Switching between voltammetry and potentiometry in order to determine H+ or OH− ion concentration over the entire pH scale by means of tungsten disk electrode

This study demonstrates that tungsten rotating disk electrode can be used for pH or H+/OH− concentration measurements in practically entire pH range, using the combination of voltammetric and potentiometric techniques. In strong acidic (c(H+) > 10−3 mol dm−3), and alkaline (c(OH−) > 10−3 mol dm−3) solutions, rotating tungsten disk electrode can be used as a maintenance-free electrode for voltammetric determination of H+ and OH− ion concentration. After an appropriate electrochemical oxidation, the same electrode, in a stationary regime, may be used as a potentiometric sensor in the range 3 < pH < 11, with the response −49.5 ± 2.3 mV per one pH unit.

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► Tungsten electrode may serve as a fast, robust maintenance–free pH sensor.
► Long flat diffusion current plateaus are found in both acidic and basic solutions.
► Electrochemically oxidized surface shows an excellent potenciometric pH response.
► By switching potentiostatic and amperometric modes entire pH range may be covered.