Objective:Determining the plasma protein binding rate of flavonoids in Compound Hongcao freeze-dried powder for injection to provide a reference for clinical safe medication and the method for the plasma protein binding. Method: The ultra-high performance liquid chromatography-mass spectrometry (UPLC-ESI-MS/MS) as a detection tool

using equilibrium dialysis method and ultrafiltration to study the plasma protein binding rate of orientin

vitexin

cynaroside and quercitrin

and compare the differences between the results. Result: When the drug-plasma concentrations were from 5-100 mg·L-1

the results showed high plasma binding ability of these compounds with two method and the binding rates were independent of the investigated concentrations. However

two method determination of vitexin and cynaroside showed statistical difference(P＜0.01). Conclusion: The established methods as equilibrium dialysis and ultrafiltration both meet the require of determination the plasma protein binding and the two method had showed difference in some compounds.