| Summary: | A portable electrochemical system based on rGO/AuNPs/Nafion was constructed for selenium (IV) field determination in coastal seawater of the North Yellow Sea, East China Sea and South China Sea. This system demonstrated a low determination limit (0.03 μg/L), a wide linear range of concentration (0.1–30 μg/L), exceptional reproducibility and repeatability, and excellent selectivity. Each individual, entire test could be accomplished within 8 min. In Yantai Sishili Bay, the Se (IV) concentrations ranged from 0.16–3.59 μg/L (average 1.43 μg/L). In Shengshan Island, the Se (IV) concentrations ranged from 0.20–5.18 μg/L (average 2.06 μg/L). In Zhelin Bay, the Se (IV) concentrations ranged from 0.87–4.87 μg/L (average 3.13 μg/L). The average concentrations of Se (IV) in surface seawater showcased an increasing trend from the north to the south of China, suggesting Zhelin Bay > Shengshan Island > Sishili Bay. The system develops a new, competitive method for water quality assessment, and contributes to the accurate study of the biogeochemical cycles of selenium.
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