Determination of Organophosphorus Compounds by HPLC with Post-Column Photochemical Degradation Followed by the Formation of Reduced Heieropolymolybdate
Date of Award
Doctor of Philosophy
Dr. James A. Howell
A novel method for the determination of organophosphorus (OP) compounds by HPLC with post-column photochemical and chemical derivatization reactions has been developed. The OP compounds eluted from the column were photochemically degraded to orthophosphate by the use of a 450 W xenon lamp in conjunction with an auxiliary photodegradation reagent. The photodegradation reaction was studied extensively by means of batch irradiations with triethylphosphate as a model compound. The effects of the initial concentrations of triethylphosphate and ammonium peroxydisulfate, and of varying the pH of the reaction medium were determined. A survey of potential interferences was performed. Copper(II) ion was found to catalyze the photodegradation, and the effect of varying the Cu(II) ion concentration and the pH dependence of the catalyzed reaction were investigated. Interference from organic solvents was found to be a serious limitation on the applicability of the photodegradation reaction. The orthophosphate resulting from the photodegradation of the eluted OP compounds was converted to reduced heteropolymolybdate and the absorbance monitored at 885 nm. The post-column detection system was extensively studied and optimized in terms of band-broadening, reaction rates, and overall performance. The interrelationships between the mobile phase and the detection system were examined during the development of chromatographic separations. Ion-exchange, ion-pair reversed phase, and cyano-phase modes of chromatography were explored. The method was applied to the determination of OP pesticide metabolites in human urine using ion-pair reversed phase chromatography. A rapid iron(III) pretreatment procedure was developed for the removal of interfering amounts of orthophosphate. Detection limits of 0.3 ppm for dimethylphosphate and 0.8 ppm for diethylphosphate were achieved. Several OP pesticides were determined in tomatoes by the use of the cyano-phase column. A simple pretreatment procedure employing a C18 Sep-Pak cartridge was developed. The recovery of dimethoate was 69% and its limit of detection was 0.09 ppm. The determination of dylox and dichlorvos was also shown to be feasible. The phosphorus-selective detection system developed in this study has strong potential for applicability to the determination of a variety of OP compounds.
Priebe, Stephen R., "Determination of Organophosphorus Compounds by HPLC with Post-Column Photochemical Degradation Followed by the Formation of Reduced Heieropolymolybdate" (1982). Dissertations. 2541.