to inject a liquid sample with large volume into a gc column of a gas chromatograph , its volatile portion is evaporated by heat , in a non - selective way , in a vaporization chamber , the vapors thus generated being fed to pre - column located upstream of the gc column and maintained at a lower temperature to that of the vaporization chamber , where such compounds are separated from the solvent vapors , which are unloaded into the atmosphere while the compounds to be analyzed are sent to the gc column .