Ascorbic Acid Determination in Commercial Fruit Juice Samples by Cyclic Voltammetry

A method was developed for assessing ascorbic acid concentration in commercial fruit juice by cyclic voltammetry. The anodic oxidation peak for ascorbic acid occurs at about 490 mV on a Pt disc working electrode (versus SCE). The influence of the potential sweep speed on the peak height was studied. The obtained calibration graph shows a linear dependence between peak height and ascorbic acid concentration in the domain (0.1-10 mmol.L(-1)). The equation of the calibration graph was y = 6.391x + 0.1903 (where y represents the value of intensity measured for the anodic peak height, expressed as muA and x the analyte concentration, as mmol.L(-1), r(2) = 0.9995, r.s.d. = 1.14%, n = 10, C(ascorbic acid) = 2 mmol.L(-1)). The developed method was applied to ascorbic acid assessment in fruit juice. The ascorbic acid content determined ranged from 0.83 to 1.67 mmol.L(-1) for orange juice, from 0.58 to 1.93 mmol.L(-1) for lemon juice, and from 0.46 to 1.84 mmol.L(-1) for grapefruit juice. Different ascorbic acid concentrations (from standard solutions) were added to the analysed samples, the degree of recovery being comprised between 94.35% and 104%. Ascorbic acid determination results obtained by cyclic voltammetry were compared with those obtained by the volumetric method with dichlorophenol indophenol. The results obtained by the two methods were in good agreement.