Electrochemical profiling and liquid chromatography-mass spectrometry characterization of synthetic cathinones: From methodology to detection in forensic samples

Simple and selective screening method for the synthetic cathinone MDPT in forensic samples using carbon nanofiber screen-printed electrodes

3',4'-Methylenedioxy-N-tert-butylcathinone (MDPT), also known as tBuONE or D-Tertylone, is a synthetic cathinone (SC) frequently abused for recreational purposes due to its potent stimulant effects and similarity to illegal substances like methamphetamine and ecstasy. The structural diversity and rapid introduction of new SC analogs to the market poses significant challenges for law enforcement and analytical methods for preliminary screening of illicit drugs. In this work, we present, for the first time, the electrochemical detection of MDPT using screen-printed electrodes modified with carbon nanofibers (SPE-CNF). MDPT exhibited three electrochemical processes (two oxidations and one reduction) on SPE-CNF. The proposed method for MDPT detection was optimized in 0.2 mol L-1 Britton-Robinson buffer solution at pH 10.0 using differential pulse voltammetry (DPV). The SPE-CNF showed a high stability for electrochemical responses of all redox processes of MDPT using the same or different electrodes, with relative standard deviations less than 4.7% and 1.5% (N = 3) for peak currents and peak potentials, respectively. Moreover, the proposed method provided a wide linear range for MDPT determination (0.90-112 μmol L-1) with low LOD (0.26 μmol L-1). Interference studies for two common adulterants, caffeine and paracetamol, and ten other illicit drugs, including amphetamine-like compounds and different SCs, showed that the proposed sensor is highly selective for the preliminarily identification of MDPT in seized forensic samples. Therefore, SPE-CNF with DPV can be successfully applied as a fast and simple screening method for MDPT identification in forensic analysis, addressing the significant challenges posed by the structural diversity of SCs.

Zwitterionic oligomers of 3-aminobenzoic acid on screen-printed electrodes: structure, properties and forensic application

The popularity and rapid spread of new psychoactive substances is why there is an urgent need for their fast monitoring in saliva in the field with electrodes modified with a selective receptor. Oligomers of electrochemically oxidized 3-aminobenzoic acid that are deposited on the surface of a graphite screen-printed electrode (o-3ABA/G/SPE) is proposed as a selector for the analyte of forensic interest. The oligomeric structure and existence of the zwitterionic form of o-3ABA on the G/SPE surface was confirmed using scanning electron microscopy, Raman spectroscopy and cyclic voltammetry techniques. The equilibrium adsorption constants between o-3ABA and 2-aminoindane (primary amine: Kads(2-AI) = 5.31 × 104) and selected synthetic cathinones (secondary amine: Kads(butylone) = 6.12 × 105, tertiary amines: Kads(MDPV) = 3.41 × 104 and Kads(naphyrone) = 1.01 × 104) were estimated using the electrochemical impedance spectroscopy (EIS) technique. The EIS technique was applied for determining a 1.0 μM concentration of 2-AI (RSD 3.5-4.0%) and butylone (RSD 4.9-6.4%) in the model and oral fluid samples.

Progress on the Electrochemical Sensing of Illicit Drugs

Illicit drugs are harmful substances, threatening both health and safety of societies in all corners of the world. Several policies have been developed over time to deal with this illicit drug problem, including supply reduction and harm reduction policies. Both policies require on-site detection tools to succeed, i.e. sensors that can identify illicit drugs in samples at the point-of-care. Electrochemical sensors are highly suited for this task, due to their short analysis times, low cost, high accuracy, portability and orthogonality with current technologies. In this chapter, we evaluate the latest trend in electrochemical sensing of illicit drugs, with a focus on detection of illicit drugs in seizures and body fluids. Furthermore, we will also provide an outlook on the potential of electrochemistry in wearable sensors for this purpose.

Forensic Analysis of Synthetic Cathinones on Nanomaterials-Based Platforms: Chemometric-Assisted Voltametric and UPLC-MS/MS Investigation

Synthetic cathinones (SCs) are a group of new psychoactive substances often referred to as "legal highs" or "bath salts", being characterized by a dynamic change, new compounds continuously emerging on the market. This creates a lack of fast screening tests, making SCs a constant concern for law enforcement agencies. Herein, we present a fast and simple method for the detection of four SCs (alpha-pyrrolidinovalerophenone, N-ethylhexedrone, 4-chloroethcathinone, and 3-chloromethcathinone) based on their electrochemical profiles in a decentralized manner. In this regard, the voltametric characterization of the SCs was performed by cyclic and square wave voltammetry. The elucidation of the SCs redox pathways was successfully achieved using liquid chromatography coupled to (tandem) mass spectrometry. For the rational identification of the ideal experimental conditions, chemometric data processing was employed, considering two critical qualitative and quantitative variables: the type of the electrochemical platform and the pH of the electrolyte. The analytical figures of merit were determined on standard working solutions using the optimized method, which exhibited wide linear ranges and LODs suitable for confiscated sample screening. Finally, the performance of the method was evaluated on real confiscated samples, the resulting validation parameters being similar to those obtained with another portable device (i.e., Raman spectrometer).

Electrochemical detection of mephedrone using a graphene screen-printed electrode: a new sensitive and selective approach to identify synthetic cathinones in forensic analysis

Mephedrone (MEP) is an illicit stimulant drug that belongs to the synthetic cathinone (SC) class, which has been widely used for recreational purposes and reported in forensic analysis. The preliminary identification of MEP and other SCs in seized samples is of great interest for forensic investigation and a fast and simple screening test for these drugs would be useful for on-site and in-house analyses. In this study, we present the electrochemical detection of MEP in forensic samples using, for the first time, independent redox processes of SCs on a graphene screen-printed electrode (SPE-GP). The proposed method for MEP detection on the SPE-GP was optimized in Britton-Robinson buffer solution (0.1 mol L^-1) at pH 10.0 with adsorptive stripping differential pulse voltammetry (AdSDPV). The use of the SPE-GP with AdSDPV provides a wide linear range for MEP determination (2.6 to 112 μmol L^-1) with a low limit of detection (LOD) (0.3 μmol L^-1). The real surface area available for adsorption on the SPE-GP was estimated to be between 3.80 and 5.70 cm², which provided high sensitivity for the proposed method. Furthermore, good stability of MEP electrochemical responses on the SPE-GP was obtained using the same or different electrodes (N = 3), with relative standard deviation (RSD) < 5.0% for both redox processes. Interference studies for a common adulterant (caffeine) and twelve other illicit drugs (phenethylamines, amphetamines, and other SCs) were performed with a highly selective response for MEP detection. Therefore, the SPE-GP with AdSDPV is demonstrated to be a selective and sensitive screening method to detect MEP and other SCs in forensic analysis, providing a fast and simple preliminary identification of these drugs in seized samples.

State-of-the-Art Analytical Approaches for Illicit Drug Profiling in Forensic Investigations

In forensic chemistry, when investigating seized illicit drugs, the profiling or chemical fingerprinting of drugs is considered fundamental. This involves the identification, quantitation and categorization of drug samples into groups, providing investigative leads such as a common or different origin of seized samples. Further goals of drug profiling include the elucidation of synthetic pathways, identification of adulterants and impurities, as well as identification of a drug's geographic origin, specifically for plant-derived exhibits. The aim of this state-of-art-review is to present the traditional and advanced analytical approaches commonly followed by forensic chemists worldwide for illicit drug profiling. We discussed numerous methodologies for the physical and chemical profiling of organic and inorganic impurities found in illicit drug. Applications of powerful spectroscopic and chromatographic tools for illicit drug profiling including isotope-Ratio mass spectrometry (IRMS), gas chromatography-mass spectrometry (GC-MS), gas chromatography-isotope ratio mass spectrometry (GC-IRMS), ultra-high-performance liquid chromatography (UHPLC), thin layer chromatography (TLC), liquid chromatography-mass spectrometry (LC-MS) and inductively coupled plasma-mass spectrometry (ICP-MS) were discussed. Altogether, the techniques covered in this paper to profile seized illicit drugs could aid forensic chemists in selecting and applying a suitable method to extract valuable profiling data.

4'-Iodo-α-Pyrrolidinononanophenone Provokes Differentiated SH-SY5Y Cell Apoptosis Through Downregulating Nitric Oxide Production and Bcl-2 Expression

Abuse of pyrrolidinophenone derivatives (PPs) is known to cause severe damage to the central nervous system due to their high lipophilicity. In this study, we compared sensitivity to toxicity elicited by 4'-iodo-α-pyrrolidinononanophenone (I-α-PNP), one of the most potent cytotoxic derivatives among PPs synthesized previously, between SH-SY5Y cells differentiated by all-trans-retinoic acid (ATRA) and the undifferentiated cells, and found that the differentiated cells are more sensitive to I-α-PNP toxicity than the undifferentiated cells. Treatment with I-α-PNP elicited some apoptotic alterations (Bax expression, loss of mitrochondrial membrane potential, and activation of caspases) in the differentiated cells, whose patterns were similar to those in the undifferentiated cells. I-α-PNP treatment resulted in no significant alteration in Bcl-2 expression in the undifferentiated cells, whereas it considerably downregulated the protein expression in the differentiated cells, suggesting that the high I-α-PNP sensitivity of the differentiated cells is mainly due to downregulation of Bcl-2 expression. I-α-PNP treatment decreased nitric oxide (NO) production and neuronal NOS (nNOS) expression in the differentiated cells, and the patterns of I-α-PNP-evoked alterations in phosphorylation of cAMP response element-binding protein (CREB) and brain-derived neurotrophic factor (BDNF) expression were almost the same as that in nNOS expression. Additionally, the addition of an NO donor restored the I-α-PNP-evoked alterations in expressions of Bcl-2, BDNF, and nNOS in the differentiated cells. These findings suggest that the downregulation of Bcl-2 expression by I-α-PNP in differentiated cells is attributed to the acceleration of two negative feedback loops (nNOS/NO/CREB loop and CREB/BDNF loop) triggered by decreased NO production.

Advances of Drugs Electroanalysis Based on Direct Electrochemical Redox on Electrodes: A Review

The strong development of mankind is inseparable from the proper use of drugs, and the electroanalytical research of drugs occupies an important position in the field of analytical chemistry. This review mainly elaborates the research progress of drugs electroanalysis based on direct electrochemical redox on various electrodes for the recent decade from 2011 to 2021. At first, we summarize some frequently used electrochemical data processing and electrochemical mechanism research derivation methods in the literature. Then, according to the drug therapeutic and application/usage purposes, the research progress of drugs electrochemical analysis is classified and discussed, where we focus on drugs electrochemical reaction mechanism. At the same time, the comparisons of electrochemical sensing performance of the drugs on various electrodes from recent studies are listed, so that readers can more intuitively compare and understand the electroanalytical sensing performance of each modified electrode for each of the drug. Finally, this review discusses the shortcomings and prospects of the drugs electroanalysis based on direct electrochemical redox research.

Real-time electrochemical screening of cocaine in lab and field settings with automatic result generation

This work presents the results of a novel application for the fast on-site screening of cocaine and its main cutting agents in suspicious and confiscated samples. The methodology behind the novel application consists of portable electrochemical detection coupled with a peak-recognition algorithm for automated result output generation, validated both in laboratory and field settings. Currently used field tests, predominantly colorimetric tests, are lacking accuracy, often giving false positive or negative results. This presses the need for alternative approaches to field testing. By combining portable electrochemical approaches with peak-recognition algorithms, an accuracy of 98.4% concerning the detection of cocaine was achieved on a set of 374 powder samples. In addition, the approach was tested on multiple 'smuggled', colored cocaine powders and cocaine mixtures in solid and liquid states, typically in matrices such as charcoal, syrup and clothing. Despite these attempts to hide cocaine, our approach succeeded in detecting cocaine during on-site screening scenarios. This feature presents an advantage over colorimetric and optical detection techniques, which can fail with colored sample matrices. This enhanced accuracy on smuggled samples will lead to increased efficiency in confiscation procedures in the field, thus significantly reducing societal economic and safety concerns and highlighting the potential for electrochemical approaches in on-the-spot identification of drugs of abuse.

Electrochemiluminescence sensors and forensic investigations: a viable technique for drug detection?

Novel psychoactive substances (NPS) are today considered one of the major ticking public health time bombs in regard to drug abuse. The inability to identify these substances with current screening methods, sees their distribution remain uninterrupted and contributes to the high death rates amongst users. To tackle this problem, it is vital that new robust screening methods are developed, addressing the limitation of those currently in place, namely colour subjectivity and lack of compatibility with the complex matrices these substances may be found within. To this avail, electrochemical methods have been assessed. These low cost and extremely portable sensors have been successfully applied for the direct detection of a broad range of compounds of interest in a range of matrices including, herbal material, commercial drinks and biological fluids (serum, saliva, sweat and urine). With their high versatility, gifted through a significant degree of flexibility in regard to electrode material a range of sensors have to date been reported. In this review the various electrochemical sensors developed to date for NPS detection will be compared and contrasted, with a special focus upon those utilising electrochemiluminescence (ECL) technology.

Rapid On-Site Detection of Illicit Drugs in Smuggled Samples with a Portable Electrochemical Device

The smuggling of illicit drugs urges the development of new tools for rapid on-site identification in cargos. Current methods rely on presumptive color tests and portable spectroscopic techniques. However, these methods sometimes exhibit inaccurate results due to commonly used cutting agents, the colorful nature of the sample or because the drugs are smuggled in common goods. Interestingly, electrochemical sensors can deal with these specific problems. Herein, an electrochemical device is presented that uses affordable screen-printed electrodes for the electrochemical profiling of several illicit drugs by square-wave voltammetry (SWV). The identification of the illicit compound is based on the oxidation potential of the analyte. Hence, a library of electrochemical profiles is built upon the analysis of illicit drugs and common cutting agents. This library allows the design of a tailor-made script that enables the identification of each drug through a user-friendly interface (laptop or mobile phone). Importantly, the electrochemical test is compared by analyzing 48 confiscated samples with other portable devices based on Raman and FTIR spectroscopy as well as a laboratory standard method (i.e., gas chromatography–mass spectrometry). Overall, the electrochemical results, obtained through the analysis of different samples from confiscated cargos at an end-user site, present a promising alternative to current methods, offering low-cost and rapid testing in the field.

Development of an Electrochemical Sensor Using a Modified Carbon Paste Electrode with Silver Nanoparticles Capped with Saffron for Monitoring Mephedrone

Mephedrone, also known as 4-methylmethcathinone, is growing into a prominent recreational drug for young people. When it came to detecting mephedrone, limited efforts were made using electrochemical sensors. As a result, this application depicts the fabrication of a new, sensitive, selective, and economical electrochemical sensor capable of detecting mephedrone by using silver nanoparticles capped with saffron produced through electropolymerization to modify carbon paste electrodes (CPEs). Silver nanoparticles (AgNPs) were capped with saffron (AgNPs@Sa) using a green method. AgNPs@Sa were studied using electron scanning microscopy (SEM) and UV-vis spectroscopy. The sensor was evaluated under the optimum condition to determine its analytical features. The results showed that this procedure had a wide linear range, low detection limit and sufficient reproducibility. Furthermore, the sensor posed sufficient stability. Moreover, it was applied in the determination of mephedrone in urine samples, showing the potential applicability of this electrochemical sensor in real sample analysis.

Tetracycline Antibiotics: Elucidating the Electrochemical Fingerprint and Oxidation Pathway

Herein, a complete study of the electrochemical behavior of the most commonly used tetracycline antibiotics (TCs) on unmodified carbon screen-printed electrodes (SPEs) is presented. In addition, the oxidation pathway of TCs on SPE is elucidated, for the first time, with liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-QTOF-MS). Square wave voltammetry (SWV) was used to study the electrochemical fingerprint (EF) of the antibiotics shaping the different oxidation processes of the TCs in a pH range from 2 to 12. Their characteristic structure and subsequent EF offer the possibility of distinguishing this class of antibiotics from other types. Under the optimized parameters, calibration curves of tetracycline (TET), doxycycline (DOXY), oxytetracycline (OXY), and chlortetracycline (CHL) in a Britton Robinson buffer solution (pH 9) exhibited a linear range between 5 and 100 µM with excellent reproducibilities (RSDTET = 3.01%, RSDDOXY = 3.29%, RSDOXY = 9.78% and RSDCHL = 6.88% at 10 µM, N = 3) and limits of detection (LOD) of LODTET = 4.15 µM, LODDOXY = 2.14 µM, LODOXY = 3.07 µM and LODCHL = 4.15 µM. Furthermore, binary, tertiary, and complex mixtures of all TCs were analyzed with SWV to investigate the corresponding EF. A dual pH screening (pH 4 and pH 9), together with the use of a custom-made Matlab script for data treatment, allowed for the successful confirmation of a single presence of TCs in the unknown samples. Overall, this work presents a straightforward study of the electrochemical behavior of TCs in SPE, allowing for the future on-site identification of residues of tetracycline antibiotics in real samples.

Human Neuronal Cell Lines as An In Vitro Toxicological Tool for the Evaluation of Novel Psychoactive Substances

Novel psychoactive substances (NPS) are synthetic substances belonging to diverse groups, designed to mimic the effects of scheduled drugs, resulting in altered toxicity and potency. Up to now, information available on the pharmacology and toxicology of these new substances is very limited, posing a considerable challenge for prevention and treatment. The present in vitro study investigated the possible mechanisms of toxicity of two emerging NPS (i) 4′-methyl-alpha-pyrrolidinoexanophenone (3,4-MDPHP), a synthetic cathinone, and (ii) 2-chloro-4,5-methylenedioxymethamphetamine (2-Cl-4,5-MDMA), a phenethylamine. In addition, to apply our model to the class of synthetic opioids, we evaluated the toxicity of fentanyl, as a reference compound for this group of frequently abused substances. To this aim, the in vitro toxic effects of these three compounds were evaluated in dopaminergic-differentiated SH-SY5Y cells. Following 24 h of exposure, all compounds induced a loss of viability, and oxidative stress in a concentration-dependent manner. 2-Cl-4,5-MDMA activates apoptotic processes, while 3,4-MDPHP elicits cell death by necrosis. Fentanyl triggers cell death through both mechanisms. Increased expression levels of pro-apoptotic Bax and caspase 3 activity were observed following 2-Cl-4,5-MDMA and fentanyl, but not 3,4-MDPHP exposure, confirming the different modes of cell death.