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Proton Transfer Reaction Mass Spectrometry


The working group "Heterogenous Reactions" has a long-standing expertise in application of Proton Transfer Reaction Mass Spectrometry (PTR-MS) to investigate the sources, sinks and chemical degradation of atmospheric trace gases. The research activities comprise:

  • the investigation of the photochemical degradation of volatile organic compounds (VOC) within the atmospheric simulation chamber SAPHIR,
  • the partitioning of semi-volatile organic compounds between the gaseous and particulate phase,
  • the measurement of plant VOC emissions,
  • the determination of the carbon balance within closed heterogeneous atmospheric systems.

The PTR-MS technique relies on soft chemical ionization to detect trace components. These are converted to product ions through the transfer of a proton from the reagent ion, H3O+. The trace gasses (M) are identified through the mass of the product ions usually being the protonated molecular mass (MH+) as shown in the equation below.

H3O+  +  M   ->   MH+  +  H2O

Two types of PTR-MS instruments are available within our working group; a quadrupole mass spectrometer system (PTR-Quad-MS) and the time-of-flight instrument (PTR-TOF, Ionicon Inc.) The PTR-TOF provides high mass resolution and enables the differentiation of isobaric compounds within a mixture. Both systems feature a switchable reagent ion source with H3O+, NO+ and O2+ as precursor ions for the measurement and identification of various trace gases.

Quadrupole mass spectrometer system and time-of-flight instrument