[Diamide] [GSH] µmol/L Precision (SD %)(d) Accuracy (RD %)(e) µmol/L(a) Obtained (b) Expected (c) 0 104 100 3.50 5.80 8.25 86.4 83.5 1.10 4.10 14.5 70.2 71.0 0.80 2.70 20.8 57.5 58.5 0.50 2.10 27.0 36.1 46.0 8.10 *25.6 33.3 22.7 33.5 5.10 *37.3 39.5 4.29 21.0 12.8 *91.9 45.5 1.51 8.50 15.2 *94.9

Table 2: Precision and accuracy of the Elman’s method in this work conditions. To a fixed concentration of GSH (100 μmol/L) was added increasing concentrations of diamide(a). The final GSH concentrations(b) presented acceptable precision (SD ≤ 12.8%)(d). When compared with to the expected by the reaction stoichiometry (1GSH:2diamide)(c) the accuracy(e) was acceptable below 57.5 μmol/L of GSH (RD% ≤ 5.80%) The GSH concentrations(b) were obtained with the absorbance of the first eight points described in figure 5 and a suitable standard curve. *RD above 5.80%.