Densitometric determination of some bioactive guanidinium compounds without post-derivatization

In this paper we present thin layer chromatographic methods suitable for determination of bioactive guanidinium compounds, saturated antibiotics with UV absorbance only in the extremely short wavelength region, below 200 nm. For elimination of disturbing impurities, arising mostly from binding agents in the precoated silica gel plates, an efficient prewashing method with methanol-formic acid, 50:50 ( v/v ) was used. In this way a smooth and straight baseline was obtained in the region of measurement even if polar mobile phases had been used. Of the compounds investigated, special attention was devoted to primycin, a macrolide antibiotic agent. Owing to the complexity of this antibiotic good separation has been a real challenge. An efficient separation system, suitable for both the quality control of the end product and for monitoring the efficiency of isolation from the fermentation liquor, has been established. Further compounds containing guanidinium groups, for example streptomycin, dihydrostreptomycin...