CHROMATOGRAPHY
The word chromatography originates from the Greek word "Khromatos" meaning "Colour writing". This is a technique used for the separation of a sample of the mixture. Chromatography involves the distribution of a solute between two phases i.e. Stationary and mobile phase. In chromatography substances are separated based on their affinity for stationary or mobile phase and this distribution is controlled by the distribution coefficient K
\[K\; =\; \frac{Concentration\: of\: a\: component\: in\: the\: moving\: phase}{Concentration\: of\: that\: component\: in\: the\: stationary\: phase}\]
The component with a small value of K remains in the stationary phase and the component with the larger value of K remains in the mobile phase.
The stationary phase may be solid or liquid as a thin film on the surface of an inert solid.
The mobile phase may be solid or liquid flowing over the surface of the stationary phase.
Types:
Absorption chromatography:
Chromatography in which the stationary phase is a solid. The substance leaves the mobile phase and is absorbed on the surface of the solid phase.
Partition chromatography:
Chromatography in which the stationary phase is a liquid. The substance is distributed in both stationary and mobile phases.