Abstract: Sample pretreatment was achieved by two different methods, solid-phase extraction and liquid-liquid extraction, before the analysis of enrofloxacin and ciprofloxacin residues in freeze-dried carp meal on UPLC-MS/MS. The analytical results were compared to examine if the two pretreatment methods influence the accuracy of determination. The solid-phase extraction procedure was composed of extraction with EDTA-Mcllvaine buffer, clean-up on HLB column and blowing to dryness under nitrogen gas. Liquid-liquid extraction pretreatment was achieved sequentially through extraction with acidified acetonitrile followed by clean-up by liquid-liquid extraction with n-hexane and evaporation to dryness in a rotary evaporator. Both residues were dissolved in 1 mL of mixed solution of acetonirile and 0.2% formic acid (1:9, V/V) prior to injection into UPLC-MS/MS system. For the quantitation of enrofloxacin and ciprofloxacin, external standard method was used. Average spike recoveries of solid-phase extraction and liquid-liquid extraction ranged from 95% to 112% and from 75% to 90%, with relative standard deviations between 2.9% and 7.4% and between 1.0% and 4.6%, respectively (n = 6). The limits of detection (LOD) of solidphase extraction for the two analytes were both 1.0μg/kg, and the LOD of liquid-liquid extraction was 0.1μg/kg for enrofloxacin and 0.2μg/kg for ciprofloxacin. As a conclusion, both methods are characterized by simplicity, rapidity, good reproducibility and high selectivity, and therefore can be used to determine enrofloxacin and ciprofloxacin residues in fish meat and freeze-dried carp meal.

Key words: enrofloxacin, ciprofloxacin, residues, freeze-dried carp meal, UPLC-MS/MS