Determination of Methyl Mercury in Water and Soil by HPLC-ICP-MS

Significance of the Topic

Mercury contamination poses serious health and environmental risks due to its bioaccumulative nature and varying toxicity depending on chemical form. Methylmercury (MeHg) is the most toxic species and readily crosses the blood–brain barrier, posing particular risk to fetal development. Accurate speciation of inorganic and organic mercury in water and soil is essential for risk assessment and regulatory compliance.

Objectives and Study Overview

This study aimed to develop and validate a robust, sensitive, and species-specific analytical method combining high-performance liquid chromatography (HPLC) with inductively coupled plasma mass spectrometry (ICP-MS) for determination of MeHg, ethylmercury (EtHg), and inorganic Hg²⁺ in aqueous and solid environmental samples. Key goals included low method detection limits (MDLs) below 10 ng/L, reliable calibration over a wide concentration range, and simple sample preparation for soil matrices.

Methodology and Used Instrumentation

• HPLC System: Agilent 1100 with a ZORBAX Eclipse XDB-C18 column (2.1×50 mm, 5 µm), degasser, quaternary pump, autosampler.
• Mobile Phase: 0.06 M ammonium acetate, 5 % methanol, 0.1 % 2-mercaptoethanol, pH 6.8; flow rate 0.4 mL/min; injection volumes 20, 100, or 1000 µL.
• ICP-MS System: Agilent 7500a with PFA concentric nebulizer, chilled Scott spray chamber (–5 °C), quartz torch; RF power 1550 W; carrier gas 0.75 L/min; sampling depth 4.5 mm.
• Water Samples: Direct injection of standards and samples; matrix tolerance tested in 3 % NaCl.
• Soil Samples: 1 g soil extracted with 7.6 % HCl and 10 % 2-mercaptoethanol, ultrasonic bath (30 min), centrifugation, pH adjustment to 6.8, dilution to 20 g, filtration (0.45 µm).

Main Results and Discussion

Chromatographic separation achieved baseline resolution for MeHg (≈2.5 min), Hg²⁺ (≈3.2 min), and EtHg (≈6.5 min). Calibration was linear over four orders of magnitude (10 ng/L to 100 µg/L) with R² > 0.9985. MDLs for all species were better than 10 ng/L without extensive preconcentration. In 3 % NaCl matrix, recoveries remained within 90–110 %. Soil spike recoveries ranged from 80 % to 120 %, confirming effectiveness of the simple acid extraction procedure.

Benefits and Practical Applications of the Method

• Element-specific detection with compound independence ensures accurate quantitation of known and unknown Hg species.
• Low MDLs and wide linear range allow direct analysis of natural waters, industrial effluents, and saline matrices without complex enrichment.
• Simple soil extraction reduces analysis time and reagent consumption compared to traditional digestion techniques.
• Method supports regulatory monitoring, food safety assessments, and environmental risk studies.

Future Trends and Potential Applications

The HPLC-ICP-MS approach may be further enhanced by automated on-line preconcentration, miniaturized extraction techniques, and coupling with species-specific derivatization for ultra-trace quantitation. Expansion to other matrices—such as sediments, biota, and food products—will address emerging regulatory needs. Integration into field-deployable platforms and real-time monitoring systems represents a promising direction.

Conclusion

A sensitive and selective HPLC-ICP-MS method for MeHg, EtHg, and inorganic Hg in water and soil has been established, achieving MDLs below 10 ng/L, excellent linearity, and reliable recoveries. The straightforward sample preparation and strong matrix tolerance make it well-suited for routine environmental speciation analysis.

References

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