Simultaneous determination of ten macrolides drugs in feeds by high performance liquid chromatography with evaporation light scattering detection

A sensitive and reproducible method based on high performance liquid chromatography with evaporation light scattering detection (ELSD) was developed for the simultaneous determination of 10 macrolides drugs such as azithromycin, tulathromycin, spiramycin, tilmicosin, tylosin, erythromycin, clarithromycin, roxithromycin, midecamycin and josamycin in feeds. Feed samples were extracted with a sodium borate buffer solution (pH 10.0) ethyl acetate. The dry extracts were dissolved in a phosphate buffer solution (pH 8.0), and then applied to an Oasis HLB solidphase extraction cartridge for cleanup. The residues were reconstituted in 0.5 mL of the mobile phase. By optimizing the main operational parameters of ELSD and chromatographic conditions, all target compounds were well separated on an Ecosil C-a - SH column (250 mm x 4.6 mm, 5 mm) using a gradient elution program. The calibration curves showed good linearity (r > 0.9985) in the range of 1200 mu g mL(-1) for ten analytes. The average recoveries of all analytes from five kinds of feeds spiked at three levels were between 60.2% and 112%, with intraday and inter day relative standard deviations below 11% and 15%, respectively. The limits of detection ranged from 0.4 to 0.8 mg kg(-1) for ten macrolides.