Determination of phenolic hydroxyl groups in residual lignin using a modified UV-method

A new modification of the UV ionization difference method has been used to determine the amount of free phenolic hydroxyl groups in isolated residual lignins from kraft pulps. The method offers a simple and rapid way to deter mine both the type and amount of phenolic hydroxyl groups in lignin. The li gnin samples were also subjected to aminolysis, a reliable but time-consumi ng method for the determination of free phenolic hydroxyl groups. The resul ts obtained with aminolysis were about 15-20% higher than the results obtai ned with the UV-method, but the correlation between the results obtained wi th the two methods was good.