The response features of C2N2, NH3, NO, N2O, and PH3 have been determined in a conventional flame ionization detector and in a flame spectrophotometer system where ion formation may be correlated with molecular emissions. The nitrile group is shown to produce ions by a different process to other organic structures, i.e., CN + 0 + 0 → CO + NO+ + e The NH3, NO, N2O and PH3 responses are much smaller, and while evidence is presented for the reaction NH2 + 0 + 0 → H2NO2+ + e as the source of ions from NH3, emission studies of NH suggest that this reaction could not be the source of ions from NO and N2O. Doubt is therefore cast on the NH3 mechanism, since NO is a major product of that oxidation.