Optimize complex fractionation/separation

For RPLC, the general strategy (Figure 3.10a) is less complex because no distinction between acidic and basic compounds is made. The optimization stage is also less complicated. In case of a baseline separation, the retention factor can be optimized based on the fact that a linear relationship is assumed between log k and the fraction... 

Cut strategy I allows a waste fraction between the product fractions, which can be either discarded or processed further (e.g. by recycling the waste fraction or by application of other separation steps, such as crystallization, to purify it). Due to the introduction of a waste fraction the optimization problem gains additional degrees of freedom, i.e. times for the beginning and the end of waste collection. These additional degrees of freedom, however, will not increase the complexity of the optimization, because they are pinpointed automatically by the purity demand, which serves as a boundary condition for the optimization problem. 

MD-HPLC can be applied to the purification of a particular natural product or comprehensive fractionation of complex natural product mixtures.60 Figure 2 illustrated an example where such approaches have been employed. The two applications have some similarities in terms of basic separation science principles however, they have fundamental differences in system design, optimization, and operation. 

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