Enantioseparation ofS-carboxymethylcysteine andN-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 electrophoresis 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 appropriate concentration of vancomycin. The presence of the chiral selector (CS) in the detector path was avoided by using the partial filling-countercurrent 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 absorption of the enantiomers studied, indirect UV detection was used in order to increase the sensitivity of the method. For method optimization the effect of several experimental parameters such as vancomycin concentration, buffer pH, and organic modifier type and concentration on enantioresolution and migration time were studied. The migration order was verified only for S-carboxymethylcysteine by injecting a mixture containing the racemic DF-1794Y spiked with the enantiomer S-carboxymethyl-L-cysteine. The L-isomer was found to migrate first.