Potentiometric open-cell titration for seawater alkalinity considering temperature dependence of titrant density and Nernst response of pH electrode

抄録

The total alkalinity (A_T) 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 A_T 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 (k_s) was measured using pH buffers for seawater and pure water. New methods for the calculation of A_T using k_s were proposed. Open-cell titrations for a certified reference material (CRM) were conducted using two electrodes with k_s 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. A_T was successfully calculated using k_s. 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.