2.4.2. ABTS radical working solution (ABTS radical cation solution)
Potassium peroxodisulfate solution (2.6 mM) was mixed with 7.4 mM ABTS solution (1:1, v/v) to react overnight at room temperature in dark to obtain ABTS radical working solution. Two concentrations working solution was prepared, their absorbance values were 1.00 ± 0.02 and 0.70 ± 0.02 at 400 nm, respectively. The fresh ABTS radical working solutions were prepared for each assay.