Product ion charge state determination via ion/ion proton transfer reactions

Proton transfer from protonated pyridine to product anions derived from quadrupole ion trap collisional activation of the triply charged anion of the oligonucleotide 5'-d(AAAA)-3' and the 6(-) charge state of oxidized bovine insulin A-chain is shown to be a rapid and effective way to determine product ion charge states. The reactions are carried out in a quadrupole ion trap as part of a procedure involving three stages of mass analysis. It is demonstrated that the reactions can be driven at rates sufficiently high to convert 30-80% of the initial product anion population to second generation products in 50-200 ms. The use of ion/ion reactions enjoys significant advantages over the use of ion/molecule proton transfer chemistry. For example, ion/ion reactions are more universal than ion/molecule reactions due to their greater exothermicity, and ion/ion reactions allow for precise control over the timing of introduction and ejection of each reactant. Despite the high exothermicity of the reactions, no significant fragmentation of product ions derived from high-mass multiply charged anions is observed.