Automated High Performance Liquid Chromatography and Liquid Scintillation Counting Determination of Pesticide Mixture Octanol/Water Partition Rates

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Abstract
Two novel methods are reported for measuring octanol/water par tition rates of pesticides. A liquid scintillation counting (LSC) method was developed for automated monitoring of14 C-labeled pesticides partitioning in biphasic water/octanol cocktail systems with limited success. A high performance liquid chromatography (HPLC) method was developed for automated partition rate moni toring of several constituents in a pesticide mixture, simultane ously. The mean log Kow ± SD determined from triplicate experi mental runs were for: 2,4-D-DMA (2,4-dichlorophenoxyacetic acid dimethylamine), 0.65 ± .17; Deet (N,N-diethyl-m-toluamide), 2.02 ± .01; Guthion (O,O-dimethyl-S-(4-oxo-1,2,3-benzotriazin- 3(4H)-ylmethyl)phosphorodithioate), 2.43 ± .03; Methyl- Parathion (O,O-dimethyl-O-(p-nitrophenyl)phosphorothioate), 2.68 ± .05; and Fenitrothion (O,O-dimethyl O-(4-nitro-m-tolyl) phosphorothioate), 3.16 ± .03. A strong positive linear correlation (r = .9979) was obtained between log Kow and log k' (log Kow = 2.35 (log k') + 0.63). The advantages that this automated procedure has in comparison with the standard manual shake-flask procedure are discussed.

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