Stir Bar Sorptive Extraction (SBSE) and GC/MS Determination of Polar and Non-polar Drugs and Pharmaceuticals in Post Mortem Brain Tissue

Importance of the Topic

Stir Bar Sorptive Extraction (SBSE) addresses key challenges in forensic and clinical analysis of drugs and pharmaceuticals in complex biological matrices. Traditional methods such as liquid–liquid extraction and solid-phase extraction are labor intensive and consume large volumes of organic solvents. SBSE offers a solvent-free alternative with minimal sample preparation, making it highly attractive for routine toxicological screening and environmental monitoring.

Study Objectives and Overview

This application note demonstrates the use of a PDMS-coated magnetic stir bar (Gerstel Twister) coupled with thermal desorption GC/MS for the extraction and determination of both polar and non-polar drugs in post mortem brain tissue. Objectives include evaluation of extraction efficiency, chromatographic cleanliness, repeatability, and capability for both target screening and non-targeted compound identification.

Methodology and Instrumentation

Sample Preparation and Extraction

• Homogenize 2 g of tissue; transfer 1 g to a 25 mL vial
• Add 5 mL Trizma buffer pH 8.5 with NaCl saturation
• Insert pre-conditioned Twister; stir at 1 000 rpm for 3 h (0.5 h for control mix)
• Remove, rinse, dry, and load Twister into TD tube

Thermal Desorption and GC/MS Conditions

• TDU: 50 °C to 280 °C at 300 °C/min, splitless
• CIS 4: trap at –100 °C, inject to 300 °C
• GC Column: Rxi-5ms, 30 m × 0.25 mm × 0.25 μm
• Carrier Gas: He at constant pressure (111.4 kPa) with retention time locking
• MSD: EI, full scan 40–570 amu

Main Results and Discussion

Target Screening

• Positive control (GTFCh mix) recovered amphetamine, ibuprofen, methadone, cocaine, diazepam and others; highly polar or GC-incompatible analytes (e.g. THC-COOH) not detected
• Chromatograms exhibited minimal fatty acid background despite complex tissue matrix
• Repeat analyses showed excellent signal reproducibility

Non-Targeted Screening

• AMDIS-based deconvolution and Agilent DRS enabled identification of over 700 library compounds
• Retention time locking improved confidence in compound matching
• Unknown workshop samples yielded identification of clomethiazole, phenprocoumon, papaverine, noscapine and xylazine

Benefits and Practical Applications

• Solvent-free, minimal sample handling and disposable consumables reduction
• Automated processing of up to 196 samples per batch using Gerstel MPS autosampler
• Broad applicability to blood, urine, liver and brain tissues in forensic, clinical and environmental laboratories

Future Trends and Potential Applications

• Integration with LC-MS workflows via solvent back-extraction from Twister
• On-bar derivatization to extend analysis to highly polar or thermally labile compounds
• Expansion of search libraries and machine learning-based deconvolution for enhanced non-target screening

Conclusion

SBSE with a PDMS-coated Gerstel Twister coupled to thermal desorption GC/MS provides a robust, solvent-free approach for screening a wide range of drugs in post mortem tissue. The technique delivers clean extracts, reliable repeatability and flexible workflows for targeted and non-targeted analysis, streamlining forensic toxicology and pharmaceutical residue testing.

References

• Sandra P, Baltussen E, David F, Hoffmann A. A Novel Extraction Technique for Aqueous Samples: Stir Bar Sorptive Extraction. GERSTEL AppNote 1/2000.
• Crifasi J, Bruder M, Long C, Janssen KJ. Performance Evaluation of Thermal Desorption System for Detection of Basic Drugs in Forensic Samples by GC–MS. J Anal Toxicol. 2006;30:1–12.
• Vendenin A, Sovorkin V, Kachur E. Stir Bar Sorptive Extraction-Thermal Desorption-Capillary GC-MS Applied for Analysis of Amphetamine Derivatives in Biological Fluids. GERSTEL AppNote 7/2004.
• Pfannkoch E, Whitecavage J, Bramlett R. Feasibility of Extraction and Quantitation of 9-Tetrahydrocannabinol in Body Fluids by SBSE and GC/MS. GERSTEL AppNote 6/2005.