Diffusion Constriction Study to Provide Virtually Limitless Resolution in Ion Mobility on Structures for Lossless Ion Manipulation (SLIM) Platforms

CARLOS LARRIBA-ANDALUZ, Mohsen Latif, Purdue University

     Abstract Number: 600
     Working Group: Instrumentation and Methods

Abstract
Ion/Electrical mobility spectrometry (IMS), especially when paired with mass spectrometry (MS), has become an essential tool for probing the structure and composition of complex molecular mixtures. By separating ions based on their shape and size (collision cross section) rather than just mass-to-charge ratio, IMS enables powerful insights across fields like aerosols and its precursors, proteomics, and small-molecule analysis. Yet, despite its versatility, IMS continues to face a major limitation: resolution. Compared to MS, IMS offers relatively modest resolution, and while increasing the path length in modern systems can improve this, it comes at a steep cost—signal loss due to axial diffusion.

While radial diffusion has largely been tamed through radiofrequency (RF) confinement at low pressures, axial diffusion remains a bottleneck. Over long separations, ion packets naturally spread, degrading signal quality and limiting the technique’s ability to distinguish closely related molecular species. In this work, we explore a new theoretical approach to overcoming this challenge. Building on the concept of diffusion autocorrection via spatially varying electric fields, we propose the use of asymmetric traveling waveforms to actively compress ion packets in the axial direction during transit. Specifically, waveforms with sharp voltage rises followed by gradual decays create a self-correcting electric field that counteracts packet broadening. Simulations based on the Nernst-Planck equation confirm that this field pattern can suppress diffusion over extended paths, preserving resolution and sensitivity far beyond what is currently achievable.

To enable this strategy, we propose a new SLIM-based architecture—CLIMB (Constricted Lossless Ion Mobility Board)—featuring densely packed electrodes and reduced inter-board spacing designed to generate near-linear field gradients over long distances. Although still at the conceptual stage, CLIMB could make it possible to baseline-separate isomers and isotopomers without relying on mass selection. If realized, this platform would represent a major leap in IMS performance and portability, opening new possibilities for high-resolution, real-time analysis in clinical, forensic, and environmental settings.