Determination of florfenicol in fish feed by liquid chromatography

A simple, accurate, and reproducible assay was developed for the determination of Florfenicol in medicated fish feed. Florfenicol was extracted from ground feed into an acetonitrile-water mixture by shaking and sonication. A portion of the centrifuged extract was passed through an Envi-Carb solid-phase extraction cartridge, through which Florfenicol eluted unretained. The collected eluant was diluted to adjust for analyte concentration, and injected into a reversed-phase liquid chromatography system. Samples were quantitated by external standard analysis versus multilevel calibration solutions. The procedure is suitable for the quantitation of samples medicated with 0.2-4 g/kg Florfenicol. Accuracy was evaluated by 2 analysts, who determined recovery of Florfenicol from feeds fortified over a range of 0.1-6.0 g/kg. The average recovery was 100.5% (relative standard deviation, 1.2%). The linearity, accuracy, precision, reproducibility (interday and analyst), and selectivity of the method are presented. The detection and quantitation limits were determined to be 0.2 and 1.0 mg/kg, respectively.