Speciation of Methyl Mercury and Mercury in Honey using High Performance Liquid Chromatography hyphenated with Inductively Coupled Plasma Mass Spectrometry

Significance of Mercury Speciation in Honey

The determination of methyl mercury and inorganic mercury in honey is essential for food safety surveillance. Mercury compounds present severe neurotoxic risks, and regulatory authorities such as FSSAI set strict limits to protect consumers.

Objectives and Study Overview

This work aimed to develop and validate a rapid, sensitive method to quantify both methyl mercury and total mercury in honey samples, in compliance with FSSAI guidelines. The study demonstrates sample pretreatment, chromatographic separation, and detection by ICP–MS.

Methodology and Instrumentation

• Sample Preparation:
  About 0.5 g of honey was diluted with 0.1 % L-cysteine mobile phase (pH 2.5), vortexed, heated at 60 °C for 2 h, then cooled and filtered through a 0.45 µm nylon membrane.
• Standards Preparation:
  Methyl mercury (II) chloride and NIST-traceable Hg standard stocks (1000 ppm) were diluted in the mobile phase to yield calibration levels from 0.1 to 10 ppb. QC checks at 0.5 ppb monitored calibration drift.
• Chromatography:
  A Shimadzu Inert LC delivered mobile phase isocratically; species separation occurred within 5 min.
• Detection:
  ICP–MS 2030 provided element-selective quantification, achieving sub-ppb detection limits and robust plasma performance.

Main Results and Discussion

The calibration curves for both mercury species exhibited excellent linearity (R² ≥ 0.999). Chromatographic peaks were baseline resolved. Initial and continuous calibration verifications showed accuracies between 90 % and 100 %, confirming system stability and washout efficiency. Spike recovery tests at levels corresponding to 0.2, 0.5, and 1.0 ppb yielded recoveries within 80–120 % and RSDs below 5 %, demonstrating method precision and extraction efficiency. Measured concentrations in honey samples were below the 4 ppb threshold.

Benefits and Practical Applications

This HPLC–ICP–MS approach offers:

• Rapid throughput: complete speciation in under 5 minutes per sample.
• High sensitivity and selectivity: reliable at low-ppb levels.
• Minimal sample preparation: simple aqueous extraction.
• Routine applicability: suitable for QA/QC in food safety laboratories.

Future Trends and Potential Uses

Emerging directions include automating sample preparation to further increase throughput, coupling with high-resolution mass spectrometers for isotopic analysis, and extending the approach to other food matrices and environmental samples. Integration with data-processing software can streamline compliance reporting.

Conclusion

The developed method effectively quantifies methyl mercury and inorganic mercury in honey with high accuracy, precision, and speed. It meets regulatory requirements and is well suited for routine monitoring to ensure consumer safety.

Instrumentation Used

• Shimadzu Inert LC system
• Shimadzu ICP–MS 2030