BORATE COMPLEXATION OF FLAVONOID-O-GLYCOSIDES IN CAPILLARY ELECTROPHORESIS .1. SEPARATION OF FLAVONOID-7-O-GLYCOSIDES DIFFERING IN THEIR FLAVONOID AGLYCONE

Capillary electrophoresis was found to give significantly greater efficiency, selectivity and speed compared with high-performance liquid chromatography for the separation of mixtures of flavonoid-0-glycosides. The migration behaviour of selected flavonoid-O-glycosides and their flavonoid aglycones in free solution capillary electrophoresis and micellar electrokinetic capillary chromatography (MECC) was investigated. A mixture of flavonoid-7-0-glycosides and their flavonoid aglycones was resolved by MECC. A 70 cm x 50 mum I.D. fused-silica capillary column and a 50 mM sodium dodecyl sulphate-20 mM Tris-HCl running buffer (pH 7.1) were used for these electrophoretic separations. Under these neutral conditions, the retention mechanism is based on hydrophobic interactions between flavonoids and the hydrophobic core of the micelles. Free zone capillary electrophoresis of borate complexes was more appropriate for the separation of a mixture of flavonoid-0-glycosides. In that case. the migration behaviour of these selected flavonoid-O-glycosides was explained by ionization of some hydroxyl groups and mainly by borate complexation of the sugar moiety. The identity of each flavonoid-0-glycoside was determined by using a fast-scanning multiple-wavelength UV detector and by recording its on-column UV spectrum in the range 190-360 nm.