Electrochemical oxidation of catecholamines on fluorine-doped SnO2 substrates. Square-wave voltammetric method for methyldopa determination in pharmaceutical dosage forms

An electrochemical study of methyldopa (MD), dopamine (DA) and adrenaline (AD) catecholamines was conducted using cyclic (CV) and square wave voltammetry (SWV). The pH-dependant electrochemical behavior of catecholamines was studied for the first time on fluorine doped tin oxide electrodes (FTO). The CV scan rate study showed the charge transfer process was diffusion controlled. Besides, electrochemical parameters such as diffusion coefficient, charge transfer coefficient and heterogeneous charge transfer rate constant were determined. The number of transferred electrons was 2. Furthermore, a method is proposed to determine MD in pharmaceutical preparations by SWV. Two linear ranges between 2.0·10−6 and 30.0 ·10−6 mol L−1 and 30.0·10−6 and 60.0·10−6 mol L−1 were found, with a limit of detection of 0.15·10−6 and 2.9·10−6 mol L−1, respectively. The method, displays good sensitivity and stability. This technique can be employed in clinical analysis, quality control and routine determination of drugs in pharmaceutical formulations.