Identification and determination of flavonoids in astragali radix by high performance liquid chromatography coupled with DAD and ESI-MS detection.

A method for the analysis of flavonoids in Astragali Radix by high-performance liquid chromatography (HPLC) combined with photodiode-array detection (DAD) and an electrospray ionization (ESI)--mass spectrometry (MS) was developed. After the samples were extracted with ethanol, the optimum separation conditions for these analytes were achieved using a gradient elution system and a 2.0 x 150 mm Shimadzu VP-ODS column. Eight flavonoids were identified to exist in Astragali Radix based on their characteristic UV data and mass spectra. The concentrations of three major components in this herb--ononin, calycosin and formononetin--were determined by LC/ESI-MS in positive selective ion monitoring (SIM) mode. The calibration curves were linear in the range of 0.9~180.0 µg·mL⁻¹ for ononin, 1.8~360.0 µg·mL⁻¹ for calycosin and 1.4~280 µg·mL⁻¹ for formononetin, respectively. The limits of quantification (LOQ) and detection (LOD) were 0.9 µg· mL⁻¹ and 0.2 µg mL⁻¹ for ononin, 1.8 µg mL⁻¹ and 0.5 µg·mL-1 for calycosin, 1.4 µg mL⁻¹ and 0.5 µg·mL⁻¹ for formononetin, respectively. The standard recoveries were between 95.4~104.7%. The developed method was proven to be useful for the quantitative and qualitative analysis of flavonoid constituents in various resources of Astragali Radix.