Separation of tetracyclines by liquid chromatography with acidic mobile phases and polymeric columns

The LC separation of selected tetracyclines has been studied using polymeric columns. Mobile phases containing acetonitrile-0.02 M sodium perchlorate, pH 2.0, were used. Asymmetry factor and number of theoretical plates were calculated for the tetracyclines investigated on four polymeric columns. The columns included: two polystyrene-divinylbenzene (PS-DVB) copolymeric columns, a PS-DVB column with octadecyl ligands and a polymethacrylate column with octadecyl ligands (PM-C18). The PLRP-S (PS-DVB) column and the PM-C18 column were found to be the most suitable for the analysis of the selected tetracyclines. Resolutions between pairs of selected tetracyclines were calculated and compared for the latter two columns, with the PLRP-S (PS-DVB) columns showing the best results. The PM-C18 column has the advantage of allowing the use of higher flow rates, which minimized analysis times. The tetracyclines included minocycline, oxytetracycline, tetracycline, demeclocycline, chlortetracycline, methacycline, doxycycline and meclocycline. Representative degradation products and impurities for selected tetracyclines were also included.