S. J. Gabriel1, R. F. Steinhoff4, M. Pabst4, C. Schwarzinger2, R. Zenobi4, U. Panne1,3, and S. M. Weidner1
- Federal Institute for Materials Research and Testing (BAM), Richard-Willstätter-Strasse 11, 12489, Berlin, Germany
- Johannes Kepler Universität Linz, Altenbergerstrasse 69, 4040, Linz, Austria
- Humboldt-Universität zu Berlin, Department of Chemistry, Brook-Taylor-Str. 2, 12489, Berlin, Germany
- Eidgenössisch Technische Hochschule Zürich, Department of Chemistry and Applied Biosciences, Vladimir Prelog Weg 3, 8093, Zürich, Switzerland
The ionization of polystyrenes in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is typically achieved by the use of silver salts. Since silver salts can cause severe problems, such as cluster formation, fragmentation of polymer chains and end group cleavage, their substitution by alkali salts is highly desirable.
The influence of various cations (Ag+, Cs+ and Rb+) on the MALDI process of polystyrene (PS) mixtures and high mass polystyrenes was examined. The sample preparation was kept as straightforward as possible. Consequently, no recrystallization or other cleaning procedures were applied.
The investigation of a polystyrene mixture showed that higher molecular polystyrenes could be more easily ionized using caesium, rather than rubidium or silver salts. In combination with the use of DCTB as matrix a high-mass polymer analysis could be achieved, which was demonstrated by the detection of a 1.1 MDa PS.
A fast, simple and robust MALDI sample preparation method for the analysis of ultra-high molecular weight polystyrenes based on the use of DCTB and caesium salts has been presented. The suitability of the presented method has been validated by using different mass spectrometers and detectors.
CovalX Technology Used (Click each option to learn more)
To prepare for MALDI mass spectrometry analysis, polymer samples were dissolved in THF at a concentration of 10 mg mL-1. The matrix solutions were also created using THF and a concentration of 100 mg mL-1 was used to ensure that spectra results would be reproducible. To promote the ionization of polystyrene, caesium salts, rubidium chloride, and silver trifluoroacetate were dissolved in THF. An ultrasonic bath was used to ensure a homogeneous mixture and a small volume of water was added to the mixture when the salt was not soluble in THF. The matrix consisted of α-Retinoic acid and 2-[(2E)-3-(4-tert-butylphenyl)-2-
methylprop-2-enylidene]malononitrile (DCTB). Using a ratio of 1:10:100 (v/v/v), salt, sample and matrix solutions were mixed. 0.5 μL of each mixture was placed on a polished MALDI steel target plate and then the droplet was dragged over the target using an Eppendorf pipette tip, creating a thin layer so that the solvent could evaporate. The plate was analyzed using a mass spectrometer that had been modified with a CovalX HM2 detection system. From this analysis, the researchers were able to determine sample preparation parameters including the ratio of matrix to analyte to salt as well as the instrumental parameters.