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An electrochemical study of three important fl-agonist drugs at unmodified and Nafion-modified carbon paste electrodes was carried out. All the compounds are oxidized irreversibly at 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.

The voltammetric characteristics of catecholamines: epinephrine (E) and norepinephrine (NE) and related compounds: isoproterenol, metanephrine, l-dopa, methyldopa, vanillylmandelic acid (VMA), and homovanillic acid (HVA) at unmodified and in situ surfactant-modified carbon paste electrodes were comparatively evaluated. For the basic and amphoteric compounds the modification of the electrode surface with submicellar concentrations of anionic surfactants (sodium dodecylsulfate, sodium decylsulfate or sodium dodecylsulfonate) produce an important current enhancement in its oxidation and reduction peak current together with the improvement in the reversibility of the processes. These effects were explained in basis on electrostatic and hydrophobic interactions. On the other hand, the oxidation of acidic metabolites, HVA and VMA, was studied at electrodes modified in situ with cationic surfactants. Under certain conditions the surfactant could stabilise some of the electrochemical reaction intermediates, thus explaining the different voltammetric behaviour of HVA and VMA.

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A simple and rapid method for the determination o f the antibiotic ciprofloxacin by differential pulse po1;irography (DW) has been developed. The changes in the voltammetric behavior o f this drug compound with plI was studied, and the most suitable pH for analytical purposes was found to be pH 8.5. The DPI' behavior o f this compound at this pll exhibited two reduction waves at -1.44 and -1.64 V. The former wave could be used t o determine ciprofloxacin between 5 X lo-' and 3 X l o w 5 M. The method was applied t o the determination o f ciprofloxacin in formulated tablets with a relative standarct deviation o f less t1i:in 0.4%.