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Fragmentation behavior of poly(methyl methacrylate) during matrix‐assisted laser desorption/ionization
Author(s) -
Iura Tomomi,
Ohtani Hajime
Publication year - 2014
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.7087
Subject(s) - chemistry , fragmentation (computing) , mass spectrometry , desorption , reagent , polymer , molecule , chain transfer , methyl methacrylate , ionization , polymerization , matrix assisted laser desorption/ionization , matrix assisted laser desorption electrospray ionization , analytical chemistry (journal) , dissociation (chemistry) , ion , electron ionization , radical polymerization , chromatography , organic chemistry , adsorption , computer science , operating system
RATIONALE Matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) has been widely utilized for the structural characterization of various synthetic polymers. However, polymer sample molecules can occasionally decompose even in the MALDI process depending on the measurement conditions. In this work, the fragmentation behavior of radically polymerized poly(methyl methacrylate) (PMMA) during laser irradiation in MALDI was investigated in detail. METHODS Two types of PMMA samples with oligomeric molar mass were examined: Sample A was synthesized with an excess content of a chain transfer reagent to form simple molecules with less labile structures. Sample B was polymerized with a greater amount of a peroxide initiator without any chain transfer reagent, which resulted in the formation of various terminal and chain structures including relatively labile ones. The original components and fragment ions for the PMMA samples were precisely assigned using a high‐resolution MALDI spiral time‐of‐flight MS system. Electrospray ionization MS measurements were also performed for comparison. RESULTS The PMMA chains underwent fragmentation during the MALDI process with high laser intensity even for the relatively stable sample A. The fragmentation reactions proceeded mainly through 1,5‐hydrogen rearrangements via a six‐membered intermediate structure. Furthermore, PMMA molecules formed via recombination termination in sample B selectively decomposed during the MALDI‐MS measurements even with low laser intensity. CONCLUSIONS It was observed that the fragmentation reactions in the PMMA chains in MALDI with high laser power were generally the same as those in the post‐source decay or collision‐induced dissociation in MALDI‐MS/MS measurements. Even with low laser intensity, less stable structures in the PMMA chain, especially head‐to‐head linkages, were readily decomposed during the MALDI process. Possible fragmentation, therefore, should be considered in the structural characterization of synthetic polymer samples by MALDI‐MS. Copyright © 2014 John Wiley & Sons, Ltd.