Determination of the standard Gibbs energies of transfer of cations across the nitrobenzenewater interface utilizing the reduction of iodine in an immobilized nitrobenzene droplet

摘要

When a nitrobenzene (NB) droplet containing iodine is attached to a graphite electrode and immersed into a chloride containingudaqueous (AQ) solution, the electrochemical reduction of iodine is accompanied by a transfer of chloride ions from NB to water.udThese chloride ions enter the NB phase in a preceding partition between the AQ and the NB phases, supported by formation ofudI2Cl� ions in NB and accompanied by the transfer of stoichiometric amounts of cations. The overall electrode reaction is of CErevudtype, where C refers to the preceding chemical step forming I2Cl�, and Erev refers to the reversible reduction of iodine at theudgraphitejNB interface and the simultaneous transfer of chloride from NB to water. If the chloride concentration in NB is insufficientudto compensate by leaving the NB the amount of electrochemically produced iodide, a second voltammetric signal occurs at moreudnegative potentials due to the transfer of iodide from NB to water. The kinetics and thermodynamics of the preceding chemical stepudC, determine the voltammetric behaviour of the system in such way that the ratio of peak currents of the first and second signalsuddepends linearly on the Gibbs energy of transfer of the co-partitioned cations. The method was validated for cations of knownudGibbs energies of transfer, and it was applied to cations of amino acids.