International Journal of Mass Spectrometry最新文献

Sesquiterpene pyridine alkaloids (SPAs) are a large group of macrocyclic dilactones formed by dihydro-β-agarofuran sesquiterpenes and pyridine dicarboxylic acids, which have aroused widespread interest in the field of medicine due to their significant biological activities. In order to achieve accurate and rapid characterization of SPAs, previous studies have systematically investigated their fragmentation patterns in MS², but there are still some problems that need to be resolved, such as distinction between wilfordate (W)- and evoninate (E)-subtypes, as well as determination of the substituent position. In this paper, a comparative analysis of W- and E-subtypes of SPAs was carried out by a product ion scanning-multistage fragmentation (PIS-MSⁿ) strategy using ultra-high-performance liquid chromatography/linear ion trap quadrupole/orbitrap mass spectrometry (UHPLC/LTQ-Orbitrap-MS). The precursor ions for MSⁿ were selected from the ions related with pyridine dicarboxylic acid moiety in MS² spectrum, such as the ions at m/z 206, 178, and 160. The results showed that the product ions at m/z 104 or 117 were produced in the MS⁴ spectra of W-subtype SPAs ([M+H]⁺ > m/z 160 > m/z 132 > m/z 104 or 117). The ion at m/z 104 was produced when acetyloxyl group was present at C-5, whereas the ion at m/z 117 was produced when hydeoxyl group was present at C-5. Neither of the above characteristic ions were produced in the MS⁴ spectra of E-subtype SPAs. The fragmentation mechanism was also deduced. In addition, 13 SPAs were identified from the root of Tripterygium wilfordii, including 1 unknown compound using the MS/MS fragmentation pattern. The findings in this study enable the differentiation between W- and E-subtypes of SPAs and, to a certain extent, solve the problem of substituent position, which is of great significance for the accurate and in-depth identification of SPAs.

The suitability of 13 Chinese silicate rock certified reference materials for Sr and Nd isotope analyses was investigated. To indicate their homogeneity and to provide information values, we report Sr and Nd isotopic data and Rb, Sr, Sm and Nd concentrations for reference materials GBW07 103–105, 109–113 and 121–125 spanning a broad compositional range. Test portions were spiked with tracers enriched in ⁸⁷Rb–⁸⁴Sr and ¹⁴⁹Sm–^145,146,150Nd and digested using HF, HNO₃, and HClO₄ acid-dissolution procedures. Chemical purification involved cation-exchange and HEHEHP or Ln resins. Analyses involved different instruments at four laboratories, including thermal ionisation mass spectrometry (TIMS) and multicollector–inductively coupled plasma–mass spectrometry (MC–ICP–MS). This study provides a comprehensive report of the Rb–Sr and Sm–Nd isotopic compositions of the reference materials, and the results indicate that the materials are comparable to those of well-characterised and widely utilized reference materials from the US Geological Survey and the Geological Survey of Japan. This is the first report of the Sr and Nd isotopic composition of standards GBW07111, GBW07112, GBW07121, GBW07122, GBW07123, GBW07124 and GBW07125. Our results are useful for quality control and assurance between laboratories and provide a robust reference-rock dataset for future studies involving classical Sr and Nd isotopic geochemistry.

Based on the laser resonance ionization mass spectrometry (LRIMS) developed in the laboratory, a preliminary method was established to determine Pu isotope ratios. A three-color-three-photon resonance ionization scheme was confirmed, and the laser wavelengths of each excitation/ionization step were λ₁ = 586.654 nm, λ₂ = 606.181 nm and λ₃ = 642.722 nm. The selective ionization of ²³⁸Pu/²³⁸U was realized by testing the Pu and U mixed sample, a selectivity ratio of over 10⁷ was obtained. More effective electrothermal atomization of Pu was implemented by loading graphene oxide solution on the Pu sample surface, and the total detection efficiency of ∼40 ng Pu sample was above 3 × 10⁻⁴, which was three orders of magnitude higher than the efficiency of the unloaded graphene oxide solution Pu sample. Results showed that the relative standard deviation of ²³⁸Pu/²³⁹Pu ratio was ∼0.20%, indicating that LRIMS could effectively avoid the isobaric interference of ²³⁸U faced by other commercial mass spectrometers such as TIMS and ICP-MS, and could achieve precise measurement of ²³⁸Pu/²³⁹Pu ratio.

Capillary vibrating sharp-edge spray ionization (cVSSI) combined with hydrogen/deuterium exchange-mass spectrometry (HDX-MS) has been utilized to characterize different solution-phase DNA conformers including DNA G-quadruplex topologies as well as triplex DNA and duplex DNA. In general, G-quadruplex DNA shows a wide range of protection of hydrogens extending from ∼12% to ∼21% deuterium incorporation. Additionally, the DNA sequences selected to represent parallel, antiparallel, and hybrid G-quadruplex topologies exhibit slight differences in deuterium uptake levels which appear to loosely relate to overall conformer stability. Notably, the exchange level for one of the hybrid sequence sub topologies of G-quadruplex DNA (24 TTG) is significantly different (compared with the others studied here) despite the DNA sequences being highly comparable. For the quadruplex-forming sequences, correlation analysis suggests protection of base hydrogens involved in tetrad hydrogen bonding. For duplex DNA ∼19% deuterium incorporation is observed while only ∼16% is observed for triplex DNA. This increased protection of hydrogens may be due to the added backbone scaffolding and Hoogsteen base pairing of the latter species. These experiments lay the groundwork for future studies aimed at determining the structural source of this protection as well as the applicability of the approach for ascertaining different oligonucleotide folds, co-existing conformations, and/or overall conformer flexibility.

Overall, the nanoflow chromatographic separation, nano-electrospray source, and Orbitrap Elite mass spectrometer with the dual-stage ion funnel that replaced the standard heated-cone inlet were used in the MS analysis of low-abundance peptide samples. The analytical advantage of the ion funnel was demonstrated in the LC-MS analysis of the HeLa protein digest mixture. Chemical noise patterns in Orbitrap, linear ion traps, and quadrupole time-of-flight mass spectrometers were compared. The chemical noise patterns in Orbitrap were found to be generally similar to those observed in linear ion traps and time-of-flight instruments, yet it was observed only under the condition of selecting a few Da mass range for the mass analysis. The Orbitrap's ultrahigh mass resolution enabled the intricate internal structure of the chemical noise to be uncovered. In addition to singly charged ions representing a bulk of chemical noise, doubly charged ions were also observed, though the intensity of the latter was found to be significantly lower, suggesting that chemical noise-limited detection levels in the MS analysis of low-abundance peptides could be significantly lower for 2+ or 3+ peptide ions compared to singly charged ones.

Electrospray ionization plays a central role in modern analytical chemistry. It is often used in combination with an HPLC system and is able to transfer large molecules, such as proteins and complexes, into the gas phase. A liquid solution containing the analyte is sprayed in a strong electric field. Charged droplets generated by this process release the analyte molecules which can ultimately be analyzed by the mass spectrometer system. However, the exact mechanisms of droplet generation and ion release are still not fully understood and are under investigation. Recent literature puts the focus on droplet disintegration and shows that the analyte ions are not exclusively released from the droplets within the ionization chamber but rather in the whole mass spectrometer system. Previous experiments allow the direct observation of the signatures of fragmented droplets within the analyzer region of a time-of-flight mass spectrometer: An oscilloscope was connected to a secondary electron multiplier which serves as an auxiliary ion detector, located downstream of the orthogonal acceleration stage of a time-of-flight mass spectrometer. The oscilloscope is thus able to monitor the time-resolved ion current in the mass analyzer region. Pulses of extraordinarily high ion currents are observable here which are attributed to aspirated charged droplets.

This work provides insights into long-term experiments with this experimental setup. There is a focus on signal stability, in the presence of such droplet signatures. It is apparent that the standby time of the instrument between individual measurements and the time since a switch of the polarity mode, has a significant influence on the signal stability. There are also indications that the observations of droplet signatures and the MS signal stability are correlated.

The plant secondary metabolite families of coumarin and 4-hydroxy coumarin have a broad pharmacological spectrum ranging from antibacterial to anticancer properties. One prominent member of this substance class is the synthetic but naturally inspired anticoagulant drug and rodenticide warfarin (coumadin). A vast number of publications focus on the identification of warfarin and its major cytochrome P450-mediated phase I metabolites by liquid chromatography (LC) with mass spectrometry (MS) and tandem mass spectrometric (MS/MS) detection techniques. For the first time, electron ionization (EI) induced high-resolution quadrupole time-of-flight mass spectrometric (HR-qToF-MS) data of in-liner derivatized warfarin and selected hydroxylated species is provided in this study as an alternative to LC-MS/MS approaches. Furthermore, the characteristic fragments and fragmentation pathways of the analyzed methyl ethers are concluded. The obtained data of analytical standards, specific deuterated and ¹³C-labeled compounds prove inductive cleavage of the acyl or acetonyl side chain, methyl migration, and H-migration, along with consequential inductive cleavage as predominant fragmentation routes. Based on the HR-spectral data, commonalities and differences between the analyzed compounds and fragment groups were evaluated with future applicability in structure elucidation and spectra prediction of related compounds.

Ionic liquids are useful for many applications and the structural diversity as a class is ever increasing. Knowledge of gas-phase dissociation pathways can inform analytical method development for the characterization of novel syntheses, degradation products, or environmental contaminants, and can inform our knowledge of the fate of ionic liquid species in the gas phase (e.g., after ejection by electrospray spacecraft thrusters). In this work, the N-heterocyclic (NHC) ions:1-butyl-1-methylpiperidinium (BMPi), 1-methyl-1-propylpiperidinium (MPPi), 1-butyl-1-methylpyrrolidinium (BMPyr), 1-ethyl-1-methylpyrrolidinium (EMPyr), 1-butylpyridinium (BPy), and 1-Butyl-1-(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl) imidazolium (BFIm) were studied. An additional fluorinated anion, nonafluorobutanesulfonate (NFBS), was also studied. Collision-induced dissociation mass spectrometry (CID-MS), as MS² and MS³ using an ion trap mass spectrometer and energy-resolved breakdown curves using a quadrupole time-of-flight mass spectrometer, were used to determine dissociation patterns. Assignment of proposed dissociation pathways were made based on the experimental results and complementary computational chemistry. It was observed that for aromatic NHCs, cleavage at the C–N bond was preferred, to generate alkene-based neutral losses. Non-aromatic NHCs typically generated both alkane- and alkene-based neutral losses. Breakdown curves, supported by theoretical thermodynamic calculations, suggest that the loss of the alkane is the favorable dissociation pathway. Additionally, some ring-opening and ring contraction reactions via C–C bond cleavage were observed in non-aromatic species, whereas the intact aromatic NHC is typically a stable terminal ion. The polyfluorinated imidazolium fragmented via the breaking of C–N, C–C, and C–F bonds. The fluorinated anion, NFBS, fragmented by C–C and C–S bond cleavage to generate fluoroalkene, sulfur dioxide, and sulfur trioxide neutral losses. Beyond these broad stroke findings, the dissociation pathways of the seven ionic liquid ions were mapped using evidence from MS³, breakdown curves, and computational chemistry together assigning product ions as either arising from competitive or sequential pathways and proposing tentative structures. Some of the ionic liquid ions showed class-based product ions which will be useful in analytical development for their characterization. Finally, these results were contextualized within previous literature reports on other ionic liquid species.

We have shown that fatty acids can be decarboxylated in the gas phase via collision-induced dissociation (CID) of ternary zinc complexes of the general formula [(L)Zn(OOCR)]⁺, where RC₃H₇, C₆H₁₃, C₇H₁₅, C₁₇H₃₅, C₁₇H₃₃, C₁₇H₃₁ and L = 1,10-phenanthroline or 2,2′:6′,2″-terpyridine. These complexes were formed by electrospray ionization of a solution mixture of zinc(II) salt, fatty acid, and the ligand. Two pathways were mapped for the resulting [(L)ZnR]⁺ organozinc ion: i) a gas-phase ion-molecule reaction with a neutral carboxylic acid R’COOH in the linear quadrupole ion trap resulted in the production of the alkane RH and formation of [(L)Zn(OOCR’)]⁺; ii) a second CID stage produced an alkene and the ion [(L)ZnH]⁺ which underwent a subsequent ion-molecule reaction with R’COOH to form [(L)Zn(OOCR’)]⁺ ion accompanied by the loss of H₂. In the case of RR’ = C₃H₇ (butyric acid), both processes presented formal catalytic cycles with the overall equations C₃H₇COOHC₃H₈+ CO₂ or C₃H₇COOHC₃H₆ + H₂+ CO₂. Theoretical DFT calculations provided the energetics of reactants/products as well as transition state energies and were in agreement with the experimental data. The work identifies Zn as a potential catalyst for deoxygenation of fatty acid with no fragmentation of the alkyl chain.

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has emerged as a robust analytical technique for the rapid and sensitive analysis of diverse biomolecules. MALDI-MS effectiveness relies on meticulous sample preparation, with a particular emphasis on achieving a uniform sample surface. Although the dried droplet (DD) method is widely utilized, it encounters challenges such as uneven sample distribution that impacts the ionization process and significantly varies ion signals across sample areas, resulting in poor data reproducibility. The uneven sample distribution can increase the time to finish mass analysis of samples and make automated analysis complicated. Automated sample deposition systems and alternative MALDI sample preparation methods show promise in overcoming the limitations of the DD method, resulting in improved reproducibility and mass spectral quality. These advancements are critical in improving the precision and reliability of quantitative measurements using MALDI-MS, propelling progress in MALDI imaging, quantitative analysis, and biomarker discovery across a wide range of scientific applications.