Separation of multicomponent mixtures of 2,4-dinitrophenyl labelled amino acids and their enantiomers by capillary zone electrophoresis

The use of capillary zone electrophoresis (CZE) for the separation of a group of 33 2,4-dinitrophenyl labeled amino acids (DNP-AA), including DNP-AA racemates, DNP-L-AA enantiomers and achiral DNP-AAs, was investigated. ?-, ?- and ?-cyclodextrins (CDs) and their derivatives (hydroxypropyl derivatives of ?-, ?- and ?-CDs, polymeric ?-CD and 6A-methylamino-?-cyclodextrin (MA-?-CD)) served as complexing agents and chiral selectors in this investigation. Although native ?- and ?-CDs and their derivatives influenced the effective mobilities of the studied DNP-AAs in different ways, they generally failed to resolve enantiomers of the individual DNP-AAs. On the other hand, ?-CD and all of its derivatives were found to be effective in this respect. Of these, the best results were achieved with a positively charged MA-?-CD and this chiral selector resolved enantiomers of ten DNP-AA racemates available for this study. However, a complete resolution of these enantiomers in one CZE run required that the effect of the chiral selector be complemented by complexing effects of polyvinyl pyrrolidone (PVP) or ?-CD. Complexing and chiral recognition capabilities of MA-?-CD combined with complexing effects of ?-CD and PVP provided separating conditions suitable for the CZE separations of multicomponent mixtures of DNP-AAs with preserved resolutions of the enantiomers. For example, a mixture consisting of 43 DNP-AA constituents was resolved using an MA-?-CD/?-CD combination with three peak overlaps.