Dissipation and Distribution Behavior of Azoxystrobin, Carbendazim, and Difenoconazole in Pomegranate Fruits

摘要

The dissipation behavior and degradation kinetics of azoxystrobin, carbendazim, and difenoconazole in pomegranate are reported. Twenty fruits/hectare (5 kg) were collected at random, ensuring sample-to-sample relative standard deviation (RSD) within 20—25%. Each fruit was cut into eight equal portions, and two diagonal pieces per fruit were drawn and combined to constitute the laboratory sample, resulting in RSDs <6% (n= 6). Crushed sample (15 g) was extracted with 10 mL of ethyl acetate (+ 10 g Na2SO4), cleaned by dispersive solid phase extraction on primary secondary amine (25 mg) and C_(18) (25 mg), and measured by liquid chromatography tandem mass spectrometry. The limit of quantification was ≤0.0025 μg g~(-1) for all the three fungicides, with calibration linearity in the concentration range of 0.001-0.025 μg mL~(-1) (r~2 ≥ 0.999). The recoveries of each chemical were 75-110% at 0.0025,0.005, and 0.010 μg g~(-1) with intralaboratory Horwitz ratio <0.32 at 0.0025 μg g~(-1). Variable matrix effects were recorded in different fruit parts viz rind, albedo, membrane, and arils, which could be correlated to their biochemical constituents as evidenced from accurate mass measurements on a Q-ToF LC-MS. The residues of carbendazim and difenoconazole were confined within the outer rind of pomegranate; however, azoxystrobin penetrated into the inner fruit parts. The dissipation of azoxystrobin, carbendazim, and difenoconazole followed first + first order kinetics at both standard and double doses, with preharvest intervals being 9, 60, and 26 days at standard dose. At double dose, the preharvest intervals extended to 20.5,100, and 60 days, respectively.