ABSTRACT
Flavonoids are a large group of phenolic plant constituents. To date, almost 6500 different avonoids have been identied. These compounds consist of two benzene rings (A and C) that are connected by an oxygen-containing pyrene ring (B). Therefore, avonoids can be regarded as chromane derivatives with a phenyl substituent in the C-2 or C-3 position. Flavonoids are often hydroxylated in positions 3, 5, 7, 3′, 4′, and/or 5′. Frequently, one or more of these hydroxyl groups is methylated, acetylated, prenylated, or sulfated. Flavonoids are mainly present in plants as O-or C-glycosides. Aglycones (the forms lacking sugar moieties) occur less frequently. At least eight different monosaccharides or combinations of these (di-or trisaccharides) can bind to the different hydroxyl groups of the avonoid aglycone. The large number of avonoids is a result of the many different combinations of avonoid aglycones and these sugars. The most common sugar moieties include d-glucose, l-rhamnose, galactose, and arabinose. The glycosides are usually O-glycosides, with the sugar moiety bound to the hydroxyl group at the C-3 or C-7 position, whereas the C-glycosides have sugar groups bound to a carbon (usually
21.1 Denition, Chemical Construction, Physicochemical Properties, and Occurrence of Flavonoids ................................................................................................... 535
21.2 Biological Meaning and Pharmacological Activities of Flavonoids .................................. 536 21.3 Analytical Methods of Flavonoid Isolation ........................................................................ 539
21.3.1 Extraction from Plant Material ............................................................................. 539 21.3.2 Sample Purication and Concentration ................................................................ 541
21.4 Column LC ......................................................................................................................... 543 21.4.1 Optimization ......................................................................................................... 543 21.4.2 Stationary Phases ..................................................................................................544 21.4.3 Mobile Phases ....................................................................................................... 545
21.5 Detection .............................................................................................................................548 21.5.1 UV-VIS Detection .................................................................................................548 21.5.2 Fluorescence Detection ......................................................................................... 549 21.5.3 Electrochemical Detection .................................................................................... 549
21.6 Hyphenated Techniques ...................................................................................................... 549 21.6.1 LC-MS and LC-MS/MS ....................................................................................... 549 21.6.2 LC-NMR ............................................................................................................... 553
21.7 The Application of HPLC of Flavonoids ............................................................................ 554 21.8 HPLC Analysis of Chiral Flavonoids ................................................................................. 555 References ...................................................................................................................................... 555
6-C or 8-C) of the aglycone [1,2]. Many avonoids can be found in monomer, dimer, or polymer forms, called monoavans, biavans, and triavans, respectively [3].
