What is the principle behind chromatography for separation?

Chromatography separates mixtures based on the different movement of individual components across a stationary phase.

Chromatography is a versatile laboratory technique used to separate and identify the components of a mixture. The principle behind chromatography is that different substances in a mixture have different affinities for two different types of material: a stationary phase and a mobile phase. The stationary phase is a solid or a liquid supported on a solid, while the mobile phase is a liquid or a gas that moves over or through the stationary phase.

The mixture to be separated is applied onto the stationary phase. The mobile phase then flows over or through the stationary phase. As this happens, the components of the mixture move at different rates over the stationary phase. This movement is due to the varying degrees of interaction between the components and the stationary phase. Those components that have a stronger interaction with the stationary phase will move more slowly, while those with a weaker interaction will move more quickly. This differential movement leads to the separation of the components.

The type of chromatography used depends on the nature of the mixture and the stationary and mobile phases. For example, in paper chromatography, the stationary phase is a piece of chromatography paper and the mobile phase is a suitable liquid solvent. In gas chromatography, the stationary phase is a high boiling point liquid and the mobile phase is an inert gas.

In summary, the principle of chromatography is based on the different affinities of the components of a mixture for a stationary and a mobile phase, which leads to their separation as the mobile phase moves over the stationary phase.