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Parallel Electrode Processes in Absence of Supporting Electrolyte. Further Strong Enhancement or Depression of Transport of Ionic Species

Nowicka A., Hyk W., Stojek Z., Ciszkowska M.

Polish Journal of Chemistry

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2004

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Vol. 78 / nr 9

1553-1565

EN

Several ferrocene derivatives, including 1,1_-ferrocenedimethanol, ferrocene, sodium ferrocenesulfonate, sodium ferroceneacetate and ferrocenylmethyltrimethylammonium hexafluorophosphate, were used to examine possible situations in voltammetry, if two of them are present together in the cell under the conditions of absence of supporting electrolyte. The pairs of ferrocene derivatives were selected for the examination in such a way that one substrate was ionic and the other one neutral. Also, the diffusion coefficients of the species in the solution were sufficiently similar to avoid the effect of nonadditive voltammetric currents. If the ion formed from the neutral substrate and the second ionic substrate are the key ions in the process of preserving the electroneutrality in the diffusion layer at the electrode surface, a significant enhancement or depression of the transport of the ionic substrate takes place. The corresponding wave heights are either much higher (different signs of the ion charges) or lower (identical signs), compared to a situation, where the ionic substrate is present alone in a solution with no supporting electrolyte. The sequence of voltammetric waves of the two substrates determines, which wave is actually affected. The situations demonstrated in the paper may be useful in analytical strategies, aiming at enhancing or depressing a particular voltammetric signal.

2

Coil-to-helix transition of anionic polysaccharides: comparisond of voltammetric and conductometric results for kappa-carrageenan

Ciszkowska M., Guillaume M. D., Kotlyar I.

Chemia Analityczna

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2000

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Vol. 45, No. 2

167-174

EN

Two electroanalytical techniques, steady-state voltammetry and conductance measurements were utilized to study the conformational coil to double helix transition of an ionic polysaccharide /cappa-carrageenan, K-car, in solutions of low ionic strengths as effected by temperature and concentration of the polyion. The interactions betweep counterions, Na+, or electroactive probe ions, Tl+, and polyanions during such transition were quantified by the ratio of the diffusion coefficient of Na+ or Tl+ ions in the polyelectrolyte solution (K-car sodium salt) to that in the solution without polyelectrolyte (NaCl or NaClO4). The results for native counterions, Na+, from conductance measurements were very close to those obtained by voltammetry of Tl+ probe ions. The conformational transition was a reversible coil-to-double helix process resulting from temperature decrease. This process did not depend on the concentration of K-car for the concentration range from 10 to 40 mmol 1-1. The charge spacing in K-car conformers was determined by employing Manning's theory for polyelectrolytes. The average charge spacing calculated from the conductivity and voltammetric results was 0.39 nm and 0.90 nm for the double helix and the coil form of K-car, respectively.

PL

Badano przejście konformacyjne jonowego polisacharydu (kappa-carrageenan, K-car) w funkcji temperatury, mocy jonowej i polijonu używając stacjonarnej woltamperometrii i konduktometrii. Oddziaływanie między polijonem i kontrjonami Na+ oraz sondującymi jonami Ti+ można było określić ilościowo ze zmian współczynników dyfuzji tych jonów. Przejście ze struktury spirali do podwójnej helisy było odwracalne i nie zależało od stężenia K-car w zakresie 10-40 mmol T1. Odległość między ładunkami obliczono używając teorii Manning'a. Otrzymano wielkości 0.39 i 0.90 nm odpowiednio dla form K-car - podwójnej helisy i spirali.

3

Steady-state current at microelectrodes for arbitrarily charged species and various concentrations of supporting electrolytes

Ciszkowska M.

Chemia Analityczna

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1999

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Vol. 44, No. 3A

391-403

EN

Equations for the dependence of the limiting steady-state current on concentration of supporting electrolyte for arbitrarily charged species were developed based on the gen-eral theory of steady-state voltammetry by Myland and Oldham [ 1 ]. The only limitations of the proposed model are that the electrode reaction must result in the neutral product and that diffusion coefficients of all species do not differ significantly. Theoretical pre-dictions presented as a ratio of the limiting current, II, to diffusional current, Id, are compared with experimental data for reduction of TI+ and Cd+2 at mercury film microele-ctrodes in solutions ofvarious concentrations and types of supporting electrolyte. Exper-imental results agree well with theoretical predictions.

PL

Opierając się- na ogólnej teorii Miland i Oldhama [I] wyprowadzono równania na zależności granicznego prądu stacjonarnego od stężenia elektrolitu podstawowego dla dowolnie wybranych ładunków jonów. Model jest ograniczony do nienaładowanych produktów reakcji elektrodowych i do zbliżonych współczynników dyfuzji. Przewi-dywania teoretyczne porównano z eksperymentalnymi falami redukcji TI+ i Cd2+ na błonkowych mikroelektrodach w roztworach różnych elektrolitów. Zgodność była dobra.