Flow injection spectrophotometric determination of ascorbic acid in soft drinks and beer

Two spectrophotometric methods, a photochemical and a non-photochemical, for the determination of ascorbic acid in soft drinks and beer using a flow-injection system are proposed. The non-photochemical method is based on the redox reaction that takes place between ascorbic acid and Fe(III), yielding dehydroascorbic acid and Fe(II). Fe(II) reacts with 1,10-phenantroline, originating the reddish orange Fe(phen)(3)(2+) complex (ferroin). This complex is spectrophotometrically monitored at 512 nm, and the signal is directly related to the concentration of ascorbic acid in the sample. The photochemical method has the same basis, nevertheless, uses the irradiation with visible light to enhance the redox reaction and so achieve higher sensitivities in the analysis. The non-photochemical method shows a linear range between 5 and 80 mu g mL(-1) with a relative standard deviation of 1.6% (n = 11), a detection limit of 2.7 mu g mL(-1) and a sample throughput of 60 samples h(-1). The photochemical method shows a linear range between 1 and 80 mu g mL(-1), with a relative standard deviation of 1.0% (n = 11), a detection limit of 0.5 mu g mL(-1) and a sample throughput of 40 samples h(-1).