Liquid Chromatography:

The simplest one with liquid as a mobile phase seems to be based on partition between the liquid supported on an inert support and the other liquid acting as a mobile phase. This is known as liquid- liquid partition chromatography. The support containing the liquid can be in the form of three dimensions (column) or two dimensions (thin layer and paper). In the 2D form, the mobile phase can move from top to bottom or bottom to top and therefore, known as descending or ascending chromatography. The two kinds of partition chromatography are also distinguishable on the basis of relative polarities of the mobile and stationary phases. Conventionally, the highly polar solvent is held on the support and the mobile phase is relatively non-polar. This is called as normal-phase chromatography. It is termed as reversed-phase chromatography if the stationary phase is non-polar and the mobile phase relatively polar. An important modification in terms of stationary phase is introduced by loading the extractant used for solvent extraction on a hydrophobized inert support and irrigating the support with aqueous solvents. This is known as extraction chromatography. At this point, it may be important to introduce liquid chromatography on bonded phases. Initially, the partition chromatography was only liquid-liquid type but now chromatography with bonded phase has gained prominence.