The excessive use of fossil resources contributes to environmental pollution that is suspected to be the main reason of global warming. It is highly relevant to find alternative renewable energy sources to mitigate global warming, which can commit over one-third of the Earth's animal and plant species into extinction within 25 years. Lignocellulosic biomass has received significant interest in recent years due to its potential application as second generation biofuels and CO2-neutral renewable feedstock for platform chemicals and materials. Lignin, being one of the three main constituents of the plant cell walls is the largest available biomass of aromatic compounds. However, it is a great challenge to produce monomers from natural or technical lignins due to their extremely complex, three-dimensional and cross-linked structure formed mainly by the radical coupling reactions of monolignols which are phydroxyphenyl (H), guaiacyl (G), and syringyl (S) units (Scheme 1). In fact, there are hundreds of research articles dedicated to the structural characterization of different lignin compounds using various chromatographic or spectroscopic techniques. Scheme 1. Major structural units in lignin compounds.