Formation of atomic hydrogen in matrix-assisted laser desorption ionization



Despite the widespread use of matrix-assisted laser desorption ionization, the processes involved in ion formation have yet to be satisfactorily explained. Several protonation processes have been suggested as possible methods for the creation of the analyte ions. In this work the existence of neutral hydrogen atoms in the ablation plume is reported. These are selectively ionized from the ground state through a (2+1) multiphoton resonant excitation scheme. The mass spectra at different delay times between the ablation and the post-ablation-ionization lasers have demonstrated the existence of hydrogen atoms with high velocities in the ablated plume.