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Molar mass distributions of polymers from size exclusion chromatography and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry: Methods for comparison



Equations are presented for calculating molar mass averages and molar mass distributions from matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) data and from size exclusion chromatography (SEC) data. The utility of polydispersity is examined as an indicator of the expectation of MALDI-TOF MS mass discrimination effects. Cumulative distributions are found to be rich in information for comparing the two techniques and are easily obtained from both SEC and MALDI-TOF MS data. Analyses of a series of narrow molar mass distribution poly(methyl methacrylate) (PMMA) standards and one polydisperse sample have been performed with both methods. MALDI-TOF MS did not detect dimer and trimer in the PMMA samples, and it often indicated lower amounts of high-molar-mass polymers than did SEC. The results showed that the distribution breadth, as evidenced by the standard deviation of the distribution (calculated from the polydispersity and number-average molar mass), correlated well with the molar mass range observed in the MALDI-TOF MS spectra, whereas the polydispersity alone did not. Ratioing the extremes in the molar mass concentrations measured with the SEC differential refractometer, which were necessary to adequately define molar mass distributions, showed that detector dynamic range values as high as approximately 370,000 were required for the polydisperse samples. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 627–639, 2005