Spectrophotometric estimation of rifampin-isoniazid mixture in dosage form

A spectrophotometric method for the simultaneous determination of rifampin and isoniazid in dosage form is described. By using a mixture of methanol and water (2 + 3) as solvent, the absorbance of the mixtures of rifampin and isoniazid is measured at 264 nm and 335 nm. The concentration of each can then be calculated by solving 2 simultaneous equations. The procedure was successfully applied to a number of commercial samples; the results agreed well with those for compendial method.