Nguyen Quy Dao

Simulation et optimisation des capteurs à fibres optiques adjacentes

The geometry of adjacent optical fiber sensors to transport the laser beam and Raman signal in Raman spectrometry is simulated and optimized. The theory of the adjacent optical fiber sensors is developed using various models and the interaction depth is calculated. The efficiency vs the interaxes distance, the diameters of the optical fibers, and the angle between the two optical fibers are also given.

Quantitative analysis of cholesterol and cholesteryl esters in human atherosclerotic plaques using near-infrared Raman spectroscopy

Raman spectroscopy is a non-destructive analytical technique and previous results have shown that qualitative analysis of the lipid component of human atheromatous arteries is feasible. In this paper, we describe a quantitative analytical method for cholesterol and cholesteryl esters in human atherosclerotic plaques, combined with Raman spectroscopic results, using partial least-squares (PLS) regression, a statistical multivariate method based on factorial analysis. Twenty-nine human atherosclerotic pooled samples were studied and the results of Raman spectroscopy coupled with the PLS method were compared to biochemical results. The standard error of prediction was 16.1, 13.6, 1.9, 3.3 and 3.4 mg/g for total cholesterol, free cholesterol, palmitate cholesteryl, oleate cholesteryl and linoleate cholesteryl, respectively. The repeatability of Raman spectroscopy was found to be excellent. Our results show that Raman spectroscopy is a promising technique to obtain a consistent and non-destructive quantitative analysis of cholesterol and cholesteryl esters in human atherosclerotic lesions. In situ and in vivo analysis is a possibility in the near future.

Normal coordinate analysis for CaNb2O6 of columbite structure

The Raman and infrared spectra of CaNb2O6 are assigned by normal coordinate analysis according to Shimanouchi’s method. The Raman spectroscopy results enabled us to refine the force field, which was then checked by the infrared spectroscopy results. The obtained force constants show that there are three different types of Nb–O bonds in the columbite structure and that the Ca–O bonds are of electrostatic nature. The potential energy distribution calculation gives us a precise assignment for all the observed frequencies.

Characterization of different bondings in some divalent metal niobates of columbite structure

Abstract The structural characteristics of the columbite niobates MNb 2 O 6 (M = Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn, Cd) from their X ray diffraction powder patterns and indexed according to the Pbcn space group are given. Cell parameters are refined for each compound. Previous spectroscopic studies by normal coordinate analysis provide the basis for a discussion of the precise nature of the NbO and MO bonds. Force constants and bond order are given and the influence of the electronegativity of the M 2+ cations upon these bonds is shown.

Etude par spectrophotométries d'absorption infrarouge et de diffusion Raman des niobates de structure columbite

Resume Infrared and Raman spectra of the niobates of columbite structure M Nb 2 O 6 ( M = Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn, Cd) were recorded in the region 1100-50 cm −1 . All of them are similar at the shorter wavelengths (> 400 cm −1 ) but depend on the cation at lower frequencies. By comparison of i.r. and Raman spectra, the main vibration frequencies have been assigned.

Normal coordinate analysis of the MNb2O6 series of columbite structure (M=Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn, Cd)

Normal coordinate analysis of the MNb2O6 series of columbite structure (M=Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn, Cd) was carried out and the results obtained permitted the assignment of all the observed vibrational bands of the columbite series. It is also shown that the force fields of the columbite series are very similar when cations are changed. The variations are interpreted as due to the mass, the electronegativity, and the positions of the cations in the periodic table. The order of the bonds is also given.

Etude par spectroscopié vibrationnelle des oxydes Pb3O4, SnPb2O4 et SnPb(Pb2O4)2

Abstract The vibrational spectra analysis of Pb 3 O 4 , SnPb 2 O 4 and SnPb(Pb 2 O 4 )2 permitted us to establish a correspondence between the frequencies of Pb 3 O 4 and SnPb 2 O 4 which are higher. A normal coordinate analysis gave us the force field of these two compounds and showed the difference of rigidity of the PbO bonds in each compound. The comparison of the stretching force constants of the two compounds suggests an explanation of the fact that SnPb 2 O 4 has not, like Pb 3 O 4 , a phase transition at 170 K.

Methode d'analyse quantitative par spectrometrie Raman-laser associee aux fibres optiques pour le suivi d'une fermentation alcoolique

Abstract Laser Raman spectrometry with a fibre-optic system is used to monitor the concentrations of ethanol, glucose and fructose at various stages of an alcoholic fermentation process. For evaluation of the data, cross-correlation and multivariate least-squares procedures are compared; the latter gives the best results. Ethanol, glucose and fructose can be determined remotely with a precision of ca. 10 g l −1 (10–15%).

Quantitative Analysis of Cholesterol and Cholesterol Ester Mixtures Using Near-Infrared Fourier Transform Raman Spectroscopy

Near-infrared Fourier transform Raman spectroscopy is a rapid and nondestructive technique that can provide reliable qualitative in situ information about the chemistry of biological samples. We have combined this technique with partial least-squares (PLS) regression to perform a quantitative determination of free and esterified cholesterol in two synthetic sample series. In 66 ternary mixtures containing various proportions of cholesterol, cholesterol linoleate, and oleate, the standard errors of prediction were 1.27, 1.17, and 0.94%, respectively. For the second series of experiments concerning the sensitive problem of quantitative analysis of cholesterol palmitate and stearate mixtures, the standard error of prediction for 49 samples was 3.02%. It is also possible to extract quantitative information for a single component of the ternary mixtures independently. These results are of great importance when—as in the case of arterial samples—many chemical species are present. Comparison between Raman spectra of ternary mixtures and atherosclerotic rabbit aorta shows that many bands, assignable to free and esterified cholesterol, are easily observed in the aorta spectrum.

New Raman Spectrometer Using a Digital Micromirror Device and a Photomultiplier Tube Detector for Rapid On-Line Industrial Analysis. Part I: Description of the Prototype and Preliminary Results

In this paper, a prototype of a new generation of Raman spectrometers, based on the use of a monochromator, a digital micromirror device as light modulator, and a photomultiplier tube as detector of the Raman light, is described. This spectrometer, containing no moving parts, is inexpensive, robust, and very precise. New in concept, this spectrometer makes it possible to record, in addition to classical Raman spectra, the intensity at several selected points of the spectrum and/or the total intensity in several selected intervals at the same time with great accuracy, thus giving new possibilities for analytical applications. Also, the work presented demonstrates the possibilities of this very simple prototype for rapid on-line industrial analysis, with an example of quantitative analysis of binary and ternary mixtures of xylene isomers. The precision obtained is satisfactory (errors of prediction ∼3% in 5–6 seconds per sample).