Flame Ionization Detector

The schematic diagram below shows a flame ionization detector for gas chromatography. The eluent from the column mixes with H₂ and is burned in the presence of excess air. Combustion of organic analytes produces a flame containing electrons and organic cations, presumably CHO⁺. Applying a potential of approximately 300 volts between the flame tip and the collector, generates a small current of roughly 10^–9 to 10^–12 amps. that, when amplified, provides a useful analytical signal proportional to the concentration of cations—and thus the concentration of analyte—in the flame.