Chapter 4 - The Column in Liquid Chromatography

Abstract

The term “liquid chromatography” encompasses a lexicon of separation techniques with a single common feature, that of a liquid mobile phase. Compared with gases, liquids provide a greater variety of solvating capabilities with more scope for selectivity optimization, while gases have more favorable kinetic properties, yielding higher efficiencies and shorter separation times. Consequently, separations in liquid chromatography are usually performed with a modest number of theoretical plates at an optimized selectivity achieved by appropriate selection of the separation mode, stationary phase structure, and mobile-phase composition. Understanding the complex relationship between the last three terms is the key to understanding how separations occur in liquid chromatography. A number of distinct separation modes are employed in liquid chromatography. This chapter also focuses on the general classification that can be made in terms of the distribution process. The main processes are interfacial adsorption, the basis of liquid–solid chromatography (LSC), restricted permeability of porous solids, the basis of size-exclusion chromatography (SEC), partition, the basis of liquid–liquid (LLC) and bonded-phase chromatography (BPC), electrostatic interactions with immobilized ionic groups, the basis of ion-exchange chromatography (lEC), and the structure-specific binding of biopolymers to immobilized molecular recognition sites, the basis of affinity chromatography (AC).