Electrocatalytic oxidation and detection of hydrazine under pH 6.0 conditions were studied with a carbon paste electrode modified with a Co(II) Schiff base complex [(CoL2)-L-II, HL = benzoic acid (2-hydroxy-3-methoxy-benzylidene)-hydrazide]. Anodic oxidation of hydrazine at the (CoL2)-L-II-modified carbon paste electrode occurred at low overpotential (0.48 V vs Ag/AgCl), and treatment of the voltammetric data showed that it was a purely diffusion-controlled reaction involving one electron in the rate-determining step. The catalytic oxidation peak current was linearly dependent on the hydrazine concentration over the wide range 5 X 10(-5) to 1 X 10(-2) M. The heterogeneous rate constant for the oxidation of hydrazine at the surface of the modified electrode was determined by rotating disk electrode voltammetry using the Koutecky-Levich plot. A Tafel plot, derived from voltammograms, indicated a one-electron charge-transfer process to be the rate-limiting step, and the overall number of electrons involved in the catalytic oxidation of hydrazine was found to be 4. The mechanism for the interaction of hydrazine with the (CoL2)-L-II complex-modified carbon paste electrode is proposed to involve the (CoL2)-L-III/(CoL2)-L-II redox process. (c) 2007 The Electrochemical Society.