A separation brought about by an exchange between a mobile gas phase and a liquid or solid stationary phase is known as Gas chromatography. They are of two types,
1. Gas Liquid Chromatography (GLC)
2. Gas Solid Chromatography (GSC)
1. Although GSC was known much earlier than GLC, the method has not developed as GLC. This is because, solid surfaces are not easily reproducible and composition of solid surface layers is not fixed. Consequently, theoretical interpretation of the retention behavior is difficult and is only approximate.
2. The GLC is more versatile than GSC because of linear isotherm obtained in GLC.
3. In GLC the isotherm are symmetrical and sharp peaks. But in GSC the isotherms are of unsymmetrical type. When the symmetrical peaks are analyzed the results are accurate and précised but unsymmetrical peaks give faulty results.
4. In GSC, distribution coefficients are much larger than those in GLC. As a result, species which are not retained in a gasliquid column can be separated by GSC. A mixture of hydrogen, oxygen, argon and nitrogen can be conveniently separated by GSC.
5. Separation of benzene (b.p. 353.1 K) and cyclohexane (b.p. 353.81 K) is possible by GLC.
6. One advantage of GSC is that since the column is packed with a solid, operation is possible at a higher temperature than in GLC. However, the components to be separated must be thermally stable.