Determining New Insecticides in Formulations and Residues

Determining New Insecticides in Formulations and Residues H. L. HALLER

Downloaded by UNIV OF MICHIGAN ANN ARBOR on May 12, 2018 | https://pubs.acs.org Publication Date: January 1, 1950 | doi: 10.1021/ba-1950-0001.ch016

Bureau of Entomology and Plant Quarantine, U. S. Department of Agriculture, Washington, D. C.

Three groups of synthetic organic insecticides have come into commercial use in the past few years— chlorinated hydrocarbons, phosphorus-containing compounds, and piperonyl derivatives. Methods for determining composition and purity of commercial grades have been developed, but only a few procedures are available for their detection and estimation in dusts, oil solutions, emulsion concentrates, and aerosols. When more than one insecticide is present in a mixture, even less is known concerning accurate determination of each component. More precise methods for determining their amount and possible degradation products are needed.

f T h e ultimate usefulness i n economic entomology of a compound possessing outstanding insecticidal properties can be determined only after numerous problems have been solved. These problems include determining the acute and chronic toxicity of the product to man, to cattle, and to other farm animals. The effect of the product on vegetation, soils, beneficial insects, and wildlife must also be ascertained. Solutions to these and related problems can be expedited b y physical and chemical studies of the product. Methods of analysis are especially important. N o t only is it necessary to have methods that will permit the analysis of the technical or commercial grade of the insecticide, but procedures should be developed for the detection and estimation of the product i n dusts, wettable powders, solutions, emulsion concentrates, and aerosols. Methods are also needed for determining the product i n combination with other insecticides and fungicides and i n spray residues. Because some new insecticides are absorbed i n animal tissues and found i n dairy products, quantitative methods must be found for determining the insecticide i n them. The importance of methods of analysis for new insecticides is evidenced b y the fact that during the past two years industry and government have cooperated i n developing methods for two of them—tetraethyl pyrophosphate and benzene hexachloride (1,2,3,4,5,6hexachlorocyclohexane) (37, 45). Among the more important synthetic organic compounds that have been developed commercially as insecticides during the past several years are certain chlorinated hydrocarbons, phosphorus-containing compounds, and piperonyl derivatives. The chlorinated hydrocarbons that have been of most practical interest are D D T , T D E ( D D D ) , methoxychlor (methoxy analog of D D T ) , benzene hexachloride, chlordan, and toxaphene (chlorinated camphene). Although methoxychlor contains oxygen, i t is included i n this group because of its close relationship to D D T . Of the organic phosphorus-containing products, hexaethyl tetraphosphate, tetraethyl pyrophosphate, and parathion have received greatest attention. The more important piperonyl compounds are piperonyl cyclonene, piperonyl butoxide, and propyl isome. 65

AGRICULTURAL CONTROL CHEMICALS Advances in Chemistry; American Chemical Society: Washington, DC, 1950.

66

ADVANCES IN CHEMISTRY SERIES

Numerous investigators have reported the entomological results obtained with these synthetic organic compounds against many different insects, both agricultural and household. I n this paper some of the analytical procedures that have been developed for these compounds and formulations of them are assembled and reviewed. The methods of analysis for the chlorinated hydrocarbons may be divided into five classes—determination of total organic chlorine, determination of hydrolyzable or labile chlorine, colorimetric methods, physical methods, and bioassays. The last mentioned is beyond the scope of this manuscript and is not considered.


Determinations of Total Organic Chlorine Chlorine makes up 5 0 % or more of the weight of all the chlorinated hydrocarbons under consideration except methoxychlor, which contains 3 0 % . Therefore, methods based on the determination of total chlorine appear appropriate. Such methods are not specific, however, and any other chlorine-containing organic compound will interfere. I n one procedure that has been widely used, the sample, after suitable treatment, is refluxed with sodium and isopropyl alcohol, after which the solution is diluted with water and the inorganic chloride is determined by standard methods (13, 54)- The method has been adopted by the Association of Official Agricultural Chemists (29, 30) as a tentative one for technical D D T and for dusts, oil solutions, and aqueous emulsions of D D T , for use in the absence of other chlorine-containing compounds. The National Association of I n secticide and Disinfectant Manufacturers has also accepted the total-chlorine method for the analysis of these preparations (28). Essentially the same procedures have been described by Donovan (22), of the Insecticide Division of the Production and Marketing Administration, for technical D D T and various commercial D D T products containing no other compounds interfering with the chlorine determination. Carter (12), of the Bureau of Entomology and Plant Quarantine, has adapted the total-chlorine method to the analysis of mixtures of D D T and benzene hexachloride i n the following manner: After determination of total chlorine in the mixture, the D D T is estimated b y the Schechter-Haller colorimetric method (47), half this value is subtracted from the total chlorine (because D D T contains 5 0 % of chlorine), and the difference is calculated as benzene hexachloride. This procedure gives no indication of the amount of the gamma isomer of benzene hexachloride. The total-chlorine method has been used extensively in the determination of spray residues of the chlorinated hydrocarbons (56). Usually the kind of insecticide applied has been known, and by means of the proper factor the chlorine values could be calculated to the insecticide originally used. This calculation is not entirely valid, as the determinations do not differentiate between the insecticide and its degradation products or other contaminants containing organic chlorine. The values obtained by the total-chlorine method are useful, however, because they indicate the magnitude of the residue and the analysis can be made i n a short time with standard laboratory equipment. A procedure that has been widely used for spray residues is the separation of the residue from the sample by extraction with an organic solvent, usually benzene. After most of the solvent has been removed, the residue is treated with sodium and isopropyl alcohol and the chloride ion is estimated by standard methods. Carter (10) has determined i n this manner D D T residues on a number of crops, and he has recommended the adoption by the Association of Official Agricultural Chemists of the method as a tentative one for D D T (11). Koblitsky and Chisholm (42) have determined D D T i n soil samples by the sodiumisopropyl alcohol procedure after removing the D D T by extraction with an azeotropic mixture of two volumes of benzene and one volume of isopropyl alcohol. The total-chlorine method for determining residues of benzene hexachloride, chlordan, and toxaphene has also been used (55) i n experiments where it was known that these i n secticides had been applied. W i t h benzene hexachloride, which is known to give off-flavor to some crops, it has not been demonstrated that a relation between organic chlorine values and off-flavor exists. I n fact, i n most cases where off-flavor was attributed to benzene hexachloride, it has not been possible to detect organically bound chlorine. AGRICULTURAL CONTROL CHEMICALS Advances in Chemistry; American Chemical Society: Washington, DC, 1950.


HALLER—DETERMINING NEW INSECTICIDES IN FORMULATIONS AND RESIDUES

67

The total-chlorine method for residues of the chlorinated hydrocarbons has also been applied to animal tissues, milk, and dairy products (9). As i n the spray-residue deter minations, the method does not differentiate between the insecticide and metabolites. Recently it was shown that when D D T , benzene hexachloride, or toxaphene is fed or applied to cattle, such organic chlorine residue as may be present i n the fatty tissues con sists essentially of unchanged insecticide. Carter (12) demonstrated their presence b y separating the fats and other oxygenated products with sulfuric acid-sodium sulfate mix ture and determining total chlorine. I n experiments with D D T Schechter (46) demon strated its presence i n fatty tissue and i n butterfat b y the Schechter-Haller colorimetric method (47). The residues were then tested for toxicity to houseflies i n comparison with the known insecticides of the same concentration. I n both cases the known insecticide gave the same mortality as the residue.

Determinations of Hydrolyzable Chlorine A l l six of the chlorinated hydrocarbons yield part of their chlorine on treatment with ethanolic alkali, but methods of analysis involving this reaction have been developed only for D D T and benzene hexachloride. This type of determination is somewhat more specific and subject to less interference than the total-chlorine method, but it must be used with discretion. When it is applied to D D T , one of the chlorine atoms is removed to form hydrogen chloride; with benzene hexachloride 3 moles of hydrogen chloride are formed. Gunther (34) was the first to develop a method using this principle for the determination of D D T i n dust and spray residues. The original procedure has been modified by substitut ing 4.5 Ν ammoniacal methanol for potassium hydroxide i n ethyl alcohol and carrying out the reaction at 45° C. instead of refluxing the solution (5). This modification has been successfully employed b y Gunther (33) for the determination of D D T residues on many different crops. L a C l a i r (44) and Solo way et al. (50) have modified the dehydrohalogenation reaction to permit the determination of ρ , ρ ' - D D T i n dusts and oil solutions containing technical D D T . The reaction between the base and the halide is carried out at 20° to 30° C , as Cristol (16) has found that under proper conditions at this temperature the ρ , ρ ' - D D T reacts completely, whereas the ο,ρ'-ΏΏΎ and most of the impurities react only slightly. The Association of Official Agricultural Chemists' (3) tentative method for the determina tion of the purity of ρ , ρ ' - D D T , which employs the dehydrohalogenation procedure, has been modified b y Fleck (30) so that the reaction is carried out at 25° C. instead of under reflux conditions. Unlike D D T , T D E does not lose one mole of hydrogen chloride when heated with ferric chloride, but rearranges to form an isomeric compound (31). It may be possible to develop this observation into an analytical method to differentiate between the two products or to detect the one i n the presence of the other. The dehydrohalogenation reaction has been applied by Goldenson and Sass (32) to the determination of benzene hexachloride in impregnated cloth. Howard (39) proposed the reaction for the determination of benzene hexachloride residues i n food, and Barlow (6) used it for benzene hexachloride i n the blood of cattle. L a C l a i r (43) has employed the dehydrohalogenation reaction to determine the gamma isomer of benzene hexachloride i n the technical product and i n dust mixtures. Two identical samples are dissolved i n 9 5 % ethyl alcohol and treated with 1 Ν ethanolic potassium hydroxide at 0° C. for 15 and 50 minutes, respectively. The 15-minute period is sufficient to dehydrochlorinate most of the alpha and the delta isomers without appre ciably affecting the gamma. In 50 minutes the gamma isomer is also dehydrochlorinated. The beta isomer does not react under these conditions, and usually the epsilon isomer is present i n quantities too small to interfere seriously.

Colorimetric Methods Methods based on color reactions have been published for several of the chlorinated hydrocarbon insecticides. Although most colorimetric methods are much more specific AGRICULTURAL CONTROL CHEMICALS Advances in Chemistry; American Chemical Society: Washington, DC, 1950.


68


than chlorine determinations, care must be exercised i n their use, as analogs and closelyrelated compounds may produce the same or similar colors. I n general, colorimetric methods are used mostly for spray-residue determinations and for qualitative tests of the insecticide i n various formulations. More experimental work has been done with D D T than with a l l the other five chlo rinated hydrocarbons combined, probably because D D T was the first of the group found to have insecticidal value. Carter (10) has summarized the several colorimetric methods for D D T . The one proposed by Stiff and Castillo (51), as modified b y Claborn (14), and the one b y Schechter and Haller (47) have probably been most widely used. I n the Stiff and Castillo method, when the D D T is heated i n pyridine solution containing xanthydrol and potassium hydroxide, a red color develops which is proportional to the quantity of D D T present. The reaction is sensitive to 10 micrograms. As T D E does not give a color with this reagent, Claborn (14) has proposed the reaction for the determination of D D T i n the presence of T D E . H e has also shown that for the development of the color the amount of water i n the pyridine is critical. The colorimetric method for D D T developed b y Schechter et al. (49) is based on i n tensive nitration of D D T with the formation of a tetranitro derivative. The product ob tained with the ρ,ρ' isomer gives an intense blue color upon addition of sodium methylate, whereas the ο,ρ' derivative produces a violet-red color. A s the method permits the esti mation of as little as 10 micrograms and none of the degradation or metabolic products of D D T interfere, i t is especially useful for work on spray residues and biological specimens. Modifications of the method that are suitable for determining D D T i n fatty materials such as milk, butter, meat, and eggs have been described b y Schechter et al. (48) and Clifford (15). Tressler (53) has adapted i t for determining D D T or its residues i n canned foods. The nitration method is more specific for D D T than any other proposed. W i t h the ex ception of T D E , which gives an almost identical color, none of the other chlorinated hydrocarbons interferes. Recently a colorimetric test for methoxychlor residues was proposed b y Fairing (27). The methoxychlor sample is treated with alcoholic potassium hydroxide, the reaction product is extracted with ether, the ether is removed, and the residue is treated with con centrated sulfuric acid. A n intense cherry-red color is developed. N o other insecticide has been found to interfere, and the reaction is sensitive to about 5 micrograms of meth oxychlor. Satisfactory colorimetric methods for benzene hexachloride, chlordan, and toxaphene are not available and are urgently needed. Davidow (19), of the Food and D r u g Administration, has described a colorimetric method applicable to technical chlordan. The method is based on the observation that when technical chlordan is heated with a mixture of diethanolamine and methanolic potassium hydroxide, a purple color is produced. When known amounts of this insecticide were added to cabbage, pears, and fresh and rancid rat fat, recoveries of 74 to 104% of the insecticide were obtained. However, because two crystalline isomers of chlordan isolated from the technical product do not give a colored reaction product with the reagent, further investigation of the method is being made. The red color obtained when technical chlor dan is heated with pyridine, alcoholic alkali, and ethylene glycol monoethyl ether, as de scribed b y A r d (2), likewise fails with the crystalline isomers of this insecticide. A method that is stated to be applicable to residues of benzene hexachloride (20) is based on the fact that benzene hexachloride yields essentially 1,2,4-trichlorobenzene on dehydrohalogenation with alkali. This product possesses a characteristic absorption band in the ultraviolet, which permits its quantitative determination.

Physicochemical Methods Methods utilizing characteristic physical properties have been developed for several chlorinated hydrocarbon insecticides. Daasch (18) has used infrared spectroscopy for the analysis of benzene hexachloride. B y this means i t is possible to determine the gammaisomer content, as well as that of the other isomers of technical benzene hexachloride, pro vided the product is substantially free of the higher chlorinated cyclohexanes. AGRICULTURAL CONTROL CHEMICALS Advances in Chemistry; American Chemical Society: Washington, DC, 1950.



69

The gamma isomer of benzene hexachloride can also be determined b y polarography (24, 40)' The method is based on the fact that, under the conditions used, the gamma isomer is the only one of the five isomers that is reduced at the dropping mercury elec trode. B o t h the infrared spectroscopic method and the polarographic method require special instruments. When instruments for both are available, the latter method seems to be pre ferred. Neither method has been found to be applicable to spray residues. Physical methods based on absorption spectra i n the infrared or ultraviolet have also been suggested for determining D D T . The method proposed b y Herriott (38) for the ρ,ρ' isomer is based on the fact that in ethyl alcohol solutions it absorbs ultraviolet light very slightly at a wave length of 250 ιημ. After dehydrochlorination b y dilute alcoholic sodium hydroxide the reaction product absorbs strongly at this wave length. The increase i n ab sorption is measured and compared with the value obtained with a similarly treated standard solution. Downing et al. (23) have shown that infrared spectroscopy can be used for the chemical characterization of technical D D T , including detection of the several isomers and impurities, and the quantitative estimation of D D T content. Neither method appears to have had widespread application. A method for determining the gamma isomer of benzene hexachloride b y partition chromatography has been developed b y Aepli et al. (1). Nitromethane and n-hexane are used as the partition solvents, and silicic acid is the supporting medium. The method a p pears to be useful for routine product analyses. A n accuracy of about 2 % of the actual gamma isomer present is claimed. A cryoscopic method for determining the gamma isomer of benzene hexachloride, developed b y Bowen and Pogorelskin (8), is based on the fact that the freezing point of a compound is lowered b y the presence of dissolved impurities. The method is useful for benzene hexachloride preparations of higher gamma-isomer content than the usual tech nical grade containing 10 to 1 2 % of the gamma isomer. The method is rapid and requires only simple, readily available equipment. Cristol et al. (17) have based a method for the determination of ρ,ρ'-DOT i n tech nical D D T on the fact that the ρ,ρ' isomer is almost insoluble i n 7 0 % aqueous ethyl alcohol and the ο,ρ' isomer is soluble. The method has not been tried with mixtures of the other chlorinated hydrocarbons. A mass-isotope dilution method for determining the gamma isomer of benzene hexachloride, i n which gamma-hexadeuterobenzene hexachloride is used as a tracer mole cule and the dilution is determined b y use of infrared spectrophotometry, has been de veloped b y Trenner et al. (52). Impurities have no effect on the accuracy of this method.

Analysis of Organic Phosphorus Compounds Of the three organic phosphorus insecticides—hexaethyl tetraphosphate, tetraethyl pyrophosphate, and parathion—the first two have been shown to be mixtures (36) that contain tetraethyl pyrophosphate as the principal active ingredient. Several methods have been proposed for the determination of this compound i n the commercial products (25, 35). A l l are based on the separation of the tetraethyl pyrophosphate from the related ethyl phosphates, followed b y its hydrolysis to diethyl orthophosphoric acid and titration with standard alkali. B o t h hexaethyl tetraphosphate and tetraethyl pyrophosphate are soluble i n water and are rapidly hydrolyzed to monoethyl and diethyl orthophosphoric acid. This rapid hydrolysis to nontoxic products greatly limits the duration of the in-* secticidal effectiveness of tetraethyl pyrophosphate, but i t also eliminates the danger of toxic residues on the crops treated. The only method that has been described for the assay of technical grades of para thion and its formulations is that of Bowen and Edwards (7). The method makes use of the polarograph. The electrolysis is carried out i n an acetone-water solution with potas sium chloride as the electrolyte and gelatin as the suppressor. A n accuracy of ± 1 % is obtained. F o r spray residues of parathion Averell and Norris (4) have developed a method that is sensitive to about 20 micrograms. The method is based on the reduction of the nitro AGRICULTURAL CONTROL CHEMICALS Advances in Chemistry; American Chemical Society: Washington, DC, 1950.


70


group to the amine, diazotization, and coupling with iV-(l-naphthyl)ethylenediamine, which gives an intense magenta color with an absorption peak at 555 ιημ. Edwards (26) has found that commercial samples of benzene, which is commonly used for stripping resi dues from plant material, give an identical color by the method. The interfering sub stance can be removed by distillation of the benzene. The oxygen analog of parathion, diethyl p-nitrophenyl phosphate, gives the same color as parathion b y the method. This oxygen analog is stated to be much more toxic to warm-blooded animals than parathion, and i t has been suggested that parathion is converted to the oxygen analog on exposure to the air. However, no definite evidence has been adduced that this compound accompanies spray residues of parathion, and laboratory experiments have failed to confirm the reac tion.

Analysis of Piperonyl Compounds Of the three piperonyl compounds that have received considerable commercial atten tion as insecticides, a method of analysis is available only for piperonyl butoxide (41). This product gives a blue color on treatment with a reagent comprising tannic acid i n a mixture of phosphoric and acetic acids. Satisfactory results can be obtained i n the pres ence of small amounts of pyrethrins, but larger amounts tend to obscure the color. A modification of the method (21) which overcomes this difficulty is the removal of the pyrethrins by saponification with alcoholic sodium hydroxide prior to carrying out the test.

Literature Cited (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21)

Aepli, O. T., Munter, P. Α., and Gall, J . F., Anal. Chem., 20, 610 (1948). Ard, J . S., Ibid., 20, 858 (1948). Assoc. Official Agr. Chemists, "Official and Tentative Methods of Analysis," 6th ed., 1945. Averell, P. R., and Norris, M . V . , Anal. Chem., 20, 753 (1948). Baier, W. E., Edmonds, E . J . , Wilson, C. W., Elliot, M . I., and Gunther, F . Α., Science, 104, 376 (1946). Barlow, F., Nature (London), 160, 719 (1947). Bowen, C . V., and Edwards, F. I., Jr., Anal. Chem., in press. Bowen, C . V., and Pogorelskin, Μ. Α., Ibid., 20, 346 (1948). Carter, R. H . , Ibid., 19, 54 (1947). Carter, R. H . , J. Assoc. Offic. Agr. Chemists, 30, 456 (1947). Ibid., 32, 353 (1949). Carter, R. H . , unpublished report. Carter, R. H . , and Hubanks, P. E., J. Assoc. Offic. Agr. Chemists, 29, 112 (1946). Claborn, Η. V., Ibid., 29, 330 (1946). Clifford, P. Α., Ibid., 30, 337 (1947). Cristol, S. J . , J. Am. Chem. Soc., 67, 1494 (1945). Cristol, S. J . , Hayes, R. Α., and Haller, H . L . , Ind. Eng. Chem., Anal. Ed., 17, 470 (1945). Daasch, L . W., Anal. Chem., 19, 779 (1947). Davidow, B., paper presented at meeting of Association of Official Agricultural Chemists, Washington, D . C., October 1948. Davidow, B., paper presented at meeting of Federation of American Societies for Biology, Detroit, Mich., April 1949. Davidson, J . C., and Terrell, H . D., paper presented at Philadelphia, Pa., meeting of AMERICAN C H E M I C A L SOCIETY, Jan. 20,

1949.

(22) Donovan, C. G., Soap and Sanit. Chem., 22 (6), 165 (1946). (23) Downing, J . R., Freed, M . V., Walker, J . F . , and Patterson, G. D., Ind. Eng. Chem., Anal. Ed., 18, 461 (1946). (24) Dragt, G . , Anal. Chem., 20, 737 (1948). (25) Dvornikoff, M . N . , and Morrill, H . L . , Ibid., 20, 935 (1948). (26) Edwards, F . I., Jr., Ibid., 21, 1415 (1949). (27) Fairing, J . D., Agr. Insect. Fungicide Assoc. News (Dec. 31, 1948). (28) Fiero, G . W., Soap and Sanit. Chem., 23 (10), 147 (1947). (29) Fleck, E. E., J. Assoc. Offic. Agr. Chemists, 30, 319 (1947). (30) Ibid., 31, 368 (1948). (31) Fleck, E . E., J. Org. Chem., 12, 708 (1947). (32) Goldenson, J . , and Sass, S., Anal. Chem., 19, 320 (1947). (33) Gunther, F . Α., Hilgardia, 18, 297 (1948). (34) Gunther, F. Α., Ind. Eng. Chem., Anal. Ed., 17, 149 (1945). (35) Hall, S. Α., and Jacobson, M . , Agr. Chemicals, 3 (7), 30 (1948).




(36) (37) (38) (39) (40) (41) (42) (43) (44) (45) (46) (47) (48) (49) (50) (51) (52) (53) (54) (55) (56)

71

Hall, S. Α., and Jacobson, M . , Ind. Eng. Chem., 40, 694 (1948). Haller, H . L . , Agr. Chemicals, 2 (9), 26 (1947). Herriott, R. M . , Science, 104, 228 (1946). Howard, Β. H . , Analyst, 72, 427 (1947). Ingram, G . B., and Southern, Η. K., Nature (London), 161, 437 (1948). Jones, Η. Α., private communication. Koblitsky, L . , and Chisholm, R. D., J. Assoc. Offic. Agr. Chemists, 32, 781 (1949). LaClair, J . B., Anal. Chem., 20, 241 (1948). LaClair, J . B., Ind. Eng. Chem., Anal. Ed., 18, 763 (1946). Rohwer, S. Α., Chem. Eng. News, 26, 2356 (1948). Schechter, M . S., unpublished report. Schechter, M . S., and Haller, H . L . , J. Am. Chem. Soc., 66, 2129 (1944). Schechter, M . S., Pogorelskin, Μ. Α., and Haller, H . L., Anal. Chem., 19, 51 (1947). Schechter, M . S., Soloway, S. B., Hayes, R. Α., and Haller, H . L., Ind. Eng. Chem., Anal. Ed., 17, 704 (1945). Soloway, S. B., Schechter, M . S., and Jones, Η. Α., Soap and Sanit. Chem., Blue Book, 18th ed., 215 (1946). Stiff, Η. Α., and Castillo, J . C., Science, 101, 440 (1945); J. Biol. Chem., 159, 545 (1945); Ind. Eng. Chem., Anal. Ed., 18, 272 (1946). Trenner, N . R., Walker, R. W., Arison, B., and Buhs, R. P., Anal. Chem., 21, 285 (1949). Tressler, C. J . , Jr., J. Assoc. Offic. Agr. Chemists, 30, 140 (1947). Umhoefer, R. R., Ind. Eng. Chem., Anal. Ed., 15, 383 (1943). Wichman, H . J . , J. Assoc. Offic. Agr. Chemists, 31, 349 (1948). Wichman, H . J . , Patterson, W. I., Clifford, P. Α., Klein, A . K., and Claborn, Η. V., Ibid., 29, 188 (1946).


Determining New Insecticides in Formulations and Residues

Recommend Documents