A column holds the stationary phase and the mobile phase carries the sample through it. Sample components that partition strongly into the stationary phase spend a greater amount of time in the column and are separated from components that stay predominantly in the mobile phase and pass through the column faster. Gas chromatography is a chromatographic technique for separating volatile compounds. A gas chromatograph consists of a flowing mobile phase, an injection port, a separation column containing the stationary phase, and a detector. Compounds injected into the flowing mobile phase separate as they pass through the column due to differences in their partitioning behavior between the mobile gas phase and the stationary phase in the column.
Mobile phases are generally inert gases such as helium, argon, or nitrogen.
The injection port consists of a rubber septum through which a syringe needle is inserted to inject the sample. The injection port is maintained at a higher temperture than the boiling point of the least volatile component in the sample mixture. Since the partitioning behavior is dependant on temperture, the separation column is usually contained in a thermostat-controlled oven. Separating components with a wide range of boiling points is accomplished by starting at a low oven temperture and increasing the temperture over time to elute the high-boiling point components. Most columns contain a liquid stationary phase on a solid support.