Hydrocarbon Flame Ionization—Positive Ions

The positive-ion-molecule reactions considered to play a role in hydrocarbon flame ionization are catalogued in Table III, and the thermochemical values used are summarized in Table IV. Many of the reactions are only moderately exothermic, so that at the high temperatures of flames, the reverse reactions can contribute significantly to ion concentrations, and often the equilibrium is such that large concentrations of both ions are present. Further, because of the large rate coefficients for ion-molecule reactions, the ion concentrations can attain equilibrium distributions with... 

In a hydrocarbon analyzer using flame ionization, the sample gas is conducted along a heated sampling line to the detector, in the hydrogen flame of which the hydrocarbons are ionized into electrons and positive ions,... 

Flame ionization detectors (FIDs) and photoionization detectors (PIDs) can be used for the detection of hydrocarbons. Both detectors have been utilized for combustibles monitoring in portable and fixed installation designs. The FID actually burns the sample in an H2 flame. A charged electrical field is positioned across the flame, and utilizing the ions in the flame can conduct a current. When most combustible materials are introduced into the flame, they produce ions in their combustion products, and these are detected by the increased flow of current across the electric field (flame). 

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