Quantification of vincristine and vinblastine in Catharanthus roseus plants by capillary zone electrophoresis

Abstract

A systematic and comprehensive study of the separation and quantification of two dimeric catharanthus alkaloids, vincristine (VC) and vinblastine (VB), in Catharanthus leaves by capillary zone electrophoresis (CZE) was conducted. Various separation parameters such as buffer concentration and pH, column internal diameter and applied voltage were studied. Due to the complexity of the samples, the optimum conditions for separating VC and VB from other alkaloids that co-exist in the plant samples are matrix-dependent. We found the following conditions, in general, gave the best results in terms of resolution and analysis time: column, 72 cm (57 cm effective length) × 75 μm I.D.; buffer, 0.2 M ammonium acetate solution, pH 6.2 and an applied voltage of 10 kV. Although the separation of VB and VC was the primary focus, the separation parameters determined in this study can be applied to the separation of other alkaloids as well. Separation of many of the other alkaloids in the plant samples was observed under conditions presented in this paper. A secondary objective of this study was to develop a method with experimental conditions which could be applied to electrophoresis-mass spectrometry. For this reason, ammonium acetate buffers, which are more compatible with mass spectrometry than the widely used phosphate buffers, were used exclusively. Also, methanol-water-acetic acid was used as external buffer for the same reason. The effects of this buffer and its compositions on the resolving power of CZE for the VB/VC pair are discussed.