Phase Selection Diagrams

Figure 5.29 Initial chromatograms for the construction of the phase selection diagram shown in Figure 5.30. Figure taken from ref. [504], Reprinted with permission.

Such an iterative procedure has been worked out in detail by Drouen et al. [576]. Refinements of the method using the phase selection diagram discussed above include the use of normalized resolution products (see section 4.3.2), shifted compositions and confidence ranges. 

Figure 5.32 Initial phase selection diagrams for three possible ternary mobile phase systems applied to the separation of five diphenyl amines. Top (Initial) retention lines. Bottom (initial) response line. Criterion normalized resolution product (r eqn.4.19 drawn line) Also shown is the response surface using the product resolution criterion (IIeqn.4.18 dashed line). The required chromatograms are shown in figure 5.33 (a, b and c). Figure taken from ref. [576]. Reprinted with permission.

In Figure 5.32 the optimum composition predicted from a combination of all three phase selection diagrams is a mixture that contains 10.4% methanol and 33.6% THF (x = 0.84). Eqn.(5.18b) then prescribes a shifted composition of 19.5% methanol and 28% THF (x = 0.7). Obviously, this composition does not fall within one of the (small) confidence regions, and therefore an experimental chromatogram is recorded at the shifted composition. This chromatogram is shown in figure 5.33 (chromatogram d). 

Method Iterative designs Includes Phase selection diagrams ... 

Partition coefficient, 9, 10 Partition ratio, 11 time optimization of, 57-58 Peak, definition of, 69 Peak capacity, 18, 19 Pellicular supports, 157 Permeability, 63-64 Phase selection diagrams, 218-219 Phase volume ratio, 11 Pinkerton (ISRP) columns, 225-226 Plate height, 17 Plate number, 14-16 Plate theory, 3, 28 Polarity index, 210, 211 Pore size of LC supports, 157 Porosity, 27 Precision, 99-100 Preparative scale ... 

A number of other methods has been used to optimize ternary solvent systems, many of them69-71 similar to the window diagram used in GC. Only one more will be described briefly here. The authors, Schoenmakers et al.,72 have prepared what they call phase selection diagrams for several reverse phase LC separations. The solvents used for their mixtures are the same ones recommended by Snyder methanol, ACN, and THF. 

Figure 9.35. Typical phase selection diagram. Reprinted with permission from ref. 72.

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