An ion sequestering apparatus and methods or systems using one or more auxiliary electrodes in an ion reaction instrument having RF electrodes adapted to guide positively-charged precursor ions along a first axis, and an electron source for introduction of an electron beam along a second axis transverse to the first axis such that electron activated dissociation of the precursor ions into reaction products can occur, the auxiliary electrode configured to apply a supplemental AC signal to permit selective extraction of reaction products while sequestering precursor ions along the second central axis. For example, the supplemental AC signal can comprises an notched white noise signal with a notch that suppresses frequencies at which the precursor ions (and/or charge reduced species that have the same molecular mass but have a different charge state) would otherwise be excited.