Bands decomposition, quantitative analysis using

Mixtures of components, that caimot be physically separated but whose molar fractions can be changed under a number of factors are considered as undefined. Such mixtures cannot be analyzed by means of classical spectrophotometric analysis (lack of calibration as shown above) and tautomeric mixtures are a typical example. Therefore, there are two approaches to treat tautomeric mixtures presented as a set of spectra with different tautomeric ratios direct quantitative analysis based on overlapping band decomposition or nonlinear optimization based on existing physical relations between the tautomeric constant and the external factor causing the shift in the equilibrium. The first one is the only option to analyze changes caused by the solvent or by salt addition. Both could be used to estimate the effects of temperature, acidity, or concentration and a critical comparison is available in Section 2.2.3 in this respect... 

On the other hand, the molar fraction must he constant in the particular solution and this is the fact when Xj is in the interval 320-360 nm, that is, statistically meaningful result can be obtained when there is a plateau. The narrowing of the decomposition interval, as shown in Figure 2.3, leads to narrowing of this plateau or even to the impossibihty to obtain statistically valid results for molar fractions. The latter happens when the band decomposition procedure is apphed only in the spectral interval 340-600 nm. Therefore, when this algorithm for quantitative analysis of tautomeric mixtures is apphed, the band decomposition interval must be as wide as the available spectral instrument and the used solvent would allow. 

From the point of view of quantitative analysis, these spectra are not suitable for simultaneous band decomposition by Fqs. (2.25) and (2.26), because the substantial reduction of the temperature causes narrowing of the vibronic bands, that is, the individual spectra of the tautomers are not temperature-independent. As a result, the spectra from Figure 2.6 were processed using the approach described... 

Using fiber optics, Groothaert et al. (2003a) monitored the decomposition of NO and of N2O on CuZSM-5. A bis(/i-oxo)dicopper species, [Cu2(iu-0)2]2+, which had been previously identified by XAFS and UV-vis analysis (Groothaert et al., 2003b), was proposed to be a key intermediate and 02-releasing species. Although no quantitative correlation was established between decomposition rate and intensity of the absorption band of the copper species, the performance appeared to be related to the intensity of this band. 

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