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Free fatty acids are involved in many metabolic regulations in the human body. In this work, an ultra-fast screening method was developed for the analysis of free fatty acids using trapped ion mobility spectrometry coupled with mass spectrometry. Thirty-three free fatty acids possessing different unsaturation degrees and different carbon chain lengths were baseline separated and characterized within milliseconds. Saturated, monounsaturated, and polyunsaturated free fatty acids showed different linearities between collision cross-section values and m/z. The establishment of correlations between structures and collision cross-section values provided additional qualitative information and made it possible to determine free fatty acids which were out of the standards pool but possessed the confirmed linearity. The gas-phase separation made the quantitative analysis reliable and repeatable at a much lower time cost than chromatographic methods. The sensitivity was comparable to and even better than the reported results. The method was validated and applied to profiling free fatty acids in human plasma. Saturated free fatty acids abundance in the fasting state was found to be lower than that in the postprandial state, while unsaturated species abundance was found higher. The method was fast and robust with minimum sample pretreatment, so it was promising in the high-throughput screening of free fatty acids.

Bio-oils, produced by biomass pyrolysis, have become promising candidates for feedstocks of high value-added chemicals and alternative sources for transportation fuels. Bio-oil is such a complicated mixture that contains nonpolar hydrocarbons and polar components which cover almost all kinds of organic oxygenated compounds such as carboxylic acids, alcohols, aldehydes, ketones, esters, furfurals, phenolic compounds, sugar-like material, and lignin-derived compounds. Comprehensive characterization of bio-oil and its subfractions could provide insight into the conversion process of biomass processing, as well as its further utilization as transportation fuels or chemical raw materials. This review focuses on advanced analytical strategies on in-depth characterization of bio-oil, which is concerned with gas chromatography, high-resolution mass spectrometry, FTIR spectroscopy and NMR spectroscopy, offering complementary information for previous reviews.