2014 Volume 48 Issue 2 Pages 153-163
The total alkalinity (AT) of seawater is one of the parameters required to characterize carbonate systems, which are essential for studying the greenhouse effects of carbon dioxide (CO2) on the Earth’s climate. The AT of seawater was measured by potentiometric open-cell titration using HCl—without the addition of sodium chloride (NaCl)—and calculated by a nonlinear least-squares regression. In addition, the equation for calculating the titrant density was studied over a range of concentrations and temperatures. The similarity of the pH electrode response to the ideal Nernst value (ks) was measured using pH buffers for seawater and pure water. New methods for the calculation of AT using ks were proposed. Open-cell titrations for a certified reference material (CRM) were conducted using two electrodes with ks of 0.997 and 0.989. The measured values for both electrodes were in good agreement with the CRM value of 2356.78 ± 0.26 μmol/kg. AT was successfully calculated using ks. The dilution effect by the titrant, free of NaCl, on electromotive force measurement was also examined and found to be negligible for the calculation of CO2 parameters.