Characterization of Dissolved Kraft Lignin by Capillary Zone Electrophoresis

Abstract

Abstract This report presents a method to characterize underivatized lignin by Capillary Zone Electrophoresis (CZE), in which separation is achieved by differences in mobility due to differences in the charge-to-size ratios of the solutes. A comparison has been made between the separation of lignin by CZE and earlier studies1 regarding the size and phenolic content of dissolved lignin. The samples were isolated at different times from a flow-through kraft cook and characterized by CZE in an alkaline solution. The resulting electropherograms show a molecular mobility distribution. The molecular mobility distribution of each fraction is in good agreement with its molecular size distribution and phenolic content. As the cook proceeds, the mobility of the lignin fragments increases with increasing phenolic content. Although the molecular size distribution shows a slight increase in molecular weight at the end of the cook according to Size Exclusion Chromatography (SEC), this does not seem to affect the mobility distribution. The change in mobility distribution may be a useful new parameter to be used in lignin characterization, as the dissolution of lignin is influenced by the number of ionized groups and by the size of the lignin fragments.