Influence of temperature on the reduction kinetics of Bi(III) ion in the presence of cystine in chlorate (VII) solutions of decreased water activity

The results of the kinetic measurements of Bi(III) electroreduction on a mercury electrode in 1–8 mol dm−3 chlorate (VII) solutions and in the presence of cystine demonstrate a dependence of the process on the temperature. The applied electrochemical techniques (DC polarography, cyclic and SWV voltammetry) allowed for the determination of the kinetic and thermodynamic parameters and their correlation with water activity. The catalytic activity of cystine was confirmed by the decrease in overall enthalpies of activation. The changes in the values of ΔH ≠ and ΔS 0 for Bi(III) electroreduction in the presence of cystine with the increase of chlorate (VII) concentration showed that the mechanism is different in solutions with low water activity as compared to those with high water activity. Probably it is connected with a different structure of the activated complexes (Bi-Hg(SR)2), mediating electron transfer.

Electrochemical Behaviour of N′-(p-toluenesulphonyl)-3-methyl-4-(4′-substituted arylhydrazono) pyrazolin-5-ones

The electrochemical behaviour of N′-(p-toluenesulphonyl)-3-methyl-4-(4′-substituted arylhydrazono) pyrazolin-5-ones has been investigated at dme and gc electrodes in buffer solutions of pH 2.0, 4.0, 6.0, 8.0 and 10.0 using dc polarography and cyclic voltammetry and coulometry. The compounds exhibit one well defined wave in the entire pH range of study. The process is irreversible and diffusion controlled. Controlled potential electrolysis indicates the involvement of four electrons in the reduction process. The effect of solvent, cations and anions, temperature and substitutents on the mechanism of reduction has been studied. Based on the results obtained the mechanism of reduction has been suggested.

DC-polarography and cyclic voltammetric studies of some mono and bis azo compounds derived from aromatic primary amines and 2,3-dihydroxynaphthalene in aqueous solutions

The DC and CV behavior of some mono and bis azo compounds based on aromatic primary amines and 2,3-dihydroxynaphthalein was investigated in Britton-Robinson buffer series. The obtained results indicated that these compounds undergo an irreversible reduction leading to cleavage of the N=N center with the formation of amine compounds. However, for the derivative m-CH3 on the aniline ring in alkaline solutions, the reduction stops at the stage for saturation of the N=N center. The E1/2 and Ep shifted to more negative potentials with rise of pH and the values of il are not much influenced except for the m-CH3 derivative. The total number of electrons involved in the reduction process was determined by controlled potential coulomety and calculated from Ilkovic equation. The effect of substituents on the electrode pathway was discussed. Based on the data obtained the electroreduction mechanism was suggested and discussed.

Kinetics and Mechanism of Zn(II) Ion Electroreduction in the Presence of Vetranal

The two-step reduction of Zn(II) ions at a dropping mercury electrode in 1 M NaClO4 with addition of vetranal was examined using dc polarography, cyclic voltammetry and impedance measurements. Small changes of reversible potential of half-wave, Er1/2, values indicate that the Zn(II)-vetranal complexes formed in the solution are very unstable. A stepwise character of electron transfer in the Zn(II) ion reduction was established. The catalytic activity of vetranal is stronger in the first step of electron transfer than in the second one. The linear dependence of the true rate constant for the forward reaction, ktf, of Zn(II) electroreduction versus relative surface excess, Γ′, of vetranal at a given potential in the reaction plane, Φr, was interpreted in terms of a "bridging model".

Voltammetric quantitation at the mercury electrode of the anticholinergic drug flavoxate hydrochloride in bulk and in a pharmaceutical formulation

Flavoxate hydrochloride, 2-piperidinoethyl 3-methyl-4-oxo-2-phenyl-4-H-chromene-8-carboxylate, is a smooth muscle antispasmodic. Its electrochemical behavior was studied at the mercury electrode in buffered solutions containing 30% (v/v) methanol using dc-polarography, differential-pulse polarography, cyclic voltammetry, and linear sweep-and square-wave adsorptive stripping voltammetry. Sensitive and precise procedures were developed for determination of bulk flavoxate hydrochloride and in the pharmaceutical formulation Genurin® S.F, without sample pretreatment or extraction. Limits of quantitation (LOQ) of 1 × 10−5, 5 × 10−6, 1 × 10−8 and 1 × 10−9 M flavoxate hydrochloride were achieved by dc-polarography, differential-pulse polarography, linear sweep and square-wave adsorptive stripping voltammetric, respectively.