Determination of Ascorbic Acid Content of Wine and Soft Drinks by Boltammetric Techniques at Glassy Carbon Electrode

Abstract

Ascorbic acid is a white crystalline powder with a molecular formula of C6H8O6 and a formula weight of 176.12 g/mol. It is a water-soluble, antioxidant vitamin, important in forming collagen, a protein that gives structure to bones, cartilages, muscles, and blood vessels. It prevents tissue damage & used in treatment of certain diseases such as scurvy, anemia, diabetes, common cold, hemorrhagic disorders, wound healing, cough, influenza, sores, gingivitis, skin diseases, diarrhea, malaria, bacterial infections, plug poisoning, liver disease, allergic reactions, arteriosclerosis as well as infertility in males. Therefore it is important to develop a method for the determination of it in different samples. A method was developed for assessing Ascorbic acid concentration in Ethiopian soft drinks such as Fanta orange, Mirinda, Pepsi and Cocacola & wines including: Gouder, Kemila and Aksumite by cyclic voltametry and square wave voltammetry. The oxidation peak for Ascorbic acid occurs at about 596 mV (versus Ag/AgCl) on a glassy carbon working electrode by using cyclic voltammetry and about 450 mV by using square wave voltammetry. For square wave voltammetry method, the influence of operational parameters like the pulse amplitude, step potential, frequency, PH dependence and concentration dependence was investigated. For cyclic voltammetry method, the influence of scan rate, concentration and PH was also investigated. The obtained calibration graph shows a linear dependence between the peak height and Ascorbic acid concentration within the range 1.0 mM - 8.0 mM with a glassy carbon working electrode for both cyclic and square wave voltammetry methods. The developed method was applied to Ascorbic acid assessment in soft drinks and wines. The Ascorbic acid content determined ranged between 2.76 mg/100 mL for sprite and 14.71mg/100 mL for  kemila white wine by using cyclic voltammetry and 4.13 mg/100 mL for sprite and  16.34 mg/100 mL for kemila white wine by using square wave voltammetry method. Different Ascorbic acid concentrations (from standard solution) were added to analyzed samples. The degree of recovery being comprised between 97.45 and 100.72 %. The results of ascorbic acid assessment by cyclic voltammetry were compared with those obtained by square wave voltammetry are in good agreement.