Characterization of lignin monomers in low rank coal humic acids using the derivatization/reductive cleavage method

Traditional CuO oxidation and thermochemolysis with tetramethylammonium hydroxide are the two main methods for lignin characterization in gymnosperm wood, and in soils and sediments formed from degraded gymnosperm wood, or for assessing the supply of terrestrial organic matter to marine sediments. In some cases, the overall lignin yield and the compound ratios used as plant source proxies have been found to be considerably different, depending on the method used. Thus, there is a need for finding efficient and more selective methods for lignin α- and β-aryl ether cleavage. Derivatization followed by reductive cleavage (the DFRC method) is suitable for lignocellulose material. Results from the DFRC method applied to the characterization of humic acids of a lignite (low rank coal) from the Czech Republic show that they contain intact lignin monomers with a dominance of coniferyl units, in accord with the gymnosperm origin of the lignite. It is expected that DFRC will be suitable also for tracing lignin in other sediments.