UV-visible light absorption is an analytical method that is commonly used to determine the concentration of lignin in solution; however, there are uncertainties with this method, particularly for use in determining lignin concentration in black liquors. To try to resolve these uncertainties, a detailed study of UV-visible absorption by lignin in solution has been made.
A dual beam UV-visible instrument capable of repetitive scan was used. The effects of lignin concentration, lignin molecular weight, molecular weight dispersion, and solvent were examined as well as the effect of the reference solvent. Measurements were made for lignin dissolved in dilute caustic, DMF, THF, and DMSO. Measurements for soft wood black liquors were also made. A refined method for determining lignin concentration in soft wood black liquors resulted that is now being used in our research to evaluate lignin concentration in soft wood black liquor.
The results of the current work have led to improvements in this analytical method so that it appears to be less affected by lignin characteristics and by solution complexities.