In 2019, Giles et al. developed cyclic ion mobility (cIM), a TWIM separator with a 'racetrack' geometry which enables scalable, multi-pass IM separations . Using the reverse sequence pentapeptides SDGRG and GRGDS, they demonstrated that the mobility resolution of cIM increases, as expected, with the square root of the number of passes around the device. Thus, by using extended IM separations, cIM has potential to offer improved LC-MS peak capacity relative to previous generation linear TWIM technology. The design, operation, and multifunctional capabilities of Cyclic IMS have been described in detail . Zöller et al. used the recently commercialised SELECT SERIES Cyclic IMS instrument with cIM technology for HDX-MS analyses of the E. coli nicotinamide nucleotide transhydrogenase . The use of HDMS E with a '1-pass' cIM routine successfully captured sequence coverage in transmembrane segments not obtained using previous-generation instrumentation. Despite this, to date, no systematic evaluation of cIM in HDX-MS has been performed, nor has its multi-pass functionality been utilised.