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41.
1-(2-pyridylazo) 2-naphtol (PAN) impregnated Ambersorb 563 resin was used as solid phase extractor of copper, nickel, cadmium, lead, chromium and cobalt ions in aqueous solutions prior to their atomic absorption spectrometric determinations. The parameters including pH, sample volume, matrix effects were also investigated. The relative standard deviation (R.S.D.) of the combined method of sample treatment, preconcentration and determination with atomic absorption spectrometry is generally lower than 10%. The limit of detection was between 0.21 and 1.4 μg l−1. The results were used for preconcentration of analyte ions from natural water samples. The method was also applied to a stream sediment standard reference material (GBW7309) for the determination of Cu, Ni, Cd, Pb, Cr and Co. 相似文献
42.
Ibrahim H. A. Badr 《Mikrochimica acta》2005,149(1-2):87-94
Membrane electrodes based on 2,2-dithiobis(benzothiazole), DTBBT, as a neutral carrier for silver ions are described. Silver-selective membrane electrodes formulated with 2wt% DTBBT ionophore and 50mol% TFPB in an FPNPE plasticized poly (vinyl chloride) exhibited near-Nernstian responses towards silver ions (60.3±0.5mVdecade–1) over a wide silver ion activity range of 0.83µM to 94mM. Increasing the amount of anionic sites, TFPB, to 100 or 150mol% (relative to the DTBBT weight) resulted in super-Nernstian responses toward silver ions. Membrane electrodes prepared using a low dielectric constant plasticizer, however, exhibited sub-Nernstian responses. Polymer membrane electrodes with optimal composition (i.e., 2wt% DTBBT, 50mol% TFPB in FPNPE plasticized poly(vinyl chloride)) exhibited high potentiometric selectivity towards silver ions over alkali, alkaline earth, transition metal ions, as well as heavy metal ions such as Hg2+ and Pb2+. A good correlation was found between the potentiometric selectivity coefficients and the change in the UV-visible spectra of the ionophore upon exposure to different metal ions. The overall performance of the silver-selective membrane electrodes based on DTBBT ionophore, which is available at low cost, was found to be comparable to the performance of silver electrodes prepared with Fluka silver ionophore-IV. A DTBBT-based silver electrode was used as an indicator electrode for titrations of silver ions using standard sodium chloride solutions. Sharp inflections occur at the end point, and the data obtained showed 99.4% recovery with a standard deviation of 0.7% (n=3). In addition, the applicability of the DTBBT-based silver-selective electrode is illustrated by measuring the silver concentrations in natural water spiked with silver nitrate and by analyzing the silver in electroplating wastewater samples. The results obtained utilizing a DTBBT-based silver electrode showed very good agreement with the standard methods of analysis. 相似文献
43.
Ibrahim MS 《Fresenius' Journal of Analytical Chemistry》2000,367(2):189-194
The electrochemical behavior of lumazine (LMZ), an important antibacterial agent, has been studied at the hanging mercury drop electrode (HMDE). The nature of the process taking place at the HMDE was clarified. Its adsorption behavior at HMDE has been studied by using a.c and cyclic voltammetry (CV). Both the molecule and its reduced product appeared to be adsorbed at the surface of the electrode. Controlled adsorptive accumulation of LMZ on the HMDE provides the basis for the direct stripping measurement of that compound in the subnanomolar concentration level. Experimental and instrumental parameters for the quantitative determination were optimized. Phase-selective a.c voltammetry provided the best signal and gave a detection limit of 0.15 microg L(-1) (9.0 x 10(-10) mol/L) LMZ in aqueous solution. Molecules or ions which may interfere were studied. 相似文献
44.
Six X-ray crystal structures are reported, all containing substituted triphenylmethanol derivative 4 either alone or as its mono or bis(chromium tricarbonyl) complexes. All four chromium complexes studied crystallize with two independent molecules in the crystallographic asymmetric unit. It is demonstrated that from the X-ray crystal structure of the acentric racemic (+/-)-(1pR,1' 'R)(1pS,1' 'S)-[Cr(CO)(3)(eta(6)-t-BuC(6)H(3)(CMeOMe)CPh(2)OH)], (+/-)-3, it is possible to deduce the 4-fold helical structure of the chiral (-)-(1pR,1' 'R) isomer, (-)-3. The bimetallic derivatives demonstrate the ability to control intermolecular interactions by the positioning of relative stereochemistry. 相似文献
45.
Mustafa R. Ibrahim Zacharia A. Fataftah Paul von Ragu Schleyer Peter D. Stout 《Journal of computational chemistry》1987,8(8):1131-1138
Sets of hydrogen molecule equivalents have been developed which permit the calculation of hydrogenation of different types of carbon-carbon bonds from ab initio total energies (3-21G and 6-31G* basis sets, and, to a more limited extent, for MP2/6-31G* data) of reactants and products. The calculated enthalpies of hydrogenation are in good agreement with experiment for unstrained molecules, with average errors on the order of 2 kcal/mol. The 6-31G* equivalents allow the enthalpies for strained molecules to be calculated accurately, but the 3-21G equivalents do not. The equivalents for both basis sets have been tested by calculating the enthalpies of hydrogenation of carbon-carbon bonds in nitrogen- and oxygen-containing organic molecules, free radicals, and classical carbocations. The results are in good agreement with experiment in most cases. 相似文献
46.
A. Jeyabharathi M. N. Ponnuswamy S. Nanjundan Hoong‐Kun Fun Suchada Chantrapromma Anwar Usman Ibrahim Abdul Razak 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(1):o26-o28
Chalcones (α,β‐unsaturated ketones) are effective antitumour agents. It has been proved that having halogen or methoxy groups substituted in various positions of the phenyl ring enhances the activity of chalcones many times. The title compounds, C21H20O5 and C19H15BrO3, respectively, were chosen for crystallographic study in order to determine their structures and conformations. In both compounds, the keto group is in the s‐cis conformation and is almost planar. There are weak intramolecular interactions in both structures. 相似文献
47.
Talaat Ibrahim El‐Emary 《中国化学会会志》2006,53(2):391-401
New derivatives of pyrazolo[3,4‐b]pyrazine and related heterocycles were prepared starting from 6‐amino‐3‐methyl‐1‐phenyl‐1H‐pyrazolo[3,4‐b]pyrazine‐5‐carbonitrile ( 2 ) and using the key intermediates 4 , 5 , 6 , 14 , 15 and 16 . Some of the prepared compounds were evaluated for their antifungal and antibacterial activities. 相似文献
48.
INTRODUCTION Epoxy resins are reactive polymers which when cured with a variety of chemicals lead to a host of useful thermosets. Since the epoxide is a strained ring, it readily undergoes addition and homopolymerization. The homopolymerization is a process catalysed by acids, bases, Lewis acids, t-amines as well as by inorganic salts. 相似文献
49.
3-[1′(1′H)-Substituent-pyrazol-5′-yl]benzo[5,6]coumarins and 3-(1′,2′-oxazol-5′-yl)benzo[5,6]coumarin were prepared via condensation of 3-(2′-formyl-1′-chlorovinyl)benzo[5,6] coumarin with hydrazine derivatives or hydroxylamine.Reaction of 3-[1′(1′H)-pyrazol-5′-yl]benzo[5,6]coumarin with alkyl halides,olefinic compunds or acid chlorides are described. 相似文献
50.
Jia‐Xiang Yang Yu‐Peng Tian Qing‐Liang Liu Yong‐Shu Xie Hoong‐Kun Fun Suchada Chantrapromma Ibrahim Abdul Razak 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(1):m43-m44
In the title compound, [Fe(C5H5)(C16H12N3OS)], the 8‐aminoquinoline and acylthiourea moieties are almost planar. There are two perpendicular arrangements of the molecules in the crystal with slightly different conformations. The two cyclopentadienyl rings in each molecule are parallel and eclipsed. 相似文献