Mechanistic Studies on Cationization in MALDI-MS Employing a Split Sample Plate Set-up
In the analysis of polymers by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), a commonly observed ionization pathway is cation-adduct formation, as polymers often lack easily ionizable (basic/acidic) functional groups. The mechanism of this process has been hypothesized to involve gas-phase cation attachment. In previous experiments, a split sample plate set-up has been introduced, enabling separate deposition of the components on individual MALDI plates. The plates are divided by a small gap of a few micrometers, allowing simultaneous laser irradiation from both plates, while precluding the possibility of any other interactions prior to ablation. Here, we extend on these studies by using different polymer-salt combinations to test the generalizability of a gas-phase ionization process. Clear evidence for in-plume ionization is presented for the model polymers poly (methyl methacrylate) and polystyrene. Furthermore, the contribution of in-plume processes to the overall ion formation by cationization is gauged, providing a first estimate for the importance of this pathway.
KeywordsMALDI mechanism Polymer cationization
We would like to express our deep gratitude to the Fonds der chemischen Industrie for financially supporting our research (Kekulé Fellowship to Jonas B. Metternich). Furthermore, the authors would like to thank Dr. Adrien Marchand and Mr. Prince Tiwari for helpful discussion. They also thank Mr. Cristian Marro, Mr. Christoph Bärtschi, and Mr. Heinz Benz for their outstanding technical support.
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