Namera A., Yashiki M., Okada K., Iwasaki Y., Kojima T.

Dept. of Legal Medicine, Hiroshima University School of Medicine, 1-2-3 Kasumi, Minami-ku, Hiroshima 734, Japan

The method for the automatic analysis of barbiturates in urine and serum was developed using a PrepStation (Hewlett Packard, USA) in combination with a gas chromatograph/mass spectrometer (GC/MS). A PrepStation can automate many pretreatment steps, such as solid phase extraction (SPE). Human interaction is only required to place samples on the auto-sampler tray.
Methods. The sample clean-up was performed by SPE on C₁₈ disposable cartridges. All the sample handling operations were effected by an auto-sampler. The SPE cartridge was preconditioned with methanol and 0.1M phosphate buffer (pH 6.0). After loading 1.5 mL of urine or diluted serum sample onto the SPE cartridge, the cartridge washed with 2.5 mL of a 10% aqueous methanol and dried. The elution step was performed with 1.0 mL of chloroform-iso-propanol (3:1). A one µl of eluate was injected into the GC/MS.
Results. Recovery of barbiturates was more than 90%. The calibration curves, using the internal standard method, demonstrated good linearity throughout the concentration range from 0.10 to 10 µg/mL for barbiturates. The proposed method was applied to some clinical cases. The total analysis time for 20 samples was approximately 14h.