Infrared spectroscopy, identification

See also Bioassays Overview. Drug Metabolism Metabolite Isolation and Identification. Infrared Spectroscopy Ovenriew. Liquid Chromatography Liquid Chromatography-Nuclear Magnetic Resonance Spectrometry Pharmaceutical Applications. Mass Spectrometry ... 

Polyester composition can be determined by hydrolytic depolymerization followed by gas chromatography (28) to analyze for monomers, comonomers, oligomers, and other components including side-reaction products (ie, DEG, vinyl groups, aldehydes), plasticizers, and finishes. Mass spectroscopy and infrared spectroscopy can provide valuable composition information, including end group analysis (47,101,102). X-ray fluorescence is commonly used to determine metals content of polymers, from sources including catalysts, delusterants, or tracer materials added for fiber identification purposes (28,102,103). 

The identification of alkanesulfonates is possible by infrared spectroscopy. Computer-supported Fourier transform infrared spectroscopy (FT-IR) allows the... 

As for other surfactants [239], infrared spectroscopy can also be used as a quick method for the identification of ether carboxylates [238]. 

Dixit, V. et al.. Identification and qnantification of industrial grade glycerol adulteration in red wine with Fourier transform infrared spectroscopy using chemometrics and artificial neural networks, Appl. Spectros., 59, 1553, 2005. 

The results presented here for silicas and aluminas illustrate that there is a wealth of structural information in the infrared spectra that has not previously been recognized. In particular, it was found that adsorbed water affects the lattice vibrations of silica, and that particle-particle Interactions affect the vibrations of surface species. In the case of alumina, it was found that aluminum oxides and hydroxides could be distinguished by their infrared spectra. The absence of spectral windows for photoacoustic spectroscopy allowed more complete band identification of adsorbed surface species, making distinctions between different structures easier. The ability to perform structural analyses by infrared spectroscopy clearly indicates the utility of photoacoustic spectroscopy. 

Spectrophotometric and spectrofluorimetric methods provide a wealth of information concerning structural determinations (identification, purity and precise measurement of concentration) and chemical changes in alkaloids. These techniques yield both quantitative and qualitative data on the effect of solvents, pH and other physiological conditions [141-143]. X-ray crystallography, H and NMR spectroscopy, infrared spectroscopy (IR) and circular dichroic spectroscopy were also used to study the physical properties... 

Infrared spectroscopy is a major tool for polymer and rubber identification [11,12]. Infrared analysis usually suffices for identification of the plastic material provided absence of complications by interferences from heavy loadings of additives, such as pigments or fillers. As additives can impede the unambiguous assignment of a plastic, it is frequently necessary to separate the plastic from the additives. For example, heavily plasticised PVC may contain up to 60% of a plasticiser, which needs to be removed prior to attempted identification of the polymer. Also an ester plasticiser contained in a nitrile rubber may obscure identification of the polymer. Because typical rubber compounds only contain some 50% polymer direct FUR analysis rarely provides a definitive answer. It is usually necessary first... 

Several additional instrumental techniques have also been developed for bacterial characterization. Capillary electrophoresis of bacteria, which requires little sample preparation,42 is possible because most bacteria act as colloidal particles in suspension and can be separated by their electrical charge. Capillary electrophoresis provides information that may be useful for identification. Flow cytometry also can be used to identify and separate individual cells in a mixture.11,42 Infrared spectroscopy has been used to characterize bacteria caught on transparent filters.113 Fourier-transform infrared (FTIR) spectroscopy, with linear discriminant analysis and artificial neural networks, has been adapted for identifying foodbome bacteria25,113 and pathogenic bacteria in the blood.5... 

Helm, D. Labischinski, H. Schallehn, G. Naumann, D. Classification and identification of bacteria by Fourier-transform infrared spectroscopy. J. Gen. Microbiol. 1991,137, 69-79. 

Infrared spectroscopy/microscopy certainly is the primary method of choice when organic substances have to be identified. Sample preparation usually is simple for identification purposes, but will be an issue for imaging experiments, and spatial resolution may then well be only in the range of a few micrometers, depending on the used experimental approach (transmission, ATR). 

The analytical techniques proposed in the literature generally give reliable information on lipids present in the paint layer. However, the presence of lipid mixtures and of particular environmental conservation conditions may affect the lipid pattern to such an extent that their identification may be very difficult and sometimes erroneous. Thus, a multianalytical approach is recommended which integrates chromatographic data with techniques such as mapping based on Fourier transform infrared spectroscopy or SIM on cross-sections, in order to better understand the distribution of lipids in the various paint layers. 

V.A. Basiuk, Pyrolysis of valine and leucine at 500°C identification of less volatile products using gas chromatography Fourier Transform infrared spectroscopy mass spectrometry, J. 

Near-infrared spectroscopy is quickly becoming a preferred technique for the quantitative identification of an active component within a formulated tablet. In addition, the same spectroscopic measurement can be used to determine water content since the combination band of water displays a fairly large absorption band in the near-IR. In one such study [41] the concentration of ceftazidime pentahydrate and water content in physical mixtures has been determined. Due to the ease of sample preparation, near-IR spectra were collected on 20 samples, and subsequent calibration curves were constructed for active ingredient and water content. An interesting aspect of this study was the determination that the calibration samples must be representative of the production process. When calibration curves were constructed from laboratory samples only, significant prediction errors were noted. When, however, calibration curves were constructed from laboratory and production samples, realistic prediction values were determined ( 5%). 

In contrast to infrared spectrometry there is no decrease in relative sensitivity in the lower energy region of the spectrum, and since no solvent is required, no part of the spectrum contains solvent absorptions. Oil samples contaminated with sand, sediment, and other solid substances have been analysed directly, after being placed between 0.5 mm 23-reflection crystals. Crude oils, which were relatively uncontaminated and needed less sensitivity, were smeared on a 2 mm 5-reflection crystal. The technique has been used to differentiate between crude oils from natural marine seepage, and accidental leaks from a drilling platform. The technique overcomes some of the faults of infrared spectroscopy, but is still affected by weathering and contamination of samples by other organic matter. The absorption bands shown in Table 9.1 are important in petroleum product identification. 

Vibrational spectroscopies such as Raman and infrared are useful methods for the identification of chemical species. Raman scattering [4] is a second-order process, and the intensities are comparatively low. A quick estimate shows that normal Raman signals generated by species at a surface or an interface are too low to be observable. Furthermore, in the electrochemical situation Raman signals from the interface may be obscured by signals from the bulk of the electrolyte, a problem that also occurs in electrochemical infrared spectroscopy (see Section 15.3)... 

Electrochemical infrared spectroscopy can be used on all kinds of electrodes and for all substances that are IR active. It is particularly useful for the identification of reaction intermediates, and has been used extensively for the elucidation of the mechanisms of technologically important reactions. A case in point is the oxidation of methanol on platinum, where linearly bonded = C = O (i.e., CO bonded to one Pt atom) has been identified as an intermediate Figs. 15.7 and 15.8 show EMIRS [6c] and IRRAS [8] spectra of this species. Near 2070 cm-1 the EMIRS spectrum shows the typical form produced by a peak that shifts with potential. This shift can be followed in the IRRAS spectrum... 

Infrared spectroscopy is utilized for identification purposes during the analysis of the drug substance, (see 2.21)... 

Summarizing, infrared spectroscopy measures, in principle, force constants of chemical bonds. It is a powerful tool in the identification of adsorbed species and their bonding mode. Infrared spectroscopy is an in situ technique, which is applicable in transmission or diffuse reflection mode on real catalysts, and in reflection-absorption mode on single crystal surfaces. Sum frequency generation is a speciality... 

In the museum context, nondestructive (or quasi-nondestructive) techniques such as X-ray fluorescence (XRF) (Chapter 5) are often preferred for the analysis of inorganic objects, although microanalysis by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) (Chapter 9) is growing in importance, since the ablation craters are virtually invisible to the naked eye. Raman and infrared spectroscopy (Chapter 4) are now being used for structural information and the identification of corrosion products to complement X-ray diffraction (Section 5.4). 

In chemistry, infrared spectroscopy is usually the first method of choice for the identification of organic functional groups and inorganic species such as CO32 in a wide range of materials. Because it can easily identify the OH- group in many materials (a broad absorption band at 3700-2700 cm ), it has proved useful for the study of corroded glass and weathered obsidian, where the corrosion... 

In general, the technique is limited to cases where the identity of the substance to be determined is known, although, in some cases identification of the separated compounds has been achieved by infrared spectroscopy or mass spectrometry of eluates of the individual separated spots isolated from the thin layer plate. 

Due to its relatively low sensitivity, the combination of gas chromatography with Fourier transform infrared spectroscopy (GC-FTIR) is not a standard technique in semiochemical research. Nevertheless, it could come in handy for the identification of some compounds with utterly uninformative mass spectra [22]. 

AHLs can be tentatively identified by comparison of the unknown with synthetic AHL standards after Thin Layer Chromatography (TLC) in which the plates are overlaid with agar containing one of the AHL biosensors described above [37,39,44,45]. However, for the unequivocal identification of AHLs the use of more powerful methods such as LC-mass spectrometry, nuclear magnetic resonance and infrared spectroscopy as described below are required. 

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