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A new electrochemical sensor with high sensitivity and selectivity for heavy-metal ions was proposed. The sensor was based on the electrochemical impedance spectroscopy (EIS) attributing to a constant phase element (CPE) behavior under dynamically controlled electrode potential. With the measurements of the CPE behavior by the surface-polarization controlling method, various heavy-metal ions could be easily detected and discriminated. No interference of counter anions such as Cl-, NO3- and CH3COO$was observed, and the same metal ions gave similar sensor response patterns regardless of the counter anions. Especially, the present method offers a high sensitivity of ppb levels for the most highly toxic elements, i.e., Hg2+ and Hg+.