ETD mass spectra of [M + Pr + H]4+ for (a) EGF(985–996), (b) hirudin(54–65), and (c) casein kinase II substrate. In the figures, the following colors are used to label the ions: non-metallated z-ions = red, non-metallated c-ions = blue, metal adducted z-ions = bright pink, metal adducted c-ions = green, and metal adducted y-ions = brown. Undissociated precursor ion is labeled in purple with a large purple diamond arrow head. Neutral loss products and electron transfer without dissociation (ETnoD) ions are labeled in black.