Assessment of Variable Traveling Wave Profiles for Small-Molecule Applications in Ion Mobility Spectrometry-Mass Spectrometry (IMS-MS)

The MOBILion MOBIE system is a relatively new platform
offering
high ion mobility spectrometry (IMS) resolving power and resolution.
While these advancements present encouraging opportunities for isomer
separations and improved molecular annotation, previous studies have
noted that collision cross section (CCS) values collected on the MOBIE
and other traveling wave (TW) systems possess bias in calculated CCS
values that limits the functionality of translating CCS libraries
across multiple IMS platforms. Though these challenges persist, MOBILion
recently released a software update (EyeOn v.2.3) that provides the
capability of utilizing variable traveling wave profiles, which modulate
the applied TW amplitude and frequency over the duration of each IMS
scan to provide optimal transmission, IMS resolution, and scan speed.
In this work, 5 variable TW profiles are assessed alongside a legacy
“static” method for application toward future small-molecule
workflows, tested herein with 3 model systems: per- and polyfluoroalkyl
substances (PFAS), bile acids, and oxylipins. Using 3 primary evaluation
metrics, including (1) ion transmission, (2) IMS resolution of isomeric
species, and (3) relative ease of CCS conversion and mobility filtering,
the collective results illustrate that the “Full” TW
profile possesses many advantages when analyzing small molecules for
nontargeted applications. Although the bias in TW-based CCS measurements
vs previous DTIMS values remains, utilizing CCS values obtained with
a consistent variable TW profile enables a linear calibration procedure,
which facilitates routine mobility filtering of IMS-MS data by CCS
and represents a needed improvement for streamlining both data acquisition
and subsequent analysis.