Column-switching high-performance liquid chromatographic assay for the determination of quercetin in human urine with ultraviolet absorbance detection

A high-performance liquid chromatographic method is described for the determination of quercetin in human urine using column-switching and ultraviolet (UV) absorbance detection. Urine samples were enzymatically hydrolysed and solid-phase extracted prior to injection onto the high-performance liquid chromatography (HPLC) system. Prior to elution of quercetin and the internal standard, fisetin, from the first column used for sample clean-up, the six-port valve was switched to the second column for analysis with UV detection. Detection of quercetin was accurate and reproducible, with a detection limit of 5 ng/ml. The method was applied to determine the urinary level of quercetin in 120 samples from an intervention study with fruit juice. (C) 1998 Elsevier Science B.V.