Experimental design-based optimization strategies for chromatographic and capillary electrophoretic separations.

To develop and optimize separations in chromatography and capillary electrophoresis (CE), different approaches are possible. Some of them (univariate, simplex and experimental design approaches) are reviewed in this chapter. During these optimizations, the factors affecting most the selectivity, i.e., the sequence in which compounds elute, are most interesting to study. In reversed-phase chromatography, for instance, these are the type of stationary phase, the mobile phase pH, the organic modifier content and the modifier composition, and to a lesser extent, some other factors, such as, for instance, gradient slope or analysis temperature. Not all factors can be optimized in one experimental setup and often a sequential approach is defined, in which in certain steps experimental designs may be applied. This chapter discusses the most common experimental designs (screening designs, response surface designs and mixture designs) applicable not only in different steps of the optimization procedure for chromatographic and electrophoretic methods but also in many other optimizations. The application of screening designs in given method validation items, such as robustness testing, is also considered. Design properties are discussed as well as the data treatment involved. Different types of screening designs (full and fractional factorial designs, Plackett–Burman designs) and the different steps in their application are addressed. The most common symmetric and nonsymmetric response surface designs are also dealt with. Finally, the transfer of CE methods after their development is also shortly addressed because these methods are much less robust than chromatographic.