Abstract: A sensitive, simple, and accurate method was developed for the determination and pharmacokinetic comparison of cinnamic acid in rat plasma after the administration of a Traditional Chinese Medicinal preparation, Di-Gu-Pi decoction, and pure cinnamic acid using RP-HPLC. Di-Gu-Pi was extracted with 5% aqueous sodium bicarbonate, which was followed by purification with ion exchange column chromatography. The plasma samples taken from rats were deproteinized with methanol. The reversed-phase(HPLC) system with a Diamonsil C₁₈ column and methanol-acetonitrile-water (8∶32∶60, volume ratio) (adjusted to pH=3.0 with glacial acetic acid) as the mobile phase was employed for the separation of cinnamic acid in the plasma samples. The detection was set at 272 nm and 3-(p-fluorophenyl)-2-propenoic acid was chosen as the internal standard. The calibration curve was linear in a range from 0.10 to 25.0 μg/mL (R²=0.9988, n=9). The precision was 3.42%-10.10%; the between-day precision was 2.84%-8.91%; the accuracy was -1.51%-1.26%; the mean recovery was 99.9%. The method was found to be sensitive, simple, accurate and appropriate for the determination of cinnamic acid.

Key words: Di-Gu-Pi decoction, Cinnam icacid, Pharm acok inetics, RP-HPLC