Gas Chromatography (GC)
Gas chromatography (GC) is a technique used to separate individual components in a complex organic mixture. The sample is injected onto one end of a fused silica wall coated open tubular column through which gas (the carrier gas) is flowing (usually nitrogen, helium or hydrogen). The column is heated in an oven through a temperature gradient, when the oven is cool (room temperature) only volatile compounds that boil from the column coating at low temperature will evaporate from the sample and travel down the column to be detected at the far end by a detector, as the oven is heated, components of the mixture that boil from the column coating at a higher temperature evaporate and are transported down the column by the flowing gas. In this way the components in the mixture are separated according to the temperatures at which they boil from the column coating.
There are several types of detector available for GC instruments of which the most common are Flame Ionisation Detectors (FID), Electrochemical Detectors (ECD) and Mass Spectrometry (MS).
GC-FID is commonly used by SGS M-Scan for the characterisation and speciation of refined product in petrochemical samples. Where further specificity is required, or where lower limits of detection are desirable, GC-MS may be more appropriate eg for the analysis of polycyclic aromatic hydrocarbon (PAH).