Potentiometric analysis of acidic lead and lead/tin plating baths

Importance of the Topic

Potentiometric titration methods are essential for precise control of plating bath compositions in electroplating operations. Accurate determination of lead, tin(II) and free fluoroboric acid ensures consistent deposit quality, optimal bath performance and compliance with environmental regulations.

Study Objectives and Overview

This bulletin presents robust analytical protocols for quantifying key species in acidic lead and lead/tin plating baths. The objectives are to establish automated titration procedures that deliver reproducible results, reduce manual intervention and adapt to industrial quality control requirements.

Methodology and Instrumentation

Three analytes are determined using dedicated titration approaches:

• Lead: complexometric titration with 0.1 mol/L Na₂EDTA at pH 10, monitored by a copper ion-selective electrode (Cu ISE).
• Tin(II): iodometric titration with 0.05 mol/L I₂ under nitrogen, using a platinum electrode (Pt Titrode).
• Free fluoroboric acid: acid–base titration with 1 mol/L NaOH, endpoint detected by a double-junction pH glass electrode at pH ≈ 3.2.

Used Instrumentation

• Metrohm Titrino or Titrando titrator with Dosino/Dosimat dosing units
• Magnetic stirrer
• Copper ion-selective electrode and double-junction Ag/AgCl reference electrode
• Combined pH glass electrode with separable ground-joint diaphragm
• Pt Titrode for redox titration
• Exchange unit for NaOH reagent delivery

Main Results and Discussion

The complexometric titration of lead shows a sharp potential jump at the EDTA equivalence point, enabling accurate quantification (1 mL EDTA = 20.72 mg Pb). Iodometric titration of Sn(II) under nitrogen yields reproducible endpoints with 1 mL I₂ = 5.93 mg Sn(II). The neutralization curve of free HBF₄ exhibits a clear inflection at pH 3.2, corresponding to 87.81 mg HBF₄ per mL NaOH.

Benefits and Practical Applications

• Automated titration reduces operator variability and increases sample throughput in QA/QC laboratories.
• Selective electrodes ensure high specificity in complex acidic matrices.
• Protocols can be transferred to other metal plating baths with minimal adaptation.

Future Trends and Opportunities

Advances in miniaturized potentiometric sensors and flow-through titration systems will enable inline, real-time monitoring of plating baths. Integration with digital laboratory information management systems (LIMS) can provide comprehensive process analytics and predictive maintenance capabilities.

Conclusion

The described potentiometric methods deliver fast, reliable and automated analysis of acidic lead and lead/tin plating baths. Their implementation supports consistent plating performance, improved process control and streamlined quality assurance.

Reference

• Metrohm Application Bulletin No. 101 Complexometric Titrations with the Cu-ISE, Metrohm Ltd., Herisau
• Metrohm Application Note T-21 Sn(II) and Sulfuric Acid in Tin Plating Bath, Metrohm Ltd., Herisau
• Metrohm Application Note T-24 Metal Contents of Alkaline Plating Baths for Cadmium, Copper, Lead or Zinc, Metrohm Ltd., Herisau
• P. W. Wild Modern Analyses for Electroplating, Eugen G. Leuze Verlag, Saulgau, 1972
• T. W. Jelinek Process-Oriented Analytics in Electroplating, Eugen G. Leuze Verlag, Saulgau, 1999