Fingerprinting biomass burning tracers: isomer-specific profiling of monosaccharide anhydrides using LC-MS/MS and GC-MS

• Reliable isomeric assignments for monosaccharide anhydrides using LC-MS/MS. • Robust dual-platform LC-MS/MS and GC–MS analytical workflow. • Column chemistry and isomer-specific MS/MS transitions govern MA identification. • Derivatized and underivatized monosaccharide anhydrides exhibit distinct stability. Monosaccharide anhydrides (MAs), levoglucosan (LVG), mannosan (MAN), and galactosan (GAN) are pyrolysis products of cellulose and hemicellulose during biomass burning (wildfires, crop residues, biofuels, fossil fuels). These molecules are widely employed to reconstruct the sources, intensity and provenance of biomass combustion in aerosols and sedimentary archives. However, previous LC-based studies have reported inconsistent elution patterns and isomeric assignments for MAN and GAN, complicating the interpretation of diagnostic MA ratios. Here, we evaluated MA’s analysis using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and gas chromatography-mass spectrometry (GC–MS). Building on commonly applied HILIC-based LC methods coupled to MS or MS/MS, we developed an optimized LC-MS/MS protocol employing distinct isomer-specific qualifier MRM transitions alongside quantifier transitions for each MA. Using these qualifier transitions, MAN and GAN were reliably distinguished despite partial overlap in quantifier signals. The protocol was applied to analytical standards and surface-sediment extracts from a Himalayan Lake, yielding reproducible isomer-specific assignments and a consistent elution order. For GC–MS, trimethylsilyl-derivatized standards and sediment extracts were analysed and quantified. Concentrations obtained by LC-MS/MS and GC–MS were comparable, but a six-month storage experiment highlighted instability of trimethylsilyl derivatives, with analyte losses of 24 ± 6% for LVG, 40 ± 3% for MAN, and 23 ± 10% for GAN. In contrast, underivatized aliquots analyzed by LC-MS/MS exhibited minimal loss/degradation (<8%). Overall, this study provides reliable isomeric assignments for LC-MS/MS and a complementary dual-platform workflow, strengthening robust biomass burning source apportionments in atmospheric chemistry and paleoenvironmental reconstructions of fire regimes and ecosystem responses.