Unusual concentration dependence of ion-exchange membrane conductivity in ampholyte-containing solutions: Effect of ampholyte nature.
In: Journal of Membrane Science, Jg. 479 (2015-04-01), S. 28-38
academicJournal
Zugriff:
Electric conductivity of homogeneous cation-exchange (CMX) and anion-exchange (AMX, AX) membranes in the salt solutions of some organic (lysine hydrogen chloride and potassium hydrogen tartrate (KHT)) and inorganic (sodium dihydrogen phosphate) ampholytes was measured as a function of their concentration. In all cases, an increase in membrane conductivity with diluting external solution was observed at concentrations <0.04 mol L –1 . This trend is not observed in the presence of strong electrolytes, such as NaCl. The effect is explained by a shift in ionic equilibriums caused by decreasing external concentration: increasing Donnan exclusion of H + ions from an anion-exchange membrane (AEM) as co-ions and increasing fraction of OH − ions in the external solution when it is diluted under a constant pH. This leads to an increase in pH of the internal charged solution in the membrane gel phase and transformation of a part of singly charged ampholyte anions (e.g. H 2 PO 4 − ) into doubly charged ones (HPO 4 2− ). The conductivity increases when one doubly charged counterion replaces two singly charged ones. The mathematical simulation of membrane conductivity concentration dependence provides a good accordance with experimental data. The effect was also simulated by measuring and calculating the conductivity of mixed KHT−K 2 T external solutions as a function of the equivalent fraction of the tartrate ion (T 2− ) under condition that the total equivalent electrolyte concentration was maintained constant. The shape of the conductivity vs. concentration curve strongly depends on the ampholyte nature, namely, on the ( pK 2 − pK 1 )/2 value. [ABSTRACT FROM AUTHOR]
Titel: |
Unusual concentration dependence of ion-exchange membrane conductivity in ampholyte-containing solutions: Effect of ampholyte nature.
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Autor/in / Beteiligte Person: | Sarapulova, V. ; Nevakshenova, E. ; Pismenskaya, N. ; Dammak, L. ; Nikonenko, V. |
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Zeitschrift: | Journal of Membrane Science, Jg. 479 (2015-04-01), S. 28-38 |
Veröffentlichung: | 2015 |
Medientyp: | academicJournal |
ISSN: | 0376-7388 (print) |
DOI: | 10.1016/j.memsci.2015.01.015 |
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