A new chemically modified electrode was synthesized for the determination of mercury(II) using differential pulse anodic stripping voltammetry (DPASV). The electrode was modified by lacunar apatite K1-xNaxCaPb3(PO4)(3) (0 <= x <= 1) synthesized using solid reaction. These powders were crystallized in the hexagonal system, space group P6(3)/m. The effect of sodium content on structural, thermodynamic and electrochemical properties of prepared apatite has been studied. Therefore, the best results was obtained using NaCaPb3(PO4)(3) (x = 1) as modifier of carbon paste electrode for the electrochemical detection of mercury(II). The later ions were preconcentrated on the surface of the modified electrode and oxidized at 0.06 V vs. Ag/AgCl. The electroanalytical procedure comprises of two steps: the chemical accumulation of the analyte under open-circuit conditions followed by the electrochemical detection of the preconcentrated species using differential pulse voltammetry. The different parameters that govern the two steps were optimized. A linear response was obtained in the concentration range from 1.0 mol L-1 x 10(-4) mol L-1 to 2.0 mol L-1 x 10(-7) mol L-1 Hg(II) after activation of the electrode surface under the optimized conditions. The standard deviation was evaluated in a high and low concentration of mercury(II). The values obtained for seven consecutive measurements were 1.24% and 5.07% of 1.0 mol L-1 x 10(-4) mol L-1 and 5.0 mol L-1 x 10(-6) mol L-1 mercury(II) solutions respectively. The detection limit and quantification limit for mercury(II), calculated from nine times standard deviation of blank/slope of the calibration graph, were 1.086 mol L-1 x 10(-8) mol L-1 and 3.62 mol L-1 x 10(-8) mol respectively. The proposed chemically modified electrode was applied to determine mercury(II) in seawater samples. (C) 2014 Elsevier Ltd. All rights reserved.