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Vol. 13, No. 9
INDUSTRIAL AND ENGINEERING CHEMISTRY
tion of the alcoholic solutions by the potentiometric method
of Tamele and Ryland (6). Alkaline solutions of mercaptans are very readily oxidized by air. Errors greater than those inherent in the method may arise from undue exposure of samples to atmospheric oxygen. B y careful manipulation as described, the errors can be kept within reasonable limits without resorting to air exclusions.
PRECISION
Sample No.
TABLEV. OF T H E METHOD Sample 0.01 N AgNO: Sample No. Sample 0.01 N A g NO8 Grams M L / 6 grams Grama M1./6 grama 5.70 6.62 9 5.18 6.56 5.00 6.61 4.96 10 6.52 5.40 6.68 11 5.38 6.65 5.41 6.68 12 5.68 6.57 5.79 6.59 13 5.00 6.63 4.73
5.32
Precision The precision of the results is difficult to estimate accurately, owing to the above-mentioned instability of dilute mercaptan solutions. Xithout taking any special precautions it was found that the standard deviation (root mean square deviation) as determined from fifteen titrations of a sample of %-butyl mercaptan with 0.01 N aqueous silver nitrate in 1.0 N sodium hydroxide and 0.05 N ammonium hydroxide was within 0.05 ml. It is believed that this figure is affected somewhat by oxidation of the standard mercaptan solution, as the results (Table V) show a slight trend to lower values as successive samples were withdrawn.
5.16
6.61 6.69 6.52
14
15
5.14 5.54
6.63 6.57
Literature Cited (1) Border, L. E., Oil Gas J.,39, 55 (1940). (2) Ellis, C., “Chemistry of Petroleum Derivatives”, p. 1157, New York, Reinhold Publishing Corp., 1937. (3) Kolthoff, I. M., and Lingane, J. J., J . Am. Chem. SOC.,58, 1528 (1936). (4) LaCroix, H. N., and Coulthurst, L. J., Refiner Natural Gasoline Mfr., 18, 90 (1939). (5) Robinson, P. M., Natl. Petroleum News, 32, No. 34, R-298 (1940) (6) Tamele, M. W., and Ryland, L. B., IND. ENG.CHEW.,ANAL.ED.. 8, 16 (1936). (7) Yabroff, D. L., IND. EXG.CHEM.,32, 257 (1940).
Sulfamic Acid Modification of the Winkler Method for Dissolved Oxygen STUART COHEN AND C. C. RUCHHOFT Stream Pollution Investigations Station, Cincinnati, Ohio
CCORDING to Gordon and Cupery (3, 4) the recent development of a practical process for commercial scale manufacture of sulfamic acid (SH2HS08)has aroused much interest in this chemical. It has long been known that nitrites react rapidly x i t h sulfamic acid to yield nitrogen and sulfuric acid. A novel industrial application of this reaction is the removal of excess nitrite following diazotization-for example, in dye and lake manufacture. Sulfamic acid is two to six times more effective on a weight basis than urea, which is commonly used for such purposes. This ability to react Tyith and destroy nitrites led to the authors’ belief that sulfamic acid might be substituted for sodium azide as a preliminary treatment for removal of nitrites in the Winkler method for dissolved oxygen.
A
Properties of Sulfamic Acid Dry sulfamic acid is a stable, nonhygroscopic, odorless, colorless, crystalline product. It is moderately soluble in water, its solubility varying from 14.68 grams at 0” to 47.08 grams at 80’ C. per 100 grams of water. Its solubility in water is decreased by presence of sulfuric acid or sodium sulfate and becomes negligible in 70 t o 100 per cent suIfuric acid. Sulfamic acid is highly ionized in aqueous solution. The strength of the acid is indicated by its reaction with basic oxides, hydroxides, and carbonates to form sulfamates. These salts are practically all soluble in water. Sulfamic acid is essentially stable in water solution at ordinary temperature. At elevated temperatures the acid is slowly hydrolyzed t o ammonium acid sulfate (3). Salts of sulfamic acid are stable in neutral or alkaline solution, and such solutions may be evaporated to dryness on the steam bath without hydrolysis of the amide group. In cold solution, chlorine, bromine, and chlorates oxidize sulfamic acid to sulfuric acid. Potassium permanganate, chromic
acid, and ferric chloride exert no oxidizing action. Sitric acid yields nitrous oxide and sulfuric acid. Nitrites react rapidly with sulfamic acid, liberating nitrogen and forming sulfuric acid. This reaction may be utilized for the analytical determination of nitrites or of sulfamic acid (2, 6). The properties indicate that sulfamic acid might prove a desirable agent for the destruction of nitrites in the determination of dissolved oxygen and biochemical oxygen demand. It has recently been shown that sodium azide is very satisfactory for this purpose in stream-pollution and sewage studies (1, 6, 7 ) . Sulfamic acid is theoretically only t x o thirds as effective as sodium azide on a weight basis, as the following equations show:
+
+ + + +
SHzSOzOH (97) HSOs -L HzSOI Nz HgO NaSa (65) HZSO, HNOZ + NZ H20 920 SaHSO,
+
+
+
However, sulfamic acid possesses the advantages of cheapness, availability, nonpoisonous nature, stability in sulfuric acid, and the formation of soluble sulfamates. Consequently, a comparative study of sulfamic acid and sodium azide for nitrite destruction in the dissolved oxygen determination i n s undertaken.
Experimental A comparative study of the reaction times of 2 per cent sodium azide and 4 per cent sulfamic acid solutions showed that the reaction between sodium azide and nitrites in acid solution proceeded more rapidly than the corresponding reaction with sulfamic acid. However, the latter reaction was sufficiently rapid to justify further experimental work on the use of sulfamic acid as a nitrite-destroying reagent.
A N A L Y T I C A L EDITION
September 15, 1941
TABLE
I. COMPAR.4TIVE DISSOLVED OXYGEX DATA
DILCTESEFAGE, AND TREATMENT PLANT --Dissolved
++ +
Water 2 p. p. m. of nitrite N Water 4 p. p. m. of nitrite N Water 6 p. p. m. of nitrite N 10 per cent sewage 10 per cent sewage 5 p. p. m. of nitrite nitrogen Activated sludge effluent Activated sludge effluent 6 p. p. m. of nitrite nitrogen Trickling filter effluent Trickling filter effluent 5 p. p. m. of nitrite nitrogen
+
+ +
a
Azide modification P.p.m. 7.74 7.92 7.85 8.10 7.96
JTATER, EFFLUESTSaMPLEs OX
Oxygen'"Sulfamic acid modificaDeviation tion P,p.m. P,p.m. 7.84 0.10 7.92 0.00 7.89 0.04 8.17 0.07 8.04 0.08
8.96 8.78
8.98 8.88
0.02 0.10
7.96
8.03 7.86
0.07 0.02
7.84
Each value is mean of three determinations.
Tables of solubility of sulfamic acid (3) in varying concentrations of sulfuric acid show that a 20 per cent sulfuric acid solution will dissolve approximately 5 grams of sulfamic acid per 100 ml. of solution at 30" C. This being true, it should be possible t o add the sulfamic acid as a solution in dilute sulfuric acid in the preliminary treatment for nitrites, Accordingly, the sulfamic solutions used in all of the following experiments, unless otherwise stated, were prepared as follows:
623
sulfamic acid produced after the final acidification did not remove it in the presence of free iodine. It is possible to apply the sulfamic acid with the manganous sulfate solution and allow time for the nitrite removal reaction before the alkaline iodide reagent is added. This was tried, employing 2 ml. of a manganous sulfate solution (480 grams of manganous sulfate tetrahydrate and 40 grams of silfamic acid per liter) in a 300-ml. sample. The data obtained in the determination of dissolved oxygen by several procedures in the presence of nitrites and copper and nitrites and organic matter are given in Table 11. They indicate that all modifications tried were satisfactory in the presence of 100 p. p. m . of copper and 14.4 p. p. m. of nitrite nitrogen. I n the presence of large amounts of organic matter the nitrites were removed effectively by all modifications tried except C, employing the manganous sulfate-containing sulfamic acid. This procedure definitely fails to remove nitrites satisfactorily in the presence of peptone or glucose. Although the so-called short Kinkler technique was employed on these samples, the effect of oxidation of pepton? and glucose during alkalinization with the subsequent reduction in the dissolved oxygen by 0.30 to 0.41 p. p. m. from the initial values in the distilled water is indicated by all satisfactory nitrite-removing modifications.
Azide and Sulfamic Acid as Preservatives for Dissolved Oxygen Samples
I n field studies of sewage-treatment plants or polluted Four grams of sulfamic acid are dissolved in 50 ml. of distilled streams, i t is sometimes desirable or necessary to delay the water and 50 ml. of cold 40 per cent sulfuric acid are added. In determination of dissolved oxygen for several hours after the this manner very little heat is evolved, thus eliminating the possibility of hydrolysis of the amino group. The solution thus samples have been collected. To do this it is necessary to prepared is slightly turbid, but this is of no consequence. One inhibit biochemical oxidation, besides taking precautions to milliliter of this solution was used as preliminary treatment for prevent gain or loss of oxygen due to temperature changes. destruction of nitrites in a 300-ml. dissolved-oxygen sample It has been shown (6) that the sulfuric acid-sodium azide bottle. As applied, this quantity of sulfamic acid will destroy 19.3 p. p. m. of nitrite nitrogen and is ample for all samples treatment is more effective for preserving the initial dissolved likely to be encountered in water and selvage work. After addioxygen values than either sulfuric acid treatment alone or the tion of the reagent the bottle is stoppered and shaken and then application of the complete Kinkler procedure followed by the allowed to stand for 10 minutes. From this point on, the proiodine titration after the interval of storage. The efficacy of cedure is identical with that of the azide modification. Solutions of varying concentrations of nitrites in distilled the sulfamic acid treatment for dissolved-oxygen sample preswater were prepared containing from 2 t o 6 p. p. m. of nitrite nitrogen. Dissolved oxygen was then determined on this water bv the azide and sulfamic acid modifications. A similar comparison TABLE 11. COMPARATIVE DISSOLVED OXYGEXRESULTS was run on sewage dilutions, trickling filter effluent, and activated sludge effluent both alone (Obtained under adverse conditions with several azide and sulfamic acid modifications) and 11 ith addition of nitrites. Initial D. 0. in Enough nitrogen was liberated in the deConcentration of InterDisfering Substances Added tilled D. 0.Results Obtained with Each Modification struction of the higher concentrations of nitrites t o Distilled Water Water A B C D E to cause the manganese hydroxide floc to rise P. p. m. P . p . m . P . p , m . P . p . m . P.p.m. P,p.m. t o the top of the bottle. However, upon re100 p. p. m. of C u + + + 7.76 7.77 7.75 7.79 7.74 7.72 1 . 7 p. p. m. of nishaking the bottles in the course of dissolvedtrite N 100 p. p. m. of C U + f~ 7.76 oxygen determinations, the bubbles were 7.75 7.75 7.88 7.76 7.80 8.4 p. p. m. of nitrite N disengaged from the precipitate, which then 100 p. p. m. of C u + + + 7.15 7.14 7.12 7.25 7.24 7.15 14.4 p. p. m. of nitrite settled well. The results are given in Table I. N 1000 p. p. m. of glucose The deviations in the results obtained with 7.80 7.51 7.44 + 1.7 p. p. m. of ni- 7.79 7.52 7 . 3 2 these modifications vary between 0.02 and 0.10 trite K 1000 p. p. m. of glucose p. p. m. and are of the same order of magnitude +, 8.4 p. p. m. of ni- 7.79 7.61 7 . 4 2 10.65 7 . 5 2 7.41 trite X whether or not nitrite was added to the sam500 p. p. m. of peptone, 7.65 7.35 7.30 ... 7.28 7.25 ples. These data demonstrate the efficacy of no nitrite 500 p. p. m. of peptone 7.65 7.33 7.27 ... 7.30 7.31 the use of sulfamic acid in the dissolved-oxygen +. 4.8Yp. p. m. of nitrite i procedure. 500 p. p. m. of peptone ... 7.28 7.24 A series of experiments was carried out toward + 9.6 Np. p. m. of 7 . 6 5 7 . 2 9 7 . 2 4 nitrite the development of a shorter, simpler procedure 7.65 500 p. p. m. of peptone 7.30 7.25 ... 7.35 7.28 +, 14.4 p. p. m. of niemploying sulfamic acid. I t was found that trite N the addition of sulfamic acid along with the A = Sulfuric acid-sodium azide preliminary treatment. alkaline iodide reagent (like the azide in the B = Sulfamio acid reliminary treatment. C = Manganous suyfate-sulfamic acid preliminary treatment original Alsterberg procedure) was valueless, D = Alsterberg azide treatment. because the sodium sulfamate formed in alkaE = C and D combined. line solution does not remove nitrite and the
INDUSTRIAL AND ENGINEERING CHEMISTRY
624
!
/
x
20
//
x
I
DEVIATIONOF AZIDE D 0. RESULTS FROM
SULFAMICACID D 0 RESULTS
I
Ii
I
'?
'\ I
;3 0
,
-2%-
-.I 0 D~SSOLVEO OXYGEN
-
DEVIATION P.P.Y.
FIGCRE1. DISSOLVED OXYGEN TABLE111. DISSOLVED OXYGEN RESULTSON PRESERV-4TION TESTS
Initial 2-hour interval 4-hour interval 24-hour interval After 2 hours After 4 hours After 24 hours
Activated Sludge EWuent 10% Sewage (lOOYg\lSulfamic famic -4zide acid Azide acid 8.24 8.27 7.57 7.60 8.19 8.15 7.44 7.48 S,l5 8.02 7.33 7.32 7.03 7.07 7.12 7.11 Loas of Dissolved Oxygen 0.05 0.10 0.12 0.13 0.12 0.31 0.25 0.09 0.24 0.28 1.21 0.65 1.20 0.45 0.49
25% Sewage Sulfamic Azide acid 8.56 8.51 8.46 8.41 8.25 8.10 7.91 7.92 0.10 0.41 0.59
Trickling Filter Effluent ( 1 0 0 7 ) SUPfamic Azide acid 7.67 7.80 7.62 7.79 7.38 7.56 7.09 7.17 0.05 0.29 0.58
0.01 0.24 0.63
Vol. 13, No. 9
Cincinnati area, settled sewage, an experimental trickling filter effluent, and activated sludge effluent. I n all, a total of 652 duplicate samples was analyzed by the two procedures and the mean results obtained are shown in Table IV. The individual differences between the initial dissolved-oxygen results obtained by these two modifications upon all the samples mere tabulated and a frequency curve for these data is plotted in Figure 1. Positive differences signify that the azide value is greater, and negative differences that the sulfamic acid result is greater. Similar plots showing the frequency distribution of the differences in the final dissolvedoxygen results and the oxygen-depletion results are shown on higher levels in the same figure. All these curves indicate practically normal probability distribution. There may be a slight tendency for a larger frequency of negative differences in the initial dissolved-oxygen data, indicating slightly higher results for the sulfamic acid modification. This tendency is not apparent in the final dissolved-oxygen data. The standard deviations obtained in each of the above sample groups and for all of the samples combined are given in Table V and are in general in very close agreement. There is, however, a slightly greater variation between the initial and final dissolved-oxygen deviations and between the initial dissolvedoxygen and oxygen-depletion deviations than between the final dissolved-oxygen and oxygen-depletion deviations. This is probably due to the added factor of bacterial action in oxygen consumption during the 5-day incubation period. The sulfamic acid method is not recommended when the sample contains interfering substances such as suspensions of river mud, quantities of ferrous and ferric iron (50 p. p. m. or less of ferric iron do not interfere), sulfite wastes, or other oxidizing and reducing agents.
Summary ervation was, therefore, compared to the sulfuric acid-sodium A modified Winkler procedure, employing a solution of 4 azide treatment. The material selected for this test was a 25 per cent sulfamic acid in 20 per cent sulfuric acid as a preper cent mixture of sewage with dilution water. This constitutes a more stringent test than is necessary for stream-pollution work. TABLEIV. MEAN COMPARATIVE DISSOLVED OXYGEN AND OXYGEN DEPLETION DATA Twenty-four bottles were put up, twelve of which were dosed with the azide reagents and (Obtained with azide and sulfamic acid modifications of Winkler method) twelve with the sulfamic acid rea ent. Of these, -Dissolved OxygenOxygen Deplesix were used for initial dissolve8 oxygen, three Initial Final tion in 5 Days0 with the sulfamic acid and three with the azide SulSul: SulNo. of famic famic famic treatment. The remainder were allowed to stand Samples Azide acid Azide acid Azide acid at room temperatures and dissolved-oxygen deterCommodlfimodlfi- modifi- modifimodifimod& minations were made on these after intervals Samples pared cation cation cation cation cation cation of 2, 4, and 24 hours. Similar tests were also made P.p.m. P.p.m. P.p.m. P.p.m. P.p.m. P.p.m. on trickling filter and activated sludge effluents. OhioRivef and 322 8.80 8.80 6.53 6.54 2.25 2.26 These results are shown in Table 111, all titration tributaries figures being the average of three determinations. Raw l,.t
