PNNL

Abstract

We describe the results of experiments designed to test several of the most widely discussed mechanistic models for matrix-assisted laser desorption and ionization. By comparing ion mass spectra from the same matrix-analyte systems across various wavelengths from ultraviolet to mid-infrared and pulse durations from nanosecond to femtosecond, we have evaluated the plausibility of such ion-formation mechanisms as multiphoton ionization, excited state ionization, and photothermal ionization. We conclude that some of these models are not plausible for the matrix-analyte systems we studied. However, the fundamental principles of the laser-materials interaction also suggest that inspection of the mass spectra alone can only serve to exclude certain mechanisms, not to establish which of several competing mechanisms is actually occurring. This is particularly true with respect to variations in pulse duration and wavelength.