Comparative analysis of alkali and alkaline-earth cations assisted transfer by monensin across the water/1,2-dichloroethane interface

S.A. DASSIE; A.M.BARUZZI

JOURNAL OF ELECTROANALYTICAL CHEMISTRY

ELSEVIER

Lugar: Amsterdam; Año: 2000 vol. 492 p. 94 - 102

0022-0728

In the first part of this paper the electrochemical transfer of alkali cations (M) assisted by monensin (HX) across the water  1,2-dichloroethane (DCE) interface at pHB5, combined with a chemical exchange reaction at 5BpHB9, is proposed as the only mechanism responsible for the transfer of these cations. At pH\9 the current is voltammetrically negligible. An equation for the dependence of Do wf1:2 on pH and Na concentration is developed. In the second part of the paper the transfer of alkaline earth cations assisted by the same ionophore is studied. The electrochemical reactions (Me(w) 2HX(o)?MeHX2 (o) ) and (Me(w) 2X (o)? MeX (o)) are responsible for the peaks observed at pHB5.0 and at pH\9.0, respectively. As expected, in both cases DEp0.030 V while at intermediate pH the electrochemical exchange reaction (Me2 (w) HX(o) ?MeX (o)H (w)) is proposed. The net charge transfer of 1 at the interface accounts for DEp0.060 V for the peak observed DEp in agreement with the hyper-Nernstian slope of 60 mV found for Ca2 and Ba2 ISE based on antibiotics with carboxylic groups at intermediate pH values. The higher selectivity for Ba2 and the tendency in selectivity at alkaline pH found in the ISEs are also observed and thus explained according to the mechanism proposed.