Speciation Analysis of Mercury in Seafood by LC-ICP-MS and Introduction of Autosampler Automatic Dilution Function

Significance of the topic

The accurate determination of mercury species in seafood is critical due to the bioaccumulative nature of mercury and its varying toxicity depending on chemical form. Methylmercury, often found in fish, poses significant health risks at low exposure levels, making speciation analysis essential for food safety, regulatory compliance, and public health protection.

Objectives and Overview

This study demonstrates a streamlined workflow for the speciation analysis of methylmercury and total mercury in seafood using a combined liquid chromatography–inductively coupled plasma mass spectrometry (LC-ICP-MS) system. A particular focus is the evaluation of an autosampler with an automatic dilution function to simplify calibration standard preparation and enhance laboratory efficiency.

Methodology

Sample preparation followed the FDA Elemental Analysis Manual (EAM 4.8). Tuna tissue (0.25 g) was homogenized, spiked for recovery testing, and extracted in 1 % L-cysteine•HCl solution at 60 °C for 120 minutes. After cooling, extracts were filtered (0.45 µm) and injected into the LC-ICP-MS system. Calibration standards for inorganic and alkyl mercuries were diluted to 0.5–20 µg/L. An internal standard (thallium, 100 µg/L) was used to correct instrumental drift. The mobile phase consisted of methanol and 0.01 M ammonium acetate (8:92) with L-cysteine at pH 7.5.

Used Instrumentation

• Inductively Coupled Plasma Mass Spectrometer: Shimadzu ICPMS-2040/2050
• High Performance Liquid Chromatograph: Shimadzu Nexera XS inert
• Chromatography Column: Shim-pack Scepter C18-120, metal-free (150 mm × 4.6 mm, 5 µm)
• Autosampler: Nexera XS inert with automatic dilution function
• Software: LabSolutions ICPMS TRM for system control and data analysis

Main Results and Discussion

Chromatographic separation of inorganic mercury, methylmercury, and ethylmercury achieved baseline resolution. Calibration curves over 0.5–20 µg/L exhibited excellent linearity (R²>0.9999). Limits of detection (3σ) were 0.02 µg/L for inorganic mercury, 0.01 µg/L for methylmercury, and 0.03 µg/L for ethylmercury. Analysis of tuna extracts yielded methylmercury at 6.16 µg/L and total mercury at 6.48 µg/L in solution, corresponding to 0.614 mg/kg and 0.646 mg/kg in tissue. Spike recoveries ranged from 102 % to 105 %, confirming method accuracy.

The automatic dilution function generated calibration standards from 0.5 to 20 µg/L by programming dilution ratios and mixing steps. Calibration prepared automatically showed high linearity (R²>0.9997) and good precision (RSD ≤4.0 %) and accuracy (1.02–1.05 %) for 1 µg/L standards.

Benefits and Practical Application

• Reliable quantification of mercury species in seafood for regulatory compliance and risk assessment
• Elimination of manual calibration preparation through autosampler automation, reducing hands-on time and potential errors
• Integrated software control for seamless operation from injection to data reporting

Future Trends and Possibilities

Advancements in autosampler robotics and in-line sample preparation are expected to further reduce manual handling and improve throughput. The integration of high-resolution ICP-MS and novel chromatographic materials may enhance sensitivity and expand speciation to other trace elements. Coupling real-time data analytics could support rapid decision-making in food safety monitoring.

Conclusion

The LC-ICP-MS method using Shimadzu’s ICPMS-2040/2050 and Nexera XS inert successfully achieved accurate speciation analysis of methylmercury and total mercury in seafood. The incorporation of an autosampler automatic dilution function simplifies calibration, maintains high analytical performance, and increases laboratory productivity.

References

• U.S. Food and Drug Administration. Elemental Analysis Manual 4.8: High Performance Liquid Chromatographic-Inductively Coupled Plasma-Mass Spectrometric Determination of Methylmercury and Total Mercury, Version 1.0, June 2008.
• Codex Alimentarius Commission. Codex General Standard for Contaminants and Toxins in Food and Feed (CODEX STAN 193-1995).