Method Validation and Residue Analysis of Mesosulfuron-Methyl and Diflufenican in Wheat Field Trial by Liquid Chromatography with Tandem Mass Spectrometry

In this study, an optimized QuEChERS method with liquid chromatography-tandem mass spectrometry (LC–MS/MS) was developed and validated for the determination of mesosulfuron-methyl and diflufenican in wheat grain and straw. At the spiking levels of 0.01, 0.02, 0.05, 0.1, and 1 mg/kg, the average recoveries of five repetitions were 74–98% with RSDs of 1–11%. The LOQs of the two herbicides were both 0.01 mg/kg for wheat grain and wheat straw. The ultimate residues of field trials in ten regions were mostly lower than LOQ (0.01 mg/kg), except that the residue of mesosulfuron-methyl in wheat straw in Hubei Province was 0.015 mg/kg and the residue of diflufenican in wheat straw in Shaanxi Province was 0.028 mg/kg. Long-term dietary risk assessment indicated that hazard quotients were 0.0014% and 0.031% for mesosulfuron-methyl and diflufenican, respectively, which means that it is safe to spray the two herbicides on wheat at the recommended dosage.