Isolation of doxycycline, 6-epidoxycycline and 2-acetyl-2- decarboxamidometacycline from commercial metacycline by preparative column liquid chromatography on silica gel.

Isolation of doxycycline, 6-epidoxycycline and 2-acetyl-2-decaboxamidometacycline from commercial metacycline was achieved by preparative column liquid chromatography on silica gel, previously impregnated with edetate (EDTA). Careful control of the pH of EDTA allowed fine tuning of the separation. The mobile phases were composed of dichloromethane, methanol and .1 mM EDTA at pH 9.0 or 6.0. Structures were confirmed with nuclear magnetic resonance spectroscopy. The presence of doxycycline and its 6-epimer in commercial metacycline has not previously been described. The presence of the 2-acetyl derivative was not surprising since analogous 2-acetyl derivatives have been identified in other tetracyclines.

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.

Assay and purity control of metacycline by thin-layer chromatography combined with UV and fluorescence densitometry--a comparison with liquid chromatography.

A thin-layer chromatographic (TLC) method involving UV and fluorescence densitometry is described for the assay and purity control of metacycline. With a mobile phase dichloromethane-methanol-water (58:35:7, v/v/v) and a silica gel thin-layer, previously sprayed with 10% sodium edetate solution adjusted to pH 9.0, all the potential impurities of metacycline were well separated from the main component and from each other. Results obtained with UV densitometry (TLC-UV) and fluorescence densitometry (TLC-F) were compared with those obtained by a liquid chromatography (LC) method using a poly(styrene-divinylbenzene) stationary phase. The correlation coefficients (r) for TLC-UV and LC or TLC-F and LC were better than 0.9999. For TLC-UV the relative standard deviation (RSD) for the assay of the main component was less than 2%, for TLC-F less than 3.0% and for LC less than 1.0%.