Ion Mobility Spectrometry A Useful Tool, But Challenges Remain

Ion mobility spectrometry can be a great tool for separating, identifying, and structurally characterizing analytes across many areas, but this process continues to have its challenges, according to a speaker at the High Performance Liquid Phase Separations and Related Techniques (HPLC 2023) conference held in Dusseldorf, Germany this week (1).

Valerie Gabelica, director of the Institut Européen de Chimie et Biologie, told the audience that collision cross-sections can help indicate gas phase compactness and different structures, but further work “needs to be done,” she said, as it relates to establishing standards for this process.

Gabelica began her talk by illustrating what the ion mobility approach actually looks like, describing a tube with buffer gas contained within, with an “entrance” and “exit” at both ends. “All the ions start at the entrance of the tube, and we measure how fast they move through the tube,” she said. “We can have a separation according to shape in the mobility cell, and we are also going to…take a collision cross-section to indicate how compact.” She noted that these measurements serve the dual purpose of separation and structural elucidation.

Ion mobility interpretation requires understanding rearrangements between the solution and gas phase, she continued. Citing a recently-published paper, Gabelica noted that the research team was curious about what was causing multimodal charge distributions from proteins that were being analyzed using electrospray. In that study, the team noted that a small percentage of the population didn’t follow the charged residue mechanism but also couldn’t ionize by pure chain ejection.

In that paper, the researchers, which included Gabelica, concluded that “a hybrid mechanism is possible, wherein globular domains are ejected one at a time from a parent droplet. The charge vs. solvent accessible surface area correlations of denatured and intrinsically disordered proteins are also compatible with this ‘bead ejection mechanism,’ which we propose as a general tenet of biomolecule electrospray" (2).

Gabelica wrapped up her talk by describing ion mass spectrometry as an “elucidation of unknown unknowns.”

References

(1) Gabelica, V. Ion mobility mass spectrometry to infer biopolymer folding and interactions. Presented at: HPLC 2023, June 18-22, 2023, Duesseldorf, Germany.

(2) Kristenko, N.; Rosu, F.; Largy, E.; Haustant, J.; Mesmin, C.; Gabelica, V. Native electrospray ionization of multidomain proteins via a bead ejections mechanism. J. Am. Chem. Soc. 2023, 145 (1), 498-506.