Highly sensitive tandem mass spectrometry detection for high resolution HILIC separation of biomass burning markers

Levoglucosan (LEV) and two of its isomers, mannosan (MAN) and galactosan (GAL), are commonly used as biomass burning tracers, however 1,6-anhydro-β-D-glucofuranose (AGF), another isomer derived from biomass burning, is rarely identified or quantified in existing literature. When present in environmental samples, AGF may be unknowingly co-eluting with another isomer, thus potentially compromising the accuracy of previously reported results. We present a novel hydrophilic interaction liquid chromatography (HILIC)-based separation method, coupled with tandem triple quadrupole mass spectrometry (MS/MS), capable of separating and quantifying all four fire-marker monosaccharide anhydrides (MAs). This separation relies on the hydrophilic penta‑hydroxy ligand functionality of HALO Penta-HILIC columns. Parameters such as mobile phase composition, column temperature, spray voltage, and selected reaction monitoring transitions were optimised to achieve a baseline separation to both confirm and improve detection of each isomer. Under optimal conditions, the limits of detection for LEV, MAN, GAL, and AGF were 0.39, 0.62, 0.52, and 0.04 µg/L, respectively. The accuracy of the method was validated via the analysis of the NIST Urban Dust 1649b certified reference material, with LEV, MAN, GAL concentrations in good agreement with previously determined results, and the concentration of AGF reported for the first time. The method was applied to a range of environmental samples (aerosols, sediments, and ice cores) to prove its applicability for different matrices. Due to its speed (< 10 min), selectivity, and sensitivity, this HILIC-MS/MS based method can be utilised in future studies to quantify all four fire-marker isomers, allowing the calculation of additional isomer ratios, which may assist with biomass burning source identification.