Paper spray and Kendrick mass defect analysis of block and random ethylene oxide/propylene oxide copolymers

Paper spray ionization coupled with a high-resolution time-of-flight mass spectrometer was applied to the analysis of 13 block and 2 random ethylene oxide/propylene oxide (EO/PO) copolymers as well as to standard samples of poly(ethylene oxide) and poly(propylene oxide) homopolymers. Paper spray mass spectra could be obtained rapidly and, unlike electrospray ionization, were not subject to contamination and sample carryover. For comparison, polyether samples were also measured on a MALDI/TOF system with ultrahigh mass resolving power. MALDI/high-resolution time-of-flight mass spectrometry exhibited single-charge ions characteristic of the polymer distributions whereas the paper spray mass spectra exhibited charge states ranging from one to six charges. Kendrick mass defect plots of the multiple-charge ions in the paper spray mass spectra exhibit isotopic splitting of the Kendrick mass defects, facilitating visualization of the number of charges in each series. The slope of the KMD plots can be used to estimate the percentage of ethylene oxide in the copolymers. In-source fragmentation permitted the distinction between block and random copolymers.