Silver nanoparticles were coated on a glass stir bar by overnight exposure of the bar to the nanoparticle solution, using 3-aminopropyltriethoxysilane as a binding agent and were used for the extraction of heavy metal Fe3+, Cu2+, Pb2+ and Zn2+ cations from water samples after their complexation with the ligand 1-(2-pyridylazo)-2-naphthol, followed by their determination by high performance liquid chromatography. Various parameters affecting the extraction were evaluated by one variable-at-a-time and Box-Behnken design methods and optimized. Six independent variables, the pH and ionic strength of the solution, the Triton X-114 (surfactant) concentration, amount of ligand, and adsorption and desorption times, were coded as A, B, C, D, E and F at three various levels (-1, 0, and 1). The linear ranges of the technique were 0.5-250.0 μg L-1 for all four analytes. Under the optimum conditions, the limits of detection were calculated as 0.08, 0.11, 0.12 and 0.17 μg L-1 for copper, iron, lead and zinc, respectively. The technique was used for the determination of these cations in drinking water samples.