Abstract: A method was developed for the determination of fipronil and its metabolites including fluorocarbonitrile, fipronil sulfone and fipronil sulfide in paddy field-cultured aquatic products by quick, easy, cheap, effective, rugged and safe (QuEChERS) extraction coupled with high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Samples were extracted using acetonitrile (containing 0.10% formic acid, V/V) as the extraction solvent with vortex shaking using a ceramic homogenizer, and purified by 0.15 g of primary secondary amine (PSA) sorbent. The target compounds were separated on an Agilent ZORBAX Extend-C18 column (2.1 mm × 100.0 mm, 1.8 μm), and was detected by using an electrospray ionization (ESI) source in the negative ion mode with multiple reaction monitoring (MRM). The analytes were quantified with external standard using the matrix-matched standard calibration curve method. The results indicated that the average spiked recoveries of fipronil, fluorocarbonitrile, fipronil sulfone and fipronil sulfide in paddy field-cultured aquatic products were 85.2%–112.6% with relative standard deviations (RSDs) of 1.2%–12.4%. Good linearity was obtained in the concentration range of 0.5–100.0 ng/mL, with correlation coefficients higher than 0.999. The limit of detection (LODs) were 1.0–1.5 μg/kg, and the limit of quantitation (LOQs) were 3.0–5.0 μg/kg, which were both lower than the maximum residue limit (10 μg/kg) for fipronil in poultry meat stipulated by the national standard GB 2763–2019 Maximum Residue Limits for Pesticides in Food. The developed method was simple, sensitive and accurate, and could be used for routine analysis of fipronil and its three metabolite residues in paddy field-cultured aquatic products.

Key words: high performance liquid chromatography-tandem mass spectrometry; QuEChERS; paddy field; aquatic products; fipronil and its metabolites