Neutral and anionic cyclodextrins in capillary zone electrophoresis: Enantiomeric separation of ephedrine and related compounds

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Abstract
Two methods for the enantiomeric separation of chiral ephedrine alkaloids (ephedrine, methylephedrine, methylpseudoephedrine and norephedrine) by capillary zone electrophoresis in uncoated capillaries were developed. Both methods were optimized to more than 100 000 theoretical plate numbers. The first method used a neutral cyclodextrin (CD) derivative: heptakis (2,6–di-O-methyl)-β-cyclodextrin at an acidic pH of 2.5 (20 mM phosphate buffer) at an 18 mM concentration. The second used a newly developed acidic CD derivative, the tetrakis[6-O-(4-sulfobutyl)]-β-cyclodextrin sodium salt. The benefits of this new reagent for the chiral separation are a wide range of basic pH available for the enantiomeric resolution. It is also useful for other cases, e.g. preventing adsorption without additives.