Facile fabrication of NaOH nanorods on pencil graphite electrode for simultaneous electrochemical detection of natural antioxidants by deep eutectic solvent

We report the application of deep eutectic solvents (DES) based on ethylene glycol and urea as low-cost, green, and suitable electrolytes for electrochemical studies. The main aim of this study was to explore the capabilities of DES as an enhancer of electrochemical detection for the natural antioxidants of ascorbic acid (AA) and gallic acid (GA). A simple fabrication of a disposable and effective electrochemical sensing platform for the simultaneous determination of AA and GA based on the one-step electrochemical deposition of NaOH nanorods on pencil graphite electrode (PGE) was performed. The electrochemical behaviour showed that the two antioxidants, AA and GA, could be electro-oxidized and discriminated simultaneously on the surface of the NaOH/PGE. The oxidation potentials of AA and GA shifted slightly towards negative, and the peak current values increased 2.0-fold in DES than in BR buffer medium.​​ Due to the strong synergistic effect between the nanostructures of NaOH (large effective surface area) and DES (high electrical conductivity), the proposed electrode led to the enhancement analytical performances towards AA and GA. Cyclic voltammetry, differential pulse voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy were used to examine the modified electrode's morphological and electrochemical characterization and performance parameters. The developed sensor exhibited good performance towards the determination of AA and GA with a low detection limit (1.4 µM for AA and 0.6 µM for GA), wide linear concentration ranges (2-200 µM for AA and 1-30 µM for GA), and good reproducibility (1.4% for AA and 0.4% for GA). The effects of possible interferences were investigated for their effect on the determination of AA and GA. With good selectivity and sensitivity, the sensor's reliability for the simultaneous detection of AA and GA in mineral water (flavored with green tea and vitamin C) was successfully tested. The mean analytical recovery was 100.4±2.5 and 96.2±0.6 for AA and GA, respectively. The results obtained with the presented sensor were confirmed by the HPLC method. This is a promising approach for the determination of the detection of AA and GA in different water samples.