A study on chloride ion-selective electrode transient potentiometry

When 0.10 mol/L KNO3 blank solution and Cl- rest solution are switched each other, day-today reproducibility of the peak height DeltaE(p) of transient signal responded by Cl--selective electrode is very good. The detection li mit of Cl--selective electrode and the intercept of DeltaE(p) similar to p( Cl) straight line accord with both values calculated by K-sp(AgCl) respecta bly. At positive activity step, the jump time of transient signal is smalle r than 1.5 s, the fast and accurate analysis of test solution in small volu me may be achieved. The potential variance velocity in different stage of t ransient signal may be explained by the variance of Cl- hydration Gibbs fre e energy, DeltaG(h) (Cl-) = DeltaG(h)(0) (Cl-) + RTln a(Cl(H2O)n)(-)/a(0)/p (Cl-g(-))/p(0), where a(0) = 1 mol/L, P-0 = 1.013 X 10(-5) Pa, DeltaG(h)(0) (Cl-) = -337 kJ/mol. At the start of positive activity step, P(Cl-g(-)) is very small, a(Cl(H2O)n)(-) larger, then \ Delta Gh(Cl-)\ the smallest. Beca use the smaller the \ DeltaG(h)(Cl-)\, the larger the hydration velocity of Cl(H2O)(n)(-), the jump of transient potential is the fastest. At the appr oach of peak potential, both p(Cl-g(-)) and \ DeltaG(h)(Cl-)\ are almost th e largest, the dehydration velocity of Cl(H2O)(n)(-) the smallest, then the jump of transient potential very slow. At the start of negative acitivity step, a(Cl(H2O)n)(-), is almost zero, p(Cl-g(-)) the largest, then \ DeltaG (h)(Cl-)\ the largest. Contrary to the dehydration of Cl(H2O)(n)(-) the hyd ration velocity of Cl-g(-) is the largest, then the jump of transient poten tial from peak potential to positive direction the fastest. With the decrea se of p(Cl-g(-)) and the increase of a(Cl(H2O)n)(-), both the \ DeltaG(h)(C l-)\ and hydration volecity of Cl-g(-) are getting smaller and smaller, so the transient potential tends slowly to the base line. The automatically sw itching setup of activity step used in this experiment is hem-made, the set up is provided with both injectors for blank and test solutions.