Nitrobenzene Interface Research Articles

Ion transfer across water/solidified nitrobenzene interface as amperometric flow detector

AbstractThe response characteristics of several ions, usually considered as electroinactive, were investigated at the thin‐layer amperometric detector based on ion transfer across the interface of water/nitrobenzene solidified by polyvinyl chloride and agar. The influence of some factors, such as applied potential, flow rate of mobile phase, and organic solvent in mobile phase, was studied by flow injection analysis of cations (choline, acetylcholine, tetramethylammonium, tetrabutylammonium, and cesium) and anions (ClO, IO, and ReO). The detection limit of the flow injection amperometric detector is in the range of 4 to 40 ng of these ions. Reversed‐phase chromatographic separation of choline and acetylcholine with amperometric detection was demonstrated.

The electron transfer at a liquid / liquid interface studied by current-scan polarography at the electrolyte dropping electrode

Some novel systems are introduced as suitable for observing the electron transfer voltammograms and/or polarograms at the aqueous (W)/nitrobenzene (NB) interface. Among them, the polarographic processes with systems composed of hexacyanoferrate(II), hydroquinone or hydroxyl ion in W/7,7,8,8-tetracyanoquinodimethane (TCNQ) in NB, hexacyanoferrate(III) or Ce 4+ in W/ferrocene (FC) or tetrathiafulvalene (TTF) in NB and permanganate in W/tetraphenylborate ion in NB were found to be reversible under appropriate conditions. The relation between the limiting currents in polarograms and the concentration of reactants either in W or NB is presented. On the basis of analysis of reversible polarograms at the W/NB interface and a comparison with voltammograms at a platinum electrode in W or in NB, the half-wave potentials are connected to the oxidation-reduction potentials of the reactants in each individual solution, W or NB.

The transfer of carboxylate and sulphonate anions at the aqueous/organic solution interface studied by polarography with the electrolyte solution dropping electrode

The transfer of carboxylate, RCOO −, and sulphonate, RSO 3 −, anions was investigated at the aqueous/1,2-dichloroethane or nitrobenzene interface, based on the half-wave potentials, Δ V 1 2 s, of the polarograms which can be related to the transfer energies, δg trs. It has been demonstrated that Δ V 1 2 is determined by the electrostatic solvation energy, Δ G solv(el), of the charged moiety in the anion, COO − or SO − 3, as well as the non-electrostatic one, Δ G solv (non-el), of the uncharged moiety, R, in both solutions when the objective anion is aliphatic carboxylate or sulphonate anion. The ϵ G solv(el) depends on the charge density of COO − or SO − 3. The non-electrostatic contribution is attributable mainly to cavity formation for the anion in the aqueous solution and hence depends on the volume of the anion. For aromatic carboxylate or sulphonate anions, whose charges are partly distributed to R due to resonance, Δ 1 2 s were less negative, i.e. Δ G trs were smaller, than those expected from Δ v 1 2 s of aliphatic anions. In this connection, the substituent effects on Δ V 1 2 s of these aromatic anions were investigated. Results obtained using chloroform as the organic solution, in which ion-pair formation is serious, are also presented as reference data. Finally, the analytical aspects of the ion transfer polarography in the determination of carboxylate and sulphonate anions are discussed.

Flow injection amperometric detection based on ion transfer across a water-solidified nitrobenzene interface for the determination of tetracycline and terramycin.

An accurate, convenient and fast method is described for the determination of tetracycline and terramycin in drugs by flow injection amperometric detection based on ion transfer across a water-nitrobenzene interface solidified with poly(vinyl chloride) and agar. When a constant potential is applied both antibiotics transfer across the interface, the process being facilitated by protons, with a linear current response for 2–200 µM solutions of tetracycline and 5–300 µM solutions of terramycin. The coefficients of variation for 22 replicate injections of 0.2 mM solutions of tetracycline and terramycin are 1.2 and 2.5%, respectively. The results obtained are in good agreement with those given by a biological assay (the relative standared deviation is less than 1%). A total of 60 samples could be determined in 1 h.

A study of proton transfer by 2,2′-bipyridine from water to nitrobenzene using chronopotentiometry with cyclic linear current-scanning and cyclic voltammetry

2,2′-Bipyridine can extract protons from the aqueous phase to nitrobenzene at pH 1.5–5.5. The extraction process has been investigated by chrono-potentiometry with cyclic linear current-scanning and cyclic voltammetry. The complex ion is formed in the aqueous phase by the reaction between hydrogen ion and 2,2′-bipyridine that has diffused from the organic phase. The transfer process is diffusion-controlled. The transfer species is a 1 : 1 proton–bipyridine complex. The formal transfer potential, Δwoϕ°tr, and the apparent Gibbs energy, ΔG°, w→otr, for the protonated bipyridine transfer at the water–nitrobenzene interface is found to be –0.005 V and –0.48 kJ mol–1, respectively. The distribution constant of free bipyridine between the two phases was calculated as log K= 1.3 ± 0.1. The diffusion coefficients of the free and protonated bipyridine in the organic and aqueous phase, DL and DHL+, are (6.4 ± 0.3)× 10–6 cm2s–1 and (7.2 ± 0.3)× 10–6 cm2 s–1, respectively.

Voltammetric study of complexing sodium cation with dibenzo-18-crown-6 in nitrobenzene phase of two-phase water-nitrobenzene extraction system

The facilitated transfer of the Na + cation through the water (w)/nitrobenzene (nb) interface affected by dibenzo-18-crown-6 dissolved in the organic phase was studied by the cyclic voltammetry in the temperature range of 5–65°C. The transfer was found to be a very fast process at each studied temperature (5, 20, 35, 50, and 65°C); the process is controlled by diffusion of the electroneutral crown ionophore from the volume of the nitrobenzene phase to the interface. Changes of thermodynamic functions characterising the studied equilibrium reaction Na + (nb) + L(nb) ⇌ NaL + (nb), where L = dibenzo-18-crown-6, were determined for a temperature of 25°C: Δ G = −36.0 kJ mol −1, Δ H = 38.9 kJ mol −1, and Δ S = −9.7 J mol −1 K −1. Further, the change of the standard Gibbs energy of the transfer of the NaL + complex from the aqueous phase into the nitrobenzene one, Δ G 0,w → nb tr, NaL + = −20.1 kJ mol −1, was calculated together with the value of the standard Galvani potential difference of the NaL + cation between the nitrobenzene and the aqueous phases, Δ nb wφ 0 NaL + = 0.208 V, and the value of Briggs' logarithm of individual extraction constant, log K i Nal + = 3.5 (L = dibenzo-18-crown-6), for the two-phase water-nitrobenzene system.

Electrochemical studies of the tetrabutyl- and tetramethyl-ammonium ion transfer across the water-1,2-dichloroethane interface: A comparison with the water—nitrobenzene interface

The results of electrochemical studies on the reaction of tetrabutyl- and tetramethylammonium (TBA + and TMA +) ion transfer from water to 1,2-dichloroethane are presented in this paper and are compared with se of the water—nitrobenzene interface. The TMA + ion transfer has been studied by the chronopotentiometric cyclic voltammetry methods and that of the TBA + ion by the chronopotentiometric method only. It has been found that the reactions are diffusion controlled over the current density range up to about 1O μA cm −2 and at polarization rates up to 0.15V s −1. Diffusion coefficients of the studied ions have been detemined, as well as their formal potentials with respect to an ion-selective tetrabutylammonium electrode to a partition electrode containing tetraethylammonium picrate whose potential is close to zero. In additon, kinetic parameters of the transfer reaction have been determined for the tetrabutylammonium ion from data obtained at current densities over 10 μA cm −2 (irreversible range).