Alkaline-earth cation transfer assisted by monensin across the water ∣ 1,2-dichloroethane interface in the presence of alkali cations

The electrochemical transfer of alkaline-earth cations (Me2+) assisted by monensin (HX) across the water ∣ 1,2-dichloroethane (DCE) in the presence of alkali cations (M+) is reported. A shift in the peak potential for Ba2+ transfer and an increase in ΔEp from 0.030 to 0.060 V are the principal effects produced by the presence of M+. These findings depend on pH and the relative concentrations of both cations. The following chemical exchange reaction M(w)++HX(c)+H2O⇄MX(o)+H3O+ coupled to the electrochemical transfer of Ba2+ accounts for ΔEp=0.060 V of the peak observed as a consequence of the net charge transfer of +1 at the interface. These results are in agreement with the hyper-Nernstian slope of 60 mV found for Ca2+ and Ba2+ ion selective electrodes based on antibiotics with carboxylic groups at intermediate pH values. A theoretical equation for the dependence of Δowφ1/2 for Me2+ with pH and M+ activity was developed.