Performance Evaluation of a Thermal Desorption System for Detection of Basic Drugs in Forensic Samples by GC/MS

Importance of the topic

The reliable detection of basic drugs in forensic samples is crucial for toxicological screening in clinical and legal investigations. Conventional solvent-based extractions involve multiple steps, organic solvents, and extensive handling, which increase analysis time and the risk of errors. The SBSE-TDU-GC/MS approach offers a solvent-free alternative that simplifies preparation, reduces matrix interferences, and improves laboratory throughput.

Objectives and study overview

This evaluation examined the performance of the GERSTEL Thermal Desorption Unit (TDU) combined with PDMS-coated Twister stir bars for extracting and screening basic drugs by GC/MS. Key aims were to compare SBSE-TDU against traditional liquid-liquid extraction (LLE), assess recovery across a broad analyte range, optimize extraction conditions, and verify bar reuse reliability.

Methodology

Fortified blood samples were diluted with various buffers or water, spiked with an internal standard, and stirred overnight with a Twister bar. Thermal desorption in splitless mode with cryofocusing preceded GC/MS analysis on a 35 m Rtx-5Sil column with helium carrier. LLE reference samples used identical chromatographic settings.

Instrumentation

• Agilent 6890 GC with PTV inlet (CIS 4) and GERSTEL TDU for SBSE samples
• Agilent 6890 GC with split/splitless inlet and 5973 MSD for LLE samples
• 35 m Rtx-5Sil column (0.20 mm i.d., 0.335 µm film) with 5 m guard

Main results and discussion

• Best extraction achieved with carbonate/bicarbonate buffer (pH 9.6) and 16 h stirring.
• Recoveries for 26 basic drugs at 0.3 mg/L ranged 23–99%, consistent with predicted values based on Ko/w.
• Of 145 compounds screened at 1 mg/L, most high-Ko/w analytes and several low-Ko/w drugs were detected.
• Case comparisons showed equivalent drug profiles for SBSE-TDU and LLE, with SBSE extracts yielding minimal cholesterol peaks.
• SBSE-TDU successfully extended to urine, bile, tissue homogenates, vitreous, and gastric contents.

Benefits and practical applications

• Eliminates organic solvents, lowering cost, waste, and exposure.
• Streamlines workflow by removing centrifugation, transfers, and concentration steps.
• Reusable Twister bars reduce consumable expenses when reconditioning is documented.
• Lower matrix background enhances sensitivity and decreases maintenance.

Future trends and applications

Automation of SBSE handling, expansion to diverse drug classes, coupling with high-resolution MS, and development of rapid or field-deployable devices are promising directions. Predictive extraction software will further accelerate method development for novel psychoactive substances.

Conclusion

The SBSE-TDU method provides a robust, solvent-free alternative for forensic basic drug screening by GC/MS. It matches traditional LLE performance, simplifies sample handling, and reduces matrix interferences. Proper bar reconditioning is key to consistent results, making this approach well suited for high-throughput toxicology laboratories.

Reference

Crifasi J.A., Bruder M.F., Long C.W., Janssen K. Performance evaluation of a thermal desorption system for basic drug screening by GC/MS. GERSTEL Application Note 11/2006.