Analysis of organic compounds with SNMS

Summary Plasma-based Secondary Neutral Mass Spectrometry (SNMS) as a depth-resolving technique was examined for the first time as a method for the quantitative analysis of heterogeneously distributed organic compounds in environmental material. Using argon ion bombardment (340 eV, 2 mA/cm²) SNMS was applied to a variety of organic compounds. Aliphatic and aromatic hydrocarbons as well as organic compounds with heteroelements yielded mass spectra with predominant atomic signals of carbon and all other elements composing the organic compound. Except for molecularly bound chlorine and nitrogen these signals were found to be governed primarily by atomic ionization probabilities, a prerequisite for elemental quantitation with low matrix dependence. For oxygen as one of these elements matrix dependent variations of the relative detection factor of ±40% were obtained in agreement with average deviations reported for alloy samples. The organic character of the samples is manifested in the appearance of C_mH_n clusters with relative yields declining with increasing number of atoms. The CH signal turned out to be proportional to the hydrogen content regardless of the molecular structure of the compound. This is of analytical importance because low mass separation usually hampers reliable detection of atomic hydrogen with quadrupole mass filters. Other heteroelemental clusters were not detected in significant amounts.     

Depth-profiling of organic layers on microparticles with SNMS

Summary Previous work on the quantification and localization of organically bound elements with plasma-based SNMS for the characterization of microparticles has been continued. Relative detection factors for 10 elements have been determined. Except for lead and bromine a principle proportionality to atomic ionization probabilities is shown. A moderate matrix dependence of less than 40% variation was found even when inorganic and organic materials are included. For depth calibration, erosion rates of organic materials were determined from the time interval necessary to sputter through planar single-layers and Langmuir-Blodgett multi-layer systems with known thickness, as well as from gravimetric powder measurements. Depth propagation rates were 0.7 nm·sec^–1 for polymers and 2.3 nm·sec^–1 for aromatic compounds, when 400 eV argon ion bombardment with 0.7 mA·cm^–2 was used. A depth resolution of 30 nm has been obtained. Model particles of 5 m size have been coated with fluoranthene. Inspection with SNMS revealed an incomplete coating covering only 20% of the microparticle surface with an average thickness of the partial coating of 300 nm. Subsequent characterization using laser-induced fluorimetry confirmed the amount of fluoranthene coating measured by SNMS.     

Comparison of the reactivity of ammonium halides using hydrogen-isotope exchange reaction in a gas-solid system

In order to reveal the behavior of the hydrogen atoms in an ammonium salt, the hydrogen-isotope exchange reaction between each of the three ammonium halides and tritiated water vapor was followed at 50–80°C. Analyzing the data obtained by theA-McKay plot method, the following has been quantitatively clarified: both the reactivity of an ammonium halide and the temperature dependence of its reactivity increase when the electronegativity of the halogen element in the ammonium halide is larger.     

Mechanisms of anion formation in O2, O2/Ar and O2/Ne clusters; the role of inelastic electron scattering

Measurements are reported on the formation of negative ions in O₂, O₂/Ar and O₂/Ne clusters aimed at establishing the mechanisms of anion formation and the role of inelastic electron scattering by the cluster constituents on negative ion formation in clusters. In the case of pure O₂ clusters the main anions we detected are of two types: O^–(O₂) _n0 and (O₂) _n ^1– . The yields of O^–(O₂) _n showed maxima at 6.3, 8.0 and 14.0 eV and the data suggest O^– as their precursor; the maxima at 8 and 14 eV are due to the production of O^– via symmetry forbidden dissociative attachment processes in O₂ at these energies which become allowed in clusters. The yields of (O₂) _n ^– showed a strong maximum at near-zero energy (0.5 eV) and also at 6.3, 8 and 14 eV. With the exception of the near-zero energy resonance, the (O₂) _n ^– anions at 6.3, 8 and 14 eV are attributed to nondissociative attachment of near-zero energy secondary electrons to O₂ clusters. The slow secondary electrons result predominantly from scattering via the O ₂ ^– negative ion states of incident electrons with energies in their respective regions. Similar results were obtained for the mixed O₂/rare gas clusters except that now a feeble and distinctly structured contribution in the yields of O^–(O₂) _n , (O₂) _n ^– (and Ar(O₂) _n ^– ) was observed at energies >10 eV. These anions are believed to have the lowest negative ion states of Ar*^– (Ne*^–) as their precursors.     

Influence of Gas Atmosphere in an Ion Source of a Laser Mass Spectrometer on the Results of Elemental Analysis

The effect of bleeding oxygen or a mixture of inert gases (Ne, Ar, and Xe) in the ion source of an EMAL-2 mass spectrometer on the results of elemental analysis (EI 696 steel, L 68 brass, and Br 663 bronze standard reference samples) was examined. Filling the ion source with gases to a pressure of 10^–2 Pa increased the number of singly charged ions and decreased the number of multiply charged ions in a laser-induced plasma. This fact allowed us to enhance analytical signals by a factor of 1.5. The effect was most pronounced for ions of elements whose second ionization potentials lie in a range of 15–20 eV. The effects were almost identical for bleeding oxygen and inert gases.     

Exchange reactions in two-phase catalytic systems. Communication 2. Ion exchange with halides between the onium salt and solid alkali metal salts

Conclusions The ion exchange reaction between solutions of tetrabutylammonium halides in toluene and solid alkali metal halides has been studied. It is shown that no ion exchange takes place between the onium salt and solid-KCl; this is in agreement with the approximate calculation of the equilibrium constant for this reaction (K_eq10^–4).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimcheskaya, No. 2, pp. 314–316, February, 1988.     

Improvements in quantification accuracy of inorganic time‐of‐flight secondary ion mass spectrometric analysis of silicate materials by using C60 primary ions

Time‐of‐flight secondary ion mass spectrometry is a very useful tool for the comprehensive characterization of samples by in situ measurements. A pulsed primary ion beam is used to sputter secondary ions from the surface of a sample and these are then recorded by a time‐of‐flight mass spectrometer. The parallel detection of all elements leads to very efficient sample usage allowing the comprehensive analysis of sub‐micrometre sized samples. An inherent problem is accurate quantification of elemental abundances which mainly stems from the so‐called matrix effect. This effect consists of changes in the sputtering and ionization efficiencies of the secondary neutrals and ions due to different sample compositions, different crystal structure or even different crystallographic orientations. Here we present results obtained using C₆₀ molecules as a new primary ion species for inorganic analyses. The results show an improvement in quantification accuracy of elemental abundances, achieving relative errors as small as the certified uncertainties for the analyzed silicate standards. This improvement is probably due to the different sputter mechanism for C primary ions from that for single atomic primary ions such as Ga⁺, Cs⁺ or Ar⁺. The C cluster breaks up on impact, distributing the energy between its constituent carbon atoms. In this way it excavates nano‐craters, rather than knocking out single atoms or molecules from the surface via a collision cascade, leading to a more reproducible sputter process and much improved quantification. Copyright © 2009 John Wiley & Sons, Ltd.     

An investigation by the NMR method of the structure of the alkaloid sophorine fromSophora alopecuroides

A new base — sophorine, with mp 59–60°C, [] _D ²³ -18.9° (c 0.98; ethanol) — has been isolated from the epigeal part of the plantSophora alopecuroides L. Its IR spectrum and the nature of its mass spectrometric composition have permitted sophorine to be assigned to the quinolizidine alkaloids. The¹³C NMR spectrum has shown the presence of 19 carbon atoms. The analysis of several of the carbon signals has confirmed the results of IR and mass spectroscopy. Additional details of the structure of sophorine have been obtained from its PMR spectrum.V. I. Lenin Tashkent State University. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 604–608, September–October, 1981.     

Negative Thermionen-Massenspektrometrie von Selen

Summary Negative thermal ionization is used to determine the selenium isotope ratios in a double-filament ion source. A thin film of barium hydroxide on the rhenium ionization filament is applied to increase the Se^– thermal ion current. The produced Se^– ion beam is by a factor of about four higher when selenious acid instead of barium selenite or sodium selenate is used. A strong dependence of the ion current on the temperature of the ionization filament is found showing the maximum ion intensity at temperatures of 970–1000 C. The different selenium isotope ratios of samples with natural isotopic abundance can be determined with relative standard deviations of 0.3–0.6%. This reproducibility is a good basis to improve the accuracy of the selenium atomic weight in the future by a calibrated measurement. An enriched ⁸²Se spike is used to analyse selenium traces in aquatic systems with isotope dilution mass spectrometry down to the pg/g level. In the concentration range of 4–23 ng/g the selenium content is determined with relative standard deviations of 0.1–5%. The results agree well with those obtained with a hydride generation atomic absorption system. It is shown that the described method of isotope dilution mass spectrometry analyses the sum of the inorganic species selenate, selenite and selenide, but not volatile organic selenium compounds.

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Herrn Prof. Dr. W. Fresenius zum 75. Geburtstag gewidmet     

Superionic conductivity in (BEDT-TTF)AgXiY

We have synthesized the organic conductor (BEDT-TTF)Ag_XI_Y (X 1.8 and Y 2.9). This compound has, in addition to high electronic conductivity (_{300 k} 5–10 ^–1 · cm^–1), significant ionic conductivity connected with the motion of silver ions. The value of this ionic conductivity at room temperature is 10^{–3 –1} · cm^–1. The activation energy for diffusion of Ag ions is equal to 0.2 eV.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 2, pp. 247–249, March–April, 1989.     

IR-Spectroscopic investigation of the hydration of tetrabutylammonium bromide in methylene chloride

The concentration dependence of the H₂O spectra in solutions of tetrabutylammonium bromide Bu₄NBr in methylene chloride was investigated by IR-spectroscopy. At low salt and H₂O concentrations the equilibrium: Br _f ^– +HOH_fBr^–HOH dominates where f indicates free or not hydrogen-bonded Br^– and H₂O. With increasing salt content, Br^–H–O–HBr^– complexes are present in addition. At high salt and H₂O content, including the saturated aqueous Bu₄NBr solution, H-bonded cyclic dimers seem to be important.Presented at the sixth Italian meeting on Calorimetry and Thermal Analysis (AICAT) held in Naples. December 4–7, 1984.     

Electronic structure,energy of hydration,and stability of metal aquo ions

The stability of metal aquo ions with respect to redox reactions is determined by the ionization energies of the atoms and the Gibbs energies of hydration for the ions(–_hG⁰). We present critically selected values of –_hG⁰ for 55 metal ions, determined from electrochemical, thermochemical, and spectra data. We consider the factors determining the values of –_hG⁰ (charges, ionic radii, electronic structure, and relativistic effects). For isoelectronic ions, we observe correlations between the ratios of the Gibbs energies of hydration for these ions with different charges and the ratios of their ionic radii. Based on the use of these correlations, we find –_hG⁰ for a number of aquo ions not observed experimentally and we estimate the unknown oxidation-reduction potentials for the pairs of ions M³⁺/M²⁺. We formulate the principles for stabilization of unstable oxidation states of the metals by including the corresponding ions in complexes with certain classes of ligands.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 30, No. 1, pp. 1–11, January–February, 1994.     

Crystal and molecular structure of the simple cation-radical salt ethylenedithiopropylenedithiotetrathiafulvalene trichloromercurate (EPT)HgCl3

The new cation-radical salt (EPT)HgCl₃ is prepared. Its structure and electrical conductivity are studied. The crystal structure of (EPT)HgCl₃ contains (EPT)⁺ in the chair conformation and trigonal planar HgCl₃ ^– packed into organic and inorganic layers alternating along thea axis. Shortened intermolecular contacts join HgCl₃ ^– into infinite chains along the c axis (Hg...Cl, 3.289 and 3.387 Å), form stacks (S...S, 3.536 and 3.597 Å) and layers (S...S, 3.427–3.498 Å) of EPT⁺ cation-radicals, and create cation-anion interactions between neighboring layers in the crystal (Cl...S, 3.396–3.521 Å, Cl...C, 3.360 Å). The configuration of the bonds around Hg in HgCl₃ ^– is distorted trigonal planar: Hg-Cl, 2.342(3)–2.449(3) Å, Cl-Hg-Cl, 110.7(1)–137.4(1). The Hg atom lies out of the plane of the Cl atoms by 0.015 Å. The conductivity of (EPT)HgCl₃ at 20°C is ₃₀₀ 5·10^–2 (·cm)^–1. The dependence of conductivity on temperature is semiconducting in nature.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2055–2061, September, 1991.     

New copper (II) complexes of tridentate dibasic ONO donor ligands derived from salicylaldehyde or substituted salicylaldehydes ando-hydroxybenzylamine

Summary Copper(II) complexes with the Schiff bases derived from Salicylaldehyde and its 5-chloro-, 5-bromo-, 5-nitro-, 3-ethoxy- and 3,5-dichloro derivatives, or from 2-hydroxy-1-naphthaldehyde ando-hydroxybenzylamine, have been synthesized and characterized on the basis of elemental analysis, i.r. and electronic spectra and magnetic susceptibility measurements. The Schiff bases behave as tridentate dibasic O, N and O donor ligands and form complexes with 11 metal: ligand stoichiometry which exhibit subnormal magnetic moments ( _eff=0.88–0.98 B.M.) and are involved in strong antifer-romagnetic exchange (–J=482–525 cm^–1). The complexes exhibit a d-d band atca. 1600 cm^–1. A dimeric structure with aminophenolic oxygen atoms as the bridging atoms is proposed on the basis of i.r. and magnetic data.     

Electron structure and reactivity of organofluorine compounds. 4. AMI calculations of anion radicals of primary,secondary, and tertiary perfluoroalkyl chlorides,bromides, and iodides

Calculations were carried out using the semiempirical quantum chemical AMI method for anion radicals (AR) of the perfluoroalkyl halides (R_FX): CF₃X, CF₃CF₂X, (CF₃)₂-CFX, and (CF₃)₃CX for X=Cl, Br, and I. All the AR's studied are thermally stable. The electron affinity of the perfluoroalkyl halides, and consequently, the thermal stability of their AR's increases in the series from F-methyl to F-tertbutyl halides and from the chlorides to bromides and iodides. During formation of an AR the spin density is preferentially localized on the * orbital of the C–X bond which leads to an increase in the distance between these atoms. Dissociation of the AR of tert-perfluorobutyl iodide to a perfluorocarbanion and an I atom is thermodynamically more favorable than dissociation with formation of a perfluoroalkyl radical and I^–.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1064–1068, May, 1990.     

Sulfurization of polymers. 5. Poly(6-methyl-5-sulfanylthieno[2,3-b]pyridine-4-thione), poly(thieno[2,3-b]azepine-4,5(6H)-dithione), and related structures from poly(2-methyl-5-vinylpyridine) and elemental sulfur

Poly(2-methyl-5-vinylpyridine) is sulfurized with elemental sulfur at 140—320 °C to release hydrogen sulfide and to give black lustrous powders (sulfur content up to 45%) possessing electric conductivity (6.4·10^–11—1.6·10^–7 S cm^–1), paramagnetism (spin concentration 6.2·10¹⁸—5.0·10¹⁹ sp g^–1, g = 2.0043—2.0046, H = 0.49—0.58 mT), and redox and complex-forming properties. Elemental analysis data, IR, ESR, and mass spectra, DSC and TGA data, electric conductivity, electrochemical activity and chemical properties (salt formation and complexation) of the materials synthesized correspond to cross-liked poly(6-methyl-5-sulfanylthieno[2,3-b]pyridine-4-thione), poly(thieno[2,3-b]azepine-4,5(6H)-dithione), and related structures.     

Silicon Carbide Modified Carbon Materials. Formation of Nanocrystalline SiC from Thermochemical Processes in the System Coal Tar Pitch/Poly(carbosilane)

Poly(carbosilane) or PCS, {–CH₂–SiH(CH₃)–} _n , is used as a Si-bearing precursor in combination with a coal tar pitch to study thermally induced transformations toward SiC-modified carbon composites. Following mixing of the components in the molten pitch at 160°C, the mixture is heated under argon atmosphere at 500°C yielding a solid carbonizate that is further subjected to separate pyrolysis experiments at 1300°C or 1650°C. At temperatures up to 500°C, the PCS reacts with suitable pitch components as well as undergoing decomposition reactions. At higher temperatures, clusters of prevailingly nanocrystalline -SiC are confirmed after the 1650°C pyrolysis step with indications that the formation of the compound starts at 1300°C. ²⁹Si MAS NMR, XRD, FT-IR, XPS, and elemental analysis are used to characterize each pyrolysis step, especially, from the viewpoint of transformation of silicon species to silicon carbide in the carbon matrix evolved from the pitch.     

Untersuchung der Anfangsstadien der Oxidation einer NiCr23-Legierung mit AES/XPS

Summary The initial stage of oxidation of NiCr23 at room-temperature and oxygen pressures between 10^–6 and 10^–5 Pa has been studied by AES and XPS. The composition of the surface during oxygen exposure was followed by continuously recording the Auger peaks of Ni (61 eV), Cr (529 eV) and O (510 eV). Photoelectron spectra from Ni 2p3/2, Cr 2p3/2 and O 1s were measured after different oxygen exposures to characterize the chemical state. The thicknesses of the oxide layers were determined by angleresolved AES. The elemental in-depth distribution was obtained by sputter depth profiling. The results are explained by an initially preferential oxidation of Cr together with an oxygen-induced segregation of Cr, followed by enrichment and oxidation of Ni at the surface. The thickness of the oxide after an exposure with 200 Langmuir oxygen was 1.3 nm, while for pure Ni it was only 0.63 nm     

Collisional process involving atomic cluster ions

Collision of Ar cluster ions, Ar _n ⁺ (n=3–16), with He and Ne atoms was investigated by use of mass spectroscopic techniques. The cross sections for the production of Ar _n ⁺ (nn) were measured as functions of the size of the parent cluster ion and the collision energy (0.1–10 eV in the center-of-mass frame). These results were analyzed in the scheme of hard-sphere spectator collision with RRK theory. It was concluded that the reaction proceeds via collisional excitation of the parent cluster ion and following sequential loss of the constituent Ar atoms.This paper was originally submitted in connection with the 2nd. Int. Conference on Atomic and Nuclear Clusters held in Santorini from 28. June-2. July 1993 and is published here as a regular article after an independent refereeing procedure according to the standards of Z. Phys. D     

A method for measuring cross sections for electron-impact excitation out of metastable levels of atoms

A method for measuring cross sections for electron-impact excitation out of the metastable levels of the He atom is described. A hollow cathode discharge is used to produce an atomic beam consisting of ground-level He atoms and the He(2¹S) and He(2³S) metastable atoms. An electron beam of energy below 20 eV crosses the atomic beam exciting the metastable atoms to higher levels, and the intensity of the radiation emitted by atoms in these higher levels is utilized to determine the cross sections. Because of the very low concentration of metastable atoms in the atomic beam, the emission signal is extremely weak. A number of special techniques have been developed to detect these very low-level signals. Absolute calibration of the cross section is accomplished by referencing the emission signal that resulted from electron excitation out of the metastable level to the emission signal that resulted from the 2³S3³P or 2¹S3¹P laser optical absorption.