Intrinsic selectivity in capillary electrophoresis for chiral separations with dual cyclodextrin systems

Area of Science:

• Analytical Chemistry
• Separation Science
• Chiral Separations

Background:

• Intrinsic selectivity quantifies analyte affinity for complexing agents.
• Multiple complexing agents in background electrolytes allow for multiple intrinsic selectivities.
• A theoretical model is presented for separations involving two complexing agents.

Purpose of the Study:

• To present a theoretical model for selectivity in separations involving two complexing agents.
• To illustrate the model using dual cyclodextrin systems for neutral enantiomer separation.
• To characterize the intrinsic selectivity of neutral cyclodextrins for neutral enantiomers.

Main Methods:

• Development of a theoretical model using apparent complex formation constants.
• Application of the model to dual cyclodextrin systems, including cationic mono(6-amino-6-deoxy)-β-cyclodextrin (β-CD-NH(2)) and neutral cyclodextrins (trimethyl-β-CD or dimethyl-β-CD).
• Experimental validation using arylpropionic acid enantiomers and benzoin derivatives at pH 2.3.

Main Results:

• A dual β-CD-NH(2)/TM-β-CD system achieved baseline resolution of arylpropionic acid enantiomers and partial resolution of benzoin derivatives.
• β-CD-NH(2) provided mobility, while TM-β-CD enabled chiral recognition for arylpropionic acids.
• Optimal separation conditions were determined by studying the influence of TM-β-CD and β-CD-NH(2) concentrations.

Conclusions:

• The theoretical model effectively characterizes intrinsic selectivity in dual complexing agent systems.
• Neutral cyclodextrins show potential as chiral selectors for neutral enantiomers when used in conjunction with other agents.
• This approach offers an alternative for separating neutral enantiomers where single agents are insufficient.