Investigation of the electrochemical behavior of metallo-tetraazaporphyrin modified silver and pyrolytic graphite electrodes in aqueous nitrite solution

Five new complexes of the type [M(OBTTAP)] (where M = Mn2+, Co2+, Ni2+, Cu2+ and Zn2+; OBTTAP = 2,3,7,8,12,13,17,18-octakis(benzylthio)-5,10,15,20-tetraazaporphyrin(2−)) were used to prepare modified silver and pyrolytic graphite electrodes and their electrochemical behavior towards the reduction of aqueous nitrite solution was investigated in acidic, neutral and alkaline medium. Of these electrodes, [Co(OBTTAP)] and [Cu(OBTTAP)] modified electrodes showed affinity for NO2- ions and thereby exhibited significantly altered cathodic responses. The [Co(OBTTAP)]/Ag electrode in acidic, neutral and also in alkaline nitrite solutions, exhibited a new one electron irreversible reduction wave at Ep,c ∼ −0.2 V vs. Ag|AgCl. The [Cu(OBTTAP)]/Ag electrode in acidic and neutral nitrite solutions also behaved in a similar manner. However, in alkaline aqueous nitrite solution it showed two successive one electron reductions, the first reversible reduction at E1/2 = −0.26 V and the second irreversible reduction at Ep,c = −0.73 V vs. Ag|AgCl. Controlled potential electrolysis of alkaline nitrite solutions using a [Cu(OBTTAP)]/Ag cathode led to isolation of a nitrosyl complex. The peak current, particularly with [Cu(OBTTAP)]/Ag microelectrode in alkaline medium, showed a linear response to [NO2-] and could be exploited in the electrochemical sensing and determination of NO2-.