Some aspects of the use of thin-layer chromatography in a limit test for related foreign steroids

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Abstract
To attain the maximum separation of the steroid impurities in pharmaceutically important synthetic corticosteroids the running of two or more chromatograms using different solvent systems is recommended. Using adsorption chromatography, solvent systems of the type 1,2-dichloroethane: methanol:water, 95:5:0·2, give the most satisfactory general separations. Some steroids can best be separated by partition chromatography, using formamide as the stationary phase and chloroform:ether:water, 80:20:0·5, or cyclohexane:tetrachloroethane:water, 50:50:0·1, as the mobile phase. A spray reagent of 0·05% tetrazolium blue and 8% sodium hydroxide in methanol is recommended. The amounts of foreign related steroids can be limited by running standard amounts of impurities alongside the steroid under test and comparing the colour intensities of the impurities in the steroid with those of the standards.