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A sensitive and reliable method using gas chromatography-negative chemical ionization mass spectrometry (GC-NCI/MS) was developed for the simultaneous determination of chloramphenicol (CAP), thiamphenicol (TAP), florfenicol (FF), and florfenicol amine (FFA) at trace levels in muscle and liver. Before extraction with ethyl acetate, CAP-d(5) was added to tissue samples as internal standard. The organic extracts were frozen to remove lipid and further purified by liquid-liquid extraction (LLE) with hexane and solid-phase extraction (SPE) using Oasis HLB cartridges. The target compounds were derivatized with BSTFA + 1% TMCS prior to GC-NCI/MS determination in selected ion monitoring mode (SIM). The recovery values ranged front 78.5 to 105.5%, with relative standard deviations (RSD) < 17%. The limits of detections (LODs) of 0.1 mu g/kg for CAP and 0.5 mu g/kg for TAP, FF, and FFA were obtain. Incurred sample and samples from local market were successfully analyzed using this method. (C) 2009 Published by Elsevier B.V.