Cobalt analysis by automated photometric titration

Importance of the Topic

Cobalt is a widely used transition metal in battery technology, catalysts, and alloys. Accurate quantification of cobalt in aqueous solutions underpins quality control in industrial processes and environmental monitoring. Automated photometric titration provides a robust, precise, and reproducible approach for routine cobalt determination.

Objectives and Study Overview

The primary aim of this study is to demonstrate an automated, photometric titration procedure using EDTA at pH 9 for direct cobalt analysis. Key goals include achieving high precision, minimizing sample preparation, and validating the method’s suitability for routine laboratory application.

Methodology and Instrumentation

A 5.0 mL aliquot of cobalt-containing sample is diluted with 90 mL of deionized water. The solution is conditioned with 5 mL of pH 9 buffer and 5 mL of murexide indicator. Titration is carried out with 0.1 M Na2EDTA. Endpoint detection is performed photometrically at 574 nm using an Optrode.
Key operational parameters:

• Titration mode: MET U
• Pause before titration: 30 s
• Stirring rate: 8
• Signal drift limit: 50 mV/min
• Minimum/maximum waiting time: 5 s / 26 s
• Volume increment: 0.1 mL
• Endpoint criterion: 15 mV, detected by the greatest change
• Stop volume: 10 mL

Instrumentation Used

• Metrohm 907 Titrando
• Metrohm 815 Robotic USB Sample Processor XL with swing head
• Metrohm Dosino units (5 mL, 10 mL, 50 mL)
• Metrohm Optrode photometric sensor (574 nm)
• Disposable 200 mL polypropylene beakers

Main Results and Discussion

Five replicate titrations yielded an average cobalt concentration of 3.205 g/L with a relative standard deviation of 1.51%. The low dispersion indicates excellent repeatability. The photometric endpoint provides clear detection without interference, and the automated dosing ensures consistent reagent delivery.

Benefits and Practical Applications

• High precision and reproducibility through automation.
• Minimal sample preparation and reagent consumption.
• Rapid analysis time suitable for high-throughput QA/QC.
• Applicability to environmental monitoring and industrial process control.

Future Trends and Potential Applications

Advancements may include coupling photometric titration with flow injection analysis, miniaturized sensor arrays for field measurements, and integration into laboratory information management systems (LIMS). Expanding the method to multi-element titrations and on-line process monitoring could further enhance its utility.

Conclusion

The automated EDTA photometric titration method at pH 9 delivers accurate, precise, and efficient cobalt analysis. Its automation and minimal user intervention make it ideal for routine laboratory work in various industrial and environmental settings.

References

• Metrohm Application Note T–143: Cobalt analysis by automated photometric titration