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 monomethylbenz[a]anthracene (MBA) isomers. Combined use of a polymeric surfactant, poly(sodium 10-undecenyl sulfate) (poly-SUS), with various types of neutral cyclodextrins (CDs) [β-CD, γ-CD, dimethyl-β-CD (DM-β-CD), trimethyl-β-CD (TM-β-CD) and hydroxypropyl-β-CD (HP-β-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 γ-CD at pH 9.75. The β-CD, γ-CD, and β-CD derivatives (DM-β-CD, TM-β-CD, HP-β-CD) were found to have different resolution and selectivity. Additionally, the tR/t0 values of isomers were found to be dependent on the type and concentration of the CD additives. In general, tR/t0 values of MBA isomers decrease with an increase in the concentration of β-CD derivatives, whereas the reversed was true when the concentrations of native β-CD and γ-CD were varied. The combination of 5 mM γ-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-β-CD under similar EKC conditions resulted in much faster separation (ca. 16 min) of 10 MBA isomers.