Evaluation of functionalized mesoporous silicas for reverse phase high performance liquid chromatography: An application for the separation of steroids

Conventional mesoporous silica (SM) and ethylene-bridged periodic mesoporous organosilica (PMO) were synthesized and modified with mono-functional octadecylsilane (C18). The materials were comprehensively characterized, before and after surface modification. Small angle X-ray diffraction, N2 adsorption-desorption measurement, scaning electron microscopy and transmission electron microscopy showed that all the prepared materials had non-symmetrical 3-D wormhole-like mesostructure and spherical morphology. Fourier transform infrared spectroscopy, 29Si MAS NMR and 13C MAS NMR spectroscopy, elemental and thermogravimetric analysis demonstrate the successful funcionalization of the materials with 0.242-0.388 and 0.204-0.402 mmol of C18 per g of SM-C18 and PMO-C18 silicas, respectively. HPLC columns packed with the prepared materials were tested by using a RP test mixture. From chromatographic parameters it was found that the separation power primarily depends on surface coverage. PMO-C18-2 and SM-C18-3 silicas were tested as a potential stationary phase for the effective separation of a mixture of five steroids. Separation for the five hormones was observed with the PMO-C18-2 column, which can be ascribed to the ethane groups in the mesoporous framework of this material.