Amperometric determination of hydrogen peroxide by direct and catalytic reduction at a copper electrode

In a buffer solution at ambient temperature and dissolved oxygen concentration, pH 6.7, copper electrodes could be cycled between the Cu(O)/Cu(II) redox states, by cycling the potential between -0.8 and + 0.3 V vs. SCE. At 1 V s(-1), the reduction of Cu(II) proceeded with a rate constant of 12.3 s(-1) (alpha(C) = 0.16, alpha(A) = 0.93). The redox couple catalysed the reduction of hydrogen peroxide, with a second-order rate constant of approx. 25 +/- 10 M(-1) s(-1). Amperometric determination of H2O2 at - 0.25 V gave a limit of detection (2 X noise) of 1.2 mu M (sensitivity = 0.211 mA mM(-1) cm(-2) up to 2.0 mM), with a response time (steady-state) of 3 to 4 s. A 1 mu M change in the O-2 concentration gave approx. a 0.04% change in the H2O2 sensitivity. The presence of H2O-soluble copper-complexing anions at low concentrations gave a change in the H2O2 response. At higher anion concentrations (>20 mM), the rate of electron transfer from the metal was faster than the rate of Cu(II) dissolution. A copper micro-band electrode was used to determine H2O2 in a mixture of glacial acetic acid and chloroform.