Polar Bonded Stationary Phases Consisting of Silica-based Monoliths for Hydrophilic Interaction Capillary Electrochromatography

Abstract

The aim of this study was to introduce novel polar stationary phases based on silica monoliths for normal-phase capillary electrochromatography (NP-CEC). The silica monoliths were produced by a sol-gel process which was optimized to allow the bonding of the polar ligands. The polar ligand investigated in this study was the 1 H -imidazole-4, 5-dicarbonitrile, which has four strong polar functions that make it possible to compensate for the low monolith surface area thus improving separation and selectivity for polar solutes. Silica-based monoliths can be produced via the sol-gel technology, which employs silica alkoxide as the sol-gel precursor and PEG as the porogen with acetic acid as the catalyst. Ammonium hydroxide can be used to adjust the size of the mesopores. Through chemical bonding reactions, the surface of the silica monolith can be modified with the desired chromatographic ligand to solve different analytical problems. The 1 H -imidazole-4, 5-dicarbonitrile modified monolithic column, which is denoted 2CN-OH-monolith, exhibited higher retentivity and selectivity than the monofunctional CN-OH-monolithic column toward a wide range of polar species including neutral (carbohydrates), ampholytes (peptides) and positively charged species (basic drugs). This study proved that the 2CN-OH-monolith is a viable stationary phase for NP-CEC. This represents a major advance in the design of polar monolithic silica columns for the normal phase chromatography in general and for NP-CEC in particular.