Characterization of synthetic polymers by MALDI-TOF/MS: investigation into new methods of sample target preparation and consequence on mass spectrum finger print

Characterization of synthetic polymers by Matrix assisted laser desorption (MALDI) is limited by the solubility of different oligomers in a suitable solvent, and the fingerprint of the mass spectrum is affected by the properties of solvents employed (eg., pH, secondary solvents, evaporation) during sample target preparation. If solvents are not used during sample target preparation, then solvent properties should not play an important role in determining the quality of the MALDI mass spectrum. We report here two solventless approaches for sample target preparation. It was observed that Poly(ethylene glycol) 6000 (PEG) showed the same molecular mass distribution in different modes of sample target preparation. Fluorinated polymer used in these studies was affected by sample target preparation protocol and by target surface. Pyrolysis of PEG oligomers was observed in all the methods of sample target preparation. The desorbed high mass neutral oligomers fragment to give small oligomers which are then cationized by the desolvation of the cationized matrix clusters. Moreover, the origin of the matrix clusters (i.e., formed in the condensed phase or in the gas phase) determines the relative intensities of PEG oligomers cationized by sodium or potassium.