Three flavonoid assays can be spectrophotomertically These are usually applied to quantify (i) flavonols using aluminium-chloride, (ii) flavanons and flavanonols using 2,4-dinitrophenyl-hydrazine or (iii) flavanols using 4-dimethylamino-cinnamaldehyde.
Methods utilizing the UV absorption of phenolic compounds were also tested and analyses of whole spectra were found more accurate than estimates based on absorptions at single wavelengths.