FTIRspectroscopie

FTIR spectroscopy, or Fourier-transform infrared spectroscopy, is an analytical technique used to obtain infrared spectra of materials in solid, liquid, or gaseous form. It relies on the interaction of infrared radiation with molecular vibrations, producing characteristic absorptions at specific wavenumbers that reflect a sample’s chemical bonds and functional groups. The resulting spectrum serves as a molecular “fingerprint” for identification and characterization.

An FTIR instrument typically includes a broadband infrared source, a Michelson-type interferometer with a moving mirror, a beamsplitter, a sample compartment, and a detector (such as DTGS or MCT). The interferometer modulates the IR signal into an interferogram, which a computer Fourier-transforms into a spectrum showing absorbance or transmittance versus wavenumber (cm−1). Measurements can be performed in several modes: transmission (often with KBr pellets for solids), attenuated total reflectance (ATR), and diffuse reflectance (DRIFTS) for powders and rough surfaces.

Spectra are analyzed by identifying absorption bands corresponding to vibrational modes of chemical bonds. The high-wavenumber region (approximately 4000–1500 cm−1) and the fingerprint region (approximately 1500–400 cm−1) are used to infer functional groups and compound identity. Quantitative analysis is possible with appropriate calibration.

Applications span polymer and material science, pharmaceuticals, environmental monitoring, forensics, and cultural heritage. Advantages include speed, minimal sample preparation, and non-destructive analysis across phases. Limitations involve overlapping bands, strong water or solvent absorptions, and reliance on reference libraries for definitive identification. FTIR remains a versatile complement to other analytical methods, including Raman spectroscopy, in providing molecular-level insights.