FTIR

FTIR stands for Fourier-transform infrared spectroscopy, a technique for obtaining infrared spectra of materials. It is used to identify and study chemical bonds and functional groups in solids, liquids, and gases. The mid-infrared region (approximately 4000 to 400 cm−1) contains many fundamental vibrational modes and is commonly employed. In addition, near-infrared (NIR) and far-infrared regions may be explored with specialized setups.

Principle: A broadband IR source irradiates a sample. An interferometer, typically a Michelson design with a moving mirror, modulates the beam and converts it to an interferogram. The detected signal is a function of optical path difference. A computer performs a Fourier transform to convert the interferogram into a spectrum of absorbance or transmittance versus wavenumber, representing molecular vibrations.

Instrumentation: Core components include a wide-band IR source, a beam splitter and moving mirror interferometer, a sample interface, a sensitive detector (such as DTGS or MCT), and a data system. Scanning speed, resolution, and apodization affect the spectrum. ATR (attenuated total reflectance) accessories allow direct measurement of solids and liquids with minimal prep.

Samples and data: Spectra display peaks at characteristic wavenumbers corresponding to stretching, bending, and other vibrational modes. The fingerprint region (roughly 600–1500 cm−1) is highly specific to a substance, while the 1500–4000 cm−1 region is often used to identify functional groups. Quantitative analyses can be performed with calibration.

Applications: FTIR supports material identification in chemistry, polymers, pharmaceuticals, food and environmental testing, forensics, and art conservation. Limitations include strong water absorption and potential overlapping bands; sample preparation and ATR geometry can influence results.