FTIR stands for Fourier transform infrared, the preferred method of infrared spectroscopy. Some of the infrared radiation is absorbed by the sample and some of it is passed through (transmitted). The resulting spectrum represents the molecular absorption and transmission response, creating a molecular fingerprint of the sample.(1) It can identify trace contaminants in high-purity gas samples and up to 30 components in gases from combustion processes, such as diesel engine emissions or continuous emissions monitoring (CEM) applications. It can quantify gas samples over large concentration spans, from parts per billion up to 99.99%.