gas chromatography

n.
Chromatography in which the substance to be separated into its components is diffused along with a carrier gas through a liquid or solid adsorbent for differential adsorption.

gas-chromatographic gas'-chro·mat'o·graph'ic

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A method for the separation and analysis of complex mixtures of volatile organic and inorganic compounds. Most compounds with boiling points less than about 250°C (480°F) can be readily analyzed by this technique. A complex mixture is separated into its components by eluting the components from a heated column packed with sorbent by means of a moving-gas phase. See also Chromatography.

Gas chromatography may be classified into two major divisions: gas-liquid chromatography, where the sorbent is a nonvolatile liquid called the stationary-liquid phase, coated as a thin layer on an inert, granular solid support, and gas-solid chromatography, where the sorbent is a granular solid of large surface area. The moving-gas phase, called the carrier gas, is an inert gas such as nitrogen or helium which flows through the chromatographic column packed with the sorbent. The solute partitions, or divides, itself between the moving-gas phase and the sorbent and moves through the column at a rate dependent upon its partition coefficient, or solubility, in the liquid phase (gas-liquid chromatography) or upon its adsorption coefficient on the packing (gas-solid chromatography) and the carrier-gas flow rate.

The apparatus used in gas chromatography consists of four basic components: a carrier-gas supply and flow controller, a sample inlet system providing a means for introduction of the sample, the chromatographic column and associated column oven, and the detector system.

Qualitative and quantitative information is obtained from analyzing the peaks appearing on a chromatogram. Combination of gas chromatography with mass spectrometry provides the ultimate in qualitative information and has been used extensively in research. See also Mass spectrometry; Qualitative chemical analysis.

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An analytical technique used to detect drugs and their metabolites. The chemical constituents of the sample are absorbed onto a stationary phase of the apparatus. A gas then displaces these chemicals at different rates under different physical conditions. The molecules leaving the apparatus are monitored and recorded on a chart. The peaks on the chart are compared with those of known standard drugs.

Gas chromatography, specifically gas-liquid chromatography, involves a sample being vaporized and injected onto the head of the chromatographic column. The sample is transported through the column by the flow of inert, gaseous mobile phase. The column itself contains a liquid stationary phase that is adsorbed onto the surface of an inert solid.

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