Abstract: The dynamic response of precipitate-based ion-selective electrodes to a sudden step change in the activity of interfering ions (Y^±) is studied in this paper. In this case the responses of AgIelectrode to Cl^-,Br^-and SCN^-, AgBr electrode to Cl^-and SCN^-, CuSelectrode to Pb²⁺, Zn²⁺, Cd²⁺, Co²⁺, Ni²⁺and Mn²⁺, PbSelectrode to Cd²⁺and CdSelectrode to Pb²⁺are all nonmonotonic overshoo-type transient signals in the presence of certain concentration of primary ion(X^±) in the solution, while all the other transient signals in the absence of primary ion in the solution are monotonictype, except the response of AgBr electrode to Cl^-. For the responses of a certain electrode to different interfering ions, the experiment discovers that both the smaller solubility product Ksp(MY) of ionexchange product (MY) and difference [ΔH_h(X^±)^° -ΔH_h(Y^±)^°] of hydration enthalpies of ions in ionexchange process, the larger the peak height ΔE_Pof transient signal responded to sudden increase in the activity of interfering ion by electrode, and the effect of [ΔH_h(X)^°-ΔH_h(Y^±) ^°] on ΔE_Pislarger than the K_SP(MY). For the responses of AgIelectrode to Br^-and SCN^-, although pK_sp(AgSCN)≈pK_sp(AgBr), ΔE_P(SCN^-)>ΔE_P(Br^-). This is probably related to [ΔH_h(I^-)^°-ΔH _h(SCN^-)^°]<[ΔH _h(I^-)^°-ΔH_h(Br^-)^°]. For CuSelectrode, pK_sp(PbS) <pK_sp(CdS) , pK_sp(MnS)<pK_sp(CoS)and pK_sp(NiS), but ΔEp_(Pb²⁺)>ΔE_p(Cd²⁺), ΔEp_(Mn²⁺) >ΔEp_{(Co²⁺ )}and ΔEp_(Ni²⁺). These are the same due to [ΔHh_(Cu²⁺)^°-ΔH_h(Pb²⁺)^°]<[ΔH_h(Cu²⁺)^°-ΔH_h(Cd²⁺)^°], [ΔH_h(Cu²⁺)^°-ΔH_{h(Mn^{2+)°]<[ΔHh(Cu2+)°-ΔH(Co2+)°] and [ΔH(Cu2+)°-ΔHh(Ni2+)°]. The relative magnitudes of differences of hydration enthalpies in positive and reverse reactions in ionexchange can also be used to explain the relative magnitudes of peak heights ΔEpand ΔE of transient signals in the positive and negative activity steps. Therefore, on the basis of the above facts, we believe that the peak potential of the transient signal responded to the interfering ion by an electrode is determined not by the velocity of ion diffusion but by that of ionexchange because the thickness of diffusion layer is infinitely thin when the solution is sprayed on the surface of electrode at a high velocity .The smaller the difference in hydration enthalpies, the larger the velocity of ionexchange, then the larger the peak height of transient signal may be. Besides, for other electrodes, except Cu Selectrode, the selectivity coefficients Kxyedetermined on the basis of the equilibrium potentials in nonmonotonic overshoottype transient signals all conform to the Ksp(MX) /Ksp(MY) values.}}

Key words: Ion-selective electrode, Electrode dynamic response, Hydration enthalpy, Ion-exchange velocity, Selectivity coefficient