Application of modified Gran functions and derivative methods to potentiometric acid titration studies of the distribution of inorganic carbon species in cultivation medium of marine microalgae Original Research Article

This paper presents an evaluation of the modified Gran functions (MGFs) and derivative methods for assessing the concentrations of inorganic carbon species, CO2, HCO3− and CO32−, in the cultivation medium of the marine microalgae Tetraselmis gracilis. Both methods were applied to simulated and experimental potentiometric titration data and were able to detect small variations of inorganic carbon species during 10 days of batch cultivation. The MGF were able to determine the concentration of an additional titratable species with pKb values between 9.5 and 9.9 that appears in the medium after the 4th day of cultivation. This species may be assigned to carboxylate groups of organic carbon compounds excreted by the algae. Treatment of the titration data with the derivative method did not permit the quantitative determination of the concentration of the additional titratable species, but no interference was observed in the results obtained for the inorganic carbon species.