Simultaneous separation and determination of four main isoflavonoids in Astragali Radix by an isocratic LC/ESI-MS method

A simple, reliable and rapid isocratic liquid chromatography (LC)-mass spectrometric detection (MS) coupled with electrospray ionization (ESI) method for simultaneous separation and determination of calycosin-7-O-β-D-glucoside, ononin, calycosin and formonometin in Astragali Radix was developed. After the samples were extracted with ethanol, the optimum separation conditions for these analytes were achieved using water and acetonitrile (70:30, v/v) containing 0.2% (v/v) acetic acid as a mobile phase and a 2.0 mm×150 mm Hypersil-Keystone C18 column. Selective ion monitoring (SIM) mode and [M+H]+ ions at m/z 447, 431, 285 and 269 were used for quantitative analysis of four main active components above mentioned. The calibration curves were linear in the range of 0.4−175.0 μg/mL for calycosin-7-O-β-D-glucoside, 0.2−146.0 μg/mL for ononin, 0.4−210.0 μg/mL for calycosin and 0.5−217.0 μg/mL for formonetion, respectively. The limits of quantification (LOQ) and detection (LOD) were 0.4 μg/mL and 0.08 μg/mL for calycosin-7-O-β-D-glucoside, 0.2 μg/mL and 0.06 μg/mL for ononin, 0.4 μg/mL and 0.1 μg/mL for calycosin, 0.5 μg/mL and 0.1 μg/mL formonetion, respectively. The standard recoveries were in the range of 96.5%−104.7%. The developed method has successfully been used for the determination of four main flavonoids in Astragali Radix from various sources and can be used for identification, differentiation and quality evaluation of Astragali Radix.