Separation of enantiomers by capillary electrophoresis–mass spectrometry employing a partial filling technique with a chiral crown ether

Enantiomer separations were performed by capillary electrophoresis–mass spectrometry (CE–MS) with (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid (18C6H4) as a chiral selector. In order to prevent the introduction of the nonvolatile chiral selector, 18C6H4, into the nozzle of the CE–MS interface and/or the orifice plate, a partial filling technique was employed in this study. By the partial filling technique, the contamination caused by the nonvolatile chiral selector was avoided not only during the analysis but also during the washing of capillary with the separation solution prior to the run. Several racemic compounds having a primary amino group were successfully separated. Racemic 3-aminopyrrolidine and racemic α-amino-ϵ-caprolactam have no strong UV absorption, but such compounds were detected with a high sensitivity by MS detection. In this paper, the effects of the length of separation zone and those of the 18C6H4 concentration were described. As the length of the separation zone was longer or as the concentration of 18C6H4 was higher, the enantiomer resolution was enhanced more and more. However, the optimization of 18C6H4 concentration was practically enough to obtain the baseline separation.