International Journal of Mass Spectrometry最新文献

Imaging mass spectrometry has emerged as a powerful tool to map the spatial distributions of lipids and metabolites in biological tissues. However, these analyses are challenged by the multitude of isobaric (i.e., same nominal mass) and isomeric compounds present in most samples. Failure to adequately separate these compounds results in inaccurate or incomplete chemical identifications and produces composite images of spatial distribution arising from multiple compounds. A number of techniques have been developed to more completely resolve and identify this complex chemical milieu. These include methods that rely on condensed-phase chemical derivatization and gas-phase ion chemistry, or some combination thereof. This Young Scientist Feature focuses on summarizing the analytical figures of merit of these tools, highlighting their relative speeds, limits of detection, molecular specificities, and eases-of-use. It will also include current challenges and future perspectives for resolving structural isomers in imaging mass spectrometry experiments.

The Sm–Nd isotopic system has been broadly utilized for dating and tracing in earth and planetary sciences. However, low Nd⁺ ionization efficiency permanently hinders precise and accurate measurements on small amounts of Nd samples. So far, isotopic measurement of micro-amount Nd sample via thermal ionization mass spectrometry (TIMS) Nd⁺ mode was mostly performed on Nd reference solutions, but less on natural rock or mineral samples. In the present study, analytical procedures to measure isotopic composition via the TIMS Nd⁺ mode were designed for natural rock powders by using 1–5 ng pure Nd. The analytical technique was refined through low-blank sample digestion, small-column chemistry for Nd extraction from matrix elements, loading Nd using purified H₃PO₄ solution, and careful heating of filaments before data acquisition. Measurements on small Nd amounts (1 ng–5 ng) of either the JNdi-1 reference solution or four reference rock powders yielded satisfactory results of ¹⁴³Nd/¹⁴⁴Nd value with respect to precision and accuracy. The analytical results agree well with the recommendation values of the reference materials within analytical errors and the internal precision is better than ±0.005 % (2RSE). When using 1 ng or 2 ng Nd amounts, ¹⁴⁴Nd ion flow can remain stable in a signal intensity of >100 mV, and without the assistance of an additional ionization enhancer. Therefore, the analytical procedure, featured by low procedural blank (about 10–22 pg), high Nd⁺ ionization efficiency, and easy operation, has broad prospects for the application of Nd isotope in single-grain minerals or micro-samples.

The Chemical Weapons Convention (CWC) is a science-based international treaty for the disarmament and non-proliferation of chemical weapons. However, reference Orgaization for prohibition of chemical weapons (OPCW) central analytical database (OCAD) of structures with mass spectra (MS) and retention indices (RI) includes only minor part of all possible chemical species defined in the Schedules of CWC. In this work we employed OCAD in silico augmentation based on chemoinformatics approach for chemical structures enumeration, MS data generation based on message passing neural network and based on P-alkyl molecular pairs RI prediction to support the verification activities as provided for in the CWC. Enumerated 879 noncyclic and 5270 monocyclic alcohols became the basis for generating hundreds of thousands molecules of Schedule 1 toxic chemicals like Sarin, Tabun, VX and Novichok. Trained on ordinary and neutral loss electron ionization mass spectrometry (EI-MS) a message-passing neural network (MPNN) outperformed other quantum chemistry and machine learning methods. Generated by this MPNN in silico EI-MS are very similar to the library's spectra and allowed to reach desired match factor above 800 within a scale of 0–1000. Statistical data for molecular pairs based on P-alkyl fragments was collected and used to predict RIs within desired 20 RI window for some toxic chemicals of Schedule 1.A.01, for which in the current OCAD version RIs are absent.

For thousands years Ephedrae herba has been used in traditional Chinese herbal medicine. Its main bioactive constituents are ephedrine and pseudoephedrine. Nowadays, these alkaloids have found application in various clinical treatments, as sports-enhancing drugs and for the illicit production of amphetamine-like drugs. Ephedrine and pseudoephedrine are diastereomers, and because of their high polarity and similar pK_a values, their chromatographic separation may be a challenge. In this study a possible application of direct infusion mass spectrometry and direct infusion tandem mass spectrometry has been proposed for differentiation of ephedrine and pseudoephedrine as well as the relative determination of the contents of these compounds in a mixture. At low collision energy condition, the ratio of relative abundances of ions [M+H–H₂O]⁺ and [M+H]⁺ permit distinction of the analyzed diastereomers, and enable evaluation of their relative content in a mixture with no need of chromatographic separation. The performed quantum chemical calculation have shown that protonated pseudoephedrine contains stronger hydrogen bond than protonated ephedrine, which can justify the observed higher relative abundance of ion [M+H–H₂O]⁺ in the mass spectrum of pseudoephedrine, in comparison to that of ephedrine.

Degradation of cyclic cyanotoxins microcystins (MCs) leads to the formation of linear MC heptapeptides. Herein, several linear MCs were identified by UHPLC-ESI-Orbitrap-MS/MS in water samples collected from Lake Erie shore during the cyanobacterial harmful algal bloom (cyanoHAB) 2022. Consequently, novel in-source fragments of linear MCs, which contain a modified Adda moiety and C-terminal arginine (Arg), were discovered and their structures were putatively assigned using high-resolution MS and MS/MS data. The fragment ion at m/z 175.11 was used as the major diagnostic ion to identify whether a MC is linear with Arg at the C-terminus. The distinguishing feature of the novel linear MC in-source fragments is the absence of the characteristic Adda fragment ion m/z 135.08. However, these contain other fragment ions formed by the remaining part of the Adda, such as m/z 135.11 and m/z 163.11. In-source fragments that were formed when C-terminal Arg-containing linear MC precursor ions lost C₆H₅-CH=CH(OCH₃) and NH₃ from the Adda moiety confirmed the presence of linear MC-RR, MC-LR, [Asp³]MC-LR, MC-YR, MC-HilR, MC-HtyR, MC-FR, and MC-HphR in Lake Erie water. The loss of specific neutral molecules during ESI assisted the identification of linear MCs and helps avoiding the missannotation of in-source fragments as precursor ions resulting from MC degradation products or other precursor molecules.

Gas-phase ion-ion reactions between the trication, [Yb(L)₃]³⁺ (where L = N,N,N′,N′-tetramethylpyridine-2,6-dicarboxamide), and the tetraphenylborate anion, [BPh₄]⁻, and its sodium bound dimer, [(BPh₄)₂Na]⁻, were examined to establish whether ion-pair formation and transmetalation from boron to ytterbium can occur. Ion clusters that were formed with the formal +3 oxidation state for the ytterbium metal centre include: the ion pair [Yb^(III)(L)₃][BPh₄]²⁺ (m/z 578, (6a)); the ion triplet [Yb^(III)(L)₃][BPh₄]₂⁺ (m/z 1475, (7a)); and [Yb^(III)(L)₃(BPh₄)₃Na]⁺ (m/z 1817, (8a)). In addition, electron transfer from [BPh₄]⁻ to [Yb(L)₃]³⁺ resulted in complexes in which the ytterbium metal centre is in the formal +2 oxidation state, which reacted further to yield the ion pairs: [Yb^(II)(L)₃][BPh₄]⁺ (m/z 1156, (7b)); [Yb^(II)(L)₂][BPh₄]⁺ (m/z 935, (8b)); and [Yb^(II)(L)][BPh₄]⁺ (m/z 714, (9b)). Selected ion pairs were mass isolated and subjected to collision-induced dissociation (CID) to examine if they underwent transmetalation from B to Yb. Most of the observed ytterbium(III) complexes were found to undergo transmetalation. Density functional theory (DFT) calculations were used to determine the energetics for the sequential ion-ion reactions associated with the formation of [Yb^(II)(L)₂][BPh₄]⁺ as well as its fragmentation reactions via ligand loss (observed experimentally) versus transmetalation (not observed experimentally).

Erastin, a classical ferroptosis inducer, exerts cytotoxicity in several types of cancer cells including gastric cancer cells. However, the mechanism of erastin in regulating metabolic pathways in gastric cancer remains largely unclear. To investigate the gastric cellular response to erastin therapy, a pseudotargeted metabolomics method was achieved on ultra-high performance liquid chromatography-hybrid triple quadrupole linear ion trap mass spectrometry (UHPLC-QTRAP MS), which was used to investigate metabolic changes between erastin-treated MGC-803 cells and the controls at different time points. We found that erastin induced tremendous impact on the metabolome of gastric cells by affecting key metabolic processes, such as cysteine and methionine metabolism, tryptophan metabolism, purine metabolism, glutathione biosynthesis, glycolysis and TCA cycle. Interestingly, S-adenosylmethionine, methionine, serine and cysteine were obviously increasing treads after erastin treatment, while S-adenosylhomocysteine and glutathione were always down-regulated up to 24 h. The results indicated that DNA methylation was activated and glutathione biosynthesis was blocked in erastin-treated MGC-803 gastric cells, highlighting the importance of erastin as a promising drug candidate for in vivo treatment of gastric tumor.

Nitrate adducts of nitroglycerin (NG) and 1,3-dinitroglycerin (1,3-DNG) were produced from atmospheric pressure chemical ionization with chloride reagent ions and in-source decomposition of M·Cl⁻. The nitrate adducts subsequently dissociated in the drift region with enthalpies of 109 ± 9 kJ mol ⁻¹ at 142–150 °C for NG·NO₃⁻ and 101 ± 8 kJ mol⁻¹ at 161–173 °C for 1,3-DNG·NO₃⁻. Similar behavior was not observed generally for other explosives although nitrate adducts of each explosive could be formed using electrospray ionization with a nitrate salt solution. Ion abundances were measured over a range of ion energies with collision induced dissociation in tandem mass spectrometry and models from Density Functional Theory were used to correlate the experimental findings to structural motifs and other adduct properties. The computational modeling showed that adduct stability is dominated by the electrostatic interaction between the nitrate ion and the dipole moment of the neutral explosive. Specifically, explosives having the ability to adapt a conformer with a large dipole moment showed the most stable adducts. Other binding contributions are possible yet were found to be minor in the explosive adducts studied here.