Ion Trapping in Spherical FAIMS

Of course, a useful trap must have an exit that can be shut to 

The performance of FAIMS trap (also called t-FAIMS ) has been evaluated for ions of doubly protonated peptide gramicidin S prefiltered by cylindrical FAIMS. The key kinetic metrics of any trap are the half-times of fill (t ) and storage (t t)—the times needed to fill an empty trap to half its capacity and for the ion population in a closed trap to halve. One normally desires to minimize and maximize t t. The ion loss due to diffusion follows the first-order kinetics (the loss per unit time is proportional to the number density N), leading to  

FIGURE 5.3 Prototype of FAIMS ion trap operating at atmospheric pressure (a) the scheme and (b) pseudopotential for gramicidin S (2+) ions computed along the axial direction marked in (a) by the dashed hne. (From Guevremont, R., Ding, L., EUis, B., Barnett, D.A., Purves, R.W., J. Am. Soc. Mass Spectrom., 12, 1320, 2001.) 

Quadrupole ion traps can eject stored ions with a given m/z value, scanning which enables MS analyses. Ions in spherical t-FAlMS are obviously radially stratified by 

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