FTIR spectrometers (Fourier Transform Infrared Spectrometer) are largely used when analyzing organic compounds to identify the functional groups and operate with solid, liquid and sometimes gaseous samples. The main components of this instrument are the source, the interferometer, the sample compartment and the detector.
The source is usually an inert solid that is heated electrically to emit steady radiation in the IR range that is intense enough to be detected. A source commonly is used is the Nernst source.
The interferometer is the core of the instrument, where a beam splitter divides one beam of light into two through a partial reflection and partial transmission. One beam encounters a stationary mirror and is reflected back, while the second one hits a moving mirror, changing the length of its path. The two beans are then recombined and depending on the position of the moving mirror, the resulting beam will have a difference in intensity. If the two mirrors are in the same position, the beam will recombine with the same wavelength as the incoming one.
The sample is hit by the recombined light and depending on its composition, will absorb part of the radiation. The sample can be either in a solid or liquid form, but in both cases needs to be dissolved in a matrix or solvent that isn’t IR active.
The detector collects the part of the wavelengths that weren’t absorbed by the sample and creates the spectrum. The Fourier transform is a mathematical model that turners these data into an actual spectrum and it’s one of the most commonly used nowadays.