Preparation and evaluation of a neutral methacrylate-based monolithic column for hydrophilic interaction stationary phase by pressurized capillary electrochromatography

Abstract

A polar and neutral polymethacrylate-based monolithic column was evaluated as a hydrophilic interaction capillary electrochromatography (HI-CEC) stationary phase with small polar–neutral or charged solutes. The polar sites on the surface of the monolithic solid phase responsible for hydrophilic interactions were provided from the hydroxy and ester groups on the surface of the monolithic stationary phase. These polar functionalities also attract ions from the mobile phase and impart the monolithic solid phase with a given zeta potential to generate electro-osmotic flow (EOF). The monolith was prepared by in situ copolymerization of a neutral monomer 2-hydroxyethyl methacrylate (HEMA) and a polar cross-linker with hydroxy group, pentaerythritol triacrylate (PETA), in the presence of a binary porogenic solvent consisting cyclohexanol and dodecanol. A typical HI-CEC mechanism was observed on the neutral polar stationary phase for both neutral and charged analytes. The composition of the polymerization mixture was systematically altered and optimized by altering the amount of HEMA in the polymerization solution as well as the composition of the porogenic solvent. The monoliths were tested in the pCEC mode. The resulting monoliths had different characteristics of hydrophilicity, column permeability, and efficiency. The effects of pH, salt concentration, and organic solvent content on the EOF velocity and the separation of nucleic acids and nucleosides on the optimized monolithic column were investigated. The optimized monolithic column resulted in good separation and with greater than 140,000 theoretical plates/m for pCEC.