A method to quantify ethanol in gasohol fuels is described by using a copper microelectrode polarised at 0.6 V vs Ag/AgCl as an amperometric sensor. The determination was performed in a I mol L-1 NaOH aqueous phase after extraction of ethanol from gasohol samples. The influence of the solution stirring on the ethanol extraction was investigated by monitoring the analyte with the sensor immersed in the aqueous phase. The electrochemical pre-treatment of the electrode surface has a great influence on the sensor response, the best sensitivity being achieved by polarising previously the electrode at -0.1 V vs Ag/AgCl. The repeatability of the amperometric method by measuring the ethanol content in a gasohol sample was found to be 3.4% (n = 10) and the limit of detection was 0.01% (v/v). Under the optimum experimental conditions, the amperometric sensor was used to monitor the concentration of ethanol in gasohol samples. (c) 2006 Elsevier Ltd. All rights reserved.