Fully Automated SPE-GC/MS Determination of Δ9-Tetrahydrocannabinol (THC) and its Metabolites in Serum Samples

Importance of the Topic

Accurate determination of Δ9-tetrahydrocannabinol (THC) and its major metabolites in blood serum is critical for forensic toxicology, clinical diagnostics and traffic safety enforcement. Conventional manual sample preparation is laborious, exposes analysts to toxic solvents and limits laboratory throughput. Fully automated workflows reduce human error, improve reproducibility and allow laboratories to meet increasing demand for high-capacity analyses.

Goals and Overview of the Study

This work describes the transfer of a validated semi-automated SPE-GC/MS method for THC, 11-hydroxy-THC and THC-COOH in serum into a fully automated platform. Objectives included reduction of sample and solvent volumes, integration of solid phase extraction and evaporation, validation according to GTFCh guidelines and demonstration of equivalent or improved performance compared to the routine method.

Methodology and Instrumentation

• Automation system: Gerstel MultiPurpose Sampler Dual Head with SPE module and MultiPosition Evaporation Station, interfaced to an Agilent 7890 GC and 5977 MSD.
• Sample preparation: 0.5 mL serum spiked with deuterated internal standards, protein precipitation in acidified water, loading onto 1 mL C18ec cartridges, washing, nitrogen drying, elution with acetonitrile, vacuum-assisted evaporation at 60 °C and derivatization with MSTFA.
• GC/MS parameters: VF-1ms column (25 m × 0.2 mm × 0.33 µm), temperature program from 160 °C to 300 °C, splitless injection, helium constant pressure, selected ion monitoring of characteristic ions for analytes and deuterated analogues.

Main Results and Discussion

• Comparative tests of Macherey & Nagel and UCT C18ec sorbents showed equivalent chromatographic response and recoveries for all three analytes.
• Method downscaling to 0.5 mL sample and 100 mg cartridges achieved comparable signal intensity, reduced background noise and halved solvent consumption.
• No measurable carry-over was observed in blank serum injections following high-level spiked samples (60 ng/mL THC/THC-OH, 600 ng/mL THC-COOH).
• Validation results: limits of quantification below 1 ng/mL for THC and THC-OH, extraction efficiencies between 70 % and 93 %, intra-day repeatability 3.3 %–10 %, inter-day repeatability 6.7 %–16.3 % in accordance with GTFCh criteria.

Benefits and Practical Applications

• Parallelized sample preparation and GC/MS analysis maximizes instrument utilization and sample throughput.
• Reduced sample and reagent volumes lower costs and minimize analyst exposure to hazardous chemicals.
• High precision and accuracy support forensic casework, workplace drug testing and clinical monitoring of cannabis consumption patterns.

Future Trends and Opportunities

Continued development of fully automated sample preparation platforms will enable broader application to complex matrices and emerging biomarkers. Integration with tandem mass spectrometry can enhance selectivity and sensitivity. Miniaturized cartridges and microfluidic approaches promise further reductions in solvent usage. Flexible software control allows rapid adaptation to new analyte panels in pharmaceutical, environmental and food analysis.

Conclusion

A robust fully automated SPE-GC/MS workflow for THC and its metabolites in serum has been established with validated performance metrics meeting forensic quality standards. The method reduces manual workload, cuts reagent consumption and offers high throughput suitable for routine toxicological laboratories.

References

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