Determination of Carboxyl Groups in Pulp via Ultraviolet Spectrophotometry

A method was established for the determination of carboxyl groups in pulp by ultraviolet (UV) spectrophotometry. The method is based on the fact that the carboxylate pretreated with diluted hydrochloric acid was completely converted to carboxylic acid in pulp. In addition, content of carboxyl groups was measured with the capacity of copper ions exchanged with the hydrogen ions of carboxylic acid by UV spectrophotometry. The data showed that the pulp was suitable to react with 30% to 50% exchanged copper ions for 4 h at 45 °C. The results indicated that the method had excellent repeatability (RSD = 1.50%) and accuracy. Compared to traditional methods, the maximum relative error was less than 4%. The method is simple and accurate, such that it can be used for the efficient determination of carboxyl groups in pulp and other researches.