Form of chromatography in which ions in solution can be paired or neutralized and separated as an ion pair on a reversed-phase column. Ion-pairing agents usually are ionic compounds that contain a hydrocarbon chain, which imparts a certain hydrophobicity so that the ion pair can be retained on a reversed-phase column. Retention is proportional to the length of the hydrophobic chain and the concentration of the ion-pair additive. Ion pairing also can occur in normal-phase chromatography when one part of the pair is dynamically loaded onto a sorbent, but this technique is not as popular as reversed-phase chromatography. Also known as ion-interaction chromatography or dynamic ion-exchange chromatography, which stresses that users sometimes do not know the precise mechanistic details of how the additive controls retention.