Gas chromatography is a form of chromatography in which a gaseous mobile phase passes through a column whose inner surface is coated with a solid stationary phase or a liquid stationary phase immobilized on an inert solid.
A gas chromatography system consists of many components. A pressurized supply of carrier gas is used to provide a constant flow of mobile phase through the column, which may be placed in an oven to change the kinetics of a particular separation. The carrier gas can be one of a variety of inert gasses depending on the type of detector used. Common carrier gasses include argon, nitrogen, helium, carbon dioxide and hydrogen. A sample injection system is needed to introduce the mixture to be separated into the flow of carrier gas at the head of the column. This injection system can be as simple as manually sticking a syringe through a septum on the injection port of an instrument, or as complex as an autosampler which can be programmed to inject hundreds of samples over a period of time using a robotic arm to move sample vials around. At the end of the column there must be some form of detector to measure the separated compounds. The most common detector is the flame ionization detector (FID). The effluent from the column is introduced into a hydrogen/air flame with a potential of several hundred volts across the burner. As compounds in the effluent burn, they form ions which can be detected by a collector electrode above the flame. Other kinds of detectors include thermal conductivity detectors, atomic emmission detectors, electron-capture detectors, and thermionic detectors. A GC system can also be paired with a mass spectrometer to form a GCMS system, a powerful instrument for identifying unknown compounds in a mixture.
Gas chromatography and GCMS have a wide range of applications, but are most commonly used in the petroleum and pharmaceutical industries.