The Mechanism of Chromatographic Retention - Chiral Chromatography > Chiral Polysiloxane Stationary Phases > Page 81

 

This change in pH has resulted in the complete resolution of the two enantiomers. However, this separation is achieved at the expense of the retention time changing from 18 min to about 32 min. The increased resolution and retention could result from either interactions between the solute and the stationary phase were much greater or the solute/mobile phase interactions had become significantly weaker. Another example of the effect of different buffer concentrations on chiral selectivity is afforded by the separations shown in figure 43. The same enantiomers are being separated as shown in figure 43, but the buffer used at different concentrations is ammonium nitrate. Although good selectivity is achieved at very low concentrations of ammonium nitrate and in the absence of the buffer, the peaks are very broad and the analysis time is long.

 

Courtesy of ASTEC Inc.

Figure 44. The Effect of Buffer Concentration on Chiral Selectivity