Simultaneous determination of gold and copper in electroplating baths and/or alloys by potentiometric titration

Significance of the topic

Precise monitoring of gold and copper levels in electroplating baths and metallic alloys is essential for ensuring consistent coating quality, minimizing material waste and maintaining process reliability. Rapid, accurate analysis supports quality control in metallurgical, electroplating and industrial laboratories.

Objectives and study overview

This application note presents a potentiometric titration method that determines gold and copper simultaneously in plating solutions or digested alloy samples. The approach exploits selective redox reactions and potential shifts to distinguish the two metals in a single procedural workflow.

Methodology and instrumentation used

The method comprises two sequential titrations using an Fe(II) standard solution as titrant. Key steps are:

• Reduction of Au(III) by Fe(II) to elemental gold, monitored potentiometrically.
• Complexation of Fe(III) with fluoride ions to shift the redox potential and prevent interference.
• Addition of iodide to reduce Cu(II) to Cu(I) and release free iodine, which is then titrated back with Fe(II).

Sample digestion involves acid treatment (HCl and HNO3) of bath samples or alloy digests under controlled evaporation. Instrumentation includes typical titration systems such as the 702 SET/MET Titrino or 716 DMS Titrino coupled with a Pt Titrode, magnetic stirrer and precision dosing modules.

Main results and discussion

The potentiometric curves furnish two well-defined equivalence points: the first for gold consumption and the second for iodine consumption corresponding to copper. Typical reagent concentrations and titrant parameters yield accurate detection limits and reproducible results. Calculations use the equivalence volume (EP1) and the known titer to derive metal concentrations in mg/L, with 1 mL of 0.1 M Fe(II) equivalent to 6.566 mg Au or 6.355 mg Cu.

Benefits and practical applications

The combined titration offers rapid throughput by avoiding separate assays for gold and copper. It is adaptable for routine quality control in plating operations and for compositional analysis of alloys after digestion. The method minimizes sample handling and reagent consumption while delivering trace-level accuracy.

Future trends and potential applications

Advances in automated titration systems, integration with flow analysis and coupling to data management platforms will further enhance method efficiency. Potential extensions include on-line monitoring of plating baths and adaptation to additional metal ions through tailored redox chemistry.

Conclusion

The described potentiometric titration method provides a reliable, cost-effective tool for simultaneous quantification of gold and copper in industrial samples. Its simplicity, speed and precision make it well-suited for quality assurance in metallurgical and plating contexts.

Used instrumentation

• Automated titrators: 702 SET/MET, 716 DMS, 736 GP, 751 GPD, 785 DMP Titrino or 726 Titroprocessor with 685 Dosimat/700 Dosino
• Pt Titrode with appropriate electrode cable
• Magnetic stirrer and exchange unit (10 mL PCTFE/PTFE stopcock)

References

• C. Mahr, B. Seeger. Titrationsverfahren mittels Redoxverschiebung. I. Die massanalytische Kupferbestimmung mit Fe(II)sulfat. Fresenius Z. Anal. Chem. 171 (1959) 343–349.
• S. K. Cirkov, V. S. Romanova. Eine elektrometrische Methode ohne Kompensation zur Goldbestimmung mit Mohr’scher Salzlösung. Zh. Anal. Khim. 14 (1959) 198–201. Ref.: Fresenius Z. Anal. Chem. 173 (1960) 233.
• S. Wolf. Die Bestimmung von Gold und Kupfer in galvanischen Bädern durch potentiometrische Titration. Galvanotechnik 63 (1962) 302–304.