Chapter 2 - The Column in Gas Chromatography

Abstract

Separations are possible in gas chromatography if the solutes differ in their vapor pressure and/or intensity of solute-stationary phase interactions. As a minimum requirement, the sample must be thermally stable at the temperature required for vaporization. The fundamental limit for sample suitability is established by the thermal stability of the sample and system suitability by the thermal stability of column materials. In contemporary practice, an upper temperature limit of about 400°C and a sample molecular weight less than 1,000 is indicated, although higher temperatures have been used and higher molecular-weight samples have been separated in a few instances. When a solid adsorbent serves as the stationary phase, the separation technique is called gas–solid chromatography (GSC). When the stationary phase is a liquid spread on an inert support or coated as a thin film onto the wall of a capillary column, the separation technique is called gas–liquid chromatography (GLC). Five types of columns are used in gas chromatography: classical packed columns, micropacked columns, packed capillary columns, SCOT (support-coated open tubular) columns, and WCOT (wall-coated open tubular) columns. The most significant difference among the various column types is their permeability.