Leveraging spectral sparsity to realize enhanced separation of gas-phase ion populations

Abstract

When coupled with mass spectrometry, gas-phase ion mobility can enable the separation of isomers provided sufficient resolution. However, traditional limits on drift tube ion mobility resolution have been imposed by thermal diffusion and the duration of the initial ion gate pulse width. We demonstrate the first application of a post processing technique, specifically basis pursuit denoising (BPDN), for multiplexed IMS–MS experiments that not only minimizes data acquisition times, but realizes resolutions that exceed traditional predicted values. The multiplexing waveform used was based upon linear frequency modulation of the ion gate producing an ion gate pulsing sequence with a 50% duty cycle. This pulsing sequence further maximizes ion transmission and improved ion statistics in the m/z domain. Traditional, single pulse (signal averaged) and multiplexing IMS acquisitions demonstrate lowered resolution at extended ion gate pulse widths and minimizing this parameter results in decreased sensitivity from gate depletion effects and lowered ion gate duty cycle. Signal processing techniques involving BPDN was demonstrated on experimentally acquired IMS–MS data using the diastereoisomer ractopamine which exhibits two distinct gas-phase conformations with K0 values differing by 0.022cm2V−1s−1. Systematically adjusting the experimental parameters related to effective ion gate pulse width, we illustrate the capacity of this method to yield peak resolutions >1.0 for ion gate pulse widths that routinely yield unresolved arrival time distributions utilizing standard deconvolution procedures or equivalent gate pulse widths that utilize traditional signal averaged IMS datasets. When viewed from the perspective of a single peak, BPDN can increase the observed resolving power by more than a factor of 2. Because resolution and ion throughput are simultaneously maximized, the application of this optimization method represents a fundamentally different approach to multiplexed IMS signal processing.