Post-column reaction detection system for the determination of organophosphorus compounds by liquid chromatography

The development and application of a post-column reaction detection system for organophosphorus compounds based upon their photodegradation to ortho-phosphate followed by the formation of reduced heteropolymolybdate is reported. Photodegradation occurs in a fused-silica tube coiled about a 450-W xenon lamp in the presence of ammonium peroxydisulfate. Photodegradation yields were practically quantitative for the organophosphates, -phosphonates, and -phosphorodithioates tested. Factors affecting the rate of the chromogenic reaction were optimized so that its contribution to the total band-broadening was negligible. The effect of interfering organic modifiers in the mobile phase was studied using the acetate ion as a model. Separations were developed using no organic solvents in the mobile phases. The determination of dialkylphosphates in urine and organophosphorus pesticides in tomatoes illustrate the potential of the methodology.