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11.
Bozlee BJ Misra AK Sharma SK Ingram M 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(10):2342-2348
In the present study, we investigated remote laser-induced fluorescence (LIF), at a distance of 4.8 m, of a variety of natural minerals and rocks, and Hawaiian Ti (Cordyline terminalis) plant leaves. These minerals included calcite cleavage, calcite onex and calcite travertine, gypsum, fluorapatite, Dover flint and chalk, chalcedony and nephelene syenite, and rubies containing rock. Pulsed laser excitation of the samples at 355 and 266 nm often resulted in strong fluorescence. The LIF bands in the violet-blue region at approximately 413 and approximately 437 nm were observed only in the spectrum of calcite cleavage. The green LIF bands with band maxima in the narrow range of approximately 501-504 nm were observed in the spectra of all the minerals with the exception of the nephelene syenite and ruby rocks. The LIF red bands were observed in the range approximately 685-711 nm in all samples. Excitation with 532 nm wavelength laser gave broad but relatively low fluorescence background in the low-frequency region of the Raman spectra of these minerals. One microsecond signal gating was effective in removing nearly all background fluorescence (with peak at approximately 610 nm) from calcite cleavage Raman spectra, indicating that the fluorescence was probably from long-lifetime inorganic phosphorescence. 相似文献
12.
Ejnik JW Todorov TI Mullick FG Squibb K McDiarmid MA Centeno JA 《Analytical and bioanalytical chemistry》2005,382(1):73-79
Urine uranium concentrations are the best biological indicator for identifying exposure to depleted uranium (DU). Internal exposure to DU causes an increased amount of urine uranium and a decreased ratio of 235U/238U in urine samples, resulting in measurements that vary between 0.00725 and 0.002 (i.e., natural and depleted uraniums 235U/238U ratios, respectively). A method based on inductively coupled plasma dynamic reaction cell mass spectrometry (ICP-DRC-MS) was utilized to identify DU in urine by measuring the quantity of total U and the 235U/238U ratio. The quantitative analysis was achieved using 233U as an internal standard. The analysis was performed both with and without the reaction gas oxygen. The reaction gas converted ionized 235U+ and 238U+ into 235UO2+ (m/z=267) and 238UO2+ (m/z=270). This conversion was determined to be over 90% efficient. A polyatomic interference at m/z 234.8 was successfully removed from the 235U signal under either DRC operating conditions (with or without oxygen as a reaction gas). The method was validated with 15 urine samples of known uranium compositions. The method detection limit for quantification was determined to be 0.1 pg U mL–1 urine and an average coefficient of variation (CV) of 1–2% within the sample measurements. The method detection limit for determining 235U/238U ratio was 3.0 pg U mL–1 urine. An additional 21 patient samples were analyzed with no information about medical history. The measured 235U/238U ratio within the urine samples correctly identified the presence or absence of internal DU exposure in all 21 patients.The opinions and assertions expressed herein are those of the authors and are not to be construed as official or as representing the views of the Armed Forces Institute of Pathology, the Department of the Army, or the Department of Defense 相似文献
13.
Chung DY Hogan TP Rocci-Lane M Brazis P Ireland JR Kannewurf CR Bastea M Uher C Kanatzidis MG 《Journal of the American Chemical Society》2004,126(20):6414-6428
The highly anisotropic material CsBi(4)Te(6) was prepared by the reaction of Cs/Bi(2)Te(3) around 600 degrees C. The compound crystallizes in the monoclinic space group C2/m with a = 51.9205(8) A, b = 4.4025(1) A, c = 14.5118(3) A, beta = 101.480(1) degrees, V = 3250.75(11) A(3), and Z = 8. The final R values are R(1) = 0.0585 and wR(2) = 0.1127 for all data. The compound has a 2-D structure composed of NaCl-type [Bi(4)Te(6)] anionic layers and Cs(+) ions residing between the layers. The [Bi(4)Te(6)] layers are interconnected by Bi-Bi bonds at a distance of 3.2383(10) A. This material is a narrow gap semiconductor. Optimization studies on the thermoelectric properties with a variety of doping agents show that the electrical properties of CsBi(4)Te(6) can be tuned to yield an optimized thermoelectric material which is promising for low-temperature applications. SbI(3) doping resulted in p-type behavior and a maximum power factor of 51.5 microW/cm.K(2) at 184 K and the corresponding ZT of 0.82 at 225 K. The highest power factor of 59.8 microW/cm.K(2) at 151 K was obtained from 0.06% Sb-doped material. We report here the synthesis, physicochemical properties, doping characteristics, charge-transport properties, and thermal conductivity. Also presented are studies on n-type CsBi(4)Te(6) and comparisons to those of p-type. 相似文献
14.
Langone Marta A. P. De Abreu Melissa E. Rezende Michelle J. C. Sant’Anna Geraldo L. 《Applied biochemistry and biotechnology》2002,98(1-9):987-996
The synthesis of monocaprin, monolaurin, and monomyristin in a solvent-free system was conducted by mixing a commercial immobilized
lipase with the organic reactants (glycerol and fatty acids) in a 20-mL batch reactor with constant stirring. The effects
of temperature, fatty acid/glycerol molar ratio, and enzyme concentration on the reaction conversion were determined. The
addition of molecular sieves in the assays of monomyristin synthesis was also evaluated. The reactions were carried out for
5 to 6 h and the nonpolar phase was analyzed by gas chromatography. The best results in terms of selectivity and conversion
(defined as the percentage of fatty acid consumed) were achieved when the stoichiometric amount of reagents (molar ratio=1)
and 9% (w/w) commercial enzyme were used and the reaction was performed at 60°C. The addition of molecular sieves did not
improve the synthesis of monomyristin. Conversions as high as 80%, with monoglycerides being the major products, were attained.
After 5 h of reaction, the concentration of monoglyceride was about twice that of diglyceride, and only trace amounts of triglyceride
were found. The results illustrate the technical possibility of producing medium chain monoglycerides in a solvent-free medium
using a simple batch reactor. 相似文献
15.
We introduce an impartial combinatorial game on Steiner triple systems called Next One to Fill Is the Loser (Nofil ). Players move alternately, choosing points of the triple system. If a player is forced to fill a block on their turn, they lose. By computing nim-values, we determine optimal strategies for Nofil on all Steiner triple systems up to order 15 and a sampling for orders 19, 21 and 25. The game Nofil can be thought of in terms of play on a corresponding hypergraph which will become a graph during play. At that point Nofil is equivalent to playing the game Node Kayles on the graph. We prove necessary conditions and sufficient conditions for a graph to reached playing Nofil. We conclude that the complexity of determining the outcome of the game Nofil on Steiner triple systems is PSPACE-complete for randomized reductions. 相似文献
16.
Suppression of non-specific adsorption using sheath flow 总被引:1,自引:0,他引:1
The use of a confining sheath fluid within a microfluidic channel in order prevent non-specific adsorption of analytes to the walls of microchannels is demonstrated. A sheath-flow channel fabricated using laser cutting of Mylar films is developed. Numerical simulations of convective and diffusive mass transport within the channel are presented. The device is characterized experimentally using epifluorescence microscopy. It is demonstrated that the device is capable of preventing the adsorption of Rhodamine B to the walls of the channel for a period that would allow for adsorption-free T-sensor measurements to be made within the core of the flow channel. Generalized scaling rules based on the diffusion coefficient, sheath thickness and affinity of the potential adsorbant for the surface material are discussed. The controlled adsorption of the protein bovine serum albumin (BSA) to a gold surface is also demonstrated using SPR microscopy. 相似文献
17.
The complex nature of biofluids demands efficient, sensitive and high-resolution analytical methodologies to examine how the 'metabolic fingerprint' changes during disease. This paper describes how sulphated beta-cyclodextrin-modified micellar electrokinetic capillary chromatography (SbetaCD-MECC) has been combined with data alignment analysis and may prove a useful new tool in urine profiling, allowing for separation of over 80 urinary analytes in under 25 min. The optimised and validated SbetaCD-MECC methodology combined with data alignment analysis provides rapid identification of 'mismatches' between urine profiles which are not easily detected with the naked eye as well as a 'similarity score' which indicates the total sum of differences between one profile and another. The combination of SbetaCD-MECC with data alignment software should prove a useful alternative tool in metabonomic studies for rapid comparison of urine profiles. 相似文献
18.
Recent advances in micellar electrokinetic chromatography 总被引:2,自引:0,他引:2
This review contains nearly 200 reference citations, and covers advances in electrokinetic capillary chromatography based on micelles, including stabilized micelle complexes, polymeric and mixed micelles from 2003-2004. Detection strategies, analyte determinations, and applications in micellar electrokinetic capillary chromatography (MEKC) are discussed. Information regarding methods of analyte concentration, analyte specific analyses, and nonstandard micelles has been summarized in tabular form to provide a means of rapid access to information pertinent to the reader. 相似文献
19.
Levason W Matthews ML Reid G Webster M 《Dalton transactions (Cambridge, England : 2003)》2004,(1):51-58
High yield syntheses for 1,2-, 1,3-, and 1,4-xylyl distibines (1,2-C6H4(CH2SbMe2)2, 1,3-C6H4(CH2SbMe2)2, 1,4-C6H4(CH2SbMe2)2, respectively) from Me2SbCl (conveniently made in situ from Me2PhSb and HClgas) and the appropriate di-Grignard are reported. The 1,3- and 1,4-phenylene distibines, 1,3-C6H4(SbMe2)2 and 1,4-C6H4(SbMe2)2, were made similarly. The new ligands have been characterised by mass spectrometry, 1H and 13C[1H] NMR spectroscopy, and by the preparation of methiodide derivatives. The crystal structures of 1,4-C6H4(CH2SbMe2)2 and [1,3-C6H4(CH2SbMe3)2]I2 have been determined. The synthesis of 1,2-C6H4(CH2SbPh2)2 has been achieved similarly in modest yield and the distibine converted into the tetra-iodo-derivative 1,2-C6H4(CH2SbPh2I2)2. The coordination modes available to these ligands have been probed by the synthesis and characterisation of complexes with nickel, iron and tungsten carbonyls. The crystal structure of [[Fe(CO)4]2[micro-1,3-C6H4(CH2SbMe2)2]] has been determined. The spectroscopic properties of these carbonyl derivatives have been compared with those of complexes of other antimony ligands, and in some cases with diphosphine and diarsine complexes, to probe the electronic properties of the new ligands. 相似文献
20.
The coupling of subcritical water separation with flame ionization detection (FID) in the split mode has been investigated in this study. In order to keep the FID system stable during subcritical water separation, a Tee union was connected between the separation column and the FID system to split the water flow. The ratio of the water flow to the FID system over the flow-rate to a waste bottle varied depending on the dimension of capillary tubings and the total water flow-rate used. Separations of several carbohydrates, carboxylic acids, and amino acids were performed on commercially available columns using a laboratory-made subcritical water chromatography-FID system. The FID system was very stable in this split mode even at total flow-rate as high as 1.24 ml/min. The linear dynamic range was up to three orders of magnitude and the limit of detection (LOD) ranged from 38 to 111 ng (306-925 ng/microl injected) with split ratios of approximately 1:10 to approximately 1:17 (FID/waste bottle) for several analytes studied. However, the LOD can be significantly lowered by adjusting the dimensions of the restrictors to allow a higher percentage of the total flow to the FID system. 相似文献