Charge determination of product ions formed from collision-induced dissociation of multiply protonated molecules via ion/molecule reactions.

The use of ion/molecule reactions involving multiply protonated ions derived from electrospray for the determination of the charges of product ions formed from collision-induced dissociation is described. The experiments are carried out with a quadrupole ion trap capable of multiple stages of mass spectrometry. The approach is illustrated with proton transfer from a product ion from quadruply protonated melittin, and from a product ion from the (M + 20H)20+ ion from horse myoglobin, to 1,6-diaminohexane. The major product ion from quadruply protonated bovine insulin is used to illustrate the use of a clustering reaction with 1,6-diaminohexane. The ion trap is shown to be a particularly useful tool for employing both collisional activation and low-energy ion/molecule reactions in the same experiment to determine product ion charge.