Glycin-bonded silica monolithic column as zwitterionic stationary phase for hydrophilic interaction pressurized capillary electrochromatography.

A novel zwitterionic monolith was prepared by in situ covalent attachment of glycin to a gamma-glycidoxypropyltrimethoxysilane-modified silica monolith. The monolith possessing in its structure bonded secondary amine groups and carboxylic acid groups was evaluated in pressurized CEC (pCEC) system using small neutral and charged solutes. Owing to the zwitterionic nature of the resulting stationary phase, the direction and magnitude of EOF in this column could be manipulated by adjusting the pH values of the mobile phase. Typical hydrophilic interaction was observed when the ACN content exceeded 45%. Separations of acidic and basic compounds were performed on the prepared column in weakly anodic and cathodic EOF modes, respectively. The organic solvent composition, the salt concentration, and the pH of the mobile phase have effects on the electrochromatographic retention. Besides the hydrophilic interaction and electrophoretic mechanism, electrostatic interactions are also involved in the separations of acids and bases on the zwitterionic column.