Kinetic determination of ansamicins in pharmaceutical formulations and human urine. Manual and semiautomatic (stopped-flow) procedures

Abstract Manual and semiautomatic kinetic methods to determine ansamicins (rifamycin SV and rifampicin), based in the catalytic effect of Cu(II) ion on the aerial oxidation of rifamycin, is described. The effect of pH, temperature and presence of foreign species are studied. A selective and fast kinetic-photometric determination of ansamicins, between 0.50 and 10 μg ml −1 , is proposed by the application of a semiautomatic procedure in which the sampling-time is 20 s per sample. The method has been applied to determine rifamycin SV and rifampicin in pharmaceutical formulations and urine. Interferences like isoniazide and pyrazinamide are avoided. Statistical comparison with a chromatographic method is reported.