Optimization and validation of an oxidation and solid-phase extraction procedure for analysis of imidacloprid and its metabolites in cereals using ultra-performance liquid chromatography tandem mass spectrometry

A simple and reliable ultraperformance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method was proposed for analysis of the total residues of imidacloprid and its 6-chloropyridinyl metabolites in cereals. The method consisted of extraction with acidic acetonitrile, conversion of the analytes into 6-chloronicotinic acid by oxidation, cleanup with C18 cartridges, and UPLC-MS/MS detection. The validation results met the requirements of the guidelines for the detection of pesticide residues in EU and China, including the linearity (R2 = 0.998), matrix effect (−0.5∼-7.1%), accuracy (75.1–109.6%), precision (3.5–13.0%), metabolite conversion efficiency (81.6–102.3%), and sensitivity (limit of detection (LOD) of 0.0015 mg/kg and limit of quantification (LOQ) of 0.0050 mg/kg). The established method met the requirements of the residue definition and the maximum residue levels (MRLs) of imidacloprid in cereals, and was further applied to investigate the residues and dissipation of imidacloprid and its metabolites in wheat samples after field application.