| Summary: | This work presents new material for solid-contact layers—hydrous iridium dioxide IrO<sub>2</sub>·2H<sub>2</sub>O, characterized by high electrical capacitance value, evaluated using chronopotentiometry (1.22 mF) and electrochemical impedance spectroscopy (1.57 mF). The remarkable electrical parameters of layers resulted in great analytical parameters of IrO<sub>2</sub>·2H<sub>2</sub>O-contacted potassium-selective electrodes. Various parameters of ion-selective electrodes were examined in the scope of this work using a potentiometry method including: linear range, repeatability, stability of potentiometric response and sensitivity to varying measurement conditions. The analytical parameters obtained for solid-contact electrodes were compared with the ones obtained for coated disc electrodes to evaluate the influence of the iridium dioxide layer. The linear range of the IrO<sub>2</sub>·2H<sub>2</sub>O-contacted K<sup>+</sup>-selective electrodes covered concentrations of K<sup>+</sup> ions from 10<sup>−6</sup> to 10<sup>−1</sup> M and the potential stability was estimated at 0.097 mV/h. The IrO<sub>2</sub>·2H<sub>2</sub>O-contacted electrodes turned out to be insensitive to varying light exposure and changes in the pH values of measured solutions (in the pH range of 2 to 10.5). A water layer test proved that, contrary to the coated disc electrode, the substantial water film is not formed between the ion-selective membrane and iridium dioxide layer.
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