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941.
The fabrication of a mini ozonizer and its application in the foam flotation-separation technique are described. The system rapidly generates ozone for instant use in small-scale oxidation processes. Its application to the separation of Ce(III) from an alkaline solution is demonstrated. 相似文献
942.
943.
Z. Iqbal V.P. Tomaselli O. Fahrenfeld K.D. Möller F.A. Ruszala E. Kostiner 《Journal of Physics and Chemistry of Solids》1977,38(8):923-927
A detailed investigation of the polarized Raman spectrum of monoclinic hydroxyapatite (OHAp) and a careful study of the low frequency infrared spectrum of polycrystalline OHAp, is reported. Most of the spectral details of Raman scattering are consistent with the local pseudo-hexagonal C6 factor group symmetry of OHAp. However, some features, for example the absence of TO-LO splitting for particular E1 phonon geometries and the splitting of the lowest frequency Raman line, are a reflection of the centrosymmetric monoclinic lattice of OHAp. Between 0 and 50cm?1, a temperature-dependent background, having E1 symmetry, and probably associated with OH? disordering flucuations, was observed in OHAp. Both OHAp and FAp displayed low frequency Raman lines which softened with decreasing temperature. However, no evidence for a phase transition was found in either OHAp or FAp in the 12–295 K temperature range. 相似文献
944.
A rapid spectrophotometric method for the determination of trace level lead using 1,5-diphenylthiocarbazone in aqueous micellar solutions. 总被引:2,自引:0,他引:2
A very simple, ultra-sensitive and fairly selective direct spectrophotmetric method is presented for the rapid determination of lead(II) at ultra-trace level using 1,5-diphenylthiocarbazone (dithizone) in micellar media. The presence of the micellar system avoids the previous steps of solvent extraction and reduces the cost and toxicity while enhancing the sensitivity, selectivity and the molar absorptivity. The molar absorptivities of the lead-dithizone complex formed in the presence of the cationic cetyltrimethylammonium bromide (CTAB) surfactants are almost ten times the value observed in the standard method, resulting in an increase in the sensitivity of the method. The reaction is instantaneous and the absorbance remains stable for over 24 h. The average molar absorption coefficient was found to be 3.99 x 10(5) L mol(-1) cm(-1) and Sandell's sensitivity was 30 ng cm(-2) of Pb. Linear calibration graphs were obtained for 0.06-60 mg L(-1) of Pb(II); the stoichiometric composition of the chelate is 1:2 (Pb:dithizone). The interference from over 50 cations, anions and complexing agents has been studied at 1 mg L(-1) of Pb(II). The method was successfully used in the determination of lead in several standard reference materials (alloys and steels), environmental water samples (potable and polluted), biological samples (human blood and urine), soil samples and solutions containing both lead(II) and lead(IV) and complex synthetic mixtures. The method has high precision and accuracy (sigma = +/-0.01 for 0.5 mg L(-1)). 相似文献
945.
Rotational and centrifugal distortion constants are determined for the ground state and several excited states of the lowest vibrational mode of l,3-dioxole-2-thione, the “envelope” ring-bending mode. The structure of the molecule is planar. The A-constant is 1% larger than that of 1,3-dioxole-2-one (vinylene carbonate), which indicates small changes in ring-geometry on substituting CS for CO. The dipole moment of 1,3-dioxole-2-thione deduced from Stark-effect measurements is (1.60 ± 0.02) × 10?29 Cm (4.81 ± 0.06 D). IR and Raman spectra lead to a complete analysis of the normal modes of vibration, based partially on a normal coordinate calculation. 相似文献
946.
C. David Gutsche Iftikhar Alam Muzaffar Iqbal Thomas Mangiafico Kye Chun Nam Janet Rogers Keat Aun See 《Journal of inclusion phenomena and macrocyclic chemistry》1989,7(1):61-72
Several facets of calixarene chemistry have been investigated including the mechanism of their formation by the base-induced condensation of phenols and formaldehyde, procedures for introducing functional groups onto the upper rim and lower rim of calixarenes, the conformational behavior of calixarene oxyanions, the formation of complexes in aqueous and nonaqueous systems, and the application of calixarenes as catalysts. 相似文献
947.
The extraction of chromium(VI) from aqueous hydrochloric, nitric and sulfuric acid solutions by diphenyl-2-pyridylmethane(DPPM)
dissolved in chloroform has been studied. Chromium(VI) is quantitatively extracted from hydrochloric acid solutions in the
range 0.1–1M. With increasing acid concentration, the extraction of chromium diminishes and in concentrated acid solutions
practically all the chromium remains in the aqueous phase. The quantitative back-extraction of chromium from the organic phase
is possible with HCl or HNO3 at concentrations higher than 5M through the use of reducing agents. The composition of the extracted chromium(VI) species
was studied in solution. The complexes (DPPMH)+HCrO
4
−
and (DPPMH)2Cr2O
7
−
are extracted for tracer and macro amounts of chromium(VI) respectively. The data have been utilized for the separation of
chromium(VI) from base metal ions. 相似文献
948.
Lead is quantitatively adsorbed as the lead N-methylethylxanthocarbamate (MEXC)-benzyldimethyltetradecylammonium (BDTA) ion pair complex on microcrystalline naphthalene in the pH range 4.0-11.0. The metal is desorbed with HCI and determined by differential pulse polarography. Alternatively lead can be quantitatively adsorbed on the adsorbent (MEXC-BDTA-naphthalene) packed in a column at a flow rate of 1-2 mL/min and determined similarly. Dissolved oxygen is removed by adding a few milliliters of 4% NaBH4 solution. The detection limit is 0.12 microg/mL at the minimum instrumental settings (signal-to-noise ratio, 2). Linearity was obtained over the concentration range 0.3-20.0 microg/mL with a correlation factor of 0.9998 and a relative standard deviation of +/- 0.98%. Various parameters, such as the effect of pH, volume of aqueous phase, flow rate, and the interference of a large number of metal ions and anions, were studied in detail to optimize the conditions for the trace determination of lead in various standard alloys, standard biological materials, and environmental samples. 相似文献
949.
Choudhary MI Begum A Abbaskhan A Ajaz A Shafique-ur-Rehman Atta-ur-Rahman 《Chemical & pharmaceutical bulletin》2005,53(11):1469-1471
A phytochemical investigation on the aerial parts of Lindelofia stylosa has resulted in the isolation of seven phenyl propanoids. This includes three analogs of lithospermic acid, along with rosmarinic acid and its ester derivatives. Compound 1 was identified as a new natural product. These compounds were studied for their antioxidant properties. 相似文献
950.
Neutron-activation analysis /NAA/ was used for the estimation of Hg, Co, Cr, Zn and Fe in leaves of various plants namelySapindus mukorossis, Alstonia scholaris andDiospyros embryopteris located in urban areas of Punjab, Pakistan. Different varities of tissues were found to have different concentration of trace elements when compared among themselves. Significant pollution has been observed. 相似文献