[Not Available].

The determinations are based on potentiometric titration data (volume of reagent, potential). To avoid any systematic error, the acidity constants are refined together with every other significant parameter (initial protolyte concentration, concentration of impurities, electrode chain characteristics ...) with the program MUPROT. Comparison of the multiparametrically adjusted results with those obtained by the usual methods reveals noticeable discrepancies. Particular attention is paid to carbonate as impurity; to take it into account, modified expressions for the titrant volume are established. The current of nitrogen used in the classical methods shifts the liquid-gas equilibrium of carbonic acid; in that case, only the approximate equations are to be considered. Working with a closed system is proposed as a more rigorous procedure.