Gas chromatography differs from other forms of chromatography in that the mobile phase is a gas and the components are separated as vapors.

It is thus used to separate and detect small molecular weight compounds in the gas phase.

The sample is either a gas or a liquid that is vaporized in the injection port. The mobile phase for gas chromatography is a carrier gas, typically helium because of its low molecular weight and being chemically inert.

The pressure is applied and the mobile phase moves the analyte through the column. The separation is accomplished using a column coated with a stationary phase. https://microbenotes.com/gas-chromatography/#what-is-gas-chromatography