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A polarizable reference electrode
Mareček, Vladimír
New concept of a reference electrode for electrochemical systems resolves a problem of a poor \npotential stability of refence electrodes based on the distribution of a strongly \nhydrophobic common cation between two immiscible electrolyte solutions (TTTES). The use of a \npolarizable metal electrode instead of a classical reference electrode is demonstrated in \n a modified conventional four-electrode cell with TTTES. A simple battery operated potentiostat \ncontrols the working electrode potential in a three-electrode configuration. The working metal \nelectrode then serves as a polarizable reference organic solvent electrode in a four-electrode \nsystem for the polarization of the water/organic solvent interface.\n\n
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Analysis of the Hydrated ions Clusters Impact on the Liquid/Liquid Interface
Mareček, Vladimír ; Samec, Zdeněk ; Trojánek, Antonín
Open circuit potential (OCP) measurements of the partition of tetrapentylammonium chloride (TPeACl) at the water/1,2-dichloroethane (DCE) interface reveal two remarkable processes. The first one is characterized by a decay of the OCP from its expected equilibrium value. This process has been ascribed to the extraction of the salt driven by its accumulation in the hydrated salt clusters in the DCE phase. The second process is characterized by the short-term potential spikes overlapping the long-term OCP records. These spikes are assumed to be associated with the collision and fusion of the hydrated salt clusters produced by the former process with the water/DCE interface.
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Mechanism of the Water Clusters Formation in the Organic Phase in the Presence of Hydrated Ions
Holub, Karel ; Samec, Zdeněk ; Mareček, Vladimír
A two-electrode cell comprising a liquid/liquid interface is used to study the water clusters formation in the organic solvent phase following the extraction of tetraalkylammonium chloride (TAACl) from the aqueous phase. The change in the concentration of the common TAA+ ion on the aqueous side of the interface is monitored by the open circuit potential measurements. It is shown that the amount of TAACl extracted into the organic phase exceeds considerably the limit determined by the concentration of Cl- in the organic phase at a given interfacial potential difference and the electroneutrality condition. A mechanism is proposed including an accumulation of the excess TAACl in the water clusters formed from the hydration shell of the Cl- ions, water already dissolved in the organic phase, and additional water extracted from the aqueous phase. At higher concentration of TAACl in the aqueous phase this process leads to the formation of emulsion in the organic phase.
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Electrochemical Monitoring of the Water Clusters Formation in an Organic Solvent in the Presence of Hydrated Ions
Mareček, Vladimír
An electrochemical method has been developed that makes it possible to monitor the\ndynamics of the co-extraction of water with hydrated chloride ions at the interface between\ntwo immiscible electrolyte solutions (ITIES). The interfacial potential was controlled by the\ndistribution of a common tetralkylammonium (TAA+) ion. Changes in the TAA+\nconcentration at the interface were monitored by measuring the open circuit potential (OCP).\nTransfer of hydrated chloride ions is accompanied by the transfer of TAA+, decreasing its\nconcentration on the aqueous side of the interface. This process involves the co-extraction of\nwater molecules with the hydrated chloride ions and the formation of water clusters in the\norganic solvent phase. The ability to monitor the process from the very beginning of interface\nformation allowed us to obtain important kinetic data.
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Noise Analysis of Ion Transfer Kinetics at the Micro Liquid/Liquid Interface
Josypčuk, Oksana ; Holub, Karel ; Mareček, Vladimír
Fluctuation analysis was utilized to determine the TEA ion transfer kinetics across the water/1,2-dichloroethane interface. The average value ks = 0.34 cm s-1 is comparable with the previously reported value ks = 0.2 cm s-1, derived from electrochemical impedance spectroscopy experiments. The experimental approach utilizing a thick wall glass microcapillary to fix the interface exhibits a very small stray capacitance value, proving this system to be suitable for determining the kinetics of the fast ion transfer across a liquid/ liquid interface. Application of a method employing a small perturbation signal prevents polarization of the inner capillary surface by current flowing through the cell. The induced polarization of the capillary can affect ion concentration at the interface due to electroosmosis and thus make the kinetics data evaluation difficult or erroneous.
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(Strept)avidin-biotin interactions at amalgam electrodes covered by thiol monolayer
Josypčuk, Bohdan ; Mareček, Vladimír ; Yosypchuk, O.
Carboxylic group of 11-mercaptoundecanoic acid (MUA) can be used to creat a peptide bond with species containing amino group, e.g., peptides, and proteins. By the help of EDC-NHS technology, streptavidin or avidin was covalently bonded with MUA-monolayer at a silver solid amalgam electrode. Such prepared electrode was used for detecting biotin and biotinylated albumin in the supporting electrolyte (0.15 M NaCl, 0.05 M TRIS, pH 7.0). Electrochemical impendance spectroscopy was performed for the biosensor response monitored by impedance spectroscopy. Binding of biotin or biotinylated albumin with (strept)avidin a change in the resistance of the sensor in the concentration range of 0.5-20 μg mL-1. Electrochemical regeneration of the amalgam electrode permits simply to renew its surface and to create the new biosensor.
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