Browsing by Author "Takayanagi, Toshio"

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    Capillary zone electrophoretic studies of ion association between inorganic anions and tetraalkylammonium ions in aqueous-dioxane media
    (2005-04) Mbuna, Julius; Takayanagi, Toshio; Oshima, Mitsuko; Motomizu, Shoji
    Ion association between inorganic anions and symmetrical tetraalkylammonium ions, R4N+ (R = Me, Et, Pr, n-Bu, n-Am, and 2-methyl butyl {isoamyl = iAm}) was investigated using ordinary silica capillary by capillary zone electrophoresis. An improved version of the Williams-Vigh method was used for the first time to measure the mobilities of the inorganic anions. Plots of log Kass against log dielectric constant in various media, revealed a smaller change in Kass compared to dielectric constant. These plots suggest that the Bjerrum's equation is inadequate in accounting for the associations of ions in a CZE setup.
  • Thumbnail Image
    Item
    Determination of bromate ion in drinking water by capillary zone electrophoresis with direct photometric detection
    (2006-09) Takayanagi, Toshio; Ishida, Makoto; Mbuna, Julius; Driouich, Rim; Motomizu, Shoji
    Bromate ion in drinking water was determined by capillary zone electrophoresis (CZE) with direct photometric detection. Bromate ion in the sample solution was introduced and concentrated into the capillary by electrokinetic injection for 50s at -10 kV. Electrophoretic separation was made at an applied voltage of -25 kV and bromate ion was detected at wavelength 193 nm, at which the baseline was stabilized with less UV-absorbing acidic phosphate buffer. Bromate ion was detected within 5 min in the electropherogram. By increasing the electric conductivity in the migrating solution with 10 mM Na2SO4, a limit of detection (LOD) of 9 x 10(-10)M (0.1 microg/L BrO3-) was achieved. The proposed method was applied to the analysis of tap water and river water samples, but bromate ion was not detected. Because the practical samples contain relatively large amount of foreign ionic substances, the tap water sample was diluted to avoid the matrix ions. Bromate ion added in a tap water at the concentration of 8 x 10(-8)M was quantitatively recovered by diluting it 1/10.
  • Thumbnail Image
    Item
    Evaluation of weak ion association between tetraalkylammonium ions and inorganic anions in aqueous solutions by capillary zone electrophoresis
    (2004-01) Mbuna, Julius; Takayanagi, Toshio; Oshima, Mitsuko; Motomizu, Shoji
    The evaluation of weak ion association between eleven (11) inorganic anions (charge -1 to -3) and five n-tetraalkylammonium ions, R4N+ (R: methyl, Me; ethyl, Et; propyl, Pr; butyl, Bu; pentyl, Am) in aqueous media at 25 degrees C was studied. The analysis of ion association equilibria was carried out under acidic condition (formate buffer, pH 3.5) at low separating potential (-10 kV) using a coated capillary with suppressed electroosmotic flow (micro = 4 x 10(-5) cm2 V(-1) s(-1)). Direct UV detection was done at anode (lambda = 220 nm). The combination of the aforementioned conditions ensured that ion association constants, Kass, between n-tetraalkylammonium ion and the small inorganic anions were reliably determined after a non-linear least squares (NLLS) treatment of the measured anion's mobility. Like their larger counterparts, small anions showed increased interaction with an increase in size of pairing ions. Moreover, for a specific cation, the interaction of small anions increased with an increase in size of the hydrated anions as reflected by the relationship between the Kass and the Stokes' radius. A favourable comparison exists between the results presented in this work and those previously documented from other analytical techniques like conductometry. Qualitatively, the mobility of the anions appeared to obey the Hückel's model more closely than the more elaborate Zwanzig and Hubbard-Onsager models.
  • Thumbnail Image
    Item
    An Investigation of Weak Ion Association Equilibria between Inorganic Anions and Tetraalkylammonium Ions in Ethanol–Aqueous Media Using Capillary Zone Electrophoresis
    (2004-07) Mbuna, Julius; Takayanagi, Toshio; Oshima, Mitsuko; Motomizu, Shoji
    Weak ion association equilibria between inorganic anions, ranging in charge from -1 to -4, and symmetrical tetra-akylammonium ions, R4N + (R = Me, Et, Pr, Bu, n-Am); were investigated in formate buffer solutions containing a variable composition of ethanol (0-62.9% (m/m)). The individual effective mobilities of the inorganic anions in a series of tetraalkylammonium chloride solutions were measured using an ordinary silica capillary maintained at 25.0 ± 0.1 °C under a negative potential (-10 kV) and direct UV detection (λ 220 nm). Under the stated experimental conditions, the association constants, Kass, showed a modest increase as the amount of ethanol in the buffer was increased. The concepts of medium effect and Gibbs free energy of transfer were applied to weak ion equilibria in order to investigate changes in association constant as the ethanol content in the buffer solutions was increased. The above treatment on selected associations revealed that the increased instability of the inorganic anion in mixed ethanolic solutions is responsible for the observed increase in Kass.
  • Thumbnail Image
    Item
    Ion-Association Analysis between Inorganic Anions and Symmetrical Tetraalkylammonium Ions in Aqueous-Acetonitrile Media by Capillary Zone Electrophoresis
    (2005-08) Mbuna, Julius; Takayanagi, Toshio; Oshima, Mitsuko; Motomizu, Shoji
    Weak ion-association equilibrium was analyzed in a water-acetonitrile solution at 25 °C by capillary zone electrophoresis using an ordinary silica capillary. The ion associates examined were formed between some inorganic anions and symmetrical tetraalkylammonium ions, where a series of acetonitrile compositions up to 62.2% (m/m) were investigated. Ion-association constants, Kass, were determined by analyzing the changes in the electrophoretic mobility; the Kass values for most of the anions increased up to about 47% (m/m) acetonitrile, beyond which they remained constant, or decreased slightly. The ion-association equilibrium between tetramethylammonium and bromide ions in aqueous-acetonitrile and in aqueous-ethanol media were compared through the Gibbs free energy of transfer, which revealed that the extent of the equilibrium in aqueous-acetonitrile media is dependent mainly on the increasing instability of Br-. On the other hand, those in aqueous-ethanol media depend on the instabilities of both tetramethylammonium and bromide ions.