Kinetic-fluorimetric determination of ascorbic acid at the nanomole level

Abstract

A kinetic-fluorimetric method is proposed for the determination of ascorbic acid. The method is based on the activating effect of ascorbic acid on the aerial oxidation of 2-hydroxynaphthaldehyde thiosemicarbazone in the presence of manganese(II), which acts as a catalyst. The reaction is monitored spectrofluorimetrically by measuring the initial rate at the excitation and emission wavelengths of the oxidation product. A linear calibration graph from 0.15 to 3 µM is obtained. The method has been applied to the determination of ascorbic acid in pharmaceuticals and fruit juices and of ascorbic acid and dehydroascorbic acid in urine.