Kiyoko Takamura

Oxo[5, 10, 15, 20-tetra(4-pyridyl)porphyrinato]titanium(IV): an ultra-high sensitivity spectrophotometric reagent for hydrogen peroxide

The water-soluble titanium(IV)–porphyrin complex, oxo[5, 10, 15, 20-tetra(4-pyridyl)porphyrinato]titanium(IV)[TiO(tpyH4)4+], was found to enhance the spectrophotometric determination of trace amounts of hydrogen peroxide. A 0.05 mol dm–3 hydrochloric acid solution containing TiO(tpypH4)4+ was used (the Ti—TPyP reagent), the absorbance of which decreased at 432 nm as hydrogen peroxide was added. This was due to the consumption of the TiO(tpypH4)4+ complex following the formation of peroxo[5, 10, 15, 20-tetra(4-pyridyl)porphyrinato]titanium(IV). The decrease in absorbance at 432 nm (ΔA432) was proportional to the concentration of hydrogen peroxide, from 1.0 × 10–8 to 2.8 × 10–6 mol dm–3, in the sample solution (25 pmol–7.0 nmol per assay). The reaction was accelerated by hydrogen ions; the presence of 1.6 mol dm–3 perchloric acid was found to promote complexation to the greatest extent. A ΔA432 of 1.9 × 105 was found for 1 mol dm–3 hydrogen peroxide. A measurement precision of 1.2% for 1.0 × 10–6 mol dm–3 hydrogen peroxide (n= 8) was obtained. The reagent can be used for the determination of hydrogen peroxide in water samples such as tap water and rainwater over the range from 1.05 × 10–7 to 3.34 × 10–5 mol dm–3.

A spectrophotometric method for the determination of free fatty acid in serum using acyl-coenzyme A synthetase and acyl-coenzyme A oxidase

A mixture of Ti(IV) and 4-(2-pyridylazo)resorcinol was found to be useful in the spectrophotometric determination of trace amounts of hydrogen peroxide. The absorbance at 508 nm was proportional to the concentration of hydrogen peroxide added. The reagent was successfully applied to the assay of free fatty acid in serum through the combined use of acyl-CoA synthetase and acyl-CoA oxidase. The latter enzyme produces H2O2. As a result, hydrogen peroxide was produced through the enzymatic oxidation of free fatty acid. It was possible to determine free fatty acid in 50 microliters of serum at concentrations ranging from 0.02 to 1.5 mM. The coefficient of variation was less than 3% at concentrations ranging from 0.1 to 1.5 mM. In the present method, there is the advantage of minimal influence from reducible substances as well as greater simplicity and accuracy.

Catalytic effects of metal submonolayers formed by faradaic adsorption on the anodic oxidation of ascorbic acid at a platinum electrode

Abstract The catalytic effects of metal ions on the anodic oxidation of ascorbic acid on a Pt electrode in 1 M HClO 4 were studied by linear sweep voltammetry. The anodic peak due to a two-electron oxidation of ascorbic acid shifts to the negative potential side on the addition of Bi 3+ . This indicates the accelerating effect of Bi 3+ on the oxidation of ascorbic acid. The presence of other metal ions, such as Pb 2+ , Hg 2+ , Tl + , Ag + and Sb 3+ , also exerts similar effects. These metal ions were adsorbed on a Pt electrode at underpotentials and the adsorbed metals (denoted as M ad ) still remain on the electrode surface until the electrode potential goes up to and beyond the peak potential of the oxidation of ascorbic acid. On the other hand, metal ions forming no adsorbed layer on Pt, such as Co 2+ , Zn 2+ , Fe 3+ and Ni 2+ , exhibit no catalytic effect. These facts suggest that the presence of a M ad on Pt is essential for the promotion of the anodic oxidation of ascorbic acid. However, there is a difference in the catalytic action among the M ad , for example, Cu ad , Cd ad , In ad , Sn ad and Mo ad display no catalytic action. The catalytic activity depends on the degree of surface coverage by the M ad . The maximal effect of the M ad is attained in the submonolayer region. The effects of metal ions were discussed on the basis that the M ad plays its major role in the removal of the adsorbed ascorbic acid occupying active sites on the electrode surface, and provides effective sites for the activation of adjacent water molecules. Furthermore, from the 13 C NMR spectra for the oxidation products, the adsorbed water on the M ad appears to function by promoting the subsequent hydration steps, following the electron-transfer step of ascorbic acid.

A review of a new voltammetric method for determining acids

A new method for determining acids based on the voltammetric reduction of quinone was developed with the objective of providing a sensitive and rapid means for acid assay superior to the conventional titration method. An assessment of this method was made for determining the free fatty acid content in fats and oils, the total acidity of beverages, and the esterase activity to demonstrate its usefulness for a wide range of applications.

Drug ion transfer across an oil—water interface and pharmacological activity

Ion transfer voltammograms of 36 cholinergic, anti-cholinergic, adrenergic, anti-adrenergic, local anesthetic and hypnotic agents were measured at a nitrobenzene—water interface. Relationships between the half-wave potential of the voltammogram and the pharmacological activity are discussed for various types of drugs. The half-wave potential of a drug is useful for evaluating its hydrophobicity, and thus the ion-transfer voltammetry of drug transfer across an oil—water interface should serve as a good method for estimating pharmacological activity.

Polymer-mediated extraction of 8-quinolinolato metal chelates for the determination of metal ions in water with graphite furnace atomic absorption spectrometry.

Water-insoluble 8-quinolinolato metal chelates were formed and were stably solubilized in the aqueous solution of a water-soluble polymer, poly (N-isopropylacrylamide)(PNIPAAm), at room temperature. When the solution was heated at 50 degrees C, PNIPAAm precipitated and then formed a gum-like aggregate (polymer phase) having a very small volume. Accompanying the polymer precipitation, hydrophobic 8-quinolinolato chelates with cobalt(II), iron(III), nickel(II), and copper(II) ions were efficiently incorporated into the polymer phase. At 0.5% (w/v) of PNIPAAm and 8.0 mM of 8-quinolinol, the recoveries in the incorporation of four metal chelates were quantitative. The fluorescence spectra of a probe suggests that the hydrated polymer in the aqueous solution provides hydrophobic portions which can incorporate hydrophobic metal chelates. The polymer phase was easily taken out from the solution and was dissolved with a small amount of acetonitrile. The resulting solution could be directly introduced into a graphite furnace of atomic absorption spectrometry. The signal intensities for the absorbance of cobalt after concentrating the chelate were 100-fold greater than those before the concentration.

Role of a surfactant in the electrical potential oscillation across a liquid membrane

Electrical potential oscillation across a liquid membrane of a water/octanol/water system, in which a surfactant and ethanol are present in one of the waters, and electrical potential between octanol and aqueous phases of the octanol/water system were measured. On using sodium dodecyl sulfate (SDS) as the surfactant, potential oscillation was initiated with a sudden potential change toward the more negative potential. The upper potential (EA,SDS) and lower potential (EB,SDS) of the first oscillation were affected by the electrolyte added to the aqueous phase containing no previous surfactant. With hexadecyltrimethylammonium bromide (CTAB) as the surfactant, direction of the pulse was opposite that when using SDS. The lower potential (EA,CTAB) and upper potential (EB,CTAB) of The first oscillation were affected by the electrolyte. For instance, EA,SDS and EB,CTAB were greatly affected by halide ion size. In contrast, EA,CTAB and EB,SDS were only slightly affected by this parameter. The effects of the electrolytes on EA,SDS and EB,SDS were essentially the same as those on potentials at the interface between the octanol and aqueous phases of the octanol/water system in the absence of SDS (EC,SDS) and presence of SDS (ED,SDS), respectively. The effects of electrolytes on EA,CTAB and EB,CTAB were also basically the same as those on the potentials at the interface between the octanol and aqueous phases of the octanol/water system in the absence of CTAB (EC,CTAB) and presence of CTAB (ED,CTAB), respectively. Potential oscillation thus appears quite likely due to the repetitive formation and destruction of the surfactant layer adsorbed on the octanol/water interface.

New electrochemical detection method in high-performance liquid chromatography for determining free fatty acids

Abstract A new electrochemical detection (ECD) method in high-performance liquid chromatography (HPLC) was developed with the objective of providing a sensitive, simple, and rapid means for determining higher fatty acids. This article reviews the assessment of this method for determining free fatty acids (FFAs) in fats and oils, and in human plasma to demonstrate its usefulness from a practical viewpoint. This method requires small sample amounts and the procedure is quite simple without derivatization of fatty acids, leading to a considerable reduction in analysis time. The method consequently permits time course measurements of free fatty acid levels in human plasma. The present method is, thus, shown to have potential for a wide range of applications in food and clinical chemistry.

Rapid determination of trace amounts of phosphate and arsenate in water by spectrophotometric detection of their heteropoly acid-malachite green aggregates following pre-concentration by membrane filtration

A simple and rapid method for the determination of trace amounts of phosphate and arsenate in water is proposed. Molybdophosphate-and molybdoarsenate-Malachite Green aggregates, formed by reaction of a reagent consisting of a mixed solution of ammonium molybdate and Malachite Green, were selectively collected on a nitrocellulose membrane filter (pore size 3 µm) and dissolved in methylcellosolve together with the membrane filter. The absorbance (λ= 627 nm), denoted A(P + As), was proportional to the sum of the concentrations of phosphate and arsenate with a molar absorptivity of 2.7 × 105 l mol–1 cm–1. Thiosulphate, a reducing agent for arsenate, was added to water samples, and the absorbance of the solution, A(P), was measured as described above. The absorbance A(P) corresponds to the concentration of phosphate alone. The difference, A(P + As)–A(P), then corresponds to the arsenate concentration. The proposed method makes it possible to determine phosphate and arsenate at levels ranging from 0.3 to 150 p.p.b.

Specular reflectivity change due to the faradaic adsorption of some metal cations on Au electrode in HClO4

Summary Current-potential (i-E) and reflectivity-potential (R/R0-E) curves have been recorded for the Au electrode in M HClO4 in the presence and in the absence of small amounts of metal cations such as Pb2+, Cd2+ and Cu2+. All the metals investigated were adsorbed on Au to form atomic submonolayers at potentials more positive than the reversible potential of the bulk phase. The formation of Pbad or Cdad gave rise to a marked increase in R/R0 at 450 nm. This returned to the original value when the adsorbed layer dissolved. The rate of adsorption was measured for Pb at constant potential. The plot of R/R0 against the square root of time gave a straight line, indicating that the rate is controlled by diffusion. At high concentration of Pb2+ (3×10−3M) the formation of another type of Pb adsorption was also observed on i-E and R/R0-E curves, but the reaction became suppressed before monolayer saturation. Deposition of Cu occurred likewise at a more positive value than the reversible potential, but the reflectivity change was not so pronounced either at 450 or 700 nm. At 450 nm, it increased while at 700 nm it decreased. The wavelength dependence of the change in R/R0 was also examined. Pb, Cd, and Cu increased the reflectivity at shorter wavelengths but only Pb and Cu decreased it at wavelengths longer than 600 nm; Cd did not change the reflectivity. The reflectivity change was explained on the basis of the difference in the wavelength dependence of the reflectivity of bulk metals.