Speciation of inorganic and organic species of mercury and arsenic in lotus root using high performance liquid chromatography with inductively coupled plasma mass spectrometric detection in one run

Abstract

Multi-elemental speciation analysis in a single run reduces costs, waste and time, and also sample consumption, which is favorable to a large set of instable samples. This work demonstrates mercury and arsenic speciation in a single run using high performance liquid chromatography with inductively coupled plasma mass spectrometric detection (HPLC/ICP-MS). Thiol compounds in mobile phases interfered with the elution of arsenite because of coordination action, which was overcome by gradient elution (elution of As(III) by thiol-free mobile phases at first). Four arsenic forms (As(III), DMA, MMA and As(V)) and three mercury species (Hg(II), MeHg and EtHg) were separated and detected by HPLC/ICP-MS using 4 mM tetrabutylammonium hydroxide (TBAH) (pH 6.0) in the first 1.0 min and 4 mM TBAH + 20 mM L-cysteine (pH 6.0) in the next 9.0 min. The detection limits were obtained at 0.078 for As(III), 0.081 for DMA, 0.078 for MMA and 0.15 μg L−1 for As(V), and 0.016 for Hg(II), 0.027 for MeHg and 0.032 μg L−1 for EtHg, and the reproducibilities (50 μg L−1 for each As-species and 10 μg L−1 for each Hg-species) were all lower than 3.7%. The proposed method was successfully applied for speciation analyses of arsenic and mercury in five lotus roots, which indicated DMA (3.5–7.9 μg kg−1) as the only arsenic species and MeHg (0.6–1.0 μg kg−1) as the only mercury species. Analyses of two certified reference materials demonstrated good agreement between determined values and certified values. All results prove its advantages including high sensitivity and high analytical efficiency, which are beneficial for routine speciation analyses of arsenic and mercury in a single run in environmental and food fields.