Reversed-phase high performance liquid chromatographic determination of rifampin in the presence of its acid-induced degradation products

The determination of rifampin in the presence of its acid-induced degradation products by reversed-phase high performance liquid chromatography is described. The method was validated as stability-indicating by forced decomposition of rifampin in acid media. Chromatographic conditions included a Nova-Pak(R) C18 (3.9 x 150 mm, 5 mu m) column and a mobile phase consisting of 0.02M Na2HPO4 and acetonitrile (65:35 v/v), apparent pH 4.5 +/- 0.2 adjusted by the addition of phosphoric acid. All analyses were done under isocratic conditions at a flow rate of 1 mL/min and at room temperature. The recovery average was 99.39% for rifampin. The method was applied to determine rifampin in commercial capsules and compared with the official method of the USP XXIII with good agreement between the results.