Analytical Methods for Pesticides and Plant Growth Regulators

Abstract

WALKER et al. methane as the carrier gas. Comparison of the same fractions from the silica gel column by both analytical methods shows large variations in the relative peak intensities. The percentage composition of several components (10, 43, 116, 139, and 165; Table I) was found by EC to be 70-130% of the corresponding values with Cl total ion current. Some smaller components (i.e., 1, 133, and 135) appeared to be in >fourfold higher amounts when analyzed by EC than by Cl-ms. It is clear that the EC response is not directly proportional to that of Cl-ms. The EC response is known to vary with isomeric compounds; for example , the a, ß, , and isomers of hexachlorocyclohex-ane differ by up to fourfold in their apparent ionization efficiencies (Ishida and Dahm, 1965). Similarly, the Cl-ms response will differ with isomeric materials since the total ion current depends on the relative intensities of the ions generated which in turn varies with different iso-mers. Attempts to quantitate using the FI detector proved fruitless due to its insensitivity with these types of compounds. The approximate composition values for toxaphene take on additional significance when one multiplies these percentage values by one billion (the number of pounds of toxaphene already used) to obtain the number of pounds of each component introduced into the environment over the past 25 years. It is cautioned, however, that the composition data are only approximate and are directly related to the Cl-ms technique used in the quantitation. It should also be noted that one batch of toxaphene may differ from another so the present composition values for individual components may vary over a small range with different batches. Toxaphene is a very complex mixture which is difficult to analyze as to composition even under idealized conditions. The complexity will be even greater on considering a mixture of these components with their metabolites and photoproducts such as may be the case under environmental conditions. It is fortunate that, at least with toxa-phene itself, most of the components undergo rapid metabolism in mammals (Casida et al., 1974; Ohsawa et al., 1974). ACKNOWLEDGMENT The authors thank William Haddon of the Western Regional Research Laboratory, U. S. Department of Agriculture , Berkeley, Calif., for providing the Elms data. An analytical method is described for the determination of urethan (ethyl carbamate) in wines. The quantitative method involves an extraction with chloroform followed by a cleanup with Flor-isil and detection by gas-liquid chromatography. A Coulson electrolytic conductivity detector is capable of detecting levels of urethan at <100 ppb. Confirmation of identity is carried out with trifluoroacetic anhydride derivatized urethan, by gas chromatography using an alkali flame ioniza-tion detector. Diethyl pyrocarbonate (DEP) has been widely used as a food additive for controlling microbiological activity in alcoholic and nonalcoholic beverages (Pauli and Genth, 1966; Fischer, 1970; Gejvall and Lófroth, 1971). Recently, however, Lófroth and Gejvall (1971) were able to show, by use of isotope dilution analysis with tritium-labeled DEP, that the DEP can result in the formation of urethan (ethyl carbamate), a known carcinogen (Nettleship et al., 1943; Mirvish, 1968). The experiments performed by Lófroth) showed that, under laboratory conditions , white wine and beer which normally contain about 5-128 mg/1. of ammonia (Muth and Malsch, 1934; Bishop, 1943) can react with DEP added in the amounts of 280-560 mg/1. to form 1.3-2.6 mg, respectively, of urethan. The reaction is pH dependent. As a result of these studies , the beverage industry has withheld any further use of DEP pending studies to see what levels of urethan can be and are produced under actual food processing conditions. Since urethan is considered a carcinogen, any levels detected could fall within the Delaney Clause, preventing the use of DEP in foods. The purpose of this study was to develop an analytical method for low levels of urethan useful for routine monitoring applications and for quantitatively studying formation of urethan under varying conditions (Ough, 1974). 944