The influence of inorganic salts with chaotropic properties on the chromatographic behavior of ropinirole and its two impurities

Chaotropic agents recently gained popularity as interesting and useful mobile phase additives in liquid chromatography due to their effect on analytes retention, peak symmetry and separation efficiency. They mimic the role of classical ion-pairing agents, but with less drawbacks, so their use becomes attractive in the field of pharmaceutical analysis. In this paper, the influence of sodium trifluoroacetate and sodium perchlorate on the chromatographic behavior of ropinirole and its impurities is examined. By the extended thermodynamic approach, it was shown that the separation in the given system was predominantly governed by electrostatic interactions between the protonated analytes and the charged surface of the stationary phase, but the ion-pair complex formation in the eluent also proved to be significant. Further, the employment of face-centered central composite design enabled the understanding of the effect of chaotropic agent concentration and its interactions with other factors (acetonitrile content and pH of the water phase) that influence the given chromatographic system. Finally, the same data was used for multi-objective optimization based on the grid point search method. After the method validation, the adequacy of the suggested approach in development of methods for routine pharmaceutical analysis was proven.