Long-Wavelength Fluorescence Detection of Flavonoids in Orange Juices by LC

A new post-column liquid chromatographic reaction system for the determination of flavonoids in orange juices is based on the use of the long wavelength fluorophor cresyl violet and cerium(IV) in a cetyl trimethylammonium bromide micellar medium. Two flavone aglycones (quercetin and kaempferol), a flavonone aglycone (naringenin), one flavone-O-glycoside (rutin) and two flavanone-O-glycosides (hesperidin and naringin) have been used as analyte models. The reaction process involves the interaction between the analyte, cerium(IV) and cresyl violet giving rise to a decrease in the fluorescence, measured at λex 585, λem 625 nm, which is proportional to the analyte concentration. Dynamic ranges of the calibration graphs and detection limits, obtained with standard solutions of the analytes are (ng mL−1): quercetin (12.2–4,000, 3.7), kaempferol (3.5–1,000, 1.0), naringenin (6.7–1,000, 2.0), rutin (5.0–800, 1.5), hesperidin (10.1–1,000, 3.0), and naringin (17.8–800, 1.8). The determination coefficients were higher than 0.993 in all instances. The precision of the method, expressed as RSD%, was established at two concentration levels, with values ranging between 2.8 and 6.2%. The practical usefulness of the developed method is demonstrated by the analysis of natural and commercial orange juices, which were filtered, diluted and directly injected into the chromatographic system, with apparent recoveries between 86.9 and 107.0%.