Simultaneous Mercury and Tin Speciation using GC-HR-ICP-MS

Importance of the Topic

Speciation of trace elements such as mercury and tin is essential for understanding their environmental behavior, toxicity and mobility. Total element concentrations alone cannot predict reactivity or bioaccumulation potential. Ultra-trace speciation is critical in water, sediments and biota to assess risks from toxic forms such as methylmercury and organotins.

Objectives and Study Overview

This study demonstrates a method for simultaneous determination of mercury and tin species at ultra-trace levels using capillary gas chromatography coupled to high-resolution sector field ICP-MS (GC-HR-ICP-MS). The aim is to achieve rapid separation, robust quantification and low detection limits for multiple toxic species in a single 14-minute run.

Methodology

• Derivatization: Aqueous calibration standards (0.1–2.0 ng mL⁻¹) are reacted with 1% sodium tetraethylborate in hexane at pH 4.9 for 5 minutes.
• GC Separation: TRACE™ TR-5 column (30 m × 0.25 mm i.d., 0.25 µm) with PTV splitless injection (1 µL), initial oven at 50 °C (1 min), ramp at 30 °C min⁻¹ to 300 °C (1 min). Carrier gas He at 2 mL min⁻¹, make-up gas Ar at 600 mL min⁻¹.
• Detection: Sector field ICP-MS operated in “Speed” mode (R = 300) monitoring isotopes 200Hg, 202Hg, 118Sn, 120Sn, 121Sb, 123Sb, 203Tl, 205Tl. Data acquired at 146 ms per scan over 14 min, with continuous infusion of 5 ng mL⁻¹ Sb/Tl standard for stability monitoring.

Instrumentation

• Thermo Scientific TRACE GC Ultra with AS3000 autosampler and GC Interface Kit
• Thermo Scientific ELEMENT 2 HR-ICP-MS
• Glass Expansion MicroMist nebulizer and Twinnabar mini-cyclonic spray chamber
• Dual-mode sample introduction for simultaneous volatile and aqueous delivery

Main Results and Discussion

The method successfully separated two mercury species (MeHg⁺, Hg²⁺) and seven tin derivatives (InSn, MBT, DBT, TBT, MPhT, DPhT, TPhT) in a single chromatogram. Limits of detection (3σ) ranged from 0.7 to 7.3 ng L⁻¹ in hexane extracts, with blank equivalent concentrations indicating sub-ppt to low-ppt background. Continuous internal standard infusion ensured consistent plasma stability and quantification precision.

Benefits and Practical Applications

• High sensitivity enables measurement at environmental ultra-trace levels, suitable for seawater, sediments and biota.
• Multi-element speciation in one run increases laboratory throughput and reduces sample volume and reagent use.
• Robust dual-mode introduction maintains plasma stability and allows real-time quality control via internal standards.

Future Trends and Potential Applications

Advances may include coupling GC-HR-ICP-MS with other separation techniques (LC-GC hyphenation), miniaturized or field-deployable interfaces, and expansion to additional trace element species (e.g., arsenic, selenium). Improved automation and data processing will further streamline ultra-trace speciation in environmental monitoring and food safety.

Conclusion

A GC-HR-ICP-MS method using the Thermo Scientific ELEMENT 2 and dedicated GC coupling achieves rapid, sensitive and reliable speciation of mercury and tin compounds at ppt levels. The approach is well suited for multi-species analysis in complex environmental matrices.

References

No external literature references were cited in this application note.