A rapid colorimetric determination for organophosphate pesticides is reported. The basis for this method is the reaction between nitrobenzyl pyridine and phosphate pesticide in a slightly basic solution at 175-180°C. The method reported is rapid and has a sensitivity of approximately 2 μg of an organophosphate pesticide. Recoveries are presented for several crops fortified at 1 ppm. Interferences were noted for some types of crops, and the need for further cleanup work was indicated.

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The recoveries of five parent organophosphate pesticides from eight different fortified crops were determined hy a “gross” cleanup technique. The primary method of analysis. was GLC. Other determinative methods used for comparison were total phosphorus determination, paper chromatography, and determination of phosphorus esters with p-nitrobenzyl pyridine reagent. The five organophosphate pesticides studied as mixtures and individually were Diazinon, methyl parathion, parathion, malathion, and Trithion. The three fortification levels in crops were 5.0, 1.0, and 0.1 ppm.

An improved paper chromatographic method, based on Cook,s serum cholinesterase inhibition spot test, can be used to detect potentially toxic organophosphate pesticide residues. A quantitative estimation requires the use of appropriate reference standards.

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