Chapter 13 - Ion exchange, ion-moderated, and ligand exchange liquid chromatography

Abstract

Ion exchange chromatography is dedicated to the separation of ionic species of the sample present in the mobile phase (water or water with a given proportion of a polar solvent). The ion species can be inorganic ions, but also organic ions such as organic acids, amines, amino acids, proteins, oligonucleotides, etc. The stationary phase is an ion exchange resin, i.e., a polymer that contains acidic groups (in case of a cation exchange) or basic groups (in case of an anion exchange) that are bonded to the resin. For example, a cation exchange material may contain covalently bonded sulfonic groups (–SO3–), carboxylic groups (–COO–), etc., and an anion exchange may contain covalently bonded quaternary amine groups (–N(CH3)3+), tertiary amines, etc. The counterion of the bonded acidic groups in the cationic resin can be H+, Na+, K+, etc., and the counterion of the bonded basic groups in the anionic resin can be OH–, Cl–, CO32−, etc. These ionic species are reversibly retained by ionic groups covalently bonded to the stationary phase.