氯离子选择电极瞬时电位分析法研究

0.1mol/L KNO3空白液与Cl^-切换时，AgCl电极响应的瞬时电位信号峰高度△Ep有非常好的再现性，40多天所测的10次标准曲线电位平衡偏差小于2.0mV，△Ep-p(Cl)^-直线平均斜率为55.4mV，其平均偏差小于1.0mV，电极响应下限和△Ep-p(Cl)^-直线截距都与经AgCl溶度积所计算的值一致，瞬时信号峰电位上升时间小于1.5s，可实现小体积试液的快速准确分析，用离子水合吉布氏自由能△Gh(Cl)^-，的变化解释了瞬时信号不同阶段的电位变化速度，实验中使用自制的活度阶梯自动切换装置，该装置具有容积比为4：1的空白液和试液两个注射泵，用该法已测定了维生素B6的含量。

A Study on Chloride Ion-selective Electrode Transient Potentiometry

When 0.10 mol/L KNO3 blank solution and Cl- test solution are switched each other, day-to-day reproducibility of the peak height ΔEp of transient signal responded by Cl--selective electrode is very good. The detection limit of Cl--selective electrode and the intercept of ΔEp～p(Cl) straight line accord with both values calculated by Ksp(AgCl) respectably. At positive activity step, the jump time of transient signal is smaller than 1.5 s, the fast and accurate analysis of test solution in small volume may be achieved. The potential variance velocity in different stage of transient signal may be explained by the variance of Cl- hydration Gibbs free energy, ΔGh(Cl-)=ΔG0h(Cl-)+RTln(aCl(H2O)-n/a0)/(p(Cl-g)/p0), where a0=1 mol/L, P0=1.013×10-5 Pa, ΔG0h(Cl-)=-337 kJ/mol. At the start of positive activity step, p(Cl-g) is very small, aCl(H2O)-n larger, then ｜ΔGh(Cl-)｜ the smallest. Because the smaller the ｜ΔGh(Cl-)｜, the larger the hydration velocity of Cl(H2O)-n, the jump of transient potential is the fastest. At the approach of peak potential, both p(Cl-g) and ｜ΔGh(Cl-)｜ are almost the 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, aCl(H2O)-n is almost zero, p(Cl-g) the largest, then ｜ΔGh(Cl-)｜ the largest. Contrary to the dehydration of Cl(H2O)-n, the hydration velocity of Cl-g is the largest, then the jump of transient potential from peak potential to positive direction the fastest. With the decrease of p(Cl-g) and the increase of aCl(H2O)-n, both the ｜ΔGh(Cl-)｜ and hydration volecity of Cl-g are getting smaller and smaller, so the transient potential tends slowly to the base line.The automatically switching setup of activity step used in this experiment is hom-made, the setup is provided with both injectors for blank and test solutions.