Attenuated total reflectance or ATR is, along with transmission, one of the most common sampling techniques in Fourier transform infrared (FTIR) spectroscopy. ATR is based on total internal reflection where infrared (IR) light and sample interact only at the point where IR light is reflected. Transmission, on the other hand, is based on IR light passing through the sample.
FTIR spectroscopy is a powerful tool to qualify and quantify organic substances in the solid, liquid, or gaseous state. However, many sampling techniques require pre-treatment of samples in order to obtain high-quality spectra. ATR FTIR spectroscopy allows solid or liquid samples to be measured with only minimal sample preparation.