Tandem mass spectrometry is an essential data acquisition mode for the analysis of environmental risk substances. This paper describes tandem mass spectrometry (MS/MS) of linear alkyl benzene sulfonate (LAS) and per- and polyfluorinated alkyl substances (PFAS). In MS/MS using negative-ion electrospray ionization, analyses of LAS is designed to use a product ion of m/z 183. Based on consideration of the fragmentation and records from public mass spectra repositories, the product ion was thought to be produced by a two-step reaction. In the analysis of PFAS, characteristic fragmentation different from hydrocarbons and surfactants that could interfere with PFAS were discussed. Analytical results on the environmental risk substances are of social interest, and it is important to have a good understanding of what is taking place in mass spectrometry during quantitative trace analyses.

Native mass spectrometry (native MS) is an analytical technique to determine molecular masses of proteins and protein complexes without crosslinking, which provides the composition and stoichiometry for their structural characterization. We have used mass spectrometry for structural biology, including native MS, to characterize proteins and protein complexes. In this paper, I present a brief overview of native MS. In addition, I highlight the structural characterization of intrinsically disordered protein complexes using ion mobility mass spectrometry and the importance of stoichiometry using native MS including the methodology of native MS in the presence of nonvolatile buffer among my researches.

In the past decade, numerous methodologies in metabolomics have emerged alongside advancements in mass spectrometry (MS) technologies. These metabolomics studies can be categorized into targeted and nontargeted methods, and having trade-offs like as lack information and quantitative reliability issues. The fundamental cause of this trade-off lies in the difficulty of collecting isotopic surrogates due to cost constraints and synthetic technological challenges. One potential solution to this issue is the utilization of stable isotope chemical-tagging (SIC). The method is based on paired SIC, i.e., one to the sample and another to a reference as surrogates. Although the matrix effect can be corrected comprehensively without isotopic surrogates, the impact of tagging efficiencies remains as a problematic issue. This study introduces a novel hole correction method, termed multiSIC (MUSIC), which addresses the recovery of tagging efficiencies to matric effects. A series of diluted MUSIC experiments can establish an internal calibration curve (ICC) with only a standard mixture (targeted function) preparation. Notably, by employing a high-resolution MS system, the ICC slope ratio can be utilized to identify similar metabolites (nontarget function). Following the validation, we applied this approach to blood samples to elucidate the relationship between metabolome fluctuations and exercise loading. Eighty-two metabolites were successfully quantitated in the serum of healthy adults who were habitually exercising. Among these, 13 metabolites were significantly fluctuated after 8-week exercise loading, and glutathione pathway was enriched from the pathway analysis.

Mass spectrometry (MS) is increasingly being utilized to monitor protein structural changes using small sample amounts. These methods involve labeling the protein surface with probes and analyzing the probe-labeled peptides by MS. However, the low specificity of the probing and high complexity of samples make it challenging to detect protein conformational changes on a proteome scale with high sensitivity. In this study, we developed an MS-based structural analysis method that utilizes site-specific probing with phosphate groups, taking advantage of the substrate recognition provided by protein kinases. The phosphate groups serve as enrichment handles, enabling selective extraction and highly sensitive analysis of labeled sites. We found that differences in substrate protein structure were reflected in in vitro phospho-probing efficiency, and based on these differences, we successfully identified protein conformational changes upon RNA digestion.

Long-range proton transfer reactions are essential across various fields. The vehicle mechanism, a type of long-range proton transfer, involves a single molecule carrying a proton. A protonated p-aminobenzoic acid (PABA·H⁺) has either N-protonated or O-protonated isomers (protomers).We have previously demonstrated that intramolecular proton transfer via the vehicle mechanism leads to the formation of the O-protomer in gas-phase bimolecular reactions between the N-protomer of PABA·H⁺ and an NH₃ molecule. Here, we combined cryogenic ion mobility-mass spectrometry (Cryo-IM-MS) with a temperature-variable ion trap to observe and identify reaction intermediates. Cryogenic conditions revealed the reaction intermediate which is confirmed by collision cross-section measurements. This study not only provides insights into the dynamics of proton transfer in non-solvent environments, but also aids in the design of new proton transfer catalysts by elucidating the mechanisms and efficiencies.

Conventional ambient mass spectrometry employs an ionization source and samples placed in an open environment under atmospheric pressure. Attempts were made in our laboratories to develop an underwater ambient mass spectrometry using remote sampling ESI. To mass analyze the chemical compounds originating from samples in an aqueous environment, ethyl acetate, which is immiscible in water was used for liquid extraction at the tip of the sampling probe. This brief report presents the preliminary result using a modified remote sampling ESI prototype for the analysis of raw aqueous solution.