Determination of flavonoids in Houttuynia cordata Thunb. and Saururus chinensis (Lour.) Bail. by capillary electrophoresis with electrochemical detection.

Four flavonoids (rutin, hyperoside, quercitrin and quercetin) in Houttuynia cordata Thunb. and Saururus chinensis (Lour.) Bail. were determined by capillary electrophoresis with wall-jet amperometric detection. The working electrode was a 500 microm diameter carbon disc electrode and the detection potential was +0.95 V (versus Ag/AgCl). Effects of several important factors, such as the running buffer and its corresponding pH and concentration, separation voltage, injection time were investigated to acquire the optimum conditions for separation of these four flavonoids. Baseline separation for the four flavonoids was obtained within 21 min in a 60 cm length capillary at a separation voltage of 15 kV with a 60 mmoL/L Na(2)B(4)O(7)-120 mmoL/L NaH(2)PO(4) buffer (pH 8.8) as running buffer. The relationship between peak currents and analyte concentrations was linear over about two orders of magnitude with detection limits (defined as S/N=3) ranging from 0.02 to 0.05 microg/mL for all analytes. This method was applied for the determination of the above four flavonoids in H. cordata Thunb. and S. chinensis (Lour.) Bail. with simple extraction procedures, and the assay results were satisfactory.