Regioisomer Differentiation of Ring-Substituted Chloromethcathinones and Bromomethcathinones Using Gas Chromatography/Electron Ionization-Triple Quadrupole Energy-Resolved Mass Spectrometry

Investigation of stereochemical stability of 2-, 3- and 4-chloromethcathinones in various biological matrixes

The stereochemical stability of the popular drugs of abuse 2-, 3- and 4-chloromethcathinone was studied in the mobile phase used for the isolation of their enantiomers by high-performance liquid chromatography, as well as in various biological matrixes such as whole blood, saliva and urine. For 2-, 3-, and 4-chloromethcathinones the rate constants and half-lives of their first order racemization reaction was assessed. It was found that at 25 °C the racemization rate constant decreases in the order 2-CMC > 3-CMC > 4-CMC while their stereochemical stability in biological matrixes decreases in the order urine > saliva > whole blood. This information must be considered for the adequate storage of purified enantiomers in the collected fractions, as well as in the studies focused on their enantioselective transformation in the human body.

Simultaneous chemo- and enantio-separation of 2-, 3- and 4-chloro-methcatinones by high-performance liquid chromatography-tandem mass spectrometry and its application to oral fluid samples

A method of analysis was developed for the simultaneous chemo- and enantioseparation of 2-, 3-, and 4-chloromethcathinones by high-performance liquid chromatography tandem mass-spectrometry. The fast method enables the reliable identification of positional isomers of chloromethcathinones in biological samples. In addition, the same method can be used for the enantioselective quantitative determination of one of these compounds and its major phase-1 metabolites in biological fluids. The developed method was applied to oral fluid samples collected by police during routine random traffic control in Belgium from January to November, 2023. It was found that 3-CMC was more frequently abused compared to 4-CMC. Although some differences were observed between the concentrations of enantiomers in OF, most likely the drugs were abused in the racemic form. No abuse of 2-CMC was detected at the timepoint of sample collection.

The differentiation of N-butyl pentylone isomers using GC-EI-MS and NMR

Forensic laboratories are faced with an ever-expanding seized drug landscape including the increasing prevalence of novel psychoactive substances (NPS), such as synthetic cathinones, that have varying potencies and scheduling. This study demonstrates a combined gas chromatography-electron ionization-mass spectrometry (GC-EI-MS) and nuclear magnetic resonance (NMR) spectroscopy approach for the differentiation of N-butyl pentylone isomers based on distinct retention times, characteristic EI mass spectra, and NMR characterization. Retention time reproducibility was assessed from 60 replicate measurements for each isomer over the course of a month. In addition, the effect of the mass spectrometer tune and the stability of an identified characteristic ion ratio using spectral data from ± 1 scan on either side of the peak apex were also statistically assessed using Welch's ANOVA testing. The presence of diastereomers for N-sec-butyl pentylone was identified using the developed GC-EI-MS method, which was confirmed using one-dimensional and two-dimensional NMR spectroscopy. The retention time reproducibility of the chromatographic method was ± 0.076% or less over the course of a month. An identified characteristic ion ratio between the abundance of the fragment ion at m/z 128 and the fragment ion at m/z 72 enabled the differentiation of the four N-butyl pentylone isomers, even when accounting for the effect of the mass spectrometer tune and mass spectral scans used to calculate the characteristic ion ratio. The 95% confidence interval mean abundance ratio of the fragment ions at m/z 128 and m/z 72 was 17.14 ± 0.14 for N-butyl pentylone, 6.44 ± 0.05 for N-isobutyl pentylone, 3.38 ± 0.02 for N-sec-butyl pentylone, and 0.75 ± 0.01 for N-tert-butyl pentylone. These results highlight the capabilities of a combined GC-EI-MS and NMR approach for the differentiation and characterization of synthetic cathinone isomers.

Influence of Metal Coordination on the Gas-Phase Chemistry of the Positional Isomers of Fluorobenzoate Complexes

The fragmentation behaviors of the o-, m-, and p-fluorobenzoate complexes of La³⁺, Ce³⁺, Fe³⁺, Cu²⁺, and UO₂²⁺ were investigated by electrospray ionization mass spectrometry, and the corresponding reaction mechanisms were explored by density functional theory (DFT) calculations. Fluoride transfer product La^IIIFCl₃^-/Ce^IIIFCl₃^- and decarboxylation product La^IIICl₃(C₆H₄F)^-/Ce^IIICl₃(C₆H₄F)^- were observed when the carboxylate precursors La^IIICl₃(C₆H₄FCO₂)^-/Ce^IIICl₃(C₆H₄FCO₂)^- were subjected to collision-induced dissociation. The variation in product ratios, which is not obvious in the meta and para cases, qualitatively follows the increasing overall energy barrier and reaction endothermicity of the two-step CO₂/C₆H₄ elimination mechanism, and this aligns with the increase in U-F distance in the ortho, meta, and para decarboxylation product isomers. In contrast, the mass spectra of Fe^IIICl₃(C₆H₄FCO₂)^-/Cu^IICl₂(C₆H₄FCO₂)^- are dominated by the reduction product FeCl₃^-/CuCl₂^- regardless of the fluorobenzoate isomer. DFT/B3LYP calculations show that the two-step CO₂/C₆H₄F elimination pathways are comparable in energy for all three positional isomers. It is energetically more favorable to give the reduction product than the fluoride transfer product, which is opposite to the lanthanum cases. Although the decarboxylation product was observed for all three U^VIO₂Cl₂(C₆H₄FCO₂)^- isomers, the ortho isomer behaves more similarly to La^IIICl₃(C₆H₄FCO₂)^-/Ce^IIICl₃(C₆H₄FCO₂)^- as evidenced by the formation of U^VIO₂FCl₂^-, and the appearance of U^VO₂Cl₂^- in the cases of the meta and para isomers indicates the similarity with Fe^IIICl₃(C₆H₄FCO₂)^-/Cu^IICl₂(C₆H₄FCO₂)^-. The shorter U-F distance in U^VIO₂Cl₂(o-C₆H₄F)^- causes the decrease in the fluoride transfer barrier and thus makes this process more favorable over o-C₆H₄F radical loss to give U^VO₂Cl₂^-.

Discrimination and quantitation of halobenzoic acid positional isomers upon Th(IV) coordination by mass spectrometry

A fast and reliable mass spectrometry-based method has been developed to discriminate the positional isomers of o-, m- and p-C₆H₄XCO₂H (X = F, Cl and Br). This is based on the distinct fragmentation patterns of isomeric ThCl₄(C₆H₄XCO₂)^- ions generated by electrospray ionization of the solutions with C₆H₄XCO₂H isomers and ThCl₄. Moreover, the composition of these positional isomers can be conveniently quantified without any pre-treatment according to the proportion of gas-phase fragmentation products.