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排序方式: 共有214条查询结果,搜索用时 39 毫秒
61.
Daniele Del Giudice Emanuele Spatola Matteo Valentini Cecilia Bombelli Gianfranco Ercolani Stefano Di Stefano 《Chemical science》2021,12(21):7460
In this report it is shown that nitroacetic acid 1 (O2NCH2CO2H) can be conveniently used to control the pH of a water solution over time. Time-programmable sequences of the kind pH1(high)–pH2(low)–pH3(high) can be achieved, where both the extent of the initial pH jump (pH1(high)–pH2(low)) and the time required for the subsequent pH rising (pH2(low)–pH3(high)) can be predictably controlled by a judicious choice of the absolute and relative concentrations of the reagents (acid 1 and NaOH). Successive pH1(high)–pH2(low)–pH3(high) sequences can be obtained by subsequent additions of acid 1. As a proof of concept, the method is applied to control over time the pH-dependent host–guest interaction between alpha-cyclodextrin and p-aminobenzoic acid.Predictable and time-programmable sequences of the kind pH1(high)–pH2(low)–pH3(high) in water solution are obtained by a judicious choice of the concentration of nitroacetic acid undergoing decarboxylation. 相似文献
62.
V. A. Semikolenov V. A. Likholobov G. Valentini G. Braca F. Ciardelli 《Reaction Kinetics and Catalysis Letters》1980,15(3):383-388
The structure of palladium acetate complexes with phosphinated polystyrene has been studied by IR and UV spectroscopy. The results indicate that on polystyrene both mono- and dinuclear palladium complexes are formed. The comparison of the catalytic properties of palladium complexes on phosphinated polystyrene with those of mono- and dinuclear complexes supported on silica confirmed the formation of dinuclear palladium complexes on polystyrene surface.
- - . , . - , , .相似文献
63.
Filippo Lo Coco Luciano Ceccon Clemente Valentini Veronica Novelli 《Journal of chromatography. A》1992,590(2):235-240
Official methods for the determination of 2-furaldehyde in spirits involve for a spectrophotometric evaluation, which is characterized by poor specificity. Gas chromatographic evaluations have also been proposed, which offer a much higher sensitivity, particularly when capillary columns are used. In this paper a high-performance liquid chromatographic (HPLC) method based on the formation of the 2,4-dinitrophenylhydrazones of carbonyl compounds and subsequent reversed-phase separation of these derivatives is described. Derivatization is carried out by utilizing an acidic solution of 2,4-dinitrophenylhydrazine in acetonitrile. Precipitation of the derivatives is avoided, and direct injection of the sample into the HPLC system is allowed. The determination ofrers a high specificity and a detection limit of the order of 10−8 mol/1. Accuracy and reproducibility data are presented. 相似文献
64.
Adina Arvinte Federica Valentini Antonio Radoi Fabiana Arduini E. Tamburri Lucian Rotariu Giuseppe Palleschi Camelia Bala 《Electroanalysis》2007,19(14):1455-1459
In this work, the capability of carbon nanofibers to be used for the design of catalytic electrochemical biosensors is demonstrated. The direct electrochemistry of NADH was studied at a glassy carbon electrode modified using carbon nanofibers. A decrease of the oxidation potential of NADH by more than 300 mV is observed in the case of the assembled carbon nanofiber‐glassy carbon electrode comparing with a bare glassy carbon electrode. The carbon nanofiber‐modified electrode exhibited a wide linear response range of 3×10?5 to 2.1×10?3 mol L?1 with a correlation coefficient of 0.997 for the detection of NADH, a high specific sensitivity of 3637.65 (μA/M cm2), a low detection of limit (LOD=3σ) of 11 μM, and a fast response time (3 s). These results have confirmed the fact that the carbon nanofibers represent a promising material to assemble electrochemical sensors and biosensors. 相似文献
65.
A sensitive electrochemical enzyme-linked immunosorbent assay (ELISA) has been used for the detection of 17beta-estradiol in waste waters. The activity of the label enzyme (horseradish peroxidase) was measured electrochemically using 3,3',5,5'-tetramethylbenzidine as electrochemical substrate. The detection limit was estimated to be 5 pg mL(-1), interday and intraday precision (RSD), ranged from 1 to 3% and from 3 to 6%, respectively. Analysis of waste waters from three different treatment plants demonstrated no matrix effect both for samples diluted 1:1 in buffer and diethyl ether extracted. Data on 36 samples analysed by an LC-ESI-MS-MS procedure and by the electrochemical ELISA assay were compared. Results correlated well. The electrochemical enzyme immunoassay appears suitable as a screening tool for analysis of estradiol in waste waters. 相似文献
66.
M. T. Valentini Ganzerli V. Crespi Caramella L. Maggi P. A. Borroni 《Journal of Radioanalytical and Nuclear Chemistry》1998,229(1-2):B39-41
Two new simple methods were studied for the analysis of radium in fresh waters by concentration and purification. Both methods
are based on the use of an inorganic selective adsorber, namely basic lead rhodizonate, LERHO, and partially reduced tin dioxide
(PRTD). The procedures were checked by using filtered fresh waters spiked with 0.1 Bq of226Ra, and in the presence of few μg/l of barium. In each experiment133Ba radioisotope was added to water samples to measure the yield of the overall procedure by γ-counting. Barium and radium
were adsorbed from basic solutions on LERHO packed chromatographic column in the first procedure, while batch experiments
were preferred for the adsorption on PRTD. After separation,226Ra and barium were eluted from the exchangers and co-precipitated onto small filters as thin film, supported on an inactive
barium sulphate substrate, to be submitted to alpha-and gamma-spectrometry. Both methods gave promising results. 相似文献
67.
Rotationally resolved, ultra-high-resolution inverse Raman spectra of CH4 have been obtained in a free-expansion jet. Using relatively mild evpansion conditions a pure methane jet has been cooled to a rotational temperature of 13 K. The limiting rotational state populations observed, however, are not Boltzmann because of nuclear spin effects. 相似文献
68.
H.-B. Valentini 《等离子体物理论文集》1979,19(3):151-175
69.
H.-B. Valentini 《等离子体物理论文集》1974,14(6):201-223
The neutral gas flux from the wall into the column - connected with the ion flux to the wall - and the anisotropy of the velocity distribution of the neutral gas are included into the theory of the steady-state positive column. d/ln and vn0/v0 occur as characteristic parameters. d denotes the radius of the column, ln the mean free path of the neutral atoms for ionization, vn0 the mean velocity of the neutral atoms re-emitted from the wall, v0 = (2kTe/M)1/2, M the ion mass, Te the electron temperature. On the axis the neutral gas density Nn is decreasing, if d/ln is rising. At the wall Nn is increasing for vn0 ? v0, but it is almost constant or decreasing for vn0 ? v0 at the same time. In the plasma the total number of the atoms and the ions is taken as constant. In the case of small vn0 the degree of ionization is high only for d ? ln. However, it is already high for d ≈ ln in the case of high vn0. Therefore, the radial profiles of the neutral gas densities of different gases in a column can differ from each other. Almost full ionization can be reached near the axis. These results hold, too, if the initial velocity of the ions and a magnetic field are taken into account. d/ln, the degree of ionization, and the electron temperature are given as functions of the electric power input and of the total number of the neutrals and the ions. The velocities of the re-emitted atoms depend on the accomodation coefficient of the ions recombining at the wall. With rising d/ln an increasing number of the neutral atoms is re-emitted with superthermal velocities and the total number of the neutrals and the ions can be decreased. The anisotropy of the velocity distribution of the neutral atoms and the ions must be taken into account for the interpretations of spectroscopical measurements. 相似文献
70.