Development and Validation of a Method for Determination of Tilmicosin Residues in Equine Plasma and Tissues Using HPLC

Abstract A sensitive liquid chromatographic method with UV detection has been developed for the analysis of tilmicosin concentrations in equine tissues and plasma. Tilmicosin is extracted from plasma or tissues using acetonitrile and a phosphate buffer. The extract is centrifuged, filtered, and cleaned up on a conditioned C18 solid phase extraction cartridge. Tilmicosin is eluted with ammonium acetate in methanol and diluted with ammonium acetate. It is analyzed by reversed phase liquid chromatography with UV detection at 287 nm. The method was shown to be suitable for detecting tilmicosin in equine plasma, muscle, liver, kidney, and lung tissues. The limit of detection of the method was 13 ng/mL in plasma and 181 ng/g in lung tissue.