(GC; gas-liquid chromatography; GLC; vapor-phase chromatography; VPC). The process in which the components of a mix are separated from one another by volatilizing the sample into a carrier gas stream that is passing through and over a bed of packing consisting of a 20–200 mesh solid support. The surface of the latter is usually coated with a relatively nonvolatile liquid (the stationary phase). This gives rise to the term gas-liquid chromatography. If the liquid is not present, the process is gas-solid chromatography, which is also widely used for analysis. Different components move through the bed of packing at different rates and so appear separately, at the effluent end, where they are detected and measured by thermal conductivity changes, density differences, or ionization detectors. Gas chromatography is advantageous as a means of analysis of minute quantities of complex mixtures from industrial, biological, and chemical sources and is also of potential value in actually preparing moderate quantities of highly purified compounds otherwise difficult to separate from the mixture in which they occur.
