Comparison of charged cyclodextrin derivatives for the chiral separation of atropisomeric polychlorinated biphenyls by capillary electrophoresis

Charged cyclodextrin (CD) derivatives were used as chiral selectors in electrokinetic chromatography (EKC) for the chiral separation of highlyhydrophobic neutral racemates such as atropisomeric polychlorinated biphenyls (PCBs). -CD-phosphated, -CD sulfated, succinylated--CD (Succ--CD) and succinylated- -CD (Succ- -CD) were used as anionic CDs. As cationic CD, 6-monodeoxy-6-monoamino- -CD ( -CD-NH2) was tested for the first time in order to separate PCBs. From the different CD derivatives employed, the best separations were obtained with the cationic CD derivative. Thus, the use of -CD-NH2 in phosphate buffer at pH 2.0 containing urea allowed the chiral recognition of eleven PCBs (45, 84, 88, 91, 95, 131, 136, 144, 149, 176, and 197). In this case, the addition of 2 M urea to the buffer solution was crucial to achieve the chiral separation of PCBs. The addition of acetonitrile to 10 mM phosphate buffer (pH 2.0) with 30 mM -CD-NH2 and 2 M urea improved considerably the chiral resolution obtained for PCBs 91, 95, 136, 144, 149, and 197 although an increase in the analysis time was also observed. All the results obtained were compared with those previously obtained with the dual CD system carboxymethyl--CD/ -CD.