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Post-Source Decay of Polystyrene Ions in Matrix-Assisted LaserDesorption/Ionization



R J. Goldschmidt, S Wetzel, William R. Blair, Charles M. Guttman


Analyte ions produced in matrix-assisted laser desorption/ionization (MALDI) are of low energy compared to those produced in many other mass spectrometricionization methods, so that there is usually little or no prompt fragmentation ofinitially formed ions. In many cases only intact molecular ions are observed in MALDI mass spectra. This is generally advantageous for analysis of large molecules, and especially synthetic polymers, since extensive fragmentation can lead to exceedingly complex mass spectra. Nevertheless some degree of fragmentation may be desirable, since it can provide important structural information. For polymer samples, for example, fragmentation could be useful in end group analysis and copolymer analysis. Methods have been developedthat can be used in conjunction with MALDI and that allow a degree of control over fragmentation. One such method is post-source decay (PSD). Althoughprompt fragmentation of analyte ions is rare in MALDI, some portion of parentions will have sufficient energy to undergo metastable decay, and fragment ions so produced can be observed under the proper operating conditions. Experimental variables such as laser fluence, accelerating voltage, and background gas pressure allow some control over the degree of decay. PSD has had valuable applications in analysis of biomolecules, e.g. in peptide sequencing, but so far has had only limited application to synthetic polymeranalysis. We have observed several unexpected series of peaks in the MALDI mass spectra of a polystyrene sample. PSD analysis has revealed that these are due to fragmentation of ions of the expected main series. The observed fragmentation depends upon both the choice of matrix and the choice of metal cation used for ionization of the polystyrene. These findings suggest an influence of matrix and cation on either the total energy of parent ions or on the fragmentation pathway. The influence of other experimental parameters onthe polystyrene fragmentation will also be presented, and the analytical and mechanistic implications will be discussed.implications will be discussed.
Post-Source Decay of Polystyrene Ions in Matrix-Assisted LaserDesorption/Ionization


MALDI, polymers, polystyrene ions, post-source decay, PSD, PSD analysis


Goldschmidt, R. , Wetzel, S. , Blair, W. and Guttman, C. (1999), Post-Source Decay of Polystyrene Ions in Matrix-Assisted LaserDesorption/Ionization, Post-Source Decay of Polystyrene Ions in Matrix-Assisted LaserDesorption/Ionization, [online], (Accessed June 15, 2024)


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Created January 1, 1999, Updated February 17, 2017