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Evidence for laser-induced redox reactions between added trifluoroacetate salts and substrate material during polystyrene/DCTB MALDI

  • Polymers, such as polystyrene, have been successfully analyzed with matrix-assisted laser desorption/ionization (MALDI) through the addition of e.g. copper or silver salts. This method is often used to establish the polydispersity index of polymer blends. However, the mechanism of cation addition and the possible interactions between the added salts and the chosen target material are still points of interest. Therefore, the addition of several trifluoroacetate salts to a mixture of polystyrene and matrix on a range of different target plate materials was systematically investigated, revealing several new interesting aspects of MALDI. Polystyrene (Mw 1,920 Da) was mixed with a range of trifluoroacetate salts (Li, Na, K, Cs, Ba, Cr, Pd, Cu, Ag, Zn, Al and In, as well as trifluoroacetic acid) and analyzed with MALDI using 2 -[2E-3-4-tert-butylphenyl)- 2- methylprop-2-enylidene]ma lononitrile DCTB) as matrix on different target plate materials (chrome, copper, silver, gold,Polymers, such as polystyrene, have been successfully analyzed with matrix-assisted laser desorption/ionization (MALDI) through the addition of e.g. copper or silver salts. This method is often used to establish the polydispersity index of polymer blends. However, the mechanism of cation addition and the possible interactions between the added salts and the chosen target material are still points of interest. Therefore, the addition of several trifluoroacetate salts to a mixture of polystyrene and matrix on a range of different target plate materials was systematically investigated, revealing several new interesting aspects of MALDI. Polystyrene (Mw 1,920 Da) was mixed with a range of trifluoroacetate salts (Li, Na, K, Cs, Ba, Cr, Pd, Cu, Ag, Zn, Al and In, as well as trifluoroacetic acid) and analyzed with MALDI using 2 -[2E-3-4-tert-butylphenyl)- 2- methylprop-2-enylidene]ma lononitrile DCTB) as matrix on different target plate materials (chrome, copper, silver, gold, Ti90/Al6/V4, Inconel® 625, Zinc and stain less steel) to evaluate the occurrence of redox-reactions. Polystyrene/salt/matrix solutions were deposited through pneumatic-assisted spraying on microscope slide -shaped target plate insets of varying material, which, secured with copper tape, fitted a milled out structure from the original target plate. Spectra, obtained on a Bruker Autoflex I MALDI-Time -of-Flight mass spectrometer, were processed with MATLAB to obtain polystyrene-and matrix -adduct ion signal intensities for direct comparison between chosen conditions. The resulting spectra shed light on the MALDI adduct formation process and the cation-polystyrene interactions. It was found that the following cation -polystyrene adducts were formed on stainless steel: Al, Li, Na, Cu and Ag, where the yield was found to depend on the sample layer thickness and possibly the cation’s ability to form a complex with either one or two of polystyrene’s phenyl rings, based on the ligand-field and the valence bond theory. With the exception of Al, these salts also formed adducts and in case of Cu and Ag also sandwich adducts with DCTB. Some alkali salts (e.g. potassium) formed clusters rather than interacting with polystyrene or DCTB, which can be explained with the HSAB theory. Application of TFA salts on a copper surface led to copper cation formation, resulting in DCTB and polystyrene copper-adduct formation. The same effect occurred for silver substrate. In the absence of copper or silver salts, it is therefore still possible to form their respective adducts by choosing the proper alternative salt (e.g. Li, Cs, Ba, Cr) in combination with either a silver or a copper substrate surface. Incubation tests with copper beads in various salt solutions, before matrix and polystyrene addition, support that copper ions are not generated during the deposition process before the MALDI experiment is carried out, except when trifluoroacetic acid, indium and aluminium trifluoroacetate are used. For all other salts used on a copper plate, it can therefore be concluded that these copper cation forming redox-reactions are enabled by the input of laser photon energy. Furthermore, it was discovered that copper beads can successfully sequester polystyrene from the sample mixture, indicating the strong bonding of polystyrene to the copper surface. These findings support that the redox-reactions occur (almost) instantaneously with laser pulse impact at the sample-coated substrate surface.zeige mehrzeige weniger

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Metadaten
Autor*innen:G. P. Zeegers
Koautor*innen:R. Steinhoff, Steffen Weidner, R. Zenobi
Dokumenttyp:Posterpräsentation
Veröffentlichungsform:Präsentation
Sprache:Englisch
Jahr der Erstveröffentlichung:2016
DDC-Klassifikation:Naturwissenschaften und Mathematik / Chemie / Analytische Chemie
Freie Schlagwörter:Cations; MALDI; Redox-reactions; Substrate
Veranstaltung:Jahrestagung der DGMS 2016
Veranstaltungsort:Hamburg, Germany
Beginndatum der Veranstaltung:28.02.2016
Enddatum der Veranstaltung:02.03.2016
Verfügbarkeit des Dokuments:Datei im Netzwerk der BAM verfügbar ("Closed Access")
Datum der Freischaltung:22.07.2016
Referierte Publikation:Nein
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