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111.
The purification of soluble fulvic acids (FA) based on a diafiltration technique is carried out on antarctic water and snow samples, characterised by low humic compound content (0.1-0.8 mg/l). Results are compared with those of FA purified with the dialysis technique that, together with ion-exchange resins, performs an often used purification process. With the adopted procedure it is possible to minimise the high content of inorganic salts deriving in part from the isolation method XAD-8 adopted, as shown by FTIR, elemental and thermogravimetric analysis. 相似文献
112.
The need for accurate (< 0.06%) isotopic blends of 6Liand 7Li is explained and their preparation is discussed. It is shown that lithium must be determined at an accuracy level better than 0.035%. Four methods — acid-base titration with hydrochloric acid or benzoic acid, and weighing as sulphate or carbonate — were tested and improved for the precise and accurate analysis of lithium hydroxide solutions. The results of these four methods for a 0.1 M solution agreed within ± 0.02%. The preparation of pure isotopically enriched lithium hydroxide solutions, with specially purified cation- and anion-exchangers, is described. The prepared products contain as little as 100 μg of other alkali metals and 50 μg of alkaline-earth metals per gram of lithium, and are sufficiently free of anions to permit accurate chemical assay of lithium. No changes in the isotopic compositions of 99% 6Li or 99.99% 7Li were detected during the treatment. 相似文献
113.
The acid catalized reaction of tri-0-acetyl-D-glucal with benzotriazole or 6-methylthiopurine in acetonitrile gave a mixture of 1',2'- and 2',3'-unsaturated nucleosides, the former predominating. The relationship between these unsaturated nucleosides is studied and an allylic carbonium ion is proposed as an intermediate for these isomerizations. The acid catalized reaction of 1',2'-unsaturated nucleosides with more benzotriazole or 6-methylthiopurine gave 1',3'-two base nucleosides. The conformation and anomeric configuration of the N-glycosyl compounds obtained were assigned by NMR spectroscopy. 相似文献
114.
Summary A reversed-phase HPLC method has been developed for the urinary determination of mutagenic 2,4- and 2,6-toluendiamines. These
amines are degradation products of polyurethane, a material used to cover textured silicone breast implants. FMOC-Cl was used
as fluorescent derivatising agent in order to obtain a limit of detection of 15 ng/ml in urine. Pre-treatment of urine samples
was by liquid/liquid extraction and urine specimens of patients after surgury were analysed. 相似文献
115.
Analytically packed columns prepared with Versamid-930, Versamid-900, XE-60, and OV-225 as stationary phases were examined for quantitative gas-liquid chromatography of the potent monamine oxydase inhibitor (MAOI) drugs iproniazid and iproclozide. With the aid of chemically related substances as internal standards, response ratios were determined and linearities calculated by regression analysis. Using the 2-butyl analogs of compounds all four column systems permit quantitation of iproniazid and iproclozide with a percent standard deviation sigmaK of about 1% or less. 相似文献
116.
Electronic structure and spectra of fused n/m ring systems with one or two bridgehead nitrogen atoms
The semiempirical ASMO-SCF-CI method has been applied to study the electronic structures and ultraviolet absorption spectra of the 4-azapentalenyl anion, 4,8-diazapentalene and related azaderivatives. The agreement between observed and calculated transition energies is, in general, satisfactory. Chemical reactivity and assignment of the observed bands are discussed.
Zusammenfassung Mit Hilfe einer semi-empirischen ASMO-SCF-CI Methode wurden Elektronenstruktur und UV Absorptionsspektren des 4-Azapentalenylanions, des 4,8-Diazapentalens und der entsprechenden Azaderivate studiert. Im allgemeinen ist die Übereinstimmung zwischen experimentellen und theoretischen Übergangsenergien zufriedenstellend. Die Zuordnung der beobachteten Banden und Reaktivitäten werden diskutiert.
Résumé La méthode semi-empirique ASMO-SCF-CI a été appliquée à l'étude de la structure électronique et des spectres d'absorption U.V. de l'anion 4-azapentalenil, du 4,8-diazapentalene et de composés aza-derivés apparentés. L'accord entre les énergies de transition observées et calculées est, dans l'ensemble, satisfaisant. La reactivité chimique et l'attribution des bandes observées ont été discutées.相似文献
117.
An alternative convention describing the (n, γ)-reaction rate suited for use in the k0-method of NAA
An alternative convention for use in the k0-method describing the (n, )-reaction rate upon reactor neutron irradiation has been derived by dividing the cross-section in a (v)=0v0/v part and a pure resonance integral, instead of splitting up the neutron spectrum. It describes the (n, )-reactions with the Westcott factor g(T)1 but without resonances below 0.35 eV, and should yield better results for those with resonances below this limit. The resulting formulas are simpler than the ones currently used. An important practical aspect of this new convention is that no irradiations under Cd-cover are needed to determine the parameters to be used in the k0-method. The parameters determined previously for (n, )-reactions with g(T)=1 can still be used. 相似文献
118.
M. Liang H. Ohm B. De Sutter K. Sistemich 《Zeitschrift für Physik A Hadrons and Nuclei》1992,344(3):357-358
Tie half-lives of 8 low lying levels of103Nb have been determined at the fission-product separator JOSEF. A B-- triple-coincidence method was used which consists in a measurement of the time delay between the feeding of the levels through the B– decay of103Zr and their decay, in coincidence with a tagging ray, with plastic, BaF2 and Ge detectors, respectively. Most of the investigated levels are members of the three known rotational bands based on the ground state and the 164 and 248 keV levels. The deformation Bq=0.31(3) of103Nb could be deduced from the half-life data. The half-lives are well reproduced through calculations in the frame of the Nilsson model.The authors thank Dr. T. Seo for valuable advise in connection with the Nilsson-model calculations. 相似文献
119.
120.
We present a multipass femtosecond amplifier pumped by a Nd-YAG laser where the gain medium is given by a variable length dye cell. This system allows amplification factors up to 5 · 106 and output pulse energies of 150 J, while restricting the contribution of amplified spontaneous emission to 0.5% of the total output energy, without using any saturable absorber stage. A detailed study of the output pulsewidth as a function of the duration of the input chirped pulse is also presented. 相似文献