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排序方式: 共有1315条查询结果,搜索用时 31 毫秒
991.
Brahim Bennani Bouchra Filali Baba Najib Ben Larbi Abdelatif Boukir Abdelali Kerbal Mostafa Mimouni Taibi Ben Hadda Bartosz Trzaskowski Abraham F. Jalbout 《Journal of heterocyclic chemistry》2007,44(3):711-716
992.
The construction and general performance of novel potentiometric membrane ion selective electrodes for determination of papaverine hydrochloride has been described. They are based on the formation of the ion association complexes of papaverine (PA) with tetraphenylborate (TPB)(I) or tetrathiocyanate (TTC)(II) counter anions as electro-active material dispersed in a PVC matrix. The electrodes show fast, stable, near Nernstian response for 1 x 10(-2) to 6 x 10(-5) M and 1 x 10(-2) to 1 x 10(-5) M for PA-TPB and PA-TTC respectively at 25 degrees C over the pH range of 3-5.0 with a cationic slope of approximately 56.5 +/- 0.5 mV/decade for both sensors respectively. The lower detection limit is 4 x 10(-5) and 8 x 10(-6) M for PA- I and PA-II respectively with fast response time ranging from 20-45 sec. Selectivity coefficients for PA relative to a number of interfering substances were investigated. There is a negligible interference from the studied cations, anions, and pharmaceutical excipients. The determination of 4.0- 3000.0 microg/ml of PA in aqueous solutions shows an average recovery of 99.1% and a mean relative standard deviation of 1.4 at 100microg/ml. The direct determination of PA in some formulations (Vasorin injection) gave results that compare favorably with those obtained using the British Pharmacopoeia method. Potentiometric titration of PA with sodium tetraphenylborate and potassium thiocyanate as titrants utilizing the papaverine electrode as an end point indicator electrode has been carried out. 相似文献
993.
A very simple liquid chromatographic technique was developed and validated for the simultaneous determination of 2 antihistaminic drugs, loratadine (LT) and terfenadine (TR), and their major active metabolites, desloratadine (DL) and fexofenadine (FX), respectively, in human serum. LT, DL, TR, and FX from directly injected serum samples were enriched on a protein-coated RP8 silica precolumn (10 x 4.6 mm id) while serum constituents, such as proteins and salts, were eluted to waste. Using an online column-switching system, the drugs and their metabolites were quantitatively transferred and separated on a second analytical column (Shim-pack 5 microm particle size cyanopropyl, 250 x 4.6 mm id) followed by ultraviolet detection at 243 nm for LT and DL and 220 nm for TR and FX. Very good precision, accuracy, and linearity were obtained over the range of 10-1000 ng/mL for LT and DL, 10-500 ng/mL for TR, and 10-3000 ng/mL for FX in human serum. High extraction recoveries from serum ranging from 96.03 to 98.19, 95.44 to 97.26, 95.61 to 98.17, and 95.60 to 97.89 for LT, DL, TR, and FX, respectively, were obtained. 相似文献
994.
Parthenolide, a germacranolide-type sesquiterpene lactone, was estimated in Tanacetum parthenium (L.) cultivated in Egypt by using colorimetric, planar chromatographic, and high-performance liquid chromatographic (HPLC) methods. Parthenolide levels in the open-field herb and aseptically germinated shoots were also compared by using the HPLC method. Parthenolide was produced and estimated for the first time in the callus culture of the plant. In addition, 2 Egyptian market preparations were analyzed for their parthenolide content by using the HPLC method. The relative standard deviations were 0.093, 0.095, and 0.098% (n = 5, 5, and 7, respectively), and the corresponding recoveries were 98.2, 98.9, and 99.4% for the colorimetric, planar chromatographic, and HPLC determinations, respectively. 相似文献
995.
Zakaria Dahbi Maron F. Anka Mostafa Mansour Moisés Rojas Clebson Cruz 《Annalen der Physik》2023,535(3):2200537
Studying quantum properties in solid-state systems is a significant avenue for research. In this scenario, double quantum dots appear as a versatile platform for technological breakthroughs in quantum computation and nanotechnology. This work inspects the thermal entanglement and quantum coherence in two-coupled DODs, where the system is exposed to an external stimulus that induces an electronic transition within each subsystem. The results show that the introduction of external stimulus induces a quantum level crossing that relies upon the Coulomb potential changing the degree of quantum entanglement and coherence of the system. Thus, the quantum properties of the system can be tuned by changing the transition frequency, leading to the enhancement of its quantum properties. 相似文献
996.
Dina Mostafa Mahmoud A. Zaky Ramy M. Hafez Ahmed S. Hendy Mohamed A. Abdelkawy Ahmed A. Aldraiweesh 《Mathematical Methods in the Applied Sciences》2023,46(1):656-674
We present a class of orthogonal functions on infinite domain based on Jacobi polynomials. These functions are generated by applying a tanh transformation to Jacobi polynomials. We construct interpolation and projection error estimates using weighted pseudo-derivatives tailored to the involved mapping. Then, using the nodes of the newly introduced tanh Jacobi functions, we develop an efficient spectral tanh Jacobi collocation method for the numerical simulation of nonlinear Schrödinger equations on the infinite domain without using artificial boundary conditions. The applicability and accuracy of the solution method are demonstrated by two numerical examples for solving the nonlinear Schrödinger equation and the nonlinear Ginzburg–Landau equation. 相似文献
997.
A new sensitive, simple, rapid, and precise RP LC method with hydrochlorothiazide as internal standard has been developed for resolving two binary mixtures, perindopril with indapamide and captopril with indapamide, in pharmaceutical formulations. The drugs were separated at room temperature on a 250 mm × 4.6 mm, 5-μm particle, cyanopropyl column with 10 mm KH2PO4, pH 6.0-methanol 55:45 (v/v) as mobile phase at a flow rate of 1 mL min?1. Detection was at 210 nm. Factors affecting the separation process were studied and optimized. The linearity, accuracy, and precision of the method were good, and the method was successfully applied to the determination of the two binary combinations in synthetic mixtures and commercial pharmaceutical products. 相似文献
998.
A stability-indicating reversed-phase liquid chromatographic (RPLC) method has been established for analysis of ramipril (RAM)
and moexipril hydrochloride (MOEX.HCl) in the presence of the degradation products generated in studies of forced decomposition.
The drug substances were subjected to stress by hydrolysis (0.1 m NaOH and 0.1 m HCl), oxidation (30% H2O2), photolysis (254 nm), and thermal treatment (80 °C). The drugs were degraded under basic and acidic conditions and by thermal
treatment but were stable under other stress conditions investigated. Successful separation of the drugs from the degradation
products was achieved on a cyanopropyl column with 40:60 (v/v) aqueous 0.01 m ammonium acetate buffer (pH 6)–methanol as mobile phase at a flow rate of 1 mL min−1. Detection was by UV absorption at 210 nm. Response was a linear function of concentration over the range 5–50 μg mL−1 (r > 0.9995), with limits of detection and quantitation (LOD and LOQ) of 0.04 and 0.09 μg mL−1, respectively, for RAM and 0.014 and 0.32 μg mL−1, respectively, for moexipril. The method was validated for specificity, selectivity, solution stability, accuracy, and precision.
Statistical analysis proved the method enabled reproducible and selective quantification of RAM and MOEX as the bulk drug
and in pharmaceutical preparations. Because the method effectively separates the drugs from their degradation products, it
can be used as stability-indicating. 相似文献
999.
Hassan S. Bazzi Siham Y. AlQaradawi Adel Mostafa El-Metwally Nour 《Journal of Molecular Structure》2008,879(1-3):60-71
The interactions of the electron donors piperazine (PIP) and N,N′-dimethylpiperazine (DMPIP) with the σ-acceptor iodine and the π-acceptors tetracyanoethylene (TCNE) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) were studied spectrophotometrically in chloroform at 25 °C. The electronic and infrared spectra of the resulting charge-transfer complexes were recorded, in addition to thermal analysis. The results obtained showed that the stoichiometries of the reactions are not fixed and depend on the nature of both the donor and the acceptor. The formed CT-complexes have the formulas of , [(PIP)(TCNE)2], [(PIP)(DDQ)2], , [(DMPIP)(TCNE)2] and [(DMPIP)(DDQ)2]. A general mechanism explaining the formation of triiodide complexes was suggested. 相似文献
1000.
Hamid Reza Azimi Mostafa Rezaei Farhang Abbasi Ali Charchi Yahya Bahluli 《Thermochimica Acta》2008,474(1-2):72-77
Methylmethacrylate-styrene (MMA-St) random copolymer was synthesized by suspension copolymerization. The thermal degradation of MMA-St copolymer and EPS lost foams was studied by non-isothermal thermal gravimetric analysis under nitrogen purge. Thermal decomposition behavior of MMA-St copolymer lost foam was examined and compared with EPS. It was found that EPS foam starts to decompose at higher temperatures than MMA-St copolymer foam in all heating rates. The apparent activation energy was calculated by the Flynn-Wall-Ozawa method. It has been concluded that the model fitting methods unable to reveal the complexity of the pyrolysis process and the model-free methods can be suggested as a reliable way of determining the kinetic parameters. 相似文献