Infrared spectroscopy compound identification

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... 

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]. 

The aim of qualitative analysis of homopolymers by infrared spectroscopy is the elucidation of polymer structure and compound identification. This often entails the identification of the functional groups and the modes of attachment to the polymer backbone [2,4,25,26], In the case of mixtures, the aim of qualitative... 

IR spectroscopy is not a very sensitive analytical tool and is, therefore, not well suited to the detection of small amounts of material. If, however, intermediates have intense and well-resolved IR absorptions, the progress of their chemical transformation can be followed by IR spectroscopy [83,88,91-93], Near-infrared spectroscopy, in combination with an acousto-optic tunable filter, can be sufficiently sensitive to enable the on-bead identification of polystyrene-bound di- and tripeptides, even if the peptides have very similar structures (e.g., Leu-Ala-Gly-PS and Val-Ala-Gly-PS) or differ only in their amino acid sequence (e.g., Leu-Val-Gly-PS and Val-Leu-Gly-PS) [94]. Special resins displaying an IR and Raman barcode have been developed, which may facilitate the deconvolution of combinatorial compound libraries prepared by the mix-and-split method [48]. 

Separation and identification of this catenation compound was effected by chromatography and infrared spectroscopy, the latter being the reason why the hydrocarbon portion of ihe catenation compound was deuterated. 

Some methods are particularly suited to the identification of compounds. For example, infrared spectroscopy is used to identify compounds by showing the presence of particular groupings of atoms (Figure 2.9). 

Infrared spectroscopy Silverstein RM, Bassler GC, Morrill TC (1981) Spectrometric identification of organic compounds, 4th edn. Wiley, New York, Chapter 3... 

An integrated GC/IR/MS instrument is a powerful tool for rapid identification of thermally generated aroma compounds. Fourier transform infrared spectroscopy (GC/IR) provides a complementary technique to mass spectrometry (MS) for the characterization of volatile flavor components in complex mixtures. Recent improvements in GC/IR instruments have made it possible to construct an integrated GC/IR/HS system in which the sensitivity of the two spectroscopic detectors is roughly equal. The combined system offers direct correlation of IR and MS chromatograms, functional group analysis, substantial time savings, and the potential for an expert systems approach to identification of flavor components. Performance of the technique is illustrated with applications to the analysis of volatile flavor components in charbroiled chicken. 

M.T. Soderstrom, H. Bjork, V.M.A. Hakkinen, O. Kostiainen, M.-L. Kuitunen and M. Rautio, Identification of compounds relevant to the chemical weapons convention using selective gas chromatography detectors, gas chromatography/Mass spectrometry and gas chromatography/Fourier transform infrared spectroscopy in an international proficiency test, J. Chromatogr., A742, 191-203 (1996). 

Infrared spectroscopy is widely used for the structural determination of tautomers, isomers conformers of various nitroimidazoles [42, 1043], Vibration spectra of different 1-alkyl [362]-, l-(trialkylsilylalkyl)-2-methyl-4-nitroimidazoles [363], allylated 4-nitroimidazoles [364], dinitroimidazoles [428] have been studied. The vibration frequencies of some medicinal compounds on the base nitroimidazoles, for example, diasteriomeric nido-carboranyl misonidazole congeners [389], antiviral agents [452], and adrenergic-receptor agonists [454] are analyzed. In the literature the number of publications devoted to vibration spectra is rather limited and, as a rule, the absorption band frequencies of nitroimidazoles are considered in synthetic works concerned with structure identification such as, for example, [354, 429, 461-464,468-471, 1044-1047],... 

Infrared spectroscopy can also be of diagnostic use for the identification of organophosphorus compounds and comprehensive data is available from several sources.18 Diagnostic absorptions include the P—H stretch, which typically occurs in the region 2460-2450 cm-1, the P=0 stretch at 1320-1200 cm-1 and the P=N at 1440-1120 cm-1. Other useful absorptions include the P—O—(C) stretch at 870-730 cm-1 and the P—O—P stretch at 800-650 cm-1 found in phosphate esters. 

The NO + MF, (except NO -f WF,) reactions proceed spontaneously at 20°. The reactions were followed tensimetrically. Gaseous products were identified by infrared spectroscopy and the solid products were examined by. y-ray powder-photography. Both ReF, and OsF, formed NO+[MF,] (cub.) salts and neither salt could be induced to combine with more NO to yield the quadrivalent (NO),MF, compound. In their reactions with nitrosyl fluoride at 20°, however, the rhenium and osmium fluorides are clearly differentiated ReF, readily forms a thermally stable 2 1 adduct, which is isomorphous with (NOjjWFg, whereas the OsF, -i- ONF reaction is complex. The identification of small quantities of nitrogen oxide trifluoride, in the gaseous product of the reaction, indicate the existence of an... 

Gas chromatography/infrared spectroscopy analysis was also used under differing operating parameters to aid in compound identification. 

Another, relatively new approach to mineral identification in pottery and stone is the use of Raman infrared spectroscopy, discussed in Sect. 4.5, which has the advantages of being both nondestructive and portable. Raman spectroscopy provides information about molecular vibrations that can be used for sample identification and quantification. IR spectroscopy provides compositional information about specific compounds, rather than elemental concentrations. IR spectroscopy works by inducing vibrations within a molecule. Specific infrared wavelengths correspond to particular modes of vibrations among particular atoms. 

Several other hyphenated systems are LC coupled with infrared spectroscopy (IR) for compound identification and LC couple with inorganic spectroscopy such as atomic absorption (AA) or inductively coupled plasma (ICP) for studies of metal speciation in samples. 

Mid-infrared (IR) spectroscopy is a well-established technique for the identification and structural analysis of chemical compounds. The peaks in the IR spectrum of a sample represent the excitation of vibrational modes of the molecules in the sample and thus are associated with the various chemical bonds and functional groups present in the molecules. Thus, the IR spectrum of a compound is one of its most characteristic physical properties and can be regarded as its "fingerprint." Infrared spectroscopy is also a powerful tool for quantitative analysis as the amount of infrared energy absorbed by a compound is proportional to its concentration. However, until recently, IR spectroscopy has seen fairly limited application in both the qualitative and the quantitative analysis of food systems, largely owing to experimental limitations. 

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