Voltammetric study of salbutamol, fenoterol and metaproterenol at unmodified and Nafion-modified carbon paste electrodes

Abstract

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.

Exploring the electrochemiluminescent behavior of procaterol hydrochloride in the presence of Ru(bpy)32+ and its analytical application in pharmaceutical preparation

“…Compared with the supporting electrolyte solution (Figure a), an irreversible oxidation peak at a potential higher than +1.0 V was observed in Ru(bpy) 3 2+ solution (Figure c), and could be assigned to the irreversible oxidation of Ru(bpy) 3 2+ to Ru(bpy) 3 3+ in the alkaline solution, where hydroxyl ions can react with Ru(bpy) 3 3+ and lead to a decrease in the redox reversibility of the Ru(bpy) 3 3+ /Ru(bpy) 3 2+ pair. As shown in Figure (b), two irreversible oxidation waves (peak I at approximately +0.45 V, peak II at approximately +0.70 V) are found in the potential range of 0.30–0.80 V. According to the molecular structure of ProH shown in Figure and previous electrochemical study, the first oxidation wave could be assigned only to oxidation of the phenolic hydroxy group; the second was due to electro‐oxidation of the aliphatic amine group. When both ProH and Ru(bpy) 3 2+ were present in the solution, the oxidation current at +1.1 V increased greatly (Figure d).…”

“…These ECL responses result from the fact that the electrochemical oxidation of amines produces strong reducing intermediates, usually neutral radical species, that react with the electrogenerated Ru(bpy) 3 3+ to produce excited state Ru(bpy) 3 2+* and lead to light emission . From the electrochemical study, it can be inferred that the aliphatic amine of ProH can be oxidized to form highly reductive radicals at a potential of approximately +0.70 V . Therefore, according to the electrochemical behavior, ECL behavior and ECL emission spectrum study, a possible mechanism for the enhanced ECL response of Ru(bpy) 3 2+ in the presence of ProH is proposed in Figure .…”

Electrochemical Behavior of Formoterol Fumarate and Its Determination in Capsules for Inhalation and Human Serum using Differential-Pulse and Square-Wave Voltammetry

“…The electrochemical oxidation of formoterol appears to be a complex process and different reaction pathways are possible. From the cyclic voltammograms and bearing in mind the main voltammetric behavior of phenolic derivatives, which are structurally related to formoterol [17,18], the mechanism of oxidation of formoterol may be postulated by oxidation of the hydroxy group on the aromatic ring [19]. Comparative study on acetanilide related for the anilide group of formoterol and anisole (phenyl methyl ether) related for the methoxy group of formoterol were done by cyclic voltammetry at the glassy carbon electrode, as a function of pH, in order to identify the other oxidation step of formoterol.…”

Fast and Accurate Analysis of Drugs Using Amperometry Associated With Flow Injection Analysis

“…Consequently, significant efforts have been devoted to sensor building and its maintenance not only for pharmaceutical analysis, but also for many other applications. These include modifications on electrode surface by recovering its surface with polymeric films,40 incorporation of enzymes,45, 46 ion‐exchange polymer,47, 48 inorganic films,49 porphyrin multi‐layer films,50, 51 immunosensors52, 53 and so on.…”