Mass spectrometry最新文献

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.

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.

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.

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.

We report a robotic sheath-flow probe electrospray ionization mass spectrometry system with a new probe design and automated positioning capabilities for pinpoint ambient mass spectrometry. The system integrates a 3-axis Cartesian robot with two cameras: a fixed global camera for coarse positioning and a movable local camera for fine alignment, enabling users to designate sampling spots by mouse-clicking on live images displayed on the graphical user interface. A microcontroller is used for voltage control, current monitoring, and the detection of probe-sample contact. Sampling, transfer, ionization, and cleaning are fully automated under computer control, and the sheath liquid is supplied by a programmable syringe pump to maintain a stable flow rate. The system successfully analyzed aqueous standards, beverages, and water-rich soft materials such as jelly and fruit slices, yielding stable ion signals with negligible carry-over between measurements.

The molecular ion M^+· was observed when the liquid sample of butyrophenone was supplied using atmospheric pressure corona discharge (APCD). In contrast, the vapor supply resulted in the formation of the protonated molecule [M+H]⁺. The mass spectrum obtained with the liquid supply showed two distinctive fragment ions at m/z 105 and 120, resulting from α-cleavage and McLafferty rearrangement (McLR), respectively. The APCD spectrum showed peaks of M^+· and the characteristic two fragment ions that were the same as the field ionization mass spectra of butyrophenone as reported by Chait et al. and Beckey et al. The formation of the molecular and fragment ions strongly indicated that high-electric field tunnel ionization (HEFTI) occurs by the HEF strength exceeding 10⁸ V/m at the tip of the corona needle in APCD. The charge and spin density distributions of the molecular and fragment ions were analyzed by quantum chemical calculations using time-dependent density functional theory (TDDFT) and natural bond orbital (NBO) analysis.

A method for the rapid determination of α-tocopherol (α-T) and its oxidative products in plant tissue has been developed using supercritical fluid extraction (SFE) coupled with supercritical fluid chromatography (SFC) and medium vacuum chemical ionization (MVCI) with tandem mass spectrometry. The method is designed to study changes in levels for α-T and its oxidative products in plant cells during photosynthesis, aiming to observe the light response curves. α-T oxidation is a non-enzymatic self-defense mechanism in plant cells. Unlike enzyme-involved reactions, it cannot be stopped, so the oxidation continues in crude extracts even after extraction. Therefore, a real-time in-situ method is essential for tracking the light response curves. To optimize the selective reaction monitoring method, the reaction mixture of α-T and singlet oxygen (¹O₂), generated by rose Bengal under light illumination, was used as the source of oxidative products. The relative abundance changes in α-tocopherylquinone and 8a-hydroperoxy tocopherone in Pisum sativum L. (Pea) leaves under excessive light illumination have been preliminarily analyzed as part of the light response curve study. The method archives a throughput of 10-15 minutes for analyzing duplicate leaf samples. This process includes cutting off the leaf, sectioning it, placing the sample in a frozen SFE vessel, and conducting SFE/SFC analysis. Consequently, the average throughput is approximately 5-7 minutes per sample.

We developed a rapid, accurate, and quantitative method for analyzing glucosinolates (GSLs) by combining column-free liquid chromatography (LC) with direct-infusion mass spectrometry (MS). Conventional methods for analyzing GSLs take a long time (20-50 min per sample) to perform compound separation on an LC column. We achieved a shortened analysis time of 30 seconds per sample using a direct-infusion method. Samples were continuously injected by a pump and autosampler on an LC system directly into the MS. Orbitrap MS detected 11 types of GSLs in the extracts of turnip hypocotyls. The calibration curve of a GSL standard showed a linear response over a 6-digit concentration range from 1 nM to 1 mM. In addition, no decrease in the detected intensity of GSL ions in 100 continuous analyses of turnip extracts was observed. This method may be applied for rapid analysis of GSLs and other health-functional or bioactive compounds.