Studies of enantiomeric degradation of the triazole fungicide hexaconazole in tomato, cucumber, and field soil by chiral liquid chromatography-tandem mass spectrometry.

Chiral pesticide enantiomers often show different bioactivity and toxicity; however, this property is usually ignored when evaluating their environmental and public health risks. Hexaconazole is a chiral fungicide used on a variety of crops for the control of many fungal diseases. This use provides opportunities for the pollution of food and soil. In this study, a sensitive and convenient chiral liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) method was developed and validated for measuring hexaconazole enantiomers in tomato, cucumber, and soil. Separation was by a reversed-phase Chiralcel OD-RH column, under isocratic conditions using a mixture of acetonitrile-2 mM ammonium acetate in water (60/40, v/v) as the mobile phase at a flow rate of 0.4 mL/min. Parameters including the matrix effect, linearity, precision, accuracy and stability were undertaken. Then the proposed method was successfully applied to investigate the possible enantioselective degradation of rac-hexaconazole in plants (tomato and cucumber) and soil under field conditions. The degradation of the two enantiomers of hexaconazole proved to be enantioselective and dependent on the media: The (+)-enantiomer showed a faster degradation in plants, while the (-)-enantiomer dissipated faster than the (+)-form in field soil, resulting in relative enrichment of the opposite enantiomer. The results of this work demonstrate that both the environmental media and environmental conditions influenced the direction and rate of enantioselective degradation of hexaconazole.