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31.
32.
Amaia Guevara-Riba Angels Sahuquillo Roser Rubio Gemma Rauret 《Accreditation and quality assurance》2007,12(5):241-248
The implementation of the European Water Framework Directive (WFD) and of the sediment-quality criteria related to the potential
disposal of dredged materials is expected to involve a substantial increase in the number of chemical analyses performed in
marine environmental control laboratories. The chemical characterization of sediments (metals, elemental composition, etc.)
and the potential release of metals under changing environmental conditions are relevant when dealing with risk assessment.
The present paper describes the preparation of a quality control material (QCM) harbor sediment carried out in a specifically
equipped laboratory at the University of Barcelona. The results of homogeneity and stability studies for total metal content
(Cd, Cr, Cu, Ni, Pb, and Zn), extractable metal following the BCR three-step sequential extraction procedure (BCR-SEP), and
total carbon content show the suitability of QCM for multi-parameter routine quality control (QC) in marine environmental
laboratories. 相似文献
33.
Comparison of the Kjeldahl method and a combustion method for total nitrogen determination in animal feed 总被引:3,自引:0,他引:3
The features of the Dumas combustion method (CM) and those of the Kjeldahl method (KM) were compared as they apply to total nitrogen determination in animal feed. Both methods achieved similar repeatability (S.D., 0.11-0.38 from Kjeldahl and 0.15-0.36 from combustion) and similar intra-laboratory reproducibility (S.D., 0.11-0.39 from Kjeldahl and 0.15-0.37 from combustion). R.S.D. is always below 2%. These results show that the CM is suitable for the analysis of protein content in animal feed (5-75% protein content). The CM is recommended owing to its shorter analysis time, its cost and its environmental suitability. 相似文献
34.
A method for the determination of arsenic species in oyster tissue is established. The extraction of arsenic species is carried out by using low‐power microwaves. Quantitative extraction is obtained at a power of 40 W, and in 5 min, using the extracting agent methanol/water (1 + 1). The measurements are carried out using liquid chromatography–UV irradiation–hydride generation–atomic fluorescence detection (LC–UV–HG–AFS). Three arsenic species were detected in oyster tissue: arsenobetaine (AsBet) (87%), a probable arsenosugar (AsS) (4.9%), and dimethylarsinate (DMA) (4.7%). No influence of the clean‐up, the microwave field or the IR drying system on the stability of the arsenic compounds was observed. The extracts can be kept stable up to 3 days at 4 °C. The performance of the method is proved on fresh samples, as they are usually analysed in routine laboratories. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
35.
Water‐Soluble Gold Nanoparticles: From Catalytic Selective Nitroarene Reduction in Water to Refractive Index Sensing
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Water‐soluble gold nanoparticles (Au NPs) stabilized by a nitrogen‐rich poly(ethylene glycol) (PEG)‐tagged substrate have been prepared by reduction of HAuCl4 with NaBH4 in water at room temperature. The morphology and size of the nanoparticles can be controlled by simply varying the gold/stabilizer ratio. The nanoparticles have been fully characterized by TEM, high‐resolution (HR) TEM, electron diffraction (ED), energy‐dispersive X‐ray spectroscopy (EDS), UV/Vis, powder XRD, and elemental analysis. The material is efficient as a recyclable catalyst for the selective reduction of nitroarenes with NaBH4 to yield the corresponding anilines in water at room temperature. Furthermore, the potential ability of the Au NPs as a refractive index sensor owing to their localized surface plasmon resonance (LSPR) effect has also been assessed. 相似文献
36.
Roser Sabater i Serra Apostolos Kyritsis Jorge L. Escobar Ivirico Andreu Andrio Balado Jose Luis Gómez Ribelles Polykarpos Pissis Manuel Salmerón-Sánchez 《Colloid and polymer science》2010,288(5):555-565
Poly(L-lactide) networks (PmLA) hydrophilized with different amounts of 2-hydroxyethyl acrylate (HEA) were investigated by
dielectric relaxation spectroscopy, thermally stimulated depolarization currents, and differential scanning calorimetry. The
incorporation of HEA units in the PmLA network, with the aim of modulating the water sorption capacity of the system, results
in a material with a complex behavior. The system consists of phase-separated microdomains richer in one or the other comonomers
that constitute the network. Initially, the addition of smalls amount of HEA units in the network gives rise to a one-phase,
two-component system; however, when the amount of HEA in the system increases, a new phase (HEA-rich one) is formed containing
some mLA chains that modify the main relaxation mode of these domains and the local dynamics of the system. The structure
of the system has been analyzed by comparing the relaxational modes in the PmLA and PHEA homonetworks with those in the copolymer
networks. 相似文献
37.
13C NMR differences of chemical shifts (delta(X) - delta(H)) of allyl carbon atoms in a series of trans-(1-(diphenylphosphino)-2-(dimethylamino)ethane)(eta(3)-1-arylallyl)palladium tetrafluoroborates, X ranging from NO(2) to OMe, correlate very well with sigma Hammett constants for C-1 and with sigma(+) for C-3, this carbon atom being in a trans relationship with the positively charged nitrogen atom. 相似文献
38.
Alejandro Marcó Ramon Companyó Roser Rubio Maite Pueyo Eugeni Vilalta 《Mikrochimica acta》2007,159(3-4):387-393
The estimation of uncertainty in organic elemental analysis for C, H, N and S is reported. Both “bottom up” and “top down”
strategies are used for uncertainty calculations. The bottom up approach used the results of C, H, N, and S obtained from
the homogeneity study of two pure chemicals (toluene-4-sulfonamide and 4(6)-methyl-2-thiouracil). Two calibration systems,
K factor and calibration curve, were applied in this study and no significant differences were obtained. For the “top down”
approach, we used the data obtained from a proficiency test on both pure chemicals from among 45 Spanish laboratories. Both
approaches are compared and discussed below. 相似文献
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