Conceptual depiction of unbalancing the RF amplitudes on the two sets of opposing poles of a quadrupole rod array. V is the RF amplitude applied on the rod, “a” is the degree of unbalance and x, y, z represents the three dimensions. Reprinted from reference [41] with permission of Elsevier from “Mutual storage mode ion/ion reactions in a hybrid linear ion trap”, by Xia Y., Wu J., McLuckey S. A., Londry F. A., Hager J. W., Journal of the American Society for Mass Spectrometry, Vol 16, pp 71–81. Copyright 2005 by the American Society for Mass Spectrometry.