A Transferable, Sample-Independent Calibration Procedure for Trapped Ion Mobility Spectrometry (TIMS)

Ion mobility spectrometry-mass spectrometry (IMS-MS) determines momentum transfer cross sections of ions to elucidate their structures. Recent IMS methods employ electrodynamic fields or nonstationary buffer gases to separate ions. These methods require a calibration procedure to determine ion mobilities from the experimental data. This applies in particular to trapped IMS (TIMS), a novel IMS method with reported high resolving powers. Here, we report the first systematic assessment of the accuracy and the limitations of mobility calibration in TIMS. Our data show that the currently used TIMS calibration approach reproduces drift tube mobilities to approximately 1% (95th percentile). Furthermore, we develop a transferable and sample-independent calibration procedure for TIMS. The central aspects of our approach are (1) a calibration function derived from a solution to the Boltzmann transport equation and (2) calibration constants based on a Taylor expansion of instrument properties (TEIP). The key advantage of our calibration approach over current ones is its transferability: one equation and one set of parameters are sufficient to calibrate ion mobilities for various instrument settings, compound classes, or charge states. Our approach is transferable over time and sufficiently accurate (∼1-2%) for structure-elucidation purposes. While we develop our calibration procedure specifically for TIMS, the approach we take is generic in nature and can be applied to other IMS systems.