Mercury analysis by automated photometric titration

Significance of the topic

Mercury is a toxic heavy metal with serious environmental and health impacts. Reliable quantification of mercury in natural and industrial samples is critical for regulatory compliance, pollution monitoring, and risk assessment. Automated photometric titration enhances precision and efficiency in routine mercury analysis.

Study objectives and overview

This application note presents an automated back-titration method for determining mercury in alkaline media. Using zinc sulfate as titrant and eriochrome black T as indicator, the procedure aims to deliver accurate and reproducible results with minimal manual intervention.

Methodology

Key steps of the titration protocol:

• Sample handling: No pre-treatment required; pipette 5 mL of 0.05 mol/L Hg solution into a 200 mL beaker.
• Reagent addition: Add 90 mL deionized water, 5 mL ammonia buffer (pH 10), 5 mL 0.1 mol/L Na2EDTA, and 1 mL eriochrome black T indicator solution.
• Back-titration: Titrate with 0.1 mol/L ZnSO4 until the photometric endpoint at 502 nm is reached.

Used Instrumentation

The automated setup included:

• 907 Titrando titrator with swing head and dedicated titration head
• 815 Robotic USB Sample Processor XL
• 800 Dosino dosing units (5×) and various volume dosing units (5 mL, 10 mL, 20 mL, 50 mL)
• 802 Stirrer and disposable 200 mL polypropylene beakers
• 6.1115.000 Optrode photometric sensor operating at 502 nm

Main results and discussion

Five replicate determinations yielded a mean mercury concentration of 8.704 g/L with a relative standard deviation of 0.47%. The high precision demonstrates the robustness of the automated photometric endpoint detection. Only Hg(II) species are quantified, since Hg(I) disproportionates in the presence of EDTA.

Benefits and practical applications

Key advantages of the method include:

• Fully automated workflow reducing operator time and errors
• Photometric endpoint detection for sharp and reproducible titration curves
• No complex sample preparation steps
• High throughput suitable for routine QA/QC laboratories

Future trends and applications

Potential developments may include coupling this titration approach with on-line sample pretreatment for speciation analysis, miniaturization in microfluidic platforms, and portable photometric titrators for field deployments.

Conclusion

The described automated photometric back-titration protocol offers a reliable, precise and efficient solution for mercury determination in alkaline media. Its ease of operation and high reproducibility make it well suited for routine environmental and industrial monitoring.

Reference

Titration Application Note T-144, Metrohm, Version 1