Regarding pH

Regarding Conductivity

On Redox Reactions

Dissolved Oxygen

FAQ

How should one select the electrode material for redox measurements: gold, silver, or platinum?

Platinum is a versatile electrode material and is unsuitable only in very few applications.

 

In an ozone (O3) or hydrogen peroxide (H2O2) environment, platinum acts as a catalyst; therefore, at low concentrations, the potential corresponding to O3 or H2O2 cannot be established in the composite layer.

 

Furthermore, platinum oxidizes in air, let alone in strong oxidizing agents. In the former case, the electrode displays an excessively high redox value, while in the latter, a memory effect occurs. In both scenarios, the response is slow.

 

In principle, platinum electrodes should not be used in applications involving ozone or peroxides.

 

Gold electrodes can be used in the aforementioned applications; moreover, gold electrodes have a more positive potential than platinum electrodes. Gold or silver electrodes also offer advantages when employed in the treatment of cyanide-containing wastewater. Cyanide exerts a mild corrosive effect on the electrode surface, which helps keep the electrode surface clean.

 

Gold should not be used in acidic solutions with high chloride concentrations, as gold forms complexes with chlorine, rendering the measurement invalid. The same principles that apply to pH measurements also apply to redox measurements, both in terms of instrument design and cable configuration: the measuring amplifier must have a very high input impedance (10¹² Ω). Redox values are typically displayed as absolute or relative “mV” readings.

 

Redox measurement is a bulk-parameter measurement and cannot be used to quantify a specific ion. Consequently, it is also impossible to determine the concentration of a particular species in a redox system, since all ions present in the solution participate in the redox process. Furthermore, the redox electrode should not be chemically cleaned in the medium being measured, because the cleaning solutions typically contain high concentrations of ions; such high ionic strength combined with the resulting potential shock results in a very slow return of the electrode potential to its original measured value.

 

If cleaning is necessary during the process, it must be performed mechanically or by ultrasonic means.

 

Before use, the electrode can be briefly immersed in a sulfite solution outside the medium being measured, followed by treatment with sulfuric acid or hydrochloric acid. Failure of a redox measurement chain typically occurs in the reference system, manifesting as zero-point drift. In such cases, zero-point calibration is required, for example using a 225 mV redox buffer solution. The slope of the redox electrode remains unchanged.

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