Residueanddissipationdynamicsofdithianonandpyraclostrobininapples

A rapid analytical method for simultaneous determination of dithianon and pyraclostrobin in apple samples was developed using ultra high liquid chromatography with photo-diode array. Residues and dissipation of dithianon and pyraclostrobin in apples were investigated. At the fortified level from 0.1 mg/kg to 5 mg/kg, the recoveries of dithianon and pyraclostrobin ranged from 72% to 98% with the relative standard deviations varied from 2.0 % to 9.7 %. The limit of quantification (LOQ) of this method was 0.1 mg/kg. The half-lives of dithianon and pyraclostrobin in apples were 3.0-6.5 d and 13.5-23.6 d, respectively. When the recommended dosage (0.43 g a.i./L) and 1.5 times of the recommended dosage (0.64 g a.i./L) of 16% pyraclostrobin·dithianon were sprayed for 3-4 times, the terminal residues of dithianon and pyraclostrobin at the 21th day after the last application ranged from < 0.1 mg/kg to 0.80 mg/kg and from < 0.1 mg/kg to 0.34 mg/kg, respectively, which were below the maximum residue limits of dithianon (5.0 mg/kg) and pyraclostrobin (0.5 mg/kg) in apples. It is recommendated that, for the prevention of anthrax of apples, the security interval of 16% pyraclostrobin·dithianon water dispersible granules is 21 days, when sprayed for 3 times at the dose of 0.43 a.i.g/L.