Flame ionization detection (FID) is the most commonly used detector for gas chromatography (GC) analysis. FID is sensitive to molecules that are ionized in a hydrogen–air flame, including most carbon-containing compounds. But there are notable exceptions (see Table I). During the operation of an FID, the carrier gas that is leaving the column is mixed with hydrogen, and the eluting compounds are burned by a flame that is surrounded by air and an oxygen-rich environment. Approximately one organic molecule in 10,000 results in the production of a gas-phase ion. These ions are detected by a collector electrode that is positioned above the flame. The magnitude of the current that is generated by these ions is related to the mass of carbon that was delivered to the detector. This signal can then be used for both the detection and quantification of organic compounds that are eluting from the column.