Residues and dissipation dynamics of six typical pesticides and three metabolites in cucumber by QuEChERS-ultra performance liquid chromatography-tandem mass spectrometry

A method for simultaneous determination of paclobutrazol, tebuconazole, prothioconazole, difenoconazole, triadimefon, cyflumetofen, and their metabolites including B-3, triadimend, CGA205375 residues in cucumber by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was established. This method was used to study the dissipation dynamics of six pesticides in cucumber at different dosages. QuEChERS method was employed for the sample preparation. The samples were extracted with acetonitrile, cleaned up with a combination of N-propyl ethylenediamine (PSA) and graphitized carbon black (GCB), detected by UPLC-MS/MS, and quantified by external standard method. The results showed that: in the range of 0.001-0.8 mg/L, the linear relationship between the mass concentration of the target analyte and its corresponding peak area was good with R² > 0.9949; at the spiking levels of 0.001, 0.01, 0.05, 0.1 and 0.5 mg/kg, the average recoveries of six pesticides and their metabolites in cucumber were 71%-105%, the relative standard deviations (RSDs, n = 5) were 1.7%-8.8%, and the limit of quantification (LOQ) was 0.001-0.01 mg/kg. The method has the advantages of good cleanup efficiency, simple and efficient operation, and high sensitivity, and it can be applied to the simultaneous detection of the six pesticides and three metabolites in cucumber. In the field trials, both the recommended dose and five times of the recommended dose of the six pesticides were applied during the fruit-bearing period of cucumbers. The dissipation dynamics of five pesticides (except for prothioconazole) in cucumber all conformed to the first-order reaction kinetic equation, and the half-lives were 3.15-9.62 d. The research results provide references for the scientific and rational use of pesticides and their risk assessment.