Preparation of mixed-mode monolithic silica capillary column with octadecyl and aminopropyl groups for liquid chromatography

Abstract

The silica monolith has been a substantial material used as stationary phase in chromatographic separation. Easy of preparation, versatile surface modification, better permeability and higher efficiency were the advantages of monolithic silica column comparing to silica packed column. In this work, The bared monolithic silica capillary column was first prepared via the sol-gel technique and followed by the post- modification with octadecylmethoxysilane and aminopropyltrimetho xysilane (C18-AP column). The chromatographic behaviors of the C18-AP column and monolithic silica capillary column modified with octadecyltrimethoxysilane (C18 column) were examined and compared according to Tanaka’s test. The hydrophobicity of the C18-AP column and the C18 column was similar while the shape selectivity of C18-AP column was better than C18 column. For ion exchange capacity and silanophilic interactions, C18-AP column showed repulsive electrostatic interactions due to the functionalized of aminopropyl groups on the stationary phase. Therefore, C18-AP column could exhibit a reversed phase and a weak anion exchange separation behavior. The separation performances of C18-AP column were then examined and compared to those of C18 column. The separation of alkylbenzenes and benzoic acid derivatives on both columns were similar which separated based on reversed phase mechanism. Inorganic anions and benzoate anions which were not separated on C18 column were successfully separated on C18-AP column because of a weak anion exchange characteristic. Moreover, the improvement of peak tailing problem for separation of basic compounds such as aniline derivatives on C18-AP column was observed. Lastly, the resolution of polyaromatic hydrocarbons (PAHs) separation on C18-AP column was better than C18 column due to the better shape selectivity of C18-AP column.