Gas chromatography (GC) is a common type of chromatography used in analytical chemistry to separate and analyze compounds that can be vaporized without decomposition. Typical uses of GC include testing the purity of a particular substance or separating the different components from a mixture (the relative amounts of such components can also be determined). In some situations, GC may help identify a compound. In preparative chromatography, GC may be used to prepare pure compounds from a mixture.
In gas chromatography, the mobile phase (or "mobile phase") is a carrier gas, usually an inert gas such as helium or a non-reactive gas such as nitrogen. Helium remains the most commonly used carrier gas in about 90% of the instruments, although hydrogen is preferred for improved separations. The stationary phase is a microscopic layer of liquid or polymer on an inert solid support within a piece of glass or metal tube called a column (homage to the fractionation column used in the distillation). The instrument used to perform gas chromatography is called a gas chromatograph (or "airbrush", "gas separator").
The gaseous compounds that are analyzed interact with the walls of the column, which is coated with a stationary phase. This causes each compound to elute at a different time, known as the retention time of the compound. The comparison of retention times is what gives GC its analytical utility.
Gas chromatography is in principle similar to column chromatography (as well as other forms of chromatography, such as HPLC, TLC), but has several notable differences. First, the separation process of the compounds in a mixture is carried out between a liquid stationary phase and a mobile phase of gas, whereas in column chromatography the stationary phase is a solid and the mobile phase is a liquid . (Thus, the full name of the procedure is "gas-liquid chromatography", referring to the mobile and stationary phases, respectively). Second, the column through which the gaseous phase passes is in an oven where the temperature of the gas can be as long as column chromatography (typically) has no such temperature control. Finally, the concentration of a compound in the gas phase is only a function of the vapor pressure of the gas.
Gas chromatography is also similar to fractional distillation, as both processes separate the components of a mixture based mainly on boiling point differences (or vapor pressure). However, fractional distillation is typically used to separate components from a large-scale blend, while GC can be used on a much smaller scale (ie, microscale).
Gas chromatography is also sometimes known as vapor phase chromatography (VPC), or gas-liquid partition chromatography (GLPC). These alternative names, as well as their abbreviations, are frequently used in the scientific literature. Strictly speaking, GLPC is the most correct terminology, and is thus preferred by many authors.
It can be understood in the following video: