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101.
M. Jochum R. Bakry I. Wartusch C. W. Huck H. Engelhardt G. K. Bonn 《Chromatographia》2002,56(5-6):263-268
Summary This paper reports on the use of a polymer-based, strong anion-exchange stationary phase for rapid, selective and sensitive
analysis of physiological important mono-, di- and oligosaccharides by high-performance anion-exchange chromatography (HPAEC)
with pulsed amperometric detection (PAD) under alkaline conditions. The adsorbent was obtained by direct nitration of 3 and
5 μm, spherical non-porous highly cross-linked, styrene-divinylbenzene copolymer (PS-DVB) beads, followed by reduction of
superficially introduced nitro groups with nascent hydrogen and quaternization of the resultant amino groups with iodomethane.
Extended exposure to high pressure and strong alkaline conditions did not have any untoward effect on mechanical stability
and chromatographic performance. A comparison of the 3 and 5 μm beads showed, that the synthesized 3 μm highly cross-linked
PS-DVB particles are the preferred phases for the separation of monosaccharides and the 5 μm particles are preferable for
the separation of oligosaccharides. To demonstrate the suitability for the analysis of complex samples, the optimized and
validated system was used for the determination of glucose, fructose and sucrose in apple juice and other soft drinks such
as Coca Cola. Finally, analysis within a few minutes without sample pretreatment down to a lower limit of detection of 0.174–0.504
μg mL−1 at a linearity with R2>0.994 and a repooducibility higher than 98% further confirmed the efficiency of these polymeric sorbents. 相似文献
102.
Photolysis of the title compounds in acidic aqueous solution results in "activation" of the distal m-methyl group, resulting in deuterium exchange (Phi approximately 0.1) when D(2)O is used. The reaction is not observed in neutral aqueous solution or in deuterated organic solvents such as CD(3)CN. The reaction is best rationalized by a mechanism involving initial protonation at the carbonyl oxygen of the triplet excited state. [reaction: see text] 相似文献
103.
Biomimetic piezoelectric quartz sensor for caffeine based on a molecularly imprinted polymer 总被引:2,自引:0,他引:2
A piezoelectric quartz sensor coated with molecularly imprinted polymer (MIP) for caffeine was developed. The MIP was prepared by co-polymerizing methacrylic acid (MAA) and ethylene glycol dimethacrylate (EDMA) in the presence of azobis(isobutyronitrile) as initiator, caffeine as template molecule, and chloroform as solvent. The MIP suspension in polyvinyl chloride/tetrahydrofuran (6:2:1 w/w/v) solution was spin coated onto the surface of the electrode of a 10 MHz AT-cut quartz crystal. The sensor exhibited a linear relationship between the frequency shift and caffeine concentration in the range of 1×10–7 mg mL–1 up to 1x10–3 mg mL–1 [correlation coefficient (r)=0.9935] in a stopped flow measurement mode. It has a sensitivity of about 24 Hz/ln(concentration, mg mL–1). A steady-state response was achieved in less than 10 min. The performance characteristic of the sensor shows a promising and inexpensive alternative method of detecting caffeine. Surface studies were carried out for the reagent phase of the sensor using SEM, AFM, and XPS analysis in order to elucidate the imprinting of the caffeine molecule. The SEM micrograph, AFM image, and XPS spectra confirmed the removal of caffeine by Soxhlet extraction in the imprinting process and the rebinding of caffeine to the MIP sensing layer during measurement. 相似文献
104.
Dimitrakakis E Haberhauer-Troyer C Abe Y Ochsenkühn-Petropoulou M Rosenberg E 《Analytical and bioanalytical chemistry》2004,379(5-6):842-848
The use of solid-phase microextraction (SPME) with gas chromatography coupled to microwave-induced plasma atomic-emission detection (GC–MIP-AED) is described for selenite [Se(IV)] speciation. Aqueous standards were derivatised with sodium tetraethyl- or tetrapropylborate and extracted by SPME. Headspace extraction of the ethyl and propyl derivatives was studied. Relevant experimental conditions were optimised, including conditions for derivatisation and extraction and those of gas chromatographic analysis. The limits of detection achieved for headspace sampling of derivatised Se(IV) were in the low ng mL–1 range for both ethylation and propylation. When the method was applied to analysis of selenite in selenised yeast reference material results were in good agreement with the indicated values. 相似文献
105.
Metabolic profiling of normal and hypertensive rat kidney tissues by hrMAS-NMR spectroscopy 总被引:5,自引:0,他引:5
Intact kidney tissue samples of normal and spontaneously hypertensive rats (SHRs) were analyzed by hrMAS-NMR spectroscopy and principal component analysis (PCA). Radial components (cortex, outer stripe of the outer medulla, inner stripe of the outer medulla, and papilla) were sampled from various regions across the kidney from multiple animals in order to establish inter- and intra-animal variability. The effects of temperature were also measured. Papilla was differentiated from the other tissue types, and this variation by tissue type was greater than the effect of temperature on the samples (spectra were compared from samples at 2 and 30 °C). This study also revealed long term stability issues of tissue storage at -80 °C. The PCA showed that the greatest differentiation between normal rats and SHRs was found in the cortex and the regions in the NMR spectra that were correlated with this variation were identified.Abbreviations hrMAS High-resolution magic angle spinning - NMR Nuclear magnetic resonance - PCA Principal component analysis - CSA Chemical shift anisotropy - DD Dipolar coupling - SHR Spontaneously hypertensive rat 相似文献
106.
Thereza Christina Vessoni Penna Marina Ishii Adalberto Pessoa Junior Laura de Oliveira Nascimento Luciana Cambricoli de Souza Olivia Cholewa 《Applied biochemistry and biotechnology》2004,114(1-3):453-468
To determine the influence of various culture conditions, transformed cells of Escherichia coli expressing recombinant green fluorescent protein (GFPuv) were grown in nine cultures with four variable conditions (storage
of inoculated broth at 4°C prior to incubation, agitation speed, isopropyl-β-d-thiogalactopyranoside [IPTG] concentration, and induction time). The pelleted cells were resuspended in extraction buffer
and subjected to the three-phase partitioning (TPP) extraction method. To determine the most appropriate purification resin,
protein extracts were eluted through one of four types of HiTrap hydrophobic interaction chromatography (HIC) columns prepacked
with methyl, butyl, octyl, or phenyl resins and analyzed further on a 12% sodium dodecylsulfatepolyacrylamidegel. With Coomassie
staining, a single band between 27 (standard GFPuv) and 29 kDa (molecular weight standard) was visualized for every HIC column
sample. TPP extraction with HIC elution provided about 90% of the GFPuv recovered and eight-fold GFPuv enrichment related
to the specific mass. Rotary speed and IPTG concentration showed, respectively, greater negative and positive influences on
GFPuv expression at the beginning of the logarithmic phase for the set culture conditions (37°C, 24-h incubation). 相似文献
107.
Christina M. Gonzalez Jeffrey Hernandez Jason G. Parsons Jorge L. Gardea-Torresdey 《Microchemical Journal》2010,96(2):324-329
Selenium (Se) is naturally occurring in the environment and is an essential nutrient in mammals. However, environmental Se can be increased to toxic levels through different industrial practices. The potential adsorption of the Se oxoanions, selenite and selenate, from aqueous solutions onto nanosynthesized MnFe2O4 was investigated using batch techniques and DRC-ICP-MS spectroscopy. The nanomaterial (NM) was laboratory synthesized through slow titration of a mixture of Fe2+ and Mn2+ ions. X-ray diffraction and Scherrer's equation were used to determine the phase of the material and crystallite size, respectively. The effects of pH, reaction time, competitive anions, and the adsorption capacity of the synthesized NM to bind selenite and selenate were investigated. The Langmuir isotherm was used to determine the binding capacity of the NM. Results showed that the phase of the nanomaterial was similar to Jacobsite with a size of 27.5 nm. Results also showed that the sorption of either 100 ppb of selenite or selenate was pH independent in the pH range 2 to 6 and occurred within 5 min of contact time. The introduction of Cl− and NO3− anions individually added to solution had no significant effect on the sorption of either selenite or selenate. However, it was found that the addition of SO42− had a competitive effect only on the sorption of selenate, first seen at 10 ppm and more pronounced at 100 ppm of SO42−. In the presence of 100 ppm of PO43−, the adsorption of selenate decreased to 87% while selenite sorption decreased to 20%. From the Langmuir isotherm equation it was determined that the nano-Jacobsite had a selenite and selenate binding capacity of 6573.76 and 769.23 mg Se/kg of NM, respectively. 相似文献
108.
This report describes the use of Pd(II)/bis-sulfoxide 1 catalyzed intra- and intermolecular allylic C-H amination reactions to rapidly diversify structures containing a sensitive β-lactam core similar to that found in the monobactam antibiotic Aztreonam. Pharmacologically interesting oxazolidinone, oxazinanone, and linear amine motifs are rapidly installed with predictable and high selectivities under conditions that use limiting amounts of substrate. Additionally, we demonstrate for the first time that intramolecular C-H amination processes may be accelerated using catalytic amounts of a Lewis acid co-catalyst [Cr(III)(salen)Cl 2]. 相似文献
109.
110.
Luis M. Fidalgo Graeme Whyte Dr. Brandon T. Ruotolo Dr. Justin L. P. Benesch Dr. Florian Stengel Chris Abell Prof. Carol V. Robinson Prof. Wilhelm T. S. Huck Prof. 《Angewandte Chemie (International ed. in English)》2009,48(20):3665-3668
Fully integrated : Mass spectrometry has been integrated into a detection scheme for microdroplets that are created within microfluidic channels (see picture, scale bar 200 μm). This technique allows droplets to be identified based on the compounds they contain, and combines fluorescence screening with MS analysis. These experiments indicate how similar approaches can be applied to the ambitious goals of on‐chip protein evolution and chemical synthesis.