Screening for Cannabinoids Using the Waters Forensic Toxicology Application Solution with UNIFI

Importance of the Topic

Cannabis and its metabolites represent one of the most frequently encountered classes of illicit substances in forensic and workplace drug testing. Accurate detection of Δ-9-tetrahydrocannabinol (THC) and its major urinary metabolite 11-nor-9-carboxy-Δ9-THC (cTHC), including its glucuronide conjugate, is critical for legal, clinical and occupational monitoring. The ability to screen negative ionizing cannabinoids in urine at concentrations below current cut-offs enhances the reliability and scope of routine toxicology workflows.

Objectives and Study Overview

This study aimed to expand the existing Waters Forensic Toxicology Application Solution with UNIFI by incorporating negative electrospray ionization (ESI–) to detect and semi-quantify key cannabinoids in urine. The work assessed method sensitivity, selectivity and concordance with an established UPLC-MS/MS assay, targeting screening thresholds below the European Workplace Drug Testing Society (EWDTS) cut-off of 50 ng/mL for cTHC.

Methodology and Instrumentation

A rapid sample preparation involved a five-fold dilution of urine with acetonitrile and formic acid containing an internal standard (deuterated cTHC). Chromatographic separation used an ACQUITY UPLC I-Class FTN system with an HSS C18 column (2.1 × 150 mm, 1.8 µm) at 50 °C, gradient elution from 87% aqueous formic acid to 5% over 4.5 min, and a total run time of 7.5 min. Mass spectrometry employed a Xevo G2-S QTof in MS^E mode with negative ESI, acquiring low- and high-energy data across m/z 50–1000. Data processing and library matching were performed in UNIFI, applying identification criteria of ≥250 counts, ±0.35 min retention time window, ≤5 ppm mass error and at least one diagnostic fragment in the high-energy function.

Main Results and Discussion

Seven cannabinoids (cTHC-glucuronide, cTHC, THC-OH, cannabidiol, cannabinol and THC) were baseline-resolved within 5.8 min. Calibration curves for cTHC and its glucuronide exhibited linearity (r² ≥ 0.995) from low nanogram levels to 500 ng/mL, with lowest positive identification at 12.5 ng/mL for cTHC and 6.25 ng/mL for cTHC-glucuronide. In 26 authentic urine samples, the MS^E assay detected cTHC in 11 and cTHC-glucuronide in 16 specimens, matching known UPLC-MS/MS results. Analysis of Bio-Rad Liquichek reference urines returned values within manufacturer specifications (11.1 vs 11.5 ng/mL; 40.5 vs 35.3 ng/mL) and provided additional fragment confirmation.

Benefits and Practical Applications

The extended solution offers rapid, high-throughput screening and semi-quantitative analysis of negative ionizing cannabinoids in urine with minimal sample preparation. Its sensitivity below standard cut-offs supports early detection and compliance monitoring. Automated data processing in UNIFI streamlines forensic workflows and reduces manual review, enhancing laboratory productivity and confidence in results.

Future Trends and Potential Applications

Further development may include full quantitative validation for regulatory compliance, expansion of the negative ion library to emerging synthetic cannabinoids, and integration with automated sample handling. Coupling high-resolution screening with targeted MS/MS quantitation in a single run could provide comprehensive toxicology panels. Machine learning tools might improve library matching and reduce false positives.

Conclusion

The Waters Forensic Toxicology Application Solution with UNIFI, enhanced for negative ESI, delivers robust screening and semi-quantitation of major urinary cannabinoids. The method demonstrates excellent linearity, sensitivity and agreement with established assays, supporting its adoption for forensic and workplace drug testing at concentrations below current screening cut-offs.

Reference

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