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11.
A highly selective, and low cost extractive spectrofluorometric method has been developed for determination of trace concentrations of chromium (III & VI) in water samples using the fluorescent reagent tetraphenylphosphonium bromide (TPP+·Br−). The method was based upon solvent extraction of the produced ion associate [TPP+·CrO3Cl−] of TPP+·Br− and halochromate in aqueous HCl and measuring the fluorescence quenching of TPP+·Br− in chloroform at λex/em = 242/305 nm. The fluorescence intensity of TPP+Br− decreased linearly on increasing the chromium (VI) concentration in the range of 1-114 μg L−1. The limits of detection (LOD) and quantification (LOQ) of chromium (VI) were 0.43 and 1.42 μg L−1, respectively. Chromium (III) species after oxidation to chromium (VI) with H2O2 in alkaline solution were also determined. Chemical speciation of chromium (III & VI) species at trace levels was achieved. The method was applied for analysis of chromium in certified reference material (IAEA Soil-7) and in tap- and wastewater samples and compared successfully (>95%) with the inductively coupled plasma-mass spectrometry (ICP-MS) results. 相似文献
12.
A comparison of the extraction of clove buds with supercritical carbon dioxide and superheated water 总被引:1,自引:0,他引:1
A. A. Clifford Annamaria Basile Salim H. R. Al-Saidi 《Analytical and bioanalytical chemistry》1999,364(7):635-637
Supercritical carbon dioxide and superheated water (subcritical water above 100 °C under pressure) have both been used to
extract the buds of cloves (Syzygium aromaticum). The yields of eugenol and eugenyl acetate obtained by these methods and also by steam distillation and liquid solvent (Soxhlet)
extraction are similar, but the yields of caryophyllene were lower for the methods using water.
Received: 23 December 1998 / Revised: 26 March 1999 / Accepted: 31 March 1999 相似文献
13.
Hisham A Rameshkumar KB Sherwani N Al-Saidi S Al-Kindy S 《Natural product communications》2012,7(5):663-666
The essential oil compositions of the rhizomes of Cyperus conglomeratus (Cyperaceae) collected from Oman and the leaves of two Annonaceae plants, Desmos chinensis var. lawii and Cyathocalyx zeylanicus collected from India were studied by GC, GC-MS and 13C NMR spectroscopy. Twenty-six compounds, representing 84.4% of the oil were identified in C. conglomeratus, where eugenol (31.3%), alpha-cyperone (10.5%) and cyperotundone (8.4%) were the major compounds. Twelve compounds, constituting 100%, were identified in D. lawii oil, of which benzyl benzoate (58.7%), beta-caryophyllene (23.2%), limonene (4.9%) and alpha-humulene (4.0%) were the major constituents. Thirty-two compounds, comprising 98.0%, were identified in C. zeylanicus oil, of which beta-caryophyllene (21.6%), alpha-pinene (20.4%) and E-beta-ocimene (11.8%) were the major components. The antibacterial and antifungal activities of the oils were tested against a panel of five bacterial and two fungal strains. The oils showed moderate activity against all the tested microbial strains. The minimum inhibitory concentrations of the oils were also determined. 相似文献
14.
Adsorption and reactions of CO(2) in the presence of H(2)O and OH species on the TiO(2) rutile (110)-(1×1) surface were investigated using dispersion-corrected density functional theory and scanning tunneling microscopy. The coadsorbed H(2)O (OH) species slightly increase the CO(2) adsorption energies, primarily through formation of hydrogen bonds, and create new binding configurations that are not present on the anhydrous surface. Proton transfer reactions to CO(2) with formation of bicarbonate and carbonic acid species were investigated and found to have barriers in the range 6.1-12.8 kcal∕mol, with reactions involving participation of two or more water molecules or OH groups having lower barriers than reactions involving a single adsorbed water molecule or OH group. The reactions to form the most stable adsorbed formate and bicarbonate species are exothermic relative to the unreacted adsorbed CO(2) and H(2)O (OH) species, with formation of the bicarbonate species being favored. These results are consistent with single crystal measurements which have identified formation of bicarbonate-type species following coadsorption of CO(2) and water on rutile (110). 相似文献
15.
Ghalib Al-Saidi Mohammad Shafiur Rahman Ahmed Al-Alawi Nejib Guizani 《Journal of Thermal Analysis and Calorimetry》2011,104(2):593-603
Gelatin extraction yield increased with the increase of acetic acid concentration and temperature. Gelatin extracted from
shaari skin using 0.1 N acid solutions and temperatures of 323 and 353 K gave highest protein content comparable to that of
commercial bovine and porcine gelatins. In general, gelatin extracted from shaari gelatin showed lower onset of glass transition
temperature than mammalian gelatins. For shaari skin gelatin, the onset of glass transition temperature decreased with the
increase of extraction temperature up to 323 K and then remained nearly constant. The decrease in glass transition was more
pronounced for gelatin extracted at 0.01 N compared to the 0.1 and 1.0 N samples. Unfolding temperature decreased exponentially
with the increase of extraction temperature. The unfolding temperature shifted to lower temperature, and the decrease was
more pronounced in the case of higher (1.0 N) concentrated samples. The extraction concentration and temperature did not show
significant effect on the onset solids-melting temperature. 相似文献
16.
Adsorption, diffusion, and dissociation of CO(2) on the anatase (101) surface were investigated using dispersion-corrected density functional theory. On the oxidized surface several different local minima were identified of which the most stable corresponds to a CO(2) molecule adsorbed at a five-fold coordinated Ti site in a tilted configuration. Surface diffusion is characterized by relatively small activation barriers. Preferential diffusion takes place along Ti rows and involves a cartwheel type of motion. The presence of a bridging oxygen defect or a surface interstitial Ti atom allows creation of several new strong binding configurations the most stable of which have bent CO(2) structures with simultaneous bonding to two surface Ti atoms. Subsurface oxygen vacancy or interstitial Ti defects are found to enhance the bonding of CO(2) molecules to the surface. CO(2) dissociation from these defect sites is calculated to be exothermic with barriers less than 21 kcal/mol. The use of such defects for catalytic activation of CO(2) on anatase (101) surface would require a mechanism for their regeneration. 相似文献
17.
The frequency-doubling performance of CdGeAs2 as a function of wavelength has been characterised using a representative selection of lines from the 9 and 10 m bands of a single mode TEA CO2 laser. Results are shown to be in good agreement with theory in which wavelength dependent absorption, most significant for the generated signal, is taken into account. 相似文献
18.
I. A. Al-Saidi 《Optics & Laser Technology》2001,33(2)
Spherical aberration phenomenon was used to convert the intensity profile of a Gaussian laser beam into a uniform beam profile. The measurements of the beam profile were obtained using a simple optical method. 相似文献
19.
Self focussing of CO2 laser radiation in ammonia gas is reported for a number of laser emissions in near coincidence with NH3 absorption lines. Detailed results for the aR(11) NH3 transition are in excellent accord with theory accounting for intensity dependent saturation of both absorption and the associated anomalous dispersion responsible for nonlinear refraction n2, giving a value for n2 of 2.375 x 10-11 esu torr-1. 相似文献
20.
The authors present phaseless auxiliary-field (AF) quantum Monte Carlo (QMC) calculations of the ground states of some hydrogen-bonded systems. These systems were selected to test and benchmark different aspects of the new phaseless AF QMC method. They include the transition state of H+H(2) near the equilibrium geometry and in the van der Walls limit, as well as the H(2)O, OH, and H(2)O(2) molecules. Most of these systems present significant challenges for traditional independent-particle electronic structure approaches, and many also have exact results available. The phaseless AF QMC method is used either with a plane wave basis with pseudopotentials or with all-electron Gaussian basis sets. For some systems, calculations are done with both to compare and characterize the performance of AF QMC under different basis sets and different Hubbard-Stratonovich decompositions. Excellent results are obtained using as input single Slater determinant wave functions taken from independent-particle calculations. Comparisons of the Gaussian based AF QMC results with exact full configuration interaction show that the errors from controlling the phase problem with the phaseless approximation are small. At the large basis-size limit, the AF QMC results using both types of basis sets are in good agreement with each other and with experimental values. 相似文献