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31.
Two new marine sediment standard reference materials (SRMs) for the determination of organic contaminants 总被引:3,自引:0,他引:3
Wise SA Poster DL Schantz MM Kucklick JR Sander LC Lopez de Alda M Schubert P Parris RM Porter BJ 《Analytical and bioanalytical chemistry》2004,378(5):1251-1264
Two new marine sediment standard reference materials (SRMs), SRM 1941b Organics in Marine Sediment and SRM 1944 New York/New Jersey Waterway Sediment, have been recently issued by the National Institute of Standards and Technology (NIST) for the determination of organic contaminants including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyl (PCB) congeners, and chlorinated pesticides. Both sediment SRMs were analyzed using multiple analytical methods including gas chromatography/mass spectrometry (GC/MS) on columns with different selectivity, reversed-phase liquid chromatography with fluorescence detection (for PAHs only), and GC with electron capture detection (for PCBs and pesticides only). SRM 1941b has certified concentrations for 24 PAHs, 29 PCB congeners, and 7 pesticides, and SRM 1944 has certified concentrations for 24 PAHs, 29 PCB congeners, and 4 pesticides. Reference concentrations are also provided for an additional 58 (SRM 1941b) and 39 (SRM 1944) PAHs, PCB congeners, and pesticides. SRM 1944, which was collected from multiple sites within New York/New Jersey coastal waterways, has contaminant concentrations that are generally a factor of 10–20 greater than SRM 1941b, which was collected in the Baltimore (Maryland) harbor. These two SRMs represent the most extensively characterized marine sediment certified reference materials available for the determination of organic contaminants.Electronic Supplementary Material Supplementary material is available in the online version of this article at . A link in the frame on the left on that page takes you directly to the supplementary material. 相似文献
32.
Anna Arkhireeva John N. Hay Jackie M. Lane Miguel Manzano Helen Masters Wilberforce Oware Steve J. Shaw 《Journal of Sol-Gel Science and Technology》2004,31(1-3):31-36
The synthesis of ORganically MOdified SILica (ORMOSIL) particles has been carried out using both the hydrolytic and non-hydrolytic sol-gel routes. The hybrid (nano)composites are organically modified with an alkyl or aryl group covalently bonded to silicon. Hybrids have been synthesised in an aqueous sol-gel process by a modified Stöber route, producing spherical nanoparticles with diameters in the range 50–300 nm. The size of the particles can be controlled by control of certain reaction parameters. Smaller ormosil nanoparticles can be synthesised by a base-catalysed emulsion polymerisation route, by varying the type and concentration of surfactant and precursor feed rate. In this case, particles in the size range 3.5–10 nm can be obtained. Hybrids have been synthesised from hyperbranched polyesters by encapsulation in a silica matrix using the hydrolytic sol-gel route. Optimisation of the reaction conditions allows the hybrids to be produced as isolated sub-micron spherical particles. Ormosil particles have also been synthesised using the non-hydrolytic sol-gel route, which may lead to products of different morphologies because of the different polarity of the reaction medium. Different reaction conditions were studied in order to optimise the size and shape of the particles, including choice of solvent, use of surfactants and addition of polystyrene. Dimethylsulfoxide acts as a novel oxygen donor for the catalyst-free formation of colourless silsesquioxanes. 相似文献
33.
Analysis of polycyclic aromatic hydrocarbons (PAHs) in environmental samples: a critical review of gas chromatographic (GC) methods 总被引:1,自引:0,他引:1
Polycyclic aromatic hydrocarbons (PAHs) are frequently measured in the atmosphere for air quality assessment, in biological
tissues for health-effects monitoring, in sediments and mollusks for environmental monitoring, and in foodstuffs for safety
reasons. In contemporary analysis of these complex matrices, gas chromatography (GC), rather than liquid chromatography (LC),
is often the preferred approach for separation, identification, and quantification of PAHs, largely because GC generally affords
greater selectivity, resolution, and sensitivity than LC. This article reviews modern-day GC and state-of-the-art GC techniques
used for the determination of PAHs in environmental samples. Standard test methods are discussed. GC separations of PAHs on
a variety of capillary columns are examined, and the properties and uses of selected mass spectrometric (MS) techniques are
presented. PAH literature on GC with MS techniques, including chemical ionization, ion-trap MS, time-of-flight MS (TOF-MS),
and isotope-ratio mass spectrometry (IRMS), is reviewed. Enhancements to GC, for example large-volume injection, thermal desorption,
fast GC, and coupling of GC to LC, are also discussed with regard to the determination of PAHs in an effort to demonstrate
the vigor and robustness GC continues to achieve in the analytical sciences. 相似文献
34.
Reaction of Tp*MoVSCl2 with a variety of phenols and thiols in the presence of triethylamine produces mononuclear, thiomolybdenyl complexes Tp*MoVSX2 [Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate; X = 2-(ethylthio)phenolate (etp), 2-(n-propyl)phenolate (pp), phenolate; X2 = benzene-1,2-dithiolate (bdt), 4-methylbenzene-1,2-dithiolate (tdt), benzene-1,2-diolate (cat)]. The complexes have been characterized by microanalysis, mass spectrometry, IR, EPR, and UV-visible spectroscopic data, and X-ray crystallography (for the etp, pp, bdt, and cat derivatives). The mononuclear, six-coordinate, distorted-octahedral Mo centers are coordinated by terminal sulfido (MoS = 2.123(1)-2.1368(8) A), tridentate facial Tp*, and monodentate or bidentate O/S-donor ligands. Multifrequency (S-, X-, Q-band) EPR spectra of the complexes and selected molybdenyl analogues were acquired at 130 K and 295 K and yielded a spin Hamiltonian of Cs symmetry or lower, with gzz < gyy < gxx < ge and Az'z' > Ax'x' approximately Ay'y', and a noncoincidence angle in the range of beta = 24-39 degrees . Multifrequency EPR, especially at S-band, was found to be particularly valuable in the unambiguous assignment of the spin Hamiltonian parameters in these low-symmetry complexes. The weaker pi-donor terminal sulfido ligand yields a smaller SOMO-LUMO gap and reduced g-values for the thiomolybdenyl complexes compared with molybdenyl analogues, supporting existing crystallographic and EPR data for an apically coordinated oxo group in the active site of xanthine oxidase. 相似文献
35.
36.
Lane W. Martin 《Surface science》2011,605(15-16):1388-1389
This perspective briefly reviews the recent developments in the study of exotic phenomena at complex oxide heterointerfaces – with special attention to results published by L. Qiao, et al. in this edition – on the LaAlO3/SrTiO3 heterointerface. The fundamental mechanisms of the observed phenomena are discussed and the results of the current study are placed in context. The importance of rigorous materials characterization and insight into fundamental limitations of modern synthesis techniques are probed. 相似文献
37.
Jane S. Murray Pat Lane Anian Nieder Thomas M. Klapötke Peter Politzer 《Theoretical chemistry accounts》2010,127(4):345-354
Si-pentaerythritol tetranitrate (PETN), Si[CH2ONO2]4, is a silicon analog of the widely used explosive PETN, C[CH2ONO2]4. Si-PETN is extremely sensitive to impact, much more so than PETN. This was attributed by Liu et al. to Si-PETN having a
much lower activation barrier to decomposition, via a facile rearrangement that is not as readily available to PETN, and which
releases considerable energy that can promote further steps. We have investigated computationally why the barrier to the rearrangement
is so much lower for Si-PETN than for PETN, using 5, (H3C)3C–CH2ONO2, and 6, (H3C)3Si–CH2ONO2, as models for PETN and Si-PETN. Reaction force analysis shows that most of the difference between the rearrangement barriers
for 5 and 6 comes about in the initial (reactant) stages of the processes, in which 6 benefits from a 1,3 electrostatic interaction involving a positive σ–hole on the silicon and the negative linking oxygen.
The analogous interaction is weaker in 5, since the central carbon does not have positive σ–holes; furthermore, this carbon is less able than silicon to temporarily
expand its coordination sphere. A similar explanation involving a positive silicon σ–hole and a linking oxygen is proposed
for Si-PETN. The greater exothermicity of the rearrangement of 6 (and also Si-PETN) can be rationalized, following Liu et al., in terms of the formation of the strong Si–O bond. 相似文献
38.
Stephen M. Lipson Ashley J. Cadby Paul A. Lane Diarmuid F. O’Brien Anna Drury Donald D. C. Bradley Werner J. Blau 《Monatshefte für Chemie / Chemical Monthly》2001,132(1):151-158
Summary. We have investigated the effect of film preparation procedures on the photoluminescence efficiency of the luminescent co-polymer
poly-(m-phenylene-co-2,5-dioctoxy-p-phenylenevinylene) (PmPV). The photoluminescence efficiency of PmPV films improved by up to 50% when the solution was degassed by bubbling argon gas through it prior to spin casting in an inert
atmosphere and baking under vacuum. Photoinduced absorption and doping measurements show that this preparation method reduces
polaron photogeneration, which reduces the photoluminescence (PL) yield through exciton quenching and excited state absorption.
It is proposed that this sample preparation method increases interchain separation, reducing the formation of polarons and
non-radiative quenching routes, thus resulting in increased PL efficiency.
Received June 23, 2000. Accepted (revised) August 3, 2000 相似文献
39.
Department of Health staff wished to use systems modelling to discuss acute patient flows with groups of NHS staff. The aim was to assess the usefulness of system dynamics (SD) in a healthcare context and to elicit proposals concerning ways of improving patient experience. Since time restrictions excluded simulation modelling, a hybrid approach using stock/flow symbols from SD was created. Initial interviews and hospital site visits generated a series of stock/flow maps. A ‘Conceptual Framework’ was then created to introduce the mapping symbols and to generate a series of questions about different patient paths and what might speed or slow patient flows. These materials formed the centre of three workshops for NHS staff. The participants were able to propose ideas for improving patient flows and the elicited data was subsequently employed to create a finalized suite of maps of a general acute hospital. The maps and ideas were communicated back to the Department of Health and subsequently assisted the work of the Modernization Agency. 相似文献
40.
Greg BG Moorhead Laura Trinkle-Mulcahy Mhairi Nimick Veerle De Wever David G Campbell Robert Gourlay Yun Wah Lam Angus I Lamond 《BMC biochemistry》2008,9(1):28