U.S. Department of Energy

Pacific Northwest National Laboratory

Ultrasensitive SLIM Serpentine Ultra-long Path with Extended Routing (SUPER) high resolution ion mobility-MS using large ion populations and peak compression



The benefits of ion mobility (IM) separations generally increase as separation power increases. However, the highest resolution IM separations reported to date have been achieved in conjunction with significant ion losses or over a very limited mobility range, substantially limiting their practicality and applicability. Limitations are not only related to the long path lengths needed for much higher resolution, but also the limited size of injected ion populations, and the decrease in IM peak intensities due to diffusion and other factors. This presentation will describe and initially demonstrate new technology and approaches achieving ultrahigh resolution IM with MS based upon use of traveling waves in long serpentine path and multi-pass Structures for Lossless Ion Manipulations (SLIM).




Long serpentine path and multi-pass SLIM designs were developed and implemented utilizing electrode arrays patterned on two surfaces spaced by ~ 3 mm. Appropriate potentials were applied to separate RF electrodes creating pseudopotentials that confine ions between the surfaces in 2 to 4 torr N2 and effectively eliminate ion losses, in conjunction with separate electrodes creating traveling waves (TW) to drive ion motion. SLIM ion switches were used to select ions for either multi-passes through the same long serpentine path (~13 m), or to shunt ions to the MS. Some SLIM designs incorporated compression ratio ion mobility programming (CRIMP) capabilities in which ion distributions could be temporally and spatially compressed. Separations were evaluated using standard samples and challenging mixtures.



Preliminary data


We initially explored TW SLIM IM approaches using short path devices (~30 cm) and showed that good performance could be achieved, with separation power comparable to conventional drift tube IM, as well as commercially available TW IM (e.g., Waters Synapt G2). We then evaluated serpentine long path (~13 m) designs and showed that the separation power achieved was consistent with expectations for the longer path length, with significant increases in resolution achieved compared to existing commercial platforms for a range of standard samples and mixtures of interest.  We then developed and explored multi-pass versions of the SLIM design, and showed that significant additional increases in resolution could be achieved for targeted applications, including many cases where new and previously unresolved or unsuspected conformers were revealed.  We have also made substantial progress in addressing three key remaining challenges for broader application and utility: (1) limitations on sensitivity and dynamic range due to the limited size of ion populations injected for separation; (2) limitations on the range of mobilities that can be studied in multi-pass separations due to the increasing separation between IM peaks; and (3) the decreasing peak intensities and growing peak width due to diffusion and related phenomena with increasing separation times. In this presentation it will be shown how CRIMP can address the first issue and greatly increase the ion population sizes in SLIM IM separations, with the potential to increase populations to >109 charges.  It will then be shown how considerably longer path length SLIM can be implemented as well as how CRIMP can be used to address the second issue.  Finally, we show that CRIMP can be used to greatly increase peak intensities (i.e. S/N ratios) in very long path separations, and in conjunction with the other developments, serve to make practical even longer path separations.



Novel aspect


The development and initial implementation of a novel long serpentine path multi-pass ultrahigh resolution and ultrasensitive SLIM IM-MS platform

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