Quantitative Analysis of Bacitracin in Porcine Edible Tissues by High-Performance Liquid Chromatography-Electrospray Ionization Tandem Mass Spectrometry and Its Application to Residue Depletion Study

The residue kinetics of bacitracin in animals has rarely been quantitatively described due to inadequate sensitivity of analytical methods. A sensitive and selective quantitative liquid chromatography coupled with electrospray ionization tandem mass spectrometry (LC-MS/MS) method was developed to determine the residue depletion kinetics of zinc bacitracin in pigs. The tissues samples were extracted with acidified methanol/water solution (v/v, 1:1, 1 % formic acid) and followed by liquid-liquid extraction with saturated solution of 0.1 mmol dithizone in chloroform. The extracts were subjected to Phenomenex Strata-X cartridges for further cleanup with 0.1 % formic acid in methanol. Analysis was performed on a C-18 column with positive-ion electrospray mass spectrometry and multiple-reaction monitoring mode. The product ions at m/z 199 and 227 were selected for bacitracin A confirmation and at 199 for quantification. The developed method was linear in the concentration ranges of 150-4000 mu g/L for bacitracin with limit of detection (LOD) and limit of quantification (LOQ) of 25 and 50 mu g/kg for kidney and 20 and 50 mu g/kg for skin with fat, liver, and muscle. The recoveries from different tissues were higher than 82.1 % at three different spiking levels with relative standard deviations (RSDs) less than 8.8 %. The residue depletion study showed that higher concentration and longer residue time were detected in kidney than in other three tissues. The elimination half-life in kidney was 0.45 days, and the recommended withdrawal period was zero. These results suggest that the established method satisfactorily enables a closer study of residue depletion kinetics of bacitracin in swine.