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A gas chromatograph is composed of three components within a single surround. These components include the injector, the column, and the detector associated with a temperature‐controlled oven that enables the column to attain high temperatures (Figure 2.1). The mobile phase that transports the analytes through the column is a gas referred to as the carrier gas. The carrier gas flow, which is precisely controlled, enables great reproducibility of the retention times.

Analysis starts when a very small quantity of sample is introduced in either liquid or gas form into the injector, which has the dual function of vaporizing the sample and mixing it with the gas flow at the head of the column. The column is usually a narrow‐bore tube that coils around itself with a length that can vary from 1 m to over 100 m, depending upon the type and the contents of the stationary phase. The column, which can serve for thousands of successive injections, is housed in a temperature‐controlled oven. At the end of the column, the mobile phase (carrier gas) passes through a detector before it exits to the atmosphere. Some gas chromatograph models of reduced size have their own electrical supply, enabling them to operate in the field (Figure 2.1).

In GC, there are four operational parameters for a given stationary phase: L, length of the column; u, velocity of the mobile phase (which affects the theoretical efficiency N); T, temperature of the column; and β, phase ratio, which affects the retention factor k. The settings of the chromatograph enable modifications in terms of T and u, and therefore both the efficiency of the column and the retention factors can be adjusted as well.

Figure 2.1 Operational diagram of a gas chromatograph and practical uses. a, b) Versatile analytical chromatogram

(Source: GC‐2010 model from Shimadzu).

The instrument represented is equipped with a sample holder (carousel), an injector, an automatic sampler, and a mass spectrometry detection system (GC‐MS). c) Portable model for analyses made in the field (volatile organic compounds, toxic industrial materials)

(Source: Hapsite ER, information courtesy of Inficon).