Characterization of polydisperse polymer systems via mass spectrometry.

摘要

This work explored and expanded the applicability of mass spectrometry (MS) as a fast and reliable tool in the study of polydisperse synthetic polymers and polysaccharides. Both electrospray ionization (ESI) and matrix-assisted laser-desorption ionization (MALDI) were employed. Since ESI-MS samples preformed ions in solution, the local pH may have a key role in the ionization and other chemistry of analyte molecules. Therefore, this work attempted to add to the current understanding of the extent to which the ions observed in an ESI-MS spectrum reflect those in the solution. Fluorescence probing the droplet pH as it travels away from the capillary tip revealed that there are clearly significant spray-induced chemical changes within the plume.; Fourier transform methods were applied to derive information from the complex, unresolved signal generated by ESI-MS of strongly ionic synthetic polymer samples. Using experimental and simulated data, this method showed promise for providing information about monomer mass, end group mass, charge distribution, and average sample mass. Applicability to copolymers was established with simulated data, but could not be tested experimentally due to the unavailability of suitable samples. Collision-induced dissociation (CID) was employed as an alternative for assessment of monomer ratios in copolymers. Utilizing CID, conditions were found where monomers or polymers could serve as standards for assessing the monomer ratios in copolymers. Differences between the fragmentation observed when sampling pure monomer versus monomer derived from CID-induced depolymerization led to the use of monomer:fragment ratios for assessing monomer contamination.; In applications to biopolymers, the response of enzymaticaIly-derived hyaluronic acid oligomers to ESI-MS and MALDI-MS revealed that it is of critical importance to consider the propensity of these fragile molecules to undergo in-source fragmentation during the ESI process. For higher molecular weight oligomers it may not be possible to avoid in-source fragmentation, even using the lowest practical CV. In such cases MALDI-MS may be the better method for characterization. For an exopolysaccharide were neither ESI-MS nor MALDI-MS spectra could not be easily interpreted, GC-MS analysis identified a rare combination of five monosaccharides including: rhamnose, galacturonic acid, glucose, N-acetyl-glucosamine, and N-acetyl-fucosamine.