Study of Retention of 31 Polyoxygenated Steroids by Normal- and Reversed-Phase Thin-Layer Chromatography

The chromatographic behavior of 31 steroidal compounds on both silica gel and RP-18 silica thin layers using nonaqueous and aqueous-organic mobile phases was investigated. It was found that an application of more polar solvent systems such as acetonitrile-dichloromethane in comparison to acetone-n-hexane resulted in stronger elution of the investigated substances in all investigated cases. Under normal-phase conditions better selectivity was achieved in acetonitrile-dichloromethane and the best in binary mixture with component ratio 1: 9 (v/v). The selectivity of the separation under reversed-phase conditions was increased with the increased fraction of water in mobile phases used. A conclusion on the influence of substance moiety on the retention behavior of the investigated substances under reversed-phase conditions could not be drawn due to complex retention mechanism. In order to find similarities and dissimilarities between normal-and reversed-phase systems used, retention parameters were investigated by principal component analysis and cluster analysis.