Selection of the receiver electrolyte for the Donnan dialysis enrichment of cations

Abstract

The Donnan dialysis of cations is typically performed with a sulphonated ion-exchange membrane. Factors that govern the selection of the receiver electrolyte when such membranes are used are described. In terms of providing high enrichment factors that are similar for a variety of cations and constituting a medium that is compatible with various quantification methods, a mixture containing 0.2 M MgSO₄ and 0.5 mM Al₂(SO₄)₃ at pH 1 is the recommended electrolyte. For use with cadmium and copper ion-selective electrodes, the pH is adjusted to 3.5–4 after the dialysis. For quantification with a lead ion-selective electrode, the receiver consists of the nitrate salts of Mg(II) and Al(III).