MATHEMATICAL-MODELING OF POTENTIOMETRIC STRIPPING ANALYSIS IN MECHANICALLY MIXED-SOLUTIONS

A mathematical model of batch potentiometric stripping analysis in a m echanically stirred measuring cell is developed both for the cases whe n the chemical stripping step takes place in the same solution where e lectrodeposition has taken place or in a new solution (medium exchange ). Analytical solutions of the model for both cases are derived. The m odel takes into account the additional mercury coating occurring durin g the electrodeposition step in the presence of mercury ions. The basi c assumptions on which the model is built are the following: (i) the m ercury film is ideally mixed during both the processes of electrodepos ition and chemical stripping; (ii) the electrode kinetics during the e lectrodeposition step can be neglected; and (iii) the bulk concentrati ons of both the analyte and the oxidant do not change as a result of t he redox processes taking place. The correctness of these assumptions is theoretically demonstrated. Potentiometric stripping experiments wi th 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 m odel can be used successfully for the quantitative description of batc h potentiometric stripping systems.