Chromatography, Liquid

Abstract

Liquid chromatography is a separation technique with three main variants: column liquid chromatography, planar (thin‐layer) chromatography, and capillary electrochromatography. Separations are achieved by the distribution of sample components between a mobile liquid phase and (generally) a porous solid stationary phase. Selectivity differences result from the differences in adsorption, partition, size exclusion, molecular recognition, and electrostatic interactions in the two phases. Defined by mechanism, the main types of liquid chromatography are known as liquid–solid (normal‐phase), reversed‐phase, size‐exclusion, ion‐exchange, affinity, chiral, hydrophilic interaction, and hydrophobic interaction liquid chromatography. These separation mechanisms are supported by a wide range of stationary phase materials whose surface chemistry and morphology are designed for optimum performance selected from porous inorganic oxide, porous organic polymers, porous graphitic carbon, chemically bonded inorganic oxides, and chemically modified porous polymers. Liquid chromatographic methods can also be classified by speed, separation performance, and scale. Here, system properties defined by instrumental parameters have to be considered simultaneously with the physical properties of the stationary phase. Analytical and preparative‐scale applications require different instrument platforms. The method used to control the mobile phase flow (capillary forces, pneumatic forces, or electroosmosis) are further important to design criteria. Liquid chromatographic methods are also sustained by a variety of detection possibilities based on the principles of bulk property and solute property methods employing spectroscopic, electrochemical, light scattering, and ion formation techniques.