U.S. Department of Energy

Pacific Northwest National Laboratory

Analysis of Structural Changes with High Resolution Structures for Lossless Ion Manipulations (SLIM) Ion Mobility-Mass Spectrometry

Introduction

 

The availability of commercial ion mobility spectrometry (IMS) instrumentation coupled to mass spectrometry (i.e. IM-MS) has resulted in an explosion of applications. For example, IM-MS has been applied to bottom up proteomics, intact protein structural analyses (e.g. including glycoforms and quaternary structure), lipidomics, metabolomics, small molecule binding interactions and kinetics, etc. However, the ability to analyze small structural changes to proteins due to e.g. small molecule binding or post-translational modifications is limited on current platforms due to insufficient ion mobility resolution in many cases for separation of key spectrum components. We will present an investigation into protein structural changes by the application of a high IMS resolution SLIM Structures for Lossless Ion Manipulations module, utilizing a multi-pass arrangement.

 

Methods

 

The high resolution multi-pass SLIM module consisted of a pair of parallel printed circuit boards spaced ~3 mm apart in ~4 Torr N2. Travelling wave (TW) potentials were applied to arrays of electrodes aligned with the ion path. Additionally, ions were confined by a combination of lateral DC-only electrodes (guards) and extended RF electrodes, also aligned with the ion path. Mixtures (either prepared by mixing purchased compounds or resulting from solution-phase fractionation) were directly infused by nanoelectrospray ionization for accumulation into an ion funnel trap before ejection (0.5 ms pulses) into the SLIM module. A SLIM ion switch controlled whether ions were sent for additional passes through the serpentine path of the module, or to the TOF MS for analysis.

 

 

Preliminary data

 

The application of SLIM for IMS has been previously reported. More recently, TW SLIM approaches have been introduced. Ion trajectory simulations were performed on several initial geometries, demonstrating that lossless ion transmission was feasible, and subsequent separations were performed using a short TW SLIM module (< 50 cm) that yielded resolutions comparable to a 1 meter drift tube IMS. The development of SLIM designs for 90 and 180° turns allowed the development of much longer path length serpentine path designs, significantly improving the resolution that can be obtained. For example, separations of peptide, lipid, and carbohydrate isomer ions have been performed in an extended path length (> 10 m) TW SLIM module. Building on this development, we have constructed a 13 m travelling wave SLIM module with the ability to switch ions either to the MS or for additional passes through the serpentine path of the SLIM.  Initial results have shown the ability to transmit ions throughout the device and switch between the two paths with high efficiency, and also that the IMS resolution increases by approximately the square root of the increase in length with multiple passes through the SLIM module. This presentation will focus on the initial applications and utility of these developments for the high resolution IM-MS analysis of proteins and the improved characterization of intact proteoforms.

 

Novel aspect

 

The ability to analyze protein structural changes and mixtures of proteoforms using high resolution IM-MS. 

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