Abstract
Since interesting selectivity for K+ over Na+ by naphtho-15-crown-5 (N15C5) has been reported in studies of ion-selective electrode and solvent extraction, the ion-transfers of alkali and alkaline earth metal cations facilitated by N15C5 have been studied electrochemically at ITIES, Interface of Two Immiscible Electrolyte Solutions between an aqueous and an organic (nitrobenzene or 1, 2-dichloroethane) phases. It is clearly observed that K+ and Ca2+ transfer across the ITIES forming 1:2 (cation to ligand) complex but the other metal ions forming 1:1 complex. Then the values of some equilibrium constant in the course of the interfacial transfer are in beautiful agreement between the electrochemical and the solvent extraction results. The stoichiometries of those complex ions have been also studied by electrospray ionization mass spectrometry directly. These results have partly supported the conclusions from the electrochemical study. Interestingly, on the other hand, it has been also observed that a bilayer phospholipid membrane doped by N15C5 selects K+ over Na+.
