n. (Chem.) an apparatus used to remove ions from a solution; a common variant contains a mixture of cation exchange resin in the acid form and anion exchange resin in the hydroxyl form inside a replaceable cartridge; ions in aqueous solution are exchanged for the elements of water by passing the solution through the mixed resin. In chemistry and biochemistry, experiments often require water free from contaminating ions, and ordinary distilled water may be further purified by passing through a deionizer in order to render the ion content sufficiently low so as not to interfere with the investigation. [ PJC ]