The liquid chromatographic properties of phenothiazines

The high-pressure liquid chromatographic behaviour of different groups of phenothiazines (drug substances) has been investigated on 10-mu m silica gel particles. Variation of the ammonia concentration between 0.5 and 1.5% in an isopropanol-diisopropyl ether (15:85) mixture permits the adjustment of the solvent system to fit the different basicities of the various groups of interest. While the capacity factors (k') for pairs of compounds in two homologous oxidation series vary considerably owing to differences in basicity, there is reasonably good agreement between the relative retention (alphs) values. This fact can be utilized in order to identify phenothiazine homologues of series that have not previously been studied. Elutropic diagrams in connection with alpha values can be used to predict the chromatographic behaviour of new groups of phenothiazines.