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1.
P. C. Hauser Thusitha W. T. Rupasinghe 《Fresenius' Journal of Analytical Chemistry》1997,357(8):1056-1060
A compact photometer is based on up to seven different light-emitting diodes whose light is guided into a photometric cell
by means of a fibre-optic coupler. The wavelength is selected by switching on the appropriate light source. The application
of this multi-wavelength photometer to the determination of binary metal ion samples is demonstrated using model mixtures.
Solutions of Fe, Co, Cu, Ni, Cr and Mn were used in combination with several photometric reagents. It was found that the instrument
yielded concentration measurements which were usually within a few percent of the correct concentration. These results are
comparable to reported data obtained with conventional instruments for similar measurements. The application of the instrument
for simultaneous determination in flow-injection analysis employing rapid computer controlled switching of the light-emitting
diodes is also demonstrated. A limitation in the use of light-emitting diodes for the simultaneous determination was found
to arise from the fact that in some instances non-linear calibration curves are obtained when employing light-emitting diodes
as light sources. This occurs when the absorptivity of the measured compound changes over the emission band of the diodes.
Multiple regression analysis is then not easily possible.
Received: 16 September 1996/Revised: 14 October 1996/Accepted: 16 October 1996 相似文献
2.
The light originating from seven light-emitting diodes of different colours is guided, one at a time, into a measuring cell by means of a fibre optic coupler. Detection is carried out with photodiodes which are connected to a log-ratio amplifier yielding direct absorbance readings. Optical filters are used to narrow the emission band from blue light emitting diodes as these bands are relatively wide compared to those of the emitters of other colours. An inexpensive and compact multi-wavelength photometer covering the visible range is thus obtained, which in many cases can replace a conventional spectrophotometer for absorbance measurements. The performance for a range of commonly used photometric analytical procedures is described and compared to conventional measurements with a spectrophotometer. 相似文献
3.
4.
Bian SW Mudunkotuwa IA Rupasinghe T Grassian VH 《Langmuir : the ACS journal of surfaces and colloids》2011,27(10):6059-6068
Metal oxide nanoparticles are used in a wide range of commercial products, leading to an increased interest in the behavior of these materials in the aquatic environment. The current study focuses on the stability of some of the smallest ZnO nanomaterials, 4 ± 1 nm in diameter nanoparticles, in aqueous solutions as a function of pH and ionic strength as well as upon the adsorption of humic acid. Measurements of nanoparticle aggregation due to attractive particle-particle interactions show that ionic strength, pH, and adsorption of humic acid affect the aggregation of ZnO nanoparticles in aqueous solutions, which are consistent with the trends expected from Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Measurements of nanoparticle dissolution at both low and high pH show that zinc ions can be released into the aqueous phase and that humic acid under certain, but not all, conditions can increase Zn(2+)(aq) concentrations. Comparison of the dissolution of ZnO nanoparticles of different nanoparticle diameters, including those near 15 and 240 nm, shows that the smallest nanoparticles dissolve more readily. Although qualitatively this enhancement in dissolution can be predicted by classical thermodynamics, quantitatively it does not describe the dissolution behavior very well. 相似文献
5.
P. C. Hauser Thusitha W. T. Rupasinghe 《Analytical and bioanalytical chemistry》1997,357(8):1056-1060
A compact photometer is based on up to seven different light-emitting diodes whose light is guided into a photometric cell
by means of a fibre-optic coupler. The wavelength is selected by switching on the appropriate light source. The application
of this multi-wavelength photometer to the determination of binary metal ion samples is demonstrated using model mixtures.
Solutions of Fe, Co, Cu, Ni, Cr and Mn were used in combination with several photometric reagents. It was found that the instrument
yielded concentration measurements which were usually within a few percent of the correct concentration. These results are
comparable to reported data obtained with conventional instruments for similar measurements. The application of the instrument
for simultaneous determination in flow-injection analysis employing rapid computer controlled switching of the light-emitting
diodes is also demonstrated. A limitation in the use of light-emitting diodes for the simultaneous determination was found
to arise from the fact that in some instances non-linear calibration curves are obtained when employing light-emitting diodes
as light sources. This occurs when the absorptivity of the measured compound changes over the emission band of the diodes.
Multiple regression analysis is then not easily possible.
Received: 16 September 1996/Revised: 14 October 1996/Accepted: 16 October 1996 相似文献
6.
Thusitha Rupasinghe Terence J. Cardwell Robert W. Cattrall Ian D. Potter Spas D. Kolev 《Analytica chimica acta》2004,510(2):225-230
A novel pervaporation-flow injection (PFI) system for the determination of As(III) in aqueous samples at μg l−1 level is described. The analytical procedure involved stopping the acceptor stream and injecting acidified As(III) samples into a 0.3 M HCl stream which was mixed with a 0.14 M sodium borohydride in 0.025 M NaOH stream. The arsine generated was transported in the pervaporation unit across a semi-permeable membrane (1.5 mm thickness) into the static acceptor solution containing 1.0×10−4 M KMnO4 in 0.1 M H2SO4 where it was oxidised. The acceptor stream was restarted after 6.5 min, and the decrease in permanganate absorbance at 528 nm was monitored to determine the initial concentration of As(III) in the samples. The method is characterised by a linear calibration range from 0.25 to 2000 μg l−1, a detection limit of 0.18 μg l−1 and a sampling frequency of 7 h−1. Samples containing As(V) were pre-treated with KI and HCl prior to injection to reduce As(V) to As(III). The effects of common anionic and cationic interferences, and the elimination of some metallic interferences using
-cysteine are discussed. The method was applied to the analysis of environmental waters and the results were in good agreement with hydride generation atomic absorption spectrometric data. 相似文献
7.
Solvent-free microwave extraction (SFME) for the isolation of essential oil from leaves of Murraya koenigii L. (Rutaceae) has been compared with the conventional hydro-distilled oil (HD) in terms of yield, composition, antioxidant activity, and antibacterial activity against Listeria innocua. The yield of essential oil obtained from 30 min of SFME was similar to that of HD for 180 min. By GC-MS analysis, the major compounds of the essential oil extracted by SFME, which were obtained in somewhat lower amounts than in the essential oil obtained by HD, were alpha-copaene (44.3%), beta-gurjunene (25.5%), isocaryophyllene (12.1%), beta-caryophyllene (8.7%) and germacrene D (2.9%). The content of oxygenated terpenes, slightly higher for the SFME-essential oil (2.3%) than the HD-essential oil (1.4%), were much lower than that of nonoxygenated terpenes in both oils. DPPH radical scavenging activities of both essential oils were relatively low (10%-24%). Complete inhibition of growth of L. innocua was observed with both SFME and HD essential oils, at 400 and 600 microg/mL (minimum inhibitory concentration), respectively. The SFME-essential oil at 300 microg/mL provided 92% inhibition, indicating its potential as a natural antimicrobial agent. 相似文献
8.
Jayasinghe L Amarasinghe NR Arundathie BG Rupasinghe GK Jayatilake NH Fujimoto Y 《Natural product research》2012,26(8):717-721
Chemical investigation of the leaves of Elaeocarpus serratus yielded myricitrin (1), mearnsetin 3-O-β-D-glucopyranoside (2), mearnsitrin (3), tamarixetin 3-O-α-L-rhamnopyranoside (4) and the fruits of Filicium decipiens yielded three flavonol glycosides, kaempferol 3-O-rutinoside (5), kaempferol 3-O-robinobioside (6) and trifolin (7). Compound 1 showed strong antioxidant activity against DPPH. 相似文献
9.
Quercetin and quercetin glycosides are physiologically active flavonol molecules that have been attributed numerous health benefits. Recovery of such molecules from plant matrices depends on a variety of factors including polarity of the extraction solvent. Among the solvents of a wide range of dielectric constants, methanol recovered the most quercetin and its glycosides from dehydrated 'Idared' apple peels. When ultra-sonication was employed to facilitate the extraction, exposure of 15 min of ultrasound wavelengths of dehydrated apple peel powder in 80% to 100% (v/v) methanol in 1:50 (w:v) solid to solvent ratio provided the optimum extraction conditions for quercetin and its glycosides. Acidification of extraction solvent with 0.1% (v/v) or higher concentrations of HCl led to hydrolysis of naturally occurring quercetin glycosides into the aglycone as an extraction artifact. 相似文献