CHROMATOGRAPHIC BEHAVIOR OF PHENYLUREA PESTICIDES IN HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY WITH NITRILE-BONDED AND AMINO-BONDED STATIONARY PHASES

The retention of phenylurea pesticides on nitrile- and amino-bonded stationary phases was measured over a broad composition range of 2-propanol-n-hexane and 2-propanol-water mobile phases. Minima of retention were observed on the nitrile phase in mobile phases containing 80-90% 2-propanol in water. In organic mobile phases, the plots of log k' versus the concentration of a-propanol in n-hexane are significantly curved. This behaviour can be attributed to combined effects of polar and hydrophobic interactions as the driving force of the retention. Simple two-parameter equations can be used to first-approximation description of retention on the nitrile bonded phase in mobile phases containing up to 50-60% 2-propanol in water and on the two bonded phases in mobile phases containing up to 60-80% 2-propanol in n-hexane. Four-parameter equations taking into account mixed mechanism of retention involving polar and hydrophobic interactions can be used to describe the retention of phenylurea compounds over the whole composition range of organic and aqueous-organic mobile phases and to allow prediction of retention and optimization of separation. The retention of phenylurea pesticides on the amino-bonded phase in mobile phase containing 2-propanol in water is too low to allow chromatographic separation of the compounds tested. The retention in aqueous-organic mobile phases is higher on the nitrile- than on the amino-bonded phase, but the selectivity of separation is unsatisfactory for most phenylurea pesticides. Most compounds tested can be separated in 2-propanol-n-hexane mobile phases, but significant differences in selectivities and even in the order of elution were observed between the two bonded phases.