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

Significance of the Topic

The accumulation of mercury in seafood presents a serious health concern, as different chemical forms exhibit distinct toxicities. Methylmercury, in particular, is highly neurotoxic and bioaccumulates in fish. Reliable speciation analysis is therefore essential to assess dietary exposure accurately and enforce safety standards.

Goals and Overview of the Study

This study aimed to develop and validate a robust method for the simultaneous speciation and quantification of inorganic mercury, methylmercury, and ethylmercury in seafood samples. The approach integrates high‐performance liquid chromatography (HPLC) with inductively coupled plasma mass spectrometry (ICP‐MS) and demonstrates an automated calibration workflow using an autosampler’s automatic dilution function.

Methodology

Sample Preparation:

• Homogenize ca. 0.25 g of tuna tissue and spike with mercury standards for recovery tests.
• Extract with aqueous 1 % (w/v) L-cysteine·HCl solution at 60 °C for 120 minutes, with intermittent mixing.
• Cool, filter (0.45 µm), and transfer the extract to HPLC vials.

Calibration and Quantification:

• Prepare calibration standards in the range 0.5–20 µg/L by diluting stock solutions of inorganic and alkyl mercury.
• Use thallium internal standard (100 µg/L) for signal correction.
• Calculate limits of detection (LOD) from repeated analysis of 0.2 µg/L standards (3σ criterion).

Autosampler Automatic Dilution:

• Program the autosampler to aspirate defined volumes of stock solution and diluent into mixing vials.
• Generate calibration standards automatically (0.5–20 µg/L), reducing manual labor and error.

Used Instrumentation

• ICPMS-2050 inductively coupled plasma mass spectrometer with cyclonic spray chamber, nickel cones, and helium collision gas.
• Nexera XS inert HPLC system equipped with an autosampler featuring an automatic dilution function.
• Shim-pack Scepter C18-120 metal-free column (150 mm×4.6 mm, 5 µm) and LabSolutions ICPMS TRM software for unified control of chromatographic and ICP-MS operations.

Main Results and Discussion

Chromatographic Separation and Calibration:

• Baseline separation of inorganic mercury, methylmercury, and ethylmercury achieved within 6 minutes.
• Calibration curves exhibited excellent linearity (r>0.9999) across all species.
• LODs: inorganic 0.02 µg/L, methyl 0.01 µg/L, ethyl 0.03 µg/L.

Seafood Analysis and Recovery:

• Methylmercury concentration in tuna extract: 6.16 µg/L (0.614 mg/kg); total mercury: 6.48 µg/L (0.646 mg/kg).
• Spike recoveries: 102 % for methylmercury; 105 % for total mercury, confirming method accuracy.

Automatic Dilution Performance:

• Calibration standards prepared automatically showed correlation coefficients >0.9997.
• Accuracy of 1 µg/L standards: 1.02 % (inorganic), 1.05 % (methyl and ethyl); repeatability RSD: 1.6–4.0 %.

Benefits and Practical Applications

The combined LC-ICP-MS system and automated dilution workflow deliver:

• High sensitivity and selectivity for mercury species in complex matrices.
• Streamlined calibration and sample preparation, reducing hands-on time and operational variability.
• Enhanced data reliability for regulatory compliance, food safety monitoring, and research applications.

Future Trends and Potential Applications

Advances may include:

• Extension to other food matrices and environmental samples for broader speciation monitoring.
• Integration with lab informatics for real‐time data processing and remote instrument control.
• Further automation of sample pretreatment and multi-element speciation workflows.

Conclusion

This study demonstrates a validated LC-ICP-MS method for accurate speciation of mercury in seafood, supported by an autosampler’s automatic dilution function. The approach achieves excellent sensitivity, linearity, and reproducibility, offering a practical solution for routine laboratory analysis and regulatory testing.

References

1. 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).
2. CODEX GENERAL STANDARD FOR CONTAMINANTS AND TOXINS IN FOOD AND FEED (CODEX STAN 193-1995).