Indirect Chiral Separation of New Recreational Drugs by Gas Chromatography-Mass Spectrometry Using Trifluoroacetyl-L-Prolyl Chloride as Chiral Derivatization Reagent

Novel ethylenediamine-β-cyclodextrin grafted membranes for the chiral separation of mandelic acid and its derivatives

In the present study, flat cellulose acetate ultrafiltration membranes were prepared first by nonsolvent induced phase separation method. Then chiral membranes for separating the enantiomers were prepared by grafting the ultrafiltration membranes using ethylenediamine-β-cyclodextrin as the chiral selector and epichlorohydrin as the spacer arm. The pure water permeability of the ultrafiltration membrane was around 115 L·m-2·h-1·bar-1. The properties of the chiral membranes were characterized using infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The chiral membrane performance in enantiomer separation was evaluated with racemates, such as mandelic acid (MA), 2-chloromandelic acid (2-ClMA), 4-chloromandelic acid (4-ClMA), and methyl mandelate (MM). The influence of feed concentration on the separation efficiency was also investigated. The results indicated that the enantiomeric excess percentages (e.e%) of the racemic mixtures for these four chiral compounds were up to 31.8%, 25.4%, 17.8%, and 32.6%, respectively. The binding free energy of the chiral selector with the (S)-enantiomer calculated by molecular dynamics simulations was stronger than that with the (R)-enantiomer, which was consistent with the experimental results (higher concentration of (R)-enantiomer in the permeate). This supports the affinity absorption-separation mechanism.

Chiral separation of propranolol by electrokinetic chromatography using nanodiamonds and human serum albumin as a pseudo-stationary phase in river water

Propranolol is currently considered as an emerging contaminant in water bodies. In this study, R- and S-propranolol were determined in river samples by electrokinetic chromatography (EKC) using nanodiamonds (NDs) and human serum albumin (HSA) as a pseudo-stationary phase in order to achieve enantioseparation. Previously, river samples were preconcentrated using a column filled with Amberlite® IR-120 and Dowex® 50WX8 resins. The setting up of influential factors such as temperature, voltage, pH, and HSA and NDs concentration is accurately described along this manuscript. A multivariate study and optimization was carried out to obtain the enantioseparation of propranolol (Rs = 2.91), which was reached under the following experimental conditions: voltage of 16 kV, temperature of 16°C, phosphate buffer pH 9.5, NDs of 0.20%, and HSA of 15 μmol l-1 . The recoveries of analytes under optimal conditions were higher than 98%. The limits of detection were 0.85 μg l-1 for R- and S-propranolol. The method was applied to real samples, and the obtained results in three different water sources studied were 1.02, 0.59, and 0.30 μg l-1 for the R-enantiomer and 0.99, 0.54, and 0.28 μg l-1 for the S-enantiomer. The accuracy of the proposed methodology (including bias and precision) has allowed us to propose it as a successful tool for the control of water quality.

Chiral resolution of (±)-flurbiprofen using molecularly imprinted hydrazidine-modified cellulose microparticles

Flurbiprofen (FP) is one of the non-steroidal anti-inflammatory drugs (NSAIDs) commonly used to treat arthritic conditions. FP has two enantiomers: S-FP and R-FP. S-FP has potent anti-inflammatory effects, while R-FP has nearly no such effects. Herein, molecularly imprinted microparticles produced from hydrazidine-cellulose (CHD) biopolymer for the preferential uptake of S-FP and chiral resolution of (±)-FP were developed. First, cyanoethylcellulose (CECN) was synthesized, and the -CN units were transformed into hydrazidine groups. The developed CHD was subsequently shaped into microparticles and ionically interacted with the S-FP enantiomer. The particles were then imprinted after being cross-linked with glutaraldehyde, and then the S-FP was removed to provide the S-FP enantio-selective sorbent (S-FPCHD). After characterization, the optimal removal settings for the S- and R-FP enantiomers were determined. The results indicated a capacity of 125 mg/g under the optimum pH range of 5-7. Also, S-FPCHD displayed a noticeable affinity toward S-FP with a 12-fold increase compared to the R-FP enantiomer. The chiral resolution of the (±)-FP was successfully attempted using separation columns, and the outlet sample of the loading solution displayed an enantiomeric excess (ee) of 93 % related to the R-FP, while the eluent solution displayed an ee value of 95 % related to the S-FP.

Protein synergistic action-based development and application of a molecularly imprinted chiral sensor for highly stereoselective recognition of S-fluoxetine

In order to improve the recognition performance of MIPs sensors in chiral drug enantiomers, a novel a highly selective molecular recognition method based on protein-assisted immobilization of chiral molecular conformation was developed. S-fluoxetine (S-FLX) as the target chiral molecule, human serum albumin (HSA), which has a high affinity and strong interactions with S-FLX, was screened from 11 proteins to serve as an auxiliary recognition unit for the fixation of chiral conformation. By incorporating HSA into the preparation of molecularly imprinted polymers (MIPs), the natural chirality and high stereoselectivity of the protein were leveraged for the induction and fixation of the stereo conformation of S-FLX, refinement of internal structures of the imprinted cavities. The sensor exhibited excellent chiral recognition ability and high detection sensitivity. The changes of probe signal intensity of the MIPs/HSA sensor were positively correlated with the logarithmic concentration of S-FLX in the range of 1.0 × 10^-16-1.0 × 10^-11 mol L^-1, where a detection limit of 6.43 × 10^-17 mol L^-1 was achieved (DL = 3δ_b/K). The selectivity of MIPs/HSA sensor in recognizing S-FLX was increased by 18.5 times and the sensitivity was increased by 2.6 times after the incorporation of HSA. The developed sensor was successfully used for the analysis of S-FLX in fluoxetine hydrochloride capsules.

Rapid discrimination of enantiomers by ion mobility mass spectrometry and chemical theoretical calculation: Chiral mandelic acid and its derivatives

Because R/S-mandelic acids (MA) and their derivatives are critical starting materials or intermediates in the synthesis of chiral drugs, their chirality discrimination is important. In this study, R/S-MA and its derivatives, including R/S-2-phenylpropionic acid (2-PPA), R/S-methoxyphenylaceticacid (MPA), and R/S-2-hydroxy-4-phenylbutyric acid (HPBA), were accurate simultaneous mobility-discriminated by forming diastereomer complexes for the first time, which were obtained by simply mixing with cyclodextrins (α, β, γ-CD) and transition-metal ions (Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺). The mass spectra revealed non-covalent diastereomer complexes formed by CD, enantiomers, and metal ions, and ion-mobility spectrometry (IMS) was performed for 109 pairs of complexes. Significant chiral discrimination was observed in the formed diastereomeric complexes, and their separation peak-to-peak resolution (R_p-p) for the enantiomers depended on the transition metal ion type. In most cases, the R_p-p value gradually increases with CD size, with quaternary complexes having the largest R_p-p value. The greatest chiral distinctions of 2-PPA, MA, MPA, and HPBA were obtained by the diastereomeric complex ions of [(2-PPA)(α)₂+Zn²⁺-H]⁺, [(MA)(α)₂+Zn²⁺-H]⁺, [(MPA)₂(β)+Co²⁺-H]⁺, and [(HPBA)(α)₂+Fe²⁺-H]⁺, with R_p-p values of 1.35, 1.57, 1.70, and 0.71, respectively. Furthermore, the favorable conformation and collisional cross section (CCS) value of the different [CD + R/S-MA + Cu-H]⁺ complexes were measured using chemical theoretical calculations to detail their intermolecular interaction, revealing that [α-CD + R/S-MA + Cu-H]⁺ has two favored gas complexes, and the CCS calculated were consistent with the TIMS observed. In addition, R² > 0.99 was obtained for the relative quantification of the chiral enantiomers. Overall, the proposed method provides a promising strategy for distinguishing the enantiomers of MA and their derivatives, with the advantages of simplicity, speed, and accuracy, without the need for complex chemical derivatization or chromatographic separation.

Synthetic Cathinones: Recent Developments, Enantioselectivity Studies and Enantioseparation Methods

New psychoactive substances represent a public health threat since they are not controlled by international conventions, are easily accessible online and are sold as a legal alternative to illicit drugs. Among them, synthetic cathinones are widely abused due to their stimulant and hallucinogenic effects. To circumvent the law, new derivatives are clandestinely synthesized and, therefore, synthetic cathinones keep emerging on the drug market, with their chemical and toxicological properties still unknown. In this review, a literature assessment about synthetic cathinones is presented focusing on the recent developments, which include more than 50 derivatives since 2014. A summary of their toxicokinetic and toxicodynamic properties are also presented. Furthermore, synthetic cathinones are chiral compounds, meaning that they can exist as two enantiomeric forms which may present different biological and toxicological activities. To analyze the enantiomers, the development of enantiomeric resolution methods for synthetic cathinones is crucial. Many methods have been reported over the years that include mostly chromatographic and electromigration techniques, with liquid chromatography using chiral stationary phases being the technique of choice. This review intended to present an overview of enantioselectivity studies and enantioseparation analysis regarding synthetic cathinones, highlighting the relevance of chirality and current trends.

Original enantioseparation of illicit fentanyls with cellulose-based chiral stationary phases under polar-ionic conditions

Fentanyl analogues used in therapy and a range of highly potent non-pharmaceutical fentanyl derivatives are subject to international control, as the latter are increasingly being synthesized illicitly and sold as 'synthetic heroin', or mixed with heroin. A significant number of hospitalizations and deaths have been reported in the EU and USA following the use of illicitly synthesized fentanyl derivatives. It has been unequivocally demonstrated that the enantiomers of fentanyl derivatives exhibit different pharmaco-toxicological profiles, which makes crucial to avail of suitable analytical methods enabling investigations at a "stereochemical level". Chromatographic methods useful to discriminate the enantioseparation of fentanyls and their derivatives are still missing in the literature. This is the first study in which the enantioseparation of four fentanyl derivatives, that is, (±)-trans-3-methyl norfentanyl, (±)-cis-3-methyl norfentanyl, β-hydroxyfentanyl, and β-hydroxythiofentanyl, has been obtained under polar-ionic conditions. Indeed, the use of ACN-based mobile phases with minor amounts of either 2-propanol or ethanol (plus diethylamine and formic acid as ionic additives) allowed obtaining enantioseparation and enantioresolution factors up to 1.83 and 7.02, respectively. For the study, the two chiral stationary phases cellulose tris(3-chloro-4-methylphenylcarbamate) and cellulose tris(4-chloro-3-methylphenylcarbamate) were used, displaying a remarkably different performance towards the enantioseparation of (±)-cis-3-methyl norfentanyl. Chiral LC analyses with a high-resolution mass spectrometry detector were also carried out in order to confirm the obtained data and demonstrate the suitability and compatibility of the optimized mobile phases with mass spectrometric systems.

Determination of the chiral status of different novel psychoactive substance classes by capillary electrophoresis and β-cyclodextrin derivatives

Besides the abuse of well‐known illicit drugs, consumers discovered new synthetic compounds with similar effects but minor alterations in their chemical structure. Originally, these so‐called novel psychoactive substances (NPS) have been created to circumvent law of prosecution because of illicit drug abuse. During the past decade, such compounds came up in generations, the most popular compound was a synthetic cathinone derivative named mephedrone. Cathinones are structurally related to amphetamines; to date, more than 120 completely new derivatives have been synthesized and are traded via the Internet. Cathinones possess a chiral center; however, only little is known about the pharmacology of their enantiomers. However, NPS comprise further chiral compound classes such as amphetamine derivatives, ketamines, 2‐(aminopropyl)benzofurans, and phenidines. In continuation of our project, a cheap and easy‐to‐perform chiral capillary zone electrophoresis method for enantioseparation of cathinones presented previously was extended to the aforementioned compound classes. Enantioresolution was achieved by simply adding native β‐cyclodextrin, acetyl‐β‐cyclodextrin, 2‐hydroxypropyl‐β‐cyclodextrin, or carboxymethyl‐β‐cyclodextrin as chiral selector additives to the background electrolyte. Fifty‐one chiral NPS served as analytes mainly purchased from online vendors via the Internet. Using 10 mM of the aforementioned β‐cyclodextrins in a 10 mM sodium phosphate buffer (pH 2.5), overall, 50 of 51 NPS were resolved. However, chiral separation ability of the selectors differed depending on the analyte. Additionally, simultaneous enantioseparations, the determination of enantiomeric migration orders of selected analytes, and a repeatability study were performed successfully. It was proven that all separated NPS were traded as racemic mixtures.

A Simple HPLC–UV Approach for Rapid Enantioseparation of Cathinones, Pyrovalerones and Other Novel Psychoactive Substances on a 2.5-µm Cellulose Tris-(3,5-dimethylphenyl-carbamate) Column

The misuse of so called novel psychoactive substances is still a challenging problem worldwide. A special attribute of a lot of these compounds is a chiral centre enabling two possible enantiomers probably related to different pharmacological and toxicological properties. The goal of the present study was to present a simple and isocratic HPLC–UV method for enantioseparation of mainly cathinone and pyrovalerone derivatives as well as selected representatives of amphetamines, ketamines, benzofuries, phenidines, phenidates, morpholines and thiophenes. A Waters Acquity UPC2® Trefoil™ CEL1 2.5 µm, 3.0 × 150 mm column served as chiral stationary phase by means of cellulose tris-(3,5-dimethylphenylcarbamate) as chiral selector. Mobile phases consisted either of n-hexane/n-butanol/diethylamine (100:0.3:0.2) or n-hexane/diethylamine (100:0.2). The method was found to be applicable for rapid simultaneous chiral separations of cathinone derivatives, to determine enantiomeric elution orders, to detect positional isomers and to identify real-life samples. Also, a repeatability study was performed successfully. 78 out of 95 compounds were separated in their enantiomers successfully, 51 of them within 6 min. It was shown that all NPS bought from online vendors or seized by police were traded as racemic mixtures.

Light-responsive vesicles for enantioselective release of chiral drugs prepared from a supra-amphiphilic M-helix

A kind of M-helix based vesicle with enantioselective release abilities towards racemic propranolol (a β-blocker) was presented.

Successful use of a novel lux® i-Amylose-1 chiral column for enantioseparation of "legal highs" by HPLC

Bath salts, fumigations, cleaners and air fresheners, behind these terms substances are hidden, which count as "Legal Highs". These fancy names are used to pretend Legal Highs as harmless compounds, to circumvent legal regulations for marketing as well as to increase the sales. Besides classic illicit drugs of synthetic origin such as amphetamines, cocaine and MDMA, the trade of these compounds, also known as new psychoactive substances (NPS), is not uncommon today. In many countries, NPS are still not subject to drug control. Among them, there are stimulants such as new amphetamine derivatives or cathinones, which possess a chiral centre. Little is known about the fact that the two possible enantiomers may differ in their pharmacological effect. The aim of this study was to test a novel HPLC column for the enantioseparation of a set of 112 NPS coming from different chemical groups and collected by internet purchases during the years 2010-2018. The CSP, namely Lux® 5 μm i-Amylose-1, LC Column 250 x 4.6 mm, was run in normal phase mode under isocratic conditions, UV detection was performed at 245 nm and 230 nm, injection volume was 10 μl and flow rate was 1 ml/min. With a mobile phase consisting of n-hexane/isopropanol/diethylamine (90:10:0.1), herein, 79 NPS were resolved into their enantiomers successfully, for 37 of them baseline resolution was achieved. After increase of lipophily of the mobile phase to 99:1:0.1, another 27 compounds were baseline separated. It was found that all separated NPS are traded as racemic compounds.

Chiral separation of cathinone derivatives using β-cyclodextrin-assisted capillary electrophoresis-Comparison of four different β-cyclodextrin derivatives used as chiral selectors

In the past decade, more than 100 different cathinone derivatives slopped over entire Europe due to their enormous popularity. Generally, these novel psychoactive substances are easily available via the internet. This fact leads to various social problems, since cathinones are substances with consciousness-changing effects and are mainly misused for recreational matters by their consumers. Cathinones possess a chiral center including two enantiomeric forms with potentially different pharmacological behavior. This fact makes analytical method development regarding their chiral separation indispensable. In this study, a chiral capillary zone electrophoresis method for the enantioseparation of 61 cathinone and pyrovalerone derivatives was developed by means of four different β-cyclodextrin derivatives. As chiral selectors, native β-cyclodextrin as well as three of its derivatives namely acetyl-β-cyclodextrin, 2-hydroxypropyl-β-cyclodextrin, and carboxymethyl-β-cyclodextrin were used. The cathinone and pyrovalerone derivatives were either purchased in internet stores or seized by police. As a result, overall 58 of 61 studied substances were partially or baseline separated by at least one of the four chiral selectors using 10 mM of β-cyclodextrin derivative in a 10 mM sodium phosphate buffer (pH 2.5). Furthermore, the method was found to be suitable for simultaneous enantioseparations, for enantiomeric purity checks and to differentiate between positional isomers. Moreover, an intra- and an interday validation was performed successfully for each chiral selector to prove the robustness of the method.

Enantiomeric separation of Novel Psychoactive Substances by capillary electrophoresis using (+)-18-crown-6-tetracarboxylic acid as chiral selector

In the recent years, hundreds of Novel Psychoactive Substances (NPS) have entered both the European and the global drug market. These drugs, which are mainly used for recreational matters, have caused serious social problems. Every year, the spectrum of these misused drugs is enlarged by new derivatives, which are produced by modifications of basic structures of already well-known substances. Additionally, a lot of them possess a stereogenic center which leads to 2 enantiomeric forms. The fact that the pharmacological effects and potencies of the enantiomers of these chiral NPS may differ can be assumed from a broad spectrum of active pharmaceutical ingredients. For this reason, analytical method development regarding enantiomeric separation for these classes of substances is of great pharmaceutical and medical interest. The aim of this work was to create an easy-to-prepare chiral capillary electrophoresis method for the enantioseparation of NPS which contains a primary amino group by means of (+)-18-crown-6-tetracarboxylic acid as chiral selector. Novel Psychoactive Substances were purchased at various Internet stores or represent samples seized by Austrian police. The effects of selector concentration, the electrolyte composition, and the addition of organic modifiers to the background electrolyte on enantioseparation were investigated. Under optimized conditions, the use of 20-mM (+)-18-crown-6-tetracarboxylic acid, 10-mM Tris, and 30-mM citric acid buffer at pH 2.10 turned out to be effective. Fifteen of 24 tested NPS were resolved in their enantiomers within 15 minutes. It was found that all NPS were traded as racemic mixtures.

Simultaneous Quantitative Determination of Synthetic Cathinone Enantiomers in Urine and Plasma Using GC-NCI-MS

Development and validation of sensitive and selective method for enantioseparation and quantitation of synthetic cathinones is reported using GC-MS triple quadrupole mass spectrometry with negative chemical ionization (NCI) mode. Indirect chiral separation of thirty-six synthetic cathinone compounds has been achieved by using an optically pure chiral derivatizing agent (CDA) called (S)-(-)-N-(trifluoroacetyl)pyrrolidine-2-carbonyl chloride (L-TPC), which converts cathinone enantiomers into diastereoisomers that can be separated on achiral columns. As a result of using Ultra Inert 60 m column and performing slow heating rate (2°C/min) on the GC oven, an observed enhancement in enantiomer peak resolution has been achieved. An internal standard, (+)-cathinone, was used for quantitation of synthetic cathinones. Method validation in terms of linearities and sensitivity in terms of limits of detection (LODs), limits of quantitation (LOQs), recoveries, and reproducibilities has been obtained for fourteen selected compounds that examined simultaneously as a mixture after being spiked in urine and plasma. It was found that the LOD of the fourteen synthetic cathinones in urine was in the range of 0.26-0.76 µg/L, and in plasma, it was in the range of 0.26-0.34 µg/L. While the LOQ of the mixture in urine was in the range of 0.86-2.34 µg/L, and in plasma, it was in the range of 0.89-1.12 µg/L. Unlike the electron impact (EI) ion source, NCI showed better sensitivity by two orders of magnitude by comparing the obtained results with the recently published reports for quantitative analysis and enantioseparation of synthetic cathinones.

1,2-Diarylethylamine- and Ketamine-Based New Psychoactive Substances

While phencyclidine (PCP) and ketamine remain the most well-studied and widely known dissociative drugs, a number of other agents have appeared since the late 1950s and early 1960s, when the pharmacological potential of this class was first realized. For example, hundreds of compounds have been pursued as part of legitimate research efforts to explore these agents. Some of these found their way out of the research labs and onto illicit markets of the 1960s and following decades as PCP analogs. Other "illicit analogs" apparently never appeared in the scientific literature prior to their existence on clandestine markets, thus originating as novel innovations in the minds of clandestine chemists and their colleagues. Like so much else in this world, new technologies changed this dynamic. In the 1990s individuals separated by vast geographical distances could now communicate nearly instantaneously with ease through the Internet. Some individuals used this newly found opportunity to discuss the chemistry and psychoactive effects of dissociative drugs as well as to collaborate on the design and development of novel dissociative compounds. Similar to modern pharmaceutical companies and academic researchers, these seekers tinkered with the structure of their leads pursuing goals such as improved duration of action, analgesic effects, and reduced toxicity. Whether all these goals were achieved for any individual compound remains to be seen, but their creations have been let out of the bag and are now materialized as defined compositions of matter. Moreover, these creations now exist not only in and of themselves but live on further as permutations into various novel analogs and derivatives. In some cases these compounds have made their way to academic labs where potential clinical applications have been identified. These compounds reached wider distribution when other individuals picked up on these discussions and began to market them as "research chemicals" or "legal highs". The result is a continuously evolving game that is being played between legislatures, law enforcement, and research chemical market players. Two structurally distinct classes that have appeared as dissociative-based new psychoactive substances (NPS) are the 1,2-diarylethylamines and β-keto-arylcyclohexylamines. Examples of the former include diphenidine and various analogs such as fluorolintane and N-ethyl-lanicemine, and examples of the latter are analogs of ketamine such as methoxetamine, deschloroketamine, and 2-fluoro-2-deschloroketamine. The subject of this chapter is the introduction to some of the dissociative NPS from these classes and their known pharmacology that have emerged on the market in recent years.

Chiral enantioresolution of cathinone derivatives present in "legal highs", and enantioselectivity evaluation on cytotoxicity of 3,4-methylenedioxypyrovalerone (MDPV)

Recently, great interest has been focused on synthetic cathinones since their consumption has increased exponentially. All synthetic cathinones exist as chiral molecules; the biological and/or toxicological properties of cathinones generally differ according to the enantiomers in human body. In this study, a chiral liquid chromatography method was developed to separate and determine the enantiomeric ratio of synthetic cathinones present in "legal highs" acquired in old smart shops or over the Internet. All the synthetic cathinones were efficiently enantio-separated with α and Rs ranging from 1.24 to 3.62 and from 1.24 to 10.52, respectively, using polysaccharide-based chiral stationary phases. All synthetic cathinones, with the exception of 4-methylethcathinone (4-MEC), were present in the commercialized "legal highs" in an enantiomeric proportion of 50:50. One of the studied chiral compounds was 3,4-methylenedioxypyrovalerone (MDPV), one of the most consumed cathinone derivative worldwide. Our research group has recently reported its hepatotoxicity in the racemic form. Thus, the analytical enantioresolution of the MDPV was scaled up to multi-milligram using a semi-preparative amylose tris-3,5-dimethylphenylcarbamate column (20 cm × 7.0 mm ID, 7 µm particle size). Both enantiomers were isolated with high enantiomeric purity (enantiomeric excess > 99 %). The toxicity of S-(-)-MDPV and R-(+)-MDPV was evaluated, for the first time, using primary cultures of rat hepatocytes. It was also possible to verify that MDPV enantiomers showed hepatotoxicity in a concentration-dependent manner, but displayed no enantioselective toxicity in this cell culture model.

A validated gas chromatography mass spectrometry method for simultaneous determination of cathinone related drug enantiomers in urine and plasma

A sensitive and selective method for detection and quantitation of 31 synthetic cathinones using GC-MS has been developed and validated. They were separated into their optical enantiomers after derivatization with L-TPC and nikethamide was used as IS.

Test purchase, synthesis, and characterization of 2-methoxydiphenidine (MXP) and differentiation from its meta- and para-substituted isomers

The structurally diverse nature of the 1,2-diphenylethylamine template provides access to a range of substances for drug discovery work but some have attracted attention as 'research chemicals'. The most recent examples include diphenidine, i.e. 1-(1,2-diphenylethyl)piperidine and 2-methoxydiphenidine, i.e. 1-[1-(2-methoxyphenyl)-2-phenylethyl]piperidine (MXP, methoxyphenidine, 2-MXP) that have been associated with uncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist activity. Analytical challenges encountered during chemical analysis include the presence of positional isomers. Three powdered samples suspected to contain 2-MXP were obtained from three Internet retailers in the United Kingdom and subjected to analytical characterization by gas chromatography (GC) and high performance liquid chromatography (HPLC) coupled to various forms of mass spectrometry (MS). Nuclear magnetic resonance spectroscopy, infrared spectroscopy and thin layer chromatography were also employed. This was supported by the synthesis of all three isomers (2-, 3- and 4-MXP) by two different synthetic routes. The analytical data obtained for the three purchased samples were consistent with the synthesized 2-MXP standard and the differentiation between the isomers was possible. Distinct stability differences were observed for all three isomers during in-source collision-induced dissociation of the protonated molecule when employing detection under HPLC selected-ion monitoring detection, which added to the ability to differentiate between them. Furthermore, the analysis of a 2-MXP tablet by matrix assisted inlet ionization Orbitrap mass spectrometry confirmed that it was possible to detect the protonated molecule of 2-MXP directly from the tablet surface following addition of 3-nitrobenzonitrile as the matrix.