Food analyses: a new calorimetric method for ascorbic acid (vitamin C) determination

The analysis of the ascorbic acid (vitamin C; A.A.) contained in some foodstuff and pharmaceutical samples was performed by a new microcalorimetric method. It uses the oxidation of the vitamin C catalysed by the enzyme ascorbate oxidase (A.O.), which gets the specificity of the reaction. The calibration curve was built under the following operative conditions: 25.00 °C, pH 5.6, [A.O.]=11 IU ml −1, the linearity range is: 3≤A.A.≤270 mg l −1. The method has been applied to many samples to determine the vitamin C quantity. Each analysis takes about 20 min (the assay time is instead about 5 min, the slow step is due to the time necessary for the calorimeter to return to the operative temperature after washing). No pre-treatments of the samples are requested, unless their solubilisation in buffer. The variations of vitamin C concentration were studied in function of storage time and light exposition. Using a known HPLC assay to compare its reliability on a drug analysis has validated the proposed method.