Nitric oxide chemical ionization ion trap mass spectrometry for the determination of automotive exhaust constituents

Nitric oxide chemical ionization in a glow discharge ionization source coupled with a quadrupole ion trap mass spectrometer has been evaluated for application to automotive exhaust measurements. Emphasis was placed on the determination of hydrocarbons at parts-per-million to parts-per-billion levels. Nitric oxide chemical ionization was found to yield diagnostic ions for alkanes, alkenes, and arenes, whereas water chemical ionization failed to provide diagnostic ions for the alkanes. The ability to measure a variety of hydrocarbons present at roughly 15 ppb at measurement rates of 3 Hz was demonstrated. All of the ions with potential to serve as parent ions in a tandem mass spectrometry experiment were found to yield parent-to-product conversion efficiencies greater than 75%. The flexibility afforded to the ion trap by the use of tailored waveforms applied to the endcaps allows parallel monitoring schemes to be devised that provide many of the advantages of tandem mass spectrometry without a major loss in measurement rate. A large loss in measurement rate would ordinarily result from the use of conventional tandem mass spectrometry experiments carried out in series for a large number of targeted components.