Determination of metacycline and related substances by column liquid chromatography on poly(styrene-divinylbenzene)

Isocratic column liquid chromatography on poly(styrene-divinylbenzene) copolymer allowed complete separation of metacycline, 4-epimetacycline, oxytetracycline, doxycycline and 6-epidoxycycline. 2-Acetyl-2-decarboxamidometacycline was eluted on the tail of metacycline. The mobile phase was 2-methyl-2-propanol-0.2 M phosphate buffer (pH 9.0)-0.01 M sodium ethylenediaminetetraacetate (pH 9.0)-water (2.5:10:10:77.5, m/v/v/v). The flow-rate was 1.0 ml/min and detection was performed at 254 nm. Official standards were compared and a number of commercial bulk samples and specialties were analysed. 2-Acetyl-2 decarboxamidometacycline, 6-epidoxycycline and doxycycline were the main impurities, while 4-epimetacycline and oxytetracycline were minor impurities.