Speciation analysis of methylmercury via species specific isotope dilution GC-ICP-MS

Importance of the Topic

The development of accurate speciation methods for methylmercury is essential due to its high toxicity, persistence and ability to bioaccumulate in food chains. Detailed knowledge of mercury species supports environmental risk assessment, regulatory monitoring and protection of human and ecosystem health.

Objectives and Study Overview

• Evaluate the coupling of a Thermo Scientific Trace 1310 GC with Element 2 high-resolution ICP-MS via the GCI 200 interface for methylmercury speciation.
• Apply species-specific isotope dilution GC-ICP-MS for quantitative analysis of methylmercury in fish, water and sediment samples.
• Assess method accuracy, precision, detection limits and robustness across diverse environmental matrices.

Used Instrumentation

• Thermo Scientific Trace 1310 Gas Chromatograph
• Thermo Scientific Element 2 High-Resolution Inductively Coupled Plasma Mass Spectrometer
• Thermo Scientific GCI 200 GC-ICP Interface

Methodology and Instrumentation

• Sample preparation included alkaline digestion of dried fish (DORM-2), acid extraction of sediments and direct spiking of water samples with Me201Hg tracer.
• Isotope dilution tracer (Me201Hg) was added to each sample to achieve a 201Hg/202Hg ratio near unity, compensating for losses and side reactions.
• Propylation was performed using sodium tetrapropylborate followed by n-hexane extraction; optional evaporative preconcentration improved low-level detection.
• GC conditions: splitless injection of 1 µL, injector at 250 °C, CP-Sil 5CB column (15 m×0.25 mm×0.25 µm), oven program from 40 °C to 180 °C at 50 °C/min.
• ICP-MS conditions: low resolution, RF power 1150 W, Pt-tipped sampler and skimmer cones, monitoring 200Hg, 201Hg and 202Hg with 50 ms integration time.

Main Results and Discussion

• Isotope ratio measurements matched reference values within 1% deviation for natural abundances and within 2.7% for the enriched spike, confirming reliable mass bias control.
• Analysis of DORM-2 (certified 4.47 ±0.32 mg/kg MeHg) yielded 4.43 ±0.01 mg/kg (RSD ≤0.27%, recovery >98%), demonstrating excellent accuracy and precision.
• Limit of quantification reached 1 ng/L MeHg (peak area ~5000); evaporative preconcentration increased peak area to ~70000 and reduced uncertainty.
• Weser River water samples contained 0.059–0.082 ng/L MeHg after evaporation, with RSDs up to 28% due to low absolute mass injected.
• Sediment samples showed 0.64–2.31 µg/kg MeHg representing 0.28–0.88% of total Hg, consistent with expected environmental levels.

Benefits and Practical Applications

• Species-specific isotope dilution corrects for nonquantitative recoveries and sample preparation artefacts.
• High sensitivity and isotope information allow detection of side products and rigorous quality control.
• Rapid analysis time (~3.8 min per run) and compatibility with varied matrices support high sample throughput.
• Applicable for environmental monitoring, food safety testing and industrial quality control of mercury species.

Future Trends and Applications

• Integration of automated extraction and preconcentration systems to further lower detection limits and improve reproducibility.
• Expansion to multi-species organomercury profiling and coupling with chromatographic techniques for broader speciation.
• Development of portable or field-deployable GC-ICP-MS interfaces for on-site environmental assessments.
• Application in large-scale monitoring programs and regulatory frameworks to track mercury cycling and remediation efficacy.

Conclusion

The Thermo Scientific Trace 1310 GC coupled to Element 2 HR-ICP-MS via the GCI 200 interface provides a robust, accurate and precise platform for methylmercury speciation using species-specific isotope dilution. The method delivers low detection limits, short run times and strong quality control across biological, water and sediment samples, supporting diverse analytical needs in environmental and food safety contexts.

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