Abstract: A method was developed for the rapid simultaneous determination of flupyradifurone and its metabolites 6-chloronicotinic acid and difluoroacetic acid in milks using ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). A simple and efficient dispersive solid phase extraction method was used to purify milk samples, and the purification strategy was evaluated. This study optimized the pretreatment and chromatography-mass spectrometry conditions, extracted with 10mL acetonitrile, vortexed and sonicated, purified with modified QuEChERS (150 mg MgSO4, 20 mg PSA, 20 mg GCB, 50mg C18) packing, and filtered with a 0.22 μm filter after nitrogen blowing and reconstitution, direct injection analysis. Using acetonitrile and 0.1% formic acid water as the mobile phase for gradient elution, Shim-pack-GIST C18 chromatographic column (100 mm×2.1 mm, 1.7 μm) for separation, electrospray ion source (ESI), and detected under the multiple reaction monitoring (MRM) mode with positive and negative ions scan simultaneously, matrix standard curve external standard method quantification. The results showed that under the optimized conditions, the target compounds had good peak shape, high response value, and good linear relationship in the range of 0.005~2.5 mg/L (R2>0.996), which could meet the requirements of quantitative analysis. The average recoveries of flupyradifurone and its metabolites varied from 70.2% to 97.6% and the relative standard deviations were between 3.6% and 5.3% at three addition levels. The limits of detection (LODs) ranged from 0.01~0.05 mg/kg. This method has high accuracy, sensitivity, and good reproducibility, and is suitable for the accurate determination of flupyradifurone and its metabolite residues in large batches of milk samples, providing reliable technical support for the supervision of the pesticide flupyradifurone.

Key words: Ultra high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), QuEChERS, flupyradifurone, metabolites, milk