Online ultrahigh resolution mass spectrometry for the molecular analysis of the atmosphere

Currently, the vast majority of online aerosol and gas phase instrumentation are equipped with time-of-flight (TOF) mass analyzers, taking advantage of their robustness in the field, their low detection limits and their rapid response. The moderate resolving power of the TOF had become the most important bottleneck in this field of research, making the identification and quantification of individual organic molecules extremely challenging. In addition, a general shortcoming of mass spectrometry is the lack of information on molecular structure and functional groups, which cannot be trivially inferred from the ion elemental composition.

Recently, we have initiated a collaboration with Ircelyon (France) to explore the much higher resolution of the Orbitrap-MS for online analysis of particle and gas phase. We have successfully reengineered the Orbitrap-MS nozzle to allow its interface with the aerosol inlet that is currently coupled with the TOF and conducted first proof-of-principle experiments (Lee et al., 2020). We demonstrate that the instrument higher resolution fundamentally alters the retrievable chemical information compared to the currently used TOF, enabling unambiguous identification of compounds’ elemental composition. Single unresolved peaks detected by the TOF contains several compounds unambiguously resolved by the Orbitrap-MS. We show that the appreciable gain in resolution does not occur at the expense of the instrument sensitivity, time resolution and robustness. The first applications of the instrument using laboratory-generated aerosols and field samples highlights the necessity of higher resolution for compound identification in the immensely complex atmospheric matrix. Another strategic feature we have explored in the instrument is the possibility to obtain tandem mass spectra for selected ions, which is highly valuable for distinguishing isomer compounds and obtaining for the first time structural information. These features will provide additional information for source characterization and for mechanistic studies. We expect such pioneering development to serve as a benchmark for atmospheric research and to open an entire range of new avenues for any discipline needing online ultrahigh resolution mass spectrometers, including environmental sciences, ecology, geochemistry and energy research, therefore going far beyond just atmospheric science.

Together with Ircelyon, we have deployed the instrument for the first time at the CLOUD chamber at CERN, to reveal the identity of the vapors forming new particles in the atmosphere. The instrument has just been deployed in China to investigate pollution sources.  

Original Publication :

Title: Online Aerosol Chemical Characterization by Extractive Electrospray Ionization - Ultrahigh Resolution Mass Spectrometry (EESI-Orbitrap)

Authors: Lee, C.-P., Riva, M., Wang, D., Tomaz, S., Li, D., Perrier, S., Slowik, J., Bourgain, F., Schmale, J., Prevot, A. S. H., Baltensperger, U., George, C., El-Haddad, I.

Journal: Environmental Science and Technology, 54, 7, 3871–3880, 2020

Acknowledgement to:

This work was financially supported by the Breakthrough grant WANTED (for Ircelyon), Swiss National Science Foundation (20020_172602, BSSGI0_155846) and European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 701647