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11.
Walter Lund 《Fresenius' Journal of Analytical Chemistry》1990,337(5):557-564
Summary The different aspects of speciation analysis are reviewed. Species-specific instrumental techniques as well as various speciation schemes are considered for the determination of species of metals and metalloids, including organometallic compounds. The application of the methods are discussed in some detail for the analysis of natural waters, air, soil, sediment and biological samples. The relationship between metal species and bioavailability is also briefly dealt with. 相似文献
12.
Gregory M. Anstead Kathryn E. Carlson Philip R. Kym Kwang-Jin Hwang John A. Katzenellenbogen 《Photochemistry and photobiology》1993,58(6):785-794
Abstract The absorption and emission characteristics of five hydroxytetrahydrochrysenes substituted with acceptor groups (nitro, cyano, methylketone, 1° amide and methyl ester) (THC-NO2, THC-CN, THC-COCH3, THC-CONH2 and THC-CO2CH3, respectively) were investigated in an extensive set of solvents. The order of absorption and fluorescence bathochromicity are: THC-NO2 > THC-COCH3 > THC-CN ≥ THC-CO2CH3 > THC-CONH2 and THC-NO2 >> THC-COCH3 > THC-CO2CH3 > THC-CN > THC-CONH2, respectively. The emission spectra of these compounds are sensitive to the solvent polarity (ET[30] scale) in the order: THC-NO2 > THC-COCH3 > THC-CO2CH3 > THC-CONH2 > THC-CN. The response of the emission maxima of these compounds to the solvent polarity and hydrogen-bond donor/acceptor properties (π*/α/β and acity/basity scales) was also determined. The emission energies of THC-NO2 were most sensitive to π*, β, acity, and basity of the solvent; those of the amide were least sensitive to the solvent π*, β, and basity. The ground- and excited-state dipole moments were determined by semiempirical molecular orbital calculations and the absorption/fluorescence solvent-shift method, respectively. THC-NO2 had the largest ground- and excitedstate moments. The ester and amide had the smallest ground- and excited-state moments, respectively. In general, unsatisfactory results were obtained for correlations of the emission and absorption energies, fluorescence solvatochromism and the ground- and excited-state dipole moments with the Hammett substituent constants of the five acceptor groups. Acceptable correlations were obtained for the absorption and emission energies and the fluorescence solvatochromism with the substituent constants if the cyano compound was excluded. 相似文献
13.
X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), rotating disc electrode-electrochemical impedance spectroscopy (RDE-EIS) and synchrotron radiation-grazing incidence X-ray diffraction (SR-GIXRD) have been used to study the response mechanism of the mercury(II) chalcogenide ion-selective electrode (ISE) in saline media. XPS and SIMS have shown that the chalcogenide surface is poisoned by silver chloride, or a mixture of silver halides, on continuous exposure to synthetic and real seawater. Significantly, the in-situ SR-GIXRD study demonstrated that electrode fouling in synthetic seawater is linked to the formation of poorly crystalline or amorphous silver chloride, and that the low level of free mercury(II) in a calibration buffer (i.e., 10(-14) M) is able to undergo metathesis with silver(II) sulfide in the membrane generating mercury(II) sulfide. Significantly, the results of this detailed surface study have shown that silver chloride fouling of the electrode is ameliorated in real seawater comprising natural organic ligands, and this has been attributed to the peptization of silver chloride by the surfactant-like nature of seawater ligands at pH 8. RDE-EIS aging studies have revealed that the chalcogenide membrane experiences a sluggish charge transfer reaction in seawater, and contrary to a previous report for a static electrode, the seawater matrix does not passivate the RDE. The results of this XPS, SIMS, RDE-EIS and SR-GIXRD study have elucidated the response mechanism of the mercury(II) ISE in saline media. 相似文献
14.
McMahon WA Aleo VA Schultz AM Horter BL Lindberg KG 《Journal of AOAC International》2003,86(5):947-953
The 3M Petrifilm Staph Express Count plate method was compared with AOAC Official Method 975.55 for the enumeration of Staphylococcus aureus in selected foods. Four foods--cooked, diced chicken; cured ham; smoked salmon; and pepperoni--were analyzed for S. aureus by 12 collaborating laboratories. For each food tested, the collaborators received 8 blind test samples consisting of a control sample, a low inoculation level, a medium inoculation level, and a medium inoculation level with background flora, each in duplicate. The mean log10 counts for the methods were comparable for all 4 foods. The repeatability and reproducibility variances of the 24 h Petrifilm Staph Express Count plate method were similar to those of the 72 h standard method. 相似文献
15.
Jibo Xia Yili Chen Kathryn M. Liberatore Barry S. Selinsky 《Tetrahedron letters》2003,44(52):9295-9297
Methyl 3,3-(ethylenedioxy)-6β-fluoro-5β-cholan-24-oate has been prepared starting from hyodeoxycholic acid and 3,3-(ethylenedioxy)-7( and β)-fluorocholestan-22-al starting from stigmasterol, using diethylaminosulfur trifluoride as the fluorinating agent. These molecules will be used to synthesize analogs of the aminosterol antibiotic squalamine. 相似文献
16.
The presence of cationic, anionic, and neutral surfactants and humic substances is shown to affect the peak heights of copper, lead and cadmium in synthetic sea-water analysed by differential pulse anodic-stripping voltammetry. At surfactant concentrations below 0.1 mg/l. the effect is insignificant, but at higher concentrations the peak heights usually decrease, although for copper an increase in the peak height was also observed. The peak heights do not depend to any great extent on the pH of the solution, except in alkaline solution and in the presence of humic substances. Adsorption and complex formation may account for the observed dependences. 相似文献
17.
Lund Myhre CE Grothe H Gola AA Nielsen CJ 《The journal of physical chemistry. A》2005,109(32):7166-7171
The complex index of refraction of liquid HNO3/H2O and H2SO4/HNO3/H2O has been obtained at different temperatures and acid concentrations. FT-IR specular reflectance spectra were obtained for 30, 54, and 64 wt % aqueous HNO3 and for four different H2SO4/HNO3/H2O mixtures in the temperature region from 293 to 183 K. The complex index of refraction was obtained from the reflectance spectra with the Kramers-Kronig transformation. The optical constants of the binary and ternary mixtures vary with the acid concentration and the temperature. The results demonstrate that vibrational bands originating from the sulfate species are more sensitive to changes in temperature than the bands originating from vibrations in the nitrate species; only minor changes in the nitrate vibrational bands are observed as the temperature decreases below 248 K. 相似文献
18.
Mei Y Wu T Xu C Langenbach KJ Elliott JT Vogt BD Beers KL Amis EJ Washburn NR 《Langmuir : the ACS journal of surfaces and colloids》2005,21(26):12309-12314
A simple yet versatile method was developed to prepare a low-density polymerization initiator gradient, which was combined with surface-initiated atom transfer radical polymerization (ATRP) to produce a well-defined poly(2-hydroxyethyl methacrylate) (HEMA) gradient substrate. A smooth variation in film thickness was measured across the gradient, ranging from 20 A to over 80 A, but we observed a nonmonotonic variation in water contact angle. Fits of X-ray reflectivity profiles suggested that at the low graft density end, the polymer chain structure was in a "mushroom" regime, while the polymer chains at high graft density were in a "brush" regime. It was found that the "mushroom" region of the gradient could be made adhesive to cells by adsorbing adhesion proteins, and cell adhesion could be tuned by controlling the density of the polymer grafts. Fibroblasts were seeded on gradients precoated with fibronectin to test cellular responses to this novel substrate, but it was found that cell adhesion did not follow the expected trend; instead, saturated cell adhesion and spreading was found at the low grafting density region. 相似文献
19.
The reaction of pyridyl functionalized porphyrins with Re(CO)(5)Cl in THF results in the formation of porphyrin dimers which, despite incorporation of rhenium into the assemblies, remain fluorescent. The rigid compounds provide an efficient geometry and/or orbital pathway for singlet energy transfer, rendering these compounds suitable, in principle, for the study of both through-bond and through-space energy transfer. Derivatives containing both metallated and freebase porphyrins connected via the metal corners display efficient porphyrin-porphyrin energy transfer. The photophysical properties of the assemblies have been studied by both steady-state and time-resolved fluorescence techniques, yielding approximate rates and efficiencies for porphyrin-porphyrin energy transfer. 相似文献
20.
T. C. Awes C. Barlag F. Berger M. A. Bloomer C. Blume D. Bock R. Bock E. -M. Bohne D. Bucher A. Claussen G. Clewing L. Dragon A. Eklund S. Garpman R. Glasow H. Gustafsson H. H. Gutbrod G. Hölker J. Idh P. Jacobs K. H. Kampert B. W. Kolb H. Löhner I. Lund F. E. Obenshain A. Oskarsson I. Otterlund T. Peitzmann F. Plasil A. M. Poskanzer M. Purschke B. Roters S. Saini R. Santo H. R. Schmidt S. P. Sørensen K. Steffens P. Steinhaeuser E. Stenlund D. Stüken G. R. Young 《Zeitschrift fur Physik C Particles and Fields》1995,65(2):207-213
Correlations between protons are studied in the target fragmentation region of reactions of protons and16O with C, Cu, Ag, Au and of32S with Al and Au at 200A GeV. The emitted protons were measured with the Plastic Ball detector in the WA80 experiment at the CERN SPS. The comparison of the correlation function with calculations, assuming a spherical, gaussian shaped source with a lifetime τ=0 fm/c, allows the extraction of radius parameters. The values are very close to those expected from the geometry of the target nuclei and increase with the target mass as αA Target 1/3 . Even in proton induced reactions the whole target nucleus is involved. The dependence of the radii on centrality, polar angleθ lab, and energy, and their relation to measured proton yields are presented. 相似文献