Stationary phase with specific surface properties for the separation of estradiol diastereoisomers

The aim of this study was to develop a procedure that enabled the separation of estradiol diastereoisomers. For this purpose a series of stationary phases with different surface properties has been utilized. Two of them contain various interaction sites, such as: cholesterol, n-acylamide, amine and silanols localised in the organic layer bonded to the surface of silica gel (SG-CHOL and SG-CHOL/AP). The other one contains mainly alkylamide ligands and also residual aminopropyl and silanol groups (SG-AP), as well as the last one consisting of hydrocarbonaceous material (SG-C18). In order to select the best type of stationary phase for this analysis, after chromatographic separation of 17-α-estradiol and 17-β-estradiol, selectivity and resolution of the analytes were compared. The best separation of hormones was obtained for SG-CHOL packing, as a consequence of the structure and the properties of this stationary phase. To better understand the retention mechanism and the properties of the stationary phases, used in the separation of steroid compounds, the functional group contributions (τ) were compared with Hansch substituent constants (π).