Retention processes on alpha 1-acid glycoprotein-bonded stationary phase.

Stereoselective separations of charged enantiomers on CHIRAL-AGP can be controlled by varying the pH and adding charged and uncharged additives to the mobile phase. The interaction with the selector, alpha 1-acid glycoprotein, was studied by monitoring the effects of the variables on retention and by indirect detection, in part using a simple multivariate design. The stereoselectivity is due to simultaneous retention processes involving ion-exchange and ion-pairing mechanisms. The predominant mode of interaction for different solutes was elucidated from variables that promote or counteract either of the processes. Considerable improvements in the stereoselectivity were achieved with chiral or achiral anionic and cationic additives that act in a synergistic or competitive mode.