Mass spectrometry最新文献

[This corrects the article DOI: 10.5702/massspectrometry.A0145.].

In matrix-assisted laser desorption ionization mass spectrometry, a suitable matrix is often selected for the analyte. Herein, we first developed a novel matrix, alkylated hydroxychalcone (AHC), which has properties similar to alkylated trihydroxyacetophenone (ATHAP) (Anal. Chem., 85: 9444-9448, 2013) developed as a matrix for hydrophobic peptides. However, the sample-to-sample reproducibility was low because of the poor crystallinity of AHC. The crystalline morphology of AHC changed when AHC/2,5-dihydroxybenzoic acid (DHB) was used as a binary matrix. As a result, the use of AHC/DHB improved sample-to-sample reproducibility and increased sensitivity for hydrophobic peptides. Mass imaging indicated that these results were due to an increased number of sweet spots wherein the analytes were detected as ion peaks, in a matrix/analyte crystal spot.

The appearance of the characteristic peak of the hydride-eliminated molecule [M-H]⁺ under a positive ion mode (positive) fast atom bombardment (FAB) ionization condition and liquid-assisted secondary ion mass spectrometry (LSIMS) conditions is known for some compounds and the mechanism of its formation has been investigated. In this study, we investigated the formation mechanism of the hydride-eliminated molecule [M-H]⁺ from 4-substituted-1-(methoxymethyl)benzene under a positive FAB ionization condition. The mass spectra of 4-methoxy-1-(methoxymethyl)benzene (1), 4-methoxy-1-(methoxymethyl-d ₂-)benzene (1-d ₂), and 4-methoxy-1-(methoxymethyl-d ₃)benzene (1-d ₃) were measured under the positive FAB conditions. [M-H]⁺ was observed for 1 and 1-d ₃, and [M-D]⁺ for 1-d ₂, indicating that the site of hydride elimination was the methylene of the 1-(methoxymethyl) moiety. Since [M-H]⁺ was hardly observed under the conditions of positive electron ionization and positive chemical ionization in the gas phase, the hydride elimination is a reaction specific to positive FAB ionization. To examine the contribution of the 4-substituent to the hydride elimination reaction, the mass spectra of (methoxymethyl)benzene (2) and 4-nitro-1-(methoxymethyl)benzene (3) were measured using the positive FAB. The ordering of the relative peak intensity of [M-H]⁺ for [M+H]⁺ in the FAB mass spectra was 1 > 2 > 3, and the results suggest that the electron-donating power of the substituents is an important factor in the formation of [M-H]⁺.

Scorpion venoms contain a variety of peptides that exhibit toxicity toward insects or mammals by acting on ion channels. We previously isolated four insecticidal peptides (Bl-1, Bl-2, Bl-3, and Bl-4) from the venom of Buthacus leptochelys. Among these, the complete amino acid sequence of Bl-1 was determined, whereas only N-terminal partial sequences were obtained for the others. In the present study, we determined the complete sequence of Bl-3 through de novo sequencing of enzymatically digested fragments. The discrimination between Leu and Ile was achieved based on side-chain fragmentation observed under high-energy collision-induced dissociation conditions. Bl-3 was identified as a 65-residue peptide containing four disulfide bonds. During the sequencing analysis, deamidation of the Asn residue at position 30 was observed, which is likely to have occurred after the purification step. Sequence comparison revealed that Bl-3 shares high similarity with α-toxins that act on sodium channels and exhibit nonselective toxicity toward both insects and mammals. These findings suggest that Bl-3 is likely to exert nonselective toxicity through a mechanism similar to that of α-toxins.

Chlorogenic acids, esters of hydroxycinnamic acids with quinic acid, are abundant plant metabolites with over 400 known derivatives. Due to the limited availability of commercial standards, mass spectrometry fragmentation data are essential for structural identification. We acquired fragmentation spectra of six chlorogenic acid homologs in both positive- and negative-ion modes using direct infusion mass spectrometry. In positive-ion mode, sodiated molecules provided additional structural information in addition to that from protonated molecules, although the difference in substitution positions had minimal effects on fragmentation patterns. In negative-ion mode, fragmentation differed significantly depending on the acyl group substitution position on the quinic acid moiety, enabling isomer differentiation. This positional selectivity in negative-ion fragmentation parallels previous observations with anhydrous monosaccharides and oligosaccharides. Comparative analysis with maltotriose and β-glucan trisaccharides demonstrated that negative-ion mode fragmentation yields more diagnostic ring cleavage information for structural characterization. This study also emphasizes that the adoption of unambiguous IUPAC (International Union of Pure and Applied Chemistry)-based nomenclature is fundamental to ensuring the reliability of mass spectra databases.

Pesticide residues in water contamination represent a significant public and political issue due to their harmful effects on the environment, biodiversity, and human health, even at low concentrations. Pesticides are chemically heterogeneous, covering a wide range of LogK _o/w values. Therefore, developing sensitive methods to detect a broad spectrum of hazardous chemicals in aqueous matrices is challenging. Gas and liquid chromatography/high-performance liquid chromatography-mass spectrometry (GC/HPLC-MS) are established tools but typically require pre-concentration steps. Stir bar sorptive extraction (SBSE) is a green, simple, automatable, and HPLC-compatible technique. This study presents a multi-residue method for determining 131 pesticides in mineral water using SBSE followed by HPLC-tandem MS. The selected pesticides, from various chemical classes, were evaluated in fortified ultra-pure and mineral water samples. The method demonstrated excellent sensitivity, with lower limits of quantification ranging from 20 to 50 ng/L for all analytes, enabling detection at trace levels. Selectivity was high (SEL% <20%), and reproducibility was confirmed with RSD% values below 20%. Intra- and interday precision tests revealed RSD% values from 0.23% to 19.81%. Trueness was validated with BIAS% below 20% at all concentrations. Uncertainty values were acceptable, with U% ranging from 1.44% to 49.24%. This SBSE-HPLC-tandem MS method is a robust, efficient, and reliable alternative to traditional approaches for routine monitoring of pesticide residues in drinking water, with quantification limits below regulatory requirements. It offers a suitable tool for public health applications, ensuring reliable pesticide detection in complex water matrices.

Temperature effects on differentiating d-amino acids using the molecular recognition ability of l-tryptophan were investigated by ultraviolet photodissociation spectroscopy in the gas phase. Temperature-dependent ultraviolet photodissociation spectra of hydrogen-bonded protonated clusters of l-tryptophan with arginine, lysine, asparagine, and glutamine enantiomers, generated via electrospray ionization, were obtained using a tandem mass spectrometer containing a variable-temperature ion trap. The spectra at 8 K differed between the amino acids and their enantiomers, indicating that l-tryptophan recognized amino acids and their enantiomers through its hydrogen bonding and electronic structure. The spectral differences observed at 100 K were significantly smaller than those at 8 K. Hot bands and entropic effects at liquid nitrogen cooling temperature prevented the differentiation of d-amino acids. To avoid these contributions in the spectra, cooling of the hydrogen-bonded clusters using a cryogenic refrigerator was necessary to distinguish amino acids and their enantiomers based on the molecular recognition of l-tryptophan.

The ion coalescence phenomenon complicates the evaluation of the effective resolution of Fourier-transform mass spectrometers. We propose an approach for confirming the resolution of an electron ionization Fourier-transform mass spectrometer using pairs of organic substances identified by automatically generated formula differences. The proposed method is compared with the search for organic substances in the National Institute of Standards and Technology (NIST) database. Under the given conditions of the mass spectrometer resolution range up to 45000-50000 at 100 m/z, 166 pairs of suitable compounds were found using the proposed method, while a search in the NIST database yielded only 88 pairs of compounds. This enabled the selection of six pairs of organic compounds that were most suitable for confirming the resolution of the high-resolution mass spectrometer using molecular ion peaks, and four pairs of compounds that allowed the resolution to be confirmed using fragment ion peaks. The resolution of the Fourier-transform mass spectrometer designed for gas analysis was experimentally evaluated by analyzing the spectra of a mixture of organic compounds selected using the proposed method.

I investigated the tandem mass spectrometry (MS/MS) fragmentation of ginsenoside glycosides using matrix-assisted laser desorption/ionization MS for ginsenosides Rg1, Rh1, Rb1, and Rb3, focusing on their sodium adduct molecules [M+Na]⁺. The glycosidic linkage at the C-20 position cleaved more readily than those at C-3 and C-6. These glycosides fragmented on their glucosyl acceptor sides, exhibiting C- and Z-type fragmentation, although generally B/Y-type fragment ions are dominant in MS/MS spectra of neutral oligosaccharides. These results suggest that, due to the hydrophobic triterpene skeleton of the aglycone, sodium cations cannot effectively coordinate with the aglycone moiety.

Polyethylene terephthalate (PET) is widely used across various industries owing to its versatility and favorable properties, including application in beverage bottles, food containers, textile fibers, engineering resins, films, and sheets. However, polymer materials are susceptible to degradation from factors such as light, oxygen, and heat. Therefore, it is crucial to understand the structural changes that occur during degradation and the extent of these changes. This report investigates the structural alterations in PET films resulting from ultraviolet (UV) irradiation utilizing pyrolysis-gas chromatography time-of-flight mass spectrometry (Py-GC-TOFMS) and matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOFMS). Using the reactive Py-GC-TOFMS, we estimated the composition of the pyrolysis products resulting from UV degradation through electron ionization, soft ionization, and exact mass measurements. Additionally, artificial intelligence (AI)-based structure analysis was performed to evaluate these compounds' structures. Notably, most degradation products were not found in the National Institute of Standards and Technology database, underscoring the effectiveness of our approach. Using MALDI-TOFMS analysis, we determine the changes in the end groups before and after UV irradiation. This analysis confirmed the generation of a series of carboxylic acid end groups as a result of degradation, a polymer series not detected by reactive pyrolysis GC-MS. We also explored degradation in the depth direction, demonstrating that degradation progresses gradually to depths of several micrometers. Our findings highlight the importance of employing mass spectrometry techniques for a comprehensive analysis of polymer degradation.