In the present paper, we describe
the fundamentals and analytical
advantages of Oversampling Selective Accumulation Trapped Ion Mobility
Spectrometry (OSA-TIMS) when coupled to ultrahigh resolution mass
analyzers (e.g., FT-ICR MS). During TIMS analysis, ion packages are
spatially resolved based on their mobilities along the TIMS analyzer
axis and multiple strategies can be utilized during the trapping and
elution of the ion population of interest. In the case of OSA-TIMS-FT-ICR
MS, the TIMS operation sequence, trapping conditions, and operations
are optimized to increase the signal-to-noise and the number of points
across the mobility domain, which leads to more accurate mobility
and mass measurements. Experimental results show that accurate ion-neutral
collision cross sections (<1%) can be measured using OSA-TIMS-FT-ICR
MS with high mobility resolving powers (<i>R</i><sub>IMS</sub> up to 250), high mass accuracy (<1 ppm), and ultrahigh mass resolution
(<i>R</i><sub>MS</sub> up to 600–1200k at <i>m</i>/<i>z</i> 400) in a single analysis. The analytical
advantages of OSA-TIMS over SA-TIMS were illustrated for the analysis
of structural peptide isomers (SDGRG and GRGDS [M + H]<sup>+</sup>), conformational isomers (AT-hook peptide 3 KRGRGRPRK [M + 2H]<sup>+2</sup>), and a complex mixture of polyaromatic hydrocarbons (PAH)
from coal tar. Baseline separation of the structural peptide isomers
SDGRG and GRGDS, [M + H]<sup>+</sup>, was observed, and three conformations
were identified for the AT-hook peptide 3 KRGRGRPRK [M + 2H]<sup>+2</sup> during OSA-TIMS-FT-ICR MS. A 2-fold increase in the number of molecular
features and a 2–6-fold signal-to-noise increase was observed
for OSA-TIMS when compared with SA-TIMS during the PAH analysis. This
work provides the proof-of-principle for further application of OSA-TIMS-FT-ICR
MS for the unsupervised analysis of complex mixtures based on the
characterization of the conformational space and the assignment of
chemical formulas in a single analysis
