Jiri Koryta

Electrolysis with electrolyte dropping electrode: II. Basic properties of the system*

Abstract In a theoretical discussion the conditions have been pointed out where an interface of two immiscible electrolyte solution behaves as an equilibrium system metal ion-metallic electrode, as an ideally polarized electrode and as an electrode under faradaic current flow. The basic equations for current-electrical potential difference across the interface have been deduced for the cases of ion as well as electron transfer. Experimentally, various base electrolyte systems were studied, the most advantageous among these are LiCl in water+tetrabutylammonium tetraphenylborate in nitrobenzene and MgCl 2 in water+tetrabutylammonium dicarbollyl cobaltate in nitrobenzene. S-shaped polarographic curves were observed with the tetramethylammonium ion. The limiting current is directly proportional to concentration. The limiting currents are somewhat higher than those predicted by the Ilkovic equation which has been ascribed to the tangential movement of the interface.

Adsorption and kinetics of oxidation of ascorbic acid at platinum electrodes

Summary As shown by cyclic voltammetry and by polarography with a rotating disc electrode, ascorbic acid is oxidized at platinum electrodes in a two-electron process. There are two reaction paths of the oxidation, one corresponding to an irreversible electrode reaction of the substance without appreciable adsorption with α n a ≈0.4, the other being the oxidation of the adsorbed substance in the potential range of Pt surface oxide formation. The adsorption of ascorbic acid is reversible and non-destructive, attaining its maximum value (68% of sites of hydrogen adsorption) even at low concentrations of ascorbic acid. The process is controlled by kinetics of adsorption proper together with diffusion. One molecule of ascorbic acid occupies two hydrogen adsorption sites.

Electro-oxidation of hydrazine on mercury, silver and gold electrodes in alkaline solutions*

Summary Polarisation curves on the dropping mercury electrode were obtained varying concentration, ionic strength and pH of the solution, and on rotating silver and gold disc electrodes varying concentration and pH of the solution, and speed of rotation of the electrode. The value of ∂E/∂ log [i/(Id−i)] is approximately 0.06 V for the mercury and gold electrodes and 0.12 V for the silver electrode. The value of ∂E1/2/∂ pH is −0.06 V for the mercury electrode and −0.05±0.01 V for the gold electrode. Polarisation curves on the silver electrode seem to be independent of pH. The half-wave potential of the oxidation of hydrazine on the mercury electrode is independent of the potential difference across the diffuse double layer, 2. The process at the silver electrode is direct discharge of the hydrazine molecule. The rate-controlling process in the oxidation at mercury and gold electrodes is either a two-electron electrode reaction with participation of hydroxide ions or a chemical volume or surface reaction of the product of a one-electron reversible oxidation.

Valinomycin mediated transfer of potassium across the water/nitrobenzene interface: A study by voltammetry at the interface between two immiscible electrolyte solutions*

The valinomycin-mediated transfer of potassium ions across the water/nitrobenzene interface was studied by potential-sweep voltammetry at this interface (ITIES). With a sweep rate 16.3 mV s−1 and at low concentrations of valinomycin reversible peak voltammograms were obtained. The charge transfer process is controlled by diffusion of valinomycin to ITIES and of the complex from ITIES into the bulk of the organic phase. The formation and the dissociation of the complex are rapid surface reactions. From the peak potential the stability constant of the valinomycin-potassium complex log KKV+=5.5 was determined.

Electrochemical reduction of monovalent cation complexes of macrocyclic ionosphores. I. crown polyether complexes

Abstract The complex formation of alkali metals Na, K, Rb, Cs and of Tl(I) with cyclic polyethers (“crowns”) and the stability of the complexes were studied in methanol and acetonitrile by the polarographic method. The influence of a number of members in the cycle and of substituents in the polyether ring on the stability of complexes was discussed. The character of the solvent was found to be an important factor in view of its ability to solvate the cation. In methanol where the alkali cations are solvated nearly as in water, the stability constants of sodium complexes are lower than those found in the present paper in acetonitrile. They are sometimes comparable or higher than the stability constants of cyclic polyethers with the potassium ion.

Charge transfer across the interface of two immiscible electrolyte solutions

Abstract The theory, experimental methods and results of the study of processes at the interface of two immiscible electrolyte solutions (ITIES) are described. The theory is concerned with equilibrium potential, double layer structure and ion transfer kinetics. Experimental methods for double layer studies as well as for transfer kinetics are discussed. Experimental results of the study of simple and facilitated ion transfer across ITIES are described. Finally, the perspective of ITIES study is discussed.

Electrochemical reduction of monovalent cation complexes of macrocyclic ionophores. II. Valinomycin and macrotetrolide complexes

Abstract The stability and selectivity of complex formation of natural macrocyclic ionophores with alkali metal ions and monovalent thallium ion was studied by polarography. With valinomycin both stability constants and homogeneous dissociation rate constants were determined from polarographic kinetic currents. The macrotetrolides gave diffusion controlled currents. The stability of their complexes increases with the degree of substitution from nonactin to trinactin. The properties of natural ionophores were compared wiht those of crown polyethers. The selectivity of complex formation of valinomycin almost coincides with its effect on the increase of the conductivity of bilayer lipid membranes.

Voltammetric study of ion transfer across the water/o-nitrophenyloctyl ether interface: Part I. Reversible process

Abstract A new method for the determination of the zero of the potential scale based on Parkers TATB assumption is proposed. It was determined from the potential sweep voltammogram of tetraphenyl-arsonium tetraphenylborate dissolved in the oil phase, in the present case, in o -nitrophenyloctyl ether (NPOE). The half-wave potentials of ions transfer across the water/NPOE interface were found using voltammetry at ITIES. The conditional Gibbs energies of transfer from water to NPOE for tetramethyl-ammonium and tetraethylammonium cations and for picrate and perchlorate anions were evaluated. The general decrease of these values is due partly to ion-pair formation in the oil phase.

Determination of Tetracycline Antibiotics by Voltammetry at the Interface of Two Immiscible Electrolyte Solutions

Abstract A method is described for determination of the antibiotics tetracycline, chlorteracycline and 6-deoxyoxytetracycline and the dehydration product, anhydrotetracycline, by voltammetry at the interface of two immiscible electrolyte solutions (ITIES) at concentrations ranging from 0.01 mmol.dm−3. The peaks obtained with cyclic voltammetry at the water/nitrobenzene interface correspond to the transfer of the cation of the antibiotic and are proportional to its concentration.

Determination of Monensin by Voltammetry at the Interface between Two Immiscible Electrolyte Solutions

Abstract The coccidiostat monensin can be determined by voltammetry at the interface between two immiscible electrolyte solutions (ITIES) in the concentration range between 0.05 mM to 3 mM. The peaks obtained with cyclic voltammetry at the water/nitrobenzene interface correspond to the transfer of sodium ions from the aqueous to the nonaqueous phase facilitated by complexation with monensin functioning as an ionophore and are proportional to its concentrations. The method was applied to the extracts from Streptomyces cultures.