Electrochemical Analysis for Total Alkalinity of Water by the Measurement of Cathodic Prepeak of Quinone Caused by Surplus Acid

Abstract

In this study, an electrochemical analysis, coupled with the concept of back neutralization titration and the voltammetric determination of surplus acid, is proposed for determining the total alkalinity of water samples. When linear sweep voltammetry of 3,5-di-tert-butyl-1,2-benzoquinone (DBBQ) with H₂SO₄ in a water and ethanol (44 : 56, v/v) mixture was carried out using a bare glassy carbon working electrode, a cathodic prepeak of DBBQ caused by H₂SO₄ was observed on the voltammogram at a more positive potential than when compared with the original cathodic peak of DBBQ. When similar voltammetry was carried out in the presence of Na₂CO₃ and H₂SO₄, the cathodic prepeak height of DBBQ was decreased with an increase in the Na₂CO₃ concentration. The decrease of the cathodic prepeak height of DBBQ was found to be linearly related to the Na₂CO₃ concentration ranging from 0.025 to 2.5 mM (r² = 0.998). The total equivalent concentrations of inorganic bases in samples of mineral water and tap water were determined, and then the results were converted to the total alkalinities of the water samples (mg/L CaCO₃). The total alkalinities of the water samples determined by the present electrochemical analysis were essentially the same compared with those by the neutralization titration method. From these results, we were able to demonstrate that the present electrochemical analysis with accuracy and precision could be applied to determine the total alkalinity, which is one of the indicators to examine water quality. The present electrochemical analysis would contribute to achieving the sustainable development goals (SDGs) of #6 and #14.