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A new type of Ag/AgCl electrodes based on a hydrophobic ionic liquid has been proposed. The electrode consists of a Ag/AgCl electrode immersed in or coated with a AgCl-saturated ionic liquid, 1-methy-3-octylimidazolium bis(trifluoromethylsulfonyl)imide ([[C.sub.8][mim.sup.+]]-[[C.sub.1][C.sub.1][N.sup.-]]), instead of the internal aqueous solution. The [[C.sub.8][mim.sup.+]]-[[C.sub.1][C.sub.1][N.sup.-] phase plays dual roles, that is, as a medium dissolving AgCl and an ionic-liquid-type salt bridge upon contact with an aqueous solution. The gelation of the [[C.sub.8][mim.sup.+]]-[[C.sub.1][C.sub.1][N.sup.-]] phase allows us to prepare coatedwire-type solid-state reference electrodes with a well-defined thermodynamic basis for the electrode potential. Both gelled and nongelled types show stable electrode potentials against the change in the concentration of KCl between 0.05 mmol [dm.sup.-3] and 2 mol [dm.sup.-3]. This new class of reference electrodes opens the way for a variety of miniaturized and solid-state reference electrodes.

The facilitated transfer of alkali metal cations ([Li.sup.+], [Na.sup.+], [K.sup.+], [Rb.sup.+], [Cs.sup.+]) by dibenzo-18-crown-6 (DB18C6) across the electrochemically polarizable interface between an aqueous solution (W) and a hydrophobic ionic liquid, N-octadecylisoquinolinium tetrakis[3,5-bis(trifluoromethyl) phenyl]borate ([[C.sub.18]Iq][TFPB]), has been studied using cyclic voltammetry at the interface formed at the tip of a micropipet. In cyclic voltammograms (CVs), the current due to the facilitated transfer of the cations by DB18C6 from W to [[C.sub.18]Iq][TFPB] can be measured within the polarized potential window of the [[C.sub.18]Iq][TFPB] IW interface. The stoichiometry of the complexes in [[C.sub.18]Iq][TFPB] for [Li.sup.+], [Na.sup.+], [K.sup.+], and [Rb.sup.+] are found to be 1:1 while for the [Cs.sup.+] transfer both 1:1 and 1:2 complexes are likely to be formed. The formation constants of the 1:1 complexes for [Li.sup.+], [Na.sup.+], [K.sup.+], and [Rb.sup.+] in [[C.sub.18]Iq][TFPB], [K.sup.R.sub.f], evaluated from CVs are log [K.sup.R.sub.f] = 5.0, 7.0, 8.2, and 7.3, respectively. The [K.sup.R.sub.f] value for [K.sup.+] is 1 order of magnitude greater than that for [Na.sup.+]. This higher selectivity of DB18C6 to [K.sup.+] over [Na.sup.+] in [[C.sub.18]Iq][TFPB] compared with that in molecular solvents suggests that the RTIL provides a unique solvation environment for the complexations of DB18C6 with the ions.

Ionic liquids composed of a hydrophobic anion, tetrakis[3,5-bis(trifluoromethyl)phenyl]borate ([TFPB.sup.-]), and various aromatic and aliphatic ammonium have been prepared. TFPB salts of N-octadecylisoquinolinium ([C.sub.18][Iq.sup.+]) and trioctylmethylammonium ([TOMA.sup.+]) 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.sub.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(pentafluoroethyl-sulfonyl)imide and of hydrophilic cations such as tetraethylammonium and acetylcholine ions.

The voltage-driven transfer of alkali and alkaline-earth metal ions across the polarized 1,2-dichloroethane (DCE)/water interface has been measured fluorometrically by using two fluorescent ionophores, coumarin 153-linked monoaza-15-crown-5 (C153-crown([O.sub.4])) and two-coumarin 153-linked diaza-18-crown-6 ([(C153).sub.2]-[K.sub.22]). The 1:1 complex formation prevails for both monovalent and divalent ion transfer, when the concentration of C153-crown([O.sub.4]) in DCE is at the micromolar level. In the [Mg.sup.2+] ion transfer, the formation of the 1:2 (metal-ligand) complex becomes significant at the millimolar level of C153-crown([O.sub.4]). C153-crown([O.sub.4]) seems to adsorb at the interface. The complexation of [Ba.sup.2+] with [(C153).sub.2]-[K.sub.22] is significantly slower than the complexation with C153-crown([O.sub.4]).

The time derivative of fluorescence vs time curves recorded with voltage-scan fluorometry (Kakiuchi, T.; Takasu, Y.; Senda, M. Anal. Chem. 1992, 64, 3096-3100) for the transfer of the divalent anionic form of Eosin B (EB) across the 1,2-dichloroethane-water interface gives curves isomorphic to the cyclic voltammograms of ion transfer of EB when the concentration of EB in the aqueous phase is in the micromolar range or lower. From the differential cyclic voltfluorograms obtained, electrochemical properties of ion transfer, e.g., the Gibbs energy of transfer of fluorescent ions and the reversibility of ion transfer, can be estimated at the nanomolar level, which is approximately 5 orders of magnitude more sensitive than conventional cyclic voltammetry of the ion transfer. Chronofluorometry, i.e., the potential-step transient of the fluorescence for the transfer of fluorescent ions, is demonstrated to be utilized as a counterpart of the chronocoulometry of ion transfer in the same low concentration range.

The application of fluorometry in detecting the transfer offluorescent Rose Bengal dianion through the 1,2-dichloroethane (DCE)-water interface is discussed. High sensitivity measurement of dye ion transfer fluoresence from the aqueous to the DCE phase was made possible by the introduction of excitation light from DCE to the interface. It was found that the sensitivity of fluorometry in ion transfer detection is three orders of magnitude more than conventional electrochemical techniques.