Phenolic Group Distribution as a Function of Molecular Weight in Lignins and Their Fractions

An analytical approach based on phenol fluorescence labeling with the dansyl fluorophore coupled with gel permeation chromatography using UV and fluorescence detection was applied in an effort to increase the understanding of the phenolic group distribution in different lignin specimens. Selective derivatization with dansyl chloride of lignin phenolic functionalities was quantitatively achieved under mild reaction conditions and was applied to acidolytic and kraft lignins from softwood and hardwood and to kraft lignin fractions obtained by solvent fractionation. Acetylated lignins and labeled lignins were analyzed to discern the lignin aromatic skeleton input from the response of dansyl-linked phenols, successively, allowing for estimation of the phenolic group distribution as a function of molecular weight for different lignins before and after solvent fractionation.