			Home About us Contact

Primary Ions (primary + ion)

Distribution by Scientific Domains

Chemistry	90%

Selected Abstracts

Comparison of mono- and polyatomic primary ions for the characterization of organic dye overlayers with static secondary ion mass spectrometry

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 3 2004
Jens Lenaerts
Organic carbocyanine dye coatings have been analyzed by time-of-flight static secondary ion mass spectrometry (TOF-S-SIMS) using three types of primary ions: Ga+ operating at 25,keV, and Xe+ and SF5+ both operating at 9,keV. Secondary ion yields obtained with these three primary ions have been compared for coatings with different layer thickness, varying from (sub)-monolayer to multilayers, on different substrates (Si, Ag and AgBr cubic microcrystals). For (sub)-monolayers deposited on Ag, Xe+ and SF5+ primary ions generate similar precursor ion intensities, but with Ga+ slightly lower precursor ion intensities were obtained. Thick coatings on Ag as well as mono- and multilayers on Si produce the highest precursor and fragment ion intensities with the polyatomic primary ion. The yield difference between SF5+ and Xe+ can reach a factor of 6. In comparison with Ga+, yield enhancements by up to a factor of 180 are observed with SF5+. For the mass spectrometric analysis of dye layers on AgBr microcrystals, SF5+ again proves to be the primary ion of choice. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Secondary ion formation of low molecular weight organic dyes in time-of-flight static secondary ion mass spectrometry

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 18 2003
Jens Lenaerts
Time-of-flight static secondary ion mass spectrometry (TOF-S-SIMS) was used to characterize thin layers of oxy- and thiocarbocyanine dyes on Ag and Si. Apart from adduct ions a variety of structural fragment ions were detected for which a fragmentation pattern is proposed. Peak assignments were confirmed by comparing spectra of dyes with very similar structures. All secondary ions were assigned with a mass accuracy better than 50,ppm. The intensity of molecular ions as well as fragment ions has been studied as a function of the type of organic dye, the substrate, the layer thickness and the type of primary ion. A large yield difference of two orders of magnitude was observed between the precursor ions of cationic carbocyanine dyes and the protonated molecules of the anionic dyes. Fragment ions, on the other hand, yielded similar intensities for both types of dye. As the dye layers deposited on an Ag substrate yielded higher secondary ion intensities than those deposited on a Si substrate, the Ag metal clearly acts as a promoting agent for secondary ion formation. The effect was more pronounced for precursor signals than for fragment ions. The promoting effect decreased as the deposited layer thickness of the organic dye layer was increased. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Analysis of hopanes and steranes in single oil-bearing fluid inclusions using time-of-flight secondary ion mass spectrometry (ToF-SIMS)

GEOBIOLOGY, Issue 1 2010
S. SILJESTRÖM
Steranes and hopanes are organic biomarkers used as indicators for the first appearance of eukaryotes and cyanobacteria on Earth. Oil-bearing fluid inclusions may provide a contamination-free source of Precambrian biomarkers, as the oil has been secluded from the environment since the formation of the inclusion. However, analysis of biomarkers in single oil-bearing fluid inclusions, which is often necessary due to the presence of different generations of inclusions, has not been possible due to the small size of most inclusions. Here, we have used time-of-flight secondary ion mass spectrometry (ToF-SIMS) to monitor in real time the opening of individual inclusions trapped in hydrothermal veins of fluorite and calcite and containing oil from Ordovician source rocks. Opening of the inclusions was performed by using a focused C60+ ion beam and the in situ content was precisely analysed for C27,C29 steranes and C29,C32 hopanes using Bi3+ as primary ions. The capacity to unambiguously detect these biomarkers in the picoliter amount of crude oil from a single, normal-sized (15,30 ,m in diameter) inclusion makes the approach promising in the search of organic biomarkers for life's early evolution on Earth. [source]

Reactions of BBrn+ (n = 0,2) at fluorinated and hydrocarbon self-assembled monolayer surfaces: observations of chemical selectivity in ion,surface scattering

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 7 2001
Nathan Wade
Abstract Ion,surface reactions involving BBrn+ (n = 0,2) with a fluorinated self-assembled monolayer (F-SAM) surface were investigated using a multi-sector scattering mass spectrometer. Collisions of the B+ ion yield BF2+ at threshold energy with the simpler product ion BF+· appearing at higher collision energies and remaining of lower abundance than BF2+ at all energies examined. In addition, the reactively sputtered ion CF+ accompanies the formation of BF2+ at low collision energies. These results stand in contrast with previous data on the ion,surface reactions of atomic ions with the F-SAM surface in that the threshold and most abundant reaction products in those cases involved the abstraction of a single fluorine atom. Gas-phase enthalpy data are consistent with BF2+ being the thermodynamically favored product. The fact that the abundance of BF2+ is relatively low and relatively insensitive to changes in collision energy suggests that this reaction proceeds through an entropically demanding intermediate at the vacuum,surface interface, one which involves interaction of the B+ ion simultaneously with two fluorine atoms. By contrast with the reaction of B+, the odd-electron species BBr+· reacts with the F-SAM surface to yield an abundant single-fluorine abstraction product, BBrF+. Corresponding gas-phase ion,molecule experiments involving B+ and BBr+· with C6F14 also yield the products BF+· and BF2+, but only in extremely low abundances and with no preference for double fluorine abstraction. Ion,surface reactions were also investigated for BBrn+ (n = 0,2) with a hydrocarbon self-assembled monolayer (H-SAM) surface. Reaction of the B+ ion and dissociative reactions of BBr+· result in the formation of BH2+, while the thermodynamically less favorable product BH+· is not observed. Collisions of BBr2+ with the H-SAM surface yield the dissociative ion,surface reaction products, BBrH+ and BBrCH3+. Substitution of bromine atoms on the projectile by hydrogen or alkyl radicals suggests that Br atoms may be transferred to the surface in a Br-for-H or Br-for-CH3 transfer reaction in an analogous fashion to known transhalogenation reactions at the F-SAM surface. The results for the H-SAM surface stand in contrast to those for the F-SAM surface in that enhanced neutralization of the primary ions gives secondary ion signals one to two orders of magnitude smaller than those obtained when using the F-SAM surface, consistent with the relative ionization energies of the two materials. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Comparison of mono- and polyatomic primary ions for the characterization of organic dye overlayers with static secondary ion mass spectrometry

Ion chemistry of chloroethanes in air at atmospheric pressure

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 20 2001
Anna Nicoletti
Ion chemistry at atmospheric pressure is of major relevance to novel methods for the abatement of volatile organic compounds (VOCs) that employ non-thermal plasmas. For this reason, positive and negative APCI (atmospheric pressure chemical ionization) mass spectra of all six di-, tri- and tetrachloroethanes diluted in air (500,1500,ppm) at atmospheric pressure were investigated at 30,°C and at 300,°C. Spectral changes due to collisional activation of the ions achieved by increasing ,V, the potential difference between sampling and skimmer cones, are informative of structures and ion-molecule reactions. Positive ion chemistry of the chloroethanes (M) can, in general, be ascribed to C-C and C-Cl cleavages of the molecular ion, M+·, never detected but likely formed via exothermic charge exchange from primary ions of the APCI plasma. Exceptions to this characteristic pattern were observed for 1,1-dichloroethane and 1,1,2,2-tetrachloroethane, which give [M,,,H]+ and [M,,,HCl]+· species, respectively. It is suggested that both such species are due to ionization via hydride transfer. Upon increasing ,V, the [M,,,HCl]+· ion formed from 1,1,2,2-tetrachloroethane undergoes the same fragmentation and ion-molecule reactions previously reported for trichloroethene. A nucleophilic reaction of water within the [C2H4Cl+](H2O)n ionic complexes to displace HCl is postulated to account for the [C2H5O+](H2O)m species observed in the positive APCI spectra of the dichloroethanes. Negative ion spectra are, for all investigated chloroethanes, dominated by Cl, and its ion-neutral complexes with one, two and, in some cases, three molecules of the neutral precursor and/or water. Another common feature is the formation of species (X,)(M)n where X, is a background ion of the APCI plasma, namely O2,,O3, and, in some cases, (NO)2,. Peculiar to 1,1,1-trichloroethane are species attributed to Cl, complexes with phosgene, (Cl,)(Cl2C=O)n(n,=,1,2). Such complexes, which were not observed for either the isomeric 1,1,2-trichloroethane or for the tetrachloroethanes, are of interest as oxidation intermediates in the corona-induced decomposition process. No conclusions can be drawn in the case of the dichloroethanes, since, for these compounds, the ions (Cl,)(Cl2C=O)n and (Cl,)(M)n happen to be isobaric. Copyright © 2001 John Wiley & Sons, Ltd. [source]

An Experimental and Theoretical Investigation of Gas-Phase Reactions of Ca2+ with Glycine

CHEMISTRY - A EUROPEAN JOURNAL, Issue 26 2006
Inés Corral Dr.
Abstract The gas-phase reactions between Ca2+ and glycine ([Ca(gly)]2+) have been investigated through the use of mass spectrometry techniques and B3-LYP/cc-pWCVTZ density functional theory computations. The major peaks observed in the electrospray MS/MS spectrum of [Ca(gly)]2+ correspond to the formation of the [Ca,C,O2,H]+, NH2CH2+, CaOH+, and NH2CH2CO+ fragment ions, which are produced in Coulomb explosion processes. The computed potential energy surface (PES) shows that not only are these species the most stable product ions from a thermodynamic point of view, but they may be produced with barriers lower than for competing processes. Carbon monoxide is a secondary product, derived from the unimolecular decomposition of some of the primary ions formed in the Coulomb explosions. In contrast to what is found for the reactions of Ca2+ with urea ([Ca(urea)]2+), minimal unimolecular losses of neutral fragments are observed for the gas-phase fragmentation processes of [Ca(gly)]2+, which is readily explained in terms of the topological differences between their respective PESs. [source]