Complete chromatographic separation of steroids, including 17α and 17β-estradiols, using a carbazole-based polymeric organic phase in both reversed and normal-phase HPLC

Poly(2-N-carbazolylethyl acrylate) with terminal trimethoxysilyl groups was prepared as an organic phase and immobilized onto silica. The retention behavior of the column packed with this carbazole-based polymer-immobilized silica (Sil-CEA) was investigated by using various estrogenic steroids and corticoids in both reversed-phase and normal-phase liquid chromatography. As a result, complete separation was confirmed for eight kinds of steroids with Sil-CEA. The most specific separation with Sil-CEA can be emphasized by the high separation factor (e.g., α = 1.39 in methanol-water (7:3, v/v) at 35 °C) for 17α and 17β-estradiols, one of the most difficult pairs of isomers in chromatographic separation, whereas for two kinds of commercially available polymeric ODS columns as references α = 1.01, only, under the same conditions. Because the excellent separation and retention order with Sil-CEA was maintained even in a normal-phase mobile phase such as a hexane-2-propanol, it is estimated that the CEA phase has multiple interaction mechanisms through stronger interactions such as dipole-dipole, carbonyl-π, and hydrogen bonding interactions than the hydrophobic effect expected with ODS.