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991.
José Neri G.?Paniz érico Marlon de M.?Flores Ayrton F.?MartinsEmail author 《Mikrochimica acta》2005,152(1-2):89-92
With the aim of avoiding cumbersome sample treatment, we present a device for the introduction of solid soil samples into
AAS-flames for gold determination, as well as the proposition of earth from anthills as a gold occurrence indicator. A previous
ground sample of anthill earth (0.50 mg) was weighed directly into a small recipient of polyethylene which was then connected
to a sampling boronsilicate glass chamber. The sample was carried by an airflow (5 L min−1) to a quartz cell positioned between the burner top and the optical beam. The generated atomic vapor produced a transient
signal which was totally integrated in three seconds. The performance was compared with conventional flame atomic absorption
spectrometry after proper sample digestion. No significant differences were observed between both procedures (mean deviation
±1.90%), and a LOQ of 0.03 μg Au was achieved using the proposed method. The anthill earth was found to be very suitable for
indication of gold occurrence in soils and related materials. 相似文献
992.
Maria de Fatima Pereira 《Tetrahedron letters》2004,45(15):3097-3099
Exploring original approaches for the synthesis of therapeutic agents having a quinazoline part, we discovered that novel 3,4-dihydro-2H-pyrazino[2,1,-b]quinazolines (3) may be rapidly and easily obtained via the chemistry of 4,5-dichloro-1,2,3-dithiazolium chloride (1). Our synthetic approach of this reaction is described with the aim of obtaining a well-controlled access to this very rarely described pyrazino[2,1,-b]quinazoline skeleton. 相似文献
993.
Wagner J. Barreto Henrique de Santana Flaveli A. S. Almeida Dilson N. Ishikawa Yoshio Kawano 《Journal of Analytical and Applied Pyrolysis》2003,70(2):719-210
The synthesis, characterization, and thermal decomposition of the [Ni(SCN)2(H+SCN)2(4-mepy)2] compound with an octahedral structure in polymeric chain were reported, in which SCN groups form bridges among Ni(II) ions. The compound decomposes in water resulting in a pH<4 solution. The FT-IR spectrum presented doublet bands at 2117; 2128 cm−1, 788; 773 cm−1 assigned to ν(C---N) and ν(C---S) stretching modes, respectively, and δ(SCN) deformation modes at 468; 476 cm−1. The Raman spectrum of the compound presented the ν(C---N) stretching as a strong doublet at 2122; 2128 cm−1, ν(C---S) at 783; 770 cm−1, and δ(SCN) at 468; 477 cm−1. No significant changes were observed in the 4-mepy ligand bands compared with the vibrational frequencies of the pure compound or the compound in aqueous solution 0.2 mol l−1. The crystal UV–vis reflectance spectrum presented two bands centered in 626 and 424 nm tentatively assigned to the d→d type transitions, 3A2g→3T1g and 3A2g→3T1g, for a symmetry close to Oh. The TG curve showed a mass loss between 120 and 200 °C assigned to the loss of the two 4-mepy molecules; from 200 to 265 °C, the loss of the two H+SCN groups; and from 265 to 450 °C, the loss of the two SCN groups that formed the bridges among the nickel atoms. Based on these mass loss data, a mechanism of thermal decomposition for the compound was proposed. 相似文献
994.
H. Abramowicz F. Dydak J. G. H. de Groot J. Knobloch J. May P. Palazzi F. Ranjard W. D. Schlatter J. Steinberger H. Taureg W. von Rüden H. Wahl J. Wotschack P. Buchholz F. Eisele H. P. Klasen K. Kleinknecht B. Pszola B. Renk H. J. Willutzki T. Flottmann C. Geweniger J. Krolikowski K. Tittel C. Guyot J. P. Merlo A. Para B. Peyaud J. Rander J. Rothberg J. P. Schuller R. Turlay J. T. He T. Z. Ruan W. M. Wu 《Zeitschrift fur Physik C Particles and Fields》1982,12(3):225-227
Right handed weak quark currents coupled to the usual left handed weak lepton current would be seen in inclusive antineutrino scattering on nuclei as a contribution at largey with the quark (not antiquark) structure function. We do not see such a term, and can therefore put an upper limit on the relative strengths of such right handed currents: \(\varrho ^2 = \frac{{\sigma _R }}{{\sigma _L }}< 0.009\) , 90% confidence. This measurement puts limits on the mixing angle of left-right symmetric models. In distinction to similar limits derived from muon decay or β decay, our limits are also valid if the right handed neutrino is heavy. 相似文献
995.
Summary In the determination of several perhalogenated compounds after gas chromatographic separation on an Apiezon L column, using
a flame ionization detector, all the compounds tested gave linear area-mass plots although the coefficients observed do not
lead to extrapolations which would permit quantitation of perhalogenated compounds for which no standard is available. Of
the compounds tested, dibromodichloromethane, tetrachloroethene and tetrabromoethene gave good linear correlations of area
ratio-mass ratio (using n-decane as the internal standard). Bromotrichloromethane and tetrabromomethane gave continuously
curving area ratio-mass ratio plots which were very reproducible and could be used for graphical interpolation. 相似文献
996.
R. S. A. de Lange K. -N. P. Kumar J. H. A. Hekkink G. M. H. van de Velde K. Keizer A. J. Burggraaf W. H. Dokter H. F. van Garderen T. P. M. Beelen 《Journal of Sol-Gel Science and Technology》1994,2(1-3):489-495
Microporous SiO2 and SiO2/MO2 (M=Ti, Zr, Al; 10 mol% MOx) materials for gas separation membrane applications have been prepared from polymeric sols. Characterization of these sols with SAXS showed that the mean fractal dimension of the SiO2 sols is 1.3–1.4 with a radius of gyration of approximately 2.5 nm. The dried and calcined films are microporous and the pore size distribution was bimodal with maxima at diameters of 0.5 nm and 0.75 nm. For the SiO2/TiO2, SiO2/ZrO2 and SiO2/Al2O3 systems, much milder reaction conditions proved to be necessary to obtain sols with comparable fractal dimensions due to the high reactivity of the Ti/Zr/Al-alkoxides. Microporous supported membranes with molecular sieve-like gas transport properties can be prepared from a relatively wide range of sol structures: from polymers too small to characterize with SAXS to structures with fractal dimensions: 1<d
f<2.04. 相似文献
997.
A method for the simultaneous spectrophotometric determination of cadmium, copper and zinc based on the formation of their complexes with 1,5-bis(di-2-pyridylmethylene)thiocarbonohydrazide is proposed. The absorption curves of these complexes overlap severely in the scanning range 380–480 nm. The analyte concentrations are calculated by a least squares fit of the pure spectra to the mixture spectra. A linear determination range of 0.1–1.7 μg/ml for cadmium, 0.1–1.3 μg/ml for copper and 0.2–1.2 μg/ml for zinc were obtained. The effect of interference was studied. The method has been applied to the determination of these metal ions in various type of materials. 相似文献
998.
Burrows HD Fernandes M Seixas de Melo J Monkman AP Navaratnam S 《Journal of the American Chemical Society》2003,125(50):15310-15311
The lowest triplet state of tris(8-hydroxyquinoline)aluminium(III) (Alq3) has been prepared by pulse radiolysis/energy transfer from appropriate donors in benzene solutions and has an absorption maximum around 510 nm with a lifetime of about 50 mus. It is quenched by molecular oxygen, leading to singlet oxygen formation. From flash photolysis and singlet oxygen formation measurements, a quantum yield of triplet formation of 0.24 was determined for direct photolysis of the complex. A value of 2.10 +/- 0.10 eV was determined for the energy of the lowest triplet state by energy transfer studies and was confirmed by phosphorescence measurements on Alq3, either in the heavy atom solvent ethyl iodide or photosensitized by benzophenone in benzene. Dexter (exchange) energy transfer was observed from triplet Alq3 to platinum(II) octaethylporphyrin. 相似文献
999.
Ingkaninan K de Best CM van der Heijden R Hofte AJ Karabatak B Irth H Tjaden UR van der Greef J Verpoorte R 《Journal of chromatography. A》2000,872(1-2):61-73
A high-performance liquid chromatography (HPLC) method with on-line coupled ultraviolet (UV), mass spectrometry (MS) and biochemical detection for acetylcholinesterase (AChE) inhibitory activity has been developed. By combining the separation power of HPLC, the high selectivity of biochemical detection, and the ability to provide molecular mass and structural information of MS, AChE inhibitors can be rapidly identified. The biochemical detection was based on a colorimetric method using Ellman's reagent. The detection limit of galanthamine, an AChE inhibitor, in the HPLC-biochemical detection is 0.3 nmol. The three detector lines used, i.e., UV, MS and Vis for the biochemical detection were recorded simultaneously and the delay times of the peaks obtained were found to be consistent. This on-line post-column detection technique can be used for the identification of AChE inhibitors in plant extracts and other complex mixtures such as combinatorial libraries. 相似文献
1000.
van den Brand J Blajiev O Beentjes PC Terryn H de Wit JH 《Langmuir : the ACS journal of surfaces and colloids》2004,20(15):6318-6326
The bonding of two types of ester group-containing molecules with a set of different oxide layers on aluminum has been investigated using infrared reflection absorption spectroscopy. The different oxide layers were made by giving typical surface treatments to the aluminum substrate. The purpose of the investigation was to find out what type of ester-oxide bond is formed and whether this is influenced by changes in the composition and chemistry of the oxide. The extent by which these bonded ester molecules resisted disbondment in water or substitution by molecules capable of chemisorption was also investigated. The ester groups were found to show hydrogen bonding with hydroxyls on the oxide surfaces through their carbonyl oxygens. For all oxides, the ester groups showed the same nu(C = O) carbonyl stretching vibration after adsorption, indicating very similar bonding occurs. However, the oxides showed differences in the amount of molecules bonded to the oxide surface, and a clear relation was observed with the hydroxyl concentration present on the oxide surface, which was determined from XPS measurements. The two compounds showed differences in the free to bonded nu(C = O) infrared peak shift, indicating differences in bonding strength with the oxide surface between the two types of molecules. The bonding of the ester groups with the oxide surfaces was found to be not stable in the presence of water and also not in the presence of a compound capable of chemisorption with the aluminum oxide surface. 相似文献