High-throughput Analysis of Softwood Lignin Using Tetra-n-butylphosphonium Hydroxide (TBPH)

The authors developed a high-throughput method for analyzing softwood lignin using tetra-n-butylphosphonium hydroxide (TBPH). Wood meal, TBPH, and hydrogen peroxide (H2O2) were introduced into a screw-capped glass test tube and allowed to react in a pressure cooker at 121 °C for 3 h to solubilize the wood meal. The solubilized polysaccharide was precipitated by the addition of a poor solvent such as methanol. After removal of the polysaccharide, the lignin concentration was measured via ultra-violet (UV) absorption spectroscopy. The series of operations performed was summarized as the TBPH method. The TBPH method was characterized as a simple and rapid procedure that used common equipment and was suitable for multiple-sample analysis. Softwood sample groups were prepared, and the lignin contents of these samples were measured by the TBPH method, the Klason method, and the acetyl bromide method to determine the accuracy of the proposed method. The TBPH method showed a high coefficient of determination (R2 = 0.94) when compared to the Klason method. By contrast, the acetyl bromide method showed a comparatively low correlation (R2 = 0.71) with the Klason method. This study revealed that the TBPH method presented high-throughput rapid analysis and good accuracy for soft wood lignin analysis.