Enantiomer Separation of Triazole Fungicides by High-Performance Liquid Chromatography

Enantiomer separation is one of the most important prerequisites for the investigation of environmental enantioselective behaviors for chiral pesticides. In the present study, the enantiomer separation of 7 triazole fungicides, i.e., hexaconazole (1), triadimefon (2), tebuconazole (3), diniconazole (4), flutriafol (5), propiconazole (6), and difenoconazole (7), were evaluated using normal phase high-performance liquid chromatography. Chrialcel OD column and Chrialcel OJ column were used. The influence of column temperature was studied for the optimization of the resolution as well as the type and percentage of organic modifier in the mobile phase. The retention factors for the enantiomers of all investigated compounds decreased as the temperature increased. The natural logarithms of the selectivity factors (ln alpha) of hexaconazole (1), tebuconazole (3), flutriafol (5), propiconazole (6) and difenoconazole (7) depended linearly on the inverse of temperature (1/T) while the corresponding values for triadimefon (2) and diniconazole (4) kept unchanged in the studied temperature range 10-35 degrees C. Van't Hoff plots afforded thermodynamic parameters, such as the apparent change in enthalpy Delta H degrees, the apparent change in entropy Delta S degrees and the apparent change in Delta Delta H degrees and Delta Delta S degrees. The thermodynamic parameters (Delta H degrees, Delta S degrees, Delta Delta H degrees and Delta Delta S degrees) were calculated in order to provide an understanding of the thermosynamic driving forces for enantio-separation. The established method shows perspective to be used for preparing micro-scale amount of pure enantiomers of the chiral triazoles studied. Chirality 21:421-427, 2009. (C) 2008 Wiley-Liss, Inc.