NIST-Sponsored Interlaboratory Comparison of Polystyrene Molecular Mass Distribution Obtained by Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry:  Statistical Analysis

Abstract

The method of preparation and methods of analysis of a narrow distribution polystyrene of ∼7 ku used in an interlaboratory comparison of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) of synthetic polymers is described. Size exclusion chromatography was used to measure the polystyrene sample variability. Fourier transform infrared spectroscopy and MALDI-TOF-MS were used to analyze end groups on the polymer. The polystyrene was analyzed by MALDI-TOF-MS and classical methods of polymer characterization. The number (M n) and mass (M w) average of the molecular mass distribution (MMD) determined by the classical methods (light scattering and NMR) were compared with those obtained by MALDI-TOF-MS. Agreement between classical methods to obtain the moments of the MMD and the MALDI is found to be good overall. However, all the experimental values obtained by MALDI fell below the classical values. A discussion of why these values are lower is included. We discuss the statistical analysis of the data from the interlaboratory comparison conducted by NIST, which includes data from 23 different laboratories. Analysis of variance is used to examine the influences of the independent parameters (laboratory, matrix, instrument manufacturer, instrument mode) on the data. The parameters, laboratory and instrument manufacturer, were determined to have an influence on the MMD, where matrix and instrument mode were found not to have a significant influence.

Characterization and relative ionization efficiencies of end-functionalized polystyrenes by matrix-assisted laser desorption/ionization mass spectrometry

“…Generally, the values for samples analyzed with AgTFA have the highest molecular weights among the groups, even given the mass contribution of the silver cation, followed by the quaternary samples, with the tertiary amine without AgTFA giving the lowest values. However, in light of a recent interlaboratory comparison in which the standard deviation observed for the number average weight of hydrogen terminated polystyrene in was 2% [17], the values in Table 5 are not significantly different. The end group functionality appears to have little difference on average molecular weight determination in this range.…”

“…Secondary series and adduct formation have been probed using post-source decay in time-of-flight MS [10], and fragmentation of PS oligomers, along with end group identification, has been examined via collision induced dissociation in tandem MS experiments [11][12][13]. Finally, biases in average molecular weights of PS have been studied with regard to increasing discrete oligomer size [14], and in comparison with classical measurements [15][16][17].…”

Overview of MS and MALDI MS for Polymer Analysis

“…In MALDI MS, molecular mass and molecular mass distribution information can be obtained for polymers of narrow polydispersity with high precision and speed. The accuracy, although diffi cult to determine due to the lack of well -characterized standards, appears to be good as well [67,68] . The MALDI analysis of polymers does not require the use of polymer standards for mass calibration.…”

Citric Acid Capped Iron Oxide Nanoparticles as an Effective MALDI Matrix for Polymers

“…MALDI signal can have limited reproducibility with variances due to laser fluence, voltages, matrix, and sample preparation. Thus, the measured mass distribution by MALDI does not necessarily reflect the true gravimetric (mass) concentration of each oligomer [12,13], which is particularly problematic for broad molecular mass distribution (MMD) polymers [14]. Nonetheless, a few studies have examined narrow MMD polymer MALDI quantitation with a closely related polymer as an internal standard [15][16][17][18].…”