Titration of free phenolic groups in pulps 10 th EWLP, Stockholm, Sweden, August 25–28, 2008

The ClO 2 titration method for in situ measurement of free phenolic groups in pulp has been improved to minimize interferences from other groups susceptible to react with ClO 2 . The method is based upon the reaction between free phenolic groups and chlorine dioxide at a temperature of 0°C, in the presence of dimethyl sulfoxide. Theoretically, one free phenolic group consumes two molecules of ClO 2 . The pH of the ClO 2 treatment was advantageously fixed at 6.7 using a phosphate buffer, and a new protocol was proposed to avoid any possible interference of quinone groups (either present in pulp or formed during the procedure) on the residual ClO 2 titration step. The results obtained on isolated lignin samples were compared to those measured by 31 P NMR spectroscopy. The ClO 2 method gave substantially higher values, for reasons which deserve further investigation.