A graphite-paraffin composite electrode has been used for the determination of ethambutol, an antituberculosis drug, in pharmaceutical samples by anodic oxidation. Voltammetric studies were used to characterise the electrochemical behaviour of the ethambutol in different pH solutions (3.0, 8.0 and 12.0). Quantification was carried out using amperometric detection. The detector was assembled in a flow injection apparatus and operated at + 1.1 V (vs. Ag/AgCl (NaCl,sat) ). The conditions for the best electrodes response were determined by studying the influence of sample volume and flow rate. The linear response for the method was extended up to a 1.5 mmol L À1 ethambutol solution with a detection limit of 0.1 mmol L À1. The repeatability for successive injections of 1.0 mmol L À1 ethambutol solution was 0.9 % (n = 26), demonstrating a good performance of the developed amperometric sensor. The analytical frequency was calculated as approximately 47 determinations h À1. Two different commercial samples were successfully analysed and the results were in good agreement with those obtained by using spectrophotometry. The advantages of the proposed amperometric method over the reference method include simplicity, low consumption of reagents and increased analytical frequency.

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