A matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) interlaboratory comparison was conducted on mixtures of synthetic polymers having the same repeat unit and closely matching molecular mass distributions but with different end groups. The interlaboratory comparison was designed to see how well the results from a group of experienced laboratories would agree on the mass fraction, and molecular mass distribution, of each polymer in a series of binary mixtures. Polystyrenes of a molecular mass near 9000 u were used. Both polystyrenes were initiated with the same butyl initiator; however, one was terminated with -H (termed PSH) and the other was terminated with -CH2CH2OH (termed PSOH). End group composition of the individual polymers was checked by MALDI-TOF MS and by nuclear magnetic resonance (NMR). Five mixtures were created gravimetrically with mass ratios between 95:5 and 10:90 PSOH:PSH.Mixture compositions where measured by NMR and by Fourier transform infrared spectrometry (FTIR). NMR and FTIR were used to benchmark the performance of these methods in comparison to MALDI-TOF MS. Samples of these mixtures were sent to any institution requesting it. A total of 14 institutions participated. Analysis of variance (ANOVA) was used to examine the influences of the independent parameters (participating laboratory, MALDI matrix, instrument manufacturer, and TOF mass separation mode) on the measured mass fractions and molecular mass distributions for each polymer in each mixture. Two parameters, participating laboratory and instrument manufacturer, were determined to have a statistically significant influence. MALDI matrix and TOF mass separation mode (linear or reflectron) were found not to have a significant influence.
Citation: Analytical Chemistry
Volume: 77 No. 14
Pub Type: Journals
analysis of variance, ANOVA, end group, interlaboratory comparison, MALDI, mass spectrometry, polymer, prepolymer, round robin