Contents of major bioactive flavones in proprietary traditional Chinese medicine products and reference herb of Radix Scutellariae

A simple and efficient HPLC/UV method for the simultaneous determination of six bioactive flavones, namely baicalein, baicalin, wogonin, wogonoside, oroxylin A and oroxylin A-7-O-glucuronide, has been developed and applied for their content determination in reference herb and proprietary traditional Chinese medicine (PTCM) products of Radix Scutellariae. The chromatographic separation was carried out on a Thermo C₁₈ column and linear gradient elution was employed with a mobile phase containing acetonitrile and 20 mM sodium dihydrogen phosphate buffer (pH 4.6). All the analytes were detected by PDA detector at a wavelength of 270 nm. Contents of the analytes in Radix Scutellariae containing PTCM products in forms of capsule, soft capsule, tablet and dripping pill and the reference herb of Radix Scutellariae were analyzed by sonicator extraction with methanol and water mixture (80:20) containing 1 mM HCl for 30 min followed by HPLC analysis. Separation of the six analytes was achieved within 25 min with good linearity (R² > 0.99). The R.S.D. of both the intra-day and inter-day precision for all the six analytes was below 10.14%. The accuracy at different concentrations was within the range of −7.83 to 4.06%. The extraction recovery was within the range of 89.22–107.33% for all the analytes. Contents of the six flavones were found to vary significantly among different products with glycosides, such as baicalin, wogonoside and oroxylin A-7-O-glucuronide, in much greater quantity than their corresponding aglycones. In addition to baicalin (18.54 ± 0.71%, w/w), the commonly used marker compound for Radix Scutellariae, wogonoside (3.54 ± 0.18%, w/w) and oroxylin A-7-O-glucuronide (2.84 ± 0.14%, w/w) also existed in abundant amount in the reference herb. Our findings suggested that wogonoside and oroxylin A-7-O-glucuronide should also be served as the chemical markers together with baicalin for the quality control of herbs and PTCM products of Radix Scutellariae.