Determination of the ionisation constants of isoflavones by capillary electrophoresis

The ionisation constants of a group of important dietary phytoestrogens wer e investigated using capillary electrophoresis, The variation in electropho retic mobilities with pH of the isoflavones genistein, daidzein, biochanin A, formononetin and glycitein along with the related compounds dihydrogenis tein and O-desmethylangolensin was examined in sodium carbonate:bicarbonate buffer across the pH range 8.5-10.5. The pK(a) values were determined by p erforming nonlinear regression on the resulting plot of electrophoretic mob ility vs. pH, Two markers of known pK(a), namely benzoic acid and resorcino l, were included to improve accuracy. The influence of isoflavone structure on electrophoretic behaviour and pK(a) has been explained. Dominant effect s over the measured pH range were attributed to substitution at the 4'-posi tion. Copyright (C) 2000 John Wiley & Sons, Ltd.