An ion-exchange separation of Cu(2+), Cd(2+), Pb(2+) and Tl(+) on silica gel with polarographic detection

The HPLC separation of heavy metal cations was studied with a column packed with Separon SGX silica gel. The retention of the cations is controlled by an ion-exchange mechanism. The ion-exchange capacity is primarily dependent on the mobile phase pH. The analyte retention is further affected by the type and concentration of the completing agent present and of the counterion. The effect of acetate, tartrate and alpha-hydroxyisobutyrate as complexing agents and that of methanol as the organic modifier were studied in detail and the results were compared with the theoretical model of ion-exchange separation. Simple mixtures of metals can be rapidly separated on a short column (30 x 3.3 mm i.d.), e.g., with a mobile phase containing 10(-2)M tartrate at pH 6.0. The metals separated can be detected by dc amperometry at a hanging mercury drop electrode. The limits of detection at an electrode potential of -0.95 V (Ag/AgCl) are in the units-tens of ng range with 20-mul samples with satisfactory precision (RSD values of 2-6%). The main advantages of the method are rapidly and simplicity because derivatization of the analytes is not required.