Abstract

European Journal of Mass Spectrometry
Volume 15 Issue 2, Pages 305–314 (2009)
doi: 10.1255/ejms.971

Dependence of the ejection velocities of laser-ablated ions on the laser wavelength and fluence

Chau-Wen Chou,^a Randall W. Nelson^b and Peter Williams^c
aProteomics Core Facility and Department of Physiology, Louisiana State University Health Sciences Center, New Orleans, LA 70112, USA
^bBiodesign Institute, Arizona State University, Tempe, AZ 85287-1604, USA
^cDepartment of Chemistry & Biochemistry, Arizona State University, Tempe, AZ 85287-1604, USA

Drift measurements of initial ejection velocities of matrix-assisted laser desorption/ionization matrix compounds have been made as a function of ablating laser wavelength and laser fluence. For pulsed laser irradiation just above the matrix ion appearance threshold, initial ejection velocities of protonated molecular ions of an anthranilic acid target increase from ~ 1350 m/s to ~ 1640 m/s (kinetic energies of 1.3 eV and 1.9 eV, respectively) when the ablation laser wavelength is changed from 355 nm to 266 nm. Increasing the laser fluence per pulse by up to a factor of 10 above threshold results in the appearance of a slower component of the ejected ion flux. The results are interpreted by a photomechanical ejection model in which a photoexcited surface molecule instantaneously becomes larger and recoils away from the surface.

Keywords: MALDI, initial velocities, laser wavelength dependence, laser fluence dependence, ion ejection mechanism

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