Analysis of glycopeptide antibiotics using micellar electrokinetic chromatography and borate complexation

Micellar electrokinetic chromatography (MEKC) was investigated as a technique for the separation and analysis of the following related glycopeptide antibiotics: alpha-avoparcin, beta-avoparcin, ristocetin A, ristocetin B and vancomycin. Sodium dodecyl sulfate (SDS) micelles were employed as the pseudostationary phase in conjunction with borate or CHES buffers at pH 9.2. A complete separation of the glycopeptides was achieved only when two separation mechanisms were employed simultaneously: (i) differential partitioning of the glycopeptides into SDS micelles; and (ii) differential complexation of the glycopeptides with the borate anion from the borate buffer. Quantitatively, linearity was confirmed for each antibiotic from 0.5 to 40 ppm, with correlation coefficients (r(2)) ranging from 0.9996 (vancomycin and beta-avoparcin) to 0.9986 (alpha-avoparcin). Detection limits ranging from 0.01 ppm (vancomycin) to 0.2 ppm (avoparcin) were achieved, and the mean recovery of avoparcin at the 10 ppm level was 99.2%.