Sample preparation flavonols

For the red wines (82-84), which were injected directly into the HPLC without sample preparation, a ternary-gradient system using aqueous acetic acid (1% and 5% or 6%), and acidified acetonitrile (acetonitrile-acetic acid-water, 30 5 6) was used for cinnamic acid derivatives, catechins, flavonols, flavonol glycosides, and proanthocyanidins. Due to the large number of peaks, the gradient was extended to 150 min for the resolution of many peaks of important phenolics. This direct injection method was able to separate phenolic acids and esters, catechins, proanthocyanidins, flavonols, flavonol glycosides, and other compounds (such as tyrosol, and rrans-resveratrol) in wine in a single analysis. However, use of acetic acid did not permit the detector (PDA) to be used to record the UV spectra of phenolics below 240 nm (84). 

Sample Preparation for Analysis of HCTA and Flavonols in Grape Extracts and Juice... 

A method of sample preparation for analysis of grape flavonols is... 

A method of wine sample preparation is to perform liquid-liquid extraction of 50 mL of wine previously concentrated to 15 mL under vacuum at 30 °C to eliminate ethanol. Two extractions with diethyl ether (3x5 mL) and ethyl acetate (3 x 15 mL) are performed. The organic phases are combined, dried with anhydrous Na2S04, the solvent is then removed under vacuum finally, the residue is dissolved in 2mL of methanol/H20 (1 1) and filtrated 0.45 pan (Monagas et al., 2005). In this analysis, several classes of nonanthocyanic phenols are detected flavan-3-ols and flavonols, hydroxycinnamoyltartaric acids, resveratrol... 

HPLC is the method of choice for the separation of complex mixtures containing non-volatile compounds such as various flavonoids in extracts prepared from different samples. A survey of literatures revealed that most researchers have used Cjg-reversed stationary phases, which proved to be superior to the normal phase technique. The reversed phases are suitable for separating flavonoids in a wide range of polarities, as Vande Casteele et al. have demonstrated the separation of 141 flavonoids from polar triglycosides to relatively non-polar polymetoxy-lated aglycones belonging to the classes of flavones, flavonols, flavanones, dihydroflavonols, chalcones, and dihydrochalcones. 

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