The mobile phase is an inert gas and as above this form of chromatography can be sub-divided according to the nature of the phase components:
Gas/liquid/ chromatography (GLC)
As indicated above the mobile phase here is a gas and the stationary phase is an immobilized liquid, either by impregnation or by bonding to an inert support which could be, quite simply, the inner surface of the column. This is the technique commonly called gas phase chromatography (GC). The gaseous sample must be brought to its vapour state. It was Martin and Synge who, in 1941, suggested the replacement of the liquid mobile phase by a gas in order to improve the separations. From this era comes the true beginnings of the development of analytical chromatography. Here once again it is the partition coefficient K that is involved.
Gas/solid chromatography (GSC)
The stationary phase is a porous solid (such as graphite, silica gel or alumina) while the mobile phase is a gas. This type of gas chromatography is very effective for analyses of gas mixtures or of compounds that have a low boiling point. The parameter concerned is the adsorption coefficient.