COMPARATIVE EVALUATION OF HIGH RESOLUTION MASS SPECTROMETRY ACQUISITION STRATEGIES FOR THE DETECTION AND ANALYSIS OF ILLICIT DRUG SUBSTANCES

Significance of the topic

Mass spectrometry-based urine drug screening underpins clinical and forensic toxicology, treatment compliance monitoring, and harm-reduction services. Traditional workflows that combine immunoassay screening and targeted LC-MS/MS confirmation provide high sensitivity for limited analyte panels but lack the breadth required to detect emerging illicit compounds and unexpected co-administered medications. High-resolution time-of-flight (Tof) mass spectrometry, operated with complementary acquisition strategies, offers the potential to combine targeted sensitivity with non-targeted discovery capability on a single platform, improving laboratory responsiveness to novel psychoactive substances and complex biological matrices.

Study objectives and overview

This work compared two Tof acquisition strategies—targeted Tof-MRM (data-dependent) and non-targeted Tof-MSE (data-independent)—to evaluate their relative analytical sensitivity, identification confidence, and practical utility for broad urinary drug screening. The study used fortified calibration samples and authentic anonymized urines to: validate limits of detection (LOD) across a panel of twenty target drugs, assess qualitative concordance between modes, and demonstrate the non-targeted method's capacity to detect additional substances outside a predefined panel.

Methodology

• Sample preparation: A commercial system suitability standard was diluted to 25 ng/mL. Calibration series were prepared in pooled blank urine spiked with twenty target analytes across 0.01–2500 ng/mL. Authentic cohort included twenty anonymized urine samples plus a commercial reference urine. Prior to analysis, all urine samples were diluted five-fold with 5 mM ammonium formate (pH 3).
• Chromatography: Both acquisition modes used a reversed-phase ACQUITY HSS C18 column with a 15-minute gradient. Mobile phases were 5 mM ammonium formate (pH 3) and acetonitrile with 0.1% formic acid. Electrospray ionization in positive mode (ESI+) was employed.
• Acquisition strategies:
  • Tof-MRM (targeted, data-dependent): Quadrupole-selected precursor isolation followed by high-resolution TOF MS detection of optimized fragment ions (quantifier and qualifier). Collision energies and cone voltages were optimized per analyte to maximize sensitivity.
  • Tof-MSE (non-targeted, data-independent): Quadrupole operated in non-selective transmission while the collision cell alternated between low energy (precursor accurate mass) and a ramped elevated energy (10–40 eV) to produce fragment ion spectra across the mass range, enabling retrospective and discovery analyses.
• Data processing: Targeted processing used MS Quan within the waters_connect platform with minimum peak area thresholds and ±0.3 min retention time windows. Non-targeted processing used the UNIFI application with compound identification supported by the Waters Toxicology Library (>2,100 compounds). Identification criteria included retention time agreement (±0.3 min) and exact mass matching of precursor and at least one fragment ion within ±2 ppm (Tof-MSE precursor tolerance).

Instrumentation

• Waters ACQUITY UPLC I-Class FTN PLUS system for chromatographic separations.
• Waters Xevo MRT MS (hybrid quadrupole multi-reflecting time-of-flight mass spectrometer) for high-resolution mass analysis.
• Software and informatics: waters_connect platform, MS Quan application for targeted data, UNIFI application for non-targeted processing, and the Waters Toxicology Library for spectral matching.

Key results and discussion

• Sensitivity: The targeted Tof-MRM workflow provided superior sensitivity, with LODs typically in the 0.05–0.5 ng/mL range for monitored analytes (examples: ketamine detected at 0.05 ng/mL; many opioids and stimulants within 0.05–0.5 ng/mL). The non-targeted Tof-MSE approach yielded LODs generally between 0.5 and 5 ng/mL.
• Analytical confidence: Both methods leveraged accurate mass precursor and fragment information plus retention time criteria to ensure reliable identifications. Tof-MSE benefitted from mass accuracy tolerances (≤2 ppm) for precursor ions, strengthening non-targeted identification despite lower sensitivity than Tof-MRM.
• Qualitative concordance: When applied to the anonymized urine cohort, both acquisition modes showed excellent qualitative agreement for the target panel. Tof-MSE additionally identified numerous compounds outside the targeted list—commonly encountered medications, benzodiazepines, antidepressants, and other illicit substances—demonstrating its value for comprehensive screening and discovery analyses.
• Practical examples: Chromatograms for low-level carfentanil (0.05 ng/mL) acquired in Tof-MRM illustrated robust quantifier and qualifier transitions with reliable calibration behavior in fortified urine. For the commercial reference urine, Tof-MSE detected a range of compounds present from sub-ng/mL (e.g., fentanyl ~0.75 ng/mL) to hundreds of ng/mL (e.g., codeine, dihydrocodeine ~225 ng/mL).

Benefits and practical applications

• Combined strategy: Operating Tof-MRM and Tof-MSE on the same platform allows laboratories to retain targeted, high-sensitivity quantitation while also acquiring comprehensive datasets that support retrospective mining and identification of unexpected or novel compounds.
• Broad applicability: The workflows are applicable to forensic and clinical toxicology, workplace drug testing, treatment compliance programs, and research settings where both sensitivity and discovery capability are required.
• Operational efficiency: A single-instrument approach simplifies laboratory infrastructure, reduces method proliferation, and enables routine parts-per-billion mass accuracy for confident identifications.

Future trends and applications

• Expanded libraries and AI-assisted annotation: Growth of curated spectral libraries and machine-learning tools will accelerate confident annotation of unknowns and reduce manual review times in non-targeted datasets.
• Hybrid acquisition optimizations: Further development of hybrid acquisition schemes that dynamically switch between high-sensitivity targeted events and broad data-independent scans could improve LODs for discovery modes while preserving comprehensive coverage.
• Regulatory and clinical translation: Standardization of identification criteria, quantitative performance metrics, and inter-laboratory validation will be necessary to support routine clinical deployment of high-resolution non-targeted workflows.
• Integration with informatics: Enhanced informatics pipelines enabling automated flagging, longitudinal surveillance for emerging substances, and integration with laboratory information management systems will increase throughput and public-health responsiveness.

Conclusions

Both Tof-MRM (targeted, data-dependent) and Tof-MSE (data-independent) acquisition strategies delivered robust and complementary performance for urinary drug screening using the Xevo MRT MS and ACQUITY UPLC platform. Tof-MRM provided lower LODs and is preferable when maximum analytical sensitivity and quantitative performance are required for a defined analyte panel. Tof-MSE supplied a richer information content that enabled reliable identification of additional compounds outside the targeted panel, supporting retrospective discovery and broader toxicological characterization. Deploying both approaches together on a single high-resolution platform provides an effective, flexible framework for modern toxicology laboratories seeking to balance sensitivity, breadth, and future-proofing against novel psychoactive substances.

References

1. N. S. Mistry, L. J. Calton, J. Cooper. The Utility of MSE for Toxicology Screening with waters_connect and the Xevo G3 QTof Mass Spectrometer. Waters Application Note, 720008045, Sept 2023.
2. N. S. Mistry, L. J. Calton, J. Cooper. The Ultimate Forensic Toxicology Screening Companion—Xevo G3 QTof. Waters Application Note, 720008033, Sept 2023.
3. N. S. Mistry, G. Hammond, R. Lieberman, V. Starkie. Forensic Toxicology Data-Independent Analysis Screening Using Xevo MRT Mass Spectrometer Delivering Routine Parts-per-Billion (ppb) Mass Accuracy. Waters Application Note, 720009219, Feb 2026.