Aspects of the mechanism of the flame ionization detector

The development of flame ionization detection took place on an empirical ba sis without a clear understanding of the mechanism. The study of flames by mass spectrometry showed that the all-important ion was the formylium ion C HO+. The pre-combustion degradation was thought to be a pyrolytic degradati on and hydrogenation at the high temperatures obtained close to the combust ion zone. Using a capillary probe inside the flame it was recently shown th at a degradation of all hydrocarbons to methane takes place at low temperat ures by the reaction of hydrogen atoms which are generated in the burning h ydrogen. The effects of heteroatoms and of H-2 substitution was studied by the same method. (C) 1999 Elsevier Science B.V. All rights reserved.