Barbara Marczewska

The influence of thiourea on the electroreduction of Zn2+ ions in various supporting electrolytes in respect to the cap-pair effect

Abstract The mechanism of the cap-pair effect was examined with respect to its acceleration of the electro-reduction of Zn 2+ ions in NaCIO 4 , NaCl and NaBr. It was found that the presence of thiourea in the solution increased the rate of the electrode process; a role is played in the acceleration by the composition of zinc complexes formed in the bulk of the solution.

Properties of ion-selective electrodes with polymer membranes for ibuprofen determination☆

Abstract Composition of a polymeric potential-determining phase for the ibuprofen selective electrode was determined. The different possibilities of using various quaternary ammonium salts — dimethyldidecylammonium bromide, methyltrioctylammonium chloride, tetraoctylammonium chloride and methyltrioctyloammonium 2-(4-isobuthylphenyl) priopionate—as anion exchangers in polymer membranes of ibuprofen electrodes were examined. The following basic electrode parameters were investigated: measurement range, slope, limit of detection, lifetime, dependence of the electrode potential on pH and selectivity coefficients in relation to some organic and inorganic anions.

Properties of naproxen ion-selective electrodes

Naproxen membrane electrodes based on different plasticizers and the quaternary ammonium salts (QASs) dimethyldidecylammonium bromide, methyltrioctylammonium chloride, or tetraoctylammonium chloride, were prepared. The following basic parameters were investigated for the optimal electrode: measurement range (10−4 − 10−1 mol L−1), slope of the linear range of the calibration curve (−58.3 mV decade−1), limit of detection (6.0 × 10−5 mol L−1), lifetime (2.5 months), dependence of the electrode potential on pH (5.5 − 9.0), reproducibility of potential (1.2 mV) and selectivity coefficients in relation to selected organic and inorganic anions. The electrode was utilized for determination of naproxen in tablets by the calibration curve method and the standard addition method.

Mechanism of the Acceleration Effect of Thiourea on the Electrochemical Reduction of Zinc(II) Ions in Binary Mixtures on Mercury Electrode

The acceleration effect of thiourea (TU) on the electroreduction of ZnII on mercury electrode surface in binary mixtures: water + methanol (MeOH), water + dimethylsulfoxide (DMSO), water + dimethylformamide (DMF) is discussed. The obtained apparent and true forward rate constants of both electrons transfered in ZnII reduction indicated that the rate constant of the first electron increases in the presence of thiourea. The acceleration effect may probably be accounted for by the concept of the formation of an active complex, presumably composed of two TU molecules and solvent molecules, on the mercury electrode.

Influence of thiourea on the electroreduction of ZN(II) at a mercury electrode from water + ethanol mixtures in relation to the “cap-pair” effect

The electroreduction process of ions at an Hg electrode is accelerated by some organic substances that meet the conditions determined by the “cap-pair” principle [l]. The process has been examined many times in aqueous solutions [l-3], but there is insufficient information about the occurrence and the possible nature of the phenomenon in non-aqueous and mixed aqueous + organic solutions. Among some organic compounds which meet the conditions of the cap-pair principle, special attention should be paid to thiourea (TU) 12,451. The electroreduction of zinc has been studied in solutions of ethanol (EtOH) and EtOH + H,O [6]. EtOH is interesting because it is a protic solvent more basic than water. The purpose of this work was to study the influence of TU on the electroreduction of Zn(I1) from H,O + EtOH + NaCIO, solutions. The choice of NaCIO, as electrolyte was determined by earlier studies in aqueous solution [21.

The Acceleration of Zn(II) Electroreduction on Mercury Electrode by 1,5‐Diaminonaphthalene and N,N′‐Diphenylthiourea, Catalytically Passive in the Aqueous Solution, in Binary Mixtures

The effect of 1,5-diaminonaphthalene (DAN) in water–methanol (MeOH) mixture and N,N′-diphenylthiourea (DFTU) in water–ethanol (EtOH) mixture on the electroreduction of ZnII on the mercury electrode is discussed. Both substances have no effect on the ZnII electroreduction process in the aqueous solution but they accelerate the process in water–alcohol mixtures. A probable mechanism of this process has been presented.