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131.
P. C. Uden Susan M. Bird Mihaly Kotrebai Paula Nolibos Julian F. Tyson Eric Block Eric Denoyer 《Fresenius' Journal of Analytical Chemistry》1998,362(5):447-456
Consumption of selenium enriched plants or yeast-based nutritional supplements has been reported to provide anticarcinogenic
benefits which are selenium compound dependent. Separation and identification of these selenium compounds is critical to understand
the activity. Plants and yeast convert inorganic selenium in the soil or growth media into organoselenium compounds, probably
following a route similar to the sulfur assimilatory pathway. Non-volatile selenium compounds produced include selenoamino
acids, some of which have shown anticarcinogenic activity. Volatile compounds produced by chemical reaction of involatile
precursors have also been found. An ion pair chromatographic method with ICP-MS detection for the separation of selenoamino
acid standards potentially present in real samples is given. The method allows separation of selenoamino acids including such
analytes as the cis-trans isomers of Se-1-propenyl-dl-selenocysteine. The method also provides the capability of determining the presence of selenoxides and possibly selenones,
and tracking of other functionalities and reactions by selective derivatization. Alternatively, selenoamino acids are treated
with ethylchloroformate to produce stable volatile derivatives which are amenable to GC separation with element specific atomic
emission detection (GC-AED). Results of total selenium determination and speciation of selenium enriched yeast-based nutritional
supplements, selenium enriched allium vegetables and bioremediation samples are presented.
Received: 16 February 1998 / Revised: 4 June 1998 / Accepted: 9 June 1998 相似文献
132.
Heating the title compound with benzene provides a mixture of dimethyl 1,3-dihydroxynaphthalene-2,4-dicarboxylate and 3-carbomethoxy-4-hydroxy-5-phenylpyrone which rearranges on melting to the aforementioned naphthalene derivative. The initial substitution reaction appears to proceed through an intermediary pyronyl cation. The scope of this potential ring annelation reaction has been investigated for a range of aromatic and heteroaromatic compounds. Heating with basic substrates converts the bisdazo compound into dimethyl 4-hydroxypyrazole-3,5-dicarboxylate, while heating with isopropanol yields dimethyl 4,5-dihydroxypyridazine-3,6-dicarboxylate. 相似文献
133.
Determination of total fumonisins in corn by competitive direct enzyme-linked immunosorbent assay: collaborative study 总被引:2,自引:0,他引:2
Bird CB Malone B Rice LG Ross PF Eppley R Abouzied MM 《Journal of AOAC International》2002,85(2):404-410
Fumonisins-mycotoxins produced by some Fusarium species-have been shown to be the causative agent of diseases in horses and other domesticated animals as well as possible carcinogens in humans. A collaborative study was conducted to evaluate the effectiveness of a competitive direct enzyme-linked immunosorbent assay (CD-ELISA) for the determination of total fumonisins (B1, B2, and B3) in corn. The test portion was extracted with methanol-water (7 + 3), filtered, diluted, and tested on the CD-ELISA. Naturally and artificially contaminated corn test portions were sent to 13 collaborators in the United States. Naturally contaminated field test portions were prepared at 3 different levels. Artificially contaminated test portions were spiked at 1.0, 3.0, and 5.0 mg/kg total fumonisins (B1, B2, and B3). Average recoveries of total fumonisins were 120, 100, and 90%, respectively. The relative standard deviations for repeatability ranged from 13.3 to 23.3% and the relative standard deviations for reproducibility ranged from 15.8 to 30.3% across all levels tested. HORRAT values, calculated for each individual sample, ranged from 1.24 to 1.94. This method demonstrated acceptable intra- and interlaboratory precision at the levels tested. 相似文献
134.
Bird MI Tait E Wurster CM Furness RW 《Rapid communications in mass spectrometry : RCM》2008,22(21):3393-3400
We report results obtained using a new technique developed to measure the stable-isotope composition of uric acid isolated from bird excreta (guano). Results from a diet-switch feeding trial using zebra finches suggest that the delta(13)C of uric acid in the guano equilibrates with the diet of the bird within 3 days of a change in diet, while the equilibration time for delta(15)N may be longer. The average carbon isotope discrimination between uric acid and food before the diet switch was +0.34 +/- 1 per thousand (1sigma) while after the diet switch this increased slightly to +0.83 +/- 0.7 per thousand (1sigma). Nitrogen isotope discrimination was +1.3 +/- 0.3 per thousand (1sigma) and +0.3 +/- 0.3 per thousand (1sigma) before and after the diet switch; however, it is possible that the nitrogen isotope values did not fully equilibrate with diet switch over the course of the experiment. Analyses of other chemical fractions of the guano (organic residue after uric acid extraction and non-uric acid organics solubilised during extraction) suggest a total range of up to 3 per thousand for both delta(13)C and delta(15)N values in individual components of a single bulk guano sample. The analysis of natural samples from a range of terrestrial and marine species demonstrates that the technique yields isotopic compositions consistent with the known diets of the birds. The results from natural samples further demonstrate that multiple samples from the same species collected from the same location yield similar results, while different species from the same location exhibit a range of isotopic compositions indicative of different dietary preferences. Given that many samples of guano can be rapidly collected without any requirement to capture specimens for invasive sampling, the stable-isotope analysis of uric acid offers a new, simple and potentially powerful tool for studying avian ecology and metabolism. 相似文献
135.
Understanding the electronic structure of organic-organic heterointerfaces is crucial for many device applications of organic semiconductors. Here we have developed a simple analytical model to describe the effect of static dipolar disorder in a polymer dielectric on the density of states of an adjacent organic semiconductor. The degree of energetic disorder varies strongly with distance from the interface. Using a simple mobility model, we have been able to explain quantitatively both the magnitude as well as the gate voltage dependence of the field-effect mobility for polymer gate dielectrics with different dielectric constants. 相似文献
136.
First measurement of the left-right cross section asymmetry in Z boson production by e+e- collisions
Abe K Abt I Acton PD Adolphsen CE Agnew G Alber C Alzofon DF Antilogus P Arroyo C Ash WW Ashford V Astbury A Aston D Au Y Axen DA Bacchetta N Baird KG Baker W Baltay C Band HR Baranko G Bardon O Barrera F Battiston R Bazarko AO Bean A Beer G Belcinski RJ Bell RA Ben-David R Benvenuti AC Berger R Berridge SC Bethke S Biasini M Bienz T Bilei GM Bird F Bisello D Blaylock G Blumberg R Bogart JR Bolton T Bougerolle S Bower GR Boyce RF Brau JE Breidenbach M Browder TE Bugg WM Burgess B Burke D 《Physical review letters》1993,70(17):2515-2520
137.
D. Levinthal F. Bird R. G. Stuart B. W. Lynn 《Zeitschrift fur Physik C Particles and Fields》1992,53(4):617-628
A study is undertaken to determine how to best extract the top quark massm
t
within the Minimal Standard Model (MSM) using a global fit to a variety of processes (including wide-angle Bhabha scattering) ine
+
e
– collisions near theZ which should be measured in the coming years. Experimental cuts are accommodated as an integral part of the analysis. It is advantageous to use the collinear radiation approximation and to cut data in rapidity, center-of-mass polar angle and minimum final state invariant mass squared,s. This avoids the need for the largest Monte Carlo acceptance correction to the data. Further, high precision cross section, calculations, (which include all one-loop electroweak and QED effects, certain higher-order improvements and perturbative QCD corrections as well as exponentiated soft and collinear photon radiation) then no longer require a Monte Carlo. This results in a speedup factor of at least fifty thousand (>5×104) in EXPOSTAR. The data (corrected only for detector cracks, resolution and small non-collinear radiation effects) can therefore be fit quickly and directly forM
z
,m
t
,m
Higgs and strong without recourse to unphysical intermediate quantities (weak mixing angles, running couplings, partial widths, *, etc.) Determination ofm
t
could be as precise as ±15 GeV (and another±20 GeV fromm
Higgs) at the end of LEP running in 1991. Longitudinally polarized beams with very small polarization error could give an error onm
t
smaller, by a factor 4 for the same luminosity. 相似文献
138.
Convenient syntheses of the epimeric 3-hydroxy-2α-carb-oxybicyclo[3.3.0]octane-4α,6α-carbolactones are described which commence from the readily available cyclopentadienone dimer. 相似文献
139.
A R Preston N R Bird P Kinchesh E W Randall W R Whalley 《Magnetic resonance imaging》2001,19(3-4):561-563
1-D STRAFI (STRAy FIeld) imaging is used to study water distribution in a sandy loam. The matric potential of the soil can be varied during acquisition of 1-D profiles. Results at a range of potentials are presented showing both the equilibrium distribution and the evolution of the profile following an abrupt change in matric potential. The air breakthrough point and variations in draining behaviour due to differences in soil compaction are identified. 相似文献
140.
Five different food types were analyzed by the Reveal for E. coli O157:H7 8-Hour Test System (Reveal 8) and either the U.S. Food and Drug Administration's Bacteriological Analytical Manual (BAM) culture method or the U.S. Department of Agriculture Food Safety Inspection Service (FSIS) culture method for the presence of E. coli O157:H7. A total of 27 laboratories representing academia and private industry in the United States and Canada participated. Food types were inoculated with E. coli O157:H7 at 2 different levels: a high level where predominantly positive results were expected, and a low level where fractional recovery was anticipated. During this study, 1,110 samples and controls were analyzed by both the Reveal 8 and by BAM or FSIS by each of the collaborators (2,220 samples in total). For each set of samples, 740 were artificially inoculated with E. coli O157:H7, and 370 were uninoculated controls. The Reveal 8 detected 528 presumptive positives of which 487 were confirmed positive by the BAM culture method. In comparison, BAM and FSIS detected 489 of the 740 artificially contaminated samples as positive. In an additional in-house study performed only on chilled and frozen raw ground beef, 240 artificially inoculated samples were analyzed by both the Reveal 8 and by FSIS. The Reveal 8 detected and confirmed 104 samples as positive compared to 79 confirmed positive by FSIS. 相似文献