Fig. 2.

The preparation methods including solid-phase extraction (SPE), methanol precipitation, acetonitrile precipitation, liquid–liquid extraction with ethyl acetate and liquid–liquid extraction with the mixture of ethyl acetate and methanol were all tried. As a result, the acetonitrile precipitation was selected considering the number of chromatography peaks and the interference from the co-eluted endogenous matrix for samples from the hepatic portal vein. (A: Flos Lonicerae extract, B: controlled rat plasma, C: rat plasma after oral administration of Flos Lonicerae extract, D: rat plasma after oral administration of Flos Lonicerae extract with COS).