Real-time analysis of polyaromatic hydrocarbons in flames using Atmospheric Pressure Ionization and tandem mass spectrometry

The use of Atmospheric Pressure Ionization followed by tandem mass spectrometry (API/MS/MS) for the analysis of flame gases was demonstrated. The hot flame gases from a methane/air laminar diffusion flame were sampled by rapid turbulent mixing with cold nitrogen gas, in a molar ratio of ca. 1:10. After 3 ms the gases underwent an additional dilution by a factor of 20 in synthetic air. The gas mixture was ionized by a corona discharge at atmospheric pressure. Subsequent chemical ionization reactions ionize mainly the polyaromatic hydrocarbons, PAHs. The PAH ions were analyzed in a triple quadrupole mass spectrometer. A sequence of PAH ions started with the perinaphthenyl cation, C 13H 9 +, and extended up to protonated coronene, C 24H 13 +, and beyond. That the observed ions were indeed protonated PAH molecules was confirmed by comparing the collision-induced dissociation spectra in the MS/MS mode with those of authentic samples. It is argued that most of the ions originate from PAHs that have substituents attached to the polyaromatic skeleton. The identities of the substituents could, however, not be determined. By rapid turbulent mixing of the flame gases with air, the PAHs were partially oxidized. The high mass region of the API spectrum was then dominated by a sequence of singly oxygenated PAHs.