Using UPLC-MS/MS for the Determination of Carboxy-THC (cTHC) in Hair for Forensic Toxicology

Importance of the Topic

Hair analysis for cannabinoids offers a non-invasive, easily stored matrix with an extended detection window, enabling differentiation of long-term usage patterns. Measurement of the metabolite 11-nor-9-carboxy-Δ9-tetrahydrocannabinol (cTHC) is essential to confirm active cannabis intake and distinguish it from passive exposure.

Goals and Overview of the Study

The study aimed to develop and validate a robust UPLC-MS/MS method for quantifying cTHC in human hair at the Society of Hair Testing confirmation cut-off of 0.2 pg/mg, ensuring high sensitivity, accuracy, and routine applicability in forensic toxicology.

Methodology and Instrumentation

Sample Preparation

• Control hair decontaminated with dichloromethane, methanol, and diethyl ether, then cut into 1–2 mm segments.
• 20 mg hair spiked with cTHC (0–10 pg/mg) and internal standard (cTHC-d3), incubated at 100 °C for 60 min with M3 reagent.
• Solid-phase extraction using OASIS PRiME HLB cartridges, washed and eluted; samples reconstituted for analysis.

Instrumentation

• UPLC: ACQUITY UPLC I-Class (FTN) with BEH C18 column, mobile phase gradient of ammonium fluoride pH 9.5 and methanol.
• MS/MS: Xevo TQ-S micro, monitoring MRM transitions 343 > 191 (quantifier), 343 > 245 (qualifier) for cTHC and 346 > 194 for cTHC-d3.

Main Results and Discussion

The method demonstrated clear chromatographic separation and a signal-to-noise ratio above forensic requirements at 0.2 pg/mg. Linearity was confirmed from 0 to 10 pg/mg with r² = 0.993. Calibration residuals remained within acceptable limits, indicating accuracy and precision at sub-pg/mg levels.

Benefits and Practical Applications

• Non-invasive hair collection with minimal privacy concerns
• Extended detection window enabling retrospective exposure assessment
• High sensitivity meeting forensic confirmation thresholds
• Simplified sample storage and handling without medical personnel

Future Trends and Applications

Advancements may include automated sample processing, higher-resolution mass analyzers for improved selectivity, segmental hair analysis for timeline reconstruction, and expanded panels for multi-drug profiling.

Conclusion

The developed UPLC-MS/MS protocol provides a sensitive, reproducible, and robust approach for forensic determination of cTHC in hair, aligning with SoHT guidelines and facilitating reliable confirmation of cannabis use.

Reference

• G.A.A. Cooper, R. Kronstrand, P. Kintz. Society of Hair Testing guidelines for drug testing in hair. Forensic Science International 218 (2012) 20–24.