Zwitterionic ion-exchangers in ion chromatography: A review of recent developments

Significant advances within the field of ion chromatography (IC) have often had their roots in research focussed on the development of new phase technologies, aimed to both simultaneously increase efficiency and vary selectivity. To increase selectivity it is necessary to develop new selective ion-exchangers, achieved by varying the nature of functional groups and the matrix of the stationary phase. In this comprehensive review, developments over the past decade in the production and application of zwitterionic and amphoteric ion-exchangers are presented and discussed. Zwitterionic and amphoteric ion-exchangers, where positive and negative charges are located in close proximity, exhibit alternative ion selectivity to standard anion and cation ion-exchangers, such as those traditionally used in IC, and have the potential for selectivity optimisation in IC due to control of the ratio of electrostatic attraction/repulsion forces between analyte ions and ion-exchange groups. This can result in the ability to utilise relatively dilute eluents, which increases detector sensitivity, with further advantages of zwitterionic ion-exchangers including their possible application to the simultaneous separation of cationic and anionic species.