Combining the Synergies of Ion Chromatography and Inductively Coupled Plasma to Identify Mercury Contamination in Herbal Medicines

Importance of the Topic

Mercury contamination in herbal medicines poses significant health risks due to the neurotoxic effects and bioaccumulation of mercury species. Rapid and accurate identification of both total mercury content and chemical form is essential to diagnose poisoning incidents, guide clinical treatment, and prevent further exposure from contaminated products.

Objectives and Study Overview

This study aimed to combine ion chromatography speciation and inductively coupled plasma mass spectrometry screening to trace the source of a mercury poisoning cluster linked to herbal medicines. Investigators sought to reconcile the disparity between high total mercury ingestion and lower observed blood levels by determining the specific mercury species present in the products.

Methodology and Instrumentation

Sample Preparation and ICP-MS Screening

• Herbal tablets were ground, extracted with acidic eluent, filtered, and diluted.
• ICP-MS analysis followed EPA guidelines to quantify total mercury and lead in blood and product extracts.

IC Speciation Method

• Mobile phase: 1.0 mM acetic acid, 1.0 mM sodium perchlorate, 5 mM cysteine, pH 4.0.
• Column: mixed cation/anion Thermo Scientific Dionex IonPac CS5A.
• Flow rate: 1.75 mL/min; injection volume: 25 μL.
• Detection by UV absorbance at 210 nm; linear response established from 1 to 10 mg/L standards.

Used Instrumentation

• Dionex ICS-1600 Integrated Ion Chromatography System
• Dionex AS-AP Autosampler
• Dionex IonPac CS5A Column (4 × 250 mm) with CG5A Guard Column
• IC Series Variable Wavelength UV Detector
• ICP-MS system for total metal analysis

Main Results and Discussion

ICP-MS screening revealed extremely high total mercury concentrations in the herbal tablets (1–10 wt%), confirming adulteration. However, IC speciation detected only inorganic mercury species at 0.04–0.2 wt% and no methylmercury. The discrepancy was attributed to mercury sulfide ore (cinnabar) used as a coloring agent in tablet production. Insoluble in neutral water, cinnabar contributed to total mercury readings but had lower bioavailability, aligning with patient blood levels and clinical symptoms.

Benefits and Practical Applications

• Rapid multi-element ICP-MS screening identifies overall contamination and guides initial diagnosis.
• IC speciation determines chemical forms, informing toxicity assessment and clinical management.
• Combined approach enables source tracing of adulterants in complex matrices.

Future Trends and Possibilities

Advancements may include direct hyphenation of IC with ICP-MS for online speciation, development of portable field-deployable systems, expanded speciation libraries for other toxic metals, and integration with high-resolution mass spectrometry for enhanced sensitivity and selectivity.

Conclusion

The synergy of ion chromatography and ICP-MS provides a comprehensive solution for complex contamination cases. Total metal screening coupled with speciation analysis enables accurate risk assessment, source identification, and effective mitigation strategies in food, environmental, and clinical contexts.

References

1. Sarzanini C, et al. Analytica Chimica Acta 1993;00:1–7.
2. Christison T, Hoefler F, Lopez L. Thermo Fisher Scientific Application Note 43130; 2012.