NMR spectroscopy of complex mixtures of petroleum organosulphur compounds

A Comprehensive Approach for Quantitative Lignin Characterization by NMR Spectroscopy

“…Earlier works on the studies of spruce MWL with quantitative 1 H and 13 C NMR ( − ) reported very high amounts of carbonyl and ester groups. However, these values are not consistent with data obtained by wet chemistry methods ( Table ) or any other reports related to 13 C NMR of spruce lignin.…”

“…In the aromatic region, signals of different moieties are partially overlapped. In addition, some calculated values are obtained after subtraction of experimental or theoretical values, which are more than 1 order of magnitude higher than the value obtained; often, calculations require assumptions or/and the use of literature data ( − ). Therefore, we consider these calculations as approximate.…”

“…For the quantitative 13 C NMR, the concentration of lignin was 20%; a 90° pulse width, a 1.4 s acquisition time, and a 1.7 s relaxation delay were used. Chromium(III) acetylacetonate (0.01 M) was added to the lignin solution to provide complete relaxation of all nuclei ( , ). A total of 20 000 scans were collected.…”

“…The development of quantitative 13 C NMR in lignin analysis () was an important milestone in lignin chemistry. However, despite the wide use of this technique for the characterization of lignin structure, there are few comprehensive works on lignin quantification with 13 C NMR ( − ). Quite often, 13 C NMR is used only for the estimation of some specific moieties ( − ).…”

Lignins from annual grassy plants

“…The number of scans was 20,000-100,000. Quantitative calculations involving 13 C NMR spectra were performed according to methods reported before [2][3][4] …”