History

Chromatography was originally used for the separation of coloured compounds (hence the name). The Russian botanist Mikkhail Tswett gave a lecture in 1903 on the separation of pigments in green leaves on a chalk column. His new method was neglected for many years, but since the 1930s it has been extensively used to identify many (biological) compounds.

Gas Chromatography was established by Martin and James in 1952.

 
   
Physics and chemistry

The rates of migration of substances in chromatographic procedures depend on the relative affinity of the substances for the stationary and mobile phase. The forces attracting solutes to the two phases are the normal forces existing between molecules - intermolecular forces. One can identify five main forces:

1. Dispersion forces (interaction between all electrons in neighbouring atoms and molecules)

2. Induction effect (polar molecules bringing a charge asymmetry in other molecules

3. Orientation effect (caused by polar molecules - alignment of dipols)

4. Hydrogen bonding (between dipolar molecules bearing positive hydrogen ions)

5. Acid-base interactions

 
   
Limitation of Gas Chromatography

The fundamental limitation of GC is that the substances must be volatile, so that a finite fraction of it is distributed in the gaseous phase. For organic substances volatility is rarely adequate if the molecular weight of the compound exceeds 500. High temperatures of up to 300°C enhance volatility, but decomposition of the substance can be the result.

 
   
Applications

Gas Chromatography is widely used for quantitative and qualitative analysis of mixtures of volatile substances. It is also used to monitor industrial processes automatically: gas streams are analysed periodically and many routine analyses are performed rapidly in medical and other fields. (By the use of only 0.1 cubic centimetre of blood, it is possible to determine the percentage of dissolved oxygen, nitrogen, carbon dioxide and carbon monoxide)

Gas Chromatography is useful in the analysis of air pollutants, alcohol in blood and many other fields.

Concerning Chromatography see also Chromatography

References: Deutsches Museum, Museumsinsel 1, 80538 Munich, Germany

 
 
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