Search results for "Spectroscopy"
showing 10 items of 10293 documents
Chemical characterization of peat fulvic acid fractions
1993
Abstract Milled peat fulvic acid (FA) preparation was fractionated by XAD-8 and conventional extraction methods. The fractions were further analyzed by IR and NMR and subjected to cupric oxide (CuO) oxidation. Carbohydrates of polydisperse FA were mostly not retained in the XAD-8 fractionation. The intensity of the signals due to double bonded carbons was much greater in the 13 C and proton NMR spectrum of the XAD-8 retained fraction than in the spectra of the XAD-8 non-retained or XAD-8 non-treated fractions. In CuO oxidation the main products of all FA fractions were 4-hydroxybenzaldehyde and 4-hydroxyacetophenone, both indicators of 4-hydroxyphenylpropane building blocks. Their concentra…
Determination of unsaturation grade and trans isomers generated during thermal oxidation of edible oils and fats by FTIR
1999
Abstract The oxidative deterioration of culinary oils and fats during episodes of heating associated with normal usage (80°C–300°C, 20–40 min) was monitored by FTIR spectroscopy. The thermal oxidation of polyunsaturated fatty acids during heating was studied by the determination of unsaturation percentage and trans isomers at various temperatures and heating times. Oils frequently used in food frying such as olive oil, sunflower oil, corn oil and seeds oil (sunflower, safflower and canola seed), and lard were studied. The Absorbance Correction Method is proposed to correct the spectral interference and allows the analytic use of signal which would not be initially valid for quantitative ana…
Analytical evaluation of polyunsaturated fatty acids degradation during thermal oxidation of edible oils by Fourier transform infrared spectroscopy
1998
The oxidative deterioration of polyunsaturated fatty acids (PUFAs) in culinary oils and fats during episodes of heating associated with normal usage (80-300 degrees C, 20-40 min) has been monitored by Fourier transform infrared spectroscopy (FTIR). The thermal oxidation of PUFAs is a free radical chain reaction, in which hydroperoxides are generally recognized as the primary major products. Hydroperoxides of PUFAs are easily decomposed into a very complex mixture of secondary products with the decrease in unsaturation. The oxidative advance of PUFAs during heating was studied by the determination of unsaturation percentage at different temperatures and heating times. Oils frequently used in…
Spectrally selective holographic optical elements based on a thick polymer medium with diffusional amplification
2000
A thick rigid polymer recording medium with self-amplification of holograms owing to diffusion of phenanthrenequinone molecules was used to find efficient holographic optical elements with high-spectral-selectivity interference filters and multiple demultiplexers. Several examples of practical applications are briefly described in this paper, showing the benefits of such optical elements for the fields of astronomy, spectroscopy and communication technologies.
Bis(3,5-dimethyl-1H-pyrazolyl)selenide--a new bidentate bent connector for preparation of 1D and 2D co-ordination polymers.
2007
The synthesis and description of eight polymeric complexes formed by transition metals with the bifurcated ligand bis(3,5-dimethyl-1H-pyrazolyl)selenide are discussed together with X-ray crystal analysis as well as variable temperature magnetic susceptibility and characterization by Mossbauer spectroscopy. Preferable types of binding patterns of the ligand were determined, which include a variation of the bridging modes (cis- and trans-) and of the separation length, where the latter parameter together with bending of the ligand molecule were found to be dependent on the type of co-ordination geometry of the central atom and the nature of the anion. A strategy for increasing the structure d…
Mono-aryltin(IV) and mono-benzyltin(IV) complexes with pyridine-2-carboxylic acid and 8-hydroxyquinoline. X-ray structure of p-chloro-phenyl-tris(8-q…
1999
Abstract Complexes RSn(O2CPy)3·2H2O and RSn(Ox)3, (PyCOOH=pyridine-2-carboxylic acid, HOx=8-hydroxyquinoline, R=o- and p-Tolyl, o- and p-ClC6H4=o- and p-ClPh, o-ClC6H4CH2=o-ClBenzyl; besides, R=Ph in RSn(Ox)3) have been synthesized and characterized by elemental analysis and determination of molecular weights in CHCl3 solutions. The structure of p-ClPhSn(Ox)3·2CHCl3 has been determined by X-ray diffractometry. The 7-coordinated tin atom of the monomeric compound is in the center of a pentagonal bipyramid formed by (p-ClPh)C and O and N atoms of the chelating Ox− ligands. The latter type of structure would hold for all complexes according to 119Sn Mossbauer (including the determination of th…
Solvation chemistry of water-soluble thiol-protected gold nanocluster Au102 from DOSY NMR spectroscopy and DFT calculations
2014
The hydrodynamic diameter of Aum(pMBA)n [(m, n) = (102, 44) and (144, 60)] clusters in aqueous media was determined via DOSY NMR spectroscopy. The apparent size of the same (n, m) cluster depends on the counter ion of the deprotonated pMBA− ligand as explained by the competing ion-pair strength and hydrogen bonding interactions studied in DFT calculations. The choice of the counter ion affects the surface chemistry and molecular structure at the organic/water interface, which is relevant for biological applications.
Inductively coupled plasma atomic emission spectrometric determination of arsenic in mussel products
1993
A precise, accurate procedure is proposed for the determination of arsenic in mussel products by inductively coupled plasma atomic emission spectrometry. Organic matter is destroyed by dry ashing. Experimental conditions for the determination of arsenic were selected and an interference study was carried out. The methodology developed has a detection limit of 0.1 μg g−1, a relative standard deviation of 3%, and a recovery percentage of 98±2%. The accuracy of the method was checked by analysis of a certified sample of NIST oyster tissue (certified 14.0±1.2 μg g−1; found 14.1±1.1 μg g−1). The proposed procedure was used to analyze real samples of mussel products.
Determination of the protein and free amino acid content in a sample using o-phthalaldehyde and N-acetyl-L-cysteine
1990
A spectrophotometric method is proposed for determining the protein content in a sample after total acid hydrolysis. In the procedure, free amino acids are caused to react with o-phthalaldehyde and N-acetyl-L-cysteine at pH 9.5, using isoleucine as the reference compound. Correction factors are used to take into account the differences between the molar absorptivities of the amino acid isoindoles and the recoveries of the amino acids after the hydrolysis treatment. The limit of detection was in the range 40-50 micrograms of protein, and the recoveries were usually 101 +/- 3% with a coefficient of variation lower than 4%. The free amino acid content in a partially hydrolysed protein was also…
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…