Quantitation of Nine Scopoletin Analogues Using an HPLC-Fluorescence Method and Its Application to <i>Morinda Citrifolia</i> (Noni) Products

Scopoletin (Sco) and its analogues (Scos) are included in various functional food materials. Quantitation of Scos in foods is useful for quality evaluation purposes. In this study, an HPLC-fluorescence method was developed for analyzing Scos emitting native fluorescence in functional food materials. Sco, esculetin (Est), umbelliferone (Umb), isoscopoletin, isofraxidin, esculin, fraxetin, fraxin, and nodakenin could be separated within a retention time of 25 min by gradient elution of a Wakopak Handy ODS column (100 × 4.6 mm i.d., 6 μm) using 15 mmol/L phosphate buffer (pH 2.5) and acetonitrile. The limits of detection for Scos at a signal-to-noise ratio of 3 ranged from 7.10×10−3 to 1.39 ng/mL. Additionally, sufficient validation parameters for quantitating Scos in Noni products were obtained, with an accuracy of 67.9-117.3 %, intra-day precision of <11.7 %, inter-day precision of 9.0 %, and recovery of 67.7-114.0 %. Moreover, the proposed method was applicable to the quantitation of Scos in four Noni products. Sco, Esn, and Umb were in the ranges 9.17-34.5 μg/mL, 39.3-210.3 ng/mL, and 54.5-227.3 ng/mL, respectively, in all samples examined. The method is thus considered useful for quantifying levels of Scos in functional food materials.