ION ION PROTON-TRANSFER KINETICS - IMPLICATIONS FOR ANALYSIS OF IONS DERIVED FROM ELECTROSPRAY OF PROTEIN MIXTURES/

Protein ions of different mass and charge but similar mass-to-charge r atios are shown to undergo significantly different rates of differenti al neutralization, defined as the rate of change of charge with time, upon initiation of reactions with oppositely charged ions in the quadr upole ion trap, Overlapping charge state distributions arising from mi xtures of ions of dissimilar charge are separated on the mass-to-charg e scale at short reactions times. It is also demonstrated that the tim e frame for near total neutralization, defined as charge reduction to the 1+ ion, is relatively insensitive to initial charge state, It is s hown, for example, that the (M + 11H)(11+)-(M + 22H)(22+)l ions derive d from horse skeletal muscle apomyoglobin yield the (M + H)(+) ion as the major ion/ion reaction product over the same reaction period that largely converts doubly protonated bradykinin to the singly protonated species, Less than 25% of the bradykinin ions are expected to be tota lly neutralized when roughly 7% of the myoglobin ions are expected to be totally neutralized, The phenomenon of significantly different init ial differential neutralization rates for ions of dissimilar charge, a nd the relative insensitivity to ion charge for total neutralization, can be used to advantage in strategies for protein ion mixture analysi s.