Check of Silver, Platinum and Gold electrodes

Significance of the Topic

Metal electrodes based on silver, platinum and gold play a crucial role in potentiometric measurements and titrimetric analyses. Ensuring their reliability is essential to maintain high accuracy and precision, avoid time-consuming error troubleshooting and prevent sample waste in quality control and research laboratories.

Objectives and Overview of the Bulletin

This bulletin presents standardized procedures for evaluating the performance of commercial silver, platinum and gold electrodes. It covers four main approaches:

• Verification with certified redox standard solution
• Measurement in self-prepared quinhydrone buffer systems
• Potentiometric titration tests for each metal type
• Bivoltammetric titration of platinum and gold electrodes

Methodology and Instrumentation

Each verification method follows a defined protocol:

• Redox potential measurement: Immerse the electrode in a temperature-controlled redox standard, record the potential under stirring and compare it against the certified value (±5 mV tolerance).
• Quinhydrone buffer test: Use saturated quinhydrone in pH 4.00 or 7.00 buffers; theoretical potentials are tabulated and deviations should remain ≤5 mV.
• Potentiometric titration: Titrate iodine with sodium thiosulfate under acidic conditions (H₂SO₄ for Au/Pt; HCl for Ag) using MET or DET modes; evaluate titrant volume (1.95–2.05 mL), titration time (<160–150 s for Au/Pt, <150 s for Ag), reproducibility (RSD <0.5 %) and potential jump (ΔU ≥ 70 mV).
• Bivoltammetric titration: Apply a constant polarization current (1 µA) in MET Ipol mode to assess double-sheet or wire electrodes of Pt/Au; similar criteria apply, with ΔU ≥ 100 mV.

Used Instrumentation

• pH meter, stirrer, water bath
• Titrators equipped with MET, DET and MET Ipol modes
• 10 mL burettes and reference electrodes (Ag/AgCl, KCl 3 mol/L or KNO₃ 1 mol/L)

Key Results and Discussion

The bulletin defines clear acceptance criteria. Electrodes that deviate beyond tolerances exhibit contamination or surface defects and require cleaning or replacement. Representative titration curves illustrate sharp equivalence points and consistent behavior across triplicate analyses. The redox potential checks reliably identify underperforming electrodes before sample analysis.

Benefits and Practical Applications

Adoption of these standardized tests:

• Improves data quality by verifying electrode condition prior to analysis
• Reduces downtime and sample loss due to faulty sensors
• Enables routine quality assurance in analytical, industrial and research settings

Future Trends and Opportunities

Electrode testing may evolve with:

• Integration of automated self-check routines in analytical instruments
• Development of novel reference systems to extend testing to less noble metals
• Miniaturized multisensor platforms combining redox, pH and conductivity checks

Conclusion

Regular validation of silver, platinum and gold electrodes using the described redox standards and titrimetric procedures ensures reliable performance, safeguarding the integrity of potentiometric and titrimetric measurements in diverse laboratory environments.

References

• Leaflet for metal electrodes (8.109.8047)
• Monograph: Electrodes in Potentiometry (8.105.5013)
• Monograph: Practical Titration (8.029.5003)
• Metrohm Application Bulletin AB-025: Coatings on silver electrode