The effects of matrix pH and cation availability on the matrix-assisted laser desorption/ionization mass spectrometry of poly(methyl methacrylate)

The matrix-assisted laser desorption/ionization (MALDI) of poly(methyl methacrylate) has been studied using time-of-flight (TOF) mass spectrometry. The effect of pH was investigated through titration of the matrix. The presence of doped alkali metal cations produced shifts in the polymer molecular weight distribution of as much as 20%. Results indicate that careful control of experimental conditions is needed to obtain reproducible mass spectra of synthetic polymers, and to critically evaluate the accuracy of polymer-size distributions measured by MALDI-TOF mass spectrometry, as the role of the matrix in desorption and ionization processes is not yet fully understood.