Determination of levamisole and tetramisole in seized cocaine samples by enantioselective high-performance liquid chromatography and circular dichroism detection

Microsampling and enantioselective liquid chromatography coupled to mass spectrometry for chiral bioanalysis of novel psychoactive substances

In this paper, the development of efficient enantioselective HPLC methods for the analysis of five benzofuran-substituted phenethylamines, two substituted tryptamines, and three substituted cathinones is described. For the first time, reversed-phase (eluents made up with acidic water-methanol solutions) and polar-ionic (eluent made up with an acetonitrile-methanol solution incorporating both an acidic and a basic additive) conditions fully compatible with mass spectrometry (MS) detectors were applied with a chiral stationary phase (CSP) incorporating the (+)-(18-crown-6)-tetracarboxylic acid chiral selector. Enantioresolution was achieved for nine compounds with α and R_S factors up to 1.32 and 5.12, respectively. Circular dichroism (CD) detection, CD spectroscopy in stopped-flow mode and quantum mechanical (QM) calculations were successfully employed to investigate the absolute stereochemistry of mephedrone, methylone and butylone and allowed to establish a (R)<(S) enantiomeric elution order for these compounds on the chosen CSP. Whole blood miniaturized samples collected by means of volumetric absorptive microsampling (VAMS) technology and fortified with the target analytes were extracted following an optimized protocol and effectively analysed by means of an ultra-high performance liquid chromatography-MS system. By this way a proof-of-concept procedure was applied, demonstrating the suitability of the method for quali-quantitative enantioselective assessment of the selected psychoactive substances in advanced biological microsamples. VAMS microsamplers including a polypropylene handle topped with a small tip of a polymeric porous material were used and allowed to volumetrically collect small aliquots of whole blood (10 μL) independently from its density. Highly appreciable volumetric accuracy (bias, in the -8.7-8.1% range) and precision (% CV, in the 2.8-5.9% range) turned out.

Cutting agents in cocaine: A temporal study of the period 2015-2017 in the Northern Region of Colombia

Cocaine is a naturally occurring psychostimulant drug available worldwide. Drug trafficking networks adulterate pure cocaine with cutting agents to increase their earnings. This study presents a descriptive statistical analysis of the cutting agents found in 2118 cocaine samples that were seized in the Northern Region of Colombia (in the period 2015-2017). The data used in this study was drawn from the GC-MS analytical reports of the National Institute of Legal Medicine and Forensic Sciences -Colombia, Northern Region. Results showed diverse cutting agents in seized cocaine samples, from which the most commonly used are caffeine, phenacetin, lidocaine, imidazole and levamisole. In addition, cocaine samples showed different mixtures of the above cutting agents, predominantly caffeine/phenacetin and caffeine/lidocaine/phenacetin mixtures.

Separation and Determination of the Enantiomeric Levamisole and Dexamisole in Equine Plasma Samples Using Chiral Polysaccharide Column/ LC-MS/MS

Background:

Drug Enforcement Administration confirmed that many manufacturers began adding tetramisole or its individual isomers to cocaine as an adulterant, and believed that tetramisole may augment cocaine’s effects. In recent times, there is an increasing trend in the usage of tetramisole and its individual enantiomer in race sports especially in horse and camel races. So it’s is very much required to confirm the stereochemistry of this illicit drug in the routine race day samples coming to the anti-doping labs in order to avoid legal arguments and challenges to the analytical findings.

Methods:

The aim of the study was to develop a simple, rapid and accurate method for the chiral separation and determination of enantiomeric mixtures of levamisole and dexamisole using Thermo Q-Exactive High-Resolution Mass Spectrometer. In order to evaluate the suitability of the method for determining the enantiomeric purity of tetramisole, validation studies were also carried out by using equine plasma.

Results:

The enantio-separation was achieved using the Lux i-cellulose-5 column. Isocratic flow was used with a 1:1 mixture of mobile phase A (10 mM ammonium acetate in water) and mobile phase B (acetonitrile), at a flow rate of 0.6 mL/min. The run time was 8.0 min, and the column temperature was 50°C. Dexamisole eluted at 5.94 min, and levamisole eluted at 6.62 min, giving the R-value of 1.50. The obtained inter-day precisions of dexamisole, levamisole were 3.16% and 2.85%, respectively. The accuracy of dexamisole was in the range of 97.78 to 102.44%, and that for levamisole was 99.16 to 102.82%. The limit of quantification value for both isomers in this method was 0.1 ng/ mL. The method was linear in the range of 0 to 50 ng/mL.

Conclusion:

Chromatographic separation was achieved using the polysaccharide cellulose chiral column, and the reverse-phase separation approach was found to have the highest potential for successful chiral resolution in LC-MS. Linearity, precision, accuracy, detection limit, recovery, and the matrix effect in equine plasma were determined. Under the optimized conditions, the validated method can be applied for the identification and detection of the tetramisole enantiomers in different sources of illicit drugs of abuse.

Stereoisomeric profiling of chiral pharmaceutically active compounds in wastewaters and the receiving environment - A catchment-scale and a laboratory study

Chiral pharmaceutically active compounds (cPACs) are not currently governed by environmental regulation yet are expected to be in the future. As cPACs can exert stereospecific toxicity in the aquatic environment, it is essential to better understand their stereoselective behaviour here. Therefore, this study aims to provide a new perspective towards comprehensive evaluation of cPACs at a river catchment level, including their stereochemistry as a chemical phenomenon driving fate of chiral molecules in the environment. A large spatial and temporal monitoring program was performed in Southwest England. It included 5 sewage treatment works and the receiving waters of the largest river catchment in Southwest England. Simultaneously, lab-scale microcosm studies in simulated activated sludge bioreactors and river water microcosm were performed to evaluate stereoselective degradation of cPACs. A multi-residue enantioselective method allowed the analysis of a total of 18 pairs of enantiomers and 3 single enantiomers in wastewater and river water samples. Our monitoring program revealed: (1) spatial and temporal variations of cPACs in influent wastewaters resulting from different patterns of usage as well as an (2) enantiomeric enrichment of cPACs, likely due to human metabolism, despite their commercialization as racemic mixtures. A similar chiral signature was observed in effluent and receiving waters. Stereoselective degradation was observed in trickling filters (TF) for naproxen, ketoprofen, cetirizine and 10,11-dihydroxy-10-hydroxycarbamazepine, in sequencing batch reactors (SBR) for ifosfamide and in activated sludge (AS) for cetirizine. The extent of enantiomer-specific fate was wastewater treatment dependent in the case of naproxen (TF showed higher stereoselectivity than AS and SBR) and cetirizine (TF and AS showed higher stereoselectivity than SBR) due to differing microbial population. Furthermore, stereoselective degradation of naproxen was highly variable among STWs using similar treatments (TF) and operating in the same region. Microbial stereoselective degradation was also confirmed by both activated and river water simulated microcosm for chloramphenicol, ketoprofen, indoprofen, naproxen and 10,11-dihydroxy-10-hydroxycarbamazepine. Results from our large scale river catchment monitoring study and lab simulated microcosm show wide-ranging implications of enantiomerism of cPACs on environmental risk assessment (ERA). As two enantiomers of the same compound show different biological effects (e.g. toxicity), their non-racemic presence in the environment might lead to inaccurate ERA. This is because current ERA approaches do not require analysis at enantiomeric level.

Cocaine adulteration with the anthelminthic tetramisole (levamisole/dexamisole): Long-term monitoring of its intake by chiral LC-MS/MS analysis of cocaine-positive hair samples

Recent studies indicate that not only the anthelminthic levamisole but also the racemate tetramisole (R-/S-phenyltetraimidazothiazole, PTHIT) was found as an adulterant for cocaine. We herein report on the investigation of the prevalence of PTHIT among cocaine-positive hair samples and the discrimination of the presence of its stereoisomers levamisole and dexamisole. Cocaine-positive hair samples were collected in a forensic context in 2015 and mainly 2017 (n = 724). Cocaine and PTHIT concentrations have been determined by achiral liquid chromatography-tandem mass spectrometry (LC-MS/MS). For distinction of levamisole/dexamisole chiral LC-MS/MS was performed. Cocaine hair concentrations ranged from 500 (cut-off) to approximately 800 000 pg/mg. The study demonstrates a strong prevalence of PTHIT in cocaine users' hair (87%, n = 627). PTHIT hair concentrations ranged from below LLOQ 3.5 to approximately 61 000 pg/mg (median: 260 pg/mg). Surprisingly, enantiomeric ratios of levamisole/dexamisole ranged from 0.17 to 1.34 (median: 0.63). Therefore, PTHIT-adulterated street cocaine samples (n = 24) seized between 2013 and 2016 were tested. Samples mainly contained racemic tetramisole (87.5%), only one sample contained levamisole only and two samples contained non-racemic PTHIT. Our experiments suggest that the presence of tetramisole in biological samples may have hitherto been underestimated. Most probably higher dexamisole than levamisole concentrations in hair specimens arise from stereoselective metabolism and/or elimination. This is particularly important in light of the different pharmacological activities of the two enantiomers and potentially different adverse effects. Toxicological interpretations in intoxication cases with adulterated cocaine should not only consider levamisole but also tetramisole and terminology in scientific contributions should be used accordingly.

Computational contribution to the electrophoretic enantiomer separation mechanism and migration order using modified β-cyclodextrins

Capillary electrophoresis (CE) is an extremely effective technique in many kinds of separations, including separation of enantiomers. Some additional techniques may be necessary to determine the enantiomer migration order (EMO) and also the mechanism involved in chiral recognition. This paper reports the development and optimization of a CE method for enantioseparation of racemic mixture of both R- and S-stereoisomers of tramadol (TRM) with a computational contribution for the EMO determination and the responsible mechanisms for chiral distinction. Parameters such as composition and concentration of background electrolyte (BGE) and type and concentration of cyclodextrins (CD) were evaluated. For calculations, a sequential methodology was used, resorting to semiempirical Parametric Model 3 (PM3) followed by calculations accomplished using density functional theory. The best results were obtained with sulfated-β-CD (s-β-CD) and carboxymethyl-β-cyclodextrin (cm-β-CD) as chiral selector. Calculations show that the inclusion of TRM is not a probable process due to the shape of the TRM molecule and the size CDs cavities. Therefore, the chiral recognition process occurs by the formation of association complexes between modified β-CD and groups of TRM molecules. The structural analysis of the fragments of complexes at a pH of 10 and a thermodynamic analysis of the complexes' formation process allows determining the EMO. Comparing results obtained experimentally and computationally, it seems that the developed method is adequate for separation of TRM enantiomers and the computational methodology is also adequate to get a sense of the system at a molecular level.

Efficient Determination of the Enantiomeric Purity and Absolute Configuration of Flavanones by Using (S)-3,3'-Dibromo-1,1'-bi-2-naphthol as a Chiral Solvating Agent

The enantiomeric purity and absolute configuration of flavanones were first determined using (S)-3,3'-dibromo-1,1'-bi-2-naphthol as a chiral solvating agent by means of (1)H NMR spectroscopy. The enantiomeric purity results closely matched those based on chiral HPLC analysis.

Multi-residue enantiomeric analysis of human and veterinary pharmaceuticals and their metabolites in environmental samples by chiral liquid chromatography coupled with tandem mass spectrometry detection

Enantiomeric profiling of chiral pharmacologically active compounds (PACs) in the environment has hardly been investigated. This manuscript describes, for the first time, a multi-residue enantioselective method for the analysis of human and veterinary chiral PACs and their main metabolites from different therapeutic groups in complex environmental samples such as wastewater and river water. Several analytes targeted in this paper have not been analysed in the environment at enantiomeric level before. These are aminorex, carboxyibuprofen, carprofen, cephalexin, 3-N-dechloroethylifosfamide, 10,11-dihydro-10-hydroxycarbamazepine, dihydroketoprofen, fenoprofen, fexofenadine, flurbiprofen, 2-hydroxyibuprofen, ifosfamide, indoprofen, mandelic acid, 2-phenylpropionic acid, praziquantel and tetramisole. The method is based on chiral liquid chromatography utilising a chiral α1-acid glycoprotein column and tandem mass spectrometry detection. Excellent chromatographic separation of enantiomers (Rs≥1.0) was achieved for chloramphenicol, fexofenadine, ifosfamide, naproxen, tetramisole, ibuprofen and their metabolites: aminorex and dihydroketoprofen (three of four enantiomers), and partial separation (Rs = 0.7-1.0) was achieved for ketoprofen, praziquantel and the following metabolites: 3-N-dechloroethylifosfamide and 10,11-dihydro-10-hydroxycarbamazepine. The overall performance of the method was satisfactory for most of the compounds targeted. Method detection limits were at low nanogram per litre for surface water and effluent wastewater. Method intra-day precision was on average under 20% and sample pre-concentration using solid phase extraction yielded recoveries >70% for most of the analytes. This novel, selective and sensitive method has been applied for the quantification of chiral PACs in surface water and effluent wastewater providing excellent enantioresolution of multicomponent mixtures in complex environmental samples. It will help with better understanding of the role of individual enantiomers in the environment and will enable more accurate environmental risk assessment.