Determination of spinosin in rat plasma by reversed-phase high-performance chromatography after oral administration of Suanzaoren decoction.

A sensitive, simple, and accurate method for determination of spinosin in rat plasma with sulfamethoxazole (SMZ) as internal standard was developed using RP-HPLC with UV detection. Sample preparations were carried out by protein precipitation with acetonitrile, followed by the evaporation of the acetonitrile to dryness. The resultant residue was then reconstituted in mobile phase and injected onto a Hypersil C(18) (200 x 4.6 mm I.D., 5 microm) analytical column. The mobile phase consisted of acetonitrile-water (15:85, v/v) with 1% glacial acetic acid. The assay was shown to be linear over the range of 18.07-903.5 ng/ml (R(2)=0.995). Mean recovery was determined as 93.6%. Within- and between-day precisions were </=8.9% RSD. The limit of quantitation was 18.07 ng/ml. The HPLC method developed has been applied to determine the pharmacokinetics of spinosin in rat plasma after having taken Suanzaoren decoction.