Anion-modulated switching of retention properties of a zwitterionic stationary phase

Abstract

Stationary phases modified by zwitterionic molecules act both as an anion- and a cation-exchanger. This characteristic property of zwitterionic stationary phases can be modulated only by changing the nature of anions added in mobile phases. Anion-exchange properties emerge when small and well hydrated anions are added in mobile phases, while cation-exchange properties appear when mobile phases contain large and poorly hydrated anions. The nature of cations is much less important than that of anions. These unusual retention properties come from the structure of a zwitterionic molecule used as a stationary phase modifier, which has an inner cationic and an outer anionic group.