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221.
In this study a new extraction–spectrophotometric method for the determination of fluoride ion in natural waters has been
presented by use of octyl chemically bonded solid phase extraction (SPE) cartridge. In this method at first aluminium–oxinate
chelate is adsorbed on SPE cartridge, then the water sample (containing fluoride ion) is passed through the SPE device. The
excess of oxine on the sorbent is washed with acetate buffer and finally the residual of aluminium–oxinate chelate on the
sorbent is eluted by ethanol and its absorbance is read at 375 nm. The decrease of adsorbed aluminium–oxinate chelate on sorbent
is proportional to the fluoride ion concentration in the water samples. The detection limit of this method is 80 ng/ml and
the linear dynamic range is between 0.1–2 μg/ml. Sensitivity of the method is excellent and absorbance variation for each
μg/ml fluoride ion is 0.6 (approximately equal to Eriochrome cyanine R-zirconium standard method and ten times better than
the Alizarin complexon standard method). Results of this method have good agreement with the Eriochrome cyanine R-zirconium
standard method. Also this method has less interferences as compared with SPADNS standard method.
Received September 6, 2000. Revision April 24, 2001. 相似文献
222.
The reaction of 3,6-diaryl-1,2,4,5-tetrazines and 2-aryl substituted acetonitriles, under basic conditions, leads unexpectedly to 3,5-diaryl-(NH)-1,2,4-triazoles in moderate yields. A mechanism is proposed. 相似文献
223.
In this paper, the liquid?Cliquid equilibria for 1-propanol, 2-propanol or 2-methyl-2-propanol + disodium hydrogen citrate aqueous two-phase systems at 298.15 K were studied. The experimental binodal curves at 298.15?K are reported, and the parameters of the Merchuk equation, modified as a nonlinear function of mixed solvent properties and used for the simultaneous correlation of the experimental binodal data. Moreover, the salting-out ability of different salts and different alcohols with different anions is discussed. Additionally, experimental tie-line data are reported at 298.15 K. The generalized electrolyte-NRTL model of the mixed solvent electrolyte systems (e-NRTL) satisfactorily used for the correlation of the tie-line compositions; restricted binary interaction parameters were also obtained. 相似文献
224.
Application of Cloud Point Extraction for Copper,Nickel, Zinc and Iron Ions in Environmental Samples
A cloud point extraction procedure was presented for the preconcentration of copper, nickel, zinc and iron ions in various samples. After complexation by 2‐(6‐(1H‐benzo[d]imidazol‐2‐yl)pyridin‐2‐yl)‐1H‐benzo[d]Imidazole (BIYPYBI), analyte ions are quantitatively extracted in Triton X‐114 following centrifugation. 1.0 mol L?1 HNO3 nitric acid in methanol was added to the surfactant‐rich phase prior to its analysis by flame atomic absorption spectrometry (FAAS). The adopted concentrations for BIYPYBI, Triton X‐114 and HNO3 and bath temperature, centrifuge rate and time were optimized. Detection limits for Cu2+, Fe3+, Zn2+ and Ni2+ ions was 1.4, 2.2, 1.0 and 1.9 ng mL?1, respectively. The preconcentration factors for all ions was 30, while the enrichment factor of Cu2+, Fe3+, Zn2+ and Ni2+ ions was 35, 25, 39 and 30, respectively. The proposed procedure was applied to the analysis of real samples. 相似文献
225.
The first comprehensive study of shallow shell vibrations subjected to as many as 21 possible boundary conditions is presented. Thin shallow shell theory is used. Relatively accurate results for natural frequencies of doubly-curved shallow shells have been obtained. These can be used for benchmarking by researchers as well as reference data for practicing engineers. The Ritz method is used to solve for natural vibrations of these shells with arbitrary boundary conditions. Natural frequencies are presented for various shell curvatures including spherical, cylindrical and hyperbolic paraboloidal shells. 相似文献
226.
Ladder operators for the radial index of the paraxial optical modes in the cylindrical coordinates are calculated. The operators obey the su(1,1) algebra commutation relations. Based on this Lie algebra, we found that coherent modes constructed as eigenstates of the destruction operator or resulting from the action of the displacement operator on the fundamental mode are different. Some properties of these two kinds of radial coherent modes are studied in detail. 相似文献
227.
Faramarz Rostami‐Charati Zinatossadat Hossaini Ebrahim Gharaee Mohammad A. Khalilzadeh 《Journal of heterocyclic chemistry》2013,50(Z1):E174-E177
A one‐pot synthesis of oxazine derivatives via reaction between activated acetylenic compounds, benzoyl cyanide, and N‐nucleophiles in water as the solvent is described?. 相似文献
228.
The 1:1 intermediate generated by the addition of an isocyanide to a dialkyl acetylenedicarboxylate is trapped by the iminium ion intermediate that forms from the reaction between an aromatic aldehyde and diethylamine. The reactions were completed in the presence of silica gel powder. The product dialkyl 2-[(alkylamino)carbonyl]-3-[(Z)-1-(diethylamino)-1-arylmethylidene]succinates, were produced in acceptable yields. The reactions are completely regio- and stereoselective. 相似文献
229.
Saieed Akbari Ebrahim Ghorbani Jack H. Koolen Mohammad Reza Oboudi 《Journal of Algebraic Combinatorics》2010,32(3):459-464
Let G be a graph of order n such that \(\sum_{i=0}^{n}(-1)^{i}a_{i}\lambda^{n-i}\) and \(\sum_{i=0}^{n}(-1)^{i}b_{i}\lambda^{n-i}\) are the characteristic polynomials of the signless Laplacian and the Laplacian matrices of G, respectively. We show that a i ≥b i for i=0,1,…,n. As a consequence, we prove that for any α, 0<α≤1, if q 1,…,q n and μ 1,…,μ n are the signless Laplacian and the Laplacian eigenvalues of G, respectively, then \(q_{1}^{\alpha}+\cdots+q_{n}^{\alpha}\geq\mu_{1}^{\alpha}+\cdots+\mu _{n}^{\alpha}\). 相似文献
230.
Ahmad Shaabani Fahimeh Rezazadeh Ebrahim Soleimani 《Monatshefte für Chemie / Chemical Monthly》2008,139(8):931-933
Ammonium chloride as a very inexpensive and readily available reagent efficiently catalyzes one-pot, three-component Groebke condensation reactions of aldehydes, isocyanides, and 2-aminopyridines or 2-aminopyrimidines in methanol to afford the corresponding
imidazo[1,2-a]pyridines in high yields at room temperature.
Correspondence: Ahmad Shaabani, Department of Chemistry, Shahid Beheshti University, PO Box 19396-4716, Tehran, Iran. 相似文献