Journal of Analytical Chemistry最新文献

A sample containing microparticles of two different uranium materials with distinct uranium isotopic compositions was analyzed during an international experiment. Mass spectrometric analysis of 25 particles revealed that, within the measurement error, six particles had an isotopic composition consistent with that of the first material, and three particles were consistent with the second material. However, the uranium isotopic composition of the remaining 16 particles did not match either of the known materials. This indicates that the preliminary examination of uranium microparticles by scanning electron microscopy can identify particles carrying information about the isotopic composition of the source materials.

Diarylheptanoids (DAH) are a class of phenolic secondary plant metabolites possessing a wide range of biological activities and pronounced antioxidant properties. This study proposes an original approach to the rapid screening of diarylheptanoids in plant extracts, based on surface-assisted laser desorption/ionization (SALDI) mass spectrometry on target plates with carbon nanocoating and cationization with lithium ions. The test sample was an extract of birch phloem containing centrolobol (CL) and platyphyllonol (PF), the structures of which were confirmed by NMR spectroscopy. The high intensity of diarylheptanoid signals in the resulting mass spectra made it possible to use tandem mass spectrometry for their search and identification. Using the developed approach, four glycosylated derivatives of CL and PF were discovered and tentatively identified in the studied extract, including those containing monosaccharide and disaccharide residues with pentose and hexose sugars.

An ion optical analysis of a static mass analyzer, based on a second-order focusing magnetic mirror, was conducted while accounting for aberrations caused by the movement of ions outside the mean plane of the mass analyzer. As part of this study, an optimization algorithm was developed for the four-dimensional acceptance of the mass analyzer at a fixed resolution, formulated within the framework of the inverse problem.

The results of measurements of ²³⁵U/²³⁸U isotope ratios in microparticles of a reference material performed by Cameca IMS-4f and Cameca IMS 1280-HR mass spectrometers are compared. Twenty-eight particles of various shapes and sizes and also one spherical uranium oxide particle approximately 0.6 μ in size were analyzed by both instruments. These particles were selected based on a preliminary SEM–EDX analysis. The results indicate that the Cameca IMS-1280 HR mass spectrometer can measure uranium isotope ratios with precision up to thousandths of percent, while the Cameca IMS-4f mass spectrometer can measure only up to tenths of percent. For measurements of uranium-235 concentrations at the 0.7% level, the error range for mass spectrometers with a “large” magnet is two orders of magnitude smaller than the errors from mass spectrometers with a “small” magnet, with measurement errors more than ten times lower. Additionally, while mass spectrometers with a small magnet cannot measure minor isotope concentrations at the 5 × 10^–3% level in submicrometer particles, mass spectrometers with a large magnet can achieve this with an error of less than 10%.

Potato, like other Solanaceae plants, have a small family of eukaryotic translation initiation factors 4E (eIF4E), including four proteins eIF4E-1, eIF4E-2, eIF(iso)4E, and the novel cap-binding protein (nCBP). These factors play roles in the process of the post-transcriptional regulation of gene expression. The eIF4Es are also used by numerous RNA viruses to synthesize their proteins. The quantitative detection of eIF4Es at the proteome level yields data about their abundances and the involvement of each factor in the process of translation initiation under normal and stress conditions. To quantify eIF4Es, we have developed a mass spectrometry protocol for the detection of isoforms in potato S. tuberosum leaf tissues by multiple reaction monitoring (MRM) assay. As a result, we have detected all potato eIF4Es and determined their amounts with the most abundant protein, eIF4E-1.

Studying the chemical composition of snow as an indicator of atmospheric pollution at high latitudes is crucial for understanding the transport processes of pollutants in the atmosphere and assessing the anthropogenic impact on Arctic ecosystems. This study proposes a method for detecting and quantifying semi-volatile micropollutants in snow by combining stir-bar sorptive extraction (SBSE) with thermal desorption (TD) gas chromatography–high resolution mass spectrometry (Orbitrap). Optimizing of SBSE conditions using 76 test priority atmospheric pollutants allowed detection limits to be achieved for most non-polar and weakly polar semi-volatile compounds at the levels ranging from 0.01 to 1 ng L^–1. The method demonstrated the ability of detecting 62 analytes and achieving the highly sensitive determination of 32 analytes, with low labor costs using a minimum amount of sample (100 g). The SBSE-TD-GC–HRMS method for snow analysis was developed and validated. Tests on real samples from the Novaya Zemlya and Franz Josef Land archipelagos detected 29 pollutants from various classes, including polycyclic aromatic hydrocarbons, phenols, phthalates, nitro- and chloro-organic compounds, and their derivatives, with concentrations ranging from 0.1 to 50 ng kg^–1.

The oxidation of hydroquinone with hydrogen peroxide in the presence of catalytic amounts of FeSO₄ results in complex mixtures of oligomers. The average composition of these products is determined by the molar ratio of reagents and varies from (C₆H₄O₄)_n at the hydroquinone to hydrogen peroxide ratio 1 : 3 to (C₆H₄O₆)_n at the ratio 1 : 5. A characteristic feature of MALDI mass spectra for polymers is the periodicity of signals. However, no such periodicity is observed for the products of hydroquinone oxidation within the m/z range <1000 Da, indicating the absence of fixed sequences of structural fragments. This unique feature arises from the variable ratios and irregular positions of polyhydroxyphenylene and polyhydroxybenzoquinone fragments. Additionally, several factors contribute to the lack of mass-spectral periodicity, namely, the potential formation of peroxides, the presence of stable hydrates, various types of linkages, and possible interactions between hydroxylated phenylene and benzoquinone fragments. In contrast, for m/z values >1000 Da, MALDI mass spectra exhibit periodicity with a mass difference of Δ(m/z) = 74. This value likely corresponds to the fragment C₂H₂O₃, which is neither a hydroquinone nor a benzoquinone structural unit. Taking into account that an equal Δ(m/z) value is observed for fragment ions in the EI mass spectrum of tetrahydroxy-p-benzoquinone, this gives indirect evidence for the presence of polyhydroxybenzoquinone fragments within the oligomers. A key issue regarding the structure of hydroquinone oxidation products is the type of linkages between the polyhydroxyphenylene and/or polyhydroxybenzoquinone units, which could involve C–C or C–O–C bonds (or both). The available spectral data do not resolve this issue conclusively. However, the presence of a sample of the composition (C₆H₄O₆)_n, in which each unit contains six oxygen atoms, suggests that at least one oxygen atom forms a bond between the units, indicating a C–O–C connection. Overall, the unique nature of oligomeric products of hydroquinone oxidation explains their high structural variability and redox properties, which likely contribute to their unique pharmacological characteristics.

Kraft (sulfate) lignin is a large-scale by-product of the pulp and paper industry and a promising renewable raw material for the production of a wide range of chemicals and materials with high added value. One of the main directions of valorization of technical lignin is conversion into low-molecular-weight phenolic products using various depolymerization methods. To solve the problems of operational control of ongoing processes and the molecular level characterization of complex mixtures of formed low-molecular-weight compounds, this study proposes the use of atmospheric pressure photoionization high-resolution mass spectrometry in combination with visualizing the resulting data sets based on elemental ratios (van Krevelen diagrams) and Kendrick mass defects. Using this methodology, the kraft lignin depolymerization products formed in a supercritical isopropanol medium were characterized, and the effect of additives of nitrogen-containing catalysts (hydroxylamine and diethylamine) on the ongoing processes and the composition of the resulting products were studied. The leading role of reduction processes in the transformation of lignin oligomers under the action of isopropanol was shown, and the characteristic differences between the products obtained in the absence and with the addition of nitrogen-containing catalysts were revealed.

This work is devoted to the analysis of the results obtained during the separation of the mass spectra of apamin and its complex after the deutero-hydrogen substitution of these molecules when leaving the electrospray ion source. The goal of the work was to determine the origin of the structural components identified in apamin and its complex. The separation method assumes that the substitution of labile hydrogen atoms with deuterium ones occurs independently, while charge carriers are retained independently too by various amino acid residues of a polypeptide with a specific structural form. This method also includes an indirect assessment of the contribution of natural isotopes to the measured data, without requiring knowledge of the elemental composition or other structural features of the biomolecule under study. Previously, we performed similar calculations by directly accounting for the contribution of natural isotopes. For apamin electrosprayed ions, after introducing a gas flow of ND₃ into the molecular ion reactor of the mass spectrometer, three main components were identified, with contributions of approximately 57, 39, and 5%. The new method yielded three components with similar contributions, which was anticipated. More noteworthy, though, and particularly relevant in various data collection and computation scenarios, is the paper’s description of the reliable identification of minor components with contributions of no more than 4%. Some of these components have almost identical formally found H/D distributions across different charges, remaining within or near the natural isotopic distribution range of apamin. This suggests that these components correspond to the structures of apamin ions and their complex in a solution without labile hydrogen atoms, such as during the formation of hydrogen bonds, or with a relatively small number of D-substituted hydrogen atoms, where protons carrying an ion charge do not participate in the exchange, particularly when more than two ion charges are present. Such a result was not anticipated in advance. This paper demonstrates the probable presence of three forms of apamin ions and its complex, each with distinct capacities for H/D exchange directly in the analyzed apamin solution. The limitations of the developed approach in decreasing the number of sites accepted to be involved in the exchange of hydrogen for deuterium, and in retaining charge carriers, are also discussed.