Selective behavior of imazalil enantiomers and its metabolites in citrus storage

The absolute configuration of imazalil and its metabolite imidazol ethanol was determined. A chiral analysis method based on high performance liquid chromatography-tandem mass spectrometry was established for the determination of imazalil and imidazol ethanol in different parts of citrus. The selective degradation behavior of imazalil during citrus storage was studied. Orange pulp, whole fruit and orange peel(Citrus reticulata Blanco cv. Ponkan) samples were extracted by acetonitrile (containing 1% acetic acid by volume). Enantiomers of imazalil and imidazol ethanol were separated by chiral column of Lux Cellulose-2 and Chiralpak IG-3, respectively. The linear range of imazalil and imidazol ethanol enantiomers was 0.001~0.5 mg/L (R² >0.9915, >0.9991). The limit of quantification (LOQ) of the method was 0.0005 mg/kg. The average recoveries of the four supplemental levels (0.0005, 0.05, 0.125 and 0.25 mg/kg) in different substrates were 78%-101% and 73%-105%, with relative standard deviations (RSDs) of 0.4%-2.9% and 0.4%-5.6%, respectively. The storage and degradation of imazalil in orange conforms to the first-order kinetic equation. The half-lives of R-imazalil in whole orange and orange peel were 136 d and 158 d, respectively, while those of S-imazalil in whole orange and orange peel were 77 d and 82 d, respectively. The degradation rate of S-imazalil was significantly faster than that of R-imazalil. The accumulation velocity of S-imidazole ethanol was higher than that of R-imidazole ethanol in different parts of orange fruits.