Chemometrical evaluation of ropinirole and its impurity's chromatographic behavior

The aim of this study was the chemometrical evaluation of ropinirole and its impurity's (4-[2-(dipropylamino)ethyl]-1H-indol-2,3-dione) chromatographic behavior in systematic and the most efficient way. For that purpose, as very descriptive, response surface designs are most preferable. Face-centered central composite design (CCD) with 23 full factorial design, ±1 star design and four replication in central point was applied for a response surface study, in order to examine in depth the effects of the most important factors. Factors—independent variables (acetonitrile content, pH of the mobile phase and concentration of sodium heptane sulfonate in water phase) were extracted from the preliminary study and as dependent variables five responses (retention factor of ropinirole, retentin factor of its impurity, resolution, symmetry of ropinirole peak and symmetry of impurity peak) were selected. For the improvement of method development and optimization step, Derringer's desirability function was applied to simultaneously optimize the five chosen responses. The procedure allowed deduction of optimal conditions and the predicted optimum was acetonitrile–5 mM of sodium heptane sulfonate (21.6:78.4, v/v), pH of the mobile phase adjusted at 2.0 with ortho   phosphoric acid. By calculating global desirability's determination coefficients (RD2), as well as by the visual inspection of 3D graphs for global desirability, robustness of the proposed method was also estimated.