Queuing theory-based predictions of ion mobility shifts via vapor clustering at arbitrary field strength

Advanced ion mobility-based separation techniques involve the measurement of gas-phase ion mobilities at high, varying electric field strengths in the presence of both a bath gas and condensable vapor molecules; the latter selectively cluster with gas-phase ions. We develop and apply a queuing theory-based approach to determine the mobilities of ions at arbitrary field strengths and in the presence of condensable vapor molecules. The theory is compared to direct molecular dynamics simulations of doubly charged bradykinin ions in the presence of methanol at variable vapor pressure, demonstrating that mobility predictions can be made with the queuing theory approach, which only requires several clearly defined input parameters.