Fast and Accurate Speciation of Mercury in Milk and Honey Food Products by HPLC-ICP-MS

Importance of the topic

Mercury is a globally recognized toxin of concern, with methylmercury ranking among the most hazardous forms due to its bioaccumulation in the food chain and neurotoxic effects. Monitoring inorganic mercury and methylmercury levels in widely consumed products such as milk and honey is critical to ensure compliance with regulatory limits and to protect public health.

Objectives and study overview

This study aimed to develop and validate a fast, accurate HPLC-ICP-MS method for speciation of inorganic mercury (Hg2+) and methylmercury (MeHg) in milk and honey, meeting the Food Safety and Standards Authority of India (FSSAI) limits (1.0 mg/kg total Hg, 0.25 mg/kg MeHg). The workflow integrates chromatographic separation and mass spectrometric detection using Agilent instrumentation.

Methodology and instrument used

Samples of full-fat milk and store-bought honey were diluted 20× in 0.1 % L-cysteine (pH 2.6) and heated with agitation. Calibration standards ranged from 0.05 to 10 µg/L.

• Chromatography: Agilent 1260 HPLC with ZORBAX SB C-18 column (4.6×250 mm, 3.5 µm), 1.2 mL/min, 50 µL injection, run time 7 min.
• Detection: Agilent 7850 ICP-MS with MicroMist nebulizer, quartz spray chamber, helium collision cell (KED), default autotune.
• Software: MassHunter for integrated HPLC control and chromatographic data analysis, including internal standard correction and automatic retention-time updates.

Main results and discussion

Calibration curves for Hg2+ and MeHg were linear (R2>0.9999) over 0.05–10 µg/L, with background equivalent concentrations of ~0.001 µg/L. Baseline separation was achieved in under 4 minutes. Limits of detection were 0.0035 µg/L for Hg2+ and 0.0038 µg/L for MeHg. No native Hg species were detected in unspiked samples. Spike recovery studies showed 98–101 % recovery in honey (n=9, RSD<2 %) and 95–102 % in milk (n=3 at 0.1, 0.5, 2.0 µg/L, RSD≤3 %). QC injections at 0.05 and 0.5 µg/L over 7 hours maintained precision below 4 % RSD.

Benefits and practical applications

This method offers:

• Rapid speciation of Hg forms in complex food matrices.
• High sensitivity and low detection limits for trace-level monitoring.
• Compliance with international and FSSAI regulations.
• Streamlined workflow with integrated software for routine QA/QC labs.

Future trends and opportunities

Advances in ICP-MS sensitivity and chromatographic media may enable simultaneous speciation of additional organometallic compounds. Automated sample preparation and data processing will further reduce analysis time and variability, supporting large-scale food safety monitoring and environmental assessments.

Conclusion

The validated HPLC-ICP-MS method on Agilent 1260/7850 instruments delivers rapid, reliable speciation of inorganic mercury and methylmercury in milk and honey, meeting regulatory requirements with excellent accuracy, precision, and throughput.

Reference

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• Food and Agriculture Organization of the United Nations. Gateway to Dairy Production and Products; accessed 2021.
• NationMaster. Natural Honey Production by Country; 2019.
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