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Relations of Permanganate and Nitrite

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  Dec., 19591 RARE EARTHS IN ZIRCONIUM AND ITS ALLOYS 731 Determination of the Permanganate Value for Waters and Sewage Effluents Containing Nitrite BY P. V. R. SUBRAHMANYAM, C. A. SASTRY AND S. C. PILLAI Department of Biochemistry, Indian Institute of Science, Bangalore, India) The results of a comparative study of the efficiencies of urea and sul- phamic acid in the destruction of nitrites added to distilled water and sea water, or present in sewage effluents, before the determination of perman- ganate values are presented and discussed. Sulphamic acid is preferred for reasons of efficiency, economy and suitability, especially when phosphoric acid is used to acidify the samples. ONE of the earliest tests for assessing the quality of sewage effluents and the pollution of water was the determination of the oxygen absorbed from acidified potassium permanganate solution. The development of this test in 1850, its continued use and its limitations have been recently reviewed.l 2 A point of considerable interest about the “permanganate value,”2 apart from its determination being simple and fairly rapid, is that it provides a continuous basis for comparison with the results accumulated over many years. G. J. Fowler, in unpublished work, observed that for many domestic sewages a 3-minute oxygen absorption of 3.6 p.p.m. indicated satisfactory purification and that for Manchester sewage, which contained much oxidisable industrial refuse, 7.1 p.p.m. might be accepted. The determination of the oxygen absorbed from permanganate in 3 minutes, i.e., practically instantaneously, gives a means of differentiating between readily or easily oxidisable substances and more slowly or difficultly oxidisable substances, which are determined by the 4-hour test, Since soon after the adoption of the test, it has been known that the presence of nitrites in the samples interferes with the determination of the permanganate value.3 Quantitative determination of the nitrite and calculation of its effect on the permanganate demand, the result being recorded as “permanganate value corrected for nitrite,” is a somewhat tedious procedure, and it is preferable.to destroy the nitrite. Jung and Otto4 tried to overcome the effect of nitrite by adding sodium azide, but found that an excess of azide affected the per- manganate demand; they recommended the addition of 50 mg of urea to a water containing 100 mg of nitrite per litre. Nolte and Bandt5 found that the destruction of nitrite by urea was slow in the cold, but could be accelerated by gently warming the mixture. Two years ago a Joint Committee of the Association of British Chemical Manufacturers and the Society for Analytical Chemistry2 recommended that 1 g of urea be added to the acidified sample containing nitrite and to the blank and that the solutions be set aside for 5 minutes before the appropriate volume of permanganate solution is added.    P  u   b   l   i  s   h  e   d  o  n   0   1   J  a  n  u  a  r  y   1   9   5   9 .   D  o  w  n   l  o  a   d  e   d   b  y   N  o  r   t   h  e  a  s   t  e  r  n   U  n   i  v  e  r  s   i   t  y  o  n   2   6   /   1   0   /   2   0   1   4   1   6  :   4   4  :   3   4 . View Article Online / Journal Homepage / Table of Contents for this issue  732 SUBFUHMANYAM, SASTRY AND PILLAI DETERMINATION OF THE PERMANGANATE [Vd. 84 In this connection we have found that sulphamic acid is more efficient than urea and that its use is more economical, especially in the analysis of saline and sea waters containing nitrite. The results of a comparative study of the use of sulphamic acid and urea in the determination of permanganate values are described in this paper. Sulphamic acid has been used in a modification of the Winkler method for determining dissolved o~ygen~,~~   its application in the oxygen-absorption test does not seem to have been attempted. MATERIALS AND METHODS Samples of distilled water and sea water to which different amounts of sodium nitrite had been added and samples of sewage effluents containing different amounts of nitrite were used for the oxygen-absorption tests. Reagents were prepared and tests were carried out as recommended by the Joint Committee.2 RESULTS Eight series of tests were carried out to study the relative efficiencies of urea and sulphamic acid for destroying nitrite in water samples and sewage effluents. In the first series, 100-ml samples of distilled water containing 1 or 2 mg of added nitrite-N were treated with l-ml portions of 0.5 M solutions of urea or sulphamic acid, i.e., 30 mg of urea or 48.5 mg of sulphamic acid. The 3-minute permanganate values were determined after the solutions had been set aside for periods of up to 5 minutes. The permanganate values of 100-ml samples containing 1 and 2 mg of nitrite-N were 11.2 and 22.5 p.p.m., respectively.) For the urea solution, the results were- Time after addition of urea solution, minutes . . .. 1 3 5 Permanganate value in presence of 1 mg of nitrite-N, p.p.m. . . 9.8 9.0 8 2 When 0 5 M sulphamic acid was used, the 3-minute permanganate value was 0.0 p.p.ni. in each test. The rate of destruction of nitrite-N in 100-ml samples of water by 1-ml portions of 0.5 M urea solution was then determined; the results were- Permanganate value in presence of 2 mg of nitrite-N, p.p.m. . 20 2 18-3 16.9 Time after addition of urea solution, Permanganate value in presence of Permanganate value in presence of minutes . .. 1 3 5 10 15 20 25 30 45 60 1 mg of nitrite-N, p.p.m. . . 9 7 9 0 8 0 6.2 4 7 3.4 2.9 2 2 1.4 0 4 2 mg of nitrite-N, p.p.m. . 20.2 18.2 16.4 12.9 10.2 8.6 6.9 5 2 3.2 1.6 The extent to which nitrite was destroyed was determined by adding increasing amounts of urea or the theoretical amounts of sulphamic acid to 100-ml samples of water containing known amounts of added nitrite-N; the results are shown in Table I. When twice the theoretical amount of sulphamic acid was added, destruction of nitrite was almost instantaneous. Different amounts of nitrite were added to 100-ml samples of distilled water and the 3-minute and 4-hour permanganate values were determined. The efficiency of sulphamic acid for destroying nitrite was then studied. The results were- Amount of nitrite-N added, mg . . 0.2 0.4 0 6 0 8 1.0 2.0 3.0 4.0 6.0 3-minute permanganate value, p,p.m. . . 2.2 4.4 6.6 9.0 11.2 22.5 34.0 44.9 65.6 4-hour permanganate value, p.p.m. 2 2 4.6 6.6 9 0 11.4 22.9 34.2 45.3 66.2 The series was then repeated, 1 ml of 0 5 M sulphamic acid being added 1 minute before the permanganate solution; in no test was either the 3-minute or the 4-hour permanganate value greater than 0.1 p.p.m. As the concentration of nitrite-N in polluted waters and sewage effluents does not normally exceed 50 p.p.m. 5 mg per 100 ml), it is suggested that 50 mg of sulphamic acid be added to 100 ml of sample containing up to 5 mg of nitrite-N and to the blank and that the mixture be set aside for 1 minute to ensure complete destruction of the nitrite. The efficiencies of urea and sulphamic acid for destroying nitrite in sewage effluent were also determined; the results are shown in Table 11.    P  u   b   l   i  s   h  e   d  o  n   0   1   J  a  n  u  a  r  y   1   9   5   9 .   D  o  w  n   l  o  a   d  e   d   b  y   N  o  r   t   h  e  a  s   t  e  r  n   U  n   i  v  e  r  s   i   t  y  o  n   2   6   /   1   0   /   2   0   1   4   1   6  :   4   4  :   3   4 . View Article Online  Dec., 19591 VALUE FOR WATERS AND SEWAGE EFFLUENTS CONTAINING NITRITE TABLE DESTRUCTION F NITRITE BY UREA AND SULPHAMIC ACID The 3-minute permanganate vaiues for water samples containing 2 and 5 mg of nitrite-N were 22.4 and 55.8 p.p.m., respectively Amount of Amount of nitrite-N reagent present in added to sample, 100 ml of mg per 100 ml sample, mg Urea added- 30 60 120 240 600 500 600 800 000 2 5 Sulphamic acid added- 7 minute, p.p.m. 20.4 18.8 16.6 12-7 4.0 20.8 16.4 11.2 7.6 3-minute permanganate value after- 733 2 minutes, 3 minutes, p.p.m. p.p.m. 18.5 14-9 11.5 6.0 0.4 4.4 2.4 1.2 0-4 1 6.93 0.2 0.0 2 13.86 0.2 0 0 3 20.79 0.4 0.0 4 27-72 0.6 0.1 5 34.65 0.6 0.2 5 minutes, p.p.m. 16.6 12.9 8.1 3.3 0.1 1.2 0.4 0.0 0.0 10 minutes, p.p.m. 12.5 9.2 3.7 0-6 0.0 0.0 0.0 0-0 0-0 TABLE 1 EFFICIENCIES F UREA AND SULPHAMIC ACID FOR DESTROYING NITRITE Sulphamic acid or urea was added 2 minutes before the permanganate solution. A 100-ml sample of effluent was used in each test IN SEWAGE EFFLUENTS Permanganate Permanganat e Permanganate Calculated value in Permanganate value in value in presence of Amount of perman- absence of urea value presence of A nitrite-N ganate or sulphamic expected 50 mg of 50 mg of present, value A),* acid B), B A), sulphamicacid, urea, mg p.p.m. p.p.m. p.p.m. p.p.m. p.p.m. Three-minute oxygen-absorption test-- 0 0 0.0 2.4 2.40 2.4 2.4 0-68 7.75 11.2 3-45 3.6 10-2 1.04 11.86 14.6 2-74 2.8 12.2 1-32 15-05 18.7 3.65 3.8 15.6 1.58 18.01 21.6 3.59 3.6 18-4 2.40 27.36 30.6 3.24 3.4 24.9 3.24 36.94 40-9 3-96 4.2 33.2 Fouv-hour oxygen-absorption test- 0.0 0-0 8.8 8.8 8.8 8.8 0.68 7.75 17.3 9.55 9.6 15.9 1.04 11-86 20.7 8.84 8 8 18.1 1-32 15.05 24.8 9-75 9.8 21.7 1-58 18.01 27.8 9.79 9.8 24.8 2.40 27-36 36.8 9.44 9-6 31.2 3-24 36.94 46.9 9.96 10.2 39.3 Amount of nitrite present, mg x 11.4. 300 mg of urea, p.p.m. 2.4 6-3 6.9 9.7 10.8 13.7 15-9 8-8 12.3 12.7 15.9 17.0 19.8 22.3 Ig of urea, p.p.m. 2-4 3.6 2.8 3.8 3-6 4.4 5.4 8 8 9.6 8-8 9.8 10.0 9.8 10.8 As phosphoric acid is used to acidify samples of sea water,9 the effect of this acid was studied. Different amounts of nitrite were added to 100-ml samples of sea water that had been acidified with phosphoric acid, and sulphamic acid or urea was added 2 minutes before the permanganate solution; the results are shown in Table 111.    P  u   b   l   i  s   h  e   d  o  n   0   1   J  a  n  u  a  r  y   1   9   5   9 .   D  o  w  n   l  o  a   d  e   d   b  y   N  o  r   t   h  e  a  s   t  e  r  n   U  n   i  v  e  r  s   i   t  y  o  n   2   6   /   1   0   /   2   0   1   4   1   6  :   4   4  :   3   4 . View Article Online  734 SUBRAHMANYAM SASTRY AND PILLAI : DETERMINATION OF THE PERMANGANATE [VOl. 84 TABLE 11 EFFECT F PHOSPHORIC ACID IN ANALYSIS OF SEA WATER 3-minute permanganate value- Amount of nitrite-N present, mg 0 1 2 3 4 r- in absence of sulphamic acid or urea, p.p.m. 0.2 11.4 22.7 34.2 45.1 55.8 in presence of 300 mg of in presence of 50 mg of urea, sulphamic acid, p.p.m. p.p.m. 0.2 9.3 32-3 45.4 Finally, the effects of phosphoric acid and sodium chloride on urea were investigated, the results being shown in Table IV. Known amounts of nitrite were added to 100-ml samples of distilled water and the 3-minute permanganate values were determined after the samples had been acidified with a) ulphuric acid and (b) phosphoric acid; 300 mg of urea were added to each sample 2 minutes before the permanganate solution. The experiment was then repeated with samples containing added sodium chloride and acidified with phosphoric acid. The 3-minute permanganate values for 100-ml samples of sea water treated with 1 g of urea and acidified with phosphoric acid and containing 5 mg of nitrite-N, after being set aside for 2 3 5 and 10 minutes before permanganate solution was added, were 15.0, 7-6 1.8 and 0-0 p.p.m., respectively. TABLE V EFFECTS F PHOSPHORIC ACID AND SODIUM CHLORIDE ON UREA 3-minute permanganate value r A \ in presence of Amount of 300 mg of nitrite-N in absence in presence of urea and 3 g present, of urea, 300 mg of of sodium mg p.p.m. urea, p.p.m. chloride,* p.p.m. Samples acidi ed with sulphuric acid-- 1 11.2 3.5 2 22.5 7-2 3 34.0 9.8 4 44.9 14.7 5 55.6 17 6 Samples acidified with phosphoric acid 1 11.0 9.1 2 22.4 17.6 3 34.0 25.8 4 44.8 32.1 5 55.4 45 2 8.3 16.8 26.2 33.2 45.4 Similar results were obtained in presence of 1 and 2 g amounts of sodium chloride. DISCUSSION F RESULTS The results indicate that it is preferable to use sulphamic acid for destroying nitrite in .waters and sewage effluents in the determination of permanganate values. In comparison with urea, a much smaller amount of sulphamic acid is needed and destruction of nitrite is more rapid, the reaction of urea being even slower when the samples are acidified with phosphoric acid. The slowness of the action of urea, even in large amounts, on nitrite added to distilled water can be seen from the results on p. 732 and in Table I, e.g. destruction of 2 mg of nitrite-N when treated with about four times the theoretical amount of urea was not complete after 1 hour, and for the complete destruction of 5 mg of nitrite-N in 3 to 5 minutes, the amount of urea required is about ninety-three times the theoretical amount. Under similar conditions, the theoretical amount of sulphamic acid was sufficient for the total destruction    P  u   b   l   i  s   h  e   d  o  n   0   1   J  a  n  u  a  r  y   1   9   5   9 .   D  o  w  n   l  o  a   d  e   d   b  y   N  o  r   t   h  e  a  s   t  e  r  n   U  n   i  v  e  r  s   i   t  y  o  n   2   6   /   1   0   /   2   0   1   4   1   6  :   4   4  :   3   4 . View Article Online
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