Gas-Phase cationization and protonation of neutrals generated by matrix-assisted laser desorption.
The ionization mechanisms involved in matrix-assisted ultraviolet laser desorption/ionization (MALDI) were studied with a time-of-flight mass spectrometer. When protonated or cationized quasimolecular ions generated by MALDI are not extracted promptly, their abundance is a function of the delay time between laser irradiation and ion extraction, maximizing at an optimum delay time (DTM) of a few hundred nanoseconds. The ion abundance at DTM exceeds that of prompt extraction by a factor of 2 or more. Increasing the cation density near the sample surface reduces the DTM, whereas increasing the desorption laser irradiance has the opposite effect. The enhancement suggests extensive gas-phase ion-molecule reactions after irradiation by the desorption laser has ceased.
Institute of Medical Physics and Biophysics, University of Muenster, Muenster, Germany.
B H
BH
Wang
K
K
Dreisewerd
U
U
Bahr
M
M
Karas
F
F
Hillenkamp