A sample is injected into a heated inlet, then the component molecules of the sample mixture are separated by interaction with a coated capillary column in the gas chromatograph. The separated molecules are detected with a mass spectrometer, allowing for identification.

GCMS is typically considered the next step after infrared analysis. While infrared can rapidly detect the major functional groups present, GCMS has lower detection limits (potentially down to parts-per-trillion) and can identify the minor species present.

Electron Ionization