ORGANIC-SURFACE ANALYSIS BY 2-LASER ION-TRAP MASS-SPECTROMETRY - 2 - IMPROVED DESORPTION PHOTOIONIZATION CONFIGURATION/

We previously described a two-laser ion trap mass spectrometer for mol ecular surface analysis of organic, biological, and polymeric surfaces (Kornienko, O.; et al. Anal. Chem. 1997, 69, 1536-1542). We have made several improvements in this instrument: a new 118-nm vacuum ultravio let (VUV) photoionization source and an improved desorption/ionization geometry in the ion trap, The improved surface analysis capabilities of this instrument are demonstrated on C-18 alkylsiloxane self-assembl ed monolayers on silicon, polypeptide thin films, mixed polystyrene th in films, and ion beam-modified polystyrene films. The new instrumenta l configuration has submonolayer sensitivity and the capability to per form tandem mass spectrometry on monolayer samples. The advantages of VUV photoionization for surface analysis studies are demonstrated to b e lower fragmentation and relatively nonselective ionization when comp ared with multiphoton ionization with ultraviolet light.