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Experimental Optimization (experimental + optimization)

Distribution by Scientific Domains

Chemistry	50%

Selected Abstracts

Performance of electrospun nanofibers for SPE of drugs from aqueous solutions

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 18 2008
Xue-jun Kang
Abstract A novel extraction technique was reported. The solid phase material, nanofiber, was prepared by electrospinning using polystyrene. Twenty different drugs (10 ,g/L in water) were extracted using 1 mg of nanofibers within 5 min. The analytes can be desorpted from the fibers with 50 ,L of the methanol and then monitored by LC coupled to a UV detector. Packed-fiber SPE (PFSPE) provide high recoveries (>50%) for some relatively non-polar drugs (log P >1.5) (n -octanol-to-water partition ratio), and relatively low recoveries (9.9,39.8%) for the drugs within the log P window below 1. Experimental optimization of the technique has been carried out using seven representative drugs, edaravone, cinchonine, quinine, voriconazole, chlordiazepoxide, verapamil, and rutonding. Except for edaravone, the maximum yields of seven drugs (0.2 ,g/L) from water samples were approximately 100%, and were 33.7,88.2% from human plasma. The advantageous aspect of the technique encompasses high throughput, high sensitivity, simplicity, low cost, and green chemistry. [source]

Comparison of various extraction techniques for isolation and determination of isoflavonoids in plants

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 1 2007
Bajer
Abstract In the present paper, the following extraction techniques have been used for extracting isoflavonoids from the species Matricaria recutita, Rosmarinus officinalis, Foeniculum vulgare, and Agrimonia eupatoria L.: supercritical fluid extraction (SFE), pressurized fluid extraction, matrix solid phase dispersion, ultrasonic extraction in an ultrasonic bath (USE) and by means of an ultrasonic homogeniser (HOM), extraction by means of Soxhlet apparatus (SOX), and solid phase extraction. Experimental optimization of all techniques has been carried out using a soybean flour. Subsequent analyses of the extracts were carried out by liquid chromatography with UV detection. The maximum yields of daidzein and genistein were obtained by extraction with the SOX, USE, and HOM techniques. The maximum yields of apigenin and biochanin A from herb samples were obtained by SFE. [source]

Experimental optimization of the 2nd loop configuration for feedforward amplifiers in terms of their efficiency and linearity

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2006
Sung-Chan Jung
Abstract In this paper, we report the results of the experimental optimization of the 2nd -loop configuration for feedforward amplifiers in terms of their efficiency and linearity. We consider two parameters in the 2nd -loop of a feedforward amplifier: (i) the size ratio between the main and error amplifiers and (ii) the coupling factor of the error signal coupler. Experiments are performed using a multicarrier down-link WCDMA signal under various configurations. The measured data, which are normalized with respect to the overall power capacity of the main and error amplifiers, show that, among the different 2nd -loop configurations, the best compromised efficiency (13.4%) at a given adjacent channel leakage ratio (ACLR) level (,50 dBc) is observed for a size ratio of around 3.0 and a coupling factor of around 7.2 dB. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 617,621, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21425 [source]

Optimization of the electrokinetic supercharging preconcentration for high-sensitivity microchip gel electrophoresis on a cross-geometry microchip

ELECTROPHORESIS, Issue 14 2004
Zhongqi Xu
Abstract We developed a novel on-line preconcentration procedure for microchip gel electrophoresis (MCGE), which enables application of electrokinetic supercharging (EKS) for highly sensitive detection of DNA fragments on a cross-geometry microchip. In comparison with conventional pinched injection using the cross microchip, the present approach allows loading a much larger amount of the sample by taking advantage of a newly developed operational mode. In order to obtain high preconcentration effect and prevent splitting of an enriched sample into subchannels, i.e., off the detector range, effects of the voltage applied on the reservoirs and the time of isotachophoretic preconcentration were examined. The optimal balance between the voltage and time was found for a high-sensitivity analysis of DNA fragments. After experimental optimization the detection limit of a 150 bp fragment was as low as 0.22 mg/L (S/N = 3) that is 10 times better than using the conventional pinched injection. [source]

Experimental optimization of the 2nd loop configuration for feedforward amplifiers in terms of their efficiency and linearity

Isolation and X-Ray Structures of Reactive Intermediates of Organocatalysis with Diphenylprolinol Ethers and with Imidazolidinones

HELVETICA CHIMICA ACTA, Issue 11 2008
5-Repulsion, A Survey, Comparison with Computed Structures, the Geminal-Diaryl Effect at Work, with 1-Acyl-imidazolidinones: The
Abstract Reaction of 2-phenylacetaldehyde with the Me3Si ether of diphenyl-prolinol, with removal of H2O, gives a crystalline enamine (1). The HBF4 salts of the MePh2Si ether of diphenyl-prolinol and of 2-(tert -butyl)-3-methyl- and 5-benzyl-2,2,3-trimethyl-1,3-imidazolidin-4-one react with cinnamaldehyde to give crystalline iminium salts 2, 3, and 4. Single crystals of the enamine and of two iminium salts, 2 and 3, were subjected to X-ray structure analysis (Figs.,1, 2, and 6), and a 2D-NMR spectrum of the third iminium salt was recorded (Fig.,7). The crystal and NMR structures confirm the commonly accepted, general structures of the two types of reactive intermediates in organocatalysis with the five-membered heterocycles, i.e., D, E (Scheme,2). Fine details of the crystal structures are discussed in view of the observed stereoselectivities of the corresponding reactions with electrophiles and nucleophiles. The structures 1 and 2 are compared with those of other diphenyl-prolinol derivatives (from the Cambridge File CSD; Table,1) and discussed in connection with other reagents and ligands, containing geminal diaryl groups and being used in enantioselective synthesis (Fig.,4). The iminium ions 3 and 4 are compared with N -acylated imidazolidinones F and G (Figs.,9, 12, and 13, and Table,3), and common structural aspects such as minimalization of 1,5-repulsion (the ,A1,3 -effect'), are discussed. The crystal structures of the simple diphenyl-prolinol,HBF4 salt (Fig.,3) and of Boc- and benzoyl-(tert -butyl)methyl-imidazolidinone (Boc-BMI and Bz-BMI, resp.; Figs.,10 and 11) are also reported. Finally, the crystal structures are compared with previously published theoretical structures, which were obtained from high-level-of-theory DFT calculations (Figs.,5 and 8, and Table,2). Delicate details including pyramidalization of trigonal N-atoms, distortions around iminium CN bonds, shielding of diastereotopic faces, and the , -interaction between a benzene ring and a Me group match so well with, and were actually predicting the experimental results that the question may seem appropriate, whether one will soon start considering to carry out such calculations before going to the laboratory for experimental optimizations. [source]