Here, we report a simple and extremely effective method to chemically grafting of o-aminophenol film (o-AP) onto glassy carbon (GC) electrode by the electrochemical reduction of the corresponding nitrophenyl diazonium salt in acidic aqueous solution for the electrocatalytic detection of hydrazine. The covalently attached o-AP enabled hydrazine to be catalytically oxidized at a greatly reduced overpotential and in a wide operational pH range. A quinoneimine structure has been proposed as the electrocatalytically active species. The kinetics of the reaction between the o-AP mediator and hydrazine has been characterized using cyclic voltammetry, chronoamperometry, and chronocoulometry and rotating disk electrode voltammetry. The o-AP modified electrode as an amperometric sensor has been characterized. The catalytic currents were proportional to the concentration of hydrazine giving rise to calibration curves characterized by two linear segments. The linear segment over the concentration range of 2.0-20.0 mu M could be used with analytical purposes to determination of hydrazine with a detection limit of 0.5 mu M and a sensitivity of 0.016 mu A/mu M. The precision of amperometry was found to be 1.7% for replicate determinations (n = 10) of a 10 mu M solution of hydrazine. The resulting modified electrode retains its initial response for at least one month if stored dry in air. (c) 2006 Elsevier B.V. All rights reserved.