Search results for "COLUMN"
showing 10 items of 1301 documents
Determination of Homovanillic Acid in Human Plasma Using HPLC with Electrochemical Detection and Automated Solid Phase Extraction
1993
Abstract An isocratic HPLC method with electrochemical detection for the quantification of homovanillic acid (HVA) is described. The method included automated solid phase extraction on C-18-reversed phase material, followed by separation on a 3-μm Nucleosil 100 C18 column (250 mm × 4.6 mm I. D.) with a 100 mM citric acid solution (pH 6.6) containing 4% acetonitrile (v/v) as eluent at a flow rate of 0.6 ml/min. Isovanillinic acid served as internal standard. Extractability of both analytes was ca. 80 %. After extraction of 1 ml of plasma, coefficients of variation of replicate analyses were below 10 % in the naturally occuring concentration range.
Über die mikrobiologische Umwandlung N-haltiger Substrate. 3. Mitt.: Über die Konstitutionsaufklärung von Umwandlungsprodukten des 5-Hydroxyindols du…
1968
In Schuttelkulturen von Cordyceps militaris entstehen aus 5-Hydroxyindol zwei neue Substanzen, die nach Chromatographie an Polyamidsaulen und nachfolgender Isolierung auf Grund ihres chemischen Verhaltens gegenuber Diazomethan sowie ihrer Elementaranalysen, IR-, Massen-und NMR-Spektren als ω-N-Acetyl-5-hydroxy-tryptophan und ω-N-Acetyl-serotonin identifiziert wurden. Two new substances are produced in submerged cultures of Cordyceps militaris fed with 5-hydroxyindole. These substances, separated by column chromatography with polyamide and isolated afterwards, have been identified as ω-N-acetyl-5-hydroxytryptophan and ω-N-acetyl-serotonin by their reaction with diazomethane, by elementary an…
Darstellung und eigenschaften von linearen oligourethanen mit phenylendgruppen und von cyclischen oligourethanen aus diäthylenglykol und hexamethylen…
1971
Es wurden lineare Oligourethane mit Phenylendgruppen und cyclische Oligourethane aus Diathylenglykol und Hexamethylendiisocyanat dargestellt. Der groste bisher isolierte Ring enthalt je sieben Grundbausteine und besitzt 119 Ringglieder bei einem Molekulargewicht von 1920. Eine gute Trennung der Oligomeren wurde durch Adsorptionssaulenchromatographie erzielt. Hierbei wurde ein Elutionsmittel mit Losungsmittelgradient verwendet. Schmelzpunkte, Umwandlungserscheinungen, Langperioden und Weitwinkeldiagramme der Oligomeren werden im Hinblick auf ihre Struktur diskutiert. Linear oligourethanes with phenylurethane endgroups and cyclic oligourethanes were prepared from diethylene glycol and hexamet…
Antibakterielle Wirkstoffe, 6. Mitt.1) 2,4-Unsymmetrisch dialkylierte Pyrimido[1,2-a]benzimidazole
1982
Durch Kondensation von 2-Aminobenzimidazol (1) mit 2,4-Hexandion (2a) entsteht das Isomerenpaar 3a/3b, mit 6-Methyl-2,4-heptandion (2b) das Isomerengemisch 3c/3d, wahrend mit 1-Phenyl-2,4-pentandion (2c) die Isomere 3e und 3f gebildet werden. Die Trennung der Isomere ist durch Saulenchromatographie, die Strukturfestlegung auf spektroskopischem Wege, moglich. 2-Imino-2H-s-triazino[2,1-b]benzoxazol weist antibakterielle Wirksamkeit auf. Antibacterial Drugs, VI: 2,4-Unsymmetrically Dialkylated Pyrimido[1,2-α]benzimidazoles Condensation of 2-aminobenzimidazole (1) with 2,4-hexanedione (2a) leads to the pair of isomers 3a/3b. Condensation with 6-methyl-2,4-heptanedione (2b) yields the isomers 3c…
Tristriazolotriazines with π-Conjugated Segments: Star-Shaped Fluorophors and Discotic Liquid Crystals
2012
C3-symmetrical tristriazolotriazines substituted with phenylene rings carrying lateral flexible alkoxy side chains were prepared via condensation/ring transformation of cyanuric chloride and tetrazoles. These star-shaped, planar compounds can form broad thermotropic mesophases. Due to the extensive π-conjugation, these compounds are highly emissive and the octupolar donor-acceptor electronic structure results in non-linear optical properties like solvatochromism. Brønstedt acids provoke halochromism of the absorption and of the fluorescence.
Methacrylate ester-based monolithic columns for nano-LC separation of tocopherols in vegetable oils
2010
The separation and determination of tocopherols (Ts) in vegetable oils by nano-LC chromatography with UV-vis detection using lauryl methacrylate ester-based monolithic columns has been developed. The separation of Ts was optimized in terms of mobile phase composition on the basis of the best compromise among efficiency, resolution and analysis time. Using a mobile phase composed of ACN/methanol/water, an excellent resolution between Ts was achieved within 18 min. The LODs were lower than 0.26 μg/mL, being repeatability values of retention time and peak area below 0.15 and 3.1%, respectively. The method was applied to the quantification of Ts and tocotrienols present in several vegetable oil…
HPLC Method for Cyst(e)ine and Methionine in Infant Formulas
1996
Cyst(e)ine and methionine were converted into cysteic acid and methionine sulfone by oxidizing with performic acid. The oxidized samples were then subjected to acid hydrolysis (6N HCl, 105-110°C/24 hr). After derivatization with phenylisothiocyanate, reverse phase HPLC separation was carried out at 48°C and with UV detection. Different gradients and pH values in the eluent were assayed to determine the best resolution. Analytical parameters, detection and quantification limits, linearity, precision and accuracy, were determined. The method was reliable and accurate for measuring cyst(e)ine and methionine in infant formulae.
Recycling and fluxes of carbon gases in a stratified boreal lake following experimental carbon addition
2014
Partly anoxic stratified humic lakes are important sources of methane (CH4) and carbon dioxide (CO2) to the atmosphere. We followed the fate of CH4 and CO2 in a small boreal stratified lake, Alinen Mustajärvi, during 2007–2009. In 2008 and 2009 the lake received additions of dissolved organic carbon (DOC) with stable carbon isotope ratio (δ13C) around 16‰ higher than that of local allochthonous DOC. Carbon transformations in the water column were studied by measurements of δ13C of CH4 and of the dissolved inorganic carbon (DIC). Furthermore, CH4 and CO2 production, consumption and emissions were estimated. Methane oxidation was estimated by a diffusion gradient method. The amount, lo…
R/C columns strengthened by means of steel angles and battens: testing, modeling and design
2010
Crystal structure of (R)-6-fluoro-2-[(S)-oxiran-2-yl]chroman
2015
The title compound, C11H11FO2, is a building block in the synthesis of the active pharmaceutical ingredient DL-nebivolol. The synthesis starting from the enantiomerically pure (R)-6-fluoro-4-oxo-3,4-dihydro-2H-chromene-2-carboxylic acid resulted in a mixture of two stereoisomers, namely (R)-6-fluoro-2-[(S)-oxiran-2-yl]chroman and (R)-6-fluoro-2-[(R)-oxiran-2-yl]chroman. The mixture was separated by column chromatography but only one stereoisomer crystallized. The X-ray structure analysis revealed that the solid consisted of theR,Sisomer. A similar procedure was repeated for (S)-6-fluoro-4-oxo-3,4-dihydro-2H-chromene-2-carboxylic acid and, in this case, theS,Risomer was produced as a crystal…