Determination of doxycycline in chicken fat by liquid chromatography with UV detection and liquid chromatography–tandem mass spectrometry

A sensitive analytical method for determination of doxycycline (DC) residues in chicken fat/fat and skin was developed. The extraction, in the presence of the internal standard (IS) minocycline (MINO), was carried out using solution of oxalic acid (pH 4.0) and ethyl acetate. The samples were cleaned up by solid phase extraction (SPE) procedure using, at first carboxylic acid and then polymeric Strata X cartridges. Chromatographic separation of DC by LC–UV was achieved on a Luna C8 analytical column and for LC–MS/MS analysis Luna C18 column was used. The presented procedures were evaluated according to the Commission Decision 2002/657/EC. Specificity, decision limit (CCα), detection capacity (CCβ), recovery (absolute and relative), precision (repeatability and reproducibility) were determined during validation process. The limit of detection (LOD) was 10 μg/kg for LC–UV and 1 μg/kg for LC–MS/MS method. The limit of quantitation (LOQ) was 15 and 2 μg/kg for LC–UV and LC–MS/MS, respectively. The absolute recovery for the LC–UV and relative recovery for the LC–MS/MS method at 300 μg/kg concentration level were 79%; 101% for fat and 82%; 99% for fat and skin, respectively. The developed liquid chromatography with ultraviolet detection (LC–UV) and liquid chromatography tandem mass spectrometry (LC–MS/MS) methods have been applied to quantitative determination of doxycycline (DC) in samples of chicken fat tissue obtained from animals treated with DC.