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

This paper presents an evaluation of the modified Gran functions (MGFs) and derivative methods for assessing the concentrations of inorganic carbon sp ecies, CO2, HCO3- and CO32-, in the cultivation medium of the marine microa lgae Tetraselmis gracilis. Both methods were applied to simulated and exper imental potentiometric titration data and were able to detect small variati ons of inorganic carbon species during 10 days of batch cultivation. The MG F were able to determine the concentration of an additional titratable spec ies with pK(b) 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 gro ups of organic carbon compounds excreted by the algae. Treatment of the tit ration data with the derivative method did not permit the quantitative dete rmination of the concentration of the additional titratable species, but no interference was observed in the results obtained for the inorganic carbon species. (C) 2001 Elsevier Science B.V. All rights reserved.