SIMULTANEOUS METHODS WITHOUT SOLUTE RECOGNITION

The simplest form of a simultaneous method follows a path in figure 5.4 that can be characterized by 1011. The term grid search forms an illustrative description of such a 

Especially for the case of figure 5.1, where the composition of the stationary phase is the continuous parameter along the horizontal axis, a large number of experiments is extremely unattractive. Fortunately, there are much more effective procedures for this kind of optimization (see section 5.5.1). 

For the important case of the optimization of the mobile phase composition in reversed phase LC (RPLC), a typical two-dimensional response surface tends to be much less rugged, especially if the number of sample components is relatively small (n 10). A typical example is shown in figure 5.5. The selection of the normalized resolution product (r, eqn.4.19) as the criterion has also contributed to the smoother appearance of figure 5.5 relative to figure 5.1. Note that the criterion r has been recommended in chapter 4 for optimization processes in which the dimensions of the column are to be optimized after completion of the procedure (table 4.11). Therefore, the grid search approach is more appropriate for this kind of optimization than for optimization processes on the final analytical column. 

Some idea of the behaviour of the response surface in figure 5.5 might be obtained by recording chromatograms at regular intervals of 10%, i.e. 11 experiments along the entire axis. By interpolation between successive data points there is a reasonable chance that the 

Number of experiments required for grid search optimization in various cases. The two numbers given for each situation refer to 10 and 5% intervals in the individual parameters. 

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Method Simultaneous methods without solute recognition Includes Grid search ... 

Simultaneous methods (without solute recognition) may be used for selectivity optimization in chromatography, but require large numbers of experiments. 

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