PTR-MS - 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.