Once the sample has been extracted and prepared it is then injected into the heated injection port of a gas chromatograph. The sample solvent is vaporized at a high temperature. A carrier gas (an inert gas such as hydrogen or helium) is used to push the sample through the chromatography column that is housed inside the GC oven. The solvent will elute very quickly from the column, but the compounds that were dissolved in the solvent begin to elute at different times, depending on their affinity (binding) to the stationary phase. The stationary phase in gas chromatography can be thought of as a gel that is coated to the inside of the long chromatography column. The time at which a compound elutes from the column is unique to each compound. This chromatography step thus serves to separate compounds. Think of the chromatography step as akin to a filter, it takes a solution containing many (sometimes thousands) distinct compounds and separates them so that they are now moving single-file, down the column, ready to be analyzed, one by one.
