Mercury Speciation Determinations in Asian Dietary Supplements

Significance of the topic

Mercury contamination in dietary supplements poses serious health risks due to the high toxicity of some organomercury species. Differentiating between inorganic and organic mercury forms is essential for accurate risk assessment and food safety evaluation.

Objectives and overview of the study

This work aimed to demonstrate cost-effective ion chromatography solutions for simultaneous determination of mercury species and counter anions in extracts from Asian dietary supplements. The study addressed the need for speciation data to explain clinical mercury poisoning incidents linked to adulterated supplements.

Methodology and instrumentation

Sample Preparation:

• Grinding of tablets into a coarse powder.
• Five-minute manual extraction in 20 mL cysteine–perchlorate buffer for mercury speciation.
• Water extraction for counter anion analysis.
• Filtration and dilution prior to injection.

Chromatographic Methods:

• Mercury speciation by ion-pairing chromatography on a mixed-mode CS5A column with 1 mM acetic acid, 1 mM sodium perchlorate and 5 mM cysteine eluent, UV detection at 210 nm.
• Counter anions and organic acids by high-capacity AS11-HC column using electrolytically generated KOH gradient, detected by suppressed conductivity.

Main results and discussion

Mercury Speciation:

• All five supplement samples contained 0.05–0.23 wt % extractable inorganic Hg (Hg2+).
• No methylmercury or ethylmercury detected above method detection limits.
• Sample 2 exhibited the highest inorganic mercury level (0.226 wt %).

Counter Anions:

• Chloride (0.08–1.62 wt %) and sulfate (0.24–1.82 wt %) were predominant.
• Minor amounts of nitrate, formate, acetate, oxalate, phosphate and citrate were observed.

Benefits and practical applications

• Provides a complete workflow for both speciation and mass balance calculations.
• Low-cost integrated IC systems deliver reliable separation and quantitation without complex eluent preparation.
• Complements ICP techniques by distinguishing mercury species, improving toxicity assessment.

Future trends and potential applications

• Integration with mass spectrometric detection for enhanced sensitivity and lower detection limits.
• Development of miniaturized or portable IC platforms for on-site screening.
• Extension to other toxic metal species in complex food and environmental matrices.
• Automation and high-throughput analysis to support large-scale quality control programs.

Conclusion

Ion chromatography methods demonstrated here offer a robust, cost-effective solution for mercury speciation and counter-anion profiling in dietary supplements. The clear identification of inorganic mercury as the sole extractable species underscores the importance of speciation in food safety evaluations.

References

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4. Dionex Application Note AN 131. Determination of Transition Metals at PPT Levels in High Purity Water and SC-2 Baths. Thermo Fisher Scientific, Sunnyvale, CA, 1998.