The use of linear potentiometric titration curves in the determination of alkalinity and acid-base properties of diluted solutions of humic substances.

A critical study of the use of Gran and modified Gran functions for the determination of alkalinity and acid-base properties of diluted solutions containing humic substances is presented. These solutions were composed of 340 muM HCO3(-)(3) in 0, 10, 20.5 and 41 mg/1. of sodium humate in order to simulate natural waters with different levels of dissolved organic carbon. The results showed that the alkalinity may be determined in good agreement with the expected value using both methodologies. The modified Gran functions give information about acid-base speciation in addition to the alkalinity. The application of the modified Gran functions for determination of humic acid pK(a)s and stoichiometry was studied under conditions simulating waters rich in natural organic matter in terms of humic acid concentrations.