Studies on the Selectivity in detecting Organophosphorus and Carbamate Pesticides by Thin-Layer Chromatographic Enzyme Inhibition Technique

Abstract

Enzymic detection of organophosphorus and carbamate pesticides by thin-layer chromatography was achieved with rat liver, rabbit liver, and rabbit serum as sources of esterase and p-nitrophenylacetate, phenylacetate and indoxylacetate as a substrate, and the selectivity to these pesticides was investigated. The possibility of selective detection of organophosphorus pesticides was also examined, using bovine pancreas chymotrypsin and 2-naphthylacetate. Organophosphorus and carbamate pesticides were developed on Avicel thin-layer plates by reverse and normal phase partition system, respectively. After development, the plates were exposed to bromine vapor if necessary. The detection was made in three steps of (1) spraying anenzyme solution, (2) incubation for 20 min at room temperature, and (3) spraying the substrate solution. The detection limits of 9 organophosphorus and 9 carbamate pesticides were determined in four combinations of enzyme, substrate, and with or without bromine treatment. Among the 20 combinations tested, N. Br-rabbit liver-IA was most selective and sensitive to phosphates and N-methylcarbamates, Br-rabbit liver-PA to all organophosphorus pesticides, N. Br-rabbit serum-IA to phosphates, and Br-rabbit liver-IA to N-methylcarbamates and all organophosphorus pesticides. The selectivity to N-phenyl and N-naphthylcarbamates was not observed. Carbamate pesticides tested were not detected after bromination by the use of chymotrypsin, and the selective detection could not be obtained because of low sensitivity of organophosphorus pesticides. The inhibitory activity of phosphorothioates and phosphorodithioates increased markedly by bromine treatment, so that they can be distinguished from phosphate and carbamate pesticides which are not affected by bromine treatment.