[Determination of R- and S-mephenytoin in human urine by gas chromatography]

The levels of R- and S-mephenytoin in human urine were determined by chiral capillary gas chromatography with nitrogen-phosphorus detector. The conditions of the chromatography and detection included a chiral capillary column (Chirasil-Val, 25 m x 0.25 mm i.d., Alltech), column temperature (T) 190 degrees C, injector T 220 degrees C, detector T 240 degrees C, and the flow-rates of 0.85, 3.5 and 120 mL/min for nitrogen, hydrogen and air respectively. Based on the above conditions, the satisfactory separation of R- and S-mephenytoin was gained, and other interference from urine sample was not found. The linear curves for both tested compounds ranged between 12.5 and 2500 microg/L, with a minimum detectable concentration of about 6 microg/L. Because of its simplicity, rapidity, sensitivity and accuracy, this method has been extensively used for testing metabolic ability of S-mephenytoin polymorphic oxidation in the Chinese populations and for the determination of the activity of hepatic drug-metabolizing enzyme CYP2C19 using mephenytoin S/R ratio of the urine samples of subjects as an indicator.