distillate materials and where elemental sulfur or highly volatile sulfur compounds are present. The carbon dioxide-oxygen combustion with the apparatus described above is recommended for precise sulfur determinations, and for analysis of heavy distillate materials. However, for the majority of routine analyses, where ASTM standards of accuracy are sufficient, the apparatus and method previously described (6), burning 0.10 to 0.20 ml. of gasoline in laboratory air, provides a more satisfactory procedure. Using this method, with two apparatus set ups. one operator can perform duplicate analyses of a sample within 12 to 15 minutes, and can average six to eight analyses per hour, with better assurance of accuracy than with the ASThl method. When halogens or other acid-forming substances are suspected in the sample, the true sulfur content may be determined, after alkalimetric titration of the absorbent, by a barium chloride turbidity method, which is sufficiently accurate for sulfur contents below 0.05%. For best accuracy a t higher sulfur contents, a gravimetric sulfate determination should be made, burning 2 to 3 ml. of sample in a larger capacity thread wick lamp.
Most heavy distillate materials may be burned directly without previous dilution in a modified thread wick lamp, thus greatly facilitating analyses. As only a few drops of material are sufficient for a series of analyses, this method is valuable \\-here sample quantities may be limited. ACKNOWLEDGMENT
The author would like to thank the management of Fletcher Oil Co. for permission to publish this paper, and to thank J. B. Gregory of Union Oil Co., Brea Research Center, for supplying the sample of pure thiophene. He also wishes to thank the following persons for providing some of the analytical data presented in this paper: C. H. Lynam, 11.11. Rhodes, and H. E. St. George, Standard Oil Co.; T. D. Bigger, General Petroleum Corp.; and J. B. Gregory, Union Oil Co. REFERENCES
(1) Altieri, V. J., “Gas Chemists’ Book of Standards for L$ht Oils and Light Oil Products, 1st ed., .pp. 119-24, American Gas Association, New York, 1943. (2) Am. Soc. Testing Materials, Method
D 1266-53T “Standards for Petrq; leum Products and Lubricants, 1953. (3) Am. Soc. Testing Materials “Standards for Petroleum Products & Lubricants,’’ p. 1337, Kovember 1949. ( 4 ) Ball, J. S., U. S. Bur. Mines, Rept. Invest. 3591 (1941). (5) Battles, IT.R., Petroleum Engr. 25, No. 12, C-47 (Sovember 1953). (6) Ibid., 27, C-41 (July 1955). ( 7 ) Edgar, G., Callingaert, G., IND.EXG. CHEM., A N A L . ED., 2, 104 (1930). (8) Fritz, J. S., Yamamura, S. S., BXAL. CHEW27, 1461 (1955). ( 9 ) Granatelli, L., Ibid., 27, 266 (1955). (10) Hudp, J. A , , hlair, R. D., Ibid., 27, 802 (1955). (11) Lane, W.H., Ibid., 20, 1045 (1048). (12) Liebhafsky, H. A., Winslow, E. H., I b i d . , 28, 583 (1956). (13) Quiram, E. R., Ibid., 27, 274 (1955). (14) Scott, S. D., “Standard Methods of Chemical Analysis,” 5th ed., 203, Van Nostrand, New Tor{; 1R X R
(15) I b L d r p : 2092. (16) Shell Oil Co., Method Series, Method S o . 303,, Shell Development Co., Emeryville, Calif. 117) Universal Oil Products Co.. “Laboratory Test Method for Sulfur and Sulfur Derivatives of Hydrocarbons in Petroleum Distillates,” A-119-40. RECEIVEDfor review October 20. 1056. -4rcepted April 23, 1957.
Colorimetric Determination of Certain Organophosphorus Compounds and Acylating Agents Use of Diisonitrosoacetone Reagent SAMUEL SASS, WILLIAM D. LUDEMANN, BENJAMIN WITTEN, VALENTINE FISCHER, ANTHONY J. SISTI1, and JACOB Chemical Research Division, Chemical Warfare laboratories, Army Chemical Center, Md.
A new reagent, diisonitrosoacetone, has been found for the detection and quantitative estimation of small quantities of organophosphorus halides, acid anhydrides, and acylating agents. Sensitivities of l y or lower can b e obtained depending on the final dilution of the color development medium. Measurements of the color are made on a spectrophotometer or colorimeter either at 486 or 580 mp.
R
has shown that organophosphorus halides, pyrophosphates, and acylating compounds can be estimated in small quantities
using a peroxide reaction with certain amines ( 1 , 2, 6). Work done in these laboratories by Jandorf (3) with hydroxylamines and by Kramer ( 5 ) m-ith ketoximes showed that these compounds reacted rapidly with diisopropyl phosphorofluoridate (DFP) and Sarin (isopropyl methylphosphonofluoridate) to produce acid.
An evtension of the titration study by the authors led to the discovery that diisonitrosoacetone (1,3-dihydroxiniino2-propanone) reacts rapidly Kith these organophosphorus halides and acylating agents to produce not only acid but also an intense magenta color. I t is believed that the reaction is of the following type:
1+
ECEKT LITERATURE
Present address, University of Michigan, Ann Arbor, Mich. 1
1346
ANALYTICAL CHEMISTRY
I. MILLER
No
CHIC + HCX
\OH
HCl
+ unidentified colored product(s)
A reagent that could be used to estimate small quantities of toxic organophosphorus compounds directly was of interest because it could be employed in a single solution reagent system. Conditions were studied for obtaining optimum results as a quantitative detection system and a n attempt was made to type the nature of compounds that could be determined with this technique. EXPERIMENTAL
Preparation of Diisonitrosoacetone and Its Monobasic Salts. Diisonitrosoacetone H I
H I
c-c-c II ti I1
HOh
0 NOH
n a s prepared by the method of Pechmann and Wehsarg ('7) and Koessler and Hanke (4) as a white crystalline solid. The product was purified in these laboratories by recrystallizing three times from water at 60" to 65" C. with decolorizing charcoal. The crystals, dried over phosphorus pentoxide in vacuo, melted a t 136" C. with decomposition when heated in a capillary tube inserted in a n oil bath preheated to 130" C. R~orosoDIuhrSALT. Sodium and absolute ethyl alcohol (50 ml. of ethyl alcohol per gram of sodium) were added to a three-necked flask fitted for anhydrous conditions. After the reaction of the sodium was complete, an equivalent quantity of diisonitrosoacetone in absolute ethyl alcohol ( 3 grams of compound per 50 ml. of solvent) was added to the stirred reaction mixture. The orange to yellow product which precipitated almost immediately was filtered and dried in vacuo over phosphorus pentoxide. This salt was also prepared in an alcohol-water medium using sodium hydroxide. A I o ~ o a a r ~SALTS. s~ iln equivalent quantity of organic base in methanol ( 5 ml. of methanol per 2 grams of diisonitrosoacetone) was added to diisonitrosoacetone ( 2 grams of compound per 20 ml. of solvent) n i t h rapid stirring. The yellow precipitate which formed almost immediately was collected and recrystallized tviice from ethyl acetate. Salts surh as monoguanidine, monodibutylamine, and the like can be prepared by this method. METHOD
Reagents. Diisonitrosoacetone, 0.4% solution in water. 2-Propanol, c.P., 99%, dried and distilled over aluminum isopropoxide. Buffer solution, pH 8.4. prepared by adding 17 ml. of 0 . 5 M aqueous sodium hydroxide to 500 ml. of 0.1M boric acid. A 27, solution of sodium bicarbonate, freshly prepared, serves equally well as a buffer. When the monobasic salts of the reagent are used, a concentration equiva-
lent to the 0.4% solution of diisonitrosoacetone (free acid basis) is maintained. This precludes the necessity for addition of buffer solution. Apparatus. Absorbance measurements were made on a Cary recording spectrophotometer and on a Beckman Model D U spectrophotometer over a range of 400 t o 700 mfi. Colorimetric measurements were made on a KletbSummerson colorimeter using filter KO. 50 (470 to 530 mp) and on a Beckman Model B spectrophotometer a t a wave length of 486 mp. 1Ieasurements can also be made a t 580 mp. The spectral characteristics, w t h concentrations adjusted to fit one graph, are shon-n in Figure 1. Procedure. Pipet 1 ml. of each sample concentration of Sarin- or DFP-type compound into a colorimeter tube such t h a t quantities in the range of 5 to 60 y are represented. Add 1 ml. of diisonitrosoacetone reagent and mix. Add 3 ml. of buffer solution, stir, and allow to stand for 7 minutes. RIeasure the color developed in a colorimeter a t 486 or 580 m l . Preparation of Standards. Prepare standards of compounds of interest in appropriate solvents such t h a t 1-ml. aliquots will represent from 5 to 60 y of material.
Table
I.
Compounds Tested with Diisonitrosoacetone Sensitivity, Color per 4 M1 Magenta 1 Tabun Magenta 1 Sarin 1 Magenta DFP 2 Magenta TEPP Methyl phospho2 Magenta nodichloridate Phosphorus 2 Magenta oxychloride Phthalic anhydride Magenta 10 S-BromoMagenta 1 fiuccinimide Benzenesulfonyl 2 Magenta chloride 2 Magenta Benzoyl chloride 15 Magenta" Paraoxon 25 Magenta" Parathion Methylphosphonic .. No color acid Diisopropyl hydro.. N o color gen phosphite Diisopropyl methyl.. phosphonate No color Isopropyl methyl.. phosphonic acid No color Diethylphosphoric .. acid No color Diethyl phthalate, .. No color phthalic acid Chloroacetophenone No color No color Phenacyl bromide No color Sodium cyanide
The 0.47, solution of diisonitrosoacetone is generally stable for several days \$hen protected from daylight. A combined solution of buffer and reagent can be used if prepared daily. I n the case of the more readily hydrolyzable compounds, such as benzenesulfonyl chloride, tetraethyl pyrophosphate (TEPP), and pentavalent phosphorus chlorides, it is essential that the compounds be dissolved in anhydrous, nonalcoholic solvents (benzene or ethers) for sampling. For best results aliquots of these compounds are added to the buffered diisonitrosoacetone solution m-ith stirring. *4cetone or alcohol can be used to make the reagent-compound solution homogeneous. Sarin, Tabun (ethyl dimethylphosphoramidocyanidate), D F P , and similar compounds can be treated in the same manner if desired.
a Paraoxon and parathion required a longer period for color development; parathion rrae the slower of the two.
Thr buffered diisonitrosoacetone, hen subjected to ultraviolet irradiation. develops a color similar to that ohtained for the compounds discuwed. Exposure T O direct sunlight during anal\-pis should, therefore, be avoided. I\
DISCUSSION
Conditions for Optimum Sensitivity. Studies made at p H from 5.0 t o 12.0 indicated that, for phosphorus compounds such as TEPP, Sarin, and DFP (Table I). and lor acylating
Figure 1 . Spectral characteristics 1. 2.
3. 4.
5.
N-Bromosuccinimide and diisonitrosoacetone Bromine and diisonitroroacetone Sarin and diisonitroroacetone Monosodium salt of diisanitrosoacetone irradiated at 2537 A. Phthalic anhydride and diironitrosoacetone I
400
500
I
\
600
WAVE LENGTH, h(jl
VOL. 2 9 ,
NO. 9 ,
SEPTEMBER 1957
1347
Table II.
Analytical Recovery of Compounds from Most Common Impurities
Compound
Compound Found, Added, y
Impurity
Sarin
Methylphosphonofluoridic acid, 150 y
Isopropyl methylphosphonic acid, 200 Diisopropyl methylphosphonate, 100 y
TEPP Diethylphosphoric acid, 200 Y
35
34
160
162
76
76
45 52 122
46 53 120
75 130 80 135 90 155 78 145 55 125
Triethyl phosphate, 200 y Benzenesulfonyl chloride Benzenesulfonic acid, 500 y Benzenesulfonic acid, 2000 y Phthalic anhydride Diethyl phthalate, 500 y Phthalic acid, 500 y
y
75 132 78 132
88
157 78 143 55 127
".a&
40
60
80
100
120
140
160
180
MOLES OF DIISONITROSOACETONE /MOLE OF SARIN
(486 M/J)
Figure 2.
Effect of reagent concentration on sensitivity
agents such as benzoyl chloride and benzenesulfonyl chloride, the optimum pH for color development-i.e., for best sensitivity and stability-was approximately 8.5. At a pH higher than 8.5 the color formed more rapidly but. persisted for a shorter period of time. Below pH 8.3 the color developed more slowly, never reaching the maximum sensitivity obtained a t the optimum pH. Between pH 8.3 and 8.5 the maximum sensitivity of color was reached within 7 minutes and this color a t peak sensitivity persisted for a t least 10 minutes. The optimum concentration of diisonitrosoacetone to compound to be determined was found to be in the range of 95 moles to 1 mole a t pH 8.5. Above or below this range of relative reagent to compound concentration, a definite gradual decrease in sensitivity was noted. These results are shown in Figure 2. 1348
ANALYTICAL CHEMISTRY
A t pH 8.3 to 8.6, final total volumes (reagent, solvent, and compound being tested) were prepared from 10 ml. to 1 ml. It was found that the sensitivities versus absorbance followed a linear 10 ml. of solution conpattern-Le., taining 10 y of Sarin showed the same approximate sensitivity as 1 ml. of solution containing 1 y of Sarin. Salts of Diisonitrosoacetone. The salts of diisonitrosoacetone were also studied. The mono salts of ammonia, sodium, cyclohexylamine, dibutylamine, and guanidine, among others, were tested by comparison with diisonitrosoacetone buffered a t pH 8.5. The sensitivities obtained in all cases were similar to those found for the buffered reagent. Of all the salts tested, the dibutylamine and guanidine salts proved to be the most stable under storage conditions. These two salts were stable for periods of greater than 2 weeks a t 50" C. without loss in
sensitivity. When kept in the dark at ambient temperature, no loss in sensitivity was noted after 1 year. A t 50" C. diisonitrosoacetone and its mono salts of sodium and ammonia decomposed within 24 hours. The cyclohexylamine salt was of intermediate stability. When used as the diisonitrosoacetone equivalent (95 moles to 1 mole of compound to be tested), any of the above-mentioned salts could be used for the quantitative detection of the compounds described in this report. These salts in their proper concentration could be used in lieu of the buffer solution described in the procedure. Characteristics of Reagent. Diisonitrosoacetone, as prepared by the procedures cited previously (4, 8), is believed t o be a mixture of several isomers. One apparent isomer, which is extractable from an aqueous solution by a minimum quantity of ether, is insensitive to ultraviolet irradiation in a basic aqueous solution. As mentioned above, the normal reagent solution is sensitive to ultraviolet irradiation in the presence of base. However, both the ether-extracted material and the normal reagent participate equally well in the reaction with the phosphorus compounds and acylating agents tested. The method for the separation of an isomer from ether is as follows. Dissolve approximately 50 grams of diisonitrosoacetone in a minimum quantity of warm water (about 50" C.). Carefully extract the aqueous solution two times, each with 200 ml. of ether. Combine the ether extracts and dry over anhydrous sodium sulfate. Add 60 ml. of petroleum ether (30" to 60' C.) and collect the colorless solid precipitate by filtration. The white crystalline product from this separation, which weighs approximately 3.5 grams, melts a t 141" C. with decomposition. (Analysis calculated for C3H4N203: C, 31.1; H, 3.4; K, 24.1; found: C, 31.1; H, 3.4; N, 24.4.) Specificity of Method. Tests were made t o determine the specificity of the diisonitrosoacetone reaction. Although Welcher (8) states that iron(I1) has been determined colorimetrically (blue color) using this reagent, the addition of a sequestering agent (Sequesterene, disodium salt) precludes any interference from iron(I1) or other cations such as copper(I1). Positive halogen compounds and chlorine and bromine in solution could also be detected with this reagent. Qualitative determinations were made on a variety of compounds that should be detectable, as well as those that would be characteristic of decomposition products of these compounds. Drop-sized quantities of liquids and approximately 0.02 gram of solids were added to 5 ml. of a solution containing 2 x 10-3 mole per liter of di-
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. I n 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 a n 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 a n 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 GEYTS.
Experiments.
REA-
Hydrogen sulfide stock solu-
VOL. 29, NO. 9, SEPTEMBER 1957
1349
