[Admixture of related substances in rifampicin preparations and methods for their determination].

Optimal conditions for separation of rifampicin in a thin layer of a sorbent were developed. This allowed one to study the quantitative content of the admixtures of the related substances in the eluates of the respective spots on chromatograms. The possible use of both the spectrophotometric method and the biological agar diffusion method for testing the eluates was shown. The method of phase solubility also provided objective characterization of the purity levels of market rifampicin. A significant increase in the level of the admixtures of the related substances in rifampicin in 150 mg capsules was found on their storage.