Chapter 23 Pharmaceutical Analysis

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Chromatographic Separation

Chromatography is based on the separation of substances of interest by their differing affinity between a mobile phase and stationary phase. The mobile phase is usually a liquid or a gas while the stationary phase is usually a solid but may be an immobilized liquid.

Relative affinity may be based on relative solubility, adsorption, size or charge. Differences in solubility are expressed by partitioning between the mobile and stationary phases. Adsorption differences cause the separation of molecules in a non aqueous environment. Permeation (gel permeation) chromatography is based on smaller molecules being retained by inclusion without smaller pores of the gel. Separation by ion-exchange chromatography is based on the exchange of ions in the mobile phase with ions on the stationary phase. As such it is better suited to purification than separation between similar materials.

Commonly used chromatography methods are high performance/pressure liquid chromatography (HPLC), gas liquid chromatography (GLC) and thin layer chromatography (TLC).

Figure 24.4.1 Column chromatography with a multi-component sample

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