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21.
22.
A simple and very sensitive spectrophotometric method for the direct determination of copper ions 总被引:1,自引:0,他引:1
A sensitive spectrophotometric method for the direct determination of copper in aqueous samples without a preconcentration step has been developed. It is based on the formation of a yellow complex with the chromogenic reagent di-2-pyridyl ketone benzoylhydrazone (dPKBH) in an alkaline medium. The complex stoichiometry was 1:2 (Cu:dPKBH) and presents maximum absorbance at 370 nm. The influence of chemical variables affecting the behaviour of the system such as pH, concentration of dPKBH, buffer solution and ethanol, order of addition of the reagents and stability of the complex, were evaluated. The molar absorptivity (epsilon) was 3.92x10(4) L mol(-1) cm(-1), and Beer's law was obeyed up to 3 mg L(-1) of copper. The relative standard deviation was 0.46% (n=11) for a sample containing 1 mg L(-1) Cu(II). The limit of detection was 2.5 micro g L(-1) and was therefore more sensitive than the direct methods reported previously. Finally, the method was successfully validated by analysing several real samples with different matrices, such as tap water, natural water or copper alloys, with an average relative error of 2.46%. 相似文献
23.
Moreno M. M. Torres Santos R. H. A. Gambardella M. T. P. Camargo A. J. da Silva A. B. F. Trsic M. 《Structural chemistry》1998,9(5):365-373
The crystal and molecular structures of the following molecules have been determined: 1-acetyl-indoline, 1-acetyl-5-nitro-indoline, l-acetyl-5-nitro-7-bromo-indoline, 1-acetyl-5-bromo-7-nitroindoline, and l-acetyl-5-bromo-7-nitro-indol. Molecular orbital calculations are performed for these compounds and two related species. 相似文献
24.
Pérez Pavón JL Guerrero Peña A García Pinto C Moreno Cordero B 《Journal of chromatography. A》2004,1047(1):101-109
The direct coupling of a headspace sampler with a mass spectrometer is proposed as a screening tool for the rapid detection of soil pollution by hydrocarbons from petroleum and derivatives. The samples are subjected to the headspace generation process, with no prior treatment, and the volatiles generated are introduced directly into the mass spectrometer, thereby obtaining a fingerprint of the sample analysed. Suitable treatment of the signal by chemometric techniques allows unequivocal characterisation of the different types of sample. The use of fast gas chromatography with a mass spectrometer detector coupled to the headspace sampler allows identification of the major hydrocarbons present in the mineral and organic polluted samples, interpretation of the results obtained, and demonstrates the analytical potential of headspace-mass spectrometry coupling. 相似文献
25.
Luís J. Moreno López Manuel Callejón Mochón Juán C. Jiménez Sánchez Alfonso Guiraúm Pérez 《Mikrochimica acta》1996,124(3-4):187-194
A method for the determination of salicylaldehyde (2 × 10–6–10–4
M) by differential-pulse polarography, based on the in situ formation of its Girard-P derivative in aqueous solution at pH 2.5, is proposed. The relative standard deviation was 1.5% (ten determinations of 4 × 10–5
M level). The applicability of this method was checked in synthetic samples containing salicyl alcohol,o-aminophenol, 2-methylphenol, salicylic acid and 4-aminobenzoic acid. 相似文献
26.
Juan Manuel Ortiz-Sánchez Ricard Gelabert Miquel Moreno José M Lluch 《Chemphyschem》2007,8(8):1199-1206
The two isoelectronic bipyridyl derivatives, [2,2'-bipyridyl]-3,3'-diamine and [2,2'-bipyridyl]-3,3'-diol, are experimentally known to undergo very different excited-state double-proton-transfer processes, which result in fluorescence quantum yields that differ by four orders of magnitude. Herein, density functional theory (DFT), time-dependent DFT (TDDFT), and complete active space self-consistent field (CASSCF) calculations are used to study the double-proton-transfer processes in the ground and first singlet pi-->pi* excited state. The quantum-chemistry calculations indicate 1) the existence of only one energy minimum in the ground electronic state corresponding to reactants (thus avoiding the possibility of a fast fluorescent relaxation process from the photoproducts region), 2) an endoergic process of the complete double proton transfer, and 3) the presence of a conical intersection in the excited intermediate region of [2,2'-bipyridyl]-3,3'-diamine. These facts explain the very low fluorescence quantum yield in [2,2'-bipyridyl]-3,3'-diamine compared to [2,2'-bipyridyl]-3,3'-diol. 相似文献
27.
Avelina Arnanz Consuelo Moreno Allan J. Lough Salomé Delgado 《Journal of organometallic chemistry》2004,689(20):3218-3231
The reaction between 2,5-bis(trimethylsilylethynyl)thiophene and Co2(CO)8 or Co2(CO)6(X), (X = dppa, dppm), gave rise to the formation of substituted ethynylcobalt complexes containing one or two Co2(CO)6 or Co2(CO)4(X) units, 2-[Co2(CO)4(X){μ2-η2-(SiMe3)C2}]-5-(Me3SiCC)C4H2S (X = 2CO (1), dppa (3) or dppm (4)) and 2,5-[Co2(CO)4(X){μ2-η2-SiMe3C2}]2C4H2S (X = 2CO (2), dppa (5) or dppm (6)). Desilylation of the non-metallated and metallated alkynes in 3, 4 and 6 occurred on treatment with KOH and tetrabutylammonium fluoride to give 2-[Co2(CO)4(μ-X){μ2-η2-SiMe3C2}]-5-(CCH)C4H2S (X = dppa (7), dppm (8)) and 2,5-[Co2(CO)4(μ-dppm){μ2-η2-HC2}]2C4H2S (9), respectively. Crystals of 6 suitable for single-crystal X-ray diffraction were grown and the molecular structure of this compound is discussed. A comparative electrochemical study of all these complexes is presented by means of the cyclic and square-wave voltammetry techniques. 相似文献
28.
J. A. Munoz Leyva M. Callejón Mochón N. Moreno Diaz A. Sánchez Misiego 《Mikrochimica acta》1984,84(3-4):295-302
Summary Dimedone bisthiosemicarbazone monohydrochloride has been examined to evaluate its usefulness as a reagent for rapid and sensitive Spectrophotometric determination of chlorate (0.5–5.0 ppm) by oxidation of the reagent in 70% perchloric acid medium and measurement of the yellow product. The molar absorptivity at 417 nm is 1.86×104 l·mole–1·cm–1. The relative standard deviation is 1.6% for 2.5 ppm of chlorate.
Spektropbotometrische Bestimmung von Chlorat mit Dimedonbisthiosemicarbazon-monocblorhydrat (I)
Zusammenfassung Die Verwendbarkeit von I als Reagens für die rasche und empfindliche spektrophotometrische Bestimmung von 0,5–5,0 ppm Chlorat durch Oxydation von I in 70%iger Perchlorsäure und Messung des gelben Reaktionsproduktes wurde untersucht. Die molare Absorptivität bei 417 nm beträgt 1,86×104 l·mol–1·cm–1. Die relative Standardabweichung beträgt 1,6% für 2,5 ppm Chlorat.相似文献
29.
A simple reverse flow-injection (rFIA) manifold for the direct determination of aluminum in drinking water is proposed. This rapid and sensitive method is based on the formation of an Al(3+) complex with salicylaldehyde picolinoylhydrazone (SAPH), which shows a maximum blue-green fluorescence (lambda(ex)=384 nm, lambda(em)= 468 nm) at pH 5.4. Operative conditions both for batch and rFIA procedures were investigated including reagent concentration, buffer solutions, injection loop, reacting coil and wavelengths used for the fluorimetric detection. The tolerance limits of foreign ions have been also evaluated, before and after the addition of masking agents. The reverse flow-injection procedure allows determination of Al(3+) at ppb level (LOD: 1.9 mug l(-1)) within a working range of 5-30 mug l(-1). The proposed method was successfully employed for the determination of Al(3+) in several commercial drinking, soft drinking (as certified reference material), and tap water samples. 相似文献
30.
We present extensive molecular dynamics simulations of the motion of a single linear rigid molecule in a two-dimensional random array of fixed overlapping disklike obstacles. The diffusion constants for the center of mass translation, D(CM), and for rotation, D(R), are calculated for a wide range of the molecular length, L, and the density of obstacles, rho. The obtained results follow a master curve Drho(micro) approximately (L(2)rho)(-nu) with an exponent micro=-3/4 and 1/4 for D(R) and D(CM), respectively, that can be deduced from simple scaling and kinematic arguments. The nontrivial positive exponent nu shows an abrupt crossover at L(2)rho=zeta(1). For D(CM) we find a second crossover at L(2)rho=zeta(2). The values of zeta(1) and zeta(2) correspond to the average minor and major axis of the elliptic holes that characterize the random configuration of the obstacles. A violation of the Stokes-Einstein-Debye relation is observed for L(2)rho>zeta(1), in analogy with the phenomenon of enhanced translational diffusion observed in supercooled liquids close to the glass transition temperature. 相似文献