A flow system using water-soluble CdSe/ZnS quantum dots modified with β cyclodextrin (β-CD) was developed for the determination of ascorbic acid. The system was based on the quenching effect produced by ascorbic acid on the fluorescence intensity of surface modified QDs with β-CD. Under the optimized conditions, the relationship between the fluorescence intensity of the β-CD-CdSe/ZnS-QDs and ascorbic acid concentration was linear in the 2–100 mg L−1 range. LOD and LOQ values of 0.6 and 2.0 mg L−1 were obtained, respectively. A reproducibility of 4.2% in terms of relative standard deviation (3.2% under repeatability conditions) was obtained. The proposed methodology was applied to the determination of ascorbic acid in fruit juices and a pharmaceutical formulation. The results obtained were in good agreement with both the titrimetric method and the amount specified by the manufacturer, thus indicating the usefulness of the proposed methodology in the alimentary field.
