U.S. Department of Energy

Pacific Northwest National Laboratory

Accumulation and Compression of Billions of Ions using CRIMP in SLIM Significantly Improves Sensitivity and Ion Mobility Resolution

Introduction

Ion mobility-mass spectrometry (IM-MS) is a highly versatile analytical tool for structural characterization of biomolecules. Recently, ultra-high IM resolution has been achieved using multi-pass SLIM designs, however, the benefits of improved resolution have been limited by the increased peak broadening due to dilution and other adverse effects which consequently degrade the overall sensitivity. Here we report a new approach Compression Ratio Ion Mobility Programming (CRIMP) within travelling wave (TW) based SLIM that enables both great trap charge capacity and efficient compression for billions of ions. An integration of the CRIMP accumulation and periodical compression process within SLIM multipass TWIM separation has the potential to achieve theoretically unlimited resolution IM separations while maintaining ultra-high sensitivity.

Methods 

The SLIM module with CRIMP used a ~13.5 m long serpentine path patterned with rf, TW, and guard electrode arrays on two surfaces with 2.75 mm spacing. Appropriate potentials were applied to rf electrodes, creating pseudopotentials that confine ions between the surfaces in 2.5 torr N2 for lossless ion manipulations. The module used two independently-controlled sections: a 9 m long section operating in a traveling trap (TT) TW mode, and a 4.5-m long section operating in stuttering trap (ST) TW mode during accumulation/compression time and then resuming to normal TT TW mode for ion ejection or maintaining the compressed ion packets. CRIMP accumulation and compression performance occurs at the TT-ST interface and was characterized using standard samples. 

Preliminary data 

CRIMP allows accumulation of extremely large ion populations in ‘TT section’ by creating a barrier at the interface of the normal TW with the second stationary wave region to accumulate ions in the first regions (typically, near the interface). We have initially investigated a range of SLIM parameters (e.g., rf, TW and guard bias) for ion accumulation. The number of charges accumulated for 40 s was estimated to be ~5×109, and much greater populations appear to be feasible. The compression process occurs at the TT-ST interface between the two TW regions, one operating conventionally and the second intermittently pausing or ‘stuttering’ to compress ions entering from the ‘TT section’, allowing the contents of multiple bins of ions to be merged into a single bin. The extent of the compression is only limited by the onset of space charge effects. Low compression ratios (CRs) allow increased peak heights without any loss of signal, excessively large CRs can lead to ion losses and other artifacts. Over 1×109 ions can be compressed in high efficiency. Larger intermittent/stuttering TW bins in ST section, as well as higher rf confinement potentials, provide greater compression performance. Importantly, the use of CRIMP within a SLIM TWIM module enabled greatly expanded ion accumulation and injection without the use of grids, and the basis for doing this in conjunction with compression in a manner that is fully compatible with TWIM separations. Thus, the integration of CRIMP accumulation and compression within multi-pass SLIM has the potential to achieve theoretically unlimited high resolution TWIM separations with ultra-high sensitivity. It is expected that these developments will result in data providing a greater depth of information for biological samples and other complex mixtures. 

Novel aspect 

A new SLIM CRIMP module capable of achieving ultrasensitive and ultra-high resolution TWIM separations

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