Electrochemical Aspects of Ionic-Liquid|Water Two-Phase Systems

Abstract

See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.R oom-temperature ionic liquids (ILs) that are salts in the liquid state have attracted much attention in a variety of areas because of their unique features, such as extremely low volatility, high polarity, and reasonable electrical conductivity (1-11).An IL with sufficient hydrophobicity forms a two-phase system upon contact with an aqueous phase (W). Among IL applications, the use of IL |W two-phase systems is one of the most promising for extraction and electroanalytical chemistry. An IL can be used as a substitute for a conventional organic solvent because its properties are similar to (but somewhat different from) those of polar molecular solvents (12, 13). However, IL|W systems have one distinct feature-when the liquids are brought into contact, ions in the IL start to dissolve in W, and a potential difference develops across the interface between the two phases. The origin of this phase-boundary potential is the difference between the affinity that the anions in the IL have for W and the affinity that the cations in the IL have for W. This is where the fundamental difference between ILs and molecular solvents emerges (14, 15).The phase-boundary potential dramatically influences the partitioning of charged components between the IL and W phases. The electrical double layers formed at the IL|W interface should affect the surface properties of the systems used in chromatography, electrophoresis, and potentiometric ion sensing. For a better understanding of the properties of IL |W two-phase systems, an electrochemical viewpoint is useful and important. In this article, some examples illustrating the importance of the phase-boundary potential are presented together with basic electrochemical concepts required in dealing with IL|W two-phase systems. Partition equilibriaThe mutual solubility of the IL and W vary considerably, depending on the ions that make up the IL. Most ILs used for extraction studies have relatively high solubility in W, on the order of a few tens of millimolar (items 1-3 in Table 1 ; 16, 19). Strongly hydrophobic ILs (items 8-10) are 3 orders of magnitude less soluble in water; moderately soluble ones (items 4-6) are in between, at a few millimolar. Although octanol-water partition coefficients IonIc-LIquId | Water Two-Phase Systems takashi KakiuchiKyoto UniversityAn electrochemical perspective is crucial for understanding such two-phase systems.Tony Fernandez S e p t e m b e r 1 , 2 0 0 7 / A n A l y t i c A l c h e m i S t r y 6 4 4 3

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Mutual Solubility of Hydrophobic Ionic Liquids and Water in Liquid-Liquid Two-phase Systems for Analytical Chemistry

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Ion Transfer Square Wave Voltammetry of Ionic Liquid Cations with a Solvent Polymeric Membrane Ion Sensor

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