Determination of Technical Benzene Hexachloride in Peanuts and Soils IRWIN HORNSTEIN Bureau of Entomology and Plant Quarantine, Agricultural Research Administration, U . S. Department of Agriculture, Beltsville, M d .
TH!
colorimetric method developed by Schechter and Hornstein ( 5 ) for the determination of benzene hexachloride is based on its dechlorination t o benzene ( 3 , 4)by means of zinc in acetic acid and the subsequent nitration of the benzene to mdinitrobenzene. The dechlorination and the nitration are carried out in a specially designed all-glass apparatus. The m-dinitrobenzene after extraction reacts with methyl ethyl ketone in the presence of strong alkali (1, $1, and the violetrred color is measured photometrically. I n many instances the analyses can be performed directly on the material being examined. Recently, in analyses of soils and peanuts, interferences were encountered that required prior treatment. The methods of separation are described below. The actual analyses, after removal of the interferences, nere made as described ( 5 ) , lvith but one change-zinc dust replaced the 80-mesh zinc used for the dechlorination. When the standard curves for the gamma isomer and for technical benzene hexachloride are being prepared, 1 gram of zinc in 10 ml. of acetic acid is used for the dechlorination. When larger volumes of acid are needed, the ratio of 1 gram of zinc t o 10 ml. of acid must be maintained. If the ratio of zinc to acid is materially decreased, low results will be obtained when technical benzene hexachloride is being analyzed. When samples of peanuts and peanut butter with no history of benzene hexachloride treatment were analyzed directly, they gave apparent benzene hexachloride values ranging from 1.0 t o 1.5 p.p,m. During the analysis the flask containing the sample and reagents as maintained under reflux a t 150' C. for about 3 hours, At higher bath temperatures greater blanks were encountered.
Table I. Technical Benzene Hexachloride Found in Untreated Check Samples of Unroasted and Roasted Peanuts and in Peanut Buttera (Weight of each sample 30 grams) Apparent Benzene Hexachloride Material Found, y
Blank, P.P.M.
When peanut butter or finell- ground roasted peanut samples were extracted with methylene chloride, and the oil extract and residue were analyzed separately, most of the interference remained in the solid residue. The apparent benzene hexachloride value of the oil extract n as about 0.3 p.p.m. and that of the residue about 1.0 p.p.m. K h e n the oil extract and the residue were deliberately charred and then analyzed, the apparent benzene hexachloride value remained unchanged, a t about 0.3 p.p,m., for the oil and increased to as high as 5.0 p.p.m. for the residues. T h e blanks obtained on the residue depended upon the degree of charring, whereas those for the oil extract were independent of the degree of char. It therefore appeared that some material insoluble in methylene chloride, perhaps a protein, could on heating yield an interfering substance. The roasting of peanuts may have the same effect as charring, but to a lesser degree. Because the precursor of the interfering material is not extracted, the amount of interference in the methylene chloride extract due t o roasting is small. Analysis of a methylene chloride extIact of unroasted peanuts gave, as expected, the least interference, a blank of about 0.1 p,p.m. being found. Some slight decomposition during the curing period and also during subsequent storage may have given this small blank. 30attempt has been made to identify the interfering substance. When 10 ml. of a methylene chloride solution containing a knoivn amount of benzene hexachloride were thoroughly stirred into 30 grams of either finely ground peanuts or peanut butter and the mixture mas extracted with methylene chloride, analysis of the extract gave quantitative recoveries of benzene hexachloride. The results of various analyses are given in Tables I and 11. The peanut butter and the roasted peanuts (Table I ) were made from the same batch of unroasted peanuts. Determinations of benzene hexachloride can be run directly on most soils v, ith little interference; however, soils high in organic content may present some difficulty. Extraction of these soils with glacial acetic acid gives a n extract that can be analyzed directly for benzene hexachloride. The results of analyses with different types of soil are sholvn in Table 111.
Peanuts Unroapted Roasted
40 43
1.33 1.43
Peanut butter
39
1.30
Peanut extract Unroasted Roasted
3 10
0.10 0.33
Model S o . 10 Oesterizer or any other satisfactory blender. A magnetic stirring apparatus. A specially designed all-glass digestion and nitrating apparatus
Peanut butter extract Xot charred Charred
9 12
0.30 0.40
A Beckman spectrophotometer, Model B, and 1-cm. absorption cells, or any suitable photometer.
Peanut residue Unroasted Roasted
29 34
0.97 1.13
APPARATUS
(5).
PROCEDURE
Peanuts.
Khole peanuts are pulverized in the blender before Peanut butter residue extraction; peanut butter samples are extracted directly. A 144 4.30 Charred 1'.00 30 Not charred sample containing approximately 50 t o 100 micrograms of benzene hexachloride is weighed directly into a 300-ml. Erlena Peanut butter and roasted peanuts were made from same batch of un. roasted peanuts. meyer flask and 90 ml, of redistilled methylene chloride are added. (This solvent is preferred because of its low boiling point; carbon tetrachloride, chloroform, and ethylene dichloride may also Table 11. Recovery of Technical Benzene Hexachloride be used.) B magnetized glass-sealed stirring bar is placed in the Added to Unroasted Peanuts and Peanut Butter liquid, and the flask, loosely stoppered, is set on the stirring ap(Analyses run on methylene chloride extracts. Weight of each sample 30 paratus. Thc suspension is stirred for 30 minutes a t room temgrams) perature. The slurry is filtered under suction and the residue Technical Benzene Hexachloride y R ~ ~ washed ~ ~ 50 ml. . of methylene ~ ~ chloride. ~ The clear amber filwith Material Added Recovered (Uncorrected), trate is transferred to a 250-ml. standard-taper Erlenmeyer flask. The solution is concentrated on a steam bath until most of the 64 103 Unroasted peanuts 62 methylene chloride has been evaporated; 100 ml. of acetic acid 90 91 101 are added, the flask is attached to an efficient fractionating column, and 20 ml. of the acid are distilled, thus removing the residPeanut butter 62 70 113 90 98 109 ual methylene chloride. The heating is done in an oil bath maintained a t about 150" C. After the solution is cooled, the ~
1036
c
1037
V O L U M E 2 4 , N O . 6, J U N E 1 9 5 2
suction and the residue washed with acetic acid. The analysis is run directly on the clear filtrate, as described (6).
Table 111. Recovery of Technical Benzene Hexachloride from Soil Samples
CONCLUSIONS
(Weight of each sample 50 grams)
Material Sandy loam Sandy loam extracto Sandy loam
Technical Benzene R ~ ~ Hexachloride, Y (cncor- Blank, Added Recovered rected). % P.P.M. 0 5 ... 0.1 0 0 .. 62 65 i 65 92 93 103
Clav soil Claj. soil extracta Clay soil Muck soil Muck soil extracta
0
3
...
0.06
0 0 62
35 0 62 88
...
0.7
100
..
90 a
...
..
98
Extracted with acetic acid.
proper amounts of zinc dust (about 8.0 grams) and malonic acid (about 5.0 grams) are added. The subsequent dechlorination and nitration are carried out in a specially designed all-glass apparatus. The final absorbancy is read on a Beckman Model B spectrophotometer or other suitable instrument. The details of the analytical procedure have been described ( 6 ) . Soils. For soils high in organic content, a sample of soil containing 50 t o 100 micrograms of benzene hexachloride is weighed directly into a 300-nil. Erlenmeyer flask and extracted with 75 ml. of glacial acetic acid for 30 minutes a t room temperature by means of a magnetic stirrer. The suspension is filtered under
~
~ Schechter-Hornstein . ~ ~ ~ The colorimetric determination of benzene hexachloride can best be carried out on a methylene chloride extract of unroasted peanuts. If extracts of roasted peanuts or of peanut butter are analyzed, corrections of about 0.3 p.p.m. have t o be made, depending perhaps on the degree of roast. This coirection may be determined by running a sample of the same variety of peanut and of approximately the same degree of roast through all the steps of the analyses and subtracting this blank benzene hexachloride value from the apparent amount of benzene hrxachloride found in the suspected sample. I n general, this colorimetric method can be applied directly t o soils. I n the one case in which a n appreciable interference was encountered, extraction n ith acetic acid folloived by direct analy?is of the extract gave satiqfactory results. LITERATURE CITED
(1) Baernstein, H. D., IND. Ex;. C m w , ANAL.ED.,15, 251 (1943). ( 2 ) Bost, R. W., and Nicholson, F., Ibid., 7 , 190 (1935). (3) Mathews, F. E., J. Chem. Soc., 61, 103 (1892). (4) Meunier, J., Compt. rend., 114, 7 5 (1892). ( 5 ) Schechter, bl. S., and Hornstein, I., .~N.AL. CHEM., 24, 544 (1952). RECEIVED for review December 8, 1951. Accepted January 24,1952.
Reduction of Carbon Disulfide at Dropping Mercury Electrode I. M. KOLTHOFF, P . E. TORES,
AND
R . W. RAMETTE
School of C h e m i s t r y , Znicersity of Minnesota, Minneapolis, M i n n .
T JVAS accidentally observed t h a t carbon disulfide yields reA study of
I duction waves a t the dropping mercury electrode. these waves is described in this paper.
-411 chemicals used were of ordinary reagent grade or better. Quantitative measurements were made n i t h a manual polarograph, while a Sargent Model X X I and a Leeds & Northrup Type E were used for qualitative work.
MOLARITY OF CARBON DISULFIDE
x
103
Figure 2. Proportionality of Current to Concentration
I -/ 0
I -I.2
I
-L 4
I
-I, 6
I
-A8
-
V O L T S VS. S.C.E
Figure 1. Cathodic Waves 1. 2. 3.
4 X 1 0 - 4 171 carbon disulfide i n 0.1 M p o t a s s i u m chloride in
presence of 0.006% gelatin and 4 X 10-4 M copper chloride S a m e , w i t h o u t copper chloride Residual current
Carbon disulfide is very volatile in aqueous solutions. I n order t o obtain reproducible results it was necessary to work a t temperatures close t o 0" C. A cracked ice bath maintained the cell temperature at about 2' C. Oxygen was removed by using 0.1 M sodium sulfite, which also served as supporting electrolyte. The solution could not be bubbled with nitrogen, as this would remove some carbon disulfide. A.solution of carbon disulfide in methanol m-as standardized by weight, and added from a microburet inserted through the stopper of the polarographic cell. The methanol content of'the resulting solution did not exceed
