ELECTROKINETIC CHROMATOGRAPHY IN SUPPRESSED ELECTROOSMOTIC FLOW ENVIRONMENT - USE OF A CHARGED CYCLODEXTRIN FOR THE SEPARATION OF ENANTIOMERS AND GEOMETRIC ISOMERS

Electrokinetic chromatography (EKC), with negatively-charged cyclodext rins (NCDs) added to the buffer, was conducted in polyacrylamide-coate d columns under suppression of electroosmotic flow. The equations of m igration and resolution for neutral solutes in this mode of chromatogr aphy, which for brevity we term NCD-EKC, are presented. The chiral sul fated cyclodextrin, beta-CD-SBE (IV), used in this study is anionic ov er the entire pH range accessible to capillary electrophoresis, and th e coated columns are stable and provide reproducible performance in th e pH range 2.5-8.8. Optimum separation was obtained in the pH range wh ere the solutes are neutral, The incorporation of an alkyl spacer betw een the sulfate ion and the rim of the cyclodextrin allows an unhinder ed approach and inclusion of neutral solutes in the cyclodextrin cavit y. Solute migration time is inversely proportional to the concentratio n of the chiral selector. Separation (relative migration time differen ce) increases with decreasing chiral selector concentration and approa ches a maximum, beyond which further decreases in chiral selector conc entration result in broad peaks and loss of resolution. A chiral selec tor concentration of 1% in a 10 mM phosphate buffer produced excellent separation of amino acids and dipeptide enantiomers. In addition to b eing chiral selectors, cyclodextrins are also known as shape selectors . NCD-EKC is particularly suited for the separation of positional isom ers of hydrophobic solutes. The separation of aflatoxin isomers and ch lorophenol congeners is presented. In the separation of chlorophenols the more hydrophobic trichlorophenols eluted first and the least hydro phobic, phenol, eluted last.