In contrast to 1-pass, cIM multi-pass routines operate such that all ions circumnavigate the mobility device repeatedly until their ejection after a specified time window has elapsed. Therefore, owing to the variability in ion size, shape and charge within complex peptide mixtures, the number of passes around the mobility device per peptide is variable and can be upscaled by increasing the duration of the mobility separation. Here, an 18.13 ms multi-pass cIM separation was applied, with number of passes for peptides likely ranging in the low to mid-single digit range . During peptide mapping, application of multi-pass cIM separations consistently underperformed relative to 1-pass (Figure ). When compared to SYNAPT G2-Si, multi-pass cIM provided 84 and 10% increases in peptide identification for SMO and XylE, respectively, but decreases of 7 and 52% for MsbA and SecYEG. This was counterintuitive, as the increased mobility separation window was expected to increase peptide identification numbers relative to 1-pass cIM owing to its increased resolution potential.