Simultaneous determination of residual thiamphenicol and florfenicol in foods of animal origin by HPLC/electrospray ionization-MS/MS.

A simple and reliable method using HPLC/MS/MS has been developed for determination of thiamphenicol and florfenicol in foods of animal origin, such as pork, porcine liver, porcine kidney, beef, bovine liver, fish, and chicken. The HPLC separation was performed on a Waters XTerra phenyl column (100 x 2.1 mm, 3.5 microm) with a gradient mobile phase system of 0.1% formic acid-methanol at a flow rate 0.35 ml/min. Negative ionization produced the molecular ions at m/z 354 and 356 for thiamphenicol and florfenicol, respectively. Two characteristic transition reactions (m/z 354-->185, 290 and m/z 356-->336, 185) in the selected reaction monitoring mode were tested for detection and confirmation of thiamphenicol and florfenicol simultaneously. The analytes were extracted with ethyl acetate and defatted with n-hexane by liquid-liquid extraction. The recoveries of thiamphenicol and florfenicol by the developed method were 72.5-97.6%. The limits of determination were 1.0 ng/g (ppb) for both compounds.

Multiclass analysis of 23 veterinary drugs in milk by ultraperformance liquid chromatography-electrospray tandem mass spectrometry.

An ultraperformance liquid chromatography-electrospray tandem mass spectrometry (UPLC-MS/MS) method for the simultaneous detection and confirmation of 23 veterinary (multiclass) drugs in milk was developed and validated. The analytes were extracted by acetonitrile, evaporated and injected into the UPLC-MS/MS system on a Waters UPLC HSS T3 column in gradient mode. Data acquisition under MS/MS was achieved by applying multiple reaction monitoring (MRM) of two ion transitions per compound to provide a high degree of specificity. Results showed good repeatability, and recoveries for the 12 macrolide, 7 ß-lactam and 2 lincosamide antibiotics and 2 other veterinary drugs (morantel, orbifloxacin) used in milk averaged 51.8-139.0%, 51.5-100.6%, 82.4-102.5% and 87.5-99.4%, respectively. The coefficients of variation (C.V.) of the recoveries were less than 15% for intraday and interday precisions. The limits of quantification (LOQs) were all lower than 5 ng/ml. This method was applied to 17 fresh milk samples and only lincomycin was found in milk samples under allowable levels. Overall, this method is a suitable and rapid tool to confirm the presence of 23 veterinary drug residues in milk.