Development of stereoselective nonaqueous capillary electrophoresis systemfor the resolution of cationic and amphoteric analytes

A stereoselective ion-pair nonaqueous capillary electrophoresis (NACE) meth od employing the partial filling technique with N-derivatized amino acids, e.g., (R)- and (S)-3,5-dinitrobenzoyl-leucine (DNB-Leu), as chiral selector for the separation of "pseudoenantiomeric" cinchona alkaloid derivatives a nd other structurally related basic compounds like the enantiomers of meflo quine is presented. Originating from NACE with cinchona alkaloid derivative s as chiral counterions, this method was developed by application of the re ciprocity principle of chiral recognition, which was proven to be valid for stereoselective ion-pair capillary electrophoresis (CE). A variety of basi c and amphoteric selectands (SAs) could be well resolved. Thereby, the sepa ration was primarily based on stereoselective ion-pair formation of corresp onding SA stereoisomers and mobility differences of free and complexed (ion -paired) SAs. Additionally, in the case of diastereomeric SAs, naturally ex isting mobility differences between the diastereomers played also a role, b ut was shown by control experiments with racemic DNB-Leu and without select or (SO) to be of minor contribution to overall separation selectivity. Due to its simplicity, speed, and good reproducibility, the established method can be utilized for fast screening of cationic as well as amphoteric chiral compounds, and therefore is a valuable tool in the development of new chir al selectors and chiral stationary phases. Small sample amounts of the SO ( 4-5 mg) and only analytical amounts of SAs are needed, and about 20-50 comp ounds per day can be tested.