Ion/ion reactions in a linear ion trap can be performed using either (a) mutual storage mode or (b), (c), (d) a form of transmission mode. (b), (c), and (d) reprinted from ref. 13 [original source “Scheme 2: Three methods for effecting transmission mode ion/ion reaction experiments in a LIT: (I) passing ions of both polarities, (II) positive ion storage/negative ion transmission, (III) positive ion transmission/negative ion storage”], Copyright 2008 Elsevier, Inc., with kind permission from Springer Science and Business Media.