Gas chromatography is a type of chromatography. The sample that is going to be tested is first turned into a gas, and then carried through a column by a nonreactive 'carrier' gas such as helium or other inert gas such as nitrogen. As the sample is carried through the column it is separated into its individual components. To achieve this the column is housed inside an oven, where the temperature is controlled to allow the individual components to exit the column at different times.