Wide Electrochemical Window at the Interface between Water and a Hydrophobic Room-Temperature Ionic Liquid of Tetrakis[3,5-bis(Trifluoromethyl)phenyl]borate

Abstract

Ionic liquids composed of a hydrophobic anion, tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB-), and various aromatic and aliphatic ammonium have been prepared. TFPB salts of N-octadecylisoquinolinium (C18Iq+) and trioctylmethylammonium (TOMA+) show low melting points of 31 and 36 degrees C, respectively, whereas TFPB-based ionic liquids of 1-alkyl-3-methylimidazolium with the alkyl chain length of 5-12 show melting points lower than 90 degrees C. The [C(18)Iq][TFPB]|water (W) and [TOMA][TFPB]|W interfaces have the polarized potential window (ppw) of 0.8 V at 56 degrees C, which is twice as wide as the ppw at the interface between W and room-temperature ionic liquids of bis(perfluoroalkylsulfonyl)imide so far reported. The extension of the ppw by more than 0.4 V to the positive direction enables voltammetric measurements of the ion transfer of relatively hydrophobic anions such as bis(trifluoromethylsulfonyl)imide and bis(pentafluoroethylsulfonyl)imide and of hydrophilic cations such as tetraethylammonium and acetylcholine ions.

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

“…We also found similar voltammograms of ion transfer at a micro liquid-liquid interface formed at the tip of a glass capillary when the capillary containing an aqueous solution was dipped in a hydrophobic RTIL, N-octadecylisoquinolinium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate. 27 The scan-rate independent plateau suggests that the shape of the capillary shank close to the orifice is not cylindrical. From numerical calculations of voltammograms, we have recently confirmed that such a steady-state current is reproduced when the tip geometry is noncylindrical, that is, conical or tapered.…”

“…However, hydrophobic RTILs are generally much more viscous than conventional solvents; the viscosity is typically two orders of magnitude greater than that of water. [21][22][23][24][25][26][27] A large solution resistance in the RTIL phase makes it diffcult to obtain voltammograms without distortion, even after applying positive-feedback compensation of the solution resistance. 17,19 For voltammetry in highly resistive media, ultramicroelectrodes are known to be useful.…”

Array of water|room temperature ionic liquid micro-interfaces

“…In particular, the group of Kakiuchi has been very active [6][7][8] since their pioneering work in 2003 [9], and the first review paper on this topic was published recently [10]. Ion transfer at the W|RTIL interface is a special case of ion transfer at the interface between two immiscible electrolyte solutions (ITIES), which enables the study and detection of ions not easily oxidisable or reducible at solid|liquid interfaces.…”

“…In this work, we report the behaviour of a W|RTIL micro-interface array formed between water and the RTIL trihexyltetradodecylphosphonium tris(pentafluoroethyl)trifluoromethylphosphate ([P 14,6,6,6 ][FAP]) within a silicon micropore membrane (consisting of 30 micropores of ca. 23 µm diameter).…”

Ionic liquids in sample preparation

“…Thus, ILs are termed "designable solvents" [8], and various applications have reported for them. In analytical chemistry, ILs were used as stationary phases in gas chromatography [9][10][11], additives for capillary electrophoresis [12][13][14][15], matrices for MALDI [16][17][18], as well as solvents for spectral analysis [19][20][21] and electrochemistry [22]. Several reviews that focus on these topics have been published recently [23][24][25][26][27].…”