Stereoselective degradation of diclofop-methyl in soil and Chinese cabbage

Abstract

The stereoselective degradation of the racemic diclofop-methyl in Chinese cabbage and several agricultural soils had been investigated. Both the enantiomers were analyzed by organic solvent extraction and validated by chiral high-performance liquid chromatography-diode array detector (DAD). Cellulose-tris-(3,5-dimethylphenylcarbamate)-based chiral column was used for the chiral separation of the two enantiomers applying a mixture of n-hexane and 2-propanol (90:10) as mobile phase at a flow rate of 1.0 mL/min. The elution order of the two enantiomers was distinguished by a JASCO 2000 HPLC-circular dichroism (CD) system and the first elution was (−)-enantiomer while the other was (+)-enantiomer. Racemic diclofop-methyl was fortified into 10 types of agricultural soils and foliar applied to Chinese cabbage. The assay method was linear over a range of concentrations (0.5–250 mg L −1) and the mean recovery was more than 80% for both enantiomers. The limit of detection for both enantiomers was 0.1 μg g −1 in soil and plant samples. The results of the stereoselectivity degradation of diclofop-methyl enantiomers in soil showed that the (−)-enantiomer was dissipated faster than the (+)-enantiomer in two typical soils and this enantioselectivity may be caused by microorganism, but no stereoselectivity was observed in other soils. In Chinese cabbage plant, (+)-enantiomer accumulated and eliminated faster than its antipode.