Selectivity in capillary electrophoresis:  application to chiral separations with cyclodextrins

Area of Science:

• Analytical Chemistry
• Separation Science

Background:

• Capillary electrophoresis (CE) and related electroseparation techniques rely on effective analyte separation.
• Accurate evaluation of electrolyte medium performance requires a clear understanding of selectivity.

Purpose of the Study:

• To propose a clear concept of selectivity in capillary electrophoresis and related electroseparation techniques.
• To define selectivity based on analyte affinity factors for separating agents.
• To illustrate this concept using chiral separations with cyclodextrins.

Main Methods:

• Defined selectivity as the ratio of affinity factors for analytes binding to a separating agent.
• Applied the concept to separations of enantiomers using mono(6-amino-6-deoxy)-β-cyclodextrin as a chiral complexing agent.
• Utilized the resolution equation from micellar electrokinetic chromatography for prediction.

Main Results:

• Selectivity is the ratio of apparent binding constants for 1:1 complexation, independent of complexing agent concentration.
• Demonstrated the concept with separations of neutral and anionic enantiomers.
• Discussed how analyte functional groups influence separation values.

Conclusions:

• The proposed concept provides a framework for evaluating electrolyte performance in CE.
• Optimum conditions for chiral separations can be predicted based on affinity factors and chiral agent concentration.
• This approach is applicable when analytes exhibit similar mobilities in free and complexed forms.