ANALYSIS OF CARBOXY-THC USING UPLC-MS/MS

Significance of Topic

The reliable detection of carboxy-Δ9-tetrahydrocannabinol (carboxy-THC) in hair is critical for forensic investigations to distinguish true cannabis use from passive exposure. Hair offers a stable matrix that can reflect drug intake over past months, facilitating long-term monitoring without invasive sampling.

Study Objectives and Overview

This work aimed to develop and validate a highly sensitive and robust UPLC-MS/MS method for quantifying carboxy-THC in human hair. The method targets the Society of Hair Testing’s confirmation cutoff (0.2 pg/mg) and ensures precise measurement across a calibration range of 0.2–10 pg/mg.

Methodology and Instrumentation

Sample preparation involved:

• Decontamination and scissor-mincing of hair (1–2 mm).
• Spiking with carboxy-THC and deuterated internal standard (carboxy-THC-D3).
• Incubation for 60 min at 100 °C with proprietary buffer.
• SPE cleanup using OASIS PRiME HLB cartridges.
• Reconstitution in 50% methanol/ammonia solution prior to injection.

Used Instrumentation:

• UPLC: ACQUITY UPLC I-Class PLUS with Premier BEH C18 column (2.1×150 mm, 1.7 µm).
• MS/MS: Xevo TQ-Absolute operating in negative ESI and MRM mode.

Main Results and Discussion

The assay demonstrated:

• Excellent linearity (R2>0.99) over 0.2–10 pg/mg.
• Limit of quantification at 0.2 pg/mg with signal-to-noise ratios >15.
• Minimal carryover, confirmed by blank injections after high-level samples.
• Matrix suppression (~36%) effectively compensated by internal standard, yielding matrix factor of 100%.
• Overall precision (total %RSD) of 8.4% and within-sample repeatability of 1.8%.

Benefits and Practical Applications

The method offers high sensitivity and reliability for forensic toxicology, enabling confident confirmation of cannabis use from hair. Its non-invasive sampling and stability support routine monitoring in clinical, forensic, and workplace settings.

Future Trends and Potential Applications

Advances may include automated on-line SPE integration, miniaturized high-resolution MS systems for multiplexed analysis, and expanded panels for simultaneous detection of multiple drug metabolites in hair.

Conclusion

This validated UPLC-MS/MS procedure fulfills stringent forensic criteria for carboxy-THC detection in hair at sub-pg/mg levels. The approach combines effective sample cleanup, isotopic standardization, and robust chromatography for reliable quantification.

References

1. Cooper G.A.A., Kronstrand R., Kintz P. Society of Hair Testing guidelines for drug testing in hair. Forensic Science International 281 (2012) 20–24.
2. Society of Hair Testing. Statements concerning the examination of drugs in human hair. (cited 14 Aug 2023).