Determination of Chemical Forms of Mercury Using High Performance Liquid Chromatography with Cold Vapour Atomic Fluorescence Spectrometric Detection (HPLC/CV-AFS)

Abstract

Sonication and microwave-assisted extractions with thioacetic acid, citric acid, cysteine, 2-sulfanylethanol, aqueous HCl, and aqueous HCl - NaCl were tested for isolation of mercury species. A mixture of 6M HCl and 0.1M NaCl was selected as the most suitable extraction agent. The extraction efficiency was about 10 % higher and RSDs were below 3.3 % when microwave-assisted extraction was used instead of sonication. The HPLC/CV-AFS method was optimized and used for separation and determination of inorganic mercury and methyl-, ethyl- and phenylmercury chloride. Isocratic elution with a mixture containing 0.05 % of 2-sulfanylethanol, acetate buffer (pH 5) and 7 % of methanol, with methanol content increasing up to 100 % MeOH, was used for separation of mercury species on a reverse phase Hypersil BDS C18 column. The limits of detection of the HPLC/CV-AFS system were estimated (in μg kg⁻¹): 0.20 (MeHgCl), 0.07 (Hg²⁺), 0.06 (PhHgCl) and 0.12 (EtHgCl). The concentrations (2.5–9.7 mg kg⁻¹ in dry matter) of total mercury and methylmercury chloride in selected fish obtained by HPLC/CV-AFS were in good agreement (but more accurate) with GC-ECD. The RSDs 3.1–8.2 % and 4.1–9.0 % of the analytical procedures for the determination of total mercury (cold vapour AAS) and methylmercury chloride (HPLC/CV-AFS) were determined, respectively.