Mass spectrometry最新文献

Ambient mass spectrometry (AMS) enables real-time analysis without sample preparation, yet atmospheric pressure corona discharge ionization (APCI)-like ion sources can oxidize analytes in-source, obscuring spectral interpretation. We investigated α-pinene using atmospheric pressure corona discharge ionization mass spectrometry (APCDI-MS; one of APCI-like AMS) and, when needed, coupled gas chromatography (GC) to separate pre-existing oxidation products from species formed inside the ion source. By comparing adduct formation and product-ion patterns, we show that oxygenated ions from primary (pre-source) and secondary (in-source) oxidation display similar ion formation behavior, notably ready NH₄ ⁺-adduct formation, whereas fragment ions rarely form NH₄ ⁺ adducts. GC-based characterization of in-source oxidation provides features that assist interpretation of APCI-like AMS spectra acquired without chromatography.

Information on candidate biomarker metabolites identified in recent disease biomarker discovery research is expected to play a key role in the future of personalized and precision medicine. Liquid chromatography mass spectrometry (LC/MS) is a powerful method for metabolomic analysis due to its comprehensive coverage and high detection sensitivity. However, the suitability of LC/MS methods for the identification and quantification of hydrophilic metabolites remains debatable. Here, we evaluated the performance of LC/MS methods combining four types of LC [hydrophilic interaction chromatography (HILIC), ion chromatography (IC) with an anion-exchange (AEX) column (AEX-IC), reversed-phase LC (RPLC) with a pentafluorophenylpropyl (PFPP) column (PFPP-RPLC), and unified-hydrophilic interaction AEX LC (unified-HILIC/AEX)], using the same Orbitrap mass spectrometer, with the aim of integrating future human plasma metabolome data. First, we conducted a qualitative performance evaluation of four LC/MS methods, HILIC/MS, AEX-IC/MS, PFPP-RPLC/MS, and unified-HILIC/AEX/MS, by analyzing 511 hydrophilic metabolite standards and NIST Standard Reference Material (SRM) 1950 (Metabolites in Frozen Human Plasma). The evaluation focused on metabolome coverage, peak width, sensitivity, and separation performance of isomers. Next, we thoroughly evaluated the quantitative performance of the four analytical methods for 63 hydrophilic metabolites in SRM 1950 using a stable isotope-labeled internal standard (SILIS) mixture derived from ¹³C-labeled Escherichia coli extracts. Furthermore, we successfully estimated new concentration values for 29 metabolites without certified values in SRM 1950 using quantitative data from the four LC/MS methods. We objectively evaluated the performance of the four LC/MS methods and demonstrated that absolute quantification using SILIS is effective for integrating hydrophilic metabolite data in metabolomics.

Carnitine (CAR) is an essential compound for animals and plays several physiological roles related to energy production. These functions are possessed by only the l-forms, while the d-forms are known to inhibit the uptake of the l-forms, thus causing a CAR deficiency. Therefore, it is required to determine dl-CAR in various samples such as foods, supplements, and drugs by an enantioselective analytical method. In this study, we developed a chiral liquid chromatography-tandem mass spectrometry (LC-MS/MS) method using derivatization. The CAR enantiomers derivatized with 4-nitrophenylhydrazine were successfully separated on a CHIRALPAK ZWIX (-) column (resolution = 1.64) and detected with high sensitivity and selectivity by MS/MS. The developed method was well validated and applied to the analysis of eight kinds of foods and an l-CAR supplement. Only the l-forms were found in all the tested food samples and were abundant in meat, milk, and yogurt. The system was also applicable for a supplement sample and could detect the d-CAR contamination at the 2.5% level, suggesting its potential for use in the purity test of CAR preparations.

We have developed a new analytical technique for the detection of volatile organic compounds (VOCs) using inductively coupled plasma tandem mass spectrometry (ICP-MS/MS). Eight VOCs of various polarities (acetic acid, 2-butanone, pyridine, 2-methylfuran, ethylene, benzene, toluene, and limonene) were introduced into the collision/reaction cell (CRC) of the ICP-MS/MS, bypassing the ICP ion source. This approach enabled a softer ionization than the typical ICP, allowing the detection of the molecules in their intact form. In this study, to explore the potential of cationization as a soft ionization approach, the interaction of the above VOCs with various elements (i.e., Li, Be, Na, Mg, V, Co, Ni, Cu, Zn, As, Rb, Sr, Y, Ru, Pd, Ag, Cd, Cs, Ba, Pt, and Hg) was investigated. The production ratio of cation adducts was evaluated using benzene as a model compound by monitoring [C₆H₆ + E]⁺/E⁺ values (E represents each element). The resulting [C₆H₆ + E]⁺/E⁺ showed a wide variation, covering ranges from 0.0001% to 1%, and the elements with ionization energies between 650 and 900 kJ mol^-1 exhibited the highest [C₆H₆ + E]⁺/E⁺ values. The data obtained here revealed that several elements, including Co, Ni, Cu, Ru, Pd, and Ag, can be suitable elements for cationization. The reduction in fragmentation resulted in easier detection of specific compounds based on their m/z values. To demonstrate the practicality of the present technique, several VOCs released from coffee beans through laser-induced evaporation were monitored. The data obtained here envisage a possibility that the detection of VOCs through cationization achieved in ICP-MS/MS can become an effective choice as a rapid analytical tool for VOCs in solid samples.

Instrumental dispersion in the ion source can severely distort fast chromatographic peaks in supercritical fluid chromatography (SFC)-mass spectrometry (MS). Despite this importance, the dispersion characteristics specific to medium-vacuum chemical ionization (MVCI) sources have not been quantitatively investigated. In this work, we combine targeted experiments with established computational tools-computational fluid dynamics (CFD) and electrostatic field simulation-to characterize ion transport in the MVCI flow tube. Arrival profiles of vitamin K₁ (VK₁) ions monitored by selected ion monitoring consistently showed a reproducible two-component structure consisting of an early narrow bandwidth ion packet followed by a delayed shoulder. CFD calculations reproduce this tailing peak profile, and electrostatic modeling further revealed that applying the same potential to the MVCI flow tube and inner cylinder generates lateral potential walls that inhibit long-residence-time ions from entering the skimmer. Introducing an appropriate potential difference between the MVCI inner cylinder and the skimmer orifice isolates the MVCI flow field from the ion guide region and suppresses long residence-time trajectories, which narrows the VK₁ peak width by more than threefold and restores the intrinsic column efficiency of a sub-2-μm SFC column (from the theoretical plate (N) = 3120 to 12079). These results provide a practical diagnostic and mitigation framework for ion-source derived dispersion in MVCI, demonstrating that modest electrostatic confinement is effective in maintaining chromatographic fidelity in high-speed SFC-MVCI-MS. The present work also highlights the utility of CFD for evaluating proposed MVCI flow designs and their influence on peak dispersion.

The stop-and-go extraction tip (StageTip) is widely used for peptide purification in bottom-up proteomics, yet the original 3M Empore disk is no longer available, prompting the need to evaluate current alternatives. Two types of commercially available poly(styrene-divinylbenzene) (SDB)-containing polytetrafluoroethylene (PTFE) disks were used to fabricate StageTips. Desalting was performed on 500 and 20 ng of HeLa tryptic peptides, and the nanoscale liquid chromatography-tandem mass spectrometry results were compared. Both StageTips demonstrated equivalent performance for the 500 ng sample, but for the 20 ng sample, one StageTip identified 1.8 times more peptides, particularly longer and more hydrophobic peptides. Physical characterization and scanning electron microscope imaging of these disks revealed that the high-performing disk contains more PTFE fibers, partially covering the SDB particle surface. This likely prevents hydrophobic peptides from being trapped in small mesopores, improving recovery from low-input samples. These findings demonstrate that disk material properties critically influence performance in trace proteomics.

Light stabilizers are additives that are widely used to improve the lifespan and performance of polymer materials. To develop advanced polymer materials, analytical techniques investigate the degradation mechanisms and distribution of additives in polymers are crucial. Herein, two extraction-ionization methods were used: tapping-mode scanning probe electrospray ionization (t-SPESI) and liquid extraction surface analysis (LESA). The distribution and molecular structure of the photodegradation products were investigated using polyethylene films containing two types of oligomeric hindered amine light stabilizers (o-HALS). In addition, to study the relationship between light irradiation time and the relative amount of photodegradation products, we developed a method for preparing films with multiple photodegradation regions. Mass spectrometry imaging (MSI) using t-SPESI (t-SPESI-MSI) revealed that the signal intensities of HALS decreased with the time of light irradiation, and its degradation products progressively changed. Moreover, tandem mass spectrometry (MS/MS) using LESA (LESA-MS/MS) revealed that degradation products were generated by HALS fragmentation in the polymer film. By integrating these results, we propose multiple and stepwise reactions for the formation of the photodegradation products. Results indicate that the combined use of t-SPESI-MSI and LESA-MS/MS can directly analyze and understand the photodegradation mechanism of o-HALS in polymer materials.

Gold nanorods (AuNRs) possess anisotropic optical and electronic properties, primarily determined by their aspect ratio and surface ligands, which make them attractive for applications in sensing, catalysis, and nanomedicine. While these nanorods are typically stabilized using cetyltrimethylammonium bromide (CTAB) to ensure colloidal dispersion, the cytotoxicity and strong surface affinity of CTAB hinder further surface modification through ligand exchange. In this study, we employed matrix-free laser desorption/ionization time-of-flight mass spectrometry (LDI-TOF-MS) to directly monitor the ligand exchange process on AuNRs. This technique enables the detection of intact CTAB, transient intermediates, and final thiol-bound ligands without requiring chemical derivatization. By correlating mass spectral data with ultraviolet-visible-near-infrared absorption and zeta potential measurements, we elucidate a stepwise ligand exchange mechanism in which CTAB is gradually displaced by a thiol-functionalized phosphorylcholine ligand, facilitated by electrostatic interaction with poly(styrene sulfonate). These findings highlight the utility of matrix-free LDI-TOF-MS as a powerful analytical tool for gaining mechanistic insights into ligand exchange reactions at the nanoscale, particularly in aqueous environments.

[This corrects the article DOI: 10.5702/massspectrometry.A0169.].