Strategy for identification of new psychoactive substances in illicit samples using attenuated total reflectance infrared spectroscopy

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Highlights

  • Strategy for the screening analysis of NPS in illicit samples has been developed.

  • The methodology based on the use of ATR-FTIR.

  • ATR-FTIR is very usable tool for the fast screening analysis of NPS.

  • Developed strategy is ready to be introduced by other laboratories.

Abstract

New strategy has been developed for the identification of novel psychoactive substances (NPS) in illicit samples. The methodology was based on the use of attenuated total reflectance Fourier transform infrared spectroscopy (ATR-IR). First pass screening by ATR-IR allows known substances to be rapidly identified, while any non-matching samples are qualified by complementary analytical techniques and then feed back into the spectral libraries. Compounds’ identification by ATR-IR was based on the correlation coefficient value. After validation, developed strategy was successfully introduced into routine analysis. Thirty one NPS have been identified in forty five samples. One new opioid was identified and new ATR-IR spectra were acquired, not reported in commercial libraries yet. ATR-IR enabled distinguishing between closely related compounds, even structural isomers. It proved to be an easy and very reproducible tool for screening analysis of NPS, in less than one minute, with no sample destruction, even for very little amount of a sample. Developed and validated strategy may be introduced by other laboratories.

Introduction

New Psychoactive Substances (NPS), often known in the media as “legal highs”, are a widespread and growing issue for the police and forensic services. The number of NPS in Europe is nowadays higher than ever. By the end of November 2018, the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) was monitoring more than 700 new substances that have appeared on Europe’s drug market over the past 20 years. Over 51 substances have been identified and reported to the EMCDDA for the first time during 2017, but the number of potential derivatives is unknown [1]. To evade legal restrictions, NPS are mislabeled by dealers as “plant food”, “bath salts” or “herbal incense” that are “not for human consumption”. Depending on their major effects on human health they may be classified as sedatives, stimulants, hallucinogens [2]. By their chemical structure NPS usually belong to one of the following groups: synthetic cannabinoids, synthetic cathinones, tryptamines, opioids, phenethylamines, piperazine derivatives, piperidines and pyrrolidines [2,3]. The adverse health effects of NPS provide an exigence for developing rapid methods to identify NPS as a public health protection issue as well as a challenge to the criminal justice system.

Identification of a particular compound (specially the new one) within a group is a continual analytical challenge [4] due to the similarities in chemical structures and/or the presence of plant matrix containing a great number of other compounds with different polarities. This makes the reproducible chromatographic separation difficult and disturbs the spectroscopic identification as well. GC–MS and LC–MS are normally employed for identification and quantification of drugs of abuse [3,5], however, mass spectra and/or retention time of isomers are very similar, which does not allow reliable identification. Also, Raman spectroscopy was used for identification and analysis of “traditional” drugs of abuse [[6], [7], [8]], but due to heating and burning by laser absorption, herbal blends cannot be measured [9]. Small scale studies on NIR [10] and MIR [11] analysis of NPS have been published as well.

Currently, the most common drug-testing practices are based on simultaneous applying of complementary techniques, approach of a rapid screening method followed by a confirmatory testing of preliminary positive screen results. In the National Medicines Institute (NMI), which is the Official Medicines Control Laboratory (OMCL) in Poland and a member of the European OMCL Network, over six thousands samples of designer drugs containing NPS were analysed between 2008 and 2015. We have applied an orthogonal approach to solve the problem of identification by liquid chromatography–electrospray ionization-quadrupole time-of-flight-mass spectrometry (LC–ESI-QTOF-MS/MS), gas chromatography–electron ionization-mass spectrometry (GC–EI-MS), and nuclear magnetic resonance (NMR) spectroscopy. These methods allow investigating the issue from different points of view, including the separation of constituents and assignment of the new chemical structures appearing on the market [3], however, each of them suffers from limitations. In LC–MS and GC–MS analysis mass spectra and / or retention time of isomers are very similar, which does not allow reliable identification. Application of NMR in such cases is quite expensive and time consuming.

In this sense, attenuated total reflectance infrared spectroscopy (ATR-IR), a Fourier-transformation technique, seems to be a very promising method for the fast preliminary investigation of NPS. The usefulness of ATR in NPS analysis has been already reported [8,[12], [13], [14]]. First, if samples are clean enough, ATR enables analysis of a sample without any sample pre-treatment (“as is”) and only very little amount of the sample is needed (like a pin head). Next, ATR is very reproducible technique, so identification of compounds can be based on the comparison between registered spectrum and reference spectra already collected in libraries or databases. In such cases possession of reference materials is not essential. The problem is, how to make such identification, if previously unknown compounds are expected to appear in the sample set preceded.

Thus, the aim of this work was to develop strategy based on ATR-IR method for the identification of NPS in such samples followed by building the ATR-IR in-house spectra library of NPS and then reporting them to the EMCDDA database.

Section snippets

Samples and reagents

All analysed samples (N = 45) were obtained in 2018 from the Polish market. Most of them (N = 31) presented as white powders packed in small plastic bags without labeling. These samples were measured in the ATR-unit, without any pretreatment. Little amount of the powder (like a pin head) was applied to the ATR diamond crystal spot and then spectrum was collected. Some samples (N = 5) presented as crystals, small ones or big ones. They were powdered in an agate mortar before measuring in the ATR unit.

Strategy for identification of NPS

The flow chart in Fig. 1 provides the strategy for identification of NPS in samples. For each sample (previously pre-treated, if applicable) ATR-IR spectrum was recorded and then it was compared to the reference spectra reported in our in-house library and in comprehensive commercial spectral libraries. Substance in a sample was identified basing on c.c. values (see Section 2.3). In the first stage, identification of NPS by ATR-IR in 22 samples was not possible because their spectra were not

Conclusions

Developed strategy, based on ATR-IR spectroscopy, offers a fast, easy and little costs alternative for the screening process of NPS in samples. First pass screening by ATR-IR allows known substances to be rapidly identified, while any non-matching samples are detected in the screening process and then taken for comprehensive identification and characterisation by different complementary analytical techniques (LC–MS/MS, GC–MS, NMR). Afterwards, it is added to spectral libraries or database as

Funding

This work was supported by the Ministry of Science and Higher Education, Poland.

Declarations of interest

None.

CRediT authorship contribution statement

K. Piorunska-Sedlak: Investigation, Validation, Data curation, Formal analysis. K. Stypulkowska: Conceptualization, Methodology, Resources, Validation, Writing - original draft, Writing - review & editing, Supervision, Project administration.

References (18)

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