A detailed investigation of the electrochemical reduction of 2-nitroimidazole (2-NIm) in a mixed aqueous medium was carried out by means of cyclic voltammetry (CV) at a mercury electrode. The voltammetric behavior of 2-NIm in 60% dimethylformamide (DMF) (0.1 M tetrabutyl ammonium perchlorate, TBAP )/40% aqueous buffer (0.3 M KCl + 0.015 M citric acid + 0.03 M boric acid) is pH-dependent, changing from one irreversible reduction peak at acid pHs to two reduction peaks at alkaline pHs. At pH 2.5 it is possible to obtain a voltammetric pK which is due to the protonation-deprotonation equilibrium produced by the hydroxylamine derivative formed from the reduction of 2-NIm. This indicates that 2-NIm is reduced to the unprotonated hydroxylamine derivative above pH 2.5 and to its protonated form below it. At pH > 7 it is possible to observe a cyclic voltammetric couple due to the one-electron reduction of 2-NIm to produce the corresponding nitro radical anion. Furthermore, the nitro radical anion disproportionates with a rate constant, k(2), of 6.78 X 10(5) M s(-1) and a half-life, t(1/2), of 1.5 ms for the first half-life. The voltammetric behavior of 2-NIm in aqueous mixed medium is substantially different from that described in nonaqueous medium; in fact, only in the aqueous medium is it possible to study in isolation the nitro radical anion. (c) 2007 The Electrochemical Society.