Potentiometric celis containing Cl“ and K+, Cu2+ ör Ca2+ ion-selective electrodes were used to construct Ecen — logCM (where M is K+, Cu2+ or Ca2+) calibration graphs of slopes 113.0, 80.5 and 78.0 mV/ Concentration decade, at 25 °C, for the three metal ions, respectively. The percent error of the determination corresponding to ± 1 mV deviation was calculated in each case and found to be much lower than the corresponding value öbtained using the con- ventional M-ion-selective electrode / calomel reference system. The Cl~and Cu2+ ion-selective electrodes employed were made by electroplating silver rod with AgCl-Ag2S and a platinum plate with CuS, respectively. The effect of pH, foreign ions, and temperature on the characteris- tics of these electrodes was studies.