Effects of Lipophilic Charged Sites on the Electromotive Behavior of Liquid Membrane Electrodes

Lipophilic salts consisting of either lipophilic cations and hydrophilic anions or hydrophilic cations and lipophilic anions act in liquid membranes as anion exchangers and cation exchangers, respectively. A large number of corresponding membrane electrodes have been described in the literature (for reviews see [2, 4, 6]). A comparison of the ion selectivities obtained with a variety of different anion exchangers corroborates the theoretical prediction that the structure of the ion exchanger molecules involved should have only minor influences on the observable ion selectivities [2,4–7]. The selectivity sequences correlate nicely with the sequence of the free energies of hydration of the ions (cf. [4–5]).