VOLTAMMETRIC STUDY OF SALBUTAMOL, FENOTEROL AND METAPROTERENOL AT UNMODIFIED AND NAFION-MODIFIED CARBON-PASTE ELECTRODES

An electrochemical study of three important beta-agonist drugs at unmodified and Nafion-modified carbon paste electrodes was carried out. All the compounds are oxidized irreversibly st high positive potentials at a bare carbon paste electrode, giving rise to sharp, well-defined peaks. A secondary oxidation process was observed at pH values above 6.0. The rate-determining step was investigated for each compound at two concentration levels. Electrochemical activation procedures were optimized to ensure reproducible signals for the construction of calibration graphs. The modification of the carbon paste surface with a Nafion film allowed a preconcentration process to take place for all compounds, such that higher sensitivities were achieved compared with the bare surface. Such modifications resulted in limits of detection for the compounds down to 2.5 X 10(-8) mol dm(-3). Optimum accumulation was obtained at low pH values (2-3). Cyclic voltammetry at two Nafion film thicknesses demonstrated that a diffusion-controlled process exists within the Nafion layer. Salbutamol showed a higher affinity for Nafion than the other two compounds, both in terms of longer linear accumulation and linear accumulation at higher concentrations.