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1.
Z. V. I. Zaretskii E. E. Kingston J. H. Beynon R. Lauber U. P. Schlunegger 《Journal of mass spectrometry : JMS》1985,20(5):336-342
Collision-induced dissociation mass-analysed ion kinetic energy spectrometry and translational energy release studies have established that provitamin D3 (7-dehydrocholesterol), provitamin D2 (ergosterol), vitamin D3 and vitamin D2 isomerizations in the mass spectrometer occur at the fragment ion level leading to [M? H2O? CH3]+ ions of identical structure. It was found that the reaction, [M]+˙→[M? H2O]+˙, plays a central role in these isomerizations. 相似文献
2.
Detection of Fragment Genesis in the Mass Spectrometer. III. Analysis of Amino-Acid Sequence in Oligopeptides and in Mixtures of Oligopeptides by DADI-Mass Spectrometry. The amino acid sequence was analysed by DADI mass spectrometry in simple oligopeptides and in mixtures containing two or three peptides. 相似文献
3.
H. J. Walther H. Eyer U. P. Schlunegger C. J. Porter E. A. Larka J. H. Beynon 《Journal of mass spectrometry : JMS》1982,17(2):81-85
Phenol and five acyclic isomeric compounds have been investigated using electron impact and field ionization techniques, mass analysed ion kinetic energy spectrometry and collision induced dissociation mass analysed ion kinetic energy spectrometry. The kinetic energy release data corresponding to the elimination of carbon monoxide from the molecular ions show that at least two structures of the reactant ion are involved. The electron impact and field ionization collision induced dissociation mass analysed ion kinetic energy spectra indicate that under electron impact conditions, the phenol ion partially isomerizes to another ion structure. An isomerization of about 40% to the structure of cis-2-hexen-4-yn-1-al is in good accordance with the spectral data. 相似文献
4.
The negative-ion chemical ionization (ammonia, 5 Pa source pressure) mass spectra of a series of substituted adenine bases, adenosine nucleosides, and the trimethylsilyl derivatives of the nucleosides are described. Selected ions from these spectra were subject to collisionally activated dissociation with mass-analysed ion kinetic energy (CAD/MIKE) analysis of the products and the spectra assessed for information content. In addition to observing strong peaks due to quasimolecular ions and heterocyclic-base ions, it proved possible to differentiate between 2'-, 3'- and 5'-deoxy and between 2'- and 3'-O-methyl isomers. The negative-ion chemical ionization spectra of four methyladenines are essentially identical, but could be clearly distinguished from each other by CAD/MIKE analysis. 相似文献
5.
Study of magnetoresistance and conductance of bicrystal grain boundary in La0.67Ba0.33MnO3 thin film
La0.67Ba0.33MnO3 (LBMO) thin film is deposited on a 36.7°C SrTiO3 bicrystal substrate using laser ablation technique. A microbridge is created across bicrystal grain boundary and its characteristics
are compared with a microbridge on the LBMO film having no grain boundary. Presence of grain boundary exhibits substantial
magnetoresistance ratio (MRR) in the low field and low temperature region. Bicrystal grain boundary contribution in MRR disappears
at temperature T>175 K. At low temperature, I-V characteristic of the microbridge across bicrystal grain boundary is nonlinear. Analysis of temperature dependence of dynamic
conductance-voltage characteristics of the bicrystal grain boundary indicates that at low temperatures (T<175 K) carrier transport across the grain boundary in LBMO film is dominated by inelastic tunneling via pairs of manganese
atoms and tunneling through disordered oxides. At higher temperatures (T>175 K), magnetic scattering process is dominating. Decrease of bicrystal grain boundary contribution in magnetoresistance
with the increase in temperature is due to enhanced spin-flip scattering process. 相似文献
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7.
A facile method based on high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (HPLC/(+)ESI-MSn) has been established for the analysis of polyoxypregnane glycosides in the stems of Marsdenia tenacissima. The data reveals the ability of MSn in the structural elucidation of polyoxypregnane glycosides including the nature of the polyoxypregnane core, the kinds of the substituents and the types of sugar residues. Offline Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) is also performed to assign accurate elemental compositions. In this study, eighteen polyoxypregnane glycosides have been investigated. Among these components, five compounds are unambiguously identified as Marsdenoside K, Tencissoside A, B, C and D; two compounds are established as novel compounds based on mass spectral data; and the other eleven compound's structures are tentatively proposed. Furthermore, breakdown curves are constructed to distinguish five pairs of isomers among these eighteen compounds. As far as our knowledge, this is the first report on identification of polyoxypregnane glycosides in the stems of M. tenacissima by HPLC/ESI-MSn directly, which could save time and material consuming efforts in traditional phytochemistry analyses. 相似文献
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9.
J. E. Szulejko I. Howe J. H. Beynon U. P. Schlunegger 《Journal of mass spectrometry : JMS》1980,15(5):263-267
The effect of the addition of argon and other gases upon the intensities of negative ion species formed in an electron impact source has been investigated. The negative ion current generated for a series of aromatic compounds has been investigated as a function both of sample and argon pressure in the ion source of a ZAB-2F mass spectrometer. For all compounds studied, a striking enhancement of molecular negative ion current occurred on increasing either the presure of the sample or of argor. The results are consistent with thermalization of the 50 eV electrons by collisions with neutral molecules in the high pressure ion source and collisional stabilization of the negative ions initially formed. Analytical applications of the technique are discussed. 相似文献
10.
UP Schlunegger M Stoeckli RM Caprioli 《Rapid communications in mass spectrometry : RCM》1999,13(18):1792-1796
An ion trap has been modified for the analysis of high mass ions generated by matrix-assisted laser desorption/ionization. Samples are deposited on a probe tip and introduced directly onto the hyperbolically shaped surface of one endcap. All three electrodes - both the endcaps and the ring electrode - are insulated so that the radio frequency (Rf) voltage may be applied to the center ring electrode and the inverted Rf voltage to the endcaps. By using low frequencies (below 100 kHz) and low amplitudes (below 200 V), high mass singly charged ions may be trapped and analyzed by a frequency sweep at constant amplitude. In the high mass range (60-160 kDa), this instrument showed good sensitivity, signal-to-noise ratios, and mass resolution. Copyright 1999 John Wiley & Sons, Ltd. 相似文献