Impact of mobile phase composition on reverse-phase separation of polar basic compounds

Abstract

Method development for determination of polar basic compounds on ion-suppression reverse-phase liquid chromatography, requires appropriate selection of stationary phase and composition and pH value of the mobile phase. The addition of the organic solvent in aqueous buffers with defined pH value, results in shift of the pH value of the mobile phase, resulting in significant change in chromatographic retention and selectivity. The aim of this study was to evaluate the impact of the variation of pH value of the mobile phase and percentage of the organic solvent, on the chromatographic separation of basic compound (octenidine dihydrochloride). The design of experiment was used for the optimization of the chromatographic conditions and selection of the most suitable mobile phase composition. The optimal composition of the mobile phase, providing satisfactory chromatographic performance based on ion-suppression reverse-phase chromatography, included 0.1M citric acid/0.2M sodium dihydrogen phosphate, pH =2.5, combined with 70% v/v organic solvent-acetonitrile. The suitability of the method was confirmed by satisfactory results for the system suitability parameters, specificity, linearity and precision. Key Words: polar basic compounds, ion-suppression, pH value, composition of mobile phase