A critical evaluation on the reliability of two aluminum chloride chelation methods for quantification of flavonoids.

Flavonols kaempferol, quercetin, myricetin and gossypetin, and flavones apigenin, acacetin, luteolin, orientin and tricin, are subjected to two AlCl(3) spectrophotometric methods used for determination of total flavonoid content. The method developed by Woisky and Salatino involves addition of AlCl(3) solution to the flavonoid solution and recording of optical density at 420nm. All flavonols except kaempferol have absorption maxima above 440nm and so readings at 420nm are erroneous. Among flavones, all except for luteolin and orientin, have absorption maxima below 400nm. Further, addition of CH(3)COOK and recording the absorbance at 415nm, as modified by Chang et al., works well for flavonols kaempferol, quercetin and myricetin, but not for gossypetin. The flavones luteolin and orientin absorbed above 400nm, whereas all others absorbed below 400nm. Examination of the results of both methods indicates they are inadequate, and should not to be considered as universal and standard methods for total flavonoid determination.