General concepts of analytical chromatography

Chromatography is a physico-chemical method of separation of components within mixtures, liquid or gaseous, in the same vein as distillation, crystallization, or the fractionated extraction. The applications of this procedure are therefore numerous since many of heterogeneous mixtures, or those in solid form, can be dissolved by a suitable solvent (which becomes, of course, a supplementary component of the mixture). 

A vertical hollow glass tube (the column) is filled with a suitable finely powdered solid, the stationary phase. 

At the top of this column is placed a small volume of the sample mixture to be separated into individual components. 

Chemical Analysis Second Edition Francis and Annick Rouessac 

The sample is then taken up by continuous addition of the mobile phase, which goes through the column by gravity, carrying the various constituents of the mixture along with it. This process is called elution. If the components migrate at different velocities, they will become separated from each other and can be recovered, mixed with the mobile phase. 

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