A simple and cheap analytical technique was developed for the measurement of total mercury in river water samples using inductively coupled plasma–mass spectrometry (ICP-MS). It is based on the direct complexation of mercury ions using iodide and a cationic surfactant in water for its subsequent solid-phase extraction. Mercury ions are retained on the silica phase as ion pairs in the presence of iodide ions and dodecyltrimethylammonium bromide. Parameters having influential influence on the retention of Hg(II) were investigated: sample flowrate, eluent type, sample volume, iodide and surfactant concentrations. The retained mercury ions are stripped off from silica phase using 10 mL of 8 mol L⁻¹ HNO₃ and quantified by ICP-MS. An enrichment factor of 50 was achieved with a maximum adsorption capacity of 718 μg Hg(II) g⁻¹. The limit of detection of Hg(II) was 8 pg mL⁻¹. The developed method was applied for the determination of total mercury in river and tap-water samples.