Multi-wavelength methods

RESULTS ILLUSTRATING THE SCOPE OF THE METHOD VARIABLE SINGLE WAVELENGTH AND MULTI-WAVELENGTH METHODS... 

Only multivariate (e.g. multi-wavelength) data are amenable to model-free analyses. While this is a restriction, it is not a serious one. The goal of the analysis is to decompose the matrix of data into a product of two physically meaningful matrices, usually into a matrix containing the concentration profiles of the components taking part in the chemical process, and a matrix that contains their absorption spectra (Beer-Lambert s law). If there are no model-based equations that quantitatively describe the data, model-free analyses are the only method of analysis. Otherwise, the results of model-... 

Recently a number of advanced detection methods have been introduced such as multi-wavelength evaluation or measuring the UV spectra by diode-array scanning [86,87]. fluorodensitometry. voltammetry, and fast atom-bombardment mass spectrometry. etc. 

The analyst can improve the identification of solutes or discrimination between samples by studying the multi-wavelength plots or spectra of the eluted components. Transformation of spectral data to yield derivative spectra have been used to improve sample discrimination, whilst a plot of the ratio of absorbances for two selected wavelengths is an excellent method for confirming the homogeneity of chromatographic peaks. However, there is a trend in forensic laboratories to use and develop techniques whereby the spectral data are reduced to a smaller number of numerical values. Results in this format at easier to compare and present in court and furthermore can be evaluated statistically. 

The deconvolution methods are multi-wavelength procedures which can be classified with regard to the selection procedure of reference spectra. These spectra can be chosen from specific compounds (Maier, 1981), from independent spectra of real samples (Thomas et al., 1993), statistically selected (Gallot and Thomas, 1993) or from a mixed choice of spectra of specific compounds and of real samples. Reference spectra are not universal recently, according to the complexity of the composition of wastewater, SECOMAM has developed UVPro software based on advanced UV spectral deconvolution (Patent 00402038-4, 17 July 2000) which allows creating dedicated models and determination of reference spectra from a set of studied water and wastewater UV spectra an automatic calibration step is carried using parameters values obtained by standard or reference method. Deconvolution is used in order to find a linear relation between measured and UV estimated values for any parameter. 

The value chosen for resolution R Is dependent upon the requirements of th separation. If co onent detection Is the sole objective, R depends upon the methods available to discriminate between adjacent components. As an example, the sophisticated multi-wavelength spectroscopic detection of overlapping chromatographic components allows the magnitude of Rj to approach very small values (3). Subtle differences In the ss spectra of eluting components can also be used to reduce R. ... 

Nakagawa A, Higuchi Y, Yasuoka N, Katsube Y, Yagi T (1990) S-class cytochromes c have a variety of folding patterns structure of cytochrome c-553 from Desulfovibrio vulgaris determined by the multi-wavelength anomalous dispersion method. J Biochem 108 701— 703... 

The word multiplex has been used indiscriminately by many authors to describe both simultaneous and rapid sequential (e.g. rotating filters, fast-scan or slow-scan systems) multi-wavelength detection methods [37]. Other specialists use this designation to refer to spectroscopic methods based on the truly simultaneous measurement of several optical signals at different wavelengths. Finally, others reserve this term for those methods which use a single detector for multi-wavelength detection [17]. 

Abstract The modified equation-of-motion coupled cluster approach of Sekino and Bartlett is extended to computations of the mixed electric-dipole/magnetic-dipole polarizability tensor associated with optical rotation in chiral systems. The approach - referred to here as a linearized equation-of-motion coupled cluster (EOM-CCl) method - is a compromise between the standard EOM method and its linear response counterpart, which avoids the evaluation of computationally expensive terms that are quadratic in the field-perturbed wave functions, but still yields properties that are size-extensive/intensive. Benchmark computations on five representative chiral molecules, including (P)-hydrogen peroxide, (5)-methyloxirane, (5 )-2-chloropropioniuile, (/ )-epichlorohydrin, and (75,45)-norbornenone, demonstrate typically small deviations between the EOM-CCl results and those from coupled cluster linear response theory, and no variation in the signs of the predicted rotations. In addition, the EOM-CCl approach is found to reduce the overall computing time for multi-wavelength-specific rotation computations by up to 34%. 

Multi-wavelength spectroscopy methods can be interpreted using Mie theory and contain information on particle counts, size distribution ... 

Multi-wavelength detection diode array rapid scan methods ... 

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