Comparison of CCS Values Determined by Traveling Wave Ion Mobility Mass Spectrometry and Drift Tube Ion Mobility Mass Spectrometry

Collision cross section (CCS, Ω)
values determined by ion
mobility mass spectrometry (IM-MS) provide the study of ion shape
in the gas phase and use of these as further identification criteria
in analytical approaches. Databases of CCS values for a variety of
molecules determined by different instrument types are available.
In this study, the comparability of CCS values determined by a drift
tube ion mobility mass spectrometer (DTIM-MS) and a traveling wave
ion mobility mass spectrometer (TWIM-MS) was investigated to test
if a common database could be used across IM techniques. A total of
124 substances were measured with both systems and CCS values of [M
+ H]+ and [M + Na]+ adducts were compared. Deviations
<1% were found for most substances, but some compounds show deviations
up to 6.2%, which indicate that CCS databases cannot be used without
care independently from the instrument type. Additionally, it was
found that for several molecules [2M + Na]+ ions were formed
during electrospray ionization, whereas a part of them disintegrates
to [M + Na]+ ions after passing through the drift tube
and before reaching the TOF region, resulting in two signals in their
drift spectrum for the [M + Na]+ adduct. Finally, the impact
of different LC-IM-MS settings (solvent composition, solvent flow
rate, desolvation temperature, and desolvation gas flow rate) were
investigated to test whether they have an influence on the CCS values
or not. The results showed that these conditions have no significant
impact. Only for karbutilate changes in the drift spectrum could be
observed with different solvent types and flow rates using the DTIM-MS
system, which could be caused by the protonation at different sites
in the molecule.