Residues and dissipation dynamics of spirotetramat and its metabolites in pear and soil

A method for the simultaneous determination of spirotetramat and its metabolites such as spirotetramat-enol-glucoside(S-glu), spirotetramat-keto-hydroxy(S-keto), spirotetramat-enol (S-enol) and spirotetramat-mono-hydroxy(S-mono) in pear and soil was developed. The residual dissipation dynamics of spirotetramat in pears was determined. The residues in samples were extracted with acetonitrile(containing 1% acetic acid) and cleaned up by dispersivemethod with N-propylethylenediamine (PSA) and anhydrous magnesium sulfate as cleaning agents. Then the samples were detected by ultra performance liquid chromatography-tandem massspectrometry under selective reaction monitoring mode, and quantified by external standard method. The results showed good linearity (R² ≥ 0.999) between mass concentration and peak area of mass spectra of each compound when the concentrations of spirotetramat ranged from 0.005 to 0.10 mg/L; S-glu from 0.005 to 0.5 mg/L; S-keto, S-enol and S-mono from 0.000 5 to 0.5 mg/L, respectively. When the fortified levels ranged from 0.005 to 0.7 mg/kg, the average fortified recoveries in pear were in the range of 84% to 109% and the reletive standard deviations (RSD) were 1.2%-3.3%. The average fortified recoveries in soil were in the range of 86% to 102% and the RSD were 1.1%-3.6%. The limits of quantification(LOQ) were 5 μg/kg. The method is rapid, sensitive and reproducible. Therefore, It is suitable for the rapid detection and identification of spirotetramat and its metabolite residues in pear and soil. According to the recommended dosage, the total residues of spirotetramat and its metabolites were 0.023-0.056 mg/kg in the fruit and 0-0.015 mg/kg in the soil when the pear was ripe and harvested. The half-life of spirotetramat in pear fruit was 12.4 d, and the half-life in soil was 7.1 d. Therefore, it is safe to use spirotetramat for the pest control of pear tree.