What is gas chromatography?

How gas chromatography works

In GC the sample is injected into a heated inlet, where volatile components vaporise. An inert carrier gas, such as helium, hydrogen, or nitrogen, then carries them through a long, narrow column whose inner wall is coated with a liquid or polymer stationary phase. Compounds that interact strongly with the stationary phase move slowly, while weakly interacting ones move quickly, so the mixture separates as it travels. The column sits in a temperature-controlled oven, because temperature strongly affects how long each compound is retained.

Retention time and detection

As each separated compound leaves the column it reaches a detector — commonly a flame ionisation detector for organic compounds or a mass spectrometer (GC-MS) for identification.

The time a compound takes to pass through the column, its retention time, is reproducible under fixed conditions and is used to identify it by comparison with standards. Peak area is proportional to amount, enabling quantification.

Uses in research

Gas chromatography is ideal for compounds that can be vaporised without decomposing, so it is widely used for solvents, fuels, flavours, fragrances, and environmental pollutants. Coupled to mass spectrometry it provides both separation and molecular identification, a combination heavily used in forensic, environmental, and food-safety analysis. Because retention times depend on column, carrier gas, and oven programme, comparable results require standardised methods and reporting.