Gas chromatography - infrared spectroscopy

Infrared spectroscopy has been. combined with various other analytical techniques. Gas chromatography-infrared spectroscopy (GC-IR) allows the identification of the components eluting froiti a gas chromatograph. GC-IR has certain advantages over, say, gas chromatography-mass spectrometry (GC-MS). While GC-MS is able to distinguish easily between compounds of different mass, it is unable to differentiate structural isomers of the same molecular mass. By comparison, GC-IR can easily distinguish such isomers. 

The nature of this technique requires that interferograms are collected in short time intervals. 

Gram-Schmidt chromatograms are created from the interferogram intensities and reflect the infrared absorption. The Gram-Schmidt traces are plots of infrared absorbance versus time. The absorbance spectra of the eluted species are calculated by performing a Fourier transformation on the interferogram. 

Infrared spectroscopy has also been combined with other established analytical techniques, e.g. thermogravimetric analysis (TGA). The latter is a technique which involves measuring the change of the mass of a sample when it is heated. While TGA can provide quantitative information about a decomposition process, it is unable to identify the decomposition products. However, TGA and infrared spectroscopy have been combined to provide a complete qualitative and quantitative characterisation of various thermal decomposition processes. 

The direct application of gas chromatography to the identification and determination of unknown additives in polymers has its limitations. Amongst these are 

Chromatographically a single peak is no criterion of purity, since more than one substance may be present, the components present could often be resolved if then-presence was suspected and alternative column operating conditions were selected. 

Confirmation of homogeneity of fractions is therefore required together with unequivocal identification and accurate quantitative determination of the product. The analytical method used should involve some property of the molecule other than boiling point. Often, only fi-actional milligram amounts of material can be recovered from a column. Of the few techniques that are applicable to these small quantities of material, mass and infrared spectroscopy are particularly suited. 

The use of fraction collecting techniques in conjunction with gas chromatography is now well established and is an attractive proposition in additive identification problems, despite the fact that little published work has yet appeared on the application of this technique to polymer additives. In this technique the separated compound as it emerges from the gas chromatographic column is swept by the carrier gas through a cold trap where it condenses. The material in the trap is then either transferred to an infrared gas cell for examination in the vapour phase, or is transferred as a liquid to a suitable micro cell or may be condensed on a cold surface as a solid for examination by conventional spectroscopic techniques. 

Volatile constituents are, however, sometimes encountered, viz expanding agents, plasticizers, lubricants, adhesives, solvents, monomers and degradation products of additives or of the polymer itself and infrared gas cell techniques can be of value in the examination of gas chromatographic fractions containing these types of substances. 

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The identity and purity of the product were determined by gas chromatography, infrared spectroscopy, and proton magnetic resonance spectroscopy by both the submitters and the checkers. 

Concrete applications of micro reactors for chemical analysis, albeit so far not a core application, have been described [5]. Among other uses in chemical analysis, micro devices for gas chromatography, infrared spectroscopy, and photoacoustic detection are mentioned. 

Pyrolysis-gas chromatography/infrared spectroscopy (Py-GCIR) A pyrolysis technique in which the volatile pyrolysates are analysed by on-line gas chromatography/infrared spectroscopy. 

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

First, we will examine the various ways of examining samples using the traditional transmission methods of infrared spectroscopy. In the second part of this ch ter we will examine the more modem reflectance methods that arh now available, such as the attenuated total reflectance, diffuse and specular reflectance methods. We ml also look at a number of more specialist techniques which you might encounter, such as photoacoustic spectroscopy, gas chromatography-infrared spectroscopy, and the use of temperature and raicrosampling cells. 

The various reflectance methods which are now widely available, such as attenuated total reflectance, specular reflectance, and diffuse reflectance spectroscopy, were also introduced. Photoacoustic spectroscopy, gas chromatography-infrared spectroscopy, temperature studies and microsampling techniques were also described. 

Among chemical analysis methods are gas chromatography, infrared spectroscopy, and mass spectroscopy for example, a TGA apparatus may be coupled with a Fourier Transform Infrared (FTIR) spectrophotometer to measure the thermal oxidative stabilities of several fluorinated polyimides." ... 

The proportion of trans isomer in a reaction mixture can be determined by gas chromatography, infrared spectroscopy, NMR, infrared attenuated total reflectance spectrometry, or by preparative silver ion chromatography (Section 4.6). 

Mossoba, M.M. Application of Gas Chromatography-Infrared Spectroscopy to the Confirmation of the Double Bond Configuration of Conjugated Linoleic Acid Isomers,... 

Mossoba, M.M. Application of gas chromatography-infrared spectroscopy to the confirmation of the double bond configuration of conjugated linoleic acid isomers. Eur. J. Lipid Sci. Technol. 2001,103, 624. 

Under normal circumstances, retention time is a good tool to identify components by GC. Often, however, retention time alone is not definitive because many compounds have similar retention times. Structural information can be obtained independently from several spectroscopic techniques. This has led to hyphenated techniques, such as gas chromatography-mass spectroscopy, gas chromatography-infrared spectroscopy and others. If spectroscopic, reference spectra are available, confirmation of analyte identity is very likely. 

Spectrometers are routinely attached to computers that can search for matches between the spectrum of an unknown and a library of known spectra. As with mass spectrometry, gas chromatographs can be attached to IR spectrometers and spectra can be determined as the individual components of a mixture elute from a column. As noted in Section 15.2, this technique is called gas chromatography/infrared spectroscopy, or GC/IR. 

METHOD 103 - IDENTIFICATION OF ADDITIVES IN POLYMERS. GAS CHROMATOGRAPHY - INFRARED SPECTROSCOPY."... 

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