PROTON-TRANSFER REACTIONS OF MASS-SELECTED MULTIPLY-CHARGED IONS

A triple-quadrupole spectrometer has been used to study proton-transfe r reactions of multiply charged ions generated by electrospray ionizat ion. Doubly and triply charged ions generated from the peptides Arg-Ly s-Glu-Val-Tyr and Met-Lys-bradykinin, respectively, were found to unde rgo proton-transfer reactions with ammonia molecules contained in the RF-only quadrupole collision-gas cell of the spectrometer. With horse- heart myoglobin in the source, ions having charges of 20+, 19+, 16+ an d 14+ were selected in turn by the first quadrupole and their proton-t ransfer reactions with ammonia investigated. For each ion, numerous pr oduct ions were detected having charges (n - 1) +, (n - 2)+, (n - 3)... where n was the charge on the reacting parent ion. The possibility of using the experimental technique to measure approximately the prot on affinities of multiply charged ions is discussed. Also, a procedure is outlined for identifying the charge states of product ions resulti ng from collision-induced dissociation of multiply charged ions.