Electrokinetic chromatography employing an anionic and a cationic β‐cyclodextrin derivative

Abstract

β‐Cyclodextrin, 1, can act as a chiral buffer additive in capillary zone electrophoresis (CZE) owing to its ability to form diastereomeric complexes with the enantiomers of ionic compounds. Reaction of 1 with 2,3‐epoxy‐propyltrimethylammonium chloride gave preponderantly 6‐O‐(2‐hydroxy‐3‐trimethyl‐ammoniopropyl) derivatives (2) of varying degrees of substitution (d.s.). Analogous reaction of 1 with 1,3‐propanesultone yielded 6‐O‐(sulfo‐n‐propyl) derivatives (SPE‐β‐CD, 3) of varying d.s. The purity and the d.s. of 2 and 3 were determined by ¹H NMR and electrospray ionization mass spectrometry (ESI‐MS). These charged β‐cyclodextrin derivatives were used for the chromatographic enantiomer separation of a series of neutral barbiturates, of chlorthalidone, terbutaline, warfarin, salbutamol and brompheniramine by cyclodextrin electrokinetic chromatography (CD‐EKC). During the separation of chlorthalidone with 3 as chiral additive, a reversible interconversion of the enantiomers (enantiomerization) was observed at temperatures below 20°C.