Molecular-Level Characterization of Native Lignin Oligomers From Flow-Through Solvolysis of Biomass by High-Performance Liquid Chromatography-Tandem Mass Spectrometry.

RATIONALE: Comprehensive characterization of lignin-derived oligomers remains a major analytical challenge because of their high structural diversity and the lack of methods capable of resolving native interunit linkages in complex biomass-derived mixtures. Molecular-level understanding of these oligomers is essential for elucidating lignin depolymerization mechanisms and guiding biomass valorization strategies.

METHODS

Lignin oligomers generated from methanol-based flow-through solvolysis of birch sawdust were analyzed by high-performance liquid chromatography coupled with ultraviolet detection and tandem mass spectrometry (HPLC-UVD/MSn). Chromatographic separation was performed on tandem reversed-phase C18 columns, and structural characterization was achieved using electrospray ionization Orbitrap mass spectrometry with higher-energy collisional dissociation (HCD).

RESULTS

Distinct chromatographic behaviors were observed for lignin-derived products with different degrees of polymerization, enabling differentiation of monomeric and oligomeric species. Tandem MS analysis of representative oligomers revealed characteristic fragmentation pathways that enabled structural elucidation of oligomers. β-O-4 linkages were identified as the predominant interunit structures, and native β-β motifs were also characterized.

CONCLUSIONS

Untargeted molecular-level characterization of lignin-derived products generated from methanol-based flow-through solvolysis of birch biomass provides direct insights into the composition and interunit linkages of native-like lignin oligomers. These findings reveal the structural diversity of biomass-derived oligomers and bridge the gap between model-compound studies and real biomass-derived lignin systems.