A novel automated direct measurement method for total antioxidant capacity using a new generation, more stable ABTS radical cation

Objectives: To develop a novel colorimetric and automated direct measurement method for total antioxidant capacity (TAC). Design and Methods: A new generation, more stable, colored 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid radical cation (ABTS*+) was employed. The ABTS*+ is decolorized by antioxidants according to their concentrations and antioxidant capacities. This change in color is measured as a change in absorbance at 660 nm. This process is applied to an automated analyzer and the assay is calibrated with Trolox. Results: The novel assay is linear up to 6 mmol Trolox equivalent/l, its precision values are lower than 3%, and there is no interference from hemoglobin, bilirubin, EDTA, or citrate. The method developed is significantly correlated with the Randox- total antioxidant status (TAS) assay (r = 0.897, P< 0.0001; n = 91) and with the ferric reducing ability of plasma (FRAP) assay (r = 0.863, P< 0.0001; n = 110). Serum TAC level was lower in patients with major depression (1.69 ± 0.11 mmol Trolox equivalent/l) than in healthy subjects (1.75 ± 0.08 mmol Trolox equivalent/l, P = 0.041). Conclusions: This easy, stable, reliable, sensitive, inexpensive, and fully automated method described can be used to measure total antioxidant capacity.