Altering the mobility-time continuum: nonlinear scan functions for targeted high resolution trapped ion mobility-mass spectrometry

Abstract

Trapped ion mobility spectrometry (TIMS) is a versatile high resolution technique that provides the user with the flexibility to adjust the mobility range of interest, duty cycle (up to 100 %), and resolving power (up to ~300) according to the application requirements. Furthermore, TIMS offers the flexibility of operating as either a mobility-selective or conventional ion funnel, thus permitting ion mobility separations to be turned on or off. Here, we extend the flexibility of TIMS by introducing multilinear and nonlinear scanning methods that allow enhanced resolution in user-defined mobility regions. The performance of the new method is demonstrated using a variety of nonlinear scan functions that allow the resolving power to be continuously varied across the mobility spectrum. Further, we demonstrate that mobility analysis can be targeted over disparate regions using a multilinear scan function. In this example, high resolution mobility analysis is targeted on two analytes on opposite ends of a mobility range, while other ions that fall between the regions of interest remain unanalyzed. Using this approach, the resolving power for targeted species was increased by a factor of two over the conventional linear scanning approach (R ~60 versus ~120) without reducing the duty cycle of the TIMS measurement. Importantly, in such an analysis, ions in the untargeted regions are not mobility analyzed, however, they are also not discarded. Rather, these ions are ejected for downstream mass analysis. In this sense, TIMS bridges the gap between dispersive and scanning mobility techniques. That is, TIMS disperses ions according to their elution voltage, however, TIMS can also perform target mobility analyses without eliminating untargeted ions.