Influence of conformation of synthetic polymers on desorption and ionization in MALDI-ToF mass spectrometrie
Analytical Chemistry
Final Report Abstract
Over the last 30 years, matrix-assisted laser desorption/ionization (MALDI) mass spectrometry has become a suitable analytical tool for determining the molar masses, molar mass distributions and end groups of synthetic polymers simultaneously. Thanks to its robustness, simple sample preparation and high sample throughput enabled by a time-of-flight mass spectrometer, polymer analysis has received a significant boost. The advantages of using this mass spectrometric technique have become particularly clear in the synthesis of new polymers. The course of polymerization (e.g. incorporation of the catalyst, chain termination reactions) can be followed in detail and side reactions (e.g. chain transfers) can be made visible. In contrast to gel permeation chromatography (GPC), the measured molar masses are structure-independent and do not require additional corrections (e.g. by determining the intrinsic viscosity). However, these advantages are overshadowed by one serious disadvantage: the lack of quantification. Furthermore, the quality of a MALDI mass spectrum is influenced by numerous parameters. These include factors based on the chemical structure of the macromolecule, as well as the actual sample preparation (e.g. the matrix used). The chemical structure of monomer units and end groups, as well as the conformation of the polymer chain, play a significant role. The extent to which the difference between the linear, branched and cyclic structures of one and the same polymer affects ionization in MALDI mass spectrometry, for example, is still largely unclear. Similar uncertainties exist with regard to the role of the end groups of linear and branched polymers. As a result, the amount of by-products in MAL- DI mass spectrometry can only be roughly estimated. The aim of this project was to improve our understanding of the desorption or ionization of polymers in the mass spectrometer source by systematically investigating the influence of polymer conformation. This would contribute to improve the quantification of the MALDI method. The main focus was on the following topics: The causes of preferential ionization of cycles in mixtures (blends) with linears (desorption and/or ionization). - The influence of the adduct cation on the preferential ionization of a structure in mixtures. - The behavior of star-shaped or other branched structures compared to strictly linear polymers in blends, and the possible influence of end groups. - The influence of molar mass on the preferential ionization of a topological structure. In addition to polylactides (PL), for which initial results have been published, these investigations should also be conducted with other polymer systems (PS, PMMA, PEG, etc.).
Publications
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Solvent‐free sample preparation for matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry of polymer blends. Rapid Communications in Mass Spectrometry, 38(12).
Dalgic, Mete Sungur & Weidner, Steffen
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Quantitative MALDI-TOF Mass Spectrometry of Star-Shaped Polylactides Based on Chromatographic Hyphenation. Journal of the American Society for Mass Spectrometry, 36(3), 613-621.
Falkenhagen, Jana; Dalgic, Mete-Sungur & Weidner, Steffen M.
