Determination of hydrochloric and nitric acid in etching baths by thermometric titration

Importance of the Topic

In industrial etching processes, precise monitoring of acid concentrations in bath solutions is crucial to maintain consistent surface treatment, protect equipment, and minimize environmental impact. Thermometric titration provides a rapid, robust, and cost-effective method to quantify total acidity and to distinguish between hydrochloric and nitric acids.

Objectives and Study Overview

This application note describes a two-step thermometric titration protocol for simulated etching baths. The first titration determines the total acid content using sodium hydroxide. The second titration selectively quantifies hydrochloric acid via precipitation with silver nitrate, with the difference yielding the nitric acid concentration.

Methodology and Instrumentation

Sample preparation is minimal: defined volumes of sample solution are diluted with deionized water. Temperature changes are recorded continuously during titrant addition to detect the exothermic endpoints.

Instrumentation:

• 859 Titrotherm system
• 804 Ti Stand
• 800 Dosino dosing units (three channels)
• 5 mL, 10 mL and 50 mL dosing units

Reagents:

• 2 mol/L NaOH (80 g NaOH per liter of deionized water)
• 1 mol/L AgNO₃ (84.935 g AgNO₃ in 500 mL of deionized water)
• 4 mol/L HNO₃ (387.75 g concentrated HNO₃ in 1 L of deionized water)

Operating parameters include stirring at 10 rpm, dosing at 4 mL/min, filter factor 60, and optimized endpoint slope criteria to ensure reproducible detection.

Results and Discussion

Spiked samples with HCl:HNO₃ ratios ranging from 90:10 to 10:90 were analyzed (n=5). Recoveries for HCl ranged from 102.2 % to 106.3 % with relative standard deviations (RSD) up to 2.56 %. Recoveries for HNO₃ ranged from 96.3 % to 104.8 % (RSD up to 2.46 %). These results demonstrate the method’s accuracy and precision across a broad composition range.

Benefits and Practical Applications

• Fast and reliable determination of total and individual acid concentrations without extensive sample treatment.
• High accuracy and precision suitable for quality control in industrial etching operations.
• Utilization of standard laboratory titration equipment and common reagents.

Future Trends and Potential Applications

Integration of automated sampling and data evaluation could enable real-time monitoring and feedback control. The approach may be extended to other mixed-acid systems and adapted for portable or in-line thermometric probes in process analytics.

Conclusion

The described thermometric titration method offers a straightforward, accurate, and reproducible solution for quantifying hydrochloric and nitric acids in etching baths, improving process control and ensuring consistent product quality.

References

• Application Note H–136: Determination of Hydrochloric and Nitric Acid in Etching Baths by Thermometric Titration, Version 1