Systematic approach to methods development for the capillary electrophoretic analysis of a minor enantiomer using a single-isomer sulfated cyclodextrin - A case study of L-carbidopa analysis

A methods development protocol - based on the charged resolving agent migration model - for the capillary electrophoretic analysis of a minor enantiomer using a single-isomer sulfated cyclodextrin is described here. The minor component of L-carbidopa was successfully assayed by capillary electrophoresis using the single-isomer heptakis-(2,3-diacetyl-6-sulfato)-beta-cyclodextrin as chiral resolving agent. Adequate separation selectivity was secured by selecting a pH 2.5 background electrolyte, operating at 16 degrees C and adjusting the concentration of the single-isomer sulfated cyclodextrin to just past the point where the migration direction of both enantiomers of carbidopa changes from cationic to anionic due to complexation with the single-isomer sulfated cyclodextrin. Once the background electrolyte composition which leads to adequate selectivity was identified, peak resolution was adjusted by optimizing the magnitude of the dimensionless normalized electroosmotic flow-rate via the addition of poly(ethylene glycol)900 which does not change separation selectivity. Rugged separation conditions permitting the fast, reproducible quantitation of the minor enantiomer in L-carbidopa preparations could be readily established. (C) 1998 Elsevier Science B.V. All rights reserved.