[A potentiometric method of quantitative analysis of rifampicin]

A potentiometric procedure for assay of rifampicin was developed. The procedure implies titration of rifampicin as a monofunctional acid by sodium hydroxide solution (0.1 mol/l) in 75 per cent aqueous methanol. The constant ionic strength of the solution is provided by addition of KCl until its concentration is 0.1 mol/l, the titrant concentration being 10 times higher than the antibiotic concentration in the solution. This provides a precise determination of the concentration ionization constant of the antibiotic as a monofunctional acid (pKa 7.33 +/- 0.01) and an insignificant dilution of the antibiotic solution during the titration promoting precise and reproducible results. The procedure error is 0.20 per cent. The variation coefficient is 0.27 per cent.