Potentiality of mass spectrometry in combustion product analysis

The analysis and characterization of flame-formed products (i.e. Polycyclic Aromatic Hydrocarbons (PAH) and soot) still represents a crucial point not only for a deepening of the knowledge on reaction pathways in flames, but also for the control and monitoring of air anthropogenic emissions due to their dangerous effect on human health and on the environment. Gas Chromatography coupled to Mass Spectrometry (GC-MS) is the analytical technique usually applied to aromatic compounds relevant in the combustion field for the qualitative and quantitative analysis of PAH, according to the UNICHIM 825/1988 and EPA (US Environmental Protection Agency) methods 8270D and 610. However, GC-MS technique is limited to the detection of PAH up to coronene (7 rings, 300 Da) and lacks in the detection of high molecular weight aromatic species (>300 Da), commonly present in complex matrixes generated from fuel-rich combustion systems [3]. This strict limitation is mainly due to the low volatility of heavy aromatic species [4], which hinders the sample vaporization necessary for the gas chromatographic analysis. Moreover, the quadrupole analyzer generally coupled with GC, presents an upper mass range limit of m/z 1000. In the present work, different kinds of ionization systems and mass analyzers for mass spectrometric techniques have been explored in order to test their potentiality in extending the detection range of combustion products analysis with respect to GC-MS. In particular, Atmospheric Pressure Photo-ionization-Mass Spectrometry (APPI-MS) and Laser Desorption Ionization-Time of Flight Mass Spectrometry (LDI-TOFMS) have been tested in the analysis of samples collected in a fuel-rich premixed flame of ethylene-oxygen.