The flame provides the energy for this ionization. This is generally speaking, a short-lived condition and the charged components quickly recombine into the products of combustion as they loose energy, moving upward, out of the flame. The Carbon molecule will readily form CO2 with the Oxygen from the surrounding air. Some variation in response occurs due to species molecule arrangement. This is a general explanation applicable to all FIDs found in hydrocarbon analyzers .
Different manufacturers use slightly differing schemes and geometries.
The FID is usually heated to prevent the formation of water vapor condensation from the FID flame, however a heated FID will have a detector and sample handling components operating at up to 200 degrees C in order to avoid both water vapor and long chain hydrocarbon condensation in the sample gas. When a hydrocarbon molecule ionizes in the FID detector of the total hydrocarbon analyzer, the positively charged portion is attracted toward the high voltage electrode where it's charge is neutralized by the high voltage power supply. The electron is attracted toward the collector electrode. The resulting charge balance occurs throught the input of a sensitive electrometer amplifier. This current is amplified and scaled to represent the volume concentration of hydrocarbon in the sample.