U.S. Department of Energy

Pacific Northwest National Laboratory

Very Long Path Length Ion Mobility Separations using Structures for Lossless Ion Manipulations

Introduction 

 

Ion mobility-based separations are of increasing importance in conjunction with MS, not only for providing additional structure-related information, but potentially more complete analysis of complex samples, detection of lower level constituents, and much greater speeds than feasible with liquid phase separations.  The benefits of mobility-based separations generally increase as separation power increases, however to date high resolution mobility separations have only been achieved in conjunction with significant ion losses and over very limited ranges of mobility, substantially limiting their practicality and range of applications.  This presentation will describe progress in new approaches capable of achieving ultrahigh resolution ion mobility separations based upon utilizing traveling waves in very long serpentine path length Structures for Lossless Ion Manipulations (SLIM) modules.

 

 Methods 

 

Extended IMS is being studied in N2 at 4 Torr in conjunction with MS using long serpentine path lengths in compact SLIM designs created using printed circuit board (PCB) technologies.  The SLIM modules consist of two PCBs spaced by ~3 mm and which have arrays of RF electrodes. The RF electrodes are used to create pseudopotentials that confine ions between the surfaces and effectively eliminate ion losses, and used in conjunction with separate traveling wave (TW) electrodes to drive ion motion. In this work very long serpentine paths (>10 m) are utilized to perform the IMS separations in SLIM modules allowing novel TW applications. Separations were evaluated based upon the resolution achieved for standard samples and various challenging mixtures.

 

Preliminary data 

 

We initially evaluated the novel TW IMS SLIM approaches using short path devices (~30 cm) and that achieved resolving powers and resolutions comparable to conventional drift tube IMS, as well as commercially available TW IMS (i.e. the Synapt II). We also evaluated, both by simulation and experiment, a range of designs, including designs having e.g. different numbers of RF electrode arrays (to adjust IMS path width), and PCB spacing.  Experimental measurements were consistent with simulations and showed that transmitted ion currents with most designs after optimization of potentials were effectively lossless. Good IMS resolution could also be achieved broadly for all the designs evaluated, with further optimization possible. Based upon simulations we developed a simple approach for ‘turning’ ions that simulations indicated avoided ion losses and also minimized any significant impacts upon resolution. We then explored several long serpentine path (> 10 m) SLIM modules using the same electrode designs, and showed that the achieved resolution was consistent with expectations.  The designs were further demonstrated for a range of challenging separations.  Finally, we have begun exploration of additional SLIM-based approaches for increasing resolution using multi-pass designs, as well as approaches for increasing the sensitivity and dynamic range of measurements.

 

Novel aspect 

 

The development of novel long path length high resolution ion mobility separations based upon novel SLIM and traveling wave approaches.

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