A sensor for in situ control of acidity level of concentrated HF solutions

Two paste electrodes: ferrocene and quinone at fixed current potentiometry composes the device and are used for the in-situ control of the acidity level of hydrofluoric acid solutions at moderate concentrations between 3.0 and 12.0 M. The influence of different factors affecting the variation of potential at imposed current were studied in previous papers published on HCl, H 3 PO 4 , H 3 PO 4 and HClO 4 as well as their mixtures. Also, the measured potential variations DE i between ferrocene and orthochloranil (oQ) electrodes are equal the values as those DE obtained by the voltamperometric curves at a fixed current. The acidity function R i (H) proposed previously is similar to that proposed by Strehlow and named R o (H); R (H) representing the H + activity is the extended pH towards concentrated acid solutions. The variation of potential determined at imposed current follows the Nernst equation and the slope of 0.058 mV is obtained.