Resonance Enhanced Multiphoton Ionization of Nucleosides by Using Pulsed-laser Desorption in Supersonic Beam Mass Spectrometry

Pulsed-laser desorption is used as a means of volatilizing nucleosides into the gas phase for entrainment into a supersonic jet expansion. These species are then studied in a time-of-flight mass spectrometer by resonance enhanced multiphoton ionization. Using this combination of techniques either relatively soft ionization or controlled fragmentation can be produced. The degree of molecular ion formation is shown to be relatively strong compared to other soft ionization methods such as FAB/MS, SIMS, FD or FI. In addition, the resulting fragmentation produces ions that are characteristic of the structure of the nucleoside. It is further demonstrated that such fragmentation can be used to discriminate between isomeric nucleosides and also between ribose and dwxyribose sugar groups.