Cadmium analysis using automated photometric titration

Importance of the topic

Cadmium is a heavy metal pollutant with significant environmental and health risks. Accurate and reliable quantification of cadmium in aqueous samples is essential for environmental monitoring, industrial quality control and regulatory compliance.

Objectives and overview

This application note describes an automated photometric back-titration method for the determination of cadmium in aqueous solutions. The procedure uses zinc sulfate as titrant, Eriochrome Black T as indicator and optical detection at 610 nm, integrated in a robotic titration system.

• Quantitative determination of Cd2+ via back-titration with ZnSO4.
• Use of Eriochrome Black T indicator monitored by an Optrode photometric sensor.
• Automation employing a robotic sample processor to enhance reproducibility and throughput.

Methodology and instrumentation

No sample pretreatment is required. A 5–15 mL aliquot of sample is pipetted into a 200 mL beaker, diluted with water, and sequentially dosed with ammonia buffer (pH 10), EDTA solution (0.1 mol/L) and indicator solution. The mixture is titrated with 0.1 mol/L ZnSO4 until the photometric endpoint at 610 nm is reached.

• Instrumentation:
• 907 Titrando titrator in MET U mode.
• 815 Robotic USB Sample Processor XL with 786 Swing head.
• 800 Dosino dosing units (5 mL, 10 mL, 50 mL) and 802 magnetic stirrer.
• Optrode photometric sensor, sample rack and disposable PP beakers.
• Reagents:
• Zinc sulfate heptahydrate titrant (0.1 mol/L) acidified with H2SO4.
• EDTA solution (0.1 mol/L).
• Ammonia buffer (pH 10) and Eriochrome Black T indicator solution.

Main results and discussion

Six replicate analyses of a 0.05 mol/L cadmium standard yielded a mean concentration of 5.87 g/L with a relative standard deviation of 1.28%. The photometric endpoint detection at 610 nm provided clear signal changes and low drift, confirming the method’s precision and robustness.

Benefits and practical applications

• Fully automated workflow reduces manual handling and operator variability.
• Photometric detection ensures precise endpoint determination.
• Applicable to environmental monitoring, industrial QA/QC and routine trace metal analysis.

Future trends and possibilities

Potential developments include on-line monitoring of cadmium in effluents, integration with flow injection analysis systems and miniaturized sensor platforms. Advances in optical detection and data processing may further enhance sensitivity and analysis speed.

Conclusion

This automated photometric back-titration method provides a reliable, precise and user-friendly approach for cadmium quantification in aqueous samples, offering significant benefits for routine laboratory and industrial applications.

Reference

• METTLER TOLEDO. Titration Application Note T–153: Cadmium analysis using automated photometric titration. Version 1.