ascorbic-acid and ferroin

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 microg mL(-1), with a relative standard deviation of 1.6% (n = 11), a detection limit of 2.7 microg mL(-1) and a sample throughput of 60 samples h(-1). The photochemical method shows a linear range between 1 and 80 microg mL(-1), with a relative standard deviation of 1.0% (n = 11 ), a detection limit of 0.5 microg mL(-1) and a sample throughput of 40 samples h(-1).

Topics: Ascorbic Acid; Beer; Beverages; Food, Fortified; Maximum Allowable Concentration; Phenanthrolines; Photochemistry; Rheology; Spain; Spectrophotometry

Tocopherols (vitamin E) located in the hydrophobic domains of biological membranes act as chain breaking antioxidants preventing the propagation of free radical reactions of lipid peroxidation. The naturally occurring form, d-alpha tocopherol is an exquisite molecule in that it is intercalated in the membrane in such a way that the hydrophobic tail anchors the molecule positioning the chromanol ring containing the hydroxyl group, which is the essence of its antioxidant function, at the polar hydrocarbon interface of phospholipid membranes. The interaction of this group with water soluble substances is not very well understood. In the present study, an investigation was made of the interaction of ascorbate and ferrous ions (Fe+2) initiators of lipid peroxidation with alpha tocopherol. The results show that tocopherol increases membrane associated iron. The formation of a tocopherol iron complex in the presence of phospholipid liposomes and ascorbate in its reduced form is indicated. These results suggest a new way in which tocopherols act to inhibit lipid peroxidation.

Topics: Ascorbic Acid; Chromatography, Gel; Hydrogen-Ion Concentration; Iron; Liposomes; Nephelometry and Turbidimetry; Phenanthrolines; Phosphatidylcholines; Phospholipids; Vitamin E