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Theory of field-amplified sample stacking (FASS) also called field-enhanced sample stacking is reevaluated considering the early work of Chien, Burgi and Helmer. The classical theory presented by Chien, Helmer and Burgi predicts the existence of maxima, which are ascribed to the counteracting principles of zone focusing and hydrodynamic dispersion. In contrast to their work, we here focus on cationic analytes separated in an acidic background electrolyte providing a very low electroosmotic flow velocity. Therefore, peak broadening due to differences in the local electroosmotic flow velocities in different compartments of the capillary can be regarded to be negligible. Consequently, peak broadening resulting from hydrodynamic dispersion will not be the dominant limitation of the accessible enrichment efficiency. In our experimental studies we, however, obtain an optimum value for the field enhancement factor (maximum of the enrichment efficiency, when varying the electric conductivity of the sample and the size of the sample injection plug) corresponding to a 10-fold dilution of the BGE in the sample solution. Comparing these experimental data with data modeled according to the revised theory, we show that this limitation of the loadability is caused by the unavoidable decrease of the analyte migration velocity in the BGE compartment of the capillary when injecting of a sample plug of lower electric conductivity (decrease in the local electric field strength). The additional diffusional band broadening limits the obtainable enrichment efficiency. 相似文献
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Eva Woltmann Hans Meyer Diana Weigel Heinz Pritzke Tjorben N. Posch Pablo A. Kler Klaus Schürmann Jörg Roscher Carolin Huhn 《Analytical and bioanalytical chemistry》2014,406(25):6347-6362
High production output of solid pharmaceutical formulations requires fast methods to ensure their quality. Likewise, fast analytical procedures are required in forensic sciences, for example at customs, to substantiate an initial suspicion. We here present the design and the optimization of an instrumental setup for rapid and non-invasive characterization of tablets by laser-induced fluorescence spectroscopy (with a UV-laser (λ ex?=?266 nm) as excitation source) in reflection geometry. The setup was first validated with regard to repeatability, bleaching phenomena, and sensitivity. The effect on the spectra by the physical and chemical properties of the samples, e.g. their hardness, homogeneity, chemical composition, and granule grain size of the uncompressed material, using a series of tablets, manufactured in accordance with design of experiments, was investigated. Investigation of tablets with regard to homogeneity, especially, is extremely important in pharmaceutical production processes. We demonstrate that multiplicative scatter correction is an appropriate tool for data preprocessing of fluorescence spectra. Tablets with different physical and chemical characteristics can be discriminated well from their fluorescence spectra by subjecting the results to principal component analysis. 相似文献
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Mariusz Mital Nina E. Wezynfeld Tomasz Frczyk Magdalena Z. Wiloch Urszula E. Wawrzyniak Arkadiusz Bonna Carolin Tumpach Kevin J. Barnham Cathryn L. Haigh Wojciech Bal Simon C. Drew 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(36):10606-10610
Accumulation of the β‐amyloid (Aβ) peptide in extracellular senile plaques rich in copper and zinc is a defining pathological feature of Alzheimer′s disease (AD). The Aβ1–x (x=16/28/40/42) peptides have been the primary focus of CuII binding studies for more than 15 years; however, the N‐truncated Aβ4–42 peptide is a major Aβ isoform detected in both healthy and diseased brains, and it contains a novel N‐terminal FRH sequence. Proteins with His at the third position are known to bind CuII avidly, with conditional log K values at pH 7.4 in the range of 11.0–14.6, which is much higher than that determined for Aβ1–x peptides. By using Aβ4–16 as a model, it was demonstrated that its FRH sequence stoichiometrically binds CuII with a conditional Kd value of 3×10−14 M at pH 7.4, and that both Aβ4–16 and Aβ4–42 possess negligible redox activity. Combined with the predominance of Aβ4–42 in the brain, our results suggest a physiological role for this isoform in metal homeostasis within the central nervous system. 相似文献
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L-Sorbose 1 was converted to 5-hydroxymethylfurfural 8 in choline chloride melts in moderate yields. A simplified synthesis of sorbosylurea tetraacetate 4 in two steps using urea melts was performed, achieving good yields. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file. 相似文献
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Frédéric Pelletier Dr. Diana Ciuculescu Jean‐Gabriel Mattei Dr. Pierre Lecante Dr. Marie‐José Casanove Dr. Nader Yaacoub Dr. Jean‐Marc Greneche Dr. Carolin Schmitz‐Antoniak Prof. Catherine Amiens 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(19):6021-6026
The effectiveness of amine–borane as reducing agent for the synthesis of iron nanoparticles has been investigated. Large (2–4 nm) Fe nanoparticles were obtained from [Fe{N(SiMe3)2}2]. Inclusion of boron in the nanoparticles is clearly evidenced by extended X‐ray absorption fine structure spectroscopy and Mössbauer spectrometry. Furthermore, the reactivity of amine–borane and amino–borane complexes in the presence of pure Fe nanoparticles has been investigated. Dihydrogen evolution was observed in both cases, which suggests the potential of Fe nanoparticles to promote the release of dihydrogen from amine–borane and amino–borane moieties. 相似文献