Development and evaluation of new imidazolium-based zwitterionic stationary phases for hydrophilic interaction chromatography

Hydrophilic interaction liquid chromatography (HILIC) has been widely used for separating polar compounds as a complement mode to reversed-phase liquid chromatography. The development of new stationary phases for HILIC is significant to improve the coverage of various polar and hydrophilic compounds. The present study described the preparation and application of novel imidazolium-based zwitterionic stationary phases. 1-Vinyl-3-(butyl-4-sulfonate) imidazolium was synthesized from 1-vinylimidazole and 1,4-butane sultone, then bonded to the surface of 3-mercaptopropyl modified silica particles (core–shell silica and totally porous silica) by “thiol-ene” click chemistry to obtain the resulting zwitterionic stationary phase with a positively charged imidazole ring and a negatively charged sulfonate group. The zwitterionic stationary phases exhibited good selectivity and favorable retention for a wide range of polar solutes (nucleosides, nucleic acid bases, benzoic organic acids, uric acid and its methyl derivatives, water-soluble vitamins) as compared to a bare silica column. The column efficiency could reach up to 100,000 theoretical plates/m with cytosine as the test solute. The retention changes of various types of test solutes were investigated under different chromatographic conditions including water content, pH, buffer salt concentration in mobile phase and column temperature. The results indicated that the retention of solutes on the stationary phase was the outcome of a mixed-mode retention mechanism (i.e. a combination of adsorptive and partitioning interactions). In conclusion, the new imidazolium-based zwitterionic stationary phases have shown excellent chromatographic behavior for a variety of polar solutes under HILIC mode, and have a great potential as a new type of stationary phases for HILIC.