ISSN:0003-2654    

DOI:10.1039/AN95782FX042

出版商:RSC    

年代:1957

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95782BX044

出版商:RSC    

年代:1957

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95782FP127

出版商:RSC    

年代:1957

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95782BP135

出版商:RSC    

年代:1957

数据来源: RSC

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OCTOBER, I957 voi. 82, NO. 979 PROCEEDINGS OF THE SOCIETY FOR ANALYTICAL CHEMISTRY ORDINARY MEETING AN Ordinary Meeting of the Society was held at 6.30 p.m. on Wednesday, October 2nd, 1957, in the meeting room of the Royal Society, Burlington House, London, W.l. The Chair was taken by the President, Dr. J. H. Hamence, M.Sc., F.R.I.C. The following papers were presented and discussed: “The Analysis of ‘Ferrites’ by Means of EDTA,” by D. G. Timms, B.Sc., A.R.I.C. ; “The Determination of Mercury by Direct Distillation in its Compounds and Preparations,” by H. E. Brooltes, B.Sc., F.R.I.C., and L. E. Solomon, BSc.; “A System for the Determination of Certain Trace Metals in Crops,” by W. D. Duffield; “Some Applications of X-ray Spectrography,” by H. I. Shalgosky, B.Sc., A.R.I.C. DEATHS WE record with regret the deaths of Archibald Prideaux Davson James Gray Adrian Joseph Clifford Lickorish, MIDLANDS SECTION AN Ordinary Meeting of the Section was held at 6.30 pm. on Thursday, September 12th, 1957, in the Mason Theatre, The University, Edmund Street, Birmingham, 3. The Chair was taken by the Vice-chairman of the Section, Dr. S. H. Jenkins, F.R.I.C., F.1nst.S.P. A discussion on “The Determination of Some Inorganic Substances in Trade Effluents,” was opened by N. T. Wilkinson, F.R.I.C. 657

ISSN:0003-2654    

DOI:10.1039/AN957820657b

出版商:RSC    

年代:1957

数据来源: RSC

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[Vol. 82 658 CHALLIS AND JONES : THE VOLUMETRIC DETERMINATION OF The Volumetric Determination of Tin in Titanium and its Alloys BY H. J. G. CHALLIS AND J. T. JONES Procedures have been established for the determination of tin in titanium and its alloys. For alloying amounts, the method involves the direct reduc- tion of tin with hypophosphite and volumetric determination with potassium iodate. Tests with solutions containing known amounts of titanium, tin and other metals indicate that recovery is satisfactory for amounts of tin above 0.2 per cent. and that no interference is caused by likely alloying metals. The recommended procedure is simple, rapid and particularly suitable for control analysis. KO difficulty has been experienced in applying the method to a wide range of titanium - tin alloys.For impurity amounts of tin below 0.2 per cent., a modification is necessary and it involves the preliminary separation of tin as sulphide in the presence of a carrier and then by reduction with hypophosphite and volumetric determination of the separated tin. Experiments have proved that recovery of tin is satisfactory for amounts as small as 0.002 per cent. TITANIUM alloys containing tin and aluminium are of increasing importance when higher creep resistance is required, and consideration has therefore been given to the determination of tin in the presence of large amounts of titanium. When this investigation was commenced, no published methods were available and a review of possible methods indicated that the hypophosphite reduction procedure1 92 offered the most promising approach.Subsequently, however, Norwitz and Codel13 recommended a method for alloying amounts of tin in titanium alloys based on the preliminary separation of tin as sulphide, but they found that copper and molybdenum (above 0.5 per cent.) inter- fered with.the determination. A later method? in which tin is reduced directly by iron powder, is stated to be ineffective in the presence of copper, and chromium and vanadium at con- centrations above 5 per cent. definitely interferee5 The experimental work described in this paper has led to the development of a rapid and direct method for tin in titanium - tin alloys, and reference is made to a modification suitable for the determination of tin present as an impurity in titanium metal.EXPERIMENTAL EFFECT OF TITANIUM- During preliminary tests on the reduction of tin in the presence of titanium and diluted hydrochloric acid (1 + l), the addition of sodium hypophosphite resulted in the formation of a dense flocculent precipitate. However, it was found that, when the solution was boiled, the precipitate dissolved to leave a clear pale-blue solution in which, after cooling, the reduced tin could be titrated with potassium iodate and the starch - iodine end-point easily observed. Further tests on solutions containing the equivalent of 0.2 or 0.5 g of titanium with various amounts of tin added, indicated that the recovery of tin by the proposed method was satis- factory over the range of 0.1 to 25 per cent., as shown by the results in Table I.EFFECT OF OTHER METALS- From previous work on copper-base alloys,2 it was known that aluminium, iron, lead, manganese and nickel do not interfere with the volumetric determination of tin, and inter- ference by precipitated arsenic, selenium and tellurium can be avoided by filtration. As titanium - tin alloys usually contain aluminium, confirmation was obtained of the non-inter- ference of up to 10 per cent. of aluminium. In addition, possible interference by other metals likely to be present in titanium alloys, namely chromium, molybdenum or vanadium, was determined for a series of solutions containing the metal under investigation with 1 to 10 per cent. of tin and the appropriate amount of titanium to bring the total sample weight to 0.2 g. In addition, the effect of copper and tungsten, which may be present as impurities, was studied and the results of these tests are given in Table 11.Oct., 19571 Metal TIN IN TITANIUM AND ITS ALLOYS TABLE I RECOVERY OF TIN ADDED TO SOLUTIONS CONTAINING TITANIUM Tin added g Nil 0~0010 0*0020 0.0030 0~0050 0*0100 0*0200 0*0500 In presence of 0.2 g of titanium- % - Nil 0.50 1.00 1.50 2.50 5.00 10.00 25.00 I n presence of 0.5 g of titanium- Xi1 0.0005 0~0010 0.0015 0.0025 0.0050 0~0100 0.0250 Nil 0.10 0.20 0.30 0.50 1.00 2.00 5.00 - Aluminium .. . . Chromium . . .. Vanadium . Molybdenum . . .. Copper Tungsten . . .. Tin recovered, % Xi1 0.49 1.00 1.42 2.45 4.90 9.98 25.00 Nil 0.12 0.20 0.26 0.49 1.03 2.00 4.97 TABLE I1 EFFECT OF METALS ON THE RECOVERY Amount of metal present Titanium present OF TIN Tin present g % Nil Nil 0.02 10.0 0.02 10.0 0.02 10.0 0.06 30.0 0.02 10.0 0.02 10.0 0.02 10.0 0.06 30.0 0.02 10.0 0.02 10.0 0.02 10.0 0.06 30.0 0.001 0.5 0.001 0.5 0.002 1.0 0.010 5.0 0,004 2.0 0.004 2.0 0,004 2.0 0.008 4.0 0.008 4.0 0.008 4.0 0.008 4.0 g Yo 0.180 90.0 0,178 89.0 0,178 89.0 0.160 80.0 0,120 60.0 0.178 89.0 0.170 85.0 0,160 80.0 0.120 60.0 0,178 89.0 0.170 85.0 0.160 80.0 0.120 60.0 0,197 98.5 0.179 89.5 0,178 89.0 0,170 85.0 0.196 98.0 0.194 97.0 0.186 93.0 0.192 96.0 0.190 95.0 0.182 91.0 0,172 86.0 g % 0.0200 10.00 0.0020 1.00 0*0020 1.00 0.0200 10.00 0.0200 10.00 0.0020 1.00 0~0100 5-00 0.0200 10.00 0*0200 10.00 0.0020 1.00 0~0100 5.00 0.0200 10.00 0.0200 10.00 0*0020 1.00 0.0200 10.00 0*0200 10.00 0.0200 10.00 Xi1 Nil 0*0020 1.00 0~0100 5.00 Nil Nil 0.0020 1.00 0~0100 5.00 0.0200 10.00 659 Tin recovered, % 9.98 1.01 1.01 9.96 9.94 1.01 5.04 9.98 9.97 1.01 4.99 9.99 9.97 1.02 10.05 10.27 10.33 Kil 1.00 5.01 Nil 1.01 4.99 9.97 The results indicated that up to 30 per cent.of chromium, molybdenum and vanadium had no effect on the determination of tin in the range of 1 to 10 per cent. A slight yellowish pink colour was noted in the presence of molybdenum, but the end-point could be easily detected. Addition of copper resulted in some fading of the end-point with consequent over-titration to the extent that 5 per cent. of copper introduced a positive error of 0.3 per cent. on 10 per cent. of tin. However, in commercial practice, only impurity amounts of copper are encountered and, as indicated in Table 11, amounts as large as 0.5 per cent.had no appreciable effect. With tungsten, a deep-blue solution was produced on reduction with sodium hypo- phosphite, but the end-point could still be discerned and the recovery of tin was satisfactory.660 REAGENTS- potassium iodide in water. dilute to 1 litre. CHALLIS AND JONES : THE VOLUMETRIC DETERMINATION OF METHOD [Vol. 82 Potassium iodate solution, 0.02 N-Dissolve 0.7134 g of potassium iodate and 10 g of Add 25 ml of sodium hydroxide solution (about 0.05 N ) and 1 ml = 1.187 mg of tin (theoretical value). Standardise the solution against a known amount (about 0.04g) of high-purity tin in the presence of 0.160 g of pure tin-free titanium by the recommended procedure. Mercuric chloride solution, saturated-Dissolve 6 g of mercuric chloride in 100 ml of boiling water, allow to cool and decant from the crystals formed.Starch solution, 1 per cent.-Make a paste of 1 g of soluble starch with cold water, pour it into 80 ml of boiling water, boil the solution for a few minutes, cool and dilute to 100 ml. This solution should be freshly prepared. PROCEDURE- For tin contents exceeding 0.5 per cent., weigh 0.2 g of sample and, for 0.2 to 0.5 per cent., weigh 0.5 g of sample; transfer it to a 100-ml beaker. Add 30 ml of dilute sulphuric acid (1 + 4) and warm gently to assist solution (see Note). Maintain the level of solution by the addition of water. When the reaction ceases, cool and oxidise with a slight excess of nitric acid, sp.gr. 1.42, added dropwise, and heat again until tin is dissolved.Evaporate to fumes of sulphur trioxide, cool, and transfer to a 500-ml conical flask, using about 50 ml of water. Add 50 ml of hydrochloric acid, sp. gr. 1.18, 1 ml of saturated mercuric chloride solution and 5 g of sodium hypophosphite. Insert a rubber bung provided with a delivery tube leading into 40 per cent. w/v sodium bicarbonate solution and boil the sample solution gently for 15 minutes. Cool to room temperature with the outlet of the delivery tube maintained below the surface of the bicarbonate solution. Add 2 g of potassium iodide, replace the rubber bung and delivery tube with an ordinary rubber bung or glass stopper, shake until the iodide has dissolved, add about 5 ml of starch solution and titrate with standard 0.02 N potassium iodate solution to the characteristic starch - iodine blue end-point.Calculate the tin content of the sample. XOTE- Alternatively, the sample may be dissolved in 50 ml of hydrochloric acid, sp.gr. 1.18, in a 500-ml conical flask. This method of solution has the advantage that evaporation t o fumes of sulphur trioxide is avoided, but care is necessary to avoid loss of hydrochloric acid, and the drillings must be finely divided. APPLICATION OF PROPOSED VOLUMETRIC METHOD The proposed procedure was applied to the determination of tin in a number of experi- mental titanium - tin alloys nominally containing from 5 to 27.5 per cent. of tin. The results, shown in Table 111, indicate that the method provides reasonably reproducible figures. TABLE I11 APPLICATION OF THE METHOD TO TITANIUM - TIN ALLOYS Nominal tin Tin content Alloy mark content, by volumetric method, % % A 5.00 4.56, 4.55 B 7.50 7.52, 7.49 C 10.00 9.54, 9.34 D 12.50 12.60, 12.30 E 17.50 17.12, 17.38 F 21.80 21.75, 21.81, 21-87 G 22.50 22.48, 22.75 H 25.00 24.83, 24.79 I 27-00 26.77, 26.94 J 27.50 27.45, 2745, 2745Oct., 19571 TIN I N TITANIUM AND ITS ALLOYS 661 DETERMINATION OF SMALL AMOUNTS OF TIN IN TITANIUM- Experience indicated that, with a sample weight of 0.2 g, the proposed direct method was only suitable for amounts of tin in excess of about 0.5 per cent.By increasing the sample weight to 0.5 g, amounts as small as 0.1 per cent. could be determined, but the end-point became increasingly difficult to detect. For amounts of tin smaller than about 0.2 per cent., a modification involving the separa- tion, or concentration, of tin was considered advisable.A tentative method was drawn up in which a larger weight of sample (up to 10 g) was used, with a single precipitation of tin as sulphide in the presence of added cadmium to act as a carrier. Preliminary tests were made to ascertain if the separated tin could be titrated with 0.005 N iodate, particularly in the presence of any small amounts of titanium that might remain owing to incomplete separation. Various amounts of tin in increments from 0.1 to 10 mg were titrated with 0.005 N iodate both in the absence of titanium and in the presence of 10 to 50 mg of titanium. The end- points were satisfactory and the results, which are shown in Table IV, indicate that recovery of tin was sufficiently accurate, provided at least 10mg of titanium were also present.Accordingly, in the proposed method, the addition of 10 mg of titanium is recommended just before the reduction with hypophosphite. TABLE IV EFFECT OF TITANIUM ON DETERMINATION OF SMALL AMOUNTS OF TIN, 0.005N IODATE BEING USED Titanium present in solution, Tin taken, Tin determined, Difference, mg mg mg mg 0.10 0.12 + 0.02 0.20 0.11 - 0.09 0.50 0.47 - 0.03 1.00 0.34 - 0.66 10.00 7-95 - 2.05 10.00 7.49 - 2.51 0.10 0.12 + 0.02 0.20 0.22 + 0.02 0.50 0.50 Nil 1.00 1.02 + 0.02 10.00 9.98 - 0.02 10*00 9.94 - 0.06 10.00 10.04 + 0.04 1 Nil 10 20 50 As it had been proved that amounts of tin as low as 0.1 mg could be reduced by hypo- phosphite and then determined satisfactorily by titration with 0.005 N iodate, the full pro- cedure, including the sulphide separation, was applied to a series of solutions containing titanium and the equivalent of 0.002 to 0.05 per cent.of tin. Ammonium citrate was added TABLE V RECOVERY OF SMALL AMOUNTS OF TIN FROM SOLUTIONS CONTAINING TITANIUM AND COPPER Weight of titanium, g Tin added, yo Tin recovered, yo (a) I n absence of coppev- 1.0 0.05 2.0 0.05 2.0 0.02 5.0 0*0040 10.0 0.0040 10.0 0.0020 10.0 0-0020 1.0 0.10 2.0 0.050 5.0 0.020 5.0 0.010 10.0 0~0020 ( b ) I n pvesence of copper equivalent to 0.1 per cent.- 0.050 0.051 0.020 0.0039 0.0039 0.0018 0.0017 0.098 0.049 0,020 0.010 0-0020662 CHALLIS AND JONES : THE VOLUMETRIC DETERMINATION O F to prevent precipitation of titanium hydroxide during neutralisation of the excess of acid with ammonia solution and 10ml of diluted sulphuric acid (1 + 1) per 400ml were added before the precipitation of tin by hydrogen sulphide. The modification for small amounts of tin under 0-l'per cent., as detailed later, was found to be reasonably convenient and the results (see Table V (a)) were sufficiently accurate to a lower limit of 0.002 per cent.Any copper present would be co-precipitated as the sulphide and, if in sufficient concen- tration, would interfere subsequently with the end-point. Some tests were carried out in which copper, equivalent to 0.1 per cent., was added to a further series of solutions containing titanium together with the equivalent of 0.01 to 0.10 per cent. of tin. In these tests, tin was separated from the combined sulphide precipitate with ammonium sulphide and subsequently determined in the copper-free solutions.The results, shown in Table V ( b ) , indicate that this additional step effectively eliminated the interference by copper and its use is recommended when the presence of copper is known or suspected from the colour of the sulphide precipitate. MODIFIED PROCEDURE FOR TIN CONTENTS BELOW 0.2 PER CENT. REAGEXTS- sulphuric acid (1 + 4), cool and dilute with water to 50 ml. 660) to a 100-ml calibrated flask and dilute to the mark with water, 1 ml G 0.297 mg of tin (theoretical value). [Vol. 82 Titanium sulphate solution-Dissolve 0.5 g of pure tin-free titanium in 30 ml of dilute Potassium iodate solution, 0.005 N-Transfer 25 ml of 0.02 N potassium iodate (see p.Cadmium sulphate solution-A 10 per cent. solution of cadmium sulphate, 3CdS0,.8H20, in water. PROCEDURE- phuric acid (1 + 4), as follows- Dissolve the recommended weight of sample in the appropriate amount of dilute sul- Tin present, yo .. .. . . 0.05 to 0.2 0.02 to 0.05 0.005 to 0.02 < 0.005 Weight of sample, g . . * . ,. 1 2 5 10 Dilute sulphuric acid ( 1 + 4) required, ml 50 100 200 300 Warm gently to assist solution and maintain the level of the solution by the addition of water. Oxidise with a slight excess of nitric acid, sp.gr. 1.42, added dropwise, and then boil for 2 to 3 minutes to remove nitrous fumes and ensure dissolution of tin. Dilute to about 300 ml, add 2 ml of cadmium sulphate solution and 5 g of ammonium citrate (10 g for the 10-g sample).Neutralise with diluted ammonium hydroxide (1 + l), using methyl red as indicator, acidify with 10 ml of diluted sulphuric acid (1 + 1) and dilute to 400 ml. Warm to 80" C and pass hydrogen sulphide through the solution for 30 minutes. Set the solution aside a t room temperature for at least 4 hours, then collect the precipitate on a Whatman No. 42 filter-paper and wash it once with cold water containing a small amount of hydrogen sulphide (see Note). Dissolve the precipitate from the filter-paper with 50 ml of warm hydrochloric acid, sp.gr. 1.18, into a 500-ml conical flask, wash the filter-paper with 50 ml of water, add 1 ml of titanium sulphate solution, 1 ml of saturated mercuric chloride solution and 5 g of sodium hypophosphite. Reduce the tin as described in the method for tin in titanium alloys and finally titrate with 0.005 N potassium iodate.Calculate the tin content of the sample. XOTE- At this stage it will be apparent if a significant amount of copper is present. If it is known or suspected that the amount of copper is greater than about half the tin content, dissolve the tin sulphide through the paper with 10 ml of warm diluted ammonium sulphide (1 + 1) into a 500-ml conical flask. Wash the copper sulphide residue with 50 ml of water containing hydrogen sulphide. Add 50 ml of hydrochloric acid, sp.gr. 1.18, to the filtrate and then 1 ml of titanium sulphate solution, 1 ml of saturated mercuric chloride solution and 5 g of sodium hypophosphite, and continue as described above. CONCLUSIONS The direct volumetric method described on p.660 is satisfactory for the determination of more than 0.2 per cent. of tin in titanium metal and alloys. Other alloying elements likely to be present, such as aluminium, chromium, iron, manganese, molybdenum and vanadium, and also impurity amounts of copper and tungsten, cause no interference; consequently theOct., 19571 TIN IN TITANIUM AND ITS ALLOYS 663 method has definite advantages over other published in which copper, molyb- denum and vanadium interfere. After solution of the sample, the proposed procedure for alloying amounts of tin takes only about 30 minutes and, being simple and direct, it can be recommended particularly for routine control analysis. The method has now been in use in a routine laboratory for over 2 years and no difficulties have been encountered, even when used by inexperienced personnel. For amounts of tin less than 0.2 per cent., preliminary sulphide separations are recom- mended, followed by reduction and volumetric determination of tin. This modified pro- cedure obviously increases the operational time, but experiments have proved that it is satisfactory for tin contents as low as 0.002 per cent. REFERENCES 1. 2. 3. Evans, B. S., Analyst, 1931, 56, 17. Bayley, W. J., Chem. 6 Ind., 1950, 34. Norwitz, G., and Codell, M., Anal. Chim. Acta, 1954, 11, 33. 4. 5, Dupraw, W. A,, Anal. Chem., 1954,26, 1642. S . Tour & Co., “Final Technical Report on Research and Development of Methods of Chemical Analysis for Titanium Metal and Alloys,” R10780, May, 1954. IMPERIAL CHEMICAL INDUSTRIES LIMITED METALS DIVISION KYNOCH WORKS WITTON BIRMINGHAM, 6 Afiril 16th, 1957

ISSN:0003-2654    

DOI:10.1039/AN9578200658

出版商:RSC    

年代:1957

数据来源: RSC

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Oct., 19571 TIN IN TITANIUM AND ITS ALLOYS 663 The Use of Paper Chromatography for the Detection and Determination of Microgram Amounts of Inorganic Fluoride BY R. J. HALL A chromatographic method is described for the isolation, detection and Recoveries of 89 A staining method determination of microgram amounts of inorganic fluoride. per cent. were obtained for amounts of less than 20 pg. for as little as 1 pg of isolated fluoride (as calcium fluoride) is described. THE determination of fluorine as inorganic fluoride presents one of the most interesting problems to the analyst. Of the methods in current use, by far the commonest is that of distillation as fluorosilicic acid, introduced by Willard and Winter,l and subsequent titration of the fluoride with thorium nitrate in the presence of an indicator such as alizarin S (sodium alizarinsulphonate) to form a thorium lake.The procedure for organically bound fluorine is to ignite the substance to be analysed with metallic sodium or potassium in a Parr-type bomb at 500" to 600" C and then to continue with the distillation. This method is tedious and difficult and not easily applicable to small amounts. During some recent work in this labora- tory, it was necessary to show the presence of microgram amounts of fluoride in a mixture of other inorganic and organic substances and to be able to determine these small amounts with a reasonable degree of accuracy. Hence the technique described, which makes use of paper chromatography and the extreme insolubility of calcium fluoride, has been developed. REAGENTS- METHOD Calcium chloride solution, 3 per cent.w / v aqueous. Calcium chloride - thorium nitrate solution-A 3 per cent. w/v solution of dried analytical-reagent grade calcium chloride containing 0.12 per cent. w/v of thorium nitrate, Th (NO,) ,.4H,O. Developing solution-A mixture of 85 parts of analytical-reagent grade acetone, 3 parts of glacial acetic acid and 12 parts of distilled water by volume. Ammonium hydroxide, 0.1 M.664 HALL: THE USE OF PAPER CHROMATOGRAPHY FOR THE DETECTION AND [VOl. 82 Boric acid solution, 0.1 N. Monochloroacetic acid bufer solution-Prepared by dissolving 22.7 g of monochloroacetic acid in 800 ml of distilled water, then slowly adding 120 ml of A' sodium hydroxide and adjusting the volume to 1 litre with distilled water. Solochrome brilliant blue BS staining solution-Prepared by dissolving 0.1 g of Solochrome brilliant blue BS in 85 ml of distilled water and adding 15 ml of monochloroacetic acid buffer solution.Silver perchlorate solution, 10 per cent. wlv. Sodium hydroxide, 0.04 N. Perchloric acid, 0.04 N. Alizarin S solution, 0.01 per cent. aqueous. Bufeeved alizarin S solzdion-Prepared by adding 10 ml of monochloroacetic acid buffer solution to 20 ml of 0.01 per cent. alizarin S solution and adjusting the volume to 100 ml with distilled water. Thorium nitrate solution, 0.002 N. Hydrochloric acid, 0.1 N. Bromophenol blue indicator solution, 0.04 per cent, aqueous. Standard lithium juoride solution-A solution containing 10 pg of fluorine per ml, pre- pared by dissolving 2.7305 mg of spectrographically pure lithium fluoride (obtained from Johnson, Matthey & Co.Ltd.) in 200 ml of distilled water. Standard juoride solution for application to chromatogram-A solution of 44.21 mg of sodium fluoride or 27.305 mg of lithium fluoride in 20 ml of water. 0.01 ml of either solution 3 10 pg of fluoride. The monochloroacetic acid buffer solution, standard lithium fluoride solution and the buffered alizarin S solution are best stored in polythene bottles. PROCEDURE FOR DETECTING FLUORIDE- Sheets of Whatman No. 531 filter-paper, 23 cm x 15 cm, are cut and marked for descend- ing-solvent chromatography. It is convenient to have the starting line some 9 to 10 cm from the end. With a Pasteur pipette, calcium chloride - thorium nitrate solution is applied to the starting line so as to form a band some 14 to 2 inches wide.This is allowed to dry in the air. The filter-papers should not be heat dried, as this produces uneven impregnation of the paper with subsequent distortion of the chromatogram. Spots of 0.005 to 0.02 ml of a solution containing 1 to 20 pg of fluorine as inorganic fluoride are applied to the paper, which is then allowed to dry. The chromatogram is developed in the descending-solvent manner for 1 to 2 hours at room temperature, after which it can be dried in the air and examined in ultra-violet light; this is useful for detecting certain components. Fluoride, calcium chloride and thorium nitrate are not themselves seen in ultra-violet light. The filter-paper is quickly rinsed in tap water and then immersed in 0.1 M ammonium hydroxide for 1 minute.It is then removed, again quickly rinsed in tap water, blotted dry and stained with Solochrome brilliant blue BS staining solution for 2 to 5 minutes. Fluoride is seen as bright violet-blue spots at the point of application. The excess of Solochrome brilliant blue BS staining solution is washed out with 0.1 N boric acid to leave a white background. Spots stained and washed in this way remain stable for a long while and as little as 1 pg of fluoride can easily be detected. PROCEDURE FOR REMOVING PHOSPHATE AND OXALATE- Several interfering radicals, including phosphates and oxalates, can be removed by pre- cipitation with silver perchlorate, a reagent employed by Armstrong2 to immobilise chloride during the distillation of fluorosilicic acid.The technique adopted for up to 3 mg of fluoride in the presence of about 30 mg of interfering substances is to add 0.5 ml of 10 per cent. w/v silver perchlorate solution to 2ml of the sample in a 5-ml calibrated flask. The mixture is made to the mark with acetone, shaken well and then centrifuged. To 4 ml of the clear supernatant solution, transferred to another 5-ml calibrated flask, is added 0.1 ml of saturated potassium chloride solution; the mixture is diluted to the mark with water, vigorously shaken and again centrifuged. Suitable volumes of the clear supernatant solution can now be used for chromatographic separation.Oct., 19571 DETERMINATION OF MICROGRAM AMOUNTS OF INORGANIC FLUORIDE 665 PROCEDURE FOR DETERMINING FLUORIDE- Whatman No.531 filter-papers are impregnated with 3 per cent. w/v calcium chloride solution and 0.005 to 0.02 ml spots are put on the papers; the chromatograms are developed and dried as before. An area of the paper is now cut out a t the point of application of the sample. For 0.005 to 0.02-ml spots a 1-inch x 1-inch area is suitable. The paper is placed in a 6-inch x $-inch test-tube with 2 ml of 0.1 N hydrochloric acid and brought just to the boil. After cooling, the paper is removed and washed with about 5 ml of water. Sufficient 0.04 N sodium hydroxide is added to bring the pH to 2.9 to 3.0, after which the fluoride is titrated with thorium nitrate. Preliminary titratio% to $H 2.9 to 3.0-A blank area of paper adjacent to one on which the fluoride is to be determined, but containing no fluoride, is cut out and extracted with 0.1 N hydrochloric acid as before.Two drops of bromophenol blue indicator solution are added and the contents are titrated with 0.04 N sodium hydroxide until the colour of the indicator, after the solution has been adjusted to 20 ml with water, matches a blank of 20 ml of water, 0.2 ml of 0.04 N perchloric acid and two drops of the bromophenol blue indicator solution. The tube containing a sample is treated in exactly the same way and should require the same volume of sodium hydroxide. This titration for the adjustment of the pH (a Doran pH meter was used to check the pH) is most important, since even small variations outside the narrow pH range affect the thorium titration.It is necessary to carry out this titration with care and to see that the colours of the blank and test solutions match exactly. A second blank area of paper, two or three test areas and two or three areas to which have been applied solutions of fluoride of known concentrations from 2 to 20 pg are now extracted and volumes of 0.04 N sodium hydroxide and perchloric acid equal to the preliminary titrations are added, but without bromophenol blue indicator solution. Thorium titration-By means of a pipette,. 5-ml portions of buffered alizarin S solution are placed in each tube. To the blank tube is added 0.15 to 0.20 ml of thorium nitrate solution from a 5-m1 microburette graduated in 0.01 ml. The tube is stoppered and mixed by gentle inversion. The solution should now assume a pale-buff colour with a distinct pink hue.The unknown solutions are titrated slowly (not more than 0.05 ml of thorium nitrate being added at a time) until the colours match that of the blank; over-titration makes the solution pinker. The titration requires practice a t first, but reproducible results should soon be achieved. The colours are best matched by holding the tubes a t an angle of 60" and looking down the depth of the solution against the bright-white matt background of Whatman No. 1 filter-paper, preferably in bright daylight or fluorescent daylight lighting, but not in direct sunlight. I t is convenient to use a stencil of Perspex having spaces of different areas. RESULTS Since thorium titrations for fluoride are not strictly stoicheiometric, it is necessary to prepare a calibration curve by applying the method to spots of standard lithium or sodium fluoride solutions.A typical calibration graph is shown in Fig. 1. Typical recoveries of fluoride are shown in Table I. TABLE I RECOVERY OF FLUORIDE FROM WHATMAN NO. 531 FILTER-PAPER Fluoride applied, Fluoride recovered, Recovery, 2 1.56 78 rg Pg % 5 4*16}4.43 4.71 10 14 12.9 92.2 12:9 92.2 2 0 18.35 91.7 18.35 91.7666 HALL: THE USE OF PAPER CHROMATOGRAPHY FOR THE DETECTION AND [Vol. 82 DEVELOPMENT OF THE METHOD Although the detection and determination of small amounts of fluoride have been of important interest for many years, surprisingly little attention appears to have been paid to the use of paper chromatography. Lederer and Ledere? detected fluoride as a white spot on a red background when the paper was sprayed with ferric salts, Mitchell4 reported fluoride to be a problem in the separation and identification of halides and Burstall, Davies, Linstead and Wells5 described the separation on paper of fluoride, chloride, bromide and iodide with acetone containing 20 per cent.of water. This technique did not satisfactorily separate fluoride from our mixtures and a method was required that would isolate the fluoride for its subsequent determination. When fluoride is applied to paper impregnated with calcium chloride, calcium fluoride is formed, which is one of the most insoluble of the calcium com- pounds and quite insoluble in dilute acetic acid. Only the oxalate and (+)-tartrate appear to have comparable solubilities and are also insoluble in dilute acetic acid.Hence in the des- cending-solvent development of the chromatogram, the calcium fluoride remains at the place of application and other substances are eluted away from it by the acidified aqueous acetone. Volume of 0'002 N thorium nitrate, ml Titration curve of fluoride spots from Whatman No. 531 filter- paper Fig. 1. The titration procedure was developed from the methods of Armstrong2 and Hoskins and Ferris,O use being made of an improvement suggested by Buffa.7 Solochrome brilliant blue BS, proposed by Milton, Liddell and Chiversa for the thorium titration, was found to be ideal for the qualitative application, but not preferable to alizarin S for the titration. Of all the radicals that interfere with the thorium titration and that form slightly soluble calcium salts, only phosphate and oxalate were found to affect the chromatographic separa- tion of fluoride as the calcium salt.This problem was overcome by using silver perchlorate in 50 per cent. acetone to remove phosphate in the presence of small amounts of fluoride. 'With as little as 60 pg of fluoride in a total of 6000 pg of phosphate, oxalate and citrate, 87 per cent. of the fluoride was recovered. When the fluoride content was 3mg as sodium fluoride in a mixture of 30 mg of other interfering acid radicals, all the fluoride was recovered and no interfering substance could be detected in the final solution to be analysed. The staining of the fluoride with Solochrome brilliant blue BS depends on the adsorption of thorium nitrate on the calcium fluoride.In a study of the staining of fluoride ions, this technique was found to be much more sensitive than any other method tried. Arsenate, tetraborate, citrate, silicate, tartrate and sulphate gave no reaction in amounts of 50 to 100 pg. In the absence of phosphate, even oxalate presented no difficulty, since it was found t o be removed by treatment with 0.0005 N potassium permanganate in 2 per cent. acetic acid at 80" C for 2 to 5 minutes. I acknowledge the constant interest that Sir Rudolph Peters, F.R.S., has shown in This in no way affected the staining of the fluoride. this work.OCt., 19571 DETERMINATION OF MICROGRAM AMOUNTS OF INORGANIC FLUORIDE 667 REFERENCES 1. 2. 3. Willard, J. H., and Winter, O.B., Ind. Eng. Chem., Anal. Ed., 1933, 5, 7. Armstrong, W. D., Ibid., 1936, 8, 348. Lederer, E., and Lederer, M., “Chromatography: A Review of Principles and Applications,” Elsevier Publishing Co. Ltd., Amsterdam and New York, and Cleaver-Hume Press Ltd., London, 19.52. 4. Iclitcheii, L. C., J . Ass. 08. Agric. Chewz., 1955, 38, 832. 5. Burstall, F. H., Davies, G. R., Linstead, R. P., and Wells, R.A., J . Chem. Soc., 1950, 516. 6. Hoskins, W. M., and Ferris, C.A., Ind. Eng. Chem., Anal. Ed., 1936, 8, 6 . 7. Buffa, P., “The Chemistry of Fluoroacetate,” Ph.D. Thesis, Oxford University, 1950. 8. Milton, R. F., Liddell, H. F., and Chivers, J. E., Analyst, 1947, 72, 43. BIOCHEMISTRY DEPARTMENT BABRAHAM, CAMBRIDGE AGRICULTURAL RESEARCH COUNCIL INSTITUTE O F ANIMAL PHYSIOLOGY April 23rd, 1957

ISSN:0003-2654    

DOI:10.1039/AN9578200663

出版商:RSC    

年代:1957

数据来源: RSC

摘要:

OCt., 19571 DETERMINATION OF MICROGRAM AMOUNTS OF INORGANIC FLUORIDE 667 The Determination of Dimefox Residues in Hops B Y K. FIELD AND E. Q. LAWS A method is described for the extraction of dimefox from hops, its separation by chromatography from interfering substances and its subsequent determination as phosphorus. THE compound tetramethylphosphorodiamidic fluoride (I) is known as dimefox. In com- mercial preparations it is also known as Hanane S-14, Terra-systam, BFPO, DIFO or Schrader’s compound 13/28. It belongs to the class of compounds known as systemic insecticides, but differs from the majority of those a t present in use by virtue of its compara- tively simple molecular structure and the fact that the molecule contains a fluorine atom bonded to phosphorus. (CH,),S 0 (1) The compound can be determined, after breakdown, as dimethylamine, inorganic fluoride or phosphoric acid.Although determination of dimethylamine would give the best quanti- tative results, it is not specific, as many plant substances decompose to give the amine. Determination of fluoride would be diagnostic of dimefox as contrasted with most other systemic insecticides, but it is not very sensitive; it has about one-tenth of the sensitivity of the phosphorus method. Determination of phosphorus is a standard procedure for this type of compound and is very sensitive but not diagnostic. The phosphorus method was selected as being the most convenient. A study of the chromatographic behaviour of dimefox shows that it is possible to separate the compound with relative ease from the other phosphorus compounds present.A simple determination of the phosphorus in the separated compound is then sufficient for its accurate quantitative evaluation. EXPERIMENTAL EXTRACTION OF DIMEFOX FROM HOPS- Hops, on account of their resinous and oily nature, are difficult to prepare for the extrac- tion of dimefox. A method described by Dupke, Heath and Otter1 involves an extraction with oil, followed by vacuum-distillation of the oil containing the dimefox. In looking for a suitable chromatographic method, it was clearly desirable that a simpler approach should be used. The method of Walker,2 originally designed for extraction of the hop resins, was found to be suitable. The method depends on the initial extraction of the dry hop material with methanol. One extraction is found to be sufficient, provided that on filtration of thevegetable residue the flask and residue are washed as indicated under “Method.” After addition of light668 FIELD AND LAWS: THE DETERMINATION OF [Vol.82 petroleum to the extract, followed by ice-cold water, a partition is effected between methanol - water on the one hand and light petroleum on the other. The advantage of this system is that dimefox is retained in the aqueous part while the hop resins go into the light petroleum layer. The aqueous layer is extracted with chloroform to remove the dimefox, together with Some of the plant substances. As the chromatography is best carried out in ether solution, the combined chloroform extracts are evaporated carefully to dryness and the solvent is replaced by ether.An extract thus obtained includes a high proportion of phosphorus- containing plant material, a relatively large amount of green colouring matter (chlorophylls), Some yellow plant pigments and carotene, contained in ether solution free from other organic solvents. THE CHROMATOGRAPHIC SEPARATION- Scliradans has been separated on alumina columns from other phosphorus compounds by using chloroform and trichloroethylene as solvents. The same system may be used for dimefox? but it is difficult to separate the compound from the vegetable extract. With a column of magnesia, the difficulties disappear and a satisfactory separation is rapidly obtained using ether as the eluent. When the solution for chromatographic separation, referred to above, is placed on a column of 5 g of magnesia that has been prepared as described under “Method,” chromato- graphic separation immediately takes place, the main portion of the colouring matter of the extract being retained a t the top of the column.With hop extracts, the chromatogram obtained has numerous coloured zones. When 100 ml of ether have been run through the column, all the dimefox and a small amount of the yellow pigment is to be found in the eluate, Washing through with a further 100ml of ether does not lead to any further recovery of dimefox, nor does the phosphorus content of the eluate increase. The yellow pigment (probably carotene) does not appear to have any phosphorus content, but in any event, it is removed in a subsequent procedure before the final determination of phosphorus.Although the method was designed for hops, it is also applicable to the chloroform extract obtained from the aqueous macerates of other vegetables, for example, brussels sprouts, cabbages and lettuces. THE DETERMIXATION OF DIMEFOX- The ether solution from the chromatographic separation contains the dimefox that was originally present in the hops. After the removal of the solvent the dimefox is dissolved in water and is subsequently treated as in the method of DupCe, Heath and 0tter.l The final determination of the phosphorus as molybdenum blue is based on the method of Berenblum and Chain,5 with a modification suggested by Martin and Doty.6 As the phosphorus concen- tration with which we are concerned is very low, the acidity and the salt concentration are factors of prime importance.The requirements are that the acidity of the final solution should lie between 0.5 and 1.5 N , and that neutral salts other than ammonium molybdate should not exceed 0.5 g in 10 ml of the test solution. METHOD The method consists in the extraction of dimefox from the plant material, its transfer to ether solution, chromatographic separation from interfering compounds and subsequent determination of the phosphorus by a spectrophotometric absorption measurement of the molybdenum-blue complex. APPARATCS- This is the solution for chromatographic separation. Unicam SP600 absorption spectrophotometer. Household slicing and grating machine. High-speed macerator. Glass tubes for chromatography, 15 cm long and 1.5 cm diameter.All the reagents used must be phosphate-free. Methanol, absolute. Light petroleum, boiling raflge 40” to 60” C. REAGENTS- periodically. Reagent blanks must be checked669 Oct., 19571 DIMEFOX RESIDUES IN HOPS Sodium chloride-Analytical-reagent grade. Ether-Use Anaesthetic Ether, B.P. Magnesium oxide-The grade “for chromatographic analysis.” Perchloric acid, N. Sulphuric acid, N. Ammonium molybdate reagent-Dissolve 50 g of. analytical-reagent grade ammonium molybdate in 400 ml of 10 N sulphuric acid and dilute to 1 litre with distilled water. isoButano1- benzene mixture-Nix equal volumes of isobutanol and benzene. Stannous chloride solution, concentrated-Dissolve 10 g of analytical-reagent grade stannous chloride dihydrate in 25 ml of concentrated hydrochloric acid.Stannous chloride solution, dilute-Dilute the concentrated solution 200-fold with N sulphuric acid. Prepare a fresh solution daily. ’ Ethanolic sulphuric acid-Mix 5 ml of concentrated sulphuric acid with 245 ml of absolute ethanol. Standard dimefox solutions-We prepared these from dimefox of 90 per cent. purity (provided by Fison’s Pest Control Ltd.). Prepare a standard solution by dissolving about 0.2 ml of the dimefox in approximately 1 litre of water and dilute the solution appropriately, so that it contains approximately 5 p g of dimefox per ml. Standardise the solution by comparison with standard phosphate solutions. PROCEDURE- Select a sample of dried hop material, and shred it into as fine a condition as possible. Macerate 10 g of the shredded material for 10 minutes with 100 ml of methanol, and set the solution aside overnight.Filter the solution through a Buchner funnel containing a Whatman No. 1 filter-paper, using slight suction. Wash the hops with a further 50ml of methanol, also collecting the washings in the Buchner flask. It may be necessary to effect a second filtration. Transfer the solution into a 500-ml separating funnel, rinsing the Buchner flask with a further small volume of methanol and then with several small volumes of light petroleum, SO that the total volume of light petroleum collected in the funnel is 100 ml. Shake the two layers together, add 200 ml of ice-cold water, and shake again. Add small amounts of sodium chloride to break up any emulsion. Transfer the lower aqueous methanol greenish yellow coloured layer into another 500-ml separating funnel and discard the upper dark green - brown coloured light petroleum layer.Extract the aqueous methanol layer five times with 50-ml portions of chloroform, collecting the lower chloroform layers after each separation. Collect the fractions in a conical flask. Combine the chloroform extracts and evaporate them to dryness: take care not to have the conical flask too hot. Immediately the chloroform has evaporated, run into the conical flask sufficient ether to form a solution. Evaporate the ether, taking similar precautions, and take up the residues in 50 ml of ether. The solution may appear cloudy. THE MAGNESIA COLUMN- Insert a cotton-wool plug into the bottom of a chromatographic tube and pour in 5 g of magnesia in a slurry with ether.Allow the magnesia to settle and then insert another cotton-wool plug on the surface of the column. Transfer the ether solution of the sample, with many rinses, on to the column. Collect the eluent in a 250-ml conical flask. Allow the green material to collect on the column before washing with ether. Wash the column with 100 ml of ether, first rinsing the original conical flask and then transferring the rinsings t o the column. As the column is washed, a wide yellow band moves down and, as the washing proceeds, the front of this band splits into two smaller bands, followed by a wide band spreading from the top of the column. A greenish coloured band persists at the surface of the magnesia. In some experiments the collected washings are colourless, in others quite yellow, depend- ing on the extent to which the small yellow bands move downwards.THE ELUATE- Stand the flask in a thermostatically controlled bath maintained at 25” aqueous solution 4ml of N perchloric acid. occasional shaking. three times with equal volumes of chloroform. Carefully distil off the ether, and immediately take up the residue in 10 ml of water. 2“ C, and add to the Set the solution aside for 20 minutes, with Transfer the solution to a 100-ml separating funnel and extract it Discard the lower chloroform layers afterA C m c) ~ B $ ._ ? 0 , 3 r 0.2 - .- 8 0 . 1 - 0.3 x ._ - .- 8 0 . 1 f 2Oct., 19571 DIMEFOX RESIDUES IN HOPS 67 1 residue contained more than 0.13 p.p.m. and most contained much less.This is the type of result usually obtained for dimefox residues when the plants are taken for analysis some weeks after treatment. The available evidence suggests that break-down of this compound is rapid in the living plant. DISCUSSION OF RESULTS The recoveries quoted are derived from experiments in which known amounts of dimefox were added to dry hops that had received no phosphorus insecticide during growth. While this procedure simulates the conditions obtaining in the case of plants grown in dimefox- treated soil, it is not identical with field conditions. There may be unknown factors influenc- ing the recovery from growing plants. Residue figures obtained by this method in treated crops are of the same order of magnitude as those obtained by the distillation method. The chromatographic separation has the advantage in simplicity and speed. In addition, the blanks obtained by the method are of the same order as the reagent blank. Recoveries are of the order of 85 to 95 per cent. of the amount added in the region 0.5 pg of dimefox on 10 g of dried hops. We thank Dr. G. M. Bennett, C.B., F.R.S., the Government Chemist, for permission to publish this paper. REFEREKCES 1. 2. 3. 4. 5. 6. 7. 8. DupBe, F., Heath, D. F., and Otter, I. K. H., J . Agvic. Food Chew&., 1956, 4, 233. Walker, T. K., J . Iizst. Brewing., 1923, 379. Heath, D. F., Lane, D. W. J., and Parks, P. O., Phil. Trans. B., 1955,239, 191. Chilwell, R. D., Fison’s Pest Control Ltd., personal communication. Berenblum, J., and Chain, E., Biochem. ,I., 1938, 32, 295. Martin, J . B., and Doty, D. M., Anal. Chcm., 1949,21, 965. Boltz, D. F., and Mellon, M. G., I b i d . , 1947, 19, 873. Leach, C. H., and Boltz, D. F., I b i d . , 1966, 28, 1168. DEPARTMENT OF THE GOVERNMENT CHEMIST STRAND, LONDON, TV.C.2 CLEMENT’S INS PASSAGE .May 20th, 1957

ISSN:0003-2654    

DOI:10.1039/AN9578200667

出版商:RSC    

年代:1957

数据来源: RSC

摘要:

Oct., 19571 DIMEFOX RESIDUES IN HOPS 67 1 Quantitative Determination of Traces of Carbon Dioxide in Wa,ter BY P. P. JENNINGS AND E. M. OSBORN An improved method for the determination of traces of carbon dioxide dissolved in water is described. 4 sample of acidified water is aspirated with air free from carbon dioxide and the carbon dioxide evolved is absorbed in sodium hydroxide solution. The alkaline solution is titrated with 0.01 N acid, the titre between pH 8.3 and pH 5.0, measured with a glass electrode system, being a measure of the carbon dioxide present. The concentrations of carbon dioxide determined were in the range 0.01 to 0.10 mg per litre. INVESTIGATIONS of the part played by carbon dioxide in the corrosion of boiler feed systems require the measurement of traces of carbon dioxide dissolved in the feed water.Previously published meth0dsl3~>~ were examined and found to be insufficiently sensitive, and a method has been developed whereby increased sensitivity has been achieved. Much attention has been given to the blank determinations in an endeavour to reduce the blank values to a minimum, and the size of the sample has been increased to increase the sensitivity. The method involves the manipulation of the sample out of contact with atmospheric carbon dioxide, the carbon dioxide in the sample being aspirated with air free from carbon dioxide and absorbed in sodium hydroxide solution. The alkaline solution is then titrated in a closed circuit to a pH of 8.3 and then in a stream of air free from carbon dioxide to a pH of 5.0, a glass electrode system being used for the pH measurements.Results with standard sodium carbonate solution over a range equivalent to 0-022 to 0.110 mg of carbon dioxide per litre gave results within 0.002 mg per litre of the concentra- tion taken, with a standard deviation of 0.0016 mg per litre. The time taken for one deter- mination is about 3 hours.672 JENNINGS AND OSBORN : QUANTITATIVE DETERMINATION OF [Vol. 82 EXPERIMENTAL In order to obtain maximum sensitivity the following sources of error have been con- sidered and reduced to a minimum. TRANSFER OF CARBON DIOXIDE FROM THE SAMPLE TO THE SODIUM HYDROXIDE SOLUTION- Errors can be caused by carbon dioxide contained in the sodium hydroxide solution, carbon dioxide leaking in or diffusing through the polythene joints, and incomplete transfer of carbon dioxide from the sample to the sodium hydroxide in the titration cell.The sodium hydroxide was originally prepared by electrolysing saturated brine with use of a mercury cathode and decomposing the amalgam with water free from carbon dioxide; this was later found to be unnecessary, sodium hydroxide “free from carbonate’’ being sufficiently pure for use. The purity of the sodium hydroxide solution can be easily tested in the apparatus to be described by the following method- Let the volume of acid used be B ml. The blank titration is then repeated with 2.0 ml of sodium hydroxide solution. Let the titre be C ml. Then C - B is a measure of the carbon dioxide present in 1 ml of sodium hydroxide solution.The second possible error is allowed for by the blank determination described in The third possible error can be eliminated by continuing the aspiration in stages, and, A blank titration is carried out as described under “Procedure.” detail later. as can be seen from Table I, p. 675, two aspirations were usually found to be sufficient. TITRATION OF THE RESULTING SODIUM CARBONATE- The carbon dioxide absorbed by the sodium hydroxide solution will be present mainly as carbonate at pH 11. Hence, 0.01 N sulphuric acid is added until the pH reaches 8.3, at which point the carbon dioxide will be present as bicarbonate; this part of the titration is carried out in a closed circuit to prevent loss of carbon dioxide from any local concen- tration of acid immediately on addition.The titration below pH 8.3 is carried out in a stream of air free from carbon dioxide, the sodium bicarbonate is decomposed, the carbon dioxide is removed to the atmosphere and the pH falls to 5.0, by which time the sodium bicarbonate is fully decomposed. INTERFERING SUBSTANCES- The preliminary concentration of the carbon dioxide by aspiration will eliminate inter- ference by most substances found in boiler feed water. Non-volatile compounds, such as boiler salts, and all basic substances, e.g., ammonia, hydrazine and amines, will be retained in the acidified sample. The only substance expected to interfere is sulphite by decomposition and aspiration of the sulphur dioxide. This effect might be reduced or eliminated by oxidation during aeration, but in view of the fact that no sulphite is present in the boiler feed water under examination this point has not, as yet, been investigated.METHOD It is essential that scrupulous attention should be given to all details of apparatus and procedure if reliable results are to be obtained. APPARATUS- The complete apparatus is shown in Figs. 1 and 2. The sample is collected and treated in a bottle, A, having a calibration mark at 10 litres. Through the rubber bung of the sample bottle are inserted (a) a glass tube, B, extending almost to the bottom of the sample bottle and having a polythene connecting tube at its upper end that can be closed by a screw clip, C ; ( b ) a glass tube, D, having two No. 2 porosity sintered-glass discs and a three-way stopcock, S,; (c) an outlet tube, E, having a three-way stopcock, S,; and ( d ) a tap funnel of 100 ml capacity, F.It is important that all flexible connections should be as short as possible, that polythene - glass connections should be as tight as possible and, where manipulation allows, sealed with poly(viny1 chloride) cement, and that every effort should be made to eliminate leakage from the system.672 JENNINGS AND OSBORN : QUANTITATIVE DETERMINATION OF [Vol. 82 EXPERIMENTAL In order to obtain maximum sensitivity the following sources of error have been con- sidered and reduced to a minimum. TRANSFER OF CARBON DIOXIDE FROM THE SAMPLE TO THE SODIUM HYDROXIDE SOLUTION- Errors can be caused by carbon dioxide contained in the sodium hydroxide solution, carbon dioxide leaking in or diffusing through the polythene joints, and incomplete transfer of carbon dioxide from the sample to the sodium hydroxide in the titration cell.The sodium hydroxide was originally prepared by electrolysing saturated brine with use of a mercury cathode and decomposing the amalgam with water free from carbon dioxide; this was later found to be unnecessary, sodium hydroxide “free from carbonate’’ being sufficiently pure for use. The purity of the sodium hydroxide solution can be easily tested in the apparatus to be described by the following method- Let the volume of acid used be B ml. The blank titration is then repeated with 2.0 ml of sodium hydroxide solution. Let the titre be C ml. Then C - B is a measure of the carbon dioxide present in 1 ml of sodium hydroxide solution.The second possible error is allowed for by the blank determination described in The third possible error can be eliminated by continuing the aspiration in stages, and, A blank titration is carried out as described under “Procedure.” detail later. as can be seen from Table I, p. 675, two aspirations were usually found to be sufficient. TITRATION OF THE RESULTING SODIUM CARBONATE- The carbon dioxide absorbed by the sodium hydroxide solution will be present mainly as carbonate at pH 11. Hence, 0.01 N sulphuric acid is added until the pH reaches 8.3, at which point the carbon dioxide will be present as bicarbonate; this part of the titration is carried out in a closed circuit to prevent loss of carbon dioxide from any local concen- tration of acid immediately on addition.The titration below pH 8.3 is carried out in a stream of air free from carbon dioxide, the sodium bicarbonate is decomposed, the carbon dioxide is removed to the atmosphere and the pH falls to 5.0, by which time the sodium bicarbonate is fully decomposed. INTERFERING SUBSTANCES- The preliminary concentration of the carbon dioxide by aspiration will eliminate inter- ference by most substances found in boiler feed water. Non-volatile compounds, such as boiler salts, and all basic substances, e.g., ammonia, hydrazine and amines, will be retained in the acidified sample. The only substance expected to interfere is sulphite by decomposition and aspiration of the sulphur dioxide. This effect might be reduced or eliminated by oxidation during aeration, but in view of the fact that no sulphite is present in the boiler feed water under examination this point has not, as yet, been investigated.METHOD It is essential that scrupulous attention should be given to all details of apparatus and procedure if reliable results are to be obtained. APPARATUS- The complete apparatus is shown in Figs. 1 and 2. The sample is collected and treated in a bottle, A, having a calibration mark at 10 litres. Through the rubber bung of the sample bottle are inserted (a) a glass tube, B, extending almost to the bottom of the sample bottle and having a polythene connecting tube at its upper end that can be closed by a screw clip, C ; ( b ) a glass tube, D, having two No. 2 porosity sintered-glass discs and a three-way stopcock, S,; (c) an outlet tube, E, having a three-way stopcock, S,; and ( d ) a tap funnel of 100 ml capacity, F.It is important that all flexible connections should be as short as possible, that polythene - glass connections should be as tight as possible and, where manipulation allows, sealed with poly(viny1 chloride) cement, and that every effort should be made to eliminate leakage from the system.Oct., 19571 TRACES OF CARBON DIOXIDE IN WATER 673 Details of the titration cell are shown in Fig. 3; this consists of a 250-ml squat spoutless beaker having (i) a No. 2 porosity sintered-glass disc for the gas inlet ; (ii) a glass electrode, a reference elcctrode and a temperature compensator; (iii) a gas outlet tube fitted with a three- way stopcor , s,; and (iv) two burettes, one containing sulphuric acid and one containing sodium hydroxide, the latter being fitted with a capillary projecting beneath the surface of the liquid in the ( I , as shown in Fig.3 (a). It is important that the burette stopcocks should not be gre d. A = Sample bottle B = Sample inlet C = Screw clip D = Air inlet E = Air outlet F = 100-ml funnel G = Pump HI and Hz I = Silica-gel container J = Titration cell S,, Sz and S, = Three-way stopcocks T = Two-way stopcock = Soda-lime containers Fig. 2. Sectional diagram of complete apparatus To pH meter yrhene leeve Rubber sleeves Water level I1 J Fig. 3(a) Fig. 3(b) Fig. 3(c) a = Calomel electrode b = Temperature compensator c = Glass electrode d = Burette containing alkali Fig. 3 ( a ) . Fig. 3 ( b ) . Titration cell Fig.3 ( c ) . Plan of rubber bung e = Burette containing acid f = Gas inlet g = Gas outlet Details of the burette containing the alkali The pump used was a Dymax diaphragm-type compressor, manufactured by Charles Two 90-cm heating tapes are wrapped round the lines from bottle to cell and from cell to The pH meter used was a Marconi mains- Austin Ltd. pump, operated type TF717A. REAGENTS- Control units are fitted to both tapes. Sodium hydroxide, 0.1 N-Free from carbonate. Sulphuric acid, 0.01 N-Free o on dioxide.674 JENNINGS AND OSBORN : QUANTITATIVE DETERMINATION OF [Vol. 82 Distilled water, free from carbon dioxide-Prepared by boiling laboratory distilled water for 30 minutes and cooling it under a guard tube. Sulphuric acid, diluted (1 + l), free from carbon dioxide-Prepared from the concentrated acid immediately before use.A cetone-Analytical-reagent grade. Soda lime-The self-indicating material. Silica gel-The self-indicating material. PROCEDURE FOR STANDARDISIXG THE pH METER- As a standard buffer solution cannot be introduced into the titration cell while an analysis is being carried out, it is necessary to determine the residual e.m.f. of the particular glass electrode being used and to utilise this value in setting up the pH meter. This procedure is sufficiently accurate for this method of determination. PROCEDURE FOR COLLECTING THE SAMPLE- The sample bottle, A, is removed in such a way that stopcocks S, and S, are still connected to the bottle. The sample enters by way of tube B, the bottle is filled and water is allowed to overflow through funnel F and stopcocks S, and S,.The contents of the bottle are displaced several times before the inlet and outlets are closed, and water is retained in the sampling tube. PROCEDURE FOR DETERMINING CARBON DIOXIDE- The sample bottle, A, is reconnected, stopcock T is opened to the atmosphere and stopcock S, is connected from the pump to the sample bottle; clip C is opened and water is pumped from the sample bottle by way of tube B and is replaced by air free from carbon dioxide. When the water level is almost down to the 10-litre mark, stopcock S, is turned to connect the sample bottle to the titration cell, stopcock S, being open to the atmosphere, and the water is allowed to syphon out of the sample bottle thereby reducing the pressure in the bottle, Clip C is closed when the correct level has been reached.A 50-ml portion of diluted sulphuric acid (1 + 1) is added through funnel F. Stopcock S, is opened to the atmosphere momentarily, to fill the line with air free from carbon dioxide, and is then closed. The electrode system is thoroughly washed with acetone and then water (this was found to increase sensitivity by removing any grease and matter adhering to the surfaces). Approx- imately 100 ml of water free from carbon dioxide are placed in the titration cell and 2 to 3 ml of 0.01 N sulphuric acid are added: air free from carbon dioxide is then bubbled through and out by way of stopcock S, for 5 to 10 minutes to ensure freedom from traces of carbon dioxide. The liquid level in the titration cell is lowered to a position fixed by the electrode system by replacing the sulphuric acid burette by a syphon inserted to the required depth and momen- tarily closing stopcock S,. It is important that the liquid should be adjusted to this level before each part of the determination.With air free from carbon dioxide flowing through the system, stopcock T, and then stopcock S,, is closed, thus allowing air to circulate under slightly reduced pressure. Then 1 ml of 0.1 N sodium hydroxide is put into the titration cell and the sample bottle is brought into the circuit by adjusting stopcock S, to connect the pump to the sample bottle and also stopcock S, to connect the sample bottle to the titra- tion cell. .The heating tapes are switched on so as to maintain a temperature of approxi- mately 40" C, which is sufficient t o prevent any condensation from forming in the tubing. Aspiration is continued for 1 hour.After aspiration of the sample, stopcock S, is adjusted so that the pump is connected directly to the titration cell and stopcock S, is closed, so that the sample bottle is cut out of the circuit. Then 0.01 N sulphuric acid is added to the titration cell until the pH is approx- imately 9. Increments of 0.1 ml of the same acid are added and the pH and burette reading are noted until the pH falls to just below 8.3. Stopcocks S, and T are then opened to allow air free from carbon dioxide to flush the system; further increments of acid are then added until the pH falls to below 5.0. The amount of acid required between pH 8.3 and 5.0 may be found by means of a graph-let this volume be A ml.The sulphuric acid burette is removed and the liquid level is re-adjusted by means of the syphon. A blank titration is now carried out. Stopcocks T and S, are closed, 1 ml of 0.1 N sodium hydroxide is run into the titration cell and the titration is again carried out. TheOct., 19571 TRACES OF CARBON DIOXIDE I N WATER 675 titre is the volume required under conditions in which carbon dioxide is absent and is usually about 0.4 to 0.5 ml of 0.01 N acid-let this volume be B ml. The liquid is again syphoned to the required level, the sample bottle is brought back into the circuit and aspiration is continued for 30 or 60 minutes as required. Titrations are carried out as before to give titres of A , and B, ml.The blank titration should be repeated after each determination, owing to a very slight loss of sensitivity at the glass electrode; this should not be more than 0.05 ml of 0.01 N acid. Aspiration 1 = A - (B + apparatus blank) = X ml. Aspiration 2 = A , - (B, + apparatus blank) = Y ml. Total 0.01 N sulphuric acid required The following decomposition takes place between pH 8.3 and pH 5.0- = X + Yml. NaHCO, + H,SO, = NaHSO, + H,O + CO,. Therefore 1 ml of 0.01 N H,SO, = 0.44 mg of CO,, i.e., 0.044 mg of CO, per litre in a 10-litre sample. PROCEDURE FOR DETERMINING THE APPARATUS BLANK- The apparatus is allowed to run on a closed circuit with the sample bottle excluded for 1 hour and a titration is carried out, followed by a blank titration as described above and the difference, usually about 0.05 ml of 0.01 N acid per hour, is noted.This is believed to be due to diffusion or leakage of carbon dioxide through the flexible joints or pump diaphragm and the result, although very small, must be included in the above calculation. TABLE I nETERMINATION OF CARBON DIOXIDE IN BOILER FEED WATER Carbon dioxide Aspiration Acid used, Total acid, found, No. Station 1- A 1 2 B 1 2 C 1 2 3 A 1 2 B 1 2 Statioiz 2- ml :::: } :::; } :::: } :::; } 0.78 0.26 } 0.02 RESULTS ml mg per litre 0.29 0.013 0.42 0.018 1.06 0,047 0.87 0.038 0.68 0,029 The method has been applied to the determination of carbon dioxide in boiler feed water, and some typical results obtained at power stations having boilers operating at 900 lb per sq.inch are given in Table I. Results of determinations of the apparatus blank were as follows- Volume of 0.01 N acid required per hour, ml . . 0.03 0.05 0.02 0.06 0.08* 0.03 Equivalent of carbon dioxide in sample, mg per litre . . . . * . * . . . 0.0013 0.0022 0.0009 0.0026 0.0035 0.0013 The method has also been checked with standard sodium carbonate solutions. The apparatus was assembled with the sample bottle filled to the 10-litre mark with acidified water aspirated free from carbon dioxide. A measured volume of 0.01 N sodium carbonate was added by means of a pipette and the carbon dioxide was determined by the proposed method. The results are given in Table 11. * This determination was made after the pump had run continuously for over 48 hours.JENNINGS AND OSBORN TABLE I1 TESTS WITH COXTROL SOLUTIONS Carbon dioxide taken, Acid used, Total acid, mg per ml ml litre :::: } 0.47 0.022 } 0.53 0.022 0.00 } 0.53 0.08 } l.04 0.08 } l.04 0.022 0.53 ;:ti } 0.96 0.044 0.044 0.96 0.044 0.96 2.02 0.05 0.46 } 2.53 0.110 [Vol.82 Volume of 0.01 N sodium carbonate taken, ml 1.0 1.0 1.0 2.0 2.0 2.0 5.0 Aspiration No. 1 2 1 2 1 2 1 2 1 2 3 Carbon dioxide found, mg Per litre 0,021 0.023 0,023 0.042 0,046 0.046 0.111 Difference, mg Per litre - 0.001 + 0.001 + 0.001 - 0.002 + 0.002 + 0.002 +0~001 DISCUSSION OF RESULTS It will be seen from the results in Table I1 that there is close agreement between the calculated and determined concentrations of carbon dioxide. The standard deviation of the carbon dioxide found from the carbon dioxide taken was 0.0016 mg per litre and the standard deviation of the apparatus blank was 0.0009 mg per litre, which indicates that the apparatus blank is the largest factor in the residual error. No determination below 0.110 mg per litre showed an error greater than 0.002 mg per litre. Work was also carried out with 2.2 and 4.4 mg of carbon dioxide, but it was found that the titration pH curve in the region of pH 8.3 was very flat and led to errors in the volume of acid, A . The results indicate that the method is capable of determining carbon dioxide in boiler feed waters with an accuracy of 0.003 mg per litre on a 10-litre sample provided that the sample does not contain more than 1 mg of carbon dioxide. We thank Mr. R. Wolforth, Divisional Chief Chemist, for his encouragement and advice and the Controller, Central Electricity Authority, Yorkshire Division, for permission to publish this paper. REFERENCES 1. 2. 3. Parkhouse, D., Chew. G. Ind., 1953, 1197. Hoemig, H. E., Mitt. Ver. Grosskesselbesitzer., 1953, 521. Smith, J. B., Gilbert, E. K., and Howie, M. P., Anal. Chem., 1954, 26, 667. CENTRAL ELECTRICITY AUTHORITY YORKSHIRE DIVISION DIVISIONAL CHEMICAL LABORATORY SKELTON GRANGE POWER STATION LEEDS April 12th, 1957

ISSN:0003-2654    

DOI:10.1039/AN9578200671

出版商:RSC    

年代:1957

数据来源: RSC

摘要:

Oct., 19571 CAMERON AND MOORE 677 The Influence of Chloride on the Dichromate-value Test BY W. M. CAMERON AND T. B. MOORE The suitability of dichromate for the determination of oxygen absorbed, by polluting matters, is confirmed. However, it is shown that errors develop in the presence of chloride and of chloride and nitrogen occurring together. These errors have a multiple effect. Correction is possible, b u t not precise. THIS paper is a record of tests carried out for the purposes of an investigation on the di- chromate-value test by Panel I of a Joint Committee of the Association of British Chemical Manufacturers and the Society for Analytical Chemistry, which was set up to enquire into analytical methods applicable to trade effluents. For the determination of oxygen absorbed (O.A.) W.A. Moore et al. employed dichromate in a method involving heating under refluxl and later incorporated the use of silver as a catalyst,2 as recommended by 311uer.~ They obtained results near to the calculated value for the oxygen required to oxidise a large number of selected organic compounds in pure solution. According to Moore et al., chloride, when present, is 100 per cent. oxidised, so that its oxygen requirements can be calculated to yield a true correction. In the present work, the method of Moore et al. was examined, and four main points emerged from the investigations, as follow- (i) The method gives results much nearer to theoretical values than the conventional British method based on permanganate, when pure solutions are being dealt with. (ii) When the silver salt is added before the chloride is oxidised, silver chloride may be precipitated in a coagulated form difficult to oxidise.(iii) The chloride present is not completely oxidised and, if this is ignored, errors may develop for which a precise correction cannot be made. (iv) Correction is more difficult when chloride and nitrogen occur together, because the nitrogenous portion may be oxidised by the free chlorine developed during the oxidation of the chloride. We recommend that sufficient dichromate should be added to oxidise the chloride, in addition to the normal 25 ml required to deal with the sample, and a period of heating under reflux should be carried out before the addition of the silver. We also suggest approximate corrections for the presence of chloride, and of chloride and nitrogen occurring together.These modifications have been incorporated into the method put forward by Panel I of the Joint Committee. OXIDATION IX PURE SOLUTION- in distilled water, of pure organic compounds. will be seen that they conform with the general thesis. EXPERIMENTAL Some comparative dichromate and permanganate values were first found for solutions, Results are given in Table I, from which it TABLE I COMPARISON OF DICHROMATE AND PERMANGANATE VALUES Ratio determined O.A. Determined O.A. calculated O.A. with- for- A P < > N / 8 N / 8 KMnO, K&r,O, N/8 N/8 Compound Calculated O.A., KMnO,, K,Cr,O,, p.p.m. p.p.m. p.p.m. Acetic acid , , .. 512 Nil 485 Nil 0.947 Phenol . . . . . . 499.6 396 512 0.793 1.024 Glycerophosphoric acid 504 220 526 0.437 1.044 Ethanol ... . 498 129.6 496 0.260 0.995 Glycerol . . , , 497-8 268.8 498 0.540 1.00 Ammonium thiocyanate 498.5 392 480 0.786 0.963 Cresol . , . . , . 478.1 267.2 508 0,559 1.062678 CAMERON AND MOORE: THE INFLUENCE OF CHLORIDE [Vol. 82 OXIDATION OF CHLORIDE IN PRESENCE OF SILVER- Chloride is commonly a constituent of natural waters and is oxidised by dichromate. Moore et al. recommended that a correction should be applied for the presence of chloride, based on 100 per cent. oxidation of the chloride. In the course of the present work, it became apparent that the degree of oxidation of chloride was generally not so complete. It was found that chloride in high concentration was not readily oxidised, since silver chloride was precipitated in a coagulated form.It was necessary under those conditions to continue the period of heating under reflux until the precipitate mas wholly dissolved, in order to complete the oxidation. In some tests 2 hours was found to be the minimum period. For example, a solution of monohydric phenols having a theoretical oxygen absorbed of 259 p.p.m. and a sodium chloride content equivalent to 1750 p.p.m. of chlorine gave the following results, the oxygen absorbed being based on the assumption of 100 per cent. oxida- tion of chloride- Time of heating under reflux, hours . . 4 1 2 Oxygen absorbed, p.p.m. . . , . 205 215 250 More satisfactory results were obtained with gas liquor, as shown by the following After 1 hour’s boiling, values for the After 1 hour’s boiling, values for the After 1 hour’s After 2 hours’ results- Sample A , 2 per cent.of 10-oz gas liquor in potable water. oxygen absorbed were 316 and 310 p,p.m., giving a mean of 313 p.p.m. Sample B , 2 per cent. of 10-oz gas liquor in potable water. oxygen absorbed were 380 and 387 p,p,m,, giving a mean of 383 p.p.m. Sample B, with added sodium chloride (equivalent to 120 p.p,m, of chloride). boiling, the oxidation of chloride was incomplete, as judged by persistent turbidity. boiling, the value for the oxygen absorbed was 381 p.p.m. REMOVAL OF CHLORIDE- Consideration was given to the removal of chloride by precipitation and filtration. However, experiments demonstrated, as was expected, that co-precipitation occurred in the presence of colloidal matter, e g ., fatty acids and proteins. The oxygen-absorbed value was thereby reduced. The results “with correction for chloride” were obtained by following the recommended method of the Joint Committee. The results “with precipitation of chloride” were obtained after the chloride had been pre- cipitated and removed by filtration. TABLE I1 RESULTS FOR OXYGEN ABSORBED WITH ADDED CHLORIDE Some results are shown in Table 11. O.A. value, Compound p.p.m. Cresylic acid . . . . 400 Soap . . . . . . 360 Soap . . .. . . 740 Soap . . . . . . 300 Glue . . . . . , 190 Chloride added, p.p.m. of oxygen absorbed 400 800 800 400 500 Oxygen absorbed with correction for chloride, p.p.m. 400 356 732 296 182 Oxygen absorbed with precipitation of chloride, p.p.m. 405 140 350 160 137 OXIDATION OF CHLORIDE IN ABSENCE OF SILVER- Another probability was that oxidation of the chloride would be readily achieved if the addition of the silver salt was delayed.Experiments with a solution of sodium chloride, silver being absent, demonstrated that maximum, but not complete, oxidation was achieved in 4 hour. The incompleteness of oxida- tion became a major point in later work, but for the sake of clarity is discussed a t this stage. In order to demonstrate the point more fully a series of tests was performed in which the back-titrations were carried out with N/80 ferrous salt. Solutions having various con- centrations of sodium chloride were heated under reflux, 25-m1 portions being taken, for 2 hours with excess of dichromate, but without the addition of silver sulphate.The results are given in Table 111. The incomplete oxidation of chloride, if ignored, leads to low oxygen-absorbed values, especially in the presence of high concentration of chloride. Hence if C is the true oxygenOct., 19571 ON THE DICHROMATE-VALUE TEST 679 equivalent of the chloride present, S the oxygen-absorbed value of the organic pollutant, both in the same terms, and P the percentage error due to the assumption of 100 per cent. oxidation of chloride, then the observed oxygen-absorbed value of the sample contains an error of CIS x P per cent. It follows that, unless P can be accurately determined, S cannot be exactly calculated for an unknown degree of organic pollution. Chloride taken, p.p.m. 225 558 1058 2112 4224 5310 TABLE I11 OXIDATION OF CHLORIDE IN ABSEKCE OF SILVER Equivalent volume of N / 8 ml 1.25 3.15 6.10 11.90 23.80 29.90 Volume of N / 8 Volume of N/80 Oxidation, K2Cr207 Fe(NH,),(SO,), added, required, ml ml % 2.0 6.3 109.7 5.0 18.75 99.2 10.0 40.10 98.1 15.0 34.40 97.4 30.0 67.90 97.4 40.0 118.75 94.0 Hence the applicability of the dichromate-value test is limited in the presence of high chloride concentrations.However, if the test is confined to the use of N / 8 dichromate, as recommended by the Panel, then it can be shown, by application of the above formula, that the concentration of chloride for organic oxygen-absorbed values of 250 to 500 p.p.m, should not exceed 1000 to 2000 p.p.m., if the resulting oxygen-absorbed value of the pollutant is to be within 5 per cent.of the true value. It further follows that, if the concentration of chloride reaches 10,000 to 20,000 p.p.m., the errors developed might be equivalent to oxygen-absorbed values of 112 p.p.m. and 224 p.p.m. Hence the test would be valid when such values are appreciable fractions of the accompanying oxygen-absorbed value of the pollutant. OXIDATION OF LACTIC ACID AND ALAXINE- The dichromate value of pure lactic acid in pure solution and in the presence of chloride was determined by using the method recommended by the Joint Committee. Typical results are given in Tables IVA and IVB, from which is seen that a serious depression in the amount of oxidation occurs a t high concentrations of chloride. TABLE IVA DETERMINATION OF THE DICHKOMATE VALUE OF LACTIC ACID Series I- (a) Lactic acid .. . . . . . . . . ( b ) Lactic acid + silver sulphate . . . . p.p.m. of chloride . . . . . . . . (c) Lactic acid + silver sulphate + 12,600 ( d ) Lactic acid + silver sulphate + 200 p.p.m. of chloride . . . . . . . . . . (a) Lactic acid + silver sulphate . . .. p.p.m. of chloride . . . . . . . . p.p.m. of chloride . . .. . . . . Series II- (h) Lactic acid + silver sulphate + 12,425 (c) Lactic acid + silver sulphate +- 12,425 Oxygen absorbed, ml of N / 8 K,Cr,O, 7.6 9.6 4.4 9.2 10.2 3.65 5*26* Theoretical oxygen absorbed, ml of N j 8 KSCr207 12.0 12.0 12.5 12.5 12.0 12.0 12.0 Amount of oxidation, % 63.0 80.0 35.4 73.5 85.0 30.4 43.8 * Mean of two tests, after aeration at the end of each test to remove any volatile oxidising agents. If the differences in absorption, in ml of N/8 potassium dichromate, between that of the pure lactic acid and those obtained when chloride was present are ascribed t o an error in the oxidation of chloride, additional oxidation of lactic acid is obtained as follows- Series I- (’) 5.2 = 41.8 per cent., to give a total of 76.8 per cent.12.5680 CAMERON AND MOORE: THE INFLUENCE OF CHLORIDE (Vol. 82 (d) L4 = 3-2 per cent., to give a total of 76.7 per cent. 12.5 The value for pure lactic acid is 80 per cent. Series II- ( b ) 6.66 = 54.7 per cent., to give a total of 85.1 per cent. 12.0 (') 494 = 41.2 per cent., to give a total of 85.0 per cent. 12.0 The value for pure lactic acid is 85 per cent. The calculation of the error and the extent of oxidation of the chloride are seen from Table IVB.TABLE IVB CALCULATION OF THE ERROR AND THE EXTENT OF OXIDATIOS Approximate Equivalent Volume of concentration, K,Cr,O, found, not absorbed, Error, Oxidation, chloride of N / 8 N / 8 K,Cr,O, p.p,m. ml ml % Yo Series I ( d ) 200 1.4 0.4 28.5 71.5 (4 12,600 71.0 5.2 7.3 92.7 Series I1 ( b ) 12,425 70.0 6.56 9.4 90.6 (4 12,425 70.0 4.94 7.1 92.9 The dichromate value of pure alanine, taken as being indicative of nitrogenous com- pounds, was similarly determined. Results are given in Table V. TABLE V DETERMINATION OF THE DICHROMATE VALUE OF ALANINE (a) Alanine + (b) Alanine + (c) Alanine + ( d ) Alanine + (e) Alanine + Oxygen absorbed, ml of Oxidation, N / 8 K,Cr,O, % silver sulphate . . . . . . * . . . 12.0 94.8 silver sulphate. . . . . . ... . .. 12.55 99.2 293 p.p,m. of chloride added as sodium chloride . . 12.85 101.5 12,753 p.p.m. of chloride added as sodium chloride 3.5 27.5 12,753 p.p.m. of chloride added as sodium chloride 4.9 38.7 The theoretical absorption for each test was equivalent to 12.65 ml of N / 8 potassium The chloride content of (c) was equivalent to 1.65 ml of N / 8 potassium dichromate If (d) and (e) are corrected in the same manner as was done for lactic acid, the following dichromate. and that of (a) and (e) to 71.85 ml of N / 8 potassium dichromate. values for these oxidations are obtained, 12.3 being taken as the mean of (a) and (b)- -- '" - 69.6 per cent., to give a total of 27.5 + 69.6 = 97.1 per cent. ~- 7'4 - 58.5 per cent., to give a total of 38.7 + 58.5 = 97.2 per cent.12.65 12.65 The oxidation of the chloride is then equivalent to- (e) 71.85 - 7.4 = 89.7 per cent. 71.85 The effect of high chloride content together with its variable oxidation is confirmed. In this case, however, the opportunity was taken to examine the oxidation from the point of view of nitrogen. In order to do this, the titrations were performed with N/8 ferrous sulphate, which was stored in an atmosphere of hydrogen. The amount of nitrogen present was 1.89 mg in each test and the amounts recovered, in mg of nitrogen, were: (a) 1.14, ( b ) 1.14, (c) 1.31, (a) 0.42 and (e) a trace.681 Oct., 19571 ON THE DICHROMATE-VALUE TEST OXIDATION OF UREA: PRESENCE OF KITROGEN AND CHLORIDE TOGETHER- The oxidation of the nitrogenous portion of the molecule indicated that the reaction was in the foregoing instance more complicated than had been supposed and further experiments were carried out to elucidate the problem.Urea was chosen for this purpose, since it is of simple chemical constitution and is a natural constituent of domestic sewage. A preliminary experiment demonstrated that some oxidation did occur directly with dichromate, but that it was enhanced in the presence of chloride. The direct oxidation was thought to follow a reaction of the type- CO(NH,), + 3 0 -+ CO, + 2H,O + N,, from which it was calculated that 12.5 ml of N / 8 potassium dichromate might directly oxidise 15.6 mg of urea. Accordingly, in a series of determinations a solution of urea con- taining 15.6 mg per 25 ml was used, together with various concentrations of chloride in the same volume. The results from these tests are given in Table VI.TABLE VI OXIDATION OF UREA IN PRESENCE OF CHLORIDE 25 ml of N / 8 K,Cr,O, = 5.2 mg of urea Absorption Chloride Total volume of as volume of present, N / 8 K,Cr,O,. N/8 FeSO,, Oxidation p.p.m. ml ml of urea, yo 266 639 1278 6327 Nil 26.5 28.6 32.2 60.7 25.0 6.5 8.5 9.7 7.14 4.2 52 68 77 57 33.6 The amount of oxidation is very variable between the tests. I t is in marked contrast to the experience with lactic acid and alanine, for with these chloride apparently causes decreased oxidation. The nitrogen determinations gave the following results, the amount of nitrogen originally present being 7.28 mg per 25 ml- Chloride present, p.p.m. . . . . 266 639 1278 6327 Nil Nitrogen recovered, mg .. . . 1.944 2.184 2.160 2.040 4.37 Oxidation, yo . . . . * . 73 70 70 72 37 Hence the higher degree of oxidation of urea appears to depend on the presence, but not the concentration, of chloride. I t would seem that the chloride a t the lower concentra- tions acts in a cyclic manner, forming free chlorine and chloride alternately, and so oxidising the urea and thereby reducing the dichromate. There are several routes by which chlorine may oxidise organically combined nitrogen, but it is thought that each involves tervalent nitrogen, therefore that is the basis of the correction offered in the Joint Committee method (i.e., 1 ml of N / 8 K,Cr,O, = 06833 mg of nitrogen). However, it should be pointed out that the correction, although based on valency, is not precise, since the nitrogen may be simultaneously directly and indirectly oxidised.The correction is given, since oxidation tests of this nature are generally con- sidered to be concerned with carbonaceous oxidation only. TABLE VII OXIDATION IN THE PRESENCE OF ORGANICALLY COMBINED CHLORINE Oxidation with Oxidation with Compound silver absent, % silver present, yo Carbon tetrachloride . . . . . . .. 6.4 6.4 Trichloroethylene . . . . . . . . 20.0 20.0 Benzoyl chloride* . . .. . . . . 94.3 94.5 Benzyl chloride . . . . . . . . . . 65.2 62.4 Chlorobenzene . . . . . . . . . . 12.0 25.6 * Owing to hydrolysis this test becomes in effect a test of benzoic acid and hydrochloric acid.682 CAMERON AND MOORE [Vol. 82 OXIDATIOX IN PRESENCE OF ORGANICALLY COMBINED CHLORINE- In an incidental manner the oxidation of chain and ring structures in which chlorine is organically combined was examined. Some results are given in Table VII.CONCLUSIONS I t has been confirmed that the results obtained in the dichromate-value test are generally close to the theoretical value, which is in marked contrast to those obtained from the per- manganate-value test. I t has also been shown that chloride, which is of common occurrence, may introduce errors that cannot be corrected in a simple manner. However, oxidation of the chloride by dichromate before the addition of silver sulphate usually reduces the error to negligible dimen- sions. Correction of the error is more difficult when chloride and nitrogenous compounds occur together. Part of the unoxidised nitrogen may be directly oxidised by the dichromate and part simultaneously oxidised by the free chlorine developed from the chloride. An empirical correction is suggested for such conditions. These corrections are the basis of the limitations placed upon the test by Panel I of the Joint Committee. Mr. W. &I. Cameron is indebted to Mr. W. T. Lockett, Chief Chemist, Main Drainage Department, Middlesex County Council, for advice and criticism, and to Mr. C. B. Townend, C.B.E., Chief Engineer of that department, for permission to publish. Thanks are also due to Mr. A. A. Kendall of the same department, who carried out the major part of the practical work. Mr. T. B. Moore wishes to thank the North Thames Gas Board for permission to take part in this work. REFERENCES 1. 2. 3. MAIN DRAINAGE DEPARTMENT ISLEWORTH Moore, W. A,, Kroner, R. C., and Ruchhoft, C. C., Anal. Chem., 1949, 21, 953. Moore, W. A,, Ludzack, F. J., and Ruchhoft, C. C., Ibzd., 1951,23, 1297. Muer, M. M., J . SOC. Chem. Ind., 1936, 55, 717. MIDDLESEX COUNTY COUNCIL MOGDEN WORKS NORTH THAMES GAS BOARD TAR AND AMMONIA PRODUCTS WORKS EAST HAM, E.6 April 30th, 1956

ISSN:0003-2654    

DOI:10.1039/AN9578200677

出版商:RSC    

年代:1957

数据来源: RSC