Flow-injection spectrophotometric determination of citric acid in beverages based on a photochemical reaction Original Research Article

A photochemical method for the determination of citric acid in beverages using a flow-injection system is proposed. The basis for the determination is the reaction that takes place between citric acid and Fe3+ upon irradiation with visible or UV light. Fe3+ is photochemically reduced by citric acid to Fe2+, which reacts with 1,10-phenanthroline, forming the reddish orange Fe(phen)2+3 complex. This complex (ferroin) is spectrophotometrically monitored at 512 nm, and the signal is directly related to the concentration of citric acid in the sample. The method shows a linear range between 1 and 120 μg ml−1, with a relative standard deviation of 2.8% and a sample throughput of 40 samples h−1.