University Centre for Pharmacy, Groningen-Utrecht Institute of Drug Exploration, Deusinglaan 1, 9713 AV Groningen, The Netherlands

Discs were SPEC.PLUS.C18AR/MP3 columns, providing hydrophobic and cation exchange interaction. Blank human urine was spiked at 2 mg/L with pentobarbital, secobarbital, methaqualone, diazepam, phencyclidine, lidocaine, methadone, imipramine and codeine, thus representing a variety of drug classes. Urine specimens (2 mL), were diluted with 2 mL phosphate buffer pH 5.0, and the mixture was applied to the preconditioned disc. Washing was done with 1 mL water. Acidic and neutral drugs were eluted with 1 mL ethyl acetate-acetone 1:1, followed by eluting basic drugs with 1 mL ammoniated ethyl acetate. Extracts were examined by GC-FID to check cleanliness, recoveries and reproducibilities.

The discs showed good extraction efficiencies for all drugs, with little or no matrix interferences. Recoveries were 75-100% with CV's around 5%. As compared to our standard SPE method mentioned above, the disc procedure allowed a reduction of both elution volumes and total processing times by some 65%.