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Dunge Ashenafi Mattias Ungerböck Jos Hoogmartens Erwin Adams 《Chromatographia》2013,76(21-22):1495-1503
A gradient liquid chromatographic (LC) method for control of emtricitabine (FTC) was validated for the analysis of FTC formulations (capsules and oral solution) and fixed-dose-combination tablets containing FTC [FTC combined with tenofovir disoproxil fumarate (TDF) and FTC combined with TDF and efavirenz (EFV)]. The method is based on the purity test recently prescribed in the International Pharmacopoeia and uses a Hypersil BDS C18 column (25 cm × 4.6 mm i.d.), 5 μm kept at a temperature of 35 °C. Other reversed-phase columns were also investigated. The mobile phases for gradient elution consist of acetonitrile, phosphate buffer and water. The flow rate is 1.0 mL min?1 and UV detection is performed at 280 nm. The method is capable of separating the main components from one another, from the inactive ingredients and from the main degradation products. The method was validated with respect to accuracy, precision, sensitivity and linearity for each component and the solution media were optimized. Finally, commercial FTC capsules, FTC oral solution, FTC/TDF tablets and FTC/TDF/EFV tablets were examined. 相似文献
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In this paper a simple and highly sensitive electroanalytical method for the determination of caffeine content using 1,4-benzoquinone modified carbon paste electrode is presented. The method is based on suppression of 1,4-benzoquinone peak current on addition of caffeine. Square-wave and cyclic voltammetric techniques were utilised for the investigation. The 1,4-benzoquinone modified electrode exhibited a well-defined peak with reproducible peak current values for repetitive measurements; and showed a decrease in peak current value with an increase in caffeine content. The result revealed two linear range regions between 0 mmol L−1 and 0.5 mmol L−1 and 0.5 mmol L−1 and 8.0 mmol L−1, with detection limits of 0.3 μmol L−1 and 5.1 μmol L−1, respectively. The method was then successfully applied to the determination of caffeine content in coffee samples. The effects of pH, electrode composition, step potential, pulse amplitude and square-wave frequency on the voltammetric responses were also investigated. 相似文献
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Aruna J. Weerasinghe Agozie N. Oyeamalu Fasil A. Abebe Andre R. Venter Ekkehard Sinn 《Journal of fluorescence》2016,26(3):891-898
Two novel sensors bearing rhodamine B and quinoline units have been synthesized. One of these, 1, allows sensitive and selective detection of Ni2+ and Cr3+ by forming non-fluorescent (1-Ni2+) and fluorescent (1-Cr3+) complexes respectively. Both metals trigger the formation of highly colored ring-open spirolactam. These form excellent probes for CN? which quenches the fluorescence of the 1-Cr3+ complex by extracting the Cr3+. Both Cr3+ and Cu2+ gave color changes with 2, but they are easily identified separately via the large fluorescence enhancement that occurs only with Cr3+. 相似文献
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Chiao-Fan Chiu Jinn-Hsuan Ho Eskedar Tessema Yijing Lu Chia-Rui Shen Chang-Wei Lin Norman Lu 《Molecules (Basel, Switzerland)》2021,26(2)
Homogeneous catalysts PtCl2[5,5′-bis-(n-ClCF2(CF2)3CH2OCH2)-2,2′-bpy] (2A) and PtCl2[5,5′-bis-(n-HCF2(CF2)3CH2OCH2)-2,2′-bpy] (2B), which contained short fluorous chains, were synthesized and used in catalysis of hydrosilylation of alkynes. In these reactions the thermomorphic mode was effectively used to recover these catalysts from the reaction mixture up to eight cycles by taking advantage of heterogeneous phase separation at ice temperature. This kind of catalysis had previously been observed in fluorous catalysts of platinum containing about 50% F-content, but in this work the percentage of F-content is decreased to only about 30%, by which we termed them as “very light fluorous”. Our new type of catalyst with limited number of F-content is considered as the important discovery in the fluorous technology field as the reduced number of fluorine atoms will help to be able to comply the EPA 8-carbon rule. The metal leaching after the reaction has been examined by ICP-MS, and the testing results show the leaching of residual metal to be minimal. Additionally, comparing these results to our previous work, fluorous chain assisted selectivity has been observed when different fluorous chain lengths of the catalysts are used. It has been found that there exists fluorous chain assisted better selectivity towards β-(E) form in the Pt-catalyzed hydrosilylation of non-symmetric terminal alkyne when the Pt catalyst contains short fluorous chain (i.e., 4 Cs). Phenyl acetylenes showed the opposite regioselectivity due to pi-pi interaction while using the same catalyst via Markovnikov’s addition to form terminal vinyl silane, which is then a major product for Pt-catalyzed hydrosilylation of terminal aryl acetylene with triethylsilane. Finally, the kinetic studies indicate that the insertion of alkyne into the Pt-H bond is the rate-determining step. 相似文献
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Glassy carbon electrode was modified by electropolymerization of 4-amino-3-hydroxynaphthalene sulfonic acid. Cyclic voltammetric study of quinine showed higher current response at the modified electrode compared to the bare and activated glassy carbon electrodes in pH 7.0 phosphate buffer solution. Under optimized conditions, a calibration curve was obtained by square wave voltammetry at the modified electrode. The linear relationship between the peak current and the concentration of quinine in the range of 1.0?×?10?7 to 1.0?×?10?5 M was I pa (in microamperes)?=?6.26C (in micromolars)?+?0.2997 (R 2?=?0.999). The detection limit calculated (S/N?=?3) was 1.42?×?10?8 M, which is much lower than similar reports. The method was successfully applied for the determination of quinine in spiked human urine, and pharmaceutical formulations and recovery values >90 % were obtained. 相似文献
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Girma Hailu Genene Tessema Balla Diop Ngom Ncholu Manyala Malik Maaza 《Applied Physics A: Materials Science & Processing》2009,96(3):685-689
The nonlinear absorption (NLA) properties of five different types of porphyrins were studied using the Z-scan technique. The
porphyrins under investigation were confined into Nafion column matrix membrane in order to protect them from possible degradation.
The results of the experiments have indicated that all the porphyrins tested exhibited interesting NLA properties. The nonlinear
absorption coefficients (β’s) were determined at different porphyrin concentrations by comparing the Z-scan data with the theoretical functions. 相似文献
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Günter Michl Dawit Abebe Franz Bucar Asfaw Debella Olaf Kunert MartinG. Schmid Efrem Mulatu Ernst Haslinger 《Helvetica chimica acta》2000,83(2):359-363
Two new bisdesmosidic triterpenoid saponins, i.e. 1 and 2 , were isolated, besides the three known saponins 3 – 5 , from the MeOH extract of the aerial parts of Achyranthes aspera Linn. (Amaranthaceae). Their structures were elucidated as β‐D ‐glucopyranosyl 3β‐[O‐α‐L ‐rhamnopyranosyl‐(1→3)‐O‐β‐D ‐glucopyranuronosyloxy]machaerinate ( 1 ) and β‐D ‐glucopyranosyl 3β‐[O‐β‐D ‐galactopyranosyl‐(1→2)‐O‐α‐D ‐glucopyranuronosyloxy]machaerinate ( 2 ) by NMR spectroscopy, including 2D‐NMR experiments (machaerinic acid=3β,21β‐dihydroxyolean‐12‐en‐28‐oic acid). The other saponins were identified as β‐D ‐glucopyranosyl 3β[O‐α‐L ‐rhamnopyranosyl‐(1→3)‐O‐β‐D ‐glucopyranuronosyloxy]oleanolate ( 3 ), β‐D ‐glucopyranosyl 3‐β‐[O‐β‐D ‐galactopyranosyl‐(1→2)‐O‐β‐D ‐glucopyranuronosyloxy]oleanolate ( 4 ), and β‐D ‐glucopyranosyl 3β‐[O‐β‐D ‐glucopyranuronosyloxy]oleanolate ( 5 ) (oleanolic acid=3β‐hydroxyolean‐12‐en‐28‐oic acid). 相似文献
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Dr. Abebe R. Woldu Pooya Talebi Asfaw G. Yohannes Jianyin Xu Xu-Dong Wu Dr. Samira Siahrostami Dr. Liangsheng Hu Prof. Xiao-Chun Huang 《Angewandte Chemie (International ed. in English)》2023,62(29):e202301621
Tin disulfide (SnS2) is a promising candidate for electrosynthesis of CO2-to-formate while the low activity and selectivity remain a great challenge. Herein, we report the potentiostatic and pulsed potential CO2RR performance of SnS2 nanosheets (NSs) with tunable S-vacancy and exposure of Sn-atoms or S-atoms prepared controllably by calcination of SnS2 at different temperatures under the H2/Ar atmosphere. The catalytic activity of S-vacancy SnS2 (Vs-SnS2) is improved 1.8 times, but it exhibits an exclusive hydrogen evolution with about 100 % FE under all potentials investigated in the static conditions. The theoretical calculations reveal that the adsorption of *H on the Vs-SnS2 surface is energetically more favorable than the carbonaceous intermediates, resulting in active site coverage that hinders the carbon intermediates from being adsorbed. Fortunately, the main product can be switched from hydrogen to formate by applying pulsed potential electrolysis benefiting from in situ formed partially oxidized SnS2−x with the oxide phase selective to formate and the S-vacancy to hydrogen. This work highlights not only the Vs-SnS2 NSs lead to exclusively H2 formation, but also provides insights into the systematic design of highly selective CO2 reduction catalysts reconstructed by pulsed potential electrolysis. 相似文献
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