[en] Preconcentration of trace elements from water samples is generally carried out by solvent extraction or sorption on suitable sorbents like silica gel, ion exchange resin or activated carbon. 100-500 ml of the aqueous solution is passed through a short column and the sorbed ions are eluted from the column in a small volume. While the accent is on quantitative recovery, the selectivity is not very good especially with respect to alkaline earth elements. A new technique is suggested in this presentation. The same amount of ion exchange resin like Chelex 100 is equilibrated with 4 or 5 successive portions of aqueous solution so that one can achieve good recovery and selectivity. Calculations show that good selectivity can be achieved if the pH and v/m (volume of solution/mass of resin) ratio are so adjusted as to giver greater than 80% recovery in a single equilibration for the ions of interest and less than 50% recovery for the ions to be discriminated against. Preliminary experiments to evaluate recoveries of Zn, Cd and Hg using Chelex 100 resin are in good agreement with the calculations. (author)