Trace determination of thiamethoxam and clothianidin in wheat leaves and wheat ears and its application

A rapid and trace analytical method was established for the determination of thiamethoxam and its metabolite clothianidin in wheat leaves and wheat ears using ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Wheat leaves and wheat ears were extracted with acetonitrile and cleaned up with NH₂/Carb solid phase extraction column to remove impurities such as chlorophyll and starch. The internal standard method was used for quantitation. The results showed that the linearity of thiamethoxam and clothianidin was good in the range of 0.001-0.5 mg/L, and the correlation coefficient was greater than 0.99. After internal standard correction, the recoveries of thiamethoxam and clothianidin in wheat leaves and wheat ears were in the range from 83.4% to 117.9% at 4 levels of 0.001, 0.01, 0.1 and 1 mg/kg, and the relative standard deviations were in the range of 1.6% to 13.0%. The limit of quantitation was 0.001 mg/kg. This method was used to determine the wheat leaves and wheat ears field samples after the wheat crops were sprayed with thiamethoxam 250 WG by unmanned aerial vehicle (UAV). The concentrations of thiamethoxam in wheat leaves and wheat ears were 4.24 and 1.34 mg/kg, respectively, at 2 h after application. On the 14th day after application, the concentrations of thiamethoxam and clothianidin were 0.097 and 0.079 mg/kg in wheat leaves, and were 0.031 and 0.046 mg/kg in wheat ears, respectively. This method can meet the detection requirements of wheat during the whole growth period, and it can also be used to study the conduction and distribution characteristics and residual metabolism of thiamethoxam and clothianidin in wheat plants.