Under usual Mass Spectrometry or MS step under the Gas Chromatography Mass Spectrometry, the compounds leaving the GC columns are fragmented by the electron impact. These charged fragments are detected gradually and the subsequent spectrum obtained is used to identify the molecules. Fragmentation patterns are reproducible and thus, can be used to create quantitative measurements.
Gas Chromatography Mass Spectrometry analysis is performed on gases, solids and liquids. For gases and liquids, the samples are usually injected directly into the Gas Chromatogram. For the solid elements, the analysis is carried our through outgrassing or desorption, solvent extraction or pyrolysis.