RP-HPLC determination and pharmacokinetic comparison of cinnamic acid in rat plasma after administration of Di-Gu-Pi decoction and pure cinnamic acid

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 C, 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 mu g/mL (R-2 = 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.