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Gaschromatographs (TCD)

Gas chromatographs are used for the separation of mixtures with volatile components. The separation process of gas chromatography is based on multiplicative distribution between the mobile and the stationary phase of the mixture, which is carried by the mobile phase through the column. Because of its high efficiency in separation, it is possible to split very complex compounds into their individual components and to analyse them with a detector. Note, however, that gas chromatography concerns gas mixtures or non-decomposed evaporateable substances.

Construction of gas chromatographs

The architecture of a gas chromatographs can be described as follows. A gas chromatograph consists of a carrier gas supply which is filled with the mobile phase, an injector, a column, which is often made of metal or glass, has a length of 10 to 200 metres and is inside a temperable oven, a detector and a data evaluation device whose results a standard computer may display. The mobile phase of gas chromatography is represented by an inert gas, p. e. helium or nitrogen, the stationary phase is represented by adsorbing solids or absorbent liquids. Gas chromatographs can consequently be classified by either a packed column or a capillary column. The rate by which the substance is transported through the column is determined basically by the flowrate of the mobile phase. The function of the stationary phase in gas chromatography is now to separate the sample into its individual components. Capillary column and packed column may be distinguished by their stationary phase. The packed column of gas chromatographs contains a solid support material, coated with a thin, liquid film, i. e. the stationary phase. The capillary column, however, may in gas chromatography be either wall-coated (WCOT column), support-coated (SCOT column) or consist of porous-layer capillaries (PLOT column).

Detectors in gas chromatography

In gas chromatography, different detectors are applied, according to the substance to be examined. Often flame ionisation detectors, thermal ionic detectors, electron capture detectors, thermal conductivity detectors or other detectors are used, such as the mass spectrometer. Often, a combination of several detectors may also be applied.

Literature

• http://de.wikipedia.org/w/index.php?title=Gaschromatographie&oldid=86925177 (called: 29.03.11).

• http://www.chemgapedia.de/vsengine/vlu/vsc/de/ch/3/anc/croma/gc_detail1.vlu.html (called: 29.03.11).