Post ion/ion reaction CID mass spectra of the [M+7H]7+ ion of ubiquitin obtained from (A) Finnigan ITMS and (B) Hitachi model M-8000 mass spectrometers. (C) and (D) show expanded mass-to-charge ratio regions from 6400 to 7400 of the data in A and B, respectively. Reprinted from reference [53] from Int. J. Mass Spectrom., Vol 222, Reid G. E., Wells J. M., Badman E. R., McLuckey S. A., Performance of a quadrupole ion trap mass spectrometer adapted for ion/ion reaction studies, pp 243–258. Copyright 2003 with permission from Elsevier.