STUDY OF A LANDOLT-TYPE REACTION WITH ASCORBIC-ACID IN A VESICULAR SYSTEM BY MEANS OF THE QUENCHING EFFECT OF IODINE

The iodine quenching effect on the fluorescence of the binaphthyl-based amphiphile C8BNC6N, was applied to the monitoring of a Landolt-type reaction between hydrogen peroxide, potassium iodide and ascorbic acid. The vesicular system presented takes advantage of both the extremely high sensitivity of iodine detection (10(-8) M level) and the micellar "concentration effect" which permits the indicator reaction to be monitored at very low concentrations of substrates. Significant differences are observed compared with the conventional Landolt reaction: first. the optimum pH range is shifted towards higher pH values (pH 4-6), and second a strong concentration effect is observed for negatively charged ions which allows the sensitive determination of catalysts and substrates. A very sensitive method for the determination of ascorbic acid at levels down to 10 ng ml(-1) is proposed. The usefulness of the method was evaluated by the determination of ascorbic acid in food and body fluid samples.