Search results for "Analytical"
showing 10 items of 9586 documents
Allylated cyclodextrins as effective affinity materials in chemical sensing of volatile aromatic hydrocarbons using an optical planar Bragg grating s…
2013
We report on the application of perallyl-substituted α-, β- and γ-cyclodextrins to an optical planar Bragg grating refractive index sensor for the effective sensitization of the sensor for airborne volatile aromatic hydrocarbons. Thereby, the emphasis of this work lies on the comparison of the different cyclodextrin types regarding their suitability as affinity material assessed by the sensors sensitivity and response behavior. The opto-chemical sensor device showed an immediate and quick response to the application of the investigated analytes benzene, toluene and m-xylene as well as a linear dependence on the concentration of those analytes. Studies on the sensors sensitivity depending on…
Modifying the reactivity of copper (II) by its encapsulation into polydimethylsiloxane: A selective sensor for ephedrine-like compounds
2018
This paper demonstrates that the reactivity of copper (II) can be modified through its entrappment in a polymeric matrix of polydimethylsiloxane (PDMS), which makes possible the reaction into the support instead of in solution. Amino-containing compounds such as amino acids, proteins and sugars, which react with Cu (II) in solution, do not react inside the polymer. As a prove of concept, a highly specific Cu (II) PDMS-based sensor for ephedrines has been developed in this work. When the sensors are put into contact with solutions of these drugs under basic conditions, a change in their color from pale green to purple is observed. This change enables the visual identification of ephedrine (E…
Separation and determination of alkylglycosides by liquid chromatography with electrospray mass spectrometric detection
2007
The separation of alkylpolyglycosides by liquid chromatography with electrospray mass spectrometric detection, using either an alkylamide or a cyanopropyl column, and acetonitrile/water mixtures as mobile phases, was developed. Using the alkylamide column and isocratic elution, the alpha- and beta-epimers and ring isomers (pyranosides and furanosides) of the alkylmonoglycosides were resolved. The ring isomers were also resolved in a much shorter time using the cyanopropyl column with gradient elution. Using these columns, the isomers of the alkyldiglycosides and alkyltriglycosides were also partially resolved. The equilibration time was much shorter with the cyanopropyl column, which was se…
Host-guest interactions for extracting antibiotics with a γ-cyclodextrin poly(glycidyl-co-ethylene dimethacrylate) hybrid sorbent
2021
Abstract A procedure for the solid-phase extraction of antibiotics (enoxacin, ofloxacin, norfloxacin, ciprofloxacin, and sparfloxacin) in water has been developed. The sorbent used is based on a poly(glycidyl-co-ethylene dimethacrylate) network, whose previously modified surface has been functionalized with γ-cyclodextrin through a click-chemistry reaction. The architecture of the material has been characterized by thermogravimetric analysis, N2 adsorption-desorption, Raman spectroscopy, confocal microscopy, and scanning electron microscopy, showing good capability to be used as a filler for extraction cartridges. The optimization of the extraction methodology shows good intra-day and inter…
Characterization of proteinaceous glues in old paintings by separation of the o-phtalaldehyde derivatives of their amino acids by liquid chromatograp…
2005
A HPLC-fluorescence method for characterization of proteinaceous glues from binding media used in pictorial works of art prior to conservation or restoration treatment is proposed. Fluorescence derivatization of amino acids released by acid hydrolysis of standard proteins is studied. The derivatization reagent was o-phtalaldehyde with 2-mercaptoethanol as catalyst. Mobile phase was a programmed gradient among two eluents (water buffered at pH 5.8 wit 5% THF, and methanol) and is able to satisfactorily resolve the amino acid derivatives in 45min. Peak area ratios among amino acid derivatives and the leucine derivative are useful to characterize the proteins. The method shows good sensitivity…
Formation rates and protonation constants of azo dyes in a sodium dodecylsulphate micellar solution.
1991
The effects of a sodium dodecylsulphate micellar solution on the coupling rates of several diazotizated arylamines with N-(1-naphthyl)-ethylenediamine and the shifts in the protonation constants of the corresponding azo dyes are quantitatively studied. Aniline, o-, m- and p-aminobenzoic acids, ethyl p-aminobenzoate and several sulphadrugs are used, and the relationships among the intensity of the effects and the molecular structure of the diazonium ions and the dyes are discussed. A single simplified procedure for the determination of all the substances at pH = 1.3 +/- 0.3, where coupling is quickly completed to directly produce the protonated form of the dyes, is established and applied to…
Anomalous diffraction profiles of alkali-halide-alkali-cyanide mixed crystals.
1986
The x-ray diffraction profiles of four mixed alkali halides-alkali cyanides have been studied. At the threshold concentration where the systems change over from ferroelastic ordering to the glass state, the profiles are highly unusual. The diffracted intensity of transverse scans along the cubic axes follows $I\ensuremath{\sim}\mathrm{exp}(\ensuremath{-}\ensuremath{\alpha}|\ensuremath{\xi}|)$, where $\ensuremath{\xi}$ is the reduced wave vector, measured from the line center.
M�ssbauer study of the spatial distribution of the active species in Cs doped Fe2O3-V2O5 catalysts
1995
From a Cs doped Fe2O3-V2O5 (Fe:V=1.4) catalyst exhibiting an inhomogeneous composition after calcination, three different fractions have been separated by visual inspection. One fraction has been found to consist of mainly α-Fe2O3, another one of mainly FeVO4. The third fraction (S1 in the text) is the catalytically most active fraction containing besides both of the former components an amorphous phase of FexVyOz and also the dopant. By combining the results from transmission and conversion electron Mossbauer spectra it has been concluded that the amorphous component is enriched in the surface region of the crystallites of the catalyst. In addition, the formation of a thin surface layer of…
Experimental and theoretical studies on corals. I. Toward understanding the origin of color in precious red corals from Raman and IR spectroscopies a…
2009
An attempt to explain the origin of the vivid red color in precious pink and red corals was undertaken. Raman and IR spectroscopies were applied to characterize white, pink and red corals. The position of the Raman signal near 1500 cm −1 of some corals and pearls was associated by several authors with the presence of the mixture of all-trans-polyenic pigments, containing 6 – 16 conjugated C C bonds or β-carotenoids. This hypothesis was examined theoretically by performing extensive B3LYP-DFT calculations of vibrational spectra of the model polyenic compounds. The B3LYP/6-311++G ∗∗ predicted positions of the dominating Raman mode depend on the number of C Cu nits (Cn parameter) and can be ac…
Structure and properties of N-methyl-N-(4-pyridyl)-nitramine and 1,4-dihydro-1-methyl-4-nitriminopyridine
2002
Abstract The molecular structure and spectral properties of N -methyl- N -(4-pyridyl)-nitramine ( 1 ) and 1,4-dihydro-1-methyl-4-nitriminopyridine ( 3 ) were investigated by the X-ray diffraction, FTIR, nuclear magnetic resonance (NMR) methods and DFT theoretical calculations. N -methyl- N -(4-pyridyl)-nitramine ( 1 ) crystallises in the orthorhombic Pbca space group. It is composed of two planar fragments; nitramino (N 2 O 2 ) group and the pirydyl ring. These two groups are twisted at about 70° with respect to each other, along the Ar–N bond. On the contrary, in compound 3 , they are coplanar to each other. Twist of the nitramino group in 1 with respect to the pirydyl ring leads to a sign…