Infrared spectrum analytical chemistry applications

Figure 8.12 Near-infrared spectrum of dehydrated tomato soup. From Davies, A. M. C. and Grant, A., Near Infrared Spectroscopy for the Analysis of Specific Molecules in Food , in Analytical Applications of Spectroscopy, Greaser, C. M. and Davies, A. M. C. (Eds), pp. 46-51 (1998). Reproduced by permission of The Royal Society of Chemistry.

The infrared spectra of most chemical compounds are unique and it is this feature that enables a spectroscopist to identify an unknown substance from its spectrum. Traditionally this identification is attempted either by direct interpretation or from a possible match to a standard reference spectrum. A positive match is obviously more desirable but this is usually limited by the availability of a wide range of reference spectra and, if performed manually, it can be a very time consuming operation. The ability of a computer to handle a large number of data files and to be able to perform high speed repetitive operations make it an ideal candidate for spectral searches. In fact, this was considered to be one of the first main applications of the computer for analytical chemistry. 

This Section Ls restricted to a description of some of the work of Ander-gon, 8-a> who has ably applied the quantitative analysis of vapors by infrared spectroscopy to analytical problems in carbohydrate chemistry, principally to the Zeisel alkoxyl determination. In this particular application, the usual Zeisel apparatus was used, and the volatile iodide liberated was carried by a flow of nitrogen into a cold trap where it was collected quantitatively Anhydrone (magnesium perchlorate) was used for removing water vapor which would otherwise interfere in the spectrum. The contents of the trap were allowed to vaporize into an evacuated gas-cell, and air was then admitted through the trap to sweep all the vapor into the gas-cell. Double-beam compensation of atmospheric water vapor and carbon dioxide was not upset by this procedure, which also served the purpose of increasing the sensitivity of the infrared method by the well known pressure-broadening effect. The complete spectrum of the vapor... 

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