Sample preparation methods for determination of quercetin and quercetin glycosides in diverse matrices

Quercetin and its glycosides have gained a lot of interest due to their potential applications in preventing and treating various diseases. Quercetin is naturally available in free and glycoside forms such as isoquercitrin, rutin, avicularin, hyperoside, quercitrin, and others. These glycosides are more soluble and hence more bioavailable than quercetin. Determining the amount of quercetin in plants and foods is crucial to assess the quality of its natural sources, because the quercetin content changes with the species, variety, and the cultivation season. Furthermore, the concentrations of quercetin and quercetin glycosides in nature and biological fluids are minimal, which makes efficient sample preparation necessary before chemical analysis. The reported sample preparation methods for quercetin and quercetin glycosides include both conventional and advanced methods. Conventional sample preparation includes liquid–liquid extraction (LLE), solid phase extraction (SPE), and supercritical fluid extraction (SFE). These traditional methods are expensive, time-consuming, laborious, and non-eco-friendly, while SFE is more environmentally friendly. Recent trends in the preparation of quercetin samples consume minimal amounts of extracting solvents or sorbents and achieve higher enrichment factors. These methods include dispersive liquid–liquid microextraction (DLLME), inverted dispersive liquid–liquid microextraction (IDLLME), single-drop microextraction (SDME), and hollow fiber liquid phase microextraction (HF-LPME). In this review, the different modes of sample preparation for quercetin samples are explained. The principle of each technique, its performance characteristics, and limitations are discussed.