Residue Analysis and Degradation Studies of Fenbuconazole and Myclobutanil in Strawberry by Chiral High-Performance Liquid Chromatography–Tandem Mass Spectrometry

A simple and sensitive enantioselective method for the determination of fenbuconazole and myclobutanil in strawberry was developed by high-performance liquid chromatography–tandem mass spectrometry (HPLC-MS/MS). Fenbuconazole and myclobutanil residues in strawberry were extracted with acetonitrile containing 1% acetic acid, and an aliquot was cleaned up with PSA (primary and secondary amine) and C18 sorbent. The direct resolution of fenbuconazole and myclobutanil enantiomers was performed on a cellulose tris (3,5-dimethylphenylcarbamate) column using acetonitrile–0.1% formic acid solution (60:40, v/v) as the mobile phase. Quantification was achieved using matrix-matched standard calibration curves, and the limits of quantification for fenbuconazole and myclobutanil enantiomers in strawberry were both 2 μg/kg. The method was successfully utilized to investigate the probable enantioselective degradation of fenbuconazole and myclobutanil in strawberry. The results showed that the degradation of the fenbuconazole and myclobutanil enantiomers in strawberry followed pseudofirst-order kinetics (R 2 > 0.97). The results from this study revealed that the degradation of fenbuconazole in strawberry was not enantioselective, while the degradation of myclobutanil was enantioselective, and the (+)-myclobutanil showed a faster degradation than (−)-myclobutanil in strawberry, resulting in the relative enrichment of (−)-myclobutanil in residue. The results could provide a reference to fully evaluate the risks of these two fungicides.