The electrochemical oxidation of dipyrone (MTM) in aqueous medium was characterized using antipyrine (AA), 4-aminoantipyrine (4AA), 4-methyl-aminoantipyrine (MAA) and 4-dimethyl-aminoantipyrine (DMAA) as model molecules for the elucidation of all MTM voltammetric signals. The MTM and the other pyrazolones show up to four oxidation electrochemical processes. The voltammograms obtained in AA solutions presented an irreversible electrochemical oxidation process involving one electron at Eap(3), which is common to all pyrazolone derivatives, while the amino pyrazolones present electrochemical oxidation processes at Eap(0) or Eap(1). The stabilization of the oxidation products depends on different effects: the proton release added to the thermodynamic stability, in the case of the imine formation at Eap(0) (4AA and MAA) and the hyperconjugation (sigma-stabilization) in the case of iminium formation (DMAA and MTM) at Eap(1). The process observed at Epa(0) corresponds to the pH-dependent oxidation of the primary and secondary enamines, while the process observed at Eap(1) occurs in the tertiary enamines, is pH independent. The oxidation peak potential follows the order: MAA < 4AA < DMAA < MTM and it was demonstrated that DMAA in an aqueous medium can simulate the MTM in an aprotic medium; therefore, the analytical MTM determination can be performed using the DMAA aqueous analytical curve. DMAA and MTM analytical curves, presented a linear range from 10 mu mol L-1 to 100 mu mol L-1 with a LOD of 1.94 and 2.97 mu M for DMAA and MTM, respectively, LOQ of 6.48 and 9.91 mu M (n = 10) and, sensitivity of 0.96 mu A/mu M for DMAA and 0.92 mu A/mu M; with a recoveries of 95-105% for MTM. (C) 2018 Elsevier Ltd. All rights reserved.