Recently, NMR spectroscopy has also been utilized to determine
some characteristics of bio-oils, such as presence of functional
groups, degrees of branching or saturation, aromatic content. The
percentages of protons based on 1H NMR spectroscopy analysis
of bio-oils grouped according to chemical shift range proposed
by Mullen et al. (2009) are given in Table 5. The most upfield region
of the spectra, from 0.5 to 1.5 ppm, represents aliphatic protons
that are attached to carbon atoms at least two bonds removed from
a C@C double bond or heteroatom (O or N). This region was the
most populated (60% of all protons) for both HTL-275 and HTL-
325 indicating their higher aliphatic content. The integrated region
from 1.5 to 3.0 ppm represents protons on aliphatic carbon atoms
that may be bonded to a C@C double bond (aromatic or olefinic) or
are two bonds away from a heteroatom. Both bio-oils again had
high levels of protons in this spectral region (25–27%). According
to Mullen et al. (2009), high amount of protons in the region both
from 0.5 to 1.5 ppm and 1.5 to 3.0 ppm describes the evidence that
bio-oil has high calorific value.