Micellar electrokinetic chromatography for the quantitative analysis of flavonoids in the radix of Astragalus membranaceus var. mongholicus

The separation and determination of eight flavonoids in the radix of Astragalus membranaceus (Fisch.) Bge var. mongholicus (Bge.) Hsiao was achieved by using micellar electrokinetic chromatography (MEKC) with a diode array detector (DAD). The influence of background electrolyte (BGE) concentrations and pH, surfactant concentrations, organic solvents, temperature, and voltage on the separate procedure was systematically investigated. The optimal resolution was obtained with a micellar phase consisting of 100 mM sodium cholate, 25 % (v/v) acetonitrile, 20 mM Na2B4O7, and 20 mM H3BO3 buffer at pH 9.2 by using a fused silica capillary at + 25 kV and 25 degrees C. A high reproducibility and good linearity ( R2 > 0.9978) were obtained over the concentration range tested. The relative standard deviations (R.S.D.s) from intra-day and inter-day precision for injection were less than 4.42 %. Six plant samples from different locations were then analyzed for the flavonoids by this newly developed MEKC method.