Search results for "Photometry"
showing 10 items of 797 documents
Steroidal saponins from the roots of Smilax aspera subsp. mauritanica
2008
Two new steroidal saponins (1, 2) were isolated from the roots of Smilax aspera subsp. mauritanica (POIR.) ARCANG. (Liliaceae), together with the known curillin G (3), asparagoside E (4), asparoside A (5), asparoside B (6) and the phenolic compound resveratrol (7). Their structures were established mainly on the basis of 600 MHz 2D-NMR spectral data. 3 exhibited antifungal activity against the human pathogenic yeasts Candida albicans, C. glabrata and C. tropicalis (minimum inhibitory concentrations of 25, 25 and 50 microg/ml, respectively) whereas the other compounds were inactive.
The determination of antimony and arsenic concentrations in fly ash by hydride generation inductively coupled plasma optical emission spectrometry
2011
Abstract Hydride generation inductively coupled plasma optical emission spectrometry (HG-ICP-OES) was used in the determination of As and Sb concentrations in fly ash samples. The effect of sample pre-treatment reagents and measurement parameters used for hydride generation was evaluated. Due to memory effects observed, the appropriate read delay time was adjusted to 60 s resulting in RSDs 0.6% and 2.3% for As and Sb, respectively. The most suitable volumes of pre-reduction reagents for 10 mL of sample were 4 mL of KI/ascorbic acid (5%) and 6 mL of HCl (conc.). The determination of Sb was significantly interfered by HF, but the interference could be eliminated by adding 2 mL of saturated bo…
Spectroelectrochemistry of cytochrome c and azurin immobilized in nanoporous antimony-doped tin oxide
2011
Stable immobilization of two redox proteins, cytochrome c and azurin, in a thin film of highly mesoporous antimony-doped tin oxide is demonstrated via UV-vis spectroscopic and electrochemical investigation.
Determination of antimony in drinking waters by an inexpensive, reproducible hydride generator for atomic spectroscopy.
1991
A method for determining antimony in drinking waters is described. In order to prevent a substantial error caused by the different oxidation states of antimony, Sb(V) is reduced to Sb(III) with potassium iodide-ascorbic acid. Covalent hydride is generated with a home made device by adding NaBH4. The hydride is then atomized in a flame-heated silica tube and atomic absorption is measured spectrophotometrically. The optimal conditions for this determination are discussed and interference effects are described. Results obtained by determining linearity range (0-200 ng), detection (LOD) and quantitation (LOQ) limits (LOD = 0.347 ng/ml, LOQ = 1.158 ng/ml), precision (instrumental CV 4.08% and me…
Increase in stability and change in supramolecular structure of β-carotene through encapsulation into polylactic acid nanoparticles
2011
International audience; β-Carotene (BC) exhibits controversial antioxidant properties as it may act also as a prooxidant. Its stability toward oxidation depends on its dispersion form and can be increased through encapsulation. In this study, oxidation of BC from synthetic and natural origins was investigated after dispersion in Tween micelles or poly lactic acid (PLA) particles. Two oxidation systems were used: autooxidation and oxidation by xanthine oxidase-generated-reactive oxygen species. Results showed that synthetic BC formed nanometric negatively-charged particles in both Tween micelle and PLA systems, whereas the natural BC sample used was shown to be already pre-oxidised, forming …
Antioxidant activities of sicilian prickly pear (Opuntia ficus indica) fruit extracts and reducing properties of its betalains: betanin and indicaxan…
2002
Sicilian cultivars of prickly pear (Opuntia ficus indica) produce yellow, red, and white fruits, due to the combination of two betalain pigments, the purple-red betanin and the yellow-orange indicaxanthin. The betalain distribution in the three cultivars and the antioxidant activities of methanolic extracts from edible pulp were investigated. In addition, the reducing capacity of purified betanin and indicaxanthin was measured. According to a spectrophotometric analysis, the yellow cultivar exhibited the highest amount of betalains, followed by the red and white ones. Indicaxanthin accounted for about 99% of betalains in the white fruit, while the ratio of betanin to indicaxanthin varied fr…
Betacyanins as phenol antioxidants. Chemistry and mechanistic aspects of the lipoperoxyl radical-scavenging activity in solution and liposomes.
2009
Reaction kinetics of betanin and its aglycone betanidin towards peroxyl radicals generated from the azo-initiated oxidation of methyl linoleate in methanol, and of a heterogeneous aqueous/soybean phosphatidylcholine liposomal system, were studied by monitoring formation of linoleic acid hydroperoxides and consumption of the pigments. Betanin was a weak retarder in methanol, and an effective chain breaking antioxidant in the liposomal model, indicating that kinetic solvent effects and partition in lipid bilayers may affect its activity. Betanidin behaved as a chain terminating antioxidant in both models. Kinetic parameters characterizing peroxyl radical-scavenging activity showed that betani…
Symbiosis between photoactive nanoparticles and their organic ligands.
2013
Photoactive spherical metal and semiconductor nanoparticles (NPs) are smart systems that exhibit unique properties, such as a high surface-to-volume ratio, a broad absorption spectrum and size-dependent properties. They are capped with a considerable number of ligands required to give rise to stable organic and aqueous NP colloidal solutions. In addition, the ligands can also be used to introduce functionality at the NP periphery. In this case, the NP could act as a 3D-scaffold, which would make a high local concentration of a functional moiety at the NP periphery possible, moreover, the photophysical properties of the NP could be tuned. The combined action of the organic capping and the in…
Simultaneous Determination of Adrenaline and Noradrenaline by First Derivative Spectrophotometry in a Fia Assembly
1996
Abstract This article deals with the design of an unsegmented-flow injection manifold for the simultaneous determination of adrenaline and noradrenaline two structurally related compounds with overlapping spectra. An FIA manifold is proposed for the simultaneous determination in which the sample solution is directly injected into a carrier-reagent stream of aqueous NaOH. The selected wavelengths (first derivative) were 394 and 342 nm, for noradrenaline and adrenaline, respectively with an integration time of 0.4 s. The calibration graphs are linear over the range 2.0–30 ppm for both drugs. The method is applied to different synthetic mixtures of both drugs.
The use of utraviolet-visible spectrophotometry in the determination of average properties of nonylphenol ethylene oxide condensates
1983
Ultraviolet spectrophotometry is usd in the determination of average molecular weight (M), average degree of polymerization (X), the hydrophilic-lipophilic balance (HLB) and ethylene oxide percentage of nonylphenol ethylene oxide condensates. The method is based on determination of the absorptivity a, expressed in g lt-1 cm−1, from the absorbances measured at 275 nm for a series of dilutions of an aqeuous ethanolic solution (60:40, v/v/) of a given product, followed by numerical interpolation of this value in the expression a = f(HLB), log a = f(log M), and log a = f(log X). These expressions are obtained from reference samples or samples previously analyzed. The proposed method gives relat…