Comparison of Reversed-Phase Liquid Chromatographic Methods for the Separation of New Quinolones

Reversed-phase high-performance liquid chromatography is widely used in the analysis of drug substances and their metabolites. The interaction of quinolones with residual silanol in a silica-based C 18 stationary phase causes peak broadening and bad peak shapes and makes it hard to resolve the peak separations. This unusual interaction is studied and finally can be removed by masking the residual silanol of a silica-based C 18 stationary phase, then good peak separation is achieved. We have chosen four new quinolones and ciprofloxacin and improved the peak shapes by optimizing the pH of the eluent and the quantity of the additive (N,N-dimethyloctylamine, approximately 0-40mM) in the monomeric C 18 stationary phase. The elution behavior of quinolones in the polymeric C 18 stationary phase is compared with that in the monomeric C 18 stationary phase under the same eluent condition. Good peak symmetry and a high plate number are achieved by this technique, which are hardly obtained with the conventional silica-based C 18 stationary phase. Based on these results, we present data of the influence of the eluent composition such as pH, buffer, and additive concentration on the peak shape.