Mitsugi Senda

Ion-transfer voltammetry at 1,6-dichlorohexane|water and 1,4-dichlorobutane|water interfaces.

The usefulness of 1,6-dichlorohexane (1,6-DCH) and 1,4-dichlorobutane (1,4-DCB) as organic solvent (O) for ion-transfer voltammetry at O|water (W) interface has been examined, and the results are compared with those with 1,2-dichloroethane (1,2-DCE). The width of potential window of the 0.1M tetraoctylammonium tetrakis(4-chlorophenyl)borate (O)|0.05M Li(2)SO(4) (W) interface increased in the sequence: O = 1,6-DCH > 1,4-DCB > 1,2-DCE. The voltammetric behavior of the transfer of various cations and anions at the 1,6-DCH|W and 1,4-DCB|W interfaces has been shown to be of reversible nature, and the midpoint potentials or the reversible half-wave potentials have been determined. The midpoint potentials of hydrophilic ions have also been determined by the analysis of anodic final rise or cathodic final decent of the voltammograms with the O|W interfaces, where the W contains a salt of the hydrophilic ion. Also, the effect of ion-pair formation in O on the midpoint potentials has also been discussed.

Electron-transfer function of NAD+-immobilized alginic acid

Polymerized NAD+ (Alg-NAD+) was prepared and its electrochemical properties were investigated. NAD+ has been covalently immobilized at the carboxyl group of alginic acid using water soluble carbodiimide (EDC) and then Alg-NAD+s of various NAD+ density were obtainable depending on NAD+ concentration in the reaction mixture. Absorbance of 260 nm of Alg-NAD+s showed that 3.4 to 17.6% of carboxyl groups of alginic acid were coupled with NAD+. The coenzyme activity of immobilized NAD+ has reached 80 to 90% on each Alg-NAD+. A cathodic peak in the cyclic voltammogram of Alg-NAD+ appeared at -1.2 V (vs. SCE) corresponding to the reduction wave of free NAD+. The anodic wave of NAD dimer was not observed in the presence of 2.0 mM methyl viologen and 5 units of diaphorase and NAD+ immobilized on the composite electrode could be reduced to the normal NADH. The ratio of apparent diffusion coefficient (Dapp.) of Alg-NAD+ and free NAD+ was evaluated from the variation of ipc with the square root of sweep rate (v 1/2). Despite the high molecular weight of Alg-NAD+, Dapp. Alg-NAD+/Dapp. free NAD+ are larger than that expected. These results indicate that electron transfer occurred effectively between each NAD+ molecule immobilized onto the polymer chain. It is also confirmed by a conjugated redox enzyme reaction with Alg-NAD+.

Voltammetric study of the transfer of heavy metal ions at the nitrobenzene | water interface assisted by 5,6-diphenyl-3-(2-pyridyl)-1,2,4-triazine ☆

The transfer of heavy metal ions across the polarized nitrobenzene water interface assisted by 5,6-diphenyl-3-(2-pyridyl)-1,2,4-triazine (DPT) present in the nitrobenzene phase has been studied by normal pulse voltammetry and cyclic voltammetry. Voltammetric waves of Pb 2 + and Cd 2 + ions were reversible, whereas that of Zn 2 + ion was quasi-reversible. Voltammetric waves of Hg 2+ , Fe 2+ , and Co 2 + ions were more or less irreversible. The voltammogram of Cu 2 + ion showed a two-step wave. The dependence of the reversible half-wave potentials of Pb 2 + , Cd 2+ , and Zn 2 + ions on the concentration of DPT in the nitrobenzene phase reveals that their ion-transfer is assisted by the formation of 1:n metal-DPT complex(es) in nitrobenzene; Pb 2+ : n = 3 and 4 with the formal formation constants (log β n O ) of log β 3 O = 18.2 ± 0.1 and log β 4 O = 20.4 ± 0.1; Cd 2+ : n = 3 with log β 3 O = 27.1 ± 0.1; and Zn 2+ : n = 3 with log β 3 O = 36.0 ± 0.1, respectively.

Voltammetric study of the partition of amines between water and an organic solvent

Ion-transfer voltammetry of organic amines at an organic solvent/water (O/W) interface is studied. A theoretical equation of the current vs. potential curve of amines at a dropping electrolyte electrode is derived. The partition processes of both protonated and neutral forms of amine at O/W interface are taken into account. Kinetics of the protonation reaction between the neutral and protonated forms in W phase is also taken into account using the reaction layer theory. The theoretical prediction is in good agreement with the experimental results obtained with procaine at nitrobenzene/water interface using a dropping electrolyte electrode. Ion-transfer voltammetry and polarography is useful for studying the partition of amines between O and W phases in both neutral and protonated forms and the protonation reaction of amines in W phase as well.

Amperometric ammonium ion sensor and its application to biosensors

Abstract A urea biosensor based on the amperometric determination of ammonia produced by hydrolytic decomposition of urea by urease is described. The urease is immobilized on the amperometric ammonium ion-selective electrode sensor. This urea sensor gives the current response proportional to the concentration of urea in the range of a few to 100 ΩM in test solutions. The response can be corrected for the residual ammonium ions. The urea sensor was successfully applied to the analysis of biological fluids. An amperometric creatinine biosensor is also described.

Theory of the double-layer effect on the rate of charge transfer across an electrolyte/electrolyte interface

Abstract Effect of the electric double-layer structure on the rate equations of charge (ion or electron) transfer across an electrolyte/electrolyte solution interface is discussed. The electric double layer is considered as composed of the inner layer sandwiched by two diffuse layers in both side. The charge transfer reaction is considered as taking place between two chemical species at the planes of contact of the inner layer with the two respective diffuse layers. A steady-state ionic transport in the diffuse layers (Levich correction) is assumed. Two ideal processes; inner layer rate-determining process and diffuse layer rate-determining process are addressed.

Mediated amperometric determination of ammonia with a methanol dehydrogenase from Pseudomonas sp. AM-1 immobilized carbon paste electrode

PQQ-dependent methanol dehydrogenase (EC 1.1.99.8) was immobilized onto the surface of a carbon paste electrode by the cross-linking method and the electrode was covered with a porous polycarbonate membrane. An electrocatalytic steady-state current for the oxidation of methanol was observed using this electrode in the presence of phenazine methosulphate as an electron transfer mediator and NH4Cl as an activator for enzyme activity. The electrocatalytic current at +0.2 V vs. Ag/AgCl was analyzed. The properties of the electrode were examined for the determination of ammonia. The electrode responded linearly to ammonia in the range of 3 to 60 mM. The assay took 40 to 50 s. The electrode was used repeatedly at room temperature for 15 days and retained 50% of its initial activity.

Effect of diffuse layer on the rate of electron transfer across an electrolyte vb electrolyte solution interface

Abstract The basic equations of the kinetics of electron transfer across an electrolyte vb electrolyte solution interface, in which the effect of diffuse layers on both sides is taken into account on a simplified model of electric double layer, are presented. Two ideal processes, an inner-layer rate-determining process and a diffuse-layer rate-determining process, are discussed. Theoretical predictions derived from the basic equations are discussed. Some abnormal transfer coefficients can be explained by the theory.

Theory of transient potential response of ion-selective electrodes based on polarizable liquid ⋯ liquid interface

Abstract The theory of the transient potential response of ion-selective electrodes is presented. The mechanism of the potential response is considered using a model of the phase-boundary potential difference, and the transient potential response is considered in terms of the electrochemical principle of ion transfer, with a single ion transfer being assumed (i.e. no interference) across the boundary interface and the electric double-layer structure of the interface. The theory predicts the effect of the ion concentrations, the ion transfer kinetics and the differential capacity of the interface on the response time of ion-selective electrodes.

Electrocapillarity and the Electric Double Layer Structure at Oil/Water Interfaces

Oil/water interfaces are classified into the ideal-polarized interface and the nonpolarized interface. The interface between a nitrobenzene solution of tetrabutylammonium tetraphenylborate and an aqueous solution of lithium chloride behaves as an ideal-polarized interface in a certain potential range. Electrocapillary curves of the interface were measured. The results are analyzed using the electrocapillary equation of the ideal-polarized interface and the Gouy-Chapman theory of diffuse double layers. The electric double layer structure consisting of the inner layer and the two diffuse double layers on each side of the interface is discussed. Electrocapillary curves of the nonpolarized oil/water interface are discussed for two cases of a nonpolarized nitrobenzene/water interface.