Determination of flumequine in channel catfish by liquid chromatography with fluorescence detection

Rapid methods are described for determination of flumequine (FLU) residues in muscle and plasma of farm-raised channel catfish (Ictalurus punctatus). FLU residues were extracted from tissues with an acidified methanol solutio n, and extracts were cleaned up on C-18 solid-phase extraction cartridges. FLU concentrations were determined by liquid chromatography (LC) using a C1 8 analytical column and fluorescence detection (excitation, 325 nm; emissio n, 360 nm). Mean recoveries of FLU from fortified muscle were 87-94% at 5 l evels ranging from 10 to 160 ppb (5 replicates per level). FLU recoveries f rom fortified plasma were 92-97% at 5 levels ranging from 20 to 320 ppb. Li mits of detection (signal-to-noise ratio, 3:1) for the method as described were 3 and 6 ppb for muscle and plasma, respectively. Relative standard dev iations (RSDs) for recoveries were less than or equal to 12%. Live catfish were dosed with C-14-labeled or unlabeled FLU to generate incurred residues . Recoveries of C-14 residues throughout extraction and cleanup were 90 and 94% for muscle and plasma, respectively. RSDs for incurred FLU at 2 levels in muscle and plasma ranged from 2 to 6%. The identity of FLU in incurred tissues was confirmed by LC/mass spectrometry.