Abstract: A gas chromatography-negative chemical ionization-tandem mass spectrometry (GC-NCI-MS/MS) method for the determination of the residues of fipronil and its four metabolites (fipronil desulfinyl, fipronil sulfone, fipronil sulfide, and fipronil carboxamide) in animal-derived foods (egg, chicken, and chicken liver) was established. The samples were extracted with acetonitrile (saturated with n-hexane), and the extract was cleaned up using the quick, easy, cheap, effective, rugged, and safe (QuEChERS) method before being detected by GC-NCI-MS/MS in the multi-reaction monitoring (MRM) mode. The matrix matched standard curve method was used for quantitation. Results showed that there was a good linearity for all analytes in the range of 1–100 μg/L with correlation coefficient (r2) higher than 0.999 0. The limit of quantitation (LOQ, RSN ≥ 10) of the method was 0.5 μg/kg for fipronil disulfonyl, fipronil, fipronil sulfide and 1.0 μg/kg for fipronil sulfone and fipronil carboxamide. The average recoveries at three spiked concentration levels (2.0, 10.0, and 20.0 μg/kg) were 80.2%–108.7% with relative standard deviations (RSDs) of 3.8%–10.2%. This method exhibited high sensitivity and accuracy, and could be used for the determination of the residues of fipronil and its four metabolites in animal-derived foods.

Key words: animal-derived foods; fipronil; metabolites; gas chromatography-negative chemical ionization-tandem mass spectrometry