Diagram of the charge neutralization chamber with (a) the corona discharge and (b) the α-particle source. Attachment to the mass spectrometer inlet via an o-ring seal greatly improved ion transmission. Reprinted from reference [24] with permission of Elsevier from “Controlling gas-phase reactions for efficient charge reduction electrospray mass spectrometry of intact proteins”, by Frey B. L., Lin Y., Westphall M. S., Smith L. M., Journal of the American Society for Mass Spectrometry, Vol 16, pp 1876–1887. Copyright 2005 by the American Society for Mass Spectrometry.