Fllterlng a 200mL water sample through a palr of Chelex-100 Ion-exchange membranes, under a 2-3 bar pressure, at pH 7 to 8 In not less than 20 mln, leads to an efflclent collection of many trace metals In a form that Is Ideal for subsequent x-ray fluorescence analysls. Slnce enrlchmenl factors around 1250 are obtalned, the detectlon llmlts are at the 1-ppb level. The preclslon Is estlmated to be In the 10-15% range. A perfectly linear relatlonshlp between concentratlon and measured x-ray yleld Is obtalned up to the total membrane palr capaclty of 0.07 mequlv. The slgnlflcant afflntly of Chelex-100 membranes for the-usually abundant-alkall and alkallne earth Ions, together wlth thelr llmlted capaclty, restrlcts the appllcablllty of the descrlbed technlque to samples wlth a very low alkall and alkaline earth content.