In situ determination of acidity level in concentrated phosphoric acid solutions by potentiometric method at imposed current intensity

The device constituted by two past electrodes: ferrocene and orthochloranil at fixed current potentiometry, can be used as a good sensor for the in-situ determination of phosphoric acid concentration (2.0-14.7 M). Good agreement was observed regarding the values obtained with our method and the spectrophotometric values in synthetic phosphoric media. Different factors affecting the variation of potential at imposed current such as current intensity, temperature, stirring rate of solution and H + ion concentrations are studied. The potential variations measured by our device between ferrocene and orthochloranil electrodes have the same values as those obtained by the voltamperometric curves. A new acidity function R i (H), which represents the determination of the H + activity has been introduced and compared to Strehlow R o (H) and Hammet H o functions. A good agreement has been observed between the R o (H) and R i (H) functions.