Analysis of combustion products using time-of-flight mass spectrometry

Time of flight mass spectrometry (TOF-MS) combined with resonant two-photon ionization is applied to detect aromatic hydrocarbons in combustion products. The sample is introduced through a heated capillary into the supersonic jet of a TOF-MS. For ionization, a tunable, frequency-doubled dye-laser is used. The inlet system allows a direct measurement of samples at atmospheric pressure. The resonant ionization can distinguish structural isomers without preceding chromatography. The short response time of the system allows for example on-line monitoring of combustion emissions. This is demonstrated by thermodesorption experiments of anthracene from activated charcoal and from diesel soot. A significant higher desorption temperature from charcoal than from diesel soot is found. In addition, examples showing selective measurements of benzene, toluene and three dimethyl-benzene isomers in the exhaust gas of a gasoline engine are presented.