A novel method for the on-line preconcentration and chromatography of trace metals, e.g., Mn, Co, Ni, Cu, Zn, Cd and Pb, on ethylenediamine triacetate-bonded silica is described. The preconcentrated metals were desorbed with 0.1 M nitric acid. Post-precolumn modification of the eluent was done by means of a tee mixer and a second high-performance liquid chromatographic pump. The modified eluent, consisting of tartaric acid and sodium nitrate, allows the separation of metals on a cation-exchange chromatographic column. The metals separated were detected by postcolumn reaction with 4-(2-pyridylazo)-resorcinol and measuring absorbances at 500 nm. Linear calibration graphs were obtained over the range 3 · 10⁻⁹−3 · 10⁻⁶M. The characteristics of this chelating silica are given and the on-line and off-line preconcentration methods were compared. Application of the method to the analysis of river water is described. The results show that the method is applicable to the determination of Co, Ni, Cu, Zn, Cd and Pb ions. It was also demonstrated that the method can be used for the determination of free metal ions and labile or moderately labile complexes.