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71.
Near-infrared reflection spectroscopy (NIRS) was used in combination with principal component analysis (PCA) and partial least squares (PLS) regression to determine the silica packing properties, whether endcapped (EC) or non-endcapped, and the amount of surface total carbon coverage (%). A preparation technique for the reproducible analysis of bulk materials is covered as well as spectral data pretreatments to enhance prediction accuracy of the PLS models. Especially derivatives and scatter correction methods turned out to be well suited. A standard error of prediction (SEP) of 0.57% C for the determination of the total carbon load of octadecylated (C18) silica was found. In case of the C18-EC silica a SEP of 0.51% carbon gives rise to a robust and accurate model. The presented method allows the simultaneous determination of several parameters, e.g. particle and pore size or surface modifications, from a single spectrum and is amenable to implementation for in-line or on-line analysis in the silica producing industry. 相似文献
72.
Horst Huck 《Analytical and bioanalytical chemistry》1994,350(10-11):599-605
The alkali instability of phenoxazine dyes was investigated with respect to their application as catalysts for anodic NADH oxidation. Spectrophotometric measurements were used in aqueous solutions at different pH values together with cyclovoltammograms of the dyes adsorbed on a graphite electrode. It is shown that the reason for desactivation in the case of Meldola Blue is a cation-pseudobase equilibrium followed by a ring-opening tautomerism. The open-ring isomer, an unstable o,p′-quinoneanile dye, could be isolated as a dark blue precipitate. Also a by-product (“dimethyl”-Nile Red V) was identified. In the case of phenoxazine dyes substituted with an amino or acylamino group in p-position to the heterocyclic nitrogen, the reason for desactivation of the electrodes is the known reversible formation of a quinone diimine as an anhydrobase. 相似文献
73.
Huck WT Stroock AD Whitesides GM 《Angewandte Chemie (International ed. in English)》2000,39(6):1058-1061
74.
Patterning electro-osmotic flow with patterned surface charge 总被引:11,自引:0,他引:11
Stroock AD Weck M Chiu DT Huck WT Kenis PJ Ismagilov RF Whitesides GM 《Physical review letters》2000,84(15):3314-3317
This Letter reports the measurement of electro-osmotic flows (EOF) in microchannels with surface charge patterned on the 200 microm scale. We have investigated two classes of patterns: (1) Those in which the surface charge varies along a direction perpendicular to the electric field used to drive the EOF; this type of pattern generates multidirectional flow along the direction of the field. (2) Those in which the surface charge pattern varies parallel to the field; this pattern generates recirculating cellular flow, and thus causes motion both parallel and perpendicular to the external field. Measurements of both of these flows agree well with theory in the limit of thin double layers and low surface potential. 相似文献
75.
76.
77.
Low-temperature synthesis of tetraalkylureas from secondary amines and carbon dioxide 总被引:1,自引:0,他引:1
The reaction of dialkylamines with CO(2) giving tetraalkylureas can be performed at 60 degrees C. The reaction requires CCl(4), is weakly promoted by DMAN or PPh(3), and is not promoted by a Pd catalyst. A two-step procedure, in which dialkylammonium dialkylcarbamate is produced in situ and then reacted with CCl(4) and free dialkylamine, gave greater yields of urea than a simple single-stage procedure. 相似文献
78.
We have achieved a significant breakthrough in the synthesis of polyelectrolyte brushes of controlled thickness and density, which has been demonstrated by the synthesis of triblock copolymer brushes composed of cationic, neutral, and anionic segments. 相似文献
79.
Summary The analysis of α, β, γ, δ-tocopherols, trienols, α-tocopheryl acetate and nicotinate (vitamin E) in complex matrices was
carried out using a new liquid chromatographic (HPLC) method giving better separation efficiency, selectivity and sensitivity
than that described in the literature. The use of normal-phase (NP)-HPLC on silica gel with issoctane-diisopropylether-1,4-dioxane
as optimized mobilepphase yielded higher resolution than conventional reversed-phase (RP)-HPLC using methanol mobile phase.
Identification of peaks was by UV-absorbance at 295 nm, diode array, or fluorescence detection (λ
ex = 295 nm,λ
ex = 330 nm). The latter was found to be more selective and ten times more sensitive than UV-absorbance detection. A quadrupole,
ion-trap mass spectrometer with an atmospheric-pressure ionization (APCl) interface was used to detect vitamin E constituents
in the femtomole range. With collision-induced dissociation (CID) in the ion source, which gave characteristic fragmentation,
the identity of the investigated compounds could be confirmed. Plots of peak area versus amount injected allowed quantitation
of α, β, γ, δ-tocopherols and-trienols, α-tocopheryl acetate and nicotinate in real samples such as peanut, almond, spinach,
spelt grain bran, latex and tablets. The method described offers fast identification and quantitation of vitamin E constituents
of complex biological origin.
Dedicated to Professor Dr. Heinz Engelhardt on the occasion of his 65th birthday. 相似文献
80.
Oberhumer PM Huang YS Massip S James DT Tu G Albert-Seifried S Beljonne D Cornil J Kim JS Huck WT Greenham NC Hodgkiss JM Friend RH 《The Journal of chemical physics》2011,134(11):114901
We present a spectroscopic and theoretical investigation of the effect of the presence and position of hexyl side-chains in the novel low-bandgap alternating donor-acceptor copolymer poly[bis-N,N-(4-octylphenyl)-bis-N,N-phenyl-1,4-phenylenediamine-alt-5,5'-4',7',-di-2-thienyl-2',1',3'-benzothiadiazole] (T8TBT). We use electronic absorption and Raman spectroscopic measurements supported by calculations of chain conformation, electronic transitions, and Raman modes. Using these tools, we find that sterically demanding side-chain configurations induce twisting in the electronic acceptor unit and reduce the electronic interaction with the donor. This leads to a blue-shifted and weakened (partial) charge-transfer absorption band together with a higher photoluminescence efficiency. On the other hand, sterically relaxed side-chain configurations promote coupling between donor and acceptor units and exhibit enhanced absorption at the expense of luminescence efficiency. The possibility of tuning the donor-acceptor character of conjugated polymers by varying the placement of side-chains has very important ramifications for light emitting diode, Laser, display, and photovoltaic device optimization. 相似文献