DETERMINATION OF CANNABINOIDS, THC AND THC-COOH, IN ORAL FLUID USING AN AGILENT 6490 TRIPLE QUADRUPOLE LC/MS

Importance of the Topic

A rapid and reliable analytical method for detecting cannabinoids in oral fluid addresses critical needs in forensic toxicology, especially in driving under the influence of drugs (DUID) testing. Oral fluid offers noninvasive collection and better blood correlation than urine, making it a preferred matrix for roadside and clinical screening.

Aims and Overview of the Study

This work aimed to develop and fully validate a simple liquid chromatography–tandem mass spectrometry (LC-MS/MS) procedure for quantifying Δ9-tetrahydrocannabinol (THC) and its primary metabolite, THC-COOH, in oral fluid. The focus was on achieving high selectivity, sensitivity, and reproducibility under forensic guidelines.

Methodology and Instrumentation

Sample preparation applied a “dilute and shoot” strategy, selecting an 1:8 dilution in water to minimize matrix effects. Chromatographic separation used an Agilent 1290 Infinity LC with a ZORBAX Eclipse Plus C18 RRHT column (2.1×100 mm, 1.8 µm), a 0.2 mL/min gradient from 30% to 95% acetonitrile with 0.1% formic acid, at 35 °C. Detection employed an Agilent 6490 Triple Quadrupole LC/MS with ESI Jet Stream, positive mode, monitoring MRM transitions for THC (315.2→193.2, 315.2→123.3) and THC-COOH (345.2→299.2, 345.2→327.2) with a deuterated internal standard (THC-COOH-D3).

Main Results and Discussion

Validation demonstrated no endogenous interferences and matrix effects controlled below 15% CV using the selected dilution. Calibration was linear for THC (0.1–10 ng/mL, R²=0.9930) and THC-COOH (0.25–10 ng/mL, R²=0.9977). Limits of quantification were 0.1 ng/mL for THC and 0.25 ng/mL for THC-COOH. Intra- and inter-day precision and accuracy met forensic criteria with RSDs ≤20% at LOQ and <15% at higher levels.

Benefits and Practical Applications

• Reduced sample preparation time through direct dilution.
• High throughput suitable for routine forensic screening.
• Simultaneous confirmation of parent drug and metabolite.
• Compliance with international forensic validation standards.

Future Trends and Applications

Emerging directions include integration with portable MS devices for on-site testing, automated sample handling to boost throughput, expansion to additional cannabinoids and metabolites, and coupling with high-resolution mass spectrometry for broad-spectrum drug screening.

Conclusion

The developed LC-MS/MS method offers a fast, sensitive, and accurate tool for forensic analysis of THC and THC-COOH in oral fluid. Its minimal sample preparation and robust validation make it an effective alternative to traditional GC-MS protocols for DUID and workplace drug testing.

References

1. Evaluation of four oral fluid devices for drugged driving screening, Forensic Sci Int., 2012.
2. Lee D., Huestis M.A., Current knowledge on cannabinoids in oral fluid, Drug Test Anal., 2013.
3. Peters F.T. et al., Validation of new methods, Forensic Sci Int., 2007.
4. Matuszewski B.K. et al., Strategies for assessment of matrix effect in quantitative HPLC-MS/MS, Anal Chem., 2003.