Simultaneous determination of seven elemental species in estuarine waters by LC-ICP-DRC-MS

A new multi-elemental speciation method was developed for seven species of three elements namely As(iii), As(vi), MMA, Cr(iii), Cr(vi), Se(iv) and Se(vi), using liquid chromatography-inductively coupled plasma-mass spectrometry. The use of dynamic reaction cell technique in removing polyatomic interference dramatically extended the detection sensitivity for all seven species with methane as the reaction gas. The developed condition offered low detection limits in ranges of 0.12-0.44 μg L^-1, 0.24-0.29 μg L ^-1 and 0.26 μg L^-1 for species of As, Cr and Se, respectively. For concise quantitative speciation, a controlled chelation condition for Cr species was optimized to minimize species interconversion. In the developed method, the seven species were baseline-separated in an 11-minute elution on an anion exchange column using NH₄NO₃/NH ₄H₂PO₄ as the mobile phase at pH 6. This efficient, high-throughput and sensitive method was fully validated and applied in quantitative speciation of river water samples collected from the Shing Mun River of Hong Kong. Most of the species were found as the toxic forms of the elements studied.