Solvent-free sample preparation for matrix-assisted laser desorption/ionization time-of-flight (MALDI TOF) mass spectrometry of polymer blends

Rationale Solvent-free sample preparation offers some advantages over solvent-based techniques, such as improved accuracy, reproducibility, and sensitivity of MALDI analysis. However, little or no information is available on the application of solvent-free techniques for the MALDI analysis of polymer blends. Methods: Solvent-free sample preparation by ball milling was applied with varying sample-to-matrix ratios for MALDI-TOF MS analysis of various polymers, including polystyrenes (PS), polymethyl methacrylates (PMMA), and polyethylene glycols (PEG). The peak intensity ratios were compared with those obtained after using the conventional dried droplet sample preparation method. In addition, solvent-assisted milling was also applied to improve sample homogeneities. Results: Depending on the sample preparation method used, different peak intensity ratios were found, showing varying degrees of suppression of the signal intensities of higher mass polymers. Ball milling for up to 30 minutes was required to achieve constant intensity ratios indicating homogenous mixtures. The use of wet-assisted grinding to improve the homogeneity of the blend was found to be disadvantageous as it caused partial degradation and mass-dependent segregation of the polymers in the vials. Conclusions: The results clearly show that solvent-free sample preparation must be carefully considered when applied to synthetic polymer blends, as it may cause additional problems with regard to homogeneity and stability of the blends.