[Diamide] [GSH] µmol/L Precision (SD %)(d) Accuracy (RD %)(e) µmol/L(a) Obtained (b) Expected (c) 0 114 120 4.50 6.50 13.3 96.2 93.5 6.00 6.70 19.5 78.2 81.0 2.10 4.40 25.8 60.3 68.5 2.10 14.5 38.2 38.1 43.6 4.40 14.5 44.4 33.8 31.2 7.90 13.6 50.8 25.9 18.4 5.20 *47.8

Table 1: Precision and accuracy of the voltammetric method proposed. To a fixed concentration of GSH (120 umol/L) was added increasing concentrations of diamide(a). The final GSH concentrations obtained(b) presented acceptable precision (SD<7.9%)(d). When compared to the expected by the reaction stoichiometry(c), the accuracy was acceptable below 33.8 μmol/L of GSH(e) (RD% ≤ 14.5). The GSH concentrations(b) were obtained using the Ip of the first seven voltammograms described in figure 6 and the standard curve described in figure 4. *RD above 14.5%.