Division of Forensic Toxicology, Armed Forces Institute of Pathology, 1413 Research Blvd., Rockville, MD 20850, USA

Urine samples were prepared by centrifuging 5 ml of urine followed by the addition of 2 ml of 100 mM phosphate buffer (pH 6.0). Blood samples were prepared by centrifuging 2 ml of blood and 3 ml DI H₂0 followed by the addition of 2 ml of 100 mM phosphate buffer (pH 6.0). Liver samples were prepared by homogenizing 3 g tissue in 6 ml DI H₂0, adding 300 µl of 1.0 M acetic acid and centrifuging for 15 min at 3000 rpm. Internal standard was added to all supernatants after being transferred to clean test tubes. Three standards containing 30 drugs were prepared in 5 ml of negative urine. Concentrations of individual drugs ranged from 0.2 mg/L to 0.8 mg/L. All samples were then extracted by the "Therapeutic and Abused Drugs" procedure found in the United Chemical Technologies, Inc. application manual. An extra wash step with 20% acetonitrile in water was required to obtain clean extracts. Samples were identified by GC-NPD and GC/MS.

The percent recovery of the thirty-drug profile varied from 73% to 100%, with the exception of diazepam. The limit of detection was found to be 0.04 mg/L to 0.16 mg/L. All 30 drugs were recovered on the GC-NPD; however, alprazolam, nordiazepam and mefloquine were not detected on the GC/MS.

All drugs that were reported positive by the liquid-liquid extraction procedure were found by both the manual and automated SPE procedures. Two drugs, caffeine and nicotine, were not always recoverable by SPE. However, the GC-NPD and GC/MS relative responses for the SPE procedure were 3 x 10⁵ and 2 x 10⁷, respectively, in comparison to 8 x 10⁴ and 1 x 10⁷ for the liquid-liquid procedure. Due to the above responses with SPE, some drugs at lower concentrations were found that were not recovered in the liquid-liquid extraction; e.g., benzoylecgonine, cotinine, desethyl-lidocaine, desmethylverapamil, desmethyltramadol, diphenhydramine, norpropoxyphene, phenyl-propanolamine, thioridazine, tramadol, trimethoprim.

Based on our results of increased response and the fact that the Rapid Trace offers a less labor-intensive extraction, the SPE procedure is preferred over the liquid-liquid procedure for basic drugs in forensic samples.