Analytical Sciences

Voltammetry of Ion Transfer across the Electrochemically Polarized Micro Liquid-Liquid Interface between Water and a Room-temperature Ionic Liquid, Tetrahexylammonium Bis(trifluoromethylsulfonyl)imide, Using a Glass Capillary Micropipette

Norihiro TSUJIOKA, Seiichi IMAKURA, Naoya NISHI, and Takashi KAKIUCHI

Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan

Ion transfer across the polarized interface between a room-temperature ionic liquid (RTIL) or room-temperature molten salt, tetrahexylammonium bis(trifluoromethylsulfonyl)imide (THAC₁C₁N), and water has been studied voltammetrically using a micro liquid-liquid interface formed at the orifice of a glass capillary micropipette. A small current of nanoampere level circumvents the problem of the iR drop in the viscous ionic liquid phase. Voltammograms for the transfer of moderately hydrophilic ions, such as BF₄^- and ClO₄^-, from the aqueous phase in the capillary to the bulk of THAC₁C₁N in which the capillary is submerged, show steady-state characteristics in that the current does not depend on the scan rate up to a few hundred millivolt per second, and the plateau in the limiting current region is proportional to the bulk concentration of analyte ions. Owing to the steady-state current, which is presumably ascribed to a noncylindrical geometry of the capillary tip, the relative magnitude of the hydrophobicity, or the affnity to the RTIL, of a series of ions can be determined from the half-wave potentials of voltammograms.

J-STAGE: View this article in J-STAGE