Approaches for Identifying New Psychoactive Substances (NPS)

Importance of the Topic

The rapid emergence of new psychoactive substances (NPS) poses significant challenges for forensic and analytical laboratories. Reliable identification of these compounds is crucial for public health, law enforcement, and regulatory compliance. This work presents a comprehensive toolkit combining mass spectrometry, spectroscopy, databases, and chemoinformatics to address “known unknowns” in seized drug analysis.

Objectives and Study Overview

This presentation by James Little (Mass Spec Interpretation Services) at the 2023 Seized Drug Analysis Symposium outlines practical workflows for identifying NPS using GC-MS, FTIR, LC-MS/MS, and complementary techniques. Case studies on fentanyl-related and PCP-related analogs illustrate the approach.

Methodology and Instrumentation

Key techniques and tools include:

• Gas Chromatography–Mass Spectrometry (GC-MS): Electron ionization (EI) and chemical ionization (CI) modes to determine fragmentation patterns and molecular weight.
• Liquid Chromatography–Tandem MS (LC-MS/MS): Accurate mass measurements and MS/MS spectra for structural elucidation.
• Fourier-Transform Infrared Spectroscopy (FTIR) and Raman Spectroscopy: Functional group confirmation.
• Nuclear Magnetic Resonance (NMR): High-field and low-field 1D/2D experiments for mixture analysis and structure confirmation.
• Hybrid Search Algorithms: NIST’s hybrid EI library search combining fragment-ion and neutral-loss matching to extend library coverage.
• Spectra-less Databases: CAS Registry and ChemSpider for candidate structures based on molecular formula and accurate mass.
• Software Packages: NIST MS Interpreter for automated fragment assignment, Wiley KnowItAll for adaptive MS/IR searching.

Main Results and Discussion

The hybrid search method dramatically increases identification confidence by proposing structurally related analogs with high match factors and calculated DeltaMass values. Two forensic examples demonstrate the workflow:

• Fentanyl-Related Compound: Hybrid search suggested a DeltaMass of 76, guiding identification of an ethyl carbamate moiety; confirmed by IR matching and NMR validation.
• PCP-Related Analog: Hybrid hit with a DeltaMass of 54 pointed to a phenylcyclohexylpiperidine core; accurate mass and DBE constraints narrowed candidate structures; final assignment verified by 2D NMR.

Benefits and Practical Applications

This multifaceted approach enables forensic scientists to identify unknown NPS rapidly, even without direct spectral matches in libraries. Combining hybrid searches, spectra-less databases, IR/NMR corroboration, and accurate mass data reduces reliance on reference standards and accelerates case turnaround.

Future Trends and Potential Applications

Emerging developments will further enhance NPS identification:

• Integration of machine-learning algorithms for improved spectral similarity scoring.
• Expansion of hybrid and spectra-less libraries with continuously updated user-generated entries.
• Increased adoption of compact, low-field NMR systems for routine mixture screening.
• Cloud-based platforms enabling real-time data sharing and remote training.

Conclusion

The hybrid search strategy, when combined with CI GC-MS, LC-MS/MS, IR, NMR, and spectra-less databases, forms a powerful toolkit for identifying new psychoactive substances. Free training materials and software tutorials support widespread implementation in forensic and QA/QC laboratories.

References

• Moorthy A, Wallace W, Kearsley AJ, Tchekhovskoi D, Stein S. Combining Fragment-Ion and Neutral-Loss Matching during Mass Spectral Library Searching: A New General Purpose Algorithm Applicable to Illicit Drug Identification. Anal. Chem. 2017;89(24):13261–13268.
• Shulgin AT, MacLean DE. Illicit Synthesis of Phencyclidine (PCP) and Several of Its Analogs. Clin. Toxicol. 1976;9(4):553–560.