Unwrapping Wrap-around in Gas (or Liquid) Chromatographic Cyclic Ion Mobility–Mass Spectrometry

Gas chromatography multiplexed with cyclic ion mobility
mass spectrometry
is a comprehensive two-dimensional separation technique that can resolve
compounds that would otherwise coelute in a single-dimension separation.
The cyclic geometry of the ion mobility cell enables ions to travel
multiple passes, increasing their drift times to the detector and
relative separation. However, the quality of the separation may be
obfuscated when “wrap-around” occurs, during which speedier
ions catch up with slower ion populations when allowed to travel through
more than one pass. Consequently, cyclic ion mobility is incorrectly
perceived as a targeted approach that requires preselection of ions
prior to separation. The present study demonstrates that “wrap-around”
can be mitigated by comparing drift times measured during single-
and multipass experiments and extrapolating the number of passes experienced
by each ion. This straightforward calculation results in the “unwrapping”
of cyclic ion mobility data so that the experiments can be interpreted
in a nontargeted way while reaping the benefit of peak capacities
that rival those achieved using other comprehensive two-dimensional
separations.