Cyclic and pulse voltammetric study of dopamine at the interface between two immiscible electrolyte solutions

The detection of dopamine by differential pulse voltammetry (DPV) and square wave voltammetry (SWV) at the interface between two immiscible electrolyte solutions (ITIES) has been studied. Voltammetry at the liquid/liquid (water/1,2-dichloroethane) interface provides a simple method for overcoming the major problem associated with dopamine detection by voltammetry at solid electrodes: the co-existence of ascorbate at higher concentrations. Selectivity for dopamine was achieved by the use of dibenzo-18-crown-6 as an ionophore for the facilitated transfer voltammetry of protonated dopamine across the ITIES. Under these conditions, ascorbate is not transferred and hence does not interfere in the ion transfer current for dopamine. By use of DPV and SWV, the lowest concentration detectable can be lowered from ca. 0.1 mM (obtained with cyclic voltammetry) to 2 microM. Evaluation of the effect of some other physiologically important species (acetylcholine, sodium, potassium and ammonium ions) on the dopamine transfer voltammetry has been studied, indicating the need for improved ionophore designs in order to achieve practically useful selectivity.