GAS-PHASE HYDROGEN DEUTERIUM EXCHANGE-REACTIONS OF PEPTIDE IONS IN A QUADRUPOLE ION-TRAP MASS-SPECTROMETER/

Hydrogen/deuterium exchange reactions of protonated and sodium cationi zed peptide molecules have been studied in the gas phase with a MALDI/ quadrupole ion trap mass spectrometer, Unit-mass selected precursor io ns were allowed to react with deuterated ammonia introduced into the t rap cell by a pulsed valve, The reactant gas pressure, reaction time, and degree of the internal excitation of reactant ions were varied to explore the kinetics of the gas phase isotope exchange, Protonated pep tide molecules exhibited a high degree of reactivity, some showing com plete exchange of all labile hydrogen atoms, On the contrary, peptide molecules cationized with sodium exhibited only very limited reactivit y, indicating a vast difference between the gas phase structures of th e two ions. (C) 1997 Wiley-Liss, Inc.