gas chromatography (GC)

Separation of mixtures of compounds in their gaseous state can be achieved by passing them in a stream of heated inert gas, called the carrier gas (usually helium or hydrogen) through a long column containing an immobilised stationary phase for which different components will have different affinities. The column is held in an oven at a carefully controlled temperature. The stationary phase can be chemically bonded to the internal wall of a silica capillary column or can be adsorbed onto a porous inert medium which is packed into a glass spiral column. The sample, either in gaseous form or dissolved in a low boiling solvent, is injected on to the top of the column into a heated chamber and the gaseous mixture is passed through the column. It is common to use a temperature gradient to heat the column. Separated components elute from the end of the column and are passed to a detector.