Analysis of HCTA and Flavonols

Because standards of HCTA are not commercially available, for quantitative analysis chlorogenic acid or free hydroxycinnamic acids are used as external standards. Standards of flavonols commercially available are quercetin and myricetin glucoside and other flavonols glycoside (e.g. rutin). Alternatively, the single HCTA and flavonols can be isolated from a grape skins extract by performing semipreparative HPLC. 

Analysis of flavonols in skins extract after hydrolysis of the glycoside forms 

Fifteen millilitres of skin extract are added of 30-40 mL of 50% (v/v) methanol aqueous solution containing HC1 (0.5 M) and morin as the internal standard the hydrolysis reaction is carried on under reflux for 1 h at 85 °C (Vuorinen et al., 2000). After cooling, the sample is filtered through a 0.45 xm membrane and analyzed by HPLC. 

Time (min) acetonitrile % aqueous 1% formic acid % flow rate (mL min-1) 

H3P04 10 3 M and B) methanol and the elution gradient program reported in Table 2.8. Detection is performed at wavelength 320 nm (sample volume injected 25 xL). 

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

Table 2.6 HPLC gradient program used for analysis of HCTA and flavonols in skins extract by a C18 (250 x 4mm, 5 pan) column (chromatograms in Figures 2.17 and 2.18) (flow rate 0.5 mL/min).

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