Unusual Fragmentation Patterns of Lignin Model Compounds with alpha-O-4 Linkages in (+) ESI/Tandem Mass Spectrometry
Lignocellulosic biomass represents a promising renewable energy resource. Conversion of lignin into useful chemicals is of great interest. Tandem mass spectrometry (MSn) is a powerful technique for the direct analysis of lignin mixtures. Due to the complex linkages present in natural lignin, the study of ionization and CAD of lignin model compounds would help us unravel the structures of lignin mixtures. In this present study, the ionization method and CAD spectra of two synthesized lignin model compounds with alpha-O-4 and beta-O-4 linkages were studied using ESI/tandem mass spectrometry. Negative ion mode is the most common ionization method for lignin compounds with free phenol group. beta-O-4 lignin compound showed most abundant [M-H]- ion. However, the alpha-O-4 lignin model compound did not show [M-H]- ion in the negative mode ESI. The possible degradation mechanism was discussed. In the positive mode ESI, both alpha-O-4 and beta-O-4 compounds showed abundant [M+Na]+ ions or [M+Li]+ ions if doped with lithium chloride. The MS2 spectra of lithiated alpha-O-4 and beta-O-4 compounds were compared, which showed significant difference. The alpha-O-4 compound showed monomer loss, whereas beta-O-4 compound only showed small neutral molecule losses. This study showed that positive ion mode with sodium or lithium attachment was an effective way to ionize lignin compounds with alpha-O-4 linkages, which could not be detected by traditional negative ion mode. The CAD of lithiated ion with alpha-O-4 linkage was useful for sequencing purpose. Further experiments on CAD of other model compounds with alpha-O-4 linkages are underway.
Researchers should cite this work as follows:
- Sheng H, Tang W, Kenttämaa HI (2013). Unusual Fragmentation Patterns of Lignin Model Compounds with β-O-4 Linkages in (+) ESI/Tandem Mass Spectrometry. 61st ASMS Conference on Mass Spectrometry and Allied Topics. Minneapolis, MN. June 9-13.