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991.
Young Hyun Cho Wanno Lee Kun Ho Chung Geun Sik Choi Chang Woo Lee 《Journal of Radioanalytical and Nuclear Chemistry》2007,274(3):531-538
The seasonal variation of the 7Be activities in air and the size distribution of the 7Be aerosols were studied by using a continuous air sampler and a five stage cascade impactor. The mean monthly activity level
of 7Be at the Korea Atomic Energy Research Institute (KAERI) site varied from 0.5 to 4.8 Bq·m−3 and revealed a seasonal variation, in which the 7Be activity levels were high in winter and low in summer. The mass size distribution showed a bi-modal distribution with a
higher peak around 0.49 μm and a smaller peak between 3 μm and 7.2 μm. The activity median aerodynamic diameter (AMAD) decreased
with increasing ambient 7Be concentrations. The mean residence times by using a mean growth rate of 0.004 μm·h−1 were estimated to be 2.5–6.4 days. The AMAD has an increasing tendency with higher relative humidity. It seemed that the
high humidity condition facilitated the growth of the aerosol, resulting in increased deposition rates of the aerosols and
the low 7Be content in the surface air. The AMAD of the 7Be aerosols increased with an increasing temperature, but the temperature dependency of AMAD should be explained with geological
and meteorological conditions. 相似文献
992.
993.
S. G. Sarkar S. V. Bandekar P. M. Dhadke 《Journal of Radioanalytical and Nuclear Chemistry》2000,243(3):803-807
Liquid-liquid extraction of Th(IV) and U(VI) has been investigated by commercial extractant PC-88A in toluene. The optimum conditions for extraction of these metals have been established by studying the various parameters like acid concentration/pH, reagent concentration, diluents and shaking time. The extraction of Th(IV) was found to be quantitative with 0.1–1.0M HNO3 acid and in the pH range 1.0–4.0 while U(VI) was completely extracted in the pH range 1.0–3.5 with 2.5·10–2M and 2.·10–2M PC-88A in toluene, respectively. The probable extracted species have been ascertained by log D-log C plot as ThR4·4HR and UO2R2·2HR, respectively. The method permits separation of Th(IV) and U(VI) from associated metals with a recovery of 99.0%. 相似文献
994.
Sushanta Saha Prodyut Kumar Sarkar Ambikesh Mahapatra 《Transition Metal Chemistry》2006,31(3):389-395
The reaction between Pd(N,N′)Cl2 [N,N′ ≡ 1-alkyl-2-(arylazo)imidazole (N,N′) and picolinic acid (picH) have been studied spectrophotometrically at λ = 463 nm in MeCN at 298 K. The product is [Pd(pic)2] which has been verified by the synthesis of the pure compound from Na2[PdCl4] and picH. The kinetics of the nucleophilic substitution reaction have been studied under pseudo-first-order conditions.
The reaction proceeds in a two-step-consecutive manner (A → B → C); each step follows first order kinetics with respect to
each complex and picH where the rate equations are: Rate 1 = {k′0 + k′2[picH]0} × [Pd(N,N′)Cl2] and Rate 2 = {k′′0 + k′′2[picH]0}[Pd(N,O)(monodentate N,N′)Cl2] such that the first step second order rate constant (k′2) is greater than the second step second order rate constant (k′′2). External addition of Cl− (as LiCl) suppresses the rate. Increase in π-acidity of the N,N′ ligand, increases the rate. The reaction has been studied
at different temperatures and the activation parameters (Δ‡H° and Δ‡S°) were calculated from the Eyring plot. 相似文献
995.
Ya-Guang Chen Fan-Xia Meng Hai-Jun Pang Dong-Mei Shi Yu Sun 《Journal of Cluster Science》2007,18(2):396-405
A novel uranyl complex with dimeric lacunary polyoxoanion like open-mouthed clam, Na5[(A-α-SiW9O33H3)2K{UO2(H2O)}2], was prepared and characterized by elemental analysis, infrared and ultraviolet–visible spectroscopy and single crystal
X-ray diffraction. In the anion, two A-α-SiW9O3410− groups share two terminal oxygen atoms Od′ derived from removal of three corner-shared W atoms from saturated α-Keggin anion, forming a dimeric anion with an open
mouth in which potassium ion and uranyl ions are coordinated. Uranium atom adopts a pentagonal bipyramidal geometry. The coordinating
anions are linked by sodium ions via coordination of terminal or bridging oxygen atoms, forming two-dimensional layer arrangement.
Between the layers are the hydrogen bonds from which a supramolecular architecture is created. UV–VIS spectrum gives W–O and
U–O charge transfer transitions at 230–265 and 432 nm, showing the change of geometry of the polyanion and weakening of the
U–O bonds of the uranyl cation.
Electronic supplementary material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
996.
Yan Xiao Jian Wang Wang Xia Guang Feng Huai You Wang 《Journal of Analytical Chemistry》2007,62(5):438-443
The maximum emission wavelength of dopamine is 317 nm with excitation at 290 nm. The relative fluorescence intensity of dopamine
decreased in the presence of enoxacin, which showed that fluorescence quenching occurred. The Stern-Volmer (S-V) plot showed
a nonlinear relationship between the relative fluorescence intensity of dopamine and the concentration of enoxain. The quenching
mechanism was studied and the results suggested that both dynamic and static quenching processes were responsible for the
observed positive deviation in the S-V plot. When the S-V plot was modified by logarithm, the linear relationship was obtained
between logF
0/F and C in the range of 0.10 to 13.0 μg/mL (where F
0 is the relative fluorescence intensity of dopamine, F is the relative fluorescence intensity of dopamine in the presence of enoxacin, and C is the concentration of enoxacin). The fluorescence quenching method for the determination of enoxacin was developed. The
linear regression equation of the calibration graph of enoxacin was C = 13.70 (logF
0/F) − 0.5836, with the correlation coefficient 0.9984. The detection limit was 2.0 ng/mL and the relative standard deviation
was 2.52%. The effects of pH, the stability of dopamine in the presence of enoxacin, and foreign ions on the determination
of enoxacin have been examined. The recovery of enoxacin was from 94.9 to 103.0% in a human serum sample and from 94.9 to
108.0% in a urine sample. The method is simple, rapid, and can be used for the determination of enoxacin in human serum and
urine samples with satisfactory results.
The text was submitted by the authors in English. 相似文献
997.
Rosa Maria Rojas K. Petrov G. Avdeev J. M. Amarilla L. Pascual J. M. Rojo 《Journal of Thermal Analysis and Calorimetry》2007,90(1):67-72
Chromium doped spinels LiCrYMn2−YO4 (0.2≤Y≤0.8) has been synthesized by the sucrose-aided combustion procedure. The thermal behaviour, phase homogeneity and structural
characteristics of the samples were studied by thermal analysis, coupled mass spectrometry, and room-and high-temperature
X-ray diffraction methods. It was found that the ‘as prepared’ samples contained residual organic impurities undetectable
for X-ray diffraction, that burn out completely at 400°C. Samples treated between 400 and 750°C are single phase spinels,
whose crystallites size increase from 10 to 50 nm on increasing the temperature. Cr-doping enhances the thermal stability
of the spinels, which augments on increasing the Cr content Y. The enhanced thermal stability of the spinels has been accounted
for based on the high excess stabilization energy of Cr3+ in octahedral ligand field. 相似文献
998.
999.
The factors influencing the electrochemical behaviour of a supercapacitor have been partly examined in this work. The effects
of so-called intrinsic parameters, i.e. exchange current density, unit cell length and double layer (DL) capacitance; as well
as the so-called application parameters, i.e. cell current, on the cell potential discharge time have been considered. The
contributions of each type of capacitors, DL capacitor and faradaic supercapacitor under various states of operation and material
have been analyzed, and the competing (compensating) effects of the two types of capacitors as regards to the discharge and
power characteristics manifested by current–potential and energy–power (Ragone plots) are elucidated. 相似文献
1000.
Capillary electrophoresis with wavelength-resolved laser-induced fluorescence detection 总被引:5,自引:0,他引:5
Capillary electrophoresis (CE) enables rapid separations with high separation efficiency and compatibility with small sample volumes. Laser-induced fluorescence detection can result in extremely low limits of detection in CE. Single-channel fluorescence detection, however, furnishes little qualitative information about a species being detected, except for its CE migration time. Use of multidimensional information often enables unambiguous identification of analytes. Combination of CE with information-rich wavelength-resolved fluorescence detection is analogous with ultraviolet-visible diode-array detection and furnishes both qualitative and quantitative chemical information about target species. This review discusses recent advances in wavelength-resolved laser-induced fluorescence detection coupled with CE, with an emphasis on instrument design. 相似文献