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Formation and reactions of cluster ions from aromatic carboxylic acids together with amino acids
Author(s) -
Meffert Anja,
Grotemeyer Jürgen
Publication year - 2001
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1560/tq7j-ja0n-djpe-c22a
Subject(s) - chemistry , ionization , mass spectrum , mass spectrometry , protonation , photochemistry , chemical ionization , matrix assisted laser desorption/ionization , ion , atmospheric pressure laser ionization , photoionization , analytical chemistry (journal) , desorption , organic chemistry , chromatography , adsorption
The cluster formation of several aromatic carboxylic acids, ferulic acid, vanillic acid, sinapinic acid, and 3,4‐dihydroxybenzoic acid was investigated by means of laser desorption into a supersonic beam followed by multiphoton ionization‐time‐of‐flight mass spectrometry. The formation of not only homogeneous clusters, but also of heterogeneous clusters with some small amino acids was studied. The different neutral clusters formed in the supersonic expansion were ionized by a multiphoton process employing either nano‐ or femtosecond laser pulses. Strong differences in the detection of cluster ions due to the laser pulse length employed for multiphoton ionization were observed. Only femtosecond activation led to mass spectra with intense signals of the cluster ions. In addition, in the case of femtosecond ionization, protonated amino acids were detected in the mass spectra. As direct ionization of the free amino acids is not possible under the chosen ionization conditions because they lack an adequate chromophore, these protonated amino acids are assumed to be formed via an intracluster proton transfer in the heterogeneous dimer and subsequent decay of the ionized cluster (dissociative proton transfer). Such well‐known processes for heterogeneous clusters consisting of a substituted aromatic molecule and small polar solvent molecules may be involved in the matrixassisted laser desorption ionization (MALDI) process.