Search results for "Concentration"
showing 10 items of 1906 documents
Determination of fluoride in rocks, soils, and fluoride-bearing minerals by separation using direct distillation in sulfuric acid medium and spectrop…
1989
Abstract An analytical method for fluoride determination in geological samples is proposed. It is based on a previous fluoride separation by distillation with a Teflon reactor. The variables that influence distillation quantitation (temperature, time, and acid concentration) are optimized. The influence of some species on fluoride recovery during distillation are studied, and conditions to avoid this influence are suggested. Fluoride determination is carried out by means of a spectrophotometric method [La(III)-F−-Alizarin complexone system] (N. T. Crosby, A. L. Dennis, and J. G. Stevens, Analyst (London), 1968, 93, 643–652). The method is applied to the analysis of soils, rocks, and fluorid…
Stability of 11-Nor-Δ9-carboxy-tetrahydrocannabinol Glucuronide in Plasma and Urine Assessed by Liquid Chromatography-Tandem Mass Spectrometry
2002
Abstract Background: Unconjugated 11-nor-Δ9-carboxy-tetrahydrocannabinol (THCCOOH) in blood and urine has been proposed as a valuable marker, but the glucuronide (THCCOOglu) is present in considerably higher concentrations than the parent drug. Acyl glucuronides have been shown to be potentially reactive conjugates, which may affect the in vitro metabolite pattern. Methods: Extraction procedures and a liquid chromatography-tandem mass spectrometry assay were developed and validated to investigate the stability of THCCOOglu in urine and plasma. Plasma and urine samples with added THCCOOglu were stored at −20, 4, 20, and 40 °C up to 10 days. Results: The glucuronide was stable at −20 °C in bo…
Viskosimetrische molekulargewichtsbestimmung von cellulose in kupfer-äethylendiamin
1955
Cellulose lost sich in Kupferathylendiamin („Cuen”) schneller und ist gegen Luftsauerstoff betrachtlich unempfindlicher als in Cuoxam. Im Gegensatz zu amerikanischen und franzosischen Arbeiten wurde festgestellt, das Losefahigkeit und Viskositatszahl weitgehend unabhangig von der Zusammensetzung des Komplexes und seiner Kupfermolaritat sind. Es wird eine Methode angegeben zur einfachen Herstellung einer Kupferathylendiaminlosung. Die viskosimetrischen Polymerisationsgr adbestimmungen von Cellulose in Cuen konnen unter Anwesenheit von Luft im Ostwald viskosimeter durchgefuhrt werden. Die dabei eryhaltenen Viskositatszahlen sind fur alle Cellulosematerialien um den Faktor 1,54 groser als die …
Monomeric vs. polymeric bonded iminodiacetate silica supports in high-performance ligand-exchange chromatography
1983
The synthesis of monomeric and polymeric bonded iminodiacetate-groups on silica supports is described. The polymeric support offers advantages over the monomeric, such as (i) preparation is much simpler, (ii) higher surface concentration of functional groups can be achieved without loss of efficiency and (iii) hydrolytic stability. Cu2+ loaded supports were examined for their kinetic performance, in particular for the C-parameter of the Knox equation, and for their hydrolytic stability. Calculation of the surface coverage shows that only a rather thin polymeric layer is formed; this is in agreement with the results of the kinetic performance. The retention of α-amino acids on the Cu2+ loade…
Hemiesters and hemiamides of maleic and succinic acid: synthesis and application of surfactants in emulsion polymerization with styrene and butyl acr…
1999
Hemiesters and hemiamides of maleic acid with different chain lengths of the hydrophobic alkyl group (R = C8H17, C10H21, C12H25, C16H33) have been synthesized and used as surfactants in the emulsion polymerization of styrene and butyl acrylate. The same polymerization experiments were also carried out using nonreactive surfactants with an analogous succinic structure. The chemical structure of the surfactants was confirmed by 1H nuclear magnetic resonance. The melting point and critical micelle concentration of the reactive surfactants described herein were measured. All of the surfactants studied provided good stability of styrene/butyl acrylate latexes, when compared with a reference late…
Rapid fluorimetric assay for primary amine groups in water samples
2003
Bond Elut C(18) solid-phase extraction cartridges were used for pre-concentration followed by derivatization with o-phthaldialdehyde-N-acetylcysteine (OPA-NAC) of primary amines in water. Optimal conditions were: conditioning the cartridges with borate buffer pH 10.4, retention of the primary amines, addition of the OPA-NAC(3.7 mmol L(-1)) 1:1 molar ratio and borate buffer pH 8, elution of the isoindol with MeOH-borate buffer (9:1) pH 10.2 and fluorescence measurement. The equations of the calibration graphs for methylamine, ethylamine, propylamine, butylamine, pentylamine, and beta-phenylethylamine at lambda(excitation)=330 nm and lambda(emission)=440 nm, in the optimal conditions are pres…
Die Beschleunigung der Polymerisation durch Hydroperoxyd und Aminsalz
1964
Di-n-butylaminhydrochlorid vergrosert die Geschwindigkeit der durch Tetralinhydroperoxyd initiierten Polymerisation von Styrol und von Methylmethacrylat. Im Bereich kleiner Konzentrationen von Hydroperoxyd und Aminsalz bis zu je etwa 5·10−4 Mol/l ist die Reaktionsgeschwindigkeit der Wurzel aus der Hydroperoxyd- und Aminsalzkonzentration jedoch der Monomerkonzentration direkt proportional. The polymerisation rate of styrene and methylmethacrylate initiated by tetraline hydroperoxide is accelerated by di-n-butylamine hydrochloride. In the range of low concentrations up to 5 · 10−4 mole/l. of each, hydroperoxide and amine salt, the rate of polymerisation is proportional to the square roote of …
Partielle spezifische volumina von m.m′-ditolyl und seinen oligomeren
1969
Das partielle spezifische Volumen von m.m′-Ditolyl in Toluol wurde durch Dichtemessungen uber den gesamten Konzentrationsbereich bei 25°C bestimmt. Das hieraus berechnete molare Uberschusvolumen betragt −0,21 cm3/Mol bei einem Volumenbruch von 0,5. Die partiellen spezifischen Volumina von Oligomeren des m.m′-Ditolyls wurden in einem niedrigen Konzentrationsbereich in Toluol, Benzol und Trichlorathylen bei 25°C bestimmt. Sie sind in erster Naherung dem Molekulargewicht umgekehrt proportional. The partial specific volume of m.m′-ditolyl in toluene was determined by means of density measurement over the entire range of concentrations at 25°C. The molar excess volume computed hereof turns out t…
Pyrene-Capped CdSe@ZnS Nanoparticles as Sensitive Flexible Oxygen Sensors in Non-Aqueous Media**
2014
A flexible, highly sensitive sensor of oxygen in non-aqueous solvents is described. It consists of CdSe/ZnS nanoparticles decorated with a considerable number of pyrene units, thus making the formation of the pyrene excimer possible. The emission of the pyrene excimer and that of the nanoparticle are suitably separated from each other and also from the excitation wavelength. This sensor can be applied as a ratiometric oxygen sensor by using the linear response of the pyrene excimer lifetime combined with the linear response of the nanoparticle excited state lifetime. This nanohybrid has been assayed in seven media with different dielectric constants and viscosities over the whole oxygen con…