Determination and identification of isoflavonoids in Radix astragali by matrix solid-phase dispersion extraction and high-performance liquid chromatography with photodiode array and mass spectrometric detection

The isoflavonoids in Radix astragali were determined and identified by HPLC–photodiode array detection–MS after extraction employing matrix solid-phase dispersion (MSPD). As a new sample preparation method for R. astragali, the MSPD procedure was optimized, validated and compared with conventional methods including ultrasonic and Soxhlet extraction. The amounts of two major components in this herb, formononetin (6) and ononin (2), were determined based on their authentic standards. Four major isoflavonoids, formononetin (6), ononin (2), calycosin (5) and its glycoside (1), and three minor isoflavonoids, (6aR,11aR)-3-hydroxy-9,10-dimethoxypterocarpan (7), its glycoside (3), and (3R)-7,2′-dihydroxy-3′,4′-dimethoxyisoflavone-7-O-β-d-glycoside (4), were identified based on their characteristic two-band UV spectra and [M+H]+, [aglycone+H]+ and [A1+H]+ ions, etc. The combined MSPD and HPLC–DAD–MS method was suitable for quantitative and qualitative determination of the isoflavonoids in R. astragali.