PMID: 11315156Apr 21, 2001Paper

Determination of avoparcin in animal formulations by capillary electrophoresis

Journal of Capillary Electrophoresis and Microchip Technology
C LucasJoe P Foley

Abstract

The separation of two closely related glycopeptides, alpha- and beta-avoparcin, which differ by the presence or absence of a Cl atom, is achieved by capillary zone electrophoresis (CZE) using 20 mM borate (pH 9.2) in bare, fused-silica capillaries. The pKa values of these two glycopeptides are determined from spectrophotometric titrations of the mixture. Absorption spectra recorded between pH 3 and 12 produced a maximum pH transition at 258 nm. Titration data fitted to two sigmoidal functions reveal pKas of 7.99 for beta-avoparcin and 10.3 for alpha-avoparcin. The differing pH dependence of the effective electrophoretic mobilities of alpha- and beta-avoparcin resulted in an optimum pH of 9.2 (roughly the average of the pKa values) for their separation. Borate is shown to be necessary for the optimal CZE separation. A linear dynamic range of 0.5-50 ppm is achieved with regression coefficients of 0.9999. The limit of detection ranges from 0.2 to 0.5 ppm using a pressure injection of 15 sec in a 50-cm (effective length) fused-silica capillary with UV detection. Finally, the effects of sodium dodecyl sulfate (SDS) concentration in the migration buffer on apparent mobility, efficiency, migration times, and resolution are discussed. ...Continue Reading

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