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31.
Salvadó N Butí S Labrador A Cinque G Emerich H Pradell T 《Analytical and bioanalytical chemistry》2011,399(9):3041-3052
Altarpieces and polychrome carved wood from the fifteenth century AD usually exhibit golden and silvery areas by the application
of a very thin foil of metal. The metal foils were normally protected from the atmosphere by a varnish or resin which maybe
either preserved or absent. Moreover, they were glued to the background surface by adhesive substances (egg yolk, drying oil
or animal glue). The high proportion of the glueing substances often renders the development of reaction compounds. With time,
silver alters blacken or simply disappear completely. In this paper, we study the alterations to metal foils from a selection
of fifteenth century artworks showing different glueing agents, organic coatings and several degrees of conservation of the
organic coatings and metal leafs. The submillimetric layered structure and the high variability and low amount of most of
the compounds present in the different layers, as well as their differing nature (organic and inorganic) make the use of micron-sensitive
high-resolution techniques essential for their study. In particular, the high resolution, high brilliance and small footprint
renders synchrotron radiation most adequate for their study. SR-XRD was performed to identify the reaction compounds formed
in the different layers; μFTIR was used at to identify the silver protecting organic coatings, the metal foil glueing layers
and the corresponding reaction compounds. The results obtained suggest that atmospheric corrosion is the dominant mechanism,
and therefore that the degree of corrosion of the metal foils is mainly related to the conservation state of the protecting
coatings. 相似文献
32.
33.
Different HPLC methodologies are employed to evaluate the separation and determination of some platinum metals (Pt, Pd, Ir and Rh) after the formation of 8-hydroxyquinolate chelates. With the aim of reducing the number of steps in treating the samples, the method developed did not include the elimination of excess chelating reagent before the analysis of metal chelates. Reversed-phase (RP), non-aqueous reversed-phase (NARP) and normal-phase (NP) HPLC are compared. The RP-HPLC method only permits the quantitative separation of Rh and Pd from the excess reagent. A silica column can be used to separate Ir and Rh by NP-HPLC. The NARP-HPLC method allows for the effective separation of the four elements tested, but the high detection limit (90 ng) for platinum and the peak width do not favour its application for quantitative measurement. Platinum group metals can be quantitatively separated and determined by NP-HPLC using a cyano column in less than 15 min. The broad linear range of all the elements (between 1 and 500 ng) is superior to that which has been previously reported and the detection limits (1.0 ng for Pt, 0.3 ng for Pd, 1.0 ng for Ir and 0.3 ng for Rh) are slightly lower. 相似文献
34.
A method based on Immobilised Metal Ion Affinity Chromatography (IMAC) using a chelating resin (Spheron Oxine 1000) loaded with Pd(II) is evaluated for the extraction and preconcentration of glyphosate and AMPA from natural water samples. The efficiency of the metal-loaded resin in retaining glyphosate and AMPA and the ability of different reagents to recover them is investigated. The most effective elution solution for the recovery of both analytes from the resin is found to be a mixture of 0.1 M HCI and 1 M NaCl. The effect of flow rate, analyte concentration, and sample volume is evaluated. The optimised experimental conditions are then used in the extraction of the analytes from spiked natural waters. The use of the Pd loaded resin led to recoveries ranging from 80-90% for glyphosate and 60-80% for AMPA. 相似文献
35.
A procedure using alkaline extraction, solid-phase extraction (SPE) and HPLC is developed to analyze the polar herbicides 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-chloro-2-methylphenoxyacetic acid (MCPA) together with their main metabolites in soils. An ion-pairing HPLC method is used for the determination as it permits the baseline separation of these highly polar herbicides and their main metabolites. The use of a highly cross-linked polystyrene-divinylbenzene sorbent (PS-DVB) gives the best results for the analysis of these compounds. This sorbent allows the direct preconcentration of the analytes at the high pH values obtained after quantitative alkaline extraction of the herbicides from soil samples. Different parameters are evaluated for the SPE preconcentration step. The high polarity of the main analytes of interest (2,4-D and MCPA) makes it necessary to work at low flow rates (< or =0.5 mL min(-1)) in order for these compounds to be retained by the PS-DVB sorbent. A two stage desorption from the SPE sorbent is required to obtain the analytes in solvents that are appropriate for HPLC determination. A first desorption with a 50:50 methanol:water mixture elutes the most polar analytes (2,4-D, MCPA and 2CP). The second elution step with methanol permits the analysis of the other phenol derivatives. The humic and fulvic substances present in the soil are not efficiently retained by PS-DVB sorbents at alkaline pH's and so do not interfere in the analysis. This method has been successfully applied in the analysis of soil samples from a golf course treated with a commercial product containing esters of 2,4-D and MCPA as the active components. 相似文献
36.
Determination of eight water- and fat-soluble vitamins in multi-vitamin pharmaceutical formulations by high-performance liquid chromatography 总被引:5,自引:0,他引:5
In the present work, a reversed-phase high-performance liquid chromatographic procedure has been developed for the determination of water-soluble vitamins (thiamine hydrochloride, pyridoxine hydrochloride, nicotinamide, riboflavin phosphoric ester and cyanocobalamine) and fat-soluble vitamins (retinol palmitate, cholecalciferol, -tocopherol acetate) in multi-vitamin pharmaceutical formulations. The sample treatment proposed consists of a solid-phase extraction with C18 AR cartridges that allow the separation of fat-soluble vitamins, which were retained on the sorbent, from water-soluble vitamins. Afterwards, the water-soluble vitamins were analysed by HPLC on a Nova-Pack C18 (150×3.9 mm, 4 μm) analytical column, using CH3OH–0.05 M CH3COONH4 as mobile phase The chromatographic analysis of the fat-soluble vitamins was carried out after their sequential elution with methanol and chloroform from C18 sorbent, on the above column. The mobile phase employed was MeOH–CH3CN (95:5, v/v) working at a flow-rate of 2 ml min−1 in isocratic mode. The solid-phase extraction for these vitamins had been previously optimised. The experimental variables studied were: application volume, elution solvents and cleaning solutions. The UV–Vis detection of vitamins was made at 270 nm for all the water-soluble vitamins (362 nm for B12) and 285 nm for the water-soluble and fat-soluble vitamins present in real samples at different concentration levels. The accuracy of the method was tested obtaining an average recovery ranging between 78 and 116%. 相似文献
37.
Belén F. Alfonso Camino Trobajo Miguel A. Salvadó Pilar Pertierra Santiago García-Granda Jesús Rodríguez-Fernández Jesús A. Blanco José R. García 《无机化学与普通化学杂志》2005,631(11):2174-2180
Polycrystalline intercalated TiMxH2−nx(PO4)2· yC3H7NH2·wH2O compounds with transition metal (TM) ions (Mn+ = Co2+, Ni2+, Fe3+ or Cr3+) have been prepared by means of an indirect route and characterised using X-ray diffraction, scanning electron microscopy, chemical and thermal analysis, X-ray absorption and magnetic measurements. These novel pillared layered materials, which were obtained from the monoclinic (P21/c space group) α-Ti(HPO4)2·H2O phase, lose its crystallinity after intercalation. However all the TM ions are octahedrally surrounded by 6 oxygen atoms, although the X-ray absorption spectra evidence a clear dependence on the temperature. Surprisingly, all the materials behave as paramagnetic down to 1.5 K, but they exhibit different colours, what means that they are optically active (Co2+: violet; Ni2+: pale green; Fe3+: yellow; Cr3+: dark green). 相似文献
38.
We study the local profiles of trees. We show that in contrast with the situation for general graphs, the limit set of k‐profiles of trees is convex. We initiate a study of the defining inequalities of this convex set. Many challenging problems remain open. 相似文献
39.
Microcrystals of Th(HPO 4) 2.H 2O were hydrothermally obtained from a Th(NO 3) 4-CO(NH 2) 2-H 3PO 3-H 2O system ( T = 180 masculineC). The structure [orthorhombic, Pbca, a = 9.1968(2) A, b = 18.6382(2) A, c = 8.7871(2) A], unlike alpha-Zr(HPO 4) 2.H 2O-type layered compounds, consists of a three-dimensional framework with PO 4 tetrahedra coordinated to Th atoms. The water molecule is also coordinated to the Th atom and projected toward small channels running along the directions of the a and c axes. The ThO 6O(w) environment could be described as a highly distorted pentagonal bipyramid. 相似文献
40.
Microcrystals of the first ammonium-thorium phosphates, (NH 4) 2Th(PO 4) 2.H 2O (tetragonal, I4 1/ amd, a = 7.0192(4) A, c = 17.9403(8) A) and NH 4Th 2(PO 4) 3 (monoclinic, C2/ c, a = 17.880(6) A, b = 6.906(1) A, c = 8.152(2) A, beta = 104.39(2) degrees ) were hydrothermally obtained from a Th(NO 3) 4-CO(NH 2) 2-H 3PO 3-H 2O system ( T = 180 degrees C). In both cases, the structure consists of a three-dimensional framework with PO 4 tetrahedra coordinated to Th atoms (ThO n polyhedra, where n = 8 or 9, for the tetragonal or monoclinic phase, respectively). The ammonium ions (and water molecules) are located in the tunnels. 相似文献