Hi.

A 7 mM ABTS aqueous solution and a 2.45 mM potassium persulfate solution are to be combined and allowed to sit overnight at ambient temperature (25 °C) in the dark to produce ABTS+ radical cations with an initial absorbance of 0.70 ± 0.02 at 734 nm (you can set this using UV spectrophotometer). In a final volume of 1 mL with the ABTS+ working standard, you must add the sample/standard concentrations. The absorbance at 734 nm can be used to measure immediately after a 6-minute incubation time at room temperature.