HPLC-UV determination of total vitamin C in a wide range of fortified food products

A HPLC method for the quantification of total ascorbic acid (AA) and isoacorbic acid (isoAA) in fortified food products, premixes and duomixes has been developed. The method is based on the acidic extraction of AA in the presence of reducing agent Tris [2-carboxyethyl] phosphine (TCEP), which maintained AA in its reduced form. The separation was performed on a C18 column with a sodium acetate eluent (pH = 5.4) containing TCEP and decylamine as ion pairing agent. The limit of detection was estimated at 0.1 mg/100 g and the recoveries were between 93% to 105% when spiking various food products with different amounts of AA. The intra-assay coefficient of variation value was 4.6% (n = 8) for infant formula and 0.8% (n = 9) for the premixes. The relative standard deviation reproducibility values obtained by 9 different laboratories ranged between 2.0% and 8.0% (n = 10). Application of the method to the analysis of 25 fortified food products, different premixes and duomixes revealed similar results to those found by the AOAC official titrimetry method.The present work shows that the proposed method can be applied to the determination of AA in different food type products and can be recommended for checking the presence of isoAA in fortified food products.