Detection of Cannabinoids in Oral Fluid Using Inert Source GC/MS

Importance of the Topic

Oral fluid is gaining support as an alternative to blood and urine in forensic and roadside drug testing because it offers noninvasive, tamper-resistant sampling with minimal biohazard risk. However, lower analyte concentrations require highly sensitive analytical methods to reliably detect cannabis constituents, including THC, its precursor THCA-A, and other cannabinoids such as cannabidiol (CBD) and cannabinol (CBN).

Objectives and Study Overview

This work aimed to develop and validate a gas chromatography/mass spectrometry (GC/MS) procedure using an inert source for the simultaneous quantification of THC, THCA-A (2-carboxy-THC), CBN and CBD in human oral fluid. By employing a collection device that delivers a known volume of neat saliva, the study addresses challenges related to sample volume, extraction efficiency, and sensitivity to meet forensic testing requirements.

Methodology

• Sample Collection: Utilized Quantisal oral fluid collector, which indicates collection of 1 mL saliva before immersion in 3 mL transport buffer, yielding a 1:3 dilution.
• Preparation: Spiked deuterated THC internal standard into 1 mL specimen; adjusted pH with acetate buffer.
• Extraction: Employed solid phase extraction (Trace N 315 SPE columns), conditioned with methanol and acetic acid, followed by washes with water/acetic acid and water/methanol, and elution with hexane/glacial acetic acid.
• Derivatization: Evaporated extract to dryness, reconstituted in ethyl acetate, and derivatized with BSTFA+1% TMCS at 60 °C for 15 minutes.
• GC/MS Analysis: Performed splitless injection (2 µL) on a DB-5 MS column; electron impact detection monitored characteristic ions for each analyte.

Instrumentation

• GC/MS System: Agilent 6890 GC coupled to 5975 MSD with inert source.
• Collection Device: Immunalysis Quantisal oral fluid collector.
• Reagents and Consumables: Deuterated THC internal standard, unlabeled standards (THC, CBN, CBD, THCA-A), BSTFA+1% TMCS derivatizing agent, Trace N 315 SPE columns.

Main Results and Discussion

• Recovery: Extraction efficiencies ranged from 71.9% (CBD) to 89.2% (THC).
• Sensitivity: Limits of quantitation were 0.5 ng/mL for THC and CBN, and 1 ng/mL for CBD and 2-carboxy-THC, with linearity (r2 ≥ 0.998).
• Precision: Intra- and inter-day coefficients of variation remained below 15% across concentration levels.
• Authentic Specimens: In a controlled smoking study, parent THC peaked above 2000 ng/mL shortly after smoking, remained detectable for 24 hours; THCA-A was observed up to 16 hours; CBD and CBN detected only in early time points.

Benefits and Practical Applications

The method offers reliable quantitation of multiple cannabinoids in oral fluid, enabling its use in roadside testing, workplace drug screening, and forensic casework. The known sample volume and validated recovery provide greater confidence in quantitative results compared to devices without volume indicators.

Future Trends and Potential Uses

Advances in microfluidic interfaces and coupling with high-resolution mass spectrometry can further enhance sensitivity and enable on-site testing. Expanding the analyte panel to include emerging cannabinoids and metabolites will support broader forensic and clinical applications.

Conclusion

A robust GC/MS protocol using an inert source and a volumetric oral fluid collector has been developed for sensitive and accurate detection of THC, THCA-A, CBD, and CBN. The approach addresses key challenges in oral fluid analysis, offering a practical solution for forensic and roadside drug testing.

References

• Moore C., Rana S., Coulter C. Detection of Cannabinoids in Oral Fluid Using Inert Source GC/MS, Agilent Technologies Application Note 5989-5860EN (2006).