Case study: Advancing Cryogenic Gas-Phase Spectroscopy of Ions

The Pagel Group at the Institute of Chemistry and Biochemistry, at Freie Universität Berlin, has developed a cutting-edge instrument for cryogenic gas-phase spectroscopy of ions in collaboration with MSVision and IsoSpec Analytics.

At the heart of the instrument is a cryogenically cooled ion trap (~40 K), filled with a helium/nitrogen gas mixture. Ions are trapped and “tagged" by nitrogen molecules at these low temperatures. When irradiated with a tunable infrared laser, resonant absorption by the ion causes the tag to detach - a process that is detected by mass spectrometry. By comparing the ratio of tagged to untagged ions after irradiation, high-resolution infrared spectra of the ions are obtained.

Figure 2. Infrared spectra of the Leucine enkephalin peptide.

What convinced me at the end was the well-designed and documented API (both C and Python) for integrating the digitizer into our own software, the pattern generator module for trigger masking and the option to firmware-upgrade the digitizer for onboard signal averaging, which would have been a good fallback option if the mass spectrometer triggering would have been too fast for moving the data between the digitizer and computer.

This advanced instrument empowers users to:

Isolate and characterize ions by mass, charge, and structure, even from complex mixtures.
Probe vibrational transitions of biomolecules, providing unique molecular fingerprints and insights into secondary and tertiary structures.
Distinguish isomers and conformers that are otherwise indistinguishable by classical mass spectrometry, such as enantiomers and diastereomers.

The approach builds on recent advances in the field, as highlighted in the literature:

Ion mobility-mass spectrometry (IM-MS) coupled with infrared action spectroscopy enables the selection and structural analysis of specific oligomers and isomers, crucial for understanding protein aggregation and glycan structures relevant to neurodegenerative diseases and cancer, [1].
Cryogenic ion traps and laser-based techniques provide highly resolved spectra, serving as benchmarks for theoretical models and facilitating the study of larger biomolecules, [2].

Building on our current achievements, the next steps for this technology could include:

Infrared spectroscopy of biomolecules to elucidate their structure and interaction sites with ligands, drugs, and even proteins.
Clinical applications where traditional mass spectrometry falls short, such as distinguishing molecules with identical masses but different IR spectra.
Accelerated and more confident molecular analysis, potentially reducing analysis time and increasing diagnostic reliability.

References:

Bakels, S. et al., “Probing High-Order Transient Oligomers Using Ion Mobility Mass Spectrometry Coupled with Infrared Action Spectroscopy," Anal. Chem. 2024.
Rizzo, T. R. et al., “Spectroscopic studies of cold, gas-phase biomolecular ions," Int. Rev. Phys. Chem. 2009.