Mathematical modelling of potentiometric stripping analysis in mechanically mixed solutions

A mathematical model of batch potentiometric stripping analysis in a mechanically stirred measuring cell is developed both for the cases when the chemical stripping step takes place in the same solution where electrodeposition has taken place or in a new solution (medium exchange). Analytical solutions of the model for both cases are derived. The model takes into account the additional mercury coating occurring during the electrodeposition step in the presence of mercury ions. The basic assumptions on which the model is built are the following: 1. (i) the mercury film is ideally mixed during both the processes of electrodeposition and chemical stripping; 2. (ii) the electrode kinetics during the electrodeposition step can be neglected; and 3. (iii) the bulk concentrations of both the analyte and the oxidant do not change as a result of the redox processes taking place. The correctness of these assumptions is theoretically demonstrated. Potentiometric stripping experiments with standard solutions of Pb(II) and Cd(II) in 0.1 M hydrochloric acid are performed. The good agreement between the experimental results and the predictions of the model confirm its validity and show that the model can be used successfully for the quantitative description of batch potentiometric stripping systems.