Adsorptive stripping voltammetry determination of methyldopa at a pencil graphite electrode modified with Fe3O4 nanoparticle/reduced graphene oxide-chitosan in biological and pharmaceutical samples

Methyldopa (MD) is a catechol derivative (catecholamine) and an old antihypertensive agent which is used in the treatment of mild to moderate hypertension. It affects nerve centers which control blood vessels in the brain. As blood vessels relax, MD relieves high blood pressure [1]. Several types of analytical procedures have been employed for the analysis of catechol derivatives in pharmaceutical formulations and or biological samples. Among techniques used in several procedures most are based on spectrofluorimetric [2], kinetic measurements [3], nuclear magnetic resonance spectroscopy [4], gas chromatography [5], high performance liquid chromatography [6], chemiluminescence [7], but electrochemical methods have attracted great interests because of their simplicity, rapidness and high sensitivity in determination of MD without any tedious pre-treatments [8]. Electrochemical techniques in the field of pharmaceutical analysis have developed due to their simplicity, reasonable accuracy and precision, low cost, and rapidity. There is no need for derivatization or time-consuming extraction steps in comparison with other techniques because of less sensitivity of electroanalytical methods to the matrix effects [9]. In this study a new, simple and disposable electrochemical sensor for the determination of MD was developed on pencil graphite electrode (PGE) via differential pulse voltammetry (DPV). We report a facile approach to synthesize nanocomposites with Fe3O4 nanopaticles (NPs) attached to reduced graphene oxide (rGO), which combines the growth of Fe3O4 NPs and the reduction of GOs in one single step.The PGEs were coated with Fe3O4 NPs/rGO-CHIT tri-component. Accumulation of MD was found to be optimized in 0.1 M phosphate buffer solution (PBS, pH=2) as an electrochemical probe. Under the optimized condition calibration curve of the MD has three linear concentration ranges from 0.001 to 0.01 μM, 0.01 to 0.1 and 0.1 to 10.0 μM with the limit of detection (LOD) of 0.2 nM. Finally, the modified electrode was successfully employed to determine MD in human urine samples.