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University, is based on the partial recombination of polypeptide cations with thermal electrons and is usually performed in the cell of an FT mass spectrometer. Positive ions become radicals and recombination energy is released. ECD is believed to follow a nonergodic mechanism, that is, "fragmentation occurs locally where the energy is released and before the energy has a chance to randomize over the whole molecule," explains Zubarev. Bonds that are closest to the energy release are broken, whereas those further away remain intact.
Using a homemade nanoelectrospray ionization source, Zubarev and his colleagues generated multiply protonated polypeptide molecules from five different glycopeptides (3 kDa range) and irradiated them with low energy electrons (
