Electrospray ionization of large multiply charged species proceeds via Dole’s charged residue mechanism Original Research Article

The maximum charge zmax on a variety of electrospray ions of globular proteins retaining their native structure, as well as naturally compact starburst dendrimers is compared to the Rayleigh charge zR (based on a water sphere with the ion mass). For most published data examined, zmax is between 65% and 110% of zR, providing strong support in favor of Dole’s charged residue mechanism, at least for masses from 3.3 kD up to 1.4 MD. Other large but less compact ions from proteins and linear chains of polyethylene glycols (PEGs) have zmax values considerably larger than zR, apparently implying that they also form as charged residues, though from non-spherical drops held together by the polymer backbone.