Study on the determination method of flavone content in tea

Polyphenols, such as hydroxybenzoic acid, cinnamic acid and proanthocyanidin, are rich in tea. They all have the structure of phenolic o-dihydroxyl, and can form complex with aluminium ions under alkaline condition, which effects the determination of flavones. A comparison was made for determination of flavones in teas by both NaNO2-Al( NO3)(3) method and AlCl3 method. It concluded that the result of NaNO2-Al (NO)(3) method was higher about 60 mg/g than that of AlCl3 method. The acidic condition is requisite for the determination for AlCl3 method, the fittest pH is 5. 0. Experiment and research on interference of tannic acid indicates that average errors is 0. 017 mg, there is no increasing trend with the rising of tannic acid. Linear equation of AlCl3 method is y =0.000638 +0.8623x (r =0. 9998), the recovery of standard addition is 98. 05%. So, the plants containing more polyphenols should be adopted AlCl3 method to determine of flavones.