A macrocyclic trinuclear complex of (1,3,5-trimethylbenzene)ruthenium(II) bridged by 2,3-dioxopyridine was synthesized, and the extraction properties for lithium and sodium picrates were investigated in a dichloromethane/water system at 25°C. The complex was found to have extremely high extractability and selectivity for lithium picrate; the logarithmic values of the extraction constants are 5.86 and 2.63 for Li⁺ and Na⁺, respectively. By using this complex as an extractant, nearly quantitative extraction and separation of Li⁺ from Na⁺ could be achieved by a single extraction.

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Liquid-liquid two-phase systems formed by a hydrophobic ionic liquid and water find several useful ways of application in analytical chemistry. One of the most important properties of such two-phase systems is the mutual solubility of the IL and water. Recent advancements on this subject have been reviewed. The solubility of ionic liquids in water is related to the standard Gibbs energies of the transfer of ions constituting the ionic liquid from the ionic liquid phase to water. Although this single ionic property cannot be measured thermodynamically and also varies from one ionic liquid to another, the standard Gibbs energy of the ion transfer from a polar aprotic solvent, such as nitrobenzene and 1,2-dichloroethane, to water is a convenient measure for it. The solubility of an ionic liquid in water and the electrochemical properties at the interface between the two phases are intimately related with each other.

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Due to their unique characteristics ionic liquids (ILs) have been extensively used as solvents in enzymatic procedures, proving to be advantageous alternatives to conventional organic solvents. The studies of enzyme behavior in ILs have increased exponentially in the last years and oxidoreductases particularly have recently started to be studied. The association of oxidoreductases with IL is very promising due to the large field of application of these enzymes. The materials are very interesting not only from the analytical point of view but also in the biocatalytic perspective. In this review, we discuss the behavior of oxidoreductases in the presence of ILs, the mechanisms involved in this association and the immobilization of oxidoreductases in composite materials with IL. The performance of proteins with peroxidase activity in ILs is also reviewed. Future trends and perspectives related with the development of biocatalytic studies involving oxidoreductases and ILs are also considered.

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Organic compounds (2-naphthol, phenol, 4-chlorophenol, 4-nitrophenol, and 1,3,5-naphthalenetrisulfonic acid) were sufficiently separated from mixtures during flow in a fused silica capillary tube (50 µm in i.d. and 45 cm in length) with an aqueous mixed solvent of an ionic liquid, 1-butyl-3-methylimidazolium chloride (BMIM⁺Cl^-), without a specific separation column. The method is based on micro-solvent cluster formation in aqueous mixed solvents of ionic liquid and preferential solvation of solvent clusters to analytes. The measurement of large angle X-ray scattering (LAXS) of aqueous mixed solvents with an ionic liquid of tetrafluoroborate (BMIM⁺BF₄^-) indicated the formation of micro-solvent clusters of water and ionic liquid in the mixed solvent. A neutral polymer (polyvinylpyrrolidone, PVP) enhanced the separation. Polarized or ionic molecules eluted slowly. The theoretical plate numbers were 6320, 22907, 63645, and 37184 for 2-naphthol, phenol, 4-chlorophenol, and 4-nitrophenol, respectively, under the conditions of 1.0 M of BMIM⁺Cl^- and 0.1 M of PVP; the flow rate was 1 µL min^-1. The separation mechanism is discussed from the viewpoint of the partition of analytes between micro-solvent clusters of water and organic solvent molecules.

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Ordered mesoporous adsorbents were prepared by physically grafting functionalized ionic liquids onto SBA-15 (a mesoporous siliceous substrate) using incipient wetness immersion method. These adsorbents were successfully applied to the selective extraction and separation of α-tocopherol (an isomer of vitamin E) from a model mixture of soybean oil deodorizer distillate. Various parameters affecting adsorption process such as adsorption time, the structures and loadings of ionic liquids, the adsorption isotherm, and the reusability of adsorbent were investigated using liquid-solid extraction. As high as 211 mg/g adsorbent of the adsorption capacity for α-tocopherol was obtained through the adsorption isotherm tests using [emim][Gly]/SBA-15 (functionalized ionic liquid 1-ethyl-3-methylimidazolium glycine which was physically coated on SBA-15) as the adsorbent, in which the functionalized ionic liquids contained the amino acid glycine as the anion. The adsorbent [emim][Gly]/SBA-15 also exhibited a very high adsorption selectivity for α-tocopherol. The extraction selectivity or the ratio of distribution coefficients between α-tocopherol and the major interference component glyceryl triundecanoate (K_{d(α-tocopherol)}/K_{d(triglyceride)}) was 10.5. The concentration of α-tocopherol was significantly increased from 15.6% in original feedstock solution that contained fatty acid methyl ester, triglyceride and a-tocopherol to 73.0% after stripping by diethyl ether. Five adsorbent recycle tests showed good reusability of the functionalized ionic liquidmodified mesoporous adsorbent.

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The extraction behavior of several divalent metal cations (M²⁺) in ionic liquid chelate extraction systems was investigated using several 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquids ([Rmim][Tf₂N]) as extraction solvent and thenoyltrifluoroacetone (Htta) as extractant. The behavior was compared with that using less hydrophobic 1-alkyl-3-methylimidazolium hexafluorophosphates ([Rmim][PF₆]). The extracted species in the [Rmim][Tf₂N] systems were neutral M(tta)₂ for M = Cu and anionic M(tta)₃^- for M = Mn, Co, Ni, Zn and Cd. Conversion of ionic liquid anion from PF₆^- to more hydrophobic Tf₂N^- resulted in changing the species extracted for Ni²⁺ from hydrated neutral complex to hydrophobic anionic one. Furthermore, the extractability for these metals was governed by the hydrophobicity of ionic liquid ions. Thus, in the ionic liquid chelate extraction system, selection of a suitable ionic liquid as extraction phase seems to be an important factor for enhancement of extraction selectivity.

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The usefulness of ion-pair reagents in selective solid reversed-phase extraction of one N-butyl-4-methylpyridinium and four short-chain alkylimidazolium ionic liquid cations from aqueous media was investigated using various concentrations of alkylsulfonates with different alkyl chain lengths. Final recoveries of the two cations with the shortest alkyl residues were poorer than those of the other, more hydrophobic compounds. Moreover, the recovery values were little affected by the different concentrations of the reagents. In nearly all cases, the best recoveries were obtained with the 1-heptanesulfonate reagent. The analytical performance parameters included excellent linearity over four orders of magnitude, with limits of detection ranging from 0.01 to 0.06 ppm, and very good precision and accuracy. The method was successfully used to extract ionic liquids from spiked seawater and freshwater samples. Recoveries and limits of detection were quite similar to those obtained with preconcentrated standard solutions.

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The distribution behavior of the salts of a series of 1-alkyl-3-methylimidazolium cations (RMeIm⁺; R = butyl, hexyl, and octyl) with tetrafluoroborate (BF₄^-), hexafluorophosphate (PF₆^-), bis(trifluoromethanesulfonyl)amide (NTf₂^-), and 2,4,6-trinitrophenolate (Pic^-) anions has been investigated in a dichloromethane-water system at 25°C. The distribution constants (K_D) of the ion pairs and the transfer activity coefficients (^oγ^w) of the single ions were determined. For the ion pairs with a given anion, the log K_D value increases linearly with the number of methylene groups (N_CH2) in the cation, which can be explained by using the regular solution theory. A similar relationship was observed between log ^oγ^w and N_CH2 for the free RMeIm⁺ ions, and the result was discussed by decomposing the transfer activity coefficient into the Born-type electrostatic contribution and the non-electrostatic one. For the free anions and their ion pairs with a given cation, the ^oγ^w and K_D values increase with increasing molar volume of the anion: i.e., BF₄^- < PF₆^- < Pic^- < NTf₂^-. The features of the RMeIm⁺ salts in the liquid-liquid distribution and the ion-pair formation in water are also discussed by comparing the present results with those of tetraalkylammonium salts previously reported.

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Grazing-incidence x-ray diffraction measurements were carried out to observe the surface structure of [bmim][PF₆]. At an incident angle of less than the critical angle, a diffraction pattern from 10 nm beneath the surface was obtained. A broad Debye-Scherrer ring was observed in the diffraction patterns, indicating that the [bmim][PF₆] molecules near the surface are randomly orientated, similar to those in the bulk liquid. The distance of the nearest anions was estimated to be 4.2 Å, which is very close to that for bulk [bmim][I], suggesting that the liquid structure of [bmim][PF₆] is determined by the packing of the cation.

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The reflection-absorption infrared (RAIRS) spectra of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM]Tf₂N) are presented for liquid as well as for amorphous and crystalline solid films. The liquid and amorphous films show rather similar spectra, indicating that the film structure is similar in both cases. On the other hand, these spectra differ considerably from those of crystalline films, indicating that the film structure is different for liquid and crystalline films. There are however indications that in all of the studied phases, including the crystalline state, the cation interaction with the SO₂ groups of the anion dominates.

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The adsorbed film of 1-decyl-3-methylimidazolium bromide (DeMIMB) at the air/water interface was investigated employing the surface tension measurement and the x-ray absorption fine structure method under the total reflection condition (TRXAFS). From the surface tension measurement, the surface excess concentrations of ions were determined. From the XAFS measurement, two solvation states of bromide ion were found in the adsorbed film, which were assigned to be “free-Br” and “bound-Br”. The hydration number of the former was estimated to be 6 while that of the latter was estimated to be 4. The results based on the XAFS analysis provided significant information on the formation of domains in the adsorbed film; the most conceivable situation is that the adsorbed molecules are definitely not homogeneously dispersed, but domains (islands or clusters) are dispersed in the adsorbed film. A regular and rather tight stacking of immidazolium rings may be formed in the domains.

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The aggregation of two imidazolium-based ionic liquids, 1-ethly-3-methylimidazolium chloride (EMI⁺Cl^-) and EMI⁺ bis-(trifluoromethanesulfonyl)amide (EMI⁺TFSA^-), in molecular liquids, water, methanol, acetonitrile, and benzene, has been studied by using the small-angle neutron scattering (SANS) technique. The SANS results have shown that the heterogeneity of EMI⁺Cl^--acetonitrile mixtures is significant at high acetonitrile contents, thus, EMI⁺Cl^- forms clusters in acetonitrile solutions. On the other hand, it has been revealed that EMI⁺Cl^- is homogeneously dissolved in water and methanol. EMI⁺TFSA^- remarkably aggregates in methanol solutions, while the mixtures of EMI⁺TFSA^- with acetonitrile and benzene are homogeneous. Furthermore, aggregation of EMI⁺Cl^- and EMI⁺TFSA^- in acetonitrile and methanol, respectively, has been examined by using ¹H NMR spectroscopy. The mechanism of aggregation of the ionic liquids in the molecular liquids has been discussed on the basis of the properties of cations, anions, and molecular liquids.

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The solvation structure of the Li(I) species in N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethane-sulfonyl) amide (DEMETFSA) was studied by measuring the Raman and multinuclear NMR spectra of DEMETFSA solutions containing LiTFSA of various concentrations (0.12 - 1.92 mol kg^-1, [TFSA^-]/[Li(I)] = 20.0 - 2.22). It was found from Raman spectra that an intense band due to the free TFSA^- anion at around 741 cm^-1 becomes weak, and a new band appears at around 747 cm^-1 with an increase in the concentrations of LiTFSA, and that the pseudoisosbestic point is observed at around 744 cm^-1 in the range of [TFSA^-]/[Li(I)] = 20.0 - 5.00. From analyses of these Raman bands, the number of TFSA^- anions bound to the Li⁺ ion was evaluated to be 1.85 ± 0.08, and hence, the Li(I) in DEMETFSA solutions was proposed to exist as [Li(TFSA)₂]^- in the range of [TFSA^-]/[Li(I)] = 20.0 - 5.00. Furthermore, in the range of [TFSA^-]/[Li(I)] = 2.86 - 2.22, the band observed at around 747 cm^-1 became more strong, and the pseudoisosbestic point disappeared. From these phenomena, it seems that the Li(I) oligomer species are formed in the higher concentration region of LiTFSA. The ¹⁹F NMR signal of the TFSA^- anion observed at 42.31 ppm in neat DEMETFSA was found to shift to a higher field linearly with an increase in the concentrations of LiTFSA ([LiTFSA] = 0.00 - 0.99 mol kg^-1, [TFSA^-]/[Li⁺] = 20.0 - 3.33), while in a higher concentration range ([LiTFSA] ≥ 1.26 mol kg^-1, [TFSA^-]/[Li⁺] ≤ 2.86), a slight deviation from linearity was observed. On the other hand, the ⁷Li NMR signal did not show an appreciable shift with increasing LiTFSA concentrations. These results support that the Li(I) species in DEMETFSA solutions exist as [Li(TFSA)₂]^- and the Li(I) oligomer species in the low and high concentration regions of LiTFSA, respectively.

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The Raman spectra for 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide [BMI][TFSA] containing alkaline metal salts of TFSA^-, MTFSA (M = Li, Na, K and Cs), were recorded in the frequency range of 200 - 1800 cm^-1, with varying salt concentrations at 298 K. With Li⁺ and Na⁺ ions, at the frequency range of 730 - 760 cm^-1, new Raman bands ascribable to the anion bound to the ions appeared at higher frequency relative to that found in the neat ionic liquid. On the other hand, with K⁺ and Cs⁺ ions, single Raman bands were solely observed. According to the difference Raman spectra for the ionic liquids containing K⁺ and Cs⁺, evaluated by subtracting Raman spectra for the neat ionic liquid, it turned out that two-state approximation, i.e., bulk TFSA^- and TFSA^- bound to K⁺ and Cs⁺ ions, could hold, as Li⁺ and Na⁺ ions. By careful analyses of Raman band intensity arising from bulk TFSA^- as a function of the salt concentration, the solvation numbers for the respective ions were successfully evaluated to be 1.95 for Li⁺, 2.88 for Na⁺, 3.2 for K⁺ and 3.9 for Cs⁺, respectively. By taking into account that TFSA^- acts as a bidentate ligand, the atomic coordination numbers are proposed to be 4, 6, 6 and 8 for Li⁺, Na⁺, K⁺ and Cs⁺, respectively. Raman shifts for the TFSA^- bound to the metal ions relative to that of the bulk TFSA^- were plotted against the ionic radii for the solvated alkaline metal ions estimated via Shannon's ionic radii, to yield a straight line with a slope of almost unity, suggesting that the electrostatic interaction predominantly operates in the ion-ion interaction between the alkaline metal ions and TFSA^-, as expected. Moreover, the Raman spectra in the frequency range of 370 - 450 cm^-1 strongly depend on the alkaline metal ions, indicating that cis TFSA^- is favored in the first solvation sphere of the Li⁺ ion of a relatively small ionic radius, and that such a preferred conformational isomerism of TFSA^- diminishes with an increase of the ionic radii of the central metal ions.

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We have investigated the aggregation behaviors of water molecules in 1-butyl-3-methylimidazolium tetrafluoroborate/water mixtures using high-pressure methods. Under ambient pressure, the IR spectra indicate that two types of O-H species: free O-H and bonded O-H, existing in ionic liquid/water mixtures. As samples were compressed, a continuous loss of the free O-H band intensity was observed. This observation may have arisen from changes in the local structures of water molecules, and the geometrical properties of the hydrogen-bond network are likely to be perturbed as the pressure is elevated. A complementary insight of the O-H spectral features is obtained by measuring the concentration-dependent variation in the mid-infrared spectra under high pressure. A sharp O-H stretching band was observed in a diluted mixture corresponding to the high order in an ice VII-like structure. Nevertheless, a very broad O-H feature was measured in a concentrated mixture, which may be attributed to the presence of more than one stable cluster.

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We have studied the cluster structure of 1-butyl-3-methylimidazolium halide, bmimX (X = Cl, Br, I), in methanol solution by means of an electrospray mass spectrometer, which is specially designed for analysis of clusters isolated from solution. In positive ion mode experiments, the ratio of solvated bmim⁺, bmim⁺(MeOH)_n and ion-pair clusters, bmim(bmim⁺X^-)_m was dependent on the counter anion. As for bmimCl solutions, few solvated bmim⁺ clusters were observed, and the ion-pair clusters were clearly observed. On the other hand, bmimBr and bmimI with large anions, the solvated bmim⁺ clusters increased obviously, and the ion-pair clusters were in turn remarkably decreased. In negative ion-mode experiments, the solvation for Br^- by the methanol is found to be the most prominent among those for Cl^-, Br^-, and I^-. These results were reasonably explained in consideration of the balance between ion-solvent and ion-counterion interactions.

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The phase-boundary potential at the interface between an aqueous KCl solution (W) and a hydrophobic room-temperature ionic liquid (RTIL), trioctylmethylammonium bis(nonafluorobutylsulfonyl)imide ([TOMA⁺][C₄C₄N^-]), containing dicyclohexano-18-crown-6 (DCH18C6), shows the nernstian response to K⁺ in W within a polarized potential window of 500 mV between [TOMA⁺][C₄C₄N^-] and W, demonstrating that hydrophobic RTILs can be used as a nonvolatile ionic medium for liquid-membrane ion-selective electrodes. The complex formation constant of K⁺ with DCH18C6 in [TOMA⁺][C₄C₄N^-] is estimated to be on the order of 10⁹ from the upper detection limit using a partition equilibrium model in the presence of a neutral ionophore. The response time of the phase-boundary potential is ∼20 min. Gelled [TOMA⁺][C₄C₄N^-] also shows the nernstian response to K⁺, although the upper limit is lower probably due to a change in the solvent properties from the non-gelled [TOMA⁺][C₄C₄N^-]. The response time of the gelled [TOMA⁺][C₄C₄N^-] is ∼5 min, shorter than that of the non-gelled [TOMA⁺][C₄C₄N^-].

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Molecular dynamics (MD) simulations have been performed to study the dynamics near the glass transition regime of molecular ions in ionic liquids. The glass transition temperature in the simulated 1-ethyl-3-methyl imidazolium nitrate (EMIM-NO₃) system was determined by plotting density against temperatures. The dynamics at several temperatures in the liquid, supercooled liquid, and glassy states have been characterized by the diffusion coefficients, fractal dimension analysis of the trajectories, and the van-Hove functions. The diffusion coefficient approximately obeys the Vogel-Fulcher-Tammann (VFT) relation. However, two power laws or two exponentials are also good descriptions of the data. The fractal dimension of the random walks is a measure of the complexity of the trajectory, which is attributed to the geometrical correlations among successive motions. Rapid increase of the fractal dimension of the random walks on decreasing temperature is found for both cations and anions. Temperature dependence of the fractal dimension of the random walks for the long range (accelerated) motion is larger than that for short range (localized) motion. This reasonably explains the change in the slopes found in the temperature dependence of the diffusion coefficients. At around the glass transition temperature, long range motion is essentially absent during the observed times, up to several nano seconds. This feature is also confirmed by the van-Hove functions. Such slowing down of the dynamics in the fragile ionic liquids is characterized by the changes from long range motion to short range motion instead of sudden changes at around T₀ in the VFT relation.

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Transient grating spectroscopy was applied to measurements of sound velocity and thermal diffusivity in binary mixture solutions of carbon dioxide (CO₂) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIm][PF₆]) along the saturated line of CO₂ at 40°C up to 20.0 MPa. The sound velocity decreased more than 10% by increasing the pressure to 10 MPa, and the pressure effect was very small above 10 MPa. The change in the thermal diffusivity was small. The translational diffusion coefficients of carbon monoxide, diphenylacetylene (DPA), and diphenylcyclopropenone (DPCP) were also determined. The diffusion coefficients increased up to 10 MPa, and the pressure effect was almost saturated above 10 MPa. The pressure dependence of the diffusion coefficients of DPCP and DPA was larger than that of carbon monoxide. The results are discussed in relation with the viscosity change caused by applying pressure.

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Thermal decomposition behaviors of a series of imidazolium-type ionic liquid samples were studied by pyrolysis-gas chromatography at 550°C using various detectors. As for the imidazolium halides, haloalkanes and 1-alkylimidazoles corresponding to the alkyl substituents were mainly formed through the nucleophilic attacks of halide ions to the alkyl groups followed by C-N bond cleavage, along with a minor amount of alkenes. Meanwhile, in the case of the ionic liquids with BF₄, PF₆ and CF₃SO₃ anions, corresponding alkenes were predominantly produced along with 1-alkylimidazoles rather than haloalkanes. No boron-containing products were found even from the samples with BF₄ anion, whereas minor but clear peaks of phosphorous-containing products were observed in the pyrograms of the samples with PF₆ anions. As for the samples with longer alkyl group, the pyrolyzates reflecting the C-C bond scissions in the alkyl groups were also formed to some extent. Meanwhile, imidazole rings did not decompose under the experimental conditions at around 550°C.

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Haloesterification of diverse diols with various carboxylic acids was achieved using potassium halides (KX) as the only halide source in ionic liquids. The best yield was obtained in [BMIM][PF₆] when 1,2-octanediol, palmitic acid and KBr were used. This yield was 85% and the regioisomer with the bromine in primary position was present in a 75:25 ratio. The regioisomeric ratio could be improved using either KCl or some phenylcarboxylic acids. [BMIM][PF₆] acts as both reaction media and catalyst of the reaction. To the best of our knowledge, this type of combined reaction using an ionic liquid is unprecedented. The other solvents tested did not lead either to the same yield or to the same regioisomeric ratio.

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Ethylammonium nitrate (EAN) is composed of C₂H₅NH₃⁺ and NO₃^- ions, which behave as an acid and a base, respectively. The ionic liquid thus involves small amounts of C₂H₅NH₂ and HNO₃ molecules owing to proton transfer from C₂H₅NH₃⁺ to NO₃^-. The equilibrium constant K_s (= [C₂H₅NH₂][HNO₃]), which corresponds to the autoprotolysis constant of water, was obtained to be ca. 10^-10 mol² dm^-6 by potentiometry using an ion-selective field-effect transistor and hydrogen electrodes at 298 K. The value indicates that C₂H₅NH₂ and HNO₃ molecules of ca. 10^-5 mol dm^-3 are involved in neat EAN. On the other hand, in an EAN-water mixture, a water molecule behaves as a base. The apparent pK_s value was determined in EAN-water mixtures of various solvent compositions. Interestingly, the pK_s value is remained at 10.5 in mixtures over the range of an EAN mole fraction of 0.05 - 0.9. The value is close to the pK_a of C₂H₅NH₂, or the acid-dissociation constant of C₂H₅NH₃⁺, in aqueous solution. This implies that the reaction C₂H₅NH₃⁺ + H₂O → C₂H₅NH₂ + H₃O⁺ is responsible for the pK_s over a wide range of solvent composition. The pK_s value in neat EAN is thus slightly smaller than that in the mixtures, implying that H₃O⁺ is a stronger acid than HNO₃ in an EAN solution, unlike water.

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That phosphonium-type ionic liquids (ILs) can be used for preparation of novel solid-phase extractants has been shown. The conditions of IL immobilization on the different matrices (polyacrilonitrile, Amberlite XAD-7, hyper cross-linked polystyrene, and multi-walled carbon nanotubes) were determined. The solid-phase extraction of Pt(IV) from 1 - 2 M HCl and Pu(IV) from 3 M HNO₃ has been investigated. The possibility of retaining ligands on the solid phases by means of ILs to prepare the complexing solid-phase extractants has been demonstrated.

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This study reports on optimization of the RP-HPLC separation of imidazolium and pyridinium ionic liquid cations using a variable-size simplex algorithm. Under the optimized conditions, all critical pairs of ionic liquids were successfully separated in a single chromatographic run. The mobile phase at the point corresponding to the optimum consisted of 10% MeOH and 90% 15 mM KH₂PO₄/H₃PO₄ with pH 3.43. The coefficients of asymmetry for all of the compounds analyzed at the simplex algorithm optimum ranged from 0.83 to 2.91.

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The usefulness of a cation exchange system followed by conductometric detection for alkylimidazolium cations separation and analysis was found for the first time. Furthermore, the possibility of simultaneously separating cations and anions typically used in ionic liquids in one chromatographic run was tested. A tandem of columns containing silica-based strong anion exchange and strong cation exchange packings was used. The study's objective was to find the optimal mobile phase: the best results were obtained with one consisting of potassium hydrogen phthalate and phthalic acid modified with acetonitrile. The method is simple and selective, and is believed to be applicable to numerous ionic liquids based on a similar design.

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The use of 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM·PF₆) as a solvent for the anodic stripping analysis of Pb(II) and Cd(II) after extraction of the iodide complexes has been investigated. This method is based on the extraction of the metal iodide complexes into BMIM·PF₆, followed by differential-pulse anodic stripping voltammetry with an in-situ plated bismuth film electrode onto an edge-plane type of pyrolytic graphite substrate. When tetra-n-propylammonium iodide at a concentration of 0.20 mol L^-1 was used as an extractant and a supporting electrolyte, the reduced lead and cadmium produced well-defined anodic peaks at -414 and -736 mV vs. Ag/AgCl, respectively. The peak currents for Pb(II) and Cd(II) were directly proportional to the initial metal concentration in the ranges of 0.01 - 0.50 µg mL^-1 and 0.05 - 1.0 µg mL^-1 under the optimized conditions. A detection limit (S/N = 3) of 0.001 µg mL^-1 Pb(II) was obtained with a volume ratio (V_aq/V_BMIM·PF6) of 2.0 at 300 s deposition time. The relative standard deviation was 3.2% on replicate runs (n = 10) for the determinations of 0.20 µg mL^-1 Pb(II).

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Self-aggregation of 1-butyl-3-methylimidazolium bromide ([bmim]Br) in D₂O has been investigated using NMR spectroscopy. The ¹H spin-lattice relaxation times (T₁) of the [bmim]⁺ increased with the decrease of concentration in the range of 0.1 - 3.0 mol dm^-3 as expected, however, in contrast, the ¹H-T₁ decreased below 0.1 mol dm^-3. The estimated ¹³C-activation energies indicated that the rotational mobility of the butyl-chain was more restricted than that of the imidazole ring at 0.1 mol dm^-3, whereas such a significant difference was not observed at 3.0 mol dm^-3. These results suggest that [bmim]⁺ forms micelle-like aggregations below 0.1 mol dm^-3 in D₂O.

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The liquid structure of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate, [BMIM]PF₆, was investigated by neutron diffraction with H/D substitution method, where the hydrogen atoms in the imidazolium ring were partially deuterated. The local structures around the ring hydrogen atoms in liquid are very similar to those estimated from the crystal structure.

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Solvation structures of manganese(II), cobalt(II), nickel(II) and zinc(II) ions in 1-ethyl-3-methylimidazolium bis(trifluoro-methanesulfonyl) amide (EMI⁺TFSA^-) have been studied by UV-Vis, FT-IR and FT-Raman spectra. The ionic liquid involves TFSA^- conformers with C₁ (cis) and C₂ (trans) symmetries, and both conformers coexist in equilibrium in the liquid state. The results showed that these metal(II) ions are all six-coordinated with three TFSA^- ions, i.e., TFSA^- ligates as a bidentate O-donor in the ionic liquid. Although the metal ion strongly prefers the C₁ conformer in crystals, the metal ion coordinates both the C₁ and C₂ conformers in the liquid state, and the conformational equilibrium in the bulk only slightly shifts to the C₁ conformer in the coordination sphere. We concluded that the conformational equilibrium in the coordination sphere is strongly temperature-sensitive.

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