Improvement of chemical analysis of antibiotics. VII. Comparison of analytical methods for determination of impurities in tetracycline pharmaceutical preparations.

In order to examine the suitability of our four established methods for the analysis of tetracyclines (high-performance liquid chromatography, reversed-phase thin-layer chromatographic densitometry, reversed-phase thin-layer chromatographic spray reagents and silica gel high-performance thin-layer chromatographic densitometry) for the determination of impurities in tetracycline pharmaceutical preparations, sixteen samples available on the Japanese market were analysed. Because these methods did not always give satisfactory results, their analytical conditions were modified. The comparative studies indicated these methods were accurate and reliable. Therefore, we recommend a combination of these methods for the analysis of impurities, in which the spray reagents are used first as a screening method, and then if the results exceed the limits, a precise determination is carried out using either high-performance liquid chromatography or reversed-phase thin-layer chromatographic densitometry.