The Mechanism of Chromatographic Retention - Chiral Chromatography > Chiral Polysiloxane Stationary Phases > Page 80

Dispersive interactions with the cyclodextrin structure are controlled with polar solvents, polar interaction controlled with dispersive solvents as with other chiral stationary phases. If ionic interactions are present, then these will be controlled by both the pH and the type of buffer that is employed. Small changes in pH can be quite critical and the effect of buffer type on chiral selectivity can be quite profound. An example of the effect of pH and buffer type is depicted in figure 43. The enantiomeric pair were Dansyl D,L-phenylalanine separated on cyclodextrin column at a flow rate of 1.5 ml/min. A change in pH from 5.0 to 4.0 is seen to produce a remarkable increase in chiral selectivity. Changing the buffer from acetic acid adjusted with caustic soda, to triethylamine adjusted with acetic acid is even more significant.


Courtesy of ASTEC Inc.

Figure 43. The Effect of pH and Buffer Type on Chiral Selectivity.