Voltammetric analysis of Cs+ -DB18C6 complex stoichiometry at the water vertical bar 1,2-dichloroethane interface

The transfer of Cs+ across the water \ 1,2-dichloroethane interface assiste d by dibenzo-18-crown-6 (DB 18C6) was studied using cyclic voltammetry in a concentration range aide enough to fulfil the following experimental condi tions: c(Cs)(w) >> c(DB18C6)(o), cCs(w) congruent to c(DB18C6)(o) and cCs(w ) << c(DB18C6)(o). In all cases, the total voltammetric current comprises t wo transfer processes which were compared with the theoretical voltammogram s for facilitated transfer by using different models. From the results obta ined, a first electrochemical step of Cs' transfer with interfacial formati on of the complex (Cs: DB18C6) 1:2 was followed by a second electrochemical step with formation of the complex 1:1. The relative contribution of each process to the global current depends on the concentration ratio (lambda = c(Cs)/c(DB18C6)) employed. At high lambda values, the 1:1 complex is formed through the interfacial destruction of the 1: 2 complex and at low lambda values, through the facilitated transfer of M(w) by L(o). An important aspe ct which results from the treatment carried out is that not only the ratio but also the concentration values determine the appearance of one or two pr ocesses. Spectroscopic UV-visible experiments corroborate this postulate. ( C) 1999 Elsevier Science S.A. All rights reserved.