排序方式: 共有65条查询结果,搜索用时 15 毫秒
21.
Benuzzi-Mounaix A Koenig M Boudenne JM Hall TA Batani D Scianitti F Masini A Di Santo D 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》1999,60(3):R2488-R2491
We show the simultaneous applicability of the frequency domain interferometry and the chirped pulse reflectometry techniques to measure shock parameters. The experiment has been realized with the laser at the Laboratoire pour l'Utilisation des Lasers Intenses (LULI) with a 550-ps pulse duration and an intensity on target approximately 5 x 10(13) W/cm(2) to produce a shock in a layered aluminum-fused silica target. A second low energy, partially compressed chirped probe beam was used to irradiate the target rear side and the reflected light has been analyzed with a spectrometer, achieving a temporal resolution of the order of 1 ps. 相似文献
22.
A critical study of the use of Gran and modified Gran functions for the determination of alkalinity and acid-base properties of diluted solutions containing humic substances is presented. These solutions were composed of 340 muM HCO3(-)(3) in 0, 10, 20.5 and 41 mg/1. of sodium humate in order to simulate natural waters with different levels of dissolved organic carbon. The results showed that the alkalinity may be determined in good agreement with the expected value using both methodologies. The modified Gran functions give information about acid-base speciation in addition to the alkalinity. The application of the modified Gran functions for determination of humic acid pK(a)s and stoichiometry was studied under conditions simulating waters rich in natural organic matter in terms of humic acid concentrations. 相似文献
23.
Determination of Cu, Pb, Cd and Zn was performed in sediment extracts obtained according to the three steps sequential extraction
procedure proposed by the European Community Standards, Measurements and Testing Program. The metal content was determined
by anodic stripping voltammetry with a thin mercury film electrode controlled by a sequential injection (SIA) system. The
proposed method improved the reproducibility of conventional anodic stripping voltammetry, as well as the sample throughput,
allowing analysis of 30 to 45 samples per hour. The influence of flow rate and sample volume was studied to achieve an adequate
sensitivity for the leachate studied. No interferences due to adsorption of organic matter, colloids, or complexes with slow
rate of dissociation were observed. The intermetallic formation of Cu-Zn was avoided by forming the mercury film in presence
of Ga(III) ions in the SIA system, resulting in low consumption of reagent in comparison to flow injection or continuous flow
systems. Results were in good agreement with those obtained by Induced Coupled Plasma – Atomic Emission Spectroscopy (ICP-
AES).
Received: 18 October 1999 / Revised: 14 December 1999 / Accepted: 19 December 1999 相似文献
24.
Marilda Rigobello-Masini José Carlos Pires Penteado Jorge Cesar Masini 《Analytical and bioanalytical chemistry》2013,405(7):2107-2122
Since “omics” techniques emerged, plant studies, from biochemistry to ecology, have become more comprehensive. Plant proteomics and metabolomics enable the construction of databases that, with the help of genomics and informatics, show the data obtained as a system. Thus, all the constituents of the system can be seen with their interactions in both space and time. For instance, perturbations in a plant ecosystem as a consequence of application of herbicides or exposure to pollutants can be predicted by using information gathered from these databases. Analytical chemistry has been involved in this scientific evolution. Proteomics and metabolomics are emerging fields that require separation, identification, and quantification of proteins, peptides, and small molecules of metabolites in complex biological samples. The success of this work relies on efficient chromatographic and electrophoretic techniques, and on mass spectrometric detection. This paper reviews recent developments in the use of monolithic columns, focusing on their applications in “top-down” and “bottom-up” approaches, including their use as supports for immobilization of proteolytic enzymes and their use in two-dimensional and multidimensional chromatography. Whereas polymeric columns have been predominantly used for separation of proteins and polypeptides, silica-based monoliths have been more extensively used for separation of small molecules of metabolites. Representative applications in proteomics and in analysis of plant metabolites are given and summarized in tables. 相似文献
25.
Goubert G Demers-Carpentier V Masini F Dong Y Lemay JC McBreen PH 《Chemical communications (Cambridge, England)》2011,47(32):9113-9115
The intermolecular structure of bimolecular complexes formed on Pt(111) at room temperature through CH···O interactions between 1-methylnaphthalene or 1-ethylnaphthalene and 2,2,2-trifluoroacetophenone is directed by the partial dehydrogenation of the alkyl groups. 相似文献
26.
Barros TC Cuccovia IM Farah JP Masini JC Chaimovich H Politi MJ 《Organic & biomolecular chemistry》2006,4(1):71-82
The study of highly conjugated, carbonyl-containing molecules such as 1,4,5,8-naphthalene tetracarboxylic dianhydride, III, is of interest since reactivity differences and transmission of electronic effects through the conjugated framework can be evidenced. The kinetics of hydrolysis of III in aqueous solution were determined from 5 M acid to pH 10. In basic solution hydrolysis of III yields, sequentially, 1,4,5,8-naphthalene diacid monoanhydride, II, and 1,4,5,8-naphthalene tetracarboxylic acid, I. The second order rate constant for alkaline hydrolysis is 200 fold higher for the first ring opening. The water-catalyzed hydrolysis of III yields a pH-dependent mixture of ionic forms of I and II. The rate constant for water-catalyzed hydrolysis of III is 25 fold higher than that for II. In concentrated acid the rates for reaching equilibrium (I, II and III) increase and III is the major product. The pK(a)s of I (3.24, 5.13 and 6.25) and II (3.05, 5.90) were determined by potentiometric, fluorescence and UV spectroscopy titrations and by quantitative fit of the kinetic and equilibrium data. The apparent, pH-dependent, equilibrium constants, K(EqII), for anhydride formation between I and II were obtained from the UV spectra. The quantitative fit of kinetic and equilibrium data are consistent with the assumption that anhydride formation only proceeds with the fully protonated species for both I and II and permitted the estimation of the equilibrium constants for anhydride formation, K(EqII). The value of K(EqII) (I <==> II) between pH 1 and 6 was ca. 5. Geometry optimization calculations in the gas phase of the reactions of III in alkaline, neutral and acid conditions, at the DFT level of theory, gave electronic distributions that were qualitatively consistent with the experimental results. 相似文献
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Marcelo S.Pinto SilvaJorge C Masini 《Analytica chimica acta》2002,466(2):345-352
The robustness of sequential injection analysis (SIA) was combined with the monosegmented flow analysis (MSFA) approach, in which there is no dispersion of the reaction zone with carrier, to develop a methodology to perform in-line dilution. This approach allows one to know accurately the dilution of sample and reagent inside the monosegment, without the need for determination of dispersion coefficients. As a consequence, the methodology allowed the mechanization of procedures to perform standard additions and to construct analytical curves using a single stock standard solution, with very simple and conventional computation of the sample concentration. The method was illustrated with experiments using the bromothymol blue (BTB) dye, in which no reactions are involved, as well as with the spectrophotometric methodology for determination of Fe(II) using o-1,10-phenanthroline as chromogenic reagent. The resulting method presented a sampling frequency of 30 analyses per hour and a detection limit of 25 μg l−1. 相似文献
30.
This paper describes the development of a sequential injection analysis method to automate the determination of picloram by square wave voltammetry exploiting the concept of monosegmented flow analysis to perform in-line sample conditioning and standard addition. To perform these tasks, an 800 μL monosegment is formed, composed by 400 μL of sample and 400 μL of conditioning/standard solution, in medium of 0.10 mol L−1 H2SO4. Homogenization of the monosegment is achieved by three flow reversals. After homogenization the mixture zone is injected toward the flow cell, which is adapted to the capillary of a hanging drop mercury electrode, at a flow rate of 50 μL s−1. After a suitable delay time, the potential is scanned from −0.5 to −1.0 V versus Ag/AgCl at frequency of 300 Hz and pulse height of 25 mV. The linear dynamic range is observed for picloram concentrations between 0.10 and 2.50 mg L−1 fitting to the linear equation Ip = (−2.19 ± 0.03)Cpicloram + (0.096 ± 0.039), with R2 = 0.9996, for which the slope is given in μA L mg−1. The detection and quantification limits are 0.036 and 0.12 mg L−1, respectively. The sampling frequency is 37 h−1 when the standard addition protocol is followed, but can be increased to 41 h−1 if the protocol to obtain in-line external calibration curve is used for quantification. The method was applied for determination of picloram in spiked water samples and the accuracy was evaluated by comparison with high performance liquid chromatography using molecular absorption at 220 nm for detection. No evidences of statistically significant differences between the two methods were observed. 相似文献