[Methodological study on the determination of oxiracetam concentration in serum and urine by HPLC].

A method was developed for the determination of oxiracetam concentration in serum and urine by HPLC. Acyclovir was used as an internal standard. The analytical column was a stainless-steel column (30 mm x 4.6 mm ID) filled with 10 microns Bondapak NH2. A mixture of acetonitrile and water (80: 20) as mobile phase was used at a flow rate of 1 ml.min-1. Detection was performed at 210 nm. The retention times were 6.3 min for oxiracetam and 8.1 min for the internal standard. The lower detection limits were 1 microgram.ml-1 for serum and 20 micrograms.ml-1 for urine. The precision and accuracy within-day and day-to-day for both serum and urine samples ranged from 5.0 to 10.7%. The mean recoveries were 99.7 +/- 5.9% and 99.0 +/- 5.6% for human serum and urine, respectively. The results showed that the method is simple, rapid, sensitive, reliable and good enough to be used in studying the clinical pharmacokinetics of oxiracetam.

[A chiral capillary gas chromatographic method for direct determination of enantiomers of mephenytoin in human urine].

A gas chromatographic method equipped with nitrogen-phosphorus detector was developed for the determination of the S- and R-enantiomers of the anticonvulsant, mephenytoin (MP) in human urine. Dichloromethane (4 ml) was added to 1 ml urine, the mixture was shaken and centrifuged. The organic phase was transferred to another tube and blown to dryness under nitrogen on water bath (37 degrees C). The residue was dissolved in 10 microliters ethylacetate and 1-2 microliters was injected into the GC. Our results showed that direct enantiomeric separation of mephenytoin was obtained by using a chiral capillary column, the retention times for S- and R-mephenytoin were 25.5 and 26.2 min respectively, with a detection limit less than 50 ng/ml of mephenytoin. Similar linear and reproducible standard curves were obtained over the concentration range of 53.2 to 2128.0 ng/ml (for S-MP, r = 0.9914 +/- 0.0070, n = 6; and for R-MP, r = 0.9939 +/- 0.0070, n = 6), and the mean recoveries of S- and R-MP were 95.4% and 95.8% respectively. The within-day relative standard deviations were less than 8.8% for both S- and R-MP, and that of between-days were less than 14.3%. There was a good reproducibility of the urine S/R mephenytoin determined in China and in Sweden by using similar method in 107 Chinese volunteers after a single oral dose of 100 mg racemic mephenytoin (r = 0.9091, P < 0.001).