Flavonoids purification

To purify, concentrate, and recover different pigments (flavonoids or anthocya-nins), various ion-changing resins were used. Recent screenings of 13 commercial resins [acrylic or styrene-divinylbenzene (SDVB)] for the purification and specific absorption of anthocyanins - used ethanol, methanol, and water mixtures as eluents at pH 3.5. DDVB resins (EXA-118 and EXA-90) were found most suitable using a mixture of methanol and water (1 1) for elution. The other routinely used resins like XAD-7 showed low efficiency. 

Procedure Flavonoids are then further purified with 2 ml of methanolic HC1 (2 N), followed by centrifugation (2 min, 15 600 g), hydrolyzation of 150 il of suspension in an autoclave (15 min, 120 C). A reverse osmosis-Millipore UF Plus water purification system is used in high performance liquid chromatography (HPLC) with an autosampler. After injections of 5 pg of samples, the mobile phases flow at a rate of 1 ml/minute with isocratic elution in a column at 30 C. 

Chen L, Jin H, Ding L, Zhang H, Li J, Qu C and Zhang H 2008. Dynamic microwave-assisted extraction of flavonoids from Herba Epimedii. Sep Purif Technol 59(1) 50—57. 

One of the major problems with the preparative separation of flavonoids is their sparing solubility in solvents employed in chromatography. Moreover, the flavonoids become less soluble as their purification proceeds. Poor solubility in the mobile phase used for a chromatographic separation can induce precipitation at the head of the column, leading to poor resolution, decrease in solvent flow, or even blockage of the column. 

Separation, purification and identification have yielded baicalein, baicalin and other Free-B-Ring flavonoids as the major active components in the organic extract from the roots of Scutellaria baicalensis, and S. orthocalyx. In Table 2, we demonstrated the potencies of five Free-B-Ring flavonoids isolated from three different Scutellaria species. 

Xiao, W. Han, L. Shi, B. 2008. Microwave-assisted extraction of flavonoids from radix astragali. Sep. Purif. Tech. 62 614-618. 

Zhang, Y. Li, S. Wu, X. 2008. Pressurized liquid extraction of flavonoids from Houttuynia cordata Thunh. Sep. Purif. Tech. 58 305-310. 

Other classical methods for the fractionation and purification of flavonoid extracts are filtrations through different Sephadex gels, that separate by a combination of adsorption, partition, and size exclusion using organic solvents (Sephadex LH-20) or aqueous solvents... 

Classical separations by open column chromatography with different stationary phases (silica gel, reversed-phase C-18 or C-8, polyamide, cellulose) and elution with appropriate solvent mixtures are also useful for flavonoid fractionation and purification. Different column systems can be used. The classical open column chromatography uses relatively large particle sizes (0.2-6 mm), with limited resolution, and solvent filtration through the column proceeds by the pressure of the solvent column placed on top of the stationary phase. In other cases, smaller... 

A general method for the evaluation of phenolic compounds in fermented beverages, fruit juices and plant extracts was developed using gradient HPLC and coulometric detection. In a 10 p,L injection it was possible to identify and determine 36 different flavonoids and simple and complex phenols, without sample extraction, purification or concentration, in several kinds of beers, red and white wines, lemon juice and soya, forsythia and tobacco extracts. This may also be useful for the characterization of beverages and extracts . 

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