Quantitation of polymer end groups using MALDI-TOF MS

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been employed to analyze polystyrene mixtures of molecular mass ca. 4000 amu. The component polymers of these mixtures are identical except for their end groups. MALDI-TOF MS with time-lag focusing (delayed extraction) enables sufficient resolution for the quantitation of polymer mixtures by giving structural of individual oligomeric species within the samples studied. The proportions of polystyrene (PS) and monohydroxy-terminated polystyrene (PSOH) were varied and analyzed by MALDI-TOF MS using dithranol and all-trans-retinoic acid matrices. The relative amount of each type of polystyrene contained in the samples have been inferred by computing the peak areas from the mass spectral data. By comparing the ratios obtained by computing the MALDI peak areas to the ratios of the components by weight, the results show that the MALDI data does not accurately represent the ratios of the components in the mixtures.