Residue and dissipation dynamics of pymetrozine in sorghum by QuEChERS and high performance liquid chromatography-tandem mass spectrometry

A QuEChERS method with high performance liquid chromatography-tandem mass spectrometry(HPLC–MS/MS) was developed and validated to simultaneously determine pymetrozine in sorghum and its straw. The samples were extracted from sorghum and its straw with acetonitrile containing 0.1% acetic acid, and the extracts were purified by PSA and C₁₈ column. The samples were then detected by the HPLC-MS/MS using positive ions electrospray scanning with multiple reaction monitoring mode. The matrix-matched external standard calibration curves were used for quantitative analysis. The satisfactory linearity (R² ≥ 0.9970) of this method was obtained for sorghum and its straw in the range of 0.001-0.2 mg/L. The intra-day average recoveries of pymetrozine in spiked samples with fortified levels of 0.002, 0.02 and 0.2 mg/kg were between 71% and 92%, and the relative standard deviation (RSD) ranged from 0.8% to 5.6% (n = 5). The inter-day average recoveries ranged from 71% to 96% and the RSD ranged from 1.2% to 4.2% (n = 15). The limits of quantification for pymetrozine in sorghum and its straw were both 0.002 mg/kg. The dissipation dynamics of pymetrozine in sorghum straw followed the first order kinetics equations, and its dissipation half-lives in the Inner Mongolia and Heilongjiang were 9.7 d and 9.0 d, respectively. The results indicated that the established method could be used to detect trace amounts of pymetrozine in sorghum. The data could also help to establish the maximum residue limits of pymetrozine on sorghum and establish the proper and safe usage of pymetrozine on sorghum plants.