Investigation of metal attachment to polystyrenes in matrix-assisted laser desorption ionization

Cationization is essential to the matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometric analysis of a variety of synthetic polymers. This work studied polystyrene cationization in MALDI using the salts of eight different metals. It was found that only the salts of silver, copper, and palladium produced good metal—polystyrene cation signals. More interestingly, it was observed that MALDI could also produce metal-rich cluster cations and that the presence of polystyrenes tended to suppress formation of the metal-rich cluster cations. Based on these results and others, we propose that polystyrene cationization may proceed through gas-phase metal attachment reactions under the conditions used. With this argument, we were able to better explain a reported experimental observation that showed a strong cation concentration effect on measured molecular weight distributions of polystyrenes.