Addressing the challenges in the analysis of poly-functional oxygenates in biomass pyrolysis oils by ultra high-resolution (FT-ICR) mass spectrometry

Biofuels from biomass pyrolysis are highly complex mixtures, which MS characterization and separation via chromatography are problematic due to their high oxygen content. Characterization of unfractionated samples by −ESI 21-tesla FT-ICR MS has revealed a strong ionization bias toward low-molecular-weight species with high oxygen numbers (˃O₆). Consequently, abundance-weighted MS-derived O/C and H/C ratios have shown discrepancies relative to quantitative values determined by combustion elemental analysis. Thus, separations are required to understand the extent of selective ionization in these complex mixtures and achieve the highest level of comprehensive molecular knowledge. The experience gained over two decades of research on fossil fuels at the National High Magnetic Field Laboratory has motivated the design and implementation of two novel biofuel separations: one is based on extrography, and the other exploits acid-base interactions. The results demonstrate that unfractionated, raw biofuels revealed up to ~14,000 unique elemental compositions and up to twenty-two oxygen atoms per molecule (O₂₂ class), assigned with an RMS error of ≤75 ppb. Furthermore, the ultra-high mass accuracy, uniquely achieved through 21-tesla FT-ICR MS, enabled the identification of boron-containing compounds (¹¹BO_X, X=4-12), which can be readily misassigned as N₂O_X species due to a mass difference of only 35 µDa. Fractionation via extrography exposed molecular features that not observable by direct MS analysis of whole samples and facilitated the identification of optimal pyrolysis and hydrotreating conditions. Additionally, an on-line LC-MS method that employs solvents doped with displacement additives provided separation based on aromaticity and oxygen content, which is currently being used to understand reaction pathways (e.g., dehydrogenation) for biomass pyrolysis, which will be discussed. Work supported by the NSF Divisions of Materials Research and Chemistry through 16-44779 and the State of Florida.