Surface-Induced Dissociation of Multiply-Protonated Proteins

A novel surface design compatible with the open cell geometry allows nonglancing angle collisions of selected ions stored in a Fourier transform mass spectrometer. Dissociation efficiencies of 36%, 22%, and 14% are achieved for gramicidin S, melittin, and carbonic anhydrase (29 kDa), respectively. Ion neutralization by the surface, which is highly competitive for many singlycharged ions, is minimal, and dissociation products of hypervalent neutral species are not detected. Instead, the spectra are similar to those from collisionally activated and infrared multiphoton dissociation; the fragmentation pathways are relatively independent of the method of energy deposition. For carbonic anhydrase, however, the single event excitation inherent to surface-induced dissociation appears to minimize secondary fragmentation, a critical advantage for tandem mass spectrometry of such large ions. Electrically floating the open cell below ground greatly enhances the collection efficiency.