Abstract:

A high performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS-MS) was developed to determine the degradation dynamics and final residues of 80% dimethomorph water dispersible granules (DWG) in ginseng root, stem, leaf and soil, and dietary risk assessment of dimethomorph was conducted. The samples were extracted with acetone, cleaned-up with GPR solid phase extraction cartridge, separated by liquid chromatography and analyzed by electron spray ionization (ESI) in positive ion multiple reaction monitoring (MRM) mode. The quantification was performed
by the external standard method. The recoveries of dimethomorph in ginseng root, stem, leaf and soil at spiked levels of 0.01–0.20 mg/kg were in the range of 82.0%–95.5% with relative standard deviation of 5.01%–7.67%. The half-life of dimethomorph was 9.13–16.35 days at spraying dosage of 800 g a.i./hm2. The final residues were below 0.024 5 mg/kg in root, 0.023 3–0.138 7 mg/kg in stem, 0.121 5–0.618 2 mg/kg in leaf and 0.008 4–0.073 8 mg/kg in soil, and the risk was very low with a risk quotient of 3.56×10–7 (much less than 1), and the residues could be reduce to a safe level after single spraying in dosage range from 533.33 to 800 g a.i./hm2 during the growth season. The MRL of dimethomorph in ginseng is suggested to be 0.05 mg/kg temporarily, and its preharvest interval is 28 days.

Key words: ginseng, dimethomorph, degradation dynamics, final residues, dietary risk assessment, high performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS-MS)