“…Thermal, catalytic, and hydrotreated bio-oils typically contain thousands of different, mostly oxygen-containing (O-containing) compounds. , In these compounds, oxygen is present as a part of one or several functional groups . In general, bio-oil compounds have a wide distribution of physical and chemical properties such as density, viscosity, polarity, boiling point, and molecular weight. , Thus, the chemical characterization of the bio-oils is very complicated. Bio-oil analytics has faced several serious challenges.…”