Enhanced selectivity for capillary zone electrophoresis using ion-pair agents

Capillary zone electrophoresis (CZE) is unique in its simplicity and versatility for liquid separations, yet selectivity for solutes with similar charge and hydrated radius is often lacking. Conventional reversed-phase liquid chromatography (RP-LC) ion-pairing agents, ionic polymers, Group I and II metal cations and dicarboxylic acids have all been effectively used over the past decade to enhance CZE resolution through a combination of complexing effects. This review summarizes the fundamental theory of ion-“ion interaction as applied to CZE separations and discusses several of the most important and diverse applications of selectivity enhancement that utilize ion-pair equilibria. In addition, the effect of ion-pair additives on electroosmotic flow and examples where changes in analyte selectivity are unrelated to ion-“ion interaction are discussed