 Fragmentation caused by ETD allows more complete protein sequence information to be obtained from ETD spectra than from CID tandem mass spectrometry.Because many peptide backbone c- and z- type ions are detected, almost complete sequence coverage of many peptides can be discerned from ETD fragmentation spectra.Sequences of 15-40 amino acids at both the N-terminus and the C-terminus of the protein can be read using mass-to-charge values for the singly and doubly charged ions.