Structural analysis of polyoxyalkyleneamines by matrix-assisted laser desorption/ionization on an external ion source FT-ICR-MS and NMR

Matrix-assisted laser desorption/ionization (MALDI) and Fourier-transform ion cyclotron mass spectrometry (FT-ICR-MS) are combined for the characterization of polyoxyalkyleneamines. ¹H and ¹³C NMR data are used to confirm and quantify structural assignments. Characterization of the molecular weight distribution, chemical composition distribution, and end group distribution of amine-terminated (co-)polymers of ethylene oxide and propylene oxide is rather complex because the convolution of these three entities yields an ensemble of structurally related molecules which is hard to characterize by conventional analytical techniques. In this study MALDI FT-ICR-MS is used to resolve intact, Na⁺ cationized, oligomer ions in the mass range from m/z 500 to 3500. This revealed the presence of various compositional distributions in the polyoxyalkyleneamines. The individual compound masses in the molecular weight distributions were measured with a mass accuracy of <20 millimass units, allowing end group and repeat unit determination with an accuracy of better than 50 millimass units. NMR is used to measure the average end group distribution to provide insight in conformational differences. In this respect, FT-ICR-MS data and NMR data are complementary. The combined results yield detailed information about chemical composition distributions of polyoxyalkyleneamines that hitherto it was not possible to obtain with either technique separately.