Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)The use of potentiometry to measure plasma antioxidant capacity to contribute to oxidative stress evaluation is presented. In this assay, plasma (n = 60) diluted (0.3 to 1 ml) in phosphate buffer, pH 7.4, NaCl 9%, was submitted to potentiometry. A platinum wire was the working electrode and saturated calomel the reference. The results are presented as the difference between sample and buffer potential (Delta E). Delta E presented a good inverse correlation with added increasing concentrations of ascorbate (2.5-75 mu mol/L; R = -0.99), urate (9.0-150 mu mol/L; R = -0.99), and bilirubin (0.78-13 mu mol/L; R = -0.99). Increase in the antioxidant capacity decreased Delta E. Depletion of the antioxidant capacity by tert-butylhydroperoxide (6.5-50 mu mol/L) presented a direct correlation (0.97) with Delta E. Furthermore, Delta E presented an inverse correlation (R = -0.99) with increased antioxidant capacity of plasma (FRAP) induced by the addition of ascorbate (2.5-75 mu mol/L). The response of the potentiometric method proved be adequate for measuring the plasma antioxidant depletion induced by acute exhaustive exercise in rats (control, n = 15; exercised, n = 15). This exercise decreased the concentration of urate (p < 0.05), decreased FRAP (p < 0.5), increased TBARS (p < 0.5), and decreased the potentiometer sensor response (p = 6.5 x 10(-3)). These results demonstrate the adequacy of potentiometry for evaluating the antioxidant capacity of blood plasma samples. (c) 2013 Elsevier Inc. All rights reserved.4412109114Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP [10/02791-7]