Electrochemical sensor in situ control of acidity level of concentrated HCl solutions

The experimental device consisting of two paste electrodes: ferrocene and quinone at fixed current potentiometry was studied for the in-situ control of the acidity level of hydrochloric acid solutions at moderate concentrations between 0.6 and 8.0 M. The influence of different factors affecting the variation of potential at imposed current were already studied in previous papers published on H3PO4, H3PO4 and HClO4. Also, the measured potential variations Ei between ferrocene and orthochloranil (oQ) or parachloranil (pQ) electrodes were equal the values as those E obtained by the voltamperometric curves at a fixed current. The acidity function Ri(H) proposed previously was similar to that proposed by Strehlow and named Ro(H); R (H) representing the H+ activity is the extended pH towards concentrated acid solutions. The variation of potential determined at imposed current obeyed the Nernst equation and the slope close 0.058 mV.