FT-IR (Fourier Transform Infrared) spectroscopy is an instrumental technique for measuring the infrared spectrum of materials. Many organic compounds have characteristic spectra that can be used for their identification, and specific functional groups (hydroxyl, carbonyl. amine, etc.) have characteristic bands at certain frequencies.

Microscopes have been coupled to FT-IR instruments and allow the IR spectrum determination of single particles. This greatly increases the identification possibilities of small particles and contaminants. These particles can be mounted on sodium chloride or potassium bromide salt crystals, since these materials are transparent to infrared radiation.