Development of a capillary electrophoretic method for the separation of the macrolide antibiotics, erythromycin,...

Capillary electrophoresis (CE) provides high separation efficiency and thus is suitable for the analysis of complex mixtures of structurally similar compounds. The versatile nature of CE can be realised by controlling the chemistry of the inner capillary wall, by modifying the electrolyte composition and by altering the physicochemical properties of the analyte. A CE method has been developed for the separation of three macrolide antibiotics, erythromycin, oleandomycin and josamycin. A systematic approach was used to maximise analyte differential electrophoretic mobility by manipulating electrolyte pH, molarity and composition. In addition, some instrumental parameters such as capillary length and diameter and applied voltage were varied. The effect of the sample solvent and on-capillary concentrating techniques such as field amplified sample injection were investigated. Also, the influence of the injection of a water plug on the quantity of sample injected was demonstrated. The macrolides were completely resolved in less than 30 min in a 100 cm x 75 microm I.D. fused-silica uncoated capillary with a Z-shaped flow cell of path-length 3 mm. The analysis was performed in a 75 mM phosphate buffer (pH 7.5) with 50% (v/v) methanol and an applied voltage of 25 kV was selected to effect the separation.