On the Possibility of Quantitative Determination of Lignin and Cellulose in Plant Materials Using IR Spectroscopy

A methodical approach to quantitative determination of lignin and cellulose in plant materials by mid-infrared FT-IR spectroscopy using the KBr tablet technique was proposed. For the prepared model binary mixtures of pure cellulose and lignin, a direct correlation was established between the concentration and intensity of the analytical absorption bands of lignin (1508–1512 cm–1) and cellulose (1059–1061 cm–1). Based on the obtained intensity–concentration plots, formulas for calculating the lignin and cellulose contents were derived. The proposed method was tested on a wide range of plant biomass samples, including 9 wood samples and 13 samples of agrowaste materials. A good suitability of the method for the quantitative determination of lignin was shown; the experimental results agree with the literature data within 1%. However, the proposed method was not suitable for the determination of cellulose, since it did not take into account the contribution from hemicellulose and extractive substances to the absorption band at 1059–1061 cm–1, which led to strongly overestimated results from the cellulose content determination.