Detection of arrival
time shifts between ion mobility spectrometry
(IMS) separations can limit achievable resolving power (Rp), particularly
when multiple separations are summed or averaged, as commonly practiced
in IMS. Such variations can be apparent in higher Rp measurements
and are particularly evident in long path length traveling wave structures
for lossless ion manipulations (SLIM) IMS due to their typically much
longer separation times. Here, we explore data processing approaches
employing single value alignment (SVA) and nonlinear dynamic time
warping (DTW) to correct for variations between IMS separations, such
as due to pressure fluctuations, to enable more effective spectrum
summation for improving Rp and detection of low-intensity species.
For multipass SLIM IMS separations, where narrow mobility range measurements
have arrival times that can extend to several seconds, the SVA approach
effectively corrected for such variations and significantly improved
Rp for summed separations. However, SVA was much less effective for
broad mobility range separations, such as obtained with multilevel
SLIM IMS. Changes in ions’ arrival times were observed to be
correlated with small pressure changes, with approximately 0.6% relative
arrival time shifts being common, sufficient to result in a loss of
Rp for summed separations. Comparison of the approaches showed that
DTW alignment performed similarly to SVA when used over a narrow mobility
range but was significantly better (providing narrower peaks and higher
signal intensities) for wide mobility range data. We found that the
DTW approach increased Rp by as much as 115% for measurements in which
50 IMS separations over 2 s were summed. We conclude that DTW is superior
to SVA for ultra-high-resolution broad mobility range SLIM IMS separations
and leads to a large improvement in effective Rp, correcting for ion
arrival time shifts regardless of the cause, as well as improving
the detectability of low-abundance species. Our tool is publicly available
for use with universal ion mobility format (.UIMF) and text (.txt)
files.