Electrochemistry of iodine and iodide in chloroaluminate melts

The electrochemical behavior of iodine and iodide has been studied in AlCl₃+NaCl mixtures with compositions ranging from NaCl saturated melts to AlCl₃+NaCl (63+37 mol %) at platinum and tungsten electrodes. Iodide is oxidized in two steps to iodine and I(I); a reduction wave to iodide and an oxidation wave to I(I) are obtained in iodine solutions. The equilibrium constant for the reaction, I^?+I(I)=I₂, is 6×10⁸ l mol^?1 in molten chloroaluminate melts at 175°C.     

Coupling chemometrics and electrochemical-based sensor for detection of bacterial population

This work describes a home-made microelectrode array, based on reticulated vitreous carbon, which has been used to record the normal pulse voltammograms with the aim of obtaining the growth curves of Escherichia coli ATCC 13706 and Pseudomonas aeruginosa ATCC 27853 chosen as test microorganisms. The electrochemical signal data have been analysed with partial least squares (PLS) regression in order to highlight the useful analytical information and correlate with the data obtained from the aerobic plate counting. The obtained PLS models generally had a low root mean square error of cross-validation (RMSECV), a cross validated explained variance percentage near 90%.     

Determination of sulphur species arising from the reaction of sulphur and sulphide in a (K, Na)SCN eutectic melt

Sulphur and sulphide ions react in (K,Na)SCN eutectic melt with the formation of polysulphide. The electrolytic oxidation of SCN(-) at 155 degrees forms S(4) which gives S(2-)(5) with S(2-); at 165 degrees the sulphur electrogenerated is S(2) that reacts according to S(2) + S(2-) = S(2-)(3). The equilibrium constants of these reactions have been obtained by voltammetric measurements. The formation of S(2) at 155 degrees by irradiation from a xenon lamp was confirmed. The S(2) reacts with S(2-) to give S(2-)(3), and the equilibrium constant for this reaction is the same as that found for the reaction at 165 degrees .     

Activation of methanol-tolerant carbon-supported RuSe<Subscript>x</Subscript> electrocatalytic nanoparticles towards more efficient oxygen reduction

An electrocatalytic system that utilizes tungsten oxide modified carbon-supported RuSe_x nanoparticles is developed and characterized here using transmission electron microscopy and such electrochemical diagnostic techniques as cyclic voltammetry and rotating ring-disk voltammetry, as well as upon its introduction (as cathode) to the low-temperature hydrogen–oxygen fuel cell. After the modification of RuSe_x catalytic centers with ultra-thin films of WO₃, the potential of oxygen reduction in 0.5 mol dm⁻³ H₂SO₄ (in the absence and presence of methanol) is shifted ca. 70 mV (under rotating disk voltammetric conditions) towards more positive values, and the percent formation (at ring) of the undesirable hydrogen peroxide has decreased approximately twice when compared to the WO₃-free system. Relative to bare electrocatalyst, an increase of power density from 75 to 100 mW cm⁻² (at 300 mA cm⁻²) has been observed upon utilization of WO₃-modified RuSe_x in polymer electrolyte membrane fuel cell at 80 °C. In comparison to Vulcan-supported Pt nanoparticles, the overall electrocatalytic performance of tungsten oxide modified carbon-supported RuSe_x nanoparticles is lower, but the latter system is practically insensitive to the presence of methanol even at 0.5 mol dm⁻³ level. Dedicated to Professor Dr. Algirdas Vaskelis on the occassion of his 70th birthday.     

Hollow-fiber flow field-flow fractionation with multi-angle laser scattering detection for aggregation studies of therapeutic proteins

The rapid development of protein-based pharmaceuticals highlights the need for robust analytical methods to ensure their quality and stability. Among proteins used in pharmaceutical applications, an important and ever increasing role is represented by monoclonal antibodies and large proteins, which are often modified to enhance their activity or stability when used as drugs. The bioactivity and the stability of those proteins are closely related to the maintenance of their complex structure, which however are influenced by many external factors that can cause degradation and/or aggregation. The presence of aggregates in these drugs could reduce their bioactivity and bioavailability, and induce immunogenicity. The choice of the proper analytical method for the analysis of aggregates is fundamental to understand their (size) dimensional range, their amount, and if they are present in the sample as generated by an aggregation or as an artifact due to the method itself. Size exclusion chromatography is one of the most important techniques for the quality control of pharmaceutical proteins; however, its application is limited to relatively low molar mass aggregates. Among the techniques for the size characterization of proteins, field-flow fractionation (FFF) represents a competitive choice because of its soft mechanism due to the absence of a stationary phase and application in a broader size range, from nanometer- to micrometer-sized analytes. In this paper, the microcolumn variant of FFF, the hollow-fiber flow FFF, was online coupled with multi-angle light scattering, and a method for the characterization of aggregates with high reproducibility and low limit of detection was demonstrated employing an avidin derivate as sample model.

Correlation of AC-impedance and in situ X-ray spectra of LiCoO2

In-situ X-ray and AC-impedance spectra have been obtained simultaneously during the deintercalation of lithium from LiCoO2 using a specially designed electrochemical cell. The AC-dispersions have been correlated with the cell parameters obtained from the X-ray spectra. The correlation confirms previous hypothesis on the interpretation of the AC-dispersions in terms of an equivalent circuit comprising an element that relates the change of the intrinsic electronic conductivity, occurring at the early stages of deintercalation, to the semiconductor to metal transition caused by the change of the cell parameters.     

Voltammetric studies in (K,Na)SCN eutectic melt

Current-potential curves are given for flow of solution containing cyanideion through a silver packed-bed electrode. It is shown that under the proper experimental conditions analyses of the free cyanide ion may be carried out. It is also shown that, within certain concentration limits, analyses of mixtures of CN^? and Cl^? may be carried out.     

Voltammetry in fused acetamide

The voltammetric behavior of Pb(II), Cd(II), Tl(I) and Ni(II) in fused acetamide at 87°Chas been studied. The measurements have been carried out using normal polarography and cyclic voltammetry either with mercury or platinum electrodes. Only Tl(I) reduction occurs reversibly while all the other cations show some degree of irreversibility.