Covalently bonded polymeric zwitterionic stationary phase for simultaneousseparation of inorganic cations and anions

A novel polymer-based zwitterionic separation material was synthesized by a two-step reaction, in which 2-hydroxyethyl methacrylate-ethylene dimethacr ylate copolymer heads were first activated with epichlorohydrin, whereafter (2-dimethylamino)ethanesulfonic acid inner salt was coupled to the epoxide groups on the activated beads in a quaternizing reaction. The resulting ma terial carried strong/strong charge zwitterionic pendant groups, whose char ge properties did not change over a wide pH range. It was capable of separa ting inorganic anions and cations both independently and simultaneously usi ng aqueous solutions of perchloric acid or perchlorate salts as eluent It w as found that the retention of cations and anions depended on the individua l ions in the analyte, not on type of salt injected, as reported for ODS co lumns dynamically coated with zwitterionic detergents using water only as e luent. This study also revealed that both the concentration and the water s tructure related properties of the eluent ions were important for the reten tion of ionic species. The mechanism appears to involve the interaction of the chaotropic anion component with the quaternary ammonium group, resultin g in an increasing cation-exchange capacity of the zwitterion up to a perch loric acid eluent concentration of similar to 10 mM. Above this concentrati on the material appears to become saturated, and the retention times of bot h cations and anions become practically independent of the HClO4 concentrat ion.