Classification According to the Mechanism of Retention

Affinity chromatography is based on the lock-and-key mechanism prevalent in biological systems. The retention mechanism is very specific, but the technique is more time-consuming and more expensive than those employing other retention mechanisms. 

The mechanisms described above form the basis for the chromatographic modes described in Chapter 2, namely, normal-phase, reversed-phase, size-exclusion, ion-exchange, and affinity chromatographies. However, other modes that are variations of those mentioned above, such as hydrophobic-interaction chromatography (HIC), chiral, ion-exclusion, and ion-pair chromatographies are also used and will be mentioned. 

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