Search results for "AH"

Role of solvent and base in the silanization reaction of silicas for reversed-phase high-performance liquid chromatography

1984

Reversed-phase packings were synthesized by reaction of n-alkyldimethylchloro- and trifluoroacetoxysilanes with silicas of 15 and 25 nm pore size, employing tetrahydrofuran, N,N-dimethylformamide, benzene, diethyl ether, dichloromethane and acetonitrile as solvents and triethylamine, pyridine, triazole, quinuclidine, 2,4- and 2,6-lutidine and imidazole as bases. With dichloromethane as solvent and 2,6- lutidine as base, n-alkyldimethyltrifluoroacetoxysilanes did not yield n-alkyl ligand densities higher than those obtained with n-alkyldimethylchlorosilanes under identical conditions. With a given base and given n-alkyldimethylchlorosilane the solvent type was found to exert a noticeable inf…

Ionomers in solution: 1. Viscometric and chromatographic studies in cononsolvent and cosolvent mixtures

1997

Abstract The viscosity and elution behaviour of polystyrene sulfonate ionomers with varying ionic content has been studied in the pure solvents chloroform (CHL), tetrahydrofuran (THF), dioxan (DIO), ethyl acetate (EA) and dimethylformamide (DMF) as well as in their cononsolvent mixtures CHL/THF (50:50), DIO/CHL (75:25) and in the cosolvent mixture EA/DMF (50:50). In the pure solvents with low dielectric constant the reduced viscosities of ionomers are lower at low concentrations and higher at moderate ones than the respective viscosities of the polystyrene precursor. These results can be explained by formation of intramolecular and intermolecular associations. Moreover, differences in visco…

Preferential solvation of a dicyanate ester monomer and poly(sulfone) in different organic solvents by size-exclusion chromatography.

2002

Preferential solvation parameters A in the ternary systems solvent (1) -monomer (2) -polymer (3) were determined as a tool to measure the compatibility between the cyanate ester monomer Arocy B10 and poly(sulfone), PSF, in the presence of three organic solvents: tetrahydrofuran, dimethylformamide and dicloromethane. The A parameter was measured by size-exclusion chromatography at different monomer-to-polymer ratios. The quantitative evaluation was rigorously made at polymer-diluted conditions. PSF was found to be preferentially solvated by the monomer. Concerning the solvent used, systems containing tetrahydrofuran showed the strongest solvation, the lowest A values being those obtained in …

Resolution assessment and performance of several organic modifiers in hybrid micellar liquid chromatography

2001

The performance of four criteria that measure the elementary resolution (modified selectivity, modified RS, peak purity, and orthogonal valley-to-peak ratio) was critically assessed using as global resolution function, the product of elementary measurements. The peak purities and valley-to-peak criteria yielded the best description of the overall separation according to the shape of the resolution surfaces compared to the peak arrangements in the chromatograms, the capability of defining unambiguously the composition regions of complete resolution, and the resolution achieved in the predicted optimums. Peak purities were used to compare the effect of five organic modifiers (1-propanol, 1-bu…

Polycyclic aromatic hydrocarbons (PAHs) in coffee brew samples: analytical method by GC-MS, profile, levels and sources.

2009

Roasting is a crucial step for the production of coffee, as it enables the development of color, aroma, and flavor, which are essential for the characterization of the coffee quality. At the same time, roasting may lead to the formation of not desirable compounds, such as polycyclic aromatic hydrocarbons (PAHs). In this paper, we report a method for PAHs determination in coffee brew, based on saponification and liquid-liquid extraction with small volumes of hexane, with exclusion of further processes of purification since we analyze the extract by gas chromatography with mass spectrometric detectors in the single ion monitoring mode (SIM). The total concentration of the 28 compounds investi…

A gallery of Chua's Attractors - Part IV

2007

Die Lehre von der Beihilfe

1892

Eine zur Erlangung des Grades eines Magisters des Strafrechts der Juristischen Fakultät der Kaiserlichen Universität zu Dorpat vorgelegte Abhandlung

IDENTIFICATION OF LECTINS IN THE KINETIDS OFTETRAHYMENA PYRIFORMIS

1997

Previously we described lectin-like molecules in the ciliate Tetrahymena pyriformis; by application of synthetic neoglycoconjugates it is now shown that T. pyriformis contains considerable amounts of both a beta-D-glucose- and a lactose-specific lectin. No evidence for the presence of alpha-D-mannose-, alpha-D-galactose- or of alpha-L-fucose-specific lectins could be obtained. The two lectins, identified in T. pyriformis, are associated with the kinetids. During cell division the lectins disappear or become masked in the fission furrow. Therefore, we assume that these lectins are involved in the organization of the distribution pattern of the kinetids during cell division perhaps due to lec…

Représenter l'irreprésentable, des abus de la rhétorique

2001

Peut-on représenter 1'irreprésentable? Par-delà la formule paradoxale, la question pose un nœud intéressant. Que prétend-il signifier, lorsqu'on parle spécifiquement de la Shoah? S'il est possible de conclure sur la représentabilité de la Shoah, nous avancerons que notre époque semble avoir saisi les risques d'une monstration sans discernement d'images reliées à la barbarie. Pudeur dans la représentation, d'un coté, et privilège cédé a la parole, de l'autre. Si l'on considère le plus gigantesque projet filmique de témoignage en cours- celui de Spielberg- il devient possible de supposer une relation entre le spectaculaire scopique et le mélodramatique d'un film comme La Liste de Schindler; d…

Representar lo irrepresentable : de los abusos de la retórica

2001

Si es posible concluir sobre la representabilidad de la Shoah, avanzaremos que nuestra época parece haber comprendido los riesgos de una mostración sin discernir imágenes relacionadas con la barbarie. Pudor en la representación, por un lado, y privilegio concedido a la palabra, por otro. Existe, al menos, una democratización de la noción de víctima que no busca la ejemplaridad, al tiempo que se olvidan en la mayoría de los casos las figuras del testigo y del verdugo. Si consideramos, tal y como lo hace Jacques Walter en el texto antes citado, el más gigantesco proyecto fílmico en curso -el de Spielberg- se hace posible suponer una relación entre la espectacularidad escópica y lo melodramáti…