Modification of the Spectrophotometric Determination of Total Flavonoids in Green Hosk of Walnuts

Significant interferences of co-existing juglone and galic acid were observed in the determination of total flavonoids in green husk of walnuts by spectrophotometry using the NaNO2-Al(NO3)3-NaOH system. To eliminate the interference, systematic tests were performed and a modification was given as follows: Two aliqucts (2.0 mL each) were taken from ethanol extract, and place separately into two 25 mL volumetric flosks. In one of the flasks, definite amount of mixed color reaction solution was added and the absorbances of A1 and A2 were measured at 15, 25 min respectively vs. reagent blank at the wavelength of 508 nm. In the other flask, 13 mL of C2H5OH(1+1) mixture and 10.0 mL of 40 g·L-1 NaOH solution were added, and its absorbance A0 was measured at 508 nm also. The absorbance of total flavonoids was calculated by the derived formula, and it content was further calculated by the regression equation. The modified method was used in the analysis of 3 samples, giving values of RSD′s (n=6) and recovery in the ranges of 0.76%-1.3% and 89.0%-105% respectively.