Electron capture induced dissociation of peptide dications

Dissociation induced by electron capture in high energy collisions between doubly protonated peptide ions and Na atoms has been investigated. The ions were produced in an electrospray ion source and accelerated to an energy of 100 keV before they were excited in collisions with a Na target gas. Electron capture was found to be the dominant reaction channel but also fragment peaks corresponding to cleavage of the backbone N-C_α bonds the so called c and z ions are prominent in the recorded mass spectra. Electron capture dissociation (ECD) where free electrons are captured by ions stored in a FTICR cell has previously been shown to result in sequence information. Similar measurements have been performed in both a Ne and a Mg target and by comparing the mass spectra for the three target gases it is concluded that electron capture by protonated peptides in high energy collisions leads to non-ergodic fragmentation of the peptide ion.