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)
The main application of Gas chromatography are:
1. Separation of benzene (b.p. 353.1 K) and cyclohexane (b.p. 353.81 K) is virtually impossible by fractional distillation. By GLC, the separation of the two can be accomplished in a few minutes.
2. Separation of hundreds of hydrocarbons in petroleum by GLC. This separation, which is now routine analysis in petroleum industries.
3. By using molecular sieves, gas-solid chromatography has been used to separate a mixture of H2, CO2, CO, O2, CH4 C2H2.
4. Volatile substances such as human breath, environmental air and urine have been analyzed by GLC. By using 300m capillary columns with methyl silicone as the stationary phase. 150 substances have been obtained in the human breath. Gas chromatography is thus increasingly being used in biomedical analysis.
5. Automobile exhaust gases, a main pollution hazard, have been analyzed by GLC.
6. Flavors and aromas of flowers and foods are the result of a combination of hundreds of organic compounds in trace amount. These have been separated by GLC.
7. The high degree of resolution of GLC allows purity of samples to be checked.
8. GLC has also been used in the separation of radioactive product.
9. Gas-liquid chromatography has been used to separate samples from less than a microgram to 100 g. Traces of components of the order of 10-15 g have been detected.
10. Gas chromatography has also been used to study reaction mechanisms.