ANALYSIS OF TILMICOSIN IN SWINE LIVER EXTRACTS BY LIQUID CHROMATOGRAPHY/ATMOSPHERIC PRESSURE CHEMICAL IONIZATION MASS SPECTROMETRY

Tilmicosin is a semisynthetic macrolide antibiotic used in the treatment of respiratory disease in cattle and swine. The technique of liquid chromatography/atmospheric pressure chemical ionization mass spectrometry (LC/APCI-MS) was employed in an on-line capacity for the analysis of tilmicosin in extracts from spiked swine liver. Increasing the potential in the cone/skimmer region of the ion source resulted in an increased abundance of unique structurally indicating fragment ions of tilmicosin. Three ions, [M + H]+ and two diagnostic fragment ions were chosen for confirmation of the presence of tilmicosin in swine liver tissue extracts using the mass spectrometer in selected-ion monitoring mode. The ion abundance ratios arising from any given combination of ions in data acquired from extracts of swine liver tissue spiked with tilmicosin at 5 and 10 ppm were within <10% of the corresponding mean standard abundance ratio, and duplicate sample analyses exhibited < 10% relative standard deviation. These results suggest the potential for the application of LC/APCI-MS as a confirmatory technique for tilmicosin in swine liver.