Isoniazid (INH) was studied with regard to its electrochemical treatment on a strongly alkaline solution of a poly (3,4-ethylenedioxythiophene)-modified gold electrode, using both cyclic voltammetry and controlled potential techniques. This composite electrode exhibited 4-fold higher oxidation of INH, in accordance with peak densities, than the bare gold electrode. It was used the central composite design method to obtain optimum experimental conditions, and used critical parameters (pH (A), scan rate (mV/s, B) and temperature (C, C) to assess the effects on amperometric response. Optimum experimental conditions were achieved by using a pH of 9.2 with a scan rate of 260 mV/s and a temperature of 30C. Under these conditions, a good linear relationship was observed between peak current densities and INH concentration in the range of 0.05-2 μM, with correlation coefficient of 0.9998. Furthermore, the method was very sensitive (limit of quantitation, 0.0043 μM), accurate (relative error, -5.65 to 4.03) and precise (relative standard deviation %, ≤7.97). The method was also applied to determine INH in pharmaceutical formulations, and statistically compared the results with the official method using the two one-sided equivalence test; the results were in good agreement with those obtained by the official and reported methods.
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