Producing an Infrared Spectrum

A beam of radiation from the infrared region of the electromagnetic spectrum is passed through the material. As the infrared light source changes in wavenumber this gives rise to certain molecular movements such as bending and stretching, and these movements absorb energy at definite values of wavenumber giving rise to peaks on the infrared spectrum, when viewed in absorbance mode. It is the position and pattern of these peaks that produces the characteristic infrared spectrum for a material.
Analysing the sample

The process of analysing the sample can be considered in two steps.

The first step is the presentation of the sample. Modern instruments, such as the one we possess at Sandberg, allow us to analyse the sample with little or no sample preparation. The sample can be placed directly onto the crystal and pressed in place by a torque limiting device. This allows us to examine very small sample sizes, say about 2mm in size. The advantages of this direct analyses are obviously in time saving, but also in its non destructive nature.

In addition to this direct approach, solvent extraction techniques do have their place especially if the sample has a high quantity of inorganic fillers that can mask the nature of the organic component of interest. This process involves dissolving the material in a solvent and placing a drop on to the germanium crystal. Evaporating the solvent off leaves a cast film of the organic component.

Another technique employed is pyrolysis of the sample and examination of the resulting pyrolysate, also useful in separating the organic component from the inorganic filler.

The second step in the analytical process is spectral interpretation. This can be carried out by manually by identifying the groups present and building up a picture of the molecule in a similar way to a jigsaw puzzle. However computer software is available to do this for you, with the computer searching data bases and coming up with a best match for the spectrum in terms of position and relative height of the peaks. The data bases are commercially available and there is even an on line searching facility, but it is often more reliable to build your own library of data so that when searching the spectra have all been obtained under the same conditions.Infrared Spectroscopy - Applications in the built environment

The range of circumstances encountered in the built environment for which analysis by infrared spectroscopy is a useful analytical technique are numerous and diverse, as the following examples demonstrate.