GCMS sample. Sample vial being selected for gas chromatography mass spectrometry (GCMS) analysis. Gas chromatography is carried out to separate complex mixtures of compounds into individual components, allowing the composition to be analysed and particular fractions isolated. As the components emerge from the top of the chromatography column they are then fed into a mass spectrometer. This ionises and fragments the molecule, and fires the fragments through a magnetic field. The amount the fragments deviate is indicative of their mass and charge. This can provide detailed information about the samples composition.