Determination of Mercury in a Certified Reference Sludge Material using the Agilent 710-ES

Significance of the Topic

A reliable determination of mercury in environmental matrices is critical because of mercury’s high toxicity and tendency to bioaccumulate. Human activities such as coal combustion, waste incineration and metal smelting have substantially increased atmospheric and aquatic mercury levels. Sewage sludge often contains elevated mercury concentrations and is increasingly used as agricultural fertilizer, raising concerns about soil contamination and subsequent exposure pathways.

Objectives and Study Overview

This study aimed to develop and validate a sensitive, interference-free procedure for quantifying total mercury in a certified reference sludge (NBS 2781) by coupling an Agilent VGA-77P vapor generation accessory with an Agilent 710-ES ICP-OES system. Results were compared against certified values using both external calibration and standard addition approaches.

Methodology and Instrumentation

Sample Preparation:

• Approximately 0.1 g of NBS 2781 sludge was digested with a 2:1 mixture of nitric and hydrochloric acids on a hot plate until fumes ceased.
• Digests were cooled, filtered, diluted to 50 mL and treated with antifoam.

Vapor Generation and ICP-OES Conditions:

• VGA carrier gas: argon.
• Reducing agent: 25 % SnCl₂ in 20 % HCl; flow rates—sample 8 mL/min, reductant 1 mL/min, acid/water 1 mL/min.
• ICP power: 0.9 kW; plasma gas 13.5 L/min; auxiliary gas 1.5 L/min; nebulizer pressure 240 kPa.
• Glass concentric nebulizer, cyclonic spray chamber, axial torch, CCD detector; replicate read time 5 s, delay 20 s, stabilization 30 s.

Main Results and Discussion

Detection limits (30 s reads) for the 184.887, 194.164 and 253.652 nm lines ranged from 0.020 to 0.023 µg/L, with the 253 nm line performing slightly better under reduced RF power. Short-term precision was 1–2 % RSD at 5 µg/L. Analysis of eight replicate aliquots of NBS 2781 yielded 3.40 ± 0.13 mg/kg Hg versus the certified value of 3.64 ± 0.25 mg/kg, corresponding to a 93 % recovery and demonstrating the method’s accuracy and lack of significant interferences.

Benefits and Practical Applications

• High sensitivity and low detection limits suitable for trace-level mercury in complex solids.
• Minimal chemical interferences evidenced by comparable slopes in external calibration and standard addition.
• Efficient sample throughput without an autosampler, thanks to stable vapor generation and optimized pump rates.

Future Trends and Possibilities

Advances may include integration of automated sample introduction, use of alternative reductants such as sodium borohydride for enhanced stability, and miniaturized field-deployable vapor generation–ICP-OES systems. Further exploration of carrier gases and lower-power plasma conditions may improve selectivity for challenging matrices.

Conclusion

The coupling of an Agilent VGA-77P vapor generator with a 710-ES ICP-OES provides a robust, accurate and sensitive approach for total mercury determination in sludge reference materials. The method’s performance aligns well with certified values, confirming its suitability for environmental monitoring and quality control.

References

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