Extraction, Separation, Detection, and Structural Analysis of Flavonoids

Flavonoids, as an important class of natural products, are the main bioactive constituents of a lot of medicinal or dietary plants. They have been reported to show extensive benefits to human health, including antioxidant, anti-inflammatory, and anti-cancer activities. In most cases, flavonoids are present in plants as a series of analogues with similar structures and physico-chemical properties. This chemical complexity renders the quality control of flavonoid-containing herbal products problematic. Therefore, rapid, accurate and sensitive analytical techniques for flavonoids are of significance. This review summarizes the advances in sample extraction, chromatographic separation, detection, and structural analysis of flavonoids in medicinal and dietary herbs since 2005. Emphasis will be put on the qualitative and quantitative analysis of flavonoids in botanical extracts by high-performance liquid chromatography (HPLC) and liquid chromatography coupled with mass spectrometry (LC/MS). New techniques like UPLC, HILIC, and 2D-HPLC have significantly improved the separation capabilities of HPLC. The versatile LC/MS does not only allow fast and accurate structural analysis of flavonoids in complicated mixtures, but also provides a rapid and sensitive technique for the quantitative detection of flavonoids in herbal extracts and even in biological matrices. These techniques will be widely used for the chemical analysis of flavonoids and for the quality control of related herbal products.