Determination of oxiracetam in plasma and urine by column-switching high-performance liquid chromatography

A column-switching high-performance liquid chromatographic method was developed for the determination of oxiracetam in plasma and urine. A sample of plasma (250 microliters) or urine (10 microliters) is mixed with the internal standard solution, 4.2 ml of acetonitrile-water (1000:4, v/v) and 0.8 ml of dichloromethane, and 1 ml of the clear solution is injected onto a first column filled with Li-Chrosorb NH2. The sample is eluted with acetonitrile-water (95:5, v/v). The portion of the eluate (heart-cutting) from this column containing the compounds of interest is selected and loaded on a Nucleosil NH2 column and eluted with acetonitrile-water (90:10, v/v). During this chromatography the first column (LiChrosorb NH2) is rinsed with acetonitrile-water (50:50, v/v). Ultraviolet detection at 200 nm is used for quantitation. The limit of quantitation of oxiracetam is ca. 1.5 microM (240 ng/ml) in plasma and 76 microM (12 micrograms/ml) in urine. Oxiracetam was stable in plasma and urine samples kept frozen at -20 degrees C for nine months and one year, respectively.