Teruo Hinoue

Voltammetry using an electrode surface continuously renewed by laser ablation and its demonstration on electro-oxidation of l-ascorbic acid

A new type of voltammetry, called laser ablation voltammetry (LAV), is demonstrated by measuring voltammograms for electro-oxidation of ascorbic acid (AA) as a model reaction which is sensitive to the condition of an electrode surface. In LAV, the electrode surface is irradiated with a laser pulse at constant intervals of a few seconds during the potential scan. Because the ablation action of the laser pulse can renew not only the electrode surface but also the electric double layer and the diffusion layer at the same time, LAV gives steady-state voltammograms under a constant condition of the electrode surface without using any forced mass transfer such as rotation of the electrode. The voltammogram exhibits a large and periodic current fluctuation concomitant with each laser pulse and thereby its shape is similar to that of the polarogram obtained with a dropping mercury electrode (DME). Because of these features of LAV, steady-state voltammograms could be obtained reproducibly even for the electro-oxidation of AA with a gold electrode without special pretreatment. Further, taking into account the similarity between LAV and polarography, the pH dependence of the half- wave potential was examined by LAV. Comparison of the pH dependence obtained in this work and reported in the literature gave fair agreement. This fact has proved that LAV is a promising voltammetric technique which is readily applicable even to voltammetric studies of electrode reactions which foul the electrode surface.

Thermal Modulation Voltammetry at a 1,2-Dichloroethane/Water Microinterface Using Visible Laser Heating with Optically Absorbing Supporting Electrolyte

Thermal modulation voltammetry (TMV) using laser heating at a liquid/liquid microinterface is a useful technique for determining the standard entropy change of ion transfer. In this work, for achieving TMV using a visible laser as a heating source at a 1,2-dichloroethane (DCE)/water microinterface, we used an optically absorbing supporting electrolyte, i.e., crystalviolet tetrakis(4-chlorophenyl)borate (CVTClPB). CVTClPB served well not only as a supporting electrolyte but also as an optical absorber in the DCE solution, and thereby, well-defined linear sweep (LS) and TM voltammograms could be obtained. On the basis of LS and thermal modulation (TM) voltammograms obtained with CVTClPB, the standard entropy changes of ion transfer for six model ions were successfully determined.

Luminol chemiluminescence under interaction with heteropoly acids.

Interaction of luminol with phosphomolybdic, phosphovanadomolybdic and silicomolybdic acids was studied by examination of chemiluminescence spectra, measurement of ESR spectra, investigation of reaction order, and elucidation of inhibition effects. A scheme of the reaction mechanism is proposed.

Ion-Transfer Voltammetry at a Water/1,2-Dichloroethane Interface Using Photoionization by Ultraviolet Irradiation: Detection of Cation Radicals of p-Phenylenediamine Derivatives

We have attempted to detect electrically neutral substances by ion-transfer voltammetry at an interface between two immiscible electrolyte solutions (ITIES), such as an interface between water and 1,2-dichloroethane (a W/DCE interface), by irradiating the interface with ultraviolet light (200 - 300 nm). In the present work, while considering the facts that p-phenylenediamine derivatives are soluble in DCE, but insoluble in water, and that cation radicals of the derivatives are fairly stable in various media, we photoionized the derivatives in a DCE phase by ultraviolet irradiation, and after that carried out ion-transfer voltammetry at a W/DCE interface. As a result, we could successfully observe ion-transfer waves of cation radicals of the derivatives from the W to DCE phase. Namely, the cation radicals are generated in the DCE phase by ultraviolet irradiation, and subsequently distributed into the W phase. In addition to these ion-transfer waves, we also found that facilitated proton-transfer waves by the derivatives were shifted to a more negative potential region after ultraviolet irradiation, because of hydrogen chloride formed from photodecomposition of DCE by ultraviolet irradiation.

Effect of Ultraviolet Irradiation on Proton Transfer Facilitated by 5,10,15,20-Tetraphenyl-21 H ,23 H -porphine and Its Metal Complexes at a Water/1,2-Dichloroethane Interface

We examined photochemical effects by ultraviolet irradiation on facilitated proton transfer at a water/1,2-dichloroethane (W/DCE) interface by ion-transfer voltammetry using a Xe flash lamp. 5,10,15,20-Tetraphenyl-21H,23H-porphine (H2TPP) or its metal complex, such as cobalt (Co(II)TPP), zinc (Zn(II)TPP), and nickel (Ni(II)TPP) complexes, was added into the DCE phase as an ionophore for the facilitated proton transfer. After we irradiated the W/DCE interface through the W phase, the voltammetric waves for proton transfer facilitated by H2TPP and Co(II)TPP were remarkably enhanced and shifted to the lower potential region, compared to those before irradiation. We confirmed from the pH and argentometric titrations that such enhancements and shifts of the waves were caused by hydrogen chloride (HCl) produced by photodecomposition of DCE. On the other hand, the waves for proton transfer facilitated by Zn(II)TPP and Ni(II)TPP were very small from the beginning, and showed neither enhancement nor any shift upon irradiation.

Evidences of Electron Transfer of a Fullerene Anion Radical (C60•−) Prepared under Visible-Light Illumination at a Nitrobenzene/Water Interface

Fullerene (C60) changes to its anion radical (C60(•-)) in the presence of tetraphenylborate (TPB(-)) under visible-light illumination. Using voltammetry at a liquid/liquid interface, we investigated the electron transfer (ET) between C60(•-), previously prepared based on this photochemical reaction, in a nitrobenzene (NB) solution and hexacyanoferrate(III) ([Fe(CN)6](3-)) or proton in an aqueous solution. We suggest that positive currents appearing in voltammograms are due to the ion transfer of decomposition products of TPB(-) and ET from C60(•-) in the NB phase to [Fe(CN)6](3-), or proton in the W phase. (11)B NMR revealed that TPB(-) decomposed to some borate anions during the photochemical reaction of fullerene. Furthermore, when the NB solution containing C60(•-) was mixed with an aqueous solution containing [Fe(CN)6](3-) or proton, absorption bands of C60(•-) in a visible/near infrared absorption spectrum disappeared. This disappearance supports the ET across the NB/W interface. This finding is significant as both an example of ET at a liquid/liquid interface including photochemical reactions and the photochemistry of C60.

Effect of nitrate ion on cathodic stripping voltammetry of uranium with trioctylphosphine oxide and determination of uranium in natural water.

つり下げ水銀滴電極を用いたトリオクチルホスフィンオキシド(TOPO)によるウランの微分パルス陰極溶出ボルタンメトリーにおいて,これに影響する諸因子を検討した。ピーク電流は支持電解質の陰イオンの種類に依存し,その値は硝酸イオン≫塩化物イオン>硫酸イオンの順となった。この傾向は支持電解質を含む水相からTOPOを含むシクロヘキサンへのウランの抽出量においても同様であった。このこととウラニルイオンと各陰イオンとの錯生成定数より,ピーク電流の支持電解質依存性は試料中のウラン(VI)のイオン種に起因すると推察された。検討した結果を基にして,海水及びかん水中のウランの定量を行った。