Measurement of antioxidant capacity of ascorbic acid against TEMPO radical scavenging using the quartz crystal micro-balance as a novel technique

Ascorbic acid is known as an important vitamin antioxidant, which has many role in the health of body cells. In this research, for the first time has been used from the quartz crystal micro-balance (QCM) technique to determine the antioxidant capacity of ascorbic acid against TEMPO radical scavenging in different concentrations in binary mixture of water-ethanol (1:2 v/v) at room temperature. In this technique, the mass changes on the quartz crystal covered by gold layer and modified by the cysteine are measured using the changes of vibrational frequency. The antioxidant capacity was measured based on the radical adsorption on the modified layer of crystal. Changes in frequency were observed proportional to the mass of the absorbed TEMPO radical. The obtained results indicate that the scavenging property of ascorbic acid is increased by increasing the concentration of TEMPO free radical. Finally, the adsorption process of TEMPO radical was evaluated by using Langmuir and Freundlich models. It was found that the adsorption of TEMPO radical on the surface of crystal follows the Langmuir isotherm.