Objective: To establish a method for determining contents of three major compounds in human plasma

namely paeoniflorin

paeonol and α-cyperone from Baixiangdan capsules

and to determine plasma protein binding rate. Method: Equilibrium dialysis method was carried to determine plasma protein binding rate.Samples were extracted by liquid-liquid extraction with ethyl acetate

LC-MS/MS was employed with a Phenomenex Luna C18 column (2.0 mm×100 mm

3 μm)

mobile phase of methanol-0.1% formic acid solution (80:20)

flow rate was 0.2 mL·min-1.Quantitation was performed on a triple quadrupole mass spectrometer employing electrospray ionization (ESI) technique

operating in multiple reaction monitoring (MRM) and positive ion mode. Result: Within low

middle and high concentration (56.2

112.5

168.8 mg·L-1) of Baixiangdan capsules

plasma protein binding rates of paeoniflorin were (24.82±3.91)%

(20.88±2.69)% and (22.40±3.33)%;binding rates of paeonol were (88.62±1.68)%

(86.16±2.36)% and (88.73±0.80)%;binding rates of α-cyperone were (80.69±1.12)%

(78.10±2.28)% and (72.57±0.30)%. Conclusion: Human protein binding rates of three major compounds in Baixiangdan capsules were decreased in the order of paeonol > α-cyperone > paeoniflorin.