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排序方式: 共有195条查询结果,搜索用时 31 毫秒
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M. Piñeiro-Iglesias M. Miñones-Vázquez E. Vázquez-Blanco S. Muniategui-Lorenzo P. López-Mahía D. Prada-Rodríguez 《Chromatographia》2002,56(7-8):483-488
Summary The aim of this work is to establish the best conditions for concentration and purification steps in the trace analysis of
aliphatic and polycyclic aromatic hydrocarbons (PAH) from atmospheric particulate matter by gas chromatography-flame ionisation
detection (GC-FID) and high performance liquid chromatography with ultraviolet and fluorescence detection (HPLC-UV-FL). The
best results for the more volatile compound were obtained with a combination of rotary evaporation and a stream of nitrogen
(near to 100% for aliphatic hydrocarbons and from 70 to 105% for PAH). Two types of solid phase extraction (SPE)cartridges
(Supelclean
tm
LC-Silica SPE tubes and Sep-Pak? Plus silica cartridges) and glass column were examined for the purification and fractionation step. Blank chromatograms of
both types of cartridges analysed by GC-FID made this study difficult, because a PSS (programmed split-splitless) injector
was employed thereby increasing the sensitivity. This problem was not observed in the HPLC-UV-FL blank chromatograms of these
cartridges. Glass columns filled with silica and alumina were chosen because no interference was found in the GC-FID blank
chromatograms and the best recoveries in the fractionation of both aliphatic hydrocarbons and PAH were achieved. This is especially
important when aliphatic hydrocarbons concentrations are lower than 1 μg mL−1. Finally, the selected conditions were applied to the analysis of hydrocarbons in real atmospheric particulate samples. 相似文献
4.
Three important characters of the suspended load of the Yellow (Huanghe) River are discussed, i.e. its temporal fluctuation as a function of solar activity, its uneven spatial distribution along the main course and the inevitability of these phenomena as a natural earth process rather than a result of disturbed ecological system caused by human activity. Implications of this understanding with regard to the control of the Yellow River are also discussed. 相似文献
5.
Hu Yang Weisi Yin Xuxin Kong Min Xu Yefeng Yao Qun Chen Rongshi Cheng 《Colloid and polymer science》2006,284(8):935-940
The compact single-chain (SC) particulates of Poly(N-isopropylacrylamide) (PNIPAM), which have been formed above its lower critical solution temperature in an aqueous solution containing the surfactant of sodium n-dodecyl sulfate (SDS), were recovered from the solution by freeze-drying. Under scanning electron microscopy, the compact particulate appears as a spherical or elliptical particulate individually dispersed in SDS, which acts as a solid solvent to prevent agglomeration. The conformation of the compact SC particulates of PNIPAM dispersed in SDS had been studied by the solid-state high-resolution 13C NMR spectroscopy. The 13C spin-lattice relaxation time T
1 of the SC sample was determined in comparison with that of the original one. It was found that the T
1 of the methyl carbon in the isopropyl group of the SC sample was about 45% higher than that in the original multichain sample, which revealed the differences in the motion of the methyl group in the different condensed states and illuminated the characteristic conformation of the compact SC globular particulates of PNIPAM. 相似文献
6.
The elemental analysis and morphology of individual particles indicate that the dominant suspended particles in river water are kaolin covered with hydrated iron(III) oxide which strongly sorbs humic substances. Suspended particles, about 1 mg, collected from 250 ml of water by centrifugation, are treated with 0.7 ml of 0.1M sodium hydroxide to desorb humic substances. Approximately 60% of copper and 30% of lead on or in suspended particles exist as humic complexes. 相似文献
7.
Shirley H. Hercules David M. Hercules 《International journal of environmental analytical chemistry》2013,93(3):169-186
The technique of electron spectroscopy (ESCA) is reviewed. Those aspects are discussed which seem to be of greatest potential interest to workers in environmental studies. Basic theory of the photoelectron ejection process is considered along with the Auger effect. Factors affecting the calculation of electron binding energies are discussed. Instrumentation utilizing both magnetic and electrostatic monochromators is discussed in some detail. The nature of ESCA data is considered, along with an extensive tabulation of chemical shifts observed for 15 elements. Application of ESCA to surface studies is reviewed, using examples like effect of layers of material on electron intensities, investigations of zeolites and some elementary catalysis studies. A review of the quantitative aspects of ESCA considers the determination of arsenic in soils and the measurement of mixed oxide ratios. 相似文献
8.
Patricia Dähmlow Torsten Trittel Kathrin May Kirsten Harth Ralf Stannarius 《Liquid crystals》2018,45(7):993-1003
Elongated freely floating smectic bubbles are observed during their relaxation to equilibrium sphere shape. Unlike soap bubbles that perform weakly damped oscillations into equilibrium, this relaxation is overdamped in smectics by internal structure reorganisation processes. The bubble area reduction of centimetre-sized freely floating bubbles with few nanometres film thickness is recorded with high-speed optical imaging in microgravity and analysed quantitatively. We find a nearly linear reduction of the film area with time, driven by capillary forces and inhibited by smectic layer reorganisations. Characteristic times are in the milliseconds range, with little correlation to the film thickness and bubble size. Instead, the homogeneity of the films and the number and sizes of islands of excess layers that spontaneously form on the films appear to have crucial influence on the dynamics. The efficiency of this process sets the time scale of the film area shrinkage. We discuss the limitations of a minimalistic model that captures smectic layer reorganisation processes. 相似文献
9.
This letter describes an original freezing process that yields homogeneous solid films at ambient temperature with preservation of the layered structure of the chiral smectic phase. One of the most remarkable features of the process is its ability to provide complexly bent films with arbitrary three-dimensional shapes. Their optical homogeneity is observed in the planar as well as in the bent films. The method is very simple. After forming the films by spreading the liquid crystal above a hole in a glass slice placed over a hot stage, the film is heated from below. The hot film is exposed to ambient temperature. Then, a solid object at room temperature with a specifically adapted shape is immersed in the liquid film. The mechanical constraints imposed by the object curves the film and stabilises various solid two- and three-dimensional structures. Their homogeneous optical properties are due to long-range organisation of the molecular orientation (tilt), which combines with a complex helical arrangement of the frozen smectic layers. 相似文献
10.
Ali Sarafraz-Yazdi Farideh Mofazzeli Zarrin Es'haghi 《International journal of environmental analytical chemistry》2013,93(14-15):1108-1118
A new sample preparation method named directly suspended droplet liquid-liquid-liquid phase microextraction was used in this research for determination of three chlorophenols in environmental water samples. The analytes (2-chlorophenol, 3-chlorophenol and 4-chlorophenol) were extracted from 4.5?mL acidic donor phase, (pH 2, P1) into an organic phase, 350?µL?of benzene/1-octanol (90?:?10 v/v, P2) and then were back-extracted into a 7?µL droplet of an basic (pH 13) aqueous solution (acceptor phase, P3). In this method, contrary to the ordinary single drop liquid-phase microextraction technique, an aqueous large droplet is freely suspended on the surface of the organic solvent, without using a microsyringe as supporting device. This aqueous microdroplet is delivered at the top-centre position of an immiscible organic solvent which is laid over the aqueous donor sample solution while the solution is being agitated. Then, the acceptor phase containing chlorophenols was withdrawn back into a HPLC microsyringe and neutralised by adding of 7?µL HCl 0.1?M. The total amount was eventually injected into the HPLC system with UV detection at 225?nm for further analysis. Parameters such as the organic solvent, phases volumes, extraction and back-extraction times, stirring rate and pH values were optimised. The calibration graphs are linear in the range of 10–2000?µg?L?1 with r?≥?0.9973. The enrichment factors were ranged from 115 to 170, and the limit of detection (LOD, n?=?7) varied from 5 to 10?µg?L?1. The relative standard deviations (RSDs, n?=?5) were found 6.8 to 7.4 at S/N?=?3. All experiments were carried out at room temperature, (22?±?0.5°C). 相似文献