Infrared spectrum, evaluation

The objectives of this study were (1) to reveal trends between selected regions of the infrared spectrum and accepted indicators of coalification (2) to determine the nature and degree of interdependency among these data using statistical analyses and (3) to evaluate the usefulness of FTIR data in measuring degree of coalification. 

TAegradation of a polymer can be evaluated by its rate of decomposi-tion. This consists of dehydrochlorination, change in color, electrical resistance, viscosity, solubility, specific weight, and infrared spectrum. The factors influencing the rate of destruction are ... 

The usual method for the spectrometric determination of hydrophobic substances in water is to extract it with a hydrophobic solvent and to evaluate its infrared spectrum (see Sec. 5.1.5.1). This discontinuous procedure cannot be applied in real time and on-line. 

Infrared spectroscopy is now nearly 100 years old, Raman spectroscopy more than 60. These methods provide us with complementary images of molecular vibrations Vibrations which modulate the molecular dipole moment are visible in the infrared spectrum, while those which modulate the polarizability appear in the Raman spectrum. Other vibrations may be forbidden, silent , in both spectra. It is therefore appropriate to evaluate infrared and Raman spectra jointly. Ideally, both techniques should be available in a well-equipped analytical laboratory. However, infrared and Raman spectroscopy have developed separately. Infrared spectroscopy became the work-horse of vibrational spectroscopy in industrial analytical laboratories as well as in research institutes, whereas Raman spectroscopy up until recently was essentially restricted to academic purposes. 

The infrared spectrum of erythromycin estolate is the most commonly accepted method for compound identification. The spectrum of a 10 mg/ml chloroform solution of erythromycin estolate from 850-4000 cm--1- is shown in Figure 1, The most characteristic difference between the infrared spectra of erythromycin base and estolate and that of anhydroerythromycin is that the latter is lacking the keto-carbonyl band at 1685 cm l (5.93 u). If a sample of erythromycin base or estolate contains at least 5 percent anhydroerythromycin, a decrease in the intensity at 1685 cm l should be observed. This decrease can most readily be detected by measuring the ratio of the absorbance at 1685 crn" -(5.93 U) to that of the ester absorbance at 1735 cm l (5.76 u). The amount of water in the sample can also be evaluated by the band at 1610 cm-1 (6.2 u). ... 

The concentration of a component in the sample analyzed can be calculated by the Lambert-Beer law, which is shown in equation (2.4). In order to evaluate quantitatively an infrared spectrum, equation (2.4) should be rewritten as equation (2.15). 

Quantitative evaluation of the infrared spectrum is done with regard to the empiric tables or digital libraries. So this can be estimated quickly. For example, if sample contains aromatic groups, information can be collected in the infrared spectrum by looking for the peaks typical of the aromatic carbon. 

The evaluation involved four basic methods and variants of them. They included the standard visual overlay method, or a modification of it that involved some linear measurements in the fingerprint region of the infrared spectrum the Brown log-ratio method (26) the vector method devised by Killeen et al. (44,45) and the standard ASTM method (22). The overlay method was the best method when used by someone experienced in interpreting weathered oils. 

Ibbitson and Moore (13) conclude that the maximum in the curve of polarization vs. concentration for ethanol in carbon tetrachloride is caused by linear multimers, and the subsequent fall in polarization is caused by an increasing amount of cyclic multimer (Figure 1). The concentration at which the maximum occurs coincides with that at which the 3350-cm.-1 band first appears in the infrared spectrum, so they have suggested that this band arises from cyclic multimers. They have fitted their data to a system containing linear dimer and trimer and cyclic tetramer only and have evaluated association constants for these species. 

The prominent new bands observed in the low-temperature infrared spectrum are due to the activation of dimer charge oscillations induced by the Au crystal components of totally symmetric (a ) intramolecular modes at frequencies somewhat lower than those of the corresponding unperturbed Ag components. The latter can be measured directly in the Raman spectrum and the set of vibronic frequency shifts (u i — n,) so derived allows one to evaluate the relative strength of the e-mv coupling constants gi of the various a intramolecular modes. This is made possible by solving... 

This method was in fact carried out around two decades ago [30, 31]. However, it was applied only in the fermentation of pure microbial cultures. In a recent report by Acros-Hernandez and coworkers [32], infrared spectroscopy was applied to quantify the PHA produced in microbial mixed cultures. Around 122 spectra from a wide range of production systems were collected and used for calibrating the partial least squares (PLS) model, which relates the spectra with the PHA content (0.03-0.58 w/w) and 3-hydroxyvalerate monomer (0-63 mol%). The calibration models were evaluated by the correlation between the predicted and measured PHA content (R ), root mean square error of calibration, root mean square error of cross validation and root mean square error of prediction (RMSEP). The results revealed that the robust PLS model, when coupled with the Fourier-Transform infrared spectrum, was found to be applicable to predict the PHA content in microbial mixed cultures, with a low RMSEP of 0.023 w/w. This is considered to be a reliable method and robust enough for use in the PHA biosynthesis process using mixed microbial cultures, which is far more complex. 

The moving mirror is a crucial component of the interferometer. It has to be accurately aligned and must be capable of scanning two distances so that the path difference corresponds to a known value. A number of factors associated with the moving mirror need to be considered when evaluating an infrared spectrum. 

Pandey and co-workers [23] describe a novel approach to the non-destructive evaluation of various physicomechanical properties of propylene copolymer. A single-step measurement of the infrared spectrum followed by chemometric operation of the predetermined... 

We next evaluate the lineshape function (8.16) for two concrete situations in gases, (The complexity of molecular motions in liquids precludes computation of their dipole correlation functions in a text of this scope.) In the first situation, we imagine that we are examining lineshapes in the far-infrared spectrum of a collision-free, rotating polar molecule. Its dipole moment /Iq is assumed to rotate classically without interruption with angular frequency cwq about an axis normal to /Iq. In a dilute gas, we would then have... 

The force constant RR of ammonia has been evaluated as 7-17 firom the infrared spectrum. Allavena calculated the same constant (with the help of an electronic wave function similar to Moccia s function, but a little less precise) and obtained a value of 9. The agreement between experiment and theory is not very satisfactory and could certainly be improved if Moccia s function itself were used. 

Measurement by IR spectroscopy is potentially promising and semi-quantitative evaluations are possible. IR methods suffer from two main drawbacks absence of suitable calibration, and thermal history effects. The second limitation is the change induced in the infrared spectrum hy thermal history effects. Thus, the IR bonds used to measure isotacticity are bonds sensitive to the formation of regular isotactic helices rather than isotacticity. As such, IR absorbance will be dependent on pretreatment and annealing, which determine the conformation and morphology of polymer chains. 

The external reflection of infrared radiation can be used to characterize the thickness and orientation of adsorbates on metal surfaces. Buontempo and Rice [153-155] have recently extended this technique to molecules at dielectric surfaces, including Langmuir monolayers at the air-water interface. Analysis of the dichroic ratio, the ratio of reflectivity parallel to the plane of incidence (p-polarization) to that perpendicular to it (.r-polarization) allows evaluation of the molecular orientation in terms of a tilt angle and rotation around the backbone [153]. An example of the p-polarized reflection spectrum for stearyl alcohol is shown in Fig. IV-13. Unfortunately, quantitative analysis of the experimental measurements of the antisymmetric CH2 stretch for heneicosanol [153,155] stearly alcohol [154] and tetracosanoic [156] monolayers is made difflcult by the scatter in the IR peak heights. 

Infrared spectroscopy of adsorbed CO is a useful characterization tool for dendrimer-templated supported nanoparticles, because it directly probes particle surface features. In these experiments, which are performed in a standard infrared spectrometer using an in-situ transmission or DRIFTS cell, a sample of supported DENs is first treated to remove the organic dendrimer. Samples are often reduced under H2 at elevated temperature, flushed with He, and cooled to room temperature. Dosing with CO followed by flushing to remove the gas-phase CO allows for the spectrum of surface-bound CO to be collected and evaluated. Because adsorbed CO stretching frequencies are sensitive to surface geometric and electronic effects, it is potentially possible to evaluate the relative effects of each on nanoparticle properties. 

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