2017 Fiscal Year Research-status Report
Energy-resolved tandem mass spectrometry for in-situ differentiation and identification of isomers
| Project/Area Number |
17K08262
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| Research Institution | Institute of Physical and Chemical Research |
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Principal Investigator |
中村 健道 国立研究開発法人理化学研究所, 環境資源科学研究センター, 専任研究員 (10360611)
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| Project Period (FY) |
2017-04-01 – 2020-03-31
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| Keywords | Energy-resolved MS/MS / Isomer Differentiation / CID / Ion Mobility / Collision Cross Section |
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| Outline of Annual Research Achievements |
Identification of isomeric organic molecules would become a big challenge for mass spectrometry with ambient in situ setup where no chromatography is available. We explore a viable generic strategy for differentiation of small isomeric metabolites in such situations; the potentials and limitations of widely available low-energy CID MS/MS and ion mobility analysis have been evaluated by using a set of isomeric C4 amino acids as a model.
Six C4 amino acids, i.e. 2-aminobutyric acid (2-ABA), 3-aminobutyric acid, 4-aminobutyric acid, 2-aminoisobutyric acid (2-AIBA), 3-aminoisobutyric acid, and N,N-dimethylglycine (DMG) are one of the simplest examples of small isomers. Among them, 2-ABA, 2-AIBA, and DMG gave similar CID spectra that were attributable to common major fragmentation pathway, loss of 46 Da (CO and H2O) from protonated molecules (m/z 104) to form m/z 58. Obviously the spectral patters were condition dependent; however, the difference in energy requirement to give m/z 58 from each isomer could be clearly visualized in breakdown diagrams obtained by ER MS/MS experiments. On the other hand, ion mobility analysis was shown to have limited discrimination power on these isomers. The predicted collision cross section (CCS) of 2-AIBA protonated molecule was roughly 2% larger than those of the other isomers whereas the predicted CCS of m/z 58 from 2-ABA was 3% larger than the CCS of m/z 58 from others.
The results show potentials and limitations of the ER-MS/MS-based integrated approach for differentiation and identification of small isomeric organic molecules.
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| Current Status of Research Progress |
Current Status of Research Progress
3: Progress in research has been slightly delayed.
Reason
In order to establish the environment for model experiments, additional gas plumbing for collision gas switching was fabricated and He, Ne, and N2 become available in addition to standard Ar on the main experimental platform, Synapt G2 instrument. Given the primary experimental platform and workflow on that have been established, we've explored viable workflow for computational studies aiming compilation of modeling data. For small molecules, it is not uncommon that just one or two primary fragmentation channels are available under a low-energy CID condition. Modeling of precursor ions and transition states in such cases open the way to estimation of energy barrier that can be correlated to collision energy. It turned out; however, multiple precursor ion structures may exist even for small molecules like C4 amino acids. Therefore, we decided to incorporate CCS in the modeling study when necessary. This caused slight delay in the accumulation of metabolites data last year.
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| Strategy for Future Research Activity |
We continue to refine the workflow for data processing and computational studies. In the meantime, compilation of experimental data will be extended to a larger number of metabolites. Regarding the computational part of the study, we start modeling and evaluation of transition-state energy barriers from the smallest metabolites (e.g., molecular mass around 100). In the meantime, in parallel to acquisition of experimental data for metabolites, we acquire data for standardization of energy axis by using thermometer ions on each experimental platform and conditions. By using those experimental data, we explore practical ways for standardize energy axis on different conditions/platforms to establish platform independent strategy for data accumulation and comparison.
There is a little concern, which has not been anticipated in the original research plan arise during some cross-platform experimental work. Some machine which would be used for the ER-MS/MS acquisition may exhibit strong mass discrimination in lower m/z range, say m/z 20 to 150, or so. Since such mass discrimination would compromise cross-platform conversion of energy axis by using small thermometer ions, close examination of possible mass discrimination and method development for y-axis standardization will be carried out if necessary.
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| Causes of Carryover |
Some hardware modifications and purchase of additional software license were planned and budgeted for the first year. Fortunately, some parts taken from an existing (decommissioning) instrument could be reused for the hardware modifications including plumbing of additional gas line for collision gas switching. In addition, it turned out that calculation of theoretical collision cross sections of ions of interests would help evaluation of modeled ion structures. Therefore, a minor change in the order of experiments has been made and calculation of CCS was carried out in parallel to the modeling study. As a result, the number of structure modeling carried out in the first year became fewer than that in the original plan and purchase of the additional software license have been postponed.
As we plan to continue the effort for acquisition and compilation of the experimental ER-MS/MS data and theoretical data in the fiscal year 2018 onward, surplus funds is planned to be used for purchase of additional software, hardware and chemicals for data compilation.
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Research Products
(3 results)
