Ion Selective Electrode Response Mechanism Study

As the activity step using wall jet can accurately record response time curves, it is an important means for probing response mechanism of ion-selective electrodes (ISEs). Three contents are contained in this paper :The transient signals of halide ISEs (LaF3> AgBr> Agl) response to primary ion were studied with activity step method, the - Gh(X~) was calculated during the change of transient potential. The smaller the | Gh(X') \ is, the fast the jump of potential in positive step is and the slower the jump of potential in negative activity step is. In equilibrium potential, AGh (X~)=G^ (X'), It proved that the potential of precipitate-based ISEs is determined by the velocity of ISEs surface reaction and the concentration of dehydration ion not by ionic diffusion through the adhering laminary layer.The precipitate-based ISEs response to interfering ion with nonmonotonic overshoot-type transient signals were studied by activity step method. Supposing that primary and interfering ions dehydrate on ISEs surface, followed by gaseous ion-exchange, The and - Gh(X~) are considered as the activation energies of ISEs surface reaction in positive and negative activity step, respectively. The general equation of ISEs transient response is derived. In equilibrium potential Ee of positive step, AGh(Y-) = AG (.Y ), the transient potential equation changes into Nicolsky equation; in equilibrium potential E\ of negative step, AG,, the transient potential equation changes into Nernst equation. These results prove thatthe rationality of described mechanism.The feasibility of activity step method used to analytical determination wasstudied. The F" contain of tap water and mineral water were successfully determined by this method. The sensitivity and accuracy of determination are better and the volume of demanded test solution is smaller than conventional potentiometry.