Greatly Increasing Trapped Ion Populations for Mobility Separations Using Traveling Waves in Structures for Lossless Ion Manipulations

Abstract

The initial use of traveling waves (TW) for ion mobility (IM) separations using structures for lossless ion manipulations (SLIM) employed an ion funnel trap (IFT) to accumulate ions from a continuous electrospray ionization source and was limited to injected ion populations of ~106 charges due to the onset of space charge effects in the trapping region. Additional limitations arise due to the loss of resolution for the injection of ions over longer periods, such as in extended pulses. In this work a new SLIM “flat funnel” (FF) module has been developed and demonstrated to enable the accumulation of much larger ion populations and their injection for IM separations. Ion current measurements indicate a capacity of ~3.2 × 108 charges for the extended trapping volume, over an order of magnitude greater than that of the IFT. The orthogonal ion injection into a funnel shaped separation region can greatly reduce space charge effects during the initial IM separation stage, and the gradually reduced width of the path allows the ion packet to be increasingly compressed in the lateral dimension as the separation progresses, allowing efficient transmission through conductance limits or compatibility with subsequent ion manipulations. This work examined the TW, rf, and dc confining field SLIM parameters involved in ion accumulation, injection, transmission, and IM separation in the FF module using both direct ion current and MS measurements. Wide m/z range ion transmission is demonstrated, along with significant increases in the signal-to-noise ratios (S/N) due to the larger ion populations injected. Additionally, we observed a reduction in the chemical background, which was attributed to more efficient desolvation of solvent related clusters over the extended ion accumulation periods. The TW SLIM FF IM module is anticipated to be especially effective as a front end for long path SLIM IM separation modules.

Squeezing of Ion Populations and Peaks in Traveling Wave Ion Mobility Separations and Structures for Lossless Ion Manipulations Using Compression Ratio Ion Mobility Programming

“…20 The SLIM designs used a pair of evenly spaced surfaces (~3 mm gap) having mirror-image arrays of six rf strip electrodes and lateral ion-confining dc “guard” electrodes, as described previously. 13,16 Five strips of segmented TW electrodes of 1.03 mm length and 0.43 mm width were interspersed between adjacent oppositely phased rf electrodes (a small portion of one surface is shown in the inset of Figure 1a).…”

New frontiers for mass spectrometry based upon structures for lossless ion manipulations

“…54 Three independently-controlled traveling waveforms provided ion transmission from the source to the trap section (i.e., ion filling), the release of ions from the trapping section (i.e., ion ejection) and transferring ions through a funnel-shaped section to a time-of-flight MS (Figure 14). The flat funnel was operated at ~3 Torr and used two TWs that were applied to two sets of interleaving TW electrodes in the trap section.…”

“…The IFT was used in continuous mode. 54 Adapted with permission from ref. 54 , Copyright (2016) American Chemical Society.…”

Ion Elevators and Escalators in Multilevel Structures for Lossless Ion Manipulations

“…10–12 The rung electrodes in the TW-SLIM used long rf electrodes separated by segmented dc electrodes. TW-SLIM IM modules were found to have similar capabilities to the uniform-field SLIM modules 10–14 and allowed for extended path lengths, thus achieving higher IM resolutions in relatively compact devices. 10–14 TW-SLIM modules were also demonstrated to enable the trapping of much larger ion populations and the ability to perform IM peak “compression”, of great utility for reversing peak diffusional growth and loss of peak intensities in extended ultrahigh resolution IM separations.…”