Certification of a Polystyrene Synthetic Polymer, SRM 2888

The certification of a polystyrene standard reference material, SRM 2888, is described. The Mw of SRM 2888 was determined by light scattering to be 7.19x10 g/mol with a sample standard deviation of 0.14 x10 g/mol. A combined expanded uncertainty for this light scattering Mw determination, including systematic and random uncertainties, was estimated to be 0.57 x10 g/mol. Mn was determined by nuclear magnetic resonance (NMR) analysis of the end groups and found to be 6.96 x10 g/mol with an estimated expanded uncertainty of 0.40 x10 g/mol. Fourier transform infrared spectroscopy (FTIR) and matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS) were used to analyze end groups on the polymer. The polystyrene was analyzed by MALDI-TOF-MS for the number (Mn) and mass (Mw) averages of the molecular mass distribution (MMD), as well as the MMD. The bottle-tobottle variation of the SRM was examined by size exclusion chromatography (SEC) and found to be negligible. This polymer was also used in an interlaboratory comparison of the analysis of polystyrene by MALDI-TOF-MS. The interlaboratory comparison and its results are described. Agreement between the MMD moments obtained by light scattering and NMR and the moments of the MMD obtained by MALDI-MS in the interlaboratory comparison is found to be good overall. However, all the experimental values obtained by MALDI-MS were lower than the classical values.