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Voltammetry of ion transfer across a polarized room-temperature ionic liquid membrane facilitated by valinomycin: Theoretical aspects and application

Analytical Chemistry, ISSN: 0003-2700, Vol: 81, Issue: 15, Page: 6382-6389
2009
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Cyclic voltammetry is used to investigate the transfer of alkali-metal cations, protons, and ammonium ions facilitated by the complex formation with valinomycin at the interface between an aqueous electrolyte solution and a room-temperature ionic liquid (RTIL) membrane. The membrane is made of a thin (∼112 μm) microporous filter impregnated with an RTIL that is composed of tridodecylmethylammonium cations and tetrakis[3,5-bis-(trifluoromethyl)phenyl] borate anions. An extension of the existing theory of voltammetry of ion transfer across polarized liquid membranes makes it possible to evaluate the standard ion-transfer potentials for the hydrophilic cations studied, as well as the stability constants (K) of their 1:1 complexes with valinomycin, as log K = 9.0 (H), 11.1 (Li), 12.8 (Na), 17.2 (K), 15.7 (Rb), 15.1 (Cs), and 14.7 (NH). These data point to the remarkably enhanced stability of the valinomycin complexes within RTIL, and to the enhanced selectivity of valinomycin for K over all other univalent ions studied, compared to the conventional K ion-selective liquid-membrane electrodes. Selective complex formation allows one to resolve voltammetric responses of K and Na in the presence of an excess of Mg or Ca, which is demonstrated by determination of K and Na in the table and tap water samples. © 2009 American Chemical Society.

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