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Two‐photon ionization thresholds of matrix‐assisted laser desorption/ionization matrix clusters
Author(s) -
Lin Qiong,
Knochenmuss Richard
Publication year - 2001
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.380
Subject(s) - chemistry , atmospheric pressure laser ionization , ionization , matrix assisted laser desorption electrospray ionization , photoionization , thermal ionization , soft laser desorption , molar ionization energies of the elements , atomic physics , chemical ionization , ambient ionization , mass spectrometry , electron ionization , ion source , ionization energy , matrix assisted laser desorption/ionization , desorption , ion , physics , organic chemistry , adsorption , chromatography
Direct two‐photon ionization of the matrix has been considered a likely primary ionization mechanism in matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry. This mechanism requires that the vertical ionization threshold of matrix materials be below twice the laser photon energy. Because dimers and larger aggregates may be numerous in the early stages of the MALDI plume expansion, their ionization thresholds are important as well. We have used two‐color two‐photon ionization to determine the ionization thresholds of jet cooled clusters of an important matrix, 2,5‐dihydroxy benzoic acid (DHB), and mixed clusters with the thermal decomposition product of DHB, hydroquinone. The thresholds of the clusters were reduced by only a few tenths of an eV compared to the monomers, to an apparent limit of 7.82 eV for pure DHB clusters. None of the investigated clusters can be directly ionized by two nitrogen laser photons (7.36 eV), and the ionization efficiency at the thresholds is low. Copyright © 2001 John Wiley & Sons, Ltd.