Estimation of DDT in Milk by Determination of Organic Chlorine R. H. C-IRTER C'nited States DeDartment of Research Administration, Bureau of Entomology and Plant " Agriculture, . Agricultural Quarantine. Beltsiille, Md.
THE
prcximately 6 grams of metallic sodium cut into small pieces. Reflux for 2 hours with moderate boiling. Add 25 ml. of ethyl nlcohol and allow to stand for a few minutes to react with all remaining metallic sodium. Dilute with 100 ml. of water poured through the condenser. Transfer the liquid to a 600-ml. beaker and evaporate most of i t on the steam bath. Make up to a volume of approximately 400 ml. with water, warming if necessary to put the soap in solution. Make acid with sulfuric acid to break up the soap and precipitate the fatty acids. Cool with ice or tap water and filter. Wash the precipitate twice with water.
he of D D T as an insecticide on forage and truck crops such u-as alfalfa, clover, and pea vines, which may be used ac: feed for livestock, particularly for beef and dairy cattle, has created a need for methods of determining D D T in milk or meat products from these animals. Methods for the determination of small amounts of D D T occurring as insecticidal residues have been reviewed by Cri-to1 and Haller ( I ) . These methods are based on the determination of total or hydrolyzable organic chlorine or on a colorimetric determination (3). The method herewith presented describes a procedure for estimation of D D T in milk and butter samples by determination of the total organic chlorine. This method is rapid, simple, and reasonably sensitive, but it is not specific for DDT. It is possible that other halogen-containing organic insecticides, fungicides, and herbicides, such as Spergon (tetrachlorobenzoquinone), 2,4dichlorophenoxyacetic acid (2,4-D) , p-dichlorobenzene, and benzene hexachloride, may also be taken up and stored in milk and meat products. Milk samples analyzed were taken from cows on diets containing DDT, and the presence of D D T in the milk was confirmed by the modified Schechter-Haller colorimetric test ( 3 ) .
Table 11. Amounts of DDT Found in Milk from Cows Receiving DDT in the Diet" Calculated from Total Organic Chlorine
Calculated from Colorimetric 'Determination b
P.p.m. 1.5 2 4
P.p.m. 3 3 3
2
a
b
A
15 17 16 23 25 Blanks less than 0.2 by both methods Determinations made by Jl.5. Schechter ( 2 ) .
1.i 19 22 23 25
REAGEXTS
Ethyl alcohol, 95y0, Ethyl ether, C.P. Petroleum ether (Skellysolve B). Isopropanol, commercial, 99%. Sodium, metallic, Silver nitrate, c.P.,0.05 or 0.025 N solution. Benzene, commercial, C.P.
Combine the aqueous filtrate and washings and extract twice with 100-ml. portions of the mixed solvent (ether-Skellysolve B). Make the aqueous sblution alkaline to phenolphthalein with 2 N potassium hydroxide. If the volume is in excess of approximately 300 ml., it should be concentrated by evaporation. 3fake the solution acid with nitric acid, adding a slight excess, and determine chloride ion by any of the standard procedures. I n their investigations the authors have determined the chloride content by electrometric titration with standard silver nitrate. The Volhard procedure is also applicable. Calculate the amount of DDT by multiplying the amount of chlorine by 2.
Table I. Percentage Recovery of Known Amounts of DDT Added to Rlilk ' Added
Found
Me.
MQ.
0.00 16 20 50
0.00
15.4 20.1 48.5
Recovery
70
Recovery of known amounts of DDT added to milk has been 95% or more, as shon-n in Table I. Determinations of organic chlorides in milk from cows on a DDT-free diet showed less than 0.2 p.p.m. of chlorine present. In milk from cows receiving D D T in the diet, the chlorine from organic chlorides ranged from approximately 1 to 12 p.p.m. Colorimetric determinations ( 2 ) have confirmed the presence of D D T in these samples in the amounts indicated by the total-chlorine determinations. These results, shown in Table 11, represent the average analyses on several samples; the differences betmen individual determinations were not significant.
96.2
100.5 97.0
PROCEDURE
1Iix 200 ml. or 200 grams of well-homogenized milk with 200 ml. of ethyl alcohol in a separatory funnel. Extract wlth 250 ml. of mixed solvent (757, eth$ ether, 25y0 SkeUysolve B). by gentle shaking. Use gentle agitation rather than violent shaking during the first extraction to prevent formation of stable emulsions. After separation of the two layers, draw off the aqueous layer and extract three times more with 100-ml. portions of the mixed solvent. Shake vigorously for 5 minutes in each of the last three extractions. Discard the aqueous phase. Combine the solutions from the four extractions in an Erlenmeyer or other suitable flask and evaporate the solvent on the steam bath. Remove the last traces of water by addition and distillation of two 50 ml. portions of benzene. To the residue in the flask add 150 ml. of isopropanol and ap-
LITERATURE CITED (1) Cristol, S.J., and Hailer, H. L., Chem. Eng. S e w s , 23,2070 ( 1 9 4 5 ) . (2) Schechter. 31. S., Pogorelskin, M . A,, and Haller, H. L., IND. ENG.CHEII,AXAL.ED.,19, 51 ( 1 9 4 7 ) .
(3) Schechter, 11. S., Solon-ay, S.B., Hayes, R. .1.,and Haller, H. L., Ibid.. 17, 704 (1945). .I.
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