Mechanism responsible for separation:

In case the mechanism responsible for separation is taken as the criteria for categorization, there will be four distinct categories of chromatography viz, adsorption, partition, ion-exchange and size exclusion. But we will have to discretely mention the competing phases.

The above discussion clearly points out that no single criteria by it will be able to effectively classify the various chromatographic techniques. We will have to take one as the main criteria and make a sub-classification based on the other yardstick. A simple approach seems to be to take the nature of the mobile phase as the main criteria and propose a sub-classification based on the various mechanisms responsible for separation. If any special feature exists within a sub-classification it may be pointed out right there.

For summing up the categorization of chromatographic methods, it emerges that there will be three kinds of chromatographic techniques.

i) Liquid chromatography.

ii) Gas chromatography, and

iii) Supercritical fluid chromatography.

We will discuss each one in brief and take into consideration the other competiting phase, the mechanism responsible for separation and the nature and shape of surface. The following sub-sections will be devoted to discussion on these lines.