Spectrophotometric Determination of Ascorbic Acid with Iron(III) and p-Carboxyphenylfluorone in a Cationic Surfactant Micellar Medium

A simple and highly sensitive spectrophotometric method for the determination of ascorbic acid (AA) was established by using iron(III) and p-carboxyphenylfluorone (PCPF) in a cationic surfactant micellar medium. The apparent molar absorptivity of the proposed method, which does not require an extraction procedure, was 2.05 × 106 dm3 mol–1 cm–1 at 655 nm. Beer’s law was obeyed in the concentration range of 0.02–0.12 µg/cm3 for AA. The procedure was successfully applied to assays of AA in pharmaceutical preparations. It is suggested that the method is based on a coupled redox-complexation reaction in which the first step is the oxidation of AA by iron(III), and the second step includes the formations of the iron(II)-PCPF (1:2) complex and the dehydroascorbic acid-iron(III)-PCPF (1:1:2) complex.