Rapid Identification of Novel Psychoactive and Other Controlled Substances Using Low-Field 1H NMR Spectroscopy

Low-field, not low quality: 1D simplification, selective detection, and heteronuclear 2D experiments for improving low-field NMR spectroscopy of environmental and biological samples

Understanding environmental change is challenging and requires molecular-level tools to explain the physicochemical phenomena behind complex processes. Nuclear magnetic resonance (NMR) spectroscopy is a key tool that provides information on both molecular structures and interactions but is underutilized in environmental research because standard "high-field" NMR is financially and physically inaccessible for many and can be overwhelming to those outside of disciplines that routinely use NMR. "Low-field" NMR is an accessible alternative but has reduced sensitivity and increased spectral overlap, which is especially problematic for natural, heterogeneous samples. Therefore, the goal of this study is to investigate and apply innovative experiments that could minimize these challenges and improve low-field NMR analysis of environmental and biological samples. Spectral simplification (JRES, PSYCHE, singlet-only, multiple quantum filters), selective detection (GEMSTONE, DREAMTIME), and heteronuclear (reverse and CH3/CH2/CH-only HSQCs) NMR experiments are tested on samples of increasing complexity (amino acids, spruce resin, and intact water fleas) at-high field (500 MHz) and at low-field (80 MHz). A novel experiment called Doubly Selective HSQC is also introduced, wherein 1H signals are selectively detected based on the 1H and 13C chemical shifts of 1H-13C J-coupled pairs. The most promising approaches identified are the selective techniques (namely for monitoring), and the reverse and CH3-only HSQCs. Findings ultimately demonstrate that low-field NMR holds great potential for biological and environmental research. The multitude of NMR experiments available makes NMR tailorable to nearly any research need, and low-field NMR is therefore anticipated to become a valuable and widely used analytical tool moving forward.

The identification of synthetic cannabinoids in English prisons

Synthetic cannabinoids (SC) are extremely prevalent within the prison system and cause problems for prisoners, law enforcement and health services. SC are often soaked into paper then posted into prisons therefore one of the aims of this research is to collaborate with Rapiscan Systems Ltd. and local prisons in England to measure the effectiveness of trace detection methods for the indication of SC in prison post using the Itemiser 3E®. To ensure compounds did not go undetected, samples with Ion Trap Mobility Spectrometry™ peaks indicative of synthetic cannabinoids on the Itemiser 3E® were analysed using Gas Chromatography-Mass Spectrometry, Liquid Chromatography-Quadrupole Time-of-Flight Mass Spectrometry and Nuclear Magnetic Resonance Spectroscopy to identify chemical characteristics which allowed comparison to reference spectra. Sample data spanning three years from one prison's Itemiser 3E® were collated to identify trends in drug prevalence and the influence of library updates. To date, the method has identified four compounds: 5F-MDMB-PICA, MMB-4en-PICA, 4F-MDMB-BUTINACA and MDMB-4en-PINACA on prison post which were not already included on, or needed confirmatory analysis to update, the Itemiser 3E® library. As a result, the libraries on prison Itemiser 3E®s have been updated to ensure future detection of such compounds. Trends and influences from the processed Itemiser 3E® data were also reported back to the West Midlands Prison Group. This research directly benefitted both the West Midlands Prison Group and Rapiscan Systems Ltd. and it is anticipated that the continuation of this research could be expanded to a national scale.

Detection, discrimination and quantification of amphetamine, cathinone and nor-ephedrine regioisomers using benchtop 1 H and 19 F nuclear magnetic resonance spectroscopy

Amphetamine and cathinone derivatives are abused recreationally due to the sense of euphoria they provide to the user. Methodologies for the rapid detection of the drug derivative present in a seized sample, or an indication of the drug class, are beneficial to law enforcement and healthcare providers. Identifying the drug class is prudent because derivatisation of these drugs, to produce regioisomers, for example, occurs frequently to circumvent global and local drug laws. Thus, newly encountered derivatives might not be present in a spectral library. Employment of benchtop nuclear magnetic resonance (NMR) could be used to provide rapid analysis of seized samples as well as identifying the class of drug present. Discrimination of individual amphetamine-, methcathinone-, N-ethylcathinone and nor-ephedrine-derived fluorinated and methylated regioisomers is achieved herein using qualitative automated ¹ H NMR analysis and compared to gas chromatography-mass spectrometry (GC-MS) data. Two seized drug samples, SS1 and SS2, were identified to contain 4-fluoroamphetamine by ¹ H NMR (match score median = 0.9933) and GC-MS (RR_t  = 5.42-5.43 min). The amount of 4-fluoroamphetamine present was 42.8%-43.4% w/w and 48.7%-49.2% w/w for SS1 and SS2, respectively, from quantitative ¹⁹ F NMR analysis, which is in agreement with the amount determined by GC-MS (39.9%-41.4% w/w and 49.0%-49.3% w/w). The total time for the qualitative ¹ H NMR and quantitative ¹⁹ F NMR analysis is ~10 min. This contrasts to ~40 min for the GC-MS method. The NMR method also benefits from minimal sample preparation. Thus, benchtop NMR affords rapid, and discriminatory, analysis of the drug present in a seized sample.

Benchtop nuclear magnetic resonance spectroscopy in forensic chemistry

Nuclear magnetic resonance (NMR) spectroscopy is a powerful technique well known for its ability to elucidate structures and analyse mixtures and its quantitative nature. However, the cost and maintenance of high field NMR instruments prevent its widespread use by forensic chemists. The introduction of benchtop NMR spectrometers to the market operating at 40-80 MHz have a small footprint, are easy to use and cost much less than high field instruments, which makes them well suited to meet the needs of forensic chemists. These modern low field spectrometers are often capable of running multiple nuclei including ¹ H, ¹³ C, ¹⁹ F and ³¹ P; 2D NMR experiments and advanced experiments such as solvent suppression and diffusion-ordered spectroscopy (DOSY) are possible. This has resulted in a number of publications in the area of forensic chemistry using benchtop NMR spectroscopy in the last 5 years that was previously missing from the literature. This mini review summarises this research including examples of benchtop NMR being used to identify and quantify compounds relevant to forensics and some advanced methods that may be used to overcome some of the limitations of these instruments for forensic analysis. Further validation and automation are likely required for widespread uptake of benchtop NMR in industry; however, it has been demonstrated as a useful complement to other analytical techniques commonplace of forensic laboratories.

Comparative study of the analysis of seized samples by GC-MS, 1H NMR and FT-IR spectroscopy within a Night-Time Economy (NTE) setting

Rapid analysis of surrendered or seized drug samples provides important intelligence for health (e.g. treatment or harm reduction), and custodial services. Herein, three in-situ techniques, GC-MS, ¹H NMR and FT-IR spectroscopy, with searchable libraries, are used to analyse 318 samples qualitatively, using technique specific library-based searches, obtained over the period 24th - 29th August 2019. 259 samples were identified as consisting of a single component, of which cocaine was the most prevalent (n = 158). Median match scores for all three techniques were ≥ 0.84 and showed agreement except for metformin (n = 1), oxandrolone (identified as vitamin K by IR (n = 4)), diazepam (identified as zolpidem by FT-IR (n = 2)) and 2-Br-4,5-DMPEA (n = 1), a structural isomer of 2C-B identified as a polymer of cellulose (cardboard) by FT-IR. 51 samples were found to consist of two or more components, of which 49 were adulterated cocaine samples (45 binary and 4 tertiary samples). GC-MS identified all components present in the 49 adulterated cocaine samples, whereas IR identified only cocaine in 88 % of cases (adulterant only = 12 %). The breakdown for ¹H NMR spectroscopy was all components identified (51 %), cocaine only (33 %), adulterant only (10 %), cocaine and one adulterant (tertiary mixtures only, 6 %).

Characterization of new psychoactive substances by integrating benchtop NMR to multi-technique databases

New psychoactive substances (NPS) have become a serious threat for public health due to their ability to be sold in the street or on internet. NPS are either derived from commercial drugs which are misused (recreational rather than medical use) or whose structure is slightly modified. To regulate NPS, it is essential to accurately characterize them, either to recognize molecules that were previously identified or to quickly elucidate the structure of unknown ones. Most approaches rely on the determination of the exact mass obtained by high‐resolution mass spectrometry requiring expensive equipment. This motivated us to develop a workflow in which the elucidation is assisted with databases and does not need the exact mass. This workflow combines 1D and 2D NMR measurements performed on a benchtop spectrometer with IR spectroscopy, for creating a multi‐technique database to characterize pure and mixed NPS. The experimental database was created with 57 entries mostly coming from seizures, mainly cathinones, cannabinoids, amphetamines, arylcyclohexylamines, and fentanyl. A blind validation of the workflow was carried out on a set of six unknown seizures. In the first three cases, AF, AB‐FUBINACA, and a mixture of 2C‐I and 2C‐E could be straightforwardly identified with the help of their reference spectra in the database. The two next samples were elucidated for the first time with the help of the database to reveal NEK and MPHP substances. Finally, a precise quantification of each characterized NPS was obtained in order to track NPS trafficking networks.

Quantification of mixtures of analogues of illicit substances by benchtop NMR spectroscopy

This paper investigates the possibility of using benchtop NMR spectroscopy for quantification of illicit drugs (methamphetamine) in binary and ternary mixtures with impurities and cutting agents (N-isopropylbenzylamine, phenethylamine and dimethylsulfone). To avoid handling regulated substances, methamphetamine in our experiments is substituted with amino-2-propanol, which has similar functional groups and chemical structure to methamphetamine and hence a related NMR spectrum. Binary and ternary mixtures at concentrations from 30 mmol/L up to 500 mmol/L for each of these species were measured using a 60 MHz benchtop spectrometer. The spectra were analysed using both integration and a model-based algorithm that relies on a full quantum mechanical description of the studied spin systems. Both techniques were able to quantify the composition of the mixtures. The root mean squared error in the measured concentration using the model-based algorithm was < 10 mmol/L, whereas the error using integration was typically > 20 mmol/L. Thus, we conclude benchtop NMR is viable for quantitative measurements of mixtures of illicit substances, particularly when coupled with a quantum mechanical model for the analysis.

Direct low field J-edited diffusional proton NMR spectroscopic measurement of COVID-19 inflammatory biomarkers in human serum

A JEDI NMR pulse experiment incorporating relaxation, diffusion and J-modulation peak editing was implemented at a low field (80 MHz) spectrometer system to quantify two recently discovered plasma markers of SARS-CoV-2 infection and general inflammation.

Recent Applications of Benchtop Nuclear Magnetic Resonance Spectroscopy

Benchtop nuclear magnetic resonance (NMR) spectroscopy uses small permanent magnets to generate magnetic fields and therefore offers the advantages of operational simplicity and reasonable cost, presenting a viable alternative to high-field NMR spectroscopy. In particular, the use of benchtop NMR spectroscopy for rapid in-field analysis, e.g., for quality control or forensic science purposes, has attracted considerable attention. As benchtop NMR spectrometers are sufficiently compact to be operated in a fume hood, they can be efficiently used for real-time reaction and process monitoring. This review introduces the recent applications of benchtop NMR spectroscopy in diverse fields, including food science, pharmaceuticals, process and reaction monitoring, metabolomics, and polymer materials.

Synthesis, characterization, and evaluation of selective molecularly imprinted polymers for the fast determination of synthetic cathinones

As a kind of new psychoactive substance (NPS), synthetic cathinones have drawn great worldwide attention. In this study, molecularly imprinted polymers (MIPs), as adsorbents for the extraction and determination of 4-methyldimethcathinone (4-MDMC), were first synthesized by coprecipitation polymerization. The physicochemical analyses of MIPs were successfully performed by XRD, FTIR, FESEM and TGA techniques. Furthermore, rebinding properties of temperature and pH dependence, and selectivity and reusability tests for MIPs and non-imprinted polymers (NIPs) were performed using an ultraviolet-visible spectrometer (UV-vis). The obtained results indicate that the imprinting efficiency has strong dependence on temperature and pH, and the optimal adsorption for targets is achieved under the condition of 318 K and pH = 6.0. This means that the combination between the polymers and 4-MDMC is a strong spontaneous and endothermic process. Compared with NIPs, MIPs exhibit prominent adsorption capacity (Q_e = 9.77 mg g⁻¹, 318 K). The selectivity coefficients (k) of MIPs for 4-MDMC, methylenedioxypentedrone (βk-MBDP), 4-ethylmethcathinone (4-EMC), methoxetamine (MXE) and tetrahydrofuranylfentanyl (THF-F) were found to be 1.70, 3.49, 7.14 and 5.82, respectively. Moreover, it was found that the adsorption equilibrium was achieved within 30 min. The aim of this work is the simple synthesis of MIPs and the optimal performance of the molecular recognition of 4-MDMC. Moreover, the synthesized MIPs can be easily regenerated and repeatedly used with negligible loss of efficiency (only 9.94% loss after six times adsorption–desorption tests). Satisfying recoveries in the range of 69.3–78.9% indicate that MIPs have good applicability for analyte removal from urine samples. Ultimately, this material shows great promise for the rapid extraction and separation of synthetic cathinones, which are dissolved in the liquid for the field of criminal sciences.

Molecularly imprinted polymers, as an adsorbent for extraction and selective recognition of 4-methyldimethcathinone, were firstly synthesized through coprecipitation polymerization.

Quantitative Monitoring of the Fermentation Process of a Barley Malt Mash by Benchtop 1H NMR Spectroscopy

In order to investigate benchtop NMR spectroscopy as a monitoring tool for fermentation processes, we used a barley malt mash and took various samples over time and analysed them by NMR spectroscopy with 3-(trimethylsilyl)-2,2,3,3-tetradeuteropropionic acid sodium salt (TSP-d4) as an internal standard for the quantification of ethanol and validated the results by two different enzymatic standard test kits for ethanol analysis. We could show that the results between NMR spectroscopy and test kits were consistent with NMR having a much lower standard deviation. Finally, we discussed the applicability of the method as well as the possibility to quantify various other substances.

Optimal control pulses for subspectral editing in low field NMR

Low field NMR is an inexpensive and low footprint technique to obtain physical, chemical, electronic and structural information on small molecules, but suffers from poor spectral dispersion, especially when applied to the analysis of mixtures. Subspectral editing employing optimal control pulses is a suitable approach to cope with the severe signal superpositions in complex mixture spectra at low field. In this contribution, the use of optimal control pulses is demonstrated to be feasible at a field strength as low as 0.5 T. The optimal control pulse shapes were calculated using the Krotov algorithm. Downsizing the complexity of the algorithm from exponential to polynomial is shown to be possible by using a system approach with each system corresponding to a (small) molecule. In this way compound selective excitation pulses can be calculated. The signals of substructures of the cyclopentenone molecule were excited using optimal control pulses calculated by the Krotov algorithm demonstrating the feasibility of subspectral editing. Likewise, for a mixture of benzoic acid and alanine, editing of the signals of either benzoic acid or alanine employing optimal control pulses was shown to be possible. The obtained results are very promising and can be extended to the targeted analysis of complex mixtures such as biofluids or metabolic samples at low field strengths opening access for benchtop NMR to point of care settings.

The impact of the 2016 Psychoactive Substances Act on synthetic cannabinoid use within the homeless population: Markets, content and user harms

BACKGROUND

On 26 May 2016, the UK introduced the Psychoactive Substances Act. The Act made it an offence to produce, supply, or offer to supply, any psychoactive substance likely to be used for its psychoactive effects. While a Home Office review of the Act in 2018 proclaimed that the Act had been successful in achieving its main goal of preventing the open sale of psychoactive substances, significantly, the review acknowledged that high levels of synthetic cannabinoid use remain amongst vulnerable user groups, in particular the homeless population.

METHODS

The research adopted an innovative interdisciplinary approach drawing on sociology and chemistry. The sociological element involved 82 face-to-face qualitative semi-structured interviews with 37 homeless synthetic cannabinoid users, 45 stakeholders, and over 100 h of fieldwork observations. The chemical analysis element involved the testing (using Gas Chromatography-Mass Spectrometry) of 69 synthetic cannabinoid street samples obtained by a local police force.

RESULTS

The introduction of the Act was associated with a number of significant changes to the synthetic cannabinoid market, including the integration of synthetic cannabinoids into the existing illicit street market, new dealers, the adoption of more targeted and aggressive supply practices, and variability in the content and potency of synthetic cannabinoids. Combined, these changes have increased the risk of harm to homeless users and homeless sector staff and resulted in a concomitant increase in the demand on emergency services.

CONCLUSION

The foreseen concerns that the Act would result in detrimental market changes and increased harms to vulnerable user groups have been manifested in the homeless population. The failure of the Act to reduce synthetic cannabinoid use within this group, combined with the increased risk of individual and societal harm, highlights the importance of reducing the demand for synthetic cannabinoids.

High-field and benchtop NMR spectroscopy for the characterization of new psychoactive substances

New psychoactive substances (NPS) have become a serious threat to public health in Europe due to their ability to be sold in the street or on the darknet. Regulating NPS is an urgent priority but comes with a number of analytical challenges since they are structurally similar to legal products. A number of analytical techniques can be used for identifying NPS, among which NMR spectroscopy is a gold standard. High field NMR is typically used for structural elucidation in combination with others techniques like GC-MS, Infrared spectroscopy, together with databases. In addition to their strong ability to elucidate molecular structures, high field NMR techniques are the gold standard for quantification without any physical isolation procedure and with a single internal standard. However, high field NMR remains expensive and emerging "benchtop" NMR apparatus which are cheaper and transportable can be considered as valuable alternatives to high field NMR. Indeed, benchtop NMR, which emerged about ten years ago, makes it possible to carry out structural elucidation and quantification of NPS despite the gap in resolution and sensitivity as compared to high field NMR. This review describes recent advances in the field of NMR applied to the characterization of NPS. High-field NMR methods are first described in view of their complementarity with other analytical methods, focusing on both structural and quantitative aspects. The second part of the review highlights how emerging benchtop NMR approaches could act as a game changer in the field of forensics.

Perspectives in process analytics using low field NMR

Low field NMR is a powerful analytical tool which creates an enormous added value in process analytics. Based on specific applications in process analytics and perspectives for low field NMR in form of spectroscopy, relaxation, diffusion, and imaging in quality control, diverse applications and technical realizations like spectrometers, time domain NMR, mobile NMR sensors and MRI will be discussed.

Low-field benchtop NMR spectroscopy: status and prospects in natural product analysis†

INTRODUCTION

Since a couple of years, low-field (LF) nuclear magnetic resonance (NMR) spectrometers (40-100 MHz) have re-entered the market. They are used for various purposes including analyses of natural products. Similar to high-field instruments (300-1200 MHz), modern LF instruments can measure multiple nuclei and record two-dimensional (2D) NMR spectra.

OBJECTIVE

To review the commercial availability as well as applications, advantages, limitations, and prospects of LF-NMR spectrometers for the purpose of natural products analysis.

METHOD

Commercial LF instruments were compared. A literature search was performed for articles using and discussing modern LF-NMR. Next, the articles relevant to natural products were read and summarised.

RESULTS

Seventy articles were reviewed. Most appeared in 2018 and 2019. Low costs and ease of operation are most often mentioned as reasons for using LF-NMR.

CONCLUSION

As the spectral resolution of LF instruments is limited, they are not used for structure elucidation of new natural products but rather applied for quality control (QC), forensics, food and health research, process control and teaching. Chemometric data handling is valuable. LF-NMR is a rapidly developing niche and new instruments keep being introduced.

High-throughput screening of argan oil composition and authenticity using benchtop 1 H NMR

We use 60-MHz benchtop nuclear magnetic resonance (NMR) to acquire 1 H spectra from argan oils of assured origin. We show that the low-field NMR spectrum of neat oil contains sufficient information to make estimates of compositional parameters and to inform on the presence of minor compounds. A screening method for quality and authenticity is presented based on nearest-neighbour outlier detection. A variety of oil types are used to challenge the method. In a survey of retail-purchased oils, several instances of fraud were found.

Demystifying NMR spectroscopy: Applications of benchtop spectrometers in the undergraduate teaching laboratory

Undergraduate students can find some aspects of NMR Spectroscopy daunting, and difficult to understand. Due to their flexibility and ease-of-use, 'benchtop' spectrometers can help to clarify key concepts and enhance learning. Here we suggest approaches to demystifying resolution, sensitivity, magnetic field variation and its consequent impact on spectra, quantitation and mixtures.

Gradient-based pulse sequences for benchtop NMR spectroscopy

Benchtop NMR spectroscopy has been on the rise for the last decade, by bringing high-resolution NMR in environments that are not easily compatible with high-field NMR. Benchtop spectrometers are accessible, low cost and show an impressive performance in terms of sensitivity with respect to the relatively low associated magnetic field (40-100 MHz). However, their application is limited by the strong and ubiquitous peak overlaps arising from the complex mixtures which are often targeted, often characterized by a great diversity of concentrations and by strong signals from non-deuterated solvents. Such limitations can be addressed by pulse sequences making clever use of magnetic field gradient pulses, capable of performing efficient coherence selection or encoding chemical shift or diffusion information. Gradients pulses are well-known ingredients of high-field pulse sequence recipes, but were only recently made available on benchtop spectrometers, thanks to the introduction of gradient coils in 2015. This article reviews the recent methodological advances making use of gradient pulses on benchtop spectrometers and the applications stemming from these developments. Particular focus is made on solvent suppression schemes, diffusion-encoded, and spatially-encoded experiments, while discussing both methodological advances and subsequent applications. We eventually discuss the exciting development and application perspectives that result from such advances.

Interpol review of controlled substances 2016-2019

This review paper covers the forensic-relevant literature in controlled substances from 2016 to 2019 as a part of the 19th Interpol International Forensic Science Managers Symposium. The review papers are also available at the Interpol website at: https://www.interpol.int/content/download/14458/file/Interpol%20Review%20Papers%202019.pdf.

City checking: Piloting the UK's first community-based drug safety testing (drug checking) service in 2 city centres

AIMS

To explore the feasibility of delivering community-based drug safety testing (drug checking), to trial service design characteristics and to compare with festival-based testing.

METHODS

In total, 171 substances of concern were submitted on 5 dates at 3 venues in 2 UK cities and tested using up to 6 analytical techniques. Test results and harm reduction advice were distributed directly to over 200 service users through 144 tailored healthcare consultations, to stakeholders, and through early warning systems, media and social media alerts.

RESULTS

The 171 samples were submitted and identified as MDMA (43.3%), cocaine (12.9%), ketamine (12.9%), various psychedelics submitted by students, and heroin and a synthetic cannabinoid submitted by rough sleeping communities, with 76% of samples' test results as expected. The 144 primary service users identified as 91.7% white, 68.1% male, with an average age of 26.7 years. Reported harm reduction intentions included alerting friends and acquaintances (37.5%), being more careful mixing that substance (35.4%), lowered dosage (27.8%), disposal of further substances (6.9%) and additionally 2.8% handed over further substances for verified destruction.

CONCLUSION

Community-based drug safety testing (drug checking) was piloted for the first time in the UK-within a drugs service, a community centre and a church-with consideration given to meso-level operational feasibility and micro-level behavioural outcomes. Service design characteristics such as venue, day of week, prior publicity, service provider, and direct and indirect dissemination of results all may impact on outcomes. Future studies should consider cost-benefit analyses of community and event-based testing and context-appropriate macro, meso and micro-level evaluations.