Quantitative analysis of a complex mixture using proton transfer reaction in an FTICR mass spectrometer

The potential of chemical ionization (CI) using proton transfer reaction associated with Fourier Transform Ion Cyclotron Resonance mass spectrometry (PTR-FTICR) for quantitative analysis was evaluated using unleaded gasoline headspace as a test mixture. A kinetic study of the reaction of H3O+ on this hydrocarbon mixture was performed in a wide range of sample pressures. Thirteen unsaturated hydrocarbons were detected as protonated species. Alkanes remain undetected since they do not react with H3O+ under FTICR conditions. The mixing ratios of the unsaturated hydrocarbons were derived from the kinetic data and varied from 0.3 to 15%. Each of them remained independent of sample pressure. Moreover, the results show that a valid concentration measurement can be drawn from only one mass spectrum, providing the reaction time is appropriately chosen. The reaction kinetics of H3O+ with selected hydrocarbons were also studied, allowing to evaluate the possible biases resulting from analyte fragmentations. Finally, the results were compared with GC/MS analysis of the same sample, showing a good consistency except for the lightest components. The origin of the differences is discussed.