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排序方式: 共有139条查询结果,搜索用时 15 毫秒
111.
A new approach for determining cyanide in microsamples is described. The method is based on capillary flow injection analysis (CFIA) with amperometric detection. The sensing electrode is a silver-plated microdisk electrode, where cyanide can react under formation of a dicyanoargentate complex. A remarkably low mass detection limit of 231 fmol cyanide is obtained for an injection volume of 60 nl. The sample throughput of the CFIA-arrangement is comparable with a conventional sized FIA-system. A practical application is given by analyzing the cyanide (amygdalin) concentration in apple kernels. 相似文献
112.
In recent years, several dual detection concepts (DDCs) for CE were developed, which consisted of at least one nondestructive detector. For these DDCs, a linear detector arrangement could be used, which is not possible when both detectors are destructive. To overcome this problem, we developed a concept for the splitting of the CE stream utilizing commercially available flow splitters (FSs) that allow the parallel positioning of two destructive detectors. In this proof-of-concept study, T- and Y-shaped FSs were characterized regarding their suitability for DDCs. To keep it simple, a UV detector (UV) and a C4D were used for the characterization. The model system consisted of an acetonitrile-based background electrolyte and the two model substances, (ferrocenylmethyl)trimethylammonium iodide and caffeine. CE hyphenated to a UV detector (CE-UV) measurements revealed that the split ratio was about 50% for both FSs. CE-C4D was used to evaluate the peak shape in front of and behind the FSs. These measurements showed that there was no significant peak broadening introduced by the FSs. Additionally, there were no changes in the LODs in front of and behind the FSs. Furthermore, the flexibility of the new FS approach allowed the usage of capillaries with different ids (25–75 µm) for injection and detection. 相似文献
113.
Eight textile dye compounds including five cationic dyes, namely, basic blue 41, basic blue 9, basic green 4, basic violet 16 and basic violet 3, and three anionic dyes, acid green 25, acid red 1 and acid blue 324, were separated and detected by non-aqueous capillary electrophoresis (NACE) with electrochemical detection. Simultaneous separations of acid and basic dyes were performed using an acetonitrile-based buffer. Particular attention was paid to the determination of basic textile dyes. The optimized electrophoresis buffer for the separation of basic dyes was a solvent mixture of acetonitrile/methanol (75:25, v/v) containing 1 M acetic acid and 10 mM sodium acetate. The limits of detection for the basic dyes were in the range of 0.1–0.7 μg mL−1. An appropriate solid-phase extraction procedure was developed for the pre-treatment of aqueous samples with different matrices. This analytical approach was successfully applied to various water samples including river and lake water which were spiked with textile dyes. 相似文献
114.
Mark Jonas Josef Peter Beutner Andrea Cindric Marija Matysik Frank-Michael 《Mikrochimica acta》2015,182(1-2):351-359
Microchimica Acta - A method is presented for conducting fast capillary electrophoresis (CE) with ultrasmall sample volumes (<10 nL) and subsequent determination of target analytes... 相似文献
115.
For several decades the plasmonic behavior of materials has been almost exclusively studied in visible region. Emerging applications require, however, the development of efficient materials operating in UV range. In UV nanoplasmonics aluminum (Al) can play a leading role due to its advantageous electronic properties. Yet, there is still lack of reproducible method to obtain Al nanostructures with desired parameters. Al nanoconcaves can provide a way to overcome these limitations. Here, two different periodicities of the Al nanoconcaves arrays were analyzed. It was observed that the Al concaves can dramatically reduce the optical reflectivity as compared to flat, unstructured Al. At the same time pronounced reflectivity dips were discernible, which were ascribed to (0,1) plasmonic mode. The positions of the dips were at around 250 nm and 350 nm for Al concaves with interpores distance (Dc) of 246.3 nm and 456.7 nm, respectively. The refractive index sensitivity (RIS) was: ∼191 nm/RIU for the Al concaves with Dc = 246.3 nm, and ∼291 nm/RIU for the Al nanoconcaves arrays with Dc = 456.7 nm. 相似文献
116.
117.
Stefan Wert Heiko Iken Michael J. Schöning Frank-Michael Matysik 《Electroanalysis》2021,33(5):1143-1151
Glucose oxidase (GOx) is an enzyme frequently used in glucose biosensors. As increased temperatures can enhance the performance of electrochemical sensors, we investigated the impact of temperature pulses on GOx that was drop-coated on flattened Pt microwires. The wires were heated by an alternating current. The sensitivity towards glucose and the temperature stability of GOx was investigated by amperometry. An up to 22-fold increase of sensitivity was observed. Spatially resolved enzyme activity changes were investigated via scanning electrochemical microscopy. The application of short (<100 ms) heat pulses was associated with less thermal inactivation of the immobilized GOx than long-term heating. 相似文献
118.
Voltammetric Determination of 8‐Nitroquinoline Using a Silver Solid Electrode and Its Application to Model Samples of Drinking and River Water
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This work is focused on the application of a silver solid electrode (AgE) for the development of modern voltammetric methods for the determination of submicromolar concentrations of biologically active compounds present in the environment. 8‐Nitroquinoline (8‐NQ), a well‐known chemical carcinogen, was chosen as a model substance. Differential pulse voltammetry (DPV) was used to study electrochemical behavior of 8‐NQ in different aqueous matrices. The following optimal conditions for determination of 8‐NQ in the concentration ranges from 2 to 100 µmol L?1 were used: Britton? Robinson (BR) buffer of pH 3.0, the regeneration potentials cycles (Ein=?1000 mV, Efin=?100 mV) and constant cleaning potential ?2000 mV. Practical applicability of AgE for the determination of micromolar concentrations of 8‐NQ was verified on model samples of drinking and river water. 相似文献
119.
Daviso E Janssen GJ Alia A Jeschke G Matysik J Tessari M 《Journal of the American Chemical Society》2011,133(42):16754-16757
Several techniques rely on electron-nuclear interactions to boost the polarization of nuclear spins in the solid phase. Averaging out of anisotropic interactions as a result of molecular tumbling strongly reduces the applicability of such hyperpolarization approaches in liquids. Here we show for the first time that anisotropic electron-nuclear interactions in solution can survive sufficiently long to generate nuclear spin polarization by the solid-state photo-CIDNP mechanism. A 10,000-fold NMR signal increase in solution was observed for a giant biomolecular complex of a photosynthetic membrane protein with a tumbling correlation time in the submicrosecond regime, corresponding to a molecular weight close to 1 MDa. 相似文献
120.
15N MAS NMR studies of cph1 phytochrome: Chromophore dynamics and intramolecular signal transduction
Rohmer T Strauss H Hughes J de Groot H Gärtner W Schmieder P Matysik J 《The journal of physical chemistry. B》2006,110(41):20580-20585
Solid-state nuclear magnetic resonance (NMR) is applied for the first time to the photoreceptor phytochrome. The two stable states, Pr and Pfr, of the 59-kDa N-terminal module of the cyanobacterial phytochrome Cph1 from Synechocystis sp. PCC 6803 containing a uniformly 15N-labeled phycocyanobilin cofactor are explored by 15N cross-polarization (CP) magic-angle spinning (MAS) NMR. As recently shown by 15N solution-state NMR using chemical shifts [Strauss, H. M.; Hughes, J.; Schmieder, P. Biochemistry 2005, 44, 8244], all four nitrogens are protonated in both states. CP/MAS NMR provides two additional independent lines of evidence for the protonation of the nitrogens. Apparent loss of mobility during photoactivation, indicated by the decrease of line width, demonstrates strong tension of the entire chromophore in the Pfr state, which is in clear contrast to a more relaxed Pr state. The outer rings (A and D) of the chromophore are significantly affected by the phototransformation, as indicated by both change of chemical shift and line width. On the other hand, on the inner rings (B and C) only minor changes of chemical shifts are detected, providing evidence for a conserved environment during phototransformation. In a mechanical model, the phototransformation is understood in terms of rotations between the A-B and C-D methine bridges, allowing for intramolecular signal transduction to the protein surface by a unit composed of the central rings B and C and its tightly linked protein surroundings during the highly energetic Pfr state. 相似文献