RESUMO
A simple and sensitive Spectrophotometric method for the determination of isoniazid [INH] that is potent antituberculosis, based on the formation of a condensation product with isatin in aqueous solution at pH 1.4, has been developed. The condensation product [isatin-isonicotinylhydrazone] was found to possess a strong absorption at 340 nm. Using 1.6 mM concentration of isatin in solution, the maximum absorbance was attained after standing for 40 min at room temperature. Calibration graph was found to be rectilinear and Beer's law was obeyed in the range 0-32 ppm of isoniazid, with the molar absorpitivity [summation] = 1.2 x 10[4] and a lower detection limit 0.5 ppm. The analysis of different forms of some pharmaceutical preparations containing isoniazid in presence of rifampicin has been carried out after the extraction of the latter with CHC13 from the sample solution containing the condensation product. The extraction of rifampicin was found to be quantitative and very rapid so that shaking for few seconds was enough. The determination of INH in presence of rifampicin in urine samples has been performed