Separation of monomethyl-benz[a]anthracene isomers using cyclodextrin-modified electrokinetic chromatography

Cyclodextrin-modified electrokinetic chromatography (CD-EKC) was investigated for the separation of 12 mono-methylbenz[a]anthracene (MBA) isomers. Combined use of a polymeric surfactant, poly(sodium 10-undecenyl sulfate) (poly-SUS), with various types of neutral cyclodextrins (CDs) [beta -CD, gamma -CD, dimethyl-beta -CD (DM-beta -CD), trimethyl-beta -CD (TM-beta -CD) and hydroxypropyl-beta -CD (HP-beta -CD)] were successful in CD-EKC separation of the MBA isomers. Baseline resolution of 10 of the 12 isomers, except for 9-MBA and 2-MBA, was achieved with gamma -CD at pH 9.75. The beta -CD, gamma -CD, and beta -CD derivatives (DM-beta -CD, TM-beta -CD, HP-beta -CD) were found to have different resolution and selectivity. Additionally, the t(R)/t(O) values of isomers were found to be dependent on the type and concentration of the CD additives. In general, t(R)/t(O) values of MBA isomers decrease with an increase in the concentration of beta -CD derivatives, whereas the reversed was true when the concentrations of native beta -CD and gamma -CD were varied. The combination of 5 mM gamma -CD, 0.5% (w/v) poly-SUS, 35% (v/v) acetonitrile at a pH of 9.75 provided the best selectivity and resolution of the MBA isomers with a separation time of 110 min. However, the use of 30 mM DM-beta -CD under similar EKC conditions resulted in much faster separation (ca. 16 min) of 10 MBA isomers. (C) 2001 Elsevier Science B.V. All rights reserved.