Automated Analysis of Organophosphorus Insecticides by Wet Digestion-Oxidation and Colorimetric Determination of the Derived Orthophosphate

Adaptation of an AutoAnalyzer system to the determination of phosphorus in organic compounds now provides an automated technique generally applicable for the analysis of organophosphorus inserticides. Following automated wet digestionoxidation of the compounds (some need preliminary alkaline hydrolysis) the resulting orthophosphate is determined automatically by a colorimetric system reading a phosphomolybdenum blue color at 815 mμ. The total system handles 10 samples per hour with a precision and sensitivity readily practical for organophosphorus insecticide analysis; the insecticidal solutions tested, at concentrations of 2 μg/ml or greater, gave repeatable responses within ± 10%. Manual cleanup procedures for most crop samples are required to remove interfering noninsecticidal phosphorus compounds before the system is applicable to total residue analyses. Thimet (phorate) and phosphamidon at 0.5 ppm in fortified stripping solutions of strawberries were analyzed separately without cleanup, however. Adsorption column chromatography on Florisil has provided rapid and efficient cleanup of fortified spinach extractives prior to automated analysis of Thimet and dimethoate. Autoanalysis of individual spots from thin layer chromatograms provides considerable specificity to this nonspecific analytical system, and for some crops provides all the cleanup necessary. Thin layer "spots" can be introduced directly into the automated system.