Enantioseparation of S-carboxymethylcysteine and N-acetamidocarboxymethylcysteine by capillary electrophoresis using vancomycin

Racemic S-carboxymethylcysteine (DF-1794Y) and N-acetamido S-carboxymethyl cysteine (DF-1796A) were resolved into their enantiomers by capillary elect rophoresis using vancomycin as a chiral selector. Electrophoretic runs were carried out in a polyacrylamide-coated capillary filled with a background electrolyte composed of sorbic acid/histidine (pH = 4.5-6.5) and the approp riate concentration of vancomycin. The presence of the chiral selector (CS) in the detector path was avoided by using the partial filling-countercurre nt method, where the CS filled only part of the capillary and was moving in the opposite direction to the analytes. Due to the relatively low absorpti on of the enantiomers studied, indirect UV detection was used in order to i ncrease the sensitivity of the method. For method optimization the effect o f several experimental parameters such as vancomycin concentration, buffer pH, and organic modifier type and concentration on enantioresolution and mi gration time were studied. The migration order was verified only for S-carb oxymethylcysteine by injecting a mixture containing the racemic DF-1794Y sp iked with the enantiomer S-carboxymethyl-L-cysteine. The L-isomer was found to migrate first.