HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY IN STABILITY STUDIES OF AN ORGANOPHOSPHORUS INSECTICIDE IN FREE-FORM AND AFTER FORMULATION AS EMULSIFIABLE CONCENTRATE - RESPONSE-SURFACE DESIGN CORRELATION OF KINETIC DATA AND PARAMETERS

DCPE lpha-(diethoxyphosphinoximino)dicycloproylmethane] is an organoph osphorus compound with good insecticidal activity. It is a yellow oily liquid, poorly soluble and unstable in aqueous media. The development of a useful, safe formulation, miscible with water, easy to use and r etaining its activity was examined. First, the kinetics of the hydroly sis of DCPE were studied in various buffer solutions over the pH range 3-11 at 20-80 degrees C by a reversed-phase HPLC method. Then the res ponse surface methodology was used to investigate how the hydrolysis r ate constant (response) was affected by temperature and pH (variables) over some specified region, and was described step by step. The degra dation product of DCPE was isolated by extraction and identified by IR and H-1 NMR spectrometry. Also, the activation energy of DCPE hydroly sis was calculated from the dependence of the observed hydrolysis rate s (k(obs)) on temperature at constant pH. Finally, 30 emulsifiable con centrate formulations of DCPE were prepared by choosing different comb inations of oil phases and emulsifiers. Five of the resulting emulsion s retained their physical stability and were examined further for chem ical stability of the active compound (DCPE) at different temperatures .