Chiral separation of local anaesthetics by a capillary electrophoresis/partial filling technique coupled on-line to micro-electrospray mass spectrometry

Abstract

A novel procedure for analysing chiral compounds is described in which a capillary electrophoresis/partial filling technique was coupled on-line to micro-electrospray mass spectrometry. Enantiomers of bupivacaine and ropivacaine were separated using methyl-β-cyclodextrin, a non-volatile buffer additive, as a chiral selector. To avoid introduction of the selector into the ion source, the capillary was coated with polyacrylamide to minimize the electroosmotic flow. Prior to sample injection, the capillary was partially filled with cyclodextrin dissolved in acetate buffer. When 30 kV was applied, the positively charged enantiomers migrated towards the mass spectrometer through the zone containing the neutral selector, which acted as a pseudo-stationary phase. A racemic mixture of bupivacaine and ropivacaine was successfully separated and an impurity of 0.25% of (R)-ropivacaine in (S)-ropivacaine could be detected. © 1998 John Wiley & Sons, Ltd.