Overview
IEC TR 62432:2006, “The rH index in aqueous and aqueous-organic media,” is a Technical Report from the International Electrotechnical Commission that defines the terminology, theory and methodology for determining the rH index (a measure of reducing power) in water and water‑rich organic solvent mixtures. The report covers the conceptual basis of rH, operational measurement approaches, recommended rH standards (notably the quinhydrone system), electrode choices, calibration principles and instrumentation considerations for rH‑metric determinations.
Key topics and requirements
- Definition of rH: rH is defined by the hydrogen pressure that would equalize a hydrogen electrode potential to the redox potential of a system; it serves as an index of reducing power in aqueous and aqueous‑organic media.
- Redox theory: Treatment of redox couples, redox equilibria and redox potentials (E) and how multiple overlapping redox couples form complex redox systems.
- Quinhydrone (QHY) standard: Use of the equimolar quinone/hydroquinone system as an operational rH reference standard (illustrated values in the report include rH ≈ 23.66 at 298.15 K for QHY and rH ≈ 41.6 for the oxygen electrode archetype).
- Electrodes and cells:
- Glass (H+) selective electrodes as practical replacements for cumbersome hydrogen gas electrodes.
- Inert noble‑metal electrodes (Pt, Au) for sensing mixed redox potentials.
- Design of calibration and measurement cells (e.g., quinhydrone vs. sample cell configurations).
- rH scales and Pourbaix diagrams: Relationships between rH, pH and redox potential (E) and how these are represented graphically for interpretation.
- Instrumentation: Guidance on analyzers, sensor units and electronic measurement units suitable for rH determinations.
- Calibration methodology: Procedures for measuring cell potential on a reference rH standard and on the sample to calculate sample rH.
Practical applications
IEC TR 62432 is applicable wherever redox conditions in aqueous or aqueous‑organic systems are important:
- Environmental and hydrological monitoring (groundwater, surface water redox status)
- Corrosion control and material compatibility assessments
- Biomedical and pharmaceutical aqueous process controls
- Food and beverage industries (winery, dairy) for process and quality monitoring
- Industrial process control where mixed solvent systems are used
Who should use this standard
- Instrument and sensor manufacturers designing rH/redox analyzers
- Analytical and water quality laboratories performing redox measurements
- Process control engineers and plant laboratories in industry sectors listed above
- Corrosion engineers and environmental scientists interpreting redox data
Related guidance
IEC TR 62432 complements standards and guidance on pH measurement, electrochemical sensors and redox electrode calibration; users should consult the report’s normative references and relevant IEC/ISO standards for electrode performance, calibration practices and instrumentation safety.