Isomeric-Level Description of Complex Bio-Oils Enabled by Gated TIMS Coupled to 18-T FTICR MS

Lignocellulosic biomass is a key renewable resource to produce biofuels via thermochemical processes such as fast pyrolysis and hydrothermal liquefaction. However, the resulting bio-oils are highly complex mixtures containing large numbers of oxygen-containing compounds, making their chemical characterization particularly challenging. While standalone Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) enables ultrahigh-accuracy molecular formula assignment, direct mass spectrometry analysis does not allow isomeric discrimination. This can be overcome by the use of an upfront separation technique such as ion mobility (IM) that separates ions as a function of their size and shape. In this work, a gated trapped ion mobility spectrometry–FTICR MS (gTIMS-FTICR MS) was used for the characterization of bio-oils. First, a mixture of 13 representative standards was analyzed, affording mobility trends for major bio-oil compound families, including carbohydrates, polyphenols, and fatty acids. The method was then applied to three pine-derived bio-oils produced by fast pyrolysis, stabilized fast pyrolysis, and hydrothermal liquefaction. Extracted ion mobilograms (EIMs) revealed extensive isomeric diversity and distinct ion mobility profiles depending on the production and stabilization processes. Descriptors derived from ion mobility distributions, such as the number of fitted Gaussians, apex component 1/K0, and the number of local maxima, provided insights into differences in molecular shape and structural diversity. Overall, gTIMS-FTICR MS proves to be a powerful multidimensional approach for resolving isomeric complexity in bio-oils and for assessing the impact of thermochemical conversion and upgrading processes.