Selectivity optimization for the separation of chlorophenols in an irregularly shaped experimental region in capillary electrophoresis

The separation of seventeen chlorophenol congeners and phenol was studied as a function of several variables. The pH and the concentration of sodium dodecylsulphate (SDS) were found to be important. During the implementation of a central composite design for the optimization of the separation it appeared that a part of the domain was not feasible as it resulted in very long migration times and extremely deformed peaks. Therefore, a D-optimal design was selected within the boundaries of the feasible region. The optimization of the selectivity did not result in selective regions for a simultaneous separation. It was, however, possible to find a region for the simultaneous separation of 15 compounds. Further optimization at these optimal conditions resulted in a separation where 17 peaks could be observed.