Ionization Of Organic Molecules Research Articles

Ionization of organic molecules with metal ions formed in the laser plasma.

A laser plasma ion source was used to ionize volatile organic compounds in a gas sample. The plasma was generated on a metal target in the intermediate vacuum region of ~0.3 Torr using a pulsed Nd:YAG laser with a wavelength of 1 μm. The resulting ions mass spectra were acquired using orthogonal time-of-flight mass spectrometer (O-TOF MS). When using a copper target, the ions formed are simple complexes (CuM+ ) of copper ions with organic molecules. The possibility of online identification of trace amounts of alkanes in nitrogen and air, with a detection limit of ~10 ppb, was demonstrated. The ionization efficiency of volatile organic compounds through the formation of clusters with metal ions is 10-4 in terms of the quasimolecular complex ions. The rate constants of ion-molecular reactions of copper ions with octane and water molecules in nitrogen and air are estimated.

Towards multiproxy, ultra-high resolution molecular stratigraphy: Enabling laser-induced mass spectrometry imaging of diverse molecular biomarkers in sediments

Mass spectrometry imaging (MSI) collects mass spectra of organic compounds from individual micrometer-sized spots and yields high-resolution images of the spatial distribution of target analytes on sample surfaces. MSI can potentially open a new avenue to ultra-high resolution molecular stratigraphy by resolving the fine-scale distribution of molecular biomarkers in geological records. However, ionization of organic molecules within their sediment matrix remains a critical challenge. Building on the recent introduction of MSI of archaeal tetraether lipids, we have extended the analytical spectrum to additional biomarkers and provide guidelines for the generation of multiproxy, ultra-high resolution paleoenvironmental records. We evaluated the addition of artificial matrices to promote ionization, defined the most suitable MS settings, and increased analytical complexity from pure compounds to their investigation in sediment. Most compounds relevant to molecular stratigraphy are not properly ionized in the presence of conventional matrices, but require atypical ones, such as those based on carbon or silver. Sediments serve as a natural matrix, directly allowing detection of many of these compounds. However, the sediment matrix also inhibits some reactions that otherwise promote detection, such as derivatization of alkenones or silver-mediated ionization of n-alkanes. The robustness of MSI-based molecular stratigraphy is enhanced by analysis of target compounds in narrow m/z ranges, and by summation of mass spectra from several coeval measurement spots. We present an initial inventory of compounds readily detected in the sediment tested, including long chain alkenones and diols, sterols, and pigments, and provide an outlook into the use of MSI in multiproxy studies.

Similarities in Kinetic Energy Distributions of Associative Fragments during Dissociative Ionization of Organic Molecules

We have performed a study of the formation of H+2 and H + 3 ions during dissociative ionization of various organic molecules under single collision conditions. The reactions are brought about by electron impact and are observed by multiparticle coincidence momentum imaging. We investigate how the presence of certain functional groups in the molecule is reflected in the kinematics of associative reactions.

Ionization of Organic Molecules by High Intense Femtosecond Laser

Ionization of Organic Molecules by High Intense Femtosecond Laser

New approach to surface ionization and drift-tube spectroscopy of organic molecules

A new physical model of ionization of organic molecules from the class of amines on the oxidized surface of transition metals is suggested. According to this model, the process involves the capture of protons or hydroxyl groups forming on the oxide surface upon water molecule adsorption. The adequacy of the model is demonstrated experimentally with test amines, such as Novocaine (procaine), bencaine, Dimedrol (diphenylhydramine), etc. A theory of drift motion of ion beams that includes the space charge effect is proposed. It is shown that the quantity P i=μj/e0 v g 2 (where μ is the ion mobility, j is the ion current density, ɛ0 is the permittivity, and v g is the longitudinal velocity of an ionized gas) plays the role of perveance for intense drift ion beams. A new type of drift-tube spectrometer that uses an ion source due to surface ionization is developed.

Use of the surface ionization of organic molecules for investigating some questions in geochemistry

The possibility of using the surface ionization of organic molecules to investigate the organic matter in carbonaceous minerals is tested. It is shown in the example of shungite that the pyrolysis of such compounds releases organic molecules or radicals into the gas phase that are capable of being ionized on the surface of oxidized tungsten.

The ionization of organic molecules by slow positrons

The ionization of organic molecules by positrons having energies above and below their positronium-formation thresholds is reviewed. The sensitivity of sub-positronium-ionization yields to chemical and structural properties of the molecules is discussed, and possible mechanisms for ionization and fragmentation are suggested. Plans are presented for future experiments to further elucidate mechanisms and to search for evidence of positronium compound formation.

Internal energy deposition into molecules upon positron-electron annihilation.

The dissociative ionization of organic molecules, induced by positrons having energies below the positronium threshold (0.5--3 eV), has been studied. Cross sections for the ionization-fragmentation processes increase as positron energies decrease. The data reveal that the energy required for dissociative ionization is supplied by the annihilation process, and that fragmentation occurs by breakage of C-C single bonds in preference to double and triple bonds.

Characterization of a glow discharge ion source for the mass spectrometric analysis of organic compounds

A glow discharge ion source has been constructed for the mass spectrometric analysis of organic compounds. Characterization of the source has been made by studying the effect of pressure and discharge current on ionic distributions by anodic ion sampling along the discharge axis. Ion and electron densities and electronic temperatures have been calculated by using the single Langmuir probe technique to correlate the extraction efficiency with measured ion distributions and gain some insight into the ionization of organic molecules. The spectra obtained for several classes of organic compounds show that formation of parent-molecular ions by proton transfer, resulting partly from the background water molecules, is a major low energy process while charge transfer, Penning ionization, and electron ionization are probably responsible for the fragmentation observed. The spectra result from the simultaneous occurrence of high and low energy reactions, and their structural information content is very high, yielding both molecular and extensive fragment ion information. The glow discharge ion source has proved to be essentially maintenance-free, easy to operate, stable, and can be used at reasonable mass resolution (up to 7000). The source also provides picogram range detection limits and has a linear response range of about six orders of magnitude, which makes it an interesting ion source for routine analysis. Preliminary work conducted with chromatographic interfaces indicates that its use can be easily extended to both gas and liquid chromatography.

Ionization of organic molecules with ultraviolet lasers: A technique for generating large, well-defined ionized volumes

In this paper we report a technique for generating a large, homogeneous volume of ionized gas and for making time-resolved measurements of its electron density. We also report absolute photoionization coefficients for a number of molecules. These coefficients will allow calculation of peak electron densities obtained in other ionization-related experiments. In our technique, the beam from a rare-gas halogen laser photoionizes organic molecules that have been seeded into a buffer gas. Ionization is accomplished by the absorption of two photons. We have analyzed the electron densities produced by photoionization with a microwave interferometer that measures the electron density in the ionized gas with a time-resolution of a few nanoseconds. Some of the organic molecules photoionized in this work produce electron-ion pairs with an efficiency more than five orders of magnitude higher than commonly used laboratory ionization sources such as ArF laser photoionization of NO. We have also studied the effect of attaching gases on the ionized mixtures and have demonstrated that addition of as little as 10 Torr of SF6 can reduce the peak electron density observed by a factor of 103.

Ionization of Organic Molecules by Fast Molecular Ion Bombardment

Abstract The bombardment of organic samples by the ionization products of trimethyl-pentaphenyl trisiloxane was found to have a strong effect on the sputtering yield of molecular parent ions of thermally labile compounds. For the tetra-saccharide stachyose an order of magnitude higher yield was obtained with fast molecular ion than with fast Hg atom bombardment. This difference decreased from tetra to disaceharides and was smallest for arginine.

The mass spectra of some chlorinated aromatic pesticidal compounds

AbstractMass spectral studies of some chlorinated aromatic pesticidal compounds are reported. The compounds studied include substituted diphenyl derivatives of methane, ethene and methanol.The diphenylmethanes are characterized by a relatively intense peak at m/e 165. Comparison of their low voltage spectra with 9‐dichloromethylfluorene indicates that this ion has a fluorenyl ion structure.The structure of the base peak (m/e 246) of the diphenylethenes was investigated by comparing competitive metastable transitions with 9‐dichloromethylenefluorene and utilizing defocusing metastables. Additional studies of model compounds suggest that the m/e 246 ion is very complex and is probably comprised of a number of structures.The mass spectra of the diphenylmethanols are significantly different from the other two groups. The hydroxyl group markedly affects the fragmentation process for these compounds; the characteristic peak is presumably the chlorobenzoyl ion and is probably precursor for other fragment ions.Mass spectral correlations of pesticidal compounds of similar structure are needed to obtain enough background to facilitate interpretation of the mass spectra of their metabolites. Furthermore, such studies make feasible the identification of characteristic product ions formed by rearrangement processes during ionization of organic molecules in the gas phase. This information can be a nucleus for correlating the other significant mass spectral data of an unknown compound. Intensive studies of carbamates,1 organophosphorus2 and bridged polycyclic chlorinated pesticidal3 compounds were invaluable in identifying metabolites of the aforementioned pesticides.4,5,6 The compounds in this magnified image magnified image Work are chlorinated aromatic pesticidal compounds which consist of a diphenylemthane, a diphenylethylene, or a diphenylmethanol structure. The compounds p,ṕ‐DDE were briefly discussed by Jorg, Houriet and Spiteller.7 The compounds examined are listed in Table 1.Treatment of data. The mass spectra of the pesticides are presented as bar graphs in Figs 1 to 12 magnified image magnified image magnified image magnified image magnified image magnified image It a metastable peak is observed, the metastable transition is indicated by m* on the figures and also by (m*) when confirmed or identified using the defocusing technique.8 Since the relative abundances of the metastable peaks for these compounds are very small (<0.1%) on special effort was made to establish their presence unless they wre pertinent.

The Role of Argon Metastable Atoms in the Ionization of Organic Molecules.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe Role of Argon Metastable Atoms in the Ionization of Organic Molecules.M. M. Shahin and S. R. LipskyCite this: Anal. Chem. 1963, 35, 11, 1562–1566Publication Date (Print):October 1, 1963Publication History Published online1 May 2002Published inissue 1 October 1963https://doi.org/10.1021/ac60204a006RIGHTS & PERMISSIONSArticle Views76Altmetric-Citations6LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (564 KB) Get e-Alerts Get e-Alerts