Preparation and characterization of a novel hydrophilic interaction/ion exchange mixed-mode chromatographic stationary phase with pyridinium-based zwitterionic polymer-grafted porous silica.

Novel zwitterionic polymer-grafted porous silica microspheres were prepared by using sodium 2-bromoethanesulfonate to quaternize the pyridyl side chains of the polymer, which is anchored on the surface of porous silica. The separation behavior for toluene and benzoic acid proved that the zwitterionic polymer-grafted porous silica worked as a stationary phase in hydrophilic interaction/ion exchange mixed-mode chromatography. Compared with a conventional sulfobetaine-based zwitterion-grafted porous silica column, the prepared poly(vinylpyridinium ethanesulfonate)-immobilized porous silica afforded the highly selective separation of benzoic acid derivatives over a wide pH range, and the separation behavior was quite sensitive to the protonation state of the carboxylic acids. The high selectivity was attributed to the multiple interactions between the guest molecule and the zwitterionic groups on the polymer chains. The new zwitterionic stationary phase demonstrated excellent selectivity for hydrophilic biorelated molecules such as nucleobases and nucleosides.