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Volume 52 (2004)
- Issue 6 Pages 307-
- Issue 5 Pages 263-
- Issue 4 Pages 159-
- Issue 3 Pages 93-
- Issue 2 Pages 57-
- Issue 1 Pages 1-
Volume 52, Issue 5
Displaying 1-7 of 7 articles from this issue
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REGULAR PAPER
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Susumu TAJIMA, Daisuke ISHIGURO, Masashi MAMADA, Satoshi NAKAJIMA2004 Volume 52 Issue 5 Pages 263-270
Published: 2004
Released on J-STAGE: October 28, 2005
JOURNAL FREE ACCESSUnimolecular reactions of diethyl malonate cation (CH3CH2OC(=O)CH2C(=O)OCH2CH3+· ; 1+·, Mw : 160) induced by electron ionization, have been investigated by use of mass-analyzed ion kinetic energy (MIKE) spectrometry and D-labeling in conjunction with thermochemistry. In the metastable time window, the molecular ions 1+· lead not only to the formation of the major fragment ions m/z 133 ([M-C2H3]+) through a McLafferty + 1 rearrangement, but also to two minor fragment ions m/z 132 ([M-C2H4]+·) through a McLafferty rearrangement (or [M-CO]+·) and m/z 88 ([M-C3H4O2]+·). These dissociations are rationalized by the idea of ion-neutral complex. The m/z 88 ions are generated via at least two different routes. The m/z 133 ([M-C2H3]+) ions decompose into the ions at m/z 115, 106, and 105 by the losses of H2O, C2H3, and C2H4, respectively. A large part of the first fragment ions would be in the keto form and it decomposes into the m/z 71 and 43 ions by the losses of CO2 and C3H4O2 (or C2O3), and a small part would be in the enol form and decomposes into the m/z 87 ions by the loss of C2H4, not CO. The m/z 43 ions are isobaric, C2H3O+ and C3H7+.View full abstractDownload PDF (298K) -
Yoko KAWAI, Satoru YAMAGUCHI, Yoshiki OKADA, Kazuo TAKEUCHI2004 Volume 52 Issue 5 Pages 271-276
Published: 2004
Released on J-STAGE: October 28, 2005
JOURNAL FREE ACCESSReaction cross sections, σr, for reactions of protonated water clusters, H+(H2O)n (n = 2 and 4), with various compounds (i.e., X = D2O, acetonitrile, acetone, dimethyl sulfide (DMS), dimethylsulfoxide (DMSO), and pyridine) were measured at the collision energies of 0.05−2.0 eV by using a guided ion beam apparatus. It was found that the σrs of H+(H2O)2 were larger than those of H+ (H2O)4 when the proton affinity of X was almost equal to or greater than that of (H2O)2. In such cases, the dominant reaction products were in the form of H+X. These findings suggest that the enhancement of σr at n = 2 was due to a reaction pathway in which a proton is transferred directly from H+(H2O)2 to X without forming an intermediate complex.View full abstractDownload PDF (237K) -
Takahiro MURAI, Haruo IWABUCHI, Toshihiko IKEDA2004 Volume 52 Issue 5 Pages 277-283
Published: 2004
Released on J-STAGE: October 28, 2005
JOURNAL FREE ACCESSLiquid chromatography/mass spectrometry (LC/MS) and liquid chromatography/nuclear magnetic resonance spectroscopy (LC/NMR) were applied to the identification of the positional isomers of gemfibrozil metabolites produced in vitro by human liver microsomes. Gemfibrozil was metabolized to two major oxidative metabolites (M1 and M2) by human liver microsomes in the presence of an nicotinamide adenine dinucleotide phosphate, reduced form (NADPH)-generating system. M1 and M2 were characterized as metabolites formed by the oxidation of the 2′,5′-dimethylphenoxy moiety, which has potentially 5 different positions for hydroxylation, based on the results of negative-ion tandem mass spectrometry in combination with those of accurate mass measurements by quadrupole time-of-flight mass spectrometry. Separation and identification of M1 and M2 were conducted by LC/NMR analyses at 500 MHz. An on-flow 1H NMR analysis demonstrated that M1 was produced by hydroxylation at either the 2′-methyl group or the 5′-methyl group and M2 by hydroxylation at either the 3′-C or the 4′-C position of the aromatic ring. A stop-flow nuclear Overhauser effect spectroscopy (NOESY) analysis demonstrated that M1 and M2 were metabolites hydroxylated at the 5′-methyl group and the 4′-C position of the aromatic ring, respectively.View full abstractDownload PDF (519K)
COMMUNICATION
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Koichi KATO, Yoshiki YAMAGUCHI, Noriko TAKAHASHI, Mamiko NISHIMURA, Sh ...2004 Volume 52 Issue 5 Pages 284-288
Published: 2004
Released on J-STAGE: October 28, 2005
JOURNAL FREE ACCESSWe report herein the first mass spectrometric analyses of isotopomers of a pyridylamino (PA)-derivatized biantennary oligosaccharide, in which one of two non-reducing terminal galactose residues is selectively enriched in 13C by an enzymatic reaction. By use of these isotopomeric PA-oligosaccharides, individual fragment ions observed in tandem mass spectra of MALDI-QIT-TOF-MS were unambiguously assigned. It was shown that the oligosaccharide ion that lacks the N-acetyllactosamine previously linked to the Manα1 →6 antenna dominates its isomeric counterpart ion. We propose that tandem mass spectrometric analyses of oligosaccharides isotopically labeled at a selected antenna would provide us with the basis of mechanisms of formation of glycosidic linkage fragment ions.View full abstractDownload PDF (246K)
REGULAR PAPER
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Masami SAWADA, Akihiro KAMEI, Hirotaka UENO, Hitoshi YAMADA, Yoshio TA ...2004 Volume 52 Issue 5 Pages 289-294
Published: 2004
Released on J-STAGE: October 28, 2005
JOURNAL FREE ACCESSThe enantiomeric excess (e.e.) determination of organic amines and dipeptides has been examined using ESI and FAB mass spectrometry. Here, an equimolar amount of labeled and unlabeled enantiomeric host pair compounds is mixed with a given e.e.-unknown guest compound. This is called the enantiomer labeled (EL)-host method. The enantiomeric host pairs employed were (1) chiral podands having galactose end-groups and (2) chiral crown ethers. Three sets of the Ie (intensity excess)-e.e. plot showed excellent linear relationships, indicating that the e.e.-value of e.e.-unknown amine compounds can be determined by the simple ESIMS or FABMS coupled with the EL-host method, within the mean error of 1.5-4%e.e.View full abstractDownload PDF (238K) -
Shigenori TSURUGA, Hiroshi FUTAMI, Hideo YAMAKOSHI, Minoru DANNO, Ichi ...2004 Volume 52 Issue 5 Pages 295-300
Published: 2004
Released on J-STAGE: October 28, 2005
JOURNAL FREE ACCESSReal-time measurement of the 1,2,4-trichlorobenzene (TCB) which is a precursor of dioxin was developed for discharge reduction of the dioxin in exhaust gas from an incinerator. The ion yield was improved using 1-photon ionization by vacuum ultraviolet (Lyman-alpha line of hydrogen (121.6nm)) and ion trap, after solid matters such as a dust were removed. Furthermore, TCB was quantitatively analyzed using the TCB fragment ion generated by ion collision in the ion trap. This method is possible to avoid the influence of much water in the exhaust gas. The calibration curve was described as Y = 0.052X + 4.2 (R2 = 0.9967), and the detection limit was approximately 80 ng/m3 N as S/N = 2. This calibration curve was sufficiently effective to practical exhaust gas of which TCB concentration is in the range between 0.0 and 6.0 μg/m3 N. It also presents the real-time monitoring of the 18 s intervals which is due to the signal output.View full abstractDownload PDF (264K)
COMMUNICATION
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Kiyotosi TAKAO, Koki HIIZUMI, Kazuo FUJITA, Masayumi ISHIDA, Toshiyasu ...2004 Volume 52 Issue 5 Pages 301-305
Published: 2004
Released on J-STAGE: October 28, 2005
JOURNAL FREE ACCESSGas-phase ion-molecule reactions in octafluorocyclopentene (C5F8) were studied with a pulsed electron beam mass spectrometer. When a few Torr of major gases, CH4, N2, Ar, or He containing ∼10 mTorr C5F8 was ionized by 2 keV electrons, C5F8+, C5F7+, C4F6+, C4F5+, and C3F3+ were formed as major positive ions. The interaction between these ions and C5F8 is found to be electrostatic. The thermochemical stabilities for these ions with C5F8 were measured. The proton affinity of C5F8 may be smaller than that of C2H4. In the negative-mode operation, the strong C5F8- ion peak was formed during the electron pulse. This indicates that C5F8 has the positive electron affinity. The C5F8- ion was quickly converted to the polymerized dimer complex C5F8-·C5F8. This dimer complex did not react further with C5F8 down to 170 K, i.e., the polymerization reaction terminates with n = 1 in the cluster ion C5F8+(C5F8)n. The nature of bonding in F-(C5F8)n changes drastically from covalent with n = 1 to electrostatic with n ≥ 2. The F- ion was found to form a covalent bond with C5F8 but the interaction in F-(C5F8)…C5F8 becomes electrostatic. The halide ions except for F- interact with C5F8 electrostatically.View full abstractDownload PDF (186K)
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