Search results for "Spectroscopy"

Improvement in sprint performance: doping or nature?

2012

Concentriols B, C and D, three squalene-type triterpenoids from the ascomycete Daldinia concentrica

2002

Abstract Three squalene-type triterpenoids named concentricols B, C and D ( 1 – 3 ) were isolated from the ethyl acetate extract of fruiting bodies of the xylariaceous ascomycete Daldinia concentrica . Their absolute structures were elucidated by analysis of 2D NMR, MS, IR and UV spectra, and the modified Mosher's method.

Trace-element composition and stable-isotope ratio for discrimination of foods with Protected Designation of Origin

2009

We review the literature on authentication of foods with Protected Designation of Origin (PDO) from their trace-element composition or stable-isotope ratios in order to evaluate the state of the art of this field and to identify the main parameters of analytical techniques and chemometric-data treatments that permit accurate discrimination of samples of different geographical origins and with different characteristics.

Towards minimization of chlorinated solvents consume in Fourier transform infrared spectroscopy determination of Propamocarb in pesticide formulation…

2008

Abstract A method has been developed for Fourier transform infrared (FTIR) spectroscopy determination of Propamocarb in emulsifiable pesticide concentrate formulations. Five microliter sample was directly injected without any pretreatment in a CHCl 3 stream at 2 mL min −1 into a closed system and the FTIR spectra of sample and standard solutions were obtained using a nominal resolution of 4 cm −1 from 4000 to 900 cm −1 spectral region and accumulating 2 scans per spectrum. Propamocarb determination was based on the measurement of flow injection analysis (FIA) recording height established from FTIR peak area measurements from 1713 to 1703 cm −1 corrected using a baseline defined at 2000 cm −…

Quantitative analysis of chromite ores using glass discs in moderate dilutions of lithium tetraborate by x-ray fluorescence spectrometry

2006

A method for the quantitative analysis of chromite ores by x-ray fluorescence spectrometry using beads is proposed. The work concerned the serious problems caused by the refractory nature of these materials which prevents the use of glass discs in x-ray fluorescence. An in-depth study was done to optimise the variables which influence the glass disc formation process. Sufficiently homogeneous glass discs were obtained under the following experimental conditions: lithium tetraborate as flux with moderate sample dilution (1:40), with the addition of one or two drops of LiBr solution(250 g l−1), at a temperature of 1200 °C for 30 min. The qualitative and semiquantitative results for the chromi…

Saturated absorption spectroscopy: elimination of crossover resonances by use of a nanocell

2007

It is demonstrated that velocity selective optical pumping/saturation resonances of reduced absorption in a Rb vapor nanocell with thickness \textit{L=} $\lambda $, 2$\lambda $, and 3$\lambda $ (resonant wavelength $\lambda $ = 780 nm) allow the complete elimination of crossover (CO) resonances. We observe well pronounced resonances corresponding to the F$_{g}=3$ $\to $ F$_{e}=2,3,4$ hyperfine transitions of the $^{85}$Rb D$_{2}$ line with linewidths close to the natural width. A small CO resonance located midway between F$_{g}=3$ $\to $ F$_{e}=3$ and F$_{g}=3$ $\to$ F$_{e}=4$ transitions appears only for \textit{L} = 4$\lambda $. The D$_{2}$ line ($\lambda $ = 852 nm) in a Cs nanocell exhi…

MgO/Ag(100): confined vibrational modes in the limit of ultrathin films

2003

The vibrational modes of clean MgO films are investigated vs film thickness by means of high-resolution electron energy-loss spectroscopy. For thin films (20\char21{}30 monolayers) we observe, in accord with the literature, the Fuchs-Kliewer phonon at $677{\mathrm{cm}}^{\ensuremath{-}1}$ and the Wallis mode at $524{\mathrm{cm}}^{\ensuremath{-}1}.$ For ultrathin films standing wave optical phonons confined in the overlayer are present, whose frequencies depend strongly on film thickness. Comparison with theoretical calculations for MgO slabs on a perfect conductor shows that the experimental frequencies are lower than expected, indicating the presence of compressive stress. At and below one-…

2019

Energy-level alignment at organic-metal interfaces plays a crucial role for the performance of organic electronic devices. However, reliable models to predict energetics at strongly coupled interfaces are still lacking. We elucidate contact formation of 1,2,5,6,9,10-coronenehexone (COHON) to the (1 1 1)-surfaces of coinage metals by means of ultraviolet photoelectron spectroscopy, x-ray photoelectron spectroscopy, the x-ray standing wave technique, and density functional theory calculations. While for low COHON thicknesses, the work-functions of the systems vary considerably, for thicker organic films Fermi-level pinning leads to identical work functions of 5.2 eV for all COHON-covered meta…

C,N-chelated organotin(IV) trifluoroacetates. Instability of the mono- and diorganotin(IV) derivatives.

2011

Abstract The C,N-chelated tri-, di- and monoorganotin(IV) halides react with equimolar amounts of CF3COOAg to give corresponding C,N-chelated organotin(IV) trifluoroacetates. The set of prepared tri-, di- and monoorganotin(IV) trifluoroacetates bearing the LCN ligand (where LCN is 2-(N,N-dimethylaminomethyl)phenyl-) was structurally characterized by X-ray diffraction analyses, multinuclear NMR and IR spectroscopy. In the case of triorganotin(IV) trifluoroacetates and (LCN)2Sn(OC(O)CF3)2, no tendency to form hydrolytic products, or instability towards the moisture was observed. LCNRSn(OC(O)CF3)2 (where R is n-Bu or Ph) and LCNSn(OC(O)CF3)3 forms upon crystallization from THF in the air mainl…

Differences in metabolic profiles of planktonic and biofilm cells in Staphylococcus aureus - (1)H Nuclear Magnetic Resonance search for candidate bio…

2013

Staphylococcus aureus is responsible for many types of infections related to biofilm presence. As the early diagnostics remains the best option for prevention of biofilm infections, the aim of the work presented was to search for differences in metabolite patterns of S. aureus ATCC6538 biofilm vs. free-swimming S. aureus planktonic forms. For this purpose, Nuclear Magnetic Resonance (NMR) spectroscopy was applied. Data obtained were supported by means of Scanning Electron Microscopy, quantitative cultures and X-ray computed microtomography. Metabolic trends accompanying S. aureus biofilm formation were found using Principal Component Analysis (PCA). Levels of isoleucine, alanine and 2,3-but…