U.S. Department of Energy

Pacific Northwest National Laboratory

Compression Ratio Ion Mobility Programming in Structures for Lossless Ion Manipulations

Introduction:

Structures for Lossless Ion Manipulations (SLIM) technology has enabled very long path length IM separations using traveling waves (TW) in serpentine and multi-pass designs, but resolutions achievable are limited by peak broadening phenomena, which increasingly inhibit detection due to peak dilution. In this work we developed a new approach for spatial and temporal peak compression that can mitigate many of the negative effects of peak broadening and demonstrate its application for the collapse of the ion distributions into tighter packets to provide higher sensitivity. The nature of fields and ion dynamics enabling peak compression will be presented. The implications of compression ratio squeezing of ion packets and programming for IM separations and other applications will be discussed.

Methods:

Theoretical and simulation methods are used to study the process of peak compression in TW SLIM. In-house computational models were used to study effects of compression. SIMION ion trajectory simulations were used to demonstrate proof-of-concept, to predict experimental performance and optimize SLIM designs. Software package OpenFOAM was used to visualize the ion confinement fields and model the ion dynamics by treating ion motion using advection-diffusion equation. Experimental implementation was performed on a 13 m long serpentine path length SLIM device with multi-pass capability, coupled to an Agilent qTOF MS.

 

Preliminary Data:

We demonstrate peak compression using a SLIM device with a TW region (R1) and another region where a stuttering wave moves only intermittently (R2). As the ions pass the interface between R1 and R2, the ion packets spanning a number of TW-created traveling traps (TT) are redistributed into fewer TT, resulting in spatial compression. The degree of spatial compression is controllable and determined by the ratio of stationary time of the TW in the second region to its moving time. This compression ratio ion mobility programming (CRIMP) approach has been implemented using SLIM in conjunction with a TOF-MS. CRIMP with the SLIM IM-MS platform is shown to provide increased peak intensities, reduced peak widths, and improved S/N ratios with MS detection. The increase in peak height is equivalent to the applied compression ratio (CR) until such a point that space charge effects lead to ion activation and/or losses. SLIM TTs keep ions confined as long as the TW is in the surfing mode, and TW produce a ion peak bin “quantization” effect which allows peak compression with integer CR. The effect of such peak compression on IM separation and resolution will be discussed from theoretical standpoint and correlated to experimental observations. TW SLIM IM separation of milk oligosaccharide isomers in conjunction with peak compression shows that two species with very similar mobilities can be fully separated by combined application of separation and compression. Also CRIMP allows injecting a wide pulse of ions that can be separated and then compressed to enable high resolution IM separations at high sensitivity. Further, insights from ion trajectories modeling on the effects of space charge during the CRIMP process will be discussed.

 

Novel Aspect:

Peak compression using CRIMP mitigates negative effects due to peak broadening in IM separations

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