Analysis of the substituent distribution in O-methyl celluloses by MALDI-FT-ICR-MS

Methyl celluloses are heterogeneous mixtures of cellulose O-methyl ethers with a variable degree of substitution at different sites of the constituing monomers. Both the degree of substitution and the substituent distribution along the backbone determine the thermogelation temperature of the compounds. The O-Me substituent distribution along the cellulose backbone has been investigated by GC of their monomers and by FAB-MS with a sector instruments of perdeuteromethylated oligomers prepared by partial hydrolysis of the samples. The distribution of the methyl groups in the perdeuteromethyl-O-methyl-cellotriose is derived from the peak intensities of the sodiated molecules in the FAB-MS spectrum. FAB-MS analysis of larger oligomers is hampered, due to the upper limit of mass resolution of the sector instrument, by the interference of fragment ions originating from sodiated oligomers with a higher degree of polymerization. Another complication in this context is the presence of FAB matrix cluster and fragment ions as a chemical background in the mass spectra.