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This work firstly reported the development of liquid chromatography coupled to an ion trap mass spectrometer (LC-MS ion trap) for the simultaneous determination of nitrofurans (e.g. nitrofurazone (NFZ), nitrofurantoin (NET), furazolidone (FZD) and furaltadone (FTD)), nitroimidazoles (e.g. metronidazole (MNZ), ronidazole (RNZ) and dimetridazole (DMZ)) and chloramphenicol (CAP) in feed water. Isotope-labeled internal standards for the corresponding target analytes were employed to prevent matrix effects that might lead to signal suppression/enhancement. High performance liquid chromatography (HPLC) analysis was performed on a Prodigy ODS-3 column, 2.0 mm x 150 mm, 5 gm with a guard cartridge at a flow rate of 0.2 mL/min, column oven temperature of 40 degrees C, and an injection volume of 10 mu L. Solid phase extraction (SPE) procedures, factors affecting HPLC separation (e.g. buffer pH and concentrations) and mass spectrometry (MS) parameters were optimized. After an off-line SPE by the OASIS HLB cartridges (with an enrichment factor of 400), the eight antimicrobial agents were separated in 18 min using a gradient elution of acetonitrile in acidified water (pH 5.0). MS detection was by an ion trap MS coupled with electrospray ionization (ESI) in tandem mass spectrometry mode (MS/MS) using the nebulizer gas at 35 psi, drying gas at 9 L/min and drying temperature of 325 degrees C. Method linearity was good (r(2) = 0.979-0.999) with acceptable precision (% RSDs = 3.4-26.6%) and accuracy (%recovery = 88.4-110.1%). Very low limits of detection (LOD) and quantitation (LOQ) were achieved in ranges of 0.002-0.06 mu g/L and 0.005-0.25 mu g/L, respectively. The established method is successfully employed by the Department of Livestock Development of Thailand for the monitoring of the drug residues in feed waterbecause of its convenience, reliability and high sensitivity. (C) 2013 Elsevier B.V. All rights reserved.