Detailed hydrocarbon analysis of gasoline by GC-MS (SI-PIONA)

A gas chromatographic – mass spectrometric (GC-MS) method has been developed for detailed analysis of the hydrocarbon content of gasoline. The method is equipped with special software and includes the analysis of oxygenated compounds in a single run. The technique utilizes three basic components: the separating power of high resolution capillary gas chromatography, a mass spectrometer with a controllable ion source and ion fragmentation ratios, and unique software for data handling and preparation of reports. The C₄ to C₁₂ range of hydrocarbons in gasoline is covered by the method. A sample of unleaded gasoline from a gas station was analyzed without sample preparation. The results are discussed.     

A derivatization assay using gaschromatography/negative chemical ionization tandem mass spectrometry to quantify 3-nitrotyrosine in human plasma

Endogenous free or protein-associated 3-nitrotyrosine (3-NT) has been proposed as a biomarker of in vivo oxidative damage caused by nitrating agents. Isotopic dilution assay gaschromatographic/mass spectrometric (GC/MS) techniques have been employed to measure endogenous 3-NT levels. However, the quantitative normal plasma values reported so far are inconsistent. The results vary between the assays; they may have been influenced by in vitro artifactual nitration of tyrosine to 3-NT. In this study, a simple and artifact-free derivatization method for quantifying the endogenous 3-NT content of biological samples by GC/negative chemical ionization MS/MS is presented. The method is based on reduction of the nitro group of the molecule by dithionite, heptafluorobutyric acylation and subsequent methyl derivatization, di-O-methyldi-N-heptafluorobutyryl being the major derivative. The results showed excellent GC and MS properties, such as low background and a favorable fragmentation pattern. Endogenous 3-NT was unequivocally quantified using collision-induced dissociation in the selected reaction monitoring mode, whereas co-elution of unknown compounds interfered in the selected-ion monitoring mode. We found that tyrosine was nitrated in the presence of nitrate anions and heptafluorobutyric anhydride, but the product appeared as a di-O-methylmono-N-heptafluorobutyryl derivative. Therefore, artifactually formed 3-NT did not contribute to the measured endogenous 3-NT level owing to its different derivative structure. The method was applied to determine endogenous 3-NT in human plasma and plasma proteins. A detection limit of 0.03 nM for (13)C(6)-labeled 3-NT in plasma samples was established and the response was linear over a concentration range of 0-50 nM (R(2) > 0.999). The endogenous free 3-NT level (mean +/- SD) in ultrafiltered plasma samples from 12 healthy adults was 0.74 +/- 0.30 nM. The mean concentration of 3-NT in their plasma total proteins was 0.60 +/- 0.40 pmol mg(-1). Hence, the described method is selective, eliminates the problem of artifactual nitration and is feasible for the quantification of free and protein-associated 3-NT in biological samples such as plasma.     

Mass spectrometry of onium compounds—XX: Ionisation potential in structural assignment of some gaseous molecules

The ionisation potentials for a series of thiazolo[3,2-a]pyridinium-3-oxides are reduced by about 1.7 to 1.8eV on introduction of an 8-OH group. The gaseous species from the former compounds are ascribed a mesoion, structure while the hydroxy-derivatives are rearranged to non charged molecules.     

Geodesic focusing and space-time topology

Given a space-timeM and a pointp inM, it is shown that, if the locus of first conjugate points ofp along future-directed null geodesics consists of a single point, thenM admits a compact (S ³) spacelike hypersurface. If in addition the null geodesics do not intersect before focusing, then, in a simply connected space-time, the spacelike hypersurface is a partial Cauchy surface.     

Excitation lines and multiple ionization in Auger spectra

Satellite lines of a new type and excessively large continuous distributions of energy degraded electrons are observed in theKLL Auger spectra of potassium, chlorine, and sulfur. The lines are tentatively interpreted as due to a process that is characteristic of the atom more than of the entire solid and the excessive number of electrons in the continuous distributions is interpreted as due to multiple ionization.     

Exact rotating and expanding radiation-filled universe

An exact rotating and expanding solution of the Einstein field equations without cosmological constant is given. The solution represents a Bianchi type VI₀ spatially homogeneous universe filled with radiation having the equation of state p = ?/3.     

Vertical phase separation in spin-coated films of a low bandgap polyfluorene/PCBM blend—Effects of specific substrate interaction

We report on the effect of the substrate on the vertical phase separation in spin-coated thin films of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-5,5-4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole] (APFO-3) blended with [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM). Compositional depth profiles of the films are measured by dynamic secondary ion mass spectrometry (SIMS). We found that changing the substrate from silicon to gold affects the composition profile near the substrate interface. This is caused by a specific interaction between the polymer (APFO-3) and the gold surface, as confirmed by X-ray photoelectron spectroscopy (XPS). The composition profile in the area away from the substrate interface, as well as the enrichment of the free surface with APFO-3, remain however unaffected by the choice of substrate. The vertical composition was also analysed for APFO-3:PCBM films spin-coated on indium tin oxide (ITO) coated with a thin layer of (3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS).     

Nitrogen-rich La-Si-Al-O-N oxynitride glass structures probed by solid state NMR

We investigate the local structures of oxynitride La-Si-(Al)-O-N glasses by ²⁹Si and ²⁷Al magic-angle spinning (MAS) solid state Nuclear Magnetic Resonance (NMR). The glasses studied span an unprecedented range of compositions, up to >50 at.% lanthanum and nitrogen out of the cations and anions, respectively, and achievable through a recently introduced glass preparation route. Transmission as well as scanning electron microscopy verified homogeneous samples over length-scales down to 20 nm. As the nitrogen content of the glasses increased, ²⁹Si NMR evidenced a progressive formation of Si-N bonds, with SiO₂N₂ tetrahedra dominating in the nitrogen-rich glass networks. In the oxygen-rich end of the series, aluminum is predominantly present in tetrahedral coordination as AlO₄, whereas the glasses with highest nitrogen contents have a major fraction of AlO₃N structural units. Trends in isotropic ²⁹Si and ²⁷Al chemical shifts and ²⁷Al quadrupolar couplings are compared with results of La-Si-Al-O glasses and are discussed in relation to the glass compositions and their proposed structures.