FTIR stands short for Fourier transform infrared spectroscopy.

​

As we explained before, FTIR measures the spectral fingerprint of a material when irradiated with infrared light. Light interacts with molecules, and it is possible to extract molecular information from theses interactions. Indeed, low energy photons, which can be associated to infrared light, may induce vibrational excitation of covalently bonded atoms and groups. To understand how this happens, one needs to picture the covalent bond as a stiff spring that can stretch, bend and twist once excited. The vibrational excitations will cause the light to be absorbed at very specific frequencies, depending on the mass of the atoms, the strength of the bonds and the environment around the molecule [1,7].

The principle of FTIR is thus that a sample is irradiated with a beam containing many frequencies of light. Part of these frequency of light are absorbed depending on the presence of vibrationally excited covalent bonds. The transmitted part of the IR radiation is gathered by a detector. Several measurements are performed in order to raster the entire frequency range (which is fixed before the experiment). Once all signals are collected, a Fourier transform is applied in order to turn the raw data into the desired results. These results are the light absorption versus the wavelength. Peaks of absorbed light at specific frequency can be correlated to specific bonds. It is therefore possible to identity a material, as each one a particular set of peaks, also called their “spectral fingerprint” [1].