Developing a sensor for determination of ascorbic acid based on immobilization of a catechol derivative on the Pt–NPs/MWCNT modified GCE surface

Ascorbic acid (AA) which is an essential nutrient for mammalian cells, has various physiological and pharmacological functions, as in collagen synthesis, intestinal absorption of iron, and drug metabolism [1]. It is also applied to supplement in adequate dietary intake and as an antioxidant. It is administered in the treatment of many disorders, including Alzheimer’s disease, atherosclerosis, cancer, and infertility as well as some clinical manifestations of HIV infections [2, 3]. Due to the mentioned importance of AA, its determination in solutions has significant importance.In this work, by immobilizing of 4-(4-nitrophenylazo)catechol, NC, at the surface of a glassy carbon electrode modified with multi-wall carbon nanotubes and platinum nanoparticles (NC–Pt–NPs/MWCNT–GCE) a new sensor has been fabricated. NC–Pt–NPs/MWCNT–GCE demonstrated a high catalytic activity for AA oxidation. Results indicated that AA peak potential at NC–Pt–NPs/MWCNT–GCE shifted 150 mV to less positive values compared to bare GCE. The kinetic parameters such as electron transfer coefficient, , and the catalytic electron transfer rate constant, kh for oxidation of AA at the proposed sensor were estimated using cyclic voltammetry. The diffusion coefficient of AA was also estimated using chronoamperometry. Differential pulse voltammetry exhibited two linear dynamic ranges of 3.6-72.6 µM and 72.6-625.0 µM and low detection limit of 1.3 µM for AA. This modified electrode is found quite effective for determination AA. The modified sensor shows high sensitivity, good stability, reproducibility and is practically very useful for the electrochemical sensing of AA in pharmaceuticals products. The results obtained, using this sensor, are in very good agreement with those declared in the label of pharmaceutical products.