Spurious infrared bands

Spurious bands can occur readily in infra-red spectra, particularly when a biological sample has undergone several purification procedures. Traces o lasticisers, surfactants, and oils left on glassware can all give rise to artefacts some spurious infrared bands are given below (after H. A. Szymanski, A Systematic Approach to the Interpretation of Infrared Spectra, Buffalo, New York, Hertillon Press, 1971). 

ORD techniques do not appear to be useful in the infrared. In the first place, optical rotation is a refraction phenomenon which is not easily studied within absorption bands because of slit-width effects these have given rise to spurious Cotton effects in infrared ORD Secondly, the multiplicity of bands in the middle IR would, at best, give ORD curves of incredible complexity. More telling is the failure of attempts to demonstrate that infrared bands could produce optical rotation in nearby regions of transparency it was found that optical rotation between 4000 and 2000 cm was still dominated by contributions from remote electronic transitions Background rotation of this nature would only make the observation of contributions from infrared bands difficult to discern. 

COMMON SPURIOUS INFRARED ABSORPTION BANDS Thomas J. Bruno and Paris D. N. Svoronos... 

In analyzing the spectrum of a substance, one occasionally finds a band or a shoulder that is very difficult to interpret. This band may, upon further consideration, be found to be spurious, that is, it does not belong to the sample under analysis, but is caused by an instrumental effect, the method of handling the sample, or some unexpected phenomenon. For example, it has been pointed out (Inchiosa, 1965) that certain disposable syringes used in clinical and laboratory medicine yielded water-soluble extractives. One of these substances was identified as 2-(methylthio)ben-zothiazole, which has fungistatic and insecticidal activity. Such extractives or their reaction products could show up in the infrared spectrum during a laboratory procedure. 

Christiansen effect A spurious band on the high frequency side of a true absorption band may sometimes be observed when examining the mulls of crystalline materials if the particle size is of the same order of magnitude as the infrared wavelength being used. 

A section dealing with spurious bands that may appear in both infrared and Raman spectra has been included in the hope that confusion may be avoid by prior knowledge of the reasons for such bands and the positions at which they may occur. 

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