Search results for "IONIZATION"
showing 10 items of 1255 documents
Gas-phase ion chemistry of protonated melatonin
2009
The gas-phase ion chemistry of protonated melatonin has been investigated by mass spectrometric (MS) techniques involving chemical ionisation, fast atom bombardment and electrospray ionisation. Either naturally-occurring or collision-induced decomposition experiments have been carried out using side chain tetra-deuterium-labelled derivatives, as well as the corresponding N–D derivatives obtained by exchange with D2O. The analysis of experimental results allows definite pathways for the formation of the ion at m/z 174 to be assigned and sheds some more light on the overall fragmentation pathways. Experiments on labelled derivatives evidenced H–D scrambling processes during fragmentation.
Degrees of freedom effect on fragmentation in tandem mass spectrometry of singly charged supramolecular aggregates of sodium sulfonates
2012
The characteristic collision energy (CCE) to obtain 50% fragmentation of positively and negatively single charged noncovalent clusters has been measured. CCE was found to increase linearly with the degrees of freedom (DoF) of the precursor ion, analogously to that observed for synthetic polymers. This suggests that fragmentation behavior (e.g. energy randomization) in covalent molecules and clusters are similar. Analysis of the slope of CCE with molecular size (DoF) indicates that activation energy of fragmentation of these clusters (loss of a monomer unit) is similar to that of the lowest energy fragmentation of protonated leucine-enkephalin. Positively and negatively charged aggregates be…
Mass Spectrometric Investigation of Noncovalent Complexation between a Tetratosylated Resorcarene and Alkyl Ammonium Ions
2004
Noncovalent complexation between tetratosylated tetraethyl resorcarene (1) and primary, secondary, and tertiary alkyl ammonium ions (mMe, dMe, tMe, mEt, dEt, tEt, dBu, and dHex) was studied by electrospray ionization Fourier transform ion cyclotron resonance (ESI-FTICR) mass spectrometry. Interactions of the noncovalent complexes were investigated by means of competition experiments, collision-induced dissociation (CID) experiments, ion-molecule reactions with tripropylamine and gas phase H/D-exchange reactions with deuteroammonia. Gas phase ion-molecule reactions gave especially valuable information about the structure and properties of the complexes. Resorcarene 1 formed relatively stable…
Response of the oxygen sensor NreB to air in vivo: Fe-S-containing NreB and apo-NreB in aerobically and anaerobically growing Staphylococcus carnosus.
2009
ABSTRACT The sensor kinase NreB from Staphylococcus carnosus contains an O 2 -sensitive [4Fe-4S] 2+ cluster which is converted by O 2 to a [2Fe-2S] 2+ cluster, followed by complete degradation and formation of Fe-S-less apo-NreB. NreB·[2Fe-2S] 2+ and apoNreB are devoid of kinase activity. NreB contains four Cys residues which ligate the Fe-S clusters. The accessibility of the Cys residues to alkylating agents was tested and used to differentiate Fe-S-containing and Fe-S-less NreB. In a two-step labeling procedure, accessible Cys residues in the native protein were first labeled by iodoacetate. In the second step, Cys residues not labeled in the first step were alkylated with the fluorescent…
Evaluation of furanocoumarins from seeds of the wild parsnip (Pastinaca sativa L. s.l.).
2018
Abstract Although the wild parsnip (Pastinaca sativa L. s.l.) fruits are known to contain linear and angular furanocoumarins, the individual components of the seeds have not been fully identified and quantitated, and, in the case of immature seeds, reported. In view of this, the main furanocoumarin compounds were extracted using pyridine, and were isolated using semi-preparative high-performance liquid chromatography. The structural elucidation of isolated compounds was done based on detailed spectral analysis conducted by liquid chromatography–electrospray ionization–mass spectrometry (LC–ESI/MS), 1H and 13C NMR and, where possible, by gas chromatography–mass spectrometry (GC–MS). The quan…
Application of Resonance Ionization Mass Spectrometry for Ultratrace Analysis of Technetium
2017
This work shows the ability of resonance ionization mass spectrometry (RIMS) to determine 99gTc at the ultratrace level. The characterization of the prepared samples by X-ray photoelectron spectroscopy (XPS) and optimization of the RIMS setup for this purpose, as well as the application of the RIMS method to a soil sample, are presented in this article. 97Tc was used as a tracer isotope to determine the amount of 99gTc in a soil sample with RIMS. With 8.8 × 1010 atoms of 97Tc as the tracer, the concentration of 99gTc was found to be 1.5 × 109 atoms per gram of dried sample material, demonstrating the sensitivity of the method. Furthermore, it could be shown that the 97Tc solution contained …
High-resolution triple-resonance autoionization of uranium isotopes
2005
Abstract The near-threshold autoionization (AI) spectrum of uranium has been investigated by triple-resonance excitation with single-mode continuous lasers. Spectra were recorded over the first ∼30 cm − 1 above the first ionization limit at a resolution of 3 × 10 − 4 cm − 1 using intermediate states with different J values (6, 7, 8) to assign AI level total angular momentum J AI = 5 to 9. Resonances with widths ranging from 8 MHz to 30 GHz were observed; the strongest ones have J AI = 9 and widths of ∼60 MHz. Hyperfine structures for 235 U and isotope shifts for 234, 235 U have been measured in the two intermediate levels and in the final AI level for the most favorable excitation path. T…
Ultratrace analysis of calcium with high isotopic selectivity by diodelaser resonance ionisation mass spectrometry
1997
A resonance ionisation mass spectrometer for the ultratrace determination of calcium isotopes is presented. It achieves high overall efficiency, ultra-high isotopic abundance sensitivity of more than 1010 and complete suppression of isobars. The system can be used for isotope ratio studies on stable and long-lived trace isotopes with the final goal of radiodating via 41Ca-determination. For the different applications optical one-, two- or three-step resonance excitation and subsequent ionisation is applied using simple and inexpensive diodelasers. Additional mass analysis is accomplished in a commercial quadrupole mass spectrometer. The experimental set-up and first results on synthetical a…
A comprehensive study on the atom flow in the cross-field discharge of a Hall thruster
2011
The flow properties of Xe atoms were investigated in the 1 kW class PPS100-ML Hall effect thruster by means of Doppler-shifted laser-induced fluorescence spectroscopy in the near infrared. Fluorescence spectra of the resonant level and the metastable level have been acquired inside and outside the thruster channel under several operating conditions. Analytical treatment and modelling of the measured lineshapes indicate the atom axial velocity increases inside the channel to a value well above the sound speed before decreasing quickly in the near-field plume. Numerical simulations performed with a fluid/kinetic hybrid approach allow us to explain the shape of the velocity profile. Atomic flo…
Higher-order Kerr terms allow ionization-free filamentation in gases.
2010
We show that higher-order nonlinear indices ($n_4$, $n_6$, $n_8$, $n_{10}$) provide the main defocusing contribution to self-channeling of ultrashort laser pulses in air and Argon at 800 nm, in contrast with the previously accepted mechanism of filamentation where plasma was considered as the dominant defocusing process. Their consideration allows to reproduce experimentally observed intensities and plasma densities in self-guided filaments.