ASSAY AND PURITY CONTROL OF OXYTETRACYCLINE AND DOXYCYCLINE BY THIN-LAYER CHROMATOGRAPHY - A COMPARISON WITH LIQUID-CHROMATOGRAPHY

A thin-layer chromatographic (TLC) method using densitometry is described for the assay and purity control of oxytetracycline and doxycycline. With a mobile phase of dichloromethane-methanol-water (59:35:6, 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 oxytetracycline or doxycycline are well separated from the main components and from each other. Results obtained with TLC are compared with those obtained by previously established liquid chromatography (LC) methods using poly(styrene-divinylbenzene) stationary phases. A good correlation was obtained (r > 0.9999). For TLC the relative standard deviation (RSD) for the assay of the main component was <2%, for LC the RSD was <1%.