Gas chromatography (GC) is a method for separating the components of a sample that contains a mixture of volatile compounds. The separations are made in order to determine the quantity of each of the sample components of interest. It has become one of the most often used procedures in analytical chemistry for separation and analysis. The reasons for its popularity can be traced to its ease of use for the separation of complex mixtures, its high sensitivity, and the small sample required for the analysis. In the elution form of GC, the sample mixture to be separated is vaporized and injected into a flowing stream of carrier gas (the mobile phase) that carries it into a column containing a so-called stationary phase. The stationary phase is a high-boiling nonvolatile liquid that is suspended on an inert solid with a large surface area or coated in a thin film on the walls of a small-bore tube (capillary, or wall-coated open tubular (WCOT) column). The support-coated solid can be packed into a fairly large-bore column (packed column) or attached to the wall of a small-bore capillary ( support-coated open tubular (SCOT) column). Similarly, a solid stationary phase (such as silica gel, alumina, or charcoal) can be packed into a column or suspended on the walls of a small-bore tube. Separations occur because the sample components have different solubilities in the liquid stationary phase or differentadsorbtivities on a solid stationary phase. Therefore, each sample component is retarded a different amount by the stationary phase and is carried down the column by the mobile phase at a different rate. Provided that a stationary phase has been selected that maximizes the solubility or absorbtivity differences, complete separation will occur with each sample component emerging from the column at a different time.