No abstract

Metal reduction at the interface between two immiscible electrolyte solutions (ITIES) has been studied with scanning electrochemical microscopy (SECM). Metal cations in the aqueous phase are reduced by 7,7,8,8‐tetracyanoquinodimethane anion (TCNQ−) residing in the oil phase, methyl isobutyl ketone (MIBK). TCNQ− is formed at the SECM tip by reducing TCNQ, which results in a positive feedback loop between the tip and the ITIES when an electron is donated to a metal cation. The effect of the Galvani potential difference on the rate of the interfacial electron transfer was investigated, establishing the potential difference either by an additional substrate electrode in the aqueous phase or by an a common ion in both phases. It is shown that the Galvani potential difference as a driving force does enable TCNQ− mediated Cu2+ reduction. Finite element method (FEM) simulations were run to provide information on the reaction kinetics and stoichiometry.

Reduction and nanoparticle nucleation of Cu 2+ by decamethylferrocene was studied with cyclic and square-wave voltammetry at a microscale liquid-liquid interface established at the tip of a micropipette. With square-wave voltammetry, two reduction steps could be distinguished as two separate current waves. Comparing the experimental results of cyclic voltammetry with finite element method simulations, particle growth could be observed as an increasing limiting current. Furthermore, kinetic parameters could be estimated with square-wave voltammetry simulations following Butler-Volmer kinetics.

Immunofixation coupled with electrophoresis is winning favor as an easy, sensitive, and versatile method for detecting specific protein fractions. Here, we discuss problems which appear when antisera are applied onto the electrophoretic medium (Cellogel or cellulose acetate). Longitudinal slits can be made in the electrophoretic medium without worsening resolution. Such longitudinally slitted electrophoretic membranes can be used in electrophoresis and specific antisera applied simply by pipetting them onto the electrophoretograms. The method has been used successfully in typing immunoglobulins.

In an immiscible water-oil system, potential determining salts can be applied to establish Galvani potential across the interface (ITIES). These salts contain a common ion in the both phases and, therefore, via a Nernstian equation, determine the Galvani potential difference that can be used to boost electron or ion transfer reactions across the ITIES [1,2]. The contribution of potential difference and potential determining salts to solvent extraction of various metals (Co, Cu, Ni, In) was investigated with cyclic voltammetry (CV) in a four-electrode cell and with shake-flask experiments; the extraction ratios were analyzed either by atomic absorption spectroscopy (AAS) or by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Di-2-(ethylhexyl)-phosphoric acid (D2EHPA) and diphenylthiocarbazone (Dithizone) were used as model ligands. While CV measurements showed ambiguous results - sometimes no ion transfer within the potential window was observed - shake-flask experiments showed clearly that the extraction ratio (co /cw ) of some metals is enhanced in the presence of potential determining salts (Fig. 1). Fig. 1. The contribution of the potential determining salt to the extraction ratio of Ni in pH 3 and 5. [1] P. Peljo, L. Murtomäki, T. Kallio, H.-J. Xu, M. Meyer, C. P. Claude, J.-M. Barbe, H. H. Girault, K. Laasonen, K. Kontturi, Biomimetic Oxygen Reduction by Cofacial Porphyrins at a Liquid-Liquid Interface, J. Am. Chem. Soc., 134, 5972-5984, 2012. [2] B. Su, R. Partovi-Nia, F. Li, M. Hojeij, M. Prudent, C. Corminboeuf, Z. Samec and H. H. Girault, H2O2 Generation by Decamethylferrocene at a Liquid|Liquid Interface, Angew. Chem., Int. Ed., 47, 2675-4678, 2008. Figure 1