Chromatographic characterization of phenothiazine drugs by a reversed-phase thin-layer technique

A reversed-phase thin-layer chromatographic technique was used for the characterization of 26 phenothiazine drugs. With two chromatographic systems having the sam stationary phase and phase volume ratio, but mobile phases of different pH, all but two of the compounds could be identified. Rf values in the different systems were standardized by applying a reference compound to the plates next to each compound under investigation; the corrected Rf values were calculated from the differences in the Rm values of the compounds and the reference compound, and the theoretical Rm value of the reference. It was shown that Rf values for different chromatographic systems with the same stationary phase could be predicted with reasonable accuracy. The pH of the mobile phase, for which a maximum difference in Rf values was obtained for pairs of compounds, could also be calculated and corresponded well with the observed values.