Multi-Pass Arrival Time Correction in Cyclic Ion Mobility\nMass Spectrometry for Imaging and Shotgun Lipidomics

Direct-infusion mass\nspectrometry (DI-MS) and mass spectrometry\nimaging (MSI) are powerful techniques for lipidomics research. However,\nannotating isomeric and isobaric lipids with these methods is challenging\ndue to the absence of chromatographic separation. Recently, cyclic\nion mobility mass spectrometry (cIM-MS) has been proposed to overcome\nthis limitation. However, fluctuations in room conditions can affect\nion mobility multipass arrival times, potentially reducing annotation\nconfidence. In this study, we developed a multipass arrival time correction\nmethod that proved effective across various dates, room temperatures,\nion mobility settings, and laboratories using mixtures of reference\nstandards. We observed slight variations in the linear correction\nlines between lipid and nonlipid molecules, underscoring the importance\nof choosing appropriate reference molecules. Based on these results,\nwe demonstrated that an accurate multipass arrival time database can\nbe constructed from corrected <i>t</i><sub>0</sub> and <i>t</i><sub>p</sub> for interlaboratory use and can effectively\nidentify isomeric lipids in MSI using only a single measurement. This\napproach significantly simplifies the identification process compared\nto determining multipass collision cross-section, which requires multiple\nmeasurements that are both sample- and time-intensive for MSI. Additionally,\nwe validated our multipass drift time correction method in shotgun\nlipidomics analyses of human and mouse serum samples and observed\nno matrix effect for the analysis. Despite variations in dates, room\ntemperatures, instruments, and ion mobility settings, our approach\nreduced the mean drift time differences from over 2% to below 0.2%.