Simultaneous Determination of Flonicamid and its Metabolites in Tea by Liquid Chromatography–Tandem Mass Spectrometry

Abstract

An analytical method was established to simultaneously quantify flonicamid and its metabolites 4-trifluoromethylnicotinic acid (TFNA), N-(4-trifluoromethylnicotinoyl) glycine (TFNG), and 4-trifluoromethylnicotinamide (TFNA-AM) in tea using orthogonal experimental design and liquid chromatography–tandem mass spectrometry (LC–MS/MS). Residues were extracted from the samples with acetonitrile containing 1% acetic acid and were purified with graphitized carbon black. The linearity of the method was excellent in the concentration range of 0.01–10 µg/mL, producing correlation coefficients greater than 0.996 for the target compounds. The limits of detection and quantification of all analytes in tea were 0.0013–0.013 mg/kg and 0.004–0.040 mg/kg, respectively. The average recoveries of flonicamid, TFNA, TFNG, and TFNA-AM ranged from 75.14 to 92.72%, with intra- and interday relative standard deviations of 1.07–9.75%. The proposed method was successfully applied to the terminal residue determination of flonicamid and its metabolites in dry tea processed from three field trials’ fresh samples. The determined total terminal residue concentrations of flonicamid 10 days after the last application at all three sites were below the maximum residue limit (MRL) set by the European Union (0.1 mg/kg) and the residues in all samples were lower than the MRL established by the United States Environmental Protection Agency (EPA) (8 mg/kg). This method may be used to meet the requirements for the determination of flonicamid and its metabolites that could provide guidance for establishing a MRL for flonicamid in tea in China.