Automated photometric determination of gallium using the Optrode

Importance of the topic

Automated photometric titration of trace metals such as gallium delivers fast, precise and reproducible results essential for quality control in semiconductor, alloy and chemical production. By combining titration with photometric endpoint detection, laboratories can minimize operator influence, increase throughput and ensure consistent data for regulatory compliance.

Objectives and Study Overview

This application note describes a back-titration method for gallium at pH 4.7 using zinc sulfate and xylenol orange as indicator. The aim is to demonstrate accurate endpoint detection with the Optrode photometric sensor at 610 nm and to provide performance data for routine analysis.

Methodology and Instrumentation

The sample (10–30 mL gallium solution) is mixed with water, buffer (pH 4.7), EDTA (0.1 M) and xylenol orange. After equilibration, the mixture is titrated with ZnSO4 (0.1 M) until the photometric signal shift signals the endpoint.

• Automated titrator: 907 Titrando
• Optrode sensor at 610 nm
• Robotic sample processor and swing head
• Dosing units (5, 10, 20, 50 mL)
• Buffer: ammonium acetate/acetic acid pH 4.7
• Titrant: ZnSO4·7 H2O (0.1 M)

Main Results and Discussion

Replicate measurements (n=3) yielded a mean gallium concentration of 0.61 g/L with a relative standard deviation of 0.51%. The photometric endpoint detection provided sharp signal jumps (>15 mV) and stable baselines, demonstrating robustness across the tested range.

Benefits and Practical Applications

This automated approach reduces manual steps, offers high precision, and integrates easily into quality assurance workflows for metal analysis. It is particularly valuable in industries requiring tight control of gallium content.

Future Trends and Applications

Advances in sensor technology and software algorithms will further enhance sensitivity and speed. Integration with inline process analytics and cloud-based data management will support real-time monitoring in manufacturing environments.

Conclusion

The described automated photometric titration method delivers reliable, reproducible gallium determination with minimal operator effort, making it suitable for high-throughput laboratories.

References

Metrohm Application Note T–158, Automated photometric determination of gallium using the Optrode. Version 1