isonitrosoacetone and 2% sodium bicarbonate. These results are shown in Table I. Quantitative estimation studies were made on a number of compounds by the procedure described above. Sarin and D F P were diluted in dry 2-propanol; TEPP and benzenesulfonyl chloride in benzene; and phthalic anhydride in acetone. 2-Propanol was added to the aqueous reagent system to ensure homogeneity whenever needed. Calibration curves were prepared for each of these compounds. In all cases a straight line plot was obtained for abForbance versus concentration. Known mixtures of these compounds and their most common hydrolysis prod-
ucts were prepared and analyzed using the diisonitrosoacetone method. The impurities caused no interference, and quantitative results could be obtained. These results are shown in Table 11. ACKNOWLEDGMENT
The authors gratefully acknowledge the technical assistance given by James E. Kearnan in connection with some of t,he experiments reported here.
Rueggeberg, W. H. C., ANAL. CHEM.29. 278 (1957). Gehauf, B.,’ Goldenson; J., Zbid., 29, 276 (1957).
Jandorf, B. J., J . Am. Chem. SOC. 78, 3686 (1956).
Koessler, K., Hanke, M., Zbid., 40, 1717 (1918).
Kramer. D. K.. Chemical Warfare Laboratories, Army Chemical Center, Md., unpublished data. Marsh, D. J., h’eale, E., Chem. &. Znd. ( L o n d o n ) 1956, 494.
Pechmann, H., Wehsarg, K., Ber.
19,
2465 (1886).
Welcher, F.,,J., “Organic Analytical Reagents, Vol. III, p. 277, Van Nostrand, New York, 1947.
LITERATURE CITED
( 1 ) Gehauf, B., Epstein, J., Wilson, G. B.,
Witten, B., Sass, S., Bauer, V. E.,
RECEIVED for review January 12, 1957. Accepted April 26, 1957.
Ultramicrodetermination of Sulfides in Air MORRIS B. JACOBS, M. M. BRAVERMAN, and SEYMOUR HOCHHEISER Bureau of laboratory, Department o f Air Pollution Control, City of New York, New York 35, N. Y.
b Hydrogen sulfide and other sulfides can be determined in the part per billion range in air if the air is bubbled through an absorption mixture of an alkaline suspension of cadmium hydroxide contained in a GreenburgSmith impinger. Rates as high as 1 cubic foot per minute can be used, or 0.1 cubic foot per minute with a midget impinger. The concentration of the trapped sulfides is then estimated by the methylene blue method. Procedures for use both in the laboratory and in the field are detailed.
H
YDROGEN SULFIDE may
be an urban as well as an industrial air pollutant. The methods customarily used for industrial-hygiene purposes are designed for the micro range and, therefore, are not suitable for the determination of hydrogen sulfide in concentrations of the order of parts per billion. Various methods of determining micro quantities of gaseous hydrogen sulfide and hydrogen sulfide evolved from sulfur and wlfides are detailed in the literature. The cadmium sulfide method of Gardner, Howell, and Jones (10) and Iloskowitz, Siegel, and Burke ( 1 7 ) , in IT hich a weakly acid or ammoniacal solution of cadmium chloride is used as the trapping agent n-ith wbsequent iodometric titration, is considered the method of choice in industrial-hygiene work. Qiiitmann (19) describes a similar method in which cadmium acetate is used a s the absorbing solution
Heinemann and Rahn (12) absorbed gaseous hydrogen sulfide evolved from various sulfides in ammoniacal chloride. The trapped sulfide was then titrated with standard iodate-iodide solution and sodium thiosulfate solution. Johnson (14) evaluated the iodometric method and the colorimetric antimony tartrate method for sulfide in sewage. The method of the Association of Official Agricultural Chemists (5) includes an iodometric method for sulfides in mineral waters. Field and Oldach (9) absorbed hydrogen sulfide in caustic soda and determined it turbidimetrically as bismuth sulfide. Ethrington, Warren, and Marsden ( 8 ) absorbed hydrogen sulfide in an arsenite solution and determined the arsenious sulfide, suspended by means of a protective colloid, colorimetrically. hlention should also be made of the nitroprusside method of Smirnov (61) and of Bell and Hall (6), in which the air or gas stream containing the sulfide is passed through a 1% solution of sodium nitroprusside containing some ammonium chloride. The color produced is then evaluated colorimetrically. None of the aforementioned methods, which are detailed by Jacobs ( I S ) , are as sensitive as that in which methylene blue is formed from the sulfide being determined. This method was studied by Mecklenburg and Rosenkranzer (16) as early as 1914. Alm? ( 6 ) , and subsequently Sheppard and devised variations ( I S ) . Hudson (%I), Pomeroy ( 1 8 ) applied the method to sewage analysis and this work subse-
quently became the standard colorimetric procedure in the methods of the American Public Health Association (3). Later Budd and Bewick ( 7 ) absorbed hydrogen sulfide in zinc acetate solution and determined it colorimetrically as methylene blue. Members of the staff of the Los Angeles Air Pollution District (1) applied this variation to air analysis using a midget impinger. A tentative method has been recommended (4) for determining sulfides in industrial waste mater. hlarbach and Doty (15) also trapped hydrogen sulfide in an alkaline suspension of cadmium hydroxide and determined the sulfide colorimetrically as methylene blue, but modified the method significantly by protecting the absorbed sulfide from oxidation by air. As none of these methods was suitable for determining hydrogen sulfide and other sulfides in the part per billion range, the following method was devised. PREVENTION OF SULFIDE OXIDATION
One of the difficulties encountered in the development of this method was the oxidation of sulfides by the relatively large volume of air sampled a t 1 cubic foot per minute. Preliminary experiments were designed to evaluate the various absorbing solutions or mixtures to find one in which sulfide oxidation was prevented. Preliminary Experiments. REAHydrogen sulfide stock solu-
GEYTS.
VOL. 29, NO. 9, SEPTEMBER 1957
1349
t,ion. .. > -1 - ml. = 100 Y hvdrozen sulfide.
Dissolve 0.71 g r a m ' o f - s o d i k sulfide, N&S.SH,O, in 1 liter of water. Standardize and adjust in the usual manner with standard iodine and thiosulfate solutions. Hydrogen sulfide test solution, 1 ml. = 1 Y of hvdroeen sulfide. Dilute 10 ml. of'stock"so1uiion to 1liter. Cadmium hydroxide absorption mixture. Dissolve 4.3 grams of cadmium sulfate, 3CdSO4.8H,0, in water. Add 0.3 gram of sodium hydroxide, dissolved in water, and dilute to 1 liter. Mix well before using. Zinc acetate absorption solution. Dissolve 20 grams of zinc acetate dihydrate and 10 grams of sodium acetate trihydrate in water and dilute to 1liter. Ammoniacal cadmium chloride solution. Dissolve 20 grams of cadmium chloride dihydrate in 400 ml. of ammonium hydroxide solution and dilute to 1 liter with water. PRocEnuRE. Air, freed from sulfides by passing it through an alkaline cadmium hydroxide solution, was aspirated through 50 ml. of each absorption solution described above a t 1 cubic foot per minute for 30 minutes. Various amounts of hydrogen sulfide, rauging from 1to 5 y , were previously added to a given absorption medium. RESULTS. The experiments were run with the aid of Greenburg-Smith impingers. The amount of hydrogen sulfide recovered, which is indicative of the efficiency of the absorbing reagent in preventing air oxidation, mas determined by the methylene blue method (described below). I n Table I the recoveries obtained with alkaline cadmium hydroxide solution are given.
Table I. Recovery of Hydrogen Sulfide with Alkaline Cadmium Hydroxide Hydrogen Sulfide, y Added Recovered 1.0
3.0 5.0
yo Recoverya
0.9 2.8 4.8
90 93 96
"Average of 30 experiments a t each concentration.
When ainr aeetat,e solution or amobtained under the conditions described ESTABLISHMENT OF TRAPPING EFFICIENCY
Although trapping efficiency at lower rates has been definitely established by various investigators, it was felt necessary to establish the efficiency of. cadmium hydroxide a t the high rate of sampling (1 cubic foot per minute)
1350
ANALYTICAL CHEMISTRY
Figure 1.
Hydrogen sulfide generator and train
used in this method. However, the usual method of testing efficiencies by making up large volumes of known gas mixtures was considered inapplicable in this case because the small amount of hydrogen sulfide would probably be quickly oxidized by the large volume of air, and thus yield low results. I n the test method finally adopted, the train (Figure 1) consisted of an impinger containing 50 ml. of alkaline cadmium hydroxide mixture to act as a wash reagent to remove any hydrogen sulfide or sulfides from the incoming air stream, a hydrogen sulfide generator, two impingers containing 50 ml. of alkaline cadmium hydroxide mixture, a flowmeter, and a vacuum pump. The vacuum pump is set to operate a t a rate of 1 cubic foot per minute, and then a small amount of sodium sulfide solution is allowed to drip and mix with the acid in the generator. The hydrogen sulfide generated is swept into the first impinger and the operation is continued for 30 minutes. At the end of that time both absorption mixtures are tested for the presence of hydrogen sulfide by the methylene blue method subsequently described. The experiment was repeated many times and for different amounts of hydrogen sulfide varying from 1 to 30 p.p.b. in the first impinger. At no time was the amount of hydrogen sulfide detected in the second impinger greater than 10% of that in the first impinger. It was felt, therefore, that proof of trapping efficiency of a high order was established. METHOD
After a procedure was established to prevent oxidation of the trapped sul-
fide, the methylene blue method was modified as follows. Reagents. All reagents should be refrigerated for optimum results. Amine-sulfuric acid stock solution. .4dd 50 ml. of concentrated sulfuric acid to 30 ml. of water and cool. Add 12 grams of N,N-dimethyl-p-phenylenediamine. Stir until solution is complete. Amine-sulfuric acid test solution. Dilute 25 ml. of stock solution to 1 liter iyith 1 to I sulfuric acid. Ferric chloride solution. Dissolve 100 grams of ferric chloride hexahydrate in enoueh water to make 100 ml. of solution: Sbsorotion mixture. Dissolve 4.3 grams df cadmium sulfate, 3CdSO4 8H,O, in water. Dissolve 0.3 gram of sodium hydroxide in water. Add to the ca.dmium solution and dilute to 1 liter. Stir well before using. Procedure. For low concentrations of hydrogen sulfide (less than 20 p.p.b.). either a colorimetric or spectrophotometric variation may be used. For the colorimetric method, place 50 ml. of absorption mixture in a large impinger and pass air through the apparatus for 30 minutes at the rate of 1 cubic foot per minute. Add 0.6 ml. of amine test solution and 1 drop of ferric chloride solution to the impinger and agitate after each addition. Transfer to a 50-ml. volumetric flask, make up to volume, and allow to stand for 30 minutes. T o 45 ml. of absorption mixture in a 50-ml. volumetric flask, add amine test reagent and ferric chloride solution, agitate after each. addition, make up to volume, let stand for 30 minutes, and use as a reference in setting the apparatus to zero. Read the absorbance of the sample and determine hydrogen sulfide concentration from the x-orking curve.
T o calculate hydrogen sulfide, use the following equation. H ~ S j
=
y HzS X 719 volume in liters
This calculation is set empirically a t 25’ C. and 760 mm., using the factor 719 ( I S , appendix). T o correct for other conditions of temperature and pressure, the usual gas law equations are used. For the spectrophotometric method, a 25-nil. alicluot is taken of both the final sample mixture and the reference blank. The final calculation is multiplied by 2. The readings should be made at 670 mp. I n both of the above methods, if the concentration of hydrogen sulfide is above the working curve, the solution is diluted to the appropriate range. An analogous dilution must also be performed on the reference reagent blank; the apparatus should be set a t zero again with this solution before measuring the absorbance of the diluted sample. For higher concentrations of hydrogen sulfide (20 p.p.b. and above). the midget impinger has been used successfully. Place 10 ml. of absorption mixture in the midget impinger and aspirate a t 0.1 cubic foot per minute through the mixture for about 15 minutes. (The midget impinger apparatus is especially useful in field work.) Add 0.6 ml. of amine test solution and 1 drop of ferric chloride solution, agitate after each addition, and transfer to a 25-m1. volumetric flask for spectrophotometric determination or to a 50-ml. volumetric flask for colorimetric determination. Dilute to the mark and allow to stand for 30 minutes. Repeat the same procedure (nithout aspiration) for the reference reagent blank, set the apparatus a t zero, and read the absorbance of the sample. Refer to the working curves for amount of hydrogen sulfide present and calculate as before. Preparation of Standard Curves. Because two methods of estimating the amount of methylene blue formed were used, two standard curves were prepared-one with the Klett-Summerson colorimeter and one n-ith the Coleman spectrophotometer. COLORIMETRIC. Add 0, 1, 3, 5 , 7 , and 9 y of hydrogen sulfide separately to 50-ml. volumetric flasks containing 4
