Simultaneous determination of flonicamid and its metabolites in cucumbers and apples by liquid chromatography-tandem mass spectrometry

A method was developed for the simultaneous determination of flonicamid and its metabolite [N-(4-trifluoromethylnicotinoyl) glycine (TFNG), 4-trifluoromethylnicotinic acid (TFNA) and 4-trifluoromethylnicotinamide (TFNA-AM)] in cucumbers and apples by liquid chromatography-tandem mass spectrometry (LC-MS/MS) with liquid-liquid extraction. The sample was extracted twice with phosphate buffer solution (pH 7.0), and the extract was adjusted to pH 1.5 - 2.0, then an aliquot of the extract (3 mL) was extracted with ethyl acetate. The final extract was dried under nitrogen and the residue was dissolved in 0.1% formic acid in water/methanol (80/20, v/v). The sample was analyzed by LC-MS/MS and quantified with the external standard calibration curve method. The detection limits of flonicamid, TFNG, TFNA and TFNA-AM were 0.17, 0.20, 0.35 and 0.60 microg/kg, respectively. The average recoveries of flonicamid and its metabolites in cucumbers and apples were 82.9% - 104.1%. In the intra-assay, the relative standard deviations were 3.6% - 6.9% at the spiked levels of 5.0 - 2 000 microg/kg. There were good linear correlations (the calibration coefficients were above 0.998) between the peak areas and the concentrations of flonicamid and its metabolites in the range of 0.5 - 200 microg/L. The volume of organic solvent used in the whole pretreatment procedure was only 6 mL. The method is accurate, highly sensitive and stable for the determination of flonicamid and its metabolites.