Energy-resolved mass spectrometry for differentiation of the fluorine substitution position on the phenyl ring of fluoromethcathinones

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^-.

Characteristics of ionization behaviors of aminonitrotoluene isomers produced by atmospheric pressure chemical ionization

RATIONALE

Six of the isomers of aminonitrotoluene (ANT) are 2-amino-3-nitrotoluene (2A3NT), 2A4NT, 2A5NT, 2A6NT, 4A2NT, and 4A3NT. Some of them can be identified by chromatography and spectroscopy. Biochemical transformation of 2,4,6-trinitrotoluene (TNT) and dinitrotoluenes (DNTs) is very complex and ANTs are decomposition products of TNT and DNTs.

METHODS

Each isomer in acetone was ionized using atmospheric pressure chemical ionization in positive and negative ion modes, and kinds and abundances of the product ions were analyzed. Energy-minimized structures of the product ions and their energies were calculated to explain the analysis results.

RESULTS

The [M + H]⁺ , [M + H + Acetone - H₂ O]⁺ , and [M + H + Acetone]⁺ ions as positive product ions were detected, while [M - H]^- , M^•- , and [M + O₂ ]^•- ions as negative ones were observed. The order of the ionization efficiencies for the positive product ions was 4A3NT > 4A2NT > 2A4NT > 2A6NT > 2A5NT > 2A3NT, while that of the negative ones was 2A5NT > 2A3NT > 4A3NT > 2A4NT > 2A6NT > 4A2NT. Ion abundance ratios for 2A3NT and 2A5NT showed very similar trends, while those of 2A6NT and 4A2NT also showed similar trends. Differences in the ionization behaviors were explained using the heats of reaction.

CONCLUSIONS

The product ions were produced by ion-molecule reactions with the reactant ions of [2Acetone + H]⁺ and [Acetone + O₂ ]^•- . The [M + H + Acetone]⁺ ion was fragmented to produce [M + H]⁺ and [M + H + Acetone - H₂ O]⁺ , while the [M + O₂ ]^•- ion was fragmented to generate the [M - H]^- and M^•- ions. Differences in the ionization behaviors of the ANTs can be used for their differentiation.

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.

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

Positional isomers o-, m-, and p-chloromethcathinones (CMCs) and m- and p-bromomethcathinones (BMCs) were effectively differentiated using gas chromatography (GC) and energy-resolved mass spectrometry (ERMS) analyses. GC demonstrated that the free bases of CMC and BMC isomers were simultaneously baseline-separated at a slow column heating rate (5 °C/min) using a conventional low-polar capillary column. ERMS showed that the trifluoroacetyl derivatives of the positional isomers differed in mass spectral abundances of both halophenyl and halobenzoyl cations. Moreover, the logarithmic plots of the abundance ratio of the two cations as a function of the collision energy (CE) exhibited marked differences among the isomers at each CE, following the order of ortho < para < meta for CMCs and para < meta for BMCs. The performed theoretical calculations of dissociation energy agreed well with the ERMS measurements. The GC and ERMS methodologies enabled unambiguous and reliable differentiation of CMC and BMC isomers. The developed approach is expected to significantly contribute to the accurate structural identification of new psychoactive substances in forensic, toxicological, and clinical fields.

Differentiation of o-, m-, and p-fluoro-α-pyrrolidinopropiophenones by Triton B-mediated one-pot reaction

Positional isomer differentiation is crucial for the analysis of forensic drugs. Presently, it is difficult to distinguish among ortho, meta, and para positional isomers of ring-fluorinated synthetic cathinones, a major class of new psychoactive substances (NPSs), because they exhibit similar chromatographic properties and mass spectral patterns. We describe herein that the ring-fluorinated synthetic cathinone positional isomers, viz. o-, m-, and p-fluoro-α-pyrrolidinopropiophenones (o-, m-, and p-FPPPs), can be discriminated by their benzyltrimethylammonium hydroxide (Triton B)-mediated one-pot reaction with methanol at ambient temperature, followed by chromatographic and mass spectral analyses of the corresponding products. For p-FPPP, fluorine was nucleophilically substituted by the methoxy group to afford p-methoxy-α-pyrrolidinopropiophenone, while o- and m-FPPPs afforded the corresponding FPPP-enamine-pyrrolidine adducts, which allowed the above positional isomers to be unambiguously differentiated by comparing the reaction product chromatograms and mass spectra. The adopted approach, which does not require excess heating or use of metallic catalysts and features the advantages of simplicity and convenience, is expected to contribute toward practical NPS identification.