Frequency encoding ion mobility information in the <i>m/z</i> domain is an effective mechanism to couple temporal ion mobility separations with mass analyzers with particular relevance to ion trapping systems. While this mode of experimental operation largely mitigates the inefficiency of traditional nested ion mobility experiments, challenges remain with respect to minimizing data acquisition time and maximizing resolving power. Traditional approaches to FT-IMS experiments involve sweeping frequencies linearly over the course of an experiment.  For higher mobility ion populations modulation frequencies that expand into multiple kHz yield appreciable levels of ion signals but these same range of frequencies prove less useful for high mobility ions (e.g. proteins). With a new found recognition that the key parameter in FT-IM is not the span of frequencies probed but the rate at which frequencies are modulated presents the experimentalist with a refined set of parameters to manipulate.<br/>Using an innovative coupling of a drift tube IM system and an Orbitrap HFX we compare the theoretical and experimental limits of speed for the FT-IM experiment. To aid in the broader objective of increasing performance we also highlight a general strategy to construct non-linear frequency modulation pulsing trains and the benefits these approaches can provide in terms of speed. In some cases, SNR values reached ~5x higher for non-linear sweeps compared to the traditional linear frequency modulation strategies. Most importantly, however, is the development of linked, ramping frequencies sweeps that extend the range of useful signals acquired in the time domain and largely mitigate the issues plaguing low mobilities species. By synchronizing the frequencies applied to the ion gates with the scanning of the mass analyzer, our preliminary data sets have demonstrated resolving powers in excess of 200 for singly charged peptides while maintaining a 25% duty cycle.

Approaching the Analytical Speed Barrier and Maximizing Resolving Power for Frequency Modulated Ion Mobility-Mass Spectrometry

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.