Objective: To optimize sample solution preparation method and establish assay method of astragaloside IV in Astragali Radix. Method: UPLC-ELSD was used to determine the content of astragaloside IV with mobile phase of acetonitrile-water(32: 68)

column temperature of 30 ℃

flow rate of 0.5 mL·min-1

temperature of ELSD at 45 ℃

carrier gas was dry compressed air with pressure of 0.5 kPa

gain value was 7.Ammonia-methanol mixture was used to ultrasonic extract of astragaloside IV as well as n-butanol extraction.Preparation method of test solution was optimized through single-factor tests. Result: Optimal preparation method was as following:added methanol 80 mL and concentrated ammonia 40 mL

ultrasonic extraction for 30 min

purification by subsequent extraction with n-butanol for four times every 40 mL in sample preparation.The content of astragaloside Ⅳ from 11 batches of Astragali Radix by this optimizing method were significantly higher than the result determined by HPLC method in 2010 edition of Chinese Pharmacopoeia. Conclusion: This optimized sample preparation method is simple with less loss of effective constituents.UPLC analysis method is accurate and reliable with high sensitivity.