Gas adsorption chromatography involves a packed bed comprised of an adsorbent used as the stationary phase. Common adsorbents are zeolite, silica gel and activated alumina. This method is commonly used to separate mixtures of gases. Gas-liquid chromatography is a more common type of analytical gas chromatography. In this type of column, an inert porous solid is coated with a viscous liquid which acts as the stationary phase.
Diatomaceous earth is the most common solid used.
Solutes in the feed stream dissolve into the liquid phase and eventually vaporize. The separation is thus based on relative volatilities. Capillary gas chromatography is the most common analytical method. Glass or fused silica comprise the capillary walls which are coated with an absorbent or other solvent. Because of the small amount of stationary phase, the column can contain only a limited capacity.