Evaluation of the extinction coefficient of the ABTS derived radical cation.

The exact knowledge of the value of the extinction coefficient of the ABTS derived radical is necessary for its quantitative use in the evaluation of the antioxidant capacity of pure compounds and/or complex mixtures. We have performed experiments in order to stablish its lower and upper limits of its value. The limits obtained, 1.0 X 10(4) M-1 cm(-1) less than or equal to epsilon(734) less than or equal to 1.6 x 10(4) M-1 cm(-1) are fully compatible with previously reported data. However, the use of these values leads to large stoichiometric coefficients for the reaction of these radicals with simple substrates, such as monophenols or tryptophan.