ABTS is oxidized to green ABTS•+ by appropriate oxidant, which can be reduced to colorless ABTS in the presence of antioxidants. The TAS of the sample can be determined and calculated by measuring the absorbance of ABTS•+ at 660 nm. Trolox is an analog of VE and has a similar antioxidant state to that of VE. Trolox is used as a reference substance for total antioxidant status.