INFLUENCE OF LIPOPHILIC INERT ELECTROLYTES ON THE SELECTIVITY OF POLYMER MEMBRANE ELECTRODES

Lipophilic inert electrolytes, i.e., salts without ion-exchange proper ties, may influence the selectivity of ionophore-based Liquid membrane electrodes by affecting the activity coefficients in the organic phas e. It is expected by a theoretical model that the addition of a lipoph ilic salt renders the ion-selective electrode more selective for dival ent over monovalent ions. These predictions are confirmed with Ca2+-re sponsive membranes containing the ionophores ETH 2120, ETH 1001, and E TH 129. The effect is especially pronounced with nonpolar membrane pha ses containing a low concentration of charged species, where up to 2 o rders of magnitude selectivity improvement is observed.