The determination of isoflavones and coumestrol by capillary electrophoresis

The separation of six isoflavones (biochanin A, isoformononetin, formononetin, prunetin, daidzein and genistein) and coumestrol on an uncoated fused-silica capillary electrophoresis column was optimised using alkaline borate buffer as electrolyte and DAD detection. A baseline separation of all analytes except a pair, formononetin-biochanin A was achieved at pH 10.5 in 25 min. Detection limits were low (0.1 µg/ml) and the linearity of the detector response was established in the concentration range 0.4–60 µg/ml (180 µg/ml for coumestrol). Coumestrol was synthesized and the carbon signals in 13C-NMR spectrum of both coumestrol and di-O-acetylcoumestrol were assigned for the first time using two-dimensional HMQC technique.