Mercury and arsenic speciation analysis by IC-ICP/MS

Importance of the topic

Trace-level speciation of mercury and arsenic is critical for environmental monitoring, food safety and public health. Different oxidation states and organic forms of these elements exhibit widely varying toxicities and mobility. Accurate measurement at sub-ppb levels helps regulators ensure drinking water and food products meet safety standards and supports research on biogeochemical cycling.

Objectives and overview of the study

This study demonstrates a single-run analytical protocol for separating and quantifying inorganic and organic species of arsenic and mercury in biological samples using ion chromatography coupled to inductively coupled plasma mass spectrometry (IC-ICP/MS). Certified tuna fish tissue (ERM-CE464) was used to validate the method, applying both external calibration and speciated isotope-dilution mass spectrometry (SIDMS) per EPA Method 6800.

Methodology and instrumentation

The protocol combines anion-exchange IC separation with ICP-MS detection. Arsenic species were resolved under alkaline eluent conditions, while mercury species (Hg2+ and CH3Hg+) were separated on a dual-mode column. Speciation accuracy was enhanced by spiking samples with enriched 199Hg2+ and CH3¹⁹⁹Hg+ isotopes before extraction, allowing correction for methylation/demethylation via SIDMS equations. Key instrument components:

• 850 Professional IC Anion – MCS
• 858 Professional Sample Processor
• 7500 ICP/MS (Agilent Technologies)

Main results and discussion

External calibration yielded quantification of Hg2+ and methylmercury within certified uncertainty margins (5.12 ± 0.16 and 5.24 ± 0.10 mg/kg). SIDMS corrected for extraction-induced transformations, confirming highest accuracy across various extraction procedures (alkaline sonication, microwave-assisted digestion, enzymatic treatment). Some protocols introduced artefactual interconversions, whereas others (procedures A–C) matched the reference values within 95 % confidence. Arsenic species (inorganic As(III), As(V) and arsenobetaine) were separated and identified based on retention time and mass spectral data.

Benefits and practical applications of the method

The combined IC-ICP/MS and SIDMS approach offers:

• Sub-ppb sensitivity and selectivity for multiple species in a single run
• Correction for species interconversion during sample preparation
• Reduced matrix interferences compared to conductivity detection
• Compliance with EPA Method 6800 for regulatory analysis

This methodology is applicable to environmental waters, food safety surveillance, and toxicological studies requiring speciation data.

Future trends and potential applications

Advances may include automation of SIDMS workflows, extension to other toxic metals (e.g., chromium, selenium), integration with high-resolution MS for structural confirmation, and miniaturized field-deployable IC‐ICP/MS units. Wider adoption of certified-reference protocols will improve interlaboratory comparability and support real-time monitoring of contaminant dynamics.

Conclusion

The IC-ICP/MS protocol, in combination with SIDMS, provides a robust, accurate and sensitive platform for simultaneous speciation of organic and inorganic mercury and arsenic. Validation with certified reference material confirms its suitability for regulatory and research laboratories.

References

1. G.M.M. Rahman et al., Anal. Bioanal. Chem., 382, 1111–1120 (2005).
2. US EPA Method 6800, Speciated isotope-dilution MS, SW-846 Update IVA (2007).
3. M. Gochfeld, Ecotoxicol. Environ. Saf., 56, 174–179 (2003).
4. C.W. Levenson & D.M. Axelrad, Nutr. Rev., 64, 139–145 (2006).
5. G.M.M. Rahman & H.M. Kingston, Anal. Chem., 76, 3548–3555 (2004).
6. G.M.M. Rahman & H.M. Kingston, J. Anal. Atomic Spectrom., 20, 183–191 (2005).
7. G.M.M. Rahman, T. Fahrenholz & H.M. Kingston, Manuscript on simultaneous transformation correction.
8. L. Reyes et al., Anal. Bioanal. Chem., 390, 2123–2132 (2008).