Electrochromatographic characterization of methacrylate-based monolith with mixed mode of hydrophilic and weak electrostatic interactions by pressurized capillary electrochromatography

A monolithic stationary phase was prepared by in situ copolymerization of 2-hydroxyethyl methacrylate (HEMA), ethylene dimethacrylate (EDMA), and methacrylic acid (MAA), in a binary porogenic solvent consisting of toluene and 1-dodecanol. The resulting monolith was evaluated as a hydrophilic interaction-capillary electrochromatography (HI-CEC) stationary phase under the mode of pressurized capillary electrochromatography (pCEC). Effects of the buffer pH, salt concentration and the mobile phase composition on the electroosmotic flow (EOF) velocity and the retention factors of the compounds were investigated. The generation of cathodic EOF under a broad pH range was attributed to the presence of the carboxyl groups on the surface of the polar stationary phase. The carboxyl groups offered at the same time the possibility of weak electrostatic interaction with analytes. The separation mechanism of the monolithic column was discussed in detail. It was found that the separation mechanism of charged solutes could be attributed to a mixed mode of HI and weak electrostatic interaction, as well as the effect of electrophoresis, while the separation of neutral solutes was based on the hydrophilic interaction at high acetonitrile (ACN) content.