Graphitic carbon nitride supported pristine carbon nanotubes for highly sensitive and selective electroanalysis of vitamin C in pharmaceutical and fruit samples

Abstract

In the human body, vitamin C or ascorbic acid (AA) plays a vital role in maintaining a strong immune system; it serves as a cofactor for enzymatic reactions, supports collagen synthesis and neutralizes free radicals. However, an abnormal concentration of this antioxidant in the body can lead to serious health concerns. Thus, keeping the AA level within the safe concentration range is crucial for promoting good health. Since AA is not produced by the human body, its accurate quantification in food and pharmaceutical formulations (through which it is ingested) constitutes a golden opportunity to make necessary actions concerning AA concentration in the body. Herein, a nanocomposite consisting of graphitic carbon nitride (gC₃N₄) and pristine multi-walled carbon nanotubes (CNTs) is proposed as an electrode material for AA electroanalysis in vitamin C tablets and orange juices. Physical characterization confirmed the successful synthesis of gC₃N₄ and the distribution of CNTs over its layers. Various electrochemical studies revealed the strong affinity of gC₃N₄ towards AA, exhibited the great ability of CNTs to enhance the electron transfer kinetics at the sensor-electrolyte interface and indicated that the overall electrochemical kinetics at the sensor surface is diffusion-controlled. Under optimal conditions, the sensor calibration, carried out in the concentration range of 1 to 9 μM, revealed a sensitivity, LOD and LOQ of 5.16 ± 0.07 μA μM⁻¹, 1 nM and 2.5 nM, respectively. Interference study and real sample analysis evidenced the high potential of the sensor for AA electroanalysis in pharmaceutical formulations and fruit juices.