Determination of roxithromycin by liquid chromatography/mass spectrometry after multiple-dose oral administration in...

A highly sensitive and specific method for the determination of roxithromycin in broiler tissues by LC/MS was developed and validated. A dichloromethane extract of the sample was separated on C18 reversed-phase column with acetonitrile-50 mM ammonium acetate (80:20, v/v) as the mobile phase and analyzed by LC/MS via atmospheric pressure ionization/electrospray ionization interface. The limit of detection and limit of quantitation were 1 ng/g and 5 ng/g. The method has been successfully applied to determine for roxithromycin in various tissues of broilers. Residue concentrations were associated with administered dose. At the termination of treatment, roxithromycin was found in all collected samples for both dose groups. Liver was detected to have the highest residual concentration of roxithromycin. Residue concentrations of roxithromycin were lower than its LOQ in all tissues from both dose groups 10 days after the treatment of roxithromycin mixed with drinking water at a dose rate of 15 mg/L or 60 mg/L to each broiler for 7 days.