Mass Spectrometry
Online ISSN : 2186-5116
Print ISSN : 2187-137X
ISSN-L : 2186-5116
Volume 8 , Issue 1
Showing 1-7 articles out of 7 articles from the selected issue
  • Hisao Nakata
    2019 Volume 8 Issue 1 Pages A0074
    Published: November 25, 2019
    Released: November 25, 2019

    Typical modes of bond cleavages of organic compounds in mass spectrometry are briefly summarized. Although these fragmentation rules can be quite useful for interpreting mass spectra of simple compounds, application to structurally complex molecules that contain multiple hetero atoms such as nitrogen or oxygen becomes increasingly difficult, because the exact location of an unpaired electron or positive or negative charges becomes obscure in precursor ions.

    About a decade ago, we proposed “a rule of mass shift,” which correctly predicts the m/z for observed peaks corresponding to singly charged even-electron fragment ions. The basis of the rule postulates that ions observed as peaks in an ordinary mass spectrum should be sufficiently stable to survive during the flight path in a mass spectrometer.

    The important recognition is that each atom in a stable ion should be in an ordinary valence state, and no free valence should be allowed. Therefore, if the cleavage of a bond leads to an ion with an unstable structure, some structural changes must take place in order for the ion to be observed in the mass spectrum. Such structural changes can be the addition of hydrogen atom(s) and/or a proton for positive ions, and the addition of a hydrogen atom and/or the elimination of two hydrogen atoms in the case of negative ions. These required structural changes in each case are schematically depicted and discussed in detail.

    Two typical examples are shown, in which m/z’s of the observed peaks are correctly predicted. The scope and limitations, as well as the significance of the rule for analyzing fragmentations in organic mass spectrometry are also discussed.

    Editor’s picks

  • MassBank Database Committee, The Mass Spectrometry Society of Japan
    2019 Volume 8 Issue 1 Pages A0076
    Published: October 25, 2019
    Released: October 25, 2019
    Editor’s picks

  • Britt S. R. Claes, Emi Takeo, Eiichiro Fukusaki, Shuichi Shimma, Ron M ...
    2019 Volume 8 Issue 1 Pages A0078
    Published: December 27, 2019
    Released: December 28, 2019
    [Advance publication] Released: November 06, 2019
    Supplementary material

    Mass spectrometry imaging is an imaging technology that allows the localization and identification of molecules on (biological) sample surfaces. Obtaining the localization of a compound in tissue is of great value in biological research. Yet, the identification of compounds remains a challenge. Mass spectrometry alone, even with high-mass resolution, cannot always distinguish between the subtle structural differences of isomeric compounds. This review discusses recent advances in mass spectrometry imaging of lipids, steroid hormones, amino acids and proteins that allow imaging with isomeric resolution. These improvements in detailed identification can give new insights into the local biological activity of isomers.

Original Article
  • Jiao Wang, Kuniyuki Kano, Daisuke Saigusa, Junken Aoki
    2019 Volume 8 Issue 1 Pages A0072
    Published: February 14, 2019
    Released: February 14, 2019

    Sphingosine-1-phosphate (S1P) acts as an extracellular signaling molecule with diverse biological functions. Tissues appear to have an S1P gradient, which is functionally relevant in the biological significance of S1P, although its existence has not been measured directly. Here, we report a highly sensitive method to determine the distribution of S1P, using a column-switching LC-MS/MS system combined with laser microdissection (LMD). Column switching using narrow core Capcell Pak C18 analytical and trap columns with 0.3 mm inner diameter improved the performance of the LC-MS/MS system. The calibration curve of S1P showed good linearity (r>0.999) over the range of 0.05–10 nM (1–200 fmol/injection). The accuracy of the method was confirmed by measuring S1P-spiked laser microdissected mice tissue sections. To evaluate our S1P analytical method, we quantified S1P extracted from micro-dissected mouse brain and spleen. These results show that this method can measure low S1P concentrations and determine S1P distribution in tissue microenvironments.

  • Nobuyuki Okahashi, Shuichi Kawana, Junko Iida, Hiroshi Shimizu, Fumio ...
    2019 Volume 8 Issue 1 Pages A0073
    Published: August 30, 2019
    Released: August 30, 2019
    [Advance publication] Released: August 01, 2019
    Supplementary material

    Isotope labeling measurements using mass spectrometry can provide informative insights on the metabolic systems of various organisms. The detailed identification of carbon positions included in the fragment ions of dicarboxylic and tricarboxylic acids in central carbon metabolism is needed for precise interpretation of the metabolic states. In this study, fragment ions containing the carbon backbone cleavage of dicarboxylic and tricarboxylic in the Krebs cycle were investigated by using gas chromatography (GC)-electron ionization (EI)-MS and GC-EI-MS/MS. The positions of decarboxylation in the dicarboxylic and tricarboxylic acids were successfully identified by analyses using position-specific 13C-labeled standards prepared by in vitro enzymatic reactions. For example, carboxyl groups of C1 and C6 of trimethylsilyl (TMS)- and tert-butyldimethylsilyl (TBDMS)-derivatized malic and citric acids were primarily cleaved by EI. MS/MS analyses were also performed, and fragment ions of TBDMS-citric and α-ketoglutaric acids (αKG) with the loss of two carboxyl groups in collision-induced dissociation (CID) were observed.

  • Kanako Sekimoto, Motoshi Sakakura, Hiroshi Hike, Takatomo Kawamukai, T ...
    2019 Volume 8 Issue 1 Pages A0075
    Published: October 25, 2019
    Released: October 25, 2019

    Herein, a dark-current discharge state created by combining argon flow with a needle electrode in ambient air is described that has an ionization efficiency and mechanism comparable to those of conventional helium direct analysis in real time (DART), without requiring dopants and DART glow discharge. Using this method, polar compounds such as α-amino acids were ionized in the dark-current argon discharge via (de)protonation, molecular anion formation, fragmentation, (de)protonation with the attachment of oxygen, deprotonation with hydrogen loss and negative ion attachment. In contrast, nonpolar compounds (e.g., n-alkanes) were detected as positive ions via hydride abstraction and oxidation. Major background ions observed were H3O+(H2O)n, O2·+, O2·−(H2O)n and CO3·−. These results indicate that the present dark-current discharge efficiently generates resonance-state argon with an internal energy of ∼14.2 eV, higher than that of the well-known metastable state (∼11.6 eV). It is therefore suggested that ionization reactions occurring there can be attributed to the Penning ionization of atmospheric H2O and O2 by resonance-state argon, analogous to helium DART.

  • Ami Kageyama (Kaneshima), Akira Motoyama, Mitsuo Takayama
    2019 Volume 8 Issue 1 Pages A0077
    Published: November 30, 2019
    Released: November 30, 2019
    [Advance publication] Released: October 10, 2019

    The influence of solvent composition and surface tension on the signal intensity of deprotonated molecules [M−H] in electrospray ionization mass spectrometry (ESI MS) was evaluated using alanine (Ala), threonine (Thr) and phenylalanine (Phe), which have differing levels of hydrophobicity. The surface tension of the ESI solution was varied by changing the ratio of the organic solvents methanol (MeOH) and acetonitrile (MeCN) in water (H2O). In ESI MS, the signal intensity of all the amino acids was increased with decreasing surface tension for the two solutions, H2O/MeOH and H2O/MeCN. The use of H2O/MeCN was more favorable for achieving a strong signal for the analytes compared to H2O/MeOH. The smaller vaporization enthalpy of MeCN compared to MeOH was proposed as one of the most plausible explanation for this. The order of the signal intensity of amino acids was Phe>Thr>Ala, the same order as their hydrophobicity. It can be practically concluded that the use of solutions with lower surface tensions and lower vaporization enthalpies would result in higher signal intensities in ESI MS.