The Estimation of Basic Groups in Wool: Possibilities and Limitations of the Orange II Method

The basic-group content of wool, like the acidic-group content, can be calculated from titration curves. However, this method is less satisfactory for the determination of basic-group content because the strongly alkaline condition required to deprotonate arginine (very basic) residues partly damages the fibre. Since the maximum binding capacity of proteins for acidic and basic dyes is a measure of the number of basic and acidic groups, respectively, a simple and more convenient procedure for the estimation of basic groups in wool, based on the measurement of the maximum binding capacity of the wool for an anionic dye (Orange II), was proposed. The method us based on the reasonable assumption that each cationic group in the fibre binds one dye anion. This procedure seems to be very simple and rapid if it is reliable. In the present authors' experiments, this method is analysed in order to demonstrate its reliability and its limitations. In the first experimental stage, the procedure was applied on untreat...