Use of MDL 63 246 (Hepta-Tyr) antibiotic in capillary zone electrophoresis. II. Chiral resolution of ?-hydroxy acids

The glycopeptide antibiotic MDL 63 246 (Hepta-Tyr), belonging to the teicoplanin family, has been adopted for the separation of several ?-hydroxy acid enantiomers by capillary zone electrophoresis (CZE). A polyacrylamide coated capillary was employed for the electrophoretic runs in order to suppress/minimize both the electroosmotic flow (EOF) and the antibiotic adsorption. The experiments were carried out using a background electrolyte (BGE) (aqueous-organic buffer) in the pH range 4-6 that allowed the analytes to reach the detector, as negatively charged species, in a relatively short time while the antibiotic moved in the opposite direction (positively charged). The chiral selector, dissolved in the BGE at relatively low concentration, filled only part of the capillary (partial filling-counter current method) allowing the detection of analytes with good sensitivity and short analysis time (5-8 min). Experimental parameters influencing the enantioresolution such as antibiotic concentration, buffer pH, organic modifier type and concentration and capillary temperature were investigated. Hepta-Tyr antibiotic exhibited a high enantiorecognition capability towards mandelic acid and their hydroxy and chloro derivatives even at very low concentration (1 mg/ml) using a background electrolyte (BGE) at pH 4 containing 20% (v/v) of methanol. On the other hand 2- and 3-phenyllactic acids were baseline resolved in their enantiomers with the same BGE containing acetonitrile and 4 mg/ml of chiral selector. Copyright (C) 1999 Elsevier Science B.V.