DETERMINATION OF METAL-IONS BY ION CHROMATOGRAPHY WITH PRECOLUMN ELECTROCHEMICAL PRECONCENTRATION

The determination of heavy metals in concentrations less than 10(-6) m ol/L by ion chromatography with conductivity detection requires a prec oncentration step. Therefore, a special electrochemical equipment and method was developed for the on-line preconcentration of the divalent metals Ni, Co, Zn and Cd and their subsequent ion chromatographic dete rmination. The loop of the injection valve of an ion chromatograph was replaced by an electrochemical flow-through-cell with a gold working electrode, a platinum auxiliary electrode and a silver/silver sulphate reference electrode. The preconcentration step consists of the deposi tion of the reduced metals on the electrode surface during a continuou s pumping of the sample solution through the cell. After switching of the mobile phase through the cell, the analytes are injected after the ir reoxidation directly into the mobile phase. A new preconcentration step is simultaneously possible during the actual chromatographic run. An effective separation of the analytes from the matrix is also possi ble with the proposed system. A maximum of metal ion accumulation was obtained after 120 min in the galvanostatic mode on a gold tube electr ode. The detection limits for Co(II), Ni(II), Zn(II) and Cd(II) were i mproved by a factor of 7.7, 10.4, 11.2, 14.0, respectively, and were i n the 0.1 mu mol/L concentration range with a RSD of 2-6%. The accumul ation of metal ions was disturbed in the presence of Cr(III).