Abstract: In this paper, a method for the simultaneous detection of pyraclostrobin and cymoxanil in cucumber and soil was developed using the quick, easy, cheap, effective, rugged and safe (QuEChERS) method coupled with high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The degradation kinetics and the final residue of pyraclostrobin-cymoxanil water dispersible granule in cucumber and soil were studied, aiming to evaluate the safety of this pesticide combination. Samples were extracted with acetonitrile and the extract was cleaned up with primary secondary amine (PSA) and C18 before being analyzed by mass spectrometry in the multiple-reaction monitoring (MRM) mode. There was a good linear relationship within the concentration range of 50–800 μg/L with correlation coefficients (R2) greater than 0.996 1. The average recoveries of two pesticides in cucumber and soil were 70.45%–107.08% at three spiked concentrations. The limit of quantification (LOQ) was 0.050 mg/kg for both. Two-year field experiments at three different locations showed that the residual concentrations of pyraclostrobin and cymoxanil were lower than the LOQ after 1 and 7 d, and 7 and 1 d after being applied at the high recommended 1.5-fold dose to cucumber and soil, respectively. When applied at the recommended dose 3 times to cucumber with a 7 d interval between each dose, the maximum residual concentrations of pyraclostrobin and cymoxanil were 0.090 and 0.060 mg/kg, respectively, which were lower than China’s maximum residue limits (MRL) for pyraclostrobin and cymoxanil in cucumber (0.5 mg/kg). The recommended safe pre-harvest interval was 3 d.

Key words: pyraclostrobin, cymoxanil, cucumber, soil, QuEChERS, high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), residue, dissipation