were titrated with 0.01 N potassium bromate and the observed current was plotted against the volume added after correcting for volume changes.Fig. 2 shows that there is a direct relationship between the quantity of bromine and the current over the range 2.5 x to 9.2 x N bromine. This agrees with the results of Kolthoff and Laitinen3 for rotating eIectrodes and it was accordingly decided that the end-point of a titration can be found by extrapolating the current - volume curve to zero current. DETERMINATION OF TERVALENT ANTIMONY- A solution of 1O-ml volume containing exactly 0.001 N potassium antimony1 tartrate, N hydrochloric acid and 0.05 N potassium bromide was measured into an open beaker con- taining the vibrating electrode and an agar- potassium chloride bridge connected to a saturated calomel half-cell. The electrode was polarised to +0.2 volt and an exactly 0.01 N solution of potassium bromate was run in from a micro-burette.Current and volume readingsNov., 19511 AMPEROMETRIC TITRATIONS. PART I1 651 were taken and plotted and the result is shown in Fig. 3, from which the end-point was read as 10.0 0.01 ml. This result is typical of a large number of determinations. DETERMINATION OF TERVALENT ARSENIC- curve gave a result of 10.0 & 0.01 ml. The same technique was followed for arsenic as for antimony; a typical current - volume Voltage Fig. 1. Current - voltage curves Curve A, supporting electrolyte alone ( N hydrochloric acid and 0.05 N potassium bromide) ; curve B, supporting electrolyte with added potassium bromate (0.6 x 10dN) Potassium bromate, ml Potassium bromate.ml Fig. 2. Diffusion current - bromine conceatra- Fig. 3. Diffusion currents measured when 100 ml of supporting electrolyte, exactly 0.001 N with respect to antimony, is titrated with 0.01 N potassium bromate tion graph Titrations were also carried out in which the concentrations of tervalent antimony and arsenic were 0.002 N and in which a 50-ml burette graduated to 0.1 ml was used. Direct proportionality was again found between diffusion current and volume. The precision is not so great, as end-points may differ by 0.1 ml, which corresponds to an accuracy of &0.5 per cent.662 CORBETT: THE ESTIMATION O F OXYGEN [Vol. 76 The authors wish to state that the experimental work was approved as part of a thesis for the degree of Master of Science of the University of L ~ n d o n . ~ They also wish t o record their thanks to Imperial Chemical Industries Ltd., for a grant used for the purchase of chemicals. REFERENCES 1. 2. 3. 4. Willard, H. H., and Diehl, H., “Advanced Quantitative Analysis,” D. van Nostrand Company Belcher, R., Anal. Chim. Acta, 1951, 5, 30. Kolthoff, I. M., and Laitinen, H. A., J . Phys. Chew., 1941, 45, 1079. Harris, E. D., M.Sc. Thesis, University of London, 1949. Inc., 1943, p. 345. S I R JOHN CASS COLLEGE LONDON, E.C.3

ISSN:0003-2654    

DOI:10.1039/AN9517600650

出版商:RSC    

年代:1951

数据来源: RSC