Flow-injection methods for the determination of antioxidant activity based on free-radical processes

Flow-injection procedures are developed for the spectrophotometry determination of the antioxidant properties of low-weight biological molecules based on their interaction with free organic radicals, namely, the on-line generated radical cation from 2,2′-azino- bis -(3-ethylbenzothiazoline-6-sulfonic acid) and the longlived 2,2′-diphenyl-1-picrylhydrazyl radical. The optical and redox properties of these radicals in aqueous and water-ethanol media are studied with and without an antioxidant in the mixture. The applicability of the methods is demonstrated on a number of exogenous antioxidants: ascorbic and uric acid, glutathione, and others, trolox, a synthetic analogue of α-tocopherol, and species of plant origin: gallic, ferulic, and caffeic acids. The comparative evaluation of the total antioxidant activity of known anti-inflammatory medicines is performed. The throughput of the methods reported is 90–200 analyses per hour.