Mercury speciation in Cuban commercial edible fish by HPLC-ICP-MS using the double spike isotope dilution analysis strategy

Abstract

A sensitive and accurate quantitative method for the speciation of inorganic Hg²⁺ and methyl-mercury by ID-HPLC–ICP-MS has been optimised and implemented for marine fish samples. Quantitative extraction of Hg species was achieved using a 0.1% (v/v) 2-mercaptoethanol, 0.05% (w/v) L-cysteine and 0.10% (v/v) HCl solution by sonication for 30 min. Chromatographic separation of mercury species was carried out on a C8 reverse phase column with 0.05% (v/v) 2-mercaptoethanol, 0.075% (w/v) L-cysteine and 0.06 mol L⁻¹ ammonium acetate as the mobile phase. A species specific isotope dilution analysis approach, using ²⁰¹CH₃Hg⁺ and ²⁰⁰Hg²⁺ was employed for the quantification of both species. Two biological Certified Reference Materials (DOLT-2, DORM-2) were analysed to assess the analytical performance. No significant differences were found between the obtained concentrations and the certified reference values for total Hg and CH₃Hg⁺. The results indicate that no species interconversion reactions occurred during the used extraction and chromatographic separation procedures. The detection limits for CH₃Hg⁺ and Hg²⁺ species were 7.7 and 5.2 ng g⁻¹, respectively. The method recovery (expressed as the sum of both species contents in relation to total Hg concentration analysed by ICP-MS) was about 97 ± 5%. The procedure was applied to speciation of mercury in 12 species of the most commonly consumed commercial fish in Cuba.

Keywords:

• fish species
• inductively coupled plasma mass spectrometry
• isotope dilution
• liquid chromatography
• mercury speciation

Acknowledgements

The authors would like to thank the IAEA TC Project CUB 5018 for providing financial support to this study. We thank Prof. J.I. García Alonso for the provision of the spread sheet for the double spike calculations and also would like to thank Thermo Fisher Scientific, Bremen for their support.