Calculation of the molar absorptivity of polyphenols by using liquid chromatography with diode array detection: the case of carnosic acid

Antioxidant activity of vegetable extracts is related to the nature and the amount of active components, mainly polyphenols; therefore, a correct quantification of these molecules should be required to define their concentration in such kind of vegetable extracts. A fast and accurate method to calculate molar absorption coefficients (ε), by using HPLC, has been tested on standard polyphenols and caffeine, and should be widely adapted for standardless quantitative analysis. Molar absorptivity (ε) of carnosic acid (CA) was determined from 200 to 300 nm, by the proposed method and those values were compared to tert-butyl-hydroxytoluene (BHT) ones for further comparative quantification.