GC - gas chromatography
Gas chromatography is analytical separation technique where gas is used as a mobile phase to separate molecules. Usually gas carrier is an inert gas - helium or hydrogen. This technique is suitable for separation of volatile organic components which are stable enough under evaporation conditions. Separation of molecules is taking place on the chromatographic column. The molecules are moving along the carrier gas path and interacting with the column stationary phase. Based on difference of this interaction and temperature of evaporation molecules or now we can call them analytes are selectively retained of released from the stationary phase thus enabling separation.
After the separation phase the analytes are entering the detector which is responsible for providing a measurable feedback of the molecule concentration in the gas phase. For the quantitative detection flame ionisation detector (FID) is typically used which signal is proportional to the number of carbon atoms present in the analyte. More advanced method of detection is the mass selective detector (MS), which offers high sensitivity and identification of the analytes at hand. This is possible by comparing fragmentation pattern (dissociation of energetically unstable molecular ions formed from passing the molecules in the ionisation chamber of a mass spectrometer, where analyte is bombarded by electrons with a predefined energy). The fragments of a molecule cause a unique pattern in the mass spectrum) between analyte and the mass library.