Detection by mass spectrometry of hydrocarbon biradicals, pyridine and aniline in a flame ionization detector

Abstract

The mass spectra of ions of > 75 in an f.i.d.-type flame with benzene additive have shown that hitherto undetected species of formulas C_llH₉⁺ and C_I3H₉⁺ are present, which may be attributed to protonation of the biradicals C₁₁H₈ and C₁₃H₈ by H₃O⁺. The remainder of the hydrocarbon ions present are attributable to protonation of aromatic compounds (e.g. naphthalene and indene) which have been detected previously in premixed benzeneloxygen flames by electron impact ionization. Addition of NH₃ to the benzene sample suppresses all the hydrocarbon peaks of m/z > 100 but generates new peaks of m/z 80 and 94, attributable to the protonation of pyridine and aniline. Aniline may be generated by addition of NH₂ radicals to benzene in the pyrolysis and reaction zones of the flame.