Determination of nickel in gold and silver plating baths by potentiometric titration

Significance of the Topic

The concentration of nickel in gold and silver plating baths is crucial to maintain plating quality, adhesion, and corrosion resistance. Precise quantification ensures consistent bath composition, reduces waste, and prevents defective coatings in industrial applications.

Objectives and Overview

This bulletin presents a potentiometric titration method for determining Ni(II) in electroplating solutions. The procedure involves removal of gold and silver interferences, complexation of nickel with cyanide, and potentiometric endpoint detection. The approach is also adaptable for nickel analysis in alloys and related matrices.

Methodology and Instrumentation

• Sample Preparation:
  – Digest 10 mL plating bath with 10 mL HCl, evaporate to one quarter volume, add HNO₃ until solids dissolve, evaporate again, and dilute to 50 mL.
• Reagents:
  – 0.2 M KCN titrant standardized against Ni standard.
  – 0.01 M Ni standard solution.
  – 2% hydrazine sulfate solution.
  – 25% NH₃ solution.
  – Concentrated HCl and HNO₃ for sample digestion.
• Titration Procedure:
  – Pipette 10 mL of prepared sample, add water, ammonia, and hydrazine, boil briefly, cool, and titrate with 0.2 M KCN while monitoring potential.

Used Instrumentation

• Titrino or Titrando titrator with Dosino/Dosimat dosing unit.
• Magnetic swing-out stirrer.
• Electrode exchange unit.
• Silver titrode coated with Ag₂S and compatible cable.

Main Results and Discussion

The method exhibits a linear titration response, where 1 mL of 0.2 M KCN corresponds to 2.935 mg Ni. A representative analysis of a silver plating bath yielded 0.56 g/L Ni, demonstrating precise endpoint detection. Chemical reduction effectively removes gold and silver interferences, providing high selectivity for nickel. The technique’s reproducibility and sensitivity align with industrial QA/QC standards.

Benefits and Practical Applications of the Method

• Rapid and reliable determination of nickel in electroplating solutions.
• High selectivity due to removal of Au and Ag interferences.
• Automatable potentiometric endpoint detection.
• Applicability to diverse sample matrices, including alloys.

Future Trends and Potential Applications

Future developments may focus on replacing toxic cyanide complexing agents with safer alternatives, integrating inline and real-time process monitoring, miniaturizing titration setups, and linking titration data with digital process control systems for enhanced bath management.

Conclusion

The described potentiometric titration method provides a robust, accurate, and efficient approach for quantifying nickel in gold and silver plating baths. Its automation potential and adaptability make it well suited for routine industrial analysis, ensuring consistent plating quality and effective process control.

Reference

• Trepka-Bloch, E. Potentiometrische Bestimmung von Nickel neben Ag, As, Bi, Co, Cu und Fe. Chemist Analyst 43 (1954) 63–65; Fresenius Z. Anal. Chem. 147 (1955) 143.
• Luke, C. L. New rapid method for the determination of nickel in ferrous and ferromagnetic metals. Anal. Chem. 33 (1961) 96–98.